Silica dispersion and curable composition

Abstract

The purpose of the present invention is to provide: a silica dispersion and a curable composition which have excellent dispersibility; and a curable composition preparation method by which a curable composition excellent in dispersibility can be prepared.　The silica dispersion comprises: silica particles having a median diameter d50 of 0.1-10.0 μm; at least one dispersant having an oxyalkylene group and selected from the group consisting of carboxylic acid esters, sulfuric acid esters, phosphoric acid esters, phosphorous acid esters, and phosphonic acid esters; and an organic solvent.

Description

Silica dispersion and curable composition

[0001] This disclosure relates to silica dispersions and curable compositions.

[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.

[0003] Semiconductor materials containing low-dielectric resins and silica particles are obtained by mixing a varnish (solution) of the low-dielectric resin with silica particles. However, if the silica particles are mixed as dry powder, aggregation may occur during mixing. Therefore, a method is sometimes employed in which the silica particles are dispersed in a solvent and mixed as a silica dispersion. Various silica dispersions and slurries containing such dispersions have been proposed.

[0004] Patent Document 1 describes a particle size of 100 nm to 2000 nm or a specific surface area of ​​2 m². ２ / g ~ 35m ２ The amount of water generated when heated at 200°C is per gram, and the amount of water generated per 1 m² of surface area. ２ A slurry for electronic materials is described, comprising silica particles surface-treated with a silane compound and having a concentration of 40 ppm or less per particle, and a liquid dispersion medium that substantially does not contain water.

[0005] Patent Document 2 describes a solution comprising spherical silica particles and a solvent, wherein the median diameter d50 of the spherical silica particles is 0.5 to 20 μm, and the specific surface area A (m²) of the spherical silica particles is 0.5 to 20 μm. ２ The product A × d50 of ( / g) and the median diameter d50 (μm) is 2.7 to 5.0 μm·m ２ A silica dispersion liquid at a concentration of / g is listed.

[0006] Patent Document 3 describes a silica particle dispersion containing hollow silica particles and a solvent, wherein the average particle size of the hollow silica particles is in the range of 0.2 to 10 μm.

[0007] Japanese Patent Publication No. 2020-097498, International Publication No. 2023 / 218949, International Publication No. 2023 / 218948

[0008] Although various silica dispersions have been proposed, there are still problems in maintaining the physical properties of silica dispersions at a high level.

[0009] In view of the above problems, an object of the present disclosure is to provide a silica dispersion and a curable composition excellent in dispersibility, and a method for producing a curable composition capable of preparing a curable composition excellent in dispersibility.

[0010] The present disclosure includes the following aspects. [1] A silica dispersion comprising silica particles having a median diameter d50 of 0.1 to 10.0 µm, at least one dispersant selected from the group consisting of carboxylic acid esters, sulfate esters, phosphate esters, phosphite esters and phosphonate esters having an oxyalkylene group, and an organic solvent. [2] The silica particles have a specific surface area S (m ２ / g) and a median diameter d50 (µm), the product S×d50 is 2.7 to 10.0 µm·m ２ / g, the silica dispersion according to [1]. [3] The silica dispersion according to [1] or [2], wherein the content of the silica particles is 30 to 75% by mass. [4] The silica particles have a particle density of 0.35 to 1.00 g / cm ３ determined by density measurement using a dry pycnometer with argon gas, the silica dispersion according to [1]. [5] The silica dispersion according to [1] or [4], wherein the content of the silica particles is 10 to 40% by mass. [6] The silica dispersion according to any one of [1] to [5], wherein the dispersant is at least one compound selected from the group consisting of carboxylic acid esters and phosphate esters having an oxyalkylene group. [7] The silica dispersion according to any one of [1] to [6], wherein the dispersant comprises at least one selected from the group consisting of an ester of an adduct of a polyhydric alcohol and an oxyalkylene, and an oxyalkylene alkyl ether phosphate. [8] The silica dispersion according to any one of [1] to [7], wherein the dispersant comprises a compound represented by the following formula (1). (R １１ O) ３ P=O ...(1) provided that, R １１Each is independently a hydrogen atom or a group represented by the following formula (1a), and at least one of them is a group represented by the following formula (1a), R １２ (OR １３ ) ｎ１ - * ... (1a) R １２ is a hydrogen atom or an alkyl group, OR １３ Each is independently an oxyalkylene group or an oxyalkylene carbonyl group, n1 is an integer from 1 to 100, and * represents the bond position. [9] A silica dispersion according to any one of [1] to [8], wherein the dispersant comprises a compound represented by the following formula (2). {R ２１ (OR ２２ ) ｎ２ -} ｍ１ Q(-C(=O)-R ２３ ) ｍ２ …(2) However, Q is a residue obtained by removing hydrogen atoms from (m1 + m2) hydroxyl groups of a polyhydric alcohol, and R ２１ Each of these is independently a hydrogen atom, or R ２３ -C (=O) - * and OR ２２ Each of these is independently an oxyalkylene group or an oxyalkylene carbonyl group, and R ２３ Each is independently an alkyl group, n2 is an integer from 1 to 100, m1 is an integer from 1 to 4, m2 is an integer from 0 to 3, and * represents the bond position.

[10] A silica dispersion according to any one of [1] to [9], wherein the content of the dispersant is less than 5% by mass.

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

[10] , wherein the viscosity at 25°C is 1 to 500 mPa·s.

[12] A silica dispersion according to any one of [1] to

[11] , wherein the organic solvent is a nonpolar solvent.

[13] A silica dispersion according to any one of [1] to

[12] , wherein the total content of the silica particles and the organic solvent is 90% by mass or more.

[14] A curable composition comprising a silica dispersion according to any one of [1] to

[13] and a thermosetting resin.

[0011] This disclosure provides a silica dispersion with excellent dispersibility, a curable composition, and a method for producing a curable composition capable of preparing a curable composition with excellent dispersibility.

[0012] Embodiments of the present disclosure will be described below, but the present invention is not limited by the examples in the following description. Embodiments of the present disclosure are not limited to the embodiments described below. In this disclosure, the "~" indicating a numerical range means that the numbers written before and after it are included as the lower and upper limits. In this disclosure, "mass" is synonymous with "weight". In this disclosure, if there are multiple identical symbols in a single chemical formula, such identical symbols may have the same structure or may have different structures within a defined range.

[0013] <Silica Dispersion> The silica dispersion of this disclosure comprises silica particles having a median diameter d50 (μm) of 0.1 to 10.0 μm, at least one dispersant (hereinafter also referred to as "the dispersant") selected from the group consisting of carboxylic acid esters, sulfate esters, phosphate esters, phosphite esters, and phosphonic acid esters having an oxyalkylene group, and an organic solvent.

[0014] A first form of the silica dispersion in this disclosure is a specific surface area S (m²). ２ The product S × d50 (saturation) of the amount (per g) and the median diameter d50 (μm) is 2.7 to 10.0 μm·m ２ One possible form is one comprising silica particles in a quantity of / g, the dispersant, and an organic solvent. Preferably, the silica particle content is 30 to 75% by mass.

[0015] While the above-mentioned specific silica particles exhibit excellent electrical properties, this also meant that they sometimes failed to exhibit sufficient dispersibility in liquids. Specifically, these specific silica particles can be considered as ranging from perfectly solid and spherical silica particles with a theoretical S×d50 value of 2.7 to highly solid and spherical silica particles with a median diameter ranging from sub-μm to several μm. Therefore, due to the true density of silica, these silica particles tend to settle easily in dispersions, and aggregation between particles is also likely to occur. The silica dispersion of this disclosure contains a dispersant which is a specific ester having an oxyalkylene group. Such a dispersant has a balanced affinity for both the dispersion medium and the silica particles due to the appropriate polarity derived from the ester structure and the action of the oxyalkylene group, while intermolecular interactions between dispersants are suppressed. Therefore, in a silica dispersion containing this dispersant, the adsorption of the dispersant onto the silica particles is promoted, and by coating their surface, the dispersion of the silica particles in liquid is promoted. Furthermore, aggregation of dispersants is suppressed, and their influence on the physical properties of the dispersion, such as viscosity and thixotropy, is minimized. As a result, not only is the dispersibility of silica particles in the silica dispersion excellent, but the particle dispersibility in the curable composition obtained by mixing the silica dispersion with the resin described later is also considered to be excellent.

[0016] A second form of the silica dispersion of this disclosure is one in which the particle density, as determined by density measurement using a dry pycnometer with argon gas, is 0.35 to 1.00 g / cm³. ３ One possible form is that which comprises silica particles, the dispersant, and an organic solvent. The silica particle content is 10 to 40% by mass.

[0017] The specific silica particles described above have a relatively low density and consequently a small specific surface area, which sometimes prevents them from exhibiting sufficient dispersibility in liquid. Furthermore, these silica particles can be considered to have a certain void or hollow structure within them, making them prone to breakage under shear conditions. For example, when such a silica dispersion is mixed with other materials, such as resins (described later), the silica particles tend to break, preventing their properties from being fully realized. The silica dispersion of this disclosure contains a dispersant that is a specific ester having an oxyalkylene group. This dispersant, due to its moderate polarity derived from the ester structure and the action of the oxyalkylene group, has a balanced affinity for both the dispersion medium and the silica particles, while suppressing intermolecular interactions between the dispersants. Therefore, in a silica dispersion containing this dispersant, the adsorption of the dispersant onto the silica particles is promoted, coating their surface and thereby promoting the dispersion of the silica particles in liquid. Additionally, aggregation of the dispersants is suppressed, and their influence on the viscosity and thixotropy of the dispersion is reduced. As a result, not only is the dispersibility of silica particles in the silica dispersion excellent, but the particle dispersibility in the curable composition obtained by mixing the silica dispersion with the resin described later is also considered to be excellent. Furthermore, since the shear required for dispersion can be suppressed, damage to silica particles in the composition can also be suppressed, making it easier to improve physical properties such as electrical properties.

