JPH10182190A - Transparent black electroconducive film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To impart low reflecting, high contrast and electromagnetic wave shielding properties to a transparent black electroconductive film by forming a lower layer containing a metallic fine powder and a black powder and a siliceous upper layer on the lower layer in a siliceous matrix on the surface of a transparent substrate. SOLUTION: This transparent black electroconductive film is a two-layer film composed of a lower layer containing an electroconductive powder in a siliceous matrix and a siliceous upper layer free of the powder. Since the lower layer is an electroconductive layer densely containing the powder, the refractive index thereof is high, whereas the upper layer has a low refractive index. When an electroconductive film having the two-layer film constitution is formed on the glass surface of a cathode-ray tube front panel, the following effects are obtained: The leakage of electromagnetic waves, sticking of dust and reflecting in of an external image deteriorating the visibility are prevented or reduced while maintaining the color tone of an image good. The contrast of the image is raised and the haze is good without darkening the image to a greater extent than that is necessary.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-reflection, high-contrast, transparent black conductive material suitable for imparting functions such as antistatic, electromagnetic wave shielding and reflection prevention to a transparent substrate such as a cathode ray tube. About the membrane.

[0002]

2. Description of the Related Art Dust easily adheres to the surface of a front panel glass, which is an image display portion of a cathode ray tube including a TV and various display CRTs, due to static electricity. There is a problem that an image becomes unclear due to reflection of light or reflection of an external image. In recent years, there has been a concern about the effect of electromagnetic waves emitted from a cathode ray tube on the human body, and standards for low-frequency leakage electromagnetic waves have been established in various countries.

In order to prevent dust from adhering and prevent electromagnetic waves from leaking, means for forming a transparent conductive film having an antistatic effect and an electromagnetic wave shielding effect on the outer surface of the screen has been generally adopted. As a measure for preventing reflection, non-glare processing 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 has a problem that the resolution of an image is deteriorated and visibility is reduced.

For this reason, recently, a two-layer film in which a low-refractive-index transparent overcoat film is formed on a high-refractive-index transparent conductive film has been provided with both antistatic (dust-prevention) and glare-prevention functions. Have been tried to. 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 light reflected from the surface of the upper low-refractive-index film will be reflected from the interface with the lower high-refractive-index film. And the reflection is prevented as a result. When the conductivity of this transparent conductive film is high, an electromagnetic wave shielding effect is also provided at the same time.

For example, Japanese Patent Application Laid-Open No. 5-290634 discloses that Sb
An alcohol dispersion obtained by dispersing a fine powder of doped tin oxide (ATO) using a surfactant is applied to a glass substrate and dried to obtain a refractive index (1.55 to 1.55 to 1.54) higher than that of the conventional conductive index (1.50 to 1.54). -2.0), and a low-refractive-index film of silica (1.45) formed of alkoxysilane, which may contain magnesium fluoride (1.38), is formed on the conductive film. A two-layer film whose ratio has been reduced to 0.7% has been proposed.

Japanese Patent Application Laid-Open No. 6-12920 discloses an optical film thickness nd (n: n) of a high refractive index layer and a low refractive index layer formed on a substrate.
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 obtained. According to this publication, the high refractive index layer is a siliceous film containing fine powder of ATO or Sn-doped indium oxide (ITO), and the low refractive index layer is a silica film.

Japanese Patent Application Laid-Open No. Hei 6-234552 also discloses a two-layer film composed of a silicate high refractive index conductive film containing ITO and a silicate glass low refractive index film. JP-A-5-107403 describes a two-layer film of a high refractive index conductive film and a low refractive index film formed by applying a liquid containing a conductive fine powder and a Ti salt.

Japanese Patent Application Laid-Open No. 6-344489 discloses a high-refractive-index first layer film composed of ATO fine powder and black conductive fine powder (preferably carbon black fine powder), which is densely filled with solids. And a blackish two-layer film comprising a silica-based low refractive index film formed thereon.

[0009]

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 the transparency. In recent years, in particular, the standards for electromagnetic waves leaked from cathode ray tubes have become more stringent, and the above-mentioned conventional technology has insufficient electromagnetic wave shielding effects, making it difficult to cope with them.Therefore, a transparent conductive film having lower resistance and a large electromagnetic wave shielding effect has been required. Have been.

An object of the present invention is to reduce the resistance so as to exhibit a high level of electromagnetic wave shielding effect, to maintain transparency and a low haze value which do not impair the visibility of the CRT, and to provide a CRT with a high contrast and an external image. An object of the present invention is to provide a transparent black conductive film having a low reflectivity capable of providing a reflection preventing function.

