JP3129110B2 - Transparent conductive film and method 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 method for forming a coating type transparent conductive film having excellent conductivity and electromagnetic field shielding properties, and a transparent conductive film obtained by this method. The transparent conductive film formed by the method of the present invention has extremely low resistance and low haze, and has high adhesion to the substrate and high film strength.
It is particularly suitable for forming a transparent conductive film for preventing static electricity on an image surface of a display or a TV cathode ray tube and for shielding an electromagnetic field, and can also be used for a transparent electrode of a display device such as a touch panel or a liquid crystal display.

[0002]

2. Description of the Related Art OA of TV cathode ray tubes, computers, etc.
2. Description of the Related Art A transparent conductive film has been formed on an image surface of a CRT (cathode ray tube) of an apparatus as an antistatic film for preventing adhesion of dust and electric shock. In recent years, these transparent conductive films have been required to have not only antistatic properties but also electromagnetic wave shielding properties.

That is, in a cathode ray tube or a CRT, electromagnetic waves generated from the vicinity of an electron gun and a deflection yoke leak to the surroundings,
It is feared that it has a bad effect on the human body. With respect to TVs, leakage electromagnetic waves increase with the increase in the size of cathode ray tubes, and with CRTs, the risk of leakage electromagnetic waves causing malfunctions of peripheral computers increases with the advancement of OA equipment. Therefore, it is necessary to block electromagnetic waves leaked from a cathode ray tube or a CRT so as to clear the safety standards. For this reason, it is desired that the transparent conductive film exhibit electromagnetic wave shielding properties.

The conductivity required of the transparent conductive film has been considered to be sufficient in terms of surface resistance in the order of 10 ⁸ Ω / square for the purpose of preventing static electricity only.
^It is necessary to further reduce the resistance to ⁵ Ω / □ or less, preferably 10 ⁴ Ω / □ or less, more preferably 10 ³ Ω / □ or less. In addition, haze (% of diffuse transmitted light with respect to direct transmitted light) is desirably as low as possible so as not to disturb the image (eg, 5% or less, particularly 1% or less), and adhesion to a substrate is naturally required. Is done.

[0005] The transparent conductive film is also used as a transparent electrode of various displays such as a touch panel, a liquid crystal display, a plasma display, an electroluminescence display and a fluorescent display which have been developed recently. The transparent conductive film used for this purpose is required to have conductivity equal to or higher than that for electromagnetic wave shielding.

The method of forming a transparent conductive film is roughly classified into a gas phase method including a CVD method and a sputtering method, and a coating method.
The vapor phase method can form a high-performance transparent conductive film, but is not suitable for mass production and is not practical.

In the coating method, the size and shape of the substrate (substrate) on which the conductive film is formed are limited, and a transparent conductive film can be formed in a large amount, simply, and at low cost without requiring a special device. The transparent conductive film is formed by a coating method by applying a transparent conductive paint to a substrate such as glass or plastic by means of coating, printing, spraying, or the like, and drying or curing the coating by heating or ultraviolet irradiation as necessary. Done.

As the transparent conductive paint, for example, JP-A-62
JP-A-232466, JP-A-63-54473, JP-A-2-77473 and JP-A-4-26768 each disclose a transparent conductive fine powder in a solvent and a polymer (resin) binder required for film formation. There is a composition containing Unlike the formation of a transparent conductive film by the sol-gel method belonging to the same application method, the formation of the transparent conductive film by applying such a paint requires a firing step at a high temperature regardless of the type of the conductive fine powder. Therefore, a transparent conductive film can be formed even on a substrate such as plastic that cannot be fired. Therefore, it is the cheapest, simplest, and widely applicable method for forming a transparent conductive film.

The transparent conductive fine powder used in the transparent conductive paint includes fine powders of conductive materials such as indium oxide containing Sn, tin oxide containing Sb, and zinc oxide containing Al and other metals. Particle size is generally 0.2 μm
m, especially 0.1 μm or less.

As the binder, an organic polymer such as an acrylic resin, a polycarbonate, or a polyester, or a polymerizable organic monomer or oligomer capable of forming an organic polymer by polymerization, and silica (siloxane-based) formed by hydrolysis and condensation of tetraalkoxysilane Organic and inorganic polymeric binders, such as polymers) are commonly used. In the present specification, the “polymer-based binder” is meant to include both inorganic and organic polymers, and polymerizable monomers and oligomers that form such polymers by polymerization. That is, not only polymers but also monomers and oligomers are included in the polymer binder. Note that the polymer binder may be simply referred to as a binder.

In order to improve the adhesion between the conductive fine powder and the binder, a suitable coupling agent (eg, vinyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-metaacryloxypropyl) It is also known to incorporate a small amount of a silane coupling agent such as trimethoxysilane) into the paint.

[0012]

However, since the transparent conductive film formed from such a transparent conductive paint has a structure in which conductive fine powder is dispersed in an insulating matrix (binder), the conductive film has a high conductivity. However, even if it can be used for antistatic purposes, it has been difficult to reduce the resistance to the level required for an electromagnetic wave shield or a transparent electrode.

Very recently, several transparent conductive paints capable of forming a transparent conductive film having electromagnetic wave shielding properties have been proposed. For example, JP-A-5-290634 discloses that Sb
An alcohol dispersion containing a mixture of fine powder of tin oxide (ATO) containing a surfactant and a surfactant is applied to a substrate, and dried to form a transparent conductive film having a high refractive index. A two-layer transparent conductive film obtained by applying and baking to form a low refractive index film is disclosed. Although it is described that this transparent conductive film exhibits practically sufficient electromagnetic wave shielding properties, the surface resistance achieved in the examples is on the order of 10 ⁷ Ω / □, which is insufficient.

