Paper Standards Measurements Final Version Eng

PaperStandards & Measurements

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The word for fine paper

THE PAPER MAKINGPROCESS

FOLDING AND CREASING

ADHESIVETECHNIQUES

MOTTLING-MOTTLEDIMPRESSION

CLIMATE AND PAPER

PAPER, INK ANDPRESS CHEMISTRY

THE PRINTING PROCESS

PROCESSINGMATT PAPERS ON-PRESS

TROUBLESHOOTING

Paper Standards Measur Umschlag 08.05.2007 15:42 Uhr Seite 2

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Xl Table of conversion factors

Most of the world has accepted the International System of “Units-Systeme International d’Unités” (SI) as the standard systemfor measurement. Test methods and standards require SI units as the primary reporting value. We trust that this guide will beuseful when converting between different units (FPS foot-pound-seconds and SI units).

Property Recommended unit or method of expression

Adhesion on strength of glue bonds kN/mof corrugated fiberboard

Air permeance µm/(Pa s)

Air resistance (Gurley) s

Apparent bulk density g/cm3

Apparent sheet density g/cm3

Ash % (mass/mass)

Bending stiffness µm, mNm, Nm

Bending stiffness index Nm7/kg3

Box compression resistance BCT kN

Breaking length km

Bulking thickness µm

Burst energy absorption Jlm2

Burst index kPa m2/g

Bursting strength kPa

Compression resistance SCT kN/m

Compression resistance SCT index kNm/kg

Conductivity of extracts mS/m

Dimensional change after immersion in water %

Dirt and shives in pulps 102 (number of specks)/kg

Drainability of pulp –"CSF" and Schopper-Riegler numerical value

Edgewise crush resistance kN/m

Electric strength kV/mm

Flat compression resistance kPa

Flat crush resistance FCT (corrugated board) kPa

Flat crush resistance of laboratory fluted corrugated medium N

Fold number, double folds numerical value

Folding endurance log10 (number of folds)

Fracture toughness J/m

Fracture toughness index Jm/kg

Friction coefficient N/N

Gloss % or numerical value

Grammage g/m2

Hygroexpansivity %

Ink absorbency “K and N” “K and N” units

Light absorption coefficient m2/kg

Light absorbing power numerical value

X Table of recommended units

We hope this list of most frequently referred units and properties within this catalogue will be a useful tool for all who are involvedin the pulp and paper field. Recommended units are from the International Standard, ISO 5651.

FPS unit Faktor Sl-unitAacres 4046.86 m2

BBtu (IT) 1.055056 kJ Btu/h 0.29307 W Btu/(h·ft·oF) 1.7307 W/(m·K) Btu/(h.ft2 . OF) 5.6783 W/(m2·K) Btu/lb 2.326 J/g Btu/(lb·oF) 4.1868 x 103 J/(kg·K)

Ffl oz (Imp) 28.413 cm3

fl oz (US) 29.574 cm3

ft H20 (39,2 °F) 2.98898 kPa ft 0.3048 m ft2 0.09290304 m2

ft3 0.02831685 m3

ft/min 5.08 mm/s ft/min 0.00508 m/s ft3/min 1.69901 m3/h ft/s 0.3048 m/s ft3/s 28.31685 l/sft·lbf 1.355818 J ft·lbf/in2 2.1015 kJ/m2

ft·lbf/ft2 14.5939 J/m2

ft·lbf/s 1.35582 W

Ggal(US) 3.785412 I gal(lmp) 4.546092 I gal(US)/d 0.00378541 m3/d gal(US)/min 3.785412 I/min gal(lmp)/min 7.5768 x 10-5 m3/s gal(US)/min 6.3090 x 10-5 m3/s grains/yd2 0.0775 g/m2

Hhp (550 ft-lbf/s) 0.7457 kW hp·h 2.68452 MJ

Iin 25.4 mm in2 6.4516 cm2

in3 16.38706 cm3

inHg (32 °F) 3.38638 kPa inHg (60 °F) 3.37685 kPa inH20 (60 °F) 0.24884 kPa in·lbf 0.1129848 N·m in·lbf 0.1129848 J in·lbf/in2 175.1268 J/m2

in·ozf 7.061552 mJ

17 18


Light scattering power numerical value

Light scattering oefficient m2/kg

Moisture content or dry matter content % (mass/mass)

