Surface-treated silica particle dispersion

Abstract

To provide a dispersion formed of silica particles surface-hydrophobized with an aryl group and an alkyl group and dispersed in a specified solvent, capable of stably dispersing silica particles for a long period of time.SOLUTION: The surface treated silica particle dispersion includes surface treated silica particles comprising an aryl group Ar and an alkyl group R present on the particle surfaces, at least one species of dispersion medium selected from the group consisting of an ether-ester based solvent, an ester-based solvent and an aromatic hydrocarbon-based solvent, and an alcohol-based solvent, in which the content of the alcohol-based solvent in 100 mass% of the surface treated silica particle dispersion is 0.20 to 5 mass%.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a surface-treated silica particle dispersion.

Background Art

[0002] A silica particle dispersion in which silica particles are dispersed in a solvent can be mixed with a resin, a resin raw material, etc. to improve properties such as strength, hardness, heat resistance, and insulation without impairing the moldability and transparency of the resin. Therefore, it is useful for applications such as adhesive materials, dental materials, optical members, coating materials (for hard coats and antiglare), and nanocomposite materials. In addition, silica particles having a minute particle size are also used as an abrasive material because of their hardness.

[0003] Since the surface of silica particles is hydrophilic, a technique for hydrophobizing the surface has been proposed in order to enhance the affinity with a highly hydrophobic dispersion medium or resin. For example, in Patent Document 1, silica particles surface-treated with phenyltrimethoxysilane and hexamethyldisilazane and aggregated and precipitated in water and isopropanol are precipitated by adding hydrochloric acid, and after obtaining a solid of the silica particles by filtration, it is mixed with methyl ethyl ketone to obtain a dispersion sample of the silica particles. Further, in Patent Document 2, phenyltrimethoxysilane and hexamethyldisilazane are added to a methanol-dispersed silica sol, a surface-treated methanol-dispersed silica sol is obtained, desolvated under reduced pressure, and dried to obtain silica powder, which is then dispersed in methyl ethyl ketone.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] A solvent dispersion of silica particles with a hydrophobic surface treatment should, of course, exhibit good dispersibility immediately after preparation, but it is also desirable that it remain well dispersed in the dispersion medium over time. However, while the aforementioned Patent Documents 1 and 2 describe the immediate dispersibility of silica particles hydrophobized with surface treatment agents such as phenyltrimethoxysilane and hexamethyldisilazane in methyl ethyl ketone, they do not examine long-term dispersion stability at all.

[0006] Therefore, the present invention aims to provide a dispersion in which silica particles whose surfaces have been hydrophobized with aryl groups and alkyl groups are dispersed in a specific solvent, and in which the silica particles can be stably dispersed over a long period of time. [Means for solving the problem]

[0007] The present invention, which has achieved the above objectives, is as follows. [1] Surface-treated silica particles having aryl groups Ar and alkyl groups R on the particle surface, A dispersion medium which is at least one selected from the group consisting of ether ester solvents, ester solvents, and aromatic hydrocarbon solvents, and A dispersion of surface-treated silica particles containing an alcohol-based solvent, A surface-treated silica particle dispersion characterized in that the content of the alcohol-based solvent in 100% by mass of the surface-treated silica particle dispersion is 0.20 to 5% by mass. [2] The surface-treated silica particle dispersion according to [1], wherein the aryl group Ar is a phenyl group which may be substituted with an alkyl group having 1 to 4 carbon atoms or an alkenyl group having 1 to 4 carbon atoms, and the alkyl group R has 1 to 4 carbon atoms. [3] The surface-treated silica particle dispersion according to [1] or [2], wherein the aryl group Ar is derived from an arylalkoxysilane. [4] The alkyl group R is derived from a hexaalkyldisilazane, the surface-treated silica particle dispersion according to any one of [1] to [3]. [5] A surface-treated silica particle dispersion according to any one of [1] to [4], wherein the ratio of the aryl group Ar to the alkyl group R (aryl group / alkyl group) is 0.01 to 3.0. [6] The surface-treated silica particle dispersion according to any one of [1] to [5], wherein when the surface-treated silica particle dispersion is 100 parts by mass, the amount of Si present in the medium other than the surface-treated silica particles is 0.05 parts by mass or less. [7] A surface-treated silica particle dispersion according to any one of [1] to [5], wherein when the surface-treated silica particle dispersion is 100 parts by mass, the amount of Si present in the medium other than the surface-treated silica particles is greater than 0.05 parts by mass. [8] The surface-treated silica particle dispersion according to any one of [1] to [7], wherein the content of surface-treated silica particles in 100% by mass of the surface-treated silica particle dispersion is 10 to 50% by mass. [9] A dispersion of surface-treated silica particles according to any one of [1] to [8], wherein the carbon concentration in 100% by mass of the surface-treated silica particles is 2 to 10% by mass.

[10] A surface-treated silica particle dispersion according to any one of [1] to [9], wherein the average primary particle diameter of the surface-treated silica particles is 10 to 100 nm. A resin composition comprising a surface-treated silica particle dispersion described in any of

[11] [1] to

[10] and a resin. [Effects of the Invention]

[0008] According to the present invention, since the dispersion contains a predetermined amount of alcohol-based solvent, surface-treated silica particles having an aryl group Ar and an alkyl group R on their particle surface can be stably dispersed over a long period of time in a dispersion medium that is at least one selected from the group consisting of ether ester-based solvents, ester-based solvents, and aromatic hydrocarbon-based solvents. [Modes for carrying out the invention]

[0009] The present invention relates to a surface-treated silica particle dispersion comprising surface-treated silica particles having an aryl group Ar and an alkyl group R on the particle surface, a dispersion medium selected from the group consisting of an ether ester solvent, an ester solvent, and an aromatic hydrocarbon solvent, and an alcohol solvent, wherein the content of the alcohol solvent in 100% by mass of the surface-treated silica particle dispersion is 0.20 to 5% by mass (hereinafter sometimes simply referred to as "dispersion").

[0010] 1. Surface-treated silica particles The surface-treated silica particles in this invention have an aryl group (Ar) and an alkyl group (R) on their surface, making the surface hydrophobic. The aryl group is sterically bulky, and even if surface treatment is performed with an amount of aryl group that is theoretically sufficient to completely cover the silica particles, the reaction rate is poor, making it difficult to impart the desired hydrophobicity. However, by having the alkyl group (R) present on the silica particle surface together with the aryl group (Ar), the particle surface becomes highly hydrophobic.

[0011] The aryl group Ar may be a phenyl group substituted with an alkyl group having 1 to 4 carbon atoms or an alkenyl group having 1 to 4 carbon atoms, preferably a phenyl group (such as a phenyl group, tolyl group, dimethylphenyl group, ethylphenyl group, or styryl group) substituted with an alkyl group having 1 to 2 carbon atoms or an alkenyl group having 1 to 2 carbon atoms, and more preferably a phenyl group. The aryl group Ar on the surface of the silica particles is preferably an aryl group directly bonded to a silicon atom.

