Silica particle dispersion, production method for silica particle dispersion, and resin composition

Abstract

The present invention provides a silica particle dispersion capable of further improving electrical characteristics of a resin composition, and a resin composition comprising the same. The present invention relates to a silica particle dispersion containing a solvent and 5 vol% or more of hollow silica particles, wherein the silica particle dispersion has a silica solid content recovery rate determined by formula (1): W1 / W×100 of 35% or less, wherein W1 is the mass of a solid content obtained by adjusting the silica particle dispersion to have a silica content of 2 mass% to obtain a dispersion for measurement, stirring the dispersion for measurement for 10 minutes under the conditions of a rotation speed of 5,000 rpm, and subjecting the same to decantation and drying by evaporation, and W is the mass of the dispersion for measurement.

Description

Silica particle dispersion, method for producing silica particle dispersion, and resin composition

[0001] The present invention relates to a silica particle dispersion, a method for producing a silica particle dispersion, and a resin composition.

[0002] Silica particles have traditionally been used in a variety of applications, including electronic materials such as printed circuit boards and packaged circuit boards, optical materials such as lenses and optical films, functional materials such as catalysts and catalyst supports, and pigments for paints and cosmetics. In particular, hollow silica particles, due to their properties such as low refractive index, low dielectric constant, and low density, are used to lower the dielectric constant, low dielectric loss tangent, and low thermal expansion coefficient of resin compositions used in insulating resin sheets such as adhesive films and prepregs, as well as in insulating layers formed on printed circuit boards.

[0003] Since silica particles tend to aggregate when used in a dry powder state, they are used in the form of dispersions in solvents such as water or resin, depending on the intended use. Various silica particle dispersions and slurries containing such dispersions have been proposed.

[0004] For example, Patent Documents 1 and 2 disclose slurries in which surface-treated silica particle material is dispersed in a dispersion medium such as water or an organic solvent.

[0005] Japanese Patent Publication No. 2020-097498 Japanese Patent Publication No. 2011-042527

[0006] In recent years, there has been a growing demand for lower dielectric constant and lower thermal expansion coefficient (low CTE) in resin components used in electronic devices, and the demand for silica particle dispersions containing hollow silica particles has also increased. Therefore, the object of the present invention is to provide a silica particle dispersion containing hollow silica particles, a method for producing the same, and a resin composition using the same, which can further improve the electrical properties of the resin composition.

[0007] As a result of diligent research, the inventors discovered that the electrical properties of molded products obtained from a silica dispersion containing hollow silica particles change depending on the amount of suspended silica solids in the silica dispersion. They then found that silica particle dispersions with a silica solid recovery rate of 35% or less, as measured by a specific measurement method I described later, have low dielectric constant and thermal expansion coefficient, thus completing the present invention.

[0008] One aspect of the present invention relates to a silica particle dispersion containing a solvent and 5% by volume or more of hollow silica particles, wherein the recovery rate of silica solids measured by the following measurement method I is 35% or less. (Measurement Method I) The silica particle dispersion is adjusted to have a silica content of 2% by mass to obtain a dispersion for measurement. The dispersion for measurement is stirred at a rotation speed of 5000 rpm for 10 minutes, decanted, and evaporated to dryness. Let W1 be the mass of the solids obtained, and W be the mass of the dispersion for measurement. The recovery rate of the silica solids is calculated using the following formula (1). Recovery rate of silica solids (%) = W1 / W × 100 ... (1)

[0009] Another aspect of the present invention relates to a method for producing a silica particle dispersion, wherein the hollow silica particle powder and a solvent are dispersed in a medialess dispersion device, and then dispersed again in a media-type dispersion device under non-pressurized conditions.

[0010] A further aspect of the present invention relates to a resin composition comprising the above-mentioned silica particle dispersion and a resin.

[0011] According to the present invention, a silica particle dispersion liquid in which both the dielectric constant and the coefficient of thermal expansion are reduced can be provided. Therefore, a resin composition containing the silica particle dispersion liquid of the present invention can form a resin component with excellent electrical properties.

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

[0013] <Silica Particle Dispersion> The silica particle dispersion according to the embodiment of the present invention contains a solvent and 5% by volume or more of hollow silica particles, and the recovery rate of silica solids measured by the following measurement method I is 35% or less. (Measurement Method I) The silica particle dispersion is adjusted to have a silica content of 2% by mass to obtain a dispersion for measurement. The dispersion for measurement is stirred at a rotation speed of 5000 rpm for 10 minutes, decanted, and evaporated to dryness. Let W1 be the mass of the solids obtained, and W be the mass of the dispersion for measurement. The recovery rate of the silica solids is calculated using the following formula (1). Recovery rate of silica solids (%) = W1 / W × 100 ... (1)

[0014] The silica content of the dispersion for measurement can be adjusted by diluting the silica particle dispersion with water or by concentrating it by heating, so that the silica content is 2% by mass. For stirring during measurement, 800 mL of the dispersion for measurement can be transferred to a cylindrical polypropylene container with an inner diameter of 95 mm and a height of 168.4 mm, and the contents of the container can be stirred. For decantation during measurement, suspended matter present in the liquid and on the liquid surface at a height of 67.4 mm or more from the bottom of the container can be removed by decantation. For evaporation to dryness during measurement, after decantation, the solvent remaining in the dispersion for measurement can be removed by distillation using a rotary evaporator to recover the solids, and the solids can be vacuum dried at 120°C for 2 hours. The mass W of the dispersion for measurement can be determined by weighing the dispersion.

[0015] The recovery rate of silica solids obtained by measurement method I is, in other words, the degree of damage to hollow silica particles in the silica particle dispersion, and can be expressed as the damage rate of hollow silica particles. When the above operation is performed on a measurement dispersion adjusted to have a silica content of 2% by mass, hollow silica particles that maintain their hollow shape are included in the suspended matter. As a result, if the recovery rate measured by measurement method I is 35% or less, it indicates that a large number of hollow silica particles are present in the silica particle dispersion while maintaining their hollow shape, and therefore the resin composition containing this silica particle dispersion can be said to have the effects of lower dielectric constant and lower thermal expansion coefficient.

[0016] In measurement method I, the recovery rate is measured using a dispersion with a silica content of 2% by mass. Therefore, the concentration is adjusted according to the solid content concentration of silica particles in the silica particle dispersion. Here, the solid content concentration of silica particles refers to the solid content concentration of all silica components contained in the silica particle dispersion. Silica components may include not only hollow silica particles but also damaged hollow silica particles and solid silica particles. Concentration adjustment is performed by either dilution with water or concentration by heating. When the silica content in the silica particle dispersion is 2% by mass, the silica particle dispersion can be used as is as the dispersion for measurement.

[0017] Furthermore, in the stirring and decantation processes of measurement method I, the hollow silica particles contain air inside and therefore float in the dispersion. The recovered solids, contained in the suspended matter, include silica particles other than the hollow silica particles and other solid substances. The solids obtained by evaporation to dryness may be completely dry or not completely dry, but when further vacuum-dried at 120°C for 2 hours, the mass loss rate is preferably 1% by mass or less, and more preferably 0.1% by mass or less.

[0018] The recovery rate of silica solids obtained by the above formula (1) is 35% or less, preferably 30% or less, more preferably 20% or less, even more preferably 15% or less, and particularly preferably 10% or less. The lower limit of the recovery rate is 0%, and may be 0.1%, 0.2%, or 0.5%. Specifically, the recovery rate is preferably between 0.1% and 35%.

[0019] Furthermore, it is preferable that the silica particle dispersion of this embodiment has a pass-through rate of 50% or more as measured by the following measurement method II. (Measurement method II) The silica particle dispersion is filtered through a filter with a mesh opening of 30 μm, and the pass-through rate is calculated using the following formula (2), with R1 being the dry mass of the filtrate and R2 being the mass of the evaporated dry filtrate. Pass-through rate (%) = R2 / (R1 + R2) × 100 ... (2)

[0020] When the pass rate measured by measurement method II is 50% or higher, there is less aggregation of hollow silica particles and the dispersibility of the hollow silica particles is high, which is effective in lowering the dielectric constant and lowering the coefficient of thermal expansion, and also improves the surface smoothness of the molded article when a molded article is obtained from the resin composition. A pass rate of 60% or higher is more preferable, 70% or higher is even more preferable, 80% or higher is even more preferable, 90% or higher is particularly preferable, and 95% or higher is most preferable. Since the dispersibility is better as the pass rate increases, there is no particular upper limit, but 100% is preferable.

