JP3460484B2 - 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 transparent conductive film having low reflectivity and low resistance, which is suitable for imparting functions such as antistatic, electromagnetic wave shield, and reflection prevention to a transparent substrate such as a cathode ray tube.

[0002]

2. Description of the Related Art The surface of a front panel glass, which is an image display portion of a cathode ray tube including a TV and a CRT for various displays, is easily dusted by static electricity and the surface is highly reflective. There is a problem that the image becomes unclear due to the reflection of light and the reflection of an external image. Recently, there has been concern about the influence of electromagnetic waves emitted from the cathode ray tube on the human body, and standards for low-frequency leakage electromagnetic waves have been established in each country.

To prevent dust from adhering and electromagnetic waves from leaking, a means for forming a transparent conductive film having an antistatic effect and an electromagnetic wave shielding effect on the outer surface of the screen is generally adopted. As a measure for preventing glare, a non-glare treatment has been generally performed in which the glass surface of the screen is subjected to fine unevenness treatment using hydrofluoric acid or the like to scatter light. But,
The non-glare processing deteriorates the resolution of the image and reduces the visibility.

Therefore, recently, a two-layer film in which a transparent overcoat film having a low refractive index is formed on a transparent conductive film having a high refractive index, imparts both functions of antistatic (prevention of dust adhesion) and reflection of glare. Is being attempted. In such a two-layer film, if the refractive index difference between the high refractive index film and the low refractive index film is large, the reflected light from the surface of the upper low refractive index film is reflected from the interface with the lower high refractive index film. Are canceled by the interference of, and as a result, glare is prevented. When the conductivity of this transparent conductive film is high, an electromagnetic wave shielding effect is also provided.

For example, Japanese Patent Laid-Open No. 5-290634 discloses Sb.
Dope tin oxide (ATO) fine powder dispersed with a surfactant is applied to an alcohol dispersion liquid, which is then dried to form a conductive film having a high refractive index and magnesium fluoride contained thereon. By forming a low refractive index film of silica formed from optionally alkoxysilane,
A two-layer film having a reflectance reduced to 0.7% has been proposed.

In JP-A-6-12920, the optical thickness nd (n: n of high refractive index layer-low refractive index layer) formed on a substrate is described.
It is described that when the film thickness and d: refractive index) are respectively set to 1 / 2λ-1 / 4λ (λ = wavelength of incident light), low reflectivity is achieved. According to this publication, the high refractive index layer is a siliceous film containing ATO or Sn-doped indium oxide (ITO) fine powder, and the low refractive index layer is a silica film.

Japanese Unexamined Patent Publication (Kokai) No. 6-234552 also discloses a two-layer film composed of an ITO-containing silicate high refractive index conductive film-silicate glass low refractive index film. Japanese Unexamined Patent Publication No. 5-107403 describes a two-layer film including a high refractive index conductive film and a low refractive index film formed by applying a liquid containing conductive fine powder and a Ti salt.

Japanese Unexamined Patent Publication (Kokai) No. 6-344489 discloses a first layer film of ATO fine powder and black electroconductive fine powder (preferably carbon black fine powder) which is densely packed with solid content and has a high refractive index. And a blackish two-layer film composed of a siliceous low-refractive index film formed thereon.

[0009]

[Problems to be Solved by the Invention] However, ATO and IT
In the case of a transparent conductive film using a semiconductor conductive powder such as O, it is difficult to reduce the resistance so as to produce the electromagnetic wave shielding effect, or even if the resistance can be reduced so as to produce the electromagnetic wave shielding effect. This significantly impairs transparency. Particularly in recent years, the standards for leaked electromagnetic waves from cathode ray tubes have become stricter, and the above-mentioned conventional techniques have an insufficient electromagnetic wave shielding effect, which makes it difficult to cope with them. Therefore, a transparent conductive film having a lower resistance and a large electromagnetic wave shielding effect is required. Has been.

An object of the present invention is to reduce the resistance so as to exhibit a high electromagnetic wave shielding effect, and to maintain high transparency and a low haze value which do not impair the visibility of a cathode ray tube.
Equipped with a low reflectance that can add a function to prevent reflection of external images on the cathode ray tube, and the reflected light is almost colorless,
It is to provide a transparent conductive film which is not bluish or reddish.

[0011]

In view of the recent severe standards for the electromagnetic wave shielding properties of cathode ray tubes, the present inventors have proposed AT as an electrically conductive powder used for a transparent electrically conductive film.
It was concluded that it is desirable to use metal fine powder having higher conductivity rather than semiconducting inorganic fine powder such as O or ITO, and as a result of further study, it was found that the lower transparent conductive film containing the metal fine powder was used. It has been found that a two-layer film provided with an upper layer film of siliceous low refractive index is suitable for this purpose.

