Transparent conductive film

Abstract

The present invention provides a transparent conductive film with excellent translucency in the near-infrared region.　A transparent conductive film according to an embodiment of the present invention comprises a base material and a conductive layer disposed on at least one side of the base material, wherein the surface resistance of the transparent conductive film is 200 Ω / sq. or less, and the transparent conductive film has a light transmittance of 85% or more in the wavelength range from 780 nm to 2500 nm.

Description

Transparent Conductive Film

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

[0002] Conventionally, transparent conductive films in which a metal oxide layer such as an indium-tin composite oxide layer (ITO layer) is formed on a resin film have been widely used as transparent conductive films for use in electrodes of touch sensors, etc. However, transparent conductive films in which a metal oxide layer is formed have low light transmittance in the near-infrared region, and there is a problem in that it is difficult to obtain a desired resistance value when the light transmittance is taken into consideration.

[0003] Special Publication No. 2009-505358

[0004] The present invention has been made to solve the above problems, and a main object of the present invention is to provide a transparent conductive film that has excellent light transmittance in the near-infrared region.

[0005] [1] A transparent conductive film according to an embodiment of the present invention includes a substrate and a conductive layer disposed on at least one side of the substrate. The surface resistance of the transparent conductive film is 200 Ω / □ or less, and the maximum light transmittance of the transparent conductive film in the wavelength range of 780 nm to 2500 nm is 85% or more. [2] The transparent conductive film of [1] above may have a surface resistance of 100 Ω / □ or less. [3] The transparent conductive film of [1] or [2] above may have a ratio (T905 / T555) of the light transmittance at a wavelength of 905 nm (T905) to the light transmittance at a wavelength of 555 nm (T555) greater than 0.95 and equal to or less than 1.1. [4] The transparent conductive film according to any one of [1] to [3] above may have a maximum light transmittance of 85% or more in the wavelength range of 900 nm to 1600 nm. [5] The transparent conductive film according to any one of [1] to [4] above may have a light transmittance of 85% or more at a wavelength of 905 nm. [6] In the transparent conductive film according to any one of [1] to [5] above, the conductive layer may contain a fibrous conductive material and a polymer matrix. [7] In the transparent conductive film according to [6] above, the fibrous conductive material may be metal nanowires. [8] The transparent conductive film according to any one of [1] to [7] above may be used for a transparent heater.

[0006] According to an embodiment of the present invention, a transparent conductive film having excellent light transmittance in the near-infrared region can be provided.

[0007] 1 is a schematic cross-sectional view of a transparent conductive film according to one embodiment of the present invention.

[0008] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

[0009] A. Overall Configuration of Transparent Conductive Film FIG. 1 is a schematic cross-sectional view of a transparent conductive film according to one embodiment of the present invention. The transparent conductive film 100 includes a substrate 10 and a conductive layer 20 disposed on at least one side of the substrate 10. In one embodiment, the conductive layer 20 includes a fiber-based conductive material 21. Examples of the fiber-based conductive material include metal nanowires and carbon nanotubes. Metal nanowires are preferably used. Although not shown, the transparent conductive film may further include any other appropriate layers.

[0010] In one embodiment, the transparent conductive film 100 includes a protective layer 30 disposed on the conductive layer 20 opposite the substrate 10. The protective layer 30 may be a layer that protects the fiber-based conductive material 21. In an embodiment of the present invention, the provision of the protective layer 30 can improve the durability of the conductive layer 20. More specifically, a conductive layer made of a fiber-based conductive material (e.g., metal nanowires) is characterized by low scratch resistance, humidity durability, etc., and the provision of a protective layer can solve these problems and improve the durability of the conductive layer (and consequently, the durability of the transparent conductive film). The conductive layer 20 may contain components that constitute the protective layer 30 (e.g., a resin that constitutes the protective layer).

