JP7502000B2 - Transparent Conductive Film - Google Patents

Description

The present invention relates to a transparent conductive film, and more specifically, to a transparent conductive film suitable for optical applications.

Transparent conductive films, in which a transparent conductive layer made of indium tin oxide (ITO) is formed into a desired electrode pattern, have traditionally been used for optical applications such as touch panels.

Such transparent conductive films typically comprise a substrate and a transparent conductive layer in that order.

Conventionally, it has been known to use a relatively thick glass substrate as the substrate.

However, using a relatively thick glass substrate as the substrate reduces flexibility, so the use of a polymer film as the substrate is being considered in order to improve flexibility.

On the other hand, by first increasing the temperature of the substrate and then depositing the film, it is possible to crystallize the ITO (also called "as-deposited crystallization") at the same time as the film is deposited. It is known that such as-deposited crystallization can reduce the surface resistance of the transparent electrode layer compared to depositing the film in amorphous form and then crystallizing it. However, in such cases, since the film is deposited by raising the temperature of the substrate to a high temperature, a polymer film cannot be used from the standpoint of the heat resistance of the polymer film.

Therefore, in order to improve flexibility while lowering surface resistance, the use of thin glass as a substrate is being considered.

For example, a transparent laminated substrate has been proposed that includes an ultra-thin transparent glass substrate and a transparent conductive oxide layer (see, for example, Patent Document 1).

JP2017-106124A

However, as in Patent Document 1, when thin glass is used as the substrate and the transparent electrode layer is crystallized at high temperatures, the transparent conductive oxide layer curls due to the difference in linear expansion coefficient between the thin glass and the transparent conductive oxide layer.

This type of curling can occur even when a polymer film is used as the substrate, but thin glass in particular is in need of even greater curl suppression than polymer films, as it can be damaged by curling.

The present invention aims to provide a transparent conductive film that can suppress curling.

The present invention [1] is a transparent conductive film that includes a glass substrate and a transparent conductive layer in this order, the thickness of the glass substrate is 150 μm or less, the transparent conductive layer is crystalline, and the residual stress of the transparent conductive layer is -100 MPa or more and 100 MPa or less.

The present invention [2] includes the transparent conductive film according to claim 1, in which the surface resistance of the transparent conductive layer is 10 Ω/□ or less.

The present invention [3] includes the transparent conductive film described in [1] or [2] above, in which the transparent conductive layer contains a metal oxide.

The present invention [4] includes the transparent conductive film described in [3] above, characterized in that the metal oxide is an indium tin composite oxide.

The transparent conductive film of the present invention comprises a glass substrate and a transparent conductive layer in that order, and the thickness of the glass substrate is 150 μm or less. Therefore, it has excellent flexibility.

In addition, in this transparent conductive film, the transparent conductive layer is crystalline. This allows the surface resistance to be reduced. In addition, in this transparent conductive film, the residual stress of the transparent conductive layer is -100 MPa or more and 100 MPa or less. This allows curling to be suppressed.

FIG. 1 shows a cross-sectional view of one embodiment of the transparent conductive film of the present invention.

One embodiment of the transparent conductive film of the present invention will be described with reference to Figure 1.

In Figure 1, the up-down direction on the paper surface is the up-down direction (thickness direction), with the upper side of the paper surface being the top side (one side in the thickness direction) and the lower side of the paper surface being the bottom side (the other side in the thickness direction). In addition, the left-right direction and the depth direction on the paper surface are surface directions that are perpendicular to the up-down direction. Specifically, they follow the directional arrows in each figure.

1. Transparent conductive film The transparent conductive film 1 has a film shape (including a sheet shape) with a predetermined thickness, extends in a plane direction perpendicular to the thickness direction, and has a flat upper surface and a flat lower surface. The transparent conductive film 1 is, for example, a part of a touch panel substrate or an electromagnetic wave shield provided in an image display device, that is, it is not an image display device. In other words, the transparent conductive film 1 is a part for producing an image display device, etc., does not include an image display element such as an OLED module, is distributed as a part alone, and is an industrially applicable device.

