Heat-stable encapsulated pigments

A method of producing a colored polyamide engineering plastic comprising a) preparing a pigment composition by mixing an organic pigment and a prepolymer in a liquid medium;

• and b) coloring a polyamide engineer plastic by processing together the pigment composition from a) and the polyamide engineering plastic at a temperature of about 220 to 350 ° C.;
• wherein the pigment composition comprises solid particles, which particles comprise from 20 to 75% by weight of an organic pigment and from 80 to 25% by weight of a crosslinked polymer, each based on the total weight of the solid particles,
• wherein the prepolymer has average molecular weight Mw from 2000 to 200000, which prepolymer comprises (a) repeating blocks of formula
• and (b1) hydroxy, epoxy or primary or secondary amino groups or (b2) unsaturated bonds, wherein R1 is H, C1-C4alkyl, C2-C4alkenyl or COOR5, R2 and R3 are independently from one another H, OR6, NHR6, C1-C4alkyl or C2-C4alkenyl, R4, R5 and R6 are independently from one another H, unsubstituted C1-C6alkyl or C2-C6alkenyl, or C2-C6alkyl or C2-C6alkenyl each substituted by one or more hydroxy and/or epoxy groups, and n is a number from 2 to 2000;
• wherein the organic pigment is selected from the group consisting of pyrrolo[3,4-c]pyrroles of the formula
• wherein R7 and R8 are each independently of the other a group of formula
• R9 and R10 are each independently of the other hydrogen, halogen, C1-C24alkyl, trifluoromethyl, C5-C6cycloalkyl, C1-C18alkoxy, C1-C18alkylthio, C1-C18alkylamino, cyano, carbamoyl, nitro, phenyl, C═N—C1-C24alkyl
• imidazolyl, pyrazolyl, triazolyl, piperazinyl, pyrrolyl, oxazolyl, benzoxazolyl, benzothiazolyl, benzimidazolyl, morpholinyl, piperidinyl or pyrrolidinyl, preferably hydrogen, halogen, cyano, carbamoyl, nitro, trifluoromethyl, phenyl, C1-C6alkyl, C1-C6alkylthio or C1-C6alkylamino;
• R11 and R12 are each independently of the other hydrogen, halogen or C1-C6alkyl;
• R13 is —CH2—, —CH(CH3)—, —C(CH3)2—, —CH═N—, —N═N—, —O —, —S—, —SO—, —SO2—NH or —NC1-C6alkyl-;
• and
• R14 and R15 are each independently of the other hydrogen, halogen, C1-C6alkyl, C1-C6alkoxy or CN;
• pyrimidopteridines of formula
• wherein R32, R33, R34 and R35 are each independently of one another NH2, OH, hydrogen, methyl, ethyl, NHCOR37, NHCOOR37, NHCONHR37, NHCONR36R37 or phenyl which is unsubstituted or substituted by OH or NH2, wherein
• R36 is C1-C4alkyl;
• phenyl which is unsubstituted or substituted by halogen, C1-C4alkyl or C1-C4-alkoxy, COR37, COOR37 or CONHR37;
• and
• R37 is C1-C4alkyl or phenyl which is unsubstituted or substituted by chloro, methyl, ethyl, methoxy or ethoxy, with the proviso that R32 and R35 are identical, and R33 and R34 are identical and at least one of the pairs R32 and R35 or R33 and R34 is NH2 or OH;