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.

NOVEL ACID-TYPE HAIR COLOR TECHNOLOGY Benzyl alcohol Ethyl alcohol Metal ion* A1Cl3 ·6H2O Acid** Glycolic acid Acid orange 7 Acid red 52 Hydroxyethyl cellulose Ager HCl Table I Formulation of Experimental Samples (w/w %) Sample A 8 20 (0.02 mol/1)*** (4 mmol/1)*** Sample B 8 20 (0.21 mol/1)*** 0.44 0.15 0.7 1.8 31 Sample Ct 8 20 0.5 1.6 0.44 0.15 0.7 1.8 Sodium lactate Ion-exchanged water pH adjusted to 3.0 Up to 100 pH adjusted to 2.3 pH adjusted to 3.5 Up to 100 Up to 100 "j" This formula is "permanent" acid-type hair color. *Metal ion: ZrC14, A1Cl3 ·6H2O, ZnC1 2 , FeC1·4H2O, CaC12·2H2O, MgCl2·6H2O, CuSO4·5H 2 O, FeSO4·7H2O, BaCl2 ·2H2O, MnCl2 ·4H2O, NaCl, or KCl. ** Acid: formic acid, glycolic acid, lactic acid, acetic acid, tertronic acid, or glycine hydrochloride. *** Final concentration. COLOR BRIGHTNESS AND COLOR LONGEVITY TEST Tresses (2 g) were treated with hair colorant (10 g) obtained as described above at 30 °C for 10 or 30 min. After the tresses were washed and dried, the colors were measured by a color analyzer (Color-Eye 7000, Sakata Inx, Tokyo). Color brightness was expressed as the degree of color changing (�E) before and after the treatment. This �E values are written as �Ed y ed hair• The Hunter Lab system was applied for calculating the �E values (12). The �E values, which express the strength of the color, are expressed by the following formulas: �E d yed = V (Ldyed - Lo) 2 + (a d y ed - ao) 2 + (bdyed - bo) 2 �£washed = V (Lwashed - Lo) 2 + (awash e d - ao) 2 + (bwash e d - bo) 2 (L d y ed : L value after dyeing. ad y e d : a value after dyeing. bd ye d : b value after dyeing. Lwashed: L value after washing. awash e d : a value after washing. bwashed: b value after washing. L0: L value of tress. a0: a value of tress. b0: b value of tress.) The tresses were then soaked in 2% SDS (100 ml), and shaken by a sample shaker (Uni Thermo Shaker NTS-3000, Eyela, Tokyo) at 30°C at 120 rpm for 10 min. The tresses were soaked by water and dried by a hairdryer. After this process was repeated six times, the colors of the tresses were measured again. This �E value is written as �Ewashed hair• SELECTION OF ACIDS The acids were investigated to obtain the best color-enhancing effect and color longevity. A concentration of 0.21 mol/1 acid (formic acid, glycolic acid, lactic acid, acetic acid, tertronic acid, or glycine hydrochloride) was added to the hair colorant of Sample B in Table I. The tresses (2 g) were treated with hair colorant (10 g), as described above, at