Discharge inks are experiencing a renewed interest among garment screen printers. This article describes the types of ink systems available, proper use of these formulations, and the safety precautions you should employ when working with them.
By Mike Ukena
Thiourea itself also warrants consideration. This chemical compound has some very unique handling and shipping requirements. It is considered to be a spontaneously combustible product. While the actual use of this product is not as dangerous as that expression may sound, there are some definite handling requirements, and it cannot be shipped without hazard packaging via UPS and Federal Express. I do not think that these challenges are impossible to overcome and believe that these products will be made easier to use and transport in the future.
Methods of using discharge
There are two distinct methods of discharge printing, both of which can be used regardless of discharge system. The traditional method is to discharge every color in the print. By discharging all colors, there is no need for an underbase screen. This technique saves a screen and does away with the need for any flashing between colors. The exception to this all-color rule is when a black-ink screen is needed. There’s no need to use discharge if the black will cover without it. If the fabric is black, any black that is part of the design can be reversed out to use the shirt color itself.
The second method is to use discharge strictly as an underbase. With this method, you can use either white discharge or natural discharge, which contains no pigment of its own and reveals the ground color of the fabric. Then, with or without flashing, the subsequent colors are printed with regular plastisol. I prefer to not flash the discharge underbase. This method saves not only the head used for the flash, but also any cooldown heads. The result is that printers can increase the number of colors they can print on dark shirts by at least one, possibly two.
The white discharge underbase works extremely well for most design types, especially spot-color work. Even though the other colors are printed using plastisol, the overall print has a less heavy feel because the underbase is basically a water-based product. If a design contains halftones or other areas with very thin ink deposits, then a natural discharge underbase may work much better. The white pigment in the white discharge underbase may mix with subsequent thin ink deposits and shift their color. But this is usually not an issue with spot colors.
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