Metal oxide fine particles and metal oxide fine particle dispersion

Abstract

To provide metal oxide fine particles capable of forming a metal oxide film having excellent heat shielding properties and visible light transmittance, and a metal oxide fine particle dispersion.SOLUTION: In a transmission spectrum measured when a dispersion liquid dispersed at a concentration of 0.7 mass% in a dispersion medium is placed in a 1 mm cell, a slope k1 obtained by linear approximation using the least squares method in a wavelength range from 290 nm to 330 nm is within a range of 0.90 or more and 1.60 or less. In a transmission spectrum measured when a dispersion liquid dispersed at a concentration of 0.7 mass% in a dispersion medium is placed in a 1 mm cell, a slope k2 obtained by linear approximation using the least squares method in a wavelength range from 310 nm to 330 nm is within a range of 0.95 or more and 2.30 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to metal oxide fine particles and a metal oxide fine particle dispersion liquid for forming a metal oxide film used as, for example, a transparent conductive film or a heat-shielding film. [Background technology]

[0002] Glass plates used for window materials for vehicles such as automobiles, trains, ships, construction equipment, and airplanes, as well as for window materials for houses and showcases, are sometimes required to have electrical conductivity for preventing static electricity and infrared blocking properties in addition to transparency. Furthermore, transparent conductive films are used as wiring in liquid crystal displays, organic EL displays, touch panels, etc. These transparent conductive films are required to have high transmittance of light in the visible light range and low electrical resistance.

[0003] Known materials for such applications include metal oxides such as tin-doped indium oxide powder, antimony-doped tin oxide powder, cesium-doped tungsten oxide powder, and aluminum-doped zinc oxide powder, as shown in Patent Documents 1 to 3, for example. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-075510 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-297414 [Patent Document 3] Patent No. 6950691 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the metal oxide powders disclosed in Patent Documents 1 to 3 suffer from scattering, reflection, and absorption of light due to the particle shape, composition, and band gap of the matrix phase, which may result in a decrease in visible light transmittance.

[0006] The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide metal oxide microparticles and a metal oxide microparticle dispersion liquid that can form a metal oxide film having excellent heat-shielding properties and visible light transmittance. [Means for solving the problem]

[0007] In order to solve the above problems, the inventors conducted extensive research and discovered that metal oxide microparticles synthesized in a mixed solvent of two or more of carboxylic acids, amines, and water have low infrared light transmittance and sufficiently high visible light transmittance, making it possible to form metal oxide films with excellent heat-shielding properties and visible light transmittance. Then, when the transmission spectrum was measured using a metal oxide microparticle dispersion liquid in which the above-mentioned metal oxide microparticles were dispersed in a dispersion medium, it was found that the transmittance increased sharply in the visible light region.

[0008] The metal oxide microparticles of aspect 1 of the present invention have been made based on the above-mentioned findings, and are characterized in that, in the transmission spectrum measured by placing a dispersion liquid dispersed at a concentration of 0.7% by mass in a dispersion medium in a 1 mm cell, the slope k1 of the linear approximation by the least squares method in the wavelength range of 290 nm to 330 nm is in the range of 0.90 to 1.60.

[0009] According to the metal oxide microparticles of aspect 1 of the present invention, in the transmission spectrum of a dispersion liquid dispersed at a concentration of 0.7 mass % in a dispersion medium, the slope k1 when linearly approximated by the least squares method in the wavelength range of 290 nm to 330 nm is in the range of 0.90 to 1.60, thereby showing a sharp improvement in transmittance in the visible light range and excellent transmittance for visible light. Therefore, it is possible to form a metal oxide film that has excellent heat-shielding properties and visible light transmittance.

[0010] The metal oxide microparticles of aspect 2 of the present invention are characterized in that, in the transmission spectrum measured by placing a dispersion liquid dispersed in a dispersion medium at a concentration of 0.7% by mass in a 1 mm cell, the slope k2 of the linear approximation by the least squares method in the wavelength range of 310 nm to 330 nm is in the range of 0.95 to 2.30.

