Ultraviolet-screening composite particulate and process for the

Details Ultraviolet-screening composite particulate and process for the Ultraviolet-screening composite particulate and process for the

1998-08-19

2000-07-18

Dodson, Shelley A.

Drug, bio-affecting and body treating compositions

Topical sun or radiation screening, or tanning preparations

106425, 106436, 106442, 424401, 424489, 424490, A61K 742, A61K 700, A61K 914, C09B 1400, C09C 136

Patent

active

060903732

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to ultraviolet shielding composite fine particles having substantially no catalytic activities, having high transparency in the visible light region, and a high shielding ability in the ultraviolet light region, and a method for producing the same.


BACKGROUND ART

Of the sunlight reaching the earth (including infrared light, visible light, and ultraviolet light), 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 cause quite some damages to a living body.
Therefore, ultraviolet shielding agents are used for protecting skin from inflammation or skin cancer due to the ultraviolet light by formulating them in the cosmetics, or they are mixed with paints to prevent a pigment from fading due to decomposition by ultraviolet light. In these cases, an unnatural skin whitening of the cosmetics and a color change of paints can be prevented by increasing the transparency 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 used as effective ingredients prevents the transmission of the ultraviolet light on account of the specific absorption of ultraviolet light by the organic compounds. For example, an ultraviolet absorbing 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 the absorbed ultraviolet light is at the same time likely to act to decompose, 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 formulated are restricted owing to effects caused on human bodies, and thus it is difficult to achieve a good shielding performance within a controlled range. Furthermore, when they are used in high proportions, stickiness increases, resulting in an unpleasant feeling.
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 bodies.
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 exhibit 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 to be highly dispersed so as to increase the ultraviolet shielding ability (absorbing ability, scattering ability). However, in the case of using such ultrafine particles, problems may arise in the dispersion stability due to the aggregation of the ultrafine particles, and in 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 selected depending upon the properties of the coating layer formed on the surfaces. Also, since t

REFERENCES:
patent: 4927464 (1990-05-01), Cowie
Japan Abstract: Ultraviolet-intercepting composite micro-particle, its production and cosmetic, JPA08012961, Jan. 16, 1996.
Japan Abstract: Spherical or randomly shaped Ti oxide of ave. particle size 30-70 nm is covered with hydrate comprising 1-4 wt. % (Si02 conversion) of silicic acid hydrate and 6-12 wt. % (AL203 conversion) of alumina hydrate, JPA3115211, May 16, 1991.

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