Patent Application
20080242772
The present invention relates to a polymeric composition and a molded body having low electric conductivity and high heat radiation.
In consideration of environmental issues such as CO2 reduction, advances are being made in reducing the fuel consumption of automobiles, and in recent years, hybrid vehicles have gained much attention. The spread of fuel cell vehicles and so on is also foreseen in the future. With respect to components related to batteries and motors, many products require low electric conductivity and high heat radiation, and various materials and shapes have been studied with a view to securing both of these characteristics.
However, it is difficult to secure both of these characteristics in a single material for practical use. The reason for this is that high thermal conductivity (which means thermal conductivity is high) is a prerequisite of high heat radiation, but almost all materials in practical use that possess high thermal conductivity also possess high electric conductivity. This will now be described more specifically.
(1) Metals possess both high thermal conductivity and high heat radiation, but also possess high electric conductivity, and therefore without modification, low electric conductivity (preferably electric insulation) cannot be secured. Accordingly, an insulating plate made of resin or the like must be provided separately, leading to problems regarding the low heat radiation of the insulating plate and the weight of the product, which increases in proportion to the weight of the insulating plate. Moreover, the specific gravity of the metal itself is high.
(2) Polymeric materials (resin, rubber) possess low electric conductivity (essentially electric insulation), but also possess low thermal conductivity, and therefore without modification, high heat radiation cannot be secured. Accordingly, the shape of the product must be manipulated (by creating air-transmitting passages) to secure high heat radiation, leading to an increase in the size of the product and a corresponding increase in the required disposal space.
(3) To solve these problems, the following composite materials have been studied.
Japanese Patent Application Publication No. JP-A-2002-88249 describes a composition formed by compounding a polymeric material with a graphitized hydrocarbon containing a boron compound.
Japanese Patent Application Publication No. JP-A-2002-3717 describes a composition formed by compounding silicone rubber with a graphitized carbon fiber and an electrical insulating thermally conductive filler.
Japanese Patent Application Publication No. JP-A-H9-321191 describes a composition formed by compounding a polymeric material with thermally conductive filler particles, the surface of which has been covered with a ceramics-based material.
Japanese Patent Application Publication No. JP-A-H7-145270 describes a composition formed by compounding a polymer such as rubber with an organic compound having a hydroxyl group and a metal oxide or the like.
Japanese Patent Application Publication No. JP-A-H7-111300 describes a composition formed by compounding silicone rubber with boron nitride.
Japanese Patent Application Publication No. JP-A-H7-33983 describes a composition formed by compounding silicone rubber with boron nitride, the surface of which has been covered with amino-modified silicone oil.
Japanese Patent Application Publication No. JP-A-2004-10880 describes a composition formed by compounding liquid silicone or the like with aluminum nitride powder and metal powder.
JP-A-2002-88249, JP-A-2002-3717, JP-A-H9-321191, JP-A-H7-145270, JP-A-H7-111300, JP-A-H7-33983, and JP-A-2004-10880 all describe composite materials in which an attempt is made to secure both low electric conductivity and high heat radiation by filling a filler constituted by a ceramics or the like for achieving high heat radiation into a polymeric material (base material) for achieving low electric conductivity. However, the following problems arise in these composite materials.
(a) High heat radiation cannot be secured unless a considerably large amount of filler is filled (unless the filler is filled at a high density).
(b) A large amount of filler is charged, and therefore the shape of the product is restricted (limited to a sheet form).
(c) The cover may break during mixing so as to expose the conductive part of the filler, and therefore reliability is lacking.
It is an object of the present invention to solve the problems described above by providing a polymeric composition and a molded body capable of securing both low electric conductivity and high heat radiation.
[A] A low electric conductivity, high heat radiation polymeric composition of the present invention comprises a polymeric material, from 10 to 35% by volume of a carbon fiber, and from 1 to 20% by volume of a ceramics.
Aspects of each element of the present invention will be illustrated below using examples.
There are no particular limitations on the polymeric material, but resin, rubber, and a thermoplastic elastomer may be mentioned as examples, and PE (polyethylene), PP (polypropylene), PPS (polyphenylene sulfide), epoxy resin, and silicone rubber are preferably used.
