Thermally expandable microspheres and use of same

Abstract

The purpose of the present invention is to provide: thermally expandable microspheres which have little change in expansibility over a wide temperature range; and use of the same.　Provided is thermally expandable microspheres which each include: an outer shell that contains a thermoplastic resin (A); and a foaming agent that is contained in the outer shell and is vaporized by heating. The thermally expandable microspheres satisfy the condition 1 described below. Condition: The glass transition point (Tg0) of a thermoplastic resin (A1) that is obtained by immersing the thermally expandable microspheres into tetrahydrofuran, and the glass transition point (Tg1) of a thermoplastic resin (A2) that is obtained by immersing a processed material, which is obtained by heating the thermally expandable microspheres at a temperature that is higher than the maximum expansion temperature thereof by 20°C for 10 minutes, into tetrahydrofuran have the relationship of formula (I). Formula (I): (Tg1)-(Tg0) > 0°C

Description

Heat-expandable microspheres and their uses

[0001] The present invention relates to heat-expandable microspheres and uses thereof.

[0002] Heat-expandable microspheres (heat-expandable microcapsules), which are microparticles with a thermoplastic resin shell and a blowing agent encapsulated inside, are characterized by their ability to expand when heated. These heat-expandable microspheres are used in a wide range of applications, for example, by being incorporated into substrates. Heat treatment during molding causes the heat-expandable microspheres to expand simultaneously with molding, thereby not only reducing the weight of the molded product but also imparting design features, cushioning properties, and the like to the molded product.

[0003] Patent Document 1 discloses such heat-expandable microspheres, each of which has an outer shell made of a thermoplastic resin obtained by polymerizing a polymerizable component that essentially contains a methacrylic acid ester monomer and a carboxyl group-containing monomer, and in which a nitrile monomer is present in an amount of 0 to 30 parts by weight per 100 parts by weight of the total amount of the methacrylic acid ester monomer and the carboxyl group-containing monomer, and in which the encapsulated blowing agent is essentially a hydrocarbon having 8 or more carbon atoms. Patent Document 2 also discloses heat-expandable microcapsules having a polymer shell encapsulating a volatile blowing agent as a core agent, the shell being formed by polymerizing a monomer composition containing a nitrile monomer, a monomer having an amide group, and a compound having a glycidyl group in its molecule, the monomer having an amide group being at least one selected from acrylamide and methacrylamide, and the monomer composition containing 0.9 to 20% by weight of the monomer having an amide group and 0.1 to 15% by weight of the compound having a glycidyl group.

[0004] International Publication No. 2015 / 17829 Japanese Patent Application Laid-Open No. 2015-172190

[0005] The heat-expandable microspheres disclosed in Patent Document 1 are nearly spherical, have excellent expandability, and are easy to work with when mixed with a resin. Furthermore, the heat-expandable microspheres disclosed in Patent Document 2 have a high expansion ratio and durability at high temperatures, and are less likely to produce coloration or odor when used in foam molding. However, when the heat-expandable microspheres disclosed in the above patent documents are expanded, there is a problem in that their expansion characteristics change significantly over a wide temperature range. Furthermore, when such heat-expandable microspheres are used to produce molded articles, there is also a problem in that the quality of the resulting molded articles is unstable.

[0006] Therefore, an object of the present invention is to provide heat-expandable microspheres whose expansion properties change little over a wide temperature range, and uses thereof.

[0007] As a result of extensive investigations, the present inventors have found that specific heat-expandable microspheres can solve the above problems, and have arrived at the present invention. Specifically, the present invention relates to heat-expandable microspheres that contain an outer shell containing a thermoplastic resin (A) and a blowing agent encapsulated in the outer shell and vaporized by heating, and that satisfy the following condition 1: Condition 1: The glass transition temperature (Tg ０ ) and the glass transition temperature (Tg １ ) have the relationship of the following formula (I): (Tg １ )-(Tg ０ ) >0 ° C. Formula (I)

[0008] The heat-expandable microspheres of the present invention preferably satisfy at least one of the following conditions 1) to 5): 1) The thermoplastic resin (A) is a polymer of a polymerizable component, and the polymerizable component contains a carboxyl group-containing monomer (a1). 2) The polymerizable component further contains a monomer (a2) containing a group reactive with a carboxyl group. 3) The weight ratio of the monomer (a1) to the polymerizable component is 20 to 70 wt %. 4) The weight ratio of the monomer (a2) to the polymerizable component is 0.1 to 10 wt %. 5) The weight ratio of the nitrile monomer (a3) ​​to the polymerizable component is 40 wt % or less.

[0009] The hollow particles of the present invention are expanded versions of the above-mentioned heat-expandable microspheres.

[0010] The composition of the present invention contains at least one selected from the group consisting of the heat-expandable microspheres and the hollow particles, and a base component. The molded article of the present invention is obtained by molding the composition.

[0011] The heat-expandable microspheres of the present invention exhibit little change in expansion properties over a wide temperature range. The hollow particles of the present invention are expanded versions of the heat-expandable microspheres and are therefore lightweight. The composition of the present invention contains at least one selected from the heat-expandable microspheres and hollow particles and therefore allows for the stable production of lightweight molded articles. The molded articles of the present invention are lightweight because they are obtained by molding the composition.

[0012] [Heat-Expandable Microspheres] The heat-expandable microspheres of the present invention comprise a shell containing a thermoplastic resin (A) and a blowing agent that vaporizes upon heating, and the microspheres as a whole exhibit heat-expandability (the property that the entire microspheres expand upon heating). The heat-expandable microspheres preferably have a core-shell structure consisting of a shell containing a thermoplastic resin and a core that essentially contains a blowing agent.

[0013] The heat-expandable microspheres of the present invention satisfy the following condition 1: the glass transition temperature (Tg ０) and the glass transition temperature (Tg １ ) have the relationship of the following formula (I): (Tg １ )-(Tg ０ ) >0 ° C. Formula (I)

[0014] The above Tg ０ The Tg indicates the glass transition temperature of the thermoplastic resin constituting the shell of the heat-expandable microspheres when the microspheres are not heated or expanded. １ indicates the glass transition temperature of the thermoplastic resin constituting the shell of the expandable body obtained when heated for 10 minutes at a temperature 20°C higher than the temperature at maximum expansion. When these glass transition temperatures satisfy the above formula (I), it is thought that the cohesive energy of the molecules (polymers) constituting the thermoplastic resin contained in the shell is large, and the shell can withstand the increase in internal pressure caused by vaporization of the blowing agent over a wide temperature range, resulting in little change in expansibility over a wide temperature range. ０ and Tg １ is obtained by the method described in the Examples. The value of the above formula (I) is preferably 1 to 50°C, more preferably 3 to 40°C, and even more preferably 5 to 35°C. A temperature of 7 to 35°C is particularly preferred.

