Substantive dye

The Direktfärbeverfahren denotes a staining method, in which the water-soluble dyes used stick by intermolecular forces without adding further chemicals directly on the material to be dyed. Particularly suitable for this process are wool and silk, as both have functional groups which react with corresponding groups of the dyes. Here can be distinguished according to the type of bond:

• In the substantive staining, the dye molecules pull on by intermolecular dipole or van der Waals forces or hydrogen bonds on the fiber. They stick with it on the surface or form aggregates in submicroscopic cavities of natural or synthetic cellulosic fibers such as cotton or rayon, but also of wool. The binding of these relatively large dye molecules on the fiber is not very strong, so that the coloring is only moderately washable. Important dyes for this method are polyazo dyes having one or more sulfo groups (e.g., Congo red ).

• In the direct staining in the narrower sense colored anions from acidic ( anionic ) dyes are bound by electrostatic forces ions to the fiber. The binding is via a salt bond with the free amino groups of wool or silk with acid dyes form a connection ( with one or more sulfo groups ). The acid dyes are mainly various azo, anthraquinone and to a lesser extent, azine dyes (eg Acidol, Isolan or nigrosin ). The basic skin substances react to leather with the sulfo groups of the acid dyes and form lightfast salts. For cationic ( basic ) dyes, the amino groups present are bound by free carboxylate ion (eg Mauvein ). While there will cationic dyes on natural fibers only moderately true- colors, but on polyacrylonitrile can be brilliant, highly lightfast colors achieve.