JPH0737494A - Method for forming field sheilding transparent conductive film - Google Patents

Abstract

PURPOSE:To obtain a method for forming a transparent conductive film, which is appropriate for the field shielding effect and for preventing the reflection, on a CRT front glass by means by of a ink applying method. CONSTITUTION:A CRT front glass is coated with the field shielding liquid, which is obtained by dispersing ITO powder of mean grain diameter of 50nm or less and alkylsilicate in a polar solvent including N-methyl-2 pyrrolydinone, and dried, Thereafter, it is over-coated with a solution including alkylsilicate, and burned in the atmosphere at 200-350C or in inert gas atmosphere and reducing gas atmosphere at 200-450C.

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 for imparting an electric field shield effect to a front glass of a cathode ray tube such as a display of an office automation equipment or a cathode ray tube of a television.

[0002]

2. Description of the Related Art On the surface of a television cathode ray tube,
It has been known for a long time that antistatic treatment is performed because dust due to electrostatic charging is apt to adhere, and when a human body comes into contact with it, it discharges and receives an electric shock. The problems associated with electrostatic charging are solved by attaching a conductive film to the glass surface of a cathode ray tube (hereinafter referred to as CRT) and grounding it.
A surface resistance of about 10 ⁸ Ω / □ is required. The conductive film here should not impair the transparency and resolution of the screen. That is, it is desirable that the amount of diffuse transmission of light passing through the film is as small as possible, and for a practical CRT, the haze value defined by the percentage of the diffuse transmission light with respect to the direct transmission light is as small as approximately 5% or less. It is required to be a value. In order to reduce the haze, it is necessary that the light scattering source in the film is small and the film thickness is as thin as possible. Also, to make the image easier to see, a CRT
It is desirable to apply antiglare treatment to the surface to suppress reflection on the screen.

With the increase in size of TVs, an increasingly large electromagnetic field tends to leak to the surroundings.
Similar to antistatic, it can be prevented by forming a conductive transparent film on the surface of the CRT glass. However, there is a large difference in the level of conductivity required for the film between the electric field shield and the antistatic property, and the surface resistance is 10 ⁸ Ω for the antistatic property.
Although about / □ is sufficient, at least 10 ⁵ Ω / □ or less, preferably 10 ³ Ω / □ to prevent a leakage electric field.
□ It is necessary to form a low resistance transparent film on the table.

[0004]

In order to meet the above requirements, several proposals have been made in the past, but among them, the present inventors have found that it is possible to realize low surface resistance at low cost. Silicate and N-methyl-2
-In a polar solvent containing pyrrolidinone as a main component, 1 to 1 tin is added.
A patent application was filed for a treatment liquid for electric field shielding in which 1 to 15 wt% of indium tin oxide powder containing 10 wt% and having an average particle size of 50 nm or less was dispersed (Japanese Patent Application No. 4-307189).
issue). After applying this treatment liquid to the CRT front glass and drying it,
By firing at a temperature of 200 ° C. or less, 10 ³ to 1
A surface resistance value of 0 ⁴ Ω / □ is obtained. This ink coating method is much simpler and has a lower manufacturing cost than other transparent conductive film forming methods such as vacuum deposition and sputtering, and C
This is an extremely advantageous method for dealing with the electric field shield of RT. However, in the surface resistance value obtained,
It has a drawback that it is slightly inferior to the vapor deposition method and the sputtering method.

The present invention, when applied to a CRT front glass, has a sufficiently low surface resistance value for the electric field shielding effect,
Another object of the present invention is to provide a method for forming a transparent conductive film having a low haze value and a high refractive index suitable for antireflection.

[0006]

As a result of various studies for achieving the above-mentioned object, the present invention has been accomplished by paying attention to the firing temperature. That is, in the present invention, an indium tin oxide powder having an average particle size of 50 nm or less and an alkyl silicate are mixed with N
-A treatment liquid for electric field shielding dispersed in a polar solvent containing methyl-2pyrrolidinone is applied to a CRT front glass and dried, and then a solution containing an alkyl silicate is overcoated, and then a temperature range of 200 to 350 ° C in the atmosphere. Or by firing in an inert gas or reducing gas atmosphere
It is characterized by firing in a temperature range of 450 ° C.

[0007]

In the present invention, the ITO powder has an average particle size of 50.
When the ITO powder is dispersed in the film, it is below nm.
Most of the scattering of light passing through the membrane is the so-called Rayle.
This is because it becomes a mode of high scattering or Mie scattering, the transparency of the object becomes extremely high, and the haze value falls to 3% or less of the practical level. The ITO powder is preferably contained in the electric field shield treatment liquid in an amount of 1 to 15% by weight.

