JP3399270B2 - Transparent conductive film and composition for forming the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transparent conductive film having low reflectivity and low resistance, which is suitable for imparting functions such as antistatic, electromagnetic wave shield, and reflection prevention to a transparent substrate such as a cathode ray tube.

[0002]

2. Description of the Related Art Dust is apt to adhere to static electricity on the gallar surface of the front panel, which is an image display portion of a cathode ray tube including a CRT for TVs and various displays, and the surface is highly reflective, so that it is not external to the screen. There is a problem that the image becomes unclear due to the reflection of light and the reflection of an external image. Recently, there has been concern about the influence of electromagnetic waves emitted from the cathode ray tube on the human body, and standards for low-frequency leakage electromagnetic waves have been established in each country.

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

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

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

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

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

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

[0009]

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

An object of the present invention is to reduce the resistance so as to exhibit a high electromagnetic wave shielding effect, and to maintain high transparency and a low haze value which do not impair the visibility of a cathode ray tube.
It is an object of the present invention to provide a transparent conductive film having low reflectivity capable of imparting a function of preventing reflection of an external image on a cathode ray tube.

[0011]

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

However, since the fine metal powder reflects visible light, the transparency of the obtained two-layer film is low, but secondary particles of the fine metal powder are dispersed to form a network structure to form a film. Then, it has been found that the visible light can pass through the holes in the mesh structure, so that the transparency is greatly improved and the above-mentioned object can be achieved.

Here, the present invention is a transparent conductive film having a two-layer structure comprising a lower layer containing fine metal powder in a siliceous matrix provided on the surface of a transparent substrate, and a siliceous upper layer provided thereon. The film is characterized in that, in the lower layer, the secondary particles of the metal fine powder are distributed so as to form a two-dimensional network structure having pores containing no metal fine powder inside. It is a transparent conductive film having low reflectivity and low resistance.

In a preferred embodiment, the average area of the pores in the mesh structure is in the range of 2,500 to 30,000 nm ² , and the pores occupy 30 to 70% of the total area of the membrane. The network structure of the secondary particles of the fine metal powder has, for example, an average primary particle diameter of 2
~ 30 nm fine metal powder containing at least one of 1-30 wt% propylene glycol methyl ether, 1-30 wt% isopropyl glycol, and 1-10 wt% 4-hydroxy-4-methyl-2-pentanone It can be formed by using a paint that is dispersed by using a dispersant in a solvent.

[0015]

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

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

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

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

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

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

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

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

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

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

The fine metal powder has an average primary particle diameter of 2 to 30 n.
Fine particles within the range of m are preferred. If the average primary particle diameter is outside this range, it becomes difficult to form the network structure of the secondary particles of the fine metal powder, which is a feature of the present invention. The average primary particle diameter is more preferably 5 to 25 nm. Such finely divided metal fine powder can be produced by utilizing a method of colloid generation (eg, reducing a metal compound to a metal with an appropriate reducing agent in the presence of a protective colloid).

As described above, in the two-layered transparent conductive film of the present invention, the fine metal powder present in the lower layer as the conductive powder has a specific distribution state. That is, submicron fine particles generally tend to take the form of secondary particles in which primary particles (individual particles) are aggregated, but in the present invention, as shown schematically in FIG. It has a two-dimensional network structure formed by two-dimensionally connecting secondary particles, and pores are present in this network structure. Such a mesh structure can be formed by the method described later.

The pores are almost completely filled with the siliceous matrix only and there is almost no fine metal powder. Therefore, this void portion of the lower layer is substantially transparent, and most of the visible light that has entered the transparent conductive film at the position of this void portion can pass through this void. As a result, the transmittance of visible light is increased and the transparency of the transparent conductive film is improved.

On the other hand, the visible light incident on the position of the portion other than the pores of the mesh structure (the portion densely filled by the secondary particles of the fine metal powder being connected) is reflected by the fine metal powder. However, in this part of the transparent conductive film,
The lower layer has a high refractive index due to the presence of fine metal powder, is siliceous, and has a large difference in refractive index from the upper layer having a low refractive index. for that reason,
The visible light incident on the transparent conductive film in this portion has low reflectivity due to the difference in refractive index between the upper layer and the lower layer, as in the conventional two-layer film.

