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Effects of coating formulation on coating thermal properties and coated paper print quality in xerography Chong Liang Ning Yan David Vidal and Xuejun Zou
KEYWORDS Paper coating Thermal conductivity
Thermal diffusivity Xerography
SUMMARY The effects of coating formulation on
thermal characteristics of coating layers (namely thermal
diffusivity specific heat capacity and heat conductivity)
were systematically studied and their impact on xerography
print quality was evaluated Model coatings were prepared
using ground calcium carbonate or kaolin pigment mixed
with styrene butadiene latex binder in various proportions
(from 6 to 25 pph) As expected porosity was shown to be
a key parameter for thermal conductivity of the coating
layers and is mainly determined by the latex concentration
Particle size distribution (PSD) and pigment morphology
also affected the thermal characteristics of the coating
layers It was found that the bulk thermal conductivity of
the coating layers can be accurately predicted by a
geometric mean model based on the pigment latex and air
contents Print quality on model coated papers was
evaluated in terms of print gloss toner adhesion and pair-
wise visual ranking It was demonstrated that print gloss is
improved by decreasing the bulk thermal conductivity of
the coatings The coating formulated with the pigments
with the steepest PSD and 10 pph of latex had a relatively
low thermal conductivity and the best print quality
ADDRESSES OF THE AUTHORS Chong Liang (cliangmascomacom) Mascoma Canada
Inc Mississauga Ontario Canada
Ning Yan (ningyanutorontoca) Faculty of Forestry
University of Toronto Toronto Ontario Canada
David Vidal (davidvidalfpinnovationsca)
Xuejun Zou (Xuejunzoufpinnovationsca) FPInnovations
Pointe-Claire Quebec Canada
Corresponding author Ning Yan
In recent years digital printing has seen the largest growth
in the printing industry This is mainly due to the
development of a new generation of large-scale high-speed
digital xerography press Xerography is an electrostatic dry-
ink printing technology which involves six steps (Duke et
al 2002)
(1) Charging a photoconductive belt
(2) Generating a latent image on the photoconductive
belt by image-wise lightlaser exposure
(3) Developing the latent image by brushing charged
pigment powders (toner) onto the image area
(4) Transferring the toner from the photoconductive belt
to substrate (paper)
(5) Fusing the toner on the paper in a fuser
(6) Discharging the photoconductive belt and cleaning
the residual toner
In xerography process toner fusion consumes the largest
amount of energy and is one of the key steps in determining
print quality When toner and paper pass through the fuser
nip formed between a heating roll and a pressure roll the
toner powders absorb the thermal energy from the heating
roll and then melt and coalesce with each other before
being fixed onto the paper surface Typically un-fused
toners on the paper are at room temperature at the entrance
of the fusing nip but have to reach their melting
temperature (could be around 110 -120C depending on the
type and manufacturer) before the nip exit Since fusing
only takes several milliseconds in a xerography printing
press an adequate heat transfer at the fuser nip is of great
importance
In many applications paper is coated with inorganic
pigments and latex binders to obtain higher smoothness
whiteness and gloss Comprehensive studies on toner
fusion in xerography printing and related heat transfer
detailing the effects of toner properties paper properties
fuser roll configurations and fusing process conditions
have been conducted by several researchers (Mitsuya
Kumasaka 1992 Sanders Rutland 1996 Bandyopadhay
et al 2001 Maijala et al 2004 Vernhes et al 2006 Gane
et al 2007 Gerstner et al 2009 Gerstner 2010)
However the contributions of the coating layer to heat
transfer toner fusion and resulting print quality have not
been fully understood In fact the thermal and surface
properties of paper can be altered significantly with the
addition of a coating layer Recent studies have shown that
the coating layer affects the effective heat transfer area for
toner and its thermal properties have an inverse effect on
the toner temperature at the toner-coating interface (Azadi
2007) Air gaps may also form at this interface due to a
ldquoheat sinkrdquo effect introduced by the coating structure
(Cormier Zou 2008) These problems may result in
insufficient toner fusion and thus a decrease in print quality
Therefore it is necessary to investigate the effects of
coating compositions on the thermal properties of coated
paper and link them to print quality
Past studies (Parker et al 1961 Morikawa Hashimoto
1998 Simula Niskanen 1998 Salazer 2003) have shown
how by measuring the thermal diffusivity D specific heat
capacity Cp and apparent (effective) density ρ of a material
its thermal conductivity K can be experimentally
determined through Eq 1
K = D ρ Cp [1]
With a systematic experimental approach this study
provides a good understanding on the effects of coating
compositions on the above thermal properties of coating
layers The relationship between the latter and the quality of
PAPER PHYSICS
Nordic Pulp and Paper Research Journal Vol 27 no22012 451
Table 1 Characteristics of Pigments
Note a Median is defined as D50 (50 percentile) b Distribution is defined as either i Percentage of particles with diameter less than 2 microm ii Width of PSD defined as (D70 ndash D30)D50
toner fusion is also studied by evaluating print quality of
coated papers This work will help papermakers engineer
optimum coatings from better raw material selection and
develop advanced coated papers to better suit high-speed
digital xerography press
Materials and Methods Materials
Three types of ground calcium carbonate (GCC) namely
Hydrocarb 90 Hydrocarb 60 and Covercarb HP and one
type of kaolin clay pigments namely Capim DG were used
in this study and their characteristics are summarized in
Table 1 (the particle size distributions were determined by
SedigraphTM
particle size analyzer) Sixteen different
coating formulations were prepared by mixing 100 pph of
one of the four pigments with 6 10 18 or 25 pph of
styrene-butadiene (SB) latex (Tg = -23C commercial
grade) with the solid content adjusted to 60 ww These
formulations are referred hereafter by their abbreviated
brand name of the pigment followed by the amount of latex
expressed in pph (eg CCHP-18 referring to a formulation
of Covercarb HP mixed with 18 pph of latex)
Formation of Standalone Coating Layers
Standalone coating layers were formed by casting model
coating colours in standard polystyrene Petri dishes which
were pre-treated by wiping a thin layer of silicone release
oil on the inner walls Approximately 40 g of coating
colour was dozed into each Petri dish and was dried under
ambient condition The resulted coating layer had a
thickness of 10 plusmn 008 mm
Measurements of Coating Layer Properties
Coating Structure Characterization by Mercury Intrusion Porosimetry
The model coating layers were characterized by mercury
intrusion porosimetry for both porosity and pore-size
distribution using an AutoPore IV 9500 mercury
porosimeter developed by Micromeritics Instrument Corp
USA The maximum applied pressure of mercury was
31000 psi (214 MPa) The mercury-intrusion measure-
ments were corrected for the compression of liquid mercury
and the expansion of the penetrometer (sample holder)
Detailed working mechanism of the mercury porosimeter
can be obtained from Micromeritics Instrument Corp
(Webb 2001)
After performing mercury intrusion porosimetry the
porosity of each coating layer was used in the calculations
for the apparent density Apparent density was obtained by
using the sample weight divided by the sample volume as
opposed to skeletal density which is defined as the sample
weight divided by the volume of the solid components only
Thermal Diffusivity Measurement
The effective thermal diffusivity of model coating layers
was measured using an LFA447 NanoFlashreg Xenon flash
apparatus developed by Netzsch Instrument Inc Germany
The working principle of this instrument was explained in
(Zhao Schabel 2006) For sample preparation coating
layers were cut into discs with a diameter of 05 inch
(127 cm) The specimens were then sprayed with 3ndash5
layers of liquid graphite The dried graphite layer ensured
consistent light energy absorption for each specimen and
the effect of its thickness was adjusted for by an internal
correction factor provided by the instrument software
(Liang 2009)
Specific Heat Capacity Measurement
The specific heat capacity of model coating layers was
measured by a Q1000 differential scanning calorimeter
from TA Instruments USA using air as a reference
material The instrument was operated under the ramp
mode for the temperature range of 10 ndash 100˚C with a steady
heating rate of 10˚Cmin
Print Quality Evaluation
For print quality evaluations 6 selected model coating
colours HC90-10 HC90-18 HC90-25 HC60-10 CCHP-
10 and CPDG-10 were applied on Xerox Digital Color
Elite Silk Cover Paper with a coat weight of 20 plusmn 07 gm2
(close to industrial standard) by a bench-top rod coating
technique The coated paper samples were dried under
ambient conditions as a low Tg latex was used and then
printed with a 100 solid black area of 8 inch x 10 inch by
a Xerox Workcentre 7345 Multifunction Copier under a
high resolution mode (with pre-set printing speed and
amount of toner used) The same solid black area was also
printed on original Xerox cover paper as control
Print Gloss Measurement
Print gloss of the coated paper samples was measured using
a RhopointTM
Novo-GlossTM
Statistical Glossmeter
developed by Rhopoint Instrumentation Ltd England The
instrument was calibrated against a standard black glass tile
with gloss units (GU) of 899 938 and 990 for the
measurement angel of 20˚ 60˚ and 75˚ respectively The
specular gloss of the 100 black print on the samples was
measured at 75˚ according to the TAPPI Test Methods T
480
Name
Particle Size Distributionb
Morphology Mediana
(microm) lt 2 microm
Width
Hydrocarb 90 (HC90)
061 951 101 Spherical
Hydrocarb 60 (HC60)
138 638 116 Spherical
Covercarb HP (CCHP)
064 977 073 Spherical
Capim DG (CPDG)
071 885 106 Platy
PAPER PHYSICS
452 Nordic Pulp and Paper Research Journal Vol 27 no22012
Toner Adhesion Test
Toner adhesion on the coated paper samples was measured
using an IGT AIC2 Printability Tester from IGT Testing
Systems Netherlands The printed coated paper specimens
were cut into strips of 15 cm wide A piece of 3M Scotch
Magic Tape 810D green tape was attached on the printed
surface of each strip and was peeled off by the IGT tester
at a constant angle with a force of 650 N and speeds from
05 to 5 ms After peeling the strips were scanned using an
Epson 4990 scanner and the images were converted to
binary black and white images to quantify the number of
white pixels (representing the quantity of toners removed)
The percentage of white pixels over the total number of
pixels on the scanned image was calculated and used to
compare how well toners adhered on each specimen
Pair-wise Visual Ranking
From the printed coated paper samples 2 areas (11 cm x 7
cm) of the solid black print were cut and mounted
individually on white card papers creating 2 batches of
samples for visual evaluation on their print quality 15
participants 6 males and 9 females with normal or
corrected to normal visions and with minimal to plentiful
visual ranking experience participated in this exercise in a
laboratory under controlled environment with a constant
light source Pair-wise method was used to visually rank the
sample prints within the same batch based on the
participantsrsquo perceptions of good print quality For each
pair of samples the number of the one with better print
quality was entered in a score matrix until all the possible
combinations of samples were compared For each sample
the number of entries on the score matrix was counted and
the sample with most entries (ie best print quality) was
given the highest ranking
Results and discussions
Effects of Coating Compositions on Coating Layer Properties
Porosity and Pore Size
Fig 1 shows that the Hydrocarb 90 (HC90) and Hydrocarb
60 (HC60) coating layers have similar porosity of ca 28
vv at 6 pph of latex and ca 3 vv at 25 pph This is
consistent with the porosity obtained by Azadi in the recent
study on coating layer compression (Azadi et al 2009)
Comparing with the Covercarb HP (CCHP) and Capim DG
(CPDG) coating layers the latter two have higher porosity
under the same latex concentration
Overall with the addition of 25 pph of latex the reduction
in porosity for all GCC coating layers (HC90 HC60 and
CCHP) is around 25 vv but is only 16 vv for clay
(CPDG) as compared to the lowest addition level of 6 pph
of latex These data suggest that as the latex concentration
in a coating layer increases its porosity decreases but the
reduction in porosity depends on the type of pigments with
the pore space between platy particles being more difficult
to fill in On the other hand Fig 2 shows that the median
Fig 1 Effect of Latex Concentration on Porosity
Fig 2 Effect of Latex Concentration on Pore Size
pore diameter of all GCC coating layers decreases only for
latex concentration greater than 10 pph This suggests that
before the latex concentration reaches 10 pph adding latex
only reduces the number of pores in the coating layer when
the latex concentration exceeds 10 pph the additional latex
starts to reduce both the number and the diameter of coating
pores This qualitatively agrees with the SEM image
analysis results given in Stroumlm et al (2010) The pore sizes
of CPDG (kaolin) coating layers remain roughly constant
indicating a different internal pore structure
Fig 1 also shows that at the same latex concentration the
HC90 and HC60 coating layers have the same porosity in
spite of their different median pigment particle sizes This
suggests that the pigment particle size has no significant
effect on the porosity of a coating layer This agrees with
the finding from Di Risio (Di Risio Yan 2006) that for
pigments with size around or below 1 microm the variation in
coating porosity due to change in pigment size is not
significant (as long as PSD width is similar) However
pigment particle size has an influence on the size of pores
formed in a coating layer Fig 2 shows that the median pore
size of HC60 coating layers is approximately twice as large
as that of HC90 corresponding to the size ratio between
HC60 and HC90 pigments This is reasonable since larger
voids will form among the larger pigment particles if the
two types of pigments have the same morphology and PSD
width Both Di Risio (2006) and Watanabe
et al (1980)
reported a similar trend on kaolin coating layers
PAPER PHYSICS
Nordic Pulp and Paper Research Journal Vol 27 no22012 453
Fig 3 Effect of Latex Concentration on Density (Descending skeletal density Ascending apparent density)
The CCHP coating layers have significantly larger
porosity than the HC90 ones due to the narrower (or steeper)
particle size distribution of CCHP The median diameter of
pores in CCHP coating layers is also larger than that of
HC90 These results are in agreement with Di Risio (2006)
Malla et al (1999) and Okomori et al
(1998) As the PSD
width decreases less fine particles are available to fill the
voids among the coarse particles thus increasing the
porosity and median pore size in a coating layer
A comparison on porosity between CPDG and HC90
coating layers shows that the former has a larger porosity
than the latter at the same latex concentration This is in
agreement with the packing simulation findings by
Vidal et
al (2004) which showed that pigment particles with larger
aspect ratio (ie kaolin) create a bulkier coating structure
Apparent Density
Since adding latex reduces the porosity of coating layers
(Fig 1) an increase in apparent density is thus obtained
(See ascending curves in Fig 3) Also as expected we
observe that pigments with a wider particle size distribution
or with a lower aspect ratio produce significantly denser
coating layers
Thermal Diffusivity
Air has a larger thermal diffusivity (ca 20 mm2s)
(Niskanen Simula 1999) than polymers (with a magnitude
of 01 mm2s) (Salazer 2003) it was shown theoretically
that the effective thermal conductivity of the coating layers
increased with the binder content up to the critical pigment
volume concentration (Vidal Zou 2004) However Fig 4
shows that the experimental thermal diffusivity values of
the HC90 HC60 and CPDG coating layers remain roughly
constant when the latex concentration exceeds 10 pph One
explanation as suggested by Salazar (2003) is that air and
latex can be very compatible in terms of diffusing heat to
each other since they might have similar thermal effusivity
a measure of a materialrsquos ability to exchange thermal
energy with its surroundings Therefore even if there are
less air pores in the coating layers when the latex content
increases heat can still diffuse through the coating layers
Fig 4 Effect of Latex Concentration on Thermal Diffusivity
effectively due to the higher amount of latex surrounding
the pigment particles
It can be seen that the thermal diffusivity of the HC90
coating layer is larger than that of HC60 when the latex
concentration is less than 10 pph but when the latex
concentration exceeds 10 pph the two have approximately
the same thermal diffusivity This might be a combined
effect due to the pigment particle size and the thermal
coupling between air and latex As the median particle size
of HC60 is twice as large as that of HC90 at a low latex
concentration it takes a longer distance for heat to
propagate through the HC60 pigment particles which has a
relatively low thermal diffusivity value (ca 2 mm2s)
(Niskanen Simula 1999) Once the latex concentration
exceeds 10 pph the effect due to the thermal coupling
between air and latex might be so strong that the obstacle
on heat propagation due to pigment particle size becomes
insignificant
Fig 4 also shows that the thermal diffusivity of the HC90
coating layer is larger than that of CCHP and CPDG
samples under the same latex concentration up to 25 pph
This can be due to the lower densities (or higher porosity)
of CCHP or CPDG samples affected by the narrower
particle size distribution or higher aspect ratio of pigments
The lower intrinsic thermal diffusivity value of clay (ca
05 mm2s) (Niskanen Simula 1999) than GCC also
contributes to this result
Specific Heat Capacity
Fig 5 shows that as the latex concentration rises the
specific heat capacity Cp of coating layers increases in a
linear fashion (represented by the solid trend lines) This
increase with additional latex can be explained by the
higher intrinsic Cp value of latex (ca 19 Jg˚C) than those
of pigment (ca 08 Jg˚C) and air (ca 10 Jg˚C) The
linearity of the trend lines is supported by the calculation of
Cp for the coating layers using the simplified 1st order
parallel model shown in Eq 2 (assuming the mass of air
pores is negligible)
latexlatexppigmentpigmentpeffp mCmCC
[2]
PAPER PHYSICS
454 Nordic Pulp and Paper Research Journal Vol 27 no22012
Fig 5 Effect of Latex Concentration on Specific Heat Capacity
where m represents the mass fraction of each coating
component and m=1 The calculated results (the dashed
lines) were found to be in close agreement with the trend
lines of the experimental data This confirms with Salazar
(2003) that the effective specific heat capacity Ceff of a
composite always follows the mixture rule