[0011]

In view of the recent strict standards for the electromagnetic wave shielding property of a cathode ray tube, the present inventors have developed AT powder as a conductive powder used for a transparent conductive film.
It was concluded that the use of metal fine powders with higher conductivity rather than inorganic fine powders of semiconductors such as O and ITO was desirable, and as a result of further study, the lower layer containing metal fine powder and black powder was examined. It has been found that the above-mentioned object can be achieved by a two-layer film in which a silica-based low-refractive-index upper film is provided on a transparent conductive film.

Here, the present invention provides a low-reflection coating comprising a lower layer containing a fine metal powder and a black powder in a siliceous matrix provided on the surface of a transparent substrate, and a siliceous upper layer provided thereon. It is a transparent black conductive film having properties, high contrast properties, and electromagnetic wave shielding properties. In a preferred embodiment, the black powder is titanium black, and the transparent substrate is a CRT image display unit.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The transparent substrate on which the transparent black conductive film of the present invention is formed is not particularly limited, and may be any transparent substrate desirably imparting low reflectivity and electromagnetic wave shielding properties. A typical transparent substrate is glass, but the transparent black conductive film of the present invention can also be formed on a substrate such as a transparent plastic.

As described above, a transparent substrate that is particularly required to have low reflectivity and electromagnetic wave shielding properties is a front panel of a cathode ray tube used as a display device of a TV or a computer. The transparent black conductive film of the present invention,
In addition to low reflection and electromagnetic shielding (low resistance), it has the feature of high contrast. Therefore, when this conductive film is formed on the glass surface of the cathode ray tube front panel, while maintaining the color tone of the image well, the leakage of electromagnetic waves which is harmful to the health and causes the malfunction of the computer, the adhesion of dust, and the visibility are improved. Deteriorating glare can be prevented or reduced, and image contrast can be increased. Further, the haze is good and the image is not darkened more than necessary.

The transparent black conductive film of the present invention is a two-layer film comprising a lower layer containing a conductive powder in a siliceous matrix and an upper layer containing no powder. The lower layer has a high refractive index because it is a conductive layer densely containing fine metal powder and black powder, while the upper layer has a low refractive index. With this two-layer film configuration, the transparent black conductive film of the present invention has characteristics of low reflectivity, low resistance, and high contrast, and can exhibit the above functions.

In the transparent black conductive film of the present invention, both the siliceous matrix of the lower conductive layer and the siliceous upper layer may be formed of alkoxysilane (more broadly, a hydrolyzable silane compound). it can.

As the alkoxysilane, at least one
Any one or more silane compounds having at least two, preferably at least two, more preferably at least three alkoxyl groups can be used. Halosilanes containing a halogen as a hydrolyzable group can also be used together with or instead of alkoxysilane.

Specific examples of the alkoxysilane include tetraethoxysilane (= ethyl silicate), tetrapropoxysilane, methyltriethoxysilane, dimethyldimethoxysilane, phenyltriethoxysilane, chlorotrimethoxysilane, and various silane coupling agents.
(E.g., 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 the least expensive and easily hydrolysable ethyl silicate.

When the coating of alkoxysilane undergoes hydrolysis, the alcohol is eliminated, and the generated OH groups are condensed to form a silica sol. When this sol is heated and baked, condensation proceeds further and finally hard silica
(SiO ₂ ) film. Therefore, the alkoxysilane can be used to form a siliceous film as an inorganic film-forming agent, and when formed into a film together with a powder, functions as an inorganic binder for binding the powder and forms a matrix of the film. Will be. In addition, although a halosilane can similarly finally form a silica film by hydrolysis, below, it demonstrates as what uses an alkoxysilane.

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

As the metal fine powder, any metal or alloy powder or a mixture of metal and / or alloy powder can be used as long as it does not adversely affect the film-forming properties of the alkoxysilane. Preferred materials for the metal fine powder include Fe, Co, Ni, Cr, W, Al, In, Zn, Pb, Sb, and B.
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 Or a mixture of alloys. Particularly preferred metal species among these are Ni, W, In, Zn, Sn, Pd, Cu,
Pt, Ag, and Au, most preferably low resistance Ag
It is. Preferred alloys are Cu-Ag, Ni-Ag, Ag-Pd, Ag
Silver alloys such as -Sn and Ag-Pb, but are not limited thereto. Ag and other metals (eg, W, In, Sn,
Pb, Cu, Bi, etc.) are also preferable as the metal fine powder.

The metal fine powder includes one or more nonmetals such as P, B, C, N and S, or alkali metals such as Na and K and / or alkaline earth metals such as Mg and Ca. Or one or more of them may be dissolved.

The particle size of the metal fine powder is selected so as not to impair the transparency of the conductive film. In this sense, preferred metal fine powders have an average primary particle diameter of 0.1 μm or less, more preferably 0.05 μm or less. The fine metal powder having such an average particle size can be produced by using a colloid generation technique (eg, reducing a metal compound to a metal with a suitable reducing agent in the presence of a protective colloid). The particle shape of the metal fine powder is not particularly limited, and may be any of a spherical shape, an irregular shape, a flat shape, and a needle shape.

