Barium titanate slurry

Abstract

This invention provides a barium titanate slurry that has a low environmental impact and excellent crushability. [Solution] The solution contains barium titanate powder, quaternary ammonium hydroxide, and a solvent containing water, and the absolute value of the zeta potential measured is 10 mV or more.

Description

[Technical Field]

[0001] This disclosure relates to a barium titanate slurry consisting of an aqueous solvent, used for forming insulators in electronic devices and inter-electrode insertion layers (dielectric layers) and internal electrode layers in multilayer ceramic capacitors. [Background technology]

[0002] Slurries and pastes containing ceramic powder have traditionally been used as materials for forming insulators in many electronic devices, such as semiconductor devices, solar cells, multilayer ceramic capacitors (MLCCs), and displays, particularly for forming dielectric layers and internal electrode layers in multilayer ceramic capacitors. Insulators and dielectric layers in electronic devices are formed from these slurries and pastes by sheet forming methods such as the doctor blade method. In addition, internal electrode layers and other components are formed by mixing a slurry containing metal powder and a slurry containing ceramic powder, printing patterns using methods such as screen printing, and then firing the mixture.

[0003] Methods using slurries and pastes have advantages over vacuum process methods such as PVD (sputtering, vacuum deposition, etc.) and CVD, which require expensive vacuum equipment, including lower costs, the ability to handle non-planar shapes, and the ability to process large areas. However, because these slurries and pastes contain many organic components, methods using slurries and pastes inherently have environmental impact issues.

[0004] Specifically, for example, multilayer ceramic capacitors have a structure in which internal electrode layers and dielectric layers are alternately stacked, but currently they are obtained by the following manufacturing process. That is, a green sheet which will become the dielectric layer is formed from a ceramic dielectric slurry containing barium titanate powder, which has a perovskite-type crystal structure and is a ferroelectric as a ceramic powder. An internal electrode paste containing nickel powder as a metal powder, and an internal electrode paste containing barium titanate powder are printed onto the obtained green sheet by methods such as screen printing. The green sheets with the printed internal electrode pastes are stacked alternately on top of each other, and the resulting laminate is heat-treated to form a multilayer structure consisting of a sintered film of ceramic powder and metal powder.

[0005] Ceramic dielectric slurries and pastes for internal electrodes contain not only particulate components such as barium titanate powder and nickel powder, which are constituent materials of the dielectric layer and internal electrodes, but also large amounts of organic components such as resin binders, organic solvents, and dispersants, which are necessary to maintain a smooth and dense film structure from the printing process to the heat treatment process. In particular, for the molding of sheets such as green sheets, organic solvent-based slurries are used as barium titanate slurries due to their ease of drying after molding.

[0006] These organic components must ultimately be removed from the film structure, and current electronic device manufacturing processes incorporate steps to thermally decompose these organic components. Therefore, current electronic device manufacturing processes, including those for multilayer ceramic capacitors, require not only the cost of organic components contained in the slurry or paste, but also a significant amount of thermal energy for removing these organic components in addition to the thermal energy required for powder sintering. This presents a major challenge in reducing environmental impact in a society where carbon neutrality is increasingly demanded.

[0007] From the perspective of reducing environmental impact, the application of aqueous slurries and pastes containing metal powders and ceramic powders, with the use of organic components minimized as much as possible, is being considered.

[0008] However, regarding the application of aqueous slurries and pastes, by making these slurries and pastes aqueous, especially in the case of ceramic powders such as barium titanate powder, the constituent components in water, specifically in the case of barium titanate, Ba 2+ It faces difficult problems such as the deterioration of particulate components due to elution and the coarsening of particulate components due to increased aggregation, making its realization not easy. In particular, particles that have coarsened along with the deterioration of particulate components become firmly bound together, making them extremely difficult to break down. Therefore, in order to apply aqueous slurries and pastes, practical properties such as the ability to easily break down aggregated particles during the process are required.

[0009] While it is possible to suppress the degradation and aggregation of particle components by applying a protective film to the particle surface with a large amount of organic components beforehand, this not only reduces the particle properties due to the replacement of constituent elements on the particle surface, but also necessitates a process to remove the large amount of organic components.

[0010] Japanese Patent Publication No. 5-208860 discloses a method for producing an aqueous suspension containing a powdered ceramic material such as barium titanate, comprising the steps of: washing solid particles in water before producing the suspension; adding an anionic compound, particularly in the form of sulfate, carbonate, iodate, chromate, oxalate, citrate and / or tartrate; producing the suspension and / or storing the finished suspension in a gaseous atmosphere where CO2 is absent; producing the suspension and storing the finished suspension at a temperature of 20°C or lower, preferably 15°C or lower; and adding an additional dispersant to the suspension when the re-aggregation of solid particles in the suspension has not yet begun or has begun. These steps are carried out individually or in combination.

