Method for producing capsules comprising at least one volatile compound, and resulting capsules

Abstract

The present invention relates to a process for preparing solid microcapsules comprising the following steps: a) preparation of a composition C1, which is either a composition C1a, comprising a single hydrophobic solid particle, or a composition C1b comprising a plurality of hydrophobic solid particles dispersed in a hydrophilic phase, b) addition with stirring of the composition C1 in a polymeric composition C2 at a temperature T.sub.b, whereby an emulsion (E1) is obtained; c) addition, with stirring, of the emulsion (E1) in a composition C3 at a temperature T.sub.c, whereby a double emulsion (E2) is obtained; d) applying a shear to the emulsion (E2), whereby a double emulsion (E3) is obtained; and e) polymerization of the composition C2, whereby solid microcapsules dispersed in the composition C3 are obtained.

Claims

1. A method for preparing solid microcapsules comprising the following steps: a) preparation of a composition C1, which is either a composition C1a, comprising a single hydrophobic solid particle, or a composition C1b comprising a plurality of hydrophobic solid particles dispersed in a hydrophilic phase, the hydrophobic solid particle(s) containing one or more lipophilic volatile compounds and one or more hydrophobic materials, solid at room temperature and liquid at a temperature above T.sub.m, b) addition, with stirring, of the composition C1 in a polymeric composition C2 at a temperature T.sub.b, the compositions C1 and C2 being immiscible with one another, the temperature T.sub.b being greater than T.sub.m when the composition C1 is a composition C1a and the temperature T.sub.b being less than T.sub.m when the composition C1 is a composition C1b, the composition C2 comprising at least one monomer or polymer, at least one crosslinking agent, and optionally at least one (photo)initiator or crosslinking catalyst, the viscosity of the composition C2 being between 500 mPa.Math.s and 100 000 mPa.Math.s at 25° C., and preferably being greater than the viscosity of the composition C1, whereby an emulsion (E1) comprising drops of composition C1a or C1b dispersed in composition C2 is obtained; c) addition, with stirring, of the emulsion (E1) in a composition C3 at a temperature T.sub.c, the compositions C2 and C3 not being miscible with each other, the temperature T.sub.c being greater than T.sub.m when the emulsion (E1) comprises drops of composition C1a dispersed in composition C2 and the temperature T.sub.c being less than T.sub.m when the emulsion (E1) comprises drops of composition C1b dispersed in the composition C2, the viscosity of the composition C3 being between 500 mPa.Math.s and 100 000 mPa.Math.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) at a temperature T.sub.d, the temperature T.sub.d being greater than T.sub.m when the composition C1 of step a) is a composition C1a and the temperature T.sub.d being less than T.sub.m when the composition C1 of step a) is a composition C1b, whereby a double emulsion (E3) is obtained comprising controlled size drops dispersed in the composition C3; and e) polymerization of the composition C2, whereby solid microcapsules dispersed in the composition C3 are obtained.

2. The method according to claim 1, wherein the hydrophobic material(s) is/are chosen from waxes, butters or pasty fatty substances, and mixtures thereof.

3. The method according to claim 1, wherein the volatile lipophilic compounds are chosen from perfuming agents, flavonoids, polyunsaturated fatty acids, and mixtures thereof.

4. The method according to claim 1, wherein the hydrophilic phase of C1b comprises at least one dispersing agent and at least one gelling agent.

5. The method according to claim 4, wherein the gelling agent is selected from branched polymers, polymers of molecular weight greater than 5000 g/mol.sup.−1, cellulose derivatives, polyacrylates, polyurethanes and their derivatives, polyethers and their derivatives, polyacrylamides, polyvinylpyrrolidone (PVP) and its derivatives, polyvinyl alcohol (PVA) and its derivatives, poly(ethylene) glycol), poly(propylene glycol) and their derivatives, polysaccharides, protein derivatives, fatty acid salts, glycerol derivatives, glycoluril derivatives, and mixtures thereof.

