Method for producing crystalline inorganic oxide particles

Abstract

To suppress adhesion between grains when firing inorganic oxide grains.SOLUTION: There is provided a method of producing inorganic oxide crystalline grains from inorganic oxide grains. In the method of producing the inorganic oxide crystalline grains, a mixture containing inorganic oxide grains and spacer grains is prepared, and the mixture is heated for firing the inorganic oxide grains to produce inorganic oxide crystalline grains.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing crystalline inorganic oxide particles.

Background Art

[0002] Inorganic oxide particles such as titanium oxide, zirconium oxide, yttrium oxide, tin oxide, silica, and alumina are widely used, for example, as materials for paints, inks, and coating materials, catalysts, ultraviolet protectants, pigments, and the like. For example, Patent Document 1 discloses that a porous titanium oxide structure is produced by preparing a titanium oxide paste containing titanium oxide particles, pore-forming resin particles, and an organic solvent, coating the paste, drying it, and then firing it.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, when producing crystalline inorganic oxide particles by firing inorganic oxide particles, if the particles of the inorganic oxide particles are joined together during firing, the particle diameter of the obtained crystalline inorganic oxide particles becomes large, and therefore there is a problem that the desired characteristics cannot be obtained.

[0005] An object of the present invention is to suppress the joining between particles during the firing of inorganic oxide particles.

Means for Solving the Problems

[0006] The present invention is a method for producing crystalline inorganic oxide particles from inorganic oxide particles, comprising preparing a mixture containing the inorganic oxide particles and spacer particles, and heating the mixture to fire the inorganic oxide particles. [Effects of the Invention]

[0007] According to the present invention, by heating a mixture containing inorganic oxide particles and spacer particles to calcine the inorganic oxide particles, bonding between inorganic oxide particles during calcination can be suppressed. [Brief explanation of the drawing]

[0008] [Figure 1] This is a scanning electron microscope image of the crystalline thin-film titanium oxide particles obtained in Example 1. [Figure 2] This is a scanning electron microscope image of the crystalline thin-film titanium oxide particles obtained in Example 2. [Figure 3] This is a scanning electron microscope image of the crystalline thin-film titanium oxide particles obtained in Comparative Example 1. [Figure 4] This is a scanning electron microscope image of the crystalline thin-film titanium oxide particles obtained in Example 3. [Figure 5] This is a scanning electron microscope image of the crystalline thin-film titanium oxide particles obtained in Example 4. [Figure 6] This is a scanning electron microscope image of the crystalline thin-film titanium oxide particles obtained in Comparative Example 2. [Figure 7] This figure shows the number distribution of film thickness for thin-film titanium oxide particles A, and for crystalline thin-film titanium oxide particles obtained in Examples 1 and 2 and Comparative Example 1. [Figure 8] This figure shows the number distribution of film thickness for thin-film titanium oxide particles B, and for crystalline thin-film titanium oxide particles obtained in Examples 3, 4, and Comparative Example 2. [Figure 9] This figure shows the X-ray diffraction patterns of thin-film titanium oxide particles A and B, Examples 1, 2, 3, and 4, and crystalline thin-film titanium oxide obtained in Comparative Examples 1 and 2. [Modes for carrying out the invention]

[0009] The embodiments will be described in detail below.

[0010] In the method for producing crystalline inorganic oxide particles according to this embodiment, crystalline inorganic oxide particles are produced from inorganic oxide particles. At that time, a mixture containing inorganic oxide particles and spacer particles is prepared, and the mixture is heated to calcine the inorganic oxide particles.

[0011] According to the method for producing crystalline inorganic oxide particles according to this embodiment, the bonding between inorganic oxide particles during firing can be suppressed by heating a mixture containing inorganic oxide particles and spacer particles to calcine the inorganic oxide particles. This is thought to be because the spacer particles are interposed between the inorganic oxide particles, physically inhibiting contact between the inorganic oxide particles, and as a result, preventing bonding between the inorganic oxide particles. In other words, in the present invention, spacer particles are particles that have the function of suppressing bonding between inorganic oxides during the calcination of the inorganic oxide particles.

