JP3141527B2 - Method for manufacturing transparent conductive film - 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 producing a transparent conductive film most suitable for use in a transparent electrode or a transparent heater of a liquid crystal display panel or a plasma display panel.

[0002]

2. Description of the Related Art In general, a transparent conductive film is formed by depositing an oxide such as indium-tin oxide (ITO) or tin-antimony oxide (ATO) on a glass substrate by sputtering or CVD. After obtaining a transparent conductive ink containing a conductive ultra-fine powder having a particle size smaller than the wavelength of visible light on a substrate such as glass and drying,
It is obtained by firing at a high temperature of 00 ° C. or higher.

[0003]

However, in the case of the former method, an expensive apparatus is required, and it is difficult to obtain a transparent conductive film at low cost because of low productivity and low product separation. Was. In addition, in the case of the latter method, since voids remain between the conductive ultrafine particles, light is scattered and optical characteristics are deteriorated. Therefore, in order to fill the voids, a method of preparing a transparent conductive film by previously adding a glass forming component to the ink has been proposed. However, the glass forming component is interposed between the conductive ultrafine particles and the surface of the conductive film. There is a problem that causes the resistance to increase, so in the latter method,
It has been difficult to simultaneously satisfy the desired conditions for the optical characteristics and the resistance value of the transparent conductive film. Further, when the transparent conductive film produced by the latter method is left in air for several months, the resistance of the film increases because the oxide in the air is gradually converted into hydroxide by absorbing moisture in the air little by little. There was also a problem in terms of weather resistance.

The present invention has been made in view of such problems of the prior art, and an object of the present invention is to provide a transparent conductive material having low surface resistance, excellent optical characteristics and excellent weather resistance. It is intended to provide a method for producing a film.

[0005]

In order to achieve the above object, a transparent conductive film according to the present invention is formed by applying a transparent conductive ink on a glass substrate, drying and firing, and then forming a transparent conductive ink thereon. It is obtained by applying and drying a paste containing glass frit, and baking the paste at a temperature equal to or higher than the softening point of the glass frit.

As glass substrates, soda lime glass (transition point 660 ° C.), low alkali glass (transition point 670)
° C), non-alkali glass (transition point 730 ° C) and the like. As the transparent conductive ink, an ultrafine oxide powder having a particle size smaller than the wavelength of visible light, such as ITO, ATO or zinc oxide-aluminum oxide, is dispersed in a solvent or a resin is further dissolved and dispersed in the solvent. Is used. Oxide-based glass is used as the glass frit. When firing at a temperature higher than the softening point of the glass frit, the temperature is obtained by raising the temperature under vacuum.

[0007]

The transparent conductive ink is applied on a glass substrate, dried, and heated to about 400 ° C. or higher in the atmosphere to completely remove the resin or the solvent. Also, at this time, sintering proceeds at the contact portion between the conductive ultrafine particles at the same time, so that the strength of the formed conductive film is increased and the degree of adhesion to the glass substrate is also improved.

Next, a paste containing glass frit is applied on the conductive film and dried. The paste is obtained by dispersing a glass frit in a solvent containing a resin, and is applied using a screen printing method, a doctor blade or the like. After applying and drying the paste, it is first heated to 300 ° C. or more, preferably to about 400 ° C. in the atmosphere, and the resin is oxidized and burned to completely remove the resin. Then, an overcoat glass layer is formed on the transparent conductive film. As a glass used for the glass frit, a lead oxide-boron oxide-silicon oxide glass having a low melting point and weather resistance is more preferable. Further, the glass frit preferably has a softening point lower than the transition point of the glass substrate.

The reason why the temperature of the glass frit is raised to a temperature higher than the softening point is that when the temperature is raised to a temperature higher than the softening point, the glass frit fuses with each other and simultaneously the glass component permeates into the voids of the conductive film, and This is because the coated glass is densified and smoothed. When raising the temperature, in order to prevent distortion from occurring in the glass used as the substrate,
It is necessary to raise the temperature below the transition point of the glass substrate.

