Water-in-oil emulsion containing gelled aqueous phase, useful as cosmetic, pharmaceutical, veterinary or detergent compositions, where the aqueous phase includes a polyelectrolyte polymer

The present invention relates to emulsions of water-in-oil type, with a high aqueous content, their preparation process and their uses.

Technological background

Emulsions make it possible to convey both water-soluble and fat-soluble substances and therefore find application in particular in the cosmetics, pharmaceutical and veterinary fields, and in the field of detergents.

In the cosmetics field, there is a requirement on the part of the user of products in the form of emulsions to have available emulsions which have appropriate sensory characteristics. Emulsions which provide a feeling of freshness and which are felt when applied to the skin as not “sticky” are particularly in demand.

Emulsions are classified according to the nature of the continuous phase (also called the external phase), in which droplets of the other phase (called the internal phase) are dispersed.

In the case where the oil droplets are dispersed in an aqueous continuous phase, the system is called an emulsion of the oil-in-water (O / W) type.

In the case where the water droplets are dispersed in an oily continuous phase, the emulsion is of the water-in-oil (W / O) type.

In general, among these two types of emulsions, it is easier to manufacture emulsions of the oil-in-water (O / W) type, because emulsions of the W / O type are inherently thermodynamically unstable. Indeed, if we mix equal quantities of water and oil, we always observe the formation of an emulsion with an aqueous continuous phase, because the cohesive forces between water molecules are stronger than those between molecules. of oil.

However, emulsions with a continuous oily phase (W / O) have many advantages:

- the separation between the water droplets reduces the possibility of proliferation of microorganisms. The use of antiseptics, essential when the continuous phase is aqueous, can be avoided;

- They keep well at low temperature, being much less sensitive in this respect than O / W type emulsions;

the continuous oily phase covers the skin and protects it from dehydration and against external substances.

In the development of a continuous oily phase emulsion system, two types of modifications have been considered:

- mechanical modifications concerning the combination of phases (order of addition of phases, flow control during the combination of phases, phase temperature, stirring speed, etc.);

- changes in the chemical constituents resulting in the stabilization of the emulsion.

Regarding mechanical modifications, the operating protocols implemented to prepare W / O generally require:

a) a significant energy input, in the form of thermal activation (the aqueous and fatty phases are typically heated to 80 ° C.), which must sometimes be followed by a well-controlled gradual cooling; and or

b) the creation of turbulence in the two-phase medium to be emulsified (high stirring speed (thousands of revolutions per minute) and high shear caused by specific geometries of the stirrers).

With regard to chemical changes, we can cite:

a) the use of microcrystalline waxes, such as ozokerite, which absorb oil and prevent its exudation;

b) the use of liquid paraffins as the fatty phase, as these are easier to emulsify;

c) the addition of inorganic salts such as in particular sodium chloride or magnesium chloride, making it possible to increase the cohesion of the interfacial film.

US Pat. No. 5,746,945 describes emulsions of the water-in-oil type which are stabilized by an emulsifying system having two components: a) a polyalkyl polyether polysiloxane copolymer and b) a derivative of phthalic anhydride (a monoamide). The method of preparing emulsions in this document consists of the gradual addition of the aqueous phase to the oily phase. The two phases are each independently heated to 160 to 165 ° F (71 to 74 ° C) before being combined to obtain the emulsion.

Document WO-97/40814 describes W / O emulsions intended in particular to be used for impregnating baby wipes. The organic phase of emulsions necessarily contains a wax. The emulsifiers used are of the carboxylic acid type, substituted by hydrocarbons, or ABA block copolymers, involving monomers such as 12-hydroxystearic acid and ethylene glycol, or an alkyldimethicone copolyol. With respect to the process used to prepare the emulsions, the fatty phase and the aqueous phase are typically heated to 160 ° F (71 ° C) and then mixed at that temperature to obtain the emulsion.

The typical procedures of the prior art therefore present a certain number of drawbacks, linked in particular to the need to provide a significant energy supply to produce the emulsion.

One problem to be solved therefore consists in providing W / O emulsions with a high aqueous content, which in particular have a fresh and non-sticky texture.

Another problem to be solved consists in having a process for preparing such emulsions, which is:

- simple, that is to say that the number of steps implemented is reduced and that factors such as the exact control of the phase introduction rates are not critical for the correct operation of the process, and

- economical, that is to say that it does not require spending a lot of energy either to heat the phases to be combined or in the vigorous stirring to be provided during the preparation of the emulsion.

Summary of the invention

It has now been discovered, and this is the basis of the present invention, that by adding an oily phase to a gelled aqueous phase, it is possible to obtain W / O emulsions having the aforementioned characteristics, without thermal input and important mechanics.

