Hollow particle, polymer composition, and polymer molded body

Abstract

Provided is a hollow particle comprising a shell containing a resin and a hollow part surrounded by the shell, wherein the porosity is 45-95%, and the shell polymer constituting the resin contains a unit derived from an aromatic vinyl compound (A) in which one vinyl group and one or more functional groups (a) represented by general formula (a) are directly bonded to an aromatic ring.　-General formula (a): -OR (In general formula (a), R is a hydrogen atom, a C1-6 alkyl group, an alkali metal atom, or an acetyl group.)

Description

Hollow particles, polymer composition and polymer molded article

[0001] The present invention relates to hollow particles, and more particularly to hollow particles that have excellent dielectric properties and can suppress deterioration of the dielectric properties under high temperature conditions.

[0002] Hollow particles, such as hollow resin particles produced by polymerizing polymerizable monomers, are particles having a cavity inside the particle, and are used as additives (additives added to resins for molding) for molded articles such as electronic materials, light reflectors, heat insulating materials, and sound insulating materials.

[0003] As a technology relating to such hollow particles, for example, Patent Document 1 discloses hollow resin particles having a shell portion and a hollow portion surrounded by the shell portion, and having a residual ethylenically unsaturated group rate of 1% to 20% and used in a resin composition for a semiconductor member.

[0004] Patent Document 2 also describes hollow particles having a shell containing a resin and a hollow portion surrounded by the shell, the porosity being 50% or more, the shell containing, as the resin, a polymer containing 91% by mass or more of hydrocarbon monomer units and 50% by mass or more of crosslinkable monomer units, at least a part of the hydrocarbon monomer units being crosslinkable hydrocarbon monomer units, the residual double bond ratio of the polymer being 30.0% or less, and the dielectric loss tangent at a frequency of 10 GHz being 3.00×10 －３ The following hollow particles are disclosed:

[0005] International Publication No. WO 2022 / 130939 International Publication No. WO 2023 / 106307

[0006] However, the hollow resin particles disclosed in Patent Document 1 suffer from a significant decrease in dielectric properties (dielectric constant and dielectric loss tangent) under high temperature conditions. Furthermore, although the hollow particles disclosed in Patent Document 2 have a reduced dielectric loss tangent at high frequencies, there is a need for further improvement in the dielectric properties, particularly for suppression of the decrease in the dielectric properties under high temperature conditions.

[0007] An object of the present invention is to provide hollow particles that have excellent dielectric properties and can suppress deterioration of the dielectric properties under high temperature conditions.

[0008] The present inventors have conducted studies to achieve the above-mentioned object, and have found that the above-mentioned object can be achieved by using a shell polymer constituting the resin in hollow particles having a shell containing a resin and a hollow portion surrounded by the shell, the shell polymer containing a unit derived from a specific aromatic vinyl compound (A), and by controlling the porosity within a predetermined range, thereby completing the present invention.

[0009] That is, the present invention provides the following hollow particles, polymer compositions, and polymer molded articles. [1] Hollow particles having a shell containing a resin and a hollow portion surrounded by the shell, the hollow particles having a porosity of 45 to 95%, and the shell polymer constituting the resin contains units derived from an aromatic vinyl compound (A) in which one vinyl group and one or more functional groups (a) represented by the following general formula (a) are directly bonded to an aromatic ring: -OR (a) (In general formula (a), R is a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkali metal atom, or an acetyl group.) [2] Hollow particles according to [1], in which the content of the units derived from the aromatic vinyl compound (A) in the shell polymer is 10 to 50 mass%. [3] Hollow particles according to [1] or [2], in which the volume average particle size is 1 to 50 μm. [4] Hollow particles according to any one of [1] to [3], in which the content of hydrocarbon monomer units in the shell polymer is 80 mass% or more. [5] The hollow particles according to any one of [1] to [4], wherein the aromatic vinyl compound (A) is a styrene compound having one vinyl group and one or more functional groups (a) directly bonded to a benzene ring. [6] The hollow particles according to [5], wherein the aromatic vinyl compound (A) is at least one styrene compound selected from the group consisting of a styrene compound (A1) represented by the following general formula (A1), a styrene compound (A2) represented by the following general formula (A2), and a styrene compound (A3) represented by the following general formula (A3): (In general formulas (A1) to (A3), R １ ~R ５are each independently a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkali metal atom, or an acetyl group.) [7] The hollow particles according to any one of [1] to [6], wherein the number of functional groups (a) directly bonded to the aromatic rings in the aromatic vinyl compound (A) is two. [8] A polymer composition comprising the hollow particles according to any one of [1] to [7], and a matrix polymer. [9] The polymer composition according to [8], wherein the matrix polymer is at least one thermosetting resin selected from the group consisting of phenolic resins, melamine resins, epoxy resins, polyurethane resins, thermosetting modified polyphenylene ether resins, thermosetting polyimide resins, benzoxazine resins, urea resins, allyl resins, maleimide resins, and unsaturated polyester resins.

[10] The polymer composition according to [9], wherein the matrix polymer is at least one thermosetting resin selected from the group consisting of epoxy resins, thermosetting modified polyphenylene ether resins, thermosetting polyimide resins, and maleimide resins.

[11] The polymer composition according to any one of [8] to

[10] , further comprising a flame retardant.

[12] A polymer molded product comprising the hollow particles according to any one of [1] to [7] and a matrix polymer.

[0010] According to the present invention, hollow particles having excellent dielectric properties and capable of suppressing deterioration of the dielectric properties under high temperature conditions can be provided.

[0011] <Hollow Particles> The hollow particles of the present invention are hollow particles having a shell containing a resin and a hollow portion surrounded by the shell, and have a porosity of 45 to 95%, and the shell polymer constituting the resin contains units derived from an aromatic vinyl compound (A) described below.

[0012] The shell of the hollow particles of the present invention contains a resin composed of a shell polymer. In the present invention, the shell polymer contains units derived from an aromatic vinyl compound (A) in which one vinyl group and one or more functional groups (a) represented by the following general formula (a) are directly bonded to an aromatic ring. Hereinafter, this aromatic vinyl compound (A) may be referred to as an "OR group-containing aromatic vinyl compound (A)": -OR (a) (In general formula (a), R is a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkali metal atom, or an acetyl group.)

[0013] The OR group-containing aromatic vinyl compound (A) used in the present invention is a compound containing an aromatic ring, and having one vinyl group and one or more functional groups (a) directly bonded to the aromatic ring. In the present invention, it is preferable to use a biologically derived raw material as the OR group-containing aromatic vinyl compound (A).

[0014] Examples of the aromatic ring contained in the OR group-containing aromatic vinyl compound (A) include aromatic hydrocarbon rings such as a benzene ring, a biphenyl ring, a naphthalene ring, an azulene ring, an anthracene ring, a phenanthrene ring, a pyrene ring, a chrysene ring, a naphthacene ring, a triphenylene ring, an o-terphenyl ring, an m-terphenyl ring, a p-terphenyl ring, an acenaphthene ring, a coronene ring, a fluorene ring, a fluoranthrene ring, a pentacene ring, a perylene ring, a pentaphene ring, a picene ring, and a pyranthrene ring; and aromatic heterocycles such as an oran ring, a thiophene ring, a pyridine ring, a pyridazine ring, a pyrimidine ring, a pyrazine ring, a triazine ring, an oxadiazole ring, a triazole ring, an imidazole ring, a pyrazole ring, a thiazole ring, an indole ring, a benzimidazole ring, a benzothiazole ring, a benzoxazole ring, a quinoxaline ring, a quinazoline ring, a phthalazine ring, a benzofuran ring, a dibenzofuran ring, a benzothiophene ring, a dibenzothiophene ring, and a carbazole ring. The OR group-containing aromatic vinyl compound (A) preferably has only one of the above aromatic rings.

[0015] Among these, the aromatic ring is preferably an aromatic hydrocarbon ring, and more preferably a benzene ring, from the viewpoint of achieving higher levels of mechanical strength, porosity, dielectric properties, and heat resistance of the hollow particles.

[0016] One or more functional groups (a) are directly bonded to the aromatic ring in the OR group-containing aromatic vinyl compound (A). The functional groups (a) are groups represented by the general formula (a): -OR (in general formula (a), R is a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkali metal atom, or an acetyl group).

[0017] The alkyl group having 1 to 6 carbon atoms represented by R may be linear or branched, or may contain a cyclic structure. Specific examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a t-butyl group, an n-pentyl group, an isopentyl group, a neopentyl group, a 1-methylpentyl group, an n-hexyl group, and an isohexyl group.

[0018] The number of carbon atoms in the alkyl group having 1 to 6 carbon atoms represented by R is not particularly limited as long as it is 1 to 6, but is preferably 1 to 4, more preferably 1 to 3, still more preferably 1 or 2 (R is a methyl group or an ethyl group), and particularly preferably 1 (R is a methyl group).

[0019] As the alkali metal atom represented by R, Li, Na and K are preferred.

[0020] As R, from the viewpoint of achieving a higher level of mechanical strength, porosity, dielectric properties, and heat resistance of the hollow particles, an alkyl group having 1 to 6 carbon atoms is preferred, a methyl group and an ethyl group are preferred, and a methyl group is more preferred.

[0021] The number of functional groups (a) directly bonded to aromatic rings in the OR group-containing aromatic vinyl compound (A) is not particularly limited as long as it is 1 or more, but is preferably 1 to 3, more preferably 1 or 2, and even more preferably 2. When the number of functional groups (a) is within the above range, the mechanical strength, porosity, dielectric properties, and heat resistance of the hollow particles are all achieved at higher levels, and in particular, deterioration of the dielectric properties under more severe conditions (for example, in a high-temperature environment of 140°C or higher) is suppressed.

[0022] When a plurality of functional groups (a) are directly bonded to the aromatic ring in the OR group-containing aromatic vinyl compound (A), the plurality of functional groups (a) may be the same or different from one another. In this case, from the viewpoint of more efficiently achieving the effects of the present invention, it is preferable that the plurality of functional groups (a) are the same.

[0023] The aromatic ring in the OR group-containing aromatic vinyl compound (A) may have a substituent other than the vinyl group and the functional group (a). Examples of such a substituent include a halogen atom, a cyano group, an alkyl group, an alkenyl group, a halogenated alkyl group, an N,N-dialkylamino group, a nitro group, an aldehyde group, a carboxy group, and a sulfo group. It is preferable that the aromatic ring in the OR group-containing aromatic vinyl compound (A) does not have a substituent other than the vinyl group and the functional group (a).

[0024] The molecular weight of the OR group-containing aromatic vinyl compound (A) is not particularly limited, but is preferably 120 to 300, more preferably 125 to 240, even more preferably 130 to 200, and particularly preferably 140 to 180. When the molecular weight of the OR group-containing aromatic vinyl compound (A) is within the above range, the mechanical strength, porosity, dielectric properties, and heat resistance of the hollow particles can all be achieved at even higher levels.

[0025] The OR group-containing aromatic vinyl compound (A) is preferably a styrene compound having one vinyl group and one or more functional groups (a) directly bonded to a benzene ring. Specifically, the OR group-containing aromatic vinyl compound (A) is preferably at least one styrene compound selected from the group consisting of a styrene compound (A1) represented by the following general formula (A1), a styrene compound (A2) represented by the following general formula (A2), and a styrene compound (A3) represented by the following general formula (A3):

[0026] (In general formulas (A1) to (A3), R １ ~R ５ are each independently a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkali metal atom, or an acetyl group.

[0027] R in general formulas (A1) to (A3)１ ~R ５ correspond to R in general formula (a). １ ~R ５ Specific examples of R include the same as those mentioned above as specific examples of R, and preferred examples are also the same.

[0028] Among these, from the viewpoint of achieving a higher level of mechanical strength, porosity, dielectric properties, and heat resistance of the hollow particles and, in particular, suppressing deterioration of the dielectric properties under more severe conditions (for example, in a high-temperature environment of 140°C or higher), the OR group-containing aromatic vinyl compound (A) is preferably at least one styrene compound selected from the group consisting of the styrene compound (A1) and the styrene compound (A2), and more preferably the styrene compound (A1).

[0029] The content of units derived from the OR group-containing aromatic vinyl compound (A) relative to all monomer units in the shell polymer is not particularly limited, but is preferably 5 to 80% by mass, more preferably 10 to 65% by mass, even more preferably 10 to 50% by mass, particularly preferably 15 to 40% by mass, and most preferably 30 to 40% by mass. When the content of units derived from the OR group-containing aromatic vinyl compound (A) is within the above range, the mechanical strength, porosity, dielectric properties, and heat resistance of the hollow particles are all achieved at higher levels, and in particular, deterioration of the dielectric properties under more severe conditions (e.g., high-temperature environments of 140°C or higher) is suppressed. Furthermore, when the content of units derived from the OR group-containing aromatic vinyl compound (A) is within the above range, breakage of the hollow particles is suppressed, and the effects of the hollow particles of the present invention are more efficiently achieved.

[0030] The shell polymer is a polymer used to form the shell of the hollow particles, and is usually obtained by polymerizing a polymerizable monomer. In the present invention, a polymerizable monomer containing an OR group-containing aromatic vinyl compound (A) is used.

[0031] The shell polymer is preferably obtained by polymerizing a crosslinkable monomer and a non-crosslinkable monomer (including an OR group-containing aromatic vinyl compound (A)) as polymerizable monomers. That is, the shell polymer preferably contains crosslinkable monomer units and non-crosslinkable monomer units (including units derived from the OR group-containing aromatic vinyl compound (A)). Here, the crosslinkable monomer is a monomer that has two or more polymerizable functional groups and forms crosslinked bonds in the resin by polymerization reaction. Furthermore, the non-crosslinkable monomer is a polymerizable monomer that has only one polymerizable functional group.

[0032] The crosslinking monomer is generally a compound having two or more ethylenically unsaturated bonds as polymerizable functional groups, and includes crosslinking hydrocarbon monomers and heteroatom-containing crosslinking monomers.

[0033] The crosslinkable hydrocarbon monomer is not particularly limited, but examples thereof include divinylbenzene, divinyldiphenyl, divinylnaphthalene, 1,3-pentadiene, 1,4-pentadiene, 1,5-hexadiene, and 1,7-octadiene, and among these, divinylbenzene is preferred.

[0034] The heteroatom-containing crosslinkable monomer is not particularly limited, and examples thereof include bifunctional heteroatom-containing crosslinkable monomers such as diallyl phthalate, allyl (meth)acrylate (meaning allyl acrylate and / or allyl methacrylate; the same applies hereinafter), ethylene glycol di(meth)acrylate, and pentaerythritol di(meth)acrylate; and trifunctional or higher functional heteroatom-containing crosslinkable monomers such as trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and dipentaerythritol poly(meth)acrylate. Among these, allyl (meth)acrylate, ethylene glycol di(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol poly(meth)acrylate, and pentaerythritol tri(meth)acrylate are preferred, allyl (meth)acrylate, ethylene glycol di(meth)acrylate, and pentaerythritol tetra(meth)acrylate are more preferred, and allyl methacrylate, ethylene glycol dimethacrylate, and pentaerythritol tetraacrylate are even more preferred. The above heteroatom-containing crosslinkable monomers may be used as protected carboxyl group-containing monomers, and in this case, the carboxyl group can be introduced into the shell polymer by deprotection after polymerization. Among the above heteroatom-containing crosslinkable monomers, allyl (meth)acrylate and ethylene glycol di(meth)acrylate are preferred as protected carboxyl group-containing monomers.

