Process for the transparent dyeing of cellulose acetate

Cellulose acetate is transparently dyed by dissolving an alcohol-soluble dyestuff in an alcohol having 1-4 carbon atoms, mixing the solution with all or part of the plasticizer necessary for plasticizing the cellulose acetate and mixing the solution so obtained with cellulose acetate. In preferred methods (a) the solution of the dyestuff in the alcohol-plasticizer mixture is added, with stirring, to a solution of cellulose acetate in solvent mixture consisting preponderantly of chlorinated methanes; (b) the solution of the dyestuff in the alcohol-plasticizer mixture is mixed, with stirring, with powdered or granulated cellulose acetate and this is then brought into solution by the slow addition of solvent. Preferably, the dyestuff is an alcohol-soluble 2:1 metal complex dyestuff. Dyes exemplified include cobalt and chromium complex dyes, and also nigrosine. Specified alcohols include ethanol, specified plasticizers include dibutyl phthalate and dioctyl phthalate, and cellulose acetate solvent mixtures include a mixture of methylene chloride and methanol. Solutions obtained may be cast to give clear, transparently dyed films, or may be used in the production of paints or of fibres.