SPTF Reports - Effects of Drying Temperature on Screen Tension

S c r e e n P r i n t i n g T e c h n i c a l F o u n d a t i o n

Abstract

The experiment used four

popular mesh counts, each

processed using three different

drying temperatures. Tension

measurements were taken at each

step of the screen making process

to identify the effects drying tem-

perature has on screen tension.

Results showed that screen tension

decreases when screens are dried

at higher temperatures.

IntroductionWithout a doubt, screen tension

is key to successful screen printing.

The importance of tension and the

uniformity of that tension cannot be

underestimated. Tension affects just

about everything, including ink

deposit, stencil uniformity, registra-

tion, print quality and ink transfer.

With this in mind, it behooves us to

explore screen processing

procedures, products and

environments that may ad-

versely affect the consistency

of tension. The production

parameter of screen drying

temperature has remained

virtually unexplored in

relation to its effects on

screen tension. This study

extends the analysis of

screen tension when screens

are processed using different

drying temperatures.

SPTF Reports

Effects of Drying Temperature on Screen Tension

The call for higher drying

temperatures is based on the fact

that hotter air holds more moisture.

Drying times will decrease when

the water can be carried out of

the screen more easily with this

moisture-hungry air. The higher

the temperature the faster the

screen dries. Unfortunately, there

are other considerations. The

industry already knows that dry-

ing a sensitized emulsion at high

temperatures can create exposure

problems. But what else does high

temperature affect on the screen?

We must understand the full im-

plications of all our processing

variables on screen stability and

performance if we are to have a

predictable process.

The Screen Printing Technical

Foundation (SPTF) designed and

ran a simple test to determine

the reaction of tension when a

Figure 1: Grunig G215 pneumatic stretcher used to tension the screens

Figure 2: Pre-testing was used to establish appropriate corner softening distances for each mesh.

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SPTF REPORTS E f f e c t s o f D r y i n g T e m p e r a t u r e o n S c r e e n T e n s i o n

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screen is exposed to various

levels of screen drying tempera-

tures typically used in the industry

during screen processing. The

study that was undertaken neither

accounted for, nor distinguished

the contributions of, the frame pro-

file/type or the adhesive response to

the temperature conditions. The

experiment was conducted in the

SPTF lab in Fairfax, Virginia.

Experimental ProcedureSPTF selected four popular

mesh counts to test, and selected

each of the four major fabric

manufacturers to provide one

of the four mesh counts. Each

mesh was stretched to the me-

dian tension of the specific manu-

facturer’s recommended tension

range. Mesh count, thread

diameter and tension parameters

are listed in Table 1.

Each test group consisted

of one screen of each mesh

count, totaling four screens.

Three test groups were con-

ducted separately, one for each

temperature condition.

Three different temperature

settings were used and are listed

and defined in Table 2. The study

used a Tetko Tekair Screen Drying

Chamber with its fan set to med-

ium during all tests to provide air-

flow on the screens, and all four

screens were placed on the top

shelf of the cabinet during each

test. Extended dry time was fac-

tored into the ambient condition to

ensure the screens dried completely.

The screen order was kept the

same for all processing steps:

#1=110.80

#2=156.64

#3=230.48

#4=380.33

TensioningTensioning was conducted on

the Grunig G215 stretcher (Figure

1). The frame size was 58 cm x 69

cm (23 in. x 27 in.). The mesh was

adhered to the frame using KIWO’s

HMT 1000 2-part adhesive.

Each mesh count was pre-tested

to establish appropriate corner soft-

ening distance (Figure 2) and pres-

sure setting (Figure 3) values. This

information is listed in Table 3.

Using these predetermined

values, a rapid tensioning technique

brought the mesh up to the target

tension initially. During a 15-minute

stabilization, the frame was brought

up to the mesh and each area of

interest (AOI) was marked using a

template (Figures 4-6). The frame

was then lowered for the remainder

of the stabilization period.

When the 15 minutes expired,

the tension was measured again

and was readjusted, if required,

to reach the target tension. The

tension was measured and recorded

in the warp and weft directions in

each AOI (Figure 7) using a SEFAR

model 75S tension meter. After

“The production parameter of screen

drying temperature has remained virtually

unexplored in relation to its effects

on screen tension.“

Figure 3: Pressure setting values were pre-established so rapid tension could be usedin the stretching process.

