Method for producing zirconium-containing metal oxide dispersion and zirconium-containing metal oxide dispersion

Abstract

To provide a metal oxide dispersion containing a zirconium element having high transparency even at high concentration and having low viscosity.SOLUTION: A method for producing a metal oxide dispersion containing a zirconium element comprises a step of heating a slurry containing a compound containing a zirconium element to carry out a hydrothermal reaction, in which the heating in the hydrothermal reaction step is carried out at a heating rate of not less than 90°C / hour.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a zirconium-containing metal oxide dispersion and a zirconium-containing metal oxide dispersion. [Background technology]

[0002] Compositions in which metal oxides are blended with resins for the purpose of improving resin properties such as mechanical strength or imparting new properties are used as materials for electronic components, optical materials, and the like. Among the metal oxides blended into resins, zirconium oxide, which can impart a high refractive index to resins, is widely used in resin compositions intended for optical material applications. When blending zirconium oxide with resins, it is often blended into the resin as a dispersion, and zirconium oxide dispersions are required to have high transparency and, further, low viscosity even at high concentrations. For this reason, various such zirconium oxide dispersions and methods for producing them have been proposed (see Patent Documents 1 to 6). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5397829 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-150066 [Patent Document 3] Japanese Patent Publication No. 2020-33195 [Patent Document 4] Japanese Patent Application Publication No. 2020-33194 [Patent Document 5] Japanese Patent Publication No. 2020-33195 [Patent Document 6] Japanese Patent Publication No. 2020-33196 Summary of the Invention [Problem to be solved by the invention]

[0004] As described above, dispersions of zirconium-containing metal oxides, such as zirconium oxide, are useful materials used in a variety of fields, including optical materials. It is generally known that the transparency of a zirconium-containing metal oxide dispersion depends on the primary particle size of the zirconium-containing metal oxide. Using a zirconium-containing metal oxide with a small primary particle size can provide a dispersion with the high transparency required for optical materials. However, zirconium-containing metal oxides with a small primary particle size have a large specific surface area, resulting in high viscosity in the dispersion state. It is particularly difficult to reduce the viscosity when the dispersion is highly concentrated. Dispersions of zirconium-containing metal oxides, particularly those used in resins, are required to have low viscosity. Therefore, there is a need for a dispersion that has high transparency even at high concentrations and low viscosity.

[0005] In view of the above-mentioned current situation, an object of the present invention is to provide a dispersion of a zirconium-containing metal oxide that has high transparency even at a high concentration and low viscosity. [Means for solving the problem]

[0006] The present inventors have investigated methods for producing a dispersion of zirconium-element-containing metal oxide that has high transparency even at high concentrations and low viscosity, and have found that when producing a dispersion of zirconium-element-containing metal oxide using a production method including a step of hydrothermally reacting a slurry containing a zirconium-element-containing compound, if the heating rate during the hydrothermal reaction is set to a predetermined rate or higher, the resulting dispersion of zirconium-element-containing metal oxide has high transparency and low viscosity even at high concentrations, and have completed the present invention.

[0007] That is, the present invention is a method for producing a zirconium-element-containing metal oxide dispersion liquid, which includes a step of heating a slurry containing a zirconium-element-containing compound as a metal element-containing compound to carry out a hydrothermal reaction, and is characterized in that the heating in the hydrothermal reaction step is carried out at a temperature increase rate of 90°C / hour or more.

[0008] The slurry preferably contains an organic acid.

[0009] The above slurry preferably contains only a zirconium-containing compound as the metal-element-containing compound.

[0010] The present invention also relates to a zirconium-containing metal oxide dispersion, characterized in that when the dispersion is a 48 wt % aqueous dispersion, the dispersion has a transmittance of 70% or more at a wavelength of 550 nm and a viscosity of 25 mPa s or less.

