JP5568459B2 - Conductive film and method for manufacturing the same, transducer using conductive film, flexible wiring board, and electromagnetic wave shield - Google Patents

Description

  The present invention relates to a conductive film suitable for stretchable electrodes, wiring, and the like, a manufacturing method thereof, a transducer using the conductive film, a flexible wiring board, and an electromagnetic wave shield.

  Development of highly flexible, small, and lightweight transducers using polymer materials such as dielectric elastomers is ongoing. Examples of the transducer include an actuator, a sensor, and a power generation element that convert mechanical energy and electrical energy, or a speaker and microphone that convert acoustic energy and electrical energy. For example, an actuator can be configured by arranging a pair of electrodes on the front and back surfaces of an elastomeric dielectric film.

  In this type of actuator, the dielectric film expands and contracts depending on the applied voltage. Therefore, the electrode is required to be able to expand and contract in accordance with the deformation of the dielectric film so as not to prevent the expansion and contraction of the dielectric film. In addition, a small change in electrical resistance is required when stretched.

  From such a viewpoint, for example, according to Patent Document 1, an electrode is formed from a paste obtained by mixing an oil or an elastomer with a conductive material such as carbon black. Patent Document 2 discloses a conductive film including an elastomer and two types of metal fillers having different shapes. On the other hand, Patent Document 3 discloses a transparent conductor including a substrate and a conductive layer including metal nanowires as a transparent electrode of a liquid crystal display or a touch panel.

JP 2009-124839 A JP 2010-153364 A Special table 2009-505358

  For example, when the elastomer is filled with carbon black, even if the carbon black is highly filled, the specific resistance of the elastomer is relatively large, about 0.1 to 1 Ω · cm. For this reason, when an electrode or wiring is formed from a paste in which a binder such as an elastomer is mixed with carbon black, there is a problem that electric resistance increases. If the electrical resistance of the electrode or wiring is high, the element is likely to deteriorate due to heat generated by the internal resistance. In addition, when the electrical resistance of the electrode or the wiring is high, the responsiveness of the actuator or the acoustic device may be lowered due to the generation of a reactance component in a high frequency region. Also, if the internal resistance is too high for the detection signal, the resolution of the sensor may be reduced.

  On the other hand, an electrode formed from a commercially available silver paste is poor in flexibility. The silver paste is formed by filling a binder resin with silver powder. In addition to the high elastic modulus of the binder itself, since the silver powder is highly filled, the elastic modulus of the formed electrode is high. For this reason, if it extends | stretches greatly, a crack will generate | occur | produce and an electrical resistance will increase remarkably. Further, when the electrode of the actuator is formed from silver paste, the electrode cannot follow the expansion and contraction of the dielectric film, which may hinder the movement of the dielectric film. In addition, in the acoustic device, in addition to the fact that the electrode cannot follow the expansion and contraction of the dielectric film, the response in the low frequency region is lowered due to the stress generated during expansion.

  Also, a conductive adhesive or the like is used to electrically connect the terminals of the circuit board. When a conventional conductive material with poor flexibility is used as the conductive adhesive, the bonded portion may be distorted when stretched, and conduction may be lost. Therefore, a conductive material having poor flexibility is not suitable for connection of a wiring body having elasticity. Similarly, a conductive material with poor flexibility is not suitable for electromagnetic shielding of devices having stretchability.

  Moreover, the metal nanowire disclosed by the said patent document 3 is easy to aggregate. For this reason, when a metal nanowire is filled in the matrix, the desired conductivity cannot be obtained with a small amount. Here, when a large amount of metal nanowires are filled in order to achieve desired conductivity, the elastic modulus of the conductive layer increases. That is, the flexibility of the conductive layer is reduced. Accordingly, cracks are likely to occur during elongation, leading to an increase in electrical resistance.

  This invention is made | formed in view of such a situation, and makes it a subject to provide the electrically conductive film which can be expanded-contracted softly and an electrical resistance does not increase easily at the time of expansion | extension, and its manufacturing method. It is another object of the present invention to provide a flexible transducer having excellent durability, a flexible wiring board, and an electromagnetic wave shield.

  (1) In order to solve the above problems, the conductive film of the present invention is a conductive film containing an elastomer and a metal fiber, and the length of the metal fiber in the longitudinal direction is 1 μm or more, and the length in the short direction is 600 nm or less, the aspect ratio is 10 or more, and the content of the metal fiber is 45 vol% or less when the volume of the conductive film is 100 vol%.

  The conductive film of the present invention includes a fiber-like conductive material (metal fiber). For this reason, there are many contact points between electrically conductive materials compared with the case where the electrically conductive materials of other shapes, such as spherical shape and flat shape, are used. Therefore, even when the conductive film is elongated, the contact state of the conductive material is easily maintained. Therefore, even when expansion and contraction is repeated, the conductivity is unlikely to decrease.

  Moreover, in the electrically conductive film of this invention, desired electroconductivity can be obtained even if content of a metal fiber is comparatively small by prescribing | regulating the magnitude | size of a metal fiber. That is, the length of the metal fiber in the longitudinal direction is 1 μm or more, the length in the short direction is 600 nm or less, and the aspect ratio is 10 or more. In the present specification, the length in the short direction of the metal fiber means the maximum length in the direction perpendicular to the long direction of the metal fiber. Hereinafter, the length in the longitudinal direction may be simply referred to as “length”, and the length in the short direction may be referred to as “thickness”. The aspect ratio is the ratio of the length in the longitudinal direction to the length in the short direction of the metal fiber (length in the longitudinal direction / length in the short direction).

  Since the length of the metal fiber is relatively long, the metal fibers are likely to contact each other. That is, a conductive path is easily formed. Further, since the thickness of the metal fiber is relatively thin, the number of metal fibers per unit weight of the conductive film can be increased. In addition, since the aspect ratio is relatively large, conductive paths are easily formed, and the number of conductive paths increases. Therefore, even when expansion and contraction is repeated, the conductivity is unlikely to decrease.

  Thus, in the conductive film of the present invention, a conductive path is efficiently formed with a relatively small amount of metal fibers. Therefore, according to the present invention, it is possible to realize a conductive film that is flexible, has high conductivity, and does not easily increase in electrical resistance when stretched.

  (2) Moreover, the manufacturing method of the electrically conductive film of the said invention WHEREIN: In the solution containing a metal compound and the reducing agent which has the reduction ability of this metal compound, a longitudinal direction length is 1 micrometer or more and a transversal direction length is. Metal fiber synthesis step for synthesizing a metal fiber having an aspect ratio of 10 or more and 600 nm or less, and the synthesized metal fiber is dispersed in a solvent capable of dissolving the rubber polymer of the elastomer component in a wet state. A conductive coating material is prepared by mixing the metal fiber dispersion preparing step for preparing the metal fiber dispersion and the rubber composition containing the rubber polymer, and the conductive coating is applied and dried to prepare the conductive film. And a conductive film forming step to be formed.

  In the manufacturing method of the electrically conductive film of this invention, the metal fiber of a predetermined magnitude | size is synthesize | combined using a well-known chemical reduction method. As an example of the chemical reduction method, Yugang Sun et al. , Chem. Mater. The synthesis method of the silver nanowire described in 2002,14,4736-4745 is mentioned. Usually, according to the chemical reduction method, the synthesized metal fiber is filtered from the solution and then dried to obtain a powder. For this reason, when preparing a conductive paint, a metal fiber is mixed with a rubber composition in a powder state. However, the thickness of the metal fiber used for the conductive film of the present invention is as thin as 600 nm or less. For this reason, metal fibers tend to aggregate. Therefore, it is difficult to uniformly disperse the metal fibers in the conductive paint.

  In this regard, according to the method for producing a conductive film of the present invention, the synthesized metal fiber is dispersed in a solvent in a wet state without being completely dried to prepare a metal fiber dispersion in advance. Then, the metal fiber dispersion is mixed with the rubber composition to prepare a conductive paint. By doing so, aggregation of the metal fibers can be suppressed, and the metal fibers can be uniformly dispersed in the conductive paint. Therefore, metal fibers can be uniformly dispersed in the formed conductive film. As a result, the conductive path can be efficiently formed. Thus, according to the manufacturing method of this invention, the said electrically conductive film of this invention can be manufactured easily.

