JP7606694B2 - Electromagnetic wave absorbing material and electromagnetic wave absorbing resin molding - Google Patents

Description

The present invention relates to an electromagnetic wave absorbing material and an electromagnetic wave absorbing resin molded body that can be used to remove electromagnetic wave noise.

Since the advent of radio wave technology of a few MHz, there has been an increasing desire to use higher frequency bands in electromagnetic wave technology, and currently research and development is being carried out with the aim of using electromagnetic waves in the 100 GHz band. In particular, millimeter wave sensors play an important role in the autonomous driving of automobiles, and millimeter wave sensing has become indispensable as the eyes of autonomous driving technology.

The distance resolution and accuracy of a millimeter wave sensor depends on the frequency used, with the higher the frequency the higher the performance. There are two types of millimeter wave radar currently in practical use: 24 GHz and 77 GHz. The distance resolution of the 24 GHz radar is 75 cm, while the distance resolution of the 77 GHz radar is 4 cm, making the performance difference about 20 times.

In fully autonomous driving, malfunctions in sensing devices can directly affect human lives, so absolutely no malfunctions can be tolerated. In other words, suppressing electromagnetic noise, which can cause sensing devices to malfunction, is an urgent issue.

The use of electromagnetic wave absorbing materials is common for reducing electromagnetic noise, and noise suppression sheets containing electromagnetic wave absorbing materials are used for personal computers, mobile phones, etc., but these electronic devices use frequency bands of up to about 5 GHz, and electromagnetic noise countermeasures up to about 5 GHz are sufficient. However, millimeter wave sensors use frequency bands of up to 100 GHz, so electromagnetic noise countermeasures also target similar frequency bands.

In response to this, for example, Patent Document 1 (JP 2019-57561 A) proposes an electromagnetic wave absorbing material containing soft magnetic metal powder, which includes copper-coated iron powder composed of the soft magnetic metal powder and a bonding material interposed between the copper-coated iron powder, and is characterized in that the copper-coated iron powder is 60% by mass or more and 95% by mass or less, and the bonding material is 5% by mass or more and 40% by mass or less.

The electromagnetic wave absorbing material described in Patent Document 1 has excellent electromagnetic wave absorbing capabilities in the high frequency range, and because it is based on relatively inexpensive iron powder, it is said that the electromagnetic wave absorbing material can be produced inexpensively.

Also, for example, Patent Document 2 (JP 2017-118073 A) proposes an electromagnetic wave absorbing material that contains an insulating material and a conductive material, has a volume resistivity of 10 ^ohm -cm or more and less than 9× ¹⁰ ohm-cm, and absorbs electromagnetic waves in a frequency range of 20 GHz or more.

In the electromagnetic wave absorbing material described in Patent Document 2, it is said that by setting the volume resistivity in the thickness direction of the film to be ^10-2 ohm-cm or more and less than 9 x ¹⁰⁵ ohm-cm, it is possible to sufficiently increase the absorption ability of electromagnetic waves in the high frequency range, such as 20 GHz or more.

JP 2019-57561 A JP 2017-118073 A

However, the electromagnetic wave absorbing material described in Patent Document 1 is intended for electromagnetic waves of 10 GHz. Also, the electromagnetic wave absorbing material described in Patent Document 2 is intended for electromagnetic waves in the high frequency range of 20 GHz or more, but the electromagnetic wave absorbing performance shown in the examples is for 20 GHz, so it is essentially an electromagnetic wave absorbing material intended for electromagnetic waves of 20 GHz.

In other words, currently available electromagnetic wave absorbing materials can only absorb electromagnetic waves with frequencies as high as 20 GHz, and the reality is that there are no inexpensive electromagnetic wave absorbing materials that can absorb electromagnetic waves in the high frequency band of 45 to 100 GHz used in millimeter wave radars, etc.

In addition, when electromagnetic wave absorbing materials are used to improve autonomous driving, they will be used as automobile parts, so it is desirable for them to be lightweight and strong.

In view of the above circumstances, the object of the present invention is to provide an inexpensive electromagnetic wave absorbing material that can efficiently absorb electromagnetic waves including those in the high frequency band of 45 to 100 GHz, and a lightweight, high-strength electromagnetic wave absorbing resin molded body that contains the electromagnetic wave absorbing material.

In order to achieve the above object, the inventors conducted extensive research into the electromagnetic wave absorption properties of carbon materials, and discovered that carbon materials whose surfaces are coated with carbon nanostructures having a graphene structure efficiently absorb electromagnetic waves in the high frequency band, thus arriving at the present invention.

