JP4450882B2 - Microcapsule manufacturing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a production method for obtaining, as uniform spherical particles, microcapsules having a function of releasing inclusions by external stimuli such as heat, pressure, acid, and alkali without releasing the inclusions during storage.
[0002]
[Prior art and problems to be solved by the invention]
Microencapsulation has been applied to the protection of unstable substances, the release control of inclusions, the surface modification of solids, etc. as a method of changing the apparent properties while maintaining the original function of the substance.
[0003]
The in situ polymerization method is a method in which microcapsules are obtained by performing polymerization in a state where oil droplets composed of encapsulated oily substances and monomers are dispersed in water, and depositing the resulting polymer around the oil droplets. It is expected that capsules having various performances can be obtained by selecting the monomer to be used. Since the encapsulation operation itself is not different from the usual suspension polymerization method, it is an advantageous method in terms of cost and productivity. For example, Japanese Examined Patent Publication No. 42-26524 discloses particles that expand by heating, in which a volatile fluid is encapsulated with a thermoplastic polymer. However, since the in situ polymerization method is difficult to control the precipitation of the polymer, it has been known in principle for a long time and has not been widely used in spite of various advantages.
[0004]
Conventionally, various methods have been taken to obtain capsules by an in situ polymerization method. For example, a method of performing redox polymerization at an interface (Japanese Patent Publication No. 44-7344), a method using a specific dispersing agent (Japanese Patent Laid-Open No. Sho). 49-14348, JP-A-60-824), a method using a specific crosslinkable monomer and a hydrophilic monomer (JP-A 61-8774), and the like. The range of conditions obtained is narrow, and an arbitrary function could not be provided. For example, in order to obtain capsules that release inclusions in an alkaline aqueous solution, it is considered that it is sufficient to copolymerize an acidic monomer such as methacrylic acid, but the particles obtained by simply attempting polymerization are porous. In other words, capsules having a homogeneous film cannot be obtained.
[0005]
In addition, the appearance of capsules may be obtained depending on the monomer composition, but many of these films have low holding power and release inclusions even when stored, so volatile liquids such as fragrances can be removed. No capsule has been obtained that can be completely trapped and released when needed.
[0006]
In addition, even if a membrane material can be encapsulated very well for a certain substance, it cannot be encapsulated at all for other substances, and each time the substance to be encapsulated changes, trial and error can occur. There was a problem that a film material had to be selected.
[0007]
An object of the present invention is to solve the above problems and provide a technique capable of encapsulating an arbitrary oily substance with an arbitrary film material. In particular, it is an object of the present invention to provide a technique for easily producing a functional microcapsule that has been difficult to obtain in the past and that does not release an inclusion during storage but releases it by an external stimulus.
[0008]
[Means for Solving the Problems]
In the present invention, an oil droplet containing an encapsulated oily substance, a vinyl monomer, and a polymer plasticizer formed from the vinyl monomer is polymerized in a state dispersed in water, and the resulting polymer is precipitated around the oil droplet. Then, a method for producing a microcapsule for removing the plasticizer is provided.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The oily substance that can be microencapsulated according to the present invention generally does not inhibit radical polymerization, has a solubility in water (25 ° C.) of 1% by weight or less, and is a monomer composition that constitutes a film material that becomes a capsule. It dissolves at the polymerization temperature.
[0010]
Examples of this material include hydrocarbons such as butane, isopentane, hexane, isooctane, decane, benzene, toluene, naphthalene, and alkylnaphthalene; esters such as ethyl acetate, butyl acetate, ethyl butyrate, fatty acid triglyceride, and tributyl phosphate; diethyl Ethers such as ether and dibutyl ether; higher alcohols having 8 or more carbon atoms, aldehydes, fatty acids, aliphatic amines, amides, nitriles; modified or unmodified silicone oils, chlorofluorocarbons, various fragrances, lubricating oils, adhesives, Adhesives, oil-soluble dyes, liquid crystal forming substances, vitamins, alkaloids, steroids, pharmaceuticals, polymers and the like can be mentioned, and one or more can be used.
[0011]
Further, even a substance having poor solubility in the monomer can be encapsulated in a state dissolved in an appropriate solvent. Furthermore, a substance that does not dissolve in the monomer or solvent, such as carbon black, a hydrophobic pigment, or a crosslinked resin bead, can be encapsulated by being dispersed in the monomer or solvent in the form of fine particles.
