How inks work with fabric
By Samit Chevli
Digital textile printing continues to gain marketplace acceptance in printing on a variety of fabrics. Markets such as apparel, home furnishings, tradeshow graphics and point of purchase displays all show rapid growth.
Creating the best image quality is obtained through proper fabric and ink selection, preprocessing and postprocessing of textiles, color software and printing equipment.
There are four basic types of inks available to digitally print on textiles: acid, disperse, pigment and reactive, and there are specific inks for specific types of textiles. Inks must be compatible with the fabric and print system, since not all ink chemistries are available for a given print system. A system that offers all the different ink chemistries will facilitate the widest selection of fabrics for printing.
Digital printing of textiles with dye-based inks requires pretreatment and posttreatment of the printed fabric for full color and durability. The chemicals in the coating permit reaction of the dye with the fiber during postprocessing. Pretreatment is an application of a solution to coat a fabric to achieve better image quality by preventing lateral bleed and for the application of necessary chemicals that are needed for the dye to exhaust onto the fabric and react with the fibers on a molecular level during the heat fixation process. Such chemicals cannot be incorporated into the ink due to the need for stringent purity and low viscosity required of an ink to sustain good quality printing.
Since universal pretreatment for all the ink types does not exist, each ink type requires its own pretreatment solution.
Once the pretreated fabric is printed, it needs to go through a fixation process, which enables exhaustion of dye from the fiber surface into the molecular structure of the fiber.
The fixation process ensures entrapment of dye colorants into the fiber structure or pigment and binder fusion to the fabric, which ensures that bright, chromatic and deep colors are obtained that do not wash off, and that printed fabric that can withstand rigors of daily use.
Wash-off is the final step in the digital printing process. It is essential for direct printing with all the dye-base inks and serves to remove excess unreacted dye, remove pretreatment or coating solution, and make the white unprinted area come out looking bright and clean.
With a variety of different textile substrates and ink chemistry available for printing, it is important to select the right substrate and ink for digitally printing onto textiles to ensure image quality.