The alkyl silicate is used to bond and fix the ITO powder on the glass surface. As such an alkyl silicate, for example, an orthoalkyl silicate or a hydrolyzate thereof is subjected to dehydration polycondensation to some extent. The advanced form is used. Examples of orthoalkyl silicates include orthomethyl silicate Si (OCH ₃ ) ₄ and orthoethyl silicate S.
i (OC ₂ H ₅ ) ₄ , orthopropyl silicate Si
(OC ₃ H ₇ ) ₄ , orthobutyl silicate Si (OC
₄ H ₉ ) ₄ or the like can be used, and an orthoalkyl silicate having two or more kinds of alkyl groups in the same molecule may be used. Further, two or more kinds of alkyl orthosilicates may be mixed and used. Orthoalkyl silicates are easily hydrolyzed in the presence of water and the alkoxyl groups become hydroxyl groups, and water is removed from the hydroxyl groups to cause dehydration polycondensation and polymerize. Those that are exposed can also be used as the alkyl silicate. In short, dehydration polycondensation progresses by heating, and finally in the form of silicate I
It suffices that it has the ability to fix the TO powder on the glass surface. In order to proceed the dehydration polycondensation reaction, a small amount of water or an acid such as hydrochloric acid or sulfuric acid as a reaction accelerator is preferably allowed to coexist. Alkyl silicate is 0.1 to 6 in the processing liquid.
It is preferable to contain it by weight%.

Any polar solvent may be used as long as it has an appropriate boiling point below the firing temperature and can disperse ITO particles efficiently. For example, N-methyl-2-pyrrolidinone and ethanol, isopropyl alcohol or dimethylformamide may be used. A preferable example is a mixed solution of (DMF), dimethylacetamide, methyl cellosolve, diacetone alcohol, acetone, tetrahydroxyfuran and the like. N-methyl-2-pyrrolidinone is ITO
It is used to promote the dispersion of the powder and is preferably contained in the electric field shield treatment liquid in an amount of 1 to 20% by weight.

In the present invention, the firing temperature is set to 200 in the atmosphere.
The temperature of ˜350 ° C. causes the shrinkage of the transparent conductive film formed as the polycondensation polymerization of the alkyl silicate or the drying is completed, so that the packing density of the ITO fine particles increases and the conductive path density increases accordingly. , Because the surface resistance value decreases. Further, the contact state between the ITO fine particles is also improved with the evaporation of the solvent component, and the change of the surface resistance value with time is also reduced. If the firing temperature is less than 200 ° C, the surface resistance value does not improve, and if it exceeds 350 ° C, the ITO powder that has already undergone a reduction treatment to introduce oxygen vacancies is oxidized and the conductivity decreases, so the surface resistance value increases. Is.

Further, the firing temperature is set to 200 to 450 ° C. in an inert gas or reducing gas atmosphere at 200 ° C.
If it is less than 450 ° C., the surface resistance will not be improved, and if it exceeds 450 ° C., it will be higher than the glass softening point of CRT.

In the present invention, a solution containing an alkyl silicate is overcoated to form a two-layer structure of an ITO film containing ITO fine particles and a silicate film on the CRT surface because of the difference in refractive index between the ITO film and the silicate film. , CR
This is because the reflectance of the T surface can be reduced. By firing at a higher temperature, the packing density of the ITO fine particles in the ITO film increases, so that the refractive index of the ITO film increases and the antireflection effect can be enhanced.

Further, since the silicate film is formed on the ITO film, the polycondensation reaction and the drying of the gel are completed by firing at a high temperature, which increases the hardness of the CRT surface.

[0014]

EXAMPLES Examples of the present invention will be shown below. The film thickness and the refractive index of the formed film were measured by an ellipsometer manufactured by Mizojiri Optical Co., Ltd. Surface resistance is Mitsubishi Yuka Co., Ltd. surface resistance meter MC
It measured using P-T200. The haze value and the transmittance were measured using a haze meter HR-200 manufactured by Murakami Color Research Laboratory.