As the conductive powder, in addition to the metal fine powder,
Inorganic oxide type transparent conductive fine powder such as ITO and ATO
(Average primary particle diameter is 0.2 μm or less, preferably 0.1 μm
The following can also be used in combination. Even in that case,
It is preferable that more than half of the conductive powder be metal fine powder.

The black powder is blended for imparting blackness to the transparent conductive film of the present invention. As the black powder, black powder having conductivity is preferable, but in the present invention, the conductivity is sufficiently imparted by the coexisting highly conductive metal fine powder, so the black powder does not have conductivity. It may be something. The average primary particle diameter of the black powder is not particularly limited, but is preferably 0.1 μm or less so as not to significantly impair the transparency.

Examples of the conductive black powder include titanium black, graphite powder, magnetite powder (Fe ₃ O ₄ ), and carbon black. Among them, titanium black is most preferred because it has a particularly high visible light absorbency. Titanium _{black, TiO x · N y (0.7} <x <2.O, y <0.2)
This is a powder of titanium oxynitride having a composition represented by the formula: and having conductivity due to oxygen defects in the crystal lattice. Particularly preferred titanium black has x of 0.8 to 1.
Two things. Ag as a non-conductive black powder
O and the like.

The mixing ratio of the metal fine powder and the black powder is preferably in the range of 5:95 to 97: 3 by weight ratio of the metal fine powder to the black powder. This weight ratio is more preferably between 15:85 and 95: 5. Part of this metal fine powder,
As described above, an inorganic oxide-based transparent conductive powder such as ATO or ITO may be used instead.

If the amount of the fine metal powder is too small, it is impossible to reduce the resistance sufficiently to secure the electromagnetic wave shielding property, and the amount of the black powder increases, so that the transparency (visible light transmittance) of the film is increased.
Decrease. If the amount of the black powder is too small, the reflectance on the short wavelength side and the long wavelength side seen in the spectral reflectance curve (reflection spectrum) in the visible region sharply increases, and the target visible light minimum reflectance of 1.0 % Or less, the reflected light takes on a blue-purple or red-yellow tint, and the visibility is significantly impaired.

The amount of the siliceous matrix in the lower conductive layer may be an amount sufficient to bind the fine metal powder and the black powder. Since this conductive layer is covered with a siliceous upper layer, it does not require particularly high film strength and hardness. Generally, the amount of siliceous matrix required to bind the powder is
15 wt% or less is sufficient, and in some cases, a small amount of about 1 wt% may be sufficient. This amount is preferably between 5 and 10% by weight.

Method for Forming Transparent Black Conductive Film The lower conductive layer containing fine metal powder and black powder in a siliceous matrix is placed in a solution of alkoxysilane (which may be hydrolyzed in advance). A coating material in which a metal fine powder and a black powder are dispersed is applied to the surface of a transparent substrate,
It can be formed by heating and baking the coating film (converting the alkoxysilane to siliceous). Thereafter, a coating composed of a solution of an alkoxysilane for forming an upper layer is applied and heated to bake the coating to form a siliceous film of the upper layer, thereby forming a transparent black conductive film having a two-layer structure of the present invention. Hereinafter, this method is referred to as a first method.

As another second method, a lower conductive layer is formed by using a paint that does not contain an alkoxysilane functioning as an inorganic binder, that is, a paint in which a metal fine powder and a black powder are dispersed in a solvent. You can also. When this paint is applied to the surface of a transparent substrate, dried and the solvent is evaporated, the powder does not contain a matrix and consists essentially of only a metal fine powder and a black powder, and the space between the particles is a void. A coating is formed on the substrate surface. Both the metal fine powder and the black powder are composed of submicron fine particles and have a strong cohesive property, and thus can be formed into a film without a binder.

Thereafter, similarly to the first method, when a paint composed of an alkoxysilane solution for forming the upper layer is applied,
Part of the applied solution penetrates into the gaps between the particles in the lower layer and functions as a binder for binding the particles. The application of the alkoxysilane solution at this time is performed so that the solution that has not completely penetrated into the lower layer film remains on the lower layer film. Then, the film is heated and baked to convert the alkoxysilane to siliceous.The alkoxysilane that has permeated between the particles in the lower layer becomes a siliceous matrix that fills the voids between the particles, and the alkoxysilane that has not completely penetrated is in the upper layer. By forming a siliceous film, a transparent black conductive film having a two-layer structure of the present invention can be obtained.