[0011] The surface resistance of the transparent conductive film is 200 Ω / □ or less, preferably 0.01 Ω / □ to 200 Ω / □, more preferably 1 Ω / □ to 180 Ω / □, particularly preferably 5 Ω / □ to 150 Ω / □, and most preferably 10 Ω / □ to 100 Ω / □. The surface resistance of the transparent conductive film may be 100 Ω / □ or less, 60 Ω / □ or less, 50 Ω / □ or less, 45 Ω / □ or less, or even 40 Ω / □. Within these ranges, a transparent conductive film particularly suitable for transparent heater applications (particularly transparent heaters for vehicles) can be obtained. In one embodiment, the surface resistance of the transparent conductive film is 20 Ω / □ or more. One factor controlling the surface resistance of a transparent conductive film is the thickness of the conductive layer (the amount of fibrous conductive material in the conductive layer). By adjusting the thickness of the conductive layer so that the surface resistance is at least a predetermined value, a transparent conductive film with excellent light transmittance (e.g., transmittance in the near-infrared region) can be obtained.

[0012] The transparent conductive film has a light transmittance of 85% or more, preferably 90% or more, in the wavelength region of 780 nm to 2500 nm. This range allows for the provision of a transparent conductive film suitable for applications that transmit laser light in the near-infrared region. For example, in the field of autonomous driving of vehicles using LiDAR (Light Detection and Ranging), a transparent conductive film suitable for components that can efficiently transmit laser light (near-infrared region) required for sensing can be provided. A transparent conductive film having a light transmittance in the wavelength region of 780 nm to 2500 nm within the above range can be obtained, for example, by forming a conductive layer containing metal nanowires. The higher the light transmittance in the wavelength region of 780 nm to 2500 nm, the more preferable it is, with the upper limit being, for example, 95% (preferably 98%). In this specification, the light transmittance in a predetermined wavelength region refers to the maximum light transmittance in that range. That is, the terms "light transmittance in the wavelength region of 780 nm to 2500 nm" and "maximum light transmittance in the wavelength region of 780 nm to 2500 nm" are synonymous. The light transmittance can be measured using a predetermined spectrophotometer.

[0013] In one embodiment, the transparent conductive film is used in a transparent heater (e.g., a transparent heater for a vehicle). The transparent heater may have any appropriate configuration. Typically, the transparent heater may be configured to generate heat by passing electricity through a transparent conductive film having a pair of electrodes arranged thereon. In the transparent heater, the transparent conductive film may be used as a heat source. A transparent conductive film having a conductive layer containing metal nanowires is advantageous in that it has excellent heat generation characteristics, and combined with its excellent near-infrared transmittance, it may be preferably used, for example, in an anti-fogging heater (transparent heater) for vehicle window glass.

[0014] The transparent conductive film preferably has a light transmittance of 80% or more, more preferably 85% or more, and particularly preferably 90% or more in the wavelength range of 900 nm to 1600 nm. Within this range, the above-described effects are prominent. The higher the light transmittance in the wavelength range of 900 nm to 1600 nm, the more preferable it is, with the upper limit being, for example, 95% (preferably 98%). The terms "light transmittance in the wavelength range of 900 nm to 1600 nm" and "maximum light transmittance in the wavelength range of 900 nm to 1600 nm" are synonymous. Furthermore, in one embodiment, the transparent conductive film has a minimum light transmittance of 80% or more in the wavelength range of 900 nm to 1600 nm. That is, the light transmittance may be 80% or more throughout the entire wavelength range of 900 nm to 1600 nm. It is more preferable that the light transmittance be 85% or more, and even more preferably 90% or more, throughout the entire wavelength range of 900 nm to 1600 nm.

[0015] The ratio (T905 / T555) of the light transmittance at a wavelength of 905 nm (T905) to the light transmittance at a wavelength of 555 nm (T555) is preferably greater than 0.95 and less than or equal to 1.2, more preferably 0.95 to 1.2, more preferably 0.98 to 1.15, even more preferably 0.99 to 1.1, still more preferably 1 to 1.1, and particularly preferably 1 to 1.05. In one embodiment, T905 / T555 is greater than 0.95 and less than or equal to 1.1. Within this range, a transparent conductive film that can preferably transmit laser light required for sensing can be obtained.

[0016] The light transmittance at a wavelength of 905 nm is preferably 85% or more, more preferably 88% or more, and even more preferably 90% or more. Within this range, a transparent conductive film suitable for transmitting laser light in the near-infrared region can be provided. The higher the light transmittance at a wavelength of 905 nm, the more preferable it is, but the upper limit is, for example, 95% (preferably 98%).

