JP5205947B2 - Resin carbon composite material - Google Patents

Description

  The present invention relates to a resin carbon composite material having high heat dissipation, electrical conductivity, electromagnetic wave shielding and strength.

  In the field of electronic equipment, heat dissipation of the heating element is an important issue. In addition, since static electricity and electromagnetic waves cause failure and malfunction of electronic devices, it is strongly required to protect the devices and elements from static electricity and electromagnetic waves.

For heat dissipation of the heat generating element, for example, a heat sink made of copper or aluminum having excellent thermal conductivity is used. Further, as the actual temperature of the heat generating element rises, the use of heat pipes loaded with a cooling liquid is increasing in addition to the heat sink. However, in the above-described heat sink made of metal such as copper or aluminum, it is necessary to make the fin of the heat sink thinner and taller in order to improve heat dissipation. At this time, an eddy current is likely to be generated, and it is necessary to separately shield an electromagnetic wave, which is a factor that hinders the cost increase and thinning of the electronic device.
In addition, since the metal heat dissipation material has a large specific gravity, it is a factor that hinders weight reduction. In addition, metal has a high thermal conductivity and is easy to move the heat of the heating element. On the other hand, it has poor self-heat dissipation and it is difficult to dissipate it even if it absorbs heat. It is necessary to always cool the surface of these metal heat sinks using a cooling fan.

As electromagnetic wave shielding bodies for shielding electromagnetic waves, metal plates, foils, meshes, conductive films, composite materials mixed with conductive fillers, conductive surface treated products such as plating, vapor deposition, and painting are usually used. ing.
Conventionally, separate members have been used for the heat radiation member and the electromagnetic wave shielding member, which has increased the cost and hindered the thickness reduction of the product.

  In order to solve the above-described problems, there are some techniques that shield electromagnetic waves and provide materials having excellent thermal conductivity. For example, Patent Literature 1 and Patent Literature 2 propose a sheet having a multilayer structure including a conductive layer, an insulating layer, and an electromagnetic wave shielding layer. Further, Patent Document 3 proposes a heat conductive sheet in which a small amount of ferrite powder and carbon nanotubes are added to a resin and excellent in heat conductivity and static electricity removing effect.

However, in the sheets of Patent Documents 1 and 2, in order to form a multilayer sheet, the adhesion of each layer becomes a problem. Moreover, since it is necessary to make each layer separately, there exists a problem that it is difficult to make thickness thin and it is difficult to produce the product of complicated shape. Moreover, since it is necessary to make each layer combining, it becomes a factor of a cost increase. Moreover, since these sheets use metal, they are poor in self-heat dissipation and are generally used in combination with a heat sink. In addition, although it has the property of shielding electromagnetic waves, it does not have the property of absorbing electromagnetic waves. Therefore, it is necessary to perform a conductive surface treatment with a metal material on the entire inner surface of the housing, which increases costs.
On the other hand, although the sheet of Patent Document 3 does not have a multilayer structure, the thermal conductivity is 5 W / m · K or less, which does not indicate a value that can be used as a heat sink, and the heat dissipation effect is not sufficient.

  In addition, there is a demand for shielding characteristics in a wide band for shielding electromagnetic waves, but there are many materials that exhibit shielding properties at a specific frequency, but a material that exhibits shielding characteristics in a wide band that exceeds 1 MHz to 1 GHz is found. This is not easy, and there is a demand for a material that is excellent in the effect of lowering heat and exhibits electromagnetic wave shielding properties in a wide band.

Also, plastic composite materials with excellent heat dissipation have been developed. However, plastic materials are easily charged due to their poor electrical conductivity, and the destruction of electronic components due to static electricity is a major problem. There are also materials that increase electrical conductivity by applying or kneading a conductive material to a conventional plastic material, but the volume resistivity is about 10 ⁵ Ω · cm, and sufficient conductivity is not obtained.

