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

Abstract

The invention provides a hollow particle with reduced dielectric loss tangent. A hollow particle having a shell containing a resin and a hollow portion surrounded by the shell, in which the proportion of particles having a roundness of 0.85 or less is 10 mass% or less, the porosity is 50% or more, and the content of an unreacted polymerizable monomer is 100 ppm or less. An aqueous dispersion of hollow particles, which is obtained by dispersing the hollow particles having a volume amount of 0.35 cm3 in 100 mL of ion-exchanged water, has an electrical conductivity of 30 [mu] S / cm or less.

Description

Technical Field

[0001] The present invention relates to hollow particles, a method for manufacturing the hollow particles, a resin composition containing the hollow particles, and a resin structure containing the hollow particles. Background Art

[0002] Since hollow particles (hollow resin particles) have voids inside the particles, they are added to resins, coatings, various molded bodies, etc. for use for purposes such as weight reduction, heat insulation, and low dielectric constant, and their uses cover a wide range of fields such as automobiles, bicycles, aviation, electrics, electronics, construction, home appliances, containers, stationery, tools, shoes, etc.

[0003] Hollow particles can be manufactured by methods such as bulk polymerization, solution polymerization, dispersion polymerization, suspension polymerization, emulsion polymerization, etc. In suspension polymerization, hollow particles can be obtained by dispersing droplets of a monomer composition containing a polymerizable monomer and a hydrophobic solvent in an aqueous medium containing a dispersion stabilizer and performing polymerization.

[0004] As a method for manufacturing hollow particles using suspension polymerization, for example, Patent Document 1 discloses a method of polymerizing a first polymerizable monomer containing a crosslinkable monomer and a second polymerizable monomer having a solubility of 0.3 g / L or more in distilled water at 20°C in two stages at a specific timing. Patent Document 1 has the following description: In the obtained hollow particles, the content ratio of unreacted polymerizable monomers is 10 to 731 ppm.

[0005] Patent Document 2 discloses a method of making a polar resin contained in a monomer composition and using a water-insoluble inorganic metal salt as a dispersion stabilizer. Patent Document 2 has the following description: In the obtained hollow particles, the residual amount of volatile compounds such as non-reactive hydrocarbon solvents and unreacted monomers used in the manufacturing process is 0.03 to 0.12% by mass.

[0006] Prior Art Documents

[0007] Patent Documents

[0008] Patent Document 1: International Publication No. 2022 / 071276;

[0009] Patent Document 2: International Publication No. 2021 / 112117. Summary of the Invention

[0010] Problems to be Solved by the Invention

[0011] For example, in the fields of electricity or electronics, there are cases where hollow particles are added to insulating materials for the purpose of reducing the dielectric constant and the dielectric loss tangent of the insulating materials. The hollow particles added for the purpose of reducing the dielectric loss tangent of various materials preferably have a lower dielectric loss tangent.

[0012] The problem of the present invention is to provide hollow particles with a reduced dielectric loss tangent, a method for manufacturing the hollow particles, a resin composition containing the hollow particles, and a resin structure containing the hollow particles.

[0013] Solution to the problem

[0014] The present inventors have found that in hollow particles in which the shell is formed of a polymer, unreacted polymerizable monomers remaining and metals or surfactants contained in a form easily soluble in water in the hollow particles easily cause an increase in the dielectric loss tangent of the hollow particles, and thus completed the present invention.

[0015] The present invention provides a hollow particle having a shell containing a resin and a hollow portion surrounded by the shell,

[0016] the proportion of particles having a roundness of 0.85 or less is 10% by mass or less,

[0017] the porosity is 50% or more,

[0018] the content of unreacted polymerizable monomers is 100 ppm or less,

[0019] in a water dispersion of the above-mentioned hollow particles obtained by dispersing the above-mentioned hollow particles having a volume of 0.35 cm 3 in 100 mL of ion-exchanged water, the conductivity is 30 μS / cm or less.

[0020] Furthermore, the present invention provides a method for manufacturing a hollow particle, which is a method for manufacturing the hollow particle of the present invention, and has the following steps:

[0021] a step of preparing a mixed liquid containing a polymerizable monomer, a hydrophobic solvent, a polymerization initiator, a dispersion stabilizer, and an aqueous medium;

[0022] a step of preparing a suspension in which droplets of a monomer composition containing the polymerizable monomer, the hydrophobic solvent, and the polymerization initiator are dispersed in the aqueous medium by suspending the above-mentioned mixed liquid;

[0023] a step of preparing a precursor composition in which precursor particles are dispersed in the aqueous medium by subjecting the above-mentioned suspension to a polymerization reaction, the precursor particles having a hollow portion surrounded by a shell containing a resin and the hollow portion being filled with the hydrophobic solvent;

[0024] A step of removing the hydrophobic solvent from the precursor particles by blowing a gas into the precursor composition while stirring the precursor composition in a stirring tank, thereby obtaining an aqueous dispersion of hollow particles;

[0025] A step of performing a cleaning for removing the dispersion stabilizer remaining in the hollow particles.

[0026] Furthermore, the present invention provides a resin composition containing the hollow particles of the present invention and a matrix resin.

[0027] Furthermore, the present invention provides a resin structure containing the hollow particles of the present invention and a matrix resin.

[0028] Advantages of the Invention

[0029] As described above, according to the present invention, it is possible to provide hollow particles having a low dielectric loss tangent. Furthermore, the present invention provides a method for manufacturing such hollow particles, a resin composition containing such hollow particles, and a resin structure containing such hollow particles. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A diagram for explaining an example of a method for manufacturing the hollow particles of the present invention.

[0031] Figure 2 A diagram for explaining an example of a stirring device used in the solvent removal step. DETAILED DESCRIPTION OF THE INVENTION

[0032] Hereinafter, the hollow particles of the present invention, the method for manufacturing the hollow particles of the present invention, the resin composition of the present invention, and the resin structure of the present invention will be described in detail.

[0033] In addition, in the present invention, "~" in a numerical range means that the numerical values described before and after it are included as the lower limit value and the upper limit value.

[0034] 1. Hollow Particles

[0035] The hollow particles of the present invention are hollow particles having a shell containing a resin and a hollow portion surrounded by the shell.

[0036] The proportion of particles having a roundness of 0.85 or less is 10% by mass or less.

[0037] The porosity is 50% or more.

[0038] The content of unreacted polymerizable monomer is 100 ppm or less.

[0039] When the volume is 0.35 cm 3In the aqueous dispersion of hollow particles obtained by dispersing the above-mentioned hollow particles in 100 mL of ion-exchanged water, the conductivity is 30 μS / cm or less.

[0040] In the aqueous dispersion obtained by dispersing hollow particles in ion-exchanged water, the more the amount of metal or ionic surfactant eluted from the hollow particles, the more the conductivity tends to increase. It is speculated that the metal and ionic surfactant eluted from the hollow particles into the aqueous dispersion adhere to the particle surface in a state where they are easily freed from the hollow particles and adhere to the particle surface when the particles are in a dry state. Therefore, the conductivity of this aqueous dispersion can be used as an index for the amount of metal and ionic surfactant adhering to the surface of the hollow particles in the dry state.

[0041] The hollow particles of the present invention have a low dielectric loss tangent. The dielectric loss tangent is "the degree to which a part of the energy is converted into heat and lost when an electric field is applied". In the hollow particles, by suppressing the molecular motion of the shell, the energy loss can be suppressed, and thus the dielectric loss tangent can be reduced. In the shell formed of a resin (polymer), the molecular motion of the polymerizable monomer remaining in an unreacted state is relatively active. It is speculated that in the hollow particles of the present invention, since the residual amount of the unreacted polymerizable monomer is small, the molecular motion of the shell is suppressed and the dielectric loss tangent is reduced. In addition, when metal adheres to the particle surface, polarization occurs when an electric field is applied, so the dielectric loss tangent of the particle increases. When a surfactant adheres to the particle surface, it easily adsorbs moisture in the air, and the moisture adhering to the particle surface increases the dielectric loss tangent of the particle. It is speculated that in the hollow particles of the present invention, since the amount of metal and surfactant adhering to the particle surface is small, the dielectric loss tangent is reduced. Furthermore, it is speculated that in the hollow particles of the present invention, due to the synergistic effect of the small residual amount of the unreacted polymerizable monomer and the small amount of metal and surfactant adhering to the surface, the dielectric loss tangent is further reduced.

[0042] In addition, the hollow particles of the present invention also have excellent dielectric properties because the proportion of particles with a roundness of 0.85 or less is small. Particles with a roundness of 0.85 or less are typically particles that have undergone deformation such as indentation or cracking, and are sometimes referred to as "abnormal-shaped particles" in the present invention. Such abnormal-shaped hollow particles have a lower porosity than spherical hollow particles, and thus have poor dielectric properties. Therefore, by reducing the proportion of abnormal-shaped particles contained in the hollow particles, the dielectric properties of the hollow particles can be improved. In addition, in the present invention, the lower the relative dielectric constant and the dielectric loss tangent, the better the dielectric properties.

[0043] In addition, compared with spherical particles, the irregularly shaped particles have problems of being prone to agglomeration and poor dispersibility when dispersed in the matrix resin. Furthermore, the irregularly shaped particles are liable to be locally applied with an external pressure, and thus have a problem of poor pressure resistance compared with spherical particles. When the irregularly shaped particles are dispersed in the matrix resin, aggregates are likely to be formed, and the aggregates are liable to be applied with an external pressure, resulting in further deterioration of the pressure resistance. Therefore, by reducing the proportion of the irregularly shaped particles contained in the hollow particles, the dispersibility and pressure resistance of the hollow particles can be improved.

[0044] In addition, in a circuit board containing hollow particles, there are problems such as abnormal ion migration. Therefore, hollow particles with excellent performance stability are required.

[0045] The inventors of the present invention have found the following tendency: when the amounts of the metal and the ionic surfactant eluted from the hollow particles into the aqueous dispersion are large, ion migration is likely to occur in the circuit board containing the hollow particles. In a circuit board in which the insulating resin layer contains hollow particles, it is presumed that when a metal or a surfactant adheres to the surface of the hollow particles, in a high-humidity environment, the metal or the surfactant is liable to adsorb moisture and ionize, and thus dendrites are likely to be generated, and therefore ion migration is likely to occur. In particular, when the ionic surfactant in the surfactant adheres to the surface of the hollow particles, since a large amount of ionic components are contained, the ionization of the metal is further promoted, and thus ion migration is more likely to occur.

[0046] The hollow particles of the present invention are hollow particles in which the contents of the metal and the surfactant contained in the hollow particles in a form easily eluted in water are sufficiently small, and the decrease in the performance stability of the hollow particles caused thereby is suppressed. In addition, in the present invention, in a material containing hollow particles, the more difficult it is to cause a change in the properties of the hollow particles, the better the performance stability of the hollow particles. The hollow particles of the present invention have an excellent effect of improving the performance stability by making the amounts of both the metal and the surfactant sufficiently small, as compared with the case of reducing only either one of them. Furthermore, the hollow particles of the present invention have a high effect of suppressing the occurrence of ion migration in a circuit board containing the hollow particles by reducing the amount of the ionic surfactant, particularly on the particle surface, in the surfactant.

[0047] In the present invention, if the conductivity of the aqueous dispersion of the hollow particles for measuring the conductivity is 2 μS / cm or less in a state without the hollow particles, a dispersant may be further contained. The type and content of the dispersant can be appropriately adjusted so that the hollow particles are uniformly dispersed. The aqueous dispersion of the hollow particles for measuring the conductivity is in a state where no powder exists visually in the upper part and all the powder is dispersed in water.

[0048] As a dispersant that can be used in an aqueous dispersion of hollow particles for measuring electrical conductivity, a dispersant can be appropriately selected such that the pH and electrical conductivity of the ion-exchanged water do not change when ion-exchanged water is added. For example, a nonionic surfactant can be used.

[0049] As the nonionic surfactant, it can be appropriately selected from known nonionic surfactants without particular limitation. Examples include: polyoxyalkylene type nonionic surfactants such as higher alcohol alkylene oxide adducts, alkylphenol alkylene oxide adducts, fatty acid alkylene oxide adducts, higher alkylamine alkylene oxide adducts, polyol aliphatic ester alkylene oxide adducts, polypropylene glycol ethylene oxide adducts, fatty acid amide alkylene oxide adducts, polyoxyalkylene styrenated phenyl ethers; polyol type nonionic surfactants such as polyethylene oxide, fatty acid esters of glycerol, alkyl glycosides, fatty acid esters of pentaerythritol, fatty acid esters of sorbitol or sorbitan, sucrose fatty acid esters, alkyl ethers of polyols, aliphatic amides of alkanolamines; nonionic high molecular compounds having both hydrophilic and hydrophobic groups such as polyvinyl alcohol and polyvinylpyrrolidone. In particular, polyoxyalkylene type nonionic surfactants can be preferably used.

[0050] In the aqueous dispersion of hollow particles, the concentration of the nonionic surfactant is not particularly limited and can be, for example, 0.05% by mass to 1% by mass.

[0051] In addition, in the present invention, the hollow particles added to the aqueous dispersion for measuring electrical conductivity are the hollow particles immediately before use. Here, the hollow particles immediately before use refer to, for example, in the hollow particles used by mixing with other materials, the hollow particles immediately before mixing with other materials. In the hollow particles used alone as a coating material or the like, the hollow particles immediately before being used for their intended purpose. In addition, in the case of measuring the above electrical conductivity for hollow particles produced in the form of a dispersion, the hollow particles separated from the dispersion are dried by the same method as the drying process in the method for producing hollow particles described later, and an aqueous dispersion is prepared by dispersing 0.35 cm 3 of the dried hollow particles in 100 mL of ion-exchanged water, and the electrical conductivity of the aqueous dispersion is measured.

[0052] In addition, in the present invention, as the hollow particles with a volume of 0.35 cm 3 , the hollow particles obtained by measuring the weight (g) calculated by the following formula (1) are used. In the following formula (1), the apparent density D of the hollow particles 1 is the same as the apparent density D of the hollow particles measured when calculating the porosity described later. 1 Same.

[0053] Formula (1):

[0054] The weight (g) of the hollow particles with a volume of 0.35 cm 3 = the apparent density D

[0055] of the hollow particles 1 (g / cm 3 )) × 0.35 (cm 3 )

[0056] The conductivity of the aqueous dispersion of the above-mentioned hollow particles only needs to be 30 μS / cm or less. However, since there is a tendency that the lower the conductivity, the more excellent the dielectric properties and performance stability of the hollow particles, it is preferably 25 μS / cm or less, more preferably 20 μS / cm or less, further preferably 15 μS / cm or less, still further preferably 10 μS / cm or less, and particularly preferably 9 μS / cm or less. The lower limit of the above-mentioned conductivity is not particularly limited, and for example, it can be 0.5 μS / cm or more.

[0057] In addition, the pH of the aqueous dispersion of the above-mentioned hollow particles for measuring the conductivity is preferably 6.5 or more and 7.5 or less. There is a tendency that the more the amount of metal dissolved from the hollow particles into water, the higher the pH of the aqueous dispersion, and there is a tendency that when the amount of the ionic surfactant reaches a certain value or more, the pH becomes alkaline (exceeds 7.5). When the pH of the aqueous dispersion of the above-mentioned hollow particles is within the above range, there is a tendency that the dielectric properties and performance stability of the hollow particles are excellent. The pH of the aqueous dispersion of the above-mentioned hollow particles is more preferably 6.6 or more and 7.4 or less, and further preferably 6.7 or more and 7.3 or less.

[0058] When the hollow particles of the present invention use tetrahydrofuran as a solvent and the mass of the residue obtained by removing tetrahydrofuran from the extract obtained by refluxing the hollow particles with a mass M1 for 6 hours using a Soxhlet extractor is taken as M2, the residual component after THF extraction, calculated as the percentage of M2 relative to M1, is preferably 80% or more, more preferably 85% or more, and further preferably 90% or more. The residual component after THF extraction can be used as an index of the crosslinking density of the resin forming the shell. There is a tendency that when the residual component after THF extraction is above the above lower limit value, the strength and dielectric properties of the hollow particles are excellent.

[0059] The upper limit of the residual component after THF extraction is not particularly limited. From the viewpoint of ease of manufacture, for example, it can be 98% or less, or can also be 96% or less.

[0060] In addition, as a method for removing tetrahydrofuran from the extract to obtain a residue, for example, the method of evaporating and removing THF from the extract to obtain a non-volatile component and drying the obtained non-volatile component in vacuo at 50 °C for 1 hour can be cited.

[0061] The hollow particles of the present invention are particles having a shell (outer shell) containing a resin and a hollow portion surrounded by the shell.

[0062] The resin contained in the shell is typically a polymer of a polymerizable monomer used in the method for manufacturing the hollow particles of the present invention described later. Conventional hollow particles formed of a polymer usually contain a small amount of polymerizable monomer remaining in an unreacted state, but in the hollow particles of the present invention, the amount of polymerizable monomer remaining in an unreacted state is reduced.

[0063] In the hollow particles of the present invention, the content of unreacted polymerizable monomer is 100 ppm or less, preferably 80 ppm or less, more preferably 70 ppm or less, still more preferably 60 ppm or less, and even more preferably 50 ppm or less, from the aspect of reducing the dielectric loss tangent of the hollow particles.

[0064] Here, the content of unreacted polymerizable monomer means the ratio of the mass of unreacted polymerizable monomer remaining in the hollow particles to the mass of the hollow particles.

[0065] The unreacted polymerizable monomer can be extracted from the hollow particles by dissolving in a solvent, and thus the content of unreacted polymerizable monomer can be determined by, for example, gas chromatography of the extract obtained by extracting the unreacted polymerizable monomer from the hollow particles.

[0066] The shell of the hollow particles of the present invention may further contain additives different from the resin within the range not impairing the effects of the present invention. When additives are contained, the content of the resin contained in the shell is preferably 96% by mass or more, more preferably 97% by mass or more, still more preferably 98% by mass or more, and even more preferably 99% by mass or more.

[0067] In the hollow particles of the present invention, the content of metal is preferably 100 ppm or less, more preferably 80 ppm or less, still more preferably 60 ppm or less, even more preferably 35 ppm or less, and particularly preferably 30 ppm or less. Here, the content of metal is the ratio of the total mass of the metal components contained in the hollow particles to the mass of the hollow particles. The metal contained in the hollow particles of the present invention usually comes from a dispersion stabilizer, and thus by sufficiently removing the dispersion stabilizer from the hollow particles, the content of metal can be made below the above upper limit value.

[0068] When the metal content in the hollow particles is below the above upper limit value, the dielectric properties and performance stability of the hollow particles can be improved, and further, in the drying process described later, the drying time can be shortened.

[0069] The metal content in the hollow particles can be determined by ICP emission spectrometry. The determination of the metal species can be carried out by X-ray fluorescence analysis (XRF). In this method, the detection limit of the metal content is usually 5 ppm.

[0070] Among the hollow particles of the present invention, the following hollow particles have a particularly low dielectric loss tangent and particularly excellent performance stability: the content of unreacted polymerizable monomer is 25 ppm or less, and in the aqueous dispersion of hollow particles obtained by dispersing 0.35 cm 3 of hollow particles in 100 mL of ion-exchanged water, the conductivity is 3.5 μS / cm or less, and the metal content is 15 ppm or less.

[0071] In the hollow particles of the present invention, the total content of the surfactant and the water-soluble polymer stabilizer of organic or inorganic type (hereinafter simply referred to as "surfactant, etc.") present on the particle surface is preferably 200 ppm or less, more preferably 100 ppm or less, and further preferably 50 ppm or less. When the content of the surfactant, etc. present on the surface of the hollow particles is below the above upper limit value, there is a tendency for the dielectric properties and performance stability to be improved. By using only an inorganic dispersion stabilizer as the dispersion stabilizer in the manufacturing process of the hollow particles described below, the content of the surfactant, etc. present on the surface of the hollow particles can be made less than the detection limit value.

[0072] In addition, in the present invention, the content of the surfactant, etc. present on the surface of the hollow particles means the ratio of the mass of the surfactant, etc. present on the surface of the hollow particles to the mass of the hollow particles. The surfactant, etc. present on the surface of the hollow particles can be extracted by, for example, subjecting the hollow particles to ultrasonic treatment in water. The types and masses of the surfactant, etc. extracted in water can be determined according to 1 the peak positions and peak intensities of the 1H-NMR spectrum. In this method, the detection limit of the amount of the surfactant, etc. present on the surface of the hollow particles is usually 0.05 ppm.

[0073] In the hollow particles of the present invention, the hollow part is a cavity-like space clearly distinguishable from the shell. The shell of the hollow particle may have a porous structure, and in this case, the hollow part has a size that can be clearly distinguished from the many minute spaces uniformly dispersed within the porous structure. From the viewpoint of dielectric properties and the like, the hollow particles of the present invention preferably have a dense shell.

[0074] Furthermore, from the aspect of exhibiting excellent dielectric properties, the hollow particles of the present invention preferably have the hollow part filled with a gas such as air.

[0075] The hollow particles of the present invention have one or more than two hollow portions. From the aspects of maintaining a good balance between high porosity and mechanical strength and improving dielectric properties, it is preferred to have only one hollow portion.

[0076] When the hollow particles of the present invention have only one hollow portion, the hollow particles of the present invention may contain a small amount of hollow particles having two or more hollow portions or particles having no hollow portion as impurities. In the hollow particles of the present invention, the number ratio of the particles having only one hollow portion is preferably 90% or more, more preferably 95% or more.

