JP4174281B2 - Method for producing indium oxide fine particles - Google Patents

Description

【００２８】
表１に示されるように、本発明に従って製造された錫ドープ酸化インジウム分散物から得られる膜は、従来技術で得られているものに比べて、透明性が高く、導電性にも優れることがわかる。
【００２９】
【発明の効果】
本発明によれば、酸化インジウムを主体とする結晶性酸化物の微粒子分散物または粉末を簡便な方法で製造できる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a novel synthesis method of a crystalline fine particle oxide mainly composed of indium oxide. More specifically, the present invention relates to a method for producing a crystalline fine particle oxide mainly composed of indium oxide, which is uniformly dispersed in a solvent or given as a powder.
[0002]
[Prior art]
Indium oxide is used for various applications as a wideband semiconductor material together with zinc oxide, tin oxide, titanium oxide, and the like, or has been studied.
The porous particle film can be used for gas sensors that utilize the change in electrical properties depending on the adsorbent on the surface, and as a photoelectrode in the same way as titanium oxide, and can be applied to photosensors and dye-sensitized solar cells. It is being considered.
Furthermore, tin-doped (ITO) can be imparted with conductivity while maintaining transparency, so it can be used as a transparent electrode in various displays as a transparent conductive material. Is also used as a heat ray-preventing film.
What formed the ITO film | membrane on the plastic with plasticity is especially useful as an electromagnetic prevention film and a heat ray prevention film which require a large area.
[0003]
Such a film is generally prepared by a vapor phase method such as a sputtering method, but this requires a vacuum apparatus, and a large equipment investment is particularly required for manufacturing a large area. There is a cost problem.
On the other hand, it is also possible to obtain a film by applying a dispersion of pre-made ITO particles. Especially for applications such as anti-electromagnetic film and heat ray-preventing film, it can be prepared by applying a particle dispersion on a plastic film. To provide this, a stable dispersion of tin-doped indium oxide fine particles can be easily prepared. A method that can be manufactured is desired.
[0004]
In recent years, it has been understood that characteristics different from the sub-micron region can be obtained by reducing the size of particles to the nanometer level. One of them is the melting point lowering effect. Constituent particles fuse at a lower temperature than conventional sub-micron-sized particles, so it is considered possible to easily form a functional thin film by fusing by applying nanoparticles and heating. It is expected as a method for forming a functional film with a low cost in terms of area.
Further, since the size is significantly smaller than the wavelength of visible light, both the dispersion and the film formed therefrom are substantially completely transparent with very little visible light scattering.
[0005]
Therefore, a method for producing a stable dispersion of indium oxide, particularly tin-doped indium oxide nano-sized particles, particularly crystalline fine particles having a size of 1 to 10 nanometers is desired.
[0006]
In addition to the use as a transparent conductive material as described above, recently, as described in Non-Patent Document 1 and Non-Patent Document 2 below, nano-sized indium oxide particles have unique properties such as exhibiting fluorescence characteristics that do not exist in bulk. The characteristics are also known, and its application development is expected as one of oxide nanoparticles.
[0007]
As described above, indium oxide nanocrystalline crystal is a material that can be applied, but as for its manufacturing method, only a limited method is known.
[0008]
In Non-Patent Document 2, indium oxide nanoparticles are prepared by laser ablation, but this is a method for obtaining an agglomerated powder of several to tens of nm, and does not give a stable particle dispersion. .
Non-Patent Document 3 below shows a method of synthesizing nanosized particles of indium oxide by the reverse micelle method. However, the reverse micelle method has a problem that the concentration that can be synthesized is low, and a step of removing the dispersant and the like is necessary.