In this regard, Patent Document 4 discloses an invention that provides a resin composition having characteristics closer to that of a filler by increasing the filling rate of the filler, and discloses a resin composition using graphite powder as an example of the filler. ing. However, when graphite powder is used, a resin composition having high electrical conductivity is considered to be obtained, but sufficient thermal conductivity can be obtained unless a graphite powder having a volume ratio of 60% by volume or more is used. However, since the strength of the molded body becomes hard and brittle due to a large amount of graphite powder, there is a problem that it is difficult to use it on a part to which an impact is applied.
JP 2001-168573 A JP 10-313191 A JP 2004-47965 A JP 2004-124037 A

  Therefore, an object of the present invention is to provide a material excellent in heat dissipation, electromagnetic wave shielding, electrical conductivity, and impact resistance.

  As a result of various studies to solve the above-mentioned problems, the inventors of the present invention have excellent heat dissipation and shield broadband electromagnetic waves by uniformly mixing carbon fiber and graphite powder into a resin at a certain ratio. In addition, the inventors have succeeded in producing a material having a low electrical resistance value, excellent electrical conductivity, high strength and excellent impact resistance, and solved the above problems.

  That is, the present invention is a resin carbon composite material in which (a) carbon fibers and (b) graphite powder are uniformly dispersed in a resin, and the proportion of (a) in the resin carbon composite material is 10% by volume. It is 60 volume% or less, the ratio of (b) is 10 volume% or more and 60 volume% or less, and the sum total of (a) and (b) is 20 volume% or more and 80 volume% or less. .

  Both carbon fiber and graphite powder are carbon materials, and are excellent in thermal conductivity and electromagnetic wave absorption. Moreover, the graphite powder has high electrical conductivity, and the carbon fiber can increase the strength of the material and improve the impact resistance. By uniformly dispersing graphite powder and carbon fiber in the above proportion in the resin, the graphite powder is uniformly dispersed in the gap between the carbon fibers, a part of the carbon fiber and the graphite powder are in contact, and the carbon fibers are intertwined. As a result, heat dissipation and electrical conductivity can be further improved.

The carbon fiber (a) preferably has a thermal conductivity of 100 W / m · K or more.
Further, by using pitch-based carbon fibers as the carbon fibers, it is possible to further improve the heat dissipation, and further, by using the carbon nanotubes in combination, the electromagnetic wave shielding characteristics can be further improved. Carbon nanotubes are effective even when added in a small amount of 2 to 5%. When the pitch-based carbon fiber and the carbon nanotube are used in combination, the ratio of the pitch-based carbon fiber in the resin carbon composite material is 10% by volume to 50% by volume, and the ratio of the carbon nanotube is 0.1% by volume to 10% by volume. Is preferred.

  Further, if a spherical graphite powder having a fixed carbon content of 95% or more is used as the graphite powder, the heat dissipation can be further improved and the electric resistance value can be reduced. Furthermore, heat dissipation and electromagnetic wave absorption characteristics can be further improved by adding carbon black. At this time, the ratio of the graphite powder in the resin carbon composite material is preferably 10% by volume to 50% by volume, and the ratio of carbon black is preferably 0.1% by volume to 10% by volume.

Molded article comprising the above resin carbon composite material is lighter than metal, by extrusion or injection molding, the products of thin products and complicated shape of the wall thickness can be integrally formed.

  The resin-carbon composite material according to the present invention has excellent heat dissipation and electromagnetic wave shielding properties, and has high conductivity and strength. In particular, the resin carbon composite material according to the present invention has good electromagnetic wave shielding characteristics in a wide band.

The resin used in the present invention may be either a thermoplastic resin or a thermosetting resin. In the thermoplastic resin, a polyolefin resin, a polyamide resin, an elastomer (styrene, olefin, PVC, urethane, ester) , Amide-based) resin, acrylic resin, engineering plastic, etc. are used. In particular, polyethylene, polypropylene, nylon resin, ABS resin, acrylic resin, ethylene acrylate resin, ethylene vinyl acetate resin, polystyrene resin, polyphenylene sulfide resin, polycarbonate resin, polyester elastomer resin, polyamide elastomer resin, and liquid crystal polymer are selected. Among these, nylon resin, polyester elastomer resin, polyamide elastomer resin, ABS resin, polypropylene resin, polyphenylene sulfide resin, and liquid crystal polymer are preferable because of heat resistance and flexibility.
Moreover, an epoxy resin, a melamine resin, a phenol resin, a silicone resin, a urethane resin, etc. are used for a thermosetting resin. Especially, an epoxy resin, a silicone resin, and a urethane resin are suitable from heat resistance and a softness | flexibility.
Dispersants, lubricants, and plasticizers may be added to these resins, and in particular, by using fatty acid esters as the dispersant, the filling rate of carbon fibers and graphite powder can be increased and the characteristics can be improved. .

