Learn ways to increase your production while reducing cost, heat, and wasted energy.
Plastisol is still the most common ink used for T-shirt printing. It cures by fusion of a resin with a liquid plasticizer. Previously, polyvinyl chloride (PVC) was the primary resin; modern inks have moved away from PVC, but the principle is still the same. Think of the resin as grains of sugar dropped into a cup of tea. The solid sugar sinks to the bottom, and as you stir the tea, the crystals dissolve. The same thing happens with plastisol. The resin begins to absorb the liquid plasticizer when the temperature reaches roughly 180 to 210 degrees F. This means all we need to do is reach that temperature in the ink film.
Plastisol is thermally sensitive: The colder it is, the stiffer the ink and the higher its viscosity. (See Figure 6.) As we heat the ink, it softens and the viscosity drops. At 90 degrees F, the viscosity stabilizes and remains constant until it reaches 135 degrees F, where it begins to slowly thicken until it gels. This information will guide you in preheating the platens.
Put the press in no-print cycle with the flash units set for a 1- to 2-second exposure, then run the press until the platen temperature reaches ±145 degrees F. (See Figure 7.) Do this with ink in the screens so the hot platens will warm it. Do not start printing or color matching until the ink temperature exceeds 90 degrees F. The goal is to minimize the difference between the temperature of the ink and the screen and the temperature at which it gels.
Preheating the platens (FIGURE 7, left) will allow for quicker flash times. Cycle the press with inks in the screens to preheat the ink as well, lessening the work the flash unit must do. With quartz units and thermo probes tied to the control panel, the flashes cycle on and off as necessary (FIGURE 8, right) to maintain the ideal temperature, making it impossible to overflash.
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