[0017] The light transmittance at a wavelength of 555 nm is preferably 80% or more, and more preferably 85% to 95%.

[0018] The thickness of the transparent conductive film is preferably 10 μm to 500 μm, more preferably 15 μm to 300 μm, and even more preferably 20 μm to 200 μm.

[0019] B. Conductive Layer In one embodiment, the conductive layer includes a fiber-based conductive material and a polymer matrix. By forming a conductive layer including a fiber-based conductive material, a transparent conductive film with excellent flexibility and light transmittance can be obtained. The fiber-based conductive material is protected by the polymer matrix. As a result, corrosion of the fiber-based conductive material is prevented, and a transparent conductive film with excellent durability can be obtained.

[0020] The thickness of the conductive layer is preferably 50 nm to 300 nm, and more preferably 80 nm to 200 nm.

[0021] (Fiber-based conductive material) Metal nanowires can be preferably used as the fiber-based conductive material.

[0022] Metal nanowires are conductive materials made of metal, shaped like needles or threads, and nanometer-sized diameters. Metal nanowires may be linear or curved. By using a conductive layer made of metal nanowires, the metal nanowires form a mesh, allowing even a small amount of metal nanowires to form a good electrical conduction path, resulting in a transparent conductive film with low electrical resistance. Furthermore, the mesh-like shape of the metal nanowires allows openings to be formed in the gaps between the meshes, resulting in a transparent conductive film with high light transmittance.

[0023] The ratio of the thickness d to the length L (aspect ratio: L / d) of the fibrous conductive material (preferably, metal nanowires) is preferably 10 to 100,000, more preferably 50 to 100,000, and particularly preferably 100 to 10,000. By using a fibrous conductive material with such a high aspect ratio, the fibrous conductive material can be well intersected, allowing a small amount of fibrous conductive material to exhibit high conductivity. As a result, a transparent conductive film with high light transmittance can be obtained. In this specification, the "thickness of the fibrous conductive material" refers to the diameter of the fibrous conductive material when the cross section is circular, the minor axis of the fibrous conductive material when the cross section is elliptical, and the longest diagonal of the fibrous conductive material when the cross section is polygonal. The thickness and length of the fibrous conductive material can be confirmed using a scanning electron microscope or a transmission electron microscope.

[0024] The thickness of the fibrous conductive material (preferably, metal nanowires) is preferably less than 500 nm, more preferably less than 200 nm, particularly preferably 10 to 100 nm, and most preferably 10 to 50 nm. Within such a range, a conductive layer with high light transmittance can be formed.

[0025] The length of the fibrous conductive material (preferably, metal nanowires) is preferably 1 μm to 1000 μm, more preferably 10 μm to 500 μm, and particularly preferably 10 μm to 100 μm. Within this range, a transparent conductive film with high conductivity can be obtained.

[0026] Any suitable metal can be used as the metal constituting the metal nanowires, as long as it is a conductive metal. Examples of metals constituting the metal nanowires include silver, gold, copper, and nickel. Materials obtained by plating these metals (e.g., gold plating) may also be used. Among these, silver, copper, or gold are preferred from the viewpoint of conductivity, and silver is more preferred.

[0027] Any suitable method can be used to produce the metal nanowires. Examples include a method of reducing silver nitrate in solution, and a method of continuously forming metal nanowires by applying a voltage or current from the tip of a probe to the surface of a precursor and drawing the metal nanowires from the tip of the probe. 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. Uniformly sized silver nanowires can be mass-produced, for example, according to the methods described in Xia, Y. et al., Chem. Mater. (2002), 14, 4736-4745 and Xia, Y. et al., Nano Letters (2003), 3(7), 955-960.

[0028] The content of the fibrous conductive material (preferably metal nanowires) in the conductive layer is preferably 30 wt % to 90 wt %, more preferably 45 wt % to 80 wt %, based on the total weight of the conductive layer. Within this range, a transparent conductive film with excellent conductivity and light transmittance can be obtained.

[0029] When the metal nanowires are silver nanowires, the density of the conductive layer is preferably 1.3 g / cm ３ ~10.5g / cm ３ and more preferably 1.5 g / cm ３ ~3.0 g / cm ３ Within this range, a transparent conductive film having excellent conductivity and light transmittance can be obtained.