As the graphite powder, spherical graphite powder or scaly graphite powder can be used. Spherical graphite powder is particularly suitable. Moreover, heat dissipation and an electrical property can be improved more by using the graphite powder whose fixed carbon amount is 95% or more. The average particle diameter of the graphite powder is preferably 0.1 μm or more and 100 μm or less. When the average particle diameter is smaller than 0.1 μm, the specific surface area increases, so that the amount that can be added to the resin decreases, and when the average particle diameter exceeds 100 μm, the powder The gap between them becomes large, and the self-heat dissipation performance decreases. In particular, in terms of characteristics, a preferable average particle size is 0.3 μm or more and 50 μm or less, more preferably 0.5 μm or more and 40 μm or less, and further preferably 1 μm or more and 20 μm or less. In the present specification, the average particle diameter of the powder means an average particle diameter measured by a laser diffraction particle size distribution measuring device.
The graphite powder contained in the resin carbon composite material of the present invention may be one kind or plural kinds, and the ratio of the graphite powder in the material is preferably 10 to 60% by volume in total. If the amount is less than 10% by volume, no effect is seen in the heat dissipation and electromagnetic wave absorption characteristics. More preferably, it is 10 to 50% by volume, and particularly preferably 15 to 40%.

Furthermore, it is preferable to use carbon black having a diameter of nanometer in addition to graphite powder. By adding carbon black, it becomes possible to increase the contact area between carbons, thereby further improving heat dissipation and electromagnetic wave absorption characteristics.
As carbon black, ketjen black having high conductivity is particularly preferable. A preferred average particle size of ketjen black is 1 nm to 100 nm, and a more preferable average particle size is 10 nm to 50 nm.

The carbon fiber according to the present invention preferably has a thermal conductivity of 100 W / m · K or more (more preferably 500 W / m · K or more). In order to maintain high thermal conductivity, it is preferable to use a carbon fiber having a diameter of 1 μm to 50 μm (more preferably a diameter of 3 μm to 20 μm) and an average length of 0.05 mm to 30 mm. . In particular, it is preferable to use carbon fibers having an average length of 0.1 mm to 25 mm (more preferably, an average length of 0.3 mm to 10 mm). Carbon fibers include PAN-based carbon fibers and pitch-based carbon fibers. In the resin carbon composite material according to the present invention, pitch-based carbon fibers and pitch-based ultrahigh modulus carbon fibers are preferable. By using pitch-based carbon fiber, it is possible to further improve heat dissipation. In the present invention, the pitch-based ultrahigh modulus carbon fiber refers to a pitch-based carbon fiber having a tensile modulus of 500 GPa or more.
Furthermore, in addition to the pitch-based carbon fibers (including pitch-based ultrahigh modulus carbon fibers), it is preferable to use a carbon nanomaterial in the form of a filament having a diameter of nanometers (including a tube shape). Examples of preferred carbon nanomaterials include carbon nanotubes or vapor grown carbon fibers. A preferable length of the filamentous carbon nanomaterial is 1 μm or more and 50 μm or less, and a preferable diameter is 5 nm or more and 100 nm or less.
In the present specification, carbon fibers having a diameter of nanometer size (1 to 999 nm) are referred to as “carbon nanomaterials”.
The length of pitch-based carbon fibers, carbon nanotubes, and the like can be measured with an electron microscope, and the diameter can also be measured with an electron microscope. The average diameter and average length can be obtained by image analysis of an electron micrograph and calculating an average value.

  Moreover, in order to improve the wettability of the surface of carbon fiber and graphite powder and resin, when these carbon fiber and graphite powder are subjected to resin coating and coupling treatment, improvement in dispersibility and improvement in material strength can be expected. . In particular, epoxy resin and polyamide resin are suitable for the resin coating, and silane coupling treatment and titanate coupling treatment are suitable for the coupling treatment.

