Transparent Conductive Film

Abstract

To provide a transparent conductive film having a transparent conductive layer containing a metal filler, the transparent conductive film having low resistance.SOLUTION: A transparent conductive film has a base material, and a transparent conductive layer disposed on at least one side of the base material, the transparent conductive layer containing a metal filler. A half-value width of distribution of the metal filler present in the thickness direction of the transparent conductive layer is 5 nm-75 nm. In one embodiment, the metal filler is a metal nanowire.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to 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 flexible displays. However, there is a problem in that it is difficult to use in applications where flexibility is required.

[0003] On the other hand, transparent conductive films containing metal fillers such as metal nanowires are known as highly flexible transparent conductive films. While such transparent conductive films have the advantages of having a predetermined transparency and conductivity as well as excellent flexibility, further improvement in conductivity (resistivity suppression) is required. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2009-505358 [Patent Document 1] 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-mentioned problems, and its object is to provide a transparent conductive film having a transparent conductive layer containing a metal filler, which has low resistance. [Means for solving the problem]

[0006] The transparent conductive film of the present invention comprises a substrate and a transparent conductive layer disposed on at least one side of the substrate, the transparent conductive layer containing a metal filler, and the half-width of the distribution of the metal filler in the thickness direction of the transparent conductive layer is 5 nm to 75 nm. In one embodiment, the metal filler is a metal nanowire. In one embodiment, the transparent conductive film of the present invention has a surface resistance value of 10 Ω / □ or more and less than 300 Ω / □. In one embodiment, the transparent conductive film of the present invention has a haze value of 20% or less. [Effects of the Invention]

[0007] According to the present invention, a transparent conductive film having a transparent conductive layer containing a metal filler and low resistance can be provided. The transparent conductive film of the present invention is useful in that it has low resistance while suppressing a decrease in transparency, compared to conventional transparent conductive films. [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. [Figure 2] 1(a) is a cross-sectional TEM photograph of the transparent conductive film obtained in Example 1. FIG. 1(b) is a cross-sectional TEM photograph of the transparent conductive film obtained in Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0009] A. Transparent conductive film 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 of the present invention comprises a substrate 10 and a transparent conductive layer 20 disposed on at least one side of the substrate 10.

[0010] In the transparent conductive film 100, the transparent conductive layer 20 contains a metal filler (not shown).

[0011] In the present invention, the half-value width of the distribution of the metal filler in the thickness direction of the transparent conductive layer is 5 nm to 75 nm. The "half-value width of the distribution of the metal filler in the thickness direction of the transparent conductive layer" refers to the half-value width at the most frequent peak (the distribution width at half the height of the distribution height at the peak position) in a plot of the distribution of the metal filler, which is determined by binarizing an image obtained by photographing a cross section of the transparent conductive layer using a TEM, with the horizontal axis representing thickness (distance from the substrate, unit: nm) and the vertical axis representing frequency (amount of metal filler present (area basis in the image)). In the present invention, the half-value width is the average of half-value widths at 10 randomly selected locations (photographing width: 1 μm).

[0012] In the present invention, since the half-width of the distribution of the metal filler particles in the thickness direction of the transparent conductive layer is within the above range, contact between the metal fillers is increased, making it possible to form a transparent conductive layer with low resistance. The transparent conductive film of the present invention, which includes such a transparent conductive layer, can achieve low resistance without increasing the metal filler content, and can exhibit excellent transparency and conductivity. Conventionally, in transparent conductive films containing metal fillers, the amount of metal filler added must be increased to improve conductivity, resulting in a trade-off between transparency and conductivity. However, in the present invention, as described above, it is possible to achieve both transparency and conductivity. This is one of the major achievements of the present invention. The half-width of the distribution of the metal filler particles in the thickness direction of the transparent conductive layer is preferably 10 nm to 70 nm, more preferably 10 nm to 60 nm, even more preferably 20 nm to 55 nm, and particularly preferably 35 nm to 55 nm. Within such ranges, the above-mentioned effects are more pronounced. The distribution of the metal filler can be controlled by the conditions (e.g., wind direction) during drying (air drying) of the coating layer when forming the transparent conductive layer, the composition and properties (e.g., viscosity) of the composition for forming the transparent conductive layer, etc. Furthermore, the metal filler can be unevenly distributed by pressing the transparent conductive layer.

