Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/18—Oxygen-containing compounds, e.g. metal carbonyls
  • C08K3/20—Oxides; Hydroxides
  • C08K3/22—Oxides; Hydroxides of metals
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
  • C01G23/00—Compounds of titanium
  • C01G23/003—Titanates
  • C01G23/006—Alkaline earth titanates
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2004/00—Particle morphology
  • C01P2004/30—Particle morphology extending in three dimensions
  • C01P2004/32—Spheres
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2004/00—Particle morphology
  • C01P2004/60—Particles characterised by their size
  • C01P2004/64—Nanometer sized, i.e. from 1-100 nanometer
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/18—Oxygen-containing compounds, e.g. metal carbonyls
  • C08K3/20—Oxides; Hydroxides
  • C08K3/22—Oxides; Hydroxides of metals
  • C08K2003/2206—Oxides; Hydroxides of metals of calcium, strontium or barium
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/18—Oxygen-containing compounds, e.g. metal carbonyls
  • C08K3/20—Oxides; Hydroxides
  • C08K3/22—Oxides; Hydroxides of metals
  • C08K2003/2237—Oxides; Hydroxides of metals of titanium
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K2201/00—Specific properties of additives
  • C08K2201/002—Physical properties
  • C08K2201/005—Additives being defined by their particle size in general

Definitions

• the objective of the present invention is to obtain spherical strontium titanate-based fine particle powder that is optimal as a filler.
• organic-inorganic hybrid materials that maintain the processability of organic resins while providing the functionality of inorganic fillers (refractive index, dielectric constant, electrical conductivity, magnetism, thermal conductivity, etc.).
• brightness enhancement films used in displays and diffractive optical elements used in AR/MR glasses etc. require a high refractive index that cannot be achieved by resin alone in order to obtain characteristics such as high brightness, thin film and improved viewing angle. For this reason, adding inorganic fillers with a high refractive index to resins to improve the refractive index of the resin film is being considered.
• TFTs thin-film transistors
• resin compositions made of resins that are easy to pattern and highly dielectric inorganic fillers are easy to pattern and highly dielectric inorganic fillers.
• strontium titanate is a compound with a perovskite structure, and is a highly functional material, so it is used in a variety of applications.
• its high refractive index makes it suitable for use as a pigment, a reflector, a light collector, and other optical applications, as well as ceramic capacitor applications due to its high dielectric constant.
• It is also used as a visible light photocatalyst due to its photocatalytic activity, and can be doped with other elements to turn it into a semiconductor, making it suitable for use in semiconductor capacitors, thermoelectric materials, electroluminescence, and light-emitting materials.
• the filler in such hybrid materials must be highly transparent and uniformly dispersible. For transparency, it must be spherical and fine, and for uniform dispersibility, it must be made of hydrophobic resin and have high dispersion stability in the solvent.
• compounds having a perovskite structure generally represented by ABO3 have an alkali metal or alkaline earth metal in the A site, and the particle surface is alkaline, so that they are highly hydrophilic, and the inorganic filler is likely to aggregate in hydrophobic resins and solvents.
• the surface area increases as the particles become more suitable for the filler, making it even more difficult to obtain dispersion stability.
• Patent Documents 1 to 3 There have been various reports on strontium titanate microparticles (Patent Documents 1 to 3).
• Patent Document 1 describes the production of fine particles of strontium titanate by reacting the hydrolysis product of a titanium compound with a water-soluble strontium salt in a strong alkaline aqueous solution, but the resulting particles are rectangular or cubic in shape and therefore unsuitable as a filler.
• Patent Documents 2 and 3 describe the production of spherical strontium titanate by adding a hydroxycarboxylic acid or a third component to a hydrolysis product of a titanium compound and a water-soluble strontium salt, and reacting them in a strong alkaline aqueous solution, but because components other than strontium titanate are present, this is not suitable as a filler.
• the technical objective of the present invention is to provide a fine spherical strontium titanate microparticle powder suitable for use as a filler in composite materials, and a dispersion with good dispersion stability.
