Garment selection and prep aren’t just important in screen printing. They are also key when using direct-to-garment technology.
• Your best bet is a natural fabric; 100-percent cotton is ideal, although there are other options, such as bamboo. It’s possible to use some synthetic blends, but the quality that’s achievable varies in indirect proportion to the percentage of cotton in them – the more natural fiber, the better the print. This is because synthetic fibers are not as absorbent and ink has a harder time penetrating them. Also, there is a tendency for dye migration to occur when heat is applied to synthetics.
• Ring-spun garments typically yield a better DTG print because they are softer and generally have a tighter weave, lending to a smoother, more uniform surface for greater ink drop accuracy and less fibrillation.
• Finishing treatments, like those for garment softening, can cause pretreating issues. Most dyes won’t create difficulties, with the exception of strong fluorescents, some of which may become discolored or spotty when treated with acetic acid-based prep fluids.
• Usually, white shirts require no preparation for DTG printing. However, a dark shirt or any garment that is going to have white ink printed on it will need to be pretreated. This allows the white ink to stay on the surface of the garment for maximum opacity. (Think of this as a “chemical flash cure.”)
• All but one method of pretreatment involves spraying a salt-based chemical on the garment and drying it prior to printing. (The exception, from Kornit, pretreats as an integral part of the workflow process, with the shirt being drawn into the back of the machine, sprayed with the company’s pretreat chemistry, and then printed directly on the wet surface.)
• In the off-line systems, pretreatment fluid can be applied manually using either a task-specific spray gun or a Wagner-type airless sprayer from a hardware store. Or it can be applied with an automatic pretreatment machine, which offers more control over the amount of chemical used and the uniformity of its application.
• After applying the pretreatment, the shirt should be dried for 15 to 30 seconds in a heat press to not only drive off the water, but to matt down the cotton fibers. While many DTG inks can now be processed through a conveyor dryer, it is still important to press the pretreated shirt before printing.
• Because of the corrosive nature of pretreatment chemistry, it is important to clean both manual and automatic equipment thoroughly with water at the end of each use to avoid corrosion.
• Shirts can be prepared a month or more prior to printing.
• It is preferable to store print-prepared shirts flat, rather than folded, as folding may cause fibers that have been matted down during the pressing process to pop up and protrude through the ink film, reducing print quality.
Thanks to Geoff Baxter, director, M&R Digital Products Division, for his assistance with this summary.
For more, check out "Understanding the Garment: Selection, Testing, and Prep" or explore our February/March 2016 issue.
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