  (3) Further, the transducer of the present invention includes an elastomer dielectric film, a plurality of electrodes disposed via the dielectric film, and a plurality of wirings connected to the plurality of electrodes, At least one of the electrode and the wiring is made of the conductive film of the present invention.

  A transducer is a device that converts one type of energy into another type of energy. As described above, the transducer includes an actuator, a sensor, a power generation element, or the like that converts mechanical energy and electrical energy, or a speaker, a microphone, or the like that converts acoustic energy and electrical energy. According to the transducer of the present invention, at least one of the electrode and the wiring is made of the conductive film of the present invention. Therefore, when the member on which the electrode or the wiring is formed is deformed, the electrode or the wiring expands and contracts following the deformation. For this reason, the movement of the transducer is difficult to be hindered by the electrodes and wiring. Moreover, in the electrode and wiring formed from the conductive film of the present invention, there is little decrease in conductivity at the time of extension, and even when repeatedly expanded and contracted, there is little heat generation due to internal resistance. Therefore, the transducer of the present invention is excellent in durability.

  (4) Moreover, the flexible wiring board of this invention is equipped with an elastic member and the wiring arrange | positioned on the surface of this elastic member, and at least one part of this wiring consists of the electrically conductive film of the said invention. It is characterized by.

  According to the flexible wiring board of the present invention, the wiring expands and contracts following the deformation of the elastic member. Even if the wiring is extended, there is little decrease in conductivity, and even when the expansion and contraction are repeated, heat generation due to internal resistance is small. Therefore, the flexible wiring board of the present invention is excellent in durability.

  (5) Moreover, the electromagnetic wave shield of this invention consists of the electrically conductive film of the said invention, It is characterized by the above-mentioned.

  The electrically conductive film of this invention can be manufactured from the electrically conductive coating material which melt | dissolved raw materials, such as a rubber polymer, in the predetermined solvent. Therefore, the conductive film of the present invention can be used as an electromagnetic wave shield by forming it at various sites where electromagnetic waves are desired to be shielded. As described above, the conductive film of the present invention is flexible and highly conductive, and the electrical resistance hardly increases even when stretched. Therefore, the electromagnetic wave shield of the present invention is suitable for a device having stretchability.

  Furthermore, the conductive film of the present invention is also suitable as a conductive adhesive. As described above, according to the conductive film of the present invention, desired conductivity can be obtained even if the content of the metal fiber is relatively small. Since the content of the metal fiber is small, it is difficult to inhibit the adhesiveness of the elastomer. Accordingly, the conductive film of the present invention is suitable as a conductive adhesive for electrically connecting a stretchable device or a strained portion.

It is a cross-sectional schematic diagram of the actuator which is 1st embodiment of the transducer of this invention, Comprising: (a) shows a voltage-off state, (b) shows a voltage-on state. It is a top view of the capacitive sensor which is 2nd embodiment of the transducer of this invention. It is III-III sectional drawing of FIG. It is a cross-sectional schematic diagram of the electric power generating element which is 3rd embodiment of the transducer of this invention, Comprising: (a) is at the time of expansion | extension, (b) shows the time of contraction. It is a perspective view of the speaker which is 4th embodiment of the transducer of this invention. It is VI-VI sectional drawing of FIG. It is an upper surface penetration figure of the flexible wiring board of the present invention.

  Hereinafter, each embodiment of the electrically conductive film of the present invention, its manufacturing method, transducer, flexible wiring board, and electromagnetic wave shield will be described. The conductive film, the manufacturing method thereof, the transducer, the flexible wiring board, and the electromagnetic wave shield of the present invention are not limited to the following embodiments, and can be changed by those skilled in the art without departing from the gist of the present invention. The present invention can be implemented in various forms with improvements and the like.

<Conductive film>
The electrically conductive film of this invention contains an elastomer and a metal fiber. The elastomer should just have rubber-like elasticity at room temperature. For example, an elastomer having a glass transition temperature (Tg) of 0 ° C. or lower is suitable because it is flexible. Moreover, since crystallinity will fall when Tg becomes low, the breaking elongation of an elastomer will become large. That is, it becomes easier to expand. In addition, since the viscosity of the elastomer increases, it is possible to impart adhesiveness to the conductive film. Adhesiveness with a base material will improve if a conductive film has adhesiveness. For example, when the adhesiveness of the conductive film formed on the surface of the elastic member is not sufficient, the tensile characteristics of the elastic member may be deteriorated. Further, when the strain is repeatedly applied, the conductive film is peeled off from the elastic member, and the mechanical reliability and the electrical reliability may be lowered. In addition, a void may enter between the elastic member and the conductive film, which may cause dielectric breakdown. Therefore, the Tg of the elastomer is desirably −20 ° C. or lower, and more preferably −35 ° C. or lower. In this specification, the midpoint glass transition temperature measured according to JIS K7121 (1987) is adopted as the glass transition temperature.

  The elastomer preferably has a functional group or structure capable of hydrogen bonding. For example, functional groups capable of hydrogen bonding have a high affinity for metal fibers. For this reason, the interface peeling between the elastomer and the metal fiber hardly occurs. Therefore, even when stretched, cracks are unlikely to occur in the conductive film, and electrical resistance is also unlikely to increase. Examples of functional groups capable of hydrogen bonding include ester groups, urethane bonds, urea bonds, halogen groups, hydroxyl groups, carboxyl groups, amino groups, sulfonic acid groups, ether bonds, and the like. Of these, those having an ester group are desirable.

  As the elastomer, one kind may be used alone, or two or more kinds may be mixed and used. For example, acrylic rubber, urethane rubber, hydrin rubber, acrylonitrile-butadiene rubber (NBR), silicone rubber, natural rubber, isoprene rubber, butyl rubber, styrene-propylene rubber, fluorine rubber, butadiene rubber, chloroprene rubber, thermoplastic elastomer, etc. are suitable. is there. Especially, since acrylic rubber has low crystallinity and weak intermolecular force, Tg is lower than other rubbers. Therefore, it is flexible and has good elongation, and is suitable for an electrode of an actuator. As an acrylic rubber, what contains 50 mol% or more of acrylate monomer units having an alkyl group having 4 or more carbon atoms is desirable. When the alkyl group is large (the number of carbon atoms is large), the crystallinity is lowered, so that the elastic modulus of the acrylic rubber becomes lower.

  The conductive film of the present invention may contain additives such as a plasticizer, a processing aid, a crosslinking agent, a crosslinking accelerator, a crosslinking aid, an antiaging agent, a corrosion inhibitor, a softening agent, and a coloring agent. For example, when a corrosion inhibitor is added, corrosion such as oxidation and sulfidation of the metal fiber can be suppressed. As the corrosion inhibitor, for example, tolyltriazole, benzotriazole, mercaptobenzotriazole, mercaptobenzotetrazole, (2-benzothiazolylthio) acetic acid, and salts of these compounds can be used. In particular, a metal fiber having a short direction length of 100 nm or less is easily oxidized and sulfided. Therefore, when employing such a thin metal fiber, it is desirable to add a corrosion inhibitor. Moreover, when a plasticizer and a softening agent are added, the processability of the elastomer is improved and the flexibility can be further improved. The plasticizer should just be excellent in compatibility with an elastomer. For example, known organic acid derivatives such as phthalic acid diester, phosphoric acid derivatives such as tricresyl phosphate, adipic acid diester, chlorinated paraffin, polyether ester and the like can be used. As the softener, a plant softener or a mineral softener may be used. Examples of plant softeners include stearic acid, lauric acid, ricinoleic acid, palmitic acid, cottonseed oil, soybean oil, castor oil, palm oil, pine tar oil, tall oil, factis and the like. Examples of mineral softeners include paraffinic, naphthenic and aroma oils.

