Transparent conductive film manufacturing method

Abstract

Provided is a method for producing a transparent conductive film which includes a metal nanowire and which has low conductive anisotropy. The method for producing a transparent conductive film according to the present invention comprises: a coating step for forming a coating layer by coating a long substrate with a composition for forming a transparent conductive layer containing a metal nanowire while conveying the substrate; and a drying step for drying the coating layer and forming a transparent conductive layer on the substrate, wherein the average inclination angle θa of the surface of the substrate is at least 0.5°.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a transparent conductive film. [Background technology]

[0002] Conventionally, in image display devices with touch sensors, transparent conductive films obtained by forming a metal oxide layer such as ITO (indium-tin oxide) on a transparent resin film have been widely used as electrodes for the touch sensors. However, transparent conductive films with such metal oxide layers tend to lose conductivity when bent, making them difficult to use in applications requiring flexibility, such as flexible displays.

[0003] On the other hand, transparent conductive films containing metal nanowires are known as highly flexible transparent conductive films. Metal nanowires are wire-shaped conductive materials with nanometer-sized diameters. In transparent conductive films made of metal nanowires, the metal nanowires form a mesh-like structure, allowing good electrical conduction paths to be formed with a small amount of metal nanowires. Furthermore, openings are formed in the gaps between the meshes, achieving high light transmittance. However, because the metal nanowires are wire-shaped, they tend to be arranged in an oriented state, which poses a problem of conductive anisotropy in transparent conductive films containing metal nanowires. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2009-505358 [Patent Document 2] Patent No. 6199034 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made to solve the above problems, and its purpose is to provide a method for producing a transparent conductive film that contains metal nanowires but has small conductive anisotropy. [Means for solving the problem]

[0006] The method for producing a transparent conductive film of the present invention includes a coating step of coating a long-sized substrate with a transparent conductive layer-forming composition containing metal nanowires onto the substrate while transporting the substrate to form a coating layer, and a drying step of drying the coating layer to form a transparent conductive layer on the substrate, wherein the average tilt angle θa of the surface of the substrate is 0.5° or more. In one embodiment, the average spacing Sm of the irregularities on the surface of the substrate is 0.4 mm or less. According to another aspect of the present invention, there is provided a transparent conductive film comprising a substrate and a transparent conductive layer disposed on one side of the substrate, wherein the average tilt angle θa of the surface of the substrate is 0.6° or more. [Effects of the Invention]

[0007] According to the present invention, a method for producing a transparent conductive film with small conductive anisotropy can be provided. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic cross-sectional view of a transparent conductive film according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] A. Manufacturing method of transparent conductive film The method for producing a transparent conductive film of the present invention includes a coating step of coating a long-sized substrate with a transparent conductive layer-forming composition containing metal nanowires onto the substrate while transporting the substrate to form a coating layer, and a drying step of drying the coating layer to form a transparent conductive layer on the substrate. Typically, the coating step and drying step are performed while the substrate in a roll state is unwound and transported, thereby forming a long-sized transparent conductive film 100 including a substrate 10 and a transparent conductive layer 20 disposed on one side of the substrate 10, as shown in FIG. 1. In one embodiment, the transparent conductive film is wound up after the drying step.

[0010] A-1. Coating process As described above, in the coating step, a composition for forming a transparent conductive layer containing metal nanowires is coated onto a long substrate while the substrate is being transported, thereby forming a coating layer.

[0011] (base material) The average tilt angle θa of the surface of the substrate is 0.5° or more. In the present invention, by using a substrate having a surface shape specified as above, the metal nanowires are well dispersed in the coating layer, causing the orientation of the metal nanowires to become disordered, thereby enabling the production of a transparent conductive film with small conductive anisotropy. In this specification, the surface of the substrate refers to the surface on which the coating layer is to be formed.

