Some General Information about Screen Printing Plastisol Inks
The most popular ink used in the garment printing industry is Plastisol ink. Screen printing plastisol ink is easy to print, does not dry in the screen, is opaque on dark garments, and features great adhesion to most t-shirt, athletic jerseys, hoodies, heat transfers, and most textiles in general.
Screen print plastisols are made up of two primary ingredients - PVC resin (a white powder) and plasticizer (a thick, clear liquid). Plastisol inks are easy to use because they don’t dry until exposed to heat in order to dry. Plastisol ink will not dry, or cure, at normal temperatures. For a proper cure, plastisols must reach a temperature of 300 - 330º F (143-166º C).
Plastisol inks can be printed on many items that can withstand the heat required to cure the ink and is porous enough to permit good ink adhesion. Plastisol inks do not dye the threads of a fabric like traditional dye stuff. Plastisol ink wraps around the fibers and makes a mechanical bond with the fabric. Screen printing plastisols will not adhere to non-porous substrates such as plastic, metal, wood and glass. They also will not adhere to waterproofed nylon material without adding a bonding agent/catalyst. General information about Screen Printing with Plastisol Ink. Drying, Curing, Additives, Emulsion Selection and more.
Mesh Selection When Printing Plastisol Inks
With so many different meshes to choose from, selecting the “best” mesh for your plastisol printing needs can be frustrating.
Use the following information as a guide for choosing your screen mesh:
- Glitter Plastisol Ink: Use 30 – 38 mesh
- Athletic Prints: Use 60 – 85 mesh
- Fleece Items: Use 60 – 110 mesh
- Puff Inks: Use 60 – 85 mesh
- Metallic Plastisol Ink: 60 – 85 mesh
- Super Opaque/Bleed Resistant Plastisol: 60 – 85 mesh
- Hot-Split Heat Transfers: 60 – 85 mesh
- General Plastisol Prints: 110 – 125 mesh
- Multi-Color, Wet-on-Wet Plastisol Printing: 180 – 200 mesh
- Nylon Jacket Printing: 180 – 230 mesh
- Simulated & 4-Color Process: 230 – 305 mesh
Emulsion Selection for Screen Printing Plastisol Inks
For plastisol inks use an SBQ or Dual-Cure Emulsion. Capillary films (like Ulano’s E-Z Films) are also ideal when printing halftones, heat transfers and when you want a very consistent film deposit. CDF film are also faster to use and eliminate pin-holds in the screen.
Plastisol Ink Additives
A word of caution about ink additives, it’s easy to upset the chemical balance of plastisol inks by using the wrong additives or by adding too much of an additive – even if it is the correct additive. The result can be ink that never cures properly, a problem that may not be discovered until your customer washes a shirt and the design falls (i.e. color lose, adhesion or cracking). To avoid this problem use only those additives recommended by the manufacturer, and read the Technical Data Sheets for each ink and additive, and carefully follow their instructions. Never add mineral spirits to plastisol ink. Although mineral spirits will make it easier to print at first, soon the ink will become even stiffer and harder to print than before. Also, it is possible that mineral spirits will prevent the ink from curing properly.
Store plastisol inks at room temperature. Prolonged exposure to temperatures above 90º F (32º C) can cause the ink to start to cure while it's still in the container.
Clean plastisol ink off your screens with either mineral spirits or any of the various brand name screen washes available from your screen printing supplier.
Controlling Dye Migration
Dye migration is the problem caused by dyes in polyester fibers transferring to and changing the color of plastisol inks. The colors most likely to migrate are red, maroon, kelly green, and some of the darker blues. Dye migration may appear immediately after the ink is cured, or hours, days, or up to two weeks later. To control dye migration use the following procedures: Print with high-opacity, low-bleed inks. Use no more heat than necessary to cure the ink. More heat means more dye migration. Print and flash-cure a low-bleed white underbase, then print the desired color over that. Avoid the problem by printing on 100% cotton fabrics.