That is, the present invention provides:
The surface of the carbon material is covered with a carbon nanostructure having a graphene structure,
The carbon nanostructure does not contain any metal element;
The present invention provides an electromagnetic wave absorbing material, characterized by:

In the electromagnetic wave absorbing material of the present invention, it is preferable that the carbon nanostructure is a carbon nanotube and/or a carbon nanowall. The reason why the electromagnetic wave absorbing material of the present invention efficiently absorbs electromagnetic waves in the high frequency band is not necessarily clear, but the carbon nanostructure having a graphene structure formed on the surface of the carbon material contributes to the absorption of electromagnetic waves, and in particular, by making the carbon nanostructure a carbon nanotube and/or a carbon nanowall, the electromagnetic wave absorbing performance can be reliably expressed.

In the electromagnetic wave absorbing material of the present invention, it is preferable that the carbon material is carbon fiber. By using carbon fiber as the carbon material, the carbon fiber alone can be easily used as an electromagnetic wave absorbing material, and can also be used as a radio wave absorbing material in the form of a reinforcing material for various substrates. Here, when using carbon fiber alone, it may be used as it is, or it may be woven two-dimensionally or three-dimensionally. When using it as a reinforcing material, it may be long fiber or short fiber.

In addition, in the electromagnetic wave absorbing material of the present invention, it is more preferable that the carbon material is milled fiber. Milled fiber is made by mechanically grinding carbon fibers into short fibers, and defects and distortions are introduced near the surface, which allows the formation of carbon nanostructures by the cleavage and recombination of C=C bonds to proceed more efficiently, allowing the carbon nanostructures to be formed more densely.

In addition, the electromagnetic wave absorbing material of the present invention preferably absorbs electromagnetic waves having a frequency of 45 to 110 GHz, and more preferably absorbs electromagnetic waves having a frequency of 75 to 110 GHz. The electromagnetic wave absorbing material of the present invention can extremely efficiently absorb electromagnetic waves having a frequency of 45 to 110 GHz by using carbon nanostructures having a graphene structure that are present on the surface of the carbon material. More specifically, by covering about 3% of the total surface area of the carbon material with carbon nanostructures having a graphene structure, it is possible to achieve high electromagnetic wave absorption performance of about -6 dB for electromagnetic waves of 45 to 110 GHz (preferably 75 to 110 GHz).

The carbon nanostructure having a graphene structure is not particularly limited as long as it is a carbon structure having a graphene structure and a size on the order of nanometers, but examples thereof include carbon nanotubes, carbon nanofibers, graphene, and carbon nanowalls, and carbon nanotubes and/or carbon nanowalls are preferred. The carbon nanostructure may be oxidized, and an example of an oxidized carbon nanostructure is graphene oxide.

In addition, in the electromagnetic wave absorbing material of the present invention, the carbon nanostructures that cover the surface of the carbon material do not contain metal elements. Generally, in gas phase methods, carbon nanostructures are formed using metal particles as a catalyst, but the carbon nanostructures in the electromagnetic wave absorbing material of the present invention are formed by the cleavage and recombination of C in the carbon material, and do not contain metal elements because no metal catalyst is used. The reason why an electromagnetic wave absorbing material having carbon nanostructures that do not contain metal elements efficiently absorbs electromagnetic waves in the high frequency band is not necessarily clear, but it is thought that the carbon nanostructures that contain metal elements are in a homogeneous state, and that conductive loss-type electromagnetic wave absorption proceeds efficiently for electromagnetic waves in the high frequency band.

The present invention further provides an electromagnetic wave absorbing resin molding, characterized in that the electromagnetic wave absorbing material of the present invention is present in a resin substrate. When the electromagnetic wave absorbing material is in the form of particles or short fibers, it can be dispersed in the resin substrate, and when the electromagnetic wave absorbing material is in the form of long fibers, it can be arranged two-dimensionally or three-dimensionally in the resin substrate.

The electromagnetic wave absorbing resin molded body of the present invention is preferably a carbon fiber reinforced thermoplastic resin. In this case, the electromagnetic wave absorbing material of the present invention may be dispersed in a general carbon fiber reinforced thermoplastic resin, or carbon fiber may be used as the electromagnetic wave absorbing material of the present invention. By making the electromagnetic wave absorbing resin molded body from a carbon fiber reinforced thermoplastic resin, it is possible to obtain a lightweight and high-strength electromagnetic wave absorbing resin molded body.

