Title:  Delivery system for inorganic sunscreens

United States Patent:  6,261,713

Assignee:  Finetex, Inc. (Elmwood, NJ)

Filed:  March 24, 2000

A novel delivery system for physical, inorganic sunscreens for use in sunscreen preparations is disclosed. One or more inorganic sunscreen agents, such as micronized zinc oxide and micronized titanium dioxide, is dispersed in a solid dispersion vehicle preferably selected from the group consisting of stearyl benzoate, behenyl benzoate and arachidyl benzoate, to thereby produce a solid dispersion of inorganic sunscreen agents for use in sun-screen preparations. The micronized sunscreens are embedded in a solid product which does not require mixing or regrinding before use. A solid formulation avoids the problems inherent in a fluid emulsion or dispersion, i.e., migration or settling out of the contents, which requires mixing and/or regrinding before use.

DETAILED DESCRIPTION OF THE INVENTION

This is accomplished by providing a novel delivery systems for physical, inorganic sunscreens. The micronized zinc oxide or titanium dioxide is mixed into a pre-melted, solid dispersion vehicle. The melting is done above the melting point of the respective vehicle. The mixture is subjected to mixing by means of a mixer for intimate blending. The mixture is then discharged and cooled on flaking equipment or on any cooled surface, especially cooled, flat, stainless steel belts. The product so cooled is a solid material, preferably in the form of flakes.

Titanium dioxide is an inorganic pigment widely used in paints, and in cosmetic products such as bar soaps, to enhance whiteness. The particle size of commonly used titanium dioxide is generally between 150 and 350 mu. Titanium dioxide also absorbs and scatters UV-radiation.

Zinc oxide is an inorganic substance which finds use as a white pigment in paints, papers and polymers, and as a physical sunblock by scattering and absorbing ultraviolet radiation.

Naturally, the grade of titanium dioxide and zinc oxide used as sunscreen agents in cosmetic preparations is different than that the grade used as a pigment in manufacturing paint, paper or plastics. The particles of inorganic sunscreen to be used in the present invention are fine, micronized particle size. If the particles are too large, over a micron, they are not effective as sunscreens. The particles may optionally be surface-treated with organic or inorganic coatings, such as aluminum stearate, or one or more oxides or hydrous oxides of aluminum, silicone, titanium, magnesium or zinc, etc., to prevent graying in sunlight.

Thus, inorganic sunscreens such as titanium dioxide or zinc oxide having a particle size less than 1 micron is used in the invention. Preferably, inorganic sunscreens having a particle size between 0.1 and 0.50 micron, and most preferably from about 10 nm to about 100 nm, are used.

Inorganic sunscreen agents such as titanium dioxide and zinc oxide have a tendency to agglomerate that reduces their efficacy, results in an unpleasant feel and gives a white appearance on the skin.

In general, the preferred method of producing the delivery system of the invention begins by melting the solid vehicle, and combining between about 10% and 60% of inorganic sunscreen agent and between about 40% and 90% of said melted vehicle, such as benzoate ester, depending upon the type of sunscreen preparation and its desired sunscreen efficacy or SPF. This mixture is then agitated and heated to a temperature and for a time sufficient to disperse the sunscreen agent in the vehicle. Any mixer or stirrer is suitable. Preferably, the temperature to which the mixture is heated will be above about 100^oC. After the inorganic sunscreen is all dispersed in the vehicle, the mixture is cooled while agitating with a mixer or stirrer to thereby form a solid dispersion of the physical sunscreen. Preferably, the temperature to which the mixture is cooled while agitating is below about 60^oC. The mixture is preferably homogenized by passing it through a homogenizer or other means, such as an in-line mill.

The solid dispersion vehicle is preferably Stearyl Benzoate (FINSOLV.RTM. 116 from Finetex Inc. of Elmwood Park, N.J., U.S. Pat. No. 4,323,694), Behenyl Benzoate (FINSOLV.RTM. 137 from Finetex Inc.), or Arachidyl Benzoate (a C-20 benzoate). Other dispersion vehicles which may be used in the process of the invention are

solid fatty alcohols such as:

Cetyl Alcohol

Stearyl Alcohol

Cetearyl Alcohol

Behenyl Alcohol

Arachidyl Alcohol or

Higher Alcohols (C22+. . . )

The foregoing list is only exemplary of the type of esters on which the delivery system may be based, and, as such, is not to be considered limiting.

