JP5397854B2 - Oxide-coated titanium oxide-containing liquid and method for producing the same - Google Patents

Description

  The present invention relates to an oxide-coated titanium oxide-containing liquid and a method for producing the same.

  In recent years, research on photocatalysts has been actively conducted in a wide range of fields. As an approach to environmental problems, research to obtain clean energy using sunlight instead of fossil fuel is being promoted. In the photocatalyst, it is possible to use sunlight as an energy source. Therefore, research on solar cells using sunlight has been conducted.

  Dye-sensitized solar cells have attracted attention from the viewpoint of cost and weight reduction, replacing conventional silicon-type solar cells. A dye-sensitized solar cell converts light energy absorbed by a sensitizing dye adsorbed on a metal oxide semiconductor into electrical energy. When the sensitizing dye absorbs light energy typified by sunlight, the energy state of electrons in the sensitizing dye becomes high, and the electrons in the sensitizing dye are excited. The excited electrons move from the sensitizing dye to the metal oxide semiconductor. The moved electrons move from the metal oxide semiconductor to the working electrode of the electrode pair, and move to the counter electrode via an external circuit. The electrons that have moved to the counter electrode return to the sensitizing dye via the electrolyte between the electrodes. Electrons emitted from the dye circulate in the system. This electron movement generates a current.

  Examples of the metal oxide semiconductor include titanium oxide and zinc oxide. With these metal oxide semiconductors as nuclei, a technique of coating metal oxides on the surface of metal oxide semiconductor particles has been attempted. As the oxide, an oxide having a conduction band with a higher energy level than that of the metal oxide semiconductor is used. Reverse injection of electrons excited and emitted from the sensitizing dye is mitigated. That is, it is known that the problem that the excited electrons are emitted to the electrolyte between the electrodes or recombined with the sensitizing dye is improved (Patent Documents 1, 2, 3, and 4). Non-patent document 1).

  When titanium oxide is used as the optical functional material, it is known that an anatase type crystal structure has high energy conversion efficiency (Patent Document 4). In the case where titanium oxide is used as an optical functional material, titanium oxide fine particles with high uniformity in particle diameter have been studied for product stability (Patent Document 5).

JP 2009-59646 A JP 2008-288477 A JP 2004-47264 A JP 2009-40622 A JP 2007-176553 A

“Effects of Cell Components in Dye-Sensitized Solar Cells” SHARP Technical Journal No. Vol.15, No.83, 49-53

  While the dye-sensitized solar cell using the oxide-coated metal oxide semiconductor has the advantage of reducing the back injection of electrons excited and emitted by the sensitizing dye as described above, There is a disadvantage that stable photoelectric conversion efficiency cannot be obtained. The following factors are considered as causes of this defect.

  In the conventional method, the oxide precursor is adsorbed on the surface of the metal oxide semiconductor particles by coating or the like. After the adsorbed oxide precursor is dried, it is fired. In this firing step, the oxide precursor is oxidized and chemically converted into an oxide. Oxidation fixes an oxide on the surface of the metal oxide semiconductor and forms an oxide film. Firing for forming the oxide coating layer is performed at a high temperature. At the same time that the oxide coating layer is formed, the metal oxide semiconductors may aggregate. Titanium oxide easily aggregates by drying, and the aggregated titanium oxide lump has a property that it is difficult to disperse once aggregated.

  Aggregation is likely to occur in the drying process and the firing process when titanium oxide is used as the core particle of the metal oxide semiconductor. Aggregation of the titanium oxide particles proceeds simultaneously with the formation of the metal oxide, or occurs before the titanium oxide particles are coated with the oxide. The aggregation of the titanium oxide particles generates an aggregate having a non-uniform diameter, and the oxide may not be coated as a uniform layer on the titanium oxide particles. Furthermore, the oxide distribution may be biased. If the distribution of the oxide is biased, a part of the titanium oxide particles may not be covered with the oxide, and the surface of the titanium oxide particles may be exposed.

  As described above, when the aggregation of the titanium oxide particles occurs, as a result, the surface area of the titanium oxide particles that can adsorb the dye becomes narrow, and the amount of the dye adsorbed on the titanium oxide particles decreases. As a result, in the dye-sensitized solar cell, the function of collecting light energy is lowered, and the photoelectric conversion efficiency is lowered.

