Hitherto, oxidative dyes have been used in permanent hair-dyeing or -coloring agents. The oxidative dye is allowed to penetrate into hairs in the state of a dye precursor, having a small size, which becomes oxidized in the hair, forming a dye molecule having a relatively large molecular size, thereby keeping the hair colored for a long period of time. However, this method has the problem that it is impossible to obtain the effect of dyeing hair in a fresh tone. Further, the safeties of a dye precursor itself, uncontrollable intermediates, and final products are currently regarded as problematic.
In the meanwhile, semi-permanent hair-dyeing or -coloring agents and temporary hair-dyeing or -coloring agents, that dye hair by applying a direct dye to hair, are used. However, these hair-dyeing agents have the drawbacks, e.g. that they have a shorter hair-color retention term, as their names imply, and that only insufficient hair-dyeing density. An attempt is made to use a nitro dye or a cationic dye as a direct dye to improve the hair-dyeing density in this method (see, for example, JP-A-6-271435 (“JP-A” means unexamined published Japanese patent application), JP-A-2001-261535, JP-T-8-501322 (“JP-T” means published searched patent publication), JP-T-8-507545, and JP-T-10-502946). However, when a nitro dye is used, it poses the problem that hair significantly fades with the lapse of time, and easily becomes darkish. On the other hand, when a cationic dye is used, it poses the problem that significant color fading is caused by shampooing hair, depending on the type of dye.
USPTO Backgrounds
USPTO Backgrounds