By thus distributing the secondary particles of the metal fine powder in the lower layer so as to form a network structure having a large number of pores inside, while maintaining the low reflectivity peculiar to the two-layer film, The presence of the holes can increase the transparency of the transparent conductive film. In order to reliably obtain this effect, it is preferable that the average area of the pores is in the range of 2,500 to 30,000 nm ² , and the pores occupy 30 to 70% of the total area of the membrane.

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

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

Method for Forming Transparent Conductive Film The method for forming the transparent conductive film having a two-layer structure of the present invention is not particularly limited, but for example, the method described below can be adopted.

First, a coating material for forming a lower layer is applied on a transparent substrate to form a film in which secondary particles of fine metal powder are distributed so as to have the above-mentioned network structure. The coating material for forming the lower layer generally comprises a dispersion liquid in which fine metal particles are dispersed in a solvent containing a dispersant. This coating may or may not contain an alkoxysilane that becomes a siliceous matrix after baking.

When the coating material for forming the lower layer does not contain an alkoxysilane serving as a binder, when this coating material is applied, dried and the solvent is evaporated, a film consisting essentially of fine metal powder is formed on the surface of the substrate. It is formed. The fine metal powder consists of submicron fine particles and has strong cohesiveness,
Can be formed into a film without the presence of a binder. After that, when a coating material composed of a solution of the alkoxysilane for forming the upper layer is applied, a part of the applied solution permeates into the voids between the particles of the metal fine powder in the lower layer and the pores of the above-mentioned network structure to form the metal fine powder. It functions as a binder that binds. The coating material for forming the upper layer is applied so that the coating material that has not completely penetrated into the lower layer film remains on the lower layer film.

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

This method requires only one baking process, which requires time and energy, and simplifies the manufacturing process. That is, in this method, the coating material is applied twice, but if it is applied by the spin coating method, the coating material for the lower layer and the coating material for the upper layer can be successively applied on one spin coater to continuously perform the coating. However, since baking is performed at a time after that, it is possible to carry out the same simple working process as that of one application in two steps.
Layer films can be formed. In addition, since there is no binder in the film of the fine metal powder that is formed first, the fine metal powder is in direct contact, and this state is maintained even after impregnation with the alkoxysilane. It is also advantageous in terms of conversion.

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

In any case, the paint for forming the lower layer is
When this coating material is applied to the surface of the substrate, the secondary particles of the fine metal powder are adjusted so as to be distributed in a network structure. When the paint is applied, the distribution state of the secondary particles of the fine metal powder in the paint is
Depends on factors such as the average primary particle size of the fine metal powder, the viscosity of the paint, and the surface tension of the solvent. Therefore, the solvent species, the average primary particle diameter of the fine metal powder, parameters such as the concentration of the fine metal powder may be selected so as to obtain the distribution state of the network structure of the secondary particles of the fine metal powder after coating. Those skilled in the art can perform the experiment.

For example, when the coating material for forming the lower layer does not contain an alkoxysilane serving as a binder, that is, is composed of a dispersion liquid in which fine metal powder is dispersed in a solvent containing a dispersant, the average primary particle of fine metal powder is At least one of propylene glycol methyl ether having a diameter of 2 to 30 nm and 1 to 30 wt% of solvent, 1 to 30 wt% of isopropyl glycol, and 1 to 10 wt% of 4-hydroxy-4-methyl-2-pentanone. When it contains a seed, the secondary particles of the fine metal powder easily form a network structure when the coating material is applied.

The remainder of the solvent is preferably composed of water and / or a lower alcohol such as methanol, ethanol, isopropanol, butanol. However, the solvent is not limited to this, and if the above network structure can be formed when the coating material is applied,
The paint can be prepared using any solvent. Other solvents that can be used include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and isophorone; toluene, xylene, hexane,
Hydrocarbons such as cyclohexane; amides such as N, N-dimethylformamide and N, N-dimethylacetamide; sulfoxides such as dimethyl sulfoxide.

Even when the coating material for forming the lower layer contains an alkoxysilane as a binder, the above-mentioned propylene glycol methyl ether, isopropyl glycol,
The use of three solvents, 4-hydroxy-4-methyl-2-pentanone, is effective in forming the network structure, but its amount may need to be changed. In any case, the solvent used may be determined experimentally.

