Hollow particles, resin composition, resin molded body, resin composition for sealing, cured product and semiconductor device

Abstract

The present invention provides hollow particles which have a reduced dielectric loss tangent, while having improved performance stability in a high humidity environment. The present invention provides hollow particles each of which comprises a shell that contains a resin and a hollow part that is surrounded by the shell, wherein: the void fraction is 50% or more; the shell contains a polymer as the resin; the content of crosslinkable monomer units in 100% by mass of all monomer units of the polymer is 60% by mass or more; the content of a surfactant that is present on the surfaces of the hollow particles is 200 ppm or less; and with respect to an aqueous dispersion of the hollow particles obtained by dispersing the hollow particles in a volume of 0.35 cm3 in 100 mL of an ion exchange water, the pH is 6.5 to 7.5 and the conductivity is 50 µS / cm or less.

Description

Hollow particles, resin composition, resin molded body, encapsulating resin composition, cured product, and semiconductor device

[0001] The present disclosure relates to hollow particles, a resin composition and a resin molded product containing the hollow particles, an encapsulating resin composition containing the hollow particles and a cured product thereof, and a semiconductor device including the cured product as an encapsulant.

[0002] Hollow particles (hollow resin particles) have cavities inside the particles and are therefore added to resins, paints, various molded products, and the like for the purposes of weight reduction, heat insulation, low dielectric constant, and the like. Their applications extend to a wide range of fields, including automobiles, bicycles, aviation, electricity, electronics, construction, home appliances, containers, stationery, tools, and footwear.

[0003] In the fields of electricity and electronics, attempts have been made to add hollow particles to insulating materials in order to lower their dielectric constants and dielectric loss tangents. For example, Patent Document 1 discloses hollow crosslinked resin particles for use in low-dielectric-constant organic insulating materials, which are obtained by polymerizing 1 to 100% by weight of a crosslinkable monomer and 0 to 99% by weight of a non-crosslinkable monomer (here, the total of the crosslinkable monomer and the non-crosslinkable monomer is 100% by weight), have an average particle size of 0.03 to 10 μm, and have an average metal ion concentration of 50 ppm or less. The hollow crosslinked resin particles in Patent Document 1 are produced by dispersing monomers in water using an emulsifier (surfactant) and then performing seed polymerization.

[0004] Patent Document 2 discloses microparticle-coated hollow particles obtained by heating and expanding heat-expandable microspheres having an ash content of 1.2 wt % or less, each of which comprises an outer shell made of a specific thermoplastic resin and a blowing agent encapsulated therein, and by depositing microparticles such as inorganic microparticles on the outer surface of the microspheres.

[0005] Patent Document 3 discloses hollow particles obtained by dispersing an organic mixed solution containing an aromatic crosslinkable monomer (a), an aromatic monofunctional monomer (b), a (meth)acrylic acid ester monomer (c) having a specific structure, a side-chain crystalline polyolefin, a polymerization initiator, and an organic solvent in an aqueous solution containing a surfactant, and then performing suspension polymerization.

[0006] Patent Document 4 discloses hollow particles obtained by dispersing an oil phase containing a hydrocarbon monomer having a crosslinkable monomer content of 70 mass% or more, a hydrocarbon solvent having 5 to 8 carbon atoms, and a polymerization initiator in an aqueous phase that is a poorly water-soluble metal hydroxide colloid, and then performing suspension polymerization.

[0007] JP 2000-313818 A JP 2015-3951 A International Publication No. 2021 / 085189 International Publication No. 2022 / 092076

[0008] Hollow particles added to various materials for the purpose of lowering their dielectric loss tangent are desirable to have a lower dielectric loss tangent. Furthermore, electronic circuit boards are also required to have stable performance in high-humidity environments, and are required to avoid problems such as ion migration (a phenomenon in which ionized metal migrates between electrodes, causing a short circuit) in high-humidity environments. However, electronic circuit boards containing hollow particles may be prone to ion migration in high-humidity environments.

[0009] An object of the present disclosure is to provide hollow particles having a reduced dielectric loss tangent and improved performance stability in high-humidity environments. Another object of the present disclosure is to provide a resin composition and a resin molded product that contain the hollow particles, thereby reducing the dielectric loss tangent while suppressing a decrease in performance stability in high-humidity environments. Another object of the present disclosure is to provide, as the resin composition and resin molded product, in particular, an encapsulating resin composition and a cured product thereof, and further to provide a semiconductor device that includes the cured product of the encapsulating resin composition as an encapsulant.

[0010] The present inventors have discovered that a metal or surfactant contained in hollow particles in a manner that makes it easy to dissolve in water tends to increase the dielectric tangent of the hollow particles and reduce performance stability in high-humidity environments, and have arrived at the present disclosure.

[0011] The present disclosure provides a hollow particle having a shell containing a resin and a hollow portion surrounded by the shell, the hollow particle having a porosity of 50% or more, the shell containing a polymer as the resin, a content of crosslinkable monomer units of 60% by mass or more relative to 100% by mass of all monomer units of the polymer, and a volume of 0.35 cm ３ The hollow particles are provided such that an aqueous dispersion of the hollow particles obtained by dispersing the hollow particles of the above formula (1) in 100 mL of ion-exchanged water has a pH of 6.5 or more and 7.5 or less and an electrical conductivity of 50 μS / cm or less.

[0012] In the hollow particles of the present disclosure, the content of hydrocarbon monomer units in 100% by mass of all monomer units of the polymer is preferably more than 50% by mass.

[0013] In the hollow particles of the present disclosure, the metal content is preferably 700 ppm or less.

[0014] In the hollow particles of the present disclosure, the content of surfactant present on the surface of the hollow particles is preferably 200 ppm or less.

[0015] In the hollow particles of the present disclosure, the dielectric loss tangent at a frequency of 10 GHz is 1.00 × 10 －３ It is preferable that:

[0016] In the hollow particles of the present disclosure, the relative dielectric constant at a frequency of 10 GHz is preferably 1.00 or more and 1.40 or less.

[0017] In the hollow particles of the present disclosure, the porosity is preferably 70% or more.

[0018] The present disclosure further provides a resin composition comprising the hollow particles of the present disclosure and a matrix resin, and a resin molded article obtained from the resin composition of the present disclosure.

[0019] The present disclosure further provides an encapsulating resin composition comprising the hollow particles of the present disclosure and an epoxy resin. The present disclosure further provides a cured product of the encapsulating resin composition of the present disclosure. The present disclosure further provides a semiconductor device comprising, as an encapsulant, the cured product of the encapsulating resin composition of the present disclosure.

[0020] The present disclosure provides hollow particles having a reduced dielectric loss tangent and improved performance stability in high-humidity environments. Furthermore, the present disclosure provides a resin composition and a resin molded product that contain the hollow particles, thereby reducing the dielectric loss tangent while suppressing a decrease in performance stability in high-humidity environments. Furthermore, the present disclosure provides, as the resin composition and resin molded product, in particular, an encapsulating resin composition and a cured product thereof, and further provides a semiconductor device that includes the cured product of the encapsulating resin composition as an encapsulant.

[0021] FIG. 1 is a diagram illustrating an example of a method for producing hollow particles according to the present disclosure.

[0022] The hollow particles disclosed herein are hollow particles having a shell containing a resin and a hollow portion surrounded by the shell, the hollow particles having a porosity of 50% or more, the shell containing a polymer as the resin, the polymer having a content of crosslinkable monomer units of 60% by mass or more relative to 100% by mass of all monomer units, and a volume of 0.35 cm ３ The hollow particles are dispersed in 100 mL of ion-exchanged water to obtain an aqueous dispersion of the hollow particles, which has a pH of 6.5 or more and 7.5 or less and an electrical conductivity of 50 μS / cm or less.

[0023] The hollow particles of the present disclosure contain sufficiently low amounts of metal and surfactant in a manner that allows them to be easily dissolved in water, thereby suppressing an increase in the dielectric tangent of the hollow particles and a decrease in the performance stability of the hollow particles in high-humidity environments due to the metal or surfactant. Because the hollow particles of the present disclosure contain sufficiently low amounts of both metal and surfactant, they are significantly more effective in reducing the dielectric tangent and improving performance stability in high-humidity environments than when only one of the two components is reduced. The hollow particles of the present disclosure have a reduced amount of ionic surfactant on the particle surface, among surfactants, thereby effectively suppressing the occurrence of ion migration in electronic circuit boards containing the hollow particles. In an aqueous dispersion of hollow particles dispersed in ion-exchanged water, the greater the amount of metal or ionic surfactant dissolved from the hollow particles, the higher the electrical conductivity tends to increase. The greater the amount of metal dissolved from the hollow particles, the higher the pH tends to increase. When the amount of ionic surfactant exceeds a certain value, the pH tends to become basic (greater than 7.5). The inventors discovered that the greater the amount of metal and ionic surfactant eluted from hollow particles into an aqueous dispersion, the higher the dielectric loss tangent of the hollow particles, which can lead to poorer performance stability in high-humidity environments, particularly in electronic circuit boards containing hollow particles, where ion migration is likely to occur. The dielectric loss tangent is the degree to which a portion of the energy is converted into heat and lost when an electric field is applied. It is believed that the metal and ionic surfactant eluted from hollow particles into an aqueous dispersion are attached to the particle surface in a state that allows them to be easily released from the hollow particles, and that they remain attached to the particle surface when the particles are dry. It is believed that the attachment of metal to the particle surface increases the dielectric loss tangent of hollow particles because polarization occurs when an electric field is applied. It is also believed that the attachment of surfactant to the particle surface increases the ability of hollow particles to adsorb moisture from the air, thereby increasing the dielectric loss tangent of hollow particles.Furthermore, in electronic circuit boards containing hollow particles in an insulating resin layer, if a metal or surfactant is attached to the surface of the hollow particles, the metal or surfactant will easily adsorb moisture and ionize in a high-humidity environment, which is thought to facilitate the formation of dendrites and therefore ion migration. Among surfactants, if an ionic surfactant is attached to the surface of the hollow particles, the ionization of the metal will be further promoted by the presence of a large amount of ionic components, making ion migration more likely to occur. The hollow particles disclosed herein are an aqueous dispersion of the hollow particles described above. By having a pH of 6.5 or more and 7.5 or less and a conductivity of 50 μS / cm or less, it is thought that the amount of metal and ionic surfactant contained in the hollow particles is reduced in a manner that is particularly likely to affect the dielectric tangent and performance stability of the hollow particles in a high-humidity environment.

[0024] The hollow particles of the present disclosure are typically produced by suspension polymerization, because this method allows for easy production of hollow particles, easy removal of impurities adhering to the surface, and easy control of particle size to a desired size. In suspension polymerization using a polymerizable monomer containing 60% by mass or more of a crosslinkable monomer, phase separation between the shell-constituting components and the hydrophobic solvent is likely to occur in droplets of the monomer composition dispersed in the suspension. Furthermore, the formation of a strong shell suppresses particle deformation, resulting in the formation of hollow portions clearly distinguishable from the shell. The hollow particles of the present disclosure are produced by suspension polymerization using a polymerizable monomer containing a high content of crosslinkable monomer, resulting in particles with a crosslinkable monomer unit content of 60% by mass or more out of 100% by mass of all monomer units constituting the shell, resulting in particles with hollow portions clearly distinguishable from the shell. Furthermore, the formation of a strong shell suppresses particle deformation, allowing for a sufficiently high porosity of 50% or more, thereby achieving a low dielectric loss tangent. The air layer has a dielectric loss tangent of 0, and the greater the proportion of the air layer in the hollow particle, the lower the dielectric loss tangent. Therefore, the higher the porosity of the hollow particle, the lower the dielectric loss tangent that can be achieved.

[0025] Furthermore, hollow particles produced by suspension polymerization can be obtained without surfactants by using an inorganic dispersion stabilizer instead of a surfactant as the dispersion stabilizer. However, when an inorganic dispersion stabilizer is used as the dispersion stabilizer, metals that can be dissolved in water tend to remain on the surface of the resulting hollow particles. In order to sufficiently reduce the amount of metals remaining on the particle surface so that the pH of the aqueous dispersion of the hollow particles described above is 6.5 to 7.5 and the electrical conductivity is 50 μS / cm or less, for example, when producing the hollow particles, it is preferable to set the polymerization temperature in the polymerization step to 80° C. or higher and to use the preferred method described below in the washing step.

[0026] In the present disclosure, the aqueous dispersion of hollow particles whose pH and electrical conductivity are measured may further contain a dispersant, as long as the electrical conductivity is 2 μS / cm or less in the state without the hollow particles. The type and content of the dispersant are appropriately adjusted so that the hollow particles are uniformly dispersed. The aqueous dispersion of hollow particles whose pH and electrical conductivity are measured is in a state in which no powder is visible at the top and all of the powder is dispersed in water.

[0027] As a dispersant that can be used in the aqueous dispersion of hollow particles for which the pH and electrical conductivity are to be measured, a dispersant that does not change the pH and electrical conductivity of ion-exchanged water when added to the ion-exchanged water can be appropriately selected and used, and for example, a nonionic surfactant can be used. The nonionic surfactant can be appropriately selected from known surfactants and is not particularly limited, but examples thereof include polyoxyalkylene-type nonionic surfactants such as higher alcohol alkylene oxide adducts, alkylphenol alkylene oxide adducts, fatty acid alkylene oxide adducts, higher alkylamine alkylene oxide adducts, polyhydric alcohol aliphatic ester alkylene oxide adducts, polypropylene glycol ethylene oxide adducts, fatty acid amide alkylene oxide adducts, and polyoxyalkylene styrenated phenyl ethers; polyhydric alcohol-type nonionic surfactants such as polyethylene oxide, glycerin fatty acid esters, alkylglycoxides, pentaerythritol fatty acid esters, sorbit or sorbitan fatty acid esters, sucrose fatty acid esters, polyhydric alcohol alkyl ethers, and alkanolamine fatty amides; and nonionic polymeric compounds having both hydrophilic and hydrophobic groups, such as polyvinyl alcohol and polyvinylpyrrolidone. Among these, polyoxyalkylene-type nonionic surfactants are preferably used. In the aqueous dispersion of hollow particles, the concentration of the nonionic surfactant is not particularly limited, but can be, for example, 0.05% by mass to 1% by mass.

[0028] In the present disclosure, hollow particles added to an aqueous dispersion for which pH and electrical conductivity are measured are those immediately before use. Here, "hollow particles immediately before use" refers to, for example, hollow particles that are to be mixed with other materials before use, and hollow particles that are to be used alone as a coating material or the like, refer to hollow particles immediately before use for that application. When measuring the pH and electrical conductivity of hollow particles produced in the form of a dispersion, dried hollow particles whose hollow portions are filled with gas are obtained from the dispersion by a method similar to the solvent removal step in the hollow particle production method described below, and a volume of 0.35 cm is measured.３ The dried hollow particles are dispersed in 100 mL of ion-exchanged water to prepare an aqueous dispersion, and the pH and electrical conductivity of the aqueous dispersion are measured. ３ The hollow particles used are those obtained by measuring the weight (g) of hollow particles calculated by the following formula (1): １ is the apparent density D of the hollow particles measured when determining the porosity described below. １ Equation (1): Volume 0.35 cm ３ Weight of hollow particles (g) = apparent density D of hollow particles １ (g / cm ３ ) x 0.35 (cm ３ )

[0029] The pH of the aqueous dispersion of the hollow particles may be 6.5 or more and 7.5 or less, but from the viewpoint of reducing the dielectric loss tangent of the hollow particles and improving the performance stability of the hollow particles under high-humidity environments, the pH is preferably 6.8 or more and 7.3 or less, and more preferably 6.9 or more and 7.2 or less.

[0030] The electrical conductivity of the aqueous dispersion of hollow particles may be 50 μS / cm or less, but from the viewpoint of reducing the dielectric loss tangent of the hollow particles and improving the performance stability of the hollow particles in a high-humidity environment, it is preferably 40 μS / cm or less, more preferably 30 μS / cm or less, and even more preferably 20 μS / cm or less. The lower limit of the electrical conductivity is not particularly limited, but may be, for example, 5 μS / cm or more or 10 μS / cm or more.

[0031] Hereinafter, an example of a method for producing hollow particles according to the present disclosure will be described, followed by a more detailed description of the hollow particles according to the present disclosure. Note that in this disclosure, the term "to" in a numerical range means that the numerical values ​​before and after it are included as the lower and upper limits.

[0032] 1. Method for Producing Hollow Particles Examples of the method for producing hollow particles according to the present disclosure include the steps of: preparing a mixed solution containing a polymerizable monomer, a hydrophobic solvent, a polymerization initiator, a dispersion stabilizer, and an aqueous medium; suspending the mixed solution to prepare a suspension in which droplets of a monomer composition containing the polymerizable monomer, the hydrophobic solvent, and the polymerization initiator are dispersed in the aqueous medium; subjecting the suspension 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 the hydrophobic solvent in the hollow portion; and washing the precursor particles.

[0033] The above-described manufacturing method is based on the basic technique of suspending a mixture containing a polymerizable monomer, a hydrophobic solvent, a polymerization initiator, a dispersion stabilizer, and an aqueous medium, thereby preparing a suspension in which the polymerizable monomer and the hydrophobic solvent phase-separate, resulting in droplets dispersed in the aqueous medium, with the polymerizable monomer unevenly distributed on the surface and the hydrophobic solvent unevenly distributed in the center. This suspension is then subjected to a polymerization reaction to harden the surfaces of the droplets, thereby forming hollow particles having hollow spaces filled with the hydrophobic solvent. In this disclosure, hollow particles whose hollow spaces are filled with the hydrophobic solvent are sometimes referred to as "precursor particles," as they are considered to be intermediates of hollow particles whose hollow spaces are filled with gas. In this disclosure, "precursor composition" refers to a composition containing precursor particles.

