By Lisa Guerriero
Fabric presents extensive opportunity for print providers. Textile graphics are everywhere, from retail displays to fashion runways. In response to demand, ink manufacturers develop and adapt products for digital textile printing.
Sublimation or dye-sublimation (dye-sub) remains a popular method. There are two kinds of dye-sub printing, transfer and direct. With transfer, the graphic is printed onto special paper and then transferred to fabric with a heat press. With direct, a heat press sublimates the print directly onto the final substrate.
Dye-sub utilizes disperse dye. By definition, sublimation is a phase transition from a solid to a gas, and does not go through a liquid phase. Disperse is an outgassing process in which the colors are set in the substrate.
Fabric is also printed on through a fixation process. Acid, pigment, and reactive ink require heat or steam to fixate the image to the fibers of the fabric.
Improvements to disperse, acid, pigment, and reactive ink allow digital fabric printing to penetrate new markets. Applications traditionally associated with other substrates and printing methods—including banners, home décor, and fine art prints—are now achievable with sublimation and fixation ink.
Disperse Dye for Sublimation
Transfer and direct dye-sub both utilize disperse dyes and print on polyester. Vendors say product improvements enable dye-sub to be used in more applications then ever before, leading to dramatic growth in this segment.
Tommy Martin, manager, textile and apparel business development group, Mimaki USA, Inc., says disperse ink is thriving because manufacturers adapted their products to advancements in technical and high-performance fabrics.
“Evolution of these fabrics is driving a change in the colors, ink performance, and the equipment, resulting in higher quality output and faster equipment speeds,” explains Martin.
Advancements in color gamut and durability play a role in dye-sub’s prevalence as well.
“Manufacturers are adding more colors—such as true black, gray, green, orange, and a number of neon shades—to expand the color gamut to cater to increasing standards,” notes Edmond Fung, director, Gunsjet by Digitex Printing Technologies Co., Ltd.
Better suspension of disperse dye allows it to perform well during printing, explains Lily Hunter, product manager, textiles and consumables, Roland DGA Corporation. “This improved suspension helps prevent settling and separation that can lead to color shifts and clogged printheads in the printer,” she says.
Because disperse dye is ideal for polyester printing, it’s used in a variety of fabric applications such as silicone edge graphics and apparel.
In addition, disperse dyes “offer high brightness and good show through—the image is visible on both sides of printed media—which is important for flags, banners, and trade show graphics,” notes Peter Saunders, business director, digital, Sun Chemical Corporation.
For soft signage, polyester is a viable and popular alternative to vinyl, and “dye-sub inks, whether direct printing or using a transfer paper, enable this shift,” explains Nufar Kiryati, marcom manager, Bordeaux Digital PrintInk Ltd.
Setting disperse dye is less challenging than other types of ink sets. Dry heat transforms the ink from solid to gas, penetrating the textile and sublimating the dye.
The sublimation process requires a heat or calendar press set at about 400 degrees Fahrenheit, for 30 to 90 seconds.
Pressure also plays a role in transfer dye-sub, suggests Jack Papaiacovou, director of technology, Hilord Chemical Corporation.
He recommends 20 to 30 PSI for typical transfer dye-sub inks, and adds that “depending on the substrate—different polyesters for example—the process may require a different set of values for temperature, time, and pressure.”
Disperse dyes enable printing on other substrates in addition to fabric. Vendors now design inks that allow print providers to utilize their dye-sub equipment for multiple applications and different vertical markets.
“They are used to print on all sorts of gift and premium products with a polyester-coated surface,” notes Fung.
Acid, Pigment, and
Acid, pigment, and reactive inks are fixated to the substrate via heat or steam versus undergoing the sublimation process like disperse dye.
A key advantage of acid dye is the ability to directly print on textiles that are difficult, or impossible, with other ink types. Acid dyes are used on synthetic polyamides like nylon, as well as select natural fabrics including silk and wool.
“With acid inks on nylon and silk, the colors are bright and the overall lightfastness is better, so the process is ideal for outdoor flag applications,” says Martin.
Because acid dyes penetrate challenging textiles, they require a lengthier and more complex fixation process compared to dye-sub. For this reason, they are used in mills and other industrial settings.
After pre-treating and printing the fabric, it must be steamed at about 215 degrees Fahrenheit with a production steamer. Steaming generally takes between 20 and 45 minutes; duration varies by ink brand and steamer type. The fabric is then washed and dried.
“The time and water usage is very significant,” for acid dyes, observes Ken Hogrefe, technical marketing, DuPont Digital Printing.
Pigment inks are printed and fixed directly on the substrate. While acid and reactive inks require steam, an oven or a heat press is used for pigment ink. Curing takes between 30 seconds and three minutes depending on the product. The curing temperature is between 325 and 375 degrees Fahrenheit, also depending on the product.
