METHOD FOR THE PRODUCE OF CAPSULES CONTAINING AT LEAST A WATER-SOLUBLE OR HYDROPHILIC SUBSTANCE AND CAPSULES PRODUCED THERETHER

Description

[0001] The present invention relates to a process for preparing capsules comprising at least one water-soluble or hydrophilic substance. It also relates to the capsules as obtained and to compositions containing them.

[0002] Many highly water-soluble or hydrophilic substances are often added to formulated products to give them interesting application properties or increase their performance. In some cases, these substances are fragile molecules that are susceptible to degradation as a result of interactions with their environment by mechanisms such as hydrolysis, thermal denaturation or oxidation, which leads to a reduction in the performance of the formulated product.

[0003] In other cases, these substances strongly modify the ionic strength of the formulated product, which has harmful consequences on the stability of the product which may, for example, undergo rapid phase separation.

[0004] In other cases, these substances react with other components of the formulated product, which also leads to adverse effects on stability and reduced performance.

[0005] The encapsulation of water-soluble or hydrophilic substances represents a very interesting way to overcome the limitation of performance or stability of the formulated products which contain them.

[0006] A large number of capsules have been developed to protect and / or isolate active ingredients in formulated products, particularly water-soluble or hydrophilic substances. These capsules result from manufacturing processes such as atomization ( spray drying), interfacial polymerization, interfacial precipitation or solvent evaporation among many others. The shell of the capsules made by these processes does not constitute a sufficiently tight barrier to the diffusion of molecules as small as the water-soluble or hydrophilic substances dissolved in their core or to the chemical species responsible for the degradation of substances such as oxygen or water. Thus, these capsules result in a relatively rapid leakage of the water-soluble or hydrophilic substances they contain, accompanied by a rapid degradation of these substances once the capsules are dispersed in the formulated product.

[0007] Document US 2004 / 234738 A1 discloses a method for preparing solid microcapsules. US 2009 / 289216 A1 discloses solid microcapsules.

[0008] The difficulty of preventing the diffusion of molecules as small as water-soluble or hydrophilic substances or chemical species responsible for the degradation of substances means that to date there is no capsule with satisfactory protection and retention properties for water-soluble or hydrophilic substances.

[0009] The present invention therefore aims to provide a method for encapsulating water-soluble or hydrophilic, or even very water-soluble or hydrophilic, substances, while avoiding the aforementioned contamination problems.

[0010] The present invention also aims to provide a double emulsion encapsulation process making it possible to obtain capsules of controlled size, in particular of a size less than 20 µm, or even 5 µm.

[0011] The present invention also aims to provide capsules containing at least one water-soluble or hydrophilic substance, or even very water-soluble or hydrophilic, having excellent retention capacities.

[0012] The present invention also aims to provide capsules containing at least one water-soluble or hydrophilic substance, or even very water-soluble or hydrophilic, having several protective barriers, in particular a steric barrier, a thermodynamic barrier and a physical barrier.

[0013] Thus, the present invention relates to a method for preparing solid microcapsules comprising the following steps: a) the preparation of a composition C1, comprising at least one water-soluble or hydrophilic substance dispersed in a hydrophobic phase, said substance having a solubility in water, measured at room temperature at 25°C ± 2°C, and at room pressure at 0.1013 MPa (1013 mbar), at least equal to 1 g / L, b) the addition with stirring of said composition C1 into a polymeric composition C2, compositions C1 and C2 not being miscible in each other, said composition C1 being at a temperature between 0°C and 100°C, composition C2 comprising at least one monomer or polymer, at least one crosslinking agent, and optionally at least one photoinitiator or crosslinking catalyst, and being at a temperature between 0°C and 100°C, the viscosity of composition C2 being between 500 mPa.s and 100,000 mPa.s at 25°C, and preferably being greater than the viscosity of composition C1, whereby an emulsion (E1) is obtained comprising drops of composition C1 dispersed in composition C2; c) the dropwise addition with stirring of the emulsion (E1) into a composition C3, compositions C2 and C3 not being miscible in each other, said emulsion (E1) being at a temperature between 15°C and 60°C and said composition C3 being at a temperature between 15°C and 60°C, the viscosity of composition C3 being between 500 mPa.s and 100,000 mPa.s at 25°C, and preferably being greater than the viscosity of the emulsion (E1), whereby a double emulsion (E2) comprising drops dispersed in the composition C3 is obtained; d) applying shear to the emulsion (E2), whereby a double emulsion (E3) comprising drops of controlled size dispersed in the composition C3 is obtained; and e) polymerizing the composition C2, whereby solid microcapsules dispersed in the composition C3 are obtained. the viscosities being measured, for a shear rate equal to 10 s- 1 , using a rheometer equipped with a cone of diameter 60 mm and angle 2 degrees, and a temperature regulation cell set at 25°C.

[0014] The process of the invention therefore makes it possible to prepare solid microcapsules comprising a core and a solid envelope completely encapsulating the core at its periphery, in which the core is a composition C1 comprising at least one water-soluble or hydrophilic substance dispersed in a hydrophobic phase.

[0015] The microcapsules obtained according to the process of the invention advantageously make it possible to protect the water-soluble or hydrophilic substances that they contain from degradation by degrading chemical species originating from the external environment of the capsules, according to 3 different mechanisms: the diffusion towards the interior of the capsule of chemical species causing the degradation of water-soluble or hydrophilic substances is advantageously limited by the rigid envelope with high crosslinking density of the capsules; the hydrophobic phase of the core constitutes an additional barrier to slow down the diffusion of hydrophilic degrading species to the water-soluble or hydrophilic substances; and when the water-soluble or hydrophilic substances are in a solid state (i.e. for example in the form of particles or crystals as described below), this state limits the quantity of material in direct contact with the degrading species: only an outer layer is in direct contact with the hydrophobic phase which contains the water-soluble or hydrophilic substances.The diffusion of chemical species inside a solid being extremely slowed down compared to a liquid, the molecules of water-soluble or hydrophilic substances, located at the center of the particles, are completely isolated from the degrading chemical species.

[0016] The capsules of the invention are particularly advantageous in that they have several retention barriers in order to achieve this level of performance: a steric barrier: due to their size, water-soluble or hydrophilic substances, in particular in solid form, in particular in the form of particles and / or in the form of a crystal, in particular a salt, preferably with an average size of less than 1 µm, cannot pass through the pores of the rigid polymer shell; a thermodynamic barrier: the solubility of water-soluble or hydrophilic substances in the hydrophobic phase of the core of the capsules is negligible, eliminating the possibility for the molecules of water-soluble or hydrophilic substances to dissolve in the core and then diffuse more quickly towards the outside of the capsule; and a physical barrier: the solid shell advantageously limits the diffusion of dissolved chemical species towards the outside of the capsule.

[0017] The process of the invention consists of producing a double emulsion composed of droplets of a hydrophobic phase containing the water-soluble or hydrophilic substances, enveloped in a crosslinkable liquid phase. These double droplets are then made monodisperse in size before being transformed by crosslinking or polymerization into rigid capsules. The preparation involves 5 steps described below in detail. Step a)

[0018] Step a) of the process according to the invention consists of preparing a composition C1 comprising at least one water-soluble or hydrophilic substance. Composition C1

[0019] Composition C1 is a dispersion and comprises at least one water-soluble or hydrophilic substance, dispersed in a hydrophobic phase.

[0020] According to the invention, the term "water-soluble or hydrophilic substance" means a substance having a solubility in water, measured at room temperature, for example T=25°C ± 2°C, in particular at 25°C, and at room pressure, for example at 0.1013 MPa (1013 mbar), at least equal to 1 gram / litre (g / L) (obtaining a macroscopically isotropic and transparent solution, coloured or not).

[0021] This solubility is preferably greater than or equal to 10 g / L, in particular greater than or equal to 50 g / L, or even greater than or equal to 100 g / L.

[0022] Furthermore, the solubility of the water-soluble or hydrophilic substance in the hydrophobic phase is advantageously less than 20 g / L, preferably less than 10 g / L, and more preferably less than 1 g / L.