[0011] In the zirconium-containing metal oxide dispersion, the zirconium-containing metal oxide preferably has an average primary particle size of 3 to 20 nm. [Effects of the Invention]

[0012] The method for producing a zirconium-containing metal oxide dispersion of the present invention is an excellent method that can produce a zirconium-containing metal oxide dispersion that has high transparency even at high concentrations and low viscosity without performing any complicated steps. The zirconium-containing metal oxide dispersion of the present invention has high transparency even at a high concentration and low viscosity, and therefore can be suitably used in various applications including optical materials. DETAILED DESCRIPTION OF THE INVENTION

[0013] Preferred embodiments of the present invention will be specifically described below, but the present invention is not limited to the following description and can be modified and applied as appropriate within the scope that does not change the gist of the present invention.

[0014] 1. Method for producing zirconium-containing metal oxide dispersion The method for producing a zirconium-containing metal oxide dispersion of the present invention is characterized in that in the step of heating a slurry containing a zirconium-containing compound to carry out a hydrothermal reaction, the heating rate for the hydrothermal reaction is 90°C / hour or more. The production method of the present invention is a useful method for producing a zirconium-containing metal oxide dispersion liquid that has high transparency even at high concentrations and low viscosity, without adding any additional steps to conventional zirconium oxide production methods. The production method of the present invention is also advantageous in that the rapid temperature rise rate in the hydrothermal reaction shortens the time required to reach a predetermined temperature, thereby reducing the amount of thermal energy used compared to conventional methods. The temperature rise rate may be 90°C / hour or more, preferably 100°C / hour or more, more preferably 110°C / hour or more, and even more preferably 120°C / hour or more. There is no particular upper limit to the temperature rise rate, but due to production equipment considerations, it is usually 250°C / hour or less. In the production method of the present invention, the temperature increase rate does not need to be constant as long as the average temperature increase rate, calculated by dividing the temperature increase from the start of temperature increase until the predetermined temperature is reached by the time required for this, is 90°C / hour or more, but from the viewpoint of producing a zirconium-containing metal oxide dispersion liquid that has high transparency even at a high concentration and low viscosity, when the time from the start of temperature increase until the predetermined temperature is reached is equally divided into five sections, the variation in the temperature increase rate among the sections is preferably within 45%, more preferably within 20%.

[0015] The temperature at which the hydrothermal reaction is carried out is preferably 170 to 230°C. By carrying out the hydrothermal reaction at such a temperature, the hydrothermal reaction can be carried out more sufficiently, and a dispersion liquid with higher water dispersibility and transparency can be obtained. The temperature at which the hydrothermal reaction is carried out is more preferably 175 to 220°C, and even more preferably 180 to 210°C. In addition, the time for carrying out the hydrothermal reaction is preferably 60 to 600 minutes, more preferably 100 to 360 minutes, and even more preferably 150 to 300 minutes, in order to allow the hydrothermal reaction to proceed more sufficiently and in consideration of production efficiency.

[0016] The zirconium-containing compound contained in the slurry containing the zirconium-containing compound is preferably a neutralized product obtained by reacting a raw material containing a zirconium compound with a basic compound in water. Therefore, the method for producing a zirconium-element-containing metal oxide dispersion of the present invention is preferably a production method comprising a step of reacting a raw material containing a zirconium compound with a basic compound in water to obtain a slurry containing a neutralized product containing zirconium element, and a step of carrying out the hydrothermal reaction using the slurry containing the zirconium-element-containing compound, which is the neutralized product containing zirconium element.

[0017] The step of reacting the raw materials containing the zirconium compound with a basic compound in water to obtain a slurry containing a neutralized product containing zirconium element may involve preparing the raw materials excluding the basic compound into an aqueous solution or aqueous dispersion, and then adding the basic compound to obtain the neutralized product; alternatively, the raw materials excluding the basic compound may be added to an aqueous solution of the basic compound to obtain the neutralized product; or the raw materials excluding the basic compound and the basic compound may be gradually added together to water to obtain the neutralized product. Among these, it is preferable to gradually add the raw materials excluding the basic compound and the basic compound together to water to obtain the neutralized product. By doing so, particles with a more uniform particle size can be produced. In this case, it is preferable to prepare the raw materials excluding the basic compound into an aqueous solution or aqueous dispersion, and also prepare the basic compound into an aqueous solution, and then gradually add them to water, in order to more uniformly proceed with the reaction.

