JP3399268B2 - Transparent black 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 black conductive material having low reflectivity and high contrast, 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. Regarding the membrane.

[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 has been 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 obtain a refractive index (1.55 higher than that of a conventional conductive refractive index (1.50 to 1.54)). ~ 2.0) and a low-refractive index film of silica (1.45) formed from an alkoxysilane that may contain magnesium fluoride (1.38) on top of it A two-layer film has been proposed in which the rate is reduced to 0.7%.

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.

The object of the present invention is to reduce the resistance so as to exhibit a high-level electromagnetic wave shielding effect, yet maintain the transparency and the low haze value which do not impair the visibility of the cathode ray tube, and provide the cathode ray tube with a high contrast and an external image. It is an object of the present invention to provide a transparent black conductive film having low reflectivity capable of imparting the anti-glare function.

[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 preferable to use a metal fine powder having higher conductivity rather than a semiconductive inorganic fine powder such as O or ITO, and as a result of further study, a lower layer containing a metal fine powder and a black powder It has been found that the above object can be achieved by a two-layer film in which a transparent conductive film is provided with an upper layer film of silica having a low refractive index.

Here, the present invention comprises a lower layer containing a metallic fine powder and a black powder in a siliceous matrix provided on the surface of a transparent substrate, and a siliceous upper layer provided thereon, which has low reflection. It is a transparent black conductive film having high properties, high contrast properties, and electromagnetic wave shielding properties. In a preferred embodiment, the black powder is titanium black and the transparent substrate is an image display part of a cathode ray tube.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION 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 for which it is desirable to impart low reflectivity and electromagnetic wave shielding property. A typical transparent substrate is glass, but the transparent black conductive film of the present invention can be formed on a substrate such as transparent plastic.

As described above, the transparent substrate which is particularly required to have low reflectivity and electromagnetic wave shielding property is a front panel of a cathode ray tube used as a display device such as a TV and a computer. The transparent black conductive film of the present invention,
In addition to low reflectivity and electromagnetic shielding (low resistance), it has high contrast. Therefore, if this conductive film is formed on the glass surface of the front panel of the cathode ray tube, the leakage of electromagnetic waves, which is harmful to health and causes malfunction of the computer, dust adhesion, and visibility are maintained while maintaining the good color tone of the image. It is possible to prevent or reduce the deterioration of glare and increase the contrast of the image. Also, 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 a siliceous upper layer containing no powder. The lower layer has a high refractive index because it is a conductive layer that contains fine metal powder and black powder densely, while the upper layer has a low refractive index. With this two-layer film structure, the transparent black conductive film of the present invention has the 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, hydrolyzable silane compound). it can.

At least one alkoxysilane is used.
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 released 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. It should be noted that halosilane can similarly be finally formed into a silica film by hydrolysis, but in the following description, it is assumed that alkoxysilane is used.

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, 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, Ag, and Au, most preferably low resistance Ag
Is. Preferred alloys are Cu-Ag, Ni-Ag, Ag-Pd, Ag
It is a silver alloy such as -Sn or Ag-Pb, but is not limited thereto. Also, Ag and other metals (eg, W, In, Sn,
A mixture with Pb, Cu, Bi, etc.) 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 particle size of the fine metal powder is such that the transparency of the conductive film is not impaired. In this sense, the fine metal powder preferably has 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 utilizing a method of colloid generation (eg, reducing a metal compound to a metal with an appropriate reducing agent in the presence of a protective colloid). The particle shape of the fine metal powder is not particularly limited, and may be spherical, irregular, flat, needle-like, or the like.

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 at least half of the conductive powder is fine metal powder.

The black powder is added in order to impart blackness to the transparent conductive film of the present invention. As the black powder, a black powder having conductivity is preferable, but in the present invention, since the coexisting highly conductive metal fine powder imparts sufficient conductivity, the black powder does not have conductivity. It may be one. The average primary particle size of the black powder is not particularly limited, but it is preferably 0.1 μm or less so as not to significantly impair the transparency.

Examples of the black powder having conductivity include titanium black, graphite powder, magnetite powder (Fe ₃ O ₄ ) and carbon black. Among them, titanium black is most preferable because it has a particularly high visible light absorption. Titanium black is TiO _x · N _y (0.7 <x <2.O, y <0.2)
It is a powder of titanium oxynitride having the composition shown by and has conductivity due to oxygen defects in the crystal lattice. Particularly preferred titanium black has x of 0.8 to 1. in the above composition.
Two things. Ag as a black powder without conductivity
O etc. are mentioned.

