JP2015032437A - Transparent electroconductive sheet and touch panel using transparent electroconductive sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transparent electroconductive sheet unlikely to entail the oxidation of a silver nanowire even if the silver nanowire is exposed to visible light.SOLUTION: The provided transparent electroconductive sheet 1 is a transparent electroconductive sheet 1 including: a substrate sheet 2; a silver nanowire retention layer 3 laminated atop the substrate sheet 2; a silver nanowire 4 laminated atop the silver nanowire retention layer 3; and an overcoat layer 5 laminated atop the silver nanowire 4 and having a surface resistivity of 3.1×10Ω/sq. or above. The overcoat layer includes not only an acrylate or methacrylate but also an isocyanate.

Description

  The present invention relates to a transparent conductive sheet used for a transparent electrode or the like, and particularly relates to a transparent conductive sheet containing silver nanowires.

A transparent conductive film in which a thin film of a conductive compound is formed on a transparent substrate is widely used in the electrical and electronic fields such as flat displays such as liquid crystal displays and EL displays, and transparent electrodes of touch panels, for example, using the conductivity. ing. As the transparent conductive film, at least one surface of a transparent substrate is made of tin oxide (SnO ₂ ), indium tin oxide (ITO), zinc oxide (ZnO), or the like, such as a vacuum deposition method, a sputtering method, or an ion plating method. Those provided by a dry process are well known.

  In addition to the dry process, a transparent conductive film by a wet process using a network structure of metal fine particles such as a conductive polymer, CNT, for example, a metal nanowire has also been proposed.

  Among them, in recent years, metal nanowires have been studied as conductive materials that are transparent in the visible light region. Since the metal nanowire has a small diameter, it has a high light transmittance in the visible light region, and is expected to be applied as a transparent conductive film in place of ITO. As one using such a metal nanowire, a transparent conductive film using a silver nanowire has been proposed (for example, Patent Document 1).

  However, when silver nanowires are used under actual conditions, there is a problem of a decrease in conductivity due to silver oxidation. In order to prevent this, for example, Patent Document 2 describes that an overcoat layer is provided against a decrease in conductivity. However, if the overcoat layer is simply provided, there is a problem that the resistance value of the transparent conductive sheet increases when visible light strikes the silver nanowire for a long time, compared with the case where the overcoat layer is not formed.

JP 2009-205924 A JP 2004-1966923 A

  Therefore, the objective of this invention is providing the transparent conductive sheet which suppresses the raise of the resistance value of a transparent conductive sheet, when visible light hits silver nanowire for a long time.

  In order to achieve the above object, the present invention is configured as follows.

According to the first aspect of the present invention, a base sheet, a silver nanowire holding layer laminated on the base sheet, a silver nanowire laminated on the silver nanowire holding layer, and the silver nanowire A transparent conductive sheet comprising an overcoat layer that is laminated and has a surface resistivity of 3.1 × 10 ¹⁴ Ω / □ or more is provided.

  According to a second aspect of the present invention, the overcoat layer provides a transparent conductive sheet containing acrylate or methacrylate.

  According to the third aspect of the present invention, the overcoat layer provides a transparent conductive sheet containing isocyanate.

  According to a fourth aspect of the present invention, there is provided a transparent conductive sheet wherein the silver nanowire has a diameter of 5 nm to 500 nm and a length of 500 nm to 50000 nm.

  According to the fifth aspect of the present invention, the silver nanowire provides a transparent conductive sheet plated with a metal other than silver.

  According to the 6th aspect of this invention, the touch panel using the said transparent conductive sheet is provided.

  The transparent conductive sheet of the present invention is a transparent conductive sheet that can suppress an increase in resistance value even when visible light is irradiated on the silver nanowire for a long time.

It is sectional drawing which concerns on a transparent conductive sheet. It is a perspective view of a touch panel. It is A-A 'sectional drawing of FIG. FIG. 4 is a B-B ′ sectional view of FIG. 3. It is a figure which shows the surface resistivity of the member used for Example 1- Comparative Example 2. FIG. It is a figure which shows the resistance value change of a transparent conductive sheet.

  Hereinafter, embodiments according to the present invention will be described in more detail with reference to the drawings. It should be noted that the dimensions, materials, shapes, relative positions, etc. of the parts and portions described in the embodiments of the present invention are not intended to limit the scope of the present invention only to those unless otherwise specified. This is just an illustrative example.

  As shown in FIG. 1, the transparent conductive sheet 1 has a configuration in which a base sheet 2, a silver nanowire holding layer 3, a silver nanowire 4, and an overcoat layer 5 are laminated in this order. The formation of the silver nanowire holding layer 3, the silver nanowire 4, and the overcoat layer 5 can be performed by a method similar to the conventional method unless otherwise specified. Examples of conventional methods include coating methods such as gravure coating, roll coating, and comma coating, printing methods such as gravure printing, and screen printing.