[0023] According to one embodiment, the water-soluble or hydrophilic substance is in a solid state (or form) in the absence of water, at room temperature, for example T=25°C ± 2°C, and at room pressure, for example 1013 mbar (or 0.1013 MPa), and in particular is in the form of particles and / or in the form of a crystal, in particular a salt, preferably with an average size of less than 1 µm.

[0024] In the context of the present invention, the term "size" designates the diameter, in particular the average diameter, of the particles and / or crystals.

[0025] According to one embodiment, among the water-soluble or hydrophilic substances, mention may be made of those chosen from the group consisting of the following compounds: ascorbic acid, in particular L-ascorbic acid, and its biologically compatible derivatives or salts, such as, for example, ethyl vitamin C; enzymes; antibiotics; components with a tensor effect; alpha-hydroxy acids and their salts; hydroxylated polyacids; sucroses and their derivatives; urea; amino acids; oligopeptides; water-soluble plant and yeast extracts; protein hydrolysates; hyaluronic acid; mucopolysaccharides; vitamins B1, B2, B3, B6, B12, H,PP; panthenol; folic acid; acetyl salicylic acid; allantoin; glycyrrhetic acid; kojic acid; hydroquinone; dihydroxyacetone (or DHA); EUK 134 (INCI name: Ethylbisiminomethylguaiacol manganese chloride); organometallic or inorganometallic catalysts of platinum, palladium, titanium, molybdenum, copper or zinc; disinfectant and antibacterial agents and in particular silver salts; brightening or lightening agents, dispersibility modifiers, stabilizers, stain removing agents in particular listed in US 6,335,315 and US 5,877,14; compounds usable as flame retardants or flame retardants such as boron salts, aluminium hydrates or magnesium hydroxides, compounds usable as phase change materials (PCMs) such as ammonium carbonate, ammonium chloride, caesium carbonate, caesium sulphate,calcium citrate, calcium chloride, calcium hydroxide, calcium phosphate, calcium saccharate, calcium sulfate, cerium phosphate, iron phosphate, lithium carbonate, lithium sulfate, magnesium chloride, magnesium sulfate, manganese chloride, manganese nitrate, manganese sulfate, potassium acetate, potassium carbonate, potassium chloride, potassium phosphate, rubidium carbonate, rubidium sulfate, disodium tetraborate, sodium acetate, sodium bicarbonate, sodium bisulfate, sodium citrate, sodium chloride, sodium hydroxide, sodium nitrate, sodium percarbonate, sodium persulfate, sodium phosphate, sodium propionate, sodium selenite, sodium silicate, sodium sulfate, sodium tellurate, sodium thiosulfate, hydrophosphate strontium, zinc acetate, zinc chloride,sodium thiosulfate, and polyethylene glycols.,

[0026] A composition C1 according to the invention may advantageously comprise from 0.1% to 40%, preferably from 0.5% to 35%, in particular from 1% to 30%, better still from 5% to 25%, and better still from 10% to 20%, by weight of water-soluble or hydrophilic substance(s) relative to the total weight of said composition C1.

[0027] According to one embodiment, for optimal protection, the hydrophobic phase of composition C1 comprises oils having medium polarity with low interfacial tension with water.

[0028] According to a preferred embodiment, the hydrophobic phase of composition C1 comprises at least one oil whose interfacial tension with water is between 25 mN / m and 50 mN / m. The interfacial tension (or surface tension) is measured according to conventional methods, in particular according to the hanging drop method or according to the Du Noüy ring method. The Du Noüy ring technique consists of immersing a platinum ring in the liquid whose surface tension is to be measured and then exerting traction on the ring towards the liquid / air interface at room temperature. The tensiometer will search for the maximum force at this interface and measure it (figure k in application FR 3 004 641). This force is written Pm and is not obtained directly; it is subject to a correction according to the geometry of the ring. The device will first calculate gs* called the measured surface tension.It is obtained by the relation: gs* = Pm / [2p(Ri + Ro)]; with Ri and Ro the radii respectively inside and outside the ring. Then, he will deduce gs from the relation: gs = gs*.F; where F is the correction factor depending on the density of the liquid as well as the ratio of the diameters of the ring. The manipulation is carried out with a Krüss K12 tensiometer, the liquid is placed in a perfectly cleaned crystallizer (46mm diameter crystallizer ref GL5 from Kruss) and the ring is made of iridium-platinum (ref R101 from Kruss). The device gives the surface tension directly in mN / m.

[0029] Preferably, the oil is chosen from vegetable, animal or synthetic oils.

[0030] These oils can be of different chemical nature such as: esters, ethers, alkanes, alcohols, alkenes, vegetable oils, of natural or synthetic origin, hydrocarbons or silicones, linear or branched, polymerized or not.

[0031] Examples of these oils include paraffin oil and polyalphaolefins.

[0032] When the water-soluble or hydrophilic substance is in a solid form, in particular in the form of particles and / or crystals, in particular with an average size of less than 1 µm, composition C1 can be prepared in several ways.

[0033] One technique involves creating water droplets containing the water-soluble or hydrophilic substance in dissolved form, and then evaporating the water.

[0034] Thus, according to a first embodiment, composition C1 is prepared by dispersing, in the hydrophobic phase, at least one solid water-soluble or hydrophilic substance in powder form, obtained in particular by atomization.

[0035] Atomization ( spray drying) in fact makes it possible to obtain particles in powder form which is then dispersed in the hydrophobic phase which will ultimately form the core of the microcapsules according to the invention.

[0036] According to another embodiment, composition C1 is obtained by preparing a nanoemulsion of water droplets in the hydrophobic phase. Nanoemulsions are a class of emulsions which generally have a number average droplet size less than or equal to 1 µm, preferably less than or equal to 800 nm.

[0037] The nanoemulsion thus obtained will form the heart of the capsules.

[0038] The nanoemulsion thus obtained can then be dried by stirring under reduced pressure and / or heating or by freeze-drying. In the case of drying by stirring under reduced pressure, the nanoemulsion, stirred using a propeller stirrer or a magnetic bar set in motion by a magnetic stirrer, is placed in an enclosure whose pressure is brought by means of a vacuum pump below 0.01 MPa (100 mbar), preferably below 0.005 MPa (50 mbar), even better below 0.001 MPa (10 mbar), thus allowing the water to evaporate from the droplets. According to a variant of the process, the enclosure can be equipped with a condensation column to maintain the vapor pressure of the water well below the saturated vapor pressure.In the case of drying by heating, the nanoemulsion, stirred by means of a propeller stirrer or a magnetic bar set in motion by a magnetic stirrer, is heated to a temperature between 30°C and 70°C, thus allowing the water to evaporate from the droplets. According to a variant of the process, drying under reduced pressure and by heating can be combined if necessary. In the case of drying by lyophilization, the nanoemulsion is introduced into a lyophilizer. This process consists of freezing the nanoemulsion at a temperature preferably higher than the solidification temperature of the hydrophobic phase of composition C1, then removing the water by sublimation.

[0039] A second technique consists of grinding a coarse powder of at least one solid water-soluble or hydrophilic substance to obtain particles of the desired size and then dispersing them in the hydrophobic phase which will ultimately form the core of the capsules.

[0040] Thus, according to yet another embodiment, composition C1 is obtained by grinding at least one solid water-soluble or hydrophilic substance and then by dispersing said ground substance in the hydrophobic phase. Step b)

[0041] Step b) of the process according to the invention consists of preparing a first emulsion (E1).

[0042] The first emulsion consists of a dispersion of droplets of composition C1 in a polymeric composition C2 immiscible with C1, created by dropwise addition of C1 into C2 with stirring.

[0043] During step b), composition C1 is at a temperature between 0°C and 100°C, preferably between 10°C and 80°C, and preferentially between 15°C and 60°C. During step b), composition C2 is at a temperature between 0°C and 100°C, preferably between 10°C and 80°C, and preferentially between 15°C and 60°C.