[0034] The above-mentioned manufacturing method includes a step of preparing a mixed solution, a step of preparing a suspension, a step of subjecting the suspension to a polymerization reaction, and a step of washing the precursor particles, and may further include other steps. Furthermore, as far as technically possible, two or more of the above steps and other additional steps may be performed simultaneously as a single step, or the order may be reversed. For example, the preparation of the mixed solution and the suspension may be performed simultaneously in a single step, such as by adding the materials for preparing the mixed solution and suspending them at the same time.

[0035] A preferred example of the method for producing hollow particles according to the present disclosure includes the following steps: (1) mixed solution preparation step: preparing a mixed solution containing a polymerizable monomer, a hydrophobic solvent, a polymerization initiator, a dispersion stabilizer, and an aqueous medium; (2) suspending step: suspending the mixed solution to prepare a suspension in which droplets of a monomer composition containing a polymerizable monomer, a hydrophobic solvent, and a polymerization initiator are dispersed in an aqueous medium; (3) polymerizing step: subjecting the suspension 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; (4) washing step: washing the precursor particles; and (5) solvent removing step: removing the hydrophobic solvent encapsulated in the precursor particles to obtain hollow particles.

[0036] FIG. 1 is a schematic diagram illustrating an example of the manufacturing method of the present disclosure. (1) to (5) in FIG. 1 correspond to the above-described steps (1) to (5). The white arrows between the diagrams indicate the order of each step. Note that FIG. 1 is merely a schematic diagram for explanatory purposes, and the manufacturing method of the present disclosure is not limited to that shown in the diagram. Furthermore, the structure, dimensions, and shape of the materials used in the manufacturing method of the present disclosure are not limited to those of the various materials shown in these diagrams. (1) in FIG. 1 is a cross-sectional schematic diagram illustrating one embodiment of a mixed solution in the mixed solution preparation step. As shown in this figure, the mixed solution contains an aqueous medium 1 and a low-polarity material 2 dispersed in the aqueous medium 1. Here, the low-polarity material 2 refers to a material that has low polarity and is difficult to mix with the aqueous medium 1. In the present disclosure, the low-polarity material 2 contains a polymerizable monomer, a hydrophobic solvent, and a polymerization initiator. (2) in FIG. 1 is a cross-sectional schematic diagram illustrating one embodiment of a suspension in the suspension step. The suspension includes an aqueous medium 1 and droplets 3 of a monomer composition dispersed in the aqueous medium 1. The droplets 3 of the monomer composition contain a polymerizable monomer, a hydrophobic solvent, and a polymerization initiator, but the distribution within the droplets is non-uniform. The droplets 3 of the monomer composition are phase-separated into a hydrophobic solvent 4a and a material other than the hydrophobic solvent, including the polymerizable monomer, 4b, with the hydrophobic solvent 4a concentrated in the center and the material other than the hydrophobic solvent 4b concentrated on the surface, and a dispersion stabilizer (not shown) attached to the surface. (3) in FIG. 1 is a cross-sectional schematic diagram illustrating one embodiment of a precursor composition obtained by a polymerization process, including precursor particles encapsulating a hydrophobic solvent in their hollow portions. The precursor composition includes an aqueous medium 1 and precursor particles 5 encapsulating a hydrophobic solvent 4a in their hollow portions, dispersed in the aqueous medium 1. The shell 6 forming the outer surface of the precursor particle 5 is formed by polymerization of the polymerizable monomer in the droplet 3 of the monomer composition, and contains a polymer of the polymerizable monomer as a resin. (4) in FIG. 1 is a cross-sectional schematic diagram showing one embodiment of a precursor particle in a washing step. (4) in FIG. 1 shows a state in which the precursor particle 5 has been separated from the state shown in (3) in FIG. 1 and reslurried with ion-exchanged water 1a. (5) in FIG. 1 is a cross-sectional schematic diagram showing one embodiment of a hollow particle after a solvent removal step. (5) in FIG. 1 shows a state in which the ion-exchanged water 1a and the hydrophobic solvent 4a have been removed from the state shown in (4) in FIG.By removing the hydrophobic solvent contained in the precursor particles, hollow particles 10 having gas-filled hollow portions 7 inside shells 6 are obtained. The above five steps and other steps will be described in order below.

[0037] (1) Mixed Liquid Preparation Step This step is a step of preparing a mixed liquid containing a polymerizable monomer, a hydrophobic solvent, a polymerization initiator, a dispersion stabilizer, and an aqueous medium. The mixed liquid may further contain other materials as long as the effects of the present disclosure are not impaired. The materials of the mixed liquid will be described in the following order: (A) polymerizable monomer, (B) hydrophobic solvent, (C) polymerization initiator, (D) dispersion stabilizer, and (E) aqueous medium.

[0038] (A) Polymerizable Monomer In the present disclosure, a polymerizable monomer is a compound having a functional group capable of addition polymerization (sometimes simply referred to as a polymerizable functional group in the present disclosure). In the present disclosure, a compound having an ethylenically unsaturated bond as a functional group capable of addition polymerization is generally used as the polymerizable monomer. In the present disclosure, any known polymerizable monomer conventionally used in the preparation of hollow polymer particles can be used as the polymerizable monomer. While not particularly limited, the polymerizable monomer preferably contains at least a crosslinkable monomer, and may further contain a non-crosslinkable monomer, in order to facilitate the formation of hollow spaces within the particles. When the polymerizable monomer contains a crosslinkable monomer, the crosslink density of the polymer precipitated on the droplet surface increases when the suspension is subjected to a polymerization reaction, and the precipitates are also crosslinked to each other, thereby increasing the crosslink density of the shell. This facilitates the formation of a shell with excellent strength, facilitates the formation of spherical hollow particles, and facilitates the formation of hollow spaces clearly distinguishable from the shell within the particles. In this disclosure, a polymerizable monomer having only one polymerizable functional group is referred to as a non-crosslinkable monomer, and a polymerizable monomer having two or more polymerizable functional groups is referred to as a crosslinkable monomer. A crosslinkable monomer is a polymerizable monomer that forms crosslinks in a resin by a polymerization reaction. In this disclosure, a polymerizable monomer consisting of carbon and hydrogen is referred to as a hydrocarbon monomer, a crosslinkable monomer consisting of carbon and hydrogen is referred to as a crosslinkable hydrocarbon monomer, and a non-crosslinkable monomer consisting of carbon and hydrogen is referred to as a non-crosslinkable hydrocarbon monomer. In addition, a polymerizable monomer having a (meth)acryloyl group as the polymerizable functional group is referred to as an acrylic monomer, a crosslinkable monomer having a (meth)acryloyl group as the polymerizable functional group is referred to as a crosslinkable acrylic monomer, and a non-crosslinkable monomer having a (meth)acryloyl group as the polymerizable functional group is referred to as a non-crosslinkable acrylic monomer. In the crosslinkable acrylic monomer, at least one polymerizable functional group may be a (meth)acryloyl group, but it is preferable that all polymerizable functional groups are (meth)acryloyl groups. In the present disclosure, "(meth)acrylate" refers to each of acrylate and methacrylate, "(meth)acrylic" refers to each of acrylic and methacrylic, and "(meth)acryloyl" refers to each of acryloyl and methacryloyl.

[0039] Examples of the crosslinkable monomer include aromatic divinyl monomers such as divinylbenzene, divinylbiphenyl, and divinylnaphthalene; diene monomers such as butadiene, isoprene, 2,3-dimethylbutadiene, pentadiene, and hexadiene; alicyclic olefins such as dicyclopentadiene, cyclopentadiene, and ethylidenetetracyclododecene; and other bifunctional crosslinkable hydrocarbon monomers; polymeric crosslinkable hydrocarbon monomers such as polybutadiene, polyisoprene, styrene-butadiene block copolymers (SBS), and styrene-isoprene block copolymers (SIS); allyl (meth)acrylate, vinyl (meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, and the like. Examples of suitable crosslinkable acrylic monomers include difunctional crosslinkable acrylic monomers such as 3-(meth)acryloyloxy-2-hydroxypropyl(meth)acrylate, trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol poly(meth)acrylate, and ethoxylated versions thereof; crosslinkable acrylic monomers such as diallyl phthalate; polymeric crosslinkable acrylic monomers such as polyphenylene ether modified at both ends with (meth)acrylic acid, and polymeric crosslinkable vinyl monomers such as polyphenylene ether modified at both ends with vinyl. These crosslinkable monomers may be used alone or in combination of two or more.

[0040] Examples of the non-crosslinkable monomer include aromatic monovinyl monomers such as styrene, vinyltoluene, α-methylstyrene, p-methylstyrene, ethylvinylbenzene, ethylvinylbiphenyl, and ethylvinylnaphthalene; monoolefin monomers such as ethylene, propylene, and butylene; and alicyclic monoolefins such as vinylcyclohexane, norbornene, and tricyclododecene; non-crosslinkable hydrocarbon monomers such as methyl(meth)acrylate, ethyl(meth)acrylate, butyl(meth)acrylate, and 2-ethylhexyl(meth)acrylate; Lauryl (meth)acrylate, t-butylaminoethyl (meth)acrylate, glycidyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-aminoethyl (meth)acrylate, (meth)acrylic acid, (meth)acrylamide, N-methylol (meth)acrylamide, N-butoxymethyl (meth)acrylamide, methoxypolyethylene glycol (meth)acrylate, ethoxypolyethylene glycol (meth)acrylate, propoxypolyethylene glycol (meth)acrylate, butoxypoly Examples of the monomer include non-crosslinkable acrylic monomers such as ethylene glycol (meth)acrylate, hexaoxy polyethylene glycol (meth)acrylate, octoxy polyethylene glycol polypropylene glycol (meth)acrylate, lauroxy polyethylene glycol (meth)acrylate, stearoxy polyethylene glycol (meth)acrylate, phenoxy polyethylene glycol polypropylene glycol (meth)acrylate, polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, polyethylene glycol propylene glycol mono(meth)acrylate, polyethylene glycol tetramethylene glycol (meth)acrylate, propylene glycol polybutylene glycol mono(meth)acrylate, and monoethylene glycol mono(meth)acrylate; vinyl carboxylate ester monomers such as vinyl acetate; halogenated aromatic vinyl monomers such as halogenated styrene; halogenated vinyl monomers such as vinyl chloride; halogenated vinylidene monomers such as vinylidene chloride; vinylpyridine; and the like.In addition, polymer-type non-crosslinkable monomers such as polystyrene having one end (meth)acrylic modified and polymethyl methacrylate having one end (meth)acrylic modified can also be used. These non-crosslinkable monomers can be used alone or in combination of two or more.

[0041] The content of the crosslinkable monomer per 100 parts by mass of the polymerizable monomer is preferably 60 parts by mass or more, more preferably 70 parts by mass or more, and even more preferably 80 parts by mass or more, from the viewpoint of improving the pressure resistance of the hollow particles and making it easier for the hollow particles to maintain a high porosity. On the other hand, from the viewpoint of making it easier for the dielectric loss tangent of the hollow particles to decrease, the content of the crosslinkable monomer per 100 parts by mass of the polymerizable monomer is preferably 96 parts by mass or less, more preferably 90 parts by mass or less, and even more preferably 85 parts by mass or less.

[0042] From the viewpoint of facilitating a stable polymerization reaction, the polymerizable monomer is preferably a polymerizable monomer whose polymerizable functional group is a (meth)acryloyl group or a vinyl group. In the present disclosure, "stable polymerization reaction" means that the reactivity of the polymerization reaction is good and the polymerization reaction proceeds uniformly. In the present disclosure, the content of the polymerizable monomer whose polymerizable functional group is a (meth)acryloyl group or a vinyl group is preferably 80 parts by mass or more, more preferably 90 parts by mass or more, and even more preferably 95 parts by mass or more, per 100 parts by mass of the polymerizable monomer.

[0043] To improve the dielectric properties of the hollow particles, the content of the hydrocarbon monomer per 100 parts by mass of the polymerizable monomer is preferably more than 50 parts by mass, more preferably 70 parts by mass or more, even more preferably 90 parts by mass or more, and even more preferably 95 parts by mass or more. The polymerizable monomer may be composed of a hydrocarbon monomer. The higher the proportion of the hydrocarbon monomer in the polymerizable monomer, the lower the relative dielectric constant and dielectric loss tangent of the hollow particles tend to be. In the present disclosure, the lower the relative dielectric constant and dielectric loss tangent, the better the dielectric properties.

[0044] From the viewpoint of achieving excellent pressure resistance while improving the dielectric properties of the hollow particles, it is preferable that the hydrocarbon monomer contains at least a crosslinkable hydrocarbon monomer. Among the crosslinkable hydrocarbon monomers, aromatic divinyl monomers are preferred, with divinylbenzene being particularly preferred. Furthermore, from the viewpoint of particularly improving the dielectric properties of the hollow particles, it is preferable that the hydrocarbon monomer contains a combination of a crosslinkable hydrocarbon monomer and a non-crosslinkable hydrocarbon monomer. Among the non-crosslinkable hydrocarbon monomers, aromatic monovinyl monomers are preferred, with at least one selected from ethylvinylbenzene and styrene being more preferred.

[0045] The content of the polymerizable monomer in the mixed solution 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 50% by mass, more preferably 20 to 40% by mass, and even more preferably 20 to 30% by mass, based on 100% by mass of the total mass of the components in the mixed solution excluding the aqueous medium. Furthermore, in order to prevent deterioration of the dielectric properties, reduction in strength, and deterioration of performance stability under high-humidity environments in the resulting hollow particles, the content of the polymerizable monomer in the mixed solution is preferably 96% by mass or more, more preferably 97% by mass or more, based on 100% by mass of the total mass of the solids, excluding the hydrophobic solvent, of the materials that form the oil phase. In the present disclosure, the solids refer to all components excluding the solvent, and liquid polymerizable monomers and the like are considered to be included in the solids.

[0046] (B) Hydrophobic Solvent The hydrophobic solvent used in the manufacturing method of the present disclosure is a non-polymerizable, poorly water-soluble organic solvent. The hydrophobic solvent acts as a spacer material that forms hollow spaces inside the particles. In the suspension process described below, a suspension is obtained in which droplets of a monomer composition containing a hydrophobic solvent are dispersed in an aqueous medium. In the suspension process, phase separation occurs within the droplets of the monomer composition, and the hydrophobic solvent, which has low polarity, tends to collect inside the droplets of the monomer composition. Ultimately, the droplets of the monomer composition contain the hydrophobic solvent inside, and other materials other than the hydrophobic solvent are distributed around the periphery according to their respective polarities. Then, in the polymerization process described below, an aqueous dispersion containing precursor particles encapsulating the hydrophobic solvent is obtained. In other words, as the hydrophobic solvent collects inside the particles, hollow spaces filled with the hydrophobic solvent are formed inside the resulting precursor particles.

[0047] The hydrophobic solvent can be appropriately selected from known hydrophobic solvents and is not particularly limited. Examples include esters such as ethyl acetate and butyl acetate; ether esters such as propylene glycol monomethyl ether acetate and propylene glycol monoethyl ether acetate; and hydrocarbon solvents, of which hydrocarbon solvents are preferred. Examples of hydrocarbon solvents include aliphatic hydrocarbons including chain hydrocarbon solvents such as pentane, hexane, heptane, octane, 2-methylbutane, 2-methylpentane, and paraffin solvents, and cyclic hydrocarbon solvents such as cyclohexane, methylcyclohexane, and cycloheptane; and aromatic hydrocarbons such as benzene, toluene, and xylene. These hydrophobic solvents can be used alone or in combination of two or more.

[0048] In the suspension step, since phase separation between the polymerizable monomer and the hydrophobic solvent is likely to occur in droplets of the monomer composition, it is preferable to select an organic solvent that has a lower solubility in water than the crosslinkable monomer contained in the polymerizable monomer as the hydrophobic solvent. Furthermore, when the polymerizable monomer contains more than 50 mass% of a hydrocarbon monomer, it is preferable to use a chain hydrocarbon solvent as the hydrophobic solvent, more preferably a chain hydrocarbon solvent having 5 to 8 carbon atoms, and even more preferably at least one selected from the group consisting of pentane, hexane, heptane, and octane.

[0049] Furthermore, although not particularly limited, the boiling point of the hydrophobic solvent is preferably 130° C. or lower, more preferably 100° C. or lower, from the viewpoint of ease of removal in the solvent removal step described below, and is preferably 50° C. or higher, more preferably 60° C. or higher, from the viewpoint of ease of inclusion in the precursor particles. When the hydrophobic solvent is a mixed solvent containing multiple types of hydrophobic solvents and has multiple boiling points, it is preferable that the boiling point of the solvent with the highest boiling point among the solvents contained in the mixed solvent is not higher than the above-mentioned upper limit, and it is preferable that the boiling point of the solvent with the lowest boiling point among the solvents contained in the mixed solvent is not lower than the above-mentioned lower limit.