In the second method, since the powder is first formed into a film without a binder, the particles of the conductive metal fine powder come into direct contact with each other without intervening silica. The structure is easily formed, which is effective for lowering the resistance. In addition, since the baking process, which requires time and energy costs, only needs to be performed once, the manufacturing process is simplified.

First method: In the first method, a paint used for forming a lower conductive layer is prepared by adding a coating solution of alkoxysilane to
It is prepared by dispersing a metal fine powder and a black powder. This dispersion of the powder can be achieved by conventional means commonly used in the manufacture of paints. The amount of the alkoxysilane is preferably in the range of 1 to 18 parts by weight based on 100 parts by weight of the total amount of the metal fine powder and the black powder in terms of SiO ₂ .

The solvent is not particularly limited as long as it can dissolve the alkoxysilane, but a preferred solvent is one or more alcohols or a mixed solvent of an alcohol and another compatible organic solvent and / or water. It is an alcoholic solvent. Alcohols include methanol, ethanol, isopropanol, butanol,
In addition to a monohydric alcohol such as hexanol, an alkoxy alcohol such as 2-methoxyethanol can be used alone or in combination with a monohydric alcohol.

The alkoxysilane is hydrolyzed in advance,
It can also be used for paints. Thereby, baking after application can be completed in a short time. In this case, the hydrolysis is preferably performed 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 performed at room temperature or under heating, and the preferred reaction temperature is in the range of 20 to 80 ° C.

In a preferred embodiment, the paint further comprises:
Alkoxy titanium (this may also be a hydrolyzate)
And at least one titanium compound selected from the group consisting of titanium coupling agents. This titanium compound acts as a film reinforcing agent, homogenizes the bonding between the particles of the metal fine powder and the black powder in the lower conductive layer,
This is effective in securing a low resistance excellent in stable reproducibility.

When this titanium compound is used, it is used in an amount of 0.1 to 5 with respect to the total amount of the fine metal powder and the black powder.
%, Preferably from 0.2 to 2% by weight. If the amount is less than 0.1% by weight, the above effect cannot be obtained. If the amount exceeds 5% by weight, the electron path between the powder particles is hindered, and the conductivity is reduced.

Examples of the alkoxytitanium that can be used in the present invention include tetraisopropoxytitanium, tetrakis (2
-Ethylhexoxy) titanium, tetraalkoxy titanium such as tetrastearoxy titanium, diisopropoxy bis (acetylacetonato) titanium, di-n-
Tri, di or monoalkoxy titanium such as butoxy bis (triethanol aminato) titanium, dihydroxy bis (lactato) titanium, titanium-i-propoxyoctylene glycolate and the like. Preferred is tetraalkoxytitanium. Alkoxytitanium can also be used as its hydrolyzate. The hydrolysis of alkoxytitanium can be carried out in the same manner as the hydrolysis of alkoxysilane.

On the other hand, examples of the titanium coupling agent include isopropyl triisostearoyl titanate, isopropyl tridecylbenzenesulfonyl titanate, isopropyl tris (dioctyl pyrophosphate) titanate, tetraisopropyl bis (dioctyl phosphite) titanate, tetraoctyl bis ( (Ditridecyl phosphite) titanate, tetra (2,2-diallyloxymethyl-1-butyl) bis (di-tridecyl) phosphite titanate, bis (dioctyl pyrophosphate) oxyacetate titanate, tris (dioctyl pyrophosphate) ethylene titanate, etc. There is.
Preferred titanium coupling agents have the following structural formula (1)
This is indicated by (8).

[0041]

Embedded image

The lower conductive layer forming paint may further contain one or more kinds of various additives which can be added to the paint if desired. Such additives include surfactants (cationic,
(Anionic, nonionic) and acids for promoting the hydrolysis of alkoxysilane.

As described later, the lower conductive layer has a thickness of 1000 nm.
Since the following thin film is sufficient, the paint is diluted as necessary so that the thin film has a viscosity that can be easily obtained by the adopted coating method. Generally, the viscosity of the paint of the present invention is
The range is preferably 0.8 to 10 cps, particularly 0.9 to 5 cps.

The coating can be applied by a spraying method, a spin coating method, an immersion method, etc., but the spin coating method is most preferable from the viewpoint of film forming accuracy. The coating is preferably performed such that a lower conductive layer having a thickness in the range of 20 to 1000 nm, particularly 30 to 600 nm is formed after drying. Film thickness
If it is less than 20 nm, conductivity and low reflectivity cannot be sufficiently imparted.
Thickness above 1000 nm, film transparency (visible light transmittance)
In addition to cracks and the like, resulting in poor adhesion and
The film is easily peeled.

In the baking after coating, particularly when the transparent substrate is a CRT, the baking is performed at a temperature of 250 ° C. or less, preferably 200 ° C. or less, more preferably 180 ° C. or less, in order to prevent the dimensional accuracy of the CRT and the phosphor from falling off. It is done by doing. If the transparent substrate is other than a cathode ray tube, a higher drying temperature may be employed within the range permitted by the material of the substrate.