[0030] In one embodiment, the conductive layer is patterned. Any appropriate method can be adopted as the patterning method depending on the form of the conductive layer. The pattern shape of the conductive layer can be any appropriate shape depending on 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 conductive layer is formed on the substrate, it can be patterned using any appropriate method depending on the form of the conductive layer.

[0031] In one embodiment, the metal nanowires in the conductive layer have a fused network structure. The metal nanowires having a fused network structure are fused to each other at their contact points. By forming a conductive layer including metal nanowires having a fused network structure, a transparent conductive film with higher conductivity can be obtained without impairing transparency.

[0032] The conductive layer containing the metal nanowires having the fused network structure can be formed, for example, by adding an additive for promoting fusion to the metal nanowire dispersion liquid used in forming the conductive layer. Examples of the additive include metal halides (e.g., LiCl, CsCl, NaF, NaCl, NaBr, NaI, KCl, MgCl, etc.). ２ , CaCl ２ , AlCl ３, AgF, etc.), inorganic acids (e.g., nitric acid, nitrous acid, sulfuric acid, etc.), organic acids (e.g., oxalic acid, citric acid, formic acid, acetic acid, lactic acid, propionic acid, butyric acid, acrylic acid, pyruvic acid, trichloroacetic acid, trifluoroacetic acid, hexanoic acid, octanoic acid, decanoic acid, dodecanoic (lauric) acid, tetradecanoic (myristic) acid, hexadecanoic (palmitic) acid, octadecanoic (stearic) acid, 2-ethylbutyric acid, 2-methylhexanoic acid, 2-ethylhexanoic acid, 2-propylpentanoic acid, pivalic acid, Examples of suitable silver salts include silver salts (e.g., silver nitrate, silver nitrite, silver lactate, silver chloride, silver sulfate, silver oxide, silver acetate, silver chlorate, silver sulfide, silver formate, silver hexanoate, silver octanoate, silver decanoate, silver dodecanoate, silver tetradecanoate, silver hexadecanoate, silver octadecanoate, silver pentanoate, silver pivalate, silver neoheptanoate, silver neononanoate, silver neodecanoate), and compounds (e.g., hydrogen chloride, sodium chloride) containing an element capable of forming a silver salt (e.g., chlorine, sulfur). Among these, metal halides are preferred, and NaCl, AgF, LiF, NaBr, or NaF is more preferred. In one embodiment, the conductive layer containing the metal nanowires having the fused network structure can be formed by applying a metal nanowire dispersion containing the additive, followed by a heat treatment and / or a pressure treatment. The temperature of the heat treatment is, for example, 50°C to 200°C.

[0033] The conductive layer containing the metal nanowires having the fused network structure may be formed by exposing a coating layer of the metal nanowire dispersion to an acid halide vapor, such as HCl, HBr, HI, or a mixture thereof.

[0034] Metal nanowires having a fused network structure and a method for producing the same are described, for example, in JP-A-2015-530693, the disclosure of which is incorporated herein by reference.

[0035] (Polymer Matrix) Any appropriate polymer can be used as the polymer constituting the polymer matrix. Examples of such polymers include acrylic polymers; polyester polymers such as polyethylene terephthalate; aromatic polymers such as polystyrene, polyvinyl toluene, polyvinyl xylene, polyimide, polyamide, and polyamideimide; polyurethane polymers; epoxy polymers; polyolefin polymers; acrylonitrile-butadiene-styrene copolymers (ABS); cellulose; silicone polymers; polyvinyl chloride; polyacetate; polynorbornene; synthetic rubber; and fluorine-based polymers. Preferably, a curable resin (preferably an ultraviolet-curable resin) composed of a polyfunctional acrylate such as pentaerythritol triacrylate (PETA), neopentyl glycol diacrylate (NPGDA), dipentaerythritol hexaacrylate (DPHA), dipentaerythritol pentaacrylate (DPPA), or trimethylolpropane triacrylate (TMPTA) is used. The polymer matrix can be the resin constituting the protective layer (details will be described later).