[0021] In this embodiment, the silica particle dispersion preferably has a viscosity of 20 to 20,000 mPa·s at 25°C when the solid content concentration of hollow silica particles is 50 vol%. If the viscosity of the silica particle dispersion with a solid content concentration of 50 vol% of hollow silica particles at 25°C is 20 mPa·s or higher, sedimentation (flotation) separation of silica can be prevented, and if it is 20,000 mPa·s or lower, the dispersion state of silica can be maintained while the dispersion is maintained. The viscosity is more preferably 50 mPa·s or higher, even more preferably 75 mPa·s or higher, particularly preferably 100 mPa·s or higher, more preferably 15,000 mPa·s or lower, even more preferably 12,000 mPa·s or lower, particularly preferably 10,000 mPa·s or lower, and most preferably 4,000 mPa·s or lower.

[0022] Here, the solid content concentration of hollow silica particles in a silica particle dispersion refers to the ratio of the volume occupied by hollow silica particles when the volume of the dispersion is set to 100. The solid content concentration of hollow silica particles can be calculated by the following formula: solid content concentration wt% = W ÷ (d・V) × 100, where W is the total mass of solids after the solvent has been removed from the silica particle dispersion using a rotary evaporator and the solids have been recovered, and then dried at 100-110°C for 2-3 hours to completely remove the solvent, d is the specific gravity of the solids Ar, and V is the total volume of the dispersion.

[0023] Next, we will explain each component contained in the silica particle dispersion.

[0024] <Hollow Silica Particles> Hollow silica particles are made from silica (SiO₂ ２These are silica particles comprising a shell layer (solid film) containing ) and having a space inside the shell layer. The presence of a space inside the shell layer of hollow silica particles can be confirmed by transmission electron microscopy (TEM) observation or scanning electron microscopy (SEM) observation. In the case of SEM observation, the hollow nature can be confirmed by observing a broken particle with a partially open portion.

[0025] In this specification, the shell layer "contains silica" means silica (SiO₂ ２ This means that it contains 50% by mass or more of ). The composition of the shell layer can be measured by ICP emission spectrometry or flame atomic absorption spectrometry. The silica content of the shell layer is preferably 80% by mass or more, and more preferably 95% by mass or more. The upper limit is theoretically 100% by mass. The silica content of the shell layer is preferably less than 100% by mass, and more preferably 99.99% by mass or less. The residue can be alkali metal oxides and silicates, alkaline earth metal oxides and silicates, carbon, etc. Furthermore, "having a space inside the shell layer" means a hollow state in which, when observing the cross-section of a single primary particle, the shell layer surrounds a single space. That is, one hollow particle has one large space and a shell layer surrounding it.

[0026] Because the hollow silica particles have a structure in which they have a space within their shell, the composition containing the silica particle dispersion of this embodiment can secure more space within the composition, and when used as an insulating layer for electronic devices, the dielectric constant and thermal expansion coefficient can be significantly reduced.

[0027] The following describes the physical properties of hollow silica particles. The properties described are those confirmed using powdered silica particles obtained by drying a silica particle dispersion.

[0028] The average particle size (D50, median diameter) of hollow silica particles is preferably 0.2 to 10 μm. Note that, due to the firing and drying processes during manufacturing, the primary particles of hollow silica particles partially bond together, so hollow silica particles are often aggregates of secondary particles formed from aggregated primary particles. Here, the average particle size of hollow silica particles refers to the particle size of the secondary particles, while primary particles refer to spherical particles with internal spaces that can be confirmed by TEM or SEM observation.

[0029] When the average particle size (D50) of hollow silica particles in a 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 prone to particle formation during coating, so that the peel strength of the resin composition is properly maintained when used as a resin composition. The average particle size (D50) is preferably 0.5 μm or more, more preferably 1 μm or more, preferably 8 μm or less, more preferably 6 μm or less, even more preferably 5 μm or less, and particularly preferably 2 μm or less.

[0030] The average particle size (secondary particle size) of hollow silica particles is preferably measured by laser scattering. Measuring the aggregation diameter by SEM is not recommended because the boundaries between particles are unclear and do not reflect the dispersion in a wet state. Furthermore, with Coulter counter measurements, the electric field changes differ between hollow and solid particles, making it difficult to obtain values ​​that correspond to those for solid particles.

[0031] The coarse particle size (D90) of the secondary particles of hollow silica particles is preferably 1 to 30 μm. From the viewpoint of production efficiency, the coarse particle size is preferably 1 μm or larger. Furthermore, if the coarse particle size is too large, it will cause granularity 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 larger, most preferably 5 μm or larger, 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.

[0032] Furthermore, as mentioned above, the coarse particle size can also be determined by measuring the particle size of secondary particles using laser scattering.

[0033] Furthermore, the size of the primary particles of hollow silica particles can be determined by directly observing their particle diameter using SEM observation, but the average value of the 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, the increase in specific surface area, oil absorption, and pore volume is suppressed, and the increase in the amount of SiOH and adsorbed water on the particle surface can be suppressed, so the dielectric loss tangent is less likely to increase. Also, when the average primary particle diameter is 10 μm or less, it is easier to handle as a filler. From the viewpoint of manufacturing reproducibility, the lower limit of the average primary particle diameter is more preferably 70 nm or more, 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.

[0034] The average primary particle diameter of hollow silica particles is determined by measuring the primary particle size of 100 particles from SEM images, and then accumulating these measurements to obtain a distribution of primary particle sizes, which is then estimated to represent the overall primary particle size distribution. SEM observation allows for the direct measurement of the primary particle diameter of particles that are difficult to deaggregate.

[0035] The hollow silica particles have the average primary particle diameter described above, and it is preferable that 40% or more of the particles have a particle diameter within ±40% of the average primary particle diameter. When the particle diameter of 40% or more of the particles is within ±40% of the average primary particle diameter, the size of the hollow silica particles becomes uniform, making it difficult for shell defects to form in the hollow silica particles. It is more preferable that 50% or more of the particles have a particle diameter within ±40% of the average primary particle diameter, even more preferable that 60% or more of the particles have a particle diameter within ±40% of the average primary particle diameter, and particularly preferable that 70% or more of the particles have a particle diameter within ±40% of the average primary particle diameter.

[0036] The hollow silica particles have a particle density (hereinafter also referred to as Ar density) of 0.30 to 0.90 g / cm³, determined by density measurement using a dry pycnometer with argon gas. ３ Preferably, the Ar density is 0.30 g / cm³. ３ As described above, particle breakage in the dispersion can be suppressed, and the specific gravity difference with the resin does not become too large, thus improving the dispersibility in the resin composition when the silica particle dispersion is mixed with the resin. Ar density is 0.90 g / cm³.３ Since it is as follows, it is easy to exhibit the effects of reducing the dielectric constant and the coefficient of thermal expansion, so it can be preferably used as a material for electronic devices. Also, since it is easy to float in the dispersion liquid, the accuracy of measurement by the above measurement method I can be improved. The Ar density is 0.40 g / cm ３ or more is more preferable, 0.50 g / cm ３ or more is even more preferable, 0.60 g / cm ３ or more is particularly preferable, 0.70 g / cm ３ or more is most preferable. Also, the upper limit is 0.85 g / cm ３ or less is more preferable, 0.80 g / cm ３ or less is even more preferable, 0.75 g / cm ３ or less is particularly preferable.

[0037] Also, the hollow silica particles have a particle density (hereinafter also referred to as He density) determined by density measurement using a dry pycnometer with helium gas of 2.00 to 2.30 g / cm ３ which is preferable. Since helium gas permeates through fine voids, the density corresponding to the true density of the silica portion of the silica particles having a space inside can be obtained. When the He density is 2.00 g / cm ３ or more, since the silica particles are dense, when the silica particle dispersion liquid is mixed with a resin and used, the peel strength of the resin composition is not reduced, and the remaining amount of silanol contained in the hollow silica particles is reduced, so it is easy to lower the dielectric tangent. To obtain a silica material having a He density exceeding 2.30 g / cm ３ requires firing at a considerably high temperature, and the particles are likely to be damaged. When the He density is 2.30 g / cm ３ or less, the space contained in the hollow silica particles can be maintained, and the Ar density is not deteriorated. The He density is 2.05 g / cm ３ or more is more preferable, 2.10 g / cm ３ or more is even more preferable, 2.15 g / cm ３ or more is particularly preferable. Also, 2.25 g / cm ３ or less is more preferable, 2.23 g / cm ３ or less is even more preferable.

