By Melissa Donovan
Part 1 of 2
Print service providers interested in printing to textiles—whether directly or through sublimation transfer—need to be educated on the ink sets available to them. Traditional ink sets designed for textile printing include acid, disperse, pigment, and reactive. Each has its own purpose and use. In this article, for each type, we share the chemical composition of the ink, typical print processed used, whether pre- or post-treatments are required, the best media pairings, ideal applications, and usage difficulty level.
Acid dye ink is used in a direct to print process and requires a pretreatment for all fabric types as well as a steam process post-print to set the ink.
The chemical composition of acid ink is described by Simon Daplyn, marketing manager, Sensient Imaging Technologies, as a soluble acid dye in water with humectants, polymer, and surfactants. These ingredients combined control flow, jetting, and wetting behavior in the printhead and on the substrate. Humectants also manage drying at the printhead nozzle to allow a good open time.
As mentioned, pretreated fabric must be used and a post-print steaming is required to set the ink. “Acid dyes require a pretreatment of the fabric to control the pH level reaction or fixation, and limit penetration and sideways bleed of the ink across the fibers,” says Daplyn.
After the print is applied directly to the fabric, it dries, and then undergoes fixation via steaming. “This occurs in a saturated steam at 100 to 102 degrees Celsius for 35 to 40 minutes. There may be unfixed dye and remaining pretreatment chemicals, so a post wash process is also required. A number of wash cycles may need to occur to achieved the required performance of the final print,” continues Daplyn.
Certain fabrics are prime contenders for acid ink. “It is ideal for protein fibers such as silk, wool, angora, alpaca, cashmere, and leather—in addition to polyamide fiber like nylon. Applications include high-end apparel, nylon flags, and high-end activewear and swimwear,” shares Victoria Harris, textile specialist, Mimaki USA, Inc.
Mark Krzywicki, associate product manager, industrial printing, Epson, agrees that acid ink is best suited for printing on nylon, silk, and wool fabric, which is used in the creation of ties, scarves, and swimwear.
A multi-step process, acid-based textile printing presents challenges for users unfamiliar with the intricacies. For example, “acid dye ink molecules breakdown in UV light faster than other ink types. If the application has high UV exposure, the inks fade more quickly,” cautions Harris.
“Due to the niche nature of some applications and the need for steaming for extended time periods, acid inks are less widely used than other variants. There is a level of skill needed to maximize performance and tune the pre- and post-treatments for optimal results,” admits Daplyn.
There are two types of disperse ink, those suited for the direct to fabric process and then there are disperse ink sets designed for dye-sublimation (dye-sub) transfer. Disperse inks are commonly referred to as sublimation ink.
“Sublimation inks require a dispersion on an insoluble disperse dye—low energy—in an ink containing water, humectants, surfactants, and additives. The dispersion is the critical part of the formulation and dictates the overall stability of the final ink. As the ink contains solid particles the ability to stop the dye from settling is key to print performance and ink shelf life,” explains Daplyn.
For direct printing capabilities, disperse dyes work well with pretreated fabrics, including polyester, triacetate, acrylic, and nylon types. Post-print, heat press fixation is commonly used, but steam fixation is also an option, according to Harris.
Krzywicki says disperse ink is best suited for polyester fabrics, which are commonly found in sports apparel, fashion apparel, and some home furnishings.
“Direct to fabric disperse inks lay more ink down onto the textile and achieve higher ink penetration. Applications such as flags, where the reverse side of the fabric is visible, are a good example of key applications. High-end activewear and swimwear are also printed with direct disperse inks because of the high ink penetration achieved,” notes Harris.
There are also disperse transfer inks used in the dye-sub transfer process, where the design is printed to sublimation paper and then transferred to the fabric with heat. “For dye-sub, we need about 400 degrees Fahrenheit for 45 to 60 seconds—depending on the fabric and color profile. This is the process of the sublimation inks dying the polyester fibers and locking in to the fabric. Dye-sub features great rub resistance because of this,” explains Lily Hunter, product manager – textiles, eCommerce, and supplies, Roland DGA Corporation.
Rub resistance in addition to high wash and colorfastness of the inks makes dye-sub transfer popular in apparel markets, adds Harris. Also, advancements in textiles made out of polyesters for the home and interior decor market continues to spark growth in utilizing dye-sub transfer inks.
Certain disperse ink sets are available for dual use—meaning direct to textile and transfer printing. For example INX Digital offers two dye-sub ink lines that “are used for printing directly on fabrics and transfer papers, and do not require a post-wash. Applications include soft banners and signage, as well as flags,” shares Marco Zanella, managing director, INX Digital Italy.
While disperse inks are generally easy to use, there is still a learning curve—especially when used for transfer dye-sub printing. Hunter believes it is because it may take time to master a heat press or calender. “The prints come out dull from the printer and the colors bloom at the heat press. Learning how to maneuver a calender to make sure you load the fabric properly and have the right tension can be difficult in the beginning.”
