Process for tanning of leather

Bisulfit-blockierte Polyether-modifizierte Polyisocyanate eignen sich in Kombination mit mineralischen Gerbstoffen hervorragend für die Ledergerbung. A tanning process comprises (1) treatment with a compound containing carbamoyl sulphonate groups and (2) treatment at a pH greater than 4 with a mineral tanning agent chosen from chromium (III), iron (II) or (III), aluminium (III), titanium (IV) or zirconium (IV) compounds, without the use of a pickling agent. The compound used in step (1) is a reaction product of the following components : (A) an organic polyisocyanate ; (B) 0.01-0.4 equivalents per isocyanate group in (A) of a polyether alcohol containing polyalkylene oxide groups, of which 40-100 mol.% are polyethylene oxide units with a sequence length of 5-70 (the equivalents are based on the hydroxyl groups in the alcohol) ; (C) optional further components which can react with isocyanate groups ; and (D) ammonium or alkali bi- or di-sulphites.