Hollow particles

Abstract

The present invention provides a hollow particle having excellent performance stability in a high humidity environment and a low relative dielectric constant. A hollow particle having a shell containing a resin, and a hollow portion surrounded by the shell, the shell containing, as the resin, a polymer containing 70 to 100 parts by mass of crosslinkable monomer units in 100 parts by mass of total monomer units, the hollow particle having a void ratio of 60% or more, a content of a surfactant present on the surface of the hollow particle of 200 ppm or less, and a relative dielectric constant of the hollow particle at a frequency of 1 MHz of 1.6 or less.

Description

Technical Field

[0001] This invention relates to hollow particles. Background Technology

[0002] Hollow granules (hollow resin granules) are granules with cavities inside. Compared to solid granules that are essentially filled with resin, they can scatter light better and reduce light transmittance. Therefore, hollow granules are widely used as organic pigments and masking agents with excellent optical properties such as opacity and whiteness in water-based coatings and paper coating compositions. In recent years, they have also been used as lightweighting agents and heat-insulating agents in resins and coatings used in various fields such as automobiles, electrical appliances, electronics, and construction.

[0003] In electronic materials applications, such as in electronic circuit boards, hollow particles are sometimes incorporated into the insulating resin layer to suppress crosstalk and reduce transmission loss. Crosstalk and transmission loss in electronic circuit boards can be suppressed by reducing the relative permittivity and dielectric loss tangent of the insulating resin layer. Since hollow particles have internal voids, efforts are underway to reduce the dielectric constant and dielectric loss tangent of the insulating resin layer by adding hollow particles.

[0004] For example, Patent Document 1 discloses hollow cross-linked resin particles for use in organic insulating materials with low dielectric constants. These particles are obtained by polymerizing 1 to 100 wt% of a cross-linking monomer with 0 to 99 wt% of a non-cross-linking monomer (here, the total of the cross-linking and non-cross-linking monomers is 100 wt%). The average particle size of these hollow cross-linked resin particles is 0.03 to 10 μm, and the average metal ion concentration present in the particles is 50 ppm or less. The hollow cross-linked resin particles of Patent Document 1 can be manufactured by using an emulsifier (surfactant) to disperse the monomer in water and perform seed polymerization.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent document 1: Japanese Patent Application Publication No. 2000-313818. Summary of the Invention

[0008] The problem the invention aims to solve

[0009] For electronic circuit boards, performance stability in high humidity environments is further required; for example, no migration or other adverse conditions are required. However, the electronic circuit board containing hollow cross-linked resin particles described in Patent Document 1 sometimes experiences migration in high humidity environments. Furthermore, the hollow cross-linked resin particles described in Patent Document 1 are not particles with a sufficiently low relative permittivity, and further reduction of the relative permittivity is required.

[0010] The purpose of this invention is to provide hollow particles with excellent performance stability and low relative permittivity in high humidity environments.

[0011] Solution for solving the problem

[0012] The inventors have discovered that residual surfactants on the surface of hollow particles contained in electronic circuit boards are one of the reasons for the migration of electronic circuit boards in high humidity environments.

[0013] The present invention provides a hollow particle having a shell containing resin and a hollow portion surrounded by the shell.

[0014] The aforementioned shell contains a polymer comprising 70 to 100 parts by mass of crosslinkable monomer units in all monomer units per 100 parts by mass as the aforementioned resin.

[0015] The porosity of the aforementioned hollow particles is over 60%.

[0016] The content of surfactant present on the surface of hollow particles is less than 200 ppm.

[0017] The relative permittivity of the aforementioned hollow particles at a frequency of 1 MHz is below 1.6.

[0018] In the hollow particles of the present invention, the volume average particle size is preferably 1 to 10 μm.

[0019] In the hollow particles of the present invention, the porosity is preferably 90% or less.

[0020] In the hollow particles of the present invention, the metal content is preferably 100 ppm or less.

[0021] Invention Effects

[0022] As described above, according to the present invention, hollow particles with excellent performance stability in high humidity environments and low relative permittivity can be provided. Attached Figure Description

[0023] Figure 1 This is a diagram illustrating an example of a method for manufacturing hollow particles according to the present invention.

[0024] Figure 2This is a schematic diagram illustrating one embodiment of the suspension in the suspension process. Detailed Implementation

[0025] Furthermore, in this invention, the "~" in the numerical range means that the values ​​recorded before and after it are included as the lower limit and upper limit values.

[0026] Furthermore, in this invention, (meth)acrylate represents each of acrylate and methacrylate, (meth)acrylic acid represents each of acrylic acid and methacrylic acid, and (meth)acryloyl group represents each of acryloyl group and methacryloyl group.

[0027] Furthermore, in this invention, a polymerizable monomer refers to a compound having a functional group capable of addition polymerization (in this invention, it is sometimes simply referred to as a polymerizable functional group). In this invention, compounds having an olefinic unsaturated bond as a functional group capable of addition polymerization are generally used as polymerizable monomers.

[0028] As polymerizable monomers, there are non-crosslinked monomers and crosslinked monomers. Non-crosslinked monomers are polymerizable monomers with only one polymerizable functional group, while crosslinked monomers are polymerizable monomers with two or more polymerizable functional groups that form crosslinks in the resin through polymerization.

[0029] The hollow particles of the present invention are characterized by having a shell containing resin and a hollow portion surrounded by the shell.

[0030] The aforementioned shell contains a polymer comprising 70 to 100 parts by mass of crosslinkable monomer units in all monomer units per 100 parts by mass as the aforementioned resin.

[0031] The porosity of the aforementioned hollow particles is over 60%.

[0032] The content of surfactant present on the surface of hollow particles is less than 200 ppm.

[0033] The relative permittivity of the aforementioned hollow particles at a frequency of 1 MHz is below 1.6.

[0034] The hollow particles of the present invention are particles having a shell (outer shell) containing resin and a hollow portion surrounded by the shell.

[0035] In this invention, the hollow portion is a void-like space that is clearly distinct from the shell of a hollow particle formed of resin material. The shell of the hollow particle may have a porous structure, in which case the hollow portion has a size that is clearly distinct from the numerous tiny spaces uniformly dispersed within the porous structure.

[0036] The hollow portion of hollow particles can be confirmed by, for example, SEM observation of the particle cross-section or TEM observation of the particle directly.

[0037] Furthermore, from the viewpoint of achieving a low dielectric constant, the hollow particles of the present invention preferably have a hollow portion filled with a gas such as air or nitrogen, or in a depressurized state close to a vacuum.

[0038] Because hollow particles have hollow interiors, materials containing them are expected to possess properties such as lightweight, heat insulation, and low dielectric constant. However, when the content of surfactants on the surface of hollow particles is high, these surfactants adsorb moisture in high humidity environments, sometimes imparting undesirable properties to the hollow particles. For example, in the case of hollow particles contained in the insulating resin layer of electronic circuit boards, where the particle surface contains a large amount of surfactant, the surfactants adsorb moisture in high humidity environments, making them prone to migration. In contrast, because the content of surfactants on the particle surface of the hollow particles of the present invention is sufficiently reduced, undesirable properties are not imparted to the hollow particles even in high humidity environments, resulting in excellent performance stability.

[0039] Furthermore, in this invention, a surfactant is a compound that simultaneously possesses both hydrophilic and hydrophobic groups in a single molecule, typically comprising compounds used as surfactants. Surfactants generally have a solubility of 1 g / L or more in water at 25°C.

[0040] Furthermore, the hollow particles of the present invention have a porosity of 60% or more, and the polymer contained in the shell contains 70 to 100 parts by mass of crosslinked monomer units out of all monomer units in 100 parts by mass, thus achieving a low dielectric constant. In hollow particles, there is a tendency for a larger internal space to result in a smaller relative dielectric constant. The hollow particles of the present invention have a porosity of 60% or more, thus achieving a low dielectric constant. When the internal space of the hollow particles decreases due to deformation or breakage, there is a tendency for the relative dielectric constant of the hollow particles to increase. However, the hollow particles of the present invention have excellent strength and are not easily deformed because of the high proportion of crosslinked monomer units in the shell and the dense covalent network distributed throughout the shell. Therefore, they can easily maintain the shape of the hollow portion and maintain a low dielectric constant.

[0041] Hereinafter, after describing an example of a method for manufacturing hollow particles according to the present invention, the hollow particles of the present invention will be described in detail.

[0042] 1. Manufacturing method of hollow particles

[0043] The hollow particles of the present invention can be obtained by a method for manufacturing hollow particles including the following steps:

[0044] The process of preparing a mixture comprising a polymerizable monomer, a hydrophobic solvent, a polymerization initiator, a dispersing stabilizer, and an aqueous medium;

[0045] The process of preparing a suspension in an aqueous medium by suspending the above-mentioned mixture, wherein droplets of a monomer composition containing the above-mentioned polymerizable monomer, the above-mentioned hydrophobic solvent, and the above-mentioned polymerization initiator are dispersed in the above-mentioned aqueous medium; and

[0046] The process of preparing a precursor composition comprising precursor particles by feeding the above suspension into a polymerization reaction, wherein the precursor particles have a hollow portion surrounded by a shell containing resin and the above hydrophobic solvent contained within the hollow portion.

[0047] The aforementioned method for manufacturing hollow particles includes a step of preparing a mixture, a step of preparing a suspension, and a step of supplying the suspension to a polymerization reaction, and may also include steps other than these. Furthermore, whenever technically possible, two or more of the aforementioned steps and other additional steps can be performed simultaneously as a single step, or their order can be changed. For example, the preparation and suspension of the mixture can be performed simultaneously in one step so that suspension occurs simultaneously with the material used to prepare the mixture.

[0048] As a preferred example of the manufacturing method of the above-mentioned hollow particles, a manufacturing method including the following steps can be cited.

[0049] (1) Mixture preparation process

[0050] The process of preparing a mixture comprising a polymerizable monomer, a hydrophobic solvent, a polymerization initiator, a dispersing stabilizer, and an aqueous medium;

[0051] (2) Suspension process

[0052] The process of preparing a suspension in an aqueous medium by suspending the above mixture, wherein droplets of a monomer composition containing a polymerizable monomer, a hydrophobic solvent and a polymerization initiator are dispersed in the mixture.

[0053] (3) Polymerization process

[0054] The process of preparing a precursor composition containing precursor particles by feeding the above suspension into a polymerization reaction, wherein the precursor particles have a hollow portion surrounded by a shell containing resin and a hydrophobic solvent contained within the hollow portion.

[0055] (4) Cleaning and solid-liquid separation process

[0056] After washing to remove residual dispersant stabilizer from the precursor composition, the precursor composition is subjected to solid-liquid separation to obtain precursor particles containing a hydrophobic solvent within a hollow portion; and

[0057] (5) Solvent removal process

[0058] The process of removing the hydrophobic solvent contained in the precursor particles obtained by the above solid-liquid separation process to obtain hollow particles.

[0059] Furthermore, in this invention, hollow particles whose hollow portion is filled with a hydrophobic solvent are sometimes considered as intermediates of hollow particles whose hollow portion is filled with gas, and are referred to as "precursor particles." In this invention, "precursor composition" means a composition containing precursor particles.

[0060] Figure 1 This is a schematic diagram illustrating an example of a method for manufacturing hollow particles according to the present invention. Figure 1 (1) to (5) in the diagram correspond to the steps (1) to (5) mentioned above. The white arrows between the diagrams indicate the order of each step. Additionally, Figure 1 These are merely illustrative diagrams, and the manufacturing methods described above are not limited to those shown in the figures. Furthermore, the structure, size, and shape of the materials used in the manufacturing methods of this invention are not limited to the structures, sizes, and shapes of the various materials depicted in these figures.

[0061] Figure 1 Figure (1) is a cross-sectional schematic diagram showing one embodiment of the mixture in the mixture preparation process. As shown in the figure, the mixture includes 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 with low polarity and difficult to mix with the aqueous medium 1. In this invention, the low-polarity material 2 includes a polymerizable monomer, a hydrophobic solvent, and a polymerization initiator.