However, this two-layer film has a minimum reflectance of 1%.
Although it is as low as or less, the reflectance increases greatly on both sides of the wavelength showing the lowest reflectance, and the reflectance increases in a sharp curve especially on the short wavelength side, so the reflected light is bluish and the color tone of the image is changed. It turned out to change. Therefore, as a result of further study, by varying the particle size distribution of the secondary particles (aggregated particles) of the fine metal powder in the dispersion liquid of the fine metal powder used for coating, unevenness is formed on the surface of the lower layer containing the fine metal powder. It has been found that the formation of the film suppresses an increase in the reflectance on both sides of the wavelength exhibiting the lowest reflectance, and greatly reduces the bluishness of the reflected light.

The present invention has a two-layered transparent structure comprising a lower layer provided on the surface of a transparent substrate and containing a fine metal powder in a siliceous matrix, and a siliceous upper layer provided thereon. The conductive film, the surface of the lower layer has irregularities, the average film thickness in the convex portion of the lower layer is 50 ~ 150 nm, the average film thickness in the concave portion is 50 ~ of the average film thickness in the convex portion. 85%, and the average pitch of the convex portions is 20 to 300 nm, which is a transparent conductive film having low reflectivity and low resistance.

The lower layer containing the fine metal powder can be formed from a dispersion liquid in which fine metal powder having an average primary particle diameter of 5 to 50 nm is dispersed in a solvent containing a dispersant. The fine metal powder of 10% has an integrated particle size of 60 nm or less, 50
When the secondary particles having a particle size distribution with a% cumulative particle size of 50 to 150 nm and a 90% cumulative particle size of 80 to 500 nm are formed, the lower layer coating having the uneven surface can be obtained.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The transparent substrate on which the transparent conductive film of the present invention is formed is not particularly limited and may be any transparent substrate for which it is desired to impart low reflectivity and electromagnetic wave shielding property. A typical transparent substrate is glass, but the transparent conductive film of the present invention can be formed on a substrate such as transparent plastic.

As described above, the transparent substrate that is particularly required to have low reflectivity and electromagnetic wave shielding property is a front panel glass of a cathode ray tube used as a display device for TVs, computers and the like. The transparent conductive film of the present invention is
In addition to low reflectivity and electromagnetic wave shielding property (low resistance), it has a flat reflection spectrum, does not have a blue-purple or red-yellowish tint like some conventional transparent conductive films, and is colorless. , Has the characteristic of good visibility. Therefore, when this conductive film is formed on the surface of the screen display part of the cathode ray tube, it is possible to prevent or reduce electromagnetic wave leakage, dust adhesion, and external image reflection that are harmful to health and cause computer malfunction. The transparency (visible light transmittance) and haze are good, and the reflected light is colorless, so the visibility of the image is kept good.

The transparent conductive film of the present invention is a lower layer containing a fine metal powder as a conductive powder in a siliceous matrix.
It is a two-layer film consisting of a (conductive layer) and a silica-based upper layer containing no powder. The lower layer has a high refractive index because it contains the fine metal powder densely, while the upper layer has a low refractive index. With this two-layer film structure, the transparent conductive film of the present invention has characteristics of low reflectivity and low resistance, and can exhibit the above-mentioned functions.

In the transparent conductive film of the present invention, both the siliceous matrix of the lower conductive layer and the siliceous upper layer can be formed of alkoxysilane (in a broader sense, a hydrolyzable silane compound).

As the alkoxysilane, at least 1
Any one or two or more silane compounds having one, preferably two or more, and more preferably three or more alkoxyl groups can be used. Halosilanes containing halogens as hydrolyzable groups can also be used with or instead of alkoxysilanes.

Specific examples of the alkoxysilane include tetraethoxysilane (= ethyl silicate), tetrapropoxysilane, methyltriethoxysilane, dimethyldimethoxysilane, phenyltriethoxysilane, chlorotrimethoxysilane and various silane coupling agents.
(Example, vinyltriethoxysilane, γ-aminopropyltriethoxysilane, γ-chloropropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane,
γ-glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, N-β-
(Aminoethyl) -γ-aminopropyltrimethoxysilane, β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane) and the like. Preferred is ethyl silicate, which is the cheapest and easiest to hydrolyze.

When a coating made of alkoxysilane is hydrolyzed, alcohol is eliminated and the generated OH groups are condensed with each other to form a silica sol. When this sol is heated and baked, condensation proceeds further and finally hard silica
(SiO ₂ ) It becomes a film. Therefore, the alkoxysilane can be used as an inorganic film forming agent to form a siliceous film, and when formed into a film together with a powder, it functions as an inorganic binder that binds the powder to form a film matrix. It will be. Similarly, halosilane can be finally formed into a silica film by hydrolysis, but the case of using alkoxysilane will be described below.

