JP3072862B2 - Method for forming 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 forming a transparent conductive film, particularly indium tin oxide (hereinafter referred to as ITO), used for a transparent electrode or an antistatic film in various display devices and the like.

[0002]

2. Description of the Related Art In recent years, flat display devices such as liquid crystal displays and electroluminescent displays have been widely used in information display devices. In this type of display, a transparent conductive film is used for an electrode of a display element or a circuit electrode. In particular, an ITO transparent conductive film is used as the transparent conductive film because of its low resistance and good transparency. It is suitable.

When forming an ITO transparent conductive film, ITO
There is a method in which a transparent conductive film is deposited on a substrate by performing sputtering using particles as a target. However, an apparatus used in this method is expensive and is not suitable for forming a film with a large deposition area. In addition, there is a problem that it is necessary to perform pattern forming by etching after film formation. Therefore, a method of forming an ITO transparent conductive film by applying or printing an ink using ITO fine powder has been developed. This method is a film formation method in which a paste is formed by mixing and uniformly dispersing the ITO fine particle powder with a resin and a solvent, the paste is printed on a substrate, and then dried (hereinafter simply referred to as a coating method). ).

[0004]

However, the conductive principle of the conductive film formed by the above-described coating method is based on the approaching action of the ITO fine particles. This was problematic because the resistance value would increase. In addition, the thickness of the conductive film increases (1 to 3 μm), and light scattering occurs due to irregularities on the surface of the conductive film and voids (voids) in the conductive film. There is a problem that the haze value (a numerical value indicating the degree of haze) is deteriorated. For this reason, a conductive film formed by such a coating method has not been put to practical use except for applications of relatively low grade, such as for antistatic purposes.

[0005] In view of such circumstances, an object of the present invention is to provide a method for forming a transparent conductive film capable of improving the optical and electrical characteristics of such a transparent conductive film.

[0006]

According to the method of forming a transparent conductive film of the present invention, an electron beam-curable ink containing ITO fine particles is printed on a resin film, then subjected to a solvent removal treatment by drying, and further subjected to a steel roll. Is performed by performing an electron beam hardening process after the rolling process.

Further, in the method of the present invention, the volume content of the ITO fine particles in the solid component of the electron beam-curable ink is 50 to 80%.

[0008]

According to the present invention, first, an ITO fine particle powder on which a transparent conductive film is to be formed is rolled by a roll of ink formed into a paste, whereby the ITO fine particles are densified. Generation of voids in the conductive film can be suppressed. Further, by performing the rolling treatment using such rolls, the surface of the conductive film is smoothed, and as a result, both the optical characteristics and the electrical characteristics of the transparent conductive film can be improved. By using the electron beam-curable ink, in the above-described rolling process performed before the ink is cured by an electron beam, the rolls during the rolling process are in a state where the electron beam-curable ink is not yet cured. Is effective even if the line pressure is set relatively low.
Densification of the TO fine particles can be achieved.

Further, according to the present invention, by setting the volume content of ITO particles in the solid component of the electron beam-curable ink applied to the substrate particularly to 50 to 80%, the electrical characteristics of the conductive film and Optical characteristics can be effectively and greatly improved. That is, a resin is required to completely fill the voids between the ITO particles to be densified when performing the rolling process. In this case, if the amount of the ITO particles is too large, the resin may completely fill the voids. Therefore, voids are generated, so that the light transmittance and the haze value are deteriorated. In addition, a so-called porous conductive film is formed and the strength is reduced. On the other hand, if the amount of ITO particles is too small,
The resin present in excess of the particles prevents the ITO particles from approaching each other, and in this case, the electrical characteristics cannot be improved even if the optical characteristics of the conductive film are good. Therefore, it is necessary to optimize the content ratio between the resin and the ITO particles in the solid component of the ink. In the method of the present invention, the volume content of the ITO particles is 50% as described above.
It is set to ~ 80%.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the method for forming a transparent conductive film according to the present invention will be described below in detail. First, the ultrafine powder of ITO, which is a component of the electron beam-curable ink to be applied on the resin film as the substrate, has an average particle diameter of 0.03 μm. Then, the ITO ultrafine particle powder is mixed with an electron beam-curable resin composed of an oligomer and a monomer, and a dispersion treatment is performed by adding a solvent of 20% based on the total weight of both, thereby obtaining an electron beam-curable resin. An ink is formed.

