JPH0986967A - Transparent conductive film and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simply obtain a transparent conductive film having a function for reducing the light reflection of a CRT display surface, having more excellent conductivity than those of conventional transparent conductive films and suitable for shielding electromagnetic fields at a low cost by a coating method. SOLUTION: This transparent conductive film formed on a glass substrate and having a film thickness of 0.31-0.62μm. The main part of the film comprises a layer wherein ITO particles having particle diameters of <=80nm are dispersed in a silicate matrix, and the ITO layer and the silicate layer do not have a clear boundary therebetween in the main part of the film. The formation of the transparent conductive film formed on the glass substrate by the method enables to obtain the film low in the surface electric resistance and in the surface reflection of light at a low cost by a low temperature baking method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to 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 OA equipment and a cathode ray tube of a television, and a manufacturing method thereof.

[0002]

2. Description of the Related Art Recent office automation (O)
A) With the introduction of many OA equipment in the office,
It is not uncommon to have an environment where you face the display of an OA device and work all day, but the cathode ray tube (C
When performing work in contact with (RT), it is required that the display screen be easy to see, that visual fatigue is not felt, and that there is no dust adhesion or electric shock due to charging of the CRT surface. In addition to this, recently, CRT
There is concern that the low-frequency electromagnetic waves generated from the human body may adversely affect the human body, and that such electromagnetic waves do not leak to the outside.
Desired for T.

Electromagnetic waves are generated from a deflection coil and a flyback transformer, and as the TV becomes larger, a larger electromagnetic wave tends to leak to the surroundings. Most of the magnetic field leakage can be prevented by changing the shape of the deflection coil. On the other hand, leakage of the electric field can be prevented by forming a conductive transparent conductive film on the front glass surface of the CTR. Although such a prevention method is in principle the same as the measures taken for the antistatic in recent years, the electroconductivity of the electroconductive coating in this case is the electroconductive coating formed for the antistatic. The surface resistance of 10 ⁸ Ω / □ is sufficient for preventing electrification, but at least 10% is necessary for preventing leakage electric field.
^It is necessary to form a transparent film having a low resistance of ⁶ Ω / □ or less, preferably 10 ³ Ω / □.

[0004]

In order to meet the above requirements, some proposals have been made in the past, but among them, ultrafine indium tin oxide is one that can realize low surface resistance at low cost. There is a method in which an ink in which (ITO) powder is dispersed in a coating liquid together with an alkyl silicate binder is applied to a CRT front glass, dried, and then baked at a temperature of 200 ° C. or lower. According to this ink coating method, a surface resistance value of 10 ³ to 10 ⁵ Ω / □ can be obtained according to the film thickness, and it is far more excellent than other transparent conductive film forming methods such as vacuum deposition and sputtering. It is a very advantageous method as a countermeasure for an electric field shield that is simple and low in manufacturing cost and capable of treating a completed CRT sphere.

On the other hand, in order to make the display screen easier to see, the surface of the face panel is subjected to an antiglare treatment to suppress the reflection of the screen. Anti-glare treatment is also carried out by a method of increasing the diffuse reflection on the surface by adding fine unevenness, but this method is not so preferable because the resolution is lowered and the image quality is deteriorated, and rather the reflected light is incident. It is preferable to carry out by an interferometry method in which the refractive index and the film thickness of the film are controlled so as to cause destructive interference with light. In order to produce a low reflection effect by such an interference method, it is generally preferable that a film having a low refractive index is coated on a film having a high refractive index, and the larger the difference in refractive index, the greater the effect. For example, in the case of a conventional two-layer film in which an ITO dispersion liquid and a silicate liquid are sequentially applied and baked, the ITO dispersion layer and the overcoat layer each have a visible light center (wavelength 550 nm) refractive index of about 1.55.
It becomes about 1.65 and 1.4. Therefore,
On a CRT panel glass having a refractive index of about 1.5, the first-order non-reflection condition of vertically incident light is satisfied at film thicknesses of 89 to 83 nm and 98 nm, respectively. In this case wavelength 550
A reflectance profile with a minimum value near nm is obtained,
A low reflection effect is produced, but the thickness of the ITO dispersion layer is 83-
With a thin film thickness of 89 nm, it was difficult to provide sufficient conductivity for the electric field shielding effect.

