JP2021184344A - Transparent conductive film - Google Patents

Abstract

To provide a transparent conductive film that is excellent in both flexibility and transparency.SOLUTION: A transparent conductive film of the present invention comprises a first transparent conductive layer, a base, and a second transparent conductive layer in this order. The first transparent conductive layer includes metal nanowires, and the second transparent conductive layer is constituted from a metal oxide. In one embodiment, the metal oxide constituting the second transparent conductive layer is an indium-tin composite oxide.SELECTED DRAWING: Figure 1

Description

The present invention relates to a transparent conductive film.

Conventionally, as a transparent conductive film used for an electrode of a touch sensor or the like, a transparent conductive film in which a metal oxide layer such as an indium tin oxide composite oxide layer (ITO layer) is formed on a resin film is often used. .. However, the transparent conductive film on which the metal oxide layer is formed has a problem that the flexibility is insufficient and cracks are likely to occur due to physical stress such as bending.

Further, as a transparent conductive film, a transparent conductive film containing metal nanowires using silver, copper or the like has been proposed. Such a transparent conductive film has an advantage of being excellent in flexibility. However, the transparent conductive film containing metal nanowires has a problem that it is difficult to obtain sufficient transparency.

Special Table 2009-505358 Gazette

The present invention has been made to solve the above problems, and an object of the present invention is to provide a transparent conductive film having excellent flexibility and transparency.

The transparent conductive film of the present invention includes a first transparent conductive layer, a base material, and a second transparent conductive layer in this order, and the first transparent conductive layer contains a metal nanowire, and the second transparent conductive layer is included. The transparent conductive layer of is composed of a metal oxide.
In one embodiment, the metal oxide constituting the second transparent conductive layer is an indium-tin composite oxide.
In one embodiment, the tensile breaking strength of the base material is 100 MPa or more.
In one embodiment, the substrate is composed of a cycloolefin resin.

According to the present invention, it is possible to provide a transparent conductive film having excellent flexibility and transparency.

FIG. 3 is a schematic cross-sectional view of a transparent conductive film according to one embodiment of the present invention.

A. Overall Configuration of the Transparent Conductive Film FIG. 1 is a schematic cross-sectional view of the transparent conductive film according to one embodiment of the present invention. The transparent conductive film 100 includes a first transparent conductive layer 10, a base material 20, and a second transparent conductive layer 30 in this order. The first transparent conductive layer 10 contains metal nanowires (not shown). The second transparent conductive layer 30 is made of a metal oxide. Although not shown, the transparent conductive film may further comprise any other suitable layer.

In the present invention, a transparent conductive film having excellent flexibility is formed by laminating a first transparent conductive layer containing metal nanowires and a second transparent conductive layer composed of a metal oxide via a base material. Can be obtained. More specifically, in the transparent conductive film of the present invention, one of the transparent conductive layers is used as a transparent conductive layer containing metal nanowires (first transparent conductive layer), that is, a transparent conductive layer that is not easily damaged by bending. With such a configuration, the first transparent conductive layer is not easily damaged (for example, cracks are unlikely to occur) when bent with the first transparent conductive layer on the outside, and has excellent flexibility.

Further, in the transparent conductive film of the present invention, the other transparent conductive layer (second transparent conductive layer) is composed of a metal oxide, and with such a configuration, a plurality of transparent conductive layers are provided. However, it has a feature of excellent transparency (for example, a small haze value). In the transparent conductive film of the present invention, if the transparent conductive film is bent with the first transparent conductive layer on the outside, the second transparent conductive layer is not stressed in the tensile direction. Therefore, Even a second transparent conductive layer made of a metal oxide can be prevented from being damaged.

The surface resistance value of the transparent conductive film of the present invention on the first transparent conductive layer side is preferably 0.01Ω / □ to 1000Ω / □, more preferably 0.1Ω / □ to 500Ω / □. Particularly preferably, it is 0.1Ω / □ to 300Ω / □, and most preferably 0.1Ω / □ to 100Ω / □.

The surface resistance value of the transparent conductive film of the present invention on the second transparent conductive layer side is preferably 0.01Ω / □ to 1000Ω / □, more preferably 0.1Ω / □ to 500Ω / □. Particularly preferably, it is 0.1Ω / □ to 300Ω / □, and most preferably 0.1Ω / □ to 100Ω / □.

The rate of increase in the surface resistance value on the first transparent conductive layer side when the transparent conductive film of the present invention is hung on a round bar having a diameter of 2 mm and bent with the first transparent conductive layer on the outside [= (Surface resistance value after bending / Surface resistance value before bending) -1) × 100] is preferably 20% or less, more preferably 15% or less, still more preferably 10% or less. As described above, the transparent conductive film of the present invention has excellent flexibility, and an increase in resistance value (that is, a decrease in conductivity) when bent is prevented.