[0038] The apparent density of hollow silica particles can also be measured using a specific gravity bottle. The sample (hollow silica particles) and organic solvent are placed in the specific gravity bottle and left to stand at 25°C for 48 hours before measurement. Depending on the density of the hollow silica particle shells, it may take time for the organic solvent to penetrate, so it is preferable to leave it standing for the above time. The results obtained by this method correspond to the results obtained by density measurement using a dry pycnometer with argon gas.

[0039] Hollow silica particles allow for adjustment of their apparent density by controlling the primary particle size and shell thickness. By changing the particle density, it's possible to control whether the particles settle, remain dispersed, or float in the solvent. For dispersion in a solvent, it's desirable that the solvent density and the particle apparent density are close. For example, a density of 1.0 g / cm³ is desirable. ３ If you want to disperse the particles in water, the Ar density of the particles should be 0.8 g / cm³. ３ 0.9g / cm or more ３ The following adjustments are preferable.

[0040] Furthermore, hollow silica particles have a BET specific surface area of ​​1 to 100 m². ２ It is preferable that the BET specific surface area is 1 m². ２ It is practically difficult to keep the amount below / g. Also, if the BET specific surface area is too large, more resins, etc. will be adsorbed onto the silica surface, but if the BET specific surface area is 100 m² ２ If the amount is less than / g, the degree of adsorption of resins, etc., can be suppressed, and the increase in viscosity when it is made into a resin composition can be suppressed. The BET specific surface area is 75 m². ２ More preferably less than / g, and 50m ２ It is even more preferable to be less than / g, and 20m ２ A value of less than or equal to 15m is particularly preferred. ２ Less than / g is most preferable. Also, a smaller BET specific surface area is preferable, but 3m ２ It may be more than / g, 5m ２ It may be 1 / g or more, and 8m ２ It may be more than / g.

[0041] Here, the BET specific surface area can be measured using a specific surface area measuring device (for example, the "Tristar II 3020" manufactured by Shimadzu Corporation). As a pretreatment, hollow silica particles are dried at 230°C until they reach 50 mTorr, and then measured using a multi-point method with nitrogen gas.

[0042] The sphericity of 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 which they come into contact in a resin composition containing a silica particle dispersion may decrease, potentially reducing the peel strength. Therefore, a sphericity of 0.75 or higher is preferred. Sphericity is expressed as the average value obtained by measuring the maximum diameter (DL) and the minimum diameter (DS) perpendicular to it for any 100 particles in a photographic projection obtained by taking a photograph with a scanning electron microscope (SEM), and calculating the ratio of the minimum diameter (DS) to the maximum diameter (DL) (DS / DL). From the viewpoint of dispersibility, a sphericity of 0.80 or higher is more preferred, 0.82 or higher is even more preferred, 0.83 or higher is even more preferred, 0.85 or higher is even more preferred, 0.87 or higher is particularly preferred, 0.90 or higher is especially preferred, and 0.95 or higher is most preferred.

[0043] The shell thickness of the hollow silica particles is preferably 0.01 to 0.3 relative to the diameter of the primary particle. When the shell thickness is 0.01 or more relative to the diameter of the primary particle, 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, and the properties due to the hollow shape can be exhibited. The shell thickness is more preferably 0.02 or more, even more preferably 0.03 or more, even more preferably 0.2 or less, and even more preferably 0.1 or less, relative to the diameter of the primary particle.

[0044] Here, the shell thickness is determined by measuring the shell thickness of individual particles using a transmission electron microscope (TEM).

[0045] Because hollow silica particles have internal spaces, they can encapsulate substances within the particles. The hollow silica particles used in this embodiment have a dense shell layer, making them resistant to the penetration of various solvents. However, if damaged particles are present, solvents will penetrate into the interior. Therefore, the amount of oil absorbed changes depending on the proportion of damaged particles.

[0046] The oil absorption capacity of hollow silica particles is preferably 15 to 1300 mL / 100 g. If the oil absorption capacity is 15 mL / 100 g or more, adhesion to the resin can be ensured when used in a resin composition, and if it is 1300 mL / 100 g or less, the strength of the resin can be ensured when used in a resin composition, and the viscosity of the composition can be reduced. Since viscosity increases with higher oil absorption, the oil absorption capacity of 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 capacity is too low, the adhesion between the powder and the resin may deteriorate, so 20 mL / 100 g or more is more preferable.

[0047] The amount of oil absorbed can be measured in accordance with JIS K 5101. Specifically, boiled linseed oil is added to the sample while kneading it until the entire sample forms a single mass. The amount of oil absorbed is expressed as the volume of boiled linseed oil per 100g of the sample when the entire sample forms a single mass.

[0048] Furthermore, based on the relationship between the proportion of damaged particles and the amount of oil absorbed as described above, the amount of oil absorbed can be adjusted by adjusting the proportion of damaged particles. In addition, since the spaces between primary particles are also spaces that can hold oil, it is conceivable that if the median diameter of the secondary particles formed by the aggregation of primary particles is large, the amount of oil absorbed will be large, and if the median diameter of the secondary particles is small, the amount of oil absorbed will be small.

[0049] 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 thus lowering the dielectric loss tangent. Metal M is incorporated into the hollow silica particles between the reaction step and the washing step. For example, metal M can be incorporated into the hollow silica particles by adding a metal salt of metal M to the reaction solution when forming the silica shell in the reaction step, or by washing the hollow silica precursor with a solution containing metal ions of metal M before firing.

[0050] 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 condensation of bonded silanol groups is promoted by the flux effect during firing, and the number of remaining silanol groups can be reduced, thereby lowering the dielectric loss tangent. If the concentration of metal M is too high, there will be many components that react with silica to form silicates, which may worsen the hygroscopicity of the hollow silica particles, so it is preferable to include it at 1% by mass or less. The concentration of metal M is more preferably 100 ppm by mass or more, even more preferably 150 ppm by mass or more, even more preferably 5000 ppm by mass or less, and most preferably 1000 ppm by mass or less.

[0051] The metal M can be measured by adding perchloric acid and hydrofluoric acid to hollow silica particles, strongly heating them to remove the main component silicon, and then measuring it by ICP emission spectrometry. Furthermore, when alkali metal silicates are used as the silica raw material, the amount of carbon (C) component derived from the raw material in the shell layer of the resulting hollow silica particles will be less compared to when silicon alkoxides are used as the silica raw material.

[0052] The hollow silica particles are preferably such that the viscosity of the following kneaded product containing the hollow silica particles is 20,000 mPa·s or less when measured by the following measurement method III. (Measurement method III) The density of the particles is determined by density measurement using a dry pycnometer with argon gas, and A (g / cm³) is used. ３As a result, 6 parts by mass of boiled linseed oil and parts by mass of hollow silica particles (6 × A / 2.2) were mixed and kneaded at 2000 rpm for 3 minutes. The resulting mixture was then measured using a rotary rheometer at a shear rate of 1 s. －１ Measure for 30 seconds and determine the viscosity at the 30-second mark.

[0053] The shear rate of the kneaded material, determined by the measurement method III described above, was 1 s. －１ If the viscosity is 20,000 mPa·s or less, the amount of solvent added during molding and film formation of the resin composition containing hollow silica particles can be reduced, the drying speed can be increased, and productivity can be improved. Furthermore, when the product of density and specific surface area according to the particle size of silica powder increases, the viscosity tends to increase when added to the resin composition, but since hollow silica particles have a small product of density and specific surface area, the increase in viscosity of the resin composition can be suppressed. The viscosity of the kneaded material 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. The shear rate of the kneaded material is 1 s －１ The lower viscosity is not particularly limited, as a lower viscosity improves the coatability of the resin composition and increases productivity.

[0054] The pore volume of hollow silica particles is 0.2 cm³. ３ It is preferable that the amount is less than or equal to / g. The pore volume is 0.2 cm³. ３ If the concentration is less than / g, it will not easily adsorb moisture, and the deterioration of dielectric loss in the resin composition can be suppressed. The pore volume is 0.15 cm³. ３ More preferably less than or equal to 0.1 cm ３ It is even more preferable to be less than or equal to 0.05 cm. ３ A value of less than or equal to / g is particularly preferred.

