JP4945079B2 - Thermally foamable microsphere and method for producing the same - Google Patents

Description

  The present invention relates to a heat-foamable microsphere having a structure in which a foaming agent is enclosed in an outer shell formed of a polymer, and more particularly, a heat-foamable microsphere with significantly improved processing characteristics, and It relates to the manufacturing method.

  Thermally foamable microspheres, also called thermally expandable microcapsules, are used in various fields such as paints and plastic fillers for weight reduction, including applications in foamed inks. ing. Thermally foamable microspheres are usually obtained by microencapsulating a volatile liquid foaming agent with a polymer. Such blowing agents are also called physical blowing agents or volatile swelling agents. If desired, a chemical foaming agent that decomposes when heated to generate gas may be used.

  Thermally foamable microspheres can generally be produced by a suspension polymerization method 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 thermally foamable microsphere having a structure in which a foaming agent is enclosed in the outer shell is obtained.

  As the polymer forming the outer shell, 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 heat-foamable microsphere is heated, the foaming agent vaporizes and expands and acts on the outer shell, but at the same time, the elastic modulus of the polymer forming the outer shell rapidly decreases. Therefore, sudden expansion occurs at a certain temperature. This temperature is called the foaming temperature. That is, when the thermally foamable microsphere is heated to the foaming temperature, it expands itself to form closed cells (foam particles).

  Thermally expandable microspheres have been developed for use in a wide range of fields as a designability-imparting agent, a functionality-imparting agent, a weight-reducing agent, and the like by utilizing the property of forming closed cells. In addition, as higher performance is required in each application field, the required level for thermally foamable microspheres is also increasing. Improvement in processing characteristics can be cited as a required performance for thermally foamable microspheres.

  For example, a composition in which a thermoplastic foam is blended with a thermoplastic resin is kneaded, calendered, extruded, or injection molded, and the thermally foamable microsphere is foamed in the process to reduce the weight. There is a method for obtaining a molded article or sheet having a design or design. However, in the case of thermally foamable microspheres, the polymer layer of the outer shell becomes very thin as the volume expands during foaming, and the elasticity of the polymer that forms the outer shell due to high temperature and high shearing force due to processing. Since the rate suddenly drops and the outer shell becomes soft, the heat-foamable microspheres were easily destroyed and it was extremely difficult to achieve the intended purpose.

  In addition, the heat-foamable microsphere has a problem that an appropriate temperature range for processing is very narrow because the temperature dependence of the elastic modulus of the polymer forming the outer shell is large. Furthermore, conventional heat-foamable microspheres have poor resistance (solvent resistance, chemical resistance) to polar solvents and plasticizers, and for example, their use in fields commonly used with polar organic solvents has been limited.

  Conventionally, a soft vinyl chloride resin composition for foam extrusion molding in which a thermally expandable microcapsule is blended with a vinyl chloride resin containing a plasticizer has been proposed (Patent Document 1). Further, as the first step, a resin composition containing a thermoplastic resin having a melting point or softening point of 100 ° C. or less and a thermally expandable microcapsule that expands at 100 to 200 ° C. is kneaded at 100 ° C. or less, and the second step As a process, a method for producing a resin composition in which the obtained resin composition is added to a thermoplastic resin and kneaded or molded has been proposed (Patent Document 2).

  However, in fact, in order for the thermally foamable microspheres to be applicable to such foam extrusion molding and kneading / molding, in addition to having an outer shell having a high foaming temperature and excellent heat resistance, The temperature dependence of the elastic modulus of the polymer forming the outer shell is small, the appropriate temperature range for processing is large, and the resistance to polar solvents and plasticizers is excellent.

  As a method for producing highly heat-resistant thermally foamable microspheres, the polymer layer of the outer shell is formed by adding a crosslinkable monomer to a polymerizable monomer composed of a vinyl monomer and polymerizing it. Have been proposed (Patent Documents 3 to 6). By using a crosslinkable monomer, a crosslinked structure is introduced into the polymer forming the outer shell, thereby improving the heat resistance and melt fluidity of the thermally foamable microsphere.

  However, when the degree of crosslinking of the polymer forming the outer shell is increased, the thermal expansion of the thermally foamable microspheres is impaired. Therefore, in each of the examples of these prior art documents, the crosslinking agent is used as a polymerizable monomer. It is only used in a very small proportion of 1% by weight or less, preferably 0.2 to 0.6% by weight. However, if the proportion of the crosslinking agent used is small, it is not possible to obtain thermally foamable microspheres with sufficiently improved processing characteristics. Moreover, since the outer shell formed from the conventional crosslinked polymer has a large temperature dependence of the elastic modulus, the appropriate temperature range for processing is very narrow and the processing characteristics are inferior.

  Furthermore, the outer shell formed from a conventional crosslinked polymer has insufficient resistance to polar solvents and plasticizers. In addition, since the outer shell formed from the conventional crosslinked polymer is actually limited to a polymer having a specific composition, the thermally foamable microsphere having excellent compatibility with the thermoplastic resin to be used. It was difficult to design.

Japanese Patent Laid-Open No. 11-60868 JP 2000-17103 A Japanese Examined Patent Publication No. 42-26524 Japanese Patent Publication No. 5-15499 Japanese Patent No. 2894990 JP-A-5-285376

  An object of the present invention is to provide a thermally foamable microsphere suitable for processing such as kneading processing, calendering processing, extrusion processing, injection molding and the like to which a strong shearing force is applied, and a method for producing the same.

  In particular, an object of the present invention is to provide a thermally foamable microsphere having a small temperature dependence of the elastic modulus of an outer shell formed from a polymer and having a wide processing temperature range and a method for producing the same.

  Another object of the present invention is to provide a heat-foamable microsphere having high resistance (chemical resistance, solvent resistance) and foaming property retention ability to polar solvents and plasticizers, and a method for producing the same. It is in.

  As a result of intensive studies to achieve the above-mentioned object, the present inventors have found that the outer shell of the thermally foamable microspheres exceeds 1% by weight based on the polymerizable monomer and the polymerizable monomer. Surprisingly, by forming a polymer obtained by polymerizing a crosslinkable monomer in a proportion of less than% by weight, the thermal foaming property has been remarkably improved without sacrificing the thermal expansibility. I found out that microspheres can be obtained. As the crosslinkable monomer, a bifunctional crosslinkable monomer is preferable, and a compound having a structure in which two polymerizable carbon-carbon double bonds are connected via a flexible chain is particularly preferable. The present invention has been completed based on these findings.

According to the present invention, in a thermally foamable microsphere having a structure in which a foaming agent is enclosed in an outer shell formed of a polymer,
(1) The outer shell formed from a polymer contains 2 polymerizable carbon-carbon double bonds in a proportion of more than 1% by weight and 5% by weight or less based on the polymerizable monomer. It is formed from a polymer obtained by polymerizing two difunctional crosslinkable monomers,
(2) polymer is, by polymerizing a mixture of vinylidene alone or vinylidene chloride and copolymerizable therewith vinyl monomer, and the crosslinkable monomer (a) as a polymerizable monomer comprising vinylidene chloride (co) and a mixture of the polymer, or (b) polymerizable as monomer (meth) acrylonitrile alone or (meth) acrylonitrile and therewith copolymerizable vinyl monomer, the crosslinking monomer (Meth) acrylonitrile (co) polymer obtained by polymerizing the body,
(3) The maximum expansion ratio is 5 times or more,
(4) When the outer shell is formed of a vinylidene chloride (co) polymer, the ratio of the expansion ratio R ₂ at a temperature 10 ° C. higher than the maximum expansion ratio R ₁ (R ₂ / R ₁ ) Is 0.8 to 0.4, and
(5) When the outer shell is formed from a (meth) acrylonitrile (co) polymer, the maximum expansion ratio ratio expansion ratio R ₂ from the temperature at that time with respect to R ₁ at 5 ° C. higher temperature (R 2 _/ R ₁ ) Thermally foamable microspheres characterized by being ₁ to 0.8 are provided.

Further, according to the present invention, the thermally foamable microsphere having a structure that a foaming agent is encapsulated in the formed outer and inner shell of a polymer, Ru der variation coefficient of the particle size distribution is less 1.50% The thermally foamable microsphere is provided.

Further, according to the present invention, in an aqueous dispersion medium, at least a blowing agent, (a) vinylidene chloride alone or a mixture of vinylidene chloride and a vinyl monomer copolymerizable therewith, or (b) (meth) acrylonitrile alone Or a polymerizable monomer which is a mixture of (meth) acrylonitrile and a vinyl monomer copolymerizable therewith , and a bifunctional crosslinkable monomer having two polymerizable carbon-carbon double bonds In a method for producing a foamable microsphere having a structure in which a foaming agent is enclosed in an outer shell formed from a polymer produced by suspension polymerization of a polymerizable mixture, the polymerizable monomer is used as a reference. A polymerizable mixture containing a bifunctional crosslinkable monomer having two polymerizable carbon-carbon double bonds in a proportion of more than 1% by weight and not more than 5% by weight, and (I) an aqueous dispersion medium and a polymerizable mixture, respectively Another flow As a method, a method of continuously feeding into a continuous high-speed rotation high shear type stirring and dispersing machine at a constant ratio, or (II) pouring an aqueous dispersion medium and a polymerizable mixture into a dispersion tank, After the primary dispersion by stirring, the droplets of the polymerizable mixture are granulated by the method of supplying the obtained primary dispersion into a continuous high-speed rotation high shear type stirring and dispersing machine, and then suspension polymerization is performed. (A) When the maximum expansion ratio is 5 times or more , and (b) when the outer shell is made of a vinylidene chloride (co) polymer, the maximum expansion ratio R _{1 is} 10 ° C. higher than the temperature at that time. the ratio of the expansion ratio _{R 2} at a temperature _(R 2 / _{R 1)} is from 0.8 to 0.4, and, when formed from (c) an outer shell (meth) acrylonitrile (co) polymer , originating at 5 ° C. higher temperatures from the temperature at that time to the maximum expansion ratio R ₁ Method for producing a thermally foamable microspheres the ratio of the magnification _{R 2 (R 2 / R 1} ) is characterized in that to obtain a thermally foamable microsphere is 1 to 0.8 is provided.

