JP3401851B2 - Method for microencapsulation of solid particles - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a method for microencapsulation of solid particles. [0003] Conventionally, a method of microencapsulation performed on inorganic solid particles as an additive such as rubber, resin, paint, etc., involves, for example, reacting a hydroxyl group on the surface of the solid particles with a coupling agent. A method in which a lipophilic group or a polymerizable group is introduced into the particle surface to selectively polymerize a polymerizable monomer on the particle surface (Japanese Patent Application Laid-Open No. Sho 62-83034). (Japanese Patent Application Laid-Open No. Sho 63-175636), a method of polymerizing a polymerizable monomer in the polymer adsorption layer and carrying out polymerization using a salt of a special cationic surfactant and a polymerization initiator on the surface of solid particles. And a method of selectively polymerizing a polymerizable monomer on the particle surface (JP-A-2-48038). However, in these microencapsulation methods, the solid particles serving as the core are not limited to inorganic solid particles,
Since the reaction occurs only on the very surface of the solid particles, there is a problem that only an extremely thin coating layer can be obtained. As a conventional method of microencapsulating organic solid particles, for example, a surfactant is added to a polymerization system to form a surfactant adsorption layer on the surface of the solid particles.
A method of microencapsulation by selectively polymerizing a polymerizable monomer in the adsorption layer (Japanese Patent Laid-Open No. 62-61)
No. 633), a method in which a polymerizable monomer is polymerized using a special water-soluble polymer as a dispersion stabilizer for solid particles to perform microencapsulation (JP-A-3-30833).
And the like. In these methods, various additives such as a surfactant and a dispersion stabilizer are used in order to stably disperse the core solid particles in a medium. However, even if these additives can previously stably disperse the core solid particles in the medium,
As the polymerization proceeds, the surface of the solid particles gradually becomes hydrophobic, and there is a problem that the dispersibility decreases and the solid particles aggregate. In addition, there is a method for improving the dispersion stability of solid particles serving as a core by increasing the amount and types of additives, but this method requires only strict adjustment of the amount and conditions of the polymerization reaction. In addition, there is a problem that a large number of polymer particles consisting only of a monomer that becomes a shell not containing solid particles are generated, and the microencapsulation rate of the solid particles is reduced. In addition, the coating layer of the microencapsulated solid particles obtained by these methods has a problem that it has to be thin in order to stably disperse the core solid particles in the medium during the polymerization reaction. It is an object of the present invention to provide a method for microencapsulating solid particles. Another object of the present invention is to control the properties of the polymer coated on the solid particles, the thickness of the coating layer, and the like, and
It is possible to efficiently and uniformly form a uniform polymer coating layer on the surface of the solid particles without agglomeration of the solid particles with the progress of microencapsulation and without generating polymer particles composed of only monomers. To provide a method for encapsulating solid particles. [0006] That is, the present invention is to form a polymer coating layer on the surface of solid particles by polymerizing a polymerizable monomer in the presence of solid particles and a surfactant. in microencapsulation processes, isobutyl as a surfactant
It has a structural unit derived from at least one monomer selected from the group consisting of prenesulfonate and alkali metal salts thereof (hereinafter, these are collectively referred to as “sulfonic acid group-containing monomers and salts thereof”). This is achieved by a microencapsulation method characterized by using a polymer (hereinafter, referred to as “specific polymer”). The solid particles used in the present invention are not particularly limited, and any organic or inorganic particles can be used as long as they are solid in the medium in which they are dispersed. Specific examples of the solid particles include metal particles such as iron, nickel, gold, silver, chromium, tungsten, copper, zinc, titanium, tin, aluminum, and silicon; iron oxide (eg, magnetite, hematite, maghemite, etc.), titanium oxide Particles of oxides, sulfides, nitrides, carbides, silicides, bromides, chlorides, etc. of metals such as tin oxide, zinc sulfide, silica, alumina, silver bromide; alloy particles such as stainless steel, brass, etc .; Inorganic or mineral powder or fibrous powder such as carbon black, gypsum, talc, sand, asbestos, mica, glass, glass fiber, asbestos, ceramics, carbon fiber, ceramic fiber; pulp, wood powder, starch, pigment Powder or natural powder such as polyvinyl chloride, polystyrene, polyethylene, polypropylene, polydivinyl Benzene, polyimide, polyamide, epoxy resin,
Particles of a synthetic polymer compound such as phenolic resin, poly (meth) acrylate, poly (meth) acrylic acid, Teflon, polyester, and polycarbonate; and composite particles of an organic substance and an inorganic substance. The shape of these solid particles may be asymmetric such as spherical or elliptical or irregular, and their particle size is equivalent to a sphere (diameter when the solid particles are spheres of the same volume). , Usually 0.01 μm to 2 mm, preferably 0.1 μm to 2 mm.