[0012] The average tilt angle θa of the surface of the substrate is preferably 0.8° or more, more preferably 1° or more, even more preferably 1.2° or more, and particularly preferably 1.4° or more. Within such a range, the effects of the present invention become more pronounced. The upper limit of the average tilt angle θa is, for example, 3° (preferably 2.5°, more preferably 2°). In this specification, the average tilt angle θa is defined by the following formula (1): θa=tan -1 Δa (1) In the above formula (1), Δa is the value obtained by dividing the sum of the differences (heights h) between the peaks of adjacent peaks and the lowest points of adjacent valleys (h1 + h2 + h3··· + hn) by the reference length L of the roughness curve specified in JIS B 0601 (1994 edition), as shown in the following formula (2). The above roughness curve is a curve obtained by removing surface waviness components longer than a specified wavelength from a profile curve using a phase difference compensation high-pass filter. The above profile curve is the outline that appears at the cut surface when the target surface is cut by a plane perpendicular to the target surface. Δa=(h1+h2+h3···+hn) / L···(2)

[0013] The average spacing Sm of the irregularities on the surface of the substrate is preferably 0.4 mm or less, more preferably 0.3 mm or less, even more preferably 0.25 mm or less, particularly preferably 0.2 mm or less, and most preferably 0.15 mm or less. The larger the average spacing Sm of the irregularities, the more likely it is that the orientation of the metal nanowires will be reduced, making it possible to produce a transparent conductive film with particularly small conductive anisotropy. Furthermore, by increasing the average spacing Sm of the irregularities, a significant reduction in conductive anisotropy can be achieved even if the average tilt angle θa is relatively small (for example, average tilt angle θa = 0.6° to 1°). The lower limit of the average spacing Sm of the irregularities is, for example, 0.03 mm (preferably 0.04 mm). The definition of the average tilt angle θa is based on JIS B 0601 (1994 edition).

[0014] The arithmetic mean surface roughness Ra of the surface of the substrate is preferably 0.05 μm to 3 μm, more preferably 0.1 μm to 1.5 μm. Within this range, a transparent conductive film with particularly small conductive anisotropy can be produced. The definition of the arithmetic mean surface roughness Ra is based on JIS B 0601 (1994 edition).

[0015] The thickness of the substrate is preferably 20 μm to 200 μm, and more preferably 30 μm to 150 μm.

[0016] The total light transmittance of the substrate is preferably 30% or more, more preferably 35% or more, and even more preferably 40% or more.

[0017] Any appropriate material can be used as the material for the substrate. Specifically, for example, a polymer substrate such as a film or plastic substrate is preferably used. This is because the substrate has excellent smoothness and wettability with respect to the transparent conductive layer-forming composition, and productivity can be significantly improved by continuous production using a roll.

[0018] The material constituting the substrate is typically a polymer film mainly composed of a thermoplastic resin. Examples of thermoplastic resins include polyester resins; cycloolefin resins such as polynorbornene; acrylic resins; polycarbonate resins; and cellulose resins. Among these, polyester resins, cycloolefin resins, and acrylic resins are preferred. These resins are excellent in transparency, mechanical strength, thermal stability, and moisture-blocking properties. The thermoplastic resins may be used alone or in combination of two or more. Optical films used in polarizing plates, such as low-retardation substrates, high-retardation substrates, retardation plates, and brightness-enhancing films, can also be used as the substrate.

[0019] Any appropriate method can be used to transport the substrate. For example, transport using transport rolls, transport using a transport belt, or a combination of these, can be used. The transport speed is, for example, 5 m / min to 50 m / min.

[0020] (metal nanowires) 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 transparent conductive layer made of metal nanowires, the metal nanowires form a mesh, allowing even a small amount of metal nanowires to form an excellent 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.

[0021] The ratio of the thickness d to the length L of the metal nanowire (aspect ratio: L / d) 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 high aspect ratio, the metal nanowires can be well intersected, enabling a small number of metal nanowires 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 metal nanowire" refers to the diameter of the metal nanowire when the cross section is circular, the minor axis of the metal nanowire when the cross section is elliptical, and the longest diagonal of the metal nanowire when the cross section is polygonal. The thickness and length of the metal nanowire can be confirmed using a scanning electron microscope or a transmission electron microscope.

[0022] The thickness of the 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 this range, a transparent conductive layer with high light transmittance can be formed.

[0023] The length of the 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. Furthermore, if the length of the metal nanowires is within this range, the effects obtained by specifying the surface shape of the substrate as described above can be enhanced.

[0024] 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.

[0025] Any suitable method can be used to produce the metal nanowires. Examples include reducing silver nitrate in solution, applying a voltage or current from the tip of a probe to the surface of a precursor, drawing the metal nanowires from 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 reducing a silver salt such as silver nitrate in the liquid phase 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.