  ADVANTAGE OF THE INVENTION According to this invention, the thermally foamable microsphere suitable for processes, such as a kneading process, a calendar process, an extrusion process, and injection molding to which a strong shear force is applied, and its manufacturing method are provided. Moreover, according to this invention, the thermal foamable microsphere with small temperature dependence of the elasticity modulus of the outer shell formed from the polymer, and its manufacturing method are provided. The heat-foamable microsphere of the present invention has a wide processing temperature range, and has high chemical resistance, solvent resistance, and a high ability to retain foaming properties. Furthermore, according to the present invention, in addition to the above-mentioned properties, a thermally foamable microsphere having a very small variation coefficient of particle size distribution and sharp foaming is provided.

1. Process for producing thermally foamable microspheres The thermally foamable microspheres of the present invention suspend a polymerizable mixture containing at least a foaming agent, a polymerizable monomer, and a crosslinkable monomer in an aqueous dispersion medium. In a method for producing a thermally foamable microsphere having a structure in which a foaming agent is enclosed in an outer shell formed from a polymer produced by suspension polymerization, the amount exceeds 1% by weight based on the polymerizable monomer. It can be obtained by suspension polymerization of a polymerizable mixture containing a crosslinking agent in a proportion of 5% by weight or less. By adjusting the kind of the polymerizable monomer, the kind of the crosslinking agent and the use ratio, etc., a thermally foamable microsphere having a maximum foaming ratio of 5 times or more, preferably 10 times or more can be obtained. In the present invention, the maximum expansion ratio means the expansion ratio at the expansion temperature at which the maximum expansion ratio of the thermally foamable microsphere is obtained. A method for measuring the maximum expansion ratio will be described later.

(1) Foaming agent The foaming agent used in 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 having a boiling point of usually 150 ° C. or lower, preferably 130 ° C. or lower, more preferably 120 ° C. or lower, particularly preferably 110 ° C. or lower is suitable.

Specific examples of the blowing agent together with the boiling point are ethane (−89 ° C.), ethylene (−102.4 ° C.), propane (−42.1 ° C.), propene (−47.7 ° C.), n-butane (− 0.5 ° C), isobutane (-12 ° C), butene (-6.47 ° C), isobutene (-6.6 ° C), n-pentane (36 ° C), isopentane (27.85 ° C), neopentane (9 0.5 ° C), 2,2,4-trimethylpentane (99.25 ° C), n-hexane (69 ° C), isohexane (60.3 ° C), petroleum ether (27-67 ° C), heptane (98.4). Hydrocarbons such as CCl ₃ F (23.8 ° C); tetraalkylsilanes such as tetramethylsilane (26.6 ° C); and the like. These foaming agents can be used alone or in combination of two or more.

  In particular, when a heat-foamable microsphere that is not easily broken under high temperature and high shear conditions during processing is desired, for example, boiling point of n-hexane, isohexane, heptane, 2,2,4-trimethylpentane, etc. Is preferably foamed using a hydrocarbon foaming agent having a temperature of 60 ° C. or higher. Among these, it is particularly preferable to use a hydrocarbon-based blowing agent having a boiling point of 70 ° C. or higher, such as heptane and 2,2,4-trimethylpentane. The boiling point range of these foaming agents is preferably 60 to 130 ° C, more preferably 60 to 120 ° C, and particularly preferably 70 to 110 ° C.

  The hydrocarbon-based blowing agents having a boiling point of 60 ° C. or higher may be used alone, but when used in combination with a hydrocarbon-based blowing agent having a boiling point of less than 60 ° C., a higher expansion ratio can be obtained. . That is, when the same amount of foaming agent is used, the low-boiling point hydrocarbon-based foaming agent of less than 60 ° C. contributes to an increase in the expansion ratio because the number of moles increases, and the hydrocarbon-based foaming having a boiling point of 60 ° C. or more. The agent contributes to heat resistance and foaming characteristics at higher temperatures. The proportion of the hydrocarbon-based blowing agent having a boiling point of 60 ° C. or higher is preferably 10% by weight to 100% by weight, more preferably 15% by weight to 95% by weight, particularly preferably, based on the total weight of the foam. 20% by weight or more and 90% by weight or less.

(2) Polymerizable monomer and polymer As the polymerizable monomer, acrylic ester such as methyl acrylate, ethyl acrylate, butyl acrylate, dicyclopentenyl acrylate; methyl methacrylate, ethyl methacrylate, methacryl Methacrylic acid esters such as butyl acid and isobornyl methacrylate; and vinyl monomers such as acrylonitrile, methacrylonitrile, vinylidene chloride, vinyl chloride, styrene, vinyl acetate, α-methylstyrene, chloroprene, neoprene, and butadiene. . These polymerizable monomers can be used alone or in combination of two or more.

  As the thermally foamable microspheres, those in which the polymer forming the outer shell is thermoplastic and has gas barrier properties are preferred. From these viewpoints, vinylidene chloride (co) polymer and (meth) acrylonitrile (co) polymer are preferable as the polymer forming the outer shell.

  As the vinylidene chloride (co) polymer, a (co) polymer obtained by using, as a polymerizable monomer, vinylidene chloride alone or a mixture of vinylidene chloride and a vinyl monomer copolymerizable therewith is used. Can be mentioned. Examples of the monomer copolymerizable with vinylidene chloride include acrylonitrile, methacrylonitrile, methacrylic acid ester, acrylic acid ester, styrene, and vinyl acetate.

  Such vinylidene chloride (co) polymers include, as polymerizable monomers, (A) 30-100% by weight of vinylidene chloride, and (B) acrylonitrile, methacrylonitrile, acrylic acid ester, methacrylic acid ester, styrene. And a (co) polymer obtained using 0 to 70% by weight of at least one monomer selected from the group consisting of vinyl acetate. If the copolymerization ratio of vinylidene chloride is less than 30% by weight, the gas barrier property of the outer shell is too low, which is not preferable.

  The vinylidene chloride (co) polymer has, as a polymerizable monomer, (A1) 40 to 80% by weight of vinylidene chloride, and (B1) at least one monomer selected from the group consisting of acrylonitrile and methacrylonitrile. A copolymer obtained by using 0 to 60% by weight of the polymer and 0 to 60% by weight of at least one monomer selected from the group consisting of (B2) acrylic acid ester and methacrylic acid ester is preferable. By setting it as such a copolymer, design of foaming temperature is easy and it is easy to achieve a high foaming ratio.

  When solvent resistance or foamability at high temperature is desired, it is preferable to form the outer shell with a (meth) acrylonitrile (co) polymer. The (meth) acrylonitrile (co) polymer is obtained by using (meth) acrylonitrile alone or (meth) acrylonitrile and a vinyl monomer copolymerizable therewith as the polymerizable monomer (co). A polymer can be mentioned. Examples of the vinyl monomer copolymerizable with (meth) acrylonitrile include vinylidene chloride, acrylic acid ester, methacrylic acid ester, styrene, and vinyl acetate.

  As such (meth) acrylonitrile (co) polymer, as a polymerizable monomer, (C) at least one monomer selected from the group consisting of acrylonitrile and methacrylonitrile, 30 to 100% by weight, (D) A (co) polymer obtained using 0 to 70% by weight of at least one monomer selected from the group consisting of vinylidene chloride, acrylic acid ester, methacrylic acid ester, styrene, and vinyl acetate is preferred. When the copolymerization ratio of (meth) acrylonitrile is less than 30% by weight, the solvent resistance and heat resistance are insufficient.

  (Meth) acrylonitrile (co) polymer has a high proportion of (meth) acrylonitrile and a high foaming temperature (co) polymer, a small proportion of (meth) acrylonitrile and a low foaming temperature (co) heavy Can be divided into coalescence. As the (co) polymer having a large use ratio of (meth) acrylonitrile, as a polymerizable monomer, at least one monomer selected from the group consisting of (C) acrylonitrile and methacrylonitrile is 80 to 100% by weight. (D) a (co) polymer obtained using 0 to 20% by weight of at least one monomer selected from the group consisting of vinylidene chloride, acrylic acid ester, methacrylic acid ester, styrene, and vinyl acetate. Can be mentioned. On the other hand, the (co) polymer with a small proportion of (meth) acrylonitrile used is at least 30% by weight of at least one monomer selected from the group consisting of (C) acrylonitrile and methacrylonitrile as a polymerizable monomer. Obtained by using less than 80% by weight and (D) at least one monomer selected from the group consisting of vinylidene chloride, acrylic acid ester, methacrylic acid ester, styrene, and vinyl acetate in excess of 20% by weight and 70% by weight or less. And a copolymer obtained.

  The (meth) acrylonitrile (co) polymer has, as a polymerizable monomer, 51 to 100% by weight of at least one monomer selected from the group consisting of (C1) acrylonitrile and methacrylonitrile, and (D1) A (co) polymer obtained using 0 to 40% by weight of vinylidene chloride and 0 to 48% by weight of at least one monomer selected from the group consisting of (D2) acrylic acid ester and methacrylic acid ester is preferable. .

  When a (co) polymer containing no vinylidene chloride is desired as the outer shell polymer, (E) at least one monomer selected from the group consisting of acrylonitrile and methacrylonitrile is used as the polymerizable monomer. (Meth) acrylonitrile (co) heavy obtained using 30 to 100% by weight of the body and 0 to 70% by weight of at least one monomer selected from the group consisting of (F) acrylates and methacrylates Coalescence is preferred. The polymerizable monomer is at least selected from the group consisting of (E1) acrylonitrile 1 to 99% by weight, (E2) methacrylonitrile 1 to 99% by weight, and (F) an acrylate ester and a methacrylate ester. Copolymers obtained using 0 to 70% by weight of a single monomer are preferred.

