New developments in textile inks include one that allows for production printing with disperse dyes, and another designed to print directly onto cotton using pigmented inks rather than with reactive dyes as shown in this sample. Image courtesy of Mimaki

Several new or improved textile inks have been introduced that caught my attention. One is a new set of disperse dye inks for production speed direct printing on synthetics. The other is the improvements in pigment inks used for printing onto garments. So in this article I’ll discuss these two technologies and how they meet the needs in printing textiles.

 

NEW DISPERSE DYE INKS 

Disperse dyes are dyes that were invented many years ago to color polyester fibers. Traditional dyes used for natural fibers simply wash off polyester. In inkjet printing most dyes are sublimation dyes whether they are used for direct printing or for transfer printing from a donor paper. Sublimation dyes are a subset of disperse dyes. They are similar in chemistry but contain smaller molecules that can be sublimed with heat (transition from solid directly to a gas) at low enough temperatures to be practical. When heated they penetrate the hot polyester and diffuse inside the fibers. 

 

However, sublimation dyes tend to suffer from poorer lightfastness than traditional disperse dyes and may continue to diffuse if reheated. Larger disperse dye molecules which do not sublime at low temperatures can diffuse directly into the fiber but usually require some moisture along with the heat. Most traditional polyester dyeing uses these larger molecules because of their enhanced permanence. 

 

For years now sublimation dye-based inkjet inks have been available for printers with Epson-based piezo printhead technology for both direct printing and by transfer using transfer paper. These inks meet the needs for short-term fabric graphics and indoor applications when only a small amount of fabric is being printed. 

 

After a long wait true disperse commercial textile dye based inkjet inks are finally available in a production speed printer. They provide the performance equal to that of traditional analog textile dyeing of synthetics. They provide excellent color gamut, high fastness and have been designed for high productivity inkjet printers incorporating industrial piezo printheads like those produced by Fujifilm Dimatix. In order for the ink to properly jet from industrial printheads a higher viscosity ink set was designed. Epson printheads require very low viscosity and those inks are not suitable for industrial printheads. 

 

The Jeti AquaJet 3324, a new 3.3 meter wide textile printer from Agfa, employs a disperse dye ink set and integrated steaming system for the printed textiles. The printer offers six-color printing, uses 24 Dimatix printheads and prints at speeds up to 650 square feet per hour.

Last year Agfa acquired Gand-innovations and its line of grand format inkjet printers. At a large digital printing trade show in Europe this year, Agfa announced a new set of disperse dyes for their 3.3 meter wide production textile printer, the Jeti AquaJet Model 3324. This printer provides 6 color printing using 24 Dimatix printheads allowing printing speeds up to 650 square feet per hour with integrated steaming of the printed textile. This printer is designed for three-shift true production printing. 

 

Agfa announced that they had formed an alliance with DuPont to provide these inks. DuPont has been providing inks for textile printing based on several dye chemistries as well as pigments. These inks use commercial textile dyes giving final properties equal to traditional screen printing. Now full-width fabrics (up to 10' 10") can be printed to meet the needs of short run textile applications.

 

TEXTILE TEES: PIGMENT PRINTING

Inkjet printing of T-shirts has become a big business and many manufacturers now offer T-shirt printers based on Epson printheads. Since most T-shirts are cotton or cotton/polyester blends, dye sublimation printing is not an option. For durability and ease of use, pigmented inks are the choice. The challenges with pigments are two-fold: washfastness and printing on colored shirts. Recently, significant progress has been made in washfastness and an improved white ink system for printing under the color ink printing on colored shirts. 

 

DuPont recently announced the development of an ink for T-shirt printers that can penetrate and bond better to the threads in cotton T-shirt, resulting in much improved washfastness. Tests using traditional textile methods indicate truly excellent performance on 100 percent cotton and very good performance on cotton blends.

The challenge in designing an ink for cotton or cotton polyester T-shirts with good lightfastness is achieving good bonding into the surface of the shirt. Cotton has hair-like fibers that protrude from the surface of the fabric. Many of these fibers will be removed during routine washing of the shirt. As a T-shirt is washed, many times the fabric becomes thinner and more translucent and the colors fade. With inkjet printing, if the pigmented ink is only bonded to these hair-like fibers on the surface and has not penetrated sufficiently to bond well to the fibers, the ink will be washed out with the fibers as they are released from the fabric during washing. 

 

The ubiquitous ink supplier to most of the T-shirt printer manufacturers is DuPont. They recently announced the development of an ink that can penetrate and bond better to the threads in the T-shirt, resulting in much improved washfastness. Test using traditional textile test methods indicate truly excellent performance on 100% cotton and very good performance on cotton blends. This performance compares very well with traditional screen printing results.

For colored shirts the issues are several-fold. First, in order to successfully print a process color image with transparent colors onto a colored background, the fabric under the area to be printed must be white or the color gamut and saturation will be poor. So a layer of white ink must be printed prior to the application of the color inks. In addition, the white ink must not penetrate into the fabric any more than necessary to bond to the fibers otherwise the hiding power of the white ink will be compromised and the print will appear dirty since the white printing is not white. 

 

For this reason a pretreatment should be used prior to printing the white and colors. This effectively “holds out” the white ink while aiding in adhesion to the fabric. This then gives a very white surface only under the areas where the image will be printed. The result is very bright and vivid colors and great washfastness. 

 

SUMMARY

With the use of commercial textile pigments and disperse dyes in the inkjet process along with additional chemistry to optimize bonding and color gamut textile printing by inkjet is improving markedly. More and more textile printing is moving from long run analog screen printing to inkjet. These performance improvements will further accelerate the adoption of inkjet printing as an attractive alternative.