WO2006003027A1

WO2006003027A1 - Cosmetic composition comprising a tensioning agent and an elastomeric film-forming polymer

Info

Publication number: WO2006003027A1
Application number: PCT/EP2005/007884
Authority: WO
Inventors: Guillaume Cassin
Original assignee: L'oreal
Priority date: 2004-07-01
Filing date: 2005-06-09
Publication date: 2006-01-12

Abstract

The present invention relates to a cosmetic composition comprising, in a physiologically acceptable medium: at least one tensioning agent, and at least one elastomeric film-forming polymer chosen such that the film obtained by drying this polymer, at ambient temperature and at a relative humidity of 55 %, has a mechanical profile defined by at least: (a) an elongation at break (ϵr) of greater than or equal to 800 %, (b) an instantaneous recovery (RI) at least equal to 75 %, after an elongation of 150 %, (c) a recovery (R300) at 300 seconds of greater than 80 %. It also relates to the use of this particular polymer for improving the remanence of the tensioning effect afforded by a tensioning agent, and also to a process for treating wrinkled skin by applying to said skin a composition as defined above.

Description

Cosmetic composition comprising a tensioning agent and an elastomeric film-forming polymer

The present invention relates to a cosmetic composition, in particular an anti-wrinkle composition, comprising, in a physiologically acceptable medium, a tensioning agent and a particular polymer capable of giving rise to remanence of the tensioning effect induced by the tensioning agent.

It also relates to the use of this particular polymer for improving the remanence of the tensioning effect afforded by a tensioning agent, and also to a process for treating wrinkled skin by applying to said skin a composition as defined above.

The general field of the invention is therefore that of ageing of the skin.

In the course of ageing of the skin, various signs appear, reflected in particular by a change in the structure and functions of the skin. One of these main signs is the appearance of fine lines and deep wrinkles, the size and the number of which increase with age. The skin microrelief becomes less uniform and has an anisotropic nature.

It is common practice to treat these signs of ageing with cosmetic compositions containing active agents capable of combating ageing, such as α-hydroxy acids, β-hydroxy acids and retinoids. These active agents act in particular on wrinkles by removing the dead cells from the skin and by accelerating the process of cell renewal. However, these active agents have the drawback of being effective in treating wrinkles only after they have been applied for a certain amount of time, i.e. an amount of time that may range from a few days to several weeks.

Now, the current needs are increasingly tending towards the production of compositions for obtaining an immediate effect, leading rapidly to smoothing-out of the wrinkles and/or fine lines and to the disappearance, even temporary, of fatigue marks. Such compositions are compositions comprising tensioning agents. It is specified that, the term "tensioning agent" is intended to mean compounds capable of having a tensioning effect, i.e. compounds that can make the skin taut and bring about a reduction in or even the immediate disappearance of wrinkles and fine lines.

These tensioning agents may in particular be polymers of natural or synthetic origin in aqueous dispersion, capable of forming a film that causes shrinkage of the stratum corneum, the superficial horny layer of the epidermis . The cosmetic or dermatological use of such polymer systems for attenuating the effects of ageing of the skin is described in patent application FR-A-2 758 083. Other tensioning agents consist of dispersions of inorganic colloidal particles, in particular of silica, as described in application EP-O 682 939, for example.

However, these tensioning agents sometimes give a sensation of discomfort to certain users, in particular those who have fragile skin. In addition, the tensioning effect that they afford does not last very long, since the film formed on the skin has a tendency to crack as a result of the facial expressions. The reason for this is that these tensioning agents form a relatively rigid and inflexible film on the skin.

The applicant has noted, surprisingly, that the use of particular elastomeric polymers as strengthening agents, in combination with a tensioning agent in a cosmetic composition, makes it possible to obtain films that have a long-lasting tensioning effect, said films being flexible and deformable from a mechanical point of view.

Some elastomeric polymers have already been described as being useful in hairstyling compositions, for maintaining the hair by forming thereon a film that is flexible and does not break (FR-2 801 202, FR-2 786 392, FR-2 786 391, FR-2 801 204) . However, these polymers have mechanical properties that are inferior to those of the strengthening polymers according to the present invention.

