Microspheres, resin composition for molding, and foam molded body

Abstract

Provided are microspheres capable of achieving a higher expansion ratio than in the past, a resin composition for molding that contains the microspheres, and a foam molded body in which the resin composition for molding is used.　Microspheres including an outer shell that contains a polymer (A) and a foaming agent (B) that is sealed within the outer shell are used, the microspheres having a foaming start temperature of 120-150°C, a median diameter of 40-60 μm, and a density after heating at 170°C for 3 minutes of 0.007 g / mL or less.　The polymer (A) preferably contains a copolymer that includes structural units (a1) derived from acrylonitrile, and the amount of the structural units (a1) derived from acrylonitrile is 55-65 parts by mass per 100 parts by mass of all structural units of the copolymer. The foaming agent (B) preferably includes a component (b1) having a boiling point of 95°C or lower, and the amount of the component (b1) having a boiling point of 95°C or lower is 67 mass% or greater relative to the total mass of the foaming agent (B).

Description

Microspheres, molding resin composition, and foam molded article

[0001] The present invention relates to microspheres, a molding resin composition containing the microspheres, and a foam-molded article using the molding resin composition.

[0002] Thermally expandable microspheres are microcapsules containing a volatile blowing agent encapsulated within a polymer shell. Taking advantage of their ability to expand upon heating, thermally expandable microspheres are used in foam molding in a variety of fields, including polymer materials, paints, and inks. In particular, the typical foaming temperature for foam molding of rubber and elastomers is around 170°C. Furthermore, microspheres with a high foaming initiation temperature are required to suppress foaming during processing, such as blending with the base resin. Minimizing shrinkage due to gas release after foaming is also essential. Furthermore, with the recent rise in environmental awareness, there is a growing demand for not only lighter weight but also resource and energy conservation, necessitating the development of microspheres with a higher expansion ratio.

[0003] For example, Patent Document 1 discloses microspheres having a foaming temperature of about 170°C and a foaming initiation temperature of about 130°C.

[0004] Japanese Patent Application Laid-Open No. 2019-173018

[0005] The microspheres disclosed in Patent Document 1 have a high acrylonitrile (AN) content to suppress gas leakage. However, although AN has high gas barrier properties, it also has a high melt viscosity, which results in a low expansion ratio. To address this issue, lowering the AN content facilitates expansion, but conventional microspheres have a small particle size, which makes them prone to gas leakage, and this creates problems such as limited process temperatures and methods.

[0006] The present invention has been made in view of the above problems, and aims to provide microspheres that exhibit a higher expansion ratio than conventional ones, a molding resin composition containing the microspheres, and a foam molded article using the molding resin composition.

[0007] As a result of extensive research to solve the above problems, the present inventors have discovered that in microspheres in which the AN content of the outer shell resin is within a predetermined range and the foaming initiation temperature is 120°C or higher and 150°C or lower, by increasing the particle size to 40 μm or higher and 60 μm or lower, a high foaming ratio can be obtained when heated at 170°C, thereby completing the present invention.

[0008] Aspects of the present invention relate to the following microspheres, molding resin compositions, and foamed molded articles. In this specification, the term "microspheres" refers to "thermally expandable microspheres" that expand when heated to form foam particles (foams).

[0009] [1] Microspheres comprising an outer shell containing a polymer (A) and a blowing agent (B) encapsulated in the outer shell, wherein the microspheres have a foaming initiation temperature of 120°C to 150°C, a median diameter of 40 μm to 60 μm, and a density of 0.007 g / ml or less after heating at 170°C for 3 minutes. [2] The microspheres according to [1], wherein the polymer (A) contains a copolymer containing a structural unit (a1) derived from acrylonitrile, and the content of the structural unit (a1) derived from acrylonitrile is 55 parts by mass to 65 parts by mass relative to 100 parts by mass of all structural units of the copolymer, and the blowing agent (B) contains a component (b1) having a boiling point of 95°C or less, and the content of the component (b1) having a boiling point of 95°C or less is 67% by mass or more relative to the total mass of the blowing agent (B). [3] The microspheres according to [2], wherein the component (b1) having a boiling point of 95°C or less is isopentane. [4] A molding resin composition comprising the microspheres according to any one of [1] to [3]. [5] A foam-molded article using the molding resin composition according to [1] to [3].