Manufacturers continue to develop pigment ink sets with broader ranges and better capacity for saturation. These inks mimic or approximate the gamut of acid and reactive inks, but offer an easier production process as well as significantly less waste.
In the past, particles suspended in pigment ink clogged printheads, but this issue is addressed with newer products. “Pigment will print on all fibers but is a very large particle, so getting maximum color with high-speed runability is a recent advancement,” says Marty Silveira, VP, sales, DigiFab Systems, Inc.
The combination of better color and easier fixation, along with improved lightfastness, allows pigment ink to compete in new arenas, particularly home furnishings and decor.
“The larger market opportunity of home goods fabrics—such as upholstery, curtains, and wallcoverings and cotton-based soft signage—primarily done in the past via reactive dye, are now migrating to new technology such as pigmented emulsion inks,” observes Craig Reid, VP, digital division, INX International Ink Co.
Durability improves. Pigment inks historically lacked washfastness, an issue new products address. Crockfastness or resistance to rubbing is also enhanced. These qualities are necessary for ink to withstand wear and tear of applications like furnishings.
“These inks offer long-term lightfastness and durability, excellent washing performance, and independence from fabric type,” notes Saunders.
Versatility is another benefit. Vendors design new pigment inks for both natural and synthetic textiles, including cotton, linen, and in some cases cotton/polyester and cotton/silk blends.
“Pigment inks can be used on a range of fabrics types with good print quality,” notes Hogrefe.
Though pre-treatment is required for dark fabric printing, recent improvements enable “greater compatibility with various types of pre-treated and non-treated fabrics,” says Hunter.
Reid notes that some vendors now offer matched pre-treatment fluids in combination with their pigment inks.
Reactive dyes are printed and fixed directly on the substrate. Though pigment inks are expanding into cotton, reactive dyes remain popular. They offer the color range and resiliency that pigment ink only recently began to approach.
Reactive dyes “have the advantage of the highest chemical bond to the fabric. These inks are mostly common for bright dyes with high light and when washfastness is required,” explains Kiryati.
In addition to cotton, reactive dye is used with other natural textiles like linen and rayon. Because it saturates the fabric, it offers a soft hand. The saturation also gives it durability, crockfastness, and lightfastness. For these reasons, it is often used for applications that people interact with, like home goods.
After pre-treatment and printing, steam sets the dye into the textile. The fixation process is similar to acid dyes, but quicker. The printed fabric requires around ten to 20 minutes—depending on the steamer—at a temperature of about 215 degrees Fahrenheit. It then requires washing and drying.
The Right Solution
Photographic Works in Tucson, AZ acquired the Roland Texart RT-640 earlier this year for transfer dye-sub printing. The print house handled fine art reproduction on paper and canvas and wanted to provide the option of metal and wood prints.
“It was perfect timing because Roland just introduced the Texart RT-640. The wider color gamut and how it lays down ink influenced us to move forward,” recalls Mary Findysz, founder and president, Photographic Works.
Roland’s Texart SBL3 disperse ink—designed specifically for use with the Texart RT-640—provides a wide gamut. After several months of dye-sub printing, Findysz and her staff love the results. “It is a whole different feel than our prints on paper. The look of metal is amazing,” she observes. She adds that there are future plans to print on fabric and tile.
Suntex Printing, Inc. of Woodruff, SC uses Mimaki disperse dye ink. It frequently prints on polyester as a contract printer for hospitality, healthcare, and retail. These environments usually require frequent washing, and Suntex Printing uses disperse dye to ensure washfastness.
“The best ink for polyester is disperse dye-sub ink because the ink is impregnated into the fibers through the heat setting process,” explains John Dill, president, Suntex Printing.
Dill says disperse dyes don’t provide ideal lightfastness but are a fit for Suntex’s output—draperies, shower curtains, bedding, and banners—offering indoor durability.
“Dye-sub still offers the best quality image in our opinion,” he adds.
As digital fabric printing grows, textile ink evolves with it. With the right ink and fabric combination, print providers can compete in a thriving segment.
Disperse dyes undergo a sublimation process with dye outgassed and set on the substrate. It is an accessible way to print on polyester. Dye-sub products provide improved color gamut and longevity.
Acid, pigment, and reactive are used in a heat or steam fixation process. Acid dyes are effective on specialty fabrics like nylon, silk, and wool that aren’t suited as well to other ink types. Pigment inks are compatible with a growing array of substrates and ink advancements enable better durability. For cotton, reactive dyes ensure a resilient print with washfastness, crockfastness, and lightfastness.
Though the four ink types vary, they all utilize a heat-based process that ensures the print performs well for the application.
Aug2015, Digital Output