[0015] The expansion initiation temperature (T ｓ ) is not particularly limited, but is preferably 120 to 200°C, more preferably 130 to 180°C, even more preferably 140 to 170°C, and particularly preferably 150 to 170°C. When the expansion onset temperature is 120°C or higher, changes in the expansion properties of the heat-expandable microspheres tend to be suppressed. When the expansion onset temperature is 200°C or lower, the expansion performance tends to be improved.

[0016] The maximum expansion temperature (T ｍａｘ) is not particularly limited, but is preferably 155°C or higher. When the maximum expansion temperature is 155°C or higher, changes in the expansion properties tend to be suppressed. The maximum expansion temperature is more preferably 155 to 250°C, even more preferably 160 to 230°C, particularly preferably 165 to 210°C, and most preferably 170 to 200°C. The expansion onset temperature (T ｓ ) and maximum expansion temperature (T ｍａｘ ) is according to the method described in the Examples.

[0017] The average particle size of the heat-expandable microspheres of the present invention is not particularly limited, but is preferably 1 to 200 μm, more preferably 5 to 100 μm, even more preferably 10 to 60 μm, and particularly preferably 10 to 50 μm. An average particle size of 1 μm or more tends to improve the expansion performance of the heat-expandable microspheres. An average particle size of 200 μm or less tends to improve the appearance of the resulting molded article. The coefficient of variation (Cv) of the particle size distribution of the heat-expandable microspheres of the present invention is not particularly limited, but is preferably 40% or less, more preferably 35% or less. The coefficient of variation is preferably 10% or more, and more preferably 15% or more. The average particle size and particle size distribution of the heat-expandable microspheres are measured according to the methods described in the Examples.

[0018] The maximum volume expansion ratio of the heat-expandable microspheres of the present invention is not particularly limited, but is preferably 5 to 200 times, more preferably 10 to 200 times, and even more preferably 15 to 200 times. An expansion ratio of 5 times or more tends to result in lightweight molded articles. On the other hand, an expansion ratio of 200 times or less tends to result in molded articles with good appearance. The heat-expandable microspheres of the present invention may be inhibited from yellowing during thermal expansion.

[0019] In the heat-expandable microspheres of the present invention, the thermoplastic resin (A) forming the outer shell is preferably a polymer of a polymerizable component containing a monomer having one polymerizable carbon-carbon double bond (hereinafter sometimes referred to as the "monomer component"), which allows the blowing agent to be efficiently encapsulated and provides high expansion performance. The polymerizable component may further contain a monomer having at least two polymerizable carbon-carbon double bonds (hereinafter sometimes simply referred to as the "crosslinking agent"). The monomer component and the crosslinking agent are components capable of undergoing an addition reaction, and the crosslinking agent is a component capable of introducing a crosslinked structure into the thermoplastic resin (A).

[0020] The monomer component is not particularly limited, but examples thereof include nitrile monomers such as acrylonitrile, methacrylonitrile, fumaronitrile, and maleonitrile; halogenated vinyl monomers such as vinyl chloride; halogenated vinylidene monomers such as vinylidene chloride; vinyl ester monomers such as vinyl acetate, vinyl propionate, and vinyl butyrate; unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, ethacrylic acid, crotonic acid, and cinnamic acid, and maleic acid, itaconic acid, fumaric acid, and citric acid. carboxyl group-containing monomers such as unsaturated dicarboxylic acids such as maleic acid and chloromaleic acid, anhydrides of unsaturated dicarboxylic acids, and unsaturated dicarboxylic acid monoesters such as monomethyl maleate, monoethyl maleate, monobutyl maleate, monomethyl fumarate, monoethyl fumarate, monomethyl itaconate, monoethyl itaconate, and monobutyl itaconate; methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, (meth)acrylic acid ester-based monomers such as acrylate, 2-ethylhexyl (meth)acrylate, stearyl (meth)acrylate, phenyl (meth)acrylate, isobornyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, and 2-hydroxyethyl (meth)acrylate; (meth)acrylamide-based monomers such as acrylamide, substituted acrylamide, methacrylamide, and substituted methacrylamide; maleimide-based monomers such as N-phenylmaleimide and N-cyclohexylmaleimide; styrene-based monomers such as styrene and α-methylstyrene; ethylenically unsaturated monoolefin-based monomers such as ethylene, propylene, and isobutylene; vinyl ether-based monomers such as vinyl methyl ether, vinyl ethyl ether, and vinyl isobutyl ether; vinyl ketone-based monomers such as vinyl methyl ketone; N-vinyl-based monomers such as N-vinylcarbazole and N-vinylpyrrolidone; and vinyl naphthalene salts. A part or all of the carboxyl groups of the carboxyl group-containing monomer may be neutralized during or after polymerization. Acrylic acid and methacrylic acid may be collectively referred to as (meth)acrylic acid, and (meth)acrylate means acrylate or methacrylate, and (meth)acrylic means acrylic or methacrylic.These monomer components may be used alone or in combination of two or more.

[0021] The polymerizable component is not particularly limited, but containing a carboxyl group-containing monomer (hereinafter sometimes referred to as monomer (a1)) as a monomer component is preferred because it improves heat resistance and solvent resistance. Furthermore, it is preferred because it facilitates the production of heat-expandable microspheres satisfying the above formula (I). When the polymerizable component contains monomer (a1) as a monomer component, the weight ratio of the carboxyl group-containing monomer in the polymerizable component is not particularly limited, but is preferably 20 to 70 wt%, more preferably 25 to 65 wt%, even more preferably 30 to 60 wt%, and particularly preferably 35 to 55 wt%. A weight ratio of 20 wt% or more tends to suppress changes in expansibility. A weight ratio of 70 wt% or less tends to improve expansibility and solvent resistance. Furthermore, satisfying the above ranges facilitates the production of heat-expandable microspheres satisfying the above formula (I).

