Coated zirconia microparticles and method for manufacturing the same

Abstract

The present invention relates to coated zirconia microparticles comprising zirconia microparticles and a coating layer covering the surface of the microparticles, wherein the coating layer comprises one or more metal elements selected from Mg, Ca, Al, and rare earth elements, and has an average particle diameter of 3 to 100 nm and a specific surface area of ​​20 to 500 m² / g.

Description

Technology Field

[0001] The present invention relates to coated zirconia microparticles and a method for manufacturing the same. Background Technology

[0002] Zirconia (ZrO2) possesses many excellent characteristics, such as high refractive index, high strength, toughness, high wear resistance, high lubricity, high corrosion resistance, high oxidation resistance, insulation, low thermal conductivity, and high transparency in the visible light range; therefore, it is used in various applications such as automotive exhaust catalysts, condensers, grinding balls, dental materials, glass additives, thermal barriers, solid electrolytes, and optical materials.

[0003] Zirconia is used to manufacture various articles, for example, by molding and sintering fine particles. However, since the elemental form exhibits a tetragonal crystal structure at high temperatures and a monoclinic structure at low temperatures, there is a problem in that the sintered body is prone to cracking and fracture due to volume expansion and contraction caused by temperature changes. For this reason, a method is generally adopted to prevent phase transitions by incorporating stabilizers such as yttria (Y2O3), calcia (CaO), magnesia (MgO), and ceria (CeO2) into the zirconia. Zirconia that has been partially stabilized by adding stabilizers is called partially stabilized zirconia.

[0004] Partially stabilized zirconia is manufactured by various methods such as neutralization, hydrolysis, hydrothermal reaction, alkoxide method, vapor phase method, and spray pyrolysis, in accordance with the manufacturing method of zirconia.

[0005] Japanese Patent Publication No. 2008-24555 discloses a method for producing fine zirconia powder containing one or more of yttria, calcia, magnesia, and ceria as stabilizers by adding a compound such as yttrium as a stabilizer to a hydrated zirconium sol, drying, and plasticizing in the range of 1000 to 1200°C.

[0006] Japanese Patent Publication No. 2010-137998 discloses a method for manufacturing partially stabilized zirconia ceramics containing zirconia and yttria within a predetermined range, wherein zirconia is obtained by heat treating a composite in which yttria fine particle powder or yttrium salts are uniformly dispersed in zirconium hydroxide as a starting material containing Zr at a temperature range of 1100 to 1400°C, and the ceramic powder obtained by grinding is molded and fired.

[0007] Japanese Patent Publication No. 2015-221727 discloses a method for manufacturing a zirconia sintered body having a yttria concentration of 2 to 4 mol% containing 0.05 to 3 mass% of alumina, wherein the average particle size of the secondary particles is 0.1 to 0.4 μm and the ratio of the average particle size of the secondary particles to the average particle size of the primary particles measured by an electron microscope is 1 to 8, and the zirconia powder having a yttria concentration of 2 to 4 mol% containing 0.05 to 3 mass% of an aluminum compound in terms of alumina is molded and pre-sintered at 1100 to 1200°C, and the obtained pre-sintered body is subjected to hot isostatic pressing at a pressure of 50 to 500 MPa and a temperature of 1150 to 1250°C.

[0008] Japanese Patent Publication No. 2009-227507 discloses a method for manufacturing zirconia composite microparticles characterized by adding an alkali carbonate solution to a zirconia acidic dispersion containing rare earth element ions and / or alkaline earth metal ions to produce a neutralized precipitate, then drying the neutralized precipitate, heat-treating the dried neutralized precipitate at a temperature of 400°C or higher and 600°C or lower, and then washing to remove the alkali carbonate component.

[0009] Japanese Patent Publication No. Hei 5-170442 discloses a method for preparing a crystalline zirconia-based sol in which a rare earth element oxide, calcia, or magnesia is dissolved, wherein a solution of zirconium salt and a solution of one salt selected from rare earth elements, calcium, or magnesium are mixed in advance, the mixed solution is added to a basic solution or a slurry of a basic substance, the obtained slurry is heat-treated at a temperature of 80 to 200°C, and then an acid is added, followed by separation and washing.

[0010] Japanese Patent Publication No. 2017-154927 discloses zirconium oxide nanoparticles coated with a carboxylic acid, wherein the zirconium oxide nanoparticles contain yttrium and also contain at least one transition metal other than a rare earth element. The problem to be solved

[0011] (Summary of the Invention)

[0012] Japanese Patent Publication No. 2008-24555, Japanese Patent Publication No. 2010-137998, Japanese Patent Publication No. 2015-221727, and Japanese Patent Publication No. 2009-227507 are methods using a neutralization method and / or a hydrolysis method, but calcination at a high temperature is required to dissolve the particles, and as a result of particle growth, the particle shape is non-uniform and the particles are prone to having poor dispersibility.

[0013] Meanwhile, Japanese Patent Publication No. Hei 5-170442 and Japanese Patent Publication No. 2017-154927 describe a method using a hydrothermal reaction method. Since this method does not require a calcination process, it is possible to obtain fine particle diameters, which is considered advantageous for obtaining zirconia fine particles at the level of tens of nanometers. However, since yttrium salts, which are frequently used as stabilizers, generally have lower solubility than zirconium salts, it is difficult to uniformly mix zirconium and yttrium at the atomic level in industrial-scale production using the hydrothermal reaction method, and yttria tends to be unevenly distributed. In addition, since the reaction requires a long time, it leaves challenges in terms of productivity. means of solving the problem

[0014] Taking these circumstances into account, the present invention provides stable zirconia microparticles and a simple method for manufacturing the same.