[0035] The crosslinkable monomer is preferably a crosslinkable hydrocarbon monomer, more preferably divinylbenzene. The crosslinkable monomers may be used alone or in combination of two or more.

[0036] The content of the crosslinkable monomer units in the shell polymer relative to all monomer units is not particularly limited, but is preferably 20 to 60% by mass, more preferably 25 to 55% by mass, and even more preferably 30 to 50% by mass. When the content of the crosslinkable monomer units is within the above range, the mechanical strength, porosity, dielectric properties, and heat resistance of the hollow particles are all achieved at higher levels, and in particular, deterioration of the dielectric properties is suppressed under more severe conditions (for example, in a high-temperature environment of 140°C or higher).

[0037] The non-crosslinkable monomer is a monomer having only one polymerizable functional group, and a compound having an ethylenically unsaturated bond as the polymerizable functional group is generally used. Examples of the non-crosslinkable monomer as the other monomer include a non-crosslinkable hydrocarbon monomer and a heteroatom-containing non-crosslinkable monomer other than the OR group-containing aromatic vinyl compound (A).

[0038] The non-crosslinkable hydrocarbon monomer is not particularly limited, but examples thereof include aromatic vinyl monomers such as styrene, ethylvinylbenzene, vinyltoluene, α-methylstyrene, p-methylstyrene, halogenated styrene, vinylbiphenyl, and vinylnaphthalene; monoolefin monomers such as ethylene, propylene, butylene, 1-pentene, 1-hexene, and 4-methyl-1-pentene; and diene monomers such as butadiene and isoprene. Of these, ethylvinylbenzene is preferred.

[0039] The heteroatom-containing non-crosslinkable monomer other than the OR group-containing aromatic vinyl compound (A) is not particularly limited, and examples thereof include hydrophilic non-crosslinkable monomers; acrylic monovinyl monomers such as methyl (meth)acrylate, ethyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, glycidyl (meth)acrylate, and 2-hydroxyethyl (meth)acrylate; amino group-containing monovinyl monomers such as dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, t-butylaminoethyl (meth)acrylate, and 4-vinylbenzylamine; carboxylic acid vinyl ester monomers such as vinyl acetate; halogenated vinyl monomers such as vinyl chloride; halogenated vinylidene monomers such as vinylidene chloride; and vinylpyridine monomers. The acrylic monovinyl monomer may be used as a protected carboxyl group-containing monomer, and in this case, the carboxyl group can be introduced into the shell polymer by deprotection after polymerization. Among the acrylic monovinyl monomers, preferred protected carboxyl group-containing monomers are methyl (meth)acrylate, ethyl (meth)acrylate, and t-butyl (meth)acrylate.

[0040] The hydrophilic non-crosslinkable monomer preferably has a solubility in water of 1% by mass or more. The hydrophilic non-crosslinkable monomer is not particularly limited, but examples thereof include non-crosslinkable monomers having a hydrophilic group, such as an acid group-containing monomer, a hydroxyl group-containing monomer, an amide group-containing monomer, and a polyoxyethylene group-containing monomer.

[0041] The acid group-containing monomer refers to a monomer containing an acid group. The acid group here includes both a proton-donating group (Brønsted acid group) and an electron pair-accepting group (Lewis acid group). By using an acid group-containing monomer as a hydrophilic monomer, the heat resistance of the resulting hollow particles can be further improved.

[0042] The acid group-containing monomer is not particularly limited as long as it has an acid group, and examples thereof include carboxyl group-containing monomers and sulfonic acid group-containing monomers.

[0043] Examples of the carboxyl group-containing monomer include ethylenically unsaturated carboxylic acid monomers such as acrylic acid, methacrylic acid, crotonic acid, cinnamic acid, itaconic acid, fumaric acid, maleic acid, and butenetricarboxylic acid; monoalkyl esters of unsaturated dicarboxylic acids such as monoethyl itaconate, monobutyl fumarate, and monobutyl maleate; etc. Examples of the sulfonic acid group-containing monomer include styrenesulfonic acid.

[0044] Examples of the hydroxyl group-containing monomer include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate.

[0045] Examples of the amide group-containing monomer include acrylamide and dimethylacrylamide.

[0046] Examples of polyoxyethylene group-containing monomers include methoxypolyethylene glycol (meth)acrylate.

[0047] The non-crosslinkable monomer is preferably a non-crosslinkable hydrocarbon monomer, more preferably ethylvinylbenzene. The non-crosslinkable monomers may be used alone or in combination of two or more.

[0048] The content of non-crosslinkable monomer units (including units derived from the OR group-containing aromatic vinyl compound (A)) relative to all polymerizable monomer units in the shell polymer is not particularly limited, but is preferably 40 to 80 mass %, more preferably 45 to 75 mass %, and even more preferably 50 to 70 mass %. When the content of non-crosslinkable monomer units is within the above range, the mechanical strength, porosity, dielectric properties, and heat resistance of the hollow particles are all achieved at even higher levels, and in particular, deterioration of the dielectric properties is suppressed under even harsher conditions (for example, in a high-temperature environment of 140°C or higher).

[0049] From the viewpoint of providing hollow particles with even better dielectric properties, the shell polymer preferably contains hydrocarbon monomer units (monomer units consisting only of carbon atoms and hydrogen atoms) as monomer units constituting the shell polymer in a proportion of 80% by mass or more. The content of hydrocarbon monomer units in the shell polymer is more preferably 85% by mass or more, and even more preferably 90% by mass or more. Examples of hydrocarbon monomers that form the hydrocarbon monomer units include the above-mentioned crosslinkable hydrocarbon monomers and the above-mentioned non-crosslinkable hydrocarbon monomers.

[0050] When extremely excellent dielectric properties are required, the content of hydrocarbon monomer units in the shell polymer is preferably 95% by mass or more, more preferably 98% by mass or more, and even more preferably 100% by mass (the shell polymer is composed only of hydrocarbon monomer units).

[0051] The shell polymer may contain a heteroatom-containing monomer unit other than the OR group-containing aromatic vinyl compound (A) as a monomer unit constituting the shell polymer. Examples of the heteroatom-containing monomer forming the heteroatom-containing monomer unit other than the OR group-containing aromatic vinyl compound (A) include the above-mentioned heteroatom-containing crosslinkable monomer and the above-mentioned heteroatom-containing non-crosslinkable monomer other than the OR group-containing aromatic vinyl compound (A).

[0052] The content of the heteroatom-containing monomer unit other than the OR group-containing aromatic vinyl compound (A) in the shell polymer is not particularly limited, but from the viewpoint of providing the hollow particles with even better dielectric properties, it is preferably 0 to 20 mass%, more preferably 0 to 15 mass%, and even more preferably 0 to 10 mass%.

[0053] When extremely excellent dielectric properties are required, the content of heteroatom-containing monomer units other than the OR group-containing aromatic vinyl compound (A) in the shell polymer is preferably 0 to 5 mass %, more preferably 0 to 2 mass %, and even more preferably 0 mass % (the shell polymer does not contain any heteroatom-containing monomer units other than the OR group-containing aromatic vinyl compound (A)).

[0054] Furthermore, the content of the carboxyl group-containing monomer units in the shell polymer is preferably 4% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less. The lower limit is 0% by mass or more. By setting the content of the carboxyl group-containing monomer units in the shell polymer within the above range, the dielectric properties of the hollow particles can be made even better.

[0055] On the other hand, when both a small particle size distribution (Dv / Dn) and a higher porosity of the hollow particles are required, the content of the carboxyl group-containing monomer unit may be 1% by mass or more, 2% by mass or more, or 3% by mass or more.

[0056] The hollow particles of the present invention are particles having a shell (outer shell) containing the above-mentioned resin and a hollow portion surrounded by the shell. In the present invention, the hollow portion is a hollow space clearly distinguishable from the shell of the hollow particle formed by the resin. The hollow particles of the present invention may have one or more hollow portions, but preferably have only one hollow portion in order to maintain a good balance between high porosity and mechanical strength. Among the hollow particles of the present invention, the proportion of particles having only one hollow portion is preferably 90% by mass or more, more preferably 95% by mass or more.

[0057] The hollow particles of the present invention usually have a shell that is free from interconnected pores and shell defects, and the hollow portion is isolated from the outside of the particle by the shell, but the shell may have one or more interconnected pores, and the hollow portion may communicate with the outside of the particle via the interconnected pores. Furthermore, the shell of the hollow particle, and when the hollow particle has two or more hollow portions, the partition walls separating adjacent hollow portions may be porous, provided that the hollow portions are of a size that can be clearly distinguished from the numerous minute spaces uniformly dispersed within the porous structure.

[0058] The hollow portion of the hollow particle of the present invention may be filled with a gas such as air, or may contain a solvent.

[0059] The shape of the hollow particles of the present invention is not particularly limited as long as a hollow portion is formed inside. The outer shape of the hollow particles is not particularly limited, but a spherical shape is preferred from the viewpoint of ease of production.

[0060] The external shape of the hollow particles can be confirmed, for example, by observing the particles with an SEM or TEM, and the internal shape of the hollow particles can be confirmed, for example, by observing the cross section of the particle with an SEM or by observing the particle with a TEM.

[0061] The porosity of the hollow particles of the present invention is 45 to 95%. If the porosity of the hollow particles is too low, the hollow particles will have poor dielectric properties. The porosity of the hollow particles is not particularly limited as long as it is 45 to 95%, but is preferably 50 to 90%, more preferably 55 to 85%, and even more preferably 60 to 80%. If the porosity is within the above range, the hollow particles can have even better dielectric properties.

[0062] The porosity (%) of the hollow particles is calculated by multiplying the apparent density D １ and true density D ０ The porosity of hollow particles (%) is calculated from the apparent density D of hollow particles by the following formula (III): １ ]÷[True density D of hollow particles ０ ]×100 (III)

[0063] The apparent density of the hollow particles D １ corresponds to the specific gravity of the entire hollow particle when the hollow portion is considered to be a part of the hollow particle, and the true density D ０ corresponds to the specific gravity of only the shell portion of the hollow particle. １ and true density D ０ Specifically, the porosity of hollow particles can be measured by the method described in the Examples. In other words, the porosity of hollow particles is the ratio of the hollow portion to the specific gravity of the hollow particles. The porosity of hollow particles can be adjusted, for example, by adjusting the composition of polymerizable monomers used in producing the hollow particles by suspension polymerization and the amount of hydrophobic solvent in the mixed solution.

[0064] The volume average particle size (Dv) of the hollow particles of the present invention is not particularly limited, but is preferably 1 to 50 μm, more preferably 1 to 30 μm, even more preferably 1 to 20 μm, and particularly preferably 1 to 10 μm. The volume average particle size (Dv) of the hollow particles can be measured, for example, by a laser diffraction particle size distribution analyzer.

[0065] The volume average particle size (Dv) of the hollow particles can be adjusted, for example, by adjusting the monomer composition of the shell polymer, the type and amount of a dispersion stabilizer used when producing the hollow particles by suspension polymerization, and the suspension conditions.

[0066] The residual double bond ratio of the shell polymer constituting the resin of the hollow particles of the present invention is not particularly limited, but is preferably 15% or less, more preferably 10% or less, more preferably 5% or less, even more preferably 4.5% or less, and particularly preferably 4% or less. When the residual double bond ratio is within the above range, the mechanical strength, porosity, dielectric properties, and heat resistance of the hollow particles are all achieved at higher levels, and in particular, deterioration of the dielectric properties under more severe conditions (e.g., high-temperature environments of 140°C or higher) is suppressed. The lower limit of the residual double bond ratio is not particularly limited, but can be, for example, 0.1% or more.

[0067] The residual double bond ratio can be determined as follows.

[0068] First, infrared absorption spectra, expressed as absorbance, are measured for the shell polymer contained in the hollow particles and the polymerizable monomer used to prepare the hollow particles before the polymerization reaction. Meanwhile, the polymerizable monomer with the highest content among the polymerizable monomers used to prepare the hollow particles is identified as the reference monomer. If there are multiple monomers with the highest content, one of them is identified as the reference monomer. From the structures of the reference monomer, one structure that does not increase or decrease before or after the polymerization reaction is selected. As the structure that does not increase or decrease before or after the polymerization reaction, it is preferable to select a structure that does not contribute to the polymerization reaction of the reference monomer, one whose peak in the infrared absorption spectrum is clearly distinguishable from the peak of the polymerizable unsaturated double bond (C═C) and has a strong intensity. The peak derived from the selected structure is used as the reference peak.

[0069] Then, in each of the infrared absorption spectrum of the shell polymer and the infrared absorption spectrum of the polymerizable monomer, the peak intensity of the reference peak is divided by the content ratio of the monomer containing the structure that exhibits the reference peak, and the calculated value is used as the reference peak intensity.

[0070] Furthermore, in each of the infrared absorption spectrum of the shell polymer and the infrared absorption spectrum of the polymerizable monomer, the peak intensity of the peak derived from the polymerizable unsaturated double bond (C═C) is measured.

[0071] The reference peak intensity (M ０ ) relative to the peak intensity (M １ ) ratio (M １ / M ０ ) is the peak intensity ratio when the residual double bond rate is 100%.

[0072] The reference peak intensity (P ０ ) relative to the peak intensity (P １ ) ratio (P １ / P ０ ) is determined in the same manner. Then, the peak intensity ratio (M １ / M ０ ) and the peak intensity ratio (P １ / P ０ ) and the residual double bond ratio can be calculated by the following formula (IV): Residual double bond ratio (%) = {(P １ / P ０ ) / (M １ / M ０ )}×100 (IV)

[0073] The peak intensity can be quantified by placing base points on the outside of both ends of the peak and measuring the height from a baseline drawn by a straight line connecting the base points to the peak top.

[0074] For example, if the polymerizable monomers used to prepare hollow particles are 95% by mass of divinylbenzene and 5% by mass of ethylvinylbenzene, the reference monomer is divinylbenzene, which has the highest content. From the structure of divinylbenzene, for example, a C-H bond in the benzene ring contained in divinylbenzene is selected as a structure that does not increase or decrease before or after the polymerization reaction. Then, the infrared absorption spectrum of the polymerizable monomer consisting of 95% by mass of divinylbenzene and 5% by mass of ethylvinylbenzene and the infrared absorption spectrum of the shell polymer contained in the hollow particles are measured. In each spectrum, the peak derived from the C-H bond in the benzene ring contained in divinylbenzene is identified as the reference peak. Since the peak derived from the C-H bond in the benzene ring contained in divinylbenzene and the peak derived from the C-H bond in the benzene ring contained in ethylvinylbenzene appear at the same position, divinylbenzene and ethylvinylbenzene are considered to be monomers containing the structure that exhibits the reference peak. Therefore, the reference peak intensity is determined by dividing the peak intensity of the reference peak by 1.00, which is the sum of the content percentages of divinylbenzene and ethylvinylbenzene. In addition, in each spectrum, the peak intensity of the peak derived from the polymerizable unsaturated double bond (C═C) contained in divinylbenzene and the polymerizable unsaturated double bond (C═C) contained in ethylvinylbenzene is measured. Then, the reference peak intensity (M ０ ) relative to the peak intensity (M １ ) ratio (M １ / M ０ ) and the reference peak intensity (P ０ ) relative to the peak intensity (P １ ) ratio (P １ / P ０ ) and calculate the residual double bond ratio according to the above formula (IV).

