Hydrophobic low-loss-tangent silica sol and production method therefor

Abstract

[Problem] to provide silica particles having a loss tangent of less than 0.01 at 1 GHz and a hydrophobicity of 40% or greater, and a dispersion thereof. [Solution] Surface modified silica particles having a hydrophobicity of 40% or greater, said silica particles being characterized in that the average primary particle size is 5-500 nm and the loss tangent is less than 0.01 at 1 GHz.

Description

Hydrophobic low dielectric loss tangent silica sol and method for producing same

[0001] The present invention relates to hydrophobized silica particles having a low dielectric loss tangent, a dispersion thereof, and a method for producing the same.

[0002] In recent years, with the increase in information communication volume in the field of communications, such as 5G, the use of high-frequency bands has become widespread in electronic devices and communication devices. Because the use of high-frequency bands poses the problem of increased circuit signal transmission loss, materials with low dielectric loss tangents are generally used for insulators that make up electrical and electronic components such as antennas, circuits, and circuit boards. Polymer materials used as insulator materials generally have low dielectric constants but high dielectric loss tangents. On the other hand, ceramic materials often have the opposite characteristics. Therefore, ceramic-filled polymer materials that combine these materials to achieve both low dielectric constants and low dielectric loss tangents have become widespread (Patent Document 1, Patent Document 2).

[0003] Fused silica with micron-order sizes is widely used as the ceramic filler (inorganic filler). However, because coarse particles generated during manufacturing have a significant impact on the performance of molded products, the separation and removal of these particles presents a challenge (see Non-Patent Document 1, Patent Document 2, Patent Document 3, and Patent Document 4). On the other hand, silica particles with nano-order average particle sizes are considered advantageous in that they are less likely to generate coarse particles during manufacturing and can be easily separated and removed by filtration or centrifugation. Nano-order particles are also considered to have various advantages, such as their applicability to transparent polymer materials and their greater composite effect compared to micro-order fillers (see Patent Documents 5 and 6). Meanwhile, proposals have been made to hydrophobize the silica particle surface to improve dispersibility in hydrophobic solvents, thereby improving the ease of storage, transportation, and mixing with resins (see Patent Documents 7 and 8).

[0004] Japanese Patent Publication No. 2014-24916, Japanese Patent No. 6793282, Japanese Patent Publication No. 2004-269636, Japanese Patent No. 6546386, Japanese Patent No. 5862886, Japanese Patent No. 6813815, Japanese Patent No. 6805538, Japanese Patent No. 6746025

[0005] Fuji Chimera Research Institute, December 2019, No. 831906736, Exhaustive search for next-generation low-dielectric materials targeting 2020-2030

[0006] As mentioned above, nano-order particles have various advantages as ceramic fillers. However, existing nano-order particles have a high dielectric loss tangent, making them difficult to apply to materials such as electronic devices that operate in high frequency bands. Furthermore, when these nano-order particles are combined with resin materials, the particles are either used as is or dispersed in a solvent and then combined with the resin material. However, inorganic particles generally lack sufficient dispersion stability, especially in highly hydrophobic solvents, resulting in sedimentation and separation, which creates issues with work efficiency and storage. Thus, it has been difficult to achieve both a low dielectric loss tangent and high hydrophobicity with existing nano-order particles.

[0007] The present invention has been made in view of the above circumstances, and aims to provide nano-order particles that are hydrophobicized particles and have a low dielectric loss tangent, specifically, silica particles and a dispersion thereof that have a dielectric loss tangent of less than 0.01 at 1 GHz and a hydrophobicity of 40% or more.

[0008] That is, according to a first aspect, the present invention provides surface-modified silica particles having a hydrophobicity of 40% or more, characterized in that the average primary particle diameter is 5 to 500 nm and the dielectric loss tangent at 1 GHz is less than 0.01. According to a second aspect, the present invention provides surface-modified silica particles according to the first aspect, characterized in that the silica particles have been freed from a surface modifier and satisfy the following items (i) and (ii): (i) a specific surface area (S Ｈ２Ｏ ) and the specific surface area by nitrogen adsorption (S Ｎ２ ) and the ratio (SH ２ O / SN ２ (ii) The total silanol group ratio, as shown in the following formula (1), is 5% or less: Total silanol group ratio (%) = (Q2 x 2 / 4 + Q3 x 1 / 4 + Q4 x 0 / 4) ... formula (1) [wherein Q2, Q3, and Q4 are respectively ２９The ratios (%) of the peak area attributable to each silicon atom structure to the total (100%) of peak areas attributable to silicon atom structures obtained by Si NMR measurement, where Q2 represents the ratio of the peak area attributable to a silicon atom structure having two oxygen atoms and two hydroxy groups bonded thereto, Q3 represents the ratio of the peak area attributable to a silicon atom structure having three oxygen atoms and one hydroxy group bonded thereto, and Q4 represents the ratio of the peak area attributable to a silicon atom structure having four oxygen atoms bonded thereto.] As a third aspect, the unit surface area (unit: nm ２the surface-modified silica particles according to the first or second aspect, characterized in that a ratio of the total number of carbon atoms per carbon atom to the total number of carbon atoms per carbon atom is 2 to 40; as a fourth aspect, the surface-modified silica particles according to any one of the first to third aspects, characterized in that at least a portion of the surface of the surface-modified silica particles is coated with at least two types of surface modifiers, and the at least two types of surface modifiers include an organosilicon compound having at least one substituent a1 selected from substituent group a consisting of an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 12 carbon atoms, and a substituent having an unsaturated bond, and an organosilicon compound having at least one substituent a2 selected from substituent group a and different from substituent a1; As a fifth aspect, the surface-modified silica particles according to any one of the first to third aspects, characterized in that the surface-modified silica particles have at least a portion of each of at least two types of surface modifiers bonded to at least a portion of the surface thereof, and the at least two types of surface modifiers include an organosilicon compound having at least one substituent a1 selected from substituent group a consisting of an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 12 carbon atoms, and a substituent having an unsaturated bond, and an organosilicon compound having at least one substituent a2 selected from substituent group a and different from substituent a1; as a sixth aspect, the surface-modified silica particles according to the fourth or fifth aspect, in which substituent group a is the group consisting of a methyl group, a phenyl group, a phenylmethyl group, and a decyl group; as a seventh aspect, the surface-modified silica particles according to any one of the fourth to sixth aspects, in which the organosilicon compound is a compound having a hydrolyzable group in addition to a substituent selected from substituent group a; According to an eighth aspect, the surface-modified silica particles according to the fourth or fifth aspect, in which the surface modifying agent is at least two compounds selected from the group consisting of compounds represented by the following formulas (a) to (c): According to a ninth aspect, the surface-modified silica particles have a surface area of ​​1 nm ２the surface-modified silica particles according to any one of the third to eighth aspects, which are particles whose surfaces are coated with the at least two types of surface modifiers or particles in which at least a part of the at least two types of surface modifiers is bound to the surface, at a ratio of 0.5 to 20 particles per particle; a silica dispersion, as a tenth aspect, in which the surface-modified silica particles according to any one of the first to ninth aspects are dispersed in at least one organic solvent selected from alcohols, ketones, hydrocarbons, amides, ethers, esters, and amines; a composite material, as an eleventh aspect, which includes the surface-modified silica particles according to any one of the first to ninth aspects, and an organic resin material or a polysiloxane; As a twelfth aspect, there is provided a composite material according to the eleventh aspect, in which the organic resin material or polysiloxane is at least one selected from the group consisting of a styrene resin, an epoxy resin, a cyanate resin, a phenolic resin, an acrylic resin, a maleimide resin, a urethane resin, a polyimide, a polytetrafluoroethylene, a cycloolefin polymer, an unsaturated polyester, a vinyl triazine, a polyphenylene sulfide, a crosslinkable polyphenylene oxide, and a curable polyphenylene ether. As a thirteenth aspect, there is provided a composite material according to the eleventh aspect or the twelfth aspect, in which the composite material has an application selected from the group consisting of a semiconductor device material, a copper-clad laminate, a flexible wiring material, a flexible display material, an antenna material, an optical wiring material, and a sensing material. As a fourteenth aspect, there is provided a composite material according to the following steps (A) to (C): Step (A): A composite material having an average primary particle diameter of 5 to 500 nm and a specific surface area (S Ｈ２Ｏ ) and the specific surface area by nitrogen adsorption (S Ｎ２ ) and the ratio (S Ｈ２Ｏ / S Ｎ２ ) is 0.6 or less, and the total silanol group ratio represented by the following formula (1) is 5% or less: total silanol group ratio (%)=(Q2×2 / 4+Q3×1 / 4+Q4×0 / 4)...formula (1) [In formula (1), Q2, Q3, and Q4 are respectively ２９These are the percentages (%) of the peak area attributable to each silicon atom structure relative to the total (100%) of peak areas attributable to silicon atom structures obtained by Si NMR measurement, where Q2 represents the percentage of the peak area attributable to a silicon atom structure having two oxygen atoms and two hydroxy groups bonded thereto, Q3 represents the percentage of the peak area attributable to a silicon atom structure having three oxygen atoms and one hydroxy group bonded thereto, and Q4 represents the percentage of the peak area attributable to a silicon atom structure having four oxygen atoms bonded thereto. and (B) a process for heating and stirring at 40 to 100°C for 0.1 to 10 hours the silica sol obtained in step (A) and at least two surface modifiers, the surface modifiers including an organosilicon compound having at least one substituent a1 selected from substituent group a consisting of an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 12 carbon atoms, and a substituent having an unsaturated bond, and an organosilicon compound having at least one substituent a2 selected from substituent group a and different from the substituent a1; and (C) a process for removing the alcohol solvent from the silica sol obtained in step (B). As a fifteenth aspect, there is provided a process for producing surface-modified silica particles according to the fourteenth aspect, wherein either or both of steps (B) and (C) are carried out under reduced pressure. As a sixteenth aspect, there is provided a method for producing surface-modified silica particles according to the fourteenth aspect, in which the silica sol prepared in the step (A) is a silica sol having a water content of 0.1 to 5 mass %. As a seventeenth aspect, there is provided a method for producing surface-modified silica particles according to the fourteenth aspect, in which the silica sol prepared in the step (A) is a silica sol obtained by subjecting an aqueous silica sol hydrothermally synthesized at 200 to 380°C and 2 to 22 MPa to solvent substitution with an alcohol having 1 to 4 carbon atoms. As an eighteenth aspect, there is provided a method for producing surface-modified silica particles according to the following steps (A), (B), and (D): Step (A): A silica sol having an average primary particle diameter of 5 to 500 nm and a specific surface area (S Ｈ２Ｏ ) and the specific surface area by nitrogen adsorption (S Ｎ２ ) and the ratio (S Ｈ２Ｏ / S Ｎ２) is 0.6 or less, and the total silanol group ratio represented by the following formula (1) is 5% or less: total silanol group ratio (%)=(Q2×2 / 4+Q3×1 / 4+Q4×0 / 4)...formula (1) [In formula (1), Q2, Q3, and Q4 are respectively ２９ These are the percentages (%) of the peak area attributable to each silicon atom structure relative to the total (100%) of peak areas attributable to silicon atom structures obtained by Si NMR measurement, where Q2 represents the percentage of the peak area attributable to a silicon atom structure having two oxygen atoms and two hydroxy groups bonded thereto, Q3 represents the percentage of the peak area attributable to a silicon atom structure having three oxygen atoms and one hydroxy group bonded thereto, and Q4 represents the percentage of the peak area attributable to a silicon atom structure having four oxygen atoms bonded thereto. (B) a step of heating and stirring at 40 to 100°C for 0.1 to 10 hours the silica sol obtained in step (A) and at least two surface modifiers, the surface modifiers including an organosilicon compound having at least one substituent a1 selected from substituent group a consisting of an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 12 carbon atoms, and a substituent having an unsaturated bond, and an organosilicon compound having at least one substituent a2 selected from substituent group a and different from the substituent a1; and (D) a step of solvent-substitution of the silica sol obtained in step (B) with at least one solvent selected from alcohols, ketones, hydrocarbons, amides, esters, ethers, and amines.

