WO2024096021A1

WO2024096021A1 - Hydrophobic low-loss-tangent silica sol and production method therefor

Info

Publication number: WO2024096021A1
Application number: PCT/JP2023/039319
Authority: WO
Inventors: 豪中田; 和也江原; 由紀松山; 雅敏杉澤
Original assignee: 日産化学株式会社
Priority date: 2022-10-31
Filing date: 2023-10-31
Publication date: 2024-05-10

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

Hydrophobized low dielectric tangent silica sol and method for producing same

The present invention relates to hydrophobized silica particles with a low dielectric tangent, a dispersion thereof, and a method for producing the same.

In recent years, with the increase in the amount of information and communication in the field of communications such as 5G, the use of high-frequency bands has become widespread in electronic devices and communications devices.
The use of high frequency bands poses the problem of increased transmission loss of circuit signals, so materials with low dielectric loss tangents are generally used for insulators that make up electrical and electronic components such as antennas, circuits, and 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. For this reason, ceramic filler-filled polymer materials that combine these materials to achieve both low dielectric constant and low dielectric loss tangent properties have become widespread (Patent Document 1, Patent Document 2).

As the above-mentioned ceramic filler (inorganic filler), fused silica having a size on the order of microns is generally widely used. However, since coarse particles generated during production have a significant effect on the performance of molded articles, separation and removal of the coarse particles has become an issue (Non-Patent Document 1, Patent Document 2, Patent Document 3, Patent Document 4).
On the other hand, silica particles with an average particle size of nano-order are considered to have an advantage in that coarse particles are less likely to be produced during production, and because filtration and centrifugation are possible, even if coarse particles are produced, they can be easily separated and removed. Nano-order particles are also considered to have various advantages, such as being applicable to transparent polymer materials and having a greater composite effect than micro-order fillers (Patent Document 5, Patent Document 6).
On the other hand, there have been proposals to hydrophobize the surfaces of silica particles to increase dispersibility in hydrophobic solvents and thereby improve the ease of storage, transportation, and mixing with resins (Patent Documents 7 and 8).

JP 2014-24916 A Patent No. 6793282 JP 2004-269636 A Patent No. 6546386 Patent No. 5862886 Patent No. 6813815 Japanese Patent No. 6805538 Japanese Patent No. 6746025

As described above, in ceramic fillers, nano-order particles have various advantages. However, existing nano-order particles have a high dielectric tangent, making them difficult to apply to materials for electronic devices and the like that operate in high frequency bands.
Furthermore, when such nano-order particles are to be composited with a resin material, the particles are either left as is or dispersed in a solvent and then composited with the resin material. However, inorganic particles generally do not have sufficient dispersion stability, particularly in highly hydrophobic solvents, and sedimentation and separation occur, leaving issues in terms of work efficiency and storage.
As described above, it has been difficult for existing nano-order particles to achieve both a low dielectric tangent and a high degree of hydrophobicity.

The present invention was made in consideration of the above circumstances, and aims to provide hydrophobic nano-order particles with a low dielectric tangent, specifically, silica particles with a dielectric tangent of less than 0.01 at 1 GHz and a hydrophobicity of 40% or more, and a dispersion thereof.

That is, in a first aspect, the present invention provides surface-modified silica particles having a hydrophobicity degree 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;
As a second aspect, the surface-modified silica particles according to the first aspect, from which a surface modifier has been removed, are characterized in that the following items (i) and (ii) are satisfied:
(i) The ratio (SH ₂ O/SN ₂ ) of the specific surface area by water vapor adsorption (S _H2O ) to the specific surface area by nitrogen adsorption (S _N2 ) is 0.6 or less.
(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) Equation (1)
[In formula (1), Q2, Q3, and Q4 each represent the percentage (%) of the peak area derived from each silicon atom structure relative to the total peak area (100%) derived from the silicon atom structure obtained by ^29Si NMR measurement, where Q2 represents the percentage of the peak area derived from a silicon atom structure having two oxygen atoms and two hydroxyl groups bonded thereto, Q3 represents the percentage of the peak area derived from a silicon atom structure having three oxygen atoms and one hydroxyl group bonded thereto, and Q4 represents the percentage of the peak area derived from a silicon atom structure having four oxygen atoms bonded thereto.]
As a third aspect, the surface-modified silica particles according to the first or second aspect, characterized in that the ratio of the total number of carbon atoms per unit surface area (unit: nm ² ) of the surface-modified silica particles is 2 to 40;
As a fourth aspect, the surface-modified silica particle according to any one of the first to third aspects, characterized in that at least a part of the surface of the surface-modified silica particle 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 the substituent a1;
As a fifth aspect, the surface-modified silica particle according to any one of the first to third aspects, characterized in that the surface-modified silica particle has 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 the substituent a1;
As a sixth aspect, the surface-modified silica particles according to the fourth or fifth aspect, in which the substituent group a is a 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 together with a substituent selected from the substituent group a.
According to an eighth aspect, the surface-modified silica particle according to the fourth or fifth aspect, in which the surface modifier is at least two types selected from the compounds represented by the following formulas (a) to (c):

As a ninth aspect, the surface-modified silica particles are particles whose surfaces are coated with the at least two types of surface modifiers at a ratio of 0.5 to 20 particles per 1 ^nm2 of the surface area of the particles, or particles whose surfaces are at least partially bound to the at least two types of surface modifiers.
The surface-modified silica particles according to any one of the third to eighth aspects,
As a tenth aspect, a silica dispersion 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;
According to an eleventh aspect, there is provided a composite material comprising the surface-modified silica particle according to any one of the first to ninth aspects and an organic resin material or a polysiloxane.
According to a twelfth aspect, the composite material according to the eleventh aspect, wherein 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 phenol 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, the composite material according to the eleventh or twelfth aspect 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, the present invention relates to a method for producing a method for producing a semiconductor device comprising the steps (A) to (C) below:
Step (A): an average primary particle size is 5 to 500 nm, the ratio (S _H2O /S _N2 ) of the specific surface area determined by water vapor adsorption (S _H2O ) to the specific surface area determined by nitrogen adsorption (S _N2 ) is 0.6 or less, and the total silanol group rate represented by the following formula (1) is 5% or less:
Total silanol group ratio (%)=(Q2×2/4+Q3×1/4+Q4×0/4) Equation (1)
[In formula (1), Q2, Q3, and Q4 each represent the percentage (%) of the peak area derived from each silicon atom structure relative to the total peak area (100%) derived from the silicon atom structure obtained by ^29Si NMR measurement, where Q2 represents the percentage of the peak area derived from a silicon atom structure having two oxygen atoms and two hydroxyl groups bonded thereto, Q3 represents the percentage of the peak area derived from a silicon atom structure having three oxygen atoms and one hydroxyl group bonded thereto, and Q4 represents the percentage of the peak area derived from a silicon atom structure having four oxygen atoms bonded thereto.]
preparing a silica sol having silica particles as a dispersoid and an alcohol having 1 to 4 carbon atoms as a dispersion medium;
Step (B): a step of heating and stirring at least two types of surface modifiers including an organosilicon compound having at least one substituent a1 selected from a 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 the substituent group a and different from the substituent a1, and the silica sol obtained in Step (A) at 40 to 100° C. for 0.1 to 10 hours; and Step (C): a step of removing the alcohol solvent from the silica sol obtained in Step (B).
including,
A method for producing surface-modified silica particles,
As a fifteenth aspect, the method for producing surface-modified silica particles according to the fourteenth aspect, in which either one or both of the step (B) and the step (C) are carried out under reduced pressure;
As a sixteenth aspect, the method for producing surface-modified silica particles according to the fourteenth aspect, in which the silica sol prepared in the step (A) has a water content of 0.1 to 5 mass %;
As a seventeenth aspect, the method for producing surface-modified silica particles according to the fourteenth aspect, in which the silica sol prepared in the step (A) is an aqueous silica sol hydrothermally synthesized at 200 to 380° C. and 2 to 22 MPa, and the aqueous silica sol is subjected to solvent substitution with an alcohol having 1 to 4 carbon atoms;
As an eighteenth aspect, the present invention provides a method for producing a method for manufacturing a semiconductor device comprising the following steps (A), (B) and (D):
Step (A): an average primary particle size is 5 to 500 nm, the ratio (S _H2O /S _N2 ) of the specific surface area determined by water vapor adsorption (S _H2O ) to the specific surface area determined by nitrogen adsorption (S _N2 ) is 0.6 or less, and the total silanol group rate represented by the following formula (1) is 5% or less:
Total silanol group ratio (%)=(Q2×2/4+Q3×1/4+Q4×0/4) Equation (1)
[In formula (1), Q2, Q3, and Q4 each represent the percentage (%) of the peak area derived from each silicon atom structure relative to the total peak area (100%) derived from the silicon atom structure obtained by ^29Si NMR measurement, where Q2 represents the percentage of the peak area derived from a silicon atom structure having two oxygen atoms and two hydroxyl groups bonded thereto, Q3 represents the percentage of the peak area derived from a silicon atom structure having three oxygen atoms and one hydroxyl group bonded thereto, and Q4 represents the percentage of the peak area derived from a silicon atom structure having four oxygen atoms bonded thereto.]
preparing a silica sol having silica particles as a dispersoid and an alcohol having 1 to 4 carbon atoms as a dispersion medium;
Step (B): a step of heating and stirring at least two types of surface modifiers including an organosilicon compound having at least one substituent a1 selected from the 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 the substituent group a and different from the substituent a1, and the silica sol obtained in step (A) at 40 to 100° C. for 0.1 to 10 hours; and (D) a step of subjecting the silica sol obtained in step (B) to solvent replacement with at least one solvent selected from alcohols, ketones, hydrocarbons, amides, esters, ethers, or amines.
The present invention relates to a method for producing a surface-modified silica dispersion, comprising the steps of:

