JP6690528B2 - Conductive film - Google Patents

Description

The first invention of the present application relates to a conductive film suitable for stretchable electrodes and wiring because it has high conductivity and can maintain high conductivity even when an external force such as extension, twist, and compression acts.
The second invention of the present application relates to a conductive film having a high conductivity, a small change in conductivity after repeated expansion and contraction, and excellent adhesion to a substrate, which is suitable for an electrode or wiring.

  Most high performance electronics are essentially rigid, planar forms and use single crystal inorganic materials such as silicon and gallium arsenide. On the other hand, when a flexible substrate is used, the wiring must have bending resistance. Further, in applications such as electrodes of actuators and transducers, and skin sensors, it is required that the electrodes and wiring be able to follow the deformation of the base material made of an elastomer or the like and the dielectric film. That is, for example, in the actuator, the dielectric film expands and contracts depending on the magnitude of the applied voltage. Therefore, the electrodes arranged on the front and back sides of the dielectric film need to be able to expand and contract according to the expansion and contraction of the dielectric film so as not to hinder the movement of the dielectric film. Further, in addition to being stretchable, it is required that the change in electric resistance when stretched is small.

In addition, many electric wires for power supply and signal transmission are used in robots and wearable electronic devices, but since the electric wires themselves generally have little elasticity, there is a margin so that they do not interfere with the movement of the robot or human. It is necessary to arrange the electric wires by holding them, which is a practical obstacle. Therefore, the demand for a stretchable electric wire is increasing.
Also in the field of healthcare, a conductive material exhibiting high elasticity is desired. For example, by using a film of a stretchable conductive material, it is possible to develop a device that can be fitted in close contact with a human body that is flexible and curved. Applications for these devices range from measuring electrophysiological signals to delivering advanced treatments and human-machine interfaces.

  One of the solutions in the development of stretchable conductive materials is the use of organic conductive materials, which have been flexible, but are not stretchable and cannot cover curved surfaces. . Therefore, it lacks performance and reliability for integration into a complicated integrated circuit. Films of other materials, such as metal nanowires and carbon nanotubes, are promising to some extent, but are difficult to develop because they are unreliable and expensive.

The stretch ratio required for the stretchable conductive film depends on the application. In applications such as wiring, antennas, and electrodes in the fields of supposed healthcare, displays, solar cells, PFIDs, etc., the specific resistance is less than 1 × 10 ⁻³ Ωcm and the extension of about 100% is possible. That is desired. Generally, in a conductive film formed by applying or printing a conductive paste in which conductive metal powder is uniformly dispersed in a resin, which can be applied or printed, the specific resistance greatly increases when subjected to an elongation action. Will end up. It is desired that the specific resistance during extension is less than 1 × 10 ⁻² Ωcm.

  Further, in consideration of the actual application, it is desired that the change in the specific resistance is small not only when the expansion and contraction action but also when an external force such as twisting or compression acts. For example, assuming wiring that is in direct contact with the human body or that is in close contact with the clothes to be worn, or wiring and sensors in the bent part of the robot, the body receives various external forces in various directions and in various directions, in response to any movement. Depending on the shape, the wire is repeatedly deformed, and the wiring itself is repeatedly expanded and contracted accordingly. Even in such a situation, it is desired that the specific resistance be small. Further, the wirings and electrodes on the base material may have a small adhesiveness between the base material and the conductive film during repeated expansion and contraction, and may cause wire breakage or the like.

  Two main methods have been reported as approaches for developing stretchable flexible wiring.

  One is a method of constructing a corrugated structure so that even a brittle material can be stretched (see Non-Patent Document 1). In this method, a metal thin film is produced on silicone rubber by performing vapor deposition, plating, photoresist treatment, and the like. Although the metal thin film shows only a few percent expansion and contraction, a zigzag-shaped or continuous horseshoe-shaped, corrugated metal thin film, or a wrinkled metal thin film obtained by forming a metal thin film on a pre-stretched silicone rubber, etc. Shows elasticity. However, in both cases, the electrical conductivity decreases by two digits or more when elongated by several tens of percent. Further, since the surface energy of silicone rubber is low, the adhesion between the wiring and the substrate is weak, so that silicone rubber has a drawback that it is easily peeled off during expansion. Therefore, with this method, it is difficult to achieve both stable high conductivity and high extensibility. Moreover, there is a problem that the manufacturing cost is high.

  The other is a composite material of a conductive material and an elastomer. The advantages of this material are its excellent printability and stretchability. Commercially available silver pastes used for electrodes and wirings have a high elastic modulus because the binder resin having a high elastic modulus is highly filled with silver powder. When stretched, cracks occur and the conductivity is significantly reduced. Therefore, in order to give flexibility, consider rubber or elastomer as a binder, and to reduce the filling degree of the conductive material, silver flakes, carbon nanotubes, metal nanowires, etc. with a large aspect ratio and high conductivity as the conductive material Is being considered. In the combination of silver particles and silicone rubber (see Patent Document 1), by providing a holding portion that further coats the conductive film on the silicone rubber substrate with the silicone rubber, the occurrence of microcracks and a decrease in electrical conductivity at the time of extension. It's suppressed. In the examples, it is noted that microcracks are generated at 80 to 100% elongation when the holding portion is not provided. With a combination of silver particles and a polyurethane emulsion (see Patent Document 2), when a conductive film is provided on a substrate, high conductivity and high elongation rate have been reported, but the specific resistance at 100% elongation is reported. Becomes larger and shows an increase ratio of more than 30 times the specific resistance in the natural state. Furthermore, since it is water-based, the method of dispersing silver particles is limited, and it is difficult to obtain a conductive film in which silver particles are sufficiently dispersed. In general, the conductive film provided on the stretchable base material relaxes tensile stress to some extent by the base material itself when it is stretched, so that the occurrence of microcracks in the conductive film is suppressed. By providing a wrapping portion such as a stretchable cover coat for wrapping, damage to the conductive film can be suppressed even at a higher degree of extension. Also, a combination of carbon nanotubes, an ionic liquid, and vinylidene fluoride (see Patent Documents 3 and 4) has been reported, but its electrical conductivity is too low, and its use is limited. As described above, it is currently difficult to achieve both high conductivity and high elasticity. On the other hand, a printable, highly conductive and stretchable composite material has been reported by combining micron-sized silver powder, carbon nanotubes surface-modified with self-assembled silver nanoparticles, and polyvinylidene fluoride. Reference 2). However, in order to mix carbon nanotubes which have a high elongation and breakage at 35% and have a large aspect ratio, the anisotropy of electrical conductivity and mechanical properties is different between the application direction and the direction perpendicular to it when forming a film by application. May occur, which is not preferable in practical use. Further, the surface modification of carbon nanotubes with silver nanoparticles is not preferable because it complicates the production and increases the cost. Further, practically, the anisotropy of the conductive film and the change in conductivity when a twisting action or a compressing action is applied are important, but almost no report has been made.