[0015] The present invention relates to a coated zirconia microparticle comprising a zirconia microparticle and a coating layer covering the surface of the microparticle, wherein

[0016] The coating layer comprises one or more metal elements selected from Mg, Ca, Al, and rare earth elements, and

[0017] The average particle diameter is 3 to 100 nm, and

[0018] Specific surface area is 20–500 m² 2 / g

[0019] This concerns coated zirconia microparticles.

[0020] In addition, the present invention relates to a method for manufacturing coated zirconia microparticles, wherein an ion of one or more metal elements selected from Mg, Ca, Al, and rare earth elements is reacted with an additive that reacts with said ions to produce a water-insoluble compound in an aqueous dispersion containing zirconia microparticles, and a compound containing said metal element is precipitated on the surface of the zirconia microparticles to obtain coated zirconia microparticles. Effects of the invention

[0021] According to the present invention, stable coated zirconia microparticles and a simple method for manufacturing the same are provided.

[0022] Compared to conventional zirconia microparticles, the coated zirconia microparticles of the present invention have the advantage of suppressing cracking and fracture of the sintered body when subjected to a firing process, thereby enabling high density, and thus are suitable for various applications such as ceramic materials, dental materials, capacitors, and coating materials. In addition, since the coated zirconia microparticles of the present invention can be manufactured by a simple method, manufacturing costs can be reduced, and they are useful for industrial-scale production. Brief explanation of the drawing

[0023] Figure 1 is a transmission electron microscope (TEM) image of coated zirconia microparticles obtained in Example 2. Figure 2 is a scanning electron microscope / energy dispersive X-ray spectroscopy (SEM-EDX) image showing the elemental distribution of zirconium and yttrium in coated zirconia microparticles obtained in Example 2 and Comparative Example 2. Specific details for implementing the invention

[0024] (Form for carrying out the invention)

[0025] [Coated Zirconia Microparticles]

[0026] The present invention relates to coated zirconia microparticles comprising zirconia microparticles and a coating layer covering the surface of the microparticles, wherein the coating layer comprises one or more metal elements selected from Mg, Ca, Al, and rare earth elements, has an average particle diameter of 3 to 100 nm, and a specific surface area of ​​20 to 500 m² 2 This concerns coated zirconia microparticles with a g content.

[0027] The specific surface area of ​​zirconia microparticles is 20–500 m² 2 / g is preferable, and 40–200m 2 / g is more preferable, and 70–150m 2 / g is more preferable. The specific surface area of ​​the zirconia microparticles is 20m² 2 If the value is 1 / g or higher, the particle diameter of the resulting coated zirconia microparticles is appropriately suppressed, making it easy to obtain a high-density sintered body. In addition, there is a tendency for the stabilization effect caused by the metallic elements in the coating layer to be more easily manifested. The specific surface area of ​​the zirconia microparticles is 500 m² 2 If the value is 1 / g or less, the particle diameter becomes appropriately large and the cohesive force does not become excessive, so monodispersion is facilitated during surface coating, and the filling ability during molding when using coated zirconia microparticles is also improved.

[0028] Here, the specific surface area of ​​the zirconia microparticles can be measured by the BET method from the adsorption and desorption of nitrogen gas on a sample degassed at 150°C using a BET specific surface area measuring device, for example, a fully automatic BET specific surface area measuring device (Macsorb HM Model-1210) manufactured by Mounttech.

[0029] The average particle diameter of the zirconia microparticles is preferably 3 to 100 nm, more preferably 5 to 50 nm, and even more preferably 7 to 20 nm. In the present invention, the average particle diameter of the zirconia microparticles can be obtained by measuring the particle diameters of 200 or more random particles from a TEM image with a magnification of 200,000 times based on observation by a transmission electron microscope, and from the average value.

[0030] The coated zirconia microparticles of the present invention have a coating layer on the surface of the zirconia microparticles comprising one or more metal elements selected from Mg, Ca, Al, and rare earth elements.

[0031] One or more metals selected from Mg, Ca, Al, and rare earth elements contribute to the stabilization of zirconia microparticles.

[0032] Y (yttrium) is a preferred rare earth element.

[0033] The coating layer may contain a compound comprising one or more metal elements selected from Mg, Ca, Al, and rare earth elements (hereinafter also referred to as a coating compound).

[0034] The coating layer may contain one or more selected from a hydroxide of one or more metal elements selected from Mg, Ca, Al, and rare earth elements, a carbonate of said metal element, and an oxide of said metal element.

[0035] The coating layer preferably contains one or more selected from a hydroxide of one or more metal elements selected from Mg, Ca, Al, and Y, a carbonate of the metal element, and an oxide of the metal element.

[0036] It is preferable for the coating layer to contain Y, and it is more preferable for it to contain yttrium compounds such as yttrium hydroxide, as well as hydroxides.

[0037] By adding the above metal element, the phase transition from tetragonal to monoclinic in the zirconia microparticles is suppressed, thereby improving strength, durability, and dimensional accuracy. In this regard, the amount of the above metal element can be adjusted. For example, in the present invention, the amount of the coating compound in the coating layer is preferably 3 to 45 mol%, more preferably 5 to 40 mol%, even more preferably 6 to 36 mol%, and even more preferably 12 to 28 mol% with respect to the zirconia of the zirconia microparticles. If the amount of the coating compound in the coating layer is greater than or equal to the above lower limit, the tetragonal modulus in the crystal structure after high-temperature sintering increases appropriately, resulting in a significant suppression effect against cracking and fracture of the sintered body, and also making it easier to manufacture the molded body. Furthermore, if the amount of the above metal element in the coating layer is less than or equal to the above upper limit, bending strength and fracture toughness can be maintained, and additionally, it becomes difficult for impurity phases derived from the stabilizer to form after high-temperature sintering, so the properties of the sintered body, such as strength and insulation, also become good. In addition, the amount of the coating compound in the coating layer can be determined by measuring it using methods such as XRF analysis. Furthermore, the estimated coating compound can be determined by calculation by specifying it based on the type and amount of the compound used for coating, and, in the case of neutralizing the compound, the type of neutralizing agent.

