化粧膜中に強力な光遮蔽層を内在した高隠蔽性化粧料の開発

Abstract

Commercial makeups for covering spots, freckles and birthmarks generally contain large amounts of high-refractive index materials such as titanium dioxide. Since covering power is proportional to the amount of titanium dioxide in the film, a thick makeup films is needed to cover serious imperfections. A thick makeup film looks artificial, unattractive and is easily rubbed off. Sometimes, even a thick makeup cannot adequately hide deep-colored birthmarks such as nevus of Ota which are not rare amoung Asian women.In searching for new materials for a better makeup for women with deep-colored facial marks, we discovered that certain metal powders could be effectively used to replace titanium dioxide for enhanced covering. One metal powder found to be very effective for this purpose consists of aluminum platelets 5 to 30 microns in size with an aspect ratio greater than 10. However, the metal platelets must be properly oriented on the skin surface to achieve maximum optical-shielding.To obtain proper platelet orientation and adehesion onto the skin, we further discovered that a copolymer of isobutyl acrylate, ethyl acrylate and acrylic acid having a molecular weight in the 10, 000-1, 000, 000 range could be used as a base coat. The polymer, having an adehesive strength of 500-2000g/25mm, was found to be ideal as it also offers flexibility, wear-resistant, water/oil-resistant properties.By applying the acrylic base film to the subject's skin and sandwitching a layer of orderly arranged metal platelets between the base and a pigment surface, a novel makeup with superior covering power was obtained. Since this tri-layered makeup film is thiner and more flexible than films formed by conventional makeups, it does not flake or rub off easily. It looks natural and effectively covers deep-colored nevus.Experimental results indicated that our tri-layered makeup, applied on a group of female subjects, lasted more than 12 hours. When applied on subjects with dark nevus, our new makeup showed ΔE, a color differential between the nevus area and the surrounding area, of less than 1.5. It was not possible to reduce ΔE to less than 2.8 when conventional makeups were used. The low ΔE value for our makeup demonstrated the superior covering effect of the film.There is no question that the new principle of multiple-layered films resulting from this research will find many applications in designing natural-looking makeups requiring super-covering and high-wear-resistant properties.