Patent GB-647898-A (GB)
Title: Improvements in the colouration of textile materials
Filed: 1947-07-28
Abstract: Textile materials of cellulose acetate (or other ester or ether of cellulose) are treated with a leuco compound of a vat dye in an aqueous medium containing sufficient water-miscible organic liquid to impart a swelling power for the cellulose derivative which is greater than that of water alone; the medium has a pH between 8 and 11.5 (preferably 10.5) due either to caustic alkali or to an alkali metal salt of an acid having a dissociation constant of less than 1 X 10-8. In the latter case, the dye liquor is prepared either by vatting the dye in water with alkali and a reducing agent and adding the organic liquid and acid of dissociation constant less than 1 X 10-8 or by vatting the dye in water with a reducing agent and the salt of the weak acid, the organic liquid being present during the vatting or added afterwards.  In the case of polybasic acids, the dissociation constant referred to is that of the first hydrogen atom.  Boric acid is preferred; other suitable acids are aminoacetic, a -amino-propionic and other a -amino-aliphatic acids; phenols may be used, e.g. phenol itself, cresols, resorcinol, hydroquinone, tannic acid and naphthols.  The acid may be used in an equimolecular proportion to the alkali or in a lesser or greater proportion.  The water-miscible organic liquid is preferably an aliphatic hydroxy or halogen compound, ketone, ester or ether, and preferably contains two such polar groups.  Diacetone alcohol is preferred, and other suitable compounds are ethylene glycol monoacetate and its methyl ether, glycerol diacetate, ethylene glycol monomethyl or ethyl ether, ethyl lactate, ethylene or propylene chlorhydrin and ethylene methylene ether.  Monohydric alcohols such as methyl, ethyl, propyl and butyl alcohols may be used, but the stability of the vat may be impaired.  An inorganic swelling agent such as a thiocyanate may be included, together with dispersing and/or wetting agents, suitable types being specified.  When working above 50 DEG  C., a formaldehyde sulphoxylate is a desirable addition.  When the material is to take up the dye substantively, suitable proportions of the organic liquid are, e.g. 10-40 per cent of ethyl alcohol or 15-25 per cent of diacetone alcohol, working at 50-80 DEG  C.  Higher proportions, e.g. 30-45 per cent of diacetone alcohol, are desirable when the dye is applied by mechanical impregnation methods, e.g. padding or printing, or a short immersion followed by centrifuging; in this case a thickening agent, e.g. a water-soluble alkyl cellulose, is preferably added, and the material may be steamed after impregnation.  Following dyeing or impregnation, the material is preferably washed (but not dried) and the dye oxidized in the usual way.  Finally it may be hot-soaped and/or steamed to develop the shade and increase the light-fastness.  The process is applicable to dyes containing two or more anthracene nuclei such as those mentioned in Specification 647,897, and to other vat dyes.  When a mixed fabric of cellulose acetate and cellulose fibres is treated, the latter may or may not be coloured simultaneously, depending on the pH and the amount of organic liquid present.  If not coloured during the process, the cellulose fibres can be dyed previously with vat dyes under conditions such that the acetate is not coloured, e.g. in a vat of low alkalinity and/or at a low temperature (cf. Specification 262,506, [Class 15 (ii)].  Alternatively, the cellulose fibres can be mechanically impregnated with a sulphuric ester of a leuco vat dye under conditions such that the acetate is not swollen, and the vat dye produced on the fibres in the usual way.  The cellulose fibres of such mixed fabrics may be of cotton or may be obtained from viscose or cuprammonium solutions or from saponification of stretched cellulose ester fibres.  When a mixed fabric of cellulose acetate and wool, silk or other animal fibre is treated, good union dyeings can be obtained by choosing the correct pH and proportion of organic liquid, especially when diacetone alcohol is used.  Examples show the colouration of cellulose acetate and of mixed cellulose acetate/wool fabrics.  The process of Specification 479,867 is disclaimed.  The Provisional Specifications contain additional examples.