• the present invention relates to a spherical strontium titanate-based fine particle powder characterized in that the perovskite compound is represented by ABO3 , has an average primary particle size of less than 50 nm, and has an A/B ratio of 0.80 or more and 0.95 or less (Invention 1).
• the present invention also relates to a dispersion containing the spherical strontium titanate-based fine particle powder described in invention 1 (invention 2).
• the present invention also relates to a resin composition containing the spherical strontium titanate-based fine particle powder described in invention 1 (invention 3).
• the spherical strontium titanate-based microparticle powder according to the present invention is a microparticle, and therefore a resin composition containing it is transparent.
• the spherical strontium titanate-based microparticle powder according to the present invention has had excess alkaline components removed from the surface, it has high dispersion stability in resins and dispersion solvents, and the filler can be uniformly dispersed in the resin, reducing bias in the properties of the composite film.
• the spherical strontium titanate-based microparticle powder according to the present invention is spherical, it can improve filling properties and is suitable as a filler for organic-inorganic hybrid materials.
• the spherical strontium titanate-based microparticle powder and dispersion according to the present invention can be processed and developed for various applications, and a resin composition containing the microparticle powder can form a functional resin composition.
• the strontium titanate-based fine particle powder according to the present invention is a spherical strontium titanate-based fine particle powder which 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 or more and 0.95 or less.
• the strontium titanate-based fine particle powder according to the present invention is spherical and has an average primary particle diameter of less than 50 nm.
• the spherical shape and average primary particle diameter within the above range, it is possible to increase the amount of filler loaded while maintaining the resin properties such as transparency. Furthermore, when the particle diameter is sufficiently smaller than the wavelength in the visible region, the light scattering intensity is significantly reduced and transparency is increased.
• the preferred average primary particle diameter is 40 nm or less, and more preferably 25 nm or less. The lower limit is about 8 nm.
• the spherical strontium titanate-based microparticle powder according to the present invention is spherical. If the filler is spherical, it is preferable because the filling rate can be increased when making a composite with a resin or the like.
• the circularity is preferably 0.80 or more. If the circularity of the strontium titanate-based microparticle powder is less than 0.80, the shape may be a rectangular parallelepiped, etc., and the filling density may decrease. A more preferable circularity is 0.82 or more, and even more preferably 0.83 to 1.0. The circularity is evaluated by the method described below.
• the spherical strontium titanate-based fine particle powder according to 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 in the A site, and some of the constituent elements can be substituted with an alkali metal or an alkaline earth metal.
• the substituted element is not particularly limited, but alkaline earth metals such as Ca and Ba are preferred.
• At least Ti is present in the B site, and some of the constituent elements may be substituted with a transition metal element such as Zr.
• composition of the spherical strontium titanate-based fine particle powder according to the present invention is evaluated by fluorescent X-rays.
• the molar ratio of A-site elements to B-site elements, represented by A/B, is 0.80 or more and 0.95 or less. If A/B is lower than 0.80, the particles have excess hydroxyl groups on the surface, which is considered to be in a highly hydrophilic state, and there is a risk of the particles agglomerating in resin or solvent. This may cause a part or all of the fluid dispersion to solidify or gel, which may result in a failure to obtain dispersion stability.
• A/B is higher than 0.95, there is a large amount of alkaline components on the particle surface, which may cause a decrease in dispersion stability in the dispersion medium or resin.
• A/B is more preferably 0.82 or more and 0.94 or less, and even more preferably 0.83% or more and 0.93 or less.
• the powder pH of the spherical strontium titanate-based microparticle powder according to the present invention is preferably close to neutral. If the powder pH is neutral, the polarity of the particle surface will be low, and compatibility with resins and solvents will be high.
• the powder pH is preferably 6.0 to 9.0, more preferably 6.3 to 8.8, and even more preferably 6.5 to 8.5.
• the powder pH can be made near neutral by setting A/B to 0.80 or more and 0.95 or less, and the excess alkaline components in the A site on the particle surface can be removed.
• A/B the excess alkaline components in the A site on the particle surface
• the polarity of the particle surface is low, and dispersion stability in a dispersion medium containing an organic solvent is obtained.
