JP3354615B2 - Method for producing composite wall microcapsules - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a composite wall microcapsule having an inner wall film and an outer wall film and having excellent mechanical stability, solvent resistance, heat resistance and the like.

[0002]

2. Description of the Related Art As one of the methods for producing microcapsules, a method has been already known in which a polymer is formed by polymerization of a monomer and at the same time a capsule wall is formed.
Typical examples are an interfacial polymerization method and an in-situ polymerization method, which have the following advantages,
In recent years, much research has been done. (1) It is relatively easy to adjust the particle size of the microcapsules. (2) It is easy to adjust the encapsulation amount of the core substance. (3) Capsule can be encapsulated at a high concentration.

The interfacial polymerization method is a method in which a hydrophobic monomer and a hydrophilic monomer are used to cause a polymerization reaction at an interface of a core substance to form a wall film. Being restricted, it is not easy to obtain a dense capsule wall, and the capsule wall is inferior in solvent resistance, and further, it is difficult to make the capsule wall thick, so that it is inferior in pressure resistance. Has disadvantages. As the in-situ polymerization method, for example, JP-A-56-1
As described in Japanese Patent No. 0489, a method of forming a capsule wall by polymerizing a monomer from the inside of a core material, or a method disclosed in JP-A-54-49984 or JP-A-
As described in JP-A-6-51238, a method of polymerizing a monomer from the outside of a core substance to form a capsule wall is known, but in each case, the obtained microcapsules are pressure-resistant, heat-resistant. Insufficient in water resistance and solvent resistance.

Further, Japanese Patent Laid-Open Publication No. Sho 56-102935 proposes a method for producing microcapsules by combining an interfacial polymerization method and an in-situ polymerization method. However, this does not make it possible to obtain microcapsules satisfying all the properties and heat resistance.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems in the conventional production of microcapsules. In particular, the present invention has an inner wall film and an outer wall film as a microcapsule wall. It is an object of the present invention to provide a method for producing a microcapsule having a composite wall having excellent solvent resistance, pressure resistance and heat resistance.

[0006]

A first aspect of the method for producing microcapsules according to the present invention is a polyvalent isocyanate compound, a radical polymerizable monomer and a radical polymerization initiator .
A hydrophobic core material containing an organic peroxide is emulsified or dispersed in an aqueous protective colloid aqueous solution in the form of droplets,
A wall film-forming substance reactive with the polyvalent isocyanate compound is added to the aqueous protective colloid aqueous solution, and an outer wall film is formed by interfacial polymerization between the polyvalent isocyanate compound and the wall film-forming substance. after forming the capsule, or while forming, in the interior of the microcapsules by polymerizing the radical polymerizable monomer by the above organic peroxides, characterized in that to form the inner wall film.

The second aspect of the method for producing microcapsules according to the present invention is a polyvalent isocyanate compound, a material for forming a wall film reactive with the polyvalent isocyanate compound, a radically polymerizable monomer, and an organic peroxy acid as a radical polymerization initiator.
A hydrophobic core material containing the compound, in an aqueous protective colloid solution is emulsified or dispersed in the droplets form, wall film having a reactivity to the polyisocyanate compound and the polyvalent isocyanate compound at this droplet in After forming the outer wall film by in-situ polymerization with the forming material to form the microcapsules, or while forming, the radical polymerizable monomer is polymerized by the organic peroxide inside the microcapsules. And forming an inner wall film.

Hereinafter, the method of the present invention will be described in detail. The polyvalent isocyanate compound used in the method according to the present invention means an organic compound having two or more isocyanate groups in a molecule. Specific examples of such a polyvalent isocyanate compound include, for example, m-phenylene diisocyanate, p-phenylene diisocyanate, 2,6
-Tolylene diisocyanate, 2,4-tolylene diisocyanate, naphthalene-1,4-diisocyanate, diphenylmethane-4,4'-diisocyanate, 3,3'-dimethoxy-4,4'-biphenyl diisocyanate, 3,3'- Dimethyldiphenylmethane-4,4'-diisocyanate, xylylene-1,4-diisocyanate, 4,4'-diphenylpropane diisocyanate, trimethylene diisocyanate, hexamethylene diisocyanate, propylene-1,
2-diisocyanate, butylene-1,2-diisocyanate, cyclohexylene-1,2-diisocyanate, diisocyanate such as cyclohexylene-1,4-diisocyanate, p-phenylenediisothiocyanate, xylylene-1,4-diisothiocyanate, Examples thereof include triisocyanates such as ethylidin diisothiocyanate and tetraisocyanates such as 4,4'-dimethyldiphenylmethane-2,2 ', 5,5'-tetraisocyanate.