Other polymers corresponding to the criteria defined in the present invention, such as the products Neorez R987 and PA Marin UA310, have been described, moreover, as constituents of hair compositions that do not contain any tensioning agent within the meaning of the present invention (FR-2 801 203) .

Finally, document FR-2 815 350 describes novel cationic polyurethanes that can be applied to the skin, in particular in make-up compositions, so as to form non-sticky, non-breakable films capable of plastic and elastic distortions. These polyurethanes have mechanical properties similar to those of the strengthening polymers according to the present invention, but combining them with tensioning agents, in particular for improving the mechanical properties of the film formed by the tensioning agent, especially in anti-wrinkle compositions, is not suggested.

Thus, according to a first subject, the invention concerns a cosmetic composition comprising, in a physiologically acceptable medium: - at least one tensioning agent, and

- at least one elastomeric film-forming polymer chosen such that the film obtained by drying this polymer, at ambient temperature and at a relative humidity of 55%, has a mechanical profile defined by at least:

(a) an elongation at break (ε_r) of greater than or equal to 800%, (b) an instantaneous recovery (R₁) at least equal to 75%, after an elongation of 150%,

(c) a recovery (R₃₀₀) at 300 seconds of greater than 80%. The constituents of the composition according to the invention will now be described in greater detail.

Tensioning agent

According to the invention, the term "tensioning agent" is intended to mean any agent that produces, at a concentration of 7% in water, a retraction of isolated stratum corneum, measured with an extensometer, of more than 1%, and preferably of more than 1.5%, at 30⁰C in a relative humidity of 40%. The principle of the method consists in measuring the length of a test sample of stratum corneum isolated from human skin originating from a surgical operation, before and after treatment with the potential tensioning agent. To do this, the test sample is placed between the two jaws of the device, one of which is fixed and the other mobile, in an atmosphere at 30°C and 40% relative humidity. A tensile stress is then exerted on the test sample, and the curve of the strength (in grams) as a function of the length (in millimetres) is recorded, the length zero corresponding to the contact between the two jaws of the device. The tangent to the curve is then plotted in its linear region. The intersection of this tangent with the x-axis corresponds to the apparent length L₀ of the test sample at zero strength. The test sample is then slackened and 2 mg/cm² of the composition to be tested (7% solution of the tensioning agent under consideration) are then applied to the stratum corneum. After drying for 15 minutes, the above steps are again carried out in order to determine the length Li of the test sample after treatment. The percentage retraction is defined: % retraction = 100 x (Li-L₀) /L₀. In order to characterize a tensioning effect, this percentage must be negative, and the greater the tensioning effect, the higher the absolute value of the percentage retraction. The tensioning agent may in particular be chosen from: a) synthetic polymers; b) polymers of natural origin, in particular plant origin; c) mixed silicates; d) wax microparticles; e) colloidal particles of inorganic fillers; and mixtures thereof.

These various categories of tensioning agents will now be described. a) Synthetic polymers

The synthetic polymers that may be used as a tensioning agent can be chosen from:

- polyurethane polymers and copolymers;

- acrylic polymers and copolymers;

- sulphoisophthalic acid polymers; - grafted silicone polymers;

- water-soluble or water-dispersible polymers comprising water-soluble or water-dispersible units and units with an LCST;

- and mixtures thereof. The polyurethane copolymers, the acrylic copolymers and the other synthetic polymers according to the invention may in particular be chosen from polycondensates, hybrid polymers and interpenetrating polymer networks (IPNs) . For the purpose of the present invention, the term "interpenetrating polymer network" is intended to mean a mixture of two intermeshed polymers, obtained by simultaneous polymerization and/or crosslinking of two types of monomer, the mixture obtained having a single glass transition temperature.

Examples of IPNs that are suitable for use in the present invention, and also the process for preparing them, are described in patents US-β,139,322 and US-β,465,001, for example. Preferably, the IPN according to the invention comprises at least one polyacrylic polymer, and it more preferably also comprises at least one polyurethane or a copolymer of vinylidene fluoride and of hexafluoropropylene.