[0038] The coated zirconia microparticles of the present invention have an average particle diameter of 3 to 100 nm, preferably 5 to 50 nm, and more preferably 7 to 20 nm. The average particle diameter of the coated zirconia microparticles is determined by measuring the particle diameters of at least 200 random particles from a TEM image at a magnification of 200,000x based on observation by a transmission electron microscope, and obtaining the average value. By controlling the particle diameter, the transparency of the composition containing these coated zirconia microparticles can be improved. In addition, low-temperature sinterability is excellent.

[0039] The coated zirconia microparticles of the present invention have a specific surface area of ​​20 to 500 m² 2 / g, and 40–200m2 / g is preferable, and 70–150m 2 / g is more preferable. The specific surface area of ​​the coated zirconia microparticles is 20 m² 2 If the value is 1 / g or higher, the particles become fine particles with appropriately suppressed diameters, making it easy to obtain a high-density sintered body. Additionally, there is a tendency for the stabilization effect caused by the metal elements in the coating layer to be more easily manifested. Furthermore, the specific surface area of ​​the coated zirconia fine particles is 500 m² 2 If it is less than / g, the particle diameter increases appropriately, and since the cohesive force does not become excessive, the filling ability during molding improves.

[0040] The coated zirconia microparticles of the present invention can be suitably used in various ceramic materials, dental materials, capacitors, coating materials, etc.

[0041] [Method for manufacturing coated zirconia microparticles]

[0042] The present invention relates to a method for manufacturing coated zirconia microparticles, wherein, in an aqueous dispersion containing zirconia microparticles, an ion of one or more metal elements selected from Mg, Ca, Al, and rare earth elements is reacted with an additive that reacts with said ions to produce a water-insoluble compound, thereby precipitating a compound containing said metal element (a coating compound) on the surface of the zirconia microparticles to obtain coated zirconia microparticles. The manufacturing method of the present invention may suitably apply the details described in the coated zirconia microparticles of the present invention. The coated zirconia microparticles of the present invention can be obtained by the manufacturing method of the present invention. For example, preferred embodiments of the raw material zirconia microparticles or said metal element are as described in the coated zirconia microparticles of the present invention.

[0043] The above additive may be, for example, an alkali agent. Examples of alkali agents include hydroxides such as NaOH and KOH, carbonates such as Na2CO3, K2CO3, ammonium carbonate, NaHCO3, and KHCO3, and ammonia. These alkali agents may be used as aqueous solutions, powders, solids, and crystals, but aqueous solutions are preferred for ease of handling. In addition, an aqueous ammonia solution may be used as an alkali agent. When the alkali agent is used as an aqueous solution, the concentration is preferably 5 to 50 mass%, more preferably 10 to 30 mass%.

[0044] In the present invention, the ions of the metal element can be introduced into the aqueous dispersion by, for example, mixing an aqueous solution of a compound containing the metal element with an aqueous dispersion of zirconia microparticles.

[0045] In the present invention, the aqueous dispersion, the aqueous solution of the compound containing the metal element, and the additive can be mixed to react the ion with the additive. In that case, the aqueous solution of the compound containing the metal element and the additive are used such that the amount of the coating compound formed from the compound and the additive is, as a maximum theoretical value, preferably 3 to 45 mol%, more preferably 5 to 40 mol%, even more preferably 6 to 36 mol%, and even more preferably 12 to 28 mol% with respect to the zirconia of the zirconia microparticles.

[0046] In the present invention, after obtaining coated zirconia microparticles, the additive can be removed from the coated zirconia microparticles. For example, after obtaining coated zirconia microparticles, the coated zirconia microparticles can be washed with water.

[0047] In the present invention, the obtained coated zirconia particles can be dried, but the temperature at that time can be set to a temperature at which the coated zirconia fine particles do not sinter, for example, 200°C or lower.

[0048] In the present invention, an alkali agent is added to an aqueous dispersion containing zirconia microparticles and mixed uniformly, and then an aqueous solution of a compound containing the metal element is added and neutralized, thereby allowing the metal compound to be uniformly coated on the surface of the zirconia microparticles.

[0049] In addition, in the present invention, an aqueous solution of a compound containing the metal element is added to an aqueous dispersion containing zirconia microparticles, and then an alkali agent is added and a neutralization reaction is carried out to uniformly coat the surface of the zirconia microparticles with a metal compound.

[0050] In addition, in the present invention, an aqueous solution of a compound containing the metal element and an alkali agent are simultaneously added to an aqueous dispersion containing zirconia microparticles and neutralized, thereby allowing the metal compound to be uniformly coated on the surface of the zirconia microparticles.

[0051] An example of a method for manufacturing coated zirconia microparticles according to the present invention is described.

[0052] First, zirconia microparticles are uniformly dispersed in water. To uniformly disperse the zirconia microparticles, pH adjustment is performed, and it is preferable to do so using a disperser such as an ultrasonic homogenizer, planetary ball mill, Henschel mixer, colloid mill, wet jet mill, or wet bead mill. Alternatively, a mechanical stirrer may be used.

