MXPA99010640A - Sunscreen composition - Google Patents

Abstract

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. A further embodiment of the invention is a method of reducing or preventing the harmful effects of solar radiation on skin by applying the inventive sunscreen formulation. A further embodiment of the invention relates to a sunscreen composition having a sun protection factor greater than 30 including zinc oxide having an average particle size of 150 to 800 nm. A still further embodiment of the invention relates to a sunscreen composition which is susbstantially transparent upon application to the skin including zinc oxide having an average particle size of 150 to 800 nm.

Description

COMPOSITION OF SOLAR FILTER DESCRIPTION OF THE INVENTION This invention relates to sunscreen formions and, more especially to a sunscreen composition that includes zinc oxide. In recent years there has been an increased perseverance of the need to use sunscreens for the protection of exposed skin. Solar radiation, particly that of the ultraviolet region, is considered to be the cause of painful sunburn, discoloration of the skin-stains and cloth and is considered to promote skin aging. In addition, exposure to strong sunlight seems to be a significant contributor to skin cancer. It should be noted that solar ultraviolet radiation contains three types of rays: UV-A, UV-B and UV-C. While UV-C rays from the sun 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 protection to REF rays: 32085 UV for the skin in the UV-A region. A commercial sunscreen formion should also provide protection in the UV-B region. There are many sunscreen formions known in the pharmaceutical and cosmetic industry. The commercialized formions 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 formions contain additional components that provide other aesthetic properties and desirable techniques. For example, moisturizers, fragrances and preservatives. "The ability of a sunscreen composition to protect the skin from the damaging effects of the sun is indicated by a sun protection factor (SPF) The higher the SPF the greater the protection produced by the sunscreen. In Australia, the SPF of a sunscreen product should be evaluated and classified according to Australian Standard AS / NZS 2604: 1993. An SPF rating allows the user to calce the amount of time he can be exposed to UV rays without significant harmful effects. For example, an SPF of 4 allows the user to spend a lot of time in the sun 4 times normally before a sunburn occurs again. It is well known in the cosmetic industry that various metal oxides have a great effect in detecting UV rays penetrating the skin. In partic, zinc oxide is known for its ability to absorb and distinguish 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 these more relevant descriptions follows: AU-B-59365/94 (671189) (Colgate-Palmolive Company) describes a sunscreen composition comprising a water-in-oil emulsion, wherein the oil phase contains oxide of nano-sized zinc defined in this document as being particles in the range of 10 to 250 nm and polyethylene. The invention is described in the discovery of a synergistic interaction between the zinc oxide of a partic particle size, polyethylene and normal sunscreen agents such as those described on page 3, lines 6-8. US 5,032,390 (Kao Corportaion) recognizes the value of using zinc oxide having a particle size of 70 to 300 nm in sunscreen compositions to diffuse or absorb UV rays, particly those in the UV-A region. US 5,066,530 (Sumitomo Chemical Company) discloses the use of a sheet comprising a lamellar substance such as a matrix and a zinc oxide (50-500 nm). US 5,575,988 (Little Point Corporation) describes a combination of sunscreen and insect repellents. The sunscreen activity can be provided by using nanomated zinc oxide having a particle size of 300 nm or less. WO 93/23482 (The Boots Company PLC) describes the preparation of ink-coated metal oxides which include zinc oxide having a particle size of less than 500 nm. These coated metal oxides are used in sunscreen formulations. In the past it has been known to use zinc oxide having a larger particle size as a sunscreen agent in "zinc creams". These creams are white or can be colored with suitable pigments and dyes and retain their color after application on the skin. These may contain up to 28-32% by weight of zinc oxide. They are normally used in the form of a face paint, but they are not aesthetically acceptable for use on the total exposed skin area. While traditional zinc oxide-based sunscreens are thixotropic and non-transparent when applied to the skin of users, modern aesthetics demand compositions of better sensation and sight. It was generally thought that in order to provide an aesthetically acceptable sunscreen that is transparent When applied, the zinc oxide used must be nanomized. This problem is discussed in AU-B-68039/90 (631704) (Johnson &Johnson Consumer Products, Ine). As stated in that patent only when "the zinc oxide particles have an average particle size around, or less than, 50 nanometers the particles lose their white appearance. A sunscreen formulation that uses suitably nanomated zinc oxide should be invisible on the skin after application and thus is aesthetically acceptable. Such formulations may contain about 4-6% by weight of nanomized zinc oxide. However, the use of nanomated zinc oxide has disadvantages associated with its high cost which, in turn, is passed on to the cost of the sunscreen. In addition, the finely divided particles of zinc oxide tend to agglomerate and thus lower their SPF classification and produce a lower product. It is the object of the present invention to provide an improved sunscreen formulation that is less expensive and has an SPF as high as possible. This preferably has a large half-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 must be controllable in the sense of its dispersibility. The invention provides a sunscreen formulation that includes conventional UVB sunscreen 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. More preferably, the 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 more preferably in the order of 200-400 nm.