[0012]
In addition, when a compound considered to be active against radicals as an encapsulated oily substance, for example, a compound containing allyl hydrogen, benzyl hydrogen, tertiary hydrogen, or the like is used, the molecular weight of the produced polymer is decreased. Since isomerization reaction may occur, care must be taken when encapsulating. However, even in such a case, encapsulation can be performed by performing polymerization at a relatively low temperature using a monomer having low reactivity of the radical of the growth species.
[0013]
The vinyl monomer of the present invention is not particularly limited as long as it has radical polymerizability and the polymer produced does not dissolve in the substance to be encapsulated and the water as the dispersion medium. Examples of such monomers include styrenes such as styrene, methylstyrene and chlorostyrene; vinyl ethers such as methyl vinyl ether and butyl vinyl ether; vinyl esters such as vinyl acetate, vinyl propionate and long chain fatty acid vinyl; vinyl chloride, Halogen group-containing monomers such as vinylidene chloride, vinylidene fluoride and perfluoroalkyl methacrylate; Conjugated diolefins such as butadiene and isoprene; Amide group-containing monomers such as N-alkylacrylamide, N-vinylpyrrolidone and N-vinylacetamide; ) Acrylonitrile, alkyl (meth) acrylates; carboxyl group-containing monomers such as (meth) acrylic acid, itaconic acid, maleic acid; styrene sulfonic acid, acrylamide-2-methylpropane sulfonic acid Acid group-containing monomers such as methacryloyloxyethyl phosphate; hydroxyl group-containing monomers such as hydroxyethyl (meth) acrylate and hydroxypropyl (meth) acrylate; dimethylaminoethyl (meth) acrylate, dimethylaminopropylacrylamide, diethylaminoethyl (meth) Amino group-containing monomers such as acrylate and vinylpyridine and quaternized products thereof; Polyethylene glycol chain-containing monomers such as polyoxyethylene mono (meth) acrylate; Glycidyl group-containing monomers such as glycidyl methacrylate and allyl glycidyl ether; Various macromonomers 1 type or more can be used.
[0014]
Moreover, a crosslinkable monomer can be used as needed. Specific examples of such a crosslinkable monomer include divinylbenzene, (poly) ethylene glycol di (meth) acrylate, methylenebisacrylamide, trimethylolpropane tri (meth) acrylate, triallyl (iso) cyanurate and the like.
[0015]
Usually, these monomers are preferably used in the range of 0.1 to 10 parts by weight with respect to 1 part by weight of the encapsulated oily substance.
[0016]
The monomer can be selected in any way, but monomers that form a skeleton such as styrene, vinyl acetate, vinyl chloride, vinylidene chloride, methyl methacrylate, acrylonitrile, etc. are used as basic components, and functional monomers are copolymerized according to the purpose. It is desirable to add functions. In particular, in order to obtain a capsule free from inclusion inclusions during storage, which is a feature of the present invention, a monomer that forms a polymer known to have a high gas barrier property, such as vinylidene chloride, acrylonitrile, etc., is a basic monomer. It is desirable to use as.
[0017]
The object of obtaining a heat sensitive release capsule is achieved by selecting the glass transition point of the membrane material. That is, since it is generally known that the material permeability of a polymer film increases rapidly above the glass transition point of the polymer film, the glass transition point of the polymer may be designed in the vicinity of the temperature to be released. Furthermore, if low boiling point hydrocarbons are encapsulated during encapsulation, the capsules expand during heating and the film thickness decreases, making it easier to release the inclusions. Capsules that release the contents in an alkaline or acidic aqueous solution can be obtained by copolymerizing a carboxyl group-containing monomer such as methacrylic acid or an amino group-containing monomer such as vinylpyridine as a monomer that forms the capsule membrane. In order to control the sustained release when used as a sustained release capsule, the affinity between the encapsulated oily substance and the capsule membrane may be changed. That is, when a relatively fast release is desired, a membrane material having a high affinity with the encapsulated oily substance may be used. Conversely, when a slow release over a long period of time is desired, a low affinity material may be used.
[0018]
In order to control the collapse pressure for the purpose of use as a pressure collapsible capsule, the diameter and film thickness of the capsule may be selected. In general, capsules that easily disintegrate are obtained when the film thickness is reduced relative to the diameter. Moreover, the pressure which collapse | crumbles can be changed also by use of a crosslinkable monomer, and molecular weight control of the production | generation polymer.
[0019]
The present invention is particularly useful when the capsule membrane is a copolymer of the carboxylic acid monomer or a crosslinked polymer.
