WO2024058165A1

WO2024058165A1 - Silicon oxide gel dispersion, transparent low-refractive-index film, and method for manufacturing silicon oxide gel dispersion

Info

Publication number: WO2024058165A1
Application number: PCT/JP2023/033175
Authority: WO
Inventors: 佳之塩谷; 洋平大久保; 朋侑八尾; 了太井筒; 大輔服部; 諒太森島; 啓介佐藤
Original assignee: 株式会社日本触媒; 日東電工株式会社
Priority date: 2022-09-12
Filing date: 2023-09-12
Publication date: 2024-03-21

Abstract

The purpose of the present invention is to provide a silicon oxide gel dispersion that has excellent ease of handling. The present invention is a silicon oxide gel dispersion that includes a silicon oxide gel and a solvent, wherein the viscosity of the dispersion is 10-2000 mPa∙s when the solid content concentration thereof is 3.0 ±0.1 mass%.

Description

Silicon oxide gel dispersion, transparent low refractive index film, and method for producing silicon oxide gel dispersion

The present invention relates to silicon oxide gel dispersions. Specifically, the present invention relates to a silicon oxide gel dispersion liquid that is easy to handle, a transparent low refractive index film, and a method for producing a silicon oxide gel dispersion liquid.

Gels are used in various fields. For example, dried gels made of silicon oxide have functional properties such as heat insulation, low dielectric constant properties, and low refractive index properties, and are used in optical materials, electronic materials, etc. It is used for various purposes. When using such a gelled product, for example, a method of preparing a dispersion in which the ground gelled product is dispersed in a solvent, applying this to a base material and drying it to form a film made of the gelled product described above. etc. are known.

Various silicon oxide gel dispersions used for producing such gelled products have been known so far.
For example, Patent Document 1 describes that a hydrophobic silica airgel film with a smooth surface was obtained by forming a film using a dispersion of organically modified silica in a ketone solvent. There is.
Further, for example, Patent Document 2 describes a gel-pulverized liquid containing Si element that is difficult to separate into solid and liquid and has excellent uniformity, and Patent Document 3 describes a gel-pulverized liquid containing Si element that is difficult to separate into solid-liquid and has excellent uniformity. A gel for producing a low refractive index film that can produce a film with a low refractive index, and a paint for producing a low refractive index film containing a pulverized product of the gel and a solvent are described.

Japanese Patent Application Publication No. 2006-151800 Japanese Patent Application Publication No. 2017-132674 International Publication No. 2017/051831

However, conventional silicon oxide gel dispersions have problems such as clogging of the circulation path when replacing the solvent or concentrating, and problems such as bubbles and clogging when pulverizing, and are not easy to handle. Ta. Furthermore, when surface treatment of silicon oxide is performed, there is a problem that the manufacturing process becomes longer.
In view of the above-mentioned current situation, an object of the present invention is to provide a silicon oxide gel dispersion having excellent handling properties.

The present inventor conducted various studies on silicon oxide gel dispersions and found that the viscosity of the gel dispersion is related to ease of handling during solvent replacement and pulverization processes. They discovered that the gel dispersion liquid has excellent handling properties, and completed the present invention.
That is, the present invention provides the following aspects of the invention.
[1] A silicon oxide gel dispersion containing a silicon oxide gel and a solvent, wherein the dispersion has a viscosity of 10 to 2000 mPa when the solid content concentration is 3.0±0.1% by mass. - A silicon oxide gel dispersion liquid characterized by being s.
[2] The silicon oxide gel dispersion as described in [1] above, wherein the silicon oxide gel has an average particle size of 1 to 99 μm.
[3] The silicon oxide gel dispersion according to [1] or [2] above, wherein the solvent is an organic solvent having a hydroxyl group.
[4] The silicon oxide according to any one of [1] to [3] above, wherein the pore volume of the dried silicon oxide gel is 0.5 to 3.0 cm ³ /g. substance gel dispersion.
[5] The silicon oxide gel dispersion according to any one of [1] to [4] above, which is used for a low refractive index material having a refractive index of 1.25 or less.
[6] A transparent low refractive index film characterized by having pores and produced using the silicon oxide gel dispersion according to any one of [1] to [5] above.
[7] A method for producing a silicon oxide gel dispersion, wherein the production method includes a step of gelling the silicon oxide dispersion while stirring. .

The silicon oxide gel dispersion of the present invention has excellent handling properties. By using the silicon oxide gel dispersion of the present invention, optical materials can be suitably obtained.

The present invention will be explained in detail below.
Note that a combination of two or more of the individual preferred embodiments of the present invention described below is also a preferred embodiment of the present invention.

<Silicon oxide gel dispersion>
The present invention provides a silicon oxide gel dispersion containing a silicon oxide gel and a solvent, wherein the dispersion has a viscosity of 10 to 10% when the solid content concentration is 3.0±0.1% by mass. This is a silicon oxide gel dispersion characterized by a pressure of 2000 mPa·s.
When the solid content concentration of the dispersion liquid is 3.0±0.1% by mass, and the viscosity is within the above-mentioned range, it can be processed while maintaining fluidity in the solvent replacement and pulverization steps, and is excellent in handleability.
Conventionally, for example, silicon oxide gel dispersions have been handled at a viscosity above a certain level (for example, about 4000 mPa・s or above) due to concerns about separation during storage; In terms of handling, there were problems such as the circulation path being blocked and the process not being able to proceed. Since the gel dispersion of the present invention has a viscosity within the above range, it can be easily handled in solvent replacement and pulverization steps.
On the other hand, if the viscosity is in a low viscosity region, for example less than 10 mPa·s, the contents will begin to settle immediately after redispersion, making it extremely difficult to handle as a uniform dispersion.

The viscosity is preferably 15 to 1,500 mPa·s, more preferably 20 to 1,000 mPa·s, even more preferably 25 to 500 mPa·s, and even more preferably 25 to 400 mPa·s. It is preferably 25 to 200 mPa·s, and most preferably 25 to 200 mPa·s.
The above viscosity can be determined by measuring at 25° C. using an E-type viscometer (product number: TV-20L, manufactured by Toki Sangyo Co., Ltd.).
Examples of methods for adjusting the solid content concentration of the dispersion to 3.0±0.1% by mass include a method of concentrating by filtration or centrifugation, and a method of diluting with a solvent contained in the dispersion.

The silicon oxide gel contained in the silicon oxide gel dispersion of the present invention is a gel-like compound of silicon oxide obtained by subjecting a silicon-containing compound to a hydrolysis/condensation reaction. The silicon-containing compound described above will be explained in the method for producing a silicon oxide gel dispersion described later.

