Common Issues with Pastisol Ink

Obtaining High Opacity on Dark Colors

Opacity is directly related to the type of ink, the thickness of the imprint, the type of textile fabric and dryer curing method. To obtain good ink coverage/opacity on the imprinted garment, please review the following topics to learn more:

Control the Thickness

Proper selection of mesh, squeegee type, and use of an opaque ink will lend to excellent coverage. The viscosity of the ink is crucial to laying the imprint on the surface of the garment. Fabric type and squeegee pressure will affect penetration of the plastisol ink into the fabric’s fibers. The best technique possible is to lay the ink layer on the surface of the garment. The thicker the imprint, the better the opacity. Often a white base image will be used to obtain good coverage on multi-colored designs. Many athletic sports jerseys are screen printed with meshes as low as 80/inch (32cm) to achieve very opaque and durable numbers.

Controlling Polyester Bleed/Dye Migration

Begin by using a good quality low bleed Ink. It is also important to recognize that fabrics will vary from one dye lot to another. It is highly recommended that a print test run is performed prior to starting production. When printing do not force the ink through the fabric. Allow as much ink as possible to sit on the material. This will give you better opacity and will allow the ink to cure faster. For better ink opacity you can print/flash/print if necessary. Cure at 325°F (163°C) or less. Cool the garments as quickly as possible: Do not stack hot. If necessary use alternating stacks with fans to allow garments to cool.

Try using Excalibur Sport Pro Inks. They are very bleed resistant and cure at lower temperatures to help avoid dye migration.

A plastisol ink goes through three stages. The first stage is the wet stage which is the state of a plastisol ink in the container or just after it has been printed on the garment prior to putting it through the dryer. The second stage is the gel stage which occurs somewhere between 180°—250°F depending upon the type of plastisol. The gel stage is the state you are trying to reach with a flash-cured underbase or conveyor-cured transfer, dry to the touch on the surface but not fully cured. The third and final stage is the cure stage. The final cure occurs when the entire ink film from top to bottom reaches 280°—320°F (depending upon the type of plastisol).

Check for Total Fusion or Cure

When the plastisol imprint reaches a temperature of 310°F – 330°F (154°C – 165°C) total cure has been achieved. Many plastisol inks are thermoplastic (soft when hot) and checks for cure must be made when the imprint is at room temperature. If the imprint cracks when flexed or stretched, improper curing is the likely problem. In cases where too much mineral spirits or non-curable reducers are added for thinning, the plastisol ink will not fuse no matter how long or how hot the cure.

1. Physically pulling and stretching the plastisol design is the best test of cure. Any cracking or crumbling indicates undercure. Check equal thickness on the entire design, as the thicker portions will cure more slowly. Abrasion resistance/scratching the design is a good method to check for proper cure.

2. Washability and/or adhesion is a good check. If plastisol was undercured the mechanical lock on the fibers will be weak and the washability poor. The definitive test to determine a fully cured print is still by washing the printed garment a minimum of three times. To perform this test use two garments that have been printed during a full production run. Do not use a shirt that has been printed and put through the oven by itself. Instead use a fully loaded belt to simulate a production situation. Unlike a conveyor belt loaded with multiple garments, a single garment requires less energy to cure because it does not have to share the heat with other garments.

3. Pigment crock or pigment migration to the surface is often confused with plastisol cure. In the majority of cases, when you are able to rub off the color, the problem is the initial mixing of the ink prior to printing. Vigorous stirring may be required. It is also a sign that the printed garment is undercured.

Other Considerations When Curing a Garment Printed with Plastisol Ink:

Left blank to keep toggle closed

Many printers think that heat is heat and the ink will cure at the exact same dryer temperature setting and belt speed for all garments. Many printers have also discovered this is a myth after undercuring garments and having to reprint the job. Fabric content will determine the length of time it takes to evaporate the moisture from the garments. Garments made from 100% cotton take longer because cotton fibers absorb and hold moisture unlike fibers of polyester or nylon. Fabric color must also be considered. The same reason you don’t want to wear a black t-shirt to the beach on the hottest summer day is the same reason dark colored garments cure quicker. Dark fabrics absorb heat instead of reflecting and will come up to temperature at a faster rate than light colored fabrics. The weight of the garment is another factor to consider in the curing process. Are you printing t-shirts, four-ply nylon reversible basketball jerseys, football jerseys or pants, sweatshirts or cut pieces that are printed prior to being sewn into a finished garment. All of these garments are of different thicknesses and the curing time for the garments will be different. The thicker the fabric the longer it takes to bring the fabric under the print up to temperature. Again, remember the moisture content we spoke of earlier. The heavyweight 100% cotton t-shirts not only take longer to bring up to temperature due to the fabric thickness but also have more surface area in which to hold in moisture which has to be evaporated before you can bring the heavier fabric under the print up to temperature.

