WO2016148173A1

WO2016148173A1 - Method for manufacturing expandable microspheres, and expandable microspheres

Info

Publication number: WO2016148173A1
Application number: PCT/JP2016/058263
Authority: WO
Inventors: 俊蔵遠藤; 哲男江尻; 義克佐竹; 修作柴田
Original assignee: 株式会社クレハ
Priority date: 2015-03-17
Filing date: 2016-03-16
Publication date: 2016-09-22

Abstract

To provide: a method for manufacturing expandable microspheres with which the start of a polymerization reaction in an oil phase at an unintended time such as while a dispersion is being prepared or prior to the start of polymerization is suppressed, the intended polymerization reaction in an oil phase is not hindered, and properties such as expansion ratio are exceptional; and expandable microspheres having excellent properties. A method for manufacturing expandable microspheres in which a foaming agent is sealed in the outer shell of a produced polymer and in which the maximum expansion ratio is 5 or higher, the method being characterized in that at least the foaming agent, a polymerizable monomer, a polymerization initiator, and a water-soluble polymerization inhibitor or a non-water-soluble polymerization inhibitor are suspended in an aqueous dispersion medium whereupon suspension polymerization is performed in the presence of the water-soluble polymerization inhibitor or the non-water-soluble polymerization inhibitor.

Description

Method for producing foamable microsphere, and foamable microsphere

The present invention relates to a method for producing foamable microspheres and foamable microspheres. More specifically, the start of a polymerization reaction at an undesired time such as during preparation of a dispersion or before the start of polymerization is sufficiently suppressed. , A method for producing foamable microspheres, in which the polymerization reaction in the oil phase is not hindered when suspension polymerization for producing foamable microspheres is performed, and physical properties such as foaming magnification are excellent, and foamable microspheres Regarding fairs.

Expandable microspheres (sometimes called "thermally expandable microcapsules") are used in various fields such as paints and plastic fillers for weight reduction, including applications in foamed inks. Applications are being developed. The foamable microspheres are usually obtained by encapsulating a volatile liquid foaming agent (sometimes referred to as “physical foaming agent” or “volatile swelling agent”) with a polymer and microencapsulating it. As the foaming agent, a chemical foaming agent that decomposes when heated to generate gas may be used as desired. In general, the foamable microspheres can be produced by a suspension polymerization of a polymerizable mixture containing at least a foaming agent and a polymerizable monomer in an aqueous medium. As the polymerization reaction proceeds, an outer shell is formed by the produced polymer, and a foamable microsphere having a structure in which the foaming agent is enclosed in the outer shell is obtained.

As the polymer forming the outer shell of the foamable microsphere, a thermoplastic resin having a good gas barrier property is generally used. The polymer forming the outer shell softens when heated. As the foaming agent, one that is gaseous at a temperature below the softening point of the polymer is selected. When the foamable microspheres are heated, the foaming agent vaporizes and expands and acts on the outer shell, and the elastic modulus of the polymer forming the outer shell decreases rapidly. Therefore, the expansion of the foamable microsphere occurs at a certain temperature. This temperature is called the foaming start temperature. When the foamable microspheres are heated to a temperature higher than the foaming start temperature, that is, the foaming temperature, the foamable microspheres expand themselves to form closed cells (such as “foam particles”, “hollow particles” or “hollow plastic balloon”). Sometimes).

In suspension polymerization performed to form foamable microspheres, a polymerizable mixture containing at least a foaming agent and a polymerizable monomer is generally added to an aqueous dispersion medium containing a dispersion stabilizer. The mixture is stirred and mixed to granulate fine droplets of the polymerizable mixture, and then heated to perform suspension polymerization. Since most of the polymerizable mixture is usually insoluble in water, an oil phase is formed in an aqueous dispersion medium, and thus, it is granulated into fine droplets by stirring and mixing. Suspension polymerization forms foamable microspheres with approximately the same particle size as these fine droplets. In the suspension polymerization method, various additives such as a dispersion stabilizer, a stabilizer (sometimes referred to as “auxiliary stabilizer”), a polymerization initiator (sometimes called “catalyst”), and a polymerization assistant. The particle shape and the particle size distribution can be adjusted by appropriately selecting and combining the types and contents, and appropriately selecting and combining the stirring and mixing conditions and the polymerization conditions.

In addition, if the polymerizable monomer may initiate a polymerization reaction at an undesired early stage (such as during the preparation of a polymerizable mixture or a dispersion), the resulting foamable microspheres are homogeneous. The desired foaming characteristics may not be achieved, and the productivity and foamed microspheres may be deteriorated. For example, when the outside air temperature is high, an undesired polymerization reaction may start. In particular, when large-scale production is performed, preparation of a polymerizable mixture and preparation of a dispersion take time. The reaction may start. For this reason, in the manufacturing method of an expandable microsphere, the polymerization inhibitory effect for 1 hour or more at the temperature of 25 degreeC, Preferably it is 2 hours or more, Furthermore, 4 hours or more is calculated | required.

In general, as a polymerization inhibitor that suppresses the polymerization of vinyl compounds such as acrylonitrile, acrylic acid ester, methacrylic acid ester, styrene, acrylic acid, methacrylic acid, quinone compounds (benzoquinone, etc.), hydroquinone compounds (called “hydroquinone”) Many compounds such as phenolic compounds (methoquinone, tocopherol, etc.), hindered amine compounds, amine compounds, phosphorus compounds, manganese salt compounds, copper diphenyldithiocarbamate, nitroso compounds, N-oxyl compounds, etc. Are known. Many of these polymerization inhibitors are used in the distillation step for the synthesis of the vinyl compound monomer and for purification after the synthesis, and are also used in a very small amount during the storage and storage of the monomer. Typically, there is a step of removing the polymerization inhibitor prior to producing the polymer from the monomer.

In manufacturing foamable microspheres, it is known to use a polymerization inhibitor in an aqueous dispersion medium. The reason is that by suppressing polymerization in an undesired aqueous phase, the liquid viscosity increases when the polymerizable mixture is stirred and polymerized in an aqueous dispersion medium, the droplets adhere to the reaction vessel, and the droplets aggregate. Is to prevent the productivity from being lowered and the quality of the foamable microspheres from being lowered. For example, Patent Document 1 includes suspension polymerization of a polymerizable mixture containing at least a foaming agent and a polymerizable monomer in an aqueous dispersion medium, and encapsulating the foaming agent in the outer shell of the resulting polymer. In a method for producing foamable microspheres, by subjecting a polymerizable mixture to suspension polymerization in the presence of alkali metal nitrite, stannous chloride, stannic chloride, water-soluble ascorbic acid, or boric acid. In addition, it is disclosed that aggregation of the generated polymer particles during polymerization and adhesion of scale to the polymerization can wall are prevented. Patent Document 2 discloses that in the method for producing hollow resin particles, an aqueous polymerization inhibitor is contained in a liquid phase (aqueous phase) in which a monomer component is insoluble. Patent Document 3 discloses that a polymerization aid (polymerization inhibitor) is generally used for suppressing the generation of an emulsion polymer in an aqueous system in suspension polymerization and preventing scale, and ascorbic acids. And alkali metal nitrites are used as polymerization inhibitors, the physical properties such as expansion ratio (synonymous with foaming ratio) are not sufficiently improved, or the thermal stability is low and the polymer decomposes during the polymerization reaction. It is disclosed that there is a problem that the property as an inhibitor is lost or the physical properties of the resulting heat-expandable microcapsules (expandable microspheres) and the hollow microparticles obtained by thermal expansion cannot be improved sufficiently. Has been.

In the method for producing foamable microspheres, the polymerization inhibitor has an effect of sufficiently suppressing the initiation of the polymerization reaction of the polymerizable monomer at an undesired time (such as during the preparation of the polymerizable mixture or the preparation of the dispersion). At the same time, it is essential to have as little addition as possible so as not to inhibit the polymerization reaction rate in the subsequent polymerization reaction such as suspension polymerization that forms the outer shell of the foamable microsphere. It is required to be. In addition, as a polymerization inhibitor used in a method for producing foamable microspheres in which a polymerizable mixture containing at least a foaming agent and a polymerizable monomer is suspended in an aqueous dispersion medium, a polymerization inhibitor is used as a product polymer. It is required that the foamable microspheres can be easily transferred to an aqueous dispersion medium without being included, and that the resulting foamable microspheres can have excellent physical properties.

That is, in a method for producing foamable microspheres, in which a polymerizable mixture is subjected to suspension polymerization in an aqueous dispersion medium to produce foamable microspheres in which a foaming agent is enclosed in the outer shell of the resulting polymer. At the time of granulation for forming droplets containing a polymerizable mixture (forms an oil phase) containing at least a polymerizable monomer and a polymerization initiator, a sufficient amount of polymerization suppression effect (for example, a temperature of 25 ° C.) in the oil phase is small. In addition, a polymerization inhibiting effect for 1 hour or longer, preferably 2 hours or longer, and further 4 hours or longer is desired), and a polymerization reaction in an oil phase by suspension polymerization to obtain foamable microspheres. Appropriate polymerization prohibition that does not hinder, can stably carry out the polymerization reaction in the oil phase, is not likely to be included in the produced polymer, and has excellent physical properties of expandable microspheres such as expansion ratio And its use has not been found.

Therefore, a suspension of a polymerizable mixture containing at least a blowing agent, a polymerizable monomer, and a polymerization inhibitor (forms an oil phase) in the aqueous dispersion medium, for example, during preparation of the dispersion or before the start of polymerization. Prior to polymerization, the initiation of the polymerization reaction in the oil phase at an undesired time is sufficiently suppressed, and the polymerization in the oil phase is performed to obtain a foamable microsphere by suspension polymerization of the polymerizable mixture There has been a demand for a method for producing foamable microspheres that are excellent in physical properties such as foaming magnification, and foamable microspheres that are excellent in physical properties such as foaming magnification without being hindered by reaction.

JP-A-11-209504 JP 2005-146223 A International Publication No. 2008-142849

The problem of the present invention is that the start of the polymerization reaction in the oil phase at an undesired time such as during the preparation of the dispersion or before the start of polymerization is suppressed, and the polymerization reaction in the desired oil phase is not inhibited, such as the expansion ratio. It is an object of the present invention to provide a method for producing foamable microspheres having excellent physical properties; and to provide foamable microspheres having excellent physical properties.

As a result of intensive studies to solve the problem, the present inventors have found that the problem can be solved by using a specific polymerization inhibitor in the oil phase, and the present invention has been completed.