[0010] According to the present invention, it is possible to provide microspheres having an expansion initiation temperature of 120°C or higher and 150°C or lower that exhibit a high expansion ratio when heated at 170°C, a molding resin composition containing the microspheres, and a foam molded article using the molding resin composition.

[0011] <Microspheres> The microspheres comprise an outer shell containing a polymer (A) and a blowing agent (B) encapsulated within the outer shell. The microspheres have a foaming initiation temperature of 120°C or higher and 150°C or lower and a median diameter of 40 μm or higher and 60 μm or lower. The density of the microspheres after heating at 170°C for 3 minutes is 0.007 g / ml or lower.

[0012] Essential and optional components contained in the microspheres are described below.

[0013] <Outer Shell> The outer shell contains a polymer (A). From the viewpoint of excellent gas barrier properties, the polymer (A) forming the outer shell preferably contains a copolymer containing a structural unit (a1) derived from acrylonitrile.

[0014] From the viewpoint of adjusting the foaming initiation temperature of the microspheres to 120°C or higher and 150°C or lower, the copolymer preferably contains structural units other than the structural unit (a1) derived from acrylonitrile (hereinafter also referred to as "other structural units"). Examples of monomers that provide other structural units include methacrylonitrile, α-chloroacrylonitrile, α-ethoxyacrylonitrile, fumaronitrile, vinyl chloride, vinylidene chloride, vinyl acetate, chloroprene, isoprene, butadiene, N-phenylmaleimide, N-naphthylmaleimide, N-cyclohexylmaleimide, methylmaleimide, (meth)acrylic acid, crotonic acid, maleic anhydride, methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, dicyclopentenyl acrylate, isobornyl methacrylate, styrene, α-methylstyrene, and halogenated styrenes, with methacrylonitrile and methyl methacrylate being particularly preferred. These may be used alone or in combination of two or more. In this specification, "(meth)acrylic" means both "acrylic" and "methacrylic." In addition, in this specification, the above-mentioned acrylonitrile and monomers that provide other structural units may be collectively referred to as "polymerizable monomers."

[0015] As the copolymer containing the other structural units, from the viewpoints of high gas barrier property and adjusting the softening point so that the foaming initiation temperature is 120°C or higher and 150°C or lower, a copolymer containing structural units derived from acrylonitrile, methacrylonitrile, and methyl methacrylate is preferred.

[0016] In the copolymer, the content of the structural unit (a1) derived from acrylonitrile is preferably 55 parts by mass or more and 65 parts by mass or less, and more preferably 56 parts by mass or more and 64 parts by mass or less, relative to 100 parts by mass of all structural units of the copolymer.

[0017] <Crosslinkable Monomer> By using a crosslinkable monomer, the copolymer may contain a crosslinked structure derived from the crosslinkable monomer. The crosslinkable monomer is a compound having two or more carbon-carbon double bonds. Examples of the crosslinkable monomer include divinylbenzene, ethylene glycol di(meth)acrylate [ethylene glycol di(meth)acrylate], diethylene glycol di(meth)acrylate [diethylene glycol di(meth)acrylate], triethylene glycol di(meth)acrylate, allyl (meth)acrylate, triallyl isocyanate, triacryl formal, trimethylolpropane tri(meth)acrylate, 1,3-butyl glycol di(meth)acrylate, pentaerythritol tri(meth)acrylate, and pentaerythritol tetra(meth)acrylate.

[0018] The content of the crosslinkable monomer is preferably 0.01 parts by mass or more and 5 parts by mass or less, more preferably 0.02 parts by mass or more and 3 parts by mass or less, and even more preferably 0.03 parts by mass or more and 2 parts by mass or less, relative to the total mass of the polymerizable monomers.

[0019] <Polymerization initiator> The copolymer may contain a structural unit derived from a polymerization initiator. Examples of the polymerization initiator include dialkyl peroxide, diacyl peroxide, peroxydicarbonate, and azo compounds. The polymerization initiator is usually used in a proportion of 0.0001 parts by mass or more and 3 parts by mass or less relative to the total mass of the polymerizable monomers.