JP, 2007-173226, A JP 2012-54192 A International publication WO2009 / 102077 JP, 2011-216562, A

Jong-Hyun Ahn and Jung Ho Je, "Stretchable electronics: materials, architectures and integrations" J. Phys. D: Appl. Phys. 45 (2012) 103001 Kyoung-Yong Chun, Youngseok Oh, Jonghyun Rho, Jong-Hyun Ahn, Young-Jin Kim, Hyoung Ryeol Choi and Seunghyun Baik, "Highly conductive, printable and stretchable composite films of carbon nanotubes and silver" Nature Nanotechnology, 5,853 ( 2010)

The present invention has been made against the background of the problems of the prior art, and an object of the first invention of the present application is a self-supporting film having high conductivity and not including a wrapping part for wrapping a base material and a conductive film. In order to provide a conductive film that can be expanded, contracted, twisted, and compressed even in this state, and that is homogeneous and has no anisotropy.
It is an object of the second invention of the present application to provide a conductive film having high conductivity, capable of expanding and contracting, having a small decrease in conductivity even after repeated expansion and contraction, and having excellent adhesion to a substrate.

The present inventor, as a result of extensive studies aimed at achieving such an object, found that the above-mentioned problems can be solved by the following means, and arrived at the present invention.
That is, the first invention of the present application comprises the following configurations (1) to (7).
(1) A conductive film containing a conductive metal powder (A) and a resin (B), having a specific resistance of less than 1.0 × 10 ⁻³ Ωcm and having an original length of 36 in at least one direction. % Or more, and the specific resistance increase ratio is less than 10 when stretched by 100% of the original length in the state of the self-supporting film without the wrapping part for wrapping the base material and the conductive film. A conductive film characterized by.
(2) Both of the two directions that are orthogonal to each other can be expanded by 36% or more of the original length. When 100% of the original length is expanded in the two directions that are orthogonal to each other, The conductive film according to (1), wherein the difference is less than 10%.
(3) In the twist test of the conductive film, the conductive film can be twisted with respect to the plane of the conductive film up to a twist angle of 3600 ° without causing film breakage, and the twist angle is from 0 ° to 3600 °. 2. The conductive film according to any one of (1) to (2), which has a specific resistance of less than 1.0 × 10 ⁻² Ωcm.
(4) The electrical conductivity according to any one of (1) to (3), which has a specific resistance of less than 1.0 × 10 ⁻³ Ωcm when compressed by 10% in the thickness direction of the electrically conductive film. film.
(5) The conductive metal powder (A) is at least one selected from the group consisting of at least silver, gold, platinum, palladium, copper, nickel, and aluminum (1) to (4). The conductive film according to any one of 1.
(6) The resin (B) is at least one selected from the group consisting of rubber containing at least a nitrile group, acrylic rubber, butyl rubber, chloroprene rubber, and chlorosulfonated polyethylene rubber (1) The conductive film according to any one of to (5).
(7) The conductive film as described in any one of (1) to (6), which is produced by coating or printing.

The second invention of the present application has the following configurations (8) to (16).
(8) A conductive film containing a conductive metal powder (A) and a resin (B), having a specific resistance of less than 1.0 × 10 ⁻³ Ωcm and having an original length of 36 in at least one direction. % Or more, and the specific resistance after repeating expansion and contraction 1000 times of returning to the original length after extending 20% of the original length is less than 1.0 × 10 ⁻² Ωcm. Membrane.
(9) The conductive film according to (8), which has a specific resistance of less than 1.0 × 10 ³ Ωcm when extended to three times the original length.
(10) The conductive film according to any one of (8) to (9), which does not break when extended to 10 times the original length.
(11) The conductive metal powder (A) is at least one selected from the group consisting of at least silver, gold, platinum, palladium, copper, nickel, and aluminum (8) to (10). The conductive film according to any one of 1.
(12) The resin (B) is at least one selected from the group consisting of rubber containing at least a nitrile group, acrylic rubber, butyl rubber, chlorosulfonated polyethylene rubber, and chloroprene rubber (8) )-(11) The conductive film according to any one of.
(13) The conductive film as described in any of (8) to (12), which is produced by coating or printing.
(14) The conductive film according to any one of (8) to (13) and the base material layer, and in a state of being extended by 36% or more of the original length, in a cross-cut test method with 100 squares, 95 / 100 or more remains, The electroconductive composite film characterized by the above-mentioned.
(15) The conductive composite film as described in (14), wherein 100/100 remains in the cross-cut test method with 100 squares.
(16) It is characterized in that 95/100 or more remain in the cross-cut test method with 100 squares after repeating expansion and contraction to return to the original length 1000 times after extending 20% of the original length (14 ) To (15), the conductive composite film according to any one of (1) to (15).

