Colorants

The dye must first be able to dissolve in the small amount of water used in the printing paste.

Both dyes and pigments may be used as colorants in the printing process, although the mechanisms by which they are fixed to the textile are quite distinct. The same forces of dye-fibre association apply to both dyeing and printing and, in principle, the dyes used to give a plain-coloured fabric could be used to print that fabric. However, there are three important characteristics a dye must possess in order to be used in the printing process.

Pigments are widely used in textile printing, with about 45% of all textile prints produced using pigments. Unlike dyes, they do not directly associate with the textile fibres but are fixed to the textile with a so-called binding agent. The binding agent is usually a copolymer which is incorporated into the printing paste and forms a three-dimensional film when heated.

Secondly, the dye must be able to diffuse at a reasonable rate from the printing paste on to the fibre, leading to preference for dye molecules with a low relative molecular mass.

Finally, the unfixed dye must be capable of being washed off satisfactorily without staining the unprinted areas of the fabric.