JP6120134B2 - Conductive film - Google Patents

Description

The present invention relates to a carbon nanotube-containing film excellent in conductivity and strength, and relates to various materials that require conductivity, electromagnetic wave shielding materials, electromagnetic wave absorbing materials, current collectors such as electric double layer capacitors, and heat dissipation sheets. Can be used.

A method for using a highly conductive film for a current collector such as an electromagnetic shielding material and an electric double layer capacitor has been proposed.

When a metal is used as the conductive material, a highly conductive film can be obtained, but there is a problem that the conductivity decreases due to oxidation. For this reason, development is progressing using the carbon-type electrically conductive material which does not change easily.

As an example for an electromagnetic shielding material, a conductive film is proposed in which a conductive material and a resin are kneaded and molded at a temperature equal to or higher than the melting temperature of the resin, and vapor-grown carbon fiber, carbon black, and a synthetic resin are melt-kneaded and molded. (Patent Document 1). However, the specific volume resistivity is on the order of 0.1 Ω · cm, and the thickness of the film is as thick as 1 mm. Moreover, there is no description about strength.

In addition, a conductive film obtained by melt-kneading graphitized vapor-grown carbon fiber, carbon black, and synthetic resin has been proposed (Patent Document 2). The specific example of the volume resistivity is as low as 0.05 Ω · cm, but the specific film thickness is as thick as 1 mm. Moreover, there is no description about strength.

Furthermore, as an example of mixing a conductive material and a resin or monomer in an organic solvent and coating it on a release film or the like, a polymerizable composition and a conductive nano-sized fibrous material that are liquid or dissolved in an organic solvent before polymerization An electromagnetic shielding material obtained by mixing a carbon material in a solution state and polymerizing and solidifying has been proposed (Patent Document 3). However, the specific volume resistivity is on the order of 0.1 Ω · cm, and the specific film thickness is as thick as 0.35 mm. In addition, there is no description about strength. And since a liquid monomer or an organic solvent is used, it is disadvantageous in terms of equipment cost, production cost and environment.

As an example for a current collector such as an electric double layer capacitor, a thermoplastic resin is dissolved in an organic solvent, and a coating liquid in which fine carbon fibers are dispersed is applied, and thermoplastic resin / (fine carbon fibers ) When the mixing volume ratio is 50/50, the volume resistance value is 0.01 to 0.03 Ω · cm, and when the mixing volume ratio is 90/10, the volume resistance value is 0.1 to 0.5 Ω · cm. A conductive film having a thickness of cm has been proposed (Patent Document 4). Specifically, the lowest volume resistivity of 0.02 Ω · cm at a thickness of 100 μm is described. However, there is no description about strength. And since an organic solvent is used, it becomes disadvantageous in terms of equipment cost, production cost and environment.

In addition, an organic solvent that dissolves or disperses the polymer component is added to the polymer containing the hydrogenated aromatic vinyl-conjugated diene block copolymer, carbon fiber, and a conductive filler other than carbon fiber, and mixed and separated. An electroconductive film obtained by coating on a mold film and drying and peeling is proposed (Patent Document 5). Specifically, although it is as thin as 30 μm and strong, the volume resistivity is on the order of 0.1 Ω · cm. And since an organic solvent is used, it becomes disadvantageous in terms of equipment cost, production cost and environment.

Furthermore, a current collector for an electric double layer capacitor that includes a conductive agent in a thermoplastic resin, has a volume resistivity of 0.01 to 5 Ω · cm, and a tensile strength of 10 to 20 MPa has been proposed (Patent Document 6). . However, the lowest volume resistivity specifically shown is as high as 0.52 Ω · cm, and the thickness is as thick as 0.3 mm.

JP 2010-260985 A JP 2010-18865 A JP 2005-191384 A JP 2004-123814 A JP 2011-68747 A JP 2004-31468 A

An object of the present invention is to provide a conductive film having a high strength and a sufficiently low volume resistivity even when the thickness is small, without using an organic solvent in the coating solution.

