ARTICLES

 

Pros and Cons of Heat Presses, Flash Cure Units and Conveyor Dryers
for Direct-to-Garment Printing

Direct-To-Garment is no longer a single type of textile printing; it's now a whole range of types, from DTG printing of up to 35 garments per hour on the most basic Epson®, Anajet® and Brother® machines, to printing 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 salability of the printed garment. Factor in recent advances in DTG-specific drying technology, and it becomes clear that a prudent dryer purchase should start with an understanding of how well the dryer will complement the printer, and how it will impact your capacity, quality and budget requirements.
 

Pretreating of fabrics prior to inkjet printing

Most Direct-To-Garment printing requires fabrics to be sprayed with a pretreatment that prevents water-based inks from being absorbed too quickly into the fabric. For white and light-colored garments, pretreatment may be unnecessary, but it is essential when inkjet printing on fabrics of darker colors. How the pretreatment is applied and/or dried greatly impacts the quality, capacity and profitability of the DTG process, as does the method employed to dry the printed image.
 

Heat Presses dry and flatten

To produce high quality printed images, the fibers of pretreated fabrics should be flattened prior to inkjet printing. This is accomplished in one of two ways depending on the type of printer employed:

Conventional DTG printers require garments to be pretreated and dried prior to printing. For the highest quality images, and to prevent clogging of inkjet print heads, raised fabric fibers should be flattened. The conventional method of simultaneously drying and flattening of pretreated fabrics is with a heat press (FIG. 1), which can also be employed to dry the printed image, minimizing capital investment and consuming only 9 square feet or less of floor space.

However, a heat press typically requires 30 to 45 seconds to dry the pretreatment, plus an additional 30 to 45 seconds if it is also used 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 of raised fibers benefits the pretreating portion of the DTG process, it also flattens the printed image, creating a shiny, too-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 salability of the printed garment.

As a result, heat presses are generally utilized for both drying of pretreatment and of the printed image only by beginning 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 previously been dried using a flash cure unit or, more commonly, an infrared conveyor dryer.
 

Kornit® machines eliminate heat press flattening of fibers

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 fibers flat. Because they are wet, the fibers 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 fibers using a heat press prior to inkjet printing, it also saturates the image area, requiring longer drying times and/or more powerful dryers than 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 color before printing another, flash cure units (FIG. 2) can also be employed as a low cost method of drying DTG printed images, albeit slowly.

Requiring less than 9 square feet 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 flattened and degrade the image in the course of drying it.

It is uncommon for flash cure units to be utilized for drying of pretreatment since they are equally as slow as heat presses and lack the ability to flatten fibers prior to printing.
 

Infrared Conveyor Dryers

Infrared conveyors dryers (FIG. 3) are larger and more costly units that require eighteen square feet 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 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 320°F (160°) in the first several inches of conveyor travel, maximizing the amount of conveyor travel during which evaporation occurs at the greatest rate. This allows the highest possible conveyor belt speeds, maximizing 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 possible using a heat press or flash cure unit. This also relegates the heat press to flattening of raised fibers 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 infrared conveyor dryer, which preserves the quality of the printed image while eliminating a capacity bottleneck common in DTG applications. This especially the case with Kornit® machines that pretreat and print with no drying in between, producing an extremely wet image area requiring a correspondingly larger dryer to match the output of the printer.
 

Dryer applications vary by DTG method, volume, budget and desired quality

For most DTG printing businesses, the production process involves several steps: spraying pretreatment, drying pretreatment, flattening fibers, 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 anticipated volume, budget and desired quality.
 

TYPICAL DTG SCENARIOS

EPSON®/
BROTHER®/
ANAJET®
Apply Pre-treatment Dry and Flatten Pre-treatment
with Heat Press
DTG Print Dry Using Heat Press $
EPSON®/
BROTHER®/
ANAJET®
Apply Pre-treatment Dry and Flatten Pre-treatment
with Heat Press
DTG Print Dry Using Flash Cure $$
EPSON®/
BROTHER®/
ANAJET®
Apply Pre-treatment Dry Pre-treatment Using Infrared Conveyor Dryer Flatten Fibers Using Heat Press 'Touch' DTG Print Dry Using Conveyor Dryer $$$
KORNIT® Apply Pre-treatment, Flatten Fibers and DTG Print Dry Using Conveyor Dryer $$$$

Pros and Cons of Heat Presses, Flash Cure Units and Conveyor Dryers for Direct-to-Garment Printing

(FIG. 1) Heat press, shown on a utility cart, can dry pretreatment, flatten raised fibers and dry the DTG printed image, at low cost but at low rates and with reduced quality.

Pros and Cons of Heat Presses, Flash Cure Units and Conveyor Dryers for Direct-to-Garment Printing

(FIG. 2) A DTG-printed garment can be placed on either rotary pallet and swiveled under the flash cure heater to dry DTG printed garments, at low rates but with high quality.

Pros and Cons of Heat Presses, Flash Cure Units and Conveyor Dryers for Direct-to-Garment Printing

(FIG. 3) Specialized infrared conveyor dryer for DTG applications pre-heats the DTG printed image to optimum curing temperature within several inches of conveyor travel, maximizing conveyor belt speed and drying capacity during the pretreatment stage of conventional DTG processes, and post printing stage of both conventional and Kornit® DTG processes.