[0077] In addition, the shell of the hollow particles of the present invention and the partition walls separating adjacent hollow portions in the case of having two or more hollow portions may be porous, and from the aspect of improving dielectric properties, it is preferably dense.

[0078] The shape of the hollow particles of the present invention may be spherical, ellipsoidal, or amorphous, etc. From the viewpoints of the dielectric properties, dispersibility, and pressure resistance of the hollow particles, it is preferably spherical.

[0079] An example of the shape of the hollow particles of the present invention is a bag formed of a thin film and inflated by gas, and its cross-sectional view is as shown in Figure 1 the hollow particle 10B in (5). In this example, a thin film is provided on the outside, and its inside is filled with gas.

[0080] In addition, the hollow portion of the hollow particles can be confirmed by, for example, observing the cross-section of the particles by SEM or directly observing the particles by TEM. The shape of the hollow particles can be confirmed by, for example, observing the hollow particles by SEM or TEM.

[0081] The hollow particles of the present invention may contain a small amount of particles with low roundness such as cracked or deformed particles as impurities. In 100% by mass of the hollow particles of the present invention, the proportion of particles with a roundness of 0.85 or less is 10% by mass or less, preferably 7% by mass or less, more preferably 5% by mass or less, further preferably 4% by mass or less, and even more preferably 3% by mass or less. By adjusting the stirring conditions in the suspension process, polymerization process, or solvent removal process described below, the proportion of particles with a roundness of 0.85 or less can be made below the above upper limit value.

[0082] Roundness is defined as the value obtained by dividing the diameter of a circle (equivalent circular area diameter) having the same area as the projected image of the particle by the diameter of a circle (equivalent circular perimeter diameter) having the same perimeter as the projected image of the particle. In the case where the particle is a perfect sphere, the roundness is 1, and the more complex the surface shape of the particle, the smaller the value of the roundness.

[0083] The average roundness of the hollow particles of the present invention can be 0.950 to 0.995.

[0084] In the present invention, the roundness is measured using a flow particle imaging measurement device at an image resolution of 0.185 μm / pixel.

[0085] As the flow particle image measurement device, it is preferably possible to use, for example, the product name "IF-3200" manufactured by JASCO INTERNATIONAL CO., LTD. The measurement sample is prepared, for example, by adding 0.10 to 0.12 g of hollow particles to an aqueous solution (concentration 0.3%) of linear alkylbenzene sulfonate and dispersing the mixture with an ultrasonic cleaner for 5 minutes.

[0086] The average roundness is the average of the roundness of optionally 1000 to 3000 particles.

[0087] The porosity of the hollow particles of the present invention is 50% or more. When the porosity is 50% or more, the dielectric properties of the hollow particles are excellent, and furthermore, the lightness and heat insulation properties are also excellent. The porosity of the hollow particles of the present invention is preferably 55% or more, more preferably 60% or more, and further preferably 70% or more. The dielectric loss tangent of the air layer is 0, and the larger the proportion of the air layer in the hollow particles, the lower the dielectric loss tangent. Therefore, the higher the porosity of the hollow particles, the lower the dielectric loss tangent can be achieved.

[0088] The upper limit of the porosity of the hollow particles is not particularly limited, and from the aspect of suppressing the reduction of the strength of the hollow particles and making them less likely to break, it is preferably 90% or less, more preferably 85% or less, and further preferably 80% or less.

[0089] The porosity of the hollow particles is calculated based on the apparent density D 1 and the true density D 0 of the hollow particles.

[0090] The method for measuring the apparent density D 1 of the hollow particles is as follows. First, about 30 cm 3 of hollow particles are filled in a volumetric flask with a capacity of 100 cm 3 , and the mass of the filled hollow particles is accurately weighed. Then, while taking care not to let air bubbles enter, isopropanol is accurately filled up to the calibration line in the volumetric flask filled with the hollow particles. The mass of the isopropanol added to the volumetric flask is accurately weighed, and the apparent density D 1 (g / cm 3 ) of the hollow particles is calculated based on the following formula (I).

[0091] Formula (I)

[0092] Apparent density D 1= [Mass of hollow particles] / (100 - [Mass of isopropanol] / [Specific gravity of isopropanol at the measurement temperature])

[0093] Apparent density D 1 It is equivalent to the specific gravity of the entire hollow particle when the hollow part is regarded as a part of the hollow particle.

[0094] True density D of hollow particles 0 The measurement method is as follows. First, crush the hollow particles, and then fill about 10 g of fragments of the hollow particles into a volumetric flask with a volume of 100 cm 3 Precisely weigh the mass of the filled fragments. Then, add isopropanol to the volumetric flask in the same manner as the measurement of the apparent density above, precisely weigh the mass of the isopropanol, and calculate the true density D of the hollow particles based on the following formula (II) 0 (g / cm 3 )

[0095] Formula (II)

[0096] True density D 0 = [Mass of fragments of hollow particles] / (100 - [Mass of isopropanol] / [Specific gravity of isopropanol at the measurement temperature])

[0097] True density D 0 It is equivalent to the specific gravity of only the shell part in the hollow particles. Obviously, from the above measurement method, when calculating the true density D 0 the hollow part is not regarded as a part of the hollow particle.

[0098] The porosity (%) of the hollow particles is calculated based on the apparent density D 1 and the true density D 0 of the hollow particles according to the following formula (III).

[0099] Formula (III)

[0100] Porosity (%) = 100 - (Apparent density D 1 / True density D 0 ) × 100

[0101] In the case where the volume-based cumulative 50% particle size is D50 and the volume-based cumulative 95% particle size is D95 for the hollow particles of the present invention, the ratio of D95 to D50 (D95 / D50) is preferably 4.0 or less, more preferably 3.5 or less, further preferably 3.0 or less, and even more preferably less than 2.0. When the above ratio (D95 / D50) is below the above upper limit value, there is a tendency for excellent dielectric properties. In addition, when the above ratio (D95 / D50) is below the above upper limit value, particles with small deviations in inter-particle properties can be obtained. In addition, when the above ratio (D95 / D50) is below the above upper limit value, for example, when manufacturing a sheet-shaped resin structure added with the hollow particles of the present invention, a product with uniform thickness can be manufactured. The lower limit of the above ratio (D95 / D50) is not particularly limited, and from the viewpoint of ease of manufacture, it can be 1.1 or more.

[0102] In addition, D50 and D95 of the hollow particles can be obtained, for example, by measuring the particle size of the hollow particles using a particle size distribution measuring machine based on the Coulter counter method and calculating from the particle size distribution based on the volume basis. The Coulter counter method is a method of measuring the particle diameter by the resistance method called the Coulter principle.

[0103] The volume-based cumulative 50% particle size (D50) of the hollow particles of the present invention is preferably 1.0 μm or more, more preferably 1.5 μm or more, further preferably 2.0 μm or more as the lower limit, and preferably 10.0 μm or less, more preferably 7.0 μm or less, further preferably 5.0 μm or less, and even more preferably 4.0 μm or less as the upper limit.

[0104] When D50 of the hollow particles is above the above lower limit value, there is a tendency that the dispersibility of the hollow particles becomes good, and in addition, it is easy to form a uniform shell, and by suppressing the deviation of the shell thickness, the pressure resistance of the hollow particles is improved. On the other hand, when D50 of the hollow particles is below the above upper limit value, the particle size is sufficiently small, so it is preferably used as a substrate material such as a circuit board, and can also be added to a thin and small substrate.

[0105] The dielectric loss tangent of the hollow particles of the present invention at a frequency of 10 GHz is preferably 1.00×10 -3 or less, more preferably 9.00×10 -4 or less, further preferably 8.00×10 -4 or less, even more preferably 6.00×10 -4 or less, and particularly preferably 4.00×10 -4 or less. The lower limit of the above dielectric loss tangent is not particularly limited and can be, for example, 1.00×10 -4 or more.

[0106] The tangent of the dielectric loss angle of the hollow particles of the present invention at a frequency of 10 GHz can be greater than 1.00×10 -3 , in which case, the tangent of the dielectric loss angle of the hollow particles of the present invention at a frequency of 10 GHz is preferably 1.00×10 -2 Hereinafter, more preferably 9.00×10 -3 Hereinafter, further preferably 8.00×10 -3 Hereinafter.

[0107] The relative dielectric constant of the hollow particles of the present invention at a frequency of 10 GHz is preferably 1.60 or less, more preferably 1.40 or less, further preferably 1.37 or less, and still further preferably 1.36 or less. The lower limit of the above relative dielectric constant is not particularly limited and can be, for example, 1.00 or more.

[0108] In the present invention, the relative dielectric constant and the tangent of the dielectric loss angle of the hollow particles are measured using a measuring device of the perturbation method.

[0109] In the present invention, the starting temperature of thermal decomposition of the hollow particles is preferably 345 °C or higher, more preferably 350 °C or higher. The hollow particles having a starting temperature of thermal decomposition of the above lower limit value or higher have excellent heat resistance. The upper limit of the starting temperature of thermal decomposition of the hollow particles is not particularly limited and can be, for example, 400 °C or lower.

[0110] In the present invention, the starting temperature of thermal decomposition of the hollow particles can be measured under the conditions of a nitrogen flow rate of 230 mL / min and a heating rate of 10 °C / min in a nitrogen atmosphere using a TG-DTA device at the temperature when the weight loss is 5%.

[0111] Examples of the uses of the hollow particles of the present invention include components such as low dielectric materials, heat insulating materials, sound insulating materials, and light reflecting materials, and light diffusing materials such as light diffusing films or light diffusing plates for various fields such as automobiles, electrics, electronics, construction, aviation, and aerospace; food containers; shoes such as sports shoes and sandals; and uses as additives in home appliance parts, bicycle parts, stationery, tools, filaments for 3D printers, buoyancy materials such as syntactic foams, etc. Among them, from the aspects of low dielectric loss tangent, excellent dielectric properties, and excellent performance stability, the hollow particles of the present invention are preferably used as highly reliable materials in the electrical or electronic fields. For example, the hollow particles of the present invention are preferably used as circuit board materials. Specifically, by making the insulating resin layer of the circuit board contain the hollow particles of the present invention, it is possible to reduce the dielectric loss tangent of the insulating resin layer while suppressing defects caused by the hollow particles. In addition, the hollow particles of the present invention are also preferably used as additives in semiconductor materials such as interlayer insulating materials, dry film resists, solder resists, bonding wires, magnet wires, semiconductor encapsulating materials, epoxy encapsulating materials, die bottom filling materials, bottom filling materials, chip bonding pastes, buffer coating materials, copper clad laminates, flexible substrates, etc., or as additives in semiconductor materials for high-frequency device modules, antenna modules, automotive radars, etc. Among them, it is particularly preferably used as an additive in semiconductor materials such as interlayer insulating materials, solder resists, magnet wires, semiconductor encapsulating materials, epoxy encapsulating materials, bottom filling materials, buffer coating materials, copper clad laminates, flexible substrates, etc., or as an additive in semiconductor materials for high-frequency device modules, antenna modules, automotive radars, etc. In addition, the hollow particles of the present invention are not limited to being used in semiconductor materials and can be used in various electronic materials.

[0112] In addition, the hollow particles of the present invention are also useful as additives for insulating resin sheets for manufacturing electronic components such as printed circuit boards. The insulating resin sheet containing the hollow particles of the present invention can be manufactured, for example, by preparing a resin composition in which a thermoplastic resin, a thermosetting resin, a thermoplastic elastomer, or a mixture thereof is mixed with the hollow particles of the present invention, and drying, extrusion molding, or molding into a sheet shape by transfer or the like by applying the resin composition to one or both sides of a sheet-like substrate. When the resin or elastomer contained in the insulating resin sheet has adhesiveness, the insulating resin sheet can be used as an adhesive sheet. Specifically, for example, it can be used as a bonding sheet. In the case of manufacturing a multilayer printed circuit board, the bonding sheet is a material for forming an insulating adhesive layer for bonding a conductor layer and an organic insulating layer.

[0113] In addition, due to the high porosity, the hollow particles of the present invention are not easily broken and have excellent heat resistance. Therefore, they meet the heat insulation and cushioning properties required for the bottom coating material and also meet the heat resistance required for thermal paper applications. In addition, the hollow particles of the present invention are also useful as plastic pigments with excellent gloss, hiding power, etc.

[0114] Furthermore, the hollow particles of the present invention can encapsulate useful components such as fragrances, chemicals, pesticides, and ink components inside them by means of impregnation treatment, reduced-pressure or pressure-impregnation treatment, etc. Therefore, they can be utilized in various applications according to the components contained inside.

[0115] Furthermore, the hollow particles of the present invention are also preferably used as rust inhibitors. The hollow particles of the present invention are also useful as additives for reducing electrical conductivity. Therefore, for example, a coating containing the hollow particles of the present invention can be used as a rust-proof coating (such as a painting primer, lubricating coating, etc.) for improving the corrosion resistance and rust prevention of steel materials, etc. In addition, rust prevention additives can also be encapsulated inside the hollow particles added to the rust-proof coating.

[0116] 2. Manufacturing method of hollow particles

[0117] The hollow particles of the present invention are manufactured by, for example, the manufacturing method described below based on the suspension polymerization method. In the manufacturing method of the hollow particles described below, by adjusting the stirring conditions in the suspension process, polymerization process, solvent removal process, etc., hollow particles with a small proportion of abnormal-shaped particles can be obtained.

[0118] As an embodiment of the manufacturing method of the hollow particles of the present invention, a manufacturing method of hollow particles having the following steps can be cited:

[0119] A step of preparing a mixed solution containing a polymerizable monomer, a hydrophobic solvent, a polymerization initiator, a dispersion stabilizer, and an aqueous medium;

[0120] A step of preparing a suspension in which droplets of a monomer composition containing the polymerizable monomer, the hydrophobic solvent, and the polymerization initiator are dispersed in the aqueous medium by suspending the above mixed solution;

[0121] A step of preparing a precursor composition in which precursor particles are dispersed in the aqueous medium by subjecting the above suspension to a polymerization reaction, wherein the precursor particles have a hollow portion surrounded by a shell containing resin and the hollow portion is filled with the hydrophobic solvent;

[0122] A step of obtaining an aqueous dispersion of hollow particles by blowing gas into the precursor composition while stirring the precursor composition in a stirring tank to remove the hydrophobic solvent from the precursor particles;

[0123] A step of performing cleaning for removing the above-described dispersion stabilizer remaining in the above-described hollow particles is carried out.

[0124] In the above-described production method, a suspension in which droplets of a monomer composition having a distribution structure in which a polymerizable monomer and a hydrophobic solvent are phase-separated, the polymerizable monomer is biased to exist on the surface side, and the hydrophobic solvent is biased to exist in the central portion are dispersed in an aqueous medium is prepared by suspending a mixture solution containing a polymerizable monomer, a hydrophobic solvent, a polymerization initiator, a dispersion stabilizer, and an aqueous medium. When this suspension is subjected to a polymerization reaction, a polymer starts to precipitate on the surface of the droplets of the monomer composition, and then, by carrying out the polymerization reaction, a shell is formed by curing the surface of the droplets, and hollow particles having a hollow portion filled with a hydrophobic solvent are obtained.

[0125] In addition, in the present invention, it is considered that hollow particles having a hollow portion filled with a hydrophobic solvent are intermediates of hollow particles having a hollow portion filled with a gas, and there are cases where they are referred to as "precursor particles". In the present invention, a "precursor composition" refers to a composition containing precursor particles.

[0126] In the production methods of hollow particles described in Patent Documents 1 and 2, after performing cleaning for removing the dispersion stabilizer, the hydrophobic solvent is removed from the precursor particles. In this method, there is a problem that aggregation of the precursor particles occurs during the cleaning step, and the cleanability deteriorates. It is speculated that since the cleaning of the precursor particles cannot be sufficiently carried out, the amounts of unreacted polymerizable monomer and metal remaining in the obtained hollow particles are large, and they cause an increase in the dielectric loss tangent of the hollow particles. The present inventors have found that in an aqueous dispersion of precursor particles used in the cleaning step, a large amount of hydrophobic solvent and unreacted polymerizable monomer becomes one of the reasons for the deterioration of cleanability, and thus have completed the above-described production method. In the above-described production method, since the hydrophobic solvent is removed from the precursor particles in the slurry and then cleaning for removing the dispersion stabilizer is carried out, the amount of unreacted polymerizable monomer remaining is also reduced by removing the hydrophobic solvent from the hollow particles before the cleaning step. Therefore, it is speculated that the hollow particles are less likely to aggregate during the cleaning step, and the cleaning of the particles can be thoroughly carried out. As a result, hollow particles with improved cleanability, very small amounts of unreacted polymerizable monomer and metal remaining after cleaning, and a low dielectric loss tangent can be obtained.

[0127] The above manufacturing method includes the steps of preparing a mixed solution, preparing a suspension, supplying the suspension to a polymerization reaction, removing a hydrophobic solvent from precursor particles, and performing a cleaning for removing a dispersion stabilizer, and may further include steps other than these. In addition, as long as it is technically feasible, two or more of the above steps and other additional steps may be carried out simultaneously as one step, or the order may be changed. For example, the preparation of the mixed solution and the suspension may be carried out simultaneously in one step in such a manner that the materials for preparing the mixed solution are introduced while performing suspension at the same time.

[0128] As a preferred example of the manufacturing method of the hollow particles of the present invention, a manufacturing method including the following steps can be cited.

[0129] (1) Mixed solution preparation step

[0130] A step of preparing a mixed solution containing a polymerizable monomer, a hydrophobic solvent, a polymerization initiator, a dispersion stabilizer, and an aqueous medium;

[0131] (2) Suspension step

[0132] A step of preparing a suspension in which droplets of a monomer composition containing a polymerizable monomer, a hydrophobic solvent, and a polymerization initiator are dispersed in an aqueous medium by suspending the above mixed solution;

[0133] (3) Polymerization step

[0134] A step of preparing a precursor composition in which precursor particles are dispersed in an aqueous medium by supplying the above suspension to a polymerization reaction, wherein the precursor particles have a hollow portion surrounded by a shell containing a resin and the hollow portion is filled with a hydrophobic solvent;

[0135] (4) Solvent removal step

[0136] A step of removing the above hydrophobic solvent from the above precursor particles while stirring the above precursor composition in a stirring tank and blowing a gas into the above precursor composition to obtain an aqueous dispersion of hollow particles; and

[0137] (5) Cleaning step

[0138] A step of performing a cleaning for removing the above dispersion stabilizer remaining in the above hollow particles.

[0139] Figure 1 is a schematic diagram showing an example of the manufacturing method of the present invention. Figure 1 In (1) to (5), they correspond to the above steps (1) to (5). The white arrows between the figures indicate the order of the steps. In addition, Figure 1This is only a schematic diagram for illustration purposes. The manufacturing method of the present invention is not limited to the manufacturing method shown in the figure. In addition, the structure, size, and shape of the materials used in the manufacturing method of the present invention are not limited to the structure, size, and shape of various materials in these figures.

[0140] Figure 1 (1) of is a cross-sectional schematic diagram showing an embodiment of the mixture in the mixture preparation step. As shown in this figure, the mixture contains an aqueous medium 1 and a low-polarity material 2 dispersed in the aqueous medium 1. Here, the low-polarity material 2 refers to a material with low polarity and difficult to mix with the aqueous medium 1. In the present invention, the low-polarity material 2 contains a polymerizable monomer, a hydrophobic solvent, and a polymerization initiator.

[0141] Figure 1 (2) of is a cross-sectional schematic diagram showing an embodiment of the suspension in the suspension step. The suspension contains an aqueous medium 1 and droplets 3 of a monomer composition dispersed in the aqueous medium 1. The droplets 3 of the monomer composition contain a polymerizable monomer, a hydrophobic solvent, and a polymerization initiator, and the distribution inside the droplets is uneven. The droplets 3 of the monomer composition have the following structure: the hydrophobic solvent 4a and the material 4b other than the hydrophobic solvent containing the polymerizable monomer are phase-separated, the hydrophobic solvent 4a tends to exist in the central part, the material 4b other than the hydrophobic solvent tends to exist on the surface side, and a dispersion stabilizer (not shown) adheres to the surface.

[0142] Figure 1 (3) of is a cross-sectional schematic diagram showing an embodiment of the precursor composition containing precursor particles obtained through the polymerization step. The above precursor particles enclose a hydrophobic solvent in the hollow part. The precursor particles 5 have a shell 6 containing resin and a hollow part filled with the hydrophobic solvent 4a. The shell 6 forming the outer surface of the precursor particles 5 is formed by the polymerization of the polymerizable monomer contained in the droplets 3 of the monomer composition. In Figure 1 (3) of, the precursor particles 5 are dispersed in the aqueous medium 1.

[0143] Figure 1 (4) of is a cross-sectional schematic diagram showing an embodiment of the aqueous dispersion of hollow particles obtained in the solvent removal step. In the solvent removal step, by removing the hydrophobic solvent from the precursor particles, hollow particles 10A having a shell 6 containing resin and a hollow part 7 filled with gas are obtained. In Figure 1 (4) of, the hollow particles 10A are dispersed in the aqueous medium 1.

[0144] Figure 1 (5) of is a cross-sectional schematic diagram showing an embodiment of the hollow particles after the cleaning step. The hollow particles 10B after the cleaning step have a reduced amount of residual polymerizable monomer and a reduced amount of residual metal compared to the hollow particles 10A before the cleaning step.

[0145] Hereinafter, the above five processes and other processes will be described in sequence.

