JP2015054789A - Method for producing crystalline metal oxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily produce a crystalline, high refractive index metal oxide comprising fine particles having high dispersibility.SOLUTION: A crystalline metal oxide production method for producing a crystalline metal oxide having an average particle diameter of primary particles of 20 nm or less includes: a first step of adding a water-containing solution to a mixed liquor containing a metalalkoxide and an organic solvent to perform reaction at a temperature of -30°C or higher and 10°C or lower; a second step of aging a reaction product after the reaction of the first step at a temperature of 20°C or higher and 30°C or lower; a third step of, when the content of the organic solvent contained in a reaction product after the aging of the second step is designated as A pts.mass and the content of water contained in the reaction product after the aging of the second step is designated as B pts.mass, adjusting a value of A/B to 2 or more and 200 or less; and a fourth step of treating a reaction product after the third step at a temperature of 100°C or higher and 200°C or lower using a solvothermal method.

Description

  The present invention relates to a method for producing a crystalline metal oxide used for a high refractive index material or the like.

Fine particles and highly crystalline titanium oxide (TiO ₂ ), zirconium oxide (ZrO ₂ ), barium titanate (BaTiO ₃ ), etc. are attracting attention as high refractive index materials for optical films and optical lenses. As the high refractive index material, materials having a particle diameter of 20 nm or more have been developed for the purpose of being used as coating materials for optical films and the like, but recently, the number of particle diameters for use in molded articles such as optical lenses has been increased. Particles on the order of nm have also been developed. However, the manufacturing method is not necessarily focused on a high refractive material, but barium titanate is used for the purpose of manufacturing a high dielectric constant material, and titanium oxide is used for materials such as piezoelectrics and phosphors. Some are for manufacturing purposes.

  For example, Patent Document 1 proposes a method in which barium titanate is synthesized and coated and then fired. However, the barium titanate crystal is in an amorphous state during synthesis, and is crystallized by subsequent firing. Yes. Patent Document 2 proposes a method in which nano-sized barium titanate particles obtained by a sol-gel method are crystal-grown to a micron size by hydrothermal synthesis.

  However, in the method of Patent Document 1, the particle diameter is increased by the sintering process, and in the method of Patent Document 2, the particle diameter is increased by the crystal growth process, and fine particles cannot be obtained by any method. In particular, if the particles are once dried by sintering or the like, it is very difficult to obtain a highly dispersed state even if the particles are dispersed thereafter.

  On the other hand, what is required of a high refractive material is crystalline particles for making the refractive index uniform, and maintaining a highly dispersed state in nano size for reducing haze of optical films and engineering lenses. . However, a method for producing a high refractive index material consisting of highly crystalline and highly dispersible fine particles has not been proposed.

JP 2005-306691 A (Patent No. 4411483) JP 2008-230959 A

  The present invention solves the above-mentioned problems and provides a method for producing a high refractive index metal oxide comprising highly crystalline and highly dispersible fine particles.

  The method for producing a crystalline metal oxide according to the present invention is a method for producing a crystalline metal oxide having an average primary particle diameter of 20 nm or less, and the mixed liquid containing the metal alkoxide and the organic solvent contains water. A first step of adding a solution and reacting at a temperature of −30 ° C. or higher and 10 ° C. or lower; a second step of aging the reaction product after the reaction in the first step at a temperature of 20 ° C. or higher and 30 ° C. or lower; When the content of the organic solvent contained in the reaction product after aging in the second step is A part by mass, and the content of water contained in the reaction product after aging in the second step is B part by mass , A third step of adjusting the value of A / B to 2 or more and 200 or less, and a fourth step of treating the reaction product after the third step at a temperature of 100 ° C. or more and 200 ° C. or less using a solvothermal method. It is characterized by including.

  According to the present invention, a high refractive index metal oxide composed of highly crystalline and highly dispersible fine particles can be easily produced.

1 is a diagram showing an X-ray diffraction chart of barium titanate obtained in Example 1, Example 8, and Comparative Example 5. FIG. FIG. 2 is a transmission electron micrograph of barium titanate obtained in Example 1.