According to a first aspect, the present application therefore relates to an emulsion consisting of an oily external phase and of a gelled aqueous phase, said aqueous phase representing from 60 to 98% by weight, preferably from 80 to 98% by weight. , of the composition, characterized in that:

- the aqueous phase comprises a polymer of polyelectrolyte type, the ionic sites of which are associated with their counterions, and

the oily phase comprises one or more oils and an emulsifying system of lipophilic nature comprising one or more emulsifying surfactants.

According to a second aspect, the present application relates to a process for preparing an emulsion of water-in-oil type with a high aqueous content comprising the following steps:

a) a fatty phase comprising one or more oils is prepared in the presence of an emulsifying system of lipophilic nature comprising one or more emulsifying surfactants;

b) independently of the fatty phase, a gelled aqueous phase containing a polymer of polyelectrolyte type is prepared;

c) the fatty phase is added to the aqueous phase.

According to a third aspect, the present application relates to cosmetic, pharmaceutical, veterinary or detergent preparations containing an emulsion as defined above.

Detailed description of the present invention

In accordance with the process of the invention, a fatty phase is first prepared comprising one or more oils chosen in particular from:

- oils of vegetable origin, such as sweet almond oil, coconut oil, castor oil, jojoba oil, olive oil, rapeseed oil, peanut oil, sunflower oil, wheat germ oil, corn germ oil, soybean oil, cottonseed oil, alfalfa oil, corn seed oil, poppy, pumpkin oil, evening primrose oil, millet oil, barley oil, rye oil, safflower oil, bancoulier oil, passionflower, hazelnut oil, palm oil, shea butter, apricot kernel oil, calophyllum oil, sysymbrium oil, avocado oil, calendula oil ;

- vegetable oils and their ethoxylated methyl esters;

- oils of animal origin, such as squalene, squalane;

- mineral oils, such as paraffin oil, petrolatum oil and isoparaffins;

- synthetic oils, in particular esters of fatty acids such as butyl myristate, propyl myristate, cetyl myristate, isopropyl palmitate, butyl stearate, hexadecyl stearate, d 'stearate isopropyl, octyl stearate, isocetyl stearate, dodecyl oleate, hexyl laurate, propylene glycol dicaprylate, esters derived from lanolic acid, such as isopropyl lanolate, lanolate isocetyl, monoglycerides, diglycerides and triglycerides of fatty acids such as glycerol triheptanoate, alkylbenzoates, polyalphaolefins, polyolefins such as polyisobutene, synthetic isoalkanes such as isohexadecane, isododecane, perfluorinated oils and silicone oils. Among the latter, mention may more particularly be made of dimethylpolysiloxanes, methylphenylpolysiloxanes, silicones modified with amines, silicones modified with fatty acids, silicones modified with alcohols, silicones modified with alcohols and fatty acids, silicones. modified with polyether groups, modified epoxy silicones, silicones modified with fluorinated groups, cyclic silicones and silicones modified with alkyl groups.

The water-in-oil emulsion generally comprises from 2 to 40% by weight, preferably from 2 to 20% by weight, of oil (s).

The fatty phase is prepared in the presence of an emulsifying system of lipophilic nature, comprising one or more emulsifying surfactants.

Among the emulsifying surfactants capable of being used in the context of the present invention, mention will in particular be made of lipoamino acids and their salts; lipopeptides and their salts; sorbitan esters, for example the product sold under the name MONTANE® 80 by the company SEPPIC; polyglycerol esters, for example the products sold under the name ISOLAN® GI34 by BASF and PLUROL® DIISOSTEARIQUE by GATTEFOSSE; ethoxylated castor oil and ethoxylated hydrogenated castor oil, for example the product sold under the name SIMULSOL® 989 by the company SEPPIC; glycerol stearate; polyglycol or polyglycerol polyhydroxystearates such as for example the products called HYPERMER® B246, ARLACEL® P135 marketed by the company UNIQEMA, the product called DEHYMULS® PGPH marketed by the company COGNIS, the product called DECAGLYN® 5HS marketed by the company NIKKO; polyethylene glycol-alkylglycol copolymers such as PEG-45 dodecylglycol copolymer such as the product sold under the name ELFACOS ST 9® by the company AKZO, ethoxylated sorbitan esters such as for example the products marketed under the name MONTANOX® by the company SEPPIC; weakly ethoxylated protein acylates (from 1 to 3 EO groups); ethoxylated beeswax, for example the product called APIFIL® sold by the company GATTEFOSSE; cationic emulsifiers such as aminoxides, quaternium 82 and the surfactants described in patent application WO 96/00719 and mainly those whose fatty chain comprises at least 16 carbon atoms; sucrose esters, ethoxylated or unethoxylated methylglucoside esters; ethoxylated fatty acids; ethoxylated fatty alcohols; anionic emulsifiers such as decylphosphate or cetearyl sulphate; aluminum polyoxystearate, such as, for example, the product sold under the name MANALOX® sold by the company RHODIA; magnesium stearate; aluminum stearate.