Lower Conductive Layer The lower conductive layer of the transparent conductive film of the present invention contains fine metal powder in a siliceous matrix. The siliceous matrix can be formed from an alkoxysilane, as described above.

As the metal fine powder, powder of any metal or alloy or a mixture of metal and / or alloy powder can be used as long as it does not adversely affect the film-forming property of alkoxysilane. Fe, Co, Ni, Cr, W, Al, In, Zn, Pb, Sb, B are preferable as the material of the metal fine powder.
One or more metals selected from the group consisting of i, Sn, Ce, Cd, Pd, Cu, Pt, Ag and Au, and / or alloys of these metals, and / or these metals and / or Alternatively, it is a mixture of alloys. Among them, particularly preferable metal species are Ni, W, In, Zn, Sn, Pd, Cu,
Pt, Bi, Ag, and Au, most preferably low resistance Ag. Preferred alloys are Cu-Ag, Ni-Ag, Ag-P
It is an Ag alloy such as d, Ag-Sn, and Ag-Pb, but is not limited thereto. Also, Ag and other metals (eg W, P
A mixture with b, Bi, Cu, In, Sn) is also preferable as the fine metal powder.

The fine metal powder includes one or more non-metals such as P, B, C, N and S, alkali metals such as Na and K, and / or alkaline earth metals such as Mg and Ca. One or more of the above may be solid-dissolved.

The fine metal powder has an average primary particle diameter of 5 to 50 n.
It is preferable to use fine particles in the range of m 2. If the average primary particle size is smaller than 5 nm, it becomes difficult to form a lower conductive layer having relatively deep surface irregularities, which is a feature of the present invention. When the average primary particle size is larger than 50 nm, surface irregularities can be formed on the lower conductive layer, but the pitch of the irregularities becomes too large. The average primary particle diameter is more preferably 8 to 35 nm. Such fine particulate metal powder can be produced by utilizing a method of colloid generation (eg, reducing a metal compound to a metal with an appropriate reducing agent in the presence of protective colloid).

As described above, in the transparent conductive film having a two-layer structure of the present invention, the conductive powder has an average primary particle diameter of 5
The surface of the lower layer (that is, the interface between the lower layer and the upper layer) containing the fine metal powder of ˜50 nm has an uneven shape, as schematically shown in FIG. Submicron particles such as this metal fine powder generally have a tendency that primary particles (individual particles) aggregate to form secondary particles (aggregated particles), but in the present invention, the thickness of the lower layer is By making the thickness almost the same as the average particle size of the secondary particles of the fine metal powder, and giving a relatively large variation in the particle size distribution of the secondary particles (that is, allowing the large secondary particles and the small secondary particles to coexist). , Causes unevenness on the surface of the lower layer. This suppresses an increase in the reflectance on both sides of the wavelength showing the lowest reflectance, and the reflected light becomes almost colorless.

Specifically, the film thickness of the lower layer having an uneven surface is such that the average film thickness at the convex portion is 50 to 150 nm and the average film thickness at the concave portion is 50 to 150 nm of the average film thickness at the convex portion. 85%, and the average pitch of the convex portions is within the range of 20 to 300 nm. The convex portion means the peak-shaped top portion of the surface unevenness, and the concave portion means the valley-shaped bottom portion of the surface unevenness. The lower layer having such surface irregularities can be formed by the method described later.

When the average film thickness at the convex portion is smaller than 50 nm,
The effect of achromaticity of reflected light due to surface irregularities is reduced. If the average film thickness at the convex portion exceeds 150 nm, the transparency of the film decreases and the visibility of the image decreases. When the average film thickness at the concave portion is less than 50% of the average film thickness at the convex portion, the unevenness is too sharp, the haze of the film increases, and the visibility of the image deteriorates.
When it exceeds%, the unevenness is too gentle, and the effect of making the reflected light colorless is hardly obtained. The average pitch of the convex parts is 20 n
When it is smaller than m, the unevenness is small and the effect of achromaticity of reflected light is small. When the average pitch of the convex portions is larger than 300 nm, the haze of the film increases, the effect of colorlessness of reflected light also decreases, and the visibility of the image decreases.

As a conductive powder, in addition to the fine metal powder,
Inorganic oxide-based transparent conductive fine powder such as ITO and ATO
(Average primary particle size is 0.2 μm or less, preferably 0.1 μm
The following) can also be used together. Even then,
It is preferable that 50% by weight or more of the electrically conductive powder is fine metal powder, and more preferably 60% by weight or more of the electrically conductive fine powder is fine metal powder.