[0062] Figure 1 (2) is a cross-sectional schematic diagram showing one embodiment of the suspension in the suspension process. The suspension includes an aqueous medium 1 and droplets 10 of a monomer composition dispersed in the aqueous medium 1. The droplets 10 of the monomer composition include a polymerizable monomer, a hydrophobic solvent, and a polymerization initiator, but the distribution within the droplets is not uniform. The droplets 10 of the monomer composition have the following structure: the hydrophobic solvent 4a separates from the material 4b containing the polymerizable monomer, excluding the hydrophobic solvent; the hydrophobic solvent 4a is predominantly present in the central part; the material 4b excluding the hydrophobic solvent is predominantly present on the surface side; and a dispersion stabilizer (not shown) is attached to the surface.

[0063] Figure 1(3) is a cross-sectional schematic diagram showing an embodiment of a precursor composition obtained by a polymerization process, comprising precursor particles containing a hydrophobic solvent within a hollow portion. The precursor composition comprises an aqueous medium 1 and precursor particles 20 dispersed in the aqueous medium 1, each containing a hydrophobic solvent 4a within a hollow portion. The shell 6 forming the outer surface of the precursor particles 20 is formed by the polymerization of polymerizable monomers in droplets 10 of the aforementioned monomer composition, wherein the polymer containing the polymerizable monomers is a resin.

[0064] Figure 1 (4) is a cross-sectional schematic diagram showing one embodiment of the precursor particles after the solid-liquid separation process. Figure 1 (4) shows the above Figure 1 The state of (3) after removing the water medium 1.

[0065] Figure 1 (5) is a cross-sectional schematic diagram showing one embodiment of hollow particles after the solvent removal process. Figure 1 (5) shows the above Figure 1 The state of (4) after removing the hydrophobic solvent 4a. By removing the hydrophobic solvent from the precursor particles, hollow particles 100 with a hollow portion 8 filled with gas inside the shell 6 are obtained.

[0066] The following sections will describe the five processes mentioned above and the other processes in turn.

[0067] (1) Mixture preparation process

[0068] This step involves preparing a mixture comprising a polymerizable monomer, a hydrophobic solvent, a polymerization initiator, a dispersant stabilizer, and an aqueous medium. Without impairing the effects of this invention, the mixture may also contain other materials.

[0069] The materials of the mixture are described in the following order: (A) polymerizable monomers, (B) hydrophobic solvents, (C) polymerization initiators, (D) dispersion stabilizers, (E) aqueous media, and (F) other materials.

[0070] (A) Polymerizing monomers

[0071] In the above manufacturing method, the polymerizable monomers in the mixture include at least crosslinking monomers, and may also include non-crosslinking monomers without impairing the effects of the present invention.

[0072] From the perspective of easy and stable polymerization reaction and obtaining hollow particles with excellent strength and heat resistance, (meth)acrylic acid-based polymerizable monomers with (meth)acryloyl groups as polymerizable functional groups are preferred as polymerizable monomers.

[0073] On the other hand, from the perspective of reducing the relative permittivity and dielectric loss tangent of hollow particles, it is preferable to use hydrocarbon monomers composed of carbon and hydrogen.

[0074] [Crosslinking monomers]

[0075] Crosslinkable monomers have multiple olefinic unsaturated double bonds, which allows them to connect with each other and increase the crosslinking density of the shell.

[0076] Examples of crosslinking monomers include: divinylbenzene, divinylbiphenyl, divinylnaphthalene, diallyl phthalate, allyl acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, and other difunctional crosslinking monomers having two polymerizable functional groups; and trifunctional or higher crosslinking monomers having three or more polymerizable functional groups, such as trimethylolpropane tri(meth)acrylate, bis(trimethylolpropane tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol poly(meth)acrylate, and their ethoxylates. These crosslinking monomers can be used alone or in combination of two or more.

[0077] As difunctional crosslinking monomers, divinylbenzene, ethylene glycol di(meth)acrylate, and pentaerythritol di(meth)acrylate are preferred from the perspectives of easy and stable polymerization reaction, obtaining hollow particles with excellent strength and heat resistance, and reducing the relative permittivity of hollow particles. Ethylene glycol di(meth)acrylate and pentaerythritol di(meth)acrylate are particularly preferred from the perspective of improving the strength and heat resistance of hollow particles. Divinylbenzene, as a hydrocarbon monomer, is preferred from the perspective of further reducing the relative permittivity and dielectric loss tangent of hollow particles.

[0078] As a crosslinking monomer with trifunctionality or higher, from the perspectives of easy and stable polymerization reaction, obtaining hollow particles with excellent strength and heat resistance, and reducing the relative permittivity of hollow particles, pentaerythritol tetra(meth)acrylate, trimethylolpropane tri(meth)acrylate, ethoxylated trimethylolpropane tri(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol poly(meth)acrylate, and more preferably trimethylolpropane tri(meth)acrylate and pentaerythritol tetra(meth)acrylate.

[0079] The content of crosslinking monomers is preferably 70 to 100 parts by mass relative to 100 parts by mass of the total mass of polymerizable monomers in the mixture. By ensuring the content of crosslinking monomers is 70 parts by mass or more, the proportion of crosslinking monomer units in the shell of the hollow particles is sufficiently large. Therefore, the covalent bond network is tightly distributed throughout the shell, resulting in a shell with excellent strength, resistance to breakage, and resistance to deformation from externally applied heat. Furthermore, by ensuring the content of crosslinking monomers is 70 parts by mass or more, the strength of the hollow particles is increased, thus suppressing the increase in relative permittivity caused by breakage or deformation of the hollow particles. The content of crosslinking monomers is preferably 80 parts by mass or more, more preferably 90 parts by mass or more.

[0080] The polymerizable monomer in the mixture preferably includes at least a difunctional crosslinking monomer as the crosslinking monomer. This facilitates the formation of hollow spaces within the particles. From the perspective of easily forming hollow spaces within the particles and further improving the shell strength, a combination of difunctional crosslinking monomers and trifunctional or higher crosslinking monomers is preferred.

[0081] The content of difunctional crosslinking monomers in 100 parts by mass of polymerizable monomers in the mixture is preferably 50 parts by mass or more, more preferably 60 parts by mass or more. When the polymerizable monomers include trifunctional or higher crosslinking monomers as crosslinking monomers, the upper limit of the content of difunctional crosslinking monomers in 100 parts by mass of polymerizable monomers in the mixture is preferably 95 parts by mass or less, more preferably 90 parts by mass or less, and even more preferably 80 parts by mass or less.

[0082] When the polymerizable monomer in the mixture includes a trifunctional or higher crosslinking monomer as a crosslinking monomer, the content of the trifunctional or higher crosslinking monomer in 100 parts by mass of polymerizable monomer in the mixture is not particularly limited. As a lower limit, it is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 20 parts by mass or more. As an upper limit, it is preferably 50 parts by mass or less, and more preferably 40 parts by mass or less.

[0083] [Non-crosslinking monomer]

[0084] Without impairing the effects of the invention, the polymerizable monomers in the mixture may also include non-crosslinked monomers.

[0085] As a non-crosslinking monomer, monovinyl monomers are preferred. A monovinyl monomer is a compound having a single polymerizable vinyl functional group. Examples of monovinyl monomers include: methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, glycidyl methacrylate, 2-hydroxyethyl methacrylate, and other (meth)acrylic acid-based monovinyl monomers; aromatic vinyl monomers such as styrene, vinyltoluene, α-methylstyrene, p-methylstyrene, ethylvinylbenzene, ethylvinylbiphenyl, ethylvinylnaphthalene, and halostyrene; monoolefin monomers such as ethylene, propylene, and butene; (meth)acrylamide monomers and their derivatives such as (meth)acrylamide, N-hydroxymethyl (meth)acrylamide, and N-butoxymethyl (meth)acrylamide; diene monomers such as butadiene and isoprene; vinyl acetate and other carboxylic acid vinyl ester monomers; haloethylene monomers such as vinyl chloride; vinylidene dihaloethylene monomers such as vinylidene chloride; and vinylpyridine monomers. These non-crosslinked monomers can be used alone or in combination of two or more.

[0086] From the perspectives of reactivity and heat resistance, (meth)acrylic acid-based monovinyl monomers are particularly preferred, and at least one selected from butyl acrylate and methyl methacrylate is more preferred. From the perspectives of reducing the relative permittivity and dielectric loss tangent of hollow particles, hydrocarbon monomers such as styrene, vinyltoluene, α-methylstyrene, p-methylstyrene, ethylvinylbenzene, ethylvinylbiphenyl, and ethylvinylnaphthalene are preferred.

[0087] The content of non-crosslinked monomers is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, even more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less, relative to 100 parts by mass of the total mass of polymerizable monomers in the mixture.

[0088] Relative to the total 100 parts by mass of polymerizable monomer and hydrophobic solvent in the mixture, the content of polymerizable monomer is preferably 15 to 50 parts by mass, more preferably 20 to 40 parts by mass, and even more preferably 20 to 30 parts by mass. When the content of polymerizable monomer is within the above range, the balance between the porosity, particle size, and mechanical strength of the hollow particles becomes good.

[0089] Furthermore, from the viewpoint of improving the mechanical strength of hollow particles, the content of polymerizable monomers is preferably 90% by mass or more, and more preferably 95% by mass or more, relative to 100% by mass of the total mass of solid components other than hydrophobic solvents in the material that becomes the oil phase in the mixture.

[0090] Furthermore, in this invention, solid components refer to all components except solvents, and liquid polymerizable monomers are included in solid components.

[0091] (B) Hydrophobic solvents

[0092] The hydrophobic solvent used in the above manufacturing method is a non-polymerizable organic solvent that is poorly soluble in water.

[0093] The hydrophobic solvent acts as a spacer material forming hollow spaces within the particles. In the suspension process described later, a suspension of droplets containing the hydrophobic solvent is obtained, dispersed in an aqueous medium. During the suspension process, phase separation occurs within the droplets of the monomer composition, resulting in the low-polarity hydrophobic solvent easily concentrating within the droplets. Ultimately, within the droplets of the monomer composition, the hydrophobic solvent is distributed internally according to its polarity, while other materials besides the hydrophobic solvent are distributed at the edges.

[0094] Furthermore, in the polymerization process described later, an aqueous dispersion containing hollow particles encapsulated with a hydrophobic solvent is obtained. That is, by concentrating the hydrophobic solvent inside the particles, a hollow portion filled with the hydrophobic solvent is formed inside the obtained precursor particles.

[0095] In the above manufacturing method, the hydrophobic solvent can be appropriately selected according to the type of polymerizable monomer, and there is no particular limitation. Known hydrophobic solvents that can be used include, for example: esters such as ethyl acetate and butyl acetate; ether esters such as propylene glycol monomethyl ether acetate and propylene glycol monoethyl ether acetate; aromatic hydrocarbons such as benzene, toluene, and xylene; and aliphatic hydrocarbons such as hexane, methylhexane, cyclohexane, and methylcyclohexane. These hydrophobic solvents can be used individually or in combination of two or more.

[0096] Particularly preferred is the selection of a hydrophobic solvent such that the HSP distance between the crosslinking monomer in the polymerizable monomer and the hydrophobic solvent is 5.80 or more and 6.50 or less. More preferably, the HSP distance is 5.85 or more and 6.40 or less, and even more preferably 5.90 or more and 6.30 or less. When the HSP distance between the crosslinking monomer and the hydrophobic solvent is within the above range, the polymerizable monomer and the hydrophobic solvent are sufficiently separated in the droplets of the monomer composition, making it easier to form hollow portions within the particles, and the thickness of the shell formed by the polymerization reaction easily becomes uniform.

[0097] HSP distance is an index used to represent the solubility between substances using the Hansen solubility parameter (HSP). It can be determined that the closer the HSP distance is to 0, the higher the miscibility of the substances. HSP is represented as a vector in three-dimensional space (Hansen space) with the dispersion term dD, polarity term dP, and hydrogen bonding term dH as coordinate axes. These three parameters, dD, dP, and dH, represent inherent values ​​for each substance. Software developed by Hansen (software name: Hansen Solubility Parameter in Practice (HSPiP)) contains a database of dD, dP, and dH values ​​for various substances. Furthermore, HSP can be calculated based on the chemical structure of a substance using HSP.

[0098] When the HSP of a mixture of multiple substances is determined, the weighted average of the dD, dP, and dH values ​​of each substance in the mixture and the proportion of each substance is calculated as the dispersion term dD, polar term dP, and hydrogen bonding term dH of the mixture, and the HSP is then determined.