[0053] An aqueous dispersion of zirconia fine particles obtained in this way is mixed with a composition containing water and ions of one or more metal elements selected from Mg, Ca, Al, and rare earth elements. The composition is preferably an aqueous solution of a compound of the metal element, for example, a salt. Examples of salts containing the metal element include inorganic salts such as sulfates, nitrates, and chlorides. In addition, organic compounds such as metal alkoxides may be used. Inorganic salts are preferred due to their solubility and ease of availability. The concentration of this aqueous solution is preferably 0.001 to 10 mol / L, more preferably 0.01 to 5 mol / L.

[0054] Next, an additive that reacts with the ions to produce a water-insoluble compound is mixed into a mixture obtained by mixing an aqueous dispersion of zirconia microparticles with a composition containing ions of the metal element and water, preferably an aqueous solution of a compound containing the metal element (e.g., a salt).

[0055] As this additive, the above-mentioned alkali agent, for example, an aqueous solution of the alkali agent, can be cited.

[0056] When using a salt containing the above metal element, the alkali agent is added in an amount such that the degree of neutralization of the salt is, for example, 0.8 or higher.

[0057] There is no specific limit on the temperature when adding the alkali agent, but for example, it should be 100°C or lower.

[0058] In the present invention, for example, from the situation of a TEM image of zirconia microparticles, it can be confirmed that the surface of the zirconia microparticles is coated with a compound containing the metal element.

[0059] An aqueous dispersion containing zirconia fine particles uniformly coated with a metal compound is appropriately subjected to treatments such as filtration, washing, drying, and crushing to obtain coated zirconia fine particles. In one example, the coating layer consists of hydroxides or carbonates of Mg, Ca, Al, and rare earth elements and is in an amorphous state. Alternatively, the coating layer may be converted to a crystalline state of oxide by performing heat treatment.

[0060] The coated zirconia microparticles of the present invention may be used in the form of powder, dispersion, nanocomposite, etc. Examples of dispersions include water or organic compounds as dispersion media. In addition, examples of nanocomposites include nanocomposites uniformly dispersed in organic compounds such as monomers, oligomers, and resins.

[0061] As an example of a manufacturing method of the present invention, a method for manufacturing coated zirconia microparticles may be provided, wherein an alkali agent is added to a mixture obtained by mixing an aqueous dispersion of zirconia microparticles with an aqueous solution of a water-soluble salt of one or more metal elements selected from Mg, Ca, Al, and rare earth elements, such that the pH of the mixture is 8 to 13, preferably 12 to 13, and a compound containing said metal element is precipitated on the surface of the zirconia microparticles to obtain coated zirconia microparticles. In this case, the alkali agent may be added such that the degree of neutralization of said water-soluble salt is 0.8 or higher. Furthermore, in the present invention, the coated zirconia microparticles may be washed with water until the detected amount of the alkali agent is 0.01 mass% or less. The water-soluble salt may be one having a solubility of 5.0 g / 100 g of water or more in water at 20°C.

[0062] According to the present invention, a method for producing zirconia microparticles is provided, wherein an ion of one or more metal elements selected from Mg, Ca, Al, and rare earth elements is reacted with an additive that reacts with said ion to produce a water-insoluble compound in an aqueous dispersion containing zirconia microparticles.

[0063] The present invention provides a method for manufacturing zirconia microparticles by mixing an aqueous dispersion of zirconia microparticles with an aqueous solution of a water-soluble salt of one or more metal elements selected from Mg, Ca, Al, and rare earth elements, and mixing an alkali agent into the mixture such that the pH of the mixture is 8 to 13, preferably 12 to 13. The aqueous solution may contain the water-soluble salt at a concentration of 0.001 to 10 mol / L. Additionally, the alkali agent may be added such that the degree of neutralization of the water-soluble salt is 0.8 or higher. Furthermore, in the present invention, the coated zirconia particles may be washed with water until the detected amount of the alkali agent is 0.01 mass% or less. Examples of the water-soluble salt may include having a solubility in water at 20°C of 5.0 g / 100 g of water or more.

[0064] The present invention provides a method for manufacturing a zirconia sintered body, comprising a process for manufacturing coated zirconia microparticles by the method of the present invention and a process for sintering the manufactured coated zirconia microparticles. The details described in the coated zirconia microparticles and the method for manufacturing coated zirconia microparticles of the present invention may be appropriately applied to the method for manufacturing the zirconia sintered body. The sintering of the coated zirconia microparticles may be performed in accordance with known zirconia microparticle sintering methods, taking into consideration the use of the sintered body. As an example, a method of sintering at 1300 to 1600°C for 1 to 15 hours may be cited.

[0065] The present invention provides a method for preparing a coated zirconia microparticle dispersion, comprising a process of dispersing the coated zirconia microparticles of the present invention in a dispersion medium (hereinafter also referred to as a dispersion medium for dispersion). The details described in the coated zirconia microparticles and the method for preparing coated zirconia microparticles of the present invention may be appropriately applied to this method for preparing the coated zirconia microparticle dispersion.

[0066] Furthermore, the present invention provides a method for manufacturing a nanocomposite having a process of dispersing the coated zirconia microparticles of the present invention in a dispersion medium (hereinafter also referred to as a dispersion medium for nanocomposites). The details described in the coated zirconia microparticles and the method for manufacturing coated zirconia microparticles of the present invention may be suitably applied to this method for manufacturing a nanocomposite.

[0067] In the method for preparing a coated zirconia microparticle dispersion and a nanocomposite of the present invention, the coated zirconia microparticles of the present invention may be treated with a surface treatment agent. Examples of surface treatment agents include the following, but are not limited thereto.