  Furthermore, in order to obtain thermally foamable microspheres with particularly excellent processability, foamability, gas barrier properties, and solvent resistance, the outer shell (meth) acrylonitrile (co) polymer is used as a polymerizable monomer. , (E1) acrylonitrile 20 to 80% by weight, (E2) methacrylonitrile 20 to 80% by weight, and (F) at least one monomer selected from the group consisting of acrylates and methacrylates 0 to 20 It is preferable that it is a copolymer obtained by using% by weight.

(3) Crosslinkable monomer In the present invention, in order to improve processing characteristics, foaming characteristics, heat resistance, solvent resistance (chemical resistance) and the like together with the polymerizable monomer as described above, a crosslinkable monomer. Use the body. As the crosslinkable monomer, a polyfunctional compound having two or more polymerizable carbon-carbon double bonds is usually used. Examples of the polymerizable carbon-carbon double bond include a vinyl group, a methacryl group, an acrylic group, and an allyl group. Two or more polymerizable carbon-carbon double bonds may be the same or different from each other.

  Specifically, examples of the crosslinkable monomer include aromatic divinyl compounds such as divinylbenzene, divinylnaphthalene, and derivatives thereof; and diethylenically unsaturated compounds such as ethylene glycol di (meth) acrylate and diethylene glycol di (meth) acrylate. Bifunctional crosslinks such as carboxylic acid esters; (meth) acrylates derived from aliphatic terminal alcohols such as 1,4-butanediol and 1,9-nonanediol; divinyl compounds such as N, N-divinylaniline and divinyl ether; Ionic monomers. Examples of the crosslinkable monomer include trifunctional or higher polyfunctional crosslinkable monomers such as trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, and triacryl formal.

  Among the crosslinkable monomers, a bifunctional crosslinkable monomer having two polymerizable carbon-carbon double bonds is preferable from the viewpoint of easily balancing the foamability and processing characteristics. In the case of a trifunctional or higher polyfunctional crosslinkable monomer, when the ratio of use increases, the polymer forming the outer shell loses its properties as a thermoplastic resin, and foaming may not occur even when heated.

  The bifunctional crosslinkable monomer may be directly or indirectly via a flexible chain derived from a diol compound selected from the group consisting of polyethylene glycol, polypropylene glycol, alkyl diol, alkyl ether diol, and alkyl ester diol. In particular, the compound is preferably a compound having a structure in which two polymerizable carbon-carbon double bonds are linked.

  When a bifunctional crosslinkable monomer having such a flexible chain is used as a crosslinkable monomer in a proportion of more than 1% by weight and 5% by weight or less, while maintaining a high expansion ratio, The temperature dependence of the modulus of elasticity of the polymer can be reduced, and even in the process of kneading, calendering, extrusion, injection molding, etc., even when subjected to shearing force, the outer shell breaks down or the inclusion gas It is possible to obtain a thermally foamable microsphere that hardly dissipates.

  When a bifunctional crosslinkable monomer having a flexible chain is used at a specific ratio, it is presumed that good scratch-hardening physical properties can be imparted to the outer shell polymer layer. Strain curability is a characteristic that requires a larger deformation stress in order to further deform as the amount of deformation increases. That is, as the foaming starts and proceeds, the outer polymer layer is stretched. At that time, not only the thinned portion of the polymer layer is stretched further by the deformation stress, but the thick portion of the polymer layer that is still small in deformation and small in deformation stress is preferentially stretched. Thereby, even if the degree of cross-linking of the outer shell polymer layer is high, a high expansion ratio can be obtained. In addition, since the thickness of the outer shell polymer layer is uniform, the temperature, shearing force, and resistance to solvents are increased. On the other hand, if the site connecting the polymerizable carbon-carbon double bonds has a rigid structure, or if the amount of the crosslinkable monomer used is too large, the curability of the strain becomes too large, and the expansion ratio If it drops significantly or is severe, it will not foam at all.

  Examples of the bifunctional crosslinkable monomer having a structure in which two polymerizable carbon-carbon double bonds are linked via the above-described flexible chain include polyethylene glycol di (meth) acrylate, polypropylene glycol di (meta) ) Acrylate, alkyl diol di (meth) acrylate, alkyl ether diol di (meth) acrylate, alkyl ester diol di (meth) acrylate, and mixtures of two or more thereof.

More specifically, examples of the bifunctional crosslinkable monomer include polyethylene glycol di (meth) acrylates such as diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, and tetraethylene glycol di (meth) acrylate [ethylene oxide Unit (—CH ₂ CH ₂ O—) is usually 2 to 15 units]; polypropylene glycol di ((dipropylene glycol di (meth) acrylate), tripropylene glycol di (meth) acrylate, tetrapropylene glycol di (meth) acrylate and the like ( meth) acrylate [propylene oxide unit _[-CH (CH 3) _CH 2 O-) or _(-CH 2 CH _(CH 3) O-] is 2-20 normal, ethylene glycol di (meth) acrylate, propylene glycol Di (meth) acrylate, 1,3-propanediol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, 1,3-butylenediol di (meth) acrylate, 1,6-hexanediol di ( (Meth) acrylate, 1,9-nonanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, 3-methyl-1,5-pentanediol di (meth) acrylate, 2-methyl-1,8-octane Alkyldiol di (meth) acrylates such as diol di (meth) acrylate, 2,4-diethyl-1,5-pentanediol di (meth) acrylate, 2-hydroxy-1,3-propanediol di (meth) acrylate ( The refractive chain is made of aliphatic carbon, and the number of carbon atoms in the linking part is usually 2-20. ); 3-oxa-1,6-alkyl ether diol di (meth) acrylates such as hexanediol di (meth) acrylate [flexible chain is composed of the aliphatic carbon and ether bonds. When there is one ether bond (—R ₁ —O—R ₂ —), usually each aliphatic carbon is not the same (R ₁ ≠ R ₂ ). ] Alkyl ester diol di (meth) acrylate such as neopentyl glycol di (meth) acrylate hydroxypivalate [a flexible chain is composed of aliphatic carbon and an ester bond. (—R ₁ —COO—R ₂ —)];

  The lower limit of the use ratio of the crosslinkable monomer is based on the polymerizable monomer (polymerizable monomer = 100 wt%), more than 1 wt%, preferably 1.1 wt%, more preferably 1.2% by weight, particularly preferably 1.3% by weight. The upper limit of the proportion of the crosslinkable monomer used is 5% by weight, preferably 4% by weight, more preferably 3% by weight. In particular, in the case of using a bifunctional copolymerizable monomer having a structure in which two polymerizable carbon-carbon double bonds are linked via the flexible chain, in many cases, a crosslinkable monomer is used. Good results can be easily obtained when the proportion of is in the range of 1.4 to 4% by weight, and further 1.5 to 3% by weight.

  When the use ratio of the crosslinkable monomer is 1% by weight or less, only processing characteristics similar to those of the conventional thermally foamable microsphere can be obtained. On the other hand, if the use ratio of the crosslinking agent is excessive, the outer shell polymer loses its thermoplasticity and foaming becomes difficult.

(4) Polymerization initiator The polymerization initiator is not particularly limited, and those generally used in this field can be used, but an oil-soluble polymerization initiator that is soluble in the polymerizable monomer is preferable. . More specifically, examples of the polymerization initiator include dialkyl peroxide, diacyl peroxide, peroxyester, peroxydicarbonate, and azo compound. The polymerization initiator is usually contained in the monomer mixture. However, when it is necessary to suppress early polymerization, a part or all of the polymerization initiator is added to the aqueous dispersion medium during or after the granulation step. It may be added and transferred into droplets of the polymerizable mixture. The polymerization initiator is usually used in a proportion of 0.0001 to 3% by weight based on the aqueous dispersion medium.

(5) Aqueous dispersion medium Suspension polymerization is usually carried out in an aqueous dispersion medium containing a dispersion stabilizer. Examples of the dispersion stabilizer include inorganic fine particles such as silica and magnesium hydroxide. In addition, auxiliary stabilizers such as a condensation product of diethanolamine and an aliphatic dicarboxylic acid, polyvinyl pyrrolidone, polyethylene oxide, various emulsifiers and the like can be used. The dispersion stabilizer is usually used at a ratio of 0.1 to 20 parts by weight with respect to 100 parts by weight of the polymerizable monomer.

  An aqueous dispersion medium containing a dispersion stabilizer is usually prepared by blending a dispersion stabilizer or an auxiliary stabilizer with deionized water. The pH of the aqueous phase at the time of polymerization is appropriately determined depending on the type of dispersion stabilizer and auxiliary stabilizer used. For example, when silica such as colloidal silica is used as a dispersion stabilizer, polymerization is performed in an acidic environment. In order to make the aqueous dispersion medium acidic, an acid is added as necessary to adjust the pH of the system to 6 or less, preferably about pH 3-4. In the case of a dispersion stabilizer that dissolves in an aqueous dispersion medium in an acidic environment such as magnesium hydroxide or calcium phosphate, the polymerization is performed in an alkaline environment.

  One preferred combination of dispersion stabilizers 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 acid value of the condensation product is preferably 60 or more and less than 95, and more preferably 65 to 90. Furthermore, when an inorganic salt such as sodium chloride or sodium sulfate is added, a thermally foamable microsphere having a more uniform particle shape can be easily obtained. As the inorganic salt, sodium chloride is usually preferably used.

  Although the usage-amount of colloidal silica changes also with the particle diameter, it is a ratio of 1-20 weight part normally with respect to 100 weight part of polymerizable monomers, Preferably it is a ratio of 2-15 weight part. The condensation product is usually used at a ratio of 0.05 to 2 parts by weight with respect to 100 parts by weight of the polymerizable monomer. The inorganic salt is used in a ratio of 0 to 100 parts by weight with respect to 100 parts by weight of the polymerizable monomer.