JP-A-6-234552 discloses a silicate film in which ultrafine particles of indium oxide (ITO) containing Sn are dispersed in the first layer, and a silicate film in which the second layer (overcoat) does not contain ITO. A transparent conductive film for electric field shielding having a layer structure is disclosed. The first layer is composed of ultrafine particles I
Since the first layer alone is formed of an ink type paint (ie, having a low ratio of silicate (= tetraalkoxysilane) as a binder) containing TO, the first layer alone has a low surface resistance.
Low resistance of the order of 10 ³ to 10 ⁴ Ω / □ can be realized. But,
The first layer alone is liable to deteriorate and has insufficient hardness.
Layer is indispensable, and when the second layer is formed, the surface resistance is 7 ×
10 ⁴ to 10 ⁷ Ω / □.

Each of these is a two-layer type transparent conductive film. Since the upper layer is insulative, the conductivity of the entire two layers is reduced, and it is not always possible to obtain sufficient conductivity for electromagnetic wave shielding. . An object of the present invention is to provide a method for forming a transparent conductive film having a high level of conductivity required for electromagnetic wave shielding, a small haze, and high adhesion to a substrate and high film strength.

[0016]

Means for Solving the Problems The present inventors have conducted various studies to achieve the above object, and as a result, have found that a solvent, a conductive fine powder,
It has been concluded that a conventional transparent conductive paint comprising a binder has a limitation in improving the conductivity and it is difficult to obtain a transparent conductive film having a reduced resistance to a target level.

Because, in the case of a transparent conductive paint, it is necessary to disperse the conductive fine powder in the paint to a state close to the primary particles in order to obtain a coating film having a small haze. But,
In a conventional paint in which a binder coexists, when the conductive fine powder is dispersed in this way, a binder component is adsorbed on the surface of each powder particle, and a coating layer made of an insulating binder is formed because the particles are coated. Is done. As a result, the direct contact between the particles of the conductive fine powder is prevented by the coating layer,
Electron transfer, which occurs through direct contact of the particles, is hindered, and the conductivity is necessarily reduced. Since a sufficient amount of binder is required to enhance the adhesion to the substrate, it is difficult to increase the conductivity of the transparent conductive film (reduce the resistance) while securing the adhesion and the low haze.

Therefore, the present inventors have searched for a method of forming a transparent conductive film without using a polymer-based binder, and have found that certain non-polymeric organic compounds (eg, 2-alkoxy alcohol, β-diketone, alkyl acetate ) Exerts a binding force, and has previously proposed a composition for forming a transparent conductive film using this organic compound as a film-forming agent. Specifically, the composition for forming a transparent conductive film contains a conductive fine powder, a solvent, and the above-mentioned non-polymer-based film forming agent, and further includes a low resistance agent and a low haze agent as optional components. A composition to which one or both are added and does not contain a polymer binder.

When this composition is applied to a substrate and the coating film is baked, the haze is 1% or less and the surface resistance is 10 ¹ to 10 ⁵ Ω /.
A transparent conductive film having a low haze and a low resistance within the range of □ can be obtained. This low haze value means that even with the above non-polymer film forming agent, the conductive fine powder can be sufficiently dispersed in a state close to the primary particles. On the other hand, the above low resistance value means that the particles are in direct contact with each other in the coating film because each particle of the dispersed conductive fine powder is not coated with the binder. However, the absence of the binder, on the other hand, causes a problem that the adhesion of the powder to the substrate and the adhesion between the powders (film strength) are reduced, and the abrasion resistance of the film becomes insufficient. There was found.

Therefore, as a result of further study, since the coating film formed from the above composition does not contain a binder, there are voids between the particles of the conductive fine powder. Impregnating the coating film, the adhesion between the powder and between the powder and the substrate can be increased without significantly impairing the advantages of low haze and low resistance of the coating film, and low haze, low resistance, and high The inventors have found that an adhesive coating film can be formed, and have reached the present invention.

According to the present invention, a first step of applying a composition for forming a transparent conductive film, which contains a conductive fine powder, a solvent, and a non-polymer-based film-forming agent and does not include a polymer-based binder, to a substrate; A second step of impregnating the coating film obtained in the first step with a liquid containing a polymer binder and having a viscosity of 25 cps or less, and drying or curing the coating film. A method of forming is provided.

However, as described above, the polymer-based binder (also simply referred to as a binder) includes not only organic and inorganic polymers but also polymerizable monomers that form such polymers by polymerization (including cross-linking). And oligomers. Further, the non-polymer film forming agent means that the film forming agent is not a polymer and has no polymerization or crosslinking reactivity.

In a preferred embodiment, one or more of the following structures can be adopted. The conductive fine powder is made of indium oxide containing Sn (hereinafter abbreviated as ITO), tin oxide containing Sb (hereinafter abbreviated as AT).
O), or a fine powder of a conductive material made of zinc oxide containing one or more selected from Al, Co, Fe, In, Sn and Ti. The non-polymeric film-forming agent is 2-alkoxyethanol,
β-diketone, and selected from the group consisting of alkyl acetate, the pH of the composition for forming a transparent conductive film is 2.0 to 7.0.
Is within the range.

