JP2006173264A - Radio wave absorbent - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio wave absorbent capable of uniformly attaining a dielectric loss with high accuracy to a high frequency, having excellent workability and capable of being easily formed in a complicated shape, lightweight, superior even in an environment, capable of being preferably used for a box body or the like for electronic equipment, capable of uniformly attaining the dielectric loss with the high accuracy to the high frequency such a radio wave as particularly 2 to 80 GHz, being easily manufactured having high versatility and proper to an industrial manufacturing. <P>SOLUTION: In the radio wave absorbent containing a thermoplastic resin and a carbon component, the content of the carbon component ranges from 30 to 80 mass%. In the radio wave absorbent, the average particle diameter of the carbon component ranges from 15 μm to 1 mm, preferably the carbon component is composed of graphite, the carbon component has a thickness at 0.01 to 1 times to the wavelength of an absorption radio wave, and the frequency of the absorption radio wave ranges from 2 to 80 GHz. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a radio wave absorber, and more particularly to a radio wave absorber that absorbs radio waves having a frequency of 2 to 80 GHz.

  In recent years, with the rapid development of IT society, high-speed processing of electronic devices has progressed, and the operating frequency of ICs such as LSIs and microprocessors has increased. In the communication field, high-speed communication networks using optical fibers have been used, and the next generation 2GHz for multimedia mobile communications, 5.8GHz for ETS (automatic toll collection system) in the field of ITS (Intelligent Tranport System), driving support road system (AHS) that measures the distance between vehicles and informs the driver In-car radar uses 76 GHz radio waves, and it is expected that the range of high-frequency usage will be further expanded in the future. Radio waves tend to emit noise as the frequency increases. On the other hand, malfunctions occur due to deterioration of the noise environment inside electronic devices due to downsizing and increasing the density of electronic devices. Negative effects are also a problem.

  Such electromagnetic wave blocking materials include electromagnetic wave blocking bodies and electromagnetic wave absorbers, and metal materials are generally used for the electromagnetic wave blocking bodies. For example, in a room where precision equipment that hates electromagnetic waves is installed, walls, etc. A metal plate is used to prevent electromagnetic waves from entering the room. In addition, in electronic devices, a plastic casing formed by conducting a conductive treatment on the surface or mixing a conductive material into a resin is used from the viewpoint of freedom of shape and weight reduction.

  In addition, as an electromagnetic wave absorber, a ferrite plate is used, a metal plate is provided with a resistance film made of a conductive loss material having a free space wave impedance value on the surface via an insulator, and is backed by a metal plate. There are also those provided with a dielectric loss material and a magnetic loss material. In such an electromagnetic wave absorber, in theory, the electromagnetic wave is partially reflected on the surface of the electromagnetic wave absorber, and the electromagnetic wave entering the absorber is reflected on the metal surface, and this reflected electromagnetic wave is reflected on the surface of the absorber, that is, A part is emitted to the outside at the interface between the absorber and free space, and is reflected again into the absorber. While this reflection is repeated and multiple reflections occur inside, the electromagnetic wave energy is converted into thermal energy, and the electromagnetic wave loses its energy. On the other hand, the electromagnetic wave reflected on the surface of the electromagnetic wave absorber was reflected on the surface of the absorber due to mutual interference with the electromagnetic wave that entered the interior and reflected on the metal surface and part of the electromagnetic wave emitted from the absorber surface. The sum of the energy density of the electromagnetic wave and the electromagnetic wave emitted from the absorber becomes 0 when viewed from free space. As described above, in the electromagnetic wave absorber, the electromagnetic wave can theoretically be subjected to multiple reflection inside the electromagnetic wave absorber and the energy of the electromagnetic wave can be extinguished by mutual interference of the reflected electromagnetic waves.