That is, according to the present invention, a polymerizable mixture containing at least a foaming agent, a polymerizable monomer, a polymerization initiator, and a water-soluble polymerization inhibitor or a water-insoluble polymerization inhibitor is suspended in an aqueous dispersion medium. Thereafter, suspension polymerization is performed in the presence of a water-soluble polymerization inhibitor or a water-insoluble polymerization inhibitor, and the maximum expansion ratio in which the foaming agent is enclosed in the outer shell of the produced polymer is 5 times or more. A method of making certain foamable microspheres is provided.

Further, according to the present invention, the following methods (1) to (6) for producing foamable microspheres are provided as specific embodiments of the invention relating to the method for producing foamable microspheres.
(1) The method for producing foamable microspheres, wherein the water-soluble polymerization inhibitor contains at least one compound selected from the group consisting of hydroquinone compounds, naphthohydroquinone compounds and N-nitroso compounds.
(2) The foaming property according to claim 1, wherein the water-insoluble polymerization inhibitor contains an oil-soluble aromatic compound having at least one selected from the group consisting of vitamin E, hydroxy group, quinone group and alkoxy group. Microsphere manufacturing method.
(3) The polymerizable monomer is at least 30 to 95% by weight of vinylidene chloride and at least selected from the group consisting of acrylonitrile, methacrylonitrile, acrylic acid ester, methacrylic acid ester, styrene, acrylic acid, methacrylic acid and vinyl acetate. The method for producing foamable microspheres as described above, which is a monomer mixture containing 5 to 70% by mass of one kind of monomer.
(4) The polymerizable monomer is at least one monomer selected from the group consisting of acrylonitrile and methacrylonitrile, 25 to 100% by mass, vinylidene chloride, acrylate ester, methacrylate ester, styrene, acrylic acid, The process for producing foamable microspheres as described above, which is a monomer mixture containing 0 to 75% by mass of at least one monomer selected from the group consisting of methacrylic acid and vinyl acetate.
(5) The aqueous dispersion medium contains at least one compound selected from the group consisting of dichromate, alkali metal nitrite, stannous chloride, stannic chloride, boric acid and water-soluble ascorbic acids. A method for producing foamable microspheres.
(6) The method for producing foamable microspheres, wherein the compound contained in the aqueous dispersion medium is an alkali metal nitrite salt.

Furthermore, according to the present invention, a polymerizable mixture containing at least a foaming agent, a polymerizable monomer, a polymerization initiator, and a water-soluble polymerization inhibitor or a water-insoluble polymerization inhibitor is suspended in an aqueous dispersion medium. Thereafter, a foamable microsphere having a maximum foaming ratio of 5 times or more obtained by enclosing a foaming agent in the outer shell of the resulting polymer obtained by suspension polymerization in the presence of a water-soluble polymerization inhibitor is provided. As a specific embodiment thereof, the above-mentioned foamable microsphere having an average particle size of 0.5 to 150 μm is provided.

According to the present invention, a polymerizable mixture containing at least a foaming agent, a polymerizable monomer, a polymerization initiator, and a water-soluble polymerization inhibitor or a water-insoluble polymerization inhibitor is suspended in an aqueous dispersion medium. Suspension polymerization in the presence of a water-soluble polymerization inhibitor, and a method for producing a foamable microsphere having a maximum foaming ratio of 5 times or more in which a foaming agent is enclosed in the outer shell of the produced polymer As a result, the start of the polymerization reaction in the oil phase at an undesired time such as during the preparation of the dispersion or before the start of the polymerization is suppressed, and the polymerization in the intended oil phase is performed to obtain foamable microspheres. The reaction is not hindered, and an effect is provided that a method for producing foamable microspheres having excellent physical properties such as foaming ratio is provided.

Further, according to the present invention, a polymerizable mixture containing at least a foaming agent, a polymerizable monomer, a polymerization initiator, and a water-soluble polymerization inhibitor is suspended in an aqueous dispersion medium, and then a water-soluble polymerization inhibitor. Or a foamable microsphere having a maximum foaming ratio of 5 times or more in which the foaming agent is enclosed in the outer shell of the resulting polymer obtained by suspension polymerization in the presence of a water-insoluble polymerization inhibitor. Thus, an effect is provided that a foamable microsphere having excellent physical properties such as a foaming ratio is provided.

I. Production method of foamable microsphere The production method of the foamable microsphere of the present invention (hereinafter sometimes referred to as “the production method of the present invention”) is at least a foaming agent and a polymerizable monomer in an aqueous dispersion medium. Suspend a polymerizable mixture containing a monomer, a polymerization initiator and a water-soluble polymerization inhibitor or a water-insoluble polymerization inhibitor, and then suspension polymerization in the presence of a water-soluble polymerization inhibitor or a water-insoluble polymerization inhibitor A method for producing foamable microspheres having a maximum foaming ratio of 5 times or more in which a foaming agent is enclosed in an outer shell of a produced polymer. In the production method of the present invention, the foaming agent, the polymerizable monomer, and other additives described later are not particularly limited, and conventionally known ones can be used. That is, the production method of the present invention can be applied to the production of all types of expandable microspheres.

1. Foaming agent The foaming agent used in the method for producing foamable microspheres of the present invention is usually a substance that becomes gaseous at a temperature below the softening point of the polymer forming the outer shell. As such a foaming agent, a low-boiling organic solvent is suitable. For example, ethane, ethylene, propane, propene, n-butane, isobutane, butene, isobutene, n-pentane, isopentane, neopentane, n-hexane, heptane , n- octane, isooctane, isododecane, petroleum ether, hydrocarbons such as isoparaffin _{_{_{_{mixture; CCl 3 F, CCl 2 F}}}} 2, CClF 3, chlorofluorocarbons such as CClF ₂ -CClF 2; tetramethylsilane, trimethylethyl silane, trimethyl And tetraalkylsilanes such as isopropylsilane and trimethyl-n-propylsilane. These can be used alone or in combination of two or more. Among these, isobutane, n-butane, n-pentane, isopentane, n-hexane, petroleum ether, isooctane, isododecane, and a mixture of two or more thereof are preferable. Further, if desired, a compound which is thermally decomposed by heating and becomes gaseous may be used. The content of the foaming agent is usually 10 to 40 parts by weight, preferably 12 to 35 parts by weight, more preferably 15 to 32 parts by weight with respect to 100 parts by weight of the total amount of polymerizable monomers described below. It is a range.

2. Polymerizable monomer As described below, the polymerizable monomer is a foamable microsphere in which a foaming agent is encapsulated in the outer shell of a product polymer obtained by suspension polymerization in an aqueous dispersion medium. As long as it can be formed, it is not particularly limited. Preferably, from the viewpoint that the outer shell of the produced polymer has gas barrier properties, solvent resistance and heat resistance, and can produce a polymer having good foamability and, if desired, foamability at high temperature. The polymerizable monomer is at least one monomer selected from the group consisting of acrylonitrile and methacrylonitrile (the monomers may be collectively referred to as “(meth) acrylonitrile”), and / or. Alternatively, it is preferable to contain vinylidene chloride.

Examples of polymerizable monomers other than (meth) acrylonitrile and / or vinylidene chloride include acrylic acid esters such as methyl acrylate, ethyl acrylate, butyl acrylate, and dicyclopentenyl acrylate; methyl methacrylate, ethyl methacrylate Methacrylic acid esters such as butyl methacrylate and isobornyl methacrylate; acrylic acid, methacrylic acid, vinyl chloride, styrene, vinyl acetate, α-methylstyrene, chloroprene, neoprene, butadiene and the like.

These polymerizable monomers can be used alone or in combination of two or more. A preferred polymerizable monomer is a monomer mixture containing (meth) acrylonitrile and / or vinylidene chloride.

[Monomer mixture containing (meth) acrylonitrile]
As the monomer mixture containing (meth) acrylonitrile, the polymerizable monomer is (meth) acrylonitrile (at least one monomer selected from the group consisting of acrylonitrile and methacrylonitrile) in a range of 25 to 100% by mass. , At least one monomer selected from the group consisting of vinylidene chloride, acrylic acid ester, methacrylic acid ester, styrene, acrylic acid, methacrylic acid and vinyl acetate (hereinafter referred to as "monomer other than (meth) acrylonitrile") A monomer mixture containing 0 to 75% by mass is preferable. In the case where the polymerizable monomer contains 100% by mass of (meth) acrylonitrile, it is not strictly a monomer mixture, but in the present invention, the monomer including this case is included. It is called a mixture.

The higher the (meth) acrylonitrile content ratio, the higher the foaming temperature of the foamable microspheres formed, and the lower the content ratio, the higher the (meth) acrylonitrile-containing monomer mixture, the lower the content ratio. Microsphere foaming temperature tends to be low. Further, the foaming temperature, the maximum foaming ratio, etc. of the foamable microsphere to be formed can be adjusted also by the type and composition of the monomer other than (meth) acrylonitrile. Therefore, desired foamable microspheres can be formed by adjusting the ratio of (meth) acrylonitrile and monomers other than (meth) acrylonitrile, and the type and composition of monomers other than (meth) acrylonitrile. can do. Preferred combinations of (meth) acrylonitrile and monomers other than (meth) acrylonitrile are (meth) acrylonitrile 25 to 99.5% by mass, preferably 30 to 99% by mass, and monomers other than (meth) acrylonitrile It is 0.5 to 75% by mass, preferably 1 to 70% by mass (the total amount is 100% by mass), and as a monomer other than (meth) acrylonitrile, particularly preferred is methyl methacrylate. When the content ratio of (meth) acrylonitrile is too low, the foaming temperature of the foamable microspheres formed may be low, or the gas barrier property may be insufficient.

[Monomer mixture containing vinylidene chloride]
As the monomer mixture containing vinylidene chloride, the polymerizable monomer is 30 to 95% by mass of vinylidene chloride, acrylonitrile, methacrylonitrile, acrylic ester, methacrylic ester, styrene, acrylic acid, methacrylic acid and A monomer mixture containing 5 to 70% by mass of at least one monomer selected from the group consisting of vinyl acetate (hereinafter sometimes referred to as “monomer other than vinylidene chloride”) is preferable. .

