Hollow particle, resin composition, and resin molded body

Abstract

Provided is a hollow particle having a low dielectric loss tangent at high frequencies. The hollow particle comprises: a resin-containing shell; and a hollow portion surrounded by the shell, and has a porosity of at least 50%, wherein the shell contains, as the resin, a polymer containing at least 91 mass% of hydrocarbon monomer units and at least 50 mass% of crosslinkable monomer units, at least a portion of the hydrocarbon monomer units are crosslinkable hydrocarbon monomer units, and the polymer has a residual double bond content of 30.0% or less and a dielectric loss tangent of 3.00×10-3 or less at a frequency of 10 GHz.

Description

Hollow particles, resin composition, and resin molded product

[0001] The present disclosure relates to hollow particles, and to a resin composition and a resin molded article containing the hollow particles.

[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 to lower their dielectric constant and dielectric loss tangent. However, hollow particles with an acrylic resin shell tend to have relatively high dielectric constants and dielectric loss tangents, which hinders the full effects of lowering the dielectric constant and dielectric loss tangent. Therefore, hollow particles using styrene-based resins have been produced to lower the dielectric constant and dielectric loss tangent of hollow particles. For example, Patent Document 1 discloses hollow particles obtained by dispersing an oil phase containing styrene, divinylbenzene, a (meth)acrylic acid ester monomer having a specific structure, a peroxide-based polymerization initiator, a side-chain crystalline polyolefin, and heptane in an aqueous phase that is an aqueous solution of a surfactant, followed by suspension polymerization. Patent Document 2 discloses hollow particles obtained by dispersing an oil phase containing divinylbenzene, a peroxide-based polymerization initiator, and hexadecane in an aqueous phase that is an aqueous solution of polyvinyl alcohol, followed by suspension polymerization.

[0004] International Publication No. 2021 / 085189 Japanese Patent Application Laid-Open No. 2002-80503

[0005] Furthermore, in recent years, efforts have been made to increase the transmission frequency in order to transmit large amounts of information in the field of information processing using electronic devices, and there is a demand for technology that can reduce the dielectric constant and dielectric loss tangent to accommodate high-frequency transmission. However, conventional hollow particles do not have sufficiently reduced relative dielectric constants and dielectric loss tangents at high frequencies of around 10 GHz, and it has been particularly difficult to reduce the dielectric loss tangent.

[0006] An object of the present disclosure is to provide hollow particles having a low dielectric tangent at high frequencies, and to provide a resin composition and a resin molded product containing the hollow particles.

[0007] The present inventors have focused on the resin composition of the shell and the amount of unreacted polymerizable functional groups remaining in the shell of hollow particles having a shell formed by polymerization of a polymerizable monomer, and have found that hollow particles exhibiting a low dielectric tangent at high frequencies such as 10 GHz can be obtained by incorporating a large amount of hydrocarbon monomer units into the polymer that forms the skeleton of the shell, adjusting the method for forming the shell to keep the residual double bond ratio at a specific amount or less, and further increasing the porosity of the hollow particles.

[0008] The present disclosure relates to hollow particles having a shell containing a resin and a hollow portion surrounded by the shell, wherein the porosity is 50% or more, the shell contains, as the resin, a polymer containing 91% by mass or more of hydrocarbon monomer units and 50% by mass or more of crosslinkable monomer units, at least a portion of the hydrocarbon monomer units being crosslinkable hydrocarbon monomer units, the polymer having a residual double bond ratio of 30.0% or less, and a dielectric loss tangent at a frequency of 10 GHz of 3.00×10 －３ Hollow particles are provided, which are:

[0009] 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.

[0010] In the hollow particles of the present disclosure, the porosity is preferably 65% ​​or more.

[0011] The hollow particles of the present disclosure preferably have a volume average particle size of 1.0 μm or more and 10.0 μm or less.

[0012] The present disclosure further provides a resin composition containing the hollow particles of the present disclosure and a matrix resin, and a resin molded product containing the hollow particles of the present disclosure and a matrix resin.

[0013] The present disclosure as described above provides hollow particles having a low dielectric loss tangent at high frequencies. The present disclosure also provides a resin composition and a resin molded product containing the hollow particles.

[0014] 1A to 1C are diagrams illustrating an example of a method for producing hollow particles according to the present disclosure.

[0015] 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. In this 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. In this disclosure, a polymerizable monomer refers to a compound having a functional group capable of addition polymerization (sometimes simply referred to as a polymerizable functional group in this disclosure). In this disclosure, a compound having an ethylenically unsaturated bond as a functional group capable of addition polymerization is generally used as the polymerizable monomer. 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 the present disclosure, a hydrocarbon monomer is a polymerizable monomer composed of carbon and hydrogen. A cross-linkable hydrocarbon monomer is a polymerizable monomer having two or more polymerizable functional groups and composed of carbon and hydrogen, and a non-cross-linkable hydrocarbon monomer is a polymerizable monomer having only one polymerizable functional group and composed of carbon and hydrogen. In the present disclosure, good dielectric properties mean low relative dielectric constant and dielectric loss tangent, and the lower the relative dielectric constant and dielectric loss tangent, the better the dielectric properties.

[0016] The hollow particles of the present disclosure are hollow particles comprising a shell containing a resin and a hollow portion surrounded by the shell, the porosity being 50% or more, the shell containing, as the resin, a polymer containing 91% by mass or more of hydrocarbon monomer units and 50% by mass or more of crosslinkable monomer units, at least a portion of the hydrocarbon monomer units being crosslinkable hydrocarbon monomer units, the polymer having a residual double bond ratio of 30.0% or less, and a dielectric loss tangent at a frequency of 10 GHz of 3.00×10 －３ The present invention is characterized by the following:

[0017] 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 that is 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.

[0018] Hollow particles obtained using hydrocarbon resins such as styrene-based resins have good dielectric properties of the resin constituting the shell, but it has been difficult to achieve a sufficiently low dielectric loss tangent at high frequencies. In contrast, the hollow particles disclosed herein have a low dielectric loss tangent even at high frequencies such as 10 GHz. It is believed that the polymer forming the shell skeleton of the hollow particles disclosed herein contains a large amount of hydrocarbon monomer units and has a low residual double bond ratio, thereby suppressing molecular motion of the shell compared to conventional hollow particles. Furthermore, the hollow particles disclosed herein have a hollow portion that is clearly distinguishable from the shell because the polymer contains 50% by mass or more of crosslinkable monomer units. The hollow particles of the present disclosure are typically obtained by suspension polymerization. In suspension polymerization using a polymerizable monomer containing 50% by mass or more of a crosslinkable monomer, phase separation between the shell-forming 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, presumably resulting in the formation of hollow particles with a hollow portion clearly distinguishable from the shell. The hollow particles of the present disclosure not only have a shell with low molecular mobility as described above, but also have a hollow portion clearly distinguishable from the shell, and further have a sufficiently high porosity, presumably resulting in a sufficiently low dielectric loss tangent even at high frequencies such as 10 GHz. Note that the dielectric loss tangent of an air layer is zero, and the greater the proportion of air layers within a hollow particle, the lower the dielectric loss tangent. Therefore, the higher the porosity of the hollow particles, the lower the dielectric loss tangent can be achieved. Below, we will describe an example of a method for producing hollow particles of the present disclosure, followed by a detailed description of the hollow particles of the present disclosure, and then further describe resin compositions and resin molded articles containing the hollow particles of the present disclosure.

[0019] 1. Method for producing hollow particles The hollow particles of the present disclosure can be produced by, for example, the following steps: 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; and 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; wherein, in 100% by mass of the polymerizable monomer contained in the mixed solution, the content of hydrocarbon monomers is 91% by mass or more and the content of crosslinkable monomers is 50% by mass or more, and at least a part of the hydrocarbon monomers is a crosslinkable hydrocarbon monomer; the polymerization initiator contained in the mixed solution is an organic peroxide; The hollow particles can be obtained by the method for producing hollow particles of the present disclosure, wherein in the step of preparing the precursor composition, the temperature of the polymerization reaction is higher than the 10-hour half-life temperature of the polymerization initiator.

[0020] The manufacturing method of the present disclosure follows a 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 are phase-separated, and droplets having a distribution structure in which the polymerizable monomer is unevenly distributed on the surface and the hydrophobic solvent is unevenly distributed in the center are dispersed in the aqueous medium, and the suspension is subjected to a polymerization reaction to harden the surfaces of the droplets and form hollow particles having hollows filled with the hydrophobic solvent. In the manufacturing method of the present disclosure, the basic technique is used to obtain hollow particles having hollows clearly distinguishable from the shell and high porosity, as described above, by using a polymerizable monomer containing 50% by mass or more of a crosslinkable monomer. Furthermore, by setting the content of the hydrocarbon monomer and the content of the crosslinkable monomer in the polymerizable monomer to be equal to or greater than the specific amount, using an organic peroxide as the polymerization initiator, and setting the polymerization temperature to a temperature higher than the 10-hour half-life temperature of the polymerization initiator, hollow particles exhibiting a low dielectric tangent even at high frequencies can be obtained. The reason why the hollow particles obtained by the manufacturing method of the present disclosure have a low dielectric loss tangent at high frequencies is believed to be as follows. First, by forming hollow portions within the particles, the porosity can be sufficiently increased, thereby sufficiently increasing the proportion of air spaces within the hollow particles, thereby achieving a low dielectric loss tangent. Furthermore, since the polymerizable monomer used to form the shell contains a large amount of hydrocarbon monomers, the resulting shell contains a large amount of hydrocarbons, resulting in a shell with lower molecular mobility than hollow particles whose shells are primarily composed of acrylic resins. This makes it easier for the dielectric loss tangent of the hollow particles to decrease, depending on the shell composition. Furthermore, by using an organic peroxide as a polymerization initiator and setting the polymerization temperature higher than the 10-hour half-life temperature of the polymerization initiator, the amount of unreacted polymerizable unsaturated bonds and decomposition products of the polymerization initiator remaining in the shell is reduced, thereby suppressing an increase in the dielectric loss tangent of the hollow particles. Unreacted polymerizable unsaturated bonds and decomposition products of the polymerization initiator increase molecular motion in the shell, and a large amount of these remaining products may increase the dielectric loss tangent of the hollow particles.When an organic peroxide is used as a polymerization initiator, the polymerization reaction is more easily promoted than when other polymerization initiators are used, and the decomposition products are easily removed and less likely to remain, so that the amount of unreacted polymerizable unsaturated bonds and the amount of remaining decomposition products of the polymerization initiator can be reduced.

