JPH0731869A - Microcapsulation of solid particle - Google Patents

Abstract

PURPOSE:To make possible a microcapsulation which enables the efficient formation of a uniform polymer-coated layer on the surface of a solid particle by using a polymer having a structural unit which originates from at least one kind of monomer selected from the group consisting of isoprene sulfonic acid and the like as a surfactant. CONSTITUTION:A polymer-coated layer is allowed to form on the surface of a solid particle by polymerizing a polymerizable monomer in the presence of the solid particle and a surfactant. A polymer used as the surfactant has a structural unit originating from at least one kind of monomer selected from the group consisting of isoprene sulfonic acid, styrene sulfonic acid, vinyl sulfonic acid, naphthalene sulfonic acid, lignin sulfonic acid, norbornene sulfonic acid and alkali salts thereof. Consequently, it is possible to adjust the quality of a polymer to be coated on the solid particle and the thickness of the coated layer and not to generate a polymer particle consisting of only a monomer without coagulating the solid particles.

Description

Detailed Description of the Invention

[0002]

FIELD OF THE INVENTION The present invention relates to a method for microencapsulating solid particles.

[0003]

2. Description of the Related Art A conventional microencapsulation method for inorganic solid particles, which is an additive for rubber, resin, paint, etc., is, for example, to react hydroxyl groups on the surface of solid particles with a coupling agent to form particles. A method of introducing a lipophilic group or a polymerizable group on the surface and selectively polymerizing a polymerizable monomer on the particle surface (JP-A-62-83034), in which a water-soluble polymer is adsorbed on solid particles, A method in which a polymerizable monomer is occluded in a polymer adsorption layer to carry out polymerization (JP-A-63-175636), and a salt of a special cationic surfactant and a polymerization initiator is formed on the surface of solid particles. Then, a method of selectively polymerizing the polymerizable monomer on the particle surface (JP-A-2-48038) can be mentioned. However, these microencapsulation methods are not only limited to inorganic solid particles as the core solid particles,
Since the reaction is carried out 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 for microencapsulating organic solid particles, for example, a surfactant is added to a polymerization system to form an adsorption layer of the surfactant on the surface of the solid particles.
A method of microencapsulating by selectively polymerizing a polymerizable monomer in the adsorption layer (JP-A-62-61).
No. 633), a method of polymerizing a polymerizable monomer using a special water-soluble polymer as a dispersion stabilizer for solid particles, and performing microencapsulation (Japanese Patent Laid-Open No. 3-30833).
And so on. In these methods, various additives such as surfactants and dispersion stabilizers are used in order to stably disperse solid core particles in a medium. However, even if these additives can previously stably disperse the solid particles serving as the core in the medium,
There is a problem that the surface of the solid particles is gradually made hydrophobic as the polymerization progresses, the dispersibility decreases and the solid particles aggregate. Further, there is a method of improving the dispersion stability of the solid particles as the core by increasing the addition amount and type of the additive, but in this method, the addition amount and the conditions of the polymerization reaction need to be adjusted quite strictly. In addition, there is a problem that a large number of polymer particles composed only of a monomer that becomes a shell without encapsulating solid particles are produced, and the microencapsulation rate of solid particles is reduced. Further, there is a problem that the coating layer of the microencapsulated product of solid particles obtained by these methods must be thinned in order to stably disperse the solid particles serving as the core in the medium during the polymerization reaction.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of microencapsulating solid particles. Another object of the present invention is to adjust the properties of the polymer coating the solid particles, the thickness of the coating layer, and the like, and
It is possible to efficiently form a uniform polymer coating layer on the surface of solid particles without agglomeration of solid particles with the progress of microencapsulation and generation of polymer particles composed of only a monomer. , To provide a method of microencapsulating solid particles.

[0006]

[Means for Solving the Problems] That is, the present invention relates to microencapsulation in which a polymerizable monomer is polymerized in the presence of solid particles and a surfactant to form a polymer coating layer on the surface of solid particles. In the method, at least one monomer selected from the group consisting of isoprene sulfonic acid, styrene sulfonic acid, vinyl sulfonic acid, naphthalene sulfonic acid, lignin sulfonic acid, norbornene sulfonic acid and their alkali metal salts as a surfactant ( Less than,
These are collectively referred to as "sulfonic acid group-containing monomer and salt thereof". And a polymer having a structural unit derived from (4) (hereinafter, referred to as "specific polymer") is used.