[0146] (1) Mixed solution preparation process

[0147] This process is a process for preparing a mixed solution containing a polymerizable monomer, a hydrophobic solvent, a polymerization initiator, a dispersion stabilizer, and an aqueous medium. Within the range that does not impair the effects of the present invention, the mixed solution may further contain other materials.

[0148] Regarding the materials of the mixed solution, they will be described in the order of (A) polymerizable monomer, (B) hydrophobic solvent, (C) polymerization initiator, (D) dispersion stabilizer, and (E) aqueous medium.

[0149] (A) Polymerizable monomer

[0150] In the present invention, the polymerizable monomer refers to a compound having a functional group capable of addition polymerization (in the present invention, there are cases where it is only called a polymerizable functional group). In the present invention, as the polymerizable monomer, a compound having an ethylenic unsaturated bond as the functional group capable of addition polymerization is usually used.

[0151] In the present invention, as the polymerizable monomer, known polymerizable monomers that have been used for the production of hollow polymer particles can be used, and there is no particular limitation. From the aspect of easily forming a hollow portion inside the particles, it is preferably at least a crosslinkable monomer, and more preferably further contains a non-crosslinkable monomer. When the polymerizable monomer contains a crosslinkable monomer, when the suspension is subjected to a polymerization reaction, the crosslinking density of the polymer precipitated on the surface of the droplets becomes higher, and further the precipitates are crosslinked with each other, so that the crosslinking density of the shell can be increased. Therefore, it is easy to form a shell with excellent strength. In addition, the hollow particles are easily spherical, and a hollow portion clearly distinguishable from the shell is easily formed inside the particles.

[0152] In addition, in the present invention, a polymerizable monomer having only one polymerizable functional group is called a non-crosslinkable monomer, and a polymerizable monomer having two or more polymerizable functional groups is called a crosslinkable monomer. The crosslinkable monomer can form a crosslinking bond in the polymer through a polymerization reaction. The crosslinkable monomer becomes a crosslinkable monomer unit in the shell, and the non-crosslinkable monomer becomes a non-crosslinkable monomer unit in the shell.

[0153] In addition, in the present invention, a polymerizable monomer composed of carbon and hydrogen is referred to as a hydrocarbon monomer, a crosslinkable monomer composed of carbon and hydrogen is referred to as a crosslinkable hydrocarbon monomer, and a non-crosslinkable monomer composed of carbon and hydrogen is referred to as a non-crosslinkable hydrocarbon monomer. Further, a polymerizable monomer having a (meth)acryloyl group as a polymerizable functional group is referred to as an acrylic monomer, a crosslinkable monomer having a (meth)acryloyl group as a polymerizable functional group is referred to as a crosslinkable acrylic monomer, and a non-crosslinkable monomer having a (meth)acryloyl group as a polymerizable functional group is referred to as a non-crosslinkable acrylic monomer. In the crosslinkable acrylic monomer, as long as at least one polymerizable functional group is a (meth)acryloyl group, it is sufficient, but it is preferred that all polymerizable functional groups are (meth)acryloyl groups.

[0154] In addition, in the present 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.

[0155] Examples of the crosslinkable monomer include aromatic divinyl monomers such as divinylbenzene, divinylbiphenyl, and divinylnaphthalene; linear or branched dienes such as butadiene, isoprene, 2,3-dimethylbutadiene, pentadiene, and hexadiene, and alicyclic dienes such as dicyclopentadiene, cyclopentadiene, and ethylidene tetracyclododecene, etc., i.e., diene-based monomers; crosslinkable macromonomers such as crosslinkable hydrocarbon monomers such as polybutadiene, polyisoprene, block copolymers of styrene and butadiene (SBS), and block copolymers of styrene and isoprene (SIS); crosslinkable acrylic monomers such as allyl (meth)acrylate, vinyl (meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, 3-(meth)acryloyloxy-2-hydroxypropyl (meth)acrylate, trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol poly(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, bisphenol A di(meth)acrylate, and their ethoxylates; crosslinkable allyl-based monomers such as diallyl phthalate; crosslinkable macromonomers such as polyphenylene ether with vinyl modification at both ends and polyphenylene ether with methacrylic acid modification at both ends. These crosslinkable monomers can be used alone or in combination of two or more.

[0156] As a crosslinkable monomer, from the aspect of reducing the dielectric loss tangent of the hollow particles, a crosslinkable hydrocarbon monomer is preferred, an aromatic divinyl monomer is more preferred, and divinylbenzene is particularly preferred.

[0157] Examples of non-crosslinkable monomers include: aromatic monovinyl monomers such as styrene, vinyltoluene, α-methylstyrene, p-methylstyrene, ethylvinylbenzene, ethylvinylbiphenyl, and ethylvinylnaphthalene; linear or branched monoolefins such as ethylene, propylene, and butene, and alicyclic monoolefins such as vinylcyclohexane, norbornene, tricyclododecene, and 1,4-methano-1,4,4a,9a-tetrahydrofluorene; non-crosslinkable acrylic monomers such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, tert-butylaminoethyl (meth)acrylate, glycidyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-aminoethyl (meth)acrylate, (meth)acrylic acid, (meth)acrylamide, N-hydroxymethyl(meth)acrylamide, N-butoxymethyl(meth)acrylamide, methoxypolyethylene glycol (meth)acrylate, ethoxypolyethylene glycol (meth)acrylate, propoxypolyethylene glycol (meth)acrylate, butoxypolyethylene glycol (meth)acrylate, hexoxypolyethylene glycol (meth)acrylate, octoxypolyethylene glycol polypropylene glycol (meth)acrylate, lauryloxypolyethylene glycol (meth)acrylate, stearyloxypolyethylene glycol (meth)acrylate, phenoxypolyethylene glycol polypropylene glycol (meth)acrylate, polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, polyethylene glycol propylene glycol mono(meth)acrylate, polyethylene glycol tetramethylene glycol (meth)acrylate, propylene glycol polybutylene glycol mono(meth)acrylate, and monoethylene glycol mono(meth)acrylate; carboxylic acid vinyl ester monomers such as vinyl acetate; halogenated aromatic vinyl monomers such as halogenated styrene; halogenated vinyl monomers such as vinyl chloride; vinylidene dihalide monomers such as vinylidene dichloride; vinylpyridine monomers; polystyrene modified at the end with (meth)acrylic acid; and non-crosslinkable macromonomers such as polymethyl methacrylate modified at the end with (meth)acrylic acid.

[0158] These non-crosslinkable monomers can be used alone or in combination of two or more.

[0159] As a non-crosslinkable monomer, from the aspect of reducing the dielectric loss tangent of the hollow particles, a non-crosslinkable hydrocarbon monomer is preferred, an aromatic monovinyl monomer is more preferred, and styrene and ethylvinylbenzene are further preferred.

[0160] In the present invention, from the aspect of improving the strength of the shell and from the aspect of facilitating the maintenance of a high porosity and good dielectric properties of the hollow particles, the content of the crosslinkable monomer in 100% by mass of the polymerizable monomer is preferably 60% by mass or more, more preferably 70% by mass or more, still more preferably 80% by mass or more, and even more preferably 90% by mass or more.

[0161] The polymerizable monomer may be a polymerizable monomer composed of a crosslinkable monomer, but there are also cases where the dielectric properties of the hollow particles are improved when a combination containing a crosslinkable monomer and a non-crosslinkable monomer is used as the polymerizable monomer. The content of the crosslinkable monomer in 100% by mass of the polymerizable monomer may be, for example, 98% by mass or less.

[0162] In addition, the content of the crosslinkable monomer in 100% by mass of the polymerizable monomer corresponds to the content of the crosslinkable monomer units in all the monomer units of 100% by mass of the polymer contained in the shell. Similarly, the content of each monomer in 100% by mass of the polymerizable monomer corresponds to the content of each monomer unit in all the monomer units of 100% by mass of the polymer contained in the shell.

[0163] From the aspect of improving the dielectric properties of the hollow particles, in 100% by mass of the polymerizable monomer, the content of the hydrocarbon monomer is preferably more than 50% by mass, more preferably 70% by mass or more, still more preferably 85% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more. The above polymerizable monomer may also be composed of a hydrocarbon monomer. There is a tendency that the higher the proportion of the hydrocarbon monomer in the polymerizable monomer, the more the dielectric properties of the hollow particles are improved.

[0164] In addition, when the content of the aromatic hydrocarbon unit in 100% by mass of the polymerizable monomer is more than 20% by mass, the content of the crosslinkable monomer in 100% by mass of the polymerizable monomer may also be less than 60% by mass. When the content of the aromatic hydrocarbon unit is more than 20% by mass, due to the occurrence of π-π interaction, even if the content of the crosslinkable monomer is less than 60% by mass, a decrease in the strength of the shell can be suppressed and the hollow particles can maintain a high porosity. Here, the aromatic hydrocarbon monomer is specifically the above aromatic divinyl monomer and aromatic monovinyl monomer.

[0165] In addition, when the content of the aromatic hydrocarbon unit is more than 20% by mass, from the aspect of improving the strength of the shell and from the aspect of facilitating the maintenance of a high porosity and good dielectric properties of the hollow particles, the content of the crosslinkable monomer in 100% by mass of the polymerizable monomer is preferably 20% by mass or more, more preferably 30% by mass or more, and still more preferably 35% by mass or more.

[0166] When the content of the crosslinkable monomer in 100% by mass of the polymerizable monomer is less than 60% by mass, from the aspect of improving the strength of the shell and from the aspect that the hollow particles are likely to maintain a high porosity and the dielectric properties are likely to be improved, the content of the aromatic hydrocarbon unit is more preferably 30% by mass or more, and further preferably 40% by mass or more.

[0167] On the other hand, from the aspect of suppressing the deterioration of the dielectric properties and the performance stability of the hollow particles, in 100% by mass of the polymerizable monomer, the content of the modified polyphenylene ether as a macromonomer is preferably 20% by mass or less, more preferably 10% by mass or less, and further preferably 5% by mass or less. In addition, through vinyl modification or (meth)acrylic acid modification, etc., the modified polyphenylene ether contains a crosslinkable macromonomer having a polymerizable functional group at at least one end and a non-crosslinkable macromonomer.

[0168] In addition, from the aspect of suppressing the increase in the conductivity of the aqueous dispersion of the hollow particles and suppressing the decrease in the performance stability of the hollow particles, in 100% by mass of the polymerizable monomer, the total content of epoxy group-containing monomers such as glycidyl (meth)acrylate and hydroxyl group-containing monomers such as 2-hydroxyethyl (meth)acrylate is preferably 20% by mass or less, more preferably 10% by mass or less, and further preferably 5% by mass or less. There is a case where the epoxy group is ring-opened to become a hydroxyl group, and the hydroxyl groups contained in the hollow particles capture metal ions. Therefore, by reducing the content of the epoxy group-containing monomer and the hydroxyl group-containing monomer, the amount of metal attached to the surface of the hollow particles can be reduced. As a result, the increase in the conductivity of the aqueous dispersion of the hollow particles can be suppressed, and in addition, the decrease in the performance stability of the hollow particles can be suppressed.

[0169] The content of the polymerizable monomer in the mixed solution is not particularly limited. From the viewpoint of the balance of the porosity, particle size, and mechanical strength of the hollow particles, it is preferably 15 to 50% by mass, more preferably 20 to 40% by mass, based on the total mass of the components in the mixed solution other than the water-based medium in 100% by mass. When the content of the polymerizable monomer in the mixed solution is within the above range, the hydrophobic solvent can be efficiently removed in the solvent removal step. As a result, the dispersion stabilizer remaining in the hollow particles can be efficiently removed in the cleaning step, and thus hollow particles having excellent dielectric properties and performance stability can be obtained.

[0170] In addition, in the obtained hollow particles, from the aspect of suppressing the deterioration of the dielectric properties and the decrease in the strength, the content of the polymerizable monomer is preferably 96% by mass or more, more preferably 97% by mass or more, based on the total mass of 100% of the solid components other than the hydrophobic solvent in the material that becomes the oil phase in the mixed solution.

[0171] In addition, in the present invention, the solid component is all components other than the solvent, and liquid polymerizable monomers and the like are included in the solid component.

[0172] (B) Hydrophobic solvent

[0173] The hydrophobic solvent used in the production method of the present invention is a non-polymerizable and water-insoluble organic solvent.

[0174] The hydrophobic solvent functions as a spacer material for forming a hollow portion inside the particles. In the suspension step described later, a suspension in which droplets of a monomer composition containing the hydrophobic solvent are dispersed in an aqueous medium is obtained. In the suspension step, phase separation occurs inside the droplets of the monomer composition, and as a result, the less polar hydrophobic solvent tends to aggregate inside the droplets. Finally, in the droplets of the monomer composition, the hydrophobic solvent is distributed inside according to its polarity, and other materials other than the hydrophobic solvent are distributed at the periphery according to their polarities.

[0175] Moreover, in the polymerization step described later, an aqueous dispersion containing precursor particles encapsulating the hydrophobic solvent is obtained. That is, the hydrophobic solvent aggregates inside the particles, thereby forming a hollow portion filled with the hydrophobic solvent inside the obtained precursor particles.

[0176] The hydrophobic solvent can be appropriately selected from known hydrophobic solvents and is not particularly limited. Examples include esters such as ethyl acetate and butyl acetate; ether esters such as propylene glycol monomethyl ether acetate and propylene glycol monoethyl ether acetate; and hydrocarbon solvents. Among them, hydrocarbon solvents are preferred, and hydrocarbon solvents having 5 to 8 carbon atoms are more preferred.

[0177] Examples of the hydrocarbon solvent include aliphatic hydrocarbons such as chain hydrocarbon solvents containing pentane, hexane, heptane, octane, 2-methylbutane, 2-methylpentane, and paraffin solvents, and cyclohexane, methylcyclohexane, and cycloheptane; and aromatic hydrocarbons such as benzene, toluene, and xylene.

[0178] These hydrophobic solvents can be used alone or in combination of two or more.

[0179] In the suspension step, from the aspect that phase separation easily occurs between the polymerizable monomer and the hydrophobic solvent inside the droplets of the monomer composition, as the hydrophobic solvent, an organic solvent having a lower solubility in water than the crosslinkable monomer contained in the polymerizable monomer is preferably selected.

[0180] In addition, when the polymerizable monomer contains a hydrocarbon compound in a proportion of more than 50%, as the hydrophobic solvent, a hydrocarbon solvent is preferred, a chain hydrocarbon solvent is more preferred, a chain hydrocarbon solvent having 5 to 8 carbon atoms is further preferred, and at least one selected from pentane, hexane, heptane, and octane is even more preferred.

[0181] In addition, the boiling point of the hydrophobic solvent is not particularly limited. From the aspect of being easily removed in the solvent removal step described later, it is preferably 130°C or lower, more preferably 100°C or lower. On the other hand, from the aspect of being easily encapsulated in the precursor particles, it is preferably 50°C or higher, more preferably 60°C or higher.

[0182] In addition, the hydrophobic solvent is a mixed solvent containing a plurality of hydrophobic solvents. In the case of having a plurality of boiling points, it is preferred that the boiling point of the solvent with the highest boiling point among the solvents contained in the mixed solvent is below the above upper limit value, and the boiling point of the solvent with the lowest boiling point among the solvents contained in the mixed solvent is above the above lower limit value.

[0183] In addition, the hydrophobic solvent preferably has a relative dielectric constant at 20°C of 2.5 or less. The relative dielectric constant is one of the indexes indicating the polarity of a compound. It is considered that when the relative dielectric constant of the hydrophobic solvent is sufficiently small to 2.5 or less, phase separation proceeds rapidly in the droplets of the monomer composition, and it is easy to form a hollow part.

[0184] Examples of the hydrophobic solvent having a relative dielectric constant at 20°C of 2.5 or less are as follows. The value in parentheses is the relative dielectric constant value.

[0185] Pentane (1.8), hexane (1.9), heptane (1.9), octane (1.9), cyclohexane (2.0).

[0186] Regarding the relative dielectric constant at 20°C, the values described in publicly known documents (for example, "Chemical Handbook Basic Edition" edited by the Chemical Society of Japan, Revised 4th Edition, Maruzen Co., Ltd., issued on September 30, Heisei 5, pages II-498 to II-503) and other technical information can be referred to. As a method for measuring the relative dielectric constant at 20°C, for example, a relative dielectric constant test carried out in accordance with 23 of JIS C2101:1999 with the measurement temperature set at 20°C can be cited.

[0187] By changing the amount of the hydrophobic solvent in the mixed liquid, the porosity of the hollow particles can be adjusted. In the suspension step described later, the polymerization reaction is carried out in a state where the hydrophobic solvent is encapsulated in the oil droplets containing the polymerizable monomer and the like. Therefore, there is a tendency that the higher the content of the hydrophobic solvent, the higher the porosity of the obtained hollow particles.

[0188] In the present invention, from the aspects of easy control of the particle size of the hollow particles, easy improvement of the porosity while maintaining the strength of the hollow particles, and easy reduction of the amount of residual hydrophobic solvent in the particles, the content of the hydrophobic solvent in the mixed solution is preferably 100 parts by mass or more and 650 parts by mass or less with respect to 100 parts by mass of the polymerizable monomer. The content of the hydrophobic solvent in the mixed solution is more preferably 120 parts by mass or more and 500 parts by mass or less, and further preferably 140 parts by mass or more and 300 parts by mass or less, with respect to 100 parts by mass of the polymerizable monomer.

[0189] (C) Polymerization initiator

[0190] In the production method of the present invention, the mixed solution preferably contains an oil-soluble polymerization initiator as the polymerization initiator. The oil-soluble polymerization initiator is not particularly limited as long as it is a lipophilic polymerization initiator having a solubility in water of 0.2% by mass or less, and examples thereof include organic peroxides such as benzoyl peroxide, lauroyl peroxide, tert-butyl peroxy-2-ethylhexanoate, tert-butyl peroxy diethylacetate, and tert-butyl peroxy pivalate; and azo compounds such as 2,2'-azobis(2,4-dimethylvaleronitrile), azobisisobutyronitrile, and 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile). Among them, from the aspect of easy improvement of the dielectric properties of the hollow particles, it is preferable to use an organic peroxide as the oil-soluble polymerization initiator. When an organic peroxide is used as the polymerization initiator, it is easy to reduce the amount of unreacted polymerizable monomer remaining in the shell. In addition, when the decomposition product of the polymerization initiator remains in the shell, there is a tendency to increase the molecular motion of the shell, but the decomposition product of the organic peroxide is easily removed. Therefore, when an organic peroxide is used as the polymerization initiator, the amount of the decomposition product of the polymerization initiator remaining in the shell can be reduced, and the increase in the molecular motion of the shell can be suppressed.

[0191] The content of the polymerization initiator is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 7 parts by mass, and further preferably 1 to 5 parts by mass, with respect to 100 parts by mass of the polymerizable monomer in the mixed solution. When the content of the polymerization initiator is above the above lower limit value, the polymerization reaction can proceed sufficiently, and when it is below the above upper limit value, after the polymerization reaction is completed, the possibility of the polymerization initiator remaining is small, and the possibility of unexpected side reactions occurring is also small.

[0192] (D) Dispersion stabilizer

[0193] The dispersion stabilizer is a preparation for dispersing the droplets of the monomer composition in the aqueous medium in the suspension step. Examples of the dispersion stabilizer include inorganic dispersion stabilizers, water-soluble polymer stabilizers of organic or inorganic systems, and surfactants.

[0194] In the present invention, from the aspects of easy control of the particle size of droplets in the suspension, easy removal of the dispersion stabilizer by the cleaning process, and suppression of the shell becoming too thin and reduction of the strength of the hollow particles, it is preferable to use an inorganic dispersion stabilizer as the dispersion stabilizer.

[0195] Examples of the inorganic dispersion stabilizer 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; metal hydroxides such as aluminum hydroxide, magnesium hydroxide, calcium hydroxide, barium hydroxide, and iron hydroxide; and inorganic compounds such as silicon dioxide. These inorganic dispersion stabilizers can be used alone or in combination of two or more.

[0196] As the inorganic dispersion stabilizer, a water-insoluble inorganic dispersion stabilizer is particularly preferably used. Here, water-insoluble preferably means that the solubility in water at 25 °C is less than 1 g / L.

[0197] Among the water-insoluble inorganic dispersion stabilizers, metal hydroxides are preferred, and magnesium hydroxide is more preferred.

[0198] In the present invention, in particular, it is preferable to use the water-insoluble inorganic dispersion stabilizer in a state where it is dispersed in the aqueous medium in the form of colloidal particles, that is, in the state of a colloidal dispersion containing water-insoluble inorganic dispersion stabilizer colloidal particles. Thereby, the inorganic dispersion stabilizer can be easily removed by the cleaning process described later.

[0199] The colloidal dispersion containing water-insoluble inorganic dispersion stabilizer colloidal particles can be prepared, for example, by reacting at least one selected from alkali metal hydroxides and alkaline earth metal hydroxides with a water-soluble polyvalent metal salt (excluding alkaline earth metal hydroxides) in an aqueous medium.

[0200] Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, potassium hydroxide, etc. Examples of the alkaline earth metal hydroxide include barium hydroxide and calcium hydroxide.

[0201] As the water-soluble polyvalent metal salt, any water-soluble polyvalent metal salt other than the compounds belonging to the above-mentioned alkaline earth metal hydroxides can be used. 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; zinc salts such as zinc chloride, zinc nitrate, and zinc acetate, etc. 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.