In all this specification, the term "pigment grade" is used to define the zinc oxide that has been produced by the French or American process. The processed zinc oxide is also known as "smoked" zinc oxide because of the process steps by which it is achieved. The "coarse" or "BP" grade is another term for the grade of zinc oxide used in the invention. The French and American processes are commonly known but are described, for example, in the article Mi tchni ck, M. A., "Zinc oxy, An Oí d Fri end to the Rescue", Cosmeti cs & Toil etri es, Vol 1 07 - October 1992. ~ Preferred formulations of the invention include one or more metal hydroxystearates. The metal tearate hydroxies used in the formulations of the invention are preferably magnesium-aluminum hydroxystearate and more preferably magnesium-aluminum hydroxystearate of the Gilugel ™ brand. 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 that provide additional protection from light in the UV-A or UV-C regions. The present invention is partially established on the unexpected discovery that when the pigment grade zinc oxide is combined with a magnesium-aluminum hydroxystearate, in particular Gilugel ™, the resulting sunscreen formulation does not retain the expected whiteness or pigmentation after application on the skin. This significant and surprising advantage is unexpected since the 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. The opacity of the ability to prevent the transmission of light either by reflection and / or absorption. The surface of the zinc oxide crystal effectively reflects the visible light. Therefore, the greater the number of surfaces, the greater the light reflected. Later, those smaller particles, with greater surface area per mass will reflect more light. This appears, however, when the particle size is plotted against the transmission, so as not to be completely correct. In particular, according to Figure 1, a graph taken from Mitchnick, M.A., "Zinc oxide, An Old Friend to the Rescue", Cosmetics &; Toiletries, Vol 107, October 1992., opacity to visible light reaches a maximum in particle size of approximately 250 nm. Particles smaller than this size actually transmit more light. It is postulated that this is because the smaller particles of 250 nm, besides reflecting light, also scatter it in all directions. Some of this scattered light is transmitted. The sunscreen formulation according to the invention is aesthetically acceptable despite including zinc oxide having a preferred average particle size in the order of 200 'to 400 nm shown in Figure 1 to transmit less light, it is say be more opaque. This surprising result is further contrasted against the existing industrial understanding illustrated in Figure 2 (from Spruce, SR, "Broad Spectrum protection with" Spectraveil "Zinc oxide and Titanium Dioxide Products-Formulation Efficacy of Zinc oxide", for Tioxide Specialties Ltd at the In-Cosmetics Meeting, Barcelona, 1994) that shows that "Fine Particle" or nanomized zinc oxide has a superior capacity to extinguish light at various wavelengths, than from pigment grade zinc oxide.