Opacity %

Picking velocity, IGT m/s

Puncture resistance J, kJ

Reflectance factor %

Reflection (optical) density numerical value

Resistance to water penetration min, h, d

Resistance to grease penetration min, h, d

Ring crush kN/m

Roughness, Print-surf µm

Roughness, Bendtsen ml/min

Saleable mass kg

Surface resistivity Ohm

Smoothness, Bekk s

Static bending force mN, N

Stock concentration %

Stretch at break %

Swelling after water immersion %

Tear index mNm2/g

Tearing strength N

Tensile index N m/g

Tensile energy absorption J/m2

Tensile stiffness N/m

Tensile stiffness index Nm/kg

Tensile stiffness orientation ° (degree with decimal (polar angle) sub-divisions)

Tensile strength kN/m

Tensile toughness index Jm/kg

Tensile toughness J/m

Thickness µm,mm

Transmission (optical) density numerical value

Volume resistivity Q m

Water absorbency g/m2

– area basis g/m2

– mass basis %

– capillary rise mm

Water vapour transmission rate g (m2 d)

z-direction strength properties kN/m2

FPS unit Faktor SI-unitKKgf/in 0.38609 kN/m

LIb 0.4535924 kg Ibf 4448.222 mN Ibf 4.448222 N Ibf·in 0.1129848 Nm Ibf/in2 6.894757 kPa Ibf/in 175.1268 N/m Ibf/in 0.1751268 kN/m Ibf/in2 6.894757 kN/m2

Ibf/in2 6.894757 kPa Ibf·ft 1.35582 N·m Ibf/ft2 47.88026 Pa Ibf/15 mm 0.29655 kN/m Ibf·s/ft2 47.88026 Pa·s Ibf/ft3 16.01846 kg/m3

Ib/1000 ft2 4.8824 g/m2

Ib/3000 ft2 1.6275 g/m2

Ib/in3 27.6799 Mg/m3

Ib/gal (US) 0.1198264 kg/l Ib/ream, 17 x 22–500 3.7597 g/m2

Ib/ream, 24 x 36–500 1.6275 g/m2

Ib/ream, 25 x 38–500 1.4801 g/m2

Mmi 1.60934 km mi2 2.589988 km2

mil (0,001 in) 25.4 IJm mil (0,001 in) 0.0254 mm

Ooz (avoir.) 28.34952 goz (US fluid) 29.57353 ml ozf 0.278014 N ozf/in 10.945 N/m oz/gal (US) 7.489152 g/l

Ppsi 6.894757 kPa

Tton (short) 0.9071847 tonnes(t) ton (short)/l 00 ft2 0.092903 t/m2

yyd 0.9144 m yd2 0.83612736 m2

yd3 0.7645549 m3

yd3/s 0.7645549 m3/s


1

Content

l Introduction 3

ll Paper Specification 4

� Basis weight 4� Thickness / Caliper 4� Specific volume 4� Relative humidity 4

III Optical Properties 5

� Gloss 5� ISO-Brightness 5� CIE-Whiteness 6� Shade (colour) 6� Opacity 6� Metamerism 6� Fluorescence 6� Yellowing 6

IV Surface Properties 7

� PPS roughness 7� Smoothness 7� Surface roughness (laser profile) 7� Picking resistance 7

IGT 7Prüfbau 7

V Strengths 8

� Tensile strength and breaking length 8� Elongation (stretch at break) 8� Tearing resistance 8� Residual strength 9� Bursting strength 9� Stiffness (rigidity) 9� Scott Bond 10� Blister test 10

Vl Absorption 11

� Water absorption Cobb 11� Oil absorption Cobb-Unger 11� Ink absorption / Set-off 11� Water absorption – Drop test (Prüfbau) 11� Ink repellence – IGT 12� Contact angle measurement 12� Penetration Dynamic Analyzer (PDA) 12

VlI Others 13

� pH value 13� Ash content 13� Mottle test 13� Ink rub resistance 14� Cracking test 14

VIIl List of Standards and Measures 15

IX Concluding remarks 16

X Table of recommended units 17

XI Table of conversion factors 18

Paper Standards & Measurements

Paper Standards Measur Inhalt 07.05.2007 16:13 Uhr Seite 1


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l Introduction

This brochure is a small summary of the very extensivepublications of DIN and ISO standards. It has been producedto help explain the most important standards and units with-out complicated mathematical formulas and with simplewords.