[0018] The water used in the aqueous solution or aqueous dispersion is not particularly limited, and examples thereof include pure water, ion-exchanged water, distilled water, industrial water, and tap water. However, the aqueous solution or aqueous dispersion may contain compounds that are soluble or miscible in water, such as methanol, ethanol, isopropanol, acetone, ethylene glycol, and diethylene glycol, to the extent that the reaction is not inhibited. The same applies to specific examples of the solvent for the slurry containing the zirconium element-containing compound to be subjected to the hydrothermal reaction step.

[0019] The concentration of the zirconium compound in the aqueous solution or dispersion of the raw material containing the zirconium compound is not particularly limited, but if it is too dilute, the amount of wastewater in the next step will be too large, and if it is too concentrated, the viscosity of the slurry containing the neutralized product will be high, making it difficult to handle the slurry, such as by stirring or transferring the solution, so the concentration is preferably 0.2 to 5 mol / L, and more preferably 0.5 to 3 mol / L.

[0020] Examples of zirconium compounds used as raw materials in producing the slurry containing the zirconium-containing compound include hydroxides, hydroxide oxides, chlorides, sulfides, sulfates, nitrates, carbonates, hydrogencarbonates, acetates, phosphates, oxalates, butyrates, selenates, iodates, fluorides, oxychlorides, etc. Among these, oxychlorides, chlorides, sulfates, nitrates, acetates, etc., which are water-soluble zirconium compounds suitable for production, are preferred.

[0021] The raw materials used to produce the slurry containing the zirconium element-containing compound may contain compounds of other metal elements as long as they contain a zirconium compound. Other metal elements include cerium and yttrium. Compounds of other metal elements include compounds similar to the zirconium compounds described above.

[0022] When the raw material contains a compound of another metal element in addition to the zirconium compound, the content of the compound of the other metal element is preferably 0.01 to 1 mole, more preferably 0.015 to 0.5 mole, and even more preferably 0.02 to 0.2 mole, per mole of zirconium element contained in the zirconium compound.

[0023] Examples of basic compounds used to neutralize the raw material containing the zirconium compound include lithium hydroxide, sodium hydroxide, potassium hydroxide, magnesium hydroxide, calcium hydroxide, barium hydroxide, lithium carbonate, sodium carbonate, potassium carbonate, sodium potassium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, ammonium hydrogen carbonate, lithium sulfite, sodium sulfite, potassium sulfite, lithium nitrite, sodium nitrite, potassium nitrite, lithium oxalate, sodium oxalate, potassium oxalate, lithium acetate, sodium acetate, potassium acetate, calcium acetate, barium acetate, lithium formate, sodium formate, potassium formate, lithium benzoate, benzoic acid ... Examples of the surfactant include sodium benzoate, potassium benzoate, lithium phenoxide, sodium phenoxide, potassium phenoxide, lithium methoxide, sodium methoxide, potassium methoxide, lithium ethoxide, sodium ethoxide, potassium ethoxide, lithium phosphate, trisodium phosphate, disodium hydrogen phosphate, tripotassium phosphate, dipotassium hydrogen phosphate, triammonium phosphate, trisodium citrate, tripotassium citrate, lithium sulfide, sodium sulfide, potassium sulfide, sodium hypochlorite, potassium hypochlorite, ammonia, methylamine, diethylamine, and hydrazine, and one or more of these can be used.

[0024] The amount of the basic compound used is not particularly limited as long as a neutralized product is obtained, but it is usually preferably 0.1 to 10 moles per mole of the total of all metal elements, including zirconium, contained in the raw materials.

