Spherical strontium titanate microparticle powder, dispersion, and resin composition

Abstract

The spherical strontium titanate-based fine particle powder according to the present invention is characterized by being spherical, having an average primary particle diameter of less than 50 nm, having a crystallinity of 86% or more as determined from the particle density, and having a high crystallinity, and thus can provide a resin composition such as a dispersion or a composite film in which the water content is low and the particles are uniformly distributed.

Description

Technical Field

[0001] An object of the present invention is to obtain spherical strontium titanate-based fine-particle powder that is most suitable as a filler. Background Art

[0002] In recent years, with the miniaturization, higher performance, and lighter weight of various electronic devices, there is an increasing demand for organic-inorganic hybrid materials that impart the functionality (refractive index, dielectric constant, electrical conductivity, magnetic properties, thermal conductivity, etc.) of inorganic fillers while maintaining the processability of organic resins.

[0003] For example, brightness-enhancing films used in displays and diffractive optical elements used in AR / MR glass require high refractive indices that cannot be achieved with a single resin component. This is to achieve properties such as high brightness, thin film thickness, and improved viewing angles. Therefore, research is underway to increase the refractive index of resin films by adding high-refractive-index inorganic fillers to the resin.

[0004] Furthermore, as electronic components become thinner, shorter, and more functional, research and development is actively underway to replace insulating films of thin film transistors (TFTs) with inorganic materials such as silicon nitride by resin compositions containing easily patternable resins and high-dielectric inorganic fillers.

[0005] On the other hand, strontium titanate is a compound with a perovskite structure and a highly functional material, making it used in a variety of applications. For example, it has optical applications such as pigments with a high refractive index, reflective materials, and light-concentrating materials, as well as ceramic capacitors due to its high dielectric constant. Furthermore, it has been used in visible light photocatalysts due to its photocatalytic activity, and in semiconductors, semiconductor capacitors, thermoelectric materials, EL, and light-emitting materials due to its semiconductorization by adding other elements.

[0006] Therefore, by forming a highly functional composite of strontium titanate and a resin, it is expected that a new material with functionality that cannot be achieved with resin alone can be produced.

[0007] The filler in such hybrid materials is dispersed in a solvent or resin for use. In addition to having a sufficiently small particle size, the inorganic filler must also be uniformly dispersible to prevent turbidity in the resulting composite film after mixing with a resin or the like and coating, ensuring transparency. Specifically, for film transparency, fine spherical particles are preferred, while for uniform dispersibility, high dispersion stability in hydrophobic resins or solvents is desirable.

[0008] However, inorganic fillers typically have defects on or within their particles, and are doped with water and hydroxyl groups, resulting in high hydrophilicity. This leads to low dispersion stability in hydrophobic resins and solvents, and the inorganic fillers are prone to aggregation. In particular, the more suitable the filler particles are, the higher the proportion of structurally unstable particle surfaces becomes, making it difficult to obtain particles with high crystallinity. This increases the number of particle defects and makes dispersion stability difficult to achieve.

[0009] Therefore, there is a need for an inorganic filler that is fine enough to achieve transparency of a composite film and satisfies both characteristics of having few particle defects and high crystallinity to achieve dispersion stability in a solvent.

[0010] There have been various reports on strontium titanate-based fine particles. Prior art literature Patent Literature

[0011] Patent Document 1: Japanese Patent Application Laid-Open No. H06-48734 Patent Document 2: Japanese Patent Application Laid-Open No. 2018-20919 Patent Document 3: International Publication No. 2015 / 152237 Summary of the Invention -Problems to be solved by the invention-

[0012] However, although strontium titanate-based fine-particle powder suitable for the above-mentioned filler is currently most desired, it has not yet been obtained.

[0013] Specifically, while Patent Document 1 describes a method for producing strontium titanate fine-particle powder with an average particle size of 0.05 μm or less, it does not consider the crystallinity of the resulting strontium titanate. Furthermore, this method requires an in-line mixer to ensure instantaneous and uniform mixing of the reactants, making the process complex and undesirable industrially.