The mixing ratio of the fine metal powder and the black powder is preferably in the range of 5:95 to 97: 3 by weight ratio of fine metal powder: black powder. This weight ratio is more preferably 15:85 to 95: 5. Part of this fine metal powder is
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 becomes impossible to lower the resistance enough to secure the electromagnetic wave shielding property, and the amount of the black powder becomes large, so that the transparency of the film (visible light transmittance) is increased.
Is reduced. If the amount of black powder is too small, the increase in reflectance on the short wavelength side and the long wavelength side seen in the spectral reflectance curve (reflection spectrum) in the visible region will increase rapidly, and the target minimum visible light reflectance of 1.0 %, The reflected light becomes blue-purple or red-yellowish, and the visual sensitivity is significantly impaired.

The amount of the siliceous matrix in the lower conductive layer may be an amount sufficient to bond the fine metal powder and the black powder. Since this conductive layer is covered with the siliceous upper layer, it does not require particularly high film strength or hardness. Generally, the amount of siliceous matrix needed to bind the powder is
15% by weight or less is sufficient, and a small amount of about 1% by weight may be used in some cases. This amount is preferably 5 to 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 previously hydrolyzed). Apply a coating in which a fine metal powder and a black powder are dispersed onto the surface of a transparent substrate,
It can be formed by heating and baking the coating film (converting alkoxysilane into siliceous material). After that, a coating material comprising an alkoxysilane solution for forming the upper layer is applied, and the coating film is heated and baked to form an upper layer siliceous film, whereby the transparent black conductive film having a two-layer structure of the present invention is formed. Hereinafter, this method will be referred to as a first method.

As another second method, the lower conductive layer is formed by using a coating material which does not contain an alkoxysilane which functions as an inorganic binder, that is, a coating material in which a fine metal powder and a black powder are dispersed in a solvent. You can also do it. When this coating material is applied to the surface of a transparent substrate and dried to evaporate the solvent, it does not contain a matrix and consists essentially of fine metal powder and black powder, and the spaces between the particles are voids. A film is formed on the surface of the substrate. Since both the fine metal powder and the black powder are composed of submicron fine particles and have strong cohesiveness, they can be formed into a film without the presence of a binder.

Thereafter, as in the case of the first method, when a coating material comprising an alkoxysilane solution for forming the upper layer is applied,
A part of the applied solution penetrates into the voids between the particles in the lower layer and functions as a binder for binding the particles. At this time, the application of the alkoxysilane solution is performed so that the solution that has not completely penetrated into the lower layer film remains on the lower layer film. Next, when the coating is heated to bake and the alkoxysilane is converted to siliceous, the alkoxysilane that has penetrated between the particles in the lower layer becomes a siliceous matrix that fills the voids between the particles, and the alkoxysilane that could not penetrate completely becomes A siliceous film is formed to obtain the transparent black conductive film having a two-layer structure of the present invention.

In this second method, since the powder is first formed into a film in the absence of a binder, the particles of the conductive fine metal powder come into direct contact with each other without interposing silica therebetween, so that the electronic path The structure is easily formed, and it is effective for lowering the resistance. Further, since the baking process which requires time and energy cost is performed only once, the manufacturing process is simplified.

First Method: In the first method, the coating material used for forming the lower conductive layer is a solution of alkoxysilane,
It is prepared by dispersing fine metal powder and black powder. Dispersion of this powder can be accomplished by conventional means commonly used in the manufacture of coatings. The amount of alkoxysilane is preferably in the range of 1 to 18 parts by weight, calculated as SiO ₂ , based on 100 parts by weight of the total amount of the fine metal powder and the black powder.

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

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.

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, and homogenizes the bonding property between the particles of the metal fine powder and the black powder in the lower conductive layer,
It is effective for ensuring low resistance with stable reproducibility.

When this titanium compound is used, it is used in an amount of 0.1 to 5 relative to the total amount of the fine metal powder and the black powder.
It is advisable to use in an amount of% by weight, preferably 0.2 to 2% by weight. If it is less than 0.1% by weight, the above effect cannot be obtained, and if it exceeds 5% by weight, the electron path between the powder particles is obstructed and the conductivity is lowered.

Examples of alkoxytitanium that can be used in the present invention include tetraisopropoxytitanium and tetrakis (2
-Ethylhexoxy) titanium, tetraalkoxy titanium such as tetrastearoxy titanium, and diisopropoxy bis (acetylacetonato) titanium, di-n-
Examples thereof include tri-, di- or mono-alkoxy titanium such as butoxy bis (triethanol aminato) titanium, dihydroxy bis (lactato) titanium and titanium-i-propoxyoctylene glycolate. Preferred is tetraalkoxytitanium. Alkoxy titanium 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 titanium coupling agents include isopropyltriisostearoyl titanate, isopropyltridecylbenzenesulfonyl 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.
A preferred titanium coupling agent has the following structural formula (1)
It is shown by (8).

