JP2020180236A - Thermoplastic resin carbon fiber composite material and shielding member shielding millimeter waves - Google Patents

Abstract

To provide a millimeter wave radar device which suppresses reception of millimeter waves reflected from other than a target obstacle, can control shielding performance of a shielding member mounted on a millimeter receiver, and improves detection accuracy.SOLUTION: A thermoplastic resin carbon composite material is composed of a thermoplastic resin carbon fiber composite material containing a thermoplastic resin and a carbon fiber, contains 5-50 wt.% of a carbon fiber, and shields millimeter waves having a ratio of carbon fibers with a fiber length of 0.01-0.5 mm of 60 wt.% or more in the total carbon fiber.SELECTED DRAWING: Figure 1

Description

The present invention relates to a thermoplastic resin carbon fiber composite material that shields millimeter waves and a shielding member using the same.

Millimeter-wave radar is used for the purpose of automatic driving of moving objects such as automobiles and motorcycles and collision prevention. The millimeter-wave radar device is mounted around the outer periphery of an automobile and has a high-frequency module incorporating an antenna for transmitting and receiving radio waves, a control circuit for controlling the radio waves, a housing for accommodating the antenna and the control circuit, and transmitting and receiving radio waves for the antenna. It is equipped with a radar dome that covers the area.

The millimeter-wave radar device configured in this way can detect the relative distance and relative speed to obstacles by transmitting and receiving millimeter waves from the antenna, and can automatically drive moving objects such as automobiles and motorcycles. Contributes to collision prevention.

However, since the antenna that receives the millimeter wave also receives the antenna that is reflected on the road surface other than the target obstacle, the detection accuracy of the device may decrease.

In order to solve such a problem, the millimeter wave radar device of Patent Document 1 is provided with a shielding member that shields radio waves between the antenna and the control circuit. It is disclosed that as a shielding member, a radio wave absorber in which a conductor layer is laminated on either a dielectric loss layer or a magnetic loss layer having a larger dielectric loss than a radar dome is used. Further, as the dielectric loss layer, one made of a carbon material selected from at least one of carbon nanotubes, carbon microcoils, shungite carbon, carbon black, expanded graphite, and carbon fibers is disclosed.

Further, Patent Document 2 discloses a method of improving radio wave shielding property by adjusting the length and concentration of carbon fibers in a thermoplastic resin.

JP-A-2007-74662 JP 2015-7216

The conventional millimeter-wave radio wave shielding performance is only made constant by the concentration of the shielding material in the resin material and the fiber length, and once a shielding member that shields radio waves is installed in the automobile, the shielding ability is increased or decreased. I couldn't. However, it is required to adjust the intensity of millimeter waves due to changes in the external environment such as fine weather, cloudy weather, rainy weather, snowfall, fog, early morning, daytime, evening, nighttime, and inside a tunnel.

That is, the subject of the present invention is to suppress the reception of millimeter waves reflected from obstacles other than the target obstacle in the millimeter wave radar device, make it possible to control the shielding performance of the shielding member attached to the millimeter wave receiving device, and improve the detection accuracy. Is to let.

In order to achieve the above object, the present invention has the following configuration.

It is composed of a thermoplastic resin carbon fiber composite material containing a thermoplastic resin and carbon fibers, and the thermoplastic resin carbon fiber composite material contains 5 to 50% by weight of carbon fibers and has a fiber length of 0.01 to 0.5 mm. A thermoplastic resin carbon fiber composite material that shields millimeter waves and has a certain carbon fiber ratio of 60% by weight or more in the total carbon fibers.

A shielding member made of a thermoplastic resin carbon fiber composite material that shields millimeter waves by stacking two or more of the thermoplastic resin carbon fiber composite materials so that the orientation directions of the carbon fibers intersect at 0 to 90 degrees.

According to the present invention, it is possible to provide a shielding member that controls the shielding of millimeter waves. By controlling the radio wave shielding rate, it is possible to correctly receive millimeter waves required when driving a car and contribute to safe driving of the car. This technology can be applied not only to automobiles, but also to motorcycles, bicycles, aircraft, helicopters, drones, ships, and submersibles.

