J. Cosmet. Sci., 56, 29-46 CTanuary/February 2005) A novel "permanent" acid-type hair color made possible with dye-metal ion complex technology M. OCHIAI, T. KAW ASOE, M. YASUDA, Y. HARADA, T. KIMURA, T. KAMBE, and J. KURITA, Product Development Center (M.O., T. Ka., Y.H., T. Karn.), Basic Research Center (M. Y., T. Ki.), and Institute of Beauty Science U. K.), Shiseido Co., Ltd., 2-2-1 Hayabuchi, Tsuzuki-ku, Yokoharna-shi, 224-8558.fapan. Accepted for publication December 14! 2004. Presented in part at the 22nd Congress of the Internationa( Federation of the Societies of Cosmetic Chemists (IFSCC), Edinburgh, Scotland, September 26, 2002. Synopsis The advantages and disadvantages of oxidative permanent and acid-type semi-permanent hair colors are evident. The former provides a longlasting "permanent" color, while the latter imparts less damage to the hair. We developed a novel acid-type hair color technology that can allow an acid dye and a metal ion ro form a complex inside the hair similar to the oxidative hair color. It is well known that acid dye diffuses into the hair and creates an ionic bond with the positively charged amino acid residues of hair protein. However, the dye can be extracted easily from the hair by daily shampooing due ro the weakness of the bond. In order to strengthen this bond and to prevent the extraction of the dye by shampooing, an aluminum chloride ion was chosen as the metal ion component to form the dye-metal complex. A proper composition of penetration enhancers, benzyl alcohol and ethyl alcohol, was required to allow acid dyes to interact with the aluminum chloride ion after each component penetrates deeply into the hair to form a complex inside the hair. To provide color brightness and a color longevity effect to hair color, glycolic acid was also selected due to the observation that a weak acid with a small molecular weight would enhance those effects. INTRODUCTION Hair coloring products can be categorized into three groups according to dyes (1,2). The first type of hair coloring product is temporary hair color, which is absorbed physically onto the surface of hair. The second type is semi-permanent hair color, whose anionic or cationic character has affinity to hair protein. The third type is oxidative or permanent hair color. In the third type, small dye molecules [e.g., p-phenylenediamine, MW: 108) diffuse into hair and produce a dye complex inside the hair cortex through chemical reactions (3-5 ). Due to its color brightness and color longevity effect, oxidative hair color is most popularly used and has a firm market position in the hair color category in Japan as well as Europe and the United States (6). On the other hand, oxidative hair color damages hair and has an irritating smell (e.g., ammonia odor) because it needs the 29

30 JOURNAL OF COSMETIC SCIENCE chemical reaction of ammonia and hydrogen peroxide to develop the color (7 ,8). It also requires an allergic patch test (9). In the semi-permanent hair color market in the US and Europe, HC (uncharged) dyes and basic dyes are mainly used. Acid dye is mainly used in Japan. HC dye simply drives into hair by a concentration gradient. In contrast, acid dye forms a hydrogen bond with charged protein. Semi-permanent hair colors are also seen in the US and Europe these days, and no outstanding problem in long-lasting effect and dyeing effect is seen. This research is targeted on the second type, semi-permanent hair color with acid dyes. Some acid dyes are approved under the Japanese cosmetic regulation. The acid dyes [e.g., acid orange 7,4-[(2-hydroxynaphth-l-yl) azo}-benzene sulfonic acid, sodium salt, MW: 350.33} penetrate into hair with the existence of a penetrating agent, benzyl alcohol. The sulfonic acid group of dyes binds with the positively charged amino group at a low pH ( 4) (3,9). It is also well known that dye in the hair can be extracted easily from hair by daily shampooing due to the weakness of the chemical bond between the dye and positively charged protein (3,9). Although acid hair dye can give vivid color and never damages hair, color brightness and color longevity attributes are required on the market (9). In this research, the authors focused on the reaction of acid dyes complexing with metal ion (10,11) and produced a novel oxidative-hair-color-like system that forms a dye­ metal complex in the hair. This novel acid hair color technology could provide color brightness and color longevity of semi-permanent acid hair color comparable to that of permanent hair color. MATERIALS AND METHODS MATERIALS Acid red 52 and acid orange 7 were purchased from Kishikasei, Tokyo, Japan, and aluminum chloride form Kishida Kagaku, Tokyo. Glycolic acid was purchased from Dupont, Wilmington, Delaware. Agar was purchased from Ina Food Industry, Tokyo. Hydroxyethyl cellulose was purchased from Hercules (Rijswijk, Netherlands). Benzyl alcohol, ethyl alcohol, and the other chemicals were of cosmetic grade. Water used in this study was ion-exchanged water. The tresses used in this study were Asian white hair unless otherwise mentioned. HAIR COLORANTS The simple-solution systems of Sample A in Table I were prepared by dissolving dyes, metal ions, and acids into a mixture of benzyl alcohol, ethanol, and water. The prepa­ ration of hair colorant in Samples B and C in Table I was as follows: agar and hydroxy­ ethyl cellulose were dissolved in water at 80 °C. Then acid, acid dyes, and metal ion were added after benzyl alcohol and ethyl alcohol were mixed. After being cooled down to room temperature, a jelly-like cake appeared in the solution. The cake was then ground by a homogenizer (Tokusyu Kika Kogyo, Osaka, Japan). The concentration of acid dye and benzyl alcohol (penetration agent) in the novel acid hair color was the same as that in conventional hair color throughout this study unless otherwise mentioned.