[0050] Furthermore, the hydrophobic solvent used in the production method of the present disclosure preferably has a dielectric constant at 20°C of 2.5 or less, more preferably 2.0 or less. The dielectric constant is one of the indicators that indicates the polarity of a compound. When the dielectric constant of the hydrophobic solvent is sufficiently small, preferably 2.5 or less, more preferably 2.0 or less, it is believed that phase separation proceeds rapidly in the droplets of the monomer composition, making it easier to form hollow spaces. Examples of hydrophobic solvents with a dielectric constant of 2.0 or less at 20°C are as follows. The values ​​in parentheses are the dielectric constant values: pentane (1.8), hexane (1.9), heptane (1.9), octane (1.9), and cyclohexane (2.0). Regarding the dielectric constant at 20°C, reference can be made to values ​​described in known literature (e.g., "Chemical Handbook: Basics," 4th Revised Edition, edited by the Chemical Society of Japan, Maruzen Co., Ltd., published September 30, 1993, pages II-498 to II-503) and other technical information. The method for measuring the relative dielectric constant at 20°C includes, for example, a relative dielectric constant test carried out in accordance with JIS C 2101:1999, 23, at a measurement temperature of 20°C.

[0051] The porosity of the hollow particles can be adjusted by changing the amount of hydrophobic solvent in the mixed solution. In the suspension process described below, the polymerization reaction proceeds with the oil droplets containing the polymerizable monomer and the like encapsulating the hydrophobic solvent. Therefore, the higher the hydrophobic solvent content, the higher the porosity of the resulting hollow particles tends to be. In the present disclosure, the content of the hydrophobic solvent in the mixed solution is preferably 50 to 500 parts by mass per 100 parts by mass of the polymerizable monomer, as this facilitates control of the particle size of the hollow particles, increases the porosity while maintaining the strength of the hollow particles, and reduces the amount of residual hydrophobic solvent within the particles. The content of the hydrophobic solvent in the mixed solution is more preferably 70 to 300 parts by mass, and even more preferably 80 to 200 parts by mass per 100 parts by mass of the polymerizable monomer.

[0052] (C) Polymerization Initiator In the production method of the present disclosure, the mixed liquid preferably contains an oil-soluble polymerization initiator as the polymerization initiator. 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. Examples of the oil-soluble polymerization initiator include organic peroxides such as benzoyl peroxide, lauroyl peroxide, t-butylperoxy-2-ethylhexanoate, t-butylperoxydiethyl acetate, and t-butylperoxypivalate; and azo compounds such as 2,2'-azobis(2,4-dimethylvaleronitrile), azobisisobutyronitrile, and 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile). Among these, organic peroxides are preferably used as the oil-soluble polymerization initiator because they tend to improve the dielectric properties of the hollow particles.

[0053] The content of the polymerization initiator relative to 100 parts by mass of the polymerizable monomer in the mixed solution is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 7 parts by mass, and even more preferably 1 to 5 parts by mass. When the content of the polymerization initiator is equal to or greater than the above-mentioned lower limit, the polymerization reaction can proceed sufficiently, while when the content is equal to or less than the above-mentioned upper limit, there is little risk of the oil-soluble polymerization initiator remaining after completion of the polymerization reaction, and there is also little risk of an unexpected side reaction proceeding.

[0054] (D) Dispersion Stabilizer The dispersion stabilizer is an agent that disperses droplets of the monomer composition in an aqueous medium during the suspension process. Examples of dispersion stabilizers include inorganic dispersion stabilizers and surfactants. In the present disclosure, inorganic dispersion stabilizers are preferably used as the dispersion stabilizer because they facilitate control of the particle size of the droplets in the suspension, narrow the particle size distribution of the resulting hollow particles, and prevent the shell from becoming too thin, thereby suppressing a decrease in the strength of the hollow particles. Examples of inorganic dispersion stabilizers include sulfates such as barium sulfate and calcium sulfate; carbonates such as barium carbonate, calcium carbonate, and magnesium carbonate; phosphates such as calcium phosphate; metal oxides such as aluminum oxide and titanium oxide; metal hydroxides such as aluminum hydroxide, magnesium hydroxide, calcium hydroxide, barium hydroxide, and ferric hydroxide; and inorganic compounds such as silicon dioxide. These inorganic dispersion stabilizers can be used alone or in combination. Among these inorganic dispersion stabilizers, poorly water-soluble inorganic dispersion stabilizers are preferred. Here, poor water solubility preferably means a solubility of 0.5 g or less in 100 g of water.Among the inorganic dispersion stabilizers, metal hydroxides are preferred, with magnesium hydroxide being more preferred.

[0055] In the present disclosure, it is particularly preferable to use a poorly water-soluble inorganic dispersion stabilizer dispersed in an aqueous medium in the form of colloidal particles, i.e., in the form of a colloidal dispersion containing poorly water-soluble inorganic dispersion stabilizer colloidal particles. This allows the inorganic dispersion stabilizer to be easily removed by the washing step described below, making it easy to adjust the pH of the aqueous dispersion of hollow particles to 6.5 or more and 7.5 or less and the electrical conductivity to 50 μS / cm or less. A colloidal dispersion containing poorly water-soluble inorganic dispersion stabilizer colloidal particles can be prepared, for example, by reacting at least one selected from alkali metal hydroxides and alkaline earth metal hydroxides with a water-soluble polyvalent metal salt (excluding alkaline earth metal hydroxides) in an aqueous medium. Examples of alkali metal hydroxides include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Examples of alkaline earth metal hydroxides include barium hydroxide and calcium hydroxide. The water-soluble polyvalent metal salt may be any water-soluble polyvalent metal salt other than the above-mentioned alkaline earth metal hydroxides. Examples include magnesium metal salts such as magnesium chloride, magnesium phosphate, and magnesium sulfate; calcium metal salts such as calcium chloride, calcium nitrate, calcium acetate, and calcium sulfate; aluminum metal salts such as aluminum chloride and aluminum sulfate; barium salts such as barium chloride, barium nitrate, and barium acetate; and zinc salts such as zinc chloride, zinc nitrate, and zinc acetate. Among these, magnesium metal salts, calcium metal salts, and aluminum metal salts are preferred, magnesium metal salts are more preferred, and magnesium chloride is particularly preferred. The method for reacting at least one selected from the above-mentioned alkali metal hydroxides and alkaline earth metal hydroxides with the above-mentioned water-soluble polyvalent metal salt in an aqueous medium is not particularly limited. For example, an aqueous solution of at least one selected from the above-mentioned alkali metal hydroxides and alkaline earth metal hydroxides may be mixed with an aqueous solution of the water-soluble polyvalent metal salt. Furthermore, colloidal silica may be used as a colloidal dispersion containing poorly water-soluble inorganic dispersion stabilizer colloidal particles.

[0056] The content of the dispersion stabilizer is not particularly limited, but is preferably 0.5 to 15 parts by mass, more preferably 1 to 10 parts by mass, per 100 parts by mass of the combined weight of the polymerizable monomer and the hydrophobic solvent. By ensuring that the content of the dispersion stabilizer is at or above the lower limit, droplets of the monomer composition can be sufficiently dispersed so as not to coalesce in the suspension. On the other hand, by ensuring that the content of the dispersion stabilizer is at or below the upper limit, an increase in the viscosity of the suspension during granulation can be prevented, thereby avoiding problems such as clogging of the suspension in the granulator. Furthermore, the content of the dispersion stabilizer is preferably 0.5 to 15 parts by mass, more preferably 0.5 to 10 parts by mass, per 100 parts by mass of the aqueous medium.

[0057] Furthermore, in the production of hollow particles according to the present disclosure, it is preferable not to use a surfactant as a dispersion stabilizer. In the present disclosure, a surfactant refers to a compound having both hydrophilic and hydrophobic groups in one molecule, and includes compounds commonly used as surfactants, such as known surfactants such as ionic surfactants and nonionic surfactants, as well as polymeric compounds that provide a dispersing effect, such as polyvinyl alcohol. Surfactants typically have a solubility of 1 g / L or more in water at 25°C. Examples of ionic surfactants include anionic surfactants, cationic surfactants, and amphoteric surfactants. Examples of anionic surfactants include carboxylates such as alkali metal salts of higher fatty acids; sulfate ester salts such as higher alcohol sulfate ester salts and higher alkyl ether sulfate ester salts; sulfonates such as alkylbenzene sulfonates, alkyl sulfonates, and paraffin sulfonates; and phosphate ester salts such as higher alcohol phosphate ester salts. Examples of cationic surfactants include quaternary ammonium salts such as alkyltrimethylammonium salts. Examples of amphoteric surfactants include amino acid-type amphoteric surfactants such as higher alkylaminopropionates, and betaine-type amphoteric surfactants such as higher alkyldimethylbetaine and higher alkyldihydroxyethylbetaine. Examples of nonionic surfactants include those similar to those usable in aqueous dispersions of hollow particles for which pH and electrical conductivity are measured. Examples of polymeric compounds that provide a dispersing effect and can be used as surfactants include polymeric compounds having both hydrophilic and hydrophobic groups, such as polyvinyl alcohol, polyvinylpyrrolidone, methyl cellulose, ethyl cellulose, polyacrylic acid, polyacrylimide, polyethylene oxide, and poly(hydroxystearic acid-g-methyl methacrylate-co-methacrylic acid) copolymer. Although not particularly limited, the molecular weight of the surfactant is typically less than 3,000.

[0058] (E) Aqueous Medium In the present disclosure, the term "aqueous medium" refers to a medium selected from the group consisting of water, a hydrophilic solvent, and a mixture of water and a hydrophilic solvent. When using a mixture of water and a hydrophilic solvent, it is important that the polarity of the entire mixture is not too low in order to form droplets of the monomer composition. In this case, for example, the mass ratio of water to hydrophilic solvent (water:hydrophilic solvent) may be 99:1 to 50:50. The hydrophilic solvent in the present disclosure is not particularly limited as long as it is sufficiently miscible with water and does not cause phase separation. Examples of hydrophilic solvents include alcohols such as methanol and ethanol; tetrahydrofuran (THF); dimethyl sulfoxide (DMSO); and the like.

[0059] The content of the aqueous medium is not particularly limited, but from the viewpoint of setting the particle size and porosity of the hollow particles within the preferred ranges described below, the lower limit is preferably 200 parts by mass or more, more preferably 400 parts by mass or more, and even more preferably 600 parts by mass or more, relative to 100 parts by mass of the polymerizable monomer contained in the mixed liquid, and the upper limit is preferably 1,000 parts by mass or less, and more preferably 800 parts by mass or less.

[0060] The mixed liquid may further contain other materials different from the above-described materials (A) to (E) as long as the effects of the present disclosure are not impaired.

[0061] A mixed liquid is obtained by mixing the above-mentioned materials and other materials as needed, and stirring appropriately. In this mixed liquid, an oil phase containing lipophilic materials such as (A) the polymerizable monomer, (B) the hydrophobic solvent, and (C) the polymerization initiator is dispersed in an aqueous phase containing (D) the dispersion stabilizer and (E) the aqueous medium, with particles of about several mm in size. The dispersion state of these materials in the mixed liquid can be observed with the naked eye, depending on the type of material. In the mixed liquid preparation step, the mixed liquid may be obtained by simply mixing the above-mentioned materials and other materials as needed, and stirring appropriately. However, in terms of making the shell more uniform, it is preferable to prepare a mixed liquid by separately preparing an oil phase containing the polymerizable monomer, the hydrophobic solvent, and the polymerization initiator, and an aqueous phase containing the dispersion stabilizer and the aqueous medium, and then mixing them. In the present disclosure, a colloidal dispersion in which a poorly water-soluble inorganic dispersion stabilizer is dispersed in the form of colloidal particles in an aqueous medium is preferably used as the aqueous phase. By preparing the oil phase and the water phase separately in advance and then mixing them, hollow particles having a uniform shell composition can be produced, and the particle size of the hollow particles can be easily controlled.

[0062] (2) Suspension Step The suspension step is a step of preparing a suspension in which droplets of a monomer composition containing a hydrophobic solvent are dispersed in an aqueous medium by suspending the mixed liquid described above. The suspension method for forming droplets of the monomer composition is not particularly limited, and any known suspension method can be used. Examples of dispersers that can be used in preparing the suspension include horizontal or vertical in-line dispersers such as Milder (product name) manufactured by Pacific Machinery Works, Ltd., Cavitron (product name) manufactured by Eurotec Co., Ltd., and in-line dispersers manufactured by IKA (e.g., DISPAX-REACTOR (registered trademark) DRS (product name)), as well as emulsifying dispersers such as the Homomixer MARK II series manufactured by Primix Corporation.

[0063] In the suspension prepared in the suspending step, droplets of the monomer composition containing the lipophilic material and having a particle size of approximately 1 to 10 μm are uniformly dispersed in the aqueous medium. Such droplets of the monomer composition are difficult to observe with the naked eye and can be observed using known observation equipment such as an optical microscope. In the suspending step, phase separation occurs in the droplets of the monomer composition, so that the hydrophobic solvent with low polarity tends 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.

[0064] The droplets of the monomer composition dispersed in an aqueous medium are formed by surrounding the oil-soluble monomer composition with a dispersion stabilizer. The droplets of the monomer composition contain an oil-soluble polymerization initiator, a polymerizable monomer, and a hydrophobic solvent. The droplets of the monomer composition are small oil droplets, and the oil-soluble polymerization initiator generates polymerization-initiating radicals inside the small oil droplets. Therefore, precursor particles of the desired particle size can be produced without excessive growth of the small oil droplets. In suspension polymerization methods using such oil-soluble polymerization initiators, there is no opportunity for the polymerization initiator to come into contact with the polymerizable monomer dispersed in the aqueous medium. Therefore, the use of an oil-soluble polymerization initiator can prevent the by-production of excess resin particles, such as dense particles with a relatively small particle size, in addition to the desired resin particles having hollow portions.

[0065] (3) Polymerization Step This step is a step of preparing 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 by subjecting the suspension obtained in the above-mentioned suspension step to a polymerization reaction. The precursor particles are formed by polymerization of a polymerizable monomer contained in droplets of the monomer composition, and the shell of the precursor particles contains a polymer of the polymerizable monomer as a resin.

[0066] The polymerization method is not particularly limited, and for example, a batch system (batch system), semi-continuous system, continuous system, etc. can be used. The polymerization temperature is not particularly limited, but is typically 40 to 90°C, and is preferably 80°C or higher from the viewpoint of reducing the amount of residual unreacted polymerizable monomer. The polymerization reaction time is typically 1 to 48 hours, and is preferably 8 hours or higher from the viewpoint of reducing the amount of residual unreacted polymerizable monomer. The upper limit of the polymerization reaction time is preferably 36 hours or less from the viewpoint of ease of production. The polymerization temperature and reaction time are preferably adjusted so that the polymerization conversion rate of the polymerizable monomer is 90% or higher. In the present disclosure, the polymerization conversion rate is calculated from the mass of the solid content of the precursor particles obtained by the polymerization reaction and the mass of the polymerizable monomer remaining unreacted after the polymerization reaction using the following formula (2). The mass of the unreacted polymerizable monomer can be measured by gas chromatography (GC) as described below. Equation (2): Polymerization conversion rate (mass %)=100−(mass of unreacted polymerizable monomer / mass of solids content of precursor particles)×100 By sufficiently reducing the amount of unreacted polymerizable monomer remaining after the polymerization step, aggregation of hollow particles in the precursor composition is suppressed. This makes it easier to remove metals and surfactants present on the surfaces of the precursor particles in the washing step described below, and therefore, in the aqueous dispersion of the hollow particles described above, hollow particles having a pH of 6.5 or more and 7.5 or less and an electrical conductivity of 50 μS / cm or less can be easily obtained.

[0067] (4) Washing Step This step is a step of washing the precursor particles obtained by the above-described polymerization step, and may be a step of removing the dispersion stabilizer. ３In an aqueous dispersion of hollow particles obtained by dispersing the hollow particles in 100 mL of ion-exchanged water, a washing step is preferably performed by the following method to adjust the pH to 6.5 to 7.5 and the electrical conductivity to 50 μS / cm or less. First, an acid or alkali is added to the precursor composition obtained by the polymerization step to dissolve the dispersion stabilizer contained in the precursor particles in the aqueous medium. If any aggregated precursor particles are present, it is preferable to deaggregate them. The precursor particles are then separated from the aqueous medium. The separated precursor particles are then dispersed in ion-exchanged water to form a reslurry, and the precursor particle separation step is repeated three or more times. If any aggregated precursor particles are present in the slurry obtained by the reslurry, it is also preferable to deaggregate them. By performing such a washing step, the dispersion stabilizer present on the surface of the precursor particles can be sufficiently removed. In the present disclosure, the number of times the precursor particles separated after the addition of an acid or alkali are reslurried and separated is referred to as the "washing count." As described above, the washing count is preferably three or more, more preferably four or more. The upper limit of the number of washings is not particularly limited, but from the viewpoint of ease of manufacturing, it may be, for example, six times or less, or five times or less.

[0068] When adding an acid or alkali to the precursor composition, if the dispersion stabilizer used is an acid-soluble inorganic dispersion stabilizer, it is preferable to add an acid to the precursor composition, while if the dispersion stabilizer used is an alkali-soluble inorganic dispersion stabilizer, it is preferable to add an alkali to the precursor composition. Furthermore, if an acid-soluble inorganic dispersion stabilizer is used as the dispersion stabilizer, it is preferable to add an acid to the precursor composition 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. However, sulfuric acid is particularly preferred because of its high dispersion stabilizer removal efficiency and its small burden on the production equipment.