[0014] Patent Document 2 describes a method for obtaining spherical strontium titanate by adding a hydroxycarboxylic acid and a third component to a hydrolyzate of a titanium compound and a water-soluble strontium salt and reacting them in a strong alkaline aqueous solution. However, no consideration is given to crystallinity.

[0015] Patent Document 3 discloses that spherical strontium titanate having an average particle size of 50 to 150 nm is obtained by a wet reaction. However, an average particle size of 50 nm or more does not provide good adhesion to resin and is therefore not suitable for use as a filler.

[0016] Therefore, an object of the present invention is to provide fine and highly crystalline spherical strontium titanate-based fine particles suitable as a filler in a composite material. -Solutions to solve the problem-

[0017] The above technical problems can be solved by the present invention as described below.

[0018] Specifically, the present invention provides a spherical strontium titanate-based fine-particle powder characterized in that the spherical strontium titanate-based fine-particle powder has an average primary particle size of less than 50 nm and a crystallinity defined by the following formula of 86% or more. Crystallinity [%] = particle density / theoretical density × 100 (Present invention 1)

[0019] The present invention also provides a dispersion containing the spherical strontium titanate-based fine particle powder according to Invention 1 (Invention 2).

[0020] Furthermore, the present invention provides a resin composition comprising the spherical strontium titanate-based fine particle powder according to Invention 1 and a resin (Invention 3). -Effects of the Invention-

[0021] According to the present invention, the spherical strontium titanate-based fine-particle powder is sufficiently fine that, when mixed with a resin or the like and coated, the resulting composite film exhibits transparency without turbidity. Furthermore, the fine-particle powder has high crystallinity, resulting in low incorporation of water and hydroxyl groups into the particles, and dispersions containing the powder exhibit excellent dispersion stability. Therefore, the powder is suitable for use as a filler in organic-inorganic hybrid materials and can be processed and applied to a variety of applications.

[0022] The dispersion containing spherical strontium titanate-based fine particle powder and the resin composition of the present invention can uniformly disperse the filler in the resin and reduce the deviation of the composite film performance, thereby forming a functional resin composition. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is an electron microscope photograph of the spherical strontium titanate fine particle powder obtained in Example 1. DETAILED DESCRIPTION

[0024] The structure of the present invention is described in detail below.

[0025] First, the spherical strontium titanate-based fine particle powder according to the present invention will be described.

[0026] The spherical strontium titanate-based fine particles of the present invention have an average primary particle size of less than 50 nm and a crystallinity defined by the following (Formula 1) of 86% or more. Crystallinity [%] = particle density / theoretical density × 100 (Formula 1)

[0027] The spherical strontium titanate-based fine particles of the present invention have an average primary particle size of less than 50 nm. By controlling the average primary particle size of the fine particles within this range, the filler loading can be increased while maintaining resin properties such as transparency, thereby achieving transparency in thin film coatings. The average primary particle size is preferably 48 nm or less, more preferably 45 nm or less, and even more preferably 30 nm or less. The lower limit is approximately 8 nm.

[0028] The spherical strontium titanate-based fine-particle powder of the present invention has a crystallinity of 86% or greater, as calculated by Formula 1. If the crystallinity is less than 86%, a large number of particle defects are present, and thus it can be considered that a large amount of water and hydroxyl groups have been incorporated, which is the main cause of particle aggregation in resins and solvents. In particular, when using fine particles with low crystallinity as a dispersion, the viscosity of the dispersion increases over time, gelling occurs, and the stability of the dispersion may not be achieved. A more preferred crystallinity is 87% or greater, and even more preferably 88% or greater. The upper limit of the crystallinity is 100%.

[0029] The spherical strontium titanate-based fine-particle powder of the present invention is spherical. Its circularity is preferably 0.80 or higher. If the circularity is less than 0.80, the powder may have a rectangular parallelepiped shape, which may result in a reduced packing density. A more preferred circularity is 0.81 or higher, and even more preferably 0.82 to 1.0.

