FR3069252A1 - PERFUME MICROCAPSULES HAVING A BICOLET STRUCTURE - Google Patents

Abstract

The present invention relates to microcapsules formed of an oily heart containing at least one perfume, surrounded by a first membrane containing at least one polymer and whose outer surface is covered with a second membrane. The second membrane comprises at least one non-silicone water-insoluble compound having a melting point of 20 to 120 ° C. These microcapsules can be in aqueous suspension. The invention further relates to the process for producing said microcapsules by in situ polymerization, as well as their uses, especially in detergent compositions.

Description

PERFUME MICROCAPSULES WITH TWO-LAYER STRUCTURE

OBJECT OF THE INVENTION

The present invention relates to microcapsules containing an oily interior phase containing a perfume, surrounded by a double envelope. It also relates to the method of manufacturing said microcapsules, as well as their uses, in particular in detergent compositions.

BACKGROUND OF THE INVENTION

It is known that the micro-encapsulation of perfumes, consisting in particular of essential oils, makes it possible to protect them, to avoid the loss of volatile aromatic ingredients, to control the release profile of the perfume and to improve its stability ( IT Carvalho et al., International Journal of Cosmetic Science, 2015, 1-11). It is thus possible to formulate these perfumes in different compositions, in particular detergents (WO 2015/104469). Most often, the encapsulation is done by the copolymerization of aldehyde and polyamine-based compounds. We mainly use the aminoplast resins obtained by polycondensation of a polyamine (in general melamine, which is a derivative of triazine) with an aldehyde (mostly formaldehyde) (US-5,137,646).

Although these resins are effective for encapsulating perfumes and their cost remains advantageous, their use remains controversial, since these resins are a source of free formaldehyde which remains in the continuous aqueous phase at the end of the process for forming capsules. Indeed, certain monomers do not react during the polymerization around the droplets of oily phase containing the perfume. Alternatively or additionally, formaldehyde can be released into the continuous aqueous phase due to the chemical equilibria taking place in the material. However, formaldehyde is a volatile, irritant compound and considered as an important carcinogen by health organizations. Therefore, its concentration in compositions is subject to regulation for many applications.

Controlling and minimizing the presence of free formaldehyde in the compositions represents a real challenge for the industry. This problem is generally resolved by adding formaldehyde inhibitors (US-7,807,076; US-4,409,156) to these compositions, such as urea or arginine, but this solution does not always sufficiently preserve the degradation of the membrane and therefore presents in some cases limited effectiveness.

In addition, there remains a need to improve the encapsulation efficiency, the protection of the perfume and the physicochemical stability of the microcapsules over time and in temperature.

Different solutions have been proposed to solve one or more of the above problems, including the use of one or more silicone membranes in place of or in addition to the aminoplast membrane (US-7,799,752; EP 2 618 927; WO 2015 / 104469). Although these solutions have made it possible to obtain more stable perfume microcapsules, in particular in the presence of detergents, the use of silicones in products of current use is increasingly contested because, on the one hand, of their bioaccumulation, especially in aquatic systems and, on the other hand, a suspicion of endocrine disrupting effect which weighs on certain silicones. It would therefore be desirable to provide microcapsules not containing silicone compounds.

In this context, the inventors have demonstrated that the presence of a second special hydrophobic membrane, crystallized on the first polymer resin membrane, improves the physicochemical stability of the microcapsules over time and in temperature and contributes to better preserving the olfactory intensity of the encapsulated perfume, especially when used in detergent compositions. In the case where the microcapsules are based on aminoplast resin, the present invention also makes it possible to limit the formation of formaldehyde over time.

SUMMARY OF THE INVENTION

The subject of the invention is microcapsules formed of a heart consisting of an oily phase containing at least one perfume, said heart being coated with a first membrane containing at least one polymer and the outer surface of which is covered with a second membrane, characterized in that the second membrane consists essentially of at least one non-silicone compound insoluble in water, having a melting point of between 20 and 120 ° C.

It also relates to a suspension of these microcapsules in an aqueous medium.