[0021] The method for producing hollow particles according to the present disclosure includes a step of preparing a mixed solution, a step of preparing a suspension, and a step of subjecting the suspension to a polymerization reaction, 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 of the steps 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.

[0022] 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) solid-liquid separation step: performing solid-liquid separation of the precursor composition to obtain precursor particles encapsulating a hydrophobic solvent in the hollow portion; and (5) solvent removal step: removing the hydrophobic solvent encapsulated in the precursor particles obtained by the solid-liquid separation step to obtain hollow particles. In the present disclosure, hollow particles whose hollow portions are filled with a hydrophobic solvent are considered to be intermediates of hollow particles whose hollow portions are filled with a gas, and may be referred to as "precursor particles." In the present disclosure, the term "precursor composition" refers to a composition containing precursor particles.

[0023] 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 8 of a monomer composition dispersed in the aqueous medium 1. The droplets 8 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 8 of the monomer composition are phase-separated into a hydrophobic solvent 4a and a material other than the hydrophobic solvent, including the polymerizable monomer, a material 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 hollow portions. The precursor composition includes an aqueous medium 1 and precursor particles 9 encapsulating a hydrophobic solvent 4a in hollow portions, dispersed in the aqueous medium 1. The shell 6 forming the outer surface of the precursor particle 9 is formed by polymerization of the polymerizable monomer in the droplet 8 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 the precursor particle after the solid-liquid separation step. (4) in FIG. 1 shows a state in which the aqueous medium 1 has been removed from the state shown in (3) in FIG. 1. (5) in FIG. 1 is a cross-sectional schematic diagram showing one embodiment of the hollow particle after the solvent removal step. (5) in FIG. 1 shows a state in which the hydrophobic solvent 4a has been removed from the state shown in (4) in FIG.By removing the hydrophobic solvent from the precursor particles, hollow particles 10 are obtained, each having a gas-filled hollow portion 7 inside a shell 6. The above five steps and other steps will be described in order below.

[0024] (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.

[0025] (A) Polymerizable Monomer The polymerizable monomer in the mixed liquid includes at least a hydrocarbon monomer and a crosslinkable monomer. Here, the hydrocarbon monomer includes a crosslinkable hydrocarbon monomer, and the crosslinkable monomer may consist of a crosslinkable hydrocarbon monomer or may be a mixture of a crosslinkable hydrocarbon monomer and a crosslinkable monomer containing a heteroatom. Furthermore, the polymerizable monomer in the mixed liquid may further include a non-crosslinkable monomer, as long as the effects of the present disclosure are not impaired. The non-crosslinkable monomer in the mixed liquid may consist of a non-crosslinkable hydrocarbon monomer or may be a mixture of a non-crosslinkable hydrocarbon monomer and a non-crosslinkable monomer containing a heteroatom.

[0026] [Hydrocarbon Monomer] The hydrocarbon monomer in the mixed liquid contains at least a crosslinkable hydrocarbon monomer, and may further contain a non-crosslinkable hydrocarbon monomer.

[0027] Examples of crosslinkable hydrocarbon monomers include aromatic divinyl monomers such as divinylbenzene, divinylbiphenyl, and divinylnaphthalene; diene monomers such as linear or branched diolefins such as butadiene, isoprene, 2,3-dimethylbutadiene, pentadiene, and hexadiene; and alicyclic diolefins such as dicyclopentadiene, cyclopentadiene, and ethylidenetetracyclododecene. Other examples include crosslinkable macromers such as polybutadiene, polyisoprene, styrene-butadiene block copolymers (SBS), and styrene-isoprene block copolymers (SIS). These crosslinkable hydrocarbon monomers can be used alone or in combination of two or more. Among these, aromatic divinyl monomers are preferred, and divinylbenzene is more preferred, because they facilitate stable polymerization reactions and enable hollow particles to be obtained that are excellent in dielectric properties, solvent resistance, strength, heat resistance, and the like.

[0028] Examples of non-crosslinkable hydrocarbon monomers include aromatic monovinyl monomers such as styrene, vinyltoluene, α-methylstyrene, p-methylstyrene, ethylvinylbenzene, ethylvinylbiphenyl, and ethylvinylnaphthalene; linear or branched monoolefins such as ethylene, propylene, and butylene; and monoolefin monomers such as alicyclic monoolefins such as vinylcyclohexane, norbornene, tricyclododecene, and 1,4-methano-1,4,4a,9a-tetrahydrofluorene. These non-crosslinkable hydrocarbon monomers can be used alone or in combination of two or more. Among these, aromatic monovinyl monomers are preferred, and ethylvinylbenzene is particularly preferred, from the viewpoint of improving the dielectric properties of hollow particles.

[0029] In the production method of the present disclosure, hollow particles with excellent dielectric properties can be obtained by setting the content of the hydrocarbon monomer, which is the sum of the crosslinkable hydrocarbon monomer and the non-crosslinkable hydrocarbon monomer, to 91% by mass or more relative to 100% by mass of the polymerizable monomer contained in the mixed solution. In order to further improve the dielectric properties of the hollow particles, the content of the hydrocarbon monomer is preferably 94% by mass or more, more preferably 96% by mass or more, and even more preferably 100% by mass. When the content of the hydrocarbon monomer is equal to or greater than the lower limit, the effect of lowering the dielectric loss tangent by reducing the residual double bond ratio is easily achieved, and the heat resistance of the hollow particles can be improved. When the polymerizable monomer in the mixed solution contains a polymerizable monomer different from the hydrocarbon monomer, the content of the hydrocarbon monomer may be, for example, 99% by mass or less, or 98% by mass or less.

[0030] The content of the crosslinkable hydrocarbon monomer is not particularly limited, but from the viewpoint of improving the dielectric properties, solvent resistance, strength, pressure resistance, etc. of the hollow particles and forming hollow portions that are clearly distinguishable from the shell, it is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 75% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more, relative to 100% by mass of the polymerizable monomer contained in the mixed liquid. It is presumed that a large amount of the crosslinkable hydrocarbon monomer increases the number of crosslinked portions, making the shell less likely to break and improving pressure resistance. The upper limit of the content of the crosslinkable hydrocarbon monomer is not particularly limited, but may be, for example, 98% by mass or less, or 96% by mass or less. The heat resistance of the hollow particles can be improved by including a combination of a crosslinkable hydrocarbon monomer and a non-crosslinkable monomer.

[0031] The content of the non-crosslinkable hydrocarbon monomer is not particularly limited, but from the viewpoint of forming a hollow portion that is clearly distinguishable from the shell, it is preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less, and even more preferably 20% by mass or less, relative to 100% by mass of the polymerizable monomer contained in the mixed liquid. The lower limit of the content of the non-crosslinkable hydrocarbon monomer is not particularly limited, and may be, for example, 2% by mass or more, or 4% by mass or more.

[0032] [Polymerizable Monomer Other Than Hydrocarbon Monomer] The polymerizable monomer in the mixed solution may further contain a polymerizable monomer other than the hydrocarbon monomer, as long as the effects of the present disclosure are not impaired. The polymerizable monomer other than the hydrocarbon monomer may be a crosslinkable monomer or a non-crosslinkable monomer. Examples of crosslinkable monomers other than hydrocarbon monomers include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tetra(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, 3-(meth)acryloyloxy-2-hydroxypropyl(meth)acrylate, trimethylolpropane tri(meth)acrylate, and ditrimethylolpropane tetra(meth)acrylate. Examples of crosslinkable acrylic monomers include ethoxylated trimethylolpropane tri(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol poly(meth)acrylate, allyl (meth)acrylate, and vinyl (meth)acrylate; crosslinkable allylic monomers such as diallyl phthalate; and the like. In addition, crosslinkable macromers such as polyphenylene ether vinyl-modified at both ends and polyphenylene ether (meth)acrylic-modified at both ends can also be used.Examples of non-crosslinkable monomers other than hydrocarbon monomers include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 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, methoxypolyethylene glycol (meth)acrylate, ethoxypolyethylene glycol (meth)acrylate, propoxypolyethylene glycol (meth)acrylate, butoxypolyethylene glycol (meth)acrylate, hexaoxypolyethylene glycol (meth)acrylate, octoxypolyethylene glycol polypropylene glycol (meth)acrylate, lauroxypolyethylene glycol (meth)acrylate, and stearoxypolyethylene glycol. Examples of suitable crosslinkable acrylic monomers include non-crosslinkable acrylic monomers such as 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; acrylamide monomers and derivatives thereof such as (meth)acrylamide, N-methylol (meth)acrylamide, and N-butoxymethyl (meth)acrylamide; vinyl carboxylic acid ester monomers such as vinyl acetate; halogenated vinyl monomers such as vinyl chloride; halogenated vinylidene monomers such as vinylidene chloride; vinylpyridine monomers; and the like. Other examples of suitable crosslinkable acrylic monomers include (meth)acrylic-terminated polystyrene and (meth)acrylic-terminated polymethyl methacrylate.

[0033] In the production method of the present disclosure, in order to form hollow portions clearly distinguishable from the shell, the content of the crosslinkable monomer, which is the sum of the crosslinkable hydrocarbon monomer and the crosslinkable monomer different from the hydrocarbon monomer, is 50% by mass or more, preferably 70% by mass or more, more preferably 75% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more, relative to 100% by mass of the polymerizable monomer contained in the mixed liquid. When the content of the crosslinkable monomer is 50% by mass or more, phase separation between the components constituting the shell and the hydrophobic solvent is facilitated in the droplets of the monomer composition. Furthermore, the formation of a shell with excellent strength suppresses particle deformation, making it easier to form hollow portions. Furthermore, increasing the content of the crosslinkable monomer increases the crosslink density of the shell, thereby improving the solvent resistance, strength, pressure resistance, and other properties of the resulting hollow particles. It is presumed that the inclusion of a large amount of the crosslinkable monomer increases the number of crosslinked portions, making the shell less susceptible to breakage and improving pressure resistance. When the polymerizable monomer in the mixed solution contains a non-crosslinkable monomer, the content of the crosslinkable monomer may be, for example, 98% by mass or less, or 96% by mass or less. By including a crosslinkable monomer and a non-crosslinkable monomer in combination, the heat resistance of the hollow particles can be improved.

