Drug – bio-affecting and body treating compositions – Topical sun or radiation screening – or tanning preparations
Patent
1997-08-27
1999-05-11
Dodson, Shelley A.
Drug, bio-affecting and body treating compositions
Topical sun or radiation screening, or tanning preparations
423462, 423592, 424 59, 424 60, 424400, 424401, A61K7/42;7/44;9/00;6/00
Patent
active
059025697
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to ultraviolet shielding composite fine particles having substantially no catalytic activity, having high transparency in the visible light region, and a high shielding ability in the ultraviolet light region. It also relates to a method for producing the composite fine particles, and cosmetics containing such composite fine particles.
BACKGROUND ART
The sunlight reaching the earth includes infrared light, visible light, and ultraviolet light, of which 5 to 6% is ultraviolet light. The ultraviolet light has short wavelengths, which are thus high-energy electromagnetic waves. Therefore, the ultraviolet light is known to decompose many kinds of materials and to damage living organisms.
Therefore, ultraviolet shielding agents are used for protecting skin from inflammation or skin cancer due to exposure of the skin to harmful ultraviolet light. For this purpose, the ultraviolet shielding agents are added to cosmetics. Also, they are used to prevent pigments from fading due to decomposition by ultraviolet light. For this purpose, the ultraviolet shielding agents are mixed with paints; however, this may cause unnatural skin whitening and a color change of paints. This can be prevented by increasing the transparency of such cosmetics or paints in the visible light region. Therefore, the ultraviolet light is desirably blocked while the transparency in the visible light region is maintained.
The ultraviolet shielding agent comprising organic compounds as effective ingredients prevents the transmission of the ultraviolet light on account of the above organic compounds which absorb the ultraviolet light. For example, an ultraviolet absorbent composition comprising substituted N,N'-bis-aromatic formamidines is known (Japanese Patent Examined Publication No. 61-09993). However, the organic ultraviolet shielding agents have the problem that although they can absorb the ultraviolet light, they are at the same time likely to be decomposed by the ultraviolet light, with the result of an undesirable lowering of the shielding ability over time. Regarding their application to cosmetics, the kinds and amounts of the ultraviolet shielding agents are restricted owing to deleterious effects caused on human bodies, and thus it is difficult to achieve a good shielding performance within a controlled range.
On the other hand, the ultraviolet shielding agent comprising an inorganic compound contains inorganic fine particles and prevents the transmission of ultraviolet light by the absorbing ability and the scattering ability of the composition. The inorganic ultraviolet shielding agent is superior to the organic ultraviolet shielding agent because the composition containing the inorganic ultraviolet shielding agent is not decomposed by the ultraviolet light with the passage of time and has little effects on the human body.
However, since the inorganic ultraviolet shielding agents are present in the form of particles, it is more difficult with inorganic ultraviolet shielding agents when compared with organic ultraviolet shielding agents to block the ultraviolet light while maintaining high transparency in the visible light region.
In order to possess an effective light shielding ability in the ultraviolet light region while maintaining high transparency in the visible light region (light wavelengths of from 400 to 800 nm), the composition has to be microgranulated to give ultrafine particles capable of being highly dispersed so as to increase the ultraviolet scattering ability. However, in the case of using ultrafine particles, dispersion stability problems may arise due to the aggregation of the ultrafine particles and the catalytic activities of the ultrafine particles.
In order to improve dispersibility, the ultrafine particle surfaces may be coated with other materials For example, skin cosmetics comprising an oily cosmetic base material and a hydrophobic titanium oxide powder are known (Japanese Patent Examined Publication No. 59-15885). However, a suitable solvent has to be selec
REFERENCES:
patent: 4927464 (1990-05-01), Cowie
patent: 5298065 (1994-03-01), Hiraoka et al.
patent: 5478550 (1995-12-01), Suzuki et al.
Hawley's Condensed Chemical Dictionary, 12th edition, revised by R.J.Lewis, Sr., Van Nostrand Reinhold Company, New York, pp. 668, 783, 784, 1113, 1993.
The Facts on File Dictionary of Chemistry, edited by J. Daintith, FactsOnFile, New York, p. 198, 1988.
Imaizumi Yoshinobu
Kozaki Shunji
Miyake Toshio
Nishimura Toru
Oshima Kentaro
Dodson Shelley A.
Kao Corporation
Lamm Marina
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