[0099] The HSP distance is the vector distance between two substances obtained from their HSPs. It is calculated using the following formula (A) from the values ​​of the dispersion term dD1, polarity term dP1, and hydrogen bonding term dH1 of one substance, and the values ​​of the dispersion term dD2, polarity term dP2, and hydrogen bonding term dH2 of the other substance.

[0100] Formula (A)

[0101] HSP distance = [4(dD1-dD2)] 2 +(dP1-dP2) 2 +(dH1-dH2) 2 ] 0.5

[0102] Furthermore, in this invention, the HSP distance is a value calculated using HSPip (version 5.3.03). In the aforementioned HSPip, the values ​​of dD, dP, and dH are represented by significant digits up to the first decimal place, and the value of the HSP distance is represented by significant digits up to the second decimal place.

[0103] Furthermore, the boiling point of the hydrophobic solvent is not particularly limited, but from the perspective of ease of removal in the solvent removal process described later, it is preferably 130°C or lower, more preferably 100°C or lower. On the other hand, from the perspective of ease of encapsulation by the precursor particles, it is preferably 50°C or higher, more preferably 60°C or higher.

[0104] Furthermore, when the hydrophobic solvent is a mixed solvent containing multiple 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 included in the mixed solvent is below the aforementioned upper limit value, and it is preferable that the boiling point of the solvent with the lowest boiling point among the solvents included in the mixed solvent is above the aforementioned lower limit value.

[0105] Furthermore, the hydrophobic solvent used in the above manufacturing method preferably has a relative permittivity of 3 or less at 20°C. The relative permittivity is one of the indicators of the polarity of a compound. It can be considered that when the relative permittivity of the hydrophobic solvent is sufficiently small (below 3), phase separation in the polymerizable monomer droplets proceeds rapidly, easily forming hollow structures.

[0106] Examples of hydrophobic solvents with a relative permittivity of 3 or less at 20°C are described below. The values ​​in parentheses are the relative permittivity values.

[0107] Pentane (1.8), Hexane (1.9), Heptane (1.9), Octane (1.9), Cyclohexane (2.0), Benzene (2.3), Toluene (2.4).

[0108] Regarding the relative permittivity at 20°C, one can refer to the values ​​and other technical information recorded in well-known literature (e.g., "Introduction to Chemistry: Fundamentals," revised fourth edition, Maruzen Co., Ltd., published September 30, 1993, pp. II-498 to II-503). As a method for determining the relative permittivity at 20°C, examples include the relative permittivity test performed according to, for example, section 23 of JIS C 2101:1999, with the measurement temperature set to 20°C.

[0109] The porosity of hollow particles can be adjusted by changing the amount of hydrophobic solvent in the mixture. In the suspension process described later, the polymerization reaction is carried out in the state where the hydrophobic solvent is encapsulated in oil droplets containing polymerizable monomers, etc. Therefore, there is a tendency that the higher the content of hydrophobic solvent, the higher the porosity of the hollow particles obtained.

[0110] In this invention, from the perspectives of easily controlling the particle size of hollow particles, increasing the porosity while maintaining the strength of hollow particles, and easily reducing the amount of residual hydrophobic solvent within the particles, it is preferable that the content of hydrophobic solvent in the mixture is 50 parts by mass or more and 500 parts by mass or less relative to 100 parts by mass of polymerizable monomer. More preferably, the content of hydrophobic solvent in the mixture is 60 parts by mass or more and 400 parts by mass or less relative to 100 parts by mass of polymerizable monomer, and even more preferably, 70 parts by mass or more and 300 parts by mass or less.

[0111] (C) Polymerization initiator

[0112] In the above manufacturing method, the mixture preferably contains an oil-soluble polymerization initiator as the polymerization initiator. Methods for suspending the mixture to polymerize droplets of the monomer composition include emulsion polymerization using a water-soluble polymerization initiator and suspension polymerization using an oil-soluble polymerization initiator, which allows suspension polymerization to be performed using an oil-soluble polymerization initiator.

[0113] There are no particular restrictions on oil-soluble polymerization initiators as long as they are lipophilic polymerization initiators with a solubility of less than 2 g / L in water at 25°C. Examples of oil-soluble polymerization initiators include benzoyl peroxide, lauroyl peroxide, tert-butyl peroxide-2-ethylhexanoate, 2,2'-azobis(2,4-dimethylpentanonitrile), azobisisobutyronitrile, and 2,2'-azobis(4-methoxy-2,4-dimethylpentanonitrile).

[0114] The content of oil-soluble polymerization initiator is preferably 0.1 to 10 parts by mass relative to 100 parts by mass of polymerizable monomers in the mixture, more preferably 0.5 to 7 parts by mass, and even more preferably 1 to 5 parts by mass. By keeping the content of oil-soluble polymerization initiator within the above range, the polymerization reaction is fully carried out, and the risk of oil-soluble polymerization initiator residue after the polymerization reaction is completed is small, as is the risk of unexpected side reactions.

[0115] Furthermore, from the perspective of reducing the metal content contained in the shell, it is preferable that the polymerization initiator does not contain metal.

[0116] (D) Dispersant stabilizer

[0117] Dispersion stabilizers are agents used in suspension processes to disperse droplets of a monomer composition in an aqueous medium. In this invention, from the viewpoint of ensuring that the content of surfactant present on the surface of the hollow particles is 200 ppm or less, it is preferable not to use surfactants as dispersion stabilizers. In this invention, inorganic dispersion stabilizers are preferably used. By using inorganic dispersion stabilizers, the droplet size can be easily controlled in the suspension, resulting in a narrower particle size distribution of the obtained hollow particles, thereby preventing the shell from becoming too thin and suppressing a decrease in the strength of the hollow particles. In particular, when inorganic dispersion stabilizers are used in combination with particle size control agents described later, the aforementioned effects of inorganic dispersion stabilizers are easily achieved.

[0118] 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 alumina and titanium oxide; and inorganic compounds such as metal hydroxides such as aluminum hydroxide, magnesium hydroxide, calcium hydroxide, barium hydroxide, and iron hydroxide. One or more of these inorganic dispersion stabilizers can be used.

[0119] Among the above-mentioned inorganic dispersing stabilizers, the preferred ones are water-insoluble metal salts such as sulfates, carbonates, phosphates, and metal hydroxides, with metal hydroxides being more preferred, and magnesium hydroxide being particularly preferred.

[0120] Furthermore, in this invention, the metal salt that is sparingly soluble in water is preferably an inorganic metal salt with a solubility of less than 5 g / L in water at 25°C.

[0121] In this invention, it is particularly preferable to use a water-insoluble inorganic dispersion stabilizer in the form of colloidal particles dispersed in an aqueous medium; that is, to use a water-insoluble inorganic dispersion stabilizer in the form of a colloidal dispersion containing water-insoluble inorganic dispersion stabilizer colloidal particles. By using a water-insoluble inorganic dispersion stabilizer in the form of a colloidal dispersion containing water-insoluble inorganic dispersion stabilizer colloidal particles, the droplet size distribution of the monomer composition can be narrowed. Furthermore, the residual amount of inorganic dispersion stabilizer in the resulting hollow particles can be easily suppressed to a low level through washing.

[0122] Colloidal dispersions containing inorganic dispersant stabilizer particles that are poorly soluble in water 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 (other than alkaline earth metal hydroxides) in an aqueous medium.

[0123] 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.

[0124] As a water-soluble polyvalent metal salt, any polyvalent metal salt exhibiting water solubility other than those belonging to the aforementioned alkaline earth metal salts of hydroxides is acceptable. 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. Furthermore, two or more water-soluble polyvalent metal salts can be used individually or in combination.

[0125] The method for reacting at least one of 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. A method of mixing an aqueous solution of at least one of the above-mentioned alkali metal hydroxides and alkaline earth metal hydroxides with an aqueous solution of the water-soluble polyvalent metal salt is also applicable. From the viewpoint of being able to appropriately control the particle size of the water-insoluble metal hydroxide colloidal particles, the following method is preferred: while stirring the aqueous solution of the water-soluble polyvalent metal salt, an aqueous solution of at least one of the above-mentioned alkali metal hydroxides and alkaline earth metal hydroxides is slowly added to the aqueous solution, thereby achieving mixing.

[0126] Furthermore, from the viewpoint of obtaining hollow particles with a volume average particle size of 1 μm or more and 10 μm or less, it is preferable to use a colloidal dispersion obtained by reacting at least one selected from alkali metal hydroxide and alkaline earth metal hydroxide with a water-soluble polyvalent metal salt in an aqueous medium at a temperature of 20°C or more and 50°C or less.

[0127] The content of the dispersant stabilizer is not particularly limited, but is preferably 0.5 to 10 parts by mass relative to the total mass of 100 parts by mass of the polymerizable monomer and the hydrophobic solvent, more preferably 1.0 to 8.0 parts by mass. By keeping the content of the dispersant stabilizer at or above the aforementioned lower limit, the droplets of the monomer composition can be sufficiently dispersed in the suspension without clogging together. On the other hand, by keeping the content of the dispersant stabilizer at or below the aforementioned upper limit, the viscosity of the suspension can be prevented from increasing during granulation, thus avoiding the undesirable situation of the suspension clogging in the granulator.

[0128] Furthermore, relative to 100 parts by weight of the aqueous medium, the content of the dispersant stabilizer is typically 2 parts by weight or more and 15 parts by weight or less, preferably 3 parts by weight or more and 8 parts by weight or less.

[0129] From the viewpoint of making the volume average particle size of the hollow particles 1 to 10 μm, it is also preferable to make the content of the dispersant stabilizer within the above range.

[0130] (E) Aquatic media

[0131] In this invention, an aqueous medium refers to a medium selected from water, hydrophilic solvents, and mixtures of water and hydrophilic solvents.

[0132] The hydrophilic solvent used in this invention is not particularly limited as long as it can be thoroughly mixed with water without phase separation. Examples of hydrophilic solvents include: alcohols such as methanol and ethanol; tetrahydrofuran (THF); and dimethyl sulfoxide (DMSO).

[0133] In aqueous media, water is preferred due to its polarity. Furthermore, ion-exchanged water is preferred to reduce the metal content contained in the shell.

[0134] When using a mixture of water and a hydrophilic solvent, from the viewpoint of forming droplets of the monomer composition, it is important that the overall polarity of the mixture does not become too low. In this case, for example, the mass ratio of water to hydrophilic solvent (water: hydrophilic solvent) can be 99:1 to 50:50.

[0135] (F) Other materials

[0136] Without impairing the effects of the present invention, the mixture may also contain other materials different from those in (A) to (E) described above.

[0137] The mixture preferably contains a particle size control agent as another material. By including the particle size control agent in the mixture, the droplet size of the monomer composition and the shell thickness of the resulting hollow particles can be appropriately adjusted.

[0138] As particle size control agents, polar resins, such as those described later, or at least one selected from rosin acid, higher fatty acids, and their metal salts, can be used. In the suspension process described later, these particle size control agents can appropriately adjust the particle size of droplets containing a monomer composition comprising a polymerizable monomer and a hydrophobic solvent. In the suspension process, droplets of the monomer composition are formed in an aqueous medium by the action of a dispersant stabilizer. In these droplets of the monomer composition, the material containing the polymerizable monomer, excluding the hydrophobic solvent, undergoes phase separation from the hydrophobic solvent; the hydrophobic solvent tends to be present in the central portion, while the material excluding the hydrophobic solvent tends to be present on the surface side. When the mixture contains a particle size control agent, it is inferred that the particle size control agent tends to be present near the surface of the droplets of the monomer composition, and the dispersant stabilizer adheres to the surface of the droplets. Such a material distribution structure is formed based on the different affinities of each material in the aqueous medium. It can be considered that by including a particle size control agent in the mixture, the droplets of the monomer composition in the suspension exhibit the material distribution structure described above, and the interaction between the dispersant stabilizer and the particle size control agent is generated on the droplet surface. Therefore, the dispersibility of the droplets caused by the dispersant stabilizer changes, and the particle size of the monomer composition droplets can be appropriately adjusted.

[0139] In this invention, polar resin refers to a polymer containing repeating units comprising heteroatoms. Specifically, examples include acrylic resins, polyester resins, and vinyl resins containing heteroatoms.

[0140] Polar resins typically have a solubility of less than 1 g / L in water. In this invention, polar resins differ from surfactants in that they are insoluble in water.