[0025] The proportion of the metal element-containing compound in the slurry containing the zirconium element-containing compound is preferably 0.1 to 20 wt %. At such a proportion, the proportion of the metal element-containing compound in the slurry is not too small, and the viscosity of the slurry is appropriate, allowing the hydrothermal reaction to proceed sufficiently and a sufficient amount of zirconium element-containing metal oxide dispersion to be obtained. Furthermore, when the slurry containing the zirconium element-containing compound is subjected to a filtering and washing process, as described below, a proportion of the metal element-containing compound in the slurry within this range allows for sufficient washing, resulting in a dispersion obtained through the hydrothermal reaction process with superior transparency at high concentrations and lower viscosity. The proportion of the metal element-containing compound in the slurry is more preferably 0.2 to 17 wt %, and even more preferably 0.5 to 15 wt %. Here, the metal element-containing compound in the slurry means a zirconium element-containing compound when the slurry contains only a zirconium element-containing compound as the metal element-containing compound, and means a zirconium element-containing compound and other metal element-containing compounds when the slurry also contains other metal element-containing compounds.

[0026] In the production method of the present invention, the slurry containing the zirconium element-containing compound to be subjected to the hydrothermal reaction preferably contains an organic acid, which causes the slurry to be acid-peptized and repels particles by electrostatic interaction, thereby providing a dispersion with high transparency. Therefore, the production method of the present invention preferably includes a step of adding an organic acid to the slurry before the hydrothermal reaction step.When the production method of the present invention includes a step of reacting a raw material containing a zirconium compound with a basic compound in water to obtain a slurry containing a neutralized product containing zirconium element, it preferably includes a step of adding an organic acid to the slurry after the step of obtaining the slurry.

[0027] The organic acid is not particularly limited, and one or more of the following can be used: monocarboxylic acids such as formic acid, acetic acid, and propionic acid, and their salts; polybasic acids such as oxalic acid, malonic acid, succinic acid, fumaric acid, and maleic acid, and their salts; and hydroxycarboxylic acids such as lactic acid, malic acid, tartaric acid, citric acid, and gluconic acid, and their salts. Examples of the salts of organic acids include alkali metal salts such as sodium salts and potassium salts, alkaline earth metal salts such as calcium salts and barium salts, and magnesium salts.

[0028] The amount of the organic acid used is preferably 0.5 to 10 moles per mole of the metal element-containing compound contained in the slurry. By using the organic acid in such a ratio, the resulting zirconium element-containing metal oxide dispersion liquid has better transparency at high concentrations. On the other hand, if the amount used is too large, the effect cannot be obtained. Therefore, the amount of the organic acid used is more preferably 1 to 5 moles, and even more preferably 1 to 3 moles, per mole of the metal element-containing compound.

[0029] The production method of the present invention preferably includes a step of filtering the slurry and a step of washing the filtered slurry after a step of reacting a raw material containing a zirconium compound with a basic compound in water to obtain a slurry containing a neutralized product containing zirconium element. For example, when a step of obtaining a slurry containing a neutralization product is performed using zirconium oxychloride as the zirconium compound contained in the raw materials and potassium hydroxide as the basic compound, potassium chloride is contained as a by-product salt in the obtained slurry. By removing the by-product salt by performing a step of filtering the slurry before the hydrothermal reaction step or a step of washing the slurry after filtration, the dispersion obtained by the hydrothermal reaction can be made into a dispersion with better dispersibility and high transparency even at a high concentration. The step of filtering the slurry containing the neutralized product containing elemental zirconium and the step of washing the filtered slurry are preferably carried out before the step of adding an organic acid to the slurry.

[0030] The production method of the present invention may include a step of washing the obtained zirconium-containing metal oxide dispersion after the hydrothermal treatment step. The washing method is not particularly limited, and filtration using an ultrafiltration membrane, ion exchange using an ion exchange resin, dialysis using a semipermeable membrane, etc. can be used, but among these, filtration using an ultrafiltration membrane is preferred. Filtration using an ultrafiltration membrane removes residual by-product salts contained in the dispersion and concentrates the dispersion to obtain a dispersion with a higher concentration. Furthermore, if necessary, the remaining by-product salt can be removed more thoroughly by adding a solvent to the dispersion liquid concentrated by filtration using an ultrafiltration membrane and then repeating the filtration using an ultrafiltration membrane again.

[0031] The production method of the present invention may include other steps in addition to the steps described above, such as a step of dissolving the raw material powder in water to prepare an aqueous solution, a step of increasing dispersibility using ultrasound or the like, a step of pulverizing the zirconium-containing metal oxide in the dispersion, a step of adjusting the pH of the dispersion, a step of adjusting the temperature of the dispersion, a step of further desalting the dispersion, and a step of additionally adding a dispersant or the like depending on the intended use of the dispersion.

