JP2009242115A - Silica sol and production method of the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a silica sol having silica fine particles as a dispersoid of the silica sol, the silica fine particles having a large specific surface area compared to a particle diameter and having a peculiar structure with a great number of acicular projections and being expected to be applied in various usages such as a catalyst carrier, an abradant, a reinforcing agent, and a filler, and to provide a production method of a silica sol for efficiently producing a silica sol having the silica fine particles dispersed therein. <P>SOLUTION: The silica sol includes the following silica fine particles dispersed in a dispersion medium; and a production method of the silica sol is also disclosed. The silica fine particles have an average particle diameter (D1) ranging from 10 to 100 nm measured by an image analysis method, a specific surface area ranging from 300 to 700 m<SP>2</SP>/g, and an apparent bulk density (ABD) ranging from 0.05 to 0.15 g/ml. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a silica sol characterized in that silica fine particles having needle-like protrusions are dispersed in a dispersion medium, and a method for producing the same.

  The shape of the silica fine particles contained in the silica sol is known to be spherical, particle-connected or chain-like, and there are reports on silica sols containing acicular or fibrous silica fine particles. Since these silica fine particles have a unique shape, they are expected to exhibit a specific effect when used as a catalyst carrier, an abrasive, a reinforcing material, a filler, and the like.

  Patent Document 1 (Japanese Examined Patent Publication No. 57-149817) discloses a method for producing a fibrous silica sol, wherein a halogen-free organosilicon compound gas is contacted with oxygen gas and thermally decomposed. Examples of the fibrous silica sol obtained by this production method include a diameter of 0.5 to 1.5 μm, a length of 0.5 mm or more (Example 1), a diameter of 0.3 to 2.0 μm, and a length of 2 mm or more. (Example 2), diameter of 0.12 to 1.0 μm, length of 1 mm or more (Example 3), and the like are disclosed.

Patent Document 2 (International Publication WO1992006920) discloses that a silicate sol is frozen in a gap between crystal planes of a crystallized sol-solvent crystal by freezing the silicate sol. A method for producing acicular silica gel is disclosed, wherein the frozen silica hydrogel is thawed, hydrothermal polymerization of the thawed silica hydrogel is performed, and the obtained silica hydrogel is dried.

Patent Document 3 (Japanese Patent Laid-Open No. 11-61043) describes a method for producing short fibrous silica obtained by hydrolyzing a specific alkoxysilane and then hydrothermally treating it at 250 ° C. or higher. Specifically, for this production method, (i) ammonia is added to a mixed solution containing water, an organic solvent, and one or more of the alkoxysilanes represented by the above general formula [1] to add alkoxy. After hydrolyzing silane to produce silica fine particles having a particle size of 10 to 30 nm, (ii) removing unreacted alkoxysilane, organic solvent and catalyst from the mixed solution after the reaction, Preparing an aqueous dispersion, (iii) adjusting the solid content concentration of silica fine particles in the aqueous dispersion to 0.1 to 5% by weight, and adjusting the ammonia concentration to 50 to 400 ppm, and (iv) the aqueous dispersion It is described that the liquid can be produced by hydrothermal treatment at a temperature of 250 ° C. or higher. The short fibrous silica obtained by this production method has an average diameter (D) of 10 to 30 nm, a length (L) of 30 to 100 nm, and an aspect ratio (L / D) of 3 to 10. It is described that it is characterized by this.

  In Patent Document 4 (Japanese Patent Laid-Open No. 2000-1309), fibrous silica gel is manufactured by dispersing raw material wollastonite in water to form a water-dispersed slurry, and blowing carbon dioxide into the water-dispersed slurry. Accordingly, a method for producing a fibrous amorphous silica having a small specific surface area, characterized by heat-treating it, is disclosed. The fibrous silica sol obtained by this production method is described as having a fiber length of 1 to 200 .mu.m, an aspect ratio of 5 to 100, and a specific surface area of 10 to 100 m @ 2 / g.

In Patent Document 5 (Japanese Patent Laid-Open No. 2006-1822), low crystalline acicular silica can be obtained by hydrothermal treatment using an aqueous solution or water slurry containing an alkaline lithium source and a silica source as a starting material. In particular, lithium hydroxide or the like is used as the alkaline lithium source, silica sol or the like is used as the silica source, or lithium silicate is used as the alkaline lithium source and the silica source, so that the diameter is 0.001 to 1 μm. An invention for producing acicular silica which is acicular silica and has an aspect ratio of 5 to 200 is disclosed.

Patent Document 6 (Japanese Patent Application Laid-Open No. 2006-265789) discloses a method for producing a siliceous fibrous aggregate obtained by acid decomposition of asbestos or asbestos-containing serpentine, in which an asbestos or asbestos-containing serpentine pulverized product is used as an acid solution. And the step of decomposing while stirring, the step of filtering the silica remaining as a residue after decomposition, the step of washing the filtered silica, and adding water to the washed silica to add 10-30% A fibrous silica comprising: a slurry solution having a concentration of 5; and a step of dispersing the fibrous silica in the slurry in water by an ultrasonic diffusion method and a step of drying the dispersion in which the silica is dispersed with a spray dryer A manufacturing method is disclosed.
Japanese Patent Publication No.57-149817 International Publication WO1992006920 Japanese Patent Laid-Open No. 11-61043 JP 2000-1309 A JP 2006-1822 A JP 2006-265789 A

  The first object of the present invention is to produce a silica sol containing fine particles having unique needle-like projections. The second problem of the present invention is that silica fine particles having a unique shape such as having a needle-like structure are dispersed in a dispersion medium, and can be suitably used as a catalyst carrier, an abrasive, a reinforcing material, a filler, and the like. It is an object to provide a silica sol that can be produced and a method for producing the same.

