Strontium titanate fine particles

Abstract

To provide strontium titanate fine particles having a small average particle diameter and excellent in crystallinity and dispersibility.SOLUTION: Strontium titanate fine particles are spherical and have an average particle diameter (D50) of 10 nm to 30 nm as measured by a laser diffraction / scattering type particle size distribution measuring device.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to strontium titanate fine particles. [Background technology]

[0002] Strontium titanate (SrTiO3) has dielectric properties, thermoelectric properties, photocatalytic activity, and a high refractive index, and is therefore expected to be used in a variety of applications as a functional material.

[0003] For example, Patent Document 1 discloses that strontium titanate having an average particle size of 50 nm or less, an average aspect ratio of 1.0 to 1.2, and a refractive index of 1.8 to 2.6 has a high refractive index. Patent Document 1 also discloses that when strontium titanate is used as a component that imparts a high refractive index, it needs to have high dispersibility so that it does not aggregate in a coating film. Furthermore, when used as such a functional material, it is necessary for the material to have crystallinity that allows high purity crystals to be obtained. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2011 / 004750 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide strontium titanate fine particles having a small average particle size and excellent crystallinity and dispersibility.

[0006] The present inventors have conducted extensive research into strontium titanate microparticles and have found that strontium titanate microparticles containing a specific amount of hydrazine or hydrazide compound and produced by reacting an organic titanate ester with a strontium compound under specified conditions (temperature and reaction time) have a small average particle size and excellent dispersibility. [Means for solving the problem]

[0007] The present invention relates to strontium titanate microparticles that are spherical and have an average particle size (D50) of 10 nm to 30 nm as measured by a laser diffraction / scattering particle size distribution analyzer. The strontium titanate microparticles of the present invention do not become cloudy when 50 mg of the strontium titanate is dissolved in 50 mL of methanol. Furthermore, the strontium titanate microparticles of the present invention preferably have a ratio of the crystallite diameter calculated by an X-ray diffractometer to the particle diameter observed by a transmission electron microscope (particle diameter observed by a transmission electron microscope / crystallite diameter calculated by an X-ray diffractometer) of 0.9 to 1.0. Furthermore, the strontium titanate microparticles of the present invention preferably have a hydrazine or hydrazide compound content of 0.1% by mass to 60% by mass relative to the strontium titanate microparticles. The strontium titanate microparticles of the present invention preferably contain an aminosilane compound, and the content of the aminosilane compound relative to the hydrazine or hydrazide compound is preferably 0.003 to 0.025 in terms of molar ratio. The strontium titanate microparticles of the present invention preferably have a circularity of 0.900 to 1.000. [Effects of the Invention]

[0008] It is possible to provide strontium titanate microparticles that have a small average particle size and excellent crystallinity and dispersibility. DETAILED DESCRIPTION OF THE INVENTION

[0009] (Strontium titanate fine particles) The strontium titanate microparticles of the present invention are spherical and have an average particle size (D50) of 10 nm to 30 nm as measured by a laser diffraction / scattering particle size distribution analyzer. The strontium titanate microparticles of the present invention have a small average particle size (D50) and are excellent in crystallinity and dispersibility.

[0010] The strontium titanate microparticles of the present invention have a spherical particle shape. Here, the term "spherical" refers not only to a perfect sphere, but also to ellipsoids, cylinders, and rounded cylinders (cylinders with rounded corners). Specifically, the circularity of the strontium titanate fine particles is 0.900 to 1.000. The circularity is calculated as follows: where S is the area of ​​a particle in an image taken with a transmission electron microscope and L is the perimeter. 2 It can be calculated as follows. The shape of the strontium titanate microparticles can be confirmed by observing them with a transmission electron microscope (JEOL Ltd., "JEM-1011") at a magnification of 300,000 times. The circularity is an average value obtained by excluding particles having a specific shape that is clearly different from the spherical shape, from among the particles that appear in an image taken by a transmission electron microscope.

[0011] The strontium titanate microparticles of the present invention have an average particle size of 10 nm to 30 nm. The average particle size is preferably 14 nm to 25 nm. By having such an average particle size, it is possible to obtain an agent having excellent dispersibility. The above average particle size refers to the average particle size (D50) measured by dissolving strontium titanate microparticles in methanol to obtain a dispersion, placing the obtained dispersion in a measurement cell, and measuring it with a laser diffraction / scattering particle size distribution analyzer (Microtrac MT3300EXII, manufactured by Nikkiso Co., Ltd.).