The subject of the invention is also the process for manufacturing these microcapsules or their suspension, comprising the following successive steps:

a) an emulsion of an oily phase containing at least one perfume is formed in an aqueous phase, in the presence of at least one surfactant and at least one monomer or prepolymer,

b) heating said emulsion with stirring so as to polymerize said monomers or prepolymers and thus to form a first membrane around the oily phase,

c) at least one hydrophobic compound in the molten state is introduced into said aqueous phase with stirring, said hydrophobic compound being a non-silicone compound insoluble in water, having a melting point of between 20 and 120 ° C.,

d) the suspension thus obtained is cooled with stirring, so as to crystallize said hydrophobic compound and thus to form a second membrane on the first membrane,

e) optionally, said microcapsules are isolated and dried.

It also relates to the use of these microcapsules as a perfume additive in a detergent, cosmetic or pharmaceutical composition or in textile materials, paper or cardboard, preferably in a detergent composition.

The present invention finally relates to a detergent composition comprising these microcapsules.

DETAILED DESCRIPTION

The present invention relates to microcapsules containing at least one perfume. In the context of this description, the term “perfume” means a single compound or a mixture of volatile and odoriferous compounds. These compounds have a vapor pressure greater than atmospheric pressure at room temperature. They are in particular listed in Merck Index, 8th Edition, Merck & Co., Inc. Rahway, N.J. These compounds can be of synthetic or natural origin. It may for example be one or more essential oils of plants, chosen for example from Asteraceae, Myrtaceae, Lauraceae, Lamiaceae, Rutaceae and Zingiberaceae, which are usually extracted from any part of these plants by extraction using a supercritical fluid, hydrodistillation, enfleurage, steam entrainment or any other process allowing the extraction of perfumed molecules from a plant.

Whether they are of synthetic or natural origin, the perfumes generally comprise compounds, possibly terpenic, chosen from alcohols, aldehydes and esters.

The following perfume compounds can in particular be used as perfume in the present invention, alone or in combination: methyl 2-methyl butyrate; isopropyl 2-methyl butyrate; ethyl 2-methyl butyrate; ethyl 2-methyl pentanoate; ethyl heptanoate; ethyl octanoate; isobutyl hexanoate; amyl butyrate; amyl heptanoate; isoamyl isobutyrate; hexyl acetate; hexyl butyrate; hexyl isobutyrate; hexyl isovalerate; hexyl propionate; ethyl 2-cyclohexyl propanoate; ethyl 3,5,5-trimethyl hexanoate; glyceryl 5-hydroxydecanoate; prenyl acetate; methyl 2-butenyl acetate; methyl 3-nonenoate; ethyl decenoate; ethyl octenoate; ethyl decadienoate; ethyl octenoate; citronellyl acetate; 2-hex-1-enyl isovalerate; 2-hexen-1-yl propionate; 2hexenen-l-yle valerate; 3-hexen-1-yl (E) -2-hexenoate; 3-hexen-1-yl 2-methyl butyrate; 3-hexen-1-yl acetate; 3-hexen-1-yl benzoate; 3-hexen-1-yl formate; 3-hexen-1-yl tiglate; 2-methyl butyl 2-methyl butyrate; butyl isovalerate; allyl cyclohexane; allyl cyclohexyl propionate; allyl cyclohexyl valerate; benzyl octanoate; gamma-decalactone; gamma-dodecalactone; jasmine lactone; jasmolactone; nonalactone; 6-acetoxydihydrotheaspirane; phenoxyethyl isobutyrate; pivacyclene; dimethyl anthranilate; methyl antranilate; octanal; nonanal; the decanal; the dodecanal; methyl nonyl acetaldehyde; methyl octyl acetaldehyde; 2,4hexadienal; intreleven; decen-l-al; nonen-l-al; aldoxal; geraldehyde; isocyclo citral; d-limonene; the ligustral; the tridecenal; the triplai; the vertoliff; cyclal C; heliotropin; neocaspirene; beta naphthol ethyl ether; beta naphthol methyl ether; the hyacinth ether; 2-heptyl cyclopentanone; undecavertol; frutonile; and their mixtures.

