JPH04237909A - Film forming method for transparent conductive film - Google Patents

Abstract

PURPOSE:To provide a transparent conductive film forming method which can improve optical characteristics and electrical characteristics especially of a transparent conductive film. CONSTITUTION:An ultravioletray-setting ink including indium-tin oxide fine particles is printed onto a resin film, subsequently de-solvent treatment is performed by drying, further a rolling process by a steel roller is applied, and is subjected to an ultravioletray-setting so as to form a transparent conductive film on the resin film.

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 made of indium tin oxide (hereinafter referred to as ITO), which is used as a transparent electrode or an antistatic film in various display devices.

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 equipment. In this type of display, transparent conductive films are used for the electrodes of display elements or circuit electrodes, and ITO transparent conductive films are particularly suitable for such transparent conductive films because of their low resistance and good transparency. suitable.

[0003] When forming an ITO transparent conductive film, ITO
There is a method of vapor depositing a transparent conductive film on a substrate by sputtering using particles as a target, but the equipment used in this method is expensive and is not suitable for film formation on a large deposition area. Further, there were problems such as the need to further perform pattern forming processing by etching after film formation. Therefore, a method of forming an ITO transparent conductive film by applying or printing ink using ITO fine particle powder has been developed. This method is a film forming method in which a paste is formed by mixing ITO fine particle powder with a resin and a solvent and uniformly dispersing it, and the paste is printed on a substrate and then dried (hereinafter referred to simply as the coating method). ).

0004

[Problems to be Solved by the Invention] However, since the conduction principle of the conductive film formed by the above-mentioned coating method is that the ITO fine particles approach each other, the electrical conductivity of the conductive film is lower than that of the above-mentioned vapor deposition method. This was a problem because the resistance value increased. In addition, as the thickness of the conductive film increases (1 to 3 μm), light scattering occurs due to unevenness on the surface of the conductive film and voids inside the conductive film, resulting in a decrease in the total light transmittance of the conductive film. There was a problem in that the haze value (a numerical value representing the degree of cloudiness) deteriorated. For this reason, conductive films formed by such coating methods have not been put into practical use except for relatively low-grade applications such as antistatic applications.

SUMMARY OF THE INVENTION In view of the above circumstances, it is an object of the present invention to provide a method for forming a transparent conductive film that can improve the optical properties and electrical properties of this type of transparent conductive film.

[0006]

[Means for Solving the Problems] The method for forming a transparent conductive film according to the present invention is to print an ultraviolet curable ink containing ITO fine particles on a resin film, perform a solvent removal treatment by drying, and then use a steel roll to remove the solvent. After the rolling process, an ultraviolet curing process is performed.

[0007] Furthermore, in the method of the present invention, the fine particles are
The average particle size is 0.1 μm or less.

Furthermore, in the method of the present invention, the volume content of the ITO fine particles in the solid component of the ultraviolet curable ink is 50 to 80%.

[0009]

[Operation] According to the present invention, first, an ink formed into a paste using ultrafine powder of ITO to form a transparent conductive film is rolled with a roll to densify the ITO fine particles. Generation of voids in the conductive film can be suppressed. Further, by performing rolling treatment using such rolls, the surface of the conductive film is smoothed, and as a result, both the optical properties and electrical properties of the transparent conductive film can be improved. By using an ultraviolet curable ink, the linear pressure of the roll during the rolling process can be reduced because the ultraviolet curable ink is not yet cured in the rolling process that is performed before the ink is cured by ultraviolet rays. Effective even if I set it relatively low.
It is possible to make the TO fine particles denser.

Further, according to the present invention, by setting the average particle size of the ITO fine particles to 0.1 μm or less, the diameter of the ITO fine particles is made to be less than the wavelength of visible light. It is possible to prevent optical properties from being impaired.

Furthermore, according to the present invention, the volume content of ITO particles in the solid component of the ultraviolet curable ink applied to the substrate is set to 50 to 80%, thereby improving the electrical properties and optical properties of the conductive film. It is possible to effectively and significantly improve the physical characteristics. In other words, enough resin is required to fill the voids between the ITO particles that are densified during the rolling process, but in this case, if the amount of ITO particles is too large, the resin may not be able to completely fill the voids. Therefore, voids are generated and the light transmittance and haze value are deteriorated, and the film becomes a so-called porous conductive film, which reduces its strength. On the other hand, if the amount of ITO particles is too small, the ITO
The resin present in excess of the particles prevents the ITO particles from approaching each other, and in this case, even if the optical properties of the conductive film are good, the electrical properties cannot be improved. Therefore, it is necessary to optimize the content ratio of the resin and ITO particles in the solid component of the ink, but in the method of the present invention, the volume content of the ITO particles is 50% as described above.
It is set to ~80%.