  Further, when the titanium oxide particles are aggregated, the scattering of incident light increases, and the titanium oxide particles coated with the oxide become opaque. When a film is formed with opaque titanium oxide particles, the film is also opaque, so that light does not reach the inside of the film. Therefore, the sensitizing dye present on the surface of the film mainly functions, and the internal sensitizing dye hardly functions, so that it is considered that the energy conversion efficiency is lowered in the dye-sensitized solar cell. The film thickness may be non-uniform, and the physical properties of the film may be reduced.

  Further, when the surface of the titanium oxide particles is exposed without being covered with an oxide, the dye comes into direct contact with the titanium oxide particles, and back injection of electrons excited and emitted by the sensitizing dye is likely to occur. In addition, since titanium oxide has a strong oxidizing ability, the dye may be oxidized when the dye contacts the titanium oxide particles for a long time. Oxidized dyes can lose their ability to collect light energy.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide means for obtaining a liquid that is contained in high dispersion without agglomeration of oxide-coated titanium oxide coated with an oxide. That is.

  In the method for producing oxide-coated titanium oxide according to the present invention, an oxide precursor is added to a dispersion of titanium oxide and heated to coat the titanium oxide with an oxide.

  The dispersion of titanium oxide particles is obtained by treating titanium oxide with a long-chain fatty acid in a solution. An oxide precursor is added to this dispersion and heated. By heating, the oxide precursor is oxidized around the titanium oxide to become an oxide. Thereby, the titanium oxide is coated with the oxide.

  Dispersion of titanium oxide in the solvent and oxidation of the oxide precursor are performed in a reaction vessel. Examples of the reaction vessel include a vessel of a size handled in a laboratory such as a three-necked flask and a separable flask, a reaction vessel for mass production, a microreactor that performs a minute amount of reaction in a minute channel, and the like. These reaction vessels preferably include a stirrer that can stir the reactants stored therein like a stirrer and a temperature control device that controls the internal temperature like an oil bath. It is preferable that the reaction vessel has a structure in which the outside air does not flow into the reaction vessel and the material can be injected into the reaction vessel during the reaction process.

  The oxidation of the oxide precursor is preferably performed in an inert gas atmosphere. This is to prevent an excess oxidation reaction or the like in the solution or the raw material from occurring due to the presence of oxygen or moisture in the atmosphere. After titanium oxide or a solution is sealed in the reaction vessel, the inside of the reaction vessel is replaced with an inert gas. For example, after the internal gas is generally removed from the reaction vessel by a method such as decompression, an operation of feeding an inert gas into the reaction vessel is repeated several times. Examples of the inert gas include argon, helium, neon and the like. The inert gas is most preferably argon in consideration of specific gravity and operability.

Titanium oxide includes, for example, anatase type, rutile type, brookite type, and mixtures thereof depending on the crystal system. In particular, when oxide-coated titanium oxide is used as an optical functional material in a solar cell, anatase-type titanium oxide is preferably used. This is because anatase-type titanium oxide has high energy conversion efficiency as a photofunctional material. Titanium oxide is not limited to spherical particles, and may be particles having an irregular shape or a certain shape.

  In the present invention, the average particle diameter of titanium oxide is preferably 100 nm or less. A more preferable average particle diameter is 50 nm or less. The polydispersity index is preferably 0.3 or less. A more preferable polydispersity index is 0.15 or less. When the average particle size and the polydispersity index are within the above ranges, the particle size of the resulting oxide-coated titanium oxide tends to be fine and uniform. Titanium oxide is preferably handled in a dispersed state in a solvent such as water. This is because titanium oxide is less likely to aggregate in a solvent such as water.

  Examples of the solvent used as the titanium oxide dispersion include hydrocarbon solvents, alcohol solvents, phenol solvents, ether solvents, ketone solvents, ester solvents, amine solvents, heterocyclic solvents, and the like. It is done. Since the oxide precursor is heated and oxidized in these solvents, it is preferable that the solvent does not evaporate at the maximum temperature of the heating step, and specific preferred solvents include 1-dodecanol.

