Method for producing potassium tantalate particles, method for producing film, potassium tantalate particles, film, anti-reflection film, optical element, and optical device

Abstract

Provided is a method for producing potassium tantalate particles, the method including a heating step for heating a mixture containing (A) an oxide including tantalum, (B) a potassium compound which is potassium hydroxide and / or potassium chloride, (C) at least one alcohol selected from the group consisting of ethylene glycol, methanol, ethanol, 1-propanol, and 2-propanol, and (D) water.

Description

[Technical Field]

[0001] The present invention relates to a method for producing potassium tantalate particles, a method for producing a film, and a method for producing a tantalate film. This invention relates to potassium particles, films, anti-reflection films, optical elements, and optical devices. This invention claims priority from Japanese Patent Application No. 2020-049969, filed on March 19, 2020, and the contents of that application are incorporated by reference into this application in designated states where incorporation by reference of documents is permitted. [Background technology]

[0002] Potassium tantalate is expected to be used as an optical material, and examples thereof include those having a perovskite crystal structure (Patent Document 1, etc.). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-076926 Summary of the Invention

[0004] A first aspect of the present invention is a method for producing potassium tantalate particles, comprising a heating step of heating a mixture containing: (A) a tantalum-containing oxide; (B) a potassium compound which is at least one of potassium hydroxide and potassium chloride; (C) at least one alcohol selected from the group consisting of ethylene glycol, methanol, ethanol, 1-propanol, and 2-propanol; and (D) water.

[0005] A second aspect of the present invention is a method for producing a film containing potassium tantalate particles, the method including: a step of obtaining potassium tantalate particles by the above-described production method; a mist-forming step of forming a dispersion liquid containing the potassium tantalate particles into a mist; a supplying step of supplying the misted dispersion liquid to a substrate; and a drying step of drying the dispersion liquid present on the substrate after the supplying step.

[0006] A third aspect of the present invention is potassium tantalate particles having an average particle size of 100 nm or less.

[0007] A fourth aspect of the present invention is a film comprising the potassium tantalate particles described above.

[0008] A fifth aspect of the present invention is an anti-reflection film comprising at least one layer of the film described above.

[0009] A sixth aspect of the present invention is an optical element comprising the above-described antireflection film.

[0010] A seventh aspect of the present invention is an optical device comprising the optical element described above. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a conceptual diagram illustrating an example of a film forming apparatus using a mist method according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment for carrying out the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail. The present embodiment is an example for explaining the present invention, and is not intended to limit the present invention to the following content. In the drawings, positional relationships such as up, down, left, and right are based on the positional relationships shown in the drawings unless otherwise specified. Furthermore, the dimensional ratios of the drawings are not limited to those shown in the drawings.

[0013] <Method of manufacturing potassium tantalate particles, potassium tantalate particles>

[0014] The method for producing potassium tantalate (KTaO) particles (hereinafter sometimes simply referred to as "particles") according to this embodiment includes a heating step of heating a mixture containing: (A) an oxide containing tantalum; (B) a potassium compound which is at least one of potassium hydroxide and potassium chloride; (C) at least one alcohol selected from the group consisting of ethylene glycol, methanol, ethanol, 1-propanol, and 2-propanol; and (D) water.

[0015] Potassium tantalate with a small average particle size has been desired for applications such as optical thin films for the purpose of suppressing light scattering, and catalyst materials requiring a large specific surface area. However, it has been difficult to obtain potassium tantalate with a small average particle size using conventional manufacturing methods.

[0016] According to the manufacturing method of this embodiment, potassium tantalate nanoparticles having an average particle diameter of 100 nm or less can be efficiently manufactured. Such potassium tantalate nanoparticles can be used not only in the film-forming technique using the mist method described below, but also in the film-forming technique using the mist method, whereby the particles can be uniformly and densely arranged, suppressing light scattering and forming a film with a high refractive index. Therefore, the potassium tantalate particles according to this embodiment can be suitably used as optical thin films that suppress light scattering.