Nonionic and anionic silicone emulsifying surfactants are also likely to be used in the context of the present invention, even if for practical reasons (they can lead to a modification of the sensory properties of the emulsions obtained), they do not represent an aspect. preferred of the invention.

It is also possible to use emulsifying surfactants of alkylpolyglycoside type, for example those described in patent application FR-A-2 790 977, in particular xylose derivatives.

It is also possible to advantageously use an emulsifier based on alkylpolyglycosides and fatty diols, comprising in particular:

- 5 to 95 parts by weight of a mixture of alkylpolyglycosides consisting of the reaction products of a saccharide and of a dimerdiol having 36 carbon atoms;

- 95 to 5 parts by weight of a dimerdiol having 36 carbon atoms.

Preferred emulsifiers, meeting the above definition include:

- 5 to 60 parts by weight of the aforementioned mixture of alkylpolyglycosides; and

- 95 to 40 parts by weight of dimerdiol having 36 carbon atoms.

The mixture of alkylpolyglycosides consisting of the reaction products of a saccharide and of a dimerdiol having 36 carbon atoms is in fact composed of a mixture in all proportions of hydroxyalkylpolyglycosides (products resulting from the acetalization of one of the two hydroxyl groups of dimerdiol) and polyglycosylalkylpolyglycosides (products resulting from the acetalization of the two hydroxyl groups of dimerdiol).

These alkylpolyglycosides can be represented, respectively by the following formulas I and II:

HO-RO (G)_not (G)_m-OR-O- (G)_p (I) (Π) in which:

G represents a saccharide residue;

R represents a disubstituted group derived from dimer alcohol from the hydrogenation of dimer acid;

n, m and p represent the average degree of polymerization of each saccharide residue.

The product known by the name dimeric acid is a dibasic acid having 36 carbon atoms, the majority compound of which can be represented by the formula:

(CH₂)₅-CH₃_XCH

CH ÇH- (CH₂)₅(-CH₃)

CH XH-CH = CH- (CH_?)₇-COOH

CH

I (CH₂)₇-COOH

The aforementioned alkylpolyglycosides may contain, as saccharide residue, a residue of glucose or dextrose, fructose, galactose, mannose, ribose, xylose, preferably a residue of glucose or xylose.

It should also be noted that each unit of the polysaccharide part of the aforementioned alkylpolyglycosides can be in α or β anomeric form, and the saccharide residue can be of furanoside or pyranoside type.

The average degree of polymerization of each saccharide residue is generally between 1.05 and 2.5, more preferably between 1.1 and 2.

The expression alkylpolyglycoside used in the context of the present application therefore denotes either an alkylmonooside (degree of polymerization equal to 1) or an alkylpolyglycoside (degree of polymerization greater than 1).

The dimerdiol used for the preparation of the above emulsifying surfactant is a diol obtained from the hydrogenation of dimer acid.

It is marketed in particular by the company COGNIS under the name SPEZIOL® C 36/2.

This compound, due to its origin, may contain minor proportions of impurities. Such impurities can be present in amounts of up to 30% by weight of the total weight of diol.

Consequently, the emulsifying surfactants based on alkylpolyglycosides and fatty diols can comprise, in corresponding minor proportions, such impurities, or the reaction products of these impurities with a saccharide.

The emulsifying surfactants based on alkylpolyglycosides and fatty diols which can be used in the context of the present invention can be prepared by simple mixing of their constituents in the desired predetermined proportions.

On an industrial scale, they will preferably be prepared according to one of the two routes conventionally used for the synthesis of alkylpolyglycosides, and for example by reaction, in an acidic medium, between the dimerdiol and a saccharide having an anomeric OH, such as than glucose or dextrose.

Where appropriate, this synthesis may be supplemented by operations of neutralization, filtration, distillation or partial extraction of the excess fatty diol or of bleaching.

