By Melissa Donovan
There is a never-ending supply of textiles designed for digital printing. If we break it down, certain fabrics are constructed to be printed well with a specific ink set. As digital printing continues to make headway into the décor and garment spaces, fabrics containing primarily cellulosic fibers and blends will increasingly need to be optimized for digital production. This includes cotton-based materials.
When direct printing, cottons and cotton blends work well with reactive dye and pigment ink. Although many times they need to be pretreated with a coating to generate optimum results. These pretreatments must be engineered in a way to add a soft hand as well as great visual quality, as many cotton materials are used in applications like drapery, upholstery, table linens, or bedding.
Each fabric type used in the digital print process always performs best when paired with the correct ink. For example, dye-sublimation techniques are ideal for polyester. When it comes to printing directly onto cotton and cotton blend materials, there are a few ink sets that meet their match.
Marty Silveira, VP – sales, DigiFab Systems, Inc., admits that markets tend to dictate the most common ink used when printing to cotton or cotton blends. For example, fashion-type applications are traditionally printed with reactive ink. “This is due to the vibrancy of color that can be achieved, as well as the way the fabrics feel after the printing, steaming, and washing processes are completed.”
Reactive dye ink is a good option—generally speaking, there is a whole host of advantages to printing with dyes, according to Hunter Ellis, president, Jacquard Inkjet Fabric Systems. “Reactive dyes form a strong covalent bond with cellulosic fibers, so they are the best choice when considering wash fastness. The colors tend to be more vibrant.”
Pigment-based ink is a more attractive alternative, mainly because the inks only need to be cured after printing—eliminating a lot of extra steps. “The post-processing requirements of reactive dyes are intense. That is why pigment inks are often the more common choice—the convenience factor is huge,” admits Ellis.
“Pigment ink is a surface ink that adheres to the cotton and many types of fabrics through a binder system so it is, in essence a surface ink, rather than a chemical reaction between the colorant and fiber. It is the preferred colorant for cotton/poly blends,” argues Mark Sawchak, partner, PremEx Solutions.
Steeped in tradition, pigment ink was originally used with cotton when printing with screen and flatbed printers. “Digitizing the pigment printing process has brought forth a new set of challenges and opportunities,” admits Kathryn Sanders, product marketing manager, apparel and home furnishings, Top Value Fabrics.
“Direct digital pigment printing requires ink and binder molecules to pass through inkjet printheads and adhere to the fabric—without clogging the inkjet printheads. Products address this printing process at its current level, improving crocking, color to wash fastness, and produce better color vibrancy and clearer print characteristics,” she continues.
Depending on the ink type, pretreatment may be necessary to enhance ink adhesion to the fabric prior to direct printing.
“All fabrics must be pretreated with the appropriate chemistry, relative to the actual ink/fabric combination. Otherwise, every property, including color, wash, and rub fastness will suffer. This statement is true for both reactive and pigment ink,” explains Dr. Jerry Pinto, president/CEO, Fabachrome.
With reactive dye, a pretreatment is generally necessary. “The chemistry of the pretreatment performs as a catalyst that assists in the reaction between the dye and the fiber,” says Sawchak.
Conversely, pigment-based inks do not require a pretreatment. However, Sawchak believes that pretreating a fabric intended for pigment printing does aid in the adhesion of the ink to the fabric to achieve optimum results, especially in regards to durability.
Silveira points out that depending on the proprietary pretreatment, it may enhance color, wash ability, or lessen the affect from rubbing when used in conjunction with a pigment ink. He does mention that depending on what the final print will be used for, it may not be necessary to treat the fabric at all.
“In the current digital pigment landscape, most printers require coated fabrics, for best results applied as a pretreatment at mill stage,” argues Sanders. She says without the coating or binder, the ink on the fabric will rub off or crock and won’t achieve crisp features or color vibrancy.
Maintaining an Aesthetic
Cotton has a connotation of soft and comforting. Adding a pretreatment to aid in ink adhesion during the direct print process should not negatively affect that aesthetic. A coating cannot poorly influence the visual quality of the print either, for example providing a glossy look when it should appear like a calico found in a quilt.
Pretreatment is specific to ink, which ensures the preferred cotton aesthetic is met. “Reactive coatings often make the fabric noticeably stiffer and slightly tinted. But these treatments are designed to be steamed and then washed out, so the end result should have no extra hand or discoloration,” shares Ellis.
Silveira takes us through the post process of a pretreated cotton printed with reactive ink. “Steam, which activates the treatment and then dye to allow the color to bloom and penetrate the fiber. Wash takes away the excess ink and treatment, leaving the original softness of the fabric along with vibrant color.”