[0075] The infrared absorption spectrum can be measured by, for example, attenuated total reflection (ATR) method. An example of an infrared absorption spectrum measuring device is Spectrum One, manufactured by Perkin Elmer.

[0076] The residual double bond ratio of the shell polymer can be adjusted, for example, by adjusting the monomer composition of the shell polymer.

[0077] Regarding the hollow particles of the present invention, the IR peak change rate ΔP ｒ is preferably 5% or less, more preferably 4% or less, and even more preferably 3% or less. ｒ When the IR peak change rate ΔP is within the above range, the deterioration of the dielectric properties under high temperature conditions is further suppressed. ｒ The lower limit of is not particularly limited, but is, for example, 0.1% or more.

[0078] IR peak change rate ΔP ｒ is the peak intensity ratio P measured by infrared spectroscopy when heat-treated in air at 130°C for 240 hours. ｒ The rate of change ΔP before and after heat treatment ｒ The peak intensity ratio P ｒ is expressed by the following formula (1): ｒ =(1680~1720cm －１ Maximum absorbance in the range of 680 to 720 cm －１ (Maximum absorbance in the range) (1)

[0079] In the above formula (1), 1680 to 1720 cm －１ The maximum absorbance in the range is the value of 1680 to 1720 cm when infrared spectroscopy is performed on hollow particles. －１ The maximum absorbance in the range of 1680 to 1720 cm －１ This is the maximum peak top intensity among the peak top intensities in the range of 1680 to 1720 cm －１The maximum absorbance in the range of 680 to 720 cm corresponds to the absorption peak derived from the carbonyl group. －１ The maximum absorbance in the range is the value measured by infrared spectroscopy of hollow particles at 680 to 720 cm －１ The maximum absorbance in the range of 680 to 720 cm －１ This is the maximum peak top intensity among the peak top intensities in the range of 680 to 720 cm. －１ The maximum absorbance in this range corresponds to the absorption peak derived from the carbon-hydrogen bond (C—H) contained in the benzene ring.

[0080] IR peak change rate ΔP ｒ The IR peak change rate ΔP can be calculated according to the following formula (2) by measuring the infrared absorption spectrum of the hollow particles before and after the heat treatment (heat treatment in air at 130° C. for 240 hours). ｒ (%) = ([peak intensity ratio of hollow particles after heat treatment] - [peak intensity ratio of hollow particles before heat treatment]) / [peak intensity ratio of hollow particles before heat treatment] × 100 (2)

[0081] IR peak change rate ΔP ｒ The hollow particles before the heat treatment and the hollow particles that had been heat treated in air at 130°C for 240 hours were measured by infrared spectroscopy. －１ and absorbance maxima in the range of 680-720 cm －１ The maximum absorbance in the range can be determined and calculated according to the above formulas (1) and (2).

[0082] IR peak change rate ΔP ｒ can be adjusted, for example, by adjusting the monomer composition of the shell polymer.

[0083] The moisture content of the hollow particles of the present invention is not particularly limited, but from the viewpoint of improving the reliability of electronic circuit boards when the hollow particles of the present invention are used as materials for electronic circuit boards, it is preferably 2.5% by mass or less, more preferably 2.0% by mass or less, and even more preferably 1.5% by mass or less. The lower limit of the moisture content of the hollow particles is not particularly limited, but from the viewpoint of improving the reliability of electronic circuit boards when the hollow particles of the present invention are used as materials for electronic circuit boards, it is preferable that the moisture content is lower.

[0084] The hollow particles of the present invention preferably have a relative dielectric constant (Dk) of 2.0 or less, more preferably 1.9 or less, and even more preferably 1.8 or less. The hollow particles of the present invention also have a dielectric loss tangent (Df) of 4.0×10 －４ Preferably, it is 3.0 × 10 or less. －４ More preferably, it is:

[0085] Examples of uses of the hollow particles of the present invention include electronic materials used in various fields such as automobiles, electricity, electronics, architecture, aviation, and space, heat insulating materials, sound insulating materials, light diffusing materials, light diffusing films, anti-glare films, piezoelectric films, electromagnetic wave absorbing sheets, vibration isolating rubber, gaskets, O-rings and other sealing materials, and light reflecting materials; additives for food containers, footwear such as sports shoes and sandals, home appliance parts, bicycle parts, stationery, tools, etc. In particular, the hollow particles of the present disclosure have excellent dielectric properties and are therefore suitable for use as additives for achieving low transmission loss in the electrical or electronic fields. For example, the hollow particles of the present invention are suitable for use as materials for electronic circuit boards. Specifically, the transmission loss of electronic circuit boards can be reduced by incorporating the hollow particles of the present invention into the insulating resin layer of the electronic circuit board.

[0086] The hollow particles of the present invention are also suitable for use as additives in semiconductor materials such as interlayer insulating materials, dry film resists, solder resists, bonding wires, bonding sheets, magnet wires, semiconductor encapsulants, epoxy encapsulants, mold underfills, underfills, die bond pastes, buffer coating materials, copper-clad laminates, flexible substrates, high-frequency device modules, antenna modules, and automotive radar. Among these, they are particularly suitable as additives in semiconductor materials such as interlayer insulating materials, solder resists, bonding sheets, magnet wires, epoxy encapsulants, underfills, buffer coating materials, copper-clad laminates, flexible substrates, high-frequency device modules, antenna modules, and automotive radar. The bonding sheet is an insulating adhesive layer-forming material used to bond a conductor layer and an organic insulating layer when producing a multilayer printed wiring board.

[0087] Furthermore, when added to a molded product, the hollow particles of the present invention are also excellent in effect as a weight-reducing material, a heat insulating material, a soundproofing material, a vibration damping material, a light diffusing agent, and the like, and are therefore suitable as an additive for molded products, and can be used, for example, as an additive for resin molded products, and can also be contained as a filler in fiber-reinforced molded products formed using a resin and reinforcing fibers. Furthermore, when used as a light diffusing agent, the hollow particles of the present invention are suitable as an additive for light diffusing materials such as light diffusion films, light diffusion plates, and antiglare films.

[0088] The hollow particles of the present invention also satisfy the heat insulating and shock absorbing properties (cushioning properties) required for undercoating materials and the heat resistance required for thermal paper applications.The hollow particles of the present invention are also useful as plastic pigments with excellent gloss, hiding power, etc.

[0089] Furthermore, the hollow particles of the present invention can be used for various purposes depending on the components contained therein, since useful components such as fragrances, medicines, agricultural chemicals, and ink components can be encapsulated therein by means of immersion treatment, reduced pressure or pressurized immersion treatment, or the like.

[0090] The hollow particles of the present invention are also suitable for use as rust inhibitors. The hollow particles of the present invention are also useful as additives that reduce electrical conductivity, so that, for example, paints containing the hollow particles of the present invention can be used as rust-preventive paints (paint primers, lubricating paints, etc.) for improving the corrosion and rust resistance of steel materials and the like. In addition, rust-preventive additives can be encapsulated in the hollow particles added to the rust-preventive paints.

[0091] The hollow particles of the present invention can be used as materials for various batteries, such as lithium ion batteries, all-solid-state batteries, and fuel cells, which are used in various fields, such as electric vehicles, power tools, auxiliary power sources, and wind power generation. More specifically, the hollow particles of the present invention can be used, for example, in conductive pastes, separator porous membranes, surface protective materials for battery packaging materials, and battery exterior materials used in lithium ion batteries, solid electrolyte separators and compositions for forming electric double layer capacitor electrodes used in all-solid-state batteries, and separators and compositions for forming microbial fuel cell electrodes used in fuel cells.

[0092] <Method for Producing Hollow Particles> The method for producing hollow particles of the present invention is not particularly limited, but hollow particles can be preferably produced by a production method including the following steps: (A) a mixed solution preparation step, (B) a suspension step, (C) a polymerization step, (D) a solid-liquid separation step, and (E) a solvent removal step.

[0093] That is, the hollow particles of the present invention can be preferably produced by a production method including: (A) a mixed solution preparation step of preparing a mixed solution containing a polymerizable monomer including an OR group-containing aromatic vinyl compound (A), a hydrophobic solvent, a polymerization initiator, and an aqueous medium; (B) a suspending step of suspending the mixed solution obtained in the mixed solution preparation step to prepare a suspension in which droplets of a polymerizable monomer composition containing the polymerizable monomer, the hydrophobic solvent, and the polymerization initiator are dispersed in an aqueous medium; (C) a polymerization step of subjecting the suspension obtained in the suspending step to a polymerization reaction to prepare a precursor composition containing precursor particles having a hollow portion surrounded by a shell containing a resin and encapsulating a hydrophobic solvent in the hollow portion; (D) a solid-liquid separation step of subjecting the precursor composition obtained in the polymerization step to solid-liquid separation to obtain precursor particles encapsulating the hydrophobic solvent; and (E) a solvent removal step of removing the hydrophobic solvent from the precursor particles encapsulating the hydrophobic solvent obtained in the solid-liquid separation step to obtain hollow particles.

[0094] (A) Mixed Liquid Preparation Step The mixed liquid preparation step is a step of preparing a mixed liquid containing a polymerizable monomer including an OR group-containing aromatic vinyl compound (A), a hydrophobic solvent, a polymerization initiator, and an aqueous medium. The hollow particles of the present invention are preferably produced by a production method including such a step.

[0095] As the polymerizable monomer, at least the above-mentioned OR group-containing aromatic vinyl compound (A) may be used, but it is preferable to use the above-mentioned OR group-containing aromatic vinyl compound (A) and the above-mentioned crosslinkable monomer. The monomer composition of the polymerizable monomer may be any monomer composition that can obtain the monomer composition of the target shell polymer.

[0096] The content of the polymerizable monomer in the mixed liquid prepared in the mixed liquid preparation step is not particularly limited, but from the viewpoint of the balance between the porosity, particle size, and mechanical strength of the hollow particles, it is preferably 15 to 55 mass%, and more preferably 25 to 50 mass%, relative to 100 mass% of the total mass of the components in the mixed liquid excluding the aqueous medium.

[0097] The hydrophobic solvent is a non-polymerizable, poorly water-soluble organic solvent, which acts as a spacer material that forms hollow spaces inside the particles.

[0098] The hydrophobic solvent is not particularly limited, but a hydrocarbon solvent can be suitably used, and specific examples thereof include saturated hydrocarbon solvents such as butane, pentane, normal hexane, cyclohexane, heptane, and octane; aromatic hydrocarbon solvents such as benzene, toluene, and xylene; and relatively volatile solvents such as carbon disulfide and carbon tetrachloride.

[0099] As the hydrophobic solvent, the proportion of saturated hydrocarbon solvents in a total amount of 100% by mass of hydrophobic solvents is preferably 50% by mass or more. This allows sufficient phase separation to occur within the droplets of the polymerizable monomer composition prepared in the suspension step described below, making it easier to obtain hollow particles having only one hollow portion and suppressing the generation of porous particles. From the viewpoint of further suppressing the generation of porous particles and from the viewpoint of making the hollow portions of each hollow particle more uniform, the proportion of saturated hydrocarbon solvents in a total amount of 100% by mass of hydrophobic solvents is preferably 60% by mass or more, more preferably 80% by mass or more.

[0100] Furthermore, as the hydrophobic solvent, a hydrocarbon solvent having 5 to 8 carbon atoms is preferred. A hydrocarbon solvent having 5 to 8 carbon atoms is easily encapsulated in the precursor particles during the polymerization step described below, and can be easily removed from the precursor particles during the solvent removal step described below. Of these, a hydrocarbon solvent having 6 to 8 carbon atoms is particularly preferred.

[0101] Furthermore, from the viewpoint of ease of removal in the solvent removal step described below, the hydrophobic solvent preferably has a boiling point of 130°C or less, more preferably 115°C or less, while from the viewpoint of ease of inclusion in the precursor particles, the hydrophobic solvent preferably has a boiling point of 30°C or more, more preferably 50°C or more.

[0102] In the present invention, when the hydrophobic solvent is a mixed solvent containing multiple types of hydrophobic solvents and has multiple boiling points, the boiling point of the hydrophobic solvent is the boiling point of the solvent with the highest boiling point among the solvents contained in the mixed solvent, i.e., the highest boiling point among the multiple boiling points.

[0103] Furthermore, the hydrophobic solvent preferably has a relative dielectric constant of 3 or less at 20°C. The relative dielectric constant is one of the indicators showing the degree of polarity of a compound. When the relative dielectric constant of the hydrophobic solvent is sufficiently small, 3 or less, it is considered that phase separation proceeds quickly in the droplets of the polymerizable monomer composition prepared in the suspension step described below, and hollow portions are likely to be formed.

[0104] Examples of hydrophobic solvents having a dielectric constant of 3 or less at 20°C include heptane (1.9), cyclohexane (2.0), benzene (2.3), toluene (2.4), etc. (The values ​​in parentheses are the dielectric constant values.) For the dielectric constant at 20°C, reference can be made to values ​​described in known literature (for example, "Chemical Handbook Basics" edited by the Chemical Society of Japan, Revised 4th Edition, Maruzen Co., Ltd., published September 30, 1993, pages II-498 to II-503) and other technical information. Examples of methods for measuring the dielectric constant at 20°C include a dielectric constant test conducted in accordance with JIS C 2101:1999-23 at a measurement temperature of 20°C.

[0105] The porosity of the hollow particles can be adjusted by adjusting the amount of the hydrophobic solvent in the mixed solution. In the polymerization step described below, the polymerization reaction proceeds in a state in which the droplets of the polymerizable monomer composition encapsulate the hydrophobic solvent, so the porosity of the resulting hollow particles tends to increase as the content of the hydrophobic solvent increases.

[0106] The content of the hydrophobic solvent in the mixed solution is preferably 50 to 500 parts by mass, more preferably 60 to 400 parts by mass, still more preferably 80 to 350 parts by mass, and particularly preferably 100 to 300 parts by mass, relative to 100 parts by mass of the total mass of the polymerizable monomers.

[0107] As the polymerization initiator, an oil-soluble polymerization initiator is preferably used. By using an oil-soluble polymerization initiator as the polymerization initiator, the polymerization initiator can be suitably incorporated into the interior of droplets of the polymerizable monomer composition in the suspension obtained in the suspension step described below.