According to a preferred embodiment, the IPN according to the invention comprises a polyurethane polymer and a polyacrylic polymer. Such IPNs are in particular those of the Hybridur series that are commercially available from the company Air Products. An IPN that is particularly preferred is in the form of an aqueous dispersion of particles with a weight-average size of between 90 and 110 nm and a number-average size of approximately 80 nm. This IPN preferably has a glass transition temperature, Tg, that ranges from approximately -60⁰C to +100⁰C. An IPN of this type is in particular sold by the company Air Products under the trade name Hybridur X-01602. Another IPN that is suitable for use in the present invention has the reference Hybridur X18693-21.

Other IPNs that are suitable for use in the present invention include the IPNs consisting of a mixture of a polyurethane with a copolymer of vinylidene fluoride and of hexafluoropropylene. These IPNs may in particular be prepared as described in patent US-5, 349, 003. As a variant, they are commercially available in the form of a colloidal dispersion in water, in a ratio of the fluoro copolymer to the acrylic polymer of between 70:30 and 75:25, under the trade names Kynar RC-10, 147 and Kynar RC-IO, 151 from the company Atofina.

Examples of grafted silicone polymers are indicated in application EP-I 038 519, which is incorporated herein by way of reference. A preferred example of a grafted silicone polymer is polysilicone-8 (CTFA name) , which is a polydimethylsiloxane onto which are grafted, via a linking chain of thiopropylene type, mixed polymer units of the poly(meth) acrylic acid type and of the poly(alkyl (meth) acrylate) type. A polymer of this type is in particular available under the trade name VS 80 (at 10% in water) or LO 21 (in pulverulent form) from the company 3M. It is a copolymer of polydimethylsiloxane containing propylthio groups, methyl acrylate, methyl methacrylate and methacrylic acid.

The abovementioned synthetic polymers may be in the form of latex. As a suitable latex that may be used according to the invention as a tensioning agent, mention may in particular be made of polyester- polyurethane and polyether-polyurethane dispersions, such as those sold under the names "Avalure UR410 and UR460" by the company Noveon, and under the names "Neorez R974", "Neorez R981" and "Neorez R970", and also acrylic copolymer dispersions such as those sold under the name "Neocryl XK-90" by the company Avecia.

Use may also be made according to the invention of water-soluble or water-dispersible polymers comprising water-soluble or water-dispersible units and comprising units with an LCST, said units with an LCST having in particular a demixing temperature in water of 5 to 4O⁰C at a mass concentration of 1%. This type of polymer is more fully described in patent application FR 2 819 429. b) Polymers of natural origin The polymers of natural origin that may be used as a tensioning agent may be chosen from: - plant proteins and plant protein hydrolysates/

- polysaccharides of plant origin, optionally in the form of microgels, such as starch;

- latices of plant origin; - and mixtures thereof.

Examples of plant proteins and plant protein hydrolysates that may be used as tensioning agents according to the invention consist of proteins and protein hydrolysates of maize, of rye, of Triticum aestivum, of buckwheat, of sesame, of spelt, of pea, of bean, of lentil, of soybean and of lupin.

The polysaccharides that are suitable for the formulation of the compositions according to the invention are polysaccharides of natural origin capable of forming heat-reversible or crosslinked gels and solutions. The term "heat-reversible" is intended to mean that the gel state of these polymer solutions is obtained reversibly once the solution has cooled to below the characteristic gelling temperature of the polysaccharide used.

A first family of polysaccharides of natural origin that may be used in the present invention consists of carrageenans and most particularly kappa- carrageenan and iota-carrageenan. These are linear polysaccharides that are present in certain red algae. They consist of alternating β-1,3 and α-1,4 galactose residues, it being possible for many galactose residues to be sulphated. This family of polysaccharides is described in the book "Food Gels" edited by Peter Harris, Elsevier 1989, chapter 3. Another family of polysaccharides that may be used consists of agars. They are also polymers extracted from red algae and they consist of alternating 1, 4-L-galactose and 1,3-D- galactose residues. This family of polysaccharides is also described in chapter 1 of the book "Food Gels" mentioned above. A third family of polysaccharides consists of the polysaccharides of bacterial origin called gellans. They are polysaccharides consisting of alternating glucose, glucuronic acid and rhamnose residues. These gellans are described in particular in chapter 6 of the book "Food Gels" mentioned above. In the case of polysaccharides that form gels of the crosslinked type, in particular induced by the addition of salts, mention will be made of polysaccharides belonging to the alginate and pectin family.