  The method for producing a crystalline metal oxide according to the present invention is a method for producing a crystalline metal oxide having an average primary particle diameter of 20 nm or less, and a solution containing water in a mixed solution containing a metal alkoxide and an organic solvent. A first step of reacting at a temperature of −30 ° C. to 10 ° C., a second step of aging the reaction product after the reaction in the first step at a temperature of 20 ° C. to 30 ° C., and the above When the content of the organic solvent contained in the reaction product after aging in the second step is A parts by mass, and the content of water contained in the reaction product after aging in the second step is B parts by mass, A third step of adjusting the value of A / B to 2 or more and 200 or less, and a fourth step of treating the reaction product after the third step using a solvothermal method at a temperature of 100 ° C. or more and 200 ° C. or less; It is characterized by providing.

  By the above production method, a metal oxide having a high refractive index composed of highly crystalline and highly dispersible fine particles can be obtained. In the present invention, the high refractive index means a refractive index of 2.0 or more. Further, if the refractive index is 2.0 or more, the type of the metal oxide is not limited, but from the viewpoint of production cost, titanium oxide, zirconium oxide and barium titanate are preferable, and there is no catalytic ability, and the refractive index. In particular, barium titanate is preferable.

  The average particle diameter of the primary particles of the metal oxide is 1 nm to 20 nm, preferably 1 nm to 15 nm, more preferably 2 nm to 10 nm, and still more preferably about 2 nm to 5 nm. When the average particle diameter is less than 1 nm, after the metal oxide is produced, the agglomeration becomes severe during actual coating preparation and tends to be difficult to disperse. On the other hand, when the average particle diameter exceeds 20 nm, it tends to be difficult to maintain optical properties such as total light transmittance and haze value when a coating film or a molded body is formed. Here, the “particle diameter” substantially means the maximum length among the lengths of the particles in all directions. The “average particle diameter” in the present specification means a value calculated by measuring the particle diameter of any 300 particles based on a transmission electron micrograph of the particles and calculating the number average thereof. .

  Hereinafter, each process of the manufacturing method of this invention is demonstrated.

<First step>
In the 1st process of this invention, the solution containing water is added to the liquid mixture containing a metal alkoxide and an organic solvent, and it is made to react at the temperature of -30 degreeC or more and 10 degrees C or less. In the first step, a hydrolysis reaction and a condensation reaction of the metal alkoxide occur.

  The kind of the metal alkoxide is not particularly limited as long as a necessary metal as a central metal exists. For example, when producing titanium oxide, titanium tetraisopropoxide, titanium tetrabutoxide, etc., when producing zirconium oxide, zirconium-n-butoxide, zirconium-tert-butoxide, etc., when producing barium titanate. Titanium tetraisopropoxide, titanium tetrabutoxide and barium ethoxide can be used.

  The organic solvent is not particularly limited as long as it is compatible with water, but an organic solvent having a hydroxy group (—OH group) is preferable. For example, alcohols having 4 or less carbon atoms such as methanol, ethanol, n-propanol, iso-propanol, n-butanol, tert-butanol, glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, and 2 -Methoxyethanol or the like can be used.

  The organic solvent used for dissolving the metal alkoxide is preferably dehydrated. This is because the metal alkoxide has a high reactivity with water and thus prevents an unexpected reaction. Further, when the metal alkoxide is dissolved in an organic solvent, it is preferably carried out in an environment with little moisture, such as in a glove box whose dew point is controlled. As a dew point, 0 degrees C or less is preferable, and -10 degrees C or less is still more preferable.

  In the first step of the present invention, the metal alkoxide is dissolved in an organic solvent to obtain a mixed solution, and then a solution containing water is added to the mixed solution. The solution containing water is mixed with the mixed solution. When the number of moles of the metal ion is C and the number of moles of added water is D, it is preferable that the C / D value be 4 or more and 30 or less. The C / D value is more preferably 4 or more and 20 or less. When the number of moles of the water is increased while keeping the amount of the metal ions constant, the particle diameter of the generated particles tends to increase. For this reason, in order to obtain particles having a small particle size, it is necessary to reduce the number of moles of the water. On the other hand, if the number of moles of water is reduced too much, the hydrolysis reaction of the metal alkoxide tends not to proceed.