[0044] Under the addition conditions of step b), compositions C1 and C2 are not miscible with each other, which means that the quantity (by weight) of composition C1 capable of being solubilized in composition C2 is less than or equal to 5%, preferably less than 1%, and preferentially less than 0.5%, relative to the total weight of composition C2, and that the quantity (by weight) of composition C2 capable of being solubilized in composition C1 is less than or equal to 5%, preferably less than 1%, and preferentially less than 0.5%, relative to the total weight of composition C1.

[0045] Thus, when composition C1 comes into contact with composition C2 under stirring, the latter is dispersed in the form of drops, called simple drops.

[0046] Composition C2 is stirred to form an emulsion comprising drops of composition C1 dispersed in composition C2. This emulsion is also called a “simple emulsion” or C1-in-C2 emulsion.

[0047] To carry out step b), any type of agitator usually used to form emulsions may be used, such as, for example, a mechanical paddle agitator, a static emulsifier, an ultrasonic homogenizer, a membrane homogenizer, a high-pressure homogenizer, a colloid mill, a high-shear disperser or a high-speed homogenizer.

[0048] Composition C1 is as defined previously. Composition C2

[0049] Composition C2 is intended to form the future solid envelope of the microcapsules.

[0050] The volume fraction of C1 in C2 can vary from 0.1 to 0.7 in order to control the thickness of the capsule shell obtained at the end of the process.

[0051] According to one embodiment, the ratio between the volume of composition C1 and the volume of composition C2 varies between 1:10 and 10:1. Preferably, this ratio is between 1:3 and 5:1, preferably between 1:3 and 3:1.

[0052] Preferably, the viscosity of composition C2 at 25°C is between 1,000 mPa.s and 50,000 mPa.s, preferably between 2,000 mPa.s and 25,000 mPa.s, and for example between 3,000 mPa.s and 15,000 mPa.s.

[0053] Preferably, the viscosity of composition C2 is greater than the viscosity of composition C1.

[0054] Viscosity is measured using a Haake Rheostress ™< 600 rheometer equipped with a 60 mm diameter cone with a 2 degree angle and a temperature control cell set at 25°C. The viscosity value is read for a shear rate equal to 10 s -1< .

[0055] According to this embodiment, the destabilization kinetics of the emulsion drops (E1) is significantly slow, which allows the shell of the microcapsules to be polymerized during step e) before the emulsion destabilizes. The polymerization, once completed, then provides thermodynamic stabilization. Thus, the relatively high viscosity of composition C2 ensures the stability of the emulsion (E1) obtained at the end of step b).

[0056] Preferably, the interfacial tension between compositions C1 and C2 is low. Typically, these interfacial tensions vary between 0 mN / m and 50 mN / m, preferably between 0 mN / m and 20 mN / m.

[0057] The low interfacial tension between compositions C1 and C2 also advantageously ensures the stability of the emulsion (E1) obtained at the end of step b).

[0058] Composition C2 contains at least one monomer or polymer, at least one crosslinking agent, and optionally at least one photoinitiator or crosslinking catalyst, thus making it crosslinkable.

[0059] According to one embodiment, composition C2 comprises from 50% to 99% by weight of monomer or polymer, or a mixture of monomers or polymers, relative to the total weight of composition C2.

[0060] According to one embodiment, composition C2 comprises from 1% to 20% by weight of crosslinking agent or a mixture of crosslinking agents, relative to the total weight of composition C2.

[0061] According to one embodiment, composition C2 comprises from 0.1% to 5% by weight of photoinitiator or a mixture of photoinitiators, relative to the total weight of composition C2.

[0062] According to one embodiment, composition C2 comprises from 0.001% to 70% by weight of crosslinking agent relative to the weight of said composition C2.

[0063] According to the invention, the term "monomer" or "polymer" designates any basic unit suitable for the formation of a solid material by polymerization, either alone or in combination with other monomers or polymers.

[0064] These monomers may be chosen from monomers comprising at least one reactive function chosen from the group consisting of acrylate, methacrylate, vinyl ether, N-vinyl ether, mercaptoester, thiolene, siloxane, epoxy, oxetane, urethane, isocyanate and peroxide functions.

[0065] In particular, the monomers may be chosen from monomers carrying at least one of the aforementioned reactive functions and also carrying at least one function chosen from the group consisting of primary, secondary and tertiary alkylamine functions, quaternary amine functions, sulfate, sulfonate, phosphate, phosphonate, carboxylate, hydroxyl, halogen functions, and mixtures thereof.

[0066] The polymers used in composition C2 may be chosen from polyethers, polyesters, polyurethanes, polyureas, polyethylene glycols, polypropylene glycols, polyamides, polyacetals, polyimides, polyolefins, polysulfides and polydimethylsiloxanes, said polymers also carrying at least one reactive function chosen from the group consisting of acrylate, methacrylate, vinyl ether, N-vinyl ether, mercaptoester, thiolene, siloxane, epoxy, oxetane, urethane, isocyanate and peroxide functions.

[0067] Examples of such polymers include, but are not limited to, the following polymers: poly(2-(1-naphthyloxy)-ethyl acrylate), poly(2-(2-naphthyloxy)-ethyl acrylate), poly(2-(2-naphthyloxy)-ethyl methacrylate), polysorbitol dimethacrylate, polyacrylamide, poly((2-(1-naphthyloxy) ethanol), poly(2-(2-naphthyloxy) ethanol), poly(1-chloro-2,3-epoxypropane), poly(n-butyl isocyanate), poly(N-vinyl carbazole), poly(N-vinyl pyrrolidone), poly(p-benzamide), poly(p-chlorostyrene), poly(p-methyl styrene), poly(p-phenylene oxide), poly(p-phenylene sulfide), poly(N-(methacryloxyethyl)succinimide), polybenzimidazol, polybutadiene, polybutylene terephthalate, polychloral, polychloro trifluoroethylene, polyether imide, polyether ketone, polyether sulfone, polyhydridosilsesquioxane, poly(m-phenylene isophthalamide), poly(methyl 2-acrylamido-2-methoxyacetate), poly(2-acrylamido-2-methylpropanesulfonic acid), poly-mono-butyl maleate, polybutylmethacrylate,poly(N-tert-butylmethacrylamide), poly(Nn-butylmethacrylamide), polycyclohexylmethacrylamide, poly(m-xylenebisacrylamide 2,3-dimethyl-1,3-butadiene,N,N-dimethylmethacrylamide), poly(n-butyl methacrylate), poly(cyclohexyl methacrylate), polyisobutyl methacrylate, poly(4-cyclohexylstyrene), polycyclol acrylate, polycyclol methacrylate, polydiethyl ethoxymethylenemalonate, poly(2,2,2-trifluoroethyl methacrylate), poly(1,1,1-trimethylolpropane trimethacrylate), polymethacrylate, poly(N,N-dimethylaniline, dihydrazide), poly(isophthalic dihydrazine), polyisophthalic acid, polydimethyl benzilketal, epichlorohydrin, poly(ethyl-3,3-diethoxyacrylate), poly(ethyl-3,3-dimethylacrylate), poly(ethyl vinyl ketone), poly(vinyl ethyl ketone), poly(penten-3-one), polyformaldehyde poly(diallyl acetal), polyfumaronitrile, polyglyceryl propoxy triacrylate, polyglyceryl trimethacrylate, polyglycidoxypropyltrimethoxysilane, polyglycidyl acrylate, poly(n-heptyl acrylate),poly(n-heptyl acrylic acid ester), poly(n-heptyl methacrylate), poly(3-hydroxypropionitrile), poly(2-hydroxypropyl acrylate), poly(2-hydroxypropyl methacrylate), poly(N-(methacryloxyethyl)phthalimide), poly(1,9-nonanediol diacrylate), poly(1,9-nonanediol dimethacrylate), poly(N-(n-propyl) acrylamide), poly(ortho-phthalic acid), poly(iso-phthalic acid), poly(1,4-benzenedicarboxylic acid), poly(1,3-benzenedicarboxylic acid), poly(phthalic acid), poly(mono-2-acryloxyethyl ester), polyterephthalic acid, polyphthalic anhydride, polyethylene glycol diacrylate, polyethylene glycol methacrylate, polyethylene glycol dimethacrylate, poly(isopropyl acrylate), polysorbitol pentaacrylate, polyvinyl bromoacetate, polychloroprene, poly(di-n-hexyl silylene), poly(di-n-propyl siloxane), polydimethyl silylene, polydiphenyl siloxane, polyvinyl propionate, polyvinyl triacetoxysilane, polyvinyl tris-tert-butoxysilane, polyvinyl butyral, polyvinyl alcohol, polyvinyl acetate,polyethylene co-vinyl acetate, poly(bisphenol-A polysulfone), poly(1,3-dioxepane), poly(1,3-dioxolane), poly(1,4-phenylene vinylene), poly(2,6-dimethyl-1A-phenylene oxide), poly(4-hydroxybenzoic acid), poly(4-methyl pentene-1), poly(4-vinyl pyridine), polymethylacrylonitrile, polymethylphenylsiloxane, polymethylsilmethylene, polymethylsilsesquioxane, poly(phenylsilsesquioxane), poly(pyromellitimide-1,4-diphenyl ether), polytetrahydrofuran, polythiophene, poly(trimethylene oxide), polyacrylonitrile, polyether sulfone, polyethylene-co-vinyl acetate, poly(perfluoroethylene propylene), poly(perfluoroalkoxyl alkane), or poly(styrene-acrylonitrile).,