[0068] For example, (meth)acryloyloxy-based silane coupling agents, vinyl-based silane coupling agents, epoxy-based silane coupling agents, amino-based silane coupling agents, uride-based silane coupling agents, etc. can be used.

[0069] Examples of (meth)acryloyloxy-based silane coupling agents include 3-(meth)acryloyloxypropyltrimethylsilane, 3-(meth)acryloyloxypropylmethyldimethoxysilane, 3-(meth)acryloyloxypropyltrimethoxysilane, 3-(meth)acryloyloxypropylmethyldiethoxysilane, and 3-(meth)acryloyloxypropyltriethoxysilane. Examples of acryloxy-based silane coupling agents include 3-acryloyloxypropyltrimethoxysilane.

[0070] Examples of vinyl-based silane coupling agents include allyltrichlorosilane, allyltriethoxysilane, allyltrimethoxysilane, diethoxymethylvinylsilane, trichlorovinylsilane, vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane, and vinyltris(2-methoxyethoxy)silane.

[0071] Examples of epoxy-based silane coupling agents include diethoxy(glycidyloxypropyl)methylsilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and 3-glycidoxypropyltriethoxysilane. Examples of styrene-based silane coupling agents include p-styryltrimethoxysilane.

[0072] Examples of amino-based silane coupling agents include N-2(aminoethyl) 3-aminopropylmethyldimethoxysilane, N-2(aminoethyl) 3-aminopropyltrimethoxysilane, N-2(aminoethyl) 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethyl-butylidene)propylamine, and N-phenyl-3-aminopropyltrimethoxysilane.

[0073] 3-ureidopropyltriethoxysilane is exemplified as a ureido-based silane coupling agent.

[0074] The following may be cited as other surface treatment agents. As a chloropropyl-based silane coupling agent, 3-chloropropyltrimethoxysilane is exemplified. As a mercapto-based silane coupling agent, 3-mercaptopropylmethyldimethoxysilane and 3-mercaptopropyltrimethoxysilane are exemplified. As a sulfide-based silane coupling agent, bis(triethoxysilylpropyl)tetrasulfide is exemplified. As an isocyanate-based silane coupling agent, 3-isocyanatepropyltriethoxysilane is exemplified. As an aluminum-based coupling agent, acetalkoxyaluminum diisopropylate is exemplified.

[0075] The dispersion medium used in the present invention is not particularly limited as long as it is capable of dispersing coated zirconia microparticles. For example, water or an organic compound may be used as the dispersion medium.

[0076] When water is used as a dispersion medium for the dispersion, it is preferable that the pH be 2 to 5 or 9 to 13 from the perspective of the dispersibility of the coated zirconia microparticles.

[0077] The organic compound used as a dispersion medium for the dispersion can be selected from compounds known as organic solvents. Specifically, preferably, examples include ethanol, isopropanol, butanol, cyclohexanol, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, ethyl acetate, propyl acetate, butyl acetate, methyl cellosolve, cellosolve, butyl cellosolve, cellosolve acetate, tetrahydrofuran, 1,4-dioxane, n-hexane, cyclopentane, toluene, xylene, N,N-dimethylformamide, N,N-dimethylacetamide, dichloromethane, trichloroethane, trichloroethylene, hydrofluoroether, etc.

[0078] There are no particular limitations on the dispersion medium for the nanocomposite, as long as it is an organic compound, such as a monomer, oligomer, or resin (polymer), capable of dispersing coated zirconia microparticles. As monomers, oligomers, resins, etc., examples include aromatic ring-containing acrylates, cycloaliphatic skeleton-containing acrylates, monofunctional alkyl (meth)acrylates, polyfunctional alkyl (meth)acrylates, and polymers thereof.

[0079] Examples of aromatic ring-containing acrylates include phenoxyethyl acrylate, phenoxy-2-methyl ethyl acrylate, phenoxyethoxyethyl acrylate, 3-phenoxy-2-hydroxypropyl acrylate, 2-phenylphenoxyethyl acrylate, benzyl acrylate, phenyl acrylate, phenylbenzyl acrylate, and paracumyl phenoxyethyl acrylate, in terms of high refractive index.

[0080] In addition, examples of acrylates containing a ring-shaped framework that have a high Abbe number and are desirable as optical materials include 2-acryloyloxyethylhexahydrophthalate, cyclohexyl acrylate, dicyclofentanyl acrylate, tetrahydrofurfuryl acrylate, dicyclofentanyl methacrylate, isobornyl methacrylate.

[0081] In addition, examples of monofunctional alkyl (meth)acrylates include, in terms of low viscosity, methyl (meth)acrylate, octyl (meth)acrylate, isostearyl (meth)acrylate, hydroxyethyl (meth)acrylate, hydroxyethyl (meth)acrylate, ethylene oxide modified alkyl (meth)acrylate, propylene oxide modified alkyl (meth)acrylate, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, etc.

[0082] In addition, as for polyfunctional alkyl (meth)acrylates, from the perspective of improving the hardness of the cured product, examples include (i) binary (meth)acrylates such as (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, and 1,9-nonanediol di(meth)acrylate; (ii) ternary or quaternary (meth)acrylates such as glycerol tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, phosphate tri(meth)acrylate, and pentaerythritol tetra(meth)acrylate; and (iii) ethylene oxide and / or propylene oxide modified products of compounds selected from (i) and (ii).