[0011] Furthermore, regarding nickel slurry, Japanese Patent Publication No. 2006-028320 discloses an aqueous electrode ink in which metal powder such as nickel powder is contained in an amount of 25% to 40% by weight relative to the total weight of the aqueous electrode ink, at least two water-soluble resins with different average molecular weights selected from water-soluble resins are contained in an amount of 3 to 6 parts by weight per 100 parts by weight of metal powder, an aqueous plasticizer is contained in an amount of 1.5 to 1.9 times the weight of the water-soluble resins, and the remainder is water, wherein the average molecular weight of one water-soluble resin is 5,000 to 10,000 and the average molecular weight of the other water-soluble resin is 150,000 to 360,000.

[0012] Japanese Patent Publication No. 2006-210301 discloses a conductive ink comprising nickel powder having an average primary particle size of 100 nm or less dispersed in a dispersion medium mainly composed of water, alcohols, glycols, and saturated hydrocarbons having a boiling point of 300°C or less at atmospheric pressure, wherein the dispersion medium contains one or more metal salts or metal oxides selected from those containing Ti, V, Ni, Cu, Zn, Y, Nb, Mo, Ag, In, Sn, Ta, and W as film density improving agents for improving the film density of a conductor formed using the conductive ink.

[0013] Japanese Patent Publication No. 2002-317201 discloses an aqueous nickel slurry comprising water, nickel fine powder in which an insoluble inorganic oxide, which is an oxide or complex oxide containing silicon, aluminum, or zirconium, is fixed to the surface of individual nickel fine particles, polyacrylic acid, its ester or a salt thereof, and organic group-substituted ammonium hydroxide. [Prior art documents] [Patent Documents]

[0014] [Patent Document 1] Japanese Patent Application Publication No. 5-208860 [Patent Document 2] Japanese Patent Publication No. 2006-028320 [Patent Document 3] Japanese Patent Application Laid-Open No. 2006-210301 [Patent Document 4] Japanese Patent Application Laid-Open No. 2002-317201 [Summary of the Invention] [Problems to be Solved by the Invention]

[0015] In Japanese Patent Application Laid-Open No. 5-208860, re-aggregation of primary particles can be prevented and the long-term stability of an aqueous suspension can be improved. However, a suspension containing a specific anion and a dispersant exhibits its intended function only under extremely strict conditions of storage in an atmosphere without carbon dioxide and at 20°C or lower, which makes it unsuitable for practical use.

[0016] In Japanese Patent Application Laid-Open Nos. 2006-028320 and 2006-210301, although particles such as nickel powder can be sufficiently dispersed in an aqueous slurry, a large amount of resin, organic salts, inorganic salts, etc. must be used as dispersion aids, which makes it difficult to reduce the energy for separating the particles and the dispersion aids.

[0017] On the other hand, in Japanese Patent Application Laid-Open No. 2002-317201, an insoluble inorganic oxide is fixed to the particle surface of nickel powder instead of an organic component. However, since the particle surface of nickel powder is covered with an insoluble inorganic oxide, the particle properties and applications are greatly limited unless it is decomposed and removed by heating or the like.

[0018] An object of the present disclosure is to provide an aqueous barium titanate slurry with a low environmental load that can easily disintegrate aggregated particles during the process without applying a protective film to the particle surface with a large amount of organic components and without causing problems such as limitations on particle properties and applications, without using an insoluble non-electrolyte fixed to the particle surface. [Means for Solving the Problems]

[0019] A barium titanate slurry according to one aspect of the present disclosure comprises barium titanate powder, a quaternary ammonium hydroxide, and a solvent containing water, and is characterized in that the absolute value of the zeta potential in zeta potential measurement is 10 mV or more.

[0020] In a barium titanate slurry according to one aspect of this disclosure, it is preferable that the quaternary ammonium hydroxide has 16 or fewer carbon atoms.

[0021] In a barium titanate slurry according to one aspect of the present disclosure, the quaternary ammonium hydroxide is preferably at least one selected from tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide.

[0022] In one embodiment of the barium titanate slurry of this disclosure, it is preferable that the pH is 10 or higher based on a liquid temperature of 25°C.

[0023] In a barium titanate slurry according to one aspect of the present disclosure, the solvent preferably includes an organic solvent with a relative permittivity of 20 or more.

[0024] In this case, the organic solvent is preferably at least one selected from methanol, ethanol, and 1-propanol.

[0025] A barium titanate slurry according to one aspect of the present disclosure preferably contains a polymer electrolyte and has an absolute value of 15 mV or more for its zeta potential.

[0026] In this case, the polymer electrolyte is preferably at least one selected from polydiallyldimethylammonium chloride, sodium polystyrene sulfonate, polyethyleneimine, sodium polyacrylate, and ammonium polyacrylate.

[0027] In a barium titanate slurry according to one aspect of the present disclosure, the number-average particle size of the barium titanate powder in terms of the equivalent circular diameter is preferably 10 nm or more and 280 nm or less.