Therefore it is reasonable that the specific heat capacity
values of HC90 and HC60 coating layers at the same latex
concentration are the same as they have same porosity and
density Hence the pigment particle size is not expected to
have a significant effect on the bulk specific heat capacity
The differences in experimental data shown in Fig 5 might
be due to the sensitivity of the DSC instrument
The Cp of CCHP and CPDG coating layers is also very
close to those of HC90 ones Since the mass fraction of air
is negligible the effects of pigment particle size distribution
or morphology on the specific heat capacity are
insignificant as expected
Bulk (Effective) Thermal Conductivity
Fig 6 shows that as the latex concentration increases up to
25 pph the bulk thermal conductivity of all coating layers
increases As explained earlier adding latex in a coating
layer results in two effects on a coating structure (1)
increasing the volume fraction of latex and thus reducing
the volume fraction of air and (2) breaking the air pores
down to smaller sizes Both latex and air have much lower
intrinsic thermal conductivity values (ca 020 WmK
(Saxaner et al 1999) and 0026 WmK (CRC 2009)
respectively) than pigments (2ndash5 WmK) (Bouguerra
1997) but the reduction in the pore volume (ie porosity) is
more significant than the increase in the latex volume In
addition having smaller pores in the coating layer means
that the pigment particles have a higher chance to be
connected creating a better channel for heat transfer
Changing the median pigment particle size between
HC90 and HC60 coating layers does not result in a change
in the apparent density specific heat capacity or thermal
diffusivity (when the latex concentration exceeds 10 pph)
of the coating layers formed Therefore the bulk thermal
Fig 6 Effect of Latex Concentration on Thermal Conductivity
conductivity of the two groups of coating layers are the
same meaning that pigment particle size alone does not
have a significant effect
Between HC90 and CCHP coating layers using pigments
with a wider particle size distribution (HC90) results in an
increased apparent density an unchanged specific heat
capacity and a higher thermal diffusivity value for the
coating layers formed Therefore the bulk thermal
conductivity of HC90 samples is higher than that of CCHP
Lastly a CPDG coating layer has lower apparent density
and thermal diffusivity but higher specific heat capacity
than a HC90 coating layer at the same latex concentration
The intrinsic thermal properties of clay (CPDG) contribute
greatly to these results However the higher aspect ratio of
the CPDG pigment does contribute to a bulkier coating
structure and therefore affects the thermal diffusivity of
the structure The combined effect is a bulk thermal
conductivity of the CPDG coating layers lower than that of
HC90
Modelling Thermal Conductivity by Geometric Mean
The theoretical bulk thermal conductivity of each coating
layer sample was modeled by calculating the geometric
mean of the K values of pigment latex and air based on
their volume fraction v as Eq 3
airlatexpigment v
air
v
latex
v
pigmenteff KKKK [3]
where Kpigment = 26 WmK for GCC or 16 WmK for
kaolin
Klatex = 020 WmK
Kair = 0026 WmK
vpigment and vlatex are derived from the porosity (vair)
and the pigment to latex mass ratio with their
individual density given 1v
Fig 7 shows that the geometric mean model provides very
good fittings of the experimental data points for the
different pigments and latex concentrations studied This
shows that the bulk thermal conductivity of the coatings
can be well predicted by the geometric mean model
Furthermore it shows that the thermal conductivity only
PAPER PHYSICS
Nordic Pulp and Paper Research Journal Vol 27 no22012 455
Fig 7 Modelling Thermal Conductivity by the Geometric Mean Model
depends on the intrinsic thermal conductivities of the
coating constituents and their respectively volume fractions
(the latter being affected by the PSD and the shape of the
pigment used) In fact this model constitutes a much
simpler model than the Lumped Parameter model proposed
recently by Gerstner (2010) while resembling the empirical
model suggested by Azadi et al (2010)
Print Quality Test Results
Print Gloss
Fig 8 shows that the average print gloss of the model
coated paper was significantly reduced as the bulk thermal
conductivity of the corresponding type of coating layer
increases This suggests that the bulk thermal conductivity
of the coating layers affect the fusing process of toner
which includes toner coalescence melting and spreading
similar to what is concluded by Azadi et al (2008) One
possible explanation is that when the coating bulk thermal
conductivity is lower the coating plays the role of a heat
barrier (dissipating less heat to the base paper) This helps
the toner layer to reach uniformly its melting temperature
and allows the toner layer to level off evenly As a result a
ldquomirror-likerdquo surface is thus created and a high print gloss
is obtained
Interestingly thermal diffusivity of the coating layer gave
a weaker correlation to print gloss with R2 around 052 It
might be due to the fact that thermal diffusivity deals
mostly with the heat flow in the coating layer itself while
print gloss is mostly determined by the heat flow at the
tonercoating interface which thermal conductivity might
be more important However this remains to be confirmed
by further studies
Toner Adhesion
The results of the toner adhesion test show that the amount
of toner removed is affected by the peeling speed of the
Scotch tape Therefore the minimum percentages of toner
remained (adhered) on the coated paper samples at all
peeling speeds were taken for the study These data are
listed in Table 2 and plotted in Fig 9 It shows no
correlation between the percentage of toners remained on
Fig 8 Effect of Bulk Thermal Conductivity of the Coating Layers on Average Print Gloss (in ) of the Coated Papers
Fig 9 Effect of Bulk Thermal Conductivity of the Coating Layers on Toner Adhesion on the Coated Papers
Table 2 Minimum Toner Adhesion on Coated Papers
the coated paper and the bulk thermal conductivity of the
corresponding type of coating layer A similar comparison
was done by Gerstner et al
(2009) and no definite
correlation was found either As explained by Kianercy
(2004) and Sipi (2001) only three factors have been found
to have significant impacts on toner adhesion which are
surface tension of paper toner viscosity at the tonerpaper
interface and fusing speed
Pair-wise Visual Ranking
The result of the visual ranking test shows that for coating
layers with 10 pph of latex the CCHP-10 coating provides
the best print quality and the CPDG-10 coating provides
the worst print quality Among the HC90 coating layers
with different latex concentrations the HC90-10 and
Sample Minimum Toner Remained ()
HC90-10 987 HC90-18 946 HC90-25 872 HC60-10 218 CCHP-10 999 CPDG-10 811
PAPER PHYSICS
456 Nordic Pulp and Paper Research Journal Vol 27 no22012
Fig 10 Effect of Bulk Thermal Conductivity of the Coating Layers on Average Ranking Score of the Printed Coated Papers
Table 3 Summary of the Print Quality Test Results
HC90-18 coating provide significantly better print quality
than the one made with 25 pph of latex However no
correlation was found between print quality (quantified by
the average ranking score) of a sample with the bulk
thermal conductivity of the coating layers see Fig 10
These findings suggest that there are other factors which
have a more significant effect on the print quality of coated
paper However this is beyond the scope of this study
A summary of the print quality test results (Table 3)
reveals that the coating layer formulated with Covercarb
HP pigment and 10 pph of latex has the best ranking in all
three tests Therefore with its relatively low thermal
conductivity this coating formulation is the best candidate
among the ones studied for use in xerography printing
Conclusions The effects of coating formulations on thermal
characteristics of the coating layers were systematically
studied for assessing their impact on xerographic toner
fusion onto the coated papers It was shown that porosity is
a key parameter in the design of a coating layer for heat
transfer applications The latex concentration in the coating
formulation plays a significant role as it determines the
overall porosity of the coating layers Therefore in order
for the coating layer to act as a heat barrier (and provide
sufficient uniform heat transfer to the toner layer) it needs
to have an acceptably high porosity or a low latex
concentration The particle size distribution (narrow PSD)
and morphology (high shape factor) of pigments also affect
positively the porosity and thus the overall thermal
characteristics of the coating layers However the median
particle size of pigments did not show any significant
effect It was also found that the bulk thermal conductivity
of the coating layers can be accurately predicted by a
simple geometric mean model based on the pigment latex
and air volume contents
A 75˚ TAPPI print gloss measurement a toner adhesion
test using an IGT printability tester and a pair-wise visual
ranking test were performed on paper samples coated with
model coating colours and printed with 100 solid black
by xerography The print gloss of coated papers was
significantly improved when the coating bulk thermal
conductivity was low This is attributed to the insulating
effect of the coating thus providing a more uniform toner
fusion No other correlation was found between the print
quality and thermal properties of the samples
Lastly it was found that the coating made of Covercarb
HP a narrow PSD pigment and 10 pph of latex gave a
relatively low thermal conductivity and the best ranking in
all three print quality tests Therefore among all the
formulations tested this coating is the best candidate for
coated paper applications in xerography
Acknowledgements The financial and technical supports from NSERC IPS Scholarship FPInnovations Xerox Research Center of Canada and Surface Science Consortium at the Pulp and Paper Centre University of Toronto are gratefully acknowledged
Literature
Azadi P (2007) Modeling of mechanical and thermal responses of paper coatings under compression using discrete element method Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada
Azadi P Yan N Farnood R (2008) Discrete Element Modeling of the Transient Heat Transfer and Toner Fusing Process in the Xerographic Printing of Coated Papers Computers amp Chemical Engineering 32(12) 3238-3245
Azadi P Nunnari S Farnood R Kortschot M Yan N (2009) High speed compression of highly filled thin composites effect of binder content and stiffness Progress in Organic Coatings 64(4) 356-360
Azadi P Farnood R Yan N (2010) FEM-DEM Modeling of Thermal Conductivity of Porous Pigmented Coatings Computational Materials Science 49(2) 392-399
Bandyopadhay A Ramarao BV Shih EC (2001) Transient response of a paper sheet subjected to a traveling thermal pulse evolution of temperature moisture and pressure fields Journal of Imaging Science and Technology 45(6) 598-608
Bouguerra A Laurent JP Goual M Queneudec M (1997) The measurement of the thermal conductivity of solid aggregates using the transient plane source technique Journal of Physics D Applied Physics 30 2900-2904
Ranking (Best to Worst)
Print Gloss
Toner Adhesion
Visual Ranking
1 CCHP-10 CCHP-10 CCHP-10 2 CPDG-10 HC90-10 HC90-10 3 HC90-10 HC90-18 HC90-18 4 HC90-18 HC90-25 HC60-10 5 HC60-10 CPDG-10 CPDG-10 6 HC90-25 HC60-10 HC90-25
PAPER PHYSICS
Nordic Pulp and Paper Research Journal Vol 27 no22012 457
Cormier L Zou X (2008) Toner fusion in electrophotographic printing ndash issues from Papricanrsquos perspectives FPInnovations Paprican Division Pointe-Claire QC February 8 2008
CRC Handbook of Chemistry and Physics (2009) 89th ed Taylor amp Francis Group
Di Risio S Yan N (2006) Characterizing Coating Pore Structures of Paper Using Scanning Probe Microscopyrdquo TAPPI Journal 5(3) 9-14
Di Risio S Yan N (2006) Characterizing Coating Layer Z-directional Binder Distribution in Paper Using Atomic Force Microscopy Colloids and Surfaces A Physicochemical and Engineering Aspects 289(1-3) 65-74
Duke CB Noolandi J Thieret T (2002) The surface science of xerography Surface Science 500 1005-1023
Gane PAC Ridgeway CJ Schoelkopf J Bousfield DW (2007) Heat transfer through calcium carbonate-based coating structures observation and model for a thermal fusing process Journal of Pulp and Paper Science 33(2) 60-70
Gerstner P Gane PAC (2009) Considerations for thermally engineered coated printing papers focus on electrophotography Journal of Pulp and Paper Science 35(3-4) 108-117
Gerstner P Paltakari J Gane PAC (2009) Measurement and modeling of heat transfer in paper coating structures Journal of Material Science 44 (2) 483-491
Gerstner P (2010) Heat Transfer Through Porous Multiphase Systems Measurement Modelling and Application in Printing of Coated Papers PhD Thesis Aalto university Helsinki Finland
Kianercy A (2004) Characterizing toner-paper adhesion in xerography Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada
Liang C (2009) Effect of coating formulations on thermal properties of coating layers Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada
Maijala J Putkisto K Pietikaumlinen R Groumln J (2004) Heat transfer during fixation of coating layers in dry surface treatment Nordic Pulp and Paper Research Journal 19(3) 291-299
Malla PB Starr RE Werkin TJ (1999) The effects of kaolin particle size structure clay loading and binder level on glossing and offset print properties ndash A CLC coating study 1999 TAPPI Coating Conference Proceedings Toronto Ontario Canada TAPPI Press
Mitsuya T Kumasaka T (1992) Heat transfer and toner melting in an electrophotographic fuser system Journal of Imaging Science and Technology 36 88-92
Morikawa J Hashimoto T (1998) Thermal diffusivity measurement of papers by an AC joule heating method Polymer International 45(2) 207-210
Niskanen K Simula S (1999) Thermal diffusivity of paper Nordic Pulp and Paper Research Journal 14(3) 236-242
Okomori K Lepoutre P (1998) Effect of pigment size and shape distribution on the cohesion of pigmented coatings 1998 TAPPI CoatingPapermakers Conference New Orleans LA USA TAPPI Atlanta GA USA 819 ndash 835
Parker WJ Jenkins RJ Butler CP Abbott GL (1961) Flash method of determining thermal diffusivity heat capacity and thermal conductivity Journal of Applied Physics 32(9) 1679-1684
Salazer A (2003) On thermal diffusivity European Journal of Physics 24(3) 351-358
Sanders DJ Rutland DF (1996) Effect of paper properties on fusing fix Journal of Imaging Science and Technology 40(2) 175-179
Saxaner NS et al (1999) Thermal conductivity of styrene butadiene rubber compounds with natural rubber prophylactics waste as filler European Polymer Journal 35 1687-1693
Simula S Niskanen K (1998) Thermal diffusivity measurement of non-impact printing paper Journal of Imaging Science and Technology 42(6) 550-553
Sipi KM (2001) Toner layer structure and toner adhesion on coated paper NIP17 International Conference on Digital Printing Technologies Fort Lauderdale FL USA 145-150
Stroumlm G Hornatowska J Changhong X Terasaki O (2010) A novel SEM cross-section analysis of paper coating for separation of latex from void volume Nordic Pulp and Paper Research Journal 25(1) 107-113
Vernhes P Blayo A Bloch J-F Pineaux B (2006) Influence of the thermal field on the fusing step in electrophotographic printing Proceedings of the Technical Association of the Graphic Arts 465-485
Vidal D Zou X Uesaka T (2004) Modeling coating structure development Monte-Carlo deposition of particles with irregular shapes Nordic Pulp and Paper Research Journal 19(4) 420ndash427
Wantanabe J Kohara Y Takahashi S (1980) Effects of clay properties on paper coating structure Tappi 63(1) 43 ndash 46
Webb PA (2001) An introduction to the physical characterization of materials by mercury intrusion porosimetry with emphasis on reduction and presentation of experimental data Micromeritics Instrument Corp January 2001 Retrieved on January 14 2009
httpwwwmicromeriticscomapplicationsarticlesaspx
Zhao S Schabel S (2006) Measurement of thermal properties of paper by a light flash method Das Papier T65 34-39
PAPER PHYSICS
458 Nordic Pulp and Paper Research Journal Vol 27 no22012
Table 1 Characteristics of Pigments
Note a Median is defined as D50 (50 percentile) b Distribution is defined as either i Percentage of particles with diameter less than 2 microm ii Width of PSD defined as (D70 ndash D30)D50
toner fusion is also studied by evaluating print quality of
coated papers This work will help papermakers engineer
optimum coatings from better raw material selection and
develop advanced coated papers to better suit high-speed
digital xerography press
Materials and Methods Materials
Three types of ground calcium carbonate (GCC) namely
Hydrocarb 90 Hydrocarb 60 and Covercarb HP and one
type of kaolin clay pigments namely Capim DG were used
in this study and their characteristics are summarized in
Table 1 (the particle size distributions were determined by
SedigraphTM
particle size analyzer) Sixteen different
coating formulations were prepared by mixing 100 pph of
one of the four pigments with 6 10 18 or 25 pph of
styrene-butadiene (SB) latex (Tg = -23C commercial
grade) with the solid content adjusted to 60 ww These
formulations are referred hereafter by their abbreviated
brand name of the pigment followed by the amount of latex
expressed in pph (eg CCHP-18 referring to a formulation
of Covercarb HP mixed with 18 pph of latex)
Formation of Standalone Coating Layers
Standalone coating layers were formed by casting model
coating colours in standard polystyrene Petri dishes which
were pre-treated by wiping a thin layer of silicone release
oil on the inner walls Approximately 40 g of coating
colour was dozed into each Petri dish and was dried under
ambient condition The resulted coating layer had a
thickness of 10 plusmn 008 mm
Measurements of Coating Layer Properties
Coating Structure Characterization by Mercury Intrusion Porosimetry
The model coating layers were characterized by mercury
intrusion porosimetry for both porosity and pore-size
distribution using an AutoPore IV 9500 mercury
porosimeter developed by Micromeritics Instrument Corp
USA The maximum applied pressure of mercury was
31000 psi (214 MPa) The mercury-intrusion measure-
ments were corrected for the compression of liquid mercury
and the expansion of the penetrometer (sample holder)
Detailed working mechanism of the mercury porosimeter
can be obtained from Micromeritics Instrument Corp
(Webb 2001)
After performing mercury intrusion porosimetry the
porosity of each coating layer was used in the calculations
for the apparent density Apparent density was obtained by
using the sample weight divided by the sample volume as
opposed to skeletal density which is defined as the sample
weight divided by the volume of the solid components only
Thermal Diffusivity Measurement
The effective thermal diffusivity of model coating layers
was measured using an LFA447 NanoFlashreg Xenon flash
apparatus developed by Netzsch Instrument Inc Germany
The working principle of this instrument was explained in
(Zhao Schabel 2006) For sample preparation coating
layers were cut into discs with a diameter of 05 inch
(127 cm) The specimens were then sprayed with 3ndash5
layers of liquid graphite The dried graphite layer ensured
consistent light energy absorption for each specimen and
the effect of its thickness was adjusted for by an internal