An upper siliceous layer is formed on the lower conductive layer containing the fine metal powder and the black powder in the siliceous matrix thus formed. The coating for forming the upper layer may be composed of a solution of alkoxysilane or a hydrolyzate thereof, and a small amount of an acid may be added to the coating to promote hydrolysis of the alkoxysilane after application. Since the paint for the upper layer does not contain powder, it is preferable to use a hydrolyzate of alkoxysilane in order to increase the viscosity. The preferred viscosity of this paint is 1-5 cps
It is. The type of the solvent and the acid, the coating method, and the baking temperature after the coating may be the same as those described for the coating for forming the lower layer.

The silica-based upper coating containing no powder is
It has a lower refractive index than the lower layer, and
As with the layer film, a low-reflection two-layer film is obtained. The preferred thickness of the upper coating for this function is 20 to 150 nm, especially 50 to 120 nm.
nm.

Second method: In the second method, the paint used for forming the lower conductive layer does not contain an alkoxysilane functioning as a binder. That is, a paint prepared by dispersing a metal fine powder and a black powder in an applicable solvent is used.

The solvent used is not particularly limited as long as the metal fine powder and the black powder can be dispersed, and may be one or more solvents selected from an organic solvent and water.
Examples of usable organic solvents include alcohols such as methanol, ethanol, isopropanol, butanol, and hexanol; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, and 4-hydroxy-4-methyl-2-pentanone. , Toluene, xylene, hexane, cyclohexane and other hydrocarbons, N, N-dimethylformamide, N, N-
Examples thereof include amides such as dimethylacetamide and sulfoxides such as dimethylsulfoxide.

Also in the second method, a preferable solvent is an alcoholic solvent, that is, one or more alcohols, or a mixture of alcohol and another organic solvent (preferably the above ketone solvent) and / or water. Solvent.

It is preferable that the solvent, especially the alcoholic solvent, contains at least one kind of alkoxyethanol or β-diketone. Alkoxyethanol and β-diketone have the effect of strengthening the bond between the conductive fine powder particles, and enhance the film-forming properties of a paint containing no binder for forming the lower conductive layer. As a result, the accuracy of film formation is improved, the surface becomes smoother, and a lower conductive layer having reduced haze and reflectance is obtained.

Examples of alkoxyethanol include 2-
Methoxyethanol, 2- (methoxyethoxy) ethanol, 2-ethoxyethanol, 2- (n-, iso-) propoxyethanol, 2- (n-, iso-, tert-) butoxyethanol, 1-methoxy-2-propanol , 1
-Ethoxy-2-propanol, 1- (n-, iso-) propoxy-2-propanol, 2-methoxy-2-propanol, 2-ethoxy-2-propanol, and the like, and examples of β-diketone include 2,4-pentanedione (=
Acetylacetone), 3-methyl-2,4-pentanedione, 3-isopropyl-2,4-pentanedione, 2,2-
Dimethyl-3,5-hexanedione and the like. As the β-diketone, acetylacetone is preferred.

As described in the first method, the coating material for forming the lower conductive layer is composed of a solvent and the above two kinds of powders.
It is preferable to contain at least one titanium compound selected from alkoxytitanium (which may be a hydrolyzate thereof) and a titanium coupling agent as a film reinforcing agent.
The type and amount of the titanium compound are as described in the first method.

The paint may further contain other additional components. Examples of such additional components include surfactants
(Cationic, anionic, nonionic), pH adjuster
(Organic acids or inorganic acids, such as formic acid, acetic acid, propionic acid, butyric acid, octylic acid, hydrochloric acid, nitric acid, perchloric acid, etc., or amines), and small amounts of organic resins.

The viscosity of the coating is preferably between 0.8 and 10 cp.
s, more preferably 0.5 to 5 cps. In order to maintain good dispersion stability between the fine metal powder and the black powder dispersed in the coating material, the pH of the liquid is preferably in the range of 4.0 to 10, particularly 5.0 to 8.5.

The method of applying the paint and the thickness of the lower layer film formed of the two types of powders may be the same as in the first method. Since the paint does not contain a binder, the thickness of the powder film formed from this paint depends on the total concentration of the fine metal powder and the black powder in the paint. Therefore, the total concentration may be selected so as to form an underlayer film having a predetermined thickness according to the coating method to be used.
-20% by weight, preferably 1.0-5% by weight
Is within the range.

After a paint containing no alkoxysilane for forming a lower conductive layer is applied to the surface of the substrate, the solvent is evaporated by appropriate means to form a film substantially consisting of the above two types of powder on the substrate. . The 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 a 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 a part of the solvent may remain.

