JP7745366B2 - Dispersion of barium titanate particles and method for producing same - Google Patents

Description

The present invention relates to a dispersion of barium titanate particles with excellent dispersion stability, and a method for producing the same.

Barium titanate (hereafter referred to as BTO) is widely known as a high-dielectric material and is used in electronic device components such as multilayer ceramic capacitors. In recent years, as multilayer ceramic capacitors have become smaller and their capacitance has increased, the dielectric layers and electrode layers have become thinner. Nano-sized BTO particles with excellent dispersion stability are required as a co-material for these dielectric layers and electrode layers, and there is also a demand for the ability to mass-produce these particles.

Conventionally, a known method for producing nano-sized BTO particles involves adding a mixture of water and a polar solvent dropwise to barium and titanium alkoxides to hydrolyze the mixture, followed by heating and aging at 10°C or higher to obtain nano-sized BTO particles (see, for example, Patent Document 1). However, the dispersion stability of these particles is insufficient. Furthermore, because this method is a so-called batch production method, mass production is difficult.

Another known method for continuously producing BTO particles involves hydrolysis in a thin film fluid to continuously produce ceramic nanoparticles (see, for example, Patent Document 2). However, the dispersion stability of the BTO particles obtained by this method is also insufficient.

Meanwhile, the present applicant has disclosed a continuous production method using a micromixing chip (see Patent Document 3). While this method can produce nano-sized BTO particles, it does not provide sufficient dispersion stability. Furthermore, this method has the risk of gel-like material clogging the flow channels during continuous production, making mass production difficult.

Furthermore, the present applicant has disclosed a method for producing BTO particles using an alkyl cellosolve solution of barium hydroxide (see Patent Document 4). While this method makes it possible to inexpensively produce nano-sized BTO particles, it does not provide sufficient dispersion stability. Furthermore, mass production is difficult, so productivity cannot be said to be sufficient.

Japanese Patent Application Laid-Open No. 2005-306691 WO2009/008392 JP 2009-172581 A JP 2012-240904 A

The smaller the particle size of BTO particles, the more likely they are to aggregate, making it difficult to store conventional nano-sized BTO particle dispersions for long periods of time. This meant that they could not be uniformly dispersed when used as co-materials for dielectric layers and electrode layers. Therefore, there is a demand for nano-sized BTO particle dispersions with excellent dispersion stability. Furthermore, conventional manufacturing methods make mass production difficult.

To solve these problems, we decided to create a dispersion of BTO particles using the following manufacturing method.

First, barium alkoxide, titanium alkoxide, and an organic solvent containing hydroxyl groups are mixed so that the atomic ratio of barium to titanium (Ba/Ti ratio) is 0.90 to 1.10 (first step). Next, the first solution obtained in the first step is held at 15°C or below for at least one hour (second step). Next, this first solution held at 15°C or below is mixed with a second solution containing water in a continuous reactor at 15°C or below (third step). Next, the third solution obtained in the third step is heated to 60°C or above (fourth step).

The dispersion of BTO particles prepared in this manner has a _D50 particle size (A) of 3 to 30 nm, a _D90 particle size (B) of 8 to 80 nm, and a crystallite size (C) of 5 to 15 nm, as measured by dynamic light scattering, and the ratio of the _D50 particle size to the crystallite size (A/C) is 0.3 to 5.0.

According to the present invention, a dispersion of nano-sized BTO particles with excellent dispersion stability can be obtained.

[Method for producing dispersion of barium titanate particles]
Hereinafter, a method for producing a dispersion (hereinafter, sometimes simply referred to as "dispersion") of barium titanate particles (hereinafter, sometimes simply referred to as "BTO particles" or "particles") according to the present invention will be described.

This manufacturing method includes the following steps, in order: a first step of preparing a first solution by mixing barium alkoxide, titanium alkoxide, and an organic solvent containing hydroxyl groups so that the atomic ratio of barium to titanium (Ba/Ti ratio) is 0.90 to 1.10; a second step of holding this first solution at 15°C or below for at least one hour; a third step of mixing the first solution obtained in this second step with a second solution containing water in a continuous reactor at 15°C or below; and a fourth step of heating the third solution obtained in this third step to 60°C or above. This results in a dispersion of nano-sized BTO particles with excellent dispersion stability. This manufacturing method also enables mass production.

Each process is described below.

[First step]
A first solution is prepared by mixing barium alkoxide, titanium alkoxide, and an organic solvent having a hydroxyl group.

The barium alkoxide and titanium alkoxide are mixed so that the atomic ratio of barium to titanium (Ba/Ti) in the first solution is 0.90 to 1.10. An atomic ratio within this range makes it possible to obtain BTO particles with a highly crystalline perovskite crystal structure. This atomic ratio is preferably 0.95 to 1.05, more preferably 0.98 to 1.02, and most preferably 1.00.