  The solvent other than water used for the solution containing water can be selected from the organic solvents used when dissolving the above-described metal alkoxide, but usually the organic solvent used when dissolving the metal alkoxide. The same organic solvent as the solvent is used.

  The reaction temperature in the 1st process of this invention shall be -30 degreeC or more and 10 degrees C or less. When the reaction temperature exceeds 10 ° C., the hydrolysis reaction and the subsequent condensation reaction proceed rapidly, and the particle diameter of the resulting metal oxide particles becomes large. On the other hand, if the reaction temperature is lower than −30 ° C. and too low, it is difficult to maintain the reaction conditions. Therefore, the reaction temperature is −30 ° C. or higher and 10 ° C. or lower, which is a temperature range that can be realized in a commercial thermostat, and preferably −30 ° C. or higher and 0 ° C. or lower. The reaction in the first step may be performed at a constant temperature within the range of the reaction temperature, or may be performed by changing the temperature within the range of the reaction temperature.

  The reaction time in the first step of the present invention may be set to 10 minutes or more and 30 minutes or less in order to terminate the hydrolysis reaction.

<Second step>
In the second step of the present invention, the reaction product after the reaction in the first step is aged at a temperature of 20 ° C. or higher and 30 ° C. or lower. In the second step, a condensation reaction of the metal alkoxide mainly occurs. The reaction product after the reaction in the first step exhibits a sol form because the condensation reaction has not been completed yet, but the reaction product after the reaction in the second step has completed the condensation reaction. Therefore, it usually exhibits a gel form. However, even a reaction product after the reaction in the second step may exhibit a sol shape depending on conditions.

  The reaction temperature in the second step of the present invention may be a so-called room temperature of 20 ° C. or higher and 30 ° C. or lower. The reaction time of the second step may be 1 hour or more and 24 hours or less in order to complete the condensation reaction of the metal alkoxide.

<Third step>
In the third step of the present invention, the content of the organic solvent contained in the reaction product after the aging in the second step is A part by mass, and the water contained in the reaction product after the aging in the second step. When the content is B parts by mass, the value of A / B is adjusted to 2 or more and 200 or less. When the content of the organic solvent is too large, the target metal oxide particles may not be obtained. When the content is too small, the average particle diameter of the obtained metal oxide particles exceeds 20 nm. There is. The value of A / B is preferably 3 or more and 150 or less, and more preferably 3 or more and 100 or less.

  Specifically, since the reaction product after the reaction in the second step is usually in a gel form, after adding an organic solvent to the reaction product to form a gel, further adding an organic solvent, the above A / B The value may be adjusted to 2 or more and 200 or less. Various organic solvents can be used as the organic solvent added in the third step, and the organic solvent used in the first step can be used as it is, or solvent substitution is performed in the third step. It is also possible. However, it is convenient and preferable to use the organic solvent used in the first step as it is without performing solvent replacement.

  The value of A / B is the theoretical amount (A part by mass) of the total organic solvent present in the reaction product at the end of the third step, and the theoretical amount of water present in the reaction product at the end of the third step (A (B parts by mass). However, in the first to third steps, calculation is performed assuming that there is no loss due to volatilization of the organic solvent and water.

  The theoretical amount (A part by mass) of the total organic solvent present in the reaction product at the end of the third step is the chemical reaction formula of the metal alkoxide in the amount of the total organic solvent used in the first to third steps. Can be determined by adding the amount of alcohol produced. The theoretical amount of water (B parts by mass) present in the reaction product at the end of the third step is based on the chemical reaction formula of the metal alkoxide from the total amount of water used in the first to third steps. It can be determined by subtracting the amount of water consumed.