[0013] In one embodiment, the metal filler is unevenly distributed on the substrate side of the transparent conductive layer. In this embodiment, the abundance ratio of the metal filler present within 50% of the transparent conductive layer from the substrate side in the thickness direction is preferably 70% or more, more preferably 80% or more, and particularly preferably 90% or more. The upper limit of the abundance ratio of the metal filler present within 50% of the transparent conductive layer from the substrate side in the thickness direction is, for example, 95% (preferably 98%, more preferably 100%). The "abundance ratio of the metal filler present within 50% of the transparent conductive layer from the substrate side in the thickness direction" is measured by binarizing an image obtained by TEM photography of a cross section of the transparent conductive layer, and is defined as the area-based proportion in the image.

[0014] Not limited to the above embodiment, the metal filler may be unevenly distributed in the center of the transparent conductive layer in the thickness direction, or may be unevenly distributed in the vicinity of the surface of the transparent conductive layer opposite to the substrate.

[0015] The surface resistance of the transparent conductive film is preferably 0.1 Ω / □ to 1000 Ω / □, more preferably 0.5 Ω / □ to 300 Ω / □, even more preferably 10 Ω / □ or more but less than 300 Ω / □, particularly preferably 10 Ω / □ to 150 Ω / □, and most preferably 10 Ω / □ or more but less than 100 Ω / □. The surface resistance can be measured using Mitsubishi Chemical Analytech's "Automatic Resistivity Measurement System MCP-S620 or MCP-S521."

[0016] The haze value of the transparent conductive film is preferably 20% or less, more preferably 10% or less, still more preferably 0.1% to 5%, and particularly preferably 0.1% to 1%.

[0017] 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.

[0018] B.Transparent conductive layer As described above, the transparent conductive layer contains a metal filler. Preferably, the transparent conductive layer contains metal nanowires as the metal filler. By forming a transparent conductive layer containing metal nanowires, a conductive film having excellent flexibility and excellent light transmittance can be obtained.

[0019] In one embodiment, the transparent conductive layer further includes a binder resin. In this embodiment, a metal filler (e.g., metal nanowires) is present in the binder resin. In a transparent conductive layer made of a binder resin, the metal filler (e.g., metal nanowires) is protected by the binder resin. As a result, corrosion of the metal filler (e.g., metal nanowires) is prevented, and a conductive film with superior durability can be obtained.

[0020] The thickness of the transparent conductive layer is preferably 10 nm to 1000 nm, more preferably 20 nm to 500 nm, and particularly preferably 20 nm to 100 nm. Within this range, a transparent conductive film having excellent durability and excellent surface contact conductivity can be obtained.

[0021] In one embodiment, the transparent conductive layer is patterned. Any appropriate method can be adopted as the patterning method depending on the form of the transparent conductive layer. The pattern shape of the transparent conductive layer can be any appropriate shape depending on the application. Examples include 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. After the transparent conductive layer is formed on the substrate, it can be patterned using any appropriate method depending on the form of the transparent conductive layer.

[0022] The total light transmittance of the transparent conductive layer is preferably 85% or more, more preferably 90% or more, and even more preferably 95% or more.

[0023] The metal nanowires are conductive materials made of metal, shaped like needles or threads, and nanometer-sized diameters. The 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 a good electrical conduction path, resulting in a 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 conductive film with high light transmittance.

[0024] 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 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 line 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.

[0025] 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 60 nm. Within this range, a transparent conductive layer with high light transmittance can be formed.

[0026] 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. If the length is within this range, a conductive film with high conductivity can be obtained.

[0027] Any suitable metal can be used as the metal constituting the metal nanowires, as long as it has high electrical conductivity. 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. The metal nanowires are preferably made of one or more metals selected from the group consisting of gold, platinum, silver, and copper.

[0028] 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 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.

[0029] The content of the metal nanowires in the transparent conductive layer is preferably 30 to 100% by weight, more preferably 30 to 90% by weight, and even more preferably 45 to 80% by weight, based on the total weight of the transparent conductive layer. Within this range, a conductive film with excellent conductivity and light transparency can be obtained.

[0030] Any suitable resin can be used as the binder resin. 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 copolymer (ABS); cellulose; silicone resins; polyvinyl chloride; polyacetate; polynorbornene; synthetic rubber; and fluorine-based resins. 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.

[0031] 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.

[0032] 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.

[0033] C. Base material 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.

[0034] 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.

[0035] The thickness of the substrate is preferably 20 μm to 200 μm, and more preferably 30 μm to 150 μm.

[0036] The total light transmittance of the substrate is preferably 30% or more, more preferably 35% or more, and even more preferably 40% or more.

