Silica particle dispersion liquid

Abstract

The present invention provides a silica particle dispersion liquid that suppresses granulation when formed into a film and that can increase detachment strength. The silica particle dispersion liquid according to the present invention contains hollow silica particles and a solvent. The average particle size of the hollow silica particles is in a range of 0.2-10 μm.

Description

Silica particle dispersion

[0001] The present invention relates to a silica particle dispersion in which silica particles are dispersed in a solvent.

[0002] Silica particles have conventionally been used in a variety of applications, including electronic materials such as printed wiring boards and package wiring boards, optical materials such as lenses and optical films, functional materials such as catalysts and catalyst carriers, and pigments for paints, cosmetics, etc. Among these, hollow silica particles, having properties such as a low refractive index, a low dielectric constant, and a low density, are used to lower the relative dielectric constant, the dielectric loss tangent, and the thermal expansion of resin compositions used in insulating resin sheets such as adhesive films and prepregs, as well as insulating layers formed on printed wiring boards.

[0003] Silica particles tend to aggregate when used in a dry powder state, and therefore are used in the form of a dispersion in which they are dispersed in a solvent such as water or a resin depending on the intended use, and various silica particle dispersions and slurries containing such silica particle dispersions have been proposed.

[0004] For example, Patent Document 1 describes a method for producing a powder having a particle size of 100 nm to 2000 nm or a specific surface area of ​​2 m ２ / g~35m ２ / g, and the amount of water generated when heated at 200°C is ２ The present invention proposes a slurry for electronic materials, which comprises a filler for electronic materials that is a silica particle material having a surface treatment with a silane compound having a vinyl group, a phenyl group, a phenylamino group, an alkyl group having 4 or more carbon atoms, a methacryl group, or an epoxy group, and which has a silica content of 40 ppm or less per 1000 ppm of the filler, and a liquid dispersion medium that is substantially free of water.

[0005] Patent Document 2 proposes a coating liquid for forming an anti-reflection film, which comprises hollow silica particles (A) having an average particle diameter (Dpa) in the range of 30 to 200 nm, solid silica particles (B) having an average particle diameter (Dpb) in the range of 5 to 80 nm, and a solvent, wherein the concentration (CA) of the hollow silica particles (A) is in the range of 0.2 to 8 wt % as solid content, the concentration (CB) of the solid silica particles (B) is in the range of 0.2 to 8 wt % as solid content, and the weight ratio (B / A) of the hollow silica particles (A) to the solid silica particles (B) is 0.25 to 4.

[0006] Furthermore, Patent Document 3 proposes a dispersion of silica-based particles containing silica-based particles having an average particle diameter of 5 to 40 nm and a ratio of the number of hollow particles to the total number of hollow particles and solid particles (hollowness) of 70% or more.

[0007] Japanese Patent Publication No. 2020-097498 Japanese Patent Publication No. 2015-102666 Japanese Patent Publication No. 2018-123043

[0008] However, when conventional silica particle dispersions are incorporated into a resin composition to form a film, the silica particles tend to become granular, resulting in low peel strength and making it difficult to achieve the effects expected from the silica particles.

[0009] The present invention has been made in view of the above problems, and an object of the present invention is to provide a silica particle dispersion liquid that can suppress granularity when a film is formed and can increase peel strength.

[0010] The present invention relates to the following (1) to (11): (1) A silica particle dispersion containing hollow silica particles and a solvent, wherein the hollow silica particles have an average particle size in the range of 0.2 to 10 μm. (2) The hollow silica particles have a particle density of 0.35 to 2.00 g / cm, as determined by density measurement using a dry pycnometer using argon gas. ３ (3) The hollow silica particles have a particle density of 2.00 to 2.30 g / cm as determined by density measurement using a dry pycnometer using helium gas. ３ (4) The silica particle dispersion liquid according to (1) or (2), wherein the hollow silica particles have a BET specific surface area of ​​1 to 100 m ２ / g. (5) The silica particle dispersion according to any one of (1) to (3), wherein the hollow silica particles have a sphericity of 0.75 to 1.0. (6) The silica particle dispersion according to any one of (1) to (5), further comprising a silane compound having at least one group selected from the group consisting of a vinyl group, a phenyl group, a phenylamino group, an alkyl group having 4 or more carbon atoms, a methacryl group, and an epoxy group. (7) The silica particle dispersion according to any one of (1) to (6), further comprising an organic thixotropic agent. (8) The silica particle dispersion according to any one of (1) to (7), wherein the solvent comprises at least one selected from the group consisting of water, hydrocarbons, alcohols, acetates, ketones, cellosolves, glycol ethers, chlorinated hydrocarbons, and polar solvents. (9) The silica particle dispersion according to any one of (1) to (8), wherein the viscosity of the silica particle dispersion at 25°C when the solid content concentration of the hollow silica particles is 50% by volume is 20 to 20,000 mPa·s. (10) A resin composition comprising the silica particle dispersion according to any one of (1) to (9). (11) A method for producing a silica particle dispersion, comprising mixing a solvent with a powder of hollow silica particles having an average particle size in the range of 0.2 to 10 μm, dispersing the mixture, and classifying the mixture to remove agglomerates of the hollow silica particles.

[0011] In the silica particle dispersion of the present invention, the hollow silica particles are uniformly dispersed in the liquid without agglomeration, and therefore, when a resin composition containing the silica particle dispersion of the present invention is formed into a film, granulation can be suppressed and the peel strength can be increased.

[0012] The present invention will be described below, but the present invention is not limited to the examples in the following description. In this specification, the term "to" indicating a range of values ​​means that the values ​​before and after it are included as the lower and upper limits. In this specification, "mass" is synonymous with "weight."

[0013] <Silica Particle Dispersion> The silica particle dispersion of the present invention contains hollow silica particles and a solvent, and the hollow silica particles have an average particle size in the range of 0.2 to 10 μm. In the silica particle dispersion of the present invention, the hollow silica particles are uniformly dispersed without agglomeration, and the dispersion stability of the hollow silica particles in the dispersion is improved. When the hollow silica particles are incorporated into a resin composition to form a film, particle formation can be suppressed and peel strength can be increased.

[0014] (Solvent) The solvent serving as the dispersion medium for the silica particle dispersion can be selected arbitrarily depending on the intended use, and examples thereof include water, hydrocarbons, alcohols, acetates, ketones, cellosolves, glycol ethers, chlorinated hydrocarbons, and polar solvents. The solvent preferably contains at least one selected from the group consisting of these.

[0015] Examples of hydrocarbons include toluene, methylcyclohexane, normal heptane, and m-xylene. Examples of alcohols include ethanol, isopropyl alcohol, 1-propyl alcohol, isobutyl alcohol, 1-butanol, and 2-butanol. Examples of acetates include propyl acetate, isobutyl acetate, and butyl acetate. Examples of ketones include methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone. Examples of cellosolves include ethylene glycol monomethyl ether and ethylene glycol monoethyl ether. Examples of glycol ethers include 1-methoxy-2-propanol, 1-methoxypropyl-2-acetate, 1-ethoxy-2-propanol, and ethyl 3-ethoxypropionate. Examples of chlorinated hydrocarbons include trichloroethylene and tetrachloroethylene. Examples of polar solvents include N-methyl-2-pyrrolidone.

[0016] The solvent may be appropriately selected depending on the field of intended use. For example, when used for an insulating layer of a wiring substrate of an electronic device, it is preferable to use ketones or hydrocarbons, specifically methyl ethyl ketone (MEK), toluene, etc.

[0017] When the silica particle dispersion of the present invention is used in a curable composition, the liquid base resin or curing agent itself may be used as a solvent. Examples of the base resin include epoxy resin, polyphenylene ether resin, polyester resin, polyimide resin, phenol resin, and orthodivinylbenzene resin. Examples of the curing agent include polyamine-based curing agents, acid anhydride-based curing agents, phenol-based curing agents, active ester-based curing agents, and peroxides.

[0018] The solvent is preferably contained in the silica particle dispersion in a range of 20 to 90% by volume. When the solvent content is 20% by volume or more, the hollow silica particles can be uniformly dispersed, and the viscosity of the dispersion does not become too high, making it easy to handle. When the solvent content is 90% by volume or less, the dispersion is in a liquid state and can be used as is. The solvent content in the silica particle dispersion is more preferably 25% by volume or more, even more preferably 30% by volume or more, more preferably 80% by volume or less, even more preferably 70% by volume or less, particularly preferably 60% by volume or less, and most preferably 50% by volume or less.

[0019] (Hollow Silica Particles) Hollow silica particles are silica particles that have a shell layer (solid film) containing silica and have a space inside the shell layer. The fact that hollow silica particles have a space inside the shell layer can be confirmed by observation with a transmission electron microscope (TEM) or a scanning electron microscope (SEM). In the case of SEM observation, it can be confirmed that the particles are hollow by observing broken particles with partial openings. The following physical properties of hollow silica particles can be confirmed by drying a silica particle dispersion to obtain powdered silica particles.

[0020] In this specification, the shell layer "contains silica" means that the shell layer contains silica (SiO ２) is contained in an amount of 50% by mass or more. The composition of the shell layer can be measured by ICP atomic emission spectrometry, flame atomic absorption spectrometry, or the like. The silica content of the shell layer is preferably 80% by mass or more, more preferably 95% by mass or more. Theoretically, the upper limit is 100% by mass. The silica content of the shell layer is preferably less than 100% by mass, more preferably 99.99% by mass or less. The remainder includes alkali metal oxides and silicates, alkaline earth metal oxides and silicates, carbon, and the like. Furthermore, "having a space inside the shell layer" means that when the cross section of a single primary particle is observed, a single space is surrounded by a shell layer, creating a hollow state. In other words, each hollow particle has one large space surrounded by a shell layer.

[0021] Since the hollow silica particles have a structure in which a space is formed within the shell, a composition containing the silica particle dispersion of the present invention can secure more space within the composition, and when used in an insulating layer of an electronic device or the like, the dielectric constant can be reduced.

[0022] The hollow silica particles dispersed in the silica particle dispersion of the present invention have an average particle size (D50, median size) of 0.2 to 10 μm. Because primary particles are partially bonded to one another during the firing and drying processes during production, the hollow silica particles often consist of aggregates of secondary particles formed by aggregation of primary particles. The average particle size of the hollow silica particles referred to here refers to the particle size of the secondary particles, and the primary particles refer to spherical particles with internal voids that can be confirmed by TEM or SEM observation.

[0023] When the average particle diameter (D50) of the hollow silica particles in the silica particle dispersion is in the range of 0.2 to 10 μm, the silica particle dispersion has a viscosity that is easy to handle and is less likely to become granular during coating, so that the peel strength of the resin composition when used as a resin composition is maintained at an appropriate level. The average particle diameter (D50) is preferably 0.5 μm or more, more preferably 1 μm or more, and is preferably 8 μm or less, more preferably 6 μm or less, and even more preferably 5 μm or less.

[0024] The average particle size of hollow silica particles (particle size of secondary particles) is preferably measured by laser scattering. Measuring the aggregate size by SEM is because the boundaries between particles are unclear and the measurement does not reflect the dispersion in a wet state. In addition, when measuring by a Coulter counter, the electric field changes differently between hollow particles and solid particles, making it difficult to obtain a value corresponding to the solid particle size.