In the present invention, the perfume is included in an oily phase which forms the heart of the microcapsule. This oily phase can consist exclusively of the perfume, that is to say one or more perfuming compounds. Alternatively, it can comprise one or more volatile and / or non-volatile oils of any kind, of vegetable and / or synthetic origin, in addition to the perfume. In the context of this description, oil is understood to mean a compound which is liquid at room temperature (25 ° C.) and atmospheric pressure (10 ⁵ Pa) which, when it is introduced at a rate of at least 1% by weight in the water at 25 ° C, is not at all soluble in water, or soluble up to less than 10% by weight, relative to the weight of oil introduced into the water. These oils can in particular be used to increase the hydrophobic nature of the oily core when the perfume is not sufficiently so, in particular in the case where the perfume comprises, or consists of, one or more essential oils. Examples of such oils include hydrocarbon oils, in particular esters of fatty acids, such as ethyl myristate and methyl stearate., The perfume can thus represent 1 to 100%, preferably 50 to 100%. weight, for example from 80 to 100% by weight or alternatively from 50 to 80% by weight, relative to the total weight of the oily phase.

Furthermore, it is preferred that the perfume and the hydrocarbon oil optionally present represent from 70 to 100%, preferably from 80 to 100%, or even from 90 to 100%, better still, from 95 to 100%, by weight of the oily phase. . The latter may optionally contain one or more antioxidant agents, viscosity agents, UV absorbers, density rectifiers, photostabilizers or any other stabilizing compound easily identifiable by those skilled in the art in addition to the aforementioned constituents.

To form a microcapsule according to the invention, each droplet of this oily phase is coated with an envelope, called the first membrane, containing at least one polymer which is capable of polymerizing in the aqueous phase, advantageously chosen from: phenolformaldehyde resins (or resins phenolic); optionally etherified aminoplast resins, in particular urea-formaldehyde, melamine-formaldehyde, melamine-urea-formaldehyde, glycoluril-formaldehyde, acetoguanamine-formaldehyde or benzoguanamine-formaldehyde, in which the urea can be replaced by an alkylene or a thiourea and / or formaldehyde can be replaced by glyoxal, as well as their methylated derivatives; polyureas; epoxy resins; polyimides; polyamides; polyurethanes, poly (meth) acrylates, without this list being exhaustive; as well as their mixtures.

It is preferred to use an aminoplast resin, preferably a urea-formaldehyde or melamine-formaldehyde or melamine-urea-formaldehyde resin, for example having a melamine / formaldehyde ratio of 1: 1.5 to 1: 6, preferably 1: 3 at 1: 6, or a polyurea.

According to a preferred embodiment of the invention, the first membrane further comprises at least one surfactant, such as an amphiphilic polymer. Examples of amphiphilic polymers suitable for this use are in particular: copolymers of acrylic acid and acrylamide; copolymers of maleic anhydride and ethylenic monomer, in particular copolymers of alkyl vinyl ether and maleic anhydride; homo- and copolymers of styrenesulfonic acid, homo- and copolymers of acrylamido-2-methylpropane sulfonic acid, cellulose derivatives such as sodium carboxymethyl cellulose;

and their mixtures.

The microcapsules according to the invention are such that the first membrane above is covered, on its outer surface, that is to say on its surface opposite to that in contact with the oily core, with a second membrane consisting essentially of a particular hydrophobic compound. By essentially constituted, it is meant that the second membrane contains from 60 to 100% by weight, preferably from 70 to 100% by weight, more preferably from 80 to 100% by weight and, better still, from 90 to 100% by weight of hydrophobic compound, relative to the total weight of the second membrane. This hydrophobic compound is a non-silicone compound insoluble in water, having a melting point of between 20 and 120 ° C, preferably from 35 to 95 ° C, more preferably from 48 to 95 ° C and, better still, from 55 at 95 ° C.

Examples of such hydrophobic compounds are:

- linear or branched alkanes, for example waxes whose crude formula is CnH2n + 2 with n between 20 and 50 such as paraffins type 6003, 5603, 4110 sold by Parafluid ™

linear fatty alcohols advantageously containing from 12 to 22, preferably from 18 to 22, carbon atoms, such as stearyl alcohol, behenyl alcohol and their mixtures,

- the fatty acids advantageously contain from 12 to 22, and preferably from 18 to 22, carbon atoms, which can be saturated or unsaturated, linear or branched (such as lauric and stearic acids), possibly hydroxylated (such as acid hydroxystearic), esterified (such as ethyl palmitate and pentaerythritol tetrabehenate), salified and / or oligomerized (in particular the dimer of linoleic acid),

- and their mixtures.

In the context of this invention, it is preferred to use the salts of fatty acids and in particular the salts of stearic acid and of ricinoleic acid, preferably magnesium stearate or zinc ricinoleate, more preferably magnesium stearate.