  Another preferred combination of the dispersion stabilizer includes a combination of colloidal silica and a water-soluble nitrogen-containing compound. Among these, a combination of colloidal silica and polyvinylpyrrolidone is preferably used. Furthermore, another preferred combination is a combination of magnesium hydroxide and / or calcium phosphate and an emulsifier.

  As a dispersion stabilizer, a hardly water-soluble metal hydroxide (for example, obtained by reaction in a water phase of a water-soluble polyvalent metal salt compound (for example, magnesium chloride) and an alkali metal hydroxide (for example, sodium hydroxide)) , Magnesium hydroxide) colloid. Moreover, as calcium phosphate, the reaction product in the aqueous phase of sodium phosphate and calcium chloride can be used.

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

  As the polymerization aid, at least one compound selected from the group consisting of alkali metal nitrite, stannous chloride, stannic chloride, water-soluble ascorbic acids, and boric acid can be present in the aqueous dispersion medium. . When suspension polymerization is performed in the presence of these compounds, polymerization particles do not agglomerate at the time of polymerization, the polymer does not adhere to the polymerization can wall, and is stable while efficiently removing heat generated by polymerization. Thus, a thermally foamable microsphere can be produced.

Among the alkali metal nitrites, sodium nitrite and potassium nitrite are preferable in terms of availability and price. Examples of ascorbic acids include ascorbic acid, metal salts of ascorbic acid, esters of ascorbic acid, and the like. Among these, water-soluble ones are preferably used. Here, the water-soluble ascorbic acids mean those having a solubility in water at 23 ° C. of 1 g / 100 cm ³ or more, and ascorbic acid and alkali metal salts thereof are preferable. Among these, L-ascorbic acid (vitamin C), sodium ascorbate, and potassium ascorbate are particularly preferably used in terms of availability, price, and action and effect. These compounds are generally used in a proportion of 0.001 to 1 part by weight, preferably 0.01 to 0.1 part by weight, per 100 parts by weight of the polymerizable monomer.

(6) Suspension polymerization The order in which each component is added to the aqueous dispersion medium is arbitrary. Usually, dispersion stability is achieved by adding water and a dispersion stabilizer, and if necessary, a stabilizing aid or a polymerization aid. An aqueous dispersion medium containing the agent is prepared. On the other hand, the foaming agent, the polymerizable monomer, and the crosslinkable monomer may be separately integrated in the aqueous dispersion medium in addition to the aqueous dispersion medium to form a polymerizable mixture (oil-based mixture). Usually, these are mixed in advance and then added to the aqueous dispersion medium. The polymerization initiator can be used by adding it to the polymerizable monomer in advance, but when it is necessary to avoid early polymerization, for example, the polymerizable mixture is added to the aqueous dispersion medium and stirred. However, a polymerization initiator may be added and integrated in an aqueous dispersion medium. The polymerization mixture and the aqueous dispersion medium may be mixed in a separate container, mixed with a stirrer or a disperser having high shearing force, and then charged into a polymerization can.

  By stirring and mixing the polymerizable mixture and the aqueous dispersion medium, droplets of the polymerizable mixture are granulated in the aqueous dispersion medium. The average particle diameter of the droplets is preferably approximately the same as the average particle diameter of the target thermally foamable microsphere, but is usually about 3 to 100 μm. In order to obtain a heat-foamable microsphere having a very 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. 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 after being stirred and dispersed.

  More specifically, in the step of supplying the aqueous dispersion medium and the polymerizable mixture into the continuous high-speed rotation high shear type stirring and dispersing machine, (I) the aqueous dispersion medium and the polymerizable mixture are separately flowed at a certain ratio. And (II) injecting the aqueous dispersion medium and the polymerizable mixture into the dispersion tank and stirring both in the dispersion tank for primary dispersion. Then, there is a method of supplying the obtained primary dispersion into a continuous high-speed rotation high-shearing type stirring and dispersing machine.

  In the method (I), for example, as shown in FIG. 2, in the step of supplying the aqueous dispersion medium and the polymerizable mixture into the continuous high-speed rotation high shear type stirring and dispersing machine, the aqueous dispersion medium 1 and the polymerizable mixture 2 Are separately fed into a continuous high speed rotating high shear type stirring and dispersing machine at a constant ratio. Specifically, the aqueous dispersion medium 1 is held in the storage tank 3, and the polymerizable mixture 2 is held in the storage tank 4. The aqueous dispersion medium 1 is supplied from the line 6 using the pump 5 and the polymerizable mixture 2 is supplied from the line 8 using the pump 7 as separate flows into the continuous high-speed rotation high shear type stirring and dispersing machine 9. The supply ratio of the aqueous dispersion medium 1 and the polymerizable mixture 2 is usually in the range of 1: 1 to 6: 1, more preferably in the range of 2: 1 to 4: 1. Both are continuously stirred and dispersed in the stirring and dispersing machine 9, and then the obtained dispersion is injected into the polymerization tank 11 through the line 10, and suspension polymerization is performed in the polymerization tank 11.

  In the method (II), as shown in FIG. 3, the aqueous dispersion medium 1 and the polymerizable mixture 2 are dispersed in the step of supplying the aqueous dispersion medium and the polymerizable mixture into the continuous high-speed rotation high shear type stirring and dispersing machine. It inject | pours in the tank 12, and stirs both in the dispersion tank 12, and makes primary dispersion | distribution. The dispersion tank 12 is usually provided with a general stirring blade. The ratio of the aqueous dispersion medium 1 to the polymerizable mixture 2 is usually in the range of 1: 1 to 6: 1, more preferably in the range of 2: 1 to 4: 1. The primary dispersion obtained by stirring in the dispersion tank is supplied into the continuous high-speed rotation high shear type stirring and dispersing machine 9 through the line 14 using the pump 13. After the primary dispersion is further stirred and dispersed in the stirring and dispersing machine 9, the obtained dispersion is poured into the polymerization tank 11 through the line 15, and suspension polymerization is performed in the polymerization tank 11. According to the method (II), a thermally foamable microsphere having a sharp particle size distribution can be stably obtained.

  By adopting such a method, the average particle size is 3 to 100 μm, and the variation coefficient of the particle size distribution is preferably 1.50% or less, more preferably 1.30% or less, and particularly preferably 1.10. It is possible to obtain thermally foamable microspheres having a sharp particle size distribution of not more than%. Thermally foamable microspheres with a sharp particle size distribution have sharp foaming and can give uniform foams and foamed molded products.

  In the present invention, a batch-type high-speed rotation high shear disperser as shown in FIG. 4 can be used. In the method using a batch-type high-speed rotation / high-shear disperser, the aqueous dispersion medium 1 and the polymerizable mixture 2 are put into the batch-type high-speed rotation / high-shear disperser 16 and stirred to disperse. The droplets are granulated, and then the dispersion is injected into the polymerization tank 11 via the line 18 using the pump 17 and suspension polymerization is performed in the polymerization tank.

  Suspension polymerization is usually performed by degassing the inside of the reaction vessel or replacing it with an inert gas and raising the temperature to 30 to 100 ° C. After suspension polymerization, the aqueous phase is removed, for example, by filtration, centrifugation, and sedimentation. The thermally foamable microspheres are collected in a wet cake state after being filtered and washed. If necessary, the thermally foamable microspheres are dried at a relatively low temperature such that the foaming agent is not gasified. The heat-foamable microspheres can be surface-treated with various compounds as desired, and inorganic fine powders can be attached thereto. Furthermore, the surface can be coated with various materials other than the inorganic fine powder.

2. Thermally foamable microsphere The thermally foamable microsphere of the present invention has a structure in which a foaming agent is enclosed in an outer shell formed from a polymer. In the present invention, a polymerizable monomer and a crosslinkable monomer amount of more than 1 wt% and not more than 5 wt% based on the polymerizable monomer are used. It is formed by polymerizing the body.

  In the thermally foamable microsphere of the present invention, the outer shell polymer is formed using a relatively large amount of a crosslinkable monomer, preferably a bifunctional crosslinkable monomer, in addition to the polymerizable monomer. Therefore, the temperature dependence of the elastic modulus of the outer shell polymer is small. Therefore, for example, when a resin composition obtained by blending the heat-foamable microspheres of the present invention with a thermoplastic resin is subjected to processing such as kneading, calendering, extrusion, injection molding, etc., destruction of the outer shell or inclusion gas Dissipation is difficult to occur.

  In addition, the thermally foamable microspheres of the present invention have a small temperature dependency of the elastic modulus of the outer shell polymer, and therefore can have a wide processing suitability temperature range for uniform foaming. In this regard, please refer to FIG. FIG. 1 is a graph showing the relationship between the elastic modulus of the outer shell polymer and the measurement temperature. The outer shell polymer (a) of the conventional heat-foamable microsphere has an elastic modulus that rapidly decreases as the temperature rises. Therefore, the temperature range (a2-a1) of the elastic modulus region in which appropriate foaming (uniform foaming) is performed. ) Is narrow. On the other hand, the outer shell polymer (b) of the heat-foamable microsphere of the present invention has a wide temperature range (b2-b1) in the elastic modulus region for appropriate foaming, so that it can foam uniformly. A wide processing suitability temperature range can be taken.

  The average particle size of the thermally foamable microspheres of the present invention is not particularly limited, but is usually 3 to 100 μm, preferably 5 to 50 μm. If this average particle size is too small, foamability becomes insufficient. If the average particle size is too large, it is not preferable because the surface becomes rough in a field where a beautiful appearance is required, and the resistance to shearing force is insufficient.