The amount of the siliceous matrix in the lower conductive layer may be an amount sufficient to bind the fine metal powder. Since this conductive layer is covered with a siliceous top layer,
It does not require particularly high film strength or hardness. Preferably, the amount of siliceous matrix is 5 to 30% by weight.

Method for Forming Transparent Conductive Film The method for forming the transparent conductive film having a two-layer structure of the present invention is not particularly limited as long as the above-mentioned surface irregularities can be formed in the lower layer. For example, it will be described below. The method can be adopted.

First, a coating material for forming a lower layer is applied on a transparent substrate to form a film in which secondary particles of fine metal powder are distributed in the above-mentioned uneven shape. The lower layer-forming coating material is preferably composed of a dispersion liquid in which metal fine particles having an average primary particle diameter of 5 to 50 nm are dispersed in a solvent containing a dispersant. It is preferable that the coating does not contain an alkoxysilane that becomes a siliceous matrix after baking.

If the lower layer-forming coating material does not contain an alkoxysilane serving as a binder, this coating material is applied,
When dried and the solvent is evaporated, a film consisting essentially of fine metal powder is formed on the surface of the substrate. The fine metal powder is composed of submicron fine particles and has strong cohesiveness, so that a film can be formed without the presence of a binder. After that, when a coating material containing an alkoxysilane solution for forming the upper layer is applied, a part of the applied solution penetrates into the voids between the particles of the lower layer metal fine powder and functions as a binder for binding the metal fine powder. The coating material for forming the upper layer is applied so that the coating material that has not completely penetrated into the lower layer film remains on the lower layer film.

Next, when the coating is heated and baked, the alkoxysilane changes to a siliceous coating, and the alkoxysilane that has penetrated between the particles in the lower layer becomes a siliceous matrix that fills the voids and pores between the particles and penetrates. The alkoxysilane that cannot be formed forms an upper siliceous film, and the transparent conductive film having a two-layer structure of the present invention can be obtained.

This method requires only one baking process, which requires time and energy cost, and simplifies the manufacturing process. That is, in this method, the coating material is applied twice, but if it is applied by the spin coating method, the coating material for the lower layer and the coating material for the upper layer can be successively applied on one spin coater to continuously perform the coating. However, since baking is performed at a time after that, it is possible to carry out the same simple working process as that of one application in two steps.
Layer films can be formed. In addition, since the binder does not exist when the fine metal powder is first formed into a film, the fine metal powder comes into direct contact with the film, and this state is maintained even after impregnating the binder with alkoxysilane. It is also advantageous in that a resistance film can be obtained.

When the coating material for forming the lower layer contains an alkoxysilane, the coating material is applied to a transparent substrate and then the coating film is baked to convert the alkoxysilane into a siliceous matrix to form a lower conductive layer. . After that, an upper layer coating material composed of an alkoxysilane solution is applied and baked again. Therefore, two baking steps are required.

In any case, the coating material for forming the lower layer (dispersion liquid of fine metal powder) is adjusted so that the secondary particles of the fine metal powder have a specific particle size distribution in this dispersion liquid. Specifically, in this dispersion, fine metal powder having an average primary particle size of 5 to 50 nm is aggregated, and the 10% cumulative particle size is 60 nm or less, the 50% cumulative particle size is 50 to 150 nm, 90%. Try to form secondary particles having a particle size distribution with an integrated particle size of 80 to 500 nm.

The state of aggregation of the fine metal powder in the dispersion (ie,
The particle size distribution of the secondary particles) depends on factors such as the average primary particle size of the fine metal powder, the surface tension of the solvent, the stirring conditions at the time of powder dispersion, the viscosity of the dispersion liquid, and additives such as a dispersant. Therefore, parameters such as solvent type, average primary particle diameter of fine metal powder, concentration of fine metal powder, stirring speed and time, type and amount of additive, and particle size distribution of secondary particles of fine metal powder are as described above. It may be selected so as to fall within the range, and this can be experimentally performed by those skilled in the art.

Suitable solvents for dispersing the fine metal powder in this way include water and / or lower alcohols.
(Methanol, ethanol, isopropanol, etc.) to 30
% Or less, especially 25% or less by weight of cellosolve solvent
A mixed solvent obtained by mixing (eg, methyl cellosolve, butyl cellosolve, etc.) is preferable. However, the solvent is not limited to this, and if the used fine metal powder can be dispersed in an agglomerated state so as to form secondary particles having the above particle size distribution, a dispersion liquid using any solvent Can be prepared. Other solvents that can be used include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone and isophorone; toluene,
Hydrocarbons such as xylene, hexane and cyclohexane;
Examples thereof include amides such as N, N-dimethylformamide and N, N-dimethylacetamide; sulfoxides such as dimethyl sulfoxide.

