JP6875247B2 - Composition - Google Patents

Description

The present invention relates to a composition containing silica particles.

Silica particles have the potential to exhibit various functions in optical materials, electronic component materials, etc., and are attracting attention in the field of various functional materials. However, since silica particles alone have insufficient dispersibility in a solvent, they often aggregate, causing problems such as a decrease in transparency and a decrease in mechanical strength.

For example, Patent Document 1 discloses a silica sol synthesized by an alkoxide method, which contains a specific dispersant and silica and uses water as a solvent, as a technique for preventing an increase in viscosity during storage of the silica sol. .. In Patent Document 2, a silica sol using water as a dispersion medium and an organic solvent are mixed and then dehydrated with an ultrafiltration membrane to produce a silica sol having excellent dispersibility using an organic solvent such as alcohol as a dispersion medium. Is disclosed.

Further, in Patent Document 3, as a technique for preventing an increase in viscosity during pulverization of silica particles, raw material silica particles obtained by a precipitation method are pulverized in alcohol in the presence of a polyvalent carboxylic acid to produce an alcohol-dispersed silica sol. It is disclosed to do. In Patent Document 4, in order to obtain stable colloidal silica for a long period of time, a first method in which a specific hydrophobizing agent is mixed with colloidal silica having a hydrophilic organic solvent as a main solvent and the hydrophilic organic solvent is used as a main solvent. A hydrophobic colloidal silica is prepared, and then the first hydrophobic colloidal silica is solvent-substituted using an ultrafiltration membrane to prepare a second hydrophobic colloidal silica using a hydrophobic organic solvent as a main solvent. ing.

Further, Patent Document 5 describes a silica sol dispersed in an organic solvent (alcohol) by subjecting associated silica or fine particle silicic acid aggregates to a mechanochemical reaction treatment in the presence of alcohol in an inert gas atmosphere. It discloses that the aggregation of silica particles in an organic solvent is suppressed. Patent Document 6 discloses powdered silica which is composed of colloidal silica particles covered with an alkoxy group having 2 to 18 carbon atoms and can be homogeneously dispersed in an organic solvent in which the alkoxy group is chemically bonded to silica. There is.

International Publication No. 2008/015943 Japanese Unexamined Patent Publication No. 2-1087 Japanese Unexamined Patent Publication No. 2013-245148 Japanese Unexamined Patent Publication No. 2001-213617 Japanese Unexamined Patent Publication No. 5-345607 Japanese Unexamined Patent Publication No. 2-1089

Silica particles may be required to have a coefficient of variation of particle size (hereinafter, may be referred to as CV value) within a specific range depending on the application. However, in Patent Documents 1 to 6 described above, the CV value of particle size is used. No consideration was given to the relationship between and dispersibility. Therefore, an object of the present invention is to clarify the relationship between the CV value of the particle size and the dispersibility, and to provide a technique for satisfactorily dispersing silica particles in a solvent.

As a result of diligently examining the effect of the coefficient of variation (CV value) of the primary particle size of silica particles on the dispersibility in a solvent, the present inventors have obtained a combination of a specific range of variation coefficient and a specific carboxylic acid and a specific solvent. It was found that a silica particle dispersion having a specific high dispersibility, almost no agglomerates, and a low viscosity can be obtained.

The present invention is as follows.
[1] A composition containing silica particles having a coefficient of variation of the primary particle size of 20% or less, at least one of a polyvalent carboxylic acid and a hydroxycarboxylic acid, and an aprotic polar solvent.
[2] The composition according to [1], wherein the average primary particle size of the silica particles measured based on a transmission electron microscope image is 10 nm or more.
[3] The composition according to [1] or [2], wherein the specific surface area of the silica particles is 200 m ^{2 / g or less.}
[4] The aprotonic polar solvent is at least selected from the group consisting of a ketone solvent, an ether solvent, a sulfoxide solvent, an amide solvent, a nitrile solvent, a carbonate solvent, a lactone solvent, and a urea solvent. The composition according to any one of [1] to [3].

Since the composition of the present invention contains silica particles having a coefficient of variation of the primary particle size of 20% or less, at least one of polyvalent carboxylic acid and hydroxycarboxylic acid, and an aprotic polar solvent, most of the aggregates are present. It is possible to easily obtain a dispersion having a low viscosity.