  The coefficient of variation of the particle size distribution of the heat-foamable microsphere of the present invention is not particularly limited, but it is preferable that the coefficient of variation is 1.50% or less particularly in applications where sharp foaming is required. The variation coefficient of the particle size distribution is more preferably 1.30% or less, and particularly preferably 1.10% or less. If this coefficient of variation is too large, large particle diameter and small particle diameter thermally foamable microspheres will be mixed. Larger particle size tends to lower the foaming start temperature than small particle size, so to prevent early foaming and obtain uniform foaming, it is desirable to reduce the coefficient of variation of the thermally foamable microspheres . Examples of the method for obtaining a thermally foamable microsphere having a very small variation coefficient of the particle size distribution include the methods (I) and (II) described above.

  In the present invention, the variation coefficient of the particle size distribution is a value calculated based on the following formulas (1) and (2).

(Where, μ = average value, x _j = particle diameter, q _j = frequency distribution)

  The content of the foaming agent in the thermally foamable microsphere of the present invention is usually 5 to 50% by weight, preferably 7 to 35% by weight, based on the total weight. If the foaming agent content is too low, the expansion ratio will be insufficient, and if it is too high, the thickness of the outer shell will be reduced, causing shearing under heating during processing and causing early foaming or rupture of the outer shell. It becomes easy. Examples of the foaming agent include a low-boiling organic solvent and a compound that decomposes by heating to generate a gas. Among these, a low-boiling organic solvent is preferable. The foaming agent is selected from those which become gaseous at a temperature below the softening point of the polymer forming the outer shell.

  The outer shell of the thermally foamable microsphere of the present invention is usually formed from a polymer having excellent gas barrier properties and heat resistance. Specifically, as described above, it can be formed using various polymerizable monomers such as acrylic acid ester, (meth) acrylonitrile, vinylidene chloride, vinyl chloride, and styrene. Among these, vinylidene chloride (co) polymers and (meth) acrylonitrile (co) polymers are preferable for highly balancing gas barrier properties, solvent resistance, heat resistance, foaming properties, and the like. According to the present invention, thermally foamable microspheres exhibiting various foaming behaviors can be obtained by controlling the combination and composition ratio of polymerizable monomers to be used and selecting the type of foaming agent.

  The thermally foamable microspheres of the present invention are particularly excellent in processing characteristics, and have a good balance between foaming characteristics (thermal expansion properties) and processing characteristics. The heat-expandable microspheres of the present invention do not lose thermal expansibility and have a maximum expansion ratio of 5 times or more despite the use of a crosslinking agent in a proportion exceeding 1% by weight. The maximum expansion ratio is preferably 10 times or more, more preferably 20 times or more. In many cases, it is possible to achieve a maximum expansion ratio of about 30 to 60 times.

  The thermally foamable microsphere of the present invention has a small temperature dependency of the elastic modulus of the outer shell formed from a polymer. Moreover, the heat-foamable microsphere of the present invention has a wide temperature range for processing. Furthermore, the thermally foamable microspheres of the present invention have high resistance (chemical resistance, solvent resistance) and foaming property retention capability against polar solvents and plasticizers. These characteristics of the thermally foamable microspheres of the present invention are specifically shown in the examples.

A specific example of the characteristics of the thermally foamable microsphere of the present invention is that the temperature dependence of foaming is small. For example, the expansion ratio of the outside case shell polymer is such vinylidene chloride (co) polymer described above, 10 ° C. higher temperatures from the temperature at that time to the maximum expansion ratio R ₁ of the thermally foamable microsphere of the present invention the ratio of _{R 2 (R 2 / R 1} ) is usually from 0.8 to 0.4, preferably 0.9 to 0.5, more preferably 1 to 0.5.

When the outer shell polymer of the thermally foamable microsphere of the present invention is a (meth) acrylonitrile copolymer (copolymerization ratio of (meth) acrylonitrile = 30 wt% or more and less than 80 wt%) as described above, the maximum foaming the ratio of the expansion ratio _{R 2} at 5 ° C. higher temperatures from the temperature at that time with respect to ratio _{R 1 (R 2 / R 1} ) is usually 1 to 0.8, preferably from 1 to 0.85, more preferably 1 to 0.9.

  When the outer shell polymer of the thermally foamable microsphere of the present invention is a (meth) acrylonitrile (co) polymer [(meth) acrylonitrile ratio = 80 to 100% by weight], particularly as a crosslinkable monomer, By using the above-mentioned bifunctional crosslinkable monomer having a flexible chain in an amount of more than 1% by weight and not more than 5% by weight, the temperature of the elastic modulus of the outer shell polymer is maintained while maintaining a high foaming property. Thermally foamable microspheres with low dependence and excellent workability and chemical resistance can be obtained.

The heat-foamable microsphere of the present invention has a high temperature and high shear when the elastic modulus of the outer shell polymer at 190 ° C. or higher is 10 ⁶ N / m ² or more and 10 ⁹ N / m ² or less. Excellent resistance. The elastic modulus of the outer shell polymer is more preferably 5.0 × 10 ⁶ N / m ² or more and 10 ⁹ N / m ² or less, particularly preferably 10 ⁷ N / m ² or more and 10 ⁸ N / m ² or less. It is.

3. Applications The thermally foamable microspheres of the present invention are used in various fields after being heated and foamed (thermally expanded) or unexpanded. Thermally foamable microspheres are used, for example, as fillers for paints for automobiles, wallpaper, foaming agents for foamed inks (relief patterns such as T-shirts), shrinkage prevention agents, etc. Is done. Thermally foamable microspheres use the volume increase caused by foaming to reduce the weight and porosity of plastics, paints, and various materials, and to provide various functions (for example, slip properties, heat insulation properties, cushion properties, and sound insulation properties). Etc.). The thermally foamable microspheres of the present invention can be suitably used in the paint, wallpaper, and ink fields that require surface properties and smoothness. Since the thermally foamable microsphere of the present invention is excellent in processing characteristics, it can be suitably applied to application fields that require processing steps such as kneading, calendering, extrusion, and injection molding.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples.
The measuring methods of physical properties and characteristics are as follows.

(1) Foaming ratio and maximum foaming ratio 0.7 g of thermally foamable microspheres are placed in a gear-type oven and heated at a predetermined temperature (foaming temperature) for 2 minutes to cause foaming. The obtained foam is put into a graduated cylinder, the volume is measured, and divided by the volume when not foamed to obtain the expansion ratio. At this time, the expansion ratio is measured by increasing the temperature from 100 ° C. in increments of 5 ° C., and the expansion ratio at the expansion temperature when the maximum expansion ratio is obtained is defined as the maximum expansion ratio.

(2) Average particle diameter Using a particle size distribution analyzer SALD-3000J manufactured by Shimadzu Corporation, the median diameter on a weight basis was measured to obtain an average particle diameter.

(3) Elastic modulus After foaming the thermally foamable microsphere and removing the encapsulated foaming agent as much as possible, a hot press sheet is prepared with a hot press machine, and a 1 cm × 1.5 cm × 0.25 cm test piece is prepared. Cut out. This test piece was heated using a rheograph solid manufactured by Toyo Seiki Seisakusho under a nitrogen atmosphere at a frequency of 10 hertz and a heating rate of 3 ° C./min, and the elastic modulus was measured.

(4) Foaming ratio in binder system An EVA emulsion (concentration 55% by weight) containing an ethylene / vinyl acetate copolymer (EVA; ethylene / vinyl acetate = 30/70% by weight) is added to 5 parts by weight of EVA. Then, 1 part by weight of thermally foamable microspheres is added to prepare a coating solution. This coating solution is applied to a double-sided art paper with a coater having a gap of 200 μm, dried, and then placed in an oven at a predetermined temperature and heated for 2 minutes. The expansion ratio is determined by the thickness ratio before and after foaming.

(5) Chemical resistance A plasticizer solution is prepared by adding 2 parts by weight of diisonolyl phthalate and 1 part by weight of thermally foamable microspheres as a plasticizer to a glass test tube. This plasticizer liquid is heated at 140 ° C. using an oil bath, and the presence or absence of foaming over time and the degree of thickening of the plasticizer liquid are observed.

(6) Foaming ratio in plasticized PVC sheet 3 parts by weight of thermally foamable microspheres were added to 50 parts by weight of polyvinyl chloride resin (S903 manufactured by Kureha Chemical Industry) and 50 parts by weight of dioctyl phthalate (DOP). Prepare the compound. The compound is roll-kneaded at 120 ° C. for 2 minutes to prepare a sheet having a thickness of 1 mm. The sheet is cut into a size of 3 × 4 cm square to make a sample, and the sample is foamed in an oven at 200 ° C. for 5 minutes and 10 minutes, respectively. The specific gravity before and after foaming is measured to calculate the foaming ratio (%).

(7) TMA (Thermo Mechanical Analysis)
TMA measurement was performed using a TMA-7 model manufactured by PerkinElmer. About 0.25 mg of sample was used. The heating rate was 5 ° C./min and 20 ° C./min.

[Comparative Example 1]
Colloidal silica with a solid content of 20% 80.5 g, diethanolamine-adipic acid condensate 50% aqueous solution 3.0 g, sodium chloride 164.1 g, potassium dichromate 2.5% aqueous solution 2.2 g, hydrochloric acid 0.1 g A total of 470 g of an aqueous dispersion medium consisting of ionic water was prepared.

  On the other hand, 141.7 g of acrylonitrile, 67.1 g of methacrylonitrile, 11.2 g of methyl methacrylate, 0.67 g of trimethylolpropane trimethacrylate as a trifunctional crosslinkable monomer, 26.1 g of n-pentane, 14.4 g of petroleum ether. A polymerizable mixture comprising 9 g and 1.1 g of azobisisobutyronitrile was prepared (weight% of monomer component = acrylonitrile / methacrylonitrile / methyl methacrylate = 64.4 / 30.5 / 5.1). The amount of crosslinkable monomer used = 0.3% by weight of the monomer component).