The coating material (dispersion liquid) for forming the lower layer preferably contains one or more of titanate-based or aluminum-based coupling agents, polymer dispersants, and surfactants. Examples of titanate-based or aluminum-based coupling agents include isopropyl triisostearoyl titanate, isopropyl tridecylbenzenesulfonyl titanate, isopropyl tris (dioctyl pyrophosphate) titanate, tetraisopropyl bis (dioctyl phosphite) titanate,
Tetraoctylbis (ditridecylphosphite) titanate, tetra (2,2-diallyloxymethyl-1-butyl) bis (di-tridecyl) phosphite titanate,
Examples thereof include bis (dioctyl pyrophosphate) oxyacetate titanate, tris (dioctyl pyrophosphate) ethylene titanate, and acetoalkoxyaluminum diisopropylate. Examples of polymer dispersants are polyvinylpyrrolidone, polyvinyl alcohol, polyethylene glycol-mono-p-nonylphenyl ether and the like. The surfactant may be nonionic, cationic, or anionic, and examples thereof include:
Examples include sodium p-aminobenzenesulfonate, sodium dodecylbenzenesulfonate, long-chain alkyltrimethylammonium salt (eg, stearyltrimethylammonium chloride) and the like. The amount of these additives added is
For example, a small amount within the range of 0.001 to 0.200% by weight of the dispersion liquid (paint) is sufficient.

The viscosity of the coating material for forming the lower layer is preferably 0.8.
-10 cps, more preferably 0.9-5 cps. The amount of fine metal powder in the paint is suitably within the range of 0.1 to 15% by weight of the paint. When the alkoxysilane is contained, the amount of the alkoxysilane (the amount converted to SiO ₂ ) is preferably in the range of 1.0 to 18% by weight with respect to the total amount of the fine metal powder.

The alkoxysilane is hydrolyzed in advance,
It can also be used in paints. Thereby, baking after application can be completed in a short time. In this case, the hydrolysis is preferably carried out in the presence of an acid catalyst (eg, an inorganic acid such as hydrochloric acid or an organic acid such as p-toluenesulfonic acid) and water in order to accelerate the reaction. The hydrolysis of the alkoxysilane can be carried out at room temperature or under heating, and the preferred reaction temperature is within the range of 20 to 80 ° C.

The coating for forming the lower layer is carried out by a spray method,
It can be performed by a spin coating method, a dipping method, or the like, but the spin coating method is preferable from the viewpoint of film formation accuracy. After drying, the average film thickness of the convex parts of the surface irregularities is 50 to 150 nm after drying.
To do so. Since this film thickness is in the same range as the 50% cumulative particle size of the secondary particles of the fine metal powder, the coating film is almost a single layer of the secondary particles, and the particle size distribution of the secondary particles is uneven as it is. Appears on the surface of the coating film. Therefore, if the secondary particles of the fine metal powder have the above-mentioned particle size distribution, it is possible to obtain the coating film of the fine metal powder having the above-mentioned surface irregularities after drying and removing the solvent.

Even if the coating material for forming the lower layer contains the alkoxysilane, since the fine metal powder has a much higher density than the alkoxysilane solution, the secondary particles of the fine metal powder settle in the coating film. In this case, the surface of the formed coating film is smooth, but the portion containing the fine metal powder has irregularities depending on the variation in the particle size of the secondary particles. The portion of the alkoxysilane solution accumulated on the concave and convex portions becomes a siliceous film containing no fine metal powder after baking, and finally integrated with the upper siliceous film to become a part of the upper layer film. . That is, of the coating film formed from the lower layer coating material, only the portion containing the fine metal powder is the lower layer, and since this portion has unevenness, the lower layer has surface unevenness.

Dispersion of fine metal powder (paint for forming lower layer)
When does not contain an alkoxysilane, the solvent is evaporated from the coating film by an appropriate means to form a film having an uneven surface substantially consisting of the fine metal powder on the substrate. This evaporation of the solvent can be carried out without heating or with heating, depending on the boiling point of the solvent used. For example, when the coating is performed by the spin coating method, depending on the type of the solvent, if the rotation time is sufficient, the solvent can be evaporated during the rotation without heating. It is not necessary to completely evaporate the solvent, and the solvent may partially remain.

When the dispersion liquid contains an alkoxysilane, baking is performed after coating to convert the alkoxysilane into silica. This baking can be performed similarly to the baking of the upper layer.