Further, as a polyvalent isocyanate compound,
Hexamethylene diisocyanate and hexanetriol adduct, 2,4-tolylene diisocyanate and prenz catechol adduct, tolylene diisocyanate and hexane triol adduct, tolylene diisocyanate and trimethylolpropane adduct, xylylene diisocyanate Polyvalent isocyanate prepolymers such as adducts of trimethylolpropane and adducts of hexamethylene diisocyanate and trimethylolpropane can also be mentioned.

[0010] In the above, a prepolymer is particularly preferably used as the polyvalent isocyanate compound.
Of course, two or more of the above-mentioned ones can be used in combination. On the other hand, examples of the wall film-forming substance reactive with the polyvalent isocyanate compound include molecules such as polyhydric alcohols, hydroxy polyesters, hydroxy polyalkylene ethers, alkylene oxide adducts of polyamines, and polyamines. And a substance having two or more active hydrogens.

The above-mentioned polyhydric alcohols may be aliphatic, aromatic or alicyclic. For example, catechol, resorcinol, 1,2-dihydroxy-4-methylbenzene, 1,3-dihydroxy-5 -Methylbenzene,
3,4-dihydroxy-1-methylbenzene, 3,5-dihydroxy-1-methylbenzene, 2,4-dihydroxyethylbenzene, 1,3-naphthalenediol, 1,5-naphthalenediol, 2,7-naphthalenediol, 2,3-naphthalene diol, o, o'-biphenol, p, p'-biphenol, bisphenol A, bis- (2-hydroxyphenyl) methane, xylylene diol, ethylene glycol, 1,3-propylene glycol, 1, 4-butylene glycol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,1,1-trimethylolpropane, hexanetriol, pentaerythritol, glycerin And sorbitol.

The hydroxypolyalkylene ethers include the above-mentioned polyhydric alcohols and polycarboxylic acids such as malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, maleic acid, isophthalic acid, terephthalic acid and gluconic acid. Examples of the obtained hydroxy polyesters include hydroxy polyalkylene ethers.Examples of the hydroxy polyalkylene ethers include hydroxypolyalkylene ethers, which are condensation products of the above-mentioned polyhydric alcohols with alkylene oxoxides such as ethylene oxide, propylene oxide, and butylene oxide. And alkylene oxide adducts of polyvalent amines as o-phenylenediamine, p-phenylenediamine, diaminonaphthalene, ethylenediamine, 1,3-propylenediamine, diethylenetriamine Triethylenetetramine, 1,6
Examples thereof include those obtained by substituting at least one or more of the hydrogen atoms of the amino group of a polyvalent amine such as hexamethylene diamine with the above-described alkylene oxide.

Further, examples of polyamines include diethylene triamine, triethylene tetramine, tetraethylene pentamine, 1,6-hexamethylene diamine,
1,8-octamethylenediamine, 1,12-dodecamethylenediamine, o-phenylenediamine, p-phenylenediamine, m-phenylenediamine, o-xylylenediamine, p-xylylenediamine, m-xylylenediamine, menthane Diamine, bis (4-amino-3-methylcyclohexylnomethane, isophoronediamine, 1,3
-Diaminocyclohexane, spiroacetal-based diamine, and the like. In addition, water can also be used as a wall-film-forming substance reactive with polyvalent isocyanate.

The radical polymerizable monomer that can be used in the present invention means a compound having a polymerizable double bond, and specifically includes unsaturated nitriles such as acrylonitrile, methacrylonitrile, crotonnitrile, and the like. , Vinyl monomers such as vinyl acetate, styrene, vinyltoluene, methylstyrene, vinyl chloride, vinylidene chloride and the like, and unsaturated amides such as acrylamide, methacrylamide, N-methylolacrylamide, N-methylolmethacryl Amides, crotonamides, maleic amides, itaconic amides, unsaturated esters such as methyl methacrylate, ethyl methacrylate, m-propyl methacrylate, methacrylates such as isopropyl methacrylate, methyl acrylate, Chill acrylate, m- propyl acrylate, isopropyl acrylate, and acrylic acid esters such as m- butyl acrylate.