The present invention was coated dry mixture of carbon nanotubes aqueous dispersion and resin water dispersion release film, in a conductive film characterized in that it is obtained by peeling off the release film, the following (1) It is the said electroconductive film which satisfy | fills the conditions of (3).
(1) The weight ratio of the carbon nanotube to the resin is 20 to 300 parts by weight in solid content of the resin with respect to 100 parts by weight of the carbon nanotube.
(2) The volume resistivity is 0.059 Ω · cm or less.
(3) The tensile strength is 5 N / 15 mm or more.

Moreover, the thickness of a film is 10-100 micrometers, It is the said electroconductive film characterized by the above-mentioned.

Further, after the coating drying a mixture of carbon nanotubes aqueous dispersion and resin water dispersion release film, in a conductive film characterized in that it is obtained by peeling off the release film, the said carbon nanotube In the conductive film, the resin has a solid content of 20 parts by weight or more and less than 100 parts by weight based on 100 parts by weight of the carbon nanotubes.

According to the present invention, it is possible to obtain a film having strength even when thin using an aqueous coating solution and having a sufficiently low volume resistivity.

The conductive material in the present invention is a carbon nanotube. The carbon nanotube production method includes a CVD method, a laser evaporation method, an arc discharge method, and the like, and may be a carbon nanotube produced by any production method. Carbon nanotubes can be either single-walled or multi-walled, and any of them may be used. Usually, the carbon nanotube has a diameter of 1 to 100 nm and a length of several μm to several hundred μm. These carbon nanotubes are manufactured and sold in the form of bundles in which many nanotubes are aggregated.

In order to prepare a coating solution, it is necessary to first disperse these aggregates one by one. For this, a dispersing agent and a dispersing device are usually used. As the dispersant, there are synthetic compounds such as sodium salt of naphthalene sulfonic acid-based formalin condensate, sodium polystyrene sulfonate, and disodium dodecyl diphenyl ether sulfonate, and water-soluble xylan as natural products. These dispersants are used alone or in combination.

The addition rate of a dispersing agent is 10-200 weight part with respect to 100 weight part of carbon nanotubes. If it is less than 10 parts by weight, dispersion becomes difficult. Even if it exceeds 200 parts by weight, it can be dispersed, but it is not preferable because the water-soluble component in the film increases.

Examples of the dispersing device include an ultrasonic homogenizer, a wet atomizer, and a high-speed stirring device.

If the dispersing agent is added and the dispersing device is used, the carbon nanotubes can be dispersed relatively easily.

Polyester aqueous dispersions, acrylic resin emulsions, styrene-butadiene copolymer resin emulsions, acrylonitrile-butadiene copolymer resin emulsions, polyurethane emulsions, natural emulsions can be added to carbon nanotube dispersions to form films. There are rubber latex.

The conductive film of the present invention can be obtained by coating and drying a mixture of a carbon nanotube aqueous dispersion and a resin aqueous dispersion on a release film and then peeling the release film.

The solid content of the resin with respect to 100 parts by weight of the carbon nanotubes is preferably 20 to 300 parts by weight. When the ratio of the solid content of the resin is less than 20 parts by weight, the strength of the film becomes weak. On the other hand, if the amount exceeds 300 parts by weight, the decrease in conductivity becomes large.

The thickness of the conductive film is preferably 10 to 100 μm. If it is less than 10 μm, the strength becomes weak. Moreover, since it will be bulky when it exceeds 100 micrometers, a use is limited.

Due to the above correspondence, a conductive film having strength and volume resistivity of the order of 10 ⁻² Ω · cm can be obtained even if it is thin.

The main components of the coating liquid are a carbon nanotube dispersion and a resin aqueous dispersion. However, subcomponents can be added to improve the coating properties, improve the physical properties of the coating film, or make it flame retardant.