The organic solvent having a hydroxyl group is preferably mixed so that the total concentration of barium alkoxide and titanium alkoxide in the first solution is 0.5 to 10.0 mol/kg. If the total concentration is less than 0.5 mol/kg, productivity may decrease. Conversely, if it exceeds 10.0 mol/kg, the dispersion stability of the BTO particle dispersion may be insufficient. This total concentration is more preferably 1.0 to 8.0 mol/kg, and even more preferably 2.0 to 5.0 mol/kg.

In this process, it is preferable to avoid contact between the metal alkoxide and water. If at least one of the barium alkoxide and titanium alkoxide is hydrolyzed with water, it may not be possible to obtain a dispersion of nano-sized BTO particles with high dispersion stability. For this reason, when preparing the first solution, it is preferable to not only avoid water contamination, but also to take care with the atmosphere.

For example, the relative humidity when mixing barium alkoxide, titanium alkoxide, and an organic solvent having a hydroxyl group is preferably 50% or less. If the relative humidity is higher than 50%, these metal alkoxides may be hydrolyzed by moisture in the air, making it difficult to obtain nano-sized BTO particles. The relative humidity is more preferably 45% or less, even more preferably 30% or less, and particularly preferably 10% or less. Suitable methods for lowering the relative humidity include replacing the inside of a glove box or tank with nitrogen gas or dry air, reducing the pressure, or adsorbing moisture in the air using silica gel or the like.

Another effective way to reduce the effects of moisture in the air is to use a container with a small surface area where the liquid surface comes into contact with the air.

Barium alkoxides and titanium alkoxides may be commercially available, or may be produced from compounds of the respective metals, hydroxides, halides, or the like, using conventional methods.

Examples of barium alkoxides include barium dimethoxide, barium diethoxide, barium dipropoxide, barium diisopropoxide, barium dibutoxide, and barium diisobutoxide. Examples of titanium alkoxides include titanium tetramethoxide, titanium tetraethoxide, titanium tetrapropoxide, titanium tetraisopropoxide, titanium tetrabutoxide, titanium tetraisobutoxide, titanium tetrastearyl alkoxide, and titanium tetrakis(2-ethyl-1-hexanolate).

These may be used as monomers or as oligomers that have been polymerized to a certain extent. They may also be used alone or in combination of two or more types.

Examples of organic solvents having a hydroxyl group include alcohols, phenols, glycols, glycol ethers, etc. Alcohols include methanol, ethanol, propanol, isopropanol, butanol, and isobutanol. Phenols include phenol, cresol, and naphthol. Glycols include ethylene glycol and propylene glycol. Glycol ethers include diethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, and propylene glycol monomethyl ether.

These may be used alone or in combination of two or more.

[Second process]
The first solution obtained in the first step is maintained at 15°C or below for at least 1 hour. This step suppresses the generation of gel-like material in the subsequent third step, improving productivity. It also improves the dispersion stability of the resulting particles. While the detailed reason for this is unclear, it is believed that in the third step, the metal alkoxide in the first solution maintained at 15°C or below is uniformly mixed with the water-containing solution at the molecular level while suppressing hydrolysis reactions.

If the temperature is higher than 15°C, the hydrolysis reaction in the third step may proceed, resulting in the generation of a gel-like substance and the risk of clogging the flow paths. This may require the production line to be stopped and cleaned to ensure proper flow paths, potentially reducing productivity. It may also reduce the dispersion stability of the resulting particles. There is no particular lower limit for this temperature as long as the solution has fluidity, but it may be -40°C, for example. Lowering the temperature below -40°C does not significantly improve the productivity or dispersion stability of the desired particles, and instead requires more expensive cooling equipment, affecting production costs. The solution temperature is preferably -20 to 10°C, more preferably -20 to 5°C.

This first solution is preferably held at 15°C or below for 3 hours or more. The exact reason for this is unknown, but a holding time of 3 hours or more makes the solution homogeneous, which prevents the formation of gel-like material in the continuous reactor and a decrease in the dispersion stability of the BTO particles in the subsequent third step. The longer the holding time, the better, with 12 hours or more being preferable, and 24 hours or more being even more preferable. There is no upper limit to the holding time, but even if it exceeds 96 hours, there is no particular improvement in the productivity or dispersion stability of the desired particles.

When maintaining the first solution at 15°C or below, it is preferable to avoid contact between the metal alkoxide and water, as in the first step. Contact with water here includes contact with moisture in the air. Contact with water accelerates hydrolysis of the metal alkoxide in the first solution, and during mixing in the third step described below, gel-like material may form in the continuous reactor, potentially clogging the flow path and reducing productivity. It may also reduce the dispersion stability of the resulting dispersion. Therefore, in the second step, the first solution may be fluidized by stirring or other means, but it is preferable to leave it undisturbed to reduce contact with moisture in the air. Furthermore, the second step is preferably carried out under the same relative humidity as the first step or at a lower relative humidity. More specifically, it is preferable to carry out the second step in a vacuum or in an atmosphere substituted with nitrogen gas or dry air, and it is preferable to use a hermetically sealed container.

