GB798780A - Improvements in or relating to the tanning of leather - Google Patents

Abstract

798,780. Tanning leather. ST. LAWRENCE CORPORATION, Ltd. Jan. 30, 1956 [Jan. 31, 1955], No. 2970/56. Addition to 777,474. Class 76. Leather stock is impregnated with an aqueous solution of a lignin, a silicate, an aldehyde and a dibasic acid amide and/or aminotriazine or a condensation product of the latter two components, and a precipitate formed in situ by the addition of sufficient acid. Lignin materials referred to are obtained by evaporation or (in the case of cellulose saccharification residues-Burgius or Scholler process) by treatment with caustic soda and acidification of, waste liquors obtained by treatment of wood with soda, calcium or magnesium bisulphites (sulphite pulping process), or soda and sodium sulphate (Kraft process). If acid liquors based on calcium or magnesium oxides are used, precipitation of the silicate must be avoided : the alkaline earth metal may be replaced or removed with ammonium or sodium, e.g. by adding a surplus of sodium silicate. The alkaline earth solids precipitate may be allowed to remain in the liquor. Other acid liquors (ammonium- or alkali metal-based) should be alkalized first, if desired with an additional quantity of the silicate. Suitable silicates are sodium and potassium silicates: they may be used in amounts sufficient to give a silica precipitate equal to “-50 per cent of the lignin-aldehydeamide precipitate, e.g. from 1-30 per cent of the other components. In examples, several of the above-mentioned lignin materials are employed with sodium silicate and (1) aqueous formaldehyde and melamine, (2) paraformaldehyde and urea, (3) aqueous formaldehyde, melamine and urea; acidification was carried out with hydrochloric acid. Specification 798,779 is referred to.