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

The viscosity of the coating material for forming the lower layer is preferably 0.8.
-10 cps, more preferably 0.9-5 cps. The amount of fine metal powder in the paint should be 0.1-15% by weight of the paint, especially 0.3
A range of up to 10% by weight is suitable. When the alkoxysilane is contained, the amount of the alkoxysilane (the amount converted to SiO ₂ ) is preferably within the range of 1 to 18% by weight with respect to the total amount of the fine metal powder.

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

The coating for forming the lower layer is carried out by a spray method,
It can be performed by a spin coating method, a dipping method, or the like, but the spin coating method is preferable from the viewpoint of film formation accuracy. The coating is preferably performed so that the lower conductive layer having a thickness of 10 to 200 nm, particularly 25 to 150 nm is formed after drying.
If the film thickness is less than 10 nm, sufficient conductivity and low reflectivity cannot be imparted, and if it exceeds 200 nm, it becomes difficult to form a network structure of secondary particles of fine metal powder.

When the coating material for forming the lower layer contains an alkoxysilane, the coating film is heated after the coating material is applied to convert the alkoxysilane to silica. Thereby, a conductive lower layer coating film in which secondary particles of fine metal powder are distributed in a network structure in the siliceous matrix is formed. The baking conditions may be the same as the baking after the application of the upper layer forming coating material described later.

When the coating material does not contain alkoxysilane, the solvent is evaporated from the coating film by an appropriate means to form a coating film consisting essentially of fine metal powder on the substrate. This evaporation of the solvent can be carried out without heating or with heating, depending on the boiling point of the solvent used. For example, when the coating is performed by the spin coating method, depending on the type of 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.

On the lower layer film thus formed, a coating material comprising an alkoxysilane solution for forming the upper layer is applied,
Bake to form a siliceous film. The alkoxysilane in this paint may be a so-called silica sol that has been previously hydrolyzed in order to accelerate the hydrolysis of the alkoxysilane after coating. The silica sol can be prepared by hydrolyzing an alkoxysilane solution 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 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 baking after the coating of this coating material is carried out at 250 ° C. or less, preferably 250 ° C. or less, particularly when the transparent substrate is a cathode ray tube in order to prevent the dimensional accuracy of the cathode ray tube and the fluorescent substance from falling off.
It is performed by heating to 200 ° C, more preferably 180 ° C or less. When the transparent substrate is other than a cathode ray tube, a drying temperature higher than this may be adopted within the range allowed by the substrate material.

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

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

As a result of investigating the cross section in the thickness direction of the transparent conductive film having the two-layer film structure of the present invention, when the coating material for forming the lower layer does not contain alkoxysilane, the content ratio of the powder in the lower conductive layer is However, it was found that the increase did not occur suddenly from the interface with the upper layer, but increased gradually. Such a two-layer film structure is characterized in that the minimum visible light reflectance does not fluctuate when the film thickness of the lower conductive layer changes. That is, as for the reflectance, the value of film thickness (nm) × refractive index is λ / 4
It becomes the minimum when (λ is equal to the wavelength <nm> of the incident light ray), but the minimum visible light reflectance can be kept low even if the film thickness of the lower layer deviates greatly from this value.

On the other hand, when the coating material for forming the lower layer contains alkoxysilane, the content ratio of the conductive powder in the lower layer sharply increases from the interface with the upper layer. In this case, it is easy to control the film thickness of each layer, and it is possible to easily control the film thickness of the upper layer and the lower layer so that the minimum visible light reflectance is minimized.

Whichever method is used, the transparent conductive film having a two-layer structure of the present invention has optical characteristics that reflected light is not bluish, is almost colorless, has high transparency, and has low reflectivity. .
Specifically, the visible light transmittance is 60% or more, preferably 70%
Above, more preferably above 75%, haze is 1%
Low as below. As for the visible light reflectance, the minimum reflectance is as low as 1%, and the reflection spectrum is flat. On the short wavelength side (eg 400 nm), which was the cause of the bluish reflected light of the conventional two-layer conductive film. The increase in reflectance is suppressed to a level not much different from that on the long wavelength side (eg, 800 nm). Therefore, the reflected light has no bluish color and is substantially colorless, and the visibility of the image is improved.

In this transparent conductive film, secondary particles of metal fine powder which is conductive powder are connected so as to form a network structure, and electricity flows through the connection structure of the metal fine powder, so that metal Despite the relatively low degree of filling of fine powder (with pores), it has a low surface resistance of the order of 10 ² to 10 ³ Ω / □, and can sufficiently fulfill the electromagnetic wave shielding function.

