JP2014133842A - Conductive resin composition - Google Patents

Abstract

A conductive resin composition having a high electromagnetic shielding effect and excellent tensile properties and moldability is provided.
A conductive resin composition containing a thermoplastic resin, carbon nanotubes, carbon black, and carbon fibers and having a volume resistivity of 1 × 10 ² Ω · cm or less.
[Selection figure] None

Description

  The present invention relates to a conductive resin composition.

  In recent years, with the development of electronic devices and the like, the influence of electromagnetic waves generated from the electronic devices and the like on the human body has become a problem. In order to solve this problem, an electromagnetic shielding material in which a conductive filler is blended with a synthetic resin has been developed. Patent Document 1 discloses a resin composition having electromagnetic wave shielding properties.

  Conventionally, power cables, particularly high-voltage power cables, have a conductive layer prepared to have conductivity inside or outside the insulator for the purpose of relaxing electric field concentration at the insulator interface and preventing partial discharge. It has the provided structure. The conductive layer is generally formed of a resin composition in which a conductive filler is blended with a synthetic resin to impart conductivity. Patent Document 2 discloses a resin composition imparted with conductivity. The resin composition used for this power cable is also required to have electromagnetic shielding properties.

Japanese Patent Laid-Open No. 2004-27017 Special table 2009-521535

  Generally, in the resin composition, it is considered effective to increase the blending amount of the conductive filler in order to improve the electromagnetic wave shielding property. However, when the compounding quantity of a conductive filler is raised, there exists a tendency for the tensile characteristic of a resin composition, a moldability, etc. to fall.

  Then, an object of this invention is to provide the conductive resin composition which has a high electromagnetic shielding effect and was excellent in the tensile characteristic and the moldability.

The present invention relates to a conductive resin composition containing a thermoplastic resin, carbon nanotubes, carbon black, and carbon fibers and having a volume resistivity of 1 × 10 ² Ω · cm or less. As a preferable aspect of the conductive resin composition of the present invention, for example, a conductive material in which the total content of carbon nanotubes, carbon black, and carbon fibers is 0.3 to 80% by mass with respect to the mass of the conductive resin composition. Resin composition; conductive resin composition in which content of carbon nanotube is 0.1 to 20% by mass with respect to mass of conductive resin composition; or content of carbon black in conductive resin composition The conductive resin composition which is 0.1-30 mass% with respect to mass is mentioned.

  According to the present invention, it is possible to provide a conductive resin composition having a high electromagnetic shielding effect and excellent tensile properties and moldability.

The present invention relates to a conductive resin composition containing a thermoplastic resin, carbon nanotubes, carbon black, and carbon fibers and having a volume resistivity of 1 × 10 ² Ω · cm or less. Hereinafter, the conductive resin composition of the present invention will be described.

[Thermoplastic resin]
There is no restriction | limiting in particular in the thermoplastic resin used for this invention, For example, olefin resin, such as polyethylene, a polypropylene, polybutadiene, polyisoprene, a propylene-butene copolymer; Poly (meth) acrylic acid, poly (meth) acrylic ester Acrylic resins synthesized by styrene resins such as polystyrene, acrylonitrile-styrene copolymer, butadiene-styrene copolymer, acrylonitrile-butadiene-styrene copolymer; polyvinylidene chloride, polyvinyl chloride, propylene-chloride Vinyl resins such as vinyl copolymers and ethylene-vinyl acetate copolymers; polyesters such as polyethylene terephthalate and polybutylene terephthalate; polyamides, polyimides, polyamideimides, polyetherimides, polycarbonates, Acetal, polyether sulfone, polyphenylene oxide, polyphenylene sulfide, polysulfone, polyurethane and the like. A thermoplastic resin may be used individually by 1 type, or 2 or more types may be mixed and used for it.

  As the thermoplastic resin, polyethylene, ethylene-vinyl acetate copolymer, and polyvinyl chloride are preferably used from the viewpoints of flexibility, flex resistance, and the like, and ethylene-vinyl acetate copolymer is particularly preferably used.

  A commercially available product can be used as the thermoplastic resin. Examples of polyethylene include “NEO-ZEX2015M” (manufactured by Prime Polymer Co., Ltd.), “Novatech UF423” (manufactured by Nippon Polyethylene Co., Ltd.), “NUC-8000” (manufactured by Nippon Unicar Co., Ltd.), ethylene-vinyl acetate Examples of polymers include “Modic EVA A543” (manufactured by Mitsubishi Chemical Corporation), “V221” (manufactured by Ube Maruzen Polyethylene Co., Ltd.), and examples of polyvinyl chloride, “Kaneka Vinyl K10L” (Co., Ltd.). Kaneka), “TE1300” (manufactured by Taiyo PVC Co., Ltd.), and “Sekisui PVC TS” (manufactured by Tokuyama Sekisui Industry Co., Ltd.).