In the monomer mixture containing vinylidene chloride, the higher the content ratio of vinylidene chloride, the higher the gas barrier property of the foamable microspheres formed, and the lower the content ratio, the lower the content of the foamable microspheres formed. The gas barrier property tends to be low. Further, the foaming temperature, the maximum foaming ratio, etc. of the foamable microspheres to be formed can also be adjusted by the type and composition of monomers other than vinylidene chloride. Therefore, desired foamable microspheres can be formed by adjusting the ratio of vinylidene chloride and monomers other than vinylidene chloride, and the type and composition of monomers other than vinylidene chloride. Preferred combinations of vinylidene chloride and monomers other than vinylidene chloride are 35 to 90% by mass, preferably 40 to 80% by mass, and monomers other than vinylidene chloride 10 to 65% by mass, preferably 20 to It is 60% by mass (the total amount is 100% by mass), and as a monomer other than vinylidene chloride, (meth) acrylonitrile and methyl methacrylate are preferable, and a monomer mixture containing vinylidene chloride is preferable. The combination is 45 to 75% by mass of vinylidene chloride, 20 to 50% by mass of (meth) acrylonitrile, and 3 to 10% by mass of methyl methacrylate (the total amount is 100% by mass). If the content ratio of vinylidene chloride is too low, the gas barrier property of the foamable microspheres to be formed may be insufficient, or the desired maximum foaming ratio may not be obtained.

3. Crosslinkable monomer A crosslinkable monomer can be used in combination with the polymerizable monomer described above in order to improve foaming characteristics and heat resistance. As the crosslinkable monomer, a compound having two or more carbon-carbon double bonds is usually used. More specifically, as the crosslinkable monomer, for example, divinylbenzene, ethylene glycol di (meth) acrylate [ethylene glycol di (meth) acrylate], diethylene glycol di (meth) acrylate [diethylene glycol di (meth) acrylate] ] Triethylene glycol di (meth) acrylate, allyl (meth) acrylate, triallyl isocyanate, triacryl formal, trimethylolpropane tri (meth) acrylate, 1,3-butyl glycol di (meth) acrylate, Examples include pentaerythritol tri (meth) acrylate and pentaerythritol tetra (meth) acrylate. The proportion of the crosslinkable monomer used is usually 0.01 to 5% by mass of the polymerizable monomer, preferably 0.05 to 2% by mass, more preferably 0.1 to 1.5% by mass, still more preferably. Is 0.15 to 1% by mass.

4). Polymerization initiator The polymerizable monomer is polymerized by contact with the polymerization initiator in a predetermined temperature environment. The polymerization initiator is not particularly limited, and those generally used in this field can be used, but an oil-soluble polymerization initiator soluble in the polymerizable monomer to be used is preferable. Examples of the polymerization initiator include dialkyl peroxide, diacyl peroxide, peroxy ester, peroxy dicarbonate, and azo compound. More specifically, dialkyl peroxides such as methyl ethyl peroxide, di-t-butyl peroxide, dicumyl peroxide; isobutyl peroxide, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, 3, 5, Diacyl peroxide such as 5-trimethylhexanoyl peroxide; t-butyl peroxypivalate, t-hexyl peroxypivalate, t-butyl peroxyneodecanoate, t-hexyl peroxyneodecanoate, 1 -Cyclohexyl-1-methylethylperoxyneodecanoate, 1,1,3,3-tetramethylbutylperoxyneodecanoate, cumylperoxyneodecanoate, (α, α-bis-neodecanoyl Peroxy) peroxy such as diisopropylbenzene Esters; bis (4-t-butylcyclohexyl) peroxydicarbonate, di-n-propyl-oxydicarbonate, di-isopropylperoxydicarbonate (hereinafter sometimes referred to as “IPP”), di (2- Peroxydicarbonates such as ethylethylperoxy) dicarbonate, di-methoxybutylperoxydicarbonate, di (3-methyl-3-methoxybutylperoxy) dicarbonate; 2,2′-azobisisobutyronitrile 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile, 2,2′-azobis (2,4-dimethylvaleronitrile), 1,1′-azobis (1-cyclohexanecarbonitrile), etc. The polymerization initiator is usually 0.01 to on a polymerizable monomer basis. It is used in a proportion of 7% by mass, preferably 0.1-3% by mass, more preferably 0.3-2% by mass.

5. Dispersion stabilizer, auxiliary stabilizer and the like Suspension polymerization is usually carried out in an aqueous dispersion medium containing a dispersion stabilizer (suspension agent). Examples of the dispersion stabilizer include silica, calcium phosphate, magnesium hydroxide, aluminum hydroxide, ferric hydroxide, barium sulfate, calcium sulfate, sodium sulfate, calcium oxalate, calcium carbonate, barium carbonate, magnesium carbonate and the like. be able to. The dispersion stabilizer is usually used at a ratio of 0.1 to 20 parts by mass with respect to 100 parts by mass of the polymerizable monomer.

In addition to dispersion stabilizers, auxiliary stabilizers such as condensation products of diethanolamine and aliphatic dicarboxylic acids, condensation products of urea and formaldehyde, polyvinylpyrrolidone, polyethylene oxide, polyethyleneimine, tetramethylammonium hydroxide, gelatin, Methyl cellulose, polyvinyl alcohol, dioctyl sulfosuccinate, sorbitan ester, various emulsifiers and the like can be used.

One preferred combination is a combination of colloidal silica and a condensation product. As the condensation product, a condensation product of diethanolamine and an aliphatic dicarboxylic acid is preferable, and a condensation product of diethanolamine and adipic acid or a condensation product of diethanolamine and itaconic acid is particularly preferable. The condensate is defined by its acid value. Preferably, the acid value is 60 mgKOH / g or more and less than 95 mgKOH / g. Particularly preferred is a condensate having an acid value of 65 mgKOH / g or more and 90 mgKOH / g or less. Furthermore, when inorganic salts such as sodium chloride and sodium sulfate are added, expandable microspheres having a more uniform particle shape are easily obtained. As the inorganic salt, sodium chloride is preferably used. The amount of colloidal silica used varies depending on the particle size, but is usually 1-20 parts by weight, preferably 1.5-10 parts by weight, based on 100 parts by weight of the polymerizable monomer. . The condensation product is usually used at a ratio of 0.05 to 2 parts by mass with respect to 100 parts by mass of the polymerizable monomer. The inorganic salt is used in a proportion of about 0 to 100 parts by mass, and in many cases about 0.5 to 50 parts by mass with respect to 100 parts by mass of the polymerizable monomer.

Other preferred combinations include a combination of colloidal silica and a water-soluble nitrogen-containing compound. Examples of water-soluble nitrogen-containing compounds include polyvinyl pyrrolidone, polyethyleneimine, polyoxyethylene alkylamine, polydialkylaminoalkyl (meth) acrylate represented by polydimethylaminoethyl methacrylate and polydimethylaminoethyl acrylate, and polydimethylaminopropyl. Examples thereof include polydialkylaminoalkyl (meth) acrylamides represented by acrylamide and polydimethylaminopropylmethacrylamide, polyacrylamide, polycationic acrylamide, polyamine sulfone, and polyallylamine. Among these, a combination of colloidal silica and polyvinylpyrrolidone is preferably used. Another preferred combination is a combination of magnesium hydroxide and / or calcium phosphate and an emulsifier.

As the dispersion stabilizer, a poorly water-soluble metal hydroxide obtained by reaction in a water phase of a water-soluble polyvalent metal compound (for example, magnesium chloride) and an alkali metal hydroxide salt (for example, sodium hydroxide) ( For example, a colloid of magnesium hydroxide can be used. In addition, as the calcium phosphate, a reaction product in an aqueous phase of sodium phosphate and calcium chloride can be used. As the emulsifier, an anionic surfactant, for example, dialkyl sulfosuccinate or polyoxyethylene alkyl (allyl) ether phosphate ester may be used.

An emulsifier is not generally used, but an anionic surfactant such as a dialkyl sulfosuccinate or a polyoxyethylene alkyl (allyl) ether phosphate may be used if desired.

Further, as a polymerization aid, in an aqueous dispersion medium (aqueous phase), from dichromate, alkali metal nitrite, stannous chloride, stannic chloride, boric acid and water-soluble ascorbic acids (vitamin C, etc.) At least one compound selected from the group consisting of: When suspension polymerization is performed in the presence of these compounds, the polymerization particles in the aqueous phase do not aggregate during polymerization, and the polymer does not adhere to the polymerization can wall, thus efficiently generating heat due to polymerization. A foamable microsphere can be produced stably while removing. In particular, the polymerizable mixture containing a polymerizable monomer contains a water-soluble polymerization inhibitor or a water-insoluble polymerization inhibitor, and at least one of the above-mentioned compounds, particularly alkali metal nitrite, in an aqueous dispersion medium. A process for producing expandable microspheres containing sulfur is preferred. Among the alkali metal nitrites, sodium nitrite and potassium nitrite are preferable in terms of availability and price. These compounds are generally used in a proportion of 0.001 to 1 part by mass, preferably 0.01 to 0.1 part by mass, with respect to 100 parts by mass of the polymerizable monomer.

6). Water-soluble polymerization inhibitor The method for producing foamable microspheres having a maximum foaming ratio of 5 times or more according to the present invention comprises at least a foaming agent, a polymerizable monomer, a polymerization initiator, and a water-soluble polymerization in an aqueous dispersion medium. It is characterized in that a polymerizable mixture containing an inhibitor is suspended and then subjected to suspension polymerization in the presence of a water-soluble polymerization inhibitor. The water-soluble polymerization inhibitor is a polymerization inhibitor having solubility in water, and means a polymerization inhibitor having a solubility in water of 1% by mass at a normal temperature of 20 ° C. Here, the solubility in water at a temperature of 20 ° C. means the mass (unit: mass%) of the polymerization inhibitor dissolved in 100 g of water at a temperature of 20 ° C. (under a pressure condition of 760 torr). “Solubility” as defined in Japanese Pharmacopoeia (16th revision) General Rules 29, ie, dissolve 1 g or 1 mL of solute (specifically, 30 minutes when shaking vigorously for 30 seconds every 5 minutes at a temperature of 20 ± 5 ° C.) It can also be determined as the amount of solvent required (unit: mL). As the water-soluble polymerization inhibitor used in the present invention, it is preferable that the solubility in water at a temperature of 20 ° C. is 5% by mass or more from the viewpoint of uniformity of foaming, and the solubility in water at a temperature of 20 ° C. It is more preferable that it is 8 mass% or more.