[0009] The surface-modified silica particles of the present invention are hydrophobic and exhibit low dielectric properties. They are also well dispersible in organic solvents. Furthermore, the silica particles of the present invention can be combined with organic resin materials or polysiloxanes to form composite materials, which may be useful in the production of semiconductor device materials.

[0010] FIG. 1 is a diagram (photograph) showing the appearance of a cured film of the composite material containing the surface-modified silica particles and the maleimide resin obtained in Example 5-1 (FIG. 1(B)), and a cured film of only the maleimide resin (FIG. 1(A)).

[0011] <Surface-modified silica particles> The surface-modified silica particles of the present invention are silica particles having an average primary particle diameter of 5 to 500 nm, a dielectric loss tangent at 1 GHz of less than 0.01, and a hydrophobicity of 40% or more (hereinafter also referred to as hydrophobic silica particles).

[0012] The surface-modified silica particles according to the present invention preferably satisfy the following requirements (i) and (II) in the silica particles from which the surface modifier has been removed. Note that "silica particles from which the surface modifier has been removed" refers to silica particles before surface modification with a surface modifier, i.e., unmodified silica particles (without surface modifying groups). (i) The specific surface area (S Ｈ２Ｏ ) and the specific surface area by nitrogen adsorption (S Ｎ２ ) and the ratio (S Ｈ２Ｏ / S Ｎ２ (ii) the total silanol group ratio represented by the following formula (1) is 5% or less: total silanol group ratio (%)=(Q2×2 / 4+Q3×1 / 4+Q4×0 / 4)...formula (1) [wherein Q2, Q3, and Q4 are respectively ２９ These are the percentages (%) of the peak area attributable to each silicon atom structure relative to the total (100%) of peak areas attributable to silicon atom structures obtained by Si NMR measurement, where Q2 represents the percentage of the peak area attributable to a silicon atom structure having two oxygen atoms and two hydroxy groups bonded thereto, Q3 represents the percentage of the peak area attributable to a silicon atom structure having three oxygen atoms and one hydroxy group bonded thereto, and Q4 represents the percentage of the peak area attributable to a silicon atom structure having four oxygen atoms bonded thereto.]

[0013] <Hydrophobicity> The hydrophobicity referred to in this specification is defined as the concentration (%) expressed in terms of the volume of methanol when silica particles begin to wet in a mixture of water and methanol (also known as methanol wettability), and is generally used as an index of the hydrophobicity of silica surfaces. The hydrophobicity measurement method is, for example, as follows. First, 0.2 g of sample particles (hydrophobized silica particles) is placed in a 200 mL container (beaker, flask, etc.) containing 50 mL of water (ion-exchanged water, etc.). Next, while stirring the sample in the water using a magnetic stirrer, etc., methanol is added dropwise from a burette, etc. When the entire amount of the sample is wetted with methanol and the sample floating on the water surface is visually determined to have completely settled, the addition of methanol is stopped, and the volume of methanol in the mixed phase of water and methanol at this time is expressed as a percentage, and this value is taken as the hydrophobicity (see formula (2) below). Hydrophobicity (%) = [V ＭｅＯＨ / (V ＭｅＯＨ +50)]×100...Formula (2) V ＭｅＯＨ : Volume of methanol dropped (unit: mL) The hydrophobicity of the hydrophobicized silica particles according to the present invention can be 40% or more, preferably 50% or more. By having a hydrophobicity of 40% or more, when dispersed in a highly hydrophobic solvent, the dispersed state can be stably maintained for a long time, and the re-stirring step before use can be simplified / labor-saving, which is expected to facilitate the preparation of composite materials.

[0014] <Average primary particle size> The average primary particle size of the hydrophobicized silica particles according to the present invention is determined by the specific surface area (S Ｎ２ The specific surface area diameter (average primary particle diameter: D (nm)) can be calculated by the specific surface area S measured by the nitrogen adsorption method (BET method). Ｎ２ (m ２The primary particle diameter is calculated from the average particle diameter (D (nm)) of the silica particles (g) by the formula D (nm) = 2720 / S, and refers to the particle diameter converted into spherical silica particles. The hydrophobized silica particles according to the present invention can have an average primary particle diameter in the range of 5 nm to 500 nm, for example, 5 nm to 250 nm, 5 nm to 200 nm, 5 nm to 120 nm, 5 nm to 100 nm, 20 nm to 500 nm, 20 nm to 100 nm, or 40 nm to 100 nm. By using hydrophobized silica particles with an average primary particle diameter of 5 nm to 500 nm, they can exhibit a low dielectric loss tangent and be well dispersed in organic solvents. Furthermore, when a composite material using the hydrophobized silica particles is molded, defects can be suppressed and high transparency can be achieved.

[0015] <Specific surface area ratio (S Ｈ２Ｏ / S Ｎ２ ) > Specific surface area by water vapor adsorption (S Ｈ２Ｏ ) and the specific surface area by nitrogen adsorption (S Ｎ２ ) and the ratio (S Ｈ２Ｏ / S Ｎ２ ) is an index of the amount of active sites (surface silanols) present per surface area of ​​the particle, and a larger value indicates that more active sites are present on the silica surface. Ｈ２Ｏ ) was measured by the BET method using water vapor as an adsorbed molecule on the particle surface, and the specific surface area (S Ｎ２ ) can be measured by the BET method using nitrogen gas as molecules adsorbed onto the particle surface. The hydrophobicized silica particles (surface-modified silica particles) according to the present invention are silica particles from which the surface modifier has been removed, and the specific surface area ratio (S Ｈ２Ｏ / S Ｎ２ ) of 0.6 or less can be used. Ｈ２Ｏ / S Ｎ２ By using silica particles having the above formula, it is possible to perform surface modification of the silica particles without increasing the dielectric tangent, and to improve the dispersibility of the silica particles in organic solvents.

[0016] <Specific surface area by water vapor adsorption (S Ｈ２ＯThe hydrophobic silica particles (surface-modified silica particles) according to the present invention are silica particles from which a surface modifier has been removed, and the specific surface area (S Ｈ２Ｏ ) is, for example, 5 to 500 m ２ / g, or 5 to 300 m ２ / g, 5-100m ３ The specific surface area (S Ｈ２Ｏ ) for 5 to 500 m ２ / g, it is possible to suppress a decrease in the dielectric loss tangent due to moisture absorption, to perform surface modification of the silica particles, and to enable good dispersibility in organic solvents.

[0017] <Specific surface area by nitrogen adsorption (S Ｎ２ The hydrophobic silica particles (surface-modified silica particles) according to the present invention are silica particles from which a surface modifier has been removed, and the specific surface area (S Ｎ２ ) is, for example, 25 to 550 m ２ / g, or 25 to 300 m ２ / g, or 25 to 250 m ２ The specific surface area (S Ｎ２ ) for 25 to 550 m ２ By setting the dielectric loss tangent at 0.15 to 0.15, a low dielectric loss tangent can be maintained.

[0018] <Total silanol group ratio> Silicon atoms in silica include silicon atoms that are not bonded to hydroxy groups and silicon atoms that are bonded to one or two hydroxy groups. That is, silicon atoms in silica have four structures, as shown in the following formulas: silicon atoms (Q2) bonded to two oxygen atoms and two hydroxy groups, silicon atoms (Q3) bonded to three oxygen atoms and one hydroxy group, and silicon atoms (Q4) bonded to four oxygen atoms. The amount of silanol (Si—OH) groups in the silica can be estimated by determining the proportions of Q2, Q3, and Q4 in the silicon atoms in the silica. In this specification, the total silanol group ratio refers to the proportion of silanol groups present in the silica particles among all silicon atoms with Q2 to Q4 structures.

[0019] The abundance of silanol groups on silicon atoms of the Q2 to Q4 structures can be determined by, for example, using a water-dispersed silica sol containing silica particles to be investigated for the abundance. ２９ Si NMR method or silica particle powder ２９ It can be measured by Si NMR. ２９ The spectrum obtained by Si NMR is subjected to waveform separation, and the peak observed between -80 ppm and -105 ppm in chemical shift is identified as being derived from the Q2 structure, the peak observed between -90 ppm and -115 ppm as being derived from the Q3 structure, and the peak observed between -95 ppm and -130 ppm as being derived from the Q4 structure. At this time, the ratio (%) of the area value of each peak Q2 to Q4 to the total area value of each peak (100%) is the content ratio (mol%) of each structure (Q2 to Q4) in the silica particles being measured. Then, using this value and the content ratio of hydroxy groups to the total number of moles of oxygen atoms and hydroxy groups in each of the structures Q2 to Q4, the total silanol group ratio (%) can be calculated according to the following formula: Total silanol group ratio (%) = (Q2 x 2 / 4 + Q3 x 1 / 4 + Q4 x 0 / 4) ... Formula (1) In the above formula, Q2, Q3, and Q4 are, respectively. ２９ The percentage (%) of the peak area attributable to each silicon atom structure relative to the total peak area (100%) attributable to the silicon atom structure obtained by Si NMR measurement, i.e., the content ratio of each structure obtained from the NMR measurement results. The surface-modified silica particles according to the present invention are silica particles from which a surface modifier has been removed, which are prepared by using a water-dispersed silica sol containing silica particles. ２９ In the Si NMR method, Q2 can be 0 to 10, 0 to 5, or 0 to 5, Q3 can be 0 to 20, 0 to 15, 1 to 15, or 5 to 15, and Q4 can be 80 to 100, or 85 to 100. In addition, in silica particles from which the surface modifier has been removed, silica particle powders were used. ２９ By Si NMR, Q2 can be 0-10, 0-5, or 0-5; Q3 can be 0-20, 0-15, 1-15, or 5-15; and Q4 can be 80-100, or 85-100.

[0020] The hydrophobicized silica particles (surface-modified silica particles) according to the present invention have a total silanol group ratio of 5% or less in the silica particles from which the surface modifier has been removed. If the total silanol group ratio is greater than 5%, the particles will not exhibit low dielectric properties, such as low dielectric constant and dielectric loss tangent.

[0021] In one embodiment of the hydrophobicized silica particles (surface-modified silica particles) according to the present invention, the unit surface area (unit: nm ２ The proportion of total carbon atoms per alkyl group is 2 to 40, for example, 2 to 20, 5 to 20, or 5 to 15.

[0022] The unmodified silica particles constituting the hydrophobic silica particles (surface-modified silica particles) according to the present invention may be produced by any method, but are preferably heat-treated in water at 200 to 380° C. The heat treatment can be carried out using a pressure-resistant vessel (autoclave).

[0023] <Surface Modifier> In a preferred embodiment, the hydrophobized silica particles of the present invention have at least a portion of their surface coated with at least two types of surface modifiers, or at least a portion of each of at least two types of surface modifiers bonded to at least a portion of their surface. In this specification, "surface modification" includes both an embodiment in which the silica particle surface is coated with a surface modifier and an embodiment in which the surface modifier is bonded to the silica particle surface, and these embodiments are collectively referred to as "surface-modified silica particles." In this specification, "at least a portion of the surface of the silica particles is coated with a surface modifier" means that at least a portion of the silica particle surface is coated with a surface modifier (such as an organosilicon compound described below), that is, it includes an embodiment in which the surface modifier covers a portion of the silica particle surface and an embodiment in which the surface modifier covers the entire surface of the silica particle. In this embodiment, it does not matter whether or not the organosilicon compound, an example of a surface modifier, is bonded to the silica particle surface. Furthermore, in the present invention, the phrase "at least a portion of a surface modifier is bonded to at least a portion of the surface of the silica particle" may mean that the surface modifier (such as an organosilicon compound described below) is bonded to at least a portion of the surface of the silica particle, i.e., includes an embodiment in which the surface modifier is bonded to a portion of the surface of the silica particle, an embodiment in which the surface modifier is bonded to a portion of the surface of the silica particle and covers at least a portion of the surface, and an embodiment in which the surface modifier is bonded to the entire surface of the silica particle and covers the entire surface.