[0055] The hollow silica particles may have their surfaces treated with a silane coupling agent. Treating the surface of the hollow silica particles with a silane coupling agent reduces the amount of remaining surface silanol groups, making the surface hydrophobic, which suppresses moisture adsorption and improves dielectric loss. Furthermore, when used in a resin composition, it improves affinity with the resin, resulting in improved dispersibility and strength after resin film formation.

[0056] There are no particular restrictions on the surface treatment conditions; general surface treatment conditions are acceptable, and either wet or dry treatment methods can be used. From the viewpoint of uniform treatment, wet treatment methods are preferred.

[0057] Examples of silane coupling agents include aminosilane coupling agents, epoxysilane coupling agents, mercaptosilane coupling agents, silane coupling agents, and organosilazane compounds. One type of silane coupling agent may be used alone, or two or more types may be used in combination.

[0058] Specifically, silane coupling agents include aminosilane-based coupling agents such as aminopropylmethoxysilane, aminopropyltriethoxysilane, ureidopropyltriethoxysilane, N-phenylaminopropyltrimethoxysilane, and N-2(aminoethyl)aminopropyltrimethoxysilane; epoxysilane-based coupling agents such as glycidoxypropyltrimethoxysilane, glycidoxypropyltriethoxysilane, glycidoxypropylmethyldiethoxysilane, glycidylbutyltrimethoxysilane, and (3,4-epoxycyclohexyl)ethyltrimethoxysilane; mercaptosilane-based coupling agents such as mercaptopropyltrimethoxysilane and mercaptopropyltriethoxysilane; silane-based coupling agents such as methyltrimethoxysilane, vinyltrimethoxysilane, octadecyltrimethoxysilane, phenyltrimethoxysilane, metaclooxypropyltrimethoxysilane, imidazolesilane, and triazinesilane; CF ３ (CF ２ ) ７ CH ２ CH ２ Si(OCH) ３ ) ３ CF ３ (CF ２ ) ７ CH ２ CH ２ SiCl ３ CF ３ (CF ２ ) ７ CH ２ CH ２ Si(CH ３ ) (OCH３ ) ２ 、CF ３ (CF ２ ) ７ CH ２ CH ２ Si (CH ３ )C1 ２ 、CF ３ (CF ２ ) ５ CH ２ CH ２ SiCS ３ 、CF ３ (CF ２ ) ５ CH ２ CH ２ Si (OCH ３ ) ３ 、CF ３ CH ２ CH ２ SiCS ３ 、CF 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 [NNHCH 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 SiCS ３ 、C ３ F７ -O-(CF(CF ３ ) CF ２ -O) ２ -CF (CF ３ )CONH-(CH ２ ) ３ Si(OCH) ３ ) ３ Examples include fluorine-containing silane coupling agents such as hexamethyldisilazane, hexaphenyldisilazane, trisilazane, cyclotrisilazane, and organosilazane compounds such as 1,1,3,3,5,5-hexamethylcyclotrisilazane.

[0059] The amount of silane coupling agent attached is preferably 1 part by mass or more, more preferably 1.5 parts by mass or more, even more preferably 2 parts by mass or more, 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, per 100 parts by mass of hollow silica particles.

[0060] The surface of hollow silica particles being treated with a silane coupling agent can be confirmed by detecting peaks corresponding to substituents of the silane coupling agent using IR (irradiation irradiation). Furthermore, the amount of silane coupling agent adhering to the surface can be measured by its carbon content.

[0061] The relative permittivity of the hollow silica particles is preferably 1.3 to 5.0 at 1 GHz. In particular, in measuring the dielectric constant of powders, the sample space becomes small and the measurement accuracy deteriorates at 10 GHz or higher, so the present invention uses the measurement value at 1 GHz. When the relative permittivity at 1 GHz is within the above range, the low relative permittivity required for electronic equipment can be achieved. It is substantially difficult to synthesize hollow silica particles with a relative permittivity of less than 1.3 at 1 GHz. The relative permittivity at 1 GHz is preferably 1.3 or higher, more preferably 1.4 or higher, more preferably 4.5 or lower, even more preferably 4.0 or lower, even more preferably 3.5 or lower, particularly preferably 3.0 or lower, and most preferably 2.5 or lower.

[0062] Furthermore, the dielectric loss tangent at 1 GHz is preferably 0.0001 to 0.05 for the hollow silica particles. A dielectric loss tangent at 1 GHz of 0.05 or less allows for the achievement of the low dielectric constant required for electronic equipment. Moreover, it is substantially difficult to synthesize hollow silica particles with a dielectric loss tangent at 1 GHz of less than 0.0001. The dielectric loss tangent at 1 GHz is more preferably 0.0002 or more, even more preferably 0.0003 or more, even 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, especially preferably 0.0015 or less, and most preferably 0.0010 or less.

[0063] The relative permittivity and dielectric loss tangent can be measured using a dedicated device (for example, the "Vector Network Analyzer E5063A" manufactured by Keycom Co., Ltd.) and the perturbation-type resonator method.

[0064] Hollow silica particles are included in the silica particle dispersion in an amount of 5% by volume or more, preferably in the range of 5 to 80% by volume, and more preferably in the range of 10 to 60% by volume. When the content of hollow silica particles 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 become too high, 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, particularly preferably 30% 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.

[0065] Furthermore, the amount of silica solids consisting of hollow silica particles in the silica particle dispersion of this embodiment is preferably 1% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more. The amount of silica solids is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 35% by mass or less.

[0066] <Solvent> The silica particle dispersion of this embodiment contains a solvent as a dispersion medium for hollow silica particles. The solvent can be arbitrarily selected depending on the purpose of use, and examples include water, hydrocarbons, alcohols, acetate esters, ketones, cellosolves, glycol ethers, chlorinated hydrocarbons, and polar solvents. Preferably, the solvent contains at least one selected from the group consisting of these.

[0067] Examples of water include distilled water, deionized water, ion-exchanged water, and tap water. Examples of hydrocarbons include toluene, methylcyclohexane, n-heptane, and m-xylene. Examples of alcohols include ethanol, isopropyl alcohol, 1-propyl alcohol, isobutyl alcohol, 1-butanol, and 2-butanol. Examples of acetate esters 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. An example of a polar solvent is N-methyl-2-pyrrolidone.

[0068] The solvent should be selected appropriately depending on the field of application. For example, when used in the insulating layer of a wiring board for electronic equipment, ketones and hydrocarbons are preferred, and specifically, methyl ethyl ketone (MEK), toluene, etc., are preferred.

[0069] Furthermore, when the silica particle dispersion of this embodiment is used in the curable composition, the liquid main component or curing agent itself may be used as the solvent. Examples of the main component include epoxy resin, polyphenylene ether resin, polyester resin, polyimide resin, phenolic resin, ortho-divinylbenzene resin, and examples of the curing agent include polyamine-based curing agents, acid anhydride-based curing agents, phenolic-based curing agents, activated ester-based curing agents, peroxides, and the like.

[0070] The solvent is preferably present in the silica particle dispersion in an amount of 95% by volume or less, more preferably 20 to 90% by volume. When the solvent content is 95% by volume or less, it remains liquid and can be used in its dispersed state. Furthermore, 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. The solvent content in the silica particle dispersion is more preferably 25% by volume or more, even more preferably 30% by volume or more, even 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.

[0071] <Silane Compounds> The silica particle dispersion of this embodiment preferably contains a silane compound, and more preferably contains a silane compound having at least one group selected from the group consisting of vinyl group, phenyl group, phenylamino group, alkyl group having 4 or more carbon atoms, methacrylic group, and epoxy group. Furthermore, the silane compound preferably has a hydrolyzable silyl group, and more preferably has a trimethoxyl group, triethoxysilyl group, methyldimethoxysilyl group, or ethyldiethoxysilyl group. By including a silane compound, when the silica particle dispersion is incorporated into the resin composition, the surface of the hollow silica particles adheres to the resin, thereby increasing the peel strength of the resin composition. Note that if the hollow silica particles have been treated with a silane coupling agent, it is not necessarily required to add a silane compound.

[0072] Examples of the silane compounds include vinylsilane, phenylsilane, phenylaminosilane, hexylsilane, decylsilane, 3-methacryloxypropyltrimethoxysilane, and aminopropylsilane. These may be used individually or in combination of two or more. Among these, from the viewpoint of interaction with the resin, silane compounds containing a vinyl group, phenyl group, methacrylic group, epoxy group, or phenylamino group are more preferred, silane compounds containing a vinyl group, phenyl group, methacrylic group, or phenylamino group are particularly preferred, and silane compounds containing a phenyl group or methacrylic group are most preferred. In this case, the dispersibility of silica particles in the silica particle dispersion of this embodiment is improved, and it is particularly easy to maintain a balance between its viscosity and the peel strength of the molded article formed therefrom.