[0022] When the polymerizable component contains a carboxyl group-containing monomer, it is preferable to further contain a monomer (a2) containing a group reactive with a carboxyl group (hereinafter, sometimes referred to as monomer (a2)) as a monomer component, as this is believed to further improve the cohesive energy of the polymer and further suppress changes in expandability. This is also preferable because it makes it easier to obtain heat-expandable microspheres that satisfy the above formula (I). The group reactive with a carboxyl group is not particularly limited, and examples thereof include methylol groups, hydroxyl groups, amino groups, epoxy groups, and isocyanate groups, and the polymerizable component may contain one or more of these groups. Furthermore, the monomer containing a group reactive with a carboxyl group is not particularly limited, and examples thereof include N-methylol(meth)acrylamide, N,N-dimethylaminoethyl(meth)acrylate, N,N-dimethylaminopropyl(meth)acrylate, vinyl glycidyl ether, propenyl glycidyl ether, glycidyl(meth)acrylate, glycerin mono(meth)acrylate, 4-hydroxybutyl acrylate glycidyl ether, 2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate, 2-hydroxybutyl(meth)acrylate, 4-hydroxybutyl(meth)acrylate, 2-hydroxy-3-phenoxypropyl(meth)acrylate, p-hydroxystyrene, etc. These monomers may be used alone or in combination of two or more.

[0023] When the polymerizable component contains the monomer (a2) as a monomer component, the weight ratio of the monomer (a2) in the polymerizable component is not particularly limited, but is preferably 0.1 to 10 wt %, more preferably 0.3 to 8 wt %, even more preferably 0.5 to 8 wt %, and particularly preferably 1 to 5 wt %. When the weight ratio is within this range, it tends to be possible to achieve both expandability and suppression of changes in expandability. Furthermore, satisfying this range makes it easier to obtain heat-expandable microspheres that satisfy the above formula (I).

[0024] The weight proportion of the nitrile monomer as a monomer component in the polymerizable component is not particularly limited, but a weight proportion of 40% by weight or less is preferred in that yellowing of the resulting heat-expandable particles and their expanded bodies is suppressed. Furthermore, a weight proportion within the above range is preferred in that heat-expandable microspheres that satisfy the above-mentioned condition 1 are easily obtained. The weight proportion is more preferably 30% by weight or less, even more preferably 20% by weight or less, particularly preferably 10% by weight or less, and most preferably 0% by weight.

[0025] The polymerizable component may contain, as a monomer component, a (meth)acrylic acid monomer having no group reactive with a carboxyl group. The inclusion of a (meth)acrylic acid monomer having no group reactive with a carboxyl group is preferred because it allows for the adjustment of the expansion properties of the heat-expandable microspheres. When the polymerizable component contains, as a monomer component, a (meth)acrylic acid monomer having no group reactive with a carboxyl group, the weight ratio of the (meth)acrylic acid monomer having no group reactive with a carboxyl group in the polymerizable component is not particularly limited, but is preferably 3 to 70 wt %, more preferably 5 to 65 wt %, even more preferably 10 to 60 wt %, and particularly preferably 15 to 55 wt %.

[0026] The polymerizable component may contain, as a monomer component, a (meth)acrylamide monomer having no group reactive with a carboxyl group. The inclusion of a (meth)acrylamide monomer having no group reactive with a carboxyl group is preferred in terms of improving the heat resistance of the heat-expandable microspheres. When the polymerizable component contains, as a monomer component, a (meth)acrylamide monomer having no group reactive with a carboxyl group, the weight ratio of the (meth)acrylamide monomer having no group reactive with a carboxyl group in the polymerizable component is not particularly limited, but is preferably 0.1 to 10 wt %, more preferably 0.5 to 8 wt %, and even more preferably 1 to 5 wt %.

[0027] As described above, the polymerizable component may contain a crosslinking agent. The crosslinking agent improves the density of the outer shell of the heat-expandable microspheres, thereby enabling the heat-expandable microspheres to expand effectively. The crosslinking agent is not particularly limited, and examples thereof include alkanediol di(meth)acrylates such as ethylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, and 1,9-nonanediol di(meth)acrylate; diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, PEG#200 di(meth)acrylate, and PEG#400 di(meth)acrylate. Polyalkylene glycol di(meth)acrylates such as acrylate, PEG#600 di(meth)acrylate, PEG#1000 di(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol#400 di(meth)acrylate, and polypropylene glycol#700 di(meth)acrylate; ethoxylated bisphenol A di(meth)acrylate (EO addition 2-30); Propoxylated bisphenol A di(meth)acrylate; Propoxylated ethoxylated bisphenol A di(meth)acrylate; Glycerin di(meth)acrylate; Polybutadiene di(meth)acrylate; Polyisoprene di(meth)acrylate; 2-hydroxy-3-acryloyloxypropyl methacrylate; Dimethylol-tricyclodecane di(meth)acrylate; Divinylbenzene; Ethoxylated glycerin triacrylate; 1,3,5-tri(meth)acrylate Examples of the crosslinking agent include difunctional monomers, trifunctional monomers, and tetrafunctional or higher functional monomers such as trimethylolpropane tri(meth)acrylate, 1,2,4-trivinylbenzene, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, and dipentaerythritol hexa(meth)acrylate. These crosslinking agents may be used alone or in combination of two or more.

[0028] The weight proportion of the crosslinking agent in the polymerizable component is not particularly limited, but is preferably 0.1 to 10% by weight, more preferably 0.15 to 5% by weight, even more preferably 0.2 to 3% by weight, particularly preferably 0.2 to 2% by weight, and most preferably 0.3 to 1.5% by weight.

[0029] The blowing agent is a component that vaporizes upon heating and is encapsulated in the outer shell of heat-expandable microspheres. This allows the heat-expandable microspheres as a whole to exhibit thermal expandability (the property of expanding the entire microsphere upon heating). The blowing agent is not particularly limited, and examples thereof include hydrocarbons having 1 to 13 carbon atoms, such as methane, ethane, propane, (iso)butane, (iso)pentane, (iso)hexane, (iso)heptane, (iso)octane, (iso)nonane, (iso)decane, (iso)undecane, (iso)dodecane, and (iso)tridecane; hydrocarbons having more than 13 but not more than 20 carbon atoms, such as (iso)hexadecane and (iso)eicosane; petroleum ethers, such as normal paraffins and isoparaffins having an initial boiling point of 150 to 260°C and / or a distillation range of 70 to 360°C; and Examples of suitable blowing agents include hydrocarbons such as distillates; halogenated hydrocarbons having 1 to 12 carbon atoms, such as methyl chloride, methylene chloride, chloroform, and carbon tetrachloride; fluorine-containing compounds such as hydrofluoroethers; silanes having an alkyl group having 1 to 5 carbon atoms, such as tetramethylsilane, trimethylethylsilane, trimethylisopropylsilane, and trimethyl-n-propylsilane; and compounds that thermally decompose to form gases upon heating, such as azodicarbonamide, N,N'-dinitrosopentamethylenetetramine, and 4,4'-oxybis(benzenesulfonylhydrazide). The blowing agent may be composed of a single compound or a mixture of two or more compounds. The blowing agent may be linear, branched, or alicyclic, with aliphatic blowing agents being preferred. Furthermore, the blowing agent preferably contains hydrocarbons having 8 or more carbon atoms, as this increases the maximum expansion temperature of the heat-expandable microspheres, and preferably contains hydrocarbons having 6 or fewer carbon atoms, as this increases the efficiency of the heat-expandable microspheres.