[Base sheet]
The substrate sheet is not particularly limited as long as it is a sheet or film. For example, ceramics such as glass and alumina, metals such as iron, aluminum and copper, polyethylene resins, polyester resins, cellulose resins, vinyl alcohol resins, vinyl chloride resins, cycloolefin resins, polycarbonate resins, acrylic resins, ABS resins, etc. These thermoplastic resins, photo-curing resins, thermosetting resins, and the like. When importance is attached to transparency, the total light transmittance is preferably 80% or more, and examples thereof include glass, polyester resin, polycarbonate resin, acrylic resin, and cellulose resin. The thickness of the base material is 10 μm to 10 mm.

[Silver nanowire holding layer]
The silver nanowire holding layer is not particularly limited as long as it is a member that can hold the silver nanowire on the base sheet. Examples of the member constituting the silver nanowire holding layer include a binder resin and a photosensitive resin. In addition, it is preferable to use photosensitive resin from a viewpoint that the thickness of a silver nanowire holding layer can be made thin.

  Examples of the binder resin include thermoplastic resins such as acrylic, polyester, polyurethane, nitrocellulose, chlorinated polyethylene, chlorinated polypropylene, and polyvinyl chloride, and curable resins such as melamine acrylate, urethane acrylate, epoxy resin, and polyimide resin. be able to.

  Photosensitive resins include thermoplastic resins such as acrylic, polyester, polyurethane, nitrocellulose, chlorinated polyethylene, chlorinated polypropylene, and polyvinyl chloride, and curable resins such as melamine acrylate, urethane acrylate, epoxy resin, and polyimide resin. Can be mentioned.

[Silver nanowires]
Silver nanowires are composed of silver. In addition, the said silver nanowire becomes a structure by which silver nanowires intertwine and the whole conducts because each silver nanowire contacts. The shape of the silver nanowire is preferably such that the ratio of the length in the minor axis direction to the length in the major axis direction (hereinafter referred to as aspect) is 10 to 10,000. When the aspect ratio is less than 10, the transmittance is lowered, and when it exceeds 10,000, the physical strength and the electrical conductivity are lowered.

In addition, 5 nm-500 nm are preferable, and, as for the length of the short axis direction of silver nanowire, More preferably, they are 5 nm-100 nm. When the length in the minor axis direction exceeds 500 nm, the transmittance of the transparent conductive sheet decreases. Further, when the length in the minor axis direction is less than 5 nm, it becomes difficult to contact the silver nanowires, and the conductivity of the transparent conductive sheet is lowered.
The length in the major axis direction is preferably 500 nm to 50000 nm, more preferably 10,000 nm to 40000 nm. When the length in the major axis direction is less than 500 nm, the conductivity of the transparent conductive sheet is lowered, and when it exceeds 50000 nm, the transmittance is lowered.

  The silver nanowire is preferably plated with a metal other than silver. When plated with a metal other than silver, oxidation of the silver nanowire can be suppressed when the silver nanowire is irradiated with visible light.

[Overcoat layer]
The overcoat layer is a member that suppresses oxidation of silver nanowires when visible light is irradiated onto the transparent conductive sheet. The overcoat layer is preferably composed of a member having a surface resistivity of 3.1 × 10 ¹⁴ Ω / □ or more. If the surface resistivity is 3.1 × 10 ¹⁴ Ω / □ or more, the silver nanowires can be prevented from being oxidized when visible light is irradiated onto the transparent conductive sheet. As a result, the resistance value of the transparent conductive sheet can be kept constant. Examples of the resin constituting such an overcoat layer include epoxy resins, urethane resins, acrylates, and methacrylates.

  Among the above members, the overcoat layer is preferably composed of a resin containing acrylate or methacrylate. If comprised from the said resin, the flaw resistance of a transparent conductive sheet will improve. The overcoat layer further preferably contains an isocyanate. When an overcoat layer contains isocyanate, said acrylate or methacrylate and isocyanate will react, and the hardness of an overcoat layer will improve.

[Touch panel]
Below, the touch panel produced using said transparent conductive sheet is demonstrated.
As shown in FIG. 2, the touch panel 100 has a configuration in which two transparent conductive sheets 10 and 20 are bonded together with an adhesive layer 30. As shown in FIG. 3, the transparent conductive sheet 10 has a configuration in which a silver nanowire holding layer 12, a silver nanowire 13, and an overcoat layer 14 are laminated on a base sheet 11 in this order. In addition, as shown in FIG. 2, a plurality of silver nanowires 13 are arranged in the Y-axis direction and form Y electrodes on the touch panel 100.

  As shown in FIG. 4, the transparent conductive sheet 20 has a configuration in which a silver nanowire holding layer 22, a silver nanowire 23, and an overcoat layer 24 are laminated on a base sheet 21 in this order. Note that a plurality of silver nanowires 23 are arranged in the X-axis direction and form X electrodes on the touch panel 100.

  As described above, the touch panel 100 is configured such that the silver nanowires 13 constituting the Y electrode and the silver nanowires 23 constituting the X electrode are covered with the overcoat layers 14 and 24, respectively. Even if it irradiates, the raise of resistance value is suppressed.

