Pretreating Garments for Direct-to-Garment Printing

June 07, 2010

When printing a garment using the direct-to-garment process, you must first pretreat it using one of three methods: indirect, manual spray; a semi-automatic offline system; or a direct, in-line system that is sometimes referred to as wet-on-wet.

The process of direct-to-garment digital printing is constructed of several crucial building blocks, and the pretreatment chemistry is truly the cornerstone of the process. This rather insipid-looking chemistry provides myriad functions that are essential in achieving a durable print.

The crucial function is the interaction between the pretreatment, garment and inks. The fixation must be absorbed into the fabric, while the inks must adhere to the pretreatment and form a bond between the two chemistries, linking them into a unified construction that is durable enough to withstand stretching, multiple machine washings, and daily wear and tear by the consumer.

A second function of the pretreatment chemistry is to provide a base on which the inks are to be projected. When you are dealing with droplets of ink (measured in Pico liters), the integrity of the surface is very important. This base provides a barrier to prevent the droplets of digital ink from falling into the natural weave of the fabric and destroying the detail of the printed image. Without this barrier, small detail (such as fine text) would be illegible, while large areas consisting of a solid color, such as a white background, would not have a uniform print appearance.

Three Pretreatment Methods
Customers currently have three methods of applying the pretreatment: the indirect, manual spray method; the semi-automatic offline system; and the fully integrated, direct in-line system, which is sometimes referred to as "wet on wet."

The traditional, indirect manual system consists of a separate process that is done outside of the direct-to-garment printer. The process is as follows: An operator takes the garment and presses it prior to the pretreatment application by placing it in a heat press for about 30 seconds. Once pressed, the operator then takes the garment and manually applies the pretreatment with a hand-held household-style sprayer. The garment is then taken back to the heat press and is re-pressed to set the pretreatment in the garment. It is important to a customer to apply the fixation as evenly and consistently as possible to ensure the wash fastness of the garment. If the garment hasn’t been pretreated sufficiently, the image will fade after a few washes.

The next method of application is by using a semi-automatic offline spraying unit. On the semi-automatic units, the garment is loaded onto a feed table after being pressed by an operator in a similar manner as in the manual process. The feed table then advances the garment through the spaying device that coats its entire front surface. The garment is then removed and, while wet, it is re-pressed under a heat press to set the fixation into the garment. Then the garment can be decorated on a direct-to-garment printer. Customers say this is more consistent than the hand-held spraying method, but the semi-automatic applicator means added investment.

There are several manufacturers of semi-automatic offline pretreatment application systems, and each manufacturer has specific procedures you should follow to properly apply the chemistry to the garment that matches their direct-to-garment equipment.

The most advanced pretreatment method is to apply the fixation automatically on the direct-to-garment printer. This process is only available on industrial versions of direct-to-garment printers from Kornit Digital, as well as its introductory-level Breeze 921 machine. This process, called “Pre T” by Kornit Digital, eliminates the additional labor of the traditional off-line operations that require an operator to hand-apply the pretreatment or undergo a secondary process. The garment is placed directly onto the printer and the proper amount of pretreatment is automatically applied immediately before printing begins.

The Wet-on-Wet Advantage
This wet-on-wet process from Kornit Digital varies from other processes, as it forms an adhesive matrix that neutralizes many variables present due to the manufacturing process of garments. It also produces a true chemical bond that connects the ink binder and the shirt itself. This process is unique to the Kornit line of direct-to-garment printers, as is the ability to load a garment directly onto the machine, automatically apply the fixation and then print immediately with white and CMYK inks while the pretreatment is still wet.

From a garment decorator’s perspective, the traditional hand-held application method is the most challenging. It compounds several variables with the operation being done completely by hand with a household-style sprayer. Plus, there is no way to certify beforehand that the correct amount pretreatment has been applied. The semi-automatic process has a much more reliable rate of application and will lay down a more consistent amount of pretreatment, but there are still two obstacles to overcome: the additional labor of performing the operation for each shirt prepared by either method and the non-quantifiable effect of the process.

The labor factor is a reality that needs to be added to the cost of each shirt printed, and little can be done to offset that burden except passing along the additional costs to the customer or cutting into the profit margins of each garment. And if the garments are pretreated too far in advance, the moisture content within the coated garment can change from the first shirt to the last shirt printed. This change could be a result of the way the shirts are stacked after coating, the length of time between spraying and the actual print process, or the amount of pretreatment applied.

Looking Ahead
The next industry advancement may be a much more localized pretreatment — one that is applied in the shape of the design so there is little waste, if any, or changes in the chemistry itself that will allow a dot-to-dot application of pretreatment to the inks in the printed image. Both provide dramatic possibilities in the way the direct-to-garment market will handle garments in the near future.

As the direct-to-garment printing industry continues to develop, so do the components that make the process more reliable and effective to use. The pretreatment — and its application — are the building blocks that will continue to improve with technology.

Paul Borucki is currently vice president of operations for Kornit Digital North America. He has more than 37 years of experience in the graphic arts industry. He has previously managed several sales organizations, and also founded an equipment manufacturing company that provided equipment to the printing industry.



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Pretreating Garments for Direct-to-Garment Printing
The process of direct-to-garment digital printing is constructed of several crucial building blocks, and the pretreatment chemistry is truly the cornerstone of the process. This rather insipid-looking chemistry provides myriad functions that are essential in achieving a durable print.
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