  The polymerizable mixture and the aqueous dispersion medium were agitated and mixed with a batch-type high-speed rotary high shear type disperser shown in FIG. 4 to granulate fine droplets of the polymerizable mixture. An aqueous dispersion medium containing fine droplets of this polymerizable mixture was charged into a polymerization can (1.5 L) equipped with a stirrer and reacted at 60 ° C. for 20 hours using a hot water bath. The obtained reaction product is repeatedly subjected to filtration using a centrifuge and washed with water to form a cake, which is dried for a whole day and night. The average particle size is about 25 μm, and the variation coefficient of the particle size distribution is 1.7%. A thermally foamable microsphere (MS-A) was obtained. The expansion ratio (maximum expansion ratio) of MS-A at 170 ° C. was about 50 times. The results are shown in Table 1. Comparative Example 1 is in accordance with Example 2 of Japanese Patent Publication No. 5-15499.

[Example 1]
In place of 0.67 g of trimethylolpropane trimethacrylate which is a trifunctional crosslinkable monomer, 3.5 g of diethylene glycol dimethacrylate which is a bifunctional crosslinkable monomer (crosslinkable monomer use amount = one monomer component) .6 wt%) in the same manner as Comparative Example 1 except that the average particle size is about 26 μm and the coefficient of variation of the particle size distribution is 1.7% (MS-1 ) The expansion ratio (maximum expansion ratio) of MS-1 at 170 ° C. was about 50 times. The results are shown in Table 1.

[Comparative Example 2]
Thermally foamable microspheres having an average particle size of about 26 μm in the same manner as in Comparative Example 1 except that the amount of trimethylolpropane trimethacrylate, a trifunctional crosslinkable monomer, was changed from 0.67 g to 3.5 g. (MS-B) was obtained. MS-B hardly foamed in any temperature range of 140 ° C. or higher because the resin component forming the outer shell layer significantly lost the properties as a thermoplastic resin. The results are shown in Table 1.

(footnote)
(* 1) Thickness ratio before and after foaming of thermally foamable microsphere-containing EVA emulsion coating layer.
(* 2) Plasticizer liquid = 2 parts of diisononyl phthalate / 1 part of thermally foamable microspheres

(Discussion)
MS-1 of Example 1 had a good maximum foaming ratio (foaming temperature of 170 ° C.) of 50 times regardless of the amount of the crosslinkable monomer used exceeding 1% by weight of the monomer component. is there. In contrast, MS-B (Comparative Example 2) using a trifunctional crosslinkable monomer in a proportion of 1.6% by weight of the monomer component is highly crosslinked by the polymer forming the outer shell layer. Thus, the thermal foaming property is substantially lost.

  In the foaming behavior in the EVA emulsion, MS-1 of Example 1 was 5.2 times the weight of the crosslinkable monomer used by MS-A of Comparative Example 1 (5 moles). (2 times), the foaming ratio at 170 ° C. at which the maximum foaming ratio was obtained was 5.5 times, and the same high foaming ratio as MS-A was maintained. Moreover, the expansion ratio of MS-1 at 190 ° C., which is even higher, is 4.3 times, indicating that the expansion ratio is less than that of MS-A and the heat resistance is excellent. .

  Comparing the elastic modulus of the outer shell polymer at 140 ° C., the MS-1 of Example 1 is less than the MS-A of Comparative Example 1 which is a typical prior art thermal foamable microsphere. .4 times the elastic modulus. That is, it can be seen that the thermally foamable microsphere of the present invention is resistant to higher shearing force and excellent in heat resistance. When compared at a higher temperature of 190 ° C., MS-1 of Example 1 has an elastic modulus of the outer shell polymer of 1.6 times that of MS-A of Comparative Example 1. This means that the thermally foamable microspheres of the present invention are less susceptible to particle shrinkage, can maintain a high expansion ratio, and can take a wider processing suitability temperature range than before.

  In the evaluation of chemical resistance, the plasticizer liquid containing MS-A of Comparative Example 1 was partially foamed after heating at 140 ° C. for 6 minutes, and the viscosity was remarkably increased. On the other hand, in the case of MS-1 of Example 1, partial foaming was not observed after heating at 140 ° C. for 6 minutes, and further, even after 7 minutes, partial foaming did not occur.

[Comparative Example 3]
A total of 520 g of an aqueous dispersion medium comprising 12 g of colloidal silica, 1.4 g of diethanolamine-adipic acid condensate, 154 g of sodium chloride, 0.12 g of sodium nitrite, 0.2 g of hydrochloric acid, and deionized water was prepared.

  On the other hand, polymerizability consisting of 130 g of acrylonitrile, 60 g of methacrylonitrile, 10 g of isobornyl methacrylate, 1 g of trimethylolpropane trimethacrylate trimethyl methacrylate, 38 g of n-pentane, and 1.2 g of azobisisobutyronitrile. A mixture was prepared (wt% of monomer component = acrylonitrile / methacrylonitrile / isobornyl methacrylate = 65/30/5, amount of crosslinkable monomer = 0.5 wt% of monomer component). The polymerizable mixture and the aqueous dispersion medium were agitated and mixed with a batch-type high-speed rotary high shear type disperser shown in FIG. 4 to granulate fine droplets of the polymerizable mixture.

  An aqueous dispersion medium containing fine droplets of this polymerizable mixture was charged into a polymerization can (1.5 L) equipped with a stirrer and reacted at 60 ° C. for 22 hours using a hot water bath. The obtained reaction product is repeatedly subjected to filtration using a centrifuge and washed with water to form a cake. The cake is dried overnight, the average particle size is about 28 μm, and the variation coefficient of the particle size distribution is 1. Thermal foaming microspheres (MS-C) of 8% were obtained. The expansion ratio (maximum expansion ratio) of MS-C at 170 ° C. was about 55 times. Comparative Example 3 is in accordance with Example 2 of JP-A-5-285376. The results are shown in Table 2.

[Example 2]
Instead of 1 g of trimethylolpropane trimethacrylate, a trifunctional crosslinkable monomer, 3.5 g of diethylene glycol dimethacrylate, a difunctional crosslinkable monomer (amount of crosslinkable monomer = 1.6 of monomer component) In the same manner as in Comparative Example 3 except that the weight%) was used, a thermally foamable microsphere (MS-2) having an average particle size of about 30 μm and a coefficient of variation of the particle size distribution of 1.6% was obtained. Obtained. The expansion ratio of MS-2 at 170 ° C. (maximum expansion ratio) was about 55 times. The results are shown in Table 2.

(Discussion)
Comparing the elastic modulus of the outer shell polymer, MS-2 of Example 2 was compared with MS-C of Comparative Example 3, which is a typical prior art thermal foaming microsphere, when the measurement temperature was 194 ° C. It was the same. However, when compared at a high measurement temperature of 210 ° C., the elastic modulus of the outer polymer of MS-2 is 2.6 times that of MS-A. In addition, in MS-2 of Example 2, the decrease in the elastic modulus of the outer shell polymer in the temperature range of 194 ° C. to 210 ° C. is extremely small. This means that the thermally foamable microspheres of the present invention are less likely to shrink particles in a high temperature range, can maintain a high expansion ratio, and can take a wider processing temperature range than in the past. From another point of view, it also means that it is resistant to higher shear forces and is heat resistant.

[Example 3]
A total of 557 g of colloidal silica (16.5 g), diethanolamine-adipic acid condensation product (1.6 g), sodium chloride (169.8 g), sodium nitrite (0.11 g), and water are added to a polymerization vessel (1.5 L) equipped with a stirrer. The aqueous dispersion medium was prepared. Hydrochloric acid was added and adjusted so that the pH of the aqueous dispersion was 3.2.

  Meanwhile, a polymerizable mixture comprising 147.4 g of acrylonitrile, 70.4 g of methacrylonitrile, 2.2 g of methyl methacrylate, 3.5 g of diethylene glycol dimethacrylate, 41.8 g of isopentane, and 1.32 g of azobisisobutyronitrile is prepared. (Wt% of monomer component = acrylonitrile / methacrylonitrile / methyl methacrylate = 67/32/1, amount of crosslinkable monomer used = 1.6 wt% of monomer component). The polymerizable mixture and the aqueous dispersion medium prepared above were agitated and mixed with a batch-type high-speed rotary high shear type disperser shown in FIG. 4 to granulate fine droplets of the polymerizable mixture.

  An aqueous dispersion medium containing minute droplets of this polymerizable mixture was charged into a polymerization can (1.5 L) equipped with a stirrer and reacted at 60 ° C. for 45 hours using a hot water bath. The obtained reaction product was repeatedly filtered and washed with water to obtain thermally foamable microspheres (MS-3) having an average particle size of about 30 μm and a coefficient of variation of the particle size distribution of 1.8%. The expansion ratio (maximum expansion ratio) of MS-3 at 170 ° C. was about 50 times. The results are shown in Table 3.

[Example 4]
The average particle size was about the same as in Example 3 except that the monomer charge amount was changed so that the monomer component charge ratio was acrylonitrile / methacrylonitrile = 70/30. A thermally foamable microsphere (MS-4) having a coefficient of variation of 30% and a particle size distribution of 2.1% was obtained. The expansion ratio (maximum expansion ratio) of this MS-4 at 170 ° C. was about 50 times. The results are shown in Table 3.

[Comparative Example 4]
Instead of 3.5 g of the difunctional crosslinkable monomer diethylene glycol dimethacrylate, the trifunctional crosslinkable monomer trimethylol propane trimethacrylate 0.6 g (crosslinkable monomer use amount = 0 of monomer component) .3 wt%) in the same manner as in Example 3, except that the average particle size was about 30 μm and the coefficient of variation of the particle size distribution was 1.6% (MS-D ) The expansion ratio (maximum expansion ratio) of this MS-D at 170 ° C. was about 50 times. The results are shown in Table 3.