As described later, the silicon oxide gel preferably contains a hydrolysis/condensation product of tetraalkoxysilane or alkylalkoxysilane, more preferably a hydrolysis/condensation product of alkylalkoxysilane, and contains alkyltrialkoxysilane. It is more preferable to include a hydrolyzed/condensed product of silane.
Preferably, the silicon oxide gel is an organosilicon oxide gel.

The shape of the silicon oxide gel is not particularly limited, but in the case of gel particles such as pulverized gel, examples include spherical and non-spherical shapes.

The average particle size of the silicon oxide gel is preferably 1 to 99 μm. When the average particle size of the silicon oxide gel is within the above range, the storage stability of the dispersion is good, and if further pulverization of the gel is required, it can be processed with a pulverizer without any problem. The average particle size is more preferably 5 to 80 μm, and even more preferably 10 to 60 μm, from the viewpoint of suppressing gel sedimentation.
The above-mentioned average particle diameter is a number average particle diameter, and can be determined using a laser diffraction particle size distribution analyzer, and specifically, can be determined by the method described in the Examples described below.

The silicon oxide gel preferably has pores. By filling the pores with air, gas, etc., the refractive index becomes low, and the above dispersion liquid can be used as a low refractive index material.
The pore volume of the dried silicon oxide gel is preferably 0.5 to 3.0 cm ³ /g. When the pore volume of the dry product of the silicon oxide gel is within the above range, a coating film with a low refractive index and high strength can be obtained. The pore volume may be appropriately selected depending on the purpose and use, but it is more preferably 0.8 to 2.8 cm ³ /g, and more preferably 1.2 to 2.5 cm ³ /g. More preferred.

The pore volume is determined by measuring the dry silicon oxide gel using a specific surface area/pore distribution measuring device (BELSORP-miniX manufactured by Microtrac Bell), and analyzing the measurement results using the BJH method. It can be found by The dried silicon oxide gel is not particularly limited as long as the solvent in the gel has completely evaporated and the silicon oxide gel has been dried, for example, by heating at 80 to 100°C for 3 to 24 hours. Examples include dried products that can be obtained, but preferably, drying is performed at 80°C for 24 hours at 0.02 MPa or less, and then further dried at 100°C for 3 hours or more at 10 Pa or less before measurement. It is a thing.
Specifically, the pore volume can be determined by the method described in Examples below.

The pore diameter of the dried silicon oxide gel is preferably 1 to 45 nm. When the pore diameter of the dried silicon oxide gel is within the above range, a coating film with a low refractive index and high strength can be obtained. The pore diameter is more preferably from 5 to 37 nm, and even more preferably from 13 to 29 nm.

The pore diameter is measured on the dried silicon oxide gel dispersion using a specific surface area/pore distribution measuring device (BELSORP-miniX manufactured by Microtrac Bell), and the measurement results are analyzed by the BJH method. It can be determined by the method and is a volume distribution. The dried silicon oxide gel described above can be prepared by a method similar to the method described above.
Specifically, the pore diameter can be determined by the method described in Examples described later.

The dry silicon oxide gel preferably has a specific surface area of 460 to 870 m ² /g. When the specific surface area of the silicon oxide gel is within the above range, a coating film with a low refractive index and high strength can be obtained. The specific surface area is preferably 530 to 800 m ² /g, more preferably 600 to 730 m ² /g.

The specific surface area is measured for the dried silicon oxide gel dispersion using a specific surface area/pore distribution measuring device (BELSORP-miniX manufactured by Microtrac Bell), and the measurement results are analyzed by the BET method. The dried product of the silicon oxide gel can be prepared by a method similar to the method described above.
Specifically, the specific surface area can be determined by the method described in Examples described later.

The amount of water in the silicon oxide gel dispersion is preferably 0.01 to 5% by mass based on 100% by mass of the gel. When the water content of the silicon oxide gel is within the above range, the gel in the dispersion is well dispersed, and a homogeneous coating film can be obtained when the dispersion is applied. The moisture content is more preferably 0.01 to 3% by mass, and even more preferably 0.01 to 1% by mass.
The above water content can be determined by the Karl Fischer method.

The above-mentioned solvent contained as a dispersion medium in the silicon oxide gel dispersion of the present invention is not particularly limited, and may be appropriately selected depending on the purpose and use of the above-mentioned silicon oxide gel dispersion. It is preferable to contain an organic solvent having a hydroxyl group in terms of good properties.

Examples of the organic solvent having a hydroxyl group include alcohols such as methanol, ethanol, isopropyl alcohol, n-butanol, 2-butanol, isobutyl alcohol, pentyl alcohol, hexanol, octanol, ethylene glycol, diethylene glycol, propylene glycol, and glycerin. Preferred examples include solvents. Among these, isopropyl alcohol, n-butanol, 2-butanol, isobutyl alcohol, and pentyl alcohol are more preferred, and isobutyl alcohol is even more preferred, since the drying rate can be easily controlled. The above solvents may be used alone or in combination of two or more.

Further, the solvent as the dispersion medium may contain other solvents in addition to the above-mentioned organic solvent having a hydroxyl group, but when it contains another solvent, the amount of the organic solvent having a hydroxyl group is It is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, based on 100% by mass of the total solvent in the dispersion.

Other solvents mentioned above include, for example, ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; ether solvents such as diethyl ether, tetrahydrofuran, dioxane, diethylene glycol dimethyl ether, diethylene glycol ethyl ether, and anisole; ethyl acetate, butyl acetate , propylene glycol monomethyl ether acetate, and 3-methoxybutyl acetate; cellosolve solvents such as methyl cellosolve, ethyl cellosolve, and butyl cellosolve; aromatic hydrocarbons such as benzene and toluene. These may be used alone or in combination of two or more.

The solid content concentration of the silicon oxide gel dispersion is preferably 1 to 10% by mass, and 2 to 8% by mass at the time the gel is dispersed in the dispersion medium containing the organic solvent having hydroxyl groups. It is more preferably 2.5 to 5% by mass, and even more preferably 2.5 to 5% by mass. The above-mentioned solid content concentration means the ratio (mass %) of the total amount of components other than the solvent which is the dispersion medium of the silicon oxide in the gel dispersion to 100 mass % of the gel dispersion. The above-mentioned solid content concentration can be determined by the method described in Examples described later.

In addition to the silicon oxide gel and solvent described above, the silicon oxide gel dispersion may contain other additives such as a catalyst, depending on the purpose and use of the silicon oxide gel dispersion. Examples of the other additives include photoactive catalysts and thermally active catalysts. Examples of the photoactive catalyst include photocatalyst generators, such as photobase generators (substances that generate basic catalysts when irradiated with light), photoacid generators (substances that generate acidic catalysts when irradiated with light), etc. are mentioned, and photobase generators are preferred.