The haze value of the transparent conductive film of the present invention is preferably 1% or less, more preferably 0.7% or less, still more preferably 0.5% or less. The smaller the haze value is, the more preferable it is, but the lower limit thereof is, for example, 0.05%.

The total light transmittance of the transparent conductive film of the present invention is preferably 80% or more, more preferably 85% or more, and particularly preferably 90% or more.

The thickness of the transparent conductive film of the present invention is preferably 10 μm to 500 μm, more preferably 15 μm to 300 μm, and further preferably 20 μm to 200 μm.

B. First Transparent Conductive Layer As described above, the first transparent conductive layer contains metal nanowires.

In one embodiment, the first transparent conductive layer further comprises a polymer matrix. In this embodiment, metal nanowires are present in the polymer matrix. In the first transparent conductive layer composed of the polymer matrix, the polymer matrix protects the metal nanowires. As a result, corrosion of the metal nanowires is prevented, and a transparent conductive film having better durability can be obtained.

The thickness of the first transparent conductive layer is preferably 10 nm to 1000 nm, more preferably 20 nm to 500 nm. When the first transparent conductive layer contains a polymer matrix, the thickness of the first transparent conductive layer corresponds to the thickness of the polymer matrix.

In one embodiment, the first transparent conductive layer is patterned. As the patterning method, any suitable method can be adopted depending on the morphology of the first transparent conductive layer. The shape of the pattern of the first transparent conductive layer can be any suitable shape depending on the application. For example, the patterns described in JP-A-2011-511357, JP-A-2010-164938, JP-A-2008-310550, JP-A-2003-511799, and JP-A-2010-541109 can be mentioned. After the first transparent conductive layer is formed on the substrate, it can be patterned by any suitable method depending on the form of the first transparent conductive layer.

The total light transmittance of the first transparent conductive layer is preferably 85% or more, more preferably 90% or more, and further preferably 95% or more.

The metal nanowire is a conductive substance whose material is metal, whose shape is needle-shaped or thread-shaped, and whose diameter is nanometer-sized. The metal nanowires may be linear or curved. If the first transparent conductive layer made of metal nanowires is used, the metal nanowires have a mesh shape, so that a good electric conduction path can be formed even with a small amount of metal nanowires, and electric resistance can be obtained. A small transparent conductive film can be obtained.

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 100. It is 10,000. By using metal nanowires having 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 film having high light transmittance can be obtained. In the present specification, the "thickness of the metal nanowire" means the diameter of the metal nanowire when the cross section is circular, and the minor diameter when the cross section of the metal nanowire is elliptical, and is polygonal. In some cases it means the longest diagonal. The thickness and length of the metal nanowires can be confirmed by a scanning electron microscope or a transmission electron microscope.

The thickness of the metal nanowires is preferably less than 500 nm, more preferably less than 200 nm, particularly preferably 10 nm to 100 nm, and most preferably 10 nm to 60 nm. Within such a range, the first transparent conductive layer having high light transmittance can be formed.

The length of the metal nanowires is preferably 1 μm to 1000 μm, more preferably 1 μm to 500 μm, and particularly preferably 1 μm to 100 μm. Within such a range, a transparent conductive film having high conductivity can be obtained.

As the metal constituting the metal nanowire, any suitable metal can be used as long as it is a highly conductive metal. Examples of the metal constituting the metal nanowire include silver, gold, copper, nickel and the like. Further, a material obtained by plating these metals (for example, gold plating) may be used. The metal nanowires are preferably composed of one or more metals selected from the group consisting of gold, platinum, silver and copper.

Any suitable method can be adopted as the method for producing the metal nanowires. For example, a method of reducing silver nitrate in a solution, a method of applying an applied voltage or a current to the surface of the precursor from the tip of the probe, pulling out a metal nanowire at the tip of the probe, and a method of continuously forming the metal nanowire can be mentioned. .. In the method of reducing silver nitrate in a 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 are available, for example, from Xia, Y. et al. et al. , Chem. Mater. (2002), 14, 4736-4745, Xia, Y. et al. et al. , Nano letters (2003) 3 (7), 955-960, can be mass-produced.

The content ratio of the metal nanowires in the first transparent conductive layer is preferably 30% by weight to 100% by weight, more preferably 30% by weight to 90% by weight, based on the total weight of the first transparent conductive layer. It is more preferably 45% by weight to 80% by weight. Within such a range, a transparent conductive film having excellent conductivity and light transmittance can be obtained.

