JPWO2007043569A1 - Transparent conductive film and method for producing the same - Google Patents

Abstract

The present invention provides a transparent conductive film having high conductivity and sufficient film strength. Specifically, a transparent conductive film composed of a metal thin film having a planar network structure, and (a) a step of applying an emulsion solution in which polymer particles are dispersed on a substrate to form a single layer film of the polymer particles, (B) heating the formed single layer film to form a single layer planar network structure, (c) applying metal nanoparticles to the substrate on which the single layer planar network structure is formed, and (d) metal nano It is a manufacturing method of a transparent conductive film including the process of heating and fusing particles.

Description

  The present invention relates to a transparent conductive film comprising a metal thin film having a specific structure and excellent conductivity, and a method for producing the transparent conductive film.

  Transparent conductive films are widely used mainly as electrode materials in familiar electronics products. As a transparent conductive film for practical electronic devices, indium tin oxide (hereinafter referred to as ITO) film, which is an oxide thin film capable of obtaining stable characteristics, occupies most, and indium zinc oxide (hereinafter referred to as IZO). Membrane etc. are used. However, both ITO and IZO films are manufactured because indium, the main raw material, is a rare metal, so the depletion problem is jeopardized, and the formation of the film requires vacuum processing and high-temperature processing. There was a problem that the process was complicated.

  Therefore, a method of manufacturing a transparent conductive film in which metal particles such as gold and silver are used in place of the ITO film and the IZO film and metal fine particles are coated on a transparent substrate has been proposed. For example, Japanese Patent Application Laid-Open Nos. 63-160140 and 9-55175 disclose a method for producing an antistatic film used on the outer surface of a cathode ray tube by applying a metal colloid solution and drying it. Has been. However, the method described in JP-A-63-160140 and JP-A-9-55175 is a method in which metal particles are dispersed on a transparent substrate, and there is a problem that the mechanical strength is low, and the electrical conductivity. There was a problem of low.

  Japanese Patent Laid-Open No. 2001-255402 discloses a film having a transparent conductive layer in which a polymer latex and metal particles are mixed in order to increase the strength of the film. The transparent conductive layer has both strength and conductivity by mixing a polymer latex. However, since the metal fine particles are dispersed in the polymer latex on the substrate, the conductivity is not sufficient. There was a problem.

  The present invention can be easily manufactured without using indium, which has been conventionally contained as a main raw material for transparent conductive films, has excellent conductivity, and has sufficient film strength. It aims at providing the transparent conductive film which has.

  The present invention relates to a transparent conductive film made of a metal thin film having a planar network structure.

  The average mesh size of the planar network structure is preferably 0.1 μm or more.

  The present invention also relates to a transparent conductive material in which the transparent conductive film is formed on a substrate.

  The present invention also includes (a) a step of applying an emulsion solution in which polymer particles are dispersed on a substrate to form a single layer film of the polymer particles, and (b) heating the formed single layer film to form a single layer. The above transparent comprising a step of forming a planar network structure, (c) a step of applying metal nanoparticles to a substrate on which a single-layer planar network structure is formed, and (d) a step of heating and fusing the metal nanoparticles. The present invention also relates to a method for manufacturing a conductive film.

  The polymer particles preferably have a particle size of 0.1 to 1000 μm.

  It is preferable that the heating temperature in a process (b) is 50-350 degreeC.

  The present invention also includes (e) a step of enclosing air or a volatile monomer together with paste-like metal nanoparticles between opposing substrates to form a planar network structure between the substrates, and (f) a formed planar network structure. And (d) the method for producing the transparent conductive film, comprising the step of heating and fusing the metal nanoparticles.

It is an electron micrograph of the surface of the transparent conductive film of this invention. It is one Embodiment of the manufacturing method of the transparent conductive film of this invention.

  The present invention relates to a transparent conductive film made of a metal thin film having a planar network structure.

  Examples of the planar network structure include a planar triangular structure, a planar square structure, a planar hexagonal structure, a planar circular structure, or a mixed structure thereof. Among these, a plane hexagonal structure is preferable from the viewpoint of ease of production and conductivity uniformity.

  The average diameter of the planar network structure varies depending on the purpose, but is preferably 0.1 μm or more. When the average mesh size is smaller than 0.1 μm, uniform mixing with metal nanoparticles becomes difficult. The upper limit of the average diameter of the mesh can be variously selected depending on the embodiment. The larger the average diameter is, the better the transmittance is, but 1000 μm or less is preferable.