  Moreover, what is necessary is just to determine suitably about the crosslinking agent, crosslinking accelerator, crosslinking adjuvant, etc. which contribute to a crosslinking reaction according to the kind etc. of elastomer. If sulfur, a sulfur compound, or an organic peroxide is used as a crosslinking agent, the metal fiber may be oxidized or sulfided. Thereby, the electrical resistance of the surface of a metal fiber may increase, and there exists a possibility that electroconductivity may fall. Therefore, it is desirable not to use any of sulfur, sulfur compounds, and organic peroxides for crosslinking the elastomer. That is, it is desirable that the conductive film of the present invention does not contain any of sulfur, sulfur compounds, and organic peroxides. In this case, the elastomer may be one or more selected from a crosslinked rubber and a thermoplastic elastomer that are crosslinked without using any of sulfur, sulfur compounds, and organic peroxides.

  The material of the metal fiber is not particularly limited. From the viewpoint of higher conductivity than carbon black and less corrosion, for example, silver, gold, copper, nickel, rhodium, palladium, chromium, titanium, platinum, iron, tin, aluminum, and alloys thereof may be appropriately selected. That's fine. Among these, silver is preferable because it has a small electric resistance and is relatively inexpensive. As a metal fiber, 1 type may be used independently and 2 or more types may be mixed and used.

  The length of the metal fiber in the longitudinal direction is 1 μm or more, the length in the lateral direction is 600 nm or less, and the aspect ratio is 10 or more. When the length in the longitudinal direction is less than 1 μm, the metal fibers are difficult to contact each other. Therefore, it is difficult to form a conductive path. Moreover, since the length of the metal fiber is short, the contact point per unit section increases. For this reason, contact resistance increases and the electroconductivity falls. In addition, since the number of conductive paths is small, it is difficult to maintain a conductive state when expansion and contraction is repeated. On the other hand, when the length of the metal fiber is too long, the dispersibility in the conductive film decreases due to the entanglement of the metal fibers. For this reason, the length of the metal fiber is desirably 100 μm or less.

  When the length of the metal fiber in the short direction exceeds 600 nm, that is, when the thickness of the metal fiber increases, the number of metal fibers per unit weight of the conductive film decreases. Therefore, it is difficult to form a conductive path. In addition, since the number of conductive paths is small, it is difficult to maintain a conductive state when expansion and contraction is repeated. In addition, if the content of the metal fiber is increased in order to secure the conductive path, the volume ratio of the elastomer is reduced accordingly. Thereby, the softness | flexibility of an electrically conductive film falls.

  When the aspect ratio of the metal fiber is less than 10, the area where the metal fibers overlap is small. Therefore, it is difficult to form conductive paths, and the number of conductive paths is reduced. For this reason, electrical resistance tends to increase at the time of expansion.

  Content of the metal fiber in the electrically conductive film of this invention is 45 vol% or less when the volume of an electrically conductive film is 100 vol%. By defining the size of the metal fiber, the conductive film of the present invention has high conductivity even if the content of the metal fiber is relatively small. From the viewpoint of further improving the flexibility of the conductive film, the content of the metal fiber is preferably 25 vol% or less, and more preferably 15 vol% or less.

  What is necessary is just to determine the thickness of the electrically conductive film of this invention suitably according to a use. From the viewpoint of forming a large number of conductive paths, the thickness of the conductive film is preferably 5 times or more the short direction length of the metal fiber.

  The conductive film of the present invention is preferably produced by applying a conductive paint obtained by mixing a metal fiber dispersion and a rubber composition containing a rubber polymer of an elastomer component to a substrate and drying it by heating. In this case, the crosslinking reaction of the rubber polymer may be allowed to proceed during heating. Here, the metal fiber dispersion is obtained by dispersing metal fibers synthesized by a chemical reduction method in a solvent capable of dissolving the rubber polymer in a wet state without being completely dried. The rubber composition is a kneaded product obtained by kneading a rubber polymer and an additive blended as necessary, or a solution obtained by dissolving a rubber polymer and an additive blended as necessary in a solvent.

  As a method for synthesizing the metal fiber, a wet method is desirable in consideration of dispersibility of the metal fiber in the elastomer. Here, examples of the reducing agent for reducing the metal compound include alcohols, polyols, alcohol amines, alkali metal borohydrides, quaternary ammonium borohydrides, citric acid, hydrazine, and the like. In the synthesis, it is desirable to use a growth regulator that grows the metal particles in a fiber form starting from the nucleus of the metal particles generated by the reduction. A suitable method for producing the conductive film of the present invention will be described in detail later.

  Moreover, what is necessary is just to form the electrically conductive film of this invention in the surface of a base material according to a use. Examples of the substrate include a flexible resin film made of polyimide, polyethylene, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), or the like. Moreover, when the electrically conductive film of this invention is formed in the surface of the elastic member made from an elastomer, the effect that a softness | flexibility is high and an electrical resistance cannot increase easily at the time of expansion | extension can be exhibited more. The elastic member includes a dielectric film in the transducer, a base material in the flexible wiring board, and the like. The thin-film elastic member can be manufactured, for example, by coating a paint for forming the elastic member on a substrate having releasability, and then cutting it into a desired shape and peeling it off.

  Also about an elastic member, the aspect which does not contain any of sulfur, a sulfur compound, and an organic peroxide like a electrically conductive film is desirable. Therefore, as the elastomer of the elastic member, one or more selected from cross-linked rubber and thermoplastic elastomer cross-linked without using any of sulfur, sulfur compounds, and organic peroxides may be adopted. The elastomer of the elastic member may be the same as or different from the elastomer of the conductive film.

<Method for producing conductive film>
The manufacturing method of the electrically conductive film of this invention has a metal fiber synthetic | combination process, a metal fiber dispersion liquid preparation process, and an electrically conductive film formation process. Hereinafter, each step will be described.

(1) Metal fiber synthesis step This step is performed in a solution containing a metal compound and a reducing agent capable of reducing the metal compound. The length in the longitudinal direction is 1 μm or more, the length in the short direction is 600 nm or less, and the aspect ratio Synthesize 10 or more metal fibers.

  In this step, a metal fiber having a predetermined size is synthesized using a known chemical reduction method. What is necessary is just to select a metal compound suitably according to the kind of metal fiber to synthesize | combine. Examples thereof include glass oxides such as silver, gold, and nickel, carbonates, hydroxides, chlorides, and sulfates. In the case of synthesizing silver fibers, silver nitrate is preferred from the viewpoint of being easily dissolved in a solvent and easily reduced.

  What is necessary is just to select a reducing agent suitably according to reaction temperature, the kind of metal compound, etc., if it has the reducing ability of a metal compound. Examples thereof include alcohol, polyol, alcohol amine, alkali metal borohydride, quaternary ammonium borohydride, citric acid, hydrazine and the like. Of these, alcohols and polyols are preferred. When alcohol or polyol is used, the thickness and length of the metal fiber can be easily controlled. In addition, safety is high. Furthermore, alcohol and polyol also serve as a solvent for dispersing the metal compound. Specifically, ethylene glycol, propylene glycol, butylene glycol, glycerin, trimethylolpropane and the like are preferable.

  For example, this step is performed by using a reducing agent having a reducing ability of a metal compound and a first solution containing a nucleating agent that generates nuclei of metal particles, the metal compound, and the metal particles starting from the generated nuclei. It is desirable to prepare a second solution containing a growth regulator that grows the fiber into a fiber shape, and drop the second solution into the first solution to synthesize the metal fiber.

  The nucleating agent serves to generate nuclei of reduced metal particles. When metal chloride is used as the nucleating agent, the length and thickness of the metal fiber can be easily controlled. For this reason, the metal fiber of the target magnitude | size can be obtained easily. Among these, platinum chloride and copper chloride are preferable from the viewpoint that metal particle nuclei can be stably generated in the solution.

  The growth regulator plays a role of growing the metal particles in a fiber shape starting from the nuclei of the generated metal particles. For example, polyvinyl pyrrolidone, polyvinyl alcohol, polyacrylamide, polyethyleneimine and the like can be mentioned. The size of the synthesized metal fiber varies depending on the content of the growth regulator, the molecular weight, and the like. For example, when polyvinyl pyrrolidone is used as the growth regulator, it is desirable to blend polyvinyl pyrrolidone in a molar ratio of 2 or more and 20 or less with respect to the metal compound. When there is too much content of polyvinylpyrrolidone, an excessive amount of polyvinylpyrrolidone will cover the produced | generated nucleus. For this reason, the growth of the metal particles becomes isotropic, and it is difficult to form a fiber. On the other hand, even if the content of polyvinyl pyrrolidone is too small, the growing metal particles cannot be sufficiently covered, so that the metal particles are unlikely to become a fiber.