1. Resin: an olefin-based resin such as PP or PE, a styrene-based resin such as PS (polystyrene), a vinyl resin such as PVC (polyvinyl chloride), PPS, LCP (liquid crystal polymer), PBT (polybutylene terephthalate), PET (polyethylene terephthalate), PA (polyamide) such as PA6 (polyamide 6), PTFE (polytetrafluoroethylene), an engineering plastic resin such as POM (polyacetal), or a thermosetting resin such as epoxy resin, phenol resin, or acrylic resin may be mentioned as examples.
2. Rubber: EPDM (ethylene propylene diene copolymer), CR (chloroprene rubber), NBR (butadiene-acrylonitrile rubber), silicone rubber, and the like may be mentioned as examples.
3. Thermoplastic elastomer: olefin-based, styrene-based, vinyl chloride-based, polyester-based, polyurethane-based, polyamide-based, and fluorine-based thermoplastic elastomers may be mentioned as examples.
There are no particular limitations on the polymeric material, but a material having a thermal conductivity of less than 1.0 W/m·K is preferable, and a material having a thermal conductivity of from 0.1 to 0.5 W/m·K is more preferable. More specifically, the materials shown in Table 1 below may be cited as examples. Further, Table 2 shows the thermal conductivity of the carbon fiber and the ceramics.
As regards the relationship between the thermal conductivity of a compound formed by filling (compounding) resin or the like with a ceramics and so on and the thermal conductivity and filling factor of the ceramics and so on, the Bruggeman formula shown below in Formula 1 exists. The thermal conductivity (shown in Table 1) of the resin or the like is smaller than the thermal conductivity (shown in Table 2) of the ceramics and carbon fiber, and therefore the effect of modifying the resin or the like on the thermal conductivity (variation in the thermal conductivity) of a compound formed by filling resin or the like with a ceramics and so on is small.
There are no particular limitations on the carbon fiber, but PAN-based carbon fiber and Pitch-based carbon fiber may be mentioned as examples, and Pitch-based carbon fiber is preferably used.
Typically, PAN-based carbon fiber uses PAN (polyacrylonitrile) fiber as a raw material, and is manufactured by subjecting the PAN fiber to calcination at from 100° C. to 1500° C. in an inert gas followed by carbonization at from 2000° C. to 3000° C.
In PAN-based carbon fiber, the graphite crystals constituting the carbon fiber are small and disposed randomly, and therefore electricity and heat pass through the fiber easily in various directions. Furthermore, PAN-based carbon fiber contains a large number of crystal defects, and therefore the thermal conductivity is lower than that of pitch-based carbon fiber.
Typically, pitch-based carbon fiber uses petroleum tar as a raw material, and is manufactured by compounding the tar with various compounding agents such as a thickening agent, forming strings at from 250 to 400° C., carbonizing the resulting substance at from 1000 to 1500° C. in an inert gas, and then baking the resulting substance at from 2500 to 3000° C.
The graphite crystals in pitch-based carbon fiber are larger than those of PAN-based carbon fiber, arranged favorably in the fiber-length direction, and have fewer defects. Hence, electricity and heat pass through pitch-based carbon fiber easily in the fiber-length direction, and as a result, the thermal conductivity is far higher than that of PAN-based carbon fiber. Note that the thermal conductivity of the pitch-based carbon fiber increases greatly depending on the orientation, to be described below, and the reason for this is that when the fiber-length direction is aligned, the thermal conduction direction is also aligned.
There are no particular limitations on the ceramics, but metal oxides, metal nitrides and metal carbides may be mentioned as examples. Preferred examples thereof include boron nitride, alumina, and aluminum nitride. There are also no particular limitations on the form of the ceramics, but particle form, fiber form and scale form may be mentioned as examples. There are also no particular limitations on the dimensions, but the average particle diameter may be between 5 and 100 μm, for example.
There are no particular limitations on the metal oxide, but alumina (Al2O3), zirconia (ZrO2) and magnesia (MgO) may be mentioned as examples.
There are no particular limitations on the metal nitride, but aluminumnitride (AlN), boronnitride (BN) andsiliconnitride (Si3N4) may be mentioned as examples.
There are no particular limitations on the metal carbide, but silicon carbide (SiC) and boron carbide (B4C) may be mentioned as examples.
The amount of carbon fiber compounded with the polymeric material is from 10 to 35% by volume, and preferably from 15 to 30% by volume, and more preferably from 15 to 25% by volume. When the compound amount is too small, it tends to be impossible to secure a sufficient heat radiation property, and when the compound amount is too large, the low electric conductivity tends to be impaired, and workability tends to lower.
