Infrared reflecting composition for topical application to the skin.

FIELD OF THE INVENTION

The present invention is directed to an infrared reflecting composition for topical application to the skin of a warm blooded animal. The composition can be used by sunbathers and those exposed to infrared radiation in their employment such as steel furnace operators, welders and the like to thereby limit exposure to infrared radiation.

BACKGROUND OF THE INVENTION

Radiant energy such as that emitted by the sun, welding arcs, light bulbs, etc. includes infrared radiation which is invisible to the naked eye and has a wavelength of at least 750nm. Localized heating occuring as a result of exposure to infrared radiation can cause serious health problems. For example, it is known from animal studies that overexposure to both infrared and ultraviolet radiation can result in tumors of the skin. Additionally, infrared radiation is known to decrease skin elasticity leading to premature aging.

Topical applications for protection against radiant energy, especially from the sun have focused on protection against ultraviolet radiation. Ultraviolet absorbers have been used in such compositions and sold commercially as topical sunscreens (<u style="single">see</u>, for example, U.S. Patent No. 4,592,906).

Protection against infrared radiation has focused primarily on the employment of infrared absorbers such as those disclosed in U.S. Patent No. 3,484,467. The infrared absorbers are incorporated into devices (e.g., sunglasses and safety lenses) which are sufficiently remote from the skin surface to insure that the heat absorbed by the infrared absorbers does not elevate skin temperature. For this reason, infrared absorbers have not been incorporated into compositions for the topical application to the skin.

Infrared reflectors are compounds which reflect infrared energy. Infrared reflecting films have been used to coat windows in high energy laser systems (see, "<u style="single">Infrared Coatings For High Energy Laser Reflectors and Windows</u>", Morris Braunstein, SPIE, Vol. 140, Optical Coatings - Applications and Utilization II, pp. 85-94 (1978)). They have also been used to construct transparent heat mirrors for architectural glass coatings, light bulb envelopes, protective lenses, solar heat devices and the like. (See, "<u style="single">Materials for Transparent Heat Mirror Coatings</u>", G. Haacke, SPIE, Vol. 324, Optical Coatings for Energy Efficiency and Solar Applications, pp. 10-15 (1982)). All of these infrared reflecting films are coated on relatively large substrates which are obviously unsuitable for topical compositions. Therefore, there is a need for a topical composition capable of protecting the skin against infrared radiation.

Applicants have discovered that an infrared reflecting composition for topical application to the skin can be prepared from infrared reflecting materials alone or by coating fine particles of an epidermally suitable substrate such as fine particles of mica or plastics with an infrared reflecting material. The resulting topical composition is easy to use and provides significant protection against infrared radiation from the sun, high energy arc lamps and the like.

It is therefore an object of the invention to provide an infrared reflecting composition for topical application to the skin.

It is another object of the invention to provide an infrared reflecting topical composition containing fine particles of an epidermally suitable substrate coated with an infrared reflecting material.

It is a further object of the invention to provide methods of protecting the skin of warm blooded animals against exposure to infrared radiation.

SUMMARY OF THE INVENTION

The present invention is directed to an infrared reflecting composition for topical application to the skin of warm-blooded animals comprising fine particles of an epidermally suitable substrate coated with at least one layer comprising an infrared reflecting effective amount of an infrared reflecting material. The present invention is also directed to methods of reflecting infrared radiation away from the skin by topically applying said compositions or an infrared reflecting material by itself to the skin.

The substrates employed in the present invention are, preferably, substantially transparent or reflect light in a manner which approximates the color tone of skin and include, by way of example, fine particles of mica or plastics such as, for example, polymethacrylate, polyethylene terephthalate and the like. The particle size of the substrate should be sufficiently small so as to enable the composition to be easily and evenly applied to the skin. The preferred particle size of the substrate is within the range of from about 20 to about 500 microns. Mica is the preferred substrate for use in the present invention.