[0073] The silane compound is preferably contained in the silica particle dispersion in an amount of 0.1 to 5% by mass. When the silane compound content is 0.1% by mass or more, the compatibility between the hollow silica particles and the resin is increased when the silica particle dispersion is incorporated into the resin composition, thereby increasing the peel strength of the resin composition. When the content is 5% by mass or less, residue in the resin composition is suppressed, reducing the impact on the physical properties of the resin composition. The silane compound content 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, more preferably 4% by mass or less, even more preferably 3% by mass or less, and particularly preferably 2% by mass or less.

[0074] <Organic synchopper> The silica particle dispersion of this embodiment preferably further contains an organic synchopper, to the extent that it does not impair the effects of the present invention. The organic synchopper is also called a wetting dispersant, and known ones can be used. In this embodiment, the organic synchopper 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 the wettability of the flux to the cured product of the resin composition or slurry.

[0075] Examples of organic synchoppers include fatty acid amides (amide waxes) 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. However, hydrogenated castor oil-based waxes, known as castor oil wax, and oxidized polyethylene-based waxes, which are produced by oxidizing polyethylene and introducing polar groups, are not included. Organic synchoppers may be used individually or in combination of two or more.

[0076] Organic oxidizers are available commercially, 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)-2009, BYK(registered trademark)-7410ET, BYK(registered trademark) Examples include )-7411ES (all manufactured by Big Chemie 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, and Flownon HR-4AF (all manufactured by Kyoeisha Chemical Co., Ltd.).

[0077] The organic oxidizer is preferably present in the silica particle dispersion in an amount of 0.01 to 5% by mass. When the organic oxidizer content is 0.01% by mass or more, aggregation of hollow silica particles in the dispersion is suppressed, which suppresses aggregation of hollow silica particles when the silica particle dispersion is stored, and suppresses the accumulation of resin between hollow silica particles when it is incorporated into a resin composition. This increases the peel strength of the resin composition. Furthermore, when the organic oxidizer content is 5% by mass or less, residue in the composition is suppressed, reducing the impact on the physical properties of the resin composition. The organic oxidizer content 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.

[0078] The silica particle dispersion of this embodiment may contain other optional components as long as they do not impair the effects of the present invention. Examples of optional components include other inorganic fillers such as alumina, curable compositions, and the like.

[0079] Furthermore, the silica particle dispersion of this embodiment may contain silica particles other than hollow silica particles. Examples of silica particles other than hollow silica particles include broken hollow silica particles that have been damaged and can no longer maintain their hollow shape, and solid silica particles. From the viewpoint of improving the electrical properties of the resin composition, it is preferable that the silica particles in the silica particle dispersion do not contain solid silica particles, more preferably that they contain only hollow silica particles and broken hollow silica particles, and most preferably that they contain only hollow silica particles.

[0080] <Method for producing silica particle dispersion> The silica particle dispersion of this embodiment can be obtained by mixing hollow silica particle powder with a solvent and dispersing the mixture. The method for producing the silica particle dispersion according to the embodiment of the present invention includes dispersing the hollow silica particle powder and solvent in a medialess dispersion device, and further dispersing them under non-pressurized conditions in a media-type dispersion device.

[0081] It is preferable to mix the hollow silica particle powder into the silica particle dispersion at a ratio of 5 to 80 volume percent. If the ratio of hollow silica particles is too low, the productivity of the subsequent concentration process will decrease, and if it is too high, the viscosity of the silica particle dispersion may increase too much, which may decrease the productivity of the dispersion process, so a range of 5 to 80 volume percent is preferable. The amount of hollow silica particles used is more preferably 10 volume percent or more, even more preferably 20 volume percent or more, particularly preferably 30 volume percent or more, more preferably 70 volume percent or less, even more preferably 60 volume percent or less, and particularly preferably 50 volume percent or less.

[0082] The solvent can be any of the solvents mentioned above. The solvent is preferably mixed into the silica particle dispersion at a ratio of 20 to 95 volume percent. If the solvent content is 20 volume percent or more, the hollow silica particles can be uniformly dispersed, and if it is 95 volume percent or less, productivity can be improved. The amount of solvent used is more preferably 25 volume percent or more, even more preferably 30 volume percent or more, even more preferably 90 volume percent or less, even more preferably 80 volume percent or less, even more preferably 70 volume percent or less, particularly preferably 60 volume percent or less, and most preferably 50 volume percent or less.

[0083] Dispersion treatment of a mixture containing a solvent and hollow silica particles can be performed using dispersion equipment used for pigment dispersion, etc. Examples of dispersion equipment include mixers such as dispersers, homomixers, and planetary mixers; homogenizers (such as M-Technic's "Clearmix," PRIMIX's "Filmix," and Silverson's "Abramix"); paint conditioners (Red Devil); colloid mills (such as PUC's "PUC Colloid Mill" and IKA's "Colloid Mill MK"), cone mills (such as IKA's "Corn Mill MKO"), ball mills, bead mills, and sand mills (Shinmaru Enterprise). Media-type dispersion devices such as Izes' "Dynomill," Attritor, Pearlmill (Eirich's "DCPmill," etc.), and Coballmill; media-less dispersion devices such as Mixrotor, Highsher mixer, and Colloid mill; wet jet mills (Genus PY, Sugino Machine, "Starburst," Nanomizer, etc.), M-Technique's "Crea SS-5," Nara Machine's "MICROS," etc.; other roll mills; kneaders, etc.

[0084] In the method for producing a silica particle dispersion of this embodiment, hollow silica particle powder and a solvent are dispersed using a medialess dispersion device, and then dispersed again using a media-type dispersion device. When processing with the media-type dispersion device, the dispersion is performed under non-pressurized conditions. By performing the dispersion treatment with the medialess dispersion device under non-pressurized conditions to promote mild solvent penetration into the hollow silica particles, and then dispersing the hollow silica particles in the solvent using the media-type dispersion device, the destruction of the hollow silica particles is suppressed, and a silica particle dispersion is obtained in which the recovery rate of silica solids according to the above measurement method I is 35% or less. In the manufacturing method of this embodiment, a high-pressure dispersion device, roll mill, kneader, etc. may be used in combination as needed.

[0085] By appropriately adjusting the dispersion conditions of the dispersion device, the silica particle dispersion can be dispersed so that the recovery rate when measured by the above measurement method I is 35% or less. For example, when using a media-type dispersion device such as a ball mill or bead mill, the size and material of the balls or beads, peripheral speed, processing time, bead filling ratio, etc., should be adjusted. In particular, when using a bead mill as a media-type dispersion device, the peripheral speed of the bead mill is preferably 1 m / s or more and less than 8 m / s, and more preferably 2 m / s or more and less than 6 m / s. Also, the bead filling ratio is preferably 30 to 90%, and more preferably 60 to 90%.

[0086] Furthermore, the dispersion treatment is preferably carried out at a temperature of 0 to 100°C. Here, the temperature during the dispersion treatment refers to the temperature range before and after the treatment. Dispersing within this temperature range maintains the viscosity of the solvent appropriately, ensuring productivity, and suppressing solvent evaporation, allowing for easy control of the solid content. The treatment temperature is more preferably 5°C or higher, even more preferably 10°C or higher, even more preferably 90°C or lower, and even more preferably 80°C or lower.

[0087] The distributed processing time can be set appropriately depending on the distributed device being used, for example, within a range of 0.5 to 60 minutes.

[0088] In this embodiment, the silica particle dispersion can be used as is after dispersion treatment, but wet classification is preferred. Wet classification can remove aggregates of hollow silica particles that were not completely dispersed during the dispersion treatment. Examples of wet classification include sieving and classification by centrifugal force. When using a sieve, it is preferable to classify using a sieve with a mesh size of 100 μm or less. As a sieve, it is preferable to use a metal with a dense lattice structure, such as an electroformed sieve.

[0089] The mesh size of the sieve 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 mesh size of the sieve is preferably 0.2 μm or more, more preferably 0.5 μm or more, and even more preferably 1 μm or more. In other words, the mesh size of the sieve is preferably in the range of 0.2 to 100 μm.

