Keepin‘ it light in terms of Ts is so last decade and digital direct-to-substrate, so past the figure it out phase, evidenced by developments being made to perfect the process. Little tweaks have us looking beyond just getting by and onto how to improve, and D2 pre-treatment is one of those ancillary assets. While the pre-treat process may not be amid the most intriguing aspects of this dynamic technology, it is of utmost importance, increasing the integrity of the print and digital-direct industry itself.
Can’t beat the pre-treat
Likening the process to that of applying primer between drywall and paint layer one, i-Group Technologies’ Brian Walker says that pre-treatment serves two functions. “One is to keep the ink from soaking into the garment. Since the inks are water based and shirts are fabric, the ink wants to soak into the shirt. This is not conducive to good white ink DTG printing.” Optical whiteness suffers, he explains, due to the ink being in and not sitting atop garment fibers. “Second, the pre-treatment actually causes a reaction with the white ink, causing it to morph so that it adheres to the fabric while simultaneously giving the CMYK inks a smooth surface on which to print and adhere.” Ultimately, pre-treating allows digital decorators with white ink capabilities to print with and onto any color.
Auto pre-treatment machines are designed to reduce labor costs, minimize pre-treatment used and provide a more even and consistent spray pattern. Image courtesy i-Group Technologies LLC
“The pre-treatment for dark shirts is a proprietary formulation that actually reacts with the chemistry of the white ink, causing it to gel on contact,” adds Geoff Baxter, The M&R Companies. “White shirts require no pre-treatment. Black and dark shirts require a pre-treatment to allow for opacity and adhesion of the white ink. Pastel shirts may require a light pre-treatment if a white highlight print is being used.”
Joe Lackey, Big Frog Custom T-Shirts of South Tampa, describes D2 pre-treat for dark shirt/white ink (DSWI) printing as the most critical step to getting a quality print. “If a shirt is not pre-treated properly, I don’t care if you print it at the U.S. Mint, it won’t print well.” At his shop, D2 pre-treatment is broken down into the aforementioned DSWI and CMYK. “CMYK printing used for white and light- to mid-colored shirts does not require pre-treat. Our DSWI printing is used for darker garments or any garment that requires white ink,” he explains.
Image courtesy Lawson Screen & Digital Products, Inc.
For certain systems, pre-treatment purposes do, however, come into play without the presence of dark shirts or white ink.
This is the case for Rob Dubow of Dubow Textile Inc., a shop that employs a digital direct-to-substrate system with the pre-treat process built right in. “We pre-treat every garment we print digitally,” Dubow reports. To him, this is a necessity for quality and vibrancy. “If something goes awry with the pre-treatment and it misses a spot, whether it’s white or dark for us, you can definitely tell.”
System discrepancies aside, any time white ink is at bat, pre-treatment is in full swing. But white ink pre-treatment is particular, and CMYK doesn’t tend to work well in conjunction. “You do not want to print straight CMYK on a pre-treatment designed for white ink,” Walker cautions, stating that washability of CMYK ink is dramatically compromised.
Images courtesy Big Frog Custom T-Shirts of South Tampa www.BigFrog.com/SouthTampa
Similarly, D2 pre-treatment for dark garments should not be used on white shirts, Baxter points out. “It may enhance the initial appearance, but will nearly always detract from wash-fastness and may yellow over time,” he remarks. “There are a number of pre-treatments on the market specifically designed to increase durability and color vibrancy on white shirts. These are optional, and it should be considered whether they might be right for a particular job.”
As for those options, Lackey predicts that pre-treating, even with CMYK, would probably always result in a better print. “Problem with that is the time it takes to do it,” he says. “Time is the big reason CMYK costs less than DSWI.” Adding to the process’ time and money costs, Lackey mentions materials like parchment paper and pre-treatment itself. “Those items do factor into the extra cost of a DSWI shirt. It takes about one minute to pre-treat a shirt, which includes drying time,” he explains. “We utilize two heat presses so we can pre-treat shirts at the same time we’re printing. This definitely cuts down on the time which, in the end, is still the most expensive part of the process.”