• the excess alkaline components react with CO2 in the air to produce carbonates. Therefore, the amount of carbonate compounds contained in the particles indicates the amount of excess alkaline components in the A site.
• the amount of carbonate compounds contained in the spherical strontium titanate-based microparticle powder according to the present invention is preferably 1% by weight or less, more preferably 0.5% by weight or less, and even more preferably 0.3% by weight or less.
• the lower limit is about 0% by weight.
• the spherical strontium titanate microparticle powder according to the present invention can be obtained by neutralizing a titanium raw material with an alkaline aqueous solution to obtain a titanium hydroxide hydrate slurry (neutralization reaction), washing the titanium hydroxide hydrate slurry with water, heating it, and adding it to a strontium hydroxide aqueous solution to carry out a wet reaction in the temperature range of 100 to 300°C.
• Titanium raw materials include titanium tetrachloride, etc.
• Alkaline raw materials include strontium hydroxide, barium hydroxide, sodium hydroxide, etc.
• the molar ratio of the titanium raw material to the alkaline aqueous solution during the neutralization reaction is preferably 1.1 to 1.8. If the ratio is less than 1.1, the production yield of strontium titanate core particles decreases, and if it exceeds 1.8, the distribution of primary particles in the strontium titanate-based fine particle powder deteriorates. A more preferable ratio is 1.25 to 1.65. If sodium hydroxide is used as the alkaline aqueous solution, the molar ratio range of twice as much as mentioned above is preferable.
• aqueous strontium hydroxide solution After the neutralization reaction, the mixture is washed with water and an aqueous strontium hydroxide solution is added.
• the amount of strontium hydroxide 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.
• aqueous strontium hydroxide solutions include aqueous strontium hydroxide solutions, and the composition can be partially substituted by adding barium hydroxide, zirconium oxychloride, etc.
• the reaction is preferably carried out under a nitrogen atmosphere and controlled so that the strontium compound does not react with carbon dioxide gas in the air.
• the reaction concentration of the reaction solution for generating strontium titanate-based microparticles is preferably 0.05 to 0.7 mol/L in terms of titanium compound. If the reaction concentration is less than 0.05 mol/L, the yield is low and not industrially viable. If the reaction concentration exceeds 0.7 mol/L, the amount of strontium hydroxide in the reaction solution exceeds the solubility, causing Sr(OH) 2 to precipitate, making it difficult to carry out a uniform liquid phase reaction.
• the reaction temperature for the wet reaction is preferably 100 to 300°C. If the reaction temperature is less than 100°C, it is difficult to obtain 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 to 280°C.
• a pH adjuster to the slurry containing the particles after the wet reaction, and after adjusting the pH to near neutral, preferably pH 5 to 8, the slurry is washed with water and dried in the usual manner.
• a pH adjuster there are no particular limitations on the pH adjuster as long as it adjusts the pH of the slurry to the above range, and examples of such an adjuster include acetic acid.
• firing treatment pulverization treatment, crushing treatment, dispersion treatment, and surface treatment may be performed.
• the dispersion medium used in the present invention can be either water-based or solvent-based.
• the dispersion medium for the aqueous dispersion may be water, or an alcohol-based solvent such as methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, or butyl alcohol; a glycol ether-based solvent such as methyl cellosolve, ethyl cellosolve, propyl cellosolve, or butyl cellosolve; an oxyethylene or oxypropylene addition polymer such as diethylene glycol, triethylene glycol, polyethylene glycol, dipropylene glycol, tripropylene glycol, or polypropylene glycol; an alkylene glycol such as ethylene glycol, propylene glycol, or 1,2,6-hexanetriol; or a water-soluble organic solvent such as glycerin or 2-pyrrolidone.
• These dispersion media for the aqueous dispersion may be used alone or in a mixture of two or more types depending on the intended use.
• Dispersion 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; ether alcohols 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; acetate esters such as ethyl acetate, butyl acetate and isobutyl acetate; lactate esters such as methyl lactate,
• the concentration of the spherical strontium titanate-based microparticle powder in the dispersion according to the present invention is preferably 5 to 60% by weight. If the concentration of the spherical strontium titanate-based microparticle powder in the dispersion is less than 5% by weight, the productivity for use in the next process is low, and if it exceeds 60% by weight, it is difficult to say that a highly fluid slurry is produced.