The weight ratio of the bifunctional urethane acrylate or bifunctional epoxy acrylate as the oligomer and the trifunctional acrylate (for example, trimethylolpropane triacrylate) as the monomer is set to about 60:40. The volume content of ITO particles in the solid components (resin component, ITO particles, additives, etc.) of such an electron beam-curable ink is preferably about 50 to 80%, but here, the urethane acrylate-based ink is 50%. , 60% and 75%, and 60% for the epoxy acrylate type, to form a total of four types of inks.

Next, each of the above-mentioned four types of electron beam-curable inks is subjected to a screen printing method to form a PET film of a substrate resin film (thickness: 100 μm, which has been subjected to a primer treatment to improve adhesion). Print on top,
Thereafter, drying is performed at a temperature of 80 ° C. for 30 minutes by infrared heating. By this drying, the solvent contained in the electron beam-curable ink is volatilized. At this point, since the other components of the electron beam-curable ink, the oligomer and the monomer, are in a liquid state, they are left on the PET film. The film is not yet cured. In addition, in each case of the above four types of electron beam-curable inks, 12 cm × 15 cm
The printing was performed after forming a printing area having a width as large as about 3 μm in the urethane acrylate ink and about 5 μm in the epoxy acrylate ink. The difference in the thickness of the coating film is caused by the difference in the viscosity of the ink used.

Further, the ink applied on the substrate resin film by the screen printing method is rolled by a steel roll. In this rolling process, two steel rolls 150 mm in diameter are hard chrome-plated on the surface. And the processing speed is about 10
The rotation speed of the steel roll was set so as to be cm / sec. In the case of performing the rolling treatment using the steel roll, it is necessary and sufficient if the linear pressure of the steel roll is 200 kgf / cm or more. Here, if the line pressure is too high, mechanical distortion occurs in the substrate resin film, but the present invention is set so as not to cause such distortion. According to the type, material and thickness of the substrate resin film to be used, the above-mentioned set value is preferable in this embodiment. And the upper limit of the linear pressure is 1000 kgf / cm
The following is preferred.

After the rolling treatment by the steel roll, the ink of this embodiment is subjected to an electron beam curing treatment in an atmosphere of an inert gas such as argon. That is, for the electron beam curable ink applied on the substrate resin film,
Irradiation dose of 10-40Mr at 175kV of electron beam acceleration voltage
The electron beam of ad is irradiated. Here, the inert gas is used as described above, for example, when the electron beam treatment is performed in the air, the oxygen in the air consumes the generated radicals, that is, the polymerization reaction is performed by the so-called oxygen inhibiting action. This is to prevent being hindered.

Since the method for forming a transparent conductive film according to the present invention is configured as described above, the optical properties of the formed ITO transparent conductive film are remarkably improved by first performing a rolling process using the steel roll. Can be done. That is, the total light transmittance of the coating film before the rolling treatment was at most only about 60%, but reached about 80% after the rolling treatment, and the haze value of the conductive film was 20%.
Was improved to about 10%. The greater the linear pressure of the steel roll in the rolling process, the greater the effect.

On the other hand, the electron beam-curable ink to be subjected to the rolling treatment usually contains 0 to 20% of a solvent. However, even after printing and drying on the substrate resin film, the solvent is removed. Not cured due to the presence of liquid oligomers and monomers. Therefore, since the rolling process is performed in such a state, even if the linear pressure of the steel roll is set relatively low, the coating film can be easily and effectively rolled, and the ITO film can be rolled.
The particles can be easily densified. The surface of the conductive film is thereby smoothed, and the optical characteristics can be improved also in this respect. However, when an ink is formed using a general thermoplastic resin, 500 k
There is an advantage that the line pressure can be set lower than when a high line pressure of gf / cm or more is required. By reducing the linear pressure in this way, it is possible to eliminate the occurrence of distortion of the substrate resin film.

Further, the electrical characteristics of the ITO transparent conductive film can be improved by the rolling treatment using the steel roll. That is, the surface resistance of the coating film reaches up to 10 to 20 kOhm / square when cured by electron beam without performing the rolling treatment, but is 200 to 60 kΩ when cured by electron beam after the rolling treatment.
0 ohm / □.