The paper properties are arranged into different groups, sothat the emphasis in the requirements of the paper be-comes clear. Therefore some overlaps cannot be avoided.


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ll Paper Specification

A paper specification is a list of characteristics with appro-priate measured values, which the paper has to fulfill. Themeasured values are indicated with their tolerances. A spe-cification is necessary, since this shows the requirements ofthe customer and forms the basis, that always the samepaper is supplied. In order to come to a specification, onemust know the intended purpose and the requirements ofthe paper. Discussions with the customer or consumer arethe correct way to co-ordinate the requirements of thepaper and the possibilities in paper production.

Basis weight ISO 536

The weight in g/m2 is understood by the basis weight of apaper under conditioned circumstances. The entire mass isthe sum of fibrous materials, fillers, process materials andwater.

Thickness / Caliper ISO 534

The thickness of a paper is measured between two evenplates, which are adjustable with a defined pressure. Be-cause of the compressibility and the inhomogeneity severalmeasurements have to be carried out and the results aver-aged. The thickness of a paper is dependent on grammageand specific volume.

Specific volume ISO 534

The thickness is expressed in micrometers (µm). To comparethe thickness of papers with different basis weights, thespecific volume is used. This is the thickness to which thebasis weight of 100 g/m2 refers. This calculation is carriedout according to the formula:Thickness (µm) divided by the basis weight is the specificvolume (cm3/g).

Relative humidity Tappi 502

The relative humidity indicates how many percent of the maxi-mum possible water vapour portion, at a certain temperatureis actually in the air (i.e. between the sheets of a stack or thewindings of a reel).

L&W Micrometer

The picture above shows the most important optical and physical characteris-tics, in so-called Datasheets are listed. These can request or with your per-sonal partner receive you at any time in the Internet.


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lII Optical Properties

The first impression of a paper is its colour, its whiteness andits gloss. The appearance of the paper is of course impor-tant when it is sold, but the optical properties are also impor-tant when the paper is printed on. In order to be able tomanufacture paper with the right optical properties, pulpand coating raw materials, paper technologists must haveaccess to good measurement methods.

The optical characteristics of the paper are affected by themeasurement of reflection, absorption or transmission oflight which strikes a sheet of paper.

Whiteness and shade of the paper do not have direct influ-ence on the printability but have an influence on the printedresult. Colour printed on bright white underground results inanother impression than printed on other white under-grounds.

The ISO12647-2 standard used for the colour managementin the graphic arts industry provides a colour-correct repro-duction with the consideration of the paper type.

Gloss ISO 8254-1 (DIN)ISO 8254-2 (Tappi)

A calendered, coated or varnished paper has a high propor-tion of direct reflection, which is commonly called gloss.Gloss is an important characteristic in the production ofcoated papers. The gloss makes paper look elegant and theproperty is therefore important for advertising print. Gloss ismeasured with special instruments where the sample is illu-minated with parallel light at a certain incidental angle. Fixedoptical geometries, incidental and reflection angles of 75, 60or 20 degrees, are usually used. A specific geometry andangle is used, based on paper quality and gloss level. Thefollowing gloss standards are common: DIN 45° or 75° andTappi 75° or 20°.

DIN standard and/or low angle are used for (ultra) high glosslevels.

Gloss can also be measured on a printed area and is calledprint gloss.

ISO-Brightness ISO 2470

The brightness is a measure for the reflection of blue light ofthe paper expressed in a percentage in comparison with anultimate reference brightness standard (IR3 standard).There are three brightness values for fluorescent papers:ISO-brightness under C-light, D65-brightness under D65light and brightness with fluorescence eliminated.

The higher the brightness value, the brighter the paper is.Papers with optical whitening agents show a peak in theblue reflection. This addition of blue reflection causes thesample to appear whiter to the observer and gives higherISO-brightness and D65-brightness values. The ultravioletenergy level of the illumination must be adjusted using afluorescent calibration standard.

L&W Gloss Tester


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CIE-Whiteness ISO 2470

Whiteness is a subjectively perceived property. Most peopleconsider that it increases when the material has a slightlyblue tone. It is thus clear that whiteness in some way is anaspect of colour perception, and that any measurement ofwhiteness must be based on colour management.