[0012] To introduce the aryl group Ar onto the silica particle surface, a surface treatment agent containing the aryl group Ar can be used, and a compound in which one silicon atom in a molecule is bonded to an aryl group-containing group and a hydrolyzable group or a hydroxyl group is preferred. The hydrolyzable group refers to a compound that can form a silanol group together with the silicon atom by hydrolysis. Examples of compounds in which one silicon atom is bonded to an aryl group-containing group and a hydrolyzable group include aryl group-containing alkoxysilanes, aryl group-containing chlorosilanes, and aryl group-containing acetoxysilanes. Examples of aryl group-containing alkoxysilanes include N-phenyl-3-aminopropyltrimethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, diphenyldimethoxysilane, and diphenyldiethoxysilane. Examples of aryl group-containing chlorosilanes include phenyltrichlorosilane, diphenyldichlorosilane, and methyldiphenylchlorosilane. Examples of aryl group-containing acetoxysilanes include phenyltriacetoxysilane and diphenyldiacetoxysilane. Examples of compounds in which an aryl group-containing group and a hydroxyl group are bonded to one silicon atom in a single molecule include diphenylsilanediol. Among these, aryl group-containing alkoxysilanes are preferred, arylalkoxysilanes in which an aryl group and an alkoxy group are directly bonded to one silicon atom are more preferred, aryltrialalkoxysilanes are even more preferred, and aryltrimethoxysilanes or aryltriethoxysilanes are particularly preferred. For example, if the aryl group Ar is a phenyl group, then phenylalkoxysilanes may be used, and phenyltrimethoxysilanes or phenyltriethoxysilanes are more preferred.

[0013] The alkyl group R on the silica particle surface is preferably an alkyl group having 1 to 4 carbon atoms, more preferably an alkyl group having 1 to 2 carbon atoms, and even more preferably a methyl group. The alkyl group R on the silica particle surface is preferably an alkyl group directly bonded to a silicon atom.

[0014] Similar to the aryl group Ar, an alkyl group R can be introduced to the silica particle surface by using a surface treatment agent containing the alkyl group R, and an alkyl group-containing silazane compound is preferred. Examples of alkyl-containing silazane compounds include alkyl-containing disilazane compounds such as 1,1,1,3,3,3-hexamethyldisilazane, 1,1,3,3-tetramethyldisilazane, 1,3-bis(3,3,3-trifluoropropyl)-1,1,3,3-tetramethyldisilazane, 1,3-bis(chloromethyl)tetramethyldisilazane, heptamethyldisilazane, 1,3-divinyl-1,1,3,3-tetramethyldisilazane, lithium hexamethyldisilazane, sodium hexamethyldisilazane, and potassium hexamethyldisilazane; alkyl-containing trisilazane compounds such as 2,2,4,4,6,6-hexamethylcyclotrisilazane and 2,4,6-trimethyl-2,4,6-trivinylcyclotrisilazane; and alkyl-containing tetrasilazane compounds such as octamethylcyclotetrasilazane. Among alkyl-containing silazane compounds, alkyl-containing disilazane compounds are preferred, hexaalkyldisilazane compounds are more preferred, and hexamethyldisilazane is even more preferred.

[0015] The ratio of the aryl group Ar to the alkyl group R (molar ratio of aryl group to alkyl group) is preferably 0.01 or higher, more preferably 0.02 or higher, even more preferably 0.03 or higher, and also preferably 3.0 or lower, more preferably 2.0 or lower, and even more preferably 1.0 or lower. The ratio of the aryl group Ar to the alkyl group R can be adjusted by the amount of surface treatment agent used, or it may be calculated from the analysis results of the obtained silica particles.

[0016] The carbon concentration in 100% by mass of surface-treated silica particles, i.e., the carbon concentration derived from the surface treatment agent, is preferably 2% by mass or more, more preferably 3% by mass or more. The upper limit is not particularly limited, but may be, for example, 10% by mass or less, or 8% by mass or less.

[0017] The average primary particle diameter of the surface-treated silica particles of the present invention is preferably 10 to 100 nm. The average primary particle diameter is more preferably 15 nm or more, still more preferably 20 nm or more, and more preferably 90 nm or less, still more preferably 80 nm or less, and particularly preferably 70 nm or less. The average primary particle diameter can be calculated by observing the particles with a scanning electron microscope (SEM) as shown in the examples described later, setting the measurement magnification so that there are 50 to 100 particles in the field of view of one photograph, taking a photograph, measuring the major axis of each of the 50 particles, and obtaining the arithmetic mean value thereof.

[0018] Also, the coefficient of variation (CV value) of the primary particle diameter of the surface-treated silica particles is preferably 15% or less, more preferably 12% or less, and still more preferably 10% or less. The lower limit of the CV value is not particularly limited, but may be, for example, 5% or less. The coefficient of variation of the primary particle diameter is a value obtained by dividing the standard deviation of the primary particle diameter by the average value of the primary particle diameter and expressing it as a percentage.

[0019] The average sphericity ratio of the surface-treated silica particles is preferably 1.2 or less, more preferably 1.1 or less, still more preferably 1.05 or less, and preferably 1 or more. The average sphericity ratio can be obtained by observing the silica particles with a transmission electron microscope (magnification 200,000 times), measuring the major axis and minor axis of one silica particle, calculating the sphericity ratio (major axis / minor axis), and averaging the sphericity ratios measured for 50 silica particles.

[0020] In 100% by mass of the dispersion of the present invention, the content of the surface-treated silica particles is preferably 10 to 50% by mass. The content of the surface-treated silica particles may be 15% by mass or more, may be 20% by mass or more, may be 45% by mass or less, or may be 40% by mass or less.

[0021] 2. Dispersion medium The dispersion medium in the present invention is at least one selected from the group consisting of ether ester solvents, ester solvents, and aromatic hydrocarbon solvents. Examples of ether ester solvents include glycol ether ester solvents such as ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, propylene glycol monobutyl ether acetate, 3-methoxybutyl acetate, and 3-methoxy-3-methylbutyl acetate, as well as 3-methoxymethylpropionate. Ethylene glycol monomethyl ether acetate or propylene glycol monomethyl ether acetate are preferred. Note that an ether ester solvent refers to a solvent that contains -COO- and -O- molecules. Examples of ester solvents include methyl formate, ethyl formate, propyl formate, butyl formate, isobutyl formate, pentyl formate, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, amyl acetate, cyclohexyl acetate, methyl lactate, ethyl lactate, and butyl lactate, with ethyl acetate being preferred. Note that an ester solvent is defined as a solvent that contains -COO- in its molecule but does not contain -O-. Examples of aromatic hydrocarbon solvents include toluene, xylene, mesitylene, pseudocumene, benzene, ethylbenzene, and cyclohexylbenzene, with toluene being preferred.

