Heat-expandable microspheres and their uses

Abstract

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. Heat-expandable microspheres comprising an outer shell containing a thermoplastic resin (A) and a blowing agent encapsulated in the outer shell and vaporized by heating, the heat-expandable microspheres satisfying the following condition 1: Condition 1: The glass transition temperature (Tg0) of a thermoplastic resin (A1) obtained by immersing heat-expandable microspheres in tetrahydrofuran satisfies the following formula (I): and the glass transition temperature (Tg1) of a thermoplastic resin (A2) obtained by heating the heat-expandable microspheres for 10 minutes at a temperature 20°C higher than their maximum expansion temperature and then immersing the treated product in tetrahydrofuran. (Tg1)-(Tg0)>0℃ Formula (I)

Description

[Technical Field]

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

[0002] Heat-expandable microspheres (heat-expandable microcapsules), which are fine particles with a thermoplastic resin outer shell and a foaming agent inside, have the characteristic of expanding when heated. These heat-expandable microspheres are used in a wide range of applications, for example, by blending them with a substrate. Heat treatment during molding causes the heat-expandable microspheres to expand simultaneously with molding, thereby contributing not only to weight reduction but also to the molded article and providing it with design features, cushioning properties, etc.

[0003] Patent Document 1 discloses such heat-expandable microspheres, which have an outer shell made of a thermoplastic resin obtained by polymerizing a polymerizable component that essentially contains a methacrylate ester monomer and a carboxyl group-containing monomer, and in which a nitrile monomer is contained in an amount of 0 to 30 parts by weight per 100 parts by weight of the total amount of the methacrylate 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 a thermally expandable microcapsule in which a volatile expanding agent is encapsulated as a core agent in a shell made of a polymer, the shell being formed by polymerizing a monomer composition containing a nitrile-based monomer, a monomer having an amide group, and a compound having a glycidyl group in the molecule, the monomer having the amide group containing at least one selected from acrylamide and methacrylamide, and the monomer composition containing 0.9 to 20% by weight of the monomer having the amide group and 0.1 to 15% by weight of the compound having the glycidyl group. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2015 / 17829 [Patent Document 2] Japanese Patent Application Publication No. 2015-172190 Summary of the Invention [Problem to be solved by the invention]

[0005] The heat-expandable microspheres disclosed in Patent Document 1 are nearly spherical, have excellent expansion properties, and are easy to work with when mixed with a resin. 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 expansion molding. However, when the heat-expandable microspheres disclosed in the above patent documents are expanded, the expansion properties change significantly over a wide temperature range, and when such heat-expandable microspheres are used to produce molded articles, 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. [Means for solving the problem]

[0007] As a result of extensive research, the present inventors have found that specific heat-expandable microspheres can solve the above problems, and have arrived at the present invention. That is, 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 (Tg0) of a thermoplastic resin (A1) obtained by immersing heat-expandable microspheres in tetrahydrofuran satisfies the following formula (I): and the glass transition temperature (Tg1) of a thermoplastic resin (A2) obtained by heating the heat-expandable microspheres for 10 minutes at a temperature 20°C higher than their maximum expansion temperature and then immersing the treated product in tetrahydrofuran. (Tg1)-(Tg0)>0℃ Formula (I)

[0008] The heat-expandable microspheres of the present invention preferably further satisfy at least one of the following requirements 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) in the polymerizable component is 20 to 70% by weight. 4) The weight ratio of the monomer (a2) in the polymerizable component is 0.1 to 10% by weight. 5) The weight ratio of the nitrile monomer (a3) ​​in the polymerizable component is 40% by weight 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 above heat-expandable microspheres and hollow particles, and a base component. The molded article of the present invention is obtained by molding the above composition. [Effects of the Invention]

[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 lightweight because they are expanded versions of the heat-expandable microspheres. The composition of the present invention contains at least one selected from the heat-expandable microspheres and hollow particles, and therefore allows stable production of lightweight molded articles. The molded article of the present invention is lightweight because it is obtained by molding the above composition. DETAILED DESCRIPTION OF THE INVENTION

[0012] [Thermally expandable microspheres] The heat-expandable microspheres of the present invention contain 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. Condition 1: The glass transition temperature (Tg0) of a thermoplastic resin (A1) obtained by immersing heat-expandable microspheres in tetrahydrofuran satisfies the following formula (I): and the glass transition temperature (Tg1) of a thermoplastic resin (A2) obtained by heating the heat-expandable microspheres for 10 minutes at a temperature 20°C higher than their maximum expansion temperature and then immersing the treated product in tetrahydrofuran. (Tg1)-(Tg0)>0℃ Formula (I)

