JP2010049869A - Transparent conductive film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transparent conductive film which is excellent in transparency and also has excellent characteristics by making use of the cohesive power of ultra-fine particles by a simple method without using a large apparatus with a vacuum device. <P>SOLUTION: The transparent conductive film is obtained by applying a colloidal solution containing 100 parts by weight of metal oxide ultra-fine particles having a number average particle diameter of 1-100 nm, preferably 1-10 nm and preferably containing zinc oxide as the main component and 1-10,000 parts by weight of solvent which is preferably methanol to a support and then removing the solvent. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a transparent conductive thin film using metal oxide ultrafine particles.

  Conventionally, transparent conductive thin films have been used for leakage electromagnetic wave shielding films such as liquid crystal display devices and electroluminescence display devices, transparent electrodes of various electronic devices, and the like. As a method for forming such a transparent conductive thin film, a transparent conductive thin film containing tin oxide or zinc oxide is formed on the surface of a transparent substrate by vapor deposition or sputtering.

  In addition, the transparent conductive thin film can be formed by a simpler sol-gel method regardless of vapor deposition, sputtering, or the like. In a normal sol-gel method, a chelating agent is added as necessary to prepare a uniform solution of these raw materials, which is applied to a substrate by spin coating or the like, dried and baked to form an oxide thin film. .

  As an example of the transparent conductive thin film by the sol-gel method, for example, indium chloride and stannous chloride or stannic chloride described in Patent Document 1 are dissolved in either alcohol or a water-alcohol mixed solution. It is known that an ITO transparent conductive film is formed by applying a coating solution obtained by adding a surfactant to the applied coating solution, followed by baking on the substrate by dip coating.

  However, in any case, a heat treatment such as a firing step is required. In the heat treatment at high temperature, it is considered unpreferable when the base material is a polymer material because it causes deformation or deterioration.

  By the way, it is known that the zinc oxide fine particles alone have a strong cohesive force and are difficult to disperse. As an example of improving this point, a small amount of silicon or aluminum is contained inside the zinc oxide particles. There exists patent document 2 which contained the oxide or hydroxide of this, and obtained the zinc oxide particle | grains with a good dispersibility of 0.03 micrometer or less.

  In forming a coating film containing such metal oxide particles, generally, this type of particles is dispersed in a solvent in which an inorganic or organic binder is dissolved, and the resulting coating is applied to various substrates. The method of apply | coating is taken. At that time, in order to obtain the transparency of the coating film, it is necessary that the particle is a so-called ultrafine particle having a diameter that does not cause light scattering, that is, a particle having a particle size of about 200 nm or less. Need to be distributed.

However, it has been pointed out that when such fine particles having a small particle diameter are used, the particles easily form secondary aggregates in the paint, making it difficult to obtain a uniform dispersion, and the transparency is rather lowered. In addition, in these methods, inorganic or organic binders are necessary to prevent aggregation, and it is impossible to overlook the possibility of adversely affecting the physical properties together with a small amount of additives such as silicon.
JP 2002-175733 A Japanese Patent Laid-Open No. 2002-201382

  An object of the present invention is to obtain a transparent conductive film having excellent characteristics by utilizing a cohesive force of ultrafine particles by a simple method without using a large-scale apparatus with a vacuum apparatus, and having excellent transparency. .

  As a result of intensive studies, the present inventor has found that if a specific colloid solution is used, a transparent conductive film having excellent characteristics can be obtained simply by applying it to a carrier and removing the solvent. Was completed.

  That is, the present invention is obtained by applying a colloidal solution containing 100 parts by weight of metal oxide ultrafine particles having a number average particle diameter of 1 to 100 nm and 1 to 10,000 parts by weight of a solvent to the support and removing the solvent. And a transparent conductive thin film.

  A preferred embodiment is that the metal oxide ultrafine particle is a transparent conductive thin film characterized by containing zinc oxide as a main component.

  A preferred embodiment is a transparent conductive thin film characterized in that the number average particle diameter is 1 to 10 nm.

  A preferred embodiment is a transparent conductive thin film characterized in that the solvent is methanol.