  In the material of the present invention, a preferable ratio of carbon fiber to graphite powder is 80:20 to 20:80, a more preferable ratio is 75:25 to 25:75, and a particularly preferable ratio is 70:30 to 30:70.

Mixing and dispersing of the thermoplastic resin, graphite powder, and carbon fiber can be performed using a heating kneader, a multi-screw extruder, a heating roll, or the like. Further, when a thermosetting resin is used as a base material, a mixer, a vacuum mixer, a multi-screw extruder, or the like can be used.
The obtained material can produce a molded article having a desired shape by injection molding, sheet molding, extrusion molding or press molding. The resulting molded product contains carbon fiber, so it has high strength, and contains a lot of graphite powder, so it prevents carbon fiber from being oriented in one direction during molding, improving the strength of the material evenly and ensuring uniform heat conduction. And absorption of electromagnetic waves can be realized.
In the molding method, in particular, by using an injection molding method, it is possible to mold a molded body having a three-dimensional complex shape at a low temperature with high dimensional accuracy as compared with a material using copper or aluminum as a raw material. Also, a three-dimensional molded product having a thickness of 1 mm or less can be easily molded with fewer burrs than when copper or aluminum is molded by the die casting method.

In order to obtain a material having heat dissipation comparable to aluminum, the amount of resin is preferably 60% by volume or less of the entire material. A preferable amount of the resin is 30 to 60% by volume of the total amount of the material, more preferably 40 to 55% by volume, and particularly preferably 45 to 50% by volume. In particular, by reducing the amount of resin to 50% by volume or less, a molding material comparable to a metallic heat dissipation material can be obtained. If the average particle size of the graphite powder is too small, it is necessary to increase the amount of the resin added. Therefore, the average particle size of the graphite powder is preferably 0.1 to 100 μm.
In particular, a spherical graphite powder having an average particle diameter of 1 μm to 40 μm is calculated and blended so that it can be finely packed, and by adding carbon fiber to this, the amount of resin can be reduced to 50% by volume or less. Thus, a molding material comparable to a metallic heat dissipation material can be obtained. In addition, the presence of carbon fibers randomly in the densely packed graphite powder can reduce the orientation of the carbon fibers produced by sheet molding, injection molding, and extrusion molding, resulting in a molded body using carbon fibers. It is possible to reduce the direction dependency of the easy heat dissipation effect, and at the same time to lower the electrical resistance, and to obtain a uniform electromagnetic wave absorption effect.

Since the resin carbon composite material according to the present invention has a density as small as about 1.5 to 1.8 g / cm ^{3 as} compared with a metal material that has been used as a heat dissipation material or an electromagnetic wave shielding material, By replacing with the material according to the invention, a weight reduction of about 40% compared to aluminum and about 80% compared to copper can be achieved.
In addition, since the carbon fiber and the graphite powder are uniformly dispersed, a molding material having excellent impact resistance can be provided.

  Hereinafter, based on an Example, the material of this invention is demonstrated in detail.

[Preparation of resin carbon composite material]
Table 1 shows the composition of the materials used in the examples. In the case of polybutylene terephthalate (PBT), 260 ° C., 250 ° C. for nylon resin (PA) and 330 ° C. for polyphenylene sulfide (PPS) resin. The mixture was mixed for 10 minutes and sufficiently melted, and then graphite powder and carbon fibers were gradually added and heated and kneaded for 1 hour. The lump taken out was made into a sheet, and then subjected to a pulverizer to obtain a molding material.
Using the obtained molding material, an injection molding machine with a clamping force of 20 tons was used to produce a molded body of 35 mm × 35 mm × thickness 2 mm for the measurement of electrical resistance and heat dissipation characteristics. For measurement of electromagnetic wave shielding properties, a molded body of 100 mm × 100 mm × thickness 1.5 mm was produced and used. For the measurement of bending strength and bending elastic modulus, strip-shaped test pieces having a length of 100 mm and a width of 5 mm were prepared and measured using a universal testing machine.
For the comparative example, a molded body was prepared by the same procedure.