  As for content of a thermoplastic resin, 20-99.7 mass% is preferable with respect to the mass of a conductive resin composition. From the viewpoint of handling properties, the content is preferably 20% by mass or more, and from the viewpoint of exhibiting characteristics such as conductivity and electromagnetic shielding properties, the content is preferably 99.7% by mass or less, 90 mass% or less is more preferable, and 70 mass% or less is further more preferable.

[carbon nanotube]
The carbon nanotube has a structure in which a graphene sheet composed of a six-membered ring of carbon is formed into a cylindrical shape. The carbon nanotube (CNT) is not particularly limited, and is a multi-wall carbon nanotube (multi-wall nanotube ( MWNT)) can be used. In the present invention, multi-walled carbon nanotubes can be preferably used from the viewpoint of dispersion efficiency. A carbon nanotube may be used individually by 1 type, or 2 or more types may be mixed and used for it.

  In the case of a single layer, the average fiber diameter is preferably 0.5 to 10 nm, more preferably 0.8 to 5 nm, and further preferably 1.0 to 2.5 nm. From the viewpoint of controlling the decrease in conductivity due to kneading, the average fiber diameter is preferably 0.5 nm or more, and from the viewpoint of dispersibility with respect to the matrix (resin), the average fiber diameter is preferably 10 nm or less. . In the case of a multilayer, the average fiber diameter (outer diameter) is preferably 1 to 150 nm, more preferably 5 to 150 nm, and still more preferably 8 to 150 nm. From the viewpoint of controlling the decrease in conductivity due to kneading, the average fiber diameter is preferably 1 nm or more, and from the viewpoint of obtaining good dispersibility in the matrix, the average fiber diameter is preferably 300 nm or less.

  The average fiber length is preferably 0.1 μm or more, more preferably 0.3 μm or more, and further preferably 0.5 μm or more. Considering the crushing of the carbon nanotubes by kneading, the average fiber length is preferably 0.1 μm or more, and from the viewpoint of dispersibility with respect to the matrix, the average fiber length is preferably 500 μm or less.

  The aspect ratio (average fiber length / average fiber diameter) is preferably 15 or more, more preferably 20 or more, and still more preferably 100 or more. From the viewpoint of forming a conductive path, the aspect ratio is preferably 5 or more, and from the viewpoint of dispersibility with respect to the matrix, the aspect ratio is preferably 10,000 or less.

  The aspect ratio is obtained by measuring the length and diameter with a scanning electron microscope (magnification 3 to 100,000 times), and calculating the ratio of the average values. The fiber length is measured by taking an observed image as image data in a CCD camera and then calculating an average fiber length using an image analyzer based on the obtained image data. The measurement of the fiber diameter is performed by randomly extracting the target carbon nanotubes to be measured with respect to the image obtained by observation with an electron microscope, measuring the fiber diameter in the vicinity of the center part, and from the obtained measurement value. The average fiber diameter is calculated.

  Carbon nanotubes obtained by any method can be used. Examples of methods for producing carbon nanotubes include laser ablation, carbon arc, and CVD. In the present invention, carbon nanotubes obtained by a CVD method can be preferably used.

  Commercially available products can be used as the carbon nanotubes. Examples of single-walled carbon nanotubes include “Iso Nanotubes-S” (manufactured by NonIntegris), “CNTS-01” (manufactured by Nanocs), “KH SWCNT HP” (manufactured by KH Chemicals), and two-layer carbon nanotubes For example, “FloTube 2000” (manufactured by CNano), “900-1500” (manufactured by SES research), “D4L1-5” (manufactured by Nano Lab), and an example of three or more layers of carbon nanotubes "VGCF-X" (manufactured by Showa Denko KK), "FLoTube 9000" (manufactured by CNano), and "CNTM15" (manufactured by Nanocs).

  The content of the carbon nanotube is preferably 0.1 to 20% by mass with respect to the mass of the conductive resin composition. From the viewpoint of obtaining an effect of improving conductivity, the content is preferably 0.1% by mass or more, more preferably 5% by mass or more, and further preferably 10% by mass or more. Further, from the viewpoint of maintaining good mechanical properties, the content is preferably 20% by mass or less.

[Carbon black]
Carbon black is not particularly limited, and examples thereof include ketjen black, acetylene black, furnace black, channel black, thermal black, and lamp black. In the present invention, ketjen black and acetylene black are preferably used, and ketjen black is more preferably used from the viewpoint that primary particles are not easily decomposed due to a shear stress applied during kneading. Carbon black may be used individually by 1 type, or 2 or more types may be mixed and used for it.