0012

[Embodiment] An embodiment of the method for forming a transparent conductive film according to the present invention will be described in detail below. First, ultrafine ITO particles having an average particle diameter of 0.03 μm are used as a component of the ultraviolet curable ink to be applied onto the resin film that is the substrate. Then, by mixing the ITO ultrafine particle powder with an ultraviolet curable resin consisting of an oligomer and a monomer, and performing a dispersion treatment by adding 20% of a solvent to the combined weight of both, an ultraviolet curable ink is produced. It is formed. In addition, this ultraviolet curable ink also contains a photoinitiator, a dispersant, etc. for promoting the polymerization reaction. The weight ratio of the photoinitiator (for example, trimethylolpropane triacrylate) and the molecular bond cleavage type initiator having an absorption region around 380 nm (for example, 1-hydroxycyclohexane) is set to about 60:35:5. The volume content of ITO particles in the solid components (resin component, ITO particles, additives, etc.) of such ultraviolet curable ink is preferably about 50 to 80%, but here it is 50%, 60% and 75%. Three types of ink were formed.

[0013] Next, each of the three types of ultraviolet curable inks described above was applied onto a PET film (100 μm thick and treated with a primer to improve adhesion) as a substrate resin film by screen printing. print on,
Thereafter, it is dried by infrared heating at a temperature of 80° C. for 30 minutes. By this drying, the solvent contained in the UV-curable ink is volatilized, but at this point, the other components of the UV-curable ink, such as oligomers and monomers, are in a liquid state, so no film is formed on the PET film. It has not hardened yet. In addition, in the case of any of the above three types of ultraviolet curable ink, the size is 12 cm x 15 cm.
The thickness of the coating film was approximately 3 μm.

Furthermore, the ink applied onto the substrate resin film by the above-mentioned screen printing method is rolled by a steel roll, and in this rolling process, two steel rolls each having a diameter of 150 mm and whose surfaces are plated with hard chrome are used. Using rolls, the processing speed is approximately 10%
The rotation speed of the steel roll was set to cm/sec. Further, when performing the rolling process using this steel roll, it is necessary and sufficient that the linear pressure of the steel roll is 100 kgf/cm or more. Here, if the linear pressure is too high, mechanical distortion will occur in the substrate resin film, but the present invention is set so that such distortion does not occur. In this embodiment, the above setting values are preferable depending on the type, material, thickness, etc. of the substrate resin film used. The upper limit of the linear pressure is preferably 1000 kgf/cm or less.

After the rolling treatment using the steel rolls, the ink of this example is subjected to ultraviolet curing treatment in an inert gas atmosphere such as argon. That is, for the ultraviolet curable ink applied on the substrate resin film,
70 seconds for 10 to 120 seconds at room temperature using a high-pressure mercury lamp.
Ultraviolet light with an illumination intensity of mW/cm2 is irradiated. The reason for using an inert gas as described above is that, for example, when UV treatment is performed in the air, the oxygen in the air consumes the radicals generated from the photoinitiator, which is the so-called oxygen inhibition effect. This is to prevent the polymerization reaction of the photoinitiator from being inhibited. Incidentally, the oxygen inhibition effect can be considerably improved by the selection of photoinitiators, photoinitiation aids (additives), etc.
Since a thin film of about several μm is susceptible to this inhibiting effect, curing in an inert gas is preferred.

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 significantly improved by first performing rolling treatment using the steel rolls described above. can be done. That is, the total light transmittance of the coating film before this rolling treatment was only about 70% at most, but after the rolling treatment it was 8.
The haze value of the conductive film was improved from about 20% to about 5%. The higher the linear pressure of the steel rolls in this rolling process, the greater the effect, but the processing temperature during the rolling process has little effect on optical properties. On the other hand, ultraviolet curable ink that is subjected to rolling treatment usually contains 0 to 20% solvent, but even after being printed and dried on the substrate resin film and then subjected to solvent removal treatment, liquid oligomers and It is not cured due to the presence of monomer. Therefore, since the rolling process is performed in such a state, the coating film can be easily and effectively rolled even if the linear pressure of the steel roll is set to a relatively low value, and the ITO particles can be easily densified. As a result, the surface of the conductive film is smoothed, and the optical properties can be improved in this respect as well. However, when the ink is formed using a general thermoplastic resin, the rolling process of the coating film requires 300 to 500 kgf/ There is an advantage that the linear pressure can be set low compared to the case where a high linear pressure of cm or more is required. By lowering the linear pressure in this way, it is possible to eliminate distortion of the substrate resin film.

[0017] Furthermore, the electrical properties of the ITO transparent conductive film can also be improved by the rolling treatment using such steel rolls. That is, the surface resistance of the coating film before this rolling treatment reached 40 to 80 kohms/square, but after the rolling treatment it decreased to 500 to 2,500 ohms (FIG. 1). Furthermore, the surface resistance as an electrical characteristic is once increased to 100-2 by ultraviolet curing treatment performed after the above-mentioned rolling treatment.
00 ohms/□, but then gradually increases and stabilizes at 300-500 ohms/□ (Figure 4).

