CN115175812A

CN115175812A - Transparent conductive film

Info

Publication number: CN115175812A
Application number: CN202180016742.1A
Authority: CN
Inventors: 长濑纯一; 茂手木佑辅
Original assignee: Nitto Denko Corp
Current assignee: Nitto Denko Corp
Priority date: 2020-02-25
Filing date: 2021-02-16
Publication date: 2022-10-11
Also published as: KR20220146457A; JP2021136085A; TW202141533A; WO2021172086A2

Abstract

The invention provides a low-resistance transparent conductive film having a transparent conductive layer containing a metal filler. The transparent conductive film of the present invention comprises a base material and a transparent conductive layer disposed on at least one side of the base material, wherein the transparent conductive layer contains a metal filler, and the semiamplitude of the distribution of the metal filler in the thickness direction of the transparent conductive layer is 5nm to 75nm. In one embodiment, the metal filler is a metal nanowire.

Description

Transparent conductive film

Technical Field

The present invention relates to a transparent conductive film.

Background

Conventionally, in an image display device having a touch sensor, a transparent conductive film obtained by forming a metal oxide layer such as ITO (indium-tin composite oxide) on a transparent resin film has been used in many cases as an electrode of the touch sensor. However, the transparent conductive film including the metal oxide layer has the following problems: it is easy to lose conductivity by bending, and it is difficult to use the flexible display for applications requiring flexibility.

On the other hand, as a transparent conductive film having high flexibility, a transparent conductive film containing a metal filler such as a metal nanowire is known. Such a transparent conductive film has advantages of having predetermined transparency and conductivity and excellent bendability, and further improvement in conductivity (suppression of resistivity) is required.

Documents of the prior art

Patent literature

Patent document 1: japanese patent laid-open publication No. 2009-505358

Patent document 2: japanese patent No. 6199034

Disclosure of Invention

Technical problem to be solved by the invention

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a low-resistance transparent conductive film including a transparent conductive layer containing a metal filler.

Means for solving the problems

The transparent conductive film of the present invention comprises a base material and a transparent conductive layer disposed on at least one side of the base material, wherein the transparent conductive layer contains a metal filler, and the semiamplitude of the distribution of the metal filler in the thickness direction of the transparent conductive layer is 5nm to 75nm.

In one embodiment, the metal filler is a metal nanowire.

In one embodiment, the surface resistance value of the transparent conductive film of the present invention is 10 Ω/sq or more and less than 300 Ω/sq.

In one embodiment, the transparent conductive film of the present invention has a haze value of 20% or less.

Effects of the invention

According to the present invention, a low-resistance transparent conductive film including a transparent conductive layer containing a metal filler can be provided. The transparent conductive film of the present invention is useful in that the decrease in transparency is suppressed and the resistance is reduced as compared with a conventional transparent conductive film.

Drawings

Fig. 1 is a schematic cross-sectional view of a transparent conductive film according to an embodiment of the present invention.

Fig. 2 (a) is a TEM (Transmission electron microscope) photograph of a cross section of the transparent conductive film obtained in example 1. (b) A cross-sectional TEM photograph of the transparent conductive film obtained in comparative example 1.

Detailed Description

A. Transparent conductive film

Fig. 1 is a schematic cross-sectional view of a transparent conductive film according to an embodiment of the present invention. The transparent conductive film 100 of the present invention includes a substrate 10 and a transparent conductive layer 20 disposed on at least one side of the substrate 10.

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

In the present invention, the half-width of the distribution of the presence of the metal filler in the thickness direction of the transparent conductive layer is 5nm to 75nm. The "semiamplitude of the distribution of the presence of the metal filler in the thickness direction of the transparent conductive layer" means the distribution of the presence of the metal filler that becomes conspicuous by binarizing an image obtained by TEM imaging the cross section of the transparent conductive layer, and the semiamplitude (distribution width at half height of the distribution height at the peak position) in the peak of the highest frequency is plotted with the horizontal axis as the thickness (distance from the base material, unit: nm) and the vertical axis as the frequency (the presence amount of the metal filler (area reference in the image)). In the present invention, the half-width is an average value of half-widths of 10 randomly selected parts (shot width: 1 μm).