[0009]
[Non-Patent Document 1]
App.Phys.Lett. (1999) 75 pages 495 [Non-Patent Document 2]
Nano Lett. (2001) Volume 1 page 287 [Non-Patent Document 3]
J.Vac, Sci.Technol B (1007) vol.15 page 1889 【0010】
[Problems to be solved by the invention]
Therefore, an object of the present invention is to easily provide a stable colloidal solution in which crystal particles mainly composed of indium oxide having a size of 1 nm to 20 nm, especially about 1 nm to 10 nm are uniformly dispersed, or a powder made of the crystal particles. It is to provide a method of manufacturing.
[0011]
[Means for Solving the Problems]
The object of the present invention has been achieved by the following items specifying the present invention and preferred embodiments thereof.
(1) A first step in which indium carboxylate is heated to reflux in a solvent represented by the following general formula I to convert indium carboxylate into a soluble alkoxide , followed by addition of the solution. And a second step of generating indium oxide having a size of 1 to 20 nm by heating at a temperature of at least 180 ° C. under pressure.
Formula I
R—O—CH ₂ CH ₂ OH
(In the formula, R represents an unsubstituted alkyl group having 1 to 4 carbon atoms or a substituted alkyl group thereof.)
(2) The method for producing a fine particle dispersion or powder according to (1) above, wherein the carboxylic acid that gives the carboxylic acid of indium is selected from acetic acid, propionic acid, and derivatives thereof.
(3) A solvent selected from 2-methoxyethanol, 2-ethoxyethanol, 2- (methoxyethoxy) ethanol, and 2- (ethoxyethoxy) ethanol is used as the solvent of the general formula I. A method for producing a fine particle dispersion or powder according to item 1).
(4) The alkoxide of a metal other than indium is added to the reaction solution in the first step in an amount of 20 mol% or less of indium, and the metal is doped into indium oxide, as described in the above item (1) A method for producing a fine particle dispersion or powder.
(5) The method for producing a crystalline fine particle dispersion or powder of doped indium oxide as described in (4) above, wherein the metal alkoxide is an alkoxide of tin, zinc, gallium, magnesium or germanium.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The crystalline oxide fine particles mainly composed of indium oxide synthesized in the present invention are suitable for synthesis of a composition in which indium of the metal elements constituting the oxide is preferably 80 atomic% or more. If the composition ratio of the indium element is too small, a stable dispersion is not obtained, and a product with a constant composition ratio is obtained. A preferred range is 85 atomic percent or more.
The kind of metal element added in addition to indium oxide can be arbitrarily selected depending on the purpose, but tin, zinc, gallium, magnesium or germanium is more preferable.
Usually, the obtained oxide particles can obtain an oxide satisfying the stoichiometric relationship, but it is also possible to obtain an oxide containing oxygen defects by adjusting the atmosphere conditions of synthesis.
[0013]
The size of the crystal particles obtained by the present invention is usually 1 nm or more and 20 nm or less, and a more preferable size is 2 nm or more and 10 nm or less. Size distribution but are not limited to, Ru monodisperse der. In the present invention, the monodisperse particles have a particle size distribution variation coefficient of preferably 30% or less, more preferably 20% or less, and most preferably 10% or less. The fine particle concentration in the fine particle dispersion of crystalline oxide mainly composed of indium oxide obtained by the present invention is preferably 1 to 40% by mass, more preferably 5 to 30% by mass.
[0014]
The raw material used in the synthesis of the present invention is preferably a salt of an indium aliphatic carboxylic acid, more preferably a salt of a compound selected from acetic acid, propionic acid and derivatives thereof, and particularly a salt of acetic acid is preferable. .
[0015]
More specifically, indium acetate hydrate, anhydrous indium acetate, indium propionate, indium hydroxyacetate, indium acetylacetate, and the like, particularly preferably anhydrous indium acetate.
[0016]
The alcohol used as the solvent is represented by the general formula I.
Formula I
R—O—CH ₂ CH ₂ OH
Here, R represents an unsubstituted alkyl group having 1 to 4 carbon atoms or a substituted alkyl group thereof. Examples of preferred substituents on the alkyl group represented by R include alkoxy groups.