The invention according to the present application has an average particle diameter (D1) measured by an image analysis method in the range of 10 to 100 nm, a specific surface area in the range of 300 to 700 m ² / g, and an apparent bulk density (A
BD) is a silica sol in which silica fine particles having a range of 0.05 to 0.15 g / ml are dispersed in a dispersion medium.

  Preferred examples of the silica sol include silica sols in which the aspect ratio of the silica fine particles is in the range of 0.7 to 1.0 and the variation coefficient of the particle diameter is in the range of 10.0 to 40.0%. it can.

Another preferred embodiment of the silica sol includes a silica sol in which silica fine particles having needle-like protrusions are dispersed in a dispersion medium.
Moreover, as another suitable aspect of the said silica sol, the silica sol whose solid content concentration of the said silica sol exists in the range of 1-50 mass% can be mentioned.

  The invention of the method for producing silica sol according to the present invention comprises 100 parts by mass of an aqueous solution containing water and a surfactant, and an oily solution 10-30 containing a surfactant other than hydrocarbon oil, an amine compound and an amine compound. The oil-in-water type (O / W) emulsion obtained by mixing with the mass part and emulsifying is maintained in a temperature range of 10 to 60 ° C., and tetraethyl orthosilicate is continuously added to the oil-in-water type (O / W) emulsion. A method for producing a silica sol, wherein a solution of a silica fine particle precursor is prepared by adding to or intermittently, and further, mechanical impact is applied to the silica fine particle precursor to generate silica fine particles.

As a suitable aspect about the manufacturing method of the silica sol which concerns on this invention, the manufacturing method of the silica sol containing the following [1]-[5] can be mentioned.
[1] 100 parts by mass of an aqueous solution containing water and a surfactant and 10 to 30 parts by mass of an oil-based solution containing a surfactant other than hydrocarbon oil, an amine compound, and an amine compound are mixed and emulsified. The oil-in-water type (O / W) emulsion thus obtained is kept in the temperature range of 10 to 60 ° C., and tetraethyl orthosilicate is continuously or intermittently added to the oil-in-water type (O / W) emulsion, Step [2] for preparing a fine particle precursor solution [2] Step for aging the silica fine particle precursor solution at 20 to 98 ° C. [3] After completion of the aging, an organic solvent is added to the silica fine particle precursor solution. Step [4] Step of washing the emulsion of the silica fine particle precursor [5] Subsequent to the previous step [5] Step of washing the solution of the silica fine particle precursor And to generate fine particles, the method for manufacturing step the silica sol to prepare a silica sol, as another preferred embodiment, there may be mentioned a method of manufacturing a silica sol for cleaning of the silica fine particles precursor by centrifugation.

Another preferred embodiment of the method for producing the silica sol includes a method for producing a silica sol in which the mechanical impact is applied by a dispersion treatment.
Another preferred embodiment of the method for producing the silica sol includes a method for producing a silica sol in which the hydrocarbon oil is kerosene.

  The silica fine particles, which are the dispersoid of the silica sol according to the present invention, have a specific surface area larger than the particle diameter and a unique structure having a large number of needle-like protrusions. It is expected to be applied to various uses such as agents or fillers. In addition, the method for producing a silica sol according to the present invention can efficiently produce a silica sol in which such silica fine particles are dispersed.

[Silica fine particles]
[Construction]
The surface structure of the silica fine particle, which is the dispersoid of the silica sol according to the present invention, has a needle-like projection and the surface of the particle is extremely undulating. Here, the acicular protrusion is a protrusion having a center line extending substantially linearly in one direction from the surface of the silica fine particle and having a generally acicular or conical shape.

  Regarding the structure of the silica fine particles according to the present invention, the appearance of the silica fine particles including needle-like protrusions is similar to a substantially spherical sea urchin or ridge. Specifically, it is preferable that the silica fine particles have an aspect ratio in the range of 0.7 to 1.0. The aspect ratio in the present application is such that the longest inner diameter of a particle is M (its length is m), and the inner diameter perpendicular to the point that divides the longest inner diameter into two equal parts on the longest inner diameter is N (its length). Is the ratio of length (n / m).

When the value of n / m is less than 0.7, it is no longer spherical or distorted, and the particle shape itself is acicular.
In the case where the particles themselves are needle-shaped, it becomes unsuitable for expressing the degree of unevenness on the particle surface by the coefficient of variation of the particle diameter defined in the present invention. As for the value of n / m, 1 is the maximum value. About n / m, the range of 0.8-1 is recommended suitably. More preferably, a range of 0.9 to 1 is recommended.

Since the needle-like protrusions have a generally triangular pyramid structure, it is not easy to specify the thickness thereof, but the needle-like protrusions have a triangular pyramid structure depending on the average particle diameter of the silica fine particles. It is preferable that the width of the bottom portion of the needle-like protrusion is approximately in the range of 1 to 10 nm.

  Regarding the length of the needle-like protrusion, it may be difficult to specify the position to be the base point on the particle surface side, and it is not easy to determine the length, but for example, the length of the longest inner diameter (M) of the silica fine particles What is 5 to 30% of range of (m) is preferable.

[Average particle size]
The silica fine particles according to the present invention have needle-like protrusions, and the shape can be regarded as spherical or indefinite. For this reason, the average particle diameter is determined by measuring the longest diameter of each of 50 arbitrary particles in a photograph projection drawing obtained by using an electron microscope and calculating the average value thereof. The value was taken as the average particle size. (In this application, this method is referred to as “image analysis method”.)
As a range of the average particle diameter of the silica fine particles, a range of 10 to 100 nm is preferable. When the average particle diameter is less than 10 nm, the shape of the silica fine particles tends to be remarkably indeterminate, which is not desirable in practice. When the average particle diameter exceeds 100 nm, it is not easy to prepare. The average particle size is more preferably in the range of 15 to 70 nm. More preferably, the range of 18 to 30 nm is recommended.