When the composition for forming a transparent conductive film is used as a haze-reducing and film-reinforcing agent, an aluminate-based coupling agent containing an acetoalkoxy group or a titanate-based coupling containing a dialkylpyrophosphate group or a dialkylphosphite group. The composition further contains an agent. The composition for forming a transparent conductive film, as a low resistance agent, Co,
Further contains mineral or organic acid salts of Fe, In, Ni, Pb, Sn, Ti, and Zn.

The polymer binder used in the second step is a hydrolysis / condensation product of tetraalkoxysilane, or Si, Ti, Zr, Al, Sn, Fe, Co, Ni, C
It is selected from mineral salts, organic acid salts, alkoxides, and complexes of u, Zn, Pb, Ag, In, Sb, Pt, and Au, and partial hydrolysates thereof.

According to the method of the present invention, the surface resistance is 10 ⁵ Ω /
□ or less, preferably 10 ¹ to 10 ⁴ Ω / □, with a haze of 1
%, Preferably 0.5% or less.

Hereinafter, the present invention will be described in detail for each component.

Materials Used in the First Step In the first step, a substrate is formed by using a composition for forming a transparent conductive film containing a conductive fine powder, a solvent, and a non-polymer-based film-forming agent and not containing a polymer-based binder. Is applied.

[Conductive Fine Powder] The type of the conductive fine powder is not particularly limited, and those which have been conventionally used for transparent conductive paints may be used. Examples of such conductive fine powders include ITO fine powder, ATO fine powder, and Al, Co, F
There is a zinc oxide fine powder containing one or more metals selected from e, In, Sn and Ti. The content of the other metal (doped metal) to be contained in each conductive fine powder is based on the total amount of the metal elements with respect to the ITO fine powder (the doped metal is S
n) 1-15 atomic%, ATO fine powder (doped metal is Sb)
1-20 atomic% for zinc oxide fine powder 1-25 atomic%
Is preferable.

The conductive fine powder has an average primary particle diameter (hereinafter, referred to as an average particle diameter) of 0.5 μm or less, more preferably 0.2 μm or less, so as not to impair the transparency of the formed film.
Particularly, those having a diameter of 0.1 μm or less are preferable. Particularly preferred conductive fine powder is ITO fine powder having an average particle size of 0.2 μm or less.

[Non-Polymer Film Forming Agent] In general, even if powder is formed into a coating material without using a binder, a film cannot be formed because of little adhesion between powder and between powder and substrate. However, the present inventors have found that certain non-polymeric organic compounds bind between the conductive fine powder and between the conductive fine powder and the substrate, and effectively function as a film-forming agent.

Non-polymeric organic compounds that have been found to function as film formers to date are 2-alkoxyethanol, β-diketone, and alkyl acetate (ie, alkyl acetate). But,
The film-forming agent used in the method of the present invention is not limited to these, and any non-polymeric organic compound may be used as the film-forming agent as long as it can bind the conductive fine powder. it can.

Specific examples of the compounds which can be used as a film-forming agent in the present invention are shown below. As 2-alkoxyethanol, 2-ethoxyethanol, 2- (methoxyethoxy) ethanol, 2- (n, iso-) propoxyethanol,
2- (n, iso-, tert-) butoxyethanol, 2-pentyloxyethanol, 2-hexyloxyethanol and the like. Examples of β-diketones are 2,4-pentanedione,
3-methyl-2,4-pentanedione, 3-isopropyl-2,4-pentanedione, 2,2-dimethyl-3,5-hexanedione and the like. Examples of alkyl acetates include methyl acetate, ethyl acetate, (n, iso-) propyl acetate, (n, iso-, tert-) butyl acetate, pentyl acetate, hexyl acetate, and the like.

[Haze Reduction / Film Reinforcing Agent] The composition for forming a transparent conductive film used in the first step is, as optional components, an aluminate-based coupling agent containing an acetoalkoxy group, and a dialkylpyrophosphate group or a dialkylpyrophosphate group. It may further contain a haze-reducing and film-reinforcing agent selected from titanate-based coupling agents containing a dialkyl phosphite group. Since this kind of coupling agent improves the haze and strength of the film, a small amount can be added particularly when it is desired to reduce the haze and / or increase the strength of the film.

Examples of the aluminate coupling agent containing an acetoalkoxy group include a compound represented by the following formula (1). Examples of titanate coupling agents having a dialkyl pyrophosphate group include the following:
There are compounds represented by the formulas (2) to (4), and examples of titanate coupling agents having a dialkyl phosphite group include compounds represented by the following formulas (5) to (7).

[0036]

Embedded image

[Low-resistance agent] The composition for forming a transparent conductive film used in the first step contains Co, Fe, I
A metal salt selected from mineral salts and organic acid salts of n, Ni, Pb, Sn, Ti, and Zn can be added as a low resistance agent. Examples of mineral acid salts are hydrochloride, sulfate, nitrate and the like, and examples of organic acid salt are acetate, propionate, butyrate, octylate, acetylacetate, naphthenate, benzoate. And so on. These are ionic compounds,
It contributes to improving the conductivity of the film.

[Solvent] As the solvent, any organic solvent capable of dissolving components other than the above-mentioned conductive fine powder (or having compatibility with liquid components) can be used. However, components used as a film forming agent in the present invention are excluded from the organic solvent.

Examples of usable organic solvents include alcohols such as methanol, ethanol, isopropanol and butanol, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone,
Ketones such as hydroxy-4-methyl-2-pentanone, hydrocarbons such as toluene, xylene, hexane, and cyclohexane; amides such as N, N-dimethylformamide and N, N-dimethylacetamide; and sulfoxides such as dimethyl sulfoxide And the like, depending on the components used,
One or more solvents are selected to dissolve them.