On the other hand, it is conceivable to increase the thickness of the film in order to improve the conductivity, but if the film is thick, it becomes difficult to satisfy the non-reflection condition, and the low reflection effect must be sacrificed. . Further, since the reflection profile shown above is a curve that is relatively steep and convex in the visible wavelength region, the product of reflectance and luminosity is defined by the value obtained by integrating the product from the wavelength of 380 nm to 780 nm. The "reflectance" does not always bring a sufficiently low value, and therefore, a film having a profile having a low reflectance over the entire visible wavelength region has been demanded. As described above, the ink coating method has many advantages, but the film conductivity and the film conductivity are better than those that can form a film in which ITO is continuously connected only at the crystal grain boundaries, such as the sputtering method and the vapor deposition method. There is a problem that the low reflection effect is insufficient.

An object of the present invention is to provide a film suitable for an electric field shield, which has a function of suppressing display reflection on a CRT screen and has conductivity superior to conventional ones, by using a coating method, simply and at low cost. Another object of the present invention is to provide a transparent conductive film that can be manufactured, and a manufacturing method thereof.

[0008]

In order to achieve the above object, a first embodiment of the present invention is a transparent conductive film formed on a glass substrate and has a film thickness of 0.31 μm or more and a thickness of 0.1.
62 μm or less, and the main part of the film has a grain size of 80 nm or less I
The transparent conductive film is a layer in which TO particles are dispersed in a silicate matrix, and is formed so that there is no clear boundary between the ITO layer and the silicate layer in the main part of the film. In the second embodiment of the present invention, an ITO dispersion liquid in which ITO fine particles having a particle size of 80 nm or less are dispersed and a treatment liquid containing an alkyl silicate partially hydrolyzed polymer are applied in this order on a glass substrate by a coating method. A method of forming a transparent conductive film by baking, wherein the silicate concentration of the treatment liquid is such that the haze value of the film produced when the silicate concentration is sequentially increased to form a minimum value for the first time It is characterized by a method of producing a transparent conductive film having a concentration of.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, ITO fine particles are used as a material for imparting transparency and conductivity, and a part of ITO is used as antimony-added tin oxide (AT).
O), aluminum-added zinc oxide (AZO), fluorine-added indium oxide, fluorine-added tin oxide, fluorine-added zinc oxide, fluorine-added ITO, fluorine-added ATO, or the like. All of these alternative substances are transparent and have conductivity, and the addition of fluorine is intended to improve the conductivity by increasing the carrier concentration. If the particle size of the ITO fine particles is too large, it causes scattering and increases the haze, so that it is usually necessary to be 80 nm or less. If this value is exceeded, the haze will increase significantly and the reflectance characteristics will deteriorate. It is to be noted that it is generally preferable that the particle size is small, but it is very difficult to produce an ITO ultrafine powder having a particle size distribution spread of less than 5 nm at the current industrial level. The lower limit of the particle size of the ITO fine particles was defined as 2 nm as the minimum particle size observed by TEM.

The silicate, which is the treatment liquid for dispersing the ITO fine particles used in the present invention (hereinafter referred to as ITO dispersion liquid), is a compound constituted by a polysiloxane bond, and dehydration condensation polymerization of silanol (Si-OH). Obtained by A part of Si of the siloxane bond may be replaced with Ti, Zr, Al or the like for adjusting the refractive index or reinforcing the strength, and even if an organic dye or pigment is added for improving contrast. I don't care.

