Clarke Joe, Lynch Colleen C. M&R Professional Screen Printing Series

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PAGE

. 13

A panel that is closer is less susceptible to drafts from open doors, windows and

the like. Further, it allows a lower operating temperature or less time to flash, and

both of these conditions are very desirable. Howeve,r if you are going to be close

to the platen, as we have advised, you must be accurate.

We recommend that you do not try to set the flash by eye, particularly if it is to

be set at a low clearance. Note that there is no focus distance required with the

M&R infrared panel flashes. You should only set the flash after the press is cali-

brated (refer to

page4.15). You will

need a 3/4 open

end wrench, a tape

measure or a ruler

and four pieces of

shim stock to

match the thickness

of the distance

from the flash to

the panel. If you

are using the rec-

ommended 3/8 as your standard, strips of squeegee blades 3/8 thick will work

well as the shim stock.

There will be times, in most shops, that the flash distance needs to be moved to

allow for thicker stock, but it is critical it remain as close to the platen as possible

for top efficiency in

production. It is

best with an Omni

or Uni flash to

move it as close as

possible. Three-

eighths of an inch

is recommended.

The graph in figure

5.13 gives a profile

Flashing

Figure 5.11 This photo-

graph shows a side view of

the Omni-Uni Flash and the

platen. In the case of panels,

you will want to be three-

eighths of an inch from the

platen. The Quartz flashes

need to be positioned two-

and-one-quarter inches from

the platen. Note that all

measurements are with the

platen in the up position.

Figure 5.12 This picture

shows the operator adjusting

the Omni-Uni Flash for par-

allelism to the platen surface.

As the panel distance

becomes closer, for more effi-

cient operation, the position

must be more accurate. A

panel that is close and out-of-

level will produce inconsistent

gel across the garment.

of each colored curved data line. The 1.0 represents the multiplier of watt density at your current distance. The 1.0 is one

hundred percent of the watt density. Travel downward and to the right on that curved line until you are directly above the

new distance, which is listed on the horizontal axis. The data point at this location is the percentage of watt density that you

will have at this distance. For example, if your current distance is three-eighths inch and you want to move farther from the

platen to one inch, the watt density is one hundred percent at three-eighths inches and will be fourteen percent at one inch.

PAGE

. 14

of the results of moving the flash closer. The difference in the operation is a

higher watt density. This allows you to operate at a lower temperature and/or

faster cycle rate.

TTeemmppeerraattuurree aanndd

WWaavveelleennggtthh

Once you select a dis-

tance, step two is to

consider the operating

temperature of the

flashit is part and par-

cel to the wavelength

generated.

The wavelength can be

determined from the

Chapter 5

Figure 5.13 This chart illus-

trates the results of moving the

flash closer to the platen. Find your

current flash-to-platen distance on

the horizontal axis of the graph.

The range is from three-eighths inch

to one-and-one-quarter inches. Look

to the bottom horizontal line in the

plot area where you will see a 1.0

at the base of each colored, curved

data line. The 1.0 represents the

multiplier of watt density at your

current distance. The 1.0 is one

hundred percent of the watt density.

Travel upward and to the left on

that curved line until you are direct-

ly above the new distance, which is

also listed on the horizontal axis.

The data point at this location is

the percentage of watt density you

will have at this distance. For

example, if your current distance is

one inch and you want to move clos-

er to the platen, to a distance of

one-half inch. Follow the green line

until it is above 0.50 on the hori-

zontal axis. The old watt density

was one-hundred percent at one

inch, and will be four times as great

at one-half inch.

Moving Flash Closer To Platen

1.0

1.7

2.7

1.5

4.0

2.2

1.4

5.4

3.0

1.9

1.3

7.1

4.0

2.5

1.7

1.3

9.0

5.0

3.2

2.2

1.6

1.2

11.1

6.2

4.0

2.7

2.0

1.5

1.2

1.0

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

11.0

12.0

0.38 0.50 0.63 0.75 0.88 1.00 1.13 1.25

Old and New Distance in Inches

Watt Density Multiplier

Figure 5.14

After the distance is

set and you are cer-

tain of parallel

planes between the

platen and the

quartz tubes or

infrared panel, it is

time to set a temper-

ature. All flash con-

trols are conveniently

located at the rear of

the flash unit.