  In such an electromagnetic wave absorber, as a dielectric loss material or a magnetic loss material, an electromagnetic wave shielding paint (Patent Document 1) in which graphite powder is mixed in a urethane resin-based paint, or protection from at least one of electrostatic interference and electromagnetic interference A composition capable of forming a conductive protective film on an object to be coated, comprising conductive fine particles and a resin as a binder, wherein the conductive fine particles are a metal, a metal oxide and a carbon-based material. Electrostatic failure using a conductive resin composition that is a fine particle of one or more materials selected from among the above, and the binder resin can be dissolved and removed by a solvent after the formation of the conductive protective film And a method for protecting against electromagnetic interference (Patent Document 2), and a fiber sheet containing synthetic fibers containing conductive powder such as carbon black powder in a layered manner and heat-sealed to each other to absorb the electromagnetic wave Forming A radio wave absorber (Patent Document 3), a radio wave absorber molded body obtained by bonding a conductive material such as carbon black and a powder of an inorganic hollow body with an inorganic adhesive, and a slurry mainly composed of sepiolite bonded thereto. An electromagnetic wave absorber (Patent Document 4) provided with a non-combustible sheet made from paper or an inorganic coating agent layer has been reported. In addition, a radio wave absorber (Patent Document 5) in which expanded graphite having an average particle size of 100 to 400 μm is dispersed in a material exhibiting rubber elasticity, or a binder containing no solvent is used. An electromagnetic wave absorber (Patent Document 6) in which expanded graphite having a particle size of 100 to 400 μm is dispersed is known.

In these radio wave absorbers, those containing a fibrous conductive material have a problem that fibers mixed with the resin are bent or cut, and a uniform dielectric loss cannot be obtained. In addition, dielectric loss and magnetic loss materials that contain metal or carbon black together with the metal have room for improvement in terms of weight reduction, environmental impact, etc. Those containing a carbon component such as have a problem that sufficient dielectric loss cannot be obtained. As a dielectric loss material in which a carbon component such as graphite is contained in a resin, if an attempt is made to increase the content of the carbon component until a sufficient dielectric loss is obtained, the production becomes difficult. For this reason, a radio wave absorber that can be easily manufactured, is suitable for industrial manufacture, and provides a sufficient dielectric loss has not been obtained. In particular, in ETS (automatic toll collection system), it is required to suppress malfunctions due to reflected radio waves with high accuracy, and in particular, dielectric loss can be achieved uniformly and accurately with respect to high frequencies, and manufacturing is possible. There is a need for an easy wave absorber.
JP-A-62-111499 JP 2001-234075 A JP 2004-247720 A JP 2000-82892 A JP 2004-39798 A JP 2004-63578 A

  The object of the present invention is to achieve a dielectric loss uniformly and accurately with respect to a high frequency, can be easily formed into a complicated shape with excellent workability, is lightweight, excellent in environment, and electronic It can be suitably used for equipment casings, etc., and dielectric loss can be achieved uniformly and with high accuracy for radio waves, especially high frequencies such as 2 to 80 GHz, and it is easy to manufacture and highly versatile, suitable for industrial manufacturing It is to provide a radio wave absorber.

  When a carbon component is used as the conductive material of the radio wave absorber, the carbon component content needs to be 30% by mass or more in order to obtain a sufficient dielectric loss in the radio wave absorber. In the process of kneading such a large amount of carbon component in the resin, the mixed state of the carbon component in the kneaded product obtained due to differences in kneading conditions such as shearing force and resin viscosity becomes unstable. As a result, the radio wave absorber has changed, and a radio wave absorber capable of obtaining a stable dielectric loss cannot be manufactured. As a result of intensive studies by the present inventors, the instability of dielectric loss that occurs in the kneaded product due to the difference in kneading conditions when a large amount of carbon component is kneaded with the resin has an average particle size of 15 μm or more with respect to the thermoplastic resin. It has been found that when a carbon component of 1 mm or less is used, the thermoplastic resin to be kneaded and the carbon component are suppressed from becoming high in viscosity and thereby eliminated. By using a carbon component having an average particle size of 15 μm or more and 1 mm or less with respect to the thermoplastic resin, a kneaded product capable of obtaining uniform dielectric loss even if kneading conditions such as shearing force and resin viscosity are different. As a result, the inventors have obtained the knowledge that a stable dielectric loss can be obtained in the radio wave absorber, thereby leading to the present invention.

  That is, the present invention is a radio wave absorber including at least one layer containing a thermoplastic resin and a carbon component, wherein the layer contains 30% by mass to 80% by mass of a carbon component having an average particle diameter of 15 μm to 1 mm. Regarding the radio wave absorber characterized by containing in a range of mass% or less, preferably, the carbon component has d002 in X-ray diffraction of 0.336 nm or more and 0.3470 nm or less, and the crystal size in the a-axis direction is Graphite that is 5 nm or more, in which the carbon component gradually decreases toward the open surface, has a thickness of 0.01 to 1 times the wavelength of the absorbed radio wave, and the frequency of the radio wave to be absorbed is 2 It relates to a radio wave absorber that is ˜80 GHz, and more preferably 5.8 GHz.