[0202] The method of reacting at least one selected from the above-mentioned alkali metal hydroxides and alkaline earth metal hydroxides with the above-mentioned water-soluble polyvalent metal salt in an aqueous medium is not particularly limited. For example, an aqueous solution of at least one selected from alkali metal hydroxides and alkaline earth metal hydroxides may be mixed with an aqueous solution of the water-soluble polyvalent metal salt.

[0203] In addition, colloidal silica can also be used as the colloidal dispersion liquid containing water-insoluble inorganic dispersion stabilizer colloidal particles.

[0204] Examples of the organic water-soluble polymer stabilizer include polyvinyl alcohol, polycarboxylic acids (such as polyacrylic acid), celluloses (such as hydroxyethyl cellulose, carboxymethyl cellulose, methyl cellulose, ethyl cellulose, etc.), polyvinylpyrrolidone, polyacrylimide, polyethylene oxide, poly(hydroxystearic acid-g-methyl methacrylate-co-methacrylic acid) copolymer, and the like.

[0205] Examples of the inorganic water-soluble polymer stabilizer include sodium tripolyphosphate and the like.

[0206] A surfactant refers to a compound having both a hydrophilic group and a hydrophobic group in one molecule, and examples thereof include known ionic surfactants such as anionic surfactants, cationic surfactants, and amphoteric surfactants, and nonionic surfactants.

[0207] In addition, the water-soluble polymer stabilizer and the surfactant usually have a solubility of 1 g / L or more in water at 25°C.

[0208] The content of the dispersion stabilizer is not particularly limited, and is preferably 0.5 to 15 parts by mass, more preferably 1 to 10 parts by mass, based on 100 parts by mass of the total mass of the polymerizable monomer and the hydrophobic solvent. By making the content of the dispersion stabilizer not less than the above lower limit value, the droplets of the monomer composition can be sufficiently dispersed in the suspension without coalescence. On the other hand, by making the content of the dispersion stabilizer not more than the above upper limit value, an increase in the viscosity of the suspension can be prevented during granulation, and an adverse condition of clogging of the granulator by the suspension can be avoided.

[0209] In addition, the content of the dispersion stabilizer is preferably 0.5 to 15 parts by mass, more preferably 0.5 to 10 parts by mass, based on 100 parts by mass of the aqueous medium.

[0210] In the hollow particles of the present invention, from the viewpoint of suppressing deterioration of dielectric properties and deterioration of performance stability, the smaller the residual amount of the dispersion stabilizer, the more preferable, and it is most preferable not to contain a dispersion stabilizer, and in particular, it is preferable not to contain an organic water-soluble polymer stabilizer, an inorganic water-soluble polymer stabilizer, and a surfactant. By using only an inorganic dispersion stabilizer as the dispersion stabilizer, hollow particles in which any one of an organic water-soluble polymer stabilizer, an inorganic water-soluble polymer stabilizer, or a surfactant is less than the detection limit value can be obtained.

[0211] (E) Aqueous medium

[0212] In the present invention, the aqueous medium refers to a medium selected from water, a hydrophilic solvent, and a mixture of water and a hydrophilic solvent.

[0213] In the case of using a mixture of water and a hydrophilic solvent, from the viewpoint of forming droplets of the monomer composition, it is important not to make the polarity of the whole mixture too low. In this case, the mass ratio of water to the hydrophilic solvent (water∶hydrophilic solvent) can be, for example, 99∶1 to 50∶50.

[0214] The hydrophilic solvent in the present invention may be any hydrophilic solvent that is sufficiently mixed with water without phase separation, and is not particularly limited. Examples of the hydrophilic solvent include alcohols such as methanol and ethanol; tetrahydrofuran (THF); dimethyl sulfoxide (DMSO), etc.

[0215] The content of the aqueous medium is not particularly limited. From the viewpoint of making the particle diameter and porosity of the hollow particles within the preferred ranges described later, as the lower limit, it is preferably 200 parts by mass or more, more preferably 400 parts by mass or more, still more preferably 600 parts by mass or more, and as the upper limit, it is preferably 1000 parts by mass or less, more preferably 800 parts by mass or less, relative to 100 parts by mass of the polymerizable monomer contained in the mixed liquid.

[0216] The mixed liquid may further contain other materials different from the above-mentioned materials (A) to (E) within a range that does not impair the effects of the present invention.

[0217] The mixed liquid is obtained by mixing the above-mentioned respective materials and other materials as required and appropriately stirring, etc. In this mixed liquid, an oil phase containing the above-mentioned (A) polymerizable monomer, (B) hydrophobic solvent, and (C) polymerization initiator and other lipophilic materials is dispersed in a water phase containing (D) dispersion stabilizer and (E) aqueous medium, etc., in a size of about several millimeters in particle diameter. The dispersion state of these materials in the mixed liquid can also be observed with the naked eye depending on the type of the materials.

[0218] In the step of preparing the mixture, the mixture can be obtained by simply mixing and appropriately stirring the above-mentioned respective materials and other materials as needed. However, from the aspect that the shell is likely to become uniform, it is preferable to prepare the mixture in the following manner: separately prepare an oil phase containing a polymerizable monomer, a hydrophobic solvent, and a polymerization initiator and an aqueous phase containing a dispersion stabilizer and an aqueous medium in advance, and mix them. In the present invention, a colloidal dispersion in which a water-insoluble inorganic dispersion stabilizer is dispersed in the aqueous medium in the form of colloidal particles can be preferably used as the aqueous phase.

[0219] In this way, on the basis of separately preparing the oil phase and the aqueous phase in advance, by mixing them, hollow particles with a uniform composition of the shell part can be prepared, and it is also easy to control the particle size of the hollow particles.

[0220] (2) Suspension step

[0221] The suspension step is a step of preparing a suspension in which droplets of a monomer composition containing a hydrophobic solvent are dispersed in an aqueous medium by suspending the above-mentioned mixture.

[0222] The suspension method for forming droplets of the monomer composition is not particularly limited, and a known suspension method can be adopted. As the disperser used when preparing the suspension, for example, horizontal or vertical pipeline-type dispersers such as Milder manufactured by Taiheiyo Kiko Co., Ltd., Cavitron manufactured by Eurotec Co., Ltd., and pipeline-type dispersers manufactured by IKA (for example, DISPAX-REACTOR (registered trademark) DRS); emulsifying dispersers such as Homomixer MARK II series manufactured by Primix Corporation, etc. can be used.

[0223] In the dispersion for preparing the suspension, from the aspect of making the particle size of the hollow particles within the above-mentioned preferred range, the front-end speed of the rotating part of the disperser is preferably 5 m / s or more, more preferably 10 m / s or more, and further preferably 15 m / s or more. On the other hand, from the aspect of reducing the proportion of abnormal particles, it is preferably 90 m / s or less, more preferably 89 m / s or less, and further preferably 88 m / s or less.

[0224] In the suspension prepared in the suspension step, droplets of the monomer composition containing the above-mentioned lipophilic material and having a particle size of about 1 to 10 μm are uniformly dispersed in the aqueous medium. Such droplets of the monomer composition are difficult to observe with the naked eye and can be observed by known observation instruments such as an optical microscope.

[0225] In the suspension step, phase separation occurs in the droplets of the monomer composition, so the less polar hydrophobic solvent tends to accumulate inside the droplets. As a result, the obtained droplets have the hydrophobic solvent distributed inside and the materials other than the hydrophobic solvent distributed on the periphery.

[0226] The droplets of the monomer composition dispersed in the aqueous medium are formed by surrounding the oil-soluble monomer composition with a dispersion stabilizer. The droplets of the monomer composition contain an oil-soluble polymerization initiator, a polymerizable monomer, and a hydrophobic solvent.

[0227] The droplets of the monomer composition are micro oil droplets, and the oil-soluble polymerization initiator generates polymerization initiating radicals inside the micro oil droplets. Therefore, the micro oil droplets will not grow excessively, and precursor particles with the target particle size can be manufactured.

[0228] In the suspension polymerization method using such an oil-soluble polymerization initiator, there is no chance for the polymerization initiator to contact the polymerizable monomer dispersed in the aqueous medium. Therefore, by using an oil-soluble polymerization initiator, it is possible to suppress the generation of unnecessary resin particles such as dense particles with a smaller particle size as by-products other than the resin particles having a hollow part as the target.

[0229] (3) Polymerization step

[0230] This step is as follows: The suspension obtained through the above suspension step is supplied to a polymerization reaction to prepare a precursor composition containing precursor particles, the precursor particles having a hollow part surrounded by a shell containing resin and the hollow part being filled with the hydrophobic solvent.

[0231] The polymerization method is not particularly limited, and known polymerization methods such as batchwise (batch), semi-continuous, and continuous can be adopted.

[0232] The upper limit of the polymerization temperature is not particularly limited. From the aspect of allowing the polymerization reaction to proceed sufficiently and reducing the content of unreacted polymerizable monomers, it is preferably 60 °C or higher, more preferably 70 °C or higher, and further preferably 80 °C or higher. From the aspect of suppressing the evaporation of the aqueous medium, it is preferably 95 °C or lower.

[0233] The reaction time of the polymerization is not particularly limited. From the aspect of allowing the polymerization reaction to proceed sufficiently and reducing the content of unreacted polymerizable monomers, it is preferably 5 hours or longer, more preferably 10 hours or longer. From the viewpoint of manufacturing efficiency, it is preferably 60 hours or shorter, more preferably 48 hours or shorter, and further preferably 36 hours or shorter.

[0234] In addition, the suspension in the polymerization reaction is usually stirred. The stirring power for this stirring is not particularly limited. From the viewpoint of promoting the polymerization reaction, it is preferably 0.01 kW / m3 More preferably, it is 0.02 kW / m or more. 3 Further preferably, it is 0.03 kW / m or more. 3 More preferably, from the aspect of reducing the proportion of irregular particles, it is 0.20 kW / m or more. 3 Preferably, it is 0.10 kW / m or less. 3 Further preferably, it is 0.05 kW / m or less. 3 Or less.

[0235] (4) Solvent removal step

[0236] In this step, the precursor composition is stirred in a stirring tank while gas is introduced into the precursor composition, thereby removing the hydrophobic solvent from the precursor particles to obtain an aqueous dispersion of hollow particles. Through this step, an aqueous dispersion of hollow particles filled with the gas introduced into the hollow part is obtained.

[0237] Introducing gas into the precursor composition can be carried out, for example, by directly introducing gas into the precursor composition, that is, directly blowing gas into the precursor composition. Alternatively, it is also possible to stir the precursor composition in a stirring tank having a liquid phase part and a gas phase part containing the precursor composition, thereby introducing the gas in the gas phase part into the precursor composition. Among them, from the aspect of efficiently removing the hydrophobic solvent encapsulated in the precursor particles and the unreacted polymerizable monomers remaining in the precursor particles, etc., it is preferably carried out in the following manner: while directly introducing gas into the precursor composition, the precursor composition is stirred in a stirring tank having a gas phase part, thereby introducing gas into the precursor composition. In addition, the gas phase part in the stirring tank is preferably filled with the gas introduced into the precursor composition in advance.

[0238] The gas introduced into the precursor composition is preferably selected from at least one of inert gases and air, more preferably an inert gas. As the inert gas, for example, nitrogen, argon, helium, etc. can be cited, and nitrogen is particularly preferred.

[0239] In this step, from the aspect of efficiently removing the hydrophobic solvent encapsulated in the precursor particles and the unreacted polymerizable monomers remaining in the precursor particles, etc., the treatment time of introducing gas into the precursor composition is preferably 2 hours or more, more preferably 5 hours or more, further preferably 10 hours or more, still more preferably 15 hours or more, and from the viewpoint of manufacturing efficiency, it is preferably 72 hours or less, more preferably 60 hours or less.

[0240] On the other hand, when the polymerization reaction time in the above polymerization step is 50 hours or more, even if the time for the air-blowing treatment in the solvent removal step is less than 2 hours, it is possible to sufficiently remove the hydrophobic solvent encapsulated in the precursor particles and the unreacted polymerizable monomers contained in the precursor particles. When the polymerization reaction time in the above polymerization step is 50 hours or more, the time for the air-blowing treatment in the solvent removal step is preferably 20 minutes or more, more preferably 30 minutes or more.

[0241] In this step, the stirring power when stirring the precursor composition is not particularly limited. From the aspect of efficiently removing the hydrophobic solvent encapsulated in the precursor particles and the unreacted polymerizable monomers remaining in the precursor particles, it is preferably 0.01 kW / m 3 or more, more preferably 0.02 kW / m 3 or more, further preferably 0.03 kW / m 3 or more. From the aspect of reducing the proportion of abnormal-shaped particles and the aspect of suppressing the foaming of the precursor composition, it is preferably 0.60 kW / m 3 or less, more preferably 0.55 kW / m 3 or less, further preferably 0.50 kW / m 3 or less, still more preferably 0.20 kW / m 3 or less, particularly preferably 0.10 kW / m 3 or less, and may also be 0.05 kW / m 3 or less.

[0242] In this step, gas is blown into the precursor composition. From the aspect of efficiently removing the hydrophobic solvent encapsulated in the precursor particles and the unreacted polymerizable monomers remaining in the precursor particles, it is preferably carried out at a pressure of 20 kPa or more and 300 kPa or less, more preferably at a pressure of 40 kPa or more and 200 kPa or less. In addition, when the pressure is above the above lower limit value, it is preferred from the aspect of improving the yield, and when the pressure is below the above upper limit value, it is preferred from the aspect of reducing the proportion of abnormal-shaped particles. Among them, from the aspect of excellent removal efficiency of the hydrophobic solvent, blowing gas into the precursor composition is preferably carried out at a pressure below atmospheric pressure, more preferably at a reduced pressure of 60 kPa or less. On the other hand, from the aspect of suppressing the foaming of the precursor composition, it is preferably carried out under a pressure of 150 kPa or more. By suppressing the foaming of the precursor composition during gas blowing, the yield of hollow particles is increased. In addition, the above pressure may also be the internal pressure of the stirring tank.

[0243] In addition, in this step, when gas is introduced into the precursor composition at a pressure higher than atmospheric pressure and not exceeding 2000 kPa, the foaming of the precursor composition is suppressed compared to the case of performing the gas introduction at a pressure below atmospheric pressure. From the aspect of suppressing the foaming of the precursor composition, it is preferable to introduce gas into the precursor composition at a pressure of 152 kPa or higher, more preferably at a pressure of 200 kPa or higher, and still more preferably at a pressure of 300 kPa or higher. On the other hand, from the viewpoint of reducing the proportion of irregular particles, it is preferable to introduce gas into the precursor composition at a pressure of 1500 kPa or lower, and preferably at a pressure of 1200 kPa or lower.

[0244] In this step, when gas is introduced into the precursor composition, it is preferable that the precursor composition contains an antifoaming agent. Thereby, the foaming of the precursor composition during gas introduction can be suppressed, and the yield of hollow particles can be increased. From the aspect of easily exerting the foaming suppression effect brought about by the antifoaming agent, it is preferable that the precursor composition contains an antifoaming agent in the case where gas is introduced into the precursor composition at a pressure of 500 kPa or lower, more preferably in the case of performing the gas introduction at a pressure below atmospheric pressure, and still more preferably in the case of performing the gas introduction under a reduced pressure of 60 kPa or lower.

[0245] In addition, when gas is introduced into the precursor composition, in order to make the precursor composition contain an antifoaming agent, the antifoaming agent can be added to the precursor composition in advance before gas introduction, or the antifoaming agent can be added to the precursor composition at the start of gas introduction or during gas introduction.

[0246] There is no particular limitation on the antifoaming agent, and examples thereof include polyether-based antifoaming agents, mineral oil-based antifoaming agents, and alcohol-based antifoaming agents. Among them, from the aspect of being difficult to remain in the hollow particles, it is preferable to use water-soluble antifoaming agents such as polyether-based antifoaming agents and alcohol-based antifoaming agents. Since the antifoaming agent remains in the hollow particles, there is a case where the tangent of the dielectric loss angle of the hollow particles increases. From the aspect of being difficult to increase the tangent of the dielectric loss angle of the hollow particles, it is particularly preferable to use polyether-based antifoaming agents.

[0247] There is no particular limitation on the addition amount of the antifoaming agent. From the aspect of sufficiently suppressing the foaming of the precursor composition, it is preferably 0.01 part by mass or more, more preferably 0.1 part by mass or more, relative to 100 parts by mass of the precursor composition (including the hydrophobic solvent and the aqueous medium). On the other hand, from the aspect of reducing the residual amount of the antifoaming agent and suppressing the increase in the tangent of the dielectric loss angle of the hollow particles, it is preferably 50 parts by mass or less, more preferably 20 parts by mass or less, and still more preferably 0.5 part by mass or less.

[0248] The flow rate of the gas introduced into the stirring tank is not particularly limited. From the aspect of efficiently removing the hydrophobic solvent encapsulated in the precursor particles and the unreacted polymerizable monomers remaining in the precursor particles, etc., the flow rate per unit time is preferably 4 L / min or more, more preferably 8 L / min or more, and further preferably 10 L / min or more. The flow rate per unit volume is preferably 200 L / (min·m 3 ) or more, more preferably 8000 L / (min·m 3 ) or more, and further preferably 10000 L / (min·m 3 ) or more. From the aspect of cost reduction, the upper limit of the gas flow rate can be, for example, 10000 L / min or less as the flow rate per unit time, and 500000 L / (min·m 3 ) or less as the flow rate per unit volume.

[0249] In addition, when using a stirring tank with a capacity of 3 to 15000 L, the gas flow rate is preferably within the above range.

[0250] In this step, it is preferred that the stirring tank has a liquid phase part and a gas phase part containing the precursor composition. This is because when there is a gas phase part in the stirring tank, the hydrophobic solvent encapsulated in the precursor particles and the unreacted polymerizable monomers contained in the precursor particles, etc. can move to the gas phase part, and thus their removal efficiency is excellent.

[0251] From the aspect of being able to efficiently remove the hydrophobic solvent encapsulated in the precursor particles and the unreacted polymerizable monomers remaining in the precursor particles, etc., the proportion of the liquid phase part relative to the whole inside the stirring tank is preferably 30% by volume or more and less than 80% by volume.

[0252] As a method of directly introducing gas into the precursor composition, for example: it is preferred to directly introduce gas into the precursor composition in the stirring tank from the side or bottom of the stirring tank, and more preferably to introduce gas from the bottom of the stirring tank. Here, the bottom of the stirring tank refers to the part of the stirring tank that can be observed looking up in the usage state. The stirring tank is typically columnar, and in the columnar stirring tank, the bottom surface on the lower side in the gravity direction is the bottom and is the deepest part.

[0253] When directly introducing gas into the precursor composition, the closer the gas introduction part is to the deepest part of the stirring tank, the easier it is for the gas to be evenly bubbled into the precursor composition, so it is preferred. When the gas is evenly bubbled into the precursor composition, the hydrophobic solvent removed from the precursor particles and the unreacted polymerizable monomers, etc. are easily moved upward to the gas phase part, and thus their removal efficiency is excellent.

[0254] In addition, from the aspect of facilitating the uniform introduction of gas into the precursor composition, the introduction of gas into the precursor composition is preferably carried out at the center of the region occupied by the precursor composition in the stirring tank. That is, when introducing gas from the bottom of the stirring tank, it is preferable to introduce the gas in the direction opposite to the direction of gravity.

[0255] In addition, in the present invention, the direction of gravity means a direction that does not have to be on the same straight line as the direction of gravity and allows an axial offset of, for example, within 30 degrees.

[0256] On the other hand, there is a case where gas is not directly introduced into the precursor composition, but only by introducing gas into the gas phase part in the stirring tank and stirring the precursor composition in the stirring tank, so as to introduce the gas in the gas phase part into the precursor composition, thereby improving the yield of hollow particles.

[0257] This step can be carried out using, for example Figure 2 the stirring device shown. In addition, Figure 2 is only a schematic diagram for illustration, and the stirring device used in the solvent removal step of the present invention is not limited to the stirring device shown in the figure. In addition, the structure, size, shape, etc. of the stirring device used in the solvent removal step of the present invention are not limited to Figure 2 the structure, size, shape, etc. shown.

[0258] In Figure 2 the stirring device shown, when the precursor composition as a slurry liquid is injected into the supply tank 12, the precursor composition is supplied from the supply tank 12 to the inside of the stirring tank 11 via the supply pipeline 16. The supply method of the precursor composition is not particularly limited, and examples thereof include a method using a liquid delivery pump. The precursor composition is supplied into the stirring tank 11 through an inner nozzle (not shown). The precursor composition 20 in the stirring tank 11 is stirred by rotating a rotor (not shown) provided in the stirring tank 11.

[0259] Gas can be introduced into the stirring tank 11 from the gas inlets 13a, 13b or 13c provided in the stirring tank 11. The gas inlet 13a is provided at the bottom of the stirring tank 11, and the gas inlet 13b is provided on the side of the stirring tank 11. When introducing gas from the gas inlet 13a or 13b, gas can be directly blown into the precursor composition 20 in the stirring tank 11 for aeration. The gas inlet 13c is provided at the upper part of the stirring tank 11. When introducing gas from the gas inlet 13c, the gas is blown into the gas phase part 21 in the stirring tank 11. By stirring the precursor composition 20 in the stirring tank 11, the gas in the gas phase part 21 is introduced into the precursor composition 20.

[0260] In Figure 2In the stirring device shown, the precursor composition 20 stirred in the stirring tank 11 can be circulated in the stirring device by returning it from the outlet 14 to the inside of the stirring tank 11 via the circulation pipeline 17a, the supply tank 12, and the supply pipeline 16.

