IT201800020872A1 - REVERSE EMULSIONS USEFUL AS THICKENERS FOR COSMETICS - Google Patents

Description

Description

REVERSE EMULSIONS USEFUL AS THICKENERS FOR COSMETICS

The present invention relates to reverse emulsions useful as thickeners in cosmetic formulations.

The reverse emulsions of the present invention comprise a cross-linked polymeric thickener obtained by polymerizing, by reverse emulsion polymerization within the same emulsion, 2-acrylamido-2-methylpropanesulfonic acid, a non-ionic acrylic associative monomer and a cross-linking agent.

The above emulsions are characterized by an excellent thickening and stabilizing efficacy and by their versatility, especially in cosmetics in the form of oil-in-water emulsion.

FIELD OF THE INVENTION

A technical problem often encountered in the cosmetic industry is that of obtaining very viscous formulations (pastes, gels) stable over time, in a wide range of physiological pH, possibly in the presence of inorganic salts and fatty phases, which are highly compatible with the skin. and hair and pleasant sensory properties.

Cosmetic products with high compatibility with the skin and hair are products that are easily absorbed through the keratin substrates, making changes to the touch, hydration and perspiration and improving the general sensory characteristics without altering the physiological pH.

An essential feature of the thickeners used in cosmetic formulations is that they show their thickening capacity without negatively altering the other properties of the formulations.

It is also highly desirable in the cosmetic field to have stable reverse emulsion liquid thickeners which, during formulation, do not require any neutralization step to develop viscosity.

The specialized literature reports many methods for thickening and regulating the rheological properties of different formulations, including the use of reverse emulsion polymers (i.e. polymers obtained by reverse emulsion polymerization)

In fact, many polyacrylic thickeners prepared by reverse emulsion polymerization (reverse emulsion polyacrylic thickeners) are already on the market and try to meet the needs of cosmetic formulators.

Unfortunately, each of them has at least one drawback: some have poor viscosity stability at acidic pH; some of them may contain traces of unwanted toxic monomers, such as acrylamide; some others suffer from poor stability at high pH or in some way from limited efficiency even at high concentration and in the presence of salts (such as NaCl).

We have now found that reverse emulsion polymers obtained from the polymerization of 2-acrylamido-2-methylpropanesulfonic acid, a non-ionic acrylic associative monomer and a cross-linking agent exhibit excellent thickening properties in aqueous solutions and in oil-in-water emulsions where they exhibit also excellent stabilization performance.

These reverse emulsion polymers are very little sensitive to pH, they maintain a satisfactory efficiency as thickeners in the presence of salts and their viscosity development, as a function of the polymer concentration, is advantageously directly proportional over a wide dosage range.

Overall, their high compatibility with skin and hair, combined with their excellent thickening and emulsifying properties, make them particularly suitable for the formulation of cosmetics, especially in the presence of inorganic salts and organic phases.

STATE OF THE ART

In the field of polyacrylic thickeners IN reverse emulsion for cosmetic use, we mention the following patents:

• EP 503853, which describes the reverse emulsion polymers containing units deriving from acrylamide, 2-acrylamido-2-methylpropanesulfonic acid and a cross-linking monomer. A disadvantage of the reverse emulsions of EP 503853 is the fact that they can contain traces of acrylamide, a toxic substance;

• US 5,721,313, which describes acrylic polymers in water-in-oil (inverse) emulsion which are the reaction products of: 50-90% by weight of a carboxylate monomer, 5-48% by weight of a non-ionic monomer 1-20% by weight of a sulfonated monomer, from 0.01 to 5% by weight of a monomer having surfactant active properties and from 0.01 to 5% by weight of a crosslinking agent; emulsions have many uses, for example in the viscosity of inks, compositions of dyes, pigments and even in cosmetics. A disadvantage of these acrylic polymers is that the carboxylated monomers provide poor viscosity performance at low pH.

• WO 99/36445, which describes cross-linked polyacrylates in reverse emulsion based on strongly acidic monomers in combination with weakly acidic monomers (acrylic acid) or neutral monomers (hydroxyethyl acrylate). The disadvantages of these polyacrylates are that the acrylic acid units provide poor viscosity performance at pH below 6, while the hydroxyethyl acrylate units have poor stability at alkaline pH.