SPTF REPORTSE f f e c t s o f D r y i n g T e m p e r a t u r e o n S c r e e n T e n s i o n

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removed from the stretching system

and the tension was measured and

recorded in each AOI as before

(Figure 10). The screen was then

placed upright, and separate, to sit

for 24 hours in ambient temperature

conditions (Figure 11). After each

screen reached its respective 24 hour

period, tension was again measured

and recorded in each AOI. Once the

final screen reached 24 hours, all

four screens were introduced in the

predetermined order

to the next processing phase.

DegreasingUlano #3 degreaser was applied

using a 10 cm (4 in.) soft bristle

brush. Using medium pressure

(bristles spread to half their maxi-

mum) the screen was brushed in

a circular pattern from top to

bottom, once on each side (Fig-

ure 12). It was then rinsed with

26.7°C (80°F) water (Figure 13).

Excess water was removed with a

screen vacuum (Figure 14) and the

tension was measured and recorded

in the warp and weft directions in

each AOI.

The screen was then placed

in the drying cabinet under the

Figure 4,5,6: During a 15 minute stabilization, the frame was brought up to the mesh and each Area Of Interest (AOI) was markedand labeled using a template.

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raising the frame, a two-part frame

adhesive was used to glue the mesh

to the frame (Figure 8). The adhe-

sive was allowed to dry for 15 min-

utes. The tension was measured

and recorded as before (Figure 9).

The stretched screen was then

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prescribed temperature conditions listed in

Table 2. After the dry time elapsed, the tension

was measured and recorded in the warp and

weft directions in each AOI.

StencilingThe screens were coated using a Grunig G405

automatic coating machine and KIWO’s Poly Plus

S-RX emulsion (Figure 15). Table 4 lists the number

of coats and coating trough radius for the substrate

and squeegee side of each mesh count. Speed and

pressure settings were constant for all screens.

The screens were again placed in the drying

cabinet under the prescribed temperature conditions

listed in Table 2. After the dry time elapsed, the

tension was measured and recorded in the warp

and weft directions in each AOI.

ExposureEach screen was exposed using an OLEC 5kW

metal halide exposure lamp, OLIX AI 121 Integrator

with an exposure distance of 91.4 cm (36 in.) (Figure

16). The image used was KIWO’s Quick Check and

KIWO’s five-step exposure calculator (Figure 17).

Exposure times are listed in Table 5.

Tape on the exposure unit’s glass ensured the

frames could be put in the same position each time.

Taping the film to the glass kept the film centered

on each screen (Figure 18).

DevelopingAfter exposure, each screen was developed using a

flat fan spray setting (Figure 19) with a spray distance

of 30.5 cm-45.7 cm (12 in.-18 in.) using 26.7°C

(80°F) water. A timer was set for two minutes and

both sides of the screen were sprayed with water to

begin softening the unexposed emulsion. After this

initial spraying, the stencil was developed from the

substrate side for the remainder of the set time.

Excess water was removed using the screen vac-

uum and the tension was measured and recorded in

the warp and weft directions in each AOI. The screen

was then placed in the drying cabinet under the tem-

perature conditions dictated by the test. After the dry

time elapsed, the tension was measured and recorded

in the warp and weft directions in each AOI.

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Figure 7: When the 15 minutes expired, tension was readjustedto reach the target, and then measured and recorded in theWarp and weft directions in each AOI.

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Figure 8: After raising the frame, a two-part frame adhesivewas used to glue the mesh to the frame.

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“Extended dry time

was factored into the

ambient condition to

ensure the screens

dried completely.“

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Screen FillerWhen all the screens were measured, the open areas

around the stencil were blocked out using screen filler

(Figure 20). The screen was then placed in the drying

cabinet under the temperature conditions dictated by

the test. After the dry time elapsed, the tension was

measured and recorded in the warp and weft directions

in each AOI.

Screens were then placed in ambient conditions and

additional tension measurements were taken after 30

and 60 minutes. A final tension was taken the next

day, approximately 18 hours later.

Temperature MeasurementsTemperature and relative humidity measurements

were taken using mobile temperature/humidity gauges

(Figure 21). These instruments were placed inside

the dryer and in the areas where the screens set in

ambient conditions.