Examples of the photobase generator include 9-anthrylmethyl N,N-diethylcarbamate (trade name WPBG-018), (E)-1-[3-(2- hydroxyphenyl)-2-propenoyl]piperidine ((E)-1-[3-(2-hydroxyphenyl)-2-propenoyl]piperidine, trade name WPBG-027), 1-(anthraquinon-2-yl)ethyl imidazole carboxy Rate (1-(anthraquinon-2-yl)ethyl imidazolecarboxylate, trade name WPBG-140), 2-nitrophenylmethyl 4-methacryloyloxypiperidine-1-carboxylate (trade name WPBG-165), 1,2-diisopropyl- 3-[bis(dimethylamino)methylene]guanidium 2-(3-benzoylphenyl)propionate (trade name WPBG-266), 1,2-dicyclohexyl-4,4,5,5-tetramethylbiguanidium n-butyl triphenylborate (trade name WPBG-300), and 1,5,7-triazabicyclo[4.4.0]dec-5-ene 2-(9-oxoxanthen-2-yl)propionic acid (Tokyo (manufactured by Kasei Kogyo Co., Ltd.), a compound containing 4-piperidinemethanol (trade name: HDPD-PB100: manufactured by Heraeus), and the like. Note that all the product names including "WPBG" mentioned above are product names of Fujifilm Wako Pure Chemical Industries, Ltd.

Examples of the photoacid generator include aromatic sulfonium salts (product name SP-170: ADEKA), triarylsulfonium salts (product name CPI101A: Sun-Apro), aromatic iodonium salts (product name Irgacure 250: Ciba Japan). Company), etc.

Further, for example, a thermally activated catalyst (or a thermal catalyst generator) may be used in the gel dispersion of the present invention. Examples of the thermally active catalyst include base catalysts such as potassium hydroxide, sodium hydroxide, and ammonium hydroxide, and acid catalysts such as hydrochloric acid, acetic acid, and oxalic acid. Among these, base catalysts are preferred.

Further, for example, a crosslinking aid may be added to the gel dispersion of the present invention. The above-mentioned cross-linking adjuvant enters between the particles, and the particles and the cross-linking adjuvant interact or bond with each other, making it possible to bond even particles that are somewhat distant, efficiently increasing the strength of the gel. It becomes possible to raise the As the crosslinking aid, a multi-crosslinked silane monomer is preferred.

Specifically, the multi-crosslinked silane monomer may have, for example, 2 or more and 3 or less alkoxysilyl groups, the chain length between the alkoxysilyl groups may be 1 or more and 10 or less carbon atoms, and an element other than carbon. may also be included. Examples of the crosslinking aid include bis(trimethoxysilyl)ethane, bis(triethoxysilyl)ethane, bis(trimethoxysilyl)methane, bis(triethoxysilyl)methane, bis(triethoxysilyl)propane, and bis(trimethoxysilyl)ethane. (trimethoxysilyl)propane, bis(triethoxysilyl)butane, bis(trimethoxysilyl)butane, bis(triethoxysilyl)pentane, bis(trimethoxysilyl)pentane, bis(triethoxysilyl)hexane, bis(trimethoxysilyl) methoxysilyl)hexane, bis(trimethoxysilyl)-N-butyl-N-propyl-ethane-1,2-diamine, tris-(3-trimethoxysilylpropyl)isocyanurate, tris-(3-triethoxysilylpropyl) ) Isocyanurate and the like.

<Method for producing silicon oxide gel dispersion>
The method for producing the silicon oxide gel dispersion of the present invention is not particularly limited, but may include, for example, a step of gelling the silicon oxide dispersion while stirring, since it can be produced efficiently. preferable. By gelling the silicon oxide dispersion while stirring, the temperature is uniformly applied to the gel, making it possible to obtain a homogeneous gel even in mass production, and a gel dispersion with a low viscosity. Furthermore, whereas conventionally a lumpy gel is obtained and a cutting step and a coarse grinding step are required, such steps can be omitted and simplified.
Such a method for producing a silicon oxide gel dispersion, which includes a step of gelling the silicon oxide dispersion while stirring, is also part of the present invention.

The gelling step (also referred to as gelling step (2)) is a step in which at least a portion of the silicon oxide contained in the silicon oxide dispersion becomes gelled.
The silicon oxide dispersion liquid is a dispersion liquid containing a hydrolyzate of a silicon-containing compound that is a raw material for a silicon oxide gel dispersion liquid. At least a portion of the hydrolyzate is dehydrated and condensed to produce a gel-like silicon oxide. Therefore, the above-mentioned gelling step is a step in which the hydrolyzate of the silicon-containing compound is condensed to form a gel of silicon oxide.

The above-mentioned stirring method is not particularly limited and includes known stirring methods, such as known stirring methods using a stirrer having stirring blades such as paddle blades, inclined paddle blades, Max Blend, anchor blades, helical ribbon blades, etc. Examples of stirring methods include:

In addition, by reducing the amount of water or gel manufacturing solvent used during production (for example, used to dilute the base catalyst), a dispersion with a predetermined viscosity can be prepared without stirring. can.

The gelation is preferably performed by adding a base catalyst to the hydrolyzate of the silicon-containing compound. By adding a base catalyst to the hydrolyzate of the silicon-containing compound, the hydrolyzate is dehydrated and condensed to form a gel.

The hydrolyzate of the silicon-containing compound can be obtained by mixing the silicon-containing compound with water, an acid catalyst, and, if necessary, a solvent other than water (solvent for gel production). The above hydrolysis may be performed by stirring the mixture.

Examples of the silicon-containing compound include a compound represented by the following formula (1).
(R ¹ ) _4-a Si(OR ² ) _a (1)
(In the formula, R ¹ and R ² are the same or different and represent a hydrogen atom or an organic group. A plurality of R ¹ and R ² may be the same or different from each other. a is , represents an integer from 1 to 4.)

The organic groups represented by R ¹ and R ² above include hydrocarbon groups that may have a substituent, hydrocarbon groups that may have a substituent, -NH-, -CO-, -O- , a group in which a divalent group such as a phenylene group is combined, and a group in which at least a part of the atoms constituting the hydrocarbon group is replaced with a nitrogen atom, an oxygen atom, or a sulfur atom.

The above hydrocarbon group may be linear, branched, or cyclic, and may be a saturated hydrocarbon group or an unsaturated hydrocarbon group. Among these, the hydrocarbon group is preferably linear or branched, more preferably linear.