[Specific surface area]
The specific surface area of the silica fine particles according to the present invention is preferably in the range of 300 to 700 m ² / g. The silica fine particles contain a large number of needle-like protrusions, and are usually less than 300 m ² / g. Further, when the specific surface area exceeds 700 m ² / g, it is not easy to produce. The specific surface area is more preferably in the range of 400 to 600 m ² / g.

[Apparent bulk density]
The silica fine particles that are the dispersoid of the silica sol according to the present invention have needle-like protrusions as described above, and the apparent bulk density (ABD) value is the same as that of ordinary spherical silica fine particles having the same average particle diameter. In comparison, the tendency to take a small value becomes stronger. Since the silica fine particles have a plurality of needle-like protrusions, it can be said that the apparent bulk density (ABD) is smaller than that of normal spherical silica fine particles.

  The apparent bulk density (ABD) of the silica fine particles according to the present invention is preferably in the range of 0.05 to 0.15 g / ml. When the apparent bulk density (ABD) is less than 0.05 g / ml, it is close to conventional hollow spherical particles. When the value of the apparent bulk density (ABD) exceeds 0.15 g / ml, the case where there is no acicular protrusion may be included. The apparent bulk density (ABD) is more preferably in the range of 0.08 to 0.13 g / ml.

[Coefficient of variation of particle size]
As for the surface state of the silica fine particles which are the dispersoid of the silica sol according to the present invention, those having a particle diameter variation coefficient (CV value) in the range of 10 to 40% are recommended.

  Here, the variation coefficient (CV value) of the particle diameter means the degree of non-uniformity of the particle diameter. Specifically, a point that bisects the longest diameter of the silica fine particles in a photographic projection view by an electron microscope is set as a central point of the spherical silica fine particles, and one direction on the longest diameter from the central point is an angle of 0 degree. The radius from 0 degree to 180 degree is measured every 10 degrees and the average value and the standard deviation of the radius are calculated from these values. Further, the radius variation coefficient is obtained by dividing the standard deviation by the average value. In the present application, a value obtained by dividing a radius variation coefficient (relative standard deviation) by 100 is displayed as a radius variation coefficient [%]. Specifically, it can be expressed as follows.

Coefficient of variation (CV value) [%] of radius (Y) = (standard deviation (σ) of radius (Y) / average value (Ya) of radius (Y)) × 100
In the present application, the coefficient of variation of each radius is obtained for arbitrary 50 particles, and the average value thereof is treated as the coefficient of variation [%] of the particle diameter.

  The silica fine particles according to the present invention have needle-like protrusions on the surface and are characterized by large fluctuations in particle diameter. Specifically, the particle diameter variation coefficient (CV value) is preferably in the range of 10.0 to 40.0%. When the variation coefficient of the particle diameter is less than 10.0, the case where there are irregularities on the particle surface but no needle-like protrusion is formed is included. Regarding the coefficient of variation of the particle diameter, it is not easy to exceed 40.0% because it is affected by the number of other needle-like protrusions and the shape of the particles themselves even when the needle-like protrusions are remarkably long. Absent. About the range of the variation coefficient of a particle diameter, the range of 12 to 30% is recommended suitably. More preferably, the range of 14 to 25% is recommended.

[Silica sol]
The silica sol according to the present invention is a silica sol in which the silica fine particles are dispersed in a dispersion medium. The dispersion medium is not particularly limited as long as the silica fine particles can be dispersed. For example, water, alcohols, ketones, or a mixed solvent thereof can be used. Examples of alcohols include methanol, ethanol, and propanol. Examples include butanol. Examples of ketones include methyl isobutyl ketone, acetone, and methyl ethyl ketone.

  About the solid content density | concentration of the silica sol which concerns on this invention, it can be normally used in 1-50 mass%. When the amount is less than 1% by mass, it is not practical for polishing use depending on the use, and in that case, it is used after being concentrated. When it exceeds 50 mass%, it may become easy to aggregate depending on temperature or pH, and is not desirable. About solid content concentration, the range of 2-40 mass% is recommended suitably. More preferably, the range of 3 to 30% by mass is recommended.

[Method for producing silica sol]
In the method for producing silica sol according to the present invention, tetraethyl orthosilicate is continuously or intermittently added to a specific oil-in-water (O / W) emulsion composed of 100 parts by weight of an aqueous solution and 10 to 30 parts by weight of an oil-based solution. It is characterized by doing.

[Oil-in-water (O / W) emulsion]
The oil-in-water emulsion in the present invention is preferably a liquid-liquid emulsion, meaning that the dispersed phase is an organic phase containing a water-insoluble liquid component and the continuous phase is an aqueous phase. A surfactant is usually used to form an oil-in-water emulsion.

[Water phase]
As an aqueous phase component, an aqueous solution containing water and a surfactant is used. About the usage-amount of surfactant, the range of 3-15 mass% is preferable in an aqueous solution. If it is less than 3% by mass, it may be difficult to produce an emulsion. When it exceeds 15 mass%, the silica sol according to the present invention may not be easily generated.

[Surfactant]
The surfactant is used for the purpose of promoting stabilization of the dispersion state of the oil-in-water emulsion. Examples of such surfactants include anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants. Regarding the use of the surfactant, one or more of the surfactants are added.

  As anionic surfactants, higher fatty acid salts, higher alkyl dicarboxylates, higher alcohol sulfates, higher alkyl sulfonates, alkyl benzene sulfonates, alkyl naphthalene sulfonates, naphthalene sulfonate salts (Na, K) , Li, Ca) formalin polycondensate, condensates of higher fatty acids and amino acids, dialkylsulfosuccinate esters, alkylsulfosuccinates, naphthenates, etc., alkyl ether carboxylates, acylated peptides, α-olefin sulfonic acids Salt, N-acylmethyl taurine, alkyl ether sulfate, secondary higher alcohol ethoxy sulfate, polyoxyethylene alkyl phenyl ether sulfate, monoglycolate, alkyl ether phosphate salt, alkyl phosphate ester salt, etc. There is not limited thereto.