[0069] The method for separating the precursor particles from the aqueous medium is not particularly limited, and examples thereof include centrifugation, filtration, and static separation. Among these, filtration is preferred due to its simple operation and high dispersion stabilizer removal efficiency. Furthermore, when separating the precursor particles from the aqueous medium, it is preferable to dehydrate the precursor particles obtained by filtration or the like using a known method. The precursor composition containing added acid or alkali, and the slurry obtained by dispersing the separated precursor particles in ion-exchanged water and reslurrying them, preferably do not exhibit aggregation of the precursor particles. That is, it is preferable that no aggregates of the precursor particles are observed with the naked eye in the slurry. To prevent aggregation of the precursor particles in the slurry, for example, it is effective to perform the polymerization reaction until the polymerization conversion rate reaches 90% or more in the polymerization step described above, thereby reducing the amount of unreacted polymerizable monomer remaining in the precursor particles, or to remove the unreacted monomer from the slurry in advance. If precursor particles aggregate in the slurry, it is difficult to clean the interior of the aggregates, which makes it easy for the dispersion stabilizer to remain in the hollow particles. Since there is no aggregation of precursor particles in the slurry, the surface of each particle can be easily washed, and the dispersion stabilizer can be easily removed. In addition, since the surface area of ​​the precursor particles in the slurry is large, the filtration speed of the slurry is slowed, and the washing time is extended, which also makes it easier to remove the dispersion stabilizer.

[0070] (5) Solvent Removal Step This step is a step of removing the hydrophobic solvent contained in the precursor particles. In the present disclosure, a method of removing the hydrophobic solvent contained in the precursor particles after solid-liquid separation from the slurry in air may be employed, or a method of removing the hydrophobic solvent contained in the precursor particles in a slurry in which the precursor particles are dispersed in an aqueous medium may be employed. The former method has the advantage of easily reducing the metal content in the resulting hollow particles, while the latter method has the advantage of reducing the amount of residual hydrophobic solvent.

[0071] The solid-liquid separation method is the same as the above-mentioned method for separating precursor particles from an aqueous medium. The precursor particles after solid-liquid separation may be pre-dried before removing the hydrophobic solvent. Pre-drying may be performed, for example, by drying the solid content containing the precursor particles obtained by solid-liquid separation using a drying device such as a dryer or a drying appliance such as a hand dryer.

[0072] In this process, "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 that the removal of the hydrophobic solvent is not affected. "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. In other words, it is important to remove the hydrophobic solvent in an environment in which the precursor particles are in direct contact with the external gas.

[0073] The method for removing the hydrophobic solvent from the precursor particles in air is not particularly limited, and known methods can be used. Examples of such methods include vacuum drying, heat drying, flash drying, or a combination of these methods. In particular, when using heat drying, the heating temperature must be above the boiling point of the hydrophobic solvent and below 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 may be, for example, 50 to 200°C, 70 to 200°C, or 100 to 200°C. By drying in air, the hydrophobic solvent inside the precursor particles is replaced with the external gas, resulting in hollow particles with a gas-filled hollow space. The drying atmosphere is not particularly limited and can be selected appropriately depending on the application of the hollow particles. Examples of suitable drying atmospheres include air, oxygen, nitrogen, and argon. Alternatively, hollow particles with a temporary vacuum interior can be obtained by first filling the interior of the hollow particles with a gas and then drying under reduced pressure.

[0074] A method for removing the hydrophobic solvent contained in the precursor particles from a slurry in which the precursor particles are dispersed in an aqueous medium can be, for example, a method of evaporating and distilling off the hydrophobic solvent contained in the precursor particles in the slurry under a predetermined pressure. More specifically, a method of evaporating and distilling off the hydrophobic solvent contained in the precursor particles by introducing an inert gas such as nitrogen, argon, or helium or water vapor into the slurry under a predetermined pressure selected from high pressure, normal pressure, and reduced pressure can be exemplified. Among these, a method of evaporating and distilling off the hydrophobic solvent contained in the hollow particles by introducing an inert gas into the slurry in which the precursor particles are dispersed under a predetermined pressure is preferred because it has excellent hydrophobic solvent removal efficiency. A preferred method for introducing an inert gas into the slurry is, for example, bubbling the inert gas into the slurry. Furthermore, the temperature when introducing the inert gas into the slurry is preferably a temperature equal to or higher than the boiling point of the hydrophobic solvent minus 35°C, from the viewpoint of reducing the residual amount of hydrophobic solvent, preferably a temperature equal to or higher than the boiling point of the hydrophobic solvent minus 30°C, and more preferably a temperature equal to or higher than the boiling point of the hydrophobic solvent minus 20°C. Here, 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 in the solvent removal step is the boiling point of the solvent with the highest boiling point among the solvents contained in the mixed solvent, that is, the highest boiling point among the multiple boiling points. Furthermore, the temperature when introducing the inert gas into the slurry is usually a temperature equal to or higher than the polymerization temperature in the polymerization step. The temperature when introducing the inert gas into the slurry is not particularly limited, but may be 50 to 100°C. The conditions for bubbling the inert gas into the slurry are appropriately adjusted depending on the type and amount of the hydrophobic solvent so as to remove the hydrophobic solvent encapsulated in the precursor particles, and are not particularly limited. For example, the inert gas may be bubbled at a rate of 1 to 3 L / min for 1 to 72 hours. By introducing the inert gas into the slurry, a slurry of hollow particles encapsulating the inert gas is obtained. The slurry is subjected to solid-liquid separation, and the remaining moisture in the obtained hollow particles is dried and removed, thereby obtaining hollow particles whose hollow portions are filled with gas.

[0075] (6) Others: As a process other than the above (1) to (5), for example, a process of substituting the interior of a particle may be added. The process of substituting the interior of a particle is a process of substituting the gas or liquid inside the hollow particle with another gas or liquid. Such a substitution can change the environment inside the hollow particle, selectively confine molecules inside the hollow particle, or modify the chemical structure inside the hollow particle according to the application.

[0076] 2. Hollow Particles The hollow particles of the present disclosure are particles having a shell (outer shell) containing a resin and a hollow portion surrounded by the shell. In the present disclosure, the hollow portion is a hollow space clearly distinguishable from the shell of the hollow particle formed from a resin material. The shell of the hollow particle may have a porous structure, but in that case, the hollow portion has a size clearly distinguishable from the numerous microscopic spaces uniformly dispersed within the porous structure. From the viewpoint of dielectric properties, the hollow particles of the present disclosure preferably have a solid shell. The hollow portion of the hollow particle can be confirmed, for example, by SEM observation of the particle cross section or by TEM observation of the particle itself. Furthermore, in order to exhibit excellent dielectric properties, the hollow portion of the hollow particle of the present disclosure is preferably filled with a gas such as air.

[0077] In order to reduce the dielectric tangent of the hollow particles and improve the performance stability of the hollow particles in a high-humidity environment, the content of surfactant present on the particle surface of the hollow particles of the present disclosure is preferably 200 ppm or less, more preferably 100 ppm or less, and even more preferably 50 ppm or less. By not using a surfactant as a dispersion stabilizer in the above-mentioned hollow particle production process, the content of surfactant present on the hollow particle surface can be made below the measurement limit. In this disclosure, the content of surfactant present on the hollow particle surface refers to the ratio of the mass of surfactant present on the hollow particle surface to the mass of the hollow particle. The surfactant present on the hollow particle surface can be extracted, for example, by ultrasonically treating the hollow particles in water. The type and mass of surfactant extracted into water are １It can be identified from the peak position and peak intensity of the H-NMR spectrum. In this method, the measurement limit of the amount of surfactant present on the hollow particle surface is usually 0.05 ppm.

[0078] In the hollow particles of the present disclosure, the metal content of the hollow particles is preferably 700 ppm or less, more preferably 400 ppm or less, and even more preferably 200 ppm or less, because the pH of the aqueous dispersion of the hollow particles described above is likely to be in the range of 6.5 to 7.5 and the electrical conductivity is likely to be 50 μS / cm or less. Here, the metal content of the hollow particles refers to the ratio of the total mass of the metal components contained in the hollow particles to the mass of the hollow particles. To achieve a metal content of the hollow particles below the upper limit, for example, it is preferable to use a metal-free polymerization initiator, use ion-exchanged water as the aqueous medium, perform the above-mentioned washing step in the production of the hollow particles, or employ a method of removing the hydrophobic solvent encapsulated in the precursor particles in air in the above-mentioned solvent removal step. The hollow particles of the present disclosure may contain a metal, as long as the pH of the aqueous dispersion of the hollow particles described above is in the range of 6.5 to 7.5 and the electrical conductivity is 50 μS / cm or less. The metal content of the hollow particles of the present disclosure may be less than the measurement limit, but may be 50 ppm or more, 80 ppm or more, 100 ppm or more, 120 ppm or more, or 150 ppm or more. The metal content of the hollow particles can be measured by inductively coupled plasma (ICP) emission spectrometry. The metal species can be identified by X-ray fluorescence analysis (XRF). In this method, the measurement limit for the metal content of the hollow particles is usually 5 ppm.

[0079] The hollow particles of the present disclosure contain a polymer of the polymerizable monomer as the main component of the shell, and the polymer forms the shell skeleton of the hollow particles. The content of the polymer of the polymerizable monomer is preferably 98% by mass or more, more preferably 99% by mass or more, and even more preferably 99.5% by mass or more, based on 100% by mass of the total solids content of the shell. By setting the content of the polymer at or above the lower limit, the hollow particles can be prevented from exhibiting deterioration in dielectric properties, a decrease in strength, and a decrease in performance stability under high-humidity environments. Furthermore, since the aqueous dispersion of the hollow particles described above is likely to have a pH in the range of 6.5 to 7.5 and a conductivity of 50 μS / cm or less, the hollow particles of the present disclosure preferably have a content of unreacted residual polymerizable monomer of 1.5% by mass or less, more preferably 1.0% by mass or less, even more preferably 0.8% by mass or less, even more preferably 0.5% by mass or less, and particularly preferably 0.15% by mass or less, based on 100% by mass of the total solids content of the shell. The content of the unreacted remaining polymerizable monomer can be determined, for example, by gas chromatography of a solution obtained by extracting the unreacted polymerizable monomer from the hollow particles. If the content of the unreacted remaining polymerizable monomer is 1.5% by mass or less, the content of each monomer unit contained in the polymer constituting the shell can be calculated from the amount of polymerizable monomer charged. Furthermore, the shell of the hollow particles of the present disclosure may further contain other materials, such as polymers different from the polymer of the above-mentioned polymerizable monomer, within a range that does not impair the effects of the present disclosure.

[0080] The composition of the polymer contained in the hollow particles of the present disclosure usually corresponds to the composition of the polymerizable monomer described above. The content of the crosslinkable monomer unit, relative to 100% by mass of all monomer units in the polymer, is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more, from the viewpoints of improving the pressure resistance of the hollow particles and making it easier for the hollow particles to maintain a high porosity. When the pressure resistance of the hollow particles is good, the hollow particles can maintain a high porosity even after being added to various materials, and therefore, the hollow particles are more likely to exhibit effects such as lowering the dielectric constant and dielectric loss tangent. On the other hand, from the viewpoint of making it easier for the dielectric loss tangent of the hollow particles to decrease, the content of the crosslinkable monomer unit is preferably 96% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less. In a shell having a crosslinkable monomer unit content of not more than the above upper limit and containing a combination of crosslinkable and non-crosslinkable monomer units, the more non-crosslinkable monomer units it contains, the fewer residual double bonds that do not contribute to the reaction, and therefore the fewer components that undergo molecular motion when an electric field is applied. This is presumably because the energy loss is reduced, resulting in a lower dielectric loss tangent of the hollow particles.

[0081] To improve the dielectric properties of the hollow particles, the content of hydrocarbon monomer units in the polymer, based on 100% by mass of all monomer units, is preferably more than 50% by mass, more preferably 70% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more. The polymer may be composed of hydrocarbon monomer units. The higher the proportion of hydrocarbon monomer units in the polymer, the lower the dielectric constant and dielectric loss tangent of the hollow particles tend to be. In recent years, efforts have been made to increase the transmission frequency in information processing using electronic devices to transmit large amounts of information, and technologies for lowering the dielectric constant and dielectric loss tangent compatible with high-frequency transmission are desired. By increasing the proportion of hydrocarbon monomer units in the polymer, hollow particles can be obtained that have sufficiently reduced dielectric constants and dielectric loss tangents even at high frequencies of around 10 GHz. To achieve excellent pressure resistance while improving the dielectric properties of the hollow particles, the hydrocarbon monomer units preferably include at least crosslinkable hydrocarbon monomer units.

[0013] In order to particularly improve the dielectric properties of the hollow particles, it is preferable to contain a combination of crosslinkable hydrocarbon monomer units and non-crosslinkable hydrocarbon monomer units. In the hollow particles of the present disclosure, the effect of reducing the dielectric tangent and the effect of improving performance stability under high humidity environments, which are achieved by having the pH of the aqueous dispersion of the hollow particles be 6.5 or more and 7.5 or less and the electrical conductivity be 50 μS / cm or less, are particularly effectively exhibited when the content of hydrocarbon monomer units in the polymer constituting the shell exceeds 50 mass%, and are further effectively exhibited when the polymer contains a combination of crosslinkable hydrocarbon monomer units and non-crosslinkable hydrocarbon monomer units.

[0082] The hollow particles of the present disclosure preferably have a dielectric loss tangent of 1.00×10 at a frequency of 10 GHz. －３ More preferably, it is 9.00×10 or less. －４ More preferably, 6.00 x 10 －４ More preferably, 4.00 x 10 －４ The lower limit of the dielectric loss tangent is not particularly limited, and is, for example, 1.00 × 10 －４ It may be more than that.

[0083] The hollow particles of the present disclosure have a relative dielectric constant at a frequency of 10 GHz of preferably 1.40 or less, more preferably 1.37 or less, and even more preferably 1.35 or less, and the lower limit is not particularly limited and may be, for example, 1.00 or more. In the present disclosure, the relative dielectric constant and dielectric loss tangent of the hollow particles are measured using a perturbation type measuring device.

[0084] The hollow particles of the present disclosure have a porosity of 50% or more, preferably 60% or more, more preferably 65% ​​or more, and even more preferably 70% or more. When the porosity is equal to or greater than the above-mentioned lower limit, the hollow particles have excellent dielectric properties, and are also excellent in terms of lightweight, heat resistance, and heat insulation. The upper limit of the porosity of the hollow particles is not particularly limited, but is preferably 90% or less, more preferably 85% or less, and even more preferably 80% or less, in order to prevent a decrease in the strength of the hollow particles and make them less likely to be crushed.

[0085] The porosity of the hollow particles is the apparent density D １ and true density D ０ The apparent density of the hollow particles D １ The measurement method is as follows: First, a volume of 100 cm ３ About 30 cm ３ The volumetric flask is filled with hollow particles, and the mass of the filled hollow particles is accurately weighed. Next, the volumetric flask filled with the hollow particles is 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 is accurately weighed, and the apparent density D of the hollow particles is calculated based on the following formula (I): １ (g / cm ３ ) is calculated by the formula (I) Apparent density D １ Apparent density D = [Mass of hollow particles] / (100 - [Mass of isopropanol] / [Specific gravity of isopropanol at measurement temperature]) 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.

[0086] True density D of hollow particles ０ The measurement method is as follows: After crushing the hollow particles in advance, ３Approximately 10 g of crushed pieces of hollow particles are filled into a measuring flask, and the mass of the crushed pieces is accurately weighed. Then, in the same manner as in the measurement of the apparent density, isopropanol is added to the measuring flask, and the mass of the isopropanol is accurately weighed. The true density D of the hollow particles is calculated based on the following formula (II): ０ (g / cm ３ ) is calculated using the formula (II) ０ = [mass of crushed pieces of hollow particles] / (100 - [mass of isopropanol] / [specific gravity of isopropanol at measurement temperature]) True density D ０ As is clear from the above measurement method, the true density D ０ In calculating the particle diameter, the hollow portion is not considered to be part of the hollow particle.

[0087] The porosity (%) of the hollow particles is calculated by multiplying the apparent density D １ and true density D ０ The porosity (%) is calculated by the following formula (III): １ / True density D ０ ) x 100

[0088] The hollow particles of the present disclosure preferably have a lower limit of the volume average particle diameter of 1.0 μm or more, more preferably 1.5 μm or more, and even more preferably 2.0 μm or more. On the other hand, the upper limit of the volume average particle diameter of the hollow particles is preferably 10.0 μm or less, more preferably 8.0 μm or less, even more preferably 6.0 μm or less, and even more preferably 4.0 μm or less. When the volume average particle diameter of the hollow particles is equal to or greater than the above lower limit, the variation in shell thickness is suppressed, making it easier to form a uniform shell, and the hollow particles are less likely to be crushed, resulting in high mechanical strength. When the volume average particle diameter of the hollow particles is equal to or less than the above upper limit, the particle diameter is sufficiently small, making them suitable for use as substrate materials for electronic circuit boards and the like, and they can be added to thin, small substrates.

[0089] The shape of the hollow particles of the present disclosure is not particularly limited as long as a hollow portion is formed inside, and examples include spherical, oval, and amorphous shapes. Among these, spherical shapes are preferred from the viewpoints of ease of production, pressure resistance, and the like. The hollow particles of the present disclosure may have one or more hollow portions. However, from the viewpoints of maintaining a good balance between high porosity and mechanical strength and improving dielectric properties, those having only one hollow portion are preferred. When the hollow particles of the present disclosure have only one hollow portion, the hollow particles of the present disclosure may contain a small amount of hollow particles having two or more hollow portions or particles having no hollow portion as impurities. In the hollow particles of the present disclosure, the proportion of particles having only one hollow portion is preferably 90% or more, and more preferably 95% or more. Furthermore, the shell of the hollow particles of the present disclosure, and the partition walls separating adjacent hollow portions when the particles have two or more hollow portions, may be porous, but are preferably solid in order to improve dielectric properties. The hollow particles of the present disclosure may have an average circularity of 0.950 to 0.995. One example of the shape of the hollow particles of the present disclosure is a bag made of a thin film and inflated with gas, and its cross-sectional view is shown in hollow particle 10 in Figure 1 (5). In this example, a single thin film is provided on the outside, and the interior is filled with gas. The particle shape can be confirmed, for example, by SEM or TEM.