  The average particle size of the primary particles of carbon black is preferably 10 nm or more, more preferably 20 nm or more, and further preferably 30 nm or more, considering the cohesive strength of carbon black.

  The aspect ratio (major axis / minor axis) of the primary particles is preferably 2 to 100 from the viewpoint that a conductive path can be suitably formed by being interposed between carbon nanotubes or carbon fibers.

  The average particle diameter and the aspect ratio can each be determined by observation using a scanning electron microscope.

DBP oil absorption of carbon black is preferably at least 100 m ² / g, more preferably at least 120 m ² / g, still more preferably at least 150m ² / g. From the viewpoints of dispersibility, workability, etc., the DBP oil supply amount is preferably 300 m ² / g or more. The DBP oil supply amount can be obtained by a measurement method according to JIS K6217-4.

  A commercially available product can be used as the carbon black. Examples of Ketjen Black include “Ketjen Black EC300J” (manufactured by Lion Corporation), “Ketjen Black 600JD” (manufactured by Lion Corporation), and examples of acetylene black “# 3030B” (Mitsubishi Chemical). And Denka Black (made by Denki Kagaku Kogyo Co., Ltd.).

  0.1-30 mass% is preferable with respect to the mass of a conductive resin composition, as for content of carbon black, 0.5-20 mass% is more preferable, and 1-10 mass% is further more preferable. From the viewpoint of conductivity, the content is preferably 0.1% by mass or more, and from the viewpoint of workability, the content is preferably 30% by mass or less.

[Carbon fiber]
In the present invention, carbon fibers other than carbon nanotubes are used as carbon fibers. Examples of carbon fibers include, for example, carbon fibers such as polyacrylonitrile (PAN), isotropic pitch, mesophase pitch, and cellulose. In the present invention, it is preferable to use a PAN-based carbon fiber from the viewpoints of cost, production quantity, and the like. A PAN-based carbon fiber is a polymer obtained by polymerizing polyacrylonitrile (PAN) from an acrylonitrile (AN) monomer to produce a long fiber called “precursor” by a dry-wet or wet-spinning method. The carbon fiber manufactured through the crystallization process, the graphitization process, the surface treatment process, and / or the sizing process. The carbon fiber may be used alone or in combination of two or more.

  The average fiber diameter of the carbon fibers is preferably 10 nm or more, more preferably 50 nm or more, and further preferably 100 nm or more. From the viewpoint of maintaining the structure during processing, the average fiber diameter is preferably 5 nm or more.

  The average fiber length is preferably 5 μm or more, more preferably 10 μm or more, and further preferably 15 μm or more. From the viewpoint of forming a conductive path, the average fiber length is preferably 1 μm or more.

  The aspect ratio (average fiber length / average fiber diameter) is preferably 3 or more, more preferably 5 or more, and still more preferably 10 or more. From the viewpoint of forming a conductive path, the aspect ratio is preferably 2 or more.

  The average fiber diameter, average fiber length, and aspect ratio can each be determined by observation using a scanning electron microscope.

  The carbon fiber may be sized. Examples of sizing agents include sizing agents such as epoxy, urethane, polyamide, and polyester.

  The carbon fiber may have a metal coating. Examples of metal coatings include nickel, copper and the like.

  A commercially available product can be used as the carbon fiber. Examples of carbon fibers include “Trecamild Fiber MLD-1000” (manufactured by Toray Industries, Inc.), “PX30MF” (manufactured by Zoltek), “K223QM” (manufactured by Mitsubishi Plastics), and examples of sized fibers. For example, “Treca Cut Fiber T008-006” (manufactured by Toray Industries, Inc.), “Tenax HT C413” (manufactured by Toho Tenax Co., Ltd.), “Panex 35” (manufactured by Zoltek), and examples of carbon fibers having a metal coating For example, “Tenax HT C903” (manufactured by Toho Tenax Co., Ltd.) is available.

  0.1-30 mass% is preferable with respect to the mass of a conductive resin composition, as for content of carbon fiber, 10-30 mass% is more preferable, and 15-25 mass% is further more preferable. From the viewpoint of obtaining an effect of improving conductivity, the content is preferably 0.1% by mass or more, and from the viewpoint of maintaining good mechanical properties, the content is preferably 30% by mass or less. preferable.