Mention may also be made of chitosans and derivatives thereof, and pullulans and derivatives thereof. The tensioning polysaccharides may be present in the form of microgels as described in FR 2 829 025.

A particularly advantageous category of polysaccharides that may be used according to the invention consists of starch and its derivatives. Starch is a natural product well known to those skilled in the art. It consists of a polymer or a mixture of polymers, that may be linear or branched, consisting of units of α-D-glucopyranosyl. Starch is in particular described in "Kirk-Othmer Encyclopedia of Chemical Technology, 3rd edition, volume 21, p. 492-507, Wiley Interscience, 1983". The starch used in the present invention may be of any origin: rice, maize, potato, cassava, pea, Triticum aestivum, oat, etc. It may be natural or optionally modified by means of a treatment such as crosslinking, acetylation or oxidation. It may optionally be grafted. As starches that may be used in the composition according to the invention, mention may, for example, be made of that sold by the company Lambert-Riviere under the name Remi Dri. c) Mixed silicates

Another class of tensioning agents that may be used according to the invention consists of mixed silicates. This expression is intended to mean any of the silicates of natural or synthetic origin containing at least two different cations chosen from alkali metals (for example Na, Li or K) or alkaline earth metals (for example Be, Mg or Ca) and transition metals .

Use is preferably made of phyllosilicates, i.e. silicates having a structure in which the SiO₄ tetrahedra are organized in lamellae between which the metal cations are enclosed.

One family of silicates that is particularly preferred as tensioning agents is the laponite family. Laponites are magnesium lithium sodium silicates that have a layer structure similar to that of montmorillonites. Laponite is the synthetic form of the natural mineral known as "hectorite". The laponite sold under the name Laponite XLS or Laponite XLG by the company Rockwood may, for example, be used, d) Wax microdispersions Yet another class of tensioning agents that may be used in the present invention consists of dispersions of wax microparticles. These are particles with a diameter of generally less than 5 μm, or better still than 0.5 μm, and consisting essentially of a wax or of a mixture of waxes chosen, for example, from carnauba wax, candelilla wax or esparto grass wax. The melting point of the wax or the mixture of waxes is preferably between 50⁰C and 150⁰C. e) Colloidal particles of inorganic fillers As another variant, use may be made, as tensioning agent according to the invention, of colloidal particles of inorganic fillers . The term "colloidal particles" is intended to mean colloidal particles in dispersion in an aqueous, aqueous- alcoholic or alcoholic medium, having a number-average diameter of between 0.1 and 100 ran, preferably of between 3 and 30 ran.

Examples of inorganic fillers comprise: silica, cerium oxide, zirconium oxide, alumina, calcium carbonate, barium sulphate, calcium sulphate, zinc oxide and titanium dioxide. An inorganic filler that is particularly preferred is silica. Colloidal silica particles are in particular available in the form of an aqueous dispersion of colloidal silica from the company Catalysts & Chemicals under the trade names Cosmo S-40 and Cosmo S-50. A particular example of colloidal particles of inorganic fillers may be silica-alumina composite colloidal particles. The term "silica-alumina composite" is intended to mean silica particles in which the aluminium atoms have been partly substituted with silica atoms. These particles are in the form of aqueous dispersions and have no thickening property in water, alcohol, oil or any other solvent. At a concentration greater than or equal to 15% by weight in water, the viscosity of the solutions thus obtained is less than 0.05 Pa. s for a shear rate equal to 10 s^"1. The measurements are carried out at 25⁰C using a Haake RheoStress RS150 rheometer in the cone-plate configuration, the measurements of the measuring cone being: diameter: 60 mm and angle: 2°.

