A Primer on Fabric Inks
With numerous fabric inks available, and with digital fabric printing becoming so popular, I thought it prudent to do some research and provide PIE Quick Tips readers with some information on the kinds of fabric inks, their uses, and their requirements for successful printing.
I found several good articles online, but the most useful was an article by Simon Eccles entitled "What You Should Know About Digital Textile Inks." It was published on the FESPA website (www.fespa.com) on May 23, 2016. I encourage you to read the article yourself. It is most comprehensive.
What Are the Issues?
First of all, the article addresses the following inks (dye sublimation/disperse dye, acid dye and reactive dye, pigment ink, latex ink, and UV cured ink), noting the textiles for which each is appropriate. (These may range from polyester to cotton to nylon to leather.) The article then notes any required pre-treatment as well as any post-processing needed to make the inks bond with the fabric.
Overall, large-format inkjet printers either print directly on textile rolls (or garments) or onto paper. In the latter case, the image is then transferred from the paper onto the fabric substrate using heat. Eccles’ article addresses which kind of application is appropriate in each case.
Finally, each of the ink categories described in "What You Should Know About Digital Textile Inks" provides sample products that would be appropriate for the particular category of ink. Some products might be more appropriate due to a better "feel" of the product (for instance, a softer feel would be required for a garment than for a flag). However, other inks might be inappropriate in certain cases (for instance, UV-cured inks may not cure completely through, and since uncured UV inks should not come into contact with human skin, they would be appropriate for signage but not clothing).
What Does Fabric Printing Include?
Today digital textile printing is a hot topic. It can be used for clothing, furnishings, signage, and flags, among other items. Some of these digital printing processes can even be used to decorate hard substrates. Simon Eccles acknowledges that his article does not address toner-based processes, although these can produce heat transfers that would also be appropriate for textile printing.
Here are the inks/processes Eccles describes:
Also known as disperse dye, this process is used for polyester fabrics (or cotton/poly blends). It offers two options for printing. The first involves initially inkjetting an image onto a transfer sheet. In a separate process, this transfer sheet is then put into direct contact with the textile, and heat is applied using calendering rollers or a heat press. The heat turns the ink directly into a gas (sublimates the ink from solid to gas without the interim liquid state). The gas permeates the polyester fabric, allowing the ink to bond with the polyester fibers. For cotton/poly blends, the more polyester in the blend, the better (the more polyester, the more intense the colors as well). In this process, the ink bonds chemically to the polyester fibers, so the colors are wash-resistant and light-fast.
The other option is to inkjet the ink directly onto the fabric and then heat-fix the ink. This requires a pre-treatment to minimize the spread of the ink into the fabric fibers before heat-fixing. A heat press then sublimates the ink so it will bond to the polyester fibers. This also intensifies the colors dramatically.
However, direct printing onto fabric risks movement of the textile, which will blur the crisp edges of type or delicate artwork. In addition, it is usually impossible to completely eliminate the wicking (i.e., spreading) of inks into the fabric during direct printing. Although some manufacturers do provide inks that minimize wicking, Eccles still finds using transfer sheets to be easier and more successful (sharper images due to little or no dot gain or bleed) than direct to fabric sublimation printing.
In addition, any pre-treatment chemistry must be washed out at the end of the process. (In contrast, no pre-treatment is needed for transfers.) Also, you can print multiple small images on a single transfer sheet and then cut them out separately for application onto multiple garments (or even onto hard substrates such as mugs), and you can print on stretchable fabrics such as Lycra.
In most cases, sublimation requires pre-treatment and also post-treatment washing after the ink sublimation process.
Acid Dye and Reactive Dye:
"What You Should Know About Digital Textile Inks" suggests using acid dyes with natural fibers such as cotton, silk, wool, synthetics like nylon and some acrylics, and leather. Inkjet presses print these inks directly onto fabrics using piezo print heads made for low-viscosity inks.
Reactive dyes are used with piezo print heads made for medium-viscosity inks. These have a different method than acid dyes for bonding with the textile fibers.
Both acid dye and reactive dye inks require fixing at high temperatures (steam heat and water washing), which also removes unfixed dye and the ink-receptive coating. This washing step uses a lot of water and energy to heat the water. Drying also takes time and requires heat, which further increases energy usage.
Eccles’ article suggests this process for natural fiber clothing and soft furnishings but notes that it is best suited to printing directly onto rolls of fabric rather than onto specific fabric items.
"What You Should Know About Digital Textile Inks" suggests this process for cotton, linen, polyester, blends, and leather, noting that printed products can include soft signage, flags, apparel, and soft furnishings.
However, since the pigment is bonded to the fibers of the fabric with heat, the color is not as brilliant as in dye-sublimated products (although this process has improved recently). Pigment inks can be used for direct-to-garment printing or for printing rolls of fabric that will be later converted into garments or furnishings.
Pretreatment is optional, but it will increase color-fastness and wash-resistance. Post-processing with dry heat and pressure (i.e., a heat press) is required.
Latex ink is water-based and environmentally friendly. It contains heat-activated polymers and pigments. These inks are odorless, and they require no solvents. However, latex inks remain on the surface of the garment rather than bonding chemically with the fibers.
According to Eccles’ article, latex inks are appropriate for both natural and synthetic fibers (but not all fabrics are "latex-capable," and there are fewer appropriate fabrics than for either dye-sublimation or acid dye and reactive dye printing). Latex inks are printed directly onto textile rolls rather than onto finished products, and pre-treatment is required (although no post-treatment is necessary).
The process requires heat to evaporate the water and activate the polymers, but the water usage is less than for acid or reactive dyes or for dye sublimation.
Latex inks can be used for soft signage, soft furnishings, and flags. However, the ink’s sitting up on the surface of the fabric would make it less appropriate for garments, which need to be soft and pliable.
UV inks cure when exposed to UV light. Modern LED curing lights do not use much energy or generate much heat when compared to the earlier metal halide lamps. The inks require no pre-treatment or post-treatment. However, UV inks cannot be guaranteed to cure all the way through and therefore cannot come into contact with human skin. Because of this, printing with UV-cured inks is suited to soft furnishings, flags, and soft-signage but not to apparel.
Printing is applied to fabric rolls from which items can be made rather than directly to the finished products. Both natural fibers and synthetics are appropriate for this technology, and the final products are especially light-fast.
[Steven Waxman is a printing consultant. He teaches corporations how to save money buying printing, brokers printing services, and teaches prepress techniques. Steven has been in the printing industry for thirty-three years working as a writer, editor, print buyer, photographer, graphic designer, art director, and production manager.]