[0036] The polymer matrix can be formed by forming a layer of fibrous conductive material on a substrate, applying a polymer solution to the layer, and then drying or curing the applied layer. This process forms a conductive layer in which fibrous conductive material is present in a polymer matrix. The polymer solution contains a polymer that constitutes the polymer matrix or a precursor of the polymer (a monomer that constitutes the polymer). The polymer solution can contain a solvent. Examples of solvents contained in the polymer solution include alcohol-based solvents, ketone-based solvents, tetrahydrofuran, hydrocarbon-based solvents, and aromatic solvents. Preferably, the solvent is volatile. The boiling point of the solvent is preferably 200°C or less, more preferably 150°C or less, and even more preferably 100°C or less.

[0037] C. Protective Layer The thickness of the protective layer is preferably 10 nm to 1000 nm, more preferably 60 nm to 800 nm. Within this range, a transparent conductive film with excellent durability can be obtained.

[0038] The total thickness of the conductive layer and the protective layer is preferably 60 nm to 1000 nm, more preferably 70 nm to 800 nm, in order to obtain a transparent conductive film having excellent durability.

[0039] Typically, the protective layer is made of a resin. Any appropriate resin can be used as the resin constituting the protective layer as long as the effects of the present invention can be obtained. Examples of such resins include acrylic resins; polyester resins such as polyethylene terephthalate; aromatic resins such as polystyrene, polyvinyl toluene, polyvinyl xylene, polyimide, polyamide, and polyamideimide; polyurethane resins; epoxy resins; polyolefin resins; acrylonitrile-butadiene-styrene copolymers (ABS); cellulose; silicone resins; polyvinyl chloride; polyacetate; polynorbornene; synthetic rubber; and fluorine-based resins.

[0040] In one embodiment, a curable resin (e.g., an active energy ray-curable resin or a thermosetting resin) is used as the resin for forming the protective layer. The protective layer made of a curable resin can be formed by curing a curable protective layer-forming composition.

[0041] In one embodiment, the curable resin is a cured product of a curable protective layer-forming composition containing a (meth)acrylate monomer and / or a (meth)acrylate oligomer. Use of such a resin allows for a protective layer with a favorably adjusted shear strength to be obtained. Specific examples of the (meth)acrylate monomer and acrylate oligomer include trimethylolpropane tri(meth)acrylate, ethylene oxide-modified trimethylolpropane tri(meth)acrylate, propylene oxide-modified trimethylolpropane tri(meth)acrylate, trimethylolpropane tetra(meth)acrylate, tris(acryloxyethyl)isocyanurate, caprolactone-modified tris(acryloxyethyl)isocyanurate, and pentaerythritol. Examples of the dipentaerythritol copolymer include dipentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, alkyl-modified dipentaerythritol tri(meth)acrylate, alkyl-modified dipentaerythritol tetra(meth)acrylate, alkyl-modified dipentaerythritol penta(meth)acrylate, and caprolactone-modified dipentaerythritol hexa(meth)acrylate. Among these, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and dipentaerythritol penta(meth)acrylate are preferred. The above-mentioned monomers and polymers may be used alone or in combination of two or more.

[0042] In one embodiment, the curable resin is a cured product of a curable protective layer-forming composition containing a urethane (meth)acrylate oligomer. Using such a resin allows a protective layer with a favorably adjusted shear strength to be obtained. Examples of urethane (meth)acrylate oligomers include oligomers obtained by reacting a polyol with a polyisocyanate, followed by a (meth)acrylate having a hydroxyl group; oligomers obtained by reacting a polyisocyanate with a (meth)acrylate having a hydroxyl group, followed by a polyol; and oligomers obtained by reacting a polyisocyanate, a polyol, and a (meth)acrylate having a hydroxyl group.

[0043] Examples of polyols include polyethylene glycol, polypropylene glycol, polytetramethylene ether glycol and copolymers thereof, ethylene glycol, propylene glycol, 1,4-butanediol, and 2,2'-thiodiethanol.

[0044] Examples of polyisocyanates include isophorone diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, 4,4'-diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, 1,3-xylylene diisocyanate, and 1,4-xylylene diisocyanate.