Any suitable polymer can be used as the polymer constituting the polymer matrix. Examples of the polymer include acrylic polymers; polyester polymers such as polyethylene terephthalate; aromatic polymers such as polystyrene, polyvinyltoluene, polyvinyl xylene, polyimide, polyamide and polyamideimide; polyurethane polymers; epoxy polymers; polyolefin polymers. Polymers; acrylonitrile-butadiene-styrene copolymer (ABS); cellulose; silicon-based polymers; polyvinyl chloride; polyacetates; polynorbornene; synthetic rubber; fluoropolymers and the like. Preferred are polyfunctionals such as pentaerythritol triacrylate (PETA), neopentylglycol diacrylate (NPGDA), dipentaerythritol hexaacrylate (DPHA), dipentaerythritol pentaacrylate (DPPA) and trimethylolpropane triacrylate (TMPTA). A curable resin composed of acrylate (preferably an ultraviolet curable resin) is used.

When the first transparent conductive layer is composed of a polymer matrix and the metal nanowires are silver nanowires, the density of the first transparent conductive layer is preferably 1.3 g / cm ^{3 to} 10.5 g / cm ^3. by weight, more preferably from ^{1.5g / cm 3 ~3.0g / cm 3} . Within such a range, a transparent conductive film having excellent conductivity and light transmittance can be obtained.

For the first transparent conductive layer, a composition for forming a first conductive layer containing metal nanowires is applied to a base material (or a laminate of the base material and another layer), and then the coated layer is dried. Can be formed.

The first conductive layer forming composition may contain any suitable solvent in addition to the metal nanowires. The composition for forming the first conductive layer can be prepared as a dispersion liquid of metal nanowires. Examples of the solvent include water, an alcohol solvent, a ketone solvent, an ether solvent, a hydrocarbon solvent, an aromatic solvent and the like. From the viewpoint of reducing the environmental load, it is preferable to use water. The first conductive layer forming composition may further contain any suitable additive depending on the purpose. Examples of the additive include a corrosion inhibitor for preventing corrosion of metal nanowires, a surfactant for preventing aggregation of metal nanowires, and the like. The type, number and amount of additives used can be appropriately set according to the purpose.

When the first transparent conductive layer contains a polymer matrix, the polymer matrix is applied onto a layer composed of metal nanowires after the composition for forming the first conductive layer is applied and dried as described above. It can be formed by applying a polymer solution (polymer composition, monomer composition) and then drying or curing the coating layer of the polymer solution. Further, the first transparent conductive layer may be formed by using the composition for forming the first conductive layer containing the polymer constituting the polymer matrix.

The dispersion concentration of the metal nanowires in the first conductive layer forming composition is preferably 0.1% by weight to 1% by weight. Within such a range, a first transparent conductive layer having excellent conductivity and light transmission can be formed.

Any suitable method can be adopted as the method for applying the first conductive layer forming composition. Examples of the coating method include spray coating, bar coating, roll coating, die coating, inkjet coating, screen coating, dip coating, letterpress printing method, intaglio printing method, gravure printing method and the like. As a method for drying the coating layer, any suitable drying method (for example, natural drying, blast drying, heat drying) can be adopted. 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.

The polymer solution contains a polymer constituting the polymer matrix or a precursor of the polymer (monomer constituting the polymer).

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

C. Substrate The substrate is typically composed of any suitable resin. Examples of the resin constituting the base material include cycloolefin resin, polyimide resin, polyvinylidene chloride resin, polyvinyl chloride resin, polyethylene terephthalate resin, polyethylene naphthalate resin and the like. Preferably, a cycloolefin resin is used. If a base material made of a cycloolefin resin is used, a transparent conductive film having excellent flexibility can be obtained.

As the cycloolefin-based resin, for example, polynorbornene can be preferably used. Polynorbornene refers to a (co) polymer obtained by using a norbornene-based monomer having a norbornene ring in a part or all of a starting material (monomer). As the polynorbornene, various products are commercially available. Specific examples include Zeon Corporation's product names "Zeonex" and "Zeonoa", JSR's product name "Arton", TICONA's product name "Topus", and Mitsui Chemicals' product name. "APEL" can be mentioned.

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 further preferably 70 ° C. to 160 ° C. A substrate having a glass transition temperature in such a range can prevent deterioration when forming the first transparent conductive layer.

The thickness of the base material is preferably 8 μm to 500 μm, more preferably 10 μm to 250 μm, further preferably 10 μm to 150 μm, and particularly preferably 15 μm to 100 μm.