The surface-modified silica particles of the present invention are hydrophobic and have the effect of exhibiting low dielectric properties. They can also be well dispersed in organic solvents. Furthermore, the silica particles of the present invention can form composite materials with organic resin materials or polysiloxanes, and are therefore expected to be used in the production of semiconductor device materials, etc.

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)).

<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 dissipation factor of less than 0.01 at 1 GHz, and a hydrophobicity of 40% or more (hereinafter also referred to as hydrophobized silica particles).

The surface-modified silica particles according to the present invention preferably satisfy the following items (i) and (II) in the silica particles from which the surface modifier has been removed: "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 ratio (S _H2O /S _N2 ) of the specific surface area by water vapor adsorption (S _H2O ) to the specific surface area by nitrogen adsorption (S _N2 ) is 0.6 or less;
(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) Equation (1)
[In formula (1), Q2, Q3, and Q4 each represent the percentage (%) of the peak area derived from each silicon atom structure relative to the total peak area (100%) derived from the silicon atom structure obtained by ^29Si NMR measurement, where Q2 represents the percentage of the peak area derived from a silicon atom structure having two oxygen atoms and two hydroxyl groups bonded thereto, Q3 represents the percentage of the peak area derived from a silicon atom structure having three oxygen atoms and one hydroxyl group bonded thereto, and Q4 represents the percentage of the peak area derived from a silicon atom structure having four oxygen atoms bonded thereto.]

<Hydrophobicity>
The degree of 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 when mixed with water and methanol (also known as methanol wettability), and is generally used as an index of the hydrophobicity of the silica surface.
The method for measuring the hydrophobicity 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 judged to have completely settled by visual observation, the dropping 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 the hydrophobicity (see formula (2) below).
Hydrophobicity (%) = [V _MeOH / (V _MeOH + 50)] × 100 ... Formula (2)
V _MeOH : Volume of methanol dropped (unit: mL)
The hydrophobic silica particles according to the present invention have a hydrophobicity of 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 a re-stirring step before use can be simplified/labor-saving, which is expected to facilitate the preparation of a composite material.

<Average primary particle size>
The average primary particle diameter of the hydrophobized silica particles according to the present invention can be a specific surface area diameter calculated from the specific surface area (S _N2 ) measured by the BET method using nitrogen gas as molecules adsorbed onto the particle surfaces.
The specific surface area diameter (average primary particle diameter: D (nm)) is the primary particle diameter calculated from the specific surface area S (m ² /g) measured by the _nitrogen adsorption method (BET method) by the formula D (nm) = 2720/S, and means the particle diameter converted into spherical silica particles.
The hydrophobized silica particles according to the present invention can have an average primary particle size 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 making the average primary particle size of the hydrophobic silica particles 5 nm to 500 nm, the particles can exhibit a low dielectric tangent and can be well dispersed in an organic solvent. Furthermore, when the hydrophobic silica particles are used to mold a composite material, defects can be suppressed and high transparency can be achieved.

<Specific surface area ratio (S _H2O /S _N2 )>
The ratio (S _H2O /S _N2 ) of the specific surface area due to water vapor adsorption (S H2O ) to the specific surface _area due to nitrogen adsorption (S _N2 ) is an indicator of the amount of active sites (surface silanols) present per unit surface area of the particle, and a larger value indicates that more active sites are present on the silica surface.
The specific surface area by water vapor adsorption (S _H2O ) can be measured by the BET method using water vapor as molecules adsorbed onto the particle surface, and as described above, the specific surface area by nitrogen adsorption (S _N2 ) can be measured by the BET method using nitrogen gas as molecules adsorbed onto the particle surface.
The hydrophobized silica particles (surface-modified silica particles) according to the present invention can be silica particles from which a surface modifier has been removed, and have the specific surface area ratio (S _H2O /S _N2 ) of 0.6 or less. By using silica particles having such a S _H2O /S _N2 ratio, the surface of the silica particles can be modified without increasing the dielectric tangent, and the dispersibility in organic solvents can be improved.

<Specific surface area by water vapor adsorption (S _H2O )>
The hydrophobized silica particles (surface-modified silica particles) according to the present invention can be silica particles from which a surface modifier has been removed, and the specific surface area (S _H2O ) determined by water vapor adsorption can be in the range of, for example, 5 to 500 m ² /g, 5 to 300 m ² /g, or 5 to 100 m ³ /g.
By setting the specific surface area (S _H2O ) to 5 to 500 m ² /g, it is possible to suppress a decrease in dielectric tangent due to moisture absorption, perform surface modification of the silica particles, and enable good dispersibility in organic solvents.

<Specific surface area by nitrogen adsorption (S _N2 )>
The hydrophobized silica particles (surface-modified silica particles) according to the present invention can be silica particles from which the surface modifier has been removed, and have a specific surface area (S _N2 ) measured by nitrogen adsorption in the range of, for example, 25 to 550 m ² /g, or 25 to 300 m ² /g, or 25 to 250 m ² /g.
By setting the specific surface area (S _N2 ) to 25 to 550 m ² /g, a low dielectric tangent can be maintained.

<Total silanol group ratio>
The silicon atoms in silica include silicon atoms that are not bonded to a hydroxy group 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: a silicon atom bonded to two oxygen atoms and two hydroxyl groups (Q2), a silicon atom bonded to three oxygen atoms and one hydroxyl group (Q3), and a silicon atom bonded to four oxygen atoms (Q4).

Then, by determining the proportions of Q2, Q3, and Q4 in silicon atoms in the silica, the amount of silanol (Si-OH) groups in the silica can be estimated.
In this specification, the total silanol group ratio refers to the ratio of silanol groups present in all silicon atoms of the Q2 to Q4 structures present in the silica particles.

The abundance ratio of silanol groups on silicon atoms having the above Q2 to Q4 structures can be measured, for example, by a ^29Si NMR method using a water-dispersed silica sol containing silica particles to be investigated for the abundance ratio, or a ^29Si NMR method using a silica particle powder.
Specifically, the spectrum obtained by the ²⁹ Si NMR method 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 (100%) of each peak is the content ratio (mol%) of each structure (Q2 to Q4) in the silica particle to be measured. Then, using this value and the content ratio of hydroxyl groups to the total number of moles of oxygen atoms and hydroxyl groups in each structure Q2 to Q4, the total silanol group ratio (%) can be calculated according to the following formula.
Total silanol group ratio (%)=(Q2×2/4+Q3×1/4+Q4×0/4) Equation (1)
In the above formula, Q2, Q3, and Q4 respectively represent the ratio (%) of the peak area attributable to each silicon atom structure to the total peak area (100%) attributable to the silicon atom structure obtained by ^29Si NMR measurement, i.e., the content ratio of each structure obtained from the above NMR measurement results.
In the surface-modified silica particles according to the present invention, in the silica particles from which the surface modifier has been removed, in a ²⁹ Si NMR method using a water-dispersed silica sol containing silica particles, 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 the silica particles from which the surface modifier has been removed, in a ²⁹ Si NMR method using a silica particle powder, 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.