[0020] <Blowing Agent (B)> The blowing agent (B) is a substance that turns into a gas when heated. As the blowing agent (B), hydrocarbons having a boiling point corresponding to the foaming initiation temperature can be used, and examples thereof include hydrocarbons such as ethane, ethylene, propane, propene, n-butane, isobutane, butene, isobutene, isopentane, n-pentane, neopentane, hexane, octane, isooctane, heptane, nonane, decane, undecane, dodecane, isododecane, petroleum ether, and isoparaffin mixtures; CCl ３ F, CCl ２ F ２ , CClF ３ , CClF ２ -CClF ２ and tetraalkylsilanes such as tetramethylsilane, trimethylethylsilane, trimethylisopropylsilane, trimethyl-n-propylsilane, etc. These may be used either alone or in combination of two or more.

[0021] Among these, hydrocarbons having 4 to 12 carbon atoms are preferred, and for example, isobutane, isopentane, n-pentane, hexane, isooctane, heptane, nonane, decane, undecane, dodecane, and isododecane are preferred.

[0022] When the hydrocarbons mentioned above are used as the blowing agent, it is preferable to use a component (b1) having a boiling point of 95° C. or less (hereinafter, sometimes referred to as a "low-boiling component"), from the viewpoint that the vapor pressure is likely to increase. Among the preferred hydrocarbons mentioned above, the low-boiling components are isobutane, isopentane, n-pentane, and hexane, and among these, isopentane and hexane, which can be handled as liquids at room temperature, are more preferable.

[0023] The content of the component (b1) having a boiling point of 95°C or less is preferably 67% by mass or more, more preferably 70% by mass or more and 100% by mass or less, even more preferably 80% by mass or more and 100% by mass or less, and particularly preferably 90% by mass or more and 100% by mass or less, based on the total mass of the blowing agent (B).

[0024] Furthermore, from the viewpoint of increasing the foaming temperature, a component (b2) having a boiling point exceeding 95°C (hereinafter, sometimes referred to as a "high-boiling component") can also be used. Of the preferred hydrocarbons, the high-boiling component is preferably a hydrocarbon having 7 to 12 carbon atoms, such as heptane, octane, isooctane, nonane, decane, undecane, dodecane, and isododecane. Of these, octane and isooctane, which have 8 carbon atoms, are more preferred.

[0025] When the component (b1) and the component (b2) are used in combination, the combination of the component (b1) and the component (b2) is preferably isopentane and isooctane, respectively.

[0026] When the component (b1) and the component (b2) are used in combination, the mass ratio (b1 / b2) of the component (b1) to the component (b2) is preferably 3 / 1 or more and 7 / 1 or less, and more preferably 4 / 1 or more and 6 / 1 or less.

[0027] The content of the blowing agent (B) is preferably 5 parts by mass or more and 50 parts by mass or less, more preferably 10 parts by mass or more and 40 parts by mass or less, and even more preferably 15 parts by mass or more and 30 parts by mass or less, relative to 100 parts by mass of the polymer (A).

[0028] In this specification, the particle size of microspheres is defined as the median diameter. The median diameter can be determined from the volume-based particle size distribution obtained by a wet laser diffraction / scattering method. The median diameter is sometimes referred to as "D50." From the viewpoint of obtaining a high expansion ratio, the median diameter of the microspheres is 40 μm or more and 60 μm or less, preferably 40 μm or more and 55 μm or less, and more preferably 40 μm or more and 50 μm or less. If it exceeds 60 μm, the expansion diameter during expansion molding will become too large, resulting in poor appearance.

[0029] The particle size (median size) of microspheres can be adjusted by the type and size of the agitator (such as a homogenizer) used for agitation and mixing during production, or the type and amount of the dispersion stabilizer described below. For example, reducing the rotation speed of the agitator tends to increase the particle size. Also, the greater the amount of dispersion stabilizer, the larger the particle size tends to be.

[0030] The foaming initiation temperature of the microspheres is 120°C or higher and 150°C or lower, preferably 125°C or higher and 140°C or lower, from the viewpoint of the processing temperature in the process before foam molding, such as kneading with the base material. This temperature range suppresses foaming of the microspheres before foam molding. The maximum foaming temperature of the microspheres is preferably 160°C or higher and 190°C or lower, more preferably 162°C or higher and 180°C or lower.

[0031] The foaming initiation temperature and maximum foaming temperature of microspheres are preferably measured using a thermomechanical analyzer (TMA). Specifically, 0.2 to 0.3 mg of a microsphere sample is placed in a container, and the temperature is increased under conditions of a load of 0.1 N and a temperature increase rate of 5°C / min. The height change of the portion occupied by the sample is continuously measured in a nitrogen atmosphere. In this case, the temperature at which the height change begins is the foaming initiation temperature (Ts), and the temperature at which the height change is greatest is the maximum foaming temperature (Tmax).