PAGE

. 15

results of the wattage or the

temperature itself. The panels

can produce a range of

infrared wavelengths but all of

the IR emitters used in the

screen-printing industry are

medium wavelength. The look

up table below lists a range of

practical temperatures and

resultant wavelengths.

The plastisol resin likes wave-

lengths around 5.0m or 600°,

but this measurement is irrel-

evant for two reasons. Until

the plasticizers are in motion,

and they like much higher

temperatures and shorter

wavelengths, you cant work

on the resin. Second, the goal

is for the flash times to be

very short, so a temperature that is too low would not make production sense

(refer to figure 5.17 for details). Cotton T-shirts like shorter wavelengths than

the resin, so scorching can be avoided by using moderate settings. Once you

have determined the distance from flash panel to platen, we suggest a wave-

Flashing

To calibrate flash distance, follow these steps:

1. Be certain the flash is disconnected from power.

2. Be certain the flash is totally cooled and at room

temperature.

3. Put the platens in the down position.

4. Place the four shims on the corners of the platen.

5. Measure or eyeball a minimum of two-and-one-half

inches clearance between the platen and the flash;

move platen accordingly.

6. Raise the platens.

7. Adjust the flash so that there is zero clearance

between the flash and the shims.

8. Drop the platens and remove the shim stock.

Note: the press must be calibrated before you calibrate

the flash distance. That is the platens must be parallel to

the flash panels or tubes.

Calabrating Flash Distance

How To

Instructions

Temperature to Wavelength

Look Up Table

600° F

650° F

700° F

750° F

800° F

850° F

900° F

950° F

5.0m

4.8m

4.6m

4.4m

4.2m

4.0m

3.9m

3.7m

1000° F

1050° F

1100° F

1150° .

1200° F

1250° F

1300° F

1350° F

3.6m

3.5m

3.4m

3.2m

3.1m

3.0m

2.9m

Figure 5.16 There is a linear relationship between wavelength and temperature. The chart above lists a range of tem-

peratures from 600° F. to 1350° and directly below the temperature lists the wavelength generated. As you can see from

the look-up table above, considering the nature of the ink, there is not a lot of change in the wavelength as compared to

the temperature. When you flash cure, you are taking the ink to a gel state. You can't work on the resin part until you get

the liquid moving. The liquids are plasticizers and they typically have peak absorption at or near 2.2 microns and 2.2-

micron wavelength equates to a 1910° F. emitter temperature, which is impractical and dangerous. Gel with the flash, cure

with the dryerthat is the way it was intended.

PAGE

. 16

length that is above scorching, yet low enough to trigger the

plasticizer at high production speeds.

TTiimmee

There is one common thread among all printers when it comes

to flash curing: no one goes fast enough. Time is the con-

straint, so the point of this exercise is to allow you to flash

more shirts per hour, with minimal downtime. Take a given

distance and a given temperature and set them against dwell

If you are using an Omni or Uni

panel type flash, we have some

sound advice. Do not run the

flash in and out at high speeds.

You will gain nothing in produc-

tion and it can rattle the flash to

death. The carriage drive on the

Gauntlet and Challenger presses is

rugged and is intended to run as

fast as you can load and unload.

All of its components are rugged

enough to withstand the shock

indefinitely. The flash panel how-

ever has thermal connections,

which given enough abuse, will

begin to erode. This erosion will

cause an amperage increase and

get worse as time goes on.

Run the panel in and out at slow

speeds as is intended, there is

absolutely no reduction in produc-

tivity and your flash will last a lot

longer.

Chapter 5

Dont Crash

The Flash

Temperature & Wavelength

600

700

800

900

1000

1100

1200

1300

1400

5.0 4.8 4.6 4.4 4.2 4.0 3.9 3.7 3.6 3.5 3.4 3.2 3.1 3.0 3.0 2.9

Wavelength in Microns

Degrees Fahrenheit

Figur5.16 This chart illustrates the relationship between degrees Fahrenheit and wavelength.

Find your temperature in degrees Fahrenheit on the vertical axis, and then move along the gray

lines to the blue dot. Drop down to the horizontal axis and read the corresponding wavelength.

Figure 15.17 This is a table to show the relationship between cycle rates, dwell set-

ting and squeegee speed. You will do well to set a low dwell time and then if additional

flash time is needed, adjust the squeegee speed to fine-tune the flash time.