The washability of properly cured direct and transfer prints are excellent. When washing, it is always recommended that the garment be turned inside out. Dry cleaning is not recommended. Do not iron the printed part of the garment.
Curing Plastisol Inks
Curing plastisol inks is a matter of exposing them to the proper amount of heat for the correct length of time. Correct curing of plastisol ink is extremely important. The most common problem encountered with plastisol inks is poor washability, color loss and cracking of the ink. In almost every case, this is due to an incomplete ink cure.
When plastisol is heated, the resin particles absorb the surrounding liquid (plasticizer) and swell, they merge with each other and form a tough, elastic film. It is generally impossible to over cure direct prints because the over cure temperature is above the scorching point of the garment. However, it is not recommended that you heat the ink layer above 350º F (176º C). Usually curing above this temperature will cause puff inks collapse. Also, problems with dye migration are greatly increased when curing at elevated temperatures – so it is best if you can cure at lower temperatures whenever possible, especially with polyester garments. Note that if the entire thickness of the ink is not brought to the correct curing temperature the ink will be under-cured (the resin has not absorbed all of the plasticizer) and the ink can crack and flake off the garment when washed.
Plastisol will start to become dry to the touch or gel (also called semi-cured) between 180-250º F (82-121º C). It becomes fully cured between 280-320º F (138-160º C), depending on the type of plastisol. The temperature at which the ink becomes fully cured is called the fusion temperature. Most plastisol inks cure at 320º F (160º C). Check the Technical Data Sheet from the manufacturer for each plastisol ink for complete instructions.
How to Test a Plastisol Direct Print for Proper Cure
The ultimate and definitive test to determine if plastisol inks are properly cured is a wash test. Wash the garment in hot water with a strong detergent. Generally it will take from 5-10 washings to fully test the cure, but if the ink is seriously under-cured, the print will show deterioration after only 1-3 washings.
There are two other tests methods that are commonly used to check for plastisol cure. The most popular test is the Stretch Test. Stretch the print about two-thirds of the total stretch of the T-shirt. If the print cracks and does not retract when the fabric is released, the ink is probably under-cured. The stretch test does not always work on really thick deposits of ink, such as athletic jerseys, where the top layer of ink may stretch but deeper layers may be under-cured.
Another test for curing is the “Ethyl Acetate Test”. Place a few drops of ethyl acetate onto the back of the ink on the inside of the garment. This spot of ink is then placed onto an area of the unprinted garment and then tightly head together for two minutes (sometimes you may lightly rub). If there is a transfer of ink to the unprinted area of the garment, then the ink is not fully cured and the garment should be dried longer. Like the stretch test, this test is not totally or always accurate. Again, the ultimate test is the “Wash Test”.
Adjusting Your Conveyor Dryer
It is critical that you fully understand your conveyor dryer and how its belt speed and temperature settings work. It is important to note you need to cure the entire film thickness of plastisol ink to achieve maximum washability. Simply drying the top surface (like you do during a spot or flash cure) will result in the plastisol ink washing out or not adhering properly.
The temperature of the plastisol ink film is determined by how much time the garment is exposed to heat and the temperature of the heater source or heat chamber. As a result, the temperature can be controlled by a combination of the belt speed and/or time in the heat chamber. If the heater temperature in a dryer or flash curing unit reaches 800º F, it is possible for the ink film on the garment to reach the full cure temperature (300º F plus) in a matter of 30-45 seconds.
Flash or Spot Cure Drying
Plastisol ink can generally be fully cured with a flash cure unit – sometimes also called a spot dryer. Set the flash cure heater to the highest temperature and placed heating element 3 inches over the garment for 25 - 35 seconds (generally speaking). For curing between colors where only a partial cure is required, the time will be less (usually between 5 – 10 seconds).
Important Drying/Curing Tips
White plastisol ink, generally speaking, requires the longest dry/cure time of any standard color. The lighter the plastisol ink color, the longer the curing time. Plastisol ink that is thicker, or printed in layers also require longer curing time than think layers of ink.
