Drug – bio-affecting and body treating compositions – Topical sun or radiation screening – or tanning preparations
Reexamination Certificate
2001-04-23
2002-09-10
Dees, Jose′ G. (Department: 1616)
Drug, bio-affecting and body treating compositions
Topical sun or radiation screening, or tanning preparations
C106S415000, C106S418000, C106S425000, C106S426000, C106S429000, C106S482000, C424S401000
Reexamination Certificate
active
06447759
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an ultraviolet absorbent with high transparency and good dispersibility, as well as good UV-A shieldability favorable for cosmetic materials. The absorbent of the invention comprises a flaky substrate coated with ultra-fine zinc oxide particles.
Energy of ultraviolet rays triggers off and causes skin aging, deterioration of coating films, deterioration and decomposition of plastics and fading of prints.
The quantity of UV rays falling within a wavelength range of from 290 to 400 nm on the ground accounts for about 6% of the overall quantity of sunlight rays, of which those falling within a short wavelength range of from 290 to 320 nm (hereinafter referred to as UV-B) are about 0.5% and those falling within a long wavelength range of from 320 to 400 nm (hereinafter referred to as UV-A) are about 5.5%. Thus, the quantity of UV-A is large. As having a longer wavelength, UV-A more easily passes through cloud and windowpanes to cause more damage to the skin in daily life, than UV-B. It is said that UV-B scatters on the surface of the skin or is absorbed in the skin to cause sunburn and the like minor inflammations of the surface of the skin, while UV-A penetrates into the dermis below the epidermis of the skin to produce radicals inside the skin tissue, and the radicals thus formed cause photo-aging of the skin to produce wrinkles, to make the skin flabby or to lower the elasticity of the skin, while additionally having some negative influences on cell membranes and genes. Accordingly, in order to protect the skin from ultraviolet rays, it is important not only to shield the skin against the entire region of ultraviolet rays but also to shield it against UV-A especially in the field of cosmetics, and an increasing interest in UV-A shielding is being taken (see the Journal of Cosmetic Technology, 31, No. 1, pp. 14.30, 1997).
Ultraviolet absorbents (UV-shielding agents) are grouped into organic compounds and inorganic compounds. As the ultraviolet absorbents of organic compounds, most typically mentioned are benzotriazole compounds. Because of their UV absorbability, organic ultraviolet absorbents are expected to exhibit quick-acting UV-shieldability, but their use is being reduced as they are problematic in their persistence (activity endurance) and safety. Accordingly, in these days, ultraviolet absorbents (UV-shielding agents) of inorganic compounds free from such problems are being widely noticed.
Most ultraviolet absorbents of inorganic compounds are to exhibit two functions, one being the ultraviolet absorbability of the inorganic compounds themselves and the other being the ability to scatter UV rays (this is referred to as Mie scattering or Rayleigh scattering) to be attained by controlling the particle size of the compound particles. As typical examples of such inorganic compounds, proposed were ultraviolet absorbents comprising metal oxides, such as titanium oxide, zinc oxide, cerium oxide and the like, of which the particle size was controlled (see, for example, Japanese Patent Application Laid-Open (JP-A) Sho-49-450, Hei-5-43682, and Japanese Patent Publication (JP-B) Hei-7-23294).
However, the ultraviolet absorbents comprising such metal oxides are problematic, as so mentioned hereinunder, and are not satisfactory. For example, titanium oxide has an effective absorption range around UV-B, and therefore its particle size must be specifically controlled in order to make it have the shieldability to scatter UV-A. It is said that fine-particle metal oxides having a mean particle size of not larger than 0.1 &mgr;m have the most effective scatterability. However, such fine-particle metal oxides easily aggregate, and therefore require dispersing prior to use. For these reasons, the practical use of the oxides is often difficult. On the other hand, zinc oxide has an effective absorption range around UV-A, and is therefore especially favorable for ultraviolet absorbents for cosmetic materials. However, the compound is problematic in that its chemical stability is poor and that its powder often aggregates. Cerium oxide is also has an effective absorption range around UV-A and is favorable to UV-A shielding. However, as being expensive, the use of the compound is limited.
In order to prevent the particle aggregation, proposed was a technique of applying ultra-fine particles of those metal oxides to particulate substrates (bases), which are larger than the ultra-fine particles, to thereby make the ultra-fine particles adhered by the larger particulate substrates.
For example, JP-B Hei-5-87545 discloses titanium oxide-coated particles; JP-B Hei-3-74641, Hei-9-188611 and JP-A Hei-5-246823 disclose zinc flower-coated or zinc carbonate-coated particles; and JP-A Hei-3-243666 discloses Zinc white-coated, transparent flaky particles.
It is said that the metal oxide-coated materials in those known techniques have transparency for visible rays and have UV-A shieldability. However, the particle size of the flaky substrate to be the base for those is not specifically defined, or, even if defined, the particle size is too large so that the transparency of the materials is poor and the specific surface area of the materials is small. Therefore, in those materials, it is difficult to enlarge the amount of the coating metal oxides which are effective for absorbing and scattering ultraviolet rays. Accordingly, the known materials could hardly exhibit their ultraviolet shieldability. Moreover, nothing is written in the published or laid-open specifications, relating to the particle size and the morphology of the metal oxide particles carried by the substrates on their surfaces; or the particle size of the metal oxide particles defined in those specifications is too large. For these reasons, the known UV absorbents could not satisfy the requirements of good transparency in the range of visible rays and good ultraviolet shieldability, especially that capable of absorbing and scattering UV-A. Specifically, even those of the known UV absorbents which are said to have UV-A shieldability and transparency are still problematic in that their transparency is not satisfactory since the particle size of the flaky substrates is too large, and that their UV-absorbing and scattering ability is not also satisfactory since the particle size of the fine-particle metal oxides adhered on the surface of the substrates is not satisfactorily controlled. Of the known UV absorbents, zinc oxide has an absorption zone near UV-A by itself, and ultra-fine particles of the oxide which are controlled to additionally have UV-A scatterability are favorable to powdery UV-A shielding agents. However, as so mentioned hereinabove, the stability and the dispersibility of the ultra-fine particles is not satisfactory, and therefore the use of the particles is limited. Accordingly, the application of the conventional powdery substances to cosmetic materials, coating compositions, plastics and ink compositions is limited with respect to the method of adding them and to their amount to be added, since the transparency and the dispersibility of the substances is not satisfactory, often resulting in that the substances added or incorporated will have some negative influences on the color tone of the resulting products and that the substances are not easy to handle.
Given that situation, we, the present inventors already proposed an ultraviolet-shielding pigment with good spreadability and adherability especially favorable to cosmetic materials. The pigment comprises a flaky powder coated with zinc oxide and barium sulfate, and has UV-A shieldability, and this is so improved that zinc oxide therein is prevented from aggregating (see JP-A Hei-9-192021).
SUMMARY OF THE INVENTION
Having further studied to improve ultraviolet absorbents of inorganic compounds, the inventors have succeeded in finding an ultraviolet absorbent which has UV-A shieldability and improved transparency and which aggregates little.
Specifically, the present invention provides a novel ultraviolet absorbent, a me
Noguchi Tamio
Watanabe Yukitaka
Dees Jose′ G.
Lamm Marina
Merck Patent Gesellschaft
Millen White Zelano & Branigan P.C.
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