Shade (colour) ISO 5631

Shade of a paper is the colour of a paper. The colour is de-scribed as blue, green, yellow or red or as a mixture of thesecolours. The colour can be described according to intensityand saturation. There are several different systems in use,but most common for the paper industry is the CIE L* a* b*.

Opacity ISO 2471

The opacity is a measurement for the light transparencydegree of the paper, expressed in a percentage in relation tothe reflected light. Paper which lets a lot of light through istransparent; paper which lets less light through is opaque.The higher the value, the more opaque the paper is.

Metamerism

Metamerism is the condition in which two colours canappear identical under certain light sources but exhibit cleardifferences in other light sources. This occurs because thereflective/reflection curves of the metameric colours are notthe same/alike over the whole spectrum.

Fluorescence

If a colour becomes more optically intensive under a certainlight source it is due to the effect of fluorescence. Thisoccurs when parts of the incident light are reflected in otherwavelengths. The impact of fluorescence is shown by theoptical brighteners used in many papers as they convert UVlight into visible light.

Yellowing DIN 6167

Degree of yellowing / discolouration of paper exposed to day-light or heat, after a specified period of time. A test piece isexposed for a specified time to UV light or heat. Colour mea-surements at specific time intervals describe the yellowing /discolouration. The degree of yellowing is expressed in a yel-lowing number.

Elrepho


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IV Surface Properties

Paper is a surface product, its surface determines the visualimpression and the feel. Beyond that, printing techniques,converting techniques and application determine the char-acteristics of the paper surface.

PPS roughness ISO 8791-4

The geometric form of a paper surface is defined as devia-tion from the ideal dead level. The more the surface ap-proaches the ideal level, the smoother the paper is. Themeasuring method (PPS) is based on the measurement ofthe air leakage between the paper surface and an evenmeasuring head. In case of the PPS roughness, the depth ofthe pores is measured by a defined circle. The higher themeasured value is, the “rougher” the paper surface is.

Smoothness ISO 879/-2/3 und ISO 5627

Definition and measuring method are comparable withthose used for roughness. Depending upon measuringtechnology either the time is measured in which a certainamount of air is used (Bekk and Gurley) or airspeed is mea-sured under a constant pressure (Bendtsen or Sheffield).

Apart from the air flow measurement principles there is alsothe optical smoothness measurement according to FOGRAand IGT method for determination of print smoothness.

Surface roughness (laser profile)

By use of a laser profile device it is possible to make a 3Dtopographical roughness profile of the paper surface. Everycomponent’s surface has some form of texture which variesaccording to its structure. These surfaces can be brokendown into three main categories: Surface roughness, Wavi-ness and Form.

With this measurement it is possible to analyze defects ofthe paper surface related to the paper machine.

Picking resistance

The picking resistance of a paper is the strength of the papersurface (Z-direction). In the offset printing process there areforces on the paper surface caused by splitting of the ink(tack) and adhesion forces of the blankets. Individual fibers,coating particles or whole surface areas can be pulled out.

The picking resistance can be determined according todifferent methods:

IGT ISO 3783The IGT and Prüfbau picking tests show rather good corre-lations with picking demands in the offset printing process.The principle of the test methods is to simulate as much aspossible the print conditions. With the IGT method oils withdifferent viscosity are used in combination with acceleratedspeed. The selection of a combination of oil and speed isdependent on the kind of paper (LWC, WFC etc.).

Prüfbau With the Prüfbau-test special test inks or commercial inkscan be used to perform a picking test. It is also possible topre-wet the paper with fountain water to determine the wetpick. The adjustable parameters such as pressure, speed,printing roller and time interval must be taken from the testprovisions and be tuned with the respective type of paperand its application.

Prüfbau


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V Strengths

The strength of paper plays an important role during pro-duction but especially at converting of the paper. Thestrength is in many cases also important for the use ofpaper. A paper, which is produced as a reel is subject to atensile force in linear direction, a paper which is produced asa sheet is subject usually to a tensile force in transverse di-rection. Depending on the forces on the paper there are testmethods, which can objectively determine if the paper’sstrength is sufficient for these demands (forces).