Walker offers additional heat press advice, suggesting it’s sometimes better to hover before making contact to start heating the pre-treatment. “Utilizing a good parchment paper or Teflon and very high pressures are required on the heat-press,” states Walker. He finds that the higher pressure will actually result in a better finish for the cured, pre-treated garment. The pressure also helps drive out any remaining moisture, which equals bad news in pre-treating, as a bone-dry shirt is optimal for most applications, reports Walker.
Dubow Textile’s printers have in-machine pre-treatment, allowing the machine to lay down a pre-treatment solution which is then checked manually to ensure an even coating on the garment. “We actually tap it down with a towel just prior to the ink being applied,” says Dubow. “We don’t stop the machine. It does the pre-treatment, we tap it down and then the ink is applied within seconds after.” A manual procedure made part of their production, operators conduct the pat-down process for both light and dark shirts.
In a different approach, Lackey’s stand-alone automatic pre-treatment machine sits right next to the printer. His pre-treat device sends a shirt through on an adult-sized platen that moves in and out of the machine at a set rate, applying an even spray to a pre-set area as the shirt exits. It can be set to start and stop spraying at desired intervals, treating areas large or small. “When the shirt is out, we squeegee it with a wide spatula-looking plastic tool that’s actually used for drywall-finishing purposes. The squeegee part is done multiple times in one direction only to smooth down the fibers of the shirt,” explains Lackey.
This shop’s direct-to-substrate pre-treatment system is built in, laying down solution for every job, white or black. (Images courtesy Dubow Textile Inc.)
According to Walker, completely manual options involve either using a roller to apply pre-treatment to a garment or utilizing a power sprayer. Automatic pre-treatment machines, on the other hand, vary in functionality and price ranges, with generally two selections: single and multi-nozzle units. Auto pre-treaters, he continues, are designed to reduce labor costs, minimize pre-treatment used and provide a more even and consistent spray pattern. “Most pre-treatment machines are going to be much faster than the printers they are supporting,” Walker adds.
In Baxter’s estimation, the most apparent advantages of automated pre-treatment systems are that they provide consistent chemical dosage and can substantially reduce cost by controlling excess or overspray. “A nice side benefit is that they limit the amount of chemical spray that the operator is exposed to.”
Walker names increased productivity and consistency as another advantage to the auto stand-alone, stating that hand-prepped shirts will most likely have more inconsistencies than would an automated system.
“Pre-treatment is basically nonionic latex polymers and cationic salts and water,” says Walker. “The polymers are there to enhance the adhesion and wash-fastness of the inks. The dry layer of pre-treatment provides a smooth surface for printing and better adhesion to the fabric.”
Baxter brings up that the pre-treatment contains a very small amount of a binder to aid in white-ink adhesion and a chemical that causes the white ink formulation to crash or gel. “This allows the very low-viscosity ink to sit on the surface of the garment rather than being absorbed into the fabric.”
Specifically designed to be used on 100 percent cotton, the formulation always works best on this fiber, Baxter says of his company’s pre-treat, which will work on some synthetics and blends at the expense of white ink bleed resistance. “What happens is that when the dyes used in blends and polyester fabrics are exposed to heat, they have a tendency to sublimate and discolor the white ink,” explains Baxter. On a red 50/50 garment, this nearly always translates to pink-tinted white ink.
Walker speaks of CMYK-specific pre-treatments to enhance washability and color intensity on poly or 50/50 fabrics. “Polyester fabrics are designed to wick moisture away from our bodies,” states Walker. “Digital inks are water based and, on a polyester fabric, will be wicked away. You can’t get nice bright colors, the washability is poorer, and you can’t maintain super high detailed images due to the wicking.” Pre-treatment is therefore designed to better hold the pigments, preventing the ink from wicking and noticeably alleviating these issues when used properly, he says, noting that currently, the technology to pre-treat dark polyester fabrics is not available…but on the horizon.
“There really are no short cuts to pre-treating,” Lackey concludes. “Naturally, the quality of the art and your printing equipment is important, but without good pre-treat, the rest doesn’t matter.”