[0034] The content of the polymerizable monomer in the mixed liquid 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, and more preferably 20 to 40% by mass, relative to 100% by mass of the total mass of the components in the mixed liquid excluding the aqueous medium. Furthermore, from the viewpoint of improving the dielectric properties of the hollow particles, the content of the polymerizable monomer in the mixed liquid, relative to 100% by mass of the total mass of the solids, excluding the hydrophobic solvent, of the materials that form the oil phase in the mixed liquid, is preferably 96% by mass or more, and more preferably 97% by mass or more. 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.

[0035] (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.

[0036] As the hydrophobic solvent, it is preferable to select an organic solvent that has a lower solubility in water at 20° C. than the crosslinkable hydrocarbon monomer contained in the mixed solution. Here, when the mixed solution contains a combination of two or more crosslinkable hydrocarbon monomers or hydrophobic solvents, it is preferable to select a hydrophobic solvent according to the type of crosslinkable hydrocarbon monomer so that the hydrophobic solvent with the highest solubility has an even lower solubility than the crosslinkable hydrocarbon monomer with the lowest solubility.

[0037] The organic solvent having a lower solubility in water at 20°C than the crosslinkable hydrocarbon monomer can be appropriately selected from known organic solvents and is not particularly limited. For example, hydrocarbon solvents can be preferably used. Hydrocarbon solvents are also preferred in that they have a lower solubility in water at 20°C than divinylbenzene, which is the crosslinkable hydrocarbon monomer preferably used in the present disclosure. Examples of hydrocarbon solvents include chain hydrocarbon solvents such as pentane, hexane, heptane, octane, 2-methylbutane, and 2-methylpentane; cyclic hydrocarbon solvents such as cyclohexane, methylcyclohexane, and cycloheptane; and aromatic hydrocarbon solvents such as benzene, toluene, and xylene. Among these, chain hydrocarbon solvents are preferred because they facilitate the formation of hollow spaces, facilitate the production of hollow particles with excellent dielectric properties, and are easily removed, thereby reducing the amount of hydrophobic solvent remaining in the hollow particles. Chain hydrocarbon solvents having 5 to 8 carbon atoms are more preferred, and at least one selected from the group consisting of pentane, hexane, heptane, and octane is even more preferred. The hydrophobic solvents may be used alone or in combination of two or more.

[0038] 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.

[0039] Furthermore, the hydrophobic solvent used in the production method of the present disclosure preferably has a dielectric constant of 2.0 or less at 20°C. 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, such as 2.0 or less, it is believed that phase separation proceeds rapidly in the droplets of the monomer composition, making it easy to form hollow spaces. Examples of hydrophobic solvents having 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), and octane (1.9). Regarding the dielectric constant at 20°C, reference can be made to values ​​described in known literature (e.g., "Chemical Handbook: Basics," edited by the Chemical Society of Japan, Revised 4th Edition, Maruzen Co., Ltd., published September 30, 1993, pages II-498 to II-503) and other technical information. 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.

[0040] 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 60 to 400 parts by mass, and even more preferably 70 to 300 parts by mass per 100 parts by mass of the polymerizable monomer.

[0041] (C) Polymerization Initiator In the manufacturing method of the present disclosure, hollow particles with a low dielectric loss tangent can be obtained by using an organic peroxide as a polymerization initiator. Because the organic peroxide is lipophilic, it is present in the droplets of the monomer composition in the suspension step described below. In the polymerization step described below, it generates polymerization initiation radicals inside the droplets of the monomer composition, thereby preventing the droplets from growing excessively and allowing precursor particles of the desired particle size to be produced. The polymerization initiator used in the present disclosure preferably has a solubility in water of 0.2% by mass or less, since it easily penetrates into the droplets of the monomer composition. Examples of organic peroxides preferably used in the present disclosure include benzoyl peroxide (benzoyl peroxide), lauroyl peroxide, t-butyl peroxide-2-ethylhexanoate, t-butyl peroxydiethyl acetate, and t-butyl peroxypivalate. Among these, at least one selected from t-butyl peroxydiethyl acetate and t-butyl peroxypivalate is preferred, and t-butyl peroxydiethyl acetate is more preferred, from the viewpoint of facilitating the production of hollow particles having excellent dielectric properties.

[0042] 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 oil-soluble polymerization initiator is equal to or greater than the above lower limit, the polymerization reaction can proceed sufficiently, while when it is equal to or less than the above upper limit, there is little risk of the polymerization initiator remaining after completion of the polymerization reaction, and there is also little risk of an unexpected side reaction proceeding.

[0043] (D) Dispersion Stabilizer The dispersion stabilizer is an agent that disperses droplets of the monomer composition in an aqueous medium during the suspension process. In the present disclosure, an inorganic dispersion stabilizer is preferably used as the dispersion stabilizer because it facilitates control of the particle size of the droplets in the suspension, narrows the particle size distribution of the resulting hollow particles, and prevents the shell from becoming too thin, thereby preventing 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 of two or more. Among the inorganic dispersion stabilizers, poorly water-soluble inorganic dispersion stabilizers are preferred, with poorly water-soluble metal salts such as the sulfates, carbonates, phosphates, and metal hydroxides mentioned above being more preferred, metal hydroxides being even more preferred, and magnesium hydroxide being particularly preferred. In the present disclosure, the poorly water-soluble inorganic dispersion stabilizer is preferably an inorganic compound having a solubility of 0.5 g or less in 100 g of water, and the poorly water-soluble metal salt is preferably an inorganic metal salt having a solubility of 0.5 g or less in 100 g of water.

[0044] 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 not only narrows the particle size distribution of the droplets of the monomer composition, but also makes it easy to reduce the amount of inorganic dispersion stabilizer remaining in the resulting hollow particles by washing. 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 water-soluble polyvalent metal salts can be used alone or in combination of two or more. 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, and examples include a method of mixing an aqueous solution of at least one selected from the alkali metal hydroxides and alkaline earth metal hydroxides with an aqueous solution of the water-soluble polyvalent metal salt. Furthermore, colloidal silica can also be used as the colloidal dispersion liquid containing poorly water-soluble inorganic dispersion stabilizer colloidal particles.

[0045] In addition, in the manufacturing method of the present disclosure, it is preferable not to use a surfactant as a dispersion stabilizer. This is because if a surfactant used as a dispersion stabilizer remains on the surface of hollow particles, it tends to increase the dielectric tangent of the hollow particles. In this disclosure, a surfactant refers to a compound having both hydrophilic and hydrophobic groups in one molecule, including compounds commonly used as surfactants. Surfactants typically have a solubility of 1 g / L or more in water at 25°C. Examples of surfactants include anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants, and may be any known surfactant. 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 nonionic surfactants include polyethylene glycol-type nonionic surfactants such as higher alcohol ethylene oxide adducts, fatty acid ethylene oxide adducts, higher alkylamine ethylene oxide adducts, and polypropylene glycol ethylene oxide adducts; and polyhydric alcohol-type nonionic surfactants such as polyethylene oxide, glycerin fatty acid esters, pentaerythritol fatty acid esters, sorbitol or sorbitan fatty acid esters, polyhydric alcohol alkyl ethers, and alkanolamine fatty amides. 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 alkyldimethylbetaines and higher alkyldihydroxyethylbetaines.In the present disclosure, surfactants also include polymeric compounds having both hydrophilic and hydrophobic groups, such as polyvinyl alcohol, 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 usually less than 3,000.

[0046] The content of the dispersion stabilizer is not particularly limited, but is preferably 0.5 to 15 parts by mass, and more preferably 1 to 10 parts by mass, per 100 parts by mass of the total mass of the polymerizable monomer and the hydrophobic solvent. By having the content of the dispersion stabilizer equal to or greater than 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 having the content of the dispersion stabilizer equal to or less than the upper limit, an increase in the viscosity of the suspension during granulation can be prevented, and the problem of the suspension clogging in the granulator can be avoided. Furthermore, the content of the dispersion stabilizer is typically 2 to 15 parts by mass, and preferably 3 to 8 parts by mass, per 100 parts by mass of the aqueous medium.

[0047] (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.

[0048] 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.

[0049] 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.

[0050] (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)); and emulsifying dispersers such as the Homomixer MARK II series manufactured by Primix Corporation.

[0051] 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.

[0052] 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.

[0053] (3) Polymerization Step This step involves subjecting the suspension obtained in the suspension step described above 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. 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. There are no particular limitations on the polymerization method, and for example, a batch method, a semi-continuous method, or a continuous method can be used.

[0054] In the production method of the present disclosure, the polymerization temperature in the polymerization step is set to a temperature higher than the 10-hour half-life temperature of the polymerization initiator. This allows the polymerization reaction to proceed sufficiently and reduces the residual double bond ratio. From the same perspective, the polymerization temperature is preferably higher than the 10-hour half-life temperature of the polymerization initiator, and the difference between the polymerization temperature and the 10-hour half-life temperature of the polymerization initiator is preferably 3°C or more, more preferably 5°C or more. When multiple polymerization initiators are used in combination, it is preferable to set the polymerization temperature as described above based on the polymerization initiator with the highest 10-hour half-life temperature. Furthermore, in order to allow the polymerization reaction to proceed sufficiently, the lower limit of the polymerization temperature is preferably 20°C or more, more preferably 65°C or more, and even more preferably 80°C or more. On the other hand, the upper limit of the polymerization temperature is appropriately adjusted so as to be a temperature at which the aqueous medium does not evaporate, and is not particularly limited. For example, when water is used as the aqueous medium, it is preferably set to be less than 100°C so as to prevent water from evaporating. The rate of temperature increase when raising the temperature to the polymerization temperature is not particularly limited, but is preferably 10°C / h to 60°C / h, more preferably 15°C / h to 55°C / h. The polymerization reaction time is preferably 7 hours or more, more preferably 15 hours or more, and even more preferably 24 hours or more, from the viewpoint of sufficiently progressing the polymerization reaction and reducing the residual double bond ratio, while it is preferably 48 hours or less, from the viewpoint of suppressing a decrease in production efficiency. In the polymerization step, the shell portion of the droplets of the monomer composition containing the hydrophobic solvent therein is polymerized, and thus, as described above, hollow portions filled with the hydrophobic solvent are formed inside the obtained precursor particles.

[0055] (4) Solid-Liquid Separation Step This step is a step of obtaining a solid content containing precursor particles by solid-liquid separation of the precursor composition containing precursor particles obtained by the above-mentioned polymerization step.

