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 particle A / B of 0.80-0.95 inclusive, and having high dispersion stability in a resin or a solvent and being capable of providing a composite film in which particles are uniformly distributed since the composition thereof is appropriately controlled.

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] In addition, 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 and 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 a hybrid material is required to have high transparency and uniform dispersibility. For transparency, fine spherical shapes are preferred, and for uniform dispersibility, high dispersion stability in a hydrophobic resin or solvent is preferred.

[0008] However, compounds with a perovskite structure typically represented by ABO3 have an alkali metal or alkaline earth metal at the A site, making the particle surface alkaline. This makes the particle highly hydrophilic and prone to agglomeration of inorganic fillers in hydrophobic resins and solvents. In particular, the larger the surface area of ​​the particles, the more suitable they are for the filler, making it difficult to achieve further dispersion stability.

[0009] Conventionally, there have been various reports on strontium titanate fine particles (Patent Documents 1 to 3). Prior art literature Patent Literature

[0010] Patent Document 1: Japanese Patent Application Laid-Open No. 2015-137208 Patent Document 2: Japanese Patent Application Publication No. 2019-151507 Patent Document 3: Japanese Patent Application Laid-Open No. 2016-69211 Summary of the Invention -Problems to be solved by the invention-

[0011] However, although strontium titanate-based fine-particle powder suitable for the above-mentioned filler is currently most desired, it has not yet been obtained.

[0012] That is, although Patent Document 1 describes that a hydrolyzate of a titanium compound and a water-soluble strontium salt are reacted in a strong alkaline aqueous solution to obtain strontium titanate fine particles, the fine particles are rectangular or cubic in shape and are therefore not suitable as fillers.

[0013] Furthermore, although Patent Documents 2 and 3 describe that spherical strontium titanate is obtained by adding a hydroxycarboxylic acid or 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, the presence of components other than strontium titanate makes it unsuitable as a filler.

[0014] Therefore, the technical problem to be solved by the present invention is to provide a fine spherical strontium titanate-based fine particle powder suitable for a filler in a composite material and a dispersion thereof having dispersion stability. -Solutions to solve the problem-

[0015] The above technical problems can be solved by the present invention as described below.

[0016] That is, the present invention is a spherical strontium titanate-based microparticle powder, characterized in that the spherical strontium titanate-based microparticle powder is a perovskite compound represented by ABO3, has an average primary particle size of less than 50nm, and has an A / B ratio of 0.80 or more and 0.95 or less (Present Invention 1).

[0017] The present invention also provides a dispersion containing the spherical strontium titanate-based fine particle powder according to Invention 1 (Invention 2).

[0018] Furthermore, the present invention provides a resin composition containing the spherical strontium titanate-based fine particle powder according to Invention 1 (Invention 3). -Effects of the Invention-

[0019] The spherical strontium titanate-based fine-particle powder of the present invention is a fine particle, so the resin composition containing it is transparent. In addition, since the spherical strontium titanate-based fine-particle powder of the present invention has removed the unnecessary alkaline components on the surface, the dispersion stability in the resin or the dispersing solvent is high, and the filler can be evenly dispersed in the resin, thereby reducing the performance deviation of the composite film. Furthermore, since the spherical strontium titanate-based fine-particle powder of the present invention is spherical, the filling property can be improved, so it is suitable for use as a filler for organic-inorganic hybrid materials. That is, the spherical strontium titanate-based fine-particle powder and the dispersion of the present invention can be processed and promoted to various uses, and the resin composition containing the above-mentioned fine-particle powder can form a functional resin composition. DETAILED DESCRIPTION

[0020] The structure of the present invention is described in detail below.

[0021] The strontium titanate-based microparticle powder of the present invention is a spherical strontium titanate-based microparticle powder. The strontium titanate-based microparticle powder is a perovskite compound represented by ABO3, has an average primary particle size of less than 50nm, and an A / B ratio of the particles is greater than 0.80 and less than 0.95.

[0022] The strontium titanate-based microparticle powder of the present invention is spherical and has an average primary particle size of less than 50 nm. By maintaining the spherical shape and the average primary particle size within the above range, the filler loading can be increased while maintaining resin properties such as transparency. Furthermore, by forming a particle size sufficiently smaller than the wavelength of the visible light region, the light scattering intensity is significantly reduced and the transparency is improved. The average primary particle size is preferably less than 40 nm, more preferably less than 25 nm. Its lower limit is approximately 8 nm.