[0141] The aforementioned polar resin can be a homopolymer or copolymer of heteroatom-containing monomers, or a copolymer of heteroatom-containing monomers and heteroatom-free monomers. When the aforementioned polar resin is a copolymer of heteroatom-containing monomers and heteroatom-free monomers, from the perspective of easily controlling the particle size of the hollow particles, the proportion of heteroatom-containing monomer units in 100% by mass of all repeating units constituting the copolymer is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more.

[0142] Examples of heteroatom-containing monomers used in polar resins include methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, acrylic acid, methacrylic acid, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 4-hydroxybutyl methacrylate, methoxy polyethylene glycol (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, and methyl propylene. Glycidyl ester, 4-hydroxybutyl acrylate glycidyl ether, etc., are monovinyl monomers of (meth)acryloyl group; aromatic vinyl monomers containing heteroatoms such as halostyrene and styrenesulfonic acid; vinyl acetate and other carboxylic acid vinyl ester monomers; vinyl chloride and other halovinyl monomers; vinylidene chloride and other dihaloethylene monomers; vinylpyridine monomers; carboxyl-containing monomers such as crotonic acid, cinnamic acid, itaconic acid, fumaric acid, maleic acid, and butene tricarboxylic acid; and epoxy-containing monomers such as allyl glycidyl ether. These heteroatom-containing monomers can be used alone or in combination of two or more.

[0143] Examples of heteroatom-free monomers used in polar resins include: aromatic vinyl monomers such as styrene, vinyltoluene, α-methylstyrene, and p-methylstyrene; monoolefin monomers such as ethylene, propylene, and butene; and diene monomers such as butadiene and isoprene. These heteroatom-free monomers can be used alone or in combination of two or more.

[0144] Regarding the aforementioned polar resin, from the perspective of high compatibility with the aforementioned polymerizable monomers and easy control of the particle size of hollow particles, it is particularly preferred that the total mass of (meth)acrylic acid monovinyl monomer units in 100% by mass of all repeating units constituting the resin is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more of an acrylic resin. It is especially preferred that all repeating units constituting the resin are acrylic resins formed from (meth)acrylic acid monovinyl monomer units.

[0145] Regarding the aforementioned polar resin, from the perspective of easily controlling the particle size of hollow particles, it is particularly preferable that the heteroatom-containing monomer unit contains a polar group-containing monomer unit, which includes a polar group selected from carboxyl, hydroxyl, sulfonic acid, amino, polyoxyethylene, and epoxy groups. Examples of polar group-containing monomers used in polar resins include, for example, monomers similar to the polar group-containing non-crosslinking monomers described later. Two or more polar group-containing monomers can be used individually or in combination. From the perspective of being able to control particle size with a small amount of addition, carboxyl and hydroxyl groups are preferred as polar groups included in the polar group-containing monomer unit contained in the polar resin.

[0146] When the above-mentioned polar resin contains monomer units with polar groups, from the perspective of the ease with which the polar resin can be disposed on the outer surface of the hollow particles and the ease with which the particle size of the hollow particles can be controlled, it is preferable that the polar groups are located at the end of the main chain or side chain or are bonded to the main chain or side chain in a pendant manner.

[0147] In the case where the polar resin does not contain the aforementioned monomer units containing polar groups, the monomer units containing heteroatoms contained in the polar resin are preferably monomer units derived from alkyl (meth)acrylates, from the perspective of high compatibility with the aforementioned polymerizable monomers and easy control of the particle size of hollow particles. From the perspective of high polarity, monomer units derived from alkyl (meth)acrylates are particularly preferred, wherein the alkyl (meth)acrylate preferably has 3 or fewer carbon atoms in the alkyl group, more preferably methyl or ethyl, and even more preferably methyl.

[0148] For the aforementioned acrylic resins as polar resins, from the perspective of high compatibility with the aforementioned polymerizable monomers and easy control of the particle size of hollow particles, polymers or copolymers containing 50.0% by mass or more of methyl methacrylate as a polar resin polymerizable monomer when the total mass of the polar resin polymerizable monomers is taken as 100% by mass are particularly preferred. Furthermore, in this invention, the polymerizable monomers used in the synthesis of polar resins are referred to as polar resin polymerizable monomers.

[0149] For the aforementioned acrylic resin as a polar resin, from the perspective of more easily controlling the particle size of the hollow particles, a copolymer containing 50.0% to 99.9% by mass of methyl methacrylate and 0.1% to 5.0% by mass of a monomer containing the aforementioned polar group is more preferred. A copolymer containing 50.0% to 99.0% by mass of methyl methacrylate and 0.1% to 5.0% by mass of a monomer containing the aforementioned polar group is even more preferred. A copolymer containing 50.0% to 98.0% by mass of methyl methacrylate is even more preferred. A copolymer comprising 1.0% by mass and 5.0% by mass of a (meth)acrylic monovinyl monomer that is different from methyl methacrylate and does not contain the aforementioned polar groups, and 0.1% by mass and 5.0% by mass of a polymerizable monomer for polar resin containing the aforementioned polar groups, particularly preferably a copolymer comprising 50.0% by mass and 98.0% by mass of methyl methacrylate, 1.0% by mass and 5.0% by mass of a (meth)acrylic monovinyl monomer that is different from methyl methacrylate and does not contain the aforementioned polar groups, and 0.2% by mass and 3.0% by mass of a polymerizable monomer for polar resin containing the aforementioned polar groups.

[0150] As a (meth)acrylic monovinyl monomer that is different from methyl methacrylate and does not contain the aforementioned polar groups, from the perspective of being able to control the glass transition temperature, it is preferably selected from at least one of ethyl acrylate and butyl acrylate, and ethyl acrylate is particularly preferred.

[0151] From the viewpoint of compatibility with polymerizable monomers in the mixture, (meth)acrylic acid monovinyl monomers containing the above-mentioned polar groups are preferred as monomers. Furthermore, from the viewpoint of being able to control particle size with a small amount of addition, (meth)acrylic acid monovinyl monomers containing carboxyl or hydroxyl groups are more preferred.

[0152] The aforementioned polar resin can be obtained, for example, by polymerizing a polar resin containing the aforementioned heteroatom-containing monomer using polymerization methods such as solution polymerization and emulsion polymerization.

[0153] Furthermore, when the aforementioned polar resin is a copolymer, the copolymer can be any one of a random copolymer, a block copolymer, or a graft copolymer, preferably a random copolymer.

[0154] Furthermore, from the perspective of improving solubility, the aforementioned polar resin is preferably pulverized into a finer powder.

[0155] The number-average molecular weight (Mn) of the aforementioned polar resin is not particularly limited, but preferably in the range of 3,000 or more and 20,000 or less, more preferably in the range of 4,000 or more and 17,000 or less, and even more preferably in the range of 6,000 or more and 15,000 or less, based on the polystyrene equivalent value determined by gel permeation chromatography (GPC) using tetrahydrofuran. By setting the number-average molecular weight (Mn) of the aforementioned polar resin to the lower limit or above, the solubility of the polar resin is improved, making it easier to control the particle size of the hollow particles. By setting the number-average molecular weight (Mn) of the aforementioned polar resin to the upper limit or below, the reduction in shell strength can be suppressed.

[0156] When using a polar resin as a particle size control agent, the content of the polar resin is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, even more preferably 0.4 parts by mass or more, and even more preferably 0.5 parts by mass or more, relative to 100 parts by mass of polymerizable monomers in the mixture. On the other hand, it is preferably 10.0 parts by mass or less, more preferably 8.0 parts by mass or less, even more preferably 5.0 parts by mass or less, and even more preferably 2.0 parts by mass or less. When the content of the polar resin is at or above the above-mentioned lower limit, it is easy to control the particle size of the hollow particles and the thickness of the shell. When the content of the polar resin is at or below the above-mentioned upper limit, it is possible to suppress the decrease in the content ratio of polymerizable monomers, and thus it is possible to suppress the decrease in shell strength.

[0157] Rosin acid can be obtained from rosins such as rosin, tall oil rosin, and wood rosin.

[0158] Examples of abietic acids derived from rosin include abietic acid, dehydroabietic acid, palustric acid, isopimaric acid, and pimaric acid. The proportions of these abietic acids are not fixed and vary depending on the type of rosin and the pine species and origin of the raw material.

[0159] As abrasive acid and its metal salt, abrasive acid and its alkali metal salt containing more than 50% by mass of abietic acid, dehydroabietic acid, longleaf abietic acid and their hydrides are preferred.

[0160] As higher fatty acids, it is preferable to have 10 to 25 carbon atoms, without a carbon atom in the carboxyl group. Examples of preferred higher fatty acids include lauric acid (CH3(CH2)). 10 COOH), tridecanoic acid (CH3(CH2)) 11 COOH), myristic acid (CH3(CH2)) 12 COOH), pentadecanoic acid (CH3(CH2)) 13COOH), palmitic acid (CH3(CH2)) 14 COOH), heptadecanoic acid (CH3(CH2)) 15 COOH), stearic acid (CH3(CH2)) 16 COOH), arachidic acid (CH3(CH2)) 18 COOH), behenic acid (CH3(CH2)) 20 COOH) and lignin (CH3(CH2)) 22 COOH, etc.

[0161] Metals used as metal salts of rosin acids or higher fatty acids include, for example, alkali metals such as Li, Na, and K, and alkaline earth metals such as Mg and Ca, with alkali metals being particularly preferred, and at least one selected from Li, Na, and K being more preferred.

[0162] When using at least one of rosin acid, higher fatty acids and their metal salts as a particle size control agent, the particle size is adjusted so that the total content of rosin acid, higher fatty acids and their metal salts on the surface of the hollow particles is less than 200 ppm.

[0163] Relative to 100 parts by mass of the polymerizable monomers and hydrophobic solvents in the mixture, the total content of rosin acid, higher fatty acids, and their metal salts is preferably 0.0001 parts by mass or more and 0.02 parts by mass or less, more preferably 0.001 parts by mass or more and 0.01 parts by mass or less, and even more preferably 0.0015 parts by mass or more and 0.006 parts by mass or less. When the above content is at or above the lower limit, it is easy to control the particle size and shell thickness of the hollow particles.

[0164] A mixture can be obtained by mixing the above-mentioned materials with other materials as needed and stirring appropriately. In this mixture, the oil phase containing the above-mentioned (A) polymerizable monomers, (B) hydrophobic solvents, and (C) polymerization initiators, etc., is dispersed in an aqueous phase containing (D) dispersion stabilizers and (E) aqueous media, etc., with a particle size of about several millimeters. The dispersion state of these materials in the mixture can also be observed with the naked eye depending on the type of material.

[0165] In the preparation process of the mixture, a mixture can be obtained by simply mixing the aforementioned materials and other materials as needed, and stirring appropriately. However, from the perspective of easily achieving homogeneity, it is preferable to prepare an oil phase containing a polymerizable monomer, a hydrophobic solvent, and a polymerization initiator, and an aqueous phase containing a dispersing stabilizer and an aqueous medium separately beforehand, and then mix them to prepare the mixture. In this invention, it is preferable to use a colloidal dispersion in which a water-poorly soluble inorganic dispersing stabilizer is dispersed in an aqueous medium in the form of colloidal particles as the aqueous phase.

[0166] By preparing the oil phase and water phase separately in advance and mixing them, it is possible to manufacture hollow particles with a uniform shell composition, and the particle size of the hollow particles can be easily controlled.

[0167] Furthermore, in the method for manufacturing hollow particles of the present invention, the content of surfactant in all solid components contained in the mixture is preferably 200 ppm or less.

[0168] Examples of surfactants include anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants, which are well-known surfactants.

[0169] Examples of anionic surfactants include: carboxylates such as alkali metal salts of higher fatty acids; sulfates such as sulfates of higher alcohols and higher alkyl ethers; sulfonates such as alkylbenzene sulfonates, alkyl sulfonates, and paraffin sulfonates; and phosphates such as phosphates of higher alcohols.

[0170] Examples of nonionic surfactants include: polyethylene glycol-type nonionic surfactants such as ethylene oxide adducts of higher alcohols, ethylene oxide adducts of fatty acids, ethylene oxide adducts of higher alkylamines, and ethylene oxide adducts of polypropylene glycol; and polyol-type nonionic surfactants such as fatty acid esters of polyethylene oxide and glycerol, fatty acid esters of pentaerythritol, fatty acid esters of sorbitol or sorbitan anhydride, alkyl ethers of polyols, and aliphatic amides of alkanolamines.

