Method for producing strontium titanate microparticles

Abstract

To provide a method for producing strontium titanate fine particles capable of producing strontium titanate fine particles excellent in dispersibility under simple conditions.SOLUTION: A method for producing strontium titanate fine particles comprises a reaction step of reacting an organic titanate ester with a strontium compound in the presence of a hydrazine or a hydrazide compound under conditions of a pH of 12 or greater, a reaction temperature of 150°C or higher and 250°C or lower, and a reaction time of 0.5 hours or longer and 2 hours or shorter, in which a molar ratio of the hydrazine or hydrazide compound to the organic titanate ester (hydrazine or hydrazide compound / organic titanate ester) is 10 to 75.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing 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.

[0004] Furthermore, as a method for producing strontium titanate, for example, Patent Document 2 discloses a method for producing strontium titanate by heat treating ammonium titanium peroxolactate and strontium hydroxide in the presence of oleic acid and hydrazine in a constant temperature bath at 200°C for 24 hours. However, the method described in Patent Document 2 takes too much time to produce strontium titanate, and therefore a simpler method for producing strontium titanate has been desired. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2011 / 004750 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-068500 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a method for producing strontium titanate microparticles that can produce strontium titanate microparticles with excellent dispersibility under simple conditions.

[0007] The present inventors have conducted extensive research into methods for producing strontium titanate microparticles and have found that by containing a specific amount of hydrazine or hydrazide compound and reacting an organic titanate ester with a strontium compound under specified conditions (temperature and reaction time), it is possible to produce strontium titanate microparticles with excellent dispersibility in a reaction time shorter than conventional methods. [Means for solving the problem]

[0008] The present invention provides a method for producing strontium titanate microparticles, which comprises 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. The method for producing strontium titanate microparticles of the present invention preferably includes 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. In the method for producing strontium titanate of the present invention, the reaction step is preferably carried out in the presence of a polyhydric alcohol, which is preferably ethylene glycol. The organic titanate ester is preferably titanium lactate. The strontium compound is preferably at least one selected from the group consisting of strontium acetate and strontium formate. The reaction step is preferably carried out in the presence of an aminosilane compound. The aminosilane compound is preferably 3-aminopropyltriethoxysilane. [Effects of the Invention]

[0009] The method for producing strontium titanate microparticles of the present invention can produce strontium titanate microparticles with excellent dispersibility under simple conditions. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention provides a method for producing strontium titanate microparticles, which comprises 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. First, various materials used in the method for producing strontium titanate microparticles of the present invention will be described.

[0011] (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.

[0012] (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.

[0013] 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 particle size within the above range, the shape of the resulting strontium titanate microparticles can be controlled.

[0014] (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.

[0015] 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.

[0016] (solvent) As the solvent used in the method for producing strontium titanate microparticles of the present invention, ion-exchanged water is preferably used. The solvent preferably contains a polyhydric alcohol.

[0017] 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.

[0018] 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.

[0019] (pH adjuster) In the method for producing strontium titanate microparticles of the present invention, 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.

[0020] When adjusting the pH, the pH is set to 12 or higher from the viewpoint of controlling the reaction rate and the shape of the resulting strontium titanate microparticles. The pH is preferably 12.5 or higher, more preferably 13 or higher, and even more preferably 13.5 or higher. The content of the pH adjuster is not limited, and may be added appropriately depending on the desired pH.

[0021] (aminosilane compound) The reaction step is preferably carried out in the presence of an aminosilane compound. By carrying out the reaction step in the presence of an aminosilane compound, the average particle size of the resulting strontium titanate microparticles can be further reduced, and dispersibility can be further improved.

[0022] 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.

[0023] The content of the aminosilane compound relative to the hydrazine or hydrazide compound is preferably 0.003 to 0.025, more preferably 0.004 to 0.019, and even more preferably 0.007 to 0.015, in terms of molar ratio (aminosilane compound / hydrazine or hydrazide compound) relative to the hydrazine or hydrazide compound.

[0024] (others) In the method for producing strontium titanate microparticles of the present invention, 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 of the present invention, it 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.

[0025] (Manufacturing method) The method for producing strontium titanate microparticles of the present invention includes a reaction step of reacting an organic titanate ester with a 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. The method for producing strontium titanate microparticles of the present invention 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.