The composition of the present invention contains silica particles having a small coefficient of variation (CV value) of the primary particle size, at least one of polyvalent carboxylic acid and hydroxycarboxylic acid, and an aprotic polar solvent. Although the cause of the specific improvement in the dispersibility of the silica particles is not clear, the present inventors speculate as follows. Generally, the larger the CV value, the larger the variation (difference in particle size) of the primary particle size of the silica particles, and the smaller the CV value, the more uniform the primary particle size of the silica particles. Further, it is considered that at least one of the polyvalent carboxylic acid and the hydroxycarboxylic acid (hereinafter, may be referred to as a specific carboxylic acid) is adsorbed on the surface of the silica particles to enhance the affinity with the solvent. Here, when the CV value is large, silica particles having a relatively small particle size and silica particles having a large particle size are present, but since the surface activities of the silica particles having different particle sizes are different, the above-mentioned specification The amount of carboxylic acid adsorbed (meaning the amount of specific carboxylic acid adsorbed per unit surface area of silica particles) is different, and uniform dispersibility cannot be imparted. On the other hand, in the case of silica particles having a small CV value, the surface activity of the silica particles is the same. Therefore, it is inferred that the amount of specific carboxylic acid adsorbed on the surface of each silica particle is almost the same, and uniform dispersibility is imparted to all the particles. Therefore, the dispersibility can be remarkably improved in the silica particles having a CV value in a specific range, and the dispersibility can be improved when at least one of a polyvalent carboxylic acid and a hydroxycarboxylic acid and an aprotic polar solvent are used. It is most effective. Hereinafter, the silica particles, the specific carboxylic acid, and the aprotic polar solvent will be described in order.

1. 1. Silica particles The silica particles in the present invention have a coefficient of variation (CV value) of the primary particle size of 20% or less. The CV value is preferably 15% or less, more preferably 10% or less. When the CV value is in the above range, the dispersibility of the silica particles can be significantly improved. The lower limit of the CV value is not particularly limited, but is, for example, 2% or more, and may be 3% or more.

The CV value is the diameter (major axis) of 50 to 100 silica particles among the silica particles contained in the obtained transmission electron microscope image obtained by observing the silica particles with a transmission electron microscope having a magnification of 200,000 times. It can be calculated by measuring the average value of the minor axis) and dividing the standard deviation by the average value based on the number of particles.

The average primary particle size of the silica particles can be measured based on a transmission electron microscope image, observed with a transmission electron microscope having a magnification of 200,000 times, and silica contained in the obtained transmission electron microscope image. Of the particles, for example, the diameter of about 300 to 2000 silica particles can be measured and calculated as an average value based on the number of the particles. The average primary particle size of the silica particles is preferably 10 nm or more, more preferably more than 10 nm, still more preferably 15 nm or more, particularly preferably 20 nm or more, and most preferably 30 nm or more. The upper limit of the average primary particle size is not particularly limited, but may be, for example, 5 μm or less, 1 μm or less, or 500 nm or less.

The specific surface area of the silica particles (specific surface area measured by the BET method) is ^{preferably 200 m 2} / g or less, more preferably 100 m ² / g or less. If the specific surface area ^{exceeds 200 m 2} / g, the intermolecular force between the silica particles becomes high, and there is a possibility that a sufficient dispersibility improving effect cannot be obtained. The lower limit of the BET specific surface area is not particularly limited, but may be, for example, 1 m ² / g or more and 2 m ² / g or more.

The method for producing the silica particles is not particularly limited as long as the CV value is within the above range, but the silicon compound having a hydrolyzable group is easy to adjust the CV value and the average primary particle size of the silica particles to the above range. Is preferably a sol-gel method for hydrolyzing and polycondensing.

The silica particles may be formed of silica alone, or may have alcohol bonded to at least a part of the surface of the silica particles. By coordinating the carboxyl group and / or hydroxy group of the specific carboxylic acid described later with the alkoxy group existing on the surface of the silica particles, the compatibility between the silica particles and the solvent is improved and the increase in viscosity is prevented. It is more effective to do.

The alcohol may be a monohydric alcohol, a polyhydric alcohol, only one type, or a combination of two or more types.

Examples of the monohydric alcohol include aliphatic 1s such as methanol, ethanol, 1-propanol, 2-propanol, 2-methyl-1-propanol, 2-methyl-2-propanol, 1-butanol, 2-butanol, and pentyl alcohol. Hyvalent alcohol; Examples thereof include aromatic monohydric alcohols such as benzyl alcohol and phenylethyl alcohol. The monohydric alcohol preferably has 1 to 4 carbon atoms, more preferably 1 to 2 carbon atoms.

Examples of the polyhydric alcohol include glycols; glycerin; sugars such as glucose, fructose, galactose, maltose and lactose; sugar alcohols such as inositol, sorbitol, mannitol and xylitol; and the like. Examples of the glycols include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, and 1,8. An aliphatic glycol such as −octanediol, 2,2-dimethyl-1,3-propanediol, diethylene glycol, pinacol; aromatic glycol such as hydrobenzoin; cyclopentane-1,2-diol, cyclohexane-1,2-diol , Cyclohexane-1,4-diol and other alicyclic glycols; and the like. The polyhydric alcohol preferably has 2 to 8 carbon atoms, more preferably 2 to 4 carbon atoms.