It may also be particularly advantageous to use an emulsifying surfactant based on alkylpolyxyloside, as described in application EP-A-1142901, of formula:

RO- (X)_P in which :

p represents a decimal number between 1 and 5,

X represents the rest of the xylose, and

R represents a branched alkyl radical:

CH (C_notH_{2n + 1})(VS_mH_{2m + 1}) -CH₂in which m is an integer between 6 and 18, n is an integer between 4 and 18 and the sum n + m is greater than or equal to 14;

or else, in a particularly preferred embodiment, a composition consisting of a mixture of at least two compounds as defined above;

or else a composition comprising more than 0% by weight and less than 100% by weight, preferably from 1% to 60% by weight, of a compound or of a mixture of compounds defined above and more than 0 % by weight and less than 100% by weight, preferably from 40% to 99% by weight, of a compound or a mixture of compounds of formula ROH in which R has the meaning mentioned above.

Particularly advantageously, a mixture of alkylpolyxyloside RO- (X) is used._P and its corresponding alcohol ROH, in the proportions indicated above.

Advantageously, an emulsifying system is used containing at least one emulsifying surfactant chosen from alkylpolyglycosides, compositions of alkylpolyglycosides and fatty alcohols, esters of polyglycerols or of polyglycols or of polyols such as polyhydroxystearates of polyglycols or of polyglycerols. .

Even more advantageously, an emulsifier system containing a polyol polyhydroxystearate or a polyglycerol ester is used, in combination with an alkylpolyglycoside and fatty alcohol composition.

The emulsions according to the present invention can contain up to 10% by weight of a co-emulsifier.

Among the co-emulsifiers which may be used in the context of the present invention, mention will in particular be made of lipoamino acids and their salts, lipopeptides and their salts, sorbitan esters, polyglycerol esters, ethoxylated hydrogenated castor oil. , glycerol stearate, cationic emulsifiers such as, for example, aminoxides, quaternium 82, sucrose esters, ethoxylated or non-ethoxylated methylglucoside esters, ethoxylated fatty acids, ethoxylated fatty alcohols, anionic emulsifiers such as decylphosphate or cetearyl sulphate.

Nonionic and anionic silicone emulsifying surfactants are also likely to be used as co-emulsifiers in the context of the present invention, even if for practical reasons (they can lead to a modification of the sensory properties of the emulsions obtained), they do not represent a preferred aspect of the invention.

Independently of the fatty phase, a gelled aqueous phase is prepared containing a polymer of polyelectrolyte type, the ionic sites of which are associated with their counterions. Among the polymers of polyelectrolyte type capable of being used in the context of the present invention, there may be mentioned:

homopolymers based on a monomer having a strong acid function, partially or totally salified,

- homopolymers based on a monomer having a weak acid function, partially or totally salified,

- homopolymers based on a cationic monomer,

- copolymers based on at least one monomer having a partially or totally salified strong acid function, copolymerized:

o either with at least one monomer having a partially or totally salified weak acid function, o or with at least one neutral monomer, ίο

- copolymers based on a cationic monomer copolymerized with at least one neutral monomer,

- copolymers based on at least one monomer having a weak acid function which is partially or totally salified, copolymerized:

o either with at least one monomer having a partially or totally salified weak acid function, o or with at least one neutral monomer.

In this context, the phrase partially or totally salified means that the strong acid or weak acid functions are partially or totally salified in particular in the form of an alkali metal salt, such as the sodium salt or the potassium salt, of an ammonium salt. or an amino alcohol salt, such as, for example, the monoethanolamine salt.

The strong acid function of the monomer can in particular be the sulphonic acid function or the phosphonic acid function, said functions being partially or totally salified.

Said monomer will be advantageously chosen from styrene sulfonic acid or 2-sulfoethyl methacrylate, styrene phosphonic acid, partially or totally salified, acid-2-methyl - [(1-oxo-2-propenyl) amino] Partially or totally salified propane sulfonic acid (AMPS) in the form of sodium salt, ammonium salt or monoethanolamine salt.

The weak acid function of the monomer can in particular be the partially or totally salified carboxylic acid function. Said monomer can in particular be chosen from acrylic acid, methacrylic acid, itaconic acid or maleic acid partially or totally salified in the form of sodium salt, potassium salt, ammonium salt or monoethanolamine salt.

When the polymer is a copolymer based on a monomer having a partially or totally salified strong acid function, copolymerized with at least one neutral monomer, said neutral monomer is in particular chosen from acrylamide, methacrylamide, vinylpyrrolidone, (2-hydroxyethyl) acrylate, (2,3-dihydroxypropyl) acrylate, (2-hydroxyethyl) methacrylate or (2,3-dihydroxypropyl) methacrylate or an ethoxylated derivative with a molecular weight between 400 and 1000, of each of these hydroxylated esters, tris (hydroxymethyl) -acrylamidomethane or tris ( hydroxymethyl) methacrylamidomethane or an ethoxylated derivative with a molecular weight between 400 and 1500, of each of these amides.