On the lower layer film thus formed, a coating material comprising an alkoxysilane solution for forming the upper layer is applied,
Bake to form a siliceous film. The alkoxysilane in this paint may be a so-called silica sol that has been previously hydrolyzed in order to accelerate the hydrolysis of the alkoxysilane after coating. Silica sol can be prepared by hydrolyzing an alkoxysilane in the presence of an acid catalyst (preferably hydrochloric acid or nitric acid) at room temperature or under heating.

When silica sol is used, the silica sol concentration in the coating material for forming the upper layer is preferably within the range of 0.5 to 2.5% by weight in terms of SiO ₂ . The viscosity of this paint is preferably
It is 0.8 to 10 cps, more preferably 1.0 to 4.0 cps. If the silica sol concentration is too low, the bonding of the powder in the lower layer and the film thickness of the upper layer will be insufficient, and if it is too high, the film forming accuracy will be reduced and it will be difficult to control the film thickness of the upper layer. If the viscosity of this paint is too high, the silica sol will not be sufficiently impregnated into the gaps between the powder particles in the lower layer, which will lower the conductivity and the film forming accuracy, making it difficult to control the film thickness of the upper layer. Becomes

The baking after the coating of this coating is carried out at 250 ° C. or lower, preferably in order to prevent the dimensional accuracy of the CRT and the fall of the phosphor, especially when the transparent substrate is a CRT.
It is performed by heating to 200 ° C, more preferably 180 ° C or less. When the transparent substrate is other than a cathode ray tube, a drying temperature higher than this may be adopted within the range allowed by the substrate material.

When the lower layer coating is formed from a coating material containing no alkoxysilane, the coating of the upper coating material causes the alkoxysilane (or its hydrolyzate, especially silica sol) in the coating material to be coated with a metal fine particle as described above. Penetrate the voids between the particles of the powder to fill these voids and form a siliceous matrix after baking. On the other hand, the paint that has not completely penetrated forms a siliceous upper layer after baking. In this case, an additive such as a surfactant for adjusting the permeability may be added to the paint.

The siliceous upper layer containing no fine metal powder has a lower refractive index than the lower layer containing fine metal powder,
As a result, as with the conventional conductive double-layer film,
A layer film is obtained. The film thickness of the upper layer (average film thickness from the protrusions on the lower layer surface) preferable for this function is 20 to 150 n.
m, more preferably 50-120 nm, most preferably 60-100
nm. The method for applying the coating material for forming the upper layer may be the same as in the case of the lower layer, but the spin coating method is preferable because the thickness can be easily controlled.

In the two-layered transparent conductive film of the present invention, since the interface between the lower layer having a high refractive index containing fine metal powder and the upper layer having a low refractive index consisting of silica has an appropriate unevenness,
In addition to having low reflectivity, the reflected light is almost colorless without bluish or reddish color, has high transparency, and has low haze. Specifically, the visible light transmittance is 55% or higher, preferably 60% or higher, and the haze is 1% or lower. As for the visible light reflectance, the minimum reflectance is as low as 1%, and the reflection spectrum is flat. On the short wavelength side (eg 400 nm), which was the cause of the bluish reflected light of the conventional two-layer conductive film. The increase in reflectance is suppressed to almost the same level as the long wavelength side (eg, 800 nm). Therefore, the reflected light has substantially no bluish color and is substantially colorless, and the visual sensitivity of the image is significantly improved. In addition, this transparent conductive film exhibits a low surface resistance of the order of 10 ² Ω / □, and can sufficiently fulfill the electromagnetic wave shielding function.

[0053]

Example: A metal fine powder was added to a solvent containing a surfactant or a polymer dispersant as a coating additive for forming a lower layer , and mixed with a paint shaker using zirconia beads having a diameter of 0.3 mm. The powder was dispersed in a solvent to prepare a coating material for forming a lower layer containing no alkoxysilane. The types of metal fine powder, dispersant and solvent used and their amounts (% by weight) in the paint were as shown in Table 1.

The fine metal powder used is a colloidal method.
(Reducing by reacting a metal compound with a reducing agent in the presence of a protective colloid), and its average primary particle size [measured by TEM (transmission electron microscope)] and in a paint (dispersion liquid). Secondary particle size distribution [10
%, 50% and 90% cumulative particle diameters, measured by UPA particle size analyzer (manufactured by Nikkiso Co., Ltd.) are also shown in Table 1.

The symbols of the dispersant and the solvent (the weight ratio in parentheses) shown in Table 1 have the following meanings. Additive: A = stearyltrimethylammonium chloride B = sodium dodecylbenzenesulfonate C = polyvinylpyrrolidone (K-30 manufactured by Kanto Kagaku).

Solvents: ethanol / methyl cellosolve (85/15), methanol / methyl cellosolve (80/20), water / butyl cellosolve (90/10), ethanol / methanol / butyl cellosolve (80/10)
/ 10), ethanol (100) water / ethanol / butyl cellosolve (80/10/10).