  Cationic surfactants include, but are not limited to, aliphatic amine salts, quaternary ammonium salts, sulfonium salts, phosphonium salts and the like. Preferable examples of the cationic surfactant include cationic surfactants such as cetyltrimethylammonium bromide (CTAB), monoalkylammonium salt, dialkylammonium salt, trialkylammonium salt and tetraalkylammonium salt. Among them, cationic surfactants such as octyltrimethylammonium bromide (OTAB), decyltrimethylammonium bromide (DeTAB), dodecyltrimethylammonium bromide (DTAB), tetradecyltrimethylammonium bromide (TTAB) and the like can be mentioned. .

Examples of amphoteric surfactants include, but are not limited to, carboxybetaine types, aminocarboxylates, and lecithin.
Nonionic surfactants include amine compounds such as dodecylamine, didodecylamine and tridodecylamine, fluorine-based or silicone-based acrylic acid copolymer, polyoxyethylene alkyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene Oxyethylene alkylphenyl ether, polyoxyethylene secondary alcohol ether, polyoxyethylene sterol ether, polyoxyethylene lanolin derivative, ethylene oxide derivative of alkylphenol formalin condensate, polyoxyethylene polyoxypropylene block polymer, polyoxyethylene polyoxypropylene Fatty acid ester type of alkyl ether polyoxyethylene compound, polyethylene oxide condensation type polyethylene glycol fatty acid ester, Examples include, but are not limited to, fatty acid monoglycerides, polyglycerin fatty acid esters, sorbitan fatty acid esters, propylene glycol fatty acid esters, sucrose fatty acid esters, fatty acid alkanolamides, polyoxyethylene fatty acid amides, and polyoxyethylene alkylamine alkylamine oxides. It is not a thing.

[Organic phase]
As a component of the organic phase, an oil-based solution containing a hydrocarbon oil, an amine-based compound and a surfactant is used. Here, a silica sol in which silica fine particles having needle-like protrusions are dispersed in a dispersion medium can be prepared by using a hydrocarbon oil and an amine compound in combination.

[Surfactant]
For surfactants other than amine compounds used in oil-based solutions, the same surfactants as the surfactants can be used.

[Hydrocarbon oil]
Examples of the hydrocarbon oil include kerosene, dimethyl silicone oil, methyl silicone oil, methyl phenyl silicone oil, methyl hydrogen silicone oil, polyether-modified silicone oil, silicone polyester copolymer, amino-modified silicone oil,
Fluorosilicone oil, castor oil, oleic acid, linolenic acid, conjugated linoleic acid, soybean fatty acid, nuka fatty acid, coconut oil fatty acid, fatty acid triglyceride, higher fatty acid, soybean oil, coconut oil, linseed oil, tall oil, rapeseed oil, cottonseed oil, olive oil , Squalane, lanolin, hydrogenated oil, chlorinated paraffin, decalin, tetralin, liquid paraffin, isoper, hydrocarbon organic solvents such as petroleum, toluene, xylene, polyoxyethylene nonylphenyl ether, polyoxyethylene higher alcohol ether, polyoxyethylene Oleyl ether, sorbitan monolaurate, lauryl alcohol, myristyl alcohol, octanol, decanol, propyl caproate, hexyl caproate, ethyl caprylate, methyl oleate, etc. The present invention is not limited to these. Of these, kerosene is particularly preferable.

[Amine compounds]
The amine compound functions as a surfactant in the method for producing a silica sol according to the present invention. For this amine compound, a primary, secondary or tertiary amine compound or a quaternary ammonium salt can be used. For example, alkylamines such as ammonium, ethylamine, triethylamine, isopropylamine, n-propylamine and n-dodecylamine, aralkylamines such as benzylamine, alicyclic amines such as piperidine, alkanols such as monoethanolamine and triethanolamine An amine etc. can be mentioned. Of these, amine compounds having a function as a surfactant are particularly preferably used. Examples of such include n-dodecylamine.

  About the ratio of the surfactant other than the hydrocarbon oil, the amine compound, and the amine compound in the organic phase, usually 70 to 90% by mass of the hydrocarbon oil, 1 to 10% by mass of the amine compound, and the interface other than the amine compound. A range of 3-15% by weight of activator is preferred.

[Method for producing oil-in-water emulsion]
The method for producing an oil-in-water (O / W) type emulsion used in the method for producing a silica sol according to the present invention is not particularly limited, and a known emulsion production method is applied. The oil-in-water emulsion can be produced by a known method such as an emulsion polymerization method using a general stirring device such as a low shearing force stirrer or a pipeline mixer. In addition, it is recommended that the emulsification treatment is preferably performed with high-speed stirring in an emulsifier such as a pressure emulsifier such as a high-pressure homogenizer, an ultrasonic emulsifier, or a high-speed rotary emulsifier.

  Specifically, an amine compound and a surfactant other than the amine compound are added to the hydrocarbon oil, and the oil solution prepared by mixing is gradually added to the aqueous solution while using an emulsifier. And then emulsifying. The ratio of hydrocarbon oil, amine compound and surfactant in the oil-based solution is usually in the range of 70 to 90% by mass of hydrocarbon oil, 5 to 10% by mass of amine compound, and 3 to 15% by mass of surfactant. Is preferred.

  The aqueous solution is usually composed of water and a surfactant. About the quantity of surfactant added to an aqueous phase, the range of 3-15 mass% is preferable normally in an aqueous phase. If it is less than 3% by mass, it may be difficult to produce an emulsion. When it exceeds 15 mass%, the silica sol according to the present invention may not be easily generated.