correction factor provided by the instrument software
(Liang 2009)
Specific Heat Capacity Measurement
The specific heat capacity of model coating layers was
measured by a Q1000 differential scanning calorimeter
from TA Instruments USA using air as a reference
material The instrument was operated under the ramp
mode for the temperature range of 10 ndash 100˚C with a steady
heating rate of 10˚Cmin
Print Quality Evaluation
For print quality evaluations 6 selected model coating
colours HC90-10 HC90-18 HC90-25 HC60-10 CCHP-
10 and CPDG-10 were applied on Xerox Digital Color
Elite Silk Cover Paper with a coat weight of 20 plusmn 07 gm2
(close to industrial standard) by a bench-top rod coating
technique The coated paper samples were dried under
ambient conditions as a low Tg latex was used and then
printed with a 100 solid black area of 8 inch x 10 inch by
a Xerox Workcentre 7345 Multifunction Copier under a
high resolution mode (with pre-set printing speed and
amount of toner used) The same solid black area was also
printed on original Xerox cover paper as control
Print Gloss Measurement
Print gloss of the coated paper samples was measured using
a RhopointTM
Novo-GlossTM
Statistical Glossmeter
developed by Rhopoint Instrumentation Ltd England The
instrument was calibrated against a standard black glass tile
with gloss units (GU) of 899 938 and 990 for the
measurement angel of 20˚ 60˚ and 75˚ respectively The
specular gloss of the 100 black print on the samples was
measured at 75˚ according to the TAPPI Test Methods T
480
Name
Particle Size Distributionb
Morphology Mediana
(microm) lt 2 microm
Width
Hydrocarb 90 (HC90)
061 951 101 Spherical
Hydrocarb 60 (HC60)
138 638 116 Spherical
Covercarb HP (CCHP)
064 977 073 Spherical
Capim DG (CPDG)
071 885 106 Platy
PAPER PHYSICS
452 Nordic Pulp and Paper Research Journal Vol 27 no22012
Toner Adhesion Test
Toner adhesion on the coated paper samples was measured
using an IGT AIC2 Printability Tester from IGT Testing
Systems Netherlands The printed coated paper specimens
were cut into strips of 15 cm wide A piece of 3M Scotch
Magic Tape 810D green tape was attached on the printed
surface of each strip and was peeled off by the IGT tester
at a constant angle with a force of 650 N and speeds from
05 to 5 ms After peeling the strips were scanned using an
Epson 4990 scanner and the images were converted to
binary black and white images to quantify the number of
white pixels (representing the quantity of toners removed)
The percentage of white pixels over the total number of
pixels on the scanned image was calculated and used to
compare how well toners adhered on each specimen
Pair-wise Visual Ranking
From the printed coated paper samples 2 areas (11 cm x 7
cm) of the solid black print were cut and mounted
individually on white card papers creating 2 batches of
samples for visual evaluation on their print quality 15
participants 6 males and 9 females with normal or
corrected to normal visions and with minimal to plentiful
visual ranking experience participated in this exercise in a
laboratory under controlled environment with a constant
light source Pair-wise method was used to visually rank the
sample prints within the same batch based on the
participantsrsquo perceptions of good print quality For each
pair of samples the number of the one with better print
quality was entered in a score matrix until all the possible
combinations of samples were compared For each sample
the number of entries on the score matrix was counted and
the sample with most entries (ie best print quality) was
given the highest ranking
Results and discussions
Effects of Coating Compositions on Coating Layer Properties
Porosity and Pore Size
Fig 1 shows that the Hydrocarb 90 (HC90) and Hydrocarb
60 (HC60) coating layers have similar porosity of ca 28
vv at 6 pph of latex and ca 3 vv at 25 pph This is
consistent with the porosity obtained by Azadi in the recent
study on coating layer compression (Azadi et al 2009)
Comparing with the Covercarb HP (CCHP) and Capim DG
(CPDG) coating layers the latter two have higher porosity
under the same latex concentration
Overall with the addition of 25 pph of latex the reduction
in porosity for all GCC coating layers (HC90 HC60 and
CCHP) is around 25 vv but is only 16 vv for clay
(CPDG) as compared to the lowest addition level of 6 pph
of latex These data suggest that as the latex concentration
in a coating layer increases its porosity decreases but the
reduction in porosity depends on the type of pigments with
the pore space between platy particles being more difficult
to fill in On the other hand Fig 2 shows that the median
Fig 1 Effect of Latex Concentration on Porosity
Fig 2 Effect of Latex Concentration on Pore Size
pore diameter of all GCC coating layers decreases only for
latex concentration greater than 10 pph This suggests that
before the latex concentration reaches 10 pph adding latex
only reduces the number of pores in the coating layer when
the latex concentration exceeds 10 pph the additional latex
starts to reduce both the number and the diameter of coating
pores This qualitatively agrees with the SEM image
analysis results given in Stroumlm et al (2010) The pore sizes
of CPDG (kaolin) coating layers remain roughly constant
indicating a different internal pore structure
Fig 1 also shows that at the same latex concentration the
HC90 and HC60 coating layers have the same porosity in
spite of their different median pigment particle sizes This
suggests that the pigment particle size has no significant
effect on the porosity of a coating layer This agrees with
the finding from Di Risio (Di Risio Yan 2006) that for
pigments with size around or below 1 microm the variation in
coating porosity due to change in pigment size is not
significant (as long as PSD width is similar) However
pigment particle size has an influence on the size of pores
formed in a coating layer Fig 2 shows that the median pore
size of HC60 coating layers is approximately twice as large
as that of HC90 corresponding to the size ratio between
HC60 and HC90 pigments This is reasonable since larger
voids will form among the larger pigment particles if the
two types of pigments have the same morphology and PSD
width Both Di Risio (2006) and Watanabe
et al (1980)
reported a similar trend on kaolin coating layers
PAPER PHYSICS
Nordic Pulp and Paper Research Journal Vol 27 no22012 453
Fig 3 Effect of Latex Concentration on Density (Descending skeletal density Ascending apparent density)
The CCHP coating layers have significantly larger
porosity than the HC90 ones due to the narrower (or steeper)
particle size distribution of CCHP The median diameter of
pores in CCHP coating layers is also larger than that of
HC90 These results are in agreement with Di Risio (2006)
Malla et al (1999) and Okomori et al
(1998) As the PSD
width decreases less fine particles are available to fill the
voids among the coarse particles thus increasing the
porosity and median pore size in a coating layer
A comparison on porosity between CPDG and HC90
coating layers shows that the former has a larger porosity
than the latter at the same latex concentration This is in
agreement with the packing simulation findings by
Vidal et
al (2004) which showed that pigment particles with larger
aspect ratio (ie kaolin) create a bulkier coating structure
Apparent Density
Since adding latex reduces the porosity of coating layers
(Fig 1) an increase in apparent density is thus obtained
(See ascending curves in Fig 3) Also as expected we
observe that pigments with a wider particle size distribution
or with a lower aspect ratio produce significantly denser
coating layers
Thermal Diffusivity
Air has a larger thermal diffusivity (ca 20 mm2s)
(Niskanen Simula 1999) than polymers (with a magnitude
of 01 mm2s) (Salazer 2003) it was shown theoretically
that the effective thermal conductivity of the coating layers
increased with the binder content up to the critical pigment
volume concentration (Vidal Zou 2004) However Fig 4
shows that the experimental thermal diffusivity values of
the HC90 HC60 and CPDG coating layers remain roughly
constant when the latex concentration exceeds 10 pph One
explanation as suggested by Salazar (2003) is that air and
latex can be very compatible in terms of diffusing heat to
each other since they might have similar thermal effusivity
a measure of a materialrsquos ability to exchange thermal
energy with its surroundings Therefore even if there are
less air pores in the coating layers when the latex content
increases heat can still diffuse through the coating layers
Fig 4 Effect of Latex Concentration on Thermal Diffusivity
effectively due to the higher amount of latex surrounding
the pigment particles
It can be seen that the thermal diffusivity of the HC90
coating layer is larger than that of HC60 when the latex
concentration is less than 10 pph but when the latex
concentration exceeds 10 pph the two have approximately
the same thermal diffusivity This might be a combined
effect due to the pigment particle size and the thermal
coupling between air and latex As the median particle size
of HC60 is twice as large as that of HC90 at a low latex
concentration it takes a longer distance for heat to
propagate through the HC60 pigment particles which has a
relatively low thermal diffusivity value (ca 2 mm2s)
(Niskanen Simula 1999) Once the latex concentration
exceeds 10 pph the effect due to the thermal coupling
between air and latex might be so strong that the obstacle
on heat propagation due to pigment particle size becomes
insignificant
Fig 4 also shows that the thermal diffusivity of the HC90
coating layer is larger than that of CCHP and CPDG
samples under the same latex concentration up to 25 pph
This can be due to the lower densities (or higher porosity)
of CCHP or CPDG samples affected by the narrower
particle size distribution or higher aspect ratio of pigments
The lower intrinsic thermal diffusivity value of clay (ca
05 mm2s) (Niskanen Simula 1999) than GCC also
contributes to this result
Specific Heat Capacity
Fig 5 shows that as the latex concentration rises the
specific heat capacity Cp of coating layers increases in a
linear fashion (represented by the solid trend lines) This
increase with additional latex can be explained by the
higher intrinsic Cp value of latex (ca 19 Jg˚C) than those
of pigment (ca 08 Jg˚C) and air (ca 10 Jg˚C) The
linearity of the trend lines is supported by the calculation of
Cp for the coating layers using the simplified 1st order
parallel model shown in Eq 2 (assuming the mass of air
pores is negligible)
latexlatexppigmentpigmentpeffp mCmCC
[2]
PAPER PHYSICS
454 Nordic Pulp and Paper Research Journal Vol 27 no22012
Fig 5 Effect of Latex Concentration on Specific Heat Capacity
where m represents the mass fraction of each coating
component and m=1 The calculated results (the dashed
lines) were found to be in close agreement with the trend
lines of the experimental data This confirms with Salazar
(2003) that the effective specific heat capacity Ceff of a
composite always follows the mixture rule
Therefore it is reasonable that the specific heat capacity
values of HC90 and HC60 coating layers at the same latex
concentration are the same as they have same porosity and
density Hence the pigment particle size is not expected to
have a significant effect on the bulk specific heat capacity
The differences in experimental data shown in Fig 5 might
be due to the sensitivity of the DSC instrument
The Cp of CCHP and CPDG coating layers is also very
close to those of HC90 ones Since the mass fraction of air
is negligible the effects of pigment particle size distribution
or morphology on the specific heat capacity are
insignificant as expected
Bulk (Effective) Thermal Conductivity
Fig 6 shows that as the latex concentration increases up to
25 pph the bulk thermal conductivity of all coating layers
increases As explained earlier adding latex in a coating
layer results in two effects on a coating structure (1)
increasing the volume fraction of latex and thus reducing
the volume fraction of air and (2) breaking the air pores
down to smaller sizes Both latex and air have much lower
intrinsic thermal conductivity values (ca 020 WmK
(Saxaner et al 1999) and 0026 WmK (CRC 2009)
respectively) than pigments (2ndash5 WmK) (Bouguerra
1997) but the reduction in the pore volume (ie porosity) is
more significant than the increase in the latex volume In
addition having smaller pores in the coating layer means
that the pigment particles have a higher chance to be
connected creating a better channel for heat transfer
Changing the median pigment particle size between
HC90 and HC60 coating layers does not result in a change
in the apparent density specific heat capacity or thermal
diffusivity (when the latex concentration exceeds 10 pph)
of the coating layers formed Therefore the bulk thermal
Fig 6 Effect of Latex Concentration on Thermal Conductivity
conductivity of the two groups of coating layers are the
same meaning that pigment particle size alone does not
have a significant effect
Between HC90 and CCHP coating layers using pigments
with a wider particle size distribution (HC90) results in an
increased apparent density an unchanged specific heat
capacity and a higher thermal diffusivity value for the
coating layers formed Therefore the bulk thermal
conductivity of HC90 samples is higher than that of CCHP
Lastly a CPDG coating layer has lower apparent density
and thermal diffusivity but higher specific heat capacity
than a HC90 coating layer at the same latex concentration
The intrinsic thermal properties of clay (CPDG) contribute
greatly to these results However the higher aspect ratio of
the CPDG pigment does contribute to a bulkier coating
structure and therefore affects the thermal diffusivity of
the structure The combined effect is a bulk thermal
conductivity of the CPDG coating layers lower than that of
HC90
Modelling Thermal Conductivity by Geometric Mean
The theoretical bulk thermal conductivity of each coating
layer sample was modeled by calculating the geometric
mean of the K values of pigment latex and air based on
their volume fraction v as Eq 3
airlatexpigment v
air
v
latex
v
pigmenteff KKKK [3]
where Kpigment = 26 WmK for GCC or 16 WmK for
kaolin
Klatex = 020 WmK
Kair = 0026 WmK
vpigment and vlatex are derived from the porosity (vair)
and the pigment to latex mass ratio with their
individual density given 1v
Fig 7 shows that the geometric mean model provides very
good fittings of the experimental data points for the
different pigments and latex concentrations studied This
shows that the bulk thermal conductivity of the coatings
can be well predicted by the geometric mean model
Furthermore it shows that the thermal conductivity only
PAPER PHYSICS
Nordic Pulp and Paper Research Journal Vol 27 no22012 455
Fig 7 Modelling Thermal Conductivity by the Geometric Mean Model
depends on the intrinsic thermal conductivities of the
coating constituents and their respectively volume fractions
(the latter being affected by the PSD and the shape of the
pigment used) In fact this model constitutes a much
simpler model than the Lumped Parameter model proposed
recently by Gerstner (2010) while resembling the empirical
model suggested by Azadi et al (2010)
Print Quality Test Results
Print Gloss
Fig 8 shows that the average print gloss of the model
coated paper was significantly reduced as the bulk thermal
conductivity of the corresponding type of coating layer
increases This suggests that the bulk thermal conductivity
of the coating layers affect the fusing process of toner
which includes toner coalescence melting and spreading
similar to what is concluded by Azadi et al (2008) One
possible explanation is that when the coating bulk thermal
conductivity is lower the coating plays the role of a heat
barrier (dissipating less heat to the base paper) This helps
the toner layer to reach uniformly its melting temperature
and allows the toner layer to level off evenly As a result a
ldquomirror-likerdquo surface is thus created and a high print gloss
is obtained
Interestingly thermal diffusivity of the coating layer gave
a weaker correlation to print gloss with R2 around 052 It
might be due to the fact that thermal diffusivity deals
mostly with the heat flow in the coating layer itself while
print gloss is mostly determined by the heat flow at the
tonercoating interface which thermal conductivity might
be more important However this remains to be confirmed
by further studies
Toner Adhesion
The results of the toner adhesion test show that the amount
of toner removed is affected by the peeling speed of the
Scotch tape Therefore the minimum percentages of toner
remained (adhered) on the coated paper samples at all
peeling speeds were taken for the study These data are
listed in Table 2 and plotted in Fig 9 It shows no
correlation between the percentage of toners remained on
Fig 8 Effect of Bulk Thermal Conductivity of the Coating Layers on Average Print Gloss (in ) of the Coated Papers
Fig 9 Effect of Bulk Thermal Conductivity of the Coating Layers on Toner Adhesion on the Coated Papers
Table 2 Minimum Toner Adhesion on Coated Papers
the coated paper and the bulk thermal conductivity of the
corresponding type of coating layer A similar comparison
was done by Gerstner et al
(2009) and no definite
correlation was found either As explained by Kianercy
(2004) and Sipi (2001) only three factors have been found
to have significant impacts on toner adhesion which are
surface tension of paper toner viscosity at the tonerpaper
interface and fusing speed
Pair-wise Visual Ranking
The result of the visual ranking test shows that for coating
layers with 10 pph of latex the CCHP-10 coating provides
the best print quality and the CPDG-10 coating provides
the worst print quality Among the HC90 coating layers
with different latex concentrations the HC90-10 and
Sample Minimum Toner Remained ()
HC90-10 987 HC90-18 946 HC90-25 872 HC60-10 218 CCHP-10 999 CPDG-10 811
PAPER PHYSICS
456 Nordic Pulp and Paper Research Journal Vol 27 no22012
Fig 10 Effect of Bulk Thermal Conductivity of the Coating Layers on Average Ranking Score of the Printed Coated Papers
Table 3 Summary of the Print Quality Test Results
HC90-18 coating provide significantly better print quality
than the one made with 25 pph of latex However no
correlation was found between print quality (quantified by
the average ranking score) of a sample with the bulk
thermal conductivity of the coating layers see Fig 10
These findings suggest that there are other factors which
have a more significant effect on the print quality of coated
paper However this is beyond the scope of this study
A summary of the print quality test results (Table 3)
reveals that the coating layer formulated with Covercarb
HP pigment and 10 pph of latex has the best ranking in all
three tests Therefore with its relatively low thermal
conductivity this coating formulation is the best candidate
among the ones studied for use in xerography printing
Conclusions The effects of coating formulations on thermal
characteristics of the coating layers were systematically
studied for assessing their impact on xerographic toner
fusion onto the coated papers It was shown that porosity is
a key parameter in the design of a coating layer for heat
transfer applications The latex concentration in the coating
formulation plays a significant role as it determines the
overall porosity of the coating layers Therefore in order
for the coating layer to act as a heat barrier (and provide
sufficient uniform heat transfer to the toner layer) it needs