[0032] The production method of the present invention is a production method that can be used not only for zirconium oxide but also for producing composite oxides containing zirconium element and other metal elements. However, the production method of the present invention is particularly suitable for producing a zirconium oxide dispersion that has high transparency even at high concentrations and low viscosity, making it suitable for optical material applications. Therefore, one preferred embodiment of the production method of the present invention is a production method in which a hydrothermal reaction step is performed using a slurry that contains only a zirconium element-containing compound as the metal element-containing compound.

[0033] 2. Zirconium-containing metal oxide dispersion The present invention also relates to a zirconium-containing metal oxide dispersion, characterized in that when the dispersion is a 48 wt % aqueous dispersion, the dispersion has a light transmittance at a wavelength of 550 nm of 70% or more and a viscosity of 25 mPa s or less. As described above, the transparency of a zirconium-containing metal oxide dispersion generally depends on the primary particle size of the zirconium-containing metal oxide. Therefore, to obtain a dispersion with high transparency, it is preferable to use a zirconium-containing metal oxide with a small primary particle size. However, since zirconium-containing metal oxides with a small primary particle size tend to aggregate, when blended with a resin, a large amount of dispersant must be used to sufficiently disperse the zirconium-containing metal oxide in the resin. Generally, dispersants have a low refractive index, which makes it difficult to improve the refractive index of the resin composition. In contrast, the zirconium-containing metal oxide dispersion of the present invention has high transparency even when made into a high-concentration aqueous dispersion, and is a low-viscosity aqueous dispersion. Therefore, when blended with a resin, a large amount of dispersant is not required, and the dispersion can be suitably used for various applications, such as optical materials. When the zirconium-containing metal oxide dispersion is prepared as a 48 wt % aqueous dispersion, the light transmittance at a wavelength of 550 nm is preferably 72% or more, more preferably 75% or more, and even more preferably 78% or more. Furthermore, the viscosity of a 48% by weight aqueous dispersion is preferably 23 mPa·s or less. The light transmittance and viscosity of the aqueous dispersion of the zirconium-containing metal oxide can be measured by the method described in the examples below.

[0034] The zirconium-containing metal oxide dispersion preferably has an average primary particle size of 3 to 20 nm. When a zirconium-containing metal oxide dispersion is used to increase the refractive index of a resin composition, the amount of dispersant used to disperse the zirconium-containing metal oxide in the resin can be reduced, thereby increasing the refractive index of the resin composition. The average primary particle size of the zirconium-containing metal oxide is more preferably 3 to 18 nm, and even more preferably 3 to 15 nm. The average primary particle size of the zirconium-containing metal oxide can be measured by a method in which the particle sizes of 200 randomly selected primary particles are measured using a transmission electron microscope and the average of the primary particle sizes is calculated.

[0035] The zirconium-element-containing metal oxide dispersion may contain other metal elements in addition to zirconium element. However, since the zirconium oxide dispersion having high transparency and low viscosity as described above is suitable for optical material applications, one preferred embodiment of the present invention is for the zirconium-element-containing metal oxide dispersion to be a zirconium oxide dispersion containing only zirconium element as the metal element. [Example]

[0036] Specific examples are given below to explain the present invention in detail, but the present invention is not limited to these examples. The methods for measuring each physical property are as follows.

[0037] The transmittance and viscosity of the aqueous zirconium oxide dispersions of the Examples and Comparative Examples were measured as follows. <Transmittance measurement> The zirconium element-containing metal oxide dispersion was placed in a glass square cell with an optical path length of 10 mm, and this cell was set in the sample chamber of a haze meter "NDH 4000" manufactured by Nippon Denshoku Industries Co., Ltd., to measure the transmittance. <Viscosity measurement> The viscosity of the zirconium-containing metal oxide dispersion was measured at room temperature using a tuning fork vibration viscometer "SV-1H" manufactured by A&D Co., Ltd.