[0057]

Example: Paint for forming lower layer Metal fine powder is added to a solvent containing a surfactant or polymer dispersant, and mixed with a paint shaker using zirconia beads having a diameter of 0.3 mm to mix the metal fine powder in the solvent. To prepare a lower layer-forming coating material containing no alkoxysilane. Type of fine metal powder, additives and solvents used and their amounts in paint (% is% by weight)
Was as shown in Table 1. The fine metal powder was prepared by a colloidal method (reducing a metal compound by reacting with a reducing agent in the presence of protective colloid), and the average primary particle size is also shown in Table 1. The symbols of additives and solvents (weight ratio in parentheses) shown in Table 1 have the following meanings.

Additive: A = stearyltrimethylammonium chloride B = sodium dodecylbenzene sulfonate C = polyvinylpyrrolidone (K-30 manufactured by Kanto Kagaku) Solvent: water / propylene glycol methyl ether / 4-hydroxy-4-methyl-2- Pentanone (85/10/5), methanol / isopropyl glycol (71/29), water / propylene glycol methyl ether (98.5 / 1.
5), ethanol / isopropyl glycol / propylene glycol methyl ether / 4-hydroxy-4-methyl-2-pentanone (84 / 1.5 / 5 / 9.5), ethanol (100), water / propylene glycol methyl ether (68/32)
.

Coating material 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 at a weight ratio of 5: 8: 1 to prepare a coating material having a SiO ₂ conversion concentration of 1.0% by weight and a viscosity of 1.65 cps.

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

Evaluation of Membrane Properties Average Area and Occupancy Ratio of Voids in Network Structure of Secondary Particles of Metallic Fine Powder: Measured from a TEM photograph of the upper surface of the membrane. Film thickness: The film thickness of each layer was measured by SEM cross section. Adhesion: Eraser ER-20R made by Lion Corp., load 1
After 50 times of reciprocation, kgf / cm ² , stroke width 5 cm, the state of scratches was visually observed. ○ means that there is no scratch, and × means that scratches are recognized.

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

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

Further, a TEM photograph of the surface of the transparent conductive film of the invention of Test No. 2 is shown in FIG. 2, its transmission spectrum and reflection spectrum are shown in FIGS. 3 (a) and 3 (b), and Test No. 11 is used.
A TEM photograph of the surface of the transparent conductive film of Comparative Example is shown in FIG. 4, and its transmission spectrum and reflection spectrum are shown in FIGS. 5 (a) and 5 (b).

[0065]

[Table 1]

As can be seen from Table 1, in the examples of the present invention, the results obtained by using the coating material prepared by dispersing the fine metal powder having the average primary particle diameter of 2 to 30 nm in the solvent satisfying the specific conditions by using the dispersant are shown. In the lower conductive layer, for example, as shown in the TEM photograph of FIG. 2, the secondary particles of the fine metal powder were distributed so as to form a network structure, and voids were present in this network structure.

However, the method of forming the transparent conductive film of the present invention is
The method is not limited to the method shown in the embodiment, and any method may be used to form the film as long as a similar network structure is generated. Further, the fine metal powder was not evenly distributed in the lower layer, and although the network structure of secondary particles was formed, the adhesion of the film was good.

On the other hand, in the comparative example, the type of the solvent or the average primary particle diameter of the fine metal powder was inappropriate, so that the secondary particles of the fine metal powder did not form a network structure, and the secondary structure of FIG.
As shown in, the distribution was relatively uneven. Further, particularly when the average primary particle size is much larger than the prescribed value of 60 nm (No. 12), the visible light transmittance and the adhesiveness of the film are remarkably lowered, and the haze is high, so that the adhesiveness for practical use is not sufficient. I couldn't get it.

In the example of the present invention, although the film thickness of the lower conductive layer covers a wide range from 28 nm to 146 nm (may deviate from λ / 4 in some cases), the obtained conductive film has a thickness of 1% or less. Minimum visible light reflectance, haze less than 1%, 60
% Or more, most of which is 70% or more of total visible light transmittance, low reflectance that can prevent glare of images, and sufficient transparency that does not interfere with image visibility. I understand.