[0020]
The plasticizer used in the present invention is one that plasticizes the produced polymer to effectively lower its glass transition point and can be removed by any method. Examples of such plasticizers include alcohols having 1 to 5 carbon atoms, glycols such as ethylene glycol, propylene glycol, and hexamethylene glycol, polyhydroxy compounds such as glycerin, trimeterolpropane, pentaerythritol, and sorbitol, and partial esters thereof. Compound: monocarboxylic acid such as acetic acid, butyric acid, valeric acid, benzoic acid, dicarboxylic acid such as succinic acid, malonic acid, glutaric acid, phthalic acid, hydroxycarboxylic acid such as glycolic acid, lactic acid, malic acid, tartaric acid, citric acid And their esterified products; polyethylene glycols such as diethylene glycol, triethylene glycol, tetraethylene glycol, cellosolve and carbitol and monoetherified products thereof; water-soluble such as tetrahydrofuran, dioxane, glyme and diglyme Ether; lower ketones such as acetone, methyl ethyl ketone, cyclohexanone; aprotic polar solvents such as dimethylformamide, dimethyl sulfoxide, acetonitrile, ethylene carbonate, N-methylpyrrolidone, dimethylimidazolidinone, hexamethylphosphonamide; pyridine, triethylamine And amine compounds such as ethylenediamine and ethanolamine.
[0021]
Among these plasticizers, hydrophilic organic compounds, particularly alcohols having 1 to 5 carbon atoms are preferable.
[0022]
The amount of the plasticizer used needs to be appropriately changed depending on the film material, the polymerization temperature, the type of the plasticizer, and the like, but it is desirable that the polymer produced at the initial stage of the polymerization is sufficiently plasticized. As a measure of the amount used, the glass transition point of the polymer may be lower than the polymerization temperature in the state containing the plasticizer and the monomer, and the range of 0.01 to 1 part by weight with respect to 1 part by weight of the film material. preferable.
[0023]
In practicing the present invention, first, oil droplets composed of an encapsulated oily substance, a monomer, and a plasticizer are dispersed in water using a suitable dispersant. Examples of the dispersant used include water-soluble polymers such as polyvinyl alcohol, polyvinyl pyrrolidone, gelatin, cationized starch, hydroxypropyl cellulose, carboxymethyl cellulose, and polyacrylic acid; sodium lauryl sulfate, alkylbenzene sulfonic acid, polyoxyethylene alkyl ether, cetyl Surfactants such as trimethylammonium halide; inorganic dispersants such as calcium carbonate, calcium phosphate, colloidal silica, montmorillonite, and the like can be used, and one or more can be used.
[0024]
An electrolyte such as sodium chloride, calcium chloride, or sodium sulfate may be added to the aqueous phase in order to suppress the distribution of the hydrophilic monomer or plasticizer to the aqueous phase, and the pH of the system may be adjusted. Various weak electrolyte salts may be added. Further, as a suspension stabilizing aid, an oxidizing agent such as potassium permanganate and potassium ferricyanide, and a polymerization inhibitor such as hydroquinone, cuperone, sodium nitrite and mercaptoethanol may be added.
[0025]
The particle size of the capsule is determined by the size of the dispersed droplets, but is usually about 1 to 1000 microns. For dispersion, in addition to stirring using a stirring blade attached to the polymerization tank, for example, a milder, a homomixer, a supersonic homogenizer, or the like is used.
[0026]
Next, polymerization is carried out while maintaining this dispersed state to form microcapsules. In carrying out the polymerization, an oil-soluble azo- or peroxide-based initiator such as azobisisobutyronitrile (AIBN), benzoyl peroxide (BPO) or the like is used as a polymerization initiator. In general, the polymerization initiator is suitably used in the range of 0.001 to 0.05 parts by weight with respect to 1 part by weight of the monomer. The initiator is preferably added to the monomer solution after preparation of the monomer solution and immediately before being dispersed in water. The polymerization temperature and time depend on the initiator used, but are generally 3 to 24 hours at 30 to 100 ° C. The polymerization is usually carried out at normal pressure. When a low boiling point compound is encapsulated or when a low boiling point monomer is used, the polymerization is carried out under pressure.
[0027]
After the polymerization is completed, the plasticizer is removed. Examples of the method for removing the plasticizer include water washing, distillation, alkali washing, and acid washing. Generally, a plasticizer having high water solubility is removed by washing with water, and a plasticizer having a low boiling point is removed by distillation. After the encapsulation, the acidic or basic plasticizer is removed by washing with the pH of the dispersion medium phase made alkaline or acidic, respectively.