[0018] The silica dispersion of this disclosure contains at least silica particles, a dispersant, and an organic solvent, and may contain other components as needed. The components that may be included in this silica dispersion are described below.

[0019] (Silica particles) In the first form, silica particles have a specific surface area S (m²). ２ The product S × d50 (saturation) of the amount (per g) and the median diameter d50 (μm) is 2.7 to 10.0 μm·m ２ It is in units of / g. The value of S × d50 is 10.0 μm·m ２ If the value is less than / g, the specific surface area per particle size decreases, and the dielectric loss tangent can be reduced. S × d50 is 8.0 μm·m ２ Preferably less than or equal to 7.0 μm·m２ More preferably less than or equal to 6.0 μm·m ２ A value of 5.0 μm·m or less is even more preferable. ２ A value of less than or equal to / g is particularly preferred. Note that the theoretical value of S×d50 is 2.7 [specific surface area = 6 / (true density of silica 2.2 (g / m³)]. ３ [Derived from () × median diameter d50 (μm))], and values ​​lower than this are practically impossible to achieve.

[0020] The physical properties of the silica particles in the first form can be confirmed by drying the silica dispersion to obtain powdered silica particles. The median diameter d50 is determined using a laser diffraction particle size distribution analyzer (e.g., Microtrac-Bell "MT3300EXII"). The specific surface area is determined by the BET method based on nitrogen adsorption using a specific surface area and pore size distribution analyzer (e.g., Microtrac-Bell "BELSORP-miniII", Micromeritic "Tristar II", etc.).

[0021] In the first embodiment, the median diameter d50 (μm) of the silica particles is 0.1 to 10.0 μm. When the median diameter d50 is within the above range, the dispersion and curable composition have a viscosity that is easy to handle. Furthermore, a curable composition containing silica particles with a median diameter d50 within the above range is less prone to granulation during coating, and therefore exhibits excellent peel strength. From the viewpoint of further improving dispersibility and peel strength, the median diameter d50 is preferably 0.2 μm or more, more preferably 0.5 μm or more, and even more preferably 1 μm. Furthermore, from the viewpoint of further improving peel strength, the median diameter d50 is preferably 8 μm or less, and more preferably 5 μm or less.

[0022] The specific surface area S of silica particles in the first form is 0.5 to 60 m². ２ A range of / g is preferred. The specific surface area is 0.5 m². ２ When the silica content is 60 m² or higher, there is sufficient contact with the resin when the silica particles are incorporated into the resin composition, resulting in good compatibility with the resin and excellent peel strength when used as a coating film. ２ If the value is less than or equal to / g, the dielectric loss tangent can be reduced and the dispersibility is improved. From the viewpoint of peel strength, the specific surface area S is 0.6 m². ２Preferably 0.8 m ２ More preferably 1.0 m ２ A value of 50 m² or more is even more preferable. Furthermore, from the viewpoint of dispersibility, the specific surface area S is 50 m². ２ It is more preferable to have a value of 40m or less. ２ It is even more preferable to be less than / g, and 10m ２ A value of less than / g is particularly preferred, and 5m ２ A value of less than or equal to / g is particularly preferred.

[0023] The shape of the silica particles in the first embodiment can be appropriately selected depending on the application of the dispersion, for example, spherical, ellipsoidal, or polyhedral shapes that approximate a sphere. From the viewpoint of low dielectric loss tangent, a spherical shape is preferred, and a sphericity of 0.75 to 1.0 is preferred. Using spherical silica particles with a sphericity of 0.75 or higher provides excellent dispersibility. Furthermore, the curable composition containing these spherical silica particles exhibits excellent peel strength when formed into a cured coating film. From the viewpoint of further improving dispersibility and peel strength, the sphericity of the silica particles is preferably 0.90 or higher, more preferably 0.93 or higher, and the closer to 1.0, the better. "Sphericity" is expressed as the average value obtained by measuring the maximum diameter (DL) and the minor axis (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).

[0024] In the first form, the silica particles preferably have a viscosity of 5000 mPa·s or less, as measured by the following measurement method. [Measurement Method] A silica dispersion is dried to obtain powdered silica particles. Eight parts by mass of the obtained powdered silica particles are mixed with six parts by mass of boiled linseed oil, and the mixture is kneaded at 2000 rpm for three minutes. The resulting mixture is measured using a rotary rheometer at 25°C and a shear rate of 1 s. －１ Measure for 30 seconds and determine the viscosity at the 30-second mark.

[0025] If the viscosity of the compound determined by the above measurement method is 5000 mPa·s or less, the silica particles are dense, and the curable composition containing the silica particles has excellent peel strength. Furthermore, since the amount of dispersion medium used in the dispersion liquid and curable composition can be reduced, the drying speed is increased during film formation, etc., and productivity can be improved. The viscosity of the compound is more preferably 4000 mPa·s or less, and even more preferably 3500 mPa·s or less. The lower limit of the viscosity of the compound is not particularly limited, as a lower viscosity improves the coatability of the curable composition and improves productivity.

[0026] In the first embodiment, the silica particles preferably have a dielectric loss tangent of 0.0020 or less in powder form at a frequency of 1 GHz, more preferably 0.0010 or less, and even more preferably 0.0008 or less. When the dielectric loss tangent of the silica particles at a frequency of 1 GHz is 0.0020 or less, an excellent dielectric loss suppression effect is obtained, resulting in substrates and sheets with improved high-frequency characteristics. The smaller the dielectric loss tangent, the more the transmission loss of the circuit is suppressed, so the lower limit is not particularly limited. The 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 resonator method.

[0027] 3746 cm⁻¹ originates from isolated silanol groups on the surface of silica particles in the first form. －１ The IR peak intensity in the vicinity is preferably 0.1 or less, more preferably 0.08 or less, and even more preferably 0.06 or less. An isolated silanol group is a silanol (Si-OH) group adsorbed onto silica particles that is not bound to water or other substances. The amount of isolated silanol (Si-OH) groups on the surface of the silica particles can be obtained by IR measurement. Specifically, the IR spectrum is measured at 800 cm⁻¹. －１ Standardized to 3800 cm －１ After aligning the baseline, 3746cm －１ The relative intensity of the nearby Si-OH peaks is determined. When there are many isolated silanol groups on the particle surface, dielectric loss tends to increase when the material mixed with resin is used in electronic applications, but the 3746 cm⁻¹ originates from the isolated silanol groups on the particle surface. －１If the IR peak intensity in the vicinity is 0.1 or less, dielectric loss can be reduced.

[0028] Furthermore, the 3300-3700 cm² originates from the bonded silanol groups on the surface of the silica particles in the first form. －１ The maximum IR peak intensity is preferably 0.2 or less, more preferably 0.17 or less, and even more preferably 0.15 or less. A bound silanol group is a silanol (Si-OH) group bound to water adsorbed on the silica particles or to silanol on the silica surface. The amount of bound silanol (Si-OH) groups on the silica particle surface can be obtained by IR measurement. Specifically, the IR spectrum is measured at 800 cm⁻¹. －１ Standardized to 3800 cm －１ After setting the baseline, 3300-3700 cm －１ The relative intensity of the bonded Si-OH peak is determined from the largest peak among those present. When there are many bonded silanol groups on the particle surface, dielectric loss tends to increase when the material mixed with the resin is used in electronic applications, but the 3300-3700 cm⁻¹ originates from the bonded silanol groups on the particle surface. －１ If the maximum IR peak intensity is 0.2 or less, dielectric loss can be reduced.

[0029] In the first embodiment, the silica particles are preferably non-porous particles. Non-porous particles reduce oil absorption, suppress the increase in viscosity in the resin, and decrease the amount of silanol groups on the surface of the silica particles, resulting in a smaller dielectric loss tangent. Specifically, the oil absorption is preferably 100 ml / 100 g or less, more preferably 70 ml / 100 g or less, and most preferably 50 ml / 100 g or less. The lower limit is not particularly limited, but it is practically difficult to reduce the oil absorption to 20 ml / 100 g or less.

[0030] Furthermore, the silica particles in the first form had a particle density of 1.00 g / cm³, determined by density measurement using a dry pycnometer with argon gas. ３The above is preferable. Density measurement using a dry pycnometer with argon gas can determine whether the silica particles are hollow or not. Argon has a larger molecular size than helium, and if the silica particles are dense, the argon cannot pass through them, allowing for the measurement of the actual particle density. Ar measurement particle density is 2.00 g / cm³. ３ If it is less than the true density of silica (approximately 2.2 g / cm³), the particle density will be less than the true density of silica. ３ Since it is smaller than ), it can be determined that there is a space inside the particle. The silica particle density is 1.00 g / cm³, considering the strength of the silica particles. ３ The above is preferable, and 1.50 g / cm³ is preferred. ３ The above is more preferable, 1.80 g / cm³ ３ The above is even more preferable, 2.00 g / cm³. ３ The above is particularly preferable. In other words, it is preferable that the silica particles are solid silica particles.