  According to the conductive film of the present invention, a conductive paste in which the conductive metal powder (B) is uniformly dispersed in the resin (A) can be prepared by coating or printing, and an effective conductive network in the conductive film can be obtained. Due to the formation of the structure, even if subjected to elongation, twisting, compression, or repeated expansion and contraction, the conductivity network does not break, so the decrease in conductivity is small, and the conductivity and extensibility are anisotropic. small.

Hereinafter, the conductive film according to the embodiment of the present invention will be described.
The conductive film of the present invention is a conductive film in which the conductive metal powder (A) and the resin (B) are contained, and the conductivity is the conductive metal powder (in the insulating resin (B) ( It depends on the formation of the conductive network of A). Generally, when the compounding amount of the conductive metal powder (A) is increased, a conductive network starts to be formed at a certain threshold value or more. When an external force is applied to the conductive film to break or break the conductive network, the conductivity of the film is reduced or lost. Therefore, it is important to impart resistance to the external force of the conductive network. The performance of the conductive film of the present invention against external force will be described below.

(1) Stretchability The stretch rate required for a stretchable conductive film varies depending on the intended use. In applications such as wiring, antennas, and electrodes in the fields of supposed healthcare, displays, solar cells, PFIDs, etc., the specific resistance is less than 1.0 × 10 ⁻³ Ωcm, and the growth is from 5% to 100%. Rate is desired. The stretchable conductive film of the present invention can be stretched by 36% or more of the original length in at least one direction, and even if it is stretched by 36% or more, the decrease in conductivity is small. The conductive film of the present invention has a specific resistance increase ratio of less than 10 according to the evaluation method described below, preferably less than 8, even when 100% stretched in a state of a self-supporting film that does not have a holding portion that encloses the conductive film. It is more preferably less than 5, and preferably, even at 100% elongation, the specific resistance is less than 1.0 × 10 ⁻² Ωcm.

(2) Homogeneity The conductive film of the present invention is produced by a printing means such as coating a conductive paste or screen printing, and is desired to have no anisotropy in many applications. If the conductivity and mechanical properties are different depending on the direction, it is not preferable as a wiring or an electrode. When a conductive filler or a non-conductive filler having a high aspect ratio such as carbon nanotubes or carbon nanophones is mixed, for example, in the case of coating, the conductive filler or the non-conductive filler is oriented in the coating direction, so that the conductive or mechanical The physical properties differ between the application direction and the direction perpendicular thereto, which is not preferable. The conductive film of the present invention can be stretched by 36% or more in each of the two directions orthogonal to each other, and the ratio of the two at the same stretch rate when stretched by 36% or more of the original length in the two directions orthogonal to each other. The difference in resistance is preferably within 10%, more preferably within 5%.

(3) Twistability The conductive film receives a twisting action as an external force depending on its use in addition to the stretching action. In a test of twisting a conductive film, for example, in the case of a conductive film having a width of 20 mm, a length of 50 mm and a thickness of 100 μm, the lower end is fixed, and when the upper end is twisted 10 times (3600 °), the film is broken up to a twist angle of 3600 °. The conductive film can be twisted without causing it, and the specific resistance is preferably less than 1.0 × 10 ⁻² Ωcm.

(4) Compressibility In addition to the stretching action, the conductive film receives a compression action as an external force depending on the application. The specific resistance is preferably less than 1.0 × 10 ⁻³ Ωcm when compressed by 10% in the thickness direction.

(5) Repeatable Stretchability It is also important to change the conductivity when the operation of stretching the conductive film by a predetermined ratio and then returning it to the original length is repeated. When the tensile stress in the conductive film at a predetermined elongation (for example, 20% elongation) does not break or break the conductive network due to the distortion of the insulating resin, when the original length is restored. However, the conductive network does not change, and the specific resistance of the conductive film is not so different from the initial specific resistance. However, in actuality, when subjected to repeated expansion and contraction, the conductive network structure is broken in whole or in part, the specific resistance increases with the number of expansions and contractions, and in some cases, microcracks occur, and finally, To break. The conductive film of the present invention is a conductive film having a high resistance to repeated expansion and contraction, and the specific resistance after repeating 20% elongation 1000 times is less than 1.0 × 10 ⁻² Ωcm. , Preferably less than 5.0 × 10 ⁻³ Ωcm.

(6) Adhesion to Substrate The conductive composite film of the present invention is a conductive composite film composed of a conductive film and a base material layer, and is not only in a natural state but also in a stretched state. Excellent adhesion between the film and substrate. If the adhesion is poor, there is a possibility that the wiring and electrodes on the base material may be broken or short-circuited during extension. As the adhesion test, generally, a cross-cut test, a peeling test, a pencil scratching method, an Erichsen test, a bending test and the like are known. Among them, the cross-cut test with 100 squares is extremely easy to operate and the coating film It is similar to the actual mechanism of loss of damage and is preferable as an evaluation method. Cut the 11 straight lines that cross at right angles to the base material with a razor on the coating film, draw 100 crosses, strongly press the adhesive tape on the cross, peel off the cross after peeling the tape Observe the condition. The conductive composite film of the present invention, in a cross-cut test with 100 squares, 95/100 or more remained when (the number of squares remaining without peeling in the test) / (the number of squares before the test) , Preferably 100/100 remains.