[0024] In one embodiment of the present invention, the surface modifier is an organosilicon compound having at least one substituent selected from Substituent Group a, which consists of alkyl groups having 1 to 20 carbon atoms, aryl groups having 6 to 12 carbon atoms, and substituents having an unsaturated bond (collectively referred to as "substituents"). In a preferred embodiment, the hydrophobized silica particles according to the present invention are surface-modified with at least two of the surface modifiers, as described above, i.e., with two or more organosilicon compounds having at least one substituent selected from Substituent Group a. More specifically, the surface-modified particles are, for example, with at least two of the following: an organosilicon compound having at least one substituent a1 selected from Substituent Group a, and an organosilicon compound having at least one substituent a2 selected from Substituent Group a and different from Substituent a1. When an organosilicon compound contains multiple substituents selected from Substituent Group a, the substituent with the greatest steric bulkiness among the substituents is treated as Substituent a1 or Substituent a2. In addition, in the two or more (plural types) of organosilicon compounds used for surface modification, for example, the substituents a1 and a2 are preferably groups having different steric bulkiness. Note that when the surface is modified with n types of surface modifiers, this means that the surface is modified with n types of organosilicon compounds having at least one substituent (a1, a2, ... an) selected from the substituent group a.

[0025] The organosilicon compound may be any compound having a substituent selected from the above-mentioned substituent group a, and examples thereof include silicon compounds having the above-mentioned substituent and a hydrolyzable group described below, organosilicon compounds having the above-mentioned substituent and an Si-O-Si bond, and organosilicon compounds having the above-mentioned substituent and an Si-N-Si bond. Surface-modified silica particles can be obtained by surface-modifying the silica particles with these organosilicon compounds.

[0026] Examples of the substituents in the substituent group a, i.e., alkyl groups having 1 to 20 carbon atoms, aryl groups having 6 to 12 carbon atoms, and substituents having an unsaturated bond, include methyl, ethyl, propyl, butyl, hexyl, octyl, nonyl, decyl, dodecyl, hexadecyl, phenyl, phenylmethyl, tolyl, xylyl, and vinyl groups. When multiple such substituents are present in the same organosilicon compound, they may be the same or different. Among these, the substituent group a can be a group consisting of methyl, octyl, decyl, dodecyl, hexadecyl, phenylmethyl, tolyl, and xylyl groups, or alternatively, a group consisting of methyl, phenyl, phenylmethyl, and decyl groups. Therefore, for example, as two or more organic silicon compounds, for example, a combination of an organic silicon compound having a methyl group and an organic silicon compound having a phenyl group, a combination of an organic silicon compound having a methyl group and an organic silicon compound having a decyl group, a combination of an organic silicon compound having a methyl group and an organic silicon compound having a phenyl group and an organic silicon compound having a decyl group, a combination of an organic silicon compound having a methyl group and an organic silicon compound having a phenylmethyl group, a combination of an organic silicon compound having a methyl group and an organic silicon compound having a tolyl group, a combination of an organic silicon compound having a methyl group and an organic silicon compound having a xylyl group, a combination of an organic silicon compound having a methyl group and an organic silicon compound having an octyl group, a combination of an organic silicon compound having a methyl group and an organic silicon compound having a dodecyl group, a combination of an organic silicon compound having a methyl group and an organic silicon compound having a hexadecyl group, etc., but are not limited to these.

[0027] The hydrolyzable group is preferably an alkoxy group, and when a plurality of groups are present, they may be the same or different. The alkoxy group is preferably an alkoxy group having 1 to 3 carbon atoms, and particularly preferably a methoxy group.

[0028] When the organosilicon compound is a silicon compound having the substituents and hydrolyzable groups, there are no particular limitations on the number of substituents and the number of hydrolyzable groups, but it is preferable that the number of substituents is 1 to 3 and the number of hydrolyzable groups is 1 to 3 (however, the total number of both groups is 4 or less) per silicon atom. Specific examples of the organosilicon compound having the substituents and hydrolyzable groups include methyltrimethoxysilane, octyltrimethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane, hexadecyltrimethoxysilane, dimethyldimethoxysilane, trimethylmethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, trimethylethoxysilane, methyltripropoxysilane, dimethyldipropoxysilane, trimethylpropoxysilane, phenyltrimethoxysilane, tolyltrimethoxysilane, xylyltrimethoxysilane, diphenyldimethylsilane, methyltrimethoxysilane, methyltripropoxy ... Examples of suitable silanes include, but are not limited to, phenyltriethoxysilane, diphenyldiethoxysilane, phenyltripropoxysilane, diphenyldipropoxysilane, phenylmethyldimethoxysilane, phenylmethyldiethoxysilane, phenyldipropoxysilane, vinyltrimethoxysilane, divinyldimethoxysilane, vinyltriethoxysilane, divinyldiethoxysilane, vinyltripropoxysilane, divinyldipropoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, and N-phenyl-3-aminopropyltriethoxysilane.

[0029] In the substituents of the organosilicon compounds having the Si-O-Si bond, the alkyl groups having 1 to 20 carbon atoms, the aryl groups having 6 to 12 carbon atoms, and the substituents having an unsaturated bond are preferably methyl, phenyl, phenylmethyl, and vinyl groups, and when multiple groups are present, they may be the same or different. A methyl group is particularly preferred, and a specific example of the organosilicon compound is hexamethyldisiloxane. In the substituents of the organosilicon compounds having the Si-N-Si bond, the alkyl groups having 1 to 20 carbon atoms, the aryl groups having 6 to 12 carbon atoms, and the substituents having an unsaturated bond are preferably methyl, phenyl, phenylmethyl, and vinyl groups, and when multiple groups are present, they may be the same or different. A methyl group is particularly preferred, and a specific example of the organosilicon compound is hexamethyldisilazane.

[0030] Among these, preferred organosilicon compounds include compounds represented by the following formulas (a) to (c), and at least one of these and another organosilicon compound, or at least two of these, can be selected.

[0031] The amount of the surface treatment (modification) with the organosilicon compound, i.e., the amount of the organosilicon compound that coats or bonds to the particle surface, is determined based on the surface area of ​​the silica particles of 1 nm ２ The number of particles per nanometer can be, for example, about 0.5 to 40 particles, or about 0.5 to 20 particles, about 0.5 to 16 particles, about 1 to 20 particles, about 2 to 20 particles, about 5 to 20 particles, or about 10 to 20 particles. ２ The number per unit area (amount of surface treatment) refers to the total number of organosilicon compounds required for surface modification, i.e., the total amount of at least two types of surface modifiers, and does not refer to the amount of surface treatment by each individual surface modifier (organosilicon compound).

[0032] <Measurement of Dielectric Properties> The dielectric constant and dielectric loss tangent of the hydrophobicized silica particles according to the present invention can be measured using a dry powder of the hydrophobicized silica particles with a dedicated device. Examples of dedicated devices include a vector network analyzer (product name: FieldFox N6626A, manufactured by KEYSIGHT TECHNOLOGIES). When composited with an organic resin material or polysiloxane and used as an insulator, the hydrophobic silica particles preferably have a dielectric loss tangent of less than 0.01, particularly 0.009 or less, at a frequency of 1 GHz. The lower limit of the dielectric loss tangent is 0.00001, 0.00005, 0.0001, or 0.0005.

[0033] <Silica Dispersion> The silica dispersion of the present invention is a dispersion obtained by dispersing the hydrophobized silica particles (surface-modified silica particles) in at least one organic solvent selected from alcohols, ketones, hydrocarbons, amides, ethers, esters, and amines. Examples of the alcohols include alcohols having 1 to 5 carbon atoms, specifically methanol, ethanol, isopropyl alcohol, and n-butanol. Examples of the ketones include ketones having 1 to 5 carbon atoms, specifically methyl ethyl ketone, methyl isobutyl ketone, γ-butyrolactone, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, and cyclohexanone. Examples of the hydrocarbons include toluene, xylene, n-pentane, n-hexane, and cyclohexane. Examples of the amides include dimethylacetamide, N,N-dimethylformamide, dimethylacrylamide, acryloylmorpholine, and diethylacrylamide. Examples of the ethers include ethylene glycol monomethyl ether and propylene glycol monomethyl ether. Examples of the esters include ethyl acetate and butyl acetate. Examples of the amines include triethylamine, tributylamine, N,N-dimethylaniline, pyridine, and picoline. The content of hydrophobized silica particles in the dispersion can be expressed as silica concentration. The silica concentration can be calculated by weighing the calcination residue obtained after calcining the silica dispersion at 1000°C. The silica concentration in the silica dispersion can be, for example, 1% to 60% by mass, 10% to 60% by mass, or 10% to 40% by mass. Furthermore, the water content of the silica dispersion is preferably 5% by mass or less. By adjusting the water content to this range, the stability of the dispersion can be improved and composite materials with organic resin materials or polysiloxanes can be more easily obtained.

[0034] <Composite Material> The composite material according to the present invention is a composite material containing the hydrophobized silica particles (surface-modified silica particles) according to the present invention and an organic resin material or polysiloxane. The organic resin material or polysiloxane can be at least one selected from the group consisting of epoxy resin, phenol resin, acrylic resin, maleimide resin, polyurethane, polyimide, polytetrafluoroethylene, cycloolefin polymer, unsaturated polyester, vinyl triazine, crosslinkable polyphenylene oxide, and curable polyphenylene ether.

[0035] The method for preparing the composite material is not particularly limited. For example, a composite material can be prepared by mixing a dispersion of hydrophobized silica particles with a solution of an organic resin material or a monomer or polymer of polysiloxane to prepare a polymerizable composition, removing excess solvent, and then curing the composition with light or heat. Alternatively, a composite material can be prepared by directly adding a powder of hydrophobized silica particles to a solution of an organic resin material or a monomer or polymer of polysiloxane to prepare a polymerizable composition, removing excess solvent, and then curing the composition with light or heat. The mixing ratio of the silica particles to the organic resin material or the monomer or polymer of polysiloxane in the polymerizable composition can be 1:100 to 0.1, e.g., 1:20 to 0.1, in terms of the mass ratio of the hydrophobized silica particles to the organic resin material or the monomer or polymer of polysiloxane.

[0036] The polymerizable composition can be cured by light or heat by using a polymerization initiator. Examples of photopolymerization initiators include photoradical polymerization initiators and photocationic polymerization initiators, and examples of thermal polymerization initiators include thermal radical polymerization initiators and thermal cationic polymerization initiators. The polymerization initiator can be used in an amount of 0.01 to 50 parts by mass per 100 parts by mass of the polymerizable compound. As optional components, conventional additives used in conventional polymerizable compositions (composite materials), such as curing-accelerating catalysts, pigments, radical scavengers (quenchers), leveling agents, viscosity modifiers, antioxidants, UV absorbers, stabilizers, plasticizers, surfactants, and other additives used in the relevant technical field, can also be mixed and used.

[0037] By selecting an appropriate organic resin material or polysiloxane depending on the intended use, the composite material of the present invention can be used as a semiconductor device material, a copper-clad laminate, an insulating film, a flexible wiring material, a flexible display material, an antenna material, an optical wiring material, or a sensing material.