  In a preferred embodiment, the coating method is a transparent conductive thin film characterized in that it is one selected from the group consisting of spin coating, dip coating, and spray coating.

  A preferred embodiment is to form a transparent conductive thin film characterized in that the solvent is reprecipitated with a poor solvent of metal oxide ultrafine particles.

  In a preferred embodiment, the method for removing the solvent comprises a transparent conductive thin film characterized by including one or more steps selected from the group consisting of heating and vacuum drying.

  The transparent conductive film of the present invention is made from a colloidal solution in which metal oxide fine particles of 1 to 100 nm that do not scatter light are monodispersed. In addition, a transparent conductive film having excellent characteristics utilizing the cohesive force of ultrafine particles can be obtained.

(Transparent conductive thin film)
The transparent conductive thin film of the present invention is obtained by applying a colloidal solution containing 100 parts by weight of metal oxide ultrafine particles having a number average particle diameter of 1 to 100 nm and 1 to 10000 parts by weight of a solvent to the support and removing the solvent. It is a transparent conductive thin film obtained by.

  Such a transparent conductive thin film of the present invention becomes an excellent inorganic transparent thin film by a simple method such as liquid application and solvent removal without using a large-scale apparatus with a vacuum apparatus such as sputtering or CVD. In addition, unlike a thin film by a general sol-gel method, fine particles having a number average particle diameter of 1 to 100 nm by a specific chemical synthesis process for obtaining highly controlled fine particles were uniformly dispersed in a solvent. Since a liquid is used as a raw material, even if there is a grain boundary in the produced transparent conductive film, basically no light is scattered and the transparency is excellent. In addition, since so-called ultrafine particles having an extremely small particle size are used as raw materials, a transparent thin film having excellent characteristics can be obtained only by a relatively low temperature treatment without a high temperature baking process due to a cohesive force derived therefrom.

(Colloid solution)
The colloidal solution according to the present invention is a mixed solution containing 100 parts by weight of metal oxide ultrafine particles having a number average particle diameter of 1 to 100 nm and 1 to 10,000 parts by weight of a solvent, preferably a metal having a particle diameter of 10 nm or less. Since the oxide fine particle colloidal solution can be easily prepared, for example, in the case of zinc oxide ultrafine particles, separately, each equivalent, ie, stoichiometric, completely dissolved methanol solution of zinc acetate, And a method of preparing a transparent and clear zinc oxide colloidal methanol solution by preparing a methanol solution of potassium hydroxide, for example, at 25 ° C. or higher at a temperature of 25 ° C. or higher and rapidly mixing the two solutions with vigorous stirring. In the present specification, this is referred to as “metal oxide ultrafine particle colloidal solution method”). Metal oxide ultrafine particles is a clear liquid is dispersed stably in.

(Metal oxide ultrafine particles)
The metal oxide ultrafine particles are preferably composed mainly of zinc oxide, since the properties such as ultraviolet absorption ability, fluorescence emission ability and photocatalytic activity can be utilized in the resin material, and are preferably dispersed in the colloidal solution. From the viewpoint of controlling the characteristics by expressing the quantum size effect, the number average particle size at 1 is required to be in the range of 1 nm to 100 nm, more preferably 30 nm or less, still more preferably 10 nm or less. is there.

  In addition, from the viewpoint of preparing a metal oxide ultrafine particle colloid solution by the above-described method, maintaining it stably, and making the transparent conductive film of the present invention more transparent, It is more preferably 20 nm or less at which scattering hardly occurs.

  Here, the number average particle diameter means a number average particle diameter calculated by measuring the particle diameter of at least 100 particles with a ruler using a photograph taken with a transmission electron microscope. However, when the photograph of the particle | grains image | photographed with the electron microscope is not circular, after calculating the area which a particle occupies, it calculates using the circle diameter at the time of replacing with the circle | round | yen which has the same area.

  As a minor component other than zinc oxide, a dope component, or an impurity, a simple substance or compound of any element may be included.