The microcapsules according to the invention have for example an oily phase / first membrane weight ratio ranging from 3: 1 to 9: 1, preferably from 4: 1 to 8: 1, and a first membrane / second membrane weight ratio of 4: 1 to 50: 1 and preferably from 5: 1 to 20: 1.

They are advantageously substantially spherical and for example have a median diameter D50 of between 1 and 50 μm, preferably from 1 to 30 μm, more preferably from 1 to 10 μm, as measured by laser diffraction using a Mastersizer® 3000 particle size analyzer of Malvern.

These microcapsules can in particular be in the form of an aqueous suspension.

Process for the preparation of microcapsules

The microcapsules according to the invention can in particular be prepared according to a coacervation (or phase separation) process, by interfacial or in situ polymerization or also by atomization or extrusion.

In the coacervation process, the oily phase is dispersed in a polymer solution, then the polymer is transformed into a coacervate, so that it forms a continuous layer around the oily phase droplets.

In the in situ polymerization process, which is preferred for the manufacture of the microcapsules according to the invention, the polymerization of the monomers or prepolymers is carried out directly on the surface of the oily phase droplets.

More particularly, the process implemented comprises a first step consisting in forming an emulsion of an oily phase containing at least one perfume in an aqueous phase of generally acidic pH, in the presence of at least one surfactant and at least one monomer or prepolymer. The emulsion can be formed by mixing, generally between 10 and 95 ° C, preferably between 20 and 50 ° C and more preferably between 20 and 35 ° C, the oily phase with an aqueous phase containing the monomer or prepolymer and the surfactant . Alternatively, the monomer or prepolymer and / or the surfactant can be included in the oily phase. The weight ratio of the aqueous phase to the oily phase can range from 1: 1 to 5: 1, preferably from 1: 1 to 3: 1 and more preferably from 1: 1 to 2: 1. In the case where the first membrane is formed from a melamine-formaldehyde resin, melamine and formaldehyde monomers or a condensate (methyolmelamine) or polycondensate (prepolymers) of these two monomers are used. It is understood, however, that several different monomers and / or prepolymers can be combined, in the case where it is desired that the first membrane of the microcapsules comprise a copolymer, a mixture of polymers or an interpenetrating network of polymers. The monomers or prepolymers can represent from 1 to 25% by weight, more preferably from 1 to 15% and preferably from 3 to 10% by weight, relative to the weight of the reaction mixture. The surfactant can be chosen from those described above. It can be used in an amount representing from 0.5 to 10%, preferably from 1 to 5% and more preferably from 1 to 3% by weight, relative to the total weight of the reaction mixture.

The emulsification step is carried out with stirring, in particular using a paddle or propeller stirrer or a homogenizer, for example at a speed of 2,000 to 15,000 rpm, preferably 4,000 to 12,000 revolutions / min and more preferably from 5,000 to 10,000 revolutions / min. Agitation is continued throughout the emulsification, which can last from a few minutes to several hours, for example from 1 to 75 minutes and preferably from 5 to 30 minutes, better still, from 10 to 15 minutes. This step is generally carried out between 10 and 95 ° C, preferably between 20 and 50 ° C and more preferably between 20 and 35 ° C.

The pH of the aqueous phase is preferably adjusted in the range from 3 to 7, more preferably from 3.5 to 6.5 and better still from 4 to 6.5, in particular by adding an organic or inorganic acid such as as citric or acetic acid. The pH can be adjusted after or before mixing the aqueous and oily phases and before or after introduction of the monomers or prepolymers and / or the surfactant into the aqueous phase, if necessary.

In the second step of the process according to the invention, the polymerization of the monomer or prepolymer is carried out by heating at a temperature ranging, for example, from 40 to 95 ° C, preferably from 85 to 95 ° C. This step is usually carried out with less agitation than the emulsification step, for example at 500-1,000 rpm, and for a period of one to several hours, for example from 2 to 4 hours. A first membrane is thus formed around each of the oily phase droplets.