[0038] <Method for producing hydrophobized silica particles (surface-modified silica particles)> The method for producing hydrophobized silica particles (surface-modified silica particles), i.e., the method for coating (surface treating) the surfaces of silica particles with the organosilicon compound, is not particularly limited. For example, by adding and mixing two or more types of surface modifiers to an organic solvent dispersion of (unmodified) silica particles, hydrolysis and condensation of the organosilicon compound occur, and the silica particles can be surface-modified.

[0039] The amount of organosilicon compound added is determined based on the surface area of ​​the silica particles. ２ For example, an organosilicon compound can be added so that the surface is modified in the range of about 0.5 to 20.0 per 1000 particles. ２The amount of organosilicon compound added here refers to the total amount (number) of the multiple organosilicon compounds added. For example, when two types of organosilicon compounds are added, it refers to the total amount (number) of the two types of organosilicon compounds added. Although excess organosilicon compound that does not contribute to surface modification may be present in the system, the preferred amount of organosilicon compound added is such that the silica particles have a surface area of ​​1 nm ２ The yield is 5.0 to 10.0 pieces per unit.

[0040] The hydrolysis of the organosilicon compound may be complete or partial, but water is required, and it is preferable to add about 1 mole or more of water per mole of hydrolyzable groups, [Si-O-Si] bonds, or [Si-N-Si] bonds of the organosilicon compound. Water contained in the organic solvent can also be utilized. When using an organosilicon compound having hydrolyzable groups, hydrolysis may be complete or partial, but water is required, and it is preferable to add about 1 mole or more of water per mole of hydrolyzable groups of the organosilicon compound. Water contained in the organic solvent can also be utilized. A catalyst can also be used during the hydrolysis and condensation. As the hydrolysis catalyst, a chelate compound, organic acid, inorganic acid, organic base, or inorganic base can be used alone or in combination. More specifically, for example, an aqueous solution of hydrochloric acid, acetic acid, or aqueous ammonia can be used.

[0041] More specifically, for example, the average primary particle diameter is 5 nm to 500 nm, and the specific surface area by water vapor adsorption (S Ｈ２Ｏ ) and the specific surface area by nitrogen adsorption (S Ｎ２ ) and the ratio (S Ｈ２Ｏ / S Ｎ２The hydrophobic silica particles (surface-modified silica particles) according to the present invention can be produced by mixing, in an organic solvent, silica particles having a silanol group ratio of 0.6 or less and a total silanol group ratio of 5% or less with a surface modifier that is at least two organosilicon compounds having an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 12 carbon atoms, and a substituent having an unsaturated bond. The organosilicon compounds that can be used are those described above, and the silica particles to be surface-modified are preferably those that have been heat-treated in water at 200 to 380°C using a pressure-resistant vessel (autoclave) or the like, as described above.

[0042] In the mixing step, the amount of the organosilicon compound added is set to a value equal to the surface area of ​​the silica particles of 1 nm ２ The amount can be set so that the surface of the silica particles is modified at a ratio of, for example, 0.5 to 20 particles per 1000 particles. ２ The organosilicon compound can be added so that the ratio of the number of particles per unit area is 0.5 to 15.0, or 1.0 to 10.0, or 3.0 to 10.0, or 5.0 to 10.0. The amount of organosilicon compound added is the total amount of two or more organosilicon compounds added; for example, when three organosilicon compounds are added, it is considered as the total amount of all three. Note that excess organosilicon compound that does not contribute to surface modification may be present in the reaction system.

[0043] The organic solvent used in the mixing step may be an organic solvent containing an alcohol and / or a ketone solvent. Examples of the alcohol include alcohols having 1 to 5 carbon atoms, such as methanol, ethanol, isopropyl alcohol, and n-butanol. Examples of the ketone solvent include ketone solvents having 1 to 5 carbon atoms, such as methyl ethyl ketone, methyl isobutyl ketone, and γ-butyl lactone.

[0044] The mixing step can be carried out at any temperature, as long as it allows the hydrolysis and condensation reaction of the organosilicon compound to proceed. For example, the temperature can be from 20°C to less than 120°C. From the standpoint of reaction efficiency, the step is preferably carried out near the boiling point of the organic solvent. For example, if an organic solvent containing methanol is used, the mixing step is preferably carried out at around 65°C. To suppress changes in the silica concentration and organosilicon compound concentration during the mixing step, the reaction may be carried out in an apparatus equipped with a reflux device, if necessary. The mixing step can be carried out multiple times at the same temperature, or multiple times at different temperatures. The mixing step can be carried out for 30 minutes to 24 hours, and from an industrial perspective, it is desirable to carry out the step within 24 hours. In the present invention, the surface modification is carried out using at least two organosilicon compounds (surface modifiers). These compounds may be added at the same time or separately. In a preferred embodiment, the at least two organosilicon compounds can be added separately. For example, the organosilicon compound having the bulkier substituent group can be added first, followed by mixing (reaction). As an example, when dimethoxyphenylmethylsilane (a compound represented by the formula (a)) and hexamethyldisiloxane (a compound represented by the formula (c)) are used as the two organosilicon compounds, dimethoxyphenylmethylsilane having a phenyl group, which is a bulkier substituent, can be added and mixed first, and hexamethyldisiloxane having a methyl group, which is less bulky than the phenyl group, can be added later, but the method is not limited to this.

[0045] Furthermore, the mixing step may include a step of adjusting the pH using an organic amine. This pH adjustment step may be performed once or multiple times before, during, or after the mixing step. The organic amine may be a secondary or tertiary amine. Examples of the secondary or tertiary amine that may be used include alkylamines, allylamines, aralkylamines, alicyclic amines, alkanolamines, and cyclic amines. Specific examples of the secondary or tertiary amine include diethylamine, triethylamine, diisopropylamine, tri-isopropylamine, di-n-propylamine, tri-n-propylamine, diisobutylamine, di-n-butylamine, tri-n-butylamine, dipentylamine, tripentylamine, di-2-ethylhexylamine, di-n-octylamine, tri-n-octylamine, N-ethyldiisopropylamine, dicyclohexylamine, N,N-dimethylbutylamine, N,N-dimethylhexylamine, N,N-dimethyloctylamine, and N,N-dimethylamine. Examples of suitable organic base compounds include ethylbenzylamine, piperidine, N-methylpiperidine, quinuclidine, diethanolamine, triethanolamine, N-methyldiethanolamine, N,N-dimethylethanolamine, N,N-diethylethanolamine, N,N-dibutylethanolamine, triisopropanolamine, imidazole, imidazole derivatives, 1,8-diaza-bicyclo(5,4,0)undec-7-ene, 1,5-diaza-bicyclo(4,3,0)non-5-ene, 1,4-diaza-bicyclo(2,2,2)octane, and diallylamine. These organic base compounds may be used alone or in combination of two or more. The amount of organic amine added may be, for example, 0.001 to 5% by mass, or 0.01 to 1% by mass, relative to the mass of the silica particles. Furthermore, by adding an organic amine, the pH of the mixed solution can be adjusted to 4.0 to 11.0, for example, pH 7.0 to 10.0, or for example, pH 8.0 to 10.0.

[0046] Furthermore, the liquid obtained after the mixing step, i.e., the liquid containing the surface-modified silica particles, can be used as a surface-modified silica dispersion in the production of the composite material described above. Furthermore, from the viewpoint of ease of production of the composite material, at least a portion of the organic solvent contained in the mixed liquid obtained by the mixing step can be replaced with another organic solvent. The other organic solvent can be at least one or more selected from the group consisting of alcohols, ketones, ethers, esters, hydrocarbons, and nitrogen-containing organic compounds. There are no particular restrictions on the type of solvent used for the replacement, as long as it is different from the organic solvent in the mixed liquid, and the replacement solvent can be selected from the viewpoint of the solubility of the organic resin material or polysiloxane to be composited. Examples of other organic solvents include alcohols such as methanol, ethanol, isopropyl alcohol, and n-butanol, ketones such as methyl ethyl ketone, methyl isobutyl ketone, γ-butyrolactone, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, and cyclohexanone, ethers such as ethylene glycol monomethyl ether, propylene glycol monomethyl ether, and propylene glycol methyl ether acetate, esters such as ethyl acetate and butyl acetate, hydrocarbons such as toluene, xylene, n-pentane, n-hexane, and cyclohexane, and nitrogen-containing organic compounds such as amides such as dimethylacetamide, N,N-dimethylformamide, N,N-dimethylformamide, dimethylacrylamide, acryloylmorpholine, and diethylacrylamide, and amines such as triethylamine, tributylamine, N,N-dimethylaniline, pyridine, and picoline. The substitution method can be a known method, and the substitution with another organic solvent can be performed by, for example, evaporation using a rotary evaporator or ultrafiltration using an ultrafiltration membrane.

[0047] A specific example of the method for producing silica particles includes the following steps (A) to (C), but is not limited to these steps. Step (A): A method for producing silica particles having an average primary particle diameter of 5 to 500 nm and a specific surface area (S Ｈ２Ｏ ) and the specific surface area by nitrogen adsorption (SＮ２ ) and the ratio (S Ｈ２Ｏ / S Ｎ２ ) is 0.6 or less, and the total silanol group ratio represented by the following formula (1) is 5% or less: total silanol group ratio (%)=(Q2×2 / 4+Q3×1 / 4+Q4×0 / 4)...formula (1) [In formula (1), Q2, Q3, and Q4 are respectively ２９ These are the percentages (%) of the peak area attributable to each silicon atom structure relative to the total (100%) of peak areas attributable to silicon atom structures obtained by Si NMR measurement, where Q2 represents the percentage of the peak area attributable to a silicon atom structure having two oxygen atoms and two hydroxy groups bonded thereto, Q3 represents the percentage of the peak area attributable to a silicon atom structure having three oxygen atoms and one hydroxy group bonded thereto, and Q4 represents the percentage of the peak area attributable to a silicon atom structure having four oxygen atoms bonded thereto. (B) a silica sol is prepared using silica particles of formula (I) as a dispersoid and an alcohol having 1 to 4 carbon atoms as a dispersion medium; (C) a surface modifier is added to the silica sol obtained in (A) at 40 to 100°C for 0.1 to 10 hours, the surface modifier comprising an organosilicon compound having at least one substituent a selected from a group a consisting of an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 12 carbon atoms, and a substituent having an unsaturated bond, and an organosilicon compound having at least one substituent a2 selected from the group a and different from the substituent a1; and (C) a surface modifier is added to the silica sol obtained in (A) at 40 to 100°C for 0.1 to 10 hours, the surface modifier comprising an organosilicon compound having at least one substituent a2 selected from the group a and different from the substituent a1; and (C) a surface modifier is added to the silica sol obtained in (B) at 40 to 100°C for 0.1 to 10 hours, the surface modifier comprising an organosilicon compound having at least one substituent a2 selected from the group a and different from the substituent a1.

[0048] The silica sol prepared in step (A) may have a water content of 0.1 to 5% by mass, for example, 3.0% by mass or less. Alternatively, the silica sol prepared in step (A) may be an aqueous silica sol obtained by hydrothermal synthesis at 200 to 380°C and 2 to 22 MPa, and then solvent-substituted with an alcohol having 1 to 4 carbon atoms.

[0049] Either or both of the steps (B) and (C) can be carried out, for example, under reduced pressure. Note that, if necessary, a step of adjusting the pH using the organic amine may be included at any one or more of the following steps: before, during, and after the step (B).

[0050] In the step (B), when at least two surface modifiers and the silica sol obtained in the step (A) are heated and stirred, multiple surface modifiers may be heated and stirred simultaneously with the silica sol, or some of the multiple surface modifiers and the remaining ones may be heated and stirred separately with the silica sol, or each of the surface modifiers may be heated and stirred individually with the silica sol. For example, the surface modifiers may be heated and stirred with the silica sol in the order of the organosilicon compounds having the most bulky substituents.

