GB568180A - Improvements in or relating to tanning compositions and processes for tanning - Google Patents

Abstract

568,180. Tanning compositions. IMPERIAL CHEMICAL INDUSTRIES, Ltd. (Du Pont de Xemours & Co., E.!.). April 3, 1943, No. 5362. [Class i6] [Also in Group III] Solid tanning compositions, adapted to be dissolved in acid to produce a modified silicic acid sol, comprise a hydrogen bonding agent and an acid-soluble double silicate of an alkali metal and aluminium, chromium, iron, zinc, titanium, or zirconium. The term " hydrogen bonding agent " is used to refer to organic compounds which form co-ordination compounds with silicic acid, and which are at least slightly soluble in water without raising the pH of the silicic acid solution above 7. A list of suitable compounds, comprising ethers, amides, ketones, alcohols and esters, is given. Examples describe the use of urea, nonaethylene glycol, tri-butyl phosphate and carbitol acetate. Silicates which may be used in the compositions are those occurring naturally, such as laumonite, analcite, natrolite, nethelite, compounds such as sodium calcium aluminium silicate, or substances prepared as described in U.S.A. Specifications 1,949,360 and 2,244,383, or by heating kaolin with sodium hydroxide solution. Sodium aluminium silicates having an Al2O3: SiO2 molar ratio from about 1 : 2 to 1 : 5 are preferably used, and may be prepared by adding a solution of any aluminium salt more soluble than the reaction product to a solution of a sodium silicate. When the SiO2 : Na2O ratio of the silicate is high, alkali, e.g. sodiwn, or potassium hydroxide, calcium oxide, barium oxide, or an organic base such as tetraethanolammonium hydroxide is added to maintain a pH of 9 or more. The use of aluminium sulphate, hydroxide, nitrate and chloride, and of sodium aluminate is referred to, and in examples, sodium silicate and metasilicate are used. Double silicates of any alkali metal and chromium, iron, zinc, titanium and zirconium may be prepared similarly. The tanning composition may also contain masking agents such as lactates, acetates, propionates, tartrates, glycollates, citrates, oxalates, adipates, succinates or glutarates of sodium, potassium, ammonium or an alkaline earth metal. Other tanning agents and assistants may be added. Acids suitable for dissolving the compositions to give tanning solutions are sulphuric, hydrochloric, nitric, acetic or lactic acids or a thionic acid. Solid acids or acid salts such as sulphamic acid, sodium bisulphate, monosodium phosphate, acid tartrates, zinc chloride, titanium, aluminium or chromium sulphates may be included in the compositions, and in this case either the acid or the silicate may be coated with an inert substance such as calcium stearate and the mixture may be compressed into briquettes to prevent segregation. In tanning with the compositions described, it is sometimes preferable that the pH of the skins to be treated should be adjusted to approximately that of the tanning solution. To increase the speed of tanning, the pH of the solution may be raised by the addition of sodium carbonate, other alkali metal or ammonium hydroxides or carbonates, or organic bases such as ethanolamines.