[0028]
In selecting the type of plasticizer and the removal method, it is necessary to consider the oily substance and membrane material to be encapsulated. In general, it is advantageous in terms of easy removal that it is more hydrophilic than the capsule membrane or has a lower boiling point than the oily substance to be encapsulated. However, a plasticizer having extremely low solubility in the polymer not only shows the effect of addition unless used in a large amount, but also should not be used to make the membrane porous when the plasticizer is removed. Further, when the oily substance or membrane material to be encapsulated has an acidic group or basic group, the inclusions are released or the capsule membrane is dissolved, so that alkali washing and acid washing cannot be performed. Also, when the oily substance or membrane material to be encapsulated has an acidic group or basic group, it is desirable not to use a plasticizer having an opposite charge that forms an ion pair with them because it is difficult to remove.
[0029]
The microcapsules obtained as described above are used as they are as suspensions or after solid-liquid separation such as filtration and centrifugation. The capsule is dried by, for example, spray drying, freeze drying, or the like.
[0030]
【Example】
Example 1
An aqueous phase consisting of 150 g of ion-exchanged water, 1.5 g of polyvinyl alcohol (manufactured by Nippon Synthetic Chemical Co., Ltd., Gohsenol GH-17), 0.0015 g of potassium ferricyanide, and 12 g of sodium chloride was prepared. An oil phase comprising 50 g of isopentane as the encapsulated oily substance, 25 g of vinylidene chloride as the monomer, 25 g of methyl methacrylate, 0.1 g of divinylbenzene and 20 g of dimethylformamide as the plasticizer was prepared.
After adding 0.5 g of diisopropyl peroxydicarbonate (Nippon Yushi Co., Ltd., Parroyl IPP, 50 wt% toluene solution) as a polymerization initiator to this oil phase and dissolving it uniformly, it is added to the previously prepared aqueous phase. The mixture was dispersed for 1 minute at 5000 rpm using a homomixer (manufactured by Special Machinery Co., Ltd.).
The dispersion was transferred to an autoclave and sealed, then heated to 50 ° C., and polymerization was carried out at that temperature for 20 hours. After the polymerization, the temperature of the reaction solution was cooled to 20 ° C., and the autoclave was opened. 500 mL of ion exchange water was added to the slurry after the reaction, and the mixture was stirred for 10 minutes, and then the filtration operation was repeated three times to remove dimethylformamide as a plasticizer. The obtained cake was dried under an air stream to obtain spherical microcapsules having an average particle size of 10 microns. Yield 70g. A microscopic photograph of the obtained microcapsule is shown in FIG.
[0031]
Example 2
50 g of methyl methacrylate as monomer component, 20 g of hydroxypropyl methacrylate, 30 g of methacrylic acid, 70 g of limonene as encapsulated oily substance, 50 g of t-butyl alcohol as plasticizer, azobisisobutyronitrile as initiator 0 A mixed solution consisting of .50 g was dispersed in 250 g of a 1.5 wt% aqueous solution of polyvinyl alcohol (Gohsenol GH-17) using a homomixer. The resulting dispersion was heated in a 1 L separable flask at 65 ° C. for 5 hours with stirring. The obtained solid was separated by filtration, redispersed in 500 mL of ion exchange water, stirred for 10 minutes, and then the filtration operation was repeated 4 times. Subsequently, spherical microcapsules having an average particle size of 10 microns were obtained by drying at 40 ° C. under reduced pressure. Yield 160g.
[0032]
Example 3
1. A mixed solution comprising 70 g of methyl methacrylate as a monomer component, 30 g of methacrylic acid, 50 g of liquid paraffin as an encapsulated oily substance, 30 g of isopropyl alcohol as a plasticizer, and 0.050 g of lauroyl peroxide as a polymerization initiator. The mixture was dispersed in 250 g of a 5% by weight aqueous polyvinyl alcohol (GOHSENOL GH-17) solution using a homomixer. The resulting dispersion was heated in a 1 L separable flask at 65 ° C. for 5 hours with stirring. The obtained solid was separated by filtration, redispersed in 500 mL of ion exchange water, stirred for 10 minutes, and then filtered. By drying at 60 ° C. under reduced pressure, spherical microcapsules having an average particle size of 15 microns were obtained. Yield 140g.