Specifically, as shown in FIG. 1, the transparent conductive film 1 comprises, in this order, a glass substrate 2 and a transparent conductive layer 3. More specifically, the transparent conductive film 1 comprises a glass substrate 2 and a transparent conductive layer 3 disposed on the upper surface (one surface in the thickness direction) of the glass substrate 2.

The thickness of the transparent conductive film 1 is, for example, 200 μm or less, preferably 150 μm or less, and, for example, 20 μm or more, preferably 30 μm or more.

2. Glass Substrate The glass substrate 2 is a transparent substrate for ensuring the mechanical strength of the transparent conductive film 1. In other words, the glass substrate 2 supports the transparent conductive layer 3.

The glass substrate 2 has a film shape. The glass substrate 2 is disposed over the entire lower surface of the transparent conductive layer 3 so as to contact the lower surface of the transparent conductive layer 3.

The glass substrate 2 is made of flexible, transparent glass.

Examples of glass include non-alkali glass, soda glass, borosilicate glass, and aluminosilicate glass.

The thickness of the glass substrate 2 is 150 μm or less, preferably 120 μm or less, and more preferably 100 μm or less. For example, it is 10 μm or more, and preferably 50 μm or more. If the thickness of the glass substrate 2 is equal to or less than the upper limit, it has excellent flexibility. If the thickness of the glass substrate 2 is equal to or more than the lower limit, it has excellent mechanical strength and can suppress breakage during transportation.

The thickness of the glass substrate 2 can be measured using a dial gauge (PEACOCK, "DG-205").

The total light transmittance (JIS K 7375-2008) of the glass substrate 2 is, for example, 80% or more, preferably 85% or more.

3. Transparent Conductive Layer The transparent conductive layer 3 is a crystalline, transparent layer that exhibits excellent electrical conductivity.

The transparent conductive layer 3 has a film shape. The transparent conductive layer 3 is disposed over the entire upper surface of the glass substrate 2 so as to be in contact with the upper surface of the glass substrate 2.

Examples of materials for the transparent conductive layer 3 include metal oxides containing at least one metal selected from the group consisting of In, Sn, Zn, Ga, Sb, Ti, Si, Zr, Mg, Al, Au, Ag, Cu, Pd, and W. If necessary, the metal oxides may be further doped with metal atoms shown in the above group.

Specific examples of the transparent conductive layer 3 include indium-containing oxides such as indium tin oxide (ITO) and antimony-containing oxides such as antimony tin oxide (ATO), and preferably indium-containing oxides, and more preferably ITO.

When ITO is used as the material of the transparent conductive layer 3, the tin oxide ( _SnO2 ) content is, for example, 0.5 mass% or more, preferably 3 mass% or more, and for example, 15 mass% or less, preferably 13 mass% or less, based on the total amount of tin oxide and _indium oxide ( _In2O3 ). If the tin oxide content is equal to or more than the above lower limit, the durability of the ITO layer can be further improved. If the tin oxide content is equal to or less than the above upper limit, the crystallization of the ITO layer can be facilitated, and the stability of the transparency and resistivity can be improved.

In this specification, "ITO" refers to a composite oxide containing at least indium (In) and tin (Sn), and may contain additional components other than these. Examples of additional components include metal elements other than In and Sn, such as Zn, Ga, Sb, Ti, Si, Zr, Mg, Al, Au, Ag, Cu, Pd, W, Fe, Pb, Ni, Nb, Cr, and Ga.

The transparent conductive layer 3 is crystalline.

If the transparent conductive layer 3 is crystalline, the surface resistivity, which will be described later, can be reduced.

The crystallinity of the transparent conductive layer 3 can be determined, for example, by immersing the transparent conductive film 1 in hydrochloric acid (20°C, concentration 5% by mass) for 15 minutes, followed by rinsing and drying, and then measuring the inter-terminal resistance at a distance of about 15 mm from the surface on the transparent conductive layer 3 side. If the inter-terminal resistance at a distance of 15 mm in the transparent conductive film 1 after the above immersion, rinsing and drying is 10 kΩ or less, the transparent conductive layer is crystalline, whereas if the resistance exceeds 10 kΩ, the transparent conductive layer 3 is amorphous.