Next, the results of measuring the optical and electrical characteristics of the ITO transparent conductive film formed according to the present invention will be described with reference to FIGS. In performing these measurements, the average particle size of the ITO particles was measured by Quantasorb QS-10 manufactured by US Counter Chrome, and the total light transmittance and haze value of the transparent conductive film were measured together with the PET film as the substrate. The surface resistance was further cut out by a direct reading haze computer HGM-ZDP manufactured by Testing Machine Co., Ltd., and the PET film was cut out to a size of 50 mm × 50 mm.
00 respectively.

FIG. 1 shows that the volume content of ITO particles was 60%.
Surface resistance and optical characteristics of ITO transparent conductive film after electron beam curing treatment formed by changing roll line pressure by steel roll using urethane acrylate-based electron beam curing type ink Ratio, haze value). According to the measurement results, a surface resistance of 500 ohm / □ or less and good optical characteristics were obtained at a roll line pressure of 200 kgf / cm or more.

FIG. 2 shows a linear pressure of 400 kgf /
cm after the electron beam curing treatment formed using three types of urethane acrylate-based electron beam curable inks having a volume content of ITO particles of 50%, 60% and 75% in cm.
The measurement results of the optical and electrical characteristics of the transparent conductive film are shown. As is clear from the figure, good film properties are obtained in any of the electron beam-curable inks. From this measurement result, the volume content of ITO particles is in the range of about 50 to 80%, and the optical properties and It is particularly preferable for improving electrical characteristics.

FIGS. 3 and 4 show the measurement results of the surface resistance and the optical characteristics (total light transmittance, haze value) of the ITO transparent conductive film when the irradiation dose of the electron beam was changed. It is shown for each of the epoxy acrylate-based inks. As is clear from FIGS. 3 and 4, the physical properties of the ITO film are not significantly affected by the irradiation amount of the electron beam, and 10 Mrad or more is sufficient. The film cured with an electron beam of 10 Mrad or more did not peel even when the coating film was rubbed 20 times with a cloth impregnated with methyl ethyl ketone. According to FIGS. 3 and 4, it can be seen that the urethane acrylate-based ink has excellent optical properties, while the epoxy acrylate-based ink has excellent electrical properties. By appropriately adjusting the mixing ratio of the epoxy acrylate-based ink, a transparent conductive film can be formed to have desired optical and electrical characteristics.

FIG. 5 shows a urethane acrylate-based and epoxy acrylate-based ITO cured by electron beam.
An example of the change with time of the transparent conductive film is shown.
Curing with an electron dose of 0 Mrad reduces the surface resistance to less than 400 ohms / □ in the case of urethane acrylates, but then increases gradually and becomes almost stable after more than 10 days, and in the case of epoxy acrylates, After curing, there is almost no change in surface resistance.

[0023]

As described above, according to the method of the present invention, by selecting an electron beam-curable resin, the electrical and optical characteristics of this kind of conductive film can be appropriately adjusted, and in particular, the surface resistance is 500 ohms. / □ or less, or total light transmittance about 80
% And excellent in solvent resistance with a haze value of 10% or less
An O transparent conductive film can be formed.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the electrical and optical properties of a urethane acrylate-based ITO transparent conductive film formed by the method of the present invention and the roll line pressure.

FIG. 2 is a graph showing the measurement results of the optical and electrical properties of an ITO transparent conductive film formed using three types of urethane acrylate-based electron beam curable inks according to the method of the present invention.

FIG. 3 is a graph showing the relationship between the optical and electrical properties of a urethane acrylate-based ITO transparent conductive film formed by the method of the present invention and the amount of electron beam irradiation.

FIG. 4 is a graph showing the relationship between the optical and electrical properties of an epoxy acrylate-based ITO transparent conductive film formed by the method of the present invention and the amount of electron beam irradiation.

FIG. 5 is a graph showing an example of a change with time of the surface resistance of an ITO transparent conductive film formed by the method of the present invention.

Continuation of the front page (56) References JP-A-4-237909 (JP, A) JP-A-4-237908 (JP, A) JP-A-60-219270 (JP, A) JP-A-62-291811 (JP) , A) JP-A-1-249436 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01B 13/00 H01B 5/14

Claims (2)

(57) [Claims] 1. An electron beam-curable ink containing fine particles of indium tin oxide is printed on a resin film, subjected to a desolvation treatment by drying, further rolled by a steel roll, and then subjected to an electron beam curing treatment. A method of forming a transparent conductive film on the resin film. 2. The volume fraction of the indium tin oxide fine particles in the solid component of the electron beam-curable ink is 50 to 8%.
The method for forming a transparent conductive film according to claim 1, wherein the content is 0%.