The fine particles of the substrate are coated with at least one layer comprising an infrared reflecting amount of an infrared reflecting material. The infrared reflecting materials are preferably substantially transparent or reflect light in a manner which approximates the color tone of skin. Under these circumstances, the present composition is substantially invisible or at least barely noticeable when applied to the skin. The infrared reflecting materials particularly suited for the present invention include metals and semiconductor materials such as doped tin oxide, doped indium oxide and cadmium orthostannate wherein the dopants are preferably selected from fluorine, phosphorous and tin. Such dopants are known to enhance the infrared reflecting properties of the semiconductor material. Of the semi-conductor type infrared reflectors, fluorine doped tin oxide is particularly preferred. In the present invention, the dopant is employed in an amount sufficient to enhance reflectance, typically no more than about 1 mol % based on the total amount of the infrared reflecting material.

The semiconductor infrared reflecting material is coated on the substrate to a thickness sufficient to insure a suitable degree of infrared reflectance. For most applications including protection from infrared radiation generated by the sun, it is preferred to coat the substrate with the semiconductor material to a thickness in the range of from about 3,000 to 4,000 Å.

The metals which are employed as infrared reflectors in the present invention include the noble metals (e.g., gold, silver, platinum, etc.), copper and aluminum. In a preferred embodiment of the invention, the metal may be coated on each of its sides with a dielectric material such as titanium dioxide or zinc sulfide or combinations thereof to obtain an infrared reflecting composition which has improved visible transparency and enhanced infrared reflectivity.

The thickness of the metal containing infrared reflecting coating is preferably in the range of from about 100 to about 300 Å.

The infrared reflecting compositions may be produced by applying a coating of the infrared reflecting material on the fine particles of the substrate by conventional methods such as chemical vapor deposition, evaporation, sputtering, spray pyrolysis and the like. Alternatively, the substrate may be coated as a sheet and then the coated sheet ground into fine particles.

The coated substrates may be applied to those areas of the skin which are exposed to infrared radiation. The coated substrates may be added to dermatologically suitable carriers if desired. Suitable carriers include SD alcohol, lanolin, glyceryl stearate, cocoa butter, sorbitan sesquioleate, propylene glycol, mineral oil, isopropyl myristate, petrolatum and Aquaphor sold by Beiersdorf (a mixture of petrolatum, mineral oil, mineral wax, wool wax and alcohol) and mixtures thereof. The amount of the carrier need only be sufficient to provide a uniform dispersion of the active ingredient when applied to the skin and to insure coverage of the skin with the infrared reflecting material, typically from about 85 to about 95 percent by weight based on the overall weight of the composition.

The composition of the present invention may contain a variety of additives including, for example, ultraviolet absorbers, stabilizers, fragrances, and the like.

Ultraviolet absorbers of the type described in U.S. Patent No. 4,592,906 incorporated herein by reference may be used to produce a composition giving protection against both ultraviolet and infrared radiation.

BRIEF DESCRIPTION OF THE DRAWINGS

<ul id="ul0001" list-style="none"><li>FIGURE 1 is a graph showing the degree of reflectance of infrared radiation of a composition of the present invention containing fluorine doped tin oxide on mica as compared with the reflectance of the uncoated substrate and unprotected human skin.</li><li>FIGURE 2 is a graph showing the degree of infrared reflectance of gold powder and a composition of gold and a dermatologically acceptable carrier as compared with unprotected human skin.</li><li>FIGURE 3 is a graph showing the degree of infrared reflectance of unprotected human skin; and</li><li>FIGURE 4 is a graph showing the degree of infrared reflectance of human skin coated with fluorine doped tin oxide alone.</li></ul>

The following examples are for illustrative purposes only and are not meant to limit the invention as set forth in the claims forming a part of the application.

EXAMPLE 1

Preparation of Doped Tin Oxide Coated Mica

A chemical vapor deposition apparatus including a resistance-heated Kanthal wire furnace (Lindberg, Model M-200) containing a 50mm × 1.8mm reaction chamber made of fused silica is loaded with a sheet of mica. Dibutyltin diacetate and trichloro-trifluoro ethane (Freon 113 sold by DuPont Canada, Inc.) as a dopant are maintained at temperatures of 100°C. and 0°C., respectively in the presence of bubbled nitrogen gas in order to maintain the desired vapor pressure for each compound.