[0037] D. Conductive film manufacturing method The conductive film of the present invention can be obtained, for example, by applying a transparent conductive layer-forming composition containing metal nanowires onto a substrate, and then drying the applied layer to form a transparent conductive layer.

[0038] 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.

[0039] 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, a transparent conductive layer in which the metal filler is well distributed unevenly can be obtained. The viscosity of the composition for forming a transparent conductive layer can be measured using a rheometer (for example, Anton Paar's MCR302).

[0040] 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, within this range, a transparent conductive layer in which the metal filler is well distributed unevenly can be obtained.

[0041] Any appropriate method may be employed as a method for applying the composition for forming a transparent conductive layer. 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. In one embodiment, a long substrate is used as the substrate, and the composition for forming a transparent conductive layer is applied to the substrate while the substrate is being transported. Any appropriate method may be employed as a method for transporting the substrate. Examples include transport using transport rolls, transport using a transport belt, and combinations thereof. The transport speed is, for example, 5 m / min to 50 m / min.

[0042] 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 2 Within this range, a transparent conductive layer in which the metal filler is unevenly distributed can be obtained.

[0043] A typical example of a method for drying the coating layer is drying by blowing air. Air can be blown onto the coating layer by any appropriate method. In one embodiment, air can be blown onto the coating layer using an air blower arranged above the coating layer (on the opposite side from the substrate). The air blowing direction can be adjusted, for example, by providing a louver on the air blower and adjusting the direction of the louver. The air blown onto the coating layer may be spiral air.

[0044] The wind speed of the wind is preferably 0.5 m / s to 10 m / s, more preferably 1 m / s to 5 m / s. Within this range, a transparent conductive layer in which the metal filler is well distributed unevenly can be obtained. The wind speed can be appropriately set depending on the solvent contained in the composition for forming a transparent conductive layer, etc. When a composition for forming a transparent conductive layer prepared with water is used, the wind speed is preferably 0.5 m / s to 10 m / s, more preferably 1 m / s to 5 m / s. In this specification, the wind speed refers to the wind speed at the time when the wind reaches the coating layer.

[0045] The temperature of the air is preferably 10°C to 50°C, and more preferably 15°C to 30°C. The air speed can be appropriately set depending on the solvent contained in the composition for forming a transparent conductive layer, etc. When a composition for forming a transparent conductive layer prepared with water is used, the temperature of the air is preferably 10°C to 50°C, and more preferably 15°C to 30°C. In this specification, the temperature of the air means the temperature of the air at the time when it reaches the coating layer.

[0046] The air blowing time is preferably 1 to 10 minutes, and more preferably 2 to 5 minutes.

[0047] In the air blowing step, air may be blown in multiple stages. For example, air may be blown in stages by dividing the zones into zones with different wind directions, wind speeds, temperatures, etc. Furthermore, the thickness of the coating layer may be reduced by oven heating, natural drying, etc. before the air blowing step. The basis weight of the coating layer at the start of the air blowing step is preferably 0.001 g / m 2 ~0.09g / m 2 and more preferably 0.005 g / m 2 ~0.05g / m 2 is.

[0048] After the air blowing step, any appropriate treatment may be performed. For example, when a composition for forming a transparent conductive layer containing a binder resin is used, a curing treatment such as ultraviolet irradiation may be performed. Furthermore, after the sending step, a drying step may be performed. Examples of drying methods include oven heating and natural drying. Furthermore, the dried coating layer may be pressed to form a transparent conductive layer. In this way, a transparent conductive layer in which the metal filler is well distributed unevenly can be obtained. [Example]

[0049] 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.

[0050] (1) 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.

[0051] (2) Haze value The haze value of the transparent conductive film was measured according to the method defined in JIS 7136 using a haze meter (manufactured by Murakami Color Science Laboratory, product name "HN-150").

[0052] (3) Half-width of the distribution of metal nanowires in the thickness direction of the transparent conductive layer The distribution of metal nanowires was revealed by binarizing the images obtained by TEM photography of the cross section of the transparent conductive layer. The horizontal axis was plotted as thickness (distance from the substrate, unit: nm) and the vertical axis was plotted as frequency (amount of metal filler present (area basis in the image)). The half-width (distribution width at half the height of the distribution height at the peak position) of the most frequent peak was calculated. The half-width was calculated as described above for 10 randomly selected locations, and the degree of uneven distribution of the metal nanowires was evaluated based on the average value.

