By Melissa Donovan
Part 1 of 2
Direct to garment (DTG) printing is commonly used for 100 percent cotton or cotton/polyester blends. There is a push to open up textile opportunities into 100 percent polyester garments. One way to do this is to use a pretreatment. Pretreatments are not new technology. When DTG printing, the liquid solution is traditionally used to enhance prints on dark/colored garments and ensure ink adhesion. It can also be applied to white garments, although it isn’t necessary.
Pretreatment options for DTG are offered for multiple reasons. Some of these include improving printing to a black/dark colored garment, increasing image quality on white garments, and most recently enabling printing directly to polyester-based garments. Pretreatments are an important part of the DTG process.
“Pretreatments are not just important, but necessary for the entire DTG industry. Without a pretreatment, an ink will not properly adhere onto the textile being decorated. In fact, pretreatment is the most important step in the process. Improper pretreatment will result in bad qualities such as poor vibrancy, staining, bad hand feel, and poor wash,” adheres Shawn Liu, director of digital technologies, Eastern Tech Company.
Timothy Check, senior product manager, professional imaging, Epson, makes the analogy of DTG pretreatment and inks to home paints—with the pretreatment the primer and the inks the paint. “Walls need to have primer applied to allow the paint to adhere and have even coverage. There can be different primers used to allow paint to adhere to different materials like drywall, metals, and plastics. Likewise, there are different DTG pretreatment liquids optimized for different fabric types and colors to allow the ink to perform its best.”
When printing on dark garments, pretreatment is essential. “Current ink technology requires a pretreatment solution to be applied to the garment for the white base layer to be durable and provide a durable backdrop to the chosen colored print design,” says Eric P. Beyeler, global marketing manager Artistri textile inks, DuPont.
Prints will “lack color vibrancy and have a washed out look,” according to Taylor Landesman, VP, Lawson Screen & Digital Products, Inc. if pretreatment isn’t used on dark garments. This is because DTG inks are water based and not naturally opaque.
Even though pretreatment isn’t required for white garments, it does offer benefits. “Other benefits for using pretreatment—even in the case of white shirts, when you are only printing CMYK—are increased image quality and durability. With the help of an excellent pretreatment, prints will last longer, even after multiple washings and regular wear,” explains Paul Crocker, marketing director, AnaJet, Inc., a Ricoh Company.
“For most printers, these benefits outweigh the cost, as they can help increase customer satisfaction—fewer product returns, and allow for faster printing using less ink,” adds Beyeler.
For a DTG printer to output on 100 percent polyester garments, pretreatment is necessary. “Printing on black/dark polyester is the next technology frontier for DTG printing. Dyed polyester fabrics provide a unique challenge as the dye tends to migrate into the white ink layer,” advises Beyeler.
Check agrees saying that when printing on polyester fabrics pretreatments prevent the ink from sinking into the fabric.
Working with Ink
Pretreatments work best with the ink set they are specifically designed for, but there are generalized solutions available.
Scientifically speaking, pretreatments contain an ink crashing mechanism, polymers for adhesion, and some liquid vehicle carrier, says Beyeler. “When the ink is jetted onto a pretreated garment, the ink solidifies or gels. This causes the ink to remain on the surface of the garment, which will give maximum color as well as control color bleed.”
Products should be tailored to the printer and ink to ensure the best match. “Because printer brands use different ink sets, it’s necessary to tailor a pretreatment to get the best results for that individual printer—not just have a general pretreatment,” shares Liu.
“For best results use pretreatment liquids designed and optimized for the specific ink from the same manufacturer. Reputable brands have a team of chemical engineers that optimize the chemistry of the ink and pretreatment to work together as a matched system,” agrees Check.
Applying the Pretreatment
Pretreatment is applied externally from the printer or inline with the printer. It depends on the ink, printer, and how the pretreatment is configured to work with them.
For external options, Liu says pretreatment in his experience is applied manually, using a hand sprayer or an automatic sprayer system.
“Spray guns are generally used in smaller print shops and can be very effective when used by an experienced operator. For such an application, it is best to isolate a spray area away from the printer, so not to affect the printer or any other equipment process,” explains Beyeler.
AnaJet users generally pretreat externally, prior to printing, through a few different methods, says Crocker. One way is a handheld HVLP Wagner power sprayer and others use a dedicated, enclosed pretreatment machine.
“Pretreatment machines were developed to make a more consistent and cleaner application. These machines use a small pump to push pretreatment through a spray nozzle. They usually include a spray box to contain overspray and keep the working area clean. These can help boost productivity for medium to larger print shops,” admits Beyeler.
The key is to apply the pretreatment consistently. “If pretreat is applied in an inconsistent manner it will affect the final print. You can see this if the colors on one area of the print look different than another. Also, applying too much can cause the DTG image to wash out prematurely,” cautions Landesman.
Steps after pretreating externally and prior to placing the pretreated garment in the printer may include a tunnel dryer or air drying, or laying the garment on a heat press—it is all dependent on the pretreatment, according to Crocker.
Pretreating externally, or a Check calls “dry printing” is beneficial because it can be done in advance of printing. It also offers superior print quality, greater workflow efficiency, and reduced costs.
Running pretreatment inline is something Check refers to as a “wet-on-wet printing process” where the pretreatment is applied to the garment while in the printer and then ink is applied to that wet surface. “The benefit is that pretreating and printing are done by a single device.”
According to Celine Tezartes Strauss, product manager, inks and consumables, Kornit Digital, an integrated process—inline pretreatment—is ideal because it eliminates any additional work.
The Importance of Pretreatment
Pretreatments for DTG printing are available for both white and dark garments as well as cotton and polyester. The nature of the ink used in DTG printing, water based, means that it requires a base in many instances to avoid the ink seeping through the garment and this is where pretreatments come into play. While not all garments require pretreatments, using them provides added benefits of enhanced image quality and increased durability.
The next article in this two-part series provides a roundup of available pretreatments for DTG printers.
Feb2019, Digital Output