One or more hydrophobic compounds as described above are then introduced into the aqueous phase. The introduction of this compound is carried out with stirring, for a period ranging for example from a few minutes to an hour, in particular from 20 to 40 minutes, at a temperature above the melting point of this hydrophobic compound or of all the compounds. hydrophobic, in the case where they are used as a mixture, for example at a temperature of 40 to 100 ° C, preferably from 50 to 100 ° C, more preferably from 60 to 100 ° C or even from 90 to 100 ° C. This hydrophobic compound can represent from 0.1 to 2% by weight, preferably from 0.3 to 1.2% by weight and, better still, from 0.4 to 1% by weight, relative to the total weight of the suspension thus formed.

The suspension obtained is then cooled while maintaining stirring, usually to room temperature, so as to crystallize said compound and thus to form a second membrane on the first membrane. During cooling or immediately after, it is possible to adjust the pH of the aqueous phase using any suitable base, to a value compatible with the application envisaged later. Alternatively or in addition, an additional surfactant can be added to the aqueous phase. In particular, an HLB surfactant greater than 8 is used which stabilizes the suspension of microcapsules. This surfactant can represent from 0.5 to 5% and preferably from 1 to 3% of the total weight of the suspension.

In a preferred embodiment of the invention, in the case where an aminoplast resin is used for the preparation of the first membrane, a formaldehyde scavenger can be added to the aqueous phase, either during the process for manufacturing the microcapsules, either later, in the suspension of microcapsules obtained. Examples of formaldehyde scavengers are urea; ethylene urea; rimidazolidin-2-one; tetrahydro-2-pyrimidone; melamine; diethanolamine; arginine; ammonia; acetylacetone; compounds comprising at least one acetoacetate function, such as methyl, tert-butyl or ethyl acetoacetate; dimethyl or methyl tert-butyl malonate; sodium sulfite; hydroxylamine hydrochloride; compounds containing from 1 to 16 carbon atoms and comprising at least one, advantageously several, hydrazide function (s), such as adipic acid dihydrazotide, isophthalic acid dihydrazide and carbodihydrazotide; and their mixtures.

The suspension of microcapsules according to the invention therefore advantageously contains in this case one or more formaldehyde scavenger (s) such as those above, which can represent for example from 0.1 to 10% by weight and preferably from 0, 4 to 5%, more preferably 0.4 to

2% by weight, relative to the total weight of the suspension, and advantageously reduces the concentration of formaldehyde dissolved in the aqueous phase.

At the end of this process, a suspension of microcapsules is obtained which can be used as such, possibly after concentration. Alternatively, the microcapsules can be collected by centrifugation or filtration, optionally washed with an appropriate solvent, then dried. They can thus be used in dry form.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 schematically illustrates the process for preparing the microcapsules according to the invention.

FIG. 2 represents the variation in the rate of encapsulation of perfume in different microcapsules containing variable amounts of magnesium stearate, stored at 70 ° C., as a function of time.

FIGS. 3A and 3B represent the alteration of the odor as a function of time (respectively before and after rubbing of a perfume encapsulated in microcapsules according to the invention and comparative microcapsules, impregnated on cardboards which were then stored at 70 ° C, by comparison with a control which is a perfume solution stored at 4 ° C.

FIG. 4 represents the alteration of the odor of a perfume encapsulated in microcapsules according to the invention and comparative microcapsules, stored at 70 ° C., then impregnated after washing on towels. FIG. 5 represents the olfactory intensity of a perfume encapsulated in microcapsules according to the invention and comparative microcapsules, after two months of storage in a softening base at room temperature, then impregnation after washing on towels washed by hand at 30 ° C.

Figure 6 illustrates the olfactory intensity, determined by a panel of experts, of a perfume encapsulated in microcapsules according to the invention and comparative microcapsules, then impregnated on towels washed in the machine and dried under different conditions.

Figure 7 illustrates the evolution of the formaldehyde concentration [F] (final concentration / initial formaldehyde concentration) as a function of time in suspensions of microcapsules according to the invention and comparative treated using two different formaldehyde scavengers (urea and tert-butyl acetoacetate).

EXAMPLES

The invention will be better understood in the light of the following examples, which are given purely by way of illustration and are not intended to limit the scope of the invention, defined by the appended claims.