The Squeegee Speeds Effect On Cycle Rate When Flashing

Dwell

Slow

Medium

Fast

56.7

65.5

65.9

49.3

53.8

54.1

41.9

42.1

42.4

34.4

34.6

34.8

27.0

27.1

27.2

PAGE

. 17

(and squeegee) time to maximize your throughput. The look-up table on the pre-

vious page will serve as a map to help you establish the optimal conditions for

your plant.

Operations

Now that you are aware of the functionality of the components of flash curing,

we can set the flash to run efficiently and quickly. The next table takes a standard

Omni or Uni flash setting and alters it based on typical conditions in most shops.

BBaasseelliinnee FFllaasshh SSeettttiinnggss

The standard setting for a flash panel (excluding quartz units) is: 950° at 3/8 for

2 seconds. This will allow the press to run at 70 dozen per hour and faster if

your blade speed, screen parameters and ink will permit. You can take advantage

of this setting if your ink deposit is approximately 2 mils and the ink that you are

flashing is designed or modified to gel fast. There are a number of things that

you can do to depart from the standard and a few of these are listed in the table

below to act not as absolutes but as a map to allow you to maneuver through a

variety of conditions with ease.

Now you know after a certain point, hotter is not so much better, and closer is

Flashing

Figure 5.17 This

picture shows the speed

controls on the

Challenger carriage

arm. The duration of

the flash is based not

only on the dwell set-

ting, but also on the

time of the slowest or

longest stroke head. You

do not have to shorten a

stroke nor run the

blades at light speed,

but you must remember

that both of these set-

tings affect the time of

flash.

PAGE

. 18

much better than farther. Begin production by letting the flash warm up until the

thermostat indicates that the flash has reached the preset temperature. You have

one of two options at the outset, either preheat the platens or begin production

at a slower rate and then as the platens heat up, increase the speed.

PPrree-HHeeaatt

This technique works best if the shop and press are very cold. It is worth the

time and effort, as it need not interfere with production. The press can warm

itself up, while you prepare for the next press run.

Turn the flashes on at the preset temperatures and put the press on automatic

mode. You will need an open press head to do this. Expect it to take about ten

minutes (of course this depends on shop ambient temperature, the dwell setting,

time of exposure, distance and initial flash temperature). Run at a slow squeegee

speed for the warm-up cycling, since longer time under the flash will elevate the

platen temperature the fastest. Bring the platen temperature up to 120° and begin

production.

When you put ink in the screen, it has specific properties that are about to radi-

cally change when the ink gets warm. At approximately 110° the ink thins and

becomes very fluid. At this stage it will tend to transfer more ink at given settings

and will leave a flatter, smoother ink film. Not until the ink reaches the range of

160° does it achieve gel state. Gel is the point when the ink can be printed upon

without any detrimental affects to its surface. You will find as the ink warms, you

Chapter 5

Standard and Adjusted Flash Settings

Variable

Standard

Thicker

Ink Deposit

Bulky

Garment

Slower

Gelling Ink

Speed Above

70 Dz./Hr.

Temperature

950

°°

1050°

1100°

1050°

Wavelength

3.7

3.5m

3.4 m

3.5 m

Panel* Distance

3/8” gap

3/8”

3/4” gap

3/8”

Flash Time

2.0 sec.

3.0 sec.

5.0 sec.

1.5 sec.

Ink Deposit

2 mil

3 mil

2 mil

Ink Gel Rate

Fast

Slow

Fast

Garment

T’s / fleece

Hoods, etc.

T’s / fleece

*Note for quartz tubes, substitute 2 1/4 and 950°.

Figure 5.18 The gray area gives a standard setting for an Omni Flash or Omni-Uni Flash. In each of the next four

columns one variable (shown in red) is changed and the temperature of the flash is adjusted to compensate. For example if

the ink deposit is thicker as indicated in Column Three, increase the flash temperature from the standard of 950° to

1050°, if you are experiencing any difficulties. You may note the only time the gel is over three seconds is with slow-gelling

ink and with such ink you will experience after-tack issues.

PAGE

. 19

are able to reduce squeegee pressure and flash

time and these adjustments are advisable.