[0026] (Composition for forming transparent conductive layer) The composition for forming a transparent conductive layer contains metal nanowires. In one embodiment, the composition for forming a transparent conductive layer is prepared by dispersing the metal nanowires in any appropriate solvent. Examples of such solvents include water, alcohol-based solvents, ketone-based solvents, ether-based solvents, hydrocarbon-based solvents, and aromatic solvents. The composition for forming a transparent conductive layer may further contain additives such as a resin (binder resin), a conductive material other than metal nanowires (e.g., conductive particles), and a leveling agent. The composition for forming a transparent conductive layer may also contain additives such as a plasticizer, a heat stabilizer, a light stabilizer, a lubricant, an antioxidant, an ultraviolet absorber, a flame retardant, a colorant, an antistatic agent, a compatibilizer, a crosslinker, a thickener, inorganic particles, a surfactant, and a dispersant.

[0027] The viscosity of the composition for forming a transparent conductive layer is preferably 5 mP·s / 25°C to 300 mP·s / 25°C, and more preferably 10 mP·s / 25°C to 100 mP·s / 25°C. Within this range, the effect obtained by specifying the surface shape of the substrate as described above is enhanced. The viscosity of the composition for forming a transparent conductive layer can be measured using a rheometer (for example, Anton Paar's MCR302).

[0028] The dispersion concentration of the metal nanowires in the composition for forming a transparent conductive layer is preferably 0.01% by weight to 5% by weight, and within this range, the effects of the present invention are significant.

[0029] The transparent conductive 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.

[0030] The basis weight of the coating layer is preferably 0.3 g / m 2 ~30g / m 2 and more preferably 1.6 g / m 2 ~16g / m 2Within such a range, the effect obtained by specifying the surface shape of the substrate as described above is significant.

[0031] The thickness of the coating layer is preferably 1 μm to 50 μm, and more preferably 2 μm to 40 μm.

[0032] A-2. Drying process As described above, in the drying step, the coating layer is dried to form a transparent conductive layer on the substrate.

[0033] The coating layer can be dried by any suitable method (e.g., natural drying, air drying, or heat drying). For example, in the case of heat drying, the drying temperature is typically 80°C to 150°C, and the drying time is typically 1 to 20 minutes.

[0034] After the drying step, any appropriate treatment may be carried out. For example, when a transparent conductive layer-forming composition containing a binder resin is used, a curing treatment such as ultraviolet irradiation may be carried out.

[0035] B. Transparent conductive film A transparent conductive film is formed by the above manufacturing method. Figure 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 transparent conductive layer 20 disposed on one side of the substrate 10.

[0036] The surface resistance of the transparent conductive film is preferably 0.1 Ω / □ to 1000 Ω / □, more preferably 0.5 Ω / □ to 300 Ω / □, and particularly preferably 1 Ω / □ to 200 Ω / □. The ratio (TD / MD) of the surface resistance in TD (the direction perpendicular to MD) to the surface resistance in MD (the machine direction) of the transparent conductive film is preferably 0.7 to 1.5, more preferably 0.8 to 1.2, and even more preferably 0.9 to 1.1. The surface resistance can be measured using Mitsubishi Chemical Analytech's "Automatic Resistivity Measurement System MCP-S620 / MCP-S521."

[0037] The haze value of the transparent conductive film is preferably 20% or less, more preferably 10% or less, and even more preferably 0.1% to 5%.

[0038] The total light transmittance of the transparent conductive film is preferably 30% or more, more preferably 35% or more, and particularly preferably 40% or more.

[0039] The average tilt angle θa of the surface of the substrate is 0.6° or more, preferably 0.8° or more, more preferably 1° or more, even more preferably 1.2° or more, and particularly preferably 1.4° or more. Within such a range, the effects of the present invention become more pronounced. The upper limit of the average tilt angle θa is, for example, 3° (preferably 2.5°, more preferably 2°). The average tilt angle θa of the surface of the substrate is measured before the transparent conductive layer is formed.

[0040] The average spacing Sm of the irregularities on the surface of the substrate is preferably 0.4 mm or less, more preferably 0.3 mm or less, even more preferably 0.25 mm or less, particularly preferably 0.2 mm or less, and most preferably 0.15 mm or less. The average spacing Sm of the irregularities on the surface of the substrate is measured before the transparent conductive layer is formed.

