WO2000021491A1 - Stable oil-in-water emulsion, method for preparing same and use in cosmetics and dermatology - Google Patents

Abstract

The invention concerns an emulsion comprising an oily phase dispersed in an aqueous phase, characterised in that the oily phase globules have an average size less than 20 microns, the oily phase constitutes at least 15 wt. % relative to the emulsion total weight and the aqueous phase contains at least a copolymer consisting of a majority fraction of C3-C6 carboxylic acid monomer with mono-olefin unsaturation or its anhydride and a minority fraction of an acrylic acid fatty chain ester monomer, and is surfactant-free. The invention also concerns the use of said emulsion in cosmetics and/or dermatology, in particular for the treatment, protection, care and/or cleaning of the skin, mucous membranes and/or hair, and/or as make-up for the skin and/or mucous membranes. The invention further concerns a method for preparing said emulsion, which consists in introducing under pressure the oily phase into the aqueous phase containing the copolymer, through a porous hydrophilic glass membrane having an average pore size ranging from 0.1 to 5 mu m and preferably from 0.3 to 3 mu m, under pressure higher than critical pressure.

Description

 Stable oil-in-water emulsion, its manufacturing process and its use in the cosmetic and dermatological fields

The invention relates to a stable oil-in-water (O / W) emulsion comprising oil globules having an average size of less than 20 microns and containing at least 15% of oily phase and at least one copolymer of fatty chain carboxylic acid. The invention also relates to the process for preparing such an emulsion and to its use in the cosmetic and / or dermatological fields. For various reasons linked in particular to their great comfort of use and their freshness, the cosmetic compositions are most often in the form of an emulsion of the oil-in-water type, comprising an oily phase dispersed homogeneously in an aqueous phase. In these conventional emulsions, the size of the globules constituting the fatty phase is generally greater than several tens of microns. Such emulsions may have insufficient cosmetic (oily feel) and physical (stability) properties. Insufficient stability results in the appearance of a phenomenon of separation (phase shift) between the aqueous and oily phases of the emuision. This instability harms the conservation of emulsions.

To obtain a stable emulsion, it is necessary to add to it emulsifying agents (or surfactants) which are put at the interface of the aqueous and oily phases. However, the presence of surfactants has several drawbacks, in particular it most often requires making the hot sauce, which in particular limits the nature of the active agents to be introduced into the sauce. In particular, this process excludes the use of heat-sensitive active ingredients. Also, are we trying to get rid of surfactants. In addition, surfactants can cause irritation, especially in people with sensitive skin. The Applicant has unexpectedly discovered that it is possible to prepare emulsions having a high level of oily phase and free of surfactant, by having oil globules having an average size of less than 20 microns and by using a copolymer constituted of a majority fraction of C ₃ -C ₆ monoolefinically unsaturated carboxylic acid monomer or of its anhydride and of a minority fraction of fatty chain ester monomer of acrylic acid.

The present invention therefore relates to an emulsion comprising an oily phase dispersed in an aqueous phase, characterized in that the globules of the oily phase have an average size of less than 20 microns, in that the oily phase constitutes at least 15% in weight relative to the total weight of the emuision and in that the aqueous phase contains at least one copolymer consisting of a majority fraction of monoolefinically unsaturated C ₃ -C ₆ carboxylic acid monomer or of its anhydride and of a minority fraction of fatty chain ester monomer of acrylic acid, and in that it is free of surfactant.

Admittedly, it is known to use polymers with a fatty chain to stabilize an emulsion, but when the quantity of oil is too large, the emulsification nevertheless tends to destabilize over time. According to the present invention, good stability is obtained even in the presence of a large amount of oil because the oil globules are sufficiently small in size. In addition, these oil globules are monodispersed, that is to say that they are practically all the same size, unlike emulsions of the prior art in which the dispersed phase particles often have quite diverse sizes.

The copolymers used in the emulsion of the invention have the advantage, compared to the surfactants usually used, not only of stabilizing the emulsion but also of gelling it. In addition, unlike surfactants, they do not penetrate the skin, which greatly reduces the risk of irritation.