It is the schematic of the thermoplastic resin carbon fiber composite material which shields a millimeter wave of this invention. It is the schematic of the sea-island structure of the thermoplastic resin carbon fiber composite material which shields a millimeter wave of this invention. It is a schematic diagram which shows the orientation of the carbon fiber of the thermoplastic resin carbon fiber composite material which shields a millimeter wave of this invention. It is a schematic diagram which shows the cross section which cut the thermoplastic resin carbon fiber composite material which shields a millimeter wave of this invention in the vertical direction. It is a schematic diagram which shows the cross section which cut | cut the thermoplastic resin carbon fiber composite material which shields a millimeter wave of this invention in the lateral direction. It is a schematic diagram which shows the cross section which cut in the horizontal direction of the thermoplastic resin carbon fiber composite material which shields a millimeter wave of this invention. It is a schematic diagram which shows the state which irradiated the thermoplastic resin carbon fiber composite material which shields a millimeter wave of this invention with millimeter wave which the orientation of carbon fiber and the linear polarization direction coincided in parallel. It is a schematic diagram which shows the state which irradiated the thermoplastic resin carbon fiber composite material which shields a millimeter wave of this invention, the millimeter wave which the orientation of carbon fiber and the linear polarization direction are orthogonal to 90 °. It is the schematic of the porous structure which processed the plurality of through holes in the thermoplastic resin carbon fiber composite material in this invention.

Hereinafter, the present invention will be described in detail.

The thermoplastic resin carbon fiber composite material of the present invention comprises a thermoplastic resin carbon fiber composite material containing a thermoplastic resin and carbon fibers, and the thermoplastic resin carbon fiber composite material contains 5 to 50% by weight of carbon fibers. However, the proportion of carbon fibers having a fiber length of 0.01 to 0.5 mm is 60% by weight or more in the total carbon fibers, and the millimeter wave is shielded (see FIG. 1).

From the viewpoint of strength, the thermoplastic resin carbon fiber composite material of the present invention contains 5 to 50% by weight of carbon fibers, more preferably 5 to 30% by weight, still more preferably 10 to 30% by weight.

From the viewpoint of moldability, the proportion of carbon fibers having a fiber length of 0.01 to 0.5 mm is 60% by weight or more based on the total carbon fibers. The fiber length is more preferably 0.1 to 0.5 mm, further preferably 0.2 to 0.5 mm.

The carbon fiber having a fiber length of 0.01 to 0.5 mm can be produced by kneading the carbon fiber and the thermoplastic resin with a twin-screw extruder. The fiber length can be adjusted by changing the rotation speed of the screw shaft, the length, thickness, groove depth, groove spacing, kneading speed, and resin temperature of the screw shaft.

The carbon fibers may be PAN-based or pitch-based, have a fiber diameter of 1 to 20 μm, and have a perfect circular or elliptical cross section. The tensile strength is preferably 2 to 4 GPa, and the tensile elastic modulus is preferably 200 to 600 GPa.

In the present invention, the thermoplastic resin carbon fiber composite material has a millimeter wave shielding performance, and the millimeter wave shielding performance is defined as the amount of transmission attenuation in the millimeter wave obtained by the measurement method of the embodiment. It is evaluated by the measurement of.

The millimeter wave in the present invention is an electromagnetic wave having a frequency of 1 to 300 GHz, and the transmission attenuation is preferably -10 dB or more, more preferably -20 dB or more, and -30 dB or more as the shielding performance of the millimeter wave. Is more preferable.

In the present invention, the thermoplastic resin contains at least a first thermoplastic resin and a second thermoplastic resin having different viscosities, and is as high as 20 to 50 ° C. from the melting point, glass transition point, or softening point of the thermoplastic resin. At temperature, the viscosity of the second thermoplastic is 3 to 70 times the viscosity of the first thermoplastic.

The thermoplastic resin carbon fiber composite material has a sea-island structure as shown in FIG. The sea phase is mainly composed of a thermoplastic resin. On the other hand, the island phase is composed of carbon fibers and a thermoplastic resin.

In the present invention, the thermoplastic resin is preferably composed of at least a first resin and a second resin having different viscosities. It is desirable that the difference in viscosity of the thermoplastic resin is 3 to 70 times, more preferably 5 to 20 times, the viscosity of the first thermoplastic resin.

In particular, in order to improve the kneadability of the carbon fiber and the resin due to the difference in viscosity at a predetermined temperature as high as 20 to 50 ° C. from the melting point of the thermoplastic resin, the viscosity of the second thermoplastic resin is that of the viscosity of the first thermoplastic resin. It is preferably 3 to 70 times, more preferably 5 to 20 times.

The low-viscosity first thermoplastic resin improves the adhesion to the carbon fibers, and the high-viscosity second thermoplastic resin improves the strength of the entire material, thereby improving the moldability of the sheet.

In the present invention, the thermoplastic resin is polyamide, polypropylene, acrylonitrile-butadiene-styrene copolymer, or polyphenylene sulfide.