7). Water-insoluble polymerization inhibitor The method for producing foamable microspheres having a maximum foaming ratio of 5 times or more according to the present invention comprises at least a foaming agent, a polymerizable monomer, a polymerization initiator and a water-insoluble solution in an aqueous dispersion medium. A polymerizable mixture containing a water-soluble polymerization inhibitor is suspended, and then suspension polymerization is performed in the presence of a water-insoluble polymerization inhibitor. The water-insoluble polymerization inhibitor is a polymerization inhibitor that is not soluble in water, and means a polymerization inhibitor having a solubility in water of 1% by mass or less at a normal temperature of 20 ° C. Here, the solubility in water at a temperature of 20 ° C. means the mass (unit: mass%) of the polymerization inhibitor dissolved in 100 g of water at a temperature of 20 ° C. (under a pressure condition of 760 torr). “Solubility” as defined in Japanese Pharmacopoeia (16th revision) General Rules 29, ie, dissolve 1 g or 1 mL of solute (specifically, 30 minutes when shaking vigorously for 30 seconds every 5 minutes at a temperature of 20 ± 5 ° C.) It can also be determined as the amount of solvent required (unit: mL). As the water-insoluble polymerization inhibitor used in the present invention, the solubility in water at a temperature of 20 ° C. is preferably 0.5% by mass or less from the viewpoint of uniformity of foaming, and the water at a temperature of 20 ° C. More preferably, the solubility in is 0.3 mass% or less.

In the method for producing a foamable microsphere having a maximum foaming ratio of 5 times or more according to the present invention, i) at least a foaming agent, a polymerizable monomer, a polymerization initiator, and a water-soluble polymerization inhibitor in an aqueous dispersion medium. Alternatively, by suspending the polymerizable mixture containing the water-insoluble polymerization inhibitor, the water-soluble polymerization inhibitor or the water-insoluble polymerization inhibitor is first dissolved in the oil phase formed by the polymerizable monomer. , The initiation of undesired polymerization reaction, in particular, the occurrence of polymerization in the polymerizable mixture such as at the time of preparing the polymerizable mixture or the preparation of the dispersion is sufficiently suppressed, and ii) the water-soluble polymerization inhibitor or During the polymerization reaction in which the outer shell of the resulting polymer encapsulating the foaming agent is formed by suspension polymerization in the presence of a water-insoluble polymerization inhibitor, a water-soluble polymerization inhibitor or a water-insoluble polymerization inhibitor is added. Due to its water solubility The polymerization reaction is not hindered by at least part of the transition to the aqueous phase, and iii) Furthermore, the water-soluble polymerization inhibitor or water-insoluble polymerization inhibitor migrates from the oil phase to the water phase due to its hydrophilicity. As a result, in the polymerization reaction, generation of new particles due to polymerization in a place other than the droplet (oil phase) containing the polymerizable mixture containing the polymerizable monomer, that is, in the aqueous dispersion medium (aqueous phase) is suppressed. Iv) The physical properties such as the maximum expansion ratio are excellent by a mechanism such that the water-soluble polymerization inhibitor or the water-insoluble polymerization inhibitor is less likely to suppress the polymerization, and the particle size is within a predetermined range if desired. It is presumed that foamable microspheres having a maximum foaming ratio of 5 times or more can be obtained.

As a water-soluble polymerization inhibitor that can be used in the method for producing foamable microspheres of the present invention, as long as it has solubility in water at a predetermined temperature of 20 ° C. and can exhibit the action described above. Although not particularly limited, it preferably contains at least one compound selected from the group consisting of a hydroquinone compound, a naphthohydroquinone compound and an N-nitroso compound, and further, the desired effect is sufficiently obtained even in the absence of oxygen. Since it can be exhibited, naphthohydroquinonesulfonic acid or a salt thereof, or a water-soluble aromatic N-nitroso compound is more preferable. In the absence of oxygen, the oxygen concentration in the reaction system or in the space of the container is determined by substituting the reaction system or the container with an inert gas such as nitrogen, helium, argon, or carbon dioxide. It refers to a sufficiently lowered condition, for example, a condition such that the oxygen concentration in the reaction system or in the space of the container is usually 1 vol% or less, preferably 0.1 vol% or less.

(1) Hydroquinone Compound Examples of the hydroquinone compound that is a water-soluble polymerization inhibitor preferably used in the method for producing foamable microspheres of the present invention include hydroquinone, methoquinone (p-methoxyphenol), catechol, resorcinol and the like. Hydroquinone and methoquinone are more preferably used. Note that tert-butyl hydroquinone does not normally correspond to the water-soluble polymerization inhibitor used in the present invention because its solubility in water at a temperature of 20 ° C. is 0.5% by mass or less.

(2) Naphthohydroquinone Compound A naphthohydroquinone compound which is a water-soluble polymerization inhibitor preferably used in the method for producing foamable microspheres of the present invention is a hydroquinone compound having a naphthalene ring which is an aromatic complex ring, and oxygen. From the viewpoint of inhibiting polymerization in the absence or from the viewpoint of water solubility, a compound having a sulfonic acid group or a carboxylic acid group in the molecule or a salt thereof may be used. More preferred naphthohydroquinone compounds include naphthohydroquinone sulfonic acid or a salt thereof. More preferred are sodium, potassium, ammonium and alkyl-substituted ammonium salts. Specifically, ammonium naphthohydroquinonesulfonate, sodium naphthohydroquinonesulfonate, potassium naphthohydroquinonesulfonate, monomethylammonium naphthohydroquinonesulfonate, monoethylammonium naphthohydroquinonesulfonate, dimethylammonium naphthohydroquinonesulfonate, trimethyl naphthohydroquinonesulfonate Ammonium, naphthohydroquinonesulfonic acid tetramethylammonium, etc. More preferred are ammonium naphthohydroquinonesulfonate, monomethylammonium naphthohydroquinonesulfonate, monoethylammonium naphthohydroquinonesulfonate, dimethylammonium naphthohydroquinonesulfonate, trimethylammonium naphthohydroquinonesulfonate, and tetramethylammonium naphthohydroquinonesulfonate. Particularly preferred is ammonium naphthohydroquinonesulfonate.

(3) N-nitroso compound The N-nitroso compound, which is a water-soluble polymerization inhibitor preferably used in the method for producing foamable microspheres of the present invention, is represented by (formula) -NN = O in the molecule. It is a water-soluble compound having an N-nitroso group. Therefore, nitrosophenol and isoamyl nitrite which are nitroso compounds do not correspond to N-nitroso compounds. In view of the effect of inhibiting polymerization in the absence of oxygen and the viewpoint of water solubility, the method for producing foamable microspheres of the present invention further comprises a water-soluble aromatic N-nitroso compound having an aromatic group in the molecule. Preferably mentioned. More specifically, N-nitrosodiphenylamine, N-nitroso-N-phenylhydroxylamine, N, N′-dinitrosophenylenediamine, N-nitrosophenylnaphthylamine, N-nitrosodinaphthylamine, or α-nitroso-β- Examples thereof include alkali metal salts, alkaline earth metal salts, ammonium salts and the like of naphthol, particularly preferably N-nitroso-N-phenylhydroxylamine salt, that is, alkali metal salt of N-nitroso-N-phenylhydroxylamine, alkali An earth metal salt, an ammonium salt, and the like, more preferably an ammonium salt of N-nitroso-N-phenylhydroxylamine, and the like.

As a water-insoluble polymerization inhibitor that can be used in the method for producing foamable microspheres of the present invention, it has a low solubility in water at a predetermined temperature of 20 ° C., and has the effects described above. Although it is not particularly limited as long as possible, the balance between the suppression effect of the polymerization reaction at an undesired time and the rapid progress of the polymerization reaction at the desired time, and the physical properties of the resulting foamable microspheres are excellent. From the viewpoint, those containing an oil-soluble aromatic compound having at least one selected from the group consisting of vitamin E, hydroxy group, quinone group and alkoxy group are preferable.

(1) Vitamin E
Vitamin E, which is a water-insoluble polymerization inhibitor preferably used in the method for producing foamable microspheres of the present invention, is a kind of fat-soluble vitamin and has tocol and tocotrienol as long as it has the physiological activity of α-tocopherol. These are phenol compounds having an antioxidant action due to the OH group in the aromatic ring of the chroman ring, generally referred to as all the derivatives of There are eight types of vitamin E, α-, β-, γ-, and δ-tocopherol and α-, β-, γ-, and δ-tocotrienol, each having an optical isomer. Natural vitamin E is d-α-tocopherol, and it is more preferable to use natural vitamin E as a water-insoluble polymerization inhibitor in the method for producing foamable microspheres of the present invention. Vitamin E belonging to the fat-soluble vitamin has a solubility in water at a temperature of 20 ° C. of less than 0.1% by mass.

(2) An oil-soluble aromatic compound having at least one selected from the group consisting of a hydroxy group, a quinone group and an alkoxy group In addition, a water-insoluble polymerization preferably used in the method for producing foamable microspheres of the present invention The oil-soluble aromatic compound having at least one selected from the group consisting of a hydroxy group, a quinone group, and an alkoxy group, which is an inhibitor, has an aromatic ring such as a benzene ring, a naphthalene ring, an anthracene ring, a hydroxy group, a quinone It is an oil-soluble compound having at least one selected from the group consisting of a group and an alkoxy group as a substituent, and its solubility in water at 20 ° C. (hereinafter sometimes simply referred to as “solubility”) is usually 1 mass. % Or less, preferably 0.5% by mass or less, more preferably 0.3% by mass or less. More preferable examples of the oil-soluble aromatic compound include (i) an oil-soluble aromatic compound having a hydroxy group, such as phenols or naphthols such as t-butylhydroquinone, t-butylcatechol, butylhydroxyanisole, 4-methoxynaphthol and the like; (ii) oil-soluble aromatic compounds having a quinone group are benzoquinones, naphthoquinones, or anthraquinones such as benzoquinone, 1,4-naphthoquinone, 1,2-naphthoquinone, 2-hydroxy -1,4-naphthoquinone, anthraquinone, etc .; or (iii) an oil-soluble aromatic compound having an alkoxy group is a benzene derivative or a naphthalene derivative such as 1,4-dimethoxynaphthalene, 1,4-diethoxynaphthalene, etc. And the like. Particularly preferable oil-soluble aromatic compounds are 4-methoxynaphthol (solubility: less than 0.1% by mass), 2-hydroxy-1,4-naphthoquinone (solubility: 0.2% by mass), 1,4 -Naphthoquinone (solubility: less than 0.1% by weight), t-butylcatechol (solubility: 0.2% by weight), butylhydroxyanisole (solubility: less than 0.1% by weight), t-butylhydroquinone (solubility: 1% by weight) %) And the like.

Furthermore, since the desired effect can be sufficiently exhibited even in the absence of oxygen, vitamin E, an oil-soluble aromatic compound having a hydroxy group is a naphthol, or an oil-soluble aromatic compound having a quinone group Naphthoquinones and anthraquinones and naphthalene derivatives which are oil-soluble aromatic compounds having an alkoxy group are more preferred. Examples of these compounds include 4-methoxynaphthol, 2-hydroxy-1,4-naphthoquinone, 1,4-naphthoquinone, 1,4-dimethoxynaphthalene, 1,4-diethoxynaphthalene and the like. In the absence of oxygen, the oxygen concentration in the reaction system or in the space of the container is determined by substituting the reaction system or the container with an inert gas such as nitrogen, helium, argon, or carbon dioxide. It refers to a sufficiently lowered condition, for example, a condition such that the oxygen concentration in the reaction system or in the space of the container is usually 1 vol% or less, preferably 0.1 vol% or less.