Results/Additional TestingThe measurement results are listed in Tables

6-9 and are illustrated graphically in Charts 1-4.

Each of the vertical blocks on the graphs represents

1 N/cm. The bottom axis represents tension meas-

urements taken at each of the processing points

previously described.

Several interesting observations emerge from these

graphs. The first, and most important to this study,

is a consistent trend that shows an increase in drying

temperature results in tension loss of 1-2 N/cm on

the screen. The trend is progressive; as the dry tem-

perature increases, tension loss increases.

Notice that these tension differences became

more apparent after the screens were removed from


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▲Figure 11: The screens were then placedupright, and separate, to sit for 24 hoursin ambient temperature conditions.

▲Figure 9: The adhesive was allowed todry for 15 minutes. The tension wasmeasured and recorded in the Warp and weft directions in each AOI.

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Figure 10: The stretched screen was thenremoved from the stretching system andthe tension was measured and recordedin each AOI as before.

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Figure 13: The screen was then rinsedwith 26.7°C (80°F) water.

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Figure 14: Excess water was removedwith a screen vacuum and the tensionwas measured and recorded in each AOI.

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Figure 12: Ulano #3 degreaser wasapplied using a 4” soft bristle brush.

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the heated drying environment

and were in ambient conditions

for 30 minutes. The screens

processed in ambient conditions

do not show this shift in tension

at this point. Also noteworthy is

the fact that these tension differ-

ences remain when the tension is

measured the next day, approxi-

mately 18 hours later.

These results occurred on all

mesh counts, indicating this is a

general reaction of all mesh.

Therefore, our conclusion is that

screen tension reacts to heat intro-

duced in processing by losing tension.

Second, the dip in tension that

was recorded after the screen was

exposed and washed out occurred

in each of the temperature condi-

tion, although the heated screens

show a greater dip than the ambient

one. Again, all mesh counts were

affected. The tension drop ranged

from 0.75 to 2.5 N/cm. However,

the tension totally recovers after

the screen is dried. A curious

phenomenon to say the least,

and one that warranted some

further verification and testing.

Additional TestingAs mentioned, the consistent

dip seen after exposure and

washout occurred in all the meshes

at all temperatures. An additional

test was performed to determine

if the reaction of the stencil caused

this fluctuation. The 230 mesh

was selected and two screens were

made and processed as in the origi-

nal test under the 95° F tempera-

ture. However, in this test one

screen was coated with emulsion

and one screen was not. An addi-

tional tension measurement was

also taken directly after exposureFigure 16: Each screen was exposed using an OLEC 5kW metal halide exposure lamp,OLIX AI 121 Integrator with an exposure Distance of 91.4 cm (36 in.).

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Figure 15: The screens were coated using a Grunig G405 automatic coating machineand KIWO’s Poly Plus S-RX emulsion.

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“An additional test was performed

to determine if the reaction of the

stencil caused this fluctuation.“


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was complete, to learn

more about when this dip was

actually occurring. Temperature

measurements were made on the

frame itself to see if excessive

temperatures were present.

Chart 5 illustrates the results.

Both screens responded simi-

larly, showing a dip both in the

measurement after exposure and

after washout. The measurement

after exposure does show a slight

drop in tension, but the most

dramatic change occurs after

washout. Frame temperature

did not shift enough to account

for these tension differences.

A second additional test

used a different frame profile

from each of the previous tests.

Using the same frame size and mesh

count, one screen was made with

a frame profile of 3.8 cm (1.5 in.)

square, compared to 2.85 cm x

3.81 cm (1.125 in. x 1.5 in.) in

the previous tests. The screen

was coated with direct emulsion.

Again, an additional measurement

was taken directly after exposure.

A comparison of the original

results, the results from the

second test (stenciled screen),

and from this test appears in Chart

6. Based on the results seen here,

the change in profile does not

appear to have a noticeable

effect on the results.

Dan Gilsdorf, Lab Manager

at SEFAR America Inc., perform-

ed a similar test to SPTF using

frame profiles of 3.81 cm and

6.35 cm (1.5 in. and 2.5 in.),

and a cyanoacrylate adhesive.

Frame size was 58 x 79 cm

(23 in. x 31 in.), and a 61

threads/cm (156 threads/in.)

mesh was used. The testing

procedures were very similar

to SPTF’s experiment. The

results closely paralleled the

results presented in this paper.