The hydrophobized silica particles (surface-modified silica particles) of the present invention have a total silanol group rate of 5% or less in silica particles from which the surface modifier has been removed. If the rate is greater than 5%, the dielectric constant and dielectric tangent will not both be low and the dielectric properties will not be exhibited.

In one embodiment of the hydrophobized silica particles (surface-modified silica particles) according to the present invention, the ratio of the total number of carbon atoms per unit surface area (unit: nm ² ) is 2 to 40, for example, 2 to 20, 5 to 20, or 5 to 15.

The unmodified silica particles constituting the hydrophobized silica particles (surface-modified silica particles) of the present invention are not particularly limited in the method of production, but are preferably heat-treated in water at 200 to 380°C. The heat treatment can be carried out using a pressure-resistant container (autoclave).

<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 have at least a portion of each of the at least two types of surface modifiers bonded to at least a portion of their surface.
In this specification, the term "surface modification" includes both an embodiment in which the surface of a silica particle is coated with a surface modifier, and an embodiment in which the surface modifier is bonded to the surface of a silica particle, and these embodiments are collectively referred to as "surface-modified silica particles".
In the present invention, "at least a part of the surface of the silica particle is coated with a surface modifier" means that the surface modifier (such as an organosilicon compound described later) coats at least a part of the surface of the silica particle, that is, it includes an embodiment in which the surface modifier covers a part of the surface of the silica particle 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, which is an example of the surface modifier, is bonded to the surface of the silica particle.
In the present invention, "at least a portion of the surface modifier is bonded to at least a portion of the surface of the silica particle" means 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., it 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 further an embodiment in which the surface modifier is bonded to the entire surface of the silica particle and covers the entire surface.

In one embodiment of the present invention, the surface modifier is an organosilicon compound having at least one substituent selected from the 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 (these may also be collectively referred to simply as "substituent").
In a preferred embodiment, the hydrophobized silica particles according to the present invention are surface-modified by at least two of the above-mentioned surface modifiers, that is, surface-modified by two or more of the organosilicon compounds having at least one substituent selected from the above-mentioned substituent group a.More specifically, for example, surface-modified by at least two of the organosilicon compounds having at least one substituent a1 selected from the above-mentioned substituent group a and having at least one substituent a2 selected from the above-mentioned substituent group a and different from the above-mentioned substituent a1.Note that, when there are multiple substituents selected from the substituent group a in one organosilicon compound, the substituent with the highest three-dimensional bulkiness among these substituents is treated as the substituent a1 or the substituent a2.
In the two or more (plural kinds) of organosilicon compounds used for surface modification, for example, the substituent a1 and the substituent a2 are preferably groups having different steric bulkiness.
In addition, when the surface is modified with n types of surface modifying agents, 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.

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 a Si-O-Si bond, and organosilicon compounds having the above-mentioned substituent and a Si-N-Si bond. By surface-modifying the silica particles with these organosilicon compounds, surface-modified silica particles can be obtained.

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 groups, ethyl groups, propyl groups, butyl groups, hexyl groups, octyl groups, nonyl groups, decyl groups, dodecyl groups, hexadecyl groups, phenyl groups, phenylmethyl groups, tolyl groups, xylyl groups, and vinyl groups. When a plurality of such substituents are present in the same organosilicon compound, they may be the same or different from each other.
Among them, the substituent group a can be a group consisting of a methyl group, an octyl group, a decyl group, a dodecyl group, a hexadecyl group, a phenylmethyl group, a tolyl group and a xylyl group, or can be a group consisting of a methyl group, a phenyl group, a phenylmethyl group and a decyl group.
Therefore, for example, as the two or more kinds of organosilicon compounds, for example, a combination of an organosilicon compound having a methyl group and an organosilicon compound having a phenyl group, a combination of an organosilicon compound having a methyl group and an organosilicon compound having a decyl group, a combination of an organosilicon compound having a methyl group, an organosilicon compound having a phenyl group and an organosilicon compound having a decyl group, a combination of an organosilicon compound having a methyl group and an organosilicon compound having a phenylmethyl group, a combination of an organosilicon compound having a methyl group and an organosilicon compound having a tolyl group, a combination of an organosilicon compound having a methyl group and an organosilicon compound having a xylyl group, a combination of an organosilicon compound having a methyl group and an organosilicon compound having an octyl group, a combination of an organosilicon compound having a methyl group and an organosilicon compound having a dodecyl group, a combination of an organosilicon compound having a methyl group and an organosilicon compound having a hexadecyl group, etc. can be mentioned, but is not limited to these.

Alkoxy groups are preferred as the hydrolyzable groups, and when multiple groups are present, they may be the same or different. As the alkoxy group, an alkoxy group having 1 to 3 carbon atoms is preferred, and a methoxy group is particularly preferred.

When the organosilicon compound is a silicon compound having the above-mentioned substituents and hydrolyzable groups, there are no particular limitations on the number of substituents and the number of hydrolyzable groups, but it is preferable for the organosilicon compound to have 1 to 3 of the above-mentioned substituents and 1 to 3 of the hydrolyzable groups (with the total number of both groups being 4 or less) per silicon atom.
Specific examples of the organosilicon compound having a substituent and a hydrolyzable group include methyltrimethoxysilane, octyltrimethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane, hexadecyltrimethoxysilane, dimethyldimethoxysilane, trimethylmethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, trimethylethoxysilane, methyltripoxysilane, dimethyldipropoxysilane, trimethylpropoxysilane, phenyltrimethoxysilane, tolyltrimethoxysilane, xylyltrimethoxysilane, diphenyldimethylsilane, and the like. Examples of the silane 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.

In the substituents of the organosilicon compounds having the above-mentioned substituents and Si-O-Si bonds, 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 groups, phenyl groups, phenylmethyl groups, and vinyl groups, and when a plurality of groups are present, they may be the same or different from each other. In particular, methyl groups are preferred, and a specific example of the organosilicon compound is hexamethyldisiloxane.
In the substituents of the organosilicon compounds having the above-mentioned substituents and Si-N-Si bonds, 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 groups, phenyl groups, phenylmethyl groups, and vinyl groups, and when a plurality of groups are present, they may be the same or different from each other. In particular, methyl groups are preferred, and a specific example of the organosilicon compound is hexamethyldisilazane.

Among these, preferred examples of the organosilicon compound include the 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, may be selected.

The amount of surface treatment (modification) with the organosilicon compound, i.e., the amount of organosilicon compound coating or bonding to the particle surface, per ^{1 nm2} of the surface area of the silica particle can be in the range of, for example, about 0.5 to 40, or alternatively about 0.5 to 20, about 0.5 to 16, about 1 to 20, about 2 to 20, about 5 to 20, or about 10 to 20. The number per ¹ nm2 of surface area (amount of surface treatment) referred to here is the number of all organosilicon compounds required for surface modification, i.e., the total amount of at least two types of surface modifiers, and does not intend the amount of surface treatment with each individual surface modifier (organosilicon compound).

<Measurement of dielectric properties>
The dielectric constant and dielectric loss tangent of the hydrophobized silica particles according to the present invention can be measured using a dry powder of the hydrophobized silica particles with a dedicated device, such as a vector network analyzer (product name: FieldFox N6626A, manufactured by KEYSIGHT TECHNOLOGIES).
When the hydrophobic silica particles are composited with an organic resin material or polysiloxane to be 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.

<Silica Dispersion>
The silica dispersion of the present invention is a dispersion in which the hydrophobized silica particles (surface-modified silica particles) are dispersed in at least one organic solvent selected from alcohols, ketones, hydrocarbons, amides, ethers, esters, and amines.
The alcohols include, for example, alcohols having 1 to 5 carbon atoms, and specific examples thereof include methanol, ethanol, isopropyl alcohol, and n-butanol.
The ketones include, for example, ketones having 1 to 5 carbon atoms, and specific examples thereof include 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 the hydrophobized silica particles in the dispersion can be expressed as a 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% by mass to 60% by mass, 10% by mass to 60% by mass, or 10% by mass to 40% by mass.
The water content of the silica dispersion is preferably 5% by mass or less. By adjusting the water content to such a level, the stability of the dispersion may be improved and a composite material with an organic resin material or polysiloxane may be easily obtained.