Coating material for forming upper layer Ethoxysilane (ethyl silicate) was hydrolyzed by heating at 60 ° C. for 1 hour in ethanol containing a small amount of hydrochloric acid and water to synthesize silica sol. The obtained silica sol solution was diluted with a mixed solvent of ethanol / isopropanol / butanol at a weight ratio of 5: 8: 1 to prepare a coating material having a SiO ₂ conversion concentration of 0.7% by weight and a viscosity of 1.65 cps.

Film forming method Soda lime glass with dimensions of 100 mm × 100 mm × thickness 3 mm
A lower layer-forming coating material and an upper layer-forming coating material were sequentially dropped onto a single surface of a (blue plate glass) substrate using a spin coater to form a film. For each paint, the dripping amount was 5 to 10 g, the rotation speed was 140 to 180 rpm, and the rotation time was 60 to 150 seconds. Then, the substrate was heated in air at 170 ° C. for 30 minutes to bake the coating film, thereby forming a transparent conductive film on the glass substrate. The characteristics of the obtained film were evaluated as follows, and the results are shown together in Table 1.

Evaluation of film characteristics Average film thickness and average pitch of convex and concave portions of surface irregularities of lower layer (layer containing fine metal powder), and film thickness of upper layer (average film thickness from lower convex portion): TEM cross-sectional photograph Measured above.

Adhesion: Using an eraser ER-20R manufactured by Lion Corporation, the state of scratches after a load of 1 kgf / cm ² , a stroke width of 5 cm, and reciprocating 50 times was visually observed. ○ means that there is no scratch, and × means that scratches are recognized.

Surface resistance: Measured by the four-probe method (Loresta AP: manufactured by Mitsubishi Yuka). Light transmittance (total visible light transmittance): Self-recording spectrophotometer (U-40
Type 00: manufactured by Hitachi, Ltd.). Haze: Measured with a haze meter (HGM-3D: manufactured by Suga Test Instruments Co., Ltd.).

Visible light reflectance: A black vinyl tape (No. 21: Nitto Denko) was attached to the back surface of the glass substrate, the temperature was kept at 50 ° C. for 30 minutes to form a black mask, and then 12 ° was measured by a spectrophotometer. The reflection spectrum in the visible wavelength range due to the regular reflection was measured. The minimum value of reflectance from this reflection spectrum
The (minimum reflectance) and the reflectance at 400 nm and 800 nm were determined and shown in Table 1 together with the wavelength at which the minimum reflectance was obtained.

The transmission spectra and reflection spectra of the transparent conductive film of the invention of Test No. 4 are shown in FIGS. 2 (a) and 2 (b), and the transmission spectra and the reflection spectra of the transparent conductive film of Comparative example of Test No. 11 are shown. The reflection spectra are shown in FIGS. 3 (a) and 3 (b).

[0064]

[Table 1]

As can be seen from Table 1, in the present invention, fine metal powder having an average primary particle diameter of 5 to 50 nm is dispersed in an agglomerated state so as to produce secondary particles having a relatively large variation in particle size distribution. As a result of using the coating material dispersed in the solvent containing the agent, in the lower conductive layer, for example, as shown schematically in FIG. 1, the lower layer containing the fine metal powder and the interface with the upper layer not containing it ( That is, the surface of the lower layer) had considerably large irregularities.

However, the method of forming the transparent conductive film of the present invention is
The method is not limited to the method shown in the embodiment, and the two-layer film may be formed by any method as long as similar surface unevenness of the lower layer is generated. Further, the adhesion of the film was good even though the fine metal powder formed relatively large secondary particles.

On the other hand, in the test No. 11 of the comparative example,
Since the integrated particle size distribution was improper (smaller by 50%), the average film thickness at the concave portion of the lower layer film was 89.1% of the average film thickness at the convex portion, and although the surface resistance was low, the reflectance at visible 400 nm Was extremely high and tinged with blue to purple. On the other hand, in Test No. 14, the 50% cumulative particle size was too large, so the visible light transmittance was remarkably reduced, and the adhesiveness for practical use was not obtained. Test No. 12
Then, although the average primary particle diameter of the fine metal powder was too large and the surface irregularities of the lower layer were sufficiently formed, the pitch thereof was too large. With these, the adhesiveness of any of the films was significantly reduced, and the adhesiveness that could be practically used was not obtained. Also,
In Test No. 13, the average primary particle size of the metal fine powder was too small, and therefore the surface irregularities of the lower layer became shallow (small).