The thermoplastic resin may be a polyolefin (eg, polyethylene, polypropylene (PP), polybutylene), a polystyrene, or a polyamide (eg, nylon 6, nylon 66, nylon 11, nylon 12, nylon 610, aromatic nylon), or Polyimide, polyamideimide, or polycarbonate, or polyester (eg, polyethylene terephthalate, polybutylene terephthalate, polypropylene terephthalate), or polyphenylene sulfide (PPS), polysulfoxide, or polytetrafluoroethylene, acronitrile butadiene styrene copolymer (eg, polyethylene terephthalate, polybutylene terephthalate, polypropylene terephthalate). ABS), polyacetal, polyether, polyether ether ketone, polyoxymethylene may be used. Further, it may be a derivative of the above-mentioned thermoplastic resin, a copolymer of the above-mentioned thermoplastic resin, or a mixture thereof.

In particular, as the thermoplastic resin, polyamide is preferable, nylon 6, nylon 66, a derivative or copolymer thereof, or a mixture containing any of the above is more preferable, and nylon 6 and nylon 66 are even more preferable.

Polyolefins are also preferable, polyethylene, polypropylene, derivatives or copolymers thereof, or mixtures containing any of the above are more preferable, and polyethylene and polypropylene are even more preferable.

Further, acronitrile butadiene styrene copolymer, a derivative or copolymer thereof, or a mixture containing any of the above is also preferable.

Further, polyphenylene sulfide, a derivative or copolymer thereof, or a mixture containing any of the above is also preferable.

In the present invention, in the thermoplastic resin carbon fiber composite material, it is preferable that 60% by weight or more of the carbon fibers are oriented in one direction within 30 ° of the total carbon fibers. That is, as shown in FIG. 3, it is preferable that 60% by weight or more of the total carbon fibers are oriented in one direction within 30 °. It is more preferably oriented in one direction within 15 °, and even more preferably oriented in one direction within 10 °.

The thermoplastic resin carbon fiber composite material in which 60% by weight or more of the carbon fibers are oriented in one direction within 30 ° is melted by a uniaxial extruder using the pellets made of the above-mentioned thermoplastic resin carbon fiber composite material. However, it can be manufactured by extruding it from a die in a certain direction and contact-fixing it to a roll.

In the present invention, the cross sections of the thermoplastic resin carbon fiber composite material cut in the vertical direction, the horizontal direction, and the horizontal direction are shown in FIGS. 4 to 6. In FIG. 4 of the vertical cross section, carbon fibers are visible in the length direction. Further, the cut surface of the carbon fiber can be seen in FIG. 5 in the cross section. Further, in FIG. 6 of the horizontal cross section, the carbon fibers spreading horizontally can be seen in the length direction.

From this, it can be seen that in the present invention, the carbon fibers are oriented in one direction inside the thermoplastic resin carbon fiber composite material.

In the present invention, the thermoplastic resin carbon fiber composite material is compared with the case where the carbon fiber orientation and the linear polarization direction of the millimeter wave are parallel to each other and the carbon fiber orientation and the linear polarization direction of the millimeter wave are 90 ° orthogonal to each other. The amount of transmission attenuation is small by 10 to 50 dB.

The thermoplastic resin carbon fiber composite material of the present invention has a shielding property against millimeter waves in a specific linearly polarized direction, similar to the function of a polarizing plate in visible light.

As shown in FIG. 7, when the orientation of the carbon fibers and the linear polarization direction of the millimeter wave coincide in parallel, the millimeter wave is transmitted. On the other hand, when the orientation of the carbon fibers and the linearly polarized direction of the millimeter wave are orthogonal to each other by 90 ° as shown in FIG. 8, the progress of the millimeter wave is hindered and a shielding property is exhibited.

The millimeter-wave shielding property can be controlled by the thickness of the thermoplastic resin carbon fiber composite material of the present invention and the ratio of carbon fibers.

In the present invention, the thermoplastic resin carbon fiber composite material may be a porous structure having a plurality of through holes, the thickness of the porous structure is 0.05 to 10 mm, the pore diameter of the through holes is 0.1 to 100 mm, and the through holes are penetrated. A porous structure having a total hole opening area of 5 to 75% of the porous structure can be used.

By punching the thermoplastic resin carbon fiber composite material of the present invention, a porous structure having through holes shown in FIG. 9 can be obtained.

The porous structure has a plurality of through holes, the thickness of the porous structure is 0.05 to 10 mm, the hole diameter of the through holes is 0.1 to 100 mm, and the total opening area of the through holes is the porous structure. 5 to 75% of the body.