[0261] Figure 2 The stirring device shown also has a spraying mechanism 15. In Figure 2 In the stirring device shown, a part of the precursor composition 20 stirred in the stirring tank 11 can be supplied from the outlet 14 to the spraying mechanism 15 via the circulation pipeline 17b and sprayed onto the liquid surface 20a of the precursor composition 20 located in the stirring tank 11.

[0262] In addition, by adjusting the flow rate of the precursor composition discharged from the stirring tank 11, the internal pressure of the stirring tank 11 can be adjusted.

[0263] In this step, during the period of blowing gas into the precursor composition, it is preferable to repeat the following operations for circulation in the stirring device: supply the precursor composition from the supply tank to the stirring tank, stir in the stirring tank, and then discharge it to the supply tank. Thereby, the hydrophobic solvent encapsulated in the precursor particles and the unreacted polymerizable monomers contained in the precursor particles can be efficiently removed. In addition, the flow rate of this circulation is not particularly limited.

[0264] In this step, when blowing gas into the precursor composition, it is preferable to supply a part of the precursor composition from the stirring tank to the spraying mechanism and spray it onto the liquid surface of the precursor composition in the stirring tank. Thereby, the hydrophobic solvent encapsulated in the precursor particles and the unreacted polymerizable monomers contained in the precursor particles can be efficiently removed, and thus the treatment time of gas blowing can be shortened.

[0265] The spraying of the precursor composition can be carried out continuously or intermittently during the period of blowing gas into the precursor composition, and it is particularly preferably carried out continuously. In the case of intermittently spraying the precursor composition, it is preferable to appropriately spray the precursor composition until the foaming disappears when the precursor composition foams and the liquid level rises. In addition, the spraying amount in the case of spraying the precursor composition is not particularly limited.

[0266] Furthermore, from the aspect of reducing the residual amount of the hydrophobic solvent, the temperature when blowing gas into the precursor composition is preferably a temperature of 35 °C or more lower than the boiling point of the hydrophobic solvent, more preferably a temperature of 30 °C or more lower than the boiling point of the hydrophobic solvent, and still more preferably a temperature of 20 °C or more lower than the boiling point of the hydrophobic solvent. Here, when the above-mentioned hydrophobic solvent is a mixed solvent containing multiple hydrophobic solvents and has multiple boiling points, the boiling point of the hydrophobic solvent in the solvent removal step refers to the boiling point of the solvent with the highest boiling point among the solvents contained in the mixed solvent, that is, the highest boiling point among the multiple boiling points.

[0267] In addition, the temperature when gas is introduced into the precursor composition is usually set to a temperature higher than the polymerization temperature in the above polymerization step.

[0268] The temperature when gas is introduced into the precursor composition is not particularly limited and can be set to 50 to 100°C.

[0269] (5) Cleaning step

[0270] The method for producing hollow particles of the present invention has a cleaning step after the above solvent removal step. The cleaning step is a step for removing the dispersion stabilizer remaining in the hollow particles obtained by the above solvent removal step, and unreacted polymerizable monomers and the like remaining in the hollow particles are also removed together.

[0271] The cleaning step is preferably carried out, for example, by repeating the following series of operations two or more times: adding an acid or a base to the aqueous dispersion of the hollow particles obtained by the solvent removal step to dissolve the dispersion stabilizer contained in the hollow particles in the aqueous medium, then separating the hollow particles from the aqueous medium, and then dispersing the separated hollow particles in ion-exchanged water and re-slurrying them, and then separating the hollow particles. From the aspect of removing more of the dispersion stabilizer and unreacted polymerizable monomers remaining in the hollow particles and easily reducing the dielectric loss tangent of the hollow particles, it is preferable to repeat the following series of operations three or more times: in the cleaning step, after adding an acid or a base and separating the hollow particles, disperse the separated hollow particles in ion-exchanged water and re-slurrying them, and then separate the hollow particles. The number of times of performing this operation is more preferably four or more times, further preferably five or more times, and the upper limit is not particularly limited. From the viewpoint of ease of manufacture, it can be, for example, ten or less times, or eight or less times.

[0272] When the dispersion stabilizer used is an inorganic dispersion stabilizer soluble in acid, it is preferable to add an acid. When the dispersion stabilizer used is an inorganic dispersion stabilizer soluble in base, it is preferable to add a base.

[0273] When the dispersion stabilizer used is an inorganic dispersion stabilizer soluble in acid, add an acid to the aqueous dispersion of the hollow particles, preferably adjust the pH to 6.5 or less, more preferably 6 or less. As the acid to be added, inorganic acids such as sulfuric acid, hydrochloric acid, and nitric acid, and organic acids such as formic acid and acetic acid can be used. From the aspect of high removal efficiency of the dispersion stabilizer and small burden on the manufacturing equipment, sulfuric acid is particularly preferred.

[0274] The method for separating the hollow particles from the aqueous medium is not particularly limited, and examples thereof include centrifugation, filtration, static separation, etc. Among them, from the viewpoints of easy operation and high removal efficiency of the dispersion stabilizer, filtration is preferred. In addition, when separating the hollow particles from the aqueous medium, it is preferable to dehydrate the hollow particles obtained by filtration or the like by a known method.

[0275] As the filtration method, any method such as natural filtration (atmospheric pressure filtration), vacuum filtration, pressure filtration, centrifugal filtration, etc. can be used. Among them, from the viewpoint of efficiently removing the dispersion stabilizer remaining in the hollow particles and unreacted polymerizable monomers, etc., pressure filtration is particularly preferred.

[0276] In the production method of the present invention, in the cleaning step, the operation of separating the hollow particles from the aqueous medium is carried out multiple times. It is preferable that pressure filtration is carried out at least once, and it is more preferable that pressure filtration is always carried out in the operation of separating the hollow particles from the aqueous medium.

[0277] In this step, the cleaning for removing the above-mentioned dispersion stabilizer remaining in the hollow particles is preferably carried out at 10°C or higher and 90°C or lower, more preferably at 30°C or higher and 90°C or lower, further preferably at 40°C or higher and 90°C or lower, and even more preferably at 60°C or higher and 90°C or lower. Here, the cleaning temperature refers to the temperature of the aqueous dispersion of the hollow particles to be cleaned. That is, the cleaning step preferably maintains the temperature of the aqueous dispersion of the hollow particles within the above range.

[0278] When the cleaning temperature is within the above range, the dispersion stabilizer remaining in the hollow particles and unreacted polymerizable monomers, etc. can be efficiently removed, so that the dielectric properties and performance stability of the hollow particles can be improved.

[0279] (6) Drying step

[0280] The drying step is a step of drying and removing the moisture remaining in the hollow particles obtained through the above-mentioned cleaning step.

[0281] The hollow particles obtained through the above-mentioned cleaning step are usually in the form of a filter cake. Therefore, in this step, the dehydrated filter cake of the hollow particles is usually dried.

[0282] The water content of the hollow particles before drying for the drying step is usually 40 - 80%. In addition, in the present invention, the water content can be calculated by the following formula (i).

[0283] Formula (i)

[0284] Water content (%) = {(w1 - w2) / w1} × 100

[0285] In the above formula (i), w1 represents the mass of the test sample to be measured, and w2 represents the mass after drying the test sample at 200 °C for 12 hours and then cooling it to 25 °C.

[0286] The method for drying and removing the moisture remaining in the hollow particles is not particularly limited, and a known method can be adopted. As such a method, for example, a reduced-pressure drying method, a heat drying method, a fluidized-bed drying method, or a combination of these methods can be cited.

[0287] Particularly in the case of using the heat drying method, it is necessary to keep the temperature below the maximum temperature at which the shell structure does not collapse. Therefore, depending on the composition of the shell, for example, the heating temperature can be set to 50 to 200 °C, can be set to 70 to 200 °C, or can be set to 100 to 200 °C.

[0288] In addition, in the drying process, pre-drying can also be carried out. The pre-drying can be performed, for example, by drying the hollow particles after the cleaning process using a drying device such as a dryer or a drying tool such as a hand dryer.

[0289] The drying atmosphere is not particularly limited and can be appropriately selected according to the use of the hollow particles. As the drying atmosphere, for example, air, oxygen, nitrogen, argon, etc. can be considered. In addition, once the inside of the hollow particles is filled with a gas, by reduced-pressure drying, hollow particles with a temporarily vacuum inside can also be obtained.

[0290] As a method with excellent drying efficiency for the moisture remaining in the hollow particles, it is also preferable to carry out drying under reduced pressure and in an inert gas stream. Here, under reduced pressure means a pressure preferably of 2 kPa or more and 35 kPa or less, more preferably of 4 kPa or more and 15 kPa or less. As the inert gas, for example, nitrogen, argon, helium, etc. can be cited, and there is no particular limitation. Nitrogen is preferably used. The flow rate of the inert gas is not particularly limited. From the aspect of improving the drying efficiency, it is preferably 30 L / min or more, more preferably 200 L / min or more, and further preferably 300 L / min or more. The upper limit of the flow rate of the inert gas is not particularly limited. From the viewpoint of manufacturing cost, it is preferably 500 L / min or less. Drying carried out under reduced pressure and in an inert gas stream can be carried out at a relatively low temperature because of its excellent drying efficiency, and can be carried out, for example, at 130 °C or lower. In this way, by carrying out drying at a relatively low temperature, the manufacturing cost can be reduced. On the other hand, from the aspect of improving the drying efficiency, the temperature of drying carried out under reduced pressure and in an inert gas stream is preferably 20 °C or more, more preferably 40 °C or more.

[0291] (7) Others

[0292] As a process other than the above (1) to (6), a replacement process inside the particles, for example, can be added. The replacement process inside the particles is a process of replacing the gas and liquid inside the hollow particles with other gases and liquids. By such replacement, the environment inside the hollow particles can be changed, or molecules can be selectively confined inside the hollow particles, or the chemical structure inside the hollow particles can be modified according to the use.

[0293] 3. Resin Composition

[0294] The resin composition of the present invention contains at least the above-described hollow particles of the present invention and a matrix resin, and is typically liquid. The resin composition of the present invention can also be used as a molding material for the resin structure described later.

[0295] Examples of the liquid resin composition include: a resin composition containing a liquid matrix resin before the curing reaction, a resin composition obtained by dissolving or dispersing each component in a solvent, etc. Here, the liquid matrix resin before the curing reaction and the matrix resin dissolved or dispersed in the solvent can be, for example, a thermosetting resin, a room-temperature curable resin, or a thermoplastic resin. Alternatively, it can also be a resin in which the resin composition becomes liquid by melting the matrix resin.

[0296] The resin composition of the present invention and the resin structure obtained by using it have a reduced dielectric loss tangent by containing the hollow particles of the present invention. In addition, since the hollow particles of the present invention have excellent dielectric properties and performance stability, the resin composition containing the hollow particles of the present invention and the resin structure obtained by using it improve the dielectric properties while suppressing a decrease in reliability.

[0297] Examples of the matrix resin include: curable resins such as thermosetting resins, photo-curable resins, and room-temperature curable resins, and thermoplastic resins. Among them, thermosetting resins, room-temperature curable resins, and thermoplastic resins can be preferably used.

[0298] In addition, the matrix resin can be an unreacted monomer, a prepolymer, or a macromonomer, can also be a polymer, or can be a precursor of a cured resin such as polyamic acid. The matrix resin contained in the resin composition of the present invention functions as a binder, for example, by curing through heating, light irradiation, or using a curing agent, a polymerization initiator, or a catalyst.

[0299] As the thermosetting resin, known thermosetting resins can be used without particular limitation, and examples thereof include: phenolic resins, melamine resins, urea resins, unsaturated polyester resins, epoxy resins, polyurethane resins, silicone resins, alkyd resins, benzoxazine resins, allyl resins, aniline resins, modified polyphenylene ether resins, thermosetting polyimide resins, maleimide resins, bismaleimide triazine resins, liquid crystalline polyester resins, vinyl ester resins, cyanate ester resins, etc., or precursors of these resins before curing.

[0300] As the room temperature curable resin, examples thereof include: epoxy adhesives, silicone adhesives, acrylic adhesives, etc., which can be cured at room temperature by adding a catalyst.

[0301] As the thermoplastic resin, examples thereof include: polyolefin resins such as polypropylene and polyethylene; polyamide resins such as PA6, PA66, and PA12; polycarbonate resins, polyphenylene sulfide resins, polyether ether ketone resins, polystyrene resins, polyphenylene ether resins, liquid crystalline polymers (LCP), polyimide, polyamideimide, polyetherimide, polyvinyl chloride, poly(meth)acrylate, polyvinylidene fluoride, acrylonitrile-butadiene-styrene copolymer (ABS), acrylonitrile-styrene copolymer (AS), polyphenylene ether, polyester, polytetrafluoroethylene, thermoplastic elastomers, etc. In addition, a thermoplastic elastomer is a substance having the following properties: it usually exhibits rubber elasticity at room temperature (25 °C) and can be plastically molded at high temperatures. Examples of the thermoplastic elastomer include: urethane elastomers, styrene elastomers, olefin elastomers, amide elastomers, and ester elastomers, etc.

[0302] In applications where low dielectric loss tangent is required, as the matrix resin, a thermosetting resin or a thermoplastic resin is preferably used, and particularly preferably used are: thermosetting resins such as epoxy resins, thermosetting polyimide resins, modified polyphenylene ether resins, silicone resins, benzoxazine resins, and melamine resins.

[0303] Examples of the epoxy resin (epoxide) include, for example, bisxylenol type epoxy resin, bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, bisphenol AF type epoxy resin, dicyclopentadiene type epoxy resin, triphenol type epoxy resin, naphthol novolak type epoxy resin, phenol novolak type epoxy resin, tert-butylcatechol type epoxy resin, naphthalene type epoxy resin, naphthol type epoxy resin, anthracene type epoxy resin, glycidylamine type epoxy resin, glycidyl ester type epoxy resin, cresol novolak type epoxy resin, phenol aralkyl type epoxy resin, biphenyl type epoxy resin, linear aliphatic epoxy resin, epoxy resin having a butadiene structure, alicyclic epoxy resin, heterocyclic epoxy resin, epoxy resin containing a spiro ring, cyclohexane type epoxy resin, cyclohexanedimethanol type epoxy resin, naphthylene ether type epoxy resin, trimethylol type epoxy resin, tetraphenylethane type epoxy resin, isocyanurate type epoxy resin, phenol phthalimide type epoxy resin, phenolphthalein type epoxy resin, etc.

[0304] These matrix resins can be used alone or in combination of two or more.

[0305] From the aspect of easily obtaining a resin composition and a resin structure excellent in dielectric properties and reliability, the matrix resin preferably contains an epoxy resin (epoxide) or a modified polyphenylene ether resin.

[0306] In the matrix resin containing an epoxy resin (epoxide), the content of the epoxy resin (epoxide) in the matrix resin of 100% by mass is preferably 70% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, and the matrix resin may be composed of an epoxy resin (epoxide).

[0307] In the matrix resin containing a modified polyphenylene ether resin, the content of the modified polyphenylene ether resin in the matrix resin of 100% by mass is preferably 70% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, and the matrix resin may be composed of a modified polyphenylene ether resin.

[0308] As the epoxy resin (epoxide), for example, from the aspects of low dielectric loss tangent and relative dielectric constant, excellent dielectric properties, and excellent reliability, bisphenol A type epoxy resin is preferred. From the aspect of good dielectric properties and reliability, cresol novolak type epoxy resin is also preferred. From the aspect of excellent dielectric properties, especially low relative dielectric constant, alicyclic epoxy resin is preferred. As the epoxy resin (epoxide), among them, from the aspects of excellent dielectric properties and reliability, bisphenol A type epoxy resin is particularly preferred.

[0309] In the resin composition of the present invention, the content of the base resin is not particularly limited. Generally, in all the solid components of 100% by mass of the resin composition, it is preferably 40 to 95% by mass, more preferably 50 to 95% by mass, further preferably 70 to 95% by mass, and may also be 85 to 95% by mass. When the content of the base resin is at least the above lower limit value, the moldability of the resin composition is excellent. In addition, the mechanical strength when the resin composition is made into a structure can be improved. When the content of the resin is at most the above upper limit value, hollow particles can be sufficiently contained. Therefore, the effects such as the reduction of the dielectric loss tangent, the reduction of the dielectric constant, the light weight, and the heat insulation of the resin composition brought by the hollow particles are excellent.

[0310] [Hollow particles]

[0311] The hollow particles contained in the resin composition of the present invention are the above-mentioned hollow particles of the present invention.

[0312] In the resin composition of the present invention, the content of the hollow particles is not particularly limited. In all the solid components of 100% by mass of the resin composition, as the lower limit, it is preferably at least 0.1% by mass, more preferably at least 1% by mass, further preferably at least 5% by mass, still more preferably at least 10% by mass. As the upper limit, it is preferably at most 50% by mass, more preferably at most 30% by mass, further preferably at most 20% by mass, still more preferably at most 15% by mass. When the content of the hollow particles is at least the above lower limit value, the effects such as the reduction of the dielectric loss tangent, the reduction of the dielectric constant, and the light weight of the resin composition brought by the hollow particles are excellent. When the content of the hollow particles is at most the above upper limit value, the base resin can be sufficiently contained in the resin composition. Therefore, the reduction of the physical properties when the resin composition is made into a structure can be suppressed and the mechanical strength can be improved.

[0313] [Solvent]

[0314] The resin composition of the present invention may further contain a solvent for dissolving or dispersing each component. As the solvent, known solvents can be used and can be appropriately selected according to the type of resin.

[0315] [Other additives]

[0316] The resin composition of the present invention may further contain additives such as a curing agent, a curing accelerator, a polymerization initiator, an ultraviolet absorber, a coloring agent, a heat stabilizer, a filler, and a flame retardant as needed within the range that does not impair the effects of the present invention.

[0317] As the filler, for example, inorganic fillers such as silica, talc, glass beads, asbestos, gypsum, diatomaceous earth, smectite, bentonite, montmorillonite, sericite, activated clay, alumina, zinc oxide, iron oxide, magnesium oxide, tin oxide, titanium oxide, calcium carbonate, magnesium carbonate, magnesium hydroxide, aluminum hydroxide, aluminum nitride, silicon nitride, barium sulfate, calcium silicate, etc. can be cited; and organic fillers such as polyester fine particles, polyurethane fine particles, vinyl polymer fine particles, acrylic polymer fine particles, etc. These fillers can be used alone or in combination of two or more. As the filler, among them, inorganic fillers are preferably used, and silica is particularly preferably used. When the resin composition of the present invention contains a filler, the processability is improved, and characteristics such as heat resistance are imparted. In particular, since silica has a low thermal expansion rate, by containing silica as the filler, a resin composition excellent in processability can be easily obtained.

[0318] The content of the filler is not particularly limited. From the aspect of the toughness of the resin composition, in all solid components of 100% by mass of the resin composition, it is preferably 1 to 80% by mass, more preferably 5 to 70% by mass.

[0319] 4. Resin structure

[0320] The resin structure of the present invention contains the above-mentioned hollow particles of the present invention and a matrix resin. In addition, in the resin structure, the matrix resin is a cured product. Since the resin structure of the present invention contains hollow particles, it is imparted with properties such as low dielectric loss tangent, low dielectric constant, light weight, heat insulation, etc. In addition, since the hollow particles of the present invention are excellent in dielectric characteristics and performance stability, the resin structure containing the hollow particles of the present invention is a resin structure that improves dielectric characteristics while suppressing a decrease in reliability. For example, prepregs, insulating layers included in metal-clad laminates, and insulating layers included in printed circuit boards, etc. are resin structures of the present invention, but the resin structures of the present invention are not limited to these.

[0321] The resin structure of the present invention can be made into a structure by curing the above-mentioned resin composition of the present invention into a desired shape, or can also be made into a structure by melt-kneading and molding the hollow particles of the present invention and a thermoplastic resin.

[0322] The base resin of the cured product is a resin cured with or without a chemical reaction, and examples thereof include: a resin cured by a curing reaction, a resin cured by drying, a resin cured by cooling a thermoplastic resin, etc. The resin structure obtained using a liquid resin composition contains, as a base resin, a cured product of a resin cured using a curing agent, a polymerization initiator, a catalyst, or the like, as needed. In this case, the base resin may contain a curing agent or the like. The resin structure obtained by melt-kneading and molding the hollow particles of the present invention with a thermoplastic resin contains, as a base resin, a cured product obtained by cooling the thermoplastic resin.

[0323] The resin structure obtained using the resin composition of the present invention described above can be obtained by curing the above-mentioned curable resin, for example. That is, the resin structure of the present invention can be a cured product of the resin composition of the present invention described above. The resin structure obtained by curing the above-mentioned curable resin using the resin composition of the present invention described above is obtained by a method including, for example, the following steps: a step of preparing a resin composition containing the hollow particles of the present invention, a base resin, and a curing agent; a step of curing the above-mentioned resin composition.

[0324] As a method for curing the curable resin, there is no particular limitation, and examples thereof include heating, light irradiation such as ultraviolet rays or electron beams, etc. Alternatively, in the case of a curable resin that cures at room temperature by adding a catalyst or the like, it can also be cured by mixing at room temperature by adding a catalyst or the like.

[0325] As a curing agent (crosslinking agent) or catalyst for curing the base resin, it can be appropriately selected from known ones according to the type of the base resin, and there is no particular limitation. As a curing agent for an epoxy resin, examples include: amines, acid anhydrides, imidazoles, thiols, phenols, naphthols, benzoxazines, cyanates, and carbodiimides, etc. These curing agents can be used alone or in combination of two or more.