[0031] In the first form, silica particles are silica (SiO ２ The particles may consist only of ) and may contain other elements as needed. The silica particles preferably contain titanium (Ti) in the range of 30 to 1500 ppm, more preferably 100 to 1000 ppm, and even more preferably 100 to 500 ppm. Including 30 ppm or more of Ti can suppress the generation of fine powder due to cracking, and if the Ti content is 1500 ppm or less, the increase in specific surface area during silica particle production is suppressed, and the amount of silanol groups on the surface of the resulting silica particles is suppressed, and the dielectric loss tangent is reduced.

[0032] The silica particles in the first embodiment may contain other elements, to the extent that they do not hinder the effects of this embodiment. Examples of other elements include alkali metals such as Na and K, alkaline earth metals such as Mg and Ca, Al and Fe, etc. The content of alkali metals and alkaline earth metals among the above other elements is preferably 2000 ppm or less, more preferably 1000 ppm or less, and even more preferably 200 ppm or less, relative to the total amount of silica particles.

[0033] In the first embodiment, the silica particles may be surface-treated with a silane coupling agent. By treating the surface of the silica particles with a silane coupling agent, the amount of residual silanol groups on the surface is reduced, the surface becomes hydrophobic, moisture adsorption is suppressed and dielectric loss is improved, and when forming a curable composition, the affinity with the resin is improved, resulting in improved dispersibility and strength after film formation.

[0034] 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.

[0035] 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.

[0036] Specifically, silane coupling agents include aminosilane-based coupling agents such as aminopropylmethoxysilane, aminopropyltriethoxysilane, ureidopropyltriethoxysilane, N-phenylaminopropyltrimethoxysilane, N-2(aminoethyl)aminopropyltrimethoxysilane, glycidoxypropyltrimethoxysilane, glycidoxypropylmethyldiethoxysilane, glycidylbutyltrimethoxysilane, and (3,4-epoxycyclohexyl)ethyltrimethoxysilane. Epoxysilane coupling agents such as silanes, mercaptosilane coupling agents such as mercaptopropyltrimethoxysilane and mercaptopropyltriethoxysilane, silane coupling agents such as methyltrimethoxysilane, vinyltrimethoxysilane, octadecyltrimethoxysilane, phenyltrimethoxysilane, methacryloxypropyltrimethoxysilane, imidazolesilane, triazinesilane, p-styryltrimethoxysilane, 7-octenyltrimethoxysilane, 8-methacryloxyoctyltrimethoxysilane, CF ３ (CF ２ ) ７CH ２ CH ２ Si (OCH ３ ) ３ 、CF ３ (CF ２ ) ７ CH ２ CH ２ SiCS ３ 、CF ３ (CF ２ ) ７ CH ２ CH ２ Si (CH ３ )(OCH ３ ) 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 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 Examples include fluorine-containing silane coupling agents, organosilazane compounds such as hexamethyldisilazane, hexaphenyldisilazane, trisilazane, cyclotrisilazane, and 1,1,3,3,5,5-hexamethylcyclotrisilazane.

[0037] The amount of silane coupling agent attached is preferably 0.01 parts by mass or more, more preferably 0.02 parts by mass or more, even more preferably 0.10 parts by mass or more, more preferably 5 parts by mass or less, and even more preferably 2 parts by mass or less, per 100 parts by mass of silica particles.

[0038] The surface of silica particles being treated with a silane coupling agent can be confirmed by detecting peaks originating from substituents of the silane coupling agent using IR (irradiation contrast). Furthermore, the amount of silane coupling agent adhering to the surface can be measured by its carbon content.

[0039] In the first form of silica dispersion, the silica particle content is preferably 30 to 75% by mass. The silica dispersion of this embodiment exhibits excellent dispersibility even when the silica particle content is high, due to its combination with the dispersant described later. If the silica particle content is 30% by mass or more, the amount of silica dispersion used when preparing the curable composition can be reduced. If the silica particle content is 75% by mass or less, the viscosity of the dispersion is suppressed, resulting in excellent handling properties. The silica particle content in the silica dispersion is more preferably 40% by mass or more, even more preferably 45% by mass or more, and particularly preferably 50% by mass or more. Furthermore, the silica particle content in the silica dispersion is preferably less than 75% by mass, and more preferably 72% by mass or less.

[0040] In the second form, the silica particles have a particle density (hereinafter also referred to as Ar density) of 0.35 to 1.00 g / cm³, determined by density measurement using a dry pycnometer with argon gas. ３ The density is 0.35 g / cm³. ３ With the above density, cracking of silica particles is suppressed, and the difference in specific gravity with the resin does not become too large, thus improving the dispersibility of silica particles in the curable composition described later. ３ The following conditions make it easier to exhibit a dielectric constant reduction effect, and therefore it is preferable to use it as a material for electronic devices. The Ar density of silica particles is 0.38 g / cm³ from the viewpoint of particle strength. ３ The above is preferable, and 0.40 g / cm³ ３ The above is more preferable, 0.45 g / cm³ ３ The above is even more preferable, 0.50 g / cm³ ３ The above is particularly preferable. Furthermore, the Ar density of the silica particles is 0.95 g / cm³, which further reduces the dielectric constant. ３ The following is preferred: 0.90 g / cm³ ３ The following is more preferable: 0.85 g / cm³ ３ The following is even more preferable: 0.80 g / cm³ ３ The following are particularly preferable.

[0041] In the second embodiment, the morphology of the silica particles may, for example, be a shell layer (solid film) containing silica and hollow silica particles having a space formed inside the shell layer. The presence of a space inside the shell layer of the silica particles can be confirmed by transmission electron microscopy (TEM) or scanning electron microscopy (SEM) observation. In the case of SEM observation, the hollowness can be confirmed by observing a broken particle with a partial opening. The physical properties of the silica particles can be confirmed by drying the silica particle dispersion to obtain powdered silica particles. Note that the shell layer "contains silica" means that 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 the cross-section of a single primary particle is observed, the shell layer surrounds a single space. That is, one hollow silica particle has one large space and a shell layer surrounding it. When a silica particle has a structure in which it has a space inside the shell, the composition containing the silica particle has more space in the composition, and when used as an insulating layer for electronic equipment, the dielectric constant can be lowered.

[0042] Furthermore, the silica particles in the second form, as determined by density measurement using a dry pycnometer with helium gas, have a particle density (hereinafter also referred to as He density) of 2.00 to 2.30 g / cm³. ３ This is preferable. Since helium gas permeates through fine voids, a density corresponding to the true density of silica present in the internal space of the silica particles can be obtained. He density of 2.00 g / cm³ ３As described above, the silica particles are relatively dense, and the coating film of the curable composition mixed with the resin exhibits excellent peel strength. Furthermore, because the amount of residual silanol in the silica particles is reduced, the He density, which tends to decrease easily, is 2.30 g / cm³. ３ The following conditions allow for the silica particles to have internal spaces, making it easier to reduce their dielectric constant: The He density of the silica particles is 2.05 g / cm³. ３ The above is more preferable, specifically 2.10 g / cm³. ３ The above is even more preferable. Furthermore, the He density of the silica particles is 2.25 g / cm³. ３ The following is more preferable: 2.23 g / cm³ ３ The following are even more preferable.

[0043] The apparent density of silica particles in the second form can also be measured using a specific gravity bottle. The sample (silica particles) and organic solvent are placed in the specific gravity bottle and left to stand at 25°C for 48 hours to allow the organic solvent to permeate the silica particles before measurement. The results obtained by this method correspond to the results obtained by density measurement using a dry pycnometer with argon gas.

[0044] In the case of hollow silica particles, the apparent density can be adjusted by adjusting the primary particle size and the thickness of the shell layer. From the viewpoint of particle dispersibility, it is desirable that the density of the dispersion medium and the apparent density of the particles are close. The apparent density of silica particles is equal to the apparent density of the dispersion medium (e.g., organic solvent) (g / cm³). ３ A range of ±20% is preferred. The ratio (T / D) of the thickness T (nm) of the shell layer of hollow silica particles to the primary particle size D (nm) of the particles is preferably 0.01 to 0.3. If the ratio (T / D) is 0.01 or higher, the silica particles have excellent strength. If the ratio (T / D) is 0.3 or lower, the space within the shell layer is secured, and the properties due to the hollow shape can be exhibited. From the viewpoint of the strength of the silica particles, the above ratio (T / D) is more preferably 0.02 or higher, and even more preferably 0.03 or higher. Also, from the viewpoint of securing the space, the above ratio (T / D) is more preferably 0.2 or lower, and even more preferably 0.1 or lower. Here, the thickness of the shell layer can be measured by a transmission electron microscope (TEM).