[0051] Furthermore, the silica sol obtained after step (B) can be used as a surface-modified silica dispersion in the production of the above-mentioned composite material, and may be subjected to solvent substitution, for example, by step (D) described below. Specifically, specific examples of the method for producing a surface-modified silica dispersion include a production method including steps (A) and (B) below, and a production method including step (D) in addition to steps (A) and (B), but are not limited to these methods (steps). Step (A): preparing a silica sol containing silica particles having an average primary particle size of 5 to 500 nm as a dispersoid and an alcohol having 1 to 4 carbon atoms as a dispersion medium; Step (B): heating and stirring at 40 to 100°C for 0.1 to 10 hours the silica sol obtained in Step (A) and at least two surface modifiers, the surface modifiers including an organosilicon compound having at least one substituent a1 selected from substituent group a consisting of an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 12 carbon atoms, and a substituent having an unsaturated bond, and an organosilicon compound having at least one substituent a2 selected from substituent group a and different from the substituent a1; and (D) performing solvent substitution on the silica sol obtained in Step (B) with at least one solvent selected from alcohols, ketones, hydrocarbons, amides, esters, ethers, and amines. Specific examples of alcohols, ketones, hydrocarbons, amides, amines (nitrogen-containing organic compounds), esters, and ethers, as well as the method of replacing the solvent, in this production method can be as described above.

[0052] EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0053] The silica sols and surface modifiers used in the examples and comparative examples are as follows. The properties of the silica particles are shown in Table 1. [Silica sol] Water-dispersed silica sol a (manufactured by Nissan Chemical Industries, Ltd., trade name: ST-OL, 45 nm, pH 3, silica concentration 20 mass%) Water-dispersed silica sol b (manufactured by Nissan Chemical Industries, Ltd., trade name: ST-O, 12 nm, pH 3, silica concentration 20 mass%) Water-dispersed silica sol c (Synthesis Example 1, 80 nm, pH 3, silica concentration 20 mass%)

[0054]

[0055] [Surface modifiers (organic silicon compounds)] DMPS: dimethoxymethylphenylsilane (manufactured by Shin-Etsu Chemical Co., Ltd., trade name: LS-2720) DTMS: decyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., trade name: KBM-3103C) HMDS: hexamethyldisiloxane (manufactured by Shin-Etsu Chemical Co., Ltd., trade name: KF-96L-0.65CS)

[0056] According to the following methods, the physical properties of the water-dispersed silica sol, the dispersions of surface-modified silica particles prepared in the Examples and Comparative Examples, and the silica sol and dispersions during the dispersion production process were measured and evaluated.

[0057] [Silica (SiO ２ The silica concentration of the water-dispersed silica sol, the methanol-dispersed silica sol, and the dispersion of surface-modified silica particles was calculated by placing the silica sol or the dispersion in a crucible, heating to remove the solvent, calcining at 1000°C, and weighing the calcination residue.

[0058] [Method for Measuring pH of Water-Dispersed Silica Sol] The pH of the water-dispersed silica sol was measured using a pH meter (MM-43X, manufactured by Toa DKK Corporation).

[0059] [Method for measuring pH of organic solvent-dispersed silica sol] The pH of the methanol-dispersed silica sol was measured using a pH meter (MM-43X, manufactured by DKK Toa Corporation) in which a target sample containing the methanol-dispersed silica sol was mixed with methanol and pure water in a mass ratio of 1:1:1. The pH measured by this method was expressed as pH (1 + 1 + 1).

[0060] [Water Content] The water content in the dispersion of surface-modified silica particles and the silica sol during the production process was measured by Karl Fischer titration using a Karl Fischer moisture meter (manufactured by Kyoto Electronics Manufacturing Co., Ltd., product name: MKA-610).

[0061] [Organic solvent content] The organic solvent content in the dispersion of surface-modified silica particles was determined by gas chromatography (Shimadzu Corporation, GC-2014s). Gas chromatography conditions: Column: 3 mm x 1 m glass column Packing: Porapack Q Column temperature: 130 to 230°C (heating rate: 8°C / min) Carrier: N ２ 40 mL / min Detector: FID Injection volume: 1 μL Internal standard: acetonitrile was used.

[0062] [Measurement of Viscosity] The viscosity of the dispersion liquid during the surface-treated silica particle production process was measured using an Ostwald viscometer (manufactured by Shibata Scientific Co., Ltd.).

[0063] [Measurement of specific surface area, specific surface area ratio and average primary particle diameter] <Specific surface area by water vapor adsorption method (S Ｈ２Ｏ Measurement of the specific surface area (S) of silica particles in a water-dispersed silica sol by water vapor adsorption method Ｈ２Ｏ ) was measured by removing water-soluble cations and anions in the water-dispersed silica sol using a cation exchange resin (manufactured by The Dow Chemical Company, trade name: Amberlite IR-120B), an anion exchange resin (manufactured by The Dow Chemical Company, trade name: Amberlite IRA400J), and a cation exchange resin (manufactured by The Dow Chemical Company, trade name: Amberlite IR-120B) in that order, and then drying the silica sol at 290°C to prepare a measurement sample, which was then measured using a water vapor adsorption specific surface area measuring device (manufactured by TS Instruments Japan, Ltd., Q5000SA).

[0064] <Specific surface area by nitrogen adsorption method (S Ｎ２ Measurement of the specific surface area (S) of silica particles in a water-dispersed silica sol by nitrogen adsorption method Ｎ２ The specific surface area of ​​a water-dispersed silica sol was measured by removing water-soluble cations in the water-dispersed silica sol with a cation exchange resin (manufactured by The Dow Chemical Company, trade name: Amberlite IR-120B), and then drying the silica sol at 290°C to prepare a measurement sample. The specific surface area of ​​the sample was measured using a Monosorb (manufactured by Quantachrome Instruments Japan, LLC) which is a nitrogen adsorption method specific surface area measuring device.

[0065] <Ratio of the specific surface area for water vapor adsorption to the specific surface area for nitrogen adsorption (S Ｈ２Ｏ / S Ｎ２Using the values ​​of the specific surface area by the water vapor adsorption method and the specific surface area by the nitrogen adsorption method obtained in the above measurement, the specific surface area ratio was calculated according to the following formula (3). Ｈ２Ｏ / S Ｎ２ ) = specific surface area by water vapor adsorption method / specific surface area by nitrogen adsorption method Equation (3)

[0066] <Average primary particle diameter> The average primary particle diameter is determined by the specific surface area S obtained by the nitrogen adsorption method. Ｎ２ (m ２ The average primary particle diameter (nm) was calculated from the average particle diameter (nm) of the polymer (g) converted into spherical particles using the following formula (4): Ｎ２ (m ２ / g)...Formula (4)

[0067] [NMR Measurement of Silica Sol or Dry Powder of Silica Sol and Calculation of Total Silanol Group Ratio] <NMR Measurement Condition A: Silica Sol ２９ Si NMR spectrum measurement> 0.5 mL of D was added to 2 mL of water-dispersed silica sol. ２ The measurement sample was prepared by adding O to the sample, which was placed in a 10 mm diameter polytetrafluoroethylene (PTFE) sample tube and measured. ２９ The Si-free probe is attached and the observed nucleus is ２９ The one-dimensional NMR spectrum of Si was measured under the following conditions: ２９ The Si resonance frequency was 99.36 MHz, the spectral width was 37.4 kHz, the X_Pulse was 90°, the Relaxation_Delay was 120 seconds, and the measurement temperature was room temperature. Data analysis was performed using JEOL Ltd.'s software "Delta 5.3.1," and waveform separation analysis was performed on each peak of the spectrum after Fourier transformation, using the center position, height, and half-width of the peak shape created using a Gaussian waveform (Gauss Model) as variable parameters. After waveform separation, the peak observed between chemical shifts of -80 ppm and -105 ppm was identified as being derived from the Q2 structure, the peak observed between -90 ppm and -115 ppm as being derived from the Q3 structure, and the peak observed between -95 ppm and -130 ppm as being derived from the Q4 structure. <NMR Measurement Condition B: Dry Powder of Silica Sol>２９ Si NMR Spectrum Measurement> The silica sol was dried in a vacuum dryer at 100°C to prepare a measurement sample. A 500 MHz nuclear magnetic resonance apparatus (model name "AVANCE III 500", manufactured by Bruker) was used, equipped with a CP / MAS probe with a diameter of 4.0 mm, and the observation nucleus was 29Si, and measurements were performed by the DD / MAS method. The measurement conditions were as follows: ２９ Si resonance frequency: 99.36 MHz ２９ Si 90° pulse width 4.6 μsec, １ The H resonance frequency was 500.13 MHz, the MAS rotation speed was 10 kHz, the spectral width was 30 kHz, and the measurement temperature was room temperature. Data analysis was performed using Bruker's software "TopSpin 3.6.0," and for each peak in the spectrum after Fourier transformation, waveform separation analysis was performed using the center position, height, and half-width of the peak shape created by mixing a Lorentzian waveform and a Gaussian waveform (Gauss / Lorentz Model) as variable parameters. After waveform separation, the peak observed between -80 ppm and -105 ppm in chemical shift was identified as originating from the Q2 structure, the peak observed between -90 ppm and -115 ppm as originating from the Q3 structure, and the peak observed between -95 ppm and -130 ppm as originating from the Q4 structure. <Total silanol group ratio> The total silanol group ratio of silica particles in the water-dispersed silica sol was determined as follows: ２９ It was calculated from the area value of each peak obtained by Si NMR spectrum measurement. The ratio (%) of the area value of each peak to the total (100%) of the area values ​​of each peak (Q2, Q3, Q4) after waveform separation was taken as the content ratio of each structure, and the total silanol group ratio was calculated using the following formula (1). In the formula, Q2, Q3, and Q4 represent the content ratio of each structure obtained from the NMR measurement results. Total silanol group ratio (%) = (Q2 x 2 / 4 + Q3 x 1 / 4 + Q4 x 0 / 4) Formula (1)

[0068] <Unit surface area of ​​silica particles (unit: nm ２ The total number of carbon atoms per unit surface area (unit: nm ) of silica particles was calculated by the following procedure. ２) and calculated the total number of carbon atoms per 1000 carbon atoms. (1) 4 mL of an organic solvent-dispersed silica sol of surface-modified silica particles was placed in a 30 cc centrifuge tube, and 20 mL of hexane was added to cause cloudiness, separation, or precipitation due to aggregation. (2) After centrifuging, the supernatant in which the unbound surface modifier had dissolved was removed. (3) 4 mL of acetone was added to redissolve the precipitate from centrifugation, and then 20 mL of hexane was added. (4) Steps (2) and (3) were repeated, and the supernatant was removed. (5) The mixture was vacuum-dried, and the resulting powder was pulverized in a mortar and dried at 150°C for 2 hours. The carbon content of this dried powder was measured using an elemental analyzer (Perkin-Elmer, model name: Elemental Analyzer 2400II). The carbon content thus obtained and the specific surface area (S) measured by the nitrogen adsorption method were then compared. Ｎ２ ) to calculate the unit surface area of ​​the silica particles (unit: nm ２ The total number of carbon atoms per unit mass was determined.

[0069] <Dynamic Light Scattering Particle Diameter> The dynamic light scattering particle diameter was measured using a dynamic light scattering particle diameter measurement device (trade name: Zetasizer Nano, manufactured by Malvern Panalytical). 0.1 g of the silica particle dispersion was dispensed into a glass cell with an optical path length of 10 mm, and the same solvent as the dispersion medium of the silica particle dispersion was further added to obtain a silica particle dispersion in which the silica concentration was adjusted so that the count rate at an attenuator of 7 was 200 to 400 kcps. The prepared silica particle dispersion was placed in the cell so that the height of the liquid surface from the bottom of the cell was approximately 1 cm, and the dynamic light scattering particle diameter of the silica particle dispersion was measured using an attenuator of 7.