At a pH of 7, the silica-alumina composite colloidal particles according to the invention have a zeta potential of less than -20 mV, and preferably less than -25 mV. The measurements are carried out at 25⁰C using a Coulter Scientific Instrument Delsa 440SX device.

As silica-alumina composite colloidal particles that may be used in the compositions according to the invention, mention may, for example, be made of those sold by the company Grace under the names Ludox AM, Ludox AM X 6021, Ludox HSA and Ludox TMA. The tensioning agent may be included in the composition according to the invention at a content ranging from 0.01 to 20% by weight of active material, preferably from 1 to 10% by weight of active material, relative to the total weight of the composition. The term "active material" is intended to exclude the medium in which the tensioning agent is optionally solubilized or in dispersion, for example in the case of latices and of dispersions of colloidal particles. Elastomeric film-forming polymer As mentioned above, the composition according to the invention contains, besides the tensioning agent as defined above, at least one particular elastomeric film-forming polymer.

This particular polymer, in combination with the tensioning agent, confers on the composition, into which it is incorporated, a remanent tensioning effect by virtue of its ability to strengthen the tensioning film while at the same time giving it properties of suppleness. This remanence is quantified according to the invention by measuring the improvement in the mechanical properties of the tensioning film (more particularly by measuring the improvement in breaking strength) , as will be explained in the protocol that appears in the experimental section of this description.

For the purpose of the invention, the term "at least one" elastomeric film-forming polymer is intended to mean one or more (2, 3 or more) elastomeric film-forming polymers.

This elastomeric film-forming polymer is chosen such that the film obtained by drying this polymer, at ambient temperature and at a relative humidity of 55%, has a mechanical profile defined by at least: (a) an elongation at break (ε_r) of greater than or equal to 800%, preferably ranging from 800% to 3000%,

(b) an instantaneous recovery (R₁) at least equal to 75%, and preferably ranging from 75% to 100%, after an elongation of 150%,

(c) a recovery (R30₀) at 300 seconds of greater than 80%, and preferably ranging from 85% to 100%. For the purposes of the present invention, the expression "film obtained by drying at ambient temperature (22⁰C + 2⁰C) and at a relative humidity of 55% + 5%" is intended to mean the film obtained, under these conditions, from a composition containing 6% by weight of active material (a.m.) of elastomeric film- forming polymer in a solvent (water or ethanol) in which the film-forming polymer is soluble or dispersible, or in a mixture of solvents, in particular a mixture consisting of 30% by weight of ethanol and of 70% by weight of water, the amount of said composition being adjusted so as to obtain, in a matrix of polytetrafluoroethylene (PTFE) , a film with a thickness of 500 μm ± 50 μm. The drying is continued until the weight of the film no longer changes, which represents approximately 12 days.

For the purpose of the present invention, the elongation at break and the recovery rate are evaluated by means of the trials described below.

In order to carry out the tensile trials, the dried film obtained as described above is cut up into rectangle-shaped test samples 80 mm long and 15 mm wide.

The trials are carried out on a device sold under the name Lloyd or sold under the name Zwick under the same temperature and humidity conditions as for the drying, i.e. a temperature of 22⁰C ± 2°C and a relative humidity of 50% ± 5%.

The test samples are pulled at a speed of 20 mm/min and the distance between the jaws is 50 ± 1 mm.

The elongation at break is determined by visualization of the appearance of the first fracture appearing in the film when it is pulled. The value given is the percentage elongation ε_r = If/lo, where Io is the initial length of the test sample and If is the length of the test sample when the first fracture in the film is observed.

The instantaneous recovery (R₁) is determined in the following manner:

- the test sample is pulled by 150% (ε_max) , i.e. 1.5 times its initial length (I₀) , - the constraint is released by applying a return speed equal to the tensile speed, i.e. 20 mm/min, and the elongation (Si) of the test sample is measured as a percentage, after returning to zero constraint.

The % instantaneous recovery (Ri) is given by the following formula: R₁ = ( (Saax-εi) /ε_max) x 100

To determine the recovery at 300 seconds, the test sample, having undergone the above operations, is maintained at zero constraint for a further 300 seconds, and its percentage elongation (S3oo_s) is measured.

