Modification study involving a Naphthol as red pigment

Abstract This paper is concerned with the modification study on a Naphthol red pigment (known in China as 808 Scarlet) synthesized by coupling aniline with Naphthol AS, on the surface of inorganic cores. We also report the use of Tobias acid to modify the aniline in the coupling step, producing a mixed coupling. As the size of the inorganic core decreases, surfaces of silica gel are fully covered with coupling component, and the resultant coated pigment is made by the naphthol coupling component reacting with the diazonium component on the inorganic core surface. The results of these experiments show that the resistance to heat, color strength, shade and dispersing stability (in aqueous media) of the modified pigment made by the “coated core” method and the mixing coupling technique are all increased.