• the concentration of the spherical strontium titanate-based microparticle powder in the dispersion is more preferably 10 to 55% by weight, and even more preferably 15 to 50% by weight.
• the dispersion according to the present invention may contain dispersants, additives (resins, defoamers, auxiliaries, etc.) as necessary, and any method may be used as long as the dispersants and additives adhere to, coat, or react with all or part of the surface of the fine particles, including, for example, a bead mill.
• the dispersants used in the present invention may be appropriately selected depending on the type of spherical strontium titanate fine particle powder or dispersion medium used, and may 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, and may be used alone or in a mixture of two or more of these.
• 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
• organosilicon compounds include alkoxysilanes such as methyltrimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, phenyltriethoxysilane, ethyltriethoxysilane, propyltriethoxysilane, butyltriethoxysilane, hexyltriethoxysilane, octyltriethoxysilane, tetraethoxysilane, and tetramethoxysilane; silane-based coupling agents such as vinyltrimethoxysilane, vinyltriethoxysilane, ⁇ -aminopropyltriethoxysilane, ⁇ -glycidoxypropyltrimethoxysilane, ⁇ -mercaptopropyltrimethoxysilane, ⁇ -methacryloyloxypropyltrimethoxysilane, N-( ⁇ -amin
• the above organic titanium compounds include isopropyl triisostearoyl titanate, isopropyl tris(dioctyl pyrophosphate) titanate, bis(dioctyl pyrophosphate)oxyacetate titanate, isopropyl tri(N-aminoethyl aminoethyl) titanate, tris(dioctyl pyrophosphate)ethylene titanate, isopropyl dioctyl pyrophosphate titanate, isopropyl tris(dodecylbenzenesulfonyl) titanate, titanium tetra-n-butoxide, titanium tetra-2-ethylhexoxy , tetraisopropyl bis(dioctyl phosphite) titanate, tetraoctyl bis(ditridecyl phosphite) titanate, tetra(2,2-diallyloxymethyl-1
• organic aluminum compounds examples include acetoalkoxyaluminum diisopropylate, aluminum diisopropoxymonoethyl acetoacetate, aluminum trisethyl acetoacetate, aluminum trisacetylacetonate, etc.
• organic zirconium compounds examples include zirconium tetrakis acetylacetonate, zirconium dibutoxy bis acetylacetonate, zirconium tetrakis ethyl acetoacetate, zirconium tributoxy monoethyl acetoacetate, zirconium tributoxy acetylacetonate, etc.
• the above surfactants include anionic surfactants such as fatty acid salts, sulfate ester salts, sulfonate salts, and phosphate ester salts; nonionic surfactants such as polyethylene glycol-type nonionic surfactants such as polyoxyethylene alkyl ethers and polyoxyethylene aryl ethers, and polyhydric alcohol-type nonionic surfactants such as sorbitan fatty acid esters; cationic surfactants such as amine salt-type cationic surfactants and quaternary ammonium salt-type cationic surfactants; and amphoteric surfactants such as alkyl betaines such as alkyl dimethylamino acetate betaines and alkyl imidazolines.
• anionic surfactants such as fatty acid salts, sulfate ester salts, sulfonate salts, and phosphate ester salts
• nonionic surfactants such as polyethylene glycol-type nonionic sur
• Polymer dispersants that can be used include styrene-acrylic acid copolymers, styrene-maleic acid copolymers, polycarboxylic acids and their salts, etc.
• the amount of dispersant added depends on the total surface area of the spherical strontium titanate-based microparticle powder in the dispersion, and may be appropriately adjusted depending on the purpose of the dispersion of the spherical strontium titanate-based microparticle powder and the type of dispersant. In general, by adding 0.01 to 100% by weight of dispersant to the spherical strontium titanate-based microparticle powder in the dispersion medium, the spherical strontium titanate-based microparticle powder can be uniformly and finely dispersed in the dispersion medium, and the dispersion stability can be improved.