[0011] According to the metal oxide microparticles of aspect 2 of the present invention, in the transmission spectrum of a dispersion liquid dispersed at a concentration of 0.7% by mass in a dispersion medium, the slope k2 when linearly approximated by the least squares method in the wavelength range of 310 nm to 330 nm is 0.95 or more and 2.30 or less, so that the transmittance is rapidly improved in the visible light range and the transmittance of visible light is excellent. Therefore, it is possible to form a metal oxide film that has excellent heat-shielding properties and visible light transmittance.

[0012] The metal oxide fine particles of embodiment 3 of the present invention are the metal oxide fine particles of embodiment 1 or 2 of the present invention, characterized in that the primary particle diameter is 50 nm or less. According to the metal oxide fine particles of aspect 3 of the present invention, the primary particle diameter is set to 50 nm or less, so that scattering of visible light can be sufficiently suppressed, and the visible light transmittance of the formed metal oxide film can be further improved.

[0013] The metal oxide fine particles of embodiment 4 of the present invention are the metal oxide fine particles of any one of embodiments 1 to 3 of the present invention, characterized in that they are made of tin oxide or tin oxide containing antimony.

[0014] The metal oxide fine particles of embodiment 5 of the present invention are the metal oxide fine particles of any one of embodiments 1 to 3 of the present invention, characterized in that they are made of indium oxide or indium oxide containing tin.

[0015] The metal oxide fine particle dispersion liquid of the sixth aspect of the present invention is characterized in that the metal oxide fine particles of any one of the first to fifth aspects of the present invention are dispersed in a dispersion medium. According to the metal oxide microparticle dispersion of aspect 6 of the invention, since the metal oxide microparticles of any one of aspects 1 to 5 of the present invention are dispersed, it is possible to form a metal oxide film having excellent heat-shielding properties and visible light transmittance.

[0016] A method for producing a metal oxide film according to a seventh aspect of the present invention is characterized by including a coating step of coating the metal oxide fine particle dispersion according to the sixth aspect of the present invention. According to the method for producing a metal oxide film of aspect 7 of the present invention, a coating step of coating the metal oxide microparticle dispersion of aspect 6 of the present invention is included, and therefore it is possible to form a metal oxide film having excellent heat-shielding properties and visible light transmittance. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide metal oxide fine particles and a metal oxide fine particle dispersion capable of forming a metal oxide film having excellent heat-shielding properties and visible light transmittance. DETAILED DESCRIPTION OF THE INVENTION

[0018] The following describes the metal oxide microparticles, metal oxide microparticle dispersion, and method for producing a metal oxide film according to embodiments of the present invention. Note that the following embodiments are specifically described to provide a better understanding of the gist of the invention, and do not limit the present invention unless otherwise specified.

[0019] The metal oxide fine particles and metal oxide fine particle dispersion according to the embodiment of the present invention are used, for example, when forming a metal oxide film used as a heat-shielding film for glass materials, a transparent conductive film, and the like. The above-mentioned metal oxide film needs to have both infrared blocking properties and high visible light transmittance in order to ensure heat shielding properties and transparency.

[0020] Here, in the metal oxide microparticles of the first embodiment of the present invention, when a dispersion liquid dispersed in a dispersion medium at a concentration of 0.7 mass % is placed in a 1 mm cell and measured, the transmission spectrum is linearly approximated by the least squares method in the wavelength range of 290 nm to 330 nm, and the slope k1 is in the range of 0.90 or more and 1.60 or less. When the slope k1 of the transmission spectrum in the near ultraviolet to visible light region of wavelengths from 290 nm to 330 nm is 0.90 or more and 1.60 or less, the transmittance increases sharply in this region, and the transmittance of visible light is particularly excellent. The lower limit of the slope k1 is preferably 0.93 or more, and more preferably 1.00 or more.