[0090] Furthermore, from the viewpoint of dielectric properties and pressure resistance, the hollow particles of the present disclosure preferably contain a small proportion of particles with a circularity of 0.85 or less. Particles with a circularity of 0.85 or less typically exhibit deformations such as dents or cracks, and are sometimes referred to as "irregularly shaped particles" in the present disclosure. These irregularly shaped hollow particles have inferior dielectric properties due to their lower porosity compared to spherical hollow particles. Therefore, reducing the proportion of irregularly shaped particles contained in the hollow particles can improve the dielectric properties of the hollow particles. Furthermore, irregularly shaped particles are more likely to aggregate when dispersed in a matrix resin than spherical particles, resulting in poor dispersibility. When irregularly shaped particles are dispersed in a matrix resin, aggregates are more likely to form, and the aggregates are more susceptible to external pressure, further reducing pressure resistance. Therefore, reducing the proportion of irregularly shaped particles contained in the hollow particles can improve the dispersibility and pressure resistance of the hollow particles. The hollow particles of the present disclosure may contain a small amount of impurities, such as particles with low circularity due to cracking or deformation. However, the proportion of particles with a circularity of 0.85 or less, based on 100% by mass of the hollow particles of the present disclosure, is preferably 10% by mass or less, more preferably 7% by mass or less, even more preferably 5% by mass or less, even more preferably 4% by mass or less, and particularly preferably 3% by mass or less. Circularity is defined as the value obtained by dividing the diameter of a circle having the same area as the projected image of the particle (equivalent circle area diameter) by the diameter of a circle having the same perimeter as the projected image of the particle (equivalent circumferential diameter). A perfectly spherical particle has a circularity of 1, and the more complex the particle's surface shape, the smaller the circularity value. In the present disclosure, circularity is measured using a flow-type particle image analyzer with an image resolution of 0.185 μm / pixel. A preferred example of a flow-type particle image analyzer is the "IF-3200" manufactured by Jasco International Co., Ltd. A measurement sample is prepared by dispersing a mixture of 0.10 to 0.12 g of hollow particles in an aqueous solution of linear alkylbenzenesulfonate (concentration: 0.3%) in an ultrasonic cleaner for 5 minutes. The average circularity is the average value of the circularity of 1,000 to 3,000 randomly selected particles.

[0091] The particle size distribution of the hollow particles (volume average particle size (Dv) / number average particle size (Dn)) may be, for example, 1.1 or more and 2.5 or less. When the particle size distribution is 2.5 or less, particles with little variation in performance among particles can be obtained. Furthermore, when, for example, a sheet-shaped resin molding containing the hollow particles of the present disclosure is manufactured, a product with a uniform thickness can be manufactured. The volume average particle size (Dv) and number average particle size (Dn) of the hollow particles can be determined, for example, by measuring the particle size of the hollow particles using a particle size distribution measuring device, calculating the number average and volume average, respectively, and using the obtained values ​​as the number average particle size (Dn) and volume average particle size (Dv) of the particles. The particle size distribution is the value obtained by dividing the volume average particle size by the number average particle size.

[0092] In the present disclosure, the thermal decomposition onset temperature of the hollow particles is preferably 150 to 400°C, more preferably 200 to 350°C. Hollow particles having a thermal decomposition onset temperature within the above range have excellent heat resistance. In the present disclosure, the thermal decomposition onset temperature of the hollow particles is the temperature at which a weight loss of 5% occurs, and can be measured using a TG-DTA device in an air atmosphere under conditions of an air flow rate of 230 mL / min and a temperature rise rate of 10°C / min.

[0093] 3. Uses of Hollow Particles Examples of uses of the hollow particles of the present disclosure include additives in components such as low-dielectric materials, heat insulating materials, sound insulating materials, and light reflecting materials used in various fields such as automobiles, electrical appliances, electronics, architecture, aviation, and spacecraft; food containers; footwear such as sports shoes and sandals; home appliance parts; bicycle parts; stationery; tools; 3D printer filaments; and buoyancy materials such as syntactic foam. In particular, the hollow particles of the present disclosure have a low dielectric loss tangent, excellent dielectric properties, and excellent performance stability in high-humidity environments, making them suitable for use as highly reliable materials in the electrical or electronic fields. For example, the hollow particles of the present disclosure are suitable for use as materials for electronic circuit boards. Specifically, by incorporating the hollow particles of the present disclosure into the insulating resin layer of an electronic circuit board, the dielectric loss tangent of the insulating resin layer can be reduced, thereby suppressing problems such as ion migration in high-humidity environments. The hollow particles of the present disclosure are also suitable for use as additives in semiconductor materials such as interlayer insulating materials, dry film resists, solder resists, bonding wires, magnet wires, semiconductor encapsulants, epoxy encapsulants, mold underfills, underfills, die bond pastes, buffer coating materials, copper-clad laminates, and flexible substrates, or in semiconductor materials used in high-frequency device modules, antenna modules, and automotive radar. Among these, the hollow particles are particularly suitable as additives in semiconductor materials such as interlayer insulating materials, solder resists, magnet wires, semiconductor encapsulants, epoxy encapsulants, underfills, buffer coating materials, copper-clad laminates, and flexible substrates, or in semiconductor materials used in high-frequency device modules, antenna modules, and automotive radar. The hollow particles of the present disclosure are not limited to semiconductor materials and can be used in various electronic materials. The hollow particles of the present disclosure are also useful as additives to insulating resin sheets used in the manufacture of electronic components such as printed wiring boards.An insulating resin sheet containing the hollow particles of the present disclosure can be produced by, for example, preparing a resin composition by mixing a thermoplastic resin, a thermosetting resin, a thermoplastic elastomer, or a mixture thereof with the hollow particles of the present disclosure, and then applying the resin composition to one or both sides of a sheet-like substrate and drying, extrusion molding, transfer molding, or the like to form a sheet. When the resin or elastomer contained in the insulating resin sheet has adhesive properties, the insulating resin sheet can be used as an adhesive sheet, specifically, for example, as a bonding sheet. A 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.

[0094] The hollow particles of the present disclosure have excellent strength due to the sufficient content of crosslinkable monomer units in the shell, and are therefore resistant to crushing when mixed with other materials and when molded after mixing, and when added to a molded product, they are effective as a low-dielectric material, weight-reducing material, heat insulating material, soundproofing material, vibration-damping material, etc. Therefore, they are suitable as additives for molded products, and can be used, for example, as additives for resin molded products. Examples of resins to which the hollow particles of the present disclosure are added, i.e., matrix resins, include thermoplastic or thermosetting resins such as polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyurethane, epoxy resin, acrylonitrile-butadiene-styrene (ABS) resin, acrylonitrile-styrene (AS) resin, poly(meth)acrylate, polycarbonate, polyamide, polyimide, polyphenylene ether, polyphenylene sulfide, polyester, polytetrafluoroethylene, maleimide resin, bismaleimide triazine resin, liquid crystalline polyester resin, phenolic resin, vinyl ester resin, unsaturated polyester resin, cyanate ester resin, polyether ketone ketone resin, and polyetherimide resin. For resin molded articles requiring a low dielectric loss tangent, insulating resins such as epoxy resin, thermosetting modified polyphenylene ether resin, thermosetting polyimide resin, silicon resin, benzoxazine resin, melamine resin, urea resin, allyl resin, phenolic resin, unsaturated polyester resin, polyurethane resin, and aniline resin are preferred as the matrix resin. When an epoxy resin is used as the matrix resin, it is preferable to mix a curing agent, a curing accelerator or a catalyst such as amines, acid anhydrides or imidazoles as appropriate.

[0095] The hollow particles of the present disclosure can also be incorporated as a filler in fiber-reinforced molded articles formed using resin and reinforcing fibers. The reinforcing fibers are not particularly limited, and examples include organic or inorganic fibers such as carbon fiber, glass fiber, aramid fiber, and polyethylene fiber. Furthermore, the hollow particles of the present disclosure have high porosity, are difficult to crush, and have excellent heat resistance, thereby satisfying the insulation and shock-absorbing properties (cushioning properties) required for undercoating materials and also meeting the heat resistance required for thermal paper applications. The hollow particles of the present disclosure are also useful as plastic pigments with excellent gloss and hiding power. Furthermore, the hollow particles of the present disclosure can be encapsulated with useful ingredients such as fragrances, pharmaceuticals, pesticides, and ink components by means of immersion treatment, reduced pressure immersion treatment, or other methods, and can be used for various applications depending on the ingredients contained therein. Furthermore, the hollow particles of the present disclosure are also suitable for use as rust inhibitors. The hollow particles of the present disclosure are also useful as an additive that reduces electrical conductivity, and therefore, for example, paints containing the hollow particles of the present disclosure can be used as anti-rust paints (paint primers, lubricating paints, etc.) for improving the corrosion resistance and rust prevention properties of steel materials, etc. Furthermore, the hollow particles added to anti-rust paints can also contain anti-rust additives.

[0096] The resin composition and resin molded article containing the hollow particles of the present disclosure will be described in further detail below.

[0097] 4. Resin Composition The resin composition of the present disclosure is characterized by containing the hollow particles of the present disclosure and a matrix resin. The resin composition of the present disclosure is typically used as a molding material for the resin molded body described below. It may be, for example, liquid or pelletized, or may be a prepreg. Examples of liquid resin compositions include those containing a liquid matrix resin before a curing reaction, and those obtained by dissolving or dispersing each component in a solvent. Here, the liquid matrix resin before a curing reaction and the matrix resin dissolved or dispersed in a solvent may be a thermosetting resin or a thermoplastic resin. Alternatively, the resin composition may be liquid due to the matrix resin being molten. Prepregs can be obtained, for example, by impregnating a substrate with a liquid resin composition and drying it. Examples of pelletized resin compositions include those obtained by melt-kneading a resin composition containing a thermoplastic matrix resin and hollow particles, and then cooling and solidifying the resulting composition to form pellets. As described above, the hollow particles of the present disclosure have a reduced dielectric tangent and improved performance stability in high-humidity environments. Conventional resin compositions and resin molded articles containing hollow particles tend to have reduced performance stability in high-humidity environments compared to those not containing hollow particles. In contrast, resin compositions and resin molded articles containing hollow particles according to the present disclosure have reduced dielectric loss tangents due to the inclusion of hollow particles according to the present disclosure, while suppressing the deterioration of performance stability in high-humidity environments.

[0098] Examples of the matrix resin contained in the resin composition of the present disclosure include the same resins as those to which the hollow particles of the present disclosure are added. A more detailed description is provided below. The matrix resin contained in the resin composition of the present disclosure may be, for example, a curable resin such as a thermosetting resin, a photocurable resin, or a room temperature curable resin, or a thermoplastic resin. Furthermore, the matrix resin contained in the resin composition of the present disclosure may be an unreacted monomer, a prepolymer, or a macromonomer, a polymer, or a precursor of a curable resin such as polyamic acid, and is not particularly limited. The matrix resin contained in the resin composition of the present disclosure may function as a binder (binding agent) by, for example, curing using heat, light irradiation, or a curing agent, polymerization initiator, or catalyst.

[0099] Known thermosetting resins can be used, and are not particularly limited. Examples 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, allyl resins, aniline resins, maleimide resins, bismaleimide triazine resins, liquid crystalline polyester resins, vinyl ester resins, unsaturated polyester resins, cyanate ester resins, polyether ketone ketone resins, polyetherimide resins, and precursors of these resins before curing. These thermosetting resins can be used alone or in combination of two or more. Examples of room temperature curing resins include adhesives that can be cured at room temperature by adding a catalyst, such as epoxy adhesives, silicone adhesives, and acrylic adhesives. Examples of thermoplastic resins include polyolefin resins, polyamide resins, polycarbonate resins, polyphenylene sulfide resins, polyether ether ketone resins, polystyrene resins, polyphenylene oxide resins, and liquid crystal polymers (LCPs). Further examples of thermoplastic resins include polyolefins such as polypropylene and polyethylene; polyamides such as PA6, PA66, and PA12; polyimides, polyamideimides, polyetherimides, polyether ketone ketones, polyvinyl chloride, polystyrene, poly(meth)acrylates, polycarbonates, polyvinylidene fluoride, acrylonitrile-butadiene-styrene copolymer (ABS) resins, acrylonitrile-styrene copolymers (AS), polyphenylene ethers, polyphenylene sulfide, polyesters, polytetrafluoroethylene, and thermoplastic elastomers. Thermoplastic elastomers generally exhibit rubber elasticity at room temperature (25°C) and are plasticized and moldable at high temperatures. Examples of thermoplastic elastomers include urethane-based elastomers, styrene-based elastomers, olefin-based elastomers, amide-based elastomers, and ester-based elastomers. The matrix resin contained in the resin composition of the present disclosure is appropriately selected depending on the application and is not particularly limited.The resin composition of the present disclosure may contain one matrix resin alone or two or more matrix resins in combination.

[0100] In the resin composition of the present disclosure, the content of the matrix resin is not particularly limited, but is preferably 20 to 99 parts by mass, more preferably 30 to 95 parts by mass, and even more preferably 40 to 95 parts by mass, per 100 parts by mass of the total solids content contained in the resin composition. When the content of the matrix resin is equal to or greater than the lower limit, the moldability when forming a resin molded article is improved, and the mechanical strength of the resulting resin molded article is improved. On the other hand, when the content of the matrix resin is equal to or less than the upper limit, the hollow particles of the present disclosure can be sufficiently incorporated, thereby allowing the hollow particles of the present disclosure to fully exhibit their effects, such as improved dielectric properties.

[0101] The resin composition of the present disclosure may further contain additives such as a curing agent, curing accelerator, curing catalyst, or initiator for promoting the curing reaction. These can be appropriately selected from known additives depending on the type of matrix resin, and are not particularly limited. The content of the curing agent is not particularly limited and may be, for example, 1 to 120 parts by mass per 100 parts by mass of the matrix resin. The content of the curing accelerator is not particularly limited and may be, for example, 0.01 to 10 parts by mass per 100 parts by mass of the matrix resin.

[0102] In the resin composition of the present disclosure, the content of hollow particles is not particularly limited, but is preferably 1 to 70 parts by mass, more preferably 3 to 50 parts by mass, and even more preferably 5 to 40 parts by mass, per 100 parts by mass of the total solids content contained in the resin composition. When the content of hollow particles is equal to or greater than the lower limit, the effects of the hollow particles of the present disclosure, such as improving dielectric properties, can be fully exerted. On the other hand, when the content of hollow particles is equal to or less than the upper limit, a sufficient amount of matrix resin can be contained, thereby improving moldability and mechanical strength.

[0103] The resin composition of the present disclosure may further contain reinforcing fibers. Examples of reinforcing fibers include organic or inorganic fibers such as carbon fibers, glass fibers, aramid fibers, polyethylene fibers, cellulose nanofibers, and liquid crystal polymer (LCP) fibers. Among these, at least one type of reinforcing fiber selected from carbon fibers and glass fibers is preferred. The reinforcing fibers contained in the resin composition of the present disclosure may be those used as a substrate for a prepreg or may be contained as a filler.

[0104] When the resin composition of the present disclosure contains reinforcing fibers, the content of the reinforcing fibers is, relative to 100 parts by mass of the total of the hollow particles and the matrix resin, preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and preferably 200 parts by mass or less, more preferably 150 parts by mass or less. When the content of the reinforcing fibers is equal to or greater than the lower limit, the strength-enhancing effect of the reinforcing fibers is excellent. On the other hand, when the content of the reinforcing fibers is equal to or less than the upper limit, the matrix resin and hollow particles can be sufficiently contained, thereby improving moldability, light weight, dielectric properties, etc.

[0105] The resin composition of the present disclosure may further contain a solvent. Known solvents can be used and are appropriately selected depending on the type of matrix resin. When the resin composition of the present disclosure contains a solvent, the solids concentration of the resin composition of the present disclosure is preferably 10 to 90 mass%. The resin composition of the present disclosure may further contain additives such as fillers, coupling agents, stress reducing agents, antifoaming agents, leveling agents, ultraviolet absorbers, foaming agents, antioxidants, colorants, heat stabilizers, and flame retardants, as necessary, within a range that does not impair the effects of the present disclosure.

[0106] The resin composition of the present disclosure can be obtained, for example, by mixing the hollow particles of the present disclosure with a matrix resin and other components added as needed. The mixing method is not particularly limited, and methods using known mixing devices such as a planetary mixer, ball mill, bead mill, planetary mixer, and roll mill can be used. When the matrix resin is a thermoplastic resin, the resin composition of the present disclosure can be obtained by adding the hollow particles of the present disclosure and other components added as needed to the molten matrix resin (thermoplastic resin) and melt-kneading them. Alternatively, a prepreg can be obtained by impregnating a substrate with a resin varnish obtained by mixing the hollow particles of the present disclosure with the matrix resin and other components added as needed and drying the resulting resin varnish. 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.