[0070] [Measurement of Dielectric Constant and Dielectric Loss Tangent] Using a cavity resonator jig for a measurement frequency of 1 GHz (manufactured by Keycom Corporation), a powder sample (silica powder obtained in Examples 2-1 to 2-5 and Comparative Examples 2-1 to 2-4 described later) was filled into a PTFE sample tube (length 30 mm, inner diameter 3 mm), and then the dielectric constant and dielectric loss tangent of the measurement sample were measured with a vector network analyzer (trade name: N5227A, manufactured by KEYSIGHT TECHNOLOGIES).

[0071] [Measurement of Hydrophobicity] The hydrophobicity was measured by placing 50 mL of pure water and 0.2 g of a powder sample (silica powder obtained in Examples 3-1 to 3-5 and Comparative Examples 3-1 to 3-4 described later) in a 200 mL beaker, adding methanol dropwise while stirring, and measuring the amount of methanol added until the sample floating on the water surface completely sinks (V ＭｅＯＨ , unit: mL) was measured and calculated using the following formula (Reference: Non-Patent Document 1): Hydrophobicity (%) = [V ＭｅＯＨ / (V ＭｅＯＨ +50)] × 100...Equation (2) <Non-Patent Document 1> Murota Seido, Tsubokawa Norio, Effect of Alkyl Chain Length on Reactivity of Ultrafine Silica with Alkylalkoxysilane in a Dry System, Journal of the Japan Society of Colour Material 74 (4), 178-184, 2001.

[0072] [Hexane Compatibility Test] The compatibility of the sample with hexane was evaluated by placing 1 mL of the sample (methyl ethyl ketone dispersions of surface-modified silica particles obtained in Examples 1-1 and 1-3 and Comparative Example 1-1, as described below) and 1 mL of hexane in a 20 mL glass bottle, shaking the bottle, and then checking the appearance. If the mixed solution of the sample and hexane gelled or aggregated after shaking, the compatibility was judged to be NG, and if neither gelling nor aggregated occurred, the compatibility was judged to be OK.

[0073] (Synthesis Example 1) Synthesis of Water-Dispersed Silica Sol c As a raw material, a water-soluble alkali metal silicate, a JIS No. 3 aqueous solution of sodium silicate was prepared. The main components of this sodium silicate aqueous solution other than water were SiO ２ The concentration is 28.8% by mass, Na ２ The sodium silicate aqueous solution was diluted with pure water to obtain a SiO ２A sodium silicate aqueous solution (a) having a concentration of 4% by mass was prepared. Next, the sodium silicate aqueous solution (a) was passed through a column packed with a hydrogen-type strongly acidic cation exchange resin (manufactured by The Dow Chemical Company, trade name: Amberlite IR-120B) at a space velocity of 4.5 per hour to remove cations, thereby preparing an activated silicic acid aqueous solution. A 10% by mass aqueous sodium hydroxide solution was added to the obtained activated silicic acid aqueous solution to adjust the pH to 8.5 to 9.5, thereby obtaining a stabilized activated silicic acid aqueous solution. The SiO of the obtained stabilized activated silicic acid aqueous solution was ２ The concentration was 3.2% by mass. 2,400 g of the stabilized activated silicic acid aqueous solution obtained above was placed in a 3 L SUS pressure vessel equipped with a stirrer, a heater, and the like, and the liquid temperature in the vessel was adjusted to 130 to 150°C by heating. After the temperature in the vessel reached 130 to 150°C, the vessel was heated for 2 hours and 30 minutes while maintaining the temperature at 130 to 150°C, thereby obtaining a colloidal silica dispersion having an average primary particle size of 10 to 15 nm. The obtained colloidal silica dispersion was filtered at room temperature using a commercially available ultrafiltration device equipped with a polysulfone ultrafiltration membrane (manufactured by Advantec Co., Ltd., product name: Q2000 150E) with a molecular weight cutoff of 200,000. ２ By concentrating the mixture to a concentration of 33 mass %, SiO ２ A colloidal silica dispersion was obtained as a precursor with an adjusted concentration. ２ The colloidal silica dispersion as a precursor with the adjusted concentration was passed through a column packed with a cation exchange resin (manufactured by The Dow Chemical Company, trade name: Amberlite IR-120B) at a space velocity of 10 per hour to remove cations, and a 10% by mass aqueous solution of sodium hydroxide was added to the resulting dispersion to adjust the pH to 7 to 8. ２The colloidal silica dispersion as a precursor with adjusted concentration and pH was placed in a reactor equipped with a stirrer, a heater, etc., in a 3 L stainless steel pressure vessel, and the temperature of the liquid in the vessel was adjusted to 250 to 260°C by heating. After the temperature in the vessel reached 250 to 260°C, the vessel was heated for 9 hours and 20 minutes while maintaining the temperature at 250 to 260°C. 50 g of the colloidal silica dispersion obtained above was placed in a 100 ml plastic vessel, and 25 ml of a cation exchange resin (manufactured by The Dow Chemical Company, trade name: Amberlite IR-120B) was added. The mixture was stirred with a magnetic stirrer for 30 minutes to remove cations. Next, 50 g of the obtained colloidal silica dispersion was placed in a 100 ml plastic container, and 25 ml of anion exchange resin (manufactured by The Dow Chemical Company, trade name: Amberlite IRA400J) was added, and the mixture was held for 30 minutes while stirring with a magnetic stirrer to remove anions. Next, 50 g of the obtained colloidal silica dispersion was placed in a 100 ml plastic container, and 25 ml of cation exchange resin (manufactured by The Dow Chemical Company, trade name: Amberlite IR-120B) was added, and the mixture was held for 30 minutes while stirring with a magnetic stirrer to remove cations. Pure water was added to the colloidal silica dispersion from which the cations and anions had been removed, and the silica concentration was adjusted to 20 mass%, to obtain water-dispersed silica sol c.

[0074] [Example 1-1] (a) Step: 2,500 g of water-dispersed silica sol a was placed in a 3 L glass reactor equipped with a stirrer, condenser, thermometer, and two injection ports, and heated to boil the silica sol. While the silica sol in the reactor was still boiling, methanol vapor generated in a separate boiler was continuously blown into the silica sol in the reactor, replacing the water dispersant with methanol. The replacement was terminated when the water content of the methanol dispersion reached 3.0% by mass or less, yielding 1,250 g of methanol-dispersed silica sol. The resulting methanol-dispersed silica sol had a silica concentration of 40.5% by mass, a water content of 1.5% by mass, and a viscosity of 2.5 mPa·s.

[0075] Step (b): 1,000 g of the obtained methanol-dispersed silica sol was placed in a 2-liter eggplant-shaped flask, and while stirring with a magnetic stirrer, 150 g of methyl ethyl ketone (MEK) was added. Further, a silica particle having a surface area of ​​1 nm determined by a nitrogen adsorption method was added. ２ DMMPS was added in an amount that gave 3 particles per 1000 particles, and the mixture was heated to 60°C and maintained for 3 hours. ２ HMDS was added in an amount that gave 5 particles per 1000 particles, and the mixture was heated to 60°C and maintained for 3 hours. Diisopropylamine was then added so that the pH (1+1+1) became 8.0 to 10.0, and the mixture was heated to 60°C and maintained for 1 hour to prepare a methanol / MEK dispersion of surface-modified silica particles.

[0076] Step (c): The eggplant-shaped flask containing the methanol / MEK dispersion of surface-modified silica particles was then placed in a rotary evaporator, and distillation was performed while supplying methyl ethyl ketone at a bath temperature of 80°C under a reduced pressure of 550 to 350 Torr. The dispersion medium was replaced with methyl ethyl ketone, yielding a methyl ethyl ketone dispersion of surface-modified silica particles. The resulting methyl ethyl ketone dispersion of surface-modified silica particles had a silica concentration of 42.7% by mass, a water content of 0.1% by mass or less, a methanol content of 0.1% by mass or less, and a total silanol ratio of 1.7% (Q2: 0%, Q3: 7.0%, Q4: 93.0%). Measurements were performed according to the procedure shown in the above-described NMR measurement conditions B, except that the methyl ethyl ketone dispersion was dried in a vacuum dryer at 100°C to prepare a measurement sample. ２９ Si NMR spectrum), the unit surface area of ​​the surface-modified silica particles (unit: nm ２ The ratio of the total number of carbon atoms per unit area was 10.

[0077] [Example 1-2] Instead of DMMPS in step (b) of Example 1-1, silica particles with a surface area of ​​1 nm contained in the silica sol were used. ２ A methanol-dispersed silica sol, a methanol / MEK dispersion of surface-modified silica particles, and a methyl ethyl ketone dispersion of surface-modified silica particles were prepared in the same manner as in steps (a) to (c) of Example 1-1, except that DTMS was added so that the amount was 1.0 particle per particle, and the mixture was similarly maintained at 60°C for 3 hours.

[0078] [Example 1-3] After adding DMMPS in step (b) of Example 1-1, the silica particles contained in the silica sol were further mixed to obtain a silica sol having a surface area of ​​1 nm ２ A methanol-dispersed silica sol, a methanol / MEK dispersion of surface-modified silica particles, and a methyl ethyl ketone dispersion of surface-modified silica particles were prepared in the same manner as in steps (a) to (c) of Example 1-1, except that DTMS was added so that the concentration was 1.0 particle per particle, the mixture was maintained at 60°C for 3 hours, and then HMDS was added.

[0079] [Example 1-4] 660 g of the water-dispersed silica sol c prepared in Synthesis Example 1 was diluted to 1,000 g with methanol, and the diluted solution was placed in a 2 L eggplant-type flask-equipped evaporator. Then, while gradually adding methanol, water was distilled off at 120 °C and 580 Torr, thereby replacing the water dispersing medium with methanol. The replacement was terminated when the water content of the methanol dispersion reached 3.0 mass% or less, yielding 1,000 g of methanol-dispersed silica sol. The resulting methanol-dispersed silica sol had a silica concentration of 13.2 mass%, a water content of 1.6 mass%, and a viscosity of 0.9 mPa·s. 20 g of the resulting methanol-dispersed silica sol was placed in a 100 mL eggplant-type flask, and while stirring with a magnetic stirrer, 3.0 g of methyl ethyl ketone (MEK) and a silica particle having a surface area of ​​1 nm determined by nitrogen adsorption were added. ２ DTMS was added in an amount that gave 3 particles per 1000 particles, and the mixture was heated to 60°C and maintained for 3 hours. ２HMDS was added in an amount that would result in 5 particles per 1000 particles, and the mixture was heated to 60°C and maintained for 3 hours. Diisopropylamine was then added so that the pH (1+1+1) was adjusted to 8.0 to 10.0, and the mixture was heated to 60°C and maintained for 1 hour to produce a methanol / MEK dispersion of surface-modified silica particles. The eggplant-shaped flask containing the methanol / MEK dispersion of surface-modified silica particles was then placed in a rotary evaporator, and distillation was carried out while supplying methyl ethyl ketone at a bath temperature of 80°C and a reduced pressure of 550 to 350 Torr. The dispersion medium was replaced with methyl ethyl ketone, yielding a methyl ethyl ketone dispersion of surface-modified silica particles. The resulting methyl ethyl ketone dispersion of surface-modified silica particles had a silica concentration of 10.1% by mass, a water content of 0.1% by mass or less, and a methanol content of 0.1% by mass or less.