The transparent conductive films of Examples of the present invention are all 1% or less in minimum visible light reflectance, 1% or less in haze, and 55% or more.
Shows the total visible light transmittance (60% or more except for one example),
It can be seen that it has low reflectivity capable of preventing the reflection of an image and sufficient transparency that does not interfere with the visibility of the image.

When the reflectances at 400 nm and 800 nm are compared, the reflectance values of both are at the same or almost the same level, and as shown in FIG. 2 (b), the reflectance spectrum shows the lowest reflectance. Both sides of the curve increased in the same curve, and the increase was relatively small. As a result, it can be seen that, in addition to having low reflectivity, the reflected light is substantially colorless and the visibility of the image is excellent. Further, as shown in FIG. 2 (a), the transmission spectrum is also very flat and the film itself is colorless.

On the other hand, in the comparative example, although the minimum reflectance is low, as shown in FIG. 3 (b), the increase of the reflectance spectrum is particularly large on the short wavelength side, and the reflectance at 400 nm is 80%.
It was more than double the reflectance at 0 nm. Therefore, the reflected light is bluish and adversely affects the visibility of the image.

In terms of conductivity, any transparent conductive film
Since the lower layer contains fine metal powder, it exhibits a low resistance on the order of 10 ² Ω / □, which is a level capable of sufficiently imparting electromagnetic wave shielding properties.

[0072]

The two-layer transparent conductive film of the present invention has a low surface resistance of the order of 10 ² Ω / □, so that the electromagnetic wave which is a problem particularly in CRTs for personal computers and cathode ray tubes for large-sized TVs. The cathode ray tube can be provided with electromagnetic wave shielding properties that can prevent leakage.

In addition, this transparent conductive film has a minimum visible light reflectance of 1% or less, although it contains fine metal powder.
It has low reflectivity and sufficient transparency with a haze of 1% or less and a total visible light transmittance of 55% or more, preferably 60% or more. Moreover, this transparent conductive film has less purple-bluish or red-yellowish reflected light, which has been a problem in the past.
The reflected light is substantially colorless.

Therefore, when the transparent conductive film of the present invention is formed in the image display portion of a cathode ray tube, the reflection of an external image due to reflection can be prevented, and at the same time, the color tone of the image is not changed, so that the image visibility is improved. Is greatly improved. Therefore, the transparent conductive film of the present invention makes it easy to see an image, and also helps prevent adverse effects on the human body due to leakage of electromagnetic waves and malfunction of a computer.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a cross-sectional structure of a transparent conductive film having a two-layer structure of the present invention.

FIG. 2 (a) shows a transmission spectrum of the transparent conductive film of the present invention produced in an example, and FIG. 2 (b) shows a reflection spectrum thereof.

FIG. 3 (a) shows a transmission spectrum of a transparent conductive film of a comparative example prepared in an example, and FIG. 3 (b) shows a reflection spectrum thereof.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI H05K 9/00 H05K 9/00 V // G02B 1/10 G02B 1/10 Z (56) Reference JP-A-61-288314 ( JP, A) JP 7-272646 (JP, A) JP 8-77832 (JP, A) JP 8-102227 (JP, A) JP 8-165147 (JP, A) JP HEI 10-182190 (JP, A) JP HEI 10-182191 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01B 5/14 H01B 1/22 C03C 17/34 C09D 5 / 24 H01J 29/88 H05K 9/00

Claims (4)

(57) [Claims] 1. A transparent conductive film having a two-layer structure, comprising a lower layer provided on the surface of a transparent substrate and containing a fine metal powder in a siliceous matrix, and a siliceous upper layer provided thereon. The surface of the lower layer has irregularities, the average film thickness at the convex portion of the lower layer is 50 to 150 nm, the average film thickness at the concave portion is 50 to 85% of the average film thickness at the convex portion, The average pitch of the protrusions is
A transparent conductive film with low reflectivity and low resistance, which is characterized by having a thickness of 20 to 300 nm. 2. The fine metal powder is Fe, Co, Ni, Cr, W, Al,
One or more metals selected from the group consisting of In, Zn, Pb, Sb, Bi, Sn, Ce, Cd, Pd, Cu, Pt, Ag and Au, and / or alloys of these metals, And /
The transparent conductive film according to claim 1, which is composed of a mixture of these metals and / or alloys. 3. The transparent conductive film according to claim 1, wherein the transparent substrate is an image display part of a cathode ray tube. 4. The lower layer is formed from a dispersion liquid in which a fine metal powder having an average primary particle diameter of 5 to 50 nm is dispersed in a solvent containing a dispersant. The powder was characterized by forming secondary particles having a particle size distribution with a 10% cumulative particle size of 60 nm or less, a 50% cumulative particle size of 50 to 150 nm, and a 90% cumulative particle size of 80 to 500 nm. To do
The transparent conductive film according to claim 1.