conductive film

Abstract

Provided is an electrically conductive film which is configured by forming a metal film on a transparent conductive layer containing metal nanowires, wherein conductivity is less likely to be reduced even when the electrically conductive film is subjected to an etching process.　This electrically conductive film comprises: a metal layer, the transparent electrically conductive layer, and a substrate, in that order. The transparent electrically conductive layer includes the metal nanowires and a polymer matrix. Some of the metal nanowires protrude from the transparent electrically conductive layer towards the metal layer side. The thickness of the transparent electrically conductive layer is 30-150 nm.

Description

Technical Field

[0001] The present invention relates to a conductive film.

Background Art

[0002] Conventionally, as a conductive film used for electrodes of touch sensors and the like, a conductive film in which a metal oxide layer such as an indium tin composite oxide layer (ITO layer) is formed on a resin film has been frequently used. However, the conductive film with a metal oxide layer has a problem of insufficient flexibility. As a conductive film with excellent flexibility, a conductive film provided with a transparent conductive layer containing metal nanowires using silver, copper, or the like has been proposed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a conductive film provided with a transparent conductive layer containing metal nanowires as described above, it is possible to form a narrow wiring by patterning by photolithography by forming a metal film on the transparent conductive layer. However, there is a problem that when etching the metal film during the photolithography, the metal nanowires are corroded and the conductivity of the conductive film is reduced.

[0005] The present invention has been made to solve the above problems, and an object thereof is to provide a conductive film formed by forming a metal film on a transparent conductive layer containing metal nanowires, which is difficult to reduce conductivity even when subjected to an etching process.

Means for Solving the Problems

[0006] The conductive film of the present invention comprises a metal layer, a transparent conductive layer, and a substrate in this order, wherein the transparent conductive layer contains metal nanowires and a polymer matrix, a portion of the metal nanowires protruding from the transparent conductive layer toward the metal layer, and the thickness of the transparent conductive layer is 30 nm to 150 nm. In one embodiment, the thickness of the transparent conductive layer is 30 nm to 120 nm. In one embodiment, the substrate is made of a cycloolefin resin. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a conductive film constructed by forming a metal film on a transparent conductive layer containing metal nanowires, which is less susceptible to deterioration in conductivity even when subjected to an etching process. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic cross-sectional view of a conductive film according to one embodiment of the present invention. [Modes for carrying out the invention]

[0009] A. Overall composition of the conductive film Figure 1 is a schematic cross-sectional view of a conductive film according to one embodiment of the present invention. The conductive film 100 comprises, in this order, a metal layer 10, a transparent conductive layer 20, and a substrate 30. The transparent conductive layer 20 includes metal nanowires 21 and a polymer matrix 22. A portion of the metal nanowires 21 protrudes from the transparent conductive layer 20 toward the metal layer 10. Although not shown, the conductive film may further include any other suitable layers.

[0010] In the present invention, the thickness of the transparent conductive layer is 30 nm to 150 nm. The thickness of the transparent conductive layer corresponds to the thickness of the polymer matrix. In the present invention, by forming a transparent conductive layer with such a thickness, the metal nanowires are effectively protected and corrosion of the metal nanowires is prevented while ensuring good surface conductivity of the transparent conductive layer. In particular, the present invention is useful in that corrosion of the metal nanowires can be prevented even when a part of the metal layer is removed by chemical means such as etching. As a result of preventing corrosion of the metal nanowires, a conductive film with a narrow wiring pattern and excellent conductivity can be obtained. In one embodiment, the conductive film (substantially a transparent conductive layer) of the present invention has corrosion resistance to an aqueous solution containing one or more selected from the group consisting of sulfuric acid, hydrogen peroxide, hydrochloric acid, cupric chloride, and ferric chloride, and the rate of change (increase) of the surface resistance value can be 20% or less even when exposed to the aqueous solution.

[0011] The surface resistance of the conductive film of the present invention is preferably 0.01Ω / □ to 1000Ω / □, more preferably 0.1Ω / □ to 500Ω / □, particularly preferably 0.1Ω / □ to 300Ω / □, and most preferably 0.1Ω / □ to 100Ω / □.

[0012] When the conductive film is immersed in a metal layer etching solution for 5 minutes, the increase in the surface resistance of the conductive film is preferably 20% or less, more preferably 15% or less, even more preferably 10% or less, and particularly preferably 5% or less. The surface resistance is determined by the resistance value calculated as (resistance after immersion / resistance before immersion - 1) × 100.