The amount of the water-soluble polymerization inhibitor or water-insoluble polymerization inhibitor used in the method for producing foamable microspheres having a maximum foaming ratio of 5 times or more according to the present invention is particularly limited as long as it meets the purpose of the present invention. Although not limited, it is usually 0.0005 to 0.5% by mass (5 to 5000 ppm), preferably 0.001 to 0.1% by mass (10 to 1000 ppm), and more based on the total amount of polymerizable monomers. Preferably 0.002 to 0.07 mass% (20 to 700 ppm), more preferably 0.003 to 0.05 mass% (30 to 500 ppm), particularly preferably 0.005 to 0.04 mass% (50 to 700 ppm). 400 ppm). The polymerizable monomer used in the method for producing foamable microspheres of the present invention does not start unintentional polymerization during transfer or storage of the polymerizable monomer, so that a polymerization inhibitor is added in advance. May be contained. At that time, when the polymerization inhibitor corresponds to the water-soluble polymerization inhibitor or water-insoluble polymerization inhibitor in the present invention, the water-soluble polymerization inhibitor or the water-soluble polymerization inhibitor in the method for producing foamable microspheres of the present invention described above. The amount of the water-insoluble polymerization inhibitor used is a polymerizable mixture containing at least a foaming agent, a polymerizable monomer, a polymerization initiator and a water-soluble polymerization inhibitor or a water-insoluble polymerization inhibitor in an aqueous dispersion medium. In consideration of the content of the polymerization inhibitor (water-soluble polymerization inhibitor or water-insoluble polymerization inhibitor) that remains in advance when suspended, the usage corresponding to the shortage or excess is offset. Thus, what is necessary is just to adjust the usage-amount of a water-soluble polymerization inhibitor. In this case, the amount of the water-soluble polymerization inhibitor or water-insoluble polymerization inhibitor used is usually 0.002 to 0.5% by mass (20 to 5000 ppm), preferably 0.005 to 0.1% by mass (50 to 50%). 1000 ppm), more preferably 0.006 to 0.05 mass% (60 to 500 ppm), and particularly preferably 0.007 to 0.05 mass% (70 to 500 ppm).

In the method for producing foamable microspheres having a maximum foaming ratio of 5 times or more according to the present invention, a dichromate or alkali metal nitrite as a polymerization aid is further contained in an aqueous dispersion medium (aqueous phase). , Containing at least one compound selected from stannous chloride, stannic chloride, boric acid and water-soluble ascorbic acids, suspending the polymerizable mixture, and then water-soluble polymerization inhibitor or water-insoluble polymerization inhibitor Suspension polymerization may be carried out in the presence. That is, the foamable microscopic material containing at least one compound selected from the group consisting of dichromate, alkali metal nitrite, stannous chloride, stannic chloride, boric acid and water-soluble ascorbic acids in an aqueous dispersion medium. By using a method for producing a sphere, in particular, by producing a foamable microsphere in which the compound contained in the aqueous dispersion medium is an alkali metal nitrite salt, The combination of the composition and / or the type and content of the foaming agent is preferable because the maximum foaming ratio and uniformity of the foamable microsphere can be adjusted.

(Polymerization inhibitory effect)
In the method for producing a foamable microsphere having a maximum foaming ratio of 5 times or more according to the present invention, an undesirable polymerization reaction is initiated by using a water-soluble polymerization inhibitor or a water-insoluble polymerization inhibitor in an oil phase. The suppressing effect can also be confirmed by the following method. That is, in a glass ampule filled with nitrogen gas (volume: 50 mL), 0.02 mass relative to a total amount of 100 mass parts of the desired combination of polymerizable monomers and polymerization initiator, and polymerizable monomers. Part (corresponding to 200 ppm) of a water-soluble polymerization inhibitor or a water-insoluble polymerization inhibitor is sealed, and the ampoule is immersed in a constant temperature water bath at a temperature of 25 ° C. Elapsed time until the white turbidity is observed by visually observing the presence or absence of white turbidity caused by the content of the ampoule being started to polymerize (hereinafter referred to as “polymerization inhibition time”). Measure. For example, if the polymerization inhibition time is 1 hour or more, it can be said that there is a polymerization inhibition effect for 1 hour or more at a temperature of 25 ° C. Therefore, when the outside air temperature is high, especially when large-scale production is performed, the polymerization property There is no possibility of starting a polymerization reaction in an undesired oil phase during the preparation of the mixture or during the preparation of the dispersion. The polymerization inhibition time is usually 1 hour or longer, preferably 2 hours or longer, more preferably 3 hours or longer, particularly preferably 4 hours or longer. If the polymerization suppression time is too long, the initiation and progress of the polymerization reaction for producing foamable microspheres having a maximum expansion ratio of 5 times or more may be hindered. It is preferable to set the time within the range of 8 hours or less.

7). Aqueous Dispersion Medium In the method for producing foamable microspheres of the present invention, suspension polymerization is carried out in an aqueous dispersion medium. As the aqueous dispersion medium, water can be used, and specifically, deionized water or distilled water can be used. The amount of the aqueous dispersion medium used relative to the total amount of the polymerizable monomers is not particularly limited, but is usually 0.5 to 10 times, and in many cases 1 to 7 times (mass ratio).

8). Suspension of polymerizable mixture, and suspension polymerization In the method for producing foamable microspheres having a maximum foaming ratio of 5 times or more according to the present invention, in an aqueous dispersion medium, at least a foaming agent, a polymerizable monomer, Suspending a polymerization mixture containing a polymerization initiator and a water-soluble polymerization inhibitor or a water-insoluble polymerization inhibitor, and then performing suspension polymerization in the presence of a water-soluble polymerization inhibitor or a water-insoluble polymerization inhibitor. It is characterized by.

(Suspension of polymerizable mixture)
In the method for producing foamable microspheres of the present invention, at least a foaming agent, a polymerizable monomer, a polymerization initiator and a water-soluble polymerization inhibitor or non-suspended in an aqueous dispersion medium prior to suspension polymerization. The preparation method of the polymerizable mixture containing the water-soluble polymerization inhibitor is not particularly limited. Usually, an aqueous dispersion medium (aqueous phase) containing a dispersion stabilizer by adding a dispersion stabilizer (suspension agent) to the aqueous dispersion medium such as water and, if necessary, an auxiliary stabilizer or a polymerization aid. To prepare. As will be described later, when suspension polymerization is performed, it is preferable to select the optimum pH condition depending on the type of dispersion stabilizer and auxiliary stabilizer used, so the pH of the system is adjusted as necessary. Also good. In addition, when using magnesium hydroxide or calcium phosphate as a dispersion stabilizer, it polymerizes in an alkaline environment. On the other hand, separately, a foaming agent, a polymerizable monomer, and a crosslinkable monomer as necessary are mixed to prepare a mixture (oil phase) containing at least the foaming agent and the polymerizable monomer. Then, the aqueous phase and the oil phase are mixed. As long as the object of the present invention is not impaired, a foaming agent, a polymerizable monomer, a crosslinkable monomer, and the like may be added to the aqueous dispersion medium containing the above dispersion stabilizer.

The water-soluble polymerization inhibitor or water-insoluble polymerization inhibitor used in the method for producing foamable microspheres of the present invention is added to the oil phase (a mixture containing at least a foaming agent and a polymerizable monomer). And contained in the polymerizable mixture. In addition, the polymerization initiator can be added to the polymerizable monomer in advance, but if it is necessary to avoid early polymerization, a mixture containing at least a foaming agent and a polymerizable monomer When (oil phase) is added to the aqueous dispersion medium containing the previous dispersion stabilizer and stirred and mixed, a polymerization initiator may be added and integrated in the aqueous dispersion medium. By these preparation methods, a polymerizable mixture containing at least a foaming agent, a polymerizable monomer, a polymerization initiator, and a water-soluble polymerization inhibitor or a water-insoluble polymerization inhibitor can be obtained. According to the present invention, the polymerizable mixture containing at least the foaming agent, the polymerizable monomer, the polymerization initiator, and the water-soluble polymerization inhibitor or the water-insoluble polymerization inhibitor is contained in an aqueous dispersion medium at a temperature of 25 ° C. In this case, the polymerization reaction is usually suppressed for 1 hour or longer, preferably 2 hours or longer, more preferably 3 hours or longer, particularly preferably 4 hours or longer. Polymerization can be performed.

Next, the obtained polymerizable mixture containing at least a foaming agent, a polymerizable monomer, a polymerization initiator, and a water-soluble polymerization inhibitor or a water-insoluble polymerization inhibitor is suspended by a method such as stirring and mixing. To do. By suspending the polymerizable mixture by stirring and mixing, an oil phase containing at least a foaming agent, a polymerizable monomer, and a polymerization initiator forms droplets in an aqueous phase containing an aqueous dispersion medium. . By selecting the conditions of stirring and mixing performed for suspending the polymerizable mixture, it can be granulated into fine droplets of a desired size. The average particle diameter of the droplets is preferably substantially the same as the average particle diameter of the target foamable microsphere, and is usually in the range of 0.2 to 500 μm, preferably about 0.5 to 150 μm. preferable. At the time of stirring and mixing, conditions such as the type of the stirrer and the number of rotations are set according to the desired particle size of the foamable microsphere. At this time, the conditions are selected in consideration of the size and shape of the polymerization can and the presence or absence of baffles. As the stirrer, a homogenizer having a high shearing force is preferable. In order to obtain foamable microspheres having an extremely sharp particle size distribution, an aqueous dispersion medium and a polymerizable mixture are fed into a continuous high-speed rotation high shear type agitator / disperser, and both are continuously fed in the agitator / disperser. After stirring and dispersing, it is preferable to employ a method in which the obtained dispersion is poured into a polymerization tank and suspension polymerization is performed in the polymerization tank. A batch-type high-speed rotation high shear disperser can also be used.