[0012] Examples of inorganic oxides constituting inorganic oxide particles include titanium oxide, zirconium oxide, yttrium oxide, tin oxide, silica, and alumina. It is preferable that the inorganic oxide particles are composed of one or more of these inorganic oxides. The inorganic oxide particles may also be composed of a composite of two or more of these inorganic oxides. The inorganic oxide particles may also be derived from an inorganic substance having hydrolyzable functional groups through a sol-gel transition involving hydrolysis and polycondensation reactions. A method for producing inorganic oxide particles using this sol-gel transition is disclosed in detail in Japanese Patent Application Publication No. 2021-54696. The crystalline form of the inorganic oxide particles is preferably amorphous.

[0013] The average particle size of the inorganic oxide particles is preferably 1 nm or larger, more preferably 0.1 μm or larger, and even more preferably 1 μm or larger, from the viewpoint of suppressing bonding between inorganic oxide particles during firing. Similarly, from the same viewpoint, it is preferably 1 mm or smaller, more preferably 500 μm or smaller, even more preferably 100 μm or smaller, and even more preferably 50 μm or smaller. This average particle size is the volume-based average particle size measured by laser diffraction scattering for dried inorganic oxide particles.

[0014] Examples of inorganic oxide particle shapes include thin films and granular shapes. When the inorganic oxide particles are thin films, their average film thickness is preferably 1 nm or more, more preferably 10 nm or more, and even more preferably 20 nm or more, from the viewpoint of suppressing bonding between inorganic oxide particles during firing. Similarly, from the same viewpoint, it is preferably 100 μm or less, more preferably 10 μm or less, even more preferably 1 μm or less, and even more preferably 500 nm or less. This average film thickness is the number average of the film thicknesses of 100 inorganic oxide particles arbitrarily selected from images obtained by scanning electron microscopy observation of dried inorganic oxide particles. The method for measuring the average particle diameter is the method described in the examples.

[0015] The ratio of the average particle diameter of thin-film inorganic oxide particles to the average film thickness (average particle diameter / average film thickness) is preferably 3 or more, more preferably 5 or more, and even more preferably 10 or more, from the viewpoint of suppressing bonding between inorganic oxide particles during firing. Similarly, from the same viewpoint, it is preferably 2000 or less, more preferably 1500 or less, even more preferably 1000 or less, even more preferably 300 or less, and even more preferably 150 or less.

[0016] The material used to form the spacer particles may be either an inorganic or organic substance. Examples of inorganic substances include silica. Examples of organic substances include thermosetting resins and thermoplastic resins. Examples of thermosetting resins include melamine resin, phenolic resin, and epoxy resin. Examples of thermoplastic resins include polymethyl methacrylate resin and polyamide resin.

[0017] The spacer particles are preferably made of a material with high heat resistance from the viewpoint of suppressing the bonding between the inorganic oxide particles during firing. On the other hand, the spacer particles preferably burn out during heating of the mixture from the viewpoint of suppressing the remaining as impurities. From these facts, the spacer particles are preferably made of an organic substance with high heat resistance, resin particles are preferred, and thermosetting resin particles are more preferred. The temperature at which the spacer particles burn out is preferably 200°C or higher, more preferably 220°C or higher, still more preferably 250°C or higher from the viewpoint of suppressing the bonding between the inorganic oxide particles during firing, and preferably 900°C or lower, more preferably 600°C or lower from the viewpoint of surely burning out during heating of the mixture. Further, the spacer particles may be hollow particles or porous particles.

[0018] The average particle diameter of the spacer particles is preferably 1 nm or more, more preferably 10 nm or more, still more preferably 20 nm or more from the viewpoint of suppressing the bonding between the inorganic oxide particles during firing, and also preferably 1 mm or less, more preferably 500 μm or less, still more preferably 100 μm or less, even more preferably 20 μm or less from the same viewpoint. This average particle diameter is the volume-based average particle diameter measured by the laser diffraction scattering method described in the examples.

