Stable emulsions useful for skin care wipes

Details Stable emulsions useful for skin care wipes Stable emulsions useful for skin care wipes

2001-09-06

2004-02-24

Page, Thurman K. (Department: 1615)

Drug, bio-affecting and body treating compositions

Preparations characterized by special physical form

Wearing apparel, fabric, or cloth

C424S400000, C424S401000, C424S078030

Reexamination Certificate

active

06696070

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to stable emulsions comprising salicylic acid and acrylates/C
10
-C
30
alkyl acrylate cross polymers which are used in combination with a substrate to form a wipe product that effectively delivers salicylic acid to the skin while being mild to the skin.
BACKGROUND OF THE INVENTION
Commercial aqueous based facial wipes which contain salicylic acid require either a high level of polyol (such as glycerol or propylene glycol), or ethanol to solubilize the salicylic acid. Unfortunately, formulations with high levels of polyol are perceived by consumers to have poor aesthetic properties (when compared to emulsion type products), while high levels of ethanol can cause irritation to the skin.
Commercial emulsions manufactured for wipe products are preferred to have a viscosity less than 1000 cps to enable impregnation in the conventional manner. Current formulation trends require a complex mixture of surfactants and emulsifiers and emulsification temperatures above 60° C. to incorporate oil phases to produce impregnates at such a viscosity.
Commercial lotions containing salicylic acid and acrylates/C
10
-
30
alkyl acrylate cross polymers are stabilized by the use of high quantities of emulsifier (usually emulsifiers which are solid at room temperature) and medium to high viscosity to prevent phase separation. A typical viscosity for such a lotion ranges from about 20,000 to about 100,000 cps.
Emulsions formed by acrylates/C
10
-
30
alkyl acrylate cross polymers (in particular those anionic in nature, with a hydrophilic backbone and hydrophobic portions to “lock” the oil in place) are sensitive to salts and soluble cations. The addition of salicylic acid to emulsions containing only acrylates/C
10
-
30
alkyl acrylate cross polymers solutions as an emulsifier causes immediate instability and results in separation of the oil and aqueous phase (creaming) or release of the oil phase from the polymer (coalescence) at a pH less than 7.
U.S. Pat. No. 5,648,083 describes personal care compositions including silicones and polymeric emulsifier for providing barrier protection against dermatitis for baby wipes. The compositions do not incorporate cationic species, such as salicylic acid or non-ionic surfactants to modify the surface tension and interact with polymeric emulsifier and oil droplets.
A study released by B F Goodrich, investigating the stability of a cationic surfactant in combination with Pemulen (an acrylates/C
10
-
30
alkyl acrylate cross polymer) states that at a pH of 5.5 the maximum concentration of cationic surfactant that remains compatible with the polymer is less than 0.25% by weight, despite increases in polymer concentration from 0.2 to 0.6%. Additional figures show that at higher pH (7.0), stability can be achieved above a viscosity of 1000 mpas. See PEMULEN Polymeric Emulsifiers, “Cationic Skin Lotions Formulated with PEMULEN Polymeric Emulsifiers”, 1995.
Polymeric Emulsifiers, “An Alternative to Traditional Emulsifiers based on Stability of Multi-Phase Systems”, Daniella R. J. Clymans, Hans M. Brand, B. F. Goodrich Chemical, discusses the use of small chain nonionic surfactants such as Poloxamer 181 (at 0.05-0.2% by weight) or similar products and the use of ethoxylated/propoxylated fatty alcohols to adjust surface properties (such as “quick break effect”) and the rheology of PEMULEN emulsions. According to the article these surfactants do not act as emulsifiers, but only reduce the surface tension of the dispersed oily phase at the use level of 0.05-0.2 & by weight.
Accordingly, there remains a need for a stable emulsion including salicylic acid and acrylates/C
10
-
30
alkyl acrylate cross polymers.
SUMMARY OF THE INVENTION
The invention relates to a wet wipe product comprising a substrate and an emulsion. The emulsion comprising: an acrylate/C