[0030] The content of the blowing agent in the heat-expandable microspheres of the present invention is defined as the percentage of the weight of the blowing agent encapsulated in the heat-expandable microspheres relative to the total weight of the heat-expandable microspheres. There are no particular limitations on the content of the blowing agent, but it is preferably 2 to 40% by weight, more preferably 4 to 35% by weight, even more preferably 5 to 30% by weight, and particularly preferably 6 to 25% by weight. When the encapsulation rate is within the above range, leakage of the blowing agent to the outside during thermal expansion tends to be less likely, and expandability tends to be improved.

[0031] The heat-expandable microspheres of the present invention can be produced by a method comprising the steps of dispersing an oily mixture containing a polymerizable component, a blowing agent, and a polymerization initiator in an aqueous dispersion medium and polymerizing the polymerizable component (hereinafter sometimes referred to as the polymerization step).

[0032] The polymerization initiator is not particularly limited, and examples thereof include peroxides, azo compounds, etc. Examples of peroxides include peroxydicarbonates such as diisopropyl peroxydicarbonate, di-sec-butyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, and dibenzyl peroxydicarbonate; diacyl peroxides such as dilauroyl peroxide and dibenzoyl peroxide; ketone peroxides such as methyl ethyl ketone peroxide and cyclohexanone peroxide; peroxyketals such as 2,2-bis(t-butylperoxy)butane; hydroperoxides such as cumene hydroperoxide and t-butyl hydroperoxide; dialkyl peroxides such as dicumyl peroxide and di-t-butyl peroxide; and peroxyesters such as t-hexyl peroxypivalate and t-butyl peroxyisobutyrate. Examples of azo compounds include 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-methylpropionate), 2,2'-azobis(2-methylbutyronitrile), and 1,1'-azobis(cyclohexane-1-carbonitrile).

[0033] The amount of the polymerization initiator to be added is not particularly limited, but in terms of achieving the effects of the present invention, it is preferably 0.05 to 10 parts by weight, more preferably 0.1 to 8 parts by weight, and even more preferably 0.2 to 5 parts by weight, relative to 100 parts by weight of the polymerizable component.

[0034] The aqueous dispersion medium used in the polymerization step is a medium containing water, such as ion-exchanged water, as its main component, for dispersing the oily mixture, and may further contain an alcohol, such as methanol, ethanol, or propanol, or a hydrophilic organic solvent, such as acetone. In the present invention, "hydrophilic" means a state in which the aqueous dispersion medium can be arbitrarily mixed with water. The amount of the aqueous dispersion medium used is not particularly limited, but is preferably 100 to 1,000 parts by weight per 100 parts by weight of the polymerizable component.

[0035] The aqueous dispersion medium may further contain an electrolyte. Examples of the electrolyte include sodium chloride, magnesium chloride, calcium chloride, sodium sulfate, magnesium sulfate, ammonium sulfate, and sodium carbonate. These electrolytes may be used alone or in combination of two or more. The content of the electrolyte is not particularly limited, but is preferably 0.1 to 50 parts by weight per 100 parts by weight of the aqueous dispersion medium.

[0036] The aqueous dispersion medium may contain at least one water-soluble compound selected from the group consisting of water-soluble 1,1-substituted compounds having a structure in which at least one hydrophilic functional group selected from a hydroxyl group, a carboxylic acid (salt) group, and a phosphonic acid (salt) group and a heteroatom are bonded to the same carbon atom, polyalkyleneimines having a structure in which an alkyl group substituted with at least one hydrophilic functional group selected from a carboxylic acid (salt) group and a phosphonic acid (salt) group is bonded to a nitrogen atom, water-soluble ascorbic acids, water-soluble polyphenols, water-soluble B vitamins, potassium dichromate, alkali metal nitrites, metal (III) halides, boric acid, and water-soluble phosphonic acids (salts). In the present invention, "water-soluble" means a state in which 1 g or more of the compound dissolves in 100 g of water. The amount of the water-soluble compound contained in the aqueous dispersion medium is not particularly limited, but is preferably 0.0001 to 1.0 part by weight, more preferably 0.0003 to 0.1 part by weight, and even more preferably 0.001 to 0.05 part by weight, relative to 100 parts by weight of the polymerizable component.

[0037] In addition to the electrolyte and water-soluble compound, the aqueous dispersion medium may contain a dispersion stabilizer or a dispersion stabilization aid. Examples of dispersion stabilizers include tribasic calcium phosphate, magnesium pyrophosphate obtained by metathesis, calcium pyrophosphate, colloidal silica, alumina sol, and magnesium hydroxide. These dispersion stabilizers may be used alone or in combination of two or more. The amount of dispersion stabilizer is not particularly limited, but is preferably 0.05 to 100 parts by weight, more preferably 0.2 to 70 parts by weight, per 100 parts by weight of the polymerizable component. Examples of dispersion stabilization aids include polymeric dispersion stabilization aids, and surfactants such as cationic surfactants, anionic surfactants, zwitterionic surfactants, and nonionic surfactants. These dispersion stabilization aids may be used alone or in combination of two or more.

[0038] The aqueous dispersion medium is prepared, for example, by blending water (ion-exchanged water) with, as necessary, an electrolyte, a water-soluble compound, a dispersion stabilizer, a dispersion stabilization assistant, etc. The pH of the aqueous dispersion medium during polymerization is appropriately determined depending on the types of the water-soluble compound, dispersion stabilizer, and dispersion stabilization assistant.

[0039] In the method for producing the heat-expandable microspheres of the present invention, polymerization may be carried out in the presence of sodium hydroxide and zinc chloride. In the method for producing the heat-expandable microspheres of the present invention, an oily mixture is suspended and dispersed in an aqueous dispersion medium so as to produce spherical oil droplets having a predetermined particle size.

[0040] Examples of methods for suspending and dispersing the oily mixture include general dispersion methods such as stirring with a homomixer (e.g., manufactured by Primix Corporation), methods using a static dispersing device such as a static mixer (e.g., manufactured by Noritake Engineering Co., Ltd.), membrane suspension, and ultrasonic dispersion. The dispersion in which the oily mixture is dispersed in the aqueous dispersion medium as spherical oil droplets is then heated to initiate suspension polymerization. It is preferable to stir the dispersion during the polymerization reaction, and the stirring may be gentle enough to prevent, for example, floating of the spherical oil droplets and settling of the heat-expandable microspheres after polymerization.