[0030] The spherical strontium titanate-based microparticle powder of the present invention preferably has a perovskite structure represented by ABO3, and one or two of the constituent elements of the strontium titanate may be substituted. At least Sr is present at the A site, and a portion of the constituent elements may be substituted with an alkali metal or alkaline earth metal. The substituting element is not particularly limited, but is preferably an alkaline earth metal such as Ca or Ba. At least Ti is present at the B site, and a portion of the constituent elements may be substituted with a transition metal such as Zr.

[0031] The composition of the spherical strontium titanate-based microparticle powder of the present invention is evaluated by fluorescent S-rays, and the molar ratio of the A-site element to the B-site element, expressed as A / B, is preferably not less than 0.80 and not more than 1.05. If A / B is less than 0.80, the particle surface has an excessive amount of hydroxyl groups, and is therefore considered to be in a highly hydrophilic state, which becomes the main reason for the particles to agglomerate with each other in the resin or solvent, and for part or all of the fluid dispersion to solidify or gel, and it is possible that dispersion stability cannot be obtained. If A / B is greater than 1.05, the alkaline components on the particle surface are high, and thus become the main reason for the reduced dispersion stability in the solvent or resin. A more preferred A / B is not less than 0.82 and not more than 1.03, and further preferably not less than 0.83 and not more than 1.02.

[0032] Next, the method for producing the spherical strontium titanate-based fine particles according to the present invention will be described.

[0033] The spherical strontium titanate-based fine particle powder of the present invention can be obtained as follows: a titanium raw material is neutralized with an alkaline aqueous solution to obtain a hydrated titanium hydroxide slurry (neutralization reaction), which is then washed with water and heated, and then added to an aqueous strontium hydroxide solution for a wet reaction.

[0034] As titanium raw materials for the neutralization reaction, titanium tetrachloride and the like can be cited, and as alkaline aqueous solutions, strontium hydroxide, barium hydroxide, sodium hydroxide and the like can be cited. The addition ratio (Sr / Ti, Ba / Ti) is preferably 1.1 to 1.8 in terms of molar ratio. If the above addition ratio is less than 1.1, the yield of strontium titanate core particles is reduced, and if it is greater than 1.8, the distribution of primary particles of strontium titanate deteriorates. A more preferred addition ratio is 1.25 to 1.65. It should be noted that when sodium hydroxide is used as the alkaline aqueous solution, a molar ratio range of twice the above is preferred.

[0035] The reaction concentration of the reaction solution for producing strontium titanate-based microparticles is preferably 0.05 to 0.7 mol / L, calculated as a titanium compound. If the reaction concentration is less than 0.05 mol / L, the yield is low, making industrialization unsuitable. If it is greater than 0.7 mol / L, the amount of strontium hydroxide in the reaction solution exceeds the solubility, causing Sr(OH)2 to precipitate, making a uniform liquid-phase reaction difficult.

[0036] After the neutralization reaction, the obtained hydrated titanium hydroxide slurry is washed with water to a degree that can fully remove impurities, and heated to reduce the temperature difference with the solution during the reaction to obtain uniform particles. The heating method is not particularly limited, and a mantle heater, an electric heater, etc. can be used. Then, the obtained hydrated titanium hydroxide slurry is added to the strontium hydroxide aqueous solution. The amount of strontium hydroxide aqueous solution added is: added to the Ti in the reaction solution in a molar ratio of Sr / Ti of 1.5 to 3.0, and a wet reaction is carried out. In addition, at this time, part of the composition can be replaced by adding barium hydroxide, zirconium oxychloride, etc.

[0037] Preferably, the wet reaction is carried out under a nitrogen atmosphere to prevent the strontium compound from reacting with carbon dioxide in the air.

[0038] Examples of wet process reactions include normal pressure reaction, pressurized reaction, and hydrothermal synthesis. One or more reaction steps may be combined, preferably with stirring. The reaction temperature of the wet process is preferably 60 to 300°C. If the reaction temperature of the wet process is less than 60°C, it is difficult to obtain a dense spherical strontium titanate-based fine particle powder. If the reaction temperature of the wet process is greater than 300°C, it is difficult to design a hydrothermal container. The reaction temperature is more preferably 65 to 280°C.