[0023] The spherical strontium titanate-based fine-particle powder of the present invention is spherical. Spherical fillers are preferred because they can increase the filling rate even when formed into a composite with a resin or the like. Their circularity is preferably 0.80 or greater. If the circularity of the strontium titanate-based fine-particle powder is less than 0.80, the shape may be rectangular, etc., and the filling density may sometimes decrease. A more preferred circularity is 0.82 or greater, and even more preferably 0.83 to 1.0. It should be noted that the circularity is evaluated using the method described below.

[0024] The spherical strontium titanate-based fine-particle powder of the present invention is a perovskite-type compound represented by ABO3, and examples thereof include strontium titanate and barium strontium titanate. At least Sr is present at the A site, and a portion of the constituent elements may be substituted by alkali metals or alkaline earth metals. 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 by transition metal elements such as Zr.

[0025] The composition of the spherical strontium titanate-based microparticle powder described in the present invention is evaluated using fluorescent X-rays, and the molar ratio of the A-site element to the B-site element, expressed as A / B, is greater than 0.80 and less than 0.95. 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, and the particles may agglomerate with each other in the resin or solvent. Therefore, it becomes the main reason for the partial or complete solidification and gelation of the fluid dispersion, and dispersion stability may not be obtained. If A / B is greater than 0.95, the alkaline components on the particle surface are high, which becomes the main reason for the reduction in dispersion stability in the dispersion medium or resin. A more preferred A / B is greater than 0.82 and less than 0.94, and further preferably greater than 0.83% and less than 0.93.

[0026] The spherical strontium titanate-based fine-particle powder of the present invention preferably has a pH near neutral. A neutral pH reduces the polarity of the particle surface, improving compatibility with resins and solvents. The pH of the powder is preferably 6.0 to 9.0, more preferably 6.3 to 8.8, and even more preferably 6.5 to 8.5.

[0027] The spherical strontium titanate-based microparticle powder of the present invention can make the powder pH value near neutral by setting A / B to 0.80 or more and 0.95 or less, thereby removing the excessive alkaline components of the A site on the particle surface. That is, it is speculated that since there are few excess components on the surface of the particles, the polarity of the particle surface is low, thereby being able to obtain dispersion stability in a dispersion medium including an organic solvent. The excessive alkaline components react with CO2 in the air to form carbonates. Therefore, the amount of carbonate compounds contained in the particles represents the amount of the excessive alkaline components of the A site. The carbonate compounds contained in the spherical strontium titanate-based microparticle powder of the present invention are preferably less than 1% by weight, more preferably less than 0.5% by weight, and further preferably less than 0.3% by weight. Its lower limit is about 0% by weight.

[0028] Next, the method for producing the spherical strontium titanate-based fine particles according to the present invention will be described.

[0029] The spherical strontium titanate-based microparticle 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), the hydrated titanium hydroxide slurry is washed with water and then heated, and then added to a strontium hydroxide-based aqueous solution, and a wet reaction is carried out in a temperature range of 100 to 300°C.

[0030] Examples of the titanium raw material include titanium tetrachloride, and examples of the alkali raw material include strontium hydroxide, barium hydroxide, and sodium hydroxide.

[0031] During the neutralization reaction, the molar ratio (Sr / Ti or Ba / Ti) of the titanium raw material to the alkaline aqueous solution is preferably 1.1 to 1.8. If this ratio is less than 1.1, the yield of strontium titanate core particles decreases, while if it exceeds 1.8, the distribution of primary particles in the strontium titanate-based microparticle powder deteriorates. A more preferred ratio is 1.25 to 1.65. When sodium hydroxide is used as the alkaline aqueous solution, a molar ratio of twice the above is preferred.

[0032] After the neutralization reaction, the mixture is washed with water and then a strontium hydroxide aqueous solution is added. The amount of the strontium hydroxide aqueous solution added is preferably such that the molar ratio of Sr / Ti relative to the Ti in the reaction solution is 1.5 to 3.0. Examples of the strontium hydroxide aqueous solution include strontium hydroxide aqueous solution, and the addition of barium hydroxide, zirconium oxychloride, etc. can partially replace the composition.