[0025] The coarse particle size (D90) of the secondary particles of the hollow silica particles is preferably 1 to 30 μm. From the viewpoint of production efficiency, the coarse particle size is preferably 1 μm or more. Furthermore, if the coarse particle size is too large, it will cause granulation when the resin composition is molded into a film, so it is preferably 30 μm or less. The lower limit of the coarse particle size is more preferably 3 μm or more, most preferably 5 μm or more, and the upper limit is preferably 30 μm or less, more preferably 25 μm or less, even more preferably 20 μm or less, and most preferably 15 μm or less.

[0026] The coarse particle size can also be determined by measuring the particle size of secondary particles by laser scattering, as described above.

[0027] The primary particle size of hollow silica particles can be determined by directly observing the particle diameter (diameter) using an SEM. The average primary particle size (average primary particle diameter) is preferably in the range of 50 nm to 10 μm. When the average primary particle diameter is 50 nm or more, increases in the specific surface area, oil absorption, and pore volume are suppressed, and increases in the amount of SiOH and adsorbed water on the particle surface are suppressed, making it difficult for the dielectric loss tangent to increase. Furthermore, when the average primary particle diameter is 10 μm or less, handling as a filler is easy. From the viewpoint of production reproducibility, the lower limit of the average primary particle diameter is more preferably 70 nm or more, and even more preferably 100 nm or more, and the upper limit is more preferably 5 μm or less, and particularly preferably 3 μm or less.

[0028] Specifically, the average primary particle diameter of the hollow silica particles is determined by measuring the primary particle sizes of 100 particles from an SEM image, aggregating the primary particle sizes, and estimating the distribution of the primary particle sizes as the overall primary particle size distribution. SEM observation allows direct measurement of the primary particle diameter of particles that are difficult to deagglomerate.

[0029] The hollow silica particles of the present invention have the above-mentioned average primary particle diameter, and it is preferable that 40% or more of the total primary particles have a particle diameter within ±40% of the average primary particle diameter. If 40% or more of the particles have a particle diameter within ±40% of the average primary particle diameter, the size of the hollow silica particles will be uniform, and defects in the shell of the hollow silica particles will be less likely to occur. It is more preferable that 50% or more of the total particles have a particle diameter within ±40%, even more preferable that 60% or more of the total particles have a particle diameter within ±40%, and particularly preferable that 70% or more of the total particles have a particle diameter within ±40%.

[0030] The hollow silica particles have a particle density (hereinafter also referred to as Ar density) of 0.35 to 2.00 g / cm as determined by density measurement using a dry pycnometer using argon gas. ３ It is preferable that the Ar density is 0.35 g / cm ３ When the Ar density is 2.00 g / cm or more, cracking of the particles in the dispersion can be suppressed, and the difference in specific gravity with the resin does not become too large, so that dispersibility in the resin composition can be improved when the silica particle dispersion is mixed with the resin. ３ When the Ar density is 0.40 g / cm or less, the effect of reducing the dielectric constant is easily exhibited, and the material can be preferably used as a material for electronic devices. ３ More preferably, the upper limit is 1.50 g / cm ３ More preferably, it is 1.00 g / cm or less. ３ More preferably, the Ar density is 0.35 to 1.50 g / cm ３ More preferably, 0.40 to 1.00 g / cm ３ is more preferable.

[0031] The hollow silica particles have a particle density (hereinafter also referred to as He density) of 2.00 to 2.30 g / cm as determined by density measurement using a dry pycnometer using helium gas. ３ Since helium gas permeates fine voids, the density of the silica particles having internal voids is preferably equal to the true density of the silica portion. ３ When the He density is 2.30 g / cm or more, the silica particles are dense, so that when the silica particle dispersion is mixed with a resin and used, the peel strength of the resin composition is not reduced, and the amount of residual silanol contained in the hollow silica particles is reduced, so that the dielectric loss tangent can be easily reduced. ３ To obtain a silica-based material with a density exceeding 2.30 g / cm3, firing at a fairly high temperature is required, and the particles are prone to breakage. ３ When the density is 2.05 g / cm or less, the spaces contained in the hollow silica particles can be maintained and the Ar density is not deteriorated. ３ More preferably, it is 2.10 g / cm or more. ３ More preferably, 2.25 g / cm ３ More preferably, it is 2.23 g / cm or less. ３ More preferably, the density of He is 2.05 to 2.25 g / cm ３ More preferably, 2.10 to 2.23 g / cm ３ is more preferable.

[0032] The apparent density of hollow silica particles can also be measured using a pycnometer. The sample (hollow silica particles) and an organic solvent are placed in the pycnometer, and the sample is left standing at 25°C for 48 hours before measurement. Since the penetration of the organic solvent may take time depending on the density of the shell of the hollow silica particles, it is preferable to leave the sample standing for the above-mentioned period. The results measured using this method correspond to the results of density measurement using a dry pycnometer using argon gas.

[0033] The apparent density of hollow silica particles can be adjusted by adjusting the primary particle diameter and shell thickness, and by changing the particle density, it is possible to adjust whether the particles settle in the solvent, remain dispersed, or float to the top. When it is desired to disperse the particles in a solvent, it is desirable that the density of the solvent and the apparent density of the particles are close to each other. For example, when the density is 1.0 g / cm ３ When it is desired to disperse the particles in water, the apparent density of the particles should be 0.8 g / cm ３ 1.2g / cm or more ３ It is preferable to adjust as follows:

[0034] The hollow silica particles have a BET specific surface area of ​​1 to 100 m ２ / g. ２ / g. If the BET specific surface area is too large, a large amount of resin or the like is adsorbed on the silica surface. ２ When the BET specific surface area is 1 to 100 m / g or less, the amount of adsorption of resins and the like can be suppressed, and an increase in viscosity when the resin composition is formed can be suppressed. ２ / g is preferred, and 1 to 50m ２ / g is more preferable, and 1 to 20m ２ / g is more preferable, and 1 to 15m ２ / g is most preferred.

[0035] Here, the BET specific surface area can be measured using a specific surface area measuring device (for example, "Tristar II3020" manufactured by Shimadzu Corporation) by pre-treating the hollow silica particles and drying them at 230°C until the pressure becomes 50 mTorr, followed by measurement by a multi-point method using nitrogen gas.

[0036] The hollow silica particles have an Ar density of A (g / cm ３ ), BET specific surface area is B (m ２ / g), the product of the Ar density and the BET specific surface area (A × B) is 1 to 120 m ２ / cm ３It is preferable that A×B is the specific surface area per volume when hollow silica particles are dispersed in a solvent, and when added to a resin, for example, it indicates the specific surface area of ​​the portion occupied by hollow silica particles in a given volume of the resin. When the hollow silica particles satisfy the above-mentioned relationship between Ar density and BET specific surface area, when a resin composition containing the hollow silica particles is used in an insulating layer, the dielectric constant of the insulating layer can be lowered and the dielectric loss can be reduced, so that a base that can fully support high-frequency circuits can be provided. If the viscosity of the resin composition increases too much, there is a risk that the dielectric loss tangent will deteriorate when used in an insulating layer, but when A×B is 120m ２ / cm ３ When A×B is 80 m or less, the specific surface area of ​​silica in the composition is small, so that the viscosity of the composition does not increase too much, and deterioration of the dielectric loss tangent can be suppressed. ２ / cm ３ Preferably it is less than 40m ２ / cm ３ Less than 20m is more preferable. ２ / cm ３ It is more preferable that A×B is less than 2 m. It is practically difficult to manufacture a product with A×B smaller than the above. ２ / cm ３ It is preferable that the length is 2.5 m or more. ２ / cm ３ More preferably, 3 m or more ２ / cm ３ The above is even more preferable.

[0037] The sphericity of the hollow silica particles is preferably 0.75 to 1.0. If the sphericity is too low, the contact area between the silica particles in the resin layer and the member in contact with the resin composition containing the silica particle dispersion may decrease, resulting in a decrease in peel strength. Therefore, the sphericity is preferably 0.75 or more. The sphericity is expressed as the average value calculated by measuring the maximum diameter (DL) and the minimum diameter (DS) perpendicular to the maximum diameter (DL) for 100 particles in a photographic projection obtained by photographing with a scanning electron microscope (SEM), and calculating the ratio (DS / DL) of the minimum diameter (DS) to the maximum diameter (DL). From the viewpoint of dispersibility, the sphericity is more preferably 0.80 or more, even more preferably 0.82 or more, even more preferably 0.83 or more, particularly preferably 0.85 or more, especially preferably 0.87 or more, and most preferably 0.90 or more.

[0038] The shell thickness of the hollow silica particles is preferably 0.01 to 0.3 relative to the primary particle diameter. When the shell thickness is 0.01 or more relative to the primary particle diameter, the strength of the hollow silica particles can be maintained. When this ratio is 0.3 or less, the internal space does not become too small, allowing the properties of the hollow shape to be exhibited. The shell thickness is more preferably 0.02 or more relative to the primary particle diameter, even more preferably 0.03 or more, and more preferably 0.2 or less, even more preferably 0.1 or less.

[0039] Here, the shell thickness is determined by measuring the shell thickness of each particle using a transmission electron microscope (TEM).

[0040] Since hollow silica particles have spaces inside, they can encapsulate substances inside the particles. The hollow silica particles of the present invention have a dense shell layer, which makes it difficult for various solvents to penetrate, but if broken particles are present, the solvent will penetrate inside. Therefore, the oil absorption capacity changes depending on the proportion of broken particles.

[0041] The oil absorption of the hollow silica particles is preferably 15 to 1300 mL / 100 g. An oil absorption of 15 mL / 100 g or more ensures adhesion to the resin when used in a resin composition, while an oil absorption of 1300 mL / 100 g or less ensures resin strength when used in a resin composition and allows for a reduction in the viscosity of the composition. Since a high oil absorption increases viscosity, the oil absorption of the hollow silica particles is more preferably 1000 mL / 100 g or less, even more preferably 700 mL / 100 g or less, particularly preferably 500 mL / 100 g or less, and most preferably 200 mL / 100 g or less. Furthermore, if the oil absorption is too low, adhesion between the powder and the resin may deteriorate, so an oil absorption of 20 mL / 100 g or more is more preferred.

[0042] In addition, based on the relationship between the proportion of broken particles and the oil absorption as described above, the oil absorption can be adjusted by adjusting the proportion of broken particles. Furthermore, since the spaces between primary particles are also spaces that can hold oil, it is thought that if the median diameter of the secondary particles formed by aggregation of primary particles is large, the oil absorption will be high, and if the median diameter of the secondary particles is small, the oil absorption will be low.

[0043] The hollow silica particles preferably contain one or more metals M selected from the group consisting of Li, Na, K, Rb, Cs, Mg, Ca, Sr, and Ba. The inclusion of metal M in the hollow silica particles acts as a flux during firing, reducing the specific surface area and the dielectric loss tangent. The metal M is incorporated between the reaction step and the washing step in the production of hollow silica particles. For example, metal M can be incorporated into the hollow silica particles by adding a metal salt of the metal M to the reaction solution used to form the silica shell in the reaction step, or by washing the hollow silica precursor with a solution containing metal ions of the metal M before sintering.