[0038] Example 1 0.24 L of a 0.6 mol / L aqueous zirconium oxychloride solution and 0.18 L of a 1.7 mol / L aqueous potassium hydroxide solution were simultaneously poured into a reaction vessel containing 0.22 L of ion-exchanged water to obtain a zirconium hydroxide slurry. The resulting slurry was filtered and washed, and 104.7 g of acetic acid (1.3 molar parts per molar part of zirconium contained in the slurry) was added and stirred to obtain 1.5 L of a slurry (zirconium oxide precursor slurry) with a zirconium hydroxide content of 10 wt%. The resulting zirconium oxide precursor slurry was poured into a pressure vessel and heated from room temperature at a rate of 180°C / hour, followed by a hydrothermal reaction at 200°C for 3 hours. This resulted in a thin, translucent aqueous zirconium oxide dispersion. This dispersion was washed using an ultrafiltration membrane to obtain a zirconium oxide dispersion with a zirconium oxide content of 30% by weight. The transmittance of this aqueous dispersion at a wavelength of 550 nm was 87.9%, and its viscosity was 5.7 mPa·s. The aqueous dispersion was further concentrated using an ultrafiltration membrane to obtain a zirconium oxide dispersion with a zirconium oxide content of 48% by weight. The transmittance of this aqueous dispersion at a wavelength of 550 nm was 84.1%, and its viscosity was 20.4 mPa·s.

[0039] Example 2 A slurry (zirconium oxide precursor slurry) with a zirconium hydroxide content of 10 wt % obtained in the same manner as in Example 1 was poured into a pressure vessel, heated from room temperature at a temperature increase rate of 165°C / hour, and subjected to a hydrothermal reaction at 200°C for 3 hours. As a result, a thin, translucent aqueous dispersion of zirconium oxide was obtained. This dispersion was washed using an ultrafiltration membrane to obtain a zirconium oxide dispersion with a zirconium oxide content of 30 wt %. The transmittance of this aqueous dispersion at a wavelength of 550 nm was 86.4%, and the viscosity was 4.6 mPa·s. The aqueous dispersion was further concentrated using an ultrafiltration membrane to obtain a zirconium oxide dispersion with a zirconium oxide content of 48 wt %. The transmittance of this aqueous dispersion at a wavelength of 550 nm was 83.1%, and the viscosity was 17.4 mPa·s.

[0040] Example 3 A slurry (zirconium oxide precursor slurry) with a zirconium hydroxide content of 10 wt % obtained in the same manner as in Example 1 was poured into a pressure vessel, heated from room temperature at a temperature increase rate of 113°C / hour, and subjected to a hydrothermal reaction at 200°C for 3 hours. As a result, a thin, translucent aqueous dispersion of zirconium oxide was obtained. This dispersion was washed using an ultrafiltration membrane to obtain a zirconium oxide dispersion with a zirconium oxide content of 30 wt %. The transmittance of this aqueous dispersion at a wavelength of 550 nm was 80.7%, and the viscosity was 6.0 mPa·s. The aqueous dispersion was further concentrated using an ultrafiltration membrane to obtain a zirconium oxide dispersion with a zirconium oxide content of 48 wt %. The transmittance of this aqueous dispersion at a wavelength of 550 nm was 76.1%, and the viscosity was 21.1 mPa·s.

[0041] Example 4 A slurry (zirconium oxide precursor slurry) with a zirconium hydroxide content of 10 wt % obtained in the same manner as in Example 1 was poured into a pressure vessel, heated from room temperature at a temperature increase rate of 96°C / hour, and subjected to a hydrothermal reaction at 200°C for 3 hours. As a result, a thin, translucent aqueous dispersion of zirconium oxide was obtained. This dispersion was washed using an ultrafiltration membrane to obtain a zirconium oxide dispersion with a zirconium oxide content of 30 wt %. The transmittance of this aqueous dispersion at a wavelength of 550 nm was 78.5%, and the viscosity was 5.7 mPa·s. The aqueous dispersion was further concentrated using an ultrafiltration membrane to obtain a zirconium oxide dispersion with a zirconium oxide content of 48 wt %. The transmittance of this aqueous dispersion at a wavelength of 550 nm was 72.8%, and the viscosity was 24.5 mPa·s.