If the ink is taken beyond the gel stage, the ink

is nearing fusion or that stage where any addi-

tional time or temperature does not improve the inks properties. This will occur

around 300° and should be avoided, even by multiple flashes, at all costs. As the

ink nears fusion, its surface alters and becomes more and more difficult to print

upon-certainly to printed upon wet-on-wet. Should you approach this stage, the

best thing to do is allow the press to totally cool and properly dispose of the

inks in the screens and try again.

Whether you call them Ink Traps or End Caps (refer to page 3.17), M&Rs

Flashing

Use the following steps when setting your flash to maxi-

mize productivity:

1. Set the flash panel as close as possible.

2. Set the quartz tube at minimal focal distance.

3. Calibrate the press.

4. Now calibrate the flash.

5. Use an ink wedge to test for proper settings.

6. Use a sharp squeegee blade and thin screen mesh.

7. Use inks with high gel, low plasticizer levels.

8. Reduce dwell time as production stabilizes.

9. Eliminate drafts around flash unit.

10. Sequence the fastest inks earliest.

11. Use heat resistant spray adhesive.

12. Install a Kool Mist between heads.

13. Use a cooling station with a curtain transvector.

14. Use flash additive, if needed.

Maximizing Productivity

With The Flash

How To

Instructions

Figure 5.19 The Kool Mist from M&R

is the failsafe answer to top production rates

with virtually any deposit, ink system or

number of flashes. It was designed and engi-

neered originally for auditory T-shirts, where

the controlled film conductive circuit was

screened directly onto the shirt. Any distur-

bance of a printed trace would alter the cir-

cuit. The Kool Mist can definitely keep your

operation cooler with water and a five-percent

solution of food-grade silicone. The unit fits

between stations, so there is no loss of color

capacity and no need to have a cool down

station.

PAGE

. 20

attachments can help you

solve the ink stability issue.

Since they keep the ink in a

confined area, they will act to

stabilize its temperature over

a longer period of time with-

out the need to overload the

screen with ink. Note that

low quantities of ink are

more apt to change faster

than large ones; just like the

road surface of the bridges

freezing faster in the winter.

OOvveerr HHeeaattiinngg

The flash is an extension of

the dryer, because heat will

build additively. For example,

if a 72° room temperature

garment goes through a dryer,

it comes out at a nominal 280°. Then put another garment under a flash and

take it to a nominal 160°. Then immediately put it through the dryer, it will exit

at 340°. The flash does not operate alone; consider it a preheat station. If you

inspect at the end of the dryer, be sure that the cause of rejects was not at the

press end. Several problems occur when the ink is over heated under a flash:

1. After tack increases (refer to sidebar on page 3.26).

2. The ink becomes less receptive to the over print color (refer to

the how-to on page 3.28).

3. Platen temperatures exceed safe limits (130°).

4. Dye migration and sublimation are at risk (refer to sidebars on

pages 3.8 and 3.9).

5. Blistering ink and scorching garments are at risk (refer to figure

5.16).

6. Garment shrinkage.

Sooner, rather than later, production must be interrupted.

Chapter 5

Use the following steps to determine proper flash set-

tings:

1. Calibrate your press.

2. Calibrate the flash distance.

3. Use the tables on pages 5.12 and 5.14.

4. Begin at 950° F. or 3.7m wavelength.

5. Preheat the flash and platens.

6. Make a note the start temperature with a heat gun.

(page5.25).

7. Run an ink wedge to relate ink, deposit and flash.

8. Adjust press dwell to minimize time.

9. Monitor the settings and results with a heat gun.

Determining Flash Settings

How To

Instructions

PAGE

. 21

FFaaccttoorrss ooff AAfftteerr TTaacckk

If you have read much of this chapter you realize that time is

the greatest enemy of successful flashing. Further, a double

stroke (which increases time) will be the demise of your ability

to predict and control your flash parameters. You may have a

tendency to approach flashing gingerly and inadvertently run

slowwrong. You must set your conditions wisely and then go

as quickly as possible to keep the time factor at a minimum.

Avoid the use of high plasticizer level inks, whether the ink

maker or you put the excess plasticizer in the pail. This

includes plasticizer reducers and curable reducers, which are

mostly plasticizers.

Be sure that you have sufficient tension and optimal off con-

tact (Refer to Chapter V for details) to allow running at high

speeds. Use a true and sharp-edged blade when ever possible,

enabling speed and a thinner deposit.