  The weight average molecular weight of polyvinyl pyrrolidone is desirably 10,000 or more and 360,000 or less. When the weight average molecular weight of polyvinylpyrrolidone is small, the thickness of the metal fiber is increased. As the metal fibers become thicker, the number of metal fibers per unit weight of the conductive film decreases. For this reason, at the time of extension, the conductive path tends to decrease, and the electrical resistance tends to increase. On the other hand, when the weight average molecular weight of polyvinylpyrrolidone is large, the thickness of the metal fiber is thin. As the metal fibers become thinner, the number of metal fibers per unit weight of the conductive film increases. For this reason, at the time of expansion, the conductive path is unlikely to decrease, and the electrical resistance is unlikely to increase. However, if the metal fiber becomes too thin, the decrease in conductivity due to surface oxidation becomes large, or dispersion in the elastomer becomes difficult.

  A solvent that can disperse the metal compound and the growth regulator may be used as the solvent of the second solution. From the viewpoint of not inhibiting the reducing action of the reducing agent by the first solution, it is desirable to use a solvent having a reducing ability of the metal compound as the solvent of the second solution. For example, ethylene glycol, propylene glycol, butylene glycol, glycerin, trimethylolpropane and the like can be mentioned. The type of the solvent may be the same as or different from the solvent of the first solution. The magnitude | size of the metal fiber synthesize | combined also changes with the dripping speed | rate of the 2nd solution with respect to a 1st solution. Therefore, it is desirable to appropriately adjust the dropping speed of the second solution so that a desired size of metal fiber is synthesized.

  The first solution is preferably heated in advance. Specifically, the temperature of the first solution is preferably 60 ° C. or higher and 180 ° C. or lower from the viewpoint that the reduction reaction of the metal compound easily proceeds. Moreover, it is desirable that the second solution is dropped while maintaining the heating temperature. And after dripping a 2nd solution to a 1st solution, it is desirable to grow a metal fiber by stirring a solution for a predetermined time, keeping the temperature. If the stirring time is short, the length of the metal fiber tends to be short.

(2) Metal Fiber Dispersion Preparation Step This step is a step of preparing the metal fiber dispersion by dispersing the synthesized metal fiber in a wet state in a solvent capable of dissolving the rubber polymer of the elastomer component.

  In this step, first, the solution after completion of the metal fiber synthesis reaction is filtered, and the metal fiber is taken out of the solution. Next, the extracted metal fiber is dispersed in a solvent in a wet state without being dried. The solvent should just be what can melt | dissolve the rubber polymer of the elastomer component used as the base material of an electrically conductive film. For example, when acrylic rubber is used as the elastomer, examples of the solvent capable of dissolving the acrylic rubber polymer include butoxyethyl acetate, butoxyethoxyethyl acetate, methyl ethyl ketone, toluene, N-methylpyrrolidone, dimethylformamide and the like. In this way, a metal fiber dispersion is prepared.

(3) Conductive film forming step In this step, the prepared metal fiber dispersion and a rubber composition containing a rubber polymer are mixed to prepare a conductive paint, and the conductive paint is applied and dried to form a conductive film. Is a step of forming.

  The rubber composition may be a kneaded product obtained by kneading a rubber polymer and an additive that is blended as necessary, or a solution in which a rubber polymer and an additive that is blended as necessary are dissolved in a solvent. The rubber composition is preferably a solution in which a rubber polymer or the like is dissolved because it is easy to mix with the metal fiber dispersion and easily disperse the metal fibers uniformly in the conductive paint. Examples of the additive include a plasticizer, a processing aid, a crosslinking agent, a crosslinking accelerator, a crosslinking aid, an antiaging agent, a corrosion inhibitor, a softening agent, and a coloring agent. What is necessary is just to mix | blend an additive as needed.

  Various known methods can be adopted as a method for applying the conductive paint. For example, in addition to printing methods such as inkjet printing, flexographic printing, gravure printing, screen printing, pad printing, and lithography, dipping, spraying, bar coating, and the like can be given. For example, when a printing method is employed, it is possible to easily separate the applied part and the non-applied part. Also, printing of large areas, thin lines, and complicated shapes is easy. Among the printing methods, a screen printing method is preferable because a conductive paint having a high viscosity can be used and the coating thickness can be easily adjusted.

  In this step, the conductive coating is applied to the substrate and then dried by heating to form a conductive film. During the heating, the crosslinking reaction of the rubber polymer may be allowed to proceed.

<Transducer>
The transducer of the present invention includes a dielectric film made of elastomer, a plurality of electrodes disposed via the dielectric film, and wirings connected to the plurality of electrodes. As the dielectric film, it is desirable to use an elastomer having a high relative dielectric constant. Specifically, an elastomer having a relative dielectric constant (100 Hz) at room temperature of 2 or more, further 5 or more is desirable. For example, an elastomer having a polar functional group such as an ester group, a carboxyl group, a hydroxyl group, a halogen group, an amide group, a sulfone group, a urethane group, or a nitrile group, or an elastomer added with a polar low molecular weight compound having these polar functional groups Should be adopted. Suitable elastomers include silicone rubber, acrylonitrile-butadiene rubber (NBR), hydrogenated acrylonitrile-butadiene rubber (H-NBR), ethylene-propylene-diene rubber (EPDM), acrylic rubber, urethane rubber, epichlorohydrin rubber, chloro Examples thereof include sulfonated polyethylene and chlorinated polyethylene. “Elastomer” means that the base material of the dielectric film is an elastomer. Therefore, other components such as additives may be included in addition to the elastomer component.

  The thickness of the dielectric film may be appropriately determined according to the use of the transducer. For example, in the case of an actuator, it is desirable that the thickness of the dielectric film is small from the viewpoints of downsizing, low potential driving, and increasing the amount of displacement. In this case, it is desirable that the thickness of the dielectric film be 1 μm or more and 1000 μm (1 mm) or less in consideration of the dielectric breakdown property. It is more preferable that the thickness is 5 μm or more and 200 μm or less.

  At least one of the electrode and the wiring is made of the conductive film of the present invention. The configuration of the conductive film of the present invention and the manufacturing method are as described above. Therefore, the description is omitted here. In the transducer of the present invention, it is desirable to employ the preferred embodiment of the conductive film of the present invention described above. Hereinafter, embodiments of an actuator, a capacitive sensor, a power generation element, and a speaker will be described as examples of the transducer of the present invention.

[First embodiment]
An embodiment of an actuator will be described as a first example of the transducer of the present invention. FIG. 1 is a schematic cross-sectional view of the actuator of this embodiment. (A) shows the voltage off state, and (b) shows the voltage on state.

  As shown in FIG. 1, the actuator 1 includes a dielectric film 10, electrodes 11a and 11b, and wirings 12a and 12b. The dielectric film 10 is made of H-NBR. The electrode 11a is disposed so as to cover substantially the entire top surface of the dielectric film 10. Similarly, the electrode 11 b is disposed so as to cover substantially the entire lower surface of the dielectric film 10. The electrodes 11a and 11b are connected to the power supply 13 via wirings 12a and 12b, respectively. The electrodes 11a and 11b are both made of the conductive film of the present invention.

  When switching from the off state to the on state, a voltage is applied between the pair of electrodes 11a and 11b. As the voltage is applied, the thickness of the dielectric film 10 is reduced, and accordingly, as shown by the white arrow in FIG. 1B, the dielectric film 10 extends in a direction parallel to the surfaces of the electrodes 11a and 11b. Thereby, the actuator 1 outputs the driving force in the vertical direction and the horizontal direction in the drawing.

  According to this embodiment, the electrodes 11a and 11b are flexible and extendable. For this reason, the electrodes 11 a and 11 b can expand and contract following the deformation of the dielectric film 10. That is, the movement of the dielectric film 10 is not easily disturbed by the electrodes 11a and 11b. Therefore, according to the actuator 1, a larger force and displacement amount can be obtained. Moreover, in the electrodes 11a and 11b, the electrical resistance hardly increases even if the electrodes 11a and 11b are extended. Therefore, there is little heat_generation | fever by internal resistance and the electrodes 11a and 11b are hard to deteriorate. Therefore, the actuator 1 is excellent in durability. The response of the actuator 1 is also good.

