JP3261720B2 - Method for reducing resistance of ITO powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reducing the resistance of an ITO powder used for forming a low-resistance transparent conductive film such as a transparent electrode or an antistatic film by coating.

[0002]

2. Description of the Related Art Recently, flat displays such as liquid crystal displays and electroluminescence displays have been widely used for information display devices. In these displays, a transparent conductive film is used for an electrode of a display element or an electrode of a driving circuit, and an ITO film is suitable for this film because of its small resistance and excellent transparency. As a method of forming the ITO film, there is a method of forming a film on a substrate by sputtering an ITO target. However, this method is expensive, and is not suitable for processing a large area. There is a problem that pattern processing by etching is required. Therefore, recently, a method of forming an ITO film by applying an ITO paste is being developed. In this method, an ITO film is formed by mixing an ITO powder, a resin, and a solvent to form a paste, printing the paste on a base material, and drying the paste. The ITO powder used in this method is not only easy to uniformly disperse in a resin, but also
In order to lower the resistance value of the O film, it is necessary that the resistance of the powder itself be low.

[0003]

However, although the conventional ITO powder for coating is satisfactory in that it is an ultra-fine powder and has no agglomerates and good dispersibility, the resistance value of the powder itself is high. Have a problem. For this reason, conventionally, a high-resistance ITO powder has been subjected to a deoxidation treatment to generate oxygen lattice defects, thereby reducing the resistance of the powder. As a conventionally known low resistance treatment method, a method of immersing ITO powder in a high-boiling organic solvent such as octanol or butanol and heating in an inert gas atmosphere to perform a deoxygenation treatment is used to reduce the resistance. It is known, however, that this method has a disadvantage that when the organic solvent evaporates, agglomeration of the ITO powder occurs, and it is difficult to completely eliminate the agglomerate even if the powder is pulverized. A method is also known in which the ITO powder is heated in a reducing gas atmosphere such as a hydrogen atmosphere or a carbon monoxide atmosphere to perform a deoxygenation treatment to reduce the resistance of the ITO powder. However, since hydrogen has a strong reducing property, there is a problem that the reduction proceeds excessively due to a slight temperature rise, so that the color of the ITO powder becomes dark, or metal indium or metal tin is deposited. When a film is formed using such ITO powder, the transparency of the film is inevitably reduced. When processing is performed in such a hydrogen atmosphere, strict temperature control is required. In addition, there is a problem that carbon monoxide is harmful to the human body and difficult to handle. Accordingly, an object of the present invention is to provide a processing method for stably reducing the resistance without causing aggregation of the ITO powder.

[0004]

According to the present invention, an ITO is provided.
The powder was treated with 5-50 mg / Nl of hydrazine hydrate gas.
200-450 ° C in an inert gas atmosphere containing a concentration
And a method for lowering the resistance of the ITO powder, characterized in that the heating is carried out at a temperature of 1.

[0005] In ITO powder present invention, ITO powder to be treated is of the coating, for example, in order to improve the dispersibility of the resin, the average particle diameter is in the range of 0.1μm Very fine ones are used. The composition varies depending on the use and the like, but generally, the indium content is 77 to 81% by weight.
And the tin content is in the range of 1-5% by weight. Also this I
TO powder usually has a high resistance value of 10 Ω.
・ It is in the range of cm or more.

[0006] In deoxidation invention, by heating in an inert gas atmosphere containing the above-described ITO powder hydrazine hydrate gas, oxygen is carried out resulting lattice defects of oxygen is, as a result The resistance of the powder is reduced.

The hydrazine hydride gas used in the above treatment exhibits a deoxidizing effect by reduction. The concentration of the hydrazine hydrate gas in the inert gas is 5 to 50 mg / Nl.
It is preferable to set the range as follows. If it is less than 5 mg / Nl, it takes more time than necessary for deoxidation, and the production efficiency is reduced. If it exceeds 50 mg / Nl, the rate of deoxygenation increases, and it becomes difficult to control the end point. The inert gas is used as a carrier gas for the hydrazine hydrate gas, and any inert gas such as a nitrogen gas and an argon gas can be used.

In the present invention, the heating in the hydrazine hydride gas-containing inert gas atmosphere is usually 200 to
It is desirable to carry out at 450 ° C., especially at 250 to 350 ° C. If the temperature is lower than 200 ° C., it is difficult to sufficiently perform deoxygenation.
It is difficult to reduce the resistance of the powder. Also 45
When the temperature exceeds 0 ° C., aggregation and sintering of the ITO powder occur, which is not desirable.

[0009] The treatment of the ITO powder by such heating is preferably carried out with stirring so that the deoxidization of the powder proceeds uniformly. Further, by this heating, the color of the ITO powder changes from yellow to yellow-green and blue-gray. ITO
The end point of the treatment is considered when the powder turns blue-grey. Even if the treatment is performed for a longer time, the resistance value of the ITO powder does not decrease, and conversely, metal indium may be deposited.

[0010] By the above-described treatment, the specific resistance at the time of pressurization is reduced to, for example, 0.01 to 0.50 Ω · cm without generating agglomerates while maintaining the ultrafine state of the ITO powder. An ITO powder is obtained. This powder is used for forming a low-resistance ITO film by a coating means known per se.

Examples 1 to 4 ITO powder (average particle size: 0.050 μm) having no agglomerates and having good dispersibility prepared by the alkoxide method was prepared by
The mixture was placed in a 1-liter separable flask, and subjected to deoxygenation treatment with nitrogen gas containing hydrazine hydrate gas while heating and stirring with a mantle heater. Table 1 shows the processing conditions at this time. I before and after processing
Table 2 shows the Sn content, the average particle size, the specific resistance under pressure, and the presence or absence of aggregates of the TO powder. The average particle size of the ITO powder was measured by Quantaso manufactured by Quanta-chrome, USA.
It was measured using rb QS-10. The pressurization specific resistance, the pressure in the cross-sectional area of the ITO powder 3g 100kgf / cm ^{2 2}
This is the value when pressure is applied to a column of cm ² . Further, the presence or absence of aggregates was determined by observing three visual fields at 10,000 times using an electron microscope and confirming the presence or absence of aggregates of 0.2 μm or more.

Comparative Examples 1 and 2 The same procedure as in Example 1 was carried out except that the heating temperature was changed among the processing conditions. Table 1 shows the processing conditions at this time. The obtained ITO powder was measured in the same manner as in Example 1. Table 2 shows the results.

[0013]

[Table 1]

[0014]

[Table 2]

[0015]

According to the processing method of the present invention, it is possible to extremely reduce the resistance of the ITO powder without agglomerating the powder. I reduced in resistance by the treatment of the present invention
The TO powder is used for forming a low-resistance ITO film by coating.

Claims (1)

(57) [Claims] 1. An ITO powder and a hydrazine hydrate gas
A method for lowering resistance of ITO powder, comprising heating at a temperature of 200 to 450 ° C. in an inert gas atmosphere containing 5 to 50 mg / Nl .