[0171] Examples of cationic surfactants include quaternary ammonium salts such as alkyltrimethylammonium salts.

[0172] Examples of amphoteric surfactants include amino acid-type amphoteric surfactants such as higher alkyl aminopropionates, and betaine-type amphoteric surfactants such as higher alkyl dimethyl betaine and higher alkyl dihydroxyethyl betaine.

[0173] Furthermore, in this invention, the surfactant also includes polymeric compounds that simultaneously possess both hydrophilic and hydrophobic groups, such as polyvinyl alcohol, methylcellulose, ethylcellulose, polyacrylic acid, polyacrylamide, polyethylene oxide, and poly(hydroxystearic acid-g-methyl methacrylate-co-methacrylic acid) copolymer.

[0174] In addition, there is no particular limitation on the molecular weight of surfactants, which is usually less than 3000.

[0175] (2) Suspension process

[0176] The suspension process is a process 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 mixture.

[0177] There are no particular limitations on the suspension method used to form droplets of monomer compositions. Devices capable of strong stirring, such as inline emulsifiers (horizontal inline dispersers manufactured by Pacific Machine Co., Ltd., trade name: Milder and Eurotec Co., Ltd., trade name: Cavitron; vertical inline dispersers manufactured by IKA, trade name: DRS 2000 / 5, etc.) and high-speed emulsifiers (manufactured by PRIMIX Co., Ltd., trade name: TKHOMOMIXER MARK II type, etc.), can be used.

[0178] In the suspension prepared by the suspension process, droplets of the monomer composition containing the aforementioned oleophilic material and having a particle size of approximately 1–10 μm are uniformly dispersed in an aqueous medium. These droplets of monomer composition are difficult to observe with the naked eye but can be observed using known observation equipment such as an optical microscope.

[0179] During the suspension process, phase separation occurs within the droplets of the monomer composition, causing the low-polarity hydrophobic solvent to tend to concentrate inside the droplets. As a result, in the resulting droplets, the hydrophobic solvent is distributed inside, while materials other than the hydrophobic solvent, such as polymerizable monomers, are distributed at the edges.

[0180] Figure 2 This is a schematic diagram illustrating one embodiment of the suspension in the suspension process. Figure 2 The cross-section of droplet 10 of the monomer composition is schematically shown. Additionally, Figure 2 This is for illustrative purposes only; the suspension in this invention is not necessarily limited to... Figure 2 The suspension shown. Figure 2 A portion corresponds to the above. Figure 1 (2)

[0181] Figure 2 The diagram shows droplets 10 of the monomer composition and polymerizable monomer 4c dispersed in an aqueous medium 1. Droplets 10 are formed by surrounding the oil-soluble monomer composition 4 with a dispersion stabilizer (not shown).

[0182] The monomer composition 4 contains an oil-soluble polymerization initiator 5, as well as a polymerizable monomer and a hydrophobic solvent (none of which are shown).

[0183] Droplet 10 is a tiny oil droplet containing monomer composition 4, and oil-soluble polymerization initiator 5 generates polymerization initiation free radicals inside the tiny oil droplet. Therefore, precursor particles with the target particle size can be produced without causing the tiny oil droplets to grow excessively.

[0184] In suspension polymerization using such an oil-soluble polymerization initiator, there is no opportunity for the polymerization initiator to come into contact with the polymerizable monomer 4c dispersed in the aqueous medium 1. Therefore, by using an oil-soluble polymerization initiator, it is possible to suppress the formation of excess resin particles, such as small, dense particles other than the target hollow resin particles, as byproducts.

[0185] (3) Polymerization process

[0186] This process involves preparing a precursor composition containing precursor particles by feeding the suspension obtained from the aforementioned suspension process into a polymerization reaction. The precursor particles have a hollow portion surrounded by a shell containing a resin, and the hollow portion contains a hydrophobic solvent. The precursor particles are formed by the polymerization of polymerizable monomers contained in droplets of a monomer composition, and the shell of the precursor particles contains the polymer of the aforementioned polymerizable monomers as a resin.

[0187] There are no particular restrictions on the aggregation method; it can be used in batch (intermittent), semi-continuous, and continuous modes, for example.

[0188] The polymerization temperature is preferably 40–80°C, and more preferably 50–70°C.

[0189] The heating rate at which the temperature is raised to the polymerization temperature is preferably 10–60 °C / hour, and more preferably 15–55 °C / hour.

[0190] The polymerization reaction time is preferably 1 to 20 hours, more preferably 2 to 15 hours.

[0191] In the polymerization process, the shell portion of a droplet containing a monomer composition with a hydrophobic solvent is polymerized, thus, as described above, a hollow portion filled with a hydrophobic solvent is formed inside the resulting precursor particles.

[0192] In this process, after the first polymerization reaction in which the suspension is fed to the polymerization reaction, a second polymerization reaction can be carried out by further adding polymerizable monomers to the precursor composition obtained from the first polymerization reaction. By carrying out the polymerization reaction in two stages in this way in the polymerization process, the solvent resistance of the hollow particles can be improved.

[0193] The first polymerization reaction described above preferably proceeds to a polymerization conversion rate of the polymerizable monomer in the suspension that is 93% by mass or more, more preferably 95% by mass or more, even more preferably 98% by mass or more, and even more preferably 99% by mass or more.

[0194] Furthermore, in this invention, the polymerization conversion rate is determined by the following formula (B): the mass of the solid component of the precursor particles in the precursor composition obtained by the first polymerization reaction, and the mass of the polymerizable monomer remaining in an unreacted state after the first polymerization reaction. Moreover, the mass of the unreacted polymerizable monomer can be determined using gas chromatography (GC).

[0195] Polymerization conversion rate (mass%) = 100 - (mass of unreacted polymerizable monomers / mass of solids component of precursor particles) x 100 (Equation B)

[0196] The reaction time for the first polymerization reaction is preferably 0.5 to 5 hours, more preferably 1 to 3 hours.

[0197] The polymerizable monomer added during the second polymerization reaction is not particularly limited. However, from the perspective of improving the solvent resistance and strength of the hollow particles, a polymerizable monomer with a solubility of 0.3 g / L or more in distilled water at 20°C is preferred, and a non-crosslinking monomer with a solubility of 0.3 g / L or more in distilled water at 20°C is more preferred. Examples of preferred polymerizable monomers added during the second polymerization reaction include, for example, alkyl (meth)acrylates having 1 to 5 carbon atoms, (meth)acrylamides and their derivatives, (meth)acrylonitrile, and non-crosslinking monomers containing polar groups. At least one selected from alkyl (meth)acrylates having 1 to 5 carbon atoms and (meth)acrylonitrile is particularly preferred, and at least one selected from methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and acrylonitrile is more preferred.

[0198] As non-crosslinking monomers containing polar groups, examples of preferred non-crosslinking monomers include those containing polar groups selected from carboxyl, hydroxyl, sulfonic acid, amino, polyoxyethylene, and epoxy groups. More specifically, examples include: olefinic unsaturated carboxylic acid monomers such as (meth)acrylic acid, crotonic acid, cinnamic acid, itaconic acid, fumaric acid, maleic acid, and butene tricarboxylic acid; hydroxyl monomers such as (meth)acrylic acid-2-hydroxyethyl ester, (meth)acrylic acid-2-hydroxypropyl ester, and (meth)acrylic acid-4-hydroxybutyl ester; sulfonic acid monomers such as styrene sulfonic acid; amino monomers such as dimethylaminoethyl (meth)acrylic acid and diethylaminoethyl (meth)acrylic acid; polyoxyethylene monomers such as methoxy polyethylene glycol (meth)acrylic acid; and epoxy monomers such as (meth)acrylic acid glycidyl ether, allyl glycidyl ether, and 4-hydroxybutyl acrylate glycidyl ether.

[0199] Furthermore, the molecular weight of the polymerizable monomer added in the second polymerization reaction is not particularly limited, but from the perspective of improving the solvent resistance and strength of the hollow particles, it is preferably 200 or less, more preferably 100 or less. The lower limit of the above molecular weight is not particularly limited, and is generally 50 or more.

[0200] From the perspective of improving the solvent resistance and strength of hollow particles, the amount of polymerizable monomer added during the second polymerization reaction is preferably 3 to 15 parts by mass, more preferably 4 to 10 parts by mass, relative to 100 parts by mass of polymerizable monomer in the mixture.

[0201] The reaction time for the second polymerization reaction is preferably 1 to 6 hours, more preferably 2 to 4 hours.

[0202] By carrying out the two-stage polymerization reaction as described above in the polymerization process, the residual amount of unreacted polymerizable monomers in the obtained hollow particles is preferably 750 ppm or less, more preferably 500 ppm or less, and even more preferably 300 ppm or less.

[0203] Furthermore, in this invention, the residual amount of unreacted polymeric monomer refers to the ratio of the mass of the polymeric monomer remaining in an unreacted state to the mass of the solid component of the hollow particles. Additionally, the mass of the unreacted polymeric monomer can be determined using gas chromatography (GC).

[0204] (4) Cleaning and solid-liquid separation process

[0205] This process is as follows: after washing to remove residual dispersant stabilizer from the precursor composition containing precursor particles obtained from the above polymerization process, the precursor composition is separated into solid and liquid components to obtain a solid component containing precursor particles.

[0206] The cleaning process for removing residual dispersant stabilizers from the precursor composition can be performed, for example, by adding an acid or a base to the precursor composition. When the dispersant stabilizer used is an inorganic compound soluble in acid, it is preferable to add an acid to the precursor composition containing the precursor particles for cleaning. Conversely, when the dispersant stabilizer used is an inorganic compound soluble in base, it is preferable to add a base to the precursor composition containing the precursor particles for cleaning.

[0207] Furthermore, when using an acid-soluble inorganic compound as a dispersant stabilizer, it is preferable to add an acid to the precursor composition containing the precursor particles to adjust the pH, preferably to 6.5 or less, and more preferably to 6 or less. As the added acid, inorganic acids such as sulfuric acid, hydrochloric acid, and nitric acid, as well as organic acids such as formic acid and acetic acid, can be used. Sulfuric acid is particularly preferred from the perspective of high removal efficiency of the dispersant stabilizer and low burden on manufacturing equipment.

[0208] By performing the above cleaning, the metal content contained in the shell can be reduced.

[0209] There is no particular limitation on the method for solid-liquid separation of the precursor composition, and known methods can be used. Examples of solid-liquid separation methods include centrifugation, filtration, and settling. Among these, centrifugation or filtration can be used, and centrifugation can be used from the viewpoint of ease of operation.

[0210] Any process, such as a pre-drying process, can be performed after the solid-liquid separation process and before the solvent removal process described later. Examples of pre-drying processes include: pre-drying the solid components obtained after the solid-liquid separation process using a drying device such as a dryer or a hand dryer.

[0211] (5) Solvent removal process

[0212] This process is to remove the hydrophobic solvent contained within the precursor particles obtained from the above solid-liquid separation process.

[0213] By removing the hydrophobic solvent encapsulated within the precursor particles in a gas and replacing the hydrophobic solvent inside the precursor particles with air, hollow particles filled with gas can be obtained.

[0214] Strictly speaking, "in the gas" in this process refers to an environment where there is absolutely no liquid component outside the precursor particles, or an environment where only a trace amount of liquid component exists outside the precursor particles, to a degree that does not affect the removal of hydrophobic solvents. "In the gas" can be interpreted as either the precursor particles not existing in the slurry or the precursor particles existing in the dry powder. That is, in this process, it is important to remove the hydrophobic solvent in an environment where the precursor particles are in direct contact with the external gas.

[0215] There is no particular limitation on the method for removing hydrophobic solvents from precursor particles in a gas, and known methods can be used. Examples of such methods include vacuum drying, heating drying, airflow drying, or a combination of these methods.

[0216] In particular, when using the heat drying method, the heating temperature needs to be above the boiling point of the hydrophobic solvent and below the highest temperature at which the shell structure of the precursor particles is not damaged. Therefore, the heating temperature varies depending on the composition of the shell in the precursor particles and the type of hydrophobic solvent; for example, the heating temperature can be 50–200°C, 70–200°C, or 100–200°C.

[0217] Through a drying process in a gas, the hydrophobic solvent inside the precursor particles is replaced by an external gas, resulting in hollow particles with gas occupying the hollow part.