<Composite materials>
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 resins, phenolic resins, acrylic resins, maleimide resins, polyurethanes, polyimides, polytetrafluoroethylene, cycloolefin polymers, unsaturated polyesters, vinyl triazines, crosslinkable polyphenylene oxides, and curable polyphenylene ethers.

The method for producing the composite material is not particularly limited, but for example, the composite material can be obtained by mixing a dispersion of hydrophobized silica particles with an organic resin material or a monomer or polymer solution of polysiloxane to prepare a polymerizable composition, removing excess solvent, and then curing with light or heat. Alternatively, the composite material can be obtained by directly adding a powder of hydrophobized silica particles to an organic resin material or a monomer or polymer solution of polysiloxane to prepare a polymerizable composition, removing excess solvent, and then curing with light or heat.
The mixing ratio of the silica particles to the organic resin material or the monomer or polymer solution of polysiloxane in the polymerizable composition can be such that the mass ratio of the hydrophobized silica particles to the organic resin material or the monomer or polymer of polysiloxane is hydrophobized silica particles:organic resin material or monomer or polymer of polysiloxane=1:100 to 0.1, for example, 1:20 to 0.1.

The polymerizable composition can be cured by light or heat by using a polymerization initiator. Examples of the photopolymerization initiator include a photoradical polymerization initiator or a photocationic polymerization initiator, and examples of the thermal polymerization initiator include a thermal radical polymerization initiator or a thermal cationic polymerization initiator. The polymerization initiator can be used in an amount of 0.01 parts by mass to 50 parts by mass relative to 100 parts by mass of the polymerizable compound.
In addition, as optional components, conventional additives used in conventional polymerizable compositions (composite materials), for example, various additives used in the relevant technical field, such as catalysts and pigments for curing acceleration, radical scavengers (quenchers), leveling agents, viscosity modifiers, antioxidants, ultraviolet absorbers, stabilizers, plasticizers, and surfactants, can also be mixed and used.

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

<Method of 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, two or more types of surface modifiers can be added to and mixed with an organic solvent dispersion of (unmodified) silica particles, thereby causing hydrolysis and condensation of the organosilicon compound to modify the surface of the silica particles.

The amount of the organosilicon compound added can be such that the surface of the silica particle is modified in a range of, for example, 0.5 to 20.0 pieces of the organosilicon compound per ^{1 nm2} of the surface area of the silica particle. For example, 0.5 to 15.0 pieces, 1.0 to 10.0 pieces, or 3.0 to 10.0 pieces per ^{1 nm2} of the surface area of the silica particle can be added. Here, the amount of the organosilicon compound added refers to the total amount (number) of the multiple types of organosilicon compounds added, and when two types of organosilicon compounds are added, for example, it refers to the total amount (number) of the two types of organosilicon compounds added. Although an excess of the organosilicon compound that does not contribute to the surface modification may be present in the system, the preferred amount of the organosilicon compound added is 5.0 to 10.0 pieces per ^{1 nm2} of the surface area of the silica particle.

The hydrolysis of the organosilicon compound may be complete or partial, but water is necessary, 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.Moisture contained in an organic solvent can also be used.
When using an organosilicon compound having a hydrolyzable group, hydrolysis may be performed completely or partially, but water is required, and it is preferable to add about 1 mole or more of water per mole of the hydrolyzable group of the organosilicon compound.Moisture contained in an organic solvent can also be used.
A catalyst may be used during hydrolysis and condensation. As the hydrolysis catalyst, a chelate compound, an organic acid, an inorganic acid, an organic base, or an inorganic base may be used alone or in combination. More specifically, for example, an aqueous solution of hydrochloric acid, an aqueous solution of acetic acid, an aqueous solution of ammonia, etc. may be used.

More specifically, the hydrophobic silica particles (surface-modified silica particles) according to the present invention can be produced by _a process including a step of mixing, in an organic solvent, silica particles having an average primary particle size of 5 nm to 500 nm, a ratio (S _H2O /S _N2 ) of the specific surface area determined by water vapor adsorption (S _H2O ) to the specific surface area determined by nitrogen adsorption (S N2 ) of 0.6 or less, and a total silanol group rate of 5% or less, and a surface modifier which is at least two types of 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 compound can be any of those described above. The silica particles to be surface-modified can be 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.

In the above mixing step, the amount of the organosilicon compound added can be an amount that allows the silica particles to be surface-modified at a ratio of, for example, 0.5 to 20 particles per 1 ^nm2 of surface area. Specifically, the organosilicon compound can be added so that the silica particles are 0.5 to 15.0 particles, 1.0 to 10.0 particles, 3.0 to 10.0 particles, or 5.0 to 10.0 particles per ¹ nm2 of surface area. The amount of the organosilicon compound added is the total amount of two or more organosilicon compounds added, and when three types of organosilicon compounds are added, it is regarded as the total amount of the three types. In addition, excess organosilicon compounds that do not contribute to surface modification may be present in the reaction system.

The organic solvent used in the mixing step may be an organic solvent containing an alcohol and/or a ketone solvent.
The alcohol may be one having 1 to 5 carbon atoms, and specific examples thereof include methanol, ethanol, isopropyl alcohol, and n-butanol.
The ketone solvent may be one having 1 to 5 carbon atoms, and specific examples thereof include methyl ethyl ketone, methyl isobutyl ketone, and γ-butyrolactone.

The mixing step can be carried out at any temperature, for example, 20° C. or higher and lower than 120° C., as long as the temperature is such that the hydrolysis and condensation reaction of the organosilicon compound proceeds.
From the viewpoint of reaction efficiency, it is preferable to carry out the reaction at a temperature near the boiling point of the organic solvent, and for example, when the mixing step is carried out using an organic solvent containing methanol, it is preferable to carry out the reaction at a temperature near 65° C. In addition, in order to suppress changes in the silica concentration and the organosilicon compound concentration during the mixing step, the reaction may be carried out in an apparatus equipped with a reflux device, etc., as necessary. The mixing step may be carried out multiple times at the same temperature, or may be carried out multiple times at different temperatures.
The mixing step can be carried out for 30 minutes to 24 hours, and from an industrial viewpoint, it is desirable to carry out the mixing step within 24 hours.
In the present invention, surface modification is carried out using at least two kinds of organosilicon compounds (surface modifiers), which may be added at once or separately. In a preferred embodiment, at least two kinds of organosilicon compounds may be added separately, for example, the organosilicon compound having the bulkier substituent may be added in order to carry out 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 two kinds of organosilicon compounds, dimethoxyphenylmethylsilane having a phenyl group, which is a bulkier substituent, may be added first and mixed, and hexamethyldisiloxane having a methyl group, which is less bulky than the phenyl group, may be added later, but is not limited thereto.

Furthermore, the mixing step may include a step of adjusting the pH using an organic amine. This pH adjustment step may be carried out once or multiple times before, during, or after the mixing step.
The organic amine may be a secondary or tertiary amine, such as an alkylamine, an allylamine, an aralkylamine, an alicyclic amine, an alkanolamine, or a cyclic amine.
Specifically, 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, N,N-dimethylamine, Examples of the 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-ene1,4-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 the organic amine added can be, for example, 0.001 to 5% by mass, or 0.01 to 1% by mass, based on the mass of the silica particles. 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, by adding the organic amine.

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 above-mentioned composite material.
From the viewpoint of ease of production of the composite material, at least a part of the organic solvent contained in the mixed liquid obtained by the mixing step can be replaced with another organic solvent. As the other organic solvent, at least one or more selected from the group consisting of alcohols, ketones, ethers, esters, hydrocarbons, and nitrogen-containing organic compounds can be used. There is no particular restriction on the type of solvent to be replaced as long as it is different from the organic solvent in the mixed liquid, and it may 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 replacement method can be a known method, for example, replacement with another organic solvent can be performed by evaporation using a rotary evaporator or the like, or ultrafiltration using an ultrafiltration membrane.