Next, measurement results regarding the optical properties and electrical properties of the ITO transparent conductive film formed according to the present invention will be explained with reference to FIGS. 1 to 4. In addition, when performing these measurements, the average particle size of the ITO particles was measured using Quantasorb QS-10 manufactured by Counterchrome Co., Ltd. of the United States, and the total light transmittance and haze value of the transparent conductive film were measured using Sugawara along with the PET film that is the substrate. Using a direct reading haze computer HGM-ZDP manufactured by Shikenki Co., Ltd., the surface resistance was further measured by cutting out the above PET film into a size of 50 mm x 50 mm, and then using a Rorestar MCP-T4 manufactured by Mitsubishi Yuka Co., Ltd.
00, respectively.

FIGS. 1 and 2 show inks before ultraviolet curing treatment, which were formed by changing rolling treatment conditions (temperature, linear pressure) with steel rolls using ultraviolet curing ink containing 60% volume content of ITO particles. This figure shows the measurement results for the surface resistance value and optical properties (total light transmittance, haze value) of the ITO transparent conductive film. In addition, since the optical properties are hardly affected by the rolling treatment temperature, the temperature in Figure 2 is room temperature, 50°C.
Three types of temperature data of 80°C and 80°C are combined and expressed. According to this measurement result, the rolling treatment temperature is room temperature and 5
In the case of 0°C, the surface resistance value can be reduced to 500 ohm/□ or less by increasing the roll line pressure (Fig. 1), and
Good optical characteristics are obtained when the linear pressure is 100 kgf/cm or more. Figure 3 shows the linear pressure of 300 during the rolling process.
IT before UV curing treatment formed using three types of UV curing inks with volume content of ITO particles of 50%, 60% and 75% at kgf/cm and processing temperature of 50°C.
The measurement results of the optical properties and electrical properties of the O transparent conductive film are shown. As is clear from the figure, good film properties are obtained for all UV-curable inks, but the measurement results show that the volume content of ITO particles in the range of about 50% to 80% has optical properties and electrical properties. It is particularly preferable in terms of improving physical characteristics.

Here, the following Table 1 shows the relationship between the type of atmosphere and the curing action in the ultraviolet curing treatment, and as is clear from Table 1, the ink of this example was By using an active gas, UV curing treatment can be effectively performed. In Table 1, cured means that the coating film does not peel off when the coating film is rubbed 20 times with a cloth containing methyl ethyl ketone. Further, depending on the type of resin constituting the ink, it can be effectively cured even in an air atmosphere.

[Table 1]

Furthermore, FIG. 4 shows ITO that has been cured by ultraviolet light.
An example of the change over time of a transparent conductive film is shown, and in this example, 3
After UV curing treatment for 0 seconds, the surface resistance value decreases to about 100 ohms/□, but after that it gradually increases and becomes almost stable after several days. This is approximately 1/2 of the state of . In the case of any type of conductive film, the surface resistance value can be reduced to about 40 to 70% by the ultraviolet curing treatment. Incidentally, the optical properties hardly change even after ultraviolet curing treatment.

[0022]

As described above, according to the method of the present invention, both the optical properties and the electrical properties of this type of conductive film can be effectively improved, and in particular, the surface resistance can be improved to 500 ohm/□.
Hereinafter, an ITO transparent conductive film having excellent solvent resistance and a total light transmittance of 80% or more and a haze value of 10% or less could be formed.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the electrical properties of an ITO transparent conductive film before ultraviolet curing treatment and rolling treatment conditions formed by the method of the present invention.

FIG. 2 is a graph showing the relationship between the optical properties of an ITO transparent conductive film before ultraviolet curing treatment formed by the method of the present invention and rolling treatment conditions.

FIG. 3 is a graph showing the measurement results of the optical properties and electrical properties of an ITO transparent conductive film before ultraviolet curing treatment, which was formed using three types of ultraviolet curable inks according to the method of the present invention.

FIG. 4 is a graph showing an example of the change over time in the surface resistance of an ITO transparent conductive film formed by the method of the present invention.

Claims (3)

[Claims] 1. After printing an ultraviolet curable ink containing fine particles of indium tin oxide on a resin film, a solvent removal treatment is performed by drying, and further, after a rolling treatment with a steel roll, an ultraviolet curing treatment is applied to the resin. A method for forming a transparent conductive film on a film. 2. The method of forming a transparent conductive film according to claim 1, wherein the indium tin oxide fine particles have an average particle size of 0.1 micrometer or less. 3. The volume content of the indium tin oxide fine particles in the solid component of the ultraviolet curable ink is 50 to 50.
2. The method for forming a transparent conductive film according to claim 1, wherein the transparent conductive film is 80%.