[0080] [Example 1-5] 660 g of the water-dispersed silica sol c prepared in Synthesis Example 1 was diluted to 1,000 g with methanol, and the diluted solution was placed in a 2 L eggplant-type flask-equipped evaporator. Then, while gradually adding methanol, water was distilled off at 120 °C and 580 Torr, thereby replacing the water dispersing medium with methanol. The replacement was terminated when the water content of the methanol dispersion reached 3.0 mass% or less, yielding 1,000 g of methanol-dispersed silica sol. The resulting methanol-dispersed silica sol had a silica concentration of 13.2 mass%, a water content of 1.6 mass%, and a viscosity of 0.9 mPa·s. 20 g of the resulting methanol-dispersed silica sol was placed in a 100 mL eggplant-type flask, and while stirring with a magnetic stirrer, 3.0 g of methyl ethyl ketone (MEK) and a silica particle surface area of ​​1 nm determined by nitrogen adsorption were added. ２ DMMPS was added in an amount that gave 6 particles per 1000 particles, and the mixture was heated to 60°C and maintained for 3 hours. ２HMDS was added in an amount that would result in 5 particles per 1000 particles, and the mixture was heated to 60°C and maintained for 3 hours. Diisopropylamine was then added so that the pH (1+1+1) was adjusted to 8.0 to 10.0, and the mixture was heated to 60°C and maintained for 1 hour to produce a methanol / MEK dispersion of surface-modified silica particles. The eggplant-shaped flask containing the methanol / MEK dispersion of surface-modified silica particles was then placed in a rotary evaporator, and distillation was carried out while supplying methyl ethyl ketone at a bath temperature of 80°C and a reduced pressure of 550 to 350 Torr. The dispersion medium was replaced with methyl ethyl ketone, yielding a methyl ethyl ketone dispersion of surface-modified silica particles. The resulting methyl ethyl ketone dispersion of surface-modified silica particles had a silica concentration of 10.3% by mass, a water content of 0.1% by mass or less, and a methanol content of 0.1% by mass or less.

[0081] Comparative Example 1-1 1,000 g of methanol-dispersed silica sol obtained in step (a) of Example 1-1 was placed in a 2-liter eggplant-shaped flask, and while stirring with a magnetic stirrer, 150 g of methyl ethyl ketone and 100 g of silica particles having a surface area of ​​1 nm determined by nitrogen adsorption method were added. ２ DMMPS was added in an amount that gave 3 particles per 1000 particles, the mixture was heated to 60°C and maintained for 3 hours, diisopropylamine was then added so that the pH (1+1+1) became 8.0 to 10.0, the mixture was heated to 60°C and maintained for 1 hour, and a methanol / MEK dispersion of surface-modified silica particles was prepared. The same procedure as in step (c) of Example 1-1 was then carried out to prepare a methyl ethyl ketone dispersion of surface-modified silica particles.

[0082] [Comparative Example 1-2] Instead of DMMPS in Comparative Example 1-1, silica particles with a surface area of ​​1 nm contained in the silica sol were used. ２ The same procedure as in Comparative Example 1-1 was carried out except that 5 particles of HMDS per particle were added, to prepare a methyl ethyl ketone dispersion of surface-modified silica particles.

[0083] Comparative Example 1-3: 1,525 g of water-dispersed silica sol b was placed in a 2-L eggplant-shaped flask-equipped evaporator, and then methanol was gradually added while distilling off the water at 600 Torr, thereby replacing the water dispersant with methanol. The replacement was terminated when the water content of the methanol dispersion reached 3.0% by mass or less, yielding 1,000 g of methanol-dispersed silica sol. The resulting methanol-dispersed silica sol had a silica concentration of 30.5% by mass, a water content of 1.7% by mass, and a viscosity of 1.6 mPa·s. Further, operations similar to steps (b) and (c) of Example 1-1 were carried out to prepare a methanol dispersion of surface-modified silica particles and a methyl ethyl ketone dispersion of surface-modified silica particles.

[0084] Comparative Example 1-4 In Comparative Example 1-4, water-dispersed silica sol b was used.

[0085] Example 2-1 The methyl ethyl ketone dispersion of the surface-modified silica particles obtained in Example 1-1 was dried in a vacuum dryer at 100°C, and the resulting silica gel was pulverized in a mortar and further dried at 150°C for 1 hour to produce silica powder. The dielectric constant and dielectric loss tangent of the obtained silica powder were measured at 23°C and a frequency of 1 GHz. The dielectric properties of the surface-modified silica particles are shown in Table 2.

[0086] [Examples 2-2 to 2-5, Comparative Examples 2-1 to 2-4] Silica powders were prepared in the same manner as in Example 2-1 from the methyl ethyl ketone dispersions of the surface-modified silica particles obtained in Examples 1-2 to 1-5 and Comparative Examples 1-1 to 1-3 and the water-dispersed silica sol b of Comparative Example 1-4, and the dielectric constant and dielectric loss tangent were measured. The dielectric properties of the surface-modified silica particles are shown in Table 2.

[0087] [Example 3-1] The methyl ethyl ketone dispersion of the surface-modified silica particles obtained in Example 1-1 was dried in a vacuum dryer at 100°C to prepare silica powder. The hydrophobicity of the obtained silica powder was measured. The hydrophobicity of the surface-modified silica particles is shown in Table 2.

[0088] [Examples 3-2 to 3-5, Comparative Examples 3-1 to 3-4] Silica powders were prepared in the same manner as in Example 3-1 for the methyl ethyl ketone dispersions of the surface-modified silica particles obtained in Examples 1-2 to 1-5 and Comparative Examples 1-1 to 1-3, and the water-dispersed silica sol b of Comparative Example 1-4, and the hydrophobicity was measured. The hydrophobicity of the surface-modified silica particles is shown in Table 2.

[0089] [Example 4-1] The hexane compatibility of the methyl ethyl ketone dispersion of the surface-modified silica particles obtained in Example 1-1 was confirmed. The hexane compatibility of the surface-modified silica particles is shown in Table 2.

[0090] [Example 4-2, Comparative Example 4-1] The hexane compatibility of the methyl ethyl ketone dispersions of surface-modified silica particles obtained in Examples 1-3 and Comparative Example 1-1 was confirmed. The hexane compatibility of the surface-modified silica particles is shown in Table 2.

[0091] Example 5-1: The compatibility of the surface-modified silica particles obtained in Example 1-1 with an organic resin material (maleimide resin) was confirmed. 50 g of the methyl ethyl ketone dispersion of the surface-modified silica particles obtained in Example 1-1 was placed in a 300 mL eggplant-shaped flask, and 20 g of a low-viscosity liquid maleimide resin (maleimide-terminated polyimide resin, product name: BMI-689, 1000-2000 cP (25°C), manufactured by DMI Corporation) was added while stirring with a magnetic stirrer. The eggplant-shaped flask containing the resulting mixture of the methyl ethyl ketone dispersion of surface-modified silica particles and the maleimide resin was then placed in a rotary evaporator, and distillation was performed at a bath temperature of 80°C under reduced pressure of 400 to 30 Torr. The dispersion medium was replaced from methyl ethyl ketone to maleimide resin, yielding a maleimide resin dispersion of surface-modified silica particles. The resulting maleimide resin dispersion of surface-modified silica particles had a silica concentration of 30.4% by mass, a water content of 0.1% by mass or less, a methanol content of 0.1% by mass or less, a methyl ethyl ketone content of 0.1% by mass or less, a viscosity of 6000 to 7000 cP (B-type viscometer, temperature 25°C), an average dispersed particle size measured by dynamic light scattering (hereinafter referred to as dynamic light scattering particle size) of 79.2 nm, and a yellow, transparent appearance. Furthermore, the resulting maleimide resin dispersion of surface-modified silica particles showed no change in appearance and no precipitate or sediment was formed even after being left to stand at room temperature for one week. The resulting maleimide resin dispersion of surface-modified silica particles was then applied to a glass substrate degreased with acetone using a hand-applied bar coater (gap: 25 μm). The substrate was then baked for 30 minutes on a hot plate heated to 100°C under a nitrogen atmosphere. The temperature of the hot plate was then further increased to 230°C, and the substrate was then baked for 120 minutes, yielding a cured film of a composite material containing surface-modified silica particles and maleimide resin (see FIG. 1(B)). The resulting cured film was yellow and transparent, and no repellency was observed with the glass substrate (for reference, in FIG. 1, the areas where the resin dispersion and the low-viscosity liquid maleimide resin described below were applied are indicated by black frames). The film thickness was measured using a constant-pressure thickness gauge (manufactured by Teclock Corporation, model: PG-01A) and was found to be 19 μm.On the other hand, as an example in which surface-modified silica particles were not used, the above-mentioned low-viscosity liquid maleimide resin (trade name: BMI-689) alone was used and applied to a glass substrate that had been degreased with acetone using a hand-applied bar coater (gap: 25 μm). The coating was then baked for 30 minutes on a hot plate heated to 100°C under a nitrogen atmosphere, and the temperature of the hot plate was further increased to 230°C, after which the coating was baked for 120 minutes, thereby obtaining a cured film of only the maleimide resin (see FIG. 1(A)). The obtained cured film was yellow and transparent, but repelling from the glass substrate was observed.

[0092] Example 5-2: The compatibility of the surface-modified silica particles obtained in Example 1-1 with an organic resin material (epoxy resin) was confirmed. 50 g of the methyl ethyl ketone dispersion of the surface-modified silica particles obtained in Example 1-1 was placed in a 300 mL eggplant-shaped flask, and 20 g of epoxy resin (Nippon Steel Chemical & Material Co., Ltd., bisphenol A-type epoxy resin, product name: YD-8125, 3900-5300 cP) was added while stirring with a magnetic stirrer. The eggplant-shaped flask containing the resulting mixture of the methyl ethyl ketone dispersion of surface-modified silica particles and the epoxy resin was then placed in a rotary evaporator, and distillation was performed at a bath temperature of 80°C under reduced pressure of 400 to 30 Torr. The dispersion medium was completely replaced from methyl ethyl ketone to epoxy resin, yielding an epoxy resin dispersion of surface-modified silica particles. The obtained epoxy resin dispersion of surface-modified silica particles had a silica concentration of 32.1% by mass, a water content of 0.1% by mass or less, a methanol content of 0.1% by mass or less, a methyl ethyl ketone content of 0.1% by mass or less, a viscosity of 14,000 to 16,000 cP (B-type viscometer, temperature 25°C), an average dispersed particle size measured by dynamic light scattering (hereinafter referred to as dynamic light scattering particle size) of 78.7 nm, an epoxy equivalent of 264 g / eq (in accordance with JIS K7236), and a white, transparent appearance. Furthermore, the obtained epoxy resin dispersion of surface-modified silica particles showed no change in appearance and no precipitate was formed even after being left to stand at room temperature for one week.

[0093]

[0094] As shown in Table 2, the surface-modified silica particles of Examples 1-1 to 1-5 had an average primary particle diameter of 5 nm to 500 nm, a dielectric loss tangent value of less than 0.01 at a frequency of 1 GHz (Examples 2-1 to 2-5), and a hydrophobicity (%) of 40 or more (Examples 3-1 to 3-5), confirming that they achieved both low dielectric properties and high hydrophobicity. The surface-modified silica particles of Examples 1-1 to 1-5 were obtained by comparing the water vapor adsorption surface area / nitrogen adsorption surface area (S Ｈ２Ｏ / S Ｎ２ ) is 0.6 or less, the total silanol group ratio is 5% or less, and the surface-modified silica particles are surface-modified silica particles treated with at least two different surface modifiers.