[0022] The total amount of the dispersion medium and the surface-treated silica particles is preferably 90% by mass or more, more preferably 93% by mass or more, and even more preferably 95% by mass or more, based on 100% by mass of the surface-treated silica particle dispersion. If the dispersion medium contains multiple types of solvents, the amount of the dispersion medium refers to the total amount of multiple types.

[0023] 3. Alcohol-based solvents In the present invention, since the surface-treated silica particle dispersion contains an appropriate amount of alcohol-based solvent, surface-treated silica particles having an aryl group Ar and an alkyl group R on their particle surface can be dispersed in the aforementioned specific dispersion medium for a long period of time. Specifically, the amount of alcohol-based solvent is (i) 0.20 to 5% by mass in 100% by mass of the surface-treated silica particle dispersion. Alternatively, instead of requirement (i) above, requirement (ii) that the amount of alcohol-based solvent is 0.3 to 5.5% by mass in 100% by mass of the total amount of the dispersion medium and alcohol-based solvent may be satisfied. Both requirements (i) and (ii) may be satisfied, and the preferred ranges described below may also be satisfied by either the preferred range of requirement (i) or the preferred range of requirement (ii), or both.

[0024] With respect to requirement (i) above, the amount of alcohol-based solvent in 100% by mass of the surface-treated silica particle dispersion is preferably 0.4% by mass or more, more preferably 0.5% by mass or more, even more preferably 0.6% by mass or more, preferably 4% by mass or less, more preferably 3% by mass or less, and even more preferably 2% by mass or less.

[0025] With respect to requirement (ii) above, the amount of alcohol-based solvent in the total amount of the dispersion medium and alcohol-based solvent (100% by mass) is preferably 0.5% by mass or more, more preferably 0.7% by mass or more, and preferably 4.5% by mass or less, and even more preferably 3.5% by mass or less.

[0026] Examples of alcoholic solvents include monools such as methanol, ethanol, propanol, isopropyl alcohol, n-butyl alcohol, t-butyl alcohol, and pentyl alcohol; diols such as ethylene glycol, propylene glycol, and 1,4-butanediol; and others. Monools are preferred, methanol or ethanol is more preferred, and methanol is even more preferred.

[0027] 4. Other ingredients The surface-treated silica particle dispersion of the present invention may contain other additives (including solvents other than the dispersion medium and alcohol-based solvent) in addition to the surface-treated silica particles, dispersion medium, and alcohol-based solvent described above. However, the total amount of other additives is preferably 5% by mass or less, more preferably 2% by mass or less, and even more preferably 0% by mass, based on 100% by mass of the surface-treated silica particle dispersion.

[0028] Of the amount of Si contained in the dispersion of the present invention, the total amount of Si contained in the medium other than the surface-treated silica particles (hereinafter referred to as residual silicon) may be more than 0.05 parts by mass per 100 parts by mass of the dispersion of the present invention. The residual silicon is that which originates from the surface treatment agent used to treat the silica particles that was unable to coat the surface of the silica particles, and it is thought that at least a portion of it is oligomerized. Such residual silicon is preferable because it is thought to contribute to the dispersibility of the surface-treated silica particles. The residual silicon can be measured by ICP-AES (inductively coupled plasma emission spectroscopy) in the manner described in the examples below.

[0029] Furthermore, the total amount of residual silicon may be 0.05 parts by mass or less per 100 parts by mass of the dispersion of the present invention. Depending on the application of the surface-treated silica particle dispersion, it is desirable to reduce the residual silicon content as much as possible. As will be described in detail below, the present invention contains an appropriate amount of alcohol-based solvent, so even with a small amount of residual silicon, sufficient dispersion stability can be ensured, and long-term dispersion stability of the dispersion can be achieved even in applications where it is desirable to reduce the residual silicon content. In the embodiment in which the residual silicon content is reduced, the total amount of residual silicon is more preferably 0.03 parts by mass or less, even more preferably 0.02 parts by mass or less, and particularly preferably 0.01 parts by mass or less per 100 parts by mass of the dispersion of the present invention. The lower limit of the total amount of residual silicon is not particularly limited, but it is also possible to set it to 0.0005 parts by mass per 100 parts by mass of the dispersion of the present invention.

[0030] Furthermore, the dispersion of the present invention preferably has a reduced content of metals as impurities (transition metals such as Fe; alkali metals such as Na; alkaline earth metals such as Ca; etc.). For example, the content of impurity metals is preferably less than 5 ppm in silica particles, and more preferably less than 1 ppm. More specifically, it is preferable that the content of alkali metals is less than 5 ppm in silica particles, or that the content of alkaline earth metals is less than 5 ppm in silica particles. Examples of metals as impurities include heavy metals such as Pb and Cr, and radioactive materials such as U and Th. It is also preferable that the content of these metals is reduced. The content of heavy metals is preferably less than 1 ppm, and the content of radioactive materials is preferably less than 0.1 ppb. The metal content as an impurity can be measured using a high-frequency inductively coupled plasma atomic emission spectrometer (SPECTRO ACROS; manufactured by Hitachi High-Tech Science, Inc., etc.). Specifically, a silica particle dispersion is evaporated to dryness, and the resulting powder sample (5g) is added to a mixture of hydrofluoric acid and nitric acid. Nitric acid and hydrogen peroxide are then sequentially added to this mixture to make a total volume of 50mL, which can then be used as the measurement sample solution.

[0031] 5. Manufacturing method The surface-treated silica particle dispersion of the present invention can be produced by a manufacturing method comprising a silica particle synthesis step (A), a surface treatment step (B), ultrafiltration and a first solvent replacement step (C), an ion exchange step (D), and a second solvent replacement step (E).

[0032] 5-1. Silica particle synthesis process (A) (also simply called process (A)) In the silica particle synthesis process (A), silica particles are produced by hydrolysis condensation of alkoxysilane in the presence of a basic catalyst and water.

[0033] The alkoxysilane is a compound having an alkoxy group as a substituent on a silicon atom. In addition to the alkoxy group, the substituent on the silicon atom may also have an alkyl group having 2 to 6 carbon atoms, or an aromatic hydrocarbon group having 6 to 10 carbon atoms. Furthermore, the hydrogen atoms of the alkyl group may be substituted with halogen atoms, vinyl groups, glycidyl groups, mercapto groups, amino groups, and the like.

[0034] Examples of alkoxysilanes include compounds in which an alkoxy group and an unsubstituted or substituted alkyl group are bonded to a silicon atom, with compounds in which an alkoxy group and an unsubstituted alkyl group are bonded to a silicon atom being more preferred. Examples include tetrafunctional alkoxysilanes such as tetramethoxysilane and tetraethoxysilane; trifunctional alkoxysilanes such as methyltrimethoxysilane and methyltriethoxysilane; difunctional alkoxysilanes such as dimethyldimethoxysilane and dimethyldiethoxysilane; and monofunctional alkoxysilanes such as trimethylmethoxysilane and trimethylethoxysilane. Among these, tetrafunctional alkoxysilanes are preferred. The more functionalities (number of alkoxy groups) an alkoxysilane has, the less likely it is that impurities will be mixed into the resulting silica calcined product. Furthermore, from the viewpoint of reactivity, the number of carbon atoms in the alkoxy group is preferably 1 to 5, more preferably 1 to 3, and even more preferably 1 to 2. In other words, the alkoxysilanes particularly preferred for use in the silica particles of the present invention are tetramethoxysilane and tetraethoxysilane.