Next, a treatment liquid containing a partially hydrolyzed polymer of an alkyl silicate to be applied on the treatment liquid in which ITO fine particles are dispersed (hereinafter referred to as a silicate treatment liquid) is an orthoalkyl silicate or is hydrolyzed to this and dehydrated to some extent. It is a solution containing as a main component a polycondensation product. As the alkyl silicate partially hydrolyzed polymer,
Orthoalkyl silicates in which water or acid catalyst is added and hydrolyzed to proceed dehydration polycondensation, or already 4 to
It is possible to use a commercially available alkyl silicate solution in which hydrolysis and polycondensation have proceeded to a pentamer, and a form in which hydrolysis and dehydration polycondensation have further proceeded. When the polycondensation progresses, the solution viscosity increases and finally solidifies. Therefore, the degree of polycondensation of the solution is used at a viscosity below the level at which the solution can be applied to the substrate. However, the degree of polycondensation is not particularly specified as long as it is at a lower level. The partially hydrolyzed alkyl silicate polymer undergoes a polycondensation reaction when it is baked and heated after coating the film to form a hard silicate.

The two treatment liquids are applied in order and then baked to complete the film. The baking temperature is usually 200 ° C. or less in consideration of the limit heating temperature of the CRT completed sphere. Even if it is more than that, it can be fired if the state of the finished CRT sphere is sufficiently taken into consideration, and the higher the heating temperature is, the more the polymerization shrinkage of the silicate used for the overcoat becomes closer to perfect one, so that the low resistance and the reflection property are improved. Therefore, it can be said that it is rather preferable, but if the temperature exceeds about 300 ° C., the resistance value tends to increase again due to reoxidation of ITO and the like, which is not preferable.

In the film according to the present invention, the film thickness is 0.3.
Although it was limited to 1 μm or more and 0.62 μm or less, this is IT
This is because both sufficient conductivity and low reflectivity of the O dispersion layer are taken into consideration. When the measured refractive index of the ITO dispersion layer is 1.63, the film thicknesses corresponding to the optical thicknesses 3λ / 4 and 5λ / 4 for low reflection are 0.23 to 0.29 μm and 0.3, respectively.
It becomes 9 to 0.48 μm. Since a thin silicate layer having a thickness of about 0.1 μm covers this, a low reflection effect occurs.

In the membrane of the present invention, IT is used in the main part of the membrane.
It is characterized by the fact that the boundary between the O layer and the upper silicate layer is not clear, which makes the reflectivity profile of the film wide open from the conventional steep one. , The actual measured value differs depending on the roughness of the interface between the ITO layer and the silicate layer. When the film thickness of the film actually formed is optically read by a spectral reflectometer and an ellipsometer, it is 0.31 to
Since the low reflection effect was obtained in the range of 0.62 μm, the film thickness was limited to the above range. When the film thickness is less than 0.31, not only the luminous reflectance increases but 10
The surface resistance on the order of ³ Ω / □ cannot be obtained, and conversely 0.6
When it exceeds 2, not only does the haze value become a non-negligible value, but also the luminous reflectance is too high to serve as a low reflection film.

Since the main part of the film has a structure in which the silicate is filled while being densely filled with ITO, the refractive index is higher than that of the silicate layer, and as a result, a low luminous reflectance is obtained. In order to obtain such a film structure, it is necessary to devise the coating conditions of the ITO dispersion liquid and the silicate treatment liquid. That is, first, it is necessary to control the concentration of the ITO dispersion liquid and the coating conditions so that the above film thickness is obtained. In addition, the silicate solids concentration of the silicate treatment liquid formed I
It is required that the fine particles of the TO film be permeated between the fine particles to just fill the film thickness of the ITO layer and be slightly left over. Since the size of the siloxane particles in the silicate treatment liquid is about 2 to 4 nm or less, it easily penetrates through the gap where the ITO fine particles having a particle diameter of 80 nm or less are deposited, but the solid content concentration of the silicate treatment liquid is low. When the solid content concentration is too high, a thick silicate layer is formed even after the ITO layer has soaked in and filled up, and the surface resistance of the film suddenly increases. And the reflectance also increases. The solid content concentration of the silicate treatment liquid has a delicate influence on the formation of the transparent conductive film of the present invention, but this optimum point can be easily determined by focusing on the haze value, which is one of the gist of the present invention. . That is, the haze value of the formed film decreases with an increase in the solid content concentration of the silicate treatment liquid, takes a minimum value when the silicate fills the ITO layer, and remains almost unchanged even if the silicate film thickness increases thereafter. Is. Therefore, the haze value was measured by gradually increasing the solid content of the silicate treatment liquid in the prototype film, and the solid content concentration at the time when it settled to the minimum value or a value in the vicinity thereof was used to easily produce the above film. It becomes possible to do. Since the solid content concentration of this silicate treatment liquid changes depending on the coating method and coating conditions, it is difficult to unify numerically, but conversely the above method using the measured haze value in advance regardless of the coating conditions. Can be determined more clearly.