[0095] On the other hand, the surface-modified silica particles of Comparative Examples 1-1 and 1-2 had an average primary particle diameter of 5 nm to 500 nm and a dielectric loss tangent value of less than 0.01 at a frequency of 1 GHz (Comparative Examples 2-1 to 2-2), but had a hydrophobicity (%) of less than 40 (Comparative Examples 3-1 to 3-2), making them silica particles with poor hydrophobicity. The surface-modified silica particles of Comparative Examples 1-1 and 1-2 had a water vapor adsorption surface area / nitrogen adsorption surface area (S Ｈ２Ｏ / S Ｎ２ ) was 0.6 or less, and the total silanol group ratio was 5% or less, and the surface-modified silica particles were 5% or less, but were surface-modified silica particles treated with one type of surface modifier. Furthermore, the surface-modified silica particles of Comparative Example 1-3 had an average primary particle diameter of 5 nm to 500 nm and a hydrophobicity (%) of 40 or more (Comparative Example 3-3), but the dielectric loss tangent value at a frequency of 1 GHz was significantly greater than 0.01 (Comparative Example 2-3), and the silica particles did not satisfy the low dielectric characteristic. The surface-modified silica particles of Comparative Example 1-3 were silica particles treated with at least two different surface modifiers, and the water vapor adsorption surface area / nitrogen adsorption surface area (S Ｈ２Ｏ / S Ｎ２) was 0.6 or more, and the total silanol group ratio was 5% or more. Furthermore, the silica particles of Comparative Examples 1-4, i.e., unmodified silica particles, had an average primary particle diameter of 5 nm to 500 nm, but the dielectric loss tangent value at a frequency of 1 GHz was significantly greater than 0.01 (Comparative Examples 2-4), and the hydrophobicity (%) was 0 (Comparative Examples 3-4). The results shown in the comparative examples above demonstrate that it is not easy to achieve nano-order silica particles that combine a low dielectric loss tangent and a high hydrophobicity.

[0096] Furthermore, as shown in Table 2, it was confirmed that the hexane compatibility of Examples 1-1 and 1-3, which are methyl ethyl ketone dispersions in which surface-modified silica particles are dispersed and which have a hydrophobicity degree of 40 or more, was OK (Examples 4-1 and 4-2).

[0097] Furthermore, when the surface-modified silica particles according to the present invention were used as a composite material with an organic resin material, neither changes in appearance nor the formation of precipitates or sediments were observed even after standing at room temperature for one week, demonstrating that the material is highly stable (Examples 5-1 and 5-2). Furthermore, as shown in Figure 1, when a cured film was formed on a glass substrate using only the organic resin material (maleimide resin), repellency occurred on the substrate (Figure 1(A)). However, when the surface-modified silica particles according to the present invention were added to the organic resin material (maleimide resin) to form a composite material, the cured film did not repellency on the glass substrate (Figure 1(B)), and a transparent film (molded product) could be formed.

[0098] The hydrophobic silica particles of the present invention achieve a high hydrophobicity of 40% or more and reduce the dielectric loss tangent of conventional hydrophobic silica sols to less than half. That is, the hydrophobicity can be improved by 20% or more while maintaining the low dielectric loss tangent of surface-modified silica particles coated with a single surface modifier. This makes the particles suitable not only for composite materials but also for high-frequency applications.

Claims

1. Surface-modified silica particles with a degree of hydrophobicity of 40% or more, characterized by an average primary particle diameter of 5 to 500 nm and a dielectric loss tangent at 1 GHz of less than 0.

01.

2. The surface-modified silica particles according to claim 1, characterized in that the silica particles from which the surface modifier has been removed satisfy the following conditions (i) and (ii). (i) Specific surface area due to water vapor adsorption (S Ｈ２Ｏ ) and specific surface area due to nitrogen adsorption (S Ｎ２ ) ratio (S Ｈ２Ｏ / S Ｎ２ ) is 0.6 or less. (ii) The total silanol group content shown in formula (1) below is 5% or less. Total silanol group percentage (%) = (Q2 × 2 / 4 + Q3 × 1 / 4 + Q4 × 0 / 4) ... Equation (1) [In equation (1), Q2, Q3, and Q4 are, respectively, ２９ Q4 represents the percentage of the peak area derived from the structure of each silicon atom relative to the total peak area derived from the structure of each silicon atom obtained by Si NMR measurement (100%), where Q2 represents the percentage of the peak area derived from the structure of a silicon atom bonded with two oxygen atoms and two hydroxyl groups, Q3 represents the percentage of the peak area derived from the structure of a silicon atom bonded with three oxygen atoms and one hydroxyl group, and Q4 represents the percentage of the peak area derived from the structure of a silicon atom bonded with four oxygen atoms.

3. The unit surface area (unit: nm) of the surface-modified silica particles ２ The surface-modified silica particles according to claim 1, wherein the ratio of the total number of carbon atoms per particle is 2 to 40.

4. The surface-modified silica particles are characterized in that at least a portion of their surface is coated with at least two types of surface modifiers. The at least two surface modifiers include an organosilicon compound having at least one substituent a1 selected from substituent group a, which consists of alkyl groups having 1 to 20 carbon atoms, aryl groups having 6 to 12 carbon atoms, and substituents having unsaturated bonds, and an organosilicon compound having at least one substituent a2 selected from substituent group a, which is different from substituent a1. Surface-modified silica particles according to claim 1.

5. The surface-modified silica particles are characterized in that at least a portion of each of at least two types of surface modifiers is bonded to at least a portion of their surface. The at least two surface modifiers include an organosilicon compound having at least one substituent a1 selected from substituent group a, which consists of alkyl groups having 1 to 20 carbon atoms, aryl groups having 6 to 12 carbon atoms, and substituents having unsaturated bonds, and an organosilicon compound having at least one substituent a2 selected from substituent group a, which is different from substituent a1. Surface-modified silica particles according to claim 1.

6. The surface-modified silica particles according to claim 4 or claim 5, wherein the substituent group a consists of a methyl group, a phenyl group, a phenylmethyl group, and a decyl group.

7. The surface-modified silica particles according to claim 4 or 5, wherein the organosilicon compound is a compound having a hydrolyzable group together with a substituent selected from the substituent group a.

8. The surface-modified silica particles according to claim 4 or claim 5, wherein the surface modifier is at least two compounds selected from those represented by the following formulas (a) to (c). 【Chemistry 1】

9. The surface-modified silica particles have a surface area of ​​1 nm ２ Each particle is either coated with at least two of the aforementioned surface modifiers at a ratio of 0.5 to 20 particles, or has at least a portion of the aforementioned at least two surface modifiers bound to its surface. Surface-modified silica particles according to claim 3.

10. A silica dispersion in which the surface-modified silica particles described in claim 1 are dispersed in at least one organic solvent selected from alcohols, ketones, hydrocarbons, amides, ethers, esters, and amines.

11. A composite material comprising surface-modified silica particles as described in claim 1 and an organic resin material or polysiloxane.

12. The composite material according to claim 11, wherein the organic resin material is at least one selected from the group consisting of styrene resin, epoxy resin, cyanate resin, phenolic resin, acrylic resin, maleimide resin, urethane resin, polyimide, polytetrafluoroethylene, cycloolefin polymer, unsaturated polyester, vinyl triazine, polyphenylene sulfide, crosslinkable polyphenylene oxide, and curable polyphenylene ether.

13. Semiconductor device materials, copper-clad laminates, insulating films, flexible wiring materials, flexible displays The composite material according to claim 11 or claim 12, having an application selected from the group consisting of play materials, antenna materials, optical wiring materials, and sensing materials.

14. The following steps (A) to (C): (A) Process: The average primary particle diameter is 5 to 500 nm, and the ratio of the specific surface area (S Ｈ２Ｏ ) by water vapor adsorption to the specific surface area (S Ｎ２ ) by nitrogen adsorption (S Ｈ２Ｏ / S Ｎ２ ) is 0.6 or less, and the total silanol group ratio represented by the following formula (1) is 5% or less: Total silanol group percentage (%) = (Q2 × 2 / 4 + Q3 × 1 / 4 + Q4 × 0 / 4) ... Equation (1) [In equation (1), Q2, Q3, and Q4 are, respectively, ２９ Q4 represents the percentage of the peak area derived from the structure of each silicon atom relative to the total peak area derived from the structure of each silicon atom obtained by Si NMR measurement (100%), where Q2 represents the percentage of the peak area derived from the structure of a silicon atom bonded with two oxygen atoms and two hydroxyl groups, Q3 represents the percentage of the peak area derived from the structure of a silicon atom bonded with three oxygen atoms and one hydroxyl group, and Q4 represents the percentage of the peak area derived from the structure of a silicon atom bonded with four oxygen atoms. A step to prepare a silica sol using silica particles as the dispersed phase and an alcohol with 1 to 4 carbon atoms as the dispersion medium. (B) Step: A step of heating and stirring at 40 to 100°C for 0.1 to 10 hours with at least two surface modifiers, each containing an organosilicon compound having at least one substituent a1 selected from substituent group a consisting of alkyl groups having 1 to 20 carbon atoms, aryl groups having 6 to 12 carbon atoms, and substituents having an unsaturated bond, and an organosilicon compound having at least one substituent a2 selected from substituent group a and different from substituent a1, and the silica sol obtained in step (A), and (C) Step: A step to remove the alcohol solvent from the silica sol after step (B). including, A method for producing surface-modified silica particles.

15. Either or both of steps (B) and (C) are carried out under reduced pressure. A method for producing surface-modified silica particles according to claim 14.

16. (A) The method for producing surface-modified silica particles according to claim 14, wherein the silica sol prepared in step (A) is a silica sol with a water content of 0.1 to 5% by mass.

17. The method for producing surface-modified silica particles according to claim 14, wherein the silica sol prepared in step (A) is a silica sol obtained by hydrothermally synthesizing an aqueous silica sol at 200 to 380°C and 2 MPa to 22 MPa, and then solvent-substituted with an alcohol having 1 to 4 carbon atoms.

18. The following steps (A), (B), and (D): (A) Process: The average primary particle diameter is 5 to 500 nm, and the specific surface area (S) is determined by water vapor adsorption. Ｈ２Ｏ ) and specific surface area due to nitrogen adsorption (S Ｎ２ ) ratio (S Ｈ２Ｏ / S Ｎ２ ) is 0.6 or less, and the total silanol group percentage shown in the following formula (1) is 5% or less: Total silanol group percentage (%) = (Q2 × 2 / 4 + Q3 × 1 / 4 + Q4 × 0 / 4) ... Equation (1) [In equation (1), Q2, Q3, and Q4 are, respectively, ２９ Q4 represents the percentage of the peak area derived from the structure of each silicon atom relative to the total peak area derived from the structure of each silicon atom obtained by Si NMR measurement (100%), where Q2 represents the percentage of the peak area derived from the structure of a silicon atom bonded with two oxygen atoms and two hydroxyl groups, Q3 represents the percentage of the peak area derived from the structure of a silicon atom bonded with three oxygen atoms and one hydroxyl group, and Q4 represents the percentage of the peak area derived from the structure of a silicon atom bonded with four oxygen atoms. Silica zo The process of preparing the ingredients, (B) Step: A step of heating and stirring at 40 to 100°C for 0.1 to 10 hours with at least two surface modifiers, each containing an organosilicon compound having at least one substituent a1 selected from substituent group a consisting of alkyl groups having 1 to 20 carbon atoms, aryl groups having 6 to 12 carbon atoms, and substituents having an unsaturated bond, and an organosilicon compound having at least one substituent a2 selected from substituent group a and different from substituent a1, and the silica sol obtained in step (A), and (D) A step of solvent replacement of the silica sol after step (B) with at least one solvent selected from alcohols, ketones, hydrocarbons, amides, esters, ethers, or amines. including, A method for producing a surface-modified silica dispersion.

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