[0044] In the present invention, the concentration of metal M contained in the hollow silica particles is preferably 50 ppm by mass or more and 1% by mass or less. When the total concentration of metal M is 50 ppm by mass or more, the flux effect during firing promotes condensation of bonded silanol groups, reducing the remaining silanol groups and thereby reducing the dielectric loss tangent. If the concentration of metal M is too high, the amount of components that react with silica to form silicate increases, which may deteriorate the hygroscopicity of the hollow silica particles, so it is preferable to contain it at 1% by mass or less. The concentration of metal M is more preferably 100 ppm by mass or more, more preferably 150 ppm by mass or more, and is preferably 1% by mass or less, preferably 5000 ppm by mass or less, and most preferably 1000 ppm by mass or less.

[0045] The metal M can be measured by adding perchloric acid and hydrofluoric acid to hollow silica particles, igniting the mixture to remove the main component silicon, and then performing ICP atomic emission spectrometry. When an alkali metal silicate is used as the silica raw material, the shell layer of the resulting hollow silica particles contains less carbon (C) components derived from the raw material than when a silicon alkoxide is used as the silica raw material.

[0046] The hollow silica particles preferably have a viscosity of 20,000 mPa·s or less when a kneaded product containing the hollow silica particles is measured by the following measurement method. (Measurement Method) The particle density, A (g / cm), obtained by density measurement using a dry pycnometer using argon gas is ３ 6 parts by mass of boiled linseed oil and 6 parts by mass of hollow silica particles (6 x A / 2.2) were mixed and kneaded at 2000 rpm for 3 minutes. The kneaded mixture was then subjected to a shear rate of 1 s using a rotational rheometer. －１ The measurement is carried out for 30 seconds, and the viscosity at the time of 30 seconds is determined.

[0047] The shear rate of the kneaded material obtained by the above measurement method is 1 s －１When the viscosity at 10000 mPa·s is 20,000 mPa·s or less, the amount of solvent added during molding and film formation of a resin composition containing hollow silica particles can be reduced, the drying speed can be increased, and productivity can be improved. Furthermore, if the product of density and specific surface area according to the particle size of silica powder becomes large, the viscosity tends to increase when added to a resin composition, but since hollow silica particles have a small product of density and specific surface area, the viscosity increase of the resin composition can be suppressed. The viscosity of the kneaded product is more preferably 8,000 mPa·s or less, even more preferably 5,000 mPa·s or less, and most preferably 4,000 mPa·s or less. At a shear rate of 1 s －１ The lower the viscosity at 200°C, the better the coatability of the resin composition and the higher the productivity, so there is no particular restriction on the lower limit.

[0048] Silica particles are ２９ In the assignment of the Si-NMR spectrum, SiO ４ They are classified into four basic structures represented by Q1 to Q4 depending on the degree of tetrahedral connectivity. Q1 to Q4 are as follows. Q1 is a structural unit that has one Si atom surrounded by oxygen atoms, and is represented by SiO ４ The tetrahedron is another SiO ４ Connected with tetrahedrons, solid ２９ It has a peak at around -80 ppm in the Si-DD / MAS-NMR spectrum. Q2 is a structural unit that has two Si atoms surrounding Si with oxygen atoms between them, and is SiO ４ The tetrahedron is the other two SiO ４ Connected with tetrahedrons, solid ２９ It has a peak at around -91 ppm in the Si-DD / MAS-NMR spectrum. Q3 is a structural unit that has three Si atoms around Si with oxygen atoms between them, and is SiO ４ The tetrahedron is the other three SiO ４ Connected with tetrahedrons, solid ２９ It has a peak at around -101 ppm in the Si-DD / MAS-NMR spectrum. Q4 is a structural unit that has four Si atoms around Si with oxygen atoms between them, and is SiO ４ The tetrahedron is the other four SiO ４ Connected with tetrahedrons, solid ２９The Si-DD / MAS-NMR spectrum has a peak at around −110 ppm.

[0049] The hollow silica particles of the present invention are solid ２９ The molar ratio (Q3 / Q4) of Q3 structures having one silanol-derived OH group to Q4 structures having no silanol-derived OH group, as measured by Si-DD / MAS-NMR, is preferably 2 to 40%. When Q3 / Q4 is 40% or less, the amount of silanol can be suppressed, improving the dielectric loss tangent. Obtaining a Q3 / Q4 ratio of less than 2% requires high-temperature calcination, which shrinks the hollow portion of the hollow silica, making it practically difficult to achieve. Furthermore, Q3 / Q4 is more preferably 30% or less, and even more preferably 20% or less.

[0050] The Q3 / Q4 ratio of hollow silica particles is measured as follows. A powder of hollow silica particles is used as a measurement sample. A 400 MHz nuclear magnetic resonance apparatus is used, and a CPSAS probe with a diameter of 7.5 mm is attached. ２９ The measurement is performed using DD / MAS under the following conditions: ２９ Si resonance frequency: 79.43 MHz ２９ The Si 90° pulse width is 5 μs, the H resonance frequency is 399.84 MHz, the H decoupling frequency is 50 kHz, the MAS rotation speed is 4 kHz, the spectral width is 30.49 kHz, and the measurement temperature is 23 ° C. Data analysis is performed for each peak in the spectrum after Fourier transformation, using the center position, height, and half-width of the peak shape created by mixing Lorentzian and Gaussian waveforms as variable parameters, and optimization calculations are performed using the nonlinear least squares method. The four structural units Q1, Q2, Q3, and Q4 are targeted, and the molar ratios of Q3 and Q4 are calculated from the obtained Q1 content, Q2 content, Q3 content, and Q4 content.

[0051] In this embodiment, the silanol group content of the silica particles is measured by the DD / MAS (Dipolar Decoupling / Magic Angle Spinning) method, not the CPSAS (Cross Polarization / Magic Angle Spinning) method.１ Since H sensitizes nearby Si for detection, the peaks obtained do not accurately reflect the contents of Q1, Q2, Q3, and Q4. On the other hand, the DD / MAS method does not have the sensitizing effect of the CPSAS method, so the peaks obtained accurately reflect the contents of Q1, Q2, Q3, and Q4, making it suitable for quantitative analysis.

[0052] The pore volume of the hollow silica particles is 0.2 cm ３ / g or less. ３ / g or less, the resin composition is less likely to adsorb moisture, and the deterioration of the dielectric loss of the resin composition can be suppressed. ３ / g or less, and more preferably 0.1 cm ３ / g or less is more preferable, and 0.05 cm ３ / g or less is particularly preferred.

[0053] The surfaces of the hollow silica particles may be treated with a silane coupling agent. Treating the surfaces of the hollow silica particles with a silane coupling agent reduces the amount of remaining silanol groups on the surface, making the surfaces hydrophobic, suppressing moisture adsorption and improving dielectric loss, and also improving affinity with resins when used in a resin composition, improving dispersibility and strength after resin film formation.

[0054] The conditions for the surface treatment are not particularly limited, and general surface treatment conditions may be used, and a wet treatment method or a dry treatment method may be used. From the viewpoint of uniform treatment, the wet treatment method is preferred.

[0055] Examples of the silane coupling agent include aminosilane coupling agents, epoxysilane coupling agents, mercaptosilane coupling agents, silane coupling agents, organosilazane compounds, etc. One type of silane coupling agent may be used alone, or two or more types may be used in combination.

[0056] Specific examples of the silane coupling agent include aminosilane-based coupling agents such as aminopropyl methoxysilane, aminopropyl triethoxysilane, ureidopropyl triethoxysilane, N-phenylaminopropyl trimethoxysilane, and N-2(aminoethyl)aminopropyl trimethoxysilane; epoxysilane-based coupling agents such as glycidoxypropyl trimethoxysilane, glycidoxypropyl triethoxysilane, glycidoxypropyl methyldiethoxysilane, glycidyl butyl trimethoxysilane, and (3,4-epoxycyclohexyl)ethyl trimethoxysilane; mercaptosilane-based coupling agents such as mercaptopropyl trimethoxysilane and mercaptopropyl triethoxysilane; silane-based coupling agents such as methyltrimethoxysilane, vinyltrimethoxysilane, octadecyltrimethoxysilane, phenyltrimethoxysilane, metachloroxypropyl trimethoxysilane, imidazole silane, and triazine silane; and CF ３ (CF ２ ) ７ CH ２ CH ２ Si(OCH ３ ) ３ , C.F. ３ (CF ２ ) ７ CH ２ CH ２ SiCl ３ , C.F. ３ (CF ２ ) ７ CH ２ CH ２ Si(CH ３ ) (OCH ３ ) ２ , C.F. ３ (CF ２ ) ７ CH ２ CH ２ Si(CH ３ ) C1 ２ , C.F. ３ (CF ２ ) ５ CH ２ CH ２ SiCl ３ , C.F. ３ (CF ２ )５ CH ２ CH ２ Si(OCH ３ ) ３ , C.F. ３ CH ２ CH ２ SiCl ３ , C.F. ３ CH ２ CH ２ Si(OCH ３ ) ３ , C ８ F １７ SO ２ N (C ３ H ７ ) CH ２ CH ２ CH ２ Si(OCH ３ ) ３ , C ７ F １５ CONHCH ２ CH ２ CH ２ Si(OCH ３ ) ３ , C ８ F １７ CO ２ CH ２ CH ２ CH ２ Si(OCH ３ ) ３ , C ８ F １７ -O-CF(CF ３ )CF ２ -O-C ３ H ６ SiCl ３ , C ３ F ７ -O-(CF(CF ３ )CF ２ -O) ２ -CF (CF ３ )CONH-(CH ２ ) ３ Si(OCH ３ ) ３ fluorine-containing silane coupling agents such as hexamethyldisilazane, hexaphenyldisilazane, trisilazane, cyclotrisilazane, 1,1,3,3,5,5-hexamethylcyclotrisilazane, and other organosilazane compounds.

[0057] The amount of the silane coupling agent attached is preferably 1 part by mass or more, more preferably 1.5 parts by mass or more, and even more preferably 2 parts by mass or more, per 100 parts by mass of the hollow silica particles, and is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and even more preferably 5 parts by mass or less.

[0058] The fact that the surface of the hollow silica particles has been treated with a silane coupling agent can be confirmed by detecting a peak due to a substituent of the silane coupling agent by IR. The amount of the silane coupling agent attached can be measured by the carbon content.

[0059] The hollow silica particles preferably have a dielectric constant of 1.3 to 5.0 at 1 GHz. In particular, when measuring the dielectric constant of powders, the sample space becomes small and measurement accuracy deteriorates at frequencies above 10 GHz, so measurements at 1 GHz are used in the present invention. A dielectric constant within the above range at 1 GHz can achieve the low dielectric constant required for electronic devices. It is practically difficult to synthesize hollow silica particles with a dielectric constant of less than 1.3 at 1 GHz. The lower limit of the dielectric constant at 1 GHz is preferably 1.3 or more, more preferably 1.4 or more. The upper limit is more preferably 4.5 or less, even more preferably 4.0 or less, even more preferably 3.5 or less, particularly preferably 3.0 or less, and most preferably 2.5 or less.

[0060] Furthermore, the hollow silica particles preferably have a dielectric dissipation factor of 0.0001 to 0.05 at 1 GHz. If the dielectric dissipation factor at 1 GHz is 0.05 or less, the low relative dielectric constant required for electronic devices can be achieved. Furthermore, it is substantially difficult to synthesize hollow silica particles having a dielectric dissipation factor of less than 0.0001 at 1 GHz. The lower limit of the dielectric dissipation factor at 1 GHz is more preferably 0.0002 or more, and even more preferably 0.0003 or more. The upper limit is more preferably 0.01 or less, even more preferably 0.005 or less, even more preferably 0.003 or less, particularly preferably 0.002 or less, even more preferably 0.0015 or less, and most preferably 0.0010 or less.