[0017] Furthermore, the potassium tantalate particles obtained by the production method according to this embodiment can be suitably used as a catalyst material, etc. Potassium tantalate is also expected to be used as a catalyst for various reactions such as organic synthesis reactions and photoreactions, and potassium tantalate particles with an average particle diameter of 100 nm or less have a large specific surface area, resulting in high contact efficiency with reactants, substrates, etc. in the system. Therefore, the potassium tantalate particles according to this embodiment can be suitably used as a catalyst with high catalytic activity.

[0018] A preferred embodiment of the manufacturing method according to the present invention is a solvothermal synthesis method. The potassium tantalate particles produced by this manufacturing method have a certain degree of dispersibility in a dispersion medium such as water. Therefore, the potassium tantalate particles according to the present invention can be applied to film formation techniques using a mist method, etc.

[0019] The following describes components that can be used in the production method according to this embodiment, production conditions, and the like.

[0020] (A) The oxide containing tantalum is not particularly limited, but from the viewpoints of availability, reaction efficiency, etc., tantalum oxide (tantalum pentoxide, Ta2O5) is preferred.

[0021] The proportion of component (A) in the mixed solution is not particularly limited, but is preferably 0.01 M or more and 1 M or less. The lower limit is more preferably 0.03 M, and even more preferably 0.05 M. The upper limit is more preferably 0.5 M, and even more preferably 0.3 M. In this embodiment, "M" refers to molar concentration (mol / L).

[0022] As the (B) potassium compound, at least one of potassium hydroxide and potassium chloride may be used. These may be used alone or in combination. Among these, potassium hydroxide is preferred from the viewpoint of basicity.

[0023] The molar ratio (B / A) of the component (B) to the component (A) is not particularly limited, but from the viewpoint of the reaction efficiency of the potassium tantalate particles and the reaction cost, it is preferably from 5 to 300. The lower limit is more preferably 10, even more preferably 20, and even more preferably 30. The upper limit is more preferably 280, even more preferably 250, and even more preferably 220.

[0024] The (C) alcohol may be at least one selected from the group consisting of ethylene glycol, methanol, ethanol, 1-propanol, and 2-propanol. These may be used alone or in combination. The use of component (C) not only increases the solubility of component (B), but also captures reactants such as cation components in the reaction system, suppressing excessive growth of the starting materials (e.g., the nucleation density of potassium tantalate particles), and inhibiting an increase in the particle size of the potassium tantalate. From these perspectives, ethylene glycol is preferred among component (C).

[0025] From the above viewpoint, increasing the proportion of component (C) in the mixed solution tends to decrease the particle size of potassium tantalate, whereas decreasing the proportion of component (C) tends to increase the particle size of potassium tantalate (however, the function of the present embodiment is not limited to this).

[0026] The proportion of component (C) in the mixed solution is not particularly limited, but is preferably from 0.1 M to 17 M. The lower limit is more preferably 1 M. The upper limit is more preferably 8 M. By setting the proportion of component (C) within this range, the average particle size of the potassium tantalate can be controlled more effectively.

[0027] In the production method according to this embodiment, at least (D) water is used as the solvent, that is, the heating step is carried out in an aqueous solvent.

[0028] In the production method according to the present embodiment, in addition to the above-described components (A) to (D), known components may be added as appropriate to the extent that they do not inhibit the synthesis of potassium tantalate, such as various catalysts for controlling the reaction rate or the basicity of the solution.

[0029] The heating temperature in the heating step is not particularly limited, but from the viewpoint of the reaction rate and the yield of potassium tantalate, it is preferably 150°C or higher, and more preferably 150°C to 300°C. The lower limit is more preferably 160°C, even more preferably 170°C, and even more preferably 200°C. The upper limit is more preferably 295°C, even more preferably 270°C, and even more preferably 260°C.

[0030] The heating time in the heating step is not particularly limited, but from the viewpoint of the reaction rate and the yield of potassium tantalate, it is preferably 30 minutes or more and 210 minutes or less. The lower limit is more preferably 40 minutes, and even more preferably 50 minutes. The upper limit is more preferably 180 minutes, and even more preferably 150 minutes.