The % recovery at 300 seconds (R3oos) is given by the formula below:

R300S ⁼ ( ( £max^~S300s ) /^£max ) ^x 100

Advantageously, the polymer (s) of the composition according to the invention is (are) such that it (they) form(s), under the conditions of the above tests, a film having an elongation at break ranging from 800% to 3000%; an instantaneous recovery of 75% to 100%; and a recovery at 300 seconds ranging from 85% to 100%.

In the compositions in accordance with the invention, the elastomeric film-forming polymer or the mixture of elastomeric film-forming polymers is preferably present at a concentration ranging from 0.05% to 20% by weight, more preferably from 0.1% to 15% by weight, and for example from 0.25% to 10% by weight, relative to the total weight of the composition.

Advantageously, the elastomeric film-forming polymer is chosen from the group comprising polyurethanes, polyvinyl alcohols, polymers comprising at least one (meth) acrylic unit, and combinations thereof. It may be in the .form of a homopolymer or a copolymer. In particular, it is in a non-crosslinked form in the composition.

It may thus be a copolymer of N-methyl- diethanolamine, of poly(tetramethylene oxide) and of isophorone diisocyanate, such as that described in Example 1 below.

As a variant, it may be the polyether-based polyurethane sold by the company Avecia under the trade name Neorez R987 or the polycarbonate-based polyurethane sold by the company Sanyo Kasei under the trade name PA-Marin UA-310.

Preferably, the elastomeric film-forming polymer (s) of the invention is (are) soluble or dispersible in an aqueous or aqueous-alcoholic medium. In particular, the elastomeric film-forming polymer (s) is (are) soluble at at least 10 g of active material in 90 g of aqueous or aqueous-alcoholic (containing 70% water and 30% ethanol) medium, at ambient temperature and atmospheric pressure.

Advantageously, the film formed has a low water-sensitivity, for example in an atmosphere with a relative humidity of 30% to 80%, i.e. the film keeps its elastomeric properties for several hours. It is flexible, non-breakable, and follows the movements of the skin well. In particular, between 30% and 80% relative humidity, the elongation at break of the film obtained does not vary by more than 50% (+ 400%) and/or its instantaneous recovery does not vary by more than 25% (18.75%); in other words, between 30% and 80% relative humidity, the elongation at break of the film obtained is between 400% and 1200% and/or its instantaneous recovery is between 57% and 93%.

The composition according to the invention is generally suitable for topical application to the skin and therefore generally comprises a physiologically acceptable medium, i.e. a medium compatible with the skin and/or its integuments. It is preferably a cosmetically acceptable medium, i.e. a medium with a pleasant colour, odour and feel, and that does not generate any unacceptable discomfort (stinging, tightness, redness) , that may turn a consumer away from using this composition.

The composition according to the invention may be in any of the pharmaceutical forms conventionally used for topical application, and in particular in the form of dispersions of the aqueous lotion or gel type, of emulsions with a liquid or semi- liquid consistency of the milk type, obtained by dispersion of a fatty phase in an aqueous phase (O/W) or vice versa (W/0) , or of suspensions or emulsions with a soft, semi-solid or solid consistency of the cream or gel type, or else of multiple emulsions (W/O/W or 0/W/O) , of microemulsions, of vesicular dispersions of ionic and/or non-ionic type, or of wax/aqueous phase dispersions. These compositions are prepared according to the usual methods.

According to a preferred embodiment of the invention, the composition is in the form of an emulsion.

This composition may also contain various adjuvants commonly used in the cosmetics field, such as emulsifiers, including fatty acid esters of polyethylene glycol, optionally polyoxyethylenated fatty acid esters of sorbitan, polyoxyethylenated fatty alcohols and fatty acid esters or ethers of sugars such as sucrose or glucose; fillers; preserving agents; sequestering agents; fragrances; and thickeners and/or gelling agents, in particular polyacrylamides and acrylic copolymers.