Example 1 Preparation of a suspension of perfumed microcapsules

An oil-in-water emulsion was prepared by mixing, in order, 60g of water, 45g of surfactant (10% solution) consisting of a poly (methylvinylether-maleic anhydride) copolymer marketed by ASHLAND INC. . under the trade name Gantrez® AN-119 BF, 100 g of perfume and 12.5 g of melamine-formaldehyde prepolymer supplied by SYRIATOS SA under the trade name WF-70®. The mixing was carried out with vigorous stirring (7,500 rpm) for 10 minutes at 70-80 ° C. The agitation was reduced to 600 rpm and continued for 3 h at 90 ° C to form the wall of the microcapsules. Still with stirring, 1.2 g of magnesium stearate in the molten state (at 95-100 ° C.) were then added to the suspension. Stirring was continued for 30 min, then the suspension was cooled to room temperature to crystallize the magnesium stearate around the microcapsules. 5g of a second surfactant (Polysorbate 85 sold by the company E.R.C.A. SpA under the trade name Ercasorb® TOE V / FD) was added to the suspension, which was neutralized using a triethanolamine solution.

A suspension of perfume microcapsules with a two-layer structure was thus obtained.

Example 2: Stability test at 70 ° C

Suspensions similar to that described in Example 1, with a pH between 5 and 6.5 and containing variable amounts of magnesium stearate, were packaged in bottles stored at 70 ° C. The samples obtained were then tested at different time intervals to assess the rate of fragrance encapsulation.

The fragrance encapsulation rate corresponds to the mass percentage of encapsulated perfume compared to the mass percentage of total perfume. It is determined using a thermogravimetric analysis device (TGA 2 from Mettler). The method consists in determining the different mass losses after heating the samples according to a temperature ramp from 25 to

500 ° C at a speed of 10 ° C / min and with a volume of N2 = 20ml / min. The loss of encapsulated perfume takes place from 240 ° C. The residue level at 240 ° C. therefore corresponds to the sum of the mass of encapsulated perfume and the mass of the membranes (which is 7 g).

The results obtained are illustrated in Figure 2 attached, in which: C7b designates microcapsules not containing a second membrane C8 designates microcapsules containing 0.1% of magnesium stearate C9 designates microcapsules containing 0.2% of stearate magnesium C10 designates microcapsules containing 0.3% magnesium stearate Cil designates microcapsules containing 0.4% magnesium stearate C12b designates microcapsules containing 0.5% magnesium stearate C13 designates microcapsules containing 1% stearate magnesium C14 designates microcapsules containing 1.5% magnesium stearate

As can be seen from this Figure, the microcapsules not comprising a second membrane (C7b) have an initial fragrance encapsulation rate lower than most of the microcapsules according to the invention. In addition, this rate drops sharply from the first days of storage at 70 ° C and remains significantly lower than that obtained with all the microcapsules according to the invention. It is also observed that the microcapsules containing from 0.4 to 1% by weight, and in particular 0.5% by weight (C7b), of magnesium stearate are the most stable over time. The following tests were therefore carried out on these microcapsules.

Example 3: Olfactory alteration test

Example 3A: Test on cardboard boxes

The suspension of microcapsules prepared in Example 1 was diluted to 20% in distilled water. 70 mg of this solution was then applied to cardboard paper (or cardboard) which was left to dry for 30 min. The cardboards were then placed in an oven at 70 ° C. Comparative scented cardboards, impregnated with microcapsules lacking a second membrane but identical if not to those used above, were prepared under the same conditions.

A sensory evaluation was carried out by two expert panelists. A maximum of 4 samples were evaluated during each test, without exceeding 5 tests per day, so as not to saturate the panellists' sense of smell. The latter evaluated the olfactory intensity of the perfume and its possible deterioration by assigning to each sample a score on a scale of 0 to 10. The perfume is considered to be altered if its odor is different from that perceived for a witness consisting of a solution of the same perfume stored at 4 ° C. The further you go from the note of the control perfume, the more the odor is altered (example: smell of burning, hot, soap, acid, chlorine, sour, etc.). For each evaluation, the samples were felt blind, randomly and at least twice to confirm the mark awarded.

The evaluation was repeated after manual rubbing of the cardboard (the cardboard is folded in half in its center, the two sides are rubbed together with constant pressure by an experienced technician).

Figures 3A and 3B illustrate the results obtained on samples stored from 14 to 28 days. As shown in FIG. 3A, the perfume contained in the microcapsules according to the invention, containing 0.5% by weight of magnesium stearate (C12b), is less altered over time than that contained in the comparative microcapsules, devoid of seconds membrane (C7b). It is the same after rubbing (Figure 3B).