• WO 99/42521, which describes 2-acrylamido-2-methylpropanesulfonic acid homopolymers prepared by reverse emulsion polymerization useful as thickeners for personal care products; the reverse emulsion polymers of WO 99/42521 are less sensitive to pH variation than the polymers of WO 99/36445.

- WO 2004/063228, which describes acrylic polymers obtained by reverse emulsion polymerization of one or more anionic acrylic monomers of which at least one containing a strongly acid functional group and a hydrophobic acrylic monomer insoluble in water to be used as thickeners for care products of the person. The reverse emulsion polymers of WO 2004/063228 are not very sensitive to pH variation and have an improved stability but, at high dosage, their viscosity performances are lower than expected.

EP 1636273 and EP 1889856, which refer to acrylic polymers in reverse emulsion obtained from acrylic and / or methacrylic acid, 2-acrylamido-2-methylpropane sulfonic acid and a cationic monomer. These polymers, in addition to having a high compatibility with the skin and hair and having good viscosity and stabilization properties over time, show a high thickening efficiency not only in aqueous solutions, but also in oil-in-water emulsions; these properties make them particularly suitable for the preparation of neutral or slightly alkaline cosmetic formulations. Unfortunately, they are not very effective as thickeners at acidic pH;

• WO 2011/138533, which refers to acrylic polymers in concentrated reverse emulsion obtained in the presence of a specific oil-in-water emulsifier from: at least one monomer containing an acid functional group, at least one neutral monomer selected from a shortlist and at least one monomer associative. In the patent application, only associative copolymers of acrylamide (undesirable in cosmetics due to the toxicity of acrylamide) and hydroxyethyl acrylate (which have poor stability at high pH) are actually described.

-WO 2006/064151, which refers to concentrated inverse emulsions containing up to 5% by weight of water and an acrylic polymer consisting of at least one associative monomer and other monomers independently selected from neutral monomers and monomers containing an acid functional group or an cationic group. The polymers actually prepared in WO 2006/064151 are made from acrylamide and / or acrylic acid, cross-linker and associative monomer and all of them suffer from at least one of the above mentioned drawbacks (presence of acrylamide and low pH sensitivity).

SUMMARY

A fundamental object of the present invention is a reverse emulsion, useful as an ingredient for the preparation of cosmetic formulations, containing an internal aqueous phase, an external oil phase, a water-in-oil emulsifier and containing from 20 to 45% by weight , on the weight of the reverse emulsion, of an acrylic polymer prepared by in situ polymerization of:

i) 95 to 99.89% by weight, preferably 98 to 99.89% by weight, of 2-acrylamido-2-methylpropanesulfonic acid,

ii) from 0.1 to 4.99% by weight, preferably from 0.1 to 1.99% by weight, of at least one unsaturated polyethoxylated monomer containing a C14-C22 hydrophobic group soluble in the aqueous phase

iii) 0.01 to 1% by weight of at least one polyfunctional unsaturated monomer,

wherein the weight ratio between aqueous phase and oil phase is from 1 to 3.

Another object of the present invention is the use of the same reverse emulsion as an ingredient in the preparation of cosmetic compositions.

DRAWINGS

Fig. 1: Thickening efficiency of Example 1, Comparative Example 2 and prior art thickeners, in water at various pHs Fig. 2: Thickening efficiency of Example 1, Comparative Example 2 and prior art thickeners, in water in the presence of NaCl

Fig. 3: thickening efficiency of Example 1, Comparative Example 2 and prior art thickeners, as a function of polymer concentration

Fig. 4: thickening efficiency of Examples 1, 4 and 5, of Comparative Example 2 and prior art thickeners, in oil in aqueous emulsions

DETAILED DESCRIPTION

In the preparation of the polymer in reverse emulsion, the 2-acrylamido-2-methylpropanesulfonic acid can be used in an acid form (not dissociated), or in a partially or totally neutralized form; it is preferably used in neutralized form in the form of sodium salt.