[Preparation of Composition for Forming Transparent Conductive Film] The composition for forming a transparent conductive film used in the first step is prepared by dispersing a conductive fine powder in a solution containing other components. It is prepared by mixing the above components. Each component can be used alone or in combination of two or more. The obtained composition preferably has a pH in the range of 2.0 to 7.0. The amount of each component is based on the weight of the conductive fine powder. The film forming agent 2-alkoxyethanol is 10 to 900%, β-diketone is 0.2 to 500%, alkyl acetate is 0.2 to 500%, and the haze is reduced.・ 5 membrane reinforcing agents
% Or less, and the resistance reducing agent is 0.2 to 15%. Composition pH
If the addition amount of each component is out of this range, the desired low haze and low resistance may not be secured.

Preferably, the pH of the composition is in the range of 6.5 to 3.0, and the amount of each component added is 15 to 200% of 2-alkoxyethanol, 0.4 to 100% of β-diketone, and 0.4 to 100% of alkyl acetate. 100100%, low haze / film reinforcing agent is 3.5% or less, low resistance agent is 0.5-10%. The amount of the solvent is not particularly limited as long as a composition having a viscosity suitable for application is obtained.

The transparent conductive film forming composition used in the present invention may further contain, if desired, additional components other than those described above (excluding the binder). Examples of such additional components include surfactants (cationic, anionic, nonionic), pH adjusters (organic or inorganic acids such as formic, acetic, propionic, butyric, octylic, hydrochloric, Nitric acid, perchloric acid, etc.).

Materials Used in the Second Step [Polymer Binder] In the second step, a liquid containing a polymer binder and having a viscosity of 25 cps or less is used for impregnation. As the polymer binder, one or more materials selected from various organic and inorganic polymers and polymerizable reactive monomers and oligomers which have been conventionally used as binders in transparent conductive paints are used. Can be. As will be described later, film properties (electrical, optical, mechanical properties) change depending on the type of binder. Therefore, an appropriate type of binder is selected according to the application. For example, organic polymers, especially thermoplastic polymers, result in highly flexible films. On the other hand, heat or ultraviolet curable organic and inorganic polymers produce hard films.

The organic polymer used as the binder is
Those having a polar functional group bonded to a carbon skeleton are preferred. As the polar functional group, a carboxyl group, an ester group, a ketone group, a nitrile group, an amino group, a phosphoric acid group, a sulfonyl group, a sulfonic acid group, a polyalkylene glycol group,
And an alcoholic hydroxyl group. Examples of polymers useful as binders include acrylics, alkyds, polyurethanes, acrylic urethanes, polycarbonates, polyesters, polystyrenes, polyacetals, polyamides, polyvinyl alcohol, polyvinyl acetate, and cellulose. Examples of the inorganic polymer include silica sol formed by hydrolysis and condensation of tetraalkoxysilane (= alkyl silicate).
(= Siloxane-based polymer).

Examples of the polymerizable organic monomer or oligomer include methyl acrylate, methyl methacrylate, methoxypolyethylene glycol methacrylate, glycidyl acrylate, ethylene oxide-modified phosphate acrylate, urethane acrylate, polyethylene glycol methacrylate, polybutadiene acrylate, and polyester acrylate. Acrylate and methacrylate type monomers and oligomers represented by, for example;
Mono (2-methacryloyloxyethyl) acid phosphate, acrylic acid, methacrylic acid, itaconic acid, acrylonitrile, methacrylonitrile, styrene, other vinyl monomers such as vinyl toluene; epoxide compounds such as bisphenol A diglycidyl ether, etc. is there.

Examples of polymerizable inorganic monomers include Si, Ti, Z
r, Al, Sn, Fe, Co, Ni, Cu, Zn, Pb, Ag, In, Sb, P
t, mineral salts of metals such as Au, organic acid salts, alkoxides,
And complexes (chelates). These are polymerized through hydrolysis or thermal decomposition, and finally inorganic substances (metal oxides,
(Hydroxide, carbide, metal, etc.), and is treated as an inorganic monomer in the present invention. These inorganic monomers can also be used in the state of a partial hydrolyzate. Next, specific examples of each metal compound will be described, but the present invention is not limited thereto.

Examples of usable silicon compounds include alkoxysilanes such as tetraethoxysilane, methylethoxysilane, dimethyldimethoxysilane and phenyltriethoxysilane; chlorosilanes such as methyltrichlorosilane, dimethyldichlorosilane and phenyltrichlorosilane; -Butyldimethylchlorosilane, N,
N-bis (trimethylsilyl) urea, N, O-bis (trimethylsilyl) acetamide, hexamethyldisilazane,
γ-chloropropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-aminopropyltrimethoxysilane, γ, glycidoxypropyltrimethoxysilane, γ-crysidoxymethyldiethoxysilane, γ- (methacryloxypropyl ) Trimethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, N-β (aminoethyl) γ-aminopropyltrimethoxysilane, N-β (aminoethyl) γ-aminopropylmethyldimethoxysilane, β- ( There are other organosilicon compounds such as 3,4 epoxycyclohexyl) ethyltrimethoxysilane, vinyltrichlorosilane, vinyltris (β-methoxyethoxy) silane, vinyltriethoxysilane, and vinyltrimethoxysilane.