[0218] There are no particular limitations on the drying atmosphere; it can be appropriately selected based on the intended use of the hollow particles. Suitable drying atmospheres include, for example, air, oxygen, nitrogen, and argon.

[0219] In addition, the hydrophobic solvent contained in the precursor particles can also be removed by, for example, the following steps: without separating the precursor composition into solid and liquid phases, the hydrophobic solvent contained in the precursor particles is replaced with the aqueous medium of the slurry in which the precursor particles and the aqueous medium are contained; from the viewpoint of reducing the metal content contained in the shell, it is preferable to remove the hydrophobic solvent contained in the precursor particles in a gas.

[0220] (6) Other

[0221] In addition to the processes described in (1) to (5) above, a re-replacement process with a hollow section may also be included.

[0222] The hollow particle re-displacement process involves replacing the gas or liquid inside the hollow particles with other gases or liquids. This displacement alters the internal environment of the hollow particles, allows for the selective encapsulation of molecules within the particles, or enables the modification of the internal chemical structure of the hollow particles according to their intended use.

[0223] 2. Hollow particles

[0224] The hollow particles of the present invention are characterized in that they have a shell containing resin and a hollow portion surrounded by the shell.

[0225] The aforementioned shell contains a polymer comprising 70 to 100 parts by mass of crosslinkable monomer units in all monomer units per 100 parts by mass as the aforementioned resin.

[0226] The porosity of the aforementioned hollow particles is over 60%.

[0227] The content of surfactant present on the surface of hollow particles is less than 200 ppm.

[0228] The relative permittivity of the aforementioned hollow particles at a frequency of 1 MHz is below 1.6.

[0229] The hollow particles of the present invention have a relative permittivity of 1.6 or less at a frequency of 1 MHz, and preferably 1.5 or less from the viewpoint of minimizing the permittivity. The lower limit of the aforementioned relative permittivity of the hollow particles of the present invention is not particularly limited, and is generally 1.0 or more.

[0230] In this invention, the relative permittivity of hollow particles is measured using a perturbation-based measuring device at a measurement frequency of 1 MHz.

[0231] The content of surfactant present on the surface of the hollow particles of the present invention is 200 ppm or less, preferably 100 ppm or less, and more preferably 50 ppm or less. When surfactants are used in the manufacturing process of hollow particles, for example, when the mixture contains surfactants, surfactant residues sometimes remain on the surface of the obtained hollow particles. By not using surfactants as dispersing stabilizers in the manufacturing process of hollow particles, the content of surfactant present on the surface of the hollow particles can be kept to 200 ppm or less.

[0232] Furthermore, in this invention, the content of surfactant present on the surface of hollow particles refers to the ratio of the mass of surfactant present on the surface of hollow particles to the mass of hollow particles. The surfactant present on the surface of hollow particles can be extracted, for example, by ultrasonic treatment of the hollow particles in water. The type and mass of surfactant extracted in water can be determined by… 1 The peak positions and intensities of the H-NMR spectrum are used to determine the peaks.

[0233] Furthermore, the metal content of the hollow particles of the present invention is preferably 100 ppm or less, more preferably 80 ppm or less, and even more preferably 70 ppm or less. Here, the metal also includes metal ions. By reducing the metal content, the performance stability of the hollow particles in high humidity environments can be improved. Furthermore, regarding the hollow particles of the present invention, when both the surfactant content and the metal content are reduced to below the aforementioned upper limits, the performance stability can be improved beyond the sum of the effects of reducing the surfactant content and reducing the metal content.

[0234] Furthermore, in this invention, the metal content in the hollow particles refers to the ratio of the total mass of the metal components contained in the hollow particles to the mass of the hollow particles.

[0235] Furthermore, the metal content contained in the hollow particles can be determined by ICP emission spectroscopy. The type of metal can be identified by X-ray fluorescence (XRF) analysis.

[0236] The hollow particles of the present invention contain a polymer as a resin in which 70 to 100 parts by mass of crosslinkable monomer units are included in all 100 parts by mass of the total monomer units. As a result, the hollow particles of the present invention have excellent strength, are not easily broken, are not easily deformed by externally applied heat, and can suppress the increase in relative permittivity caused by the breakage or deformation of the hollow particles.

[0237] The polymer described above is a polymer that forms the skeleton of the shell of hollow particles. In the polymer described above, when the content of crosslinked monomer units is less than 100 parts by mass, the monomer units other than the crosslinked monomer units are non-crosslinked monomer units.

[0238] In the hollow particles of the present invention obtained by the above-described method for manufacturing hollow particles, the polymer contained in the shell is obtained by polymerization of the above-described polymeric monomers, wherein the crosslinked monomer units or non-crosslinked monomer units contained in the polymer are derived from the above-described polymeric monomers. Therefore, the content of each monomer unit in the polymer can be calculated from the amount of each polymeric monomer supplied to the polymerization reaction.

[0239] The polymer described above may have all monomer units as crosslinked monomer units. When the combination includes crosslinked monomer units and non-crosslinked monomer units, the content of crosslinked monomer units in 100 parts by mass of all monomer units is preferably 80 parts by mass or more, more preferably 90 parts by mass or more, and preferably 99 parts by mass or less, more preferably 97 parts by mass or less, as a lower limit.

[0240] The polymers described above preferably contain at least a difunctional crosslinking monomer unit as the crosslinking monomer unit. From the perspective of further improving the strength of hollow particles, it is more preferable to combine a difunctional crosslinking monomer unit and a trifunctional or higher crosslinking monomer unit.

[0241] In 100 parts by mass of the above polymer, the content of difunctional crosslinkable monomer units is not particularly limited, but as a lower limit, it is preferably 50 parts by mass or more, more preferably 60 parts by mass or more, and as an upper limit, it is preferably 90 parts by mass or less, more preferably 80 parts by mass or less.

[0242] When the polymer contains trifunctional or higher crosslinkable monomer units, the content of trifunctional or higher crosslinkable monomer units in all monomer units of 100 parts by mass of the polymer is not particularly limited. As a lower limit, it is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 20 parts by mass or more. As an upper limit, it is preferably 40 parts by mass or less, and more preferably 30 parts by mass or less.

[0243] In the above polymer, the content of non-crosslinked monomer units in 100 parts by mass of all monomer units is 30 parts by mass or less. From the perspective of improving the strength of hollow particles and suppressing the increase of relative permittivity caused by the breakage or deformation of hollow particles, the upper limit is preferably 20 parts by mass or less, more preferably 10 parts by mass or less. From the perspective of improving solvent resistance, the lower limit is preferably 1 part by mass or more, more preferably 3 parts by mass or more.

[0244] In the hollow particles of the present invention, the content of the aforementioned polymer is preferably 90% by mass or more, more preferably 95% by mass or more, in 100% by mass of the total solid component of the shell. By setting the content of the aforementioned polymer to the aforementioned lower limit or above, the strength of the hollow particles can be improved, and the increase in the relative permittivity caused by the breakage or deformation of the hollow particles can be suppressed.

[0245] The shell of the hollow particles of the present invention may also contain the above-mentioned polar resin or at least one selected from rosin acid, higher fatty acids and their metal salts as a particle size control agent.

[0246] When the shell of the hollow particles of the present invention contains the above-mentioned polar resin as a particle size control agent, the content of the above-mentioned polar resin in 100% by mass of the total solid components of the shell is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, further preferably 0.4% by mass or more, and even more preferably 0.5% by mass or more. On the other hand, it is preferably 10.0% by mass or less, more preferably 8.0% by mass or less, further preferably 5.0% by mass, and even more preferably 2.0% by mass or less.

[0247] When the shell of the hollow particles of the present invention contains at least one selected from rosin acid, higher fatty acids and their metal salts as a particle size control agent, the total content of rosin acid, higher fatty acids and their metal salts in 100% by mass of the total solid content of the shell is preferably 0.0001 to 0.02% by mass, more preferably 0.0010 to 0.01% by mass, and even more preferably 0.0015 to 0.006% by mass.

[0248] Furthermore, the presence of particle size control agents in the shell of hollow particles and their content can be confirmed by, for example, thermal decomposition gas chromatography.

[0249] The lower limit of the volume average particle size of the hollow particles of the present invention is preferably 1 μm or more, more preferably 1.5 μm or more, and even more preferably 2 μm or more. On the other hand, the upper limit of the volume average particle size of the hollow particles is preferably 10 μm or less, more preferably 8 μm or less, and even more preferably 6 μm or less. When the volume average particle size of the hollow particles is above the above-mentioned lower limit, the agglomeration of the hollow particles is reduced, thus exhibiting excellent dispersibility. When the volume average particle size of the hollow particles is below the above-mentioned upper limit, shell thickness deviation is suppressed, a uniform shell is easily formed, and high mechanical strength is achieved. The hollow particles are not easily broken, thus suppressing the increase in relative permittivity caused by the breakage or deformation of the hollow particles. Furthermore, even if hollow particles with a volume average particle size within the above-mentioned range are contained in the insulating resin layer of the electronic circuit board, it will not cause wiring defects. Therefore, hollow particles with a volume average particle size within the above-mentioned range are preferably used as materials for electronic circuit boards.

[0250] In order to make the volume average particle size of the hollow particles within the preferred range described above, for example, it is preferable to use the combination of the preferred dispersant stabilizer and particle size control agent described above in the mixture preparation process, and further use the preferred hydrophobic solvent described above.

[0251] The shape of the hollow particles of the present invention is not particularly limited as long as a hollow portion is formed inside; examples include spherical, ellipsoidal, and amorphous shapes. Among these, spherical shapes are preferred from the perspective of ease of manufacture.

[0252] The hollow particles of the present invention may have one or more hollow portions, but from the perspective of maintaining a good balance between high porosity and mechanical strength and low dielectric constant, it is preferable to have only one hollow portion.

[0253] The average roundness of the hollow particles of the present invention can be 0.950 to 0.995.

[0254] A vivid example of the shape of the hollow particles of the present invention is a bag formed by a thin membrane and inflated by gas, as shown in the cross-sectional view below. Figure 1 Hollow particles 100 in (5). In this example, a thin membrane is provided on the outside, and its interior is filled with gas.

[0255] Furthermore, the particle shape can be confirmed using methods such as SEM and TEM. Additionally, the internal shape of the particles can be confirmed using SEM and TEM after slicing the particles into circular pieces using known methods.

[0256] The particle size distribution (volume average particle size (Dv) / number average particle size (Dn)) of the hollow particles can be, for example, 1.05 or more and 2.5 or less. By making this particle size distribution 2.5 or less, particles with small deviations in compressive strength and heat resistance between particles can be obtained. Furthermore, by making this particle size distribution 2.5 or less, products with uniform thickness can be manufactured, for example, when manufacturing sheet-like molded articles.

[0257] The volume-average particle size (Dv) and number-average particle size (Dn) of hollow particles can be determined by measuring the particle size of the hollow particles, for example, using a particle size distribution measuring device. The number-average and volume-average values ​​are then calculated, and these values ​​are used as the number-average particle size (Dn) and volume-average particle size (Dv) of the particle. Particle size distribution is the value of volume-average particle size divided by number-average particle size.

[0258] The hollow particles of the present invention have a porosity of 60% or more, preferably 65% ​​or more. By making the porosity above the aforementioned lower limit, the relative permittivity of the hollow particles is sufficiently reduced, and they exhibit excellent lightweight, heat resistance, and thermal insulation properties. The upper limit of the porosity of the hollow particles of the present invention is not particularly limited, but from the perspective of suppressing the reduction in the strength of the hollow particles, it is preferably 90% or less, more preferably 85% or less.

[0259] The porosity of the hollow particles of the present invention can be calculated from the apparent density D1 and true density D0 of the hollow particles.

[0260] The method for determining the apparent density D1 of hollow particles is as follows. First, in a volume of 100 cm³... 3 Fill the volumetric flask with approximately 30cm 3 The hollow granules were precisely weighed, and the mass of the filled hollow granules was accurately measured. Next, in a volumetric flask filled with the hollow granules, isopropanol was precisely filled to the mark, taking care not to introduce air bubbles. The mass of isopropanol added to the volumetric flask was accurately weighed, and the apparent density D1 (g / cm³) of the hollow granules was calculated based on the following formula (I). 3 ).