[0019] The ratio of the average particle diameter of the inorganic oxide particles to the average particle diameter of the spacer particles (average particle diameter of inorganic oxide particles / average particle diameter of spacer particles) is preferably 0.001 or more, more preferably 0.01 or more, still more preferably 0.1 or more, even more preferably 1 or more from the viewpoint of suppressing the bonding between the inorganic oxide particles during firing, and preferably 1000 or less, more preferably 500 or less, still more preferably 100 or less, even more preferably 50 or less from the same viewpoint.

[0020] In a mixture of inorganic oxide particles and spacer particles, the mass ratio of the inorganic oxide particle content to the spacer particle content (inorganic oxide particle content / spacer particle content) is preferably 0.01 or more, more preferably 0.05 or more, and even more preferably 0.1 or more, from the viewpoint of suppressing bonding between inorganic oxide particles during firing. Similarly, it is preferably 1000 or less, more preferably 100 or less, even more preferably 50 or less, and even more preferably 10 or less.

[0021] The preparation of the mixture is preferably carried out by mixing inorganic oxide particles and spacer particles via a solvent, from the viewpoint of suppressing bonding between inorganic oxide particles during firing. Examples of solvents used at this time include organic solvents such as water and ethanol. From the viewpoint of suppressing bonding between inorganic oxide particles during firing, the mass ratio of the inorganic oxide particle content to the solvent content in the mixture (inorganic oxide particle content / solvent content) is preferably 0.001 or more, more preferably 0.005 or more, even more preferably 0.01 or more, and from the same viewpoint, preferably 10 or less, more preferably 5 or less, even more preferably 1 or less, and even more preferably 0.2 or less.

[0022] The mixture may contain, in addition to inorganic oxide particles and spacer particles, other materials such as crystalline inorganic oxides.

[0023] From the viewpoint of suppressing bonding between inorganic oxide particles during firing, the heating temperature of the mixture is preferably 200°C or higher, more preferably 220°C or higher, and even more preferably 250°C or higher. Similarly, from the same viewpoint, it is preferably 1200°C or lower, more preferably 1100°C or lower, and even more preferably 1000°C or lower.

[0024] The average particle size of crystalline inorganic oxide particles obtained by calcining inorganic oxide particles is often smaller than the average particle size of the inorganic oxide particles themselves. The average particle size of crystalline inorganic oxide particles is preferably 1 nm or larger, more preferably 0.1 μm or larger, even more preferably 1 μm or larger, and also preferably 1 mm or smaller, more preferably 500 μm or smaller, even more preferably 100 μm or smaller, and even more preferably 50 μm or smaller. This average particle size is the volume-based average particle size measured by laser diffraction scattering.

[0025] Thin-film crystalline inorganic oxide particles can be obtained from thin-film inorganic oxide particles. In this case, the average film thickness of the crystalline inorganic oxide particles is often smaller than the average film thickness of the inorganic oxide particles. The average film thickness of the crystalline inorganic oxide particles is preferably 1 nm or more, more preferably 10 nm or more, even more preferably 20 nm or more, and also preferably 100 μm or less, more preferably 10 μm or less, even more preferably 1 μm or less, and even more preferably 500 nm or less. This average film thickness is the number average of the film thicknesses of 100 crystalline inorganic oxide particles arbitrarily selected from images obtained by scanning electron microscopy observation.

[0026] The ratio of the average particle diameter to the average film thickness (average particle diameter / average film thickness) of the resulting thin-film crystalline inorganic oxide particles is preferably 3 or more, more preferably 5 or more, even more preferably 10 or more, and also preferably 2000 or less, more preferably 1500 or less, even more preferably 1000 or less, even more preferably 300 or less, and even more preferably 150 or less.

[0027] Examples of crystalline inorganic oxide particles include rutile, anatase, and brookite forms for titanium oxide. Of these, the rutile form is preferred for crystalline inorganic oxide particles. This crystal form is analyzed by X-ray crystal structure analysis.

[0028] Crystalline inorganic oxide particles can be used, for example, as materials for paints, inks, and coatings, as catalysts, UV protection agents, pigments, and the like. [Examples]

[0029] As described in Examples 1 to 4 and Comparative Examples 1 to 2 below, experiments were conducted to produce crystalline thin-film titanium oxide particles from thin-film titanium oxide particles. The average particle size and average film thickness of the thin-film titanium oxide particles and the crystalline thin-film titanium oxide particles were measured, and the crystal type of the crystalline thin-film titanium oxide particles was analyzed. The details of each are also shown in Tables 1 and 2.