[0013] The thickness of the conductive film of the present invention is preferably 10 μm to 500 μm, more preferably 15 μm to 300 μm, and even more preferably 20 μm to 200 μm.

[0014] B. Metal layer The above metal layer is composed of a conductive metal. Examples of the metal constituting the metal layer include, for example, copper, silver, aluminum, nickel alloy, copper alloy, titanium alloy, silver alloy, etc. Among them, copper is particularly preferred.

[0015] The thickness of the above metal layer is preferably 10 to 1000 nm, more preferably 50 to 300 nm.

[0016] As the method for forming the above metal layer, any appropriate method can be adopted. Examples of the method for forming the metal layer include vapor deposition methods represented by vacuum evaporation method and sputtering method, wet methods represented by electrolytic plating and electroless plating, etc.

[0017] C.Transparent conductive layer As described above, the transparent conductive layer includes metal nanowires and a polymer matrix.

[0018] The thickness of the above transparent conductive layer is, as described above, 30 nm to 150 nm, preferably 30 nm to 140 nm, more preferably 30 nm to 130 nm, and particularly preferably 30 nm to 120 nm. In one embodiment, the thickness of the above transparent conductive layer is preferably 55 nm to 150 nm, more preferably 55 nm to 140 nm, still more preferably 60 nm to 130 nm, and particularly preferably 65 nm to 120 nm. Within the above range, the above effects of the present invention become remarkable. When the transparent conductive layer is thinner than 30 nm, the metal nanowires may not be sufficiently protected, and there is a risk that the corrosion of the metal nanowires cannot be prevented. Also, when it is thicker than 150 nm, there is a risk that surface conduction cannot be achieved sufficiently.

[0019] In one embodiment, the transparent conductive layer is patterned. As the patterning method, any appropriate method can be adopted according to the form of the transparent conductive layer. The shape of the pattern of the transparent conductive layer can be any appropriate shape according to the application. For example, the patterns described in JP-T-2011-511357, JP-A-2010-164938, JP-A-2008-310550, JP-T-2003-511799, and JP-T-2010-541109 can be mentioned. After the transparent conductive layer is formed on the substrate, it can be patterned using any appropriate method according to the form of the transparent conductive layer.

[0020] The total light transmittance of the transparent conductive layer is preferably 85% or more, more preferably 90% or more, and even more preferably 95% or more.

[0021] The metal nanowire refers to a conductive substance whose material is metal, shape is needle-like or thread-like, and diameter is in the nanometer size. The metal nanowire may be linear or curved. By using a transparent conductive layer composed of metal nanowires, the metal nanowires form a mesh-like pattern, so that even a small amount of metal nanowires can form a good electrical conduction path, and a conductive film with low electrical resistance can be obtained.

[0022] The ratio (aspect ratio: L / d) of the thickness d to the length L of the metal nanowire is preferably 10 to 100,000, more preferably 50 to 100,000, and particularly preferably 100 to 10,000. By using metal nanowires with such a large aspect ratio, the metal nanowires can cross well, and a small amount of metal nanowires can exhibit high conductivity. As a result, a transparent conductive layer with high light transmittance can be obtained. In this specification, the "thickness of the metal nanowire" means the diameter when the cross section of the metal nanowire is circular, the minor axis when it is elliptical, and the longest diagonal line when it is polygonal. The thickness and length of the metal nanowire can be confirmed by a scanning electron microscope or a transmission electron microscope.

[0023] The thickness of the above-mentioned metal nanowire is preferably less than 500 nm, more preferably less than 200 nm, particularly preferably between 10 nm and 100 nm, and most preferably between 10 nm and 60 nm. Within this range, a transparent conductive layer with high light transmittance can be formed.

[0024] The length of the above-mentioned metal nanowire is preferably 1 μm to 1000 μm, more preferably 1 μm to 500 μm, and particularly preferably 1 μm to 100 μm. Within this range, a highly conductive film can be obtained.

[0025] Any suitable metal can be used as the metal constituting the above-mentioned metal nanowire, as long as it is a metal with high conductivity. Examples of metals that can be used to constitute the above-mentioned metal nanowire include silver, gold, copper, and nickel. Materials that have been plated (for example, gold plated) may also be used. Preferably, the metal nanowire is composed of one or more metals selected from the group consisting of gold, platinum, silver, and copper.