Of course, those skilled in the art will take care to choose this or these optional additional compound(s) and/or the amount thereof in such a way that the advantageous properties of the composition according to the invention are not, or are not substantially, impaired by the envisaged addition. The composition according to the invention may also contain anti-ageing active agents having an effect complementary to the polymers defined above, such as at least one compound chosen from desquamating agents, moisturizers, agents for stimulating keratinocyte proliferation and/or differentiation, agents for stimulating collagen and/or elastin synthesis or for preventing degradation thereof, depigmenting agents, anti-glycation agents, agents for stimulating glycosaminoglycan synthesis, dermo- decontracting agents or muscle-relaxing agents, antioxidants and free-radical scavengers, and mixtures thereof.

A subject of the present invention is also the use of an ethylenic polymer as defined above, for improving the remanence of the tensioning effect afforded by a tensioning agent.

Finally, a subject of the present invention is a process for cosmetically treating wrinkled skin, comprising a step consisting in applying to said skin a composition as defined above.

The application is carried out according to the usual techniques, for example by application of creams, gels, sera or lotions to the skin intended to be treated, in particular the skin of the face and/or of the neck, in particular the skin around the eyes. In the context of this process, the composition may, for example, be a care composition or a make-up composition, in particular a foundation composition.

The invention will now be described with reference to the following examples given by way of non-limiting illustration.

EXAMPLES

Example 1; Synthesis of a polyurethane-based elastomeric film-forming polymer

The following monomers and solvents are introduced into a thermostated reactor equipped with a mechanical stirring system and a condenser:

- 1 mol of a mixture of monomers of diol type, i.e. of a mixture of N-methyldiethanolamine and of poly (tetramethylene oxide) with a weight-average molar mass equal to 2900, the N-methyldiethanolamine/ poly(tetramethylene oxide) molar ratio being equal to 3, and

- an amount of methyl ethyl ketone such that the concentration of monomers of diol type is equal to 75% by weight.

The mixture is heated with stirring up to a temperature of 70°C, and then a small molar excess, i.e. 1.03 mol, of isophorone diisocyanate is introduced dropwise, with stirring, over a period of approximately 2 hours. During this addition, an increase in the temperature up to the reflux of the solvent is observed. A sample is taken at regular intervals, and an IR absorption spectrum for said sample is plotted in order to follow the disappearance of the band corresponding to the isocyanate functions (2260 cm^"1) . When the absorption band for the -NCO functions no longer decreases, which is generally the case after approximately 5 hours, the reaction mixture is allowed to cool to ambient temperature and is then diluted with acetone until a concentration of polymer of approximately 40% by weight is obtained.

20 ml of ethanol are then added to the mixture obtained, in order to deactivate the residual -NCO functions, and the stirring is continued at ambient temperature until complete disappearance of the -NCO functions, i.e. of the IR absorption band at 2260 cm^"1.

A hydrochloric acid solution (2 mol/1) is added in an amount such that the amine groups are neutralized to the desired degree. The various organic solvents (methyl ethyl ketone, acetone and ethanol) are then eliminated by distillation under vacuum at a temperature of 40°C.

After elimination of the organic phase, water is added to the aqueous solution of polymer in an amount sufficient to obtain a concentration of polymer in water of approximately 25% by weight.

The polyurethane copolymer thus obtained consists of a copolymer of N-methyldiethanolamine, of poly(tetramethylene oxide) having a weight-average mass of 2900 and of isophorone diisocyanate, in a 3/1/4 molar ratio, and it has the following characteristics, measured as indicated above: ε_r = 1500%

Ri = 82%

R₃₀₀ = 92%.

Example 2 : Preparation of a cosmetic anti- wrinkle composition

The compositions A and B below were prepared in a manner that is conventional for those skilled in the art.

AM means "in terms of active material"

^(1> Dispersion at 41% by weight in water of colloidal silica particles having a mean particle diameter of 18 nm (Cosmo S-40 from Catalysts & Chemicals)

Example 3: Evaluation of the remanence of the tensioning effect The tensioning effect of the dispersion of colloidal silica has already been evaluated in application FR-2 823 113. The ability of the polymers according to the invention to increase the fissuring strength of the tensioning film formed by the colloidal silica is evaluated here. Protocol

The strengthening potential of the elastomeric film-forming polymers was quantified from the measurement of the breaking strength of a material consisting of composition A or B of Example 2.

