Modification study involving a Naphthol as red pigment

This paper is concerned with the modification study on a Naphthol red pigme nt (known in China as 808 Scarlet) synthesized by coupling aniline with Nap hthol AS, on the surface of inorganic cores. We also report the use of Tobi as acid to modify the aniline in the coupling step, producing a mixed coupl ing. As the size of the inorganic core decreases, surfaces of silica gel ar e fully covered with coupling component, and the resultant coated pigment i s made by the naphthol coupling component reacting with the diazonium compo nent on the inorganic core surface. The results of these experiments show t hat 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. (C) 1999 Elsevier Sci ence Ltd. All rights reserved.