A specific example of the method for producing silica particles includes a production method including the following steps (A) to (C), but is not limited to these methods (steps).
Step (A): an average primary particle size is 5 to 500 nm, the ratio (S _H2O /S _N2 ) of the specific surface area determined by water vapor adsorption (S _H2O ) to the specific surface area determined by nitrogen adsorption (S _N2 ) is 0.6 or less, and the total silanol group rate represented by the following formula (1) is 5% or less:
Total silanol group ratio (%)=(Q2×2/4+Q3×1/4+Q4×0/4) Equation (1)
[In formula (1), Q2, Q3, and Q4 each represent the percentage (%) of the peak area derived from each silicon atom structure relative to the total peak area (100%) derived from the silicon atom structure obtained by ^29Si NMR measurement, where Q2 represents the percentage of the peak area derived from a silicon atom structure having two oxygen atoms and two hydroxyl groups bonded thereto, Q3 represents the percentage of the peak area derived from a silicon atom structure having three oxygen atoms and one hydroxyl group bonded thereto, and Q4 represents the percentage of the peak area derived from a silicon atom structure having four oxygen atoms bonded thereto.]
preparing a silica sol having silica particles as a dispersant and an alcohol having 1 to 4 carbon atoms as a dispersion medium;
Step (B): a step of heating and stirring at least two types of surface modifiers including an organosilicon compound having at least one substituent a selected from the 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 the silica sol obtained in step (A) at 40 to 100° C. for 0.1 to 10 hours;
Step (C): A step of removing the alcohol solvent from the silica sol after step (B).
The amount of organosilicon compound added in this production method and the conditions for step (B), i.e., hydrolysis, can be as described above.

The silica sol prepared in the step (A) may have a water content of 0.1 to 5% by mass, for example, 3.0% by mass or less.
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-substitution with an alcohol having 1 to 4 carbon atoms.

Either or both of the steps (B) and (C) can be carried out, for example, under reduced pressure.
In addition, a step of adjusting the pH using the above-mentioned organic amine may be included, as necessary, at any one or more of the steps before, during, and after the step (B).

In addition, in the step (B) above, when at least two types of surface modifiers and the silica sol obtained in the step (A) are heated and stirred, multiple types of surface modifiers may be heated and stirred simultaneously with the silica sol, or some types of the multiple types and the remaining types may be heated and stirred separately with the silica sol, or each type 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 starting with the organosilicon compound having the bulkier substituent.

Furthermore, the silica sol obtained after the 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 replacement, for example, by the step (D) described below.
Specifically, specific examples of the method for producing a surface-modified silica dispersion include a production method including the following steps (A) and (B), 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): a step of heating and stirring at least two types of 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 the substituent group a and different from the substituent a1, and the silica sol obtained in step (A) at 40 to 100°C for 0.1 to 10 hours; 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, or amines.
Specific examples of alcohols, ketones, hydrocarbons, amides, amines (nitrogen-containing organic compounds), esters, and ethers in this production method, as well as the method of replacing the solvent, can be as described above.

The present invention will be explained in more detail below with examples and comparative examples, but the present invention is not limited to the following examples.

The silica sol 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 (Nissan Chemical Industries, Ltd., product name: ST-OL, 45 nm, pH 3, silica concentration 20% by mass)
Water-dispersed silica sol b (Nissan Chemical Industries, Ltd., product name: ST-O, 12 nm, pH 3, silica concentration 20% by mass)
Water-dispersed silica sol c (Synthesis Example 1, 80 nm, pH 3, silica concentration 20% by mass)

[Surface modifier (organosilicon compound)]
DMMPS: dimethoxymethylphenylsilane (manufactured by Shin-Etsu Chemical Co., Ltd., product name: LS-2720)
DTMS: decyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., product name: KBM-3103C)
HMDS: hexamethyldisiloxane (manufactured by Shin-Etsu Chemical Co., Ltd., product name: KF-96L-0.65CS)

The physical properties of the above 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 manufacturing process were measured and evaluated according to the following methods.

[Measurement of Silica (SiO ₂ ) Concentration]
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.

[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 DKK-Toa Corporation).

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

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

[Organic solvent content]
The content of the organic solvent in the dispersion of the 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 material: Polapack Q
Column temperature: 130 to 230°C (heating rate: 8°C/min)
Carrier: _N2 40mL/min
Detector: FID
Injection volume: 1 μL
The internal standard was acetonitrile.

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

[Measurement of specific surface area, specific surface area ratio and average primary particle size]
<Measurement of specific surface area (S _H2O ) by water vapor adsorption method>
The specific surface area (S _H2O ) of the silica particles in the water-dispersed silica sol by the water vapor adsorption method was measured by removing the water-soluble cations and anions in the water-dispersed silica sol using a cation exchange resin (manufactured by The Dow Chemical Company, product name: Amberlite IR-120B), anion exchange resin (manufactured by The Dow Chemical Company, product name: Amberlite IRA400J), and cation exchange resin (manufactured by The Dow Chemical Company, product 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 specific surface area measuring device by the water vapor adsorption method (manufactured by TS Instruments Japan, Ltd., Q5000SA).

<Measurement of specific surface area (S _N2 ) by nitrogen adsorption method>
The nitrogen adsorption specific surface area (S _N2 ) of the silica particles in the water-dispersed silica sol was measured by removing the water-soluble cations in the water-dispersed silica sol with a cation exchange resin (manufactured by The Dow Chemical Company, product name: Amberlite IR-120B), drying the silica sol at 290°C to prepare a measurement sample, and using a nitrogen adsorption specific surface area measuring device, Monosorb (manufactured by Quantachrome Instruments Japan, LLC), to measure the specific surface area.

<Ratio of specific surface area for water vapor adsorption to specific surface area for nitrogen adsorption (S _H2O /S _N2 )>
Using 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).
Specific surface area ratio of water vapor/nitrogen adsorption (S _H2O /S _N2 )=specific surface area of water vapor adsorption method/specific surface area of nitrogen adsorption method (Equation (3))

<Average primary particle size>
The average primary particle size was calculated from the specific surface area S _N2 (m ² /g) obtained by the nitrogen adsorption method described above, using the following formula (4) in terms of spherical particles.
Average primary particle diameter (nm)=2720/S _N2 (m ² /g) (4)

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

<Total number of carbon atoms per unit surface area (unit: nm ² ) of silica particles>
The total number of carbon atoms per unit surface area (unit: nm ² ) of the silica particles was calculated by the following procedure.
(1) 4 mL of an organic solvent dispersion silica sol of surface-modified silica particles was placed in a 30 cc centrifuge tube, and 20 mL of hexane was added to cause clouding due to aggregation, separation, or precipitation.
(2) After centrifuging, the supernatant in which the unbound surface modifier was dissolved was removed.
(3) 4 mL of acetone was added to redissolve the precipitate from the centrifugation, and then 20 mL of hexane was added.
(4) (2) to (3) were repeated, and the supernatant was removed.
(5) The mixture was dried in a vacuum, and the 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 total number of carbon atoms per unit surface area (unit: nm ² ) of the silica particles was quantified from the carbon content and the specific surface area (S _N2 ) measured by the nitrogen adsorption method.

<Dynamic Light Scattering Particle Size>
The dynamic light scattering particle size was measured using a dynamic light scattering particle size measuring device (manufactured by Malvern Panalytical, product name: Zetasizer Nano). 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 when the attenuator was 7 was 200 to 400 kcps. The prepared silica particle dispersion was adjusted in the cell so that the height of the liquid surface from the bottom of the cell was about 1 cm, and the dynamic light scattering particle size of the silica particle dispersion was measured with the attenuator 7.

[Measurement of dielectric constant and dielectric loss tangent]
Using a cavity resonator jig for measuring frequency 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) using a cavity resonator jig for measuring frequency 1 GHz (manufactured by Keycom Corporation), and then the dielectric constant and dielectric loss tangent of the measurement sample were measured using a vector network analyzer (product name: N5227A, manufactured by KEYSIGHT TECHNOLOGIES).

[Measurement of hydrophobicity]
The degree of hydrophobicity was calculated from the following formula (Reference: Non-Patent Document 1) 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, dropping methanol into it with stirring, and measuring the amount of methanol dropped until the sample floating on the water surface completely sank (V _MeOH , unit: mL).
Hydrophobicity (%) = [V _MeOH / (V _MeOH + 50)] × 100 Formula (2)
Non-Patent Document 1:
A. Murota, N. Tsubokawa, Effect of alkyl chain length on the reactivity of ultrafine silica particles with alkylalkoxysilanes in a dry system, Journal of the Japan Society of Colour Material 74 (4), 178-184, 2001.