Among them, aliphatic monohydric alcohols, aromatic monohydric alcohols, or aliphatic glycols are preferable, aliphatic monohydric alcohols or aliphatic glycols are more preferable, and methanol, ethanol, propanol, 2-propanol, 1-butyl alcohol, 2 -Olipid monohydric alcohols such as methyl-2-propanol and pentyl alcohol; aliphatic glycols such as ethylene glycol, propylene glycol and 1,4-butanediol; are even more preferred; methanol, ethanol, 1-propanol, 2- An aliphatic monohydric alcohol such as propanol, 2-methyl-1-propanol, 2-methyl-2-propanol, 1-butanol, or 2-butanol is more preferable, and methanol or ethanol is particularly preferable.

Whether or not alcohol is bound can be measured by the following procedure. First, the silica particle dispersion is centrifuged at a centrifugal force of 100,000 G or more for 1 hour, and the extracted precipitate is dried at 80 ° C. for 10 hours under the condition of 50 Torr (6.7 kPa). Next, the suspension obtained by stirring about 1 g of silica particles and 50 mL of a 0.05 N sodium hydroxide aqueous solution at room temperature for 10 hours is centrifuged at a centrifugal force of 100,000 G or more for 60 minutes to separate the supernatant. The supernatant can be taken and analyzed by gas chromatography according to JIS K 0114 to confirm that the alcohol is bound. A hydrogen flame ionization detector (FID) is used as the detector of the gas chromatograph.

The silica particle concentration in the composition of the present invention is, for example, 10% by mass or more, preferably 20% by mass or more, more preferably 30% by mass or more, still more preferably 35% by mass or more, and the upper limit. Is not particularly limited, but is, for example, 60% by mass or less. In the present invention, since the specific carboxylic acid and the specific solvent described later are used, aggregation of silica particles can be prevented even if the concentration of silica particles is high, and a composition having a low viscosity can be obtained.

2. Specific Carboxylic Acid The carboxylic acid used in the present invention is at least one of polyvalent carboxylic acid and hydroxycarboxylic acid. It is considered that these carboxylic acids improve the dispersibility of the silica particles and can function as a dispersant. A polyvalent carboxylic acid is a carboxylic acid having two or more carboxyl groups in one molecule, and a hydroxycarboxylic acid is a compound having one or more hydroxy groups and one or more carboxyl groups in one molecule. Only one type of polyvalent carboxylic acid and hydroxycarboxylic acid may be used, or two or more types may be used in combination.

The number of carboxyl groups in one molecule of the polyvalent carboxylic acid may be 4 or less, preferably 3 or less. The polyvalent carboxylic acid may be an aliphatic polyvalent carboxylic acid or an aromatic polyvalent carboxylic acid, and is preferably an aromatic polyvalent carboxylic acid. As the polyvalent carboxylic acid, an aromatic polyvalent carboxylic acid having 2 or more and 4 or less carboxyl groups in one molecule is particularly preferable, and phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, pyromellitic acid, and naphthalenedicarboxylic acid are preferable. Examples thereof include phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid and pyromellitic acid. As the aromatic polyvalent carboxylic acid, phthalic acid, isophthalic acid, terephthalic acid and trimellitic acid are more preferable, and phthalic acid is particularly preferable.

The number of hydroxy groups in one molecule of hydroxycarboxylic acid may be 3 or less, more preferably 2 or less. The number of carboxyl groups in one molecule of hydroxycarboxylic acid may be 4 or less, more preferably 3 or less. The hydroxycarboxylic acid may be an aromatic hydroxycarboxylic acid, may be an aliphatic hydroxycarboxylic acid, and is preferably an aliphatic hydroxycarboxylic acid. As the aliphatic hydroxycarboxylic acid, an aliphatic hydroxycarboxylic acid having 1 to 4 carbon atoms excluding carbon in the carboxyl group and 3 or less carboxyl groups in one molecule is preferable, and for example, glycolic acid and lactic acid. , Malic acid, tartaric acid, citric acid and the like.

The amount of the specific carboxylic acid is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, and further preferably 1 part by mass or less (particularly less than 1 part by mass) with respect to 100 parts by mass of the silica particles. The lower limit of the amount of the specific carboxylic acid is, for example, 0.1 part by mass or more, preferably 0.3 part by mass or more, and more preferably 0.5 part by mass or more with respect to 100 parts by mass of the silica particles.

3. 3. Solvents Examples of aprotonic polar solvents include ketone solvents, ether solvents, sulfoxide solvents, amide solvents, nitrile solvents, carbonate solvents, lactone solvents, and urea solvents, and at least one of these. Is preferably used.