[0033] Preferably, the reaction is carried out under a nitrogen atmosphere to prevent the strontium compound from reacting with carbon dioxide in the air.

[0034] 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 impossible. If the reaction concentration is greater than 0.7 mol / L, the amount of strontium hydroxide in the reaction solution exceeds its solubility, causing Sr(OH)2 to precipitate and making a uniform liquid-phase reaction difficult.

[0035] Examples of wet process reactions include normal pressure wet reaction, pressurized reaction, and hydrothermal synthesis. One or more reaction steps may be combined. The reaction temperature for the wet process is preferably 100-300°C. If the reaction temperature is less than 100°C, it is difficult to obtain a dense, spherical strontium titanate-based fine particle powder. If the reaction temperature exceeds 300°C, it is difficult to design a hydrothermal vessel. The reaction temperature is more preferably 105-280°C.

[0036] Preferably, a pH adjuster is added to the slurry containing the wet-reacted particles to adjust the pH to near neutral, preferably to pH 5-8, followed by water washing and drying according to conventional methods. The pH adjuster is not particularly limited as long as it adjusts the pH of the slurry to within the above range; examples include acetic acid. Adjusting the pH of the slurry and then washing with water can remove excess carbonate compounds from the particle surface, bringing the powder pH to near neutral. Furthermore, impurities such as Na, K, and Cl can be removed simultaneously.

[0037] In the present invention, calcination treatment, pulverization treatment, disintegration treatment, dispersion treatment, and surface treatment may be performed.

[0038] Next, the dispersion containing the spherical strontium titanate-based fine particle powder according to the present invention will be described.

[0039] As the dispersion medium of the present invention, either an aqueous system or a solvent system can be used.

[0040] As the dispersing medium 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 media can be used alone or in combination, depending on the intended use.

[0041] Dispersing media for 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 media for solvent-based dispersions can be used alone or in combination of two or more, depending on the intended use.

[0042] 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.

[0043] The dispersion of the present invention may further include dispersants, additives (resins, defoamers, auxiliary agents, etc.) as needed. The method for attaching, coating, or reacting the dispersants and additives to the entire or a portion of the surface of the particles is not limited, and examples thereof include a bead mill, etc. The dispersant of the present invention may be appropriately selected based on the type of spherical strontium titanate-based fine particle powder and dispersion medium 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. These dispersants may be used singly or in combination.

[0044] 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.

[0045] 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.

[0046] Examples of the organoaluminum compound include acetoalkoxyaluminum diisopropylate, aluminum diisopropoxymonoethyl acetoacetate, aluminum trisethyl acetoacetate, and aluminum trisacetyl acetonate.

[0047] Examples of the organic zirconium compound include zirconium tetrakisacetylacetonate, zirconium dibutoxybisacetylacetonate, zirconium tetrakisethyl acetoacetate, zirconium tributoxy monoethyl acetoacetate, and zirconium tributoxy acetylacetonate.

[0048] 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.

[0049] As the polymer dispersant, styrene-acrylic acid copolymer, styrene-maleic acid copolymer, polycarboxylic acid and its salt, etc. can be used.

[0050] The amount of dispersant added depends on the total surface area of ​​the spherical strontium titanate-based fine particles in the dispersion and can be appropriately adjusted based on the intended use of the dispersion and the type of dispersant. Generally, adding 0.01 to 100% by weight of dispersant relative to the spherical strontium titanate-based fine particles in the dispersion medium allows the spherical strontium titanate-based fine particles to be uniformly and finely dispersed in the dispersion medium, while also improving dispersion stability. Furthermore, the dispersant can be added directly to the dispersion medium or pre-treated within the spherical strontium titanate-based fine particles.

[0051] Next, the resin composition containing the spherical strontium titanate-based fine particle powder according to the present invention will be described.

[0052] The resin used is not particularly limited, and acrylic resin, polycarbonate, polystyrene resin, polyester resin, polyimide resin, polymethyl methacrylate (PMMA), AS resin, silicone resin, fluororesin, etc. can be used.