The fact that the aqueous phase of the emulsions according to the present invention comprises a polyelectrolyte whose ionic sites are associated with their counterions contributes to the fact that the additional supply of inorganic salts is not necessary.

The polymers mentioned above can be branched or crosslinked. The term “branched polymer” denotes a nonlinear polymer which has pendant chains so as to obtain, when this polymer is dissolved in water, a strong state of entanglement leading to very high low gradient viscosities. The term “crosslinked polymer” denotes a nonlinear polymer in the form of a three-dimensional network which is insoluble in water, but swellable in water and therefore leading to the production of a chemical gel.

When the polymer is crosslinked and / or branched, the crosslinking agent and / or the branching agent is in particular chosen from diethylenic and polyethylenic compounds, and most particularly from diallyloxyacetic acid or one of its salts and in particular its salt. sodium, triallylamine, trimethylol propanetriacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, diallylurea or methylene bis (acrylamide).

The crosslinking and / or branching agent is generally used in the molar proportion expressed relative to the monomers used, from 0.005% to 1%, in particular from 0.01% to 0.2% and more particularly from 0, 01% to 0.1%.

In general, the polymers of polyelectrolyte type which are suitable for producing emulsions according to the present invention are therefore copolymers or homopolymers, which may or may not be crosslinked or branched, comprising monomers having a strong acid or weak acid function partially or totally. salified, or a cationic function.

Among the polymers of polyelectrolyte type which are very particularly suitable for carrying out the process of the present invention, we can cite the derivatives of acrylamide, of acrylic acid and of vinylpyrolidone, such as copolymers of acrylic acid. and 2-methyl - [(1-oxo-2propenyl) amino] 1-propanesulfonic acid (AMPS), copolymers of acrylamide and 2-methyl acid - [(1-oxo- 2-propenyl) amino] 1-propane sulfonic acid, copolymers of 2-methyl - [(1-oxo-2-propenyl) amino] 1-propanesulfonic acid and (2-hydroxyethyl) acrylate, the homopolymer of 2-methyl acid - [(1-oxo2-propenyl) amino] 1-propane sulfonic acid, the homopolymer of acrylic acid, the copolymers of acryloyl ethyl trimethyl ammonium chloride and of acrylamide, the copolymers of AMPS and vinylpyrrolidone, copolymers of acrylic acid and of alkyl acrylates whose carbon chain comprises between ten and thirty carbon atoms, copolymers of AMPS and of alkyl acrylates whose carbon chain comprises between ten and thirty carbon atoms.

Such polymers are generally prepared by a reverse phase polymerization process, and are in particular marketed respectively under the names SIMULGEL® EG, SEPIGEL® 305, SIMULGEL® NS, SIMULGEL® 800 and SIMULGEL® A by the company SEPPIC. They involve partially or fully salified forms of acidic monomers. The corresponding monomer (s) is (are) dissolved in drops of water dispersed in a fatty phase using a surfactant. In this type of polymerization, each drop of water in the water-in-oil emulsion in itself constitutes a small reactor. This system minimizes the probabilities of termination reactions and results in polymer chains of higher molecular weight. At the end of the reaction, a hydrophilic surfactant and water are added. The polymer expands, no longer being constrained by the size of the drop of water in which it was synthesized, resulting in a soft solid, characterized by a three-dimensional structure.

This preparation process uses surfactants, such as sorbitan esters, mannitan esters, polyhydroxystearates of polyglycols, polyglycerols or polyols, alkanolamides on linear or branched fatty chains, ethoxylated sorbitan esters, esters ethoxylated mannitan, ethoxylated nonylphenols, ethoxylated octylphenols. As a result, the surfactants mentioned above can be present in the gelled aqueous phase during the implementation of the process of the invention.

Advantageously, the dry weight of said polyelectrolyte constitutes between 0.1% and 4% and preferably between 0.5% and 2% of the weight of the aqueous phase, if the process for preparing such a polyelectrolyte results from a polymerization process precipitous; or the dry weight of said polyelectrolyte constitutes between 0.25% and 4% and preferably between 0.5% and 2% of the weight of the aqueous phase if the process for preparing such a polyelectrolyte results from a process for the preparation of reverse emulsion polymerization.

The polyelectrolyte type polymers used in the process of the present invention have shear thinning (non-Newtonian) behavior, that is to say that the observed viscosity varies as a function of the shear gradient.

