Patent ID: 7517397

Claim:
A mixture consisting of (a) a color developer (1a) wherein A′ stands for a unsubstituted or substituted divalent aromatic radical, R 7 and R 8 are independent of each other and stand for —OH, unsubstituted or substituted C 1 -C 8 alkyl, unsubstituted or substituted C 1 -C 8 alkoxy, unsubstituted or substituted phenyl or naphthyl, —COOR 1a , wherein R 1a stands for hydrogen, unsubstituted or substituted C 1 -C 8 alkyl, benzyl or unsubstituted or substituted phenyl, —C(O)R 1a , or —NR 1a R 1b , wherein R 1b , independently from R 1a , stands for hydrogen, unsubstituted or substituted C 1 -C 8 alkyl, benzyl or unsubstituted or substituted phenyl, s stands for 0, 1, 2, 3, 4 or 5, t stands for 0, 1, 2, 3, 4, or 5, and (b) a compound of formula (2) wherein D stands for wherein D′ stands for a unsubstituted or substituted divalent aromatic radical, R 13 stands for a substituent as defined for R 7 , R 14 stands for a substituent as defined for R 8 , x1 stands for 0, 1, 2, 3, 4 or 5, x2 stands for 0, 1, 2, 3, 4, or 5, and wherein the weight ratio of (1a) to (2) is chosen in the range from 99.9:0.1 to 0.1:99.9.