Additives which offer additional dispersing effects to the sunscreen compositions may be added in the vehicle delivery system at the time of melting of the dispersion vehicle. These are liquid emollients which may be added to the system in small quantities and do not affect the solid characteristics of the vehicle delivery system. Among them are:

C_12-15 Alkyl Benzoate (FINSOLV.RTM. TN from Finetex Inc., U.S. Pat. No. 4,323,694)

Octyl Dodecyl Benzoate (FINSOLV.RTM. BOD from Finetex Inc.)

PPG-15 Stearyl Ether Benzoate (FINSOLV.RTM. P from Finetex Inc., U.S. Pat. No. 4,791,097)

Dipropylene Glycol Dibenzoate (FINSOLV.RTM. PG-22 from Finetex Inc.)

The above and similar compounds are liquid emollients which promote the dispersion of the particulate inorganic sunscreen in the dispersion vehicle. Their addition is preferred but is not required. The quantity of the dispersing agent used depends on various factors but generally an amount from 1% to 20%, preferably from 1% to 10% by weight based on the weight of the particulate matter may be added.

These benzoate additives offer a processing benefit for the use of the solid vehicle delivery of micronized zinc oxide and titanium dioxide. Benzoate esters offer dispersing effects to the sunscreen compositions. The liquid benzoate esters identified above offer particularly effective dispersing effects and emolliency in the final compositions.

The micronized physical sunscreens of this invention in the solid dispersed form as prepared by the invention process may be incorporated into various cosmetic and personal care products such as hand and body creams, a suspension or dispersion in solvents or fatty substances, or alternatively, as lotions, ointments, oils, gels, emulsions such as a cream or a milk, solid sticks, facial cosmetics, lip balm products and the like, and may optionally be packaged as an aerosol or in the form of a foam or a spray.

The amount used in such compositions is dependent on the type of composition, the type and quantity of other ingredients, such as cosmetic ingredients used, and the amount and type of functional additives that are utilized. Typically, the percent concentration of the micronized zinc oxide or titanium dioxide used may very from 0.5% to 65%, by weight, depending upon the intended use of the particular sunscreen composition. For instance, low amounts are required in suntanning products which are not intended to prevent the sun's rays from reaching the skin. More substantial amounts are required for sunblocks products which are intended to prevent substantially all of the sun's rays from contacting the skin. A preferred, usable form carries about 60 parts of micronized zinc oxide or titanium dioxide per 40 parts of the benzoate ester or other dispersion vehicle.

The delivery system of the invention is advantageous as it results in micronized physical sunscreens which are:

non-dusting

non-agglomerating

easily re-meltable

easily dispersible in the commonly used systems for sunscreen applications

easily admixable in the oil phases of the cosmetic creams, lotions, etc.; and

easily grindable, if necessary.

Another advantage is that the delivery system of the invention allows for pre-mixed, pre-dispersed sunscreen compositions suitable for long-term storage as stable, solid dispersions. Such compositions preferably comprise 10% to 60% by weight of inorganic sunscreen agents in a solid dispersion.

Another advantage is the solid dispersion has excellent homogeneity, i.e., the inorganic sunscreen pigments are very well dispersed in the solid dispersion, and when mixed into a sunscreen preparation for topical application.

Thus, the present invention provides novel stable and homogeneous sunscreen compositions comprising inorganic sunscreen pigments in a cosmetically acceptable vehicle of the solid dispersant type.

The delivery system of the invention makes the zinc oxide or titanium dioxide particles more dispersible, so that higher concentrations than were possible before may now be incorporated into stable fluid emulsions, dispersions, creams, lotions, ointments, etc. Thus, the delivery system of the invention enhances the dispersibility of the inorganic sunscreen particles, contributing to an improvement in the UV sunscreening efficiency and long-term stability of sunscreen compositions incorporating same.

Once the solid dispersion of zinc oxide or titanium dioxide in the dispersion vehicle, preferably a solid benzoate ester, has been prepared, it is ready for use in cosmetic sunscreen preparations as the active sunscreen ingredient.