[0031] The pressure in the heating step is not particularly limited, but is preferably higher than atmospheric pressure from the viewpoint of the reaction rate and the yield of potassium tantalate. When heating is performed at a pressure higher than atmospheric pressure, it is preferable to perform the heating step using an autoclave or the like. Specifically, for example, a high-temperature acid decomposition vessel or the like can be used.

[0032] In the production method according to the present embodiment, if necessary, a cooling step of cooling the mixed liquid may be performed after the heating step. The cooling means is not particularly limited, and known methods such as water cooling and air cooling can be used.

[0033] The potassium tantalate particles obtained by the production method according to this embodiment can have an average particle size of 100 nm or less, or may have an average particle size of 80 nm or less or 50 nm or less depending on the application.

[0034] In this embodiment, the "average particle diameter" refers to the particle diameter of each particle when observed with a TEM (transmission electron microscope) at a magnification of 120k (120,000 times), with the particles present in one field of view being the measurement target, and the arithmetic mean of the major and minor axes of each particle being the particle diameter of the particle, and the arithmetic mean of the particle diameters of each particle being the "average particle diameter." Note that the "major axis" refers to the longest axis of the particle, and the "minor axis" refers to the shortest axis of the particle. Furthermore, particles of which only a portion is visible in one field of view are excluded from the measurement target.

[0035] <Method of manufacturing a film containing potassium tantalate particles, and the film>

[0036] The method for producing a film containing potassium tantalate particles according to this embodiment (hereinafter, sometimes simply referred to as "film") includes a heating step of heating a mixture containing (A) an oxide containing tantalum, (B) a potassium compound which is at least one of potassium hydroxide and potassium chloride, (C) at least one alcohol selected from the group consisting of ethylene glycol, methanol, ethanol, 1-propanol, and 2-propanol, and (D) water to obtain potassium tantalate particles, a mist-forming step of misting a dispersion liquid containing the potassium tantalate particles, a supplying step of supplying the misted dispersion liquid to a substrate, and a drying step of drying the dispersion liquid present on the substrate after the supplying step.

[0037] The potassium tantalate particles according to this embodiment have high dispersibility in aqueous solvents, and therefore, it is possible to form a nanoparticle film by the above-described method. The nanoparticle film can be produced, for example, by spraying a nanoparticle-containing mist, which is obtained by atomizing a dispersion containing potassium tantalate particles using the vibration of an ultrasonic pendulum in the MHz range, onto a substrate.

[0038] Furthermore, the above-described method does not require heat treatment of the substrate at high temperatures, which alleviates restrictions on the substrate material. For example, it is possible to form a film on a flexible substrate made of a resin material with a low softening point.

[0039] Each step will be described below.

[0040] (1) For the heating step, the conditions described for the heating step carried out in the method for producing potassium tantalate particles can be adopted.

[0041] The mist-forming step (2) may be any method for misting (atomizing) the dispersion liquid containing the potassium tantalate particles obtained in the step (1). Note that the mist-forming step may also include an operation of adding the potassium tantalate particles obtained in the step (1) to a dispersion medium to prepare the dispersion liquid.

[0042] As a method for generating mist, known methods can be used, such as a pressurized method, a rotating disk method, an ultrasonic method, an electrostatic method, an orifice vibration method, and a steam method. In this embodiment, since the dispersion liquid is a potassium tantalate particle dispersion, a method of physically generating mist (atomization) is preferred. This makes it easy to control the temperature of the liquid and the size of the droplets.

[0043] In the mist-forming step, the mist of the dispersion liquid can be carried to the subsequent supply step by using a carrier gas, such as an inert gas such as argon, helium, or nitrogen.

[0044] Furthermore, between the steps (2) and (3), a step of homogenizing the mist using a mist trap or a retention step of providing a retention period (retention portion) for the mist may be performed.