The hole diameter of the through hole is preferably 0.1 to 100 mm. 1 to 10 mm is more preferable, and 2 to 5 mm is even more preferable. Further, the shape of the hole may be circular, elliptical or polygonal.

Further, a porous structure having through holes can also be obtained by expanding the thermoplastic resin carbon fiber composite material of the present invention.

The porous structure obtained by the expanding process has rhombic or hexagonal through holes, the thickness of the porous structure is 0.05 to 10 mm, and the opening area of one through hole is 0.02 to 39000 mm. ^2. The total opening area of the through holes is 5 to 90% of the porous structure.

The pore opening ratio and the pore size of the porous structure are related to the millimeter wave shielding property. If the pore opening ratio and the pores are small, the shielding property is improved, and if it is too large, unnecessary millimeter waves are transmitted.

Further, if the aperture ratio or the pores are too large, the strength of the porous structure is lowered and damage occurs. Therefore, it is preferable that the total opening area of the through holes is 5 to 75% with respect to the porous structure. It is more preferably 15 to 60%, and even more preferably 30 to 50%.

In the present invention, a shielding member made of a thermoplastic resin carbon fiber composite material that shields millimeter waves by stacking two or more thermoplastic resin carbon fiber composite materials and intersecting the directions of carbon fibers at 0 to 90 degrees. It becomes.

The thermoplastic resin carbon fiber composite material of the present invention is made of a thermoplastic resin carbon fiber composite material that shields millimeter waves by stacking two or more sheets and intersecting the orientation directions of carbon fibers at 0 to 90 degrees. It is preferable to use it as a member.

In the thermoplastic resin carbon fiber composite material of the present invention, since the carbon fibers are oriented in one direction, the millimeter wave of specific linearly polarized light is shielded, but the millimeter wave of non-polarized light is not regular. Millimeter waves pass through the portion where the orientation of the carbon fibers and the linearly polarized light of the millimeter waves match.

Therefore, by stacking two thermoplastic resin carbon fiber composite materials and making one of them orthogonal so that the orientation is 90 degrees, the shielding property of millimeter waves is improved. Further, when three or four sheets are stacked, the shielding property is improved. On the other hand, the transparency of millimeter waves to be transmitted is improved by matching the orientation of carbon fibers with the direction of linearly polarized waves.

Further, the permeability is improved by using the porous structure. Further, it is more effective to stack two or more porous structures, and the shielding property can be controlled by changing the hole size, the hole pitch, the aperture ratio, and the angle.

That is, by using the thermoplastic resin carbon fiber composite material that shields the millimeter wave in the present invention, the reception of the millimeter wave reflected from other than the target obstacle in the millimeter wave radar device is shielded and the laminated heat is laminated. By introducing a mechanism that partially rotates the thermoplastic resin carbon fiber composite material, it is possible to provide a shielding member that can control the shielding property of millimeter waves according to the external environment, which contributes to the safe driving of automobiles. Can be done.

Hereinafter, the present invention will be described in detail based on Examples and Comparative Examples. Unless otherwise specified, the test conditions in each Example and Comparative Example are basically the same as those in Example 1.

(Material used)
(A) Carbon fiber A carbon fiber having a fiber diameter of 7 μm.

(B) First thermoplastic resin B1: Nylon 6 (melting point: 225 ° C., viscosity at 275 ° C.: 80 poise)
B2: PP (polypropylene) (melting point: 170 ° C, viscosity at 220 ° C: 75 poise)
B3: ABS (acrylonitrile butadiene styrene copolymer) (glass transition point (softening point): viscosity at 190 ° C. and 240 ° C.: 490 poise)
B4: PPS (polyphenylene sulfide) (melting point: 285 ° C., viscosity at 335 ° C.: 150 poise).

(C) Second thermoplastic resin C1: Nylon 6 (melting point: 225 ° C., viscosity at 275 ° C.: 1,150 poise)
C2: PP (polypropylene) (melting point: 170 ° C, 220 ° C viscosity: 1,700 poise)
C3: ABS (Acrylonitrile-butadiene-styrene copolymer) (Glass transition point (softening point): Viscosity at 190 ° C. and 240 ° C.: 2,600 poise)
C4: PPS (polyphenylene sulfide) (melting point: 285 ° C., viscosity at 335 ° C.: 8,100 poise)
(D) Pellet of Thermoplastic Resin Carbon Fiber Composite Material D1: Contains 20% by weight of carbon fiber, 50% by weight of the first thermoplastic resin B1, and 30% by weight of the second thermoplastic resin C1.