[0032] The density of the microspheres after heating at 170°C for 3 minutes is 0.007 g / ml or less, preferably 0.006 g / ml or less, and more preferably 0.005 g / ml or less. The expansion ratio of the microspheres can be calculated by dividing the density of the unfoamed microspheres by the density of the foamed microspheres after heating. Since the density of the unfoamed microspheres does not change significantly within the range of the polymer (A) and the foaming agent (B), a low density after heating indicates a high expansion ratio.

[0033] The density of the unfoamed microspheres and the density of the foamed material can be determined by Archimedes' method.

[0034] <Method for producing microspheres> Microspheres can be produced by suspension polymerization of the polymerizable monomers used as raw materials for the copolymer described above together with the blowing agent (B) in an aqueous dispersion medium containing a dispersion stabilizer. The specific production method is not particularly limited, and known methods can be used.

[0035] Examples of the dispersion stabilizer include silica such as colloidal silica, calcium phosphate, magnesium hydroxide, aluminum hydroxide, ferric hydroxide, barium sulfate, calcium sulfate, sodium sulfate, calcium oxalate, calcium carbonate, barium carbonate, magnesium carbonate, etc. The dispersion stabilizer is usually used in a proportion of 0.1 parts by mass or more and 20 parts by mass or less per 100 parts by mass of the total amount of the polymerizable monomers.

[0036] In addition to the dispersion stabilizer, a co-stabilizer such as a condensation product of diethanolamine and an aliphatic dicarboxylic acid may be added. When colloidal silica is used as the dispersion stabilizer, it is preferable to use a condensation product of diethanolamine and an aliphatic dicarboxylic acid as the co-stabilizer.

[0037] At least one compound selected from the group consisting of alkali metal nitrite, stannous chloride, stannic chloride, water-soluble ascorbic acids, and boric acid may be added as a polymerization aid. When suspension polymerization is performed in the presence of these compounds, aggregation of polymer particles does not occur during polymerization, the polymer does not adhere to the polymerization vessel wall, and microspheres can be produced stably while efficiently removing heat generated by polymerization. Among alkali metal nitrite salts, sodium nitrite or potassium nitrite is preferred in terms of availability and cost. These compounds are typically used in an amount of 0.001 to 1 part by weight, preferably 0.01 to 0.1 parts by weight, per 100 parts by weight of the total polymerizable monomers.

[0038] <Uses of Microspheres> Taking advantage of the above-mentioned properties of forming foam particles, microspheres are used, for example, as weight-reducing agents, moldability improving agents (sink mark prevention agents), heat insulating agents, sound absorbing agents, etc. Specifically, microspheres are added to polymer materials such as synthetic resins (thermoplastic resins and thermosetting resins) and rubbers to obtain foamed molded articles.

[0039] <Foam Molded Article> A foam molded article can be obtained by a method using a mixture of simply mixing microspheres and a base resin, a mixture of masterbatch pellets and a base resin, or a molding resin composition obtained by melt-kneading microspheres and a base resin. The foam molded article is lightweight due to foam molding using the microspheres, and can be designed as needed. The shape of the foam molded article is not particularly limited, and may be any of a sheet, rod, pipe, block, and any other shape.

[0040] The method for producing the foamed molded article is not particularly limited, and molding methods such as extrusion molding, injection molding, etc. The microspheres may be introduced into the molding machine as powder or as masterbatch pellets, and then dry-blended with other raw materials, or a molding resin composition may be used.

[0041] <Base Resin> The base resin is at least one selected from the group consisting of thermoplastic resin (A), thermoplastic elastomer (TPE), and thermosetting resin. The thermoplastic resin (A) is not particularly limited, and examples thereof include polypropylene (PP), low-density polyethylene (LDPE), ethylene-α-olefin copolymer (LLDPE), polyvinyl chloride (PVC), ethylene-vinyl acetate copolymer (EVA), ethylene-methyl methacrylate copolymer (EMMA), polystyrene (PS), and acrylonitrile-butadiene-styrene copolymer (ABS). Thermoplastic elastomer (TPE) refers to a substance that exhibits the properties of an elastomer, i.e., vulcanized rubber, at room temperature and thermoplastic properties at high temperatures. The thermoplastic elastomer is not particularly limited, and examples thereof include olefin-based thermoplastic elastomers (TPO, TPV), styrene-based thermoplastic elastomers (TPS), and urethane-based thermoplastic elastomers (TPU). The thermosetting resin is not particularly limited, and examples thereof include ethylene-propylene-diene rubber (EPDM), silicone rubber, and epoxy resin.

