Images Magazine November 18

TIPS & TECHNIQUES www.images-magazine.com 28 images NOVEMBER 2018 D irect-to-garment is no longer a single type of textile printing; it now encompasses a whole range from printing up to 35 garments per hour on the most basic Epson, Anajet and Brother machines up to as many as 220 garments per hour on high-capacity Kornit machines – and everything in between. Methods of drying the pretreatment and the printed image also run the gamut, and affect not only the output of a DTG system, but also the appearance and saleability of the printed garment. Heat presses dry and flatten Conventional DTG printers require garments to be pretreated and dried prior to printing. To produce high quality printed images, and to prevent clogging of inkjet print heads, the fibres of pretreated fabrics should be flattened prior to pressing ‘print’. The conventional method of simultaneously drying and flattening pretreated fabrics is with a heat press, which can also be used to dry the printed image, minimising both capital investment and floor space usage. However, a heat press typically requires 30 to 45 seconds to dry the pretreatment, plus an additional 30 to 45 seconds to dry the printed image. Both wait times require an operator’s attention unless the heat press is equipped with an auto-release. Perhaps the most significant downside of drying printed images using a heat press is the visual result. While flattening raised fibres benefits the pretreating portion of the DTG process, it also flattens the printed image, creating a shiny, overly-smooth, ironed-on appearance that fails to reproduce the depth and vibrancy of the original art. Heat presses may also leave an impression or ‘halo‘ around the image that can also impair the appearance and saleability of the printed garment. As a result, heat presses are generally utilised for both drying of pretreatment and of the printed image only by DTG printers with low volumes, budget constraints and space limitations that outweigh quality concerns. Conventional DTG printers with low- medium to high capacity requirements also rely on heat presses, but only to quickly flatten pretreated fabrics that have been dried using a flash cure unit or, more commonly, an infrared conveyor dryer. Inline pretreatment Unlike stand-alone DTG inkjet printers, high capacity Kornit-type machines both pretreat and print with no drying in between, by first spraying the fabric with pretreatment and then passing it under a plastic squeegee that lays the fibres flat. Because they are wet, the fibres remain flat, allowing the unit to then inkjet onto the flattened surface. While this method eliminates the need to dry the pretreatment and/or flatten fibres using a heat press prior to inkjet printing, it also saturates the image area, requiring longer drying times and/or more powerful dryers than for those images printed onto pretreated fabric that has been dried prior to printing. Flash cure units More commonly used in screen printing to partially dry one colour before printing another, flash cure units can also be employed as a low cost method of drying DTG printed images, albeit slowly. Requiring less than a square metre of floor space, they radiate infrared heat to cure one DTG-printed garment at a time with good edge-to-edge consistency, producing a higher quality result than Mark Vasilantone, president of Vastex International, debates the pros and cons of using heat presses, flash cure units and conveyor dryers in DTG printing A specialised infrared conveyor dryer for DTG applications pre-heats the DTG printed image to optimum curing temperature within several centimetres of conveyor travel, maximising conveyor belt speed and drying capacity during the pretreatment stage of conventional DTG processes, and the post printing stage of both conventional and Kornit DTG processes Mark Vasilantone