A leveling agent can be added in order to improve the leveling property when the mixed solution of the carbon nanotube dispersion and the resin aqueous dispersion is applied to the release film. Fluorine and silicone surfactants and acrylic polymers can be used alone or in combination as leveling agents. An addition amount of 1% or less is sufficient with respect to the solid content of the coating liquid main component.

A crosslinking agent can be used to improve the strength of the film or the solvent resistance. Specifically, there is an isocyanate.

A flame retardant can be used to make the film flame retardant. As the flame retardant, a type having a fine particle size, water-insoluble or hardly soluble, infusible or having a high melting point and capable of being uniformly dispersed in the coating liquid is preferable. Specific examples include melamine cyanurate, melamine polyphosphate, and surface-treated ammonium polyphosphate.

A coating layer is obtained by coating this liquid on a release film and drying. For the coating, a wire bar coater, knife coater, air knife coater, blade coater, reverse roll coater, die coater or the like can be used.

If the desired thickness or performance cannot be obtained by a single coating, it may be applied multiple times.

When a dispersant (low molecular dispersant) that is relatively easily dissolved in water is used as the dispersant, the dispersant can be eluted by dipping in water after coating and drying. This improves the ratio of carbon nanotubes in the film.

A conductive film can be obtained by peeling the coating layer from the release film after the coating drying operation or after the water elution treatment.

The present invention will be specifically described below with reference to examples. In addition, the physical property in the Example of this invention was measured with the following method.

[Film thickness]
Measurement was performed using a digital micrometer.

[Volume resistivity]
The resistance was measured by JIS K 7194 (four-probe method), and the volume resistivity was calculated by the following equation (1).
Volume resistivity = resistance × correction coefficient × film thickness (1)

[Tensile strength]
It was measured according to JIS K 7127.

[Flame retardance]
It was measured by the UL94 50W vertical combustion test method.

[Electromagnetic shielding]
The electric field shielding property was measured by the KEC method.

[Thermal conductivity]
It was measured by a periodic heating method.

Example 1
Showa Denko multi-walled carbon nanotube VGCF-X was dispersed with an ultrasonic homogenizer using IPE water-soluble xylan as a dispersant to prepare a dispersion of carbon nanotubes 3.5% and water-soluble xylan 1.0%. To this dispersion, Toyobo's water-dispersed polyester resin Vylonal MD-1930 was added to 100 parts by weight of carbon nanotubes so that the solid content was 100 parts by weight, and a small amount of Neos FT-100 was added as a leveling agent. The mixture was stirred to prepare a coating solution. This was applied to a release PET film three times with a wire bar # 90 and dried, the release PET film was peeled off, and the physical properties were measured. This is shown in Table 1.

Example 2
Nanosil multi-wall carbon nanotubes NC-7000 were dispersed with an ultrasonic homogenizer using Kao-made Demol N as a dispersant to prepare a dispersion of 3.8% carbon nanotubes and 1.9% Demol MS. To this dispersion, Mitsui Chemicals acrylic resin emulsion Bonlon S-1294 is added to 100 parts by weight of carbon nanotubes so that the solid content is 100 parts by weight, and a small amount of FT-100 is added and stirred to form a coating solution. Was prepared. This was coated four times on a release PET film with a wire bar # 70, immersed in water each time the coating was dried, the dispersant was eluted and dried, the release PET film was peeled off, and the physical properties were measured. This is shown in Table 1.

Example 3
Carbon nanotube NC-7000 was dispersed with an ultrasonic homogenizer using water-soluble xylan as a dispersant to prepare a dispersion of 3.0% carbon nanotubes and 1.0% water-soluble xylan. To this dispersion liquid, natural rubber LA-NR39 made by Resitex was added so that the solid content was 100 parts by weight with respect to 100 parts by weight of carbon nanotubes, and a small amount of FT-100 was further added and stirred to prepare a coating liquid. . This was applied to the release PET film three times with a wire bar # 90, and the release PET film was peeled off to measure the physical properties. This is shown in Table 1.