[0026] Any suitable method can be used to manufacture the above-mentioned metal nanowires. For example, methods include reducing silver nitrate in solution, applying a voltage or current from the tip of a probe to the surface of a precursor, drawing out metal nanowires at the tip of the probe, and continuously forming the metal nanowires. In the method of reducing silver nitrate in solution, silver nanowires can be synthesized by liquid-phase reduction of a silver salt such as silver nitrate in the presence of a polyol such as ethylene glycol and polyvinylpyrrolidone. Silver nanowires of uniform size can be mass-produced according to methods described, for example, in Xia, Y. et al., Chem. Mater. (2002), 14, 4736-4745, and Xia, Y. et al., Nano letters (2003) 3(7), 955-960.

[0027] The metal nanowire content in the transparent conductive layer described above is preferably 30% to 100% by weight, more preferably 30% to 90% by weight, and even more preferably 45% to 80% by weight, relative to the total weight of the transparent conductive layer. Within this range, a transparent conductive layer with excellent conductivity and light transmittance can be obtained.

[0028] Any suitable polymer can be used as the polymer constituting the polymer matrix described above. Examples of such polymers include acrylic polymers; polyester polymers such as polyethylene terephthalate; aromatic polymers such as polystyrene, polyvinyltoluene, polyvinylxylene, polyimide, polyamide, and polyamideimide; polyurethane polymers; epoxy polymers; polyolefin polymers; acrylonitrile-butadiene-styrene copolymer (ABS); cellulose; silicone polymers; polyvinyl chloride; polyacetate; polynorbornene; synthetic rubber; and fluorine polymers. Preferably, a curable resin (preferably an ultraviolet-curable resin) composed of polyfunctional acrylates such as pentaerythritol triacrylate (PETA), neopentyl glycol diacrylate (NPGDA), dipentaerythritol hexaacrylate (DPHA), dipentaerythritol pentaacrylate (DPPA), and trimethylolpropane triacrylate (TMPTA) is used.

[0029] The density of the transparent conductive layer is preferably 1.3 g / cm³. 3 ~10.5g / cm 3 More preferably 1.5 g / cm³ 3 ~3.0g / cm 3 Within this range, a transparent conductive layer with excellent conductivity and light transmittance can be obtained.

[0030] A transparent conductive layer can be formed by applying a conductive layer-forming composition containing metal nanowires to a substrate (or a laminate of a substrate and other layers), and then drying the applied layer.

[0031] The above-mentioned conductive layer-forming composition may contain any suitable solvent in addition to metal nanowires. The conductive layer-forming composition can be prepared as a dispersion of metal nanowires. Examples of the solvent include water, alcohol-based solvents, ketone-based solvents, ether-based solvents, hydrocarbon-based solvents, and aromatic solvents. From the viewpoint of reducing environmental impact, it is preferable to use water. The above-mentioned conductive layer-forming composition may further contain any suitable additives depending on the purpose. Examples of the additives include corrosion inhibitors that prevent corrosion of metal nanowires and surfactants that prevent aggregation of metal nanowires. The type, number, and amount of additives used can be appropriately set depending on the purpose.

[0032] If the transparent conductive layer includes a polymer matrix, the polymer matrix may be formed by applying and drying the conductive layer-forming composition as described above, then applying a polymer solution (polymer composition, monomer composition) onto a layer made of metal nanowires, and then drying or curing the polymer solution layer. Alternatively, the transparent conductive layer may be formed using a conductive layer-forming composition containing the polymer that constitutes the polymer matrix.

[0033] The dispersion concentration of metal nanowires in the above-mentioned conductive layer-forming composition is preferably 0.1% to 1% by weight. Within this range, a transparent conductive layer with excellent conductivity and light transmittance can be formed.

[0034] Any suitable method can be used to apply the above-mentioned conductive layer-forming composition. Examples of application methods include spray coating, bar coating, roll coating, die coating, inkjet coating, screen coating, dip coating, letterpress printing, intaglio printing, and gravure printing. Any suitable drying method (e.g., natural drying, forced-air drying, and heat drying) can be used to dry the coated layer. For example, in the case of heat drying, the drying temperature is typically 50°C to 200°C, preferably 80°C to 150°C. The drying time is typically 1 to 10 minutes.

[0035] The above polymer solution contains the polymer constituting the above polymer matrix, or a precursor of the polymer (a monomer constituting the polymer).

