Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-10-03
2002-05-07
Yoon, Tae H. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S135000, C523S201000, C524S458000, C424S059000, C424S060000, C424S078170
Reexamination Certificate
active
06384104
ABSTRACT:
BACKGROUND
This invention relates to an improvement in the known process for enhancing the ultraviolet (UV) radiation absorption of personal care formulations, such as sunscreen compositions, where voided latex polymer particles are added to personal care compositions containing at least one UV radiation-absorbing agent. The improvement involves the use of selected polymer compositions for the latex polymer particles that results in extended stability as measured by retention of the SPF (Sun Protection Factor) enhancement and effectiveness under storage and use conditions.
Six percent of the solar energy reaching the earth's surface is ultraviolet (UV) radiation having a wavelength of 290-400 nanometers (nm). This radiation has two components: 5.5% UVA having a wavelength of 320-400 nm and 0.5% UVB having a wavelength of 290-320 nm. While the UV portion of the solar energy is relatively small, it induces nearly 99% of all the side effects of sunlight. UVB radiation, for example, is responsible for producing sunburn, aging and cancer of the skin. UVA radiation, for example, causes direct tanning and erythema (abnormal redness) and contributes to aging of the skin.
By avoiding exposure to sunlight, people can avoid the serious effects caused by UV radiation. However, because of the nature of their work, some people cannot avoid exposure to the sun. In addition, others voluntarily expose their skin to the sun to tan, sometimes to extremes. Therefore, protection against the harmful effects of the sun is important.
Protection from these harmful effects of UV radiation exposure is available in the form of topically applied formulations containing at least one physical blocker, or at least one chemical absorber, or combinations thereof. Physical blockers include active ingredients such as red petrolatum, titanium dioxide and zinc oxide. Chemical absorbers include active ingredients, such as para-aminobenzoic acid (more commonly known as PABA), which are generally transparent when applied and act by absorbing UV radiation, offering selective protection against certain UV wave bands.
The effectiveness of a sunscreen formulation is generally assessed by how well it protects the skin in terms of a Sun Protection Factor (SPF) which is defined as the ratio of the amount of energy required to produce a minimal erythema on sunscreen protected skin to the amount of energy required to produce the same level of erythema on unprotected skin.
A number of the chemical absorbers and physical blockers, hereafter referred to as “UV radiation-absorbing agents,” typically used in sunscreen to formulations have adverse toxicological effects. Therefore, it is desirable to reduce the level of UV radiation-absorbing agents present in a sunscreen formulation without reducing the level of protection.
European Patent Applications EP 669,124 and EP 761,201 and U.S. Pat. No. 5,663,213 disclose the use of voided latex polymer particles having selected particle sizes to improve the absorbance of UV radiation in compositions containing one or more UV radiation-absorbing agents. U.S. Pat. No. 4,427,836 discloses processes for preparing core-shell polymers containing voids that are suitable for use as opacifying agents in coating compositions.
Although previous methods that reduce the level of UV radiation-absorbing agents in personal care formulations enhance initial SPF performance, there is a need for improved formulations that have extended lifetime and durability of the enhancement effect. The problem addressed by the present invention is to provide extended stability as measured by retention of the SPF (Sun Protection Factor) enhancement and effectiveness under storage and use conditions for the personal care formulations containing the particles and UV active ingredients.
STATEMENT OF INVENTION
The present invention provides a method for providing storage stability of UV radiation-absorption compositions, comprising adding to the compositions 5 to 70 percent of latex polymer particles, based on total weight nonvolatiles, to increase the UV radiation absorption of the compositions, wherein (a) the composition comprises at least one UV radiation-absorbing agent; (b) the latex polymer particles contain a void and have a particle size from 50 to 1000 nanometers; and (c) the latex polymer particles comprise a shell portion prepared by one or more steps selected from: (i) polymerization to incorporate from 4 to 80 percent monomeric units, based on total weight of the shell portion, of one or more polyethylenically unsaturated monomers; and (ii) polymerization to incorporate from 4 to 80 percent monomeric units, based on total weight of the shell portion, of one or more multifunctional monomers having at least one functional group capable of vinyl copolymerization and at least one functional group capable of reaction with a reactive molecule effective to produce post-polymerization crosslinking.
The present invention further provides a personal care composition comprising (a) at least one UV radiation-absorbing agent; and (b) from 5 to 70 percent of latex polymer particles, based on total weight nonvolatiles, comprising a shell portion prepared by polymerization to incorporate from 4 to 80 percent monomeric units, based on total weight of the shell portion, of one or more multifunctional monomers having at least one functional group capable of vinyl copolymerization and at least one functional group capable of reaction with a reactive molecule effective to produce post-polymerization crosslinking; wherein the composition has an SPF Enhancement Retention value of at least 40.
DETAILED DESCRIPTION
The compositions of the present invention are useful for improving the storage stability of personal care formulations containing at least one UV radiation-absorbing agent and latex polymer particles. We have found that selected crosslinker levels used in the shell portion of the latex polymer particles are particularly effective for this purpose and result in unexpectedly improved storage stability (as measured by the retention of SPF enhancement) and effectiveness of the personal care formulation as compared with the use of prior art latex polymer particles having little or no crosslinking in the shell portion of the polymer particles. These selected crosslinked shell compositions are based on (1) monomeric compositions containing polyethylenically unsaturated monomers, (2) monomeric compositions containing multifunctional monomers having at least one functional group capable of vinyl copolymerization and at least one functional group capable of reaction with suitable reactive molecules to produce post-polymerization crosslinking, or (3) combinations thereof.
As used herein, the term “(meth)acrylic” refers to either the corresponding acrylic or methacrylic acid and derivatives; similarly, the term “alkyl (meth)acrylate” refers to either the corresponding acrylate or methacrylate ester. As used herein, all percentages referred to will be expressed in weight percent (%), based on total weight of polymer or composition involved, unless specified otherwise. As used herein, the term “copolymer” or “copolymer material” refers to polymer compositions containing units of two or more different monomers. As used herein, the term “nonvolatiles” refers to solid or liquid components of the personal care formulation that do not readily evaporate at ambient temperatures due to their vapor pressure (such as polymer particles, UV radiation-absorbing agents and conventional adjuvants).
For the purposes of the present invention, the terms, “sheath” and “shell” are considered synonymous and refer to the total shell polymer composition (not including the core portion) prepared from single or multistage polymerizations.
For the purposes of the present invention, “SPF Enhancement Retention” (SER) refers to the retention (as a function of storage time) of the %SPF enhancement (%SE) of a sample containing latex particles relative to a control formulation containing no latex particles, expressed as a % value.
The method of the present inventi
Chang Ching-Jen
Jones Charles Elwood
Weinstein Barry
Howell Thomas J.
Rohm and Haas Company
Yoon Tae H.
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