D2: Contains 5% by weight of carbon fiber, 15% by weight of the first thermoplastic resin B1, and 80% by weight of the second thermoplastic resin C1.

D3: Contains 50% by weight of carbon fiber, 20% by weight of the first thermoplastic resin B1, and 30% by weight of the second thermoplastic resin C1.

D4: Contains 20% by weight of carbon fiber, 50% by weight of the first thermoplastic resin B2, and 30% by weight of the second thermoplastic resin C2.

D5: Contains 20% by weight of carbon fiber, 50% by weight of the first thermoplastic resin B3, and 30% by weight of the second thermoplastic resin C3.

D6: Contains 20% by weight of carbon fiber, 50% by weight of the first thermoplastic resin B4, and 30% by weight of the second thermoplastic resin C4.

(Equipment used for measuring viscosity)
Capillary Rheometer Capillary Graph 1D manufactured by Toyo Seiki Seisakusho
(Equipment used to measure the proportion of carbon fibers with a fiber length of 0.01 to 0.5 mm)
KEYENCE Digital Microscope VHX-5000
PC for image analysis.

(Measuring method for the proportion of carbon fibers with a fiber length of 0.01 to 0.5 mm)
The thermoplastic resin carbon fiber composite material is subjected to combustion treatment or solution extraction treatment to separate only the carbon fibers contained therein, and then only the carbon fibers are photographed with a digital microscope, and the number of carbon fibers for each carbon fiber length is determined by image processing software. The carbon fiber length distribution was determined by measurement.

(Equipment used to measure the proportion of carbon fibers oriented in one direction within 30 °)
Yamato Scientific X-ray CT device TDM1000-IS
PC for orientation analysis.

(Measuring method of the ratio of carbon fibers oriented in one direction within 30 °)
The CT data of the thermoplastic resin carbon fiber composite material was measured with an X-ray CT apparatus, and the orientation direction of the carbon fibers was analyzed with the orientation analysis software.

(Equipment used to measure the transmission attenuation of millimeter waves)
KEYSIGHT network analyzer N5227A
Millimeter wave module WR10-VNAX manufactured by Virginia Dimensions.

(Measurement method of transmission attenuation)
A sample made of a thermoplastic resin carbon fiber composite material is installed between the millimeter wave modules on the transmitting side and the receiving side installed so as to face each other. Millimeter waves of a specific frequency and a specific polarization emitted from the transmission side millimeter wave module pass through the sample and are detected by the reception side millimeter wave module. The transmission attenuation was measured by a network analyzer connected to the receiving millimeter wave module.

(Example 1)
The first thermoplastic resin B1 made of nylon 6, the second thermoplastic resin C1 and the carbon fiber were put into an extruder and heated and kneaded to obtain pellets D1 of the thermoplastic resin carbon fiber composite material.

The pellet D1 is put into an extruder, extruded in a certain direction from a die while melting, and contact-fixed to a roll to form a sheet-shaped thermoplastic resin carbon fiber composite material having a thickness of 0.3 mm, a width of 640 mm, and a length of 1000 mm. I made one.

In the obtained thermoplastic resin carbon fiber composite material, the proportion of carbon fibers having a fiber length of 0.01 to 0.5 mm is 73% by weight, and 84 carbon fibers oriented in one direction within 30 ° are 84. It was% by weight.

Using this thermoplastic resin carbon fiber composite material, the transmission attenuation of the millimeter wave at 70 to 90 GHz was measured so that the orientation of the carbon fiber and the linearly polarized direction of the millimeter wave coincided in parallel. It was 1 dB.

(Example 2)
Using the pellet D1 obtained by the method described in Example 1, a sheet-shaped thermoplastic resin carbon fiber composite material having a thickness of 0.3 mm, a width of 640 mm, and a length of 1000 mm was prepared.

In the obtained thermoplastic resin carbon fiber composite material, the proportion of carbon fibers having a fiber length of 0.01 to 0.5 mm is 74% by weight, and 85 carbon fibers oriented in one direction within 30 ° are 85. It was% by weight.

Using this thermoplastic resin carbon fiber composite material, the transmission attenuation of the millimeter wave at 70 to 90 GHz was measured so that the orientation of the carbon fiber and the linearly polarized direction of the millimeter wave were orthogonal to each other by 90 °. It was 3 dB.

(Example 3)
Using the pellet D2 obtained by the same method as in Example 1, one sheet-shaped thermoplastic resin carbon fiber composite material having a thickness of 0.3 mm, a width of 640 mm, and a length of 1000 mm was prepared.