[0041] The polymerization temperature can be freely set depending on the type of polymerization initiator, but is preferably controlled within a range of 30 to 100°C, more preferably 40 to 90°C. The time for maintaining the reaction temperature is preferably about 1 to 20 hours. The initial polymerization pressure is not particularly limited, but is in the range of 0 to 5 MPa, more preferably 0.1 to 3 MPa, in gauge pressure.

[0042] The resulting slurry is filtered using a centrifuge, pressure press, vacuum dehydrator, or the like to obtain a wet powder with a moisture content of 10 to 50% by weight, preferably 15 to 45% by weight, and more preferably 20 to 40% by weight. The resulting wet powder is then dried using a tray dryer, indirect heating dryer, fluidized bed dryer, vacuum dryer, vibration dryer, flash dryer, or the like to obtain a dry powder. The moisture content of the resulting dry powder is preferably 8% by weight or less, more preferably 5% by weight or less. To reduce the content of ionic substances, the resulting wet or dry powder may be washed with water and / or redispersed, then refiltered and dried. The slurry may also be dried using a spray dryer, fluidized bed dryer, or the like to obtain a dry powder. The wet powder and dry powder can be selected appropriately depending on the intended use.

[0043] [Hollow Particles] The hollow particles of the present invention are expanded bodies obtained by thermally expanding the heat-expandable microspheres described above. The hollow particles are lightweight and exhibit excellent material properties when contained in compositions or molded articles. The hollow particles of the present invention are expanded bodies obtained by thermally expanding the heat-expandable microspheres having the specific properties described above, and exhibit excellent stability of specific gravity. Furthermore, yellowing may be suppressed.

[0044] The average particle size of the hollow particles of the present invention can be freely designed depending on the application and is not particularly limited, but is preferably 3 to 1,000 μm, more preferably 5 to 300 μm, even more preferably 10 to 200 μm, and particularly preferably 20 to 150 μm. The coefficient of variation (CV) of the particle size distribution of the hollow particles of the present invention is not particularly limited, but is preferably 40% or less, more preferably 35% or less. The coefficient of variation is preferably 10% or more, and more preferably 15% or more.

[0045] The true specific gravity of the hollow particles of the present invention is not particularly limited, but in terms of achieving the effects of the present invention, it is preferably 0.001 to 0.6 g / mL, more preferably 0.0015 to 0.4 g / mL, and even more preferably 0.002 to 0.3 g / mL. When the true specific gravity is 0.001 g / mL or more, the stability of the specific gravity tends to be improved. Furthermore, when the true specific gravity is 0.6 g / mL or less, the weight reduction effect tends to be improved.

[0046] The hollow particles of the present invention can be obtained by thermally expanding the above-described heat-expandable microspheres, preferably at a temperature of 100 to 400° C. The thermal expansion method is not particularly limited, and may be either a dry thermal expansion method or a wet thermal expansion method.

[0047] The hollow particles of the present invention may be composed of fine particles adhered to the outer surface of the shell. Such a form may be referred to as fine particle-adhered hollow particles hereinafter. The term "adhered" here means that the fine particles are simply adsorbed to the outer surface of the hollow particle's shell, or that the thermoplastic resin constituting the shell near the outer surface is melted by heating, causing the fine particles to sink into the outer surface of the hollow particle's shell and become fixed. The fine particles may have an irregular or spherical shape. When hollow particles are mixed with a base component to prepare a composition, the fine particles to be mixed into the composition may be adhered to the outer surface of the hollow particles before mixing.

[0048] The average particle size of the fine particles is also appropriately selected depending on the hollow particles constituting the particles, and is not particularly limited, but is preferably 0.001 to 30 μm, more preferably 0.005 to 25 μm, and even more preferably 0.01 to 20 μm. The average particle size of the fine particles is preferably 1 / 10 or less of the average particle size of the fine particle-coated hollow particles. Here, the average particle size refers to the average particle size of the primary particles.

[0049] Various types of fine particles can be used, and may be made of either inorganic or organic materials. Examples of the shape of the fine particles include spherical, needle-like, and plate-like. The organic material constituting the fine particles is not particularly limited, and examples thereof include metal soaps such as magnesium stearate, calcium stearate, zinc stearate, barium stearate, and lithium stearate; synthetic waxes such as polyethylene wax, lauric acid amide, myristic acid amide, palmitic acid amide, stearic acid amide, and hydrogenated castor oil; and organic polymers such as polyacrylamide, polyimide, nylon, polymethyl methacrylate, polyethylene, and polytetrafluoroethylene. The inorganic substance constituting the fine particles is not particularly limited, and examples thereof include talc, mica, bentonite, sericite, carbon black, molybdenum disulfide, tungsten disulfide, graphite fluoride, calcium fluoride, boron nitride, silica, alumina, mica, colloidal calcium carbonate, heavy calcium carbonate, calcium hydroxide, calcium phosphate, magnesium hydroxide, magnesium phosphate, barium sulfate, titanium dioxide, zinc oxide, ceramic beads, glass beads, quartz beads, etc. The inorganic and organic substances constituting the fine particles may be treated with a surface treatment agent such as a silane coupling agent, paraffin wax, fatty acid, resin acid, urethane compound, fatty acid ester, etc., or may be untreated.

[0050] When the hollow particles are microparticle-coated hollow particles, they are useful as coating compositions or adhesive compositions when incorporated into the compositions described below. Microparticle-coated hollow particles can be obtained, for example, by heating and expanding microparticle-coated heat-expandable microspheres. Examples of methods for producing microparticle-coated hollow particles include a process comprising the steps of: mixing heat-expandable microspheres with microparticles (a mixing process); and heating the mixture obtained in the mixing process to a temperature above the softening point to expand the heat-expandable microspheres and adhere microparticles to the outer surfaces of the resulting hollow particles (an adhering process).

[0051] The true specific gravity of the fine particle-coated hollow particles is not particularly limited, but is preferably 0.01 to 0.6 g / mL, more preferably 0.03 to 0.5 g / mL, even more preferably 0.05 to 0.4 g / mL, and particularly preferably 0.07 to 0.3 g / mL. When the true specific gravity is 0.01 g / mL or more, the durability of the hollow particles tends to be improved. When the true specific gravity is 0.6 g / mL or less, the weight reduction effect tends to be improved.