  10-100 nm is preferable and, as for the film thickness of a metal thin film, 10-50 nm is more preferable. When the film thickness is smaller than 10 nm, generally, the electron orbit is distorted in the vicinity of the metal film interface. Therefore, the proportion of the distorted region is increased, and the conductivity tends to decrease and the conductivity is not exhibited. . On the other hand, if the film thickness is larger than 100 nm, the transmittance tends to be small, and the shape of fine lines of metal nanoparticles forming a planar network structure tends to be seen.

  Specifically, the metal used for the metal thin film may be conductive nanoparticles such as gold, silver, copper, aluminum, iron, nickel, palladium, and platinum. Among these, gold and silver are preferable in terms of low reactivity and low surface resistance.

  The transmittance of the transparent conductive film is more preferably 50% or more, further preferably 70% or more, and particularly preferably 90% or more. When the transmittance is less than 50%, the value as a permeable film is low even though it can be used as a conductive film.

  The surface resistance of the film produced according to the present invention is preferably 100Ω / □ or less, more preferably 10Ω / □ or less, and further preferably 1Ω / □ or less. When the surface resistance is larger than 100Ω / □, the value as a conductive film is lowered.

  FIG. 1 shows an electron micrograph of the transparent conductive film of the present invention. As can be seen from FIG. 1, the transparent conductive film of the present invention has a planar network structure, and even if any part of the mesh is disconnected, the overall conductivity is hardly affected.

  The transparent conductive film of the present invention comprises (a) a step of applying an emulsion solution in which polymer particles are dispersed on a substrate to form a monolayer film of the polymer particles, and (b) heating the formed monolayer film. Forming a single-layer planar network structure, (c) applying metal nanoparticles to the substrate on which the planar network structure is formed, and (d) heating and fusing the metal nanoparticles. Manufactured by.

  Hereinafter, an embodiment of the method for producing a transparent conductive film of the present invention will be described with reference to FIG.

  First, in the step (a), an emulsion solution in which polymer particles are dispersed is applied onto the substrate 1, and each polymer particle is packed so as to be densely arranged on the substrate 1, thereby forming a polymer particle monolayer film 2. Is done.

  As the polymer particles in the step (a), the melting softening point temperature needs to be higher than normal temperature and lower than the melting temperature of the metal nanoparticles, and electrostatic repulsion between the polymer particles and the metal nanoparticles is strong, As in the case of metal nanoparticles, those having a negative charge in water are preferred in that a highly accurate network structure is formed. As a specific example, when a polymer latex particle such as polystyrene or polymethacrylic acid having a negative charge forms a single layer film, it is preferable in that a regular structure of particles having no cracks can be produced over a wide range.

  The particle diameter of the polymer particles is preferably 0.1 to 1000 μm, more preferably 0.1 to 5 μm, and further preferably 1 to 3 μm. When the particle diameter is smaller than 0.1 μm, the transmittance tends to decrease. On the other hand, when the particle diameter is larger than 1000 μm, the transmittance increases, but the fine line becomes too thick and the shape of the planar network structure tends to be seen.

  As the solvent for dispersing the polymer particles, a polar solvent which does not dissolve the polymer particles and has a low boiling point and a high vapor pressure is used. Examples of the polar solvent include water, methanol, ethanol, propyl alcohol, dimethyl sulfoxide, dimethylformamide and the like, and it is preferable to use water because it is easy to handle.

  As the substrate, a glass substrate, a plastic substrate, or the like can be used.

  The blending amount of the polymer particles in the emulsion solution is preferably 5 to 30% by weight and more preferably 15 to 30% by weight with respect to the emulsion solution. If the blending amount is less than 5% by weight, the filling rate tends to decrease and a wide range and a large number of voids tend to appear. On the other hand, if the blending amount is greater than 30% by weight, there is a tendency for multiple arrangement. In addition, in order to prepare an emulsion solution, you may add an emulsifier suitably.

  Examples of the method for applying the emulsion solution on the substrate include a shear coating method, a dip coating method, a spin coating method, an advection accumulation method, and a microchannel method.

  Next, in the step (b), the polymer particle monolayer film is heated to near the softening and melting temperature, whereby the contact area of each polymer particle is increased and a single-layer planar network structure is formed. The single-layer planar network structure becomes a so-called template for forming a planar network structure of metal nanoparticles in a later step.