The copolymers used in the emulsions according to the present invention are prepared by polymerizing a preponderant amount of monoolefinically unsaturated carboxylic acid monomer or its anhydride to a smaller amount of fatty chain acrylic ester monomer. The term fatty chain is understood to mean a linear or branched alkyl radical containing from 8 to 30 carbon atoms. The amount of carboxylic acid monomer or its anhydride is preferably from 80 to 98% by weight and more particularly 90 to 98% by weight while ^'that the acrylic ester is present in amounts ranging from 2 to 20% by weight and more particularly from 1 to 10% by weight, the percentages being calculated relative to the total weight of the two monomers.

The preferred carboxylic monomers are chosen from those corresponding to the following formula (I):

RI CH ₂ r = C-COOH (I)

where R denotes hydrogen, a halogen, a hydroxyl group, a lactone group, a lactam group, a cyanogenic group (-C = N), a monovalent alkyl group, an aryl group, an alkylaryl group, an aralkyl group or a cycloaliphatic group. The particularly preferred carboxylic monomers are chosen from acrylic acid, methacrylic acid or their mixtures.

The fatty chain acrylic ester monomers are preferably chosen from those corresponding to formula (II) below:

CH ₂ = C-COOR ₂ ^(ll)

where R, is chosen from the group formed by hydrogen, the methyl radical and the ethyl radical, and R ₂ is a C ₈ -C ₃₀ alkyl group.

Particularly preferred ester monomers are those for which R. 1 is hydrogen or a methyl radical and R ₂ is a C ₁₀ -C ₂₂ alkyl group.

The copolymer used in the emulsion of the invention can optionally be crosslinked using a crosslinking agent used in an amount ranging from 0.1 to 4%, preferably from 0.2 to 1% by weight relative to the total weight of carboxylic monomers and acrylic ester monomers. The crosslinking agent can be chosen in particular from polymerizable monomers containing a polymerizable CH ₂ = C- group and at least another polymerizable group, the unsaturated bonds of which are not conjugated with respect to each other.

These copolymers are described in document EP-A-0268164 and are obtained according to the preparation methods described in this same document.

Use is made more particularly of the copolymers having a viscosity measured with the BROOKFIELD viscometer in a solution of water at 2% and at 25 ° C., less than or equal to 5000 cPs (5 Pa.s) and more preferably of the order of approximately 3000 cPs (3 Pa.s), and more especially the acrylate / C ₁₀ -C ₃₀ -alkylacrylate copolymers such as the products sold under the names PEMULEN TR1, PEMULEN TR2 and CARBOBOL 1382 by the company GOODRICH, or their mixtures.

The copolymer is used in the emulsion according to the invention in concentrations preferably ranging from 0.1 to 4% by weight and more particularly from 0.1 to 2% by weight relative to the total weight of the emulsion.

The emulsion of the invention is free of surfactant. Thus, due to the absence of surfactant, this emulsion has the advantage of allowing the incorporation of heat-sensitive active agents and of not being irritating for particularly sensitive skin.

Furthermore, the average size of the oily phase globules, measured in number by a laser diffraction method, is less than 20 microns, and it preferably ranges from 0.5 to 15 microns. Due to the fineness of these oil globules, the emulsion obtained has particularly satisfactory sensory and visual qualities.

The nature of the oily phase of the emulsion according to the invention is not critical. The oily phase can thus consist of all fatty substances and in particular oils, conventionally used in the cosmetic and dermatological fields.

Among the oils which can be used in the emulsion of the invention, mention may in particular be made, for example, of vegetable oils (jojoba, avocado), mineral oils (petroleum jelly), synthetic oils (ethylhexyl palmitate, isopropyl myristate) , volatile (cyclomethicone) or non-volatile silicone oils and fluorinated oils. The other fatty substances likely to be present in the oily phase can be for example fatty acids, fatty alcohols and waxes (liquid jojoba wax).

The oily phase of the emuision may represent from 15 to 45% by weight and better still from 20 to 30% by weight of the total weight of the emuision.

The emulsion according to the invention can be used in all areas where this type of dosage form is advantageous, and in particular in the cosmetic and dermatological fields. When it constitutes a cosmetic and / or dermatological composition, it also advantageously contains a physiologically acceptable medium, that is to say compatible with the skin, mucous membranes, nails and / or hair.