[0035] In the reaction solution for hydrolysis and condensation of alkoxysilane, the concentration of alkoxysilane is, for example, 0.1 mmol / g or higher and 3 mmol / g or lower. When the concentration of alkoxysilane in the reaction solution is within this range, the reaction rate can be easily controlled, and the particle size can be made uniform.

[0036] Furthermore, the concentration of water in the reaction solution is preferably 2 mmol / g to 25 mmol / g. However, since the amount of water changes due to the hydrolysis and condensation of alkoxysilane, the amount at the time of charging (before the start of hydrolysis and condensation) should be used as the basis. The molar ratio of water to alkoxysilane (water / alkoxysilane) is preferably 4 to 10. When the molar ratio of water to alkoxysilane is within this range, the amount of silanol groups remaining inside the silica particles is easily reduced.

[0037] Examples of the basic catalyst include ammonia compounds, amines, and quaternary ammonium compounds. Among these, ammonias and amines are preferred from the viewpoint of easy control of particle size. Furthermore, from the viewpoint of increasing the purity of the resulting silica particles, it is preferable that the catalyst is easily removed from the silica. Specifically, ammonias and amines are preferred, and ammonia and aliphatic amines are more preferred. Furthermore, from the viewpoint of combining catalytic effect and ease of removal, ammonias are preferred, and ammonia is particularly preferred.

[0038] In the reaction solution, the concentration of the basic catalyst is preferably 0.8 mmol / g to 2 mmol / g. Furthermore, the mass ratio of the basic catalyst to the total mass of the basic catalyst and water (basic catalyst / (basic catalyst + water)) is preferably 0.2 or higher, and preferably 0.32 or lower.

[0039] When hydrolyzing and condensing alkoxysilane, a diluent may be added. The presence of a diluent facilitates the mixing of the hydrophobic alkoxysilane with water, allowing for a more uniform rate of hydrolysis and condensation of the alkoxysilane in the reaction solution, and improving the dispersibility of the resulting silica particles. A water-soluble organic solvent is preferred as the diluent. Examples of water-soluble organic solvents include alcohol solvents such as methanol, ethanol, propanol, isopropyl alcohol, n-butyl alcohol, t-butyl alcohol, and pentyl alcohol (monools); ethylene glycol, propylene glycol, and 1,4-butanediol (diols); and others. Monools are preferred, methanol or ethanol is more preferred, and methanol is even more preferred.

[0040] In the reaction solution, the diluent is preferably 40% by mass or more and 80% by mass or less. Furthermore, the diluent is preferably 120 parts by mass or more and 500 parts by mass or less per 100 parts by mass of the total of alkoxysilane and water. The more diluent there is, the easier it is to make the reaction proceed more uniformly, and the less diluent there is, the faster the reaction rate can be increased. However, since the amount of alcohol changes due to the hydrolysis and condensation of alkoxysilane, the amount of diluent should be based on the amount at the time of charging (before the start of hydrolysis and condensation).

[0041] The reaction solution may contain hydrophobic organic solvents such as ketones (acetone, methyl ethyl ketone, etc.), esters (ethyl acetate, etc.), paraffins (isooctane, cyclohexane, etc.), ethers (dioxane, diethyl ether, etc.), aromatic hydrocarbons (benzene, toluene, etc.). When using these hydrophobic organic solvents, surfactants may be added to improve dispersibility.

[0042] The above components may be mixed in any order, but for example, a pre-mixed solution may be prepared by first mixing the components other than alkoxysilane, and then the alkoxysilane may be added to this pre-mixed solution. The alkoxysilane may also be mixed with a diluent beforehand and then mixed with the pre-mixed solution.

[0043] When hydrolyzing and condensing alkoxysilanes, the reaction temperature is preferably 20 to 70°C, and the hydrolysis and condensation duration is preferably 30 minutes to 100 hours.

[0044] 5-2. Surface treatment process (B) In the surface treatment step (B), it is preferable to add the surface treatment agent containing the aryl group Ar and the surface treatment agent containing the alkyl group R to the reaction solution obtained after hydrolysis and condensation of the alkoxysilane in step (A).

[0045] The order in which the surface treatment agent containing the aryl group Ar and the surface treatment agent containing the alkyl group R are added is not particularly limited, but it is preferable to add the surface treatment agent containing the aryl group Ar first, followed by the surface treatment agent containing the alkyl group R. After adding the surface treatment agents, it is preferable to stir for about 5 to 20 hours, and the temperature in step (B) is preferably 20 to 70°C.

[0046] The amount of surface treatment agent containing the aryl group Ar is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and preferably 15 parts by mass or less, and more preferably 13 parts by mass or less, per 100 parts by mass of alkoxysilane.

[0047] The amount of surface treatment agent containing alkyl group R is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more, and preferably 8 parts by mass or less, and more preferably 6 parts by mass or less, per 100 parts by mass of alkoxysilane.

[0048] The molar ratio (aryl group / alkyl group) of the amount of aryl group Ar in a surface treatment agent containing an aryl group Ar to the amount of alkyl group R in a surface treatment agent containing an alkyl group R is preferably 0.01 or more, more preferably 0.02 or more, even more preferably 0.03 or more, and also preferably 3.0 or less, more preferably 2.0 or less, and even more preferably 1.0 or less.

[0049] 5-3. Ultrafiltration and first solvent replacement step (C) In step (C), a first solvent exchange is performed, and ultrafiltration is carried out as needed. After step (B), in which a surface treatment agent is added to the reaction solution after hydrolysis and condensation, the solution is filtered using an ultrafiltration membrane. This removes water, basic catalysts, diluents added as needed, ketones, etc., that were present in the reaction solution after hydrolysis and condensation, as well as any excess surface treatment agent (the residual silicon mentioned above) that could not be used to coat the silica particle surface in step (B). In step (C), while filtering with an ultrafiltration membrane, a dispersion medium different from the dispersion medium (reaction solvent) of the reaction solution may be added. In this way, a dispersion in which surface-treated silica particles are dispersed in a solvent different from the reaction solvent can be obtained. Furthermore, in the dispersion of the present invention, if the residual silicon content is to be above a predetermined level as described above, ultrafiltration may be omitted, and only the first solvent substitution may be performed. In the present invention, the solvent added for the first solvent substitution in step (C) may be an alcohol-based solvent, and this alcohol-based solvent may be the alcohol-based solvent contained in the dispersion of the present invention. In step (C), it is preferable to perform solvent replacement (preferably with an alcohol-based solvent) and concentrate the surface-treated silica particles until the concentration reaches about 5 to 20% by mass to obtain a dispersion of surface-treated silica particles.