[0036] The polymer solution may contain a solvent. Examples of solvents included in the polymer solution include alcohol-based solvents, ketone-based solvents, tetrahydrofuran, hydrocarbon-based solvents, or aromatic solvents. Preferably, the solvent is volatile. The boiling point of the solvent is preferably 200°C or lower, more preferably 150°C or lower, and even more preferably 100°C or lower.

[0037] D. Base material The above-mentioned substrate is typically composed of any suitable resin. Examples of resins that constitute the above-mentioned substrate include cycloolefin resins, polyimide resins, polyvinylidene chloride resins, polyvinyl chloride resins, polyethylene terephthalate resins, polyethylene naphthalate resins, and the like. Preferably, cycloolefin resins are used. By using a substrate composed of a cycloolefin resin, a conductive film with excellent flexibility can be obtained.

[0038] As the cycloolefin resin mentioned above, polynorbornene can be preferably used, for example. Polynorbornene refers to a (co)polymer obtained using a norbornene monomer having a norbornene ring as part or all of the starting material (monomer). Various products of the above polynorbornene are commercially available. Specific examples include the trade names "Zeonex" and "Zeonor" from Nippon Zeon Corporation, "Arton" from JSR Corporation, "Topas" from TICONA Corporation, and "APEL" from Mitsui Chemicals Corporation.

[0039] The glass transition temperature of the resin constituting the above-mentioned substrate is preferably 50°C to 200°C, more preferably 60°C to 180°C, and even more preferably 70°C to 160°C. A substrate having a glass transition temperature within this range can prevent degradation when forming the transparent conductive layer.

[0040] The thickness of the above-mentioned substrate is preferably 8 μm to 500 μm, more preferably 10 μm to 250 μm, even more preferably 10 μm to 150 μm, and particularly preferably 15 μm to 100 μm.

[0041] The total light transmittance of the above substrate is preferably 80% or more, more preferably 85% or more, and particularly preferably 90% or more. Within this range, a conductive film suitable for use as a conductive film in touch panels and the like can be obtained.

[0042] The above-mentioned base material may further contain any suitable additives as needed. Specific examples of additives include plasticizers, heat stabilizers, light stabilizers, lubricants, antioxidants, UV absorbers, flame retardants, colorants, antistatic agents, compatibilizers, crosslinking agents, and thickeners. The type and amount of additives used may be appropriately determined depending on the purpose.

[0043] If necessary, various surface treatments may be performed on the above substrate. Any appropriate method can be used for the surface treatment depending on the purpose. Examples include low-pressure plasma treatment, ultraviolet irradiation treatment, corona treatment, flame treatment, and acid or alkali treatment. In one embodiment, the transparent substrate is surface-treated to make the surface of the transparent substrate hydrophilic. By making the substrate hydrophilic, the processability when coating with a transparent conductive layer-forming composition prepared with an aqueous solvent is improved. Furthermore, a conductive film with excellent adhesion between the substrate and the transparent conductive layer can be obtained. [Examples]

[0044] The present invention will be specifically described below with reference to examples, but the present invention is not limited in any way to these examples. The evaluation methods in the examples and comparative examples are as follows.

[0045] (1) Resistance increase rate The initial resistance (R0) of a conductive film was measured using the eddy current method with a non-contact surface resistance meter, product name "EC-80," manufactured by Napson Corporation. Next, the conductive film was immersed in a metal layer etching solution at room temperature for 5 minutes, then dried at room temperature for 30 minutes, and the resistance (R) was measured again. The resistance increase rate R / R0 was calculated from the initial resistance (R0) and the resistance (R).

[0046] (2) Surface conductivity A conductive film (50mm x 50mm) with a metal film formed on a transparent conductive layer was masked at both ends (10mm each), the metal layer was removed, and then the metal layer at both ends was checked for continuity using a tester. If continuity was possible, it was considered OK; if not, it was considered NG.