[0107] 5. Resin Molded Article The resin molded article of the present disclosure is a resin molded article obtained from the resin composition of the present disclosure described above. The method for obtaining a resin molded article from the resin composition of the present disclosure is appropriately selected from known methods depending on the type of matrix resin contained in the resin composition, the form of the resin composition, etc., and is not particularly limited. When the resin composition of the present disclosure contains a curable resin as the matrix resin, the resin molded article of the present disclosure includes a cured product of the resin composition.

[0108] When the resin composition of the present disclosure is a varnish, for example, the resin composition can be applied to a support, dried, and cured as necessary to obtain a resin molded product. The support may be made of, for example, resin or metal, and the surface of the support may be coated with a release agent. Known methods can be used to apply the resin composition, including dip coating, roll coating, curtain coating, die coating, slit coating, and gravure coating. When the resin composition contains a solvent, it is preferable to dry the resin composition after application. The drying temperature is preferably a temperature at which the matrix resin does not harden, typically 20°C or higher and 200°C or lower, preferably 30°C or higher and 150°C or lower. The drying time is typically 30 seconds to 1 hour, preferably 1 minute to 30 minutes. The curing reaction of the resin composition is carried out by a method appropriate for the type of matrix resin and is not particularly limited. When a matrix resin that cures upon heating is included, the heating temperature for the curing reaction is adjusted appropriately depending on the type of resin and is not particularly limited, but is usually from 30°C to 400°C, preferably from 70°C to 300°C, and more preferably from 100°C to 200°C. The curing time is from 5 minutes to 5 hours, preferably from 30 minutes to 3 hours. The heating method is not particularly limited, and may be performed using, for example, an electric oven.

[0109] When the resin composition of the present disclosure is a prepreg, a resin molded article can be obtained by curing the prepreg. The preferred conditions for curing the prepreg are the same as the preferred conditions for curing the resin composition described above.

[0110] When the resin composition of the present disclosure is a pellet-like resin composition containing a thermoplastic matrix resin, the resin composition can be melt-kneaded and then molded into a desired shape by a known molding method such as extrusion molding, injection molding, press molding, or compression molding to obtain the resin molded article of the present disclosure. The temperature during melt-kneading is not particularly limited as long as it is a temperature at which the thermoplastic resin used can be melted. Kneading can be performed by a known method and is not particularly limited, but can be performed using a kneading device such as a single-screw kneader or a twin-screw kneader.

[0111] The shape of the resin molded body of the present disclosure is not particularly limited and can be any moldable shape, such as a sheet, a film, a plate, a tube, or any other three-dimensional shape.

[0112] Examples of uses of the resin composition and resin molded article of the present disclosure include the uses of the hollow particles of the present disclosure described above, in which the resin composition or resin molded article can be used. Among the uses described above, one embodiment of the resin composition of the present disclosure used as a semiconductor encapsulant (hereinafter referred to as an "encapsulating resin composition") will be described in detail below.

[0113] 6. Encapsulating Resin Composition The encapsulating resin composition of the present disclosure is a resin composition of the present disclosure used as an encapsulant for semiconductor devices and the like. The encapsulating resin composition of the present disclosure is characterized by including an epoxy resin as a matrix resin. That is, the encapsulating resin composition of the present disclosure is characterized by including the hollow particles of the present disclosure and an epoxy resin. By using an epoxy resin as the matrix resin, a resin composition can be obtained that satisfies the moisture resistance, heat resistance, and other properties required of an encapsulant. The encapsulating resin composition of the present disclosure further contains the hollow particles of the present disclosure described above, and therefore has improved dielectric properties and excellent performance stability in high-humidity environments.

[0114] [Epoxy Resin] The epoxy resin contained in the encapsulating resin composition of the present disclosure can be a compound having one or more epoxy groups in its molecule. Furthermore, from the viewpoint of workability during production and curing of the encapsulating resin composition of the present disclosure, the epoxy resin is preferably liquid at room temperature (25°C). The encapsulating resin composition of the present disclosure preferably contains at least an alicyclic epoxy resin as the epoxy resin. This can improve the moisture resistance, dielectric properties, heat resistance, and other performance properties of the resin composition. An alicyclic epoxy resin is a compound having one or more alicyclic rings (aliphatic hydrocarbon rings) and one or more epoxy groups in its molecule. Among alicyclic epoxy compounds, (i) a compound having at least one alicyclic epoxy group in its molecule is preferred in terms of the above-mentioned excellent performance. Furthermore, such a compound is more preferably one having two or more alicyclic epoxy groups in its molecule. In the (i) compound having at least one alicyclic epoxy group in its molecule, the alicyclic epoxy group is an epoxy group composed of two adjacent carbon atoms and an oxygen atom that constitute an alicyclic ring. The alicyclic epoxy group is not particularly limited, but from the viewpoint of curability, a cyclohexene oxide group, i.e., an epoxy group composed of two adjacent carbon atoms and an oxygen atom constituting a cyclohexane ring, is preferred. As the compound (i) having at least one alicyclic epoxy group in the molecule, from the viewpoint of the heat resistance of the cured product, a compound having two or more cyclohexene oxide groups in the molecule is preferred, and a compound represented by the following formula (A) is more preferred. Note that one or more of the carbon atoms constituting the alicyclic epoxy group in the following formula (A) may be bonded to a substituent such as an alkyl group having 1 to 6 carbon atoms.

[0115]

[0116] In the above formula (A), X represents a single bond or a linking group, and is preferably a linking group. Here, the linking group is a divalent group having one or more atoms. Examples of the linking group include a divalent hydrocarbon group, a carbonyl group, an ether bond, an ester bond, a carbonate group, an amide bond, and a group in which two or more of these are linked. Among these, the linking group is preferably a linking group containing an oxygen atom, and more preferably a linking group containing an ester bond. In particular, a group in which at least one ester bond is linked to a linear alkylene group having 1 to 18 carbon atoms is preferred, and more preferably a group in which one ester bond is linked to a linear alkylene group having 1 to 6 carbon atoms.

[0117] The compound represented by formula (A) is not particularly limited, but examples thereof include (3,3',4,4'-diepoxy)bicyclohexyl, 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate, ε-caprolactone-modified 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate, 2,2-bis(3,4-epoxycyclohexylmethyl)propane, bis(3,4-epoxycyclohexylmethyl)ether, 1,2-bis(3,4-epoxycyclohexane-1-yl)ethane, 1,2-epoxy-1,2-bis(3,4-epoxycyclohexane-1-yl)ethane, etc. Among these, 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate is particularly preferred. As the compound represented by formula (A), for example, commercially available products such as "Celloxide 2021P" (compound name: 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate), "Celloxide 2081" (compound name: caprolactone-modified 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate), "Celloxide 8000" (compound name: (3,3',4,4'-diepoxy)bicyclohexyl), and "Epolead GT401", all manufactured by Daicel Corporation, can also be used.

[0118] Among the compounds (i) having at least one alicyclic epoxy group in the molecule, compounds having two or more alicyclic epoxy groups in the molecule include, in addition to the compound represented by formula (A), compounds having a cyclohexene oxide group and a cyclopentene oxide group in the molecule. Examples of such compounds include Epocalic (registered trademark) THI-DE, DE-102, and DE-103, both of which are products of ENEOS Corporation.

[0119] Among the compounds (i) having at least one alicyclic epoxy group in the molecule, examples of the compound having one alicyclic epoxy group in the molecule include products manufactured by Daicel Corporation under the trade names "Cyclomer M100" and "Celloxide 2000".

[0120] The alicyclic epoxy compound may also be (ii) a compound having an epoxy group directly bonded to an alicyclic ring via a single bond. Examples of such compounds include, but are not limited to, 1,2-epoxy-4-(2-oxiranyl)cyclohexane adduct of 2,2-bis(hydroxymethyl)-1-butanol (e.g., product name "EHPE3150" manufactured by Daicel Corporation).

[0121] As the alicyclic epoxy compound, (iii) a compound having an alicyclic ring and a glycidyl group can also be used. The compound is not particularly limited, but examples thereof include 2,2-bis[4-(2,3-epoxypropoxy)cyclohexyl]propane, 2,2-bis[3,5-dimethyl-4-(2,3-epoxypropoxy)cyclohexyl]propane, hydrogenated bisphenol A type epoxy resin, bis[2-(2,3-epoxypropoxy)cyclohexyl]methane, [2-(2,3-epoxypropoxy)cyclohexyl][4-(2,3-epoxypropoxy)cyclohexyl]methane, bis[4-(2,3-epoxypropoxy)cyclohexyl]methane, bis[3,5-dimethyl-4-(2,3-epoxypropoxy)cyclohexyl]methane, hydrogenated bisphenol F type epoxy resin, hydrogenated biphenol type epoxy resin, hydrogenated novolac type epoxy resin, and hydrogenated naphthalene type epoxy resin. The alicyclic epoxy resins may be used alone or in combination of two or more.

[0122] The encapsulating resin composition of the present disclosure may contain an epoxy resin that does not have an alicyclic structure as the epoxy resin. By appropriately selecting and using an epoxy resin that does not have an alicyclic structure, desired properties can be imparted to the encapsulating resin composition of the present disclosure. For example, by selecting and using a highly flexible resin as the epoxy resin that does not have an alicyclic structure, stress relaxation properties can be imparted to the encapsulating resin composition of the present disclosure. The epoxy resin not having an alicyclic structure is not particularly limited, but examples thereof include bixylenol-type epoxy resins, bisphenol A-type epoxy resins, bisphenol F-type epoxy resins, bisphenol S-type epoxy resins, bisphenol AF-type epoxy resins, trisphenol-type epoxy resins, naphthol novolac-type epoxy resins, phenol novolac-type epoxy resins, tert-butyl-catechol-type epoxy resins, naphthalene-type epoxy resins, naphthol-type epoxy resins, anthracene-type epoxy resins, glycidylamine-type epoxy resins, glycidyl ester-type epoxy resins, cresol novolac-type epoxy resins, biphenyl-type epoxy resins, biphenylaralkyl-type epoxy resins, linear aliphatic epoxy resins, epoxy resins having a butadiene structure, heterocyclic epoxy resins, spiro ring-containing epoxy resins, naphthylene ether-type epoxy resins, trimethylol-type epoxy resins, and tetraphenylethane-type epoxy resins. Among these, bisphenol A-type epoxy resins are preferred from the viewpoint of improving conformability to irregularities, i.e., irregularity embedding ability, when encapsulating semiconductor elements and the like. On the other hand, biphenyl aralkyl epoxy resins are preferred from the viewpoint of heat resistance. Furthermore, epoxy resins without an alicyclic structure preferably have two or more epoxy groups in the molecule from the viewpoint of reactivity. The epoxy resins without an alicyclic structure may be used alone or in combination of two or more.

[0123] In the encapsulating resin composition of the present disclosure, the content of the alicyclic epoxy resin per 100 parts by mass of the epoxy resin is preferably 10 parts by mass or more, more preferably 30 parts by mass or more, and even more preferably 50 parts by mass or more, from the viewpoint of improving performance such as moisture resistance, dielectric properties, and heat resistance. In the encapsulating resin composition of the present disclosure, the content of 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate per 100 parts by mass of the epoxy resin is preferably 30 parts by mass or more, more preferably 40 parts by mass or more, and even more preferably 50 parts by mass or more, from the viewpoint of improving performance such as moisture resistance, dielectric properties, and heat resistance.

[0124] In the encapsulating resin composition of the present disclosure, the content of the epoxy resin is not particularly limited, but from the viewpoint of the ability to fill irregularities, it is preferably 20 parts by mass or more, more preferably 30 parts by mass or more, and even more preferably 40 parts by mass or more relative to 100 parts by mass of the total solid content contained in the encapsulating resin composition; on the other hand, from the viewpoint of suppressing deterioration of the dielectric properties, it is preferably 95 parts by mass or less, more preferably 90 parts by mass or less, and even more preferably 80 parts by mass or less.

[0125] [Hollow Particles] The hollow particles contained in the encapsulating resin composition of the present disclosure are the hollow particles of the present disclosure described above. In the encapsulating resin composition of the present disclosure, the content of the hollow particles is not particularly limited, but is preferably 1 to 70 parts by mass per 100 parts by mass of the total solid content contained in the resin composition, from the viewpoint of improving the dielectric properties of the resin composition while suppressing a decrease in performance stability. The lower limit of the hollow particle content is more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, from the viewpoint of improving the dielectric properties of the resin composition. The upper limit of the hollow particle content is more preferably 50 parts by mass or less, and even more preferably 40 parts by mass or less, from the viewpoint of suppressing a decrease in performance stability of the resin composition and a decrease in the ability to embed uneven surfaces.

[0126] [Curing Accelerator] The encapsulating resin composition of the present disclosure typically contains a curing accelerator. The curing accelerator can be appropriately selected from those commonly used as curing accelerators for epoxy resins, and is not particularly limited. Examples of the curing accelerator include phosphorus-based curing accelerators, amine-based curing accelerators, imidazole-based curing accelerators, guanidine-based curing accelerators, and metal-based curing accelerators. The curing accelerators can be used alone or in combination of two or more.

[0127] In the present disclosure, the curing accelerator is not particularly limited, but imidazole-based curing accelerators are preferably used because they make it easier to obtain a resin composition with excellent heat resistance. Examples of imidazole-based curing accelerators include 2-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-methylimidazole, and 1-benzyl-2-furan. phenylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-phenylimidazolium trimellitate, 1-cyanoethyl-2-phenylimidazolium trimellitate, 2,4-diamino-6-[2'-methylimidazolyl- (1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-undecylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanuric acid adduct, 2-phenylimidazole isocyanuric acid adduct, Examples of the imidazole compounds include 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2,3-dihydro-1H-pyrrolo[1,2-a]benzimidazole, 1-dodecyl-2-methyl-3-benzylimidazolium chloride, 2-methylimidazoline, and 2-phenylimidazoline, as well as adducts of imidazole compounds with epoxy resins. Among these, at least one selected from the group consisting of 2-ethyl-4-methylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, and 2-heptadecylimidazole is preferred.

[0128] In the encapsulating resin composition of the present disclosure, the content of the curing accelerator is adjusted appropriately depending on the type of the curing accelerator, and is not particularly limited, but is preferably 0.1 to 7 parts by mass, more preferably 0.5 to 5 parts by mass, relative to 100 parts by mass of the epoxy resin. When the content of the curing accelerator is equal to or greater than the above lower limit, the curing acceleration effect is excellent.

[0129] [Curing Agent] The encapsulating resin composition of the present disclosure preferably contains a curing agent. The curing agent can be appropriately selected from those commonly used as curing agents for epoxy resins, and is not particularly limited. Examples of the curing agent include amine-based curing agents, acid anhydride-based curing agents, imidazole-based curing agents, thiol-based curing agents, phenol-based curing agents, naphthol-based curing agents, benzoxazine-based curing agents, cyanate ester-based curing agents, and carbodiimide-based curing agents. The curing agents can be used alone or in combination of two or more.

[0130] In order to improve the storage stability of the encapsulating resin composition of the present disclosure, an acid anhydride curing agent is preferably used as the curing agent. The acid anhydride curing agent is not particularly limited, but examples thereof include hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, 1,2,3,6-tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylendomethylenetetrahydrophthalic anhydride, cyclohexane-1,2,4-tricarboxylic acid-1,2-anhydride, dodecenylsuccinic anhydride, succinic anhydride, hydrogenated pyromellitic anhydride, hydrogenated biphenyl dianhydride, phthalic anhydride, tetrahydrophthalic anhydride, and methylcyclohexene dicarboxylic anhydride. Among these, in order to improve the storage stability of the encapsulating resin composition, at least one selected from methylhexahydrophthalic anhydride and methyltetrahydrophthalic anhydride is preferred.

[0131] In the encapsulating resin composition of the present disclosure, the content of the curing agent is adjusted appropriately depending on the type of curing agent and is not particularly limited, but is preferably 0.5 to 1.5 equivalents, and more preferably 0.8 to 1.2 equivalents, of the curing agent relative to 1 equivalent of the epoxy group of the epoxy resin. In the case of an acid anhydride-based curing agent, one acid anhydride group is calculated as 1 equivalent. In the encapsulating resin composition of the present disclosure, the content of the curing agent is preferably 50 to 200 parts by mass, and more preferably 70 to 120 parts by mass, relative to 100 parts by mass of the epoxy resin.

[0132] [Other Additives] The encapsulating resin composition of the present disclosure may further contain additives commonly used in semiconductor encapsulants, such as a release agent, a plasticizer, a filler, an antioxidant, a light stabilizer, an antifoaming agent, a leveling agent, a coupling agent, a surfactant, a flame retardant, a colorant, an ion adsorbent, and the like.

[0133] The release agent is not particularly limited, but examples thereof include long-chain carboxylic acids or metal salts thereof such as stearic acid, behenic acid, and montanic acid; higher alcohols such as stearyl alcohol; amides such as stearyl bisamide; esters such as carnauba wax and phosphate esters; paraffin; and silicone oils such as dimethyl silicone oil and methyl phenyl silicone oil. These can be used alone or in combination of two or more. The content of the release agent is not particularly limited, but can be, for example, 1 to 8 parts by mass per 100 parts by mass of the epoxy resin. By including a release agent in the encapsulating resin composition of the present disclosure, the slip properties of the cured product can be improved.

[0134] The plasticizer is not particularly limited, but examples thereof include polyhydric alcohols. Examples of polyhydric alcohols include glycerin, sorbitol, polyglycerin, pentaerythritol, and trimethylolpropane. The content of the plasticizer is not particularly limited, but can be, for example, 5 to 30 parts by mass per 100 parts by mass of the epoxy resin.