[0028] In a barium titanate slurry according to one aspect of the present disclosure, the content of the barium titanate powder is preferably 0.5% by mass or more and 40% by mass or less, and more preferably 1% by mass or more and 20% by mass or less, based on the total amount of the barium titanate slurry. [Effects of the Invention]

[0029] Barium titanate slurry according to one aspect of this disclosure has a low environmental impact, excellent pulverizability, and can be applied to the manufacturing process of electronic devices such as multilayer ceramic capacitors, in line with a carbon-neutral society. [Modes for carrying out the invention]

[0030] The inventors of this disclosure diligently investigated means to realize an easily cleavable aqueous barium titanate slurry without using insoluble non-electrolytes that adhere to the particle surface. They found that including a quaternary ammonium hydroxide in the aqueous barium titanate slurry is effective, and thus completed this disclosure.

[0031] A barium titanate slurry according to one aspect of the present disclosure comprises barium titanate powder, a quaternary ammonium hydroxide, and a solvent containing water, and is characterized in that the absolute value of the zeta potential in zeta potential measurement is 10 mV or more.

[0032] The components and properties of a barium titanate slurry according to an example of one aspect of this disclosure will be described below.

[0033] (1) Barium titanate powder Barium titanate powder is a ferroelectric material and is used as an insulator in electronic devices, as well as as a dielectric material for the inter-electrode insertion layer and internal electrode layer of multilayer ceramic capacitors (MLCCs).

[0034] When applying barium titanate powder to an aqueous slurry, as described above, Ba 2+ Since it is more difficult to suppress the deterioration and aggregation of particulate components due to the elution of certain substances, applying the barium titanate slurry in this example is advantageous.

[0035] Furthermore, with the increasing miniaturization of electronic devices such as multilayer ceramic capacitors, there is a demand for thinner ceramic dielectric layers and internal electrode layers.

[0036] Therefore, in the barium titanate slurry of this example, the number-average particle size of the barium titanate powder contained in the barium titanate slurry in terms of the equivalent circular diameter is preferably 10 nm or more and 280 nm or less, and more preferably 20 nm or more and 100 nm or less.

[0037] If the number-average particle diameter at the equivalent circle diameter is less than 10 nm, problems such as powder re-aggregation may occur. On the other hand, if the number-average particle diameter at the equivalent circle diameter exceeds 280 nm, problems such as difficulty in achieving uniform thickness may occur when forming internal electrodes using barium titanate slurry or a conductive paste to which the barium titanate slurry is added may occur.

[0038] The number-average particle diameter in terms of the equivalent circle diameter is obtained by selecting 100 observable primary particles of barium titanate powder using image analysis with observation images acquired using a scanning electron microscope (SEM), measuring their equivalent circle diameters (diameters of circles with equal area), and calculating the number-average value.

[0039] The amount of barium titanate powder in the barium titanate slurry in this example can be any amount depending on the intended use of the barium titanate slurry. For example, the amount of barium titanate powder can be any amount, but is not limited to this, and can be within a concentration range that can be crushed by a crusher. More specifically, the amount of barium titanate powder is preferably 0.5% by mass or more and 40% by mass or less, and more preferably 1% by mass or more and 20% by mass or less, relative to the total amount of barium titanate slurry.

[0040] The barium titanate powder applicable to the barium titanate paste in this example is not particularly limited, and any barium titanate powder can be used. For example, either experimentally synthesized or commercially available products may be used.

[0041] For example, barium titanate powder can be produced by known granulation methods using solid-phase or liquid-phase reactions. Specifically, known methods for producing barium titanate include the hydrothermal method, solid-phase method, oxalate method, and alkoxide method. In the hydrothermal method, barium titanate crystals are precipitated in an autoclave under high temperature and high pressure conditions. In the solid-phase method, barium titanate is synthesized by mixing titanium oxide powder and barium carbonate powder and heat-treating them at a temperature of approximately 1000°C.

[0042] Furthermore, the particle size of the barium titanate powder can be appropriately controlled by known methods depending on the granulation method.

[0043] (2) Quaternary ammonium hydroxide The barium titanate slurry of this disclosure contains a quaternary ammonium hydroxide. The quaternary ammonium hydroxide has the general formula: [R 1 , R 2 , R 3 , R 4 N + ][OH - It has the composition represented by [ ]. In the general formula, R represents an alkyl group.

[0044] Quaternary ammonium hydroxide almost completely ionizes in an aqueous solution to simultaneously generate hydroxide ions and ammonium ions. The hydroxide ions make the pH of the aqueous solution alkaline, that is, the pH is 7 or higher, and it becomes possible to suppress the progress of aggregation due to the elution of Ba 2+ in an acidic atmosphere. Furthermore, due to the interposition of charged quaternary ammonium ions between the particles constituting the barium titanate powder, the aggregability of the barium titanate powder is relaxed, and it becomes possible to facilitate its disintegration treatment.

[0045] In order to effectively exhibit such an effect, it is preferable that it has a high degree of dissociation in an aqueous solution and at the same time the length of the alkyl group is such that the action of the positive charge of the nitrogen atom is not hindered by steric hindrance.