<Example 1>
The transparent conductive sheet of Example 1 was prepared as follows.

  A film in which a silver nanowire holding layer and a silver nanowire were laminated on a base sheet made of a biaxially stretched polyethylene terephthalate film having a thickness of 50 μm was prepared (manufactured by Cambrios: ClearOhm).

Next, an overcoat layer having a thickness of 10 μm was formed on the silver nanowire using a urethane resin having a surface resistivity of 8.6 × 10 ¹⁶ Ω / □. The surface resistivity was measured by applying a urethane resin on a PET film so as to have a thickness of about 10 μm, and applying DC500V to the urethane resin. Note that a high resistance meter (manufactured by Agilent Technologies) was used for the measurement.

<Example 2 to Comparative Example 2>
About the transparent conductive sheet of Example 2-Comparative Example 2, the transparent conductive sheet was created by the method similar to Example 1 except having used resin from which surface resistivity differs for an overcoat layer. In Comparative Example 1, no overcoat layer is formed. In addition, the resin used for Examples 1-4 and the comparative example 2 and the surface resistivity of the used resin are shown in FIG.

<Evaluation of resistance value suppression effect of Example 1 to Comparative Example 2>
The transparent conductive sheets of Example 1 and Comparative Example 2 were evaluated based on the following criteria.
First, using a xenon lamp (SX-75, manufactured by Suga Test Instruments Co., Ltd.), the transparent conductive sheet was irradiated with light for 250 hours (test conditions are black panel temperature: 60 ° C., humidity: 50%). . On the way, the resistance value of the transparent conductive sheet at each time was measured using a non-contact resistance meter (NC-10E manufactured by Napson). The measurement was performed at 25 ° C.

And R / _R0 in each time was computed based on the following formula, irradiation time (h) was plotted on the horizontal axis, and R / _R0 was plotted on the vertical axis. The result is shown in FIG.
R / R ₀ = resistance value (R) / initial resistance value (R ₀ )

Finally, evaluation was performed according to the following classification based on the value of R / R ₀ 250 hours after irradiation with visible light. The result is shown in FIG.
○: 1 ≦ R / R ₀ <2
Δ: 2 ≦ R / R ₀ <5
×: 5 ≦ R / R ₀

As shown in FIG. 5 and FIG. 6, when light is applied to the transparent conductive sheet, a member having a surface resistivity of 3.1 × 10 ¹⁴ Ω / □ or more is used for the overcoat layer. The increase in the resistance value of the transparent conductive sheet was suppressed as compared with the case where it was not provided (Examples 1 to 4). Further, when a member having a surface resistivity of 2.3 × 10 ¹⁶ Ω / □ or more was used for the overcoat layer, the increase in the resistance value was further suppressed (Examples 1 and 2). In addition, when a member having a surface resistivity of 2.5 × 10 ¹⁴ Ω / □ or less was used for the overcoat layer, the resistance value of the transparent conductive sheet increased as compared with the case where no overcoat layer was provided (Comparative Example). 2). From the above, it has been clarified that when a resin having a surface resistivity of 3.1 × 10 ¹⁴ Ω / □ is used for the overcoat layer, an increase in the resistance value of the transparent conductive sheet is suppressed.

From the above, it is preferable to use a member having a surface resistivity of 3.1 × 10 ¹⁴ Ω / □ or more, and it is more preferable to use a member having 2.3 × 10 ¹⁶ Ω / □ or more for the overcoat layer. It was revealed. On the other hand, when a member having a surface resistivity of 2.5 × 10 ¹⁴ Ω / □ or less is used as the overcoat layer, the resistance value of the transparent conductive sheet increases more than when no overcoat layer is provided, which is not preferable. It became clear.

1: Transparent conductive sheet 2: Base sheet 3: Silver nanowire holding layer 4: Silver nanowire 5: Overcoat layer 10: Transparent conductive sheet 11: Base sheet 12: Silver nanowire holding layer 13: Silver nanowire 14: Adhesive layer 20 : Transparent conductive sheet 21: Base sheet 22: Silver nanowire holding layer 23: Silver nanowire 24: Adhesive layer 30: Adhesive layer 100: Touch panel

Claims (6)

A base sheet;
A silver nanowire holding layer laminated on the base sheet;
Silver nanowires laminated on the silver nanowire holding layer;
A transparent conductive sheet comprising an overcoat layer laminated on the silver nanowire and having a surface resistivity of 3.1 × 10 ¹⁴ Ω / □ or more.   The transparent conductive sheet according to claim 1, wherein the overcoat layer contains acrylate or methacrylate.   The transparent conductive sheet according to claim 2, wherein the overcoat layer contains isocyanate.   The diameter of the said silver nanowire is 5 nm-500 nm, and length is 500 nm-50000 nm, The transparent conductive sheet of Claims 1-3.   The transparent conductive sheet according to claim 1, wherein the silver nanowire is plated with a metal other than silver.   A touch panel using the transparent conductive sheet according to claim 1.

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