The polyethoxylated unsaturated monomer containing a C14-C22 hydrophobic group (associative monomer) is non-ionic, soluble in the aqueous phase of the emulsion and preferably soluble in all ratios in water.

The associative monomer is selected from allyl ethers and esters of (meth) acrylic acid, more preferably from esters of (meth) acrylic acid, of C14-C22 alkyl or alkenyl monoethers of a polyethylene glycol having at least 10 oxyethylene units , more preferably having from 10 to 50 oxyethylene units, or even more preferably from 15 to 30 oxyethylene units and in particular from 20 to 25 oxyethylene units.

In accordance with the preferred embodiments, the hydrophobic groups are C14-C22 alkyls, i.e. linear or branched, preferably linear alkyl groups, having from 14 to 22 carbon atoms, more preferably they are C16-C22 alkyl groups, for example groups C18, C20, C22 alkyls; the linear C16-C18 alkyl groups are particularly preferred.

The highly preferred polyethoxylated unsaturated monomers are the (meth) acrylic acid esters of the C16-C18 alkyl monoethers of a polyethylene glycol having 20 to 25 oxyethylene units, such as the methacrylic ester of 25 moles ethoxylated stearyl alcohol.

Different associative monomers can be used and not all their hydrophobic groups need to be the same.

The polyfunctional unsaturated monomer iii) contains two or more unsaturated reactive groups and is typically selected from methylenebisacrylamide, triallylamine, ethylene glycol dimethacrylate, tetraalliiloxyethane, ethylene glycol diacrylate, diallylurea, trimethylolpropane triacrylate, or a mixture of these compounds.

Preferably, the polyfunctional monomer is methylenebisacrylamide, used in a concentration from 0.05 to 0.3% by weight of the total weight of the monomers.

According to the preferred embodiments, the reverse emulsion polymer is obtained only from the monomers referred to in points i), ii) and iii), i.e. only from them or in the presence of negligible quantities of other monounsaturated monomers (0.01-1 % by weight), which would not significantly affect the viscosity efficiency of the polymer, in water and in water-in-oil (W / O) emulsions.

The oil phase of the reverse emulsions comprises a liquid organic medium which is insoluble in water (oil) and the water-in-oil emulsifier. Suitable oils include: mineral oils containing saturated hydrocarbons such as paraffins, isoparaffins or cycloparaffins with a boiling point of approximately 150 ° C to approximately 300 ° C, for example Isopar® M, MARCOL® 52 or MARCOL® 82, sold by Exxon Chemical; hydrocarbons, esters and ethers of plant origin, such as Cetiol® Ultimate (INCI name: Undecane (and) Tridecane), Cetiol® C5 (INCI: Coco Caprylate) and Cetiol® OE (INCI: Dicaprylyl Ether), sold by BASF; vegetable oils, such as methyl- or glycerolesters of fatty acids of vegetable origin; synthetic oils such as isohexadecane, hydrogenated polyisobutene or hydrogenated polydecene; blends of these oils.

Plant-based hydrocarbons and isohexadecane are the preferred oils. The aqueous phase of the reverse emulsion comprises water, the polymer and, optionally, one or more oil-in-water emulsifiers and other water-soluble compounds.

In the reverse emulsion of the present invention, the weight ratio between the aqueous phase and the oily phase is from 1 to 3, preferably from 1.5 to 2.5.

In the reverse emulsion, the water-in-oil emulsifier consists of a single emulsifier or a mixture of emulsifiers having a low HLB value, capable of stabilizing water-in-oil emulsions.

Water-in-oil emulsifiers are those normally used for this purpose.

Examples of water-in-oil emulsifiers which can be used are sorbitan esters, for example sorbitan oleate, sorbitan isostearate, sorbitan monolaurate, sorbitan monopalmitate, sorbitan stearate; polyethoxylated sorbitan esters, for example pentaethoxylated sorbitan monooleate or pentaethoxylated sorbitan isostearate; dialcanol fatty amides; low molecular weight polyesters produced by the condensation of a poly (isobutenyl) succinic acid or its anhydride, such as Hypermer® 2296 sold by the company Croda.