In the present invention, together with the above-mentioned radically polymerizable monomers, polyfunctional and, therefore, crosslinkable monomers such as methylene bisacrylamide, divinylbenzene, tripropylene glycol diacrylate, and bisphenol A diamine. Glycidyl ether diacrylate, trimethylolpropane triacrylate, acrylate cyanurate and the like can also be used.

And Oite, a radical polymerization initiator [0016] The present invention
Te, organic peroxides, e.g., lauroyl peroxide,
Benzoyl peroxide, methyl ethyl ketone peroxide, cyclohexanone peroxide, 2,2-bis (t
-Butylperoxy) valate, di-t-butyl peroxide, dicumyl peroxide, octanoyl peroxide and the like are used .

Examples of the protective colloid agent usable in the present invention include a water-soluble polymer compound and a water-insoluble inorganic fine powder. Specific examples of these include, for example, carboxymethylcellulose, polyvinyl alcohol, hydroxypropylmethylcellulose, methylcellulose, polyacrylic acid, gum arabic, gelatin, and the like.
Examples include talc, bentonite, organic bentonite, white carbon, colloidal silica, colloidal alumina, fine particle silica, calcium carbonate, calcium sulfate, and the like.

The first of the microcapsule manufacturing methods according to the present invention basically includes the following steps. First Step An aqueous protective colloid aqueous solution containing a protective colloid agent is prepared. Here, according to the present invention, as a protective colloid agent,
When a water-soluble polymer is used, 0.2 to 10 parts by weight, preferably 0.5 to 5 parts by weight of a water-soluble polymer is used with respect to 100 parts by weight of water. When the inorganic fine powder is used, 0.1 parts by weight of water is used.
It is appropriate to use from 100 to 100 parts by weight, preferably from 1 to 50 parts by weight of inorganic fine powder.

Second step A mixture of a hydrophobic core substance and a polyvalent isocyanate compound, a radical polymerizable monomer and a radical polymerization initiator is emulsified or dispersed in the aqueous protective colloid aqueous solution prepared in the first step. Disperse. Here, the amount of the polyvalent isocyanate compound used is in the range of 1 to 50 parts by weight, preferably 5 to 20 parts by weight, based on 100 parts by weight of the mixed solution. The amount of the radical polymerizable monomer used is in the range of 1 to 100 parts by weight, preferably 5 to 50 parts by weight, based on 100 parts by weight of the mixed solution. The amount of the radical polymerization initiator used is not particularly limited, but is usually 0.1 to 10 parts by weight, preferably 0.1 to 5 parts by weight, based on 100 parts by weight of the radical polymerizable monomer. Range.

Third Step The above-mentioned polyisocyanate-reactive wall film forming substance is added to the aqueous protective colloid aqueous solution obtained in the second step, and the mixture is heated under stirring to increase the hydrophobicity. A microcapsule is formed by forming an outer shell wall made of a polymer such as polyurethane or polyurea at the interface between the droplets containing the wicking substance. Here, the amount of the wall film forming substance used is 5 to 100 parts by weight, preferably 5 to 100 parts by weight, based on 100 parts by weight of the polyvalent isocyanate compound.
It is in the range of 50 weight. In the third step, a dispersion of microcapsules can be obtained.

Fourth Step The microcapsule dispersion obtained in the third step is further heated to a temperature not lower than the starting temperature of the radical polymerization initiator, whereby the inner layer of the polymer of the radical polymerizable monomer is formed by radical polymerization. A wall is formed inside the adventitia wall. However, according to the method of the present invention, the radical polymerization initiator is appropriately selected, and simultaneously with the formation of the outer membrane wall, the radical polymerization monomer is polymerized by the polymerization of the radical polymerizable monomer. May be used to form an intimal wall made of a polymer.

The second method of manufacturing a microcapsule according to the present invention basically includes the following steps. First Step An aqueous protective colloid aqueous solution containing a protective colloid agent is prepared. Second step A mixed solution obtained by adding a polyvalent isocyanate, a radical polymerizable monomer, a radical polymerization initiator, and a wall film-forming substance having reactivity to the polyvalent isocyanate to a hydrophobic core substance was prepared in the first step. It is emulsified or dispersed in the form of droplets in an aqueous protective colloid aqueous solution.