[0045] As the dispersion medium, organic solvents such as ethanol, methanol, and propanol may be used in addition to water. For example, the above-mentioned component (C) or component (D) may be used as the dispersion medium. The dispersion medium may be one type alone or two or more types may be used in combination. The frequency band for atomization is not limited to the above bands as long as it is suitable for each dispersion medium. The material of the substrate is not limited, and may be glass, resin, metal, etc., and it is preferable to provide a process for hydrophilizing the surface, such as UV irradiation.

[0046] (3) The supplying step is not particularly limited as long as it is a method for supplying a mist to a substrate, and known techniques can be used. For example, a method in which the fine droplets obtained in the mist-forming step are sprayed onto the substrate by a mist method can be mentioned. Examples of the mist method include ultrasonic spraying, mist CVD, the Sonia source method, and the hot wall method. These methods can be selected taking into consideration the film thickness of the film to be formed on the substrate, the size of the droplets to be sprayed, and the like.

[0047] The supply step may be carried out under atmospheric pressure, reduced pressure, or vacuum, but is preferably carried out under atmospheric pressure from the viewpoint of simplicity.

[0048] Alternatively, the film containing potassium tantalate particles may be patterned by spraying the mist of the dispersion onto a masked substrate in accordance with a predetermined pattern, thereby enabling highly accurate dimensional control.

[0049] For example, a material that becomes relatively hydrophilic upon light irradiation may be used as the masking material. By irradiating the material with light corresponding to a predetermined pattern, relatively hydrophilic regions and relatively water-repellent regions are formed, and by spraying the mist of the dispersion liquid in this state, the mist of the dispersion liquid can be deposited only in the hydrophilic regions.

[0050] Furthermore, since material restrictions on the substrate are relaxed, thin, highly flexible film substrates (sometimes called "sheet substrates") can be used as the substrate. Furthermore, continuous production such as roll-to-roll production becomes possible.

[0051] The substrate may be made of known materials, such as glass, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethersulfone (PES), polyetherimide, polyetheretherketone, polyphenylene sulfide, polyarylate, polyimide, polycarbonate (PC), cellulose triacetate (TAC), and cellulose acetate propionate (CAP).

[0052] (4) In the drying process, the dispersion medium of the dispersion liquid sprayed onto the substrate is removed. For example, the dispersion medium is vaporized by irradiation with infrared light or heating, thereby forming a film containing potassium tantalate particles on the surface of the substrate. The heating temperature can be set taking into consideration the boiling point of the solvent, the softening point of the substrate, and other physical properties that affect the physical properties of the film. The softening point of the substrate here refers to the temperature at which the substrate softens and begins to deform when heated, and can be determined, for example, by a test method conforming to JIS K7191-1.

[0053] After the step (4), if necessary, a UV irradiation step or the like may be carried out for the purpose of modifying the substrate, such as by imparting hydrophilicity.

[0054] Here, an example of a film forming apparatus that can be used in the manufacturing method according to this embodiment will be described.

[0055] FIG. 1 is a conceptual diagram showing an example of a film forming apparatus using a mist method according to this embodiment.

[0056] The film forming apparatus 1 has a first tank for misting a dispersion liquid containing potassium tantalate particles, a second tank which is a mist trap for homogenizing the mist, and a third tank for spraying the mist onto the substrate 10.

[0057] The first tank contains the dispersion liquid S containing the potassium tantalate particles described above.

[0058] Air 20 is flowed through the first tank to form a flow path for the mist.

[0059] The first tank is equipped with an ultrasonic vibrator 30. The ultrasonic vibrator 30 turns a dispersion liquid containing potassium tantalate particles into mist. The particle size of the mist is not particularly limited, but is preferably 10 μm or less (for example, 1 to 10 μm). The mist generated in the first tank is transported to the second tank via a pipe provided in the first layer. In the second tank, excess mist accumulates at the bottom of the tank, and mist with a more uniform particle size is transported to the third layer via a pipe provided in the second tank. It is preferable that the configuration be such that mist with a particle size of 5 μm or less (for example, 1 to 5 μm) is transported from the second tank to the third tank.