[0030] Here, the average particle size of thin-film titanium oxide particles and crystalline thin-film titanium oxide particles was measured using a laser diffraction / scattering particle size distribution analyzer (LA-960, Horiba, Ltd.) and the volume-based average particle size was determined by the laser diffraction / scattering method. A flow cell was used for the measurement, the medium was water, and the refractive index was set to the relative refractive index: 1.12 when measuring thin-film titanium oxide before firing, and 2.0 when measuring crystalline thin-film titanium oxide. The aqueous dispersion containing the titanium particles was added to the flow cell, and measurements were performed at a concentration that showed a transmittance of approximately 95%, and the volume-based average particle size was determined.

[0031] For the average film thickness of thin-film titanium oxide particles, the number average of the film thicknesses of 100 randomly selected thin-film titanium oxide particles dried at 105°C using a scanning electron microscope was calculated. For the average film thickness of crystalline thin-film titanium oxide particles, the number average of the film thicknesses of 100 randomly selected crystalline thin-film titanium oxide particles using a scanning electron microscope was calculated.

[0032] The crystalline structure of thin-film titanium oxide particles was analyzed by X-ray crystallography after drying at room temperature. The crystalline structure of crystalline thin-film titanium oxide particles was analyzed by X-ray crystallography of the powder after calcination. A desktop X-ray diffractometer (MiniFlex 600, Rigaku) ​​was used for the X-ray crystallography. The measurement conditions were: X-ray source: Cu / Kα-radiation, tube voltage: 40kV, tube current: 15mA, measurement range: diffraction angle 2θ = 20~60°, X-ray scan speed: 10° / min. In X-ray diffraction, those showing a diffraction peak at a diffraction angle (2θ) of 25.4±0.3° were considered to be of the anatase type, and those showing a diffraction peak at a diffraction angle (2θ) of 27.5±0.3° were considered to be of the rutile type.

[0033] (Manufacturing of crystalline thin-film titanium oxide particles) <Example 1> Thin-film titanium oxide particles were prepared based on the method disclosed in Japanese Patent Publication No. 2021-54696. The thin-film titanium oxide particles had an average particle diameter of 14 μm and an average film thickness of 282 nm. The crystalline form of the thin-film titanium oxide particles was amorphous. Hereinafter, these thin-film titanium oxide particles will be referred to as "thin-film titanium oxide particles A".

[0034] A dispersion containing 5% by mass of thin-film titanium oxide particles A was prepared by dispersing thin-film titanium oxide particles A in water. To this dispersion, 5 parts by mass of melamine-formaldehyde resin particles (Epostor S6, manufactured by Nippon Shokubai Co., Ltd., average particle size: 0.42 μm, burning temperature 300°C) were added per 100 parts by mass of the dispersion to prepare a mixture.

[0035] The particle size of the spacer particles was determined using a laser diffraction / scattering particle size distribution analyzer (LA-960, Horiba, Ltd.) and the volume-based average particle size was measured by the laser diffraction / scattering method. A batch cell was used for the measurement, the solvent was ethanol, and the refractive index was set to 1.22 relative refractive index. The spacer particles were added to the batch cell, and measurements were performed at a concentration that showed a transmittance of approximately 90%, and the volume-based average particle size was determined.

[0036] The mass ratio of the content of thin-film titanium oxide particles A in the mixture to the content of spacer particles is 1. The mass ratio of the content of thin-film titanium oxide particles A in the mixture to the content of water is 0.05.

[0037] The mixture was subjected to ultrasonic cleaning using an ultrasonic cleaner (VS-100III, manufactured by AS ONE Corporation) at a frequency of 28 kHz for 1 minute, dispersing thin-film titanium oxide particles A and spacer particles.