Prior to deposition, the substrate is preheated for about five minutes under a nitrogen gas flow. Tin oxide is coated on the mica sheet by exposing the mica sheet to approximate flow rates respectively as follows: 400 m./min nitrogen carrier gas, 550 ml/min oxygen, 1.14 liter/min nitrogen through the dibutyltin diacetate reactor and 25 to 280 ml/min of nitrogen through the Freon 113 reactor.

After deposition, the sheet of mica was cut into fine particles of mica (about 500 microns²) and then applied to human skin and tested for infrared reflectance by a Perken Elmer Lambda 9 UV-Visible NIR-Spectrophotometer and the results are shown in FIGURE 1.

As shown in FIGURE 1, the coated mica particles exhibited significantly greater reflection of infrared radiation than uncoated mica and unprotected skin.

EXAMPLE 2

Preparation of A Sandwich Film of Titanium Dioxide (Dielectric) and Gold

A sheet of mica is ultrasonically cleaned in a heated decontamination solution (DECONTAM sold by Electronic Space Products, Inc., Los Angeles, California), rinsed in deionized water and blown dry in nitrogen gas.

A TiO₂ target is presputtered at 1.6 W/cm² in an Argon-oxygen mixture (10 vol % Oxygen) for 15 minutes, then in Argon for 15 minutes. The flow rates of the Argon-Oxygen mixture and Argon are kept at about 74 cm³/min The sputtering pressure is 7-10×10⁻³ Torr.

A TiO₂ film having a thickness of about 180 N is deposited on the sheet of mica by sputtering at 0.8 W/cm² for 7.5 minutes in Argon at a flow rate of about 74 cm³/min at the same sputtering pressure employed above.

A film of gold approximately 180 Å thick is deposited by sputtering at 0.4 W/cm² for 35 seconds in Argon and the same flow rate and sputtering pressure described above for depositing the TiO₂ film.

Another TiO₂ film is deposited on the gold film in the same manner as described above for the deposition of the initial TiO₂ film. The resulting product reflects at least about 75% infrared radiation in the near IR region (750-1000 nm) and approaches 100% reflectance at about 3,000 nanometers.

EXAMPLE 3

Gold Coated Mica

A piece of gold wire 19.2 mm long and 0.2mm wide weighing about 8 mg was twisted around a tungsten filament secured within a Denton Vacuum Machine Model No. DV-502. The filament was connected to two electrodes and a petri dish containing fine particles of mica (e.g., 20 to 500 microns) was placed about 5 to 7.5 cm below the filament.

The gold wire was heated and subsequently evaporated onto the mica particles at a vacuum pressure of 10⁻⁵ Torr at 20 amps and 45 volts for 3 seconds.

The gold coated fine particles of mica were combined with Aquaphor at a weight ratio of about 1:10 (10mg gold coated mica:100 mg Aquaphor) and mixed until the gold coated mica was uniformly dispersed in the Aquaphor to produce an infrared reflecting composition for topical application. The composition was applied to human skin and tested for infrared reflectance in the same manner as in Example 1. The results are shown in FIGURE 2.

The experiment is repeated except that the gold coated mica was not combined with Aquaphor. The gold coated mica alone was applied to human skin and tested for infrared reflectance in the same manner as Example 1. The results are shown in FIGURE 2.

As shown in FIGURE 2, the gold coated mica alone and the gold coated mica combined with Aquaphor exhibited significantly greater infrared reflectance than unprotected skin.

EXAMPLE 4

Preparation of Doped Tin Oxide Crystals

Fluorine doped tin oxide is coated on a sheet of mica employing the same method described in Example 1. The doped tin oxide coating was separated from the mica sheet using a fine knife to obtain fine particles of doped tin oxide which were applied to the skin as a topical composition. The degree of infrared reflectance of the coated skin as shown in FIGURE 4 is significantly greater than the infrared reflectance of uncoated skin as shown in FIGURE 3.