Preferably, the saturated hydrocarbon group is an aliphatic hydrocarbon group.
Examples of the aliphatic hydrocarbon groups include linear alkyl groups such as methyl, ethyl, propyl, and butyl; branched alkyl groups such as isopropyl and isobutyl; and cycloalkyl groups such as cyclohexyl. ; etc.

Examples of the unsaturated hydrocarbon group include linear alkenyl groups such as vinyl group, n-propenyl group, 1-butenyl group, 2-butenyl group, and 1-pentenyl group; branched alkenyl groups such as isopropenyl group. Aryl groups such as phenyl, tolyl, and xylyl groups; aralkyl groups such as benzyl and phenethyl groups; and aromatic hydrocarbon groups such as styryl groups.

The hydrocarbon group preferably has 1 to 6 carbon atoms, more preferably 1 to 3 carbon atoms, and even more preferably 1 to 2 carbon atoms.

Examples of the substituents that the hydrocarbon group may have include epoxy groups, (meth)acryloyl groups, amino groups, isocyanate groups, mercapto groups, succinic anhydride groups, and isocyanurate substituents. It will be done.

Among these, R ¹ is preferably an aliphatic hydrocarbon group from the viewpoint of membrane strength and stability of primary particles within the gel, and preferably an aliphatic hydrocarbon group having 1 to 3 carbon atoms. More preferred is a methyl group, and even more preferred is a methyl group.

The above R ² is preferably a hydrogen atom or an aliphatic hydrocarbon group, preferably a hydrogen atom or an aliphatic hydrocarbon group having 1 to 3 carbon atoms, and a hydrogen atom or an aliphatic hydrocarbon group having 1 to 3 carbon atoms. More preferably, it has 1 to 2 aliphatic hydrocarbon groups.

a in the above formula (1) represents an integer of 1 to 4, preferably 2 to 4, and more preferably 3 to 4. In addition, in the above formula (1), when a is 1, it is "monofunctional", when a is 2, it is "bifunctional", and when a is 3, it is "trifunctional" silicon-containing compound. becomes.
Among these, the silicon-containing compound is preferably di- to tetrafunctional, more preferably trifunctional, from the standpoint of maintaining high film strength and flexibility.

Specific examples of the silicon-containing compounds include tetraalkoxysilanes such as tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, and tetrabutoxysilane; methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, and ethyl Alkyltrialkoxysilanes such as triethoxysilane, propyltrimethoxysilane, propyltriethoxysilane, hexyltrimethoxysilane, hexyltriethoxysilane, and alkylalkoxysilanes such as alkyldialkoxysilanes such as dimethyldimethoxysilane and dimethyldiethoxysilane. ; Aryl alkoxysilane such as phenyltrimethoxysilane, phenyltriethoxysilane, diphenyldimethoxysilane, diphenyldiethoxysilane; Vinyl group-containing alkoxysilane such as vinyltrimethoxysilane, vinyltriethoxysilane; 2-(3,4-epoxy Epoxies such as cyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, etc. Group-containing alkoxysilane; Styryl group-containing alkoxysilane such as p-styryltrimethoxysilane; 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropylmethyldiethoxysilane (Meth)acryloyl group-containing alkoxysilanes such as roxypropyltriethoxysilane and 3-acryloxypropyltrimethoxysilane; N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl) -3-Aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethyl-butylidene)propylamine, N-phenyl-3 - Amino group-containing alkoxysilanes such as aminopropyltrimethoxysilane and N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane; isocyanurate alkoxysilanes such as tris-(trimethoxysilylpropyl)isocyanurate ; Ureido alkoxysilane such as 3-ureidopropyltrialkoxysilane; Mercapto group-containing alkoxysilane such as 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane; Isocyanate group-containing alkoxy such as 3-isocyanatepropyltriethoxysilane Silane: Examples include alkoxysilanes containing acid anhydride groups such as 3-trimethoxysilylpropylsuccinic anhydride. Further, the silicon-containing compound may be a salt such as a hydrochloride of these silane compounds. Among these, the silicon-containing compound is preferably at least one selected from the group consisting of tetraalkoxysilane and alkylalkoxysilane, more preferably alkylalkoxysilane, from the viewpoint of maintaining high film strength and flexibility. More preferred are trialkoxysilanes. The above silicon-containing compounds may be used alone or in combination of two or more.

The above-mentioned water is not particularly limited, and may be any water such as distilled water, ion-exchanged water, and pure water.
The amount of water used is not particularly limited, but for example, it is preferably 20 to 400 parts by weight, more preferably 40 to 200 parts by weight, and 60 to 100 parts by weight, based on 100 parts by weight of the silicon-containing compound. More preferably, it is parts by mass.

Examples of the acid catalyst include hydrochloric acid, oxalic acid, and sulfuric acid.
The amount of the acid catalyst used is not particularly limited, but for example, it is preferably 0.001 to 0.5 parts by mass, and 0.01 to 0.2 parts by mass, based on 100 parts by mass of the silicon-containing compound. It is more preferable that the amount is 0.02 to 0.1 parts by mass.

The solvent other than water (solvent for gel production) is not particularly limited, and known solvents commonly used for gel production can be used, such as dimethyl sulfoxide (DMSO), N-methylpyrrolidone ( Aprotic polar solvents such as NMP), N,N-dimethylacetamide (DMAc), dimethylformamide (DMF), γ-butyllactone (GBL), acetonitrile (AN), acetone, and ethylene glycol monoethyl ether (EGEE); Examples include protic polar solvents such as alcoholic solvents such as methanol, ethanol, isopropyl alcohol, isobutyl alcohol, and n-butyl alcohol.
Among these, as the solvent other than water, aprotic polar solvents are preferred from the viewpoint of ensuring the stability and transparency of the primary particles of silicon oxide gel, such as N-methylpyrrolidone (NMP) and dimethylsulfoxide (DMSO). , dimethylformamide (DMF), γ-butyllactone (GBL), and N,N-dimethylacetamide (DMAc) are more preferred, and dimethyl sulfoxide is even more preferred.
The solvents other than water may be used alone or in combination of two or more.

The amount of the solvent other than water used is not particularly limited, but for example, it is preferably 50 to 600 parts by mass, more preferably 100 to 400 parts by mass, based on 100 parts by mass of the silicon-containing compound. More preferably, the amount is 150 to 250 parts by mass.

The reaction temperature for the above hydrolysis is preferably 10 to 60°C, more preferably 15 to 50°C, even more preferably 20 to 40°C. Further, the reaction time is preferably 0.1 to 40 hours, more preferably 0.2 to 20 hours, and even more preferably 0.5 to 10 hours.