[0038] Then, in an environment where nitrogen was flowed at a flow rate of 5 L / min, the mixture was heated at 850°C for 60 minutes to calcine the thin-film titanium oxide particles A to obtain crystalline thin-film titanium oxide particles, while also burning off the spacer particles.

[0039] Figure 1 shows the obtained crystalline thin-film titanium oxide particles. The crystalline thin-film titanium oxide particles obtained in Example 1 had an average particle diameter of 9.5 μm and an average film thickness of 238 nm. The crystalline form of the crystalline thin-film titanium oxide particles was a mixture of rutile and anatase forms.

[0040] <Example 2> Crystalline thin-film titanium oxide particles were obtained in the same manner as in Example 1, except that polymethyl methacrylate resin particles (NMB-0220C, manufactured by ENEOS Liquid Crystal Co., Ltd., average particle size: 2.6 μm, burn-out temperature 340°C) were used as thin-film titanium oxide particles A and spacer particles.

[0041] The particle size of the spacer particles was determined using a laser diffraction / scattering particle size distribution analyzer (LA-960V2, Horiba, Ltd.) and the volume-based average particle size was measured by laser diffraction / scattering. A batch cell was used for the measurement, with water as the solvent, the solvent refractive index set to 1.333, and the solute refractive index set to 1.49. The spacer particles were added to the batch cell, and measurements were performed at a concentration that showed a transmittance of approximately 90%, and the volume-based average particle size was determined.

[0042] Figure 2 shows the obtained crystalline thin-film titanium oxide particles. The crystalline thin-film titanium oxide particles obtained in Example 2 had an average particle diameter of 12.5 μm and an average film thickness of 262 nm. The crystal type of the crystalline thin-film titanium oxide particles was rutile.

[0043] <Comparative Example 1> Crystalline thin-film titanium oxide particles were obtained in the same manner as in Example 1, except that thin-film titanium oxide particles A were used and spacer particles were not used.

[0044] Figure 3 shows the obtained crystalline thin-film titanium oxide particles. The crystalline thin-film titanium oxide particles obtained in Comparative Example 1 had an average particle diameter of 13.8 μm and an average film thickness of 334 nm. The crystal type of the crystalline thin-film titanium oxide particles was rutile.

[0045] [Table 1]

[0046] <Example 3> Thin-film titanium oxide particles were prepared based on the method disclosed in Japanese Patent Publication No. 2021-54696. The thin-film titanium oxide particles had an average particle diameter of 16 μm and an average film thickness of 163 nm. The crystalline form of the thin-film titanium oxide particles was amorphous. Hereinafter, these thin-film titanium oxide particles will be referred to as "thin-film titanium oxide particles B".

[0047] A dispersion containing 4% by mass of thin-film titanium oxide particles B was prepared by dispersing thin-film titanium oxide particles B in water. To this dispersion, 4 parts by mass of melamine-formaldehyde resin particles, which are spacer particles, were added per 100 parts by mass of the dispersion to prepare a mixture.

[0048] The mass ratio of the content of thin-film titanium oxide particles B in the mixture to the content of spacer particles is 1. The mass ratio of the content of thin-film titanium oxide particles B in the mixture to the content of water is 0.04.

[0049] The mixture was subjected to ultrasonic waves at a frequency of 28 kHz for 1 minute using an ultrasonic cleaner, and thin-film titanium oxide particles B and spacer particles were dispersed in it.

[0050] Then, in an environment where nitrogen was flowed at a flow rate of 5 L / min, the mixture was heated at 850°C for 300 minutes to calcine the thin-film titanium oxide particles B, thereby obtaining crystalline thin-film titanium oxide particles and burning off the spacer particles.

[0051] Figure 4 shows the obtained crystalline thin-film titanium oxide particles. The crystalline thin-film titanium oxide particles obtained in Example 3 had an average particle diameter of 13.3 μm and an average film thickness of 218 nm. The crystal type of the crystalline thin-film titanium oxide particles was rutile.

[0052] <Example 4> Crystalline thin-film titanium oxide particles were obtained in the same manner as in Example 3, except that thin-film titanium oxide particles B were used, and the amount of melamine-formaldehyde resin particles added as spacer particles was 19 parts by mass per 100 parts by mass of the dispersion. The mass ratio of the content of thin-film titanium oxide particles B in the mixture to the content of spacer particles was 0.21.