[0050] 5-4. Ion exchange process (D) The surface-treated silica particle dispersion after the ultrafiltration step (C) can be further treated with a cation exchange resin to remove basic catalysts and other substances adsorbed on the particle surface. Conventional cation exchange resins can be used, and either weakly acidic or strongly acidic cation exchange resins may be used. Examples of weakly acidic cation exchange resins include Amberlite IRC-76 (Organo Corporation), Diaion WK10, WK20 (Mitsubishi Chemical Corporation), and Levatit CNP80 (Bayer Ltd.). Examples of strongly acidic cation exchange resins include Amberlist 16, Amberlite IR-120B (Organo Corporation), Diaion PK-208, PK-228, PK-216 (Mitsubishi Chemical Corporation), Duolite C-26, Duolite ES-26 (Sumitomo Chemical Corporation), and MSC-1, 88 (Dow Corporation).

[0051] 5-5. Second solvent replacement step (E) In the second solvent replacement step (E), the solvent of the surface-treated silica particle dispersion obtained in the ion exchange step (D) is removed by solid-liquid separation means such as centrifugation or solvent removal by vacuum distillation, and at least one of the dispersion media for the dispersion of the present invention, i.e., selected from the group consisting of ether ester solvents, ester solvents, and aromatic hydrocarbon solvents, is added to replace the solvent in step (D) with the dispersion media for the dispersion of the present invention. If the first solvent replacement in step (C) is replaced with an alcohol-based solvent, the solvent in step (D) is also an alcohol-based solvent, and by appropriately adjusting the degree of concentration in the solid-liquid separation means in step (E), the content of the alcohol-based solvent contained in the final dispersion of the present invention can be adjusted to an appropriate range.

[0052] Resin compositions comprising the dispersion of the present invention and polymerizable monomers and / or polymer materials (resins) are also included in the technical scope of the present invention.

[0053] The concentration of surface-treated silica particles is, for example, 3% by mass or more and 70% by mass or less, based on 100% by mass of the resin composition.

[0054] The polymerizable monomer can be one or more types, including monofunctional monomers and crosslinkable monomers. The monofunctional monomer may be any compound having one polymerizable carbon-carbon double bond, and one or more types may be used. Examples include (meth)acrylic acid esters; styrene monomers such as styrene, p-tert-butylstyrene, α-methylstyrene, m-methylstyrene, p-methylstyrene, p-chlorostyrene, and p-chloromethylstyrene; carboxyl group-containing monomers such as (meth)acrylic acid; and hydroxyl group-containing monomers such as 2-hydroxyethyl (meth)acrylate, 3-hydroxy-2-hydroxypropyl (meth)acrylate, and 3-phenoxy-2-hydroxypropyl (meth)acrylate.The above-mentioned (meth)acrylic acid esters specifically include, for example, alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and lauryl (meth)acrylate; cycloalkyl (meth)acrylates such as cyclohexyl (meth)acrylate; 2 aryl esters of (meth)acrylates such as ,4-dibromo-6-sec-butylphenyl(meth)acrylate, 2,4-dibromo-6-isopropylphenyl(meth)acrylate, phenyl(meth)acrylate, 2,4,6-tribromophenyl(meth)acrylate, pentabromophenyl(meth)acrylate; aralkyl esters of (meth)acrylates such as benzyl(meth)acrylate, pentabromobenzyl(meth)acrylate; phenoxyethyl(meth)acrylate, phenoxyethyl Examples include (meth)acrylic acid esters having aryloxy units such as hydroxy-2-methylethyl (meth)acrylate, 2,4,6-tribromophenoxyethyl (meth)acrylate, 2,4-dibromophenoxyethyl (meth)acrylate, 2-bromophenoxyethyl (meth)acrylate, 1-naphthyloxyethyl (meth)acrylate, 2-naphthyloxyethyl (meth)acrylate, phenoxy-2-methylethyl (meth)acrylate, and phenoxyethoxyethyl (meth)acrylate; (meth)acrylic acid esters having arylthiooxy groups such as phenylthioethyl (meth)acrylate, 1-naphthylthioethyl (meth)acrylate, and 2-naphthylthioethyl (meth)acrylate; alkylene glycol mono(meth)acrylates such as methoxypolyethylene glycol (meth)acrylate and phenoxypolyethylene glycol (meth)acrylate; and (meth)acrylic acid esters having glycidyl groups such as glycidyl (meth)acrylate.

[0055] A crosslinkable monomer can be any compound containing multiple carbon-carbon double bonds. One or more types of crosslinkable monomers can be used, for example alkylene glycol poly(meth)acrylates such as ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, tetramethylene glycol di(meth)acrylate; neopentyl glycol poly(meth)acrylates such as neopentyl glycol di(meth)acrylate, dineopentyl glycol di(meth)acrylate; trimethylolpropane tri(meth)acrylate, ethoxylated (3) trimethylolpropane tri(meth)acrylate, propoxylated (3) trimethylolpropane tri(meth)acrylate, epoxidized (3) trimethylol Trimethylolpropane poly(meth)acrylates such as methylpropane tri(meth)acrylate and ditrimethylolpropane tetra(meth)acrylate; glyceryl poly(meth)acrylates such as glyceryl tri(meth)acrylate and ethoxylated glyceryl tri(meth)acrylate; pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, propoxylated pentaerythritol Polyfunctional (meth)acrylates such as thol tri(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and other pentaerythritol poly(meth)acrylates; polyfunctional styrene monomers such as divinylbenzene; polyfunctional allyl ester monomers such as diallyl phthalate, diallyl isophthalate, triallyl cyanurate, and triallyl isocyanurate; 2-(2-vinyloxyethoxy)ethyl (meth)acrylate;Examples include urethane acrylate oligomers (e.g., Shiko® series (manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), CN series (manufactured by Sartomer Inc.), Unidic® series (manufactured by DIC Corporation), KAYARAD® UX series (manufactured by Nippon Kayaku Co., Ltd.), etc.).

[0056] The polymerizable monomer content is, for example, 1 part by mass or more and 500 parts by mass or less per 100 parts by mass of surface-treated silica particles.

[0057] The aforementioned polymer material (resin) can be one or more types, and examples include polyamides such as 6-nylon, 66-nylon, and 12-nylon; polyimides; polyurethanes; polyolefins such as polyethylene and polypropylene; polyesters such as PET, PBT, and PEN; polyvinyl chlorides; polyvinylidene chlorides; polyvinyl acetates; polystyrenes; (meth)acrylic resin polymers; ABS resins; fluororesins; phenol-formaldehyde resins; phenolic resins such as cresol-formaldehyde resins; epoxy resins; urea resins; melamine resins; amino resins such as guanamine resins; polyvinyl butyral resins; polyurethane resins; ethylene-vinyl acetate copolymer resins; and soft and hard resins such as ethylene-(meth)acrylic acid ester copolymer resins. Among the above, polyimides, polyurethanes, polyesters, (meth)acrylic resin polymers, phenolic resins, amino resins, and epoxy resins are more preferred.