The thermal expansion coefficient of the overcoat glass is preferably equal to or slightly smaller than the thermal expansion coefficient of the glass substrate. If the thermal expansion coefficient of the overcoat glass is small, compressive stress remains in the overcoat glass and the strength of the overcoat glass increases.
On the other hand, when the thermal expansion coefficient of the overcoat glass is large, tensile stress remains in the overcoat glass and the overcoat glass is easily broken.

When the temperature is maintained at a temperature equal to or higher than the softening point of the glass frit, fine bubbles generated by the fusion of the glass frit escape, and the overcoat glass fills the gap between the conductive ultrafine particles, so that the gap becomes transparent. As a result, the optical characteristics of the transparent conductive film are significantly improved. However, if the heating is continued for an excessively long time, the reaction between the overcoat glass and the conductive ultrafine particles or the reaction between the overcoat glass and the substrate glass softens the substrate surface to which the transparent conductive film is attached, and the transparent conductive film is formed. Since it comes off from the substrate, the surface resistance of the transparent conductive film increases, which is not preferable. That is, when the overcoat glass is formed at about 550 ° C., if the heating is continued for 40 minutes or more, the surface resistance sharply increases. Therefore, the shorter the baking time of the overcoat glass, the better.

It is preferable to raise the temperature above the softening point of the glass frit in a vacuum, since air bubbles in the overcoat glass can be removed in a short time. In addition, since all the bubbles remaining in the overcoat glass disappear by switching from vacuum to an inert gas, no time is required for defoaming by using this method, and the overcoat glass is removed in a short time. Baking becomes possible. Further, by heating the glass frit to a temperature equal to or higher than the softening point, and fusing the glass frit together, and then firing under an inert gas atmosphere,
A transparent conductive film having a low surface resistance can be obtained.

Also, since the transparent conductive film is covered with the overcoat glass, the penetration of moisture in the air into the conductive film is prevented, so that the surface resistance does not change even if left in the air for a long time. The weather resistance is significantly improved.

[0014]

Example 1 An ITO transparent conductive ink (DX-101, manufactured by Tohoku Kako Co., Ltd.) in which ultrafine ITO powder was dispersed in a solvent was applied to a wire bar having a wire diameter of 0.1 mm and a size of 75 mm × 75 mm. The composition was applied on a soda lime glass substrate (thickness: 1 mm) and dried at 80 ° C. Next, on this, as shown in FIG.
(Dotite D-1230 (revised) manufactured by Fujikura Kasei Co., Ltd.) was screen-printed on a 200-mesh plate, leveled at room temperature for 10 minutes, and then dried at 120 ° C. for 20 minutes. This was baked at 550 ° C. for 20 minutes in the air and then cooled to form a transparent conductive film, and its surface resistance and optical characteristics were measured. The results are as shown in Table 1. On this conductive film, a glass paste GP (PLS-3 manufactured by NEC Corporation)
130, softening point 485 ° C) with a 200 mesh plate
As shown in the figure, screen printing, leveling at room temperature for 10 minutes, and drying at 120 ° C. for 10 minutes. This was heated to 580 ° C. in the atmosphere and held for 20 minutes, then switched to a nitrogen atmosphere, and fired for 20 minutes. After cooling, a portion including the silver electrode portion SP and the glass overcoat portion GP was cut out from the glass substrate P, and the resistance and the optical characteristics (total light transmittance, haze value) were measured. The results are as shown in the attached table.

Example 2 As a glass paste, a glass frit (GA-9 manufactured by NEC Corporation, softening point: 430 ° C.) dispersed in terpineol dissolved in ethyl cellulose was used.
The calcination was performed in the same manner as in Example 1 except that calcination was performed at 550 ° C. in the air for 20 minutes and in a nitrogen gas atmosphere for another 20 minutes.
An O film was obtained. The measured values are as shown in the attached table.