(7) Electrical Conductivity and Mechanical Properties at High Elongation The stretchable conductive film may be subjected to a large elongation action in rare cases depending on the application, and at that time, it is preferably conductive without breaking. Is required to be maintained to some extent. The conductive film of the present invention preferably has a specific resistance of less than 1.0 × 10 ³ Ωcm even when stretched 3 times, and more preferably does not break even when stretched 10 times.

Hereinafter, embodiments of the conductive film of the present invention will be described in order.
The conductive film of the present invention is a conductive film containing a conductive metal powder (A) and a resin (B), and preferably the conductive metal powder (A) is uniformly dispersed in the resin (B). In the case of a conductive film, the conductive metal powder (A) and the resin (B) are not particularly limited, but preferred embodiments will be shown below.

  The conductive metal powder (A) is used for imparting conductivity to the conductive film or conductive pattern to be formed.

  The conductive metal powder (A) is preferably a noble metal powder such as silver powder, gold powder, platinum powder or palladium powder, or a base metal powder such as copper powder, nickel powder, aluminum powder or brass powder. Further, there may be mentioned a plating powder obtained by plating different particles made of an inorganic substance such as a base metal or silica with a noble metal such as silver, a base metal powder alloyed with a noble metal such as silver, and the like. These metal powders may be used alone or in combination. Among these, those containing silver powder and / or copper powder as a main component (50% by weight or more) are particularly preferable from the viewpoint of easily obtaining a coating film having high conductivity and the cost. Silver powder is particularly preferable in terms of conductivity, processability, reliability and the like.

  Examples of the shape of the conductive metal powder (A) are known flakes (scaly particles), spherical particles, dendritic particles (dendritic particles), and aggregates (spherical primary particles are three-dimensionally aggregated). And so on. Among these, for example, in the case of silver powder, irregular-shaped agglomerated silver powder and flake-shaped silver powder are preferable, and they are used to impart conductivity to the conductive film or conductive pattern to be formed. The irregular-shaped aggregated silver powder is a three-dimensional aggregate of spherical or irregularly shaped primary particles. Amorphous agglomerated silver powder and flake-shaped silver powder have a larger specific surface area than spherical silver powder, etc., so that a conductive network can be formed even with a low filling amount, and the conductive film is subjected to external forces such as stretching, twisting, or compression. However, it is preferable because the conductive network can be maintained. Since the irregular-shaped agglomerated silver powder is not in a monodisperse form, the particles are in physical contact with each other, so that a conductive network work is easily formed, which is more preferable.

  The particle diameter of the conductive metal powder (A) is not particularly limited, but an average diameter of 0.5 to 10 μm is preferable from the viewpoint of imparting fine patternability. When a metal powder having an average diameter of more than 10 μm is used, the shape of the formed pattern is bad and the resolution of the patterned fine line may be reduced. If the average diameter is smaller than 0.5 μm, when a large amount is mixed, the cohesive force of the metal powder may be increased to deteriorate the printability, and it is expensive, which is not preferable in terms of cost.

  The blending amount of the conductive metal powder (A) in the conductive paste is determined in consideration of conductivity and elasticity. When the volume% in the solid content is large, the conductivity is high, but the amount of rubber is small and the elasticity is poor. When the volume% is small, the elasticity is improved, but it is difficult to form a conductive network and the conductivity is lowered. Therefore, the content of the conductive metal powder (A) in the solid content of the conductive paste is 20 to 50% by volume (70 to 90% by weight), preferably 25 to 40% by volume (78 to 88% by weight). . The volume% of the solid content is determined by measuring the weight of each solid content of each component contained in the paste and calculating (weight of each solid content / specific gravity of each solid content). It can be determined by calculating the volume.

  The conductive film of the present invention may further contain metal nanoparticles as a conductive metal powder for the purpose of improving conductivity and printability. Since the metal nanoparticles have a function of imparting conductivity between the conductive networks, improvement in conductivity can be expected. Further, it can be blended for the purpose of adjusting the rheology of the conductive paste for improving printability. The average particle size of the metal nanoparticles is preferably 2 to 100 nm. Specific examples thereof include silver, bismuth, platinum, gold, nickel, tin, copper, and zinc. From the viewpoint of conductivity, copper, silver, platinum, and gold are preferable, and silver and / or copper are the main components (50 It is particularly preferable that the amount is at least wt%.

  Since metal nanoparticles are also generally expensive, it is preferable that the amount is as small as possible. The compounding amount of the metal nanoparticles in the solid content of the conductive paste is preferably 0.5 to 5% by volume.

  Examples of the resin (B) include a thermoplastic resin, a thermosetting resin, rubber and the like, but rubber is preferable in order to exhibit the stretchability of the film. Examples of the rubber include urethane rubber, acrylic rubber, silicone rubber, butadiene rubber, nitrile group-containing rubber such as nitrile rubber and hydrogenated nitrile rubber, isoprene rubber, sulfide rubber, styrene butadiene rubber, butyl rubber, chlorosulfonated polyethylene rubber, ethylene propylene. Examples thereof include rubber and vinylidene fluoride copolymer. Among these, nitrile group-containing rubber, acrylic rubber, butyl rubber, chloroprene rubber, and chlorosulfonated polyethylene rubber are preferable, and nitrile group-containing rubber is particularly preferable.