Specifically, there was no dis-

cernable difference between

the two frame profiles, and

the tension dip from exposure

and washout was present

as before.

Figure 17: KIWO’s Quick Check and KIWO’s 5 step exposure calculator were exposedon each screen.

▲Figure 18: Tape marks were created on the exposure unit’s glass so the frames couldbe put in the same position each time.

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Laura Unterbrink, Applications Lab Manager at

KIWO also conducted a similar test to investigate this

effect. She tested thirteen mesh counts, and took addi-

tional readings before the screen was vacuumed and

directly after exposure. All the screens exhibited a

drop in tension after exposure washout, and a subse-

quent increase in tension after they were dry, just as

in SPTF’s study. There were also other small tension

drops at various points with some of the meshes, but

no other clear or consistent pattern was easily seen.

KIWO’s suggested explanation was that the water

absorption of the polyester influenced the tension at

these points where moisture was introduced, and then

removed. This is certainly a possibility, but more

research is needed to support this claim.

Without further testing, no conclusive explanation

for this odd tension dip can be offered. However, the

data does seem to eliminate the stencil, frame profile

and adhesive type from the list of possible causes.

The tension dip seen, while puzzling, should not be

a point of concern, as recovery of tension has been

seen on all tests.

DiscussionSPTF results provide some insight into the original

question: Does drying temperature effect screen ten-

sion? However, the test undertaken here did not

include printing these new screens. It is conceivable

that the higher temperatures actually encourage the

screen to stabilize in tension before a new mesh is put

on press. The answer would lie in the tension levels

seen on these screens after they were printed. If the

ambient screen dropped in tension after printing to

a greater degree than the screens exposed to heat,

this screen reaction may actually be a desirable one.

Unfortunately, this was beyond the scope of the study

and further study would be needed to determine if

this effect is good or bad.

We must also interpret the results of the study

in light of other known processing limitations. For

example, using excessive temperatures to dry stencils

is highly detrimental to their exposure performance.

Most stencil manufacturers specify a maximum drying

temperature of 32.2°C to 37.8°C (90°F to 100°F).

On the flip side, it is also understood that raising tem-

perature speeds the drying process so screens can be

Figure 20: After measuring the screens, the open areas aroundthe stencil were blocked out using screen filler.

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Figure 19: After exposure, each screen was developed using aflat fan spray setting with a spray distance of 30.5 cm-45.7 cm(12 in.-18 in.) using 26.7°C (80°F) water. Stencil was developed for a total of two minutes.

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“It is conceivable that

the higher temperatures actually

encourage the screen to

stabilize in tension before a

new mesh is put on press.“


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created more quickly - an important

need in production. We can see this

played out in the relative humidity

measurements that were taken at

the three temperature settings test-

ed, shown in Table 2.

As we have seen, our ability to

raise the drying temperature comes

at a cost, not only from stencil per-

formance, but also possibly from

screen tension loss. We must weigh

the need for speed with quality.

Knowing the end effects of process-

ing variables is an important part of

creating procedures that will yield

consistent screens, and ultimately

quality products.

The test results SPTF obtained in

this study are limited in scope to

the variables and procedures used

in the experiment. Other areas

such as thread thickness relative to

mesh count, tension level, various

frame adhesives, frame type, size

and profile have not been adequate-

ly investigated as far as their

response to tension and drying tem-

peratures. Therefore it is important

to keep in mind that results may

vary in actual practice.

ConclusionsThe results of these measure-

ments show that higher drying

temperatures cause greater tension

loss over the course of the screen

making process. These results

were consistent regardless of

mesh count tested, indicating it

is an overall trend within the

confines of the experimental

method used. As to what specific

effect or phenomena caused the

tension shift (frame, adhesive or

mesh), it cannot be determined

from this particular investigation.

RecommendationsBased on the preliminary indi-

cations suggested from this study,

the following recommendations

are suggested.

1. Dry screens in 30°C-40°C (86°F-

104°F) at 40-50% relative

humidity with moderate airflow

to maintain screen tension and

stencil reliability.

2. Use a dehumidifier to reduce the

moisture in the air to speed dry-

ing times instead of raising the

temperature excessively.