[0017]
Preferred alcohols include 2-methoxyethanol, 2-ethoxyethanol, 2- (methoxymethoxy) ethanol, 2- (methoxyethoxy) ethanol, 2- (ethoxyethoxy) ethanol, 2-isopropoxyethanol, 2-butoxyethanol. I can list them. These alcohol solvents can be used alone or in admixture of two or more. Further, the second solvent can be supplementarily mixed and used in a volume equal to or less than that of the alcohol. For example, it is a solvent miscible with alcohol such as dioxane, acetone, dimethylformamide, dimethylsulfoxide.
The amount of the solvent of the general formula I is not particularly limited, but is usually a solvent in which the concentration of indium carboxylate in the obtained solvent solution is 0.02 to 0.5 M (mol / l). Used in quantity. For example, the solvent of the general formula I can be used in an amount of 100 to 1000 times mol of indium carboxylate.
[0018]
In the synthesis method of the present invention, in the first step of heating an alcohol solution in which indium carboxylate (preferably indium aliphatic carboxylate) is dissolved, indium carboxylate is converted into soluble alkoxide, In the second step of heating the solution at a high temperature, the alkoxide is considered to decompose and form an oxide.
The heating in the first step is preferably refluxed at normal temperature and at the boiling point of the solvent. The heating time is arbitrarily adjusted depending on the types of the raw material and the solvent, but usually, conditions ranging from 3 hours to 7 hours at the reflux temperature are used. Further, it is preferable to distill off a part of the solvent during the refluxing process.
[0019]
In the second step, the liquid obtained in the first step is poured into a pressure resistant container and heated at a temperature of 180 ° C. or higher. The pressure during heating is appropriately determined depending on the type and temperature of the solvent used. For example, when the solvent is 2-ethoxyethanol, it is heated under a pressure of about 4 to 6 Pa.
The heating temperature is preferably 180 ° C. or higher and 300 ° C. or lower, and more preferably 190 ° C. to 250 ° C. The heating time is usually selected in the range of 30 minutes to 6 hours.
[0020]
In the present invention, it is preferable to prevent unwanted moisture from entering from the outside. For this reason, it is also preferable to dehydrate and use the solvent alcohol as necessary. It is also preferable that the reaction vessel is connected to a trap that avoids the influence of humidity in the atmosphere if necessary, and that dry air and dry nitrogen gas are circulated.
[0021]
Depending on the purpose, the oxide particle dispersion produced according to the present invention can be made into a higher concentration dispersion by distilling off the solvent or taken out as a powder. There are a method by centrifugal separation and a method by ultrafiltration. The method by ultrafiltration is more preferable in that it can be concentrated without secondary aggregation of particles.
[0022]
In order to contain (dope) other metal elements in addition to indium, it is preferable to add this metal alkoxide compound to the reaction solution in the first step. The type of metal alkoxide is arbitrary, but for example, ethoxide, butoxide, isopropoxide, methoxyethoxide, ethoxyethoxide and the like are used.
[0023]
【Example】
The present invention will be described in more detail below based on examples, but the present invention should not be limited thereto.
[0024]
Example 1
10 g of anhydrous indium acetate was added to a 500 ml three-necked flask, and 500 ml of 2-ethoxyethanol was added thereto. While stirring with a stirrer, 100 ml was distilled off while refluxing the suspension. At this stage, the liquid turned yellow and became transparent. After removing a slight insoluble matter with a 0.2 micrometer pore size filter, it was added to a stainless steel pressure vessel and heated with an external heater at 200 ° C. for 1 hour under a pressure of 4 to 6 Pa.
The obtained liquid was yellow and transparent, and the powder obtained by evaporating the solvent with an evaporator was confirmed to be cubic indium oxide from the X-ray diffraction pattern. The crystal grain size was 2 nm. From observation with a high-resolution electron microscope, fine particles having a uniform particle size of 2 nm were observed. That is, it was found that each particle was a single crystal particle. The coefficient of variation in particle size was about 25%, indicating high monodispersity.