[0016]

EXAMPLES Examples of the present invention will be shown below.

(Example 1) 1 g of an ITO fine particle dispersion liquid containing 6 wt% of ITO having an average particle diameter of 20 nm manufactured by Sumitomo Metal Mining Co., Ltd. in a solid content of 6 wt% and ethanol was used as a diluting solution.
It was dropped from a beaker on a plate glass substrate of 200 × 150 × 3 mm rotating at 60 rpm. The plate glass was dried while being rotated for 8 minutes as it was, and the rotation was stopped. Then, the plate glass was baked in an explosion-proof dryer at 160 ° C. for 30 minutes to form a single-layer film.
Next, as a two-layer film, an ITO fine particle dispersion is dropped to form a 8 layer film.
After drying while rotating for 1 minute, 10 g of the silicate treatment liquid was continuously added, rotation was stopped after 1 minute, and the plate glass was baked at 160 ° C. for 30 minutes in an explosion-proof dryer. As the silicate treatment liquid, 10 parts of ethyl silicate 40 manufactured by Tama Chemical Industry, 48 parts of ethanol, 26 parts of 5% hydrochloric acid aqueous solution, and 16 parts of distilled water were used to prepare a SiO ₂ solid content concentration of 4%. SiO ₂ solid content is 1.30, 1.50, 1.75, 1.90, 2.00,
It diluted with ethanol so that it might become 2.20, 2.50, 3.00, 4.00%, and produced 9 different density | concentrations.

(Example 2) ITO of ITO fine particle dispersion liquid
Ten kinds of membranes were prepared in exactly the same manner as in Example 1 except that the solid content was 7 wt%.

(Comparative Example 1) ITO of ITO fine particle dispersion liquid
Ten kinds of membranes were prepared in exactly the same manner as in Example 1 except that 2% by weight of solid content was included.

Comparative Example 2 Ten kinds of films were prepared in exactly the same manner as in Example 1 except that coarse ITO particles having an average particle diameter of 100 nm were used as the ITO fine particles.

The surface resistance, haze, film thickness and reflectance of the films obtained in Examples 1 and 2 and Comparative Examples 1 and 2 were measured, and the results are shown in Table 1 and FIGS. . As for the results of Comparative Examples 1 and 2, only those in which the luminous reflectance was minimum are shown. The surface resistance was measured using a surface resistance meter Loresta MCP-T200 manufactured by Mitsubishi Petrochemical Co., Ltd., and the haze was measured using a haze meter HR-200 manufactured by Murakami Color Research Laboratory. The reflectance was measured using a spectrophotometer manufactured by Shimadzu Corporation. The film thickness is measured by first measuring the refractive index n when only the ITO layer is formed by an ellipsometer manufactured by Mizojiri Optical Co., Ltd., and using the formula nd = (odd number) λ / 4 from the maximum position of the reflectance profile. An estimated thickness value was obtained. For those with a silicate coating, d obtained by a simulation calculation using the above n so that the minimum value comes to the 3λ / 4 position of the reflectance profile was taken as the total thickness.

Luminous refl
ectance) Ref _1m , for 1924CI
E, calculated based on 1933 CIPM (International Committee for Weights and Measures) adoption data (Optical Technology Handbook, pp387-421, Asakura Shoten) by the following mathematical formula 1.

[0023]

[Equation 1]

Here, S (λ): Spectral distribution of standard illumination defined by CIE. B light source is used here. ρ (λ): Measured spectral reflectance. V (λ): Standard relative luminous efficiency (s according to 1924CIE
spectral luminous efficien
cy).

