GB892258A - Process for preparing stable aqueous pigment dispersions - Google Patents

Abstract

An "aqueous filter cake of an organic pigment" is mixed with a non-ionic polyglycol ether dispersant which is soluble in an acid to weakly alkaline medium but insoluble in concentrated aqueous alkalis and to the resulting mixture containing the dispersant in aqueous solution is added an amount of alkali metal hydroxide sufficient to cause the dispersant to separate from the aqueous alkaline solution and to form a separate phase. Thereafter the organic pigment is transferred by mechanical treatment into the dispersant phase, the bulk of the resulting pigment-free aqueous alkaline solution is separated and the dispersant is reconverted into an aqueous solution which contains the pigment in a very finely dispersed state. "Aqueous filter cake of an organic pigment" is defined as an aqueous cake which is alkali resistant and is obtained by filtering an aqueous slurry of a pigment resulting from the manufacture or conditioning of an organic pigment, e.g. aqueous pigment filter cakes of water-insoluble azo dyestuffs, oxazine dyestuffs, vat dyestuffs or of halogenated copper phthalocyanines. Non-ionic polyglycol ether dispersants referred to include those made by reacting ethylene oxide with lauryl alcohol, myristyl alcohol, cetyl alcohol, octadecyl alcohol, oleyl alcohol, arachidyl alcohol, linoleyl alcohol, ricinoleyl alohol, dihydroricinoleyl alcohol, hydroabietyl alcohol, naphthene alcohol, cetylamine, octadecylamine, octadecenylamine, methyloctadecylamine, hydroabietylamine, octadecyl-p-tolindine, cetyl mercaptan, dodecyl mercaptan, hexadecyl mercaptan, lauric acid, palmitic acid, ricinoleic acid, oleic acid, p-tert.-amyl phenol, isohexylphenol, p-tert.-octylphenol, thymol, p-nonylphenol, isooctylresorcinol, 2:6-di-tert.-butyl-p-cresol, dodecyl phenol, octadecylphenol or castor oil. The dispersant may be reconverted into an aqueous solution by (1) addition of an acid, e.g. acetic acid, (2) dilution with water or (3) addition of an anion-active dispersant, e.g. 2-heptadecyl-N-benzyl-benzimidazole disulphonate. Additionally the stable aqueous pigment dispersion may contain aminoplast resins, solvents and plasticizers. Specified pigments are 4:41,7:71-tetrachloro-thioindigo, b -copper phthalocyanine, chlorinated copper phthalocyanine, the pigment from diazotised 2:5-dichloroaniline and 2:3-hydroxynaphthoic acid-o-methoxyphenylamide, a -copper phthalocyanine and the pigments of formulae <FORM:0892258/III/1> <FORM:0892258/III/2> <FORM:0892258/III/3> <FORM:0892258/III/4> Examples are given.