to have an acceptably high porosity or a low latex
concentration The particle size distribution (narrow PSD)
and morphology (high shape factor) of pigments also affect
positively the porosity and thus the overall thermal
characteristics of the coating layers However the median
particle size of pigments did not show any significant
effect It was also found that the bulk thermal conductivity
of the coating layers can be accurately predicted by a
simple geometric mean model based on the pigment latex
and air volume contents
A 75˚ TAPPI print gloss measurement a toner adhesion
test using an IGT printability tester and a pair-wise visual
ranking test were performed on paper samples coated with
model coating colours and printed with 100 solid black
by xerography The print gloss of coated papers was
significantly improved when the coating bulk thermal
conductivity was low This is attributed to the insulating
effect of the coating thus providing a more uniform toner
fusion No other correlation was found between the print
quality and thermal properties of the samples
Lastly it was found that the coating made of Covercarb
HP a narrow PSD pigment and 10 pph of latex gave a
relatively low thermal conductivity and the best ranking in
all three print quality tests Therefore among all the
formulations tested this coating is the best candidate for
coated paper applications in xerography
Acknowledgements The financial and technical supports from NSERC IPS Scholarship FPInnovations Xerox Research Center of Canada and Surface Science Consortium at the Pulp and Paper Centre University of Toronto are gratefully acknowledged
Literature
Azadi P (2007) Modeling of mechanical and thermal responses of paper coatings under compression using discrete element method Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada
Azadi P Yan N Farnood R (2008) Discrete Element Modeling of the Transient Heat Transfer and Toner Fusing Process in the Xerographic Printing of Coated Papers Computers amp Chemical Engineering 32(12) 3238-3245
Azadi P Nunnari S Farnood R Kortschot M Yan N (2009) High speed compression of highly filled thin composites effect of binder content and stiffness Progress in Organic Coatings 64(4) 356-360
Azadi P Farnood R Yan N (2010) FEM-DEM Modeling of Thermal Conductivity of Porous Pigmented Coatings Computational Materials Science 49(2) 392-399
Bandyopadhay A Ramarao BV Shih EC (2001) Transient response of a paper sheet subjected to a traveling thermal pulse evolution of temperature moisture and pressure fields Journal of Imaging Science and Technology 45(6) 598-608
Bouguerra A Laurent JP Goual M Queneudec M (1997) The measurement of the thermal conductivity of solid aggregates using the transient plane source technique Journal of Physics D Applied Physics 30 2900-2904
Ranking (Best to Worst)
Print Gloss
Toner Adhesion
Visual Ranking
1 CCHP-10 CCHP-10 CCHP-10 2 CPDG-10 HC90-10 HC90-10 3 HC90-10 HC90-18 HC90-18 4 HC90-18 HC90-25 HC60-10 5 HC60-10 CPDG-10 CPDG-10 6 HC90-25 HC60-10 HC90-25
PAPER PHYSICS
Nordic Pulp and Paper Research Journal Vol 27 no22012 457
Cormier L Zou X (2008) Toner fusion in electrophotographic printing ndash issues from Papricanrsquos perspectives FPInnovations Paprican Division Pointe-Claire QC February 8 2008
CRC Handbook of Chemistry and Physics (2009) 89th ed Taylor amp Francis Group
Di Risio S Yan N (2006) Characterizing Coating Pore Structures of Paper Using Scanning Probe Microscopyrdquo TAPPI Journal 5(3) 9-14
Di Risio S Yan N (2006) Characterizing Coating Layer Z-directional Binder Distribution in Paper Using Atomic Force Microscopy Colloids and Surfaces A Physicochemical and Engineering Aspects 289(1-3) 65-74
Duke CB Noolandi J Thieret T (2002) The surface science of xerography Surface Science 500 1005-1023
Gane PAC Ridgeway CJ Schoelkopf J Bousfield DW (2007) Heat transfer through calcium carbonate-based coating structures observation and model for a thermal fusing process Journal of Pulp and Paper Science 33(2) 60-70
Gerstner P Gane PAC (2009) Considerations for thermally engineered coated printing papers focus on electrophotography Journal of Pulp and Paper Science 35(3-4) 108-117
Gerstner P Paltakari J Gane PAC (2009) Measurement and modeling of heat transfer in paper coating structures Journal of Material Science 44 (2) 483-491
Gerstner P (2010) Heat Transfer Through Porous Multiphase Systems Measurement Modelling and Application in Printing of Coated Papers PhD Thesis Aalto university Helsinki Finland
Kianercy A (2004) Characterizing toner-paper adhesion in xerography Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada
Liang C (2009) Effect of coating formulations on thermal properties of coating layers Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada
Maijala J Putkisto K Pietikaumlinen R Groumln J (2004) Heat transfer during fixation of coating layers in dry surface treatment Nordic Pulp and Paper Research Journal 19(3) 291-299
Malla PB Starr RE Werkin TJ (1999) The effects of kaolin particle size structure clay loading and binder level on glossing and offset print properties ndash A CLC coating study 1999 TAPPI Coating Conference Proceedings Toronto Ontario Canada TAPPI Press
Mitsuya T Kumasaka T (1992) Heat transfer and toner melting in an electrophotographic fuser system Journal of Imaging Science and Technology 36 88-92
Morikawa J Hashimoto T (1998) Thermal diffusivity measurement of papers by an AC joule heating method Polymer International 45(2) 207-210
Niskanen K Simula S (1999) Thermal diffusivity of paper Nordic Pulp and Paper Research Journal 14(3) 236-242
Okomori K Lepoutre P (1998) Effect of pigment size and shape distribution on the cohesion of pigmented coatings 1998 TAPPI CoatingPapermakers Conference New Orleans LA USA TAPPI Atlanta GA USA 819 ndash 835
Parker WJ Jenkins RJ Butler CP Abbott GL (1961) Flash method of determining thermal diffusivity heat capacity and thermal conductivity Journal of Applied Physics 32(9) 1679-1684
Salazer A (2003) On thermal diffusivity European Journal of Physics 24(3) 351-358
Sanders DJ Rutland DF (1996) Effect of paper properties on fusing fix Journal of Imaging Science and Technology 40(2) 175-179
Saxaner NS et al (1999) Thermal conductivity of styrene butadiene rubber compounds with natural rubber prophylactics waste as filler European Polymer Journal 35 1687-1693
Simula S Niskanen K (1998) Thermal diffusivity measurement of non-impact printing paper Journal of Imaging Science and Technology 42(6) 550-553
Sipi KM (2001) Toner layer structure and toner adhesion on coated paper NIP17 International Conference on Digital Printing Technologies Fort Lauderdale FL USA 145-150
Stroumlm G Hornatowska J Changhong X Terasaki O (2010) A novel SEM cross-section analysis of paper coating for separation of latex from void volume Nordic Pulp and Paper Research Journal 25(1) 107-113
Vernhes P Blayo A Bloch J-F Pineaux B (2006) Influence of the thermal field on the fusing step in electrophotographic printing Proceedings of the Technical Association of the Graphic Arts 465-485
Vidal D Zou X Uesaka T (2004) Modeling coating structure development Monte-Carlo deposition of particles with irregular shapes Nordic Pulp and Paper Research Journal 19(4) 420ndash427
Wantanabe J Kohara Y Takahashi S (1980) Effects of clay properties on paper coating structure Tappi 63(1) 43 ndash 46
Webb PA (2001) An introduction to the physical characterization of materials by mercury intrusion porosimetry with emphasis on reduction and presentation of experimental data Micromeritics Instrument Corp January 2001 Retrieved on January 14 2009
httpwwwmicromeriticscomapplicationsarticlesaspx
Zhao S Schabel S (2006) Measurement of thermal properties of paper by a light flash method Das Papier T65 34-39
PAPER PHYSICS
458 Nordic Pulp and Paper Research Journal Vol 27 no22012
Toner Adhesion Test
Toner adhesion on the coated paper samples was measured
using an IGT AIC2 Printability Tester from IGT Testing
Systems Netherlands The printed coated paper specimens
were cut into strips of 15 cm wide A piece of 3M Scotch
Magic Tape 810D green tape was attached on the printed
surface of each strip and was peeled off by the IGT tester
at a constant angle with a force of 650 N and speeds from
05 to 5 ms After peeling the strips were scanned using an
Epson 4990 scanner and the images were converted to
binary black and white images to quantify the number of
white pixels (representing the quantity of toners removed)
The percentage of white pixels over the total number of
pixels on the scanned image was calculated and used to
compare how well toners adhered on each specimen
Pair-wise Visual Ranking
From the printed coated paper samples 2 areas (11 cm x 7
cm) of the solid black print were cut and mounted
individually on white card papers creating 2 batches of
samples for visual evaluation on their print quality 15
participants 6 males and 9 females with normal or
corrected to normal visions and with minimal to plentiful
visual ranking experience participated in this exercise in a
laboratory under controlled environment with a constant
light source Pair-wise method was used to visually rank the
sample prints within the same batch based on the
participantsrsquo perceptions of good print quality For each
pair of samples the number of the one with better print
quality was entered in a score matrix until all the possible
combinations of samples were compared For each sample
the number of entries on the score matrix was counted and
the sample with most entries (ie best print quality) was
given the highest ranking
Results and discussions
Effects of Coating Compositions on Coating Layer Properties
Porosity and Pore Size
Fig 1 shows that the Hydrocarb 90 (HC90) and Hydrocarb
60 (HC60) coating layers have similar porosity of ca 28
vv at 6 pph of latex and ca 3 vv at 25 pph This is
consistent with the porosity obtained by Azadi in the recent
study on coating layer compression (Azadi et al 2009)
Comparing with the Covercarb HP (CCHP) and Capim DG
(CPDG) coating layers the latter two have higher porosity
under the same latex concentration
Overall with the addition of 25 pph of latex the reduction
in porosity for all GCC coating layers (HC90 HC60 and
CCHP) is around 25 vv but is only 16 vv for clay
(CPDG) as compared to the lowest addition level of 6 pph
of latex These data suggest that as the latex concentration
in a coating layer increases its porosity decreases but the
reduction in porosity depends on the type of pigments with
the pore space between platy particles being more difficult
to fill in On the other hand Fig 2 shows that the median
Fig 1 Effect of Latex Concentration on Porosity
Fig 2 Effect of Latex Concentration on Pore Size
pore diameter of all GCC coating layers decreases only for
latex concentration greater than 10 pph This suggests that
before the latex concentration reaches 10 pph adding latex
only reduces the number of pores in the coating layer when
the latex concentration exceeds 10 pph the additional latex
starts to reduce both the number and the diameter of coating
pores This qualitatively agrees with the SEM image
analysis results given in Stroumlm et al (2010) The pore sizes
of CPDG (kaolin) coating layers remain roughly constant
indicating a different internal pore structure
Fig 1 also shows that at the same latex concentration the
HC90 and HC60 coating layers have the same porosity in
spite of their different median pigment particle sizes This
suggests that the pigment particle size has no significant
effect on the porosity of a coating layer This agrees with
the finding from Di Risio (Di Risio Yan 2006) that for
pigments with size around or below 1 microm the variation in
coating porosity due to change in pigment size is not
significant (as long as PSD width is similar) However
pigment particle size has an influence on the size of pores
formed in a coating layer Fig 2 shows that the median pore
size of HC60 coating layers is approximately twice as large
as that of HC90 corresponding to the size ratio between
HC60 and HC90 pigments This is reasonable since larger
voids will form among the larger pigment particles if the
two types of pigments have the same morphology and PSD
width Both Di Risio (2006) and Watanabe
et al (1980)
reported a similar trend on kaolin coating layers
PAPER PHYSICS
Nordic Pulp and Paper Research Journal Vol 27 no22012 453
Fig 3 Effect of Latex Concentration on Density (Descending skeletal density Ascending apparent density)
The CCHP coating layers have significantly larger
porosity than the HC90 ones due to the narrower (or steeper)
particle size distribution of CCHP The median diameter of
pores in CCHP coating layers is also larger than that of
HC90 These results are in agreement with Di Risio (2006)
Malla et al (1999) and Okomori et al
(1998) As the PSD
width decreases less fine particles are available to fill the
voids among the coarse particles thus increasing the
porosity and median pore size in a coating layer
A comparison on porosity between CPDG and HC90
coating layers shows that the former has a larger porosity
than the latter at the same latex concentration This is in
agreement with the packing simulation findings by
Vidal et
al (2004) which showed that pigment particles with larger
aspect ratio (ie kaolin) create a bulkier coating structure
Apparent Density
Since adding latex reduces the porosity of coating layers
(Fig 1) an increase in apparent density is thus obtained
(See ascending curves in Fig 3) Also as expected we
observe that pigments with a wider particle size distribution
or with a lower aspect ratio produce significantly denser
coating layers
Thermal Diffusivity
Air has a larger thermal diffusivity (ca 20 mm2s)
(Niskanen Simula 1999) than polymers (with a magnitude
of 01 mm2s) (Salazer 2003) it was shown theoretically
that the effective thermal conductivity of the coating layers
increased with the binder content up to the critical pigment
volume concentration (Vidal Zou 2004) However Fig 4
shows that the experimental thermal diffusivity values of
the HC90 HC60 and CPDG coating layers remain roughly
constant when the latex concentration exceeds 10 pph One
explanation as suggested by Salazar (2003) is that air and
latex can be very compatible in terms of diffusing heat to
each other since they might have similar thermal effusivity
a measure of a materialrsquos ability to exchange thermal
energy with its surroundings Therefore even if there are
less air pores in the coating layers when the latex content
increases heat can still diffuse through the coating layers
Fig 4 Effect of Latex Concentration on Thermal Diffusivity
effectively due to the higher amount of latex surrounding
the pigment particles
It can be seen that the thermal diffusivity of the HC90
coating layer is larger than that of HC60 when the latex
concentration is less than 10 pph but when the latex
concentration exceeds 10 pph the two have approximately
the same thermal diffusivity This might be a combined
effect due to the pigment particle size and the thermal
coupling between air and latex As the median particle size
of HC60 is twice as large as that of HC90 at a low latex
concentration it takes a longer distance for heat to
propagate through the HC60 pigment particles which has a
relatively low thermal diffusivity value (ca 2 mm2s)
(Niskanen Simula 1999) Once the latex concentration
exceeds 10 pph the effect due to the thermal coupling
between air and latex might be so strong that the obstacle
on heat propagation due to pigment particle size becomes
insignificant
Fig 4 also shows that the thermal diffusivity of the HC90
coating layer is larger than that of CCHP and CPDG
samples under the same latex concentration up to 25 pph
This can be due to the lower densities (or higher porosity)
of CCHP or CPDG samples affected by the narrower
particle size distribution or higher aspect ratio of pigments
The lower intrinsic thermal diffusivity value of clay (ca
05 mm2s) (Niskanen Simula 1999) than GCC also
contributes to this result
Specific Heat Capacity
Fig 5 shows that as the latex concentration rises the
specific heat capacity Cp of coating layers increases in a
linear fashion (represented by the solid trend lines) This
increase with additional latex can be explained by the
higher intrinsic Cp value of latex (ca 19 Jg˚C) than those
of pigment (ca 08 Jg˚C) and air (ca 10 Jg˚C) The
linearity of the trend lines is supported by the calculation of
Cp for the coating layers using the simplified 1st order
parallel model shown in Eq 2 (assuming the mass of air
pores is negligible)
latexlatexppigmentpigmentpeffp mCmCC
[2]
PAPER PHYSICS
454 Nordic Pulp and Paper Research Journal Vol 27 no22012
Fig 5 Effect of Latex Concentration on Specific Heat Capacity
where m represents the mass fraction of each coating
component and m=1 The calculated results (the dashed
lines) were found to be in close agreement with the trend
lines of the experimental data This confirms with Salazar
(2003) that the effective specific heat capacity Ceff of a
composite always follows the mixture rule
Therefore it is reasonable that the specific heat capacity
values of HC90 and HC60 coating layers at the same latex
concentration are the same as they have same porosity and
density Hence the pigment particle size is not expected to
have a significant effect on the bulk specific heat capacity
The differences in experimental data shown in Fig 5 might
be due to the sensitivity of the DSC instrument
The Cp of CCHP and CPDG coating layers is also very
close to those of HC90 ones Since the mass fraction of air
is negligible the effects of pigment particle size distribution
or morphology on the specific heat capacity are
insignificant as expected
Bulk (Effective) Thermal Conductivity
Fig 6 shows that as the latex concentration increases up to
25 pph the bulk thermal conductivity of all coating layers
increases As explained earlier adding latex in a coating
layer results in two effects on a coating structure (1)
increasing the volume fraction of latex and thus reducing
the volume fraction of air and (2) breaking the air pores
down to smaller sizes Both latex and air have much lower
intrinsic thermal conductivity values (ca 020 WmK
(Saxaner et al 1999) and 0026 WmK (CRC 2009)
respectively) than pigments (2ndash5 WmK) (Bouguerra
1997) but the reduction in the pore volume (ie porosity) is
more significant than the increase in the latex volume In
addition having smaller pores in the coating layer means
that the pigment particles have a higher chance to be
connected creating a better channel for heat transfer
Changing the median pigment particle size between
HC90 and HC60 coating layers does not result in a change
in the apparent density specific heat capacity or thermal
diffusivity (when the latex concentration exceeds 10 pph)
of the coating layers formed Therefore the bulk thermal
Fig 6 Effect of Latex Concentration on Thermal Conductivity
conductivity of the two groups of coating layers are the
same meaning that pigment particle size alone does not
have a significant effect
Between HC90 and CCHP coating layers using pigments
with a wider particle size distribution (HC90) results in an
increased apparent density an unchanged specific heat
capacity and a higher thermal diffusivity value for the
coating layers formed Therefore the bulk thermal
conductivity of HC90 samples is higher than that of CCHP
Lastly a CPDG coating layer has lower apparent density
and thermal diffusivity but higher specific heat capacity
than a HC90 coating layer at the same latex concentration
