One of the main challenges is to have a textile colorant bound to the textile. After the coloration is complete, the colorant must withstand washing cycles, and, when exposed outdoors, be stable to weather elements such as rain and sun. This is particularly challenging as the colorants are often applied as a solution/dispersion in water! Many technologies have been invented to convert the dye from soluble to insoluble form. For example, one can make the dye water soluble at higher temperatures, apply it to a textile and then have it made bound/insoluble in water at lower temperatures, at which the garments are used (or washed). These sparingly water-soluble dyes are called disperse dyes. Alternatively, one can rely on a partial conversion of the dye/pigment into an acid form to react with amino groups (in, e.g. Nylon) on the contact with textile (acid dyes) . Yet another option is to convert a water-insoluble dye into a water soluble form in a basic solution, with the following oxidation step to convert it back to water-insoluble form (vat dyes). Does it have to be so complicated? Direct dyes on the other hand can have enough affinity to textile by itself, without the stages pre-and post-treatment; however their waterfastness tends to be poor. Many textile dye chemistries are now available and are catalogued in Colour Index, first published in 1924. In the old times, dye chemical structures were heavily guarded by the manufacturers and the Colour Index database served as an intermediary between the dye manufacturers and the textile colorists. This produced many cryptic dye names (e.g. Acid Red 52) that do not disclose the dye structure. While it is still true for some dyes and pigments, many structures are now in public domain and can be found in monographs or on internet.
The textiles can be colored monochrome (single color) at the stage of the fiber manufacturing or immediately after; this process is known as dyeing, as opposed to textile printing, when the parts can be made in multiple colors by using more advanced printing methods such as screen printing. Inkjet recently has become available as one of the methods of direct printing on textile.
- Industrial Dyes: Chemistry , Properties, applications. K. Hunger, Ed., Wiley-`VCH, 2003