The solid particles used in the present invention are not particularly limited, and both organic and 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), titanium oxide. , Particles of metal oxides such as tin oxide, zinc sulfide, silica, alumina and silver bromide, sulfides, nitrides, carbides, silicides, bromides, chlorides; alloy particles such as stainless steel and brass; graphite, Inorganic or mineral powders or fibrous powders such as carbon black, gypsum, talc, sand, asbestos, mica, glass, glass fiber, asbestos, ceramics, carbon fiber, ceramic fiber; pulp, wood powder, starch, pigment Natural product powder or fibrous powder such as polyvinyl chloride, polystyrene, polyethylene, polypropylene, polydivinyl Benzene, polyimide, polyamide, epoxy resin,
Examples thereof include particles of synthetic polymer compounds such as phenol resin, poly (meth) acrylic acid ester, poly (meth) acrylic acid, Teflon, polyester, and polycarbonate; or composite particles of organic substance and inorganic substance.

The shape of these solid particles may be an asymmetrical shape such as a sphere or an ellipse, or an indefinite shape, and their particle diameters are sphere-equivalent diameters (diameters when the solid particles have the same volume). , Usually 0.01 μm to 2 mm, preferably 0.1
μm to 200 μm. These solid particles alone
Alternatively, two or more kinds may be used in combination.

In the present invention, the polymerizable monomer used for microencapsulation of solid particles is 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) acrylic acid ester monomers such as methylethylaminoethyl (meth) acrylate; vinyl cyan monomers such as acrylonitrile and methacrylonitrile; vinyl chloride, vinylidene chloride, vinyl methyl ethyl ketone, vinyl methyl ether, vinyl acetate , Vinyl formate,
Substituted vinyl monomers such as allyl acetate, methallyl acetate, acrylamide, methacrylamide, N-methylol acrylamide, glycidyl acrylate, acrolein and allyl alcohol; ethylene oxide,
Cyclic ether monomers such as propylene oxide, tetrahydrofuran, styrene oxide, butylene oxide; divinylbenzene, (poly) ethylene glycol di (meth) acrylate, 1,3-butylene glycol di (meth) acrylate, glycerol di (meth) Examples thereof include monomers having two or more unsaturated double bonds such as acrylate, trimethylolpropane tri (meth) acrylate, and allyl (meth) acrylate. 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 and (poly) ethylene glycol di (meth). An acrylate etc. can be mentioned.

Further, in the present invention, a polycapsule of solid particles produced by using a polyfunctional monomer in the total polymerizable monomer is preferably 30% by weight or more, more preferably 50% by weight or more. Even when the compound is brought into contact with an organic solvent, the components of the solid particles do not migrate or elute, and the microencapsulated product 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 with respect to the solid particles is 1 to 500 parts by weight, preferably 2 to 100 parts by weight, based on 100 parts by weight of the solid particles. If the amount is less than 1 part by weight, the coating layer of the microencapsulated solid particles may be too thin to serve the role of protecting the solid particles, and if it exceeds 500 parts by weight, the solid particles serving as the core may be included. It is easy to generate polymer particles consisting of only polymerizable monomer, and it becomes difficult to control the thickness of the coating layer of the microencapsulated solid particles.

The specific polymer used in the present invention is
Although it has a structural unit derived from a sulfonic acid group-containing monomer and its salt, it can be copolymerized with other monomers 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 may be used alone or in combination of two or more. The amount of these other monomers used is 70% by weight or less, preferably 50% by weight or less, and more preferably 30% by weight or less based on the specific monomer.

In the present invention, the molecular weight of the specific polymer used and the amount used with respect to the solid particles vary depending on the type of solid particles, the particle size, or the type of medium in which the solid particles are dispersed. The absolute molecular weight measured by a light scattering method is preferably 500 to 1,000,000, more preferably 1
000 to 500,000, the specific polymer is solid particles 1
Preferably 0.1 to 200 parts by weight with respect to 00 parts by weight,
More preferably 0.5 to 100 parts by weight is used.

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 higher fatty acid alkali salts such as sodium oleate; alkylsulfates such as sodium dodecyl sulfate, sodium lauryl sulfate and sodium stearyl sulfate; sodium dodecylbenzenesulfonate. 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 alkoxy propyl ammonium salts A cationic surfactant such as an organic acid salt or an inorganic acid salt of alkyl propylene diamine, an amphoteric surfactant such as an alkyl glycine, an alkyl betaine, an alkyl alanine or an alkyl imidazoline, an alkyl polyoxyethylene ether; an alkyl Phenyl polyoxyethylene ethers; polyethylene glycol alkyl ethers; alkylcarbonyloxy polyethylenes; N, N-di (polyoxyethylene) alkane amides; N, N- (Alkanol) alkane amides; 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, alkyl Cellulose, polyvinyl alcohol, polyvinylpyrrolidone, poly (meth)
Examples thereof include polymer dispersion stabilizers such as acrylic acid, polyacrylamide, polyethylene oxide, polyvinyl acetate, gelatin and starch.