[Comparative Example 5]
Instead of 3.5 g of the difunctional crosslinkable monomer diethylene glycol dimethacrylate, the trifunctional crosslinkable monomer trimethylol propane trimethacrylate 0.6 g (crosslinkable monomer use amount = 0 of monomer component) .3 wt%) in the same manner as in Example 4 except that the average particle size was about 30 μm and the coefficient of variation of the particle size distribution was 1.9% (MS-E ) The expansion ratio (maximum expansion ratio) of this MS-E at 170 ° C. was about 50 times. The results are shown in Table 3.

(footnote)
(* 1) A sheet of 1 mm thickness prepared by kneading 100 g of a mixture of 50 parts PVC / 50 parts DOP / 3 parts thermally foamable microspheres with a 120 ° C. rotating roll for 2 minutes.
(* 2) A 3 × 4 cm square sheet was foamed in an oven at 200 ° C., and the foaming ratio (%) was calculated from the measured specific gravity before and after foaming.

(Discussion)
Each plasticized PVC sheet containing the thermally foamable microspheres (MS-3 and MS-4) of Examples 3 and 4 showed a high foaming ratio after 200 ° C / 5 minutes, respectively, and 200 ° C / 10 minutes. The high expansion ratio is maintained afterwards. On the other hand, each plasticized PVC sheet containing the thermally foamable microspheres (MS-D and MS-E) of Comparative Examples 4 and 5 was significantly foamed at 120 ° C., after 200 ° C./5 minutes. The foaming ratio was small, and the foaming ratio after 200 ° C./10 minutes was remarkably lowered, so-called sag phenomenon was observed.

[Comparative Example 6]
An aqueous dispersion medium was prepared by weighing 5 g of colloidal silica, 0.5 g of diethanolamine-adipic acid condensation product, 0.12 g of sodium nitrite, and 600 g in total. Hydrochloric acid was added and adjusted so that the pH of the aqueous dispersion medium was 3.2.

  On the other hand, acrylonitrile 120 g, methyl methacrylate 120 g, trifunctional crosslinkable monomer trimethylol propane trimethacrylate 0.4 g, isopentane 70 g, and 2,2′-azobis (2,4-dimethylvaleronitrile) 1.2 g A polymerizable mixture was prepared (weight% of monomer component = acrylonitrile / methyl methacrylate = 50/50, amount of crosslinkable monomer used = 0.2% by weight of monomer component). The polymerizable mixture and the aqueous dispersion medium were stirred and mixed with a batch-type high-speed rotary high shear type disperser shown in FIG. 4 to prepare fine droplets of the polymerizable mixture.

  An aqueous dispersion medium containing fine droplets of this polymerizable mixture was charged into a polymerization can equipped with a stirrer (1.5 L) and reacted at 53 ° C. for 22 hours using a hot water bath. The obtained reaction product having a pH of 6.3 was filtered and washed with water, and this was repeated, followed by drying, and a thermally foamable microscopic product having an average particle size of 14 μm and a coefficient of variation of the particle size distribution of 1.6%. Fair (MS-F) was obtained. The expansion ratio of MS-F at 145 ° C. (maximum expansion ratio) was about 18 times, and the expansion ratio at 150 ° C. was about 12 times. The results are shown in Table 4.

[Example 5]
Instead of 0.4 g of trimethylolpropane trimethacrylate, a trifunctional crosslinkable monomer, 3.2 g of diethylene glycol dimethacrylate, a bifunctional crosslinkable monomer (crosslinkable monomer use amount = one monomer component) .6 wt%), the same as Comparative Example 6, except that the average particle size is about 15 μm, and the coefficient of variation of the particle size distribution is 1.7% (MS-5) Got. The expansion ratio of MS-5 at 145 ° C. (maximum expansion ratio) was about 40 times, and the maximum expansion ratio of about 40 times was maintained even when the foaming temperature was increased to 150 ° C. The results are shown in Table 4.

[Comparative Example 7]
An aqueous dispersion medium was prepared by weighing 8.8 g of colloidal silica, 0.8 g of a diethanolamine-adipic acid condensation product, 0.13 g of sodium nitrite, and 528 g of water in total.

  On the other hand, a polymerizable mixture comprising 143 g of vinylidene chloride, 66 g of acrylonitrile, 11 g of methyl methacrylate, 0.33 g of trimethylolpropane trimethacrylate, 2.2 g of isopropyl peroxydicarbonate, and 35.2 g of isobutane was prepared (monomer % By weight of component = vinylidene chloride / acrylonitrile / methyl methacrylate = 65/30/5, amount of crosslinkable monomer = 0.15% by weight of monomer component). Next, the polymerizable mixture and the aqueous dispersion medium prepared above were stirred and mixed with a batch-type high-speed rotary high shear type disperser shown in FIG. 4 to granulate fine droplets of the polymerizable mixture. The polymerization can was charged and reacted at 50 ° C. for 22 hours. The obtained reaction product was repeatedly filtered and washed with water to obtain thermally foamable microspheres (MS-G) having an average particle size of about 15 μm and a coefficient of variation of the particle size distribution of 1.6%. This MS-G had a foaming ratio at 120 ° C. (maximum foaming ratio) of about 50 times, but when the foaming temperature was raised to 130 ° C., the foaming ratio was significantly reduced to about 18 times. The results are shown in Table 5.

[Example 6]
Instead of 0.33 g of trimethylolpropane trimethacrylate, a trifunctional crosslinkable monomer, 3.5 g of diethylene glycol dimethacrylate, a bifunctional crosslinkable monomer (the amount of crosslinkable monomer used = one monomer component) .6 wt%) was obtained in the same manner as in Comparative Example 7 to obtain a thermally foamable microsphere MS-6 having an average particle size of about 15 μm and a coefficient of variation of the particle size distribution of 1.7%. It was. The expansion ratio of MS-6 at 120 ° C. (maximum expansion ratio) was about 50 times, and even when the foaming temperature was increased to 130 ° C., a high expansion ratio of about 35 times was exhibited. The results are shown in Table 5.

[Example 7]
In place of 0.67 g of trimethylolpropane trimethacrylate which is a trifunctional crosslinkable monomer, 3.5 g of diethylene glycol dimethacrylate which is a bifunctional crosslinkable monomer (crosslinkable monomer use amount = one monomer component) 6 wt%), when stirring and mixing the polymerizable mixture and the aqueous dispersion medium, as shown in FIG. 2, the aqueous dispersion medium and the polymerizable mixture are respectively held in separate tanks, and these In the same manner as in Comparative Example 1 except that the suspension polymerization is carried out after continuously passing through a continuous high-speed rotation high-shear stirring and dispersing machine at a certain ratio. A thermally foamable microsphere (MS-7) having a coefficient of variation in diameter distribution of 0.3% was obtained. The expansion ratio (maximum expansion ratio) of MS-7 at 170 ° C. was about 50 times. This plasticizer liquid containing MS-7 did not partially foam even when held at 140 ° C. for 8 minutes. On the other hand, in the case of MS-1 of Example 1, partial foaming was slightly recognized after 8 minutes. This is due to the fact that the particle size distribution of MS-7 is sharper than that of MS-1 in addition to the effects of the type and amount of crosslinkable monomer.

[Example 8]
When stirring and mixing the polymerizable mixture and the aqueous dispersion medium, as shown in FIG. 2, the aqueous dispersion medium and the polymerizable mixture are held in separate tanks, and these are continuously added at a certain ratio. The average particle size is about 30 μm and the coefficient of variation of the particle size distribution is 0.3% in the same manner as in Example 3 except that the suspension polymerization is performed after passing through a continuous high-speed rotation high shear type disperser. Thus, a thermally foamable microsphere (MS-8) having a sharp particle size distribution was obtained. The expansion ratio (maximum expansion ratio) of MS-8 at 170 ° C. was about 50 times.

  The plasticized PVC sheet containing MS-3 of Example 3 (see Table 3) was prepared by kneading with a rotating roll at 120 ° C. for 2 minutes, so that the thickness of the 1 mm thick sheet does not contain MS-3. The thickness increased by about 10% compared to the modified PVC sheet. On the other hand, the plasticized PVC sheet containing MS-8 is a plasticized PVC sheet containing 1-8 mm thick prepared by kneading for 2 minutes with a rotating roll at 120 ° C. There was almost no change in thickness. That is, it can be said that MS-8 is excellent in partial foaming characteristics during roll kneading (partial foaming is difficult).

[Example 9]
When stirring and mixing the polymerizable mixture and the aqueous dispersion medium, as shown in FIG. 2, the aqueous dispersion medium and the polymerizable mixture are held in separate tanks, and these are continuously added at a certain ratio. The average particle size was about 15 μm and the coefficient of variation in particle size distribution was 0.5%, as in Example 5, except that the suspension polymerization was performed after passing through a continuous high-speed rotation high shear type disperser. Thus, a thermally foamable microsphere (MS-9) having a sharp particle size distribution was obtained. The expansion ratio of MS-9 at 145 ° C. (maximum expansion ratio) was about 40 times, and even when the foaming temperature was increased to 150 ° C., the maximum expansion ratio of about 40 times was maintained.

  MS-9 and MS-5 (Example 5) were each applied to double-sided art paper according to the method for measuring the expansion ratio in a binder system. When these wet coated papers were dried with a dryer at a rate of 1 ° C./min, MS-5 foamed at a lower temperature than MS-9. This means that when a thermally foamable microsphere having a sharp particle size distribution such as MS-9 is used, the processing speed can be increased (can be dried at a high temperature in a short time).