[0039] The reaction time of the wet reaction is preferably 1 to 24 hours. If the reaction time is shorter than 1 hour, sufficient crystallinity may not be achieved, while if it is longer than 24 hours, productivity is poor and industrialization is not possible. The reaction time is more preferably 1.5 to 16 hours, and even more preferably 2 to 12 hours.

[0040] After the wet reaction, the product is washed with water and dried. Furthermore, the pH can be adjusted to approximately 4.0 to 8.0 using a pH adjuster such as acetic acid before washing. Excess strontium and impurities such as Na, K, and Cl can also be removed by washing. Heat treatment, pulverization, fragmentation, classification, or surface treatment can then be performed as needed.

[0041] Next, the dispersion containing the spherical strontium titanate-based fine particle powder according to the present invention will be described.

[0042] As the dispersion solvent in the present invention, either an aqueous system or a solvent system can be used.

[0043] As the dispersing solvent for the aqueous dispersion, water, alcoholic solvents such as methanol, ethanol, propanol, isopropanol, and butanol; glycol ether solvents such as methyl cellosolve, ethyl cellosolve, propyl cellosolve, and butyl cellosolve; ethylene oxide or propylene oxide addition polymers such as diethylene glycol, triethylene glycol, polyethylene glycol, dipropylene glycol, tripropylene glycol, and polypropylene glycol; alkylene glycols such as ethylene glycol, propylene glycol, and 1,2,6-hexanetriol; and water-soluble organic solvents such as glycerol and 2-pyrrolidone can be used. These dispersing solvents for the aqueous dispersion can be used alone or in combination of two or more, depending on the intended use.

[0044] Examples of dispersing solvents used in solvent-based dispersions include aromatic hydrocarbons such as toluene and xylene; ketones such as methyl ethyl ketone and cyclohexanone; amides such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone; alcohol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, propylene glycol monomethyl ether, and propylene glycol monoethyl ether; ether acetates such as ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, and propylene glycol monoethyl ether acetate; acetates such as ethyl acetate, butyl acetate, and isobutyl acetate; lactic acid esters such as methyl lactate, ethyl lactate, and propyl lactate; cyclic esters such as ethylene carbonate, propylene carbonate, and γ-butyrolactone; and various monomers. These dispersing solvents used in solvent-based dispersions can be used alone or in combination of two or more, depending on the intended use.

[0045] The concentration of the spherical strontium titanate-based fine particles in the dispersion of the present invention is preferably 5 to 60% by weight. If the concentration of the spherical strontium titanate-based fine particles in the dispersion is less than 5% by weight, the productivity of the subsequent process is low, while if it is greater than 60% by weight, it is difficult to say that the slurry has high fluidity. The concentration of the spherical strontium titanate-based fine particles in the dispersion is more preferably 10 to 55% by weight, and even more preferably 15 to 50% by weight.

[0046] The dispersion of the present invention may further include dispersants, additives (resins, defoamers, auxiliary agents, etc.) as needed. The dispersant may improve dispersion stability by adsorption, bonding, or coating on a portion or all of the surface of the spherical strontium titanate-based fine particles. The dispersant in the present invention may be appropriately selected based on the type of spherical strontium titanate-based fine particles and the type of the dispersion solvent used. Examples of the dispersant include organic silicon compounds such as alkoxysilanes, silane coupling agents, and organopolysiloxanes, organic titanium compounds such as titanate coupling agents, organic aluminum compounds such as aluminate coupling agents, organic zirconium compounds such as zirconate coupling agents, surfactants, or polymer dispersants. One of these dispersants may be used or a mixture of two or more may be used based on the purpose and application.

[0047] Examples of the organosilicon compound include alkoxysilanes such as methyltrimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, phenyltriethoxysilane, ethyltriethoxysilane, propyltriethoxysilane, butyltriethoxysilane, hexyltriethoxysilane, octyltriethoxysilane, tetraethoxysilane, and tetramethoxysilane; vinyltrimethoxysilane, vinyltriethoxysilane, γ-aminopropyltriethoxysilane, γ-epoxypropyltriethoxysilane, and the like; Silane coupling agents such as oxypropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, and γ-chloropropyltrimethoxysilane; organopolysiloxanes such as polysiloxane, methylhydrogenpolysiloxane, and modified polysiloxane.