[0061] The relative dielectric constant and the dielectric loss tangent can be measured by a perturbation resonator method using a dedicated device (for example, "Vector Network Analyzer E5063A" manufactured by Keycom Corporation).

[0062] The hollow silica particles are preferably contained in the silica particle dispersion in a range of 5 to 80% by volume. When the hollow silica particle content is 5% by volume or more, the desired peel strength can be imparted with a small amount of silica particle dispersion added to the resin composition, and when it is 80% by volume or less, the viscosity of the dispersion does not increase too much, making it easy to handle. The content of hollow silica particles in the silica particle dispersion is more preferably 10% by volume or more, even more preferably 20% by volume or more, more preferably 70% by volume or less, even more preferably 60% by volume or less, and particularly preferably 50% by volume or less.

[0063] (Silane Compound) The silica particle dispersion of the present invention preferably contains a silane compound having at least one group selected from the group consisting of a vinyl group, a phenyl group, a phenylamino group, an alkyl group having 4 or more carbon atoms, a methacryl group, and an epoxy group.By containing the silane compound, when the silica particle dispersion is contained in a resin composition, the surface of the hollow silica particles is compatible with the resin, so that the peel strength of the resin composition can be further improved.In addition, when the hollow silica particles are treated with a silane coupling agent, it is not necessarily necessary to add a silane compound.

[0064] Examples of the silane compound include vinyl silane, phenyl silane, phenylamino silane, hexyl silane, decyl silane, 3-methacryloxypropyl trimethoxy silane, and aminopropyl silane. These compounds may be used alone or in combination of two or more. Among these, from the viewpoint of interaction with the resin, silane compounds containing a vinyl group, a phenyl group, a methacryl group, an epoxy group, or a phenylamino group are preferred, silane compounds containing a vinyl group, a phenyl group, a methacryl group, or a phenylamino group are more preferred, and silane compounds containing a phenyl group or a methacryl group are even more preferred. In this case, the dispersibility of the silica particles in the silica particle dispersion of the present invention is improved, and it is particularly easy to maintain a balance between the viscosity and the peel strength of a molded article formed therefrom.

[0065] The silane compound is preferably contained in the silica particle dispersion in a range of 0.1 to 5% by mass. When the silane compound content is 0.1% by mass or more, when the silica particle dispersion is incorporated into a resin composition, the compatibility between the hollow silica particles and the resin is improved, thereby increasing the peel strength of the resin composition. When the silane compound content is 5% by mass or less, the silane compound is prevented from remaining in the composition, thereby reducing its impact on the physical properties of the resin composition. The content of the silane compound in the silica particle dispersion is more preferably 0.2% by mass or more, even more preferably 0.3% by mass or more, particularly preferably 0.5% by mass or more, and more preferably 4% by mass or less, even more preferably 3% by mass or less, and particularly preferably 2% by mass or less.

[0066] (Organic Thixotropic Agent) The silica particle dispersion of the present invention preferably further contains an organic thixotropic agent, which is added to suppress aggregation and precipitation of hollow silica particles in the silica particle dispersion and the resin composition or slurry containing the silica particle dispersion, and to improve wettability of the flux to the cured resin composition or slurry.

[0067] Examples of organic thixotropic agents include fatty acid amides (amide wax-based) synthesized from vegetable oil fatty acids and amines; surfactants such as fatty acid esters, polyethers, sulfated oils, and higher alcohol sulfates; polycarboxylic acid esters; polycarboxylic acid amides; and urea-modified compounds, but do not include hydrogenated castor oil-based agents known as castor oil waxes or oxidized polyethylene-based waxes obtained by oxidizing polyethylene and introducing polar groups. One type of organic thixotropic agent may be used alone, or two or more types may be used in combination.

[0068] Organic thixotropic agents are commercially available, for example, BYK (registered trademark)-R606, BYK (registered trademark)-405, BYK (registered trademark)-R605, BYK (registered trademark)-R607, BYK (registered trademark)-410, BYK (registered trademark)-411, BYK (registered trademark)-415, BYK (registered trademark)-430, BYK (registered trademark)-431, BYK (registered trademark)-7410ET, and BYK (registered trademark)-7411E. S (all manufactured by BYK Japan), TALEN 1450, TALEN 2000, TALEN 2200A, TALEN 7200-20, TALEN 8200-20, TALEN 8300-20, TALEN 8700-20, TALEN BA-600, FLOWNON SH-290, FLOWNON SH-295S, FLOWNON SH-350, FLOWNON HR-2, FLOWNON HR-4AF (all manufactured by Kyoeisha Chemical Co., Ltd.).

[0069] The organic thixotropic agent is preferably contained in the silica particle dispersion in a range of 0.01 to 5% by mass. When the organic thixotropic agent content is 0.01% by mass or more, aggregation of hollow silica particles in the dispersion is suppressed, and aggregation between hollow silica particles is suppressed during storage of the silica particle dispersion. When the organic thixotropic agent is contained in a resin composition, accumulation of resin between hollow silica particles can be suppressed. This increases the peel strength of the resin composition. Furthermore, when the organic thixotropic agent content is 5% by mass or less, residue in the composition can be suppressed, reducing the impact on the physical properties of the resin composition. The content of the organic thixotropic agent in the silica particle dispersion is more preferably 0.015% by mass or more, even more preferably 0.05% by mass or more, more preferably 3% by mass or less, even more preferably 2.5% by mass or less, and particularly preferably 2% by mass or less.

[0070] The silica particle dispersion of the present invention may contain other optional components, such as other inorganic fillers such as alumina, curing compositions, etc., as long as the effects of the present invention are not impaired.

[0071] (Physical Properties of Silica Particle Dispersion) The silica particle dispersion of the present invention preferably has a viscosity of 20 to 20,000 mPa·s at 25°C when the solids concentration of hollow silica particles is 50% by volume. If the viscosity of a silica particle dispersion having a solids concentration of hollow silica particles of 50% by volume at 25°C is 20 mPa·s or more, sedimentation (floating) separation of the silica can be prevented, and if it is 20,000 mPa·s or less, the dispersion state of the silica can be maintained while the dispersion can be maintained. The viscosity is more preferably 50 mPa·s or more, even more preferably 75 mPa·s or more, particularly preferably 100 mPa·s or more, and more preferably 15,000 mPa·s or less, even more preferably 12,000 mPa·s or less, and particularly preferably 10,000 mPa·s or less.

[0072] <Method for producing silica particle dispersion> The silica particle dispersion of the present invention is obtained by dispersing a powder of hollow silica particles in a solvent. The hollow silica particles may be obtained by manufacturing, or commercially available hollow silica particles may be used. Below, a method for producing hollow silica particles and a method for producing a silica particle dispersion using the hollow silica particles will be described.

[0073] (Method for Producing Hollow Silica Particles) Examples of methods for producing hollow silica particles include a method in which an oil-in-water emulsion containing an aqueous phase, an oil phase, and a surfactant is used to obtain a hollow silica precursor in the emulsion, and hollow silica particles are obtained from this precursor. This oil-in-water emulsion is an emulsion in which an oil phase is dispersed in water, and when a silica raw material is added to this emulsion, the silica raw material adheres to the oil droplets, forming oil-core-silica shell particles.

[0074] A method for producing hollow silica particles includes preparing an oil-in-water emulsion containing an aqueous phase, an oil phase, and a surfactant, allowing the oil-in-water emulsion to stand for 0.5 to 240 hours to obtain hollow silica precursors in which a silica-containing shell layer is formed around the core in the oil-in-water emulsion, removing the core from the hollow silica precursor, and heat-treating the resulting particles. When obtaining the hollow silica precursor, it is preferable to add a first silica raw material to the oil-in-water emulsion to form a first shell, and then add a second silica raw material to the emulsion with the first shell formed to form a second shell, thereby forming a shell layer around the core. Hereinafter, the oil-in-water emulsion will also be referred to simply as "emulsion." Furthermore, the dispersion of oil core-silica shell particles formed by adding the first silica raw material and before adding the second silica raw material, and the dispersion of oil core-silica shell particles after adding the second silica raw material, may also be referred to as "emulsion." The dispersion in which the oil core-silica shell particles are dispersed after the latter second silica raw material is added may be the same as the hollow silica precursor dispersion.

[0075] [Formation of First Shell] First, the first silica raw material is added to an oil-in-water emulsion containing a water phase, an oil phase, and a surfactant to form the first shell.

[0076] The aqueous phase of the emulsion mainly contains water as a solvent. To the aqueous phase, additives such as a water-soluble organic liquid and a water-soluble resin may be further added. The proportion of water in the aqueous phase is preferably 50 to 100% by mass, more preferably 90 to 100% by mass.

[0077] The oil phase of the emulsion preferably comprises a water-insoluble organic liquid that is incompatible with the aqueous phase components, which forms droplets in the emulsion and form the oil-core portion of the hollow silica precursor.

[0078] Examples of organic liquids include aliphatic hydrocarbons such as n-hexane, isohexane, n-heptane, isoheptane, n-octane, isooctane, n-nonane, isononane, n-pentane, isopentane, n-decane, isodecane, n-dodecane, isododecane, and pentadecane, or mixtures thereof, such as paraffinic base oils; alicyclic hydrocarbons such as cyclopentane, cyclohexane, and cyclohexene, or mixtures thereof, such as naphthenic base oils; benzene, toluene, xylene, ethylbenzene, propylbenzene, cumene, and methacrylic acid; Examples of suitable solvents include aromatic hydrocarbons such as ethylene, tetralin, and styrene; ethers such as propyl ether and isopropyl ether; esters such as ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, n-amyl acetate, isoamyl acetate, butyl lactate, methyl propionate, ethyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, and butyl butyrate; vegetable oils such as palm oil, soybean oil, and rapeseed oil; and fluorine-based solvents such as hydrofluorocarbons, perfluorocarbons, and perfluoropolyethers. Polyoxyalkylene glycols that become hydrophobic liquids at the shell formation reaction temperature can also be used. Examples include polypropylene glycol (molecular weight 1000 or more) and polyoxyethylene-polyoxypropylene block copolymers having an oxyethylene unit ratio of less than 20% by mass and a cloud point (1% by mass aqueous solution) of 40°C or less, preferably 20°C or less. Among these, polyoxypropylene-polyoxyethylene-polyoxypropylene block copolymers are preferred. These may be used alone or in combination of two or more kinds so long as they form a single oil phase.

[0079] As the organic liquid, a hydrocarbon having 8 to 16 carbon atoms, particularly 9 to 12 carbon atoms, is preferred. The organic liquid is selected taking into consideration a comprehensive range of factors, including operability, safety against fire, separability between the hollow silica precursor and the organic liquid, shape characteristics of the hollow silica particles, and solubility of the organic liquid in water. The hydrocarbon having 8 to 16 carbon atoms may be linear, branched, or cyclic, as long as it has good chemical stability, and a mixture of hydrocarbons with different carbon numbers may also be used. As the hydrocarbon, a saturated hydrocarbon is preferred, and a linear saturated hydrocarbon is more preferred.