  First, the oil-based solution is gradually added while stirring the aqueous solution with an emulsifier, and emulsification is performed. The emulsification treatment time is not particularly limited, but is performed in the range of 10 minutes to 3 hours.

Although it does not restrict | limit especially about the temperature of the solution at the time of performing an emulsification process, Usually, it carries out in the range of 20 to 40 degreeC.
About the addition amount of the said aqueous solution and the said oil-based solution, an organic phase is added with respect to 100 mass parts of aqueous phases by adding the range of 10-30 mass parts of oil-based solutions with respect to 100 mass parts of aqueous solutions. Of 10 to 30 parts by weight of an oil-in-water (O / W) emulsion. By adding tetraethyl orthosilicate to such an oil-in-water emulsion in a later step, a silica fine particle precursor that can finally become silica fine particles having needle-like protrusions on the surface can be obtained. When the ratio of the oil-based solution to 100 parts by mass of the aqueous solution is less than 10 parts by mass, acicular protrusions are hardly generated on the core particles. Moreover, even when it exceeds 30 mass parts, it becomes difficult to produce | generate an acicular processus | protrusion on a nucleus particle. About the ratio of the oil-based solution with respect to 100 mass parts of aqueous solutions, the range of 12-25 mass parts is recommended suitably. More preferably, the range of 15 to 20 parts by mass is recommended.

[Addition of tetraethylorthosilicate]
By adding tetraethyl orthosilicate continuously or intermittently to the oil-in-water (O / W) emulsion, a gel is formed. (Hereinafter, this gel-like material may be referred to as “silica fine particle precursor”.) The gel-like material (silica fine particle precursor) is subjected to mechanical impact in a later step to have needle-like protrusions. By producing silica fine particles, the silica sol according to the present invention can be obtained.

  About the temperature range of an oil-in-water type (O / W) emulsion at the time of adding tetraethyl orthosilicate, the range of 10-60 degreeC is preferable. When the temperature is lower than 10 ° C., the generation efficiency of the silica fine particle precursor is lowered. Heating at a temperature exceeding 60 ° C. is not necessarily required. About the temperature range of an oil-in-water (O / W) emulsion, the range of 15-50 degreeC is recommended suitably. More preferably, the range of 18 to 48 ° C. is recommended.

  As for the addition of tetraethyl orthosilicate to the oil-in-water emulsion, it is necessary to add tetraethyl orthosilicate continuously or intermittently to the oil-in-water emulsion. “Continuous” means that the entire amount added is not added all at once in a short time, but is continuously added over a certain period of time without being substantially interrupted. Intermittent means that the total amount added is divided into several times and added in small portions over a certain period of time. The addition time is preferably 1 to 20 hours. More preferably, a range of 2 to 15 hours is recommended.

  Although the amount of tetraethyl orthosilicate added is not particularly limited, it can be usually prepared by adding 1 to 10 parts by mass with respect to 100 parts by mass of the oil-in-water emulsion. preferable.

  Tetraethyl orthosilicate may be added after dilution with a solvent, or may be added without dilution. When the solvent is diluted, it is adjusted to 1 to 30% by mass with a solvent such as ethanol and added. Moreover, when performing the addition operation of the tetraethyl orthosilicate to an oil-in-water emulsion, it is preferable to carry out in inert atmosphere, such as dried air, nitrogen, and argon.

[Aging]
The silica fine particle precursor solution after the addition of tetraethyl orthosilicate is preferably aged at a temperature of 20 to 98 ° C. for 1 hour to 200 hours. By aging, the skeleton stability of the silica fine particles is improved, and a silica sol having practical strength can be obtained.

When the aging temperature is less than 20 ° C., the reaction of unreacted components may not proceed, and may not contribute to the stability of the particle skeleton, which is not desirable. Aging at temperatures above 98 ° C. is not necessarily required. About aging temperature, the range of 18-50 degreeC is recommended suitably.

  With respect to the aging time, if it is less than 1 hour, the reaction of the unreacted components may not sufficiently proceed. For aging over 200 hours, it is not necessarily required. About the time to age | cure | ripen, the range for 10 to 100 hours is recommended suitably.

[Addition of organic solvent]
For the silica fine particle precursor solution that has been aged, the emulsion is desirably destroyed by adding an organic solvent to promote oil-water separation.

  The type of organic solvent used here is not particularly limited, but usually the alcohols or the ketones are used. The addition amount of the organic solvent is not particularly limited, but an organic solvent equivalent to the solution of the silica fine particle precursor is usually added.

[Washing]
It is preferable to wash the silica fine particle precursor solution after breaking the emulsion of the silica fine particle precursor solution by adding an organic solvent. This washing is preferably performed by centrifugation. About centrifugation processing, it is desirable to repeat about 2 to 10 times if desired. It should be noted that an organic solvent may be appropriately added when repeating the centrifugation process.

[Formation of silica fine particles]
The silica fine particles are generated by applying a mechanical impact to the silica fine particle precursor after the washing step. The method for applying the mechanical impact is not particularly limited as long as the silica fine particles having the needle-like projections can be generated, and examples thereof include ultrasonic treatment. By applying such a mechanical impact, a silica sol in which silica fine particles having needle-like protrusions on the surface are dispersed in a dispersion medium can be obtained from a gel-like silica fine particle precursor. When ultrasonic treatment is used as a method of applying a mechanical impact, silica fine particles having needle-like projections can be efficiently obtained and dispersion treatment can be performed simultaneously, so that a silica sol having a good dispersion state can be obtained. There is an advantage that can be.

  For ultrasonic treatment, specifically, an approximately equal amount of an organic solvent is added to the washed silica fine particle precursor (gel-like material), and the ultrasonic treatment is usually performed in an ultrasonic bath. The output and frequency of the ultrasonic wave are not particularly limited as long as the silica fine particle precursor itself is separated and silica fine particles having needle-like protrusions are generated, and an ultrasonic wave having a commercially available ultrasonic processing function. Any disperser can be used.