As long-chain fatty acids, aliphatic monocarboxylic acids, aliphatic dicarboxylic acid fatty acids and their amine derivatives are preferred, and salts thereof are also preferred. Examples include myristic acid, palmitic acid, palmitoleic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, arachidonic acid, arachidic acid, icosapentaenoic acid, docosapentaenoic acid, docosahexaenoic acid, and the like. A hydrocarbon portion having a certain length is preferable because it can easily build a self-assembly such as a micelle in a solution. As long-chain fatty acid salts, the above-mentioned alkali metal salts and alkaline earth metal salts of fatty acids are preferred from the viewpoint of easy availability. Specific examples include sodium salts, potassium salts, magnesium salts, calcium salts, and the like. Of these long-chain fatty acids, aliphatic monocarboxylic acids or aliphatic dicarboxylic acid fatty acids are preferred, and a particularly preferred long-chain fatty acid is oleic acid in terms of ease of handling and availability.

  As the oxide precursor, it is preferable that the conduction band level of the oxide when oxidized is higher than the conduction band level of titanium oxide. This is because reverse injection is prevented when the oxide is treated as a semiconductor.

  In the present invention, the above-described titanium oxide and solvent are placed in a reaction vessel and stirred. These mixing ratios are preferably 10 parts by weight or less of titanium oxide with respect to 100 parts by weight of the solvent. Then, the atmosphere in the reaction vessel is replaced with an inert gas. A long chain fatty acid is dropped into the reaction vessel in an inert gas atmosphere at 2 mL / min. These mixing ratios are preferably 100 parts by weight or more of long-chain fatty acids with respect to 100 parts by weight of titanium oxide. This is because it is considered that all the titanium oxide is covered with the long chain fatty acid by sufficiently increasing the amount of the long chain fatty acid with respect to the titanium oxide. The liquid in which the titanium oxide and the long chain fatty acid are mixed is stirred, and in the liquid, the titanium oxide forms micelles covered with the long chain fatty acid.

  Long chain fatty acids collect and adsorb on the surface of titanium oxide with titanium oxide as a nucleus. The titanium oxide particles are separated from each other without being aggregated by being covered with the long-chain fatty acid. That is, the presence of the long chain fatty acid between the titanium oxide particles reduces the possibility that the titanium oxide particles are in direct contact with each other, thereby preventing aggregation. In this way, a dispersion of titanium oxide is obtained.

  When water is used as the solvent described above, the long-chain fatty acid is added to the water mixed with titanium oxide and stirred, and then allowed to stand. Titanium oxide mixed in water is covered with long chain fatty acids. In addition, with the passage of time, water and long-chain fatty acids are separated into two layers. Titanium oxide covered with long chain fatty acids migrates to the layer of long chain fatty acids. The long chain fatty acid layer is recovered and the solvent described above is added and stirred. Then, by removing moisture by reducing the pressure, a dispersion of titanium oxide covered with long-chain fatty acids can be obtained.

  An oxide precursor is added to the titanium oxide dispersion. These mixing ratios are preferably 50 parts by weight or more of the oxide precursor with respect to 100 parts by weight of titanium oxide. After the oxide precursor is added, the dispersion is heated with stirring. The pressure in the reaction vessel is maintained at atmospheric pressure while the inert gas is continuously supplied. The reaction temperature is preferably 200 ° C. or higher and 400 ° C. or lower, more preferably 300 ° C. or higher and 350 ° C. or lower. By making the reaction temperature lower than before, collision between the titanium oxide particles hardly occurs, and aggregation of the titanium oxide particles is suppressed. In addition, when the reaction temperature is 200 ° C. or higher, preferably 300 ° C. or higher, the oxidation of the oxide precursor is promoted, and the generation of amorphous components and unreacted materials after heating is suppressed. By this heating, the oxide precursor is oxidized around the titanium oxide particles to form oxide-coated titanium oxide. This oxide-coated titanium oxide is maintained in a dispersed state in the aforementioned solvent.