[0058] The content of the above polymer material (resin) is, for example, 1 part by mass or more and 500 parts by mass or less per 100 parts by mass of surface-treated silica particles.

[0059] If the resin composition of the present invention contains a polymerizable monomer, it may further contain a polymerization initiator. Examples of polymerization initiators include photopolymerization initiators and thermal polymerization initiators, which may be used individually or in combination. Some photopolymerization initiators act as thermal polymerization initiators, and some thermal polymerization initiators act as photopolymerization initiators, so those having both properties can cure the active energy ray curable aqueous resin composition by light irradiation or heating. Among polymerization initiators, photopolymerization initiators are preferred because they do not impart a thermal history to the formed film or the substrate to which the active energy ray curable aqueous resin composition is applied.

[0060] Examples of thermal polymerization initiators include oil-soluble initiators such as 2,2'-azobis-(2-methylbutyronitrile), 2,2'-azobisisobutyronitrile, 2,2'-azobis-(2,4'-dimethylvaleronitrile), benzoyl peroxide, 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, and tert-butylperoxy-2-ethylhexanoate; persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate; water-soluble peroxides such as hydrogen peroxide; and water-soluble azo compounds such as 2,2'-azobis(2-amidinopropane) dihydrochloride. However, the present invention is not limited to these examples. These thermal polymerization initiators may be used individually or in combination of two or more types.

[0061] Examples of photopolymerization initiators include benzophenone, 1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propan-1-one, oxyphenyl acetate acid 2-[2-oxo-2-phenylacetoxyethoxy]-ethyl ester, oxyphenyl acetate acid 2-[2-hydroxyethoxy]-ethyl ester, 1-hydroxycyclohexylphenyl ketone, 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide. Examples of photopolymerization initiators include 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-(4-isopropylphenyl)2-hydroxy-2-methylpropan-1-one, 2-methyl-1-[4-(methylthio)phenyl]2-morpholinopropan-1-one, 2-morpholinopropan-1-one, iodonium, sulfonium salts, diazonium salts, (4-methylphenyl[4-(2-methylpropyl)phenyl])-hexafluorophosphate, diethylthioxanthone, isopropylthioxanthone, etc., but the present invention is not limited to these examples. These photopolymerization initiators may be used individually or in combination of two or more types.

[0062] The amount of polymerization initiator is, for example, 0.5 parts by mass or more and 20 parts by mass or less per 100 parts by mass of polymerizable monomer.

[0063] The resin composition can be produced by mixing the silica particle dispersion with a polymerizable monomer and / or a polymer material (resin). The solvent may be removed if necessary.

[0064] The surface-treated silica particle dispersion of the present invention can stably disperse silica particles over a long period of time and is useful for applications such as forming precise microstructures in adhesive materials, dental materials, optical components, coating materials (for hard coatings and anti-glare coatings), nanocomposite materials, abrasives, and resists. [Examples]

[0065] The present invention will be described in more detail below with reference to examples. The present invention is not limited by the following examples, and it is certainly possible to implement it with appropriate modifications within the scope that is consistent with the spirit described below, and all such modifications are included within the technical scope of the present invention.

[0066] The examples and comparative examples described below were evaluated using the following method.

[0067] [Average primary particle size and coefficient of variation (CV value)] Surface-treated silica particles were imaged using a JEOL JSM-7600F scanning electron microscope. The diameters of 50 randomly selected particles from the captured SEM images were measured using calipers, and the arithmetic mean of these 50 diameters was defined as the average primary particle diameter. The scanning electron microscope image capture was performed with a magnification setting such that 50 to 100 particles were contained within the field of view of each image. Furthermore, the coefficient of variation (CV value) for the primary particle diameters of the 50 measured particles was calculated based on the following formula. CV value (%) = Standard deviation of primary particle diameter / Average primary particle diameter × 100

[0068] [Silica particle content in silica particle dispersion] 5.0g each of the silica particle dispersions (dispersions 1-8 described below) was measured out into aluminum cups, and the amount of silica particles (solid content) in the silica particle dispersion was calculated from the weight remaining after heating on a hot plate preheated to 150 degrees Celsius for 30 minutes.

[0069] [Carbon concentration] 5.0 g each of silica particle dispersions (dispersions 1-8 described below) was weighed into aluminum cups and heated for 30 minutes on a hot plate preheated to 150 degrees Celsius. The carbon concentration per unit mass of the remaining surface-treated silica particles was measured using a MICRO CORDER JM10 manufactured by J-Science Lab Co., Ltd.

[0070] [Residual silicon content] 15 mL of the silica particle dispersion from each example and comparative example was placed in a centrifuge tube and centrifuged at 15000 G, 25°C, and for 60 minutes. After repeating the above centrifugation procedure three times, the supernatant was taken from the centrifuge tube and the silicon concentration not derived from the surface-treated silica particles, i.e., the residual silicon content, was measured using an ICP analyzer (SPECTRO ARCOS, Hitachi High-Tech Science Corporation).

[0071] [Content of alcohol-based solvents] The alcohol-based solvent content in the silica particle dispersion in each example and comparative example was measured using gas chromatography. 0.2 g of the particle dispersion and 0.02 g of diethylene glycol diethyl ether as an internal standard were mixed with 5 g of n-butanol. The mixture was filtered through a 0.45 μm pore size filter, and the alcohol-based solvent content in the filtrate was determined by a calibration curve (internal standard) using gas chromatography. The gas chromatography conditions were as follows: Equipment: GC-2014 (manufactured by Shimadzu Corporation) Column: Capillary column InertCap Pure-WAX (GL Sciences Co., Ltd., column length: 30m, column inner diameter: 0.25mm, capillary inner film thickness: 0.25μm) Carrier gas: Helium Column temperature: Hold at 50°C for 5 minutes, increase temperature at 10°C / min, hold at 240°C for 6 minutes. Inlet temperature: 280℃ Detector temperature: 280℃ (FID) Examples of detected substances and their retention times: methanol (2.5 min), diethylene glycol diethyl ether (12.3 min)

[0072] [Dispersion stability evaluation using grind gauge (grain gauge)] To estimate the maximum particle size of aggregated particles contained in the silica particle dispersion, the silica particle dispersion was evaluated using a grind gauge (particle gauge) with a width of 40 mm, a length of 170 mm, and a maximum depth of 50 μm, based on JIS-K5101. Specifically, the dispersions obtained in the examples and comparative examples were left at 23°C and 50% RH for one or two weeks, placed on the particle gauge, and a scraper was applied vertically and slid along the groove to scrape off the dispersion. The resulting linear marks were observed, and the scale at the position where the linear marks began to be observed (i.e., the maximum particle size of aggregated particles) was read. In Table 1 below, "None" indicates that no linear marks were observed even at the "0 μm" position.

