Title: Method for colouring hair with removable hair colour
Claimed is a composition that will colour hair to the same degree as permanent hair colour but can be removed from the hair when desired. Also claimed is a method for colouring hair that provides the same degree of gentleness as found in semi-permanent hair colour, yet provides the relative permanence found with oxidative hair colour.
Hair is coloured with an aqueous composition comprising a reducing agent capable of reducing the --S--S-- bonds on the hair fibre surface to form reactive --SH groups and a dye molecule containing chemical groups reactive with the --SH groups. When the hair colour composition is applied to the hair at ambient conditions --S--S-- bonds are formed between the dye molecule and the hair surface. Atmospheric oxygen will cause the disulfide bonds to reform between the dye molecule and the hair surface, such that the dye molecule is bonded to the hair and is expected to remain so for a period of four to six weeks unless removed by disruption of the --S--S-- bond.
The dye molecules may be present in the form of complex molecules or polymers, or may be a chromophore compound substituted with the requisite --SH group or protected --SH groups as found in Bunte or isothiouronium salts. Any chromophore that provides colour to the hair is suitable for use provided it contains at least one free --SH group. Suitable compounds include acid dyes, basic dyes, disperse dyes and HC dyes, as well as dyes typically used for oxidative dyeing of the hair such as aminophenols and nitrophenols.
The hair colour composition comprises a reducing agent that is capable of reacting with the disulfide bonds on the hair fibre surface to cause formation of --SH groups. The preferred reducing agents are glyceryl thioglycollate and thioglycolic acid. The compositions may also contain other ingredients to improve the aesthetics of the formula, or provide other effects and include humectants, pH adjusters, hair conditioning agents and biological products.
The colour is removed from the hair with a composition containing a reducing agent in aqueous media and may be in the form of a shampoo, conditioner or hair treatment product. In addition to the reducing agent the colour removing composition may contain one or more ancillary ingredient that improve the aesthetics and performance of the composition. Preferably, the reducing agent used is different from the reducing agent used in the hair colour composition and the most preferred is sodium sulphite.