[0053] Figure 5 shows the obtained crystalline thin-film titanium oxide particles. The crystalline thin-film titanium oxide particles obtained in Example 4 had an average particle diameter of 10.7 μm and an average film thickness of 164 nm. The crystalline form of the crystalline thin-film titanium oxide particles was a mixture of rutile and anatase forms.

[0054] <Comparative Example 2> Crystalline thin-film titanium oxide particles were obtained in the same manner as in Example 3, except that thin-film titanium oxide particles B were used and spacer particles were not used.

[0055] Figure 6 shows the obtained crystalline thin-film titanium oxide particles. The crystalline thin-film titanium oxide particles obtained in Comparative Example 2 had an average particle diameter of 6.9 μm and an average film thickness of 321 nm. The crystal type of the crystalline thin-film titanium oxide particles was rutile.

[0056] [Table 2]

[0057] (Experimental results) Figure 7 shows the number distribution of film thickness for thin-film titanium oxide particles A, and for crystalline thin-film titanium oxide particles obtained in Examples 1, 2, and Comparative Example 1. Figure 8 shows the number distribution of film thickness for thin-film titanium oxide particles B, and for crystalline thin-film titanium oxide particles obtained in Examples 3, 4, and Comparative Example 2. Figure 9 shows the X-ray diffraction patterns of crystalline thin-film titanium oxide obtained in thin-film titanium oxide particles A and B, Examples 1, 2, 3, and 4, and Comparative Examples 1 and 2.

[0058] According to Figures 7 and 8, in Examples 1 to 4 using spacer particles, the film thickness of the thin-film titanium oxide particles A and B before firing and the film thickness of the crystalline thin-film titanium oxide particles after firing have almost the same number distribution. On the other hand, in Comparative Examples 1 and 2, which do not use spacer particles, the film thickness of the crystalline thin-film titanium oxide particles after firing shows that the number distribution is wider towards the thicker side than the film thickness of the thin-film titanium oxide particles A and B before firing. [Industrial applicability]

[0059] This invention is useful in the field of methods for producing crystalline inorganic oxide particles.

Claims

1. A method for producing crystalline inorganic oxide particles from inorganic oxide particles, The inorganic oxide particles are thin-film titanium oxide particles, and the crystalline inorganic oxide particles are crystalline thin-film titanium oxide particles. A method for producing crystalline inorganic oxide particles, comprising mixing the inorganic oxide particles and resin spacer particles through a solvent to prepare a mixture, and heating the mixture to calcine the inorganic oxide particles.

2. The method for producing crystalline inorganic oxide particles according to claim 1, wherein the crystalline form of the inorganic oxide particles is amorphous.

3. A method for producing crystalline inorganic oxide particles according to claim 1 or 2, wherein the spacer particles are burned off when the mixture is heated.

4. A method for producing crystalline inorganic oxide particles according to any one of claims 1 to 3, wherein the temperature at which the spacer particles burn out is 200°C or higher.

5. A method for producing crystalline inorganic oxide particles according to any one of claims 1 to 4, wherein the inorganic oxide particles are induced from an inorganic substance having hydrolyzable functional groups by a sol-gel transition involving a hydrolysis reaction and a polycondensation reaction.

6. A method for producing crystalline inorganic oxide particles according to any one of claims 1 to 5, wherein the average particle diameter of the inorganic oxide particles is 1 nm or more and 1 mm or less.

7. A method for producing crystalline inorganic oxide particles according to any one of claims 1 to 6, wherein the average particle diameter of the spacer particles is 1 nm or more and 1 mm or less.

8. A method for producing crystalline inorganic oxide particles according to any one of claims 1 to 7, wherein the mass ratio of the content of the inorganic oxide particles in the mixture to the content of the solvent is 0.001 or more and 10 or less.

9. A method for producing crystalline inorganic oxide particles according to any one of claims 1 to 8, wherein the mass ratio of the content of the inorganic oxide particles in the mixture to the content of the spacer particles is 0.01 or more and 1000 or less.

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