[0060] Substrate 10 is placed in the third tank, and the mist transported from the second tank is sprayed onto the substrate. In the third tank, the mist is sprayed onto substrate 10 for a predetermined time. Then, the dispersion medium of the mist that has adhered to substrate 10 evaporates, forming a film containing potassium tantalate particles on the surface of substrate 10. Note that, if a certain amount of time has passed since spraying, new mist will adhere to substrate 10 before the mist evaporates, causing the droplets of the dispersion liquid to flow down, preventing the formation of a uniform film on substrate 10. The time to stop spraying the mist onto substrate 10 may be the time when the mist containing potassium tantalate fine particles liquefies and flows down from substrate 10, or the time when a film of the desired thickness has been formed on substrate 10.

[0061] If the substrate 10 is heated excessively in the third tank, it may be softened and deformed. Therefore, it is preferable that the mist is sprayed in the third tank at a temperature lower than the softening point of the substrate to form a film. Furthermore, if the substrate 10 is heated to a temperature higher than a predetermined temperature when the mist is sprayed, the potassium tantalate particles adhering to the substrate 10 will aggregate, deteriorating the uniformity of the film. Therefore, it is more preferable that the mist is sprayed at a temperature of 40°C or lower (for example, 10 to 40°C) to form a film.

[0062] When selectively forming a film on the substrate 10, a water-repellent film is selectively formed on the substrate 10 in advance, so that the mist is deposited only on relatively hydrophilic regions. In this case, if the substrate 10 is placed horizontally, the mist adhering to the relatively water-repellent regions is less likely to be repelled, and it may be impossible to selectively form a film. For this reason, in the third tank, it is preferable to spray the mist onto the substrate 10 that is tilted relative to the horizontal plane.

[0063] Similarly, in the third tank, it is preferable that the mist be sprayed onto the substrate 10 that is tilted with respect to a plane perpendicular to the direction of mist spraying. This is because the force of the mist spray removes excess fine particles that have adhered to areas that are relatively water-repellent.

[0064] The film forming apparatus may omit the mist trap in the second tank.

[0065] In addition to the ultrasonic vibrator 30 described above, other methods for generating mist include an electrostatic method in which a voltage is applied directly to a capillary tube that sprays droplets to generate mist; a pressure method in which pressure is applied to increase the flow rate of gas and the resulting mist is dispersed by colliding it with the liquid; a rotating disk method in which droplets are dropped onto a rapidly rotating disk and the resulting mist is dispersed by centrifugal force; and an orifice vibration method in which droplets are passed through an orifice plate with micro-sized holes, and the droplets are cut by applying vibrations using a piezoelectric element or the like to generate micro-sized droplets. These methods can be selected as appropriate depending on cost, performance, and other factors. Furthermore, mist can be generated by combining multiple of the above methods.

[0066] A suitable example of a film obtained by the above-described production method is a film containing potassium tantalate particles with an average particle size of 100 nm or less. Such a film can be suitably used as an anti-reflection film, etc., as described below.

[0067] The film according to this embodiment may be a film in which potassium tantalate particles are dispersed in a resin material. The components of the resin material can be selected appropriately depending on the application of the film. Examples of the resin material include polymethyl methacrylate resin.

[0068] <Anti-reflective film>

[0069] A preferred example of the film according to this embodiment is a film containing potassium tantalate particles, and therefore can be suitably used, for example, as an optical thin film that suppresses light scattering. Therefore, the film according to this embodiment can be suitably used as a layer constituting an antireflection film. Such an antireflection film may have a single-layer structure or a multi-layer structure of two or more layers. For example, the antireflection film may include at least one layer of the film according to this embodiment.

[0070] The antireflection film according to this embodiment can be provided on the surface of an optical element such as an optical lens of various optical devices such as a camera, a microscope, etc. The optical element such as an optical lens provided with such an antireflection film can suppress surface reflection, thereby eliminating stray light. [Example]

[0071] The present invention will be explained in more detail with reference to the following examples and comparative examples, but the present invention is not limited to the following examples.