The Fabric

Ink Film Thickness & Type of Ink

Different ink film thicknesses cure differently for the same reason different fabric thicknesses cure differently. There is more volume to be brought up to temperature. Even though the recommended cure temperature is 320° F for both inks, the thick athletic uniform print requires more time and heat than a soft hand print on a white t-shirt. Glitter or shimmer inks require more time and temperature but for a different reason. The metallic characteristics of these inks tend to reflect infra-red heat and require a longer time in the dryer as well as more heat to reach their required curing temperatures.

Room Temperature & Humidity

Having the doors and windows open creates a draft that sucks heat from your dryer and out the open windows or doors. The printed garment now has to compete with the outside elements to receive enough heat to become fully cured. Many shops use fans to try to keep the ambient temperature down. Avoid fans directly blowing into to dryer chambers or at flash cure units.
In high humidity conditions, heavier cotton garments can absorb moisture from the air. Running moisture layden garments through the dryer can delay cure times as well. Always test for cure under these conditions.

How Do I Measure Ink Film Temperature?

Most shops measure their ink film temperature with either a donut probe, temperature tapes or a non-contact infra-red thermometer. However, these methods only provide a reference for setting dryer temperatures and should not be used as a final test for determining cure. There are marked differences of opinion throughout the industry as to which of these types is most effective in helping the screen printer set his equipment temperatures most accurately.

Temperature Tapes

Pressure sensitive pieces of tape that are placed next to the print. One model has a coating with one temperature (270° F.) that is grey in appearance at room temperature but turns black and stays black when the temperature reaches that particular level. The second type has five fixed temperature levels on each tape. These five levels come in temperature ranges of 240—280°, 290—330° F., and 340—380° F. and also blacken and stay black when the temperature reaches that level. Even though many say these tapes are inaccurate because they only measure the temperature of the tape and not the ink film they are still commonly used due to their low cost. However, it is difficult to dispute chemists and printers who say that the technique of placing the temperature tape inside the garment underneath the ink area is the only way you can prove the entire ink film above the tape has reached the required temperature. Many industry experts suspect the accuracy of these tapes to be somewhere around + or – 10% so you must be careful that an indication of 330° F. is not actually 10 percent less or closer to 297° F. where the ink film may not fully cure.

Donut Probe

A round, teflon ring with two wires that cross in the center of the ring. The ring is connected to a hand-held thermometer by a teflon coated wire. The donut is placed on the print with the two wires actually sitting in the wet ink. As the garment travels though the dryer the actual ink film temperature appears on the screen of the hand held thermometer. This is considered to be a very accurate measurement of ink film temperature because you are seeing the temperature deeply into the as the wires sink through the ink and touch the garment. However, the accuracy of this method has also proven to be somewhat suspect depending upon the length of the dryer and by how well shops keep the contact point (where the wires cross) free of oil and ink residue to prevent false readings.

Non-Contact Infra-Red Thermometer

(sometimes called a raygun because of the manufacturers name)

These devices are hand-held and when aimed at the print from a distance of 6-12 inches provide a good reference point for the temperature of your ink film. Like the previous two methods the non-contact thermometer is not without a disclaimer also. It only measures the surface temperature of the ink film and does not tell you the temperature in the middle of the ink film or at the bottom where the ink film actually touches the shirt. You must make sure you are aiming accurately at the printed design. Even with these disclaimers, there are many who claim that its speed and accuracy make it the current way to go.

Overcuring and Overflashing

When printing on 100% polyester try not to exceed 330°F. Even though the ink film may be fully cured at this temperature, the components used to give the inks their low-bleed characteristics do not stand a chance if too much heat is applied to the garment. Remember that these inks are low-bleed inks, not no-bleed inks. When printing any polyester blended garment you will not only have to ensure a full cure but also ensure that you do not overcure.

Overflashing can cause a problem with the adhesion of the top colors adhering to the underbase color. If for some reason a printer would actually cure the underbase print he would get what is called poor “intercoat adhesion” of the top colors to the underbase colors. Recommended gel or flash cure temperatures of inks commonly used to underbase are approximately 240—250°.