The intrinsic thermal properties of clay (CPDG) contribute
greatly to these results However the higher aspect ratio of
the CPDG pigment does contribute to a bulkier coating
structure and therefore affects the thermal diffusivity of
the structure The combined effect is a bulk thermal
conductivity of the CPDG coating layers lower than that of
HC90
Modelling Thermal Conductivity by Geometric Mean
The theoretical bulk thermal conductivity of each coating
layer sample was modeled by calculating the geometric
mean of the K values of pigment latex and air based on
their volume fraction v as Eq 3
airlatexpigment v
air
v
latex
v
pigmenteff KKKK [3]
where Kpigment = 26 WmK for GCC or 16 WmK for
kaolin
Klatex = 020 WmK
Kair = 0026 WmK
vpigment and vlatex are derived from the porosity (vair)
and the pigment to latex mass ratio with their
individual density given 1v
Fig 7 shows that the geometric mean model provides very
good fittings of the experimental data points for the
different pigments and latex concentrations studied This
shows that the bulk thermal conductivity of the coatings
can be well predicted by the geometric mean model
Furthermore it shows that the thermal conductivity only
PAPER PHYSICS
Nordic Pulp and Paper Research Journal Vol 27 no22012 455
Fig 7 Modelling Thermal Conductivity by the Geometric Mean Model
depends on the intrinsic thermal conductivities of the
coating constituents and their respectively volume fractions
(the latter being affected by the PSD and the shape of the
pigment used) In fact this model constitutes a much
simpler model than the Lumped Parameter model proposed
recently by Gerstner (2010) while resembling the empirical
model suggested by Azadi et al (2010)
Print Quality Test Results
Print Gloss
Fig 8 shows that the average print gloss of the model
coated paper was significantly reduced as the bulk thermal
conductivity of the corresponding type of coating layer
increases This suggests that the bulk thermal conductivity
of the coating layers affect the fusing process of toner
which includes toner coalescence melting and spreading
similar to what is concluded by Azadi et al (2008) One
possible explanation is that when the coating bulk thermal
conductivity is lower the coating plays the role of a heat
barrier (dissipating less heat to the base paper) This helps
the toner layer to reach uniformly its melting temperature
and allows the toner layer to level off evenly As a result a
ldquomirror-likerdquo surface is thus created and a high print gloss
is obtained
Interestingly thermal diffusivity of the coating layer gave
a weaker correlation to print gloss with R2 around 052 It
might be due to the fact that thermal diffusivity deals
mostly with the heat flow in the coating layer itself while
print gloss is mostly determined by the heat flow at the
tonercoating interface which thermal conductivity might
be more important However this remains to be confirmed
by further studies
Toner Adhesion
The results of the toner adhesion test show that the amount
of toner removed is affected by the peeling speed of the
Scotch tape Therefore the minimum percentages of toner
remained (adhered) on the coated paper samples at all
peeling speeds were taken for the study These data are
listed in Table 2 and plotted in Fig 9 It shows no
correlation between the percentage of toners remained on
Fig 8 Effect of Bulk Thermal Conductivity of the Coating Layers on Average Print Gloss (in ) of the Coated Papers
Fig 9 Effect of Bulk Thermal Conductivity of the Coating Layers on Toner Adhesion on the Coated Papers
Table 2 Minimum Toner Adhesion on Coated Papers
the coated paper and the bulk thermal conductivity of the
corresponding type of coating layer A similar comparison
was done by Gerstner et al
(2009) and no definite
correlation was found either As explained by Kianercy
(2004) and Sipi (2001) only three factors have been found
to have significant impacts on toner adhesion which are
surface tension of paper toner viscosity at the tonerpaper
interface and fusing speed
Pair-wise Visual Ranking
The result of the visual ranking test shows that for coating
layers with 10 pph of latex the CCHP-10 coating provides
the best print quality and the CPDG-10 coating provides
the worst print quality Among the HC90 coating layers
with different latex concentrations the HC90-10 and
Sample Minimum Toner Remained ()
HC90-10 987 HC90-18 946 HC90-25 872 HC60-10 218 CCHP-10 999 CPDG-10 811
PAPER PHYSICS
456 Nordic Pulp and Paper Research Journal Vol 27 no22012
Fig 10 Effect of Bulk Thermal Conductivity of the Coating Layers on Average Ranking Score of the Printed Coated Papers
Table 3 Summary of the Print Quality Test Results
HC90-18 coating provide significantly better print quality
than the one made with 25 pph of latex However no
correlation was found between print quality (quantified by
the average ranking score) of a sample with the bulk
thermal conductivity of the coating layers see Fig 10
These findings suggest that there are other factors which
have a more significant effect on the print quality of coated
paper However this is beyond the scope of this study
A summary of the print quality test results (Table 3)
reveals that the coating layer formulated with Covercarb
HP pigment and 10 pph of latex has the best ranking in all
three tests Therefore with its relatively low thermal
conductivity this coating formulation is the best candidate
among the ones studied for use in xerography printing
Conclusions The effects of coating formulations on thermal
characteristics of the coating layers were systematically
studied for assessing their impact on xerographic toner
fusion onto the coated papers It was shown that porosity is
a key parameter in the design of a coating layer for heat
transfer applications The latex concentration in the coating
formulation plays a significant role as it determines the
overall porosity of the coating layers Therefore in order
for the coating layer to act as a heat barrier (and provide
sufficient uniform heat transfer to the toner layer) it needs
to have an acceptably high porosity or a low latex
concentration The particle size distribution (narrow PSD)
and morphology (high shape factor) of pigments also affect
positively the porosity and thus the overall thermal
characteristics of the coating layers However the median
particle size of pigments did not show any significant
effect It was also found that the bulk thermal conductivity
of the coating layers can be accurately predicted by a
simple geometric mean model based on the pigment latex
and air volume contents
A 75˚ TAPPI print gloss measurement a toner adhesion
test using an IGT printability tester and a pair-wise visual
ranking test were performed on paper samples coated with
model coating colours and printed with 100 solid black
by xerography The print gloss of coated papers was
significantly improved when the coating bulk thermal
conductivity was low This is attributed to the insulating
effect of the coating thus providing a more uniform toner
fusion No other correlation was found between the print
quality and thermal properties of the samples
Lastly it was found that the coating made of Covercarb
HP a narrow PSD pigment and 10 pph of latex gave a
relatively low thermal conductivity and the best ranking in
all three print quality tests Therefore among all the
formulations tested this coating is the best candidate for
coated paper applications in xerography
Acknowledgements The financial and technical supports from NSERC IPS Scholarship FPInnovations Xerox Research Center of Canada and Surface Science Consortium at the Pulp and Paper Centre University of Toronto are gratefully acknowledged
Literature
Azadi P (2007) Modeling of mechanical and thermal responses of paper coatings under compression using discrete element method Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada
Azadi P Yan N Farnood R (2008) Discrete Element Modeling of the Transient Heat Transfer and Toner Fusing Process in the Xerographic Printing of Coated Papers Computers amp Chemical Engineering 32(12) 3238-3245
Azadi P Nunnari S Farnood R Kortschot M Yan N (2009) High speed compression of highly filled thin composites effect of binder content and stiffness Progress in Organic Coatings 64(4) 356-360
Azadi P Farnood R Yan N (2010) FEM-DEM Modeling of Thermal Conductivity of Porous Pigmented Coatings Computational Materials Science 49(2) 392-399
Bandyopadhay A Ramarao BV Shih EC (2001) Transient response of a paper sheet subjected to a traveling thermal pulse evolution of temperature moisture and pressure fields Journal of Imaging Science and Technology 45(6) 598-608
Bouguerra A Laurent JP Goual M Queneudec M (1997) The measurement of the thermal conductivity of solid aggregates using the transient plane source technique Journal of Physics D Applied Physics 30 2900-2904
Ranking (Best to Worst)
Print Gloss
Toner Adhesion
Visual Ranking
1 CCHP-10 CCHP-10 CCHP-10 2 CPDG-10 HC90-10 HC90-10 3 HC90-10 HC90-18 HC90-18 4 HC90-18 HC90-25 HC60-10 5 HC60-10 CPDG-10 CPDG-10 6 HC90-25 HC60-10 HC90-25
PAPER PHYSICS
Nordic Pulp and Paper Research Journal Vol 27 no22012 457
Cormier L Zou X (2008) Toner fusion in electrophotographic printing ndash issues from Papricanrsquos perspectives FPInnovations Paprican Division Pointe-Claire QC February 8 2008
CRC Handbook of Chemistry and Physics (2009) 89th ed Taylor amp Francis Group
Di Risio S Yan N (2006) Characterizing Coating Pore Structures of Paper Using Scanning Probe Microscopyrdquo TAPPI Journal 5(3) 9-14
Di Risio S Yan N (2006) Characterizing Coating Layer Z-directional Binder Distribution in Paper Using Atomic Force Microscopy Colloids and Surfaces A Physicochemical and Engineering Aspects 289(1-3) 65-74
Duke CB Noolandi J Thieret T (2002) The surface science of xerography Surface Science 500 1005-1023
Gane PAC Ridgeway CJ Schoelkopf J Bousfield DW (2007) Heat transfer through calcium carbonate-based coating structures observation and model for a thermal fusing process Journal of Pulp and Paper Science 33(2) 60-70
Gerstner P Gane PAC (2009) Considerations for thermally engineered coated printing papers focus on electrophotography Journal of Pulp and Paper Science 35(3-4) 108-117
Gerstner P Paltakari J Gane PAC (2009) Measurement and modeling of heat transfer in paper coating structures Journal of Material Science 44 (2) 483-491
Gerstner P (2010) Heat Transfer Through Porous Multiphase Systems Measurement Modelling and Application in Printing of Coated Papers PhD Thesis Aalto university Helsinki Finland
Kianercy A (2004) Characterizing toner-paper adhesion in xerography Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada
Liang C (2009) Effect of coating formulations on thermal properties of coating layers Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada
Maijala J Putkisto K Pietikaumlinen R Groumln J (2004) Heat transfer during fixation of coating layers in dry surface treatment Nordic Pulp and Paper Research Journal 19(3) 291-299
Malla PB Starr RE Werkin TJ (1999) The effects of kaolin particle size structure clay loading and binder level on glossing and offset print properties ndash A CLC coating study 1999 TAPPI Coating Conference Proceedings Toronto Ontario Canada TAPPI Press
Mitsuya T Kumasaka T (1992) Heat transfer and toner melting in an electrophotographic fuser system Journal of Imaging Science and Technology 36 88-92
Morikawa J Hashimoto T (1998) Thermal diffusivity measurement of papers by an AC joule heating method Polymer International 45(2) 207-210
Niskanen K Simula S (1999) Thermal diffusivity of paper Nordic Pulp and Paper Research Journal 14(3) 236-242
Okomori K Lepoutre P (1998) Effect of pigment size and shape distribution on the cohesion of pigmented coatings 1998 TAPPI CoatingPapermakers Conference New Orleans LA USA TAPPI Atlanta GA USA 819 ndash 835
Parker WJ Jenkins RJ Butler CP Abbott GL (1961) Flash method of determining thermal diffusivity heat capacity and thermal conductivity Journal of Applied Physics 32(9) 1679-1684
Salazer A (2003) On thermal diffusivity European Journal of Physics 24(3) 351-358
Sanders DJ Rutland DF (1996) Effect of paper properties on fusing fix Journal of Imaging Science and Technology 40(2) 175-179
Saxaner NS et al (1999) Thermal conductivity of styrene butadiene rubber compounds with natural rubber prophylactics waste as filler European Polymer Journal 35 1687-1693
Simula S Niskanen K (1998) Thermal diffusivity measurement of non-impact printing paper Journal of Imaging Science and Technology 42(6) 550-553
Sipi KM (2001) Toner layer structure and toner adhesion on coated paper NIP17 International Conference on Digital Printing Technologies Fort Lauderdale FL USA 145-150
Stroumlm G Hornatowska J Changhong X Terasaki O (2010) A novel SEM cross-section analysis of paper coating for separation of latex from void volume Nordic Pulp and Paper Research Journal 25(1) 107-113
Vernhes P Blayo A Bloch J-F Pineaux B (2006) Influence of the thermal field on the fusing step in electrophotographic printing Proceedings of the Technical Association of the Graphic Arts 465-485
Vidal D Zou X Uesaka T (2004) Modeling coating structure development Monte-Carlo deposition of particles with irregular shapes Nordic Pulp and Paper Research Journal 19(4) 420ndash427
Wantanabe J Kohara Y Takahashi S (1980) Effects of clay properties on paper coating structure Tappi 63(1) 43 ndash 46
Webb PA (2001) An introduction to the physical characterization of materials by mercury intrusion porosimetry with emphasis on reduction and presentation of experimental data Micromeritics Instrument Corp January 2001 Retrieved on January 14 2009
httpwwwmicromeriticscomapplicationsarticlesaspx
Zhao S Schabel S (2006) Measurement of thermal properties of paper by a light flash method Das Papier T65 34-39
PAPER PHYSICS
458 Nordic Pulp and Paper Research Journal Vol 27 no22012
Fig 3 Effect of Latex Concentration on Density (Descending skeletal density Ascending apparent density)
The CCHP coating layers have significantly larger
porosity than the HC90 ones due to the narrower (or steeper)
particle size distribution of CCHP The median diameter of
pores in CCHP coating layers is also larger than that of
HC90 These results are in agreement with Di Risio (2006)
Malla et al (1999) and Okomori et al
(1998) As the PSD
width decreases less fine particles are available to fill the
voids among the coarse particles thus increasing the
porosity and median pore size in a coating layer
A comparison on porosity between CPDG and HC90
coating layers shows that the former has a larger porosity
than the latter at the same latex concentration This is in
agreement with the packing simulation findings by
Vidal et
al (2004) which showed that pigment particles with larger
aspect ratio (ie kaolin) create a bulkier coating structure
Apparent Density
Since adding latex reduces the porosity of coating layers
(Fig 1) an increase in apparent density is thus obtained
(See ascending curves in Fig 3) Also as expected we
observe that pigments with a wider particle size distribution
or with a lower aspect ratio produce significantly denser
coating layers
Thermal Diffusivity
Air has a larger thermal diffusivity (ca 20 mm2s)
(Niskanen Simula 1999) than polymers (with a magnitude
of 01 mm2s) (Salazer 2003) it was shown theoretically
that the effective thermal conductivity of the coating layers
increased with the binder content up to the critical pigment
volume concentration (Vidal Zou 2004) However Fig 4
shows that the experimental thermal diffusivity values of
the HC90 HC60 and CPDG coating layers remain roughly
constant when the latex concentration exceeds 10 pph One
explanation as suggested by Salazar (2003) is that air and
latex can be very compatible in terms of diffusing heat to
each other since they might have similar thermal effusivity
a measure of a materialrsquos ability to exchange thermal
energy with its surroundings Therefore even if there are
less air pores in the coating layers when the latex content
increases heat can still diffuse through the coating layers
Fig 4 Effect of Latex Concentration on Thermal Diffusivity
effectively due to the higher amount of latex surrounding
the pigment particles
It can be seen that the thermal diffusivity of the HC90
coating layer is larger than that of HC60 when the latex
concentration is less than 10 pph but when the latex
concentration exceeds 10 pph the two have approximately
the same thermal diffusivity This might be a combined
effect due to the pigment particle size and the thermal
coupling between air and latex As the median particle size
of HC60 is twice as large as that of HC90 at a low latex
concentration it takes a longer distance for heat to
propagate through the HC60 pigment particles which has a
relatively low thermal diffusivity value (ca 2 mm2s)
(Niskanen Simula 1999) Once the latex concentration
exceeds 10 pph the effect due to the thermal coupling
between air and latex might be so strong that the obstacle
on heat propagation due to pigment particle size becomes
insignificant
Fig 4 also shows that the thermal diffusivity of the HC90
coating layer is larger than that of CCHP and CPDG
samples under the same latex concentration up to 25 pph
This can be due to the lower densities (or higher porosity)
of CCHP or CPDG samples affected by the narrower
particle size distribution or higher aspect ratio of pigments
The lower intrinsic thermal diffusivity value of clay (ca
05 mm2s) (Niskanen Simula 1999) than GCC also
contributes to this result
Specific Heat Capacity
Fig 5 shows that as the latex concentration rises the
specific heat capacity Cp of coating layers increases in a
linear fashion (represented by the solid trend lines) This
increase with additional latex can be explained by the
higher intrinsic Cp value of latex (ca 19 Jg˚C) than those
of pigment (ca 08 Jg˚C) and air (ca 10 Jg˚C) The
linearity of the trend lines is supported by the calculation of
Cp for the coating layers using the simplified 1st order
parallel model shown in Eq 2 (assuming the mass of air
pores is negligible)
latexlatexppigmentpigmentpeffp mCmCC
[2]
PAPER PHYSICS
454 Nordic Pulp and Paper Research Journal Vol 27 no22012
Fig 5 Effect of Latex Concentration on Specific Heat Capacity
where m represents the mass fraction of each coating
component and m=1 The calculated results (the dashed
lines) were found to be in close agreement with the trend
lines of the experimental data This confirms with Salazar
(2003) that the effective specific heat capacity Ceff of a
composite always follows the mixture rule
Therefore it is reasonable that the specific heat capacity
values of HC90 and HC60 coating layers at the same latex
concentration are the same as they have same porosity and
density Hence the pigment particle size is not expected to
have a significant effect on the bulk specific heat capacity
The differences in experimental data shown in Fig 5 might
be due to the sensitivity of the DSC instrument
The Cp of CCHP and CPDG coating layers is also very
close to those of HC90 ones Since the mass fraction of air
is negligible the effects of pigment particle size distribution
or morphology on the specific heat capacity are
insignificant as expected
Bulk (Effective) Thermal Conductivity
Fig 6 shows that as the latex concentration increases up to
25 pph the bulk thermal conductivity of all coating layers
increases As explained earlier adding latex in a coating
layer results in two effects on a coating structure (1)
increasing the volume fraction of latex and thus reducing
the volume fraction of air and (2) breaking the air pores
