Sunscreen Emulsions

The invention relates generally to topical radiation screening and tanning preparations, and more specifically to sunscreen emulsions including zinc oxide in the emulsion's continuous phase, and titanium dioxide in the emulsion's discontinuous phase.

It is well known that light radiation having a wavelength of between 280 and 320 nm causes erythema and skin bums, the effects of which increase according to the length of exposure. A suitable protective agent should accordingly absorb light radiation in the zone from about 280 to 320 nm. "Emulsions," as used herein, is a system which includes a liquid (e.g. an oil) dispersed in an immersible liquid (e.g. water). As such, an emulsion has two phases, a continuous phase and a discontinuous phase. In the case of an oil-in-water emulsion, oil is the discontinuous phase, and water is the continuous phase. Hydrophobic constituents of the emulsion tend to concentrate in the oil phase, while hydrophilic constituents tend to concentrate in the water (or aqueous) phase. Water-in-oil emulsions have been described for use as vehicles for sunscreen agents. When water-in-oil emulsions are applied to the skin, the water-phase droplets are believed to be suspended in a film of oil. This film is believed to create a moisturizing and non-hygroscopic barrier, which does not take up water, thus deterring the emulsion from being washed off.

U.S. Pat. No. 4,284,630 to Yu et al. (Aug. 18, 1981) discloses stable water-in-oil emulsions useful as vehicles for cosmetics or for application of medicinal compositions. The emulsions use magnesium oxide or magnesium hydroxide as a stabilizing agent, which permit the incorporation of up to 70% water in the total composition without loss of shelf-life stability. The emulsions create a water non-washable dispersion medium, which possess substantiation and occlusion properties after application to the skin.

U.S. Pat. No. 4,781,914 to Deckner (Nov. 1, 1988) discloses a moisture-resistant skin treatment composition in the form of a sprayable oil-in-water emulsion that inverts to a water-in-oil emulsion upon being robbed onto the skin. The invention uses polyglyceril-8 oleate as an emulsifier to impart moisture resistance to the skin treatment composition.

U.S. Pat. No. 5,256,422 to Albert et al. (Oct. 26, 1993) discloses a water-in-oil emulsion having a discontinuous aqueous phase dispersed within a continuous oil phase. The aqueous droplets forming the discontinuous aqueous phase have intact liposomes dispersed therein, thus forming a type of oil-in-water-in-oil emulsion. The invention allows incorporation of aqueous soluble materials into either the aqueous phase external to the lipid vesicles or into the lipid vesicles themselves. Likewise, any oil soluble materials can be included into the emulsion via the continuous oil phase or the lipid vesicles.

Sunscreen preparations, which extend the time of exposure needed to produce a sunburn, are also commercially available. Such preparations contain ultraviolet absorbing chemicals such as the alkyl esters of aminosalicylic acid disclosed in U.S. Pat. No. 4,036,951 to Halpern et al. (Jul. 19, 1977), the benzoxazole derivatives in U.S. Pat. No. 4,250,315 to Poncioni (Feb. 10, 1981), and the coffee bean oil in U.S. Pat. No. 4,793,990 to Grollier et al. (Dec. 27, 1988).

Physical sunscreens generally include heavy creams or pastes containing such compounds as ZnO and TiO.sub.2. Although physical sunscreens reflect and scatter radiation effectively, such sunscreens create an opaque film and thus lack cosmetic appeal.

The art is not believed to suggest that by carefully choosing various ingredients and incorporating them into specific phases of a selected emulsion that a synergistic combination would result.

Surprisingly, it has been found that by incorporating TiO.sub.2 into the discontinuous phase of an emulsion, and ZnO in the continuous phase of the same emulsion, that a synergistic combination results.

Further, it has been found that a water-in-oil emulsion containing titanium dioxide in the water phase of the emulsion, zinc oxide in the oil phase of the emulsion, together with a compound such as tridecyl neopentanoate (e.g. C.sub.12-5 alkyl benzoate or octyl neopentanoate), and sunblocking agents, results in an especially advantageous emulsion having an exceedingly high sun protection factor (SPF) value. In particular, the invention concerns the use of ZnO, TiO.sub.2, and organic agents for the purpose of enhancing the SPF of a water-in-oil emulsion. The SPF value is the ultraviolet energy required to produce a minimal erythema dose ("MED") on protected skin, divided by the ultraviolet energy required to produce an MED on unprotected skin. An MED is the smallest dose of ultraviolet radiation that produces redness reaching the borders of the exposure site. The emulsion is primarily useful as a sun screening agent and moisturizer for application to the skin.