The amount of ceramics compounded with the polymeric material is from 1 to 20% by volume, and preferably from 5 to 15% by volume.
The carbon fiber compounded with the polymeric material may be used after being oriented by a magnetic field or the like. With this orientation, the thermal conductivity can be raised even when the compounding amount of the carbon fiber remains the same, or when the same thermal conductivity is sufficient, the compounding amount of the carbon fiber can be decreased. Orientation indicates a state in which carbon fiber is arranged regularly and in a specific direction within a polymeric material serving as a base material.
The orientation can be confirmed using the following two methods and evaluated using Method 1 in particular, for example.
In carbon fiber, for example, graphite crystals are arranged regularly in a fiber-length direction, and by measuring the azimuth intensity distribution of the graphite crystal (0. 0. 2) surface through X-ray diffraction analysis (as in
Degree of orientation=(180°−full width at half maximum)/180° <Formula 2>
2. Visual Confirmation Through Observation with Microscope Etc.
A molded body is cut along a surface on which the orientation is to be confirmed, and the direction of the carbon fiber is observed using a scanning electron microscope or the like. Note, however, that it is difficult to evaluate the degree of orientation quantitatively from this observation.
There are no particular limitations on the direction in which the carbon fiber in the polymeric material is oriented, but when the molded body includes a plate-form portion, for example, the carbon fiber may be oriented in either direction along the surface of the plate-form portion or in the thickness direction of the plate-form portion.
There are no particular limitations on the method of orienting the carbon fiber, but the following magnetic field method and processing method may be cited as examples.
In this method, a molded body or a molded body serving as a material of the molded body is molded using the low electric conductivity, high heat radiation polymeric composition described above, and the carbon fiber in the polymeric material of the molded body is oriented using a magnetic field when the polymeric material is in a fluid state. The carbon fiber is oriented in the direction of the magnetic field (the direction of the line of magnetic force). Following orientation, the polymeric material is cooled or the like and hardened. There are no particular limitations on the intensity of the magnetic field, but a strong magnetic field of at least 1 T (tesla) is preferable. According to this method, various orientation directions including the orientation direction described above as an example can be realized simply by aligning the orientation direction with the direction of the magnetic field.
Here, there are no particular limitations on the fluid state of the polymeric material, but examples thereof include a molten state, a state prior to cross-linking, and a state prior to polymerization or the like.
In this method, a molded body or a molded body serving as a material of the molded body is molded using the low electric conductivity, high heat radiation polymeric composition described above, and the carbon fiber in the polymeric material of the molded body is oriented by deforming at least a part of the molded body in an elongated manner through processing performed when the polymeric material is in a fluid state. Thus, the carbon fiber is oriented in the elongation direction. Following orientation, the polymeric material is cooled or the like and hardened.
Note that in the methods described above, a molded body serving as a material of the molded body denotes a precursory molded body in a case where a plurality of molding stages is performed, for example a sheet member in a case where a molded body is molded into a three-dimensional shape by subjecting sheet members to vacuum molding or the like.
[B] A low electric conductivity, high heat radiation molded body of the present invention is molded using the low electric conductivity, high heat radiation polymeric composition described above.
There are no particular limitations on the specific products formed by the molded body, but the following products may be mentioned as examples.
(a) An insulating plate 12 or a battery case 13, for insulating battery elements in a battery pack 11 of an electrically driven vehicle such as a hybrid vehicle or a fuel cell vehicle, as shown in
(b) A motor coil insulator/sealing material or the like for the motor of an electrically driven vehicle or the like.
(c) An inverter case for an electrically driven vehicle, a household appliance, or the like.
(d) A radiation sheet, a casing, or the like for a household appliance, personal computer, or the like.
The developmental background and actions of the present invention are as follows.
A carbon fiber has high thermal conductivity (and therefore high heat radiation), and has a reinforcing property in relation to polymeric material, and is therefore suitable for the present invention. However, a carbon fiber also has high electric conductivity, and therefore an object of the present invention was to suppress the electric conductivity of the composition formed by compounding the carbon fiber.
As a result of various investigations, it was found that by combining carbon fiber with various insulating ceramics and compounding the result with a polymeric material, a novel composition exhibiting both low electric conductivity and high heat radiation was obtained.
According to the polymeric composition and molded body of the present invention, both low electric conductivity and high heat radiation can be secured.