[0045] The specific surface area S of silica particles in the second form is 1 to 60 m².２ A range of / g is preferred. Specific surface area of ​​1 m² ２ When the silica particle content is 60 m² or higher, there is sufficient contact with the resin when the silica particles are incorporated into the curable composition, resulting in good compatibility with the resin and excellent peel strength when formed into a coating film. ２ If the value is less than or equal to / g, the dielectric loss tangent can be reduced and the dispersibility is improved. From the viewpoint of peel strength, the specific surface area S is 2m ２ Preferably 5 m ２ More preferably 10 m ２ A value of 50 m² or more is even more preferable. Furthermore, from the viewpoint of dispersibility, the specific surface area S is 50 m². ２ It is more preferable to have a value of 40m or less. ２ It is even more preferable to be less than / g, and 10m ２ A value of less than / g is particularly preferred, and 5m ２ A value of less than or equal to / g is particularly preferred. Here, the specific surface area can be measured using a specific surface area measuring device (for example, "Tristar II 3020" manufactured by Shimadzu Corporation), after pre-treating the silica particles by drying them at 230°C until they reach 50 mTorr, and then measuring them using a multi-point method with nitrogen gas.

[0046] In the second form, the silica particles have an Ar density of A (g / cm³). ３ ) and the above specific surface area S (m ２ The product of (A × S) is between 1 and 120 m ２ / cm ３ It is preferable that this is the case. The above product (A × S) represents the specific surface area per unit volume of hollow silica particles. When the product (A × S) is 1 to 120 m ２ / cm ３ An insulating layer formed using a curable composition containing silica particles has a low dielectric constant, can suppress dielectric loss, and can provide a substrate suitable for high-frequency circuits. Furthermore, the above product (A × S) is 120 m ２ / cm ３ The following curable composition containing silica particles has a low specific surface area, resulting in relatively little contact with the resin and suppressed viscosity increase, thus keeping the dielectric loss tangent low. The above product (A × S) is 80 m ２ / cm ３ The following is preferable: 40m ２ / cm ３The following is more preferable: 20m ２ / cm ３ The following is even more preferable. Also, the above product (A × S) is 2m ２ / cm ３ The above is preferable, 2.5m ２ / cm ３ The above is more preferable, 3m ２ / cm ３ The above is even more preferable.

[0047] The shape of the silica particles in the second embodiment can be appropriately selected depending on the application of the dispersion, for example, spherical, ellipsoidal, or polyhedral shapes that approximate a sphere. From the viewpoint of low dielectric loss tangent, a spherical shape is preferred, and a sphericity of 0.75 to 1.0 is preferred. Using spherical silica particles with a sphericity of 0.75 or higher provides excellent dispersibility. Furthermore, the curable composition containing these spherical silica particles exhibits excellent peel strength when formed into a cured coating film. From the viewpoint of further improving dispersibility and peel strength, the sphericity of the silica particles is preferably 0.90 or higher, more preferably 0.93 or higher, and the closer to 1.0, the better. "Sphericity" is expressed as the average value obtained by measuring the maximum diameter (DL) and the minor axis (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).

[0048] In the second embodiment, the median diameter d50 (μm) of the silica particles is 0.1 to 10.0 μm. When the median diameter d50 is within the above range, the dispersion and curable composition have a viscosity that is easy to handle. Furthermore, a curable composition containing silica particles with a median diameter d50 within the above range is less prone to granulation during coating, and therefore exhibits excellent peel strength. From the viewpoint of further improving dispersibility and peel strength, a median diameter d50 of 0.2 μm or more is preferable, 0.5 μm or more is more preferable, and 1 μm is even more preferable. Also from the viewpoint of further improving peel strength, a median diameter d50 of 8 μm or less is preferable, and 5 μm or less is more preferable. Note that the silica particles may be dispersed in the dispersion as secondary particles. In this case, the particle size and median diameter d50 of the silica particles refer to the particle size and median diameter of the secondary particles. The particle size of the silica particles (particle size of secondary particles) is preferably measured by laser scattering in order to reflect the state in the dispersion.

[0049] In the second embodiment, the coarse particle size (d90) of the secondary silica particles is preferably 10 times or less, and more preferably 5 times or less, than the median diameter d50, from the viewpoint of production efficiency. Furthermore, the coarse particle size is preferably 1 time or more than the median diameter d50. In this case, grain separation is easily suppressed when the curable composition is formed into a film.

[0050] Furthermore, the size of the primary particles of the silica particles in the second embodiment is determined by directly observing their particle size (diameter) using SEM observation. The average primary particle size of the silica particles is preferably in the range of 50 nm to 10 μm. If the average primary particle size 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, making it difficult for the dielectric loss tangent to increase. Also, if the average primary particle size is 10 μm or less, it is easier to handle as a filler. From the viewpoint of manufacturing reproducibility, the average primary particle size of the silica particles in the second embodiment is more preferably 70 nm or more, and even more preferably 100 nm or more. Furthermore, the average primary particle size of the silica particles is more preferably 5 μm or less, and even more preferably 3 μm or less.

[0051] In the second form, the average primary particle size of silica particles is calculated by measuring the size of 100 primary particles from SEM images, aggregating these measurements to obtain a distribution of primary particle sizes, and then estimating the overall primary particle size distribution from this. This method allows for the direct measurement of the primary particle size of particles that are difficult to deaggregate.

[0052] In the second embodiment, it is preferable that 40% or more of the silica particles have a particle size within ±40% of the average primary particle size. A group of silica particles satisfying this condition has a relatively uniform particle size, making it less likely for shell defects to form in the silica particles. Furthermore, it is more preferable that 50% or more of the particles have a particle size within ±40% of the average primary particle size, even more preferable that 60% or more of the particles have a particle size within ±40% of the average primary particle size, and particularly preferable that 70% or more of the particles have a particle size within ±40% of the average primary particle size.

[0053] In the second form, hollow silica particles have internal spaces, allowing them to encapsulate substances. While the hollow silica particles of this invention have a dense shell layer that makes them resistant to solvent penetration, the presence of damaged particles allows solvents to penetrate. Therefore, the amount of oil absorbed changes depending on the proportion of damaged particles.

[0054] In the second form, the silica particles have a relatively low density and therefore contain internal spaces, which can encapsulate other substances. The oil absorption capacity of the silica particles in the second form is preferably 15 to 1300 mL / 100 g. If the oil absorption capacity is 15 mL / 100 g or more, the adhesion to the resin in the curable composition described later is excellent. If the oil absorption capacity is 1300 mL / 100 g or less, the increase in viscosity of the curable composition is suppressed, and when formed into a coating film, the peel strength is excellent. From the viewpoint of suppressing the increase in viscosity of the curable composition, the oil absorption capacity of the 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 extremely preferably 200 mL / 100 g or less. Furthermore, from the viewpoint of improving adhesion to the resin, the oil absorption capacity of the silica particles is more preferably 20 mL / 100 g or more.

[0055] In the second form, silica particles are silica (SiO ２The particles may consist only of ) and may contain other elements as needed. The silica particles in the second form preferably contain one or more metals M selected from the group consisting of Li, Na, K, Rb, Cs, Mg, Ca, Sr, and Ba. The metal M acts as a flux during calcination in the manufacturing process of the silica particles, and silica particles with a low specific surface area can be produced. The content of the metal M is preferably 50 ppm by mass or more and 1% by mass or less. If the content of metal M is 50 ppm by mass or more, silica particles with a low specific surface area and a low dielectric loss tangent can be obtained. If the content of metal M is 1% by mass or less, the silicate component in the silica particles is suppressed and the hygroscopicity (solvent absorption) is improved. The content of metal M in the silica particles is more preferably 100 ppm by mass or more, and even more preferably 150 ppm or more. Furthermore, the content of metal M in the silica particles is more preferably 5,000 ppm by mass or less, even more preferably 2,000 ppm by mass or less, and particularly preferably 1,000 ppm by mass or less.

[0056] Metal M can be measured by ICP emission spectrometry after removing silicon, the main component, by strongly heating silica particles with perchloric acid and hydrofluoric acid.

[0057] In the second form, the silica particles preferably have a viscosity of 20,000 mPa·s or less, as measured by the following measurement method. [Measurement Method] Mix 6 parts by mass of boiled linseed oil and (6 × A / 2.2) parts by mass of silica particles, knead at 2000 rpm for 3 minutes, and measure the viscosity of the resulting mixture using a rotary rheometer at 25°C and a shear rate of 1 s. －１ The measurement is taken for 30 seconds, and the viscosity at the 30-second mark is determined. However, A is the argon density A (g / cm³). ３ )

[0058] If the viscosity of the kneaded material determined by the above measurement method is 20,000 mPa·s or less, the amount of dispersion medium used in the dispersion liquid and curable composition can be reduced, thereby increasing the drying speed during film formation and improving productivity. 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 particularly preferably 4,000 mPa·s or less. The lower limit of the viscosity of the kneaded material is not particularly limited, as a lower viscosity improves the coatability when used as a curable composition.

[0059] In the second embodiment, the silica particles preferably have a relative permittivity of 1.3 to 5.0 at 1 GHz. A relative permittivity within this range at 1 GHz can achieve the low relative permittivity required for electronic equipment. A relative permittivity of 1.3 or higher is preferred, and 1.4 or higher is more preferred. Furthermore, a relative permittivity of 4.5 or lower at 1 GHz is more preferred, 4.0 or lower is even more preferred, 3.5 or lower is particularly preferred, 3.0 or lower is extremely preferred, and 2.5 or lower is most preferred.

[0060] Furthermore, the silica particles in the second embodiment preferably have a dielectric loss tangent of 0.0001 to 0.05 at 1 GHz. A dielectric loss tangent of 0.05 or less at 1 GHz can achieve the low dielectric constant required for electronic equipment. A dielectric loss tangent of 0.0002 or more at 1 GHz is more preferable, and 0.0003 or more is even more preferable. A dielectric loss tangent of 0.01 or less at 1 GHz is more preferable, 0.005 or less is even more preferable, 0.003 or less is even more preferable, 0.002 or less is particularly preferable, 0.0015 or less is extremely preferable, and 0.0010 or less is most preferable.