3. Keep drying temperature consis-

tent so screen tension will stay

consistent from screen to screen.

The information and recommendationscontained in this report are believed to bereliable and accurate. The authors andpublishers make no warranty, guaranteenor representation as to the correctness ofthis information for any given purpose nordo they assume any responsibility for theuse of information presented here, or forresults obtained or not obtained, and here-by disclaim all liability in regard to suchuse and/or results.

ACKNOWLEDGMENTSSpecial thanks to the followingcompanies for providing equipmentand supplies for this SPTF researcheffort:

Autotype Americas, Inc.

Chemical Consultants, Inc.

Diamond Chase Div. of OLEC

DYNAMESH, Inc.

Grunig Interscreen AG

Industrial Fabrics Corporation

KIWO Inc.

Olec Corporation

RhinoTech, Inc.

SaatiPrint USA

Sefar America, Inc.

SPE Incorporated

Ulano Corporation

UV Process Supply, Inc.

Figure 21: Temperature and relative humidity measurements were taken using mobiletemperature/humidity gauges.

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RegentsSefar America Inc.3M Commercial Graphics

Division/TCM

FellowsAvery Dennison Graphics Division

North AmericaSaatiPrint USA

AmbassorsMII International Inc.NazdarStout Marketing

CounselorsAdvance Process Supply Co.Autotype Americas Inc.Patrick CorcoranKay Premium Marking Films Ltd.KIWO Inc (Kissel & Wolf GmbH)M & R Printing Equipment Inc.Frank G & Marian A MayerNor-Cote International Inc.Rutland Plastic Technologies Inc.Solutions Unlimited

DiplomatsColor Arts Inc.DYNAMESH Inc.GFX International IncHarbor Graphics Corp.F B Johnston GroupKansas City Poster Display Co.Lowen CorporationModagraficsPosters IncScreen Printing MagazineSemaSys Inc.Sericol Inc.Summit Screen Inks

Union Ink Company Inc.Visual Marking Systems Inc.Wilflex

SponsorsAmerican Trim LLCAlbert Basse Associates Inc.Chemical Consultants Inc.Coates Screen Inc.Color Craft Inc.Commercial Screen Supply Inc.Daytona TrophyDecals Inc.FimorFirst Impressions Ltd.Forest CorporationGillespie Decals Inc.Globe Poster Corp.Grady McCauley Inc.Graphic Solutions Group Inc.Gregory Inc.Intercontinental Chemical Corp.Intergraphics Decal LimitedJohn Deal Co.Joliet Pattern Inc.Lawson Screen Products Inc.M & M Displays Inc.Mandel Graphic SolutionsMasterscreen Products Inc.Midwest Sign & Screen Printing

Supply CoMorgan Adhesives CompanyMorrison & Burke Inc.National Banner Company Inc.National ScreenPrinters Inc.Pratt CorporationRockford Silkscreen Process Inc.Rose Poster PrintingSaturn Rack CompanySelecto-Flash Inc.SGI Integrated Graphic SystemsSignet Graphic Products Inc.Spectra Inc.

STM GraphicsSuperior Imaging GroupSuperior Silk Screen Inc.TEKRA CorporationThermal Trade GraphicsTri-Tech Graphics Inc.Yunker Industries

BenefactorsAction Graphics Inc.Bovie Screen Process PrintingW. H. Brady CompanyBurlington Graphic Systems Inc.Canadian Screen Printing

IndustryThe Chromaline CorpDahlstrom Display Inc.Deco-Chem Inc.Design Mark GroupEuropean Screen Printing

Manufacturers AssociationExcel Graphics Inc.Globe ScreenPrintIDS MurfinLiberty International

Technology Inc.The Mitographers Inc.ModernisticMultigraphics Inc.National Screen Printing

EquipmentP P S Inc.Ivan, Avis and Wade PetersonPrime Source Inc.Romo Inc.Signdesign Inc.Neal H. SkinnerT S Designs Inc.Tapecon® Inc.Transport Graphics Inc.Ulano Corporation

As of June, 2002

Screen PrintingTechnical Foundation10015 Main StreetFairfax, Virginia, 22031-3489 USATelephone: 703-385-1417Fax: 703-273-0456

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SPTF Reports - Effects of Drying Temperature on Screen Tension