[0261] Formula (I)

[0262] Apparent density D1 = [mass of hollow particles] / (100 - [mass of isopropanol] ÷ [specific gravity of isopropanol at the measurement temperature])

[0263] Apparent density D1 is equivalent to the overall density of the hollow particle when the hollow part is considered as part of the hollow particle.

[0264] The method for determining the true density D0 of hollow granules is as follows. After the hollow granules are pre-crushed, the density is measured in a 100 cm³ container. 3 Approximately 10 g of hollow particle powder was filled into a volumetric flask, and the mass of the powder was accurately weighed. Then, isopropanol was added to the volumetric flask in the same manner as the apparent density determination described above, and the mass of the isopropanol was accurately weighed. Based on the following formula (II), the true density D0 (g / cm³) of the hollow particles was calculated. 3 ).

[0265] Equation (II)

[0266] True density D0 = [mass of the hollow particle fragments] / (100 - [mass of isopropanol] ÷ [specific gravity of isopropanol at the measurement temperature])

[0267] True density D0 corresponds to the specific gravity of the shell portion only in a hollow particle. As clearly demonstrated by the above measurement method, the hollow portion is not considered part of the hollow particle when calculating true density D0.

[0268] The porosity (%) of the hollow particles is calculated using the following formula (III) based on the apparent density D1 and true density D0 of the hollow particles.

[0269] Equation (III)

[0270] Porosity (%) = 100 - (apparent density D1 / true density D0) × 100

[0271] In other words, the porosity of hollow particles is the proportion of the hollow portion in the total weight of the hollow particles.

[0272] The hollow particles of the present invention exhibit excellent strength due to the ample inclusion of cross-linked monomer units within their shells. Therefore, they are less prone to breakage during compounding with other materials and during molding after compounding. When added to molded articles, they perform excellently as lightweight materials, heat-insulating materials, sound-insulating materials, and shock-absorbing materials. Furthermore, because the hollow particles of the present invention have reduced residual hydrophobic solvents, they will not cause fires or smoke when compounded with resins or other materials. Therefore, the hollow particles of the present invention are particularly preferred as additives for molded articles, and particularly preferred as additives for resin-molded articles.

[0273] The molded body containing the hollow particles of the present invention may contain, for example, thermoplastic or thermosetting resins such as polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyurethane, epoxy resin, acrylonitrile-butadiene-styrene (ABS) resin, acrylonitrile-styrene (AS) resin, poly(meth)acrylate, polycarbonate, polyamide, polyimide, polyphenylene ether, polyphenylene sulfide, polyester, polytetrafluoroethylene, maleimide resin, bismaleimide triazine resin, liquid crystal polyester resin, phenolic resin, vinyl ester resin, unsaturated polyester resin, cyanate ester resin, polyetherketoneketone resin, and polyetherimide resin. Furthermore, when using epoxy resin as the resin component, it is preferable to mix in curing agents or catalysts such as amines, acid anhydrides, and imidazoles. In addition, the molded body containing the hollow particles of the present invention may also contain organic or inorganic fibers such as carbon fiber, glass fiber, aramid fiber, and polyethylene fiber. The hollow particles of the present invention can be contained as fillers in molded articles formed using thermoplastic or thermosetting resins, and in molded articles formed using materials comprising thermoplastic or thermosetting resins and fibers.

[0274] Applications of resin molded articles containing the hollow particles of the present invention include components such as light-reflecting materials, heat-insulating materials, sound-insulating materials, and low-dielectric materials used in various fields such as automobiles, electrical engineering, electronics, construction, aviation, and aerospace; food containers; shoes such as athletic shoes and sandals; household appliance parts; bicycle parts; stationery; and tools. The hollow particles of the present invention exhibit excellent performance stability in high-humidity environments and have a low relative permittivity, making them particularly preferred as low-dielectric-constant and highly reliable materials in the electrical or electronic fields. For example, the hollow particles of the present invention are preferably used as electronic circuit board materials. Specifically, by containing the hollow particles of the present invention in the insulating resin layer of the electronic circuit board, the relative permittivity of the insulating resin layer can be reduced, suppressing adverse conditions such as migration in high-humidity environments.

[0275] Furthermore, the hollow particles of the present invention are also preferably used as interlayer insulating materials, dry film resists, solder resists, bonding wires, electromagnetic wires, semiconductor sealing materials, epoxy sealing materials, molding underfills, die bond pastes, buffer coating materials, copper-clad laminates, flexible substrates, high-frequency device assemblies, antenna assemblies, automotive radar, and other semiconductor materials. Among these, they are particularly preferred as interlayer insulating materials, solder resists, electromagnetic wires, epoxy sealing materials, underfills, buffer coating materials, copper-clad laminates, flexible substrates, high-frequency device assemblies, antenna assemblies, automotive radar, and other semiconductor materials.

[0276] Furthermore, the hollow particles of this invention have a high porosity, are not easily broken, and exhibit excellent heat resistance, thus meeting the requirements for heat insulation and cushioning in primer materials, as well as the heat resistance required for use in thermal paper. In addition, the hollow particles of this invention can also be used as plastic pigments with excellent gloss and hiding power.

[0277] Furthermore, the hollow particles of the present invention can be used to seal useful components such as fragrances, pharmaceuticals, pesticides, and ink ingredients into the interior through impregnation, depressurization, or pressurization impregnation, thus enabling them to be used for various purposes depending on the components contained therein.

[0278] Example

[0279] The present invention will be further described in detail below with examples and comparative examples, but the present invention is not limited to these examples. Furthermore, unless otherwise specified, parts and percentages are based on mass.

[0280] [Manufacturing Example 1: Manufacturing of Polar Resin A (MMA / AA / EA Copolymer)]

[0281] 200 parts of toluene were added to a reaction vessel. While stirring the toluene, the reaction vessel was thoroughly purged with nitrogen. The temperature was then raised to 90°C. After 2 hours, a mixed solution of 96.2 parts of methyl methacrylate (MMA), 0.3 parts of acrylic acid (AA), 3.5 parts of ethyl acrylate (EA), and 2.8 parts of tert-butyl peroxide-2-ethylhexanoate (manufactured by Nippon Oil Co., Ltd., trade name: PERBUTYL O) was added dropwise to the reaction vessel. The polymerization was then completed by reflux of toluene for 10 hours. The solvent was then removed by distillation under reduced pressure to obtain polar resin A (MMA / AA / EA copolymer).

[0282] Of the total mass of repeating units constituting the obtained polar resin A (MMA / AA / EA copolymer), 96.2% were from MMA, 0.3% were from AA, and 3.5% were from EA. Furthermore, the obtained polar resin A is insoluble in water and has a number-average molecular weight of 10,000.

[0283] In addition, the number-average molecular weight was determined by gel permeation chromatography (GPC) using tetrahydrofuran as a carrier at a flow rate of 0.35 ml / min, and the molecular weight was calculated as the equivalent of that of polystyrene. The apparatus used was an HLC8220 manufactured by Tosoh Corporation, and the chromatographic column was a three-column Shodex KF-404HQ column manufactured by Showa Denko Corporation (column temperature 40°C). Differential refractive index detectors and ultraviolet detectors were used. Molecular weight correction was performed using 12 standard polystyrene samples (from 5 million to 3 million) manufactured by Polymer Laboratories Ltd.

[0284] [Example 1]

[0285] (1) Mixture preparation process

[0286] First, the mixture of the following materials is used as the oil phase.

[0287] 31.9 parts of ethylene glycol dimethacrylate

[0288] 13.7 parts of trimethylolpropane triacrylate

[0289] 0.2 parts of polar resin A (MMA / AA / EA copolymer)

[0290] 1.04 parts of 2,2'-azobis(2,4-dimethylvalerate) (oil-soluble polymerization initiator, manufactured by Fujifilm and Koh Genuine Chemicals Co., Ltd., trade name: V-65)

[0291] Hydrophobic solvent: 54.5 parts cyclohexane

[0292] On the other hand, in a stirred tank at room temperature, 7.8 parts of magnesium chloride (a water-soluble polyvalent metal salt) were dissolved in 225 parts of ion-exchanged water. Under stirring, an aqueous solution containing 5.5 parts of sodium hydroxide (an alkali metal hydroxide) dissolved in 55 parts of ion-exchanged water was slowly added to the above-obtained aqueous solution to prepare a magnesium hydroxide colloid (a water-insoluble metal hydroxide colloid) dispersion (4.0 parts of magnesium hydroxide) as the aqueous phase.

[0293] A mixture is prepared by mixing the aqueous phase and the oil phase.

[0294] (2) Suspension process

[0295] The mixture obtained in the above-mentioned mixture preparation process was stirred for 1 minute at 4000 rpm using a disperser (manufactured by PRIMIX Co., Ltd., trade name: HOMOMIXER) to suspend it, thus preparing a suspension in which monomer droplets containing hydrophobic solvent are dispersed in water.

[0296] (3) Polymerization process

[0297] The suspension obtained in the above suspension process was heated from 40°C to 65°C (heating rate: 50°C / hour) for 30 minutes under a nitrogen atmosphere. The mixture was then stirred at 65°C for 1 hour and 30 minutes to carry out the first polymerization reaction. Next, 2.3 parts of methyl acrylate were added to the stirred tank, and the mixture was stirred at 65°C for 2 hours and 30 minutes under a nitrogen atmosphere to carry out the second polymerization reaction. Through the first and second polymerization reactions, a precursor composition was prepared as a slurry containing precursor particles of an encapsulated hydrophobic solvent dispersed in water.

[0298] (4) Cleaning and solid-liquid separation process

[0299] The precursor composition obtained in the above polymerization process was washed with dilute sulfuric acid at 25°C for 10 minutes to bring its pH to below 5.5. Next, after separating the water by filtration, 200 parts of ion-exchanged water were added for re-slurrying. The water washing process (washing, filtration, dehydration) was repeated multiple times at 25°C, and the solid component was obtained by filtration separation. The obtained solid component was dried in a dryer at 40°C to obtain precursor particles containing a hydrophobic solvent.

[0300] (5) Solvent removal process

[0301] The precursor particles obtained in the above solid-liquid separation process were heated for 6 hours under vacuum conditions at 200°C using a vacuum dryer. Then, nitrogen was introduced to bring the pressure to atmospheric pressure, and the particles were cooled to room temperature, thereby obtaining the hollow particles of Example 1. Observations using a scanning electron microscope and the porosity values ​​confirmed that these particles were spherical and possessed hollow portions.

[0302] [Example 2]

[0303] In Example 1, when preparing the oil phase in the above (1) mixture preparation process, the amount of polymerizable monomer and hydrophobic solvent added was changed according to Table 1. Otherwise, the hollow particles of Example 2 were manufactured using the same steps as in Example 1.

[0304] [Example 3]

[0305] In Example 1, when preparing the aqueous phase in the above (1) mixture preparation process, the amount of magnesium chloride (water-soluble polyvalent metal salt) added was changed from 7.8 parts to 15.7 parts, and the amount of sodium hydroxide (alkali metal hydroxide) added was changed from 5.5 parts to 11.0 parts, so that the amount of magnesium hydroxide in the magnesium hydroxide colloid was 8.0 parts. Otherwise, the hollow particles of Example 3 were manufactured using the same steps as in Example 1.

[0306] [Comparative Example 1]

[0307] Hollow particles of Comparative Example 1 were manufactured in the same manner as those of Manufacturing Example 1 in Japanese Patent Application Publication No. 2000-313818.

[0308] Specifically, 70 parts of styrene, 27 parts of butadiene, 3 parts of itaconic acid, and 12 parts of tert-dodecyl mercaptan were added to an aqueous solution obtained by dissolving 0.5 parts of the reactive emulsifier SE10N (manufactured by ADEKA) and 1.0 part of ammonium persulfate in 200 parts of distilled water. While stirring the solution, polymerization was carried out at 75°C for 8 hours to obtain polymer particles. These polymer particles were then used as seed polymers for the following polymerization: 10 parts of the polymer particles, 0.1 parts of polyoxyethylene nonylphenyl ether as a surfactant, 0.4 parts of lauryl sulfate, and 0.5 parts of ammonium persulfate were dispersed in 900 parts of distilled water. A mixture of 50 parts of methyl methacrylate, 40 parts of divinylbenzene, 10 parts of α-methylstyrene, and 20 parts of toluene was added to the resulting solution, and polymerization was carried out at 75°C for 5 hours, resulting in a dispersion of precursor particles containing toluene within the particles. The obtained precursor particles were spray-dried to obtain the hollow particles of Comparative Example 1.