[0061] The pore volume of the silica particles in the second form is 0.2 cm³. ３ Preferably less than / g. Pore volume of 0.2 cm³. ３ If the amount is less than / g, water adsorption is suppressed, and the deterioration of dielectric loss 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.

[0062] In the second embodiment, the silica particles may be surface-treated with a silane coupling agent. By treating the surface of the silica particles with a silane coupling agent, the amount of residual silanol groups on the surface is reduced, the surface becomes hydrophobic, moisture adsorption is suppressed and dielectric loss is improved, and when forming a curable composition, the affinity with the resin is improved, resulting in improved dispersibility and strength after film formation.

[0063] 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.

[0064] Examples of silane coupling agents include the silane coupling agent in the second embodiment. 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, and more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less, per 100 parts by mass of silica particles.

[0065] The surface of silica particles being treated with a silane coupling agent can be confirmed by detecting peaks originating from substituents of the silane coupling agent using IR (irradiation contrast). Furthermore, the amount of silane coupling agent adhering to the surface can be measured by its carbon content.

[0066] In the second form of silica dispersion, the silica particle content is preferably 10 to 40% by mass. The silica dispersion of this embodiment exhibits excellent dispersibility even when the silica particle content is high, due to its combination with the dispersant described later. If the silica particle content is 10% by mass or more, the amount of silica dispersion used when preparing the curable composition can be reduced. If the silica particle content is 40% by mass or less, the viscosity of the dispersion is suppressed, resulting in excellent handling properties. The silica particle content in the silica dispersion is more preferably 10% by mass or more, even more preferably 15% by mass or more, and particularly preferably 20% by mass or more. Furthermore, the silica particle content in the silica dispersion is preferably 38% by mass or less, and more preferably 35% by mass or less.

[0067] (Dispersant) The silica dispersion of this disclosure contains at least one dispersant selected from the group consisting of carboxylic acid esters, sulfate esters, phosphate esters, phosphite esters, and phosphonic acid esters, which have an oxyalkylene group. Due to the oxyalkylene group of this dispersant, the dispersant has excellent compatibility with organic solvents and curable resins described later. As a result, aggregation of the dispersants is presumed to be suppressed. Furthermore, the ester structure of the dispersant is presumed to easily adsorb the dispersant onto silica particles. From these points, it is presumed that the dispersant is efficiently adsorbed onto silica particles with suppressed aggregation of the dispersants themselves, and that it is compatible with solvents and resins, thereby significantly improving the dispersibility of silica particles. Note that one type of dispersant may be used alone, or two or more types may be used in combination.

[0068] The above-mentioned oxyalkylene group may be present in the dispersant as one or more, or two or more may be linked together to form a polyoxyalkylene group (polyoxyalkylene chain). When there are two or more oxyalkylene groups, the multiple oxyalkylene groups may be the same or different. The alkylene groups constituting the oxyalkylene group may have branched chains and may have substituents such as oxo groups (=O). That is, the oxyalkylene group may be an oxyalkylene carbonyl group.

[0069] The dispersant may contain one or more ester portions selected from carboxylic acid esters, sulfate esters, phosphate esters, phosphite esters, and phosphonic acid esters. If there are two or more such ester portions, the esters may be the same or different. In order to suppress the increase in viscosity of the silica dispersion and improve the dispersibility of silica particles, the number of ester portions in the dispersant is preferably 1 to 3, more preferably 1 to 2, and preferably 1. Furthermore, in order to suppress the increase in viscosity of the silica dispersion and improve the dispersibility of silica particles, the ester portion is preferably a carboxylic acid ester, a phosphate ester, or a phosphite ester, and more preferably a carboxylic acid ester or a phosphate ester.

[0070] As a phosphate ester having an oxyalkylene group, oxyalkylene alkyl ether phosphate is preferred from the viewpoint of compatibility, dispersibility of silica particles, and suppression of viscosity of the dispersion, and the compound represented by the following formula (1) (hereinafter also referred to as compound (1)) is more preferred. (R １１ O) ３ P = O ... (1) where R １１ Each is independently a hydrogen atom or a group represented by the following formula (1a), and at least one of them is a group represented by the following formula (1a), R １２ (OR １３ ) ｎ１ - * ... (1a) R １２ is a hydrogen atom or an alkyl group, OR １３ Each of these is independently an oxyalkylene group or an oxyalkylene carbonyl group, n1 is an integer from 1 to 100, and * represents the bond position.

[0071] R １１ This is a hydrogen atom or a group represented by the above formula (1a) (hereinafter also referred to as group (1a)). From the viewpoint of improving the dispersibility of silica particles, the number of groups (1a) in one molecule is preferably 1 to 3, and more preferably 1 to 2. Compound (1) with 1 to 2 groups (1a) is presumed to be more easily adsorbed onto silica particles.

[0072] R １２ R is a hydrogen atom or an alkyl group. R is used to suppress the increase in viscosity of the silica dispersion and improve the dispersibility of silica particles. １２ Alkyl alkyl groups are preferred. These alkyl groups may be linear, branched, or have a ring structure. From the viewpoint of compatibility with organic solvents and resins, R １２ The alkyl group is preferably a linear or branched alkyl group, and more preferably a linear alkyl group. From the viewpoint of compatibility with organic solvents and resins, １２The number of carbon atoms in the alkyl group is preferably 1 to 60, more preferably 1 to 36, even more preferably 1 to 24, and particularly preferably 1 to 18. Specific examples of alkyl groups include methyl group, ethyl group, n-butyl group, tert-butyl group, n-hexyl group, cyclohexyl group, n-octyl group, n-dodecyl group (lauryl group), and n-octadecyl group (stearyl group).

[0073] OR １３ OR is an oxyalkylene group or an oxyalkylene carbonyl group. １３ The alkylene group contained may be linear or branched. From the viewpoint of compatibility with organic solvents and resins, the number of carbon atoms in the alkylene group is preferably 1 to 18, more preferably 1 to 12, even more preferably 1 to 6, and particularly preferably 2 to 4. A specific example of an oxyalkylene group is -OCH ２ -, -OCH ２ CH ２ -, -OCH ２ CH (CH ３ )-,-O(CH ２ ) ３ -, -O(CH ２ ) ４ -, -O(CH ２ ) ６ -, -OCH(CH ３ )CH(CH ３ Examples include -OC(=O)- and -OC(=O)CH. ２ -, -OC(=O)CH ２ CH ２ -, -OC(=O)CH ２ CH ２ CH ２ - are some examples. Also, if n1 is 2 or more, - OR １３ OR １３ - of "R" １３ O" may constitute an oxyalkylene carbonyl group. In this case, R １３ Specific examples of O include -C(=O)O- and -CH ２ C(=O)O-, -CH ２ CH ２ C(=O)O-, -CH ２ CH２ CH ２ Examples include C(=O)O-. From the standpoint of improving the dispersibility of silica particles, OR １３ The oxyalkylene group is preferred, and the oxyalkylene group having 1 to 6 carbon atoms is more preferred, -OCH ２ CH ２ - or - OCH ２ CH (CH ３ ) - is even more preferable.

[0074] n1 is an integer from 1 to 100. From the viewpoint of the dispersibility of silica particles, n1 is preferably 1 to 80, more preferably 1 to 60, even more preferably 1 to 40, and particularly preferably 2 to 20.

[0075] Furthermore, (OR １３ ) ｎ１ From the viewpoint of the dispersibility of silica particles, the polyoxyalkylene group is preferable, and a polyoxyalkylene group containing ethylene oxide and propylene oxide is more preferable.

[0076] As the carboxylic acid ester having the oxyalkylene group described above, from the viewpoint of compatibility, dispersibility of silica particles, and suppression of viscosity of the dispersion, the ester of the adduct of a polyhydric alcohol and an oxyalkylene is preferred, and the compound represented by the following formula (2) (hereinafter also referred to as compound (2)) is more preferred. {R ２１ (OR ２２ ) ｎ２ -} ｍ１ Q(-C(=O)-R ２３ ) ｍ２ …(2) However, Q is a residue obtained by removing hydrogen atoms from (m1 + m2) hydroxyl groups of a polyhydric alcohol, and R ２１ Each of these is independently a hydrogen atom, or R ２３ -C (=O) - * and OR ２２ Each of these is independently an oxyalkylene group or an oxyalkylene carbonyl group, and R ２３ Each of these is an alkyl group, n2 is an integer from 1 to 100, m1 is an integer from 1 to 4, m2 is an integer from 0 to 3, and * represents the bond position.

[0077] Q is a residue obtained by removing hydrogen atoms from (m1 + m2) hydroxyl groups of a polyhydric alcohol. Examples of polyhydric alcohols include aliphatic alcohols such as ethylene glycol, propylene glycol, and glycerin; sugar alcohols such as sorbitol, erythritol, pentaerythritol, xylitol, and mannitol; disaccharides such as saccharose, trehalose, isotrehalose, and isosaccharose; and trisaccharides such as gentianose, raffinose, meletitose, and planteose. Among these, non-reducing disaccharides or trisaccharides are preferred in terms of suppressing an increase in the viscosity of the silica dispersion and improving the dispersibility of silica particles, with saccharose, trehalose, gentianose, raffinose, and planteose being more preferred, saccharose or trehalose being even more preferred, and saccharose being particularly preferred.