The raw materials used in the examples and comparative examples are as follows.
As the graphite powder, spherical graphite powder (fixed carbon content 98%) having an average particle diameter of 10 μm was used.
Ketjen black EC-600JD having an average particle diameter of 40 nm was used as carbon black.
Carbon fiber includes pitch-based carbon fiber K6331T: 140 W / m · K (average length: 6.3 mm, sizing agent [epoxy resin] attachment rate 2 wt%), pitch-based carbon fiber, pitch-based carbon fiber Mitsubishi Chemical Corporation K223HG: 700 W / m · K (average length: 6 mm, no sizing agent added), which is an elastic carbon fiber, and multi-walled carbon nanotubes (average length: Nanocarbon Technologies), which are carbon nanotubes About 20 μm).

[Measurement of characteristics]
Regarding the measurement of electromagnetic waves, an electromagnetic shielding characteristic of 1 MHz to 1 GHz was measured using a spectrum analyzer R3132 manufactured by Advantest. The electromagnetic wave shielding property shown in the table is transmission loss, and shows a decrease value of the transmission amount in the sheet of the example or the comparative example with the transmission amount in the sheet made of only the corresponding resin as a reference value.
About the measurement of the thermal radiation characteristic, it measured by the method shown below. A copper plate having a width of 15 mm, a thickness of 2 mm, and a length of 100 mm was heated to 80 ° C. using a heat source, and after confirming soaking for 30 minutes, a sample (35 mm square, 2 mm thickness) was placed on the copper plate. The temperature after 30 minutes of the copper plate 5 mm behind the sample was measured.
The electrical resistance value was measured using a four-probe type measuring instrument (DC four-terminal method measuring device manufactured by Mitsubishi Chemical Corporation).
For the measurement of bending strength and flexural modulus, a bending test piece was prepared and tested according to JISK7171.

Table 1 shows the results of the examples and Table 2 shows the results of the comparative examples.

From the measurement results, all the materials according to the present invention are excellent in heat dissipation, with the temperature of the copper plate after 30 minutes being 71 ° C. or less, and excellent in electromagnetic shielding between about 1 MHz and 1 GHz in a wide band of around −30 dB. It was confirmed that the film showed an electromagnetic shielding property. When the copper plate was measured under the same conditions, the heat dissipation characteristic was 71 ° C., and that of aluminum was 73 ° C. It was found that the material according to the present invention has a heat dissipation characteristic (heat absorption effect) equal to or higher than that of aluminum and copper. It was.
Also in the electrical resistance value, the volume specific resistance value is 3 Ω · cm or less in all the examples, and in Examples 3 and 6 to 9, particularly less than 1 Ω · cm, which is a very low value as a resin molding material. It was. Thereby, it turns out that the resin carbon composite material concerning this invention has high electrical conductivity.
In addition, regarding the bending strength and the flexural modulus, results comparable to those of the conventional plastic composite material were obtained.

On the other hand, in the case of a material in which only graphite powder is kneaded with a resin (Comparative Example 1), the bending strength is 100 or less and the bending elastic modulus is 10 or less. Was easily destroyed. Further, the electric resistance value was 10 ² Ω · cm, which was higher than that of the example.
Further, in the case of a material in which only carbon black is kneaded with a resin (Comparative Examples 4 and 5), the average particle diameter is very small and the surface area is large. It was difficult. Moreover, although it was excellent in electrical conductivity, the bending strength of the molded bodies was 100 or less and the bending elastic modulus was 10 or less in Comparative Example 4, and sufficient strength was not obtained.

On the other hand, in the case of a material in which only pitch-based carbon fibers are kneaded with a resin (Comparative Example 2), the fibers are bulky and it is difficult to produce a molding material by reducing the amount of resin added to less than 60% by volume. . Moreover, although the obtained molded article was excellent in strength, the electrical resistance value was as high as 10 ² Ω · cm, and the electrical conductivity was inferior.
Further, in the case of a material in which only carbon nanotubes are kneaded with a resin (Comparative Example 3), the carbon nanotubes are very bulky, and it is difficult to produce a molding material with the amount of resin added being 60% by volume or less. . Moreover, since it is difficult to uniformly disperse the carbon nanotubes, the bending strength of the molded body was as low as 100 or less. Further, the electrical resistance value was as high as 10 ² Ω · cm, and the electrical conductivity was inferior.