[0090] The solution may then be diluted or concentrated as needed to adjust it to an appropriate concentration. Methods of concentration include vaporization and solid-liquid separation.

[0091] In the method for producing the silica particle dispersion of this embodiment, a silane coupling agent may be added to the mixture of the solvent and hollow silica particles. Examples of silane coupling agents include those mentioned above.

[0092] <Resin Composition> The silica particle dispersion of this embodiment is suitable for use in combination with a resin. The resin composition according to the embodiment of the present invention comprises the silica particle dispersion of this embodiment and a resin. The resin composition preferably contains hollow silica particles in an amount of 5 to 70% by mass, and more preferably 10 to 50% by mass. Furthermore, the content of hollow silica particles in the resin composition is preferably 10 to 60% by volume, and more preferably 10 to 50% by volume. Furthermore, the content of resin in the resin composition is preferably 10 to 60% by mass, and more preferably 20 to 50% by mass.

[0093] As resins, one or more of the following can be used: epoxy resin, silicone resin, phenolic resin, melamine resin, urea resin, unsaturated polyester, fluororesin, polyimide, polyamideimide, polyetherimide and other polyamides; polyesters such as polybutylene terephthalate and polyethylene terephthalate; polyphenylene sulfide, aromatic polyester, polysulfone, liquid crystal polymer, polyethersulfone, polycarbonate, maleimide-modified resin, ABS resin, AAS (acrylonitrile-acrylic rubber / styrene) resin, AES (acrylonitrile-ethylene-propylene-diene rubber / styrene) resin, polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-ethylene copolymer (ETFE), etc. The dielectric loss tangent in the resin composition also depends on the properties of the resin, so the resin to be used should be selected considering these factors. The resin may be used alone, or a resin varnish in which the resin is dissolved or dispersed in a solvent may be used.

[0094] The resin composition may contain any components other than the resin described above. Examples of optional components include dispersants, surfactants, and fillers other than silica.

[0095] Furthermore, when a resin film is made using the resin composition of this embodiment, its relative permittivity is preferably 2.0 to 3.5 at a frequency of 10 GHz. The lower limit of the relative permittivity at a frequency of 10 GHz is more preferably 2.2 or higher, even more preferably 2.3 or higher, and particularly preferably 2.4 or higher. The upper limit is more preferably 3.2 or lower, even more preferably 3.0 or lower, even more preferably 2.9 or lower, particularly preferably 2.7 or lower, and most preferably 2.5 or lower. When the relative permittivity of the resin film at a frequency of 10 GHz is within the above range, it exhibits excellent electrical properties and can be expected to be used in electronic equipment, communication equipment, and the like.

[0096] Furthermore, 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 of the resin film at a frequency of 10 GHz is within the above range, it exhibits excellent electrical properties and can be expected to be used in electronic equipment and communication devices. The smaller the dielectric loss tangent, the lower the transmission loss in the circuit, so the lower limit is not particularly limited.

[0097] The relative permittivity and dielectric loss tangent can be measured using a split-post dielectric resonator (SPDR) (for example, manufactured by Agilent Technologies).

[0098] Furthermore, it is preferable that the average linear expansion coefficient of the resin film is 10 to 80 ppm / °C. When the average linear expansion coefficient is within the above range, it is close to the thermal expansion coefficient of copper foil, which is widely used as a base material, 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, particularly preferably 20 ppm / °C or higher, more preferably 70 ppm / °C or lower, even more preferably 60 ppm / °C or lower, and particularly preferably 55 ppm / °C or lower.

[0099] The average coefficient of linear expansion is determined by measuring the coefficient of linear expansion in the Z direction (z-CTE) between 50°C and 100°C, in accordance with IPC-TM-650 2.4.24, and calculating the average.

[0100] Furthermore, when a plate-shaped molded article is produced using the resin composition of this embodiment, it is preferable that its surface roughness Rz is 6 μm or less. When the surface roughness Rz of the molded article is 6 μm or less, the surface smoothness of the molded article is high, and it can accommodate high density when used in electronic devices and electronic circuit boards. A surface roughness Rz of 5 μm or less is more preferable, 3 μm or less is even more preferable, 2 μm or less is particularly preferable, and 1 μm or less is most preferable. Since a smaller value for surface roughness Rz is preferable, there is no particular lower limit.

[0101] <Applications> The silica particle dispersion of this embodiment can be used, for example, in metal substrates such as electronic circuit boards used in electronic devices such as personal computers, laptop computers, and digital cameras, as well as communication devices such as smartphones and game consoles. It can be suitably used as a filler in resin compositions used in the manufacture of electronic devices and metal substrates. Specifically, the silica particle dispersion of this embodiment is expected to be applied to resin compositions, prepregs, metal foil laminates, printed circuit boards, resin sheets, adhesive layers, adhesive films, solder resists, bump preflow materials, rewiring insulating layers, die bond materials, encapsulants, underfills, molded underfills, and laminated inductors, etc., for the purpose of lowering dielectric constant, lowering transmission loss, lowering moisture absorption, and improving peel strength.

[0102] As described above, the present invention includes the following configurations [1] to

[15] . [1] A silica particle dispersion comprising a solvent and 5% by volume or more of hollow silica particles, wherein the recovery rate of silica solids measured by the measurement method I below is 35% or less. (Measurement method I) The silica particle dispersion is adjusted to obtain a dispersion for measurement by adjusting the silica content to 2% by mass, the dispersion for measurement is stirred for 10 minutes under conditions of a rotation speed of 5000 rpm, decanted, and evaporated to dryness, with W1 being the mass of the solids obtained and W being the mass of the measurement dispersion, and the recovery rate of the silica solids is calculated by the following formula (1). Recovery rate of silica solids (%) = W1 / W × 100 ... (1) [2] The silica particle dispersion according to [1] above, wherein the pass-through rate measured by the measurement method II below is 50% or more. (Measurement Method II) The silica particle dispersion is filtered through a filter with a mesh size of 30 μm, and the pass rate is determined by the following formula (2), with R1 being the dry mass of the filtrate and R2 being the mass of the evaporated dry filtrate. Pass rate (%) = R2 / (R1 + R2) × 100 ... (2) [3] The silica particle dispersion according to [1] or [2] above, wherein the recovery rate is 0.1 to 35%. [4] The silica particle dispersion according to any one of [1] to [3] above, which contains 10 to 60 volume% of the hollow silica particles. [5] The particle density of the hollow silica particles, as determined by a dry pycnometer using argon gas, is 0.30 to 0.90 g / cm³. ３ A silica particle dispersion according to any one of the above [1] to [4]. [6] The BET specific surface area of ​​the hollow silica particles is 1 to 100 m². ２A silica particle dispersion according to any one of [1] to [5] above, wherein the amount is / g. [7] A silica particle dispersion according to any one of [1] to [6] above, wherein the solvent comprises at least one selected from the group consisting of water, hydrocarbons, alcohols, acetate esters, ketones, cellosolves, glycol ethers, chlorinated hydrocarbons, and polar solvents. [8] A silica particle dispersion according to any one of [1] to [7] above, further comprising a silane compound, wherein the silane compound has at least one group selected from the group consisting of vinyl group, phenyl group, phenylamino group, alkyl group having 4 or more carbon atoms, methacrylic group, and epoxy group. [9] A silica particle dispersion according to any one of [1] to [8] above, further comprising an organic thixotrope.

[10] A silica particle dispersion according to any one of [1] to [9] above, wherein the viscosity of the silica particle dispersion at 25°C is 20 to 20,000 mPa·s when the solid content concentration of the hollow silica particles is 50% by volume.

[11] A silica particle dispersion according to any one of [1] to

[10] above, used for mixing with a resin.

[12] A method for producing a silica particle dispersion according to any one of [1] to

[11] above, comprising dispersing a hollow silica particle powder and a solvent in a medialess dispersion device, and further dispersing them under non-pressurized conditions in a media-type dispersion device.

[13] A resin composition comprising a silica particle dispersion according to any one of [1] to

[11] above and a resin.

[14] A resin composition according to

[13] above, wherein the resin content is 10 to 60% by mass.

[15] The resin composition according to

[13] or

[14] above, wherein the content of the hollow silica particles is 10 to 60 volume percent.

[0103] The present invention will be described in 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 for common components. Also, Examples 1 to 8 are examples, and Examples 9 to 11 are comparative examples.