  Although the heating temperature in a process (b) changes with softening points of a polymer particle, 50-350 degreeC is preferable and 150-250 degreeC is more preferable. When the heating temperature is lower than 50 ° C., no melt deformation of the particles is observed, and there is a tendency that the nanoparticles do not accumulate and are not thinned. On the other hand, when the heating temperature is higher than 350 ° C., the polymer particles tend to burn out.

  The heating time is preferably 5 to 60 seconds, and more preferably 15 to 30 seconds. When the heating time is shorter than 5 seconds, melting deformation of the particles is not recognized, and the particles tend to peel off and generate structural defects.

  Furthermore, in the step (c), the metal nanoparticles 4 are applied on the polymer particles 3 on which the template having a single-layer planar network structure is formed. Then, since the metal nanoparticles 4 enter a narrow boundary region between adjacent polymer particles, the metal nanoparticles 4 form a planar network structure.

  1-100 nm is preferable, as for the particle diameter of a metal nanoparticle, 10-50 nm is more preferable, and 10-20 nm is further more preferable. When the particle diameter is smaller than 1 nm, a single-layer network structure can be manufactured in principle, but the stability is poor and the operability tends to be poor. When the particle diameter is larger than 100 nm, it is difficult to make a thin line and the transmittance is lowered.

  The metal nanoparticles are preferably dispersed and applied in a solvent. Examples of the solvent include organic solvents such as alcohol, water, and the like, but water is preferable because of easy handling.

  The compounding amount of the metal nanoparticles is preferably 1 to 30% by weight, and more preferably 10 to 20% by weight when gold is used as the metal of the metal nanoparticles. If the blending amount is less than 1% by weight, the conductivity tends to decrease. On the other hand, if the blending amount is greater than 30% by weight, the fluidity tends to decrease and the productivity tends to decrease.

  Examples of the method for applying the metal nanoparticles include a shear coating method, a dip coating method, a spin coating method, an advection accumulation method, and a spray method.

  Next, in the step (d), the metal nanoparticles 4 having the planar network structure are heated, so that the metal nanoparticles 4 are fused to each other. At that time, the polymer particles 3 forming a template having a single-layer planar network structure are removed by heating to form voids 5, and as a result, a transparent conductive film 6 made of a metal thin film having a planar network structure is formed.

  200-450 degreeC is preferable and the fusion temperature in a process (d) has more preferable 400-450 degreeC. When the fusing temperature is lower than 200 ° C., polymer particles tend to remain. On the other hand, if the fusion temperature is higher than 450 ° C., the substrate tends to be softened and deformed.

  In addition, after forming a single-layer planar network composed of polymer particles on a substrate, a planar network structure is formed by coating polymer particles and metal nanoparticles on the substrate at the same time, instead of applying metal nanoparticles. May be. That is, a step of applying an emulsion mixed solution in which polymer particles and metal nanoparticles are dispersed on a substrate to form a polymer particle monolayer film containing metal nanoparticles, and the formed polymer particle monolayer film is a softening point of the polymer particles The transparent conductive film of the present invention can also be produced by a method including a step of heating to the vicinity to form a planar network structure and a step of heating to fuse the metal nanoparticles.

  In addition, the single layer structure in the production method of the present invention occurs when the drying rate and the supply rate of the polymer dispersion are in equilibrium. Therefore, by changing the drying speed (accumulation speed) of the polymer particles, it is possible to obtain a polymer particle ordered structure film having a multilayer structure of two layers, three layers or more. Thereby, it is possible to produce a transparent conductive film having a three-dimensional network structure. A transparent conductive film having a three-dimensional network structure is preferable in that it has a large specific surface area.

  Further, the transparent conductive film of the present invention includes (e) a step of enclosing air or a volatile monomer together with paste-like metal nanoparticles between opposing substrates to form a planar network structure between the substrates, (f) It can also be produced by a method comprising a step of freeze-drying the formed planar network structure and a step of (d) heating and fusing the metal nanoparticles.

  In the step (e), a planar network structure of the metal nanoparticles is formed between the substrates by bubbles generated when the paste-like metal nanoparticles and air are mixed and sealed between the substrates. For example, a channel that can be sealed while mixing paste-like metal nanoparticles and air between opposing substrates is provided, and the paste and air are mixed in the channel to generate fine bubbles. Let me. After that, when the bubbles in the flow path are sealed between the substrates, the bubbles are filled so as to be densely arranged, and the metal nanoparticles present at the boundary portion of each bubble form a planar network structure.