When the reflectances at 400 nm and 800 nm were compared with the minimum reflectance, the reflectance at 400 nm was higher for all transparent conductive films, but the reflectance values were relatively high. It was small and the reflection spectrum was relatively flat, as shown in FIG. 3 (b). That is, it can be seen that, in addition to having low reflectivity, the reflected light has no bluish color and the visual sensitivity of the image is excellent.
Further, as shown in FIG. 3 (a), the transmission spectrum is also very flat and the film itself is colorless.

On the other hand, in the comparative example, the total visible light transmittance is low, the transparency of the film is inferior, and the minimum reflectance is low, but as shown in FIG. Is large (the reflection spectrum is not flat), and the reflectance at 400 nm is larger than that of the examples of the present invention. Therefore, the reflected light is bluish and adversely affects the visibility of the image.

From the viewpoint of conductivity, the surface resistance of the transparent conductive film of the present invention is on the order of 10 ² to 10 ³ Ω / □, and it has high conductivity capable of sufficiently imparting electromagnetic wave shielding property. On the other hand, in the transparent conductive film of the comparative example, even though the metal fine powders were used in the same amount, the metal fine powders were not connected in the mesh structure and were distributed in a random manner. , The surface resistance value was 10 ⁴ to 10 ⁵ Ω / □, and the conductivity was greatly reduced.

[0073]

The two-layer structure transparent conductive film of the present invention has a low surface resistance of 10 ² to 10 ³ Ω / □ even though the filling degree of the fine metal powder is relatively low. In particular, the cathode ray tube can be provided with an electromagnetic wave shielding property capable of preventing the leakage of electromagnetic waves, which is a problem particularly in CRTs for personal computers and cathode ray tubes for large TVs.

Further, this transparent conductive film has a minimum visible light reflectance of 1% or less, despite containing fine metal powder.
It has low reflectivity and sufficient transparency with a haze of 1% or less and a total visible light transmittance of 60% or more, preferably 70% or more. Moreover, this transparent conductive film has less purple-bluish or red-yellowish reflected light, which has been a problem in the past.
The reflected light is substantially colorless.

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

[Brief description of drawings]

FIG. 1 is an explanatory view showing a two-dimensional network structure of fine metal powder in a lower layer of a transparent conductive film having a two-layer structure of the present invention.

FIG. 2 is a TEM of a transparent conductive film of the present invention manufactured in an example.
It is a photograph.

FIG. 3 (a) shows a transmission spectrum of the transparent conductive film of the present invention produced in the example, and FIG. 3 (b) shows a reflection spectrum thereof.

FIG. 4 is a TEM of a transparent conductive film of a comparative example manufactured in an example.
It is a photograph.

FIG. 5 (a) shows a transmission spectrum of a transparent conductive film of a comparative example produced in the example, and FIG. 5 (b) shows a reflection spectrum of the same.

Continuation of 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-63-160140 (JP, A) JP8-290943 (JP, A) JP8-295513 (JP, A) JP10-1777 (JP, A) Nakajima Keiji et al., EMC directive, future electromagnetic wave shield against electromagnetic environment deterioration Materials CRT electromagnetic wave reduction wet coating, 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 (4)

(57) [Claims] 1. A two-layered transparent conductive film comprising a lower layer containing fine metal powder in a siliceous matrix provided on the surface of a transparent substrate, and a siliceous upper layer provided thereon. In the lower layer, the secondary particles of the fine metal powder are distributed so as to form a two-dimensional network structure having pores that do not contain the fine metal powder, and the flat particles of the pores of the network structure are distributed.
The uniform area is in the range of 2,500 to 30,000 nm ² , and the pores are
30 to 70% of the total area of the transparent conductive film with low reflectivity and low resistance. 2. The fine metal powder is Fe, Co, Ni, Cr, W, A.
l, In, Zn, Pb, Sb, Bi, Sn, Ce, Cd, Pd, Cu, Pt, Ag
The transparent conductive film according to claim 1, which comprises 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. 3. The transparent conductive film according to claim 1, wherein the transparent substrate is a cathode ray tube image display section. 4. The coating material used for forming the lower layer comprises a dispersion liquid in which fine metal powder having an average primary particle diameter of 2 to 30 nm is dispersed in a solvent containing a dispersant, and the solvent is 1 to 30 wt%. 4. Propylene glycol methyl ether, 1 to 30 wt% isopropyl glycol, and 1 to 10 wt% 4-hydroxy-4-methyl-2-pentanone at least one of claims 1 to 3. Transparent conductive film.