[0083] In the method for preparing a dispersion of coated zirconia microparticles and a method for preparing a nanocomposite according to the present invention, a dispersant may be used as needed. The dispersant is not particularly limited, provided that it is a compound containing a group having an affinity for coated zirconia microparticles, for example; however, preferred dispersants include anionic dispersants having acid groups such as carboxylic acids, sulfuric acids, sulfonic acids, phosphoric acids, or salts thereof. Among these, a phosphate ester-based dispersant is preferably used. Regarding the amount of dispersant used, it is not particularly limited, but 0.1 to 30 mass% is preferred relative to the coated zirconia microparticles.

[0084] Examples

[0085] Hereinafter, the coated zirconia microparticles of the present invention and the method for manufacturing the same will be described by way of examples, but the present invention is not limited to these examples.

[0086] In addition, various instrument analyses were performed using the following methods.

[0087] (1) X-ray diffraction (XRD)

[0088] Measurements were taken using a Bruker AX X-ray diffraction apparatus (D8 ADVANCE / V), and qualitative analysis or quantitative analysis was performed by Rietveld analysis (tetragonal, monoclinic, etc.).

[0089] (2) Measurement of the amount of coating metal compound in coated zirconia microparticles (XRF analysis)

[0090] Using a fluorescence X-ray analyzer (S8 TIGER) manufactured by Bruker AXS, the amount of each element in the coated inorganic fine particles was quantified.

[0091] (3) Measurement of specific surface area (SSA)

[0092] Coated zirconia microparticles degassed at 150°C were used, and the specific surface area was measured by the BET method from the adsorption and desorption of nitrogen gas using a fully automatic BET specific surface area measuring device (Macsorb HM Model-1210) manufactured by Mounttech.

[0093] (4) Measurement of average particle diameter, evaluation of particle shape and uniformity

[0094] Using a transmission electron microscope (H-7600) manufactured by Hitachi High Technologies, images of particles were acquired at a magnification of 30,000 to 200,000 times, and the major axes of more than 200 particles were measured, and the average particle diameter was measured by calculating the average value. Particle shape was evaluated from observation of the TEM images, and uniformity was evaluated from the measured average particle diameter.

[0095] (5) Evaluation of surface coating uniformity

[0096] Using a field emission scanning electron microscope (SU8220) and an energy dispersive X-ray analyzer (EX-370X-MAX50) manufactured by Hitachi High Technologies, images of particles were acquired at a magnification of 3000x, and the elemental distribution was observed and evaluated by EDX mapping.

[0097] [Preparation of Coated Zirconia Microparticles]

[0098] <Example 1>

[0099] To 27.7 g (225 mmol) of zirconia fine particle powder (manufactured by Kanto Denka Kogyo Co., Ltd.) with an average particle diameter of 10 nm, pure water was added to achieve a powder concentration of 20 mass%, and the mixture was stirred with a mechanical stirrer for 1 hour to prepare a zirconia aqueous slurry. To this slurry, a 1 mol / L aqueous solution of yttrium nitrate was added dropwise to achieve a concentration of 13.5 mmol in terms of yttrium nitrate, and the mixture was stirred for 1 hour. Subsequently, a 25 mass% aqueous solution of sodium hydroxide was added dropwise to achieve a degree of neutralization of 0.8 or higher and a pH of 12 to 13, and the mixture was stirred for about 1 hour. The obtained slurry was filtered by suction, washed with water until no Na was detected by XRF measurement, and then dried at 150°C until the moisture content was 1% or less. The obtained solid was ground in a mortar and pestle and subjected to classification (75 μm mesh).

[0100] <Examples 2–13, Comparative Example 1>

[0101] Various coated zirconias were prepared in accordance with Example 1 and the formulations shown in Table 1. In addition, in Example 6, commercially available zirconia microparticles, mainly monoclinic, were used as raw materials. In addition, in Example 7, neutralization was performed with sodium carbonate. In addition, in Example 8, calcium chloride was used instead of yttrium nitrate. In addition, in some examples, the second compound was used.

[0102] TEM images of the coated zirconia microparticles of Example 2 are shown in Fig. 1. Also, SEM-EDX mapping images of the coated zirconia microparticles of Example 2 are shown in Fig. 2. From the TEM images, it can be seen that the particles obtained in Example 2 are spherical, and from the measured average particle diameter, it can be seen that they have good uniformity.

[0103] <Comparative Example 2>

[0104] To 27.7 g (225 mmol) of powdered zirconia fine particles with an average particle diameter of 5 to 10 nm (manufactured by Kanto Denka Kogyo Co., Ltd.), pure water was added to make 20 mass% and stirred with a mechanical stirrer for 1 hour. 3.1 g of yttria (Y2O3) was added to the slurry containing the obtained zirconia fine particles and stirred for 1 hour. The obtained slurry was filtered by suction, washed with water, and then heated and dried at 150°C until the moisture content was 1% or less. The obtained solid was ground in a mortar and pestle and passed through a sieve with a mesh size of 74 μm. SEM-EDX mapping images of the coated zirconia of Comparative Example 2 are shown in Figure 2.

[0105] [Sintering and Crystal Structure Changes of Coated Zirconia Microparticles]

[0106] The crystal structure of the coated zirconia microparticles obtained in Examples 1 to 13 and Comparative Examples 1 to 2 after firing at 1000°C was evaluated by the following method.

[0107] Coated zirconia microparticles were heated from 20°C to 1000°C for 4 hours in an air atmosphere, and then sintered at 1000°C for 3 hours. The crystal structure of the obtained powder was evaluated by X-ray diffraction (XRD) measurement. In addition, physical properties such as the crystal structure of the coated zirconia microparticles changed significantly depending on the sintering conditions (temperature, time).

[0108]

[0109] ※ 1 mol% is the mol% relative to zirconia, and represents the amount of the coating compound depending on the type and amount of raw material, the type of neutralizing agent, etc.

