United States Patent:  6,001,379

Assignee:  L'Oreal (Paris, FR)

Filed:  September 21, 1998

Oil-in-water type emulsions having a pH below or equal to 3.5, especially a pH below or equal to 3, and comprising as a stabilizing agent a substantially water-soluble crosslinked anionic copolymer consisting of units derived from the reaction between (i) acrylamide, (ii) 2-acrylamido-2-methylpropanesulfonic acid and (iii) at least one compound possessing multiple olefinic unsaturation (crosslinking agent), in which the compound possessing multiple olefinic unsaturation is present in the copolymer at a concentration of between 0.06 and 1 mmol per mole of the collective monomer units, are stable.

SUMMARY OF THE INVENTION

Accordingly, it is one object of the present invention to provide novel stable acidic oil-in-water emulsions.

It is another object of the present invention to provide oil-in-water emulsions which have a pH of less than or equal to 3.5 and which are stable.

It is another object of the present invention to provide oil-in-water emulsions which have a pH of less than or equal to 3 and which are stable.

It is another object of the present invention to provide novel compositions containing such an emulsion.

It is another object of the present invention to provide a novel method for stabilizing oil-in-water emulsions which are acidic.

It is another object of the present invention to provide a method for stabilizing oil-in-water emulsions which have a pH of less than or equal to 3.5.

It is another object of the present invention to provide a method for stabilizing oil-in-water emulsions which have a pH of less than or equal to 3.

These and other objects, which will become apparent during the following detailed description, have been achieved by the inventor's discovery that unexpectedly and surprisingly, by employing a specific polymer which is introduced into an oil-in-water type emulsion initially possessing a pH below or equal to 3.5 and in an unstable state, it is possible to obtain a final emulsion which is also of the oil-in-water type, having the same pH, but which is completely stable.

This discovery has made the present invention possible.

According to one of the objects of the present invention, stable oil-in-water type emulsions having a pH below or equal to 3.5, especially a pH below or equal to 3, are hence now provided. Specifically, the present emulsions comprise as a stabilizing agent a substantially water-soluble crosslinked anionic copolymer consisting of units derived from the reaction between (i) acrylamide (monomer 1), (ii) 2-acrylamido-2-methylpropanesulfonic acid (monomer 2, hereinafter designated AMPS for convenience) and (iii) at least one compound possessing multiple olefinic unsaturation (monomer 3, here constituting the crosslinking agent), in which the compound possessing multiple olefinic unsaturation is present in the copolymer at a concentration of between 0.06 and 1 mmol per mole based on the total monomer units.

Another aspect of the present invention is the use of a polymer as defined above for stabilizing oil-in-water type emulsions possessing a pH below or equal to 3.5, especially below or equal to 3, as well as the stabilization process resulting therefrom. According to the present invention, the present method simply involves introducing the copolymer into the initial acidic emulsion to be stabilized.

It will be noted already that the present invention is of very general scope, that is to say the present method is appropriate for the stabilization of any acidic emulsion (having a pH below or equal to 3.5) of the oil-in-water type, already known per se or otherwise, the composition of the latter not assuming, in fact, any critical character.

Lastly, another aspect of the present invention consists of the various compositions, cosmetic, dermatological, and pharmaceutical, prepared and obtained from the emulsions according to the invention. In this connection, the present invention is especially well suited to the preparation of compositions which take the form of emulsions of the above type and which contain cosmetic and/or therapeutic active agents possessing markedly acid character.

Claim 1 of 31 Claims

1. A method for preparing an oil-in-water emulsion having a pH of 3 or below, comprising combining the following:

a) an oily phase;

b) an aqueous phase;

c) an acid; and

d) a polyacrylamide copolymer comprising polymerized units of acrylamide and 2-acrylamido-2-methylpropanesulfonic acid or salt thereof and crosslinked with at least one crosslinking agent possessing, in monomer form, multiple olefinic unsaturation;

wherein, when combined, said oily phase (a) is dispersed in said aqueous phase (b), said oil-in-water emulsion has a pH of 3 or below, and wherein

said acid is selected from the group consisting of ascorbic acid, kojic acid, caffeic acid, salicylic acid, lactic acid, methyllactic acid, glucuronic acid, glycolic acid, pyruvic acid, 2-hydroxybutanoic acid, 2-hydroxypentanoic acid, 2-hydroxyhexanoic acid, mandelic acid, benzylic acid, phenyllactic acid, gluconic acid, galactauronic acid, citric acid, aleuritic acid, tartronic acid, tartaric acid, malic acid, fumaric acid, benzene-1,4-bis(3-methylidene-10-camphorsulfonic) acid, mixtures thereof, and plant and fruit extracts containing said acids.

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