[Third step]
In the second step, the first solution maintained at 15°C or below is mixed with the second solution containing water to prepare a third solution. A continuous reactor is used for this mixing. A continuous reactor can quantitatively mix and react the solutions at a constant ratio. In this way, the quantitative supply, mixing, reaction, and discharge of the solutions can be continuously performed, thereby achieving stable quality and mass production of BTO particles. Examples of continuous reactors include a continuous flow microreactor, a forced thin film microreactor, and a line mixer.

Continuous flow microreactors that can be used include, for example, the microreaction device disclosed in Patent Document 3 by the present applicant, and the SMCR stacked multi-channel reactor manufactured by Kobe Steel, Ltd. Furthermore, forced thin film microreactors that can be used include, for example, the ULREA series manufactured by M Technique Co., Ltd.

When the first solution and the second solution are mixed, the temperature of the reaction site (mixing temperature) is 15°C or lower. A reaction temperature of 15°C or lower suppresses the formation of gel-like material. If the reaction temperature is higher than this temperature, gel-like material may form in the continuous reactor, clogging the flow path and reducing productivity. The temperature of the third solution may also exceed 15°C. This may result in the average particle size of the resulting dispersion becoming too large or the dispersion stability decreasing. There is no particular lower limit for this temperature, but it is, for example, -40°C for the same reasons as for the first solution in the second step. The reaction temperature is more preferably 10°C or lower, and even more preferably 5°C or lower.

If the mixing temperature of the first solution and the second solution is 15°C or less, the temperature of the third solution discharged from the continuous reactor can easily be kept at 15°C or less. If this temperature is higher than 15°C, gel-like material may form in the continuous reactor, clogging the flow path and reducing productivity. There is also a risk that the average particle size of the particles in the resulting dispersion may become too large or that dispersion stability may decrease. There is no particular lower limit for this temperature as long as the solution has fluidity, but for the same reasons as for the first solution in the second step, it may be, for example, -40°C. The temperature of the discharged mixed solution is more preferably 10°C or less, and even more preferably 0 to 10°C.

The ratio of the total number of moles of barium alkoxide and titanium alkoxide contained in the first solution to the number of moles of water in the second solution (water/(barium alkoxide + titanium alkoxide)) to be mixed in the continuous reactor is preferably 1 to 10. If the molar ratio is less than 1, hydrolysis of these metal alkoxides will be insufficient, making it difficult to obtain highly crystalline BTO particles. Conversely, if the molar ratio exceeds 10, gel-like matter may be generated in the continuous reactor, reducing productivity, the crystallite size of the particles in the resulting dispersion may become too large, and dispersion stability may be reduced. The molar ratio (water/(barium alkoxide + titanium alkoxide)) is more preferably 2 to 8, and even more preferably 3 to 6.

Here, it is preferable to use a solution in which the mass ratio of water to alcohol (water/alcohol) is 0.05 to 1.00 as the second solution. A mass ratio within this range can suppress a rapid hydrolysis reaction, resulting in BTO particles with the desired crystallite size and average particle size.

Here, even if the mass ratio is less than 0.05, it is unlikely that the crystallite size or average particle size can be adjusted to be any smaller. Rather, the concentration of the resulting third solution will be too low, which could result in a decrease in productivity. Conversely, if the mass ratio is higher than 1.00, it is essentially the same as using water directly. As a result, gel-like matter may form in the continuous reactor, resulting in a decrease in productivity. There is also a risk that the crystallite size and average particle size of the BTO particles may become too large.

Preferably, the alcohol used is a lower alcohol such as methanol, ethanol, propanol, isopropanol, or butanol. These may be used alone or in combination of two or more. The mixture may also contain organic solvents other than alcohol (e.g., glycols or glycol ethers), surfactants, dispersants, etc. The mass ratio of water to alcohol is more preferably 0.10 to 0.80, and even more preferably 0.30 to 0.60.

The feed rate of the first solution is preferably 4 L/Hr or more. If it is less than 4 L/Hr, productivity will not be sufficient on an industrial level. There is no specific upper limit to this feed rate, but considering the capacity of the commercially available continuous reactors mentioned above, it is, for example, 20 L/Hr. However, if a larger device is used for production or multiple devices are arranged in parallel for production, it may be possible to exceed 20 L/Hr.

In order to control the "temperature of the third solution discharged from the continuous reactor" and the "temperature of the reaction site," it is more preferable that the temperatures of the "first solution" and the "second solution" mixed in the continuous reactor are both 15°C or below. When the temperatures of these solutions are within this range, it is easy to keep the temperature of the third solution discharged from the continuous reactor at 15°C or below. If the temperatures of these solutions deviate from this temperature, the temperature of the reaction site may also deviate from the specified temperature, and the temperature of the third solution discharged from the continuous reactor may also deviate from the specified temperature. In this state, gel-like material may form in the continuous reactor, clogging the flow path of the equipment and reducing productivity. Furthermore, even if a dispersion is obtained, the average particle size of the particles may become too large, or dispersion stability may be reduced.