[0080] The flash point of the organic liquid is preferably 20° C. or higher, and more preferably 40° C. or higher. When an organic liquid with a flash point of less than 20° C. is used, the flash point is too low, and therefore measures to prevent fire and improve the working environment are necessary.

[0081] The emulsion contains a surfactant to enhance emulsion stability. The surfactant is preferably water-soluble or water-dispersible, and is preferably added to the aqueous phase. A nonionic surfactant is preferred. Examples of nonionic surfactants include the following surfactants: Polyoxyethylene-polyoxypropylene copolymer surfactants, polyoxyethylene sorbitan fatty acid ester surfactants: polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitan monooleate, polyoxyethylene higher alcohol ether surfactants: polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene oleyl ether, polyoxyethylene octylphenol ether, polyoxyethylene nonylphenol ether, polyoxyethylene aliphatic ester surfactants: polyoxyethylene glycol monolaurate, polyoxyethylene glycol monostearate, polyoxyethylene glycol monooleate, glycerin fatty acid ester surfactants: monoglyceride stearate, monoglyceride oleate, etc. Furthermore, polyoxyethylene sorbitol fatty acid ester surfactants, sucrose fatty acid ester surfactants, polyglycerin fatty acid ester surfactants, polyoxyethylene hydrogenated castor oil surfactants, etc. may also be used. These may be used alone or in combination of two or more.

[0082] Among the nonionic surfactants described above, sorbitan fatty acid esters and polyoxyethylene-polyoxypropylene copolymer surfactants are preferably used. Polyoxyethylene-polyoxypropylene copolymers are block copolymers in which a polyoxyethylene block (EO) and a polyoxypropylene block (PO) are bonded. Examples of block copolymers include EO-PO-EO block copolymers and EO-PO block copolymers, with EO-PO-EO block copolymers being preferred. The proportion of oxyethylene units in the EO-PO-EO block copolymer is preferably 20% by mass or more, more preferably 30% by mass or more. The weight-average molecular weight of the polyoxyethylene-polyoxypropylene copolymer is preferably 3,000 to 27,000, more preferably 6,000 to 19,000. The total amount of polyoxyethylene blocks is preferably 40 to 90% by mass, and the total amount of polyoxypropylene blocks is preferably 10 to 60% by mass, based on the entire polyoxyethylene-polyoxypropylene copolymer.

[0083] The amount of surfactant used varies depending on conditions such as the type of surfactant, HLB (Hydrophile-Lipophile Balance), which is an index indicating the degree of hydrophilicity or hydrophobicity of the surfactant, and the particle size of the target silica particles, but the content in the aqueous phase is preferably 500 to 20,000 ppm by mass, and more preferably 1,000 to 10,000 ppm by mass. A content in the aqueous phase of 500 ppm by mass or more can further stabilize the emulsion. Furthermore, a content of 20,000 ppm by mass or less can reduce the amount of surfactant remaining in the hollow silica particles.

[0084] The water phase and the oil phase may be mixed in a mass ratio of 200:1 to 5:1, preferably 100:1 to 9:1.

[0085] Methods for preparing oil-in-water emulsions are not limited to the following. The aqueous and oil phases can be prepared in advance, and then the oil phase is added to the aqueous phase and thoroughly mixed or stirred. Other methods that apply strong physical shear forces include ultrasonic emulsification, stirring emulsification, and high-pressure emulsification. Other methods include membrane emulsification, in which a finely divided oil phase is dispersed in an aqueous phase through a membrane with micropores; phase inversion emulsification, in which a surfactant is dissolved in an oil phase and then an aqueous phase is added to emulsify; and phase inversion temperature emulsification, in which a surfactant changes from water-soluble to oil-soluble at a temperature near its cloud point. These emulsification methods can be appropriately selected depending on the desired particle size, particle size distribution, and the like.

[0086] In order to reduce the particle size of the resulting hollow silica particles and narrow the particle size distribution, it is preferable that the oil phase is sufficiently dispersed and emulsified in the aqueous phase. For example, the mixture can be emulsified using a high-pressure homogenizer at a pressure of preferably 10 bar or more, more preferably 20 bar or more.

[0087] In the first-stage shell formation step, it is preferable to perform a step of aging the obtained oil-in-water emulsion. By performing aging, fine emulsions grow preferentially, the primary particle size of the obtained hollow silica becomes uniform, and the distribution of primary particle sizes becomes narrow. This makes it possible to reduce the product (A x B) of the Ar density A and the BET specific surface area B. The aging time is 0.5 to 240 hours. An aging time of 0.5 hours or more improves the uniformity of the particle size of the primary particles, and an aging time of 240 hours or less improves productivity. The aging time is preferably 0.5 to 96 hours, and most preferably 0.5 to 48 hours. The aging temperature is preferably 5 to 80°C, more preferably 20 to 70°C, and most preferably 20 to 55°C.

[0088] In the first shell formation step, a first silica raw material is added to the oil-in-water emulsion. Examples of the first silica raw material include an aqueous solution of water-soluble silica, an aqueous dispersion of solid silica, a mixture of these, and one or more selected from the group consisting of alkali metal silicates, active silicic acid, and silicon alkoxides, or their aqueous solutions or dispersions. Among these, one or more selected from the group consisting of alkali metal silicates, active silicic acid, and silicon alkoxides, or their aqueous solutions or dispersions, are preferred because of their high availability.

[0089] Examples of solid silica include silica sol obtained by hydrolysis of an organic silicon compound and commercially available silica sol. The alkali metal of the alkali metal silicate includes lithium, sodium, potassium, rubidium, etc., and among them, sodium is preferred for easy availability and economic reasons. That is, sodium silicate is preferred as the alkali metal silicate. Sodium silicate is Na ２ O.nSiO ２ ・mH ２ The composition is represented by the formula: Na SiO ... ２ O / SiO ２ The molar ratio n is preferably 1.0 to 4.0, more preferably 2.0 to 3.5.

[0090] Activated silicic acid is obtained by subjecting alkali metal silicate to cation exchange treatment to replace the alkali metal with hydrogen, and an aqueous solution of this activated silicic acid exhibits weak acidity. A hydrogen-type cation exchange resin is preferably used for cation exchange. The alkali metal silicate and activated silicic acid are preferably dissolved or dispersed in water and then added to the emulsion. The concentrations of the alkali metal silicate and activated silicic acid aqueous solution are determined by the SiO ２ The concentration is preferably 3 to 30% by mass, more preferably 5 to 25% by mass.

[0091] As the silicon alkoxide, for example, tetraalkylsilanes such as tetramethoxysilane, tetraethoxysilane, and tetrapropoxysilane are preferably used. Furthermore, composite particles can also be obtained by mixing other metal oxides with the silica raw material. Examples of other metal oxides include titanium dioxide, zinc oxide, cerium oxide, copper oxide, iron oxide, and tin oxide.

[0092] As the first silica raw material, the above-mentioned silica raw materials may be used alone or in combination of two or more. Among them, it is preferable to use an alkali metal silicate aqueous solution, particularly a sodium silicate aqueous solution, as the first silica raw material.

[0093] The first silica raw material is preferably added to the oil-in-water emulsion under acidic conditions. By adding the silica raw material in an acidic environment, silica fine particles are generated to form a network, thereby forming a first-stage coating. The reaction temperature is preferably 80°C or less in order to maintain the stability of the emulsion, more preferably 70°C or less, even more preferably 60°C or less, particularly preferably 50°C or less, and most preferably 40°C or less. Furthermore, from the viewpoint of controlling the network formation rate of the silica fine particles to achieve a uniform coating thickness, the temperature is preferably 4°C or more, more preferably 10°C or more, even more preferably 15°C or more, particularly preferably 20°C or more, and most preferably 25°C or more.

[0094] The pH of the oil-in-water emulsion is more preferably less than 3, even more preferably 2.5 or less, and even more preferably 1 or more, from the viewpoint of making the coating thickness more uniform and making the silica shell layer of the resulting hollow silica more dense.

[0095] The pH of the oil-in-water emulsion can be made acidic by adding an acid, such as hydrochloric acid, nitric acid, sulfuric acid, acetic acid, perchloric acid, hydrobromic acid, trichloroacetic acid, dichloroacetic acid, methanesulfonic acid, or benzenesulfonic acid.

[0096] In the addition of the first silica raw material, the amount of the first silica raw material added is 100 parts by mass of the SiO in the first silica raw material relative to 100 parts by mass of the oil phase contained in the emulsion. ２ is preferably 1 to 50 parts by mass, more preferably 3 to 30 parts by mass.

[0097] In the addition of the first silica raw material, after the addition of the first silica raw material, the pH of the emulsion is maintained at an acidic level, and the state is preferably maintained for 1 minute or more, more preferably 5 minutes or more, and even more preferably 10 minutes or more.

[0098] Next, it is preferable to maintain the pH of the emulsion to which the first silica raw material has been added at 3 or more and 7 or less (weakly acidic to neutral). This allows the first silica raw material to be immobilized on the surface of the oil droplets. For example, there is a method of adjusting the pH of the emulsion to 3 or more by adding a base to the emulsion to which the first silica raw material has been added.

[0099] Examples of the base include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, alkaline earth metal hydroxides such as magnesium hydroxide and calcium hydroxide, ammonia, amines, etc. Alternatively, a method of exchanging anions such as halogen ions for hydroxide ions by anion exchange treatment may be used.

[0100] When adding the base, it is preferable to gradually add the base while stirring the emulsion to which the first silica raw material has been added, thereby gradually increasing the pH of the emulsion. If the stirring is weak or a large amount of base is added all at once, the pH of the emulsion may become non-uniform, which may result in non-uniform thickness of the first coating layer.

[0101] The emulsion is preferably maintained while being stirred. The maintenance time may be 10 minutes or more, preferably 1 hour or more, or may be 4 hours or more. The maintenance temperature is preferably 100°C or less in order to maintain the stability of the emulsion, more preferably 95°C or less, even more preferably 90°C or less, and particularly preferably 85°C or less. In order to promote aging, the maintenance temperature is preferably 35°C or more, more preferably 40°C or more, and particularly preferably 45°C or more.

[0102] [Formation of the Second Shell] Next, a second silica raw material is added to the emulsion in the presence of alkali metal ions, thereby obtaining a hollow silica precursor dispersion. Here, the hollow silica precursor is in the form of oil core-silica shell particles.

[0103] The addition of the second silica raw material to the emulsion is preferably carried out under alkaline conditions. In the addition of the first silica raw material, a method is used in which the emulsion is first acidified and then the pH is adjusted to 3 or more and 7 or less (weakly acidic to neutral) in order to more uniformly adhere the first silica raw material to the oil droplets. The first silica layer obtained by this method is porous and has insufficient density, resulting in low strength. By making the emulsion alkaline in the addition of the second silica raw material, a high-density second silica layer can be formed on the first silica layer obtained earlier.

[0104] In order to suppress the generation of new fine particles, the pH of the emulsion when the second silica raw material is added is preferably 8 or more, more preferably 8.5 or more, even more preferably 8.7 or more, particularly preferably 8.9 or more, and most preferably 9 or more. Moreover, since the solubility of silica increases if the pH is too high, the pH is preferably 13 or less, more preferably 12.5 or less, more preferably 12 or less, particularly preferably 11.5 or less, and most preferably 11 or less.