[0053] The viscosity of the dispersion containing the spherical strontium titanate-based fine particle powder and the resin composition of the present invention may be such that the fluidity is maintained without sedimentation, separation, solidification or gelation. [Example]

[0054] Examples of the present invention are described below, but the present invention is not limited thereto.

[0055] 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 calculated as (4π×area) / perimeter of the particle measured based on the above-mentioned electron microscope photograph. 2 express.

[0056] The Sr / Ti molar ratio represented by A / B was measured using a fluorescent X-ray analyzer (ZSXPrimusII manufactured by Rigaku Corporation).

[0057] The amount of carbonate compound contained in the spherical strontium titanate-based fine particle powder was measured using an X-ray diffractometer D8-ADVANCE (manufactured by Bruker Japan Co., Ltd.) (tube: Cu) within the range of 2θ of 10 to 90° and calculated using the Rietveld method.

[0058] The pH value of the spherical strontium titanate-based fine-particle powder was evaluated by the following method: 2.5 g of the fine-particle powder was added to 50 ml of pure water, boiled for 10 minutes, cooled to room temperature, filtered, and the pH value of the filtrate was measured.

[0059] The dispersion stability of spherical strontium titanate-based fine-particle powder was evaluated using the following method. 5 g of the fine-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. Spherical strontium titanate-based fine-particle powder that did not gel after 10 days or longer and maintained fluidity was rated as "○." Spherical strontium titanate-based fine-particle powder that gelled within 10 days or less was rated as "X."

[0060] The transparency of a coating film containing a dispersion of spherical strontium titanate fine particles was evaluated using the following method. 1 g of spherical strontium titanate fine particles, 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 for 60 minutes using a paint shaker to obtain a dispersion. This dispersion was applied to a PET film at a thickness of 12 μm using a rod coater. Each coating film was visually observed; a transparent, non-turbid coating film was rated as ○, while a turbid coating film was rated as ×.

[0061] Example 1 To a titanium tetrachloride aqueous solution having a Ti molar concentration of 2.10 mol / l, a 20 wt% strontium hydroxide aqueous solution was added so that the Sr / Ti molar ratio was 1.37, to obtain a titanium hydroxide slurry, which was then washed with water. The obtained titanium hydroxide slurry was placed in a strontium hydroxide aqueous solution. At this time, the Sr / Ti molar ratio of the strontium hydroxide aqueous solution was 2.0. In addition, the concentration during the reaction was 0.28 mol / l in terms of strontium titanate concentration. Then, the mixture was stirred continuously at 180°C for 8 hours to carry out a hydrothermal reaction. After the hydrothermal reaction, the mixture was cooled to room temperature to obtain a slurry, acetic acid was added to the slurry to adjust the pH to 5.0, and then the mixture was washed with water, filtered, and dried using a Nutsche filter to obtain a white powder of spherical strontium titanate particles.

[0062] The obtained strontium titanate fine-particle powder was observed under an electron microscope to be spherical particles with an average primary particle size of 17.4 nm. Furthermore, fluorescent X-ray measurement showed that the Sr / Ti ratio (A / B) was 0.835, and the pH value of the powder was 8.3.

[0063] Example 2 Spherical strontium titanate fine particle powder was obtained in the same manner as in Example 1 except that the pH of the slurry after the hydrothermal reaction was adjusted to 6.0.

[0064] Electron microscopic observation of the resulting strontium titanate fine-particle powder revealed spherical particles with an average primary particle size of 17.4 nm. Furthermore, X-ray fluorescence analysis revealed an Sr / Ti ratio of 0.883. The pH of the powder was 8.2.

[0065] Example 3 Spherical strontium titanate fine particle powder was obtained in the same manner as in Example 1 except that the hydrothermal reaction temperature was set to 260°C.

[0066] The obtained strontium titanate fine-particle powder was observed under an electron microscope to be spherical particles with an average primary particle size of 22.1 nm. Furthermore, fluorescent X-ray measurement showed an Sr / Ti ratio of 0.866 and a pH value of 8.5.

[0067] Example 4 Spherical strontium titanate fine particle powder was obtained in the same manner as in Example 3 except that the pH of the slurry after the hydrothermal reaction was adjusted to 6.0.