[0108] The oil-soluble polymerization initiator is not particularly limited as long as it is lipophilic and has a solubility in water of 0.2% by mass or less, and examples of the oil-soluble polymerization initiator include benzoyl peroxide, lauroyl peroxide, t-butyl peroxide-2-ethylhexanoate, t-butyl peroxydiethyl acetate, t-butyl peroxypivalate, 2,2'-azobis(2,4-dimethylvaleronitrile), and azobisisobutyronitrile.

[0109] The content of the polymerization initiator is preferably 0.5 to 20 parts by mass, more preferably 1 to 15 parts by mass, and even more preferably 2 to 12 parts by mass, relative to 100 parts by mass of the total mass of the polymerizable monomers in the mixed solution. By setting the content of the polymerization initiator within the above range, the polymerization reaction can be sufficiently progressed, and there is little risk of the polymerization initiator remaining after completion of the polymerization reaction, and there is also little risk of an unexpected side reaction proceeding.

[0110] The aqueous medium may be a medium selected from the group consisting of water, a hydrophilic solvent, and a mixture of water and a hydrophilic solvent.

[0111] The hydrophilic solvent is not particularly limited as long as it is sufficiently miscible with water and does not cause phase separation, and examples thereof include alcohols such as methanol and ethanol; tetrahydrofuran (THF); dimethyl sulfoxide (DMSO); and the like.

[0112] Among aqueous media, water is preferred due to its high polarity. When a mixture of water and a hydrophilic solvent is used, it is preferable that the polarity of the entire mixture is not too low, from the viewpoint of properly forming droplets of a polymerizable monomer composition containing a polymerizable monomer, a hydrophobic solvent, and a polymerization initiator. When a mixture of water and a hydrophilic solvent is used, it is preferable that the mixing ratio (mass ratio) of water to hydrophilic solvent is 99:1 to 50:50.

[0113] In addition, in the mixed solution preparation step, it is preferable to use a dispersion stabilizer in addition to the polymerizable monomer, hydrophobic solvent, polymerization initiator, and aqueous medium. That is, the mixed solution preparation step is preferably a step of preparing a mixed solution containing the polymerizable monomer, hydrophobic solvent, polymerization initiator, aqueous medium, and dispersion stabilizer.

[0114] The dispersion stabilizer is a compound that disperses droplets of the polymerizable monomer composition in an aqueous medium in the suspension step described below, and may be either an inorganic dispersion stabilizer or an organic dispersion stabilizer.

[0115] Examples of inorganic dispersion stabilizers include colloidal silica, magnesium hydroxide, calcium phosphate, calcium carbonate, barium sulfate, calcium oxalate, calcium carbonate, magnesium carbonate, barium carbonate, tricalcium phosphate, aluminum hydroxide, magnesium hydroxide, ferric hydroxide, hydroxyapatite, diatomaceous earth, clay, and bentonite.

[0116] Examples of organic dispersion stabilizers include methyl cellulose, hydroxypropyl methyl cellulose, carboxymethyl cellulose, and starch.

[0117] Among these, inorganic dispersion stabilizers are preferred from the viewpoint of having a high dispersion stabilizing effect and making it easier to control the particle size of droplets of a polymerizable monomer composition containing a polymerizable monomer, a hydrophobic solvent, and a polymerization initiator. Among inorganic dispersion stabilizers, metal-containing dispersion stabilizers are preferred, and poorly water-soluble inorganic metal salts are more preferred. Furthermore, poorly water-soluble inorganic metal salts are preferably inorganic metal salts having a solubility of 0.5 g or less in 100 g of water, such as magnesium hydroxide, calcium hydroxide, barium hydroxide, calcium phosphate, etc., and among these, magnesium hydroxide is more preferred. Each dispersion stabilizer can be used alone or in combination of two or more.

[0118] In addition, from the viewpoint of further enhancing the dispersion stabilizing effect, it is preferable to use the dispersion stabilizer in the form of a dispersion or solution by dispersing or dissolving it in an aqueous medium. That is, in the mixed liquid preparation step, it is preferable to obtain the mixed liquid by mixing the dispersion stabilizer in the form of a dispersion or solution with the polymerizable monomer, the hydrophobic solvent, and the polymerization initiator. Note that the above-mentioned aqueous medium can be used.

[0119] In the dispersion or solution of the dispersion stabilizer, the mixing ratio of the dispersion stabilizer to the aqueous medium, in terms of the mass ratio of "dispersion stabilizer:aqueous medium", is preferably 0.7:100 to 7:100, more preferably 1.0:100 to 5:100, and even more preferably 1.4:100 to 4:100. By setting the mixing ratio of the dispersion stabilizer to the aqueous medium within the above range, the dispersion stabilization effect can be more appropriately enhanced.

[0120] As a method for preparing a dispersion or solution of a dispersion stabilizer, a method of directly mixing a dispersion stabilizer with an aqueous medium may be adopted, but a method of mixing two or more compounds that serve as precursors of the dispersion stabilizer (i.e., two or more precursor compounds) in an aqueous medium to cause a reaction and thereby produce the dispersion stabilizer is preferred.

[0121] The precursor compounds used when mixing two or more precursor compounds in an aqueous medium are not particularly limited. For example, when a poorly water-soluble hydroxide salt such as magnesium hydroxide, calcium hydroxide, or barium hydroxide is used as the dispersion stabilizer, examples of the two or more precursor compounds include a combination of a water-soluble polyvalent metal salt and an alkali metal hydroxide.

[0122] Examples of water-soluble polyvalent metal salts include hydrochlorides, sulfates, nitrates, acetates, etc. of polyvalent metals such as magnesium, calcium, aluminum, iron, copper, manganese, nickel, and tin. Among these, water-soluble salts of magnesium and calcium are preferred. Examples of alkali metal hydroxides include sodium hydroxide, potassium hydroxide, and lithium hydroxide. For example, when magnesium hydroxide is used as the dispersion stabilizer, a combination of magnesium chloride and sodium hydroxide is preferred as the two or more precursor compounds.

[0123] The method for mixing two or more precursor compounds in an aqueous medium is not particularly limited. However, in the case of a combination of a water-soluble polyvalent metal salt and an alkali metal hydroxide, a method is preferred in which an aqueous medium solution of the alkali metal hydroxide is added dropwise to an aqueous medium solution of the water-soluble polyvalent metal salt under stirring.

[0124] The content of the water-soluble polyvalent metal salt in the aqueous medium solution is preferably 2 to 15 parts by weight, more preferably 3 to 12 parts by weight, per 100 parts by weight of the aqueous medium solution. The content of the alkali metal hydroxide in the aqueous medium solution is preferably 6 to 30 parts by weight, more preferably 8 to 25 parts by weight, per 100 parts by weight of the aqueous medium solution. The aqueous medium may be any of those described above.

[0125] In the mixed solution preparation step, the above-mentioned components are mixed by stirring or the like to obtain a mixed solution. In this case, in addition to the above-mentioned components, other materials may be mixed as needed. In the mixed solution preparation step, a mixed solution is prepared in which an oil phase containing a polymerizable monomer, a hydrophobic solvent, and a lipophilic material such as a polymerization initiator is dispersed in an aqueous medium and an aqueous phase containing a dispersion stabilizer used as needed, with particles having a particle size of about several μm. The dispersion state of these components in the mixed solution can be observed with the naked eye, depending on the type of each component.

[0126] In addition, in the mixed solution preparation step, from the viewpoint that the composition of the shell portion is likely to be uniform, it is preferable to prepare the mixed solution by previously preparing an oil phase containing a polymerizable monomer, a hydrophobic solvent, and a polymerization initiator, and mixing this with a dispersion or solution obtained by dispersing or dissolving a dispersion stabilizer in an aqueous medium.

[0127] (B) Suspension Step The suspension step is a step of preparing a suspension in which droplets of a polymerizable monomer composition containing a polymerizable monomer, a hydrophobic solvent, and a polymerization initiator are dispersed in an aqueous medium by suspending the mixed liquid obtained in the mixed liquid preparation step described above.

[0128] The suspension method for forming droplets of the polymerizable monomer composition is not particularly limited, but a method in which the mixed solution obtained in the mixed solution preparation step described above is stirred using a stirrer capable of strong stirring is preferred. The stirrer used in the suspension step is not particularly limited, but for example, a stirrer equipped with a stirring blade or a rotor and a supply tank for supplying the mixture to the stirrer can be used. The stirrer is not particularly limited as long as it is equipped with a stirring blade or a rotor. However, from the viewpoint of efficiently forming a suspension, a stirrer having a combination of a rotor and a stator that are comb-tooth concentric rings is preferred, in which the rotor is rotated at high speed to circulate the dispersion from the inside of the rotor to the outside of the stator, and the dispersion is stirred in the gap between the rotor and the stator.

[0129] An example of an agitator having such a configuration is an in-line emulsifying disperser, and examples of the in-line emulsifying disperser include those with the product name "Cavitron" (manufactured by Eurotech), the product name "Milder" (manufactured by Pacific Machinery Works), the product name "Ebara Milder" (manufactured by Ebara Corporation), the product name "TK Pipeline Homomixer" (manufactured by Tokushu Kika Kogyo Co., Ltd.), the product name "Colloid Mill" (manufactured by Kobe Steel Pantech Co., Ltd.), the product name "Slasher" (manufactured by Nippon Coke and Engineering Co., Ltd.), the product name "Trigonal Wet Fine Pulverizer" (manufactured by Mitsui Miike Chemical Engineering Co., Ltd.), and the product name "Fine Flow Mill" (manufactured by Pacific Machinery Works).

[0130] In the suspending step, a suspension can be obtained in which droplets of the polymerizable monomer composition containing the lipophilic material are uniformly dispersed in an aqueous medium. Such droplets of the polymerizable monomer composition are difficult to observe with the naked eye and can be observed using known observation equipment such as an optical microscope. Furthermore, in the suspending step, phase separation occurs in the droplets of the polymerizable monomer composition, which makes it easier for the hydrophobic solvent with low polarity to collect inside the droplets. As a result, the resulting droplets contain the hydrophobic solvent in their interiors and materials other than the hydrophobic solvent distributed around their peripheries.

[0131] (C) Polymerization Step The polymerization step is a step of subjecting the suspension obtained in the suspension step to a polymerization reaction to prepare a precursor composition containing precursor particles having a hollow portion surrounded by a shell containing a resin and encapsulating a hydrophobic solvent in the hollow portion.

[0132] In the polymerization process, the polymerizable monomer in the droplets of the polymerizable monomer composition is polymerized while the droplets still contain the hydrophobic organic solvent, thereby forming precursor particles having a shell containing a resin, which is a polymer of the polymerizable monomer, and a hollow portion filled with the hydrophobic organic solvent.

[0133] In the polymerization step, droplets of the polymerizable monomer composition are subjected to the polymerization reaction while encapsulating the hydrophobic organic solvent, which facilitates the polymerization reaction while maintaining the shape, and facilitates the adjustment of the size and porosity of the precursor particles. Furthermore, since the polymerizable monomer and the hydrophobic organic solvent are used in combination, the polarity of the hydrophobic organic solvent is low relative to the shell of the precursor particles, and the hydrophobic organic solvent is not easily compatible with the shell, which leads to sufficient phase separation and the formation of only one hollow portion.

[0134] The polymerization method is not particularly limited, and for example, a batch method, a semi-continuous method, a continuous method, etc. can be used. The polymerization temperature is preferably 40 to 90°C, more preferably 50 to 80°C. The polymerization reaction time is preferably 1 to 48 hours, more preferably 3 to 30 hours.

[0135] The polymerization step may include a plurality of polymerization steps. For example, the polymerization step may include the following (C-1) first polymerization step and (C-2) second polymerization step. In this case, in the (A) mixed solution preparation step, only the first polymerizable monomer to be polymerized in the (C-1) first polymerization step is used as the polymerizable monomer.

[0136] (C-1) a first polymerization step in which the suspension obtained in the suspension step is subjected to a polymerization reaction to carry out a first polymerization reaction, thereby preparing a first precursor composition containing first precursor particles, the first precursor composition having a shell containing a polymer comprising monomer units composed of a first polymerizable monomer and a hollow portion filled with a hydrophobic solvent; and (C-2) a second polymerization step in which a non-crosslinkable monomer as a second polymerizable monomer is further added to the first precursor composition prepared in the first polymerization step, and a second polymerization reaction is carried out, thereby preparing a second precursor composition containing second precursor particles having a shell containing a polymer comprising monomer units composed of the first polymerizable monomer and monomer units composed of a second polymerizable monomer and a hollow portion filled with a hydrophobic solvent.

[0137] (C-1) First Polymerization Step The first polymerization step is a step of subjecting the suspension prepared in the above-described suspension step to a polymerization reaction to carry out a first polymerization reaction, thereby preparing a first precursor composition containing first precursor particles having a shell containing a polymer including monomer units formed from a first polymerizable monomer and a hollow portion filled with a hydrophobic solvent.

[0138] In the first polymerization reaction, the polymerization method is not particularly limited, and for example, a batch method, a semi-continuous method, a continuous method, etc. can be used, with a batch method being preferred. The polymerization temperature in the first polymerization reaction is preferably 40 to 100°C, more preferably 60 to 90°C. The temperature increase rate when raising the temperature to the polymerization temperature in the first polymerization reaction is preferably 10°C / h to 60°C / h, more preferably 15°C / h to 55°C / h.

[0139] The polymerization time in the first polymerization reaction is preferably 0.1 to 4 hours, more preferably 0.25 to 3 hours, and even more preferably 0.5 to 2 hours. The polymerization time in the first polymerization reaction is the time from when the polymerization temperature is reached to when the second polymerizable monomer described below is added and the second polymerization step is started.

[0140] (C-2) Second Polymerization Step The second polymerization step is a step of further adding a non-crosslinkable monomer as a second polymerizable monomer to the first precursor composition prepared in the first polymerization step, and carrying out a second polymerization reaction, thereby preparing a second precursor composition containing second precursor particles having a shell containing a polymer including monomer units composed of the first polymerizable monomer and monomer units composed of the second polymerizable monomer, and a hollow portion filled with a hydrophobic solvent.

[0141] That is, in the manufacturing method of the present invention, after performing the polymerization reaction for the predetermined time in the first polymerization step, a non-crosslinkable monomer as the second polymerizable monomer is added, and the polymerization reaction is further continued to prepare a second precursor composition containing second precursor particles. Specifically, the polymerization reaction in the first polymerization step is performed under conditions of preferably 0.1 to 4 hours, more preferably 0.25 to 3 hours, and more preferably 0.5 to 2 hours to form a first precursor composition containing first precursor particles. The non-crosslinkable monomer as the second polymerizable monomer is then added to the first precursor composition, and the polymerization reaction is further continued to prepare a second precursor composition containing second precursor particles. The timing for adding the non-crosslinkable monomer as the second polymerizable monomer is preferably when the polymerization conversion rate in the first polymerization reaction reaches 10 to 80%, more preferably when it reaches 15 to 70%, even more preferably when it reaches 20 to 60%, and particularly preferably when it reaches 30 to 55%.

[0142] The amount of the second polymerizable monomer added is preferably 15 to 80 parts by mass, more preferably 17.5 to 70 parts by mass, and even more preferably 20 to 65 parts by mass, per 100 parts by mass of the first polymerizable monomer.