6. The method according to claim 4, wherein the dispersing agent is selected from the group consisting of surfactants; polyacrylates; sugar/polysaccharide esters and fatty acid(s); polyamides; polyethers and polyesters of silicone; ethoxylated alcohols; and mixtures thereof.

7. The method according to claim 1, wherein, when the composition C1 is a composition C1a, step a) comprises a step of heating the hydrophobic material or materials at a temperature above T.sub.m, followed by a step of adding the lipophilic volatile compound(s), and a step of mixing the assembly at a temperature greater than T.sub.m.

8. The method according to claim 1, wherein, when the composition C1 is a C1b composition, step a) further comprises a step of dispersing the composition C1a in the hydrophilic phase, followed by a cooling step of the dispersion thus obtained at a temperature below T.sub.m, whereby hydrophobic solid particles dispersed in said hydrophilic phase are obtained.

9. The method according to claim 1, wherein the step d) consists in applying a homogeneous controlled shear to the emulsion (E2), with the said shear rate applied between 1000 s.sup.−1 and 100,000 s .sup.−1.

10. The method according to claim 1, wherein the viscosity of the composition is greater than 2000 mPa.Math.s at 25° C., the step d) consists in applying to the emulsion (E2) a shear rate of less than 1000 s.sup.−1.

11. The method according to claim 1, 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.

12. The method according to claim 1, in which, when the composition C2 does not comprise a photoinitiator, the step e) is a polymerisation step, without exposure to a light source.

13. A series of solid microcapsules, susceptible to be obtained with the method according to claim 1, in which each microcapsule includes: a core comprising of a composition C1 as defined according to any one of claims 1 to 8; and a solid enveloping shell that completely encapsulates at its periphery the core; 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% or less than 1 μm.

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

15. A cosmetic composition comprising a series of solid microcapsules according to claim 13, further comprising at least one physiologically acceptable medium.

16. A method of releasing a volatile compound, comprising a step of applying mechanical shear stress to a composition comprising a series of solid microcapsules according to claim 14.

17. The method according to claim 2, wherein the volatile lipophilic compounds are chosen from perfuming agents, flavonoids, polyunsaturated fatty acids, and mixtures thereof.

18. A method of releasing a volatile compound, comprising a step of applying mechanical shear stress to a composition comprising a series of solid microcapsules according to claim 15.

Description

EXAMPLES

Example 1: Manufacture of Solid Capsules According to the Invention

(1) A mechanical agitator (Ika Eurostar 20) equipped with a deflocculating type propeller stirrer is used to carry out all the stirring/agitation steps.

(2) Step a): Creation of the Core of the Capsules (Dispersion of Particles—Composition C1b)

(3) TABLE-US-00001 Weight (g) % Composition Fragrance 21.6 54 C1a Saturated triglyceride wax (Suppocire 2.4 6 DM wax, Gattefosse) Composition B Dispersant 0.8 2 (Tween 80, Sigma Aldrich) Deionized water 15.2 38 Total 40 100

(4) The composition C1a is placed in a bath thermostated at 35° C. and stirred at 500 rpm until complete dissolution of the wax. Composition B is placed in a bath thermostated at 35° C. and stirred at 200 rpm until complete homogenization. The composition C1a is then added to the composition B dropwise with stirring at 2000 rpm, still at 35° C. The mixture is stirred at 2000 rpm for 5 minutes and then sonicated (Vibra-cell 75042, Sonics) for 20 minutes (pulse 5 s/2 s) at 30% amplitude. If the temperature exceeds 35° C. during sonication, the mixture is cooled using ice.

(5) After cooling, 1.2 g of gelling agent (modified polyethylene glycol, Aculyn 44N, Dow) are added to the mixture with stirring at 500 rpm until gelation. Alternatively, Aculyn 44N can be replaced by a carbomer (Tego Carbomer 340 FD). The composition C1b is thus obtained.

