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

Подождите немного. Документ загружается.

PAGE

. 3

Flash Curing

Although most T-shirt plasti-

sols are printed wet-on-wet,

there are a variety of times

that you will need to flash.

Even though a job may actu-

ally run faster with a flash, it

is wise not to overuse the

flashing option. The only

times you are guaranteed not

to require a flash are; single

color jobs or colors printed

last. Nonetheless, there are

many times that you will need

to flash. The primary prob-

lem scenarios are listed below.

Colors that are not printed

last in sequence and:

1. Under-bases.

2. High value, high-chroma inks on darks.

3. Opaque inks on darks.

4. Opaque fluorescent inks.

5. High density or puff inks.

7. Metallic or pearlescent inks.

WWhheenn TToo FFllaasshh CCuurree

The times when you can be sure you will need to flash your print are under-base

colors, white inks or otherwise. Those bright, near-white colors of high-value,

high-chroma, when printed in large areas on dark garments. Opaque colors,

when printed on a dark background and sometimes on an under-base often

times require flashing. Opaque, fluorescent colors are probably the worst of the

bunch, and do poorly without a flash. High density or puff inks requiring third

dimensional relief, need to be flashed. Finally metallic colors, if over printed

while they are wet, lose their shimmering affect unless flashed.

Flashing

To properly print an under-base follow these steps:

1. Use inks with minimum plasticizer levels.

2. Use moderate viscosity, short-bodied inks.

3. Apply with a thin, large opening screen mesh,150 S

to 380 S are suitable.

4. Sharpened squeegee blade with a true edge.

5. Set off contact for zero mesh lag and zero stretch.

6. Angle the blade to control opacity and deposit.

7. Set the flash panel to 950° (3.7m) and 3/8-inch.

8. Preheat flash panel for fifteen minutes or set the

quartz flashes to 350° and 2 ¼ inches.

9. Preheat for fifteen seconds.

Printing Under-Bases

How To

Instructions

PAGE

. 4

UUnnddeerr-BBaassee IInnkkss

An under-base is a thin coat of white or pastel color, which lightens the value of

a dark T-shirt and builds a smooth surface for wet-on-wet printing. The most fre-

quently used color is white-that is a mixed blessing. It is truly opaque, unlike

many lead-free yellows and reds, but its pigmentation is the problem. White pig-

ment is microscopic in size, nearly a perfect sphere and at a very high loading

(percentage) in the ink-usually between 17 percent and 25 percent. When you

print, pump or stir white ink, it thickens and becomes resistant to flow. White ink

should have a high thix index and the mesh should have a large opening and thin

threads (refer to the sidebars on page 3.14 and page 3.28 for details).

The under-base should be printed through a thin-thread mesh. Unless the white

is visible in the final print, do not try to totally alter the value of the dark sub-

strate. For example, let the white turn the black T-shirt to a gray. This allows a

thinner white; one that is easier to print upon. Under-basing is usually done with

screen mesh counts between 150 and 380 (refer to the how-to on page 3.30 for

details). Always try to run opaque, or at least semi-opaque, colors as your over-

print set. These are much easier to deal with than transparent inks.

If the garment is 50/50 poly-cotton there are two guidelines. First, they are often

lower fabric mass, so mat down is more difficult. You may find that you need a

thicker deposit than for cotton. Second, it is very important to keep the fiber

hair below the surface of the garment to control surface bleeding (refer to the

how-to on page 3.16 for details.)

If the under-base is not visible in the final print and the overprint colors are not

too transparent, try this: use a small amount of blue-shade-black pigment in the

white ink to make it a 30 percent gray (refer to the sidebar on page 3.28 for

details). This will clear the mesh at higher speeds, print more smoothly and flash

faster. The surface will also have a propensity to hide flaws, like you tend to get,

when you print a royal blue over a stark white under-base.

The highest productivity on a long press run comes from running a second white

(versus double stroke or revolver mode), if the press and the run length permit.

You may want to review page 6.13 on pricing and cycle rates for assistance on

making the decision whether to run a second white. Ask your supplier for a white

intended for flash-cured under-bases. It should be low gloss, high thix index,

smooth finish and dry to the touch if it is to perform well.

HHiigghh-VVaalluuee,, HHiigghh-CChhrroomm

aa IInnkkss OOnn DDaarrkkss

High-value colors are nearest to white; they include yellows and pastels, even light

Chapter 5

PAGE

. 5

grays. High-chroma colors are the ones in the center of the PMS® column, the

ones that have no white or black added and little opacity or hiding power. A per-

fect example is a lead-free chrome yellow on a navy-blue T-shirt. The yellow is

clean, free of black or white and the shirt is its complementary color. The two

are complimentary-directly across from each other on the color wheel, so any

trace of blue will be immediately detected. Artists know to make shadows they

combine complimentary colors, so if yellow is not totally opaque, it will appear

dark and dingy. Such a color/garment combination would not run well without a

flash. If it is not flashed or run last, the force of the screen and blade on subse-

quent colors will push the ink into the garment and destroy its contrast. In fact,

this combination may need to be flashed, even if printed on an under-base.