[0135] The filler may be either inorganic or organic, but inorganic fillers are preferred. Examples of inorganic fillers include, but are not limited to, barium sulfate, barium titanate, silica (amorphous silica, crystalline silica, fused silica, spherical silica, etc.), talc, clay, magnesium carbonate, calcium carbonate, aluminum oxide, aluminum hydroxide, silicon nitride, and aluminum nitride. Among these, silica is preferred because of its good dispersibility, relatively small thermal expansion coefficient, and ease of achieving desired cured film properties. The filler may be surface-modified. While the surface modification method is not particularly limited, surface modification using a silane coupling agent is preferred because it is simple, has a wide variety of functional groups, and is easy to impart desired properties. The filler content is not particularly limited, but can be, for example, 30% by volume or more and 85% by volume or less based on the total solids content contained in the encapsulating resin composition.

[0136] [Method for Producing Encapsulating Resin Composition] The encapsulating resin composition of the present disclosure can be obtained, for example, by mixing the above-described epoxy resin, hollow particles, and curing accelerator, and further, if necessary, a curing agent and other additives, by known means. Examples of the mixing method include methods using known mixing or kneading devices such as a planetary mixer, ball mill, bead mill, planetary mixer, roll mill, kneading extruder, and kneader. The encapsulating resin composition of the present disclosure may further contain a solvent, if necessary. Furthermore, the encapsulating resin composition of the present disclosure may be in a B-stage state.

[0137] [Cured Product] A cured product of the encapsulating resin composition of the present disclosure can be obtained, for example, by heating the encapsulating resin composition of the present disclosure described above. The heating temperature, curing time, and heating method for curing the encapsulating resin composition of the present disclosure are the same as those for the resin composition of the present disclosure described above.

[0138] 7. Semiconductor Device The semiconductor device of the present disclosure is characterized by including a cured product of the encapsulating resin composition of the present disclosure as an encapsulant. The semiconductor device of the present disclosure generally has a structure in which a semiconductor element is disposed on a substrate and the semiconductor element is encapsulated with an encapsulant. The method for encapsulating the semiconductor element disposed on the substrate using the encapsulating resin composition of the present disclosure is not particularly limited, and various molding methods such as transfer molding or casting can be used.

[0139] The present disclosure will be described in more detail below with reference to examples and comparative examples, but the present disclosure is not limited to these examples. Note that parts and percentages are by mass unless otherwise specified.

[0140] Example 1 (1) Mixed Liquid Preparation Step First, the following materials were mixed to form an oil phase: 37.5 parts divinylbenzene, 1.6 parts ethylvinylbenzene, 0.89 parts t-butylperoxydiethyl acetate, and 60.8 parts hydrophobic solvent: heptane. Next, in a stirring vessel, an aqueous solution prepared by dissolving 15.7 parts magnesium chloride (a water-soluble polyvalent metal salt) in 225 parts ion-exchanged water and 11.0 parts sodium hydroxide (an alkali metal hydroxide) in 55 parts ion-exchanged water was gradually added under stirring to prepare a magnesium hydroxide colloid (poorly water-soluble metal hydroxide colloid) dispersion (8 parts magnesium hydroxide), which served as the aqueous phase. The resulting aqueous phase and oil phase were mixed to prepare a mixed liquid.

[0141] (2) Suspension step The mixture obtained in the mixture preparation step was suspended by stirring for 1 minute using an emulsifying disperser (manufactured by Primix Corporation, product name: Homomixer) at a rotation speed of 4,000 rpm to prepare a suspension in which droplets of the monomer composition encapsulating the hydrophobic solvent were dispersed in water.

[0142] (3) Polymerization step: The suspension obtained in the suspension step was heated to 80° C. in a nitrogen atmosphere and stirred for 24 hours at a temperature of 80° C. to carry out a polymerization reaction. Through this polymerization reaction, a precursor composition was obtained, which was a slurry liquid in which precursor particles encapsulating a hydrophobic solvent were dispersed in water.

[0143] (4) Washing Step The precursor composition obtained in the polymerization step was treated with dilute sulfuric acid (25 ° C, 10 minutes) to adjust the pH to 5.5 or less. Thereafter, a nonionic surfactant was added to improve compatibility at the interface between the water and the precursor particles, thereby eliminating the aggregation of the precursor particles, and a pH-adjusted slurry was obtained. Next, the precursor particles were separated from the pH-adjusted slurry by filtration at room temperature (25 ° C), and the separated precursor particles were dehydrated. 200 parts of ion-exchanged water was added to the dehydrated precursor particles to re-slurry them, and the aggregation of the precursor particles was eliminated in the same manner as above, followed by filtration and dehydration. This series of steps of re-slurrying the precursor particles, eliminating the aggregation, filtration, and dehydration was repeated three times (three washings) to obtain precursor particles containing a hydrophobic solvent.

[0144] (5) Solvent Removal Step The precursor particles obtained in the washing step were pre-dried by drying in a dryer at a temperature of 40° C. Next, the precursor particles were heat-treated in a vacuum dryer at 200° C. for 12 hours under vacuum conditions to remove the hydrophobic solvent contained in the particles, thereby obtaining hollow particles of Example 1.

[0145] Example 2 Hollow particles of Example 2 were produced in the same manner as in Example 1, except that the number of washings in the "(4) washing step" was changed from three to four.

[0146] [Examples 3 to 5] Hollow particles of Examples 3 to 5 were produced in the same procedure as in Example 1, except that in the above "(1) mixed solution preparation step", the type and amount of polymerizable monomer added to the oil phase were changed according to Table 1, and in the above "(4) washing step", the number of washings was changed from three to four.

[0147] Comparative Example 1 The hollow particles of Comparative Example 1 were produced in the same manner as in Example 1, except that in the above "(4) washing step", the precursor composition obtained in the polymerization step was treated with dilute sulfuric acid (at 25°C for 10 minutes) to adjust the pH to 5.5 or less, and then the precursor particles were separated by filtration and dehydrated.

[0148] Comparative Example 2 Hollow particles of Comparative Example 2 were produced in the same manner as in Example 1, except that in the above "(4) washing step", the number of washings was changed from three to one.

[0149] Comparative Example 3 Hollow particles of Comparative Example 3 were produced in the same manner as in Example 1, except that in the above "(4) washing step", the number of washings was changed from three to two.

[0150] Comparative Example 4 Hollow particles of Comparative Example 4 were produced in the same manner as in Example 1, except that 0.313 parts of an anionic surfactant was added to the aqueous magnesium chloride solution when preparing the aqueous phase in the above-mentioned "(1) mixed solution preparation step", and further, the number of washings was changed from three to two in the above-mentioned "(4) washing step".

[0151] Comparative Example 5 Hollow particles for Comparative Example 5 were produced in the same manner as in Production Example 1 of Patent Document 1 (JP 2000-313818 A). Specifically, an aqueous solution of 70 parts of styrene, 27 parts of butadiene, 3 parts of itaconic acid, and 12 parts of t-dodecyl mercaptan, 0.5 parts of a reactive emulsifier SE10N (manufactured by Adeka) and 1.0 parts of ammonium persulfate in 200 parts of distilled water was polymerized at 75°C for 8 hours while stirring to obtain polymer particles. Next, using these polymer particles as a seed polymer, the following polymerization was carried out. Specifically, 10 parts of these polymer particles, 0.1 parts of a surfactant polyoxyethylene nonylphenyl ether, 0.4 parts of ammonium lauryl sulfate, and 0.5 parts of ammonium persulfate were dispersed in 900 parts of distilled water. A mixture of 50 parts of methyl methacrylate, 40 parts of divinylbenzene, 10 parts of α-methylstyrene, and 20 parts of toluene was added to the mixture and polymerized at 75° C. for 5 hours, yielding a dispersion of precursor particles containing toluene inside the particles. The resulting precursor particles were spray-dried to obtain hollow particles of Comparative Example 5.

[0152] [Comparative Example 6] Hollow particles of Comparative Example 6 were produced as hollow particles corresponding to Patent Document 3 (WO 2021 / 085189). First, the following materials were mixed to form an oil phase. Styrene 12.5 parts Divinylbenzene 16.2 parts Ethylvinylbenzene 3.8 parts HS Crysta 4100 (: product name, side chain crystalline polyolefin, manufactured by Toyokuni Oil Mills Co., Ltd.) 3.3 parts Blenmar (registered trademark) 50PEP-300 (: product name, polyethylene glycol propylene glycol monomethacrylate, manufactured by NOF Corporation) 3.3 parts Perloyl L (: product name, polymerization initiator, manufactured by NOF Corporation) 1.07 parts Hydrophobic solvent: heptane 26.04 parts Next, 370 parts of ion-exchanged water and 0.18 parts of Rapisol A-80 (surfactant, manufactured by NOF Corporation) were mixed to prepare an aqueous phase. The oil phase was added to the aqueous phase, and a suspension was prepared using an ultrasonic homogenizer. The resulting suspension was heated at 70°C for 4 hours to polymerize the mixture, yielding a slurry. The resulting slurry was heated at 100°C for 24 hours to yield hollow particles of Comparative Example 6.

[0153] [Comparative Example 7] The hollow particles of Comparative Example 7 were produced in the same manner as in Example 1, except that in the above "(1) mixed solution preparation step", the types and amounts of polymerizable monomers and hydrophobic solvents added to the oil phase were changed according to Table 1, in the "(3) polymerization step", the polymerization temperature was changed to 40°C and the polymerization time to 4 hours, and in the above "(4) washing step", no nonionic surfactant was added to the slurry after pH adjustment and the slurry after reslurrying to eliminate aggregation between precursor particles.

[0154] [Evaluation] The hollow particles obtained in the above-mentioned examples and comparative examples were subjected to the following measurements and evaluations. The results are shown in Table 1.

[0155] 1. Volume Average Particle Size (Dv) The volume average particle size (Dv) of hollow particles was measured using a particle size distribution analyzer (manufactured by Beckman Coulter, Inc., product name: Multisizer 4e) using the Coulter Counter method. The measurement conditions were aperture diameter: 50 μm, dispersion medium: Isoton II (product name), concentration: 10%, and number of particles measured: 100,000. Specifically, 0.2 g of particle sample was placed in a beaker, and a surfactant aqueous solution (manufactured by Fujifilm Corporation, product name: Drywell) was added as a dispersant. 2 ml of dispersion medium was added to wet the particles, and then 10 ml of dispersion medium was added. The mixture was dispersed in an ultrasonic disperser for 1 minute, and then measured using the particle size distribution analyzer.

[0156] 2. Porosity 2-1. Measurement of apparent density of hollow particles First, a volume of 100 cm ３ About 30 cm ３ The 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 the 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 was calculated using the formula (I). １ = [Mass of hollow particles] / (100 - [Mass of isopropanol] / [Specific gravity of isopropanol at measurement temperature])

[0157] 2-2. Measurement of true density of hollow particles After crushing the hollow particles in advance, 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. Then, in the same manner as in the measurement of the apparent density, 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 ) was calculated. ０ = [Mass of crushed hollow particle fragments] / (100 - [Mass of isopropanol] / [Specific gravity of isopropanol at measurement temperature])

[0158] 2-3. Calculation of porosity Apparent density D of hollow particles １ and true density D ０ The porosity of the hollow particles was calculated based on the following formula (III): Formula (III) Porosity (%) = 100 - (apparent density D １ / True density D ０ ) x 100

[0159] 3. Residual Monomer Amount In measuring the residual monomer amount, hollow particles (precursor particles encapsulating a hydrophobic solvent) after the cleaning process were prepared as measurement samples in each Example and Comparative Example. The residual monomer amount in each measurement sample was measured using the following method. 3 g of the solid content of the hollow particles was collected and weighed to the nearest 1 mg. 27 g of ethyl acetate was added and stirred for 15 minutes, after which 13 g of methanol was added and stirred for an additional 10 minutes. The resulting solution was allowed to stand to precipitate the insoluble matter, and the supernatant of this solution was collected as the measurement sample. The measurement sample was injected into a gas chromatograph, and the amount of unreacted polymerizable monomer in the measurement sample was quantified by gas chromatography (GC) under the following conditions. The content of unreacted polymerizable monomer in the solid content of the hollow particles was calculated to determine the residual monomer amount. (Analysis conditions) Apparatus: GC-2010 (Shimadzu Corporation) Column: DB-5 (Agilent Technologies Inc.) Film thickness: 0.25 μm, inner diameter: 0.25 mm, length: 30 m Detector: FID Carrier gas: nitrogen (linear velocity: 28.8 cm / sec) Injection port temperature: 200° C. Detector temperature: 250° C. Oven temperature: increased from 40° C. to 230° C. at a rate of 10° C. / min, and held at 230° C. for 2 minutes Sampling volume: 2 μL

[0160] 4. pH and Electrical Conductivity of Hollow Particle Aqueous Dispersion A 0.35 cm3 volume of an aqueous solution (electrical conductivity 1 μS / cm or less) of a nonionic surfactant (product name: SN Deformer 180, manufactured by San Nopco, polyether type) dissolved in ion-exchanged water at a concentration of 0.1% by mass was added to 100 mL of the aqueous solution. ３The hollow particles were placed in a container and stirred at 300 rpm for 3 hours at room temperature (25°C), to obtain an aqueous dispersion of hollow particles. The pH and electrical conductivity of the obtained aqueous dispersion of hollow particles were measured. The obtained aqueous dispersion of hollow particles was visually inspected to see that no powder was present at the top, and the powder was entirely dispersed in water. Furthermore, a volume of 0.35 cm ３ The hollow particles used were those weighed out and calculated using the following formula (1): Formula (1): Volume 0.35 cm ３ Weight of hollow particles (g) = apparent density D of hollow particles １ (g / cm ３ ) x 0.35 (cm ３ )

[0161] 5. Surfactant Content on Particle Surface 50 ml of ultrapure water and 5 g of hollow particles were precisely weighed and mixed thoroughly. Ultrasonic waves were irradiated for 30 minutes, and the mixture was filtered through a syringe membrane filter with a diameter of 0.45 μm. The filtrate was freeze-dried, and the residue was dissolved in 1 g of tetramethylsilane (TMS) solvent under the following conditions: １ H-NMR measurement was carried out. １ For the surfactant identified from the H-NMR spectrum, a calibration curve based on TMS intensity was prepared, and the amount of surfactant extracted from the hollow particle surface was calculated. The calibration curve was prepared from the ratio of the TMS intensity and the peak intensity derived from the surfactant. The ratio of the amount of surfactant extracted from the hollow particle surface to the mass of the hollow particle was calculated, and this was taken as the content of surfactant present on the hollow particle surface. １ Particles in which no surfactant was detected from the H-NMR spectrum were recorded as not detected (ND). １ H-NMR measurement conditions> Device name: FT-NMR device Resonance frequency: 400 MHz Measurement mode: 1H-NMR Pulse width: 5.0 μs (pulse angle: 90°) Measurement range: 26 ppm (frequency range: 10,500 Hz) Number of accumulations: 1,024 Measurement temperature: 40°C Solvent: deuterated chloroform (TMS (tetramethylsilane) 1%) Reference substance: tetramethylsilane-derived peak: 0.00 ppm (internal standard method)

[0162] 6. Metal Content in Particles Using a microwave (PerkinElmer, Multiwave 3000), 10 g of precisely weighed hollow particles were wet decomposed, and the resulting decomposition product was subjected to ICP emission analysis using an ICP emission analyzer (PerkinElmer, Optima 2100 DV) to measure the total mass of metals. The metal species were identified by elemental analysis using X-ray fluorescence analysis (XRF). The ratio of the total mass of metals in the decomposition product to the mass of the hollow particles was calculated and used as the metal content in the hollow particles.

[0163] 7. Dielectric Constant (Dk) and Dielectric Loss Tangent (Df) The dielectric constant and dielectric loss tangent of the hollow particles 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).

[0164] 8. Void Maintenance Rate in Molded Article 90 parts of polypropylene (Novatec PP MA1B manufactured by Japan Polypropylene Corporation) and 10 parts of hollow particles were mixed in a blender. The resulting mixture was then placed in a mold and heated to 230°C. After the polypropylene had dissolved, the mixture was removed and the temperature was lowered to 130°C. A molded article was then produced by applying 15 MPa (surface pressure) using a press. The void maintenance rate (%) of the hollow particles was calculated from the specific gravity of the resulting molded article and the specific gravity of the hollow particles. The higher the void maintenance rate of the hollow particles, the more excellent their pressure resistance can be evaluated.

[0165] 9. Reliability Test in High-Humidity Environment 9-1. Preparation of Hollow Particle-Containing Resin Varnish First, 90 parts of a brominated epoxy resin (manufactured by Tohto Kasei Co., Ltd., product name: YDB-500EK75, epoxy equivalent: 500, solid content: 75% by mass) and 10 parts of a cresol novolac epoxy resin (manufactured by Tohto Kasei Co., Ltd., product name: YDCN220EK75, epoxy equivalent: 210, solid content: 75% by mass) were dissolved in a mixed solvent (room temperature) of 20 parts of dimethylformamide (DMF) and 6 parts of methyl ethyl ketone (MEK), and then 2 parts of dicyandiamide (DICY) (manufactured by Nippon Carbide Corporation) and 0.1 parts of 2-ethyl-4-methylimidazole (product name: Curesol (registered trademark) 2E4MZ, manufactured by Shikoku Chemicals Corporation) were added, followed by stirring and mixing to prepare a resin varnish. Next, 95 parts of the resin varnish cooled to room temperature and 5 parts of the hollow particles were mixed by stirring using a disper at 3,000 rpm for 30 minutes to obtain a hollow particle-containing resin varnish.