[0048] Examples of the organic titanium compound include isopropyl triisostearoyl titanate, isopropyl tris(dioctyl pyrophosphate) titanate, bis(dioctyl pyrophosphate)oxy acetate titanate, isopropyl tris(N-aminoethyl-aminoethyl) titanate, tris(dioctyl pyrophosphate)ethylene titanate, isopropyl dioctyl pyrophosphate titanate, isopropyl tris(dodecyl benzenesulfonyl) titanate, titanium tetra-n-butoxide, titanium tetra-2-ethylhexyl oxide, and titanium tetra-n-butoxide. tetra-2-ethylhexoxide), tetraisopropyl bis(dioctyl phosphite)titanate, tetraoctyl bis(ditridecyl phosphite)titanate, tetra(2,2-diallyloxymethyl-1-butyl)bis(ditridecyl)phosphite titanate, tetraoctyl bis(ditridecyl phosphite)titanate, tetra(2,2-diallyloxymethyl-1-butyl)bis(ditridecyl)phosphite titanate, tetraoctyl bis(ditridecyl phosphite)titanate, tetra(2-2-diallyloxymethyl-1-butyl)bis(ditridecyl)phosphite titanate, bis(dioctyl pyrophosphate)oxyacetate titanate, bis(dioctyl pyrophosphate)vinyl titanate, and the like.

[0049] Examples of the organoaluminum compound include acetoalkoxyaluminum diisopropylate, aluminum diisopropoxymonoethyl acetoacetate, aluminum trisethyl acetoacetate, and aluminum trisacetyl acetonate.

[0050] Examples of the organic zirconium compound include zirconium tetrakisacetylacetonate, zirconium dibutoxybisacetylacetonate, zirconium tetrakisethyl acetoacetate, zirconium tributoxy monoethyl acetoacetate, and zirconium tributoxy acetylacetonate.

[0051] Examples of the surfactant include anionic surfactants such as fatty acid salts, sulfates, sulfonates, and phosphates; nonionic surfactants such as polyethylene glycol nonionic surfactants such as polyoxyethylene alkyl ethers and polyoxyethylene aryl ethers, and polyol nonionic surfactants such as sorbitan fatty acid esters; cationic surfactants such as amine salt cationic surfactants and quaternary ammonium salt cationic surfactants; and amphoteric surfactants such as alkyl betaines such as alkyl dimethylaminoacetic acid betaine and alkyl imidazolines.

[0052] As the polymer dispersant, styrene-acrylic acid copolymer, styrene-maleic acid copolymer, polycarboxylic acid and its salt, etc. can be used.

[0053] The amount of dispersant added depends on the total surface area of ​​the strontium titanate-based fine-particle powder in the dispersion and can be appropriately prepared according to the purpose of the dispersion of the strontium titanate-based fine-particle powder and the type of dispersant. Generally, by adding 0.01 to 100 weight % of dispersant relative to the strontium titanate-based fine-particle powder in the dispersion solvent, the strontium titanate-based fine-particle powder can be uniformly and finely dispersed in the dispersion solvent, and the dispersion stability can also be improved.

[0054] In addition to being added directly to the dispersion solvent, the dispersant can also be pre-treated in the spherical strontium titanate-based fine-particle powder. Furthermore, any method capable of surface treatment to coat a portion or all of the surface of the spherical strontium titanate-based fine-particle powder is not particularly limited. However, a method in which the strontium titanate-based fine particles are disintegrated by mechanical force using a bead mill, homogenizer, or the like, followed by mixing with the surface treatment agent for surface treatment is preferred. The dispersion time is not particularly limited, but preferably, the mixture is stirred and mixed at room temperature for approximately 30 minutes.

[0055] Next, the resin composition containing the spherical strontium titanate-based fine particle powder according to the present invention will be described.