[0053] (4) The proportion of metal nanowires present within 50% of the transparent conductive layer on the substrate side in the thickness direction The distribution of metal nanowires was plotted in the same manner as in (3) above, and the proportion of metal nanowires present within 50% of the transparent conductive layer on the substrate side in the thickness direction was determined. The proportions of the metal nanowires present at 10 randomly selected locations were calculated as described above, and the average value was used to evaluate the degree of uneven distribution of the metal nanowires.

[0054] [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.

[0055] [Example 1] A PET film (manufactured by Mitsubishi Plastics, product name "S100") was used as the substrate. While this substrate was being transported using a transport roll, the transparent conductive layer-forming composition prepared in Production Example 1 was applied onto the substrate using a bar coater (manufactured by Daiichi Rika Co., Ltd., product name "Bar Coater No. 16") to form a coating layer with a wet film thickness (measured by an optical interference film thickness meter) of 12 μm. Thereafter, while transporting the substrate on which the coating layer had been formed, rectified air was blown onto the coating layer to dry the coating layer, forming a transparent conductive layer, and a transparent conductive film comprising the substrate and the transparent conductive layer was obtained. In the transparent conductive layer of the obtained transparent conductive film, the metal nanowires were unevenly distributed, as shown in the cross-sectional TEM photograph of Figure 2(a). Furthermore, when the Ag amount (metal nanowire amount) was measured by ICP measurement, it was found to be 15.3 mg / m 2 It was. The obtained transparent conductive film was subjected to the above evaluations (1) to (4). The results are shown in Table 1.

[0056] [Example 2] A transparent conductive film was obtained in the same manner as in Example 1, except that the wet thickness of the coating layer was 15 μm. The Ag amount (amount of metal nanowires) measured by ICP measurement was 17.4 mg / m 2 The obtained transparent conductive film was subjected to the above evaluations (1) to (4). The results are shown in Table 1.

[0057] [Example 3] A transparent conductive film was obtained in the same manner as in Example 1, except that the wet thickness of the coating layer was 17 μm. The Ag amount (amount of metal nanowires) measured by ICP measurement was 18.7 mg / m 2 The obtained transparent conductive film was subjected to the above evaluations (1) to (4). The results are shown in Table 1.

[0058] [Comparative Example 1] A coating layer was formed in the same manner as in Example 1. Thereafter, the substrate on which the coating layer was formed was placed in an oven at an oven temperature of 100°C for 2 minutes to obtain a transparent conductive film. The Ag amount (amount of metal nanowires) measured by ICP was 15.4 mg / m 2The obtained transparent conductive film was subjected to the above evaluations (1) to (4). The results are shown in Table 1. FIG. 2(b) shows a cross-sectional TEM photograph of the transparent conductive layer.

[0059] Comparative Example 2 A transparent conductive film was obtained in the same manner as in Example 1, except that the wet thickness of the coating layer was 15 μm. The Ag amount (amount of metal nanowires) measured by ICP measurement was 17.5 mg / m 2 The obtained transparent conductive film was subjected to the above evaluations (1) to (4). The results are shown in Table 1.

[0060] Comparative Example 3 A transparent conductive film was obtained in the same manner as in Example 1, except that the wet thickness of the coating layer was 17 μm. The Ag amount (amount of metal nanowires) measured by ICP measurement was 18.5 mg / m 2 The obtained transparent conductive film was subjected to the above evaluations (1) to (4). The results are shown in Table 1.

[0061] [Table 1]

[0062] As is clear from the comparison between Example 1 and Comparative Example 1, the comparison between Example 2 and Comparative Example 2, and the comparison between Example 3 and Comparative Example 3, the transparent conductive films of the Examples have a haze value equivalent to that of the transparent conductive films of the Comparative Examples, but a low surface resistance value. That is, according to the present invention, a transparent conductive film having excellent transparency and excellent conductivity can be obtained. [Explanation of symbols]

[0063] 10 Base material 20 Transparent conductive layer 100 Transparent conductive film

Claims

1. A substrate and a transparent conductive layer disposed on at least one side of the substrate, the transparent conductive layer contains a metal filler; the half-value width of the distribution of the metal filler in the thickness direction of the transparent conductive layer is 5 nm to 75 nm; the metal filler is a metal nanowire; The content of the metal nanowires in the transparent conductive layer is 45% by weight to 80% by weight based on the total weight of the transparent conductive layer. Transparent conductive film.

2. The transparent conductive film according to claim 1, having a surface resistance of 10 Ω / □ or more and less than 300 Ω / □.

3. The transparent conductive film according to claim 1 or 2, which has a haze value of 20% or less.

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