With the increase of molecular weight, the former has much lower solvent resistance and migration resistance than the latter, such as C.I. Pigment Yellow 1 and C.I. Pigment Yellow 12. The results show that the solvent resistance and migration resistance of mono azo red naphthol as pigments are much lower than those of red condensed azo pigments, such as C.I. Pigment Red 2 and C.I. Pigment Red 166. Therefore, increasing the molecular weight of pigments is helpful to improve the solvent resistance and migration resistance of organic pigments. Reducing the solubility of organic pigment in the application medium can not only improve the solubility of the derivative in the application medium, but also reduce the solubility of the derivative in the application medium. The simplest chemical modification is the introduction of substituents into organic pigment molecules. It is known that the introduction of long carbon chain alkyl, alkoxy and alkylamino groups into organic pigment molecules can improve its solubility in organic solvents.
On the contrary, the introduction of amide group, nitro group and halogen lamp polar group into organic pigment molecule will reduce its solubility in organic solvent. For example, for C.I. Pigment Red 3, C.I. Pigment Red 13, C.I. Pigment Red 170, and C.I. Pigment Red 187, their solubility in organic solvents decreases with the increase of the number of amide groups in the molecule. According to the fact that the introduction of amide groups into organic pigment molecules has a significant effect on reducing its solubility in organic solvents, some heterocyclic amide groups have been designed and introduced into coupling components. As a result, the molecular design has a significant effect on reducing the solubility of pigments in organic solvents. According to the idea, the amide groups of heterocyclic structures are benzimidazolidone, phthalimide, benzotetrahydropyridazinones, benzotetrahydropyrimidinones and benzotetrahydropyrazinone. Among them, the pigment with benzimidazolidone as coupling component has the lowest solubility in organic solvents, and has excellent solvent resistance and migration resistance.