  The resin (B) is required to have good affinity with the conductive metal powder (B) in order to achieve uniform dispersion of the conductive metal powder (A). The nitrile group has a high affinity for metals, and the strong affinity of the nitrile group for metal particles also increases the affinity for the conductive metal powder (B), which is effective for developing conductivity and exerts an external force. It is possible to form a conductive network that is not easily cut or destroyed. Therefore, it is preferable to contain a rubber containing a nitrile group as the resin (B). As a result, the conductive film of the present invention has high conductivity and is strong against external force such as extension, twist, and compression, so that it can maintain high conductivity even when an external force acts. The metal powder (B) preferably has an average particle size of 0.5 μm to 10 μm, and is preferably selected from flake-shaped metal powder or agglomerated metal powder. In addition, metal nanoparticles having an average particle size of 100 nm or less can be further included.

  The nitrile group-containing rubber is not particularly limited as long as it is a nitrile group-containing rubber or elastomer, but nitrile rubber and hydrogenated nitrile rubber are preferable. Nitrile rubber is a copolymer of butadiene and acrylonitrile. When the amount of bound acrylonitrile is large, the affinity with metals increases, but the rubber elasticity that contributes to stretchability decreases conversely. Therefore, the amount of bound acrylonitrile in the acrylonitrile butadiene copolymer rubber is preferably 18 to 50% by weight, particularly preferably 40 to 50% by weight.

  In the amount of the resin (B) blended in the conductive paste, when the volume% in the solid content is small, the conductivity is high, but the elasticity is poor. On the other hand, when the volume% is large, the elasticity is improved, but the conductivity is lowered. Therefore, the compounding amount of the resin (A) in the solid content of the conductive paste is 50 to 80% by volume (10 to 30% by weight), and preferably 60 to 75% by volume (12 to 22% by weight).

  It should be noted that the conductive paste forming the conductive film of the present invention may be blended with other resins within a range that does not impair the performance of the stretchable conductive film, the coating property and the printability.

  An inorganic substance can be added to the conductive film of the present invention within a range that does not impair the conductivity, stretchability, homogeneity, twistability, and compressibility. As the inorganic substance, various carbides such as silicon carbide, boron carbide, titanium carbide, zirconium carbide, hafnium carbide, vanadium carbide, tantalum carbide, niobium carbide, tungsten carbide, chromium carbide, molybdenum carbide, calcium carbide and diamond carbon lactam; boron nitride , Various nitrides such as titanium nitride and zirconium nitride, various borides such as zirconium boride; various oxidations such as titanium oxide (titania), calcium oxide, magnesium oxide, zinc oxide, copper oxide, aluminum oxide, silica and colloidal silica Compounds; various titanic acid compounds such as calcium titanate, magnesium titanate and strontium titanate; sulfides such as molybdenum disulfide; various fluorides such as magnesium fluoride and carbon fluoride; aluminum stearate, calcium stearate Um, zinc stearate, various metal soaps such as magnesium stearate and the like; may be used talc, bentonite, talc, calcium carbonate, bentonite, kaolin, glass fiber, mica or the like. By adding these inorganic substances, it may be possible to improve printability, heat resistance, mechanical properties and long-term durability.

  Also, thixotropic agents, defoamers, flame retardants, tackifiers, hydrolysis inhibitors, leveling agents, plasticizers, antioxidants, ultraviolet absorbers, laser light absorbers, flame retardants, pigments, dyes, etc. It can be blended.

  The conductive paste forming the conductive film of the present invention preferably contains an organic solvent. The organic solvent used preferably has a boiling point of 100 ° C or higher and lower than 300 ° C, more preferably 150 ° C or higher and lower than 290 ° C. If the boiling point of the organic solvent is too low, the solvent may volatilize during the paste manufacturing process or the paste is used, and the component ratio of the conductive paste may change. On the other hand, if the boiling point of the organic solvent is too high, a large amount of the solvent may remain in the coating film when a low temperature drying step is required (for example, 150 ° C. or lower), which lowers the reliability of the coating film. I have a concern.

  Examples of such a high boiling point solvent include cyclohexanone, toluene, isophorone, γ-butyrolactone, benzyl alcohol, Solvesso 100, 150, 200 manufactured by Exxon Chemical, propylene glycol monomethyl ether acetate, terpionel, butyl glycol acetate, and diamylbenzene ( Boiling point: 260-280 ° C), triamylbenzene (boiling point: 300-320 ° C), n-dodecanol (boiling point: 255-29 ° C), diethylene glycol (boiling point: 245 ° C), ethylene glycol monoethyl ether acetate (boiling point: 145) ° C), diethylene glycol monoethyl ether acetate (boiling point 217 ° C), diethylene glycol monobutyl ether acetate (boiling point: 247 ° C), diethylene glycol dibutyl ether (boiling point) : 255 ° C.), diethylene glycol monoacetate (boiling point: 250 ° C.), triethylene glycol diacetate (boiling point: 300 ° C.) triethylene glycol (boiling point: 276 ° C.), triethylene glycol monomethyl ether (boiling point: 249 ° C.), triethylene Glycol monoethyl ether (boiling point: 256 ° C), triethylene glycol monobutyl ether (boiling point: 271 ° C), tetraethylene glycol (boiling point: 327 ° C), tetraethylene glycol monobutyl ether (boiling point: 304 ° C), tripropylene glycol (boiling point) : 267 ° C.), tripropylene glycol monomethyl ether (boiling point: 243 ° C.), 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate (boiling point: 253 ° C.) and the like. Further, as petroleum hydrocarbons, AF solvent No. 4 (boiling point: 240 to 265 ° C.), No. 5 (boiling point: 275 to 306 ° C.), No. 6 (boiling point: 296 to 317 ° C.) manufactured by Nippon Oil Corp. , No. 7 (boiling point: 259 to 282 ° C.), and No. 0 solvent H (boiling point: 245 to 265 ° C.) and the like, and two or more of them may be included as necessary. Such an organic solvent is appropriately contained so that the conductive paste has a viscosity suitable for printing and the like.