Example 3B: Test on towels

A solution containing 1% suspension of microcapsules according to Example 1, stored at 70 ° C. for 30 days, was prepared in an unscented softening base (commercial) which will be used for washing in the machine. Towels were placed tied in the drum of a washing machine. 25 g of this basic softener solution were added to the softener compartment of the machine, which was set to a softening program lasting approximately 15 min. The towels were then dried for 24 hours at room temperature. Comparative scented towels, impregnated with microcapsules lacking a second membrane but identical if not to those used above, were washed and dried under the same conditions.

The change in odor of the perfume was evaluated in the same way as above, using as a control a towel washed with the same program, using a softening base solution containing 1% of perfume under free form, stored at 4 ° C (fragrance identical to that encapsulated), and dried as above.

The results of this evaluation are shown in Figure 4. As shown in this Figure, the odor present on the towels treated with the microcapsules according to the invention (C 12b) is less altered than that present on the treated towels using comparative microcapsules, not comprising a second membrane (C7b).

These tests make it possible to conclude that the perfume microcapsules according to the invention are more stable in temperature than identical microcapsules but which do not contain a second membrane.

Example 4: Olfactory properties

Example 4A: Hand wash

A solution comprising 0.2% suspension was prepared according to Example 1 in a commercial softening base. This solution was stored for 2 months at room temperature, then 5 g of this solution were added to IL of tap water at 30 ° C. A small towel was immersed in the solution and stirred for 2 min before allowing it to soak for 15 min. The towel was then wrung and dried for 24 hours at room temperature. Comparative towels, impregnated with microcapsules lacking a second membrane but identical if not to those used above, were washed and dried under the same conditions.

A sensory evaluation was carried out by two expert panelists. A maximum of 4 samples were evaluated during each test, without exceeding 5 tests per day, so as not to saturate the panellists' sense of smell. The latter evaluated the olfactory intensity of the perfume by assigning each sample a score on a scale of 0 to 10. For each evaluation, the samples were smelled blind, randomly and at least twice to confirm the assigned rating.

The results of this evaluation are presented in Figure 5. As appears from this Figure, the odor present on the towels treated with the microcapsules according to the invention (C 12b) is more intense than that present on the towels treated using comparative microcapsules, not comprising a second membrane (C7b), after washing by hand at 30 ° C.

Example 4B: Machine wash

A solution was prepared by diluting 1% of suspension according to Example 1 in an unscented softening base. Towels were placed tied in the drum of a washing machine. 25g of this softener base was added to the softener compartment of the machine, which was set to a softener program lasting approximately 15 min. The towels were then dried either at room temperature for 24 hours, or in the dryer for 2 hours at 70 ° C or for 1 hour at 80 ° C. An additional sample was prepared using 2% suspension of microcapsules, which was dried for 3 h at 80 ° C. Comparative scented towels, impregnated with microcapsules lacking a second membrane but identical if not to those used above, were washed and dried under the same conditions.

The intensity of the scent of the perfume was evaluated in the same way as above.

The results of this evaluation are presented in Figure 6. As shown in this Figure, the odor present on the towels treated with the microcapsules according to the invention (C12b) is more intense than that present on the towels treated with using comparative microcapsules, not comprising a second membrane (C7b), whatever the drying method used.

These tests make it possible to conclude that the perfume microcapsules according to the invention are more effective, in a linen treatment application, than identical microcapsules but not containing a second membrane.

EXAMPLE 5 Measurement of the Free Formaldehyde Level

The suspension of microcapsules of Example 1 was divided into two samples treated respectively with two different formaldehyde traps: urea (U) (1.2% by weight) or tert-butyl acetoacetate (TBAA) ( 5.3% by weight). Two suspension samples of comparative microcapsules were prepared, containing microcapsules identical to those of Example 1 but lacking a second membrane, and mixed with the same formaldehyde scavengers in the same proportions.

The level of free formaldehyde in each of the samples was measured at different time intervals, using MQuant® analytical test kits supplied by MERCK KGa. The results of this test are shown in Figure 7. As shown in this Figure, the microcapsules according to the invention release less formaldehyde than the comparative microcapsules after 15 days of storage at room temperature.

Example 6: Detergent compositions

The compositions below were prepared in a conventional manner for a person skilled in the art, by mixing their constituents, designated here by their INCI names, in the proportions indicated.