As the titanium compound, titanium tetraisopropoxide, tetrakis (2-ethylhexoxy) titanium, tetrastearoxytitanium, diisopropoxy.
Bis (acetylacetonato) titanium, di-n-butoxybis (triethanolaminate) titanium, dihydroxybis (lactato) titanium, titanium-i-propoxyoctylene glycolate, titanium stearate and the like can be used.

Examples of zirconium compounds include alkoxides such as zirconium tetraisobutoxide. Examples of aluminum compounds include aluminum isopropoxide, acetoalkoxy aluminum diisopropylate and the like. Examples of tin compounds are di-n-butoxy tin,
And tetraisoamyloxytin.

Other metals (Fe, Co, Ni, Cu, Zn, Pb,
Ag, In, Sb, Pt, Au) are also mineral salts such as nitrates (eg, indium nitrate) and chlorides (eg, zinc chloride), and organic acid salts such as carboxylate (eg, indium octylate). Further, it can be used as an inorganic monomer in the form of a complex with a chelating agent such as acetylacetonate and ethylenediamine.

Preferred polymer binders are inorganic binders. That is, a hydrolysis / condensation product of an inorganic polymer, tetraalkoxysilane, or an inorganic monomer, Si, Ti, Zr, Al, Sn, Fe, Co, Ni, Cu, Zn, P
Preferred are b, Ag, In, Sb, Pt, and Au mineral salts, organic acid salts, alkoxides, or complexes, or partial hydrolysates thereof. Among them, inorganic monomers, especially In, Zn,
When a compound of each metal of Co, Sb, Ag, and Pb is used as a polymer-based binder, a transparent conductive film having a very low resistance can be formed.

[Impregnating liquid] The above-mentioned polymer binder
(Polymer, monomer or oligomer) is dissolved or diluted with an organic solvent if necessary,
A liquid having a viscosity of 25 cps or less, preferably 10 cps or less, is prepared and used for impregnation of the coating film formed in the first step. When the viscosity of the liquid is higher than 25 cps, the liquid does not sufficiently penetrate into the coating film to reach the substrate during impregnation of the coating film, and the desired effects of improving the adhesion and the film strength cannot be obtained. In addition, when the liquid has a high viscosity, excessive liquid is deposited on the coating film formed in the first step to form an insulating layer containing no conductive fine powder. descend.

The organic solvent used for dissolution or dilution is not particularly limited. In addition to the various organic solvents exemplified in relation to the first step, the liquid organic compound used as a film-forming agent in the first step and water are also solvents. Can be used as

If necessary, a curing catalyst (for thermal curing), a photopolymerization initiator (for ultraviolet curing) may be added to the impregnating liquid.
, Crosslinking agent, hydrolysis catalyst (eg, acid), surfactant, p
An H adjuster or the like can be added.

Method for Forming Transparent Conductive Film According to the method of the present invention, the first step of applying the composition for forming a transparent conductive film, which does not contain the above-mentioned polymer-based binder, to a substrate is carried out.
Step and impregnating the coating film obtained in this step with a liquid containing a polymer binder and having a viscosity of 25 cps or less, and performing a second step of drying or curing the coating film,
A transparent conductive film is formed on a substrate.

The application of the composition for forming a transparent conductive film in the first step is carried out by employing any commonly used application method such as spraying, dipping, bar coating, roll coating, flow coating, spin coating and the like. Can be. The thickness of the coating film formed by this coating is preferably 0.
02 to 1 μm, more preferably 0.05 to 0.5 μm. When the film thickness is 1 μm or more, it becomes difficult for the binder-containing liquid to penetrate into the substrate in the second step, and the adhesion may be insufficient.

After the application, the solvent is removed by standing or heating / baking if necessary, and the coating film is dried. As a result, a coating film in which the conductive fine powder is combined with the film forming agent is obtained. When baking is performed, the heating temperature is preferably in the range of 80 to 500 ° C., and the atmosphere is not particularly limited, and may be any of air, an inert atmosphere, and a reducing atmosphere. The coating film may be irradiated with ultraviolet rays instead of or in combination with baking after coating. By the ultraviolet irradiation, the residue found at the contact interface between the conductive fine powders in the coating film is decomposed,
The film characteristics are further improved.

The impregnation of the polymer-based binder-containing liquid in the second step can also be performed by the above-mentioned coating method. Since the impregnating liquid has a low viscosity and a thin film thickness, the impregnating liquid can penetrate into the coating film to reach the substrate even when impregnation is performed by a coating method with a short contact time such as spin coating. it can. The impregnating liquid is used in excess so that the entire coating is impregnated. Because of the low viscosity of the impregnating liquid, excess liquid that has not been impregnated is easily removed from the coating, and any impregnating liquid remaining on top of the coating is very thin. Therefore, the coating operation is performed twice,
The finally obtained coating film is substantially one layer.

The drying or curing of the coating film in the second step can be performed by any of leaving (air drying), baking, and ultraviolet irradiation, or a combination thereof, depending on the kind of the polymer binder used. The baking conditions (temperature and atmosphere) are appropriately selected according to the type of the binder. Generally the baking temperature is below 700 ° C, preferably 80
~ 500 ° C. When the substrate is made of a material having relatively low heat resistance such as plastic, it is necessary to select the type of the binder used in the second step in consideration of the required baking temperature. The baking atmosphere may be any of air, an inert atmosphere, and a reducing atmosphere.