  The radio wave absorber of the present invention can achieve a dielectric loss uniformly and accurately with respect to a high frequency, can be easily formed into a complicated shape with excellent workability, is lightweight, and is environmentally friendly. It is also preferable, has high mechanical strength, can be suitably used for a housing of an electronic device, etc., is easy to manufacture, is versatile and suitable for industrial manufacture, and is particularly high for high frequencies of 2 to 80 GHz. Dielectric loss can be achieved with high accuracy.

  The radio wave absorber of the present invention is a radio wave absorber having at least one layer containing a thermoplastic resin and a carbon component, and the layer has 30% by mass of a carbon component having an average particle diameter of 15 μm or more and 1 mm or less. The content is not particularly limited as long as it is contained in the range of 80% by mass or less.

  Examples of the thermoplastic resin used in the radio wave absorber of the present invention include almost all known thermoplastic resins, regardless of whether they are monomeric polymers or copolymers. Such heat-composable resin preferably has a heat distortion temperature of 50 ° C. or higher and 200 ° C. or lower, more preferably 60 ° C. or higher and 180 ° C. or lower. When the heat distortion temperature of the thermoplastic resin is 200 ° C. or lower, a high temperature is not required when kneading carbon, the heating capacity of the apparatus is not excessive, and the thermal decomposition of the resin can be suppressed. If the heat distortion temperature of the thermoplastic resin is 180 ° C. or lower, the above effects can be obtained more remarkably. On the other hand, if the thermoplastic resin has a heat distortion temperature of 50 ° C. or lower, it has a hardness that can be used for the radio wave absorber, and if it is 60 ° C. or higher, such an effect can be obtained more remarkably. Here, the heat distortion temperature indicates a value measured by the test method of ASTM D648.

  Furthermore, the thermoplastic resin used in the present invention preferably has a bending strength of 10 MPa or more, more preferably 30 MPa. When the thermoplastic resin has a bending strength of 10 MPa or more, mechanical strength can be obtained in the radio wave absorber. If the thermoplastic resin has a bending strength of 30 MPa or more, the above effects can be obtained more remarkably. Here, the bending strength indicates a value measured by a test method of ASTM D790.

  Examples of the thermoplastic resin include high density polyethylene (HDPE), low density polyethylene (LDPE), vinyl acetate copolymer resin (EVA), acrylic acid copolymer resin (EAA), and ethyl acrylate copolymer resin (EEA). , Polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), acrylonitrile-butadiene-styrene copolymer resin (ABS), acrylonitrile-styrene copolymer resin (AS), polycarbonate (PC), polyacetal (polyoxymethylene) ) (POM), poly (ethylene terephthalate) (PET), poly (butylene terephthalate) (PBT), polyphenyloxide (PPO), polyamide (PA), polyphenylene sulfide (PPS), polysulfone (PSF), polyether sulfone ( ES), polyether-etherketone (PEEK), polyarylate (PAR), aromatic polyester (POB), aromatic polyamide, polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene copolymer resin (ETFE), tetra Fluoroethylene-perfluoropropylene copolymer resin (FEP), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC), polyvinyl alcohol (PVA), polyvinyl acetate (PVAc), polyvinyl Examples include formal (PVFM), polyvinyl butyral (PVB), polymethyl methacrylate (PMMA), and poly (cellulose acetate) (CA). The thermoplastic resin to be applied are not limited to, or may be a combination of two or more of these.

  The carbon component used in the radio wave absorber of the present invention may contain a trace amount of other atoms as long as the carbon atoms are aggregated regardless of crystalline or amorphous. Examples include fullerene compounds such as graphite, diamond-like carbon, carbon nanotubes, and carbon nanohorns, and amorphous carbon such as carbon black. Among these, graphite or graphite containing carbon as a part thereof is preferable.