10
-C
30
alkyl acrylate cross polymer emulsifier; salicylic acid; a nonionic surfactant; and a lipophillic component. The nonionic surfactant is selected from the group consisting of (i) a polymeric ether, (ii) a mixture of laurate esters of sorbitol and sorbital anhydrides condensed with ethylene oxide; and (iii) mixtures thereof.
The invention also relates to a method for depositing salicylic acid to mammalian skin comprising topically applying the wipe product described above to the skin to be treated.
The emulsion according to the invention produces an aesthetically pleasing product, capable of removing non-water proof make-up and able to deliver salicylic acid to the skin and is mild on the skin.
DETAILED DESCRIPTION
As discussed above, the invention relates to a wet wipe product comprising a substrate and an emulsion, said emulsion comprising:
(a) an acrylate/C
10
-C
30
alkyl acrylate cross polymer emulsifier;
(b) salicylic acid; and
(c) a nonionic surfactant selected from the group consisting of (i) polymeric ether, (ii) a mixture of laurate esters of sorbitol and sorbitol anhydrides condensed with ethylene oxide; and (iii) mixtures thereof.
The acrylate/C
10
-C
30
alkyl acrylate cross polymer is a white solid powder commercially available from B F Goodrich under the name PEMULEN. It is a high molecular weight cross linked poly(acrylic acid) polymer which contains a hydrophilic back bone and hydrophobic portions which stabilize the oil and lock it in place. The polymer is anionic in nature and can be the only emulsifier used to emulsify the lipophillic components. In a preferred embodiment the acrylates/C
10
-C
30
alkyl acrylate cross polymer is present in an amount ranging from about 0.05 to about 2.0% by weight, more preferably from about 0.12 to about 0.13% by weight.
The emulsions of the present invention further comprise at least one emulsion stabilizer. Examples of suitable emulsion stabilizers include small chain nonionic surfactants, such as polymeric ethers, including, for example, polyoxyethylene-polyoxypropylene block polymers and nonionic surfactant consisting of a mixture of laurate esters of sorbitol and sorbitol anhydrides, condensed with approximately ethylene oxide. Particularly preferred nonionic surfactants useful as emulsion stabilizers include (1) Poloxamer 124 : A non-ionic surfactant which belongs to the chemical class of polymeric ethers, consisting of a polyoxyethylene, polyoxypropylene block polymer and (2) Polysorbate 20: a nonionic surfactant consisting of a mixture of laurate esters of sorbitol and sorbitol anhydrides, condensed with approximately 20 moles of ethylene oxide.
Although not wishing to be bound by any theory, the proposed mechanism of stabilization is (1) by protection of the hydrophilic backbone by the small chain non-ionic particles to hinder shrinkage and reactions to the salicylic acid; (2) stabilization of the oil droplet at the C
10
-C
30
alkyl acrylate cross polymer/lipophillic interface by lowering the surface tension and hence nullifying the effects of salicylic acid.; or a combination of both 1 and 2.
In a particularly preferred embodiment, the nonionic surfactant is a mixture of (i) a polyoxyethylene-polyoxypropylene block polymer and (ii) a mixture of laurate esters of sorbitol and sorbital anhydrides condensed with 20 moles of ethylene oxide and is present in amount ranging from about 0.01 to about 10.0% by weight, preferably from about 0.03 to about 0.08% by weight.
The emulsions used in the wipe product of the invention further comprise a cationic active ingredient such as salicylic acid. Preferably, salicylic acid is incorporated for its keratolytic action for the prevention and treatment of comodons and for its slight antibacterial properties. Suitable amounts of salicylic acid range for example, from about 0.05 to about 0.5% by weight, preferably from about 0.05 to about 0.5% by weight.
The emulsions of the invention further comprise a lipophillic component to contribute to the aesthetics of the product. Suitable lipophillic components include as emollients such as C
12
-C
15
alkyl benzoate; cyclomethicone, dimethicone, and mixtures thereof. The emollients are generally present in an amount ranging from ab

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