The emulsions which are the subject of the invention find their application in a large number of cosmetic and / or dermatological treatments of the skin, mucous membranes and hair, including the scalp, in particular for the protection, care, cleaning and / or make-up of the skin and / or mucous membranes, for the protection, care and / or hair cleaning and / or for the therapeutic treatment of the skin, hair and / or mucous membranes (lips).

The emulsions according to the invention can for example be used as care and / or cleaning products for the face in the form of creams or milks or as makeup products (skin and lips) by incorporation of fillers, pigments or dyes .

Also, the subject of the invention is also the cosmetic use of the emulsion as defined above for the treatment, protection, care and / or cleaning of the skin, mucous membranes and / or the hair, and / or for making up the skin and / or mucous membranes.

The subject of the invention is also the use of the emulsion as defined above for the manufacture of a dermatological composition intended for the treatment and / or the protection of the skin, mucous membranes and / or the hair.

In addition, in known manner, the emulsions of the invention may contain adjuvants customary in the cosmetic or dermatological field, such as hydrophilic or lipophilic active agents, preservatives, antioxidants, perfumes, solvents, fillers, filters , coloring matters, basic agents (triethanolamine) or acids and also lipid vesicles. These adjuvants are used in the usual proportions in the cosmetic or dermatological field, and for example from 0.01 to 30% of the total weight of the emulsion, and they are, depending on their nature, introduced into the aqueous phase or into the phase oily emulsion, or in vesicles. These adjuvants and their concentrations must be such that they do not modify the property sought for the emulsion.

If you want to obtain a less fluid emulsion, you can add one or more gelling agents such as clays, polysaccharide gums (xanthan gum), carboxyvinyl polymers or carbomers. These gelling agents are used at concentrations ranging from 0.1 to 10%, preferably 0.1 to 5% and better still from 0.1 to 3% of the total weight of the composition. The emulsions of the invention can optionally be free of solvent. This also goes in the direction of a slightly aggressive and non-irritating emulsion capable of being used by people with sensitive skin. However, if necessary, they can contain a solvent, in particular a lower alcohol containing from one to six carbon atoms, more particularly ethanol. The amount of solvent can range up to 30% of the total weight of the composition.

The emulsions according to the invention can be prepared by any suitable means making it possible to obtain sizes of oily globules of less than 20 microns. According to a preferred embodiment of the invention, they are prepared using a microporous membrane, this technique making it possible to obtain a size of globules particularly suited to the aim of the invention and in particular of calibrated, monodispersed oil globules. Such a technique is described for example in document EP-A-546,174. Also, the subject of the invention is also a process for manufacturing the emulsion as defined above, consisting in introducing under pressure the oily phase into the aqueous phase containing the copolymer, through a porous glass membrane hydrophilic having an average pore size ranging from 0.1 to 5 μm and preferably from 0.3 to 3 μm, at a pressure greater than the critical pressure.

Preferably, the membrane is previously treated under vacuum and ultrasound in demineralized water containing approximately 2 grams per liter of aqueous phase of the composition according to the invention, this treatment lasting approximately one hour.

The term “critical pressure” is understood to mean the minimum pressure necessary for the introduction of a phase dispersed in a continuous phase through a porous glass membrane having a determined pore size. The critical pressure (in kPa) is defined by the following equation:

Pc = 4γ _ow cosθ / D _m , in which γ _ow is the interfacial tension (mN / m), θ is the contact angle (rad) and D _m is the average pore size (μm) of the glass membrane porous ...

In the process of the invention, the pressure used is preferably Pc + 20 kPa. A membrane having a pore size ranging from 0.1 to 5 μm can be used, for example, using a pressure preferably ranging from 350 to 30 kPa (3.5 to 0.3 bars). Preferably, the membrane used has a pore size of 0.3 μm, 0.7 μm or 2.8 μm and a pressure ranging from 220 to 320 kPa (2.2 to 3.2 bar) is then used. ), from 140 to 200 kPa (1, 4 to 2 bars) and from 30 to 70 kPa (0.3 to 0.7 bars).

