Drug – bio-affecting and body treating compositions – Topical sun or radiation screening – or tanning preparations
Patent
1997-07-14
2000-09-26
Cook, Rebecca
Drug, bio-affecting and body treating compositions
Topical sun or radiation screening, or tanning preparations
514937, 514938, A61K 742
Patent
active
061239275
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a cosmetic composition having a UV blocking action in a wide region from UVB to UVA and capable of preventing erythema and melanism due to burning by the sun.
BACKGROUND ART
In the past, sun screens, foundations, etc. have been known as cosmetic compositions for preventing sunburn. In these cosmetic compositions UV absorbents and UV blocking agents are formulated as substances for blocking UV rays. In these, fine particles of titanium dioxide having an average particle size of 0.03 to 0.05 .mu.m have been generally used as UV blocking agents. The applicant of the present invention previously obtained a cosmetic composition having a high UV protective effect by formulating a combination of spherical fine particles of titanium dioxide having an average particle size of 0.01 to 0.10 .mu.m and needle type (spindle shaped) fine particles of titanium dioxide having a short diameter of 0.005 to 0.02 .mu.m and a long diameter of 0.01 to 0.10 .mu.m (Japanese Patent Application No. 5-340571 (i.e., JP-A-7-165532)).
However, these fine particles of titanium dioxide are hard to disperse in the single particle state in a cosmetic composition since the particle size is small. Therefore, in actuality, they exist as considerably large aggregates. Further, when metal oxides having a large relative particle size are formulated in a cosmetic composition, the metal oxides form the nucleus for easy formation of aggregates and the effect for preventing UV rays inherently exhibited remarkably falls. In particular, in a solid foundation, since the components are a powder and oil in a paste composition, the fine particles of powder easily aggregate as nuclei the relatively large particle size powder. The above trend becomes particularly conspicuous. Accordingly, even if fine particles of titanium dioxide are formulated in the cosmetic composition, it is hard to obtain the desired UV protecting effect. Even if the amount of formulation is increased, the effect for protecting the UV rays will not rise, the feeling to the skin will become poorer, the finish will become powdery, and other defects will appear.
Further, fine particles of titanium dioxide have the effect for blocking UVB of the region of 290 nm to 320 nm, but are insufficient in the effect for blocking UVA having a region of 320 nm to 400 nm, and therefore, have had the defect of not being able to prevent skin disorders due to UVA--which have recently been taken up as an issue.
DISCLOSURE OF INVENTION
The present inventors newly designed the fine particles of titanium dioxide so as to overcome the above-mentioned defects in fine particles of titanium dioxide. That is, the present inventors conducted theoretical calculations based on the Mie theory (P. Stamatakis et al., J. Coatings Teck., 62 (10), 95 (1990) on the dependency of the titanium dioxide optical scattering and UV protection effect on the particle size. As a result, it was found that, at a wavelength of 300 nm, a particle size having 0.03 to 0.06 .mu.m gave the highest blocking effect, at 350 nm, a particle size of 0.08 .mu.m was optimal, and at 400 nm, a particle size of 0.12 .mu.m was optimal. Further, as a result of the verification of the effect of the particle shape which was supposed to reduce the aggregation of powder in the cosmetic composition, it was discovered that the dispersion of the particles having the spindle shape rather than a spherical shape was high and the UV blocking effect was high. Therefore, the present inventors designed spindle shaped fine particles of titanium dioxide having a long diameter of an optimal particle size for blocking the UVA, that is, approximately 0.10 .mu.m, and a short diameter of an optimal particle size for blocking the UVB, that is, of 0.03 to 0.06 .mu.m. Further, the present inventors found that fine particles of titanium dioxide synthesized faithfully to the particle design are not that susceptible to the effects of the metal oxides having a relatively large particle size in the cosmetic composition and are
REFERENCES:
patent: 4810490 (1989-03-01), Dixon
patent: 4927464 (1990-05-01), Cowie
patent: 5443759 (1995-08-01), Dahms
patent: 5516457 (1996-05-01), Dahms
patent: 5543135 (1996-08-01), Dahms
Kumagaya Shigenori
Ogawa Katsuki
Takata Sadaki
Cook Rebecca
Shiseido Company Ltd.
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