Dissociative Azo Dyes for Oxidative Hair Coloring Products and Their Visual Effect

Abstract

Hair coloring products adopt various type of dyes with different characteristics. The mainly used oxidative dyes show promising basic performance, while typically giving dull color look. Dissociative azo dyes; HC Red 18, HC Blue 18 and HC Yellow 16, which have high chroma, and work in alkaline peroxide system were developed. In addition to the known challenges of the conventional direct dyes, such as dyeing level and skin-staining, stability to the alkaline peroxide was carefully considered. As a result, the dyes can be used in the same way as oxidative dyes, that is, simultaneous bleaching and coloring of the hair. An anionic charge on the hydroxyl group of the dyes can be delocalized onto their conjugated system. The said delocalized charge distribution allowed the dyes to penetrate to the hair cortex and enabled their long-lasting color durability. Cross-sectional observation of the dyed hair showed multi-layered penetration pattern of the dyes in the hair cortex. This penetration pattern provides “Moving Color” effect, which is, angle-dependent hair color look depending on the hair/observer’s position.