The temperatures of these "first solution" and "second solution" may be the same or different. The lower limit of the temperature of these solutions is not particularly set as long as they have fluidity, but for the same reasons as for the first solution in the second step, it is, for example, -40°C. The temperature of these solutions before being mixed in the continuous reactor is more preferably -20 to 10°C, and even more preferably -20 to 5°C.

[Fourth step]
The third solution is heated to 60°C or higher. This heating promotes the hydrolysis reaction and dehydration condensation reaction of barium alkoxide and titanium alkoxide, resulting in a dispersion of nano-sized BTO particles with high dispersion stability. If the heating temperature is below 60°C, the dispersion stability may be reduced. There is no particular upper limit for the heating temperature, but it is, for example, 200°C. If the temperature exceeds 200°C, an expensive pressure-resistant container is required, and the crystallinity and dispersion stability of the particles will not be further improved. The heating temperature is preferably 60 to 130°C, more preferably 70 to 100°C.

The heating time is preferably 2 hours or more. By heating for 2 hours or more, a dispersion of BTO particles with high dispersion stability can be easily obtained. However, if the heating time is less than 2 hours, sufficient crystallization may not occur or the dispersion stability may be reduced. The heating time is more preferably 12 hours or more, and even more preferably 24 hours or more.

[Other steps]
The dispersion thus obtained may be subjected to a dispersion treatment, a washing treatment, a surface treatment, and a concentration adjustment treatment, as required.

If the aggregated particles are broken down by the dispersion treatment, the particle size distribution becomes sharper than before the dispersion treatment, and the _D50 particle size and _D90 particle size can be reduced. The dispersion treatment may be, for example, simple stirring, or a conventionally known ultrasonic agitator, homogenizer, homomixer, bead mill, or the like may also be used.

By washing the dispersion, it is possible to reduce particles and impurities (especially halogen elements) in the dispersion. Examples of washing methods include the conventionally known filtration washing method using an ultrafiltration membrane, the ion exchange method using an ion exchange resin, and the centrifugal washing method, which involves centrifugal sedimentation and the replacement of the supernatant.

The use of surface-treated particles improves mixing stability with other components used in the high-dielectric layer and electrode layers of multilayer ceramic capacitors, as well as with UV-curable resins or additives used in the high-refractive-index film. There are no particular restrictions on the surface treatment agent, as long as it is a conventionally known surface treatment agent that can be used with nano-sized metal oxide particles, and examples include silane coupling agents, titanate coupling agents, surfactants, and organic acids.

The solids concentration of the dispersion is preferably 60% by mass or less. If this concentration is too low, the storage and transportation costs of the dispersion will increase, so the solids concentration may be increased by concentration adjustment. Conversely, if the solids concentration exceeds 60% by mass, the dispersion stability of the dispersion may decrease. Furthermore, the dispersion stability of the coating solution using this dispersion may also decrease. Methods for adjusting the solids concentration include concentrating the dispersion using ultrafiltration membranes, distillation, or vacuum distillation, or diluting the dispersion by adding a solvent. Solvent substitution may also be performed simultaneously with concentrating or diluting the dispersion. Examples of solvents that can be used include water, alcohols, ketones, esters, glycols, glycol ethers, glycol ether acetates, and monoterpene alcohols, and can be selected appropriately depending on the application. Any conventionally known solvent can be used without any particular restrictions. There is no specific lower limit for the solids concentration, but it is, for example, approximately 10% by mass. If a lower concentration is required, it can be achieved by diluting with an appropriate solvent. The solids concentration of the dispersion is more preferably 20 to 60% by mass, and even more preferably 25 to 40% by mass.

[BTO Particle Dispersion]
The dispersion of BTO particles of the present invention has an average particle size ( _D50 particle size (A)) of 3 to 30 nm, a _D90 particle size (B) of 8 to 80 nm, and a crystallite size (C) of 5 to 15 nm, as measured by dynamic light scattering, and a ratio of the _D50 particle size (A) to the crystallite size (A/C) of 0.3 to 5.0. The crystalline structure of the particles can be confirmed by X-ray diffraction. Such a dispersion can be obtained by the production method described above.

Here, the _D50 particle size refers to the particle size when the cumulative distribution of particles is 50%, and the _D90 particle size refers to the particle size when the cumulative distribution of particles is 90%.

If the _D50 particle size (A) is less than 3 nm, the dispersion stability may be reduced. Conversely, if it exceeds 30 nm, it may be difficult to uniformly disperse the particles when used as a co-material for the electrode layer of a thin-film ceramic capacitor. Furthermore, when forming a high refractive index film, a transparent film may not be obtained. The _D50 particle size is preferably 5 to 20 nm.