Example 4
Carbon nanotube NC-7000 was dispersed with an ultrasonic homogenizer using water-soluble xylan as a dispersant to prepare a dispersion of 3.0% carbon nanotubes and 1.0% water-soluble xylan. Byronal MD-1930 was added to this dispersion so that the solid content was 100 parts by weight with respect to 100 parts by weight of the carbon nanotubes. Further, an aqueous dispersion of melamine cyanurate STABACE MC-5F manufactured by Sakai Chemical Industry Co., Ltd. was added so that the solid content was 80 parts by weight with respect to 100 parts by weight of Bayronal MD-1930, and a small amount of FT-100 was further added. The mixture was stirred to prepare a coating solution. This was applied to a release PET film three times with a wire bar # 90 and dried, the release PET film was peeled off, and the physical properties were measured. This is shown in Table 1.

Example 5
Carbon nanotube VGCF-X was dispersed with an ultrasonic homogenizer using Kao-made Demol MS as a dispersant to prepare a dispersion of 4.0% carbon nanotube and 2.0% Demol MS. To this dispersion, Mitsui Chemicals acrylic resin emulsion Bonron S-415 was added to 100 parts by weight of carbon nanotubes to a solid content of 100 parts by weight, and a small amount of FT-100 was added and stirred to coat. A working solution was prepared. This was applied once to a release PET film with a wire bar # 90 and dried, immersed in water, the dispersant was eluted and dried, the release PET film was peeled off, and the physical properties were measured. This is shown in Table 1.

Example 6
Carbon nanotube NC-7000 was dispersed with an ultrasonic homogenizer using Demol MS as a dispersing agent to prepare a dispersion of 4.0% carbon nanotube and 2.0% Demol MS. To this dispersion, Bonlon S-415 was added so that the solid content was 300 parts by weight with respect to 100 parts by weight of the carbon nanotubes, and a small amount of FT-100 was further added and stirred to prepare a coating solution. This is applied to the release PET film three times with wire bar # 90, and each time the coating is dried, it is immersed in water to elute the dispersant and dry, and then the release PET film is peeled to measure the physical properties. did. This is shown in Table 1.

Example 7
Carbon nanotube NC-7000 was dispersed with an ultrasonic homogenizer using water-soluble xylan as a dispersant to prepare a dispersion of 3.2% carbon nanotubes and 1.0% xylan. To this dispersion, Bonlon S-415 was added so that the solid content was 20 parts by weight with respect to 100 parts by weight of the carbon nanotubes, and a small amount of FT-100 was further added and stirred to prepare a coating solution. This was coated and dried four times on a release PET film with a wire bar # 90, immersed in water for each coating drying operation, the dispersant was eluted and dried, the release PET film was peeled off, and the physical properties were measured. This is shown in Table 1.

Example 8
Carbon nanotube NC-7000 was dispersed with an ultrasonic homogenizer using Demol MS as a dispersant to prepare a dispersion of 4.6% carbon nanotube and 2.3% Demol MS. To this dispersion, Bonlon S-415 was added so that the solid content was 200 parts by weight with respect to 100 parts by weight of the carbon nanotubes, and a small amount of FT-100 was further added and stirred to prepare a coating solution. This was coated and dried once on a release PET film with a wire bar # 90, dipped in water, the dispersant was eluted and dried, the release PET film was peeled off, and the physical properties were measured. This is shown in Table 2.

Example 9
Carbon nanotube NC-7000 was dispersed with an ultrasonic homogenizer using Demol MS as a dispersant to prepare a dispersion of 3.5% carbon nanotubes and 1.7% Demol MS. To this dispersion, Bonlon S-415 was added so that the solid content was 100 parts by weight with respect to 100 parts by weight of the carbon nanotubes, and a small amount of FT-100 was further added and stirred to prepare a coating solution. This was applied to a release PET film four times with a wire bar # 90, and each time the coating was dried, it was immersed in water and the dispersant was eluted and dried, and then the release PET film was peeled to measure the physical properties. . This is shown in Table 2.