(Suspension polymerization)
After suspending a polymerizable mixture containing at least a foaming agent, a polymerizable monomer, a polymerization initiator and a water-soluble polymerization inhibitor or a water-insoluble polymerization inhibitor in an aqueous dispersion medium, a water-soluble polymerization inhibitor or Suspension polymerization is performed in the presence of a water-insoluble polymerization inhibitor. The suspension polymerization is carried out in an aqueous dispersion medium, and is usually carried out in an aqueous dispersion medium containing a dispersion stabilizer (suspension agent). In carrying out the suspension polymerization, it is preferable to select optimum pH conditions depending on the type of dispersion stabilizer and auxiliary stabilizer used. For example, when silica such as colloidal silica is used as the dispersion stabilizer, it is preferable to carry out the polymerization in an acidic environment, so that the aqueous dispersion containing the dispersion stabilizer in advance prior to the suspension of the polymerizable mixture described above. The pH of the system may be adjusted to about 3 to 4 by adding an acid to the medium. When magnesium hydroxide or calcium phosphate is used as the dispersion stabilizer, the polymerization is performed in an alkaline environment.

The polymerization (suspension polymerization) reaction is carried out in the presence of a water-soluble polymerization inhibitor or a water-insoluble polymerization inhibitor, usually in the absence of oxygen, for example, degassed or replaced with an inert gas such as nitrogen gas. The polymerization can is carried out at 40 to 80 ° C., preferably 50 to 70 ° C. with stirring for 1 to 40 hours, preferably 3 to 30 hours. Since the foamable microspheres formed by polymerization form a fine particle solid, the aqueous phase containing the aqueous dispersion medium is separated from the foamable microsphere by a known separation method such as filtration, centrifugation, sedimentation, or the like. Separated and removed from the fair. At that time, the water-soluble polymerization inhibitor or the water-insoluble polymerization inhibitor easily shifts to the aqueous phase at the beginning of the polymerization, so that the polymerization is less likely to be suppressed, and as a result, the maximum foaming that has excellent physical properties such as foaming characteristics. A foamable microsphere having a magnification of 5 times or more is obtained. The resulting foamable microsphere is dried at a relatively low temperature so that the foaming agent is not gasified, if necessary.

II. Foamable microspheres According to the present invention, at least a foaming agent, a polymerizable monomer, a polymerization initiator, and a water-soluble polymerization inhibitor are produced in an aqueous dispersion medium by the method for producing foamable microspheres described above. Or in the outer shell of the resulting polymer obtained by suspending a polymerizable mixture containing a water-insoluble polymerization inhibitor and then subjecting it to suspension polymerization in the presence of a water-soluble polymerization inhibitor or water-insoluble polymerization inhibitor. A foamable microsphere having a maximum foaming ratio of 5 times or more in which a foaming agent is enclosed is provided.

[Maximum foaming ratio]
The maximum expansion ratio of the expandable microsphere having a maximum expansion ratio of 5 or more according to the present invention is determined by the expansion ratio (coating method) measured by the following method. That is, the foamable microspheres in terms of solid content are converted to EVA aqueous emulsion (concentration 55% by weight) containing an ethylene / vinyl acetate copolymer (EVA; ethylene / vinyl acetate = 30/70 mass%). Add 5: 1 to adjust the coating solution. This coating solution is applied to double-sided art paper with a coater having a gap of 200 μm, and then placed in an oven and dried at a temperature of 90 ° C. for 5 minutes. After measuring the thickness of the coating film after drying, it is placed in a plurality of ovens at a predetermined temperature from the vicinity of the foaming start temperature to a higher temperature, and heated for 2 minutes for foaming. The coating thickness after foaming is measured, the foaming ratio at each predetermined temperature is determined from the coating pressure ratio before and after foaming, and the measured maximum foaming ratio is taken as the maximum foaming ratio of the foamable microsphere. The maximum expansion ratio of the foamable microsphere of the present invention having a maximum expansion ratio of 5 times or more is preferably 6 times or more, more preferably 7 times or more. The maximum expansion ratio has no particular upper limit, but is usually 30 times or less, and in most cases 20 times or less, from the viewpoint of the strength of foam particles or expandable microspheres, the uniformity or stability of foaming, and the like. is there.

[Average particle size]
The average particle diameter of the foamable microspheres having a maximum foaming ratio of 5 times or more according to the present invention is preferably 0.5 to 150 μm from the viewpoint of handleability, foaming uniformity or stability. More preferably, it is 1 to 120 μm. The average particle size of the foamable microspheres is measured using a laser diffraction particle size distribution measuring device (such as SALD series manufactured by Shimadzu Corporation), and is an integrated percentage of the particle size (sphere equivalent diameter). 50% particle diameter (sometimes referred to as “median diameter”, sometimes referred to as “average particle diameter (D50)”) obtained based on a particle size distribution curve (volume basis and logarithmic scale). Unit: μm). If the average particle size is too small, the cushioning property and weight reduction may be insufficient. If the average particle size is too large, the foamed foam has too large bubbles, resulting in fatigue resistance or strength against repeated compression. May be insufficient.

The foamable microspheres having a maximum foaming ratio of 5 times or more obtained by the present invention are used in various fields after being foamed (expanded) or unfoamed. The foamable microspheres are used, for example, as paint fillers for automobiles, foaming inks for foaming inks (wallpaper, relief patterns such as T-shirts), anti-shrinkage agents, etc. Is done. In addition, foamable microspheres use the volume increase caused by foaming to make plastics, paints, various materials lighter and more porous, and to provide various functions (for example, slip, heat insulation, cushion, sound insulation) Used for the purpose of sex. In particular, the foamable microspheres according to the present invention can be suitably used for paints and ink fields that require surface properties and smoothness, and weight reduction of plastic molded products (for example, interior materials).

In contrast, a polymerizable mixture containing at least a foaming agent, a polymerizable monomer and a polymerization initiator is suspended in an aqueous dispersion medium without containing a water-soluble polymerization inhibitor or a water-insoluble polymerization inhibitor. The foamable microspheres, which are turbid and then obtained by suspension polymerization in the absence of a water-soluble polymerization inhibitor or a water-insoluble polymerization inhibitor, in which the foaming agent is encapsulated in the outer shell of the resulting polymer, The maximum expansion ratio may be less than 5 times, or the particle size, the maximum expansion ratio, and the foaming start temperature may vary, which may not meet the purpose of use. Furthermore, when producing foamable microspheres, the progress of the polymerization reaction may be too slow, an uncontrollable abnormal reaction may occur, or a large amount of deposits may be generated in the polymerization vessel. .

The form for implementing this invention can also take the following structures.
[1]
Suspend a polymerizable mixture containing at least a foaming agent, a polymerizable monomer, a polymerization initiator, and a water-soluble polymerization inhibitor in an aqueous dispersion medium, and then suspension polymerize in the presence of the water-soluble polymerization inhibitor. It is characterized by
A method for producing foamable microspheres, wherein the foaming agent is enclosed in the outer shell of the resulting polymer and the maximum foaming ratio is 5 times or more.
[2]
The method for producing foamable microspheres according to [1], wherein the water-soluble polymerization inhibitor has a solubility in water at a temperature of 20 ° C. of more than 1% by mass.
[3]
The method for producing foamable microspheres according to [2], wherein the water-soluble polymerization inhibitor has a solubility in water at a temperature of 20 ° C. of 5% by mass or more.
[4]
The water-soluble polymerization inhibitor contains at least one compound selected from the group consisting of a hydroquinone compound, a naphthohydroquinone compound, and an N-nitroso compound, and the foamable microinjector according to any one of [1] to [3] A method for producing a sphere.
[5]
The method for producing foamable microspheres according to [4], wherein the water-soluble polymerization inhibitor contains naphthohydroquinonesulfonic acid or a salt thereof.
[6]
The method for producing foamable microspheres according to [4], wherein the water-soluble polymerization inhibitor contains a water-soluble aromatic N-nitroso compound.
[7]
The polymerizable monomer is 30 to 95% by mass of vinylidene chloride, and at least one kind selected from the group consisting of acrylonitrile, methacrylonitrile, acrylic acid ester, methacrylic acid ester, styrene, acrylic acid, methacrylic acid and vinyl acetate. The method for producing expandable microspheres according to any one of [1] to [6], which is a monomer mixture containing 5 to 70% by mass of a monomer.
[8]
The polymerizable monomer is at least one monomer selected from the group consisting of acrylonitrile and methacrylonitrile, 25 to 100% by mass, vinylidene chloride, acrylate ester, methacrylate ester, styrene, acrylic acid, methacrylic acid and The foamable microsphere according to any one of [1] to [6], which is a monomer mixture containing 0 to 75% by mass of at least one monomer selected from the group consisting of vinyl acetate. Manufacturing method.
[9]
The aqueous dispersion medium contains at least one compound selected from the group consisting of dichromate, alkali metal nitrite, stannous chloride, stannic chloride, boric acid and water-soluble ascorbic acids, [1] to [1] to [8] The method for producing a foamable microsphere according to any one of [8].
[10]
The method for producing foamable microspheres according to [9], wherein the compound contained in the aqueous dispersion medium is an alkali metal nitrite.
[11]
Suspend a polymerizable mixture containing at least a foaming agent, a polymerizable monomer, a polymerization initiator, and a water-soluble polymerization inhibitor in an aqueous dispersion medium, and then perform suspension polymerization in the presence of the water-soluble polymerization inhibitor. A foamable microsphere having a maximum foaming ratio of 5 times or more in which a foaming agent is enclosed in the outer shell of the resulting polymer.
[12]
The foamable microsphere according to [11], having an average particle size of 0.5 to 150 μm.