Third Step The temperature of the aqueous protective colloid aqueous solution obtained in the second step is increased with stirring, so that the outer membrane wall made of a polymer such as polyurethane or polyurea is formed at the interface of the mixed solution containing the core substance. To form microcapsules. Thus, in this third step, a dispersion of microcapsules is obtained. Fourth Step The microcapsule dispersion obtained in the third step is further heated to a temperature equal to or higher than the starting temperature of the radical polymerization initiator, thereby radically polymerizing the radically polymerizable monomer. A membrane wall is formed inside the outer membrane wall. The amounts of various samples used in this step are the same as those in the above-described steps. As described above, by appropriately selecting the radical polymerization initiator, the inner shell wall is formed simultaneously with the formation of the outer shell wall and the polymerization of the radical polymerizable monomer. It can also be done.

In the method of the present invention, the particle size of the obtained composite wall microcapsules is not particularly limited, and is the same as that of ordinary microcapsules, and is usually several μm to several hundred μm.
m. The amount of the core substance in the obtained composite wall microcapsule is 30 to 95% of the total capsule weight.
% By weight, preferably 40 to 70% by weight. The core substance that can be included in the microcapsule of the present invention may be either solid or liquid, but is preferably one soluble in the radical polymerizable monomer used. According to the method of the present invention, since the microcapsules are formed in an aqueous medium, the solubility of the core substance in water is 0.2% by weight.
The following is preferred. As described above, the composite wall microcapsules obtained according to the method of the present invention exhibit particularly excellent properties in solvent resistance, pressure resistance and water resistance.

[0025]

EXAMPLES The present invention will be described below with reference to examples.
The present invention is not limited by these examples. In the following, parts and% mean parts by weight and% by weight, respectively. The core substance content of the obtained microcapsules was determined by a high performance liquid chromatogram. The particle size was calculated from the particle size distribution diagram using a sedimentation type particle size distribution analyzer. The solvent resistance, pressure resistance and heat resistance of the microcapsules were determined by the following methods.

Solvent resistance 100 parts of a solvent (toluene, 1,1,1-trichloroethane, cyclohexane or methanol) contains 3 microcapsules.
The solution to which 0 part was added was sealed in an ampoule and stirred at 40 ° C. for about 5 hours. Thereafter, the microcapsules were sedimented and separated by centrifugation, and the amount of the microcapsule core substance in the supernatant was quantified using a high performance liquid chromatogram to determine the residual ratio of the microcapsule core substance.

20 parts of pressure-resistant microcapsules are dispersed in 30 parts of a 10% aqueous solution of polyvinyl alcohol, and applied to a typewriter paper using an applicator so that the applied amount of the microcapsules is 5.0 g / m ^2. After drying at 10 ° C. for 10 minutes, a sheet was prepared. After a load of 100 kg / cm ² was applied to the sheet for 10 minutes, the state of the sheet surface was determined by finger touch. The criterion is: ×: a liquid substance (core substance) is visually observed on the sheet surface, and
Stickiness is felt, Δ: no liquid substance is visually observed, but stickiness is felt by finger touch, ○: no stickiness is observed by either visual or finger touch. did.

Heat resistance The microcapsules were heat-treated in air at 150 ° C. for 5 hours, and the residual ratio of the core substance was determined by the following equation. Residual rate (%) = [(content after heat treatment / content before heat treatment)
× 100

Example 1 48 parts of methyl methacrylate, 2 parts of divinylbenzene, 0.2 part of lauroyl peroxide, adduct of 3 mol of tolylene diisocyanate / 1 mol of trimethylolpropane 11.1
Of the core substance was uniformly dissolved in 50 parts of chlorinated paraffin (manufactured by Ajinomoto, salt para L-50) to prepare an oil phase.

Next, an aqueous phase was prepared comprising 800 parts of distilled water and 8 parts of polyvinyl alcohol (Poval 220E, manufactured by Kuraray Co., Ltd.). Subsequently, the oil phase and the aqueous phase were mixed at 8000 rpm using a homomixer (manufactured by Tokushu Kika Co., Ltd.), and the mixture was charged into a polymerization reactor equipped with a reflux tube, a stirrer, a dropping funnel, and a nitrogen introduction tube. . Separately, 50 ml of an aqueous solution containing 5.6 parts of triethylenetetramine was prepared and added to the emulsion in the reactor using a dropping funnel.
Interfacial polymerization was performed at 0 ° C. for 5 hours.