[0073] [Synthesis Example 1] Project 1A In a 50L stainless steel container equipped with a stirrer, dropping nozzle, and thermometer, 16,500g of methanol, 3,200g of water, 1,300g of 25% aqueous ammonia, and 110g of acetone were added and stirred for 30 minutes to obtain a homogeneous mixed solution. The temperature of the above mixed solution was adjusted to 49-51°C, and while stirring, 5,700g of tetramethyl orthosilicate (TMOS) was added dropwise through the dropping nozzle over 90 minutes. After the addition was complete, stirring was continued for another 30 minutes while maintaining the above temperature to obtain an alcoholic suspension of silica particles (suspension 1A).

[0074] Project 1B The suspension 1A obtained in step A was heated to 50°C again while stirring, and 660g of phenyltrimethoxysilane (KBM-103, manufactured by Shin-Etsu Chemical Co., Ltd.) was added dropwise through the dropping port over 120 minutes while maintaining the liquid temperature and stirring. Subsequently, 270g of hexamethyldisilazane (SZ-31, manufactured by Shin-Etsu Chemical Co., Ltd.) was added dropwise through the dropping port over 15 minutes. After the addition was completed, stirring was continued for 15 hours while maintaining the above liquid temperature to obtain an alcoholic solution suspension (suspension 1B) of silica particles having phenyl and methyl groups on the particle surface.

[0075] Project 1C The suspension 1B obtained in step B was subjected to solvent replacement using a commercially available ultrafiltration membrane equipped with a ceramic tubular ultrafiltration membrane with a fractional molecular weight of approximately 10,000, while adding methanol as appropriate at room temperature, and concentrated until the SiO2 concentration reached approximately 11%, thereby obtaining a methanol suspension (suspension 1C) of silica particles having phenyl groups and methyl groups on the particle surface.

[0076] [Synthesis Example 2] Project 2A In a 50L stainless steel container equipped with a stirrer, dropping nozzle, and thermometer, 16,400g of methanol, 2,700g of water, 2,000g of 25% aqueous ammonia, and 110g of acetone were added and stirred for 30 minutes to obtain a homogeneous mixed solution. The temperature of the above mixed solution was adjusted to 49-51°C, and while stirring, 5,700g of tetramethyl orthosilicate (TMOS) was added dropwise through the dropping nozzle over 90 minutes. After the addition was complete, stirring was continued for another 30 minutes while maintaining the above temperature to obtain an alcoholic suspension of silica particles (suspension 2A).

[0077] Project 2B The suspension 2A obtained in step 2A was heated to 50°C again while stirring, and 260g of phenyltrimethoxysilane (KBM-103, manufactured by Shin-Etsu Chemical Co., Ltd.) was added dropwise through the dropping port over 40 minutes while maintaining the liquid temperature and stirring. Subsequently, 110g of hexamethyldisilazane (SZ-31, manufactured by Shin-Etsu Chemical Co., Ltd.) was added dropwise through the dropping port over 5 minutes. After the addition was completed, stirring was continued for 15 hours while maintaining the above liquid temperature to obtain an alcoholic solution suspension (suspension 2B) of silica particles having phenyl and methyl groups on the particle surface.

[0078] Engineering 2C The suspension 2B obtained in step 2B was subjected to solvent replacement using a commercially available ultrafiltration membrane equipped with a ceramic tubular ultrafiltration membrane with a fractional molecular weight of approximately 10,000, while adding methanol as appropriate at room temperature, and concentrated until the SiO2 concentration reached approximately 11%, thereby obtaining a methanol suspension of silica particles having phenyl groups and methyl groups on the particle surface (suspension 2C).

[0079] [Synthesis Example 3] Project 3A In a 50L stainless steel container equipped with a stirrer, a dropping nozzle, and a thermometer, 16100g of methanol, 2200g of water, 2700g of 25% aqueous ammonia, and 110g of acetone were added and stirred for 30 minutes to obtain a homogeneous mixed solution. The temperature of the above mixed solution was adjusted to 49-51°C, and while stirring, 5700g of tetramethyl orthosilicate (TMOS) was added dropwise through the dropping nozzle over 90 minutes. After the addition was complete, stirring was continued for another 30 minutes while maintaining the above temperature to obtain an alcoholic solution suspension of silica particles (suspension 3A).

[0080] Project 3B The suspension 3A obtained in step 3A was heated to 50°C again while stirring, and 190g of phenyltrimethoxysilane (KBM-103, manufactured by Shin-Etsu Chemical Co., Ltd.) was added dropwise through the dropping port over 30 minutes while maintaining the liquid temperature and stirring. Subsequently, 80g of hexamethyldisilazane (SZ-31, manufactured by Shin-Etsu Chemical Co., Ltd.) was added dropwise through the dropping port over 15 minutes. After the addition was completed, stirring was continued for 15 hours while maintaining the above liquid temperature to obtain an alcoholic solution suspension (suspension 3B) of silica particles having phenyl and methyl groups on the particle surface.

[0081] Engineering 3C The suspension 3B obtained in step 3B was subjected to solvent replacement using a commercially available ultrafiltration membrane equipped with a ceramic tubular ultrafiltration membrane with a fractional molecular weight of approximately 10,000, while adding methanol as appropriate at room temperature, and concentrated until the SiO2 concentration reached approximately 11%, thereby obtaining a methanol suspension (suspension 3C) of silica particles having phenyl and methyl groups on the particle surface. The sphericity ratio of the silica particles obtained in Synthesis Example 3 was 1.03.

[0082] [Synthesis Example 4] Project 4A The same procedure as in step 3A of synthesis example 3 was performed to obtain an alcoholic solution suspension of silica particles (suspension 4A).

[0083] Project 4B The suspension 4A obtained in step 4A was heated to 50°C while stirring again, and 160g of hexamethyldisilazane (SZ-31, manufactured by Shin-Etsu Chemical Co., Ltd.) was added dropwise through the dropper port over 30 minutes while maintaining the liquid temperature and stirring. After the addition was completed, stirring was continued for 15 hours while maintaining the above liquid temperature to obtain an alcoholic solution suspension (suspension 4B) of silica particles having methyl groups on the particle surface.

[0084] Engineering 4C In step 3C of the above synthesis example 3, the same procedure was performed except that suspension 3B was changed to suspension 4B, to obtain a methanol suspension of silica particles having methyl groups on the particle surface (suspension 4C).

[0085] [Synthesis Example 5] Engineering 5A The same procedure as in step A of synthesis example 3 was performed to obtain an alcoholic solution suspension of silica particles (suspension 5A).