The amount of these surfactants or dispersion stabilizers used varies depending 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. Although it cannot be determined specifically, it is usually 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 carried out in an aqueous medium. Here, the aqueous medium refers to water or a mixed medium of water and an organic solvent soluble in water, but the latter is preferable. 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 dimethylformamide; dimethyl sulfoxide and the like. Can be mentioned. The aqueous medium preferably does not dissolve the polymer that microcapsulates the solid particles, and as the most preferably used organic solvent contained in the aqueous medium,
Methyl alcohol, ethyl alcohol, 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. To be 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 being previously dissolved or dispersed in the above-mentioned organic solvent or the like, is 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 with respect to 100 parts by weight of water contained in the aqueous medium. Parts by weight. The amount of 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 they vary depending on the solid particles, the medium in which the solid particles are dispersed, the polymerization initiator, the type and amount of the polymerizable monomer used, and the like. However, usually, the reaction temperature is preferably 0 ° C to 120 ° C.
℃, more preferably 20 ℃ ~ 100 ℃, the reaction time is preferably 1 hour to 30 hours, more preferably 2
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-2-2-imidazoline-2
Azo initiators such as -yl-propane (dihydrochloride); benzoyl peroxide, cyclohexanone peroxide, lauroyl peroxide, dicumyl peroxide, cumene hydroxyperoxide, di-
Organic peroxides such as t-butyl peroxide; inorganic persulfates such as potassium persulfate and ammonium persulfate; and commonly used redox initiators composed of the above organic peroxides and iron (II) compounds You can list them. Further, these polymerization initiators are preferably 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 with respect to 100 parts by weight of the polymerizable monomer. It is 5 to 10 parts by weight.

In the present invention, the equivalent spherical diameter of the microencapsulated product of the obtained solid particles can be adjusted by adjusting the amount of the polymerizable monomer used with respect to the solid particles.
The equivalent sphere diameter of the microencapsulated product of the solid particles is usually 1.01 to 3 times, preferably 1.02 to 2.5 times the equivalent sphere diameter of the solid particles to be the core.

[0023]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples as long as the gist thereof is not exceeded.

Example 1 1 g of spherical particles having a styrene / divinylbenzene content of 45/55 (weight ratio) and an average particle size of 5.1 μm,
0.36 g of sodium polyisoprene sulfonate having an absolute molecular weight of 20,000 measured by a light scattering method was added to 70 g of deionized water, and well stirred to completely disperse solid particles in water. Then, a solution prepared 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 particles were gradually added to the dispersion liquid with good stirring, and then the liquid temperature was adjusted to 50 ° C. in a nitrogen atmosphere to carry out polymerization for 8 hours. The polymerization conversion rate was 85%, and no particles consisting of polymethylmethacrylate (hereinafter referred to as "PMMA") were observed. PMMA produced by polymerization of MMA was used for microencapsulation of solid particles. It was The resulting microencapsulated particles are spherical and have an average particle size of 5.
It was 3 μm. The surface of the microencapsulated particles was observed with a scanning electron microscope, and it was found to be smooth and uniform. The microencapsulated solid particles are sprayed and adhered onto a glass substrate, and the whole glass substrate is heated at 180 ° C.
Heated for 10 minutes in a preheated 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 in the vicinity of the contact point between the glass substrate and the solid particles. It was cured and solid particles were firmly fixed on the glass substrate. In this way, the solid particles microencapsulated with a thermoplastic polymer are used to keep the gap between the substrates of the liquid crystal display constant because the solid particles are firmly fixed on the glass substrate by heating. It is useful as a spacer particle having adhesiveness.