[0046] From this point of view, the quaternary ammonium hydroxide preferably has 16 or more carbon atoms. When the carbon number is in the range of 4 or more and 16 or less, due to the synergistic effect of forming an alkaline environment in an aqueous solution and the interposition of charged quaternary ammonium ions between particles, the aggregability of barium titanate particles in the barium titanate slurry is remarkably relaxed. Therefore, even if the addition amount of quaternary ammonium hydroxide to the total amount of the solvent is very small, it is possible to provide an aqueous barium titanate slurry that is easily disintegrated.

[0047] General formula representing quaternary ammonium hydroxide: [R 1 , R 2 , R 3 , R 4 N + [OH - In this formula, R 1 , R 2 , R 3 , R 4 are each preferably an alkyl group having 1 or more and 4 or less carbon atoms, and are preferably composed of the same or different alkyl groups from each other.

[0048] Examples of quaternary ammonium hydroxides with such a structure include tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, trimethylethylammonium hydroxide, trimethylpropylammonium hydroxide, dimethyldipropylammonium hydroxide, monomethyltriethylammonium hydroxide, and monomethyltripropylammonium hydroxide. These quaternary ammonium hydroxides may be used individually or in combination of two or more.

[0049] For reasons unknown, among these, those in which the charge is easily distributed isotropically when ionized in a solvent are preferred. More specifically, the quaternary ammonium hydroxide is preferably at least one selected from tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide.

[0050] The content of quaternary ammonium hydroxide in the barium titanate slurry in this example is restricted to an amount that can set the absolute value of the zeta potential to 10 mV or more, preferably an amount that can set the absolute value of the zeta potential to 10 mV or more and the pH to 10 or more based on a liquid temperature of 25°C.

[0051] In other words, when preparing the barium titanate slurry in this example, a quaternary ammonium hydroxide is added to a water-containing solvent until the absolute value of the zeta potential is 10 mV or more, preferably until the absolute value of the zeta potential is 10 mV or more and the pH is 10 or more.

[0052] Specifically, although it varies depending on factors such as the amount of carbon dioxide dissolved in the solvent from the atmosphere, the concentration of quaternary ammonium hydroxide in barium titanate slurry is approximately several tens of millimol / L.

[0053] (3) pH The barium titanate slurry in this example contains quaternary ammonium hydroxide, and therefore its pH is 7 or higher at a liquid temperature of 25°C.

[0054] The pH of the barium titanate slurry is preferably 10 or higher at a liquid temperature of 25°C. If the pH is less than 10, acidification by dissolved carbon dioxide in the water and reaction with dissolved oxygen will occur, resulting in the loss of barium from the barium titanate powder. 2+ As the substance leaches out, aggregation becomes more likely. The aggregated and coarser particles, resulting from the degradation of the particulate components, become firmly bound together, which may make them difficult to break down. However, depending on the application and storage period of the barium titanate slurry, the pH of the barium titanate slurry at a liquid temperature of 25°C can be set to 10 or below.

[0055] While there is no particular upper limit to the pH of barium titanate slurry at a liquid temperature of 25°C, a pH above 13 is undesirable because it may increase the measurement error (alkalinity error) when using a pH meter with a typical glass electrode.

[0056] (4) Solvent The solvent used in the barium titanate slurry in this example is an aqueous solution of water mixed with a quaternary ammonium hydroxide. For the quaternary ammonium hydroxide to dissociate sufficiently, the solvent must be a polar solvent with a remarkably high dielectric constant, such as water.

[0057] In the barium titanate slurry of this example, the solvent may include an organic solvent with a relative permittivity of 20 or higher. That is, from the viewpoint of not excessively inhibiting the ionization of the electrolyte in the aqueous solution, a mixed solution containing an organic solvent with lower polarity than water can be used as the solvent. However, in order for the solvent to retain the properties of water, it is preferable to use an organic solvent whose volume ratio to the total solvent is less than 50% and which has a relative permittivity of 20 or higher.

[0058] Examples of organic solvents with a relative permittivity of 20 or higher include methanol, ethanol, and 1-propanol. These organic solvents may be used individually or in combination of two or more.

[0059] (5)Polymer electrolyte The barium titanate slurry in this example may contain a polymer electrolyte. By adding a polymer electrolyte that is highly dissociable in aqueous solution and carries a positive or negative charge, the agglomeration relaxation effect due to interparticle mediation can be enhanced together with the charged quaternary ammonium ions, thereby further improving the ease of disintegration of the barium titanate slurry.

[0060] Examples of polymer electrolytes include polydiallyldimethylammonium chloride, sodium polystyrene sulfonate, polyethyleneimine, sodium polyacrylate, and ammonium polyacrylate. These polymer electrolytes may be used individually or in combination of two or more types.

[0061] The amount of polymer electrolyte added is preferably in the range of 0.01% to 10% by mass relative to the barium titanate powder, and more preferably 0.1% to 5% by mass.

[0062] Furthermore, inorganic bases such as sodium hydroxide may promote aggregation by increasing the ionic strength of the aqueous solution simply by making the pH alkaline; therefore, it is preferable that the barium titanate slurry in this example does not contain inorganic bases.