[0056] The method for solid-liquid separation of the precursor composition is not particularly limited, and known methods can be used. Examples of solid-liquid separation methods include centrifugation, filtration, and static separation. Among these, centrifugation or filtration can be used, and centrifugation may be used from the viewpoint of ease of operation. After the solid-liquid separation step, an optional step such as a pre-drying step may be performed before performing the solvent removal step described below. Examples of the pre-drying step include a step of pre-drying the solid content obtained after the solid-liquid separation step using a drying device such as a dryer or a drying appliance such as a hand dryer.

[0057] (5) Solvent Removal Step This step is a step of removing the hydrophobic solvent contained in the precursor particles obtained by the solid-liquid separation step. For example, by removing the hydrophobic solvent contained in the precursor particles in air, the hydrophobic solvent inside the precursor particles is replaced with air, and hollow particles filled with gas are obtained.

[0058] 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, in this process, it is important to remove the hydrophobic solvent in an environment in which the precursor particles are in direct contact with the external gas.

[0059] 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 equal to or higher than the boiling point of the hydrophobic solvent and equal to or lower than the maximum temperature at which the shell structure of the precursor particles does not collapse. Therefore, depending on the shell composition and the type of hydrophobic solvent in the precursor particles, the heating temperature may be, for example, 50 to 200°C, 70 to 200°C, or 100 to 200°C. The drying operation in air replaces the hydrophobic solvent inside the precursor particles with the external gas, resulting in hollow particles whose hollow portions are filled with gas.

[0060] The drying atmosphere is not particularly limited and can be appropriately selected depending on the application of the hollow particles. Examples of the drying atmosphere include air, oxygen, nitrogen, argon, etc. Hollow particles with a temporary vacuum inside can also be obtained by filling the inside of the hollow particles with a gas and then drying under reduced pressure.

[0061] Alternatively, the hydrophobic solvent may be removed from the slurry containing precursor particles and an aqueous medium without solid-liquid separation of the slurry-like precursor composition obtained in the polymerization step. In this method, for example, the hydrophobic solvent encapsulated in the precursor particles can be removed by bubbling an inert gas through the precursor composition at a temperature equal to or higher than the boiling point of the hydrophobic solvent minus 35°C. Here, when the hydrophobic solvent is a mixed solvent containing multiple hydrophobic solvents and has multiple boiling points, the boiling point of the hydrophobic solvent in the solvent removal step is the boiling point of the solvent with the highest boiling point among the solvents contained in the mixed solvent, i.e., the highest boiling point among the multiple boiling points. The temperature at which the inert gas is bubbled through the precursor composition is preferably equal to or higher than the boiling point of the hydrophobic solvent minus 30°C, more preferably equal to or higher than the boiling point of the hydrophobic solvent, in order to reduce the amount of hydrophobic solvent remaining in the hollow particles. The bubbling temperature is typically equal to or higher than the polymerization temperature in the polymerization step. Although not particularly limited, the temperature during bubbling may be 50°C or higher and 100°C or lower. The inert gas to be bubbling is not particularly limited, but examples thereof include nitrogen, argon, etc. The bubbling conditions are appropriately adjusted depending on the type and amount of hydrophobic solvent so as to remove the hydrophobic solvent encapsulated in the precursor particles. Although not particularly limited, for example, the inert gas may be bubbled at a rate of 1 to 3 L / min for 1 to 10 hours. This method produces an aqueous slurry of hollow particles encapsulating an inert gas. The hollow particles obtained by solid-liquid separation of this slurry are dried, and the aqueous medium remaining in the hollow particles is removed, thereby producing hollow particles whose hollow portions are filled with gas.

[0062] Comparing a method of obtaining hollow particles having hollow spaces filled with gas by performing solid-liquid separation on a slurry-like precursor composition and then removing the hydrophobic solvent in the precursor particles in air, with a method of obtaining hollow particles having hollow spaces filled with gas by removing the hydrophobic solvent encapsulated in precursor particles in a slurry containing the precursor particles and an aqueous medium, performing solid-liquid separation, and removing the aqueous medium remaining in the particles in air, the former method has the advantage that the hollow particles are less likely to be crushed in the step of removing the hydrophobic solvent, while the latter method has the advantage that the amount of remaining hydrophobic solvent is reduced by performing bubbling with an inert gas. Alternatively, as a method for removing the hydrophobic solvent encapsulated in the precursor particles after the polymerization step and before the solid-liquid separation step without subjecting the slurry precursor composition obtained in the polymerization step to solid-liquid separation, for example, a method for evaporating and distilling off the hydrophobic solvent encapsulated in the precursor particles from the precursor composition under a predetermined pressure (high pressure, normal pressure, or reduced pressure); or a method for introducing an inert gas such as nitrogen, argon, or helium, or water vapor, into the precursor composition under a predetermined pressure (high pressure, normal pressure, or reduced pressure) and evaporating and distilling off the hydrophobic solvent may be used.

[0063] (6) Others Steps other than the above steps (1) to (5) may include, for example, the following (6-a) washing step and the following (6-b) particle internal substitution step. (6-a) Washing Step The washing step is a step of adding an acid or alkali to wash the precursor composition containing precursor particles before the solvent removal step in order to remove any dispersion stabilizer remaining in the precursor composition. When the dispersion stabilizer used is an acid-soluble inorganic dispersion stabilizer, it is preferable to add an acid to the precursor composition containing precursor particles to perform washing. On the other hand, when the dispersion stabilizer used is an alkali-soluble inorganic compound, it is preferable to add an alkali to the precursor composition containing precursor particles to perform washing. Furthermore, when an acid-soluble inorganic dispersion stabilizer is used as the dispersion stabilizer, it is preferable to add an acid to the precursor composition containing precursor particles to adjust the pH to preferably 6.5 or less, more preferably 6 or less. Examples of the acid to be added include inorganic acids such as sulfuric acid, hydrochloric acid, and nitric acid, and organic acids such as formic acid and acetic acid. However, sulfuric acid is particularly preferred due to its high dispersion stabilizer removal efficiency and its small burden on production equipment.

[0064] (6-b) Particle Interior Substitution Process The particle interior substitution process is a process in which the gas or liquid inside the hollow particles is replaced with another gas or liquid. This substitution can change the environment inside the hollow particles, selectively confine molecules inside the hollow particles, or modify the chemical structure inside the hollow particles to suit the application.

[0065] 2. Hollow Particles 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, as the resin, a polymer containing 91% by mass or more of hydrocarbon monomer units and 50% by mass or more of crosslinkable monomer units, at least a portion of the hydrocarbon monomer units being crosslinkable hydrocarbon monomer units, the polymer having a residual double bond ratio of 30.0% or less, and a dielectric loss tangent at a frequency of 10 GHz of 3.00 × 10 －３ The present invention is characterized by the following:

[0066] The hollow particles of the present disclosure contain a polymer of the above-described polymerizable monomer as the main component of the shell, and the polymer forms the skeleton of the shell of the hollow particle. In the hollow particles of the present disclosure, the content of hydrocarbon monomer units is 91% by mass or more relative to 100 parts by mass of all structural units in the polymer contained in the shell, thereby improving dielectric properties. To further improve the dielectric properties of the hollow particles, the content of hydrocarbon monomer units is preferably 94% by mass or more, more preferably 96% by mass or more, and even more preferably 100% by mass. When the content of hydrocarbon monomer units is equal to or greater than the above lower limit, the effect of reducing the residual double bond ratio and thereby lowering the dielectric loss tangent is easily achieved, and the heat resistance of the hollow particles can be improved. When the polymer contains a monomer unit other than the hydrocarbon monomer unit, the content of the hydrocarbon monomer unit may be, for example, 99% by mass or less, or 98% by mass or less.

[0067] In the hollow particles of the present disclosure, the content of crosslinkable monomer units is 50% by mass or more relative to 100 parts by mass of all structural units in the polymer contained in the shell, thereby enabling the hollow particles to be clearly distinguished from the shell and providing excellent solvent resistance, strength, pressure resistance, etc. The content of crosslinkable monomer units is preferably 70% by mass or more, more preferably 75% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more. The upper limit of the content of the crosslinkable monomer units is not particularly limited, but may be, for example, 98% by mass or less, or 96% by mass or less. The heat resistance of the hollow particles can be improved by including a combination of crosslinkable monomer units and non-crosslinkable monomer units.

[0068] Furthermore, in the hollow particles of the present disclosure, in order to improve dielectric properties, solvent resistance, strength, pressure resistance, etc., and to have a hollow portion that is clearly distinguishable from the shell, the content of crosslinkable hydrocarbon monomer units relative to 100 parts by mass of all structural units in the polymer contained in the shell is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 75% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more. The upper limit of the content of the crosslinkable hydrocarbon monomer units is not particularly limited, but may be, for example, 98% by mass or less or 96% by mass or less. The heat resistance of the hollow particles can be improved by including a combination of crosslinkable hydrocarbon monomer units and non-crosslinkable monomer units.

[0069] In the hollow particles of the present disclosure, when the polymer contained in the shell contains a non-crosslinkable hydrocarbon monomer unit, the content of the non-crosslinkable hydrocarbon monomer unit is not particularly limited, but in order to have a hollow portion that is clearly distinguishable from the shell, it is preferably 50 mass% or less, more preferably 40 mass% or less, even more preferably 30 mass% or less, and even more preferably 20 mass% or less, relative to 100 mass parts of all structural units in the polymer contained in the shell. The lower limit of the content of the non-crosslinkable hydrocarbon monomer unit is not particularly limited, and may, for example, be 2 mass% or more, or 4 mass% or more.

[0070] In the hollow particles according to the present disclosure, the content of the polymer of the polymerizable monomer is preferably 96% by mass or more, more preferably 97% by mass or more, even more preferably 98% by mass or more, and still more preferably 99% by mass or more, based on 100% by mass of the total solid content of the shell. By ensuring that the content of the polymer is equal to or greater than the lower limit, the dielectric properties and strength of the hollow particles can be improved.

[0071] In the hollow particles of the present disclosure, the polymer contained in the shell has a residual double bond ratio of 30.0% or less, preferably 20.0% or less, and more preferably 15.0% or less. It is believed that the residual double bond ratio of the hollow particles of the present disclosure, being equal to or less than the upper limit, contributes to improved dielectric properties. Furthermore, a residual double bond ratio of equal to or less than the upper limit results in hollow particles with excellent heat resistance. The lower limit of the residual double bond ratio is not particularly limited, and a lower residual double bond ratio is preferable in terms of improving the dielectric properties of the hollow particles. From the viewpoint of ease of production, the lower limit of the residual double bond ratio may be, for example, 1% or more, 3% or more, or 5% or more. The residual double bond ratio can be determined as follows. First, infrared absorption spectra, expressed as absorbance, are measured for the polymer contained in the hollow particles and the polymerizable monomer used to produce the hollow particles before the polymerization reaction. Meanwhile, the polymerizable monomer with the highest content among the polymerizable monomers used to produce the hollow particles is identified as the reference monomer. When there are multiple monomers with the highest content, one of them is identified as the reference monomer. From the structures of the reference monomer, one structure that does not increase or decrease before or after the polymerization reaction is selected. As the structure that does not increase or decrease before or after the polymerization reaction, it is preferable to select a structure that does not contribute to the polymerization reaction among the structures of the reference monomer, such that the peak that appears in the infrared absorption spectrum can be clearly distinguished from the peak of the polymerizable unsaturated double bond (C=C) and is a peak with high intensity. The peak derived from the selected structure is used as the reference peak. Then, in each of the infrared absorption spectrum of the polymer and the infrared absorption spectrum of the polymerizable monomer, the peak intensity of the reference peak is divided by the content ratio of the monomer containing the structure that appears the reference peak, and the calculated value is used as the reference peak intensity. Furthermore, in each of the infrared absorption spectrum of the polymer and the infrared absorption spectrum of the polymerizable monomer, the peak intensity of the peak derived from the polymerizable unsaturated double bond (C=C) is measured. The reference peak intensity (M ０ ) relative to the peak intensity (M １ ) ratio (M １ / M ０) is the peak intensity ratio when the residual double bond ratio is 100%. ０ ) relative to the peak intensity (P １ ) ratio (P １ / P ０ ) is determined in the same manner. Then, the peak intensity ratio (M １ / M ０ ) and the peak intensity ratio (P １ / P ０ ) can be calculated by the following formula (A): Residual double bond ratio (%) = {(P １ / P ０ ) / (M １ / M ０)} × 100. The peak intensity can be quantified as the height from the baseline, which is formed by connecting the base points outside both ends of the peak with a straight line, to the peak top. The peak intensity and peak intensity ratio values ​​used to calculate the residual double bond ratio are rounded to three significant figures in accordance with Rule B of JIS Z8401:1999, and the residual double bond ratio is rounded to one decimal place. For example, if the polymerizable monomers used to prepare hollow particles are 95% by mass of divinylbenzene and 5% by mass of ethylvinylbenzene, the reference monomer is divinylbenzene, which has the highest content. From the structure of divinylbenzene, for example, the C-H bond of the benzene ring contained in divinylbenzene is selected as a structure that does not increase or decrease before or after the polymerization reaction. The infrared absorption spectrum of the polymerizable monomer consisting of 95% by mass of divinylbenzene and 5% by mass of ethylvinylbenzene and the infrared absorption spectrum of the polymer contained in the hollow particles are then measured. In each spectrum, the peak derived from the C-H bond of the benzene ring contained in divinylbenzene is specified as the reference peak. Since the peak derived from the C-H bond of the benzene ring contained in divinylbenzene and the peak derived from the C-H bond of the benzene ring contained in ethylvinylbenzene appear at the same position, divinylbenzene and ethylvinylbenzene are monomers containing a structure that exhibits the above-mentioned reference peak. Therefore, the reference peak intensity is determined by dividing the peak intensity of the reference peak by 1.00, which is the sum of the content ratio of divinylbenzene and the content ratio of ethylvinylbenzene. Furthermore, in each spectrum, the peak intensities of the peaks derived from the polymerizable unsaturated double bond (C=C) contained in divinylbenzene and the polymerizable unsaturated double bond (C=C) contained in ethylvinylbenzene are measured. Then, the reference peak intensity (M ０ ) relative to the peak intensity (M １ ) ratio (M １ / M ０ ) and the reference peak intensity (P ０ ) relative to the peak intensity (P １ ) ratio (P１ / P ０ ) and calculate the residual double bond ratio using the above formula (A). The infrared absorption spectrum can be measured, for example, by attenuated total reflection (ATR) method. An example of an infrared absorption spectrum measuring device is Spectrum One, manufactured by Perkin Elmer.

[0072] Furthermore, in the hollow particles of the present disclosure, in order to prevent deterioration of dielectric properties, the content of components other than the polymer is preferably 4% by mass or less, more preferably 3% by mass or less, even more preferably 2% by mass or less, and even more preferably 1% by mass or less, based on 100% by mass of the total solids content of the shell. Examples of components other than the polymer contained in the hollow particles of the present disclosure include unreacted residual polymerizable monomers, polymers other than the polymers of the polymerizable monomers, decomposition products of polymerization initiators, and low-molecular-weight compounds contained as impurities in the raw materials for the polymerizable monomers. Low-boiling components (e.g., boiling points of 200°C or less) are usually removed during the production process of hollow particles, but high-boiling components (e.g., boiling points of 250°C or more) may remain unremoved.

[0073] From the viewpoint of improving dielectric properties, the hollow particles of the present disclosure preferably have a surfactant content present on the hollow particle surface of 500 ppm or less, more preferably 200 ppm or less, even more preferably 100 ppm or less, and even more preferably 50 ppm or less. When a surfactant is used in the hollow particle production process, for example, when a surfactant is added to a mixed liquid, the surfactant may remain on the surface of the resulting hollow particles. However, by not using a surfactant as a dispersion stabilizer in the hollow particle production process, the surfactant content present on the hollow particle surface can be reduced to 10 ppm or less, more preferably 1 ppm or less. In the present disclosure, the surfactant content present on the hollow particle surface refers to the ratio of the mass of the 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 the surfactant extracted into water can be determined as follows: １It can be identified from the peak position and peak intensity in the H-NMR spectrum.

[0074] From the viewpoint of improving dielectric properties, the hollow particles of the present disclosure preferably have a metal content of 100 ppm or less, more preferably 80 ppm or less, and even more preferably 70 ppm or less. Here, metal includes metal ions. Furthermore, when the hollow particles of the present disclosure have both the surfactant content and the metal content reduced to the above-mentioned upper limit or less, the dielectric properties can be improved beyond the sum of the effects of reducing the surfactant amount and the metal content. In this disclosure, the metal content in 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 above upper limit or less, it is preferable to use, for example, a metal-free polymerization initiator, use ion-exchanged water as the aqueous medium, perform the above-mentioned washing step in the production of hollow particles, or employ a method of removing the hydrophobic solvent contained in the precursor particles in air in the above-mentioned solvent removal step in the production of hollow particles. The metal content in the hollow particles can be measured by ICP atomic emission spectrometry. The metal species can be identified by X-ray fluorescence analysis (XRF).

[0075] The hollow particles of the present disclosure have a dielectric loss tangent of 3.00×10 at a frequency of 10 GHz. －３ or less, preferably 2.60 × 10 －３ or less, more preferably 2.50 × 10 －３ More preferably, 1.00 x 10 －３ More preferably, 8.00 x 10 －４ Particularly preferably, 7.50 x 10 －４ The lower limit is not particularly limited, and is, for example, 1.00 × 10 －４The hollow particles according to the present disclosure may have a relative dielectric constant at a frequency of 10 GHz of preferably 1.50 or less, more preferably 1.45 or less, and even more preferably 1.40 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 measurement device at a measurement frequency of 10 GHz.

[0076] 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 furthermore, are excellent in terms of lightweightness and heat insulation properties. 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.

[0077] 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.

[0078] 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.

[0079] 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

[0080] 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, and even more preferably 6.0 μm or less. When the volume average particle diameter of the hollow particles is equal to or greater than the above lower limit, the tendency for the hollow particles to aggregate with each other is reduced, thereby enabling excellent dispersibility to be exhibited. When the volume average particle diameter of the hollow particles is equal to or less than the above upper limit, variation in shell thickness is suppressed, making it easier to form a uniform shell. Furthermore, the hollow particles are less likely to be crushed, resulting in high mechanical strength. Furthermore, hollow particles having a volume average particle diameter within the above range are sufficiently small in particle diameter that they are suitable for use as substrate materials for electronic circuit boards and the like, and can be added to thin, small substrates.

[0081] 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 thereof 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. The proportion of hollow particles of the present disclosure having only one or two hollow portions is preferably 90% by mass or more, more preferably 95% by mass or more. Furthermore, the proportion of particles having only one hollow portion is preferably 90% by mass or more, more preferably 95% by mass or more. Furthermore, the shell of the hollow particles of the present disclosure, and the partition walls separating adjacent hollow portions when the hollow particles have two or more hollow portions, may be porous, but are preferably solid from the viewpoint of improving 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, the cross-sectional view of which is shown as hollow particle 10 in (5) of Figure 1. 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.

[0082] 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 molded product 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.

[0083] Furthermore, the hollow particles of the present disclosure have excellent dielectric properties due to the low proportion of particles with a circularity of 0.85 or less. Particles with a circularity of 0.85 or less typically have 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 have a lower proportion of hollow portions and a higher proportion of resin than spherical hollow particles, resulting in faster weight loss due to thermal decomposition and a lower thermal decomposition onset temperature. Therefore, reducing the proportion of irregularly shaped particles contained in the hollow particles can improve the heat resistance of the hollow particles. Furthermore, irregularly shaped particles have a tendency to aggregate more easily when dispersed in a matrix resin than spherical particles, resulting in poor dispersibility. Furthermore, irregularly shaped particles are more susceptible to localized external pressure, resulting in poorer pressure resistance compared to spherical particles. When irregularly shaped particles are dispersed in a matrix resin, agglomerates are likely to form, and the agglomerates are more susceptible to external pressure, further reducing pressure resistance. Therefore, reducing the proportion of irregularly shaped particles contained in 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 particles with low circularity due to cracking, deformation, etc. as impurities. However, the proportion of particles with a circularity of 0.85 or less per 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 diameter of a circle having the same area as the projected image of the particle (equivalent circle area diameter) divided 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, the circularity is measured using a flow-type particle image analyzer with an image resolution of 0.185 μm / pixel. As the flow-type particle image analyzer, for example, the product name "IF-3200" manufactured by Jasco International Co., Ltd. can be preferably used.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.

[0084] In the present disclosure, the thermal decomposition onset temperature of the hollow particles is preferably 150 to 400°C, and is preferably 335°C or higher, more preferably 340°C or higher, and even more preferably 345°C or higher. The thermal decomposition onset temperature of the hollow particles may be 370°C or lower, or may be 350°C or lower. The higher the thermal decomposition onset temperature, the more excellent the heat resistance of the hollow particles. 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 heating rate of 10°C / min.