down to smaller sizes Both latex and air have much lower
intrinsic thermal conductivity values (ca 020 WmK
(Saxaner et al 1999) and 0026 WmK (CRC 2009)
respectively) than pigments (2ndash5 WmK) (Bouguerra
1997) but the reduction in the pore volume (ie porosity) is
more significant than the increase in the latex volume In
addition having smaller pores in the coating layer means
that the pigment particles have a higher chance to be
connected creating a better channel for heat transfer
Changing the median pigment particle size between
HC90 and HC60 coating layers does not result in a change
in the apparent density specific heat capacity or thermal
diffusivity (when the latex concentration exceeds 10 pph)
of the coating layers formed Therefore the bulk thermal
Fig 6 Effect of Latex Concentration on Thermal Conductivity
conductivity of the two groups of coating layers are the
same meaning that pigment particle size alone does not
have a significant effect
Between HC90 and CCHP coating layers using pigments
with a wider particle size distribution (HC90) results in an
increased apparent density an unchanged specific heat
capacity and a higher thermal diffusivity value for the
coating layers formed Therefore the bulk thermal
conductivity of HC90 samples is higher than that of CCHP
Lastly a CPDG coating layer has lower apparent density
and thermal diffusivity but higher specific heat capacity
than a HC90 coating layer at the same latex concentration
The intrinsic thermal properties of clay (CPDG) contribute
greatly to these results However the higher aspect ratio of
the CPDG pigment does contribute to a bulkier coating
structure and therefore affects the thermal diffusivity of
the structure The combined effect is a bulk thermal
conductivity of the CPDG coating layers lower than that of
HC90
Modelling Thermal Conductivity by Geometric Mean
The theoretical bulk thermal conductivity of each coating
layer sample was modeled by calculating the geometric
mean of the K values of pigment latex and air based on
their volume fraction v as Eq 3
airlatexpigment v
air
v
latex
v
pigmenteff KKKK [3]
where Kpigment = 26 WmK for GCC or 16 WmK for
kaolin
Klatex = 020 WmK
Kair = 0026 WmK
vpigment and vlatex are derived from the porosity (vair)
and the pigment to latex mass ratio with their
individual density given 1v
Fig 7 shows that the geometric mean model provides very
good fittings of the experimental data points for the
different pigments and latex concentrations studied This
shows that the bulk thermal conductivity of the coatings
can be well predicted by the geometric mean model
Furthermore it shows that the thermal conductivity only
PAPER PHYSICS
Nordic Pulp and Paper Research Journal Vol 27 no22012 455
Fig 7 Modelling Thermal Conductivity by the Geometric Mean Model
depends on the intrinsic thermal conductivities of the
coating constituents and their respectively volume fractions
(the latter being affected by the PSD and the shape of the
pigment used) In fact this model constitutes a much
simpler model than the Lumped Parameter model proposed
recently by Gerstner (2010) while resembling the empirical
model suggested by Azadi et al (2010)
Print Quality Test Results
Print Gloss
Fig 8 shows that the average print gloss of the model
coated paper was significantly reduced as the bulk thermal
conductivity of the corresponding type of coating layer
increases This suggests that the bulk thermal conductivity
of the coating layers affect the fusing process of toner
which includes toner coalescence melting and spreading
similar to what is concluded by Azadi et al (2008) One
possible explanation is that when the coating bulk thermal
conductivity is lower the coating plays the role of a heat
barrier (dissipating less heat to the base paper) This helps
the toner layer to reach uniformly its melting temperature
and allows the toner layer to level off evenly As a result a
ldquomirror-likerdquo surface is thus created and a high print gloss
is obtained
Interestingly thermal diffusivity of the coating layer gave
a weaker correlation to print gloss with R2 around 052 It
might be due to the fact that thermal diffusivity deals
mostly with the heat flow in the coating layer itself while
print gloss is mostly determined by the heat flow at the
tonercoating interface which thermal conductivity might
be more important However this remains to be confirmed
by further studies
Toner Adhesion
The results of the toner adhesion test show that the amount
of toner removed is affected by the peeling speed of the
Scotch tape Therefore the minimum percentages of toner
remained (adhered) on the coated paper samples at all
peeling speeds were taken for the study These data are
listed in Table 2 and plotted in Fig 9 It shows no
correlation between the percentage of toners remained on
Fig 8 Effect of Bulk Thermal Conductivity of the Coating Layers on Average Print Gloss (in ) of the Coated Papers
Fig 9 Effect of Bulk Thermal Conductivity of the Coating Layers on Toner Adhesion on the Coated Papers
Table 2 Minimum Toner Adhesion on Coated Papers
the coated paper and the bulk thermal conductivity of the
corresponding type of coating layer A similar comparison
was done by Gerstner et al
(2009) and no definite
correlation was found either As explained by Kianercy
(2004) and Sipi (2001) only three factors have been found
to have significant impacts on toner adhesion which are
surface tension of paper toner viscosity at the tonerpaper
interface and fusing speed
Pair-wise Visual Ranking
The result of the visual ranking test shows that for coating
layers with 10 pph of latex the CCHP-10 coating provides
the best print quality and the CPDG-10 coating provides
the worst print quality Among the HC90 coating layers
with different latex concentrations the HC90-10 and
Sample Minimum Toner Remained ()
HC90-10 987 HC90-18 946 HC90-25 872 HC60-10 218 CCHP-10 999 CPDG-10 811
PAPER PHYSICS
456 Nordic Pulp and Paper Research Journal Vol 27 no22012
Fig 10 Effect of Bulk Thermal Conductivity of the Coating Layers on Average Ranking Score of the Printed Coated Papers
Table 3 Summary of the Print Quality Test Results
HC90-18 coating provide significantly better print quality
than the one made with 25 pph of latex However no
correlation was found between print quality (quantified by
the average ranking score) of a sample with the bulk
thermal conductivity of the coating layers see Fig 10
These findings suggest that there are other factors which
have a more significant effect on the print quality of coated
paper However this is beyond the scope of this study
A summary of the print quality test results (Table 3)
reveals that the coating layer formulated with Covercarb
HP pigment and 10 pph of latex has the best ranking in all
three tests Therefore with its relatively low thermal
conductivity this coating formulation is the best candidate
among the ones studied for use in xerography printing
Conclusions The effects of coating formulations on thermal
characteristics of the coating layers were systematically
studied for assessing their impact on xerographic toner
fusion onto the coated papers It was shown that porosity is
a key parameter in the design of a coating layer for heat
transfer applications The latex concentration in the coating
formulation plays a significant role as it determines the
overall porosity of the coating layers Therefore in order
for the coating layer to act as a heat barrier (and provide
sufficient uniform heat transfer to the toner layer) it needs
to have an acceptably high porosity or a low latex
concentration The particle size distribution (narrow PSD)
and morphology (high shape factor) of pigments also affect
positively the porosity and thus the overall thermal
characteristics of the coating layers However the median
particle size of pigments did not show any significant
effect It was also found that the bulk thermal conductivity
of the coating layers can be accurately predicted by a
simple geometric mean model based on the pigment latex
and air volume contents
A 75˚ TAPPI print gloss measurement a toner adhesion
test using an IGT printability tester and a pair-wise visual
ranking test were performed on paper samples coated with
model coating colours and printed with 100 solid black
by xerography The print gloss of coated papers was
significantly improved when the coating bulk thermal
conductivity was low This is attributed to the insulating
effect of the coating thus providing a more uniform toner
fusion No other correlation was found between the print
quality and thermal properties of the samples
Lastly it was found that the coating made of Covercarb
HP a narrow PSD pigment and 10 pph of latex gave a
relatively low thermal conductivity and the best ranking in
all three print quality tests Therefore among all the
formulations tested this coating is the best candidate for
coated paper applications in xerography
Acknowledgements The financial and technical supports from NSERC IPS Scholarship FPInnovations Xerox Research Center of Canada and Surface Science Consortium at the Pulp and Paper Centre University of Toronto are gratefully acknowledged
Literature
Azadi P (2007) Modeling of mechanical and thermal responses of paper coatings under compression using discrete element method Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada
Azadi P Yan N Farnood R (2008) Discrete Element Modeling of the Transient Heat Transfer and Toner Fusing Process in the Xerographic Printing of Coated Papers Computers amp Chemical Engineering 32(12) 3238-3245
Azadi P Nunnari S Farnood R Kortschot M Yan N (2009) High speed compression of highly filled thin composites effect of binder content and stiffness Progress in Organic Coatings 64(4) 356-360
Azadi P Farnood R Yan N (2010) FEM-DEM Modeling of Thermal Conductivity of Porous Pigmented Coatings Computational Materials Science 49(2) 392-399
Bandyopadhay A Ramarao BV Shih EC (2001) Transient response of a paper sheet subjected to a traveling thermal pulse evolution of temperature moisture and pressure fields Journal of Imaging Science and Technology 45(6) 598-608
Bouguerra A Laurent JP Goual M Queneudec M (1997) The measurement of the thermal conductivity of solid aggregates using the transient plane source technique Journal of Physics D Applied Physics 30 2900-2904
Ranking (Best to Worst)
Print Gloss
Toner Adhesion
Visual Ranking
1 CCHP-10 CCHP-10 CCHP-10 2 CPDG-10 HC90-10 HC90-10 3 HC90-10 HC90-18 HC90-18 4 HC90-18 HC90-25 HC60-10 5 HC60-10 CPDG-10 CPDG-10 6 HC90-25 HC60-10 HC90-25
PAPER PHYSICS
Nordic Pulp and Paper Research Journal Vol 27 no22012 457
Cormier L Zou X (2008) Toner fusion in electrophotographic printing ndash issues from Papricanrsquos perspectives FPInnovations Paprican Division Pointe-Claire QC February 8 2008
CRC Handbook of Chemistry and Physics (2009) 89th ed Taylor amp Francis Group
Di Risio S Yan N (2006) Characterizing Coating Pore Structures of Paper Using Scanning Probe Microscopyrdquo TAPPI Journal 5(3) 9-14
Di Risio S Yan N (2006) Characterizing Coating Layer Z-directional Binder Distribution in Paper Using Atomic Force Microscopy Colloids and Surfaces A Physicochemical and Engineering Aspects 289(1-3) 65-74
Duke CB Noolandi J Thieret T (2002) The surface science of xerography Surface Science 500 1005-1023
Gane PAC Ridgeway CJ Schoelkopf J Bousfield DW (2007) Heat transfer through calcium carbonate-based coating structures observation and model for a thermal fusing process Journal of Pulp and Paper Science 33(2) 60-70
Gerstner P Gane PAC (2009) Considerations for thermally engineered coated printing papers focus on electrophotography Journal of Pulp and Paper Science 35(3-4) 108-117
Gerstner P Paltakari J Gane PAC (2009) Measurement and modeling of heat transfer in paper coating structures Journal of Material Science 44 (2) 483-491
Gerstner P (2010) Heat Transfer Through Porous Multiphase Systems Measurement Modelling and Application in Printing of Coated Papers PhD Thesis Aalto university Helsinki Finland
Kianercy A (2004) Characterizing toner-paper adhesion in xerography Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada
Liang C (2009) Effect of coating formulations on thermal properties of coating layers Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada
Maijala J Putkisto K Pietikaumlinen R Groumln J (2004) Heat transfer during fixation of coating layers in dry surface treatment Nordic Pulp and Paper Research Journal 19(3) 291-299
Malla PB Starr RE Werkin TJ (1999) The effects of kaolin particle size structure clay loading and binder level on glossing and offset print properties ndash A CLC coating study 1999 TAPPI Coating Conference Proceedings Toronto Ontario Canada TAPPI Press
Mitsuya T Kumasaka T (1992) Heat transfer and toner melting in an electrophotographic fuser system Journal of Imaging Science and Technology 36 88-92
Morikawa J Hashimoto T (1998) Thermal diffusivity measurement of papers by an AC joule heating method Polymer International 45(2) 207-210
Niskanen K Simula S (1999) Thermal diffusivity of paper Nordic Pulp and Paper Research Journal 14(3) 236-242
Okomori K Lepoutre P (1998) Effect of pigment size and shape distribution on the cohesion of pigmented coatings 1998 TAPPI CoatingPapermakers Conference New Orleans LA USA TAPPI Atlanta GA USA 819 ndash 835
Parker WJ Jenkins RJ Butler CP Abbott GL (1961) Flash method of determining thermal diffusivity heat capacity and thermal conductivity Journal of Applied Physics 32(9) 1679-1684
Salazer A (2003) On thermal diffusivity European Journal of Physics 24(3) 351-358
Sanders DJ Rutland DF (1996) Effect of paper properties on fusing fix Journal of Imaging Science and Technology 40(2) 175-179
Saxaner NS et al (1999) Thermal conductivity of styrene butadiene rubber compounds with natural rubber prophylactics waste as filler European Polymer Journal 35 1687-1693
Simula S Niskanen K (1998) Thermal diffusivity measurement of non-impact printing paper Journal of Imaging Science and Technology 42(6) 550-553
Sipi KM (2001) Toner layer structure and toner adhesion on coated paper NIP17 International Conference on Digital Printing Technologies Fort Lauderdale FL USA 145-150
Stroumlm G Hornatowska J Changhong X Terasaki O (2010) A novel SEM cross-section analysis of paper coating for separation of latex from void volume Nordic Pulp and Paper Research Journal 25(1) 107-113
Vernhes P Blayo A Bloch J-F Pineaux B (2006) Influence of the thermal field on the fusing step in electrophotographic printing Proceedings of the Technical Association of the Graphic Arts 465-485
Vidal D Zou X Uesaka T (2004) Modeling coating structure development Monte-Carlo deposition of particles with irregular shapes Nordic Pulp and Paper Research Journal 19(4) 420ndash427
Wantanabe J Kohara Y Takahashi S (1980) Effects of clay properties on paper coating structure Tappi 63(1) 43 ndash 46
Webb PA (2001) An introduction to the physical characterization of materials by mercury intrusion porosimetry with emphasis on reduction and presentation of experimental data Micromeritics Instrument Corp January 2001 Retrieved on January 14 2009
httpwwwmicromeriticscomapplicationsarticlesaspx
Zhao S Schabel S (2006) Measurement of thermal properties of paper by a light flash method Das Papier T65 34-39
PAPER PHYSICS
458 Nordic Pulp and Paper Research Journal Vol 27 no22012
Fig 5 Effect of Latex Concentration on Specific Heat Capacity
where m represents the mass fraction of each coating
component and m=1 The calculated results (the dashed
lines) were found to be in close agreement with the trend
lines of the experimental data This confirms with Salazar
(2003) that the effective specific heat capacity Ceff of a
composite always follows the mixture rule
Therefore it is reasonable that the specific heat capacity
values of HC90 and HC60 coating layers at the same latex
concentration are the same as they have same porosity and
density Hence the pigment particle size is not expected to
have a significant effect on the bulk specific heat capacity
The differences in experimental data shown in Fig 5 might
be due to the sensitivity of the DSC instrument
The Cp of CCHP and CPDG coating layers is also very
close to those of HC90 ones Since the mass fraction of air
is negligible the effects of pigment particle size distribution
or morphology on the specific heat capacity are
insignificant as expected
Bulk (Effective) Thermal Conductivity
Fig 6 shows that as the latex concentration increases up to
25 pph the bulk thermal conductivity of all coating layers
increases As explained earlier adding latex in a coating
layer results in two effects on a coating structure (1)
increasing the volume fraction of latex and thus reducing
the volume fraction of air and (2) breaking the air pores
down to smaller sizes Both latex and air have much lower
intrinsic thermal conductivity values (ca 020 WmK
(Saxaner et al 1999) and 0026 WmK (CRC 2009)
respectively) than pigments (2ndash5 WmK) (Bouguerra
1997) but the reduction in the pore volume (ie porosity) is
more significant than the increase in the latex volume In
addition having smaller pores in the coating layer means
that the pigment particles have a higher chance to be
connected creating a better channel for heat transfer
Changing the median pigment particle size between
HC90 and HC60 coating layers does not result in a change
in the apparent density specific heat capacity or thermal
diffusivity (when the latex concentration exceeds 10 pph)
of the coating layers formed Therefore the bulk thermal
Fig 6 Effect of Latex Concentration on Thermal Conductivity
conductivity of the two groups of coating layers are the
same meaning that pigment particle size alone does not
have a significant effect
Between HC90 and CCHP coating layers using pigments
with a wider particle size distribution (HC90) results in an
increased apparent density an unchanged specific heat
capacity and a higher thermal diffusivity value for the
coating layers formed Therefore the bulk thermal
conductivity of HC90 samples is higher than that of CCHP
Lastly a CPDG coating layer has lower apparent density
and thermal diffusivity but higher specific heat capacity
than a HC90 coating layer at the same latex concentration
The intrinsic thermal properties of clay (CPDG) contribute
greatly to these results However the higher aspect ratio of
the CPDG pigment does contribute to a bulkier coating
structure and therefore affects the thermal diffusivity of
the structure The combined effect is a bulk thermal
conductivity of the CPDG coating layers lower than that of
HC90
Modelling Thermal Conductivity by Geometric Mean
The theoretical bulk thermal conductivity of each coating
layer sample was modeled by calculating the geometric
mean of the K values of pigment latex and air based on
their volume fraction v as Eq 3
airlatexpigment v
air
v
latex
v
pigmenteff KKKK [3]
where Kpigment = 26 WmK for GCC or 16 WmK for
kaolin
Klatex = 020 WmK
Kair = 0026 WmK
vpigment and vlatex are derived from the porosity (vair)
and the pigment to latex mass ratio with their
individual density given 1v
Fig 7 shows that the geometric mean model provides very
good fittings of the experimental data points for the
different pigments and latex concentrations studied This
shows that the bulk thermal conductivity of the coatings
can be well predicted by the geometric mean model
Furthermore it shows that the thermal conductivity only
PAPER PHYSICS
Nordic Pulp and Paper Research Journal Vol 27 no22012 455
Fig 7 Modelling Thermal Conductivity by the Geometric Mean Model
depends on the intrinsic thermal conductivities of the
coating constituents and their respectively volume fractions