The reverse emulsion generally contains between 0.5% and 10% by weight, preferably between 2 and 5% by weight, of water-in-oil emulsifiers.

The reverse emulsion can optionally contain one or more oil-in-water (high HLB) emulsifiers; among the usable oil-in-water emulsifiers, we mention linear or branched ethoxylated fatty alcohols, fatty esters of polyglycerols and alkyl polyglycosides.

The reverse emulsion generally contains between 1% and 10% by weight, preferably between 1.5% and 5% by weight, of the oil-in-water emulsifiers.

The procedure for preparing the reverse emulsions is known in the art and typically comprises the following steps:

to. an aqueous solution is prepared, typically containing from 30 to 65% by weight of the monomers i), ii) and iii);

b. optionally a base is added to the solution to adjust the pH between 4 and 10;

c. an oil phase is prepared containing the oil and one or more water-in-oil emulsifiers;

d. the solution obtained in a is introduced. or in b. in the organic phase prepared in c., or vice versa, and the two phases are emulsified by vigorous stirring;

And. the radical polymerization initiators are added to the emulsion;

f. polymerization is started and completed at a temperature typically between 30 ° C and 95 ° C;

g. the reaction mixture is cooled and optionally an oil-in-water emulsifier is added.

Among the radical polymerization initiators that can be used for the preparation of the acrylic polymer are ammonium, potassium or sodium peroxide, water-soluble organic peroxides, by way of example hydrogen peroxide and peracetic acid, azobisisobutyronitrile, redox couples and other initiators known in the art.

The reverse emulsions of the invention can further contain the additives commonly used in radical polymerization; by way of example sequestering agents, such as sodium diethylenetriamine pentaacetate.

The reverse emulsions of the present invention are particularly useful as viscosifiers and emulsifiers in cosmetic compositions. They can be present in the cosmetic compositions in concentrations preferably between 1% and 10% by weight with respect to the total weight of the compositions, and more preferably between 2% and 8% by weight.

Reverse emulsions can be used in cosmetic compositions for their viscosity enhancing and stabilizing properties, especially in the preparation of cosmetic skin care compositions.

Examples of cosmetic compositions that can be viscous and stabilized by reverse emulsions are creams and lotions for the body, hands and face, skin conditioners, sunscreen compositions, cleansing, moisturizing and anti-perspirant fluids, perfumes, soaps, but also hair gels and lotions (such as styling and fixative lotions and conditioners), hair dyes and bleaching creams, shampoos, two-in-one shampoos, and other products for similar applications. Reverse emulsions can be easily incorporated into cosmetic compositions, without the need for any pH adjustment, and their thickening effect is not compromised by the presence of surfactants, which are normally present in cosmetic and home care compositions.

The cosmetic compositions, alongside the inverse emulsions of the invention, contain the usual ingredients, such as surfactants, moisturizers, emollients, sunscreens, hydrophilic or lipophilic actives such as ceramides, anti-free radical agents, insect repellents, skin refreshers, deodorants , active antiperspirants, agents for hair treatment, agents for the care of oral hygiene, slimming agents, bactericides, sequestering agents, anti-dandruff agents, antioxidants, preservatives, basifying or acidifying agents, perfumes, fillers, dyes, other polymers and emulsifiers , gelling agents, foaming agents.

Cosmetic compositions usually also contain a suitable liquid medium; the suitable medium can represent from 5% to 98% of the total weight of the compositions. The typical suitable medium is water.

Suitable organic solvents can replace or partially replace water.

The organic solvents can be hydrophilic organic solvents, lipophilic organic solvents, amphiphilic solvents or mixtures thereof.

Examples of hydrophilic organic solvents are short linear or branched mono-alcohols having from 1 to 8 carbon atoms, such as ethanol, propanol, butanol, isopropanol and isobutanol; polyethylene glycols having from 6 to 80 ethylene oxide units; polyols such as propylene glycol, butylene glycol, glycerol and sorbitol; mono- or dialkyl isosorbides in which the alkyl groups have 1 to 5 carbon atoms, such as dimethyl isosorbide; glycol ethers such as diethylene glycol monomethyl ether or monoethyl ether and dipropylene glycol methyl ether.