[0041] The arithmetic mean surface roughness Ra of the surface of the substrate is preferably 0.05 μm to 3 μm, and more preferably 0.1 μm to 1.5 μm. The arithmetic mean surface roughness Ra of the surface of the substrate is measured before the transparent conductive layer is formed.

[0042] The basis weight of the transparent conductive layer is preferably 0.001 g / m 2 ~0.09g / m 2 and more preferably 0.005 g / m 2 ~0.05g / m 2 is.

[0043] The content of the metal nanowires in the transparent conductive layer is preferably 0.1 to 50 parts by weight, more preferably 0.1 to 30 parts by weight, relative to 100 parts by weight of the binder resin constituting the transparent conductive layer. Within this range, a transparent conductive film with excellent conductivity and light transmittance can be obtained. [Example]

[0044] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The evaluation methods in the examples are as follows. The thickness was measured using a scanning electron microscope "S-4800" manufactured by Hitachi High-Technologies Corporation, after embedding the sample in epoxy resin and cutting it with an ultramicrotome to form a cross section.

[0045] (1) Shape of the substrate surface According to JIS B0601 (1994 edition), the average inter-convexity distance Sm (mm) and the arithmetic mean surface roughness Ra (μm) were measured. Specifically, a glass plate (MICRO SLIDE GLASS, manufactured by MATSUNAMI Co., Ltd., product number S, thickness 1.3 mm, 45 × 50 mm) was attached to the opposite side of the measurement surface with an adhesive to prepare a sample. The surface profile of the antiglare layer of the sample was measured in a certain direction using a stylus-type surface roughness measuring instrument (manufactured by Kosaka Laboratory Co., Ltd., high-precision micro-profile measuring instrument, product name "Surfcorder ET4000") with a diamond-tipped stylus having a curvature radius R = 2 μm under the conditions of a scanning speed of 0.1 mm / s, a cutoff value of 0.8 mm, and a measurement length of 4 mm. The average inter-concave spacing Sm was determined, and the average slope angle θa (°) was also calculated from the obtained surface roughness curve.

[0046] (2) Surface resistance The surface resistance values (MD and TD surface resistance values) of the transparent conductive film were measured by an eddy current method using a non-contact surface resistance meter, product name "EC-80", manufactured by Napson Co., Ltd. The measurement temperature was 23°C.

[0047] [Production Example 1] Preparation of composition for forming transparent conductive layer Silver nanowires were synthesized based on the method described in Chem. Mater. 2002, 14, 4736-4745. The silver nanowires obtained above were dispersed in pure water to a concentration of 0.2 wt % and dodecyl-pentaethylene glycol to a concentration of 0.1 wt %, to obtain a composition for forming a transparent conductive layer.

[0048] [Example 1] A coating solution containing 100 parts by weight of an acrylic monomer (Osaka Organic Chemical Industry Co., Ltd., product name "Viscoat #300", solids content 56 wt%), 30 parts by weight of particles (Sekisui Chemical Co., Ltd., product name "Techpolymer SSX-105"), 0.5 parts by weight of an initiator (BASF, product name "Irgacure 127"), and 35 parts by weight of butyl acetate was applied to a PET film (Toray Industries, Inc., product name "U40", thickness: 23 μm), dried at 100°C for 2 minutes, and then irradiated with 300 mJ of ultraviolet light to form substrate A (thickness: 20 μm) on the PET film. The transparent conductive layer-forming composition prepared in Production Example 1 was applied to the substrate A peeled from the PET film using a bar coater (manufactured by Daiichi Rika Co., Ltd., product name "Bar Coater No. 16") and dried for 2 minutes in a 120°C air dryer to form a transparent conductive layer, thereby obtaining a transparent conductive film comprising a substrate and a transparent conductive layer. The average inclination angle θa of the surface of substrate A on which the transparent conductive layer was formed was 1.5°, and the average spacing Sm of the irregularities was 0.05 mm. The obtained transparent conductive film was subjected to the above evaluation (2), and the results are shown in Table 1.

