Hair Colouring by Using Catechins from Green Tea and Chemical Oxidants

摘要

The hair dyeing using green tea extracts containing high amount of catechins in combination with chemical oxidants such as O_2, H_2O_2 and NaIO_4 was attempted in order to establish a novel hair dyeing technique without using aromatic amines contained in commercial oxidation dye products. The new hair dyeing technique consists of a two-step colouration system. The first step is treatment of hair with tea extract solution and the second one is oxidation treatment. Three kinds of oxidation methods such as (1) treating hair with basic dyeing solution (pH=11.5) supplied with large amount of O_2 gas (O_2 method), (2) treating hair with H_2O_2 solution (pH=9.5) (H_2O_2 method), (3) treating hair with NaIO_4 solution (pH = 7) (NaIO_4 method) were attempted as the second oxidation treatment. The results show that once dyed hair is discoloured by H_2O_2 in the oxidation process and white hair is hardly coloured by the method. In contrast, white hair is dyed brown by the O_2 or NaIO_4 method, and the dyeability increases with increasing temperature of the first tea extract treatment. This may be due to the increase in the amount of dye precursors adsorbed onto hair by heating. Colour fastness of the hair samples dyed by the 0_2 and NaIO_4 method to washing is almost same level as that by the commercial oxidation dyes. The NaIO_4 method is more useful than the O_2 method because the supply of O_2 gas is unnecessary for the NaIO_4 one and it uses the neutral solution.