The reaction product thus obtained was observed by an optical microscope, and it was confirmed that the reaction product was a microcapsule composed of a single wall of polyurethaneurea. Next, nitrogen was introduced into the polymerization apparatus containing the above product, polymerization was carried out at 80 ° C. for 5 hours, and separation and washing were repeated by a centrifugal separator, followed by drying to form free-flowing particulate matter. I got something. When the particles were measured by a sedimentation type particle size distribution analyzer, the average particle size was 7 μm. These samples were evaluated for solvent resistance, pressure resistance and heat resistance. Table 1 shows the results.

Example 2 Except that diisopropylnaphthalene was used instead of chlorinated paraffin as the core substance, the same treatment as in Example 1 was performed.

Example 3 48 parts of methyl methacrylate, 2 parts of divinylbenzene, t
0.5 parts of butyl peroxylaurate, 11.1 g of an adduct of 3 mol of tolylene diisocyanate / 1 mol of trimethylolpropane, and 5.6 g of polytetramethylene glycol (PTMG-1000, manufactured by Sanyo Chemical) as a core substance An oily phase was prepared by uniformly dissolving in 50 parts of paraffin.

Next, an aqueous phase comprising 800 parts of distilled water and 8 parts of polyvinyl alcohol was prepared. Subsequently, the oil phase and the aqueous phase were mixed at 8000 rpm using a homomixer, and the mixture was charged into a polymerization reactor equipped with a reflux tube, a stirrer, and a nitrogen introduction tube, and was then in-situ at 70 ° C. for 10 hours. Polymerized. The reaction product thus obtained was observed by an optical microscope, and as a result, it was confirmed that the reaction product was a microcapsule having a single wall of polyurethane urea. Next, nitrogen was introduced into the polymerization apparatus containing the above product, and 95
After polymerization at 10 ° C. for 10 hours, separation and washing by a centrifugal separator were repeated and then dried to obtain a free-flowing particulate product. When the particles were measured by a sedimentation type flow distribution measuring device, the average particle size was 10 μm. This sample was evaluated for solvent resistance, pressure resistance and heat resistance. Table 1 shows the results.

Example 4 The same treatment as in Example 3 was performed except that diisopropylnaphthalene was used instead of chlorinated paraffin as the core substance.

Example 5 In Example 1, 35 parts of acrylonitrile and 13 parts of methyl methacrylate were used in place of 48 parts of methyl methacrylate.
Except for using a mixture consisting of the above components, the same processing as in Example 1 was performed.

Comparative Example 1 An oil phase was prepared by uniformly dissolving 3 parts of tolylene diisocyanate / 20 parts of trimethylolpropane adduct in 50 parts of chlorinated paraffin as a core substance. Next, an aqueous phase composed of 800 parts of distilled water and 8 parts of polyvinyl alcohol was prepared. Subsequently, the oil phase and the aqueous phase were mixed at 8000 rpm using a homomixer, and this was mixed with a reflux tube.
The polymerization reactor was equipped with a stirrer and a dropping funnel.

Separately, 50 ml of an aqueous solution containing 10 parts of triethylenetetramine was prepared and added to the reactor using a dropping funnel, followed by interfacial polymerization at 80 ° C. for 5 hours.
Next, about the obtained microcapsule dispersion liquid, after repeating separation and washing by a centrifuge, dried,
A free flowing particulate product was obtained. When the particles were measured by a sedimentation type particle size distribution analyzer, the average particle size was 12 μm. These samples were evaluated for solvent resistance, pressure resistance and heat resistance. Table 1 shows the results.