[0021] In addition, in the metal oxide microparticles which are the second embodiment of the present invention, when a dispersion liquid dispersed in a dispersion medium at a concentration of 0.7% by mass is placed in a 1 mm cell and measured, the transmission spectrum is linearly approximated by the least squares method in the wavelength range of 310 nm to 330 nm, and the slope k2 is in the range of 0.95 or more and 2.30 or less. When the slope k2 of the transmission spectrum in the visible light region of wavelengths from 310 nm to 330 nm is 0.95 or more and 2.30 or less, the transmittance increases sharply in this region, and the transmittance of visible light is particularly excellent. The lower limit of the slope k2 is preferably 0.96 or more, and more preferably 1.00 or more.

[0022] Here, it is preferable to appropriately select the dispersion medium that can sufficiently disperse the metal oxide microparticles. For example, if the metal oxide microparticles are sufficiently dispersible in water, the transmission spectrum of an aqueous dispersion in which the metal oxide microparticles are dispersed at a concentration of 0.7% by mass using water as the dispersion medium can be measured. Furthermore, if the metal oxide microparticles are sufficiently dispersible in toluene, the transmission spectrum of a toluene dispersion in which the metal oxide microparticles are dispersed at a concentration of 0.7% by mass using toluene as the dispersion medium can be measured.

[0023] Here, in the metal oxide fine particles of this embodiment, the primary particle diameter is preferably within the range of 2.0 nm or more and 50 nm or less. When the primary particle diameter of the metal oxide fine particles is relatively small, at 50 nm or less, scattering of visible light by the metal oxide fine particles can be suppressed, and the transmittance of visible light can be further improved. The upper limit of the primary particle diameter of the metal oxide fine particles is more preferably 20 nm or less, and although there is no particular lower limit to the primary particle diameter of the metal oxide fine particles, it is substantially 1 nm or more.

[0024] Examples of metal oxides that can be used to form the metal oxide particles include tin oxide, tin oxide containing antimony (antimony-doped tin oxide), indium oxide, and indium oxide containing tin (tin-doped indium oxide).

[0025] In tin oxide containing antimony (antimony-doped tin oxide), the content of antimony is preferably in the range of more than 0 atomic % to 30 atomic % or less relative to tin. In indium oxide containing tin (tin-doped indium oxide), the tin content is preferably in the range of more than 0 atomic % to 30 atomic % or less relative to the indium.

[0026] In the metal oxide fine particle dispersion liquid of this embodiment, the metal oxide fine particles of this embodiment are dispersed in a dispersion medium. In the metal oxide fine particle dispersion liquid of this embodiment, for example, water, ethanol, isopropanol, toluene, or the like can be used as the dispersion medium. In the metal oxide fine particle dispersion liquid of this embodiment, the content of the metal oxide fine particles of this embodiment is preferably in the range of 0.1% by mass to 80% by mass.

[0027] The metal oxide fine particles of this embodiment can be produced by synthesizing metal oxide fine particles in a mixed solvent of two or more selected from carboxylic acid, amine, and water. For example, a mixed solvent of a carboxylic acid (e.g., acetic acid) and an amine (e.g., monoethanolamine) is heated, and a tin source (e.g., tin(IV) chloride pentahydrate) and an antimony source (e.g., antimony(III) chloride) are mixed into this mixed solvent, followed by a heat treatment (heating temperature: 100°C or higher and 300°C or lower, holding time: 10 minutes or longer) to produce the metal oxide microparticles of this embodiment, which are made of antimony-doped tin oxide.

[0028] The metal oxide fine particle dispersion liquid of this embodiment can be produced by dispersing the above-described metal oxide fine particles of this embodiment in a dispersion medium.

[0029] According to the metal oxide microparticles of the first embodiment of the present invention configured as described above, in the transmission spectrum of a dispersion liquid dispersed at a concentration of 0.7 mass% in a dispersion medium, the slope k1 when linearly approximated by the least squares method in the wavelength range of 290 nm to 330 nm is in the range of 0.90 or more and 1.60 or less, so that the transmittance is sharply improved in the visible light range, and the transmittance is excellent for visible light without transmitting infrared light. Therefore, it is possible to form a metal oxide film that has excellent heat-shielding properties and visible light transmittance.