Example 2 PMMA was prepared in the same manner as in Example 1 except that 1 g of spherical particles having a styrene / divinylbenzene copolymer ratio of 45/55 (weight ratio) and an average particle diameter of 3.1 μm were used. Microencapsulated particles were obtained. Polymerization conversion rate is 82%
In the same manner as in Example 1, formation of particles consisting of PMMA alone 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 styrene-based spherical particles having a styrene / divinylbenzene copolymer ratio of 45/55 (weight ratio) and an average particle diameter of 5.1 μm, and an absolute molecular weight of 2000 measured by a light scattering method.
Sodium polyisoprene sulfonate 0.5
g, 0.01 g of potassium persulfate, and 0.5 g of MMA were added to 100 g of deionized water, and the liquid temperature was adjusted to 70 under a nitrogen atmosphere.
Polymerization was carried out for 8 hours with stirring adjusted to 0 ° C. The polymerization conversion rate was 92%, and the formation of particles consisting of PMMA alone was not observed. PMMA produced by polymerization of MMA was all used for microencapsulation of solid particles. The resulting microencapsulated particles are spherical and have an average particle size of 5.3μ.
It was m. The surface of the microencapsulated particles was observed with a scanning electron microscope, and it was found to be smooth and uniform.

Example 4 A styrene / divinylbenzene 45/55 (weight ratio) copolymer having an average particle size of 5.1 μm and a styrene-based spherical particle surface having a thickness of 0.1 μm of iron oxide (magnetite). 3 g of an iron oxide composite particle having an average particle size of 7.1 μm and having a coating layer of 2 and an absolute molecular weight of 200 measured by a light scattering method.
Sodium polyisoprene sulfonate (00) (1 g) was added to deionized water (210 g) and sufficiently stirred to disperse the iron oxide composite particles. Next, a solution prepared 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, It was slowly added to the above dispersion while stirring well. Then, the dispersion was subjected to polymerization for 10 hours while stirring while adjusting the liquid temperature to 80 ° C. under a nitrogen atmosphere. Polymerization conversion rate is 8
At 3%, no formation of particles consisting only 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 microencapsulated particles produced were spherical and had an average particle size of 7.4 μm when observed with a transmission electron microscope.
Met. The surface of the microencapsulated solid particles was observed with a scanning electron microscope to find that it was a smooth and uniform surface. When measured by X-ray photoelectron spectroscopy, iron oxide was not detected at all, and the particle surfaces were all organic. Turned out to be a layer. The surface of the microencapsulated solid particles has an appropriate hydrophilicity, and the dispersibility in water is good. Further, 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 the sodium polyisoprene sulfonate used in Example 3, 0.1 g of an alkylated polyoxyethylene / allyl alcohol / maleic anhydride / styrene copolymer (Marialim AKM-0851 manufactured by NOF Corporation) was used. Microencapsulation was performed in the same manner as in Example 3 except that the solid particles were rapidly aggregated 3 hours after the initiation of the reaction. When this agglomerate was finely crushed and observed with a scanning electron microscope, it was aggregated in such a state that the coating layers of the polymer formed on the surface of the solid particles were fused to each other, and the fine particles of PMMA alone containing no solid particles were observed. Many large particles were generated.

Comparative Example 2 Instead of the sodium polyisoprene sulfonate used in Example 3, sodium dodecylbenzene sulfonate 0.
Microencapsulation was carried out in the same manner as in Example 3 except that 05 g was used, and 1 hour after the start of the reaction, solid particles began to aggregate, and 8 hours later, the solid particles were completely aggregated. When the aggregates were finely crushed and observed with a scanning electron microscope, it was found that the polymer coating layers formed on the surfaces of the solid particles were aggregated in a state of being fused. Further, when the amount of sodium dodecylbenzenesulfonate added was increased to 0.1 g and microcapsulation 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 the solid particles was considerably improved. However, PMMA does not include solid particles in the aggregate.
A large number of single fine particles were confirmed.

[0030]

The method for encapsulating solid particles according to the present invention makes it possible to control the properties of the polymer coated on the solid particles, the thickness of the coating layer, etc. It is possible to efficiently form a uniform polymer coating layer on the surface of solid particles without agglomeration of particles and generation of polymer particles composed of only a monomer. The obtained microencapsulated solid particles are useful for adhesive spacer particles, magnetic diagnostic agents, etc. depending on the coated components.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kenji Yasuda 2-11-24 Tsukiji, Chuo-ku, Tokyo Within Nippon Synthetic Rubber Co., Ltd.

Claims (1)

[Claims] 1. A microencapsulation method of polymerizing a polymerizable monomer in the presence of solid particles and a surfactant to form a polymer coating layer on the surface of solid particles, wherein isoprenesulfonic acid is used as a surfactant. At least 1 selected from the group consisting of styrene sulfonic acid, vinyl sulfonic acid, naphthalene sulfonic acid, lignin sulfonic acid, norbornene sulfonic acid and alkali metal salts thereof.
A method for microencapsulation, which comprises using a polymer having structural units derived from one kind of monomer. [0001]