[0014] The Tg0 indicates the glass transition temperature of the thermoplastic resin constituting the shell of unheated, unexpanded heat-expandable microspheres. On the other hand, the Tg1 indicates the glass transition temperature of the thermoplastic resin constituting the shell of the expanded microspheres obtained when the expanded microspheres are heated for 10 minutes at a temperature 20°C higher than the temperature at maximum expansion. When these glass transition temperatures satisfy the formula (I), the cohesive energy of the molecules (polymers) constituting the thermoplastic resin in the shell is large, which is thought to enable the shell to withstand the increase in internal pressure caused by vaporization of the blowing agent over a wide temperature range, resulting in little change in expandability over a wide temperature range. Tg0 and Tg1 are determined 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. It is particularly preferably 7 to 35°C.

[0015] The expansion starting 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 starting temperature is 120°C or higher, changes in the expansion properties of the heat-expandable microspheres tend to be suppressed. When the expansion starting 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 expansibility 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 starting 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, and more preferably 10% or more, and even more preferably 15% or more. The average particle size and particle size distribution of the heat-expandable microspheres are determined by 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, more preferably 10 to 200, and even more preferably 15 to 200. An expansion ratio of 5 or more tends to result in a lightweight molded article. On the other hand, an expansion ratio of 200 or less tends to result in a molded article with a good appearance. The heat-expandable microspheres of the present invention may be prevented from yellowing when expanded by heating.

[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 a 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 a 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; vinyl halide monomers such as vinyl chloride; vinylidene halide 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; 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] Although the polymerizable component is not particularly limited, it is preferable to include a carboxyl group-containing monomer (hereinafter sometimes referred to as monomer (a1)) as a monomer component, since this improves heat resistance and solvent resistance, and also makes it easier to obtain heat-expandable microspheres that satisfy the above formula (I). When the polymerizable component contains the 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 expandability. A weight ratio of 70 wt% or less tends to improve expandability and solvent resistance. Satisfying the above range also facilitates the production of heat-expandable microspheres that satisfy 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, since this is believed to further improve the cohesive energy of the polymer and further suppress changes in expandability. It 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, but examples thereof include a methylol group, a hydroxyl group, an amino group, an epoxy group, an isocyanate group, etc., and may be composed of one or more types. Furthermore, the monomer containing a group reactive with a carboxyl group is not particularly limited, but 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 the above range, it tends to be possible to achieve both expansion and suppression of changes in expansion. Furthermore, satisfying the above 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-based monomer having no group reactive with a carboxyl group, which is preferable in that the expansion of the heat-expandable microspheres can be adjusted. When the polymerizable component contains, as a monomer component, a (meth)acrylic acid-based monomer that does not have a group that reacts with a carboxyl group, the weight ratio of the (meth)acrylic acid-based monomer that does not have a group that reacts 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, which is preferable in that the heat resistance of the heat-expandable microspheres is improved. When the polymerizable component contains, as a monomer component, a (meth)acrylamide-based monomer that does not have a group that reacts with a carboxyl group, the weight ratio of the (meth)acrylamide-based monomer that does not have a group that reacts 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, which improves the density of the outer shell of the heat-expandable microspheres and allows 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; polyalkylene glycol di(meth)acrylates such as diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, PEG#200 di(meth)acrylate, PEG#400 di(meth)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 to 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)acryl Examples of crosslinking agents include difunctional, trifunctional, and tetrafunctional or higher functional monomers such as methyltrimethylolpropane tri(meth)acrylate, methyltrimethylolpropane tetra(meth)acrylate, methyltrimethylolpropane tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, etc. These crosslinking agents may be used alone or in combination.