The present invention is a low electric conductivity, high heat radiation polymeric composition which comprises a polymeric material compounded with from 15 to 30% by volume of a carbon fiber and from 5 to 15% by volume of a ceramics.
The present invention is also a molded body having low electric conductivity and high heat radiation using this low electric conductivity, high heat radiation polymeric composition.
The following Table 3 shows the composition and physical properties of first through fifteenth examples and first through five comparative examples, which were formed using a polyethylene (PE) resin (manufactured by Sumitomo Chemical Co., Ltd., product name “Sumikasen G807”) as the base polymeric material 1. In the first through fifteenth examples, predetermined amounts of the carbon fiber 2 and ceramics 3 were compounded with the polyethylene resin, and in the first through five comparative examples, predetermined amounts of carbon fiber and so on were compounded with the polyethylene resin.
In the first through eleventh examples, carbon fiber and boron nitride were compounded. In the twelfth through fourteenth examples, carbon fiber and alumina were compounded. In the fifteenth example, carbon fiber and aluminum nitride were compounded.
Meanwhile, in the first comparative example, the polyethylene resin was used alone. In the second and third comparative examples, only carbon fiber was compounded. In the fourth and fifth comparative examples, only boron nitride was compounded. Table 4 below shows the composition and physical properties of sixteenth through forty-third examples and sixth through eighth comparative examples using polypropylene (PP) resin (manufactured by Japan Polypropylene Corporation, product name “Novatec PP”), polyphenylene sulfide (PPS) resin (manufactured by Toray Industries Inc., product name “Torelina A900”), silicone rubber (manufactured by Shin-Etsu Chemical Co., Ltd., product name “KE106”) or bisphenol A-type epoxy resin (manufactured by Refine-Tec, product name “Epo-mount”) instead of polyethylene (PE) resin as the base polymeric material 1.
The base polymeric material used in each of the samples was polypropylene resin in the sixteenth through twenty-fourth examples and the sixth comparative example, PPS resin in the twenty-fifth through thirty-third examples and the seventh comparative example, silicone rubber in the thirty-fourth through forty-second examples and the eighth comparative example, and bisphenol A-type epoxy resin in the forty-third example.
Further, the sixteenth through nineteenth, twenty-fifth through twenty-eighth, and thirty-fourth through thirty-seventh examples employed a compound of carbon fiber and boron nitride, the twentieth through twenty-third, twenty-ninth through thirty-second, thirty-eighth through forty-first, and forty-third examples employed a compound of carbon fiber and alumina, and the twenty-fourth, thirty-third, and forty-second examples employed a compound of carbon fiber and aluminum nitride.
Note that the carbon fiber used in this test is a pitch-based carbon fiber manufactured by Mitsubishi Chemical Functional Products, Inc. under the product name of “Dialead K223HGM” (average particle diameter: Φ10×50 μm), the boron nitride (BN) used in the test is manufactured by GE Specialty Materials under the product name of “PT110” (average particle diameter 50 μm), the alumina (Al2O3) used in the test is manufactured by Denki Kagaku Kogyo under the product name of “DAW10” (average particle diameter 10 μm), and the aluminum nitride (AlN) used in the test is manufactured by Toyo Aluminum under the product name of “FAN-f80” (average particle diameter 80 μm).
The compounded materials of each example and comparative example were mixed by a Segment mixer (model number “KF70V”) of a Laboplastomill manufactured by Toyo Seiki Seisaku-Sho Ltd. under the following conditions: temperature 210° C. (polyethylene resin), 200° C. (polypropylene resin), 320° C. (PPS resin), room temperature (silicone rubber and bisphenol A-type epoxy resin); rotation speed 100 rpm; time 10 minutes; filling rate 70%. Each mixed material was press-molded by a hand press device at a pressure of 20 MPa under the following conditions:
polyethylene resin: at 210° C. for 5 minutes,
polypropylene resin: at 200° C. for 5 minutes,
PPS resin: at 320° C. for 5 minutes,
silicone rubber: at 150° C. for 30 minutes,
bisphenol A-type epoxy resin: at room temperature for 24 hours, whereby a test piece measuring 25 mm×25 mm×(thickness) 2 mm was created.
The physical properties of each test piece were measured using the following method.
A measuring device with the product name of “Xe Flash Analyzer LFA447 Nanoflash”, manufactured by NETZSCH, was used, and measurement was performed at 25° C. (room temperature). The direction of the thermal conductivity corresponds to the thickness direction of the test piece.