[0078] R ２１ is a hydrogen atom, or R ２３ -C(=O)-*, and from the standpoint of silica particle dispersibility, at least one is R ２３ It is preferable that -C(=O)-*.

[0079] OR ２２ OR is an oxyalkylene group or an oxyalkylene carbonyl group. ２２ The oxyalkylene group and oxyalkylene carbonyl group in the OR １３ It is the same as in the case of R, and the preferred embodiment is also the same. ２３ The alkyl group in R １２ This is similar to the case in [the relevant section], and the preferred embodiment is also similar.

[0080] n2 is an integer between 1 and 100. From the viewpoint of the dispersibility of silica particles, n2 is preferably between 2 and 98, more preferably between 5 and 95, and even more preferably between 7 and 90. m2 is an integer between 0 and 3, preferably between 0 and 2, and more preferably between 0 and 1.

[0081] The dispersant may be obtained by synthesis or as a commercially available product. A method for synthesizing compound (1) is, for example, a method in which phosphoric acid and a dihydric alcohol are dehydrated and then added by addition polymerization of an alkylene oxide. A method for synthesizing compound (2) is to add polymerization of an alkylene oxide to a polyhydric alcohol and then esterify it with a carboxylic acid. A commercially available product of compound (1) is, for example, Antox EHD-400 (manufactured by Nippon Emulsifier Co., Ltd.). A commercially available product of compound (2) is, for example, SN Dispersant 9228 (manufactured by Sunopco Corporation).

[0082] In the silica dispersion, the dispersant content is less than 5% by mass. The silica dispersion of this embodiment exhibits excellent dispersibility even with a dispersant content of less than 5% by mass because the dispersant has excellent silica dispersion performance. From the viewpoint of improving dispersibility, the dispersant content is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, even more preferably 0.1% by mass or more, particularly preferably 0.5% by mass or more, and extremely preferably 1% by mass or more. Furthermore, from the viewpoint of the peel strength of the curable composition, the dispersant content is preferably 4.5% by mass or less, more preferably 4% by mass or less, particularly preferably 3% by mass or less, and extremely preferably less than 2% by mass.

[0083] (Organic solvent) The silica dispersion of this disclosure contains an organic solvent as a dispersion medium. The organic solvent can be arbitrarily selected depending on the application of the dispersion, and examples include hydrocarbons, alcohols, acetates, ketones, cellosolves, glycol ethers, chlorinated hydrocarbons, and amides. The solvent may be used alone or as a mixture of two or more solvents.

[0084] 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. Examples of amides include N,N-dimethylformamide, dimethylacetamide, and N-methyl-2-pyrrolidone. In this silica dispersion, a nonpolar solvent is preferred as the organic solvent. Examples of nonpolar solvents include the hydrocarbons mentioned above.

[0085] The organic 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, cyclohexanone, etc. are preferred.

[0086] Furthermore, when the silica dispersion of this disclosure is used as a curable composition as described later, a liquid main component may be used instead of, or in combination with, the above-mentioned organic solvent. Examples of liquid main components include epoxy resins, polyphenylene ether resins, polyester resins, polyimide resins, phenolic resins, ortho-divinylbenzene resins, and examples of curing agents include polyamine-based curing agents, acid anhydride-based curing agents, phenolic-based curing agents, activated ester-based curing agents, peroxides, and the like.

[0087] The organic solvent is preferably present in the silica dispersion in an amount of 20 to 70% by mass. When the solvent content is 20% by mass or more, the 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 70% by mass or less, it remains in liquid form and can be used in its dispersed state. The solvent content in the silica dispersion is more preferably 25% by mass or more. Furthermore, the organic solvent content is preferably 70% by mass or less, more preferably 65% ​​by mass or less, even more preferably 60% by mass or less, and particularly preferably 55% by mass or less.

[0088] Furthermore, the silica dispersion of this disclosure preferably contains 90% by mass or more, and more preferably 92% by mass or more, of silica particles and the organic solvent. This makes it possible to increase the content ratio of silica particles and curable resin in the curable composition described later, and to form a coating film with excellent peel strength.

[0089] (Optional components) The silica dispersion of this disclosure may contain other components as needed. Examples of optional components include other inorganic fillers such as alumina.

[0090] (Physical Properties of Silica Dispersion) The silica dispersion of this disclosure preferably has a viscosity of 1 to 500 mPa·s at 25°C. If the viscosity is 1 mPa·s or higher, sedimentation (floating) separation of silica particles can be prevented, and if it is 500 mPa·s or lower, the dispersion stability of silica is excellent. From the viewpoint of suppressing the separation of the silica dispersion, the viscosity of the silica dispersion is preferably 1.5 mPa·s or higher, and more preferably 2.0 mPa·s or higher. Furthermore, from the viewpoint of the dispersion stability of silica particles, the viscosity of the silica dispersion is preferably 400 mPa·s or lower, more preferably 200 mPa·s or lower, even more preferably 100 mPa·s or lower, particularly preferably 50 mPa·s or lower, and extremely preferably 25 mPa·s or lower. When the viscosity of the silica dispersion is within the specified range and sedimentation (floating) separation of silica particles is suppressed, the preparation of the curable composition described later becomes easier. The silica dispersion of this embodiment is obtained by dispersing silica particle powder in a solvent. Known silica particles can be used, for example, the silica particles described in International Publication No. 2023 / 218949 and International Publication No. 2023 / 218948.

[0091] (Preparation of Silica Dispersion) The silica dispersion of this disclosure can be prepared, for example, by mixing an organic solvent containing a dispersant with silica particles, dispersing the mixture, and classifying it as necessary to remove aggregates of silica particles. Dispersion of the mixture containing the solvent and silica particles can be performed using dispersion equipment used for pigment dispersion, etc. For example, mixers such as dispersers, homomixers, and planetary mixers, homogenizers (such as M-Technic's "Clearmix," PRIMIX's "Filmix," Silverson's "Abramix," etc.), paint conditioners (Red Devil), colloid mills (such as PUC's "PUC Colloid Mill," IKA's "Colloid Mill MK"), cone mills (such as IKA's "Corn Mill MKO"), ball mills, sand mills Examples include media-type dispersers such as dynomills (manufactured by Shinmaru Enterprises, Inc.), attritors, pearl mills (manufactured by Eirich, Inc. 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.The dispersion time should be set appropriately according to the dispersion equipment used to prevent particle breakdown, but it is preferably 0.5 to 60 minutes, more preferably 0.5 to 10 minutes, and even more preferably 0.5 to 5 minutes. After that, aggregates of silica particles that were not dispersed during the dispersion process are wet-classified. Wet classification can be done using sieves or centrifugal force. When using sieves, it is preferable to classify using sieves with a mesh size of 100 μm or less. As for the sieves, it is preferable to use metal with a dense lattice structure, such as electroformed sieves. After that, the solution may be diluted or concentrated as needed to adjust to an appropriate concentration. Concentration methods include vaporization concentration and solid-liquid separation. In addition, when preparing the silica dispersion, a silane coupling agent may be added to the mixture of organic solvent, dispersant, and silica particles.

[0092] The silica dispersion of this disclosure can be used as various fillers, and is particularly suitable as a filler for resin compositions used in the manufacture of 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. Specifically, the silica dispersion of this embodiment is expected to be applied to curable compositions, prepregs, metal foil-clad 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 reducing dielectric loss tangent, reducing transmission loss, reducing moisture absorption, and improving peel strength.

[0093] <Curable Composition> The curable composition of this disclosure is characterized by comprising the above-mentioned silica dispersion and a thermosetting resin. By using the above-mentioned silica dispersion, this curable composition exhibits excellent dispersibility of silica particles, is less prone to granular formation when a coating film is formed, and has excellent peel strength.

[0094] (Thermosetting Resin) The curable composition of this disclosure contains a thermosetting resin. One thermosetting resin may be used, or two or more may be used in combination. Examples of thermosetting resins include epoxy resins, polyphenylene ether resins, polyimide resins, phenolic resins, and ortho-divinylbenzene resins. From the viewpoint of adhesion, heat resistance, etc., the thermosetting resin is preferably an epoxy resin, a polyphenylene ether resin, or an ortho-divinylbenzene resin. The thermosetting resin is preferably a resin containing at least one selected from the group consisting of phenyl groups and phenylene groups.

[0095] Examples of epoxy resins include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, alicyclic epoxy resin, phenol novolac type epoxy resin, cresol novolac type epoxy resin, bisphenol A novolac type epoxy resin, diglycidyl ether derivatives of polyfunctional phenols, and diglycidyl ether derivatives of polyfunctional alcohols. The polyphenylene ether resin may be a modified polyphenylene ether or an unmodified polyphenylene ether, but from the viewpoint of adhesion, the modified polyphenylene ether is preferred. The modified polyphenylene ether has a polyphenylene ether chain or a substituent bonded to the end of the polyphenylene ether chain. The substituent is preferably a reactive group, and more preferably a vinyl group, a (meth)acryloyloxy group, or an epoxy group.

[0096] The hydrogen atoms of the phenylene group in the polyphenylene ether chain may be substituted with alkyl groups, alkenyl groups, alkynyl groups, formyl groups, alkylcarbonyl groups, alkenylcarbonyl groups, or alkynylcarbonyl groups.