The transparent conductive film obtained by the method of the present invention generally has a haze of less than 1%, preferably less than 0.5%,
It has a surface resistance of 10 ⁵ Ω / □ or less, preferably 10 ¹ to 10 ⁴ Ω / □, and has improved the adhesion between the conductive fine powders and between the fine powders and the substrate. High strength and excellent scratch resistance. The conductivity of the transparent conductive film varies depending on the baking atmosphere. When the atmosphere is an inert or reducing atmosphere, particularly a reducing atmosphere containing hydrogen or carbon monoxide, the conductivity is further improved.

The transparent conductive film formed by the method of the present invention comprises:
Since the adhesiveness to the substrate and the film strength are sufficiently high, it can be used for various applications as it is without overcoating, but may be further coated with an overcoat if desired. However, when the overcoat is an insulating film, the overcoat is preferably made as thin as possible in order to prevent a decrease in conductivity. A suitable overcoat is a silica film formed by hydrolysis of an alkoxysilane or the like.

[0062]

In the conventional transparent conductive paint, as described above,
As a result of the dispersion of the conductive fine powder, each powder particle is coated with the binder, which is an insulator. As a result, the conductivity is reduced, and it has been difficult to reduce the resistance while maintaining low haze and adhesion.

On the other hand, according to the method of the present invention, the first
In the step, the conductive fine powder is formed into a paint using a non-polymer-based film forming agent, and is applied to a substrate. The coating film thus formed is
Since the binder is not present, the conductive fine powder has a coating film structure in which each particle of the conductive fine powder is in direct contact without any intervening insulator. Even if the film forming agent is slightly adsorbed on the surface of the conductive fine powder, the adsorption is not so strong that it does not hinder the direct contact of the powder particles. Then, the binder is impregnated in the gaps between the conductive fine powders in the second step. Since this binder is used in the form of a liquid having a very low viscosity, the binder easily reaches the substrate, the conductive fine powder is integrated with the substrate,
An adhesive film is obtained. When the binder cures,
It is presumed that the contact pressure between the conductive fine powders is further increased due to the volume shrinkage (internal stress) of the binder, and ideal electron transfer is developed, so that excellent conductivity can be exhibited.

[Application Examples] The transparent conductive film formed by the method of the present invention is suitable for the display of OA equipment (CRT, liquid crystal display, etc.) and the antistatic of the image surface of a TV cathode-ray tube, and electromagnetic wave shielding. In this case, the composition for forming a transparent conductive film used in the first step contains a haze-reducing and film-reinforcing agent in addition to the conductive fine powder, the solvent, and the non-polymer-based film-forming agent, which are essential components. Are preferred. After applying this composition by a method such as spraying, spin coating, or dipping, in a second step, for example, a low-viscosity silica (siloxane-based polymer of 10 cps or less obtained by hydrolyzing and condensing tetraethoxysilane. ) The alcohol solution is applied in the same manner as described above, the liquid is impregnated into the coating film, and then baked at a relatively low temperature of about 80 to 250 ° C., the haze is 0.5% or less and the surface resistance is 10 ^3. Ω /
□ A transparent conductive film with excellent adhesion to the table is formed on the display or CRT surface. Although baking is sufficient in the air, baking in a reducing atmosphere can stably realize a low resistance of the order of 10 ³ Ω / □ even with a thin film of about 0.1 μm.

After the composition for forming a transparent conductive film is applied to a substrate, the composition is impregnated with a low-viscosity solution of a metal compound (inorganic monomer) such as In, Zn, Co, Sb, Ag, or Pb, and is then heated to 300 ° C. or more. When baking is performed at a high temperature, a transparent conductive film having a very low resistance of the order of 10 ¹ Ω / □ and excellent adhesion can be obtained.

The transparent conductive film formed by the method of the present invention comprises:
It can also be used as a transparent electrode and a transparent surface heating element for touch panels and various display devices. In applications where flexibility is required (eg, touch panel), it is preferable to use an organic binder as the binder used for impregnation.

The transparent conductive film formed by the method of the present invention comprises:
In addition to applications utilizing the conductivity, it can also be used for applications utilizing other characteristics of the conductive fine powder. For example, when the conductive fine powder used is an ITO fine powder having a function to cut off near infrared rays or a zinc oxide type fine powder having a function to cut off near ultraviolet rays, each has a low haze with respect to visible light. It is useful as a near-infrared cut-off film or a near-infrared cut-off film having high transparency and excellent adhesion. Also in this case, a transparent film having a high cutoff effect can be obtained as compared with a film formed from a conventional paint.

[0068]

【Example】

[Preparation of Transparent Conductive Film Forming Composition] As shown in Table 1, the following components (in Table 1, the numbers or symbols in <>) are used to form the transparent conductive film forming composition. Was prepared. In order to achieve the compounding ratio shown in Table 1 these components,
Put in a 100 cc glass bottle with a total amount of 60 g and a diameter of 0.
Each composition for forming a transparent conductive film was obtained by dispersing 100 g of 3 mm zirconia beads (Microhaica, manufactured by Showa Shell Sekiyu Sekiyu) with a paint shaker for 6 hours.