The following examples illustrate the invention. In these examples, the percentages are given by weight.

Example 1:

Phase A Pemulen TR2 0.75% Triethanolamine 0.75% Preservatives 0.2% Demineralized water qs 100%

Phase B

Volatile silicone oil (cyclopentasiloxane) 20% Procedure: A membrane having a pore size of 0.7 μm is immersed in one liter of demineralized water containing 2 grams of phase A, then it is placed under vacuum and ultrasound for one o'clock.

After this treatment of the membrane, phase A is pumped to pass inside the membrane. Phase B is pressurized up to the critical pressure of 170 kPa (1.7 bar). Phase B is then emulsified in phase A under a pressure of 190 kPa (1.9 bars).

A very fine emulsion which is very pleasant to apply is obtained.

Claims

1. Emulsion comprising an oily phase dispersed in an aqueous phase, characterized in that the globules of the oily phase have an average size of less than 20 microns, in that the oily phase constitutes at least 15% by weight relative to the total weight of the emulsion and in that the aqueous phase contains at least one copolymer consisting of a majority fraction of monoolefinically unsaturated C ₃ -C ₆ carboxylic acid monomer or of its anhydride and of a minority fraction of fatty chain ester monomer acrylic acid, and in that it is free of surfactant. 2. Emulsion according to claim 1, characterized in that the quantity of carboxylic acid monomer or of its anhydride in the copolymer varies from 80 to 98% by weight and that the quantity of ester monomer varies from 20 to 2% by weight, the weight percentages being expressed relative to the total weight of the two monomers. 3. Emulsion according to claim 1 or 2, characterized in that the carboxylic acid monomer is a compound of formula (I): R CH „= C-COOH (0 where R is hydrogen, halogen, hydroxyl group, lactone group, iactam group, cyanogen group, monovalent alkyl group, aryl group, alkylaryl group, aralkyl group or cycloaliphatic group and the monomer ester is a compound of formula (II):

where R-, is chosen from the group formed by hydrogen, a methyl radical and an ethyl radical and R ₂ is a C ₈ -C ₃₀ alkyl group. 4. Emulsion according to the preceding claim, characterized in that the carboxylic acid monomer is chosen from acrylic acid, methacrylic acid or their mixtures, and that the ester monomer is chosen from the monomers of formula (II) in which R ^ is hydrogen or methyl and R ₂ is a Cιo ^_ ₂₂ alkyl group. 5. Emulsion according to any one of the preceding claims, characterized in that the copolymer is present in an amount ranging from 0.1 to 4% by weight and preferably from 0.1 to 2% by weight of the total weight of l 'emulsion. 6. Emulsion according to any one of the preceding claims, characterized in that the average size of the oily phase globules ranges from 0.5 to 15 microns. 7. Emulsion according to any one of the preceding claims, characterized in that the oily phase of the emulsion represents from 15 to 45% by weight and preferably from 20 to 30% by weight of the total weight of the emulsion. 8. Emulsion according to any one of the preceding claims, characterized in that it constitutes a cosmetic and / or dermatological composition. 9. Emulsion according to any one of the preceding claims, characterized in that it contains at least one additive chosen from hydrophilic active agents, lipophilic active agents, preservatives, antioxidants, perfumes, solvents, fillers, filters sunscreen, pigments, coloring matters, basic agents, acid agents, lipid vesicles and gelling agents. 10. Cosmetic use of the emulsion according to any one of claims 1 to 9 for the treatment, protection, care and / or cleaning of the skin, mucous membranes and / or hair, and / or for make-up. of the skin and / or mucous membranes. 11. Use of the emulsion according to any one of claims 1 to 9 for the manufacture of a dermatological composition intended for the treatment and / or the protection of the skin, mucous membranes and / or the hair. 12. A method of manufacturing an emulsion as defined in claims 1 to 9, consisting in introducing under pressure the oily phase into the aqueous phase containing the copolymer, through a hydrophilic porous glass membrane having an average pore size ranging from 0.1 to 5 μm and preferably from 0.3 to 3 μm, at a pressure higher than the critical pressure. 13. The manufacturing method according to claim 12, characterized in that the pressure ranges from 30 to 350 kPa.