[0052] [Composition and Molded Article] The composition of the present invention contains at least one selected from the heat-expandable microspheres and hollow particles described above, and a base component. The base component is not particularly limited, and examples thereof include rubbers such as natural rubber, butyl rubber, silicone rubber, and ethylene-propylene-diene rubber (EPDM); thermosetting resins such as unsaturated polyester, epoxy resin, and phenolic resin; waxes such as polyethylene wax and paraffin wax; thermoplastic resins such as ethylene-vinyl acetate copolymer (EVA), ionomer, polyethylene, polypropylene, polyvinyl chloride (PVC), acrylic resin, thermoplastic polyurethane, acrylonitrile-styrene copolymer (AS resin), acrylonitrile-butadiene-styrene copolymer (ABS resin), polystyrene (PS), polyamide resins (such as nylon 6 and nylon 66), polycarbonate, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyacetal (POM), and polyphenylene sulfide (PPS). Examples of suitable base materials include: resins; thermoplastic elastomers such as olefin elastomers and styrene elastomers; bioplastics such as polylactic acid (PLA), cellulose acetate, polybutylene succinate (PBS), polyhydroxyalkanoate (PHA), and starch resins; sealing materials such as silicones, modified silicones, polysulfides, modified polysulfides, urethanes, acrylics, polyisobutylenes, and butyl rubbers; liquid components such as emulsions and plastisols of urethanes, ethylene-vinyl acetate copolymers, vinyl chlorides, and acrylics; inorganic materials such as cement, mortar, and cordierite; and organic fibers such as cellulose, kenaf, wheat bran, aramid fibers, phenolic fibers, polyester fibers, acrylic fibers, polyolefin fibers such as polyethylene and polypropylene, polyvinyl alcohol fibers, and rayon. These base materials may be used alone or in combination.

[0053] The composition of the present invention can be prepared by mixing at least one selected from heat-expandable microspheres and hollow particles with a base component. Alternatively, the composition obtained by mixing at least one selected from heat-expandable microspheres and hollow particles with a base component can be further mixed with another base component to prepare the composition of the present invention. In addition to the heat-expandable microspheres, hollow particles, and base component, the composition of the present invention may contain other components depending on the intended use.

[0054] The weight ratio of at least one selected from heat-expandable microspheres and hollow particles in the composition is not particularly limited, but is preferably 0.01 to 70 wt %, more preferably 0.05 to 60 wt %, even more preferably 0.1 to 50 wt %, and particularly preferably 0.3 to 40 wt %. When the weight ratio is within this range, a lightweight composition can be obtained that maintains the physical properties of the base component.

[0055] The composition of the present invention may be prepared by a conventionally known method, for example, by mechanically mixing the components uniformly using a mixer such as a homomixer, static mixer, Henschel mixer, tumbler mixer, planetary mixer, kneader, roll, mixing roll, mixer, single-screw kneader, twin-screw kneader, multi-screw kneader, etc. Examples of the composition of the present invention include a rubber composition, a molding composition, a coating composition, a clay composition, an adhesive composition, and a powder composition.

[0056] The composition of the present invention, particularly when it contains, together with heat-expandable microspheres, a compound and / or a thermoplastic resin having a melting point lower than the expansion-initiation temperature of the heat-expandable microspheres as a base component, can be used as a masterbatch for molding resins and / or rubbers. The thermoplastic resin constituting the base component contained in the masterbatch is not particularly limited, and examples thereof include waxes such as polyethylene wax and paraffin wax; thermoplastic resins such as ethylene-vinyl acetate copolymer (EVA), polyethylene, modified polyethylene, polypropylene, modified polypropylene, modified polyolefin, polyvinyl chloride (PVC), acrylic resin, thermoplastic polyurethane, acrylonitrile-styrene copolymer (AS resin), acrylonitrile-butadiene-styrene copolymer (ABS resin), polystyrene (PS), polycarbonate, polyethylene terephthalate (PET), and polybutylene terephthalate (PBT); ionomer resins such as ethylene-based ionomers, urethane-based ionomers, styrene-based ionomers, and fluorine-based ionomers; and thermoplastic elastomers such as olefin-based elastomers, styrene-based elastomers, and polyester-based elastomers, and these may be used alone or in combination of two or more.

[0057] The molding masterbatch is utilized in injection molding, extrusion molding, press molding, etc., and is suitably used as a bubble-introducing agent. The base component used in resin molding or rubber molding is not particularly limited as long as it is selected from the base components described above, and examples thereof include ethylene-vinyl acetate copolymer (EVA), polyethylene, modified polyethylene, polypropylene, modified polypropylene, modified polyolefin, polyvinyl chloride (PVC), acrylic resin, thermoplastic polyurethane, acrylonitrile-styrene copolymer (AS resin), acrylonitrile-butadiene-styrene copolymer (ABS resin), polystyrene (PS), polyamide resin (nylon 6, nylon 66, etc.), modified polyamide, polycarbonate, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyacetal (POM), ... Examples of such rubbers include phenylene sulfide (PPS), polyphenylene ether (PPE), modified polyphenylene ether, ionomer resin, olefin-based elastomer, styrene-based elastomer, polyester-based elastomer, polylactic acid (PLA), cellulose acetate, polybutylene succinate (PBS), polyhydroxyalkanoate (PHA), starch resin, natural rubber, isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), chloroprene rubber (CR), nitrile rubber (NBR), butyl rubber, silicone rubber, acrylic rubber, urethane rubber, fluororubber, and ethylene-propylene-diene rubber (EPDM), and these may be used alone or in combination of two or more.

[0058] The composition of the present invention may contain other components as described above, such as fibrous materials such as glass fiber, carbon fiber, and natural fiber; inorganic powders such as talc, titanium oxide, silica, and inorganic pigments; polymeric fine particles such as acrylic fine particles, styrene fine particles, urethane fine particles, and silicone fine particles; organic pigments; organic powders; flame retardants; and chemical foaming agents.

[0059] The molded article of the present invention is obtained by molding the composition described above, and exhibits little change in expansion ratio or specific gravity, excellent foaming stability, and is lightweight. Furthermore, yellowing may be suppressed. Examples of the molded article of the present invention include coating films and molded articles. The molded article of the present invention has improved physical properties such as light weight, porosity, sound absorption, heat insulation, low thermal conductivity, low dielectric constant, design, impact absorption, strength, and chipping resistance. In addition to these, effects such as stabilization against sink marks and warpage, reduced molding shrinkage, and dimensional stability are also expected. A molded article containing an inorganic substance as a substrate component can be further fired to obtain a ceramic filter, etc.