Thereafter, a paint for forming the upper layer is applied. This coating material consists of a solution of alkoxysilane or a hydrolyzate thereof in the same manner as the first method, and the solvent used is the first solvent.
The same may be used as the paint used in the method. In the second method, the paint for forming the upper layer penetrates into the gaps between the particles of the lower powder coating, and the upper and lower layers are baked at once after application of the paint, whereby the powder is tightly bound with silica. A lower conductive layer having a high refractive index is formed. On the other hand, the upper layer paint that has not penetrated into the lower layer forms the low refractive index silica-based upper layer that covers this conductive layer, so that the desired low reflectivity is ensured. If desired, additives such as surfactants for adjusting the permeability can be added to the paint.

In the second method, since the lower layer and the upper layer are baked at a time, it is preferable to use the alkoxysilane as a hydrolyzate in order to accelerate the hydrolysis of the alkoxysilane during the baking, and it is particularly called a silica sol. It is preferable to use one in a state. Silica sol can be prepared by hydrolyzing 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 concentration of silica sol in the coating material for forming the upper layer is preferably in the range of 0.5 to 2.5% by weight in terms of SiO ₂ . The viscosity of the paint is preferably
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 become insufficient, and if it is too high, the film forming accuracy decreases,
It is difficult to control the thickness of the upper layer. Further, if the viscosity of the paint is too high, the silica sol will not sufficiently impregnate the gaps between the powder particles in the lower layer, and the conductivity will be reduced, and the film forming accuracy will be reduced, and it will be difficult to control the film thickness of the upper layer. Becomes The method of coating the upper layer, the film thickness, and the baking temperature after coating may be the same as those in the first method. In the second method, the paint is applied twice,
If the coating is performed by a spin coating method, the coating for the lower layer and the coating for the upper layer can be continuously performed by sequentially dropping the coating for the lower layer and the coating for the upper layer on one spin coater. It can be carried out in the same simple working process as a single application.

As a result of examining the cross section in the thickness direction of the transparent black conductive film having the two-layer film structure of the present invention formed by the second method,
It was found that the content of the powder in the lower conductive layer did not show a sudden increase from the interface with the upper layer, but increased gradually. On the other hand, when formed by the first method,
The content of the conductive powder in the lower layer rapidly increases from the interface with the upper layer.

The two-layer film structure formed by the second method is
It is characterized in that there is little change in the visible light minimum reflectance when the film thickness of the lower conductive layer changes. That is, the reflectivity is
The value of (nm) × refractive index is λ / 4 (λ is the wavelength of incident light <nm>)
When the film thickness of the lower layer greatly deviates from this value, the visible light minimum reflectance can be kept low in the two-layer film formed by the second method. On the other hand, the first method is characterized in that the thickness of each layer can be easily controlled, and the thicknesses of the upper layer and the lower layer can be easily controlled so that the lowest visible light reflectance is minimized.

Whichever method is used, the transparent black conductive film having a two-layer structure of the present invention has optical characteristics such as low resistance, blackish transparency, and low reflectivity. . Conductivity of the transparent black conductive film is greatly vary depending on the type and amount of the metal micropowder of the lower layer (the ratio of the black powder), the surface resistance of the film is generally from 10 ⁰ Ω / □ platform 10 ⁵ Ω
It changes within the range of / □. Therefore, the type and amount of the metal fine powder may be selected according to the required degree of electromagnetic wave shielding. When ITO powder was used as the conductive powder, the surface resistance was in the order of 10 ³ Ω / □ at most. Therefore, by using the metal fine powder according to the present invention,
Further conductivity can be increased to 10 ⁰ Ω / □ pedestal surface resistance.

Further, since the transparent black conductive film of the present invention contains black powder in the lower conductive layer, the blue-purple or red-yellow tint of the conventional two-layer film is eliminated, and the transparent black conductive film is substantially free from the problem. Colorless. This conductive film has practically sufficient transparency such as a haze of less than 1% and a total light transmittance of 60% or more, although the lower layer contains metal fine powder or black powder densely. And a low-refractive-index silica layer as an upper layer, it can exhibit a low visible light minimum reflectance of less than 1%. In addition, by being blackish,
The contrast of the image can be increased.

[0065]

【Example】

(Example 1) In this example, a transparent black conductive film having a two-layer structure was formed on a glass substrate by the above-described second method.

Paint for forming the lower layer In a mixed solvent of isopropanol / 2-iso-propoxyethanol in a weight ratio of 80/20, a metal fine powder and a black powder in the types and ratios shown in Table 1 were used, and in some cases, the types shown in Table 1 were used. The two types of powders were dispersed in a solvent by mixing with a zirconia bead having a diameter of 0.3 mm and using a paint shaker to prepare a coating material for forming a lower layer containing no alkoxysilane. Both the fine metal powder and the black powder in this paint have an average primary particle size of 0.1 μm or less, and the paint is a sum of these two powders.
0.7 to 3.2% by weight, paint viscosity is 1.0 to 1.
It was in the range of 6cps.