Example 1 1 ITO ultrafine powder (ITO-UFP) manufactured by Sumitomo Metal Mining Co., Ltd. having a specific surface area of 27.5 cm ² and an average particle size of 25.3 nm (evaluated by a transmission electron microscope) was used.
5 g, N-methyl-2-pyrrolidone (NMP) 20
g, N, N-dimethylformamide (DMF) 7
g and 4-hydroxy-4-methyl-2-pentanone (diacetone alcohol) 70 g were mixed to prepare an ITO dispersion solution. On the other hand, while stirring a mixed solution of 1.5 g of ethyl silicate 40 manufactured by Tama Chemical Industry Co., Ltd. having an average degree of polymerization of 4 to 5, 16 g of diacetone alcohol, and 1.5 g of distilled water, 3 g of 5% hydrochloric acid aqueous solution, diacetone. A mixed solution of 2 g of alcohol and 2.4 g of distilled water was added dropwise to prepare an ethyl silicate solution. Two liquids of the ITO separation solution and the ethyl silicate solution were mixed and rotated at 150 rpm, and the solution was dropped from a beaker onto a plate glass of 200 × 200 × 3 mm.

After coating the first layer film on the plate glass, it is dried for 2 minutes as it is, and then only the ethyl silicate solution used for the first layer is used as an overcoat solution.
It dripped from the beaker on the plate glass rotated at 0 rpm.
Then, each was baked in the air at a baking temperature of 250 ° C. for 30 minutes to form a two-layer film. The evaluation results are shown in Table 1.

(Example 2) A film was formed in the same manner as in Example 1 except that the baking conditions were 300 ° C / 30 minutes.
Characterized. The evaluation results are shown in Table 1. (Example 3) Except that the firing conditions were 350 ° C./30 minutes,
A film was formed and the characteristics were evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1. (Example 4) The firing conditions were 450 ° C / 30 in a nitrogen atmosphere.
A film was formed and the characteristics were evaluated in the same manner as in Example 1 except that the amount was changed. The evaluation results are shown in Table 1. (Example 5) As a firing condition, in a 10% hydrogen-mixed argon gas atmosphere, the material was gradually heated and first held at 250 ° C for 30 minutes, and then held at 450 ° C for 30 minutes and gradually cooled. A film was formed in the same manner as in Example 1 except for the above, and characteristics were evaluated. The evaluation results are shown in Table 1.

(Comparative Example 1) The firing conditions were 80 ° C. in the air /
A film was formed and the characteristics were evaluated in the same manner as in Example 1 except that the time was 30 minutes. The evaluation results are shown in Table 1. (Comparative Example 2) A film was formed and the characteristics were evaluated in the same manner as in Example 1 except that the firing conditions were 160 ° C./30 minutes in the atmosphere. The evaluation results are shown in Table 1. (Comparative Example 3) A film was formed and the characteristics were evaluated in the same manner as in Example 1 except that the firing conditions were 400 ° C / 30 minutes in the atmosphere. The evaluation results are shown in Table 1. (Comparative Example 4) A film was formed and the characteristics were evaluated in the same manner as in Example 1 except that the firing conditions were 450 ° C / 30 minutes in the atmosphere. The evaluation results are shown in Table 1.

[0019]

[Table 1]

From Table 1, I is formed by firing the treatment liquid for electric field shielding in the atmosphere at 200 to 350 ° C. or in the atmosphere of inert gas or reducing gas at 200 to 450 ° C.
The transparent conductive film having a two-layer structure of a TO film and a silicate film has a surface resistance value of 3 to 5 × 10 ³ Ω / □ and ITO.
The refractive index difference between the film and the silicate film is high, the haze value,
It can be seen that the total light transmittance and pencil strength are also excellent.

[0021]

According to the present invention, a transparent conductive film having a surface resistance value extremely suitable for the electric field shielding effect of a CRT front glass and a refractive index suitable for antireflection can be formed. Compared with the method, the transparent conductive film for electric field shield can be manufactured easily and at low cost.

Continued Front Page (72) Keiichi Orita Inventor Keiichi Orita 7-9-4 Nishigotanda, Shinagawa-ku, Tokyo Tohoku Kako Co., Ltd.

Claims (2)

[Claims] 1. A cathode ray tube front glass is coated with an electric field shielding treatment liquid comprising an indium tin oxide powder having an average particle diameter of 50 nm or less and an alkyl silicate dispersed in a polar solvent containing N-methyl-2pyrrolidinone. A method for forming a transparent conductive film for electric field shielding, which comprises drying, then overcoating with a solution containing an alkyl silicate, and then baking in a temperature range of 200 to 350 ° C. in the atmosphere. 2. The method according to claim 1, wherein the firing is performed in an inert gas and / or reducing gas atmosphere at a pressure of 200 to 45.
A method for forming a transparent conductive film for electric field shielding, which is performed in a temperature range of 0 ° C.