Patent GB-674638-A (GB)
Title: Process for dyeing skins and furs with insoluble azo-dyestuffs
IPC: D06P3/30
Filed: 1949-08-23
Abstract: Skins or furs are dyed with insoluble azo dyestuffs by applying a strongly caustic alkaline solution of a component (e.g. of the benzene, naphthalene, anthracene or higher carbocyclic or heterocyclic series) coupling in o-position to a hydroxy group (the concentration of caustic alkali corresponding to those usual on cellulose fibres), in the presence of formaldehyde in a concentration sufficient to protect the material from detrimental attack by the caustic alkali, and developing the dyestuff by treatment with a solution of a diazonium compound (e.g. of the benzene, diphenyl, terphenyl, naphthalene, carbazole, quinoline, indole, indazole, fluorene, diphenylene oxide or azobenzene series).  Fancy effects may be produced by locally brushing, scraping on, spraying or printing on the skins a solution of the coupling component containing caustic alkali, formaldehyde and, if desired, solvents, wetting and thickening agents, whilst multi-coloured fancy effects may be produced by applying different coupling components side-by-side or by locally applying a second coupling component on a material pre-treated with a coupling component.  The process is applicable to raw or fleshed skins or furs, either immediately or after dressing and killing, and, if desired, after a formaldehyde tanning (in which case further formaldehyde need not be added if the concentration is already sufficient).  When the skins or furs have been dressed (e.g. with a strongly acid Leipzig dressing), a preliminary neutralization with an alkaline-reacting agent (e.g. sodium carbonate solution or caustic alkali) is necessary.  When the diazonium compound contains a strongly-negative substituent, the skin or fur is preferably pre-treated with an agent yielding oxygen, such as hydrogen peroxide or sodium peroxide, or with a solution of sodium hypochlorite or hypochlorite of lime.  In examples: (1) raw fleshed rabbit skins are treated with a solution of dried sulphite waste liquor (freed from iron and calcium salts), sodium carbonate, sodium chloride and formaldehyde, with subsequent addition of an aqueous alcoholic caustic soda solution of 1-(Bz-21-hydroxy-111 : 211-benzocarb azole-31-carboylamino)-4-methoxybenzene containing more formaldehyde, and a black dyeing is developed by treatment with a solution of the zinc chloride double salt of 4-amino-3 : 5-dichlorobenzene-1-diazonium chloride and a dodecyl alcohol-ethylene oxide condensation product, followed by pickling in a solution of sodium chloride, ammonium chloride and sulphuric acid; (2) Leipzig dressed rabbit skins are killed in sodium carbonate solution and treated with a solution of 1 - (21 - hydroxycarbazole - 31 - carboylamino) - 4 - chlorobenzene, sodium turkey red oil, caustic soda, sodium chloride and formaldehyde, and a brown dyeing is developed with diazotized 4-chloro-2-methylaniline; (3) the wetting agent in the first treatment in (1) is replaced by oleylmethyltaurine and sulphite waste liquor and the coupling component by 1-(21 : 31-hydroxynaphthoylamino) - 2 - o  - dimethylaminomethylbenzene, yielding a dark brown dyeing; (4) rabbit skins are mordanted with formaldehyde, dressed with a pickle of sodium chloride and sulphuric acid, killed with sodium carbonate solution, brushed with an ammoniacal solution of hydrogen peroxide and treated with an aqueous alcoholic caustic soda solution of the coupling component of (1), turkey red oil and formaldehyde, and a black dyeing is developed with the zinc chloride double salt of 2-methoxy-4 - nitrobenzene - 1 - diazonium chloride; other skins, e.g. lamb or calf, may be similarly dyed; (5) rabbit skins are locally brushed or sprayed with a solution of 1-(Bz-21-hydroxy-111 : 211-benzocarbazole - 31 - carboylamino) - 2 - methyl-4-methoxybenzene, ethylene diglycol, caustic soda, the sodium salt of sulphonated castor oil, formaldehyde and tragacanth thickening, and black fancy effects are developed with 4-amino-3 : 5 - dichlorobenzene - 1 - diazonium chloride.  Lists of additional components are given.  The Specification as open to inspection under Sect. 91 comprises also the addition of chromium acetate to promote coupling with certain classes of diazonium compounds (e.g. those of diphenylamines), the treatment with which is advantageously carried out at elevated temperature.  An additional example describes the dyeing of fleshed lamb skins by this method, the diazonium compound being 41-methoxydiphenylamine-41-diazonium chloride.  This subject-matter does not appear in the Specification as accepted.