In sum, the delivery system of the invention provides a means for delivering micronized inorganic sunscreens embedded in a Finsolv.RTM. benzoate ester product. There are currently no other solid dispersions of physical sunscreens on the market of the type of this invention. Liquid dispersions have drawbacks as the micronized sunscreen settles out over time, and must be stirred vigorously before use. In contrast, the invention contemplates a homogeneous, solid material into which the micronized physical sunscreen has been dispersed, which does not require mixing or regrinding prior to use.

The solid dispersions of physical sunscreens so prepared provide a convenient form of sunscreen which may be mixed with one or more cosmetically acceptable materials in the customary manner to formulate various types of sunscreen compositions. These may be used for cosmetic and/or dermatologic protection from the sun, and for the treatment, care and cleansing of the skin or hair, and as make-up. The formulation may take the form of anhydrous gel-type sunscreen compositions, oil in water emulsions and water in oil emulsions. There are no limitations on the use of the solid dispersions of the invention in sunscreen compositions. The cosmetic and dermatologic preparations are used by applying them to the skin and/or the hair in effective amounts in the customary manner.

Preferred compositions include emollients, selected from the group consisting of lanolin, isopropyl myristate, glycerlyl stearate, cetyl alcohol, and dimethicone, and combinations thereof. The compositions may include further ingredients such as customarily used in such preparations, i.e., conventional adjuvants, including organic or inorganic sunscreens, fragrances, preservatives, bactericides, emulsifying agents, stabilizers, dispersants, anti-oxidants, thickeners, moisturizers, moisture-retaining agents, fats, oils, waxes, foam stabilizers, electrolytes, water-proofing agents, fillers, humectants, corrosion inhibitors, solubilizing agents, coloring pigments, vitamins, deodorizing agents, anti-perspirants, insect repellents, alkalinizing or acidifying agents, shaping agents, propellants, or any other ingredient generally used in the cosmetic field, as is known in the art.

Typically, in a general method for preparing a sunscreen lotion, hydroxyethyl cellulose (Natrosol.RTM. from Hercules, Inc. of Wilmington, Del.) is dispersed in water and heated to 75^oC. to form a first Phase A. A second Phase B is prepared by separately heating glyceryl monostearate, DEA Oleth-3 phosphate, and cyclomethicone (345) to 75^oC., and then adding Phase B to Phase A with mixing. Phase C, comprising the solid dispersion of inorganic sunscreen prepared as described above, is added in small portions with vigorous stirring by means of a mixer over a period of one hour. The mixture is cooled with stirring to 40^oC. The loss of water is adjusted. When the temperature reaches 40^oC., Phase D comprising propyleneglycol, diazolidinylurea, methyl paraben and propyl paraben (Germaben II from ISP, Wayne, N.J.) is added. The lotion is then homogenized with a hand homogenizer.

The ingredients and quantities used in any particular sunscreen composition will depend on the type of sunscreen, and the degree of SPF desired.

A further advantage of the delivery system of the invention is that lotions prepared thereby are invisible, i.e., do not have a whitening effect on the skin.

Another advantage is that sunscreen compositions made using the method of the invention have a pleasing appearance, because the benzoate ester provides a generally translucent medium. As a result, the composition can include dyes and the like to confer desirable colors to the composition.

Yet another advantage is that the compositions have been found to possess high substantivity, i.e., retention on the skin, even when reasonably immersed in water for 30 -60 minutes or more.

A further advantage of the invention is that the consistency, i.e., the viscosity and homogeneity, of the composition is stable over a wide range of temperatures. The preferred composition of the invention is generally stable at temperatures below 0^oC. and above about 55^oC. It will not liquify in high temperatures or freeze in low temperatures.

The delivery system of the invention provides a convenient and economical method for producing a wide variety of sunscreens.

Claim 1 of 18 Claims

We claim:

1. A method of preparing a solid dispersion of physical inorganic sunscreens for use in sunscreen preparations comprising the steps of:

a. melting a solid dispersion vehicle;

b. adding one or more inorganic sunscreen agents to said melted dispersion vehicle;

c. stirring and heating the mixture to a temperature and for a time sufficient to disperse said sunscreen agent in said dispersion vehicle;

d. after the sunscreen agent is dispersed in said dispersion vehicle, cooling the mixture while stirring to thereby produce a solid dispersion of said one or more inorganic sunscreen agents for use in sunscreen preparations.

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