[0326] The content of the curing agent is appropriately adjusted according to the type of the base resin, and there is no particular limitation. For example, it can be 5 to 120 parts by mass relative to 100 parts by mass of the resin (main agent).

[0327] When curing a liquid resin composition, for example, the resin composition can be coated on a support, dried as needed, and then cured under curing conditions.

[0328] Examples of the material of the above-mentioned support include: resins such as polyethylene terephthalate and polyethylene naphthalate; metals such as copper, aluminum, nickel, chromium, gold, and silver, etc. A release agent can also be coated on the surface of the support. As a method for coating the liquid resin composition, known methods can be used, and examples include: dip coating, roll coating, curtain coating, die coating, slot coating, gravure coating, etc.

[0329] Alternatively, when curing the liquid resin composition, the resin composition can be impregnated into a sheet-like fiber substrate, dried as needed, and then cured under curing conditions.

[0330] When the resin composition contains a solvent, it is preferable to dry the resin composition after the above coating or impregnation. From the viewpoint of removing the solvent from the resin composition in an uncured or semi-cured state, the drying temperature is preferably set to a temperature at which the resin composition does not cure, usually 20°C or higher and 200°C or lower, preferably 30°C or higher and 150°C or lower. In addition, the drying time is usually 30 seconds or longer and 1 hour or shorter, preferably 1 minute or longer and 30 minutes or shorter.

[0331] The temperature during curing of the resin composition is appropriately adjusted according to the type of matrix resin and is not particularly limited. In the case of a thermosetting resin, it is usually 30°C or higher and 400°C or lower, preferably 70°C or higher and 300°C or lower, more preferably 100°C or higher and 200°C or lower. The heating method is not particularly limited, and for example, an electric oven can be used.

[0332] In addition, the curing time is usually 5 minutes or longer and 5 hours or shorter, preferably 30 minutes or longer and 3 hours or shorter.

[0333] In the resin structure of the present invention obtained by melt-kneading and molding the hollow particles of the present invention with a thermoplastic resin, as the thermoplastic resin, known thermoplastic resins can be used without particular limitation. Examples thereof include the same thermoplastic resins as those that can be used in the resin composition of the present invention described above.

[0334] The temperature during the above melt-kneading only needs to be a temperature at which the thermoplastic resin used can be melted and is not particularly limited. It can be, for example, 150°C or higher. On the other hand, from the aspect of suppressing the breakage of the hollow particles, it is preferably 300°C or lower.

[0335] The above kneading can be carried out by a known method and is not particularly limited. For example, a kneading device such as a single-screw kneader or a twin-screw kneader can be used.

[0336] The method of the above molding is not particularly limited, and known molding methods such as extrusion molding, injection molding, and compression molding can be adopted.

[0337] In the resin structure of the present invention, the content of the base resin contained in the resin structure is not particularly limited. From the aspect of suppressing the reduction of the physical properties of the resin structure and improving the mechanical strength, it is preferably 30% by volume or more, more preferably 40% by volume or more. From the aspect of sufficiently containing hollow particles, it is preferably 90% by volume or less, more preferably 80% by volume or less.

[0338] The content of the hollow particles contained in the resin structure of the present invention is not particularly limited. As the lower limit, it is preferably 10% by volume or more, more preferably 20% by volume or more. As the upper limit, it is preferably 80% by volume or less, more preferably 70% by volume or less, and further preferably 60% by volume or less. When the content of the hollow particles is above the above lower limit value, the effects such as low dielectric loss tangent, low dielectric constant, light weight, and heat insulation brought by the hollow particles are excellent. When the content of the hollow particles is below the above upper limit value, the base resin can be sufficiently contained in the resin structure, so that the reduction of the physical properties of the resin structure can be suppressed and the mechanical strength can be improved.

[0339] The resin structure of the present invention may further contain additives as needed. As the additives, the additives that can be used in the resin composition of the present invention can be used in the same manner.

[0340] In addition, the resin structure of the present invention may also be a resin structure containing organic or inorganic reinforcing fibers such as carbon fiber, glass fiber, aromatic polyamide fiber, polyethylene fiber, cellulose nanofiber, and liquid crystalline polymer (LCP) fiber. The reinforcing fibers contained in the resin structure of the present invention can be used as the base material of the prepreg or can be contained as a filler.

[0341] The shape of the resin structure is not particularly limited, and it can be made into various shapes that can be molded, such as sheet shape, film shape, or plate shape. When the resin structure contains fibers, the fibers in the resin structure can be in the form of non-woven fabric. In addition, the resin structure of the present invention can be a structure in which the hollow particles of the present invention are added to a fiber-reinforced plastic.

[0342] The dielectric loss tangent of the resin structure of the present invention at a frequency of 10 GHz is preferably less than 1.20×10 -2 , more preferably less than 9.70×10 -3 , further preferably 5.00×10 -3 or less, and even more preferably 4.50×10 -3 or less, particularly preferably 4.30×10 -3 or less. The lower limit of the above dielectric loss tangent is not particularly limited and can be, for example, 1.00×10 -3 or more.

[0343] The relative dielectric constant of the resin structure of the present invention at a frequency of 10 GHz is preferably 2.50 or less, more preferably 2.30 or less, and still more preferably 2.20 or less. The lower limit of the relative dielectric constant is not particularly limited and may be, for example, 1.00 or more.

[0344] In the present invention, the relative dielectric constant and the dielectric loss tangent of the resin structure are measured using a perturbation method measuring device.

[0345] Examples of the uses of the resin composition and the resin structure of the present invention include the same uses as those for which the hollow particles of the present invention are used. Since the resin composition and the resin structure of the present invention are excellent in dielectric properties and performance stability, they are particularly preferably used in the electrical or electronic field, and are particularly preferably used as a circuit board material.

[0346] Examples

[0347] Hereinafter, examples and comparative examples are given to more specifically illustrate the present invention, but the present invention is not limited only to these examples. In addition, unless otherwise specified, parts and % are based on mass.

[0348] [Example 1]

[0349] 1. Preparation of hollow particles

[0350] (1) Mixed solution preparation step

[0351] First, the following materials are mixed to form an oil phase.

[0352] Divinylbenzene (DVB): 37.5 parts;

[0353] Ethyl vinylbenzene (EVB): 1.6 parts;

[0354] tert-Butyl peroxy diethylacetate: 0.89 part;

[0355] Hydrophobic solvent (heptane): 60.8 parts.

[0356] Next, in a stirring tank, an aqueous solution obtained by dissolving 15.7 parts of magnesium chloride (water-soluble polyvalent metal salt) in 225 parts of ion-exchanged water is slowly added to an aqueous solution obtained by dissolving 11.0 parts of sodium hydroxide (alkali metal hydroxide) in 55 parts of ion-exchanged water while stirring to prepare a magnesium hydroxide colloid (water-insoluble metal hydroxide colloid) dispersion (8 parts of magnesium hydroxide), and an aqueous phase is formed.

[0357] The obtained aqueous phase and oil phase are mixed to thereby prepare a mixed solution.

[0358] (2) Suspension step

[0359] The mixture obtained in the above mixture preparation step was stirred for 1 minute using an emulsifying disperser (manufactured by Spectrum Mix Co., Ltd., product name: Homomixer) under the condition that the front-end speed of the rotating part was 88 m / s, thereby performing a suspension treatment to prepare a suspension in which droplets of the monomer composition encapsulating the hydrophobic solvent were dispersed in water.

[0360] (3) Polymerization step

[0361] The suspension obtained in the above suspension step was heated to 80 °C in a nitrogen atmosphere, and the stirring power of the stirring blade was set to 0.04 kW / m 3 , and stirred for 24 hours to carry out a polymerization reaction. Through this polymerization reaction, a precursor composition was obtained as a slurry liquid in which precursor particles encapsulating the hydrophobic solvent were dispersed in water.

[0362] (4) Solvent removal step

[0363] The solvent removal step was carried out in the following order using the stirring device shown in Figure 2 . In addition, as the stirring tank, a stirring tank with a capacity of 3.6 L was used, and the inside of the stirring tank was made into a nitrogen atmosphere when supplying the precursor composition.

[0364] 2.6 L of the precursor composition obtained in the above polymerization step was supplied from the supply tank to the stirring tank. The stirring power of the stirring blade provided in the stirring tank was set to 0.04 kW / m 3 , while stirring the precursor composition in the stirring tank, the precursor composition was heated to 95 °C and the inside of the stirring tank was depressurized to 40 kPa. While blowing nitrogen directly into the precursor composition at a flow rate of 10 L / min (since the gas phase part is 1 L, so it is 10000 L / (min·m Figure 2 )) in the direction opposite to the direction of gravity from the gas inlet ( 3 ) at the bottom of the stirring tank, while stirring the precursor composition in the stirring tank, a bubbling treatment was carried out for 15 hours. In this treatment, the precursor composition injected into the stirring tank was circulated in the stirring device by repeating the following operation: after stirring in the stirring tank, it was discharged to the supply tank and then supplied to the stirring tank again from the supply tank. In addition, during this treatment, a part of the precursor composition injected into the stirring tank was supplied to the spraying mechanism, and continuously sprayed onto the liquid surface of the precursor composition in the stirring tank. Through the above treatment, an aqueous dispersion of hollow particles with the hollow part filled with nitrogen was obtained.

[0365] (5) Cleaning step

[0366] In an environment at 25°C, dilute sulfuric acid was added to the aqueous dispersion of hollow particles obtained in the above solvent removal step and stirred for 10 minutes, thereby obtaining a pH-adjusted slurry with a pH adjusted to 5.5 or less. The obtained pH-adjusted slurry was still pressurized and filtered at 25°C, and a dehydrated cake of hollow particles was obtained by dehydration. A series of steps of washing the obtained dehydrated cake with 400 parts of ion-exchanged water, pressurized filtration, and dehydration were repeated 6 times.

[0367] In addition, in Tables 1 to 4, the number of times of performing a series of steps of washing the dehydrated cake with ion-exchanged water, pressurized filtration, and dehydration is shown as the "number of washing times".

[0368] (6) Drying step

[0369] After pre-drying the dehydrated cake (with a moisture content of 67% and a thickness of 2 cm) after the above washing step at a temperature of 40°C using a dryer, the moisture remaining in the particles was removed by heat treatment for 12 hours under vacuum conditions of 200°C and 4 kPa using a vacuum dryer, and the hollow particles of Example 1 were obtained.

[0370] [Example 2]

[0371] In Example 1, in the above "(4) Solvent removal step", the time of the air-blowing treatment was changed to 20 hours, and the spraying of the precursor composition from the spraying mechanism was not performed. Except for this, the hollow particles of Example 2 were manufactured in the same steps as Example 1.

[0372] [Example 3]

[0373] In Example 1, in the above "(4) Solvent removal step", the gas inlet located at the upper part of the stirring tank ( Figure 2 the gas inlet 13c in it) was used as the gas inlet, while introducing nitrogen gas into the gas phase part in the stirring tank and stirring the precursor composition in the stirring tank, thereby performing an air-blowing treatment for 20 hours, and the spraying of the precursor composition from the spraying mechanism was not performed. Except for this, the hollow particles of Example 3 were manufactured in the same steps as Example 1.

[0374] [Example 4]

[0375] In Example 1, in the above "(4) Solvent removal step", the inside of the stirring tank was in an atmospheric pressure state, the time of the air-blowing treatment was changed to 20 hours, and the spraying of the precursor composition from the spraying mechanism was not performed. Except for this, the hollow particles of Example 4 were manufactured in the same steps as Example 1.

[0376] [Example 5]

[0377] In Example 1, in the above-mentioned "(4) Solvent removal step", the precursor composition was not circulated but left in the stirring tank, the spraying of the precursor composition from the spraying mechanism was not carried out, and the time of the aeration treatment was changed to 20 hours. Except for this, the hollow particles of Example 5 were manufactured in the same steps as Example 1.

[0378] [Example 6]

[0379] In Example 1, in the above-mentioned "(4) Solvent removal step", the time of the aeration treatment was changed to 10 hours, the spraying of the precursor composition from the spraying mechanism was not carried out. Except for this, the hollow particles of Example 6 were manufactured in the same steps as Example 1.

[0380] [Example 7]

[0381] In Example 1, in the above-mentioned "(4) Solvent removal step", the pressure in the stirring tank was increased to 200 kPa, the time of the aeration treatment was changed to 20 hours, and the spraying of the precursor composition from the spraying mechanism was not carried out. Except for this, the hollow particles of Example 7 were manufactured in the same steps as Example 1.

[0382] [Example 8]

[0383] In Example 1, in the above-mentioned "(3) Polymerization step", the time of the polymerization reaction was changed to 60 hours. In the above-mentioned "(4) Solvent removal step", the time of the aeration treatment was changed to 30 minutes, and the spraying of the precursor composition from the spraying mechanism was not carried out. Except for this, the hollow particles of Example 8 were manufactured in the same steps as Example 1.

[0384] [Example 9]

[0385] In Example 1, in the above-mentioned "(1) Mixed solution preparation step", the amounts of divinylbenzene (DVB) and ethyl vinylbenzene (EVB) added to the oil phase were changed according to Table 1. Except for this, the hollow particles of Example 9 were manufactured in the same steps as Example 1.

[0386] [Example 10]

[0387] In Example 1, in the above-mentioned "(4) Solvent removal step", the stirring power of the stirring blade was changed to 0.57 kW / m 3 , and except for this, the hollow particles of Example 10 were manufactured in the same steps as Example 1.

[0388] [Example 11]

[0389] In Example 1, in the above-mentioned "(5) Cleaning process", the number of a series of processes of cleaning the obtained dewatered filter cake with 400 parts of ion-exchanged water, pressure filtration, and dehydration was changed from 6 times to 3 times. Except for this, the hollow particles of Example 11 were manufactured in the same steps as in Example 1.

[0390] [Comparative Example 1]

[0391] In Example 1, in the above-mentioned "(1) Mixed solution preparation process", the amounts of divinylbenzene (DVB) and ethyl vinylbenzene (EVB) added to the oil phase were changed according to Table 2. Except for this, the hollow particles of Comparative Example 1 were manufactured in the same steps as in Example 1.

[0392] [Comparative Example 2]

[0393] In Example 1, in the above-mentioned "(4) Solvent removal process", the time of the air-blowing treatment was changed to 30 minutes. Except for this, the hollow particles of Comparative Example 2 were manufactured in the same steps as in Example 1.

[0394] [Comparative Example 3]

[0395] In Example 1, in the above-mentioned "(3) Polymerization process", the stirring power of the stirring blade was changed to 0.30 kW / m 3 , and in the above-mentioned "(4) Solvent removal process", the stirring power of the stirring blade was also changed to 0.30 kW / m 3 . Except for this, the hollow particles of Comparative Example 3 were manufactured in the same steps as in Example 1.

[0396] [Comparative Example 4]

[0397] In Example 1, in the above-mentioned "(5) Cleaning process", the number of a series of processes of cleaning the obtained dewatered filter cake with 400 parts of ion-exchanged water, pressure filtration, and dehydration was set to only once. Except for this, the hollow particles of Comparative Example 4 were manufactured in the same steps as in Example 1.

[0398] [Comparative Example 5]

[0399] In Example 1, in the above-mentioned "(4) Solvent removal process", the time of the air-blowing treatment was changed to 30 minutes, and in the above-mentioned "(5) Cleaning process", the number of a series of processes of cleaning the dewatered filter cake with 400 parts of ion-exchanged water, pressure filtration, and dehydration was changed to 10 times. Except for this, the hollow particles of Comparative Example 5 were manufactured in the same steps as in Example 1.

[0400] [Example 12]

[0401] In Example 1, in the above-mentioned “(4) Solvent removal step”, 0.19 part of a polyether-based antifoaming agent (trade name: SN DEFOAMER PC, manufactured by San Nopco Ltd.) was added to 100 parts of the precursor composition in the stirring tank, the cleaning temperature in the above-mentioned “(5) Cleaning step” was changed from 25°C to 90°C, and in the above-mentioned “(6) Drying step”, instead of heat-treating for 12 hours under vacuum conditions of 200°C and 4 kPa, heat treatment was carried out for 12 hours at 120°C, 4 kPa under vacuum conditions and in a nitrogen gas stream (flow rate 400 L / min) using a vacuum dryer. Except for this, hollow particles of Example 12 were manufactured in the same steps as in Example 1.

[0402] [Example 13]

[0403] In Example 12, 0.38 part of a mineral oil-based antifoaming agent (trade name: SN DEFOAMER 479, manufactured by San Nopco Ltd.) was used instead of 0.19 part of the polyether-based antifoaming agent. Except for this, hollow particles of Example 13 were manufactured in the same steps as in Example 12.

[0404] [Example 14]

[0405] In Example 12, 0.03 part of an alcohol-based antifoaming agent (trade name: DAPPO H-312, manufactured by San Nopco Ltd.) was used instead of 0.19 part of the polyether-based antifoaming agent. Except for this, hollow particles of Example 14 were manufactured in the same steps as in Example 12.

[0406] [Example 15]

[0407] In Example 1, in the above-mentioned “(4) Solvent removal step”, 0.19 part of a polyether-based antifoaming agent (trade name: SN DEFOAMER PC, manufactured by San Nopco Ltd.) was added to 100 parts of the precursor composition in the stirring tank, the inside of the stirring tank was pressurized to 500 kPa, the cleaning temperature in the above-mentioned “(5) Cleaning step” was changed from 25°C to 90°C, and in the above-mentioned “(6) Drying step”, instead of heat-treating for 12 hours under vacuum conditions of 200°C and 4 kPa, heat treatment was carried out for 12 hours at 120°C, 4 kPa under vacuum conditions and in a nitrogen gas stream (flow rate 400 L / min) using a vacuum dryer. Except for this, hollow particles of Example 15 were manufactured in the same steps as in Example 1.

[0408] [Example 16]

[0409] In Example 15, the pressure inside the stirring tank was changed from 500 kPa to 900 kPa. Except for this, hollow particles of Example 16 were manufactured in the same steps as in Example 15.

[0410] [Example 17]

[0411] In Example 15, no polyether defoamer was added, and further, the pressure in the stirring tank was changed from 500 kPa to 900 kPa. Except for this, the hollow particles of Example 17 were manufactured in the same steps as Example 15.

[0412] [Example 18]

[0413] In Example 12, the cleaning temperature in the cleaning process was changed from 90 °C to 50 °C. Except for this, the hollow particles of Example 18 were manufactured in the same steps as Example 12.

[0414] [Example 19]

[0415] In Example 12, the flow rate of nitrogen in the drying process was changed from 400 L / min to 200 L / min. Except for this, the hollow particles of Example 19 were manufactured in the same steps as Example 12.

[0416] [Example 20]

[0417] In Example 1, in the above-mentioned “(1) Mixed solution preparation process”, 32.7 parts of DVB, 1.4 parts of EVB, and 5 parts of a modified polyphenylene ether oligomer (trade name: OPE-2St 1200, manufactured by Mitsubishi Gas Chemical Co., Ltd.) were used instead of 37.5 parts of DVB and 1.6 parts of EVB as polymerizable monomers. In the above-mentioned “(4) Solvent removal process”, 0.19 part of a polyether defoamer (trade name: SN DEFOAMER PC, manufactured by San Nopco Ltd.) was added relative to 100 parts of the precursor composition in the stirring tank. The cleaning temperature in the above-mentioned “(5) Cleaning process” was changed from 25 °C to 90 °C. In the above-mentioned “(6) Drying process”, instead of heating treatment at 200 °C and 4 kPa under vacuum conditions for 12 hours, it was heated and treated at 120 °C, 4 kPa under vacuum conditions and nitrogen gas flow (flow rate 400 L / min) for 12 hours using a vacuum dryer. Except for this, the hollow particles of Example 20 were manufactured in the same steps as Example 1.

[0418] [Example 21]

[0419] In Example 20, 5 parts of glycidyl methacrylate were used instead of 5 parts of the modified polyphenylene ether oligomer. Except for this, the hollow particles of Example 21 were manufactured in the same steps as Example 20.

[0420] [Example 22]

[0421] In Example 1, in the above-mentioned “(1) Mixed solution preparation step”, 16.9 parts of ethylene glycol dimethacrylate, 12.7 parts of styrene, and 12.7 parts of methyl methacrylate were used instead of 37.5 parts of DVB and 1.6 parts of EVB as polymerizable monomers, and 57.6 parts of hexane was used instead of 60.8 parts of heptane as a hydrophobic solvent. In the above-mentioned “(4) Solvent removal step”, 0.19 part of a polyether-based antifoaming agent (trade name: SNDEFOAMER PC, manufactured by San Nopco Ltd.) was added relative to 100 parts of the precursor composition in the stirring tank. The cleaning temperature in the above-mentioned “(5) Cleaning step” was changed from 25°C to 90°C. In the above-mentioned “(6) Drying step”, a vacuum dryer was used to heat-treat for 12 hours under a vacuum condition of 120°C and 4 kPa and a nitrogen gas flow (flow rate 400 L / min) instead of heat-treating for 12 hours under a vacuum condition of 200°C and 4 kPa. Except for this, hollow particles of Example 22 were manufactured in the same steps as in Example 1.

[0422] [Comparative Example 6]

[0423] In Comparative Example 6, a polyether-based antifoaming agent was not added. In the cleaning step, the number of a series of steps of washing the obtained dehydrated filter cake with 400 parts of ion-exchanged water, pressure filtration, and dehydration was changed from 6 times to 1 time. Except for this, hollow particles of Comparative Example 6 were manufactured in the same steps as in Example 22.