When the volume specific resistance was equal to or lower than 106 Ω·cm, a measuring device with the product name of “Loresta GP”, manufactured by Dia Instruments Co., Ltd. was used, and measurement was performed using a four-terminal method. Both the separation direction of the electric current application terminals (the electric current direction) and the separation direction of the potential taps (the potential difference direction) correspond to the thickness direction of the test piece. When the volume specific resistance was higher than 106 Ω·cm, a measuring device with the product name of “Hiresta UP”, manufactured by Dia Instruments Co., Ltd. was used, and measurement was performed using a double ring method (conforming to JISK6911).
All of the example products secure both low electric conductivity (volume specific resistance is equal to or more than 1×102 Ω·cm) and high heat radiation (thermal conductivity is equal to or more than 0.5 W/m·K). On the other hand, the first, and sixth though eighth comparative examples secure low electric conductivity but exhibits poor heat radiation. The second and third comparative examples secure high heat radiation but exhibit extremely poor low electric conductivity. The fourth and fifth comparative examples secure both low electric conductivity and high heat radiation, but are lacking in mechanical strength and are therefore not suitable for practical application.
Note that when evaluating the heat radiation and electric conductivity of the various compound materials, the fact that the required levels of high heat radiation and low electric conductivity differ according to the specific product type of the low electric conductivity, high heat radiation molded body to be molded from the compound materials must be taken into account.
First, a preliminary test was performed to confirm that the carbon fiber could be oriented using a magnetic field. Five compositions, formed by respectively compounding 15% by volume, 25% by volume, 30% by volume and 35% by volume of pitch-based carbon fiber with a polyethylene resin and compounding 15% by volume of pitch-based carbon fiber with 5% by volume of alumina having an average particle diameter of 10 μm, were mixed under similar conditions to those described above and molded into a 25 mm×25 mm×2 mm test piece, whereupon a magnetic field was applied to the compound examples containing 15% by volume, 25% by volume and 35% by volume of carbon fiber and the example containing carbon fiber and alumina (a magnetic field was not applied to the compound example containing 30% by volume of carbon fiber, and a test in which a magnetic field was not applied to the compound example containing 25% by volume of carbon fiber was also performed). More specifically, orientation was performed using the following devices and procedures, as shown in
(1) A cooling type superconducting magnet device (HF10-100VHT), manufactured by Sumitomo Heavy Industries, Ltd., was used as a magnetic field generating unit.
(2) An electric heater 23 was disposed in the lower portion of a space 22 (bore) positioned in a central magnetic field portion of this device 21, and test pieces 24 described above were set on the electric heater 23 one by one such that the test piece thickness direction corresponded to the magnetic field direction (the direction of the magnetic force line).
(3) The test piece 24 was heated in the space by the electric heater 23 to a temperature region (during implementation, 220° C.) for melting polyethylene resin, and the polyethylene resin serving as the base material of the test piece was melted. At this time, the test piece was held so as to maintain the dimensions described above.
(4) The device was activated while maintaining the heating and temperature described above to apply a magnetic field (during implementation, 8 T (tesla)) to the test piece, and the test piece 24 was left within the magnetic field for one hour.
(5) Heating was then halted, and the test piece 24 was left for 0.5 hours to cool naturally so that the polyethylene resin base material of the test piece hardened.
(6) The test piece 24 was extracted from the space 22 in the device 21 and the orientation of the carbon fiber was confirmed.
The orientation of the carbon fiber was confirmed using the following two methods.
The azimuth intensity distribution on the surface of the graphite crystals (0. 0. 2) of the carbon fiber was measured in the manner described above, i.e. through X-ray diffraction analysis using an X-ray diffraction analysis device, in relation to the compound example containing 30% by volume of carbon fiber to which the magnetic field was not applied, the compound example containing 15% by volume of carbon fiber to which the magnetic field was applied, the compound example containing 35% by volume of carbon fiber to which the magnetic field was applied, and the example containing carbon fiber and alumina to which the magnetic field was applied. The measurement results are shown in
The test pieces of the compound example containing 25% by volume of carbon fiber to which the magnetic field was not applied and the compound example containing 25% by volume of carbon fiber to which the magnetic field was applied were cut in the thickness direction, and the thickness direction orientation of the carbon fiber was observed using a scanning electron microscope. The resulting microphotographs are shown in
[Examples in which Carbon Fiber is Oriented]
Having confirmed that the carbon fiber can be oriented favorably in the preliminary test, examples 1a, 2a, 3a, 5a, 6a, 12a, 13a, 14a, and 15a and comparative examples 1a, 2a, 3a, 4a, and 5a were implemented using the same material compositions and molding methods as examples 1, 2, 3, 5, 6, 12, 13, 14, and 15, and comparative examples 1, 2, 3, 4, and 5, respectively, but differing therefrom in that the carbon fiber in the base polymeric material (polyethylene resin) was oriented using a magnetic field. Note that in these examples, the carbon fiber contained therein was particularly well oriented (the degree of orientation determined from the above Formula 2 was from 0.9 to 1).