(the latter being affected by the PSD and the shape of the
pigment used) In fact this model constitutes a much
simpler model than the Lumped Parameter model proposed
recently by Gerstner (2010) while resembling the empirical
model suggested by Azadi et al (2010)
Print Quality Test Results
Print Gloss
Fig 8 shows that the average print gloss of the model
coated paper was significantly reduced as the bulk thermal
conductivity of the corresponding type of coating layer
increases This suggests that the bulk thermal conductivity
of the coating layers affect the fusing process of toner
which includes toner coalescence melting and spreading
similar to what is concluded by Azadi et al (2008) One
possible explanation is that when the coating bulk thermal
conductivity is lower the coating plays the role of a heat
barrier (dissipating less heat to the base paper) This helps
the toner layer to reach uniformly its melting temperature
and allows the toner layer to level off evenly As a result a
ldquomirror-likerdquo surface is thus created and a high print gloss
is obtained
Interestingly thermal diffusivity of the coating layer gave
a weaker correlation to print gloss with R2 around 052 It
might be due to the fact that thermal diffusivity deals
mostly with the heat flow in the coating layer itself while
print gloss is mostly determined by the heat flow at the
tonercoating interface which thermal conductivity might
be more important However this remains to be confirmed
by further studies
Toner Adhesion
The results of the toner adhesion test show that the amount
of toner removed is affected by the peeling speed of the
Scotch tape Therefore the minimum percentages of toner
remained (adhered) on the coated paper samples at all
peeling speeds were taken for the study These data are
listed in Table 2 and plotted in Fig 9 It shows no
correlation between the percentage of toners remained on
Fig 8 Effect of Bulk Thermal Conductivity of the Coating Layers on Average Print Gloss (in ) of the Coated Papers
Fig 9 Effect of Bulk Thermal Conductivity of the Coating Layers on Toner Adhesion on the Coated Papers
Table 2 Minimum Toner Adhesion on Coated Papers
the coated paper and the bulk thermal conductivity of the
corresponding type of coating layer A similar comparison
was done by Gerstner et al
(2009) and no definite
correlation was found either As explained by Kianercy
(2004) and Sipi (2001) only three factors have been found
to have significant impacts on toner adhesion which are
surface tension of paper toner viscosity at the tonerpaper
interface and fusing speed
Pair-wise Visual Ranking
The result of the visual ranking test shows that for coating
layers with 10 pph of latex the CCHP-10 coating provides
the best print quality and the CPDG-10 coating provides
the worst print quality Among the HC90 coating layers
with different latex concentrations the HC90-10 and
Sample Minimum Toner Remained ()
HC90-10 987 HC90-18 946 HC90-25 872 HC60-10 218 CCHP-10 999 CPDG-10 811
PAPER PHYSICS
456 Nordic Pulp and Paper Research Journal Vol 27 no22012
Fig 10 Effect of Bulk Thermal Conductivity of the Coating Layers on Average Ranking Score of the Printed Coated Papers
Table 3 Summary of the Print Quality Test Results
HC90-18 coating provide significantly better print quality
than the one made with 25 pph of latex However no
correlation was found between print quality (quantified by
the average ranking score) of a sample with the bulk
thermal conductivity of the coating layers see Fig 10
These findings suggest that there are other factors which
have a more significant effect on the print quality of coated
paper However this is beyond the scope of this study
A summary of the print quality test results (Table 3)
reveals that the coating layer formulated with Covercarb
HP pigment and 10 pph of latex has the best ranking in all
three tests Therefore with its relatively low thermal
conductivity this coating formulation is the best candidate
among the ones studied for use in xerography printing
Conclusions The effects of coating formulations on thermal
characteristics of the coating layers were systematically
studied for assessing their impact on xerographic toner
fusion onto the coated papers It was shown that porosity is
a key parameter in the design of a coating layer for heat
transfer applications The latex concentration in the coating
formulation plays a significant role as it determines the
overall porosity of the coating layers Therefore in order
for the coating layer to act as a heat barrier (and provide
sufficient uniform heat transfer to the toner layer) it needs
to have an acceptably high porosity or a low latex
concentration The particle size distribution (narrow PSD)
and morphology (high shape factor) of pigments also affect
positively the porosity and thus the overall thermal
characteristics of the coating layers However the median
particle size of pigments did not show any significant
effect It was also found that the bulk thermal conductivity
of the coating layers can be accurately predicted by a
simple geometric mean model based on the pigment latex
and air volume contents
A 75˚ TAPPI print gloss measurement a toner adhesion
test using an IGT printability tester and a pair-wise visual
ranking test were performed on paper samples coated with
model coating colours and printed with 100 solid black
by xerography The print gloss of coated papers was
significantly improved when the coating bulk thermal
conductivity was low This is attributed to the insulating
effect of the coating thus providing a more uniform toner
fusion No other correlation was found between the print
quality and thermal properties of the samples
Lastly it was found that the coating made of Covercarb
HP a narrow PSD pigment and 10 pph of latex gave a
relatively low thermal conductivity and the best ranking in
all three print quality tests Therefore among all the
formulations tested this coating is the best candidate for
coated paper applications in xerography
Acknowledgements The financial and technical supports from NSERC IPS Scholarship FPInnovations Xerox Research Center of Canada and Surface Science Consortium at the Pulp and Paper Centre University of Toronto are gratefully acknowledged
Literature
Azadi P (2007) Modeling of mechanical and thermal responses of paper coatings under compression using discrete element method Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada
Azadi P Yan N Farnood R (2008) Discrete Element Modeling of the Transient Heat Transfer and Toner Fusing Process in the Xerographic Printing of Coated Papers Computers amp Chemical Engineering 32(12) 3238-3245
Azadi P Nunnari S Farnood R Kortschot M Yan N (2009) High speed compression of highly filled thin composites effect of binder content and stiffness Progress in Organic Coatings 64(4) 356-360
Azadi P Farnood R Yan N (2010) FEM-DEM Modeling of Thermal Conductivity of Porous Pigmented Coatings Computational Materials Science 49(2) 392-399
Bandyopadhay A Ramarao BV Shih EC (2001) Transient response of a paper sheet subjected to a traveling thermal pulse evolution of temperature moisture and pressure fields Journal of Imaging Science and Technology 45(6) 598-608
Bouguerra A Laurent JP Goual M Queneudec M (1997) The measurement of the thermal conductivity of solid aggregates using the transient plane source technique Journal of Physics D Applied Physics 30 2900-2904
Ranking (Best to Worst)
Print Gloss
Toner Adhesion
Visual Ranking
1 CCHP-10 CCHP-10 CCHP-10 2 CPDG-10 HC90-10 HC90-10 3 HC90-10 HC90-18 HC90-18 4 HC90-18 HC90-25 HC60-10 5 HC60-10 CPDG-10 CPDG-10 6 HC90-25 HC60-10 HC90-25
PAPER PHYSICS
Nordic Pulp and Paper Research Journal Vol 27 no22012 457
Cormier L Zou X (2008) Toner fusion in electrophotographic printing ndash issues from Papricanrsquos perspectives FPInnovations Paprican Division Pointe-Claire QC February 8 2008
CRC Handbook of Chemistry and Physics (2009) 89th ed Taylor amp Francis Group
Di Risio S Yan N (2006) Characterizing Coating Pore Structures of Paper Using Scanning Probe Microscopyrdquo TAPPI Journal 5(3) 9-14
Di Risio S Yan N (2006) Characterizing Coating Layer Z-directional Binder Distribution in Paper Using Atomic Force Microscopy Colloids and Surfaces A Physicochemical and Engineering Aspects 289(1-3) 65-74
Duke CB Noolandi J Thieret T (2002) The surface science of xerography Surface Science 500 1005-1023
Gane PAC Ridgeway CJ Schoelkopf J Bousfield DW (2007) Heat transfer through calcium carbonate-based coating structures observation and model for a thermal fusing process Journal of Pulp and Paper Science 33(2) 60-70
Gerstner P Gane PAC (2009) Considerations for thermally engineered coated printing papers focus on electrophotography Journal of Pulp and Paper Science 35(3-4) 108-117
Gerstner P Paltakari J Gane PAC (2009) Measurement and modeling of heat transfer in paper coating structures Journal of Material Science 44 (2) 483-491
Gerstner P (2010) Heat Transfer Through Porous Multiphase Systems Measurement Modelling and Application in Printing of Coated Papers PhD Thesis Aalto university Helsinki Finland
Kianercy A (2004) Characterizing toner-paper adhesion in xerography Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada
Liang C (2009) Effect of coating formulations on thermal properties of coating layers Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada
Maijala J Putkisto K Pietikaumlinen R Groumln J (2004) Heat transfer during fixation of coating layers in dry surface treatment Nordic Pulp and Paper Research Journal 19(3) 291-299
Malla PB Starr RE Werkin TJ (1999) The effects of kaolin particle size structure clay loading and binder level on glossing and offset print properties ndash A CLC coating study 1999 TAPPI Coating Conference Proceedings Toronto Ontario Canada TAPPI Press
Mitsuya T Kumasaka T (1992) Heat transfer and toner melting in an electrophotographic fuser system Journal of Imaging Science and Technology 36 88-92
Morikawa J Hashimoto T (1998) Thermal diffusivity measurement of papers by an AC joule heating method Polymer International 45(2) 207-210
Niskanen K Simula S (1999) Thermal diffusivity of paper Nordic Pulp and Paper Research Journal 14(3) 236-242
Okomori K Lepoutre P (1998) Effect of pigment size and shape distribution on the cohesion of pigmented coatings 1998 TAPPI CoatingPapermakers Conference New Orleans LA USA TAPPI Atlanta GA USA 819 ndash 835
Parker WJ Jenkins RJ Butler CP Abbott GL (1961) Flash method of determining thermal diffusivity heat capacity and thermal conductivity Journal of Applied Physics 32(9) 1679-1684
Salazer A (2003) On thermal diffusivity European Journal of Physics 24(3) 351-358
Sanders DJ Rutland DF (1996) Effect of paper properties on fusing fix Journal of Imaging Science and Technology 40(2) 175-179
Saxaner NS et al (1999) Thermal conductivity of styrene butadiene rubber compounds with natural rubber prophylactics waste as filler European Polymer Journal 35 1687-1693
Simula S Niskanen K (1998) Thermal diffusivity measurement of non-impact printing paper Journal of Imaging Science and Technology 42(6) 550-553
Sipi KM (2001) Toner layer structure and toner adhesion on coated paper NIP17 International Conference on Digital Printing Technologies Fort Lauderdale FL USA 145-150
Stroumlm G Hornatowska J Changhong X Terasaki O (2010) A novel SEM cross-section analysis of paper coating for separation of latex from void volume Nordic Pulp and Paper Research Journal 25(1) 107-113
Vernhes P Blayo A Bloch J-F Pineaux B (2006) Influence of the thermal field on the fusing step in electrophotographic printing Proceedings of the Technical Association of the Graphic Arts 465-485
Vidal D Zou X Uesaka T (2004) Modeling coating structure development Monte-Carlo deposition of particles with irregular shapes Nordic Pulp and Paper Research Journal 19(4) 420ndash427
Wantanabe J Kohara Y Takahashi S (1980) Effects of clay properties on paper coating structure Tappi 63(1) 43 ndash 46
Webb PA (2001) An introduction to the physical characterization of materials by mercury intrusion porosimetry with emphasis on reduction and presentation of experimental data Micromeritics Instrument Corp January 2001 Retrieved on January 14 2009
httpwwwmicromeriticscomapplicationsarticlesaspx
Zhao S Schabel S (2006) Measurement of thermal properties of paper by a light flash method Das Papier T65 34-39
PAPER PHYSICS
458 Nordic Pulp and Paper Research Journal Vol 27 no22012
Fig 7 Modelling Thermal Conductivity by the Geometric Mean Model
depends on the intrinsic thermal conductivities of the
coating constituents and their respectively volume fractions
(the latter being affected by the PSD and the shape of the
pigment used) In fact this model constitutes a much
simpler model than the Lumped Parameter model proposed
recently by Gerstner (2010) while resembling the empirical
model suggested by Azadi et al (2010)
Print Quality Test Results
Print Gloss
Fig 8 shows that the average print gloss of the model
coated paper was significantly reduced as the bulk thermal
conductivity of the corresponding type of coating layer
increases This suggests that the bulk thermal conductivity
of the coating layers affect the fusing process of toner
which includes toner coalescence melting and spreading
similar to what is concluded by Azadi et al (2008) One
possible explanation is that when the coating bulk thermal
conductivity is lower the coating plays the role of a heat
barrier (dissipating less heat to the base paper) This helps
the toner layer to reach uniformly its melting temperature
and allows the toner layer to level off evenly As a result a
ldquomirror-likerdquo surface is thus created and a high print gloss
is obtained
Interestingly thermal diffusivity of the coating layer gave
a weaker correlation to print gloss with R2 around 052 It
might be due to the fact that thermal diffusivity deals
mostly with the heat flow in the coating layer itself while
print gloss is mostly determined by the heat flow at the
tonercoating interface which thermal conductivity might
be more important However this remains to be confirmed
by further studies
Toner Adhesion
The results of the toner adhesion test show that the amount
of toner removed is affected by the peeling speed of the
Scotch tape Therefore the minimum percentages of toner
remained (adhered) on the coated paper samples at all
peeling speeds were taken for the study These data are
listed in Table 2 and plotted in Fig 9 It shows no
correlation between the percentage of toners remained on
Fig 8 Effect of Bulk Thermal Conductivity of the Coating Layers on Average Print Gloss (in ) of the Coated Papers
Fig 9 Effect of Bulk Thermal Conductivity of the Coating Layers on Toner Adhesion on the Coated Papers
Table 2 Minimum Toner Adhesion on Coated Papers
the coated paper and the bulk thermal conductivity of the
corresponding type of coating layer A similar comparison
was done by Gerstner et al
(2009) and no definite
correlation was found either As explained by Kianercy
(2004) and Sipi (2001) only three factors have been found
to have significant impacts on toner adhesion which are
surface tension of paper toner viscosity at the tonerpaper
interface and fusing speed
Pair-wise Visual Ranking
The result of the visual ranking test shows that for coating
layers with 10 pph of latex the CCHP-10 coating provides
the best print quality and the CPDG-10 coating provides
the worst print quality Among the HC90 coating layers
with different latex concentrations the HC90-10 and
Sample Minimum Toner Remained ()
HC90-10 987 HC90-18 946 HC90-25 872 HC60-10 218 CCHP-10 999 CPDG-10 811
PAPER PHYSICS
456 Nordic Pulp and Paper Research Journal Vol 27 no22012
Fig 10 Effect of Bulk Thermal Conductivity of the Coating Layers on Average Ranking Score of the Printed Coated Papers
Table 3 Summary of the Print Quality Test Results
HC90-18 coating provide significantly better print quality
than the one made with 25 pph of latex However no
correlation was found between print quality (quantified by
the average ranking score) of a sample with the bulk
thermal conductivity of the coating layers see Fig 10
These findings suggest that there are other factors which
have a more significant effect on the print quality of coated
paper However this is beyond the scope of this study
A summary of the print quality test results (Table 3)
reveals that the coating layer formulated with Covercarb
HP pigment and 10 pph of latex has the best ranking in all
three tests Therefore with its relatively low thermal
conductivity this coating formulation is the best candidate
among the ones studied for use in xerography printing
Conclusions The effects of coating formulations on thermal
characteristics of the coating layers were systematically
studied for assessing their impact on xerographic toner
fusion onto the coated papers It was shown that porosity is
a key parameter in the design of a coating layer for heat
transfer applications The latex concentration in the coating
formulation plays a significant role as it determines the
overall porosity of the coating layers Therefore in order
for the coating layer to act as a heat barrier (and provide
sufficient uniform heat transfer to the toner layer) it needs
to have an acceptably high porosity or a low latex
concentration The particle size distribution (narrow PSD)
and morphology (high shape factor) of pigments also affect
positively the porosity and thus the overall thermal
characteristics of the coating layers However the median
particle size of pigments did not show any significant
effect It was also found that the bulk thermal conductivity
of the coating layers can be accurately predicted by a
simple geometric mean model based on the pigment latex
and air volume contents
A 75˚ TAPPI print gloss measurement a toner adhesion
test using an IGT printability tester and a pair-wise visual
ranking test were performed on paper samples coated with
model coating colours and printed with 100 solid black
by xerography The print gloss of coated papers was
significantly improved when the coating bulk thermal
conductivity was low This is attributed to the insulating
effect of the coating thus providing a more uniform toner
fusion No other correlation was found between the print
quality and thermal properties of the samples
Lastly it was found that the coating made of Covercarb
HP a narrow PSD pigment and 10 pph of latex gave a
relatively low thermal conductivity and the best ranking in
all three print quality tests Therefore among all the
formulations tested this coating is the best candidate for
coated paper applications in xerography
Acknowledgements The financial and technical supports from NSERC IPS Scholarship FPInnovations Xerox Research Center of Canada and Surface Science Consortium at the Pulp and Paper Centre University of Toronto are gratefully acknowledged
Literature
Azadi P (2007) Modeling of mechanical and thermal responses of paper coatings under compression using discrete element method Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada
Azadi P Yan N Farnood R (2008) Discrete Element Modeling of the Transient Heat Transfer and Toner Fusing Process in the Xerographic Printing of Coated Papers Computers amp Chemical Engineering 32(12) 3238-3245
Azadi P Nunnari S Farnood R Kortschot M Yan N (2009) High speed compression of highly filled thin composites effect of binder content and stiffness Progress in Organic Coatings 64(4) 356-360
Azadi P Farnood R Yan N (2010) FEM-DEM Modeling of Thermal Conductivity of Porous Pigmented Coatings Computational Materials Science 49(2) 392-399
