Patent GB-777699-A (GB)
Title: Tanning process
IPC: C14C3/18
Filed: 1953-01-27
Abstract: 777,699. Tanning leather. BOEME FETTCHEMIE GES. Jan. 27, 1953 [March 31, 1952], No. 2279/53. Class 76. Hides and skins are tanned by consecutively applying thereto a nitrogen containing artificial resin pre-condensate and a water-soluble surface-active compound containing an aliphatic, cycloaliphatic or araliphatic radical of at least 6 carbon atoms, and during the treatment or subsequent thereto converting the watersoluble artificial resin pre-condensate into an insoluble form. The water-soluble surface-active compound may be anion-active, cation-active or electro-neutral. The anion-active compounds are fatty alcohol sulphonates, water-soluble salts of alkyl or alkyl-aryl sulphonic acids or of sulphonated oils or fats, or water-soluble salts of fatty acids, resin acids and wax acids, or water-soluble condensation products of proteins or their degradation products with fatty acid halides, or with sulphonic acid halides which contain radicals of at least 6 carbon atoms or with high molecular weight halogen fatty acid esters or amides. The cation-active compounds are quaternary ammonium compounds and the corresponding phosphonium or sulphonium compounds which contain at least one high molecular weight lipophilic radical, for example trimethyl octadecyl ammonium chloride, dodecyl pyridinium bisulphate and dimethyl cyclo hexyl octadecyl ammonium chloride. Electro-neutral compounds are polyalkylene oxide addition products, such as ethylene oxide addition products, of high molecular weight carboxylic acids, amines, mercaptans or of high molecular weight aliphatic or aliphatic-aromatic sulphonic acids or sulphonamides, or the corresponding water-soluble condensation products with polyvalent alcohols such as ethylene glycol, glycerol, pentaerythritol, and sorbitol. The water-soluble nitrogen containing artificial resin precondensates are those obtained from urea, thiourea, cyanamide, methylene diurea, guanidine, alkyl guanidines, dicyandiamide, dicyandiamidine, and melamine by condensation with aldehydes particularly formaldehyde or acetaldehyde. The resinous tanning agent is generally employed in an amount between 2 and 10 per cent by weight of the unhaired hides whilst the water-soluble surface active compounds may constitute 2 to 5 per cent. The conversion of the water-soluble resin pre-condensate into insoluble form may be effected by alkaline or acid reagents or by heat. There may be employed in addition to, or as partial replacement for, the water-soluble surface-active compounds, substances such as animal or vegetable fatty acids, for example olein, animal or vegetable fats or oils such as train oil, tall oil and resin oil, mineral oils or fats, fatty acids or sulphonic acid chlorides such as alkyl benzene sulphonic acid chlorides, or other substances containing fatty radicals with reactive halogen atoms such as high molecular weight halogen fatty acid esters or amides. According to examples: (1) sheepskins were defatted, delimed and drenched and then treated at 18 to 20‹ C. for 2 hours with 4 per cent of a water-soluble melamineformaldehyde pre-condensate and 80 per cent of water. The tanning liquor was then replaced by 5 per cent of an alkyl sodium sulphate mixture and 20 per cent water, and after one-and-a-half hours the leathers showed a pH of 6.2, the resin precondensate having been converted to insoluble form to complete the tanning. (2) Dehaired goatskins were treated with 3 to 4 per cent of a water-soluble dicyandiamide-formaldehyde condensate and 80 to 100 per cent of water at 10‹ to 20‹ C. the leather having a final pH of 6 to 6.8, whereby the conversion of the resin precondensate into insoluble form commenced. The liquor was then replaced by 3 to 4 per cent of a water-soluble ethylene oxide addition product to an alkyl benzene sulphonamide mixture and 20 per cent water and allowed to stand for an hour, by which time the leather had a pH of about 6 and the conversion of the resin precondensate into insoluble form was completed. (3) Dehaired calfskins were treated with 4 per cent of a water-soluble urea formaldehyde precondensate and thereatter with a solution of 6 to 12 per cent of sodium alkyl benzene sulphonato and 20 per cent of water at normal temperature, the pH finally being adjusted to 4.5 to 5 by the addition of an organic acid such as formic acid which converted the resin precondensate into insoluble form. (4) Dehaired lambskins were treated with 2 to 3 per cent of a water-soluble melamine-formaldehyde pre-condensate at 18‹ to 20‹ C., the leather having a final pH of 6.9. The tanning liquor was then replaced by 2 per cent of an alkyl sulphate mixture neutralized by triethanolamine and after treatment the leather had a pH of 5.8 to 6.4. Potash, alum and common salt were then added to lower the pH to 4 to 4.4 whereby the resin pre-condensate was converted to insoluble form. (5) Sheeps pelts after heating were treated with a pickle containing cooking salt, sulphuric acid and formic acid and thereafter treated at 20‹ C. with an aqueous solution of oleyl sodium sulphate. Subsequently they were treated with 4 per cent of a condensation product of dicyandiamide and formaldehyde which was converted into the insoluble form since the pH of the pelts was already in the acid range.