Among the usable amphiphilic organic solvents we mention polyols such as the derivatives of polypropylene glycol (PPG), such as fatty acid esters of polypropylene glycol and fatty alcohol ethers of PPG.

Usable lipophilic organic solvents are, for example, fatty esters such as diisopropyl adipate, dioctyl adipate and alkyl benzoates.

Reverse emulsions are particularly useful for thickening and stabilizing cosmetic compositions containing fatty ingredients, such as oils, vitamins and emollients, preserving the persistence of their perfumes and fragrances while providing an effective thickening effect.

Advantageously, the reverse emulsions are therefore used in the preparation of cosmetic compositions which contain an oil, in particular at least 5% by weight of an oil, such as a mineral oil, a vegetable oil, an animal oil, a synthetic oil, a silicone, an oil of vegetable origin, a mixture of these. Specific examples of usable oils are paraffin, petroleum gel, jojoba oil, coconut oil, sweet almond oil, olive oil, rapeseed oil, castor oil, sesame oil, avocado oil, peanut oil, isoparaffin , amodimethicones, dimethiconols, cyclopentasiloxanes, and mixtures thereof.

The cosmetic compositions containing the inverse emulsions of the invention can be in the form of solution, emulsion, dispersion, gel, cream, paste, bar or wet wipe; because of the excellent emulsifying properties of the reverse emulsion, they are preferably in the form of an emulsion, in particular an oil-in-water emulsion.

The reverse emulsions are normally compatible with the other usual ingredients of the cosmetic compositions.

In the following examples, reverse emulsions according to the invention and various reverse emulsions according to the known art are reported, together with some tests which show the very high viscosity efficiency and versatility of the emulsions of the present invention, in aqueous solution and especially in oil-based emulsified systems. in water.

EXAMPLES

The following abbreviations are used:

AMSA: 2-acrylamide-2-methylpropanesulfonic acid

AMSA-Na: 2-acrylamide-2-methylpropansulfonic acid, sodium salt SMA 25EO: methacrylic ester of ethoxylated stearyl alcohol 25 moles LMA 4EO: methacrylic ester of lauryl alcohol ethoxylated 4 moles MBA: methylenebisacrylamide

IHD: isohexadecane

C11-13: Cetiol® Ultimate from BASF (INCI name: Undecane (and) Tridecane)

Dry matter is measured by thermogravimetric analysis at 160 ° C.

EXAMPLES 1-5

The reverse emulsions of Examples 1-5 were prepared using the method described in Example 1 of EP 186361.

The polymerization was carried out at pH 9.2.

After polymerization, some of the water was distilled off to obtain a dry matter concentration of about 42-44% by weight, as reported in Table 1, and an alkyl polyglucoside was added as an oil-in-water emulsifier.

Table 1 also reports the polymeric compositions and other characteristics of the reverse emulsions of Examples 1-5. The effect of using even a very small amount of SMA 25EO is a notable increase in the viscosity performance of the polymer; the use of LMA

4EO, on the other hand, did not produce any noticeable effect.

Table 1

*Comparative

1) dry matter

2) sodium salt

3) aqueous phase / oil phase weight ratio

Evaluation of the properties of the reverse emulsions of the examples by comparison with commercial reverse emulsion thickeners The commercial thickeners tested are as follows:

SML-EG, a reverse emulsion containing a reverse emulsion polymer based on acrylic acid and AMS.

SML-INS and SML-NS, reverse emulsions containing reverse emulsion polymers of hydroxyethylacrylate and AMS.

SPL-305, a reverse emulsion containing a polymer made from AMS and acrylamide.

SPS-S, a concentrated reverse emulsion containing a reverse emulsion polymer made from hydroxyethyl acrylate, AMS and 4 mol acrylate ethoxylated lauryl alcohol.

a) Efficiency of viscosity in water at various pH

The Brookfield® viscosities of aqueous solutions at 1.3% by weight of dry matter of the reverse emulsions, at 25 ° C, rotor 6, 5 revolutions per minute and various pH, were measured and reported in Table 1 and in Fig. 1.