  The total content of carbon nanotubes, carbon black, and carbon fibers is preferably 0.3 to 80% by mass, more preferably 20 to 60% by mass, and 30 to 50% by mass with respect to the mass of the conductive resin composition. Further preferred. From the viewpoint of conductivity and electromagnetic shielding characteristics, the content is preferably 0.3% by mass or more, and from the viewpoint of moldability, the content is preferably 80% by mass or less.

[Optional ingredients]
In addition to the thermoplastic resin, carbon nanotube, carbon black, and carbon fiber, the conductive resin composition of the present invention can contain any component. Examples of optional components include inorganic fillers (talc, kaolin, titanium oxide, potassium titanate, glass fibers, glass flakes), flame retardants (silicone flame retardants, halogen flame retardants, magnesium hydroxide, aluminum hydroxide, Organic phosphate ester, red phosphorus), mold release agent (saturated fatty acid ester, unsaturated fatty acid ester, paraffin wax), colorant (organic dye, pigment), antioxidant (phenolic antioxidant, amine antioxidant) ), UV absorbers (benzotriazole UV absorbers, triazine UV absorbers, benzophenone UV absorbers), antistatic agents, antibacterial agents, antifouling agents, infrared absorbers, anti-coloring agents, dispersants, etc. be able to.

  Especially, it is preferable to use a dispersing agent for the improvement of the dispersibility of a carbon nanotube, carbon black, and a carbon fiber. Examples of the dispersant include acrylic dispersants, fatty acid ester dispersants, polyethylene glycol dispersants, nonionic surfactants, amphiphilic triphenylene derivatives, and pyrene derivatives.

[Volume resistivity]
The conductive resin composition of the present invention has a volume resistivity of 1 × 10 ² Ω · cm or less. Volume resistivity can be measured using the conductive resin composition after molding. Specifically, it may be measured using a molded product obtained by molding a thermoplastic resin, carbon nanotubes, carbon black, and carbon fiber, and optionally mixing arbitrary components. From the viewpoint of obtaining a conductive resin composition having more excellent various characteristics, it is preferably 1 × 10 ⁰ Ω · cm or less, more preferably 1 × 10 ⁻¹ Ω · cm or less. The volume resistivity can be measured by a four-terminal method in room temperature air (25 ± 2 ° C., humidity 50 ± 5%), for example, with a measurement length of about 100 mm.

  In order to bring the volume resistivity within the above range, a method of appropriately adjusting the blending amount of carbon nanotube, ketjen black, and carbon fiber can be taken. For example, by increasing the compounding amount of the carbon nanotube, the volume resistivity can be greatly reduced and the electromagnetic shielding effect can be improved. Further, the volume resistivity can be reduced by increasing the blending amount of carbon black. Furthermore, by increasing the compounding amount of the carbon fiber, the volume resistivity can be reduced and the electromagnetic shielding effect can be improved.

  Carbon nanotubes are known as materials with excellent electrical conductivity, but due to the high aspect ratio, the dispersibility in the resin is inferior and the particles are very small, resulting in a conductive network in the resin. There was a tendency to be difficult to form. In the present invention, as a conductive material, a combination of carbon black and carbon fiber is used in combination with carbon nanotubes, so that the contact between the conductive materials is close and a high electromagnetic shielding effect is obtained without reducing tensile properties and moldability. It is realized. Therefore, the conductive resin composition of the present invention can be preferably used as a shielding material excellent in conductivity, electromagnetic shielding properties, tensile properties, and moldability.

[Method for producing conductive resin composition]
The method for obtaining the conductive resin composition of the present invention is not particularly limited, and a conventionally known method for obtaining a thermoplastic resin composition can be used. In the present invention, a method by melt kneading is preferred. For melt kneading, for example, a uniaxial kneader, a biaxial kneader, a Banbury mixer, a roller, a kneader, or the like can be used.

  As a kneading method, even if a thermoplastic resin and carbon nanotubes, carbon black, and carbon fiber are mixed at once, or a part of the thermoplastic resin is mixed with carbon nanotubes, carbon black, and carbon fiber, The remaining thermoplastic resin may be added and further mixed.

  The temperature at the time of kneading can be set to 150 to 250 ° C., for example, from the viewpoint of lowering the viscosity of the thermoplastic resin.

[Method for Molding Conductive Resin Composition]
The method for molding the conductive resin composition of the present invention is not particularly limited, and a conventionally known method for molding a thermoplastic resin composition can be used. For molding, for example, injection molding, extrusion molding, sheet molding, rotational molding, press molding, or the like can be applied.

[Usage]
The conductive resin composition of the present invention is suitable for electric and electronic parts, machine parts, automobile parts and the like. Particularly preferably, it is used for shielding automobile parts, shielding layers for electric wires, and the like.