If the _D90 particle size (B) is less than 8 nm, the dispersion stability may be reduced. Conversely, if it exceeds 80 nm, it may be difficult to uniformly disperse the particles when used as a co-material for the electrode layer of a thin-film ceramic capacitor. Furthermore, when forming a high refractive index film, a transparent film may not be obtained. The _D90 particle size is preferably 15 to 50 nm.

If the crystallite diameter (C) is less than 5 nm, dispersion stability is likely to be low, and crystallinity may be insufficient, making it difficult to achieve a high dielectric constant. Conversely, if it exceeds 15 nm, it may be difficult to achieve uniform dispersion when used as a co-material in the electrode layer of a thin-film ceramic capacitor. Furthermore, when forming a high-refractive-index film, a transparent coating may not be obtained. The crystallite diameter is preferably 7 to 12 nm.

A ratio (A/C) of less than 0.3 is difficult to achieve. Conversely, a ratio (A/C) of more than 5.0 indicates a high degree of particle aggregation in the dispersion, and there is a risk that the particles may not be uniformly dispersed in the film. As a result, when used as a co-material in an electrode layer, there is a risk that the electrode layer may not be uniform, or that the haze of the coated film may increase. The ratio (A/C) is preferably 0.3 to 3.0.

The content of halogen elements in the dispersion is preferably less than 500 ppm relative to the solid content of the dispersion. If this content is 500 ppm or more, when used as a co-material in the electrode layer of a multilayer ceramic capacitor, there is a risk that the capacitor may crack or deform. The content of halogen elements is more preferably less than 100 ppm. Here, halogen elements refer to F, Cl, Br, and I.

By keeping the solids concentration of the dispersion at 60% by mass or less, it is possible to prevent a decrease in the dispersion stability of the dispersion or coating liquid. The solids concentration is set taking into account the required particle blending amount and workability depending on the application, so there is no specific lower limit for the solids concentration, but considering storage and transportation costs, it is approximately 10% by mass. If a lower concentration is required, this can be achieved by diluting with an appropriate solvent. The solids concentration of the dispersion is more preferably 20 to 50% by mass, and even more preferably 25 to 40% by mass.

Solvents for this dispersion include, for example, water, alcohols, ketones, esters, glycols, glycol ethers, glycol ether acetates, and monoterpene alcohols, and can be selected appropriately depending on the application. Selecting the right solvent can improve the mixing stability with, for example, the high dielectric layer of a multilayer ceramic capacitor, other components used in the electrode layer, and UV-curable resins and additives used in the high refractive index film. If the solvent needs to be changed, known solvent substitution methods can be used.

Furthermore, the dispersion of the present invention preferably has a ratio (E/C) of the _D50 particle size (E) to the aforementioned crystallite size (C) of 0.3 to 7.0. The _D50 particle size (E) is the _D50 particle size determined by dynamic light scattering after heating a dispersion prepared by using ethanol as the solvent and adjusting the solid content concentration to 30% by mass at 50°C for 3 hours. If the solvent type or solid content concentration of the original dispersion is different, the solvent is replaced with ethanol, and the solid content concentration is adjusted to 30% by mass before evaluation.

However, the higher the solids concentration of a dispersion, and the greater the thermal history it is subjected to, the lower its stability tends to be. This ratio (E/C) is a value determined by measuring a dispersion adjusted to a specific state as described above, and serves as an index of the dispersion stability of the dispersion. The lower this value, the better the dispersion stability.

It is difficult to obtain a ratio (E/C) of less than 0.3. Conversely, a ratio higher than 7.0 has poor dispersion stability, making it difficult to store the dispersion for long periods of time or to achieve uniform dispersion when used as a co-material in the electrode layers of thin-film ceramic capacitors. The ratio (E/C) is more preferably 0.5 to 5.0.

The following describes an example of the present invention.

[Example 1]
[First step]
Nitrogen gas was added to a 30 L tank, and the relative humidity was adjusted to 25%. 14.9 kg of ethylene glycol monomethyl ether was placed in the tank, and the temperature was adjusted to 25°C. While stirring, 6.6 kg of barium diethoxide was added over 5 minutes. Subsequently, 8.3 kg of titanium tetraisopropoxide was added over 10 minutes to prepare a first solution.

The properties of each step and the solution are shown in Tables 1 and 2 (the same applies to the following Examples and Comparative Examples).

[Second process]
This first solution was transferred to a sealable container adjusted to a relative humidity of 25%. Nitrogen gas was sealed into the container so that the relative humidity after cooling would be 25% or less, and the container was cooled to -10°C while maintaining the sealed state and left to stand for 24 hours.

[Third step]
A second solution was prepared by adding 3.8 kg of pure water to 9.0 kg of methanol with stirring and adjusting the temperature to 3°C. The first solution obtained in the second step was also adjusted to 3°C. Next, using the microreactor for micro-reactions described in Patent Document 3 as a continuous flow microreactor, the first solution was delivered at 5.0 L/Hr and the second solution at 2.4 L/Hr while maintaining the micromixing chip in the reaction field at 4°C, to prepare a third solution. Continuous operation was performed under these conditions for 6.4 hours, and the entire amount was delivered.