(6) Step b): Preparation of the First Emulsion (E1)

(7) TABLE-US-00002 Weight (g) % Total Composition C1b 4 40 Composition C2 6 60 Composition C2 CN2203 5.72 (Polyester acrylate oligomer, Sartomer) CN381 0.1 (modified amine polyether oligomer, Sartomer) Darocur 1173 0.18 (photoinitiator, BASF) Total 10 100

(8) The composition C1 is added dropwise to the composition C2 with stirring at 2000 rpm, at a temperature T.sub.b=20° C. The first emulsion (E1) is thus obtained.

(9) Step c): Preparation of the Second Emulsion (E2)

(10) TABLE-US-00003 Weight (g) % total First emulsion 5 5 Composition C3 Sodium alginate 9.5 9.5 (Sigma Aldrich) Deionized water 85.5 85.5 Total 100 100

(11) The composition C3 is placed under agitation at 1000 rpm until complete homogenization is obtained and then allowed to stand for a period of one hour at ambient temperature. The first emulsion (E1) is then added to the composition C3 under stirring at 1000 rpm, at a temperature T.sub.c=20° C. The second emulsion (E2) is thus obtained.

(12) Step d): Size Refinement of the Second Emulsion

(13) The second polydisperse emulsion obtained in the preceding step is agitated at 1000 rpm for a period of 10 minutes, at a temperature T.sub.d=20° C. A monodisperse emulsion (E3) is thus obtained.

(14) Step e): Cross-Linking of the Enveloping Shell of the Capsules

(15) The second monodisperse emulsion (E3) obtained in the previous step is irradiated for a period of 15 minutes by using a UV light source (Dymax LightBox ECE 2000) having a maximum luminous intensity of 0.1 W/cm.sup.2 at a wavelength of 365 nm.

(16) The solid microcapsules according to example 1 present a good size distribution, that is to say, an average size of 7.9 μm and a standard deviation of 3.8 μm that is 48%.

(17) Furthermore, the quality of encapsulation of the volatile lipophilic compound, namely the perfuming agent, with the microcapsules according to Example 1 was studied by incubation at 50° C. for 30 days with a suspension of the microcapsules of Example 1 in a carbomer solution (Tego carbomer 750FD, Evonik) at 0.3%.

(18) There is no change in color or smell emanation, especially the encapsulated perfume agent, even after stirring. It is also noted that the viscosity of the suspension does not undergo a significant decrease, indicating the absence of leakage of the perfuming agent outside the capsules where it would cause the coagulation of the carbomer causing a drop in viscosity.

(19) The solid microcapsules according to Example 1 thus prove to be particularly suitable for effectively encapsulating a volatile lipophilic compound, in particular a perfuming agent.

Example 2: Manufacture of Solid Capsules According to the Invention

(20) Example 2 differs from Example 1 only in the nature of composition C2, as described below. All the other parameters, protocols, steps, compositions described in example 1 remain identical.

(21) TABLE-US-00004 % Ratio Raw materials for C2 C1-C2 Composition C1b — 4 Composition C2 CN 981 87 6 (aliphatic polyester/ether urethane acrylate oligomer, Sartomer) SR238 10 (1,6-hexanediol diacrylate, Sartomer) Darocur 1173 3 (2-Hydroxy-2-methyl-1-phenyl- propan-1-one, photoinitiator, BASF) Total 100 10

Example 3: Manufacture of Solid Capsules According to the Invention

(22) Example 3 differs from Examples 1 and 2 only in the nature of composition C3, as described below. All the other parameters, protocols, steps, compositions described in example 1 remain identical.

(23) Step c): Preparation of the Second Emulsion (E2)

(24) TABLE-US-00005 Weight (g) % total First emulsion (E1) 5 5 Composition C3 Modified polyethylene 2.85 2.85 glycol gelling agent (Aculyn 44N, Dow) Deionized water 92.15 92.15 Total 100 100