[0045] Preferably, the composition for forming a curable protective layer contains any appropriate photopolymerization initiator. Examples of the photopolymerization initiator include benzoin ethers such as benzoin normal butyl ether and benzoin isobutyl ether, benzil ketals such as benzil dimethyl ketal and benzil diethyl ketal, acetophenones such as 2,2-dimethoxyacetophenone and 2,2-diethoxyacetophenone, 1-hydroxycyclohexyl phenyl ketone, [2-hydroxy-2-methyl-1-(4-ethylenephenyl)propan-1-one], 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propan-1-one, and 2-hydroxy-2-methyl-1-(4-isopropylphenyl)propan. Examples of the hydroxyalkylphenone include α-hydroxyalkylphenones such as pan-1-one, α-aminoalkylphenones such as 2-methyl-1-[4-(methylthio)phenyl]-1-morpholinopropane and 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-1-butanone, monoacylphosphine oxides such as 2,4,6-trimethylbenzoyldiphenylphosphine oxide and 2,4,6-trimethylbenzoylphenylethoxyphosphine oxide, and monoacylphosphine oxides such as bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide.

[0046] D. Substrate The substrate is typically made of any appropriate resin. Examples of resins constituting the substrate include cycloolefin-based resins, polyimide-based resins, polyvinylidene chloride-based resins, polyvinyl chloride-based resins, polyethylene terephthalate-based resins, and polyethylene naphthalate-based resins. Preferably, a cycloolefin-based resin is used.

[0047] The glass transition temperature of the resin constituting the substrate is preferably 50°C to 200°C, more preferably 60°C to 180°C, and even more preferably 70°C to 160°C.

[0048] The thickness of the substrate is preferably 8 μm to 500 μm, more preferably 10 μm to 250 μm, still more preferably 10 μm to 150 μm, and particularly preferably 15 μm to 100 μm.

[0049] The total light transmittance of the substrate is preferably 80% or more, more preferably 85% or more, and particularly preferably 90% or more. Within such a range, a transparent conductive film suitable for use in a transparent heater or the like can be obtained.

[0050] The tensile breaking strength of the substrate at 23°C is preferably 30 MPa to 100 MPa, more preferably 50 MPa to 95 MPa, and even more preferably 70 MPa to 90 MPa. According to the present invention, even if a film with poor flexibility is used, it is possible to ensure that the transparent conductive film exhibits sufficient flexibility. The tensile breaking strength is measured at room temperature (23°C) in accordance with JIS K 7161.

[0051] The substrate may further contain any appropriate additives as necessary. Specific examples of additives include plasticizers, heat stabilizers, light stabilizers, lubricants, antioxidants, UV absorbers, flame retardants, colorants, antistatic agents, compatibilizers, crosslinkers, and thickeners. The type and amount of additives used may be appropriately determined depending on the purpose.

[0052] If necessary, the substrate may be subjected to various surface treatments. Any appropriate surface treatment method may be adopted 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 hydrophilize the surface of the transparent substrate. Hydrophilizing the substrate improves processability when applying a conductive layer-forming composition prepared using an aqueous solvent. Furthermore, a transparent conductive film with excellent adhesion between the substrate and the conductive layer can be obtained. The substrate may also have a multilayer structure, and may be composed of, for example, a resin film and another layer formed on the resin film.

[0053] E. Method for Producing a Transparent Conductive Film The transparent conductive film can be produced by any appropriate method. In one embodiment, the transparent conductive film can be formed by coating a substrate with a conductive layer-forming composition containing metal nanowires, and then coating a protective layer-forming composition (polymer liquid). Alternatively, the transparent conductive film can be obtained by incorporating metal nanowires into the protective layer-forming composition and coating the protective layer-forming composition containing the metal nanowires onto the substrate.

[0054] The conductive layer-forming composition may contain any appropriate solvent in addition to the metal nanowires. The conductive layer-forming composition may be prepared as a dispersion of the 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 conductive layer-forming composition may further contain any appropriate additive depending on the purpose. Examples of the additive include a corrosion inhibitor that prevents corrosion of the metal nanowires and a surfactant that prevents aggregation of the metal nanowires. The type, number, and amount of the additive used may be appropriately determined depending on the purpose.

[0055] The dispersion concentration of the metal nanowires in the conductive layer-forming composition is preferably 0.1% by weight to 1% by weight, which allows the formation of a conductive layer with excellent conductivity and light transparency.