[0097] From the viewpoint of dielectric properties and the like, the weight-average molecular weight of the thermosetting resin is preferably 1,000 to 7,000, more preferably 1,000 to 5,000, and even more preferably 1,000 to 3,000.

[0098] From the viewpoint of adhesion to metal substrate layers and the like provided in wiring boards such as prepregs obtained from the curable composition of this disclosure, the content of the curable resin relative to the total mass of the composition is preferably 10 to 40% by mass, more preferably 15 to 35% by mass, and even more preferably 20 to 30% by mass.

[0099] The curable composition of this disclosure may contain one or more curing accelerators. Examples of curing accelerators include triallyl isocyanurate compounds such as triallyl isocyanurate, polyfunctional acrylic compounds having two or more acryloyl or methacryloyl groups in the molecule, polyfunctional vinyl compounds having two or more vinyl groups in the molecule, and vinylbenzyl compounds such as styrene having a vinylbenzyl group in the molecule. The content of the curing accelerator per 100 parts by mass of thermosetting resin is preferably 10 to 100 parts by mass.

[0100] The curable composition of this disclosure may contain one or more plasticizers. Examples of plasticizers include butadiene styrene copolymer. The content of plasticizers per 100 parts by mass of thermosetting resin is preferably 10 to 50 parts by mass, and more preferably 20 to 40 parts by mass.

[0101] In addition to the above-mentioned components, the curable composition of this disclosure may further contain other components such as surfactants, thixotropic agents, pH adjusters, pH buffers, viscosity modifiers, defoamers, silane coupling agents, dehydrating agents, weathering agents, antioxidants, heat stabilizers, lubricants, antistatic agents, whitening agents, colorants, conductive materials, mold release agents, surface treatment agents, flame retardants, and various organic or inorganic fillers, to the extent that they do not impair the effects thereof.

[0102] (Method for producing a curable composition) The method for producing a curable composition according to the present disclosure comprises mixing a silica dispersion according to the present disclosure with a thermosetting resin. The method for producing a curable composition according to the present disclosure involves mixing a thermosetting resin with a silica dispersion having silica particles in a state with excellent dispersion performance due to the adsorption of a dispersant, so that a curable composition can be prepared while maintaining the excellent dispersibility of the silica particles. The mixing method is not particularly limited, and for example, the above-mentioned dispersing group may be used for mixing.

[0103] The curable composition according to this disclosure can be suitably used, for example, as a prepreg that can be processed into printed circuit boards, or as an electrical insulating layer for resin-coated metal substrates.

[0104] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples. Examples relating to the first embodiment and examples relating to the second embodiment are shown in order below. Note that each embodiment is independent.

[0105] (Examples relating to the first embodiment) <Components used> [Silica particles] Silica particles Aα: As a spherical silica precursor, 150 g of silica powder 1 (manufactured by AGC SI-TEC, Inc.: H-31, d50: 3.5 μm) produced by a wet process was packed into an alumina crucible, heated at an electric furnace temperature of 1200 °C for 1 hour, cooled to 25 °C, and ground in an agate mortar to obtain 100 g of silica particles. 1 g of 3-methacryloxypropyltrimethoxysilane and 50 ml of isopropanol were added and mixed, dried at 120 °C for 2 hours, and 43 g of toluene was added to the resulting 100 g of surface-treated silica particles. The mixture was then ejected 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.) to obtain a silica dispersion. The surface-treated silica particles in the dispersion are referred to as silica particle A. Silica particle Bα: SO-C2 manufactured by Admatex Co., Ltd. Silica particle Cα: FB-5SDC manufactured by Denka Co., Ltd. Silica particle Dα: FB-3SDC manufactured by Denka Co., Ltd. Silica particle Eα: As a spherical silica precursor, 15 g of silica powder 1 (manufactured by AGC SI-TEC Co., Ltd.: H-31, d50: 3.5 μm) produced by a wet process was packed into an alumina crucible, heated at an electric furnace temperature of 1200°C for 1 hour, cooled to 25°C, and ground in an agate mortar to obtain silica particles. Silica particle Fα: SP-01M manufactured by Tokuyama Co., Ltd. Silica particle Gα: YA050C manufactured by Admatex Co., Ltd.

[0106] The median diameter d50 and specific surface area S of each silica particle were determined using the BET method based on nitrogen adsorption, with a laser diffraction particle size distribution analyzer (MT3300EXII, Microtrac-Bell, Inc.) and a specific surface area / pore size distribution analyzer (BELSORP-miniII, Microtrac-Bell). The results are shown in Table 1.

[0107] [Organic solvents] Toluene (Tol): Boiling point 111°C Methyl ethyl ketone (MEK): Boiling point 80°C Cyclohexanone (CHN): Boiling point 156°C [Dispersants] Dispersant A: Phosphate ester dispersant having an oxyalkylene group B: Carboxylic acid ester dispersant having an oxyalkylene group C: Sulfate ester dispersant having an oxyalkylene group D: Phosphite ester dispersant having an oxyalkylene group E: Polyacrylic acid (a dispersant that does not fall under the dispersants of this embodiment) Dispersant A is Antox EHD-400 (trade name) manufactured by Nippon Emulsifier Co., Ltd. and corresponds to compound (1), and dispersant B is SN Dispersant 9228 (trade name) manufactured by Sunopco Corporation and corresponds to compound (2).

[0108] [Example 3α: Preparation of silica dispersion] 1 part by mass of dispersant A was dissolved in 29 parts by mass of toluene, and then 70 parts by mass of silica particles Aα were added to obtain the silica dispersion of Example 3.

[0109] [Examples 1α to 2α, 4α to 18α: Preparation of silica dispersions] Each silica dispersion was obtained in the same manner as in Example 3α, except that the components were changed as shown in Table 1.

[0110] <Settling Test> 10 ± 0.1 ml of the silica dispersions of Examples 1α to 18α above were filled into a 10 ml graduated cylinder conforming to JIS R3505 Class A standards. The cylinder was then covered with plastic wrap and aluminum foil, sealed, and left to stand for 7 ± 0.1 days in an environment of 25 ± 2°C and RH 50 ± 20%, protected from vibration and direct sunlight. The distance (mm) from the top of the 10 ml cylinder to the settling top (the point where the opposite side could no longer be seen) was measured.

[0111] <Viscosity> The viscosity of the silica dispersions of Examples 1α to 18α above was measured at 10 Hz using a B-type viscometer.

[0112] [Preparation of curable compositions, prepregs, and resin-coated metal substrates] 59 parts by mass of polyphenylene ether resin, 15 parts by mass of butadiene-styrene random copolymer, 25 parts by mass of triallyl isocyanurate, 1 part by mass of α,α'-di(t-butylperoxy)diisopropylbenzene, and each silica dispersion of Examples 1 to 18 were blended so that the silica content was 55 parts by mass. 30 parts by mass of toluene were added to a poly bottle, and a Φ20 mm alumina ball was added and mixed at 30 rpm for 12 hours. The alumina ball was then removed to obtain the curable compositions of Examples 1α to 18α.

[0113] Each curable composition was impregnated and coated onto IPC Spec 2116 glass cloth, and then heated and dried at 160°C for 4 minutes to obtain a prepreg. 18 μm thick copper foil (Mitsui Mining & Smelting Co., Ltd., HS1-VSP) was laminated to both sides of the prepreg, and then heated at 230°C and a pressure of 30 kg / cm². ２ The material was then heated and molded for 120 minutes to obtain a resin-coated metal substrate.

[0114] [Measurement of Peel Strength] In accordance with IPC-TM650-2.4.8, the peel strength between the prepreg and the copper foil with carrier was measured using a Tensilon universal tester (A&D Corporation, RTC-1250A). The measurement results are summarized in Table 1.

[0115] [Float Test] The copper foil on one side of the obtained resin-coated metal substrate was etched off and dried at 130°C for 2 hours. The resulting resin-coated single-sided metal material was then immersed in a solder bath at 288±5°C for 10 seconds, and the appearance of the resulting substrate was observed. A: No bubbles B: Bubble diameter 5 mm or less and 5 or fewer bubbles C: Bubble diameter greater than 5 mm or more than 5 bubbles

[0116]

[0117] As shown in Table 1, the silica dispersion according to the first embodiment exhibits excellent dispersibility of silica particles, and the resin composition prepared using this silica dispersion exhibits excellent peel strength.

[0118] (Examples relating to the second embodiment) [Production of silica particles Aβ] (1) Preparation of emulsion 4 g of EO-PO-EO block copolymer (Pluronic® F68, manufactured by ADEKA Corporation) 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 (Ionet S-80, manufactured by Sanyo Chemical Industries) 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 (LAB1000, manufactured by SMT Corporation) to prepare a fine emulsion with an emulsion diameter of 1 μm. The obtained fine emulsion was aged by standing at 40°C for 12 hours. EO stands for ethylene oxide and PO stands for propylene oxide.

[0119] (2) Add a diluted sodium silicate aqueous solution (SiO₂) to 1300 g of the emulsion after the first stage shell formation aging 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.

[0120] (3) Second stage shell formation The entire amount of 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 (SiO ２ Concentration 10.4% by mass, Na ２ 330 g of 3.6% by mass of 0 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 silica precursor dispersion.

