Patent GB-641835-A (GB)
Title: Improvements in the colouration of cellulose ester or ether textile materials
IPC: D06P1/28
Filed: 1948-02-23
Abstract: Cellulose ether and ester fibres (especially cellulose acetate) are coloured by impregnation with a solution, free from discharging agents, of an ester of a leuco vat dye in a mixture of water and an organic liquid containing urea, and steaming to convert the ester into the parent vat dye; the urea may be replaced by one of its water-soluble alkyl derivatives or by a water-soluble ester of carbamic acid or by a water-soluble carboxylic amide.  The material may be in the form of yarn, staple fibres or fabric and may be associated with other fibres, e.g. cotton and regenerated cellulose. Sulphuric and phosphoric acid esters of the leuco vat dye are preferred.  The leuco esters may be of indigoid or anthraquinone dyes, a number being specified. The organic liquid may be a hydroxy compound, ketone, ester or ether or may contain two or more such groups with or without another polar group or atom such as a halogen atom; suitable compounds are mentioned, ethyl alcohol being preferred.  A thiocyanate may also be present.  A preferred composition consists of ethyl alcohol of 60-70 per cent strength by weight containing 10-15 per cent of urea and 1-5 per cent (e.g. 3 per cent) of ammonium thiocyanate based on the weight of water and alcohol. The solutions of the leuco esters are preferably applied by mechanical impregnation (padding or printing) in conjunction with a thickener, e.g. water-soluble methyl cellulose.  The material is preferably dried before steaming, and then the leuco ester is oxidized to the parent dye, for example with acidified sodium nitrite or a chromate.  After oxidation, the material is soaped, and the shade and light-fastness improved by a further steaming. When mixed fabrics of cellulose and cellulose acetate are treated by the process of the invention, a more or less solid shade is usually obtained. With certain dyestuffs, however, it is possible to wash out the leuco ester from the cellulose fibres before the first steaming so that after oxidation only the cellulose acetate is coloured.  The cellulose may then be coloured in any way, e.g. with direct dyes or by vat dyes applied from weakly alkaline vats.  A convenient method, however, is to impregnate the material with an aqueous solution of a leuco ester which does not swell the cellulose acetate and oxidize the two simultaneously.  By using the same leuco ester as was used for the cellulose acetate, but in a different proportion, tone-in-tone effects can be produced, or alternatively a different leuco ester or a mixture of leuco esters may be employed.  Besides cellulose acetate, the process of the invention is applicable to cellulose formate, propionate, butyrate, aceto-propionate and acetobutyrate, and to ethyl cellulose.  Examples show: (1) padding cellulose acetate with Indigosol Golden Yellow IRK; (2) printing cellulose acetate with a mixture of Indigosol Bordeaux I 2RN and Indigosol Golden Yellow IRK; and (3) padding a mixed cellulose acetate/cotton fabric with a mixture of Soledon Red 3BS and Indigosol Golden Yellow IRK, washing the leuco esters from the cotton fibres and padding again with a mixture of Soledon Jade Green XS and Indigosol Golden Yellow IRK, whereby the two fibres are coloured differently.  Specifications 462,222, 583,349 and 594,722 are referred to.