  The carbon component may be any of those obtained from coke, such as calcined coke whose degree of graphitization does not reach 100% in addition to graphitized coke whose degree of graphitization is 100%. There may be. As such carbon, a carbon having an interplanar spacing (d002) measured by X-ray crystal structure analysis of 0.3360 nm or more and 0.3470 nm or less and a crystal size in the a-axis direction (La110) of 5 nm or more is preferable, and more preferably Examples thereof include carbon having an interplanar spacing (d002) of 0.3360 nm or more and 0.3450 nm or less and an a-axis direction crystal size (La110) of 7 nm or more. By using such carbon, it is possible to obtain extremely stable dielectric loss with respect to a high frequency of 2 to 80 GHz in the radio wave absorber.

  In the carbon component, the average particle size is 15 μm or more, preferably 30 μm or more, more preferably 50 μm or more. If the average particle diameter of the carbon component is 15 μm or more, stable absorption performance can be obtained in the radio wave absorber, and if it is 30 μm or more, and further 50 μm or more, this effect can be obtained more remarkably. On the other hand, the carbon component has an average particle diameter of 1 mm or less, preferably 0.8 mm or less, more preferably 0.5 mm or less. If the average particle diameter of the carbon component is 1 mm or less, mechanical strength can be obtained in the radio wave absorber, and if it is 0.8 mm or less and further 0.5 mm or less, higher mechanical strength can be obtained.

  In the radio wave absorber of the present invention, the content of the carbon component is 30% by mass or more, preferably 40% by mass or more. If the content of the carbon component in the radio wave absorber is 30% by mass or more, a stable dielectric loss can be obtained in the radio wave absorber, and if it is 40% by mass or more, this effect can be obtained more remarkably. it can. Moreover, content in the electromagnetic wave absorber of a carbon component is 80 mass% or less, Preferably it is 70 mass% or less, More preferably, it is 60 mass% or less. When the content of the carbon component in the radio wave absorber is 80% by mass or less, kneading into the resin does not become difficult and can be easily manufactured, and the mechanical strength of the obtained radio wave absorber is obtained. be able to. If a carbon component is 70 mass% or less and 60 mass% or less, the effect can be acquired more notably.

  In addition to the above components, for example, a rubber component can be added to the layer containing the thermoplastic resin and the carbon component in the radio wave absorber of the present invention in a range that does not inhibit the function of these components. Further, a lubricant, a plasticizer and the like can be contained.

  The layer containing the thermoplastic resin and the carbon component in the radio wave absorber of the present invention is not particularly limited as long as it contains the thermoplastic resin and the carbon component, and is in a sheet form such as a plate, a sheet, or a film. can do.

  The radio wave absorber of the present invention has at least one of the above layers. On the layer containing the thermoplastic resin and the carbon component, a layer having a low carbon component content is directed toward the surface. Thus, it may be laminated in multiple layers so that the content of the carbon component gradually decreases. In the radio wave absorber of the present invention, it is preferable that the carbon component gradually decreases toward the surface, and the content of the carbon component gradually decreases toward the surface, so that stable radio wave absorption can be performed in the radio wave absorber. .

  Such a shape of the radio wave absorber of the present invention may be any shape such as an injection molded product, a sheet, a film, a deformed product, a thermoformed product, and a resin obtained by melt spinning and forming a fiber. It may be a mixture. In addition, the radio wave absorber of the present invention can be applied to a housing of an electronic device.

  In the radio wave absorber of the present invention, the frequency of radio waves to be absorbed can be adjusted by controlling the material of the radio wave absorber, that is, the complex dielectric constant, the thickness, and the layer structure of the material, The frequency of radio waves to be absorbed to which the radio wave absorber of the present invention is applied is preferably 2 to 80 GHz, and particularly preferably 2 to 10 GHz. When the thickness of the radio wave absorber of the present invention that absorbs radio waves of such a frequency is equivalent to 0.01 times or more the wavelength of radio waves to be absorbed, the radio wave absorption performance can be maintained. preferable. More preferably, the thickness of the radio wave absorber is 0.02 or more, more preferably 0.03 or more, the wavelength of the target radio wave. With such a thickness, the above effect can be obtained more remarkably. it can. Further, if the thickness is less than 1 times the wavelength of the radio wave to be absorbed, it is lightweight and easy to handle. The thickness of the radio wave absorber of the present invention is more preferably 0.8 times or less, more preferably 0.5 times or less with respect to the wavelength of the radio wave to be absorbed. By having such a thickness, The above effects can be obtained more remarkably. Specific examples of the thickness of the radio wave absorber of the present invention include 0.03 mm to 15 cm.

