GB568182A - Improvements relating to the treatment of skin and leather materials - Google Patents

Abstract

568,182. De-tanning leather. VIGODNY, A., HERDAN, B., and LEVY, E. April 21, 1943, No. 6368. [Class 76] In the treatment of chrome tanned leather materials or waste alternately with acid and alkali liquors as a preliminary to the extraction of glue or gelatine, the acid liquors are such as to lower the pH of the materials distinctly below 3, or more preferably below 2, and contain a soluble salt such as sodium chloride, sodium sulphate, or magnesium chloride, or soluble non-electrolytes such as sugar, or mixtures of these substances, in order to lessen the swelling of the leather materials under acid conditions. Examples describe the use of suspensions of lime or barium hydroxide (the pH of the bath being kept above 11 and preferably above 12), solutions of sodium carbonate or sodium hydroxide, and sulphuric and hydrochloric acids. Reference is also made to the use of strontium hydroxide, caustic alkali, soda ash, formic, lactic, citric, tartaric acids and sodium bisulphate. After acid treatment, the material may be washed with water or a solution of the substances specified above for addition to the acid bath. After alkaline treatment, washing may be carried out with water or, especially when a sparingly soluble base has been used, with salts of weak bases, e.g. ammonium chloride, or with acids, e.g. boric acid. or with mixtures of these substances, the pH not being allowed to drop substantially below 5. Neutralization of the material with milk of lime, sodium carbonate solution, a suspension of barium carbonate, caustic alkali or ammonia may follow a final acid treatment. A treatment may also be given with solutions or suspensions of soluble carbonates, barium carbonate, barium hydroxide, or soluble barium compounds such as the chloride in order to convert calcium sulphate into calcium carbonate or barium sulphate and prevent it being carried forward into the glue or gelatine. Reference is also made to treating the material, before soaking in acid and alkali, by washing with water, which may be hot, or with a solution of ammonia or sodium bicarbonate. A wetting agent, e.g. a sulphonated oil or a sulphonated fatty alcohol, may be added at this stage. The Provisional Specification is not limited to the treatment of chrome tanned leather, and describes the process as applied to skin and leather materials in general.