[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 when heated and is encapsulated in the outer shell of the heat-expandable microspheres, which allows the entire microsphere to exhibit thermal expandability (the property of expanding when heated). 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; Examples include hydrocarbons such as distillates; halides of 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 produce gas when heated, such as azodicarbonamide, N,N'-dinitrosopentamethylenetetramine, and 4,4'-oxybis(benzenesulfonylhydrazide). The blowing agent may be composed of one type of compound or a mixture of two or more types of compounds. The blowing agent may be linear, branched, or alicyclic, with aliphatic blowing agents being preferred. The blowing agent preferably contains a hydrocarbon having 8 or more carbon atoms, which increases the maximum expansion temperature of the heat-expandable microspheres, and preferably contains a hydrocarbon having 6 or less carbon atoms, which increases the efficiency of the expansion 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. The content of the blowing agent is not particularly limited, but 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, the blowing agent is less likely to leak to the outside during thermal expansion, 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, but examples thereof include peroxides and azo compounds. 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, per 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 a 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 medium can be arbitrarily mixed with water. The amount of the aqueous dispersion medium used is not particularly limited, but is preferably 100 to 1000 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, sodium carbonate, etc. 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 relative to 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 solubility means a state in which at least 1 g 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] The aqueous dispersion medium may contain a dispersion stabilizer or a dispersion stabilization aid in addition to the electrolyte and the water-soluble compound. Examples of the dispersion stabilizer include tribasic calcium phosphate, magnesium pyrophosphate obtained by a metathesis method, calcium pyrophosphate, colloidal silica, alumina sol, magnesium hydroxide, etc. These dispersion stabilizers may be used alone or in combination of two or more. The amount of the dispersion stabilizer to be added 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 the dispersion stabilization aid include surfactants such as polymer-type dispersion stabilization aids, cationic surfactants, anionic surfactants, zwitterionic surfactants, nonionic surfactants, etc. 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 an electrolyte, a water-soluble compound, a dispersion stabilizer, a dispersion stabilization assistant, etc., as necessary. The pH of the aqueous dispersion medium during polymerization is determined appropriately depending on the types of the water-soluble compound, dispersion stabilizer, and dispersion stabilization assistant.

[0039] In the production method of the heat-expandable microspheres of the present invention, the 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 prepare spherical oil droplets having a predetermined particle size.

[0040] Examples of methods for suspending and dispersing an oily mixture include general dispersion methods such as stirring with a homomixer (e.g., manufactured by Primix Corporation), methods using a static dispersion device such as a static mixer (e.g., manufactured by Noritake Engineering Co., Ltd.), membrane suspension methods, and ultrasonic dispersion methods. The suspension polymerization is then initiated by heating the dispersion in which the oily mixture is dispersed as oil globules in the aqueous dispersion medium. During the polymerization reaction, the dispersion is preferably stirred gently, for example, to a degree sufficient to prevent the floating of the oil globules and the 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 the range of 30 to 100°C, and more preferably 40 to 90°C. The reaction temperature is preferably maintained for about 1 to 20 hours. The initial polymerization pressure is not particularly limited, but is in the range of 0 to 5 MPa, and more preferably 0.1 to 3 MPa, in gauge pressure.

[0042] The obtained slurry is filtered using a centrifuge, pressure press, vacuum dehydrator, etc. 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 obtained wet powder is then dried using a tray dryer, indirect heating dryer, fluidized bed dryer, vacuum dryer, vibration dryer, flash dryer, etc. to obtain a dry powder. The moisture content of the obtained dry powder is preferably 8% by weight or less, more preferably 5% by weight or less. To reduce the content of ionic substances, the obtained wet or dry powder may be washed with water and / or redispersed, then re-filtered and dried. Alternatively, the slurry may be dried using a spray dryer, fluidized bed dryer, or the like to obtain a dry powder. The wet or 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 have excellent stability of specific gravity and may be inhibited from yellowing.

[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 1000 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, and more preferably 10% or more, and even 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 heat-expandable microspheres described above, 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 attached to the outer surface of the shell, and such a configuration may be referred to as fine particle-attached hollow particles hereinafter. The term "adhesion" as used herein means that the fine particles may simply be adsorbed onto the outer surface of the shell of the hollow particle, 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 shell of the hollow particle and become fixed thereto. The shape of the fine particles may be either amorphous or spherical. When hollow particles are mixed with a base component to form a composition, it is also possible to attach fine particles to be mixed into the composition 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. The shape of the fine particles may be spherical, needle-like, or plate-like. The organic substance constituting the microparticles is not particularly limited, but 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, and quartz beads. The inorganic or organic material 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, or fatty acid ester, or may be untreated.

[0050] When the hollow particles are fine particle-coated hollow particles, the fine particle-coated hollow particles are blended as hollow particles in a composition described below, and are useful as a coating composition or adhesive composition. The microparticle-coated hollow particles can be obtained, for example, by heating and expanding microparticle-coated heat-expandable microspheres. The method for producing the microparticle-coated hollow particles includes a step of mixing heat-expandable microspheres with microparticles (mixing step), and a step of heating the mixture obtained in the mixing step to a temperature above the softening point to expand the heat-expandable microspheres and to cause microparticles to adhere to the outer surfaces of the obtained hollow particles (adhesion step).