Hydrolysis of the silicon-containing compound produces a hydrolyzate in which at least a portion of "(OR ² ) _a " in formula (1) representing the silicon-containing compound becomes "(OH) _a ".

As described above, the method for producing the silicon oxide gel dispersion preferably includes the step (1) of hydrolyzing the silicon-containing compound before the gelling step (2).

Examples of the chlorine catalyst include ammonia, potassium hydroxide, sodium hydroxide, and the like. When mixing the base catalyst, the base may be diluted with a solvent or water in advance.
The amount of the base catalyst used is preferably 0.1 to 50 parts by weight, more preferably 1 to 30 parts by weight, and 10 to 20 parts by weight based on 100 parts by weight of the silicon-containing compound. It is even more preferable.

The temperature of the gelling step is preferably 10 to 80°C, more preferably 15 to 70°C, and even more preferably 20 to 60°C.

After the gelling step (2), the method may further include a step (3) of aging the silicon oxide gel. A crosslinking reaction progresses through aging, and the skeleton of the silicon oxide gel becomes stronger.

The aging step (3) is preferably carried out with stirring for the same reason as the gelling step (2) described above. Examples of the above-mentioned stirring method include the same method as the stirring method in the gelling step described above.

The temperature of the aging reaction is not particularly limited, but is preferably the same as the gelling step described above. The reaction time is preferably 1 to 40 hours, more preferably 2 to 35 hours, and still more preferably 3 to 30 hours, including the gelation step.

The gelling step (or also including the aging step) produces a gel-like silicon oxide. The above silicon oxide is a compound (siloxane compound) having a siloxane bond (Si--O--Si bond).
The siloxane compound may be a compound having a chain-like (straight-chain or branched), ladder-like, network-like, cyclic, cage-like, cubic-like, random-like structure, or the like. Preferably, the siloxane compound is polysilsesquioxane.

(Solvent replacement step)
It is preferable that the above manufacturing method further includes a solvent replacement step. After the gelling step (or aging step), the resulting gel or gel solution contains the solvent used during gel production. By replacing the solvent used during gel production with a desired solvent for the dispersion to be finally obtained, the silicon oxide gel dispersion can be made suitable for the purpose and use. In addition, by replacing the solvent, not only the unnecessary solvent during gel production but also the remaining amount of catalyst and generated by-products can be reduced, improving the storage stability of the resulting gel dispersion and improving its properties. can be more fully demonstrated.

The method for replacing the solvent is not particularly limited, and may be carried out by any known method such as contacting the silicon oxide gel obtained in the gelling step (or aging step) with a replacement solvent. For example, the silicon oxide gel is immersed in or brought into contact with a replacement solvent to dissolve the gel manufacturing solvent in the gel, the alcohol component produced by the condensation reaction, water, etc. in the replacement solvent, and then, Examples include a method in which the above-mentioned replacement solvent in which the gel is immersed or brought into contact is discarded, and the above-mentioned gel is immersed in or brought into contact with a new replacement solvent again. The gel may be immersed or brought into contact with the gel once or repeatedly several times.

Another method for replacing the solvent in the silicon oxide gel is a method using a filtration membrane, and specifically, for example, by adding a replacement solvent to the silicon oxide gel and filtering it. , a filtration method in which the gel manufacturing solvent, alcohol component, etc. dissolved in the replacement solvent are continuously passed through a membrane.
Among these, as the method for the solvent replacement, a filtration method is preferred in terms of good solvent replacement efficiency, and cross-flow filtration is more preferred.

The above-mentioned cross-flow filtration is a method of filtration in which the liquid direction is perpendicular to the filtration direction, and is not particularly limited as long as it is such a cross-flow type filtration method, and it can be performed by a known method. Can be done. In cross-flow filtration, efficient filtration can be achieved by circulating the liquid to be filtered and bringing it into contact with a filtration membrane.

The filtration membrane used in the cross-flow filtration is not particularly limited, and includes polysulfone, polyacrylonitrile, polyethylene, tetrafluoroethylene, polypropylene, polyethersulfone, aluminum oxide, zirconium oxide, titanium oxide, stainless steel, glass, ceramic, and metal. A filtration membrane made of a known material such as mesh can be used. Among these, filtration membranes made of ceramic are preferred because they have high corrosion resistance, high heat resistance, and high strength.

The pore size of the filtration membrane may be selected appropriately depending on the size of the gel, but is preferably 0.005 to 10 μm, more preferably 0.01 to 5 μm, and 0.05 to 3 μm. It is even more preferable.

The above-mentioned filtration membrane may be a commercially available product. Examples of the filtration membrane that can be used in the present invention include a ceramic membrane filter manufactured by NGK Insulators, a ceramic filter manufactured by Noritake Company, and a ceramic membrane filter manufactured by Nippon Pall. etc.
The above-mentioned filtration conditions are not particularly limited, and may be appropriately selected from known methods.

The solvent replacement described above may be performed by directly replacing the solvent for gel production with the target solvent, or by replacing the solvent in multiple steps. Among these, from the viewpoint of production efficiency, it is preferable to perform solvent replacement in one step.

The above-mentioned replacement solvent is not particularly limited and may be appropriately selected depending on the purpose and use of the dispersion, and examples thereof include the solvent as the dispersion medium of the gel dispersion of the present invention described above.

(Crushing process)
The above manufacturing method may further include a pulverization step. By pulverizing the gel, the particle size of the gel particles can be adjusted, and the desired gel dispersion can be efficiently produced. Moreover, the amount of gel manufacturing solvent and by-products can be reduced more efficiently.

The pulverization method is not particularly limited as long as it can be pulverized to the desired particle size of the gel particles, and includes emulsifying and dispersing machines such as homomixers, milders, ultrasonic homogenizers, and high-speed rotation homogenizers, ball mills, bead mills, and sand mills. Known pulverization methods such as a media pulverizer such as .

The above-mentioned pulverization step may be performed in a solvent. The solvent used for pulverization may be the same as the above-mentioned gel manufacturing solvent or substitution solvent, or may be a mixture thereof. Further, pulverization may be performed by appropriately adding these solvents.

The pulverizing step may be performed before or after the solvent replacement step, or may be performed before or after the solvent replacement step.

In addition to the steps described above, the method for producing the dispersion liquid may include other commonly known steps such as a concentration step, a purification step, a washing step, and the like.

The residual amount of the gel manufacturing solvent in the silicon oxide gel dispersion obtained by the above manufacturing method is preferably 20,000 ppm or less, more preferably 10,000 ppm or less, even more preferably 5,000 ppm or less, and 1,000 ppm or less. It is even more preferable that it is below, and particularly preferably that it is 500 ppm or less.