Comparative Example 2 An oil phase was prepared by dissolving 3 parts of tolylene diisocyanate / 20 parts of adduct of trimethylolpropane and 10 parts of polytetramethylene glycol in 50 parts of chlorinated paraffin as a core substance. Next, an aqueous phase composed of 800 parts of distilled water and 8 parts of polyvinyl alcohol was prepared. Subsequently, the oil phase and the aqueous phase were mixed at 8000 using a homomixer.
After mixing at rpm, the mixture was charged into a polymerization reactor equipped with a reflux tube and a stirrer, and was subjected to in-situ polymerization at 70 ° C. for 10 hours. Next, the obtained microcapsule dispersion liquid was repeatedly separated and washed by a centrifuge, and then dried to obtain a free-flowing particulate product. When the particles were measured by a sedimentation type particle size distribution analyzer, the average particle size was 7 μm. These samples were evaluated for solvent resistance, pressure resistance and heat resistance. Table 1 shows the results.

Comparative Example 3 An oil phase was prepared by uniformly dissolving 48 parts of methyl methacrylate, 2 parts of divinylbenzene and 0.2 part of lauroyl peroxide in 50 parts of chlorinated paraffin as a core substance.
Next, an aqueous phase composed of 800 parts of distilled water and 8 parts of polyvinyl alcohol was prepared. Subsequently, the oil phase and the aqueous phase were mixed at 8000 rpm using a homomixer, and the mixture was charged into a polymerization reactor equipped with a reflux tube, a stirrer, and a nitrogen introduction tube, and polymerized at 70 ° C. for 5 hours under stirring. I let it. The product thus obtained was repeatedly filtered and washed with water using a centrifuge, and then dried to obtain a solid product. However, this solid product had remarkable secondary aggregation. These samples were evaluated for solvent resistance, pressure resistance and heat resistance. Table 1 shows the results.

Comparative Example 4 20 parts of chlorinated paraffin was added to a 10% aqueous gelatin solution 100
Mix at 8000 rpm with a homomixer in the
A 0 / W emulsion was prepared. Thereafter, the emulsion was heated to a temperature of 50 ° C. and stirred for 2 hours.
50 parts of a 0% gum arabic aqueous solution was added, and the pH was adjusted to 4.4 with a 5% acetic acid aqueous solution. This is cooled to 5 ° C and 3
5 parts of a 3% formalin aqueous solution was added, the pH was raised to 9 with a 10% aqueous sodium hydroxide solution, a crosslinking treatment was carried out for about 5 hours, and the temperature was returned to room temperature to obtain a microcapsule slurry.
The microcapsule slurry thus obtained was repeatedly filtered by centrifugation and washed with water, and then dried to obtain a powdery product having an average particle size of 18 μm. These samples were evaluated for solvent resistance, pressure resistance and heat resistance. Table 1 shows the results.

[0042]

[Table 1]

[0043]

The microcapsule according to the method of the present invention has, as the microcapsule wall, a composite wall composed of an inner membrane wall and an outer membrane wall, and has any of solvent resistance, pressure resistance and heat resistance to various solvents. It is also excellent.

Continuation of front page (56) References JP-A-4-290538 (JP, A) JP-A-2-46468 (JP, A) JP-A-4-277027 (JP, A) (58) Fields investigated (Int .Cl. ⁷ , DB name) B01J 13/02-13/22

Claims (2)

(57) [Claims] 1. A hydrophobic core substance containing a polyvalent isocyanate compound, a radical polymerizable monomer and an organic peroxide as a radical polymerization initiator is emulsified or dispersed in an aqueous protective colloid aqueous solution in the form of droplets, Next, a wall film-forming substance reactive with the polyvalent isocyanate compound is added to the aqueous protective colloid aqueous solution, and an outer wall film is formed by interfacial polymerization between the polyvalent isocyanate compound and the wall film-forming substance. , after forming the microcapsules, or while forming the inside of the microcapsules
A method for producing a composite wall microcapsule, comprising polymerizing the radical polymerizable monomer with an organic peroxide to form an inner wall film. 2. A polyvalent isocyanate compound, a material for forming a wall film reactive with the polyvalent isocyanate compound, a radically polymerizable monomer, and an organic peroxide as a radical polymerization initiator.
A hydrophobic core substance containing an oxide is emulsified or dispersed in an aqueous protective colloid aqueous solution in the form of droplets, and the polyvalent isocyanate compound and a wall having reactivity with the polyvalent isocyanate compound in the droplets. In-situ with film-forming substances
After forming the outer wall film by polymerization to form the microcapsules, or while forming, polymerize the radical polymerizable monomer with the organic peroxide inside the microcapsules to form the inner wall film. A method for producing a composite wall microcapsule, comprising: