Hollow particles, method for producing hollow particles, and resin composition

Abstract

The present invention provides hollow particles which have improved adhesion to a resin. The present invention provides hollow particles, each of which comprises a shell that contains a resin and a hollow part that is surrounded by the shell. The shell contains, as the resin, a polymer that contains 60% by mass or more of a crosslinkable monomer unit; the surfaces of the hollow particles have an amino group; and the amount of amine per unit area as calculated from the amine value of the hollow particles and the specific surface area of the hollow particles by formula (A) (amount of amine (µmol / m2)) = (amine value (µmol / g)) / (specific surface area (m2 / g)) is 5.00 µmol / m2 or more.

Description

Hollow particles, method for producing hollow particles, and resin composition

[0001] The present disclosure relates to hollow particles, a method for producing the same, and a resin composition 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 order to improve the effects of various compositions and molded articles containing hollow particles, such as weight reduction, heat insulation, and low dielectric constant, it is desirable that the hollow particles maintain a high porosity when kneaded with other materials and when molded after kneading. For example, Patent Documents 1 and 2 disclose hollow particles that can maintain porosity by suppressing deformation of the hollow particles, and have a shell containing a polymer obtained by polymerizing a reactive monomer having a radically polymerizable functional group and a crosslinkable functional group such as an epoxy group, and then crosslinking the polymer with a crosslinking agent such as a polyamine compound.

[0004] International Publication No. 2019 / 177006 Japanese Patent Application Laid-Open No. 2006-89648

[0005] However, conventional resin compositions containing hollow particles have the problem of lower physical properties related to strength against external forces, such as tensile strength and flexural strength, compared to resin compositions that do not contain hollow particles. Furthermore, when conventional resin compositions containing hollow particles are used as insulating resins or sealing resins for electronic components such as electronic circuit boards, there are problems such as insufficient copper foil peel strength due to poor adhesion between the resin layer containing the hollow particles and copper foil, and problems such as a tendency for malfunctions due to moisture absorption to occur in reliability tests such as PCT (pressure cooker test). These problems are thought to be caused by insufficient adhesion between the hollow particles in the resin composition and the resin.

[0006] An object of the present disclosure is to provide hollow particles that can improve adhesion to resins, a method for producing the hollow particles, and a resin composition containing the hollow particles.

[0007] The present inventors have found that when the amount of amine per unit area on the surface of hollow particles is equal to or greater than a specific amount, adhesion to resins can be improved.

[0008] The present disclosure provides hollow particles having a shell containing a resin and a hollow portion surrounded by the shell, wherein the shell contains, as the resin, a polymer containing 60 mass % or more of crosslinkable monomer units, the hollow particles have amino groups on their surfaces, and the amount of amine per unit area calculated from the amine value of the hollow particles and the specific surface area of ​​the hollow particles using the following formula (A) is 5.00 μmol / m ２ The hollow particles are provided such that the amine amount (μmol / m ２ ) = amine value (μmol / g) / specific surface area (m ２ / g)

[0009] In the hollow particles of the present disclosure, it is preferable that the polymer contains an amino group-containing monomer unit, and that the amino group-containing monomer unit is derived from an amino group-introducing monomer that contains a radical polymerizable group and an amino group.

[0010] In the hollow particles of the present disclosure, the amino groups present on the surfaces of the hollow particles are preferably amino groups contained in the amino group-containing monomer units.

[0011] In the hollow particles of the present disclosure, the content of the amino group-containing monomer units is preferably 2% by mass or more and 40% by mass or less relative to 100% by mass of all monomer units contained in the polymer.

[0012] In the hollow particles of the present disclosure, the content of hydrocarbon monomer units may be more than 50% by mass relative to 100% by mass of all monomer units contained in the polymer, or the content of acrylic monomer units may be more than 50% by mass relative to 100% by mass of all monomer units contained in the polymer.

[0013] In the hollow particles of the present disclosure, the porosity is preferably 50% or more.

[0014] The present disclosure relates to a method for producing hollow particles of the present disclosure, the method comprising the steps of: preparing a mixed solution containing a skeleton-forming 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 skeleton-forming monomer, the hydrophobic solvent, and the polymerization initiator are dispersed in the aqueous medium; and subjecting the suspension to a polymerization reaction, and when a polymerization conversion rate of the skeleton-forming monomer reaches 1% by mass or more and 99% by mass or less, adding an amino group-introducing monomer containing a radical polymerizable group and an amino group, and further carrying out a polymerization reaction, thereby preparing a precursor composition containing precursor particles having a shell containing a polymer of the skeleton-forming monomer and the amino group-introducing monomer and having an amino group on an outer surface, and a hollow portion surrounded by the shell, with the hydrophobic solvent encapsulated in the hollow portion. The method for producing hollow particles further provides a method for producing hollow particles, wherein the solubility of the amino group-introducing monomer in water at 20°C is greater than that of the hydrophobic solvent and is 0.5 g / L to 1000 g / L, the skeleton-forming monomer includes a crosslinkable monomer, and the content of the crosslinkable monomer is 60 mass% or more relative to 100 mass% in total of the skeleton-forming monomer and the amino group-introducing monomer.

[0015] The present disclosure provides a resin composition containing the hollow particles of the present disclosure and a binder resin having a functional group capable of reacting with an amino group.

[0016] The present disclosure as described above provides hollow particles that can improve adhesion to resins, and further provides a method for producing the hollow particles and a resin composition containing the hollow particles.

[0017] 1A to 1C are diagrams illustrating an example of a method for producing hollow particles according to the present disclosure.

[0018] 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 addition, in the present disclosure, good dielectric properties means low relative permittivity and dielectric loss tangent, and the lower the relative permittivity and dielectric loss tangent, the better the dielectric properties.

[0019] The hollow particles of the present disclosure are hollow particles having a shell containing a resin and a hollow portion surrounded by the shell, wherein the shell contains, as the resin, a polymer containing 60 mass % or more of crosslinkable monomer units, the hollow particles have amino groups on their surfaces, and the amount of amine per unit area calculated from the amine value of the hollow particles and the specific surface area of ​​the hollow particles by the formula (A) described below is 5.00 μmol / m ２ The present invention is characterized in that:

[0020] When the hollow particles of the present disclosure are used in combination with a resin having functional groups reactive with amino groups, the amino groups on the surface of the hollow particles can react with the functional groups on the resin to form crosslinks, thereby improving the adhesion at the interface between the hollow particles and the resin. Here, the reaction between the amino groups on the hollow particles and the functional groups on the resin can be a reaction that forms a covalent bond. Furthermore, when hollow particles of the present disclosure having amino groups on their surface are dispersed in a resin having functional groups reactive with amino groups, the particles and the resin have similar polarities and high affinity, resulting in good dispersibility of the hollow particles. If the hollow particles aggregate in a molded product containing hollow particles, pressure is likely to be applied to the aggregated areas when the molded product is pressed, causing the hollow particles to collapse. However, when the hollow particles of the present disclosure are incorporated into a resin having functional groups, the hollow particles are more likely to be uniformly dispersed and aggregation of the hollow particles is suppressed, making it easier to apply pressure evenly when pressed. Furthermore, in a molded article obtained by incorporating the hollow particles of the present disclosure into a resin having functional groups, the amino groups of the hollow particles and the functional groups of the resin are crosslinked to form a three-dimensional crosslinked structure near the particle surface, resulting in improved pressure resistance and reduced crushing of the hollow particles.

[0021] The hollow particles of the present disclosure are particles having a shell (outer shell) containing a resin and a hollow portion surrounded by the shell. In the present disclosure, the hollow portion is a hollow space clearly distinguishable from the shell of the hollow particle formed from a resin material. The shell of the hollow particle may have a porous structure, but in that case, the hollow portion has a size clearly distinguishable from the numerous microscopic spaces uniformly dispersed within the porous structure. From the viewpoint of dielectric properties, etc., 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. Below, an example of a method for producing hollow particles of the present disclosure is described, followed by a detailed description of the hollow particles of the present disclosure, and further a description of a resin composition containing the hollow particles of the present disclosure.

[0022] 1. Method for producing hollow particles The method for producing hollow particles according to the present disclosure includes, for example, the steps of: preparing a mixed solution containing a skeleton-forming 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 skeleton-forming monomer, the hydrophobic solvent, and the polymerization initiator are dispersed in the aqueous medium; and subjecting the suspension to a polymerization reaction, and when the polymerization conversion rate of the skeleton-forming monomer reaches 1% by mass or more and 99% by mass or less, adding an amino group-introducing monomer containing a radical polymerizable group and an amino group, and further carrying out a polymerization reaction, thereby preparing a precursor composition containing precursor particles having a shell containing a polymer of the skeleton-forming monomer and the amino group-introducing monomer and having an amino group on the outer surface, and a hollow portion surrounded by the shell, with the hydrophobic solvent encapsulated in the hollow portion. The hollow particles can be obtained by the method for producing hollow particles disclosed herein, in which the solubility of the amino group-introducing monomer in water at 20°C is greater than that of the hydrophobic solvent and is 0.5 g / L to 1000 g / L, the skeleton-forming monomer includes a crosslinkable monomer, and the content of the crosslinkable monomer is 60 mass% or more relative to 100 mass% in total of the skeleton-forming monomer and the amino group-introducing monomer.

[0023] 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 phase-separate, forming droplets having a distribution structure in which the polymerizable monomer is concentrated on the surface and the hydrophobic solvent is concentrated in the center, and then subjecting this suspension to a polymerization reaction to harden the surfaces of the droplets and form hollow particles having hollows filled with the hydrophobic solvent. In the above-described basic technique, when an amino group-containing monomer is added to the suspension in advance, it is difficult to position the amino groups of the amino group-containing monomer on the outer surface of the shell. Even when the content of the amino group-containing monomer is increased, it is difficult to ensure that a sufficient number of amino groups are present on the surface of the hollow particles. Furthermore, the dielectric properties of hollow particles tend to deteriorate as the amino group content in the shell increases, which presents a problem of difficulty in improving adhesion to resins while maintaining the dielectric properties of the hollow particles. In contrast, in the production method of the present disclosure, an amino group-introducing monomer containing a radical polymerizable group and an amino group and having moderate water solubility is added to the suspension during the polymerization reaction, and the polymerization reaction is further carried out, thereby efficiently introducing monomer units derived from the amino group-introducing monomer onto the outer surface of the shell. In the production method of the present disclosure, the amino group-introducing monomer is added during the polymerization reaction, and because the amino group-introducing monomer has moderate water solubility, it is presumed that the added amino group-introducing monomer is likely to be located on the surface of the shell during the polymerization reaction. Furthermore, the amino group-introducing monomer has a radical polymerizable group as a polymerizable functional group, and due to the high reactivity of this radical polymerizable group, it is presumed that it easily reacts with unreacted backbone-forming monomer located on the surface of the shell. Therefore, in the production method of the present disclosure, it is presumed that the amino group-introducing monomer added during the polymerization reaction is bonded to the surface of the shell by addition polymerization, thereby efficiently introducing amino groups onto the outer surface of the shell. Even if the polymerization conversion rate of the backbone-forming monomer is relatively low when the amino group-introducing monomer is added, the polymer composed of the backbone-forming monomer reacts with the amino group-introducing monomer in the oil droplets.It is believed that the amino group-containing reactant increases polarity and makes it more likely to be present on the outermost surface of the droplets, allowing the amino group-introducing monomer to be introduced onto the shell surface. According to the manufacturing method of the present disclosure, amino groups can be efficiently introduced onto the surface of hollow particles, minimizing the amount of amino group-introducing monomer added and providing the necessary amount of amino groups on the surface of hollow particles to improve adhesion to resins. This allows the relative content of skeleton-forming monomer units to be increased, and by adjusting the composition of the skeleton-forming monomer, hollow particles with desired physical properties can be obtained. For example, hollow particles with excellent dielectric properties can be obtained by using a large amount of hydrocarbon monomer as the skeleton-forming monomer. Furthermore, according to the manufacturing method of the present disclosure, spherical hollow particles having a hollow portion clearly distinguishable from the shell can be formed by setting the content of crosslinkable monomer to 60% by mass or more relative to 100% by mass of the total of the skeleton-forming monomer and the amino group-introducing monomer. This is presumably because the polymerizable monomer used to form the shell contains a sufficient amount of crosslinkable monomer, which makes it easier for the components that make up the shell and the hydrophobic solvent to phase separate in the droplets of the monomer composition dispersed in the suspension, and also because a shell with excellent strength is formed, which suppresses deformation of the particles.

[0024] 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 preparing a precursor composition, 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.

[0025] 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 skeleton-forming 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 the skeleton-forming monomer, the hydrophobic solvent, and the polymerization initiator are dispersed in an aqueous medium; (3) precursor composition preparation 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 may be considered as intermediates of hollow particles whose hollow portions are filled with a gas and may be referred to as "precursor particles." In the present disclosure, a "precursor composition" refers to a composition containing precursor particles. In the manufacturing method of the present disclosure, in the precursor composition preparation step (3), an amino group-introducing monomer that contains a radical polymerizable group and an amino group and has suitable water solubility is added during the polymerization reaction of the suspension, and the polymerization reaction is further carried out to form precursor particles having a shell that contains a polymer of a skeleton-forming monomer and an amino group-introducing monomer and has amino groups on the outer surface.

[0026] 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 the steps. 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 includes a skeleton-forming 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 skeleton-forming 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 materials other than the hydrophobic solvent, including the skeleton-forming monomer, 4b, with the hydrophobic solvent 4a concentrated in the center and the materials 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 the precursor composition preparation step, 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 skeleton-forming monomer in the droplet 8 of the monomer composition and the amino group-introducing monomer added during the polymerization reaction, and contains a polymer of the skeleton-forming monomer and the amino group-introducing monomer as a resin. (4) in Figure 1 is a cross-sectional schematic diagram showing one embodiment of the precursor particle after the solid-liquid separation step. (4) in Figure 1 shows the state in which the aqueous medium 1 has been removed from the state shown in (3) in Figure 1. (5) in Figure 1 is a cross-sectional schematic diagram showing one embodiment of the hollow particle after the solvent removal step.1 (5) shows the state after removing the hydrophobic solvent 4a from the state shown in FIG. 1 (4). By removing the hydrophobic solvent from the precursor particles, hollow particles 10 having gas-filled hollow portions 7 inside the shells 6 are obtained. The above five steps and other steps will be described below in order.

[0027] (1) Mixed Liquid Preparation Step This step is a step of preparing a mixed liquid containing a skeleton-forming 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) skeleton-forming monomer, (B) hydrophobic solvent, (C) polymerization initiator, (D) dispersion stabilizer, and (E) aqueous medium.

[0028] (A) Skeleton-Forming Monomer The skeleton-forming monomer may be any known polymerizable monomer conventionally used in the preparation of hollow particles. While not particularly limited, it is preferable for the skeleton-forming monomer to contain a crosslinkable monomer. When the skeleton-forming monomer contains a crosslinkable monomer, the resulting hollow particles tend to be spherical, and hollow portions that are clearly distinguishable from the shell tend to form within the particles. Furthermore, in order to obtain hollow particles with excellent dielectric properties, it is preferable for the skeleton-forming monomer to contain a hydrocarbon monomer. On the other hand, acrylic monomers are preferably used because they facilitate stable polymerization reactions. In the present disclosure, a polymerizable monomer consisting of carbon and hydrogen is referred to as a hydrocarbon monomer, a crosslinkable monomer consisting of carbon and hydrogen is referred to as a crosslinkable hydrocarbon monomer, and a non-crosslinkable monomer consisting of carbon and hydrogen is referred to as a non-crosslinkable hydrocarbon monomer. In the present disclosure, a polymerizable monomer having a (meth)acryloyl group as a polymerizable functional group is referred to as an acrylic monomer, a crosslinkable monomer having a (meth)acryloyl group as a polymerizable functional group is referred to as a crosslinkable acrylic monomer, and a non-crosslinkable monomer having a (meth)acryloyl group as a polymerizable functional group is referred to as a non-crosslinkable acrylic monomer. In the crosslinkable acrylic monomer, it is sufficient that at least one polymerizable functional group is a (meth)acryloyl group, but it is preferable that all of the polymerizable functional groups are (meth)acryloyl groups.

[0029] [Crosslinkable Monomer] 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. In addition, crosslinkable macromers such as polybutadiene, polyisoprene, styrene-butadiene block copolymers (SBS), and styrene-isoprene block copolymers (SIS) can also be used. 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. Examples of crosslinkable acrylic monomers include bifunctional ones such as allyl(meth)acrylate, vinyl(meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, and 3-(meth)acryloyloxy-2-hydroxypropyl(meth)acrylate; and trifunctional or higher ones such as trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol poly(meth)acrylate, and ethoxylated versions of these. In addition, crosslinkable macromers such as polyphenylene ether, both ends of which are (meth)acrylic-modified, can also be used. Among these, ethylene glycol di(meth)acrylate and pentaerythritol di(meth)acrylate are preferred, and ethylene glycol di(meth)acrylate and pentaerythritol di(meth)acrylate are more preferred, since the polymerization reaction is likely to be stable and hollow particles having excellent strength can be obtained.Further examples of the crosslinkable monomer include crosslinkable allylic monomers such as diallyl phthalate, and crosslinkable macromers such as polyphenylene ether vinyl-modified at both ends. These crosslinkable monomers can be used alone or in combination of two or more. From the viewpoint of improving the strength of the hollow particles, it is also preferable to use a combination of a bifunctional crosslinkable monomer having only two polymerizable functional groups and a trifunctional or higher crosslinkable monomer having three or more polymerizable functional groups. Preferred bifunctional crosslinkable monomers are as described above. As the tri- or higher functional crosslinkable monomer, pentaerythritol tetra(meth)acrylate, trimethylolpropane tri(meth)acrylate, ethoxylated trimethylolpropane tri(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, and dipentaerythritol poly(meth)acrylate are preferred, and pentaerythritol tetra(meth)acrylate and trimethylolpropane tri(meth)acrylate are more preferred.

[0030] The content of the crosslinkable monomer is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and even more preferably 90% by mass or more, relative to 100% by mass of the skeleton-forming monomer. When the content of the crosslinkable monomer is equal to or greater than the above-mentioned lower limit, hollow portions are easily formed within the particles, the particles are easily spherical, and the crosslinking density of the shell can be increased, which has the advantage of improving the solvent resistance, strength, pressure resistance, heat resistance, etc. of the hollow particles. When the skeleton-forming monomer 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, relative to 100% by mass of the skeleton-forming monomer.

[0031] When the crosslinkable monomer contained in the skeleton-forming monomer contains a combination of a bifunctional crosslinkable monomer and a tri- or higher functional crosslinkable monomer, the content of the trifunctional crosslinkable monomer is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and even more preferably 30 parts by mass or more, relative to 100% by mass of the total mass of the crosslinkable monomers, and is preferably 70 parts by mass or less, more preferably 60 parts by mass or less, and even more preferably 50 parts by mass or less, in order to improve the strength of the hollow particles.

[0032] [Non-crosslinkable monomer] The skeleton-forming monomer may contain a non-crosslinkable monomer. Examples of non-crosslinkable hydrocarbon monomers include aromatic monovinyl monomers such as styrene, vinyltoluene, α-methylstyrene, p-methylstyrene, ethylvinylbenzene, ethylvinylbiphenyl, and ethylvinylnaphthalene; monoolefin monomers such as linear or branched monoolefins such as ethylene, propylene, and butylene, and alicyclic monoolefins such as vinylcyclohexane, norbornene, tricyclododecene, and 1,4-methano-1,4,4a,9a-tetrahydrofluorene; and the like. Among these, aromatic monovinyl monomers are preferred, and ethylvinylbenzene is particularly preferred, from the viewpoint of improving the dielectric properties of the hollow particles. Examples of non-crosslinkable acrylic monomers include (meth)acrylic acid alkyl esters such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and lauryl (meth)acrylate; glycidyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, (meth)acrylic acid, (meth)acrylamide, N-methylol (meth)acrylamide, and N-butoxymethyl (meth)acrylamide.Further examples include 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, stearoxypolyethylene glycol (meth)acrylate, phenoxypolyethylene 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, monoethylene glycol mono(meth)acrylate, etc. In addition, non-crosslinkable macromers such as (meth)acrylic-modified polystyrene and (meth)acrylic-modified polymethyl methacrylate can also be used. Among them, (meth)acrylic acid alkyl esters are preferred, and butyl acrylate and methyl methacrylate are more preferred, because they facilitate stable polymerization reactions.Furthermore, examples of non-crosslinkable monomers include carboxylic acid vinyl ester monomers such as vinyl acetate; halogenated aromatic vinyl monomers such as halogenated styrene; halogenated vinyl monomers such as vinyl chloride; halogenated vinylidene monomers such as vinylidene chloride; vinylpyridine monomers; and the like.These non-crosslinkable monomers can be used alone or in combination of two or more.

[0033] From the viewpoint of obtaining hollow particles with excellent dielectric properties, it is preferable to use a hydrocarbon monomer as the main component of the skeleton-forming monomer. In this case, the content of the hydrocarbon monomer is preferably more than 50% by mass, more preferably 60% by mass or more, even more preferably 80% by mass or more, and even more preferably 90% by mass or more, relative to 100% by mass of the skeleton-forming monomer. It is particularly preferable that the skeleton-forming monomer consists of a hydrocarbon monomer. Note that a polymerizable monomer containing a heteroatom may be included within a range that does not significantly impair the dielectric properties of the hollow particles. For example, the content of the hydrocarbon monomer may be 99% by mass or less, or 98% by mass or less, relative to 100% by mass of the skeleton-forming monomer.

[0034] From the viewpoint of the reactivity of the polymerization reaction, it is preferable to use an acrylic monomer as the main component of the skeleton-forming monomer. In this case, the content of the acrylic monomer relative to 100% by mass of the skeleton-forming monomer is preferably 40% by mass or more, more preferably more than 50% by mass, even more preferably 70% by mass or more, and even more preferably 90% by mass or more. It is particularly preferable that the skeleton-forming monomer consists of an acrylic monomer. Note that, as long as the stability of the polymerization reaction is not significantly impaired, a polymerizable monomer other than the acrylic monomer may be contained. For example, the content of the acrylic monomer relative to 100% by mass of the skeleton-forming monomer may be 99% by mass or less, or 98% by mass or less. In order to suppress deterioration of the dielectric properties, the content may be 90% by mass or less, 80% by mass or less, 70% by mass or less, or 60% by mass or less.

[0035] The content of the skeleton-forming 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 30 to 60% by mass, and more preferably 40 to 50% 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 the mechanical strength of the hollow particles, the content of the skeleton-forming monomer 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 95% 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.

[0036] (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 precursor composition preparation 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.

[0037] As the hydrophobic solvent, it is preferable to select an organic solvent that has lower solubility in water than the crosslinkable monomer contained in the backbone-forming monomer. Known hydrophobic solvents can be appropriately selected depending on the type of crosslinkable monomer, and are not particularly limited. Examples of hydrophobic solvents include esters such as ethyl acetate and butyl acetate; ether esters such as propylene glycol monomethyl ether acetate and propylene glycol monoethyl ether acetate; and hydrocarbon solvents, of which hydrocarbon solvents are preferred. Examples of hydrocarbon solvents include aliphatic hydrocarbons, including chain hydrocarbon solvents such as pentane, hexane, heptane, octane, 2-methylbutane, and 2-methylpentane, and cyclic hydrocarbon solvents such as cyclohexane, methylcyclohexane, and cycloheptane; and aromatic hydrocarbons such as benzene, toluene, and xylene. These hydrophobic solvents can be used alone or in combination of two or more. Among the hydrophobic solvents, when the skeleton-forming monomer contains more than 50% by mass of a hydrocarbon monomer, chain hydrocarbon solvents are preferred, 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, because they facilitate the formation of hollow portions and are easily removed, thereby reducing the amount of hydrophobic solvent remaining in the hollow particles. On the other hand, from the same viewpoint as above, when the skeleton-forming monomer contains more than 50% by mass of an acrylic monomer, hydrocarbon solvents having 4 to 7 carbon atoms are preferred, and hydrocarbon solvents having 5 or 6 carbon atoms are more preferred. Here, the hydrocarbon solvent may be either an aromatic hydrocarbon or an aliphatic hydrocarbon, with aliphatic hydrocarbons being preferred.

[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 manufacturing method of the present disclosure preferably has a dielectric constant of 2.5 or less at 20°C, and more preferably 2.0 or less. The dielectric constant is one of the indicators of the polarity of a compound. When the dielectric constant of the hydrophobic solvent is sufficiently small, such as 2.5 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), octane (1.9), and cyclohexane (2.0). Regarding the dielectric constant at 20°C, reference can be made to values ​​described in known literature (e.g., "Chemical Handbook: Basics," 4th Revised Edition, edited by the Chemical Society of Japan, Maruzen Co., Ltd., published September 30, 1993, pages II-498 to II-503) and other technical information. The method for measuring the relative dielectric constant at 20°C includes, for example, a relative dielectric constant test carried out in accordance with JIS C 2101:1999, 23, at a measurement temperature of 20°C.

[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 hydrophobic solvent encapsulated in oil droplets containing the skeleton-forming monomer and the like. 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 skeleton-forming monomer and the amino group-introducing monomer, because this makes it easier to control the particle size of the hollow particles, increase the porosity while maintaining the strength of the hollow particles, and reduce the amount of residual hydrophobic solvent within the particles. In particular, from the viewpoint of achieving a porosity within the preferred range described below, the content of the hydrophobic solvent in the mixed solution is more preferably 70 to 300 parts by mass, and even more preferably 90 to 200 parts by mass, per 100 parts by mass of the skeleton-forming monomer and the amino group-introducing monomer.

[0041] (C) Polymerization Initiator In the production method of the present disclosure, the mixed liquid preferably contains an oil-soluble polymerization initiator as a polymerization initiator. Methods for polymerizing droplets of the monomer composition after suspending the mixed liquid include emulsion polymerization using a water-soluble polymerization initiator and suspension polymerization using an oil-soluble polymerization initiator. Suspension polymerization can be carried out using an oil-soluble polymerization initiator. The oil-soluble polymerization initiator is not particularly limited as long as it is lipophilic and has a solubility in water of 0.2% by mass or less. Examples of the oil-soluble polymerization initiator include organic peroxides such as benzoyl peroxide, lauroyl peroxide, t-butyl peroxide-2-ethylhexanoate, t-butyl peroxydiethyl acetate, and t-butyl peroxypivalate; and azo compounds such as 2,2'-azobis(2,4-dimethylvaleronitrile), azobisisobutyronitrile, and 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile). Of these, in the production method of the present disclosure, it is preferable to use an organic peroxide as a polymerization initiator. Organic peroxides can easily accelerate the polymerization reaction, thereby reducing the amount of unreacted polymerizable functional groups, and are less likely to leave decomposition products after the polymerization reaction, thereby preventing deterioration of the dielectric properties of hollow particles. Unreacted polymerizable functional groups and decomposition products of the polymerization initiator remaining in the shell increase the molecular mobility of the shell, so if these remain in large amounts, the dielectric loss tangent of the hollow particles may increase.

[0042] The content of the polymerization initiator relative to 100 parts by mass of the skeleton-forming monomer in the mixed solution is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 7 parts by mass, and even more preferably 1 to 5 parts by mass. When the content of the polymerization initiator is equal to or greater than the above-mentioned lower limit, the polymerization reaction can proceed sufficiently, while when the content is equal to or less than the above-mentioned upper limit, there is little risk of the oil-soluble polymerization initiator remaining after completion of the polymerization reaction, and there is also little risk of an unexpected side reaction proceeding.

[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. Examples of dispersion stabilizers include inorganic dispersion stabilizers, organic or inorganic water-soluble polymer stabilizers, and surfactants. In the present disclosure, inorganic dispersion stabilizers are preferably used as the dispersion stabilizer because they facilitate control of the particle size of the droplets in the suspension, narrow the particle size distribution of the resulting hollow particles, and prevent the shell from becoming too thin, thereby suppressing a decrease in the strength of the hollow particles. Examples of inorganic dispersion stabilizers include sulfates such as barium sulfate and calcium sulfate; carbonates such as barium carbonate, calcium carbonate, and magnesium carbonate; phosphates such as calcium phosphate; metal oxides such as aluminum oxide and titanium oxide; metal hydroxides such as aluminum hydroxide, magnesium hydroxide, calcium hydroxide, barium hydroxide, and ferric hydroxide; and inorganic compounds such as silicon dioxide. These inorganic dispersion stabilizers can be used alone or in combination of two or more. Among the inorganic dispersion stabilizers, poorly water-soluble inorganic dispersion stabilizers are preferred, and poorly water-soluble metal salts such as the sulfates, carbonates, phosphates, and metal hydroxides mentioned above are more preferred, metal hydroxides are even more preferred, and magnesium hydroxide is 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. 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.Examples of organic water-soluble polymer stabilizers include polyvinyl alcohol, polycarboxylic acids (such as polyacrylic acid), celluloses (such as hydroxyethyl cellulose, carboxymethyl cellulose, methyl cellulose, and ethyl cellulose), polyvinylpyrrolidone, polyacrylimide, polyethylene oxide, and poly(hydroxystearic acid-g-methyl methacrylate-co-methacrylic acid) copolymers. Examples of inorganic water-soluble polymer compounds include sodium tripolyphosphate. Surfactants are compounds that have both hydrophilic and hydrophobic groups in one molecule, and examples include known ionic surfactants such as anionic surfactants, cationic surfactants, and amphoteric surfactants, as well as nonionic surfactants.

[0045] 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 skeleton-forming monomer and hydrophobic solvent. By having the content of the dispersion stabilizer equal to or greater than the above-mentioned 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 above-mentioned 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.

[0046] (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.

[0047] 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.

[0048] A mixed solution is obtained by mixing the above-mentioned materials and, if necessary, other materials and stirring them appropriately. In this mixed solution, an oil phase containing lipophilic materials such as (A) the skeleton-forming monomer, (B) the hydrophobic solvent, and (C) the polymerization initiator is dispersed in an aqueous phase containing, for example, (D) the dispersion stabilizer and (E) the aqueous medium, with particles of about several millimeters in size. The dispersion state of these materials in the mixed solution can be observed with the naked eye, depending on the type of material. In the mixed solution preparation step, the mixed solution may be obtained by simply mixing the above-mentioned materials and, if necessary, other materials and stirring appropriately. However, in terms of facilitating the formation of a uniform shell, it is preferable to prepare a mixed solution by separately preparing an oil phase containing the skeleton-forming monomer, the hydrophobic solvent, and the polymerization initiator and an aqueous phase containing the dispersion stabilizer and the aqueous medium in advance and 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.

[0049] (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 above-mentioned mixed liquid. 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 those manufactured by Pacific Machinery Works, Ltd. (product name: Milder), those manufactured by Eurotec Co., Ltd. (product name: Cavitron), and those manufactured by IKA (product name: DISPAX-REACTOR (registered trademark) DRS series); and emulsifying dispersers such as those manufactured by Primix Corporation (homomixer MARK II series).

[0050] 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 50 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.

[0051] 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 skeleton-forming 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 skeleton-forming 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.

[0052] (3) Precursor Composition Preparation Step This step involves subjecting the suspension obtained in the suspension step described above to a polymerization reaction, adding an amino group-introducing monomer during the polymerization reaction, and further carrying out the polymerization reaction to prepare a precursor composition containing precursor particles having a shell containing a polymer of a backbone-forming monomer and an amino group-introducing monomer and having an amino group on its outer surface, and a hollow portion surrounded by the shell and containing a hydrophobic solvent in the hollow portion. The precursor particles are formed by polymerization of the backbone-forming monomer contained in droplets of the monomer composition and the amino group-introducing monomer added during the polymerization reaction. Note that in the present disclosure, the polymerization reaction before the addition of the amino group-introducing monomer may be referred to as the first polymerization reaction, and the polymerization reaction after the addition of the amino group-introducing monomer may be referred to as the second polymerization reaction.

[0053] As the amino group-introducing monomer, a polymerizable monomer containing a radical polymerizable group and an amino group is used. Here, as the radical polymerizable group, from the viewpoint of excellent reactivity, at least one selected from a (meth)acryloyl group, a vinyl group, and an allyl group is preferable, and a (meth)acryloyl group is more preferable. As the amino group, a monovalent functional group (-NH ２ , -NHR, -NRR') may be used, but in particular, -NH ２ or -NHR is preferred. Here, R and R' in -NHR and -NRR' represent organic groups. From the viewpoint of improving the adhesion of the hollow particles to the resin, R and R' are preferably alkyl groups having 6 or less carbon atoms, and more preferably alkyl groups having 4 or less carbon atoms. Furthermore, R is also preferably an organic group containing a radically polymerizable group. Among the organic groups containing a radically polymerizable group, allyl groups, (meth)acryloyl groups, and groups in which the terminal hydrogen atom of an alkyl group is substituted with at least one radically polymerizable group selected from (meth)acryloyl groups, vinyl groups, and allyl groups are preferred. Here, the number of carbon atoms in the alkyl group is preferably 1 to 6, and more preferably 1 to 4.

[0054] Furthermore, in order to improve the adhesion of hollow particles to resins, it is preferable that the amino group-introducing monomer has a radically polymerizable group at one end and an amino group at the other end via a linking group. Examples of the linking group include a linking group containing a chain structure, preferably having 2 to 10 atoms, more preferably 3 to 6 atoms, a linking group containing a cyclic structure such as a cyclohexane or benzene ring, and combinations thereof. The chain structure may have a branched chain or a substituent, and the cyclic structure may have a substituent. The linking group may be composed of a hydrocarbon or may contain a heteroatom. The linking group preferably contains an alkylene group having 1 to 6 carbon atoms, and more preferably an alkylene group having 2 to 4 carbon atoms. When an amino group-introducing monomer having a radically polymerizable group at one end and an amino group at the other end is introduced to the surface of hollow particles via a linking group, the adhesion between the hollow particles and the resin is likely to be improved. Since the amino group is present at the end of the linking group extending from the particle surface, it is presumed that the amino group is more likely to react with the functional group of the resin. Therefore, hollow particles into which amino groups have been introduced using such amino group-introducing monomers have excellent adhesion to resins even if the amount of amine per unit area is relatively small.

[0055] Furthermore, as the amino group-introducing monomer, a polymerizable monomer having multiple radical polymerizable groups and an amino group is also preferably used. It is presumed that such an amino group-introducing monomer easily reacts on the shell surface due to the multiple radical polymerizable groups, and therefore easily introduces an amino group onto the shell surface.

[0056] The amino group-introducing monomer has a solubility in water at 20°C that is greater than that of the hydrophobic solvent and is 0.5 g / L to 1000 g / L, preferably 0.5 g / L to 80 g / L. This allows the amino group-introducing monomer to be easily incorporated into the surface of the shell during the polymerization reaction. The solubility of the amino group-introducing monomer in water at 20°C is preferably 70 g / L or less, more preferably 60 g / L or less, and even more preferably 50 g / L or less, and is preferably 1.0 g / L or more, more preferably 2.0 g / L or more.

[0057] In addition, since the amino group-introducing monomer is easily incorporated into the surface of the shell during the polymerization reaction, the molecular weight of the amino group-introducing monomer is preferably 300 or less, more preferably 200 or less. The lower limit of the molecular weight of the amino group-introducing monomer is not particularly limited, and is usually 50 or more.

[0058] Examples of amino group-introducing monomers having a radical polymerizable group at one end and an amino group at the other end via a linking group include 2-(tert-butylamino)ethyl (meth)acrylate, 4-vinylbenzylamine, dimethylaminoethyl (meth)acrylate, and diethylaminoethyl (meth)acrylate. Among these, from the viewpoint of improving the adhesion of hollow particles to resin, 2-(tert-butylamino)ethyl (meth)acrylate and 4-vinylbenzylamine are preferred, and 2-(tert-butylamino)ethyl (meth)acrylate is more preferred. Note that 2-(tert-butylamino)ethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, and diethylaminoethyl (meth)acrylate have a (meth)acryloyl group at one end and -O-(CH ２ ) ２ 4-Vinylbenzylamine has a vinyl group at one end and an amino group at the other end via -Ph-CH ２- (where Ph is a p-phenylene group) and has an amino group at the other end. As an amino group-introducing monomer having a plurality of radical polymerizable groups and an amino group, for example, diallylamine can be preferably used.

[0059] The amount of the amino group-introducing monomer added is preferably 2% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more relative to 100% by mass of the total of the backbone-forming monomer and the amino group-introducing monomer contained in the mixed solution in order to introduce a sufficient amount of amino groups onto the surface of the hollow particles from the viewpoint of adhesion to the resin. The upper limit is preferably 40% by mass or less, more preferably 30% by mass or less relative to 100% by mass of the total of the backbone-forming monomer and the amino group-introducing monomer contained in the mixed solution in order to obtain performance such as dielectric properties attributable to the composition of the backbone-forming monomer.

[0060] Furthermore, in the production method of the present disclosure, in order to obtain spherical hollow particles having hollow portions therein, the content of the crosslinkable monomer is set to 60% by mass or more relative to 100% by mass of the total of the skeleton-forming monomer and the amino group-introducing monomer, and further, from the viewpoint of improving the solvent resistance, strength, pressure resistance, heat resistance, etc. of the hollow particles, the content is preferably 70% by mass or more, more preferably 80% by mass or more. The upper limit of the content of the crosslinkable monomer is not particularly limited, and when the skeleton-forming monomer or the amino group-introducing monomer contains a non-crosslinkable monomer, the content may be 98% by mass or less, 95% by mass or less, 90% by mass or less, or 85% by mass or less relative to 100% by mass of the total of the skeleton-forming monomer and the amino group-introducing monomer.

[0061] In the manufacturing method of the present disclosure, the suspension obtained in the suspension step is subjected to a polymerization reaction. When the polymerization conversion rate of the skeleton-forming monomer in the suspension reaches 1% by mass or more and 99% by mass or less, the amino group-introducing monomer is added to further carry out the polymerization reaction. From the viewpoints of efficiently introducing amino groups onto the surfaces of the hollow particles and improving the dielectric properties of the hollow particles, the polymerization conversion rate of the skeleton-forming monomer in the suspension when the amino group-introducing monomer is added is preferably 3% by mass or more, more preferably 5% by mass or more, even more preferably 10% by mass or more, still more preferably 15% by mass or more, and may even be 40% by mass or more. Meanwhile, the polymerization conversion rate is preferably 90% by mass or less, more preferably 80% by mass or less, even more preferably 70% by mass or less, and even more preferably 60% by mass or less. The polymerization conversion rate of the backbone-forming monomer when adding an amino group-introducing monomer having a radical polymerizable group at one end and an amino group at the other end via a linking group is preferably 5 to 90% by mass, more preferably 10 to 70% by mass. The polymerization conversion rate of the backbone-forming monomer when adding an amino group-introducing monomer having multiple radical polymerizable groups and an amino group is preferably 3 to 75% by mass, more preferably 10 to 70% by mass. In the present disclosure, the polymerization conversion rate can be calculated using the following formula (C) from the mass of the backbone-forming monomer contained in the suspension before the addition of the amino group-introducing monomer and the mass of the unreacted backbone-forming monomer contained in the suspension immediately before the addition. Here, the mass of the backbone-forming monomer contained in the suspension before the addition of the amino group-introducing monomer is the total mass of the backbone-forming monomer after the polymerization reaction and the unreacted backbone-forming monomer. The mass of the unreacted backbone-forming monomer can be measured using gas chromatography (GC). Equation (C): Polymerization conversion rate (mass %)=100−(mass of unreacted skeleton-forming monomer / mass of skeleton-forming monomer contained in suspension)×100

[0062] In the production method of the present disclosure, the polymerization method for the polymerization reaction is not particularly limited, and for example, a batch method, a semi-continuous method, a continuous method, etc. can be employed. The polymerization temperature is preferably 40 to 90°C, more preferably 50 to 80°C. The temperature increase rate when raising the temperature to the polymerization temperature is preferably 10 to 60°C / h, more preferably 15 to 55°C / h. The polymerization reaction time, which is the total time of the first polymerization reaction carried out before adding the amino group-introducing monomer and the second polymerization reaction carried out after adding the amino group-introducing monomer, is preferably 1 to 48 hours, more preferably 4 to 36 hours. The reaction times for the first and second polymerization reactions may be appropriately adjusted so that the polymerization conversion of the backbone-forming monomer at the time of adding the amino group-introducing monomer falls within the preferred range described above, and are not particularly limited, but for example, after the suspension is heated to the polymerization temperature, the first polymerization reaction is carried out preferably for 1 minute to 8 hours, more preferably for 20 minutes to 8 hours, and even more preferably for 30 minutes to 4 hours, and after the amino group-introducing monomer is added, the second polymerization reaction is carried out preferably for 1 to 48 hours, more preferably for 2 to 44 hours. In the precursor composition preparation step, the shell portion of the droplets of the monomer composition containing the hydrophobic solvent therein is polymerized, and therefore, as described above, hollow portions filled with the hydrophobic solvent are formed inside the obtained precursor particles.

[0063] (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 in the precursor composition preparation step described above.

[0064] 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.

[0065] (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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] Alternatively, the hydrophobic solvent may be removed from the slurry containing precursor particles and an aqueous medium without solid-liquid separation of the precursor composition obtained in the precursor composition preparation 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 of the polymerization reaction performed in the precursor composition preparation 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.

[0070] 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 precursor composition preparation step and before the solid-liquid separation step, without performing solid-liquid separation on the slurry precursor composition obtained in the precursor composition preparation step, 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.

[0071] (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.

[0072] (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.

[0073] 2. Hollow Particles The hollow particles of the present disclosure are hollow particles having a shell containing a resin and a hollow portion surrounded by the shell, wherein the shell contains, as the resin, a polymer containing 60% by mass or more of crosslinkable monomer units, the hollow particles have amino groups on their surfaces, and the amount of amine per unit area calculated from the amine value of the hollow particles and the specific surface area of ​​the hollow particles using the following formula (A) is 5.00 μmol / m ２ Formula (A): Amine amount (μmol / m ２ ) = amine value (μmol / g) / specific surface area (m ２ / g)

[0074] In the hollow particles of the present disclosure, the amount of amine per unit area is 5.00 μmol / m ２ However, from the viewpoint of further improving the adhesion to the resin, it is preferably 6.00 μmol / m ２ More preferably, 6.20 μmol / m ２ The upper limit of the amount of amine per unit area is not particularly limited, but from the viewpoint of obtaining performance such as dielectric properties resulting from the composition of the skeleton-forming monomer, it is preferably 70 μmol / m ２ or less, more preferably 50 μmol / m ２ More preferably, 30 μmol / m or less ２ More preferably, 20 μmol / m or less ２ In the present disclosure, the amine value of the hollow particles is measured by potentiometric titration in accordance with JIS K 7237. In addition, in the present disclosure, the specific surface area of ​​the hollow particles is determined by the volume average particle size and the apparent density D of the hollow particles, assuming that the hollow particles are spherical. １ The volume average particle diameter used in the following formula (B) is a value in units of "m", and the apparent density D １ The unit is "g / m ３ " Formula (B): Specific surface area (m ２ / g) = 6 / (volume average particle size (m) × apparent density D １ (g / m ３ ))

[0075] The hollow particles of the present disclosure typically contain a polymer of the above-described skeleton-forming monomer and amino group-introducing monomer as the main component of the shell. Since the polymer forms the skeleton of the hollow particle shell, the shell of the hollow particles of the present disclosure contains amino group-containing monomer units derived from the above-described amino group-introducing monomer. Preferably, the amino groups present on the surface of the hollow particles of the present disclosure are amino groups contained in the amino group-containing monomer units. In the hollow particles of the present disclosure, the content of the amino group-containing monomer units derived from the amino group-introducing monomer is preferably 2% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more, based on 100% by mass of all monomer units in the polymer contained in the shell, from the viewpoint of adhesion to resins. On the other hand, from the viewpoint of obtaining performance such as dielectric properties attributable to the composition of the skeleton-forming monomer units, the content is preferably 40% by mass or less, more preferably 30% by mass or less.

[0076] In the hollow particles of the present disclosure, the content of the crosslinkable monomer units relative to 100% by mass of all monomer units in the polymer contained in the shell is 60% by mass or more in order to make the hollow particles of the present disclosure spherical and hollow, and is preferably 70% by mass or more, more preferably 80% by mass or more in order to improve the solvent resistance, strength, pressure resistance, heat resistance, etc. of the hollow particles. The upper limit of the content of the crosslinkable monomer units is not particularly limited, and when the polymer contains non-crosslinkable monomer units, the content may be 98% by mass or less, 95% by mass or less, 90% by mass or less, or 85% by mass or less, relative to 100% by mass of all monomer units in the polymer.

[0077] In order to provide the hollow particles of the present disclosure with good dielectric properties, the content of hydrocarbon monomer units is preferably more than 50% by mass, more preferably 60% by mass or more, even more preferably 70% by mass or more, and even more preferably 80% by mass or more, based on 100 parts by mass of all monomer units in the polymer contained in the shell. In the hollow particles of the present disclosure containing hydrocarbon monomer units as the main component, the upper limit of the content of hydrocarbon monomer units is preferably 95% by mass or less, more preferably 90% by mass or less, based on 100 parts by mass of all monomer units in the polymer, in order to ensure a sufficient content of the amino group-containing monomer units.

[0078] In the hollow particles of the present disclosure obtained using an acrylic monomer as a skeleton-forming monomer, the content of the acrylic monomer units relative to 100 parts by mass of all monomer units in the polymer contained in the shell is not particularly limited, but is preferably more than 50% by mass, more preferably 60% by mass or more, even more preferably 70% by mass or more, and even more preferably 80% by mass or more. In this case, the upper limit of the content of the acrylic monomer units is not particularly limited, and the polymer may be composed of acrylic monomer units, may be 95% by mass or less, or may be 90% by mass or less. From the viewpoint of suppressing deterioration of dielectric properties, it may be 80% by mass or less, 70% by mass or less, or may be 60% by mass or less.

[0079] In the hollow particles of the present disclosure, the content of the polymer of the skeleton-forming monomer and the amino group-introducing 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 solids content of the shell. By ensuring that the content of the polymer is equal to or greater than the lower limit, the dielectric properties, strength, pressure resistance, etc. of the hollow particles can be improved.

[0080] 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 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 backbone-forming monomers or amino-group-introducing 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.

[0081] The hollow particles of the present disclosure preferably have a relative dielectric constant of 2.00 or less, more preferably 1.60 or less, and even more preferably 1.40 or less at a frequency of 1 GHz, and the lower limit is not particularly limited, and may be, for example, 1.00 or more. The hollow particles of the present disclosure preferably have a dielectric loss tangent of 3.00×10 at a frequency of 1 GHz. －２ or less, more preferably 5.00 x 10 －３ More preferably, 2.50 x 10 －３ More preferably, 1.00 x 10 －３ The lower limit is not particularly limited, and is, for example, 1.00 × 10 －４ In the present disclosure, the relative permittivity and dielectric loss tangent of hollow particles are measured using a perturbation type measuring device.

[0082] The hollow particles of the present disclosure preferably have a porosity of 50% or more, more preferably 60% or more, even more preferably 65% ​​or more, and even more preferably 70% or more. When the porosity is equal to or greater than the above-mentioned lower limit, the hollow particles have excellent dielectric properties, and are also excellent in terms of lightweightness and heat insulation. The upper limit of the porosity of the hollow particles is not particularly limited, but is preferably 90% or less, more preferably 85% or less, and even more preferably 80% or less, in order to prevent a decrease in the strength of the hollow particles and make them less likely to be crushed.

[0083] The porosity of the hollow particles is the apparent density D１ 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 using 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.

[0084] True density D of hollow particles ０ The measurement method is as follows: After crushing the hollow particles in advance, ３ Approximately 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): True density D 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.

[0085] The porosity (%) of the hollow particles is calculated by multiplying the apparent density D １ and true density D ０The porosity (%) is calculated by the following formula (III): １ / True density D ０ ) x 100

[0086] The volume average particle diameter of the hollow particles of the present disclosure can be adjusted appropriately depending on the application and is not particularly limited. However, the lower limit is preferably 1.00 μm or more, more preferably 1.50 μm or more, and even more preferably 2.00 μm or more. When the volume average particle diameter of the hollow particles is equal to or greater than the above-mentioned lower limit, the tendency for the hollow particles to aggregate with each other is reduced, thereby enabling excellent dispersibility to be exhibited. The upper limit of the volume average particle diameter of the hollow particles of the present disclosure is preferably 10.00 μm or less, more preferably 8.00 μm or less, and even more preferably 5.00 μm or less, for hollow particles used to reduce the dielectric constant or dielectric loss tangent. Hollow particles having a volume average particle diameter equal to or less than the above-mentioned upper limit are sufficiently small that they are suitable for use as substrate materials for electronic circuit boards and the like, and can be added to thin, small substrates. On the other hand, from the viewpoint of a balance between pressure resistance and mechanical strength, the volume average particle diameter is preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 20 μm or less.

[0087] 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.

[0088] 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 compressive strength characteristics and heat resistance can be obtained. Furthermore, when manufacturing a sheet-shaped resin molded product containing the hollow particles of the present disclosure, 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.

[0089] 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 tend to aggregate more easily than spherical particles when dispersed in a binder resin, 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 binder resin, aggregates tend to form, and the aggregates are more susceptible to external pressure, further worsening the pressure resistance. Therefore, reducing the proportion of irregularly shaped particles contained in the hollow particles can improve the dispersibility and pressure resistance of the hollow particles. The hollow particles of the present disclosure may contain a small amount of impurities, such as particles with low circularity due to cracking or deformation. However, the proportion of particles with a circularity of 0.85 or less, based on 100% by mass of the hollow particles of the present disclosure, is preferably 10% by mass or less, more preferably 7% by mass or less, even more preferably 5% by mass or less, even more preferably 4% by mass or less, and particularly preferably 3% by mass or less. Circularity is defined as the value obtained by dividing the diameter of a circle having the same area as the projected image of the particle (equivalent circle area diameter) by the diameter of a circle having the same perimeter as the projected image of the particle (equivalent circumferential diameter). A perfectly spherical particle has a circularity of 1, and the more complex the particle's surface shape, the smaller the circularity. In the present disclosure, circularity is measured using a flow-type particle image analyzer with an image resolution of 0.185 μm / pixel. A preferred example of a flow-type particle image analyzer is the "IF-3200" manufactured by Jasco International, Inc. 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.

[0090] In the present disclosure, the thermal decomposition onset temperature of the hollow particles is preferably 150 to 400°C, more preferably 200 to 350°C. Hollow particles having a thermal decomposition onset temperature within the above range have excellent heat resistance. In the present disclosure, the thermal decomposition onset temperature of the hollow particles is the temperature at which a weight loss of 5% occurs, and can be measured using a TG-DTA device in an air atmosphere under conditions of an air flow rate of 230 mL / min and a temperature rise rate of 10°C / min.

[0091] Examples of uses of the hollow particles of the present disclosure include additives for low-dielectric, heat-insulating, sound-insulating, and light-reflecting components 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. The hollow particles of the present disclosure are resistant to crushing during mixing with other materials and molding after mixing, and when added to molded bodies, they exhibit excellent effects as lightweight materials, heat-insulating materials, soundproofing materials, and vibration-damping materials, making them suitable as additives for molded bodies. They are also resistant to crushing during mixing with resins and molding after mixing, and have excellent adhesion to resins, making them suitable as additives for resin molded bodies. The hollow particles of the present disclosure can also be incorporated as a filler in fiber-reinforced molded bodies formed using resin and reinforcing fibers. The hollow particles of the present disclosure, which have excellent dielectric properties, are suitable for use in electrical or electronic fields as additives for achieving low dielectric constants or low transmission losses, for example, as materials for electronic circuit boards. Specifically, by incorporating the hollow particles of the present disclosure into an insulating resin layer of an electronic circuit board, the relative dielectric constant of the insulating resin layer can be reduced, thereby reducing the transmission loss of the electronic circuit board. 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 substrates, high-frequency device modules, antenna modules, and automotive radar. Among these, the hollow particles are particularly suitable as additives in semiconductor materials such as interlayer insulating materials, solder resists, magnet wires, 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 have high porosity, are difficult to crush, and have excellent heat resistance, so they meet the heat insulation and shock-absorbing properties (cushioning properties) required for undercoating materials and also meet the heat resistance required for thermal paper applications.The hollow particles of the present disclosure are also useful as plastic pigments that are excellent in 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.

[0092] 3. Resin Composition The resin composition of the present disclosure contains the hollow particles of the present disclosure and a binder resin having a functional group capable of reacting with an amino group.

[0093] [Binder Resin] The binder resin having a functional group reactive with an amino group only needs to have a functional group reactive with an amino group when mixed with the hollow particles of the present disclosure. After the amino group of the hollow particle reacts with the functional group of the binder resin to form a crosslinked bond, the binder resin does not need to have the functional group. In the present disclosure, the reaction between the amino group on the surface of the hollow particle and the functional group of the binder resin may be a reaction that forms a covalent bond, such as an addition reaction, a substitution reaction, a dehydration condensation reaction, or an aminolysis reaction. Furthermore, the binder resin having a functional group reactive with an amino group may be an unreacted monomer, prepolymer, or macromonomer, a polymer, or a precursor of a curable resin such as polyamic acid, when mixed with the hollow particles of the present disclosure.

[0094] Examples of functional groups reactive with amino groups include epoxy groups; acidic groups such as carboxy groups, carboxylic acid anhydride groups, and sulfo groups; isocyanate groups; and alkoxycarbonyl groups having 1 to 4 carbon atoms. Among these, at least one selected from the group consisting of epoxy groups, carboxy groups, and carboxylic acid anhydride groups is preferred from the viewpoint of reactivity. Binder resins having these functional groups can be appropriately selected from known resins and are not particularly limited. Examples of preferred binder resins include epoxy resins, polyimide resins, urethane resins, and their precursors or raw materials. Epoxy resins have epoxy groups at least before the curing reaction with a curing agent. Polyimide resins have carboxy groups in the polyamic acid state before the curing reaction (imidization reaction), and the tetracarboxylic acid component, which is the raw material for the polyamic acid, has carboxy groups or carboxylic acid anhydride groups. Urethane resins are obtained by reacting a polyol component having a hydroxyl group with a polyisocyanate component having an isocyanate group, and therefore have hydroxyl groups and isocyanate groups before the curing reaction. Examples of resins having an alkoxycarbonyl group having 1 to 4 carbon atoms include polymethyl (meth)acrylate. Binder resins having these functional groups may be thermosetting resins, thermoplastic resins, adhesives that can be cured at room temperature, or photocurable resins. The binder resin contained in the resin composition of the present disclosure may function as a binder (binding agent) by being cured by heating, light irradiation, or using a curing agent, polymerization initiator, catalyst, or the like. Furthermore, epoxy-based resins, polyimide-based resins, and urethane-based resins have good dielectric properties and are therefore preferably used in applications requiring low dielectric constants and low dielectric loss tangents.

[0095] Examples of epoxy resins include bixylenol type epoxy resins, bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol S type epoxy resins, bisphenol AF type epoxy resins, dicyclopentadiene type epoxy resins, trisphenol type epoxy resins, naphthol novolac type epoxy resins, phenol novolac type epoxy resins, tert-butyl-catechol type epoxy resins, naphthalene type epoxy resins, naphthol type epoxy resins, anthracene type epoxy resins, glycidylamine type epoxy resins, and glycidyl ester type epoxy resins. , cresol novolac type epoxy resins, phenol aralkyl type epoxy resins, biphenyl type epoxy resins, linear aliphatic epoxy resins, epoxy resins having a butadiene structure, alicyclic epoxy resins, heterocyclic epoxy resins, spiro ring-containing epoxy resins, cyclohexane type epoxy resins, cyclohexane dimethanol type epoxy resins, naphthylene ether type epoxy resins, trimethylol type epoxy resins, tetraphenylethane type epoxy resins, isocyanurate type epoxy resins, phenolphthalimidine type epoxy resins, phenolphthalein type epoxy resins, etc. These epoxy resins can be used either alone or in combination of two or more.

[0096] Examples of polyol components used in urethane-based resins include ethylene glycol, propylene glycol, glycerin, trimethylolpropane, pentaerythritol, sorbitol, sucrose, polyoxypropylene triol, polyester polyol, etc. Examples of polyisocyanate components used in urethane-based resins include aliphatic polyisocyanates and aromatic polyisocyanates. Examples of the aliphatic polyisocyanate include polyisocyanates having a chain structure such as tetramethylene diisocyanate, hexamethylene diisocyanate, dodecamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, 2-methylpentane-1,5-diisocyanate, and 3-methylpentane-1,5-diisocyanate; and polyisocyanates having a cyclic structure such as isophorone diisocyanate, hydrogenated xylylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, 1,4-cyclohexane diisocyanate, methylcyclohexylene diisocyanate, and 1,3-bis(isocyanatemethyl)cyclohexane. Examples of aromatic polyisocyanates include tolylene diisocyanate, 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-dibenzyl diisocyanate, 1,5-naphthylene diisocyanate, xylylene diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, dialkyldiphenylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, and α,α,α,α-tetramethylxylylene diisocyanate.

[0097] Polyamic acid, a precursor of polyimide resins, is obtained by reacting a tetracarboxylic acid component, such as a tetracarboxylic acid dianhydride, a tetracarboxylic acid, or a tetracarboxylic acid derivative such as a tetracarboxylic acid diester, with a diamine component. Examples of the tetracarboxylic acid component include benzophenonetetracarboxylic acid dianhydride, 4,4'-oxydiphthalic anhydride, pyromellitic acid and its dianhydride, and 3,3',4,4'-biphenyltetracarboxylic acid and its dianhydride. Examples of the diamine component include paraphenylenediamine and 4,4'-diaminodiphenyl ether.

[0098] Furthermore, examples of binder resins having functional groups reactive with amino groups include modified resins modified with the functional groups. Examples of such modified resins include modified polyolefin resins such as acid-modified polyolefin resins and epoxy-modified polyolefin resins. For example, when the hollow particles of the present disclosure are mixed into a molten modified polyolefin resin, the mixing occurs at a high temperature, and the heat causes a reaction between the functional groups of the modified polyolefin resin and the amino groups of the hollow particles, resulting in the formation of crosslinks.

[0099] The resin composition of the present disclosure may further contain a binder resin not having the functional group in addition to the binder resin having the functional group, as long as the effects of the present disclosure are not impaired. The binder resin not having the functional group can be appropriately selected from, for example, known thermosetting resins, thermoplastic resins, thermoplastic elastomers, and the like. Specific examples include polyethylene, polypropylene, acrylonitrile-butadiene-styrene copolymers (ABS resins), styrene-isoprene-styrene block copolymers (SIS), styrene-butadiene-styrene block copolymers (SBS), styrene-ethylene-propylene-styrene block copolymers (SEPS), and styrene-ethylene-butylene-styrene block copolymers (SEBS). From the viewpoint of improving adhesion between the binder resin and the hollow particles, the content of the binder resin not having the functional group is preferably 90 parts by mass or less, more preferably 50 parts by mass or less, per 100 parts by mass of the binder resin having the functional group.

[0100] The content of the binder resin in 100% by mass of the total solid content of the resin composition is not particularly limited, but the lower limit is preferably 50% by mass or more, more preferably 60% by mass or more, from the viewpoint of improving mechanical strength, while the upper limit is preferably 95% by mass or less, more preferably 90% by mass or less, from the viewpoint of sufficiently containing hollow particles.

[0101] [Curing Agent] The resin composition of the present disclosure may further contain a curing agent for curing the binder resin. The curing agent can be appropriately selected from known curing agents depending on the type of binder resin, and is not particularly limited. However, examples of curing agents for epoxy resins 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 binder resin.

[0102] [Catalyst] The resin composition of the present disclosure may further contain a catalyst for curing the binder resin. Examples of catalysts used for curing the polyimide resin, i.e., the imidization reaction, include a combination of an organic acid anhydride and an organic base. Examples of organic acid anhydrides include acetic anhydride, propionic anhydride, maleic anhydride, and phthalic anhydride. Examples of organic bases include heterocyclic compounds such as pyridine and picoline; and tertiary amines such as triethylamine and N,N-dimethylaniline. The content of the catalyst is adjusted appropriately depending on the type of binder resin and is not particularly limited.

[0103] [Hollow Particles] The hollow particles contained in the resin composition of the present disclosure are the hollow particles of the present disclosure described above. In the resin composition of the present disclosure, the content of the hollow particles is not particularly limited, but is preferably 5 to 50 mass%, more preferably 5 to 30 mass%, and even more preferably 5 to 15 mass%, based on 100 mass% of the total solids content of the resin composition. When the content of hollow particles is at least the above-mentioned lower limit, the resin composition can be improved in terms of low dielectric constant, weight reduction, heat insulation, and other effects. When the content of hollow particles is at most the above-mentioned upper limit, the resin composition can be sufficiently contained with the binder resin, thereby suppressing deterioration in physical properties when formed into a molded product and improving mechanical strength. Furthermore, although not particularly limited, from the viewpoint of improving adhesion between the binder resin and the hollow particles, the content of hollow particles per 100 parts by mass of the binder resin having a functional group reactive with an amino group is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and preferably 50 parts by mass or less, more preferably 40 parts by mass or less.

[0104] [Other Additives] 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, and a solvent, as necessary, 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 contain organic or inorganic reinforcing fibers such as carbon fiber, glass fiber, aramid fiber, and polyethylene fiber.

[0105] The resin composition of the present disclosure can be obtained, for example, by mixing the hollow particles of the present disclosure, the binder resin, and further additives that are added as needed, a solvent, etc. When the binder resin in the resin composition of the present disclosure is a thermoplastic resin, the hollow particles of the present disclosure and further additives that are added as needed may be added to a molten thermoplastic resin and mixed by melt-kneading.

[0106] The resin composition of the present disclosure may be a resin composition before crosslinking occurs through the reaction of amino groups on the surface of hollow particles with functional groups on the binder resin. In this case, during the process of curing or molding the resin composition of the present disclosure, the amino groups on the surface of hollow particles react with functional groups on the binder resin to form crosslinks, thereby providing excellent adhesion at the interface between the binder resin and the hollow particles. Furthermore, even when the resin composition of the present disclosure contains components other than the hollow particles and the binder resin having functional groups, the adhesiveness at the interface between the binder resin and the hollow particles can be excellent. This is presumably because the functional groups on the binder resin have a high affinity with the amino groups on the surface of the hollow particles, which allows the binder resin having functional groups to be unevenly distributed around the hollow particles in the resin composition, thereby allowing crosslinking between the functional groups and the amino groups on the surface of the hollow particles. Examples of methods for forming crosslinks by reacting amino groups on the surfaces of hollow particles with functional groups on the binder resin include heating the resin composition of the present disclosure. Here, heating may be, for example, heating to reduce the melt viscosity of the resin for molding when the binder resin is a thermoplastic resin, heating to cure the resin when the binder resin is a thermosetting resin, or heating to dry the resin composition when the resin composition contains a solvent. The heating conditions are adjusted appropriately depending on the purpose of heating and are not particularly limited. However, from the viewpoint of reacting the amino groups on the hollow particles with the functional groups on the binder resin, heating is preferably performed at a temperature of 50 to 300°C for a total of 1 to 24 hours. Alternatively, the hollow particles and binder resin may be mixed and the binder resin cured at room temperature, whereby crosslinks are formed by reacting the amino groups on the surfaces of the hollow particles with the functional groups on the binder resin during the curing reaction.

[0107] The resin composition of the present disclosure may be a liquid resin composition. The binder resin contained in the liquid resin composition may be a liquid binder resin before a curing reaction, may be dissolved or dispersed in a solvent, or may be a molten thermoplastic resin. The resin composition of the present disclosure may be a resin molded product obtained by forming the liquid resin composition into a resin molded product by a known method.

[0108] The resin molded product of the present disclosure comprises hollow particles derived from the hollow particles of the present disclosure and a binder resin, wherein the shells of the hollow particles are cross-linked to the binder resin. The binder resin contained in the resin molded product of the present disclosure is a solidified product. The solidified binder resin is a resin that has solidified with or without a chemical reaction, such as a resin that has hardened by a curing reaction, a resin that has solidified by drying, or a thermoplastic resin that has solidified by cooling. The resin molded product obtained using the above-described resin composition contains, as the binder resin, a cured product of a resin that has been cured using a curing agent, a polymerization initiator, a catalyst, or the like, as necessary. In this case, the binder resin may contain a curing agent, etc. The resin molded product of the present disclosure obtained by melt-kneading and molding the hollow particles of the present disclosure with a thermoplastic resin contains, as the binder resin, a solidified product of the thermoplastic resin that has solidified by cooling. In the resin molded article of the present disclosure, the hollow particles impart properties such as low dielectric constant, weight reduction, and heat insulation, and further, the excellent adhesion between the binder resin and the hollow particles suppresses deterioration of the resin properties.

[0109] The method for producing a resin molded product of the present disclosure includes, for example, a step of mixing the hollow particles of the present disclosure with a binder resin having a functional group reactive with an amino group (hereinafter referred to as step 1), a step of solidifying the binder resin (hereinafter referred to as step 2), and a step of reacting the amino group of the hollow particles with the functional group of the binder resin (hereinafter referred to as step 3). In the method for producing a resin molded product of the present disclosure, the order of steps 1, 2, and 3 is not particularly limited. For example, steps 2 and 3 may be performed after step 1. In this case, the order of steps 2 and 3 is not particularly limited. If technically possible, steps 2 and 3 may be performed simultaneously. Alternatively, steps 1 and 3 may be performed simultaneously before step 2.

[0110] In the first step, a mixture containing at least the hollow particles of the present disclosure and a binder resin having a functional group capable of reacting with an amino group is prepared. The first step may be a step of preparing the resin composition of the present disclosure.

[0111] In the second step, the mixture obtained in the first step is solidified with or without a chemical reaction, thereby solidifying the binder resin. When the binder resin is cured by a curing agent or a catalyst, the curing agent or catalyst may be added in the second step. When the binder resin is a curable resin, the curing method for the curable resin is not particularly limited, and examples include heating and irradiation with light such as ultraviolet light or electron beams. Alternatively, the binder resin may be cured by adding a catalyst and mixing at room temperature.

[0112] In the third step, the amino groups of the hollow particles are reacted with the functional groups of the binder resin in the mixture obtained in the first step, or in a mixture obtained by further adding a curing agent or catalyst, or in the solidified product obtained in the second step, thereby crosslinking the shells of the hollow particles and the binder resin. The third step may be performed in conjunction with the curing reaction of the binder resin in the second step. For example, if the curing reaction of the binder resin and the reaction between the amino groups of the hollow particles and the functional groups of the binder resin both proceed at room temperature by the addition of a curing agent or catalyst, the second and third steps can be performed simultaneously by adding a curing agent or catalyst to the resin composition of the present disclosure and then curing the resin composition. Alternatively, if the curing reaction of the binder resin and the reaction between the amino groups of the hollow particles and the functional groups of the binder resin both proceed by heat, the second and third steps can be performed simultaneously by heating the resin composition of the present disclosure. When a thermoplastic resin is used as the binder resin, the kneading of the hollow particles with the thermoplastic resin and the subsequent molding are carried out at high temperatures. Therefore, when the binder resin is a thermoplastic resin and the reaction between the amino groups of the hollow particles and the functional groups of the binder resin proceeds due to heat, the third step can be carried out simultaneously with the first or second step.

[0113] The resin molded article of the present disclosure may be, for example, a resin molded article obtained by forming the liquid resin composition of the present disclosure described above into a resin molded article using a known method. In the process of converting the liquid resin composition into a resin molded article, the aforementioned heating or room temperature curing reaction is typically carried out. In the resin molded article, the curing reaction involves the reaction of amino groups present on the hollow particles with functional groups present on the binder resin to form crosslinks. The surfaces of the hollow particles are covalently bonded to the binder resin, resulting in excellent interfacial adhesion between the binder resin and the hollow particles. For example, a liquid resin composition containing hollow particles or the like in a liquid binder resin before the curing reaction, or a liquid resin composition obtained by dissolving or dispersing each component in a solvent, can be applied to a support, and then dried and cured as necessary to obtain the resin molded article of the present disclosure. 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 can be used to apply the liquid resin composition, including dip coating, roll coating, curtain coating, die coating, slit coating, and gravure coating. Alternatively, a resin molded product can be obtained by impregnating a substrate with the liquid resin composition and, if necessary, drying and curing it. Examples of the substrate include inorganic fibers such as carbon fiber, glass fiber, metal fiber, and ceramic fiber, and organic synthetic fibers such as polyamide fiber, polyester fiber, polyolefin fiber, and novoloid fiber. Glass fiber (glass cloth) is preferred. The substrate may be in any form, including woven fabrics and nonwoven fabrics. When the liquid resin composition contains a solvent, it is preferable to dry the liquid resin composition after application or impregnation. The drying temperature is preferably set to a temperature that does not harden the binder resin, 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 that depends on the type of binder resin, and is not particularly limited.When a binder 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. However, it is typically 30°C to 400°C, preferably 70°C to 300°C, and more preferably 100°C to 200°C. The curing time is 5 minutes to 5 hours, preferably 30 minutes to 3 hours. The heating method is not particularly limited, and may be performed using, for example, an electric oven. The liquid binder resin before the curing reaction and the binder resin dissolved or dispersed in a solvent may be a thermosetting resin or a thermoplastic resin. Alternatively, a resin composition containing a thermoplastic resin as a binder resin may be molded into a desired shape using a known molding method such as extrusion molding, injection molding, press molding, or compression molding to obtain a resin molded product. The temperature during melt-kneading is not particularly limited, as long as it is a temperature at which the thermoplastic resin used can be melted. The kneading can be carried out by a known method, and is not particularly limited, but can be carried out using a kneading device such as a single-screw kneader or a twin-screw kneader.

[0114] The shape of the resin molded body is not particularly limited and can be any moldable shape, such as a sheet, a film, a plate, a tube, or any other three-dimensional shape. When the resin molded body contains fibers, the fibers in the resin molded body may be in the form of a nonwoven fabric. When the resin molded body contains fibers, the resin molded body may be a molded body 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.

[0115] 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.

[0116] 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.

[0117] Example 1 (1) Mixed Liquid Preparation Step First, the following materials were mixed to form an oil phase: Divinylbenzene 83.7 parts Ethylvinylbenzene 3.5 parts t-Butylperoxydiethyl acetate (oil-soluble polymerization initiator) 2.3 parts Hydrophobic solvent: Heptane (solubility in water at 20°C: 2.2 mg / L, boiling point 98.4°C) 155.7 parts Next, in a stirring vessel, an aqueous solution prepared by dissolving 19.6 parts of magnesium chloride (a water-soluble polyvalent metal salt) in 225 parts of ion-exchanged water was gradually added with stirring to prepare a magnesium hydroxide colloid (poorly water-soluble metal hydroxide colloid) dispersion (magnesium hydroxide 10 parts), which served as the aqueous phase. The resulting aqueous phase and oil phase were mixed to prepare a mixed liquid.

[0118] (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.

[0119] (3) Precursor Composition Preparation Step: The suspension obtained in the suspension step was heated to 80°C in a nitrogen atmosphere and stirred for 1 hour at 80°C, thereby carrying out a first polymerization reaction. The polymerization conversion rate at the end of the first polymerization reaction was 50%. Subsequently, 12.8 parts of 2-(tert-butylamino)ethyl methacrylate (t-BAEMA) (solubility in water at 20°C: 18 g / L) was added to the stirring tank as an amino group-introducing monomer, and the mixture was stirred for 23 hours at 80°C under a nitrogen atmosphere. This second polymerization reaction yielded a precursor composition that was a slurry liquid in which precursor particles containing a hydrophobic solvent and having amino groups on their surfaces were dispersed in water.

[0120] (4) Washing Step and Solid-Liquid Separation Step The precursor composition obtained in the precursor composition preparation 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 fresh ion-exchanged water was added to re-slurry the mixture. The water washing treatment (washing, filtration, dehydration) was repeated several times at room temperature (25°C), and the mixture was filtered to obtain a solid fraction. The obtained solid fraction was dried in a dryer at a temperature of 40°C to obtain precursor particles encapsulating the hydrophobic solvent.

[0121] (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.

[0122] [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", the amount of divinylbenzene added was changed to 71.4 parts, the amount of ethylvinylbenzene added was changed to 3.0 parts, and in the "(3) precursor composition preparation step", the amount of t-BAEMA added was changed from 12.8 parts to 25.6 parts.

[0123] [Example 3] Hollow particles of Example 3 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 the amount of t-BAEMA added in the "(3) precursor composition preparation step" was changed from 12.8 parts to 22.0 parts. The mixed solution preparation step of Example 3 was carried out as follows. First, the following materials were mixed to form an oil phase. Ethylene glycol dimethacrylate 78.0 parts 2,2'-azobis(2,4-dimethylvaleronitrile) (oil-soluble polymerization initiator) 2.3 parts Hydrophobic solvent: cyclohexane 119.8 parts Next, in a stirring tank, at room temperature, an aqueous solution obtained by dissolving 17.1 parts of magnesium chloride (a water-soluble polyvalent metal salt) in 225 parts of ion-exchanged water was gradually added with stirring to prepare a magnesium hydroxide colloid (poorly water-soluble metal hydroxide colloid) dispersion (magnesium hydroxide 4 parts), which served as the aqueous phase. The resulting aqueous phase and oil phase were mixed to prepare a mixed liquid.

[0124] Example 4 The hollow particles of Example 4 were produced in the same manner as in Example 1, except that in the above "(1) mixed solution preparation step", the amount of divinylbenzene added was changed to 91.2 parts, the amount of ethylvinylbenzene added was changed to 3.8 parts, the amount of t-BAEMA added was changed from 12.8 parts to 5.0 parts, the reaction time of the first polymerization reaction was changed from 1 hour to 0.5 hours, and the reaction time of the second polymerization reaction was changed from 23 hours to 23.5 hours.

[0125] [Example 5] Hollow particles of Example 5 were produced in the same manner as in Example 4, except that the reaction time of the first polymerization reaction was changed from 0.5 hours to 4 hours and the reaction time of the second polymerization reaction was changed from 23.5 hours to 20 hours.

[0126] [Example 6] Hollow particles of Example 6 were produced in the same procedure as in Example 1, except that in the above "(3) Preparing precursor composition step" in Example 1, the reaction time of the first polymerization reaction was changed from 1 hour to 0.2 hours, and the reaction time of the second polymerization reaction was changed from 23 hours to 23.8 hours.

[0127] Example 7 The hollow particles of Example 7 were produced in the same manner as in Example 1, except that in the above "(1) mixed solution preparation step", the amount of divinylbenzene added was changed to 81.4 parts, the amount of ethylvinylbenzene added to 3.4 parts, and the amount of heptane added to 204 parts, and in the above "(3) precursor composition preparation step", the amount of t-BAEMA added was changed from 12.8 parts to 15.2 parts, the reaction time of the first polymerization reaction was changed from 1 hour to 1.5 hours, and the reaction time of the second polymerization reaction was changed from 23 hours to 22.5 hours.

[0128] [Example 8] The hollow particles of Example 8 were produced in the same procedure as in Example 3, except that in the above "(3) precursor composition preparation step", the reaction time of the first polymerization reaction was changed from 1 hour to 0.1 hour, and the reaction time of the second polymerization reaction was changed from 23 hours to 23.9 hours.

[0129] Example 9 The hollow particles of Example 9 were produced in the same procedure as in Example 3, except that in the above "(1) mixed solution preparation step", the amount of ethylene glycol dimethacrylate added was changed to 90.0 parts, in the above "(3) precursor composition preparation step", the amount of t-BAEMA added was changed from 22.0 parts to 10.0 parts, the reaction time of the first polymerization reaction was changed from 1 hour to 0.1 hour, and the reaction time of the second polymerization reaction was changed from 23 hours to 23.9 hours.

[0130] Example 10 The hollow particles of Example 10 were produced in the same manner as in Example 3, except that in the above "(1) mixed solution preparation step", the amount of ethylene glycol dimethacrylate added was changed to 95.0 parts, in the above "(3) precursor composition preparation step", the amount of t-BAEMA added was changed from 22.0 parts to 5.0 parts, the reaction time of the first polymerization reaction was changed from 1 hour to 4 hours, and the reaction time of the second polymerization reaction was changed from 23 hours to 20 hours.

[0131] Example 11 Hollow particles of Example 11 were produced in the same manner as in Example 1, except that in the above "(3) precursor composition preparation step", 12.8 parts of diallylamine (solubility in water at 20°C: 90 g / L) was added instead of 12.8 parts of t-BAEMA, the reaction time of the first polymerization reaction was changed from 1 hour to 0.15 hours, and the reaction time of the second polymerization reaction was changed from 23 hours to 23.85 hours.

[0132] Example 12 Hollow particles of Example 12 were produced in the same manner as in Example 3, except that in the above "(3) precursor composition preparation step", 22 parts of diallylamine was added instead of 22.0 parts of t-BAEMA, the reaction time of the first polymerization reaction was changed from 1 hour to 3 hours, and the reaction time of the second polymerization reaction was changed from 23 hours to 21 hours.

[0133] Example 13 The hollow particles of Example 13 were produced in the same procedure as in Example 1, except that in the above "(1) mixed solution preparation step", 83.7 parts of divinylbenzene and 3.5 parts of ethylvinylbenzene were replaced with 25.7 parts of divinylbenzene, 18.0 parts of ethylvinylbenzene, 22.2 parts of ethylene glycol dimethacrylate, and 20.0 parts of A-TMMT, the amount of t-butylperoxydiethyl acetate added was changed from 2.3 parts to 2.0 parts, and 92.3 parts of hexane was used instead of 155.7 parts of heptane, and in the above "(3) precursor composition preparation step", the reaction time of the first polymerization reaction was changed from 1 hour to 0.2 hours, and the reaction time of the second polymerization reaction was changed from 23 hours to 23.8 hours.

[0134] Comparative Example 1 Hollow particles of Comparative Example 1 were produced in the same manner as in Example 1, except that in the "(1) mixed solution preparation step", the amount of divinylbenzene added was changed to 96.0 parts, and the amount of ethylvinylbenzene added was changed to 4.0 parts, and in the "(3) precursor composition preparation step", t-BAEMA was not added.

[0135] Comparative Example 2 The hollow particles of Comparative Example 2 were produced in the same manner as in Example 2, except that 25.6 parts of t-BAEMA was added to the oil phase in the "(1) mixed solution preparation step" and that t-BAEMA was not added in the "(3) precursor composition preparation step."

[0136] Comparative Example 3 The hollow particles of Comparative Example 3 were produced in the same manner as in Example 1, except that in the "(1) mixed solution preparation step", the amount of divinylbenzene added was changed to 95.0 parts, the amount of ethylvinylbenzene added was changed to 4.0 parts, in the "(3) precursor composition preparation step", the amount of t-BAEMA added was changed from 12.8 parts to 1.0 part, the reaction time of the first polymerization reaction was changed from 1 hour to 4 hours, and the reaction time of the second polymerization reaction was changed from 23 hours to 20 hours.

[0137] Comparative Example 4 Hollow particles for Comparative Example 4 were produced by the following method corresponding to Example 1 of Patent Document 2 (JP 2006-89648 A). First, the following materials were mixed to form an oil phase: 50 parts glycidyl methacrylate, 1.7 parts 2,2'-azobis(isobutyronitrile) (oil-soluble polymerization initiator), and 115 parts hydrophobic solvent: heptane. Next, in a stirring tank, 666.7 parts ion-exchanged water was added at room temperature with 3.3 parts sodium dodecylbenzenesulfonate and 3.3 parts acetyl alcohol to prepare an aqueous solution, which served as the water phase. The resulting water phase and oil phase were mixed to prepare a mixed solution. The resulting mixed solution was stirred for 60 minutes using an ultrasonic homogenizer to obtain a dispersion, which was then stirred for 4 hours at 60°C in a nitrogen atmosphere to carry out a polymerization reaction. Next, 50 parts of diethylenetriamine was added as a crosslinking agent, and the crosslinking reaction was carried out for 6 hours at 80°C, after which the mixture was cooled to room temperature to obtain a slurry. The obtained slurry was dialyzed and filtered to obtain particles containing the hydrophobic solvent, and then vacuum dried to remove the hydrophobic solvent contained in the particles, thereby obtaining hollow particles of Comparative Example 4.

[0138] <Measurement of Polymerization Conversion Rate> In the precursor composition preparation step of each Example and Comparative Example 3, 50 g of the suspension was sampled immediately before the addition of the amino group-introducing monomer, the pH of the suspension was adjusted to 5 to 6, and the suspension was subjected to pressure filtration to separate the polymer precipitate (including water and the hydrophobic solvent) contained in the suspension. After removing the water and hydrophobic solvent by drying at 200°C for 2 hours, the mass of the polymer precipitate was precisely weighed and used as the mass of the skeleton-forming monomer contained in the suspension (the total mass of the skeleton-forming monomer after the polymerization reaction and the unreacted skeleton-forming monomer). This polymer precipitate was dispersed in ethyl acetate, and 2 μL of the resulting dispersion was sampled as a measurement sample. The mass of the unreacted skeleton-forming monomer in the measurement sample was quantified by gas chromatography (GC) under the following conditions, and the mass of the unreacted skeleton-forming monomer contained in the suspension was calculated. The polymerization conversion rate was calculated using the mass of the skeleton-forming monomer contained in the suspension, i.e., the mass of the polymer precipitate, and the mass of the unreacted skeleton-forming monomer contained in the suspension, i.e., the mass of the unreacted skeleton-forming monomer measured by GC, using the following formula (C). Alternatively, if no polymer precipitate was formed, the suspension was adjusted to pH 5 to 6 and separated into two phases, and the oil phase was isolated. 2 μL of the resulting oil phase was collected as a measurement sample, and the amount of polymerized or unreacted skeleton-forming monomer in the measurement sample was quantified by gas chromatography (GC) under the following conditions, and the mass of polymerized or unreacted skeleton-forming monomer contained in the oil phase was calculated. At this time, the non-reactive encapsulating solvent (hydrophobic solvent) contained in the oil phase is divided (divided) to calculate the mass of the unreacted skeleton-forming monomer contained in the oil phase alone. The polymerization conversion rate was calculated from the mass of the skeleton-forming monomer contained in the suspension, i.e., the total mass of the skeleton-forming monomer after the polymerization reaction and the unreacted skeleton-forming monomer contained in the suspension, and the mass of the unreacted skeleton-forming monomer contained in the suspension, using the following formula (C): Formula (C): Polymerization conversion rate (mass %) = 100 - (mass of unreacted skeleton-forming monomer / mass of skeleton-forming monomer contained in suspension) x 100 (GC conditions) Column: TC-WAX (0.25 mm x 30 m) Column temperature: 80°C Injection temperature: 200°C FID detection side temperature: 200°C

[0139] [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, 2 and 3.

[0140] 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])

[0141] 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 using the formula (II): True density D ０ = [Mass of crushed hollow particle fragments] / (100 - [Mass of isopropanol] / [Specific gravity of isopropanol at measurement temperature])

[0142] 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

[0143] 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.

[0144] 3. Measurement of Amine Amount 3-1. Measurement of Amine Value The amine value was measured by potentiometric titration in accordance with JIS K 7237. The specific measurement method is as follows. 2 g of hollow particles were added to 65 mL of a mixed solution of 2-nitrotoluene and acetic acid (volume ratio of 2-nitrotoluene:acetic acid 9:4) and mixed to obtain a sample solution containing hollow particles. The sample solution containing hollow particles was subjected to potentiometric titration using a potentiometric measuring device AT-710 (manufactured by Kyoto Electronics Manufacturing Co., Ltd.) and a 0.1 mol / L perchloric acid / acetic acid solution as the titrant, and the obtained inflection point was taken as the endpoint. Separately from this main test, a blank test was conducted on a solution to which no hollow particles had been added, and the amine value was calculated using the following formula. Amine value (mmol / g) = (V1 - V0) x N x f / S S: Mass of sample solution (g) V1: Volume of titrant in this test (mL) V0: Volume of titrant in blank test (mL) N: Concentration of titrant (mol / L) f: Factor of titrant

[0145] 3-2. Measurement of specific surface area The volume average particle diameter and apparent density D of the hollow particles measured above １ From the above formula (B), the specific surface area (m ２ / g) was calculated.

[0146] 3-3. Calculation of Amine Amount The amine amount per unit area of ​​the hollow particles (μmol / m) was calculated from the amine value of the hollow particles and the specific surface area of ​​the hollow particles using the above formula (A). ２ ) was calculated. In accordance with Rule B of JIS Z8401:1999, the amine value and specific surface area were rounded to two decimal places, and the amine amount was rounded to two decimal places. The amine value used in the above formula (A) was a value converted into the unit "μmol / g".

[0147] 4. Measurement of Dielectric Constant (Dk) and Dielectric Loss Tangent (Df) of Hollow Particles The dielectric constant and dielectric loss tangent of the hollow particles were measured at a frequency of 1 GHz and room temperature (25°C) using a measuring device (manufactured by AET Co., Ltd., model: ADMS01Nc).

[0148] 5. Adhesion to Resin 0.2 g of hollow particles was added to 0.8 g of Agent A (main component: 4,4'-isopropylidenediphenol and 1-chloro-2,3-epoxypropane polycondensate (bisphenol A liquid epoxy resin)) of an epoxy adhesive (product name: Quick 5, manufactured by Konishi Co., Ltd.) and mixed until uniform. 0.9 g of Agent B (curing agent: a mixture of polythiol (curing agent), polyamidoamine (curing agent), tertiary amine (curing agent), and silica) was then added and mixed to form a resin composition. The resulting resin composition was thinly spread to a thickness of approximately 2 mm and left at room temperature for 24 hours to harden and form a molded product. The resulting molded product was split, and the state of the interface between the hollow particles and the resin (epoxy resin) in the cross section was observed using an SEM. More than 100 hollow particles were observed, and the percentage of hollow particles that had undergone cohesive failure was calculated. Adhesion was evaluated according to the following evaluation criteria. Note that hollow particles that have undergone cohesive failure are those in which the shell has been broken, and the higher the adhesion at the interface between the hollow particles and the resin, the more likely cohesive failure occurs. In each example, the hollow particles that have undergone cohesive failure have had their shells broken, but the shape of the hollow portion was maintained. (Adhesion evaluation criteria) A: 90% or more of the hollow particles have undergone cohesive failure B: 70% or more but less than 90% of the hollow particles have undergone cohesive failure C: 50% or more but less than 70% of the hollow particles have undergone cohesive failure D: 20% or more but less than 50% of the hollow particles have undergone cohesive failure E: Less than 20% of the hollow particles have undergone cohesive failure

[0149]

[0150]

[0151]

[0152] Tables 1, 2, and 3 show the amount (parts by mass) of each material added, and the results of each measurement or evaluation. In Tables 1, 2, and 3, the dielectric loss tangent values ​​are expressed in exponential notation as specified in JIS X 0210 for simplification. For example, "1.33 x 10 －３ " is expressed as "1.33E-03". In Tables 1, 2 and 3, the meanings of the abbreviations are as follows: EGDMA: ethylene glycol dimethacrylate t-BAEMA: 2-(tert-butylamino)ethyl methacrylate A-TMMT: pentaerythritol tetraacrylate GMA: glycidyl methacrylate AIBN: 2,2'-azobis(isobutyronitrile)

[0153] [Discussion] In Comparative Example 1, hollow particles were prepared without adding an amino group-introducing monomer in the precursor composition preparation step. Therefore, the resulting hollow particles did not have amino groups on their surfaces and exhibited poor adhesion to resins. In Comparative Example 2, no amino group-introducing monomer was added in the precursor composition preparation step, and t-BAEMA was used as the skeleton-forming monomer. As a result, the resulting hollow particles had an insufficient amount of amine and exhibited poor adhesion to resins. In Comparative Example 2, it is presumed that the amine amount was insufficient because few of the t-BAEMA-derived monomer units were located on the shell surface. The dielectric properties of the hollow particles in Comparative Example 2 were comparable to those of the hollow particles in Example 2. This demonstrated that the dielectric properties were comparable between particles having amino groups on the shell surface and particles having amino groups inside the shell. In Comparative Example 3, although t-BAEMA was added as an amino group-introducing monomer in the precursor composition preparation step, the amount added was small, so the resulting hollow particles had an insufficient amount of amine and exhibited poor adhesion to the resin. In Comparative Example 4, a shell was formed by polymerizing glycidyl methacrylate and then crosslinking with diethylenetriamine, but the resulting hollow particles had an insufficient amount of amine and exhibited poor adhesion to the resin. It is believed that most of the amino groups of the diethylenetriamine used in Comparative Example 4 were used to react with the epoxy groups of glycidyl methacrylate, and therefore insufficient amino groups were present on the surfaces of the hollow particles.

[0154] In contrast, the hollow particles obtained in each example had an amine amount per unit area of ​​5.00 μmol / m ２As described above, the particles had a sufficient amount of amino groups on their surface, and therefore had excellent adhesion to the resin. In each example, in the precursor composition preparation step, when the polymerization conversion rate of the skeleton-forming monomer was 1 to 99 mass %, a sufficient amount of an amino group-introducing monomer containing a radical polymerizable group and an amino group and having suitable water solubility was added and the polymerization reaction was further carried out, which is thought to have enabled a sufficient amount of amino groups to be introduced onto the particle surface. Furthermore, in Examples 1 to 10 and 13, the amino group-introducing monomer had a radical polymerizable group at one end and -O-(CH ２ ) ２It is believed that the use of t-BAEMA, which has an amino group at the other end via a -, facilitates the reaction of the amino group on the particle surface with the functional group of the resin, thereby improving adhesion to the resin. In Examples 11 and 12, diallylamine having multiple radically polymerizable groups and an amino group was used as the amino group-introducing monomer, and amino groups were efficiently introduced onto the particle surfaces. Meanwhile, a comparison of Examples 6 and 11 showed that t-BAEMA had a better amino group introduction efficiency than diallylamine. This is believed to be due to the higher reactivity of methacryloyl groups than allyl groups. Furthermore, the hollow particles obtained in each Example were spherical and hollow, and had a high porosity. This is presumably because the crosslinkable monomer was at least 60% by mass relative to the total of 100% by mass of the skeleton-forming monomer and amino-group-introducing monomer used to prepare the hollow particles. This resulted in sufficient phase separation between the shell-constituting components and the hydrophobic solvent during the suspension process, resulting in the formation of a shell with excellent strength. Furthermore, the dielectric properties of hollow particles tend to deteriorate as the content of amino-group-containing monomer units increases. This tendency is particularly pronounced as the polymer contains more hydrocarbon monomer units. In each example, the amount of amino-group-introducing monomer added was minimized while achieving a sufficient amount of amine per unit area. Therefore, the hollow particles obtained in each example exhibited minimal deterioration in their dielectric properties and an excellent balance between adhesion to resin and their dielectric properties. In particular, the hollow particles of Examples 1, 2, 4 to 7, and 11, whose shells contained a large amount of hydrocarbon monomer units, exhibited low relative permittivity and dielectric loss tangent, resulting in excellent dielectric properties. Among them, Examples 4 and 5 had relatively poor adhesion to the resin due to a relatively small amount of amine, but had a particularly high proportion of hydrocarbon monomer units, resulting in a low dielectric tangent and particularly excellent dielectric properties. Regarding the hollow particles obtained in each Example, 3,000 randomly selected particles were examined, and in all Examples, the proportion of particles with a circularity of 0.85 or less was 10% by mass or less, and the proportion of particles having only one or two hollow portions was 90% by mass or more.

[0155] 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 shell contains, as the resin, a polymer containing 60% by mass or more of a crosslinkable monomer unit, The hollow particles have amino groups on their surfaces, The amount of amine per unit area calculated from the amine value of the hollow particles and the specific surface area of ​​the hollow particles by the following formula (A) is 5.00 μmol / m ２ That's it, hollow particles. Formula (A): Amount of amine (μmol / m ２ ) = amine value (μmol / g) / specific surface area (m ２ / g)

2. 2. The hollow particle according to claim 1, wherein the polymer contains an amino group-containing monomer unit, and the amino group-containing monomer unit is derived from an amino group-introducing monomer that contains a radical polymerizable group and an amino group.

3. 3. The hollow particle according to claim 2, wherein the amino group present on the surface of the hollow particle is an amino group contained in the amino group-containing monomer unit.

4. 4. The hollow particle according to claim 2, wherein the content of the amino group-containing monomer unit is 2% by mass or more and 40% by mass or less relative to 100% by mass of all monomer units contained in the polymer.

5. 4. The hollow particle according to claim 1, wherein the content of hydrocarbon monomer units is more than 50% by mass relative to 100% by mass of all monomer units contained in the polymer.

6. 4. The hollow particle according to claim 1, wherein the content of acrylic monomer units is more than 50% by mass relative to 100% by mass of all monomer units contained in the polymer.

7. The hollow particle according to any one of claims 1 to 3, which has a porosity of 50% or more.

8. A method for producing hollow particles according to any one of claims 1 to 3, comprising the steps of: A step of preparing a mixed liquid containing a skeleton-forming monomer, a hydrophobic solvent, a polymerization initiator, a dispersion stabilizer, and an aqueous medium; a step of suspending the mixed liquid to prepare a suspension in which droplets of a monomer composition containing the skeleton-forming monomer, the hydrophobic solvent, and the polymerization initiator are dispersed in the aqueous medium; and subjecting the suspension to a polymerization reaction, and when the polymerization conversion rate of the skeleton-forming monomer reaches 1% by mass or more and 99% by mass or less, adding an amino group-introducing monomer containing a radical polymerizable group and an amino group, and further carrying out a polymerization reaction, thereby preparing a precursor composition containing precursor particles which contain a polymer of the skeleton-forming monomer and the amino group-introducing monomer, a shell having an amino group on the outer surface, and a hollow portion surrounded by the shell, and which encapsulates the hydrophobic solvent in the hollow portion, the solubility of the amino group-introducing monomer in water at 20°C is greater than that of the hydrophobic solvent and is 0.5 g / L to 1000 g / L; the backbone-forming monomer includes a crosslinkable monomer, and the content of the crosslinkable monomer is 60% by mass or more relative to 100% by mass of the total of the backbone-forming monomer and the amino group-introducing monomer.

9. A method for producing hollow particles according to any one of claims 1 to 3, comprising the steps of: A step of preparing a mixed liquid containing a skeleton-forming monomer, a hydrophobic solvent, a polymerization initiator, a dispersion stabilizer, and an aqueous medium; a step of suspending the mixed liquid to prepare a suspension in which droplets of a monomer composition containing the skeleton-forming monomer, the hydrophobic solvent, and the polymerization initiator are dispersed in the aqueous medium; and subjecting the suspension to a polymerization reaction, and when the polymerization conversion rate of the skeleton-forming monomer reaches 40% by mass or more and 99% by mass or less, adding an amino group-introducing monomer containing a radical polymerizable group and an amino group, and further carrying out a polymerization reaction, thereby preparing a precursor composition containing precursor particles which contain a polymer of the skeleton-forming monomer and the amino group-introducing monomer, a shell having an amino group on the outer surface, and a hollow portion surrounded by the shell, and which encapsulates the hydrophobic solvent in the hollow portion, the solubility of the amino group-introducing monomer in water at 20°C is greater than that of the hydrophobic solvent and is 0.5 g / L to 80 g / L; the backbone-forming monomer includes a crosslinkable monomer, and the content of the crosslinkable monomer is 60% by mass or more relative to 100% by mass of the total of the backbone-forming monomer and the amino group-introducing monomer.

10. A resin composition comprising the hollow particles according to any one of claims 1 to 3 and a binder resin having a functional group capable of reacting with an amino group.

11. The resin composition according to claim 10, wherein the functional group of the binder resin is at least one selected from the group consisting of an epoxy group, a carboxy group, and a carboxylic anhydride group.