Orientation using a magnetic field was performed in a similar manner to the preliminary test described above, using the devices and procedures illustrated in
Further, the melt flow rate (MFR) of each sample was measured in compliance with JISK7210-1999 using the “Melt Indexer model P-001”, manufactured by Toyo Seiki Co., Ltd., at a test temperature of 220° C. and a test load of 2.16 kgf (21.18N). The results are shown in Table 6 below.
(B) Base Using Resin or the Like Other than Polyethylene Resin
Similarly to the polyethylene resin samples described above, examples 16a though 43a and comparative examples 6a though 8a were also implemented using the same material compositions and molding methods as examples 16 though 43 and comparative examples 6 though 8, in which the base polymeric material is not polyethylene resin, respectively, but differing therefrom in that the carbon fiber in the base polymeric material was oriented using a magnetic field. To orient the carbon fiber, the polypropylene resin samples and PPS resin samples were heated to 220° C. and 320° C., respectively such that orientation of the carbon fiber was performed in a molten state. While the silicone rubber and bisphenol A-type epoxy resin samples were not heated into a molten state such that orientation of the carbon fiber was performed in a state prior to polymerization or the like. The results are shown in Table 7. Note that orientation method and physical property tests performed were the same as those of the samples having polyethylene resin as the base polymeric material.
Further, measurement of the melt flow rate (MFR) of the samples of examples 16a through 24a and comparative example 6a (using polypropylene resin as the base polymeric material) was performed under the same conditions as the samples having polyethylene resin as the base polymeric material, while the melt flow rate (MFR) of the samples of examples 25a through 33a and comparative example 7a (using PPS resin as the base polymeric material) was measured at a test temperature of 320° C. and a test load of 5 kgf (49.03N) (the other conditions being identical to those of examples using polypropylene resin as the base polymeric material). Further, the viscosity of the samples of examples 34a through 42a and comparative example 8a (using silicone rubber as the base polymeric material) and example 43a (using bisphenol A-type epoxy resin as a base polymeric material) in a state prior to polymerization or the like was measured using an E-type viscosity meter (manufactured by Metoc) The results are shown in Table 7.
By orienting the carbon fiber, the following effects were obtained.
(1) All of the examples secure both low electric conductivity (volume specific resistance is equal to or more than 1×102 Ω·cm) and high heat radiation (thermal conductivity is equal to or more than 0.5 W/m·K).
(2) In examples, a large improvement was achieved in relation to high heat radiation (thermal conductivity). The low electric conductivity in some cases deteriorated slightly, but the required performance was secured.
(3) In comparative example 2a, on the other hand, a large improvement was achieved in relation to high heat radiation, but the low electric conductivity deteriorated further. In comparative example 3a, the low electric conductivity deteriorated further.
(B) Samples Employing a Resin or the Like Other than Polyethylene Resin as the Base Polymeric Material
(1) All of the examples secure both low electric conductivity (volume specific resistance is equal to or more than 1×102 Ω·cm) and high heat radiation (thermal conductivity is equal to or more than 0.5 W/m·K).
(2) In examples having a carbon fiber compound amount from 15 to 30% by volume, the high heat radiation improved. Particularly, in the examples having a carbon fiber compound amount from 15 to 20% by volume, a large improvement was achieved in relation to high heat radiation.
(3) In examples having a carbon fiber compound amount from 15 to 20% by volume (except the thirty-eighth and thirty-ninth examples), the low electric conductivity improved.
The present invention is not limited to the examples described above, and may be modified appropriately for implementation within a scope that does not depart from the spirit of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-080490 | Mar 2007 | JP | national |
| 2008-055563 | Mar 2008 | JP | national |