  Such a wave absorber of the present invention is preferably lined with a metal. Any metal may be used, but for example, a metal plate such as iron, nickel, aluminum, zinc, and stainless steel is preferable. The thickness of the metal used for the radio wave absorber may be any thickness as long as it can reflect radio waves, and may be, for example, 50 μm to 1 mm.

  The manufacturing method of the electromagnetic wave absorber of this invention is demonstrated.

  The method for producing a radio wave absorber according to the present invention can be carried out by kneading a carbon component having an average particle diameter of 15 μm or more and 1 mm or less into a thermoplastic resin. Kneading can be performed using a general kneading machine such as a roll, a Banbury mixer, a single-screw extruder, a twin-screw extruder, and the like by blending a predetermined amount of a thermoplastic resin and a carbon component. The kneading temperature is not restricted by the viscosity of the resin in the kneading, and therefore may be at or above the melting temperature of the thermoplastic resin, and can be performed for a desired time. The resin can be dissolved in a solvent and mixed with the carbon component. The shearing force for kneading, that is, the shearing amount and the shearing speed can be selected as appropriate because the dielectric loss of the radio wave absorber does not become unstable due to the difference. Thus, even if the conditions for kneading are different, the obtained kneaded product has a stable dielectric loss. It is also possible to melt and mix in a solvent.

  Any method can be used as the method for molding the radio wave absorber of the present invention, for example, using methods such as injection molding, calender molding, blow molding, extrusion molding, thermoforming, foam molding, melt spinning and the like. In addition, molded articles such as injection molded articles, sheets, films, deformed articles, thermoformed articles, and fibers can be obtained.

  The radio wave absorber of the present invention described above can obtain a uniform dielectric loss containing a thermoplastic resin and a carbon component, and contains a carbon component according to the radio wave to be absorbed. Further, by adjusting the thickness, layer structure, the absorptance can be adjusted high.

Hereinafter, the present invention will be described in more detail with reference to examples.
Various physical properties are measured by the following methods.
(1) Average particle diameter It measured using the Malvern company laser diffraction type particle size distribution analyzer (master sizer). The measurement method and conditions were the standard conditions recommended by Malvern. That is, a sample of a micropartel was dispersed in a small amount of water using a surfactant and charged into the apparatus, and further dispersed by applying ultrasonic waves for 60 seconds while circulating. Thereafter, the ultrasonic irradiation was stopped, the measurement was performed, the particle size distribution was obtained, and the median value (d50) was taken as the measured value.
(2) X-ray diffraction of graphite Using an X-ray diffraction measurement device, measurement and data processing are performed in accordance with the “Measuring method of lattice constant and crystallite size of artificial graphite” established by the Japan Society for the Promotion of Science 117th Committee. The interplanar spacing d002 and the crystal size La011 were obtained. The X-ray diffraction measurement conditions are as follows.
X-ray source: CuKα, 50 KV, 200 mA
Measurement range: 2θ = 10-40deg
Scanning speed: 1 deg / min
Slit: DS = 1/2 deg, SS = 1/2 deg, RS = 0.15 mm
Sample holder: A cylindrical glass plate having a diameter of 46 mm and a thickness of 3 mm, in which a recess having a diameter of 26 mm and a depth of 0.2 mm was dug (the recess was filled with a sample).
(3) Dielectric constant Prepare a sample with a thickness of 2 to 3 mm, and use a rectangular waveguide (47.55 mm x 22.15 mm) at 5.8 GHz. The complex dielectric constant was calculated from the field strength ratio and the position of the node, and the field strength ratio between the node and the antinode of the standing wave when the data was placed in front of the metal plate and the position of the node. For details of measurement, see "Material Constant Measurement Method" p45-65, Osamu Hashimoto, Morikita Publishing (2003).
According.
(4) Radio wave absorption rate Measurement was performed at 1 to 18 GHz using a “lens antenna type oblique incidence type radio wave absorber (radio wave absorbing material) / reflection attenuation measuring device” manufactured by Keycom.
[Example 1]
After 10 kg of petroleum coke was pulverized for 5 hours using a ball mill BM50 manufactured by Oshima Tekko Co., Ltd. and then heat treated at 1500 ° C. for 10 hours, carbon particles having an average particle size of 15 μm were obtained. As a result of X-ray diffraction, the interplanar spacing d002 was 0.345 nm, and the crystal size in the a-axis direction was 8 nm. 1200 g of this carbon was kneaded under conditions shown in Table 1 using 800 g of PET resin (Teijin Chemical TR-8550) and KRC S1 Kneader manufactured by Kurimoto Iron Works, and compositions 1-1, 1-2, and 1-3 were mixed. Obtained. Using these compositions, test pieces having a thickness of 2 mm and 47.55 mm × 22.15 mm were prepared, and the complex dielectric constant measured at 5.8 GHz by the waveguide method is shown in Table 1.