The surface resistivity of the upper surface of the transparent conductive layer 3 is, for example, 30 Ω/□ or less, preferably 10 Ω/□ or less, and for example, 1 Ω/□ or more. The surface resistivity can be measured by a four-terminal method in accordance with JIS K7194.

If the surface resistivity is equal to or less than the upper limit, the transparent conductive film 1 can be suitably used for large touch panels, etc.

The residual stress of the transparent conductive layer 3 is -100 MPa or more, preferably -50 MPa or more, more preferably -30 MPa or more, even more preferably -10 MPa or more, and is 100 MPa or less, preferably 60 MPa or less, more preferably 10 MPa or less, even more preferably -5 MPa or less.

Note that negative residual stress means residual stress in the compression direction, and positive residual stress means residual stress in the elongation direction.

Residual stress can be determined by X-ray diffraction, as described in detail in the examples below.

Specifically, the residual stress can be determined in accordance with the residual stress measurement method described in JP 2017-106124 A.

The residual stress can be adjusted to the above range by adjusting the amount of reactive gas introduced, the deposition pressure, and the substrate temperature, all of which will be described in detail later.

The transparent conductive layer 3 has a thickness of, for example, 15 nm or more, preferably 30 nm or more, more preferably 100 nm or more, and for example, 300 nm or less, preferably 250 nm or less, more preferably 150 nm or less. The thickness of the transparent conductive layer 3 can be measured by observing a cross section of the transparent conductive film 1 using, for example, a transmission electron microscope.
4. Manufacturing method of transparent conductive film To manufacture the transparent conductive film 1, for example, in a roll-to-roll process, a transparent conductive layer 3 is provided on the upper surface of a glass substrate 2. Specifically, while the long glass substrate 2 is fed from a feed roll and transported downstream in the transport direction, the transparent conductive layer 3 is provided on the upper surface of the glass substrate 2, and the conductive film 1 is taken up by a take-up roll. This will be described in detail below.

First, a long glass substrate 2 is prepared and wound around a delivery roll, and then the glass substrate 2 is transported so that it is wound around a take-up roll.

The conveying speed is, for example, 0.1 m/min or more, preferably 0.2 m/min or more, and, for example, 1.0 m/min or less, preferably 0.5 m/min or less.

After that, if necessary, from the viewpoint of adhesion between the glass substrate 2 and the transparent conductive layer 3, the surface of the glass substrate 2 may be subjected to an etching treatment or an undercoat treatment, such as sputtering, corona discharge, flame, ultraviolet irradiation, electron beam irradiation, chemical conversion, or oxidation. In addition, the glass substrate 2 may be cleaned by solvent washing, ultrasonic washing, or the like to remove dust and clean it.

Next, a transparent conductive layer 3 is provided on the upper surface of the glass substrate 2. For example, the transparent conductive layer 3 is formed on the upper surface of the glass substrate 2 by a dry method.

Dry methods include, for example, vacuum deposition, sputtering, and ion plating. Sputtering is preferred. This method makes it possible to form a thin transparent conductive layer 3 with a uniform thickness.

In the sputtering method, a target and an adherend (glass substrate 2) are placed facing each other in a vacuum chamber, and gas is supplied while a voltage is applied from a power source to accelerate the gas ions and irradiate the target, ejecting the target material from the target surface and depositing the target material on the adherend surface.

Examples of sputtering methods include bipolar sputtering, ECR (electron cyclotron resonance) sputtering, magnetron sputtering, and ion beam sputtering. Magnetron sputtering is preferred.

When the sputtering method is employed, examples of the target material include the above-mentioned metal oxides constituting the transparent conductive layer 3, and preferably ITO. The tin oxide concentration of ITO is, from the viewpoint of durability, crystallization, etc. of the ITO layer, for example, 0.5% by mass or more, preferably 3% by mass or more, and for example, 15% by mass or less, preferably 13% by mass or less.