  Here, the particle size of the bubbles filled between the substrates is preferably 0.4 μm or more, and more preferably 0.8 μm or more. When the bubble particle size is smaller than 0.4 μm, the transmittance tends to be remarkably lowered.

  Here, the distance between the substrates is preferably 0.4 to 200 μm. When the distance is smaller than 0.4 μm, the amount of metal constituting the film tends to decrease and the conductivity tends to decrease. On the other hand, if the distance is larger than 200 μm, the film thickness inevitably increases and tends to be visible.

  A volatile monomer that is insoluble in a solvent may be encapsulated instead of air. Specifically, if the solvent is water, a styrene monomer can be encapsulated.

  Paste-like metal nanoparticles are formed by adding metal nanoparticles and, if necessary, an emulsifier in an organic solvent such as alcohol or a solvent such as water.

  The compounding amount of the metal nanoparticles is preferably 1 to 30% by weight with respect to the paste, and particularly 10 to 30% by weight when the metal is silver. If the blending amount is less than 1% by weight, the conductivity tends to decrease. On the other hand, if the blending amount is larger than 30% by weight, the fluidity tends to decrease.

  An emulsifier is appropriately added in order to stabilize the bubbles encapsulated between the substrates and forming a planar network structure. The emulsifier is preferably a volatile liquid, and specific examples include polyethylene glycol lauryl ether, polyethylene glycol oleyl ether, and sodium lauryl sulfate.

  The blending amount of the emulsifier is preferably 0.1 to 5% by weight with respect to the paste, and particularly preferably 1 to 2% by weight when the metal is silver. If the blending amount is less than 0.1% by weight, the bubbles tend to coalesce and become non-uniform. On the other hand, if the blending amount is larger than 5% by weight, the fluidity tends to decrease and the productivity tends to decrease.

  The flow rate at which the paste-like metal nanoparticles are sealed is preferably 0.01 to 0.5 ml / min, more preferably 0.1 to 0.2 ml / min. When the flow rate is less than 0.01 ml / min, the bubbles tend to coalesce and become non-uniform. On the other hand, when the flow rate is higher than 0.5 ml / min, the bubble size tends to be small.

  The flow rate for enclosing air is preferably 0.05 to 2.5 ml / min, and more preferably 0.5 to 1 ml / min. When the flow rate is less than 0.05 ml / min, the amount of bubbles tends to decrease and the transmittance tends to decrease. On the other hand, when the flow rate is higher than 2.5 ml / min, the bubbles tend to coalesce and become non-uniform.

  The gas to be sealed is not limited to air, but may be nitrogen, argon, or the like.

  In the step (f), a planar network structure formed of metal nanoparticles is formed, then frozen, and then vacuum dried to remove the solvent and immobilize the planar network structure. The freezing temperature may be any temperature below the freezing point of the solvent used.

  In the step (d), the metal nanoparticles having the planar network structure are fused by heating, and the solvent or emulsifier other than the metal is removed by heating to form a metal thin film having a planar network structure of metal nanoparticles.

  In addition, in order to make metal particles into nanoparticles, aggregation must be avoided. Methods for stabilizing nanoparticles include attaching a dissociation group to the surface and preventing aggregation by electrostatic repulsion, and wrapping with a polymer or surfactant to prevent aggregation by steric repulsion. It is done. However, when stabilization is performed as in the method, when gold nanoparticles are aligned and fused in a single layer to form a thin film, particle gaps are formed, so that fusion does not occur. In addition, when gold nanoparticles are arranged in multiple layers, they are fused but the transparency is lost. Therefore, according to the production method of the present invention, the metal nanoparticles can be brought into contact with each other and fused by applying an external pressure to the metal nanoparticles using a deformation process of particles such as a polymer or bubbles.

  In addition to the above-described method, the transparent conductive film of the present invention is a mixture of paste-like metal nanoparticles and a foaming agent, sealed between substrates, and foaming the internal foaming agent by heating or the like, A planar network composition of metal nanoparticles may be formed between the substrates. Examples of the foaming agent include inorganic foaming agents such as sodium bicarbonate, ammonium carbonate, ammonium bicarbonate, ammonium nitrite, amide compound, sodium borohydride; isocyanate compounds, azodicarbonamide, azobisisobutyronitrile, barium Azo compounds such as azodicarboxylate, hydrazine derivatives such as p, p′-oxybisbenzenesulfonyl hydrazide, hydrazine derivatives such as p-toluenesulfonyl hydrazide, semicarbazide compounds, aziso compounds, nitroso compounds such as dinitrosopentamethylenetetramine, triazole compounds, etc. An organic foaming agent is mentioned, It can also use combining these various foaming agents 2 or more types.

