Mark Vasilantone, president of Vastex International, debates the pros and cons of using heat presses, flash cure units and conveyor dryers in DTG printing
Direct-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 heat presses, which flatten and degrade the image in the course of drying it. It is uncommon for flash cure units to be used to dry pretreatment since they are equally as slow as heat presses and lack the ability to flatten fibres prior to printing.
A heat press can dry pretreatment, flatten raised fibres and dry the DTG printed image, at low cost, but at low rates and with reduced quality.
Infrared conveyor dryers
Infrared conveyors dryers are larger and more costly units that require two square metres or more of floor space, and consist of a heating chamber positioned above a conveyor belt. These machines use infrared radiation to rapidly raise the temperature of the ink (not the air in the heating chamber) to evaporate moisture as the garment is conveyed.
Some infrared conveyor dryers such as the Vastex LittleRed X2D and X3D models are designed specifically for DTG applications and feature a pre-heating zone that boosts the ink to its ideal evaporation temperature of approximately 160°C in the first several centimetres of conveyor travel, maximising the amount of conveyor travel during which evaporation occurs at the greatest rate. This allows the highest possible conveyor belt speeds, maximising the rate at which garments can be dried before exiting the heating chamber.
The efficiency afforded by DTG-specific infrared conveyor dryers can benefit the pretreatment phase of the DTG process by drying pretreated garments many times faster than is possible when using a heat press or flash cure unit. This also relegates the heat press to flattening of raised fibres prior to printing, accomplished in a one-second ‘touch’ per garment. Drying of the DTG-printed image also benefits from the speed and efficiency of a DTG-specific conveyor dryer, which preserves the quality of the printed image while eliminating a capacity bottleneck common in DTG applications. Another benefit of the conveyor dryer is that it allows the curing to be unattended. Once it is set up properly, the garments are simply placed on the belt, and the rest is automatic.
Applications and choice
For most DTG printing businesses, the production process involves several steps: spraying pretreatment, drying pretreatment, flattening fibres, inkjet printing of the garment and drying of the printed garment. The selection of a heat press, flash cure unit or conveyor dryer, alone or in combination, should hinge on your print shop’s anticipated volume, your budget and the desired print quality.