Examples of the ketone solvent include methyl ethyl ketone and 4-methyl-2-pentanone, and methyl ethyl ketone is more preferable.
Examples of the ether solvent include ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and 1,4-dioxane.
Examples of the sulfoxide solvent include dimethyl sulfoxide and sulfolane.
Examples of the amide solvent include N, N-dimethylformamide, N, N-dimethylacetamide, N, N-diethylformamide, N-methylpyrrolidone, N-methylpiperidone and the like, and N, N-dimethylformamide, N, N. -Dimethylacetamide and N-methylpyrrolidone are more preferable.
Examples of the nitrile solvent include acetonitrile, propionitrile and the like, and acetonitrile is more preferable.
Examples of the carbonate solvent include diethyl carbonate, ethylene carbonate, propylene carbonate and the like.
Examples of the lactone-based solvent include β-propiolactone, γ-butyrolactone, δ-valerolactone and the like, and γ-butyrolactone is more preferable.
Examples of the urea solvent include 1,3-dimethylimidazolidinone, 1,3-dimethylpropylene urea and the like.

The aprotonic polar solvent is preferably at least one of an amide solvent, a nitrile solvent, a carbonate solvent, a lactone solvent, and a urea solvent, and more preferably at least one of an amide solvent, a nitrile solvent, and a lactone solvent. It is one kind, and more preferably an amide-based solvent (particularly N, N-dimethylacetamide).

Next, the procedure for producing the composition of the present invention containing the above-mentioned silica particles, the specific carboxylic acid and the solvent will be described.

The method for producing silica particles used in the present invention is not limited as long as the CV value of the primary particle size can be adjusted to 20% or less, but it is preferable to use the sol-gel method. In the sol-gel method, wet silica particles can be obtained by hydrolyzing and condensing a hydrolyzable silicon compound. A hydrolyzable silicon compound has at least one hydrolyzable group bonded to the silicon atom, such as a hydrogen atom, a halogen atom, a hydroxyl group, an alkoxy group having 1 to 4 carbon atoms, and an acyloxy group having 2 to 5 carbon atoms. Means a compound that is present. By using such a silicon compound, the metal content as an impurity in the obtained silica particles can be reduced. As the hydrolyzable group, an alkoxy group is preferable. Further, in addition to the hydrolyzable group, an alkyl group having 1 to 10 carbon atoms (particularly, an alkyl group having 1 to 6 carbon atoms) and an aryl group having 6 to 10 carbon atoms may be bonded to the silicon atom. Good. Further, the hydrogen atom of the alkyl group may be substituted with a halogen atom, a vinyl group, a glycidyl group, a mercapto group, an amino group, a (meth) acryloyloxy group or the like.

Examples of the silicon compound in which only a hydrolyzable group is bonded to a silicon atom include tetrafunctional alkoxysilanes such as tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, tetrabutoxysilane, and dimethoxydiethoxysilane. Examples of the silicon compound in which an alkoxy group and an unsubstituted alkyl group are bonded to a silicon atom include trifunctional alkoxysilanes such as methyltrimethoxysilane and methyltriethoxysilane; and 2 such as dimethyldimethoxysilane and dimethyldiethoxysilane. Functional alkoxysilanes; monofunctional alkoxysilanes such as trimethylmethoxysilane and trimethylethoxysilane; and the like. Further, examples of the silicon compound in which an alkoxy group and a substituted alkyl group are bonded to a silicon atom include chloroalkyl group-containing alkoxysilanes such as 3-chloropropylmethyldimethoxysilane and 3-chloropropyltrimethoxysilane; vinyltrimethoxysilane and vinyl. Vinyl group-containing alkoxysilanes such as triethoxysilane; aromatic group-containing alkoxysilanes such as phenyltrimethoxysilane, phenyltriethoxysilane, diphenyldimethoxysilane and diphenyldiethoxysilane; 3-glycidoxypropyltrimethoxysilane, 3- Glycidyl group-containing alkoxysilanes such as glycidoxypropylmethyldimethoxysilane and 3-glycidoxypropylmethyldiethoxysilane; mercapto group-containing alkoxysilanes such as 3-mercaptopropyltrimethoxysilane; 3-aminopropyltrimethoxysilane, 3 -(2-Aminoethylamino) Amino group-containing alkoxysilanes such as propyltrimethoxysilane; and the like.

Among them, 1 to 4 functional alkoxysilanes are preferable, 3 to 4 functional alkoxysilanes are more preferable, and tetrafunctional alkoxysilanes are even more preferable. The larger the functional number (the number of alkoxy groups) of the alkoxysilane, the less likely it is that impurities will be mixed into the obtained silica fired body. From the viewpoint of reactivity, the alkoxy group preferably has 1 to 5 carbon atoms, more preferably 1 to 3 carbon atoms, and even more preferably 1 to 2 carbon atoms. That is, the alkoxysilanes particularly preferably used in the production of the silica particles of the present invention are tetramethoxysilane and tetraethoxysilane. Of these, tetramethoxysilane is the most preferable.

The concentration of the silicon compound in the reaction solution for hydrolyzing and condensing the silicon compound is preferably 0.05 mmol / g or more, more preferably 0.1 mmol / g or more, and the upper limit is not particularly limited, but for example. It is preferably 3 mmol / g or less, and more preferably 1 mmol / g or less. When the concentration of the silicon compound in the reaction solution is in this range, the reaction rate can be easily controlled and the particle size can be made uniform.