OOppaaqquuee IInnkkss OOnn DDaarrkkss

These are in the maybe category for flash or no-flash. If the ink is very opaque,

with white added to the formula, you are not too particular about a slight shift in

the final color, and the color is not printed too early in the sequence, then you

may not need to flash. These colors include most grays, light blues and many pas-

tels. All of them rely on white pigment or some other attempt to whiten the

Flashing

Figure 5.1 The

L*a*b* color model

shows the three primary

color attributes in an

opposed format. If your

ink color is light, or

nearer the white

extreme and being

printed on a comple-

mentary garment color,

you may need to flash.

For example lets take a

yellow, which is always

high value, or near the

white position. Print it

on a dark blue T-shirt.

Since blue is opposite

yellow on the color

model: this is very

demanding to print.

The same is true for

red and green. You can

use this model to pre-

dict degrees of difficulty

in pairing ink and gar-

ment colors.

PAGE

. 6

color (refer to page 3.30 for details). This type of ink will tend to print extremely

well on the thinnest of under-bases and are often easy to overprint (refer to

Targets photo).

OOppaaqquuee FFlluuoorreesscceenntt IInnkkss

This is perhaps the worst-case scenario for potential build-up, mottling and loss

of contrast. The fluorescent resin is very tacky and yet will separate. It is made to

be opaque by the addi-

tion of white and or

blowing agents (refer to

page 3.30 for details) and

both of these tend to

build up. They are sus-

ceptible to both high-

shear build up, as well as

absorptive build up

(refer to page 3.31 for

details). Further these

inks tend to mottle like a

stucco ceiling when they

are printed upon, so

almost always, you will

want to flash them.

HHiigghh DDeennssiittyy OOrr PPuuffff IInnkkss

The nature of these ink

systems is to build a high

relief, so any overprint-

ing without a flash

would be counter pro-

ductive. Both of these

systems are designed to flash well, under reasonable conditions.

eettaalllliicc OOrr PPeeaarrlleesscceenntt IInnkkss

Much of the shimmering effect that is so desirable in a metallic or a pearlescent

is lost if overprinted while wet. An overprint screen crushes the structure of the

surface and the metallic goes from silver to pewter or lead. To allow them to fuse

in the dryer at normal times and temperatures, they often contain soft resins and

hot plasticizersthe perfect recipe for high after flash tack. Whenever possible

you will want to run your metallic colors dead last in the sequence.

Chapter 5

Figure 5.2 This is a high opacity print on a 50/50 (poly-cotton) swatch. The

fabric mass was low and the process color inks were totally transparent. This

meant that the white had to have sufficient opacity and bleed resistance or the col-

ors would be lost. Flashing was critical to this print, compliments of Target

Graphics Ltd.

PAGE

. 7

WWhheenn NNoott TToo FFllaasshh

It is unwise to use flashing long term to solve problems created by other facets of

the process. The list of problem scenarios appearing at the beginning of this

chapter, are legitimate and require a flash, but if you dont see your cause for

flashing on the list-beware. The flash in your case may be a very expensive band-

aid. For example, if the ink is building up-fix the ink, dont waste your time

(other than to get the job out the door) flashing. If you have smearing, review

chapters one and five on screens and press calibration. If you cant get quality

coverage, it may be your ink or printing technique, refer to pages 3.16 and 3.30

for details.

You should not need to flash white shirts, exceptions being metallic inks, high

density, and under-bases. Even if the image is a four-color process, if it looks

better flashed, something is wrong with your parameters and they should be cor-

rected, so the press can be run at top speed. Gauntlets and Challengers are capa-

ble of printing process color on white T-shirts at 70 dozen per hour or higher,

without any flashing.

FFllaasshh CCuurree RReessuullttss

I hope by now you are getting the message-flash curing should be limited.

However, when it is necessary you will find the possible results of flash curing

are few, but critical to your productivity. In the real world, there are only three

possibilities for flash curing, they are:

Flashing

Figure 5.3

Compliments of Liberty

Screen Print the high-den-

sity print shows off the

deposit that is critical to

the effect. This type of

printing involves multiple

flashes. To bring a screen

down on top of the wet

thick ink deposit would

ruin the relief of the

image.

PAGE

. 8

Under gelnever happens, the ink would still be wet.