[0056] The resin used in the resin composition is not particularly limited. Acrylic resin, polycarbonate, polystyrene resin, polyester resin, polyimide resin, polymethyl methacrylate (PMMA), AS resin, silicone resin, fluororesin, etc. can be used. One of these resins can be appropriately selected or two or more can be mixed and used according to the purpose and application.

[0057] The solid content, i.e., the concentration of the strontium titanate-based fine particle powder in the resin composition of the present invention, is not particularly limited as long as it is dispersed in the resin, but is preferably approximately 10 to 60% by weight. If the solid content of the resin composition is less than 10% by weight, the productivity of the subsequent process is low. If it is greater than 60% by weight, fluidity may not be achieved. [Example]

[0058] Examples of the present invention are described below, but the present invention is not limited thereto.

[0059] For the photograph (25,000 times) obtained by observing the spherical strontium titanate-based fine-particle powder using a transmission electron microscope (JEM-F200 manufactured by JEOL Ltd.), the average primary particle size was measured from about 300 primary particles. Here, the average primary particle size refers to the particle size obtained by averaging the diameter of a circle with the same area as the area obtained from the photograph for each particle relative to all the particles measured. In addition, the particle shape is judged by the above-mentioned electron microscope photograph. Furthermore, the circularity is determined by (4π×area) / perimeter of the particle measured based on the above-mentioned electron microscope photograph. 2 express.

[0060] The composition of the spherical strontium titanate-based fine particle powder was measured using an S-ray diffractometer D8-ADVANCE (manufactured by Bruker Japan Co., Ltd.) (tube: Cu) within a 2θ range of 10 to 90° and calculated using the Rietveld method.

[0061] The compositional molar ratios of Sr / Ti, (Ba+Sr) / Ti, and Sr / (Ti+Zr) represented by A / B were measured using a fluorescent S-ray analyzer (ZSXPrimusII manufactured by Rigaku Corporation).

[0062] Particle density was measured using a "Particle Density Meter BELPYCNO" (manufactured by Microtrac Bell Co., Ltd.). For strontium titanate alone, the theoretical density was 5.13 g / cc. For barium solid solution, the theoretical density of barium titanate was 6.02 g / cc, and for zirconium solid solution, the theoretical density of strontium zirconate was 5.47 g / cc. The density was calculated using the following equation using the composition ratio with strontium titanate. Theoretical density of barium solid solution (BaxSryTiO3) = 6.02×x+5.13×y (Formula 2) Theoretical density of zirconium solid solution (SrTixZryO3) = 5.13×x+5.47×y (Formula 3)

[0063] The transparency of the coating films of the dispersions containing each particle powder was evaluated using the following method. 1 g of each particle powder, 9 g of propylene glycol monomethyl ether acetate (PGMEA), and 0.1 g of a polymer dispersant (Disperbyk-180, manufactured by BYK Chemie Japan Co., Ltd.) were dispersed in a paint shaker for 60 minutes. This dispersion was then applied to a PET film using a rod coater to form a 12 μm thick coating. Each coating film was visually inspected; transparent, non-turbid coatings were rated as "○," while turbid coatings were rated as "×."

[0064] The dispersion stability of dispersions containing each particle powder was evaluated using the following method. 5 g of each particle powder was mixed with 5 g of propylene glycol monomethyl ether acetate (PGMEA) and 0.5 g of a polymer dispersant (Disperbyk-180, manufactured by BYK Chemie Japan Co., Ltd.) and dispersed using a paint shaker for 60 minutes. The dispersion was allowed to stand at room temperature. Dispersions that did not gel after four days or more were rated as positive, while those that gelled within four days were rated as negative.