<4th process>
In the fourth step of the present invention, the reaction product after the third step is treated at a temperature of 100 ° C. or higher and 200 ° C. or lower using a solvothermal method. In the fourth step, the reactant is crystallized to obtain the target metal oxide.

  The solvothermal method differs from the hydrothermal synthesis method in that it contains a liquid other than water as a reaction medium. However, basically, the reaction apparatus, operation procedure and reaction conditions of the hydrothermal synthesis method can be used for the solvothermal method.

  The heating means in the solvothermal method is not particularly limited. If the solvent can be heated, a thermostatic bath, a microwave hydrothermal reactor, or the like can be used. The thermostatic bath is an external heating type device in which the inside of the bath is heated by an external heater and the reaction vessel is heated by the heat. On the other hand, the microwave hydrothermal reaction device is irradiated with microwaves to react with the reaction vessel. It is an internal heating type that directly heats the solvent inside.

  The treatment temperature in the solvothermal method is 100 ° C. or more and 200 ° C. or less. If the treatment temperature is too low, crystallization will be insufficient. Conversely, if the treatment temperature is too high, particle growth will proceed too much and the particle size of the primary particles will increase. The treatment temperature is preferably 120 ° C. or higher and 180 ° C. or lower. The treatment time in the solvothermal method varies depending on the heating method and treatment temperature, but is usually about 15 minutes to 2 hours, preferably 20 minutes to 1 hour 30 minutes.

  Hereinafter, the present invention will be described in detail based on examples. However, the present invention is not limited to the following examples.

Example 1
<First Step: Preparation of Sol Solution by Sol-Gel Method>
40 ml of a mixed solvent of methanol: 2-methoxyethanol = 3: 2 by volume as an organic solvent was prepared and left for 24 hours or more using dehydrated molecular sieve 3A to remove moisture in the mixed solvent. In this mixed solvent, 9.1 g of barium diethoxide (manufactured by High Purity Chemical Laboratory) and 11.4 g of titanium tetraisopropoxide (manufactured by Wako Pure Chemical Industries) as metal alkoxide in a glove box having a dew point of −20 ° C. To prepare a mixed solution. This mixed solution was cooled in a constant temperature bath set to −30 ° C. until the temperature of the mixed solution became −30 ° C. Thereafter, a solution prepared in such a manner that the molar ratio of water: methanol = 7: 3 and the amount of water is 8 times the molar amount of the above-mentioned titanium tetraisopropoxide (the above-mentioned C / D value is 8) The solution was dropped into the prepared mixed solution and reacted for 10 minutes while cooling at −30 ° C. to obtain a sol solution.

<Second step: Gelation by aging>
Next, the sol solution was allowed to stand at room temperature for 12 hours. Gelation proceeded during standing, and a gelled product that was completely gelled was obtained after completion of the standing.

<Third Step: Adjustment of A / B Value>
Next, 2-methoxyethanol was added to the gelled product to make a total of 90 g, and pulverized in an ultrasonic bath to obtain a sol solution again. Thereafter, 10 g of the sol solution was separated from the sol solution, and 10 g of 2-methoxyethanol was added thereto.

  Here, the theoretical amount (A part by mass) of all organic solvents present in the sol solution fractionated at the end of the third step is the theory of water present in the sol solution fractionated at the end of the third step. When the value of A / B was determined by dividing by the amount (B parts by mass), it was 21.4.

  The theoretical amount (A part by mass) of the total organic solvent present in the reaction product at the end of the third step is the amount of the total organic solvent used in the first to third steps as described above. It can obtain | require by adding the quantity of produced | generated alcohol based on the following chemical reaction formula. The theoretical amount of water (B parts by mass) present in the reaction product at the end of the third step is calculated from the total amount of water used in the first to third steps according to the following chemical reaction formula of the metal alkoxide. Based on this, it can be obtained by subtracting the amount of water consumed.