Furthermore, the form for implementing this invention can also take the following structures.
[1]
Suspend a polymerizable mixture containing at least a foaming agent, a polymerizable monomer, a polymerization initiator and a water-insoluble polymerization inhibitor in an aqueous dispersion medium, and then suspend in the presence of a water-insoluble polymerization inhibitor. Characterized by polymerization,
A method for producing foamable microspheres, wherein the foaming agent is enclosed in the outer shell of the resulting polymer and the maximum foaming ratio is 5 times or more.
[2]
The water-insoluble polymerization inhibitor is a method for producing foamable microspheres according to [1], wherein the solubility in water at a temperature of 20 ° C. is 1% by mass or less.
[3]
The method for producing foamable microspheres according to [1] or [2], wherein the water-insoluble polymerization inhibitor contains vitamin E.
[4]
The water-insoluble polymerization inhibitor includes any one of [1] to [3], which contains an oil-soluble aromatic compound having at least one selected from the group consisting of a hydroxy group, a quinone group, and an alkoxy group. A process for producing the expandable microspheres as described.
[5]
The method for producing foamable microspheres according to [4], wherein the oil-soluble aromatic compound having a hydroxy group is phenols or naphthols.
[6]
The method for producing foamable microspheres according to [4], wherein the oil-soluble aromatic compound having a quinone group is benzoquinones, naphthoquinones, or anthraquinones.
[7]
The method for producing foamable microspheres according to [4], wherein the oil-soluble aromatic compound having an alkoxy group is a benzene derivative or a naphthalene derivative.
[8]
The polymerizable monomer is 30 to 95% by mass of vinylidene chloride, and at least one kind selected from the group consisting of acrylonitrile, methacrylonitrile, acrylic acid ester, methacrylic acid ester, styrene, acrylic acid, methacrylic acid and vinyl acetate. The method for producing expandable microspheres according to any one of [1] to [7], which is a monomer mixture containing 5 to 70% by mass of a monomer.
[9]
The polymerizable monomer is at least one monomer selected from the group consisting of acrylonitrile and methacrylonitrile, 25 to 100% by mass, vinylidene chloride, acrylate ester, methacrylate ester, styrene, acrylic acid, methacrylic acid and The foamable microsphere according to any one of [1] to [7], which is a monomer mixture containing 0 to 75% by mass of at least one monomer selected from the group consisting of vinyl acetate. Manufacturing method.
[10]
The aqueous dispersion medium contains at least one compound selected from the group consisting of dichromate, alkali metal nitrite, stannous chloride, stannic chloride, boric acid and water-soluble ascorbic acids, [1] to [1] to [8] The method for producing a foamable microsphere according to any one of [8].
[11]
The method for producing foamable microspheres according to [10], wherein the compound contained in the aqueous dispersion medium is an alkali metal nitrite salt.
[12]
Suspend a polymerizable mixture containing at least a foaming agent, a polymerizable monomer, a polymerization initiator and a water-insoluble polymerization inhibitor in an aqueous dispersion medium, and then suspend in the presence of a water-insoluble polymerization inhibitor. A foamable microsphere having a maximum foaming ratio of 5 times or more in which a foaming agent is enclosed in an outer shell of a product polymer obtained by polymerization.
[13]
The foamable microsphere according to [12], which has an average particle size of 0.5 to 150 μm.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to the examples. A method for measuring the characteristics of the foamable microsphere according to the present invention is as follows.

[Maximum foaming ratio]
The maximum expansion ratio of the foamable microsphere is determined by measuring the expansion ratio (coating method) described above by foaming for 2 minutes in an oven at each temperature in increments of 5 ° C from 100 ° C. Asked.

[Average particle diameter (D50)]
The average particle size (D50) of the foamable microspheres was measured using a laser diffraction particle size distribution analyzer SALD-3000J manufactured by Shimadzu Corporation.

(Polymerization inhibitory effect)
In the method for producing foamable microspheres, the polymerization inhibiting effect that suppresses the initiation of an undesirable polymerization reaction was confirmed by the following method. That is, 0.02 parts by mass (corresponding to 200 ppm) with respect to a total amount of 100 parts by mass of a desired combination of polymerizable monomers, a polymerization initiator, and a polymerizable monomer in a glass ampule (volume 50 mL). The water-soluble polymerization inhibitor was added and purged with nitrogen, and the ampoule was immersed in a constant temperature water bath at a temperature of 25 ° C. The polymerization inhibition time (unit: hours) was measured by visually observing the presence or absence of white turbidity caused by the content of the ampoule starting polymerization. When no cloudiness was observed after 4 hours, the polymerization inhibition time was determined to exceed 4 hours.

[I] Confirmation of polymerization inhibitory effect [Example 1]
Glass ampule filled with nitrogen gas (volume 50 mL), polymerizable monomer vinylidene chloride / acrylonitrile / methyl methacrylate (mass ratio 65/30/5), and total amount of polymerizable monomer 100 0.02 parts by mass of N-nitroso-N-phenylhydroxylamine ammonium salt (Q-1300 manufactured by Wako Pure Chemical Industries, Ltd., hereinafter referred to as “NPHAA”) The solubility in water at a temperature of 20 ° C. is 9.2 mass%), and 1 part by mass of IPP as a polymerization initiator is enclosed, and the ampoule is placed in a constant temperature water bath at a temperature of 25 ° C. When the polymerization inhibition time was measured by dipping, the polymerization inhibition time exceeded 4 hours. In addition, these purchased polymerizable monomers contain in advance methoquinone (solubility in water at a temperature of 20 ° C. is 3.8% by mass), which is a polymerization inhibitor, It was 0.0013 mass part with respect to 100 mass parts of polymerizable monomers total amount, ie, 13 ppm.

[Example 2]
Instead of NPHAA, 1,4-naphthohydroquinone-2-sulfonic acid ammonium (prepared by the method described in Example 3 of JP-A-8-59600. The solubility in water at a temperature of 20 ° C. was 10% by mass. The ampoule is placed in a constant temperature water bath at a temperature of 25 ° C. in the same manner as in Example 1 except that 0.02 part by mass is enclosed with respect to 100 parts by mass of the total amount of polymerizable monomers. When the polymerization inhibition time was measured by dipping, the polymerization inhibition time exceeded 4 hours.

[Example 3]
Instead of NPHAA, 0.02 part by mass of hydroquinone (solubility in water at a temperature of 20 ° C. is 5.9% by mass) is added to 100 parts by mass of the total amount of polymerizable monomers. Except for this, the ampoule was immersed in a constant temperature water bath at a temperature of 25 ° C. in the same manner as in Example 1, and the polymerization inhibition time was measured. As a result, the polymerization inhibition time exceeded 4 hours.

[Example 4]
In place of NPHAA, the ampoule was kept at a temperature of 25 ° C. in the same manner as in Example 1 except that 0.02 parts by mass of methoquinone was enclosed with respect to 100 parts by mass of the total amount of polymerizable monomers. When the polymerization inhibition time was measured by immersing the film in the solution, the polymerization inhibition time was more than 4 hours.

[Example 5]
In place of NPHAA, the ampoule was kept at a constant temperature of 25 ° C. in the same manner as in Example 1 except that 0.02 part by mass of natural vitamin E was enclosed with respect to 100 parts by mass of the total amount of polymerizable monomers. When the polymerization inhibition time was measured by dipping in a water tank, the polymerization inhibition time was more than 2 hours.

[Example 6]
Except that 0.02 parts by mass of t-butylhydroquinone (hereinafter sometimes referred to as “t-BuHQ”) was enclosed instead of NPHAA with respect to 100 parts by mass of the total amount of polymerizable monomers. The ampoule was immersed in a constant temperature water bath at a temperature of 25 ° C. in the same manner as in Example 1, and the polymerization inhibition time was measured. As a result, the polymerization inhibition time exceeded 2 hours.

[Comparative Example 1]
When the ampoule was immersed in a constant temperature water bath at a temperature of 25 ° C. and the polymerization inhibition time was measured in the same manner as in Example 1 except that NPHAA was not enclosed, the polymerization inhibition time was less than 5 minutes. .

[II] Production of foamable microspheres [Example 7]
(Suspension of polymerizable mixture)
65 g of polymerization monomer vinylidene chloride (hereinafter sometimes referred to as “VD”), 30 g of acrylonitrile (hereinafter sometimes referred to as “AN”) and methyl methacrylate (hereinafter sometimes referred to as “MMA”). .) 5 g (mass ratio: VD / AN / MMA = 65/30/5), 0.2 g of ethylene glycol dimethacrylate (EDMA) as a crosslinkable monomer, and 0.02 g of NPHAA as a water-soluble polymerization inhibitor (0.02 parts by mass with respect to 100 parts by mass of the total amount of polymerizable monomers; hereinafter referred to as “0.02% by mass of monomer”), 16 g of isobutane as a foaming agent, and polymerization initiation A polymerizable mixture (oil phase) was prepared by mixing 1 g of IPP as an agent, and the polymerizable mixture was stored at a temperature of 25 ° C. In addition, the purchased polymerizable monomer previously contains methoquinone which is a polymerization inhibitor, and the content thereof is 0.0013 parts by mass with respect to 100 parts by mass of the total polymerizable monomers, that is, It was 13 ppm. On the other hand, 2.0 g of colloidal silica (supplied as a 20 mass% colloidal silica dispersion), 0.375 g of diethanolamine-adipic acid condensation product (acid value = 78 mg KOH / g) (supplied as a 50 mass% aqueous solution), After mixing 0.06 g of sodium nitrite and 240 g of water, hydrochloric acid (5 mass% aqueous solution) was added to adjust the pH to 3.2 to prepare an aqueous dispersion medium containing a dispersion stabilizer. .

By mixing the polymerizable mixture stored at a temperature of 25 ° C. for 3 hours with the aqueous dispersion medium, and stirring and mixing with a homogenizer, at least a foaming agent, a polymerizable monomer, and a polymer in the aqueous dispersion medium. A polymerizable mixture containing an initiator and a water-soluble polymerization inhibitor was suspended, and fine droplets of the polymerizable mixture were granulated in an aqueous dispersion medium.

(Suspension polymerization)
An aqueous dispersion medium containing fine droplets of a polymerizable mixture is charged into a polymerization can (1.5 L) equipped with a stirrer and heated at a temperature of 50 ° C. for 22 hours using a hot water bath, thereby inhibiting a water-soluble polymerization inhibitor. Suspension polymerization in the presence of After the polymerization, the slurry containing the foamable microspheres produced was filtered, washed with water, and dried to obtain foamable microspheres. About the obtained foamable microsphere, the result (displayed for temperatures 120, 130, 140 and 150 ° C.), the maximum foaming ratio, and the average particle size (D50) (hereinafter simply referred to as the coating method) were measured. Table 1 shows the results of measurement of “sometimes referred to as“ average particle size ”” (hereinafter collectively referred to as “measurement results of expansion ratio and average particle size”).

[Example 8]
By performing suspension polymerization and suspension polymerization of the polymerizable mixture in the same manner as in Example 5 except that hydroquinone was used instead of NPHAA as a water-soluble polymerization inhibitor, foamable microspheres were obtained. Obtained. Table 1 shows the measurement results of the expansion ratio and average particle size of the obtained foamable microspheres.

[Example 9]
By performing suspension polymerization and suspension polymerization of the polymerizable mixture in the same manner as in Example 5 except that methoquinone was used instead of NPHAA as a water-soluble polymerization inhibitor, foamable microspheres were obtained. Obtained. Table 1 shows the measurement results of the expansion ratio and average particle size of the obtained foamable microspheres.