The emulsion typically contains ZnO and an agent such as tridecyl neopentanoate in the oil phase of the emulsion, TiO.sub.2 in the water phase of the emulsion, and sunblocking agents as basic ingredients. Other ingredients which also may be included are thickeners, emulsifying agents, moisturizers, emollients, preservatives, coloring agents, fragrances, antioxidants and the like.

Surprisingly, the water-in-oil emulsion displays an improved "SPF" value, which is higher than the value seen in analogous emulsions having ZnO and TiO.sub.2 in the opposite phases (i.e. ZnO in the water phase and TiO.sub.2 in the oil phase) in a water-in-oil emulsion having TiO.sub.2 and ZnO in the same phases or in an oil-in-water emulsion having similar ingredients. The emulsion filters light radiation from about 280 to about 320 nm. Additionally, the emulsion creates a transparent (i.e. non-whitening), moisture-resistant medium, which possesses occlusive and moisturizing properties after application to the skin.

The invention also includes processes of making and using such emulsions. The process may be used to manufacture an emulsion for the prevention of a sunburn. An inventive emulsion may be topically applied to a mammal, such as a human, before prolonged exposure to light radiation to prevent the erythema normally observed after such exposure.

FIG. 1 is a graph depicting the SPF values of various emulsions comprising various organic agents, alone or in combination with TiO.sub.2 and ZnO.

The emulsion includes sufficient amounts of the selected ingredients in the appropriate phases to attain a composition having a desired SPF value. In this regard, the emulsion can contain ZnO in an amount up to about 25% and TiO.sub.2 in an amount up to about 25%, by weight, of the total emulsion and tridecyl neopentanoate in combination with one or more organic agents. Preferably greater than, 90% of the ZnO will reside in the continuous phase, and 90% of the TiO.sub.2 will reside in the discontinuous phase. Percent, as used throughout this specification, refers to weight percent, based on the total weight of the emulsion. The emulsion will preferably contain sufficient amounts of sunblocking agents and oil phase emulsion components to form an oil phase that will produce an emulsion having a smooth, continuous appearance when combined with a water phase.

Preferred organic sunblocking agents include benzophenone-3 (oxybenzone), menthyl anthranilate, octocrylene, octyl methoxycinnamate, and mixtures thereof. Other sunblocking agents such as octyl salicylate, PABA and derivatives may be used. When the emulsion contains octyl methoxycinnamate ("OMC"), an amount up to 7.5%, by weight of the total emulsion may be used. When the emulsion includes benzophenone-3, the emulsion may contain benzophenone-3 in an amount from up to about 6% by weight of the total emulsion.

Preferred oil phase emulsion components include cetyl dimethicone copolyol, cyclomethicone, cetyl dimethicone, hydrogenated castor oil, aloe oil, microcrystalline wax and mixtures thereof.

A preferred method for producing the emulsion involves heating a dispersion medium to the point of melting and then admixing zinc oxide with the dispersion medium. Titanium dioxide is incorporated into a water phase solution. The water phase solution may also include hyaluronic acid and sodium chloride and other water soluble ingredient (e.g. sodium PCA and polyphenon-G). The dispersion medium is then cooled to the approximate temperature of the water phase and both phases are mixed. Alternatively, the water phase may be heated to the approximate temperature of the dispersion medium. To the combined water phase and dispersion medium are then added aluminum starch octenylsuccinate, and preservatives such as propylene glycol, diazolidinyl urea, methylparaben, and propylparaben (Germaben II). A fragrance can also be added, if desired. The resulting emulsion is homogenized for about two minutes.

The dispersion medium may contain tridecyl neopentanoate (or C.sub.12-15 alkyl benzoate, octyl neopentanoate, or mixtures thereof), benzophenone-3, menthyl anthranilate, octocrylene, octyl methoxycinnamate, cetyl dimethicone copolyol, cyclomethicone, cetyl dimethicone, hydrogenated castor oil, aloe oil, and microcrystalline wax.

The amount of compound such as tridecyl neopentanoate will be sufficient to boost the SPF value, which will typically vary from 0.5 to 20% by weight of the total emulsion, preferably 4 to 10% by weight.

Preferably, the method will use micronized ZnO in an amount from about 1 to about 5% and micronized and coated (e.g. with glycerol, trimethylolethane or dimethicone) TiO.sub.2 in an amount from about 1 to 5%, by weight, of the total emulsion. The dispersion medium can usually be melted by heating it to a temperature of about 80.degree. C. The titanium dioxide, hyaluronic acid, and sodium chloride can be readily incorporated into aqueous solution. The water is slowly added to the dispersion medium with rapid stirring. Preferably, the water phase and dispersion medium should be mixed when both are below about 40.degree. C.

TiO.sub.2 and ZnO are commercially available under the trade designations "UV-Titan 212", from Presperse Inc., South Plainfield, N.J., and "Z-Cote", from Sun Smart, Inc. of Wainscott, N.Y., respectively.

The following illustrative EXAMPLES represent preferred embodiments of the invention.

A sunscreen formulation in the form of a water-in-oil emulsion was prepared as follows.

Phase A was prepared by melting the listed ingredients together at a temperature of 80.degree. C. Once Phase A melted and mixed, Phase B was added to Phase A with constant stirring. Phase C was then prepared by simple mixing of the ingredients to the deionized water. Once the combined Phase A-B was cooled to below 40.degree. C., Phase C was mixed into the combined Phase A-B. Phase D and Phase E were incorporated into Phase A-B-C by rapid stirring. The resulting mixture was homogenized for two minutes on a Ross mixer.

The SPF value of the formulation (26.4) was determined via an Optometrics SPF-290 Analyzer (available from Optometrics USA, Inc., Ayer, Mass., 01432).

The resulting water-in-oil emulsion is a light tan, viscous liquid, which readily rubbed onto the skin and demonstrated no whitening effect after application. The emulsion was stable.

A sunscreen formulation in the form of a water-in-oil emulsion, having an SPF value of 30.3 was prepared using the methods as described in EXAMPLE I. The ingredients are listed by weight basis in grams. The SPF value was determined in the same manner as in EXAMPLE I.

The emulsion of EXAMPLE H was a white viscous liquid similar to EXAMPLE I, except for the added benefit of a higher SPF value.

A sunscreen formulation in the form of a water-in-oil emulsion, having an SPF value of 24.6 was prepared using the methods similar to those of EXAMPLE I. The SPF value was determined in the same manner as in EXAMPLE I.

The method of EXAMPLE III resulted in a lustrous, white, soft cream. Upon an additional two minute period of homogenization on a Ross mixer, the cream became thinner, readily rubbed onto the skin, and had a creamy but non-greasy feel. The cream does not create a white film when applied to the skin. The SPF value of the cream in this example was lower than the SPF value of EXAMPLE I.

A sunscreen formulation in the form of a water-in-oil emulsion, having an SPF value of 15.1 was prepared using the methods as described in EXAMPLE I. The SPF value was determined in the same manner as in EXAMPLE I.

The emulsion of EXAMPLE IV was substantially indistinguishable from the emulsion described in EXAMPLE III except for having a lower SPF value.

A sunscreen formulation in the form of a water-in-oil emulsion, having an SPF value of 21.1 was prepared using the methods similar to those of EXAMPLE I. The SPF value was determined in the same manner as in EXAMPLE I.

The emulsion of EXAMPLE V was substantially indistinguishable from the emulsion described in EXAMPLE 3 except for having a lower SPF value.

A sunscreen formulation in the form of a water-in-oil emulsion, having an SPF value of 15.1 was prepared in a manner similar to EXAMPLE I. The SPF value was determined in the same manner as in EXAMPLE I.

The emulsion of EXAMPLE VI was substantially indistinguishable from the emulsion described in EXAMPLE III, except for having a lower SPF value.

A sunscreen formulation in the form of a water-in-oil emulsion, having an SPF value of 8.9 was prepared using the identical methods as described in EXAMPLE I. The ingredients are listed by weight basis in grams. The SPF value was determined in the same manner as in EXAMPLE I.

The emulsion of EXAMPLE VII was substantially indistinguishable from the emulsion described in EXAMPLE 3, except for having a much lower SPF value.

A sunscreen formulation in the form of a water-in-oil emulsion, having an SPF value of 33 was prepared using the methods similar to those of EXAMPLE I. The ingredients are listed by weight basis in grams. The SPF value was determined in the same manner as in EXAMPLE I.

The emulsion of EXAMPLE VIII was substantially indistinguishable from the emulsion described in EXAMPLE llI, except for having a higher SPF value.

A sunscreen formulation in the form of a water-in-oil emulsion, having an SPF value of 13.7 was prepared using methods similar to those of EXAMPLE I. The SPF value was determined in the same manner as in EXAMPLE I.

The emulsion of EXAMPLE IX was substantially indistinguishable from the emulsion described in EXAMPLE 1II, except for having a lower SPF value.

In this EXAMPLE, the same methods and ingredients were used as described in EXAMPLE VIII except that the ZnO and TiO.sub.2 were introduced into the reverse phases. 25 grams of TiO.sub.2 replaced the ZnO in Phase B and 25 grams of ZnO replaced the TiO.sub.2 in Phase C. The emulsion of EXAMPLE X was substantially indistinguishable from the emulsion of EXAMPLE VIII except for a decrease in SPF from 33, seen in the emulsion of EXAMPLE VIII, to 21.5.

In this EXAMPLE, the same methods and ingredients were used as described in EXAMPLE VIII except that the ZnO and TiO.sub.2 were both introduced into the same phase. Phase B consisted of 25 grams of TiO.sub.2 and ZnO, respectively. The emulsion of EXAMPLE XI was substantially indistinguishable from the emulsion described in EXAMPLE VIII except for a decrease in SPF from 33, seen in the emulsion of EXAMPLE VIII, to 23.

A sunscreen formulation in the form of a water-in-oil emulsion, having an SPF value of 9.7 was prepared using the methods similar to those of EXAMPLE I. The SPF value was determined in the same manner as in EXAMPLE I.

A sunscreen formulation in the form of a water-in-oil emulsion, having an SPF value of 10 was prepared using methods similar to those as described in EXAMPLE I. The ingredients are listed by weight basis in grams. The SPF value was determined in the same manner as in EXAMPLE I.

Phase A was heated to melt the solid ingredients and then stirred to cool. Phase B was added slowly with rapid stirring followed by C and then D. The product is a lustrous, off-white, soft cream with an easy rob-in and soft dry after feel.

A five panel skin test of the emulsion of EXAMPLE VIII was conducted according to the "Proposed Monograph for UTC Sunscreen Products" issued by the Food & Drug Administration, Aug. 25, 1978, Federal Register, 43 (166): 38206-38269. An SPF value of 30.2 was measured.

An oil-in-water emulsion containing 3% ZnO in the oil phase, 3% TiO.sub.2 in the water phase, and 3% octylmethoxycinnamate and 1% benzophenone-3 was made. It had an SPF value of 17.7.

Phase A was heated to melt the ingredients (80.degree. C.) and B added with stirring. Phase C was stirred magnetically and heated to 75.degree. C. While being constantly stirred, it was added to the A-B mixture. Phase D was added and stirred to cool (.about.40.degree. C.). No Dry Flo was added. The thin white liquid was hand homogenized twice and 1% sepigel 305 added to thicken.

An oil-in-water emulsion containing 3% ZnO in the water phase, 3% TiO.sub.2 in the oil phase, and 3% octyl methoxycinnamate and 1% benzophenone was made. It had an SPF value of 19.2.

Phase A was heated to melt the ingredients (80.degree. C.) and B added with stirring. Phase C was stirred magnetically and heated to 75.degree. C. While being constantly stirred, it was added to the A-B mixture. Phase D was added and stirred to cool (.about.40.degree. C.). No Dry Flo was added. The thin white liquid was hand homogenized twice and 1% Sepigel 305 added to thicken. References herein to specific EXAMPLES or embodiments should not be interpreted as limitations to the invention's scope, which is to be determined by the claims.