[0042] <Masterbatch Pellets> The masterbatch pellets refer to a resin composition containing a high concentration of microspheres in a resin composition of a thermoplastic resin (B) and microspheres. The use of masterbatch pellets can enhance the dispersibility of the microspheres. The proportion of microspheres contained in the masterbatch pellets can be 10% by mass or more and 70% by mass or less, preferably 20% by mass or more and 65% by mass or less, and more preferably 30% by mass or more and 60% by mass or less. The thermoplastic resin (B) used in the masterbatch pellets is not particularly limited as long as it is a resin that can be processed under conditions that do not cause foaming of the microspheres, and examples thereof include low-density polyethylene (LDPE), ethylene-α-olefin copolymer (LLDPE), ethylene-vinyl acetate copolymer (EVA), and ethylene-methyl methacrylate copolymer (EMMA).

[0043] <Molding Resin Composition> The method for producing the molding resin composition includes a step of kneading the microspheres with the base resin before foam molding. At this time, processing aids such as flame retardants, plasticizers, antioxidants, and colorants may be added and kneaded together. The kneading method is not particularly limited, and examples thereof include extrusion molding (compounding). A specific example of extrusion molding is a method in which the microspheres are blended with at least one resin selected from the group consisting of the thermoplastic resin and the thermosetting resin, and pellets are produced by extrusion molding.

[0044] The present invention will be described in more detail below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0045] Examples 1 and 2 and Comparative Examples 1 to 3 (1) Preparation of aqueous dispersion medium An aqueous dispersion medium was prepared by mixing 4.4 parts of colloidal silica (20 wt % aqueous dispersion), 0.44 parts of a diethanolamine-adipic acid condensation product (50 wt % aqueous solution, acid value = 78 mg KOH / g), 0.06 parts of sodium nitrite, 89 parts of sodium chloride, and 300 parts of water. A 5 wt % aqueous solution of hydrochloric acid was added to this aqueous dispersion medium to adjust the pH to 3.5.

[0046] (2) Preparation of Polymerizable Mixtures 1 to 2 and 4 to 6 Acrylonitrile, methacrylonitrile, methyl methacrylate, isopentane, isooctane, diethylene glycol dimethacrylate, and 2,2'-azobisisobutyronitrile were mixed in the parts by mass shown in Table 1 to prepare Polymerizable Mixtures 1 to 2 and 4 to 6.

[0047] (3) Suspension Polymerization: The aqueous dispersion medium prepared above and each of Polymerizable Mixtures 1-2 and 4-6 were mixed and stirred using a homogenizer to form fine droplets of Polymerizable Mixtures 1-2 and 4-6 in the aqueous dispersion medium. Each aqueous dispersion medium containing the fine droplets of the polymerizable mixture was placed in a polymerization vessel equipped with a stirrer and heated in a hot water bath at 60°C for 13.5 hours and then at 70°C for 10.5 hours to allow the reaction to proceed. Eight and a half hours after the start of polymerization, 12.15 parts by mass of a hydrochloric acid solution at pH 3.5 and 0.1 parts by mass of 3-methacryloxypropyltrimethoxysilane, a silane coupling agent having a polymerizable reactive group, were dispersed in water at pH 3.5 to form a 10 wt% aqueous solution, and the resulting solution was added to the polymerization vessel. After polymerization, the resulting slurry containing microspheres was filtered, washed with water, and dried to obtain the microspheres of Examples 1-2 and Comparative Examples 1-3.

[0048] Example 3 Microspheres were obtained in the same manner as in Examples 1 and 2 and Comparative Examples 1 to 3, except that in the preparation of the aqueous dispersion medium, colloidal silica (20 wt % aqueous dispersion) was used in an amount of 2.8 parts and the rotation speed of the stirrer during stirring and mixing was reduced to 47% of that in Example 1.

[0049] Comparative Example 4 Microspheres were obtained in the same manner as in Examples 1 and 2 and Comparative Examples 1 to 3, except that the amount of colloidal silica (20% by weight aqueous dispersion) was changed to 3.3 parts in the preparation of the aqueous dispersion medium.