[Second Embodiment]
As a second example of the transducer of the present invention, an embodiment of a capacitive sensor will be described. First, the configuration of the capacitive sensor of this embodiment will be described. FIG. 2 shows a top view of the capacitive sensor. FIG. 3 is a cross-sectional view taken along the line III-III in FIG. As shown in FIGS. 2 and 3, the capacitive sensor 2 includes a dielectric film 20, a pair of electrodes 21a and 21b, wirings 22a and 22b, and cover films 23a and 23b.

  The dielectric film 20 is made of H-NBR and has a strip shape extending in the left-right direction. The thickness of the dielectric film 20 is about 300 μm.

  The electrode 21a has a rectangular shape. Three electrodes 21a are formed on the upper surface of the dielectric film 20 by screen printing. Similarly, the electrode 21b has a rectangular shape. Three electrodes 21b are formed on the lower surface of the dielectric film 20 so as to face the electrode 21a with the dielectric film 20 interposed therebetween. The electrode 21 b is screen-printed on the lower surface of the dielectric film 20. Thus, three pairs of electrodes 21a and 21b are arranged with the dielectric film 20 in between. The electrodes 21a and 21b are made of the conductive film of the present invention.

  The wiring 22a is connected to each of the electrodes 21a formed on the upper surface of the dielectric film 20. The electrode 21a and the connector 24 are connected by the wiring 22a. The wiring 22a is formed on the upper surface of the dielectric film 20 by screen printing. Similarly, the wiring 22b is connected to each of the electrodes 21b formed on the lower surface of the dielectric film 20 (indicated by a dotted line in FIG. 2). The electrode 21b and the connector (not shown) are connected by the wiring 22b. The wiring 22b is formed on the lower surface of the dielectric film 20 by screen printing. The wirings 22a and 22b are made of the conductive film of the present invention.

  The cover film 23a is made of acrylic rubber and has a strip shape extending in the left-right direction. The cover film 23a covers the top surfaces of the dielectric film 20, the electrode 21a, and the wiring 22a. Similarly, the cover film 23b is made of acrylic rubber and has a strip shape extending in the left-right direction. The cover film 23b covers the lower surface of the dielectric film 20, the electrode 21b, and the wiring 22b.

  Next, the movement of the capacitive sensor 2 will be described. For example, when the capacitive sensor 2 is pressed from above, the dielectric film 20, the electrode 21a, and the cover film 23a are united and curved downward. The thickness of the dielectric film 20 is reduced by the compression. As a result, the capacitance between the electrodes 21a and 21b increases. By this capacitance change, deformation due to compression is detected.

  Next, the function and effect of the capacitive sensor 2 of the present embodiment will be described. According to the present embodiment, the dielectric film 20, the electrodes 21a and 21b, the wirings 22a and 22b, and the cover films 23a and 23b are all made of an elastomer material. Therefore, the entire capacitive sensor 2 is flexible and can be expanded and contracted. Further, the electrodes 21 a and 21 b and the wirings 22 a and 22 b can be deformed following the deformation of the dielectric film 20. Furthermore, the electrodes 21a and 21b and the wirings 22a and 22b have high conductivity, and even if they are elongated, their electrical resistance is unlikely to increase. Therefore, the response of the capacitive sensor 2 is good. In the capacitive sensor 2 of the present embodiment, three pairs of electrodes 21a and 21b facing each other with the dielectric film 20 narrowed are formed. However, the number, size, arrangement, etc. of the electrodes may be appropriately determined according to the application.

[Third embodiment]
An embodiment of a power generation element will be described as a third example of the transducer of the present invention. In FIG. 4, the cross-sectional schematic diagram of the electric power generation element in this embodiment is shown. (A) shows the time of expansion, and (b) shows the time of contraction.

  As shown in FIG. 4, the power generating element 3 includes a dielectric film 30, electrodes 31a and 31b, and wirings 32a to 32c. The dielectric film 30 is made of H-NBR. The electrode 31 a is disposed so as to cover substantially the entire top surface of the dielectric film 30. Similarly, the electrode 31 b is disposed so as to cover substantially the entire lower surface of the dielectric film 30. Wirings 32a and 32b are connected to the electrode 31a. That is, the electrode 31a is connected to an external load (not shown) through the wiring 32a. The electrode 31a is connected to a power source (not shown) through the wiring 32b. The electrode 31b is grounded by the wiring 32c. The electrodes 31a and 31b are both made of the conductive film of the present invention.

  4A, when the power generating element 3 is compressed and the dielectric film 30 is extended in a direction parallel to the surfaces of the electrodes 31a and 31b, the thickness of the dielectric film 30 decreases, and the electrode Charge is stored between 31a and 31b. Thereafter, when the compressive force is removed, the dielectric film 30 contracts due to the elastic restoring force of the dielectric film 30 as shown in FIG. At this time, the stored charge is released through the wiring 32a.

  According to this embodiment, the electrodes 31a and 31b are flexible and extendable. For this reason, the electrodes 31 a and 31 b can expand and contract following the deformation of the dielectric film 30. That is, the movement of the dielectric film 30 is not easily disturbed by the electrodes 31a and 31b. Further, the electrical resistance of the electrodes 31a and 31b hardly increases even when the electrodes 31a and 31b are extended. For this reason, even when repeatedly deformed, heat generation due to internal resistance is small. Therefore, the power generating element 3 is excellent in durability.

[Fourth embodiment]
An embodiment of a speaker will be described as a fourth example of the transducer of the present invention. First, the configuration of the speaker of this embodiment will be described. FIG. 5 shows a perspective view of the speaker of this embodiment. FIG. 6 is a cross-sectional view taken along the line VI-VI in FIG. As shown in FIGS. 5 and 6, the speaker 4 includes a first outer frame 40a, a first inner frame 41a, a first dielectric film 42a, a first outer electrode 43a, a first inner electrode 44a, One diaphragm 45a, a second outer frame 40b, a second inner frame 41b, a second dielectric film 42b, a second outer electrode 43b, a second inner electrode 44b, a second diaphragm 45b, A bolt 460, eight nuts 461, and eight spacers 462 are provided.

  The first outer frame 40a and the first inner frame 41a are each made of resin and have a ring shape. The first dielectric film 42a is made of H-NBR and has a circular thin film shape. The first dielectric film 42a is stretched between the first outer frame 40a and the first inner frame 41a. That is, the first dielectric film 42a is sandwiched and fixed by the front-side first outer frame 40a and the back-side first inner frame 41a in a state in which a predetermined tension is secured. The first diaphragm 45a is made of resin and has a disk shape. The first diaphragm 45a has a smaller diameter than the first dielectric film 42a. The first diaphragm 45a is disposed approximately at the center of the surface of the first dielectric film 42a.

  The first outer electrode 43a has a ring shape. The first outer electrode 43a is attached to the surface of the first dielectric film 42a. The first inner electrode 44a also has a ring shape. The first inner electrode 44a is adhered to the back surface of the first dielectric film 42a. The first outer electrode 43a and the first inner electrode 44a face away from each other across the first dielectric film 42a. Both the first outer electrode 43a and the first inner electrode 44a are made of the conductive film of the present invention. As shown in FIG. 6, the first outer electrode 43a includes a terminal 430a. The first inner electrode 44a includes a terminal 440a. A voltage is applied to the terminals 430a and 440a from the outside.

  The configuration of the second outer frame 40b, the second inner frame 41b, the second dielectric film 42b, the second outer electrode 43b, the second inner electrode 44b, and the second diaphragm 45b (hereinafter collectively referred to as “second member”). The first outer frame 40a, the first inner frame 41a, the first dielectric film 42a, the first outer electrode 43a, the first inner electrode 44a, the first diaphragm 45a (hereinafter referred to as “first member”). This is the same as the configuration, material, and shape. The arrangement of the second member is symmetrical with the arrangement of the first member in the front and back direction. Briefly, the second dielectric film 42b is made of H-NBR, and is stretched between the second outer frame 40b and the second inner frame 41b. The second diaphragm 45b is disposed substantially at the center of the surface of the second dielectric film 42b. The second outer electrode 43b is printed on the surface of the second dielectric film 42b. The second inner electrode 44b is printed on the back surface of the second dielectric film 42b. Both the second outer electrode 43b and the second inner electrode 44b are made of the conductive film of the present invention. A voltage is applied from the outside to the terminal 430b of the second outer electrode 43b and the terminal 440b of the second inner electrode 44b.