[0026] 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.

[0027] 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. Furthermore, it is 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.

[0028] 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.

[0029] In the reaction step, the organic titanate ester and the strontium compound are reacted under conditions of pH 12 or higher, reaction temperature of 150° C. to 250° C., and reaction time of 0.5 to 2 hours.

[0030] The reaction temperature is 150°C or higher and 250°C or lower. If the reaction temperature is below 150°C, the reaction will not proceed and the desired strontium titanate microparticles will not be obtained. If the reaction temperature exceeds 250°C, the reaction efficiency will decrease and the resulting strontium titanate microparticles will become larger and less dispersible. The reaction temperature is preferably 180 to 250°C, and more preferably 200 to 240°C.

[0031] The reaction time is from 0.5 hours to 2 hours. If the reaction time is less than 0.5 hours, the reaction will not proceed and the desired strontium titanate microparticles will not be obtained. If the reaction time exceeds 2 hours, the reaction efficiency will decrease and the resulting strontium titanate microparticles will become larger and less dispersible. The reaction time is preferably 1 to 2 hours.

[0032] 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.

[0033] 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.

[0034] (Strontium titanate fine particles) The strontium titanate microparticles obtained by the method for producing strontium titanate microparticles of the present invention have the following properties.

[0035] The strontium titanate fine particles preferably 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, this means that the circularity of the strontium titanate fine particles is 0.900 to 1.000. 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 of the strontium titanate microparticles is expressed as follows: where S is the area of ​​the microparticle in the image taken by the transmission electron microscope and L is the perimeter. 2 It can be calculated as follows. 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.

[0036] The strontium titanate fine particles preferably have an average particle size of 10 nm to 30 nm, more 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.).

[0037] The strontium titanate fine particles 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.

[0038] The strontium titanate fine particles 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.

[0039] The strontium titanate fine particles preferably contain 0.1% by mass to 60% by mass of the hydrazine or hydrazide compound relative to the strontium titanate fine particles. Such a content will result in good dispersibility. [Example]

[0040] 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."

[0041] 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.)

[0042] Example 1 0.584 g of titanium lactate (Orgatix TC-310, component concentration 44 wt%, manufactured by Matsumoto Fine Chemical Co., Ltd.) was mixed with 3.0 g of purified water and 3.0 g of hydrazine hydrate (manufactured by 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.

[0043] (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 microparticles were not obtained.

[0044] <Evaluation method> (particle shape) The fine particles obtained in the examples and comparative examples were collected and observed under a transmission electron microscope (JEOL Ltd., "JEM-1011") 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.

[0045] (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

[0046] (Average particle size) 50 mg of the fine particles 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").

[0047] (dispersibility) 50 mg of the fine particles 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.

[0048] [Table 1]

[0049] 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 in which 3-aminopropyltriethoxysilane was added, 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]

[0050] The method for producing strontium titanate microparticles of the present invention is useful in that it can produce strontium titanate microparticles that 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. a mixing step of mixing an organic titanate ester with a hydrazine or hydrazide compound in a solvent to obtain a mixed solution; and an adjusting step of adjusting the pH of the mixed solution to 12 or more; In the presence of hydrazine or a hydrazide compound, under the conditions of a pH of 12 or higher, a reaction temperature of 150°C or higher and 250°C or lower, a pressure of 2 MPa or higher, and a reaction time of 0.5 hours or higher and 2 hours or lower, The method includes a reaction step of reacting an organic titanate ester with a strontium compound in the presence of a polyhydric alcohol, 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; Method for producing strontium titanate microparticles.

2. 2. The method for producing strontium titanate microparticles according to claim 1, wherein the polyhydric alcohol is ethylene glycol.

3. 3. The method for producing strontium titanate microparticles according to claim 1, wherein the organic titanate ester is titanium lactate.

4. 4. The method for producing strontium titanate microparticles according to claim 1, wherein the strontium compound is at least one selected from the group consisting of strontium acetate and strontium formate.

5. 5. The method for producing strontium titanate microparticles according to claim 1, wherein the reaction step is carried out in the presence of an aminosilane compound.

6. 6. The method for producing strontium titanate microparticles according to claim 5, wherein the aminosilane compound is 3-aminopropyltriethoxysilane.

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