[0085] Examples of uses of the hollow particles of the present disclosure include additives for low-dielectric, heat-insulating, sound-insulating, 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; and 3D printer filaments. In particular, the hollow particles of the present disclosure have excellent dielectric properties and are therefore suitable for use as additives for achieving low transmission loss in the electrical or electronic fields. For example, the hollow particles of the present disclosure are suitable for use as electronic circuit board materials. Specifically, the hollow particles of the present disclosure can be incorporated into the insulating resin layer of an electronic circuit board to reduce transmission loss. 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, flexible circuit boards, high-frequency device modules, antenna modules, and automotive radar. Among these, the hollow particles of the present disclosure are particularly suitable as additives for semiconductor materials such as interlayer insulating materials, solder resists, magnet wires, epoxy encapsulants, underfills, buffer coating materials, copper-clad laminates, flexible substrates, high-frequency device modules, antenna modules, and automotive radar. Furthermore, the hollow particles of the present disclosure are suitable as additives for molded bodies because, when added to molded bodies, they exhibit excellent effects as lightweight materials, heat insulating materials, soundproofing materials, and vibration damping materials. For example, they can be used as additives for resin molded bodies, and can also be incorporated as fillers in fiber-reinforced molded bodies formed using resin and reinforcing fibers. Furthermore, the hollow particles of the present disclosure have high porosity, are difficult to crush, and have excellent heat resistance, thereby satisfying the heat insulating and shock-absorbing properties (cushioning properties) required for undercoat 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, hiding power, etc.Furthermore, the hollow particles of the present disclosure can be encapsulated with useful ingredients such as fragrances, pharmaceuticals, pesticides, and ink components by immersion, vacuum immersion, or pressure immersion, and can be used for a variety of purposes 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 additives that reduce electrical conductivity, and therefore, for example, paints containing the hollow particles of the present disclosure can be used as rust-preventive paints (paint primers, lubricating paints, etc.) to improve the corrosion and rust resistance of steel materials and the like. Furthermore, rust-preventive additives can also be encapsulated in the hollow particles added to rust-preventive paints.

[0086] 3. Resin Composition The resin composition of the present disclosure contains the hollow particles of the present disclosure and a matrix resin. The resin composition of the present disclosure may be a liquid resin composition or a resin molded product. Examples of liquid resin compositions include those containing a liquid matrix resin before a curing reaction, those obtained by dissolving or dispersing each component in a solvent, and those in which the matrix resin is a thermoplastic resin and the resin is melted, thereby making the resin composition liquid. Examples of resin molded products include those obtained by molding the liquid resin composition described above using a known method.

[0087] The matrix resin contained in the liquid resin composition of the present disclosure is not particularly limited and 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. The matrix resin contained in the resin composition of the present disclosure may function as a binder (binding agent) by, for example, curing by heating, light irradiation, or using a curing agent, polymerization initiator, catalyst, or the like.

[0088] 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, 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, liquid crystal polymers (LCPs), etc. These matrix resins can be used either alone or in combination of two or more.

[0089] The thermoplastic resin used when melt-kneading and molding a resin composition containing the hollow particles of the present disclosure and a thermoplastic resin can be any known thermoplastic resin, and is not particularly limited, but examples include polyolefins such as polypropylene and polyethylene; polyamides such as PA6, PA66, and PA12; polyimide, polyamideimide, polyetherimide, polyetherketoneketone, polyvinyl chloride, polystyrene, poly(meth)acrylate, polycarbonate, polyvinylidene fluoride, acrylonitrile-butadiene-styrene copolymer (ABS), acrylonitrile-styrene copolymer (AS), polyphenylene ether, polyphenylene sulfide, polyester, polytetrafluoroethylene, thermoplastic elastomers, etc. These thermoplastic resins can be used alone or in combination of two or more.

[0090] In applications requiring a low dielectric constant or a low dielectric loss tangent, insulating resins such as epoxy resins, thermosetting modified polyphenylene ether resins, thermosetting polyimide resins, silicon resins, benzoxazine resins, melamine resins, urea resins, allyl resins, phenol resins, unsaturated polyester resins, polyurethane resins, and aniline resins are preferably used as the matrix resin, and among these, epoxy resins, thermosetting polyimide resins, modified polyphenylene ether resins, silicon resins, benzoxazine resins, and melamine resins are preferably used. These insulating resins can be used alone or in combination of two or more.

[0091] The content of the matrix resin in the resin composition of the present disclosure, based on 100% by mass of the total solids, is not particularly limited, but is preferably 50 to 95% by mass. Having a matrix resin content equal to or greater than the lower limit provides excellent moldability when formed into a resin molded article, and the resulting resin molded article has excellent mechanical strength. On the other hand, having a matrix resin content equal to or less than the upper limit allows the hollow particles of the present disclosure to be sufficiently incorporated, thereby allowing the hollow particles of the present disclosure to fully exhibit their effects, such as a low dielectric tangent.

[0092] The resin composition of the present disclosure may further contain additives such as a curing agent, a curing catalyst, or an initiator for promoting a curing reaction, depending on the type of resin. Examples of curing agents include amines, acid anhydrides, imidazoles, thiols, phenols, naphthols, benzoxazines, cyanate esters, and carbodiimides. The content of the curing agent is not particularly limited and may be, for example, 5 to 120 parts by mass per 100 parts by mass of the matrix resin.

[0093] The content of the hollow particles of the present disclosure is not particularly limited, but is preferably 5 to 50 mass% relative to 100 mass% of the total solid content of the resin composition of the present disclosure. When the content of the hollow particles is equal to or greater than the lower limit, the hollow particles of the present disclosure can fully exhibit their effects, such as lowering the dielectric tangent. On the other hand, when the content of the hollow particles is equal to or less than the upper limit, the matrix resin can be sufficiently contained, thereby improving moldability and mechanical strength.

[0094] The resin composition of the present disclosure may further contain additives such as a compatibilizer, an ultraviolet absorber, a colorant, a heat stabilizer, a filler, a flame retardant, a solvent, etc., as needed, within a range that does not impair the effects of the present disclosure. Furthermore, when the resin composition of the present disclosure is formed into a resin molded product, it may further contain organic or inorganic fibers such as carbon fibers, glass fibers, aramid fibers, and polyethylene fibers.

[0095] The resin composition of the present disclosure can be obtained, for example, by mixing the hollow particles of the present disclosure, a matrix resin, and optionally further additives, solvents, etc. When the matrix resin in the resin composition of the present disclosure is a thermoplastic resin, the hollow particles of the present disclosure and optionally further additives may be added to a molten thermoplastic resin, and the mixture may be melt-kneaded.

[0096] The method for producing a resin molded article of the present disclosure is not particularly limited. For example, a liquid resin composition containing hollow particles or the like in a liquid matrix resin before a curing reaction, or a liquid resin composition obtained by dissolving or dispersing each component in a solvent, can be applied to a support, followed by drying and curing as necessary to obtain a resin molded article. Examples of materials for the support include resins such as polyethylene terephthalate and polyethylene naphthalate; and metals such as copper, aluminum, nickel, chromium, gold, and silver. These supports may have a release agent applied to their surfaces. Known methods for applying the liquid resin composition can be used, including dip coating, roll coating, curtain coating, die coating, slit coating, and gravure coating. Alternatively, a resin molded article can be obtained by impregnating a substrate with the liquid resin composition, followed by drying and curing as necessary. Examples of the substrate include inorganic fibers such as carbon fibers, glass fibers, metal fibers, and ceramic fibers, and organic synthetic fibers such as polyamide fibers, polyester fibers, polyolefin fibers, and novoloid fibers, with glass fibers (glass cloth) being preferred. The form of the substrate is not limited, and woven fabrics and nonwoven fabrics can be used. When the liquid resin composition contains a solvent, it is preferable to dry the resin composition after the application or impregnation. The drying temperature is preferably a temperature at which the matrix resin does not harden, typically 20°C to 200°C, preferably 30°C to 150°C. 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.The liquid matrix resin before the curing reaction and the matrix resin dissolved or dispersed in a solvent may be a thermosetting resin or a thermoplastic resin. Alternatively, the resin molded article of the present disclosure may be obtained by molding a liquid resin composition containing a thermoplastic resin as the matrix resin into a desired shape using a known molding method such as extrusion molding, injection molding, press molding, or compression molding. The temperature during melt-kneading is not particularly limited as long as it can melt the thermoplastic resin used. Kneading can be performed using 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.

[0097] The resin molded product of the present disclosure includes hollow particles of the present disclosure and a matrix resin. The matrix resin included in the resin molded product is a solidified product. The solidified matrix resin is a resin that has solidified with or without undergoing a chemical reaction, such as a resin cured by a curing reaction, a resin solidified by drying, or a thermoplastic resin solidified by cooling. The molded product obtained using the resin composition described above contains, as the matrix resin, a cured product of a resin cured using a curing agent, a polymerization initiator, a catalyst, or the like, as needed. In this case, the matrix resin may contain a curing agent or the like. The molded product obtained by melt-kneading and molding the hollow particles of the present disclosure and a thermoplastic resin contains, as the matrix resin, a solidified product of the thermoplastic resin that has solidified by cooling.

[0098] The resin molded article of the present disclosure has excellent dielectric properties due to the inclusion of the hollow particles of the present disclosure. The resin molded article of the present disclosure has a dielectric loss tangent of preferably 1.50×10 at a frequency of 10 GHz. －２ or less, more preferably 1.00 x 10 －２ More preferably, 9.50 x 10 －３ More preferably, 9.00 x 10 －３ The lower limit is not particularly limited, and is, for example, 1.00 × 10 －４The resin molded product of the present disclosure has a relative dielectric constant at a frequency of 10 GHz of preferably 2.50 or less, more preferably 2.40 or less, and even more preferably 2.30 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 resin molded product are measured using a perturbation type measuring device under a measurement frequency condition of 10 GHz.

[0099] The shape of the resin molded product of the present disclosure is not particularly limited and can be any moldable shape, such as a sheet, film, plate, tube, or any other three-dimensional shape. When the resin molded product contains fibers, the fibers in the resin molded product may be in the form of a nonwoven fabric. When the resin molded product contains fibers, the resin molded product may be a molded product of a resin composition in which hollow particles of the present disclosure are added to a fiber-reinforced plastic containing the resin and fibers as described above.