Examples of the gas include inert gases such as Ar. If necessary, reactive gases such as oxygen gas can be used in combination.

The ratio of reactive gas introduced to the inert gas (hereinafter referred to as reactive gas introduction amount) is, for example, 0.1 vol.% or more, preferably 1 vol.% or more, and, for example, 10 vol.% or less, preferably 3 vol.% or less, and more preferably less than 2.5 vol.%.

The air pressure during sputtering (hereinafter referred to as the film formation air pressure) is, for example, 1 Pa or less, preferably 0.5 Pa or less, and for example, 0.1 Pa or more, preferably 0.2 Pa or more.

The power source may be, for example, a DC power source, an AC power source, an MF power source, or an RF power source, or a combination of these.

In this sputtering process, the glass substrate 2 is heated to a high temperature beforehand. This places the particles that form the transparent conductive layer 3 on the surface of the glass substrate 2 in a high energy state, allowing them to crystallize (as-deposited crystallization) simultaneously with the film formation by sputtering.

The heating temperature of the glass substrate 2 (hereinafter referred to as substrate temperature) is, for example, 350°C or higher and, for example, 600°C or lower, preferably 550°C or lower.

The heating time of the glass substrate 2 is, for example, 10 seconds or more, preferably 20 seconds or more, and, for example, 120 seconds or less, preferably 60 seconds or less.

From the viewpoint of adjusting the residual stress of the transparent conductive layer 3 to the above-mentioned predetermined range, it is preferable to adjust the amount of reactive gas introduced, the film formation pressure, and the substrate temperature to the above-mentioned predetermined range.

Specifically, when the substrate temperature is 350°C or more and less than 450°C, the amount of reactive gas introduced is, for example, 1% by volume or more and 3% by volume or less, and the deposition pressure is, for example, 0.2 Pa or more and 0.5 Pa or less.

When the substrate temperature is 450°C or higher and 550°C or lower, the amount of reactive gas introduced is, for example, 1.5% by volume or higher and less than 2.5% by volume, and the deposition pressure is, for example, 0.1 Pa or higher and 0.5 Pa or lower. When the substrate temperature is 450°C or higher and 550°C or lower, the amount of reactive gas introduced is, for example, 2.5% by volume or higher and 3.5% by volume, and the deposition pressure is, for example, 0.1 Pa or higher and 0.2 Pa or lower.

This allows the residual stress of the transparent conductive layer 3 to be adjusted to the specified range described above.

Then, after the transparent conductive layer 3 is heated, the transparent conductive layer 3 is cooled.

As a result, a transparent conductive layer 3 is formed on the upper surface of the glass substrate 2, and a transparent conductive film 1 is obtained which comprises the glass substrate 2 and the transparent conductive layer 3 in that order.

The obtained transparent conductive film 1 has a thickness of, for example, 2 μm or more, preferably 20 μm or more, and for example, 100 μm or less, preferably 50 μm or less.
5. Effects The transparent conductive film 1 includes a glass substrate 2 and a transparent conductive layer 3 in this order, and the glass substrate 2 has a thickness of 150 μm or less. Therefore, the film has excellent flexibility.

In addition, in the transparent conductive film 1, the transparent conductive layer 3 is crystalline. This allows the surface resistance to be reduced.

In addition, in the transparent conductive film 1, the residual stress of the transparent conductive layer 3 is -100 MPa or more and 100 MPa or less.

In this transparent conductive film 1, the substrate temperature is raised to a high temperature in order to sufficiently crystallize the transparent conductive layer 3.

However, if the substrate temperature is high, the transparent conductive layer 3 may curl due to the difference in the linear expansion coefficient between the glass substrate 2 and the transparent conductive layer 3.