Pigment ink is a direct print process that continues to grow in popularity, mainly because pretreatment of fabrics is not considered mandatory compared to other ink sets.
Atalia Attar, product marketing manager for consumables, Kornit Digital, notes that because pretreatment isn’t necessary, it makes pigment inks versatile, allowing for printing on a range of fabrics without the need for a separate pretreatment process or system reconfiguration.
While not necessary, “coating the fabric does increase the ink’s penetration, saturation, and color development, as well as the fastness properties of the ink,” adds Harris.
The chemical composition of pigment ink plays a role in its fabric compatibility. “It consists of an organic pigment that needs to be carefully dispersed prior to the addition of the other materials needed to make a digital ink. The quality of the dispersion is key to print and application performance. Pigments are inert and do not react to fix to a fabric and a polymeric binder is needed to physically bond the ink to the textile,” explains Daplyn.
After printing when using pigment ink, a thermal fixation process is suggested. Daplyn recommends fixation either through a heat press or drying oven. A post wash isn’t necessary, but the fabric may undertake a softening process to improve its hand.
Kodak’s proprietary pigment ink set is water based and designed for direct to textile printing. “Thermal post-processing is required. Its best media pairing is with natural fibers, which do require a pretreatment. Ideal applications include apparel, finished garments, interiors, and soft signage,” says Grant French, direct of digital ink sales, Eastman Kodak Company.
Specific fabrics best suited for pigment include cotton, viscose, and blended materials, according to Krzywicki, and are used in home furnishings and some apparel applications.
“Textile pigment inks are ideal for home furnishing and interior decor applications because of their high colorfastness. Additionally, most interior decor fabrics for furniture and linen are not concerned with the penetration through to the reverse side of the textiles, which makes them ideal with pigments, since pigments sit on the surface of the fabrics,” agrees Harris.
Pigment inks are heavily favored in the direct to garment market for printing directly to t-shirts. “This is predominantly for printing t-shirts in specifically designed garment printers and often includes the printing of a white base layer to allow decoration of pre-dyed shirts,” adds Daplyn.
When compared to other ink sets, “printing with pigment inks can be considered less complex due to fewer steps in the process, and lower overall investment required to start,”explains Krzywicki.
However, that doesn’t mean there aren’t challenges associated with pigment inks. “Proper daily and weekly printer maintenance is important with heavy production using textile pigment inks, which include a binder. It operates like a glue to bind the inks to the surface of the textile and can clog nozzles over time if proper care and maintenance of the machine is not upheld,” suggests Harris.
Similar to acid and disperse inks that are printed directly to fabric, a pretreatment is required when printing with reactive ink. Post-processing includes steaming and washing.
Reactive dye-based inks consist of reactive dye, water, humectants, and surfactants. Two different types of dye are common choices, and the composition varies depending on the printhead and print system being used due to the viscosity, surface tension, and compatibility, shares Daplyn.
Pretreated fabric is required to ensure dye fixation and control drop spreading, he says. Post-print, the ink is fixated using saturated steam at 102 to 104 degrees Celsius for eight to ten minutes. “The steam concentration is typically 400 to 800 kilograms per hour. Steamers can be adapted at a small scale, but typically industrial application use a large scale loop steamer,” adds Daplyn.
Natural cellulose fabrics such as cotton, linen, bamboo, rayon, lyocell, hemp, and ramie are used with reactive ink, as are protein fiber-based materials like silk, wool, cashmere, angora, alpaca, and nylon, notes Harris.
Krzywicki says reactive ink is best for cotton and viscose fabrics, are also be used on silk and wool fabrics, and often found in fashion and apparel markets.
“Reactive inks are widely used for fashion and fast fashion markets globally. Once you have the workflow in place, they are easy to use with low maintenance requirements, but there are limitations in terms of the amount of equipment needed. The capital investment can be high for the full process equipment requirements,” admits Daplyn.
This ink type’s advantages are vast. “Most of the world’s textiles are printed with reactive inks, which offer the highest washfastness of all ink types, due to the reactive inks covalently bonding to the fabric during the post-steaming process. These inks have the tightest bond possible between two molecules. Reactive inks also feature a very large and bright color gamut,” shares Harris.
All four ink options have their own advantages and disadvantages. Pigment ink, used in a direct to print process, is popular because it doesn’t necessarily require pretreated fabric, opening up many material possibilities.
Acid, disperse, and reactive inks are all recommended for use with a pretreated fabric when run in a direct print process. Based on the ink set’s molecular makeup, the three vary in terms of applicable materials, standout features, and post-treatment factors. It is important to note disperse ink sets are also available for transfer dye-sub printing.
The next article in this two-part series looks at available acid, disperse, pigment, and reactive ink sets for textiles.
Jun2020, Digital Output