  Moreover, even in the case of a material obtained by kneading graphite powder and carbon fiber with a resin, the bending strength was poor when the amount of carbon fiber was less than 10% by volume (Comparative Example 6).

  Further, in each of Comparative Examples 1 to 6, the heat dissipation characteristics were inferior to those of aluminum (73 ° C.), the electromagnetic wave shielding property was as low as −15 dB or less, and the heat radiation characteristics and electromagnetic wave shielding properties were clearly inferior to those of the examples. .

From the above results, it can be seen that the resin-carbon composite material according to the present invention is a resin-carbon composite material that has excellent heat dissipation, high electromagnetic shielding properties, low electrical resistance, high strength, and high impact resistance. .
In addition, since the copper plate emits almost no infrared rays, taking data with infrared thermography makes the measurement temperature much lower than the actual temperature, but with the material according to the present invention, the thermographic temperature and the actual temperature are almost the same. Therefore, it was confirmed that the thermal emissivity is close to 1. For this reason, it is considered that the heat dissipation characteristics of the material according to the present invention (the effect of reducing the heat of the other party [endothermic effect]) are caused by the high self-heat dissipation property (effect of dissipating its own heat) due to thermal radiation.
Moreover, since carbon fiber and graphite powder are excellent in electromagnetic wave absorption characteristics, it is considered that the resin carbon composite material according to the present invention is excellent not only in electromagnetic wave shielding properties but also in electromagnetic wave absorption properties. When electromagnetic waves are incident on the sample, the relationship of incident amount = reflection amount + absorption amount + transmission amount is satisfied, but high electromagnetic wave shielding means that the transmission amount is small, and electromagnetic wave absorption is high. Means not only a small amount of transmission but also a small amount of reflection. Therefore, the resin-carbon composite material according to the present invention, which is considered to have high electromagnetic wave absorbability, can also prevent adverse effects due to reflection interference.

  Since the material according to the present invention has high heat dissipation, electromagnetic wave shielding, and electrical conductivity, it is possible to integrate a plurality of parts conventionally used, and it is excellent in strength, so that the product is thin. Can be achieved. In addition, since the material according to the present invention has electromagnetic wave shielding properties in a wide band, it is also suitable for use only for electromagnetic wave shielding. For example, with the recent development of communication technology, it has been pointed out that electromagnetic waves generated from mobile phones, personal computers, game machines, etc. may adversely affect the human body, but the present invention aims to protect against such electromagnetic waves. It can also be used. In addition, since it is lighter than metal, it is possible to reduce the weight by about 40% by replacing a metal material that has been conventionally used with the material according to the present invention.

Claims (4)

A resin carbon composite material in which (a) carbon fiber having a thermal conductivity of 100 W / m · K or more and (b) spherical graphite powder having a fixed carbon content of 95% or more are uniformly dispersed in a resin, is the ratio 10 to 60% by volume of (a) in the middle, the fraction is 10 to 60 vol% of (b), Ri total from 20 to 80 vol% der in (a) and (b), further The carbon fibers of (a) are pitch-based carbon fibers and carbon nanotubes, the proportion of pitch-based carbon fibers in the resin carbon composite material is 10 to 50% by volume, and the proportion of carbon nanotubes is 0.1 to Resin carbon composite material characterized by being 10% by volume . Furthermore, carbon black is contained, The ratio of the graphite powder in the said resin carbon composite material is 10-50 volume%, The ratio of carbon black is 0.1-10 volume%, It is characterized by the above-mentioned. The resin carbon composite material described. The average length of the pitch-based carbon fibers 0.05Mm～30mm, wherein the average particle size of the graphite powder is approximately 0.1-100 [mu] m, the resin carbon composite according to claim 1 or 2 material. Molding, characterized in that it is manufactured by extrusion or injection molding a resin carbon composite material according to any one of claims 1-3.