GB427248A - Improvements in or relating to the production of cellulosic pigments - Google Patents

Abstract

A process for the production of cellulose pigments suitable for paints, printing inks, printing of wall paper or colouring of plastics, includes the step of regenerating the cellulose in a finely divided form from a solution of a soluble cellulose derivative in the presence of or with the subsequent addition of a solution of a dye which is stable to hydrolysis and which has an affinity for cellulose, but which is other than an ester salt of a body, yielding by oxidation a coloured compound. In a preferred form, the cellulose is regenerated by heating an alkaline aqueous solution of an alkali soluble salt of a cellulose mono-ester of a dicarboxylic acid, for example sodium cellulose phthalate, in the presence of excess alkali to a temperature high enough to hydrolyze the ester, for example above 50 DEG C. The regenerated cellulose may be filtered. The dye solution may be present during the regeneration, or may be added subsequently to the regenerated cellulose suspension, or the cellulose may be separated and separately treated with the dye. The term "solution of a dye" covers solutions not only of dyes as such, e.g. direct azo dyes but also of the leuco vat dyes. Specific examples are: (1) To a solution of 5 parts of Ponsol Blue GD, 6,4 parts sodium hydroxide and 5 parts sodium hydrosulphite in 1000 parts of water at 50 DEG C. is added a solution of 21 parts of sodium cellulose phthalate in 1000 parts of water, and the whole is heated to 90 DEG C. with the addition of a further 10 parts of sodium hydroxide. When hydrolysis is complete, the product is cooled, filtered, and washed. To ensure complete oxidation of the dye the product may be suspended in water through which air is passed or oxidizing agents such as mixtures of acetic acid and sodium or potassium bichromate, sodium perborate or hydrogen peroxide may be employed. Other similar examples are given employing alkaline solutions of ethyl cellulose hydrogen quinolate or cellulose benzoate hydrogen phthalate with a variety of other vat dyes, and of sodium cellulose phthalate with azo and sulphur dyes. Especially advantageous results are obtained with cellulose mono-ester of dicarboxylic acids which form inner anhydrides, e.g. the mono-esters obtained by reacting cellulose with phthalic succinic, quinolic, maleic or adipic anhydride in presence of a tertiary amine. Suitable alkali-soluble salts of these mono-esters are sodium, potassium, lithium and ammonium salts. The desired alkalinity of the solution may be maintained with any of the common alkalies.