[0105] The pH of the oil-in-water emulsion can be made alkaline by adding a base, and the same compounds as those mentioned above can be used as the base.

[0106] As the second silica raw material, the same materials as those used for the first silica raw material described above can be used alone or in combination of two or more. Among these, at least one of an aqueous sodium silicate solution and an aqueous activated silicic acid solution is preferably used for adding the second silica raw material. When adding the second silica raw material to the emulsion under alkaline conditions, a method of adding an alkali metal hydroxide simultaneously with the second silica raw material may be used. Alternatively, a method of using sodium silicate as the alkali metal silicate in the second silica raw material may be used. In this case, sodium silicate, an alkaline component, is added to the weakly acidic emulsion whose pH is adjusted to 5 or higher after the addition of the first silica raw material, so that the pH of the emulsion can be maintained alkaline while the second silica raw material is added. Furthermore, alkali metal ions become present in the emulsion.

[0107] In addition, when an aqueous solution of sodium silicate is used as the second silica raw material, if the pH becomes too high, an acid may be added to adjust the pH. The acid used here may be the same acid as that used when adding the first silica raw material.

[0108] The second silica raw material is preferably added in the presence of alkali metal ions. The alkali metal ions may be derived from the first silica raw material, the second silica raw material, or a base added for pH adjustment, and may also be added by adding an additive to the emulsion. For example, this is the case when an alkali metal silicate is used as at least one of the first silica raw material and the second silica raw material. Also, this is the case when an alkali metal halide, sulfate, nitrate, fatty acid salt, etc. is used as an additive to the emulsion.

[0109] The second silica raw material may be added, for example, by adding either one or both of an aqueous sodium silicate solution and an aqueous active silicic acid solution to the emulsion after the addition of the first silica raw material. When both are added, the aqueous sodium silicate solution and the aqueous active silicic acid solution may be added all at once or in order.

[0110] For example, the addition of the second silica raw material can be carried out by repeating the steps of adding an aqueous sodium silicate solution and adding an aqueous activated silicic acid solution once or twice or more times while adjusting the pH to promote adhesion of the silica raw material onto the first silica layer.

[0111] The second silica raw material is preferably added to the heated emulsion to promote adhesion of the silica raw material onto the first silica layer. The heating temperature is preferably 30°C or higher, more preferably 35°C or higher, even more preferably 40°C or higher, particularly preferably 45°C or higher, and most preferably 50°C or higher, in order to suppress the generation of new fine particles. Since the solubility of silica increases as the temperature increases, the temperature is preferably 100°C or lower, more preferably 95°C or lower, even more preferably 90°C or lower, particularly preferably 85°C or lower, and most preferably 80°C or lower. When a heated emulsion is used, it is preferable to gradually cool the resulting emulsion to room temperature (approximately 23°C) after adding the second silica raw material. That is, the heating temperature is preferably in the range of 30 to 100°C.

[0112] In the addition of the second silica raw material, the amount of the second silica raw material added is 100 parts by mass of SiO in the second silica raw material relative to 100 parts by mass of the oil phase. ２ is preferably adjusted to 20 to 500 parts by mass, more preferably 40 to 300 parts by mass. In the addition of the second silica raw material, it is preferable to maintain the pH of the emulsion alkaline for 10 minutes or more after the addition of the second silica raw material.

[0113] Through the addition of the first silica raw material and the second silica raw material, the total amount of the first silica raw material and the second silica raw material added is 100 parts by mass of the SiO in the first silica raw material relative to 100 parts by mass of the oil phase. ２ and SiO in the second silica raw material ２ The total amount is preferably adjusted to 30 to 500 parts by mass, and more preferably adjusted to 50 to 300 parts by mass.

[0114] The silica shell layer of the present invention is mainly composed of silica, but may contain other metal components such as Ti and Zr as needed to adjust the refractive index, etc. The method for containing other metal components is not particularly limited, but for example, a method such as adding a metal sol liquid or an aqueous metal salt solution simultaneously in the step of adding the silica raw material may be used.

[0115] In this manner, a hollow silica precursor dispersion is obtained.

[0116] Methods for obtaining hollow silica precursors from hollow silica precursor dispersions include, for example, filtering the dispersion, heating to remove the aqueous phase, separating the precursor by sedimentation or centrifugation, etc. One example is a method of filtering the dispersion using a filter of about 0.1 μm to 5 μm, and drying the filtered hollow silica precursor.

[0117] If necessary, the obtained hollow silica precursor may be washed with water, an acid, an alkali, an organic solvent, or the like.

[0118] [Heat Treatment of Hollow Silica Precursor] Then, the oil core is removed from the hollow silica precursor and heat treated. Methods for removing the oil core include, for example, a method of calcining the hollow silica precursor to combustibly decompose the oil, a method of volatilizing the oil by drying, a method of decomposing the oil by adding an appropriate additive, and a method of extracting the oil using an organic solvent, etc. Among these, the method of calcining the hollow silica precursor with little oil residue to combustibly decompose the oil is preferred.

[0119] Hereinafter, a method of calcining a hollow silica precursor to remove the oil core and then heat-treating the resulting hollow silica particles will be described as an example. In the method of calcining a hollow silica precursor to remove the oil core and obtain hollow silica particles, it is preferable to perform heat treatment in at least two stages at different temperatures. The first stage of heat treatment removes the oil core, and the second stage of heat treatment densifies the shell layer of the hollow silica particles.

[0120] The first-stage heat treatment removes organic components from the oil core and surfactant. Since it is necessary to thermally decompose the oil in the hollow silica precursor, it is preferably carried out at 100°C or higher, more preferably 200°C or higher, and most preferably 300°C or higher. If the first-stage heat treatment is too high, the silica shell becomes more densified, making it difficult to remove the internal organic components. Therefore, it is preferably carried out at less than 700°C, preferably 550°C or lower, more preferably 530°C or lower, even more preferably 520°C or lower, particularly preferably 510°C or lower, and most preferably 500°C or lower. That is, it is preferable to carry out the first-stage heat treatment at a temperature in the range of 100°C or higher but lower than 700°C. The first-stage heat treatment may be carried out once or multiple times. The first-stage heat treatment time is preferably 30 minutes or longer, preferably 1 hour or longer, more preferably 2 hours or longer, and preferably 48 hours or shorter, more preferably 24 hours or shorter, and more preferably 12 hours or shorter. That is, the first stage heat treatment time is preferably in the range of 30 minutes to 48 hours.

[0121] The second heat treatment densifies the hollow silica particles to form a dense shell. The second heat treatment also reduces the number of silanol groups on the particle surface, lowering the dielectric loss tangent. The second heat treatment is preferably performed at a higher temperature than the first heat treatment.

[0122] When the second-stage heat treatment is performed by the static method, it is preferably performed at 700°C or higher, more preferably 800°C or higher, even more preferably 900°C or higher, and most preferably 1000°C or higher. Furthermore, if the temperature is too high, crystallization of the amorphous silica occurs, increasing the dielectric constant. Therefore, it is preferably performed at 1200°C or lower, more preferably 1150°C or lower, and most preferably 1100°C or lower. That is, the second-stage heat treatment is preferably performed in the range of 700 to 1200°C. The second-stage heat treatment temperature is preferably 200°C or higher, more preferably 200 to 800°C higher, and even more preferably 400 to 700°C higher than the first-stage heat treatment temperature. The second-stage heat treatment may be performed once or multiple times. The heat treatment time is preferably 10 minutes or longer, more preferably 30 minutes or longer, and is preferably 24 hours or shorter, more preferably 12 hours or shorter, and most preferably 6 hours or shorter. That is, the second stage heat treatment time is preferably in the range of 10 minutes to 24 hours.

[0123] The second-stage heat treatment may be performed using a spray combustion method. The flame temperature is preferably 1000°C or higher, more preferably 1200°C or higher, and most preferably 1400°C or higher. The flame temperature is preferably 2000°C or lower, more preferably 1800°C or lower, and most preferably 1600°C or lower. In other words, when the spray combustion method is used for the second-stage heat treatment, the flame temperature is preferably in the range of 1000 to 2000°C.

[0124] After the first-stage firing, the hollow silica precursor may be returned to room temperature before the second-stage heat treatment, or the temperature may be raised to the second-stage heat treatment temperature while maintaining the first-stage firing temperature.

[0125] The hollow silica particles obtained by the above steps may be aggregated due to the drying or calcination steps, so they may be crushed to make the aggregate size easier to handle, but in the present invention, they are directly mixed with a solvent to obtain a silica particle dispersion. Examples of the crushing method include a method using a mortar, a method using a dry or wet ball mill, a method using a shaking sieve, and a method using a crusher such as a pin mill, a cutter mill, a hammer mill, a knife mill, a roller mill, or a jet mill.

[0126] In this manner, the hollow silica particles used in the silica particle dispersion of the present invention are obtained.

[0127] (Preparation of Silica Particle Dispersion) The obtained hollow silica particles are mixed with a solvent to obtain a silica particle dispersion. The method for producing a silica particle dispersion of the present invention includes mixing a solvent with a powder of hollow silica particles having an average particle size in the range of 0.2 to 10 μm, dispersing the mixture, and classifying it to remove aggregates of the hollow silica particles. The type and amount of the solvent, the physical properties and amount of the hollow silica particles, etc. are as described above.

[0128] The hollow silica particle powder is preferably mixed in the silica particle dispersion at a ratio of 5 to 80% by volume. If the ratio of hollow silica particles is too low, productivity in the subsequent concentration step decreases, while if it is too high, the viscosity of the silica particle dispersion increases too much, which may decrease productivity in the dispersion treatment. Therefore, the range of 5 to 80% by volume is preferable. The amount of hollow silica particles used is more preferably 10% by volume or more, even more preferably 20% by volume or more, and more preferably 60% by volume or less, and even more preferably 50% by volume or less.

[0129] For the dispersion treatment of the mixed solution containing the solvent and hollow silica particles, a dispersing device used for pigment dispersion etc. can be used. For example, mixers such as a Disper, Homomixer, Planetary Mixer, etc., homogenizers (M Technique's "Clearmix", PRIMIX, etc., and Silverson's "Abramix", etc.), paint conditioners (Red Devil), colloid mills (PUC's "PUC Colloid Mill", IKA's "Colloid Mill MK"), cone mills (IKA's "Cone Mill MKO", etc.), ball mills, sand mills, etc. Examples of suitable dispersers include media-type dispersers such as a wet jet mill (such as "Dynomill" manufactured by Shinmaru Enterprises), an attritor, a pearl mill (such as "DCP Mill" manufactured by Eirich), and a Coball mill; media-less dispersers such as a wet jet mill (such as "Zenus PY" manufactured by Genus, "Starburst" manufactured by Sugino Machine, and "Nanomizer" manufactured by Nanomizer), a "Clear SS-5" manufactured by M Technique, and a "MICROS" manufactured by Nara Kikai; and other roll mills and kneaders. Among these, those that do not use grinding media (such as balls and beads) are preferred. This is because the use of grinding media raises concerns about contamination from worn media. Specifically, media-less dispersers such as a wet jet mill (such as "Zenus PY" manufactured by Genus, "Starburst" manufactured by Sugino Machine, and "Nanomizer" manufactured by Nanomizer), a "Clear SS-5" manufactured by M Technique, and a "MICROS" manufactured by Nara Kikai are preferred.