[0121] (4) Preparation of silica particles Aβ The entire silica precursor dispersion was neutralized to pH 2 with 2M hydrochloric acid and then filtered using quantitative filter paper 5C. Then, 350 ml of ion-exchanged water at 80°C was added and the mixture was pressure filtered again to wash the 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 silica precursor. The obtained silica precursor was calcined at 1000°C for 1 hour (heating rate 10°C / min) to sinter the shell and obtain calcined silica particles.

[0122] (5) Surface treatment with silane coupling agent 10 g of the above-mentioned silica calcined particles, 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 poly bottle and stirred at 30 rpm for 2 hours using a mix rotor. The resulting mixture was heated at 80°C for 1 hour, then cooled, and the mixture was ejected 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 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% by mass. The silica particles after surface treatment are designated as silica particles Aβ.

[0123] [Silica Particles Bβ] Throughria 4110 (manufactured by JGC Catalysts & Chemicals, average primary particle size 60 nm) was vacuum dried at 200°C for 2 hours to obtain silica particles Bβ.

[0124] [Silica Particles Cβ] Silica particles Cβ were obtained in the same manner as in the production of silica particles Aβ, except that in (1) of the production of silica particles Aβ above, the amount of EO-PO-EO block copolymer added was changed to 10 g, sorbitanic acid monooleate was not used, the pressure was changed to 100 bar, and in (5) the electroformed sieve was changed to a mesh size of 15 μm.

[0125] [Silica particles Dβ] Glass Bubbles iM30K manufactured by 3M was used.

[0126] [Silica Particles Eβ] Silica particles Eβ were obtained in the same manner as in the production of silica particles Aβ, except that step (4) of the production of silica particles Aβ was changed from firing at 1000°C for 1 hour to firing at 700°C for 1 hour.

[0127] [Silica Particles Fβ] Silica particles Fβ were obtained by omitting (5) surface treatment with a silane coupling agent in the production of the above silica particles Aβ.

[0128] The median diameter d50 and specific surface area S of each silica particle were determined using the BET method based on nitrogen adsorption, with a laser diffraction particle size distribution analyzer (MT3300EXII, Microtrac-Bell, Inc.) and a specific surface area / pore size distribution analyzer (BELSORP-miniII, Microtrac-Bell). The Ar density of each silica particle was measured using a dry pycnometer with argon gas. The results are shown in Table 1.

[0129] [Organic solvents] Toluene (Tol): boiling point 111°C Methyl ethyl ketone (MEK): boiling point 80°C Cyclohexanone (CHN): boiling point 156°C [Dispersants] Dispersant A: Phosphate ester dispersant having an oxyalkylene group B: Carboxylic acid ester dispersant having an oxyalkylene group C: Sulfate ester dispersant having an oxyalkylene group D: Phosphite ester dispersant having an oxyalkylene group E: Polyacrylic acid (a dispersant that does not fall under the dispersants of this embodiment) Note that dispersant A is Antox EHD-400 (trade name) manufactured by Nippon Emulsifier Co., Ltd. and corresponds to compound (1), and dispersant B is SN Dispersant 9228 (trade name) manufactured by Sunopco Corporation and corresponds to compound (2).

[0130] [Example 3β: Preparation of silica dispersion] 1 part by mass of dispersant A was dissolved in 69 parts by mass of toluene, and then 30 parts by mass of silica particles Aβ were added to obtain the silica dispersion of Example 3β.

[0131] [Examples 1β to 2β, 4β to 17β: Preparation of silica dispersions] Except for changing each component as shown in Table 1 in Example 3β above, each silica dispersion was obtained in the same manner as in Example 3.

[0132] <Settling Test> 10 ± 0.1 ml of silica dispersions of Examples 1β to 17β were filled into a 10 ml graduated cylinder conforming to JIS R3505 Class A standards. The cylinder was then covered with plastic wrap and aluminum foil, sealed, and left to stand for 7 ± 0.1 days in an environment of 25 ± 2°C and RH 50 ± 20%, protected from vibration and direct sunlight. The distance (mm) from the top of the 10 ml cylinder to the settling top (the point where the opposite side is no longer visible) was measured.

[0133] <Viscosity> The viscosity of the silica dispersions of Examples 1β to 17β above was measured at 10 Hz using a B-type viscometer.

[0134] [Preparation of curable compositions, prepregs, and resin-coated metal substrates] 59 parts by mass of polyphenylene ether resin, 15 parts by mass of butadiene-styrene random copolymer, 25 parts by mass of triallyl isocyanurate, 1 part by mass of α,α'-di(t-butylperoxy)diisopropylbenzene, and 30 parts by mass of silica in each of the silica dispersions of Examples 1 to 18 were added to a poly bottle, 20 mm diameter alumina balls were added and mixed at 30 rpm for 12 hours, and the alumina balls were removed to obtain the curable compositions of Examples 1β to 17β.

[0135] Each curable composition was impregnated and coated onto IPC Spec 2116 glass cloth, and then heated and dried at 160°C for 4 minutes to obtain a prepreg. 18 μm thick copper foil (Mitsui Mining & Smelting Co., Ltd., HS1-VSP) was laminated to both sides of the prepreg, and then heated at 230°C and a pressure of 30 kg / cm². ２ The material was then heated and molded for 120 minutes to obtain a resin-coated metal substrate.

[0136] [Measurement of Peel Strength] In accordance with IPC-TM650-2.4.8, the peel strength between the prepreg and the copper foil with carrier was measured using a Tensilon universal tester (A&D Corporation, RTC-1250A). The measurement results are summarized in Table 1.

[0137] [Float Test] The copper foil on one side of the obtained resin-coated metal substrate was etched off and dried at 130°C for 2 hours. The resulting resin-coated single-sided metal material was then immersed in a solder bath at 288±5°C for 10 seconds, and the appearance of the resulting substrate was observed. A: No bubbles B: Bubble diameter 5 mm or less and 5 or fewer bubbles C: Bubble diameter greater than 5 mm or more than 5 bubbles

[0138]

[0139] As shown in Table 2, the silica dispersion according to the second form exhibits excellent dispersibility of silica particles, and the curable composition prepared using this silica dispersion exhibits excellent peel strength.

[0140] This application claims priority based on Japanese Patent Applications No. 2025-043257 and No. 2025-043258, filed on 18 March 2025, and incorporates all of their disclosures herein.

Claims

A silica dispersion comprising silica particles having a median diameter d50 of 0.1 to 10.0 μm, at least one dispersant selected from the group consisting of carboxylic acid esters, sulfate esters, phosphate esters, phosphite esters, and phosphonic acid esters having an oxyalkylene group, and an organic solvent. 　 The silica particles have a specific surface area S (m²). ２ The product S × d50 (saturation) of the amount (per g) and the median diameter d50 (μm) is 2.7 to 10.0 μm·m ２ A silica dispersion according to claim 1, wherein the silica particles are in a quantity of / g. 　 The silica dispersion according to claim 2, wherein the silica particle content is 30 to 75% by mass. 　 The silica particles, as determined by density measurement using a dry pycnometer with argon gas, have a particle density of 0.35 to 1.00 g / cm³. ３ A silica dispersion according to claim 1, wherein the silica particles are silica particles. 　 The silica dispersion according to claim 4, wherein the silica particle content is 10 to 40% by mass. 　 The silica dispersion according to claim 1, wherein the dispersant is at least one compound selected from the group consisting of carboxylic acid esters and phosphate esters having an oxyalkylene group. 　 The silica dispersion according to claim 1, wherein the dispersant comprises at least one selected from the group consisting of esters of polyhydric alcohols and oxyalkylene adducts and oxyalkylene alkyl ether phosphates. 　 The silica dispersion according to claim 1, wherein the dispersant comprises a compound represented by the following formula (1). (R １１ O) ３ P=O …(1) however, R １１ Each of these is independently a hydrogen atom or a group represented by the following formula (1a), and at least one of them is a group represented by the following formula (1a), R １２ (OR １３ ) ｎ１ -* …(1a) R １２ is a hydrogen atom or an alkyl group, OR １３ Each of these is independently an oxyalkylene group or an oxyalkylene carbonyl group. n1 is an integer between 1 and 100. * indicates the joining position. 　 The silica dispersion according to claim 1, wherein the dispersant comprises a compound represented by the following formula (2). {R ２１ (OR ２２ ) ｎ２ -} ｍ１ Q(-C(=O)-R ２３ ) ｍ２ …(2) however, Q is a residue obtained by removing hydrogen atoms from the (m1 + m2) hydroxyl groups of a polyhydric alcohol, and R ２１ Each of these is independently a hydrogen atom, or R ２３ -C (=O) - *, OR ２２ Each of these is independently an oxyalkylene group or an oxyalkylene carbonyl group. R ２３ Each of them is independently an alkyl group, n² is an integer between 1 and 100. m1 is an integer between 1 and 4. m2 is an integer between 0 and 3. * indicates the joining position. 　 The silica dispersion according to claim 1, wherein the content of the dispersant is less than 5% by mass. 　 The silica dispersion according to claim 1, wherein the viscosity at 25°C is 1 to 500 mPa·s. 　 The silica dispersion according to claim 1, wherein the organic solvent is a nonpolar solvent. 　 The silica dispersion according to claim 1, wherein the total content of the silica particles and the organic solvent is 90% by mass or more. 　 A curable composition comprising a silica dispersion according to any one of claims 1 to 13 and a thermosetting resin.

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