[Hexane compatibility test]
The compatibility of the sample with hexane was evaluated by placing 1 mL of the sample (a methyl ethyl ketone dispersion 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 after shaking showed gelation or aggregates, the compatibility was judged as NG, and if no gelation or aggregates were found, the compatibility was judged as OK.

(Synthesis Example 1) Synthesis of Water-Dispersed Silica Sol c As a raw material water-soluble alkali metal silicate, a sodium silicate aqueous solution of JIS No. 3 was prepared. In the main components other than water of this sodium silicate aqueous solution, the _SiO2 concentration was 28.8 mass% and the _Na2O concentration was 9.47 mass%.
The above sodium silicate aqueous solution was diluted with pure water to prepare a sodium silicate aqueous solution (a) having a _SiO2 concentration of 4 mass%.
Next, the above-mentioned aqueous sodium silicate 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 aqueous activated silicic acid solution.
The obtained active silicic acid aqueous solution was adjusted to pH 8.5 to 9.5 by adding 10% by mass of sodium hydroxide aqueous solution to obtain a stabilized active silicic acid aqueous solution. The _SiO2 concentration of the obtained stabilized active silicic acid aqueous solution was 3.2% by mass.
2,400 g of the stabilized activated silicic acid aqueous solution obtained above was placed in a reaction apparatus comprising a 3 L SUS pressure vessel equipped with a stirrer, a heater, etc., 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 in the vessel 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 concentrated to a SiO2 concentration of 33 mass% at room temperature using a commercially available ultrafiltration device equipped with a polysulfone ultrafiltration membrane with a molecular weight cutoff of 200,000 (manufactured by Advantec Co., Ltd., product name: Q2000 150E), thereby obtaining a colloidal _silica dispersion as a precursor with an adjusted _SiO2 concentration.
The above-mentioned colloidal silica dispersion as a precursor with the adjusted _SiO2 concentration was passed through a column packed with a cation exchange resin (manufactured by The Dow Chemical Company, product 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 obtained dispersion to adjust the pH to 7 to 8.
The colloidal silica dispersion as a precursor with the _SiO2 concentration and pH adjusted obtained above was placed in a reaction apparatus equipped with a stirrer, a heater, etc., in a 3 L SUS pressure-resistant container, and the liquid temperature in the container was adjusted to 250 to 260° C. by heating. After the temperature in the container reached 250 to 260° C., the container was heated for 9 hours and 20 minutes while maintaining the temperature in the container at 250 to 260° C.
50 g of the colloidal silica dispersion obtained above was placed in a 100 ml plastic container, 25 ml of a cation exchange resin (manufactured by Dow Chemical Company, product name: Amberlite IR-120B) was added, and the mixture was held for 30 minutes while stirring with a magnetic stirrer to remove cations. Next, 50 g of the colloidal silica dispersion obtained was placed in a 100 ml plastic container, 25 ml of anion exchange resin (manufactured by Dow Chemical Company, product 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 a 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% by mass, to obtain water-dispersed silica sol c.

[Example 1-1]
Step (a): 2,500 g of water-dispersed silica sol a was charged into a 3 L glass reactor equipped with a stirrer, a condenser, a thermometer and two inlets, and the silica sol was boiled by heating. While the silica sol in the reactor was boiling, methanol steam generated in another boiler was continuously blown into the silica sol in the reactor, replacing the water, which was the dispersion medium, with methanol. When the water content of the methanol dispersion became 3.0 mass% or less, the replacement was terminated, and 1,250 g of methanol-dispersed silica sol was obtained.
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.

(b) step: 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) and DMMPS were added in an amount that would result in 3 particles per ^{1 nm2} of the surface area of the silica particles as determined by the nitrogen adsorption method, and the mixture was heated to 60°C and held for 3 hours. Thereafter, HMDS was added in an amount that would result in 5 particles per ^{1 nm2} of the surface area of the silica particles, and the mixture was heated to 60°C and held for 3 hours. Thereafter, diisopropylamine was added so that the pH (1+1+1) was 8.0 to 10.0, and the mixture was heated to 60°C and held for 1 hour to prepare a methanol/MEK dispersion of surface-modified silica particles.

Step (c): Thereafter, the recovery flask containing the methanol/MEK dispersion of the surface-modified silica particles was set in a rotary evaporator, and distillation was performed 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, thereby obtaining a methyl ethyl ketone dispersion of the surface-modified silica particles.
The obtained methyl ethyl ketone dispersion of the 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, a total silanol ratio of 1.7% (Q2: 0%, Q3: 7.0%, Q4: 93.0%, calculated from the 29Si NMR spectrum measured using the procedure shown in the above-mentioned NMR measurement condition B, except that the above methyl ethyl ketone dispersion was dried in a vacuum dryer at ¹⁰⁰ °C to prepare a measurement sample), and the ratio of the total number of carbon atoms per unit surface area (unit: ^nm2 ) of the surface-modified silica particles was 10.

[Example 1-2]
Instead of DMMPS in step (b) of Example 1-1, DTMS was added so that the amount of DTMS was 1.0 particle per ^nm2 of the surface area of the silica particles contained in the silica sol, and the mixture was similarly maintained at 60° C. for 3 hours. Except for this, operations were carried out in the same manner as in steps (a) to (c) of Example 1-1 to prepare 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.

[Examples 1-3]
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 by carrying out the same operations as in steps (a) to (c) of Example ^1-1 , except that after the addition of DMMPS in step (b) of Example 1-1, DTMS was additionally added so that the amount of DTMS was 1.0 particle per nm2 of the surface area of the silica particles contained in the silica sol, the mixture was maintained at 60° C. for 3 hours, and then HMDS was added.

[Examples 1 to 4]
660 g of the water-dispersed silica sol c prepared in Synthesis Example 1 was diluted with methanol to 1,000 g, and this was placed in a 2 L eggplant-shaped flask-equipped evaporator, and then methanol was gradually added while distilling off water at 120° C. and 580 Torr, thereby replacing the water, which was the dispersion medium, with methanol. When the water content of the methanol dispersion became 3.0 mass % or less, the replacement was terminated, and 1,000 g of methanol-dispersed silica sol was obtained.
The resulting methanol-dispersed silica sol had a silica concentration of 13.2% by mass, a water content of 1.6% by mass, and a viscosity of 0.9 mPa·s.
20 g of the obtained methanol-dispersed silica sol was placed in a 100-mL eggplant-shaped flask, and while stirring with a magnetic stirrer, 3.0 g of methyl ethyl ketone (MEK) and DTMS were added in an amount that would result in 3 particles per 1 ^nm2 of the surface area of the silica particles as determined by the nitrogen adsorption method, and the mixture was heated to 60°C and held for 3 hours. Then, HMDS was added in an amount that would result in 5 particles per ¹ nm2 of the surface area of the silica particles, and the mixture was heated to 60°C and held for 3 hours. Then, diisopropylamine was added so that the pH (1+1+1) was 8.0 to 10.0, and the mixture was heated to 60°C and held for 1 hour to prepare a methanol/MEK dispersion of surface-modified silica particles.
Next, the recovery flask containing the methanol/MEK dispersion of the surface-modified silica particles was set in a rotary evaporator, and distillation was performed while supplying methyl ethyl ketone at a bath temperature of 80°C and a reduced pressure of 550 to 350 Torr, replacing the dispersion medium with methyl ethyl ketone to obtain a methyl ethyl ketone dispersion of the surface-modified silica particles.
The obtained methyl ethyl ketone dispersion of the 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.

