GB599608A - Improvements in or relating to the production of monazo and disazo pigments - Google Patents

Abstract

Monoazo and disazo pigments of clean colour and high tinctorial strength are manufactured by effecting coupling of a diazo or tetrazo compound with an acetoacetic arylide or pyrazolone coupling component by feeding the diazo or tetrazo compound and the coupling component into an aqueous reaction bath in substantially equivalent reacting proportions while maintaining the concentration of the reactants low and keeping the pH of the bath below about 5.0, preferably between 3.5 and 4.3, e.g. by the use of a buffer salt. Preferably, the amount of water is kept low and the concentrations of the separate solutions of the components high, and the rate of feed is controlled so that reaction takes place substantially instantaneously. It is, however, advantageous to have the coupling component always present in slight excess, e.g. of an amount up to 20 per cent of the diazo or tetrazo compound during the major part of the process, which condition may be brought about by initially introducing part of the coupling component alone, then simultaneously introducing the reactants in equivalent reacting proportions until all the coupling component has been added and finally adding the remainder of the diazo or tetrazo compound. After completion of the coupling, the pigment particles may be resinated by raising the temperature of the reaction bath to about 60-65 DEG C. and the pH to about 6.5 and adding a resin and a material reactive therewith to form a precipitate, this step being advantageously effected in the presence of alumina hydrate, which may be used in an amount between 1 and 100 per cent of the amount of resinate, and may be added to the reaction bath before or after the coupling. In examples: (1) a solution of tetrazotized 3 : 31-dichlorobenzidine and a solution of acetoacetanilide made slightly alkaline with caustic soda are introduced (the latter to the extent of 15 per cent of the total before any of the former) into a dilute solution of sodium acetate and acetic acid, at 0-3 DEG C. with final heating to 60-65 DEG C.; (2) the tetrazo compound in (1) is replaced by diazotized o-nitro-p-toluidine and the proportion of coupling component added initially is reduced to 10 per cent; (3) the pigment p-chloro-o-nitraniline --> acetoacet-o-chloranilide is similarly prepared; (4) the product of (1) is resinated by adjusting the pH of the bath to about 6.5 with caustic soda and adding alumina hydrate and a solution or dispersion of water white rosin in aqueous caustic soda, followed by an aqueous solution of aluminium sulphate; (5) the coupling component in (1) is replaced by 1-phenyl-3-methyl-5-pyrazolone. A printing ink is described in which the product of (2) is incorporated with chrome orange, alumina hydrate and zinc sulphide in a linseed oil varnish.