The chemical reaction formula of the metal alkoxide in Example 1 is as follows.
Ba (OC ₂ H ₅ ) ₂ + Ti (OCH (CH ₃ ) ₂ ) ₄ + 3H ₂ O
→ BaTiO ₃ + 2C ₂ H ₅ OH + 4CH (CH ₃ ) ₂ OH

<Fourth step: Crystallization by solvothermal method>
The sol solution fractionated in the third step was placed in a high-pressure reaction vessel, heated to 150 ° C. with a microwave high-pressure reactor (trade name “MicroSYNTH” manufactured by Milestone General), and reacted for 0.5 hours. After cooling, the reaction solution was taken out from the high pressure reaction vessel. Next, the reaction solution was centrifuged with a centrifuge and then the supernatant was discarded three times, and the washed reaction solution was filtered to obtain fine particles.

  Next, the fine particles were analyzed by a powder X-ray diffraction method to obtain an X-ray diffraction chart. The X-ray diffraction chart is shown in FIG. From FIG. 1, a crystal diffraction pattern of barium titanate was obtained, and it was confirmed that barium titanate was generated. The average particle diameter of primary particles calculated by measuring the particle diameter of 300 fine particles by transmission electron microscope measurement and calculating the number average thereof was 5.2 nm. FIG. 2 shows a transmission electron micrograph of the fine particles. Table 1 shows the production conditions of Example 1 and the characteristics of the produced barium titanate.

(Examples 2 to 8)
Barium titanate was produced in the same manner as in Example 1 except that the production conditions of barium titanate were changed as shown in Table 1. Further, the characteristics of barium titanate obtained in Examples 2 to 8 were measured in the same manner as in Example 1, and the results are also shown in Table 1. FIG. 1 shows an X-ray diffraction chart of the fine particles produced in Example 8. It can be seen from FIG. 1 that the fine particles produced in Example 8 are almost barium titanate but contain a small amount of TiO ₂ .

Example 9
As a heating method in the fourth step, barium titanate was produced in the same manner as in Example 1 except that a thermostatic bath was used instead of the microwave high-pressure reactor and the reaction time was changed to 1 hour. The characteristics of barium titanate obtained in Example 9 were also measured in the same manner as in Example 1. The results are also shown in Table 1.

(Comparative Example 1)
Fine particles were produced in the same manner as in Example 1 except that the A / B value was set to 223 and the C / D value was changed to 3.5. The obtained fine particles were analyzed by the powder X-ray diffraction method in the same manner as in Example 1 to obtain an X-ray diffraction chart. As a result, a crystal diffraction pattern of barium titanate was obtained on the X-ray diffraction chart, but at the same time, an unidentified peak was obtained. From this, it was presumed that the obtained fine particles were a mixed crystal of barium titanate and an unidentified substance. Moreover, the average particle diameter of the primary particles measured in the same manner as in Example 1 was 4.6 nm.

(Comparative Example 2)
Fine particles were produced in the same manner as in Example 1, except that the A / B value was set to 1.7 and the C / D value was changed to 4.5. The obtained fine particles were analyzed by the powder X-ray diffraction method in the same manner as in Example 1 to obtain an X-ray diffraction chart. As a result, a crystal diffraction pattern of barium titanate was obtained on the X-ray diffraction chart, and it was confirmed that barium titanate was generated. Moreover, the average particle diameter of the primary particles measured in the same manner as in Example 1 was 25 nm.

(Comparative Example 3)
Fine particles were produced in the same manner as in Example 1 except that the treatment temperature in the fourth step was set to 60 ° C. The obtained fine particles were analyzed by the powder X-ray diffraction method in the same manner as in Example 1 to obtain an X-ray diffraction chart. As a result, a broad peak was observed in the X-ray diffraction chart, and it was confirmed that the obtained product was amorphous.

(Comparative Example 4)
Fine particles were produced in the same manner as in Example 1 except that the treatment temperature in the fourth step was set to 250 ° C. The obtained fine particles were analyzed by the powder X-ray diffraction method in the same manner as in Example 1 to obtain an X-ray diffraction chart. As a result, a crystal diffraction pattern of barium titanate was obtained on the X-ray diffraction chart, and it was confirmed that titanium barium oxide was generated. Moreover, the average particle diameter of the primary particles measured in the same manner as in Example 1 was 25 nm.