[0063] (6) Absolute value of the zeta potential In this example, the barium titanate slurry has an absolute zeta potential of 10 mV or higher when measured. The zeta potential is the potential of the slip surface where liquid flow begins to occur in the electric double layer formed around particles in an aqueous solution. When the zeta potential approaches zero, the repulsive force between particles weakens, causing them to aggregate. In other words, if the interparticle mediation of quaternary ammonium hydroxide is normal, the absolute zeta potential of the barium titanate slurry will be 10 mV or higher, and if it is less than 10 mV, there is a possibility that the interparticle mediation of quaternary ammonium hydroxide is not functioning properly.

[0064] When the barium titanate slurry in this example contains a polymer electrolyte, the interparticle interaction of the polymer electrolyte also contributes to making it possible to achieve an absolute value of 15 mV or higher, preferably 20 mV or higher, in terms of zeta potential.

[0065] The zeta potential can be measured using any known method, such as electrophoresis, electroacoustics, or colloidal vibrational current spectroscopy.

[0066] (7) Decomposition In the barium titanate slurry of this example, known methods can be used to crush the barium titanate powder. Examples of crushing methods include ultrasonic homogenizers, ball mills, bead mills, automatic mortars, and thin-film swirling high-speed mixers.

[0067] (8) Uses of barium titanate slurry The barium titanate slurry in this example can be used in the same way as slurry and paste materials for electronic materials.

[0068] When manufacturing a dielectric paste using the barium titanate slurry in this example, the barium titanate powder in the barium titanate slurry is crushed by any method, and then a binder such as cellulose resin (ethylcellulose, nitrocellulose, etc.), acrylic resin, or phenolic resin is added to form a paste. Furthermore, by adding metal powder such as nickel powder, a conductive paste can also be produced.

[0069] The barium titanate slurry of this example and the barium titanate paste or conductive paste manufactured using this barium titanate can be used, for example, as dielectric material for the dielectric layer and internal electrode layer of multilayer ceramic capacitors, or as insulating material in electronic devices including multilayer ceramic capacitors.

[0070] In these applications, known methods can be used to apply the barium titanate slurry of this example and the barium titanate paste or conductive paste produced using this barium titanate slurry to various substrates. Such application methods include, for example, gravure printing, screen printing, spray coating, spin coating, dip coating, bar coating, knife coating, offset printing, flexographic printing, inkjet printing, and dispenser printing. Of these, dip coating or spin coating is preferred from the viewpoint of efficiently forming a coated film. [Examples]

[0071] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0072] First, the evaluation methods used in this embodiment and comparative example will be described.

[0073] (1) Method for measuring the number-average particle size The "number-average particle diameter" was obtained by performing image analysis using observation images captured with a scanning electron microscope (SEM: JEOL Ltd., model: JSM-7200F), arbitrarily selecting 100 observable primary particles of barium titanate powder, measuring their equivalent circle diameters (diameters of circles with equal area), and calculating the number-average value.

[0074] (2) Method for measuring zeta potential The "zeta potential" was measured using an electroacoustic zeta potential meter (Colloidal Dynamics LLC, model: ZetaProbe) while stirring the slurry at 250 rpm.

[0075] (3) Method for evaluating disintegration ability The barium titanate powder in the barium titanate slurry was crushed using a thin-film swirling high-speed mixer (Primix Corporation, model: Filmix 30-L) at a rotation speed of 22,000 rpm for 5 minutes.

[0076] Ten mL of the slurry after crushing was filtered through a membrane filter with a pore size of 0.5 μm or 1.0 μm (both manufactured by Merck KGaA). Undisintegrated particles larger than the pore size of each membrane filter were captured on the filter, and the amount of these undisintegrated particles was calculated by ICP emission spectrometry (inductively coupled plasma emission spectrometry) of a solution containing all of the undisintegrated particles dissolved in acid.

[0077] If the content of undisintegrated particles in the barium titanate slurry in a 1.0 μm pore size filter was less than 100 ppm, the disintegration performance was judged to be good. For both 1.0 μm and 0.5 μm pore size filters, if the content of undisintegrated particles in the barium titanate slurry was less than 100 ppm, the disintegration performance was judged to be excellent. For both 1.0 μm and 0.5 μm pore size filters, if the content of undisintegrated particles in the barium titanate slurry was 100 ppm or more, the disintegration performance was judged to be poor.

[0078] [Example 1] A barium titanate slurry was prepared containing water as the solvent and tetraethylammonium hydroxide (which has 8 carbon atoms) as the quaternary ammonium hydroxide.

[0079] (1) Barium titanate powder Commercially available barium titanate powder (manufactured by Toda Kogyo Co., Ltd., product number: T-BTO-020RF) was used as the barium titanate powder. Observation by scanning electron microscope (SEM) revealed that the particle shape was approximately spherical. Image analysis of the observed image showed that the number mean of the equivalent circle diameter was 40 nm.

