Leather dyes refer to dyes with an affinity to leather and for leather coloring. Based on solvent types, it can be divided into two categories: non-water-soluble dyes and water-soluble dyes. Non-water-soluble dye comprises: sulfur dyes soluble in aqueous solution of sulfide; fat-soluble oil-soluble dye; alcohol-soluble dye soluble in alcohol. Water-soluble dyes include: anionic acid dyes, direct dyes, dye leather special dye; amphoteric metal complex dyes, triphenylmethane dyes of sulfite; cationic alkaline dyes.
Leather dyeing can be divided into two categories including dip-dye and surface coloring dye (including finishing and spray dyeing). Dyes suitable for leather disseminated coloring belong to D series; dyes suitable for leather spray coloring belong to SP series. In recent years, the popular aniline leather and nappa leather are light leather with only minor or no finishing. It is required to be well combined with the leather fibers with a high degree of fastness and good levelness and color and so on. Garment leather also requires dye has excellent performance on resistance to dry cleaning (solvent).
Shoes-special grained leather are usually finished with paint with just surface coloring while clothing leather is subject to overall dyeing with the color of the cut area being the same as that of the surface. The leather dyeing mainly apply acidic and direct dyes, sometimes with alkaline, mordant, reactive dyes and oil-soluble, mostly picked out from the textile dyes. With the improvement of living standards and the development of science and technology, there is an corresponding increase on the demand on the leather dyes, the demand for the light-resistance, abrasion resistance as well as resistance to dry-cleaning solvents for garment leather is also increasing. In order to maintain the leather surface "natural look", there has emerged the so-called “aniline leather” which doesn’t need paint finishing but only dyeing with synthetic dyes, proposing new demand for the dyes dedicated to leather. Metal complex dyes play an important role in the leather dye.