[0047] [Manufacturing Example 1] (Manufacturing of metal nanowires) In a reaction vessel equipped with a stirring device, at 160°C, 5 ml of anhydrous ethylene glycol and 0.5 ml of anhydrous ethylene glycol solution of PtCl2 (concentration: 1.5 × 10⁻⁴ mol / L) were added. After 4 minutes, 2.5 ml of anhydrous ethylene glycol solution of AgNO₃ (concentration: 0.12 mol / L) and 5 ml of anhydrous ethylene glycol solution of polyvinylpyrrolidone (MW: 55000) (concentration: 0.36 mol / L) were simultaneously added dropwise over 6 minutes to the resulting solution. After this addition, the mixture was heated to 160°C and the reaction was carried out for more than 1 hour until AgNO₃ was completely reduced to produce silver nanowires. Next, acetone was added to the reaction mixture containing the silver nanowires obtained as described above until the volume of the reaction mixture was increased fivefold. The reaction mixture was then centrifuged (2000 rpm, 20 minutes) to obtain silver nanowires. A silver nanowire dispersion was prepared by dispersing the silver nanowire (concentration: 0.2 wt%) and pentaethylene glycol dodecyl ether (concentration: 0.1 wt%) in pure water.

[0048] [Example 1] (Preparation of transparent conductive layer-forming composition (PN)) A transparent conductive layer-forming composition (PN) with a solid content of 0.05% by weight was prepared by diluting the above silver nanowire dispersion with 25 parts by weight of pure water and 75 parts by weight. (Preparation of monomer composition a) One part by weight of pentaerythritol triacrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd., trade name "Viscote #300") and 0.2 parts by weight of a photopolymerization initiator (manufactured by BASF, trade name "Irgacure 907") were diluted with 80 parts by weight of isopropyl alcohol and 19 parts by weight of diacetone alcohol to obtain a monomer composition with a solid content of 1% by weight. (Fabrication of conductive film) The transparent conductive layer-forming composition (PN) was applied to one side of a substrate (polycycloolefin film (manufactured by Zeon Corporation, product name "ZEONOR®", thickness 25 μm) and dried. Furthermore, the monomer composition was applied on the PN coating layer, dried at 90°C for 1 minute, and then subjected to a 300 mJ / cm² test. 2 A transparent conductive layer (thickness: 55 nm) was formed by irradiating it with ultraviolet light. Furthermore, a metal layer made of copper was formed on the transparent conductive layer by sputtering. A conductive film was obtained as described above. The obtained conductive film was subjected to evaluations (1) and (2) above. The results are shown in Table 1.

[0049] [Example 2] A conductive film was obtained in the same manner as in Example 1, except that the thickness of the transparent conductive layer was set to 90 nm. The obtained conductive film was subjected to evaluations (1) and (2) described above. The results are shown in Table 1.

[0050] [Example 3] A conductive film was obtained in the same manner as in Example 1, except that the thickness of the transparent conductive layer was set to 130 nm. The obtained conductive film was subjected to evaluations (1) and (2) described above. The results are shown in Table 1.

[0051] [Example 4] (Preparation of monomer composition b) One part by weight of urethane acrylate (manufactured by DIC, trade name "Luxidia 17-806") and 0.2 parts by weight of a photopolymerization initiator (manufactured by BASF, trade name "Irgacure 907") were diluted with 80 parts by weight of isopropyl alcohol and 19 parts by weight of diacetone alcohol to obtain a monomer composition with a solid content of 1% by weight. (Fabrication of conductive film) A conductive film was obtained in the same manner as in Example 1, except that monomer composition b was used instead of monomer composition a, and the thickness of the transparent conductive layer was set to 90 nm. The obtained conductive film was subjected to the evaluations (1) and (2) described above. The results are shown in Table 1.

[0052] [Comparative Example 1] A conductive film was obtained in the same manner as in Example 1, except that the thickness of the transparent conductive layer was set to 200 nm.

[0053] [Comparative Example 2] A conductive film was obtained in the same manner as in Example 1, except that no monomer composition was applied, i.e., a transparent conductive layer without a polymer matrix was formed.

[0054] [Table 1] [Explanation of Symbols]

[0055] 10 metal layer 20 Transparent conductive layer 30 Base material 100 conductive film

Claims

1. The structure comprises a metal layer, a transparent conductive layer, and a substrate in this order. The metal layer is composed of copper, silver, aluminum, nickel alloy, copper alloy, titanium alloy, or silver alloy. The transparent conductive layer comprises metal nanowires and a polymer matrix. A portion of the metal nanowire protrudes from the transparent conductive layer toward the metal layer. The thickness of the transparent conductive layer is 60 nm to 130 nm. The content ratio of the metal nanowire in the transparent conductive layer is 45% to 90% by weight relative to the total weight of the transparent conductive layer. Conductive film.

2. The conductive film according to claim 1, wherein the substrate is made of a cycloolefin resin.

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