  The first member and the second member are fixed by eight bolts 460 and eight nuts 461 via eight spacers 462. A set of “bolt 460 -nut 461 -spacer 462” is arranged in the circumferential direction of the speaker 4 at a predetermined interval. The bolt 460 penetrates from the surface of the first outer frame 40a to the surface of the second outer frame 40b. The nut 461 is screwed to the penetrating end of the bolt 460. The spacer 462 is made of resin and is mounted around the shaft portion of the bolt 460. The spacer 462 ensures a predetermined interval between the first inner frame 41a and the second inner frame 41b. The back surface of the central portion of the first dielectric film 42a (the back side of the portion where the first diaphragm 45a is disposed) and the back surface of the central portion of the second dielectric film 42b (the back side of the portion where the second diaphragm 45b is disposed). And are joined. Therefore, a biasing force is accumulated in the first dielectric film 42a in the direction indicated by the white arrow Y1a in FIG. Further, an urging force is accumulated in the second dielectric film 42b in the direction indicated by the white arrow Y1b in FIG.

  Next, the movement of the speaker of this embodiment will be described. Through the terminals 430a and 440a and the terminals 430b and 440b, the first outer electrode 43a and the first inner electrode 44a, and the second outer electrode 43b and the second inner electrode 44b are in an initial state (offset state). A predetermined voltage (offset voltage) is applied. When the speaker 4 is in operation, voltages having opposite phases are applied to the terminals 430a and 440a and the terminals 430b and 440b. For example, when the offset voltage + 1V is applied to the terminals 430a and 440a, the thickness of the portion of the first dielectric film 42a disposed between the first outer electrode 43a and the first inner electrode 44a is thin. Become. In addition, the portion extends in the radial direction. At the same time, an antiphase voltage (offset voltage -1 V) is applied to the terminals 430b and 440b. Then, the film thickness of the part arrange | positioned between the 2nd outer electrode 43b and the 2nd inner electrode 44b among the 2nd dielectric films | membranes 42b becomes thick. In addition, the portion contracts in the radial direction. Thus, the second dielectric film 42b is elastically deformed by its own urging force in the direction indicated by the white arrow Y1b in FIG. 6 while pulling the first dielectric film 42a. On the other hand, when the offset voltage + 1V is applied to the terminals 430b and 440b and the reverse phase voltage (offset voltage -1V) is applied to the terminals 430a and 440a, the first dielectric film 42a pulls the second dielectric film 42b. However, it is elastically deformed by its own urging force in the direction indicated by the white arrow Y1a in FIG. In this way, the first diaphragm 45a and the second diaphragm 45b are vibrated to vibrate air and generate sound.

  Next, the effect of the speaker 4 of this embodiment is demonstrated. According to this embodiment, the first outer electrode 43a, the first inner electrode 44a, the second outer electrode 43b, and the second inner electrode 44b (hereinafter referred to as “electrodes 43a, 44a, 43b, 44b” as appropriate) are flexible. It can be expanded and contracted. Therefore, the first outer electrode 43a and the first inner electrode 44a can expand and contract following the deformation of the first dielectric film 42a. Similarly, the second outer electrode 43b and the second inner electrode 44b can expand and contract following the deformation of the second dielectric film 42b. That is, the movement of the first dielectric film 42a and the second dielectric film 42b is not easily hindered by the electrodes 43a, 44a, 43b, and 44b. Therefore, the responsiveness of the speaker 4 is good even in the low frequency region. In addition, the electrodes 43a, 44a, 43b, and 44b are unlikely to increase in electrical resistance even when they are extended. For this reason, even when repeatedly deformed, heat generation due to internal resistance is small. Therefore, the speaker 4 is excellent in durability.

<Flexible wiring board>
The flexible wiring board of this invention is equipped with an elastic member and the wiring arrange | positioned on the surface of this elastic member. The material of the elastic member is not particularly limited. For example, silicone rubber, ethylene-propylene copolymer rubber, natural rubber, styrene-butadiene copolymer rubber, acrylonitrile-butadiene rubber (NBR), acrylic rubber, epichlorohydrin rubber, chlorosulfonated polyethylene, Examples include chlorinated polyethylene, urethane rubber, fluorine rubber, chloroprene rubber, isobutylene isoprene rubber, and various thermoplastic elastomers.

  At least a part of the wiring is made of the conductive film of the present invention. The configuration of the conductive film of the present invention and the manufacturing method are as described above. Therefore, the description is omitted here. Moreover, also in the flexible wiring board of this invention, it is desirable to employ | adopt the suitable aspect of the electrically conductive film of this invention mentioned above. Hereinafter, embodiments of the flexible wiring board of the present invention will be described.

  First, the structure of the flexible wiring board of this embodiment is demonstrated. In FIG. 7, the upper surface transparent view of the flexible wiring board of this embodiment is shown. In FIG. 7, the electrodes and wirings on the back side are indicated by thin lines. As shown in FIG. 7, the flexible wiring board 6 includes an elastic member 60, front-side electrodes 01X to 16X, back-side electrodes 01Y to 16Y, front-side wirings 01x to 16x, back-side wirings 01y to 16y, and front-side wiring connectors. 61 and a backside wiring connector 62.

  The elastic member 60 is made of urethane rubber and has a sheet shape. A total of 16 front side electrodes 01X to 16X are arranged on the upper surface of the elastic member 60. The front side electrodes 01X to 16X each have a strip shape. The front side electrodes 01X to 16X each extend in the X direction (left-right direction). The front-side electrodes 01X to 16X are arranged in the Y direction (front-rear direction) so as to be substantially parallel to each other at a predetermined interval. Similarly, a total of 16 back-side electrodes 01Y to 16Y are arranged on the lower surface of the elastic member 60. The back side electrodes 01Y to 16Y each have a strip shape. The back-side electrodes 01Y to 16Y each extend in the Y direction. The back-side electrodes 01Y to 16Y are arranged in the X direction so as to be substantially parallel to each other at a predetermined interval. As shown by hatching in FIG. 7, a detection unit for detecting a load or the like is formed by a portion where the front side electrodes 01X to 16X and the back side electrodes 01Y to 16Y intersect (overlapping portions) with the elastic member 60 interposed therebetween. Yes.

  A total of 16 front side wirings 01x to 16x are arranged on the upper surface of the elastic member 60. The front side wirings 01x to 16x each have a linear shape. The front side wirings 01x to 16x are made of the conductive film of the present invention. The front wiring connector 61 is disposed at the left rear corner of the elastic member 60. The front side wirings 01x to 16x connect the left ends of the front side electrodes 01X to 16X and the front side wiring connector 61, respectively. Further, the upper surface of the elastic member 60, the front side electrodes 01X to 16X, and the front side wirings 01x to 16x are covered with a front side cover film (not shown) from above.

  A total of 16 back-side wirings 01y to 16y are arranged on the lower surface of the elastic member 60. The back side wirings 01y to 16y each have a linear shape. The back side wirings 01y to 16y are made of the conductive film of the present invention. The back side wiring connector 62 is disposed at the left front corner of the elastic member 60. The back side wirings 01y to 16y connect the front ends of the back side electrodes 01Y to 16Y and the back side wiring connector 62, respectively. Further, the lower surface of the elastic member 60, the back side electrodes 01Y to 16Y, and the back side wirings 01y to 16y are covered with a back side cover film (not shown) from below.

  Each of the front side wiring connector 61 and the back side wiring connector 62 is electrically connected to a calculation unit (not shown). The impedance in the detection unit is input from the front side wirings 01x to 16x and the back side wirings 01y to 16y to the arithmetic unit. Based on this, the surface pressure distribution is measured.