μm to 200 μm. These solid particles alone,
Alternatively, two or more kinds may be used in combination. In the present invention, the polymerizable monomers used for microencapsulation of solid particles include styrene,
aromatic vinyl monomers such as α-methylstyrene, vinyltoluene, p-methylstyrene and chlorostyrene; mono- or dicarboxylic acids or dicarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid and itaconic acid Acid anhydride; methyl (meth) acrylate,
Ethyl (meth) acrylate, n-butyl (meth) acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl methacrylate, dimethylaminoethyl (meth)
Acrylate, diethylaminoethyl (meth) acrylate, dipropylaminoethyl (meth) acrylate,
(Meth) acrylate monomers such as methylethylaminoethyl (meth) acrylate; vinylcyan monomers such as acrylonitrile and methacrylonitrile; vinyl chloride, vinylidene chloride, vinyl methyl ethyl ketone, vinyl methyl ether, and vinyl acetate , Vinyl formate,
Substituted vinyl monomers such as allyl acetate, methallyl acetate, acrylamide, methacrylamide, N-methylol acrylamide, glycidyl acrylate, acrolein, allyl alcohol; ethylene oxide;
Cyclic ether monomers such as propylene oxide, tetrahydrofuran, styrene oxide and butylene oxide; divinylbenzene, (poly) ethylene glycol di (meth) acrylate, 1,3-butylene glycol di (meth) acrylate, glycerol di (meth) Monomers having two or more unsaturated double bonds, such as acrylate, trimethylolpropane tri (meth) acrylate, and allyl (meth) acrylate, can be mentioned. These polymerizable monomers may be used alone or in combination of two or more. Of these polymerizable monomers, preferred are styrene, (meth) acrylic acid, methyl (meth) acrylate, diethylaminoethyl (meth) acrylate, divinylbenzene, (poly) ethylene glycol di (meth) Acrylate and the like can be mentioned. In the present invention, microcapsules of solid particles produced by using a polyfunctional monomer in all polymerizable monomers, preferably at least 30% by weight, more preferably at least 50% by weight. Even when the compound is brought into contact with an organic solvent, the components of the solid particles do not migrate and elute, and the microencapsulated material of the solid particles can be prevented from being deformed by heat. Specific examples of these polyfunctional monomers include monomers having two or more unsaturated double bonds. The amount of the polymerizable monomer used is 1 to 500 parts by weight, preferably 2 to 100 parts by weight, per 100 parts by weight of the solid particles. If the amount is less than 1 part by weight, the thickness of the coating layer of the microencapsulated solid particles may be so small that the role of protecting the solid particles may not be fulfilled. If the amount exceeds 500 parts by weight, the solid particles serving as the core are included. Polymer particles consisting only of non-polymerizable monomers are easily generated, and it is difficult to control the thickness of the coating layer of the microencapsulated solid particles. The specific polymer used in the present invention is:
It has a structural unit derived from a sulfonic acid group-containing monomer and a salt thereof, but can be copolymerized with another monomer as long as the effects of the present invention are not impaired. Examples of the other copolymerizable monomer include the same as those exemplified as the polymerizable monomer. These other monomers can be used alone or in combination of two or more. The amount of these other monomers to be used is 70% by weight or less, preferably 50% by weight or less, more preferably 30% by weight or less of the specific monomer. In the present invention, since the molecular weight of the specific polymer used and the amount used for the solid particles vary depending on the type and size of the solid particles or the type of the medium in which the solid particles are dispersed, these values must be uniquely defined. The absolute molecular weight measured by the light scattering method is usually preferably 5 to 1,000,000, and more preferably 1 to 1.
