GB807089A - Manufacture of readily dispersible dry dyestuff preparations - Google Patents

Abstract

Readily dispersible dry dyestuff preparations are prepared by a process wherein an aqueous dyestuff suspension is frozen and then dried in the frozen state (i.e. a lyophilization process) and, if desired, the residual moisture is removed at a temperature above 0 DEG C. under reduced or ordinary pressure. The process may be carried out by freezing a dyestuff paste, introducing the frozen paste into a refrigerator connected to a low-temperature condenser (about - 70 DEG C.) and performing the lyophilization process at about - 10 DEG C. and at a pressure of about 0.5-0.05 mm. of mercury. In the second stage the temperature is raised to about 30-50 DEG C. and reduced and ordinary pressure may be applied alternately. The aqueous dyestuff suspension may contain dispersing or other auxiliary agents. In examples: (1) a vat dyestuff obtained by condensing 3 : 9-dibrombenzanthrone with pyrazolanthrone and 1-aminoanthraquinone with subsequent carbazolation is wet ground together with the condensation product from formaldehyde and naphthalene-2-sulphonic acid and with sodium di-butylnaphthalene sulphonate, the paste obtained is frozen and dried at a pressure of 0.5 mm. of mercury the temperature being raised first to 40 DEG and then to 50 DEG C. in the second stage; (2) an aqueous paste containing the vat dyestuff obtained by melting 1 : 4 : 5 : 8-tetra-(alpha-anthraquinonyl) - amino - anthraquinone with aluminium chloride together with the auxiliary agents specified in (1) is dried in a manner similar to (1). In further examples aqueous pastes containing the following dyestuffs and other ingredients are dried in the frozen state: the leuco acid of thio-indigo and molasses; dibromo - 3 : 4 : 8 : 9 - dibenzopyrenequinone-(5 : 10), the condensation product from formaldehyde and naphthalene-2-sulphonic acid, glucose, the reaction product of ethylene oxide and ammonia and sodium di-butylnaphthalene sulphonate; the azo dye 1-amino-2-methoxybenzene - 5 - sulphondiethylamide --> 1-(21 : 31 - hydroxynaphthoylamino) - 2 : 4 - dimethoxy - 5 - chlorobenzene with the auxiliary agents as in (1); 3 : 4 : 8 : 9-dibenzopyrenequinone - (5 : 10) and sorbitol; the azo dye 1-amino - 2 - nitro - 4 - methyl - benzene --> acetoacetanilide; the azo dye 1-amino-3-nitro-2 - methylbenzene --> 1 - (21 : 31 - hydroxynaphthoylamino) - 4 - chlorobenzene; 5 : 51 - dichloro-7 : 71-dimethyl-thio-indigo.