[Preferred embodiment 1 of the present invention]
A silica sol having the following features 1) to 5) and having silica fine particles having needle-like protrusions on the surface thereof dispersed in a dispersion medium, wherein the solid content concentration is in the range of 1 to 50% by mass.
1) Range of average particle diameter (D1) measured by image analysis method of 10 to 100 nm 2) Range of aspect ratio of 0.7 to 1.0 3) Range of specific surface area of 300 to 700 m ² / g 4) Range of apparent bulk density (ABD) of 0.05 to 0.15 g / ml 5) Range of variation coefficient of particle diameter of 10.0 to 40.0%

[Preferred embodiment 2 of the present invention]
A silica sol having the following features 1) to 5) and having silica fine particles having needle-like protrusions on the surface thereof dispersed in a dispersion medium, wherein the solid content concentration is in the range of 1 to 50% by mass.
1) Average particle diameter (D1) measured by image analysis method is in the range of 15 to 70 nm 2) Aspect ratio is in the range of 0.8 to 1.0 3) Specific surface area is in the range of 400 to 600 m ² / g 4) Range of apparent bulk density (ABD) of 0.08 to 0.13 g / ml 5) Range of variation coefficient of particle diameter of 12 to 30%

[Preferred embodiment 3 of the present invention]
A silica sol having the following features 1) to 5) and having silica fine particles having needle-like protrusions on the surface thereof dispersed in a dispersion medium, wherein the solid content concentration is in the range of 1 to 50% by mass.
1) Average particle diameter (D1) measured by image analysis method is in the range of 18-30 nm 2) Aspect ratio is in the range of 0.9-1.0 3) Specific surface area is in the range of 400-600 m ² / g 4) The apparent bulk density (ABD) is in the range of 0.08 to 0.13 g / ml 5) The variation coefficient of the particle diameter is in the range of 14 to 25%

[Preferred embodiment 4 of the present invention]
The method for producing a silica sol according to claim 1, comprising the following [1] to [5].
[1] 100 parts by weight of an aqueous solution containing water and a surfactant and 10 to 30 parts by weight of an oily solution containing a surfactant other than kerosene, an amine compound and an amine compound are mixed and emulsified. [2] Step of preparing silica fine particle precursor solution by maintaining an oil-in-water (O / W) emulsion in a temperature range of 10 to 60 ° C. and continuously or intermittently adding tetraethyl orthosilicate A step of aging the fine particle precursor solution at 20 to 98 ° C. [3] A step of breaking the emulsion by adding an organic solvent to the silica fine particle precursor solution after completion of the aging [4] Following the previous step Step 5 of washing silica fine particle precursor solution by centrifugal separation treatment [5] Following the previous step, the silica fine particle precursor is subjected to a dispersion treatment by ultrasonic treatment to obtain a silica sol. Preparing

(Example)
[Measurement and analysis method]
[1] Average particle size measurement by image analysis method Arbitrary image projection in a photograph obtained by photographing a sample at a magnification of 250,000 using a transmission electron microscope (model number H-800, manufactured by Hitachi, Ltd.) About 50 particles, the longest diameter was measured, respectively, the average value was calculated, and the value was taken as the average particle diameter.

[2] Specific surface area measurement by the BET method 50 ml of silica sol was adjusted to pH 3.5 with HNO ₃ , 40 ml of 1-propanol was added, and the sample dried at 110 ° C. for 16 hours was pulverized in a mortar and then 500 ° C. in a muffle furnace. The sample was baked for 1 hour to obtain a measurement sample. And the specific surface area was computed by the BET 1-point method from the adsorption amount of nitrogen using the BET method by nitrogen adsorption | suction using the specific surface area measuring apparatus (The product made from Yuasa Ionics, model number multisorb 12). Specifically, 0.5 g of a sample is taken in a measurement cell, degassed for 20 minutes at 300 ° C. in a mixed gas stream of nitrogen 30 v% / helium 70 v%, and then the sample is liquidized in the mixed gas stream. Keep nitrogen temperature and allow nitrogen to equilibrate to sample. Next, the sample temperature was gradually raised to room temperature while flowing the mixed gas, the amount of nitrogen desorbed during that time was detected, and the specific surface area of the silica sol was calculated using a calibration curve prepared in advance.

[3] Apparent bulk density [ABD] (g / cm ³ )
The silica sol is pretreated and calcined at 500 ° C. for 1 hour, and then 100.0 g of a sample cooled in a desiccator and cooled to room temperature is collected and transferred to a 250 ml graduated cylinder. Cover the graduated cylinder gently and repeat it upside down, then let it sit and read the sample volume. This operation was repeated 5 times, and the average capacity (Vcm ³ ) of 5 times of data was obtained and calculated by the following formula.
ABD = 100.0 (g) / V (cm ³ )

[4] Calculation of coefficient of variation of particle diameter Spherical shape in a photographic projection obtained by photographing a sample silica sol at a magnification of 250,000 to 500,000 with a transmission electron microscope (H-800, manufactured by Hitachi, Ltd.) A point that divides the longest diameter of the silica fine particle into two equal parts is a central point of the spherical silica fine particle, and one direction on the longest diameter from the central point is an angle of 0 degrees, and 10 degrees from there to 0 degrees to 180 degrees Measure the radius. And the average value and standard deviation of a radius are calculated from the value. Furthermore, the coefficient of variation (relative standard deviation) of the particle diameter was determined by dividing the standard deviation by the average value. This measurement and calculation were performed on arbitrary 50 particles, and the average value of the coefficient of variation in particle diameter was taken, and the value was taken as the coefficient of variation (CV value) in particle diameter.