[0042] Comparative Example 1 1.5 L of a slurry (zirconium oxide precursor slurry) with a zirconium hydroxide content of 10 wt %, obtained in the same manner as in Example 1, was poured into a pressure vessel and heated at a temperature increase rate of 75°C from room temperature. A hydrothermal reaction was carried out at 200°C for 3 hours. As a result, a translucent aqueous zirconium oxide dispersion was obtained. This dispersion was washed using an ultrafiltration membrane to obtain a zirconium oxide dispersion with a zirconium oxide content of 30 wt %. This aqueous dispersion had a light transmittance of 73.6% at a wavelength of 550 nm and a viscosity of 5.9 mPa·s. Further desalination of this aqueous dispersion using an ultrafiltration membrane yielded a zirconium oxide dispersion with a zirconium oxide content of 48 wt %. This aqueous dispersion had a light transmittance of 66.4% at a wavelength of 550 nm and a viscosity of 30.1 mPa·s.

[0043] Comparative Example 2 1.5 L of a slurry (zirconium oxide precursor slurry) with a zirconium hydroxide content of 10 wt %, obtained in the same manner as in Example 1, was poured into a pressure vessel and heated at a temperature increase rate of 80°C from room temperature. A hydrothermal reaction was carried out at 200°C for 3 hours. As a result, a translucent aqueous dispersion of zirconium oxide was obtained. This dispersion was washed using an ultrafiltration membrane to obtain a zirconium oxide dispersion with a zirconium oxide content of 30 wt %. This aqueous dispersion had a light transmittance of 75.4% at a wavelength of 550 nm and a viscosity of 5.5 mPa·s. This aqueous dispersion was further desalted using an ultrafiltration membrane to obtain a zirconium oxide dispersion with a zirconium oxide content of 48 wt %. This aqueous dispersion had a light transmittance of 69.0% at a wavelength of 550 nm and a viscosity of 29.2 mPa·s.

[0044] [Table 1]

[0045] As shown in Table 1, it was confirmed that the zirconium oxide dispersions of Examples 1 to 4, which were produced by carrying out the hydrothermal reaction step at a heating rate corresponding to the production method of the present invention, had high transparency not only at normal concentrations but also at high concentrations, compared to the zirconium oxide dispersions of Comparative Examples 1 and 2, which were produced by carrying out the hydrothermal reaction step at a heating rate not corresponding to the production method of the present invention. Furthermore, it was confirmed that the viscosity at normal concentrations was similar for the zirconium oxide dispersions of Examples 1 to 4 and the zirconium oxide dispersions of Comparative Examples 1 and 2, but that at high concentrations the viscosity increased more significantly than for the zirconium oxide dispersions of Examples 1 to 4. These results confirmed the effectiveness of production by the production method of the present invention.

Claims

1. A method for producing a zirconium-containing metal oxide dispersion for optical materials, comprising: The production method includes a step of heating a slurry containing a zirconium-element-containing compound as a metal-element-containing compound to carry out a hydrothermal reaction, The heating in the hydrothermal reaction step is carried out at a temperature increase rate of 90°C / hour or more.

1. A method for producing a zirconium-containing metal oxide dispersion for optical materials, comprising:

2. 2. The method for producing a zirconium-containing metal oxide dispersion for optical materials according to claim 1, wherein the slurry contains an organic acid.

3. 3. The method for producing a zirconium-containing metal oxide dispersion for optical materials according to claim 1, wherein the slurry contains only a zirconium-containing compound as the metal-element-containing compound.

4. A zirconium-containing metal oxide dispersion for optical materials, characterized in that when the dispersion is made into a 48 wt % aqueous dispersion, the transmittance of light having a wavelength of 550 nm is 70% or more and the viscosity is 25 mPa·s or less.

5. 5. The zirconium-containing metal oxide dispersion for optical materials according to claim 4, wherein the zirconium-containing metal oxide has an average primary particle size of 3 to 20 nm.

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