(Preparation of metal oxide ultrafine particles)
As long as the metal oxide ultrafine particles according to the present invention form a colloidal solution with 100 parts by weight of the solvent and 1 to 10,000 parts by weight of the solvent, the ultrafine particles of commonly used ultrafine particles such as the gas phase method and the liquid phase method are used. What was synthesize | combined using the manufacturing method can be used. The production method is illustrated below.

  As a method for producing ultrafine particles, a method in which an aqueous raw material solution is present in a reverse micelle of a nonpolar organic solvent and crystal growth is performed (reverse micelle method), and a method in which a thermally decomposable raw material is grown in a liquid organic solvent at high temperature (Hot soap method), a method of growing a crystal by converting a raw material complex into a hydroxide complex by an acid-base reaction and then dehydrating the hydroxide complexes with each other (sol generation method), etc. If these methods are used, it is preferably used because the particle size control of the ultrafine particles obtained is easy.

  It is particularly preferable to use the metal oxide ultrafine particles obtained by the above-described metal oxide ultrafine particle colloidal solution method, without undergoing operations such as solvent conversion, and without causing unexpected aggregation. The colloidal solution according to the present invention can be easily obtained.

(solvent)
The solvent of the colloidal solution according to the present invention can maintain the dispersion state of the metal oxide ultrafine particles, does not react with the metal oxide ultrafine particles and the base material, and gives a viscosity that can be applied as a colloidal solution. Preference is given to those which can be easily removed completely by vacuum drying and which do not evaporate rapidly at room temperature and pressure. Therefore, water, alcohols, ketones, esters, carbonates, aldehydes, amines and amides are preferred. It is preferably at least one selected from the group consisting of alcohols, of which alcohols are the main components, and methanol is the main component.

(Carrier / Use)
Examples of the support according to the present invention include glass plates, plastic plates / films / sheets, rubber plates / films / sheets, ceramics / ceramics, etc. Among them, the present invention is basically an inorganic substance. From the viewpoint of utilizing the light resistance of the transparent conductive film, a glass plate is preferable, and from the viewpoint of utilizing the characteristics of the present invention that a highly transparent transparent conductive film is obtained by agglomeration at low temperature, a plastic plate, film, sheet, etc. Is preferred.

  Depending on such a carrier, a glass plate, a plastic plate or the like containing the transparent conductive film of the present invention is suitably used as a touch panel electrode, a photoelectric conversion substrate, a printable electronics substrate, or the like.

(Coating process)
The coating step according to the present invention is preferably carried out by one method selected from the group consisting of spin coating, dip coating, and spray coating, and from the viewpoint of forming a more uniform film, among these, spin coating is performed. Is preferred.

(Solvent removal step)
The solvent removal step according to the present invention is preferably performed in an apparatus such as a vacuum oven, a vacuum furnace, etc. The temperature is preferably room temperature to 300 ° C., the time is 0.1 to 10 hours, and the degree of vacuum is 0. Although it is carried out at 0.0001 atm to normal pressure, a high-quality transparent conductive film can be easily obtained in a short time. It is preferable to implement.

  Hereinafter, examples will be shown to further clarify the features of the present invention.

(Explanation of measurement)
The surface resistance was measured using a surface resistance value measuring device (manufactured by Mitsubishi Chemical Corporation).

  The pencil hardness was measured according to a standard method.

  The appearance including transparency was visually evaluated. The formed thin film was transparent with no coloration, and it was judged as good if there was no change except that the thin film was formed on the carrier.

  The thickness of the glass plate or the like was measured using a data base K405A and a displacement meter KG3001A (both manufactured by Anritsu). The thickness of the film was calculated by comparing the thickness before coating with the thickness after coating and heat treatment.

(Production Example 1) Preparation of 0.2 M zinc oxide ultrafine particle methanol colloid solution 11.2 g of potassium hydroxide (85%, manufactured by Nacalai Tesque) was dissolved in 250 mL of methanol (manufactured by Wako Pure Chemical Industries) at room temperature. A potassium hydroxide solution was prepared. Separately, 21.95 g (0.1 mol) of zinc acetate dihydrate (manufactured by Nacalai Tesque) was dissolved in 250 mL of methanol (manufactured by Wako Pure Chemical Industries) at room temperature in a separate container. A zinc solution was prepared.

