Patent ID: 6916348

Claim:
A process for dyeing tanned leather, which comprises either (a1) allowing ammonia, primary amines or a mixture of ammonia and primary amines in an aqueous and alkaline medium to act on the tanned leather and (a2) treating this leather in an aqueous and alkaline medium in the presence of ammonia, primary amines or a mixture of ammonia and primary amines with a polyfunctional organic compound comprising at least one aldehyde group as a functional group, or (b1) allowing a part or all of a polyfunctional organic compound comprising at least one aldehyde group as a functional group to act on the tanned leather in an aqueous and acidic medium and (b2) allowing ammonia, primary amines or a mixture of ammonia and primary amines in an aqueous and alkaline medium and then, if necessary, the remainder of the polyfunctional organic compound to act on the tanned leather; (c) allowing a dye comprising at least one functional group to act on the treated leather in an aqueous and alkaline medium, wherein this functional group is capable of reacting with one of the functional groups of the organic compound forming a covalent bond; and (d) draining the dye liquor and washing the dyed leather with water with the proviso that the pH value in (c) is over 8 when using an anionic tanned or retanned leather, if an anionic dye is used.