[0041]

[Chemical 1]

The lower conductive layer-forming coating material may further contain one kind or two or more kinds of various additives which can be added to the coating material, if desired. As such an additive, a surfactant (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 coating material is diluted as necessary so that the thin film has a viscosity that can be easily obtained by the coating method adopted. Generally, the viscosity of the coatings of the present invention is
The range of 0.8 to 10 cps, particularly 0.9 to 5 cps is preferable.

The coating material can be applied by a spray method, a spin coating method, a dipping method or the like, but the spin coating method is most preferable from the viewpoint of film forming accuracy. The coating is preferably performed so that a lower conductive layer having a thickness 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,
Transparency of film (visible light transmittance) above 1000 nm
In addition, the adhesion is deteriorated by causing cracks and the like,
The film is easily peeled off.

When the transparent substrate is a cathode ray tube, the baking after coating is performed at 250 ° C. or lower, preferably 200 ° C. or lower, more preferably 180 ° C. or lower in order to prevent dimensional accuracy of the cathode ray tube and to prevent the fluorescent substance from falling off. By doing. 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.

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 material for forming the upper layer may be composed of a solution of an alkoxysilane or a hydrolyzate thereof, and a small amount of acid may be added to the coating material in order to accelerate the hydrolysis of the alkoxysilane after coating. Since the coating material 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
Is. The type of solvent and acid, the coating method, and the baking temperature after coating may be the same as those described for the lower layer-forming coating material.

The siliceous upper layer film containing no powder is
It has a lower refractive index than the lower layer, which makes it more
Similar to the layer film, a low-reflection two-layer film is obtained. The preferred upper layer thickness for this function is 20 to 150 nm, especially 50 to 120 nm.
nm.

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

The solvent used is not particularly limited as long as it can disperse the metal fine powder and the black powder, and may be one or more solvents selected from organic solvents 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. Hydrocarbons such as toluene, xylene, hexane, cyclohexane, N, N-dimethylformamide, N, N-
Examples thereof include amides such as dimethylacetamide and sulfoxides such as dimethyl sulfoxide.

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 (the above-mentioned ketone solvent is preferable) and / or water. It is a 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 a function of strengthening the bond between the conductive fine powder particles, and enhance the film forming property of the coating material containing no binder for forming the lower conductive layer. As a result, the film forming accuracy is improved, the surface is made smoother, and the lower conductive layer with 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 can be mentioned.Examples of β-diketones include 2,4-Pentanedione (=
Acetylacetone), 3-methyl-2,4-pentanedione, 3-isoprop-2,4-pentanedione, 2,2-
Examples include dimethyl-3,5-hexanedione. Acetylacetone is preferred as the β-diketone.

As described in the first method, the coating material for forming the lower conductive layer is not limited to the solvent and the above two kinds of powder,
As the membrane reinforcing agent, it is preferable to contain at least one titanium compound selected from alkoxytitanium (which may be a hydrolyzate thereof) and a titanium coupling agent.
The kind and the amount of addition of the titanium compound are as described in the first method.

The coating composition may further contain other additive components. Examples of such additive components include surfactants.
(Cationic, anionic, nonionic), pH adjuster
(Organic acid or inorganic acid such as formic acid, acetic acid, propionic acid, butyric acid, octylic acid, hydrochloric acid, nitric acid, perchloric acid, etc., or amine), and a small amount of organic resin.

The viscosity of this paint is preferably 0.8-10 cp
s, more preferably 0.5 to 5 cps. In order to maintain good dispersion stability of the fine metal powder and the black powder dispersed in the paint, the liquid pH is preferably in the range of 40 to 10, and particularly 5.0 to 8.5.

The coating method of this coating and the film thickness of the lower layer coating composed of the two kinds of powders formed may be the same as in the first method. Since the paint does not contain a binder, the film 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, this total concentration may be selected so as to form a lower layer film having a predetermined thickness depending on the coating method used, but is usually 0.5.
~ 20% by weight, preferably 1.0 to 5% by weight
Within the range of.

A coating for forming a lower conductive layer, which does not contain an alkoxysilane, is applied to the surface of the substrate, and then the solvent is evaporated by an appropriate means to form a film consisting essentially of the above two kinds of 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.