All of these compositions are expected to absorb a radio wave of around 5.8GHz with a thickness of 2.02mm. Therefore, a 40cm x 40cm sheet is formed by press molding, and a 1mm thick iron plate is attached to the back surface. When absorption was measured, absorption was able to be confirmed as shown in FIG.
[Example 2]
After 10 kg of petroleum coke was pulverized in a dry system for 1 hour using a ball mill BM50 manufactured by Oshima Iron Works, carbon particles having an average particle size of 15 μm were obtained by heat treatment at 1900 ° C. for 10 hours. As a result of X-ray diffraction, the interplanar spacing d002 was 0.340 nm, and the crystal size in the a-axis direction was 50 nm. 1000 g of this carbon was kneaded under the conditions shown in Table 2 using 1000 g of polycarbonate resin (Teijin Chemicals Panlite L1225Y) and KRC S1 kneader manufactured by Kurimoto Iron Works, and compositions 2-1, 2-2, and 2-3 were Obtained. Using these compositions, test pieces having a thickness of 2 mm and 47.55 mm × 22.15 mm were prepared, and the complex dielectric constant measured at 5.8 GHz by the waveguide method is shown in Table 2.

All of these compositions are expected to absorb radio waves in the vicinity of 5.8GHz with a thickness of 2.15mm. Therefore, a 40cm x 40cm sheet is formed by press molding, and a 1mm thick iron plate is attached to the back surface to generate radio waves. When the absorption was measured, the absorption could be confirmed as shown in FIG.
[Example 3]
10 kg of petroleum coke was coarsely pulverized in a mortar, sieved, and heat-treated at 2800 ° C. for 2 hours to obtain carbon particles having an average particle size of 1000 μm. As a result of X-ray diffraction, the interplanar spacing d002 was 0.336 nm, and the crystal size in the a-axis direction was 120 nm. 800 g of this carbon was kneaded under the conditions shown in Table 3 using 1200 g of polycarbonate resin (Teijin Chemicals Panlite L1225Y) and KRC S1 kneader manufactured by Kurimoto Iron Works, and compositions 3-1, 3-2 and 3-3 were prepared. Obtained. Using these compositions, test pieces having a thickness of 2 mm and 47.55 mm × 22.15 mm were prepared, and the complex dielectric constant measured at 5.8 GHz by the waveguide method is shown in Table 3.

All of these compositions are expected to absorb radio waves in the vicinity of 5.8 GHz with a thickness of 2.33 mm. Therefore, a 40 cm x 40 cm sheet is formed by press molding, and a 1 mm thick iron plate is attached to the back surface to generate radio waves. When absorption was measured, absorption was able to be confirmed as shown in FIG.
[Comparative Example 1]
The carbon used in Example 3 was pulverized in a dry manner for 1 hour using a ball mill BM50 manufactured by Oshima Tekko, and carbon having an average particle size of 15 μm was obtained. 500 g of this carbon was kneaded under the conditions shown in Table 4 using 1500 g of polycarbonate resin (Teijin Chemicals Panlite L1225Y) and KRC S1 Kneader manufactured by Kurimoto Iron Works, and compositions 4-1, 4-2, and 4-3 were mixed. Obtained. Using these compositions, test pieces having a thickness of 2 mm and 47.55 mm × 22.15 mm were prepared, and the complex dielectric constant measured at 5.8 GHz by the waveguide method is shown in Table 4.