[0033]
Example 4
50 g of methyl methacrylate as a monomer component, 50 g of methacrylic acid, 50 g of silicone oil (KF-96 manufactured by Shin-Etsu Chemical Co., Ltd.) as an encapsulated oily substance, 40 g of t-butyl alcohol as a plasticizer, azo as an initiator A mixed solution composed of 0.50 g of bisisobutyronitrile was dispersed in 250 g of an aqueous solution of 1.5% by weight of polyvinyl alcohol (GOHSENOL GH-17) using a homomixer. The resulting dispersion was heated in a 1 L separable flask at 65 ° C. for 5 hours with stirring. The obtained solid was separated by filtration, redispersed in 500 mL of ion exchange water, stirred for 10 minutes, and then filtered. By drying at 60 ° C. under reduced pressure, spherical microcapsules having an average particle size of 10 microns were obtained. Yield 135g.
[0034]
Example 5
50 g of methyl methacrylate as monomer component, 20 g of hydroxypropyl methacrylate, 30 g of methacrylic acid, 50 g of 2-hydroxy-4-methoxybenzophenone as encapsulated oily substance, 20 g of tetrahydrofuran as plasticizer, dimethyl 2, as initiator A mixed solution composed of 0.50 g of 2′-azobisisobrate was dispersed in 250 g of a 1.5 wt% aqueous solution of polyvinyl alcohol (Gosenol GH-17) using a homomixer. The dispersion was heated in a 1 L separable flask at 60 ° C. for 5 hours with stirring. After filtering off the obtained solid, it was redispersed in 500 mL of ion exchange water, stirred for 10 minutes, and then suitable for filtration. By drying at 40 ° C. under reduced pressure, spherical microcapsules having an average particle size of 10 microns were obtained. Yield 140g.
[0035]
Comparative Example 1
Polymer particles were prepared in the same manner as in Example 1 except that dimethylformamide as a plasticizer in Example 1 was removed. The obtained polymer particles were deformed as shown in FIG. 2, and desired microcapsules were not obtained.
[0036]
Comparative Example 2
Polymer particles were prepared in the same manner as in Example 2, except that t-butyl alcohol as a plasticizer in Example 2 was removed. The obtained polymer particles were irregular particles having irregularities, and desired microcapsules could not be obtained.
[0037]
Comparative Example 3
Polymer particles were prepared in the same manner as in Example 3 except that isopropyl alcohol as a plasticizer in Example 3 was removed. The obtained polymer particles were amorphous particles, and the desired microcapsules were not obtained.
[0038]
Comparative Example 4
Preparation of polymer particles was attempted in the same manner as in Example 4 except that t-butyl alcohol as a plasticizer in Example 4 was excluded. However, the polymer particles were aggregated without becoming microcapsules. This is thought to be due to the large deformation during the particle formation process and the release of the encapsulated oily substance.
[0039]
Comparative Example 5
An attempt was made to prepare polymer particles in the same manner as in Example 5 except that tetrahydrofuran as a plasticizer in Example 5 was excluded. However, the polymer particles were aggregated without becoming microcapsules. This is thought to be due to the large deformation during the particle formation process and the release of the encapsulated oily substance.
[0040]
[Effect of the present invention]
According to the method of the present invention, functional microcapsules useful in various industrial fields can be easily and economically produced. In particular, a capsule in which the inside and the outside are completely blocked, which has been difficult to obtain in the past, is obtained, which is useful for the encapsulation of volatile liquids, substances that are easily oxidized, and the like.
[Brief description of the drawings]
1 is an electron micrograph (magnification X400) showing the particle structure of a microcapsule obtained in Example 1. FIG.
2 is an electron micrograph (X400 magnification) showing the particle structure of the polymer particles obtained in Comparative Example 1. FIG.

Claims (3)

At least one encapsulated oily substance selected from isopentane, limonene, and 2-hydroxy-4-methoxybenzophenone , a vinyl monomer, and at least one selected from alcohols having 1 to 5 carbon atoms, dimethylformamide, and tetrahydrofuran An oil droplet containing a seed plasticizer (0.2 to 1 part by weight with respect to 1 part by weight of vinyl monomer) is polymerized in a state dispersed in water, and the resulting polymer is precipitated around the oil droplet, and then washed with water. To make microcapsules.   The process according to claim 1, wherein the plasticizer is at least one selected from t-butyl alcohol and isopropyl alcohol. The process according to claim 1 or 2 , wherein the vinyl monomer is at least one selected from vinylidene chloride, divinylbenzene, methacrylic acid, methyl methacrylate and hydroxypropyl methacrylate.

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