Tensile strength and breaking length ISO 1924-2

The testing of the paper on tensile strength takes place viatear test under a defined increasing force. The measuredtensile strength value is the quotient of the force (N) at themoment of break and the width of the test strip. The tensilestrength index is the quotient of the tensile strength and thegrammage (g/m2) of the paper.

The breaking force (N) and the grammage are the basis forcalculating the breaking length. The breaking length is thelength of a strip of paper with a defined width, when, freelysuspended, it tears due to its own weight.

Elongation (stretch at break) ISO1924-2

The elongation at rupture defines the stretch of a paper inpercentage (%) at the time of tearing in relation to the un-loaded length. The elongation at rupture is simultaneouslymeasured with the breaking force. From the breaking forceand elongation graph the elasticity module can be calculated.This elasticity module is related to the dimensional stabilityof the paper in different printing and converting processes.

Tearing resistance ISO 1974

The mean force required to continue the tearing of an initialcut in a single sheet of paper is expressed as the internaltearing resistance. If the initial slit is made in the machinedirection, the result is given as machine direction tearingresistance and similarly for the cross machine direction.

Tearing Tester

Tensile Tester


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Residual strength FOGRA

Residual strength is an important characteristic for web off-set papers. In web offset the paper is printed, heated andfolded. During this process the paper should have a specificresidual strength to prevent web breaks and breaks on thefold.

Under standardized circumstances a paper is heated andfolded. Directly afterwards the tensile strength of the testpiece is determined.

A general method for residual strength is the FOGRAmethod. With this method the residual strength of the papershould be higher than a minimum value of 0.67 kN/m.

Bursting strength ISO 2758

The bursting strength is expressed as the maximum uni-formly distributed pressure, applied at right angles to itssurface that a single sample piece can withstand under testconditions. The Burst index is the bursting strength dividedby the grammage.

Stiffness (rigidity) ISO 5628

The stiffness is an important characteristic of the paper,because it has substantial influence on the runability proper-ties during the printing process and on the requirements forconverting (folding, creasing etc.). Stiffness is defined asresistance against bending in the elastic area of the paper.Beside grammage and thickness there are other itemswhich have influence on the stiffness, such as choice of rawmaterials, refining degree of the fibers, quality and amount offiller and moisture content. The extent of the bend followsthe laws of mechanics, which means the paper is not dam-aged when stretched on the outside and compressed onthe inside. There are different methods available to deter-mine the stiffness but the most used method in the paperindustry is the 2-points load method. With this method theforce needed to bend a rectangular test piece to a specifiedangle is measured. The stiffness in machine direction andcross direction are the key factors.

Bursting Strength Tester


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Scott-Bond Tappi T 569ZDT Tappi T 541

Internal bond strength (paper’s strength in its thicknessdirection) is an important characteristic during printing andconverting processes. Internal bond strength is the maxi-mum load that single ply or multiple paper or boxboard canwithstand when loaded with a force directed at right anglesto the surface of the sample material. The paper’s ability towithstand these forces depends on factors such as choiceof pulp, degree of beating and refining, paper machine set-tings and choice of additives.

The Z-directional tensile and Scott Bond tests are differentmethods. The ZD-tensile measures the maximum force tosplit the sample at a low standardized test speed perpen-dicular to the test surface. The Scott Bond method mea-sures the energy needed to split the sample at a speed severalthousand times higher.

Internal bond is related to several phenomena duringprinting and converting such as delaminating, blistering,creasability etc.

Blister test

With the Blister test the drying section of a HSWO printingpress is simulated. The blister oil test has proven to be agood test to determine the blister resistance in practice. Thepaper is put in an oil bath with a specific temperature andthe water located in the paper evaporates, just as happensin the drying section of the HSWO printing press. Blisteringcan occur if the temperature is too high, the internal bondtoo low or the vapour permeability too low. Printed areaswith a high coverage of ink (300–400%) are more sensitivefor blistering. Papers used for HSWO should show noblistering at a temperature of 160–170°C or 340-360°F.

Scott-Bond Tester


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Vl Absorption

Types of paper for offset printing should have a certainabsorption to give the ink a good adhesion and to store thefountain water (temporarily). The absorption level should notbe so high that printing ink and fountain water show throughthe paper. The absorption is an important property of thepaper during the printing process and is a crucial factor forpaper-ink-fountain water interaction studies.