[0110] ※2 Although it contains an extremely small amount of Hf, the amount including that amount is expressed as the amount of Zr in mass %.

[0111] As shown in Comparative Example 1, zirconia microparticles not coated with a metal compound had a tetragonal determinance of 0%, i.e., a monoclinic determinance of 100%, after firing at 1000°C, whereas Examples 1 to 13 showed a tetragonal determinance of 20% or more.

[0112] As shown in Examples 1 to 3, it can be seen that the tetragonal lattice after calcination increases by increasing the content of yttrium hydroxide, which is a coating compound. In particular, under these calcination conditions, as shown in Examples 2 and 3, when the content is 12 mol% or more in terms of yttrium hydroxide, the tetragonal lattice after calcination becomes 95% and 93%, respectively, and it is presumed that Y entered the zirconia crystal lattice and effectively acted as a tetragonal stabilizing element.

[0113] As shown in Comparative Example 2, when coated directly with yttria without passing through Y ions, the tetragonal rate was 64%, which is about 30% lower than Example 2, where the surface was coated via an aqueous solution of Y ions. This is thought to be because the Y coating became non-uniform, as shown in the SEM-EDX mapping image of Fig. 2, and it can be easily inferred that the physical properties are unstable. In addition, since impurity phases originating from the stabilizer were generated, there is concern that this will affect the degradation of properties such as strength when the body is sintered.

[0114] As shown in Examples 4 to 10, metal compounds acting as stabilizers may include not only Y, but also hydroxides and carbonates of Mg, Ca, and Al (including hydrates of carbonates). It is also possible to combine these metal compounds.

[0115] As shown in Example 6, even when monoclinic raw material particles (particle diameter: 20 nm) were used as raw material particles, the crystal structure after firing at 1000°C showed a tetragonal modulus of 95%, which was equivalent to the result of Example 4.

[0116] As shown in Example 11, it was possible to coat zirconia fine particles even with a small amount of yttrium nitrate charged.

[0117] As shown in Examples 12 and 13, coating of zirconia microparticles was possible even with a large amount of yttrium nitrate charged. In Examples 12 and 13, it was inferred from the observation of the XRD pattern of yttria that undissolved yttria was also produced.

[0118] <Examples 14–21, Comparative Example 3>

[0119] The influence of the size of the zirconia microparticles (hereinafter referred to as raw material microparticles) used in the coating process is explained. Since raw material microparticles with a wide particle size distribution are also used, the particle size was evaluated here based on the specific surface area.

[0120] Coated zirconia microparticles were obtained by applying Example 2 and using the raw material microparticles with the specific surface areas shown in Table 2. The raw material microparticles were the raw material microparticles used in Example 14 (specific surface area: 140 m²). 2 The specific surface area was adjusted by calcining (g). The coating compound was uniformly set to 12 mol% in terms of yttrium hydroxide. The obtained coated zirconia microparticles were calcined at 1000°C as in Examples 1 to 13, and the crystal structure was evaluated by XRD measurement. The tetragonal modulus after calcination and the specific surface area of ​​the raw microparticles are shown in Table 2.

[0121]

[0122] ※1 Specific surface area (m²) of zirconia microparticles used in the coating process or zirconia microparticles after coating 2 / g)

[0123] ※2 Tetragonal modulus (mass%) of coated zirconia fine particles after firing at 1000℃ for 3 hours

[0124] As shown in Table 2, it can be seen that the tetragonal modulus increases as the specific surface area of ​​the raw material fine particles increases. Under these firing conditions, particularly for Examples 14 to 17, i.e., with a specific surface area of ​​75 to 140 m² 2 In the range of / g, the tetragonal stability is about 90%, indicating that Y acts more effectively as a tetragonal stabilizing element. This is thought to be because as the particle diameter decreases, Y becomes uniformly dissolved at the molecular level.

[0125] <Reference Examples 1–4>

[0126] The degree of densification of a sintered body made of coated zirconia microparticles was evaluated.

[0127] [Sintering Body Fabrication]

[0128] A molded body was fabricated using 4g of coated zirconia fine powder under a pressure of 0.5t using a uniaxial press. As an evaluation of densification, the molded body was measured with a vernier caliper before and after sintering, and the density of the molded body was compared to the theoretical density of zirconia (6.0 g / cm³). 3 The relative density (%) was calculated by dividing by ). The sintering temperatures were set to 200℃ for 1 hour, 1000℃ for 3 hours, and 1200℃ for 3 hours, and the heating rate was set to 4℃ / min from 20℃ to 1000℃ and 2℃ / min from 1000℃ to 1200℃. Table 3 shows the relative density, etc. of the sintered bodies.

[0129] In Reference Example 1, zirconia microparticles not coated with a stabilizer (Comparative Example 1) were used; in Reference Example 2, the coated zirconia microparticles of Example 1 were used; in Reference Example 3, the coated zirconia microparticles of Example 4 were used; and in Reference Example 4, commercially available partially stabilized zirconia was used.

[0130]

[0131] ※1 Relative density (%) = (W / V) / d0 × 100

[0132] W: Mass of coated zirconia fine powder (g)

[0133] V: Volume of the molded body (cm²) 3 )

[0134] d0: Theoretical density of zirconia (=6.0 g / cm³) 3 )

[0135] ※2 The content of the commercially available product in Reference Example 4 is (1) converted to Y2O3 and (2) converted to Al2O3.

[0136] As shown in Reference Example 1, zirconia microparticles not coated with a stabilizer could not produce the molded body itself, whereas when zirconia microparticles coated only with yttria in Reference Example 2 were used, a sintered body could be produced without cracking or fracture.