[0049] [Example 2] Substrate B (thickness: 20 μm) was formed in the same manner as in Example 1, except that 5 parts by weight of particles (manufactured by Soken Chemical Co., Ltd., product name "SX-350H") were used instead of 30 parts by weight of particles (manufactured by Sekisui Chemical Co., Ltd., product name "Techpolymer SSX-105"), and 0.2 parts by weight of a thixotropic agent (manufactured by Kunimine Industries Co., Ltd., product name "SAN") was added to the coating liquid. Thereafter, a transparent conductive layer was formed in the same manner as in Example 1, and a transparent conductive film comprising the substrate and the transparent conductive layer was obtained. The average inclination angle θa of the surface of substrate D on which the transparent conductive layer was formed was 0.9°, and the average spacing Sm of the irregularities was 0.15 mm. The obtained transparent conductive film was subjected to the above evaluation (2), and the results are shown in Table 1.

[0050] [Example 3] Substrate C (thickness: 20 μm) was formed in the same manner as in Example 2, except that the amount of particles (manufactured by Soken Chemical Co., Ltd., product name "SX-350H") added was 10 parts by weight. Thereafter, a transparent conductive layer was formed in the same manner as in Example 1, to obtain a transparent conductive film including a substrate and a transparent conductive layer. The average inclination angle θa of the surface of substrate C on which the transparent conductive layer was formed was 1.5°, and the average spacing Sm of the irregularities was 0.12 mm. The obtained transparent conductive film was subjected to the above evaluation (2), and the results are shown in Table 1.

[0051] [Comparative Example 1] A transparent conductive film was obtained in the same manner as in Example 1, except that a PET film (manufactured by Toray Industries, Inc., product name "U40", thickness: 23 μm, average tilt angle: 0.1°, average spacing Sm of irregularities: 0.04 mm) was used as substrate B instead of substrate A. The obtained transparent conductive film was subjected to the above evaluation (2). The results are shown in Table 1.

[0052] Comparative Example 2 Substrate D (thickness: 20 μm) was formed in the same manner as in Example 1, except that 15 parts by weight of particles (manufactured by Sekisui Chemical Co., Ltd., product name "Technopolymer SSX-101") were used instead of 30 parts by weight of particles (manufactured by Sekisui Chemical Co., Ltd., product name "Techpolymer SSX-105"). Thereafter, a transparent conductive layer was formed in the same manner as in Example 1, and a transparent conductive film comprising a substrate and a transparent conductive layer was obtained. The average inclination angle θa of the surface of substrate D on which the transparent conductive layer was formed was 0.3°, and the average spacing Sm of the irregularities was 0.19 mm. The obtained transparent conductive film was subjected to the above evaluation (2), and the results are shown in Table 1.

[0053] [Table 1]

[0054] [Reference example 1] A coating solution containing 100 parts by weight of an acrylic monomer (manufactured by Osaka Organic Chemical Industry Co., Ltd., trade name "Viscoat #300", solids content 56 wt%), 10 parts by weight of particles (manufactured by Sekisui Chemical Co., Ltd., trade name "Techpolymer SSX-101"), 0.5 parts by weight of an initiator (manufactured by BASF, trade name "Irgacure 127"), and 35 parts by weight of butyl acetate was applied to a PET film, dried at 100°C for 2 minutes, and then irradiated with 300 mJ of ultraviolet light to form substrate C (thickness: 20 μm) on the PET film. The transparent conductive layer-forming composition prepared in Production Example 1 was applied to the substrate C peeled from the PET film using a bar coater (manufactured by Daiichi Rika Co., Ltd., product name "Bar Coater No. 16") and dried for 2 minutes in a 120°C air dryer to form a transparent conductive layer, thereby obtaining a transparent conductive film comprising a substrate and a transparent conductive layer. The average inclination angle θa of the surface of substrate C on which the transparent conductive layer was formed was 0.1°, and the average spacing Sm of the irregularities was 0.27 mm. The obtained transparent conductive film was subjected to the above evaluation (2), and the surface resistance value in MD was 41Ω and the surface resistance value in TD was 62Ω. [Explanation of symbols]

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

Claims

1. a coating step of coating a transparent conductive layer-forming composition containing metal nanowires onto a long substrate while transporting the substrate to form a coating layer; a drying step of drying the coating layer to form a transparent conductive layer on the substrate, The average inclination angle θa of the surface of the substrate is 1.2° to 3°. A method for producing a transparent conductive film.

2. The method for producing a transparent conductive film according to claim 1 , wherein the average spacing Sm of the irregularities on the surface of the substrate is 400 μm or less.

3. A substrate; a transparent conductive layer disposed on one side of the substrate and including metal nanowires; The average inclination angle θa of the surface of the substrate is 1.2° to 3°. Transparent conductive film.

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