[0424] [Evaluation]

[0425] The following measurements and evaluations were carried out on the hollow particles obtained in each example and each comparative example. The results are shown in Tables 1 to 4.

[0426] 1. SEM observation of hollow particles

[0427] 100 hollow particles obtained in each example and each comparative example were each observed by SEM, and the presence or absence of pores of 100 nm or more was confirmed on the surface of each particle. When the number of hollow particles with pores of 100 nm or more was less than 5, it was evaluated as “no” particle breakage, and when the number of hollow particles with pores of 100 nm or more was 5 or more, it was evaluated as “yes” particle breakage.

[0428] 2. Proportion of abnormal-shaped particles

[0429] A mixed solution containing 0.10 - 0.12 g of hollow particles was added to an aqueous solution of sodium linear alkylbenzene sulfonate (concentration 0.3%) and dispersed using an ultrasonic cleaner for 5 minutes to prepare a measurement sample. Using a flow particle image measuring device (manufactured by JASCO INTERNATIONAL CO., LTD., trade name: IF-3200), the roundness of each particle contained in the measurement sample was measured under the following measurement conditions. Calculate the proportion of particles with a roundness of 0.85 or less based on mass, and use this as the proportion of irregularly shaped particles.

[0430] In addition, the smaller the particle size, the larger the number of particles contained in the measurement sample, and each of the examples and comparative examples was in the range of 1000 - 3000.

[0431] (Measurement conditions)

[0432] Thickness of the flow cell spacer: 50 μm

[0433] Telecentric zoom lens magnification: 4.5 times

[0434] Total magnification: 9.0 times

[0435] Measurement volume: 0.5 mL

[0436] Image resolution: 0.185 μm / pixel

[0437] Detection algorithm: Ghost detection

[0438] Threshold: 15%

[0439] 3. Particle size and particle size distribution

[0440] Using a particle size distribution measuring machine based on the Coulter counting method (product name: Multisizer 4e, manufactured by Beckman Coulter), the volume-based particle size distribution of the hollow particles was obtained, and the cumulative 50% particle size (D50) and the cumulative 95% particle size (D95) based on volume were calculated, and the ratio of D95 to D50 (D95 / D50) was calculated.

[0441] The measurement conditions were set as follows: aperture: 50 μm, dispersion medium: ISOTON II (product name), concentration 10%, number of measured particles: 100,000. Specifically, 0.2 g of the particle sample was placed in a beaker, and an aqueous surfactant solution (product name: DRIWEL, manufactured by Fujifilm Corporation) was added as a dispersant. Then, 2 ml of the dispersion medium was further added, and after wetting the particles, 10 ml of the dispersion medium was added. After dispersing for 1 minute using an ultrasonic disperser, the measurement was performed using the above particle size distribution measuring machine.

[0442] 4. Porosity

[0443] 4-1. Determination of the Apparent Density of Hollow Particles

[0444] First, fill about 30 cm 3 of hollow particles into a volumetric flask with a capacity of 100 cm 3 . Accurately weigh the mass of the filled hollow particles. Then, in the volumetric flask filled with hollow particles, carefully fill it with isopropyl alcohol up to the calibration mark while preventing air bubbles from entering. Accurately weigh the mass of the isopropyl alcohol added to the volumetric flask, and calculate the apparent density D 1 (g / cm 3 ) based on the following formula (I).

[0445] Formula (I)

[0446] Apparent density D 1 = [Mass of hollow particles] / (100 - [Mass of isopropyl alcohol] / [Specific gravity of isopropyl alcohol at the measurement temperature])

[0447] 4-2. Determination of the True Density of Hollow Particles

[0448] After previously crushing the hollow particles, fill about 10 g of fragments of the hollow particles into a volumetric flask with a capacity of 100 cm 3 . Accurately weigh the mass of the filled fragments.

[0449] Then, add isopropyl alcohol to the volumetric flask in the same manner as in the determination of the apparent density above, accurately weigh the mass of the isopropyl alcohol, and calculate the true density D 0 (g / cm 3 ) based on the following formula (II).

[0450] Formula (II)

[0451] True density D 0 = [Mass of fragments of hollow particles] / (100 - [Mass of isopropyl alcohol] / [Specific gravity of isopropyl alcohol at the measurement temperature])

[0452] 4-3. Calculation of Porosity

[0453] Calculate the porosity of the hollow particles from the apparent density D 1 and the true density D 0 based on the following formula (III).

[0454] Formula (III)

[0455] Porosity (%) = 100 - (Apparent density D 1 / True density D 0 ) × 100

[0456] 5. pH and Conductivity of the Aqueous Dispersion of Hollow Particles

[0457] Dissolve a nonionic surfactant (product name: SN DEFOAMER 180, manufactured by San Nopco Ltd., polyether type) in 100 mL of an aqueous solution (conductivity 1 μS / cm or less) of ion-exchanged water at a concentration of 0.1% by mass, and add hollow particles with a volume of 0.35 cm 3 . Stir at 300 rpm for 3 hours at room temperature (25°C) to obtain an aqueous dispersion of the hollow particles. Measure the pH and conductivity of the obtained aqueous dispersion of the hollow particles. In addition, the obtained aqueous dispersion of the hollow particles is in a state where no powder is present in the upper part as observed with the naked eye, and all the powder is dispersed in water. Furthermore, as the hollow particles with a volume of 0.35 cm 3 , use the hollow particles whose weight (g) was measured by the following formula (1).

[0458] Formula (1):

[0459] Weight (g) of hollow particles with a volume of 0.35 cm 3 = Apparent density D of hollow particles 1 (g / cm 3 )) × 0.35 (cm 3 )

[0460] 6. Residual monomer content

[0461] Measure the amount of unreacted polymerizable monomers contained in the hollow particles obtained in each example and each comparative example by the following method.

[0462] Precisely weigh 3 g of the solid content of the hollow particles to the nearest 1 mg unit, add 27 g of ethyl acetate and stir for 15 minutes, then add 13 g of methanol and stir for another 10 minutes. Let the obtained solution stand to precipitate the insoluble components, and collect the supernatant of this solution as the test sample for measurement. Inject the test sample for measurement into a gas chromatograph, and quantify the amount of unreacted polymerizable monomers in the test sample by gas chromatography (GC) under the following conditions. Calculate the content ratio of the unreacted polymerizable monomers contained in the hollow particles, and use it as the residual monomer content.

[0463] (Analysis conditions)

[0464] Apparatus: GC-2010 (manufactured by Shimadzu Corporation)

[0465] Column: DB-5 (manufactured by Agilent Technologies, Inc.)

[0466] Film thickness 0.25 μm, inner diameter 0.25 mm, length 30 m

[0467] Detector: FID

[0468] Carrier gas: Nitrogen (linear velocity: 28.8 cm / sec)

[0469] Inlet temperature: 200 °C

[0470] Detector temperature: 250 °C

[0471] Oven temperature: Rising from 40 °C to 230 °C at a rate of 10 °C / min and holding at 230 °C for 2 minutes. Sampling volume: 2 μL

[0472] 7. Residual components extracted by THF

[0473] Take the result of weighing 0.8 - 1.0 g of hollow particles as M1. Put the weighed hollow particles into a cylindrical filter paper (manufactured by Advantech Co., Ltd.: No. 84) and set it in a Soxhlet extractor. Use 100 ml of tetrahydrofuran (THF) as the solvent and carry out reflux for 6 hours to obtain an extract. Evaporate THF from the extract to obtain non-volatile components, and dry the obtained non-volatile components in vacuo at 50 °C for 1 hour to obtain a residue. Take the result of weighing the above residue as M2. Calculate the residual components after THF extraction of the hollow particles according to the following formula (2).

[0474] Formula (2):

[0475] Residual components after THF extraction (%) = (M2 / M1) × 100

[0476] 8. Residual metal content

[0477] Use a microwave digestion instrument (manufactured by PerkinElmer, model: Multiwave 3000) to wet-digest 10 g of accurately weighed hollow particles. Use an ICP emission analyzer (manufactured by PerkinElmer, model: Optima 2100DV) to perform ICP emission analysis on the obtained digest to measure the total mass of metals. In addition, the determination of metal types is carried out by elemental analysis based on X-ray fluorescence analysis (XRF). Calculate the ratio of the total mass of metals in the digest to the mass of the hollow particles as the residual metal content in the hollow particles.

[0478] 9. Relative dielectric constant (Dk) and dielectric loss tangent (Df)

[0479] Use a measurement device in perturbation mode (manufactured by AET Co., Ltd., model: ADMS01Nc) to measure the relative dielectric constant and dielectric loss tangent of the hollow particles at a frequency of 10 GHz, a temperature of 30 °C, and a humidity of 50%.

[0480] 10. Performance stability

[0481] Preparation of Resin Composition Containing Hollow Particles

[0482] Dissolve 90 parts of brominated epoxy resin (manufactured by Tohto Kasei Co., Ltd., product name: YDB-500EK75, epoxy equivalent 500, solid content 75% by mass) and 10 parts of cresol novolak type epoxy resin (manufactured by Tohto Kasei Co., Ltd., product name: YDCN220EK75, epoxy equivalent 210, solid content 75% by mass) in a mixed solvent of 20 parts of dimethylformamide (DMF) and 6 parts of methyl ethyl ketone (MEK) (room temperature). Further, add 2 parts of dicyandiamide (DICY) (manufactured by Nippon Carbide Industries Co., Ltd.) and 0.1 part of 2-ethyl-4-methylimidazole (product name: CUREZOL (registered trademark) 2E4MZ, manufactured by Shikoku Kasei Kogyo Co., Ltd.), and stir and mix them to prepare a resin varnish.

[0483] Next, use a disperser to stir and mix 95 parts of the resin varnish cooled to room temperature and 5 parts of hollow particles at 3000 rpm for 30 minutes to obtain a resin composition containing hollow particles.

[0484] 10-2. Production of Prepreg Containing Hollow Particles

[0485] Immerse the obtained resin composition containing hollow particles in a glass cloth (manufactured by Nitto Boseki Co., Ltd., product name: WEA116E), and heat and dry it at 150 to 170 °C for 3 to 10 minutes to remove the solvent, thereby obtaining a prepreg containing hollow particles.

[0486] 10-3. Production of Double-Sided Copper-Clad Laminate Containing Hollow Particles

[0487] Place 35-μm-thick copper foils on both sides of a single obtained prepreg containing hollow particles, and heat and press it under the curing conditions of 180 °C, 2 hours, and a pressure of 2.94 MPa (30 kg / cm 2 ) to obtain a double-sided copper-clad laminate with a thickness of 0.13 mm, having copper foils on both sides of a cured layer containing hollow particles.

[0488] 10-4. Reliability Test

[0489] Use a highly accelerated life test device (manufactured by ESPEC Corporation) to conduct a HAST test on the obtained double-sided copper-clad laminate under the conditions of 110 °C, 85% RH, and 100 hours of treatment. Apply a voltage of 50 V to the double-sided copper-clad laminate after this test for a specified time, measure the resistance value, confirm whether there is any abnormality, and evaluate it according to the following evaluation criterion I. In addition, consider a change in the resistance value as an abnormality. The change in the resistance value is considered to be caused by ion migration.

[0490] (Performance Stability Evaluation Criterion I)

[0491] AA: There is no abnormality even when the voltage is applied for 400 hours.

[0492] A: There is no abnormality even when the voltage is applied for 300 hours, but an abnormality occurs when the voltage application time reaches 400 hours.

[0493] B: There is no abnormality even when the voltage is applied for 200 hours, but an abnormality occurs when the voltage application time reaches 300 hours.

[0494] C: An abnormality occurs when the voltage application time reaches 200 hours.

[0495] When the evaluation result of the above Performance Stability Evaluation Criterion I is AA, the performance stability is further evaluated by the following Evaluation Criterion II.

[0496] (Performance Stability Evaluation Criterion II)

[0497] AAA: There is no abnormality even when the voltage is applied for 500 hours.

[0498] AA: There is no abnormality even when the voltage is applied for 400 hours, but an abnormality occurs when the voltage application time reaches 500 hours.

[0499] [Table 1]

[0500]

[0501] [Table 2]

[0502] Table 2

[0503]

[0504] [Table 3]

[0505]

[0506] [Table 4]

[0507] Table 4

[0508]

[0509] In addition, in Tables 1 to 4, for simplicity, the values of the dielectric loss tangent are expressed using the exponential notation specified in JIS X 0210. For example, "3.24×10 -4 " is denoted as "3.24E-04".

[0510] In addition, regarding the hollow particles obtained in each of the examples and comparative examples, based on the SEM observation results and the porosity values, it was confirmed that any of the hollow particles was spherical and had only one hollow part. In addition, among the hollow particles obtained in each example, the proportion of particles having only one hollow part was 90% or more.

[0511] [Examination]

[0512] Since the porosity of the hollow particles of Comparative Example 1 was less than 50%, the tangent of the dielectric loss angle and the relative dielectric constant were high, and the dielectric properties were poor.

[0513] Since the content of the unreacted polymerizable monomer in the hollow particles of Comparative Example 2 was greater than 100 ppm, and in the aqueous dispersion of hollow particles obtained by dispersing 0.35 cm 3 of hollow particles in 100 mL of ion-exchanged water, the conductivity was greater than 30 μS / cm, the tangent of the dielectric loss angle was large, and abnormalities were likely to occur in the reliability test of the double-sided copper-clad laminate containing the hollow particles, and the performance stability was poor. It is considered that in Comparative Example 2, since the hydrophobic solvent and the unreacted polymerizable monomer could not be sufficiently removed from the precursor particles in the solvent removal step, the cleanability in the cleaning step deteriorated, and the dispersion stabilizer (magnesium hydroxide) remaining in the hollow particles could not be sufficiently removed.

[0514] Since the proportion of particles having a roundness of 0.85 or less in the hollow particles of Comparative Example 3 was greater than 10% by mass, the tangent of the dielectric loss angle was large.

[0515] Since the conductivity of the hollow particles of Comparative Example 4 was greater than 30 μS / cm, the tangent of the dielectric loss angle was large, and abnormalities were likely to occur in the reliability test of the double-sided copper-clad laminate containing the hollow particles, and the performance stability was poor. It is considered that in Comparative Example 4, since the number of cleaning times in the cleaning step was reduced, the dispersion stabilizer (magnesium hydroxide) remaining in the hollow particles could not be sufficiently removed.

[0516] Since the content of the unreacted polymerizable monomer in the hollow particles of Comparative Example 5 was greater than 100 ppm, the tangent of the dielectric loss angle was large. It is considered that in Comparative Example 5, the unreacted polymerizable monomer could not be sufficiently removed from the precursor particles in the solvent removal step.

[0517] In contrast, for the hollow particles of each example, since the proportion of particles having a roundness of 0.85 or less was 10% by mass or less, the porosity was 50% or more, the content of the unreacted polymerizable monomer was 100 ppm or less, and when the volume was 0.35 cm 3In the aqueous dispersion of hollow particles obtained by dispersing the hollow particles in 100 mL of ion-exchanged water, the conductivity is 30 μS / cm or less, so the dielectric loss tangent is low. In each of the examples, it is considered that since the hydrophobic solvent and unreacted polymerizable monomer can be sufficiently removed from the precursor particles in the solvent removal step, the cleanability in the cleaning step is excellent, and in the cleaning step, the dispersion stabilizer (magnesium hydroxide) and unreacted polymerizable monomer remaining in the hollow particles can be efficiently removed. When compared with Comparative Examples 2, 4, and 5, the following is shown: compared with the case where the unreacted polymerizable monomer is more than 100 ppm and the above conductivity is more than 30 μS / cm (Comparative Example 2), the case where the unreacted polymerizable monomer is reduced to 100 ppm or less (Comparative Example 4), and the case where the above conductivity is reduced to 30 μS / cm or less (Comparative Example 5) each reduce the dielectric loss tangent, and in each of the examples, the unreacted polymerizable monomer is reduced to 100 ppm or less and the above conductivity is reduced to 30 μS / cm or less, and thus, due to the synergistic effect, the dielectric loss tangent is significantly reduced.

[0518] In addition, it is difficult for the hollow particles of each example to cause abnormalities in the reliability test of the double-sided copper-clad laminate containing the hollow particles, and the performance stability is excellent.

[0519] Among them, for the hollow particles of Examples 1 to 5, 7, 9, 10, and 11, the content of the unreacted polymerizable monomer is 80 ppm or less, the conductivity of the aqueous dispersion of the hollow particles is 20 μS / cm or less, and the dielectric loss tangent is even lower. It is considered that in these examples, since more hydrophobic solvent and unreacted polymerizable monomer can be removed from the precursor particles in the solvent removal step, the cleanability in the cleaning step is improved, and more dispersion stabilizer (magnesium hydroxide) and unreacted polymerizable monomer remaining in the hollow particles can be removed.

[0520] Furthermore, in Examples 1 to 5, 10, and 11, the content of the unreacted polymerizable monomer is 80 ppm or less, the conductivity of the aqueous dispersion of the hollow particles is 10 μS / cm or less, and it is even more difficult to cause abnormalities in the reliability test of the double-sided copper-clad laminate containing the hollow particles, and the performance stability is even more excellent. It is considered that in these examples, the solvent removal step is carried out at a pressure below atmospheric pressure and the time of the air bubbling treatment is long, so that more hydrophobic solvent and unreacted polymerizable monomer can be removed from the precursor particles in the solvent removal step, and thus the cleanability in the cleaning step is further improved, and more dispersion stabilizer (magnesium hydroxide) and unreacted polymerizable monomer remaining in the hollow particles can be removed.

[0521] In addition, in Example 11, even if the number of cleaning times in the cleaning step is reduced, the content of unreacted polymerizable monomers and the conductivity of the aqueous dispersion of the hollow particles can be reduced. Therefore, it is obvious that the cleanability in the cleaning step is excellent.

[0522] Furthermore, regarding the hollow particles of Examples 1 to 2, the content of unreacted polymerizable monomers is 60 ppm or less, the conductivity of the aqueous dispersion of the hollow particles is 9 μS / cm or less, the proportion of particles with a roundness of 0.85 or less is 5% by mass or less, the dielectric loss tangent is lower, and the performance stability is excellent. It is considered that in these examples, the solvent removal step is carried out under reduced pressure, gas is introduced from the bottom of the stirring tank, and while circulating the precursor composition in the stirring device, gas is blown into the precursor composition. As a result, more hydrophobic solvents and unreacted polymerizable monomers can be removed from the precursor particles in the solvent removal step. Therefore, the cleanability in the cleaning step is further improved, and more dispersing stabilizer (magnesium hydroxide) and unreacted polymerizable monomers remaining in the hollow particles can be removed. In addition, when comparing Examples 1 to 2 with Example 10, the following is shown: in Examples 1 to 2, by reducing the stirring power during solvent removal, the proportion of particles with a roundness of 0.85 or less is reduced, and as a result, the dielectric properties are improved.

[0523] When comparing Example 1 with Example 2, the content of unreacted polymerizable monomers in the hollow particles of Example 1 is less, the conductivity is lower, and the dielectric properties are more excellent. It is considered that in Example 1, during the gas blowing in the solvent removal step, the precursor composition is sprayed on the liquid surface of the precursor composition. As a result, more hydrophobic solvents and unreacted polymerizable monomers can be removed from the precursor particles compared to Example 2. Therefore, the cleanability in the cleaning step is further improved, and more dispersing stabilizer (magnesium hydroxide) and unreacted polymerizable monomers remaining in the hollow particles can be removed.

[0524] In Examples 12 to 19, by adding an antifoaming agent to the precursor composition when blowing gas in the solvent removal step, or by carrying out the solvent removal step under pressure, foaming of the precursor composition is suppressed, and the yield of the hollow particles is increased. In addition, by carrying out the cleaning step at a high temperature, the cleaning efficiency is improved, and more dispersing stabilizer (magnesium hydroxide) and unreacted polymerizable monomers remaining in the hollow particles can be removed. Furthermore, by carrying out the drying step under reduced pressure and in an inert gas stream, the drying efficiency is improved, so that the drying step can be carried out at a relatively low temperature of 120 °C. Regarding the hollow particles obtained in Examples 12 to 19, the content of unreacted polymerizable monomers is 45 ppm or less, the conductivity of the aqueous dispersion of the hollow particles is 4.0 μS / cm or less, the metal content is 13 ppm or less, the dielectric loss tangent is low, and the performance stability is excellent.

[0525] Among them, in Example 12 and Examples 15 to 19 where a polyether-based antifoaming agent is used as an antifoaming agent in the solvent removal step or the solvent removal step is carried out under pressure without using an antifoaming agent, the tangent of the dielectric loss angle of the obtained hollow particles is further reduced, and the performance stability is also excellent. On the other hand, among Examples 12 to 19, the tangent of the dielectric loss angle of the hollow particles obtained in Examples 13 to 14 is relatively high. It is considered that this is the influence of the remaining mineral oil-based or alcohol-based antifoaming agent. Regarding the hollow particles obtained in Example 12 and Examples 15 to 18, the content of unreacted polymerizable monomer is 25 ppm or less, the conductivity of the aqueous dispersion of the hollow particles is 3.5 μS / cm or less, and the metal content is 15 ppm or less. They are hollow particles with particularly excellent dielectric properties and performance stability in both aspects.

[0526] In Examples 20 to 22, similar to Example 12, when gas is bubbled in the solvent removal step, the foaming of the precursor composition is suppressed by making the precursor composition contain a polyether-based antifoaming agent, the cleaning efficiency is improved by performing the cleaning step at a high temperature, and further, the drying efficiency is improved by performing the drying step under reduced pressure and in an inert gas stream.