  Next, the effect of the flexible wiring board 6 of this embodiment is demonstrated. According to the present embodiment, the front-side wirings 01x to 16x and the back-side wirings 01y to 16y are each flexible and extendable. For this reason, the front side wirings 01x to 16x and the back side wirings 01y to 16y can be deformed following the deformation of the elastic member 60. Further, the front-side wirings 01x to 16x and the back-side wirings 01y to 16y hardly increase in electrical resistance even if they are extended. For this reason, even when repeatedly deformed, heat generation due to internal resistance is small. Therefore, the flexible wiring board 6 is excellent in durability.

<Electromagnetic wave shield>
The electromagnetic wave shield of the present invention comprises the conductive film of the present invention. The electromagnetic wave shield plays a role in suppressing electromagnetic waves generated inside the electronic device from leaking to the outside or making it difficult for electromagnetic waves from the outside to enter the inside. For example, when an electromagnetic wave shield is disposed on the inner peripheral surface of the casing of the electronic device, the conductive paint for forming the conductive film of the present invention is applied to the inner peripheral surface of the casing of the electronic device and dried. You can do it. Further, an electromagnetic wave shield can be disposed on the capacitive sensor shown as the second embodiment of the transducer. For example, an electromagnetic wave shield may be disposed so as to cover the upper surface of the cover film 23a and the lower surface of the cover film 23b (see FIGS. 2 and 3). In this case, the conductive paint for forming the conductive film of the present invention may be applied to the upper surface of the cover film 23a and the lower surface of the cover film 23b and dried. Furthermore, in the case of arranging as a gasket in a gap between electronic devices, the conductive film of the present invention may be used after being formed into a desired shape.

  Next, the present invention will be described more specifically with reference to examples.

<Synthesis of silver fiber>
[Silver fiber A]
First, 350 ml of ethylene glycol was heated to 150 ° C., 7.5 mg of platinum chloride was added with stirring, and stirred for 1 hour to prepare a first solution. Next, 12 g of polyvinyl pyrrolidone (weight average molecular weight 24,500) and 9 g of silver nitrate were dissolved in 450 ml of ethylene glycol to prepare a second solution. Subsequently, while stirring the first solution at 150 ° C., the second solution was added dropwise to the first solution at a rate of 7.5 ml / min. After completion of the dropwise addition, stirring was further continued at 150 ° C. for 2 hours. Then, the solution was filtered to separate the synthesized silver fiber (the obtained silver fiber is referred to as silver fiber A). Then, silver fiber A was dispersed in butoxyethyl acetate in a wet state without drying to prepare a silver fiber A / butoxyethyl acetate dispersion. In addition, when the silver fiber A was observed separately with a scanning electron microscope (SEM), the length was about 15 μm and the thickness was about 300 nm. Therefore, the aspect ratio of the silver fiber A is 50.

[Silver fiber B]
A silver fiber B is synthesized and a silver fiber B / butoxyethyl acetate dispersion is prepared in the same manner as the synthesis of the silver fiber A except that the stirring time after dropping the second solution is changed to 0.5 hour. did. When the silver fiber B was observed by SEM, the length was about 3 μm and the thickness was about 300 nm. Therefore, the aspect ratio of the silver fiber B is 10.

[Silver fiber C]
A silver fiber C was synthesized in the same manner as the synthesis of the silver fiber A, except that the polyvinyl pyrrolidone (growth regulator) in the second solution was changed to one having a weight average molecular weight of 10,000. / Butoxyethyl acetate dispersion was prepared. When the silver fiber C was observed by SEM, the length was about 15 μm and the thickness was about 600 nm. Therefore, the aspect ratio of the silver fiber C is 25.

[Silver fiber D]
A silver fiber D was synthesized in the same manner as the synthesis of the silver fiber A except that the polyvinyl pyrrolidone (growth regulator) in the second solution was changed to one having a weight average molecular weight of 360,000. / Butoxyethyl acetate dispersion was prepared. When the silver fiber D was observed by SEM, the length was about 12 μm and the thickness was about 40 nm. Therefore, the aspect ratio of the silver fiber D is 300.

[Silver fiber E]
A silver fiber E was synthesized in the same manner as the synthesis of the silver fiber A except that the polyvinyl pyrrolidone (growth regulator) in the second solution was changed to one having a weight average molecular weight of 3,500. / Butoxyethyl acetate dispersion was prepared. When the silver fiber E was observed by SEM, the length was about 6 μm and the thickness was about 1100 nm. Therefore, the aspect ratio of the silver fiber E is about 5.5.

<Preparation of rubber composition>
First, two types of monomers were subjected to suspension polymerization to produce an acrylic rubber polymer. As monomers, n-butyl acrylate (BA) and allyl glycidyl ether (AGE) were used. The blending ratio of the monomer was 98% by mass for BA and 2% by mass for AGE. When the weight average molecular weight of the obtained acrylic rubber polymer was measured by gel permeation chromatography (GPC), it was about 900,000. The Tg of the acrylic rubber polymer was -46 ° C.

  Next, 100 parts by mass of the manufactured acrylic rubber polymer, 1 part by mass of processing aid stearic acid ("Lunac (registered trademark) S30" manufactured by Kao Corporation), and sodium benzoate (Ouchi Shinsei Chemical) as a crosslinking agent 1 part by mass of “Barnock (registered trademark) AB-S” manufactured by Kogyo Co., Ltd. was mixed with a roll kneader. The obtained kneaded material was dissolved in butoxyethyl acetate as a solvent to prepare an acrylic rubber solution (rubber composition).

  Moreover, a thermoplastic urethane elastomer ("Thermoplastic urethane N5193" manufactured by Nippon Polyurethane Industry Co., Ltd.) was prepared as a rubber composition.

<Manufacture of conductive film>
[Examples 1-8, Comparative Examples 3-4, 6]
First, a predetermined amount of any one of the above silver fiber A to E / butoxyethyl acetate dispersion was added to an acrylic rubber solution, and kneaded with a three roll to prepare a conductive paint. Next, the conductive paint was applied to the surface of the acrylic resin substrate by a bar coating method. Thereafter, the base material on which the coating film was formed was allowed to stand in a drying furnace at about 150 ° C. for about 30 minutes to dry the coating film, and the crosslinking reaction was advanced to obtain a conductive film. The thickness of the obtained conductive film was about 20 μm.

[Example 9]
First, a predetermined amount of the above-mentioned silver fiber D / butoxyethyl acetate dispersion was added to a thermoplastic urethane elastomer, and kneaded with a three roll to prepare a conductive paint. Next, the conductive paint was applied to the surface of the acrylic resin substrate by a bar coating method. Thereafter, the base material on which the coating film was formed was allowed to stand in a drying furnace at about 150 ° C. for about 30 minutes, and the coating film was dried to obtain a conductive film. The thickness of the obtained conductive film was about 20 μm.

[Comparative Example 1]
A conductive film having a thickness of about 20 μm was formed from a commercially available silver paste (“Dotite (registered trademark) FA-353N” manufactured by Fujikura Kasei Co., Ltd.).

[Comparative Example 2]
A conductive film having a thickness of about 20 μm was formed from a commercially available silver paste (“DW-250H-5” manufactured by Toyobo Co., Ltd.).

[Comparative Example 5]
In the synthesis of the silver fiber A, the silver fiber A separated from the solution by filtration was completely dried. After drying, the obtained silver fiber A powder was directly added to the acrylic rubber solution and kneaded with a three-roll to prepare a conductive paint. Thereafter, a conductive film was produced in the same manner as in Examples 1-8.

In Table 1, the compounding quantity of silver fiber with respect to an acrylic rubber polymer in the electrically conductive film of Examples 1-9, and content of silver fiber are shown. In Table 2, the compounding quantity of silver fiber with respect to an acrylic rubber polymer in the electrically conductive film of Comparative Examples 3-6, and content of silver fiber are shown.

<Evaluation method>
The flexibility and conductivity of the conductive films of Examples and Comparative Examples were evaluated. Hereinafter, each evaluation method will be described.

[Flexibility]
The conductive film was subjected to a tensile test according to JIS K7127 (1999). The shape of the test piece was test piece type 2. The elastic modulus of the conductive film was calculated from the obtained stress-elongation curve. Further, the elongation at break (Eb) of the conductive film was measured according to JIS K 6251 (2004). The shape of the test piece was dumbbell-shaped No. 5.