Without wishing to be bound by any particular theory, it is believed that this shear-thinning (non-Newtonian) behavior is likely related to the three-dimensional structure of polyelectrolyte-type polymers, which also influences the physical properties of emulsions. There is therefore a correlation between the behavior of polymers in terms of viscosity and their ability to facilitate the formation of emulsions.

Advantageously, the polymers of polyelectrolyte type which can be used in the context of the present invention exhibit a non-Newtonian rheological behavior in solution, characterized by a gradient index of between 0.1 and 0.7, and preferably between 0.2 and 0.5.

Advantageously, the gelled aqueous phase obtained by dissolving the polyelectrolyte-type polymer will have a viscosity of between 0.5 and 300 Pa.s, preferably between 1.0 and 150 Pa.s and more particularly between 5 and 100 Pa.s. , measured on a BROOKFIELD LV viscometer (6 rpm, 20 ° C).

The water-in-oil emulsion according to the present invention may also optionally contain up to 10% by weight of a stabilizer.

Among the stabilizing agents which may be used in the context of the present invention, mention may be made of hydrogenated castor oil; stearic acid and its metal salts such as aluminum stearate; hydrophobic silicas; polymers such as the products sold under the name KRATON® POLYMERS by the company KRATON; clays such as hectorite or bentonite; hydrophobic modified starches such as, for example, the product sold under the name DRY FLO PC® by the company NATIONAL STARCH; polymethylmethacrylates, whether or not crosslinked, such as MICROPEARL sold by the company SEPPIC, polyamides, such as Orgasol 2002 sold by the company ATOCHEM.

Waxes of plant, animal or mineral origin, such as beeswax, carnauba wax or ozokerite, are also likely to be used in the context of the present invention, even if for practical reasons, they do not represent a preferred aspect of the invention.

In a manner known per se, these emulsions can also comprise one or more compounds chosen from humectants, such as for example glycerin, preservatives such as for example the products known under the name SEPICIDE® and marketed by the company SEPPIC, the products. dyes, perfumes, cosmetic active ingredients, mineral or organic sun filters, mineral fillers such as iron oxides, titanium oxides and talc, synthetic fillers such as nylons and poly (methyl methacrylate) crosslinked or not, silicone elastomers, sericite and plant extracts.

The water-in-oil emulsion can also comprise one or more electrolyte mineral salts, such as for example magnesium chloride, magnesium sulfate, sodium borate or sodium chloride, in an amount ranging from 0.1% at 5% by weight. These electrolytes are not, however, essential for obtaining the emulsions in accordance with the invention.

These compounds can be introduced into the aqueous phase or into the oily phase, depending on their affinity for these phases.

The emulsions according to the invention are obtained by adding the fatty phase to the aqueous phase. It is possible to operate at temperatures up to 80 ° C. However, it is advantageous to minimize the energy expenditure represented by the heating of the phases and it will therefore be preferable to produce the emulsion at a temperature below 55 ° C. Even more preferably, the fatty phase will be added to the gelled aqueous phase at a temperature between 20 ° C and 35 ° C, that is to say at room temperature.

The emulsion according to the invention can be produced by mixing the two phases at a stirring speed exceeding 1500 revolutions per minute. However, it is advantageous to minimize the energy expended in the agitation used to produce the emulsion. A stirring speed of less than 1000 revolutions per minute will therefore be preferred, and a stirring speed of between 80 and 800 revolutions per minute will be most particularly preferred. Even more preferably, a stirring speed of between 80 and 450 revolutions per minute will be chosen, most particularly between 80 and 330 revolutions per minute.

The emulsions in accordance with the invention, which are stable over time, advantageously exhibit a polydispersity index greater than 41%, preferably greater than 45% and more preferably greater than or equal to 51%.

In this context, the polydispersity is determined by particle size analysis on a dilute form of the emulsion using a laser particle size analyzer of the MALVERN MASTERSIZER type.

In particular, by implementing the operating conditions of the process of the present invention, it is possible:

- to combine the fatty and aqueous phases which are both at room temperature,

- carry out this combination of phases without constraint as to the rate of introduction of one phase into the other

- to produce the emulsion with a gentle relative stirring by means of stirring systems of simple geometry (anchor, marine propeller, Rayneri type deflocculator),

avoiding the use of additional substances which are often essential for the preparation of W / O emulsions with a high aqueous phase content of the prior art, such as in particular microcrystalline waxes and inorganic electrolyte salts.

In addition, in the process according to the invention the order of addition of the phases is reversed with respect to the usual order of preparation of a water-in-oil (W / O) type emulsion. The fact of adding the fatty phase to the aqueous phase represents a gain in productivity in itself. Indeed, the fatty phase is of a smaller volume than the aqueous phase, which can allow the use of a single preparation tank 10, and has a much lower viscosity.