In the obtained thermoplastic resin carbon fiber composite material, the proportion of carbon fibers having a fiber length of 0.01 to 0.5 mm is 80% by weight, and 81 carbon fibers oriented in one direction within 30 ° are 81. It was% by weight.
Using this thermoplastic resin carbon fiber composite material, the transmission attenuation of millimeter waves at 70 to 90 GHz was measured so that the orientation of the carbon fibers and the linearly polarized direction of the millimeter waves coincided in parallel. It was 8 dB.

(Example 4)
Using the pellet D2 obtained by the same method as in Example 1, one sheet-shaped thermoplastic resin carbon fiber composite material having a thickness of 0.3 mm, a width of 640 mm, and a length of 1000 mm is prepared.
In the obtained thermoplastic resin carbon fiber composite material, the proportion of carbon fibers having a fiber length of 0.01 to 0.5 mm is 82% by weight, and 78 carbon fibers oriented in one direction within 30 ° are produced. It was% by weight.

Using this thermoplastic resin carbon fiber composite material, the transmission attenuation of millimeter waves at 70 to 90 GHz was measured so that the orientation of the carbon fibers and the linearly polarized direction of the millimeter waves were orthogonal to each other by 90 °. It was 7 dB.

(Example 5)
Using the pellet D3 obtained by the same method as in Example 1, one sheet-shaped thermoplastic resin carbon fiber composite material having a thickness of 0.3 mm, a width of 640 mm, and a length of 1000 mm was prepared.

In the obtained thermoplastic resin carbon fiber composite material, the proportion of carbon fibers having a fiber length of 0.01 to 0.5 mm is 76% by weight, and 77 carbon fibers oriented in one direction within 30 ° It was% by weight.

Using this thermoplastic resin carbon fiber composite material, the transmission attenuation of millimeter waves at 70 to 90 GHz was measured so that the orientation of the carbon fibers and the linearly polarized direction of the millimeter waves coincided in parallel. The average was -50 dB or more. It exceeded the measurement limit.

(Example 6)
Using the first thermoplastic resin B2 made of polypropylene, the second thermoplastic resin C2, and the pellet D4 obtained from carbon fiber in the same manner as in Example 1, the thickness is 0.3 mm, the width is 640 mm, and the length is 640 mm. A 1000 mm sheet-shaped thermoplastic resin carbon fiber composite material was prepared.

In the obtained thermoplastic resin carbon fiber composite material, the proportion of carbon fibers having a fiber length of 0.01 to 0.5 mm is 81% by weight, and 79 carbon fibers oriented in one direction within 30 ° It was% by weight.

Using this thermoplastic resin carbon fiber composite material, the transmission attenuation of the millimeter wave at 70 to 90 GHz was measured so that the orientation of the carbon fiber and the linearly polarized direction of the millimeter wave were orthogonal to each other by 90 °. It was 0 dB.

(Example 7)
Using a first thermoplastic resin B3 made of an acrylonitrile butadiene styrene copolymer, a second thermoplastic resin C3, and pellets D5 obtained from carbon fibers in the same manner as in Example 1, the thickness was 0.3 mm. , A sheet-shaped thermoplastic resin carbon fiber composite material having a width of 640 mm and a length of 1000 mm was prepared.

In the obtained thermoplastic resin carbon fiber composite material, the proportion of carbon fibers having a fiber length of 0.01 to 0.5 mm is 78% by weight, and 78 carbon fibers oriented in one direction within 30 ° are 78. It was% by weight.

Using this thermoplastic resin carbon fiber composite material, the transmission attenuation of the millimeter wave at 70 to 90 GHz was measured so that the orientation of the carbon fiber and the linearly polarized direction of the millimeter wave were orthogonal to each other by 90 °. It was 6 dB.

(Example 8)
Using the first thermoplastic resin B4 made of polyphenylene sulfide, the second thermoplastic resin C4, and the pellet D6 obtained from carbon fiber in the same manner as in Example 1, the thickness is 0.3 mm, the width is 640 mm, and the length is long. A sheet-shaped thermoplastic resin carbon fiber composite material having a size of 1000 mm was prepared.

In the obtained thermoplastic resin carbon fiber composite material, the proportion of carbon fibers having a fiber length of 0.01 to 0.5 mm is 76% by weight, and 83 carbon fibers oriented in one direction within 30 ° are produced. It was% by weight.