Bandyopadhay A Ramarao BV Shih EC (2001) Transient response of a paper sheet subjected to a traveling thermal pulse evolution of temperature moisture and pressure fields Journal of Imaging Science and Technology 45(6) 598-608
Bouguerra A Laurent JP Goual M Queneudec M (1997) The measurement of the thermal conductivity of solid aggregates using the transient plane source technique Journal of Physics D Applied Physics 30 2900-2904
Ranking (Best to Worst)
Print Gloss
Toner Adhesion
Visual Ranking
1 CCHP-10 CCHP-10 CCHP-10 2 CPDG-10 HC90-10 HC90-10 3 HC90-10 HC90-18 HC90-18 4 HC90-18 HC90-25 HC60-10 5 HC60-10 CPDG-10 CPDG-10 6 HC90-25 HC60-10 HC90-25
PAPER PHYSICS
Nordic Pulp and Paper Research Journal Vol 27 no22012 457
Cormier L Zou X (2008) Toner fusion in electrophotographic printing ndash issues from Papricanrsquos perspectives FPInnovations Paprican Division Pointe-Claire QC February 8 2008
CRC Handbook of Chemistry and Physics (2009) 89th ed Taylor amp Francis Group
Di Risio S Yan N (2006) Characterizing Coating Pore Structures of Paper Using Scanning Probe Microscopyrdquo TAPPI Journal 5(3) 9-14
Di Risio S Yan N (2006) Characterizing Coating Layer Z-directional Binder Distribution in Paper Using Atomic Force Microscopy Colloids and Surfaces A Physicochemical and Engineering Aspects 289(1-3) 65-74
Duke CB Noolandi J Thieret T (2002) The surface science of xerography Surface Science 500 1005-1023
Gane PAC Ridgeway CJ Schoelkopf J Bousfield DW (2007) Heat transfer through calcium carbonate-based coating structures observation and model for a thermal fusing process Journal of Pulp and Paper Science 33(2) 60-70
Gerstner P Gane PAC (2009) Considerations for thermally engineered coated printing papers focus on electrophotography Journal of Pulp and Paper Science 35(3-4) 108-117
Gerstner P Paltakari J Gane PAC (2009) Measurement and modeling of heat transfer in paper coating structures Journal of Material Science 44 (2) 483-491
Gerstner P (2010) Heat Transfer Through Porous Multiphase Systems Measurement Modelling and Application in Printing of Coated Papers PhD Thesis Aalto university Helsinki Finland
Kianercy A (2004) Characterizing toner-paper adhesion in xerography Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada
Liang C (2009) Effect of coating formulations on thermal properties of coating layers Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada
Maijala J Putkisto K Pietikaumlinen R Groumln J (2004) Heat transfer during fixation of coating layers in dry surface treatment Nordic Pulp and Paper Research Journal 19(3) 291-299
Malla PB Starr RE Werkin TJ (1999) The effects of kaolin particle size structure clay loading and binder level on glossing and offset print properties ndash A CLC coating study 1999 TAPPI Coating Conference Proceedings Toronto Ontario Canada TAPPI Press
Mitsuya T Kumasaka T (1992) Heat transfer and toner melting in an electrophotographic fuser system Journal of Imaging Science and Technology 36 88-92
Morikawa J Hashimoto T (1998) Thermal diffusivity measurement of papers by an AC joule heating method Polymer International 45(2) 207-210
Niskanen K Simula S (1999) Thermal diffusivity of paper Nordic Pulp and Paper Research Journal 14(3) 236-242
Okomori K Lepoutre P (1998) Effect of pigment size and shape distribution on the cohesion of pigmented coatings 1998 TAPPI CoatingPapermakers Conference New Orleans LA USA TAPPI Atlanta GA USA 819 ndash 835
Parker WJ Jenkins RJ Butler CP Abbott GL (1961) Flash method of determining thermal diffusivity heat capacity and thermal conductivity Journal of Applied Physics 32(9) 1679-1684
Salazer A (2003) On thermal diffusivity European Journal of Physics 24(3) 351-358
Sanders DJ Rutland DF (1996) Effect of paper properties on fusing fix Journal of Imaging Science and Technology 40(2) 175-179
Saxaner NS et al (1999) Thermal conductivity of styrene butadiene rubber compounds with natural rubber prophylactics waste as filler European Polymer Journal 35 1687-1693
Simula S Niskanen K (1998) Thermal diffusivity measurement of non-impact printing paper Journal of Imaging Science and Technology 42(6) 550-553
Sipi KM (2001) Toner layer structure and toner adhesion on coated paper NIP17 International Conference on Digital Printing Technologies Fort Lauderdale FL USA 145-150
Stroumlm G Hornatowska J Changhong X Terasaki O (2010) A novel SEM cross-section analysis of paper coating for separation of latex from void volume Nordic Pulp and Paper Research Journal 25(1) 107-113
Vernhes P Blayo A Bloch J-F Pineaux B (2006) Influence of the thermal field on the fusing step in electrophotographic printing Proceedings of the Technical Association of the Graphic Arts 465-485
Vidal D Zou X Uesaka T (2004) Modeling coating structure development Monte-Carlo deposition of particles with irregular shapes Nordic Pulp and Paper Research Journal 19(4) 420ndash427
Wantanabe J Kohara Y Takahashi S (1980) Effects of clay properties on paper coating structure Tappi 63(1) 43 ndash 46
Webb PA (2001) An introduction to the physical characterization of materials by mercury intrusion porosimetry with emphasis on reduction and presentation of experimental data Micromeritics Instrument Corp January 2001 Retrieved on January 14 2009
httpwwwmicromeriticscomapplicationsarticlesaspx
Zhao S Schabel S (2006) Measurement of thermal properties of paper by a light flash method Das Papier T65 34-39
PAPER PHYSICS
458 Nordic Pulp and Paper Research Journal Vol 27 no22012
Fig 10 Effect of Bulk Thermal Conductivity of the Coating Layers on Average Ranking Score of the Printed Coated Papers
Table 3 Summary of the Print Quality Test Results
HC90-18 coating provide significantly better print quality
than the one made with 25 pph of latex However no
correlation was found between print quality (quantified by
the average ranking score) of a sample with the bulk
thermal conductivity of the coating layers see Fig 10
These findings suggest that there are other factors which
have a more significant effect on the print quality of coated
paper However this is beyond the scope of this study
A summary of the print quality test results (Table 3)
reveals that the coating layer formulated with Covercarb
HP pigment and 10 pph of latex has the best ranking in all
three tests Therefore with its relatively low thermal
conductivity this coating formulation is the best candidate
among the ones studied for use in xerography printing
Conclusions The effects of coating formulations on thermal
characteristics of the coating layers were systematically
studied for assessing their impact on xerographic toner
fusion onto the coated papers It was shown that porosity is
a key parameter in the design of a coating layer for heat
transfer applications The latex concentration in the coating
formulation plays a significant role as it determines the
overall porosity of the coating layers Therefore in order
for the coating layer to act as a heat barrier (and provide
sufficient uniform heat transfer to the toner layer) it needs
to have an acceptably high porosity or a low latex
concentration The particle size distribution (narrow PSD)
and morphology (high shape factor) of pigments also affect
positively the porosity and thus the overall thermal
characteristics of the coating layers However the median
particle size of pigments did not show any significant
effect It was also found that the bulk thermal conductivity
of the coating layers can be accurately predicted by a
simple geometric mean model based on the pigment latex
and air volume contents
A 75˚ TAPPI print gloss measurement a toner adhesion
test using an IGT printability tester and a pair-wise visual
ranking test were performed on paper samples coated with
model coating colours and printed with 100 solid black
by xerography The print gloss of coated papers was
significantly improved when the coating bulk thermal
conductivity was low This is attributed to the insulating
effect of the coating thus providing a more uniform toner
fusion No other correlation was found between the print
quality and thermal properties of the samples
Lastly it was found that the coating made of Covercarb
HP a narrow PSD pigment and 10 pph of latex gave a
relatively low thermal conductivity and the best ranking in
all three print quality tests Therefore among all the
formulations tested this coating is the best candidate for
coated paper applications in xerography
Acknowledgements The financial and technical supports from NSERC IPS Scholarship FPInnovations Xerox Research Center of Canada and Surface Science Consortium at the Pulp and Paper Centre University of Toronto are gratefully acknowledged
Literature
Azadi P (2007) Modeling of mechanical and thermal responses of paper coatings under compression using discrete element method Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada
Azadi P Yan N Farnood R (2008) Discrete Element Modeling of the Transient Heat Transfer and Toner Fusing Process in the Xerographic Printing of Coated Papers Computers amp Chemical Engineering 32(12) 3238-3245
Azadi P Nunnari S Farnood R Kortschot M Yan N (2009) High speed compression of highly filled thin composites effect of binder content and stiffness Progress in Organic Coatings 64(4) 356-360
Azadi P Farnood R Yan N (2010) FEM-DEM Modeling of Thermal Conductivity of Porous Pigmented Coatings Computational Materials Science 49(2) 392-399
Bandyopadhay A Ramarao BV Shih EC (2001) Transient response of a paper sheet subjected to a traveling thermal pulse evolution of temperature moisture and pressure fields Journal of Imaging Science and Technology 45(6) 598-608
Bouguerra A Laurent JP Goual M Queneudec M (1997) The measurement of the thermal conductivity of solid aggregates using the transient plane source technique Journal of Physics D Applied Physics 30 2900-2904
Ranking (Best to Worst)
Print Gloss
Toner Adhesion
Visual Ranking
1 CCHP-10 CCHP-10 CCHP-10 2 CPDG-10 HC90-10 HC90-10 3 HC90-10 HC90-18 HC90-18 4 HC90-18 HC90-25 HC60-10 5 HC60-10 CPDG-10 CPDG-10 6 HC90-25 HC60-10 HC90-25
PAPER PHYSICS
Nordic Pulp and Paper Research Journal Vol 27 no22012 457
Cormier L Zou X (2008) Toner fusion in electrophotographic printing ndash issues from Papricanrsquos perspectives FPInnovations Paprican Division Pointe-Claire QC February 8 2008
CRC Handbook of Chemistry and Physics (2009) 89th ed Taylor amp Francis Group
Di Risio S Yan N (2006) Characterizing Coating Pore Structures of Paper Using Scanning Probe Microscopyrdquo TAPPI Journal 5(3) 9-14
Di Risio S Yan N (2006) Characterizing Coating Layer Z-directional Binder Distribution in Paper Using Atomic Force Microscopy Colloids and Surfaces A Physicochemical and Engineering Aspects 289(1-3) 65-74
Duke CB Noolandi J Thieret T (2002) The surface science of xerography Surface Science 500 1005-1023
Gane PAC Ridgeway CJ Schoelkopf J Bousfield DW (2007) Heat transfer through calcium carbonate-based coating structures observation and model for a thermal fusing process Journal of Pulp and Paper Science 33(2) 60-70
Gerstner P Gane PAC (2009) Considerations for thermally engineered coated printing papers focus on electrophotography Journal of Pulp and Paper Science 35(3-4) 108-117
Gerstner P Paltakari J Gane PAC (2009) Measurement and modeling of heat transfer in paper coating structures Journal of Material Science 44 (2) 483-491
Gerstner P (2010) Heat Transfer Through Porous Multiphase Systems Measurement Modelling and Application in Printing of Coated Papers PhD Thesis Aalto university Helsinki Finland
Kianercy A (2004) Characterizing toner-paper adhesion in xerography Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada
Liang C (2009) Effect of coating formulations on thermal properties of coating layers Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada
Maijala J Putkisto K Pietikaumlinen R Groumln J (2004) Heat transfer during fixation of coating layers in dry surface treatment Nordic Pulp and Paper Research Journal 19(3) 291-299
Malla PB Starr RE Werkin TJ (1999) The effects of kaolin particle size structure clay loading and binder level on glossing and offset print properties ndash A CLC coating study 1999 TAPPI Coating Conference Proceedings Toronto Ontario Canada TAPPI Press
Mitsuya T Kumasaka T (1992) Heat transfer and toner melting in an electrophotographic fuser system Journal of Imaging Science and Technology 36 88-92
Morikawa J Hashimoto T (1998) Thermal diffusivity measurement of papers by an AC joule heating method Polymer International 45(2) 207-210
Niskanen K Simula S (1999) Thermal diffusivity of paper Nordic Pulp and Paper Research Journal 14(3) 236-242
Okomori K Lepoutre P (1998) Effect of pigment size and shape distribution on the cohesion of pigmented coatings 1998 TAPPI CoatingPapermakers Conference New Orleans LA USA TAPPI Atlanta GA USA 819 ndash 835
Parker WJ Jenkins RJ Butler CP Abbott GL (1961) Flash method of determining thermal diffusivity heat capacity and thermal conductivity Journal of Applied Physics 32(9) 1679-1684
Salazer A (2003) On thermal diffusivity European Journal of Physics 24(3) 351-358
Sanders DJ Rutland DF (1996) Effect of paper properties on fusing fix Journal of Imaging Science and Technology 40(2) 175-179
Saxaner NS et al (1999) Thermal conductivity of styrene butadiene rubber compounds with natural rubber prophylactics waste as filler European Polymer Journal 35 1687-1693
Simula S Niskanen K (1998) Thermal diffusivity measurement of non-impact printing paper Journal of Imaging Science and Technology 42(6) 550-553
Sipi KM (2001) Toner layer structure and toner adhesion on coated paper NIP17 International Conference on Digital Printing Technologies Fort Lauderdale FL USA 145-150
Stroumlm G Hornatowska J Changhong X Terasaki O (2010) A novel SEM cross-section analysis of paper coating for separation of latex from void volume Nordic Pulp and Paper Research Journal 25(1) 107-113
Vernhes P Blayo A Bloch J-F Pineaux B (2006) Influence of the thermal field on the fusing step in electrophotographic printing Proceedings of the Technical Association of the Graphic Arts 465-485
Vidal D Zou X Uesaka T (2004) Modeling coating structure development Monte-Carlo deposition of particles with irregular shapes Nordic Pulp and Paper Research Journal 19(4) 420ndash427
Wantanabe J Kohara Y Takahashi S (1980) Effects of clay properties on paper coating structure Tappi 63(1) 43 ndash 46
Webb PA (2001) An introduction to the physical characterization of materials by mercury intrusion porosimetry with emphasis on reduction and presentation of experimental data Micromeritics Instrument Corp January 2001 Retrieved on January 14 2009
httpwwwmicromeriticscomapplicationsarticlesaspx
Zhao S Schabel S (2006) Measurement of thermal properties of paper by a light flash method Das Papier T65 34-39
PAPER PHYSICS
458 Nordic Pulp and Paper Research Journal Vol 27 no22012
Cormier L Zou X (2008) Toner fusion in electrophotographic printing ndash issues from Papricanrsquos perspectives FPInnovations Paprican Division Pointe-Claire QC February 8 2008
CRC Handbook of Chemistry and Physics (2009) 89th ed Taylor amp Francis Group
Di Risio S Yan N (2006) Characterizing Coating Pore Structures of Paper Using Scanning Probe Microscopyrdquo TAPPI Journal 5(3) 9-14
Di Risio S Yan N (2006) Characterizing Coating Layer Z-directional Binder Distribution in Paper Using Atomic Force Microscopy Colloids and Surfaces A Physicochemical and Engineering Aspects 289(1-3) 65-74
Duke CB Noolandi J Thieret T (2002) The surface science of xerography Surface Science 500 1005-1023
Gane PAC Ridgeway CJ Schoelkopf J Bousfield DW (2007) Heat transfer through calcium carbonate-based coating structures observation and model for a thermal fusing process Journal of Pulp and Paper Science 33(2) 60-70
Gerstner P Gane PAC (2009) Considerations for thermally engineered coated printing papers focus on electrophotography Journal of Pulp and Paper Science 35(3-4) 108-117
Gerstner P Paltakari J Gane PAC (2009) Measurement and modeling of heat transfer in paper coating structures Journal of Material Science 44 (2) 483-491
Gerstner P (2010) Heat Transfer Through Porous Multiphase Systems Measurement Modelling and Application in Printing of Coated Papers PhD Thesis Aalto university Helsinki Finland
Kianercy A (2004) Characterizing toner-paper adhesion in xerography Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada
Liang C (2009) Effect of coating formulations on thermal properties of coating layers Thesis for the Degree of Master of Applied Science University of Toronto Toronto Canada
Maijala J Putkisto K Pietikaumlinen R Groumln J (2004) Heat transfer during fixation of coating layers in dry surface treatment Nordic Pulp and Paper Research Journal 19(3) 291-299
Malla PB Starr RE Werkin TJ (1999) The effects of kaolin particle size structure clay loading and binder level on glossing and offset print properties ndash A CLC coating study 1999 TAPPI Coating Conference Proceedings Toronto Ontario Canada TAPPI Press
Mitsuya T Kumasaka T (1992) Heat transfer and toner melting in an electrophotographic fuser system Journal of Imaging Science and Technology 36 88-92
Morikawa J Hashimoto T (1998) Thermal diffusivity measurement of papers by an AC joule heating method Polymer International 45(2) 207-210
Niskanen K Simula S (1999) Thermal diffusivity of paper Nordic Pulp and Paper Research Journal 14(3) 236-242
Okomori K Lepoutre P (1998) Effect of pigment size and shape distribution on the cohesion of pigmented coatings 1998 TAPPI CoatingPapermakers Conference New Orleans LA USA TAPPI Atlanta GA USA 819 ndash 835
Parker WJ Jenkins RJ Butler CP Abbott GL (1961) Flash method of determining thermal diffusivity heat capacity and thermal conductivity Journal of Applied Physics 32(9) 1679-1684
Salazer A (2003) On thermal diffusivity European Journal of Physics 24(3) 351-358
Sanders DJ Rutland DF (1996) Effect of paper properties on fusing fix Journal of Imaging Science and Technology 40(2) 175-179
Saxaner NS et al (1999) Thermal conductivity of styrene butadiene rubber compounds with natural rubber prophylactics waste as filler European Polymer Journal 35 1687-1693
Simula S Niskanen K (1998) Thermal diffusivity measurement of non-impact printing paper Journal of Imaging Science and Technology 42(6) 550-553
Sipi KM (2001) Toner layer structure and toner adhesion on coated paper NIP17 International Conference on Digital Printing Technologies Fort Lauderdale FL USA 145-150
Stroumlm G Hornatowska J Changhong X Terasaki O (2010) A novel SEM cross-section analysis of paper coating for separation of latex from void volume Nordic Pulp and Paper Research Journal 25(1) 107-113
Vernhes P Blayo A Bloch J-F Pineaux B (2006) Influence of the thermal field on the fusing step in electrophotographic printing Proceedings of the Technical Association of the Graphic Arts 465-485
Vidal D Zou X Uesaka T (2004) Modeling coating structure development Monte-Carlo deposition of particles with irregular shapes Nordic Pulp and Paper Research Journal 19(4) 420ndash427
Wantanabe J Kohara Y Takahashi S (1980) Effects of clay properties on paper coating structure Tappi 63(1) 43 ndash 46
Webb PA (2001) An introduction to the physical characterization of materials by mercury intrusion porosimetry with emphasis on reduction and presentation of experimental data Micromeritics Instrument Corp January 2001 Retrieved on January 14 2009
httpwwwmicromeriticscomapplicationsarticlesaspx
Zhao S Schabel S (2006) Measurement of thermal properties of paper by a light flash method Das Papier T65 34-39
PAPER PHYSICS
458 Nordic Pulp and Paper Research Journal Vol 27 no22012