[Conductivity]
The volume resistivity of the conductive film was measured according to the parallel terminal electrode method of JIS K6271 (2008). The volume resistivity was measured only with the conductive film without using an insulating resin support for supporting the conductive film (test piece). The volume resistivity was measured twice according to the presence or absence of elongation. That is, the measurement was performed once in a natural state (no elongation), and was measured once in an expanded state with an elongation rate of 100%. Here, the expansion rate is a value calculated by the following equation (I).
Elongation rate (%) = (ΔL ₀ / L ₀ ) × 100 (I)
[L ₀ : Distance between marked lines of test piece, ΔL ₀ : Increase due to extension of distance between marked lines of test piece]
<Evaluation results>
The evaluation result of the electrically conductive film of an Example and a comparative example is put together in the said Table 1 and Table 2, and is shown. As shown in Table 1, the conductive films of the examples were all flexible and exhibited good elongation. In particular, for the conductive film of Example 9 using a thermoplastic urethane elastomer, the elongation at break was large. Moreover, all the electrically conductive films of an Example have high electroconductivity in a natural state. And even if it extended | stretched the electrically conductive film of an Example, the increase in electrical resistance was small. Further, when the applicability to a flexible wiring board was evaluated based on whether or not the volume resistivity of the conductive film stretched at a stretch rate of 100% was 1 × 10 ⁻¹ Ω · cm or less, Example These conductive films can be said to be suitable for flexible wiring boards.

  For example, when the conductive films of Examples 1 to 3 were compared, as the silver fiber content decreased, the elastic modulus decreased and the elongation at break increased. Moreover, in the electrically conductive film of Example 3, favorable electroconductivity was maintained even if content of silver fiber was as small as 11.6 vol%. Similar results were obtained for the conductive films of Examples 4 to 6. Moreover, in the Example using an acrylic rubber, about the electrically conductive film of Example 8 in which the thickness of a silver fiber is thinner than other Examples, the increase in the electrical resistance at the time of expansion | extension was the smallest.

  In addition, when the conductive film of Example 2 and the conductive film of Example 7 having the same silver fiber content and different thicknesses are compared, the conductive film of Example 7 having a large silver fiber thickness is electrically conductive. Decreased. The reason for this is thought to be that as the thickness of the silver fiber increases, the number of silver fibers per unit weight of the conductive film decreases, and the number of conductive paths decreases.

  On the other hand, in Table 2, in the conductive film of Comparative Example 5, the electrical resistance at the time of elongation was significantly increased as compared with the conductive films of Examples 2, 5, and 7 having the same silver fiber content. The conductive film of Comparative Example 5 is manufactured using a dried silver fiber. For this reason, it is considered that the silver fibers aggregated in the conductive paint, and the dispersibility of the silver fibers in the elastomer deteriorated.

  Moreover, about the electrically conductive film of the comparative examples 1 and 2 formed from the silver paste, an elasticity modulus is very high and its flexibility is scarce. Therefore, although the electrical conductivity in the natural state is high, the volume resistivity significantly increased during elongation. Moreover, about the electrically conductive film of the comparative examples 3 and 4, content of silver fiber is over 45 vol%. Therefore, the flexibility was poor, and the volume resistivity was remarkably increased during elongation. Moreover, also about the electrically conductive film of the comparative example 6, the volume resistivity increased significantly at the time of expansion | extension compared with the electrically conductive film of Example 1, 4 with the same silver fiber content. The thickness of the silver fiber in the conductive film of Comparative Example 6 exceeds 600 nm. For this reason, it is considered that the number of silver fibers per unit weight of the conductive film is small and the conductive path is not sufficiently formed.

  As described above, by uniformly dispersing metal fibers of a predetermined size in the elastomer, a conductive film that has excellent conductivity even when the metal fiber content is small and does not easily increase electrical resistance when stretched. Can be realized.

  The conductive film of the present invention is suitable for electrodes and wiring of flexible transducers using an elastomer. Further, it is suitable for wiring of a flexible wiring board used for control of movable parts of robots and industrial machines, wearable devices, bendable displays and the like. Furthermore, it is also suitable as an electromagnetic wave shield and a conductive adhesive.

  The conductive film of the present invention is excellent in flexibility and conductivity. For this reason, it can be used for members that require electrical control and flexible contact. For example, it is suitable for an electrode layer and a surface layer in a developing roll, a charging roll, a transfer roll, a paper feeding roll, a toner layer forming member, a cleaning blade, a charging blade and the like used in OA (Office Automation) equipment such as a laser beam printer.

1: Actuator (transducer) 10: Dielectric film 11a, 11b: Electrode 12a, 12b: Wiring 13: Power supply 2: Capacitance type sensor (transducer) 20: Dielectric film 21a, 21b: Electrode 22a, 22b: Wiring 23a, 23b : Cover film 24: connector 3: power generation element (transducer) 30: dielectric film 31a, 31b: electrodes 32a to 32c: wiring 4: speaker (transducer)
40a: first outer frame 40b: second outer frame 41a: first inner frame 41b: second inner frame 42a: first dielectric film 42b: second dielectric film 43a: first outer electrode 43b: second outer electrode 44a: First inner electrode 44b: Second inner electrode 45a: First diaphragm 45b: Second diaphragm 430a, 430b, 440a, 440b: Terminal 460: Bolt 461: Nut 462: Spacer 6: Flexible wiring board 60: Elastic member 61 : Front side wiring connector 62: Back side wiring connector 01X to 16X: Front side electrode 01Y to 16Y: Back side electrode 01x to 16x: Front side wiring 01y to 16y: Back side wiring

Claims (11)

An electrically conductive film containing an elastomer and a metal fiber,
The metal fiber has a length in the longitudinal direction of 1 μm or more, a length in the short direction of 600 nm or less, and an aspect ratio of 10 or more.
Content of this metal fiber is 45 vol% or less when the volume of a conductive film is 100 vol%, The electrically conductive film characterized by the above-mentioned.   The metal fiber synthesized by the chemical reduction method was mixed in a wet state with a metal fiber dispersion in which the rubber polymer of the elastomer component was dispersed in a solvent capable of dissolving, and a rubber composition containing the rubber polymer. The conductive film according to claim 1, which is formed from a conductive paint.   The conductive film according to claim 1, wherein the metal fiber includes silver.   The said elastomer is 1 or more types chosen from the crosslinked rubber bridge | crosslinked without using any of sulfur, a sulfur compound, and an organic peroxide, and a thermoplastic elastomer. Conductive film.   Furthermore, the electrically conductive film in any one of the Claims 1 thru | or 4 containing the corrosion inhibitor which suppresses corrosion of the said metal fiber.   The conductive film according to claim 1, wherein the conductive film is formed on a surface of the elastic member. The elastic member is made of an elastomer,
The conductive film according to claim 6, wherein the elastomer of the elastic member is at least one member selected from a crosslinked rubber that is crosslinked without using any of sulfur, a sulfur compound, and an organic peroxide, and a thermoplastic elastomer. It is a manufacturing method of the electrically conductive film according to claim 1,
Metal fiber for synthesizing a metal fiber having a length in the longitudinal direction of 1 μm or more, a length in the short direction of 600 nm or less, and an aspect ratio of 10 or more in a solution containing the metal compound and a reducing agent capable of reducing the metal compound A synthesis process;
A metal fiber dispersion preparation step of preparing the metal fiber dispersion by dispersing the synthesized metal fiber in a wet state in a solvent capable of dissolving the rubber polymer of the elastomer component;
A conductive film forming step of preparing the conductive paint by mixing the metal fiber dispersion and the rubber composition containing the rubber polymer, and applying the conductive paint and drying to form a conductive film;
The manufacturing method of the electrically conductive film characterized by having. A dielectric film made of an elastomer, a plurality of electrodes arranged via the dielectric film, and a wiring connected to each of the plurality of electrodes,
8. A transducer characterized in that at least one of the electrode and the wiring is made of the conductive film according to claim 1. An elastic member, and wiring disposed on the surface of the elastic member,
A flexible wiring board, wherein at least a part of the wiring is made of the conductive film according to any one of claims 1 to 7.   An electromagnetic wave shield comprising the conductive film according to claim 1.

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