• the dispersant may be added directly to the dispersion medium, or may be pretreated with the spherical strontium titanate-based microparticle powder.
• resin there are no particular limitations on the resin that can be used, but examples that can be used include acrylic resin, polycarbonate, polystyrene resin, polyester resin, polyimide resin, polymethyl methacrylate (PMMA), AS resin, silicone resin, and fluororesin.
• the viscosity of the dispersion or resin composition containing the spherical strontium titanate microparticle powder according to the present invention may be such that it maintains fluidity without causing settling, separation, solidification or gelation.
• the average primary particle diameter was measured from approximately 300 primary particles in a photograph (25,000x) of the spherical strontium titanate microparticle powder taken with a transmission electron microscope (JEM-F200, manufactured by JEOL Ltd.).
• the average primary particle diameter is the particle diameter calculated by averaging the diameter of a circle having the same area as that determined from the photograph for each particle for all particles measured.
• the particle shape was determined from the electron microscope photograph.
• the circularity was expressed as (4 ⁇ ⁇ area)/ perimeter2 of the particle measured from the electron microscope photograph.
• the amount of carbonate compounds contained in the spherical strontium titanate microparticle powder was measured using an X-ray diffractometer D8-ADVANCE (manufactured by Bruker Japan, Ltd.) (tube: Cu). Measurements were taken in the 2 ⁇ range of 10 to 90°, and calculations were made using the Rietveld method.
• the powder pH of the spherical strontium titanate microparticle powder was evaluated using the following method. 2.5 g of the microparticle powder was added to 50 ml of pure water, boiled for 10 minutes, cooled to room temperature, filtered, and the pH of the filtrate was measured.
• the dispersion stability of the spherical strontium titanate microparticle powder was evaluated by the following method. 5 g of the microparticle powder, 5 g of propylene glycol monomethyl ether acetate (PGMEA), and 0.5 g of a polymer dispersant (Disperbyk-180, manufactured by BYK Japan Co., Ltd.) were mixed and dispersed for 60 minutes using a paint shaker. The dispersion was left to stand at room temperature, and those that were not gelling and had fluidity after 10 days or more were marked with an O, and those that gelled in less than 10 days were marked with an X.
• PMEA propylene glycol monomethyl ether acetate
• a polymer dispersant Disperbyk-180, manufactured by BYK Japan Co., Ltd.
• the coating transparency of dispersions containing spherical strontium titanate microparticle powder was evaluated using the following method. 1 g of spherical strontium titanate microparticle powder, 9 g of propylene glycol monomethyl ether acetate (PGMEA), and 0.1 g of polymer dispersant (Disperbyk-180, manufactured by BYK Japan Co., Ltd.) were dispersed for 60 minutes using a paint shaker to obtain a dispersion. This dispersion was applied to a PET film with a thickness of 12 ⁇ m using a bar coater. Each coating was visually observed, and transparent and non-cloudy coatings were rated as ⁇ , and cloudy coatings were rated as ⁇ .
• PMEA propylene glycol monomethyl ether acetate
• Dispersion was applied to a PET film with a thickness of 12 ⁇ m using a bar coater. Each coating was visually observed, and transparent and non-cloudy coatings were rated as ⁇ , and cloudy coating
• Example 1 A 20 wt% aqueous solution of strontium hydroxide was added to an aqueous titanium tetrachloride solution with a molar concentration of Ti of 2.10 mol/l 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 poured into an aqueous strontium hydroxide solution. The aqueous strontium hydroxide solution had a Sr/Ti molar ratio of 2.0. The concentration during the reaction was 0.28 mol/l as the strontium titanate concentration. The mixture was then stirred at 180°C for 8 hours to perform a hydrothermal reaction.
• the slurry was cooled to room temperature, and acetic acid was added to adjust the pH to 5.0, followed by washing with water using a Nutsche filter, filtration, and drying to obtain a white powder of spherical strontium titanate microparticles.
• strontium titanate fine particle powder When the obtained strontium titanate fine particle powder was observed under an electron microscope, it was found to be spherical particles with an average primary particle size of 17.4 nm. Furthermore, fluorescent X-ray measurement revealed that A/B, Sr/Ti, was 0.835, and the powder pH was 8.3.