[0065] Example 1 A titanium tetrachloride aqueous solution is mixed with water to a molar concentration of Ti of 2.10 mol / l to obtain a mixed solution. A 20 wt% strontium hydroxide aqueous solution is added to the mixed solution to obtain a Sr / Ti molar ratio of 1.32 to obtain a titanium hydroxide slurry, which is then washed with water. The resulting titanium hydroxide slurry is placed in a strontium hydroxide aqueous solution pre-dissolved in a reaction vessel. At this time, the Sr / Ti molar ratio of the strontium hydroxide aqueous solution is adjusted to 2.0. In addition, the concentration during the reaction is 0.28 mol / l in terms of strontium titanate concentration. Then, the mixture is stirred continuously at 180°C for 8 hours to carry out a hydrothermal reaction. After the reaction, the mixture is cooled to room temperature, then washed with water, filtered, and dried to obtain a white spherical strontium titanate microparticle powder.

[0066] Electron microscopic observation of the resulting spherical strontium titanate fine particle powder revealed spherical particles with an average primary particle size of 17.4 nm. Furthermore, X-ray diffraction analysis indicated a single phase of strontium titanate (theoretical density 5.13 g / cc). The particle density of the resulting powder was measured to be 4.57 g / cc, and the crystallinity calculated from equation (1) was 89.1%.

[0067] Examples 2 to 5 Spherical strontium titanate fine particle powder was obtained in the same manner as in Example 1 except that the reaction temperature and reaction time were changed as shown in Table 1. S-ray diffraction measurement showed a single phase of strontium titanate (theoretical density 5.13 g / cc).

[0068] The production conditions are shown in Table 1, and the powder properties and evaluation results of the obtained fine-particle powder are shown in Table 2.

[0069] Example 6 Spherical strontium titanate fine particle powder was obtained in the same manner as in Example 1 except that acetic acid was added to the slurry after the hydrothermal reaction to adjust the pH of the slurry to 5.

[0070] Electron microscopic observation of the resulting spherical strontium titanate fine-particle powder revealed spherical particles with an average primary particle size of 17.4 nm. Furthermore, S-ray diffraction analysis revealed a single phase of strontium titanate (theoretical density 5.13 g / cc). The particle density of the resulting powder was measured to be 4.43 g / cc. Therefore, the crystallinity calculated from equation (1) was 86.4%.

[0071] Example 7 During the wet reaction, the molar ratio Sr / Ti of the strontium hydroxide aqueous solution was set to 1.0, barium hydroxide was added at a molar ratio Ba / Ti of 1.0, and the reaction temperature was set to 150°C. Except for this, a spherical strontium titanate microparticle powder containing barium solid solution was obtained in the same manner as in Example 1.

[0072] The obtained spherical barium solid solution strontium titanate fine particle powder is a spherical fine particle with a particle size of 19.2nm. S-ray diffraction measurement shows that it is a single phase of barium strontium titanate. In addition, Rietveld analysis shows that its composition is Sr 0.8 Ba 0.2 TiO3. According to equation (2), the theoretical density at this time is 5.33 g / cc. The particle density was measured to be 4.76 g / cc, and the crystallinity calculated according to equation (1) was 89.3%.

[0073] Example 8 Spherical zirconium solid-solution strontium titanate fine particles containing zirconium in a solid solution were obtained in the same manner as in Example 1 except that zirconium oxychloride was added during the wet reaction so as to adjust the molar ratio Zr / Ti to 0.1 and the reaction temperature was set to 260°C.

[0074] The obtained spherical zirconium solid solution strontium titanate fine particles are spherical particles with a particle size of 20.0nm. X-ray diffraction analysis shows that it is a single phase. In addition, Rietveld analysis shows that its composition is SrTi 0.94 Zr 0.06 O3. According to equation (3), the theoretical density at this time is 5.15 g / cc. The particle density was measured to be 4.67 g / cc. According to equation (1), the crystallinity is 90.7%.

[0075] Comparative Example 1 Strontium titanate fine particle powder was prepared with reference to Example 19 of Patent Document 1. That is, a titanium tetrachloride aqueous solution was added to pure water and stirred for 1 hour. 5% ammonia water was added dropwise to the aqueous solution to obtain a white slurry with a pH of 7.8. After filtering and washing the slurry with water, the slurry was made into a slurry again, heated to 60°C, acetic acid was added, and aged at pH 6.0 for 40 minutes. After aging, the slurry was filtered and washed with water to obtain a hydrated titanium hydroxide gel cake. After adding pure water to the hydrated titanium hydroxide gel cake, the boiled slurry and the strontium hydroxide aqueous solution were adjusted to an Sr / Ti ratio of 1.2, mixed by a line mixer, and then refluxed at 80°C for 4 hours for aging. After aging, the slurry was filtered, washed with water, and dried.