[0030] According to the second embodiment of the present invention, the metal oxide microparticles dispersed in a dispersion medium at a concentration of 0.7% by mass exhibit a transmission spectrum in which the slope k2 of a linear approximation by the least squares method in the wavelength range of 310 nm to 330 nm is 0.95 or more and 2.30 or less, and therefore transmittance is sharply improved in the visible light range, and the microparticles exhibit excellent transmittance for visible light without transmitting infrared light. Therefore, it is possible to form a metal oxide film that has excellent heat-shielding properties and visible light transmittance.

[0031] In the metal oxide fine particles of this embodiment, when the primary particle diameter is 50 nm or less, scattering of visible light can be sufficiently suppressed, and the visible light transmittance of the formed metal oxide film can be further improved.

[0032] When the metal oxide fine particles of this embodiment are made of tin oxide or tin oxide containing antimony, it is possible to form a metal oxide film that is excellent in heat-shielding properties and visible light transmittance.

[0033] When the metal oxide fine particles of this embodiment are made of indium oxide or indium oxide containing tin, it is possible to form a metal oxide film that is excellent in heat-shielding properties and visible light transmittance.

[0034] According to the metal oxide microparticle dispersion of this embodiment, the metal oxide microparticles of this embodiment are dispersed in a dispersion medium, making it possible to form a metal oxide film with excellent heat-shielding properties and visible light transmittance.

[0035] Although one embodiment of the present invention has been described above, the present invention is not limited to this and can be modified as appropriate within the scope of the technical idea of ​​the invention. [Example]

[0036] A confirmation experiment conducted to confirm the effectiveness of the present invention will be described.

[0037] (Examples 1-11 of the present invention) A carboxylic acid and an amine shown in Table 1 were mixed to prepare a mixed solvent, and the mixed solvent was heated to 80°C. The tin raw material and the antimony raw material shown in Table 1 were added and stirred to obtain a raw material suspension. This raw material suspension was heat treated under the conditions shown in Table 1 to produce metal oxide fine particles of antimony-doped tin oxide (doping concentration: 10 atomic %).

[0038] [Table 1]

[0039] (Examples 12 and 13) 1.99 g of potassium stannate was dissolved in 10 mL of water, and 0.40 g of antimony (V) chloride and 2 mL of acetic acid were added to obtain a raw paste. After washing the raw paste with water, 10 mL of a 0.7 mol% aqueous methylamine solution was added to obtain a raw suspension. This raw material suspension was heat-treated under specified conditions (holding at 200°C for 6 hours in Inventive Example 12, and at 230°C for 2 hours in Inventive Example 13) to produce metal oxide microparticles consisting of antimony-doped tin oxide (doping concentration 16 atomic %).

[0040] (Example 14) 4.55 mmol of indium octoate, 0.51 mmol of stannous octoate, 41.94 mmol of oleylamine, and 158.38 mmol of octyl ether were heated in vacuum (100 kPa or less) at 80°C for 1 hour, then heated in a nitrogen atmosphere at 150°C for 1 hour, and then at 280°C for 1 hour, to produce metal oxide microparticles consisting of tin-doped indium oxide (doping concentration 10 atomic %).

[0041] (Comparative Examples 1 and 2) 92 g of a 5 mass% tin (IV) chloride solution, 14 g of 17 mass% hydrochloric acid, and an antimony (III) chloride solution at a ratio of 5 to 30 atomic % relative to tin (Comparative Example 1: 5 atomic %, Comparative Example 2: 18 atomic %) were mixed, and added dropwise together with a 25 mass% sodium hydroxide solution to 1 L of water kept at 60°C. The pH was kept at 5 to 6. The remaining salt was removed from the obtained hydroxide by decantation, filtered, dried, and then calcined in air at 700 to 900°C for 2 hours.