“The hand of the fabric can be engineered to be soft by using the optimum chemistry in the pretreatment. The polymers in the ink could add hand and there are some differences among different brands. Proper selection of an optimum ink, fabric, and coating chemistry gives good hand, durability, and color,” advises Sawchak.
When all components are paired correctly, the right pretreatment will not affect the soft hand expected of cottons or deter the visual qualities. If performed correctly, visual qualities are enhanced, which “allow colors to fully bloom,” says Sanders.
Cotton and cotton blends are prevalent in décor and garment applications.
Interior home décor that benefits from cotton fabrics include drapery, bedding, and upholstery. “The cotton offers some advantages in terms of breathability, softness, and hand that is not achievable with most synthetic fibers,” adds Sawchak.
Sanders sees cottons used most prevalently in the apparel market. “Consumers typically gravitate towards wearing natural fibers, often for ecological or comfort reasons. If you look at the tags on your clothes, you’ll quickly realize that most of your garments are made from natural fibers and blends, which makes direct digital pigment printing all the more significant.”
Ellis believes cotton is not ideal for applications that require high crock fastness or high light fastness. “Pigments, which are inherently more light fast than dyes, tend to have poor crocking resistance. Reactive dyes, which have good crock fastness, fade in the sunlight. Thus, you are forced to choose which fastness property you want to prioritize.”
Types of applications not ideal include outdoor, performance, or technical, lists Pinto.
Quick Note on Certifications
Cotton and cotton blends optimized for direct digital printing technology require additional post processing to achieve classifications like fire retardants or water and stain repellency. Other certifications are also attractive to various buyers.
On the topic of fire retardants, “it is not a strong property for cotton fabrics, unless the fabric is treated specifically for this property,” advises Sawchak.
Silveira notes that it really depends on the needs of each application. For example, a cotton would require flame retardant processing if used in a public or commercial location, but not necessarily for home or clothing. The same can be said for water or stain repellency.
Pinto suggests awareness of The Global Organic Textile Standard (GOTS). It is a worldwide textile processing standard for organic fibers, including ecological and social criteria, backed by independent certification of the entire textile supply chain.
According to the GOTS website, on-site inspection and certification of processors, manufacturers, and traders performed by independent specially accredited bodies is the basis of the GOTS monitoring system in order to provide a credible assurance for the integrity of GOTS certified textiles.
To become GOTS certified, textile products must contain a minimum of 70 percent organic fibers. The GOTS website states, “all chemical inputs such as dyestuffs and auxiliaries used must meet certain environmental and toxicological criteria. The choice of accessories is limited in accordance with ecological aspects as well. A functional waste water treatment plant is mandatory for any wet-processing unit involved and all processors must comply with social criteria.”
Print providers can visit the GOTS website—global-standard.org—and search the public database to find out more about GOTS-certified entities, their location, fields of operation, and certified products.
Additional Cotton Awareness
Cotton and cotton blends are complicated materials. There are other challenges that print providers should be aware of in addition to ink type and whether pretreatments or certifications are necessary. Most importantly, issues related to the actual material itself.
“Printers should be aware that cotton is a natural fiber, and variation will occur between lots even with the same mill and weave specifications. It is also generally important to source ‘contamination-free’ cotton—cotton guaranteed to be free from foreign fibers. Domestically grown cotton is usually contamination free, while foreign grown cotton can often have stray pieces of polyester or nylon mixed in with cotton threads,” warns Ellis.
He stresses the importance of consistency, repeatability, and accountability as key components to a cotton supply chain.
“Print providers need to have a strong understanding of color to crock fastness, color to wash fastness, and fabric shrinkage pre- and post-printing results before performing jobs. It’s vital to do thorough testing in these areas and know how printers, fabrics, and coatings impact the final product,” advises Sanders.
Silveira agrees, saying cotton and cotton-blend fabrics can sell at a premium, but knowledge of the materials is strongly required for all.
Cotton Under Control
Cotton and cotton-based fabrics optimized for direct digital printing are ideal for décor and apparel. Common applications found in both of these segments, for example drapes and linens or scarves and t-shirts, are regularly made up of cotton. The correct pairing of ink, fabric, and pretreatment makes today’s options viable for mass market production as well as more specific one-off and specialty pieces.
However, technology has not plateaued. Sanders believes that direct digital pigment printing is the way of the future in regards to cotton fabric. “Ultimately, we are waiting for chemistry and/or inkjet printhead innovations that will take direct digital pigment printing to the next level—and likely revolutionize our industry.”
Jul2019, Industrial Print Mgazine