Digital Textile Inks: Reactive, Acid, Sublimation, Dispersion, Pigment
For many in the industry particularly in the Visual Communication or Soft Signage, “dye sublimation” is synonymous with digital textile printing, but in reality sublimation is just one of several processes that can be used. Theoretically any large format printer that can print on fabric can be called a fabric printer, but for the purposes of this blog we are speaking only about true digital textile printers that are engineered to bond or infuse ink into fabric rather than technologies such as latex or UV that lay ink on top of the surface of fabric. All of the inks we refer to below utilize water-soluble dyes.
Invented in 1956, contains dyes that create chemical bonds with cellulose when applied to pretreated fabric and then fixated. The fiber reactive dyes react with the textile fiber forming a covalent bond. The have a very bright shades and after the complete process a good wash fastness.
The major processing points have the purpose to make the fabric fiber to be reactive. During the preparation of them the textile media is pretreated with alkali, urea and anti-migrant, depending on the pretreatment, after the printing, the fabric must be either steamed for 8-12minutes or alternatively is thermo-fixed at 160-200°C, one to four minutes. Before steaming it is very important that the ink on the media surface is completely dry and it is better to perform the steaming process within, at the maximum, 24 ours after the printing.
Fabric with reactive ink must be washed after transfer to remove any residue. Reactive and acid-based inks also have to be set into the fabrics with a post-processing heating procedure to permanently set the dyes.
Reactive inks do best on cotton, linen, rayon, nylon and other cellulose materials.
They require pretreated fabric for fixation and are printed directly to the textile then steamed to set the ink. The dyes that make up acid ink create ionic (anionic, negative charged)or electrostatic bonds with textiles such as silk, wool, and nylon. Acid inks are generally brightly colored and will form an ionic bond in the presence of acid. Fabric with acid ink must be washed after transfer to remove any residue. Reactive and acid-based inks also have to be set into the fabrics with a post-processing heating procedure to permanently set the dyes.
Are the most commonly known type of digital textile inks in the Soft Signage Market, and this is what is used in the dye-sublimation ink process. Dispersed inks infuse into and actually dye the fabric, becoming part of the textile itself.
Disperse inks are not anymore dye inks but more appropriately they are a dispersion of micro particles in the ink.
They will literally sublime (from solid int to gaseous) upon heating forming a gaseous dye, the gaseous dye is extremely attracted to and soluble in polyester, upon cooling the now solid dye is entrapped in the polyester fiber.
Disperse dye has good wash fastness and light fastness that increase as energy level increases.
Disperse inks are broken down into low-energy, medium-energy and high-energy dispersion. Our commonly used “dye sublimation inks” are actually a low-energy dye dispersion, most typically used for transfer printing from paper to fabric. The sublimation process requires the use of a calendar to deliver heat and pressure.
When the ink and carrier is heated to a high temperature (typically around 180-200 °C) the carrier evaporates and the dye turns to gas. The synthetic fibers “open” to receive the gas and when they cool, they close and encapsulate the colorant, which then returns to a solid, actually dyeing the material.
There are two ways for the fixation of the disperse dye:
a) Steaming 8 min at 170-180 C° whit steam overheated and in high pressure;
b) Thermo fixation 1-2 min at 180-210 C°
Disperse and sublimation inks are used to print of fabric targeted to the markets of: 1) Soft Signage or Visual Communication; 2) Sportswear; 3) Apparel or fashion; 4) 3D printing;
Disperse and sublimation inks are used as well for direct printing in this emerging markets; 1) Outdoor furnishing; 2) Outdoor awnings; Automotive interiors; Home textiles, Flags and Banner; Sun Umbrellas.
They are finely ground powders suspended in liquid carriers with binders. As pointed out with the disperse inks pigment inks are not anymore dye inks but more appropriately they are a dispersion of micro particles in the ink.
Where sublimation creates permanency when the dye is encapsulated into a polymer, pigments are bonded to natural fabrics using binders and a heat calender process. Digitally printed natural fabrics are in high demand, so this is an area we expect to see significant growth in in coming years.
Here is a summary of which inks are best for particular types of fabric:
Disperse and sublimation are used on polyester, acetate rayon, poly-Lycra® and acrylics and require post treatment heat
Reactive dyes are for cotton, linen, rayon, nylon and other cellulosic materials and require pre- and post treatment
Acid dyes are best for wool, silk, polyamides, cashmere, angora and nylon and require post treatment
Pigment works on cotton and natural fabrics and requires post treatment heat