Second, the invention is partially established on the discovery that there appears to be a synergistic increase in the SPF classification provided by a sunscreen formulation containing zinc oxide, a conventional UVB sunscreen agent and metal hydroxystearate. It could have been expected normally that the SPF classification of the total sunscreen formulation containing zinc oxide, a UVB agent and magnesium-aluminum hydroxystearate could be the sum of the effect of agents having the sunscreen capacity present in the formulation and in particular the combination of Gilugel ™ and zinc oxide and the UVB agent. However, from the initial tests, the SPF of the total sunscreen formulation is significantly higher than that of the sum dp of the agents that have solar filter capacity. From a physical perspective, it is speculated that the magnesium-aluminum hydroxystearate in its capacity as an oil phase thickener, also acts to keep the sunscreen formulation in a layer of sufficient thickness that allows the Law of Beer-Lambert can be exploited for the benefit of the user, particularly by the absorption of UVB light by the UVB filter agent present in the composition. The Beer-Lambert Law states that the intensity of radiation falls off exponentially with the thickness of the sample, and depends on the concentration of the absorbing species, in this case the UVB filter agent, and its ability to absorb light in the frequency that is used, in this case, UV light. In particular it is thought that if the length of the path of the UV light through the formulation can be maximized, the radiation reaching the surface of the skin is minimized. It is thought that pigment grade zinc oxide performs the function of path light extension. A schematic illustration of this principle, also applicable to titanium dioxide which is commonly used as a sunscreen together with or instead of zinc oxide, is provided by Figure 3. A further embodiment of the invention is a method for reducing or avoiding the damaging effects of solar radiation on the skin by applying the inventive sunscreen formulation. This is a method to reduce or prevent the damaging effects of solar radiation on the skin by applying a sunscreen formulation that includes zinc oxide having an average particle size in the order of 150 to 800 nm. Preferably the zinc oxide used in pigment grade as defined hereinabove. Preferably the sunscreen formulation will include one or more metal hydroxystearates, more preferably magnesium-aluminum hydroxystearate and more preferably magnesium-aluminum hydroxystearate of the Gilugel ™ brand. More preferably, the average particle size of the zinc oxide particles is 200-400 nm. A further embodiment of the invention relates to a sunscreen composition having a sun protection factor greater than 30 which includes zinc oxide having an average particle size of 150 to 800 nm. Preferably the zinc oxide used is pigment grade as defined hereinabove. Preferably the sunscreen formulation will include one or more metal hydroxystearates, more preferably magnesium-aluminum hydroxystearate and more preferably magnesium-aluminum hydroxystearate of the Gilugel ™ brand. More preferably, the average particle size of the zinc oxide particles is 200-400 nm. A still further embodiment of the invention relates to a sunscreen composition that is substantially transparent with skin application that includes zinc oxide having an average particle size of 150 to 800 nm. Preferably the zinc oxide used is pigment grade as defined hereinabove. Preferably the sunscreen formulation will include one or more metal hydroxystearates, more preferably magnesium-aluminum hydroxystearate and more preferably magnesium-aluminum hydroxystearate of the Gilugel ™ brand. More preferably, the average particle size of the zinc oxide particles is 200-400 nm. The amount of zinc oxide present in the formulation affects the SPF of the formulation. While the nanomized zinc oxide used in the prior art formulations is expensive, the pigment grade zinc oxide is not, and thus an upper limit is determined for aesthetic reasons only. A minimum amount of pigment grade zinc oxide is required since without it, or in the case where it is not properly dispersed throughout the formulation, it is found that insufficient diffraction of light occurs so that acceptable grades of