[0068] The obtained strontium titanate fine-particle powder was observed under an electron microscope to be spherical particles with an average primary particle size of 22.1 nm. Furthermore, fluorescent X-ray measurement showed an Sr / Ti ratio of 0.879 and a pH value of 8.1.

[0069] Example 5 Spherical strontium titanate fine particle powder was obtained in the same manner as in Example 3 except that the pH of the slurry after the hydrothermal reaction was adjusted to 7.0.

[0070] The obtained strontium titanate fine-particle powder was observed under an electron microscope to be spherical particles with an average primary particle size of 22.1 nm. Furthermore, fluorescent X-ray measurement showed an Sr / Ti ratio of 0.929 and a pH value of 8.9.

[0071] Comparative Example 1 Strontium titanate fine-particle powder was obtained in the same manner as in Example 1 except that the slurry after the hydrothermal reaction was washed with water and dried without undergoing pH adjustment.

[0072] The obtained strontium titanate fine-particle powder was observed under an electron microscope to be spherical particles with an average primary particle size of 17.4 nm. Furthermore, fluorescent X-ray measurement showed an Sr / Ti ratio of 0.980 and a pH value of 10.4.

[0073] Comparative Example 2 Strontium titanate fine-particle powder was obtained in the same manner as in Example 3 except that the slurry after the reaction was washed with water and dried without pH adjustment.

[0074] The obtained strontium titanate fine-particle powder was observed under an electron microscope to be spherical particles with an average primary particle size of 22.1 nm. Furthermore, fluorescent X-ray measurement showed an Sr / Ti ratio of 0.978 and a pH value of 10.8.

[0075] Comparative Example 3 Strontium titanate fine-particle powder was obtained in the same manner as in Example 2 except that the reaction temperature was set to 90° C. and the reaction time was set to 3 hours.

[0076] Electron microscopic observation of the resulting strontium titanate fine-particle powder revealed spherical particles with an average primary particle size of 12.5 nm. Furthermore, X-ray fluorescence analysis revealed an Sr / Ti ratio of 0.747 and a powder pH of 8.6. Although Comparative Example 3 contained little carbonate (residual SrCO₃) and had a low powder pH, the A / B ratio was also low, resulting in a "Poor" evaluation for dispersion stability.

[0077] The various properties, dispersion stability, and coating transparency of the spherical strontium titanate fine particle powders obtained in each Example and Comparative Example are shown in Table 1. The dispersions in the Examples all exhibited dispersion stability for more than 10 days, while the dispersions in the Comparative Examples gelled in less than 10 days, exhibiting low dispersion stability.

[0078] [Table 1]

[0079] The spherical strontium titanate fine-particle powder obtained in the examples has a powder pH close to neutral, and residual SrCO3 has been removed. Therefore, it is speculated that the dispersion containing the spherical strontium titanate fine-particle powder of the present invention can maintain a stable dispersion state for a longer period of time than the particles obtained in the comparative examples. Therefore, the spherical strontium titanate fine-particle powder of the present invention is transparent due to its fineness, and has a neutral powder pH due to an A / B ratio of 0.80 to 0.95, thereby exhibiting dispersion stability. Therefore, even when mixed with a solvent or resin as a filler, aggregation can be suppressed, enabling the production of uniform composite films, particularly thin films. -Industrial Applicability-

[0080] The spherical strontium titanate-based fine-particle powder of the present invention can control the average particle size according to the purpose, is finely spherical, and has an appropriately controlled A / B ratio, thereby having the characteristics of high transparency and dispersion stability. Therefore, the spherical strontium titanate-based fine-particle powder of the present invention is most suitable for use as a high-refractive-index inorganic filler for high-refractive-index resin compositions used in brightness enhancement films for displays, diffractive optical elements used in AR / MR glass, etc., or as a high-dielectric inorganic filler for high-dielectric resin compositions used in electronic components such as thin-film transistors (TFTs).

Claims

1. A spherical strontium titanate-based fine particle powder, wherein: The spherical strontium titanate-based fine particle powder is a perovskite compound represented by ABO3, has an average primary particle size of less than 50 nm, and has an A / B ratio of 0.80 to 0.

95.

2. A dispersion, wherein The dispersion contains the spherical strontium titanate-based fine particle powder according to claim 1.

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

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