GB1160688A - Improvements in and relating to Chrome Tanning - Google Patents

Abstract

1, 160, 688. Pickling and tanning skins. UGINE KUHLMANN. Nov. 28, 1966 [Dec. 3, 1965], No. 53105/66. Heading C6C. In a process for chrome-tanning skins without basification, the skins, e.g. cleaned, softened, lime-depilated, fleshed and de-limed skins, are pickled in an aqueous liquor comprising sodium chloride, an acid or an acidic salt and a synthetic tanning agent, the pickling liquor is then drained off, and the pickled skins are tanned with a chromium salt, e.g. chromic cloride, chromic sulphate or a chromium alum, having a basicity of at least 45 degrees Schorlemmer, e. g. 55 degrees or 65 degrees Schorlemmer, water being added at the start of or during the tanning operation. The synthetic tanning agent may be an organometal compound, e. g. the reaction product of a water-soluble chromium salt with the condensation product of formaldehyde and #-naphthol sulphonic acid, or with the condensation product of formaldehyde and an alkali metal bisulphite and a diphenol having the formula: wherein X represents either SO 2 or the group: wherein Y and Z each represent H of CH 3 , as described in French Specification 1, 364, 655. A suitable organo-metal compound is obtained by treating chromium sulphate with the product resulting from the condensation of: formaldehyde, sodium bi-sulphite and 4, 4'-dihyroxydiphenyl propane, as exemplified in said French Specification. Alternatively, the synthetic tanning agent may be an auxiliary synthetic tanning agent, such as the ammonium salt of dinaphthylmethane di-sulphonic acid, or of a product made by condensing formaldehyde with phenol sulphonic acid or naphthalene sulphonic acid. Some of the chromium salt having a basicity of at least 45 degrees Schorlemmer may be introduced during pickling. Suitable acids and acidic salts for use in pickling are: sulphuric acid, hydrochloric acid, sodium bisulphate, ammonium bisulphate.