[0143] In the second polymerization step, by timing the addition of the second polymerizable monomer and the start of the second polymerization step as described above, the polymerization reaction can proceed with the second polymerizable monomer incorporated into the shell of the first precursor particle. In particular, in the second polymerization step, by adding the second polymerizable monomer during the polymerization reaction of the first polymerizable monomer, i.e., when the shell of the first precursor particle formed by polymerizing the first polymerizable monomer is relatively flexible, the second polymerizable monomer is incorporated into the shell, and the second polymerizable monomer can react with a portion of the crosslinkable monomer constituting the first polymerizable monomer (e.g., a functional group of the crosslinkable monomer that is not subjected to crosslinking) within and on the shell.

[0144] The addition of the second polymerizable monomer and the start of the second polymerization step are set at the above-mentioned timing, and the amount of the second polymerizable monomer added is set at the above-mentioned amount, whereby the IR peak change rate ΔP ｒ can be controlled.

[0145] In the present invention, even in a polymerization method that does not include the first polymerization step (C-1) and the second polymerization step (C-2) (i.e., a polymerization method in which a non-crosslinkable monomer is not added during the polymerization), the IR peak change rate ΔP ｒ can be adjusted within the above preferred range.

[0146] As the second polymerizable monomer, it is preferable to use the above-mentioned non-crosslinkable monomer, and more preferable to use the above-mentioned OR group-containing aromatic vinyl compound (A).

[0147] The method for adding the second polymerizable monomer is not particularly limited, and may be any of a lump-sum addition method, a divided addition method, a continuous addition method, etc., but a lump-sum addition method is preferred.

[0148] The polymerization method for the second polymerization reaction carried out after the addition of the second polymerizable monomer is not particularly limited, and for example, the same polymerization method as that used for the first polymerization reaction can be adopted. The polymerization temperature for the second polymerization reaction is desirably the same as that for the first polymerization reaction, and is preferably 40 to 100°C, and more preferably 60 to 90°C. The reaction time for the second polymerization reaction is preferably 1 hour or more, more preferably 2 hours or more, and particularly preferably 4 hours or more. The upper limit of the reaction time for the second polymerization reaction may be determined depending on the total reaction time of the polymerization reactions in the entire polymerization step, and is not particularly limited, but can be, for example, within 24 hours.

[0149] The polymerization step may include the following third polymerization step (C-3) in addition to the first polymerization step (C-1) and the second polymerization step (C-2).

[0150] (C-3) Third Polymerization Step The third polymerization step is a step in which, after the second polymerization step, a functional group-containing polymerizable monomer is further added as a third polymerizable monomer to carry out a third polymerization reaction.

[0151] In the third polymerization step, it is desirable to add the third polymerizable monomer after the first polymerization reaction and the second polymerization reaction have progressed sufficiently and a covalent bond network has been densely spread throughout the shell of the second precursor particle. This allows the introduction of desired functional groups onto the shell surface of the second precursor particle, thereby increasing the affinity of the hollow particles of the present invention with a resin or the like for molding when blended with the resin or the like.

[0152] As the third polymerizable monomer, it is preferable to use a functional group-containing polymerizable monomer. The functional group-containing polymerizable monomer is a monomer having a polymerizable functional group and a functional group other than the functional group involved in polymerization. As the functional group-containing polymerizable monomer, the above-mentioned crosslinkable hydrocarbon monomer, heteroatom-containing crosslinkable monomer, heteroatom-containing non-crosslinkable monomer, etc. can be used.

[0153] The crosslinkable hydrocarbon monomer is preferably divinylbenzene.

[0154] The heteroatom-containing crosslinkable monomer is preferably a protected carboxyl group-containing monomer, more preferably allyl(meth)acrylate and ethylene glycol di(meth)acrylate, and even more preferably allyl methacrylate and ethylene glycol dimethacrylate. The protected carboxyl group contained in the protected carboxyl group-containing monomer is preferably a group that is deprotected by hydrolysis under acidic or basic conditions to form a carboxyl group.

[0155] As the heteroatom-containing non-crosslinkable monomer, an amino group-containing monovinyl monomer and a protected carboxyl group-containing monomer are preferred.

[0156] Examples of the amino group-containing monovinyl monomer include dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, t-butylaminoethyl (meth)acrylate, and 4-vinylbenzylamine.

[0157] Protected carboxyl group-containing monomers include methyl (meth)acrylate, ethyl (meth)acrylate, and t-butyl (meth)acrylate.

[0158] Among these, from the viewpoint of improving the adhesion of the hollow particles to the resin, amino group-containing monovinyl monomers are more preferred, t-butylaminoethyl (meth)acrylate and 4-vinylbenzylamine are even more preferred, and t-butylaminoethyl (meth)acrylate is particularly preferred.

[0159] The protected carboxyl group contained in the protected carboxyl group-containing monomer is preferably a group that is deprotected by hydrolysis under acidic or basic conditions to form a carboxyl group.

[0160] The amount of the third polymerizable monomer added is preferably 1 to 20 parts by mass, more preferably 2 to 20 parts by mass, and even more preferably 3 to 15 parts by mass, per 100 parts by mass of the first polymerizable monomer.

[0161] The timing of adding the third polymerizable monomer is preferably between 1 and 12 hours, more preferably between 1 and 10 hours, even more preferably between 2 and 10 hours, and particularly preferably between 4 and 8 hours from the start of the second polymerization reaction, from the viewpoint of being able to increase the affinity of the hollow particles with a resin or the like for molding when blended with the resin or the like.

[0162] The timing of adding the third polymerizable monomer may be determined depending on the polymerization conversion rate in the second polymerization reaction, from the viewpoint of increasing the affinity of the hollow particles with a molding resin or the like when the hollow particles are blended with the resin or the like. The timing is preferably when the polymerization conversion rate in the second polymerization reaction is 20 to 99%, more preferably when it is 30 to 99%, even more preferably when it is 40 to 99%, particularly preferably when it is 60 to 99%, particularly preferably when it is 80 to 99%, and most preferably when it is 90 to 99%.

[0163] The method for adding the third polymerizable monomer is not particularly limited, and may be any of a lump-sum addition method, a divided addition method, a continuous addition method, etc., but a lump-sum addition method is preferred.

[0164] The third polymerization reaction carried out after the addition of the third polymerizable monomer is not particularly limited in terms of the polymerization method, and may be, for example, the same polymerization method as that used in the first and second polymerization reactions. The polymerization temperature in the third polymerization reaction may be the same as that in the first and second polymerization reactions, but is preferably 40 to 100°C, and more preferably 60 to 90°C. The reaction time for the third polymerization reaction is preferably 1 hour or more, more preferably 2 hours or more, even more preferably 5 hours or more, particularly preferably 10 hours or more, and particularly preferably 15 hours or more. The upper limit of the reaction time for the third polymerization reaction may be determined based on the total reaction time of the entire polymerization process, and is not particularly limited, but may be, for example, within 24 hours.

[0165] The polymerization step yields a second precursor composition in which precursor particles encapsulating a hydrophobic solvent are dispersed in an aqueous phase containing an aqueous medium as the main component.

[0166] (D) Solid-Liquid Separation Step The solid-liquid separation step is a step of obtaining precursor particles encapsulating a hydrophobic solvent by separating the precursor composition obtained in the above-described polymerization step into solid form.

[0167] The method for solid-liquid separation of the precursor composition is not particularly limited, and any known method can be used. Examples of the solid-liquid separation method include centrifugation, filtration, and static separation. Among these, centrifugation or filtration can be used, and centrifugation may be used from the viewpoint of ease of operation.

[0168] After the solid-liquid separation step, an optional step such as a pre-drying step may be carried out before the solvent removal step described below is carried out. Examples of the pre-drying step include a step of pre-drying the solid content obtained after the solid-liquid separation step using a drying device such as a dryer or a drying appliance such as a hand dryer.

[0169] (E) Solvent Removal Step The solvent removal step is a step of removing the hydrophobic solvent from the precursor particles encapsulating the hydrophobic solvent obtained by the solid-liquid separation step described above. By removing the hydrophobic solvent encapsulated in the precursor particles in air, the hydrophobic solvent inside the precursor particles is replaced with air, and hollow particles filled with gas are obtained.

[0170] In the solvent removal step, "in the air" strictly refers to an environment in which no liquid is present outside the precursor particles, or an environment in which only a trace amount of liquid is present outside the precursor particles, so as not to affect the removal of the hydrophobic solvent. "In the air" can also be referred to as a state in which the precursor particles are not present in a slurry, or a state in which the precursor particles are present in a dry powder. That is, in the solvent removal step, it is desirable to remove the hydrophobic solvent in an environment in which the precursor particles are in direct contact with the external gas.

[0171] The method for removing the hydrophobic solvent from the precursor particles in air is not particularly limited, and known methods can be used, such as vacuum drying, heat drying, and flash drying, which may be used in combination. In particular, when heat drying is used, the heating temperature must be equal to or higher than the boiling point of the hydrophobic solvent and equal to or lower than the maximum temperature at which the shell structure of the precursor particles does not collapse. Therefore, depending on the shell composition and the type of hydrophobic solvent in the precursor particles, the heating temperature is preferably 50 to 200°C, more preferably 70 to 200°C, and even more preferably 100 to 200°C. The drying operation in air replaces the hydrophobic solvent inside the precursor particles with the external gas, resulting in hollow particles whose hollow portions are filled with gas.

[0172] The drying atmosphere is not particularly limited and can be appropriately selected depending on the application of the hollow particles. Examples of the drying atmosphere include air, oxygen, nitrogen, argon, etc. Alternatively, hollow particles with a temporary vacuum inside can be obtained by filling the inside of the hollow particles with a gas and then drying under reduced pressure.

[0173] Alternatively, the hydrophobic solvent may be removed by replacing the hydrophobic solvent encapsulated in the precursor particles with the aqueous medium of the slurry in a slurry containing precursor particles and an aqueous medium without performing solid-liquid separation of the slurry-like precursor composition obtained in the polymerization step. In this method, the amount of hydrophobic solvent remaining in the hollow particles can be reduced by bubbling an inert gas through the precursor composition at a temperature equal to or higher than the boiling point of the hydrophobic solvent minus 35°C. Here, if the hydrophobic solvent is a mixed solvent containing multiple hydrophobic solvents and has multiple boiling points, the boiling point of the hydrophobic solvent in the solvent removal step refers to the boiling point of the solvent with the highest boiling point among the solvents contained in the mixed solvent, i.e., the highest boiling point among the multiple boiling points.

[0174] The temperature at which the inert gas is bubbled into the precursor composition is preferably at least 30°C below the boiling point of the hydrophobic solvent, more preferably at least 20°C below that, in order to reduce the amount of hydrophobic solvent remaining in the hollow particles. The bubbling temperature is usually equal to or higher than the polymerization temperature in the polymerization step. Although not particularly limited, the bubbling temperature may be 50°C or higher and 100°C or lower. The inert gas to be bubbled is not particularly limited, but examples thereof include nitrogen and argon.

[0175] The bubbling conditions are appropriately adjusted depending on the type and amount of hydrophobic solvent so as to remove the hydrophobic solvent contained in the precursor particles, and are not particularly limited. For example, a method in which an inert gas is bubbled at a rate of 1 to 3 L / min for 1 to 10 hours is preferred. This method produces an aqueous slurry in which the aqueous medium is contained in the precursor particles. The slurry is subjected to solid-liquid separation to obtain hollow particles, which are then dried and the aqueous medium is removed from the hollow particles, yielding hollow particles whose hollow portions are filled with gas.

[0176] Comparing a method of obtaining hollow particles having hollow spaces filled with gas by performing solid-liquid separation on a slurry-like precursor composition and then removing the hydrophobic solvent in the precursor particles in an air atmosphere, and a method of obtaining hollow particles having hollow spaces filled with gas by replacing the hydrophobic solvent contained in precursor particles with the aqueous medium of the slurry in a slurry containing the precursor particles and the aqueous medium, performing solid-liquid separation, and removing the aqueous medium in the precursor particles in an air atmosphere, the former method has the advantage that the hollow particles are less likely to be crushed in the step of removing the hydrophobic solvent, and the latter method has the advantage that the amount of residual hydrophobic solvent is reduced by performing bubbling with an inert gas.

[0177] Alternatively, as a method for removing the hydrophobic solvent contained in the precursor particles after the polymerization step and before the solid-liquid separation step without performing solid-liquid separation on the slurry precursor composition obtained in the polymerization step, for example, a method for evaporating and distilling off the hydrophobic solvent contained in the precursor particles from the precursor composition under a predetermined pressure (high pressure, normal pressure, or reduced pressure); or a method for introducing an inert gas such as nitrogen, argon, or helium, or water vapor, into the precursor composition under a predetermined pressure (high pressure, normal pressure, or reduced pressure) and evaporating and distilling off the hydrophobic solvent may be used.

[0178] (F) Other Steps The above manufacturing method may also include other steps, such as (F-1) a cleaning step, (F-2) a hollow portion re-replacement step, and (F-3) a surface treatment step.

[0179] (F-1) Washing Step The above-described production method preferably includes a washing step before or after the solid-liquid separation step. For example, when a dispersion stabilizer is used, it is preferable to include a washing step in which an acid or alkali is added to wash the hollow particle slurry containing hollow particles and an aqueous medium before the recovery step in order to remove any dispersion stabilizer remaining in the hollow particle slurry. When the dispersion stabilizer used is an acid-soluble dispersion stabilizer, it is preferable to add an acid to the precursor composition containing the precursor particles to perform washing. On the other hand, when the dispersion stabilizer used is an alkali-soluble dispersion stabilizer, it is preferable to add an alkali to the precursor composition containing the precursor particles to perform washing.

[0180] Furthermore, when an acid-soluble dispersion stabilizer is used as the dispersion stabilizer, it is preferable to add an acid to the precursor composition containing the precursor particles to adjust the pH to preferably 6.5 or less, more preferably 6 or less. The acid to be added may be an inorganic acid such as sulfuric acid, hydrochloric acid, or nitric acid, or an organic acid such as formic acid or acetic acid, but sulfuric acid is particularly preferable because it has a high efficiency in removing the dispersion stabilizer and places a small burden on the production equipment.

[0181] (F-2) Hollow Portion Re-Substitution Process The hollow portion re-substitution process is a process of substituting the gas or liquid inside the hollow particles with another gas or liquid. This substitution can change the environment inside the hollow particles, selectively confine molecules inside the hollow particles, or modify the chemical structure inside the hollow particles to suit the application.

[0182] (F-3) Surface Treatment Step The hollow particles may be subjected to a surface treatment. That is, the hollow particles of the present invention may be surface-treated. Examples of the surface treatment method include surface oxidation treatment, boron treatment, surface coupling treatment, fluorine coating, and diamond coating.

[0183] <Polymer composition> A polymer composition containing the hollow particles of the present invention and a polymer (matrix polymer) can be obtained by adding the hollow particles of the present invention to a polymer material. The polymer composition usually comprises the hollow particles of the present invention dispersed in the matrix polymer.