[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. If the true specific gravity is 0.01 g / mL or more, the durability of the hollow particles tends to be improved. If 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 material 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; and thermoplastics 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 resin (nylon 6, nylon 66, etc.), polycarbonate, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyacetal (POM), and polyphenylene sulfide (PPS). Examples of suitable substrate 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 substrate components 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. The composition of the present invention may contain other components in addition to the heat-expandable microspheres, hollow particles and base component depending on the intended use.

[0054] The weight proportion 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%. A weight proportion within this range allows for a lightweight composition 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, or multi-screw kneader. 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 an air bubble introducing agent. The base material component used in resin molding or rubber molding is not particularly limited as long as it is selected from the above-mentioned base material components, 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), polyolefin, etc. 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 light weight. Also, yellowing may be suppressed. Examples of the molded article of the present invention include coating films, molded articles, etc. 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, designability, impact absorption, strength, and chipping resistance. In addition to these, effects such as stabilization against sink marks and warpage, reduction of molding shrinkage, and dimensional stability are also expected. The molded body containing an inorganic substance as a base component can be further fired to obtain a ceramic filter or the like. [Example]

[0060] Examples of the heat-expandable microspheres of the present invention will now be described in detail. 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] [Temperature at which thermally expandable microspheres begin to expand (T s ) and maximum expansion temperature (T max ) A 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. The sample was heated from 20°C to 350°C at a temperature increase rate of 10°C / min while a force of 0.01 N was applied using the pressure probe, 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 onset temperature (T s ) and the temperature at which the maximum displacement occurred was the maximum expansion temperature (T max ) was decided.

[0062] [Measurement of mean 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 Microtrack Bell Co., Ltd. The D50 value measured by volumetric standard measurement 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 disperse the microspheres uniformly. The dish was then left to stand at room temperature for 2 hours to immerse the microspheres in tetrahydrofuran. The dish was then heated in a far-infrared dryer at 110°C for 2 hours to evaporate the tetrahydrofuran, producing the residue, Thermoplastic Resin A1. On the other hand, a flat-bottomed box measuring 12 cm in length, 13 cm in width, and 9 cm in height was made from aluminum foil, 0.5 g of microspheres was placed evenly in the box, and the box was covered with aluminum foil. The box was placed in a gear oven and heated to the maximum expansion temperature (T max ) for 10 minutes at a temperature 20°C higher than the initial temperature 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] [Measurement of glass transition temperatures Tg0 and Tg1] The glass transition temperatures Tg0 and Tg1 of the obtained thermoplastic resins A1 and A2 were measured in accordance with JIS K7121:2012. Specifically, the measurement was carried out 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, and 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, and the prepared sample was held at 60°C for 3 minutes, 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. Among the DSC curves observed during the temperature rise process, the intersection (mid-glass transition temperature) between the step-change partial curve and the straight line equidistant from each baseline in the vertical direction was taken as the glass transition point (Tg) of the thermoplastic resin.

[0065] [Expansion maintenance evaluation method] A flat-bottomed box measuring 12 cm in length, 13 cm in width, and 9 cm in height 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 then placed in a gear oven and heated to (1) the maximum expansion temperature (T max The expanded bodies were obtained by heating for 4 minutes at three temperatures: (1) a temperature 10°C higher than the maximum expansion temperature, and (2) a temperature 20°C higher than the maximum expansion temperature. The true specific gravity of the expanded hollow particles was measured using the following 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, dried, and 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, dried, and then weighed. 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 not to introduce air bubbles, and the weight (WS3) was then weighed. The obtained WB1, WB2, WS1, WS2, and WS3 were then introduced into the following equation to calculate the true specific gravity (d) of the particle sample. d(g / mL)={(WS2-WS1)×(WB2-WB1) / 100} / {(WB2-WB1)-(WS3-WS2)} The measured true specific gravity was judged based on the following evaluation criteria, with ◯ or higher being considered acceptable. ◎: 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 expansion properties and excellent suppression of changes in expansion properties over a wide temperature range. Good: The ratio ((3) / (1)) 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) is less than 1.7, and the hollow particles are somewhat excellent at suppressing changes in expansion over a wide temperature range. ×: The ratio ((3) / (1)) 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) is 1.7 or more, and the expansion change cannot be suppressed over a wide temperature range.