Perfect gelnot in the real world.

Over gelthe only real possibility.

Since the best-case scenario is bound to be excessive, you want

to do everything possible to keep from a runaway flash. If

there is too much time or temperature (and time is the greater

enemy) you wont reach stability; the heat will rise until you are

forced to stop the press. Then you must wait until the flash

cools, hardly an efficient prospect.

M&R Flash Models

All M&R flash units, panels and quartz tubes, are medium-

wavelength-infrared emitters. Infrared is a specific wavelength

of energy that is emitted from the panel or quartz tube and is

absorbed by the garment and the ink. As the garment and ink

absorb this energy, it is converted to thermal energy.

Chapter 5

If you must flash, then you must

select the right ink for optimum

results. Choose an ink with the

following characteristics:

1. Low plasticizer level.

2. Fine grind of 5.0 or

above.

3. High critical surface

tension.

4. Low surface tension.

5. Low plastic viscosity.

6. High relative viscosity.

Finally, review chaper six, on inks,

for a better understanding of this

list.

Selecting Ink

Characteristics Suitable

For Flashing

Figure 5.5 This photo shows two white T-shirts, one finely detailed line art with gradients

and the second a process color job. Neither of these two prints warrants a flash. If you need to

flash this type of work, your process conditions are out of spec. We suggest you review this

manual.

PAGE

. 9

Flash curing is intended to take the ink to a state of gel. This is the level of

melting that combines resin and plasticizer to the point when the ink film is

dry to the touch. Once exposed to infrared, the plasticizer or liquid phase

becomes hot and only then, aggressive enough to flux (melt) the resin, the solid

phase of the ink. The fluxing process combines the plasticizer and resin into a

vinyl sheet. This transformation is complete as the ink reaches a temperature of

approximately 300° (refer to Chapter Three for details).

OOmmnnii FFllaasshh

ää PPaanneell

The Omni is the entry-level infrared panel and fits neatly into the carriage drive

of any press head on a Gauntlet or Challenger. It uses the same microprocessor

technology and heating system of all M&R panel flash units. The standard size

Omni flash runs on a standard 30 Amp 208/240VAC circuit. Larger sizes are

available and electrical ratings will differ based on the final size. Height adjust-

ment is done with an open-end wrench and the flash shuttles in and out as need-

ed. This flash requires an available press head to operate.

OOmmnnii-UUnnii FFllaasshh

ää PPaanneell

The Uni Flash is a step ahead of the Omni Flash with convenient, no tools

height adjustment wheel and an insulated cabinet. The panel is synchronized to

shuttle in and out with the press operation, and has a maximum operating tem-

perature of 1100°F. The standard Uni flash runs on 30 Amp, 120 VAC circuits,

larger sizes are available. This flash requires an available press head to operate

automatically, operating in synch with the press. It can be positioned over an

open platen. But if so, must be manually removed when the press stops for

longer than a dwell setting.

Flashing

Figure 5.5 Shown is the Omni flash with floor stand.

This unit provides a quality flash without all of the conven-

ience of the more expensive models. For automatic press use

only, the Omni is available in a cage mount. The flash as

shown, can be positioned strategically over an open station

and must be moved when the press stops. The cage mount

Omni functions automatically with the press carriage-drive

and decommissions one color from the press.

PAGE

. 10

QQuuaarrttzz FFllaasshh

ää TTuubbeess

The Quartz Flash is a step-up from the Uni Flash configuration. The Quartz

Flash monitors the temperature of the garment during production to ensure con-

sistent results. Since there is no hard

connection to the press they can be

moved from position, to position,

easily. It can be used in full auto-

matic synch with the press opera-

tion either, at a press head, or over

an open platen. Once the unit is

preheated for approximately 15 sec-

onds, it is instant on and off. At

two and a quarter inch distance,

there are no hot or cool spots-the

unit is in focus. The Quartz Flash

takes up far less space than the Uni

Flash for operator convenience, as

well as use in cramped quarters.

Flash Calibration

Every bit as important as the

selection of the flash unit is

ensuring your press is cali-

brated and your flash is cali-

brated to the press. The

parameters that need to be

controlled and adjusted for

are; time, temperature and

distance between the emitter

and the platen. Each of these

variables will be reviewed in

detail.

DDiissttaannccee

The following paragraphs will detail how to optimize the flash settings. All M&R

panels are designed to allow the highest productivity at minimal energy levels.

Chapter 5

Figure 5.7 The

Quartz Flash can

prove far more energy

efficient, particularly on

short runs where stop

and start are the norm.