[Fourth step]
This third solution was heated to 70° C. and maintained at this temperature for 24 hours to produce a dispersion of BTO particles according to the present invention.

Next, to evaluate the properties of this dispersion, the dispersion was concentrated using a rotary evaporator to a solids concentration of 30% by mass.

The properties of this dispersion were measured using the following methods. The dispersion preparation conditions and measurement results are shown in Tables 1 and 2 (the same applies to the following Examples and Comparative Examples).

(1) _D50 particle size (A), _D90 particle size (B)
The _D50 particle size (A) and _D90 particle size (B) of the particles in the dispersion were measured using a particle size distribution analyzer (NANOTRAC-WAVE II manufactured by Microtrac-Bell) using a dynamic light scattering method. The refractive index of the particles used in the measurement was 1.93 and the density was 6.00.

(2) Crystal structure and crystallite size (C)
The dispersion was dried at 150°C for 1 hour, and the resulting powder was crushed in a mortar. The crystal structure was identified using an X-ray diffractometer (RINT1400 manufactured by Rigaku Denki Co., Ltd.). The half-width of the peak of the (110) plane near 2θ = 31.5° was measured, and the crystallite size was calculated using the following Scherrer formula.

D = κλ/β cos θ
(In the formula, D is the crystallite diameter (Å), κ is the Scherrer constant, λ is the wavelength (Å), β is the half-width (dimensionless), and θ is the reflection angle (rad).)

(3) Solid Content Concentration 5 g of the dispersion was collected, precisely weighed into a porcelain crucible, dried, and then fired at 1000°C for 1 hour. After cooling to room temperature in a desiccator containing a desiccant, the dispersion was precisely weighed again, and the solid content was determined from the mass of the ignition residue.

(4) Halogen Elements The amount of halogen elements in the dispersion was measured using an ICP emission spectrometer (Shimadzu Corporation, ICPS-8100) to determine the content of halogen elements relative to the solid content in the dispersion.

(5) _D50 particle size after heat treatment (E)
10 g of a dispersion liquid adjusted to a solids concentration of 30% by mass using ethanol as a solvent was placed in a sealed container and heated at 50°C for 3 hours. After heating, the _D50 particle size (E) of the dispersion liquid was measured by dynamic light scattering in the same manner as described above. The ratio (E/C) was calculated from this value (E) and the above-mentioned crystallite size (C).

(6) Applicability of Mass Production In this example, if the operation of the third step could be continued for 5 hours or more, it was determined that mass production was possible.

Third process continuous operation for 5 hours or more: ○
Continuous operation of the third process is less than 5 hours: ×

[Example 2]
The dispersion of BTO particles obtained in the same manner as in Example 1 was subjected to ultrasonic treatment for 30 minutes, and then the solvent was replaced with ethanol using an ultrafiltration membrane to obtain an ethanol dispersion of BTO particles with a solid content concentration of 30% by mass.

[Example 3]
30 g of anion exchange resin (SA-20A manufactured by Mitsubishi Chemical Corporation) was added to 100 g of an ethanol dispersion of BTO particles obtained in the same manner as in Example 2. The mixture was stirred at room temperature for 30 minutes, and then the ion exchange resin was separated. Subsequently, 3 g of methyltrimethoxysilane was added as a surface treatment agent, and the mixture was stirred at 30°C for 18 hours. The mixture was then concentrated using an ultrafiltration membrane to obtain a dispersion of surface-treated BTO particles with a solids concentration of 30% by mass.

[Example 4]
A first solution was prepared in the same manner as in Example 1, except that in the first step, the relative humidity was adjusted to 50% and 6.3 kg of barium diethoxide and 8.6 kg of titanium tetraisopropoxide were used.

In the second step, this first solution was transferred to a sealable container adjusted to a relative humidity of 50%. Nitrogen gas was sealed into the container so that the relative humidity after cooling would be 50% or less, and the container was cooled to 12°C while maintaining the seal and left to stand for 24 hours.

In the third step, 3.7 kg of pure water was added to 8.9 kg of methanol while stirring to prepare the second solution. Next, the third solution was prepared in the same manner as in Example 1, except that the temperature of this solution, the first solution obtained in the second step, and the temperature of the micromixing tip were adjusted to 15°C. Continuous operation was carried out under these conditions for 6.4 hours, and the entire amount was transferred.

In the fourth step, a dispersion of BTO particles of the present invention was produced in the same manner as in Example 1, except that this third solution was used. Next, the dispersion was concentrated using a rotary evaporator, and then the solvent was replaced with ethanol using an ultrafiltration membrane, yielding a dispersion with a solids concentration of 30% by mass.

[Example 5]
A first solution was prepared in the same manner as in Example 1, except that 6.9 kg of barium diethoxide and 7.8 kg of titanium tetraisopropoxide were used in the first step.