[0527] In Examples 20 and 21, a modified polyphenylene ether oligomer or glycidyl methacrylate is used as the polymerizable monomer. As a result, compared with the hollow particles obtained in Example 12, the dielectric properties and performance stability are poor. However, regarding the hollow particles obtained in Examples 20 and 21, the proportion of particles with a roundness of 0.85 or less is 10% by mass or less, the porosity is 50% or more, the content of unreacted polymerizable monomer is 100 ppm or less, and the conductivity of the aqueous dispersion of the hollow particles is 30 μS / cm or less. Therefore, compared with hollow particles obtained using the same polymerizable monomer and not satisfying at least any one of these characteristics, they are hollow particles with a reduced tangent of the dielectric loss angle and excellent performance stability.

[0528] In Example 22, the type of the polymerizable monomer was changed from Example 12, and as a result, the dielectric properties and performance stability were inferior compared to the hollow particles obtained in Example 12. However, regarding the hollow particles obtained in Example 22, the proportion of particles with a roundness of 0.85 or less was 10% by mass or less, the porosity was 50% or more, the content of unreacted polymerizable monomer was 100 ppm or less, and the conductivity of the aqueous dispersion of the hollow particles was 30 μS / cm or less. Therefore, compared to hollow particles obtained using the same polymerizable monomer and not satisfying at least any one of these characteristics, the hollow particles had a reduced dielectric loss tangent and excellent performance stability. Comparative Example 6 was hollow particles obtained using the same polymerizable monomer as in Example 22, and the conductivity of the aqueous dispersion of the hollow particles was greater than 30 μS / cm. The hollow particles of Example 22 had an extremely low dielectric loss tangent and improved performance stability compared to the hollow particles of Comparative Example 6.

[0529] [Example 23]

[0530] (1) Preparation of resin composition

[0531] To 100 parts of bisphenol A liquid epoxy resin (manufactured by Mitsubishi Chemical Corporation, product name: jER (registered trademark) 828, epoxy equivalent: 184 to 194), 4 parts of 2-ethyl-4-methylimidazole (trade name: CUREZOL 2E4MZ, manufactured by Shikoku Kasei Kogyo Co., Ltd.), 17 parts of the hollow particles obtained in Example 1, and 50 parts of an inorganic filler (silica manufactured by Admatechs Company) were added and uniformly dispersed using a planetary stirring and degassing device (manufactured by Kurashiki Boseki Co., Ltd., product name: MAZERUSTAR), thereby preparing the resin composition of Example 23.

[0532] (2) Production of resin film

[0533] An aluminum foil was affixed to a glass plate without wrinkles, and the resin composition obtained in (1) above was coated on the aluminum foil using a bar coater No. 75 to form a coating film. The coating film was cured by heating at 150 °C for 3 hours in a nitrogen atmosphere to form a resin cured layer on the aluminum foil. The laminate of the resin cured layer and the aluminum foil was immersed in 1N hydrochloric acid aqueous solution overnight to remove the aluminum foil and obtain only the resin cured layer. The obtained resin cured layer was washed with ion-exchanged water and dried to obtain a resin film. In the obtained resin film, the content of the hollow particles was 40% by volume relative to 100% by volume of the resin film.

[0534] (3) Production of prepreg

[0535] After impregnating the resin composition obtained in the above (1) into a glass cloth (manufactured by Nitto Boseki Co., Ltd., product name: WEA116E), it is heated and dried at 150 to 170 °C for 3 to 10 minutes to obtain a prepreg containing hollow particles.

[0536] (4) Fabrication of a double-sided copper-clad laminate

[0537] Copper foils with a thickness of 35 μm are disposed on both sides of one sheet of the prepreg obtained in the above (3), and are heated and pressed under the curing conditions of 180 °C, 2 hours, and a pressure of 2.94 MPa (30 kg / cm 2 ), thereby obtaining a double-sided copper-clad laminate with a thickness of 0.13 mm having copper foils on both sides of a cured layer containing hollow particles.

[0538] [Example 24]

[0539] In Example 23, the hollow particles obtained in Example 12 were used instead of the hollow particles obtained in Example 1, and except for this, the resin composition, resin film, prepreg, and double-sided copper-clad laminate of Example 24 were produced in the same steps as in Example 23.

[0540] In the obtained resin film, the content of the hollow particles is 40% by volume with respect to 100% by volume of the resin film.

[0541] [Example 25]

[0542] In Example 23, the hollow particles obtained in Example 20 were used instead of the hollow particles obtained in Example 1, and except for this, the resin composition, resin film, prepreg, and double-sided copper-clad laminate of Example 25 were produced in the same steps as in Example 23.

[0543] In the obtained resin film, the content of the hollow particles is 40% by volume with respect to 100% by volume of the resin film.

[0544] [Example 26]

[0545] In Example 23, the hollow particles obtained in Example 21 were used instead of the hollow particles obtained in Example 1, and except for this, the resin composition, resin film, prepreg, and double-sided copper-clad laminate of Example 26 were produced in the same steps as in Example 23.

[0546] In the obtained resin film, the content of the hollow particles is 40% by volume with respect to 100% by volume of the resin film.

[0547] [Example 27]

[0548] In Example 23, the hollow particles obtained in Example 22 were used instead of the hollow particles obtained in Example 1, and in addition, the resin composition, resin film, prepreg, and double-sided copper-clad laminate of Example 27 were produced in the same steps as in Example 23.

[0549] In the obtained resin film, the content of the hollow particles was 37% by volume with respect to 100% by volume of the resin film.

[0550] [Comparative Example 7]

[0551] In Example 23, the hollow particles obtained in Example 1 were not added, and in addition, the resin composition, resin film, prepreg, and double-sided copper-clad laminate of Comparative Example 7 were produced in the same steps as in Example 23.

[0552] [Example 28]

[0553] (1) Preparation of Resin Composition

[0554] 90 parts of a brominated epoxy resin solution (manufactured by Tohto Kasei Co., Ltd., product name: YDB-500EK75, epoxy equivalent 500, solid content 75% by mass) and 10 parts of a cresol novolak type epoxy resin solution (manufactured by Tohto Kasei Co., Ltd., product name: YDCN220EK75, epoxy equivalent 210, solid content 75% by mass) were dissolved in a mixed solvent (room temperature) of 20 parts of dimethylformamide (DMF) and 6 parts of methyl ethyl ketone (MEK). Further, 2 parts of dicyandiamide (DICY) (manufactured by Nippon Carbide Industries Co., Ltd.) and 0.1 part of 2-ethyl-4-methylimidazole (trade name: CUREZOL 2E4MZ, manufactured by Shikoku Chemicals Corporation) were added, and the mixture was stirred and mixed to prepare a resin varnish.

[0555] Next, 95 parts of the resin varnish cooled to room temperature and 5 parts of the hollow particles were stirred and mixed at 3000 rpm for 30 minutes using a disperser to obtain the resin composition of Example 28. In addition, the amounts of the brominated epoxy resin and the cresol novolak type epoxy resin with respect to 5 parts of the hollow particles are shown in Table 5.

[0556] (2) Production of Resin Film

[0557] The aluminum foil was pasted on the glass plate without wrinkles, and the resin composition obtained in the above (1) was coated on the aluminum foil using a rod coater No. 75 to form a coating film. By curing it in a nitrogen atmosphere in the order of heating at 80 °C for 1 hour, heating at 120 °C for 30 minutes, heating at 160 °C for 30 minutes, and heating at 200 °C for 1 hour, a resin cured layer was formed on the aluminum foil. By immersing the laminate of the resin cured layer and the aluminum foil in 1N hydrochloric acid aqueous solution overnight, the aluminum foil was removed to obtain only the resin cured layer. By washing the obtained resin cured layer with ion-exchanged water and drying it, a resin film was obtained. In the obtained resin film, the content of the hollow particles was 30% by volume relative to 100% by volume of the resin film.

[0558] (3) Production of prepreg

[0559] Using the resin composition obtained in the above (1), a prepreg containing hollow particles was obtained by the same steps as in Example 23.

[0560] (4) Production of double-sided copper-clad laminate

[0561] Using the prepreg obtained in the above (3), a double-sided copper-clad laminate was obtained by the same steps as in Example 23.

[0562] [Example 29]

[0563] In Example 28, the hollow particles obtained in Example 12 were used instead of the hollow particles obtained in Example 1, and in addition, the resin composition, resin film, prepreg, and double-sided copper-clad laminate of Example 29 were produced by the same steps as in Example 28.

[0564] In the obtained resin film, the content of the hollow particles was 30% by volume relative to 100% by volume of the resin film.

[0565] [Example 30]

[0566] In Example 28, the hollow particles obtained in Example 12 were used instead of the hollow particles obtained in Example 1, and further, 67.5 parts of alicyclic epoxy resin 1 (trade name: CELLOXIDE 2021P, manufactured by Daicel Corporation) was used instead of 90 parts of brominated epoxy resin solution. Except for this, the resin composition, resin film, prepreg, and double-sided copper-clad laminate of Example 30 were produced by the same steps as in Example 28.

[0567] In addition, the amounts of alicyclic epoxy resin 1 and cresol novolac epoxy resin relative to 5 parts of the hollow particles are shown in Table 5.

[0568] In the obtained resin film, the content of the hollow particles was 20% by volume relative to 100% by volume of the resin film.

[0569] [Example 31]

[0570] In Example 28, the hollow particles obtained in Example 12 were used instead of the hollow particles obtained in Example 1. Furthermore, 67.5 parts of an alicyclic epoxy resin 2 (trade name: CYCLOMER M100, manufactured by Daicel Corporation) was used instead of 90 parts of a brominated epoxy resin solution. Except for this, the resin composition, resin film, prepreg, and double-sided copper-clad laminate of Example 31 were produced in the same steps as in Example 28.

[0571] In addition, the amounts of the alicyclic epoxy resin 2 and the cresol novolak type epoxy resin with respect to 5 parts of the hollow particles are shown in Table 5.

[0572] In the obtained resin film, the content of the hollow particles is 20% by volume with respect to 100% by volume of the resin film.

[0573] [Example 32]

[0574] (1) Preparation of resin composition

[0575] Measure 20 parts of a toluene solution of a modified polyphenylene ether modified with a vinyl group-containing functional group (manufactured by Mitsubishi Gas Chemical Company, Inc., product name: OPE-1200, iodine value: 43 g / 100 g, number average molecular weight: 1200, solid content 65% by mass) in a cup, add 11 parts of the hollow particles obtained in Example 1, 13 parts of an inorganic filler (silica manufactured by Admatechs Co., Ltd.), and further add 0.15 parts of dicumyl peroxide (manufactured by NOF Corporation, product name: PERCUMYL D). Uniformly disperse using a planetary stirring and defoaming device (manufactured by Kurashiki Boseki Co., Ltd., product name: MAZERUSTAR) to prepare the resin composition of Example 32.

[0576] (2) Production of resin film

[0577] Affix the aluminum foil to the glass plate without wrinkles, and coat the resin composition obtained in (1) above on the aluminum foil using a bar coater No. 75 to form a coating film. Cure it in a nitrogen atmosphere in the order of heating at 80°C for 1 hour, heating at 120°C for 30 minutes, heating at 160°C for 30 minutes, and heating at 200°C for 1 hour to form a resin cured layer on the aluminum foil. Immerse the laminate of the resin cured layer and the aluminum foil in 1N hydrochloric acid aqueous solution overnight to remove the aluminum foil and obtain only the resin cured layer. Wash the obtained resin cured layer with ion-exchanged water and dry it to obtain a resin film. In the obtained resin film, the content of the hollow particles is 75% by volume with respect to 100% by volume of the resin film.

[0578] (3) Production of prepreg

[0579] Using the resin composition obtained in the above (1), a prepreg containing hollow particles was obtained through the same steps as in Example 23.

[0580] (4) Production of double-sided copper-clad laminate

[0581] Using the prepreg obtained in the above (3), a double-sided copper-clad laminate was obtained through the same steps as in Example 23.

[0582] [Relative dielectric constant (Dk) and dielectric loss tangent (Df) of resin film]

[0583] Using a measuring device of the perturbation method (manufactured by AET Co., Ltd., model: ADMS01Nc), the relative dielectric constant and dielectric loss tangent of the resin film were measured at a frequency of 10 GHz and room temperature (25 °C), and the relative dielectric constant and dielectric loss tangent were evaluated based on the following evaluation criteria. The evaluation results are shown in Table 5.

[0584] (Evaluation criteria for relative dielectric constant (Dk) of Examples 23 to 31 and Comparative Example 7)

[0585] A: Less than 2.35

[0586] B: 2.35 or more and less than 2.38

[0587] C: 2.38 or more and less than 2.41

[0588] D: 2.41 or more

[0589] (Evaluation criteria for dielectric loss tangent (Df) of Examples 23 to 31 and Comparative Example 7)

[0590] A: Less than 9.70×10 -3

[0591] B: 9.70×10 -3 or more and less than 1.20×10 -2

[0592] C: 1.20×10 -2 or more and less than 1.70×10 -2

[0593] D: 1.70×10 -2 or more

[0594] (Evaluation criteria for relative dielectric constant (Dk) of Example 32)

[0595] A: Less than 2.18

[0596] B: 2.18 or more and less than 2.23

[0597] C: Above 2.23 and less than 2.28

[0598] D: Above 2.28

[0599] (Evaluation Criteria for Dielectric Loss Tangent (Df) of Example 32)

[0600] A: Less than 1.50×10 -3

[0601] B: 1.50×10 -3 or more and less than 2.00×10 -3

[0602] C: 2.00×10 -3 or more and less than 2.45×10 -3

[0603] D: 2.45×10 -3 or more

[0604] [Reliability Test of Double-Sided Copper-Clad Laminate]

[0605] The obtained double-sided copper-clad laminate was subjected to a reliability test in the same manner as the above-mentioned "10-4. Reliability Test" to confirm the presence or absence of abnormalities, and the reliability was evaluated according to the following evaluation criteria. The evaluation results are shown in Table 5.

[0606] (Reliability Evaluation Criteria)

[0607] AAA: No abnormality even when a voltage is applied for 500 hours.

[0608] AA: No abnormality even when a voltage is applied for 400 hours, but an abnormality occurs when the voltage application time reaches 500 hours.

[0609] A: No abnormality even when a voltage is applied for 300 hours, but an abnormality occurs when the voltage application time reaches 400 hours.

[0610] B: No abnormality even when a voltage is applied for 200 hours, but an abnormality occurs when the voltage application time reaches 300 hours.

[0611] C: An abnormality occurs when the voltage application time reaches 200 hours.

[0612] [Table 5]

[0613]

[0614] [Discussion]

[0615] Since the resin compositions and resin structures obtained in Examples 23 to 27 contain the hollow particles of the present invention, the relative dielectric constant and the tangent of the dielectric loss angle are reduced compared with the resin compositions and resin structures of Comparative Example 7 having the same composition except for not containing the hollow particles, and the reduction in reliability is suppressed.

[0616] Since the resin compositions and resin structures obtained in Examples 28 to 32 also contain the hollow particles of the present invention, the relative dielectric constant and the tangent of the dielectric loss angle are reduced compared with the resin compositions and resin structures having the same composition except for not containing the hollow particles, and the reduction in reliability is suppressed.

[0617] Explanation of reference numerals

[0618] 1: Aqueous medium;

[0619] 2: Low-polarity material;

[0620] 3: Droplets of monomer composition;

[0621] 4a: Hydrophobic solvent;

[0622] 4b: Materials other than the hydrophobic solvent;

[0623] 5: Precursor particles;

[0624] 6: Shell;

[0625] 7: Hollow part;

[0626] 10A: Hollow particles after the solvent removal step;

[0627] 10B: Hollow particles after the cleaning step;

[0628] 11: Stirring tank;

[0629] 12: Supply tank;

[0630] 13a, 13b, 13c: Gas inlets;

[0631] 14: Outlet;

[0632] 15: Spraying mechanism;

[0633] 16: Supply pipeline to the stirring tank;

[0634] 17a, 17b: Circulation pipelines;

[0635] 20: Precursor composition;

[0636] 21: Gas phase part.

Claims

1. A hollow particle having a shell containing a resin and a hollow portion surrounded by the shell, wherein the proportion of particles having a roundness of 0.85 or less is 10% by mass or less, the porosity is 50% or more, the content of unreacted polymerizable monomer is 100 ppm or less, In a aqueous dispersion of the hollow particles obtained by dispersing the hollow particles having a volume of 0.35 cm 3 in 100 mL of ion-exchanged water, the electric conductivity is 30 μS / cm or less.

2. The hollow particle according to claim 1, wherein, the shell contains a polymer as the resin, and in all monomer units of 100% by mass of the polymer, the content of crosslinkable monomer units is 60% by mass or more.

3. The hollow particle according to claim 1, wherein, the shell contains a polymer as the resin, and in all monomer units of 100% by mass of the polymer, the content of crosslinkable monomer units is less than 60% by mass, and the content of aromatic hydrocarbon monomer units is more than 20% by mass.

4. The hollow particle according to any one of claims 1 to 3, wherein, when using tetrahydrofuran as a solvent and taking the mass of the residue obtained by removing tetrahydrofuran from the extract obtained by refluxing the hollow particles with a mass of M1 for 6 hours using a Soxhlet extractor as M2, the residue component remaining after THF extraction, calculated as a percentage of M2 relative to M1, is 80% or more.

5. The hollow particle according to any one of claims 1 to 3, wherein, the metal content is 100 ppm or less.

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

7. The hollow particle according to claim 1 or 3, wherein, The dielectric loss tangent at a frequency of 10 GHz is greater than 1.00×10 -3 and is 1.00×10 -2 or less.

8. The hollow particle according to any one of claims 1 to 3, wherein, the relative permittivity at a frequency of 10 GHz is 1.00 or more and 1.60 or less.

9. A method for manufacturing a hollow particle, which is the hollow particle according to claim 1, and the manufacturing method has the following steps: a step of preparing a mixed solution containing a polymerizable monomer, a hydrophobic solvent, a polymerization initiator, a dispersion stabilizer, and an aqueous medium; a step of preparing a suspension in which droplets of a monomer composition containing the polymerizable monomer, the hydrophobic solvent, and the polymerization initiator are dispersed in the aqueous medium by suspending the mixed solution; a step of preparing a precursor composition in which precursor particles are dispersed in the aqueous medium by subjecting the suspension to a polymerization reaction, the precursor particles having a hollow portion surrounded by a shell containing a resin and the hollow portion being filled with the hydrophobic solvent; a step of obtaining an aqueous dispersion of hollow particles by stirring the precursor composition in a stirring tank and blowing a gas into the precursor composition to remove the hydrophobic solvent from the precursor particles; a step of performing a cleaning for removing the dispersion stabilizer remaining in the hollow particles.

10. The method for manufacturing a hollow particle according to claim 9, wherein, the cleaning is performed at 10°C or higher and 90°C or lower.

11. The method for manufacturing a hollow particle according to claim 9 or 10, wherein, after the step of performing the cleaning, there is further a step of drying and removing the water remaining in the hollow particles obtained by this step, and the drying is performed under reduced pressure and in an inert gas stream.

12. The manufacturing method of the hollow particles according to claim 9 or 10, wherein, a process of blowing gas into the precursor composition is carried out for 2 hours or more.

13. The manufacturing method of the hollow particles according to claim 9 or 10, wherein, The stirring power during stirring of the precursor composition is 0.01 kW / m 3 or more and 0.60 kW / m 3 or less.

14. The manufacturing method of the hollow particles according to claim 9 or 10, wherein, blowing gas into the precursor composition is carried out under a pressure of 20 kPa or more and 300 kPa or less.

15. The manufacturing method of the hollow particles according to claim 9 or 10, wherein, blowing gas into the precursor composition is carried out under a pressure of 20 kPa or more and below atmospheric pressure.

16. The manufacturing method of the hollow particles according to claim 9 or 10, wherein, blowing gas into the precursor composition is carried out under a pressure higher than atmospheric pressure and 2000 kPa or less.

17. The manufacturing method of the hollow particles according to claim 9 or 10, wherein, when blowing gas into the precursor composition, the precursor composition contains an antifoaming agent.

18. The manufacturing method of the hollow particles according to claim 9 or 10, wherein, when blowing gas into the precursor composition, the gas is introduced from the bottom of the stirring tank storing the precursor composition.

19. The manufacturing method of the hollow particles according to claim 9 or 10, wherein, during the period of blowing gas into the precursor composition, the following operation is repeated to circulate in the stirring device: the precursor composition is supplied from the supply tank to the stirring tank, stirred in the stirring tank, and then discharged to the supply tank.

20. The manufacturing method of the hollow particles according to claim 9 or 10, wherein, in the stirring tank storing the precursor composition, there is a liquid phase part and a gas phase part containing the precursor composition. When blowing gas into the precursor composition, a part of the precursor composition is supplied from the stirring tank to the spraying mechanism and sprayed onto the liquid surface of the precursor composition in the stirring tank.

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

22. The resin composition according to claim 21, wherein, in all solid components of 100% by mass of the resin composition, the content of the hollow particles is 0.1% by mass or more and 30% by mass or less.

23. The resin composition according to claim 21, wherein, the matrix resin contains an epoxy compound.

24. A resin structure comprising the hollow particles according to any one of claims 1 to 8 and a matrix resin.

25. A resin structure which is a cured product of the resin composition according to claim 21.

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