  The oxide-coated titanium oxide is confirmed by, for example, XRD (X-ray diffraction method). XRD identifies a substance. If a titanium oxide peak and an oxide peak are detected at the same position on the image, it is assumed that the titanium oxide is covered with the oxide. Titanium oxide is formed at the same position on the same line by line measurement using a transmission electron microscope (hereinafter also referred to as TEM) by energy dispersive X-ray spectroscopy (hereinafter also referred to as EDX). The presence or absence of metal atoms of titanium and oxide inside is confirmed. In addition, the measurement using TEM is performed at three points on the outer side, the end (surface), and the inner side of the oxide-coated titanium oxide on the image, whereby the elements present at the positions of the three points are detected. By these measurement methods, it is confirmed that titanium oxide is coated with an oxide.

  The oxide-coated titanium oxide has a structure in which titanium oxide is used as a nucleus and the periphery thereof is coated with an oxide. The particle diameter of the oxide-coated titanium oxide is determined by the particle diameter of the core titanium oxide and the thickness of the oxide coating layer. Therefore, the particle diameter and polydispersity index of the oxide-coated titanium oxide obtained by the production method according to the present invention include the size (particle diameter) of titanium oxide particles used as a raw material, the mixing ratio of oxide precursors, and the like. Can be adjusted to some extent. Therefore, according to the production method of the present invention, an oxide-coated titanium oxide having an average particle diameter of 5 nm to 100 nm and a polydispersity index of 0.1 to 0.3 can be obtained. It is also possible to obtain oxide-coated titanium oxide having an average particle diameter of 5 nm to 50 nm and a polydispersity index of 0.1 to 0.15.

  The average particle diameter and polydispersity index of the oxide-coated titanium oxide can be obtained by measuring the oxide-coated titanium oxide with a particle size distribution measuring device and analyzing the measurement result by a dynamic scattering method. It is estimated that the smaller the average particle size and the more uniform the particle size, the more highly dispersed titanium oxide is without aggregation. The presence or absence of aggregation can be determined, for example, by observing the oxide-coated titanium oxide with a scanning electron microscope (hereinafter also referred to as “SEM”). Moreover, it can be judged that uniformity is so high that a polydispersity index is small.

  The oxide-coated titanium oxide particles in the present invention have a higher particle size uniformity than particles produced by conventional methods. Specifically, the oxide-coated titanium oxide obtained by the conventional method includes particles having a polydispersity index of 0.3 or more and a particle diameter of 500 nm or more.

  The oxide-coated titanium oxide according to the present invention is processed into a thin layer for the purpose of being used in, for example, a solar cell. As a method for forming this thin layer, screen printing or the like can be mentioned. When processed into a thin layer, the oxide-coated titanium oxide is made into a paste. Since the oxide-coated titanium oxide according to the present invention has a fine average particle diameter and high uniformity, the oxide-coated titanium oxide does not clog the holes of the plate used in screen printing, and the paste is applied onto the printing object. Is uniformly applied. That is, the omission is good. Further, since the oxide-coated titanium oxide particles are fine, the paste can be applied thinly. In addition, since the particle diameter of the oxide-coated titanium oxide is uniform, unevenness and unevenness are less likely to occur in the thin layer. Thereby, a thin layer is stabilized and, as a result, a solar cell with stable quality can be obtained.

When the oxide-coated titanium oxide according to the present invention is used in a dye-sensitized solar cell, the dye is adsorbed on the surface of the oxide-coated titanium oxide particles. Since the oxide-coated titanium oxide according to the present invention is uniform and fine particles, the total surface area of all the particles is larger than those having a non-uniform or large particle size. As a result, since the amount of the dye adsorbed on the surface of the particles increases, sensitization by the dye increases, and as a result, the conversion efficiency of the dye-sensitized solar cell increases.

  In the oxide-coated titanium oxide-containing liquid or paste-like thin film according to the present invention, the particle diameter of the oxide-coated titanium oxide is small and the uniformity is high, so that irregular reflection of incident light hardly occurs. Therefore, the incident light passes through the oxide-coated titanium oxide-containing liquid and the thin film in a straight line. That is, the oxide-coated titanium oxide-containing liquid or thin film according to the present invention has high light transmittance. In this specification, the transmittance is the proportion of light that has been transmitted to the material without being absorbed or irregularly reflected. That is, the ratio of transmitted light to incident light. As incident light, light having a wavelength belonging to the visible light region is used.