[5] Aspect ratio of silica fine particles (minor axis / major axis ratio)
Using a transmission electron microscope (model number H-800, manufactured by Hitachi, Ltd.), for each of 50 arbitrary particles in a photographic projection obtained by photographing a sample at a magnification of 250,000 times, The diameter perpendicular to the center point was measured, the aspect ratio (minor axis / major axis ratio) was calculated, and the average value of 50 particles was taken as the aspect ratio (minor axis / major axis ratio).

[6] n-dodecylamine such as surfactant used in Examples (manufactured by Kanto Chemical Co., Inc.)
Polyoxyethylene sorbitan monooleate (Kanto Chemical Co., Inc., Twin 80)
Sorbitan monooleate (manufactured by Kanto Chemical Co., Span 80)
N-Hexadecyltrimethylammonium bromide (CTAB, manufactured by Kanto Chemical Co., Inc.)
Polyoxyethylene octyl phenyl ether (N-862, manufactured by Nippon Emulsifier Co., Ltd.)
Hexane (Kanto Chemical Co., Ltd.)
Kerosene (Kanto Chemical Co., Ltd.)

[Preparation of O / W emulsion]
After putting 2500 ml of distilled water into a 7 L reaction vessel set in a high-temperature tank set at 25 ° C., 185 g of cetyltrimethylammonium bromide (CTAB) was added and stirred at a rotational speed of 400 rpm to obtain an aqueous solution. Was prepared.

An oil-based solution was prepared by dissolving 7.5 g of n-dodecylamine and 40.25 g of polyoxyethylene octylphenyl ether in 400 g of kerosene.
Next, while stirring the aqueous solution at 15 Krpm with a disperser HG92 (manufactured by SMT), the oil-based solution was gradually added and emulsified for 30 minutes to prepare 3132 g of an O / W emulsion.

(Preparation of silica sol)
While maintaining 3132 g of the O / W emulsion at 25 ° C. and stirring at a stirring speed of 200 rpm, 108.95 g of tetraethyl orthosilicate (TEOS) was continuously added over 7.5 hours using an addition pump. did. And it matured at 25 degreeC over 72 hours in the stationary state.

Further, 3000 ml of ethanol was added to break the emulsion, followed by centrifugation four times to separate the gel. This gel-like material is washed with ethanol to remove the remaining surfactant, catalyst, kerosene, etc., and then the same amount of ethanol as the washed gel-like material is added, and an ultrasonic bath (ultrasonic output; over 150 W) A mechanical impact was applied using a sound wave frequency (19.5 kHz) to obtain a silica sol in which silica fine particles were dispersed in ethanol. This silica sol was made into an aqueous solvent silica sol (solid content concentration 20 mass%) by ultrafiltration. The production conditions of the silica sol are shown in Tables 1 and 2, and the properties of the silica sol are shown in Table 3. A scanning electron micrograph (magnification 250,000 times) of this silica sol is shown in FIG.

[Preparation of O / W emulsion]
After putting 2500 ml of distilled water into a 7 L reaction vessel set in a high-temperature tank set at 25 ° C., 185 g of cetyltrimethylammonium bromide (CTAB) was added and stirred at a rotational speed of 400 rpm to obtain an aqueous solution. Was prepared.

An oil-based solution was prepared by dissolving 7.5 g of n-dodecylamine and 40.25 g of polyoxyethylene octylphenyl ether in 400 g of kerosene.
Next, while stirring the aqueous solution at 15 Krpm with a disperser HG92 (manufactured by SMT), the oil-based solution was gradually added and emulsified for 30 minutes to prepare 3132 g of an O / W emulsion.

(Preparation of silica sol)
While maintaining 3132 g of the O / W emulsion at 25 ° C. and stirring at a stirring speed of 200 rpm, 108.95 g of tetraethylorthosilicate (TEOS) was continuously added over 3 hours using an addition pump. And it matured at 25 degreeC over 72 hours in the stationary state.

  Further, 3000 ml of ethanol was added to break the emulsion, followed by centrifugation four times to separate the gel. This gel-like material is washed with ethanol to remove the remaining surfactant, catalyst, kerosene, etc., and then the same amount of ethanol as the washed gel-like material is added, and an ultrasonic bath (ultrasonic output; over 150 W) A mechanical impact was applied using a sound wave frequency (19.5 kHz) to obtain a silica sol in which silica fine particles were dispersed in ethanol. This silica sol was made into an aqueous solvent silica sol (solid content concentration 20 mass%) by ultrafiltration. The production conditions of the silica sol are shown in Tables 1 and 2, and the properties of the silica sol are shown in Table 3.

[Comparative Example 1]
[Preparation of W / O type emulsion]
200 ml of distilled water is put into a 5 L reaction vessel set in a high-temperature tank set at 25 ° C., and then 14.8 g of cetyltrimethylammonium bromide (CTAB) is added and stirred at a rotational speed of 400 rpm. To prepare an aqueous solution.

An oil-based solution was prepared by dissolving 15 g of n-dodecylamine and 80.5 g of polyoxyethylene octylphenyl ether in 800 g of kerosene.
Next, while the oil-based solution was stirred at 15 Krpm with a disperser HG92 (manufactured by SMT), the aqueous solution was gradually added and emulsified for 30 minutes to prepare 1110 g of a W / O emulsion.

(Preparation of silica sol)
While maintaining 1110 g of the W / O type emulsion at 25 ° C. and stirring at a stirring speed of 200 rpm, 186 g of tetraethyl orthosilicate (TEOS) was continuously added over 7.5 hours using an addition pump. . And it matured at 25 degreeC over 72 hours in the stationary state.