[0100] Examples of uses of the resin composition and resin molded article of the present disclosure include uses in which the resin composition or resin molded article can be used, among the uses of the hollow particles of the present disclosure described above.

[0101] 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.

[0102] 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 (10-hour half-life temperature: 75°C), and 60.8 parts hydrophobic solvent: heptane (solubility in water at 20°C: 2.2 mg / L, boiling point: 98.4°C). 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 was gradually added with 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.

[0103] (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.

[0104] (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.

[0105] (4) Washing step and solid-liquid separation step The precursor composition obtained in the polymerization step was washed with dilute sulfuric acid (25°C, 10 minutes) to adjust the pH to 5.5 or less. Next, after separating the water by filtration, 200 parts of ion-exchanged water was added to re-slurry the mixture. The water washing treatment (washing, filtration, dehydration) was repeated several times at room temperature (25°C), and the mixture was filtered to obtain a solid. The obtained solid was dried in a dryer at 40°C to obtain precursor particles encapsulating the hydrophobic solvent.

[0106] (5) Solvent Removal Step The precursor particles obtained in the solid-liquid separation step were heat-treated in a vacuum dryer at 200°C for 12 hours to remove the hydrophobic solvent contained in the particles, thereby obtaining hollow particles of Example 1. From the results of observation with a scanning electron microscope and the porosity value, it was confirmed that the obtained hollow particles were spherical and had hollow portions.

[0107] [Example 2] Hollow particles of Example 2 were produced in the same manner as in Example 1, except that in the "(1) mixed solution preparation step", octane (solubility in water at 20°C: 0.7 mg / L, boiling point: 125.6°C) was used instead of heptane as the hydrophobic solvent, and further, in the "(3) polymerization step", the polymerization temperature was changed as shown in Table 1.

[0108] [Example 3] The hollow particles of Example 3 were produced in the same procedure as in Example 1, except that in the above "(1) mixed solution preparation step", t-butyl peroxypivalate (10-hour half-life temperature: 55°C) was used as the polymerization initiator instead of t-butyl peroxydiethyl acetate, the amounts of magnesium chloride and sodium hydroxide used in preparing the aqueous phase were changed as shown in Table 1, and further, in the above "(3) polymerization step", the polymerization temperature was changed as shown in Table 1.

[0109] [Example 4] Hollow particles of Example 4 were produced in the same procedure as in Example 1, except that in the above "(1) mixed solution preparation step", the amount of divinylbenzene added was changed to 24.6 parts, the amount of ethylvinylbenzene added was changed to 14.5 parts, and further, the amounts of magnesium chloride and sodium hydroxide used in preparing the aqueous phase were changed as shown in Table 1.

[0110] [Example 5] The hollow particles of Example 5 were produced in the same procedure as in Example 1, except that in the above "(1) mixed solution preparation step", the amount of divinylbenzene added was changed to 35.6 parts, the amount of ethylvinylbenzene added was changed to 1.5 parts, 2.0 parts of ethylene glycol dimethacrylate was added to the oil phase, and the amounts of magnesium chloride and sodium hydroxide used in preparing the aqueous phase were changed as shown in Table 1.

[0111] [Example 6] Hollow particles of Example 6 were produced in the same procedure as in Example 1, except that in the above "(1) mixed solution preparation step", the amount of divinylbenzene added was changed to 22.3 parts, the amount of ethylvinylbenzene added was changed to 15.6 parts, and further, the amounts of magnesium chloride and sodium hydroxide used in preparing the aqueous phase were changed as shown in Table 1.

[0112] [Example 7] The hollow particles of Example 7 were produced in the same procedure as in Example 1, except that in the above "(1) mixed solution preparation step", the amount of divinylbenzene added was changed to 31.6 parts, the amount of ethylvinylbenzene added was changed to 1.3 parts, 0.75 parts of t-butylperoxydiethyl acetate and 1.07 parts of t-butylperoxypivalate were used as polymerization initiators, the amount of heptane was changed to 67.1 parts, and further, the amounts of magnesium chloride and sodium hydroxide used in preparing the aqueous phase were changed as shown in Table 1.

[0113] [Example 8] The hollow particles of Example 8 were produced in the same manner as in Example 1, except that in the above "(1) mixed solution preparation step", the amounts of magnesium chloride and sodium hydroxide used in preparing the aqueous phase were changed as shown in Table 1, the polymerization temperature in the above "(3) polymerization step" was changed as shown in Table 1, and further, a nonionic surfactant was added during reslurrying in "(4) washing step and solid-liquid separation step" to eliminate aggregation between particles, and the number of water washing treatments was further increased.

[0114] [Comparative Example 1] Hollow particles of Comparative Example 1 were produced in the same procedure as in Example 1, except that the "(1) mixed solution preparation step" in Example 1 was changed as follows, and further, the polymerization temperature in the "(3) polymerization step" was changed as shown in Table 2. The mixed solution preparation step of Comparative Example 1 was carried out as follows. First, the following materials were mixed to form an oil phase. Ethylene glycol dimethacrylate 31.85 parts Trimethylolpropane triacrylate 13.65 parts 2,2'-azobis(2,4-dimethylvaleronitrile) (10-hour half-life temperature: 51 ° C.) 1.04 parts Hydrophobic solvent: cyclohexane 54.5 parts Next, in a stirring tank, an aqueous solution obtained by dissolving 23.5 parts of magnesium chloride (water-soluble polyvalent metal salt) in 225 parts of ion-exchanged water was gradually added with stirring to an aqueous solution obtained by dissolving 16.5 parts of sodium hydroxide (alkali metal hydroxide) in 55 parts of ion-exchanged water, to prepare a magnesium hydroxide colloid (poorly water-soluble metal hydroxide colloid) dispersion (magnesium hydroxide 12 parts), which served as an aqueous phase. The resulting aqueous phase and oil phase were mixed to prepare a mixed liquid.

[0115] [Comparative Example 2] First, the following materials were mixed to form an oil phase. Styrene (St) 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, yielding a slurry. The obtained slurry was heated at 100° C. for 24 hours to produce hollow particles of Comparative Example 2.

[0116] Comparative Example 3 First, the following materials were mixed to form an oil phase: 48.0 parts divinylbenzene, 2.0 parts ethylvinylbenzene, 1.0 part benzoyl peroxide (10-hour half-life temperature: 74°C), and 50.0 parts hexadecane. Next, in a stirring tank, 10 parts polyvinyl alcohol (PVA) was dissolved in 3,000 parts ion-exchanged water to prepare an aqueous solution, which served as the aqueous phase. The resulting aqueous phase and oil phase were mixed to prepare a mixed solution. The resulting mixed solution was suspended using the same method as in the suspension step of Example 1 to prepare a suspension in which droplets of the monomer composition encapsulating the hydrophobic solvent were dispersed in water. The resulting suspension was heated to 70°C in a nitrogen atmosphere and stirred for 24 hours at 70°C to carry out a polymerization reaction. This polymerization reaction yielded a slurry in which precursor particles encapsulating the hydrophobic solvent were dispersed in water. The resulting slurry was then filtered using filter paper to isolate the precursor particles encapsulating the hydrophobic solvent. The precursor particles were dried under conditions of a temperature of about 70° C. and a pressure of about 100,000 Pa (atmospheric pressure) to remove the hydrophobic solvent contained in the particles, thereby producing hollow particles of Comparative Example 3.

[0117] [Evaluation] The hollow particles obtained in each Example and Comparative Example were subjected to the following measurements and evaluations. The results are shown in Tables 1 and 2.

[0118] 1. Density and porosity of hollow particles 1-1. Measurement of apparent density of hollow particles First, a 100 cm ３ About 30 cm ３ The hollow particles were packed into the measuring flask, and the mass of the packed hollow particles was accurately weighed. Next, the measuring flask packed 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 measuring flask was accurately weighed, and the apparent density D of the hollow particles was calculated based on the above 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])

[0119] 1-2. 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])

[0120] 1-3. 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

[0121] 2. Measurement of Volume Average Particle Size (Dv) and Number Average Particle Size (Dn), and Calculation of Particle Size Distribution (Dv / Dn) The volume average particle size (Dv) and number average particle size (Dn) of hollow particles were measured using a particle size distribution analyzer (manufactured by Beckman Coulter, Inc., product name: Multisizer 4e), and the particle size distribution (Dv / Dn) was calculated. 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 further 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.

[0122] 3. Measurement of Residual Double Bond Ratio Using an ATR-IR (Perkin Elmer, product name: Spectrum One), infrared absorption spectra, expressed as absorbance, were measured for the polymerizable monomers used to prepare the hollow particles before the polymerization reaction and the polymers contained in the hollow particles. Measurements of the polymerizable monomers before the polymerization reaction were performed by placing 0.1 g of a measurement sample consisting of the same type and content of polymerizable monomers as the polymerizable monomers used to prepare the hollow particles on the top of a cell and bringing the measurement sample into contact with a crystal. Measurements of the polymers contained in the hollow particles were performed by placing 0.1 g of hollow particles on the top of a cell and tightening the compression bearing from above to bring the crystal into contact with the hollow particles. From the obtained infrared absorption spectra, the residual double bond ratio was calculated using the method described above. For example, in Example 5, the residual double bond ratio was calculated as follows. In Example 5, 35.6 parts of divinylbenzene, 1.5 parts of ethylvinylbenzene, and 2.0 parts of ethylene glycol dimethacrylate were used as the polymerizable monomers. Divinylbenzene (91% by mass), which had the highest content, was used as the reference monomer, and the C-H bond of the benzene ring contained in divinylbenzene was selected as the structure that did not change before or after the polymerization reaction. In the infrared absorption spectrum of the polymerizable monomer before the polymerization reaction and the infrared absorption spectrum of the polymer, the peak derived from the C-H bond of the benzene ring contained in divinylbenzene was identified as the reference peak. Because the peak derived from the C-H bond of the benzene ring contained in divinylbenzene and the peak derived from the C-H bond of the benzene ring contained in ethylvinylbenzene appear at the same position, the peak intensity of the reference peak was determined by dividing the peak intensity by the sum of the content percentage of divinylbenzene and the content percentage of ethylvinylbenzene (0.95). The reference peak intensity obtained from the infrared absorption spectrum of the polymerizable monomer before the polymerization reaction was 0.167, and the reference peak intensity obtained from the infrared absorption spectrum of the polymer was 0.0760. Next, in each infrared absorption spectrum, the peak intensities of the peaks derived from the polymerizable unsaturated double bonds (C═C) derived from divinylbenzene, ethylvinylbenzene, and ethylene glycol dimethacrylate were measured.The peak intensity of the peak derived from the polymerizable unsaturated double bond (C=C) obtained from the infrared absorption spectrum of the polymerizable monomer before the polymerization reaction was 0.0724, and the peak intensity of the peak derived from the polymerizable unsaturated double bond (C=C) obtained from the infrared absorption spectrum of the polymer was 0.00438. Therefore, the reference peak intensity (M ０ ) relative to the peak intensity (M １ ) ratio (M １ / M ０ The reference peak intensity (P) calculated from the infrared absorption spectrum of the polymer was 0.0724 / 0.167, which was 0.434. ０ ) relative to the peak intensity (P １ ) ratio (P １ / P ０ ) was 0.00438 / 0.0760, which was calculated as 0.0576. １ / M ０ ) and the peak intensity ratio (P １ / P ０ ) was applied to the above formula (A), and the residual double bond ratio was calculated to be 13.3% from the calculation formula (0.0576 / 0.434) × 100.