[0076] The obtained strontium titanate fine particle powder was observed under an electron microscope and was found to be spherical particles with an average primary particle size of 29.4 nm, a particle density of 4.30 g / cc, and a crystallinity of 83.8% as determined by equation (1).

[0077] Comparative Example 2 Strontium titanate fine-particle powder was prepared with reference to Example 1 of Patent Document 3. Specifically, a titanium tetrachloride aqueous solution having a Ti molar concentration of 1.35 mol / l was prepared. A 20 wt% aqueous strontium hydroxide solution was added to the aqueous solution to achieve an Sr / Ti molar ratio of 1.45, thereby obtaining a titanium hydroxide slurry. This slurry was placed in a nitrogen-purged reaction vessel and heated to 90°C while stirring. A 20 wt% aqueous strontium hydroxide solution was then added to achieve an Sr / Ti molar ratio of 1.2. Stirring was then continued at 90°C for 3 hours to terminate the reaction. After the reaction, the slurry was filtered, washed with water, and dried.

[0078] The obtained strontium titanate fine particle powder was observed under an electron microscope and was found to be spherical particles with an average primary particle size of 52.6 nm, a particle density of 4.30 g / cc, and a crystallinity of 83.8% as determined by equation (1).

[0079] [Table 1]

[0080] [Table 2]

[0081] Since the strontium titanate-based fine particles obtained in Examples 1 to 8 were all spherical and fine, the filler-filled films were colorless, transparent, and free of turbidity. On the other hand, the film containing the strontium titanate fine particle powder with an average primary particle size of 50 nm or greater obtained in Comparative Example 2 was turbid and lacked transparency.

[0082] Furthermore, the dispersions of the spherical strontium titanate-based fine-particle powders obtained in Examples 1 to 8 all had the same fluidity as when they were prepared after being allowed to stand for more than four days after being prepared, demonstrating dispersion stability. On the other hand, the dispersions containing the granular powders obtained in Comparative Examples 1 and 2 gelled two days after being prepared, demonstrating low dispersion stability. Specifically, the spherical strontium titanate-based fine-particle powders of the present invention have few intragranular voids, little residual moisture and hydroxyl groups, and high crystallinity, and therefore it is inferred that dispersions containing these granular powders can maintain a stable dispersion state. Therefore, the spherical strontium titanate-based fine-particle powders of the present invention can suppress aggregation even when mixed with resin as a filler, allowing for the production of uniform composite films. -Industrial Applicability-

[0083] Spherical strontium titanate based particulate powder of the present invention is fine spherical, therefore can obtain transparent composite film, because particle defect is also seldom and crystallinity is high, so the dispersion stability of dispersion and resin combination is high.In addition, can control average grain diameter according to purpose, easily improve the packing density of filler in composite film.Therefore, spherical strontium titanate based particulate powder of the present invention is most suitable for the resin combination in the used diffraction optical element of the used brightness enhancement film of display, XR (AR, MR, VR) glass etc., for the high refractive index inorganic filler of high refractive indexization or can be used for the high dielectric inorganic filler of the high dielectric resin composition of electronic components such as thin film transistor (TFT).

Claims

1. A spherical strontium titanate-based fine particle powder, characterized in that: The spherical strontium titanate-based fine-particle powder has an average primary particle size of less than 50 nm and a crystallinity defined by the following formula of 86% or more. Crystallinity [%] = particle density / theoretical density × 100 2. A dispersion, characterized in that The dispersion contains the spherical strontium titanate-based fine particle powder according to claim 1.

3. A resin composition, characterized in that The resin composition contains the spherical strontium titanate-based fine particle powder according to claim 1 and a resin.

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