Using this thermoplastic resin carbon fiber composite material, the transmission attenuation of millimeter waves at 70 to 90 GHz was measured so that the orientation of the carbon fibers and the linearly polarized direction of the millimeter waves were orthogonal to each other by 90 °. It was 5 dB.

(Example 9)
Using the pellet D1 obtained by the method described in Example 1, a sheet-shaped thermoplastic resin carbon fiber composite material having a thickness of 0.5 mm, a width of 640 mm, and a length of 1000 mm was prepared.

The obtained thermoplastic resin carbon fiber composite material was perforated using a punching machine to prepare one porous structure.

In the obtained porous structure, the proportion of carbon fibers having a fiber length of 0.01 to 0.5 mm was 78% by weight, and the proportion of carbon fibers oriented in one direction within 30 ° was 83% by weight. It was.

The shape of the opening of the through hole of the porous structure is a perfect circle with a diameter of 3.0 mm, the distance from the center of the opening to the center of the adjacent opening is 4 mm, and the width between the holes is It was 1 mm. The arrangement of the through holes was a 60 ° staggered arrangement, and the opening ratio was 51.0%.

Using this thermoplastic resin carbon fiber composite material, the transmission attenuation of millimeter waves at 70 to 90 GHz was measured so that the orientation of the carbon fibers and the linearly polarized direction of the millimeter waves were orthogonal to each other by 90 °. It was 8 dB.

(Example 10)
Using the pellet D1 obtained by the method described in Example 1, two sheet-shaped thermoplastic resin carbon fiber composite materials having a thickness of 0.3 mm, a width of 640 mm, and a length of 1000 mm were prepared.

In the obtained thermoplastic resin carbon fiber composite material, the proportion of carbon fibers having a fiber length of 0.01 to 0.5 mm is 75% by weight, and 84 carbon fibers oriented in one direction within 30 ° are 84. It was% by weight.

The two thermoplastic resin carbon fiber composite materials are laminated so that the orientations of the carbon fibers are parallel to each other, and the millimeter waves of 70 to 90 GHz are aligned so that the orientations of the carbon fibers and the linear polarization directions of the millimeter waves are parallel to each other. When the transmission attenuation of the above was measured, it was -27.0 dB on average.

(Example 11)
Using the pellet D1 obtained by the method described in Example 1, two sheet-shaped thermoplastic resin carbon fiber composite materials having a thickness of 0.3 mm, a width of 640 mm, and a length of 1000 mm were prepared.

In the obtained thermoplastic resin carbon fiber composite material, the proportion of carbon fibers having a fiber length of 0.01 to 0.5 mm is 75% by weight, and 84 carbon fibers oriented in one direction within 30 ° are 84. It was% by weight.

Two pieces of the thermoplastic resin carbon fiber composite material are stacked so that the carbon fiber orientations are orthogonal to each other by 90 °, and the carbon fiber orientation of one of the thermoplastic resin carbon fiber composite materials and the linear polarization direction of the millimeter wave coincide in parallel. As a result, the transmission attenuation of the millimeter wave of 70 to 90 GHz was measured and found to be -46.6 dB on average.

(Example 12)
Using the pellet D1 obtained by the method described in Example 1, a sheet-shaped thermoplastic resin carbon fiber composite material having a thickness of 1.0 mm, a width of 640 mm, and a length of 1000 mm was prepared.

In the obtained thermoplastic resin carbon fiber composite material, the proportion of carbon fibers having a fiber length of 0.01 to 0.5 mm is 77% by weight, and 86 carbon fibers oriented in one direction within 30 ° are 86. It was% by weight.

Using this thermoplastic resin carbon fiber composite material, the transmission attenuation of 70 to 90 GHz millimeter waves was measured so that the orientation of the carbon fibers and the linearly polarized direction of the millimeter waves were orthogonal to each other by 90 °. As a result, the average was -50 dB or more. The measurement limit was exceeded.

(Comparative Example 1)
A second thermoplastic resin C1 made of nylon 6 is put into an extruder, extruded in a certain direction from a die while being melted, and contact-fixed to a roll to obtain a sheet having a thickness of 1.0 mm, a width of 640 mm, and a length of 1000 mm. I made one piece of material.

When the transmission attenuation of a millimeter wave of 70 to 90 GHz was measured using this material, it was an average of -2.6 dB.

(Comparative Example 2)
By the method described in Comparative Example 1, one sheet-like material having a thickness of 1.0 mm, a width of 640 mm, and a length of 1000 mm was prepared using a second thermoplastic resin C2 made of polypropylene.
When the transmission attenuation of a millimeter wave of 70 to 90 GHz was measured using this material, it was 1.9 dB on average.