[0042] (Comparative Example 3) 55 mL of aqueous indium chloride solution and 4.38 g of tin(II) chloride dihydrate were mixed. This mixture and aqueous ammonia solution were simultaneously added dropwise to 500 mL of water, adjusted to pH 7, and allowed to react at 30°C for 30 minutes. The precipitated hydroxide was repeatedly washed with ion-exchanged water until the electrical conductivity of the supernatant liquid reached 100 μS / cm or less. The hydroxide was filtered, and the solid-liquid separated hydroxide was dried at 110°C overnight and then calcined in air at 550°C for 3 hours. The calcined aggregates were crushed to obtain golden yellow tin-doped indium oxide powder. This tin-doped indium oxide powder was impregnated in a surface treatment solution (ethanol:distilled water = 95:5 by weight) and then placed in a glass Petri dish and heated at 330°C for 2 hours under a nitrogen gas atmosphere to obtain the desired tin-doped indium oxide powder.

[0043] The metal oxide fine particles of Inventive Examples 1 to 14 and Comparative Examples 1 to 3 obtained as described above were evaluated for each item by the following methods. The evaluation results are shown in Table 2.

[0044] (Transmission spectrum of dispersion of metal oxide fine particles) The metal oxide fine particles were dispersed in the dispersion medium shown in Table 2, and the concentration of the metal oxide fine particles was adjusted to 0.7 mass %. At this time, a dispersant (such as an alkyl succinate or a phosphate ester) may be added as appropriate. The obtained dispersion of metal oxide fine particles was placed in a 1 mm cell, and the transmission spectrum was measured using a spectrophotometer (UH4150, Hitachi High-Tech Corp.) From the measured transmission spectrum, the slope k1 when linearly approximating the wavelength range from 290 nm to 330 nm using the method of least squares, and the slope k2 when linearly approximating the wavelength range from 310 nm to 330 nm using the method of least squares, were calculated.

[0045] (Primary particle diameter of metal oxide fine particles) Images of the particles were taken at a magnification of 100,000 times using a transmission electron microscope (JEM-210F manufactured by JEOL Ltd.). Using the image processing software ImageJ, the primary particle diameter was calculated from the average particle area of ​​50 particles, assuming that all particles were spherical.

[0046] [Table 2]

[0047] As shown in Table 2, in Comparative Examples 1 to 3, in the transmission spectrum of the dispersion liquid dispersed in a dispersion medium at a concentration of 0.7% by mass, the slope k1 when linearly approximated by the least squares method in the wavelength range of 290 nm to 330 nm was less than 0.90, and the slope k2 when linearly approximated by the least squares method in the wavelength range of 310 nm to 330 nm was less than 0.95, indicating insufficient visible light transmittance.

[0048] In contrast, in Examples 1 to 14 of the present invention, in the transmission spectrum of the dispersion liquid dispersed at a concentration of 0.7% by mass in a dispersion medium, the slope k1 when linearly approximated by the least squares method in the wavelength range of 290 nm to 330 nm was 0.90 or more, and the slope k2 when linearly approximated by the least squares method in the wavelength range of 310 nm to 330 nm was 0.95 or more, indicating excellent visible light transmittance.

[0049] As described above, it has been confirmed that the present invention can provide metal oxide microparticles and a metal oxide microparticle dispersion capable of forming a metal oxide film having excellent heat-shielding properties and visible light transmittance.

Claims

1. The slope k of the transmission spectrum measured in a 1 mm cell after dispersing a dispersion at a concentration of 0.7% by mass in a dispersion medium is calculated by linear approximation using the least squares method in the wavelength range from 290 nm to 330 nm. １ is in the range of 0.90 or more and 1.60 or less.

2. The slope k of the transmission spectrum measured in a 1 mm cell after dispersing a dispersion at a concentration of 0.7% by mass in a dispersion medium is calculated by linear approximation using the least squares method in the wavelength range from 310 nm to 330 nm. ２ is in the range of 0.95 or more and 2.30 or less.

3. 3. The metal oxide fine particles according to claim 1, wherein the primary particle diameter is in the range of 2.0 nm to 50 nm.

4. 3. The metal oxide fine particles according to claim 1, which are made of tin oxide or tin oxide containing antimony.

5. 3. The metal oxide fine particles according to claim 1, which are made of indium oxide or indium oxide containing tin.

6. 3. A metal oxide fine particle dispersion liquid, comprising the metal oxide fine particles according to claim 1 or 2 dispersed in a dispersion medium.

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