<Application>
The silicon oxide gel dispersion of the present invention can be suitably used as an optical silicon oxide gel dispersion.

The silicon oxide gel dispersion of the present invention is preferably used for a low refractive index material having a refractive index of 1.25 or less. The low refractive index material having a refractive index of 1.25 or less means that the refractive index of the dry product of the low refractive index material is 1.25 or less. Examples of the dried material include a film-like material. For example, by using the silicon oxide gel dispersion described above, a low refractive index film having a refractive index of 1.25 or less can be obtained.

Examples of the method for producing a low refractive index film using the silicon oxide gel dispersion of the present invention include a method of applying the silicon oxide gel dispersion to a base material and drying the coated material. It will be done.

The above-mentioned base material is not particularly limited, and includes, for example, a glass base material; an inorganic base material such as silicon; a thermoplastic resin base material such as polyethylene terephthalate, acrylic, cellulose acetate propionate, polyethylene phthalate, polyethylene, and polypropylene; Examples include carbon fiber base materials.
Examples of the form of the base material include a film, sheet, plate, and the like.

The coating method is not particularly limited, and includes known coating methods such as dip coating, spray coating, and die coating.

The drying method is not particularly limited, and includes known drying means such as leaving drying, blow drying, and heating drying.
In the case of heating drying, the heating temperature may be appropriately selected depending on the boiling point of the solvent contained in the gel dispersion, but for example, it is preferably 80 to 110°C, and preferably 85 to 100°C. The temperature is more preferably 90 to 95°C.
Although the heating time is not particularly limited, for example, it is preferably 1 hour or less, more preferably 0.5 hour or less, and even more preferably 0.1 hour or less.

The thickness of the low refractive index film formed on the base material is not particularly limited, but is preferably 0.01 to 100 μm, more preferably 0.05 to 10 μm, and 0.1 to 3 μm. It is more preferable that

The refractive index of the low refractive index film is preferably 1.25 or less, more preferably 1.23 or less, and even more preferably 1.21 or less.
The above-mentioned refractive index can be determined by the method described in Examples described later.

The low refractive index film preferably has pores. Having pores can provide a low refractive index.
The porosity of the low refractive index film is preferably 40 to 65%, more preferably 45 to 62%, and even more preferably 50 to 60%.
The porosity can be calculated from the measured value of the refractive index using the Lorentz-Lorentz equation.

The total light transmittance of the low refractive index film is preferably 80% or more, more preferably 85% or more, and even more preferably 88% or more in terms of excellent transparency.
The total light transmittance can be measured using a haze meter HM-150 (manufactured by Murakami Color Research Institute), and specifically, can be determined by the method described in Examples.

Such a low refractive index film produced using the silicon oxide gel dispersion and characterized by having pores is also one of the preferred embodiments of the present invention. In this specification, the above-mentioned low refractive index film is also referred to as a "low refractive index film." A transparent low refractive index film characterized by having pores and produced using the silicon oxide gel dispersion is also part of the present invention.

Furthermore, the silicon oxide gel dispersion of the present invention is useful not only for optical (material) applications as described above, but also for heat insulating materials and low dielectric materials.

The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited to these Examples. In addition, unless otherwise specified, "part" means "part by mass" and "%" means "% by mass", respectively.

(viscosity)
E-type viscometer (manufactured by Toki Sangyo Co., Ltd.: TV-20L, low viscosity area: 1° 34' x R24 rotor, or high viscosity area: 3° x R9.7 rotor, upper limit of viscosity of the rotor for low viscosity area) (607.6 mPa・s, if the viscosity is higher, use a rotor for high viscosity range) at 25°C and a rotational speed of 5 rpm, and 2.5 minutes after the start of the measurement. The value was adopted.

(pore volume)
The gel dispersion was dried at 80° C. under reduced pressure conditions (0.02 MPa or less) for 24 hours, and a dried gel obtained was used as a measurement sample. The pore volume was calculated by measuring using a specific surface area/pore distribution measuring device (BELSORP-miniX manufactured by Microtrac Bell Co., Ltd.) and analyzing the measurement results by the BJH method. The above measurement was performed as a pretreatment after drying the measurement sample at 10 Pa or less and 100° C. for 3 hours or more before the measurement.

(Specific surface area)
The gel dispersion was dried at 80° C. under reduced pressure conditions (0.02 MPa or less) for 24 hours, and a dried gel obtained was used as a measurement sample. The specific surface area was measured using a specific surface area/pore distribution measuring device (BELSORP-miniX manufactured by Microtrac Bell Co., Ltd.), and the measurement results were analyzed by the BET method to calculate the specific surface area. Note that the above measurement was performed as a pretreatment after drying the measurement sample at 10 Pa or less and 100° C. for 3 hours or more before the measurement.

(pore diameter)
The gel dispersion was dried at 80° C. under reduced pressure conditions (0.02 MPa or less) for 24 hours, and a dried gel obtained was used as a measurement sample. The pore diameter was calculated by measuring using a specific surface area/pore distribution measuring device (BELSORP-miniX manufactured by Microtrac Bell Co., Ltd.) and analyzing the measurement results by the BJH method. Note that the above measurement was performed as a pretreatment after drying the measurement sample at 10 Pa or less and 100° C. for 3 hours or more before the measurement.

(Number average particle diameter)
Using a dispersion obtained by diluting the gel dispersion 3 to 10 times with isobutyl alcohol as a measurement sample, the number average particle diameter was determined using a laser diffraction particle size distribution analyzer ("Mastersizer 3000" manufactured by Malvern).

(solid content)
Solid content was measured by the following method.
1. The aluminum plate was accurately weighed.
2. A sample (gel dispersion liquid) whose solid content was to be measured was placed on an accurately weighed aluminum plate, and the sample was accurately weighed.
3. On a hot plate adjusted to 180°C, 2. The accurately weighed sample was placed in the aluminum dish for 1 hour.
4. After 1 hour, the aluminum plate and the component whose solid content was to be measured were removed from the hot plate and allowed to cool.
5. After cooling, the aluminum plate and the sample (after drying) whose solid content was to be measured were accurately weighed.
6. Using the weight measured above, the solid content was calculated using the following formula.
Solid content (%) = {[(Weight obtained with the precision scale in 5 above) - (Weight of the aluminum plate obtained with the precision scale in 1 above)] / [(Weight obtained with the precision scale in 2 above) ) - (Weight of the aluminum plate obtained using the precision scale in 1 above)]} x 100