The test consists in applying a compression stress, to breaking, to the material deposited, by means of a film-drawing device, at the surface of a supple and deformable foam consisting of neoprene 13 mm thick, the amount of material deposited being such that it makes it possible to obtain a film having a thickness of 15 to 30 μm after drying for 24 h. The use of this foam support makes it possible to impose a considerable distortion on the material deposited at the surface, and therefore to quantify its breaking strength. The mechanical compression stress is exerted after drying of the film, by means of a cylindrical punch 1 mm in diameter; the displacement rate of the punch being 0.1 mm/s. The test is carried out using a TA-XT21 texture analyser sold by the company Stable Micro System. A curve of force F (in N) as a function of displacement d (in mm) is thus obtained, from which it is possible to determine the breaking point of the material.

Results The results obtained are given in the table below:

Composition Fbreak (N) Wbreak (J/M²) tested

Composition A Does not fracture Does not fracture

Composition B 0.14 ± 0. 01 23 ± 2

These results demonstrate the strengthening role of the polymer used in the composition according to the invention, in the presence of a tensioning agent such as colloidal silica. The applicant also verified, in vitro, that composition A always exhibited a tensioning effect.

Claims

1. Cosmetic composition comprising, in a physiologically acceptable medium:

- at least one tensioning agent, and - at least one elastomeric film-forming polymer chosen such that the film obtained by drying this polymer, at ambient temperature and at a relative humidity of 55%, has a mechanical profile defined by at least: (a) an elongation at break (ε_r) of greater than or equal to 800%,

(b) an instantaneous recovery (Rj) at least equal to 75%, after an elongation of 150%,

(c) a recovery (R₃₀₀) at 300 seconds of greater than 80%.

2. Composition according to Claim 1, characterized in that the tensioning agent is chosen from:

- synthetic polymers; - polymers of natural origin;

- mixed silicates;

- wax microparticles;

- colloidal particles of inorganic fillers;

- and mixtures thereof.

3. Composition according to Claim 2, characterized in that the synthetic polymers are chosen from: - polyurethane polymers and copolymers;

- acrylic polymers and copolymers;

- sulphoisophthalic acid polymers;

- grafted silicone polymers; - water-soluble or water-dispersible polymers comprising water-soluble or water-dispersible units and units with an LCST;

- and mixtures thereof.

4. Composition according to Claim 2, characterized in that the polymers of natural origin are chosen from:

- plant proteins and plant protein hydrolysates;

- latices of plant origin;

- and mixtures thereof.

5. Composition according to Claim 2, characterized in that the mixed silicates are chosen from laponites.

6. Composition according to Claim 2, characterized in that the wax microparticles are chosen from: particles of carnauba wax, of candelilla wax or of esparto grass wax, having a particle diameter of less than 5 μm.

7. Composition according to Claim 2, characterized in that the colloidal particles of inorganic fillers are colloidal particles of silica or of silica-alumina composite.

8. Composition according to any one of Claims 1 to I₁ characterized in that said tensioning agent is included in the composition in an amount ranging from 1% to 10% by weight of active material, relative to the total weight of the composition.

9. Composition according to any one of Claims 1 to 8, characterized in that said polymer is a copolymer of N-methyldiethanolamine, of poly(tetra- methylene oxide) and of isophorone diisocyanate.

10. Composition according to any one of Claims 1 to 9, characterized in that said polymer is such that it forms a film having an elongation at break ranging from 800% to 3000%; an instantaneous recovery of 75% to 100%; and a recovery at 300 seconds ranging from 85% to 100%.

11. Composition according to any one of Claims 1 to 10, characterized in that the elastomeric film-forming polymer is present at a concentration ranging from 0.25% to 10% by weight, relative to the total weight of the composition.

12. Use of an ethylenic polymer as defined in any one of Claims 1, 9 and 10, for improving the remanence of the tensioning effect afforded by a tensioning agent as defined in any one of Claims 1 to 7.

13. Process for cosmetically treating wrinkled skin, comprising a step consisting in applying to said skin a composition as defined in any one of Claims 1 to 11.