However, in this transparent conductive film 1, the residual stress of the transparent conductive layer 3 is adjusted to be in the range of -100 MPa or more and 100 MPa or less, so that curling can be suppressed.
In the above description, the transparent conductive film 1 is composed of the glass substrate 2 and the transparent conductive layer 3. However, an intermediate layer may be interposed between the glass substrate 2 and the transparent conductive layer 3.

An example of the intermediate layer is a hard coat layer.

The hard coat layer is a protective layer for preventing scratches on the glass substrate 2 when the transparent conductive film 1 is manufactured. The hard coat layer is also an abrasion-resistant layer for preventing scratches on the transparent conductive layer 3 when the transparent conductive film 1 is laminated.

The hard coat layer is formed, for example, from a hard coat composition.

The hard coat composition contains a resin component.

Examples of resin components include curable resins and thermoplastic resins (e.g., polyolefin resins).

The hard coat composition may also contain particles.

Examples of particles include organic particles such as cross-linked acrylic particles, and inorganic particles such as silica particles.

From the viewpoint of scratch resistance, the thickness of the hard coat layer is, for example, 0.1 μm or more, preferably 0.5 μm or more, and, for example, 10 μm or less, preferably 3 μm or less. The thickness of the hard coat layer can be calculated, for example, based on the wavelength of the interference spectrum observed using an instantaneous multi-photometer system (for example, "MCPD2000" manufactured by Otsuka Electronics Co., Ltd.).

Another example of an intermediate layer is an optical adjustment layer.

The optical adjustment layer is a layer that adjusts the optical properties (e.g., refractive index) of the transparent conductive film 1 in order to suppress the visibility of the pattern of the transparent conductive layer 3 and to suppress reflection at the interface within the transparent conductive film 1 while ensuring excellent transparency of the transparent conductive film 1.

The optical adjustment layer is formed, for example, from an optical adjustment composition.

The optical adjustment composition contains the above-mentioned resin component and the above-mentioned particles.

The thickness of the optical adjustment layer is, for example, 5 nm or more, preferably 10 nm or more, and, for example, 200 nm or less, preferably 100 nm or less. The thickness of the optical adjustment layer can be calculated, for example, based on the wavelength of the interference spectrum observed using an instantaneous multi-photometer system.

In other words, the transparent conductive film 1 can have a hard coat layer or an optical adjustment layer interposed between the glass substrate 2 and the transparent conductive layer 3, and the transparent conductive film 1 can have a hard coat layer and an optical adjustment layer interposed between the glass substrate 2 and the transparent conductive layer 3.

Preferably, the transparent conductive film 1 has an optical adjustment layer between the glass substrate 2 and the transparent conductive layer 3, and more preferably, the transparent conductive film 1 does not have a hard coat layer or an optical adjustment layer between the glass substrate 2 and the transparent conductive layer 3, i.e., the transparent conductive film 1 consists of the glass substrate 2 and the transparent conductive layer 3.

More specifically, the transparent conductive film 1 uses a glass substrate 2 as the substrate, and therefore has excellent adhesion and transparency, even without an intermediate layer (particularly a hard coat layer) between the glass substrate 2 and the transparent conductive layer 3, compared to a case in which a polymer film is used as the substrate.

The present invention will be described in more detail below with reference to examples and comparative examples. The present invention is not limited to the examples and comparative examples. The specific numerical values of the blending ratio (content ratio), physical property values, parameters, etc. used in the following description can be replaced with the upper limit (a numerical value defined as "less than" or "less than") or lower limit (a numerical value defined as "more than" or "exceeding") of the corresponding blending ratio (content ratio), physical property values, parameters, etc. described in the above "Form for carrying out the invention".
1. Production of Transparent Conductive Film Example 1
As the glass substrate, a long transparent glass substrate (thickness: 50 μm, manufactured by Nippon Electric Glass Co., Ltd., "G-Leaf") wound in a roll shape was prepared.