[0184] The polymer composition may be a liquid polymer composition or a polymer molded body. Examples of liquid polymer compositions include those containing a liquid matrix polymer before a curing reaction, those obtained by dissolving or dispersing each component in a solvent, and those in which the matrix polymer is a thermoplastic resin and the resin is melted, thereby making the resin composition liquid. Examples of polymer molded bodies include those obtained by molding the above-mentioned liquid polymer composition by a known method.

[0185] Examples of polymers include thermosetting resins, thermoplastic resins, and rubbers. The polymer composition may also contain unreacted monomers, prepolymers, or macromonomers as precursors of the polymer. For example, the polymer composition may contain a precursor of a curable resin such as polyamic acid. The polymer may be used alone or in combination of two or more types.

[0186] The thermosetting resin may be any known one and is not particularly limited, but examples thereof include phenolic resins, melamine resins, urea resins, unsaturated polyester resins, epoxy resins, polyurethane resins, silicon resins, alkyd resins, thermosetting modified polyphenylene ether resins, thermosetting polyimide resins, benzoxazine resins, urea resins, allyl resins, aniline resins, maleimide resins, bismaleimide triazine resins, liquid crystalline polyester resins, vinyl ester resins, unsaturated polyester resins, cyanate ester resins, polyetherimide resins, etc. These thermosetting resins may be used alone or in combination of two or more.

[0187] The thermosetting resin is preferably at least one selected from the group consisting of phenolic resins, melamine resins, epoxy resins, polyurethane resins, thermosetting modified polyphenylene ether resins, thermosetting polyimide resins, benzoxazine resins, urea resins, allyl resins, maleimide resins, and unsaturated polyester resins, and more preferably at least one selected from the group consisting of epoxy resins, thermosetting modified polyphenylene ether resins, thermosetting polyimide resins, and maleimide resins.

[0188] The thermoplastic resin may be any known one and is not particularly limited, but examples thereof include polyolefins such as polypropylene and polyethylene; polyamides such as PA6, PA66, and PA12; polyimide, polyamideimide, polyetherimide, polyetherketoneketone, polyvinyl chloride, polystyrene, poly(meth)acrylate, polycarbonate, polyvinylidene fluoride, acrylonitrile-butadiene-styrene copolymer (ABS), acrylonitrile-styrene copolymer (AS), polyphenylene ether, polyphenylene sulfide, polyester, polytetrafluoroethylene, thermoplastic elastomers, etc. These thermoplastic resins may be used either alone or in combination of two or more.

[0189] In applications requiring a low dielectric constant or a low dielectric loss tangent, insulating resins such as epoxy resins, thermosetting modified polyphenylene ether resins, thermosetting polyimide resins, silicon resins, benzoxazine resins, melamine resins, urea resins, allyl resins, phenol resins, unsaturated polyester resins, polyurethane resins, and aniline resins are preferably used as the resin, and among these, epoxy resins, thermosetting polyimide resins, modified polyphenylene ether resins, silicon resins, benzoxazine resins, and melamine resins are preferably used. These insulating resins can be used either alone or in combination of two or more.

[0190] The thermoplastic elastomer may be a thermoplastic elastic polymer that has been conventionally used as a molding resin, such as a urethane-based elastomer, a styrene-based elastomer, an olefin-based elastomer, an amide-based elastomer, or an ester-based elastomer. A thermoplastic elastomer generally exhibits rubber elasticity at room temperature (25°C) and has the property of being plasticized and moldable at high temperatures. The thermoplastic elastomer may be used alone or in combination of two or more types.

[0191] Examples of rubber include silicone rubber, acrylonitrile-butadiene copolymer rubber (NBR), natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), ethylene-propylene-diene terpolymer (EPDM), fluororubber, etc. The rubbers may be used alone or in combination of two or more.

[0192] The polymer composition may contain other ingredients in addition to the polymer and hollow particles, as long as the object of the present invention is not impaired.

[0193] For example, the polymer composition may further contain additives such as a curing agent, a curing catalyst, or an initiator for promoting a curing reaction, depending on the type of polymer. Examples of curing agents include amines, acid anhydrides, imidazoles, thiols, phenols, naphthols, benzoxazines, cyanate esters, and carbodiimides. The content of the curing agent is not particularly limited, and may be, for example, 5 to 120 parts by mass per 100 parts by mass of the polymer (matrix polymer).

[0194] The polymer composition may further contain a flame retardant (excluding the hollow particles of the present invention). Examples of the flame retardant include halogen-based flame retardants such as brominated bisphenol compounds and chlorinated paraffins, phosphorus-based flame retardants such as phosphite compounds and phosphate esters, nitrogen-based flame retardants, metal hydroxide-based flame retardants such as magnesium hydroxide and aluminum hydroxide, antimony compounds such as antimony trioxide, and hindered phenol-based flame retardants.

[0195] Examples of commercially available flame retardants include AO-20 (manufactured by Adeka Corporation), AO-30 (manufactured by Adeka Corporation), AO-330 (manufactured by Adeka Corporation), PEP-8 (manufactured by Adeka Corporation), PEP-36 (manufactured by Adeka Corporation), PX-200 (manufactured by Daihachi Chemical Industry Co., Ltd.), HCA-HQ (manufactured by Sankosha), XZ92741 (manufactured by Dow Chemical Company), FX-305 (manufactured by Nippon Steel & Sumitomo Metal Chemical Co., Ltd.), and OP-930 (manufactured by Clariant).

[0196] The content of the flame retardant in the polymer composition is not particularly limited, but is preferably 0.3 to 30 parts by mass, more preferably 1 to 20 parts by mass, and even more preferably 2 to 15 parts by mass, relative to 100 parts by mass of the polymer (matrix polymer).

[0197] Other compounding materials may include fillers including organic and inorganic fillers, colorants including dyes and pigments, antistatic agents, end-capping agents, UV absorbers, UV inhibitors, heat stabilizers, light stabilizers, anti-fogging agents, anti-fog agents, plasticizers, color inhibitors, antioxidants, release agents, moisture-proofing agents, oxygen barrier agents, crystal nucleating agents, compatibilizers, crosslinking agents, and crosslinking aids. The polymer composition may further contain organic or inorganic fibers such as carbon fibers, glass fibers, aramid fibers, and polyethylene fibers. The above compounding materials may be used alone or in combination of two or more.

[0198] The content of the hollow particles in the polymer composition is not particularly limited, but is preferably 1 to 50 parts, more preferably 3 to 40 parts, and even more preferably 5 to 35 parts, per 100 parts by mass of the polymer (matrix polymer). By setting the content of the hollow particles within the above range, the effects of the hollow particles of the present invention can be more efficiently exhibited.

[0199] The polymer composition can be obtained, for example, by mixing the hollow particles of the present invention, a polymer, and any optional additives. When a thermoplastic resin is used as the polymer, the hollow particles of the present invention and any optional additives can be added to a molten thermoplastic resin and melt-kneaded. Alternatively, the hollow particles of the present invention, a polymer solution, and any optional additives can be mixed, and then the solvent can be removed. The polymer composition obtained in this manner may be a liquid polymer composition, or it may be a polymer molded product obtained by molding the liquid polymer composition by a known method.

[0200] The method for producing a polymer molded body is not particularly limited, and for example, a liquid polymer composition obtained by incorporating hollow particles or the like into a liquid matrix polymer before a curing reaction, or a liquid polymer composition obtained by dissolving or dispersing each component in a solvent, is applied to a support, and if necessary, dried and cured, thereby obtaining a polymer molded body.

[0201] Examples of the material for the support include resins such as polyethylene terephthalate and polyethylene naphthalate, and metals such as copper, aluminum, nickel, chromium, gold, and silver. The surface of these supports may be coated with a release agent.

[0202] The liquid polymer composition can be applied by any known method, such as dip coating, roll coating, curtain coating, die coating, slit coating, or gravure coating.

[0203] Alternatively, a polymer molded article can be obtained by impregnating a substrate with the liquid polymer composition, and then drying and curing the composition as necessary. Examples of the substrate include inorganic fibers such as carbon fiber, glass fiber, metal fiber, and ceramic fiber, and organic synthetic fibers such as polyamide fiber, polyester fiber, polyolefin fiber, and novoloid fiber. Glass fiber (glass cloth) is particularly preferred. The form of the substrate is not limited, and woven fabrics and nonwoven fabrics can be used.

[0204] When the liquid polymer composition contains a solvent, it is preferable to dry the polymer composition after the coating or impregnation. The drying temperature is preferably a temperature at which the matrix polymer does not harden, and is usually 20° C. to 200° C., preferably 30° C. to 150° C. The drying time is usually 30 seconds to 1 hour, preferably 1 minute to 30 minutes.

[0205] The curing reaction of the polymer composition is carried out by a method depending on the type of polymer, and is not particularly limited. When a polymer that cures by heating is included, the heating temperature for the curing reaction is appropriately adjusted depending on the type of polymer, and is not particularly limited, but is usually 30°C or higher and 400°C or lower, preferably 70°C or higher and 300°C or lower, and more preferably 100°C or higher and 200°C or lower. The curing time is 5 minutes or higher and 5 hours or lower, preferably 30 minutes or higher and 3 hours or lower. The heating method is not particularly limited, and may be carried out using, for example, an electric oven.

[0206] Alternatively, a resin molded body may be obtained by molding a liquid resin composition containing a thermoplastic resin as a polymer and obtained by melting the resin into a desired shape using a known molding method such as extrusion molding, injection molding, press molding, or compression molding.

[0207] The shape of the polymer molded body is not particularly limited and can be any moldable shape, such as a sheet, film, plate, tube, or any other three-dimensional shape. When the polymer molded body contains fibers, the fibers in the polymer molded body may be in the form of a nonwoven fabric. When the polymer molded body contains fibers, the polymer molded body may be a molded body of a polymer composition in which hollow particles of the present disclosure are added to a fiber-reinforced plastic containing the polymer and fibers as described above.

[0208] Examples of uses of the polymer composition include those uses of the hollow particles of the present invention described above in which the polymer composition can be used.

[0209] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. Note that "parts" and "%" are by mass unless otherwise specified. Various measurements were carried out according to the following methods.

[0210] <Volume average particle diameter (Dv) of hollow particles> The particle diameter of each hollow particle was measured using a laser diffraction particle size distribution analyzer (manufactured by Shimadzu Corporation, product name: SALD-2000), and the volume average was calculated assuming that the hollow particles were spherical, thereby determining the volume average particle diameter (Dv) of the hollow particles.

[0211] <Porosity of hollow particles> The porosity of hollow particles is determined by first calculating the apparent density D １ and true density D ０ The apparent density D １ and true density D ０ was calculated from

[0212] Apparent density D １ First, measure the volume of 100 cm ３ About 30 cm ３The volumetric flask was filled with hollow particles, and the mass of the filled hollow particles was accurately weighed. Next, the volumetric flask filled with the hollow particles was accurately filled with isopropanol up to the marked line, taking care not to introduce air bubbles. The mass of isopropanol added to the volumetric flask was accurately weighed, and the apparent density D of the hollow particles was calculated based on the following formula (I): １ (g / cm ３ The apparent density D １ = [Mass of hollow particles] / (100 - [Mass of isopropanol] ÷ [Specific gravity of isopropanol at measurement temperature]) (I)

[0213] ・True density D ０ Measurement of the volume of 100 cm ３ Approximately 10 g of crushed pieces of hollow particles was filled into a measuring flask, and the mass of the crushed pieces was accurately weighed. Next, in the same manner as in the measurement of the apparent density described above, isopropanol was added to the measuring flask, and the mass of the isopropanol was accurately weighed. The true density D of the hollow particles was calculated based on the following formula (II): ０ (g / cm ３ The true density D ０ = [mass of crushed hollow particle fragments] / (100 - [mass of isopropanol] ÷ [specific gravity of isopropanol at measurement temperature]) (II)

[0214] Calculation of void ratio Apparent density D measured above １ The true density D measured above ０ The result was divided by 100, and the resulting value was subtracted from 100 to obtain the measured porosity (%) of the hollow particles.

[0215] <Residual Double Bond Ratio> Using an ATR-IR (manufactured by PERKIN ELMER, product name: Spectrum One), infrared absorption spectra, expressed as absorbance, were measured for the polymerizable monomers used to prepare the hollow particles before the polymerization reaction and the shell polymers constituting the hollow particles. Measurement of the polymerizable monomers before the polymerization reaction was performed by placing 0.1 g of a measurement sample consisting of polymerizable monomers of the same type and content as the polymerizable monomers used to prepare the hollow particles on the top of a cell, and bringing the measurement sample into contact with a crystal. Measurement of the shell polymers constituting the hollow particles was performed by placing 0.1 g of hollow particles on the top of a cell, and tightening a compression bearing from above to bring the crystal into contact with the hollow particles. From the obtained infrared absorption spectra, the residual double bond ratio was calculated as follows.

[0216] In Examples 1 to 6 and 8 and Comparative Examples 1 to 4, divinylbenzene was used as the reference monomer, and the C-H bond of the benzene ring contained in divinylbenzene was selected as a structure that does not increase or decrease before or after the polymerization reaction. In each of the infrared absorption spectrum of the polymerizable monomer before the polymerization reaction and the infrared absorption spectrum of the shell polymer constituting the hollow particles, a peak derived from the C-H bond of the benzene ring contained in divinylbenzene was identified as the reference peak. The peak derived from the C-H bond of the benzene ring contained in divinylbenzene, the peak derived from the C-H bond of the benzene ring contained in ethylvinylbenzene, the peak derived from the C-H bond of the benzene ring contained in styrene, the peak derived from the C-H bond of the benzene ring contained in 3,4-dimethoxystyrene, and the peak derived from the C-H bond of the benzene ring contained in 4-methoxystyrene appear at the same position, and therefore the value obtained by dividing the peak intensity of the reference peak by the sum of the content percentage of divinylbenzene, the content percentage of ethylvinylbenzene, the content percentage of styrene, the content percentage of 3,4-dimethoxystyrene, and the content percentage of 4-methoxystyrene was used as the reference peak intensity.

[0217] Next, in each infrared absorption spectrum, the peak intensity of the peak derived from the polymerizable unsaturated double bond (C=C) derived from all the polymerizable monomers was measured. ０) relative to the peak intensity (M １ ) ratio (M １ / M ０ ) was determined, and the ratio of these peak intensities was defined as the peak intensity ratio when the residual double bond ratio was 100%. ０ ) relative to the peak intensity (P １ ) ratio (P １ / P ０ ) was calculated in the same way.

[0218] Then, the peak intensity ratio (M １ / M ０ ) and the peak intensity ratio (P １ / P ０ ) and the residual double bond ratio was calculated by the following formula (IV): Residual double bond ratio (%) = (P １ / P ０ ) / (M １ / M ０ ) × 100 (IV)

[0219] In Example 7, the residual double bond ratio was determined in the same manner as above, except that 3,4-dimethoxystyrene was used as the reference monomer.