  When the molded product obtained from the resin composition of the present invention is used as a substitute for metal, effects such as reduction in product weight, improvement in productivity, and reduction in material cost fluctuation can be obtained.

  Hereinafter, the present invention will be described using examples. The present invention is not limited to the following examples.

(Examples 1-36)
An ethylene-vinyl acetate copolymer (EVA), carbon black, carbon fiber, and carbon nanotube are put in this order into a kneader (KH-1-S, manufactured by Inoue Seisakusho Co., Ltd.) and kneaded at a kneading temperature of 200 ° C. for 9 minutes. As a result, a conductive resin composition was obtained. Thereafter, the conductive resin composition was formed into a sheet shape at a processing temperature of 200 ° C. using a press machine (manufactured by Shindo Metal Industry Co., Ltd., SFA-50) to obtain a sample sheet (150 mm × 150 mm × thickness 1 mm). It was. The blending ratio of each component is as shown in Table 1.

(Comparative Examples 1-29)
In the same manner as in the Examples, a conductive resin composition was obtained using the components shown in Table 2, and formed into a sheet shape.

  The volume resistivity of the conductive resin compositions obtained in the examples and comparative examples was evaluated by the four-terminal method. Specifically, the sheet obtained above was cut into a length of 150 mm and a width of 20 mm to prepare a sample for volume resistivity evaluation. Copper tape (E13CA2020, manufactured by Seiwa Electric Co., Ltd.) was wound around 20 to 25 mm and 40 to 45 mm from both ends of the sample. The volume resistivity was measured in an environment of room temperature 23 ° C. and humidity 50% using a resistance meter (DMM 4040, manufactured by Tektronix) and a measurement electrode (P-617, manufactured by Kawaguchi Electric).

The conductive resin compositions obtained in Examples and Comparative Examples were evaluated by the following methods.
(1) Tensile properties The sheet obtained above was punched into a dumbbell shape (parallel portion thickness 1 mm x parallel portion width 4 mm, standard distance 20 mm) to prepare a sample for tensile property evaluation. A tensile tester (manufactured by Intesco, IM-20) was used for the measurement.
The evaluation results based on the following criteria are shown in Tables 1 and 2.
Tensile strength ○: 15 MPa or more, Δ: 10 MPa or more and less than 15 MPa, ×: less than 10 MPa Elongation ○: 200% or more, Δ: 100% or more and less than 200%, ×: less than 100%

(2) Electromagnetic wave shielding characteristics Electromagnetic wave shielding characteristics were evaluated by the KEC method. The sheet obtained above was used as a sample for evaluating electromagnetic wave shielding characteristics. The electromagnetic wave shielding characteristics were evaluated by measuring the attenuation (frequency: 500 MHz) of electromagnetic waves transmitted through the sample according to the KEC method. The apparatus used for the measurement is shown below.
Standard signal generator: HP 8648A (manufactured by Hewlett-Packard)
Power amplifier: A250L-SMA (HP8590 manufactured by Agilent)
Preamplifier: EM648A (manufactured by Sonoma INSTRUMENT 310)
EMC analyzer: HP8590 series (manufactured by Hewlett-Packard)
The evaluation results based on the following criteria are shown in Tables 1 and 2.
○: 40 dB or more, Δ: 20 dB or more and less than 40 dB, ×: less than 20 dB

(3) Formability In the above, when the conductive resin composition was formed into a sheet using a press, the formability was evaluated.
The evaluation results based on the following criteria are shown in Tables 1 and 2.
○: Press molding is possible after kneader kneading, X: Press molding is not possible after kneader kneading

(4) Total evaluation The evaluation results based on the following criteria are shown in Tables 1 and 2.
◯: There are no Δ and × in the evaluation results of the above (1) to (3).
X: There exists (triangle | delta) and x in the evaluation result of said (1)-(3).

  As shown in Table 1, the conductive resin compositions of Examples 1 to 36 showed excellent results in all of the electromagnetic shielding effect, tensile properties, and moldability.

Claims (4)

A conductive resin composition comprising a thermoplastic resin, carbon nanotubes, carbon black, and carbon fibers and having a volume resistivity of 1 × 10 ² Ω · cm or less.   The conductive resin composition according to claim 1, wherein the total content of carbon nanotubes, carbon black, and carbon fibers is 0.3 to 80 mass% with respect to the mass of the conductive resin composition.   The conductive resin composition according to claim 1 or 2, wherein the content of the carbon nanotube is 0.1 to 20% by mass with respect to the mass of the conductive resin composition.   Content of carbon black is 0.1-30 mass% with respect to the mass of a conductive resin composition, The conductive resin composition in any one of Claims 1-3.