[0012] The strontium titanate fine particles of the present invention have excellent dispersibility. Here, dispersibility can be determined by whether or not cloudiness occurs when 50 mg of strontium titanate microparticles are dissolved in 50 mL of methanol to obtain a dispersion, the resulting dispersion is placed in a screw cap bottle, black paper is placed on the back, and the state of the dispersion is visually confirmed. If cloudiness does not occur, it can be evaluated as having excellent dispersibility, and can be suitably applied to, for example, high refractive index materials, etc.

[0013] The strontium titanate fine particles of the present invention preferably have good crystallinity. The crystallinity of the strontium titanate microparticles is judged to be good if the crystallite diameter calculated by X-ray diffractometer is the same as the particle diameter observed by transmission electron microscope [particle diameter ratio (particle diameter observed by transmission electron microscope / crystallite diameter calculated by X-ray diffractometer) is 0.9 to 1.0], and is judged to be poor if the ratio is smaller or if no crystals are observed.

[0014] The strontium titanate microparticles of the present invention preferably contain 0.1% to 60% by mass of the hydrazine or hydrazide compound, and more preferably 1% to 30% by mass, based on the strontium titanate microparticles. Such a content will result in good dispersibility.

[0015] The strontium titanate microparticles of the present invention preferably contain an aminosilane compound, and the content of the hydrazine or hydrazide compound is preferably 0.003 to 0.025 in terms of molar ratio (aminosilane compound / hydrazine or hydrazide compound) relative to the strontium titanate microparticles. By including the aminosilane compound in the above range, the average particle size of the strontium titanate fine particles can be suitably controlled.

[0016] The content of the aminosilane compound is more preferably 0.004 to 0.019, and even more preferably 0.007 to 0.015, in terms of molar ratio relative to the hydrazine or hydrazide compound.

[0017] (Method of producing strontium titanate microparticles) The strontium titanate microparticles of the present invention can be produced, for example, by the following method. The method includes a reaction step of reacting an organic titanate ester with a strontium compound in the presence of a hydrazine or hydrazide compound under conditions of a pH of 12 or higher, a reaction temperature of 150°C to 250°C, and a reaction time of 0.5 hours to 2 hours, wherein the molar ratio of the hydrazine or hydrazide compound to the organic titanate ester (hydrazine or hydrazide compound / organic titanate ester) is 10 to 75.

[0018] (organic titanate ester) Examples of the organic titanate ester include tetraethyl titanate, tetraisopropyl titanate, tetra-normal-butyl titanate, butyl titanate dimer, tetra(2-ethylhexyl) titanate, and polymers thereof; titanium acetyl titanate, polytitanium acetylacetonate, titanium octylglycinate, titanium lactate, titanium lactate ethyl ester, titanium triethanolamine, and titanium phosphate complexes and other titanium chelate compounds. Among these, titanium lactate is preferred from the viewpoint of hydrophilicity.

[0019] (hydrazine or hydrazide compounds) Examples of the hydrazide compounds include 1-monomethylhydrazine, 1,1-dimethylhydrazine, 1-ethyl-2-methylhydrazine, adipic acid dihydrazide, oxalic acid dihydrazide, malonic acid dihydrazide, succinic acid dihydrazide, glutaric acid dihydrazide, isophthalic acid dihydrazide, sebacic acid dihydrazide, maleic acid dihydrazide, fumaric acid dihydrazide, and itaconic acid dihydrazide. Among these, hydrazine is preferred because it is relatively easy to handle and has an excellent effect of controlling the shape of the resulting strontium titanate microparticles. The hydrazine or hydrazide compound may be in a hydrogenated state.

[0020] The content of the hydrazine or hydrazide compound is 10 to 75, preferably 30 to 65, in terms of a molar ratio (hydrazine or hydrazide compound / organic titanate ester) relative to the organic titanate ester. By setting the content within the above range, the shape of the obtained strontium titanate microparticles can be suitably controlled.

[0021] (strontium compounds) Examples of the strontium compound include strontium nitrate, strontium hydroxide, strontium carbonate, strontium peroxide, strontium formate, strontium acetate, strontium lactate, strontium oxalate, strontium chloride, strontium fluoride, strontium iodide, strontium bromide, strontium chlorate, strontium iodate, strontium perchlorate, etc. These may be used as hydrates. Among these, from the viewpoint of hydrophilicity, at least one selected from strontium acetate and strontium formate is preferred, and strontium acetate is more preferred.