[0220] <Dielectric Constant (Dk) and Dielectric Loss Tangent (Df) of Hollow Particles> The dielectric constant (Dk) and dielectric loss tangent of hollow particles were measured at a frequency of 1 GHz and room temperature (25°C) using a measuring device (manufactured by AET Co., Ltd., model: ADMS01Nc). The lower the dielectric constant (Dk), the better the dielectric properties. Furthermore, the lower the dielectric loss tangent (Df), the better the dielectric properties.

[0221] <Water Content> First, 10 μl of pure water was precisely weighed out using a microsyringe, and the amount of water (mg) per 1 ml of Karl Fischer reagent was calculated from the amount of reagent titration required to remove this water. Next, 100 to 200 mg of hollow particles were precisely weighed out and left to stand in an environment of 30°C and 80% RH for 2 hours, and then thoroughly dispersed in a measuring flask for 5 minutes using a magnetic stirrer. Next, measurement was started using a Karl Fischer moisture meter (Kyoto Electronics Manufacturing Co., Ltd., MKA-3p), and the amount of Karl Fischer reagent titration required for titration (ml) was determined. The amount of water (mg) and water content (%) of the hollow particles were calculated using the following formula: Water Amount (mg) = Reagent Consumption (ml) × Reagent Titer (mgH ２ Water content (%) = {water content (mg) / sample weight (mg)} × 100

[0222] <IR peak change rate ΔP ｒ > The infrared absorption spectrum of the hollow particles was measured using an ATR-IR (manufactured by PERKIN ELMER, product name: Spectrum One). Measurement of the hollow particles was performed by placing 0.1 g of hollow particles on the top of a cell and tightening the compression bearing from above to bring the crystal and hollow particles into contact. From the infrared absorption spectrum of the hollow particles, a peak was observed in the 680-720 cm －１ The maximum absorbance in the range (P ２ ) to 1680-1720 cm －１ The maximum absorbance in the range (P ３ ) peak intensity ratio (P ３ / P ２ ) was sought.

[0223] Next, the hollow particles were left in an air environment at 130° C. for 240 hours to heat-treat the hollow particles. The infrared absorption spectrum of the heat-treated hollow particles was measured in the same manner as before the heat treatment. From the infrared absorption spectrum of the heat-treated hollow particles, －１ The maximum absorbance in the range (P ４ ) to 1680-1720 cm －１ The maximum absorbance in the range (P ５ ) peak intensity ratio (P ５ / P ４) was sought.

[0224] Then, the peak intensity ratio (P ３ / P ２ ) and the peak intensity ratio after the heat treatment (P ５ / P ４ ) and the peak intensity ratio P ｒ The rate of change ΔP before and after heat treatment ｒ The peak intensity ratio P ｒ The rate of change ΔP before and after heat treatment ｒ (%) = {(P ５ / P ４ )-(P ３ / P ２ ) / (P ３ / P ２ ) x 100 (2)

[0225] <Heating Test 1 (130°C, 240H)> The hollow particles were left in air at 130°C for 240 hours to thermally deteriorate the hollow particles. Next, using a measuring device (manufactured by AET, model: ADMS01Nc) at a frequency of 1 GHz and room temperature (25°C), the dielectric constant and dielectric loss tangent (Df) of the hollow particles after the heat treatment were measured. The rate of change in the dielectric constant (Dk) of the hollow particles after the heat deterioration test was calculated relative to the measured value obtained in the measurement of the dielectric constant (Dk) of the hollow particles. The change in the dielectric loss tangent (Df) of the hollow particles after the heat deterioration test was calculated relative to the measured value obtained in the measurement of the dielectric loss tangent (Df) of the hollow particles. The smaller the rate of change in the dielectric constant (Dk) and the amount of change in the dielectric loss tangent (Df), the more suppressed the deterioration of the dielectric properties of the hollow particles under high-temperature conditions can be judged.

[0226] <Heating Test 2 (140°C, 240H)> A heating test at a higher temperature was conducted using the hollow particles of Examples 1 to 8. Specifically, the test was conducted in the same manner as Heating Test 1, except that the heating temperature was changed from 130°C to 140°C. It can be determined that the smaller the rate of change in relative permittivity (Dk) and the amount of change in dielectric dissipation factor (Df), the more suppressed the deterioration of the dielectric properties of the hollow particles under high-temperature conditions.

[0227] Example 1 (1) Mixture Preparation Step First, the following materials were mixed, and the resulting mixture was used as an oil phase: 33 parts of "DVB630" (trade name, first polymerizable monomer, manufactured by Nippon Steel Chemical & Material Co., Ltd., divinylbenzene 63%, ethylvinylbenzene 37%) (divinylbenzene 20.79 parts, ethylvinylbenzene 12.21 parts) 0.89 parts of t-butylperoxydiethyl acetate (oil-soluble polymerization initiator, manufactured by Nouryon Chemical Co., Ltd., trade name "Trigonox 27") 67.0 parts of heptane (hydrophobic solvent)

[0228] Next, in a stirring tank, at a temperature of 40°C, an aqueous solution of 19.59 parts of magnesium chloride (a water-soluble polyvalent metal salt) dissolved in 225 parts of ion-exchanged water was gradually added with stirring to an aqueous solution of 13.72 parts of sodium hydroxide (an alkali metal hydroxide salt) dissolved in 55 parts of ion-exchanged water to prepare a magnesium hydroxide colloid (a poorly water-soluble metal hydroxide colloid) dispersion. 15 minutes after the addition, stirring was stopped to form an aqueous phase. The obtained magnesium hydroxide colloid dispersion contained 10 parts of magnesium hydroxide per 280 parts of ion-exchanged water. The obtained aqueous phase and oil phase were mixed to prepare a mixed liquid.

[0229] (2) Suspension step The mixture obtained in the above (1) Mixture preparation step was subjected to a suspension treatment by stirring for 1 minute using an emulsifying disperser (manufactured by Primix Corporation, product name: Homomixer) under the condition of a tip speed of the rotating part of 88 m / s, thereby preparing a suspension in which droplets of the monomer composition encapsulating the hydrophobic solvent were dispersed in water.

[0230] (3) Polymerization Step (3-1) First Polymerization Step The suspension obtained in the suspension step (2) above was heated from 40°C to 80°C in a nitrogen atmosphere, and stirred for 1 hour under the temperature condition of 80°C to carry out a first polymerization reaction, thereby preparing a first precursor composition which was a slurry liquid in which first precursor particles encapsulating a hydrophobic solvent were dispersed in water.

[0231] (3-2) Second Polymerization Step Subsequently, 20.00 parts of 3,4-dimethoxystyrene (styrene compound (A1)) as a second polymerizable monomer was added to the first precursor composition prepared in (3-1) above, and the mixture was stirred for 24 hours under a nitrogen atmosphere at a temperature of 80°C, thereby carrying out a second polymerization reaction. This polymerization reaction yielded a second precursor composition that was a slurry liquid in which second precursor particles encapsulating a hydrophobic solvent were dispersed in water. Note that the polymerization conversion rate in the first polymerization reaction when the second polymerizable monomer was added was 50%.

[0232] (4) Washing Step / Solid-Liquid Separation Step The second precursor composition obtained in the second polymerization step (3-2) above was washed with dilute sulfuric acid (25°C, 10 minutes) to adjust the pH to 5.5 or less. Next, after separating the water by filtration, 200 parts of fresh ion-exchanged water was added to re-slurry the mixture. The water washing treatment (washing, filtration, dehydration) was repeated several times at room temperature (25°C), and the mixture was filtered to obtain a solid fraction. The obtained solid fraction was dried in a dryer at a temperature of 40°C to obtain precursor particles encapsulating a hydrophobic solvent.

[0233] (5) Solvent Removal Step The precursor particles obtained in the above (4) Washing Step / Solid-Liquid Separation Step were heat-treated under vacuum conditions in a vacuum dryer at 200°C for 6 hours to remove the hydrophobic solvent contained in the particles, thereby obtaining hollow particles of Example 1. From the results of observation of the obtained hollow particles using a scanning electron microscope and the porosity value, it was confirmed that the particles were spherical and had hollow portions. The polymerization conversion rate was nearly 100%, and the monomer composition of the shell polymer in the obtained hollow particles generally matched the composition of the polymerizable monomers used in the polymerization. (This was also the case in each of the Examples and Comparative Examples described below.)

[0234] The obtained hollow particles were used to measure the volume average particle diameter (Dv), porosity, residual double bond ratio, relative dielectric constant, dielectric loss tangent, water content, and IR peak change rate ΔP ｒ The values ​​were measured, and heating tests 1 and 2 were carried out. The results are shown in Table 1.

[0235] Example 2 (1) Hollow particles were obtained in the same manner as in Example 1, and evaluated in the same manner, except that 33 parts of "DVB690" (trade name, manufactured by Nippon Steel Chemical & Material Co., Ltd., divinylbenzene 69%, ethylvinylbenzene 31%) (divinylbenzene 22.77 parts, ethylvinylbenzene 10.23 parts) were used instead of "DVB630" in the mixed solution preparation step. The polymerization conversion rate in the first polymerization reaction when the second polymerizable monomer was added was 50%. The results are shown in Table 1.

[0236] Example 3 (1) Hollow particles were obtained in the same manner as in Example 1, and evaluated in the same manner, except that 33 parts of "DVB810" (trade name, manufactured by Nippon Steel Chemical & Material Co., Ltd., divinylbenzene 81%, ethylvinylbenzene 19%) (divinylbenzene 26.73 parts, ethylvinylbenzene 6.27 parts) were used instead of "DVB630" in the mixed solution preparation step. The polymerization conversion rate in the first polymerization reaction when the second polymerizable monomer was added was 50%. The results are shown in Table 1.

[0237] Example 4 (3-2) Hollow particles were obtained and evaluated in the same manner as in Example 1, except that the amount of 3,4-dimethoxystyrene added to the first precursor composition in the second polymerization step was changed from 20.00 parts to 9.00 parts. The polymerization conversion rate in the first polymerization reaction when the second polymerizable monomer was added was 50%. The results are shown in Table 1.

[0238] Example 5 (1) Hollow particles were obtained and evaluated in the same manner as in Example 4, except that the amount of "DVB630" used in the mixed solution preparation step was changed from 33 parts to 38.8 parts (divinylbenzene 24.44 parts, ethylvinylbenzene 14.36 parts) and the amount of heptane used was changed from 67.0 parts to 61.2 parts. The polymerization conversion rate in the first polymerization reaction when the second polymerizable monomer was added was 40%. The results are shown in Table 1.

[0239] Example 6 (1) Mixed Liquid Preparation Step A mixed liquid was prepared in the same manner as in Example 1, except that the following materials were mixed and the resulting mixture was used as the oil phase: 33 parts of "DVB630" (trade name, first polymerizable monomer, manufactured by Nippon Steel Chemical & Material Co., Ltd., divinylbenzene 63%, ethylvinylbenzene 37%) (divinylbenzene 20.79 parts, ethylvinylbenzene 12.21 parts) 20.00 parts of 3,4-dimethoxystyrene (styrene compound (A1)) 0.89 parts of t-butylperoxydiethyl acetate (oil-soluble polymerization initiator, manufactured by Nouryon Chemical Co., Ltd., trade name "Trigonox 27") Heptane (hydrophobic solvent) 67.0 parts (2) Suspension Step A suspension in which droplets of a monomer composition encapsulating a hydrophobic solvent were dispersed in water was prepared in the same manner as in Example 1, except that the mixed liquid obtained in the above (1) mixed liquid preparation step was used. (3) Polymerization Step (3-1) First Polymerization Step The suspension obtained in the above (2) Suspension Step was heated from 40°C to 80°C in a nitrogen atmosphere and stirred at 80°C for 25 hours to carry out a polymerization reaction. This polymerization reaction yielded a first precursor composition, which was a slurry liquid in which precursor particles encapsulating a hydrophobic solvent were dispersed in water. (4) Washing Step / Solid-Liquid Separation Step and (5) Solvent Removal Step Hollow particles were obtained in the same manner as in Example 1, except that the first precursor composition obtained in the above (3-1) Polymerization Step was used, and evaluation was carried out in the same manner. The results are shown in Table 1.

[0240] Example 7 (1) Mixture preparation step (3-2) Hollow particles were obtained and evaluated in the same manner as in Example 6, except that the amount of 3,4-dimethoxystyrene added to the first precursor composition in the second polymerization step (3-2) was changed from 20.00 parts to 50.00 parts. The results are shown in Table 1.

[0241] Example 8 (3-2) Hollow particles were obtained in the same manner as in Example 1, except that in the second polymerization step, 4-methoxystyrene (styrene compound (A3)) was used instead of 3,4-dimethoxystyrene as the second polymerizable monomer, and the obtained hollow particles were evaluated in the same manner. When the second polymerizable monomer was added, the polymerization conversion rate in the first polymerization reaction was 50%. The results are shown in Table 1.

[0242] Comparative Example 1 (1) Mixed Liquid Preparation Step A mixed liquid was prepared in the same manner as in Example 1, except that the following materials were mixed and the resulting mixture was used as the oil phase: 44.3 parts of "DVB960" (trade name, first polymerizable monomer, manufactured by Nippon Steel Chemical & Material Co., Ltd., divinylbenzene 96%, ethylvinylbenzene 4%) (divinylbenzene 42.53 parts, ethylvinylbenzene 1.77 parts) 0.89 parts t-butylperoxydiethyl acetate Hydrophobic solvent: heptane 55.7 parts (2) Suspension Step A suspension in which droplets of a monomer composition encapsulating a hydrophobic solvent were dispersed in water was prepared in the same manner as in Example 1, except that the mixed liquid obtained in the mixed liquid preparation step (1) above was used. (3) Polymerization Step (3-1) First Polymerization Step The suspension obtained in the suspension step (2) above was heated from 40°C to 80°C in a nitrogen atmosphere and stirred at 80°C for 25 hours to carry out a polymerization reaction. This polymerization reaction yielded a first precursor composition, which was a slurry liquid in which precursor particles encapsulating a hydrophobic solvent were dispersed in water. (4) Washing Step / Solid-Liquid Separation Step and (5) Solvent Removal Step Hollow particles were obtained in the same manner as in Example 1, except for the first precursor composition obtained in the above (3-1) polymerization step. The obtained hollow particles were then used to measure the volume average particle size (Dv), porosity, residual double bond ratio, relative dielectric constant, dielectric loss tangent, water content, and IR peak change rate ΔP ｒ The results are shown in Table 2.

[0243] <Comparative Example 2> (1) Hollow particles were obtained and evaluated in the same manner as in Comparative Example 1, except that 44.3 parts of "DVB630" (27.91 parts of divinylbenzene, 16.39 parts of ethylvinylbenzene) was used instead of "DVB960" in the mixed solution preparation step. The results are shown in Table 2.

[0244] <Comparative Example 3> (1) In the mixed solution preparation step, the amount of "DVB630" used was changed from 44.3 parts to 39.1 parts (divinylbenzene 24.60 parts, ethylvinylbenzene 14.50 parts) and the amount of heptane used was changed from 55.7 parts to 60.8 parts, respectively. Except for this, hollow particles were obtained in the same manner as in Comparative Example 2, and evaluation was performed in the same manner. The results are shown in Table 2.