The same procedure as in Example 1 was followed, except that in the second step, the temperature was cooled to -18°C and left to stand for 3 hours.

In the third step, 3.7 kg of pure water was added to 8.9 kg of methanol while stirring to prepare the second solution. The temperature of this solution and the first solution obtained in the second step were adjusted to -18°C, and the temperature of the micromixing tip was set to -10°C. The third solution was prepared in the same manner as in Example 1, except that the system was operated continuously under these conditions for 6.3 hours, and the entire amount was pumped.

In the fourth step, a dispersion of BTO particles of the present invention was produced in the same manner as in Example 1, except that the third solution was heated to 60°C and maintained at this temperature for 3 hours. The dispersion was then concentrated using a rotary evaporator, and the solvent was replaced with ethanol using an ultrafiltration membrane to obtain a dispersion with a solids concentration of 30% by mass.

[Example 6]
A first solution was prepared in the same manner as in Example 1, except that in the first step, the relative humidity was adjusted to 10% and 10.8 kg of ethylene glycol monomethyl ether, 12.0 kg of barium diethoxide, and 14.7 kg of titanium tetraisopropoxide were used.

In the second step, this first solution was transferred to a sealable container adjusted to a relative humidity of 10%. Nitrogen gas was sealed into the container so that the relative humidity after cooling would be 10% or less, and the container was cooled to 0°C while maintaining the seal and allowed to stand for 96 hours.

In the third step, 6.8 kg of pure water was added to 16.1 kg of methanol with stirring to prepare the second solution, which was then adjusted to 8°C. The first solution obtained in the second step was also adjusted to 8°C. Next, using a ULREA SS-11 forced thin film reactor manufactured by M Technique Co., Ltd., the first solution was pumped at 5.0 L/Hr and the second solution at 3.4 L/Hr while maintaining the reaction temperature at 8°C, to prepare the third solution. Continuous operation was carried out under these conditions for 8.0 hours, and the entire amount was pumped.

In the fourth step, this third solution was placed in a pressure-resistant container and heated to 125°C. This temperature was maintained for 48 hours to produce a dispersion of BTO particles of the present invention. The dispersion was then concentrated using a rotary evaporator, and the solvent was replaced with ethanol using an ultrafiltration membrane to obtain a dispersion with a solids concentration of 30% by mass.

[Example 7]
A first solution was prepared in the same manner as in Example 1, except that a 200 L tank was used and 105.0 kg of ethylene glycol monomethyl ether, 6.0 kg of barium diethoxide, and 7.5 kg of titanium tetraisopropoxide were used in the first step.

The same procedure as in Example 1 was followed, except that in the second step, the temperature was cooled to 7°C.

In the third step, 7.6 kg of pure water was added to 76.0 kg of methanol with stirring to prepare a second solution, which was then adjusted to 7°C. The first solution obtained in the second step was adjusted to 5°C. Next, while maintaining the temperature of the reaction site at 7°C, the first solution was pumped at 20.0 L/Hr and the second solution at 16.3 L/Hr to prepare a third solution. Continuous operation was carried out under these conditions for 6.4 hours, and the entire amount was pumped.

In the fourth step, a dispersion of BTO particles of the present invention was produced in the same manner as in Example 1, except that this third solution was used. The dispersion was then concentrated using a rotary evaporator to obtain a dispersion with a solids concentration of 30% by mass.

[Comparative Example 1]
A first solution was prepared in the same manner as in Example 1, except that 7.2 kg of barium diethoxide and 7.5 kg of titanium tetraisopropoxide were used in the first step.

The third solution was prepared in the same manner as in Example 1, except that this first solution was used in the second and third steps. Under these conditions, the production line became clogged (blocked) 4.2 hours after the start of operation of the third step, so the production line was cleaned and the liquid flow was resumed.

In the fourth step, a dispersion of BTO particles of the present invention was produced in the same manner as in Example 1, except that this third solution was used. Next, the dispersion was concentrated using a rotary evaporator, and then the solvent was replaced with ethanol using an ultrafiltration membrane, yielding a dispersion with a solids concentration of 30% by mass.

[Comparative Example 2]
A first solution was prepared in the same manner as in Example 1, except that in the first step, 14.7 kg of ethylene glycol monomethyl ether, 5.75 kg of barium diethoxide, and 9.0 kg of titanium tetraisopropoxide were used.

The second step was carried out in the same manner as in Example 1, except that this first solution was used.

In the third step, a second solution was prepared by adding 3.7 kg of pure water to 8.8 kg of methanol while stirring, and the temperature was adjusted to 3°C. A third solution was prepared in the same manner as in Example 1, except that this second solution was used. Under these conditions, the production line became clogged 3.1 hours after the start of operation, so the production line was cleaned and liquid flow was resumed.

