Drug – bio-affecting and body treating compositions – Topical sun or radiation screening – or tanning preparations
Reexamination Certificate
2001-02-26
2002-04-09
Dodson, Shelley A. (Department: 1616)
Drug, bio-affecting and body treating compositions
Topical sun or radiation screening, or tanning preparations
C424S060000, C424S400000, C424S401000, C514S241000
Reexamination Certificate
active
06368578
ABSTRACT:
The present invention relates to cosmetic and dermatological light protection preparations, in particular skin-care cosmetic and dermatological light protection preparations.
The harmful effect of the ultraviolet part of solar radiation on the skin is generally known. The rays have various effects on the skin as an organ depending on their particular wavelength; so-called UV-C radiation with a wavelength below 290 nm is absorbed by the ozone layer in the earth's atmosphere and therefore has no physiological significance. By contrast, rays in the range between 290 nm and 320 nm, the so-called UV-B range, cause erythema, simple sunburn or even more or less severe burns. The narrower range around 308 nm is stated to be a maximum for the erythema activity of sunlight.
Numerous compounds are known for protecting against UV-B radiation, examples thereof being derivatives of 3-benzylidenecamphor, of 4-aminobenzoic acid, of cinnamic acid, of salicylic acid, of benzophenone, of 2-phenylbenzimidazole and of s-triazine.
It has long been incorrectly assumed that the long-wavelength UV-A radiation with a wavelength between 320 nm and 400 nm has only a negligible biological effect. However, it has now been proved by many studies that UV-A radiation is far more hazardous than UV-B radiation in relation to the initiation of photodynamic, specifically phototoxic, reactions and chronic changes in the skin.
Thus, it has been proved, inter alia, that even UV-A radiation under entirely normal everyday conditions is sufficient to damage within a short time the collagen and elastin fibers which are of essential importance for the structure and firmness of the skin. This results in chronic light-induced skin changes—the skin “ages” prematurely. The clinical appearance of skin aged by light includes, for example, creases and wrinkles and an irregular, furrowed relief. In addition, the areas affected by light-induced skin aging may have irregular pigmentation. The formation of brown spots, keratoses and even carcinomas or malignant melanomas is also possible. Skin aged prematurely by everyday exposure to UV is additionally distinguished by a lower activity of the Langerhans cells and a slight chronic inflammation.
About 90% of the ultraviolet radiation which reaches the earth consists of UV-A rays. Whereas UV-B radiation varies greatly depending on a large number of factors (for example season and time of day or latitude), UV-A radiation remains relatively constant from day to day irrespective of seasonal and diurnal or geographic factors. At the same time, most of the UV-A radiation penetrates into living epidermis, while about 70% of UV-B rays are retained by the stratum corneum.
It is therefore of fundamental importance that cosmetic and dermatological light protection preparations provide adequate protection both against UV-B and against UV-A radiation.
In general, the light absorption characteristics of light protection filter substances are very well known and documented, especially since most industrialized countries have positive lists for the use of such substances, which impose very strict standards on the documentation.
The use concentration of known light protection filter substances is, however, frequently limited in particular in combination with other substances present as solids. There are thus certain technical difficulties in formulating to achieve higher sun protection factors and effective UV-A protection.
Various authors have introduced UV filter substances having the structural motif
Both symmetrical substitution and asymmetrical substitution in relation to the C
3
axis of the triazine basic structure are conceivable. In this sense, symmetrically substituted s-triazines have three identical subsituents R
1
, R
2
and R
3
, while asymmetrically substituted s-triazine accordingly have different substituents, thus destroying the C
3
symmetry. For the purpose of the present invention, “asymmetric” always means asymmetric in relation to the C
3
axis of the triazine basic structure, unless anything else is expressly mentioned.
Asymmetrically substituted triazine derivatives display a good light protection effect. Their main disadvantage is, however, that their solubility is low in conventional oil components. Well-known solvents can dissolve only up to a maximum of 15% by weight of these compounds, which usually corresponds to a concentration of about 1 to 1.5% by weight of dissolved (=active) filter substance in the complete cosmetic or dermatological preparation.
One disadvantage of the prior art is accordingly that generally only comparatively low sun protection factors have been achievable with these filter substances because their solubility or dispersibility in the formulations is too low, i.e. they can be satisfactorily incorporated into such formulations only with difficulty or not at all.
Even if it is also possible in principle to achieve a certain UV protection when the solublity is limited, another problem frequently occurs, that is recrystallization. Substances of low solubility in particular recrystallize comparatively rapidly, which may be induced by fluctuations in temperature or other influences. Uncontrolled recrystallization of an essential ingredient of a preparation such as a UV filter has, however, extremely disadvantageous effects on the properties of the given preparation and, not least, on the desired light protection.
It was an object of the present invention to obtain in a simple manner preparations which are distinguished by an increased content of asymmetrically substituted triazine derivatives and a correspondingly high sun protection factor.
It was, however, surprising and not predictable for the skilled worker that the disadvantages of the prior art are remedied by active ingredient combinations effective for light protection and composed of
(a) one or more UV filter substances selected from the group of asymmetrically substituted triazine derivatives and
(b) one or more dialkyl naphthalates having the structural formula
in which R
1
and R
2
are, independently of one another, selected from the group of branched and unbranched alkyl groups having 6 to 24 carbon atoms.
Also according to the invention is, in particular, the use of one or more dialkyl naphthalates having the structural formula
in which R
1
and R
2
are, independently of one another, selected from the group of branched and unbranched alkyl groups having 6 to 24 carbon atoms, as solvent, solution aid, solubilizer or stabilizer for asymmetrically substituted triazine derivatives.
In a particularly advantageous embodiment, the present invention relates to the use of one or more dialkyl naphthalates having the structural formula
in which R
1
and R
2
are, independently of one another, selected from the group of branched and unbranched alkyl groups having 6 to 24 carbon atoms, for achieving or increasing the solubility of asymmetrically substituted triazine derivatives in
(a) either an isolated oil component or
(b) at least one oil phase of a disperse two-phase or multiphase system which may additionally comprise one or more aqueous phases.
It is preferred according to the invention for the disperse two-phase or multiphase systems which, besides one or more oil phases, may additionally comprise one or more aqueous phases to be constituted in the form of cosmetic or dermatological emulsions—for example of the W/O, O/W, W/O/W or O/W/O type. Such emulsions may preferably also be a microemulsion, a Pickering emulsion or a sprayable emulsion. It may, however, also be advantageous for the preparations of the invention to be a solution, a hydrodispersion, an aerosol, a foam or else a stick.
Dialkyl naphthalates advantageous for the purpose of the present invention are those where R
1
and/or R
2
are branched alkyl groups having 6 to 10 carbon atoms. Diethylhexyl naphthalate is very particularly preferred.
Advantageous asymmetrically substituted s-triazine derivatives within the meaning of the present invention are, for example, those described in EP-A-570 838, whose chemical struc
Gers-Barlag Heinrich
Grundt Wiebke
Wendel Volker
Beiersdorf AG
Dodson Shelley A.
Norris & McLaughlin & Marcus
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