The W / O emulsion in accordance with the invention can advantageously be used in a cosmetic, dermocosmetic, pharmaceutical or veterinary preparation. The W / O emulsion according to the invention can also be used in a detergent preparation.

The invention will be illustrated by the following examples.

EXAMPLES

EXAMPLE 1 Preparation of a W / O emulsion

Two phases are prepared separately having the following compositions:

Fat phase

<td>Alkyl polyxylosides on Isofol® 20 prepared according to EPI 142901 PEG45 dodecylglycol copolymer (ELFACOS® ST9) Triglyceride C8-C10</td><td> 1,6 % 0,4 % 8,0 %</td>

<td>Aqueous phase Water Glycerine SIMULGEL® EG</td><td>qs 100% 5% 2%</td>

The fatty phase is heated moderately (50 ° C max.) Until the mixture of the three constituents is limpid. This fatty phase can be stored at room temperature for several days without causing crystallization of the various surfactants present.

The aqueous gel comprising water, a water-soluble polymer presented in reverse emulsion under the trade name Simulgel® EG, and glycerin is prepared at room temperature with conventional stirring for this type of preparation (RAYNERI deflocculator), at a temperature of 18 -25 ° C, with a stirring speed of 300 revolutions / min.

The fatty phase is added all at once to the gel, at room temperature and at a moderate stirring speed (200 to 300 revolutions / min.) With a stirrer equipped with an anchor-type mobile. This stirring is then maintained for ten minutes and no cooling step is necessary.

Furthermore, the emulsion obtained is a water-in-oil emulsion which, because of its high water content, has a strong shear-thinning character associated with a non-sticky and cool feel.

EXAMPLE 2 Preparation of a W / O emulsion

The same operating mode as that described in Example 1 is used in an 8 kg pilot reactor, equipped with a planetary mixer. The speed of emulsification with such a system was 100 revolutions / min and the maintenance phase, after the end of the addition of the fatty phase, lasted thirty minutes.

EXAMPLE 3 Influence of the energy provided by the quality of the agitation

The conditions of Example 1 were reproduced using a rotor stator type stirrer, operating at a speed of 4000 revolutions / minute, to produce the emulsion.

EXAMPLE 4: Combined Influences of Stirring Quality and Emulsification Temperature

The fatty phase is heated to 80 ° C. until the mixture of the three constituents is limpid.

The aqueous gel comprising water, a water-soluble polymer presented in reverse emulsion under the trade name Simulgel® EG, and glycerin is prepared at room temperature with conventional stirring for this type of preparation (RAYNERI deflocculator). It is then heated to 80 ° C.

The fatty phase is added all at once to the gel, and the stirring conditions of Example 3 were reproduced.

The emulsion is then cooled with moderate stirring with an anchor for 20 minutes.

The properties of the emulsions obtained according to Examples 1 to 4 are collated in Table 1.

Table 1

<td></td><td>Example 1</td><td>Example 2</td><td>Example 3</td><td>Example 4</td>

<td>Quantity produced</td><td>200g</td><td>8kg</td><td>200g</td><td>200g</td>

<td>Emulsification temperature</td><td>20-25 ° C</td><td>20-25 ° C</td><td>20-25 ° C</td><td>80 ° C</td>

<td>Stirring speed during emulsification</td><td>300 rpm</td><td>100 rpm</td><td>4000 rpm</td><td>4000 rpm</td>

<td>Characteristics of the emulsion obtained / SENSE (1)</td><td>E / H</td><td>E / H</td><td>E / H</td><td>E / H</td>

<td>VISCOSITY (2)</td><td>55.6 Pa.s</td><td>58.0 Pa.s</td><td>51.2 Pa.s</td><td>51.2 Pa.s</td>

(1) method: 1g of emulsion is diluted in 5g of demineralized water. If the emulsion is immiscible with water, it is W / O.

(2) method: BROOKFIELD LV 6rpm (at 20 ° C)

The comparison of Examples 3 and 4 with Example 1 shows that the direction of the W / O emulsion and the order of magnitude of the viscosity of the emulsion obtained are similar regardless of the amount of energy supplied to the system. .

On the other hand, the comparison of Examples 1 and 2 shows that the extrapolation of the process to a “pilot” scale results in similar performances, without significant modification of the operating conditions relating to the emulsification phase.

EXAMPLE 5; Study of the rheological behavior of an aqueous gel which can be used in the context of the present invention

The rheological behavior of different gelled aqueous phases, containing a polymer of polyelectrolyte type, was studied in the absence of an organic phase using a CSL500 imposed stress rheometer, sold by the company TA Instruments. The viscosity measurements are carried out at 20 ° C. The gradient indices, shown in Table 2, are obtained by calculating the convexity of the curve analyzed according to the mathematical model of the power law.

