| 摘要 |
The invention relates to monoazo pigments prepared from dichloroanilines as diazo components and CH-acidic coupling components of the acetoacetarylamide or naphthol series, these pigments only containing an extremely low level of polychlorinated biphenyls (PCBs) (at most 25 mu g per g of pigment). The process for preparing the pigments takes the form of an azo coupling in an aqueous medium, wherein a) azo coupling is effected by adding the diazonium salt solution to a suspension or solution of the coupling component or by simultaneously metering the aqueous suspensions or solutions of the diazonium salt and of the coupling component into the reaction mixture, b) azo coupling is effected at a pH or within a pH range of less than pH 7 and b1) between pH 4 and 7 during and after azo coupling less than 0.05 mol-%, b2) at pH 2 to 4 during azo coupling less than 5 mol-%, and b3) at pH<2 during azo coupling less than 25 mol-%, of diazonium salt is detectable in the reaction mixture and in pH ranges b2) and b3) more than 0.05 mol-% of diazonium salt is not present for longer than a total of 8 hours, more than 5 mol-% diazonium salt is not present for longer than a total of 4 hours and more than 15 mol-% of diazonium salt is not present for longer than a total of 2 hours, the mol-% ages of diazonium salt each being based on the total number of moles of coupling component present in the reaction mixture and pigment already formed, c) azo coupling is effected at a temperature or temperatures of 0 DEG to 50 DEG C., preferably 20 DEG to 40 DEG C., d) azo coupling is effected in the absence of nitrite ions, and e) azo coupling is carried out in the absence or presence of coupling assistants or coupling accelerants. The monoazo pigments, like existing monoazo pigments of corresponding structures, are useful for coloring natural and synthetic materials. |