Glitter, shimmer, reflective and metallic inks require much longer curing times because the pigments used in these inks tend to reflect infrared/heat away from the garment. Likewise, garments that are “reflective” like dazzle cloth or garments that are moisture-laden also require longer drying/ curing times.
When printing, the print should be cured shortly after the printing process - within a minute of printing. If you delay drying the plastisol ink, the plasticizer in the ink may start to leach out of the ink and into the t-shirt or garment. Plastizer looks like an oil around the print.
Temperature tapes are a great way to monitor the temperature of the dryer. Of course the best method of testing for proper plastisol ink cure is to the wash test and then determine how well the garment launders.
It is important to remember that the dryer temperature (and ultimately your cure) can vary greatly with changes in belt speed, the type of garment you are printing on, the method of garment loading on the dryer belt, the type of ink you are using, the screen mesh you print with, room temperature, air movement, or fluctuations in incoming voltage – just to name some of the more important curing variables. So test, test, test.
Screen Printing Plastisol Heat Transfer Printing
Most plastisol heat transfers fall into one of two (2) categories, hot-split, and cold-peel. When hot-split transfers are applied, the paper is stripped off the garment immediately after the heat transfer press is opened up. The plastisol ink layer separates from the paper transfer sheet (splits), leaving part of the ink on the garment and part on the transfer paper. Hot-split transfers are similar to a soft-hand direct print. When cold-peel transfers are applied, the heat transfer is allowed to cool before the paper is removed (usually around 30 seconds). All of the ink transfers from the paper to the garment. Cold-peel transfers have a glossy surface and are typically preferred for athletic-looking prints. Some heat transfers can be either hot-split or cold-peeled. Heat Transfers are usually not as durable as a direct screen print.
Curing Plastisol Heat Transfers
When printing heat transfers, plastisol ink should only be gelled or brought to a semi-cure. This occurs between 180-250º F (82-121º C), just past the “wet” state. Transfers that have been semi-cured become fully cured when they are applied to the garment via a heat transfer press. If they are over-cured, the ink will not transfer well to the garment.
Testing for Proper Heat-Transfer Plastisol Cure
To determine the dryer settings for curing heat transfer plastisol ink, you may need to increase the conveyor speed, or decrease the temperature of the dryer until the stacked heat transfers begin to stick together or show a slight amount of set-off on the back of the upper sheet. Then decrease the conveyor speed enough to eliminate the sticking. Another test for gel (though not always accurate) is to peel the ink off the release paper and roll it into a ball. If the ball unrolls when laid down, the transfer is over-cured. A third test is the stretch test. The gelled ink layer should be cured just enough that you can peel it off the paper, but if you try to stretch it, it should break with very little stretch.
Always Test Screen Printing Plastisol Inks Before Using In Production
Always test inks to determine their suitability for your particular need and applications. Before printing a production run, print a sample and test for adhesion, bleeding, crocking, opacity, washability and any other specific requirements you may require.
Safety, Health and Environmental Concerns
Screen print plastisol inks are safe when used with reasonable care. Most plastisol inks used in screen printing contain no air-polluting volatile organic compounds (solvents). The manufacture, transportation, storage, use, and disposal of plastisol inks do not cause injury, illness, or environmental contamination as long as the appropriate safety and environmental protection procedures are followed. Most plastisol inks used for screen printing have a Health Rating of 1 (hazard - slight), a Flammability Rating of a 0 or 1 (hazard - slight), a Reactivity Rating of 0 (hazard - minimal) and a Personal Protection Rating of B (wear safety glasses and gloves).
For more information about screen printing and plastisol inks, give us a call at 314-382-9300. For technical questions or in-depth discussions, ask for David Landesman.
Lawson Screen & Digital Products believes the information contained herein is accurate and the opinions expressed here are those of qualified experts regarding the results of the tests conducted and data presented are not to be taken as a warranty or representation for which Lawson assumes any legal responsibility. This information is offered solely for your consideration, investigation, and verification. Always pretest inks yourself prior to running production.