The concentration of water in the reaction solution is preferably 0.3 mmol / g or more, more preferably 0.4 mmol / g or more, preferably 15 mmol / g or less, and more preferably 10 mmol. It is / g or less, more preferably 5 mmol / g or less. However, since the amount of water changes due to the hydrolysis / condensation of the silicon compound, the amount at the time of preparation (before the start of hydrolysis / condensation) is used as a reference. The molar ratio of water to silicon compound (water / silicon compound) is preferably 1 or more, more preferably 1.5 or more, preferably 20 or less, more preferably 15 or less, still more preferably 10 or less.

When hydrolyzing and condensing a silicon compound, it is preferable that a catalyst coexists. Silicon compounds can be hydrolyzed and condensed even in the absence of a catalyst, but by using a catalyst, the reaction can be easily controlled, and the particle size and residual amount of silanol groups can be adjusted. The catalyst is preferably a basic catalyst from the viewpoint of increasing the reaction rate, and examples of the basic catalyst include ammonia, amines, and quaternary ammonium compounds. Examples of the ammonia include ammonia; an ammonia generating agent such as urea; and the like. Examples of the amines include aliphatic amines such as methylamine, ethylamine, propylamine, n-butylamine, dimethylamine, dibutylamine, trimethylamine and tributylamine; alicyclic amines such as cyclohexylamine; aromatics such as benzylamine. Group amines; alkanol amines such as monoethanolamine, diethanolamine, triethanolamine; and the like. Examples of the quaternary ammonium compound include tetramethylammonium hydroxide and tetrabutylammonium hydroxide.

Of these, ammonia and amines are preferable from the viewpoint of easy control of particle size. Further, from the viewpoint of increasing the purity of the obtained silica particles, a catalyst that can be easily removed from the silica is preferable, specifically, ammonia and amines are preferable, and ammonia and aliphatic amines are more preferable. Further, from the viewpoint of having both a catalytic effect and ease of removal, ammonia is preferable, and ammonia is particularly preferable.

The concentration of the catalyst in the reaction solution is preferably 0.1 mmol / g to 3 mmol / g. The mass ratio of the catalyst to the total of the catalyst and water (catalyst / (catalyst + water)) is preferably 0.1 or more, more preferably 0.2 or more, and 0.4 or less. Is preferable, and 0.32 or less is more preferable.

Further, when hydrolyzing / condensing the silicon compound, it is preferable to coexist with a reaction diluent. By containing the reaction diluent, the hydrophobic silicon compound and water can be easily mixed, the progress of hydrolysis / condensation of the silicon compound can be made uniform in the reaction solution, and the obtained unbaked silicon compound can be obtained. The dispersibility of silica is improved. As the reaction diluent, an appropriate water-soluble organic solvent can be used, and alcohol is preferable. As the alcohol, any of the above-mentioned alcohols exemplified as the alcohol which may be bonded to a part of the surface of the silica particles can be used, and methanol or ethanol is particularly preferable.

The diluent is preferably 60 parts by mass or more, more preferably 100 parts by mass or more, still more preferably 120 parts by mass or more, and 500 parts by mass with respect to 100 parts by mass of the total of the silicon compound and water. It is preferably less than or equal to, more preferably 300 parts by mass or less, still more preferably 200 parts by mass or less. The larger the amount of diluent, the easier it is to make the progress of the reaction uniform, and the smaller the amount of diluent, the higher the reaction rate.

Each of the above components may be mixed in an appropriate order, but for example, a premixed solution in which at least a part of each of the above components (for example, water, a catalyst, a diluent, etc.) is mixed in advance is prepared, and then a silicon compound is prepared. May be mixed with. Further, it is preferable to add the silicon compound to the premixture, and the addition method may be either batch addition or sequential addition (continuous addition or intermittent addition), but sequential addition is preferable. The silicon compound may be mixed with the diluent in advance and then mixed with the premixture.

In order to reduce the CV value of the obtained silica particles, it is preferable that this reaction is carried out as uniformly as possible at the start of the hydrolysis / condensation reaction of the silicon compound. For example, the stirring speed of the reaction solution immediately after the addition of the silicon compound. The CV value can be adjusted by adjusting.

When hydrolyzing and condensing a silicon compound, the reaction temperature is preferably 0 to 100 ° C, more preferably 10 to 60 ° C, and even more preferably 10 to 45 ° C. The duration of hydrolysis / condensation is preferably 30 minutes to 100 hours, more preferably 50 minutes to 20 hours, and even more preferably 1 to 10 hours.