[0056] Any appropriate method can be used as a method for applying the conductive layer-forming composition. Examples of the application method include spray coating, bar coating, roll coating, die coating, inkjet coating, screen coating, dip coating, letterpress printing, intaglio printing, and gravure printing. Any appropriate drying method (e.g., natural drying, air drying, and heat drying) can be used as a method for drying the coating layer. For example, in the case of heat drying, the drying temperature is typically 50°C to 200°C, and preferably 80°C to 150°C. The drying time is typically 1 minute to 10 minutes.

[0057] The protective layer-forming composition contains a resin that forms the protective layer, or a precursor thereof (monomer, oligomer). The protective layer-forming composition may further contain any appropriate additives as needed. For example, a photopolymerization initiator, a coupling agent, etc. may be contained. The protective layer-forming composition may also contain any appropriate solvent for dilution. Examples of such solvents include toluene, butyl acetate, isobutanol, ethyl acetate, cyclohexane, cyclohexanone, methylcyclohexanone, hexane, acetone, methyl ethyl ketone, methyl isobutyl ketone, propylene glycol monomethyl ether, diethyl ether, and ethylene glycol.

[0058] The protective layer-forming composition may be applied by any suitable method, such as spray coating, bar coating, roll coating, die coating, inkjet coating, screen coating, dip coating, letterpress printing, intaglio printing, or gravure printing.

[0059] When a curable protective layer-forming composition is used, the composition is applied and then cured. Any appropriate method is adopted as the curing method depending on the composition of the curable protective layer-forming composition. For example, the curing method may be a method of heating and drying the solvent, followed by curing the composition with an ultraviolet ray irradiator at 500 mW / cm. ２ ~3000mW / cm ２ At an irradiation intensity of 50 mJ / cm ２ ~400 mJ / cm ２ One method is to irradiate the surface with ultraviolet light.

[0060] The present invention will be described in detail below using examples, but the present invention is not limited to these examples. The measurement methods for each property are as follows. Unless otherwise specified, "parts" and "%" in the examples and comparative examples are based on weight. (1) Surface Resistance: The surface resistance of the transparent conductive film was measured using a NAPSON EC-80 spectrophotometer. The measurement temperature was 23°C. (2) Transmittance: The transmittance in the wavelength range of 780 nm to 2500 nm was measured at room temperature using the transmittance measurement mode of a Hitachi High-Tech Science U-4100 spectrophotometer. Table 1 shows the transmittances at wavelengths of 555 nm and 905 nm, their ratio (T905 nm / T555 nm), and the maximum and minimum transmittances in the range of 900 nm to 1600 nm.

[0061] [Production Example 1] (Synthesis of Silver Nanowires and Preparation of Silver Nanowire Dispersion) In a reaction vessel equipped with a stirrer, 5 ml of anhydrous ethylene glycol, PtCl ２ anhydrous ethylene glycol solution (concentration: 1.5 × 10 －４ After 4 minutes, 0.5 ml of AgNO was added to the resulting solution. ３ 2.5 ml of anhydrous ethylene glycol solution (concentration: 0.12 mol / L) of AgNO3 and 5 ml of anhydrous ethylene glycol solution (concentration: 0.36 mol / L) of polyvinylpyrrolidone (MW: 55000) were simultaneously added dropwise over 6 minutes. After this addition, the mixture was heated to 160°C and stirred for 1 hour or more. ３ The reaction was carried out until the silver nanowires were completely reduced, producing 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 five times that of the reaction mixture, and the reaction mixture was then centrifuged (2000 rpm, 20 minutes) to obtain silver nanowires. The resulting silver nanowires had a minor axis of 30 nm to 40 nm, a major axis of 30 nm to 50 nm, and a length of 5 μm to 50 μm. The silver nanowires (concentration: 0.2 wt %) and pentaethylene glycol dodecyl ether (concentration: 0.1 wt %) were dispersed in pure water to prepare silver nanowire dispersion I.