  Next, the zinc acetate solution was quickly charged into the reactor containing the potassium hydroxide solution and stirred well at room temperature. After stirring for 3 hours, a part of the solution was taken, diluted with methanol, and UV spectrum and PL spectrum were measured to confirm that ultrafine zinc oxide particles were formed. In this manner, a methanol colloid solution of zinc acetate ultrafine particles (0.2 M, 500 mL, 0.1 mol as zinc oxide) was prepared.

Example 1 Preparation of Transparent Conductive Film First, isopropanol and hexane were mixed so that the volume ratio = isopropanol: hexane was 1: 5 to prepare a mixed solvent thereof.

  Next, 1 L of the mixed solvent was put into a 1 L flask, 100 mL of the colloidal solution prepared in Production Example 1 was added and stirred gently, and then left for a while to generate a white precipitate. That is, the isopropanol / hexane mixed solvent is a poor solvent of metal oxide ultrafine particles mainly composed of zinc produced in Production Example 1, and the colorless and transparent colloidal solution obtained in Production Example 1 was reprecipitated.

  Next, after removing 1 L of the supernatant liquid, 100 mL of the mixed solvent was further added to the remaining liquid containing the white precipitate, and the mixture was gently stirred and washed. Was removed. Methanol 40mL was added there, and it was set as the transparent colloid solution again.

  Subsequently, this solution was applied to a glass plate (manufactured by Corning, number 1737, 0.7 mm × 100 mm × 50 mm). A glass plate was attached to a spin coater (manufactured by Mikasa, 1H-DX2), and an appropriate amount of the solution was dropped, followed by treatment at 1000 rpm for 30 seconds.

  Finally, the coated glass plate was set in a vacuum oven (manufactured by ASONE, VO-400) at 60 ° C. and treated under reduced pressure corresponding to about 0.1 atm for 3 hours. In this way, a transparent conductive film was obtained. The obtained samples with a transparent conductive film were evaluated for conductivity, hardness and transparency.

(Examples 2 and 3)
Samples of Example 2 and Example 3 were prepared in the same manner except that the processing temperature in the vacuum oven of Example 1 was set to 150 ° C. (Example 2) and 270 ° C. (Example 3). Evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

Example 4
The sample of Example 4 was prepared in the same manner except that the processing temperature in the oven of Example 1 was 500 ° C., the oven was an electric furnace (KDF, S90), and normal pressure instead of reduced pressure. Evaluation was performed in the same manner as in 1. The results are shown in Table 1. In the sample of Example 4, although it was a transparent film, since the drying treatment temperature was high, the surface of the glass substrate was distorted.

（比較例１）
市販の酸化亜鉛（亜鉛華、ハクスイテック）１ｇに、メタノール１００ｍLを加えて攪拌したが、均一な溶液は得られなかった。

(Comparative Example 1)
Although 100 mL of methanol was added to 1 g of commercially available zinc oxide (Zinc Hana, Hakusuitec) and stirred, a uniform solution was not obtained.

Claims (7)

  A transparent conductive thin film obtained by applying a colloidal solution containing 100 parts by weight of metal oxide ultrafine particles having a number average particle diameter of 1 to 100 nm and 1 to 10,000 parts by weight of a solvent to a carrier and removing the solvent.   The transparent conductive thin film according to claim 1, wherein the metal oxide ultrafine particles contain zinc oxide as a main component.   The transparent conductive thin film according to claim 1, wherein the number average particle diameter is 1 to 10 nm.   The transparent conductive thin film according to claim 1, wherein the solvent is methanol.   The transparent conductive thin film according to claim 1, wherein the coating method is one selected from the group consisting of spin coating, dip coating, and spray coating.   The transparent conductive thin film according to any one of claims 1 to 5, wherein the solvent is reprecipitated with a poor solvent of metal oxide ultrafine particles.   The transparent conductive thin film according to claim 1, wherein the method for removing the solvent includes one or more steps selected from the group consisting of heating and vacuum drying.