[0086] Project 5B The suspension 5A obtained in step 5A was heated to 50°C while stirring again, and 380g of phenyltrimethoxysilane (KBM-103, manufactured by Shin-Etsu Chemical Co., Ltd.) was added dropwise through the dropper port over 60 minutes while maintaining the liquid temperature and stirring. After the addition was completed, stirring was continued for 10 hours while maintaining the above liquid temperature to obtain an alcoholic solution suspension (suspension 5B) of silica particles having phenyl groups on their surface. Suspension 5B was white and showed a tendency to thicken and aggregate.

[0087] Engineering 5C When the suspension 5B obtained in step 5B was subjected to solvent replacement using a commercially available ultrafiltration membrane equipped with a ceramic tubular ultrafiltration membrane with a fractional molecular weight of approximately 10,000, while adding methanol as appropriate at room temperature, the ultrafiltration membrane became clogged during solvent replacement, and it was not possible to obtain a methanol suspension of silica particles having phenyl groups on the particle surface (suspension 5C).

[0088] Example 1 The suspension 1C obtained in Synthesis Example 1 was passed through a column packed with the hydrogen-type strongly acidic cation exchange resin Amberlite IR-120B (Organo) at room temperature at a flow rate of 3 space velocity per hour (Step D). 1800 g of the suspension 1C after passing through was weighed, and the solvent in the suspension was replaced with PGMEA by sequentially adding propylene glycol monomethyl ether acetate (PGMEA) while concentrating the solvent by vacuum distillation at a reduced pressure of 30-300 hPa and 40°C using a rotary evaporator (Step E). By concentrating to an SiO2 concentration of approximately 30%, a PGMEA dispersion of silica particles having phenyl and methyl groups on the particle surface (Dispersion 1) was obtained. The evaluation results of the obtained dispersion 1 are shown in Table 1.

[0089] Example 2 In Example 1, the same procedure was followed except that the suspension used was changed from 1C to 2C, and a PGMEA dispersion of silica particles having phenyl and methyl groups on the particle surface (Dispersion 2) was obtained. The evaluation results of the obtained Dispersion 2 are shown in Table 1.

[0090] Example 3 In Example 1, the same procedure was followed except that the suspension used was changed from 1C to 3C, and a PGMEA dispersion of silica particles having phenyl and methyl groups on the particle surface (Dispersion 3) was obtained. The evaluation results of the obtained dispersion 3 are shown in Table 1.

[0091] Example 4 In Example 3, the same procedure was followed except that PGMEA in step E was replaced with ethyl acetate to obtain an ethyl acetate dispersion (dispersion 4) of silica particles having phenyl and methyl groups on the particle surface. The evaluation results of the obtained dispersion 4 are shown in Table 1.

[0092] Example 5 In Example 3, the same procedure was followed except that PGMEA in step E was replaced with ethylene glycol monoethyl ether acetate to obtain an ethylene glycol monoethyl ether acetate dispersion (dispersion 5) of silica particles having phenyl and methyl groups on the particle surface. The evaluation results of the obtained dispersion 5 are shown in Table 1.

[0093] Example 6 In Example 3, the same procedure was followed except that PGMEA in step E was replaced with toluene to obtain a toluene dispersion (dispersion 6) of silica particles having phenyl and methyl groups on their particle surfaces. The evaluation results of the obtained dispersion 6 are shown in Table 1.

[0094] Comparative Example 1 In Example 1, the same procedure was followed except that the suspension used was changed from 1C to 3C, and the degree of concentration of suspension 3C in step E was changed, to obtain a PGMEA dispersion (dispersion 7) of silica particles having phenyl and methyl groups on the particle surface. The evaluation results of the obtained dispersion 7 are shown in Table 1.

[0095] Comparative Example 2 In Example 1, the same procedure was followed except that the suspension used was changed from 1C to 4C, and a PGMEA dispersion of silica particles having methyl groups on the particle surface (dispersion 8) was obtained. The evaluation results of the obtained dispersion 8 are shown in Table 1.

[0096] Comparative Example 3 In the above synthesis example 5, since a methanol suspension of silica particles 5C could not be obtained, steps D and E could not be carried out.

[0097] [Table 1]

[0098] Table 1 shows that in Examples 1-6, where the dispersion contained 0.20% by mass or more of an alcohol-based solvent, no aggregation of surface-treated silica particles was observed even after two weeks, indicating good dispersion. On the other hand, in Comparative Example 1, where the amount of alcohol in the dispersion was small, aggregation of surface-treated silica particles occurred after two weeks, with the maximum particle size being 40 μm. Similarly, in Comparative Example 2, where the particle surface was treated only with alkyl groups, aggregation of surface-treated silica particles occurred after two weeks, just like in Comparative Example 1. Furthermore, in Comparative Example 3, where the particle surface was treated only with aryl groups, solvent replacement in step C could not be performed due to the effects of thickening and aggregation at step B.

Claims

1. Surface-treated silica particles having aryl groups Ar and alkyl groups R on their surface. A dispersion medium which is at least one selected from the group consisting of ether ester solvents, ester solvents, and aromatic hydrocarbon solvents, A dispersion of surface-treated silica particles containing an alcohol-based solvent, A surface-treated silica particle dispersion characterized in that the content of the alcohol-based solvent in 100% by mass of the surface-treated silica particle dispersion is 0.20 to 5% by mass.

2. The surface-treated silica particle dispersion according to claim 1, wherein the aryl group Ar is a phenyl group which may be substituted with an alkyl group having 1 to 4 carbon atoms or an alkenyl group having 1 to 4 carbon atoms, and the alkyl group R has 1 to 4 carbon atoms.

3. The surface-treated silica particle dispersion according to claim 1 or 2, wherein the aryl group Ar is derived from an arylalkoxysilane.

4. The surface-treated silica particle dispersion according to claim 1 or 2, wherein the alkyl group R is derived from a hexaalkyldisilazane.

5. The surface-treated silica particle dispersion according to claim 1 or 2, wherein the ratio of the aryl group Ar to the alkyl group R (aryl group / alkyl group) is 0.01 to 3.

0.

6. The surface-treated silica particle dispersion according to claim 1 or 2, wherein when the surface-treated silica particle dispersion is 100 parts by mass, the amount of Si present in the medium other than the surface-treated silica particles is 0.05 parts by mass or less.

7. The surface-treated silica particle dispersion according to claim 1 or 2, wherein when the surface-treated silica particle dispersion is 100 parts by mass, the amount of Si present in the medium other than the surface-treated silica particles is greater than 0.05 parts by mass.

8. The surface-treated silica particle dispersion according to claim 1 or 2, wherein the content of surface-treated silica particles in 100% by mass of the surface-treated silica particle dispersion is 10 to 50% by mass.

9. The surface-treated silica particle dispersion according to claim 1 or 2, wherein the carbon concentration in 100% by mass of the surface-treated silica particles is 2 to 10% by mass.

10. The surface-treated silica particle dispersion according to claim 1 or 2, wherein the average primary particle diameter of the surface-treated silica particles is 10 to 100 nm.

11. A resin composition comprising a surface-treated silica particle dispersion according to claim 1 or 2 and a resin.

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