In the present invention, when the half width of the distribution of the presence of the metal filler in the thickness direction of the transparent conductive layer is set to the above range, the metal fillers are in contact with each other more, and the transparent conductive layer having low resistance can be formed. The transparent conductive film of the present invention having such a transparent conductive layer can realize a low resistance without increasing the content of the metal filler, has excellent transparency, and can exhibit excellent conductivity. Conventionally, in a transparent conductive film containing a metal filler, since it is necessary to increase the amount of the metal filler to be added in order to improve the conductivity, there is a trade-off relationship between the transparency and the conductivity, but in the present invention, as described above, both the transparency and the conductivity can be achieved. This is a great result of the present invention. The half-width value of the distribution of the metal filler in the thickness direction of the transparent conductive layer is preferably 10nm to 70nm, more preferably 10nm to 60nm, still more preferably 20nm to 55nm, and particularly preferably 35nm to 55nm. Within such a range, the above-described effects become more remarkable. The distribution of the metal filler can be controlled by the conditions (for example, wind direction) of drying (air drying) the coating layer when forming the transparent conductive layer, the composition and properties (for example, viscosity) of the composition for forming the transparent conductive layer, and the like. In addition, the metal filler may be biased by pressing the transparent conductive layer.

In one embodiment, the metal filler is biased toward the substrate side of the transparent conductive layer. In this embodiment, the proportion of the metal filler present in the range of 50% on the substrate side in the thickness direction of the transparent conductive layer is preferably 70% or more, more preferably 80% or more, and particularly preferably 90% or more. The upper limit of the proportion of the metal filler present in the range of 50% on the substrate side in the thickness direction of the transparent conductive layer is, for example, 95% (preferably 98%, more preferably 100%). The "proportion of the metal filler present in the range of 50% on the substrate side in the thickness direction of the transparent conductive layer" is measured by binarizing an image obtained by TEM imaging of a cross section of the transparent conductive layer, and is defined as the proportion based on the area in the image.

The metal filler may be present not only in the center of the transparent conductive layer in the thickness direction but also in the vicinity of the surface of the transparent conductive layer opposite to the substrate.

The surface resistance value of the transparent conductive film is preferably 0.1. Omega./sq to 1000. Omega./sq, more preferably 0.5. Omega./sq to 300. Omega./sq, still more preferably 10. Omega./sq or more and less than 300. Omega./sq, particularly preferably 10. Omega./sq to 150. Omega./sq, and most preferably 10. Omega./sq or more and less than 100. Omega./sq. The surface resistance value can be measured by "automatic resistivity measurement system MCP-S620 model MCP-S521 model" manufactured by Mitsubishi chemical ANALYTECH.

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%.

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.

B. Transparent conductive layer

As described above, the transparent conductive layer contains a metal filler. Preferably, the transparent conductive layer contains metal nanowires as a metal filler. When the transparent conductive layer including the metal nanowires is formed, a conductive film having excellent flexibility and excellent light transmittance can be obtained.

In one embodiment, the transparent conductive layer further comprises a binder resin. In this embodiment, a metal filler (e.g., metal nanowires) is present in the adhesive resin. In the transparent conductive layer composed of the binder resin, the metal filler (e.g., metal nanowires) is protected by the binder resin. As a result, a conductive film which prevents corrosion of the metal filler (for example, metal nanowires) and has more excellent durability can be obtained.

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

In one embodiment, the transparent conductive layer is patterned. As the method of patterning, any suitable method may be employed depending on the form of the transparent conductive layer. The pattern shape of the transparent conductive layer may be any suitable shape according to the use. Examples thereof include: the pattern described in Japanese patent laid-open publication Nos. 2011-511357, 2010-164938, 2008-310550, 2003-511799, and 2010-541109. After the transparent conductive layer is formed on the substrate, patterning may be performed by any suitable method according to the form of the transparent conductive layer.

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

The metal nanowire is a conductive material having a material of metal, a needle-like or wire-like shape, and a diameter of nanometer. The metal nanowires can be linear or curved. When the transparent conductive layer made of the metal nanowires is used, even if the number of the metal nanowires is small, the metal nanowires can be formed into a mesh shape to form a good conductive path, and a conductive film with low resistance can be obtained. Further, by forming the metal nanowires in a mesh shape, a conductive film having openings formed in the gaps of the mesh and having high light transmittance can be obtained.

The ratio of the thickness d to the length L (aspect ratio: L/d) of the metal nanowire is preferably 10 to 100000, more preferably 50 to 100000, and particularly preferably 100 to 10000. When such a metal nanowire having a large aspect ratio is used, the metal nanowire is favorably crossed, and high conductivity can be exhibited by a small amount of the metal nanowire. As a result, a conductive film having high light transmittance can be obtained. In the present specification, the term "thickness of the metal nanowire" means a diameter when the cross section of the metal nanowire is circular, a minor diameter when the cross section of the metal nanowire is elliptical, and a longest diagonal line when the cross section of the metal nanowire is polygonal. The thickness and length of the metal nanowire can be confirmed by a scanning electron microscope or a transmission electron microscope.