• Example 2 A 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.
• strontium titanate microparticle powder When the obtained strontium titanate microparticle powder was observed under an electron microscope, it was found to be spherical particles with an average primary particle size of 17.4 nm. Furthermore, fluorescent X-ray measurement revealed that the Sr/Ti ratio was 0.883. The powder pH was 8.2.
• Example 3 A spherical strontium titanate fine particle powder was obtained in the same manner as in Example 1, except that the hydrothermal reaction temperature was 260°C.
• strontium titanate fine particle powder When the obtained strontium titanate fine particle powder was observed under an electron microscope, it was found to be spherical particles with an average primary particle size of 22.1 nm. Furthermore, fluorescent X-ray measurement revealed that the Sr/Ti ratio was 0.866 and the powder pH was 8.5.
• Example 4 A 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.
• strontium titanate microparticle powder When the obtained strontium titanate microparticle powder was observed under an electron microscope, it was found to be spherical particles with an average primary particle size of 22.1 nm. Furthermore, fluorescent X-ray measurement revealed that the Sr/Ti ratio was 0.879 and the powder pH was 8.1.
• Example 5 A 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.
• strontium titanate fine particle powder When the obtained strontium titanate fine particle powder was observed under an electron microscope, it was found to be spherical particles with an average primary particle size of 22.1 nm. Furthermore, fluorescent X-ray measurement revealed that the Sr/Ti ratio was 0.929 and the powder pH was 8.9.
• Comparative Example 1 A 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 not adjusted and the slurry was washed with water and dried.
• strontium titanate microparticle powder When the obtained strontium titanate microparticle powder was observed under an electron microscope, it was found to be spherical particles with an average primary particle size of 17.4 nm. Furthermore, fluorescent X-ray measurement revealed that the Sr/Ti ratio was 0.980 and the powder pH was 10.4.
• Comparative Example 2 A fine strontium titanate powder was obtained in the same manner as in Example 3, except that the pH of the slurry after the reaction was not adjusted and the slurry was washed with water and dried.
• strontium titanate fine particle powder When the obtained strontium titanate fine particle powder was observed under an electron microscope, it was found to be spherical particles with an average primary particle size of 22.1 nm. Furthermore, fluorescent X-ray measurement revealed that the Sr/Ti ratio was 0.978 and the powder pH was 10.8.
• Comparative Example 3 A strontium titanate fine particle powder was obtained in the same manner as in Example 2, except that the reaction temperature was 90° C. and the reaction time was 3 hours.
• Table 1 shows the various properties, dispersion stability, and coating transparency of the spherical strontium titanate microparticle powder obtained in each Example and Comparative Example. All of the dispersions in the Examples showed dispersion stability for 10 days or more, but the dispersions in the Comparative Examples gelled in less than 10 days, indicating low dispersion stability.
• the spherical strontium titanate microparticle powder obtained in the examples has a powder pH close to neutral, and residual SrCO3 has been removed. Therefore, it is presumed that the dispersion containing the spherical strontium titanate microparticle powder according to the present invention can maintain a stable dispersion state for a longer period of time than the microparticles obtained in the comparative examples. Therefore, the spherical strontium titanate microparticle powder according to the present invention is transparent because it is fine, and has a neutral powder pH and dispersion stability because A/B is 0.80 or more and 0.95 or less. Therefore, aggregation is suppressed even when mixed with a solvent or resin as a filler, and a uniform composite film, especially a thin film, can be produced.
• the spherical strontium titanate-based fine particle powder of the present invention is characterized by its average particle size being controllable according to the purpose, being fine and spherical, and having transparency and high dispersion stability due to the appropriate control of A/B. Therefore, the spherical strontium titanate-based fine particle powder of the present invention is optimal for a high refractive index inorganic filler for increasing the refractive index of a resin composition in a brightness improvement film used in a display, a diffractive optical element used in an AR/MR glass, etc., or a high dielectric inorganic filler for a high dielectric resin composition usable in an electronic component such as a thin film transistor (TFT).
• TFT thin film transistor

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