The tensile breaking strength of the base material is preferably 50 MPa or more, more preferably 70 MPa or more, and further preferably 100 MPa or more. Within such a range, a transparent conductive film having particularly excellent flexibility can be obtained. The tensile breaking strength can be measured at room temperature according to JIS K 7161.

The total light transmittance of the base material 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 as a transparent conductive film provided for a touch panel or the like can be obtained.

The substrate may further contain any suitable additive, if desired. Specific examples of additives include plasticizers, heat stabilizers, light stabilizers, lubricants, antioxidants, UV absorbers, flame retardants, colorants, antistatic agents, compatibilizers, cross-linking agents, and thickeners. And so on. The type and amount of the additive used can be appropriately set according to the purpose.

If necessary, various surface treatments may be applied to the base material. Any appropriate method is adopted for the surface treatment depending on the purpose. For example, low pressure plasma treatment, ultraviolet irradiation treatment, corona treatment, flame treatment, acid or alkali treatment can be mentioned. In one embodiment, the transparent substrate is surface-treated to make the surface of the transparent substrate hydrophilic. If the base material is made hydrophilic, the processability when applying the composition for forming a transparent conductive layer prepared by an aqueous solvent is excellent. Further, it is possible to obtain a transparent conductive film having excellent adhesion between the base material and the transparent conductive layer.

D. Second Transparent Conductive Layer As described above, the second transparent conductive layer is composed of a metal oxide. Examples of the metal oxide include indium oxide, tin oxide, zinc oxide, indium-tin composite oxide, tin-antimon composite oxide, zinc-aluminum composite oxide, indium-zinc composite oxide and the like. Of these, indium-tin composite oxide (ITO) is preferable. The metal oxide may be a crystallized metal oxide. As will be described later, the crystallized metal oxide means a metal oxide obtained by forming a metal oxide film and then heating (for example, heating at 120 ° C. to 200 ° C.).

The total light transmittance of the second transparent conductive layer is preferably 80% or more, more preferably 85% or more, still more preferably 90% or more.

As a method for forming the second transparent conductive layer, for example, a metal oxide layer is formed by any appropriate film forming method (for example, vacuum vapor deposition method, sputtering method, CVD method, ion plating method, spray method, etc.). A method of forming a second transparent conductive layer can be mentioned. The metal oxide layer may be used as it is as a second transparent conductive layer, or may be further heated to crystallize the metal oxide. The heating temperature is, for example, 120 ° C to 200 ° C.

The thickness of the second transparent conductive layer is preferably 50 nm or less, more preferably 40 nm or less. Within such a range, a transparent conductive film having excellent light transmission can be obtained. The lower limit of the thickness of the conductive layer is preferably 1 nm, more preferably 5 nm.

The second transparent conductive layer may be patterned. As the patterning method, any suitable method can be adopted depending on the morphology of the conductive layer. For example, it can be patterned by an etching method, a laser method, or the like. The shape of the pattern of the second transparent conductive layer can be any suitable shape depending on the application. For example, the patterns described in JP-A-2011-511357, JP-A-2010-164938, JP-A-2008-310550, JP-A-2003-511799, and JP-A-2010-541109 can be mentioned.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples. The evaluation methods in the examples and comparative examples are as follows.

(1) Haze value The haze value of the transparent conductive film was measured using a haze meter (manufactured by Murakami Color Science Laboratory Co., Ltd., trade name "HN-150") by the method specified by JIS 7136.

(2) Flexibility The flexibility of the transparent conductive film was evaluated based on the conductivity after bending the transparent conductive film. The specific evaluation method is as follows.
A test piece was obtained by applying Ag paste to both ends of the transparent conductive film (length 100 mm × width 20 mm) in the longitudinal direction on the first conductive layer side. This test piece was hung on a stainless steel round bar (diameter: 2 mm) with the first conductive layer on the outside, and bent 180 ° along the round bar so as to bend in the longitudinal direction. Next, weights (500 g each) were lowered to both ends in the longitudinal direction via clips and held in that state for 10 seconds.
After the above operation, the weight and clip were removed, and the continuity between the Ag paste parts was confirmed with a tester. If continuity was possible, it was OK, and if continuity was not possible, it was NG.