[0050] <Evaluation> The particle diameter (D50), expansion initiation temperature (Ts), maximum expansion temperature (Tmax), expanded particle density, and expansion ratio of the obtained microspheres of the Examples and Comparative Examples were measured according to the following methods.

[0051] (Measurement of particle diameter (D50)) The particle diameters of the microspheres of the Examples and Comparative Examples were measured by a laser diffraction / scattering method (based on JIS Z8825) using a particle size distribution analyzer (SALD2300, manufactured by Shimadzu Corporation). The samples used were prepared by adding the microspheres of the Examples and Comparative Examples to 20 ml of water and dispersing them by ultrasonic treatment for 2 minutes. The results are shown in Table 1.

[0052] (Measurement of foaming initiation temperature (Ts) and maximum foaming temperature (Tmax)) The foaming initiation temperature and maximum foaming temperature of the microspheres in the examples and comparative examples were measured using a thermomechanical analyzer (TMA / SDTA840, manufactured by Mettler Toledo K.K.). Specifically, 0.2 to 0.3 mg of sample was placed in a container, and the temperature was raised under conditions of a load of 0.1 N and a temperature rise rate of 5°C / min, and the height displacement of the part occupied by the sample was continuously measured in a nitrogen atmosphere. The temperature at which the height displacement started was taken as the foaming initiation temperature (Ts), and the temperature at which the height displacement was greatest was taken as the maximum foaming temperature (Tmax).

[0053] (Measurement of Expansion Ratio) The expansion ratio was determined by dividing the density of the unfoamed material by the density of the foam. The density of the unfoamed material and the density of the foam were measured by Archimedes' method.

[0054] Density in unfoamed state: 30 g of the microspheres of the Examples and Comparative Examples was placed in a 100 ml measuring flask and diluted to 100 ml with isopropanol. The amount of isopropanol required for diluting was calculated from the difference between the sample weight and the weight after diluting, and the density in the unfoamed state was determined using the density of isopropanol.

[0055] Foam density: 0.2 g of microspheres from the Examples and Comparative Examples and 1.0 g of silicone oil were weighed into an aluminum cup, mixed thoroughly, and heated for 3 minutes in a gear oven heated to a predetermined temperature (160°C, 170°C, 180°C) to obtain a foam. The obtained foam was placed in a 100 ml measuring flask and diluted to 100 ml with isopropanol. The amount of isopropanol required to make the solution was calculated from the difference between the sample weight and the weight after dilution, and the density of the foam was determined using the density of isopropanol.

[0056] Based on the obtained expansion ratio at 170°C, the expansion ratio was judged into three levels: ○ (expansion ratio: good), △ (expansion ratio: same as conventional), and × (expansion ratio: poor). The criteria for the judgment were ○ for an expansion ratio of 200 times or more, △ for an expansion ratio of more than 100 times and 200 times or less, and × for an expansion ratio of less than 100 times.

[0057]

[0058] From Table 1, it can be seen that when microspheres having an AN content in the shell resin within a predetermined range and a median diameter (D50) of 40 μm or more and 60 μm or less are used, a high expansion ratio is exhibited.

Claims

1. Microspheres comprising an outer shell containing a polymer (A) and a blowing agent (B) encapsulated within the outer shell, wherein the foaming initiation temperature is 120°C or higher and 150°C or lower, the median diameter is 40 μm or higher and 60 μm or lower, and the density after heating at 170°C for 3 minutes is 0.007 g / ml or lower.

2. The microspheres according to claim 1, wherein the polymer (A) contains a copolymer containing a structural unit (a1) derived from acrylonitrile, and the content of the structural unit (a1) derived from acrylonitrile is 55 parts by mass or more and 65 parts by mass or less, based on 100 parts by mass of all structural units of the copolymer; and the blowing agent (B) contains a component (b1) having a boiling point of 95°C or less, and the content of the component (b1) having a boiling point of 95°C or less is 67% by mass or more, based on the total mass of the blowing agent (B).

3. The microspheres according to claim 2, wherein the component (b1) having a boiling point of 95°C or less is isopentane.

4. A molding resin composition comprising the microspheres according to any one of claims 1 to 3.

5. A foamed molded article using the microspheres according to any one of claims 1 to 3.

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