[0104] (Example 1) "Emulsion Preparation" 4 g of EO-PO-EO block copolymer (ADEKA Corporation's "Pluronic F68") was added to 1250 g of pure water and stirred until dissolved. 42 g of n-decane in which 4 g of sorbitanic acid monooleate (Sanyo Chemical Industries' "Ionet S-80") was dissolved was added to this aqueous solution, and the mixture was stirred using an IKA homogenizer until the entire liquid was homogenized to prepare a crude emulsion. This crude emulsion was emulsified at a pressure of 50 bar using a high-pressure emulsifier (SMT Corporation's LAB1000) to prepare a fine emulsion with an emulsion diameter of 1 μm.

[0105] "Emulsified liquid aging" The obtained fine emulsion was left to stand at 40°C for 12 hours to obtain an aged emulsion.

[0106] "First stage shell formation" Add a diluted sodium silicate aqueous solution (SiO₂) to 1300g of the aged emulsion obtained, so that the pH is 2. ２ Concentration 10.4% by mass, Na ２ 23 g of 3.6% by mass of 0.0% and 2 M hydrochloric acid were added, and the mixture was thoroughly stirred while maintaining the temperature at 30°C. While stirring the mixture well, 1 M sodium hydroxide aqueous solution was slowly added dropwise until the pH reached 6, to obtain an oil core-silica shell particle dispersion. The obtained oil core-silica shell particle dispersion was held and allowed to mature.

[0107] "Second stage shell formation" The entire volume of the oil core-silica shell particle dispersion obtained in the first stage shell formation was heated to 70°C, and 1 M NaOH was slowly added while stirring to adjust the pH to 9. Next, diluted sodium silicate aqueous solution (SiO2) was added. ２ Concentration 10.4% by mass, Na ２ 330 g of 3.6% by mass O was gradually added along with 0.5 M hydrochloric acid to a pH of 9. This suspension was kept at 80°C for 1 day, then cooled to room temperature to obtain a hollow silica precursor dispersion.

[0108] "Filtration, Washing, Drying, and Calcination" The entire hollow silica precursor dispersion was neutralized to pH 2 with 2M hydrochloric acid, and then filtered using quantitative filter paper 5C. After that, 350 ml of ion-exchanged water at 80°C was added and the mixture was pressure filtered again to wash the hollow silica cake. The filtered cake was dried under a nitrogen atmosphere at 100°C for 1 hour, followed by 400°C for 2 hours (heating rate 10°C / min) to remove organic components and obtain the 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 and obtain hollow silica particles.

[0109] "Preparation of Dispersion 1" 40 g of the obtained hollow silica particles and 140 ml of methyl ethyl ketone (MEK) were placed in a 250 ml poly bottle (30 vol% hollow silica particles, 70 vol% MEK), and stirred at 30 rpm for 2 hours using a medialess dispersion device, the Mix Rotor. Furthermore, the obtained mixture was dispersed for 3 minutes at a peripheral speed of 2 m / s under non-pressurized conditions using a media-type dispersion device, the Bead Mill (IMEX "RMB II" type, 300 ml vessel). Zirconia beads with a diameter of Φ2 mm were used as dispersion beads, with a bead filling rate of 50%. The obtained slurry was passed through a nylon mesh with a mesh opening of 20 μm to obtain a silica particle dispersion with a solid content of 20 mass%.

[0110] (Example 2) The procedure was carried out under the same conditions as in Example 1, except that the amount of EO-PO-EO block copolymer (ADEKA's "Pluronic F68") added was changed to 2 g, and the amount of sorbitanic acid monooleate (Sanyo Chemical's "Ionet S-80") added was changed to 2 g to produce hollow silica particles.

[0111] (Example 3) The procedure was carried out under the same conditions as in Example 1, except that the obtained hollow silica precursor was calcined at 800°C for 1 hour (heating time 10°C / min) to produce hollow silica particles.

[0112] (Example 4) Using the hollow silica particles prepared in Example 1, a silica particle dispersion was prepared according to "Preparation of Dispersion 2" below. "Preparation of Dispersion 2" 40 g of the hollow silica particles obtained in Example 1 and 140 ml of methyl ethyl ketone (MEK) were placed in a 250 ml poly bottle (30 vol% hollow silica particles, 70 vol% MEK), and stirred at 30 rpm for 2 hours using a media-less dispersion device, a Mix Rotor. The resulting mixture was dispersed for 3 minutes at a peripheral speed of 2 m / s under non-pressurized conditions using a media-type dispersion device, a bead mill (IMEX "RMB II" type, 300 ml vessel). Zirconia beads with a diameter of Φ0.1 mm were used as dispersion beads, with a bead filling rate of 50%. The obtained slurry was passed through a nylon mesh with a mesh opening of 20 μm to obtain a silica particle dispersion with a solid content of 20 mass%.

[0113] (Example 5) The procedure was carried out under the same conditions as in Example 1, except that 40 g of hollow silica particles, 140 ml of methyl ethyl ketone (MEK), and 0.040 g of DYSPERBY K-161 (manufactured by Big Chemie) were placed in a 250 ml poly bottle and stirred.

[0114] (Example 6) In "Preparation of Dispersion 2" of Example 4, the procedure was carried out under the same conditions as in Example 4, except that 40 g of hollow silica particles, 140 ml of methyl ethyl ketone (MEK), and 1 g of KBM-503 were placed in a 250 ml poly bottle and stirred.

[0115] (Example 7) Using the hollow silica particles prepared in Example 1, a silica particle dispersion was prepared according to "Preparation of Dispersion 3" below. "Preparation of Dispersion 3" 40 g of the hollow silica particles obtained in Example 1 and 140 ml of methyl ethyl ketone (MEK) were placed in a 250 ml poly bottle (30 vol% hollow silica particles, 70 vol% MEK), and stirred at 30 rpm for 2 hours using a media-less dispersion device, a Mix Rotor. The resulting mixture was dispersed for 60 minutes at a peripheral speed of 2 m / s under non-pressurized conditions using a media-type dispersion device, a bead mill (IMEX "RMB II" type, 300 ml vessel). Zirconia beads with a diameter of Φ2 mm were used as dispersion beads, with a bead filling rate of 50%. The obtained slurry was passed through a nylon mesh with a mesh opening of 20 μm to obtain a silica particle dispersion with a solid content of 20 mass%.

[0116] (Example 8) Using the hollow silica particles prepared in Example 1, a silica particle dispersion was prepared according to "Preparation of Dispersion 4" below. "Preparation of Dispersion 4" 40 g of the hollow silica particles obtained in Example 1 and 140 ml of methyl ethyl ketone (MEK) were placed in a 250 ml poly bottle (30 vol% hollow silica particles, 70 vol% MEK), and stirred at 30 rpm for 2 hours using a media-less dispersion device, a Mix Rotor. The resulting mixture was dispersed for 5 minutes at a peripheral speed of 4 m / s under non-pressurized conditions using a media-type dispersion device, a bead mill (IMEX "RMB II" type, 300 ml vessel). Zirconia beads with a diameter of Φ0.5 mm were used as dispersion beads, with a bead filling rate of 50%. The obtained slurry was passed through a nylon mesh with a mesh opening of 30 μm to obtain a silica particle dispersion with a solid content of 20 mass%.

[0117] (Example 9) Instead of hollow silica particles, solid silica particles (Admatex "SO-C2", deflagration silica with a median diameter of 0.5 μm) were used, and a silica dispersion was prepared according to "Preparation of Dispersion 1" in Example 1. However, in Example 9, the slurry was passed through an electroformed sieve with a mesh size of 30 μm.

[0118] (Example 10) Using the hollow silica particles prepared in Example 1, a silica particle dispersion was prepared according to "Preparation of Dispersion 5" below. "Preparation of Dispersion 5" 10 g of the hollow silica particles obtained in Example 1 and 200 ml of methyl ethyl ketone (MEK) were placed in a 250 ml poly bottle (7 vol% hollow silica particles, 93 vol% MEK), and stirred at 30 rpm for 2 hours using a medialess dispersion device, the Mix Rotor. The resulting mixture was ejected three times from a φ0.1 mm nozzle under pressurized conditions (pressure 50 MPa) using a wet micronization device (Sugino Machine Co., Ltd. "Starburst Mini", model number: HJP-25001). The obtained slurry was passed through an electroformed sieve with a mesh size of 10 μm to obtain a silica particle dispersion with a solid content of 6.2 mass%.