[Example 10]
When stirring and mixing the polymerizable mixture and the aqueous dispersion medium, as shown in FIG. 2, the aqueous dispersion medium and the polymerizable mixture are held in separate tanks, and these are continuously added at a certain ratio. The average particle size is about 15 μm and the coefficient of variation of the particle size distribution is 0.2% in the same manner as in Example 6 except that the suspension polymerization is performed after passing through the continuous high-speed rotation high shear type disperser. Thus, a thermally foamable microsphere (MS-10) having a sharp particle size distribution was obtained. The expansion ratio of MS-10 at 120 ° C. (maximum expansion ratio) was about 50 times, and even when the foaming temperature was increased to 130 ° C., the maximum expansion ratio of about 35 times was maintained. When the foaming behavior was observed while raising the temperature at a rate of 5 ° C./min with a microscope with a hot stage, the temperature at which MS-10 foamed was higher than that of MS-6 in Example 6. Therefore, MS-10 is judged to be sharply foaming.

[Example 11]
The average particle size was about the same as in Example 8 except that 66 g of isopentane / 2,2,4-trimethylpentane (weight ratio = 20/10) was used as a blowing agent instead of 41.8 g of isopentane. A thermally foamable microsphere (MS-11) having a coefficient of variation of 30% and a particle size distribution of 0.5% was obtained. The expansion ratio of MS-11 at 180 ° C. was about 40 times.

  As for the plasticized PVC sheet containing MS-11, the thickness of a 1 mm-thick sheet prepared by kneading for 2 minutes with a rotating roll at 120 ° C. is almost the same as that of a plasticized PVC sheet not containing MS-11. There wasn't. That is, it can be said that MS-11 is excellent in partial foaming characteristics during roll kneading (partial foaming is difficult).

[Example 12]
The average particle size was about the same as in Example 8 except that 66 g of isopentane / 2,2,4-trimethylpentane (weight ratio = 15/15) was used as a blowing agent instead of 41.8 g of isopentane. A thermally foamable microsphere (MS-12) having a coefficient of variation of 31 μm and a particle size distribution of 0.4% was obtained.

  The plasticized PVC sheet containing MS-12 has a thickness of 1 mm thick prepared by kneading for 2 minutes with a rotating roll at 120 ° C., and the thickness changes almost as compared with the plasticized PVC sheet not containing MS-12. There wasn't. That is, it can be said that MS-12 is excellent in partial foaming characteristics during roll kneading (partial foaming is difficult).

[Example 13]
The average particle size was about the same as in Example 8 except that 66 g of isopentane / 2,2,4-trimethylpentane (weight ratio = 10/20) was used as a blowing agent instead of 41.8 g of isopentane. A heat-foamable microsphere (MS-13) having 30 μm and a coefficient of variation of the particle size distribution of 0.3% was obtained.

  The plasticized PVC sheet containing MS-13 has a thickness of 1 mm, which is prepared by kneading for 2 minutes with a rotating roll at 120 ° C., and the thickness of the plasticized PVC sheet is almost the same as that of the plasticized PVC sheet not containing MS-13. There wasn't. That is, it can be said that MS-13 is excellent in partial foaming characteristics during roll kneading (partial foaming is difficult).

[Example 14]
The average particle size was about the same as in Example 8 except that 66 g of isopentane / 2,2,4-trimethylpentane (weight ratio = 6/24) was used as a blowing agent instead of 41.8 g of isopentane. A thermally foamable microsphere (MS-14) having a coefficient of variation of 30% and a particle size distribution of 0.5% was obtained.

[Example 15]
In the same manner as in Example 3 except that 66 g of 2,2,4-trimethylpentane was used as a foaming agent in place of 41.8 g of isopentane, the average particle size was about 29 μm and the variation coefficient of the particle size distribution was 0. Thermally foamable microspheres (MS-15) of 2% were obtained.

[Example 16]
Thermal foaming having an average particle size of about 32 μm and a coefficient of variation of the particle size distribution of 0.3% in the same manner as in Example 3 except that 66 g of heptane was used as the blowing agent instead of 41.8 g of isopentane. Microspheres (MS-16) were obtained.

[Example 17]
TMA measurement was performed on samples MS-3 and MS-11 to MS-15 prepared in the above examples. The results are shown in Table 6.

(*) Relative comparison of displacement due to expansion

[Example 18]
1 g of MS-D prepared in Comparative Example 4 and MS-14-16 prepared in Examples 14-16 were dispersed in 99 g of water and then boiled at 100 ° C. for 10 minutes. It was observed whether the foamed particles floated on the water surface, and the results are shown in Table 7.

  The thermally foamable microspheres of the present invention can be used in various fields such as applications of foamed inks, paints for the purpose of reducing weight, and fillers for plastics.

FIG. 1 is a graph showing the relationship between the elastic modulus of the outer shell polymer of the thermally foamable microsphere and the measurement temperature. FIG. 2 is an explanatory diagram showing an example of a method for producing thermally foamable microspheres using a continuous high-speed rotating high-shear disperser. FIG. 3 is an explanatory view showing another example of a method for producing thermally foamable microspheres using a continuous high-speed rotation high shear type disperser. FIG. 4 is an explanatory diagram showing an example of a method for producing thermally foamable microspheres using a batch-type high-speed rotation high shearing disperser.

Explanation of symbols

1: Aqueous dispersion medium 2: Monomer mixture 3: Tank 4: Tank 5: Pump 6: Line 7: Pump 8: Line 9: Continuous high-speed rotation high shear type stirring and dispersing machine 10: Line 11: Polymerization tank 12: Dispersion tank 13: Pump 14: Line 15: Line 16: Batch type high speed rotation high shear type disperser 17: Pump 18: Line

Claims (6)

In a thermally foamable microsphere having a structure in which a foaming agent is enclosed in an outer shell formed of a polymer,
(1) The outer shell formed from a polymer contains 2 polymerizable carbon-carbon double bonds in a proportion of more than 1% by weight and 5% by weight or less based on the polymerizable monomer. It is formed from a polymer obtained by polymerizing two difunctional crosslinkable monomers,
(2) polymer is, by polymerizing a mixture of vinylidene alone or vinylidene chloride and copolymerizable therewith vinyl monomer, and the crosslinkable monomer (a) as a polymerizable monomer comprising vinylidene chloride (co) and a mixture of the polymer, or (b) polymerizable as monomer (meth) acrylonitrile alone or (meth) acrylonitrile and therewith copolymerizable vinyl monomer, the crosslinking monomer (Meth) acrylonitrile (co) polymer obtained by polymerizing the body,
(3) The maximum expansion ratio is 5 times or more,
(4) When the outer shell is formed of a vinylidene chloride (co) polymer, the ratio of the expansion ratio R ₂ at a temperature 10 ° C. higher than the maximum expansion ratio R ₁ (R ₂ / R ₁ ) Is 0.8 to 0.4, and
(5) When the outer shell is formed from a (meth) acrylonitrile (co) polymer, the maximum expansion ratio ratio expansion ratio R ₂ from the temperature at that time with respect to R ₁ at 5 ° C. higher temperature (R 2 _/ R ₁ ) Thermally foamable microspheres characterized by being ₁ to 0.8. The bifunctional crosslinkable monomer has two polymerizable properties via a flexible chain derived from a diol compound selected from the group consisting of polyethylene glycol, polypropylene glycol, alkyl diol, alkyl ether diol, and alkyl ester diol. carbon - thermally foamable microspheres according to claim 1, wherein carbon double bond is a compound of the connecting structure. The compound which is a bifunctional crosslinkable monomer includes polyethylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, alkyl diol di (meth) acrylate, alkyl ether diol di (meth) acrylate, and alkyl ester diol. The thermally foamable microsphere according to claim 2 , which is at least one compound selected from the group consisting of di (meth) acrylates. In thermally foamable microspheres having a structure foaming agent is encapsulated in the formed outer and inner shell of a polymer, heat-expandable according to claim 1, wherein the variation coefficient of the particle size distribution is Ru der less 1.50% Microsphere. In an aqueous dispersion medium, at least a blowing agent, (a) vinylidene chloride alone or a mixture of vinylidene chloride and a copolymerizable vinyl monomer, or (b) (meth) acrylonitrile alone or (meth) acrylonitrile and A polymerizable mixture containing a polymerizable monomer that is a mixture with a polymerizable vinyl monomer and a bifunctional crosslinkable monomer having two polymerizable carbon-carbon double bonds is subjected to suspension polymerization. In the method for producing a foamable microsphere having a structure in which a foaming agent is enclosed in an outer shell formed from the produced polymer, 1% by weight and 5% by weight or less based on the polymerizable monomer A polymerizable mixture containing a bifunctional crosslinkable monomer having two polymerizable carbon-carbon double bonds at a ratio of (I), a constant ratio with the aqueous dispersion medium and the polymerizable mixture as separate streams Ream A method of continuously feeding into a continuous high-speed rotation high shear type stirring and dispersing machine, or (II) injecting an aqueous dispersion medium and a polymerizable mixture into a dispersion tank, and stirring both in the dispersion tank for primary dispersion. After that, the resulting primary dispersion is granulated into droplets of the polymerizable mixture by a method of supplying the obtained primary dispersion into a continuous high-speed rotation high shear type stirring and dispersing machine, and then suspension polymerization is performed. (A) Maximum foaming When the magnification is 5 times or more and (b) the outer shell is formed of a vinylidene chloride (co) polymer , the expansion ratio R ₂ at a temperature 10 ° C. higher than the maximum expansion ratio R _{1 at} that time. the ratio is _(R 2 / _{R 1)} is from 0.8 to 0.4, and, for the case, the maximum expansion ratio _{R 1} which is formed from (c) an outer shell (meth) acrylonitrile (co) polymer the ratio of the expansion ratio R ₂ at 5 ° C. higher temperatures from the temperature at that time (R ₂ / Thermally foamable microspheres manufacturing method _{of 1),} characterized in that to obtain a thermally foamable microsphere is 1 to 0.8. The compound which is a bifunctional crosslinkable monomer includes polyethylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, alkyl diol di (meth) acrylate, alkyl ether diol di (meth) acrylate, and alkyl ester diol. The production method according to claim 5 , which is at least one compound selected from the group consisting of di (meth) acrylates.

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