We have generally recommended plain-woven mesh, but for

flashing, it is imperative. Twill mesh puts more mesh in con-

tact with the flashed print at any one time and this allows dif-

fusion adhesion.

The worst news is that the better you make your stencil, the

more affinity it will have for the flashed, hot under-printer. But

under no circumstances should you consider altering the sten-

cil. Remember identify, and then fix, the problem, not what

surrounds it.

Flash curing successfully relies upon the balance of inks, flash

and press. If you have adhered to the recommendations given

in this book and are still having problems on the press, change

inks.

IInnccrreeaassee SSppeeeedd

Begin at a slower speed for the first five-minutes. Then every

five-minutes you can increase the speed of the press (see fig-

ure 5.21). Remember that cycle rate is a combination of dwell

time and squeegee speed (refer to page 6.7 for details on pro-

duction rates and cycle times). If you start at 72° with a stan-

After-flash tack is a form of dif-

fusion adhesion. This is a tempo-

rary bond between two hot, flat,

compatible plastic surfacesthe

ink and the stencil. The solution is

as multifaceted as the causes and

depending on the setting, may be

very complex. One method of

eliminating ink-to-screen sticking

is adding, flash additive to the

under-printing color.

Flash additive is similar to the

resin your plastisol is made from.

It is PVC (poly vinyl chloride)

blending resin. Named so due to

its primary usage, to modify a fin-

ished plastisol for specific per-

formance properties.

This particular resin is large

enough to be properly stirred into

the ink. The resin proceeds to

use-up the excess plasticizer in the

system.

Before you add flash additive to

your ink, be certain the ink has

been thoroughly stirred. Flash

additive is very efficient, requiring

only a small amount, so it should

always be added by weight. Since

it affects the ratio of available-to-

absorbed plasticizer it should be

added at least 24 hours, and

preferably 72 hours, before going

to press. This gives the ink a

chance to achieve equilibrium and

you will find you will need less

resin to solve your problems.

Adding resin worsens the hand

and drape. You know you have

added too much when it com-

promises squeegee speed. Now

time becomes the problem. If you

add too much flash additive, dis-

pose of it and begin again.

Flashing

Use of Flash A

dditiv

PAGE

. 22

dard flash setting (see figure

5.23), the platens will be at

90° in seven-minutes and up

to 120° in fifteen-minutes. Of

course this depends on shop

ambient temperature, the

dwell setting, time of expo-

sure, distance and initial flash

temperature. If you are dou-

ble stroking and trying to

flash (refer to pages 6.5 and

6.5), then review the table

below. Time is the deadliest

enemy with flash curing, not

only does it cost productivity

and money, but it is like a jet

airplane-they dont fly very

well at slow speeds.

SSeeqquueennccee tthhee FFaasstteesstt IInnkkss FFiirrsstt

We have discovered some

interesting facts; the only pos-

sible real-world flash technique is unfortunately over flashing. Heat has an addi-

tive property and preheating affects the final outcome. We know sticking occurs

more often at elevated temperatures.

Therefore, the first color flashed, is the most critical. It is our chance to keep

the heat at a minimum level, to finish from the dryer at a lower temperature

point. Consequently, it is best to run the fastest flashing colors, earliest in the

sequence.

These fast-flashing colors will generally be the ones with the lowest plasticizer

level. This is information you will want to get from your ink supplier. If the

plasticizer level is too high, the addition of flash additive (refer to page 3.26 for

details) may be helpful in reducing the flash time and temperature.

The benchmark for addition of flash additive is when the ink will not run at top

speed. In this scenario, the solution becomes the problem. If you have to run

slower, the addition of flash additive may have been self-defeating, as time is a

greater enemy than temperature.

Chapter 5

To minimize flash tempertures follow these steps:

1. Calibrate press and flash.

2. Use low plasticizer level ink.

3. Add flash additive if needed.

4. Minimize flash to platen distance.

5. Engineer for single stroke.

6. Minimize dwell time as run progresses.

7. Maximize squeegee and flood speed.

8. Minimize ink deposit.

9. Use a thin flat screen mesh.

10. Prepare a sharp, true-edged squeegee blade.

Minimizing Flash Temperatures

How To

Instructions

Clarke Joe, Lynch Colleen C. M&amp;R Professional Screen Printing Series

Подождите немного. Документ загружается.

Clarke Joe, Lynch Colleen C. M&R Professional Screen Printing Series