[0022] The content of the strontium compound is preferably such that the molar ratio (strontium compound / organic titanate) to the organic titanate is 1.0 or more. By setting the content within the above range, the progress of crystallization can be suitably controlled. Moreover, from the viewpoint of reducing raw material costs, the molar ratio (strontium compound / organic titanate ester) is more preferably 2.0 or less.

[0023] (aminosilane compound) Examples of the aminosilane compound include 3-aminopropyltrimethoxysilane, 3-aminopropylethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, and N-phenyl-3-aminopropyltrimethoxysilane. Of these, 3-aminopropyltriethoxysilane is preferred.

[0024] (solvent) As the solvent used in the method for producing the strontium titanate microparticles, water is preferably used. The solvent preferably contains a polyhydric alcohol.

[0025] Examples of the polyhydric alcohol include dihydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, butanediol, pentanediol, hexanediol, heptanediol, nonanediol, decanediol, and neopentyl glycol, and trihydric or higher polyhydric alcohols such as glycerin, trimethylolpropane, and pentaerythritol. Among these, from the viewpoint of adjusting the particle size of the resulting strontium titanate microparticles and maintaining favorable dispersibility in the reaction system, at least one selected from ethylene glycol, propylene glycol, diethylene glycol, and 1,3-propanediol is preferred, and ethylene glycol is more preferred.

[0026] The content of the polyhydric alcohol is preferably 1 to 20% by mass, more preferably 3 to 15% by mass, and even more preferably 7 to 12% by mass, based on the total amount of the solvent.

[0027] (pH adjuster) In the method for producing strontium titanate microparticles, it is preferable to adjust the pH using a pH adjuster. Examples of the pH adjuster include lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, and ammonium hydroxide. Among these, potassium hydroxide is preferred from the viewpoint of solubility in the above solvent.

[0028] When adjusting the pH, it is preferable to set the pH to 12 or higher from the viewpoint of controlling the reaction rate and the shape of the resulting strontium titanate microparticles. The pH is more preferably 12.5 or higher, even more preferably 13 or higher, and particularly preferably 13.5 or higher. The content of the pH adjuster is not limited, and may be added appropriately depending on the desired pH.

[0029] (others) In the above method for producing strontium titanate microparticles, it is not necessary to add an amphiphilic compound. In conventional methods for producing strontium titanate microparticles, the particle size and shape are precisely controlled by carrying out the reaction in the presence of an amphiphilic compound, thereby imparting particle dispersibility. On the other hand, if the amphiphilic compound is added in the method for producing strontium titanate microparticles, the compound will be dispersed non-uniformly in the system, resulting in an increase in the average particle size of the resulting strontium titanate microparticles. Examples of the amphiphilic compound include saturated fatty acids such as propionic acid, butyric acid, valeric acid, caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, and lignoceric acid; and unsaturated fatty acids such as α-linolenic acid, stearidonic acid, eicosapentaenoic acid, docosahexaenoic acid, linoleic acid, γ-linolenic acid, dihomo-γ-linolenic acid, arachidonic acid, oleic acid, elaidic acid, erucic acid, and nervonic acid.

[0030] The method for producing the strontium titanate microparticles preferably includes, for example, a mixing step of mixing an organic titanate ester with a hydrazine or hydrazide compound in a solvent to obtain a mixed solution, an adjustment step of adjusting the pH of the mixed solution to 12 or higher, and the reaction step.

[0031] The mixing step is a step of adding an organic titanate ester and a hydrazine or hydrazide compound to a solvent. It is presumed that the mixing step causes hydrazine to be coordinated to the organic titanate ester. In the mixing step, the method for adding the various materials is not particularly limited, and the materials may be added, stirred, or the like by a known method.

[0032] In the preparation step, the pH is adjusted, which makes it possible to suitably control the reaction rate and the shape of the resulting strontium titanate microparticles. It is also believed that the mixing step controls the increase in the average particle size of the organic titanate ester coordinated with hydrazine, and as a result, the average particle size of the resulting strontium titanate microparticles can be controlled within a suitable range. The pH is preferably adjusted using the above-mentioned pH adjuster. When the aminosilane compound is added, it is preferably added together with the pH adjuster in the adjustment step.

[0033] The crystal growth of strontium titanate fine particles is accelerated in the presence of a large amount of water, while the hydrophobicity of the solvent increases, accelerating aggregation due to the hydrophilic surface of the strontium titanate fine particles. On the other hand, the polyhydric alcohol is preferably added in the preparation step because it is hydrophilic and has the effect of suppressing crystal growth. In the preparation process, the method for adding the various materials is not particularly limited, and the materials may be added, stirred, or the like by a known method.