[0166] The obtained hollow particle-containing resin varnish was impregnated into a glass cloth (manufactured by Nitto Boseki Co., Ltd., product name: WEA116E), and then the solvent was removed by heating and drying at 150 to 170°C for 3 to 10 minutes, thereby obtaining a prepreg.

[0167] 9-3. Preparation of double-sided copper-clad laminates 35 μm thick copper foil was placed on both sides of one of the obtained prepregs, and the laminate was heated at 180° C. for 2 hours under a pressure of 2.94 MPa (30 kg / cm ２ ) under the curing conditions of 1.05 to 2.5 mm, and then heated and pressed to obtain a double-sided copper-clad laminate having a thickness of 0.13 mm.

[0168] 9-4. Reliability Test The obtained double-sided copper-clad laminate was subjected to a pressure cooker treatment (110°C, 85% RH, 100 hours). A voltage of 50 V was applied to the double-sided copper-clad laminate after this treatment for a predetermined time, and the resistance value was measured. The presence or absence of abnormalities was confirmed and evaluated according to the following evaluation criteria. A change in the resistance value was deemed to be abnormal. The change in resistance value is thought to be due to corrosion of the copper substrate. (Reliability Test Evaluation Criteria) A: No abnormality even after 400 hours of voltage application. B: No abnormality even after 300 hours of voltage application, but abnormality occurs before the voltage application time reaches 400 hours. C: No abnormality even after 200 hours of voltage application, but abnormality occurs before the voltage application time reaches 300 hours. D: No abnormality even after 100 hours of voltage application, but abnormality occurs before the voltage application time reaches 200 hours. E: Abnormality occurs before the voltage application time reaches 100 hours.

[0169]

[0170] Table 1 shows the amount (parts by mass) of each material added and the results of each measurement or evaluation. In Table 1, the dielectric loss tangent values ​​are expressed in exponential notation as specified in JIS X 0210 for simplification. For example, "8.44 x 10 －４ " is expressed as "8.44E-04". In Table 1, the meanings of the abbreviations are as follows: DVB: divinylbenzene EVB: ethylvinylbenzene St: styrene MMA: methyl methacrylate α-MSt: α-methylstyrene 50PEP-300: polyethylene glycol propylene glycol monomethacrylate (manufactured by NOF Corporation, product name: Blemmer (registered trademark) 50PEP-300)

[0171] In addition, SEM observations of the particle surfaces and cross sections of the hollow particles obtained in each Example and Comparative Example were performed. From the SEM observation results and porosity values, it was confirmed that the hollow particles obtained in each Example and Comparative Example except Comparative Example 6 were spherical and had only one hollow portion. The hollow particles obtained in Comparative Example 6 had cracks or dents. The proportion of particles having only one hollow portion was 90% or more in all Examples. Furthermore, 3,000 randomly selected particles were examined for the hollow particles obtained in each Example. In all Examples, the proportion of particles with a circularity of 0.85 or less was 10% by mass or less.

[0172] [Discussion] The hollow particles obtained in Comparative Examples 1 to 7 had a volume of 0.35 cm ３ In an aqueous dispersion of hollow particles obtained by dispersing the hollow particles of Example 1 in 100 mL of ion-exchanged water, the pH exceeded 7.5 and the electrical conductivity exceeded 50 μS / cm. Therefore, compared with the hollow particles obtained in each Example, the dielectric tangent was high and abnormalities were likely to occur in reliability tests, i.e., the performance stability in a high-humidity environment was poor. Furthermore, the hollow particles obtained in Comparative Examples 5 and 6 had a crosslinkable monomer unit content of less than 60 mass%, and therefore had poor pressure resistance. The hollow particles obtained in Comparative Example 7 had a large amount of residual monomer, and therefore had poor pressure resistance. In contrast, the hollow particles obtained in each Example had a volume of 0.35 cm ３The hollow particles obtained by dispersing the hollow particles in 100 mL of ion-exchanged water had a pH of 6.5 to 7.5 and a conductivity of 50 μS / cm or less, resulting in a low dielectric loss tangent and a low incidence of abnormalities in reliability tests, i.e., excellent performance stability in high-humidity environments. Furthermore, the hollow particles obtained in each Example had a crosslinkable monomer unit content of 60% by mass or more based on 100% by mass of all monomer units of the polymer contained in the shell, resulting in excellent pressure resistance and a porosity of 50% or more. The low dielectric loss tangent of the hollow particles obtained in each Example is presumably due in part to the sufficiently high porosity. The low dielectric loss tangent of the hollow particles obtained in each Example is presumably due in part to the high content of hydrocarbon monomer units. The hollow particles obtained in Examples 3 to 5 contained a combination of crosslinkable hydrocarbon monomer units and non-crosslinkable hydrocarbon monomer units, and the proportion of non-crosslinkable hydrocarbon monomer units was increased. Therefore, compared with the hollow particles obtained in Examples 1 and 2, the dielectric loss tangent was further reduced and the dielectric properties were particularly excellent.

[0173] [Example 6] (1) Preparation of resin composition The same hollow particle-containing resin varnish prepared in "9-1. Preparation of hollow particle-containing resin varnish" of "9. Reliability test under high humidity environment" in Example 2 was used as the resin composition of Example 6. The amount of each material added was adjusted so that the total solid content in the resin composition was 100 parts by mass. That is, first, 90 parts of a brominated epoxy resin (manufactured by Tohto Kasei Co., Ltd., product name: YDB-500EK75, epoxy equivalent: 500, solid content: 75% by mass) and 10 parts of a cresol novolac epoxy resin (manufactured by Tohto Kasei Co., Ltd., product name: YDCN220EK75, epoxy equivalent: 210, solid content: 75% by mass) were dissolved as a matrix resin in a mixed solvent (room temperature) of 20 parts of dimethylformamide (DMF) and 6 parts of methyl ethyl ketone (MEK). Further, 2 parts of dicyandiamide (DICY) (manufactured by Nippon Carbide Corporation) as a curing agent and 0.1 parts of 2-ethyl-4-methylimidazole (product name: Curesol (registered trademark) 2E4MZ, manufactured by Shikoku Chemicals Corporation) as a curing accelerator were added, and the mixture was stirred and mixed to prepare a resin varnish. Next, 118 parts of the resin varnish (solid content 94 parts) cooled to room temperature and 6 parts of the hollow particles prepared in Example 2 were stirred and mixed using a disper at 3,000 rpm for 30 minutes to prepare a resin composition of Example 6. Table 2 shows the content (parts by mass) of each component contained in the resulting resin composition.

[0174] (2) Preparation of resin molded body (cured product) The obtained resin composition was filled into an aluminum mold frame lined with a Teflon (registered trademark) sheet, and then heat-cured in an oven under a nitrogen atmosphere at 180°C for 3 hours to prepare a sheet-like resin molded body, which was a cured product of the resin composition obtained above.

[0175] [Example 7] The resin composition of Example 7 and its cured product, a resin molded body, were prepared in the same manner as in Example 6, except that the amount of resin varnish added was changed to 122.5 parts (solid content 98 parts) and the amount of hollow particles added was changed to 2 parts.

[0176] [Example 8] The resin composition of Example 8 and its cured product, a resin molded body, were prepared in the same manner as in Example 6, except that the amount of resin varnish added was changed to 106.5 parts (solid content 85 parts) and the amount of hollow particles added was changed to 15 parts.

[0177] Example 9 (1) Preparation of Encapsulating Resin Composition 48.8 parts of an alicyclic epoxy resin (product name: CELLOXIDE 2021P, manufactured by Daicel Corporation) as a matrix resin, 44.3 parts of methylhexahydrophthalic anhydride (product name: RIKACID (registered trademark) MH, manufactured by New Japan Chemical Co., Ltd.) as an acid anhydride curing agent, and 0.89 parts of 1-benzyl-2-methylimidazole (product name: CUREZOL (registered trademark) 1B2MZ, manufactured by Shikoku Chemical Industries, Ltd.) as a curing accelerator were mixed and stirred for 15 minutes using a planetary mixer. The resulting mixture was cooled to room temperature, and then 6 parts of the hollow particles prepared in Example 2 were added to the mixture. The mixture was mixed and stirred at 3,000 rpm for 30 minutes using a disper to prepare the encapsulating resin composition of Example 9.

[0178] (2) Preparation of Cured Product The obtained encapsulating resin composition was filled into an aluminum mold frame lined with a Teflon (registered trademark) sheet, and then heat-cured in an oven under a nitrogen atmosphere at 180°C for 3 hours to prepare a sheet-like cured product of the encapsulating resin composition.

[0179] Examples 10 to 15 Encapsulating resin compositions and cured products thereof of Examples 10 to 15 were prepared in the same manner as in Example 9, except that the type and amount of matrix resin, the amount of acid anhydride curing agent (RIKACID (registered trademark) MH) added, or the amount of curing accelerator (1B2MZ) added was changed according to Table 2.

[0180] Comparative Example 8 An encapsulating resin composition and a cured product thereof of Comparative Example 8 were prepared in the same manner as in Example 9, except that the hollow particles prepared in Comparative Example 2 were used instead of the hollow particles prepared in Example 2 in Example 9, and the type and amount of matrix resin, the amount of acid anhydride curing agent (RIKACID (registered trademark) MH) added, and the amount of curing accelerator (1B2MZ) added were changed according to Table 2.

[0181] [Evaluation] The following measurements and evaluations were carried out on the resin compositions and cured products obtained in Examples 6 to 15 and Comparative Example 8. The results are shown in Table 2.

[0182] 10. Void Retention Rate The void retention rate (%) of the hollow particles in the cured product was calculated from the specific gravity of the cured products obtained in Examples 6 to 15 and Comparative Example 8 and the specific gravity of the hollow particles added to each cured product.

[0183] 11. Rate of Decrease in Dielectric Loss Tangent Small pieces measuring 2.6 mm wide, 80 mm long, and 40 μm thick were cut from the cured products obtained in Examples 6 to 15 and Comparative Example 8 to serve as measurement samples. The dielectric loss tangents of these measurement samples were measured at a frequency of 10 GHz and room temperature (25°C) using a cavity resonator perturbation dielectric constant / dielectric loss tangent measuring device. Meanwhile, cured products containing no hollow particles were prepared using the same procedure as in Examples 6 to 15 and Comparative Example 8, except that no hollow particles were added. The dielectric loss tangents of the cured products containing no hollow particles obtained in Examples 6 to 15 and Comparative Example 8 were measured in the same manner as above. The rate of decrease in dielectric loss tangent of the cured products containing hollow particles obtained in Examples 6 to 15 and Comparative Example 8 was calculated using the following formula and evaluated according to the following evaluation criteria. In the formula, the dielectric loss tangent of the cured product containing hollow particles is designated Df1, and the dielectric loss tangent of a cured product prepared under the same conditions except that no hollow particles were added is designated Df2. Decrease rate of dielectric tangent (%) = {(Df2 - Df1) / Df2} x 100 (Evaluation criteria) A: Decrease rate of dielectric tangent is 12% or more B: Decrease rate of dielectric tangent is 6% or more and less than 12% C: Decrease rate of dielectric tangent is less than 6%

[0184] 12. Reliability test under high-humidity environment Prepregs were obtained using the resin compositions obtained in Examples 6 to 15 and Comparative Example 8 in the same procedure as in "9-2. Preparation of prepreg" in "9. Reliability test under high-humidity environment" above. Using the obtained prepregs, double-sided copper-clad laminates were obtained in the same procedure as in "9-3. Preparation of double-sided copper-clad laminate" in "9. Reliability test under high-humidity environment" above. Using the obtained double-sided copper-clad laminates, evaluations were carried out using the same procedures and evaluation criteria as in "9-4. Reliability test" in "9. Reliability test under high-humidity environment" above.

[0185]

[0186] In Table 2, the abbreviations have the following meanings. YDB-500EK75: Product name "YDB-500EK75", manufactured by Tohto Kasei Co., Ltd., brominated epoxy resin YDCN220EK75: Product name "YDCN220EK75", manufactured by Tohto Kasei Co., Ltd., cresol novolac epoxy resin CEL2021P: Product name "Celloxide 2021P", manufactured by Daicel Corporation, compound represented by the following formula (B) EHPE3150: Product name "EHPE3150", manufactured by Daicel Corporation, compound represented by the following formula (C) CEL2081: Product name "Celloxide 2081", manufactured by Daicel Corporation, compound represented by the following formula (D) GT401: Product name "Epolead GT401", manufactured by Daicel Corporation, compound represented by the following formula (E) THI-DE: Product name "Epocalic (registered trademark) THI-DE", manufactured by ENEOS Corporation, a compound represented by the following formula (F) jER828EL: Product name "jER828EL", manufactured by Mitsubishi Chemical Corporation, a bisphenol A type epoxy compound, epoxy equivalent 189 NC-3000-L: Product name "NC-3000-L", manufactured by Nippon Kayaku Co., Ltd., a biphenyl aralkyl type epoxy compound, epoxy group equivalent 269 2E4MZ: Product name "Curezol (registered trademark) 2E4MZ", manufactured by Shikoku Chemicals Corporation, 2-ethyl-4-methylimidazole 1B2MZ: Product name "Curezol (registered trademark) 1B2MZ", manufactured by Shikoku Chemicals Corporation, 1-benzyl-2-methylimidazole DICY: Dicyandiamide Rikacid, manufactured by Nippon Carbide Corporation MH: Product name "Rikacid MH", manufactured by New Japan Chemical Co., Ltd., methylhexahydrophthalic anhydride

[0187]

[0188] n in the formula (C) and n in the formula (D) are each an integer of 1 or more, and n1, n2, n3, and n4 in the formula (E) are each an integer of 0 or more.

[0189] [Discussion] The resin composition obtained in Comparative Example 8 and its cured product, a resin molded article, contained the hollow particles of Comparative Example 2. The hollow particles of Comparative Example 2 had an aqueous dispersion with a pH exceeding 7.5 and an electrical conductivity exceeding 50 μS / cm. Therefore, the resin composition obtained in Comparative Example 8 and its cured product, a resin molded article, were prone to abnormalities in reliability tests, i.e., had poor performance stability in high-humidity environments. Furthermore, in Comparative Example 8, the rate of decrease in dielectric loss tangent was smaller than in Examples in which the same amount of hollow particles was added, and the hollow particles were also inferior in their effect of reducing the dielectric loss tangent. In contrast, the resin compositions obtained in Examples 6 to 15 and their cured products, a resin molded article, contained the hollow particles of Example 2. The hollow particles of Example 2 had a pH of 6.5 or more and 7.5 or less and a conductivity of 50 μS / cm or less in their aqueous dispersion, and therefore the resin compositions and cured resin molded articles obtained in Examples 6 to 15 had a large reduction in dielectric tangent due to the hollow particles and were less likely to develop abnormalities in reliability tests, i.e., had excellent performance stability in high-humidity environments. This demonstrates that the resin compositions and resin molded articles of the present disclosure, which contain hollow particles and a matrix resin, have a reduced dielectric tangent due to the inclusion of hollow particles, while suppressing a decrease in performance stability in high-humidity environments.

[0190] REFERENCE SIGNS LIST 1 Aqueous medium 1a Ion-exchanged water 2 Low-polarity material 3 Droplets of monomer composition 4a Hydrophobic solvent 4b Material other than hydrophobic solvent 5 Precursor particle 6 Shell 7 Hollow portion 10 Hollow particle with the hollow portion filled with gas

Claims

1. A hollow particle comprising a resin-containing shell and a hollow portion surrounded by the shell, wherein the porosity is 50% or more. The shell contains a polymer as the resin, and the content of crosslinkable monomer units is 60% by mass or more of the total monomer units of the polymer by mass. Volume: 0.35 cm³ ３ In an aqueous dispersion of hollow particles obtained by dispersing the hollow particles in 100 mL of deionized water, the pH is 6.5 or higher and 7.5 or lower, and the conductivity is 50 μS / cm or less.

2. The hollow particle according to claim 1, wherein the content of hydrocarbon monomer units exceeds 50% by mass in 100% by mass of the total monomer units of the polymer.

3. The hollow particle according to claim 1 or 2, wherein the metal content is 700 ppm or less.

4. The hollow particle according to claim 1 or 2, wherein the surfactant content present on the surface of the hollow particle is 200 ppm or less.

5. The dielectric loss tangent at a frequency of 10 GHz is 1.00 × 10⁻⁶. －３ The hollow particle according to claim 1 or 2, which is as follows:

6. A hollow particle according to claim 1 or 2, wherein the relative permittivity at a frequency of 10 GHz is 1.00 or more and 1.40 or less.

7. The hollow particle according to claim 1 or 2, wherein the porosity is 70% or more.

8. A resin composition comprising hollow particles according to claim 1 or 2 and a matrix resin.

9. A resin molded article obtained from the resin composition described in claim 8.

10. A sealing resin composition comprising hollow particles according to claim 1 or 2 and an epoxy resin.

11. The sealing resin composition according to claim 10, wherein the epoxy resin includes an alicyclic epoxy resin.

12. The sealing resin composition according to claim 11, further comprising an epoxy resin that does not have an alicyclic structure as the epoxy resin.

13. Furthermore, the encapsulating resin composition according to claim 10, further comprising a curing accelerator.

14. The sealing resin composition according to claim 10, wherein the content of the hollow particles is 1 to 70 parts by mass with respect to 100 parts by mass of the total solid content contained in the sealing resin composition.

15. A cured product of the sealing resin composition according to claim 10.

16. A semiconductor device comprising the cured product described in claim 15 as a sealing material.