[Example 10]
(Suspension of polymerizable mixture)
65 g of polymerization monomer vinylidene chloride (hereinafter sometimes referred to as “VD”), 30 g of acrylonitrile (hereinafter sometimes referred to as “AN”) and methyl methacrylate (hereinafter sometimes referred to as “MMA”). .) 5 g (mass ratio: VD / AN / MMA = 65/30/5), 0.2 g of ethylene glycol dimethacrylate (EDMA) which is a crosslinkable monomer, and natural vitamin which is a water-insoluble polymerization inhibitor E0.02 g (0.02 parts by mass with respect to 100 parts by mass of the total amount of polymerizable monomers; hereinafter, sometimes referred to as “0.02% by mass of monomer”), 16 g of isobutane as a foaming agent, Then, 1 g of IPP as a polymerization initiator was mixed to prepare a polymerizable mixture (oil phase), and the polymerizable mixture was stored at a temperature of 25 ° C. In addition, the purchased polymerizable monomer previously contains methoquinone which is a polymerization inhibitor, and the content thereof is 0.0013 parts by mass with respect to 100 parts by mass of the total polymerizable monomers, that is, It was 13 ppm. On the other hand, 2.0 g of silica (supplied as a 20% by mass colloidal silica dispersion), 0.375 g of diethanolamine-adipic acid condensation product (acid value = 78 mg KOH / g) (supplied as a 50% by mass aqueous solution), After mixing 0.06 g of sodium nitrate and 240 g of water, hydrochloric acid (5 mass% aqueous solution) was added to adjust the pH to 3.2 to prepare an aqueous dispersion medium containing a dispersion stabilizer.

By mixing the polymerizable mixture stored at a temperature of 25 ° C. for 2 hours with the aqueous dispersion medium and stirring and mixing with a homogenizer, at least a foaming agent, a polymerizable monomer, and a polymer in the aqueous dispersion medium. A polymerizable mixture containing an initiator and a water-insoluble polymerization inhibitor was suspended, and fine droplets of the polymerizable mixture were granulated in an aqueous dispersion medium.

(Suspension polymerization)
A water-based dispersion medium containing minute droplets of a polymerizable mixture is charged into a polymerization can equipped with a stirrer (1.5 L) and heated at a temperature of 50 ° C. for 22 hours using a hot water bath to inhibit water-insoluble polymerization. Suspension polymerization was performed in the presence of an agent (natural vitamin E). After the polymerization, the slurry containing the foamable microspheres produced was filtered, washed with water, and dried to obtain foamable microspheres. About the obtained foamable microsphere, the result (displayed for temperatures 120, 130, 140 and 150 ° C.), the maximum foaming ratio, and the average particle size (D50) (hereinafter simply referred to as the coating method) were measured. Table 1 shows the results of measurement of “sometimes referred to as“ average particle size ”” (hereinafter collectively referred to as “measurement results of expansion ratio and average particle size”).

[Example 11]
By performing suspension and suspension polymerization of the polymerizable mixture in the same manner as in Example 11 except that t-BuHQ was used in place of natural vitamin E as the water-insoluble polymerization inhibitor, foaming was performed. Sex microspheres were obtained. Table 1 shows the measurement results of the expansion ratio and average particle size of the obtained foamable microspheres.

[Comparative Example 2]
When suspension polymerization was started after suspending the polymerizable mixture in the same manner as in Example 7 except that NPHAA which is a water-soluble polymerization inhibitor was not used, a precipitate was generated in a short time. Thus, foamable microspheres could not be obtained (measurement results of foaming magnification and average particle diameter of the foamable microspheres could not be obtained).

From Table 1, suspend a polymerizable mixture containing at least a foaming agent, a polymerizable monomer, a polymerization initiator, and a water-soluble polymerization inhibitor in an aqueous dispersion medium, and then in the presence of the water-soluble polymerization inhibitor. According to the method for producing foamable microspheres of Examples 7 to 9, which is characterized by suspension polymerization, the initiation of the polymerization reaction in the oil phase at an undesired time such as during the preparation of the dispersion or before the start of polymerization. In addition, the polymerization reaction in the desired oil phase is not inhibited, and the maximum foaming ratio obtained by measurement of the foaming ratio (coating method) is 5 times or more, specifically 8.8 times, 7. It was found that expandable microspheres having excellent physical properties such as expansion ratio, which are 3 times or 7.2 times, can be obtained.

In addition, from Table 1, a polymerizable mixture containing at least a foaming agent, a polymerizable monomer, a polymerization initiator, and a water-insoluble polymerization inhibitor is suspended in an aqueous dispersion medium, and then a water-insoluble polymerization inhibitor is used. According to the method for producing foamable microspheres of Examples 10 and 11, characterized in that suspension polymerization is carried out in the presence of an oil phase or an aqueous phase at an undesired time such as during the preparation of the dispersion or before the start of polymerization. Initiation of the polymerization reaction in the oil phase is suppressed, the polymerization reaction in the desired oil phase is not inhibited, and the maximum foaming ratio determined by measurement of foaming ratio (coating method) is 5 times or more, specifically It was found that a foamable microsphere having excellent physical properties such as a foaming ratio of 10.2 times or 7.8 times can be obtained.

In particular, according to the method for producing foamable microspheres of Example 7 using a water-soluble polymerization inhibitor (NPHAA) having a solubility in water at 20 ° C. of 5% by mass or more, specifically 8% by mass or more. For example, since the average particle diameter (D50) is 11.7 μm and a fine foamable microsphere, and the maximum foaming ratio obtained by measuring the foaming ratio (coating method) is 8.8 times. Even when compared with Examples 8 and 9, it was found that foamable microspheres having particularly excellent physical properties such as foaming ratio were obtained. Further, the hydroquinone of Example 8 having a solubility in water at a temperature of 20 ° C. of 5% by mass or more has a smaller particle diameter [average particle diameter (D50)] than that of the methoquinone of Example 9 having a solubility of less than 5% by mass. Regardless, it was found that foamable microspheres having excellent physical properties such as expansion ratio can be obtained.

In particular, according to the method for producing effervescent microspheres of Example 10 using a water-insoluble polymerization inhibitor (natural vitamin E) having a solubility in water at a temperature of 20 ° C. of less than 0.1% by mass, Since the average particle size (D50) is 13.0 μm and a fine foamable microsphere, and the maximum foaming ratio determined by measurement of the foaming ratio (coating method) is 10.2 times, Compared with Example 11 using a water-insoluble polymerization inhibitor (t-BuHQ) having a solubility of 1% by mass, foamable microspheres having particularly excellent physical properties such as expansion ratio can be obtained. I understood.

On the other hand, a polymerizable mixture containing at least a foaming agent, a polymerizable monomer, and a polymerization initiator in an aqueous dispersion medium without containing a water-soluble polymerization inhibitor or a water-insoluble polymerization inhibitor. According to the method for producing the foamable microspheres of Comparative Example 2, which is suspended and then suspension-polymerized in the absence of a water-soluble polymerization inhibitor or a water-insoluble polymerization inhibitor, during the preparation of the dispersion or before the start of the polymerization It is impossible to obtain foamable microspheres with excellent physical properties such as expansion ratio without inhibiting the initiation of the polymerization reaction in the oil phase at undesired times and without inhibiting the polymerization reaction in the desired oil phase. I understood that.

The present invention suspends a polymerizable mixture containing at least a foaming agent, a polymerizable monomer, a polymerization initiator and a water-soluble polymerization inhibitor or a water-insoluble polymerization inhibitor in an aqueous dispersion medium, and then water-soluble. Suspension polymerization is carried out in the presence of a polymerization inhibitor or a water-insoluble polymerization inhibitor, and the foaming micro has a maximum foaming ratio of 5 times or more in which the foaming agent is enclosed in the outer shell of the produced polymer. By the sphere manufacturing method, the start of the polymerization reaction in the oil phase at an undesired time such as during the preparation of the dispersion or before the start of the polymerization is suppressed, and the intended process for obtaining foamable microspheres is performed. Since the polymerization reaction in the oil phase is not inhibited and a method for producing foamable microspheres having excellent physical properties such as foaming ratio can be provided, the industrial applicability is high.

Further, the present invention suspends a polymerizable mixture containing at least a foaming agent, a polymerizable monomer, a polymerization initiator and a water-soluble polymerization inhibitor or a water-insoluble polymerization inhibitor in an aqueous dispersion medium, A foaming micro that is obtained by suspension polymerization in the presence of a water-soluble polymerization inhibitor or a water-insoluble polymerization inhibitor and has a maximum foaming ratio of 5 times or more in which the foaming agent is enclosed in the outer shell of the resulting polymer. Since it is a sphere, it is possible to provide a foamable microsphere having excellent physical properties such as a foaming ratio, so that the industrial applicability is high.

Claims

In a water-based dispersion medium, suspend a polymerizable mixture containing at least a foaming agent, a polymerizable monomer, a polymerization initiator, and a water-soluble polymerization inhibitor or a water-insoluble polymerization inhibitor, and then suspend the water-soluble polymerization inhibitor. Suspension polymerization in the presence,
A method for producing foamable microspheres having a maximum foaming ratio of 5 times or more in which a foaming agent is enclosed in an outer shell of a produced polymer.
The foamable micros of any one of claims 1 to 3, wherein the water-soluble polymerization inhibitor contains at least one compound selected from the group consisting of hydroquinone compounds, naphthohydroquinone compounds and N-nitroso compounds. The manufacturing method of a fair.
2. The foamable micro of claim 1, wherein the water-insoluble polymerization inhibitor contains an oil-soluble aromatic compound having at least one selected from the group consisting of vitamin E, hydroxy group, quinone group and alkoxy group. A method for producing a sphere.
The polymerizable monomer is 30 to 95% by mass of vinylidene chloride and at least one selected from the group consisting of acrylonitrile, methacrylonitrile, acrylic acid ester, methacrylic acid ester, styrene, acrylic acid, methacrylic acid and vinyl acetate. The process for producing expandable microspheres according to any one of claims 1 to 3, which is a monomer mixture containing 5 to 70% by mass of monomers.
The polymerizable monomer is 25 to 100% by mass of at least one monomer selected from the group consisting of acrylonitrile and methacrylonitrile, vinylidene chloride, acrylic ester, methacrylic ester, styrene, acrylic acid, methacrylic acid. The foamable microsphere according to any one of claims 1 to 3, which is a monomer mixture containing 0 to 75 mass% of at least one monomer selected from the group consisting of vinyl acetate and vinyl acetate. Production method.
In the aqueous dispersion medium, a polymerizable mixture containing at least a foaming agent, a polymerizable monomer, a polymerization initiator and a water-soluble polymerization inhibitor or a water-insoluble polymerization inhibitor is suspended, and then a water-soluble polymerization inhibitor. A foamable microsphere having a maximum foaming ratio of 5 times or more in which a foaming agent is encapsulated in the outer shell of the resulting polymer, obtained by suspension polymerization in the presence of.