[0137] As shown in Reference Example 3, a sintered body was produced using zirconia fine particles surface-coated with aluminum hydroxide as well as yttrium hydroxide, and densification was achieved more than that of the commercial product shown in Reference Example 4.

[0138] <Example 22>

[0139] 100 g of the powder of coated zirconia microparticles obtained in Example 4 was mixed with 500 g of pure water, and acetic acid was added dropwise to achieve a pH of 4 to prepare a mixture. The obtained mixture was stirred with a dispersion stirrer for 30 minutes to perform coarse dispersion. The obtained mixture was then subjected to dispersion treatment using a media-type wet disperser. By performing the dispersion treatment while checking the particle diameter during the process, the dispersion of Example 22 was obtained. The dispersion particle size of the coated zirconia microparticles in the obtained dispersion was measured by the following method. Additionally, as Reference Example 5, the same evaluation was performed on a dispersion prepared in the same manner using uncoated raw zirconia microparticles instead of the coated zirconia microparticles of Example 4. The results are shown in Table 4.

[0140] <Example 23>

[0141] 120 g of powdered coated zirconia microparticles obtained in Example 4, 30.0 g of 3-methacryloyloxypropyltrimethoxysilane (product name: KBM-503, manufactured by Shin-Etsu Kagaku Kogyo Co., Ltd.), and 250 g of methyl ethyl ketone (MEK) were mixed and stirred with a dispersion stirrer for 30 minutes to perform coarse dispersion. The resulting mixture was dispersed using a media-type wet disperser. By performing the dispersion treatment while checking the particle diameter during the process, the dispersion of Example 23 was obtained. The dispersion particle size of the coated zirconia microparticles in the obtained dispersion was measured by the following method. In addition, as Reference Example 6, the same evaluation was performed on a dispersion prepared in the same manner using uncoated raw zirconia microparticles instead of the coated zirconia microparticles of Example 4. The results are shown in Table 4.

[0142] Method for Measuring the Dispersion Particle Size of Coated Zirconia Microparticles in a Dispersion

[0143] The dispersion particle size of coated or uncoated zirconia microparticles in a dispersion solution one day after preparation (stored at 25°C) was measured at 25°C using a dynamic light scattering particle size distribution measuring device LB-500 manufactured by Horiba Seisakusho Co., Ltd. The results are shown in Table 4. It was found that even when using the coated zirconia microparticles of the present invention, a dispersion solution with a good dispersion state can be prepared, just like with uncoated zirconia microparticles.

[0144]

Claims

Claim 1 A coated zirconia microparticle comprising a zirconia microparticle and a coating layer covering the surface of the microparticle, wherein the coating layer comprises one or more metal elements selected from Mg, Ca, Al, and rare earth elements, and said metal element comprises at least Y, the average particle diameter is 3 to 50 nm, and the specific surface area is 20 to 500 m² 2 Coated zirconia microparticles in g. Claim 2 In claim 1, the coating layer contains a compound comprising one or more metal elements selected from Mg, Ca, Al, and rare earth elements, and the metal element comprises at least Y, a coated zirconia microparticle. Claim 3 In claim 1, the coating layer contains one or more compounds selected from a hydroxide of one or more metal elements selected from Mg, Ca, Al and rare earth elements, a carbonate of said metal element, and an oxide of said metal element, and the metal element comprises at least Y, a coated zirconia microparticle. Claim 4 In claim 1, the coating layer contains 3 to 45 mol% of a compound comprising one or more metal elements selected from Mg, Ca, Al, and rare earth elements relative to the zirconia of the zirconia microparticles, and the metal element comprises at least Y. Claim 5 A method for manufacturing coated zirconia microparticles, wherein, in an aqueous dispersion containing zirconia microparticles, ions of one or more metal elements selected from Mg, Ca, Al, and rare earth elements are reacted with an additive that reacts with said ions to produce a water-insoluble compound, thereby precipitating a compound containing said metal element on the surface of the zirconia microparticles to obtain coated zirconia microparticles, wherein said metal element comprises at least Y, the average particle diameter of said zirconia microparticles is 3 to 50 nm, and the specific surface area of ​​said zirconia microparticles is 20 to 500 m² 2 Method for manufacturing coated zirconia microparticles with a weight of / g. Claim 6 A method for manufacturing coated zirconia microparticles in which the additive in paragraph 5 is an alkali agent. Claim 7 A method for manufacturing coated zirconia microparticles according to claim 5, wherein after obtaining coated zirconia microparticles, the additive is removed from the coated zirconia microparticles. Claim 8 A method for manufacturing coated zirconia microparticles according to claim 5, wherein the coated zirconia microparticles are obtained and then the coated zirconia microparticles are washed with water. Claim 9 A method for manufacturing coated zirconia microparticles according to claim 5, wherein the obtained coated zirconia particles are dried at 200°C or lower. Claim 10 A method for manufacturing coated zirconia microparticles according to claim 5, wherein the above aqueous dispersion, the aqueous solution of the compound containing the above metal element, and the above additive are mixed. Claim 11 A method for manufacturing a zirconia sintered body having a process for manufacturing coated zirconia microparticles by a method described in any one of claims 5 to 10, and a process for sintering the manufactured coated zirconia microparticles. Claim 12 A method for manufacturing a coated zirconia microparticle dispersion having a process of dispersing coated zirconia microparticles described in any one of claims 1 to 4 in a dispersion medium. Claim 13 A method for manufacturing a nanocomposite having a process of dispersing coated zirconia microparticles described in any one of claims 1 to 4 in a dispersion medium. Claim 14 delete Claim 15 delete

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