[0080] (2) Preparation of barium titanate slurry A 10% by mass barium titanate slurry was prepared by adding tetraethylammonium hydroxide to water used as a solvent using a pH meter (Horiba, Ltd., model: LAQUAact D-73) while measuring the pH at a liquid temperature of 25°C until the pH reached 12. 12.6 g of this aqueous solution was mixed with 1.4 g of barium titanate powder, and then subjected to crushing treatment using a thin-film swirling high-speed mixer (Primix Corporation, Filmix 30-L). The amount of tetraethylammonium hydroxide added to the water was 17 mmol / L. The amount of slurry required for evaluation was repeatedly prepared using the above procedure.

[0081] (3) Evaluation (a) Zeta potential measurement of barium titanate slurry The zeta potential of the barium titanate slurry obtained during the preparation process was analyzed using an electroacoustic zeta potential meter and found to be -10.0 mV.

[0082] (b) Evaluation of the disintegration properties of barium titanate slurry using a 1.0 μm pore size filter. When the disintegration properties of the barium titanate slurry were analyzed by filtering it through a membrane filter with a pore size of 1.0 μm, the content of undisintegrated particles was found to be less than 100 ppm.

[0083] (c) Evaluation of the disintegration properties of barium titanate slurry using a 0.5 μm pore size filter. Analysis of the disintegration properties of barium titanate slurry by filtering it through a 0.5 μm pore size membrane filter revealed that it contained more than 100 ppm of undisintegrated particles.

[0084] Table 1 shows the preparation conditions for the barium titanate slurry, and Table 2 shows the evaluation results of the obtained barium titanate slurry. The same applies to Examples 2-11 and Comparative Examples 1-5.

[0085] [Example 2] A barium titanate slurry was prepared in the same manner as in Example 1, except that commercially available barium titanate powder (manufactured by Sakai Chemical Industry Co., Ltd., product number: BT-03, number average value of the equivalent circle diameter is 280 nm) was used as the barium titanate powder, and tetrabutylammonium hydroxide, which has 16 carbon atoms, was added as a quaternary ammonium compound in the barium titanate slurry preparation step. The amount of tetrabutylammonium hydroxide added to water was 17 mmol / L.

[0086] The zeta potential of the barium titanate slurry was -15.3 mV. Analysis after filtration with a 1.0 μm pore size filter showed that the undisintegrated particle content in the barium titanate slurry was less than 100 ppm, while analysis after filtration with a 0.5 μm pore size filter showed that the undisintegrated particle content in the barium titanate slurry was 100 ppm or more.

[0087] [Example 3] Barium titanate slurry was prepared in the same manner as in Example 1, except that commercially available barium titanate powder (manufactured by Toda Kogyo Co., Ltd., product number: T-BTO-60RF, number average value of the equivalent circle diameter was 70 nm) was used as the barium titanate powder, and in the preparation step of the barium titanate slurry, water and 1-propanol used as the solvent were mixed in a volume ratio of 9:1, and then tetrapropylammonium hydroxide, which has 12 carbon atoms, was added as a quaternary ammonium compound until the pH reached 10. The amount of tetrapropylammonium hydroxide added to water was 1.5 mmol / L.

[0088] The zeta potential of the barium titanate slurry was -15.9 mV. Analysis after filtration with a 1.0 μm pore size filter showed that the undisintegrated particle content in the barium titanate slurry was less than 100 ppm, while analysis after filtration with a 0.5 μm pore size filter showed that the undisintegrated particle content in the barium titanate slurry was 100 ppm or more.

[0089] [Example 4] As barium titanate powder, we used powder recovered from a commercially available 20% by mass barium titanate dispersion (manufactured by Daiken Chemical Industry Co., Ltd., product number: DLB-003-30TO40NAE). The procedure for recovering the barium titanate powder involved first mixing methanol with the barium titanate dispersion in a volume ratio of 5:5, and then centrifuging at 10,000 rpm for 10 minutes to separate the supernatant from the powder. Subsequently, methanol was added to the powder and ultrasonically dispersed, followed by another 10-minute centrifugal separation at 10,000 rpm. By performing the methanol supernatant-to-powder separation operation a total of three times, we obtained washed barium titanate powder. Observation by scanning electron microscope (SEM) revealed that the particle shape was approximately spherical. Image analysis of the observed images showed that the number-average value of the equivalent circle diameter was 10 nm.

[0090] Barium titanate slurry was prepared in the same manner as in Example 1, except that the barium titanate powder obtained from this recovery was used as the barium titanate powder, and in the preparation step of the barium titanate slurry, water and methanol used as the solvent were mixed in a volume ratio of 6:4, and then tetramethylammonium hydroxide, which has 4 carbon atoms, was added as a quaternary ammonium compound until the pH reached 13. The amount of tetramethylammonium hydroxide added to the water was 90 mmol / L.

