Drug – bio-affecting and body treating compositions – Topical sun or radiation screening – or tanning preparations
Reexamination Certificate
1999-11-15
2001-07-31
Dodson, Shelley A. (Department: 1616)
Drug, bio-affecting and body treating compositions
Topical sun or radiation screening, or tanning preparations
C106S014340, C106S014390, C106S018270, C423S621000, C423S622000, C424S060000, C424S400000, C424S401000
Reexamination Certificate
active
06267949
ABSTRACT:
This invention relates to sunscreen formulations and, more especially to a sunscreen composition including zinc oxide.
In recent years there has been an increasing awareness of the need to use sunscreens for the protection of exposed skin. Solar radiation, in particular that in the ultra-violet region, is considered to be the cause of the painful sunburn, skin discolouration—blotches and freckles and is considered to promote skin aging. In addition, exposure to strong sunlight seems to be a significant contributing factor to skin cancer. It is should be noted that solar ultra-violet radiation contains three types of rays: UV-A, UV-B and UV-C. Whilst the sun's UV-C rays are absorbed by the atmosphere and therefore are not normally a problem, they can be produced in artificial sources, such as arc welding. Zinc oxide provides a high level of UV-ray protection for the skin in the UV-A region. A commercial sunscreen formulation should also provide protection in the UV-B region.
There are many sunscreen formulations known in the pharmaceutical and cosmetic industry. Commercialised formulations are usually in the form of a cream or lotion and contain a number of active components designed to protect the user against various wavelengths of light. In addition these commercial formulations contain further components which provide other desirable aesthetic and technical properties. For example, moisturisers, fragrances and preservatives.
The ability of a sunscreen composition to protect the skin from the harmful effects of the sun is indicated by a sun protection factor (SPF). The higher the SPF the greater the protection afforded by the sunscreen. In Australia, the SPF of a sunscreen product should be evaluated and classified in accordance with the Australian Standard AS/NZS 2604:1993. An SPF rating allows the user to calculate the amount of time he can spend exposed to UV rays without significant deleterious effect. For example an SPF of 4 enables the user to spend 4 times as long in the sun as he normally would before getting sunburnt.
It is well known in the cosmetic industry that various metal oxides have great effect in stopping UV rays from penetrating the skin. In particular, zinc oxide is known for its ability to absorb and scatter UV rays by virtue of Beers Law and its use in sunscreens has been the subject of a number of patent applications. A brief description of the most relevant of these disclosures follows:
AU-B-59365/94 (671189) (Colgate-Palmolive Company) describes a sunscreen composition comprising a water-in-oil emulsion, wherein the oil phase contains nanomised zinc oxide defined in this document as being particles in the range of 10 to 250 nm and polyethylene. The invention is predicated on the discovery of a synergistic interaction between zinc oxide of a particular particle size, polyethylene and normal sunscreening agents such as are described at page 3, lines 6-8.
U.S. Pat. No. 5,032,390 (Kao Corporation) recognises the value of using zinc oxide having a particle size from 70 to 300 nm in sunscreen compositions to scatter or absorb UV rays, particularly those in the UV-A region.
U.S. Pat. No. 5,066,530 (Sumitomo Chemical Company) discloses the use of a lamina comprising a laminar substance as a matrix and zinc oxide (50-500 nm).
U.S. Pat. No. 5,575,988 (Little Point Corporation) describes a combination sunscreen and insect repellent. The sunscreen activity may be provided by using nanomised zinc oxide having a particle size of 300 nm or less.
WO 93/23482 (The Boots Company PLC) describes the preparation of dye coated metal oxides including zinc oxide having a particle size less than 500 nm. These coated metal oxides are used in sunscreen formulations.
In the past it is has been known to use zinc oxide having a larger particle size as a sunscreen agent in “zinc creams”. These creams are white or may be coloured with suitable pigments and dyes and retain their colour after application on the skin. They may contain up to 28-32% by weight of zinc oxide. They are normally used in the manner of a face paint, but are not aesthetically acceptable for use over the entire exposed skin area.
Whilst traditional zinc oxide-based sunscreens were thixotropic and non-transparent when applied to the users skin, modern aesthetics demand better feeling and better looking compositions. It is generally thought that in order to provide an aesthetically acceptable sunscreen which is transparent when applied the zinc oxide used must be nanomised. This problem is discussed in AU-B-68039/90 (631704) (Johnson & Johnson Consumer Products, Inc). As noted in that patent only when the zinc oxide particles have an average particle size about, or less than, 50 nanometers do the particles lose their white appearance. A sunscreen formulation using suitably nanomised zinc oxide will be invisible on the skin after application and thus is aesthetically acceptable. Such formulations may contain approximately 4-6% by weight of nanomised zinc oxide.
However, the use of nanomised zinc oxide has disadvantages associated with its high cost which is, in turn transmitted to the cost of the sunscreen. In addition, finely divided particles of zinc oxide tend to agglomerate and this will decrease their SPF rating and produce an inferior product.
It is the objective of the present invention to provide an improved sunscreen formulation which is less expensive and has as high an SPF as possible. It preferably has a long shelf life and is aesthetically acceptable in order to be commercially viable. The sunscreen formulation is ideally cosmetically acceptable, non-toxic and non-irritating to the skin. It should also be controllable in the sense of its spreadability.
The invention provides a sunscreen formulation including conventional UVB sunscreening agents and zinc oxide having an average particle size in the order of 150 to 800 nm. Preferably the zinc oxide used is pigment grade. Most preferably, zinc oxide prepared by the French process is used, although that produced by the American process is also suitable. The average particle size of the zinc oxide is most preferably in the order of 200-400 nm.
Throughout this specification, the term “pigment grade” is used to define zinc oxide that has been produced by the French or American process. French processed zinc oxide is also known as “fumed” zinc oxide by reason of the process steps by which it is achieved. “Coarse” or “BP” grade is another term for the grade of zinc oxide utilised in the invention. The French and American processes are commonly known but are described, for example, in the article Mitchnick, M. A., “Zinc oxide, An Old Friend to the Rescue”,
Cosmetics
&
Toiletries
, Vol 107, October 1992.
The formulations of the invention preferably include one or more metal hydroxystearates The metal hydroxystearates used in the formulations of the invention are preferably magnesium aluminium hydroxystearate and more preferably Gilugel™ brand magnesium aluminium hydroxystearate. The metal hydroxystearate is preferably present in an amount of 2-20% w/w, more preferably, 5-15% w/w.
Preferably, the composition may include active ingredients providing additional protection from light in the UV-A or UV-C regions.
The present invention is partly predicated on the unexpected discovery that when pigment grade zinc oxide is combined with a magnesium aluminium hydroxystearate, in particular Gilugel™, the resultant sunscreen formulation does not retain the expected whiteness or pigmentation after application onto the skin. This significant and surprising advantage is unexpected as pigment grade zinc oxide usually has an average particle size in the order of 100 to 500 nm, results in a generally opaque film and is very visible on the skin when applied as a cream or lotion. Opacity is the ability to prevent light transmission by either reflection and/or absorption. The surface of the zinc oxide crystal effectively reflects visible light. Therefore, the greater the number of surfaces, the more light is reflected. It follows then, that smaller particles, with higher s
Dodson Shelley A.
Ostrolenk Faber Gerb & Soffen, LLP
Soltec Research Pty Ltd.
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