[0066] Example 1 To 230 parts of ion-exchanged water, 60 parts of sodium chloride, 19 parts of colloidal silica containing 20% ​​active ingredient, 0.6 parts of polyvinylpyrrolidone, 0.8 parts of an aqueous solution of ethylenediaminetetraacetic acid tetrasodium salt containing 5% active ingredient, and 0.2 parts of an aqueous solution of aluminum chloride containing 10% active ingredient were added, and the pH of the resulting mixture was adjusted to 2.8 to 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 oil 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. This 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 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. In Tables 1 and 2, the following abbreviations are used: HOP: 2-hydroxypropyl methacrylate GMA: Glycidyl methacrylate 4EG-A:PEG200#diacrylate OPP: Di(2-ethylhexyl) peroxydicarbonate

[0068] [Table 1]

[0069] [Table 2]

[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, and the kneaded mixture was extruded and shaped into pellets to prepare a masterbatch. Next, 6 parts by weight of the obtained masterbatch was mixed with 94 parts by weight of a styrene-based thermoplastic elastomer (AR-SC-15, specific gravity 0.89, manufactured by Aron Kasei Co., Ltd.) to prepare a composition. The obtained composition was supplied to the hopper of an injection molding machine (J85AD-110H, mold 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 body thickness: 7.0 mm. The molding temperature was set at the maximum expansion temperature (T maxInjection molding was performed at three temperatures: (1) a temperature 10°C higher than the maximum expansion temperature; and (2) a temperature 20°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 body 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 in Example A 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] Measurements were performed using a Shimadzu top-pan electronic analytical balance (AX200, manufactured by Shimadzu Corporation) in solid specific gravity measurement mode.

[0073] [Table 3]

[0074] Examples 1 to 10 confirm that heat-expandable microspheres that satisfy the above condition 1 exhibit little change in expandability. On the other hand, it has been confirmed that heat-expandable microspheres that do not satisfy the above condition 1 undergo large changes in expandability.

Claims

1. Heat-expandable microspheres comprising an outer shell containing a thermoplastic resin (A) and a blowing agent encapsulated in the outer shell and vaporized by heating, the thermoplastic resin (A) is a polymer of a polymerizable component, the polymerizable component contains a carboxyl group-containing monomer (a1) and a monomer (a2) containing a group reactive with a carboxyl group, the weight ratio of the monomer (a1) in the polymerizable component is 29.94 to 70% by weight, and the weight ratio of the monomer (a2) in the polymerizable component is 0.5 to 8% by weight, the weight ratio of the nitrile monomer (a3) ​​in the polymerizable component is 40% by weight or less, Heat-expandable microspheres satisfying the following condition 1: Condition 1: A thermoplastic resin (A1) is obtained by adding 30 mL of tetrahydrofuran to 0.5 g of heat-expandable microspheres, uniformly dispersing the microspheres, allowing the mixture to stand at room temperature for 2 hours, immersing the microspheres in tetrahydrofuran, and then evaporating the tetrahydrofuran. The glass transition point (Tg0) of the thermoplastic resin (A1) is then obtained. A thermoplastic resin (A2) is obtained by adding 30 mL of tetrahydrofuran to 0.5 g of a treated product obtained by heating the heat-expandable microspheres for 10 minutes at a temperature 20°C higher than their maximum expansion temperature, uniformly dispersing the treated product in tetrahydrofuran, allowing the mixture to stand at room temperature for 2 hours, immersing the treated product in tetrahydrofuran, and then evaporating the tetrahydrofuran. The glass transition point (Tg1) of the thermoplastic resin (A2) satisfies the following formula (I): (Tg1)-(Tg0)>0℃ Formula (I) 2. The heat-expandable microspheres according to claim 1, wherein the group reactive with the carboxyl group is at least one selected from the group consisting of a hydroxyl group and an epoxy group.

3. The heat-expandable microspheres according to claim 1, wherein the monomer (a1) comprises at least one selected from acrylic acid and methacrylic acid.

4. 3. The heat-expandable microspheres according to claim 1, wherein the polymerizable component further comprises a monomer having at least two polymerizable carbon-carbon double bonds.

5. Hollow particles, which are expanded bodies of the heat-expandable microspheres according to claim 1.

6. A composition comprising at least one selected from the heat-expandable microspheres of claim 1 or 2 and the hollow particles of claim 5, and a base component.

7. A molded article obtained by molding the composition according to claim 6.

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