After producing the silica particles by the above method, the wet silica particles may be separated from the reaction solution, the wet silica particles may be dried or fired, and then mixed with a specific carboxylic acid and a solvent. From the viewpoint of suppressing aggregation and sticking during drying, the wet silica particles may be separated from the reaction solution by filtration, centrifugation, solvent evaporation (concentration), etc., and in particular, separated by solvent evaporation (concentration). It is preferable to keep it. Further, the reaction solution may be filtered with a filter prior to separating the wet silica particles from the reaction solution.

In order to dry the wet silica particles, for example, it is preferable to adopt an air flow drying method. In the air-flow drying method, the wet silica particles during drying are dispersed by the air flow or collide with the inner wall of the drying device, so that the aggregation of the silica particles can be suppressed while drying. When drying the reaction solution (concentrated solution) by the air flow drying method, either the direct heating method (a method using a heated air flow) or the indirect heating method (heating the heat transfer plate (preferably the inner wall of the drying device) of the drying device) May be selected. When the direct heating method is adopted, the high-temperature airflow generated from the hot air generator or the like comes into contact with the reaction liquid (concentrated liquid) to evaporate the solvent and dry the wet silica particles, and at the same time, the wet silica being dried by the high-temperature airflow. The particles are crushed and the aggregation of the dried silica particles can be suppressed. Further, when the indirect heating method is adopted, the reaction solution (concentrated solution) is heated through the heat transfer plate (preferably the inner wall), so that the solvent evaporates and the wet silica particles are dried, and at the same time, they are introduced from the outside. Wet silica particles during drying are crushed by the air flow or the air flow circulating inside, and the aggregation of the dried silica particles is suppressed. Above all, the indirect heating method is preferable.

As described above, the silica particles in the composition of the present invention have a coefficient of variation of the primary particle size of 20% or less, and a preferable average primary particle size of 10 nm or more, in order to satisfy such requirements. The coefficient of variation of the particle size and the average primary particle size of the above-mentioned hydrolyzed / reduced-polymerized silica particles or dried silica particles may be 20% or less and 10 nm or more, respectively. The preferred range of the variation coefficient of the particle size and the average primary particle size of the silica particles and the dried silica particles after hydrolysis / contraction polymerization is the variation coefficient of the particle size of the silica particles and the average primary particle size in the composition of the present invention. Similar to range.

The dried silica particles thus obtained can be used as a raw material for the composition of the present invention. By the way, as described above, it is preferable that alcohol is bonded to the surface of the dried silica particles. Silica particles having alcohol bonded to the surface can be produced by adding alcohol in the production process at the latest by the completion of the drying process. When the silica particles containing alcohol are dried, the alcohol binds to the surface of the silica particles.

The mixing order of the silica particles, the specific carboxylic acid and the solvent for obtaining the composition of the present invention is not particularly limited, and the specific carboxylic acid may be added to the liquid in which the silica particles and the solvent are mixed, or the specific carboxylic acid and the specific carboxylic acid may be added. Silica particles may be added to the solution mixed with the solvent. Examples of the mixing method include stirring and mixing using a stirrer, a shaker, a kneading machine and the like, crushing and mixing using a crusher, and the like. Above all, it is preferable to pulverize and mix using a pulverizer. Examples of the crusher used in this case include a high-pressure homogenizer, an ultra-high pressure homogenizer, a pressure-type disperser such as a star burst, a media mill such as a ball mill, a bead mill, and a planetary ball mill, an impact shear crusher such as a micros, and an ultra Examples thereof include a sound wave disperser, a pressure type disperser is preferable, and a star burst is more preferable.

Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited by the following examples, and it is of course possible to carry out the invention with appropriate modifications within the range that can be adapted to the above-mentioned purpose, and all of them are technical of the present invention. Included in the range. In the following, unless otherwise specified, "part" means "part by mass" and "%" means "% by mass".

The measurement methods used in the following examples and comparative examples are as follows.

[Measurement of average primary particle size]
The average primary particle size is 5 or more visual fields obtained by observing arbitrarily collected silica particles using a transmission electron microscope at a measurement magnification in which the number of silica particles contained in one visual field is 100 to 300. In the transmission electron microscope image, it can be obtained as the number average value of the primary particle diameters of all the particles contained in the electron microscope image.

[Measurement of coefficient of variation of primary particle size]
The coefficient of variation of the primary particle size can be calculated based on the following formula using the standard deviation between the average primary particle size and the primary particle size.
Coefficient of variation (%) = (standard deviation of primary particle size / average primary particle size) x 100

[Measurement of specific surface area]
After vacuum-drying the silica particles at 110 ° C., the specific surface area of the silica particles was measured by the BET method using a MacSorb 1210 fully automatic gas adsorption amount measuring device manufactured by Mountec Co., Ltd.