[0091] The zeta potential of the barium titanate slurry was -19.8 mV. Analysis after filtration with a 1.0 μm pore size filter showed that the undisintegrated particle content in the barium titanate slurry was less than 100 ppm, while analysis after filtration with a 0.5 μm pore size filter showed that the undisintegrated particle content in the barium titanate slurry was 100 ppm or more.

[0092] [Example 5] Barium titanate slurry was prepared in the same manner as in Example 1, except that 0.05 g of polydiallyldimethylammonium chloride (molecular weight 8500) was added to the aqueous solution as a polymer electrolyte in the preparation step of each barium titanate slurry.

[0093] The zeta potential of the barium titanate slurry was +20.2 mV. Furthermore, analysis after filtration with a 1.0 μm pore size filter and a 0.5 μm pore size filter revealed that the content of undissolved particles was less than 100 ppm in both cases.

[0094] [Example 6] Barium titanate slurry was prepared in the same manner as in Example 1, except that 0.05 g of sodium polystyrene sulfonate (molecular weight 10000) was added to the aqueous solution as a polymer electrolyte in the preparation step of each barium titanate slurry.

[0095] The zeta potential of the barium titanate slurry was -43.0 mV. Furthermore, analysis after filtration with a 1.0 μm pore size filter and a 0.5 μm pore size filter revealed that the content of undissolved particles was less than 100 ppm in both cases.

[0096] [Example 7] In the preparation of each barium titanate slurry, water and ethanol used as solvents were mixed in a volume ratio of 8:2, then tetraethylammonium hydroxide was added, and 0.05 g of polyethyleneimine (molecular weight 1200) was added to the aqueous solution as a polymer electrolyte. Except for these differences, the barium titanate slurry was prepared in the same manner as in Example 1.

[0097] The zeta potential of the barium titanate slurry was +15.0 mV. Furthermore, analysis after filtration with a 1.0 μm pore size filter and a 0.5 μm pore size filter revealed that the content of undissolved particles was less than 100 ppm in both cases.

[0098] [Example 8] Barium titanate slurry was prepared in the same manner as in Example 1, except that 0.05 g of sodium polyacrylate (molecular weight 3500) was added to the aqueous solution as a polymer electrolyte in the preparation step of each barium titanate slurry.

[0099] The zeta potential of the barium titanate slurry was -61.8 mV. Furthermore, analysis after filtration with a 1.0 μm pore size filter and a 0.5 μm pore size filter revealed that the content of undissolved particles was less than 100 ppm in both cases.

[0100] [Example 9] Barium titanate slurry was prepared in the same manner as in Example 1, except that 0.05 g of ammonium polyacrylate (molecular weight 6000) was added to the aqueous solution as a polymer electrolyte in the preparation step of each barium titanate slurry.

[0101] The zeta potential of the barium titanate slurry was -62.3 mV. Furthermore, analysis after filtration with a 1.0 μm pore size filter and a 0.5 μm pore size filter revealed that the content of undissolved particles was less than 100 ppm in both cases.

[0102] [Example 10] In the preparation of each barium titanate slurry, 14.85 g of an aqueous solution prepared by adding tetraethylammonium hydroxide to water used as the solvent until the pH reached 12 was mixed with 0.15 g of barium titanate powder, and then subjected to a crushing treatment using a thin-film swirling high-speed mixer to prepare a 1% by mass barium titanate slurry. The barium titanate slurry was prepared in the same manner as in Example 1, except that in the preparation step of each barium titanate slurry, 0.15 g of barium titanate powder was mixed with tetraethylammonium hydroxide to water until the pH reached 12, and then subjected to a crushing treatment using a thin-film swirling high-speed mixer. The amount of tetraethylammonium hydroxide added to the water was 17 mmol / L.

[0103] The zeta potential of the barium titanate slurry was -10.2 mV. Analysis after filtration with a 1.0 μm pore size filter showed that the undisintegrated particle content in the barium titanate slurry was less than 100 ppm, while analysis after filtration with a 0.5 μm pore size filter showed that the undisintegrated particle content in the barium titanate slurry was 100 ppm or more.

[0104] [Example 11] In the preparation of each barium titanate slurry, 3 g of barium titanate powder was mixed with 12 g of an aqueous solution prepared by adding tetraethylammonium hydroxide to water used as the solvent until the pH reached 12, and then subjected to a crushing treatment using a thin-film swirling high-speed mixer to prepare a 20% by mass barium titanate slurry. The barium titanate slurry was prepared in the same manner as in Example 1, except that in the preparation process of each barium titanate slurry, 3 g of barium titanate powder was mixed with tetraethylammonium hydroxide to 12 g of an aqueous solution prepared with water used as the solvent, and then subjected to a crushing treatment using a thin-film swirling high-speed mixer. The amount of tetraethylammonium hydroxide added to the water was 17 mmol / L.

[0105] The zeta potential of the barium titanate slurry was -10.1 mV. Analysis after filtration with a 1.0 μm pore size filter showed that the undisintegrated particle content in the barium titanate slurry was less than 100 ppm, while analysis after filtration with a 0.5 μm pore size filter showed that the undisintegrated particle content in the barium titanate slurry was 100 ppm or more.