absorption of harmful radiation that reaches the surface of the skin. It is preferable that the amount of zinc oxide present is in the range of about 0.05-25% w / w by weight. More preferably zinc oxide is present in the range of 0.5-15% w / w by weight. It has also been found that the sunscreen formulations according to the invention are sufficiently waterproof without the addition of a waterproof polymer as required, for example, in the formulations of AU-B-59365. / 94 (671189) in the name of the Colgate Palmolive Company discussed earlier herein. The sunscreen formulation can be constituted in any form. However, it is preferred that the sunscreen formulation is in the form of an emulsion, more particularly a water-in-oil emulsion. Emulsions are a useful and effective carrier for zinc oxide. The zinc oxide may be suspended in the oil phase of the emulsion. The sunscreen formulation is preferably sold in any cosmetically acceptable form, such as a lotion, cream, gel or oil. It is preferred to use an emulsion when a sunscreen formulation is produced in the form of a cream, gel or lotion for the purposes of sensation and dispersibility. Some examples of ingredients that are active in the UVB region include titanium oxide, oxybenzene, octyl salicylate, octyl methoxycinnamate, octyl dimethyl p-aminobenzoic acid, octocrylene (2-ethylhexyl-2-cyano-3, 3-diphenylacrylate) , methyl benzylidene camphor, 2-phenyl-benzimidazole-5-sulfuric acid, benzophenone-2, benzophenone-6, benzophenone-12, benzophenone-3, benzophenone-4, benzophenone-8, DEA methoxycinnamate, ethyl dihydroxypropyl PABA, PABA of glyceryl, homosalate, menthyl anthranilate, octocrylene, PABA, phenylbenzimidazole sulfonic acid, TEA salicylate, isopropyl dibenzoyl methane, butyl methoxy-dibenzoylmethane, ethacrylene, PABA PEG-25, octyl triazone, wax wax beline, yellow beeswax filtered and orange wax. Preferred UVB absorbers according to the invention are octyl methoxycinnamate and methylbenzylidene camphor. These UVB protective components can be present in an amount of 0-15% w / w, preferably 2.0-8.0% w / w. In addition to the known agents that have a synergistic effect they can also be included in the sunscreen formulation. For example, the use of polyethylene in the sunscreen formulations containing zinc oxide and a number of the above sunscreen agents have been shown to synergistically improve the SPF classification of the total formulation. Other known ingredients commonly used in sunscreens may be added to the sunscreen formulation of the invention. Examples of such ingredients include emollients, dispersants, emulsifiers, stabilizers, humectants, antioxidants, preservatives and agents which provide water resistance, improve the "feel" for the skin and aid in the formation of the film, perfumes and dyes. they are isopropyl myristate, isopropyl palmitate, liquid paraffin, alkyl benzoate of 12 to 15 carbon atoms, fatty acid esters, triglycerides. Examples of dispersants include lecithin and solulate PB20. Any suitable emulsifiers can be used. Exemplary emulsifiers are ethoxylated fatty alcohols, acids and their esters, sorbitan esters, ethoxylated glycerides, glyceryl monostearate, polysorbates, cetyldimethicone copolyols and cyclomethicone / -dimethicone polyols. Preferred emulsifiers according to the invention are Arlacel 989MR and Abil WE 09MR which may be present in an amount of 1.0-10% w / w, preferably 2.0-8.0% w / w. Preferred stabilizers include magnesium sulfate, sodium chloride and sodium citrate. The preferred humectants are glycerin, 1, 3-butylene glycol, propylene glycol, D-panthenol, stearic acid, stearyl alcohol, oleic acid, octyl dodecanol, lanolin and alcohols and lanolin oils and dimethicone silicone. Several antioxidants can be included in the formulation. Examples are butylated hydroxytoluene and tocopherol. It is also desirable to include one or more preservatives in the formulation. Examples of suitable preservatives include bronopol, imidazolidinyl urea, diazolidinyl urea, sodium dehydroacetate, phenoxyethanol and parabens. A number of other agents useful in the formulation may be included. For example agents for water resistance such as PVP hexadecene copolymer and silicone oil, skin improving agents such as cyclomethicone and film-forming agents such as polyethylene and alkylated polyvinylpyrrolidone.