  The content of the organic solvent in the conductive paste is determined by the method of dispersing the conductive metal powder, the viscosity of the conductive paste suitable for the method of forming the conductive film, the drying method, and the like. The conductive paste for forming the conductive film of the present invention can uniformly disperse the conductive metal powder in the resin by using a conventionally known method of dispersing powder in a liquid. For example, metal powder, a dispersion liquid of a conductive material, and a resin solution can be mixed and then uniformly dispersed by an ultrasonic method, a mixer method, a three-roll mill method, a ball mill method, or the like. It is also possible to use a plurality of these means in combination.

  The conductive paste for forming the conductive film of the present invention is applied or printed on a substrate to form a coating film, and then the organic solvent contained in the coating film is volatilized and dried to give a conductive film or A conductive pattern can be formed. Further, a conductive pattern can be formed by laser etching the coating film. Although the range of the film thickness is not particularly limited, it is preferably 1 μm to 1 mm. If it is less than 1 μm, film defects such as pinholes are likely to occur, which may cause a problem. If it exceeds 1 mm, the solvent tends to remain inside the film, and the reproducibility of the film physical properties may be poor.

  The base material to which the conductive paste is applied is not particularly limited, but a flexible or elastic base material is preferable in order to take advantage of the elasticity of the elastic conductive film. Generally, in a conductive film provided on a stretchable base material, the base material itself relaxes tensile stress to some extent during stretching, so that generation of microcracks in the conductive film is suppressed. Examples of the flexible substrate include paper, cloth, polyethylene terephthalate, polyvinyl chloride, polyethylene and polyimide. Examples of the stretchable base material include polyurethane, polydimethylsiloxane (PDMS), nitrile rubber, butadiene rubber, SBS elastomer, SEBS elastomer, spandex cloth, and knit cloth. It is preferable that these base materials can be creased and can be expanded and contracted in the plane direction. In that respect, a base material made of rubber or elastomer is preferable.

  In the present invention, particularly in the second aspect of the present invention, the conductive composite film preferably has good adhesion between the conductive film and the substrate. If the adhesiveness is poor, the wiring made of the conductive film may be peeled off from the substrate due to the stretching action or the repeated stretching action to cause a problem such as disconnection or short circuit.

  The step of applying the conductive paste onto the base material is not particularly limited, but can be performed by, for example, a coating method, a printing method, or the like. Examples of the printing method include a screen printing method, a lithographic offset printing method, an inkjet method, a flexographic printing method, a gravure printing method, a gravure offset printing method, a stamping method, a dispensing method and a squeegee printing method.

  The step of heating the base material coated with the conductive paste can be performed in the air, a vacuum atmosphere, an inert gas atmosphere, a reducing gas atmosphere, or the like. The heating temperature is in the range of 20 to 200 ° C. and is selected in consideration of the required conductivity and heat resistance of the base material. The organic solvent is volatilized, the curing reaction proceeds under heating in some cases, and the conductivity, adhesion and surface hardness of the conductive film after drying are improved. If the temperature is lower than 20 ° C., the solvent may remain in the coating film and the conductivity may not be obtained. Although it exhibits conductivity when treated for a long time, the specific resistance may be significantly inferior. The preferred heating temperature is 70 to 180 ° C. If the temperature is lower than 70 ° C, the heat shrinkage of the coating film becomes small, the conductive network of silver powder in the coating film cannot be sufficiently formed, and the specific resistance may increase. In some cases, due to the denseness of the coating film, the elongation rate and the repeated stretchability also deteriorate. If the temperature exceeds 180 ° C., the base material is limited due to heat resistance, and if treated for a long time, the rubber (B) containing a nitrile group may be thermally deteriorated, and the elongation rate and the cyclic stretchability may be deteriorated.

  A wrapping portion such as a stretchable cover coat may be provided on the conductive film on the base material. By providing the holding portion, damage to the conductive film can be suppressed even at a higher degree of extension, and functions such as waterproofness and insulation can be imparted. The cover coat material is not particularly limited as long as it is a stretchable material having good adhesion to the conductive film. As a preferable material, the resin (B) of the present invention can be mentioned.

The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto. In addition, Example 3 is Comparative Example 12, Example 4 is Comparative Example 13, Example 7 is Comparative Example 14, Example 8 is Comparative Example 15, Example 9 is Comparative Example 16, and Example 12 is Example 12. Read as Comparative Example 17.

[Preparation of conductive paste]
(Examples 1 to 4, Comparative Examples 1 to 5)
The resin was dissolved in Solvesso. However, as the solvent, isophorone was used for NBR (nitrile rubber), and 4-methyl-2-pentanone was used for PVDF (vinylidene fluoride copolymer). Silver particles, and optionally carbon nanotubes or vapor-grown carbon fibers were further added to this solution so that each of the components had a volume% in the solid content shown in Table 1, and the mixture was kneaded with a three-roll mill, A conductive paste was obtained.
(Examples 5-12, Comparative Examples 6-11)
The resin was dissolved in ethylene glycol monomethyl ether acetate, and a liquid in which silver particles were uniformly dispersed in this solution was blended so that each component had a volume% in the solid content shown in Table 2 or Table 3, and 3 It kneaded with this roll mill to obtain a conductive paste.

[Preparation of conductive film]
(Examples 1 to 7, Comparative Examples 6 to 7)
The conductive paste was formed on a Teflon (registered trademark) sheet with a wire bar and dried at 150 ° C. for 30 minutes to prepare a sheet-like conductive film having a thickness of 100 μm. Tests of specific resistance, homogeneity, twistability and compressibility were conducted using a conductive film.
The specific resistance of the conductive film was evaluated by the method described below when a natural state and an external force acted. Table 1 shows the compositions of the conductive films of Examples 1 to 4 and Comparative Examples 1 to 5 and the evaluation results thereof. Further, the conductive film was subjected to an elongation test and a repeated expansion and contraction test by the method described below. Table 2 shows the compositions of the conductive films of Examples 5 to 7 and Comparative Examples 6 to 7 and the evaluation results thereof.