[0025]
Example 2 (Synthesis of tin-doped indium oxide fine particles)
10 g of anhydrous indium acetate was added to a 500 ml three-necked flask, and 500 ml of 2-methoxyethanol was added thereto. While the suspension was refluxed under heating, 100 ml was distilled off over about 3 hours. After removing a slight insoluble matter by filtration, 1.7 g of tetra-t-butoxytin was added and the mixture was further refluxed for 1 hour. This liquid was added to a stainless steel pressure-resistant airtight container and left under pressure at a temperature of 200 ° C. for 1 hour. The resulting liquid was a pale yellow transparent liquid.
After cooling, the liquid was taken out and concentrated by about 10 times by distilling off the solvent.
From observation with a high-resolution electron microscope, fine particles having a uniform particle size of 2 nm were observed.
This liquid was filtered with a regenerated cellulose ultrafiltration membrane having a molecular weight cut off of 30,000, and the amounts of unreacted indium and tin in the filtrate were measured. Both were less than 1% of the charged amount. The yield of the target product was as high as 99% or more.
[0026]
Test example 1
The solution prepared in Example 2 was applied to a thickness of about 900 nm by spin coating on a 2.5 cm square glass substrate, and then heat treated at a temperature of 500 ° C. for 1 hour. The obtained film is designated as sample A.
For comparison, a liquid in which SUFD-HX (trade name, commercially available ITO) manufactured by Sumitomo Metal Mining Co., Ltd. was dispersed in cyclohexanol and acetylacetone was applied in the same manner, and heat treatment was performed at the same temperature. The obtained film is designated as Sample B.
The results of measuring the light transmittance and sheet resistance of these samples are shown in Table 1.
[0027]
[Table 1]

[0028]
As shown in Table 1, the film obtained from the tin-doped indium oxide dispersion produced according to the present invention has higher transparency and better conductivity than those obtained by the prior art. Recognize.
[0029]
【The invention's effect】
According to the present invention, a fine particle dispersion or powder of a crystalline oxide mainly composed of indium oxide can be produced by a simple method.

Claims (7)

The first step of heating and refluxing the indium carboxylate in a solvent represented by the following general formula I to convert the indium carboxylate to a soluble alkoxide , followed by the solution at least under pressure: And a second step of producing indium oxide having a size of 1 to 20 nm by heating at a temperature of 180 ° C. or higher.
Formula I
R—O—CH ₂ CH ₂ OH
(In the formula, R represents an unsubstituted alkyl group having 1 to 4 carbon atoms or a substituted alkyl group thereof.) The method for producing a fine particle dispersion according to claim 1, wherein the carboxylic acid that gives the indium carboxylate is selected from acetic acid, propionic acid, and derivatives thereof. 2. The solvent according to claim 1, wherein a solvent selected from 2-methoxyethanol, 2-ethoxyethanol, 2- (methoxyethoxy) ethanol, and 2- (ethoxyethoxy) ethanol is used as the solvent of the general formula I. A method for producing a fine particle dispersion. 2. The fine particle dispersion according to claim 1, wherein an alkoxide of a metal other than indium is added to the reaction liquid in the first step in an amount of 20 mol% or less of indium, and the metal is doped into indium oxide . Production method. The method for producing a crystalline fine particle dispersion of doped indium oxide according to claim 4, wherein the metal alkoxide is an alkoxide of tin, zinc, gallium, magnesium, or germanium. 6. The production method according to claim 1, wherein the crystalline fine particle dispersion of indium oxide is an indium oxide crystalline fine particle dispersion. A method for producing indium oxide crystalline fine particle powder, wherein the indium oxide crystalline fine particle dispersion is taken out from the indium oxide crystalline fine particle dispersion.