Drug – bio-affecting and body treating compositions – Topical sun or radiation screening – or tanning preparations
Reexamination Certificate
1999-07-16
2001-01-09
Dodson, Shelley A. (Department: 1616)
Drug, bio-affecting and body treating compositions
Topical sun or radiation screening, or tanning preparations
C423S622000, C424S060000, C424S400000, C424S401000
Reexamination Certificate
active
06171580
ABSTRACT:
TECHNICAL FIELD
The present invention relates to zinc oxide exhibiting an excellent screening effect, particularly against long-wavelength ultraviolet rays (UV-A), as well as to a composition containing the zinc oxide.
More particularly, the present invention relates to zinc oxide in the form of primary particles having an average particle diameter of 50-100 nm and forming a planar shape, which zinc oxide exerts an excellent screening effect against ultraviolet(UV) rays, particularly against long-wavelength UV rays, and excellent visible-light transmission. The present invention also relates to a UV-screening composition containing the zinc oxide and applicable to, e.g., a composition for external use.
BACKGROUND ART
Recently, adverse effects on the human body of ultraviolet rays included in sunlight have become widely known, and various measures directed toward alleviating or preventing the adverse effects have been considered.
Ultraviolet rays are divided into three categories based on dermatological effects, i.e., long-wavelength ultraviolet rays (UV-A) (320-400 nm), medium-wavelength ultraviolet rays (UV-B) (290-320 nm), and short-wavelength ultraviolet rays (UV-C) (shorter than 290 nm).
Of these, UV-C can cause fatal harm to living things, including human beings. So far, UV-C has been absorbed by the ozone layer of the upper atmosphere before reaching the earth (However, there is concern that recent depletion of the ozone layer may allow UV-C to damage living things on the earth).
UV-A and UV-B reach the earth, and human beings are exposed to them. UV-A and UV-B have a number of effects on the human body.
UV-A and UV-B have many more adverse effects rather than beneficial effects, such as promotion of production of vitamin D in the body.
The development of agents for preventing harm caused by UV-B started earlier and was carried out more actively than that for preventing harm caused by UV-A. However, adverse effects caused by UV-A, such as accelerated aging of the skin, have been noted recently, and a number of measures to effectively screen UV-A have been proposed.
Presently, when an inorganic substance is used to screen ultraviolet rays in sunlight, a metal oxide having an excellent UV-screening effect such as titanium dioxide or zinc oxide is incorporated into a composition for external use, such as a cosmetic composition, to thereby make use of the UV-screening effect of the metal oxide for protection of the human body from UV rays in sunlight. However, when the metal oxide is used to improve a screening effect against UV-A, whose wavelength range includes a wavelength proximate to the wavelengths of visible light, there arises a problem that the application area of the skin appears unnaturally white due to a characteristic of metal oxides scattering visible light. Therefore, the content of the metal oxide incorporated into a composition for external use is limited. As a result, a composition for external use has not yet led to exerting a sufficient screening effect against UV-A.
At present, measures for screening UV-A have not been fully established.
In view of the foregoing, an object of the present invention is to provide a metal oxide which enables effective UV-screening, i.e., which has excellent screening ability against UV rays, particularly UV-A, as well as excellent transmission with respect to visible light. Another object of the present invention is to provide a UV-screening composition that contains the metal oxide and can be applied to external use.
DISCLOSURE OF THE INVENTION
The present inventors have carried out extensive studies, and have found that zinc oxide that can be produced by a particular method and that has a characteristic form has excellent UV-A-screening ability as well as excellent visible-light transmission. The present invention has accomplished based on this finding.
Accordingly, in the present invention, there is provided zinc oxide in the form of primary particles having an average particle diameter of 50-100 mm and forming a planar shape, the zinc oxide having a ratio represented by lnT
360nm
/lnT
400nm
(T
xnm
: transmittance of transmitted light of X nm) of 10 or more.
Particularly, there is provided zinc oxide having the following morphological characteristics:
(1) the zinc oxide is in the form of primary particles having an average particle diameter of 50-100 nm and forming a planar shape, the zinc oxide having a roughness corresponding to the diameter of one such primary particle;
(2) the longest dimension of the above zinc oxide is 0.01-5 &mgr;m; and
(3) the edge portion of the zinc oxide as described in (1) and (2) above has indentures having a depth of 10-200 nm, at intervals of 10-200 nm.
In the present description, the term “the longest dimension” of the zinc oxide is a distance between two points on a plane formed of the zinc oxide primary particles selected such that the distance is maximized.
The zinc oxide according to the present invention (hereinafter referred to as the zinc oxide of the present invention) is produced by crushing the zinc oxide aggregate produced in the following manner.
Specifically, zinc ions (Zn
2+
: supplied by a strong acid salt of zinc such as zinc chloride, zinc sulfate, or zinc nitrate), carbonate ions (CO
3
2−
: supplied by a carbonate salt such as sodium carbonate or potassium carbonate), and hydroxide ions (OH
−
: supplied by a strong base such as sodium hydroxide or potassium hydroxide) are allowed to react in water, preferably at 40° C.-70° C., while the pH of the aqueous reaction solution is maintained at 7-9 and the mole ratio of hydroxide ion to carbonate ion is fixed to be not greater than 4 (preferably approximately 2.5-3.5, although the amount of hydroxide ion may be 0). Basic zinc carbonate formed in the aqueous reaction solution is calcinated (150° C.-450° C.) to thereby generate the zinc oxide aggregate according to the present invention (hereinafter referred to as “the zinc oxide aggregate of the present invention”).
The present invention also provide a UV-screening composition containing the zinc oxide of the present invention that may be applied to a composition for external use such as make-up cosmetics or sunscreen cosmetics, as well as a UV-screening composition containing the zinc oxide aggregate of the present invention.
When the UV-screening composition containing the zinc oxide aggregate is used as a composition for external use, the zinc oxide aggregate contained in the composition is crushed on the skin by friction generated during application of the composition to the skin, to thereby develop, on the skin of the user of the composition, transparency and UV-screening ability induced by the resultant zinc oxide represented by lnT
360nm
/lnT
400nm
(T
xnm
: transmittance of transmitted light of X nm) of 10 or more.
Thus, the present invention is also directed to a method for use of the external-use composition according to the present invention.
REFERENCES:
patent: 5527519 (1996-06-01), Miksits et al.
patent: 5744126 (1998-04-01), Horino et al.
Katsuyama Tomoyuki
Kimura Asa
Dodson Shelley A.
Shiseido Company Ltd.
Townsend & Banta
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