EXAMPLES OF THE INVENTION The invention is further illustrated by, but not limited to, the following examples.

Example 1 A test formulation was prepared by combining pigment grade zinc oxide (10% by weight) with octyl methoxycinnamate (7.5% by weight). The formulation was found to have an SPF before swimming (measured according to the standard referred to above herein) of 41.

Examples 2 - 7 The test formulations were prepared according to the following table, and the SPF is measured before swimming (measured as described hereinabove). The results are also tabulated.

It will be appreciated that example 2 in which the pigment grade zinc oxide is not present has a relatively low SPF of 16.0. Example 6 does not incorporate metal hydroxystearate, but zinc oxide at 5% w / w has an SPF of 14.1 while example 5 includes both zinc oxide at 5% w / w and Gilugel ™ at 11% p / p has an SPF of 34.2. All formulations are transparent when applied to the user's skin. The commercial form of the formulation according to the invention (example 4) contains 7.5% of octyl methoxycinnamate and 5.0% of pigment grade zinc oxide produces an SPF before swimming of more than 41.3, an SPF after swimming (after 2 hours of immersion in water) of more than 38.9, and an SPF after swimming (after 4 hours of immersion in water) of 31.

Examples 8 - 12 The examples are tabulated below in which the formulations are identical regardless of the percentage w / w of the zinc oxide present in the formulations. In each formulation a UVB agent has been used as it has a metal hydroxystearate. SPF has been generated when tested on human subjects.

Example Number% w / w of Zinc Oxide Grade Pigment Classification of SPF 8 0.5 25. 0 9 1.0 28. 2 10 2.0 25. 0 11 4.0 41. 5 12 3.0 + 2.0% zinc oxide 25. 0 nanamide coated with silicone The composition of the solar filter with 5% zinc oxide pi-grade according to the invention produces an SPF of 41 or more, as does the sunscreen having pigment-grade zinc oxide at 4% of Example 11 in the table previously described. It is evident that the addition of the silicon coated nanomized zinc oxide in example 12 can in fact be subtracted from the SPF of the formulation rather than being added thereto. It is also evident that nanomized zinc oxide does not serve to diffract UV light as apparently made by pigment grade zinc oxide. A very small amount of pigment grade zinc oxide (0.5%) is shown to substantially strengthen the SPF of the formulation.

Examples 13-15 As an alternative to the octyl methoxycinnamate used in Examples 4-7, tests are also performed using Methyl Benzylidene Camphor (MBC) as the UVB absorbent sunscreen component. The SPF classifications are determined by application of the formulations to humans, which are identical but for the indicated variations and include magnesium-aluminum hydroxystearate.

Number of% w / w% of MBC Classification of SPF Example zinc oxide Before Swimming After Swimming 2 h 13 10.00 4 > 39.4 37.7 14 0 4 16.0 15 5.0 4 28.0 It is thus shown that the presence of the pigment grade zinc oxide in the formulations together with a UV absorbing compound and magnesium-aluminum hydroxystearate produces the SPF which is substantially greater than that which belongs to the formulations in which there is no oxide zinc grade pigment present.

Examples 16 - 19 These examples demonstrate the apparent synergy that occurs between the metal hydroxystearate, the pigment grade zinc oxide and the UVB absorbing agent in the compositions according to the invention. Example 16 is absent from the UVB absorbing agent. It is postulated that in this case, the composition is able to diffract the UV light but does not allow it to be absorbed due to the absence of the UVB absorbent component. Example 17 demonstrates the absence of the metal hydroxystearate. In this case, it is thought that the physical structure of the formulation collapses, and little or no absorption can occur. Example 18 demonstrates the absence of pigment grade zinc oxide. In this case, none of the formulation acts to diffract light through the formulation. It can be seen in Example 19 that the total formulation gives an SPF much greater than the additive effects of the three components.