[0068] By "crosslinking agent" is meant a compound carrying at least two reactive functions capable of crosslinking a monomer or a polymer, or a mixture of monomers or polymers, during its polymerization.

[0069] The crosslinking agent may be chosen from molecules carrying at least two functions chosen from the group consisting of acrylate, methacrylate, vinyl ether, N-vinyl ether, mercaptoester, thiolene, siloxane, epoxy, oxetane, urethane, isocyanate and peroxide functions.

[0070] As crosslinking agents, we can notably cite: diacrylates, such as 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, polyethylene glycol dimethacrylate, 1,9-nonanediol dimethacrylate, 1,4-butanediol dimethacrylate, 2,2-bis(4-methacryloxyphenyl) propane, 1,3-butanediol dimethacrylate, 1,10-decanediol dimethacrylate, bis(2-methacryloxyethyl) N,N'-1,9-nonylene biscarbamate, 1,4-butanediol diacrylate, ethylene glycol diacrylate, 1,5-pentanediol dimethacrylate, 1,4-Phenylene diacrylate, allyl methacrylate, N,N'-methylenebisacrylamide, 2,2-bis[4-(2-hydroxy-3-methacryloxypropoxy)phenyl]propane, tetraethylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, triethylene glycol dimethacrylate, polyethylene glycol diglycidyl ether, N,N-diallylacrylamide, 2,2-bis[4-(2-acryloxyethoxy)phenyl]propane, glycidyl methacrylate;multifunctional acrylates such as dipentaerythritol pentaacrylate, 1,1,1-trimethylolpropane triacrylate, 1,1,1-trimethylolpropane trimethacrylate, ethylenediamine tetramethacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate; acrylates also having another reactive function, such as propargyl methacrylate, 2-Cyanoethyl acrylate, tricyclodecane dimethanol diacrylate, hydroxypropyl methacrylate, N-acryloxysuccinimide, N-(2-Hydroxypropyl)methacrylamide, N-(3-aminopropyl)methacrylamide hydrochloride, N-(t-BOC-aminopropyl)methacrylamide, 2-aminoethyl methacrylate hydrochloride, monoacryloxyethyl phosphate, o-nitrobenzyl methacrylate, acrylic anhydride, 2-(tert-butylamino)ethyl methacrylate, N,N-diallylacrylamide, glycidyl methacrylate, 2-hydroxyethyl acrylate, 4-(2-acryloxyaehoxy)-2-hydroxybenzophenone, N-(Phthalimidomethyl)acrylamide, cinnamyl methacrylate.;

[0071] By "photoinitiator" we mean a compound capable of fragmenting under the effect of light radiation.

[0072] The photoinitiators that can be used according to the present invention are known in the art and are described, for example, in "Photoinitiators in the crosslinking of coatings", G. Li Bassi, Double Liaison - Chimie des Peintures, No. 361, November 1985, pp. 34-41; "Industrial applications of photoinduced polymerization", Henri Strub, L'Actualité Chimique, February 2000, pp. 5-13; and "Photopolymers: theoretical considerations and setting reaction", Marc, JM Abadie, Double Liaison - Chimie des Peintures, No. 435-436, 1992, pp. 28-34.

[0073] These photoinitiators include: α-hydroxyketones, such as 2-hydroxy-2-methyl-1-phenyl-1-propanone, marketed for example under the names DAROCUR ®< 1173 and 4265, IRGACURE ®< 184, 2959, and 500 by the company BASF, and ADDITOL ®< CPK by the company CYTEC; α-aminoketones, in particular 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1, marketed for example under the names IRGACURE ®< 907 and 369 by the company BASF; aromatic ketones marketed for example under the name ESACURE ®< TZT by LAMBERTI; or thioxanthones marketed for example under the name ESACURE ®< ITX by LAMBERTI, and quinones. These aromatic ketones most often require the presence of a hydrogen donor compound such as tertiary amines and in particular alkanolamines. We can notably cite the tertiary amine ESACURE ®< EDB marketed by the company LAMBERTI. α-dicarbonyl derivatives, the most common representative of which is benzyldimethylketal marketed under the name IRGACURE ®< 651 by BASF. Other commercial products are marketed by the company LAMBERTI under the name ESACURE ®< KB1, and acylphosphine oxides, such as, for example, bis-acylphosphine oxides (BAPO) marketed for example under the names IRGACURE ®< 819, 1700, and 1800, DAROCUR ®< 4265, LUCIRIN ®< TPO, and LUCIRIN ®< TPO-L by the company BASF.

[0074] Among the photoinitiators, aromatic ketones such as benzophenone, phenylglyoxylates, such as phenyl glyoxylic acid methyl ester, oxime esters, such as [1-(4-phenylsulfanylbenzoyl)heptylideneamino]benzoate, sulfonium salts, iodonium salts and oxime sulfonates may also be mentioned.

[0075] According to one embodiment, composition C2 may further comprise an additional monomer or polymer capable of improving the properties of the shell of the microcapsules and / or of giving new properties to the shell of the microcapsules.

[0076] Among these additional monomers or polymers, we can cite monomers or polymers carrying a group sensitive to pH, temperature, UV or IR.

[0077] These additional monomers or polymers can induce the rupture of solid microcapsules and subsequently the release of their contents, after stimulation via pH, temperature, UV or IR.

[0078] These additional monomers or polymers may be chosen from monomers or polymers carrying at least one reactive function chosen from the group consisting of acrylate, methacrylate, vinyl ether, N-vinyl ether, mercaptoester, thiolene, siloxane, epoxy, oxetane, urethane, isocyanate and peroxide functions, and also carrying one of the following groups: a hydrophobic group such as a fluorinated group, for example, trifluoroethyl methacrylate, trifluoroethyl acrylate, tetrafluoropropyl methacrylate, pentafluoropropyl acrylate, hexafluorobutyl acrylate, or fluorophenyl isocyanate; a pH-sensitive group such as primary, secondary, or tertiary amines, carboxylic acids, phosphate, sulfate, nitrate, or carbonate groups; a UV-sensitive or UV-cleavable group (or photochromic group) such as azobenzene, spiropyran, 2-diazo-1,2-naphthoquinone, o-nitrobenzyl, thiol, or 6-nitro-veratroyloxycarbonyl groups, for example, poly(ethylene oxide)-block-poly(2-nitrobenzylmethacrylate), and other block copolymers, as described in particular in Liu et al., Polymer Chemistry 2013, 4, 3431-3443; an IR-sensitive or IR-cleavable group such as o-nitrobenzyl or 2-diazo-1,2-naphthoquinone, e.g., the polymers described in Liu et al., Polymer Chemistry 2013, 4, 3431-3443; and a temperature-sensitive group such as poly(N-isopropylacrylamide). . Step c)

[0079] Step c) of the process according to the invention consists of preparing a second emulsion (E2).