The reverse emulsion of Example 1 has the highest viscosifying efficiency and excellent stability over the entire pH range.

Table 1 - Viscosity (mPa * s), effect of pH

*comparative

b) Viscosizing efficiency in the presence of NaCl

Table 2 and Fig. 2 report the Brookfield® viscosity of the aqueous solutions of the reverse emulsions with 1.3% by weight of dry matter at 25 ° C, in the presence of 0.10 and 0.25% by weight of NaCl.

Only SPL-305 (which is acrylamide based) has a better performance than the reverse emulsion of Example 1 at 0.1% by weight of salt and close to it at 0.25% by weight of salt.

Table 2 - Viscosity (mPa * s), effect of salt

c) Viscosity efficiency as a function of the polymer concentration Table 3 and Fig. 3 report the Brookfield® viscosities of the aqueous solutions of the products at various concentrations (dry matter, weight percentage) at 25 ° C.

The viscosifying effect of the reverse emulsion polymer of Example 1 has a better response to increasing the concentration in the whole group of products tested.

Table 3 - Viscosity (mPa * s), effect of the polymer concentration

d) Thickening efficiency in oil-in-water emulsions

The oil-in-water (o / w) emulsions are prepared with each of the commercial products, with the inverse emulsions of Examples 1-2, 4-5, with the following composition (weight%):

Water 78%

Oil phase 20%

Products of the examples at 0.86% dry matter

Table 4 reports the Brookfield® viscosities of the emulsions.

The reverse emulsions of the examples according to the invention have the best viscosifying performance in all oils, despite their different polarity.

Table 4 - Viscosity (mPa * s) o / w emulsions - oil effect

e) Stability of thickened emulsions

The stability of the emulsions tested above in point d) is evaluated with the separation test in the centrifuge, at 25 ° C and 6000 rpm for 1 hour.

Table 5 reports the stability index of the emulsions.

Table 5 - Emulsion stability index <1)>, oil effect

1) 0 = no phase separation

1 = phase separation <2 mm

2 = phase separation between 3 and 5 mm

3 = phase separation between 6 and 10 mm

4 = phase separation> 10 mm

Claims (10)

CLAIMS 1. Reverse emulsion containing an internal aqueous phase, an external oil phase, a water-in-oil emulsifier, in which the weight ratio between the aqueous phase and the oil phase is from 1 to 3 and containing in the internal aqueous phase from 20 45% by weight, based on the weight of the reverse emulsion, of an acrylic polymer prepared by polymerization of: i) from 95 to 99.89% by weight of 2-acrylamido-2-methylpropanesulfonic acid, ii) from 0.1 to 4.99% by weight of at least one unsaturated polyethoxylated monomer containing a C14-C22 hydrophobic group soluble in the phase aqueous iii) from 0.01 to 1% by weight of at least one polyfunctional unsaturated monomer. 2. Reverse emulsion according to claim 1 wherein the monomer ii) is selected from allyl ethers and (meth) acrylic esters of C14-C22 alkyl or alkenyl monoethers of a polyethylene glycol having at least 10 oxyethylene units. 3. Reverse emulsion according to claim 2 wherein the monomer ii) is selected from the (meth) acrylic esters of C14-C22 alkyl or alkenyl monoethers of a polyethylene glycol having at least 10 oxyethylene units. 4. Reverse emulsion according to claim 3 wherein the monomer ii) is a (meth) acrylic ester of C14-C22 alkyl or alkenyl monoethers of a polyethylene glycol having 10 to 50 oxyethylene units. 5. Reverse emulsion according to claim 4 wherein the monomer ii) is a (meth) acrylic ester of C16-C18 alkyl monoethers of a polyethylene glycol having 20 to 25 oxyethylene units. Use of the reverse emulsion of any one of claims 1 to 5 as an ingredient in the preparation of cosmetic compositions. Use according to claim 6 wherein the cosmetic compositions are skin care compositions. Use according to claim 6 wherein the cosmetic compositions contain at least 5% by weight of an oil. Use according to claim 8 wherein the cosmetic compositions are in the form of an emulsion. Use according to claim 6 wherein the cosmetic compositions contain inorganic salts.