Ingredient Ejepplo 16 Ejepplo 17 Ejenplo 18 Ejepplo 19% p / p% p / p% p / p% p / p Abil WE 99 5.0 5.0 5.0 5.0 Finsolv TN 6.5 6.5 6.5 6.5 Octyl methoxycinnamate 0 0.00 7.5 7.5 7.5 Isopropyl Palmitate 2 255..00 19.7 22.5 17.5 Paraben esters 0.3 0.3 0.3 0.3 Gilugel OS 11.0 0.0 11.0 11.0 Octyl stearate 0.0 8.8 0.0 0.0 Propylene glycol 2.0 2.0 2.0 2.0 Phenoxyethanol 0.6 0.6 0.6 0.6 Methyl paraben 0.1 0.1 0.1 0.1 Water 44.1 44.1 44.1 44.1 Zinc oxide 5.0 5.0 0.0 5.0 Sodium Chloride 0.4 0.4 0.4 0.4 Total 100 100 100 100 SPF before swimming 3.4 12.8 16.0 > 41.3 It will be appreciated by an expert to handle a variety of other ingredients that can be included in the formulations and the invention includes such formulations. In addition, a variety of the above ingredients can be replaced by commonly accepted substitute ingredients. The invention also includes formulations wherein substitute ingredients have been used. Finally, as set forth above, the examples illustrate but do not limit the present invention. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (19)

RE IVINDICATIONS
1. Having described the invention as above, the content of the following claims is claimed as property: 1. A sunscreen formulation, characterized in that it includes at least one UVB sunscreen agent and zinc oxide having an average particle size of 150 to 800 nm.
2. 2. A sunscreen formulation according to claim 1, characterized in that the zinc oxide is pigment grade zinc oxide.
3. 3. A sunscreen composition according to claim 1 or 2, characterized in that it also includes at least one metal hydroxystearate in a synergistically effective amount.
4. 4. A sunscreen composition according to claim 3, characterized in that the metal hydroxystearate is magnesium-aluminum hydroxystearate.
5. 5. A sunscreen composition according to claim 3 or 4, characterized in that the metal hydroxystearate is present in an amount of 2-20% w / w.
6. 6. A sunscreen composition according to any of claims 1-5, characterized in that the UVB sunscreen agent is selected from the group consisting of octyl methoxycinnamate and methylbenzylidene camphor.
7. 7. A sunscreen composition according to any of claims 1 to 6, characterized in that the zinc oxide is present in an amount of 0.05-25% w / w.
8. 8. A sunscreen composition according to any of claims 1 to 7, characterized in that the zinc oxide is present in an amount of 0.5-15% w / w.
9. 9. A sunscreen composition according to any of claims 3 to 8, characterized in that it includes pigment grade zinc oxide, octyl methoxycinnamate and magnesium-aluminum hydroxystearate.
10. 10. A sunscreen composition according to any of claims 1 to 9, characterized in that the average particle size of the zinc oxide is 200-400 nm.
11. 11. A sunscreen composition, characterized in that it has a sun protection factor greater than 30 which includes zinc oxide having an average particle size of 150 to 800 nm.
12. 12. A sunscreen composition according to claim 11, characterized in that the zinc oxide is pigment grade.
13. 13. A sunscreen composition according to claim 11 or 12, characterized in that it also includes at least one metal hydroxystearate in a synergistically effective amount.
14. 14. A sunscreen composition, characterized in that it is substantially transparent with the application to the skin including zinc oxide having an average particle size of 150 to 800 nm.
15. 15. A sunscreen composition according to claim 14, characterized in that the zinc oxide is pigment grade.
16. 16. A sunscreen composition according to claim 14 or 15, characterized in that it also includes at least one metal hydroxystearate in a synergistically effective amount.
17. 17. A method to reduce or avoid the damaging effects of solar radiation on the skin by applying to the skin requiring such treatment a sunscreen formulation, characterized in that it includes zinc oxide having an average particle size in the order of 150 to 800 nm.
18. 18. A method according to claim 17, characterized in that the zinc oxide is pigment grade.
19. 19. A method according to claim 17 or 18, characterized in that the sunscreen composition further includes a metal hydroxystearate in a synergistically effective amount.