  The transmittance can be measured by a spectrophotometer. As the sample, for example, an oxide-coated titanium oxide-containing liquid having a concentration of 0.02 g / mL is used. The thickness at which light is transmitted to the oxide-coated titanium oxide-containing liquid is 10 mm, and the transmittance is measured by irradiation with light having a visible light wavelength band of 630 nm. The transmittance | permeability of the oxide coating titanium oxide containing liquid which concerns on this invention is 90% or more, More preferably, it is 95% or more. With this transmittance, an optical functional material having high translucency can be obtained. When an optically functional material with high translucency is used in a dye-sensitized solar cell, light reaches the inside of the film containing oxide-coated titanium oxide in the optically functional material. It is considered that sensitization is realized not only by the oxide-coated titanium oxide present in the film, but also by the dye adsorbed on the surface of the oxide-coated titanium oxide present in the film, thereby increasing the energy conversion efficiency.

  The oxide-coated titanium oxide-containing liquid according to the present invention can wash the oxide-coated titanium oxide present in the liquid by centrifugation. When the oxide-coated titanium oxide-containing liquid is centrifuged, the oxide-coated titanium oxide precipitates in the liquid. When the supernatant is discarded by decantation, a liquid in which the oxide-coated titanium oxide is concentrated is obtained. A new low-polar solvent is added to the concentrated liquid and stirred. For example, hexane or toluene is preferable as the low-polarity solvent because it is easy to handle. By repeating such concentration and dilution operations, unreacted substances and other excess substances in the oxide-coated titanium oxide-containing liquid are discarded. That is, the oxide-coated titanium oxide is cleaned.

  Since the oxide-coated titanium oxide-containing liquid according to the present invention is obtained as a liquid, the oxide-coated titanium oxide is not agglomerated even when it is treated as a material such as a solar cell in which drying due to storage or storage is suppressed. Can be used.

  According to the present invention, an oxide-coated titanium oxide having a fine particle size and a uniform particle size can be obtained. Moreover, according to this invention, the oxide coating titanium oxide containing liquid with a high translucency is obtained.

1 is a TEM spectrum obtained by performing line analysis of the oxide-coated titanium oxide according to Example 1. FIG. FIG. 2 is a TEM image of the oxide-coated titanium oxide according to Example 1. FIG. 3 is a TEM spectrum of the oxide-coated titanium oxide according to Example 1. (A) is a TEM spectrum at point A in FIG. 2, (B) is a TEM spectrum at point B in FIG. 2, and (C) is a TEM spectrum at point C in FIG. 4 is an SEM image of a film formed by applying a paste of oxide-coated titanium oxide according to Example 1. FIG. FIG. 5 is an SEM image of a film formed by applying the oxide-coated titanium oxide paste according to Comparative Example 1.

  In the following, preferred embodiments of the invention will be described. It should be noted that each embodiment described below is merely an example of the present invention, and it is needless to say that the embodiment of the present invention can be appropriately changed without departing from the gist of the present invention.

[Example 1]
As Example 1, oxide-coated titanium oxide was synthesized by the production method according to the present invention. Specifically, 12 g (150 mmol) of titanium oxide aqueous dispersion (manufactured by Sakai Corporation, particle diameter 20 nm to 40 nm) and 180 mL of pure water were added to a three-necked flask and diluted, and 60 mL of oleic acid was further added and stirred. The mixture was allowed to stand overnight to separate the oleic acid and water into two layers. After the supernatant oleic acid layer was collected in another three-necked flask, 1-octadecene was added to the oleic acid layer, and the inside of the three-necked flask was depressurized with an evaporator for dehydration. Thereafter, the atmosphere inside the three-necked flask was removed by a vacuum pump (GLD-201B manufactured by ULVAC Kiko Co., Ltd.), and then argon gas was introduced into the three-necked flask. The gas in the three-necked flask was replaced with argon gas by repeating the removal of the gas in the three-necked flask and the inflow of argon gas several times.

  While stirring the oleic acid layer in a three-necked flask under an argon gas atmosphere (300 ° C., 150 rpm), 355 g (1.91 mol) of 1-dodecanol and 44 g (75 mmol) of magnesium oleate were added to the three-necked flask. The argon solution was circulated through the three-necked flask at 50 mL / min, and the liquid inside was stirred at 300 ° C. for 60 minutes (150 rpm), and then stirred at 40 ° C. overnight (150 rpm).