[Examples 1 to 5]
660 g of the water-dispersed silica sol c prepared in Synthesis Example 1 was diluted with methanol to 1,000 g, and this was placed in a 2 L eggplant-shaped flask-equipped evaporator, and then water was distilled off at 120° C. and 580 Torr while gradually adding methanol, thereby replacing the water, which was the dispersion medium, with methanol. When the water content of the methanol dispersion became 3.0 mass % or less, the replacement was stopped, and 1,000 g of methanol-dispersed silica sol was obtained.
The resulting methanol-dispersed silica sol had a silica concentration of 13.2% by mass, a water content of 1.6% by mass, and a viscosity of 0.9 mPa·s.
20 g of the obtained methanol-dispersed silica sol was placed in a 100-mL eggplant-shaped flask, and while stirring with a magnetic stirrer, 3.0 g of methyl ethyl ketone (MEK) and DMMPS were added in an amount that would result in 6 particles per ^{1 nm2} of the surface area of the silica particles as determined by the nitrogen adsorption method, and the mixture was heated to 60°C and held for 3 hours. Then, HMDS was added in an amount that would result in 5 particles per ¹ nm2 of the surface area of the silica particles, and the mixture was heated to 60°C and held for 3 hours. Then, diisopropylamine was added so that the pH (1+1+1) was 8.0 to 10.0, and the mixture was heated to 60°C and held for 1 hour to prepare a methanol/MEK dispersion of surface-modified silica particles.
Next, the recovery flask containing the methanol/MEK dispersion of the surface-modified silica particles was set in a rotary evaporator, and distillation was performed while supplying methyl ethyl ketone at a bath temperature of 80°C and a reduced pressure of 550 to 350 Torr, replacing the dispersion medium with methyl ethyl ketone to obtain a methyl ethyl ketone dispersion of the surface-modified silica particles.
The obtained methyl ethyl ketone dispersion of the 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.

[Comparative Example 1-1]
1,000 g of the 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 an amount of DMMPS such that the number of particles becomes 3 per 1 ^nm2 of the surface area of the silica particles determined by a nitrogen adsorption method were added, and the mixture was heated to 60° C. and maintained for 3 hours. Thereafter, diisopropylamine was 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.
Thereafter, the same operation as in step (c) of Example 1-1 was carried out to prepare a methyl ethyl ketone dispersion of surface-modified silica particles.

[Comparative Example 1-2]
A methyl ethyl ketone dispersion of surface-modified silica particles was prepared by carrying out the same operation as in Comparative Example 1-1, except that 5 particles of HMDS per ¹ nm2 of the surface area of the silica particles contained in the silica sol were added instead of DMMPS in Comparative Example 1-1.

[Comparative Example 1-3]
1,525 g of water-dispersed silica sol b was put into a 2 L eggplant-shaped flask-equipped evaporator, and then methanol was gradually added while distilling off water at 600 Torr, thereby replacing the water, which was the dispersion medium, with methanol. When the water content of the methanol dispersion became 3.0 mass% or less, the replacement was stopped, and 1,000 g of methanol-dispersed silica sol was obtained.
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.
Furthermore, operations similar to those in 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.

[Comparative Examples 1 to 4]
As Comparative Example 1-4, water-dispersed silica sol b was used.

[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 obtained silica gel was pulverized in a mortar and further dried at 150° C. for 1 hour to prepare 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.

[Examples 2-2 to 2-5, Comparative Examples 2-1 to 2-4]
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 in Comparative Example 1-4, silica powders were prepared in the same manner as in Example 2-1, and the dielectric constant and dielectric loss tangent were measured. The dielectric properties of the surface-modified silica particles are shown in Table 2.

[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.

[Examples 3-2 to 3-5, Comparative Examples 3-1 to 3-4]
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 in Comparative Example 1-4, silica powders were prepared in the same manner as in Example 3-1, and the hydrophobicity was measured. The hydrophobicity of the surface-modified silica particles is shown in Table 2.

[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.

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

[Example 5-1]
The compatibility of the surface-modified silica particles and an organic resin material (maleimide resin) was confirmed for the surface-modified silica particles obtained in Example 1-1. 50 g of the methyl ethyl ketone dispersion of the surface-modified silica particles obtained in Example 1-1 was charged into a 300-milliliter eggplant-shaped flask, and 20 g of a low-viscosity liquid maleimide resin (maleimide-terminated polyimide resin, product name: BMI-689, 1000 to 2000 cP (25° C.), manufactured by DMI Co., Ltd.) was added while stirring with a magnetic stirrer. Thereafter, the eggplant-shaped flask containing the mixture of the obtained methyl ethyl ketone dispersion of the surface-modified silica particles and the maleimide resin was set in a rotary evaporator, and distillation was performed at a bath temperature of 80° C. and a reduced pressure of 400 to 30 Torr, and the dispersion medium was replaced from methyl ethyl ketone to maleimide resin, thereby obtaining a maleimide resin dispersion of the surface-modified silica particles.
The obtained 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 obtained maleimide resin dispersion of surface-modified silica particles showed no change in appearance even after being left to stand at room temperature for one week, and no precipitate was formed.
The obtained maleimide resin dispersion of surface-modified silica particles was applied to a glass substrate degreased with acetone using a hand-applied bar coater (gap: 25 μm), baked for 30 minutes on a hot plate heated to 100° C. under a nitrogen atmosphere, and then baked for 120 minutes after raising the temperature of the hot plate to 230° C. to obtain a cured film of a composite material containing surface-modified silica particles and maleimide resin (see FIG. 1(B)). The obtained cured film was yellow and transparent, and no repellency was observed with the glass substrate (note that in FIG. 1, the periphery of the portion where the resin dispersion and the low-viscosity liquid maleimide resin described below were applied is indicated by a black frame for reference). The film thickness was measured with a constant pressure thickness meter (manufactured by Teclock Corporation, model: PG-01A) and was 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 (product name: BMI-689) alone was used and applied to a glass substrate degreased with acetone using a hand-applied bar coater (gap: 25 μm), followed by baking for 30 minutes on a hot plate heated to 100° C. under a nitrogen atmosphere, and then further increasing the temperature of the hot plate to 230° C. and baking 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.

[Example 5-2]
The compatibility of the surface-modified silica particles and an organic resin material (epoxy resin) was confirmed for the surface-modified silica particles obtained in Example 1-1. 50 g of the methyl ethyl ketone dispersion of the surface-modified silica particles obtained in Example 1-1 was charged into a 300-milliliter eggplant-shaped flask, and 20 g of an epoxy resin (manufactured by Nippon Steel Chemical & Material Co., Ltd., bisphenol A-type epoxy resin, product name: YD-8125, 3900 to 5300 cP) was added while stirring with a magnetic stirrer. Thereafter, the eggplant-shaped flask containing the mixture of the obtained methyl ethyl ketone dispersion of the surface-modified silica particles and the epoxy resin was set in a rotary evaporator, and distillation was performed at a bath temperature of 80° C. and a reduced pressure of 400 to 30 Torr, and the dispersion medium was entirely replaced from methyl ethyl ketone to epoxy resin, thereby obtaining an epoxy resin dispersion of the 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 method (hereinafter, dynamic light scattering particle size) of 78.7 nm, and an epoxy equivalent of 264 g/eq (in accordance with JIS K7236), and was white and transparent in appearance.
Furthermore, the obtained epoxy resin dispersion of surface-modified silica particles showed no change in appearance even after being left to stand at room temperature for one week, and no precipitate was formed.

As shown in Table 2, the surface-modified silica particles of Examples 1-1 to 1-5 had an average primary particle size 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 degree (%) 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 had a water vapor adsorption surface area/nitrogen adsorption surface area (S _H2O /S _N2 ) of 0.6 or less and a total silanol group ratio of 5% or less in the silica particles (silica sol a, silica sol c) before surface modification, and were surface-modified silica particles treated with at least two different surface modifiers.

On the other hand, the surface-modified silica particles of Comparative Examples 1-1 and 1-2 had an average primary particle size 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 ) of the silica particles (silica sol a) before surface modification of 0.6 or less and a total silanol group ratio of 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.
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 degree (%) of 40 or more (Comparative Example 3-3), but the dielectric 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 ) of the silica particles (silica sol c) before surface modification was 0.6 or more, and the total silanol group ratio was 5% or more.
Furthermore, the silica particles of Comparative Example 1-4, i.e., the unmodified silica particles, had an average primary particle diameter of 5 nm to 500 nm, but the dielectric tangent value at a frequency of 1 GHz was significantly greater than 0.01 (Comparative Example 2-4), and the hydrophobicity (%) was 0 (Comparative Example 3-4).
The results shown in the comparative examples above indicate that it is not easy to realize nano-order silica particles that have both a low dielectric tangent and a high degree of hydrophobicity.