000 to 500,000, the solid polymer 1
0.1 to 200 parts by weight based on 00 parts by weight,
More preferably, it is used in an amount of 0.5 to 100 parts by weight. In the present invention, a generally known surfactant or dispersion stabilizer may be added to further improve the dispersibility of the solid particles. Specific examples of these surfactants or dispersion stabilizers include alkali salts of higher fatty acids such as sodium oleate; alkyl sulfates such as sodium dodecyl sulfate, sodium lauryl sulfate, and sodium stearyl sulfate; and sodium dodecyl benzene sulfonate. Alkylaryl sulfonates; dioctyl sulfosuccinates such as dioctyl sodium sulfosuccinate; anionic surfactants such as alkylamine oxides; higher alkyl ammonium salts such as dodecyl ammonium chloride; quaternary N such as dodecyl pyridinium chloride
-Alkylpyridinium salts; quaternary N-alkylpicolinium salts such as dodecylpicolinium chloride;
Quaternary alkyl ammonium salts such as cetyl trimethyl ammonium bromide; quaternary alkyl imidazolinium salts; quaternary polyoxyethylene alkyl diammonium salts; quaternary polyoxyethylene alkyl ammonium salts; quaternary alkoxypropyl ammonium salts Cationic surfactants such as organic acid salts or inorganic acid salts of alkyl propylene diamine, amphoteric surfactants such as alkyl glycines, alkyl betaines, alkyl alanines and alkyl imidazolines; alkyl polyoxyethylene ethers; Phenyl polyoxyethylene ethers; polyethylene glycol alkyl ethers; alkylcarbonyloxy polyethylenes; N, N-di (polyoxyethylene) alkaneamides; (Alkanol) alkaneamides; fatty acid polyhydric alcohol esters such as polyethylene glycol fatty acid ester, sorbitan fatty acid ester, fatty acid monoglyceride, fatty acid sucrose ester; nonionic surfactants such as fatty acid polyhydric alcohol polyoxyethylene ethers; Cellulose, polyvinyl alcohol, polyvinylpyrrolidone, poly (meth)
Examples include polymer dispersion stabilizers such as acrylic acid, polyacrylamide, polyethylene oxide, polyvinyl acetate, gelatin, and starch. The amount of the surfactant or dispersion stabilizer used depends on the type of surfactant or dispersion stabilizer used, the type of solid particles, the particle size, or the type of medium in which the solid particles are dispersed. Usually, it is preferably 100 parts by weight or less, more preferably 50 parts by weight or less, based on 100 parts by weight of the solid particles. The microencapsulation in the present invention is performed in an aqueous medium. Here, the aqueous medium refers to water or a mixed medium of water and an organic solvent soluble in water, and is preferably the latter. Specific examples of water-soluble organic solvents include alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, ethyl cellosolve, and ethylene glycol; ketones such as acetone and methyl ethyl ketone; methyl acetate; tetrahydrofuran methylformamide; dimethyl sulfoxide and the like. Can be mentioned. Preferably, the aqueous medium does not dissolve the polymer that microencapsulates the solid particles, and most preferably used as the organic solvent contained in the aqueous medium,
Methyl alcohol, ethyl alcohol and isopropyl alcohol. The microencapsulation in the present invention is achieved by dispersing solid particles in an aqueous medium containing a specific polymer, then adding a polymerizable monomer and a polymerization initiator, and preferably performing polymerization with stirring. Is done. On this occasion,
The method of adding the polymerization initiator and the polymerizable monomer to the aqueous medium is not particularly limited, and as it is or after previously dissolving or dispersing in the above-described organic solvent or the like, collectively or divided into several times Or continuously added to the aqueous medium. In the microencapsulation of the present invention, the amount of the organic solvent contained in the reaction system is preferably 90 parts by weight or less, more preferably 10 to 80 parts by weight, based on 100 parts by weight of water contained in the aqueous medium. Parts by weight. The amount of the solid particles used is preferably 0.1 to 50 parts by weight, more preferably 0.5 to 30 parts by weight, based on 100 parts by weight of the aqueous medium. The polymerization conditions for microencapsulating the solid particles are not uniquely determined because the solid particles, the medium in which the solid particles are dispersed, the polymerization initiator, the type and amount of the polymerizable monomer, and the like are different. However, usually, the reaction temperature is preferably 0 ° C to 120 ° C.
° C, more preferably 20 ° C to 100 ° C, and the reaction time is preferably 1 hour to 30 hours, more preferably 2 hours.
