Paul Borucki, of Kornit Digital, explains the company’s unique garment-pretreatment system
The process of Direct to Garment digital printing is constructed of several crucial building blocks, and the fixation chemistry is truly the cornerstone of the process. This rather insipid-looking chemistry provides a myriad of functions that are essential in
achieving a durable print.
The crucial function is the interaction between the fixation, the garment and the inks. The fixation must be able to be absorbed into the fabric and the inks must be able to adhere to the fixation 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 fixation chemistry is to provide a base on which the inks are to be
projected. When you are dealing with droplets of ink that are measured in picolitres, 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 and large areas consisting of a solid colour, such as a white background, would not have a uniform print appearance.
Customers currently have three methods of applying the fixation: the indirect, manual spray method, the semi-automatic offline system and the fully integrated, direct in-line system, 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. An operator takes the
garment and presses it prior to the application of the fixation, by placing it in a common heattransfer press for approximately 30 seconds. Once pressed, the operator takes the garment and manually sprays it with a hand-held, householdstyle sprayer. The garment is then taken back to the heat-transfer press and is repressed to set the fixation 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 fixation is too little, the image will fail after a few washes.
The next method of application is by using a semi-automatic, off-line spraying unit. On semiautomatic units the garment, after being pressed by an operator as in the manual process, is loaded on to a feed table. The feed table then advances the
garment through the spaying device, which coats the entire front surface of the garment. The garment is then removed and, while wet, is re-pressed under a heat-transfer machine to set the fixation into the garment. Then the garment can be taken to the DTG printer and printed. Customers say this is more consistent than the hand-held spraying method but adds an additional investment for the semiautomatic applicator. There are several manufacturers of the offlinefixation application systems, hand-held or semiautomatic, and each manufacturer has specific procedures to follow to properly apply the chemistry to the garment in a way that matches their direct-togarment equipment.
The most advanced pretreatment method is to apply the fixation automatically, on-press. This process was only found on industrial versions of the Direct-On-Garment printers from Kornit Digital, but is now also being offered in an introductory-level
machine, the Breeze 921, also from Kornit. This process, named ‘Pre T’ by Kornit Digital, eliminates all the additional labour of the traditional off-line operations that require an operator to hand apply the fixation solution or process a garment
through a secondary operation. The garment is placed directly on to the printer and the proper amount of fixation is applied automatically, immediately prior to the print process. This wet-on-wet process from Kornit Digital varies dramatically from other processes, as it forms an adhesive matrix that acts to neutralise the many variables in the manufacturing process of the garments and then produces a true chemical bond that connects the ink binder and the shirt itself. This process is unique to the Kornit line of direct-togarment printers – to be able to load a garment directly to the machine, automatically apply the fixation and then print immediately on the wet fixation with white and CMYK inks.
From an owner’s perspective, the traditional hand-held application method is the most worrisome. This method compounds several variables, with the operation being done completely by hand with a household-style sprayer. There is little verification that the process has applied the correct amount of fixation. The semi-automatic process has a much more reliable rate of application and will lay down a more consistent amount of fixation, but there are still looming obstacles to overcome: the additional labour added to the operation, for each shirt prepared by either method, and then the nonquantifiable effect of the process. The labour is a reality that needs to be added to the cost of each shirt printed and little can be done to offset the additional labour burden, except to either pass along the additional costs to the customer or cut into the
profit margins of each garment.
Concerning the application of the fixation, if the garments are prepared too far in advance the moisture content within the coated garment can change from the first shirt to the last shirt printed. This change can be a result of the way the shirts are stacked after coating, the length of time between spraying and the actual print process, and the amount of fixation applied.
The next advancement may be a much more localised fixation – one that is applied in the shape of the design, so there is little if any waste or changes in the chemistry itself, and that will allow a dot-to-dot application of fixation to the inks in the printed image. Both provide dramatic possibilities in the way the DTG market will handle garments in the near future.
As the direct-to-garment industry continues to develop, so do the components that make the process more reliable and effective to use. The fixation and the application of the fixation are the building blocks that will continue to improve with technology.
Digital Textile Magazine, UK
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