(Residual DMSO amount)
Approximately 1 g of the gel dispersion and 1 g of acetone were mixed and allowed to stand for over an hour. The mixed solution was filtered, and the filtrate was taken into a sample tube and accurately weighed. The same weight of acetonitrile and 0.1 g of diethylene glycol diethyl ether (internal standard) were added and the mixture was used as a measurement sample. The conditions for gas chromatography were as follows.
Equipment: GC-2014 (manufactured by Shimadzu Corporation)
Column: DB-WAX (manufactured by Agilent Technologies)
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°C
Detector temperature: 320℃ (FID)
Detected substances and retention times: diethylene glycol diethyl ether (12 minutes), dimethyl sulfoxide (14 minutes)

(Refractive index)
A film with a low refractive index layer cut into a size of 25 mm x 50 mm was bonded to the surface of a glass plate (thickness: 3 mm) via an adhesive. The center part (about 20 mm in diameter) of the back surface of the glass plate was filled in with black marker to prepare a sample that did not reflect on the back surface of the glass plate. The sample was set in an ellipsometer (manufactured by J.A. Woollam Japan: VASE), and the refractive index was measured at a wavelength of 550 nm and an incident angle of 50 to 80 degrees.

(Total light transmittance)
The side surface of the film with a low refractive index layer is pasted on a slide glass (total light transmittance of 92% or more), and the side surface of the low refractive index layer of the resulting laminate is measured using a haze meter HM-150 (Murakami Color Technology). (manufactured by Kenkyusho Co., Ltd.).

Example 1
In a four-necked flask equipped with a cooling tube, a thermometer, and a dripping port, 208 parts of dimethyl sulfoxide, 23 parts of ion-exchanged water, and 100 parts of methyltrimethoxysilane (trade name KBM-13, manufactured by Shin-Etsu Chemical Co., Ltd.) were charged. The internal temperature was adjusted to 30°C while stirring using a three-one motor (manufactured by Shinto Kagakusha). After 53 parts of a 0.015M oxalic acid aqueous solution was dropped into the temperature-controlled mixed solution from the dropping port while stirring was continued, methyltrimethoxysilane was hydrolyzed by keeping the internal temperature at 30° C. for 45 minutes. A mixture of 918 parts of dimethyl sulfoxide, 121 parts of ion-exchanged water, and 58 parts of a 25% ammonia aqueous solution was added to the obtained hydrolyzed solution, and the mixture was kept at an internal temperature of 40°C for 20 hours with continuous stirring. , gelation and aging were performed.

100 parts of isobutyl alcohol was added to 100 parts of the obtained gel slurry, and the mixture was pulverized for 5 minutes at 25° C. and 8000 rpm using a Homomixer MARKII model 2.5 manufactured by Primix, to obtain a stirred aged gel slurry containing gel particles. Then, the obtained stirring aged gel slurry is placed in a cross-flow type filtration device equipped with a ceramic precision filtration membrane (manufactured by NGK Insulators) with a pore size of 0.1 μm, and 1900 parts of isobutyl alcohol is continuously added and filtered. By replacing the solvent and performing a concentration process, an isobutyl alcohol-substituted silicon oxide gel dispersion was obtained. The resulting gel dispersion had a solid content of 3.09% by mass, a residual DMSO amount of 99 ppm, and a viscosity of 25 mPa·s. The number average particle diameter of the gel particles was 44 μm. Moreover, the pore volume of the dried gel was 2.2 cm ³ /g, the specific surface area was 714 m ² /g, and the pore diameter was 18.4 nm.

The obtained gel dispersion was treated with a mixer (model: high-speed homogenizer HF93, manufactured by SMT Co., Ltd.) at 9000 rpm for 5 minutes, and then treated with an ultra-high pressure wet atomization device (Nano Veita, manufactured by Yoshida Kikai Kogyo Co., Ltd.) at 100 MPa, 50 MPa, It was pulverized three times under the condition of 50 MPa to obtain a nano-pulverized liquid (average particle size of gel particles 0.2 μm). The average particle diameter of the gel particles of the nano-pulverized liquid was measured using a dynamic light scattering particle size distribution meter NICOMP manufactured by MS Scientific.

To 0.75 g of the obtained nano-pulverized liquid, 0.062 g of a 1.5% by mass MEK (methyl ethyl ketone) solution of a photobase generator (Fujifilm Wako Pure Chemical Industries, Ltd.: trade name WPBG266) was added, and bis(trimethoxy A 5% MEK solution of (silyl) hexane was added at a ratio of 0.036 g to obtain a gel dispersion coating solution.
Next, the obtained gel dispersion coating liquid was applied onto an acrylic base material (total light transmittance: 92%) and dried at 100° C. for 2 minutes. As a result, a film with a low refractive index layer was obtained.
The thickness of the low refractive index layer was 0.9 μm, the refractive index was 1.163, and the total light transmittance was 91%.

Example 2
Example 1 was carried out in the same manner as in Example 1, except that the amounts of dimethyl sulfoxide and ion-exchanged water added after hydrolysis were changed to 1335 parts and 210 parts, respectively, to obtain an isobutyl alcohol-substituted silicon oxide gel dispersion. The resulting gel dispersion had a solid content of 3.1% by mass, a residual DMSO amount of 43 ppm, and a viscosity of 105 mPa·s. The number average particle diameter of the gel particles was 41 μm. Further, the pore volume of the dried gel was 2.0 cm ³ /g, the specific surface area was 707 m ² /g, and the pore diameter was 18.4 nm.

The obtained gel dispersion was treated with a mixer (model: high-speed homogenizer HF93, manufactured by SMT Co., Ltd.) at 9000 rpm for 5 minutes, and then treated with an ultra-high pressure wet atomization device (Nano Veita, manufactured by Yoshida Kikai Kogyo Co., Ltd.) at 150 MPa, 150 MPa, It was pulverized three times under the condition of 50 MPa to obtain a nano-pulverized liquid (average particle size 0.1 μm).

The same operation as in Example 1 was performed to obtain a film with a low refractive index layer. The thickness of the low refractive index layer was 0.9 μm, the refractive index was 1.166, and the total light transmittance was 91%.

Example 3
In Example 1, the amounts of dimethyl sulfoxide and ion-exchanged water added after hydrolysis were changed to 733 parts and 82 parts, respectively, and the stirring operation was not performed during aging. I got it. The obtained aged gel was coarsely ground using a spatula and a plastic container, 100 parts of isobutyl alcohol was added to 100 parts of the coarsely ground gel, and the mixture was ground for 5 minutes at 25°C and 8,000 rpm using a homomixer MARKII model 2.5 manufactured by Primix. By doing so, a stirred and aged gel slurry containing gel particles was obtained. Thereafter, as in Example 1, solvent replacement was performed to obtain an isobutyl alcohol-substituted silicon oxide gel dispersion. The resulting gel dispersion had a solid content of 3.10% by mass, a residual DMSO amount of 109 ppm, and a viscosity of 476 mPa·s. The number average particle diameter of the gel particles was 71 μm. The dried gel had a pore volume of 1.4 cm ³ /g, a specific surface area of 803 m ² /g, and a pore diameter of 12.1 nm.