Table 2

<td>POLYELECTROLYTE STUDY</td><td>QUANTITY BY DRY WEIGHT IN AQUEOUS PHASE (%)</td><td>Gradient index</td><td>Brookfield Viscosity LV 6 RPM (Pa.s)</td>

<td>Copolymer of AMPS and acrylic acid</td><td> 0,96</td><td> 0,28</td><td> 70</td>

<td>Copolymer of AMPS and acrylamide</td><td> 0,8</td><td> 0,32</td><td> 60</td>

<td>Copolymer of AMPS and HydroxyEthyl Acrylate</td><td> 1,06</td><td> 0,31</td><td> 73</td>

<td>AMPS homopolymer</td><td> 0,95</td><td> 0,34</td><td> 61</td>

<td>Copolymer of AMPS and vinyl pyrolidone</td><td> 0,9</td><td> 0,34</td><td> 70</td>

<td>Copolymer of acrylic acid and C10-30 alkylacrylates</td><td> 0,7</td><td> 0,4</td><td> 69</td>

<td>Acrylic acid homopolymer</td><td> 1,5</td><td> 0,48</td><td> 61</td>

These results show that the aqueous gels, obtained from polymers of polyelectrolyte type, exhibit shear thinning. This profile is illustrated by the measurement of the gradient index

It is observed that the gradient index is generally less than 0.5 for gels based on polyelectrolyte polymers. Other studies, the results of which are not indicated, show that the aqueous gels obtained from polyethylene glycols have a gradient index close to 1, thus reflecting an almost Newtonian character.

EXAMPLE 6 Study of the polydispersity of an emulsion according to the present invention

Two phases are prepared separately having the following compositions:

Oily phase • FLUIDANOV® 20X¹ 0.50% (polyxyloside octyldodecanol and octyldodecanol) • ARLACEL® P 135 0.10% (PEG 1500 polyhydroxystearate) • LANOL® 99 4.40% (isononyl isononanoate)

Aqueous phase • SIMULGEL® EG 2.85% (sodium acrylate / sodium acryloyl dimethyl taurate / isohexadecane / Polysorbate 80) • Water

92,15% ¹ Prepared according to EP-A-1142901

These two phases were combined by following the procedure of Example 1 above.

The polydispersity of the water-in-oil emulsion obtained was measured according to the method indicated above (particle size analysis on a dilute form of the emulsion using a laser particle size analyzer of the MALVERN MASTERSIZER type).

The polydispersity index of the emulsion was greater than 51%. On the other hand, the gradient index of the aqueous phase of this water-in-oil emulsion was 0.28.

EXAMPLE 7 Influence of the viscosity of the aqueous gel on the direction of the emulsion

Two phases are prepared separately having the following compositions:

Fat phase

Alkyl polyxylosides on Isofol® 20 prepared according to EP1142901 2.4%

PEG45 dodecylglycol copolymer (ELFACOS® ST9) 0.6%

Triglyceride C8-C10 12.0%

Aqueous phase

Water qs 100%

SIMULGEL® EG x%

The conditions of Example 1 were reproduced using an anchor-type stirrer, operating at a speed of 300 revolutions / minute, to produce the emulsion.

The viscosity of the aqueous phase and the resulting direction of the emulsion, prepared according to the procedure described above, are given in Table 3.

Table 3

<td>Number of SIMULGEL® EG Employee (1)</td><td>Quantity of polyelectrolyte Used (1)</td><td>Viscosity of the aqueous phase Not</td><td>Characteristic of the emulsion / Direction (2)</td>

<td> 2,55 %</td><td> 1,0 %</td><td> &gt; 100</td><td>E / H</td>

<td> 1,70 %</td><td> 0,67 %</td><td> 65</td><td>E / H</td>

<td> 1,27 %</td><td> 0,50 %</td><td> 40</td><td>E / H</td>

<td> 0,85 %</td><td> 0,33 %</td><td> 2,0</td><td>E / H</td>

<td> 0,61 %</td><td> 0,24 %</td><td> 0,4</td><td>HEY</td>

(1) quantity expressed in% by mass relative to the total mass of the emulsion (2) method: lg of emulsion is diluted in 5g of demineralized water. If the emulsion is immiscible with water, it is W / O.

These results show that an aqueous phase whose viscosity is less than 0.5 Pa.s does not make it possible to produce a water-in-oil emulsion under the conditions of the invention.