[0245] Comparative Example 4 (1) Mixture Preparation Step First, the following materials were mixed, and the resulting mixture was used as an oil phase. "DVB810" 1.85 parts (first polymerizable monomer, divinylbenzene 1.50 parts, ethylvinylbenzene 0.35 parts) Styrene 1.15 parts Polyethylene glycol propylene glycol monomethacrylate (manufactured by NOF Corporation, trade name "BLEMMER 50PEP-300") 0.60 parts t-Butylperoxydiethyl acetate 0.89 parts Hydrophobic solvent: heptane 2.4 parts

[0246] Next, 34 parts of ion-exchanged water and 0.017 parts of "Rapisol A-80" (trade name, surfactant, manufactured by NOF Corporation) were mixed in a stirring tank to obtain a mixture called an aqueous phase. The obtained aqueous phase and oil phase were mixed to prepare a mixed liquid.

[0247] (2) Suspension step, (3) Polymerization step, (4) Washing step / solid-liquid separation step, and (5) Solvent removal step. Except for using the mixed liquid obtained in the above (1) mixed liquid preparation step, hollow particles were obtained in the same manner as in Comparative Example 1, and evaluation was performed in the same manner. The results are shown in Table 2.

[0248]

[0249]

[0250] As shown in Table 1, hollow particles having a shell containing a resin and a hollow portion surrounded by the shell, in which the porosity is 45 to 95%, and in which the shell polymer constituting the resin contains units derived from the OR group-containing aromatic vinyl compound (A), were excellent in dielectric properties and were able to suppress deterioration of the dielectric properties under high temperature conditions (Examples 1 to 8).

[0251] On the other hand, as shown in Table 2, hollow particles in which the shell polymer does not contain units derived from the OR group-containing aromatic vinyl compound (A) were inferior in dielectric properties, and the dielectric properties were significantly reduced after the heat degradation test (Comparative Examples 1 to 4).

[0252] <Production and Evaluation of Resin Composition, Resin Film, and Molded Article> In Examples 9 to 15 and Comparative Examples 5 to 17, resin compositions, resin films, and molded articles were produced and evaluated. The flame retardants used in the production of the resin compositions were as follows. Example 9, Comparative Example 13: Aromatic condensed phosphate ester, manufactured by Daihachi Chemical Industry Co., Ltd., product name: PX-200 Example 10: Phosphite-based flame retardant, manufactured by Adeka Corporation, product name: PEP-36 Example 11: Hindered phenol-based flame retardant, antioxidant, manufactured by Adeka Corporation, product name: AO-20

[0253] Examples 9 to 11 (1) Preparation of Resin Composition 100 parts of a 65% toluene solution of modified polyphenylene ether (modified PPE) modified with a functional group having a vinyl group (manufactured by Mitsubishi Gas Chemical Company, Inc., product name: OPE-1200, iodine value: 43 g / 100 g, number average molecular weight: 1200) was weighed into a cup, and 11 parts of the hollow particles obtained in Example 1, 0.63 parts of dicumyl peroxide (manufactured by NOF Corporation, product name: Percumyl D) and 5 parts of a flame retardant listed in Table 4 were added, and the mixture was uniformly dispersed using a planetary stirring degassing apparatus (manufactured by Kurabo Industries, Ltd., product name: Mazerustar) to prepare a liquid resin composition.

[0254] (2) Preparation and Evaluation of Resin Films Aluminum foil was attached to a glass plate without any wrinkles, and the resin composition obtained in (1) above was applied to the aluminum foil using a No. 75 bar coater to form a coating film. The coating film was cured by heating in a nitrogen atmosphere at 80°C for 1 hour, 120°C for 30 minutes, 160°C for 30 minutes, and 200°C for 1 hour, forming a resin film on the aluminum foil. The laminate of the resin film and aluminum foil was immersed in a 1N aqueous hydrochloric acid solution overnight to remove the aluminum foil and obtain only the resin film. The obtained resin film was washed with ion-exchanged water and dried to obtain a resin film. The hollow particle content of the obtained resin film was 40% by volume relative to 100% by volume of the resin film.

[0255] The resin film obtained above was cut into a width of 3 mm and a length of 80 mm to obtain a measurement sample. The relative dielectric constant and dielectric loss tangent of the obtained measurement sample were measured at a frequency of 10 GHz and room temperature (25°C) using a perturbation type measuring device (manufactured by AET Co., Ltd., model: ADMS01Nc). The results are shown in Table 4.

[0256] (3) Preparation and Evaluation of Polymer Molded Articles Five test pieces measuring 125 mm x 13 mm x 0.2 mm were cut from the resin film obtained in (2) above. A vertical combustion test was conducted using the obtained test pieces. Specifically, each test piece was attached vertically to a clamp and exposed to a 20 mm flame for 5 seconds twice, and the test results were judged based on the combustion behavior in accordance with the test standard. The evaluation criteria are shown in Table 3. The evaluation results showed that "V-1" was superior to "V-2," and "V-0" was superior to "V-1."

[0257]

[0258] Example 12 (1) Preparation of Resin Composition 100 parts of a 65% toluene solution of modified polyphenylene ether (modified PPE) modified with a functional group having a vinyl group (manufactured by Mitsubishi Gas Chemical Company, Inc., product name: OPE-1200, iodine value: 43 g / 100 g, number average molecular weight: 1200) was weighed into a cup, and 11 parts of the hollow particles obtained in Example 1 and 0.63 parts of dicumyl peroxide (manufactured by NOF Corporation, product name: Percumyl D) were added, and the mixture was uniformly dispersed using a planetary stirring degassing apparatus (manufactured by Kurabo Industries, Ltd., product name: Mazerustar) to prepare a liquid resin composition.

[0259] (2) Preparation and Evaluation of Resin Films Aluminum foil was attached to a glass plate without any wrinkles, and the resin composition obtained in (1) above was applied to the aluminum foil using a No. 75 bar coater to form a coating film. The coating film was cured by heating under a nitrogen atmosphere at 80°C for 1 hour, 120°C for 30 minutes, 160°C for 30 minutes, and 200°C for 1 hour, forming a resin film on the aluminum foil. The laminate of the resin film and aluminum foil was immersed in a 1N aqueous hydrochloric acid solution overnight to remove the aluminum foil and obtain only the resin film. The obtained resin film was washed with ion-exchanged water and dried to obtain a resin film. The hollow particle content of the obtained resin film was 40% by volume relative to 100% by volume of the resin film. The obtained resin film was evaluated in the same manner as in Example 9. The results are shown in Table 4.

[0260] (3) Preparation and Evaluation of Polymer Molded Articles Preparation and evaluation of polymer molded articles were carried out in the same manner as in Example 9, except that the resin composition obtained in (1) above was used. The results are shown in Table 4.

[0261] Example 13 (1) Preparation of Resin Composition Four parts of 2-ethyl-4-methylimidazole (2E4MZ) (manufactured by Shikoku Chemicals Corporation) and 17 parts of the hollow particles obtained in Example 1 were added to 100 parts of a bisphenol A liquid epoxy resin (manufactured by Mitsubishi Chemical Corporation, product name: jER (registered trademark) 828, epoxy equivalent: 184 to 194), and the mixture was uniformly dispersed using a planetary stirring degassing apparatus (manufactured by Kurabo Industries Co., Ltd., product name: Mazerustar), thereby preparing a liquid resin composition.

[0262] (2) Preparation and Evaluation of Resin Films Aluminum foil was attached to a glass plate without any wrinkles, and the resin composition obtained in (1) above was applied to the aluminum foil using a bar coater No. 75 to form a coating film. The coating film was cured by heating at 150°C for 3 hours under a nitrogen atmosphere, forming a resin film on the aluminum foil. The laminate of the resin film and aluminum foil was immersed in a 1N aqueous hydrochloric acid solution overnight to remove the aluminum foil and obtain only the resin film. The obtained resin film was washed with ion-exchanged water and dried to obtain a resin film. The hollow particle content of the obtained resin film was 40% by volume relative to 100% by volume of the resin film. The obtained resin film was evaluated in the same manner as in Example 9. The results are shown in Table 4.

[0263] Example 14 (1) Preparation of Resin Composition 50 g of a polyamic acid solution (manufactured by Ube Industries, Ltd., product name: U-Varnish-A) was weighed into a cup, and 2.5 g of the hollow particles obtained in Example 1 was added thereto. The mixture was uniformly dispersed in a planetary stirring degassing apparatus (manufactured by Kurabo Industries, Ltd., product name: Mazerustar) to obtain a liquid resin composition.

[0264] (2) Preparation and Evaluation of Resin Films Aluminum foil was attached to a glass plate, and the resin composition obtained in (1) above was applied to the aluminum foil using a No. 75 bar coater to form a coating film. The coating film was heated in a nitrogen atmosphere at 120°C for 30 minutes, 150°C for 10 minutes, 200°C for 10 minutes, and 250°C for 30 minutes, successively to polyimideate the polyamic acid and harden the coating film, forming a polyimide film containing hollow particles on the aluminum foil. The laminate of the film and aluminum foil was immersed in a 1N aqueous hydrochloric acid solution overnight to remove the aluminum foil and obtain the film alone. The obtained film was washed with ion-exchanged water and dried to obtain a polyimide film containing hollow particles. The hollow particle content of the obtained resin film was 40% by volume relative to 100% by volume of the resin film. The obtained resin film was evaluated in the same manner as in Example 9. The results are shown in Table 4.

[0265] Example 15 (1) Preparation of Resin Composition 100 parts of a 70% MEK solution of maleimide resin (manufactured by Nippon Kayaku Co., Ltd., product name: MIR-3000-70MT, number average molecular weight: 1200) was weighed into a cup, and 12.3 parts of the hollow particles obtained in Example 1 and 0.7 parts of dicumyl peroxide (manufactured by NOF Corporation, product name: Percumyl D) were added thereto, and the mixture was uniformly dispersed using a planetary stirring degassing apparatus (manufactured by Kurabo Industries Co., Ltd., product name: Mazerustar) to prepare a liquid resin composition.

[0266] (2) Preparation and Evaluation of Resin Films Aluminum foil was attached to a glass plate without any wrinkles, and the resin composition obtained in (1) above was applied to the aluminum foil using a No. 75 bar coater to form a coating film. The coating film was cured by heating under a nitrogen atmosphere at 80°C for 1 hour, 120°C for 30 minutes, 160°C for 30 minutes, and 200°C for 1 hour, forming a resin film on the aluminum foil. The laminate of the resin film and aluminum foil was immersed in a 1N aqueous hydrochloric acid solution overnight to remove the aluminum foil and obtain only the resin film. The obtained resin film was washed with ion-exchanged water and dried to obtain a resin film. The hollow particle content of the obtained resin film was 40% by volume relative to 100% by volume of the resin film. The obtained resin film was evaluated in the same manner as in Example 9. The results are shown in Table 4.

[0267] Comparative Examples 5 to 8 Resin compositions and resin films were produced in the same manner as in Examples 12 to 15, except that hollow particles were not used. The obtained resin films were evaluated in the same manner as in Example 9. The results are shown in Table 5.

[0268] Comparative Examples 9 to 12 Resin compositions and resin films were produced in the same manner as in Examples 12 to 15, except that silica particles (manufactured by Admattex Co., Ltd., product name: SC-2500 SXJ, particle size: 0.5 μm) were used instead of the hollow particles. The obtained resin films were evaluated in the same manner as in Example 9. The results are shown in Table 5.

[0269] Comparative Example 13 A resin composition, a resin film, and a polymer molded article were produced in the same manner as in Example 9, except that the hollow particles were changed to the hollow particles obtained in Comparative Example 1. The obtained resin film and polymer molded article were evaluated in the same manner as in Example 9. The results are shown in Table 5.

[0270] Comparative Examples 14 to 17 Resin compositions and resin films were produced in the same manner as in Examples 12 to 15, except that the hollow particles were changed to the hollow particles obtained in Comparative Example 1. The obtained resin films were evaluated in the same manner as in Example 9. The results are shown in Table 5.

[0271]

[0272]

[0273] As shown in Table 4, when hollow particles having a resin-containing shell and a hollow portion surrounded by the shell, with a porosity of 45 to 95%, and the shell polymer constituting the resin containing units derived from the OR group-containing aromatic vinyl compound (A) were used, polymer compositions (resin compositions and resin films) with excellent dielectric properties were obtained (Examples 9 to 15). Furthermore, the resulting polymer compositions (polymer molded articles) also had excellent flame retardancy.

[0274] On the other hand, as shown in Table 5, the polymer compositions obtained when the above hollow particles were not used (Comparative Examples 5 to 8) or when particles other than the above hollow particles were used (Comparative Examples 9 to 17) each had inferior dielectric properties compared to the polymer compositions obtained when the above hollow particles were used (Examples 9 to 15).

Claims

1. Hollow particles having a shell containing a resin and a hollow portion surrounded by the shell, the porosity being 45 to 95%, and the shell polymer constituting the resin containing units derived from an aromatic vinyl compound (A) in which one vinyl group and one or more functional groups (a) represented by the following general formula (a) are directly bonded to an aromatic ring: -OR(a) (In general formula (a), R is a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkali metal atom, or an acetyl group.) 2. The hollow particle according to claim 1, wherein the content of units derived from the aromatic vinyl compound (A) in the shell polymer is 10 to 50% by mass.

3. The hollow particles according to claim 1 or 2, which have a volume average particle size of 1 to 50 μm.

4. The hollow particle according to any one of claims 1 to 3, wherein the content of hydrocarbon monomer units in the shell polymer is 80 mass % or more.

5. The hollow particles according to any one of claims 1 to 4, wherein the aromatic vinyl compound (A) is a styrene compound having one vinyl group and one or more functional groups (a) directly bonded to a benzene ring.

6. The hollow particle according to claim 5, wherein the aromatic vinyl compound (A) is at least one styrene compound selected from the group consisting of a styrene compound (A1) represented by the following general formula (A1), a styrene compound (A2) represented by the following general formula (A2), and a styrene compound (A3) represented by the following general formula (A3): (In general formulas (A1) to (A3), R １ ~R ５ are each independently a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkali metal atom, or an acetyl group.

7. The hollow particle according to any one of claims 1 to 5, wherein the number of functional groups (a) directly bonded to the aromatic ring in the aromatic vinyl compound (A) is two.

8. A polymer composition comprising the hollow particles according to any one of claims 1 to 7 and a matrix polymer.

9. The polymer composition according to claim 8, wherein the matrix polymer is at least one thermosetting resin selected from the group consisting of phenolic resins, melamine resins, epoxy resins, polyurethane resins, thermosetting modified polyphenylene ether resins, thermosetting polyimide resins, benzoxazine resins, urea resins, allyl resins, maleimide resins, and unsaturated polyester resins.

10. The polymer composition according to claim 9, wherein the matrix polymer is at least one thermosetting resin selected from the group consisting of epoxy resins, thermosetting modified polyphenylene ether resins, thermosetting polyimide resins, and maleimide resins.

11. The polymer composition according to any one of claims 8 to 10, further comprising a flame retardant.

12. A polymer molded article comprising the hollow particles according to any one of claims 1 to 7 and a matrix polymer.

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