Hours to 24 hours. As the polymerization initiator, 2,2′-azobisisobutyronitrile, 2,2′-azobis-2,
4-dimethylvaleronitrile, 2,2'-azobis-4
-Methoxy-2,4-dimethylvaleronitrile, 1-azobis-1-cyclohexanecarbonitrile, 4,4 '
-Azobis-4-cyanovaleric acid, 2,2'-azobis-
2-methylpropionamidine (dihydrochloride), 2,2'-azobis-2-imidazoline-2
Azo initiators such as -yl-propane (dihydrochloride); benzoyl peroxide, cyclohexanone peroxide, lauroyl peroxide, dicumyl peroxide, cumene hydroxy peroxide, di-
Organic peroxides such as t-butyl peroxide; inorganic persulfates such as potassium persulfate and ammonium persulfate; and commonly used redox initiators comprising the above organic peroxides and iron (II) compounds. Can be mentioned. Further, it is desirable that these polymerization initiators are soluble in an aqueous medium containing a polymerizable monomer. In the present invention, the amount of the polymerization initiator used for microencapsulating the solid particles is preferably 0.1 to 20 parts by weight, more preferably 0.1 to 20 parts by weight, based on 100 parts by weight of the polymerizable monomer. It is 5 to 10 parts by weight. In the present invention, the sphere equivalent diameter of the microencapsulated solid particles obtained can be adjusted by adjusting the amount of the polymerizable monomer used relative to the solid particles.
The equivalent sphere diameter of the microencapsulated solid particles is usually 1.01 to 3 times, preferably 1.02 to 2.5 times the equivalent sphere diameter of the core solid particles. EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples unless it exceeds the gist thereof. Example 1 1 g of spherical particles having a 45/55 (weight ratio) styrene / divinylbenzene copolymer having an average particle size of 5.1 μm,
0.36 g of sodium polyisoprenesulfonate having an absolute molecular weight of 20,000 as measured by a light scattering method was added to 70 g of deionized water, and the mixture was thoroughly stirred to completely disperse the solid particles in water. Then, a solution obtained by completely dissolving 0.5 g of methyl methacrylate (hereinafter, referred to as “MMA”) and 0.025 g of 2,2′-azobis-2,4-dimethylvaleronitrile in 30 g of ethanol was used as the solid. The solution was gradually added to the particle dispersion with good stirring, and then the polymerization was carried out for 8 hours by adjusting the liquid temperature to 50 ° C. under a nitrogen atmosphere. The polymerization conversion rate was 85%, and the formation of particles consisting only of polymethyl methacrylate (hereinafter referred to as “PMMA”) was not observed. All PMMA generated by polymerization of MMA was used for microencapsulation of solid particles. Was. The resulting microencapsulated particles are spherical with an average particle size of 5.
It was 3 μm. When the surface of the microencapsulated particles was observed with a scanning electron microscope, the surface was smooth and uniform. The microencapsulated solid particles are sprayed and attached on a glass substrate,
For 10 minutes in a heated oven. After that, when the adhesion state of the particles on the glass substrate was observed by a scanning electron microscope, the coating layer of the microencapsulated solid particles was melted by heat and flowed near the contact point between the glass substrate and the solid particles. It hardened and solid particles were firmly fixed on the glass substrate. In this way, the solid particles microencapsulated with the thermoplastic polymer are firmly fixed on the glass substrate by heating, and are used to keep the gap between the substrates of the liquid crystal display constant. It is useful as an adhesive spacer particle. Example 2 PMMA was prepared in the same manner as in Example 1 except that 1 g of spherical particles having a styrene / divinylbenzene ratio of 45/55 (weight ratio) and an average particle size of 3.1 μm were used. Microencapsulated particles were obtained. 82% polymerization conversion
In the same manner as in Example 1, generation of particles composed of only PMMA was not observed. The resulting microencapsulated particles were spherical particles having an average particle size of 3.5 μm and a smooth surface. Example 3 1 g of a styrene / divinylbenzene copolymer having a weight ratio of 45/55 (weight ratio), 1 g of styrene-based spherical particles having an average particle size of 5.1 μm, and an absolute molecular weight of 2,000 measured by a light scattering method was 2,000.
Sodium polyisoprenesulfonate which is 0 0.5
g, potassium persulfate (0.01 g) and MMA (0.5 g) were added to deionized water (100 g).
The polymerization was carried out for 8 hours while adjusting the temperature to ° C and stirring. The polymerization conversion was 92%, and no formation of particles consisting of PMMA alone was observed. All PMMA produced by polymerization of MMA was used for microencapsulation of solid particles. The resulting microencapsulated particles are spherical with an average particle size of 5.3μ.
m. When the surface of the microencapsulated particles was observed with a scanning electron microscope, the surface was smooth and uniform. Example 4 A styrene / divinylbenzene copolymer having a weight ratio of 45/55 (weight ratio) was coated on a surface of styrene-based spherical particles having an average particle diameter of 5.1 μm on a surface of iron oxide (magnetite) having a thickness of 0.1 μm. 3 g of an iron oxide composite particle having an average particle size of 7.1 μm having a coating layer formed thereon and an absolute molecular weight of 200 measured by a light scattering method.