[0119] (Example 11) Using the hollow silica particles prepared in Example 1, a silica particle dispersion was prepared according to "Preparation of Dispersion 6" below. "Preparation of Dispersion 6" 40 g of the hollow silica particles obtained in Example 1 and 140 ml of methyl ethyl ketone (MEK) were placed in a 250 ml poly bottle (30 vol% hollow silica particles, 70 vol% MEK), and stirred at 30 rpm for 2 hours using a media-less dispersion device, a Mix Rotor. The resulting mixture was dispersed for 20 minutes at a peripheral speed of 8 m / s under non-pressurized conditions using a media-type dispersion device, a bead mill (IMEX "RMB II" type, 300 ml vessel). Zirconia beads with a diameter of Φ0.1 mm were used as dispersion beads, with a bead filling rate of 50%. The obtained slurry was passed through a nylon mesh with a mesh opening of 20 μm to obtain a silica particle dispersion with a solid content of 20 mass%.

[0120] The following measurements were performed on the silica particle dispersions of Examples 1 to 11. The results are shown in Table 1.

[0121] 1. The recovery rate was measured using measurement method I described above. 2. The pass rate was measured using measurement method II described above.

[0122] 3. Measurement of Average Particle Size (D50) The silica particle dispersion was dried at 200°C for 12 hours and then cooled to below 100°C to obtain silica particle (secondary particle) powder. The obtained silica particle powder was measured using a diffraction scattering particle size distribution analyzer (MT3300) manufactured by Microtrac-Bell, 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.

[0123] 4. Density Measurement Using a Dry Pycnometer The silica particle dispersion was dried at 200°C for 12 hours and then cooled to below 100°C to obtain silica particle (secondary particle) powder. The density of the silica particles obtained above was measured using a dry pycnometer (AccuPyc II 1340, 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; Purge filling pressure: 135 kPag; Number of cycles: 10; Cycle filling pressure: 135 kPag; Pressure equilibrium rate: 0.05 kPag / min

[0124] 5. Measurement of specific surface area: The silica particle dispersion was dried at 200°C for 12 hours, cooled to below 100°C, and measured from the silica particle (secondary particle) powder.

[0125] 6. Measurement of Sphericity: The silica particle dispersion was dried at 200°C for 12 hours, cooled to below 100°C, and measured from scanning electron microscope (SEM) images of the silica particle (secondary particle) powder.

[0126] 7. Viscosity of Silica Particle Dispersion The silica particle dispersion was concentrated using a rotary evaporator to obtain a concentrated dispersion with a silica particle solid content of 50% by volume. The concentrated dispersion was sprayed three times from a φ0.1 mm nozzle at a pressurized pressure of 50 MPa using a wet micronization device (Starburst Mini, model number: HJP-25001, manufactured by Sugino Machine Co., Ltd.). The obtained slurry was adjusted to 25°C, and its viscosity was measured for 30 seconds at a shear rate of 1 rpm using a rotary rheometer (e.g., Modular Rheometer PhysicaMCR-301, manufactured by Anton Paar, Inc.), and the viscosity at 30 seconds was determined.

[0127] 8. Measurement of the relative permittivity and average linear expansion coefficient of the resin composition 12.5 parts by mass of polyphenylene ether resin, 12.5 parts by mass of low dielectric resin (JSR Corporation's "HC-G0037"), 50 parts by mass of butadiene-styrene random copolymer, 0.75 parts by mass of α,α'-di(t-butylperoxy)diisopropylbenzene, a silica particle dispersion in a quantity such that the solid content of silica particles is 40% by volume of the total, and 10 parts by mass of toluene were placed in a rotary-orbit mixer (Thinky Corporation's "Awatori Rentaro ARE-310") and mixed at 2000 rpm for 30 minutes to obtain a resin composition. The obtained resin composition was vacuum-dried at 120°C for 1 hour. 5 g was taken and placed in a 0.3 mm thick x 80 mm square mold. Low-profile copper foil (Mitsui Mining & Smelting Co., Ltd. "3EC-M3-V-18", thickness: 18 μm, Rz: 3.5 μm) was laminated on the top and bottom. The resulting laminate was heated to 200°C at a heating rate of 5°C / min and held at a pressure of 10 MPa for 120 minutes to heat-molde and obtain a resin-coated metal substrate. The obtained resin-coated metal substrate was etched with an etching solution (Sunhayato Corporation "H-1000A"), dried in a 100°C oven for 1 hour, and then the relative permittivity at a frequency of 10 GHz was measured using a split-post dielectric resonator (SPDR) (Agilent Technologies). Furthermore, the etched substrate was cut, and the coefficient of linear expansion in the Z direction (z-CTE) was measured between 50°C and 100°C in accordance with IPC-TM-650 2.4.24, and its average value was calculated.

[0128] 9. Measurement of Surface Roughness Rz The resin composition prepared in "8. Measurement of Relative Permittivity and Average Linear Expansion Coefficient of Resin Composition" was vacuum-dried at 120°C for 1 hour. 3 g was then taken and placed in a 0.1 mm thick x 80 mm square mold. It was vacuum-pressed at 200°C and a surface pressure of 10 MPa for 1 hour to obtain a plate-shaped molded body. The surface roughness Rz (μm) of the plate-shaped molded body was measured using a contact-type surface roughness meter (SURFCOM NEX001, manufactured by Tokyo Seimitsu Co., Ltd.).

[0129]

[0130] Examples 1 to 8 showed a relative permittivity of 3.0 or less and an average coefficient of linear expansion (z-CTE) of 50 to 60, demonstrating that both low relative permittivity and low thermal expansion coefficient were achieved. In contrast, Example 9 was a comparative example using solid silica particles, resulting in a higher relative permittivity. Example 10 showed a higher average coefficient of linear expansion, and Example 11 showed high relative permittivity and high average coefficient of linear expansion.

[0131] 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 without departing from the spirit and scope of the invention. This application is based on Japanese Patent Application No. 2024-208728, filed on 29 November 2024, the contents of which are incorporated herein by reference.

Claims

1. A silica particle dispersion containing a solvent and 5% by volume or more of hollow silica particles, wherein the recovery rate of silica solids measured by the following measurement method I is 35% or less. (Measurement method I) The silica particle dispersion is adjusted to have a silica content of 2% by mass to obtain a dispersion for measurement. The dispersion for measurement is stirred at a rotation speed of 5000 rpm for 10 minutes, decanted, and evaporated to dryness. Let W1 be the mass of the solids obtained, and W be the mass of the dispersion for measurement. The recovery rate of the silica solids is calculated using the following formula (1). Recovery rate of silica solids (%) = W1 / W × 100 ... (1) 2. The silica particle dispersion according to claim 1, wherein the pass rate measured by the measurement method II below is 50% or more. (Measurement method II) The silica particle dispersion is filtered through a filter with a mesh size of 30 μm, and the pass rate is determined by the following formula (2), with R1 being the dry mass of the filtrate and R2 being the mass of the evaporated dry filtrate. Pass rate (%) = R2 / (R1 + R2) × 100 ... (2) 3. The silica particle dispersion according to claim 1, wherein the recovery rate is 0.1 to 35%.

4. The silica particle dispersion according to claim 1, comprising 10 to 60 volume% of the hollow silica particles.

5. The particle density of the hollow silica particles, as determined by a dry pycnometer using argon gas, is 0.30 to 0.90 g / cm³. ３ The silica particle dispersion according to claim 1.

6. The BET specific surface area of ​​the hollow silica particles is 1 to 100 m². ２ A silica particle dispersion according to claim 1, wherein the amount is / g.

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

8. The silica particle dispersion according to claim 1, further comprising a silane compound, wherein the silane compound has 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 methacrylic group, and an epoxy group.

9. The silica particle dispersion according to claim 1, further comprising an organic thixotrope.

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

11. A silica particle dispersion according to claim 1, used for mixing with a resin.

12. A method for producing a silica particle dispersion according to any one of claims 1 to 11, comprising dispersing a hollow silica particle powder and a solvent in a medialess dispersion device, and further dispersing them under non-pressurized conditions in a media-type dispersion device.

13. A resin composition comprising a silica particle dispersion and a resin according to any one of claims 1 to 11.

14. The resin composition according to claim 13, wherein the resin content is 10 to 60% by mass.

15. The resin composition according to claim 13, wherein the content of the hollow silica particles is 10 to 60% by volume.

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