  The transparent conductive film of the present invention can be used as a transparent conductive material by being formed on a substrate. Applications include, for example, liquid crystal display (LCD), plasma display (PDP), field emission display (FED), organic EL display, transparent electrode material constituting flat panel display (FPD) such as electronic paper, solar cell electrode Use for building materials such as functional glass windows, application to high-density optical discs such as DVDs, optical filters, light control films, transparent electromagnetic wave shields, transparent heaters, touch panels, and transparent wave absorbers It is done.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

Example 1
(I) Production of Polystyrene Single Layer Film 4 g of polystyrene latex particles having a particle size of 2.2 μm were dispersed in 10 g of water and coated on the glass plate surface by a shear coating method to form a single layer film. Subsequently, it heated on 150 degreeC on the hotplate for 30 second, and was set as the single layer plane hexagon structure by the thermal deformation of the latex particle.

(Ii) Production of transparent conductive film 0.1 g of gold particles having a particle diameter of 20 nm was dispersed in 0.9 g of water, and applied to the glass plate on which the polystyrene single-layer film was formed 10 times by a shear coating method. Infiltrated. By heating to 450 ° C. with a heater, the gold particles were fused and the latex particles were removed by heating to produce a transparent conductive film having a planar hexagonal structure of gold particles.

(Iii) Physical property evaluation The transmittance | permeability and surface resistance of the manufactured transparent conductive film were measured using the following apparatuses.
Transmittance: UV1200 spectrophotometer, manufactured by Shimadzu Corporation Surface resistance: Loresta EP surface resistance meter, manufactured by Mitsubishi Chemical Corporation This transparent conductive film has a transmittance of 62% and a surface resistance of less than 0.1Ω / □ ( The electrical resistance was almost 0).

Example 2
A silver paste was prepared by dispersing 0.3 g of 10 nm silver particles and 0.02 g of polyethylene glycol lauryl ether in 0.7 g of water. The silver paste is mixed at 0.03 ml / min and air at 0.15 ml / min in a 200 μm × 200 μm flow path, and is directly discharged into a 5 mm × 200 μm flow path sandwiched between glass plates. A planar network structure consisting of silver and bubbles was formed. This was frozen at −10 ° C., vacuum-dried at 0 ° C., and then heated to 250 ° C. with a heater to fuse silver particles to obtain a transparent conductive film having a planar network structure.

  When the transmittance and surface resistance of the formed transparent conductive film were measured using the same apparatus as in Example 1, this transparent conductive film had a transmittance of 50% and a surface resistance of less than 0.1Ω / □ (electricity The resistance was almost 0).

  Since the transparent conductive film of the present invention is composed of a metal thin film having a planar network structure, excellent conductivity and transparency can be obtained. Moreover, since the manufacturing method is also easy, a transparent conductive film with a large area can be manufactured at low cost. Furthermore, when gold or silver is used as the film material, a transparent conductive film having an electric resistance approximately two orders of magnitude lower than that of the ITO film can be obtained.

Claims (7)

  A transparent conductive film comprising a metal thin film having a planar network structure.   The transparent conductive film according to claim 1, wherein the average mesh size of the planar network structure is 0.1 μm or more.   A transparent conductive material, wherein the transparent conductive film according to claim 1 or 2 is formed on a substrate. (A) applying an emulsion solution in which polymer particles are dispersed on a substrate to form a single layer film of the polymer particles;
(B) heating the formed single layer film to form a single layer planar network structure;
3. The method according to claim 1, comprising: (c) a step of applying metal nanoparticles to a substrate having a single-layer planar network structure; and (d) a step of heating and fusing the metal nanoparticles. Manufacturing method of transparent conductive film.   The method for producing a transparent conductive film according to claim 4, wherein the polymer particles have a particle size of 0.1 to 1000 µm.   The method for producing a transparent conductive film according to claim 4 or 5, wherein the heating temperature in the step (b) is 50 to 350 ° C. (E) A step of enclosing air or a volatile monomer together with paste-like metal nanoparticles between opposing substrates to form a planar network structure between the substrates,
The method for producing a transparent conductive film according to claim 1 or 2, comprising: (f) a step of freeze-drying the formed planar network structure; and (d) a step of heating and fusing the metal nanoparticles. .

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