In the fourth step, a dispersion of BTO particles of the present invention was produced in the same manner as in Example 1, except that this third solution was used. Next, the dispersion was concentrated using a rotary evaporator, and then the solvent was replaced with ethanol using an ultrafiltration membrane, yielding a dispersion with a solids concentration of 30% by mass.

[Comparative Example 3]
In the first step, a first solution was prepared in the same manner as in Example 1.

In the second step, this first solution was transferred to a sealable container adjusted to a relative humidity of 25%. Nitrogen gas was sealed into the container so that the relative humidity at 25°C was 25% or less, and the container was kept sealed and kept at 25°C for 24 hours.

In the third step, the third solution was prepared in the same manner as in Example 1, except that the first solution obtained in the second step was used. Under these conditions, the production line became clogged 4.2 hours after the start of operation, so the production line was cleaned and the liquid flow was resumed.

In the fourth step, a dispersion of BTO particles of the present invention was produced in the same manner as in Example 1, except that this third solution was used. Next, the dispersion was concentrated using a rotary evaporator, and then the solvent was replaced with ethanol using an ultrafiltration membrane, yielding a dispersion with a solids concentration of 30% by mass.

[Comparative Example 4]
The first and second steps were carried out in the same manner as in Example 1.

In the third step, the third solution was prepared in the same manner as in Example 1, except that the second solution and the first solution were adjusted to 20°C. Under these conditions, the production line became clogged 2.0 hours after the start of operation, so the production line was cleaned and the liquid flow was resumed.

In the fourth step, a dispersion of BTO particles of the present invention was produced in the same manner as in Example 1, except that this third solution was used. Next, the dispersion was concentrated using a rotary evaporator, and then the solvent was replaced with ethanol using an ultrafiltration membrane, yielding a dispersion with a solids concentration of 30% by mass.

[Comparative Example 5]
A dispersion of BTO particles of the present invention was produced in the same manner as in Example 1, except that steps up to the third step were carried out, and in the fourth step, the third solution was heated to 50° C. and maintained at this temperature for 12 hours. Next, the dispersion was concentrated using a rotary evaporator, and then the solvent was replaced with ethanol using an ultrafiltration membrane, yielding a dispersion with a solids concentration of 30% by mass.

Claims (10)

a first step of mixing the barium alkoxide, the titanium alkoxide, and an organic solvent having a hydroxyl group in an atmosphere of a relative humidity of 50% or less so that the atomic ratio of barium to titanium (Ba/Ti ratio) is 0.90 to 1.10 and the total concentration of the barium alkoxide and the titanium alkoxide is 0.5 to 10.0 mol/kg;
a second step of maintaining the first solution obtained in the first step at −40 to 12° C. for 3 hours or more;
a third step of mixing the first solution obtained in the second step with a second solution containing water in a continuous reactor at 15°C or less;
a fourth step of heating the third solution obtained in the third step to 60°C or higher;
A method for producing a dispersion of barium titanate particles, comprising the steps of: The method for producing a dispersion of barium titanate particles described in claim 1, characterized in that in the second step, the first solution is maintained at -18 to 12°C for 3 hours or more. The method for producing a dispersion of barium titanate particles described in claim 1, characterized in that in the second step, the first solution is maintained at -18 to 12°C for 3 to 96 hours. The method for producing a dispersion of barium titanate particles described in claim 1, characterized in that the molar ratio (water/(barium alkoxide + titanium alkoxide)) of the number of moles of water in the second solution (used in the third step) to the sum of the number of moles of barium alkoxide and titanium alkoxide in the first solution is 1 to 10. The method for producing a dispersion of barium titanate particles described in claim 1, characterized in that the second solution contains alcohol, and the mass ratio of water to alcohol (water/alcohol) is 0.05 to 1.00. The method for producing a dispersion of barium titanate particles described in claim 1, characterized in that in the third step, the flow rate of the first solution is 4 L/Hr or more. 2. The method for producing a dispersion liquid of barium titanate particles according to claim 1, wherein the first solution and the second solution are at 15° C. or less in the third step. The method for producing a dispersion of barium titanate particles described in claim 1, characterized in that the solids concentration is adjusted to 20 to 60 mass % after the fourth step. A dispersion of barium titanate particles, the particles having a _D50 particle size (A) of 3 to 30 nm, a _D90 particle size (B) of 8 to 80 nm, and a crystallite size (C) of 5 to 15 nm, as measured by a dynamic light scattering method, and a ratio (A/C) of the _D50 particle size to the crystallite size of 0.3 to 5.0,
The dispersion is adjusted to a solid content concentration of 30% by mass using ethanol as a solvent, and the dispersion is heated at 50°C for 3 hours. After that, the ratio (E/C) of the _D50 particle size (E) obtained by a dynamic light scattering method to the crystallite size (C) is 0.3 to 7.0.
A dispersion of barium titanate particles, characterized in that the content of halogen elements relative to the solid content in the dispersion is less than 500 ppm. The dispersion of barium titanate particles according to claim 9, characterized in that the solids concentration is 10 to 60 mass%.