Example 3 An ITO film was obtained in the same manner as in Example 1 except that the ITO transparent conductive ink was applied on a soda lime glass plate P (FIG. 1) with a wire bar having a wire diameter of 0.15 mm. . The measured values are as shown in the attached table.

An ink (X-101, manufactured by Tohoku Kako Co., Ltd.) in which ultrafine ITO powder was dispersed in a solvent in which a resin was dissolved was applied to 27 inks.
An ITO film was obtained in the same manner as in Example 1 except that screen printing was performed using a 0-mesh plate. The measured values are as shown in the attached table.

Example 5 A glass paste GP (FIG. 1) was screen-printed and dried in the same manner as in Example 1, and then heated to 400.degree.
Then, the temperature was raised to 580 ° C. in vacuum, and after the temperature was raised, the atmosphere was switched to a nitrogen gas atmosphere and baked for 20 minutes, to thereby obtain an ITO film in the same manner as in Example 1. The obtained ITO
A voltage V was applied to the film as shown in FIG. 2 and the surface temperature was measured with a thermocouple TC to test the performance as a transparent heater. That is, an AC voltage V (60 Hz: 20 volts, 15 volts, 10 volts) was applied between the silver electrodes SP on both side ends of the overcoat ITO film GP, and the surface temperature was measured by a foil thermocouple TC. FIG. 3 shows the measurement results. As is clear from FIG. 3, even when the surface temperature of the ITO film is increased by adjusting the voltage applied to the ITO film, disconnection or sparking may occur. It can be seen that the surface resistance is stable without performing. FIG.
Is a method of forming a glass overcoat ITO film and an overcoat-free ITO film as in this embodiment in the air (20 to 25 ° C.,
(Relative humidity RH 50 to 70%) shows the change in the resistance value when the transparent conductive film according to the present invention is left in the air for 6 months or more. It does not change.

Comparative Example An ITO film was obtained in the same manner as in Example 1 except that the overcoat glass was baked in the air at 580 ° C. for 40 minutes and in a nitrogen gas atmosphere at 580 ° C. for 20 minutes. The measured values are as shown in the attached table.

The total light transmittance and the haze value were measured by a direct reading haze computer HGM-ZD manufactured by Suga Test Machine Co., Ltd.
P was measured together with the substrate, and the surface resistance was measured using a Loresta MCP-T400 manufactured by Mitsubishi Yuka Corporation.

[Appendix]

[0022]

As described above, according to the method of the present invention, a high-quality transparent conductive film having low resistance, excellent transparency and excellent weather resistance can be provided.

[Brief description of the drawings]

FIG. 1 is a plan view showing a process for producing a transparent conductive film according to the method of the present invention.

FIG. 2 is a plan view for explaining a method for measuring a relationship between an applied voltage and a surface temperature of a transparent conductive film manufactured by the method of the present invention.

FIG. 3 is a characteristic diagram showing a relationship between an applied voltage and a surface temperature of a transparent conductive film manufactured by the method of the present invention.

FIG. 4 is a diagram showing a change with time of the surface resistance of the ITO film.

[Explanation of symbols]

 P ITO Glass substrate coated with transparent conductive ink GP Glass paste (glass overcoat part) SP Silver paste (silver electrode part) TC Thermocouple

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Claims (3)

(57) [Claims] A transparent conductive ink in which ultrafine oxide powder is dispersed in a solvent is applied on a glass substrate, dried and baked to form a conductive film made of ultrafine oxide powder. A paste containing glass frit is applied to the conductive film, dried, and baked at a temperature equal to or higher than the softening point of the glass frit, so that gaps between the ultrafine oxide powders are removed.
Conductive film filled with glass component of lath frit and on the conductive film
Layer composed of overcoat glass layer formed on
A method for manufacturing a transparent conductive film which is capable of obtaining a film . 2. The method according to claim 1, wherein the glass frit is an oxide glass. 3. The method for producing a transparent conductive film according to claim 1, wherein when firing at a temperature higher than the softening point of the glass frit, the temperature is raised to a temperature higher than the softening point of the glass frit under vacuum.