[0025]

[Table 1]

As can be seen from Table 1 and FIG. 3, when the solid content of the ITO dispersion liquid is 6%, the surface resistance of the ITO dispersion liquid is in the range of 1.5 to 2.0 of the solid content of the silicate treatment liquid. When the solid content is 7%, the solid content of the silicate treatment liquid is 1.3.
The values in the range of up to 2.2 are in the order of 10 ³ Ω / □, and when the solid content of the ITO dispersion is as small as 2 wt%, the film of Comparative Example 1 has a thickness of 0.17 μm and a thickness of 8.2. × 10 ⁴ Ω
It is a very low value compared to / □. 10
The difference between the ⁴ Ω / □ range and the 10 ³ Ω / □ range appears as a large difference in the electric field shielding effect.

The luminous reflectance is shown in Table 1 and FIG.
As can be seen from the above, the minimum value is taken in the vicinity of the silicate concentration where the surface resistance value is low. For example, when the solid content of the ITO dispersion liquid is 6%, 1.508 when the solid content concentration of the silicate treatment liquid is 1.75%, ITO When the solid content of the dispersion liquid is 7%, it is 1.430 when the solid content concentration of the silicate treatment liquid is 1.90.
Value, which is slightly less than the luminous reflectance of 1.251 of the film of Comparative Example 1, but far higher than the luminous reflectances of 2 to 6 when the solid content concentration of the other silicate-treated liquid is used. It has a low value, and has a sufficiently low reflection effect.

Further, it can be seen from FIG. 4 that the solid content concentration of the silicate-treated liquid in which the surface resistance and the luminous reflectance are minimum values is in the vicinity where the haze value of the film settles to the minimum value. The change in haze is monotonous, and ITO
It decreases as the amount of silicate seeping into the layer increases, and
When the thickness of the silicate film permeates into the TO layer to form a new silicate film, the thickness does not substantially change. Therefore, the optimum solid content concentration of the silicate treatment liquid can be determined by using the concentration in the vicinity of the lower haze value, and the value is 1.75 when the solid content of the ITO dispersion liquid is 6%, for example.
%, When the solid content of the ITO dispersion is 7%, it is 1.90%.

When the particle size of the ITO fine particles used as in Comparative Example 2 is as large as 100 nm, the surface resistance is 3.49.
It is as high as × 10 ⁴ Ω / □, and haze and luminous reflectance are increased, resulting in a film with poor characteristics.

[0030]

As described above, by forming the transparent conductive film of the present invention on a glass substrate, a film having low surface resistance and low surface reflection can be obtained at low cost and at low temperature. Is.

[Brief description of drawings]

FIG. 1 is a view showing a measured reflectance profile (ITO solid content: 6 wt%) of a trial film.

FIG. 2 is a diagram showing a measured reflectance profile (ITO solid content: 7 wt%) of a prototype film.

FIG. 3 is a graph showing a change in bilayer film surface resistance depending on a silicate ink concentration.

FIG. 4 is a graph showing a change in haze of a two-layer film depending on a silicate ink concentration.

FIG. 5 is a graph showing a change in luminous reflectance of a two-layer film depending on the concentration of silicate ink.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication H01J 9/24 H01J 9/24 A 29/88 29/88 H05K 9/00 H05K 9/00 S

Claims (2)

[Claims] 1. A transparent conductive film formed on a glass substrate, having a film thickness of 0.31 μm or more and 0.62 μm or less, and a main part of the film having ITO fine particles having a particle diameter of 80 nm or less dispersed in a silicate matrix. And a transparent conductive film formed so that there is no clear boundary between the ITO layer and the silicate layer in the main part of the film. 2. A particle size of 80 on a glass substrate by a coating method.
A method for forming a transparent conductive film by coating and baking an ITO dispersion liquid in which ITO fine particles having a particle size of not more than 10 nm are dispersed and a treatment liquid containing an alkyl silicate partial hydrolysis polymer in order, and a silicate concentration of the treatment liquid. The method for producing a transparent conductive film is characterized in that the haze value of the film produced when the film is formed by increasing the concentration in order is a concentration in the vicinity of the minimum value for the first time.