(Comparative Example 5)
Fine particles were produced in the same manner as in Example 1 except that the reaction temperature in the first step was set to 25 ° C. The obtained fine particles were analyzed by the powder X-ray diffraction method in the same manner as in Example 1 to obtain an X-ray diffraction chart. As a result, a crystal diffraction pattern other than barium titanate was obtained on the X-ray diffraction chart, and it was presumed that titanium oxide was probably produced, but could not be assigned completely. FIG. 1 shows an X-ray diffraction chart of Comparative Example 5. Moreover, the average particle diameter of the primary particles measured in the same manner as in Example 1 was 20 nm.

  From Table 1, it can be seen that the fine particles obtained in Examples 1 to 9 are almost barium titanate crystals, and the average primary particle diameter is 20 nm or less. Further, from the results of Example 1, Example 8 and Comparative Example 5 in which the reaction temperature of the first step was changed, the reaction temperature of the first step needs to be set to −30 ° C. or more and 10 ° C. or less. I understand.

(Reference example)
Using the barium titanate particles produced in Example 1, a coating film having a high refractive index was produced as follows. First, without drying the barium titanate particles produced in Example 1, 2-methoxyethanol was added to prepare a mixed solution adjusted so that the content of barium titanate particles was 10% by mass. This mixed solution was applied to a dispersing apparatus to disperse the barium titanate particles to obtain a dispersion. Next, an ultraviolet curable resin “KAYARAD DPHA” (trade name) manufactured by Nippon Kayaku Co., Ltd. was added to this dispersion so that the mass ratio was barium titanate: “KAYARAD DPHA” = 9: 1. Furthermore, 1 part by mass of “Irgacure 819” (trade name) manufactured by Ciba Specialty Chemicals as a reaction initiator was added to the solid content (barium titanate and “KAYARAD DPHA”) to prepare a coating material. Subsequently, the prepared paint was applied to a PET resin film using a bar coater and dried at 120 ° C. for 2 minutes. Thereafter, the resin was cured by irradiating ultraviolet rays with an ultraviolet lamp to prepare a coating film.

  When the prepared coating film was measured using a reflection spectral film thickness meter “FE-3000” (trade name) manufactured by Otsuka Electronics, the film thickness was 140 nm and the refractive index of light at 550 nm was 1.83. . Thus, it was found that a coating film having a high refractive index can be obtained using the barium titanate particles produced by the production method of the present invention.

Claims (5)

A method for producing a crystalline metal oxide having an average primary particle size of 20 nm or less,
A first step of adding a solution containing water to a mixed solution containing a metal alkoxide and an organic solvent and reacting at a temperature of −30 ° C. or higher and 10 ° C. or lower;
A second step of aging the reaction product after the reaction in the first step at a temperature of 20 ° C. or higher and 30 ° C. or lower;
When the content of the organic solvent contained in the reaction product after aging in the second step is A part by mass, and the content of water contained in the reaction product after aging in the second step is B part by mass , A third step of adjusting the value of A / B to 2 or more and 200 or less,
And a fourth step of treating the reactant after the third step at a temperature of 100 ° C. to 200 ° C. using a solvothermal method.   In the first step, the solution containing water has a C / D value of 4 or more and 30 or less, where C is the number of moles of metal ions in the mixed solution and D is the number of moles of water to be added. The method for producing a crystalline metal oxide according to claim 1, which is added in the step.   The method for producing a crystalline metal oxide according to claim 1 or 2, wherein a reaction time of the first step is 30 minutes or less, and an aging time of the second step is 1 hour or more and 24 hours or less.   The method for producing a crystalline metal oxide according to any one of claims 1 to 3, wherein a refractive index of the crystalline metal oxide is 2.0 or more.   The method for producing a crystalline metal oxide according to any one of claims 1 to 4, wherein the crystalline metal oxide is any one selected from the group consisting of titanium oxide, zirconium oxide, and barium titanate. .