The Quartz Flash does

not need to be hard

wired to the press and

can be placed at any

open station. The tubes

are instant-on as need-

ed. We recommend a

one-time fifteen second

preheat cycle prior to

each use. This negates

the start-up curve asso-

ciated with fused

quartz units.

Figure 5.6 All M&R Quartz flashes have been designed

with lamp positioning so that there are no hot or cool spots with

a distance of lamp to platen of 2.25 from the quartz tube to

the platen when the platen is in the up position. Closer and you

will find lines of hot spots, farther and you will not gain the full

efficiency of the lamps.

PAGE

. 11

You will want to take advantage of the selective control offered by the press and

its flash curing equipment. The first step is to establish a distance between the

flash panel and the platen. To help you

do so, we will look at the effects of

distance on watt density at the surface

of the panel and then at the surface of

the garment.

WWaattttaaggee aanndd WWaatttt DDeennssiittyy

The watt density or how many watts in

a given area can be determined by the

following equation: watt density =

(voltage * amperage) / (panel length *

panel width). Watt density is measured

at the surface of the panel itself and

can be used to compare the output

efficiency of panel-to-panel. More

important on the production floor is

the relative surface density of the

wattage. In other words, how much of it is hitting the ink on the shirt. With all

M&R panels, the energy is evenly distributed so there are no effective hot

spots; you can put the panel as close as 3/8.

Although there is more to flash-curing ink than the watt density of the flash at

the platen surface, the distance sets the range of performance. For highest out-

put, energy efficiency and most stable results, put the flash panel as close as prac-

tical to the platen. Note, the distances below are with the indexer and platens in

the UP Position. The following look-up table allows you to compare relative lev-

els of watt density at the surface of the T-shirt as the panel is moved closer and

farther from the platen, or when you have an uncalibrated press (one corner

lower than the others).

It may be obvious that accuracy in the flash setting is critical and becomes even

more critical the closer you get to the platen. If you were at one and one-eighth

inch on one end and one inch at the other, the closer of the two ends has a sur-

face watt density twenty percent greater than the farther setting. But if the closer

end was three-eighths inch and the farther end one half inch, the closer end has a

forty-four percent greater surface density. With this level of variability-consistent

gel is impossible.

Flashing

Figure 5.8 The Uni Flash connects to the press to func-

tion on automatic mode. The panel stays on during the press

run and automatically shuttles in at the start of a run and

out at the end of the run or for interruptions. During the

press run it stays in the slash position.

PAGE

. 12

Chapter 5

Figure 5.9 The look-up table above shows the relationship between distances ranging from three-eighths of an inch to one

and one-quarter inches (shown across the top of the table) and how the surface watt density increases or decreases. The best

distance and surface watt density are on the left side progressively getting worse as you move to the right. The starting distance

is listed as start in bold black type. For example, if your starting distance is ¾ between the bottom of the flash panel

and the platen and you were to adjust it closer, to ½ from the platen, the increase in surface density would be 2.2 times as

high. If you were close, at 3/8 and you were running zippered fleece and had to increase the clearance and moved to 1,

the surface density would drop to a mere 14 percent of the closer setting. Closer is more efficient, increasing production of

dozens per hour. This table also demonstrates how uncalibrated presses can easily over gel one corner and under gel another.

The closer your distance between the flash and the platen, the more critical press calibration becomes.

Surface Watt Density

Based on Panel Distance Change

3/8”

½”

5/8”

¾”

7/8”

1.0”

1 1/8”

1 ¼”

0.375”

0.500”

0.625”

0.750”

0.875”

1.000”

1.125”

1.250”

Start

56%

36%

25%

18%

14%

11%

1.7

Start

64%

44%

32%

25%

19%

16%

2.7

1.5

Start

69%

51%

39%

30%

25%

4.0

2.2

1.4

Start

73%

56%

44%

36%

5.4

3.0

1.9

1.3

Start

76%

60%

49%

7.1

4.0

2.5

1.7

1.3

Start

79%

64%

9.0

5.0

3.2

2.2

1.6

1.2

Start

81%

11.1

6.2

4.0

2.7

2.0

1.5

1.2

Start

Moving Flash Further From Platen

1.0

0.6

0.4

0.3

0.2

0.1

1.0

0.6

0.4

0.3

0.2

1.0

0.7

0.5

0.4

0.3

1.0

0.7

0.6

0.4

1.0

0.8

0.6

0.5

1.0

0.8

0.6

1.0

0.8

1.0

0.14

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.38 0.50 0.63 0.75 0.88 1.00 1.13 1.25

Original & New Distance in Inches

Watt Density Multiplier

Figure 5.10 This chart illustrates the results of moving the flash farther away from 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 top perimeter of the plot area, directly above your current distance, where you will see a 1.0 at the top

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