[0034] In the reaction step, it is preferable to react the organic titanate ester with the strontium compound under conditions of a pH of 12 or higher, a reaction temperature of 150°C to 250°C, and a reaction time of 0.5 hours to 2 hours.

[0035] The reaction temperature is preferably 150°C or higher and 250°C or lower. If the reaction temperature is below 150°C, the reaction may not proceed and the desired strontium titanate microparticles may not be obtained. If the reaction temperature exceeds 250°C, the reaction efficiency may decrease and the resulting strontium titanate particles may become larger and less dispersible. The reaction temperature is preferably 180 to 250°C, and more preferably 200 to 240°C.

[0036] The reaction time is preferably 0.5 hours or more and 2 hours or less. If the reaction time is less than 0.5 hours, the reaction may not proceed and the desired strontium titanate microparticles may not be obtained. If the reaction time exceeds 2 hours, the reaction efficiency may decrease and the resulting strontium titanate particles may become larger and less dispersible. The reaction time is preferably 1 to 2 hours.

[0037] The pressure during the reaction may be, for example, about 2 to 5 MPa, and it is not necessary to apply a pressure exceeding 10 MPa.

[0038] The method for carrying out the reaction step is not particularly limited, and any method may be used as long as it satisfies the above conditions. For example, a pressure reactor or the like can be used. [Example]

[0039] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, "%" means "% by mass" and "parts" means "parts by mass."

[0040] The materials used in the examples and comparative examples are as follows. (organic titanate ester) Titanium lactate (Orgatics TC-310, component concentration 44 wt%, manufactured by Matsumoto Fine Chemical Co., Ltd.) Titanium phosphate complex (Orgatics TC-1040, component concentration 75 wt%, manufactured by Matsumoto Fine Chemical Co., Ltd.) (hydrazine or hydrazide compounds) Hydrazine hydrate (Nippon Carbide Industries Co., Ltd.) (strontium compounds) Strontium acetate 0.5 hydrate (Fujifilm Wako Pure Chemical Industries, Ltd.) Strontium formate dihydrate (solvent) ethylene glycol Propylene glycol Purified water (ion-exchanged water) (pH adjuster) Potassium hydroxide (aminosilane compound) 3-Aminopropyltriethoxysilane (Tokyo Chemical Industry Co., Ltd.)

[0041] Example 1 0.584 g of titanium lactate (Orgatix TC-310, component concentration 44 wt%, Matsumoto Fine Chemical Co., Ltd.) was mixed with 3 g of purified water and 3.0 g of hydrazine hydrate (Nippon Carbide Industries Co., Ltd.) to prepare a yellow, transparent solution. Next, a solution prepared from 0.48 g of potassium hydroxide, 0.432 g of ethylene glycol, and 5.088 g of purified water was added to the above yellow transparent solution to obtain a cloudy white solution. Then, 0.429 g of strontium acetate 0.5-hydrate (Fujifilm Wako Pure Chemical Industries, Ltd.) was added to the resulting cloudy solution and stirred at room temperature for 30 minutes to obtain a clear solution. The resulting clear solution was placed in a pressure reactor and reacted at 230°C for 1 hour. The pressure was approximately 2.8 MPa. The solution containing the reactants was centrifuged (model name SIGMA 3-30KS, conditions 15,000 rpm, 5 minutes) to separate and purify the unreacted material by settling the fine particles. A re-dispersed solution of the fine particles was prepared in purified water, and the centrifugal separation to settle the fine particles was repeated three times to complete the separation and purification. The resulting fine particles were collected and observed with an X-ray diffractometer (Rigaku Corporation, "MiniFlex600-C"), and were confirmed to be fine particles of strontium titanate.

[0042] (Examples 2 to 8, Comparative Examples 1 to 6) Strontium titanate microparticles were produced in the same manner as in Example 1, except that the blending amounts of various materials and the reaction conditions were changed as shown in Table 1. In Examples 5 and 6, 3-aminopropyltriethoxysilane was added together with the pH adjuster (potassium hydroxide). The obtained fine particles were collected and observed with an X-ray diffractometer (Rigaku Corporation, "MiniFlex600-C"), and it was confirmed that in Examples 2 to 8 and Comparative Example 4, the fine particles were strontium titanate fine particles. On the other hand, in Comparative Examples 1 to 3, 5 and 6, the reaction did not proceed and strontium titanate was not obtained.