Solvent (1) Isopropanol <IPA> (2) Mixed solvent of isopropanol / ethanol / N, N-dimethylformamide (weight ratio 10: 10: 1) <Mixed 1> (3) Mixed solvent of isophorone / xylene ( (Weight ratio 4: 1) <Mixed 2> (4) Toluene <T> Conductive fine powder (average particle size 0.02 μm) (1) Sn: Indium oxide fine powder containing 5 atom% <IT
O> (2) Sb: fine powder of tin oxide containing 10 atomic% <ATO> (3) Al: fine powder of zinc oxide containing 5 atomic% <AZO> (4) Fe: 2 atomic% and Al: 1 Atomic% zinc oxide fine powder <F-AZO> (5) In: Zinc oxide fine powder containing 4 atomic% <IZO> (6) Sn: Zinc oxide fine powder containing 3 atomic% <TZO > Non-polymer type film forming agent (1) 2-ethoxyethanol / 2,4-pentanedione mixture
(Weight ratio 6: 1) <a> (2) 2-isopropoxyethanol / 2,4-pentanedione / ethyl acetate mixed solution (weight ratio 6: 1: 2) <b> (3) 2,4-pentane Dione <c> Low haze / film reinforcing agent Aluminum-based or titanate-based coupling agent represented by the above formulas (1) to (7) <(1) to (7)> [Preparation of binder-containing impregnation liquid] Each of the following polymer binder components and one of the above-mentioned solvents (both are indicated by numbers or symbols in <> in Table 1) are mixed at the compounding ratio shown in Table 1, and the impregnating liquid containing the binder is mixed. Was prepared. E-type viscometer for this liquid (Type ELD: manufactured by Tokimec)
Table 1 shows the viscosities at room temperature measured by the above.

Polymer type binder (1) Siloxane-based polymer obtained by hydrolysis and condensation of tetraethoxysilane (solid content in terms of SiO ₂ : 20% by weight) <P-1> Preparation method: water-cooled in a 500 mL four-necked flask Install condenser, stirring propeller and mantle heater,
385 g of tetraethoxysilane (manufactured by Colcoat) and a mixed solvent of ethanol / isopropanol (weight ratio 2: 1) 105
650 g of ion-exchanged water containing 1 g of concentrated hydrochloric acid was added dropwise with stirring at 180 rpm, and the mixture was reacted at 60 ° C. for 1 hour.

(2) Acrylic resin solution (solid content 38% by weight:
<P-2> Monomer type binder (1) Tetraethoxysilane <M-1> (2) Mixture of tetraethoxysilane / aluminum isopropoxide and zirconium isobutoxide (weight ratio: 1)
0: 2: 1) <M-2> (3) Mixture of mono (2-methacryloyloxyethyl) acid phosphate / 2-ethylhexyl methacrylate / glycerin diglycidyl ether / methyl ethyl ketone peroxide (weight ratio 4: 20: 6: 1) <M-3> (4) Mixture of mono (2-methacryloyloxyethyl) acid phosphate / 2-ethylhexyl methacrylate / benzyldimethyl ketal (weight ratio 8: 40: 1) <M-4> (5) Acetic acid Lead <M-5> (6) Indium nitrate <M-6> (7) Zinc octylate <M-7> (8) Cobalt naphthenate <M-8> [Conventional transparent conductive paint] (1) <Transparent Conductive paint A>
10 g of ITO> 7 g, 49.75 g of the above <mixture 2> as a solvent, and 3.25 g of the above <P-2> (60 g in total) as a binder.
The mixture was placed in a 0 cc glass bottle and dispersed with a paint shaker for 4 hours using 100 g of zirconia beads having a diameter of 0.3 mm.

(2) <Transparent conductive paint B> 7 g of the above <ATO> as a conductive fine powder, 49.75 g of the above <IPA> as a solvent,
<P-1> as binder and 5g (48g in total)
Was placed in a 100 cc glass bottle, and dispersed with a paint shaker for 6 hours using 100 g of zirconia beads having a diameter of 0.3 mm.

[Preparation of Transparent Conductive Film] Glass plate (length 75 mm ×
(Width 55mm x thickness 2mm, visible light transmittance 91%, haze 0.0%)
The composition for forming a transparent conductive film and the binder-containing liquid for impregnation are sequentially applied at room temperature using any of the following film forming methods, and then baked or cured by ultraviolet irradiation under any of the following curing conditions. Was cured to form a transparent conductive film.

Film formation conditions (1) were spin-coated / spin-coated / cured. <Film formation 1> (2) was spin-coated / in a reducing atmosphere of 10% H ₂ + N ₂ 2
Baking at 00 ° C for 5 minutes / spin coating / curing <Film formation 2> (3) dip coating / dip coating / curing <Film formation 3> (4) Spin coating / curing <Film formation 4> (5 ) Was bar-coated / cured. <Film formation 5> In addition, except for (2), the coating was allowed to dry (eg, for 1 to 3 minutes) after the application, and then applied.

Curing conditions (1) Baking in air at 100 ° C. for 30 minutes <Curing 1> (2) Baking in air at 160 ° C. for 30 minutes <Curing 2> (3) Baking in air at 350 ° C. for 30 minutes < Curing 3> (4) Baking in air at 550 ° C for 30 minutes <Curing 4> (5) Baking in a reducing gas atmosphere of 10% H ₂ + N ₂ at 160 ° C for 30 minutes <Curing 5> (6) Inert (N ₂ ) baking in a gas atmosphere at 250 ° C for 30 minutes <Curing 6> (7) Baking in an inert (N ₂ ) gas atmosphere at 650 ° C for 30 minutes <Curing 7> (8) High-pressure mercury lamp at room temperature in air at 600 mJ / UV irradiation cm ² <curing 8> (9) 5% H 2 + N 2 of 450 ° C. in a reducing gas atmosphere, 30 minutes of baking <hardening 9> obtained film of the transparent conductive film Thickness by SEM (cross section)
Haze is measured with a haze meter (HGM-3D: manufactured by Suga Test Machine) using the four-point probe method (Loresta AP: manufactured by Mitsubishi Yuka).
Cross-cut test (1mm x 1m)
m, the number of squares (total 100) remaining after tape peeling)
Was measured by The measurement results are also shown in Table 1.