[0309] [Comparative Example 2]

[0310] In Comparative Example 1, the amount of polyoxyethylene nonylphenyl ether added was changed from 0.1 parts to 0.3 parts, and 0.4 parts of sodium lauryl sulfate was used instead of 0.4 parts of ammonium lauryl sulfate. Otherwise, the hollow particles of Comparative Example 2 were manufactured using the same steps as in Comparative Example 1.

[0311] [evaluate]

[0312] The hollow particles obtained in each embodiment and comparative example were measured and evaluated as follows. The results are shown in Table 1.

[0313] 1. Volume average particle size

[0314] The volume average particle size of hollow particles was determined using a particle size analyzer (Beckman Coulter, trade name: Multisizer 4e). The measurement conditions were: pore size: 50 μm, dispersion medium: ISOTONII (trade name), concentration: 10%, and number of particles measured: 100,000.

[0315] Specifically, 0.2 g of particle sample was taken into a beaker, and an aqueous surfactant solution (manufactured by Fujifilm Corporation, trade name: DRIWEL) was added as a dispersant. Then, 2 ml of dispersion medium was added to wet the particles, followed by 10 ml of dispersion medium. The particles were dispersed using an ultrasonic disperser for 1 minute, and then measured using the particle size distribution analyzer described above.

[0316] 2. Porosity

[0317] 2-1. Determination of the apparent density of hollow particles

[0318] First, in a capacity of 100cm 3 Fill the volumetric flask with approximately 30cm 3 The hollow granules were precisely weighed, and the mass of the filled hollow granules was accurately measured. Next, isopropanol was precisely filled to the mark into a volumetric flask containing the hollow granules, taking care to avoid introducing air bubbles. The mass of isopropanol added to the volumetric flask was accurately weighed, and the apparent density D1 (g / cm³) of the hollow granules was calculated based on the following formula (I). 3 ).

[0319] Formula (I)

[0320] Apparent density D1 = [mass of hollow particles] / (100 - [mass of isopropanol] ÷ [specific gravity of isopropanol at the measurement temperature])

[0321] 2-2. Determination of the true density of hollow particles

[0322] After pre-crushing the hollow granules, in a volume of 100cm³ 3 Fill a volumetric flask with approximately 10g of hollow granulated powder and accurately weigh the mass of the powder.

[0323] Then, in the same manner as the apparent density determination described above, isopropanol is added to the volumetric flask, the mass of isopropanol is accurately weighed, and the true density D0 (g / cm³) of the hollow particles is calculated based on the following formula (II). 3).

[0324] Equation (II)

[0325] True density D0 = [mass of the hollow particle fragments] / (100 - [mass of isopropanol] ÷ [specific gravity of isopropanol at the measurement temperature])

[0326] 2-3. Calculation of porosity

[0327] Based on the following equation (III), the porosity of the hollow particles is calculated from the apparent density D1 and true density D0 of the hollow particles.

[0328] Equation (III)

[0329] Porosity (%) = 100 - (apparent density D1 / true density D0) × 100

[0330] 3. Determination of relative permittivity

[0331] The relative permittivity of hollow particles at a frequency of 1 MHz and room temperature (25 °C) was measured using a perturbation-based measuring device (manufactured by AET Corporation, model: ADMS01Nc).

[0332] 4. Surfactant content on particle surface

[0333] Accurately weigh 50 ml of ultrapure water and 5 g of hollow granules, and mix thoroughly. Irradiate with ultrasound for 30 minutes, and filter using a 0.45 μm diameter syringe membrane filter. Freeze-dry the filtrate, and dissolve 1 g of tetramethylsilane (TMS) in the residue. Proceed under the following conditions. 1 H-NMR determination. For those derived from 1 A calibration curve was constructed using the surfactant as a TMS intensity reference determined by H-NMR spectroscopy, and the amount of surfactant extracted from the surface of the hollow particles was calculated. Additionally, a calibration curve was constructed using the ratio of TMS intensity to the peak intensity from the surfactant. The proportion of the amount of surfactant extracted from the surface of the hollow particles relative to the mass of the hollow particles was calculated as the surfactant content present on the surface of the hollow particles.

[0334] In addition, from 1 Particles of surfactant not detected by H-NMR spectroscopy are considered as undetected (ND).

[0335] < 1 H-NMR measurement conditions >

[0336] Device Name: FT-NMR Device

[0337] Resonant frequency: 400MHz

[0338] Measurement mode:1 H-NMR

[0339] Pulse width: 5.0 μs (pulse angle: 90°)

[0340] Measurement range: 26 ppm (frequency range: 10500 Hz)

[0341] Total number of times: 1024

[0342] Measurement temperature: 40℃

[0343] Solvent: Deuterated chloroform (TMS (tetramethylsilane) 1%)

[0344] Reference material: Peak from tetramethylsilane: 0.00 ppm (internal standard method)

[0345] 5. Metal content in particles

[0346] Wet digestion of 10g of precisely weighed hollow particles was performed using a microwave digester (PerkinElmer Multiwave 3000). The decomposition products were analyzed by ICP emission spectroscopy using an ICP emission spectrometer (PerkinElmer Optima 2100DV) to determine the total mass of metals. Furthermore, the metal species were identified by elemental analysis using X-ray fluorescence (XRF). The ratio of the total mass of metals in the decomposition products to the mass of the hollow particles was calculated as the metal content in the hollow particles.

[0347] 6. Reliability testing in high humidity environments

[0348] <Preparation of Resin Varnish Containing Hollow Particles>

[0349] First, 90 parts of brominated epoxy resin (manufactured by Toto Chemical Co., Ltd., trade name: YDB-500EK75, epoxy equivalent 500, solid content 75% by mass) and 10 parts of cresol phenolic varnish type epoxy resin (manufactured by Toto Chemical Co., Ltd., trade name: YDCN220EK75, epoxy equivalent 210, solid content 75% by mass) and 0.1 parts of 2-ethyl-4-methylimidazolium (manufactured by Shikoku Chemical Industry Co., Ltd.) were dissolved in a mixed solvent (room temperature) of 20 parts of dimethylformamide (DMF) and 6 parts of methyl ethyl ketone (MEK), and 10 parts of cresol phenolic varnish type epoxy resin (manufactured by Toto Chemical Co., Ltd., trade name: YDCN220EK75, epoxy equivalent 210, solid content 75% by mass) were further added. Then, 2 parts of dicyandiamide (DICY) (manufactured by Carbide Co., Ltd., Japan) and 0.1 parts of 2-ethyl-4-methylimidazolium (2E4MZ) (manufactured by Shikoku Chemical Industry Co., Ltd.) were added and stirred to prepare a resin varnish.

[0350] Next, 95 parts of the resin varnish cooled to room temperature and 5 parts of hollow particles were stirred and mixed at 3000 rpm for 30 minutes using a disperser to obtain a resin varnish containing hollow particles.

[0351] <Preparation of Prepreg>

[0352] After impregnating the obtained resin varnish containing hollow particles with glass cloth (Nittobo, trade name: WEA116E), it is heated and dried at 150-170°C for 3-10 minutes to remove the solvent and obtain a prepreg.

[0353] <Fabrication of Double-Sided Copper-Clad Laminates>

[0354] A 35 μm thick copper foil (ST foil) was deposited on both sides of a prepreg and subjected to a temperature of 180°C for 2 hours and a pressure of 2.94 MPa (30 kg / cm²). 2 The curing conditions are heated and pressurized to obtain a double-sided copper-clad laminate with a thickness of 0.13 mm.

[0355] <Reliability Testing>

[0356] The obtained double-sided copper-clad laminate was subjected to pressure steam treatment (110°C, 85% RH, 100 hours). A 50V voltage was applied to the treated double-sided copper-clad laminate for a specified time, and the resistance value was measured to confirm the presence of any abnormalities. Evaluation was conducted according to the following criteria. Furthermore, any change in resistance value was considered abnormal. Changes in resistance value can be considered to be caused by corrosion of the copper substrate.

[0357] (Reliability Test Evaluation Standards)

[0358] ◎: No abnormalities were observed after applying voltage for 300 hours.

[0359] ○: No abnormalities were observed after applying voltage for 100 hours.

[0360] ×: An anomaly occurred before the voltage application time reached 100 hours.

[0361] [Table 1]

[0362] Table 1

[0363]

[0364] Additionally, the abbreviations in Table 1 are explained below.

[0365] EGDMA: Ethylene glycol dimethacrylate

[0366] TMPT: Trimethylolpropane triacrylate

[0367] MA: Methyl acrylate

[0368] MMA: Methyl methacrylate

[0369] DVB: Divinylbenzene

[0370] α-MSt: α-methylstyrene

[0371] V-65: 2,2'-Azobis(2,4-dimethylvalerate) (Oil-soluble polymerization initiator, manufactured by Fujifilm and Koh Genuine Chemicals Co., Ltd., trade name: V-65)

[0372] [Inspection]

[0373] Regarding the hollow particles obtained in Comparative Examples 1 and 2, the proportion of crosslinked monomer units was less than 70 parts by mass relative to 100 parts by mass of all monomer units of the polymer contained in the shell, the porosity was less than 60%, and the content of surfactant present on the particle surface was greater than 200 ppm. Therefore, in the reliability test, the hollow particles obtained in Comparative Examples 1 and 2 exhibited abnormalities before the voltage application time reached 100 hours, had poor performance stability in high humidity environments, and had a relative permittivity greater than 1.6. Furthermore, the surfactants detected on the surface of the hollow particles obtained in Comparative Example 1 were polyoxyethylene nonylphenyl ether (solubility in water at 25°C: ≥1 g / L) and ammonium lauryl sulfate (solubility in water at 25°C: 100 g / L). The surfactants detected on the surface of the hollow particles obtained in Comparative Example 2 were polyoxyethylene nonylphenyl ether (solubility in water at 25°C: ≥1 g / L) and sodium lauryl sulfate (solubility in water at 25°C: 100 g / L).

[0374] In contrast, the hollow particles obtained in the various embodiments are as follows: the polymer contained in the shell contains 70-100 parts by mass of crosslinked monomer units per 100 parts by mass of all monomer units, with a porosity of 60% or more, and the content of surfactant present on the particle surface is less than 200 ppm. Therefore, in reliability tests, no abnormalities were observed when a 300-hour voltage was applied, exhibiting excellent performance stability in high humidity environments, and having a relative permittivity of less than 1.6, which is low. Furthermore, no surfactant was detected on the surface of the hollow particles obtained in the various embodiments.

[0375] Explanation of reference numerals in the attached figures

[0376] 1: Aquatic medium;

[0377] 2: Low polarity materials;

[0378] 4: Monomer composition;

[0379] 4a: Hydrophobic solvent;

[0380] 4b: Materials other than hydrophobic solvents;

[0381] 4c: Polymerizable monomers dispersed in aqueous media;

[0382] 5: Oil-soluble polymerization initiators;

[0383] 6: Shell;

[0384] 8: Hollow section;

[0385] 10: Droplets;

[0386] 20: Precursor particles;

[0387] 100: Hollow particles whose hollow interior is filled with gas.

Claims

1. A hollow particle having a shell containing resin and a hollow portion surrounded by said shell, The shell contains a polymer comprising 70 to 100 parts by mass of crosslinking monomer units in 100 parts by mass of all monomer units as the resin, wherein the crosslinking monomer units include difunctional crosslinking monomer units as monomer units derived from difunctional crosslinking monomers and trifunctional or higher crosslinking monomer units as monomer units derived from trifunctional or higher crosslinking monomers. In 100 parts by weight of all monomer units of the polymer, the content of the difunctional crosslinkable monomer unit is 50 parts by weight or more and 90 parts by weight, and the content of the trifunctional or higher crosslinkable monomer unit is 5 parts by weight or more and 40 parts by weight. The hollow particles have a porosity of over 60%. The content of surfactant present on the surface of hollow particles is less than 200 ppm. The metal content of the hollow particles is below 70 ppm, and the metal content is determined by ICP emission spectroscopy. The hollow particles have a relative permittivity of less than 1.6 at a frequency of 1 MHz. The volume average particle size of the hollow particles is 1–8 μm.

2. The hollow particles according to claim 1 have a porosity of 90% or less.

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