[Manufacturing Example 1]
(Manufacturing of metal nanowires)
In a reaction vessel equipped with a stirrer, 5 ml of anhydrous ethylene glycol and 0.5 ml of an anhydrous ethylene glycol solution of PtCl2 (concentration: 1.5 × 10-4 mol / L) were added at 160 ° C. After 4 minutes, 2.5 ml of an anhydrous ethylene glycol solution of AgNO3 (concentration: 0.12 mol / l) and an anhydrous ethylene glycol solution of polyvinylpyrrolidone (MW: 55000) (concentration: 0.36 mol / l) were added to the obtained solution. l) 5 ml was added dropwise over 6 minutes at the same time. After this dropping, the mixture was heated to 160 ° C. for 1 hour or more and _{reacted until AgNO 3} was completely reduced to produce silver nanowires. Then, acetone was added to the reaction mixture containing the silver nanowires obtained as described above until the volume of the reaction mixture was increased by 5 times, and then the reaction mixture was centrifuged (2000 rpm, 20 minutes). Obtained silver nanowires. The silver nanowire (concentration: 0.2% by weight) and pentaethylene glycol dodecyl ether (concentration: 0.1% by weight) were dispersed in pure water to prepare a silver nanowire dispersion liquid.

[Example 1]
(Preparation of composition (PN) for forming a transparent conductive layer)
A composition (PN) for forming a transparent conductive layer having a solid content concentration of 0.05% by weight was prepared by diluting with 25 parts by weight of the silver nanowire dispersion liquid and 75 parts by weight of pure water.
(Preparation of monomer composition)
1 part by weight of pentaerythritol triacrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd., trade name "Viscoat # 300"), 0.2 parts by weight of photopolymerization initiator (manufactured by BASF, trade name "Irgacure 907") by 80 parts by weight of isopropyl alcohol Dilute with 19 parts by weight of diacetone alcohol to obtain a monomer composition having a solid content concentration of 1% by weight.
(Manufacturing of transparent conductive film)
The composition for forming the transparent conductive layer as the first composition for forming the transparent conductive layer on one side of the base material (polycycloolefin film (trade name "ZEONOR (registered trademark)" manufactured by Nippon Zeon Corporation, thickness 25 μm)). The product (PN) was applied and dried. Further, the above-mentioned monomer composition was applied onto the first transparent conductive layer forming composition (PN) coating layer, dried at 90 ° C. for 1 minute, and then dried. A first transparent conductive layer was formed by irradiating with ultraviolet rays of 300 mJ / cm ^2. Next, a second transparent conductive layer made of an indium tin oxide layer having a thickness of 30 nm was sputtered on the other side of the base material. The conductive film thus obtained was wound around a plastic winding core to prepare a conductive film roll.
A transparent conductive film was obtained as described above. The obtained transparent conductive film was subjected to the above evaluations (1) and (2). The results are shown in Table 1.

[Comparative Example 1]
A transparent conductive layer made of an indium tin oxide oxide layer on both sides of a base material (polycycloolefin film (trademark "ZEONOR (registered trademark)" manufactured by Nippon Zeon Corporation, thickness 25 μm) (thickness of each layer: 30 nm)). Was formed to obtain a transparent conductive film.
A transparent conductive film was obtained as described above. The obtained transparent conductive film was subjected to the above evaluations (1) and (2). The results are shown in Table 1.

[Comparative Example 2]
The composition for forming the transparent conductive layer as the first composition for forming the transparent conductive layer on one side of the base material (polycycloolefin film (trade name "ZEONOR (registered trademark)" manufactured by Nippon Zeon Corporation, thickness 25 μm)). The product (PN) was applied and dried. Further, the above-mentioned monomer composition was applied onto the first transparent conductive layer forming composition (PN) coating layer, dried at 90 ° C. for 1 minute, and then dried. The first transparent conductive layer was formed by irradiating with ultraviolet rays of 300 mJ / cm ^2.
The transparent conductive layer forming composition (PN) was also applied to the other side of the base material as the second transparent conductive layer forming composition and dried. Further, the above-mentioned monomer composition is applied onto the second transparent conductive layer forming composition (PN) coating layer, dried at 90 ° C. for 1 minute, and then irradiated with ultraviolet rays of ^{300 mJ / cm 2 to obtain the first.} A transparent conductive layer was formed.
A transparent conductive film was obtained as described above. The obtained transparent conductive film was subjected to the above evaluations (1) and (2). The results are shown in Table 1.

10 First transparent conductive layer 20 Base material 30 Second transparent conductive layer 100 Transparent conductive film

Claims (4)

A first transparent conductive layer, a base material, and a second transparent conductive layer are provided in this order.
The first transparent conductive layer contains metal nanowires and contains.
The second transparent conductive layer is made of a metal oxide.
Transparent conductive film. The transparent conductive film according to claim 1, wherein the metal oxide constituting the second transparent conductive layer is an indium-tin composite oxide. The transparent conductive film according to claim 1 or 2, wherein the tensile breaking strength of the base material is 100 MPa or more. The transparent conductive film according to any one of claims 1 to 3, wherein the base material is made of a cycloolefin resin.

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