For reference, FIG. 1A shows an SEM photograph of the dried coating film after the first application of the composition for forming a transparent conductive film, and FIG. S of the paint film
Each EM photograph is shown. From FIG. 1 (a), it can be seen that after the first application, the conductive fine powder is densely filled, and a coating film in which the fine powders are in direct contact with each other is formed. From FIG. 1 (b), it can be seen that the binder permeated into the voids of the coating film formed by the first coating and reached the substrate by the second coating. In addition, a layer consisting only of the binder is not formed on the surface, and the transparent conductive film is substantially a single layer.

[0077]

[Table 1]

[0078]

According to the method of the present invention, a transparent conductive film having a lower haze, a lower resistance and an excellent adhesion as compared with a film obtained by applying and curing a conventional transparent conductive paint containing a binder. Can be formed. Specifically, the haze is 1% or less, preferably 0.5% or less, and the surface resistance is 10 ⁵ Ω / □ or less, preferably 10 ¹ to 10 ⁴ Ω / □.
A transparent conductive film having a platform and adhesion (cross-cut test result) of 50/100 or more, preferably 100/100, was formed. In addition, by adjusting the presence / absence of a haze-reducing and film reinforcing agent and the setting of curing conditions, it is possible to greatly change the surface resistance value in particular by using a composition having the same basic composition. A transparent conductive film satisfying the required characteristics can be provided.

In particular, a haze-reducing and film reinforcing agent is added to the composition for forming a transparent conductive film used in the first step, and tetraalkoxysilane is hydrolyzed and condensed as a binder used in the impregnation in the second step. with siloxane-based polymer, or subjected to baking at a relatively low temperature (250 ° C. or less), or an in, Zn, Co, Sb, Ag, when subjected to baking at an elevated temperature with a compound of a metal such as Pb, 10 ¹ It is possible to obtain a transparent conductive film which has a very low resistance of about 10 ³ Ω / □ and satisfies the performance required for the electromagnetic wave shielding film of OA equipment displays and TV cathode-ray tubes.

According to the present invention, using a simple and efficient coating method, a high-performance transparent conductive material that cannot be obtained by the conventional coating method and can be used for shielding electromagnetic waves such as cathode ray tubes. The film can be formed at low cost.

[Brief description of the drawings]

FIG. 1A is a scanning electron microscope (SEM) of a dried coating film after a composition for forming a transparent conductive film containing no polymer binder is applied to a substrate according to the method of the present invention.
The photograph, FIG. 1 (b), is an SEM photograph after the binder is impregnated by the second application and the film is cured.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H01B 13/00 H01B 1/22 H01B 5/14 C09D 5/24

Claims (8)

(57) [Claims] 1. A first step of applying a composition for forming a transparent conductive film, which contains a conductive fine powder, a solvent, and a non-polymer-based film-forming agent and does not contain a polymer-based binder, to a substrate, and in the first step, A method of forming a transparent conductive film, comprising: impregnating the obtained coating film with a liquid containing a polymer binder having a viscosity of 25 cps or less and drying or curing the coating film. (However, the polymer-based binder is meant to include polymers and polymerizable monomers and oligomers.) 2. The method according to claim 1, wherein the conductive fine powder is composed of indium oxide containing Sn, tin oxide containing Sb, and Al, Co, F
2. A fine powder of one or more conductive materials selected from the group consisting of zinc oxide containing one or more selected from e, In, Sn and Ti. The method for forming a transparent conductive film of the above. 3. The non-polymeric film-forming agent is selected from the group consisting of 2-alkoxyethanol, β-diketone, and alkyl acetate, and the pH of the composition for forming a transparent conductive film is in the range of 2.0 to 7.0. The method for forming a transparent conductive film according to claim 1. 4. The group comprising the composition for forming a transparent conductive film, comprising: an aluminate-based coupling agent containing an acetoalkoxy group; and a titanate-based coupling agent containing a dialkylpyrophosphate group or a dialkylphosphite group. The method for forming a transparent conductive film according to any one of claims 1 to 3, further comprising one or more compounds selected from the group consisting of: 5. The composition for forming a transparent conductive film, the composition comprising Co, F
The method according to claim 1, further comprising one or more compounds selected from the group consisting of mineral salts and organic acid salts of e, In, Ni, Pb, Sn, Ti, and Zn as a low resistance agent. 5. The method for forming a transparent conductive film according to any one of 1 to 4. 6. The method for forming a transparent conductive film according to claim 1, wherein the polymer binder used in the second step is a hydrolysis / condensation product of tetraalkoxysilane. 7. The polymer binder used in the second step is composed of Si, Ti, Zr, Al, Sn, Fe, Co, Ni, Cu, Zn,
The mineral salt, the organic acid salt, the alkoxide, and the complex of Pb, Ag, In, Sb, Pt, and Au, and any one selected from the group consisting of the partial hydrolyzate thereof. 3. The method for forming a transparent conductive film according to item 2. 8. A transparent conductive film having a surface resistance of not more than 10 ⁵ Ω / □ and a haze of 1% or less, formed by the method according to claim 1.