Water absorption Cobb ISO 535

Dependent on the intended purpose, different measuringmethods for the determination of the water absorption abilitywere developed. An old method is with the help of a pullingfeather/spring to apply a coloured ink on the paper with aspecific increasing width and observe if the ink spreads outor shows through. With the ink swimming test the measureof gluing is likewise tested. Both testing methods are limitedto printing and writing papers.

For papers which are printed in offset the absorption is oftendetermined with the Cobb test. The water absorption is de-termined by measuring the amount of water, which is takenup by the paper within a specific time. The Cobb test givesonly reliable values, if the paper is not fully soaked throughwith water.

Oil absorption Cobb-Unger FOGRA

The Cobb test can also be used for the measurement of oilabsorption instead of water and is called the Cobb-Unger.

Ink absorption / Set-off

The set-off of paper describes the absorption of ink on thepaper. The speed of absorption is determined by the timethat the ink needs to penetrate into the paper. For the offsetprocess this property is very important. An absorption whichis too slow, may result in smearing because the ink does notdry fast enough. An absorption which is too fast, may resultin a reduction of the dry ink properties.

The set-off of paper can be measured with a test printingmachine like Prüfbau or IGT.

A sample is printed with a standard ink. After several timeintervals, a part of the printed sample is countered against ablank counter sheet of the same paper (top on bottom inorder to simulate a pile). The density of the transferred ink ofeach area on the counter sheet is measured and plottedagainst time.

The shorter the time from high ink transfer to no ink transferof the counter sheet the faster the set-off.

Water absorption – Drop test (Prüfbau)

The drop test is carried out using the Prüfbau printingmachine. A drop of a defined Isopropylalcohol solution isapplied to the paper sample by means of a micro-pipetteand the paper is immediately printed with an ink. The inkdensities in the pre-wetted and dry printed areas are mea-sured. The ink density in the pre-wetted area is expressedas a percentage of the ink density in the dry printed area.The higher the value, the lower is the ink repellence of thepaper.

Cobb Sizing Tester


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Ink repellence – IGT

If the flow rate of fountain solution is high and/or the paperhas poor water-absorbing characteristics, the film of foun-tain solution on the surface of the paper results in repulsionof the ink in the following printing unit. Depending on the ex-tent of the repulsion, solid areas can show an uneven print-out.

The ink repellence test is carried out using the IGT test-print-ing machine. Dampening is performed using an engravedsteel roller dampened with fountain solution. The printingunit of the IGT tester is situated below the dampening unit,which allows the first section of the paper strip to be printeddry. The second section of the paper strip is printed afterdampening and is designated as the first interval. There is atime interval of 0.05 seconds between wetting and printing.The printing densities of the solid area (dry printing) and thepre-wetted area are measured. The mean value of thedampening interval is expressed as a percentage of themean value of the solid area. The higher these values are,the lower is the ink repellence of the paper.

Contact angle measurement Tappi-558

With determination of the absorptive capacity of paper forliquid it is necessary to define clearly, which liquid it con-cerns, how long the time of contact will be and under whichconditions the test is implemented. In most cases where aliquid droplet is applied to a solid material, an angle isformed at the point of contact between droplet and solid,the so called wettability angle or contact angle. This contactangle is an indication of the wetting performance of liquidsapplied to solids. This contact angle must be determined im-mediately, because the liquid could penetrate rapidly into thepores of the paper. Many printing inks, oils, paraffins andsimilar products have rather a low surface tension and arespreading immediately on the paper surface. Contact anglemeasurements and wetting studies can be performed usingan automated contact angle tester.

Penetration Dynamic Analyzer (PDA)

With this test it is possible to measure process relevantparameters of paper, coating colours or chemicals like glueand ink with the aim of predicting printability, glueability andability for coating.

A paper sample is brought into contact with liquid in a mea-suring cell. From the moment of liquid contact, it is radiatedin the Z-direction with high-frequency low-energy ultrasonicsignals. These signals are received by a highly sensitivesensor before they are processed in the device and trans-mitted to a personal computer. The main advantage of thismethod compared to other methods is that the penetrationdynamics can be tracked in real time with millisecond timeresolution.