[0080] The second emulsion consists of a dispersion of droplets of the first emulsion in a composition C3 immiscible with C2, created by dropwise addition of the emulsion (E1) into C3 under stirring.

[0081] During step c), the emulsion (E1) is at a temperature between 15°C and 60°C. During step c), the composition C3 is at a temperature between 15°C and 60°C.

[0082] Under the addition conditions of step c), compositions C2 and C3 are not miscible with each other, which means that the quantity (by weight) of composition C2 capable of being solubilized in composition C3 is less than or equal to 5%, preferably less than 1%, and preferentially less than 0.5%, relative to the total weight of composition C3, and that the quantity (by weight) of composition C3 capable of being solubilized in composition C2 is less than or equal to 5%, preferably less than 1%, and preferentially less than 0.5%, relative to the total weight of composition C2.

[0083] Thus, when the emulsion (E1) comes into contact with the composition C3 under stirring, the latter is dispersed in the form of drops, called double drops, the dispersion of these drops of emulsion (E1) in the continuous phase C3 being called emulsion (E2).

[0084] Typically, a double drop formed during step c) corresponds to a single drop of composition C1 as described above, surrounded by an envelope of composition C2 which completely encapsulates said single drop.

[0085] The double drop formed during step c) may also comprise at least two single drops of composition C1, said single drops being surrounded by an envelope of composition C2 which totally encapsulates said single drops.

[0086] Thus, said double drops comprise a core consisting of one or more single drops of composition C1, and a layer of composition C2 surrounding said core.

[0087] The resulting emulsion (E2) is usually a polydisperse double emulsion (C1-in-C2-in-C3 emulsion or C1 / C2 / C3 emulsion), meaning that the double drops do not have a clear size distribution in the emulsion (E2).

[0088] The immiscibility between compositions C2 and C3 makes it possible to avoid mixing between the layer of composition C2 and composition C3 and thus ensures the stability of the emulsion (E2).

[0089] The immiscibility between compositions C2 and C3 also makes it possible to prevent the water-soluble or hydrophilic substance of composition C1 from migrating from the core of the drops to composition C3.

[0090] To carry out step c), any type of agitator usually used to form emulsions may be used, such as, for example, a mechanical paddle agitator, a static emulsifier, an ultrasonic homogenizer, a membrane homogenizer, a high-pressure homogenizer, a colloid mill, a high-shear disperser or a high-speed homogenizer. Composition C3

[0091] According to one embodiment, the viscosity of composition C3 at 25°C is greater than the viscosity of emulsion (E1) at 25°C.

[0092] According to the invention, the viscosity of composition C3 at 25°C is between 500 mPa.s and 100,000 mPa.s.

[0093] Preferably, the viscosity of composition C3 at 25°C is between 3000 mPa.s and 100,000 mPa.s, preferably between 5,000 mPa.s and 80,000 mPa.s, for example between 7,000 mPa.s and 70,000 mPa.s.

[0094] According to this embodiment, given the very high viscosity of the continuous phase formed by composition C3, the destabilization rate of the double drops of the emulsion (E2) is significantly slow compared to the duration of the process of the invention, which then provides kinetic stabilization of the emulsions (E2) then (E3) until the polymerization of the capsule shell is complete. The capsules, once polymerized, are thermodynamically stable.

[0095] Thus, the very high viscosity of composition C3 ensures the stability of the emulsion (E2) obtained at the end of step b).

[0096] The high viscosity of composition C3 advantageously ensures the kinetic stability of the double emulsion (E2), preventing it from separating during the manufacturing process.

[0097] Preferably, the interfacial tension between compositions C2 and C3 is low. The low interfacial tension between compositions C2 and C3 also advantageously ensures the stability of the emulsion (E2) obtained at the end of step c).

[0098] The volume fraction of first emulsion (E1) in C3 can be varied from 0.05 to 0.5 in order to improve the production yield and to vary the average diameter of the capsules. At the end of this step, the size distribution of the second emulsion is relatively broad.

[0099] According to one embodiment, the ratio between the volume of emulsion (E1) and the volume of composition C3 varies between 1:10 and 10:1. Preferably, this ratio is between 1:9 and 3:1, preferably between 1:9 and 1:1.

[0100] According to one embodiment, composition C3 further comprises at least one branched polymer, preferably with a molecular weight greater than 5,000 g.mol -1< , and / or at least one polymer with a molecular weight greater than 5,000 g.mol -1< , and / or solid particles such as silicates.

[0101] According to one embodiment, composition C3 comprises at least one branched polymer, preferably with a molecular weight greater than 5,000 g.mol -1< , preferably between 10,000 g.mol -1< and 500,000 g.mol -1< , for example between 50,000 g.mol -1< and 300,000 g.mol -1< .

[0102] Branched polymer means a polymer having at least one branch point between its two terminal groups, a branch point (also called a branch point) being a point on a chain to which a side chain, also called a branch or pendant chain, is attached.

[0103] Among the branched polymers, we can for example cite grafted polymers, comb polymers or even star polymers or dendrimers.

[0104] According to one embodiment, the composition C3 comprises at least one polymer with a molecular weight greater than 5,000 g.mol -1< , preferably between 10,000 g.mol -1< and 500,000 g.mol -1< , for example between 50,000 g.mol -1< and 300,000 g.mol -1< .

[0105] As polymers that can be used in composition C3, the following compounds can be mentioned, used alone or mixed together: cellulose derivatives, such as cellulose ethers: methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, methylhydroxyethyl cellulose, ethylhydroxyethyl cellulose, carboxymethyl cellulose, hydroxypropyl cellulose or methylhydroxypropyl cellulose; polyacrylates (also called carbomers), such as polyacrylic acid (PAA), polymethacrylic acid (PMAA), poly(hydroxyethyl methacrylate) (pHEMA), poly(N-2-hydroxypropyl methacrylate) (pHPMA); polyacrylamides such as poly(N-isopropylacrylamide) (PNIPAM); polyvinylpyrrolidone (PVP) and its derivatives; polyvinyl alcohol (PVA) and its derivatives; polyethylene glycol, polypropylene glycol and their derivatives, such as polyethylene glycol acrylate / methacrylate, polyethylene glycol diacrylate / dimethacrylate, polypropylene carbonate;polysaccharides such as carrageenans, locust bean gums or tara gums, dextran, xanthan gums, chitosan, agarose, hyaluronic acids, gellan gum, guar gum, gum arabic, tragacanth gum, diutan gum, oat gum, karaya gum, ghatti gum, curdlan gum, pectin, konjac gum, starch; protein derivatives such as gelatin, collagen, fibrin, polylysine, albumin, casein; silicone derivatives such as polydimethylsiloxane (also called dimethicone), alkyl silicones, aryl silicones, alkyl aryl silicones, polyethylene glycol dimethicones, polypropylene glycol dimethicone;waxes, such as diester waxes (alkanediol diesters, hydroxyl acid diesters), triester waxes (triacylglycerols, 1,2-alkanediol, ω-hydroxy acid and fatty acid triesters, hydroxymalonic acid, fatty acid and alcohol esters, hydroxyl acid, fatty acid and fatty alcohol triesters, fatty acid, hydroxyl acid and diol triesters) and polyester waxes (fatty acid polyesters). Fatty acid esters which can be used as waxes in the context of the invention are, for example, cetyl palmitate, cetyl octanoate, cetyl laurate, cetyl lactate, cetyl isononanoate, cetyl stearate, stearyl stearate, myristyl stearate, cetyl myristate, isocetyl stearate, glyceryl trimyristate, glyceryl tripalmitate, glyceryl monostearate or glyceryl cetyl palmitate;fatty acids usable as waxes such as cerotic acid, palmitic acid, stearic acid, dihydroxystearic acid, behenic acid, lignoceric acid, arachidic acid, myristic acid, lauric acid, tridecyclic acid, pentadecyclic acid, margaric acid, nonadecyclic acid, heneicosylic acid, tricosylic acid, pentacosylic acid, heptacosylic acid, montanic acid or nonacosylic acid; fatty acid salts, in particular aluminum salts of fatty acids such as aluminum stearate, hydroxyl aluminum bis(2-ethylhexanoate); isomerized jojoba oil; hydrogenated sunflower oil; hydrogenated coconut oil; hydrogenated lanolin oil; castor oil and its derivatives, in particular modified hydrogenated castor oil or compounds obtained by esterification of castor oil with fatty alcohols; polyurethanes and their derivatives; styrenic polymers such as styrene butadiene;polyolefins such as polyisobutene.;

[0106] According to one embodiment, composition C3 comprises solid particles such as clays, silicas and silicates.