[0072] <Measurement method>

[0073] ·XRD measurement: The measurement was performed using a multipurpose X-ray diffractometer (Rigaku Corporation's "Ultima-IV") under the following conditions: a CuKα source, an output of 40 kV, 40 mA, and a "D / teX Ultra" detector.

[0074] ·ICP measurement: The measurement device used was an ICP emission spectrometer (PerkinElmer "Optima 3300").

[0075] ·TEM measurement: A transmission electron microscope (TEM; Hitachi, Ltd., "JEM-2100") was used as the measuring device, and measurements were performed at a magnification of 120k (120,000).

[0076] Particle shape evaluation: The TEM images of the particles were processed using the image processing software "imageJ 1.51j8." Specifically, the scale of one pixel was adjusted to correspond to the actual image, and the image was binarized.

[0077] The average particle diameter was then calculated according to the following method. First, the sample was centrifuged to extract particles. Then, when the particles were observed using a TEM at a magnification of 120k (120,000 times), the particles present in one field of view were measured, and the arithmetic mean of the long and short axes of each particle was taken as the particle diameter of the particle, and the arithmetic mean of the particle diameters of each particle was taken as the "average particle diameter." Note that the "longest axis" refers to the longest axis of the particle, and the "short axis" refers to the shortest axis of the particle. Furthermore, particles in which only a portion was visible in one field of view were excluded from the analysis.

[0078] <Examples 1 to 24> Tantalum oxide (tantalum pentoxide, Ta2O5) and 5 mL of ethylene glycol were added to 5 mL of 10 M potassium hydroxide aqueous solution to give the concentrations shown in Table 1, and the mixture was heated using a high-temperature pressurized acid decomposition vessel (manufactured by Parr) under the conditions shown in Table 1. After heating, it was confirmed by the above-mentioned measurements whether potassium tantalate (KTaO3) had been obtained, and its average particle size was determined using the above-mentioned method.

[0079] <Comparative Example 1> Except for not adding ethylene glycol, particle production was attempted under the same conditions as in Example 7. As a result, the average particle size of the potassium tantalate particles was 101 nm.

[0080] [Table 1]

[0081] From the above, it was at least confirmed that this example makes it possible to efficiently produce potassium tantalate particles having a small average particle size. [Explanation of symbols]

[0082] 1...film forming device, 10...substrate, 20...air, 30...ultrasonic vibrator, S...raw material solution

Claims

1. The method includes a heating step of heating a mixture containing: (A) an oxide containing tantalum; (B) a potassium compound which is at least one of potassium hydroxide and potassium chloride; (C) at least one alcohol selected from the group consisting of ethylene glycol, methanol, ethanol, 1-propanol, and 2-propanol; and (D) water. Method for producing potassium tantalate particles.

2. In the heating step, heating is performed at 150°C or higher. The method of claim 1.

3. In the heating step, heating is performed at 300°C or less. The method according to claim 1 or 2.

4. In the heating step, heating is performed for 30 minutes or more and 210 minutes or less. The method according to claim 1 or 3.

5. The (A) oxide containing tantalum is tantalum oxide (Ta ２ O ５ ) The method according to any one of claims 1 to 4.

6. The potassium compound (B) is potassium hydroxide. The method according to any one of claims 1 to 5.

7. The (C) alcohol is ethylene glycol. The method according to any one of claims 1 to 6.

8. The heating step is carried out at a pressure higher than atmospheric pressure. The method according to any one of claims 1 to 7.

9. a molar ratio (B / A) of the potassium compound (B) to the tantalum-containing oxide (A) is 5 or more and 300 or less; The method according to any one of claims 1 to 8.

10. A step of obtaining potassium tantalate particles by the production method according to any one of claims 1 to 9; a mist-forming step of forming a dispersion liquid containing the potassium tantalate particles into a mist; a supplying step of supplying the mist-formed dispersion onto a substrate; a drying step of drying the dispersion liquid present on the substrate after the supplying step, A method for producing a film containing potassium tantalate particles.

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