Covalent fixation of drum dyes on collagen

Covalent fixation of performance chemicals on various substrates of natural or synthetic origin is a well-known and thoroughly investigated principle since decades. Taking a deeper look into the literature of collagen, though, there are only a few examples found to this topic. Immobilisation of process chemicals is of great importance for leather as well. Especially dyes play a crucial role, since their mobility within the substrate matrix my lead to visible staining of other materials upon contact. In order to meet these challenges in leather manufacturing a new dyeing concept has been developed: covalent fixation of drum dyes to the collagen fibre. The dyes react with collagen under mild alkaline conditions at moderately elevated temperatures, thus reaching a fixation rate of above 95%. Due to the fact that only covalently fixed dye molecules remain in leather, unprecedented fastness properties are achieved even on leather dyed to very deep shades.