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

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

As the metal constituting the metal nanowire, any suitable metal can be used as long as it is a metal having high conductivity. Examples of the metal constituting the metal nanowire include silver, gold, copper, and nickel. In addition, a material obtained by subjecting these metals to plating treatment (e.g., gold plating treatment) can also be used. The metal nanowire is preferably composed of 1 or more metals selected from gold, platinum, silver, and copper.

As the method for producing the metal nanowire, any suitable method can be adopted. Examples thereof include: a method of reducing silver nitrate in solution; and a method of applying an applied voltage or current to the surface of the precursor from the tip of the probe to pull out the metal nanowire from the tip of the probe, thereby continuously forming the metal nanowire. In a method of reducing silver nitrate in a solution, silver nanowires can be synthesized by performing liquid-phase reduction of a silver salt such as silver nitrate in the presence of a polyhydric alcohol such as ethylene glycol and polyvinylpyrrolidone. Uniformly sized silver nanowires can be mass produced according to methods described in, for example, xia, y.et., chem.mater. (2002), 14,4736-4745, xia, y.et., nano letters (2003) 3 (7), 955-960.

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

As the binder resin, any suitable resin may be used. Examples of the resin include: an acrylic resin; polyester resins such as polyethylene terephthalate; aromatic resins such as polystyrene, polyvinyltoluene, polyvinylxylene, polyimide, polyamide, and polyamideimide; a polyurethane resin; an epoxy resin; a polyolefin-based resin; acrylonitrile-butadiene-styrene copolymer (ABS); cellulose; a silicon-based resin; polyvinyl chloride; a polyacetate; polynorbornene; synthesizing rubber; fluorine-based resins, and the like. It is preferable to use 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), trimethylolpropane triacrylate (TMPTA).

The weight per unit area of the transparent conductive layer is preferably 0.001g/m ² ～0.09g/m ² More preferably 0.005g/m ² ～0.05g/m ² 。

The content ratio of the metal nanowires in the transparent conductive layer is preferably 0.1 to 50 parts by weight, and more preferably 0.1 to 30 parts by weight, based on 100 parts by weight of the binder resin constituting the transparent conductive layer. Within such a range, a transparent conductive film having excellent conductivity and light transmittance can be obtained.

C. Base material

Any suitable material may be used for the material constituting the substrate. Specifically, for example, a polymer substrate such as a film or a plastic substrate is preferably used. This is because the smoothness of the substrate and the wettability of the composition for forming a transparent conductive layer are excellent, and the productivity can be greatly improved by continuous production using a roll.

The material constituting the substrate is typically a polymer film containing a thermoplastic resin as a main component. Examples of the thermoplastic resin include: a polyester resin; cycloolefin resins such as polynorbornene; an acrylic resin; a polycarbonate resin; cellulose-based resins, and the like. Among them, polyester resins, cycloolefin resins, or acrylic resins are preferable. These resins are excellent in transparency, mechanical strength, thermal stability, moisture barrier properties, and the like. The thermoplastic resin can be used alone, or more than 2 kinds of combination. In addition, as the substrate, an optical film used for a polarizing plate, for example, a low retardation substrate, a high retardation substrate, a retardation plate, a luminance improving film, or the like can be used.

The thickness of the substrate is preferably 20 to 200. Mu.m, more preferably 30 to 150. Mu.m.

The total light transmittance of the substrate is preferably 30% or more, more preferably 35% or more, and further preferably 40% or more.

D. Method for producing conductive film

The conductive film of the present invention can be obtained, for example, by applying a composition for forming a transparent conductive layer containing metal nanowires on a substrate, and then drying the applied layer to form a 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 metal nanowires in any suitable solvent. Examples of the solvent include: water, alcohol solvents, ketone solvents, ether solvents, hydrocarbon solvents, aromatic solvents, and the like. The composition for forming a transparent conductive layer may further contain additives such as a resin (binder resin), a conductive material (for example, conductive particles) other than the metal nanowires, and a leveling agent. The composition for forming a transparent conductive layer may further contain additives such as plasticizers, heat stabilizers, light stabilizers, lubricants, antioxidants, ultraviolet absorbers, flame retardants, colorants, antistatic agents, compatibilizers, crosslinking agents, tackifiers, inorganic particles, surfactants, and dispersants.