[0060] Examples of the heat-expandable microspheres of the present invention are described below. However, the present invention is not limited to these examples. In the following examples and comparative examples, "%" means "% by weight" and "parts" means "parts by weight" unless otherwise specified. Furthermore, hereinafter, heat-expandable microspheres may be simply referred to as "microspheres."

[0061] [Expansion start temperature of thermally expandable microspheres (T ｓ ) and maximum expansion temperature (T ｍａｘ ) DMA (DMA Q800 manufactured by TA Instruments) was used as the measuring device. 0.5 mg of microspheres was placed in an aluminum cup with a diameter of 6.0 mm and a depth of 4.8 mm, and an aluminum lid (diameter 5.6 mm, thickness 0.1 mm) was placed on top of the microsphere layer to prepare a sample. The sample height was measured while a force of 0.01 N was applied from above using a pressure probe. With a force of 0.01 N applied using the pressure probe, the sample was heated from 20°C to 350°C at a temperature increase rate of 10°C / min, and the displacement of the pressure probe in the vertical direction was measured. The temperature at which displacement in the forward direction began was defined as the expansion beginning temperature (T ｓ ) and the temperature at which the maximum displacement occurred was the maximum expansion temperature (T ｍａｘ )

[0062] [Measurement of average particle size (D50) and particle size distribution of heat-expandable microspheres] The average particle size (D50) and particle size distribution were measured using a laser diffraction / scattering particle size distribution analyzer (MT3000II) manufactured by Microtrac-Bell Co., Ltd. The D50 value measured on a volume basis was used as the average particle size.

[0063] [Method for producing thermoplastic resins (A1) and (A2)] 0.5 g of microspheres were placed in a stainless steel evaporating dish with a diameter of 80 mm and a depth of 15 mm, and 30 mL of tetrahydrofuran was added to uniformly disperse the microspheres. The dish was then left to stand at room temperature for 2 hours, allowing the microspheres to immerse in tetrahydrofuran. The tetrahydrofuran was then evaporated by heating at 110°C for 2 hours in a far-infrared dryer, producing the residue, Thermoplastic Resin A1. Meanwhile, a box with a flat bottom, 12 cm long, 13 cm wide, and 9 cm high, was made using aluminum foil, and 0.5 g of the microspheres were placed therein uniformly and covered with aluminum foil. This box was placed in a gear oven, and the maximum expansion temperature (T ｍａｘ The resulting mixture was heated at a temperature 20°C higher than the initial temperature for 10 minutes to produce a heat-treated product. 0.5 g of the resulting treated product was placed in a stainless steel evaporating dish with a diameter of 80 mm and a depth of 15 mm, and 30 mL of tetrahydrofuran was added to uniformly disperse the mixture. The mixture was then left to stand at room temperature for 2 hours, after which the treated product was immersed in tetrahydrofuran. The mixture was then heated in a far-infrared dryer at 110°C for 2 hours to evaporate the tetrahydrofuran, producing the residue, Thermoplastic Resin A2.

[0064] [glass transition temperature Tg ０ and Tg １ Measurement of the glass transition point Tg of each of the obtained thermoplastic resins A1 and A2 ０ , Tg １was measured in accordance with JIS K7121:2012. Specifically, the procedure was as follows. 10 mg of the obtained thermoplastic resin was placed in an aluminum cup with an inner diameter of 3.5 mm and a depth of 1.63 mm. An aluminum lid with a diameter of 2.88 mm and a thickness of 0.1 mm was placed on top of the thermoplastic resin and the lid was closed with a hand press to prepare a sample. Next, a PerkinElmer differential scanning calorimeter (Jade DSC) was used as the measuring device. The prepared sample was held at 60°C for 3 minutes, and then heated from 60°C to 300°C at a rate of 10°C / min to obtain a DSC curve. Alumina was used as the reference material. The intersection (mid-glass transition temperature) of the step-change portion of the DSC curve observed during the temperature rise process with the straight lines equidistant from each baseline in the vertical direction was taken as the glass transition point (Tg) of the thermoplastic resin.

[0065] [Method for evaluating expansion retention] A box with a flat bottom, 12 cm long, 13 cm wide, and 9 cm high, was made from aluminum foil, and 1.0 g of heat-expandable microspheres was placed evenly inside the box and covered with aluminum foil. The box was placed in a gear oven and measured for (1) the maximum expansion temperature (T ｍａｘ(1) The expanded hollow particles were heated for 4 minutes at three temperatures: (1) a temperature 10°C higher than the maximum expansion temperature; and (2) a temperature 10°C higher than the maximum expansion temperature. The expanded hollow particles were then heated for 4 minutes at each of these three temperatures to obtain an expanded body. The true specific gravity of the resulting expanded hollow particles was measured using the following measurement method. The true specific gravity was measured by the immersion method (Archimedes' method) using isopropyl alcohol in an atmosphere with an ambient temperature of 25°C and a relative humidity of 50%. Specifically, a 100 mL volumetric flask was emptied and dried, and the weight of the volumetric flask (WB1) was then weighed. The weighed volumetric flask was then filled with isopropyl alcohol exactly up to the meniscus, and the weight of the volumetric flask filled with 100 mL of isopropyl alcohol (WB2) was then weighed. The 100 mL volumetric flask was also emptied and dried, and the weight of the volumetric flask (WS1) was then weighed. Approximately 50 mL of particle sample was filled into the weighed volumetric flask, and the weight of the volumetric flask filled with the particle sample (WS2) was then weighed. The volumetric flask filled with the particle sample was then filled with isopropyl alcohol exactly up to the meniscus, taking care to prevent air bubbles from entering, and the weight (WS3) was then measured. The obtained WB1, WB2, WS1, WS2, and WS3 were then introduced into the following formula to calculate the true specific gravity (d) of the particle sample: d (g / mL) = {(WS2 - WS1) x (WB2 - WB1) / 100} / {(WB2 - WB1) - (WS3 - WS2)} The measured true specific gravity was evaluated based on the following evaluation criteria, with a score of 0 or higher being considered a pass. ◎: The true specific gravity of the hollow particles obtained at the heating temperature (1) is less than 0.02 g / mL, and the ratio of the true specific gravity of the hollow particles obtained at the heating temperature (3) to the true specific gravity of the hollow particles obtained at the heating temperature (1) ((3) / (1)) is less than 1.7, indicating excellent expandability and excellent suppression of changes in expandability over a wide temperature range. ◯: The ratio of the true specific gravity of the hollow particles obtained at the heating temperature (3) to the true specific gravity of the hollow particles obtained at the heating temperature (1) ((3) / (1)) is less than 1.7, indicating moderately excellent suppression of changes in expandability over a wide temperature range. ×: The ratio of the true specific gravity of the hollow particles obtained at the heating temperature (3) to the true specific gravity of the hollow particles obtained at the heating temperature (1) ((3) / (1)) is 1.7 or more, indicating failure to suppress changes in expandability over a wide temperature range.