Drop test: Paper with a bad water absorption

Drop test: Paper with a good water absorption


13

Vll Others

pH value ISO 6588

The pH value in the data sheets defines the pH value of thesurface. The pH values are indicated on a scale from 0 to 14.The measuring value 7 marks the neutral point which corre-sponds to distilled water. Values below 7 refer to “increas-ingly acid”, values above 7 stand for “increasingly alkaline”.Papers should be close to, if possible, next to the neutralarea or in the slightly alkaline range to have ideal require-ments for printing and further treatment.

Ash content ISO 2144

The ash content is the remaining residue as percentage ofdry paper after ignition at 900°C. The ash content is the totalof inorganic material, like carbonate, kaolin etc. in the paper(including filler). Fillers have an important influence on thepaper quality (for instance opacity) and are dosed with caredepending on the application of the paper.

Mottle test

Mottling is the uneven print appearance, mostly in solidareas: small dark and light areas in the surface of paper(board) caused by ink, paper or printing press. Mottle is in-fluenced by many parameters: e.g. ink, colour sequence,construction of printing press, speed, rubber blanket andfountain water. Variations in the surface characteristics suchas absorption and smoothness play an important roleregarding mottle and are caused by the production processand the components within the paper.

There can be three kinds of mottle:

Backtrap mottleInk applied to paper surface on a preceding printing unit of amulti-colour press will split onto the blanket in a subsequentunit and then be re-deposited onto the next sheet. If thisoccurs unevenly, the print can become mottled.

This backtrap mottle can be simulated on a test printingmachine by printing the paper and countering the paper inpre-defined times against a clean blanket reel.

Water interference mottleWater transferred to paper surface on a preceding printingunit of a multi-colour press should be absorbed by the coat-ing before it reaches a subsequent printing unit. If it is notabsorbed it will prevent even transfer of the ink. A mottledprint can result.

The method IGT ink repellence (see chapter VI Absorption)is used to test this phenomenon.

Midtone mottle (screen mottle)This is an uneven print in 30–60% screens, caused by differ-ences in the scattering and absorption behaviour of basepaper and/or coating. This effect can occur in one colourprinting and even in case of perfectly formed dots of equaldensity (optical effect).

Midtone mottle can be evaluated by printing a screen withthe test printing machine or with help of a plastic screenwhich is put on top of the paper. The level of screen mottlecan be evaluated visually or with help of image analysis.


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Ink rub resistance Prüfbau

Rubbing is the effect of repeated relative shifting of twotouching surfaces under a certain amount of pressure. Themeasure of resistance of a printed material to this rubbingeffect is known as ink rub resistance.

Ink rub resistance can be determined with the Prüfbau inkrub tester. 48 hours after printing the ink rub resistance isvisually evaluated. It is also possible to evaluate the ink rubresistance with a spectrophotometer or with image analysis.

Cracking test DIN 55437

After the printing process the paper is mostly converted tobrochures, books, maps etc.

During converting when the paper is folded, cracking of thecoating can occur at the folds.

Papers below 170g/m2 are directly folded, whereas papersequal or above 170g/m2 are creased before folding. Foldingcan be carried out with the Fogra folding tester. Fold isvisually evaluated for cracking.

The creasability of a paper is tested with a special machine,which has a creasing knife and different rules.

Papers which can be creased within a wide range (combina-tions depths and widths) without showing faults, have agood creasability level. Papers that can only be creasedwithout showing faults within a small range have a badcreasability level.


15

Vlll List of Standards and Measures

Selection of ISO/DIN/TAPPI and FOGRA test methods

Unit Europe USPaper SpecificationBasis weight g/m2 ISO 536 Tappi T 410Thickness / Caliper µm ISO 534 Tappi T 411Specific volume cm2/g ISO 534 Tappi T 500Relative humidity % Tappi 502 Tappi T 502

Optical PropertiesGloss % ISO 8254 – 1 and 2 Tappi T 480ISO-Brightness % ISO 2470 Tappi T 452CIE-Whiteness ISO 11475 Tappi T 562Shade ISO 5631 Tappi T 524 or T 527Opacity % ISO 2471 Tappi T 425MetamerismFluorescentYellowing DIN 6167

Surface PropertiesRoughness PPS µm ISO 8791-4 Tappi T 555Smoothness Bekk sec. ISO 8791-2/3 and ISO 5627 Tappi T 479Surface roughness (laser profile)Picking resistanceIGT ISO 3783 Tappi T 514Prüfbau

