They are used to dye
paper, polyacrylonitrile, modified nylons, and modified polyesters. In solvents
other than water, they form writing and printing inks. The principal
chemical classes are triaryl methane or xanthenes. Basic brown 1
is an example of a cationic dye that is readily protonated under the pH
2 to 5 conditions of dyeing.
Basic dyes are water-soluble and produce colored
cations in solution. They are mostly amino and substituted amino compounds
soluble in acid and made insoluble by the solution being made
basic. They become attached to the fibers by formation of salt linkages
(ionic bonds) with anionic groups in the fiber.