Also, as shown in Table 2, it was confirmed that Example 1-1 and Example 1-3, which are methyl ethyl ketone dispersions containing surface-modified silica particles with a hydrophobicity of 40 or more, were judged to be OK in terms of hexane compatibility (Examples 4-1 and 4-2).

Furthermore, when the surface-modified silica particles according to the present invention were used as a composite material with an organic resin material, there was no change in appearance or the occurrence of precipitates or sediments even after leaving the material at room temperature for one week, and it was confirmed that the material is highly stable (Examples 5-1 and 5-2). As shown in FIG. 1, when a cured film was formed on a glass substrate, the organic resin material (maleimide resin) alone resulted in repelling the substrate (FIG. 1(A)). However, by adding the surface-modified silica particles according to the present invention to the organic resin material (maleimide resin) to form a composite material, the cured film did not repel the glass substrate (FIG. 1(B)), and a transparent film (molded product) could be formed.

The hydrophobic silica particles according to the present invention are particles that realize a high hydrophobicity of 40% or more and reduce the dielectric loss tangent of conventional hydrophobic silica sol to less than half. In other words, 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, making them suitable not only for use in composite materials but also for use in high frequency applications.

Claims

Surface-modified silica particles with a hydrophobicity of 40% or more, characterized by an average primary particle diameter of 5 to 500 nm and a dielectric tangent of less than 0.01 at 1 GHz.
2. The surface-modified silica particles according to claim 1, wherein the silica particles from which the surface modifier has been removed satisfy the following requirements (i) and (ii):
(i) The ratio (SH 2 O/SN 2 ) of the specific surface area by water vapor adsorption (S H2O ) to the specific surface area by nitrogen adsorption (S N2 ) is 0.6 or less.
(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) Equation (1)
[In formula (1), Q2, Q3, and Q4 each represent the percentage (%) of the peak area derived from each silicon atom structure relative to the total peak area (100%) derived from the silicon atom structure obtained by 29Si NMR measurement, where Q2 represents the percentage of the peak area derived from a silicon atom structure having two oxygen atoms and two hydroxyl groups bonded thereto, Q3 represents the percentage of the peak area derived from a silicon atom structure having three oxygen atoms and one hydroxyl group bonded thereto, and Q4 represents the percentage of the peak area derived from a silicon atom structure having four oxygen atoms bonded thereto.]
3. The surface-modified silica particles according to claim 1, wherein the ratio of the total number of carbon atoms per unit surface area (unit: nm 2 ) of the surface-modified silica particles is 2 to 40.
The surface-modified silica particles are characterized in that at least a part of the surface thereof is coated with at least two types of surface modifiers;
the at least two types of surface modifiers include an organosilicon compound having at least one substituent a1 selected from the 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 the substituent group a and different from the substituent a1;
The surface-modified silica particle according to claim 1 .
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 the surface of the surface-modified silica particles;
the at least two types of surface modifiers include an organosilicon compound having at least one substituent a1 selected from the 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 the substituent group a and different from the substituent a1;
The surface-modified silica particle according to claim 1 .
The surface-modified silica particles according to claim 4 or 5, wherein the substituent group a is a group consisting of a methyl group, a phenyl group, a phenylmethyl group, and a decyl group.
The surface-modified silica particles according to any one of claims 4 to 6, wherein the organosilicon compound is a compound having a hydrolyzable group together with a substituent selected from the substituent group a.
6. The surface-modified silica particles according to claim 4, wherein the surface modifier is at least two types selected from the compounds represented by the following formulas (a) to (c):
The surface-modified silica particles are particles whose surfaces are coated with the at least two types of surface modifiers at a ratio of 0.5 to 20 particles per 1 nm2 of the surface area, or particles whose surfaces are at least partially bound to the at least two types of surface modifiers.
The surface-modified silica particle according to any one of claims 3 to 8.
A silica dispersion in which the surface-modified silica particles according to any one of claims 1 to 9 are dispersed in at least one organic solvent selected from alcohols, ketones, hydrocarbons, amides, ethers, esters, and amines.
A composite material comprising the surface-modified silica particles according to any one of claims 1 to 9 and an organic resin material or a polysiloxane.
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, phenol resin, acrylic resin, maleimide resin, urethane resin, polyimide, polytetrafluoroethylene, cycloolefin polymer, unsaturated polyester, vinyl triazine, polyphenylene sulfide, crosslinkable polyphenylene oxide, and curable polyphenylene ether.
The composite material according to claim 11 or 12, which has an application selected from the group consisting of semiconductor device materials, copper-clad laminates, insulating films, flexible wiring materials, flexible display materials, antenna materials, optical wiring materials, and sensing materials.
The following steps (A) to (C):
Step (A): an average primary particle size is 5 to 500 nm, the ratio (S H2O /S N2 ) of the specific surface area determined by water vapor adsorption (S H2O ) to the specific surface area determined by nitrogen adsorption (S N2 ) is 0.6 or less, and the total silanol group rate represented by the following formula (1) is 5% or less:
Total silanol group ratio (%)=(Q2×2/4+Q3×1/4+Q4×0/4) Equation (1)
[In formula (1), Q2, Q3, and Q4 each represent the percentage (%) of the peak area derived from each silicon atom structure relative to the total peak area (100%) derived from the silicon atom structure obtained by 29Si NMR measurement, where Q2 represents the percentage of the peak area derived from a silicon atom structure having two oxygen atoms and two hydroxyl groups bonded thereto, Q3 represents the percentage of the peak area derived from a silicon atom structure having three oxygen atoms and one hydroxyl group bonded thereto, and Q4 represents the percentage of the peak area derived from a silicon atom structure having four oxygen atoms bonded thereto.]
preparing a silica sol having silica particles as a dispersoid and an alcohol having 1 to 4 carbon atoms as a dispersion medium;
Step (B): a step of heating and stirring at least two types of surface modifiers including an organosilicon compound having at least one substituent a1 selected from a 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 the substituent group a and different from the substituent a1, and the silica sol obtained in Step (A) at 40 to 100° C. for 0.1 to 10 hours; and Step (C): a step of removing the alcohol solvent from the silica sol obtained after Step (B).
including,
A method for producing surface-modified silica particles.
Either or both of the steps (B) and (C) are carried out under reduced pressure;
The method for producing the surface-modified silica particles according to claim 14.
The method for producing surface-modified silica particles according to claim 14, wherein the silica sol prepared in step (A) has a water content of 0.1 to 5 mass %.
The method for producing surface-modified silica particles according to claim 14, wherein the silica sol prepared in step (A) is an aqueous silica sol hydrothermally synthesized at 200 to 380°C and 2 to 22 MPa, and the solvent is replaced with an alcohol having 1 to 4 carbon atoms.
The following steps (A), (B) and (D):
Step (A): an average primary particle size is 5 to 500 nm, the ratio (S H2O /S N2 ) of the specific surface area determined by water vapor adsorption (S H2O ) to the specific surface area determined by nitrogen adsorption (S N2 ) is 0.6 or less, and the total silanol group rate represented by the following formula (1) is 5% or less:
Total silanol group ratio (%)=(Q2×2/4+Q3×1/4+Q4×0/4) Equation (1)
[In formula (1), Q2, Q3, and Q4 each represent the percentage (%) of the peak area derived from each silicon atom structure relative to the total peak area (100%) derived from the silicon atom structure obtained by 29Si NMR measurement, where Q2 represents the percentage of the peak area derived from a silicon atom structure having two oxygen atoms and two hydroxyl groups bonded thereto, Q3 represents the percentage of the peak area derived from a silicon atom structure having three oxygen atoms and one hydroxyl group bonded thereto, and Q4 represents the percentage of the peak area derived from a silicon atom structure having four oxygen atoms bonded thereto.]
preparing a silica sol having silica particles as a dispersoid and an alcohol having 1 to 4 carbon atoms as a dispersion medium;
Step (B): a step of heating and stirring at least two types of surface modifiers including an organosilicon compound having at least one substituent a1 selected from the 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 the substituent group a and different from the substituent a1, and the silica sol obtained in step (A) at 40 to 100° C. for 0.1 to 10 hours; and (D) a step of subjecting the silica sol obtained in step (B) to solvent replacement 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.