[0123] 4. Measurement of Metal Content 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.

[0124] 5. Measurement of Relative Dielectric Constant (Dk) and Dielectric Loss Tangent (Df) of Hollow Particles The relative 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).

[0125] 6. Heat Resistance Approximately 3 mg of hollow particles were placed in a sample pan, and measurements were performed in an air atmosphere using a TG-DTA device (manufactured by Rigaku Corporation, product name: Thermo Plus EVO2) at a heating rate of 10°C / min and an air flow rate of 230 mL to determine the temperature at which 5% weight loss (Td5). The higher the Td5, the better the heat resistance of the hollow particles. (Heat Resistance Evaluation Criteria) A: Td5 is 345°C or higher B: Td5 is 340°C or higher but lower than 345°C C: Td5 is 335°C or higher but lower than 340°C D: Td5 is lower than 335°C

[0126] 7. Measurement of the relative permittivity (Dk) and dielectric dissipation factor (Df) of polyimide films containing hollow particles 7-1. Preparation of polyimide films containing hollow particles 50 g of polyamic acid solution (Ube Industries, Ltd., product name: U-Varnish-A) was weighed into a cup, 2.5 g of hollow particles were added, and the mixture was uniformly dispersed using a planetary stirring degassing device (Kurabo Industries, Ltd., product name: Mazerustar) to obtain a resin composition. Next, aluminum foil was attached to a glass plate, and the obtained resin composition was applied to the aluminum foil using a bar coater No. 75 to form a coating film. The coating film was heated in a nitrogen atmosphere at 120°C for 30 minutes, 150°C for 10 minutes, 200°C for 10 minutes, and 250°C for 30 minutes in that order to polyimidize the polyamic acid and harden the coating film, forming a polyimide film containing hollow particles on the aluminum foil. The laminate of the film and aluminum foil was immersed in a 1N hydrochloric acid solution overnight to remove the aluminum foil, and the film alone was obtained. The obtained film was washed with ion-exchanged water and dried to obtain a polyimide film containing hollow particles.

[0127] 7-2. Measurement of the dielectric constant (Dk) and dielectric loss tangent (Df) of the film The hollow particle-containing polyimide film obtained above was cut into a width of 3 mm and a length of 80 mm to obtain a measurement sample. The dielectric constant and dielectric loss tangent of the obtained measurement sample were measured at a frequency of 10 GHz and room temperature (25°C) using a perturbation type measuring device (manufactured by AET Co., Ltd., model: ADMS01Nc). In addition, as Reference Example 1, the dielectric constant and dielectric loss tangent of a polyimide film containing no hollow particles were measured in the same manner.

[0128]

[0129]

[0130] Tables 1 and 2 show the amount (parts by mass) of each material added and the results of each measurement or evaluation. In Tables 1 and 2, the dielectric loss tangent values ​​are expressed in exponential notation as specified in JIS X 0210 for simplification. For example, "2.41 x 10 －３ " is expressed as "2.41E-03". In Tables 1 and 2, the meanings of the abbreviations are as follows: EGDMA: ethylene glycol dimethacrylate TMPT: trimethylolpropane triacrylate St: styrene 50PEP-300: polyethylene glycol propylene glycol monomethacrylate (manufactured by NOF Corporation, product name: Blenmar (registered trademark) 50PEP-300) HS4100: side chain crystalline polyolefin (manufactured by Toyokuni Oil Mills Co., Ltd., product name: HS Crystal 4100) PVA: polyvinyl alcohol A-80: anionic surfactant, sulfosuccinic acid diester salt (manufactured by NOF Corporation, product name: Rapisol A-80)

[0131] [Discussion] The hollow particles obtained in Comparative Example 1 were formed using an acrylic monomer and had poor dielectric properties and were also poor in their effect of lowering the dielectric constant and dielectric dissipation factor of a polyimide film. The hollow particles obtained in Comparative Example 1 were formed because the polymer in the shell did not contain hydrocarbon monomer units, which is thought to have led to poor dielectric properties of the shell and poor dielectric properties of the particles as a whole. Comparative Example 2 corresponds to Example 1 of Patent Document 1. The hollow particles obtained in Comparative Example 2 had poor dielectric properties and were also poor in their effect of lowering the dielectric constant and dielectric dissipation factor of a polyimide film. The hollow particles obtained in Comparative Example 2 were formed because the polymer in the shell contained a small amount of hydrocarbon monomer units, which led to poor dielectric properties of the shell. Furthermore, the low porosity also worsened the dielectric properties, which is thought to have led to poor dielectric properties of the particles as a whole. The hollow particles obtained in Comparative Example 3 had a high residual double bond rate in the polymer contained in the shell, which led to poor dielectric properties and poor effect of lowering the dielectric constant and dielectric dissipation factor of a polyimide film. The hollow particles obtained in Comparative Example 3 had a surfactant (PVA) content of 3,000 ppm present on the particle surface. The hollow particles obtained in Comparative Example 3 had a high residual double bond ratio in the polymer contained in the shell, which resulted in poor shell dielectric properties. Furthermore, it is presumed that the PVA used in the manufacturing process remained on the particle surface, which also deteriorated the dielectric properties of the hollow particles. The high residual double bond ratio of the hollow particles obtained in Comparative Example 3 is presumed to be due to the low polymerization temperature.

[0132] In contrast, the hollow particles obtained in each example were spherical hollow particles having a hollow portion, a porosity of 50% or more, a shell containing a polymer as a resin containing 91% by mass or more of hydrocarbon monomer units and 50% by mass or more of crosslinkable monomer units, a residual double bond ratio of the polymer being 30.0% or less, and a dielectric loss tangent at a frequency of 10 GHz being 3.00×10 －３The dielectric constant of the hollow particles obtained in each Example was low, or less, and the hollow particles had excellent dielectric properties. The reason why the hollow particles obtained in each Example had excellent dielectric properties even at a frequency of 10 GHz is presumably because the polymer forming the shell skeleton contained a large amount of hydrocarbons and the polymer had a low residual double bond ratio, resulting in low molecular mobility of the shell and a sufficiently high porosity. Furthermore, the hollow particles obtained in each Example had a low amount of residual decomposition products of the polymerization initiator, no surfactant was present on the particle surface, and a low metal content, which are also thought to have contributed to the improved dielectric properties. Since the hollow particles obtained in each Example were obtained without the use of a surfactant, no surfactant was detected on the particle surface. Furthermore, the hollow particles obtained in each Example were also excellent in reducing the dielectric constant and dielectric loss tangent of polyimide films. Furthermore, the dielectric properties of the hollow particles obtained in Examples 1 to 4 were superior to those of the hollow particles obtained in Examples 5 and 6. This is presumably because the polymer forming the shell skeleton contained a particularly high content of hydrocarbon monomer units, and the raw materials contained few impurities, resulting in a particularly low content of components other than the polymer in the shell. The particularly superior dielectric properties of the hollow particles obtained in Example 7 are presumably due to their high porosity. The low dielectric tangent of the hollow particles obtained in Example 8 is presumably due to the removal of a large amount of impurities in the washing process, thereby suppressing an increase in the dielectric tangent due to moisture absorption by the impurities. Furthermore, when 1,000 to 3,000 randomly selected hollow particles obtained in each Example were examined, the proportion of particles with a circularity of 0.85 or less was 7% by mass or less, and the proportion of particles having only one or two hollow portions was 95% by mass or more in all Examples.

[0133] REFERENCE SIGNS LIST 1 aqueous medium 2 low-polarity material 4a hydrophobic solvent 4b material other than hydrophobic solvent 6 shell 7 hollow portion 8 droplet 9 precursor particle 10 hollow particle with hollow portion filled with gas

Claims

1. A hollow particle having a shell containing a resin and a hollow portion surrounded by the shell, The porosity is 50% or more, the shell contains, as the resin, a polymer containing 91% by mass or more of hydrocarbon monomer units and 50% by mass or more of crosslinkable monomer units, at least a part of the hydrocarbon monomer units are crosslinkable hydrocarbon monomer units, and the polymer has a residual double bond ratio of 30.0% or less; The dielectric loss tangent at a frequency of 10 GHz is 3.00 x 10 －３ Below are hollow particles.

2. 2. The hollow particle according to claim 1, having a relative dielectric constant at a frequency of 10 GHz of 1.00 or more and 1.40 or less.

3. The hollow particle according to claim 1 or 2, wherein the porosity is 65% or more.

4. 3. The hollow particles according to claim 1, wherein the volume average particle size is 1.0 μm or more and 10.0 μm or less.

5. A hollow particle as described in claim 1 or 2, wherein the content of the crosslinkable hydrocarbon monomer units is 50 mass% or more relative to 100 mass% of all structural units in the polymer contained in the shell.

6. The hydrocarbon monomer units further contain non-crosslinkable hydrocarbon monomer units, 3. The hollow particle according to claim 1, wherein the content of the non-crosslinkable hydrocarbon monomer unit is 2% by mass or more and 50% by mass or less, relative to 100% by mass of all structural units in the polymer contained in the shell.

7. Hollow particles described in claim 1 or 2, having a metal content of 100 ppm or less.

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

9. A resin molded product comprising the hollow particles according to claim 1 or 2 and a matrix resin.

10. The resin molded article according to claim 9, wherein the dielectric loss tangent at a frequency of 10 GHz is 1.50×10 −2 or less.

11. A resin molded body as described in claim 9, having a relative dielectric constant of 2.50 or less at a frequency of 10 GHz.