The meanings of the symbols of the titanium compounds used in Table 1 are as follows. a: isopropyl tris (dioctyl pyrophosphate) titanate [compound of the above structural formula (3)], b: tetra (2,2-diallyloxymethyl-1-butyl)
Bis (di-tridecyl) phosphite titanate [compound of the above structural formula (8)], c: bis (dioctyl pyrophosphate) oxyacetate titanate [compound of the above structural formula (1)].

For comparison, paints containing the following ITO powder or ATO powder instead of metal fine powder were prepared in the same manner. ITO powder: Sn doping amount 5 mol%, average primary particle diameter 0.02
μm, ATO powder: Sb doping amount 5 mol%, average primary particle diameter 0.02
μm.

The coating ethoxysilane (ethyl silicate) for forming the upper layer was hydrolyzed by heating at 60 ° C. for 1 hour in ethanol containing a small amount of hydrochloric acid and water to synthesize a silica sol. The resulting 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 concentration of 0.70% by weight in terms of SiO ₂ and a viscosity of 1.65 cps.

[0070] film-forming method 100 mm × 100 mm × dimensions of 3mm thick soda lime glass
On one surface of a substrate made of (blue glass), a lower layer forming paint and an upper layer forming paint were sequentially dropped using a spin coater to form a film. The amount of each of the paints dropped was 5 to 10 g, the rotation speed was 140 to 180 rpm, and the rotation time was in the range of 60 to 180 seconds. Thereafter, the substrate was heated at 170 ° C. for 30 minutes in the air to bake the coating film, thereby forming a transparent black conductive film on the glass substrate. The characteristics of the obtained film were evaluated as follows.

Evaluation of film properties Film thickness: The film thickness of each layer was measured by SEM cross section. Surface resistance: Measured by a four-probe method (Loresta AP: manufactured by Mitsubishi Yuka). Light transmittance (total visible light transmittance): Self-recording spectrophotometer (U-40
00 type: manufactured by Hitachi, Ltd.). Haze: Measured with a haze meter (HGM-3D: manufactured by Suga Test Instruments).

Minimum visible light reflectance: on the back of the glass substrate,
Attach black vinyl tape (No.21: Nitto Denko) and apply at 50 ° C
After keeping the temperature for 30 minutes to form a black mask, the reflection spectrum of the visible wavelength region due to regular reflection at 12 ° was measured by a self-recording spectrophotometer. From this reflection spectrum, the minimum value of the reflectance at 500 to 600 nm with high visibility was determined, and this was defined as the minimum reflectance.

The above test results are also shown in Table 1. Further, the transmission spectrum and reflection spectrum of the transparent black conductive film (containing Ag fine powder and titanium black powder) of the example of the present invention in Test No. 7 are shown in FIGS. 1 (a) and (b).
The transmission spectrum and reflection spectrum of the transparent black conductive film (containing ITO powder and titanium black powder) of Comparative Example 3 are shown in FIGS. 2 (a) and 2 (b).

[0074]

[Table 1]

As can be seen from Table 1, in the example of the present invention, although the thickness of the lower conductive layer extends over a wide range of about 65 to 600 nm (may deviate greatly from λ / 4), it can be obtained. The conductive film has a visible light minimum reflectance of 1% or less,
It shows a haze of 1% or less and a total visible light transmittance of 60% or more, indicating that the film is a low-reflection film excellent in visibility.
The surface resistance of the film, the ratio of the metal fine powder type and a black powder were vary widely from 10 ⁰ Ω / □ pedestal to 10 ⁵ Ω / □ platform. That is, it is possible to change the conductivity of the film in accordance with the electromagnetic wave shielding properties to be required, with a tight electromagnetic shielding required to meet the 10 ⁰ ~10 ¹ Ω / □ pedestal surface resistance, very low It can be seen that a transparent black conductive film having resistance can be obtained.

On the other hand, when ITO powder is used as the conductive powder, the transparency is high, but the conductivity is as low as at most 10 ³ Ω / □, and strict electromagnetic wave shielding requirements are required. It turns out that it cannot be satisfied. When ATO powder is used, the surface resistance is 10 ⁶ Ω
/ □ Very high, indicating that even if antistatic ability can be imparted, electromagnetic wave shielding properties cannot be exhibited.