After that, a coating material for forming the upper layer is applied. This coating consists of a solution of an alkoxysilane or its hydrolyzate as in the first method, and the solvent used is the first
It may be the same as the paint used in the above method. In the second method, the coating material for forming the upper layer penetrates into the gaps between the particles of the powder coating of the lower layer, and the upper layer and the lower layer are baked at once after the coating of the coating material, so that the powder is tightly bound with silica. A lower conductive layer having a high refractive index is formed. On the other hand, the upper coating material that has not penetrated into the lower layer forms an upper layer of siliceous material having a low refractive index and covering the conductive layer, so that the desired low reflectivity is secured. 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 the same time, it is preferable to use the alkoxysilane as a hydrolyzate in order to accelerate the hydrolysis of the alkoxysilane during baking, and it is particularly called silica sol. It is preferable to use the one in the state. 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 decrease,
It becomes 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 coating method of 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 coating is applied twice,
If the coating is performed by the spin coating method, the coating for the lower layer and the coating for the upper layer can be successively applied on one spin coater in order, and the coating can be continuously performed at a time. It can be carried out by a simple working process similar to one-time application.

As a result of investigating 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 does not show a sharp increase from the interface with the upper layer but gradually increases. On the other hand, when formed by the first method,
The content of the conductive powder in the lower layer sharply increases from the interface with the upper layer.

The two-layer film structure formed by the second method is
It is characterized in that the minimum visible light reflectance does not fluctuate when the film thickness of the lower conductive layer fluctuates. That is, the reflectance is the film thickness
(nm) × refractive index value is λ / 4 (where λ is the wavelength of incident light <nm>)
However, in the two-layer film formed by the second method, the minimum visible light reflectance can be kept low even when the film thickness of the lower layer deviates greatly from this value. On the other hand, the first method is characterized in that the film thickness of each layer can be easily controlled and the film thicknesses of the upper layer and the lower layer can be easily controlled so that the minimum visible light reflectance is minimized.

Whichever method is used, the transparent black conductive film having a two-layer structure of the present invention has the optical characteristics of 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
/ Changes within the range of □. Therefore, the type and blending amount of the fine metal powder may be selected according to the required degree of electromagnetic wave shielding properties. When ITO powder was used as the conductive powder, the surface resistance on the order of 10 ³ Ω / □ was at most, so by using the fine metal powder according to the present invention,
Further conductivity can be increased to 10 ⁰ Ω / □ pedestal surface resistance.

In addition, 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 it is substantially It is colorless. This conductive film has sufficient transparency for practical use that the haze is less than 1% and the total light transmittance is 60% or more, even though the lower layer densely contains fine metal powder or black powder. In addition, since it has a low refractive index silica layer as an upper layer, it can exhibit a minimum visible light reflectance of less than 1%. Also, because it has a black tint,
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 second method described above.

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

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 (dioctylpyrophosphate) oxyacetate titanate [compound of the above structural formula (1)].

For comparison, a coating material containing the following ITO powder or ATO powder instead of the fine metal powder was similarly prepared. 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.

Coating for forming the 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 in a weight ratio of 5: 8: 1 to prepare a coating material having a SiO ₂ conversion concentration of 0.70% 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 180 seconds. Then, the substrate was heated in air at 170 ° C. for 30 minutes to bake the coating film to form 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 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.).

Minimum visible light reflectance: on the back surface of the glass substrate,
Apply black vinyl tape (No.21: Nitto Denko) at 50 ℃
After keeping the temperature for 30 minutes to form a black mask, the reflection spectrum of visible wavelength by 12 ° specular reflection was measured by a self-recording spectrophotometer. From this reflection spectrum, the minimum value of the reflectance in the range of 500 to 600 nm, which has high luminosity, was obtained, and this was taken as the minimum reflectance.

The above test results are also shown in Table 1. The transmission spectrum and reflection spectrum of the transparent black conductive film (containing Ag fine powder and titanium black powder) of the present invention of Test No. 7 are shown in FIGS. 1 (a) and 1 (b).
Transmission spectra and reflection spectra 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, it was obtained even though the film thickness of the lower conductive layer was in a wide range of about 65 to 600 nm (may deviate greatly from λ / 4). The conductive film has a minimum visible light reflectance of 1% or less,
It shows that the film has a haze of 1% or less and a total visible light transmittance of 60% or more, and is a low-reflectivity film having excellent 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. In other words, the conductivity of the film can be changed according to the required electromagnetic wave shielding property, and the surface resistance of 10 ⁰ to 10 ¹ Ω / □ level required to satisfy the severe electromagnetic wave shielding property is required. It can be seen that a transparent black conductive film having resistance can also be obtained.