[0107] As solid particles that can be used in composition C3, mention may be made of clays and silicates belonging in particular to the category of phyllosilicates (also called layered silicas). As examples of silicates that can be used in the context of the invention, mention may be made of Bentonite, Hectorite, Attapulgite, Sepiolite, Montmorillonite, Saponite, Sauconite, Nontronite, Kaolinite, Talc, Sepiolite, Chalk. Synthetic pyrogenic silicas can also be used. The clays, silicates and silicas mentioned above can advantageously be modified by organic molecules such as polyethers, ethoxylated amides, quaternary ammonium salts, long-chain diamines, long-chain esters, polyethylene glycols, polypropylene glycols.

[0108] These particles can be used alone or mixed together.

[0109] According to one embodiment, composition C3 comprises at least one polymer with a molecular weight greater than 5,000 g.mol -1< and solid particles. Any mixture of the compounds mentioned above can be used. Step d)

[0110] Step d) of the method according to the invention consists of refining the size of the drops of the second emulsion (E2).

[0111] This step may consist of applying a homogeneous controlled shear to the emulsion (E2), said applied shear rate being between 10 s -1< and 100,000 s -1< .

[0112] According to one embodiment, the polydisperse double drops obtained in step c) are subjected to size refining consisting of subjecting them to shearing capable of fragmenting them into new double drops of homogeneous and controlled diameters. Preferably, this fragmentation step is carried out using a high shear cell of the Couette type according to a method described in patent application EP 15 306 428.2.

[0113] According to one embodiment, in step d), the second emulsion (E2), obtained at the end of step c), consisting of polydisperse double drops dispersed in a continuous phase, is subjected to shearing in a mixer, which applies homogeneous controlled shearing.

[0114] Thus, according to this embodiment, step d) consists of applying a homogeneous controlled shear to the emulsion (E2), said applied shear rate being between 1,000 s -1< and 100,000 s -1<.

[0115] According to this embodiment, in a mixer, the shear rate is said to be controlled and homogeneous, independently of the duration, when it passes to an identical maximum value for all parts of the emulsion, at a given instant which can vary from one point of the emulsion to another. The exact configuration of the mixer is not essential according to the invention, as long as the entire emulsion has been subjected to the same maximum shear on leaving this device. Mixers suitable for carrying out step d) are described in particular in document US 5,938,581.

[0116] The second emulsion can undergo homogeneous controlled shear as it flows through a cell formed by: two concentric rotating cylinders (also called a Couette-type mixer); two parallel rotating discs; or two parallel oscillating plates.

[0117] According to this embodiment, the shear rate applied to the second emulsion is between 1,000 s -1< and 100,000 s -1< , preferably between 1,000 s -1< and 50,000 s -1< , and preferentially between 2,000 s -1< and 20,000 s -1< .

[0118] According to this embodiment, during step d), the second emulsion is introduced into the mixer and is then subjected to shearing which results in the formation of the third emulsion. The third emulsion (E3) is chemically identical to the second emulsion (E2) but consists of monodisperse double drops whereas the emulsion (E2) consists of polydisperse double drops. The third emulsion (E3) typically consists of a dispersion of double drops comprising a core consisting of one or more drops of composition C1 and a layer of composition C2 encapsulating said core, said double drops being dispersed in the composition C3.

[0119] The difference between the second emulsion and the third emulsion is the size variance of the double drops: the drops of the second emulsion are polydisperse in size while the drops of the third emulsion are monodisperse, due to the fragmentation mechanism described above.

[0120] Preferably, according to this embodiment, the second emulsion is introduced continuously into the mixer, which means that the quantity of double emulsion (E2) introduced at the inlet of the mixer is the same as the quantity of third emulsion (E3) at the outlet of the mixer.

[0121] Since the droplet size of the emulsion (E3) essentially corresponds to the droplet size of the solid microcapsules after polymerization, it is possible to adjust the microcapsule size and the shell thickness by adjusting the shear rate during step d), with a strong correlation between the decrease in droplet size and the increase in shear rate. This allows the resulting microcapsule dimensions to be adjusted by varying the shear rate applied during step d).

[0122] According to a preferred embodiment, the mixer used during step d) is a Couette type mixer, comprising two concentric cylinders, an external cylinder of internal radius R o and an internal cylinder of external radius R i , the external cylinder being fixed and the internal cylinder being rotating with an angular speed ω.

[0123] A Couette type mixer suitable for the process of the invention can be supplied by the company TSR France.

[0124] According to one embodiment, the angular speed ω of the rotating internal cylinder of the Couette type mixer is greater than or equal to 30 rad.s -1< .

[0125] For example, the angular velocity ω of the rotating inner cylinder of the Couette-type mixer is about 70 rad.s -1< .

[0126] The dimensions of the fixed outer cylinder of the Couette type mixer can be chosen to modulate the space (d = R o - R i ) between the rotating inner cylinder and the fixed outer cylinder.

[0127] According to one embodiment, the space (d = R o - R i ) between the two concentric cylinders of the Couette type mixer is between 50 µm and 1000 µm, preferably between 100 µm and 500 µm, for example between 200 µm and 400 µm.

[0128] For example, the distance d between the two concentric cylinders is equal to 100 µm.

[0129] According to this embodiment, during step d), the second emulsion is introduced at the inlet of the mixer, typically via a pump, and is directed towards the space between the two concentric cylinders, the outer cylinder being fixed and the inner cylinder being rotating at an angular speed ω.

[0130] When the double emulsion is in the space between the two cylinders, the shear rate applied to said emulsion is given by the following equation: γ = R i ω R o − R i in which: ω is the angular velocity of the rotating inner cylinder, R o is the inner radius of the fixed outer cylinder, and R i is the outer radius of the rotating inner cylinder.

[0131] According to another embodiment, when the viscosity of composition C3 is greater than 2,000 mPa.s at 25°C, step d) consists of applying to the emulsion (E2) a shear rate of less than 1,000 s -1< .

[0132] According to this embodiment, the fragmentation step d) can be carried out using any type of mixer usually used to form emulsions with a shear rate of less than 1,000 s -1< , in which case the viscosity of the composition C3 is greater than 2,000 mPa.s, namely under conditions such as those described in patent application FR 16 61787.

[0133] The geometric characteristics of the double drops formed at the end of this stage will dictate those of the future capsules.

[0134] According to this embodiment, in step d), the emulsion (E2), consisting of polydisperse drops dispersed in a continuous phase, is subjected to shearing, for example in a mixer, at a low shear rate, namely less than 1000 s -1< .

[0135] According to this embodiment, the shear rate applied in step d) is for example between 10 s -1< and 1000 s -1< .

[0136] Preferably, the shear rate applied in step d) is strictly less than 1000 s -1< .

[0137] According to this embodiment, the emulsion drops (E2) can only be efficiently fragmented into fine, monodisperse emulsion drops (E3) if a high shear stress is applied to them.