Example 10
Carbon nanotube VGCF-X was dispersed with an ultrasonic homogenizer using demole N as a dispersion to prepare a dispersion of carbon nanotubes 3.5% and demole N 1.7%. To this dispersion, Bonlon S-415 was added so that the solid content was 100 parts by weight with respect to 100 parts by weight of the carbon nanotubes, and a small amount of FT-100 was further added and stirred to prepare a coating solution. This is applied to the release PET film 8 times with wire bar # 90, and after each drying operation, the dispersion is eluted and dried, and the release PET film is peeled off to measure the physical properties. did. This is shown in Table 2. Although the thermal conductivity itself is not so high, the thermal resistance is sufficiently low because it is thin.

Example 11
Disperse with water-soluble xylan and demole MS using single-walled carbon nanotube super-growth manufactured by AIST as a dispersant to obtain a dispersion of carbon nanotubes 0.5%, water-soluble xylan 0.3%, demole MS 0.7% Prepared. To this dispersion, Bonlon S-119H was added to 100 parts by weight of carbon nanotubes so that the solid content was 100 parts by weight, and a small amount of FT-100 was further added and stirred to prepare a coating solution. This was coated and dried 5 times with a wire bar # 90 on a release PET film, immersed in water for every coating drying operation, the dispersant was eluted and dried, the release PET film was peeled off, and the physical properties were measured. . This is shown in Table 2. The thermal conductivity itself is not so high, but the thermal resistance is sufficiently low because the film is thin.

Comparative Example 1
Add non-dispersed powdered carbon nanotubes NC-7000 to water to 4%, add Bonron S-415 to 100 parts by weight of carbon nanotubes in solids, and add FT-100 in a small amount. The coating liquid was prepared by stirring. This was coated on a release PET film with a wire bar # 90 and dried. The carbon nanotubes in the coating layer were granular and uneven, and a uniform coating layer could not be obtained and could not be peeled off from the release film. This is shown in Table 2.

Comparative Example 2
A small amount of FT-100 was added to Bonlon S-1294 resin alone to prepare a coating solution, and the release film was coated and dried once with wire bar # 90, peeled off from the release film, and measured for physical properties. This is shown in Table 2.

Comparative Example 3
A small amount of FT-100 was added to Bonlon S-415 resin alone to prepare a coating solution, and the release film was coated and dried twice with wire bar # 70, peeled off from the release film, and measured for physical properties. This is shown in Table 2.

Although the conductive film of the present invention is thin, the volume resistivity is low and the strength is high, so various materials that require high conductivity, electromagnetic wave shielding materials, electromagnetic wave absorbing materials, current collectors such as electric double layer capacitors, It can be used as a heat dissipation material.

Claims (3)

After coating drying a mixture of carbon nanotubes aqueous dispersion and resin water dispersion release film, in a conductive film characterized in that it is obtained by peeling off the release film, the following (1) - (3 The said conductive film which satisfy | fills the conditions of).
(1) The weight ratio of the carbon nanotube to the resin is 20 to 300 parts by weight in solid content of the resin with respect to 100 parts by weight of the carbon nanotube.
(2) The volume resistivity is 0.059 Ω · cm or less.
(3) The tensile strength is 5.0 N / 15 mm or more. The conductive film according to claim 1, wherein the film has a thickness of 10 to 100 μm. A conductive film obtained by coating a mixed film of a carbon nanotube aqueous dispersion and a resin aqueous dispersion on a release film and then drying the release film, wherein the release film is peeled off. The conductive film, wherein the resin has a solid content of 20 parts by weight or more and less than 100 parts by weight with respect to 100 parts by weight of the carbon nanotubes.