  The liquid in the three-necked flask was collected and centrifuged, and the supernatant was discarded by decantation. Then, hexane was added to the remaining liquid and stirred. This operation was repeated several times to obtain an oxide-coated titanium oxide-containing liquid.

[Comparative Example 1]
After adding 100 mL of water to 12 g of titanium oxide powder (manufactured by Sakai Corporation, particle diameter 20 nm to 40 nm), 6.5 g of magnesium methoxide was added and stirred at room temperature for 1 hour. Furthermore, after stirring for 30 minutes at 70 ° C., the solvent was removed by an evaporator and dried to obtain a powdered oxide-coated titanium oxide.

[Confirmation test of oxide-coated titanium oxide]
The oxide-coated titanium oxide particles according to Example 1 were evaluated by SEM (S-5200 manufactured by Hitachi High-Technologies), XRD (RINT-TTRIII-AX2 manufactured by Rigaku) and TEM (JEM-4000 manufactured by JEOL Ltd.). Scanning was performed while traversing the particles along the white line shown on the TEM image of FIG. In addition, the measurement was performed at three points shown on the TEM image in FIG. 2, that is, outside the particle (point A), at the end of the particle (point B), and at the center of the particle (point C). The measurement result is shown in FIG.

  In the analysis results by XRD, a titanium oxide peak of 25.3 ° and a magnesium oxide peak of 42.6 ° were observed at the same position. Further, from the measurement results shown in FIG. 3, the elements of Mg and Ti are not recognized outside the particle (point A), and Mg and Ti are observed at the end of the particle (point B) and the center of the particle (point C). Both elements were observed, and in particular, the strength of the Ti element was detected at the center of the particle. From these results, it was confirmed that the particles obtained in Example 1 were titanium oxide particles coated with magnesium oxide.

[Physical property test of oxide-coated titanium oxide]
(Average particle size)
The oxide-coated titanium oxide obtained in Example 1 and Comparative Example 1 was measured by Malvern Instruments (manufactured by Ltd., Nano-ZS). By analyzing the measurement results by the dynamic scattering method, the average particle diameter of the oxide-coated titanium oxide was obtained. The average particle size of the oxide-coated titanium oxide of Example 1 was 43.7 nm. For Comparative Example 1, pure water was added to the oxide-coated titanium oxide of Comparative Example 1 to prepare a liquid having the same concentration as in Example 1. The oxide-coated titanium oxide in pure water was ground in a mortar and then dispersed by ultrasonic waves to obtain an oxide-coated titanium oxide-containing liquid of Comparative Example 1. The average particle diameter of the oxide-coated titanium oxide in the oxide-coated titanium oxide-containing liquid of Comparative Example 1 was 2.3 μm.

(Polydispersity index)
The oxide-coated titanium oxide obtained in Example 1 and Comparative Example 1 was measured by Malvern Instruments (manufactured by Ltd., Nano-ZS). The polydispersity index was obtained by analyzing the measurement results by the dynamic scattering method. The polydispersity index of the oxide-coated titanium oxide-containing liquid of Example 1 was 0.12, and the polydispersity index of the oxide-coated titanium oxide-containing liquid of Comparative Example 1 was 0.32. In addition, as for the oxide coating titanium oxide containing liquid of Example 1 and Comparative Example 1, both the same samples as those used for the above-mentioned measurement of the average particle diameter were used.

(Transmittance)
Using the oxide-coated titanium oxide of the oxide-coated titanium oxide-containing liquid of Example 1, a sample having a concentration of oxide-coated titanium oxide of 0.02 g / mL and a transmission thickness of 10 mm was prepared. For Comparative Example 1, pure water was added to the oxide-coated titanium oxide of Comparative Example 1 to prepare a liquid having the same concentration as the sample of Example 1. The oxide-coated titanium oxide in pure water was ground in a mortar and then dispersed by ultrasonic waves to obtain an oxide-coated titanium oxide-containing liquid. A sample having a transmission thickness of 10 mm was prepared using this oxide-coated titanium oxide-containing liquid. And the transmittance | permeability was obtained by irradiating each sample with visible light with a wavelength of 630 nm, and measuring transmitted light with a spectrophotometer (the JASCO make, V-650). The transmittance of the sample of Example 1 was 90.6%, and the transmittance of the sample of Comparative Example 1 was 74.8%.