[0138] The shear stress σ applied to an emulsion drop (E2) is defined as the tangential force per unit drop area resulting from the macroscopic shear applied to the emulsion during its stirring during step d).

[0139] The shear stress σ (expressed in Pa), the viscosity of composition C3 η (expressed in Pa s) and the shear rate γ (expressed in s -1< ) ​​applied to the emulsion (E2) during its stirring during step d) are related by the following equation: σ = ηγ

[0140] Thus, according to this embodiment, the high viscosity of composition C3 makes it possible to apply a very high shear stress to the emulsion drops (E2) in the mixer, even if the shear rate is low and the shear inhomogeneous.

[0141] To carry out step d) according to this embodiment, any type of agitator usually used to form emulsions can be used, such as for example a mechanical paddle agitator, a static emulsifier, an ultrasonic homogenizer, a membrane homogenizer, a high pressure homogenizer, a colloidal mill, a high shear disperser or a high speed homogenizer.

[0142] According to a preferred embodiment, a simple emulsifier such as a mechanical paddle stirrer or a static emulsifier is used to carry out step d). Indeed, this is possible because this embodiment requires neither controlled shear nor shear greater than 1000 s -1< . Step e)

[0143] Step e) of the process of the invention consists of crosslinking and therefore the formation of the envelope of the solid microcapsules according to the invention.

[0144] This step allows both to achieve the expected performance of protection and retention of the capsules and to ensure their thermodynamic stability, by definitively preventing any destabilization mechanism such as coalescence or ripening.

[0145] According to one embodiment, when composition C2 comprises a photoinitiator, step e) is a photopolymerization step consisting of exposing the emulsion (E3) to a light source capable of initiating the photopolymerization of composition C2, in particular to a UV light source preferably emitting in the wavelength range between 100 nm and 400 nm, and in particular for a duration of less than 15 minutes.

[0146] According to this embodiment, step e) consists of subjecting the emulsion (E3) to photopolymerization, which will allow the photopolymerization of the composition C2. This step will make it possible to obtain microcapsules encapsulating the water-soluble substance as defined above.

[0147] According to one embodiment, step e) consists of exposing the emulsion (E3) to a light source capable of initiating the photopolymerization of the composition C2.

[0148] Preferably, the light source is a UV light source.

[0149] According to one embodiment, the UV light source emits in the wavelength range between 100 nm and 400 nm.

[0150] According to one embodiment, the emulsion (E3) is exposed to a light source for a duration of less than 15 minutes, and preferably for 5 to 10 minutes.

[0151] During step e), the shell of the aforementioned double drops, consisting of photocrosslinkable composition C2, is crosslinked and thus converted into a viscoelastic polymeric shell, encapsulating and protecting the water-soluble substance from its release in the absence of mechanical triggering.

[0152] According to another embodiment, when composition C2 does not comprise a photoinitiator, step e) is a polymerization step, without exposure to a light source, the duration of this polymerization step e) preferably being between 8 hours and 100 hours and / or this step e) being carried out at a temperature between 20°C and 80°C.

[0153] According to this embodiment, the polymerization is initiated for example by exposure to heat (thermal initiation), or by simply bringing the monomers, polymers and crosslinking agents into contact with each other, or with a catalyst. The polymerization time is then generally greater than several hours.

[0154] Preferably, step e) of polymerization of composition C2 is carried out for a period of between 8 hours and 100 hours, at a temperature of between 20°C and 80°C.

[0155] The composition obtained at the end of step e), comprising solid microcapsules dispersed in composition C3, is ready to use and can be used without any additional post-treatment step of the capsules being required.

[0156] The thickness of the shell of the microcapsules thus obtained is typically between 0.1 µm and 20 µm, preferably between 0.2 µm and 10 µm, preferentially between 0.2 µm and 8 µm.

[0157] According to one embodiment, the solid microcapsules obtained at the end of step e) are devoid of surfactant, in particular at the interface between the solid envelope and the external medium (or continuous phase) represented by composition C3.

[0158] The process of the invention has the advantage of not requiring a surfactant in any of the steps b) to e) of forming the shell of the solid microcapsules. The process of the invention thus makes it possible to reduce the presence of additives which could modify the properties of the final product obtained after release of the water-soluble substance.

[0159] The present invention also relates to a series (or set) of solid microcapsules, capable of being obtained according to the process as defined above, in which each microcapsule comprises: a core comprising a composition C1 as defined above, comprising at least one water-soluble or hydrophilic substance dispersed in a hydrophobic phase, the water-soluble or hydrophilic substance being in solid form at room temperature and atmospheric pressure, and a solid envelope completely encapsulating the core at its periphery, said solid envelope being obtained from composition C2 as defined in claim 1, said composition C2 comprising at least one monomer or polymer, at least one crosslinking agent, and optionally at least one photoinitiator or crosslinking catalyst, and being at a temperature between 0°C and 100°C, wherein the average diameter of said microcapsules is between 1 µm and 30 µm, the thickness of the rigid shell is between 0.1 µm and 20 µm and the standard deviation of the diameter distribution of the microcapsules is less than 50%, in particular less than 25%, or less than 1 µm, the size distribution of the solid microcapsules being measured by light scattering technique as defined in the description.

[0160] As indicated above, the method of the invention makes it possible to obtain monodisperse particles. Also, the above-mentioned series of solid microcapsules is formed from a population of particles monodisperse in size. Thus, the standard deviation of the distribution of the diameter of the microcapsules is less than 50%, in particular less than 25%, or less than 1 µm.

[0161] The size distribution of solid microcapsules can be measured by light scattering technique using a Mastersizer 3000 (Malvern Instruments) equipped with a Hydro SV measuring cell.

[0162] According to the invention, the above-mentioned solid microcapsules comprise a solid shell composed entirely of crosslinked polymer (obtained from composition C2).

[0163] As indicated above, the method of the invention makes it possible to obtain solid microcapsules. The present application also describes solid microcapsules comprising a core and a solid shell completely encapsulating the core at its periphery, in which the core is a composition C1 as defined above, dispersed in a hydrophobic phase, and in which said rigid shell is made of crosslinked polymer, the diameter of said microcapsule being between 1 µm and 30 µm and the thickness of the rigid shell being between 0.1 µm and 20 µm.

[0164] The present invention also relates to a composition comprising a series of solid microcapsules as defined above.

[0165] The capsules of the invention can advantageously be used to protect the active ingredients used in polymer, elastomer, rubber, paint, adhesive, sealant, mortar, paper, varnish or coating formulations; in synthetic chemical products; in detergents, detergents, laundry care and household care products; in agrochemical products such as fertilizers, herbicides, insecticides, fungicides or pesticides; textiles; petrochemical products such as lubricants, fuels, bitumens, drilling and well stimulation fluids.

[0166] The present application also describes a method for releasing a water-soluble or hydrophilic substance, in particular in solid form at room temperature and atmospheric pressure, in particular in the form of particles and / or in the form of a crystal, in particular a salt, preferably with an average size of less than 1 µm, comprising a step of applying a mechanical shear stress to a composition comprising a series of solid microcapsules as defined above.

[0167] The expressions "between ... and ...", "from ... to ..." and "ranging from ... to ..." must be understood inclusively, unless otherwise specified.

[0168] The following examples illustrate the present invention without limiting its scope. EXAMPLES Example 1: Manufacture of solid capsules according to the invention

[0169] A mechanical agitator (Ika Eurostar 20) equipped with a deflocculating type stirring propeller is used to carry out all the stirring steps. Step a): Creation of the particle dispersion (composition C1) by nanoemulsion

[0170] Raw materials % Composition A Paraffin oil 48 Abil Em 90 (Cetyl PEG / PPG-10 / 1 Dimethicone, Evonik) 2 Composition B Calcium Chloride 5 Deionized water 45 Total 100

[0171] Composition A is stirred at 1000 rpm until completely homogenized.

[0172] Composition B is stirred at 1000 rpm until completely homogenized.