[0066] Example 1: 60 parts of sodium chloride, 19 parts of colloidal silica (20% active ingredient), 0.6 parts of polyvinylpyrrolidone, 0.8 parts of an aqueous solution of ethylenediaminetetraacetic acid tetraNa salt (5% active ingredient), and 0.2 parts of an aqueous solution of aluminum chloride (10% active ingredient) were added to 230 parts of ion-exchanged water, and the pH of the resulting mixture was adjusted to 2.8-3.2 to prepare an aqueous dispersion medium. Separately, 35 parts of acrylic acid, 13 parts of methacrylic acid, 2 parts of glycidyl methacrylate (GMA), 50 parts of methyl methacrylate, 0.2 parts of PEG200# diacrylate (4EG-A), 1.5 parts of di(2-ethylhexyl) peroxydicarbonate (OPP), and 30 parts of isopentane were mixed to prepare an oily mixture. The aqueous dispersion medium and the oily mixture were mixed, and the resulting mixture was dispersed in a Clearmix (M Technique Co., Ltd.) at 15,000 rpm for 20 seconds to prepare a suspension. The suspension was transferred to a 1.5-liter pressure reactor and purged with nitrogen. The initial reaction pressure was adjusted to 0.3 MPa, and polymerization reaction was carried out at 60°C for 15 hours with stirring at 100 rpm. After polymerization, the product was filtered and dried to obtain heat-expandable microspheres 1. The physical properties of the resulting heat-expandable microspheres are shown in Table 1.

[0067] Examples 2 to 10 and Comparative Examples 1 to 3 Heat-expandable microspheres were obtained in the same manner as in Example 1, except for changing the reaction conditions as shown in Tables 1 and 2. The physical properties of the obtained heat-expandable microspheres are shown in Tables 1 and 2. The following abbreviations are used in Tables 1 and 2: HOP: 2-hydroxypropyl methacrylate GMA: glycidyl methacrylate 4EG-A: PEG200# diacrylate OPP: di(2-ethylhexyl) peroxydicarbonate

[0068]

[0069]

[0070] Example A: First, a masterbatch containing the microspheres 1 obtained in Example 1 was prepared. Specifically, 50 parts of ethylene-vinyl acetate copolymer (melting point 61°C) and 50 parts of the microspheres 1 were mixed and kneaded in a pressure kneader at 75°C for 1 minute. The kneaded mixture was then extruded and shaped into pellets to prepare a masterbatch. Next, 6 parts by weight of the masterbatch was mixed with 94 parts by weight of a styrene-based thermoplastic elastomer (AR-SC-15, specific gravity 0.89, manufactured by Aronkasei Co., Ltd.). The resulting composition was fed into the hopper of an injection molding machine (J85AD-110H, clamping force 85 tons, manufactured by The Japan Steel Works, Ltd.), melt-kneaded, and injection-molded by the short-shot method to obtain a plate-shaped molded product. The molding conditions were as follows: injection filling time: 1 second, injection speed: 200 mm / sec, mold surface temperature: 30°C, and molded product thickness: 7.0 mm. The molding temperature is the maximum expansion temperature (T ｍａｘ (1) Injection molding was performed at three temperatures: (1) a temperature 10°C higher than the maximum expansion temperature; and (2) a temperature 10°C higher than the maximum expansion temperature. The physical properties of the resulting molded articles were evaluated. The results are shown in Table 3. The specific gravity of the molded articles was measured by the following procedure.

[0071] Example B: Plate-shaped molded articles were obtained by injection molding in the same manner as in Example A, except that the heat-expandable microspheres used were microspheres 9 and the molding temperature was changed to the maximum expansion temperature of microspheres 9, a temperature 10°C higher than the maximum expansion temperature, and a temperature 20°C higher than the maximum expansion temperature. The physical properties of the obtained molded articles were evaluated in the same manner as in Example A. The results are shown in Table 3.

[0072] [Measurement of specific gravity] Measurement was carried out using a Shimadzu top-pan electronic analytical balance (AX200, manufactured by Shimadzu Corporation) in the solid specific gravity measurement mode.

[0073]

[0074] Examples 1 to 10 confirm that heat-expandable microspheres that satisfy the above condition 1 exhibit little change in expansion properties, whereas heat-expandable microspheres that do not satisfy the above condition 1 exhibit significant change in expansion properties.

Claims

1. An outer shell containing a thermoplastic resin (A), and thermally expandable microspheres containing a blowing agent encapsulated in the outer shell and vaporizing by heating, the thermally expandable microspheres satisfying the following condition 1. Condition 1: The glass transition point (Tg ０ ) of the thermoplastic resin (A1) obtained by immersing the thermally expandable microspheres in tetrahydrofuran, and the glass transition point (Tg １ ) of the thermoplastic resin (A2) obtained by immersing a treated product obtained by heating the thermally expandable microspheres at a temperature 20 ° C higher than its maximum expansion temperature for 10 minutes in tetrahydrofuran have the relationship of the following formula (I). (Tg １ ) - (Tg ０ ) > 0 ° C Formula (I) 2. The thermally expandable microspheres according to claim 1, wherein the thermoplastic resin (A) is a polymer of polymerizable components, and the polymerizable components include a carboxyl group-containing monomer (a1).

3. The thermally expandable microspheres according to claim 2, wherein the polymerizable components further include a monomer (a2) containing a group that reacts with a carboxyl group.

4. The thermally expandable microspheres according to claim 2 or 3, wherein the weight ratio of the monomer (a1) in the polymerizable components is 20 to 70% by weight.

5. The thermally expandable microspheres according to claim 3 or 4, wherein the weight ratio of the monomer (a2) in the polymerizable components is 0.1 to 10% by weight.

6. The thermally expandable microspheres according to any one of claims 2 to 5, wherein the weight ratio of the nitrile-based monomer (a3) in the polymerizable components is 40% by weight or less.

7. Hollow particles which are expanded bodies of the thermally expandable microspheres according to any one of claims 1 to 6.

8. A composition comprising at least one selected from the thermally expandable microspheres according to any one of claims 1 to 6 and the hollow particles according to claim 7 and a base material component.

9. A molded article obtained by molding the composition according to claim 8.

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