[0062] Example 1 The silver nanowire dispersion I obtained in Production Example 1 was applied to a substrate (polyethylene terephthalate film, manufactured by Mitsubishi Chemical Corporation, product name "T910E125," thickness 125 μm) using a die coater so that the resistance value after film formation would be 100 Ω / □, and heated at 120° C. for 2 minutes to form a film. Furthermore, a monomer composition having a solids concentration of 1 wt % obtained by diluting 1 part by weight of pentaerythritol triacrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd., product name "Viscoat #300") and 0.1 part by weight of a photopolymerization initiator (manufactured by BASF, product name "Irgacure 907") with 59 parts by weight of isopropyl alcohol and 25 parts by weight of diacetone alcohol was applied to the silver nanowire ink-coated surface using a spin coater so that the dry film thickness would be 70 nm, and after heating at 80° C. for 1 minute, the film was exposed to an integrated exposure dose of 200 mJ / cm using a high-pressure mercury lamp. ２ The film was irradiated with ultraviolet light of 1000 kJ / cm to obtain a transparent conductive film consisting of a substrate, a conductive layer and a protective layer.

[0063] Example 2 A transparent conductive film was obtained in the same manner as in Example 1, except that the silver nanowire dispersion liquid I obtained in Production Example 1 was applied to a substrate (a cycloolefin (norbornene)-based resin film (manufactured by Zeon Corporation, product name "ZEONOR ZF16", thickness 40 μm) using a die coater so that the resistance value after film formation would be 37 Ω / □.

[0064] [Example 3] A transparent conductive film was obtained in the same manner as in Example 2, except that the silver nanowire dispersion liquid I obtained in Production Example 1 was applied using a die coater so that the resistance value after film formation was 25 Ω / □.

[0065] [Example 4] A transparent conductive film was obtained in the same manner as in Example 2, except that the silver nanowire dispersion liquid I obtained in Production Example 1 was applied using a die coater so that the resistance value after film formation was 20 Ω / □.

[0066] [Example 5] A transparent conductive film was obtained in the same manner as in Example 2, except that the silver nanowire dispersion liquid I obtained in Manufacturing Example 1 was applied using a die coater so that the resistance value after film formation was 18 Ω / □.

[0067] [Example 6] A transparent conductive film was obtained in the same manner as in Example 2, except that the silver nanowire dispersion liquid I obtained in Production Example 1 was applied using a die coater so that the resistance value after film formation was 13 Ω / □.

[0068] Comparative Example 1: A sintered target containing indium oxide and tin oxide in a weight ratio of 90:10 or 96.7:3.3 was loaded into a parallel-plate, winding-type magnetron sputtering apparatus. Then, in an atmosphere of 80% argon gas and 20% oxygen gas at 5.3 × 10-1 Pa, a film was formed on one side of a substrate (polyethylene terephthalate film, manufactured by Mitsubishi Chemical Corporation, product name "T910E125," thickness 125 μm) by reactive sputtering. A transparent conductive layer was formed so that the post-film resistance was 40 Ω / □. The light transmittance of the transparent conductive film obtained as described above in the wavelength range of 780 nm to 2500 nm was less than 85%.

[0069]

[0070] As is clear from Table 1, the present invention can provide a transparent conductive film having excellent light transmittance in the near-infrared region. The transparent conductive films of the examples are suitable for components that can efficiently transmit laser light (near-infrared region) required for sensing, for example, in the field of autonomous driving of vehicles using LiDAR (Light Detection and Ranging).

[0071] 10: Substrate 20: Conductive layer 30: Protective layer 100: Transparent conductive film

Claims

1. A transparent conductive film comprising a substrate and a conductive layer disposed on at least one side of the substrate, the transparent conductive film having a surface resistance of 200 Ω / □ or less, and a maximum light transmittance of 85% or more in the wavelength region of 780 nm to 2500 nm.

2. The transparent conductive film according to claim 1, having a surface resistance of 100 Ω / □ or less.

3. The transparent conductive film according to claim 1, wherein the ratio (T905 / T555) of the light transmittance at a wavelength of 905 nm (T905) to the light transmittance at a wavelength of 555 nm (T555) is greater than 0.95 and less than or equal to 1.

1.

4. The transparent conductive film according to claim 1, having a maximum light transmittance of 85% or more in the wavelength region of 900 nm to 1600 nm.

5. The transparent conductive film according to claim 1, which has a light transmittance of 85% or more at a wavelength of 905 nm.

6. The transparent conductive film of claim 1, wherein the conductive layer comprises a fibrous conductor and a polymer matrix.

7. The transparent conductive film according to claim 6, wherein the fiber-based conductive material is a metal nanowire.

8. The transparent conductive film according to claim 1, which is used for a transparent heater.

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