6A - Softening composition

INCI % AQUA 82.8 DITALLOWOYLETHYL HYDROXYETHYLMONIUM methosulfate 16.5 CALCIUM CHLORIDE DIHYDRATE 0.6 benzisothiazolone 0.1

6B- Liquid detergent

INCI % AQUA 67.35 SODIUM HYDROXIDE (50%) 3.4 DODECYLBENZENE SULFONICACID 7 COCONUT ACID 3.2 CITRATE SODIUM 2.6 GLYCERETH -6 COCOATE 8.4 SODIUM LAURETH SULFATE 7 EDTA 1 benzisothiazolone 0.05

Claims (10)

1. Microcapsules formed of a heart consisting of an oily phase containing at least one perfume, said heart being coated with a first membrane containing at least one polymer and the outer surface of which is covered with a second membrane, characterized in that that the second membrane consists essentially of at least one non-silicone compound insoluble in water, having a melting point of between 20 and 120 ° C. 2. Microcapsules according to claim 1, characterized in that the non-silicone compound is chosen from linear or branched alkanes, linear fatty alcohols and saturated or unsaturated, linear or branched fatty acids, optionally hydroxylated, esterified, salified and / or oligomerized, and mixtures thereof. 3. Microcapsules according to claim 1 or 2, characterized in that the fatty acid salt is chosen from the salts of stearic acid and ricinoleic acid, preferably magnesium stearate or zinc ricinoleate, more preferably stearate magnesium. 4. Microcapsules according to any one of claims 1 to 3, characterized in that the polymer of the first membrane is chosen from: phenol-formaldehyde resins; optionally etherified aminoplast resins, in particular urea-formaldehyde, melamineformaldehyde, melamine-urea-formaldehyde, glycoluril-formaldehyde, acetoguanamineformaldehyde or benzoguanamine-formaldehyde, in which the urea can be replaced by an alkylene or a thiourea and / or formaldehyde replaced by glyoxal, as well as their methyl derivatives; polyureas; epoxy resins; polyimides; polyamides; polyurethanes, poly (meth) acrylates; as well as their mixtures. 5. Microcapsules according to claim 4, characterized in that the polymer of the first membrane is chosen from aminoplast resins, preferably ureaformaldehyde or melamine-formaldehyde or melamine-urea-formaldehyde resins, and polyureas. 6. Suspension of microcapsules, characterized in that it comprises microcapsules according to any one of claims 1 to 5 in an aqueous medium. 7. Suspension of microcapsules according to claim 6, characterized in that it also contains at least one formaldehyde trapper chosen from: urea; ethylene urea; rimidazolidin-2-one; tetrahydro-2-pyrimidone; melamine; diethanolamine; arginine; ammonia; acetylacetone; compounds comprising at least one acetoacetate function, such as methyl, tert-butyl or ethyl acetoacetate; dimethyl or methyl tert-butyl malonate; sodium sulfite; hydroxylamine hydrochloride; compounds containing from 1 to 16 carbon atoms and comprising at least one, advantageously several, hydrazide function (s), such as adipic acid dihydrazotide, isophthalic acid dihydrazide and carbodihydrazotide; and their mixtures. 8. A method of preparing the microcapsules according to any one of claims 1 to 5 or of the suspension according to claim 6 or 7, characterized in that it comprises the following successive steps: a) an emulsion of an oily phase containing at least one perfume is formed in an aqueous phase, in the presence of at least one surfactant and at least one monomer or prepolymer, b) heating said emulsion with stirring so as to polymerize said monomers or prepolymers and thus to form a first membrane around the oily phase, c) at least one hydrophobic compound in the molten state is introduced into said aqueous phase with stirring, said hydrophobic compound being a non-silicone compound insoluble in water, having a melting point of between 20 and 120 ° C., d) the suspension thus obtained is cooled with stirring, so as to crystallize said hydrophobic compound and thus to form a second membrane on the first membrane, e) optionally, said microcapsules are isolated and dried. 9. Use of the microcapsules according to any one of claims 1 to 5 or of the suspension according to claim 6 or 7 as a scent additive in a detergent, cosmetic or pharmaceutical composition or in textile materials, paper or cardboard, preferably in a detergent composition. 10. A detergent composition comprising microcapsules according to any one of claims 1 to 5 or the suspension according to claim 6 or 7.