The obtained gel dispersion was treated with a mixer (model: HF93, manufactured by SMT Co., Ltd.) at 9000 rpm for 5 minutes, and then treated at 100 MPa, 50 MPa, and 50 MPa using an ultra-high pressure wet atomization device (Nano Veita, manufactured by Yoshida Kikai Kogyo Co., Ltd.). The nano-pulverized liquid was obtained by pulverizing three times under the following conditions.

The same operation as in Example 1 was performed to obtain a film with a low refractive index layer. The thickness of the low refractive index layer was 0.9 μm, the refractive index was 1.178, and the total light transmittance was 91%.

Example 4
In a four-necked flask equipped with a cooling tube, thermometer, and dropping port, add 208 parts of 90% dimethyl sulfoxide, 23 parts of ion-exchanged water, and 100 parts of methyltrimethoxysilane (trade name KBM-13, manufactured by Shin-Etsu Chemical Co., Ltd.). , 10 parts of tetraethoxysilane (manufactured by Tokyo Chemical Industry Co., Ltd.) were charged, and the internal temperature was adjusted to 30° C. while stirring using a three-one motor (manufactured by Shinto Kagaku Co., Ltd.). After dropping 53 parts of a 0.015M oxalic acid aqueous solution from the dropping port into the temperature-controlled mixed solution with continuous stirring, the mixture was maintained at an internal temperature of 30°C for 45 minutes to hydrolyze methyltrimethoxysilane and tetraethoxysilane. . A mixture of 1334 parts of 90% dimethyl sulfoxide, 210 parts of ion-exchanged water, and 58 parts of a 25% ammonia aqueous solution was added to the obtained hydrolyzed solution, and the mixture was kept at an internal temperature of 40°C for 20 hours with continuous stirring. This allowed for gelation and aging.

48 parts of isobutyl alcohol was added to 100 parts of the obtained gel slurry, and the mixture was pulverized at 25° C. and 8000 rpm for 5 minutes using a Homomixer MARKII model 2.5 manufactured by Primix, to obtain a stirred aged gel slurry containing gel particles. Then, the obtained stirring aged gel slurry is placed in a cross-flow type filtration device equipped with a ceramic precision filtration membrane (manufactured by NGK Insulators) with a pore size of 0.1 μm, and 1418 parts of isobutyl alcohol is continuously added and filtered. By replacing the solvent and performing a concentration process, an isobutyl alcohol-substituted silicon oxide gel dispersion was obtained. The resulting gel dispersion had a solid content of 3.06% by mass, a residual DMSO amount of 55 ppm, and a viscosity of 52 mPa·s. The number average particle diameter of the gel particles was 56 μm. Further, the pore volume of the dried gel was 1.7 cm ³ /g, the specific surface area was 708 m ² /g, and the pore diameter was 12.7 nm.

The obtained gel dispersion was treated with a mixer (model: high-speed homogenizer HF93, manufactured by SMT Co., Ltd.) at 9000 rpm for 5 minutes, and then treated with an ultra-high pressure wet atomization device (Nano Veita, manufactured by Yoshida Kikai Kogyo Co., Ltd.) at 150 MPa, 150 MPa, It was pulverized three times under the condition of 50 MPa to obtain a nano-pulverized liquid (average particle size of gel particles 0.1 μm). The average particle diameter of the gel particles of the nano-pulverized liquid was measured using a dynamic light scattering particle size distribution meter NICOMP manufactured by MS Scientific.

To 300 g of the obtained nano-pulverized liquid, 48 g of a 1.5% by mass MEK (methyl ethyl ketone) solution of a photobase generator (Fuji Film Wako Pure Chemical Industries, Ltd.: trade name WPBG266) and bis(trimethoxysilyl)hexane were added. A 5% MEK solution was added at a ratio of 14.40 g to obtain a gel dispersion coating solution.

Next, the obtained gel dispersion coating liquid was applied onto an acrylic base material (total light transmittance: 92%) and dried at 100° C. for 2 minutes. As a result, a film with a low refractive index layer was obtained.
The thickness of the low refractive index layer was 0.9 μm, the refractive index was 1.236, and the total light transmittance was 91%.

Comparative example 1
A dispersion of isobutyl alcohol-substituted silicon oxide gel was obtained in the same manner as in Example 1, except that the stirring operation was not performed during ripening and coarse pulverization was performed before dilution with isobutyl alcohol. The resulting gel dispersion had a solid content of 3.11% by mass, a residual DMSO amount of 64 ppm, and a viscosity of 4250 mPa·s. The pressure loss of the cross-flow type filtration device was large, and it appeared that the liquid was not circulating sufficiently. Furthermore, a large amount of isobutyl alcohol-substituted silicon oxide gel dispersion remained in the apparatus and could not be recovered.
From this, it was recognized that when the viscosity of the silicon oxide gel dispersion liquid is high, the handling property in cross-flow filtration becomes low. It is a finding obtained for the first time in the present invention that the viscosity of the gel dispersion is related to the ease of handling in cross-flow filtration.

Claims

A silicon oxide gel dispersion containing a silicon oxide gel and a solvent,
A silicon oxide gel dispersion characterized in that the dispersion has a viscosity of 10 to 2000 mPa·s when the solid content concentration is 3.0±0.1% by mass.
The silicon oxide gel dispersion according to claim 1, wherein the silicon oxide gel has an average particle size of 1 to 99 μm.
The silicon oxide gel dispersion according to claim 1 or 2, wherein the solvent is an organic solvent having a hydroxyl group.
The silicon oxide gel dispersion according to any one of claims 1 to 3, wherein the pore volume of the dried silicon oxide gel is 0.5 to 3.0 cm 3 /g.
The silicon oxide gel dispersion according to any one of claims 1 to 4, which is used for a low refractive index material having a refractive index of 1.25 or less.
A transparent low refractive index film characterized by having pores and produced using the silicon oxide gel dispersion according to any one of claims 1 to 5.
A method for producing a silicon oxide gel dispersion, the method comprising:
A method for producing a silicon oxide gel dispersion, characterized in that the production method includes a step of gelling the silicon oxide dispersion while stirring.