The viscosity of the composition for forming a transparent conductive layer is preferably 5 mPs/25 to 300 mPs/25 ℃, and more preferably 10 mPs/25 to 100 mPs/25 ℃. Within such a range, a transparent conductive layer in which the metal filler is favorably present can be obtained. The viscosity of the composition for forming a transparent conductive layer can be measured by a rheometer (e.g., MCR302 from Anton Paar).

The dispersion concentration of the metal nanowires in the composition for forming a transparent conductive layer is preferably 0.01 to 5 wt%. Within such a range, a transparent conductive layer in which the metal filler is favorably present can be obtained.

As a method for applying the composition for forming a transparent conductive layer, any suitable method can be used. Examples of the coating method include: spray coating, bar coating, roll coating, die coating, ink jet coating, screen coating, dip coating, relief printing, gravure printing, and the like. In one embodiment, a long-sized base material is used as the base material, and the composition for forming a transparent conductive layer is applied while the base material is conveyed. As a method of transporting the base material, any suitable method can be adopted. Examples thereof include: conveyance by a conveyance roller, conveyance by a conveyor belt, a combination thereof, and the like. The conveying speed is, for example, 5 to 50m/min.

The weight per unit area of the coating layer is preferably 0.3g/m ² ～30g/m ² More preferably 1.6g/m ² ～16g/m ² . Within such a range, a transparent conductive layer in which the metal filler is favorably present can be obtained.

As a typical method for drying the coating layer, drying by air blowing is exemplified. The air supply to the coating layer may be performed by any suitable method. In one embodiment, the air supply to the coating layer may be performed using an air blower disposed above the coating layer (on the side opposite the substrate). The air blowing direction may be adjusted by, for example, providing a louver on the air blower and adjusting the direction of the louver. The wind applied to the coating layer may be a wind blowing spirally.

The wind speed is preferably 0.5 to 10m/s, more preferably 1 to 5m/s. Within such a range, a transparent conductive layer in which the metal filler is favorably present can be obtained. The wind speed may be appropriately set according to the solvent and the like contained in the composition for forming a transparent conductive layer. When the composition for forming a transparent conductive layer prepared from water is used, the wind speed is preferably 0.5 to 10m/s, more preferably 1 to 5m/s. In the present specification, the wind speed refers to the wind speed at the time when the coating layer is reached.

The temperature of the air is preferably 10 to 50 ℃, and more preferably 15 to 30 ℃. The wind speed may be appropriately set according to the solvent and the like contained in the composition for forming a transparent conductive layer. When the composition for forming a transparent conductive layer prepared from water is used, the temperature of the air is preferably 10 to 50 ℃, more preferably 15 to 30 ℃. In the present specification, the temperature of the wind refers to the temperature of the wind at the time when the wind reaches the coating layer.

The air blowing time is preferably 1 minute to 10 minutes, more preferably 2 minutes to 5 minutes.

In the air blowing step, air blowing can be performed in multiple stages. For example, the air may be blown in stages by dividing the area into different regions according to the wind direction, the wind speed, the temperature, and the like. In addition, the thickness of the coating layer may be reduced by a method such as oven heating or natural drying before the air blowing step. The weight per unit area of the coating layer at the start of the air blowing step is preferably 0.001g/m ² ～0.09g/m ² More preferably 0.005g/m ² ～0.05g/m ² 。

Any appropriate treatment may be performed after the air blowing step. For example, when a composition for forming a transparent conductive layer containing a binder resin is used, curing treatment can be performed by ultraviolet irradiation or the like. Further, the drying step may be performed after the air blowing step. Examples of the drying method include: oven heating, natural drying, etc. Alternatively, 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 favorably distributed can be obtained.

Examples

The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples at all. The evaluation methods in the examples are as follows. Further, the thickness is measured in the following manner: after the embedding treatment with epoxy resin, the cross section was formed by cutting with a microtome, and the measurement was performed using a scanning electron microscope "S-4800" manufactured by hitachi high and new technologies.

(1) Surface resistance value

The surface resistance values (surface resistance values in MD and TD) of the transparent conductive film were measured by the eddy current method using a non-contact surface resistance meter manufactured by Napson corporation, trade name "EC-80". The measurement temperature was set at 23 ℃.

(2) Haze value

The haze value of the transparent conductive film was measured by a method prescribed in JIS 7136 using a haze meter (product name "HN-150" manufactured by color science research institute in village).