[0043] <Evaluation method> (particle shape) The strontium titanate microparticles obtained in the examples and comparative examples were collected and observed under a transmission electron microscope (Hitachi High-Technologies Corporation, H-800) at a magnification of 300,000 times to confirm the particle shape. The microparticles were evaluated as spherical when the circularity of the microparticles was confirmed to be 0.900 to 1.000.

[0044] (crystalline) The microparticles obtained in the examples and comparative examples were observed with a transmission electron microscope (JEOL Ltd., "JEM-1011") and an X-ray diffractometer (Rigaku Corporation, "MiniFlex600-C") and evaluated according to the following criteria. 〇: The ratio of the crystallite size calculated by X-ray diffractometer to the particle size observed by transmission electron microscope is 0.9 to 1.0 △: The ratio of the crystallite size calculated by an X-ray diffractometer to the particle size observed by a transmission electron microscope is less than 0.9 ×: No crystals formed

[0045] (Average particle size) 50 mg of the strontium titanate microparticles obtained in the examples and comparative examples were dissolved in 50 mL of methanol to obtain a dispersion. The resulting dispersion was placed in a measurement cell, and the average particle diameter (D50) was measured using a laser diffraction / scattering particle size distribution analyzer (manufactured by Nikkiso Co., Ltd., "Microtrac MT3300EXII").

[0046] (dispersibility) 50 mg of the strontium titanate microparticles obtained in the examples and comparative examples were dissolved in 50 mL of methanol to obtain a dispersion. The obtained dispersion was placed in a screw cap bottle, and black paper was placed on the backside of the bottle. The state of the dispersion was visually confirmed and evaluated according to the following criteria. ◯: The obtained dispersion was a transparent solution. ×: The obtained dispersion was a cloudy solution.

[0047] [Table 1]

[0048] The strontium titanate microparticles obtained in the examples were confirmed to have a spherical particle shape, an average particle diameter of 14 nm to 30 nm, and excellent crystallinity and dispersibility. In particular, in Examples 5 and 6 containing 3-aminopropyltriethoxysilane, strontium titanate microparticles with a small average particle size and excellent dispersibility were obtained. In Example 7, which used a phosphate ester titanium complex, and Example 8, which used propylene glycol as the solvent, the transparency of the dispersion was slightly lower than in the other Examples, and the dispersibility was slightly lower than in the other Examples. On the other hand, in Comparative Examples 1 to 3, 5 and 6, the reaction did not proceed and strontium titanate microparticles were not obtained. Furthermore, the microparticles obtained in Comparative Examples 1 to 3, which did not contain hydrazine or hydrazide compounds or in which the amount added was outside the specified range, had a large average particle size and poor dispersibility (the dispersion liquid was cloudy). Furthermore, the strontium titanate microparticles obtained in Comparative Example 4, in which the reaction temperature was not within the predetermined range, had insufficient crystallinity. Furthermore, the fine particles obtained in Comparative Example 5, in which the reaction time was too long, had a large average particle size and poor dispersibility (the dispersion liquid was cloudy). In Comparative Example 6, in which the reaction time was long and the pH was low, the reaction did not proceed and fine particles were not obtained. [Industrial Applicability]

[0049] The strontium titanate microparticles of the present invention are useful in that they can be used as functional materials such as refractive index increasing agents, thermoelectric conversion materials, photocatalysts, ion conductive materials, ferroelectric materials, magnetic materials, catalytic materials, oxygen electrode materials, piezoelectric materials, pyroelectric materials, nonlinear optical materials, and fillers.

Claims

1. The particles are spherical and have an average particle size (D50) of 10 nm to 30 nm as measured by a laser diffraction / scattering particle size distribution analyzer; Contains aminosilane compounds Strontium titanate microparticles.

2. 2. The strontium titanate microparticles according to claim 1, wherein no turbidity occurs when 50 mg of said strontium titanate is dissolved in 50 mL of methanol.

3. 3. The strontium titanate microparticles according to claim 1, wherein the ratio of the crystallite diameter calculated by an X-ray diffractometer to the particle diameter observed by a transmission electron microscope (particle diameter observed by a transmission electron microscope / crystallite diameter calculated by an X-ray diffractometer) is 0.9 to 1.

0.

4. 4. The strontium titanate microparticles according to claim 1, wherein the content of the hydrazine or hydrazide compound is 0.1% by mass to 60% by mass relative to the strontium titanate microparticles.

5. 5. The strontium titanate microparticles according to claim 1, wherein the content of said aminosilane compound is 0.003 to 0.025 in terms of molar ratio to said hydrazine or hydrazide compound.

6. 6. The strontium titanate microparticles according to claim 1, having a circularity of 0.900 to 1.000.

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