1 g of sodium polyisoprenesulfonate (00) was added to 210 g of deionized water, and sufficiently stirred to disperse the iron oxide composite particles. Next, a solution obtained by completely dissolving 2.8 g of styrene, 0.2 g of methacrylic acid (hereinafter, referred to as “MAA”) and 0.05 g of 2,2′-azobisisobutyronitrile in 90 g of ethanol was used. It was slowly added to the dispersion with good stirring. Subsequently, the dispersion was polymerized for 10 hours with stirring and stirring at a liquid temperature of 80 ° C. in a nitrogen atmosphere. Polymerization conversion is 8
At 3%, no formation of particles consisting solely of polymer without inclusion of iron oxide composite particles was observed, and the copolymer of styrene and MAA was all used for microencapsulation of solid particles. The resulting microencapsulated particles were observed under a transmission electron microscope and were spherical, with an average particle size of 7.4 μm.
Met. When the surface of the microencapsulated solid particles was observed with a scanning electron microscope, the surface was smooth and uniform. When measured by X-ray photoelectron spectroscopy, no iron oxide was detected, and the surface of the particles was entirely organic. It turned out to be a layer. The surface of the microencapsulated solid particles is moderately hydrophilic, and has good dispersibility in water. Furthermore, the microencapsulated solid particles are easily magnetized in a magnetic field by a magnet or the like, and those dispersed in water can be used as magnetic diagnostic agent particles. Comparative Example 1 Instead of sodium polyisoprenesulfonate used in Example 3, 0.1 g of an alkylated polyoxyethylene / allyl alcohol / maleic anhydride / styrene copolymer (Mariarim AKM-0851 manufactured by NOF Corporation) was used. When microencapsulation was carried out in the same manner as in Example 3 except that the solid particles were used, the solid particles rapidly began to aggregate 3 hours after the start of the reaction. When the aggregates were crushed into fine pieces and observed with a scanning electron microscope, the polymer coating layers formed on the surfaces of the solid particles were aggregated in a state where they were fused together, and the fine particles of PMMA alone that did not contain the solid particles were contained. Many particles were generated. COMPARATIVE EXAMPLE 2 Instead of sodium polyisoprenesulfonate used in Example 3, sodium dodecylbenzenesulfonate 0.1% was used.
When microcapsulation was performed in the same manner as in Example 3 except that 05 g was used, aggregation of solid particles started 1 hour after the start of the reaction, and solid particles completely aggregated 8 hours later. The aggregate was finely crushed and observed with a scanning electron microscope. As a result, it was found that the polymer coating layers formed on the surface of the solid particles were aggregated in a state where they were fused together. When the amount of sodium dodecylbenzenesulfonate added was increased to 0.1 g and microencapsulation was performed in the same manner, the aggregation start time was about 3 hours after the start of the reaction, and the dispersion stability of solid particles was considerably improved. PMMA that does not include solid particles in agglomerates
Many single fine particles were confirmed. According to the method for microencapsulation of solid particles of the present invention, the properties of the polymer to be coated on the solid particles, the thickness of the coating layer, etc. can be adjusted, and the microencapsulation proceeds. Accordingly, a uniform polymer coating layer can be efficiently formed on the surface of the solid particles without agglomeration of the solid particles and generation of polymer particles composed of only monomers. The obtained microencapsulated solid particles are useful as adhesive spacer particles, magnetic diagnostic agents, and the like depending on the components coated.

Continuation of the front page (56) References JP-A-4-227845 (JP, A) JP-A-3-228066 (JP, A) JP-A-6-175390 (JP, A) JP-A-6-312127 (JP) , A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01J 13/14 C08F 2/00

Claims (1)

(57) [Claim 1] A microencapsulation method in which a polymerizable monomer is polymerized in the presence of a solid particle and a surfactant to form a polymer coating layer on the surface of the solid particle. At
A microencapsulation method comprising using, as a surfactant, a polymer having a structural unit derived from a monomer selected from the group consisting of isoprenesulfonic acid and an alkali metal salt thereof.