(Manufacturing of silica particles)
Manufacturing example 1
A glass reactor with a capacity of 20 L equipped with a stirrer, a dropping device and a thermometer was charged with 3300 g of methyl alcohol as an organic solvent and 730 g of 25 wt% aqueous ammonia (water and catalyst), and the liquid temperature was adjusted to 41 while stirring. The temperature was adjusted to ± 0.5 ° C. On the other hand, 2500 g of tetramethoxysilane as a silicon compound was charged into the dropping device. Tetramethoxysilane was added dropwise from the dropping device over 3 hours with stirring at 430 rpm. After completion of the dropping, the mixture was further stirred for 1 hour to hydrolyze and condense tetramethoxysilane to obtain a suspension of silica particles.
The obtained suspension was dried using an instantaneous vacuum evaporator to take out powdered silica particles. As the instantaneous vacuum drying device, a cracks system 8B type (manufactured by Hosokawa Micron Co., Ltd., airflow drying method, indirect heating method) was used. Further, as drying conditions, a heating tube temperature of 175 ° C. and a reduced pressure of 200 Torr were adopted. The above-mentioned instantaneous vacuum evaporator includes a stainless steel pipe having an inner diameter of 8 mm and a length of 9 m covered with a jacket to which heated steam is supplied, a supply unit that supplies a suspension to one end of the steel pipe, and the other end of the steel pipe. It was provided with a powder collection chamber in a reduced pressure state, which was connected to a section and provided with a bag filter for separating powder and steam. Then, the suspension supplied from the supply unit is heated when passing through the steel pipe and separated into powder and steam, the powder is collected by the bag filter, the steam is condensed, and then the apparatus. It was configured to be discharged to the outside.

Production Example 2 to Production Example 5
Amount of methyl alcohol as an organic solvent, amount of water and aqueous ammonia as a catalyst, liquid temperature when stirring methyl alcohol and aqueous ammonia, amount of tetramethoxysilane as a silicon compound, dropping time of tetramethoxysilane, completion of dropping Silica particles were produced in the same manner as in Production Example 1 except that the subsequent stirring times were changed as shown in Table 1.

Production example 6
2040 g of methyl alcohol as an organic solvent and 470 g of 25 wt% aqueous ammonia (water and catalyst) were charged in a glass reactor having a capacity of 20 L equipped with a stirrer, a dropping device and a thermometer, and the liquid temperature was raised to 20 while stirring. The temperature was adjusted to ± 0.5 ° C. On the other hand, 2600 g of tetramethoxysilane as a silicon compound was charged into the dropping device. Tetramethoxysilane was added dropwise from the dropping device over 4 hours. The first 5 minutes were stirred at 20 rpm and the remaining dropping time was stirred at 430 rpm. After completion of the dropping, the mixture was further stirred for 1 hour to hydrolyze and condense tetramethoxysilane to obtain a suspension of silica particles. The obtained suspension was dried using an instantaneous vacuum evaporator in the same manner as in Production Example 1 to take out powdered silica particles.

Production example 7
Amount of methyl alcohol as an organic solvent, amount of water and aqueous ammonia as a catalyst, liquid temperature when stirring methyl alcohol and aqueous ammonia, amount of tetramethoxysilane as a silicon compound, dropping time of tetramethoxysilane, completion of dropping Silica particles were produced in the same manner as in Production Example 6 except that the subsequent stirring times were changed as shown in Table 1.

In Table 1, the CV value and the average particle size of the silica particles obtained in Production Examples 1 to 7 are also shown.

(Preparation of composition)
Example 1-1
In a 20 mL screw tube, 4.0 g of the silica particles obtained in Production Example 1, 6.0 g of γ-butyrolactone as an organic solvent, and 0.9 part (0.036 g) of citric acid with respect to 100 parts of the silica particles were added. , Stirrer was stirred at a rotation speed of 150 rpm for 5 minutes to prepare a solvent dispersion having a silica concentration of 40%.

Examples 1-2-1-5
A solvent dispersion having a silica concentration of 40% was prepared in the same manner as in Example 1-1 except that the specific carboxylic acid shown in Table 2 was used instead of citric acid.

Examples 2-1 to 2-5
In a 20 mL screw tube, 4.0 g of the silica particles obtained in Production Example 2, 6.0 g of N, N-dimethylformamide as an organic solvent, and 0.9 of the specific carboxylic acid shown in Table 2 with respect to 100 parts of the silica particles. Part (0.036 g) was added and stirred with a stirrer at a rotation speed of 150 rpm for 5 minutes to prepare a solvent dispersion having a silica concentration of 40%.

Example 3, Example 4
In a 20 mL screw tube, 4.0 g of the silica particles obtained in Production Example 3 and 6.0 g of acetonitrile (Example 3) or N-methylpyrrolidone (Example 4) citric acid as a solvent were added to 100 parts of the silica particles. 0.9 part (0.036 g) was added and stirred with a stirrer at a rotation speed of 150 rpm for 5 minutes to prepare a solvent dispersion having a silica concentration of 40%.

