LAKED SULFONIC ACID GROUP-CONTAINING AZO DYE

This invention relates to a method of dyeing thermoplastics with sulfonated monoazo colorant lakes having a sulfophenyl pyrazole substituent, of general formula (I) wherein R is CH3 or COO-; X is Cl, CH3, CH3O, C2H5O, C2H5CONH, NH2CONH, C6H5CONH, CH3SO2NH, C6H5SO2NH, CH3CONH, or hydrogen; Y is hydrogen, Cl, or CH3; Z is hydrogen or Cl, n is 0, 1 or 2; and Me+ is one equivalent of a cation selected from the group consisting of NH4+, Li+, K+, Na+, 1/2Sr2+, 1/2Mn2+, 1/2Ni2+, 1/2Ba2+, 1/2Mg2+ and 1/2Ca2+; with the proviso that if R is COO-, the additional equivalent charge is compensated by a further equivalent of said or another cation. These compounds, which are insoluble in organic solvents and sparingly soluble in water, are useful as lakes with good pigmentary characteristics and possessing very good lightfastness in plastics, such as polyolefins, polyvinyl chloride, polystyrene, and ABS. They are also useful in surface coatings, and particularly suitable for coloring thermoplastics. Noteworthy is their good plasticizer fastness, their high stability to heat and the absence of blooming they produce when used.