(Membrane formation)
A thin film was formed using the oxide-coated titanium oxide obtained in Example 1 and Comparative Example 1, respectively. Specifically, ethyl cellulose, propylene glycol monomethyl ether acetate and terpineol were added to the oxide-coated titanium oxide-containing liquid of Example 1 concentrated with an evaporator, and mixed in a mortar to obtain a paste. The obtained paste was applied on a glass substrate and dried to obtain a thin film. Further, ethyl cellulose, propylene glycol monomethyl ether acetate and terpineol were added to the powder of Comparative Example 1, and mixed in a mortar to obtain a paste. Further, a three-roll mill (NR-42A manufactured by Noritake Co., Ltd.) was used to pulverize the aggregated particles in the paste, and then the paste was applied onto a glass substrate and dried to obtain a thin film. Each thin film was measured by SEM. The SEM image of the thin film of Example 1 is shown in FIG. 4, and the SEM image of the thin film of Comparative Example 1 is shown in FIG.

[Evaluation]
When comparing the average particle diameter of each oxide-coated titanium oxide of Example 1 and Comparative Example 1, the average particle diameter of the oxide-coated titanium oxide of Example 1 is larger than that of the oxide-coated titanium oxide of Comparative Example 1. small. In terms of the polydispersity index, the oxide-coated titanium oxide of Example 1 is smaller than the oxide-coated titanium oxide of Comparative Example 1. Thus, it can be said that the oxide-coated titanium oxide according to Example 1 has finer and more uniform particles than the oxide-coated titanium oxide according to Comparative Example 1. This is because the oxide-coated titanium oxide of Comparative Example 1 was agglomerated and the particles were large and non-uniform, whereas the oxide-coated titanium oxide of Example 1 was fine and uniform without agglomeration. Presumed to be.

  Further, when the transmittances of the samples of Example 1 and Comparative Example 1 are compared, the sample of Example 1 has a higher transmittance than the sample of Comparative Example 1. Thereby, it can be said that the sample of Example 1 has high transparency. Moreover, when each thin film of Example 1 and Comparative Example 1 was visually observed, the thin film of Example 1 was transparent, but the thin film of Comparative Example 1 was cloudy.

Claims (6)

A titanium oxide dispersion containing a hydrocarbon, alcohol, phenol, ether, ketone, ester, amine, or heterocyclic solvent, a long chain fatty acid, and an oxide precursor. A heating step of obtaining a liquid containing oxide-coated titanium oxide in which the titanium oxide is coated with an oxide by heating at a temperature of 200 ° C. or higher and 400 ° C. or lower in an inert gas atmosphere;
The solvent is one that does not vaporize at the highest temperature adopted in the temperature range of 200 ° C. or more and 400 ° C. or less in the heating step,
The long chain fatty acid is myristic acid, palmitic acid, palmitoleic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, arachidonic acid, arachidic acid, icosapentaenoic acid, docosapentaenoic acid, docosahexaenoic acid, and amine derivatives thereof, And a method for producing an oxide-coated titanium oxide which is at least one of these salts.   The method for producing oxide-coated titanium oxide according to claim 1, wherein the oxide-coated titanium oxide has an average particle size of 100 nm or less and a polydispersity index of the liquid is 0.3 or less.   The method for producing oxide-coated titanium oxide according to claim 1 or 2, wherein a transmittance of light having a wavelength of 630 nm with respect to the liquid having a concentration of 0.02 g / mL and a transmission thickness of 10 mm is 90% or more. The method for producing oxide-coated titanium oxide according to any one of claims 1 to 3 , wherein the oxide precursor is magnesium oleate. The oxide-coated titanium oxide having an average particle size of 100 nm or less is oxidized by the method for producing an oxide-coated titanium oxide according to any one of claims 1 to 4 , wherein the polydispersity index is dispersed to 0.3 or less. Product coating titanium oxide containing liquid. 6. The oxide-coated titanium oxide-containing liquid according to claim 5 , wherein a transmittance of light having a wavelength of 630 nm with respect to the oxide-coated titanium oxide-containing liquid having a concentration of 0.02 g / mL and a transmission thickness of 10 mm is 90% or more. .