Example 5-1
A slurry is obtained by pre-dispersing 300.0 g of silica particles obtained in Production Example 4 by mixing and stirring with 450.0 g of N, N-dimethylacetamide as an organic solvent so as to have a concentration of 40%. It was. This slurry was then pulverized and mixed using a pulverizing mixer (“Starburst” manufactured by Sugino Machine Limited). To the pulverized and mixed slurry obtained above, 0.9 part (2.7 g) of citric acid was added to 100 parts of silica particles and stirred under mixing and stirring, and a solvent dispersion having a silica concentration of 40% was added. Got

Examples 5-2-5-8
A solvent dispersion having a silica particle concentration of 40% was obtained in the same manner as in Example 5-1 except that the type and amount of the specific carboxylic acid were set to the values shown in Table 2.

Example 6
Using the silica particles obtained in Production Example 5, a solvent dispersion having a silica particle concentration of 40% was obtained in the same manner as in Example 5-1 except that the organic solvent was methyl ethyl ketone.

Example 7
Using the silica particles obtained in Production Example 3, a solvent dispersion having a silica particle concentration of 40% was obtained in the same manner as in Example 5-1 except that the solvent was 4-methyl-2-pentanone.

Comparative Example 1
A solvent dispersion having a silica concentration of 40% was obtained in the same manner as in Example 1-1 except that the specific carboxylic acid was not used.

Comparative Example 2
A solvent dispersion having a silica concentration of 40% was obtained in the same manner as in Example 5-1 except that the specific carboxylic acid was not used.

Comparative Example 3, Comparative Example 4
Examples except that the silica particles obtained in Production Example 6 (Comparative Example 3) or the silica particles obtained in Production Example 7 (Comparative Example 4) were used and N, N-dimethylformamide was used as a solvent. A solvent dispersion having a silica concentration of 40% was obtained in the same manner as in 1-1.

The silica solvent dispersions obtained in Examples and Comparative Examples were evaluated by the following methods.

[Dispersion evaluation of solvent dispersion A]
Take 10 g of the silica particle dispersion dispersed in each solvent in a 20 mL screw tube, stir it by hand up and down 10 times, let it stand, visually check the state of the dispersion, and evaluate as follows according to the state of bubble formation. did. The higher the viscosity, the more air is entrained during stirring to form bubbles, and the bubbles once formed are less likely to disappear, but the lower the viscosity, the less bubbles are formed during stirring.
◯: Almost no bubbles are seen immediately after standing overnight △: Almost no bubbles are seen after standing overnight ×: Bubbles are seen after standing overnight

[Dispersion evaluation B of solvent dispersion]
10 g of the silica particle dispersion dispersed in each solvent is taken in a 20 mL screw tube, dispersed with a stirrer for 10 minutes, and then 1 g of the dispersion is dropped onto a slide glass (MICRO SLIDE GLASS thickness 1 mm, manufactured by Matsunami Glass Industry Co., Ltd.). Cover with a cover glass (COVER GLASS thickness 0.15 mm) and visually confirm the presence of aggregates with a microscope (magnification 400 times).
◯: Almost no agglomerates △: Slight agglomerates are seen ×: Many agglomerates are seen

The results are shown in Table 2.

In Examples 1 to 7 using the silica particles, the specific carboxylic acid, and the solvent specified in the present application, the dispersibility evaluation B was ◯, and the evaluation A was ◯ or Δ. On the other hand, in Comparative Examples 1 and 2 in which the specific carboxylic acid was not used, evaluations A and B were both ×, and in Comparative Examples 3 and 4 in which the CV value of the silica particles exceeded 20%, the dispersion evaluation B was ×. It was.

The composition containing silica particles of the present invention is a hard coat material used for various display devices, resin products, etc .; an anti-blocking agent and a slipper-imparting agent for various films such as polyester film, polyimide film, and fluororesin film; liquid crystal. In-plane spacers for display elements, seal part spacers for liquid crystal display elements, spacers for EL display elements, spacers for touch panels, spacers such as gap retainers between various substrates such as ceramics and plastics; encapsulants for semiconductors, seals for liquid crystals Encapsulants for various electronic parts such as materials and encapsulants for LED light emitting elements; light diffusing agents such as light diffusing films, light diffusing plates, light guide plates, antiglare films; cosmetic additives such as white extender pigments; dentistry It is preferably used as a material.

Claims (4)

Silica particles with a coefficient of variation of the primary particle size of 20% or less,
With at least one of polyvalent carboxylic acid and hydroxycarboxylic acid,
A composition comprising an aprotic polar solvent. The composition according to claim 1, wherein the average primary particle diameter of the silica particles measured based on a transmission electron microscope image is 10 nm or more. The composition according to claim 1 or 2, wherein the specific surface area of the silica particles is 200 m ^{2 / g or less.} The aprotonic polar solvent is at least one selected from the group consisting of a ketone solvent, an ether solvent, a sulfoxide solvent, an amide solvent, a nitrile solvent, a carbonate solvent, a lactone solvent, and a urea solvent. The composition according to any one of claims 1 to 3.