On the other hand, when ITO powder is used as the conductive powder, the transparency is high, but the conductivity is low at the surface resistance of the order of 10 ³ Ω / □, and a severe electromagnetic wave shielding property is required. It turns out that we cannot meet. Surface resistance is 10 ⁶ Ω when ATO powder is used
It is as high as / square, and although it can give antistatic ability, it cannot exhibit electromagnetic wave shielding properties.

From the transmission spectrum of the transparent black conductive film of the present invention (conductive powder is Ag powder) of the present invention shown in FIG. 1 (a), the transmittance is suppressed to about 65% in the entire visible region and is kept substantially constant. Therefore, it can be seen that the film has a blackish 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 is lower in the conductive film of the present invention example than in the comparative example, and the effect of improving visibility due to the low reflectivity is IT
It can be seen that it becomes larger than when O powder is used.

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

Coating material for forming the lower layer Tetraethoxysilane (ethyl silicate) was added as a binder at a ratio 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 added. Example 1 except that a small amount of hydrochloric acid was added as
Was similar to.

Coating for forming the upper layer The same as in Example 1. Film forming method: After coating the lower layer forming coating material on the substrate with the spin coater and before applying the upper layer forming coating material with the spin coater, the lower layer is baked by heating at 50 ° C. for 5 minutes in the atmosphere. The same as in Example 1.

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

[0082]

[Table 2]

[0083]

EFFECT OF THE INVENTION The transparent black conductive film of the present invention depends on the type and blending amount of the fine metal powder used as the conductive powder.
^It has a wide range of surface resistance values from ⁰ Ω / □ to 10 ⁵ Ω / □, and its conductivity can be adjusted according to the required level of electromagnetic shielding properties, so that it can meet strict electromagnetic shielding requirements. Can also respond.

This transparent black conductive film does not have the reflected light of purple to bluish or red to yellowish, which has been a problem in the past, and has the lowest visible light reflection despite containing fine metal powder. It has low reflectivity and sufficient transparency such that the rate is 1% or less, the haze is 1% or less, and the total visible light transmittance is 60% or more, preferably 70% or more. Therefore, by forming the transparent black conductive film of the present invention on the glass surface of the front panel of the cathode ray tube, it is possible to prevent the reflection of an external image due to reflection, and at the same time, it becomes a problem especially in a CRT for a personal computer and a cathode ray tube for a large TV. The cathode ray tube can be provided with a high degree of electromagnetic wave shielding property that can surely prevent the leakage of electromagnetic waves. Also, since the film is blackish,
The image contrast is improved.

Therefore, the transparent black conductive film of the present invention not only makes the image easier to see by improving the visibility and contrast of the cathode ray tube, but also helps prevent adverse effects on the human body due to electromagnetic wave leakage and malfunction of the computer.

[Brief description of drawings]

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

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

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI G09F 9/00 318 H01B 1/22 B H01B 1/22 5/14 A 5/14 H01J 9/20 A H01J 9/20 29 / 88 29/88 H04N 5/64 541D H04N 5/64 541 H05K 9/00 V H05K 9/00 G02B 1/10 A (56) Reference JP-A-8-77832 (JP, A) JP-A-7-48543 (JP, A) JP-A-6-344489 (JP, A) JP-A-6-212125 (JP, A) Nakajima Keiji et al., EMC Directive, future electromagnetic wave shield material CRT electromagnetic wave reduction wet coating against deterioration of electromagnetic environment, Industrial Materials, August 1, 1996, vol. 44 No. 9, p68-71 (58) Fields investigated (Int.Cl. ⁷ , DB name) C03C 15/00-23/00 B32B 1/00-35/00 C09D 1/00-10/00 H01B 1/00- 1/24 JOIS

Claims (6)

(57) [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 on it,
A transparent black conductive film with high contrast and electromagnetic wave shielding properties. 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 cathode ray tube front panel. 4. The fine metal powder is Fe, Co, Ni, Cr, W, A.
l, In, Zn, Pb, Sb, Bi, Sn, Ce, Cd, Pd, Cu, Pt, Ag
4. Any one of claims 1 to 3 consisting of one or more metals selected from the group consisting of and Au, and / or alloys of these metals, and / or mixtures of these metals and / or alloys. Item 1. The transparent black conductive film according to item 1. 5. The metal fine powder is contained in a proportion of 5 to 97% by weight with respect to the total amount of the metal fine powder and the black powder, and the film thickness of the lower layer is 20 to 1000 nm. The transparent black conductive film according to any one of 1. 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 and its hydrolyzate and a titanium coupling agent, and the metal fine powder and the black powder. The transparent black conductive film according to any one of claims 1 to 5, wherein the transparent black conductive film is formed from a coating material which is contained in an amount of 0.1 to 5% by weight based on the total amount of the powder.