From the transmission spectrum of the transparent black conductive film (conductive powder is Ag powder) of the example of the present invention shown in FIG. 1 (a), it can be seen that the transmittance is almost constant at about 65% in the entire visible region. It can be seen that the film has a black tint. Also,
Comparing the reflection spectrum of this transparent black conductive film shown in FIG. 1 (b) with the reflection spectrum of the comparative example (conductive powder is ITO powder) shown in FIG. 2 (b), 400 nm and 800 nm at the end of the visible region. The reflectance in the vicinity of the conductive film of the present invention is lower than that of the comparative example.
It can be seen that the size becomes larger than when O powder is used.

(Embodiment 2) In this embodiment, the first
A transparent black conductive film having a two-layer structure was formed on a glass substrate by the method described in (1).

Tetraethoxysilane (ethyl silicate) was added as a paint binder for forming the lower layer in an amount of 10 parts by weight in terms of SiO ₂ per 100 parts by weight of the total amount of the fine metal powder and the black powder, and the hydrolysis catalyst was further added. Example 1 except that a small amount of hydrochloric acid was added as
Was similar to

Paint for forming upper layer Same as in Example 1. After application of the coating material for lower layer formed on the substrate in the film forming process a spin coater, a paint for the upper layer formed prior to coating with a spin coater, except carrying out the underlying baked by heating for 5 minutes to 50 ° C. in air And the same as in Example 1.

Table 2 summarizes the film structure and test results of the obtained black conductive fine powder having a two-layer structure. From Table 2,
It can be seen that the first method also provides a transparent black conductive film having the same properties as those formed by the second method shown in Example 1.

[0082]

[Table 2]

[0083]

According to the present invention, the transparent black conductive film can be prepared according to the kind and amount of the metal fine powder used as the conductive powder.
^It has a wide range of surface resistance from ⁰ Ω / □ to 10 ⁵ Ω / □, and its conductivity can be adjusted according to the required level of electromagnetic shielding. Can also respond.

Further, the transparent black conductive film has no violet-bluish or red-yellow reflected light, which has conventionally been a problem, and has a minimum visible light reflection despite containing metal fine powder. It has low reflectivity and sufficient transparency, with a ratio of 1% or less, a haze of 1% or less, and a total visible light transmittance of 60% or more, preferably 70% or more. Accordingly, by forming the transparent black conductive film of the present invention on the glass surface of the front panel of a cathode ray tube, reflection of an external image due to reflection can be prevented, and at the same time, it becomes a problem particularly in a CRT for a personal computer and a cathode ray tube for a large TV. A high degree of electromagnetic wave shielding that can reliably prevent the leakage of the electromagnetic wave can be imparted to the cathode ray tube. Also, because the film is blackish,
Image contrast is improved.

Therefore, the transparent black conductive film of the present invention not only improves the visibility of a cathode ray tube and improves the visibility of a CRT but also makes it easier to see an image, and also helps to prevent adverse effects on the human body due to leakage of electromagnetic waves and malfunction of a computer.

[Brief description of the drawings]

FIG. 1 (a) shows the transmission spectrum of the transparent black conductive film of the present invention produced in the example, and FIG. 1 (b) shows the reflection spectrum.

FIG. 2 (a) shows a transmission spectrum of a comparative transparent black conductive film produced in an example, and FIG. 2 (b) shows a reflection spectrum.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H01B 1/22 H01B 5/14 A 5/14 H01J 9/20 A H01J 9/20 29/88 29/88 H05K 9/00 V H05K 9/00 G02B 1/10 A

Claims (6)

[Claims] 1. A lower layer containing a fine metal powder and a black powder in a siliceous matrix provided on the surface of a transparent substrate,
Low reflectivity, consisting of a siliceous upper layer provided thereon,
Transparent black conductive film with high contrast and electromagnetic wave shielding. 2. The transparent black conductive film according to claim 1, wherein the black powder is titanium black. 3. The transparent black conductive film according to claim 1, wherein the transparent substrate is a front panel of a cathode ray tube. 4. The method according to claim 1, wherein the metal fine powder is Fe, Co, Ni, Cr, W, A
l, In, Zn, Pb, Sb, Bi, Sn, Ce, Cd, Pd, Cu, Pt, Ag
And one or more metals selected from the group consisting of Au and Au, and / or alloys of these metals, and / or mixtures of these metals and / or alloys. 2. The transparent black conductive film according to item 1. 5. The method according to claim 1, wherein the metal fine powder is contained in a proportion of 5 to 97% by weight based on the total amount of the metal fine powder and the black powder, and the lower layer has a thickness of 20 to 1000 nm. The transparent black conductive film according to any one of the above. 6. The lower layer comprises, in addition to the metal fine powder and the black powder, at least one titanium compound selected from the group consisting of alkoxytitanium, a hydrolyzate thereof, and a titanium coupling agent. The transparent black conductive film according to any one of claims 1 to 5, wherein the transparent black conductive film is formed from a paint containing 0.1 to 5% by weight based on the total amount of the powder and the powder.