[Preparation of conductive composite film]
(Examples 8-12, Comparative Examples 8-11)
A conductive paste was applied on a stretchable urethane sheet or silicon sheet having a thickness of 1 mm with a wire bar and dried at 150 ° C. for 30 minutes to prepare a conductive composite film containing a 100 μm conductive film. Using this conductive composite film, an elongation test, a repeated expansion and contraction test, a cross-cut test by 100 squares, a 3 times extension test, and a 10 times extension test were carried out by the methods described below. Table 3 shows the compositions of the conductive composite films of Examples 8 to 12 and Comparative Examples 8 to 11 and the evaluation results thereof.

Details of 1) to 11) in Table 1 are as follows.
1) Aggregated silver powder: G-35 (average particle size 5.9 μm, manufactured by DOWA Electronics)
2) Flake silver powder: FA-D-3 (average particle size 1.6 μm, manufactured by DOWA Electronics Co., Ltd.)
3) VGCF: vapor grown carbon fiber (fiber diameter 150 nm, fiber length 15 μm, Showa Denko KK)
4) CNT-A: carbon nanotube (SWeNT MW100 (multi-wall carbon nanotube, diameter 6 to 9 nm, length 5 μm, aspect ratio 556 to 833, manufactured by Southwest Nano Technologies, Inc.)
5) CNT-B: Produced according to the production method described in Non-Patent Document 2. SWeNT MW100 was dispersed by sonication in a silver nanoparticle dispersion made from benzyl mercaptan and silver nitrate. Then, filtration and washing are performed to obtain carbon nanotubes CNT-B modified with silver nanoparticles.
6) CSM: Chlorosulfonated polyethylene rubber (CSM-TS530, manufactured by Tosoh Corporation)
7) NBR: Nitrile rubber (Nipol DN003, acrylonitrile content 50% by weight, manufactured by Zeon Corporation)
8) CR: Chloroprene rubber (DOR-40, manufactured by Denka)
9) UR: Urethane rubber (Coatlon KYU-1, manufactured by Sanyo Chemical Co., Ltd.)
10) EPDM: ethylene propylene rubber (EP11, manufactured by JSR)
11) PVDF / ionic liquid: vinylidene fluoride copolymer (Dayer G-801, manufactured by Daikin) / 1-butyl-methylpyridinium tetrafluoroborate (50 wt / 50 wt)

The evaluation methods of the conductive films of Examples 1 to 4 and Comparative Examples 1 to 5 are as follows.
[Evaluation of resistivity]
A test piece was prepared by cutting the conductive film into a width of 20 mm and a length of 50 mm. The sheet resistance and the film thickness of the conductive film test piece in the natural state (extension rate 0%) were measured, and the specific resistance was calculated. The film thickness was measured using a thickness gauge SMD-565L (manufactured by TECLOCK), and the sheet resistance was measured on four test pieces using Loresta-GP MCP-T610 (manufactured by Mitsubishi Chemical Analytech), and the average value was used. . The specific resistance was calculated by the following formula.
Specific resistance (Ω · cm) = Rs (Ω / □) × t (cm)
Here, Rs indicates the sheet resistance measured under each condition, and t indicates the film thickness measured under each condition.
Then, in the same manner as in the natural state (extension rate 0%), when using a universal testing machine (manufactured by Shimadzu Corporation, Autograph AG-IS), when extended to 20%, 35%, 50%, 100% (extension rate A specific resistance of 60 mm / min) was measured. The elongation rate was calculated by the following formula.
Note that the elongation evaluation of the conductive film is performed in two extending directions, one in which the direction in which the conductive paste is applied is the extending direction of the test piece and the other in which the direction orthogonal to the applying direction is the extending direction of the test piece. It was carried out in.
Elongation rate (%) = (ΔL ₀ / L ₀ ) × 100
Here, L ₀ is the distance between the marked lines of the test piece, and ΔL ₀ is the increase in the marked line Korean distance of the test piece. The sheet resistance during stretching was read 30 seconds after reaching a predetermined degree of stretching.
Further, the specific resistance increase ratio at 100% elongation was calculated by the following formula.
Specific resistance increase ratio = (R ₁₀₀ / R ₀ ) × 100 (%)
Here, R ₁₀₀ is the resistivity after 100% elongation, and R ₀ is the resistivity in the natural state.

[Evaluation of homogeneity]
The conductive film was cut into a width of 20 mm and a length of 50 mm in the application direction and the direction perpendicular to the application direction to prepare a sample piece. Using each test piece, the specific resistance was measured at elongation rates of 20%, 35%, 50% and 100%. The homogeneity was evaluated by comparing the difference in the specific resistance between the test pieces in the application direction and the direction perpendicular to the application direction.

[Evaluation of twistability]
The conductive film was cut into a piece of 20 mm in width and 50 mm in length. The specific resistance was measured when one end of the sample piece was fixed and the other end was twisted once (360 °) and ten times (3600 °).

[Evaluation of compressibility]
Ten conductive film test pieces (thickness 100 μm, diameter 200 mm) were stacked to obtain a test piece. A universal tester (manufactured by Shimadzu Corporation, Autograph AG-IS) was used for the compression operation. The test piece was attached to a compression jig for foam rubber and a sample holder via electrodes (copper foil) respectively, and the specific resistance was measured from the resistance between the electrodes when compressed by 10%.