From the results, it was estimated that any of the compositions had insufficient dielectric loss, and radio wave absorption was measured for a molded article having a thickness of 2.8 mm. However, as shown in FIG.
[Comparative Example 2]
The carbon used in Example 3 was pulverized in a dry manner for 4 hours using a ball mill BM50 manufactured by Oshima Tekko, and carbon having an average particle size of 10 μm was obtained. 600 g of this carbon was kneaded under the conditions shown in Table 5 using 1700 g of a polycarbonate resin (Teijin Chemicals Panlite L1225Y) and a KRC S1 kneader manufactured by Kurimoto Iron Works, and compositions 5-1, 5-2, and 5-3 were mixed. Obtained. Using these compositions, test pieces having a thickness of 2 mm and 47.55 mm × 22.15 mm were prepared, and the complex dielectric constants measured at 5.8 GHz by the waveguide method are shown in Table 5.

As a result, it has been found that the dielectric loss greatly depends on the kneading conditions. Radio wave absorption was measured for a molded product having a thickness of 2.2 mm, and it was found that the absorption changes greatly depending on the kneading conditions as shown in FIG.
[Comparative Example 3]
After 10 kg of petroleum coke was heat treated at 1500 ° C. for 10 hours, it was coarsely pulverized in a mortar and sieved to obtain carbon particles having an average particle diameter of 1000 μm. As a result of X-ray diffraction, the interplanar spacing d002 was 0.345 nm, and the crystal size in the a-axis direction was 8 nm. This carbon 1700g was kneaded with 300g of polycarbonate resin (Teijin Kasei Panlite L1225Y) and Kurimoto Iron Works KRC S1 kneader to obtain a composition. There wasn't.
[Comparative Example 4]
After heat-treating 10 kg of petroleum coke at 1200 ° C. for 10 hours, it was pulverized in a dry manner for 1 hour using a ball mill BM50 manufactured by Oshima Tekko, and carbon having an average particle size of 15 μm was obtained. As a result of X-ray diffraction, the interplanar spacing d002 was 0.350 nm, and the crystal size in the a-axis direction was 5 nm. 1500 g of this carbon was kneaded under the conditions shown in Table 6 using 500 g of polycarbonate resin (Teijin Chemicals Panlite L1225Y) and KRC S1 Kneader manufactured by Kurimoto Tekkosho, and compositions 6-1 6-2, and 6-3 were mixed. Obtained. Using these compositions, test pieces having a thickness of 2 mm and 47.55 mm × 22.15 mm were prepared, and the complex dielectric constants measured at 5.8 GHz by the waveguide method are shown in Table 6.

  From the results, it was estimated that any of the compositions had insufficient dielectric loss, and radio wave absorption was measured for a molded article having a thickness of 2.0 mm. However, as shown in FIG.

It is a figure which shows the electromagnetic wave absorption of an example of the electromagnetic wave absorber of this invention. It is a figure which shows the electromagnetic wave absorption of an example of the electromagnetic wave absorber of this invention. It is a figure which shows the electromagnetic wave absorption of an example of the electromagnetic wave absorber of this invention. It is a figure which shows the electromagnetic wave absorption of the electromagnetic wave absorber of a prior art example. It is a figure which shows the electromagnetic wave absorption of the electromagnetic wave absorber of a prior art example. It is a figure which shows the electromagnetic wave absorption of the electromagnetic wave absorber of a prior art example.

Claims (6)

  An electromagnetic wave absorber having at least one layer containing a thermoplastic resin and a carbon component, wherein the layer has a carbon component having an average particle diameter of 15 μm or more and 1 mm or less in a range of 30% by mass or more and 80% by mass or less. An electromagnetic wave absorber characterized by containing.   The carbon component is graphite having an interplanar spacing (d002) of 0.3360 nm or more and 0.3470 nm or less in X-ray diffraction, and a crystal size (La110) in the a-axis direction of 5 nm or more. 1. The radio wave absorber according to 1.   3. The radio wave absorber according to claim 1, wherein the carbon component gradually decreases toward the open surface.   The wave absorber according to any one of claims 1 to 3, wherein the wave absorber has a thickness of 0.01 to 1 times the wavelength of the absorbed radio wave.   The radio wave absorber according to any one of claims 1 to 4, wherein the frequency of the radio wave to be absorbed is 2 to 80 GHz.   The radio wave absorber according to claim 5, wherein the frequency of the radio wave to be absorbed is 5.8 GHz.

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