StrengthsTensile strength and breaking length kN/m – km ISO 1924-2 Tappi T 494Elongation % ISO 1924-2 Tappi T 494Tear resistance mN ISO 1974 Tappi T 414Residual strength kN/m FOGRABursting strength kPa ISO 2758 Tappi T 403Stiffness mN.m ISO 5628 Tappi T 556Scott Bond / ZD Tensile J/m2 – kPa Tappi T 569 – Tappi T 541 Tappi T 569 – Tappi T 541Blister test ° Tappi T 526

AbsorptionWater absorption Cobb g/m2 ISO 535 Tappi T 441Oil absorption Cobb-Unger g/m2 FOGRAInk absorption / set-off test (Prüfbau) Water absorption (Drop test)Ink repellence – IGTContact angle measurement Tappi T 558 Tappi T 558Penetration Dynamic Analyzer

OtherspH-Value ISO 6588 Tappi T 509Ash content % ISO 2144 Tappi T 211 and T 413Mottle testInk rub resistanceCracking test DIN 55437


16

lX Concluding remarks

The contents of this brochure result from extensive researchwork, closely linked with practice and with practical experi-ence.

We would like to take this opportunity to thank the followingcompany for their support and assistance

Lorentzen & Wettre16493 KISTA, Schweden

All statements and information are correct to the best of ourknowledge. All liability for losses associated with sugges-tions given in this brochure is excluded, regardless of thelegal basis. The right is reserved to make technical changesto our grades in the course of further development.

All rights reserved© 2007 by Sappi Europe SA

ImprintSappi Fine Paper Europe

Text and Editing: Herrmann Nax, Maurice van Duuren












Ash % (mass/mass)




Breaking length km






















Grammage g/m2

Hygroexpansivity %









fl oz (US) 29.574 cm3

ft H20 (39,2 °F) 2.98898 kPa ft 0.3048 m ft2 0.09290304 m2

ft3 0.02831685 m3


ft·lbf/ft2 14.5939 J/m2

ft·lbf/s 1.35582 W



Iin 25.4 mm in2 6.4516 cm2

in3 16.38706 cm3


in·ozf 7.061552 mJ

17 18





Opacity %







Ring crush kN/m



Saleable mass kg


Smoothness, Bekk s



Stretch at break %


Tear index mNm2/g

Tearing strength N

Tensile index N m/g








Thickness µm,mm




– area basis g/m2

– mass basis %







Ib/1000 ft2 4.8824 g/m2

Ib/3000 ft2 1.6275 g/m2

Ib/in3 27.6799 Mg/m3


Ib/ream, 24 x 36–500 1.6275 g/m2

Ib/ream, 25 x 38–500 1.4801 g/m2

Mmi 1.60934 km mi2 2.589988 km2



Ppsi 6.894757 kPa


yyd 0.9144 m yd2 0.83612736 m2

yd3 0.7645549 m3

yd3/s 0.7645549 m3/s












Ash % (mass/mass)




Breaking length km






















Grammage g/m2

Hygroexpansivity %









fl oz (US) 29.574 cm3

ft H20 (39,2 °F) 2.98898 kPa ft 0.3048 m ft2 0.09290304 m2

ft3 0.02831685 m3


ft·lbf/ft2 14.5939 J/m2

ft·lbf/s 1.35582 W



Iin 25.4 mm in2 6.4516 cm2

in3 16.38706 cm3


in·ozf 7.061552 mJ

17 18





Opacity %







Ring crush kN/m



Saleable mass kg


Smoothness, Bekk s



Stretch at break %


Tear index mNm2/g

Tearing strength N

Tensile index N m/g








Thickness µm,mm




– area basis g/m2

– mass basis %







Ib/1000 ft2 4.8824 g/m2

Ib/3000 ft2 1.6275 g/m2

Ib/in3 27.6799 Mg/m3


Ib/ream, 24 x 36–500 1.6275 g/m2

Ib/ream, 25 x 38–500 1.4801 g/m2

Mmi 1.60934 km mi2 2.589988 km2



Ppsi 6.894757 kPa


yyd 0.9144 m yd2 0.83612736 m2

yd3 0.7645549 m3

yd3/s 0.7645549 m3/s



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Documents

Paper Standards Measurements Final Version Eng