  Then, 2000 ml of ethanol was further added to break the emulsion, followed by centrifugation four times to separate the gel. This gel-like material is washed with ethanol to remove the remaining surfactant, catalyst, kerosene, etc., and then the same amount of ethanol as the washed gel-like material is added, and an ultrasonic bath (ultrasonic output; over 150 W) A mechanical impact was applied using a sound wave frequency (19.5 kHz) to obtain a silica sol in which silica fine particles were dispersed in ethanol. This silica sol was made into an aqueous solvent silica sol (solid content concentration 20 mass%) by ultrafiltration. The production conditions for the silica sol are shown in Tables 1 and 2, and the properties of the silica sol are shown in Table 3.

[Comparative Example 2]
[Preparation of O / W emulsion]
After putting 2500 ml of distilled water into a 5 L reaction vessel set in a high temperature tank set at 25 ° C., 185 g of cetyltrimethylammonium bromide (CTAB) was added and stirred at a rotational speed of 400 rpm to prepare an aqueous solution. Was prepared.

An oil-based solution was prepared by dissolving 8.13 g of polyoxyethylene sorbitan monooleate and 4.078 g of sorbitan monooleate in 395 g of hexane.
Next, while stirring the aqueous solution at 15 Krpm with a disperser HG92 (manufactured by SMT), the oil-based solution was gradually added and emulsified for 30 minutes to prepare 3132 g of an O / W emulsion.

(Preparation of silica sol)
While maintaining 3025 g of the O / W type emulsion at 25 ° C. and stirring at a stirring speed of 200 rpm, 108.95 g of tetraethyl orthosilicate (TEOS) was continuously added over 3 hours using an addition pump. . And it matured at 25 degreeC over 72 hours in the stationary state.

  Further, 3000 ml of ethanol was added to break the emulsion, followed by centrifugation four times to separate the gel. This gel-like material is washed with ethanol to remove the remaining surfactant, catalyst, kerosene, etc., and then the same amount of ethanol as the washed gel-like material is added, and an ultrasonic bath (ultrasonic output; over 150 W) A mechanical impact was applied using a sound wave frequency (19.5 kHz) to obtain a silica sol in which silica fine particles were dispersed in ethanol. This silica sol was made into an aqueous solvent silica sol (solid content concentration 20 mass%) by ultrafiltration. The production conditions of the silica sol are shown in Tables 1 and 2, and the properties of the silica sol are shown in Table 3.

  The silica sol of the present invention is expected to exhibit a new effect derived from its unique structure (acicular protrusions) in many applications. In the field of utilizing the silica sol of the present invention as a filler or additive, specifically, a new function may be imparted as an additive to a resin additive, paint additive or film forming agent (coating agent). Be expected. In addition, examples of fields in which the silica fine particles according to the present invention are used as carriers include catalysts and antibacterial agents. In addition, it is expected to show excellent effects in applications such as cosmetics, abrasives, or conductivity imparting agents.

  According to the production method of the present invention, tetraethyl orthosilicate is continuously added to a predetermined water-in-oil (O / W) emulsion prepared from 100 parts by weight of an aqueous solution and 10 to 30 parts by weight of an oil-based solution. Alternatively, a silica sol in which silica fine particles having needle-like protrusions on the surface are dispersed in a dispersion medium can be produced by intermittent addition.

1 is a scanning electron micrograph (magnification 250,000 times) of the silica sol produced in Example 1. FIG.

Claims (9)

The average particle diameter (D1) measured by the image analysis method is in the range of 10 to 100 nm, the specific surface area is in the range of 300 to 700 m ² / g, and the apparent bulk density (ABD) is 0.05 to 0.
. A silica sol obtained by dispersing silica fine particles in a range of 15 g / ml in a dispersion medium.   2. The silica sol according to claim 1, wherein the silica fine particles have an aspect ratio in the range of 0.7 to 1.0 and a particle diameter variation coefficient in the range of 10.0 to 40.0%.   The silica sol according to claim 1 or 2, wherein the silica fine particles have needle-like protrusions.   The silica sol according to any one of claims 1 to 3, wherein the solid content concentration of the silica sol is in the range of 1 to 50 mass%.   100 parts by weight of an aqueous solution containing water and a surfactant and 10 to 30 parts by weight of an oil-based solution containing a surfactant other than hydrocarbon oil, an amine compound and an amine compound are mixed and emulsified. By maintaining the oil-in-water type (O / W) emulsion in the temperature range of 10 to 60 ° C., and adding tetraethyl orthosilicate continuously or intermittently to the oil-in-water type (O / W) emulsion, The method for producing a silica sol according to any one of claims 1 to 4, wherein a solution of the precursor is prepared, and the silica fine particle precursor is further subjected to mechanical impact to produce silica fine particles. The method for producing a silica sol according to any one of claims 1 to 4, comprising the following [1] to [5].
[1] 100 parts by mass of an aqueous solution containing water and a surfactant and 10 to 30 parts by mass of an oil-based solution containing a surfactant other than hydrocarbon oil, an amine compound, and an amine compound are mixed and emulsified. The oil-in-water type (O / W) emulsion thus obtained is kept in the temperature range of 10 to 60 ° C., and tetraethyl orthosilicate is continuously or intermittently added to the oil-in-water type (O / W) emulsion, Step [2] for preparing a fine particle precursor solution [2] Step for aging the silica fine particle precursor solution at 20 to 98 ° C. [3] After completion of the aging, an organic solvent is added to the silica fine particle precursor solution. Step [4] Step of washing the emulsion of the silica fine particle precursor [5] Subsequent to the previous step [5] Step of washing the solution of the silica fine particle precursor And to generate fine particles, preparing a silica sol   The method for producing a silica sol according to claim 6, wherein the silica fine particle precursor is washed by a centrifugal separation process.   The method for producing a silica sol according to any one of claims 5 to 7, wherein the mechanical impact is applied by ultrasonic treatment.   The method for producing a silica sol according to any one of claims 5 to 8, wherein the hydrocarbon oil is kerosene.