(Comparative Example 3)
By the method described in Comparative Example 1, one sheet-like material having a thickness of 1.0 mm, a width of 640 mm, and a length of 1000 mm was prepared by using a second thermoplastic resin C3 made of an acrylonitrile-butadiene-styrene copolymer. did.

When the transmission attenuation of a millimeter wave of 70 to 90 GHz was measured using this material, it was an average of −2.0 dB.

(Comparative Example 4)
By the method described in Comparative Example 1, one sheet-like material having a thickness of 1.0 mm, a width of 640 mm, and a length of 1000 mm was prepared using a second thermoplastic resin C4 made of polyphenylene sulfide.

When the transmission attenuation of millimeter waves of 70 to 90 GHz was measured using this material, it was an average of −2.5 dB.

Table 1 shows the properties and physical properties of the materials and composite materials used in the above Examples and Comparative Examples.

1 Thermoplastic resin Carbon fiber composite material 2 Sea island structure 3 Carbon fiber 4 First thermoplastic resin 5 Second thermoplastic resin 6 Thermoplastic resin 7 Vertical direction 8 Horizontal direction 9 Horizontal direction 10 Vertical cross section 11 Horizontal cross section 12 Horizontal cross section 13 Carbon fiber orientation 14 Linearly polarized millimeter wave 15 Porous structure 16 Through hole

Claims (8)

It is composed of a thermoplastic resin carbon fiber composite material containing a thermoplastic resin and carbon fibers, and the thermoplastic resin carbon fiber composite material contains 5 to 50% by weight of carbon fibers and has a fiber length of 0.01 to 0.5 mm. A thermoplastic resin carbon fiber composite material that shields millimeter waves and has a carbon fiber ratio of 60% by weight or more in the total carbon fibers. The thermoplastic resin contains at least a first thermoplastic resin and a second thermoplastic resin having different viscosities, and has a high predetermined temperature of 20 to 50 ° C. from the melting point of the thermoplastic resin, the glass transition point, or the softening point. The thermoplastic resin carbon fiber composite material according to claim 1, wherein the viscosity of the second thermoplastic resin is 3 to 70 times the viscosity of the first thermoplastic resin. The thermoplastic resin carbon fiber composite according to claim 1 or 2, wherein the first thermoplastic resin and the second thermoplastic resin are polyamide, polypropylene, acronitrile butadiene styrene copolymer, and polyphenylene sulfide. Material. The heat for shielding millimeter waves according to any one of claims 1 to 3, wherein in the thermoplastic resin carbon fiber composite material, 60% by weight or more of the carbon fibers in the total carbon fibers are oriented in one direction within 30 °. Thermoplastic resin Carbon fiber composite material. In the thermoplastic resin carbon fiber composite material, when the carbon fiber orientation and the linear polarization direction of the millimeter wave are parallel, the transmission attenuation is compared with the case where the carbon fiber orientation and the linear polarization direction of the millimeter wave are orthogonal to each other by 90 °. The thermoplastic resin carbon fiber composite material that shields millimeter waves according to any one of claims 1 to 4, wherein the amount is as small as 10 to 50 dB. The thermoplastic resin carbon fiber composite material is a porous structure having a plurality of through holes, the thickness of the porous structure is 0.05 to 10 mm, the pore diameter of the through holes is 0.1 to 100 mm, and the through holes The thermoplastic resin carbon fiber composite material that shields millimeter waves according to any one of claims 1 to 5, wherein the total opening area is 5 to 75% with respect to the porous structure. By stacking two or more thermoplastic resin carbon fiber composite materials for shielding millimeter waves according to any one of claims 1 to 6 and intersecting the directions of carbon fibers at 0 to 90 degrees, millimeter waves are shielded. A shielding member made of a thermoplastic resin carbon fiber composite material. Thermoplastic resin pellets containing 5 to 50% by weight of carbon fibers in which 60% by weight or more of the total fibers have a fiber length of 0.01 to 0.5 mm are melted by an extruder and oriented in a certain direction from the die. A method for producing a thermoplastic resin carbon fiber composite material that is extruded and contact-fixed to a roll, wherein the thermoplastic resin contains at least a first thermoplastic resin and a second thermoplastic resin having different viscosities, and is thermoplastic. Thermoplasticity in which the viscosity of the second thermoplastic resin is 3 to 70 times the viscosity of the first thermoplastic resin at a predetermined temperature as high as 20 to 50 ° C. from the melting point of the resin, the glass transition point, or the softening point. A method for producing a resin carbon fiber composite material.