[0106] [Comparative Example 1] Barium titanate slurry was prepared in the same manner as in Example 1, except that, in the preparation step of the barium titanate slurry, only water was used as the solvent, without adding a quaternary ammonium hydroxide.

[0107] The zeta potential of the barium titanate slurry was +18.6 mV. Furthermore, analysis after filtration with a 1.0 μm pore size filter and a 0.5 μm pore size filter revealed that the content of undissolved particles was 100 ppm or more in both cases.

[0108] [Comparative Example 2] Barium titanate slurry was prepared in the same manner as in Comparative Example 1, except that an aqueous solution of water with sodium hydroxide added to adjust the pH to 12 was used as the solvent in the preparation step of the barium titanate slurry.

[0109] The zeta potential of the barium titanate slurry was -8.4 mV. Furthermore, analysis after filtration with a 1.0 μm pore size filter and a 0.5 μm pore size filter revealed that the content of undissolved particles was 100 ppm or more in both cases.

[0110] [Comparative Example 3] Barium titanate slurry was prepared in the same manner as in Example 2, except that trioctylmethylammonium chloride, a quaternary ammonium compound but not a quaternary ammonium hydroxide with 25 carbon atoms, was added to the water at a concentration of 17 mmol / L without pH adjustment.

[0111] The zeta potential of the barium titanate slurry was +19.5 mV. Furthermore, analysis after filtration with a 1.0 μm pore size filter and a 0.5 μm pore size filter revealed that the content of undissolved particles was 100 ppm or more in both cases.

[0112] [Comparative Example 4] Barium titanate slurry was prepared in the same manner as in Example 3, except that quaternary ammonium hydroxide was not added during the preparation of the barium titanate slurry.

[0113] The zeta potential of the barium titanate slurry was +16.3 mV. Furthermore, analysis after filtration with a 1.0 μm pore size filter and a 0.5 μm pore size filter revealed that the content of undissolved particles was 100 ppm or more in both cases.

[0114] [Comparative Example 5] Barium titanate slurry was prepared in the same manner as in Example 4, except that quaternary ammonium hydroxide was not added during the preparation of the barium titanate slurry.

[0115] The zeta potential of the barium titanate slurry was +15.7 mV. Furthermore, analysis after filtration with a 1.0 μm pore size filter and a 0.5 μm pore size filter revealed that the content of undissolved particles was 100 ppm or more in both cases.

[0116] [Table 1]

[0117] [Table 2]

[0118] [Discussion on the evaluation results] Table 2 shows that the examples satisfying the composition of the barium titanate slurry according to one aspect of this disclosure exhibit superior disintegration properties compared to the comparative examples. The reason why the examples, despite being aqueous barium titanate slurries, exhibit such excellent disintegration properties is understood from the comparison between Examples 1, 3, and 4 and Comparative Examples 1, 4, and 5. This is because the synergistic effect of the formation of an alkaline environment in the aqueous solution of quaternary ammonium hydroxide and the interparticle interposition of charged quaternary ammonium ions significantly reduces the aggregation of barium titanate particles in the barium titanate slurry, resulting in an easily disintegrable aqueous barium titanate slurry.

[0119] It is understood that the effects of this disclosure cannot be obtained when simply making the pH alkaline with a typical inorganic salt, as in Comparative Example 2, or when the quaternary ammonium compound has 25 carbon atoms and does not contain a hydroxide, as in Comparative Example 3.

Claims

1. A barium titanate slurry comprising barium titanate powder, quaternary ammonium hydroxide, and a solvent containing water, wherein the absolute value of the zeta potential measured is 10 mV or more.

2. The barium titanate slurry according to claim 1, wherein the quaternary ammonium hydroxide has 16 or fewer carbon atoms.

3. The barium titanate slurry according to claim 2, wherein the quaternary ammonium hydroxide is at least one selected from tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide.

4. The barium titanate slurry according to claim 1, wherein the pH is 10 or higher based on a liquid temperature of 25°C.

5. The barium titanate slurry according to claim 1, wherein the solvent comprises an organic solvent with a relative dielectric constant of 20 or more.

6. The barium titanate slurry according to claim 5, wherein the organic solvent is at least one selected from methanol, ethanol, and 1-propanol.

7. The barium titanate slurry according to claim 1, comprising a polymer electrolyte, wherein the absolute value of the zeta potential is 15 mV or more.

8. The barium titanate slurry according to claim 7, wherein the polymer electrolyte is at least one selected from polydiallyldimethylammonium chloride, sodium polystyrene sulfonate, polyethyleneimine, sodium polyacrylate, and ammonium polyacrylate.

9. The barium titanate slurry according to claim 1, wherein the number-average particle size of the barium titanate powder in the equivalent circular diameter is 10 nm or more and 280 nm or less.

10. The barium titanate slurry according to claim 1, wherein the content of the barium titanate powder is 0.5% by mass or more and 40% by mass or less based on the total amount of the barium titanate slurry.

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