This transparent glass substrate was set on a delivery roll, sent out at a conveying speed of 0.27 m/min, passed through a sputtering device (target section), and wound on a take-up roll. A 130 nm thick ITO layer (transparent conductive layer) was formed on the upper surface of the glass substrate by DC sputtering. Sputtering was performed under a vacuum atmosphere of 0.3 Pa (film formation pressure) with 98% argon gas and 2% oxygen gas (i.e., oxygen gas introduction amount 2% by volume). The discharge output was 3 kW. The target used was a sintered body of 87.5% by mass indium oxide and 12.5% by mass tin oxide. In addition, before sputtering, an infrared heater (heating section) was operated in the sputtering device, the heater temperature (substrate temperature) was set to 500°C, and the glass substrate was heated for 25 seconds.

This resulted in the production of a transparent conductive film that had a glass substrate and an ITO layer and was wound into a roll.

Examples 2 to 4 and Comparative Examples 1 to 4
A transparent conductive film was produced in the same manner as in Example 1, except that the substrate temperature, film formation pressure, and oxygen gas introduction amount were changed according to Table 1.
2. Evaluation 1) Surface Resistivity The surface resistivity of the ITO layer of each Example and Comparative Example was measured by a four-terminal method in accordance with JIS K7194. The results are shown in Table 1.
2) Residual Stress The residual stress of the ITO layer in each of the examples and comparative examples was indirectly determined from the crystal lattice distortion of the ITO film by an X-ray scattering method.

Specifically, first, the diffraction intensity was measured at 0.04° intervals in the measurement scattering angle range 2θ = 59 to 62° using a powder X-ray diffraction device manufactured by Rigaku Corporation. The integration time (exposure time) at each measurement angle was 100 seconds.

The crystal lattice spacing d of the ITO film was calculated from the peak angle 2θ of the obtained diffraction image (peak of the (622) plane of ITO) and the wavelength λ of the X-ray source, and the lattice distortion ε was calculated based on d. The following formulas (1) and (2) were used for the calculation.

Here, λ is the wavelength (=0.15418 nm) of the X-ray source (Cu Kα ray), and d ₀ is the lattice spacing (=0.15241 nm) of ITO in a stress-free state. Note that d ₀ is a value obtained from the ICDD (The International Centre for Diffraction Data) database.

The above X-ray diffraction measurement was performed for angles Ψ between the film plane normal and the ITO crystal plane normal of 45°, 50°, 55°, 60°, 65°, 70°, 77°, and 90°, and the lattice strain ε was calculated for each angle Ψ. The angle Ψ between the film plane normal and the ITO crystal plane normal was adjusted by rotating the sample around the TD direction as the rotation axis. The residual stress σ in the ITO film in-plane direction was calculated from the slope of the straight line plotting the relationship between sin ² Ψ and the lattice strain ε using the following formula (3).

In the above formula, E is the Young's modulus of ITO (116 GPa), and ν is the Poisson's ratio (0.35). These values are known measured values described in D. G. Neerinck and T. J. Vink, "Depth profiling of thin ITO films by grazing incident X-ray diffraction," Thin Solid Films, 278 (1996), pp. 12-17.

The resulting residual stresses are shown in Table 1.
3) Amount of curl First, the transparent conductive film was cut to a width of 100 mm and a length of 100 mm, and the cut transparent conductive film was placed on a smooth table. Next, the distance that each corner of the cut transparent conductive film was lifted from the table was measured, and the average value of the four corners was calculated, which was taken as the amount of curl. The results are shown in Table 1.

1 Transparent conductive film 2 Glass substrate 3 Transparent conductive layer

Claims (4)

A glass substrate and a transparent conductive layer are provided in this order,
The thickness of the glass substrate is 150 μm or less,
the transparent conductive layer is crystalline,
A transparent conductive film, characterized in that the transparent conductive layer has a residual stress of -100 MPa or more and 100 MPa or less. The transparent conductive film according to claim 1, characterized in that the surface resistance of the transparent conductive layer is 10 Ω/□ or less. The transparent conductive film according to claim 1 or 2, characterized in that the transparent conductive layer contains a metal oxide. 4. The transparent conductive film according to claim 3, wherein the metal oxide is an indium tin composite oxide.

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