(3) Half-amplitude value of existence distribution of metal nanowires in thickness direction of transparent conductive layer

The distribution of metal nanowires that became evident by binarizing an image obtained by TEM imaging the cross section of the transparent conductive layer was plotted with the thickness (distance to the base material, unit: nm) on the horizontal axis and the frequency (amount of metal filler present (area standard in the image)) on the vertical axis, and the half-width of the peak with the highest frequency (distribution width at half height of the distribution height at the peak position) was determined.

The half-amplitude values were obtained as described above for the randomly selected 10 sites, and the degree of localization of the metal nanowire was evaluated using the average value thereof.

(4) The ratio of metal nanowires present in the range of 50% on the substrate side in the thickness direction of the transparent conductive layer

The existence distribution of the metal nanowires was plotted in the same manner as in (3) above, and the existence ratio of the metal nanowires existing in the range of 50% on the substrate side in the thickness direction of the transparent conductive layer was determined.

For the randomly extracted 10 sites, the presence ratio was determined as described above, and the average value was used to evaluate the degree of localization of the metal nanowire.

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 thus obtained were dispersed in pure water so that the concentration of the silver nanowires was 0.2 wt% and the concentration of the dodecyl-pentaethylene glycol was 0.1 wt%, thereby obtaining a composition for forming a transparent conductive layer.

[ example 1]

A PET film (trade name "S100" manufactured by mitsubishi resin corporation) was used as the base material. The composition for forming a transparent conductive layer prepared in production example 1 was applied onto the substrate using a bar coater (product name "bar coater No.16", manufactured by first Clavician corporation) while conveying the substrate using a conveying roll, and a coating layer having a wet film thickness (measured by an optical interference film thickness meter) of 12 μm was formed. Then, while the substrate on which the coating layer is formed is conveyed, a flow-adjusting air is blown to the coating layer to dry the coating layer, thereby forming a transparent conductive layer, and a transparent conductive film including the substrate and the transparent conductive layer is obtained.

As shown in the cross-sectional TEM photograph of fig. 2 (a), the metal nanowires were biased in the transparent conductive layer of the obtained transparent conductive film. Further, the amount of Ag (amount of metal nanowires) was measured by ICP measurement, and found to be 15.3mg/m ² 。

The obtained transparent conductive film was subjected to the above evaluations (1) to (4). The results are shown in Table 1.

[ 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 set to 15 μm. The amount of Ag (amount of metal nanowires) obtained by ICP measurement was 17.4mg/m ² . The obtained transparent conductive film was subjected to the above evaluations (1) to (4). The results are shown in Table 1.

[ 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 set to 17 μm. The amount of Ag (amount of metal nanowires) obtained by ICP measurement was 18.7mg/m ² . The obtained transparent conductive film was subjected to the above evaluations (1) to (4). The results are shown in Table 1.

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 put into an oven at an oven temperature of 100 ℃ for 2 minutes, thereby obtaining a transparent conductive film. The amount of Ag (amount of metal nanowires) obtained by ICP measurement was 15.4mg/m ² . The 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.

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 set to 15 μm. The amount of Ag (amount of metal nanowires) obtained by ICP measurement was 17.5mg/m ² . Subjecting the obtained solution toThe bright conductive films were subjected to the above evaluations (1) to (4). The results are shown in Table 1.

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 set to 17 μm. The amount of Ag (amount of metal nanowires) obtained by ICP measurement was 18.5mg/m ² . The obtained transparent conductive film was subjected to the above evaluations (1) to (4). The results are shown in Table 1.

TABLE 1

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 film of the example has a haze value equal to that of the transparent conductive film of the comparative example, but has a small surface resistance value. That is, according to the present invention, a transparent conductive film having excellent transparency and excellent conductivity can be obtained.

Description of the symbols

10 base material

20 transparent conductive layer

100 transparent conductive film

Claims

1. A transparent conductive film having a high transparency and a high dielectric constant,

which comprises a base material and a transparent conductive layer disposed on at least one side of the base material,

the transparent conductive layer contains a metal filler,

the half-amplitude of the presence distribution of the metal filler in the thickness direction of the transparent conductive layer is 5nm to 75nm.

2. The transparent conductive film according to claim 1, wherein the metal filler is a metal nanowire.

3. The transparent conductive film according to claim 1 or 2, wherein the surface resistance value is 10 Ω/sq or more and less than 300 Ω/sq.

4. The transparent conductive film according to any one of claims 1 to 3, wherein the haze value is 20% or less.