Details of 21) to 31) in Tables 2 and 3 are as follows.
21) Aggregated silver powder: G-35 (average particle size 5.9 μm, manufactured by DOWA Electronics)
22) Flake silver powder: FA-D-3 (average particle size 1.6 μm, manufactured by DOWA Electronics Co., Ltd.)
23) AR: acrylic rubber (Nipol AR51, manufactured by Zeon Corporation)
24) IIR: Butyl rubber (BUTYLO065, manufactured by JSR)
25) NBR: Nitrile rubber (Nipol DN003, acrylonitrile content 50% by weight, manufactured by Zeon Corporation)
26) CSM: Chlorosulfonated polyethylene rubber (CSM-TS530, manufactured by Tosoh Corporation)
27) CR: Chloroprene rubber (DOR-40, manufactured by Denka)
28) UR: Urethane rubber (Coatlon KYU-1, Sanyo Kasei Co., Ltd.)
29) EPDM: ethylene propylene rubber (EP11, manufactured by JSR)
30) Urethane rubber sheet: thickness 1 mm, (manufactured by Tigers Polymer Co., Ltd.)
31) Silicone rubber sheet: thickness 1 mm (manufactured by AS ONE)

  The evaluation methods of the conductive films and the conductive composite films of Examples 5 to 12 and Comparative Examples 6 to 12 were the same as those of Examples 1 to 4 for the evaluation of the specific resistance. Other evaluation methods are as follows.

[Evaluation of repeatability]
Using a repeating durability tester (TIQ-100, manufactured by Lesca), electrodes were provided on the chuck portions holding both ends of the conductive film test piece and the conductive composite film test piece, and the electrode was extended by 20% of the original length. , And the sheet resistance in the state of returning to the original length was measured by the two-terminal method. The extension speed and the speed for returning to the original length were both 60 mm / min. During the sheet resistance measurement, the value was read 30 seconds after reaching the natural state (0% elongation) and 20% elongation. After repeating this stretching operation 1000 times, the specific resistance in the natural state was measured.

[Evaluation of adhesion]
It was conducted by a cross-cut test with 100 squares. Eleven straight lines that cross the conductive sheet of the conductive composite film and reach the base sheet with a razor are cut at 1 mm intervals to draw 100 squares, and adhesive tape (cellophane tape (registered trademark) is drawn on the squares. , (Manufactured by Nichiban Co., Ltd.) was strongly pressure-bonded, and after peeling off the tape, the peeled state of the grid pattern was observed. The numerical values of the results in Table 1 represent (the number of cells remaining without peeling in the test) / (the number of cells before the test).

[Evaluation of extensibility]
The conductive composite film test piece was measured for specific resistance of the conductive film when stretched 3 times (extension rate 200%), and the appearance of the conductive film when extended 10 times (extension rate 900%) was observed.

  As is clear from the results in Table 1, the conductive films of Examples 1 to 4 can maintain not only good conductivity in a natural state but also high conductivity even when stretched by 36% or more, and thus the homogeneity can be improved. Excellent in twistability and compressibility. On the other hand, the conductive films of Comparative Examples 1 to 5 have higher specific resistance or poor homogeneity as compared with Examples 1 to 4, and the specific resistance is significantly increased by the stretching action, the twisting action, and the compression action.

As is clear from the results of Table 2, the electroconductive films of Examples 5 to 7 can maintain high electroconductivity even at the time of elongation and have electroconductivity after repeated expansion and contraction as compared with Comparative Examples 6 to 7. The drop is small.
Further, as is clear from the results of Table 3, the conductive composite films of Examples 8 to 12 can maintain high conductivity even when stretched, the conductivity is not significantly reduced even after repeated expansion and contraction, and the adhesion is improved. Almost no decrease is seen. On the other hand, in the conductive films of Comparative Examples 8 to 11, compared with Examples 8 to 12, breakage occurs due to elongation, or adhesion is greatly reduced due to repeated expansion and contraction.

  The conductive paste of the present invention has high conductivity and high stretchability, excellent repeat stretchability, and excellent multi-adhesiveness with the base material, so that a foldable display using a rubber or elastomer material, stretchable LED arrays, stretchable solar cells, stretchable antennas, stretchable batteries, actuators, healthcare devices and medical sensors, wearable computers, electrodes and wiring, and the like.

Claims (4)

A conductive film containing a conductive metal powder (A) and a resin (B), having a specific resistance of less than 1.0 × 10 ⁻³ Ωcm and extending by 36% or more of the original length in at least one direction. It is possible, and in a state of a self-supporting film in which a wrapping part for wrapping a base material and a conductive film is not provided, a specific resistance increase ratio at a time of 100% extension of the original length is less than 10. In the conductive film to
The conductive metal powder (A) is silver powder having an agglomerate shape, and the resin (B) is nitrile group-containing rubber or chlorosulfonated polyethylene rubber,
In the twist test of the conductive film, it is possible to twist the conductive film with respect to the plane of the conductive film up to a twist angle of 3600 ° without causing film breakage, and when the twist angle is from 0 ° to 3600 °, the specific resistance is Of less than 1.0 × 10 ⁻² Ωcm.   36% or more of the original length can be extended in each of the two directions orthogonal to each other. When 100% of the original length is extended in the two directions orthogonal to each other, the difference in specific resistance between the two is 10 at the same extension rate. %, The conductive film according to claim 1. When compressed by 10% in the thickness direction of the conductive film, a conductive film according to claim 1 or 2, wherein the resistivity is less than 1.0 × 10 ^-3 Ωcm. Conductive film according to any one of claims 1 to 3, characterized in that is manufactured by coating or printing.