[0130] The temperature during dispersion treatment is preferably 0 to 100°C. Here, the temperature during dispersion treatment refers to the temperature range before and after treatment. By performing dispersion treatment within this temperature range, the viscosity of the solvent is maintained at an appropriate level, productivity is maintained, and evaporation of the solvent is suppressed, making it possible to easily control the solid content. The treatment temperature is more preferably 5°C or higher, even more preferably 10°C or higher, and more preferably 90°C or lower, and even more preferably 80°C or lower.

[0131] The time for the dispersion treatment may be appropriately set depending on the dispersing device used so as not to destroy the hollow structure of the hollow silica particles, but is preferably 0.5 to 60 minutes, more preferably 0.5 to 10 minutes, and even more preferably 0.5 to 5 minutes.

[0132] Thereafter, the remaining agglomerates of hollow silica particles that were not completely dispersed by the dispersion treatment are subjected to wet classification. Examples of wet classification include classification using a sieve or centrifugal force. When using a sieve, classification is preferably performed using a sieve with a mesh size of 100 μm or less. As the sieve, for example, a metal sieve with a dense lattice structure, such as an electroformed sieve, is preferably used.

[0133] The sieve opening is preferably 100 μm or less, more preferably 75 μm or less, even more preferably 50 μm or less, and particularly preferably 35 μm or less. The lower limit of the sieve opening is preferably 0.2 μm or more, more preferably 0.5 μm or more, and even more preferably 1 μm or more. That is, the sieve opening is preferably in the range of 0.2 to 100 μm.

[0134] Thereafter, the mixture may be diluted or concentrated as necessary to adjust the concentration to an appropriate level. Concentration methods include evaporation concentration and solid-liquid separation.

[0135] In the method for producing a silica particle dispersion of the present invention, a silane coupling agent may be added to the mixture of the solvent and the hollow silica particles. Examples of the silane coupling agent include the silane coupling agents described above.

[0136] <Resin Composition> The silica particle dispersion of the present invention can be mixed with a resin to form a resin composition. The resin composition preferably contains hollow silica particles in an amount of 5 to 70% by mass, more preferably 10 to 50% by mass.

[0137] Examples of resins that can be used include epoxy resins, silicone resins, phenolic resins, melamine resins, urea resins, unsaturated polyesters, fluororesins, polyamides such as polyimides, polyamideimides, and polyetherimides; polyesters such as polybutylene terephthalate and polyethylene terephthalate; polyphenylene sulfide, aromatic polyesters, polysulfones, liquid crystal polymers, polyethersulfones, polycarbonates, maleimide-modified resins, ABS resins, AAS (acrylonitrile-acrylic rubber-styrene) resins, AES (acrylonitrile-ethylene-propylene-diene rubber-styrene) resins, polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers (PFA), tetrafluoroethylene-hexafluoropropylene copolymers (FEP), and tetrafluoroethylene-ethylene copolymers (ETFE). The dielectric loss tangent of a resin composition also depends on the properties of the resin, so the resin to be used should be selected taking these factors into consideration.

[0138] The resin composition may contain any component other than the above resin, such as a dispersing aid, a surfactant, or a filler other than silica.

[0139] When a resin film is produced using the resin composition of the present invention, the relative dielectric constant thereof is preferably 2.0 to 3.5 at a frequency of 10 GHz, with the lower limit being more preferably 2.2 or more, and even more preferably 2.3 or more, and the upper limit being more preferably 3.2 or less, and even more preferably 3.0 or less. When the relative dielectric constant of the resin film at a frequency of 10 GHz is within the above range, the resin film has excellent electrical properties and is therefore expected to be used in electronic devices, communication devices, etc.

[0140] The dielectric loss tangent of the resin film is preferably 0.01 or less at a frequency of 10 GHz, more preferably 0.008 or less, and even more preferably 0.0065 or less. When the dielectric loss tangent at a frequency of 10 GHz is within the above range, the resin film has excellent electrical properties and is therefore expected to be used in electronic devices, communication devices, etc. The smaller the dielectric loss tangent, the more the circuit transmission loss can be suppressed, so the lower limit is not particularly limited.

[0141] The dissipation factor can be measured using a split post dielectric resonator (SPDR) (eg, manufactured by Agilent Technologies).

[0142] The resin film preferably has an average linear expansion coefficient of 10 to 50 ppm / °C. When the average linear expansion coefficient is within this range, it is close to the thermal expansion coefficient of copper foil, which is widely used as a substrate, and therefore has excellent electrical properties. The average linear expansion coefficient is more preferably 12 ppm / °C or higher, even more preferably 15 ppm / °C or higher, and more preferably 40 ppm / °C or lower, even more preferably 30 ppm / °C or lower.

[0143] The average linear expansion coefficient can be determined by using a thermomechanical analyzer (for example, "TMA-60" manufactured by Shimadzu Corporation) to heat the resin film under a load of 5 N at a temperature increase rate of 2°C / min, measuring the dimensional change of the sample from 30°C to 150°C, and calculating the average.

[0144] The silica particle dispersion of the present invention can be used as various fillers, and is particularly suitable as a filler for resin compositions used in the production of electronic substrates for electronic devices such as personal computers, notebook computers, and digital cameras, and communication devices such as smartphones and game consoles. Specifically, the silica particle dispersion of the present invention is expected to be applied to resin compositions, prepregs, metal foil-clad laminates, printed wiring boards, resin sheets, adhesive layers, adhesive films, solder resists, bump reflow materials, rewiring insulating layers, die bond materials, encapsulants, underfills, mold underfills, and laminated inductors, etc., in order to reduce dielectric constant, reduce transmission loss, reduce moisture absorption, and improve peel strength.

[0145] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the following description, the same components are used. Examples 1 to 10 are examples, and Examples 11 to 13 are comparative examples.

[0146] Test Example 1 In Test Example 1, hollow silica particles were prepared, and a silica particle dispersion was prepared using the obtained hollow silica particles.

[0147] Example 1 "Preparation of Emulsion" 4 g of EO-PO-EO block copolymer (Pluronic F68, manufactured by ADEKA Corporation) was added to 1,250 g of pure water and stirred until dissolved. 42 g of n-decane in which 4 g of sorbitan acid monooleate (IONET S-80, manufactured by Sanyo Chemical Industries, Ltd.) had been dissolved was added to this aqueous solution, and the mixture was stirred using an IKA homogenizer until the entire solution became uniform, producing a coarse emulsion. This coarse emulsion was emulsified using a high-pressure emulsifier (LAB1000, manufactured by SMT Corporation) at a pressure of 50 bar, producing a fine emulsion with an emulsion diameter of 1 μm.

[0148] "Emulsion Aging" The obtained fine emulsion was allowed to stand at 40°C for 12 hours to obtain an aged emulsion.

[0149] "First-stage shell formation" 1,300 g of the obtained emulsion after aging was diluted with an aqueous sodium silicate solution (SiO ２ Concentration 10.4% by mass, Na ２ 23 g of 2M hydrochloric acid (O concentration 3.6 mass%) was added and the mixture was stirred thoroughly while maintaining the temperature at 30°C. 1M aqueous sodium hydroxide solution was slowly added dropwise to the mixture while maintaining the pH at 6, thereby obtaining an oil core-silica shell particle dispersion. The obtained oil core-silica shell particle dispersion was maintained and aged.

[0150] "Second-stage shell formation" The entire oil core-silica shell particle dispersion obtained in the first-stage shell formation was heated to 70°C, and 1M NaOH was slowly added with stirring to adjust the pH to 9. Next, a diluted aqueous sodium silicate solution (SiO ２ Concentration 10.4% by mass, Na ２ 330 g of a solution of 1,000 sachets (3.6 mass%) was gradually added together with 0.5 M hydrochloric acid to adjust the pH to 9. The suspension was kept at 80° C. for 1 day and then cooled to room temperature to obtain a hollow silica precursor dispersion.

[0151] "Filtration, washing, drying, and calcination" The entire hollow silica precursor dispersion was neutralized to pH 2 with 2 M hydrochloric acid and then filtered using quantitative filter paper 5C. Then, 350 ml of 80°C ion-exchanged water was added, and the mixture was again pressure-filtered to wash the hollow silica cake. The filtered cake was dried in a nitrogen atmosphere at 100°C for 1 hour and then at 400°C for 2 hours (heating rate 10°C / min) to remove organic components, thereby obtaining hollow silica precursor. The obtained hollow silica precursor was calcined at 1000°C for 1 hour (heating rate 10°C / min) to sinter the shell, thereby obtaining calcined hollow silica particles.

[0152] "Dispersion in Solvent" 10 g of the obtained hollow calcined silica particles and 200 ml of methyl ethyl ketone (MEK) were placed in a 250 ml plastic bottle (7 vol% hollow calcined silica particles, 93 vol% MEK) and stirred at 30 rpm for 2 hours using a mix rotor. The resulting mixture was sprayed three times from a φ0.1 mm nozzle using a wet microparticulation device (Starburst Mini, manufactured by Sugino Machine Co., Ltd., model number: HJP-25001) at a pressure of 50 MPa. The resulting slurry was passed through an electroformed sieve with 10 μm openings to obtain a silica particle dispersion with a solids content of 6.2 mass%.

[0153] Example 2 The same conditions as in Example 1 were repeated except that the amount of EO-PO-EO block copolymer ("Pluronic F68" manufactured by ADEKA Corporation) added was changed to 2 g, and the amount of sorbitan acid monooleate (Ionet S-80 manufactured by Sanyo Chemical Industries, Ltd.) added was changed to 2 g to prepare hollow silica particles.

[0154] (Example 3) An experiment was carried out under the same conditions as in Example 1, except that the amount of EO-PO-EO block copolymer ("Pluronic F68" manufactured by ADEKA Corporation) added was changed to 10 g, sorbitan acid monooleate (IONET S-80 manufactured by Sanyo Chemical Industries, Ltd.) was not used, emulsification was carried out at a pressure of 100 bar to produce hollow silica particles, and the slurry was passed through an electroformed sieve with 15 μm openings.

[0155] (Example 4) The same conditions as in Example 1 were repeated except that the obtained hollow silica precursor was calcined at 1,100°C for 1 hour (heating rate: 10°C / min) to produce hollow silica particles, and the slurry was passed through an electroformed sieve with 15 µm openings.

[0156] Example 5 The same conditions as in Example 1 were used except that the obtained hollow silica precursor was calcined at 800° C. for 1 hour (heating rate: 10° C. / min) to produce hollow silica particles.

[0157] Example 6 The same conditions as in Example 1 were used except that the obtained hollow silica precursor was calcined at 700° C. for 1 hour (heating rate: 10° C. / min) to produce hollow silica particles.

[0158] Example 7 The same conditions as in Example 1 were used for filtering and washing the hollow silica precursor, except that 350 ml of tap water was used instead of ion-exchanged water.

[0159] Example 8: 10 g of hollow calcined silica particles obtained in the same manner as in Example 1, 200 ml of methyl ethyl ketone (MEK), and 0.10 g of KBM-503 (3-methacryloxypropyltrimethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd.) were placed in a 250 ml polyvinyl chloride bottle and stirred at 30 rpm for 2 hours using a mixing rotor. The resulting mixture was heated at 80°C for 1 hour, cooled, and then sprayed three times from a φ0.1 mm nozzle at a pressure of 50 MPa using a wet microparticle generator (Starburst Mini, manufactured by Sugino Machine Co., Ltd., model number: HJP-25001). The resulting slurry was passed through an electroformed sieve with 10 μm openings to obtain a silica particle dispersion with a solids content of 6.2% by mass.