[0173] Composition B is then added dropwise to composition A while stirring at 2000 rpm. Stirring is maintained for 5 minutes after addition and then sonicated (Vibra-cell 75042, Sonics) for 3 minutes (pulse 5s / 2s) for 3 minutes at amplitude 30%.

[0174] The resulting nanoemulsion is then placed under reduced pressure and heating (25 mbar, 40°C) until the water has completely evaporated. This gives composition C1. Step b): Preparation of the first emulsion (E1)

[0175] Raw materials % Composition C2 CN 9800 (silicone urethane acrylate oligomer, Sartomer) 92 CN381 (amine-modified polyether oligomer, Sartomer) 5 Darocur 1173 (photoinitiator, BASF) 3 Total 100

[0176] Composition C1 is added dropwise to composition C2 while stirring at 2000 rpm with a ratio of 3:7. This gives the first emulsion (E1). Step c): Preparation of the second emulsion (E2)

[0177] Raw materials % First emulsion - 5 Composition C3 Sodium alginate (Sigma Aldrich) 9,5 Deionized water 85,5 Total 100

[0178] Composition C3 is stirred at 1000 rpm until completely homogenized and then left to stand for one hour at room temperature. The first emulsion (E1) is then added dropwise to composition C3 while stirring at 1000 rpm. This gives the second emulsion (E2). Step d) : Refining the size of the second emulsion

[0179] The second polydisperse emulsion (E2) obtained in the previous step is stirred at 1000 rpm for 10 minutes. This gives a monodisperse emulsion (E3). Step e): Crosslinking of the capsule shell

[0180] The second monodisperse emulsion (E3) obtained in the previous step is irradiated for 10 minutes using a UV light source (Dymax LightBox ECE 2000) having a maximum light intensity of 0.1 W / cm 2< at a wavelength of 365 nm.

[0181] The obtained microcapsules have a good size distribution, namely an average size of 8.7 µm and their size distribution has a standard deviation of 2.1 µm or 24%.

[0182] Furthermore, the quality of encapsulation of calcium chloride with the microcapsules according to Example 1 was studied by monitoring the viscosity of the capsule suspension for 20 days at room temperature. It was found that the viscosity did not undergo a significant increase, indicating the absence of leakage of calcium chloride outside the capsules where it would cause gelation of the alginate. The microcapsules of Example 1 therefore prove to be particularly suitable for effectively encapsulating a water-soluble substance in the form of particles.

Claims

1. A method for preparing solid microcapsules that comprises of the following steps: a) the preparation of a composition C1, comprising at least one water-soluble or hydrophilic substance dispersed in a hydrophobic phase, said substance having a solubility in water, measured at ambient temperature, at T = 25°C ± 2°C, and at ambient pressure, at 0.1013 MPa (or 1,013 mbar), at least equal to 1 g / L; b) the dropwise addition, under agitation, of said composition C1 in a polymeric composition C2, the compositions C1 and C2 being immiscible with each other, said composition C1 being at a temperature comprised from 0°C to 100°C, the composition C2 comprising at least one monomer or polymer, at least one crosslinking agent, and optionally at least one photoinitiator or a crosslinking catalyst, and being at a temperature comprised from 0°C to 100°C; the viscosity of the composition C2 being comprised between 500 mPa.s and 100 000 mPa.s at 25°C, and preferably being greater than the viscosity of the composition C1, whereby an emulsion (E1) is obtained comprising droplets of the composition C1 dispersed in the composition C2; c) the dropwise addition, under agitation, of the emulsion (E1) in a composition C3, the compositions C2 and C3 being immiscible with each other, said emulsion (E1) being at a temperature comprised from 15°C to 60°C and said composition C3 being at a temperature comprised between 15°C and 60°C; the viscosity of the composition C3 being comprised between 500 mPa.s and 100,000 mPa.s at 25°C, and preferably being greater than the viscosity of the emulsion (E1); whereby a double emulsion (E2) is obtained comprising droplets dispersed in the composition C3; d) the application of a shear to the emulsion (E2); whereby a double emulsion (E3) is obtained comprising size controlled droplets dispersed in the composition C3; and e) the polymerisation of the composition C2, whereby solid microcapsules dispersed in the composition C3 are obtained, the viscosities being measured, for a shear rate equal to 10 s-1, by means of a rheometer, equipped with a cone having 60 mm diameter and 2 degrees cone angle, and a temperature control cell set at 25°C.

2. The method according to claim 1, in which the water-soluble or hydrophilic substance is in solid form at ambient temperature and atmospheric pressure, in particular in the form of particles and / or in the form of a crystal, in particular of a salt, preferably having an average size of less than 1 µm.

3. The method according to claim 2, in which the composition C1 is prepared, either by dispersing, in the hydrophobic phase, at least one water-soluble or hydrophilic solid substance in the form of a powder, obtained in particular by atomisation, or by preparing a nanoemulsion of droplets of water in the hydrophobic phase.

4. The method according to any one of claims 2 or 3, in which the composition C1 is obtained by means of grinding at least one solid water-soluble or hydrophilic substance and then dispersing the said ground substance in the hydrophobic phase.

5. The method according to any one of claims 1 to 4, in which the hydrophobic phase comprises at least one oil whose interfacial tension with water is comprised between 25 mN / m and 50 mN / m, said interfacial tension being measured according to the Du Noüy ring method.

6. The method according to claim 5, in which the oil is selected from among plant, animal or synthetic oils.

7. The method according to any one of claims 1 to 6, in which the composition C2 comprises from 0.001% to 70% by weight of crosslinking agent(s) in relation to the total weight of said composition.

8. The method according to any one of claims 1 to 7, in which the step d) consists in applying a homogeneous controlled shear to the emulsion (E2), with the said shear rate applied comprised between 1,000 s-1 and 100,000 s-1.

9. The method according to any one of claims 1 to 7, in which when the viscosity of the composition C3 is greater than 2,000 mPa.s at 25°C, the step d) consists in applying to the emulsion (E2) a shear rate of less than 1,000 s-1.

10. The method according to any one of claims 1 to 9, in which, when the composition C2 comprises a photoinitiator, the step e) is a step of photopolymerisation consisting in exposing the emulsion (E3) to a light source that is capable of initiating the photopolymerisation of the composition C2, in particular to a UV light source emitting preferably in the wavelength range of between 100 nm and 400 nm, and this being in particular for a time period of less than 15 minutes.

11. The method according to any one of claims 1 to 9, in which, when the composition C2 does not comprise a photoinitiator, the step e) is a polymerisation step, without exposure to a light source, with the duration of this step e) of polymerisation preferably being comprised between 8 hours and 100 hours and / or this step e) being carried out at a temperature comprised between 20°C and 80°C.

12. The method according to any one of claims 1 to 11, in which the composition C3 comprises in addition at least one branched polymer, preferably having a molecular weight greater than 5,000 g.mol-1, and / or at least one polymer having a molecular weight greater than 5,000 g.mol-1, and / or solid particles such as silicates.

13. A series of solid microcapsules, susceptible to be obtained with the method according to any one of claims 1 to 12, in which each microcapsule includes: - a core comprising of a composition C1 as defined according to any one of claims 1 to 6, comprising at least one water-soluble or hydrophilic substance dispersed in a hydrophobic phase, the water-soluble or hydrophilic substance being in solid form at ambient temperature and atmospheric pressure; and - a solid enveloping shell that completely encapsulates at its periphery the core, said solid enveloping shell being obtained from the composition C2 as defined in claim 1, said composition C2 comprising at least one monomer or polymer, at least one crosslinking agent, and optionally at least one photoinitiator or a crosslinking catalyst, and being at a temperature comprised from 0°C to 100°C; in which the mean diameter of the said microcapsules is comprised between 1 µm and 30 µm, the thickness of the rigid enveloping shell is comprised between 0.1 µm and 20 µm and the standard deviation of the distribution of the diameter of microcapsules is less than 50%, in particular less than 25%, or less than 1 µm, the distribution of the size of the solid microcapsules being measured by the light diffusion method as defined in the specification.

14. A composition comprising a series of solid microcapsules according to claim 13.