[0160] Example 9: 10 g of hollow calcined silica particles obtained in the same manner as in Example 1, 200 ml of methyl ethyl ketone (MEK), and 0.020 g of BYK®-R606 (a polyhydroxycarboxylic acid ester, manufactured by BYK-Chemie) were placed in a 250 ml plastic bottle and stirred at 30 rpm for 2 hours using a mix rotor. The resulting mixture was sprayed three times from a 0.1 mm diameter nozzle at a pressure of 50 MPa using a wet microparticle generator (Starburst Mini, manufactured by Sugino Machine Co., Ltd., model number HJP-25001). The resulting slurry was passed through an electroformed sieve with 10 μm openings to obtain a silica particle dispersion with a solids content of 6.2% by mass.

[0161] Example 10 A silica particle dispersion was obtained in the same manner as in Example 8, except that KBM-503 was changed to 0.10 g of KBM-103 (trimethoxyphenylsilane, manufactured by Shin-Etsu Chemical Co., Ltd.).

[0162] (Example 11) The same conditions as in Example 1 were repeated except that SO-C2 (deflagration method silica, solid silica, with a median diameter of 0.5 μm, manufactured by Admatechs Co., Ltd.) was used instead of the hollow fired silica particles, and the slurry was passed through an electroformed sieve with an opening of 30 μm.

[0163] Example 12 The same conditions as in Example 1 were repeated, except that iM16K (glass balloons with a median diameter of 18 μm, manufactured by 3M) was used instead of the hollow fired silica particles, and the slurry was passed through an electroformed sieve with a mesh size of 30 μm.

[0164] Example 13 10 g of the hollow calcined silica particles obtained in Example 1 was used as is.

[0165] The hollow silica particles prepared in each of the above examples were measured for average particle diameter (D50), Ar density, He density, specific surface area, sphericity, and viscosity of a 50% by volume dispersion as follows, and the results are shown in Table 1.

[0166] 1. Average particle diameter (D50) Hollow silica particles (secondary particles) were measured using a diffraction / scattering particle size distribution analyzer (MT3300) manufactured by Microtrac Bell, Inc., and the median value (median diameter, D50) of the particle size distribution (diameter) was measured. The measurement was performed twice, and the average value was calculated.

[0167] 2. Density Measurement Using a Dry Pycnometer The density of the hollow silica particles was measured using a dry pycnometer (AccuPycII 1340 manufactured by Micromeritics). The measurement conditions were as follows: Sample cell: 10 cm ３ Cell Sample weight: 1.0 g Measurement gas: helium or argon Number of purges: 10 times Purge treatment filling pressure: 135 kPag Number of cycles: 10 times Cycle filling pressure: 135 kPag Rate to complete pressure equilibration: 0.05 kPag / min

[0168] The hollow silica particles were dried under reduced pressure at 230°C to completely remove moisture, and used as a sample. The specific surface area of ​​this sample was measured by the multipoint BET method using nitrogen gas with an automatic specific surface area and pore distribution measuring device "Tristar II" manufactured by Micromeritics.

[0169] 4. Sphericity A scanning electron microscope image (SEM image) of hollow silica particles was obtained using an S4800 manufactured by Hitachi High-Technologies Corporation, observed at an accelerating voltage of 5 kV. The diameter of the circumscribed circle (DL) and the diameter of the inscribed circle (DS) were measured for 100 particles selected from the SEM image, and the ratio (DS / DL) of the diameter of the inscribed circle (DS) to the diameter of the circumscribed circle (DL) was calculated, and the sphericity was determined from the average value.

[0170] 5. Viscosity of Silica Particle Dispersion The viscosity of a silica particle dispersion with a solid concentration of hollow silica particles of 50% by volume was measured as follows. 100 ml of hollow silica particles and 100 ml of methyl ethyl ketone (MEK) were placed in a 250 ml polyvinyl alcohol bottle and stirred at 30 rpm with a mix rotor for 2 hours. Note that the 100 ml of hollow silica particles was measured at a density d (g / cm) of the calcined hollow silica particles. ３The resulting mixture was prepared by 100×d (g) calculated from the mass of the slurry. The resulting mixture was sprayed three times from a φ0.1 mm nozzle using a wet atomization device (Starburst Mini, model number HJP-25001, manufactured by Sugino Machine Co., Ltd.) at a pressure of 50 MPa. The resulting slurry was adjusted to 25°C, and its viscosity was measured for 30 seconds using a rotational rheometer (e.g., Modular Rheometer Physica MCR-301, manufactured by Anton Paar) at a shear rate of 1 rpm, and the viscosity at 30 seconds was determined.

[0171] Test Example 2 (Preparation of Evaluation Sample A (Resin Film)) A resin film was prepared using the silica particle dispersions of Examples 1 to 12 and the hollow silica particles of Example 13. 25 parts by mass of biphenyl-type epoxy resin (epoxy equivalent: 276, "NC-3000" manufactured by Nippon Kayaku Co., Ltd.) was dissolved in 13 parts by mass of methyl ethyl ketone (MEK) by heating while stirring. After cooling to room temperature, 32 parts by mass of an active ester curing agent ("HP8000-65T" manufactured by DIC Corporation, active group equivalent weight 223, toluene solution with 65% by mass of non-volatile components) was mixed therein, and the mixture was kneaded for 5 minutes at 2000 rpm using a foaming mixer. 0.9 parts by mass of 4-dimethylaminopyridine (DMAP) and 1.6 parts by mass of 2-ethyl-4-methylimidazole ("2E4MZ" manufactured by Shikoku Chemicals Corporation) were then mixed therein as curing accelerators, and the mixture was mixed for 5 minutes at 2000 rpm using a homodisper. The density of the particles was determined by density measurement using a dry pycnometer using argon gas, and the density was measured as A (g / cm ３ The silica particle dispersion or hollow silica particles were weighed and mixed so as to obtain a particle powder of (30×A / 2.2) parts by mass, and the mixture was mixed using a homodisper at 2000 rpm for 5 minutes.

[0172] Next, a release-treated transparent polyethylene terephthalate (PET) film ("PET5011 550" manufactured by Lintec Corporation, thickness 50 μm) was prepared. The obtained varnish was applied to the release-treated surface of this PET film using an applicator so that the thickness after drying would be 40 μm, and after drying for 10 minutes in a gear oven at 100 ° C, it was cut to produce an uncured laminate film comprising an uncured resin film (B-stage film) measuring 200 mm in length x 200 mm in width x 40 μm in thickness. The obtained uncured laminate film was heated for 90 minutes in a gear oven set at 190 ° C to cure the uncured resin film, and a cured film was produced.

[0173] (Preparation of Evaluation Sample B (Laminate)) (1) Lamination Process: A single-sided roughened copper foil (F0-WS, thickness 18 μm, surface roughness Rz = 1.2 μm, manufactured by Furukawa Electric Co., Ltd.) was prepared. Using a batch vacuum laminator MVLP-500-IIA manufactured by Meiki Seisakusho Co., Ltd., the uncured laminate film prepared above was laminated onto this copper foil so that the surface of the uncured resin film (B-stage film) faced the roughened surface of the copper foil, thereby obtaining a laminate structure consisting of copper foil / B-stage film / PET film. The lamination conditions were as follows: the pressure was reduced for 30 seconds to a pressure of 13 hPa or less, and then the laminate was pressed at 100 ° C and a pressure of 0.8 MPa for 30 seconds. (2) Film Peeling Process: The PET film of the laminate structure was peeled off. (3) Curing Process: The laminate was placed in a gear oven with an internal temperature of 180 ° C for 30 minutes, and the B-stage film was cured to form an insulating layer.

[0174] (Evaluation) 1. Measurement of peel strength A 1 cm wide rectangular cut was made on the copper foil side of Evaluation Sample B. The substrate was set in a 90° peel tester, and the end of the copper plating where the cut had been made was picked up with a gripping tool, and the copper plating was peeled off by 20 mm to measure the peel strength (N / cm).

[0175] 2. Granularity of the coating film The appearance of the uncured laminate film was observed to evaluate the granularity of the coating film. The evaluation criteria are as follows. A and B ratings were judged to be practical. [Evaluation criteria] A (good): No granularity. B (fair): Fine irregularities were observed after coating. C (unfair): Streaks were observed due to adhesion of coarse particles during coating.

[0176] The test results are shown in Table 1.

[0177]

[0178] From Table 1, it can be seen that Examples 1 to 10 had higher peel strength and stronger adhesive strength than Examples 11 and 13. Furthermore, Examples 1 to 10 also had good coating film granularity, and all were suitable for practical use. In contrast, Examples 11 and 13 had low peel strength and coating film granularity was observed. Furthermore, in Example 12, after coating and drying, the coating film peeled off when touched with the hand, and when observed under a microscope, the particles were found to have broken into fragments. Therefore, further evaluation was not possible.

[0179] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made thereto without departing from the spirit and scope of the present invention. This application is based on a Japanese patent application (Patent Application No. 2022-077092) filed on May 9, 2022, the contents of which are incorporated herein by reference.

Claims

1. A silica particle dispersion comprising hollow silica particles and a solvent, the hollow silica particles having an average particle size in the range of 0.2 to 10 μm.

2. The hollow silica particles have a particle density of 0.35 to 2.00 g / cm as determined by density measurement using a dry pycnometer using argon gas. ３ The silica particle dispersion according to claim 1 ,

3. The hollow silica particles have a particle density of 2.00 to 2.30 g / cm as determined by density measurement using a dry pycnometer using helium gas. ３ The silica particle dispersion according to claim 1 ,

4. The hollow silica particles have a BET specific surface area of ​​1 to 100 m ２ The silica particle dispersion according to claim 1 , wherein the silica particle dispersion has a molecular weight of 1000 to 10000.

5. 2. The silica particle dispersion according to claim 1, wherein the hollow silica particles have a sphericity of 0.75 to 1.

0.

6. The silica particle dispersion liquid according to claim 1 , further comprising a silane compound having at least one group selected from the group consisting of a vinyl group, a phenyl group, a phenylamino group, an alkyl group having 4 or more carbon atoms, a methacryl group, and an epoxy group.

7. The silica particle dispersion according to claim 1 , further comprising an organic thixotropic agent.

8. 2. The silica particle dispersion liquid according to claim 1, wherein the solvent comprises at least one selected from the group consisting of water, hydrocarbons, alcohols, acetates, ketones, cellosolves, glycol ethers, chlorinated hydrocarbons, and polar solvents.

9. 2. The silica particle dispersion according to claim 1, wherein the silica particle dispersion has a viscosity of 20 to 20,000 mPa·s at 25° C. when the solid content concentration of the hollow silica particles is 50% by volume.

10. A resin composition comprising the silica particle dispersion according to any one of claims 1 to 9.

11. A method for producing a silica particle dispersion liquid, comprising mixing a solvent with a powder of hollow silica particles having an average particle size in the range of 0.2 to 10 μm, dispersing the mixture, and classifying the mixture to remove agglomerates of the hollow silica particles.