In addition, the electromagnetic wave absorbing resin molded body of the present invention is preferably used for shielding electromagnetic interference from outside electronic circuits in automobile applications. In an embodiment, it can be used, for example, in emblems or bumpers to prevent electromagnetic waves such as millimeter wave radar from being reflected in the front grille or rear grille and becoming a noise source. It can also be used as an electromagnetic noise shield to electromagnetically shield part or all of the parts having electronic circuits in an automobile. Furthermore, as applications other than automobiles, it can be used in situations where electromagnetic shielding is required, such as reducing noise in the high frequency range of 45 to 110 GHz, such as ETC, aircraft, long-distance wireless communication, and the construction of electromagnetic anechoic chambers for measuring electromagnetic waves. The electromagnetic wave absorbing resin molded body of the present invention can efficiently absorb electromagnetic waves having a frequency of 45 to 110 GHz, and can be suitably used as an electromagnetic wave absorbing material for automobiles where millimeter wave radar having a frequency of up to 81 GHz is also a noise source. In addition, it is expected that electromagnetic waves in the 100 GHz band will be used in the future, and the electromagnetic wave absorbing material and electromagnetic wave absorbing resin molded body of the present invention can efficiently absorb electromagnetic waves in this frequency band as well.

The present invention provides an inexpensive electromagnetic wave absorbing material that can efficiently absorb electromagnetic waves, including those in the high frequency band of 45 to 100 GHz, and a lightweight, high-strength electromagnetic wave absorbing resin molded body that contains the electromagnetic wave absorbing material.

1 is a schematic cross-sectional view of an electromagnetic wave absorbing material of the present invention. 1 is a schematic cross-sectional view of an electromagnetic wave-absorbing resin molding of the present invention. FIG. 2 is a schematic diagram showing an example of a situation in which surface modification is performed on carbon fibers. 1 is a SEM photograph of carbon felt after surface treatment in an example. 4 shows the electromagnetic wave absorption characteristics of the carbon felt subjected to the surface treatment in the embodiment.

A preferred embodiment of the electromagnetic wave absorbing material and electromagnetic wave absorbing resin molded body of the present invention will be described in detail below, taking as an example a case where the carbon material is carbon fiber. Note that the following description merely shows one embodiment of the present invention, and the present invention is not limited thereto, and duplicated descriptions may be omitted.

(1) Electromagnetic Wave Absorbing Material The electromagnetic wave absorbing material of the present invention is characterized in that the surface of a carbon material is covered with a carbon nanostructure having a graphene structure, and the carbon nanostructure does not contain any metal elements.

Figure 1 shows a schematic cross-sectional view of the electromagnetic wave absorbing material of the present invention when the carbon material is carbon fiber. In the electromagnetic wave absorbing material 2, carbon nanostructures 6 are formed on the surface of carbon fibers 4 having a diameter of 1 to 20 μm. The length of the carbon fibers 4 is not particularly limited, and generally known long fibers or short fibers can be used. Here, the carbon nanostructures 6 are densely formed and preferably cover the entire surface of the carbon fibers 4, but may cover only a part of the surface of the carbon fibers 4. Here, since the carbon nanostructures 6 are formed by C near the surface of the carbon fibers 4, the carbon fibers 4 and the carbon nanostructures 6 have relatively good adhesion, and when the carbon fibers 4 are used as a reinforcing material for various matrices, the interaction between the carbon fibers 4 and various matrices can be increased (the mechanical properties of the carbon fibers 4 can be better reflected).

The carbon nanostructure 6 is a carbon structure having a size on the order of nanometers, and basically has a graphene structure. There are no particular limitations on the carbon nanostructure 6, and examples of the carbon nanostructure 6 include carbon nanotubes (single-layer or multi-layer) and carbon nanowalls in which several graphene sheets are stacked. The carbon nanostructure 6 may also be oxidized, and an example of the oxidized carbon nanostructure 6 is graphene oxide.

In addition, the carbon nanostructure 6 does not contain any metal elements. Generally, in gas phase methods, carbon nanostructures are formed using metal particles as a catalyst, but the carbon nanostructure 6 is formed by the cleavage and recombination of C near the surface of the carbon fiber 4, and does not contain any metal elements. In other words, it has homogeneous properties compared to carbon nanostructures that contain metal elements.

The carbon fibers 4 are preferably short fibers, and more preferably milled fibers. Milled fibers are carbon fibers that have been mechanically crushed to produce short fibers, and because defects and distortions are introduced near the surface, the formation of carbon nanostructures 6 through the cleavage and recombination of C=C bonds can proceed more efficiently, allowing more carbon nanostructures 6 to be formed on the surface.

Furthermore, carbon fiber 4 having carbon nanostructures 6 on its surface can extremely efficiently absorb electromagnetic waves having a frequency of 45 to 110 GHz. The reason why carbon fiber 4 having carbon nanostructures 6 on its surface can extremely efficiently absorb electromagnetic waves having a frequency of 45 to 110 GHz is not entirely clear, but it is believed that electromagnetic waves having a frequency of 45 to 110 GHz are extremely efficiently absorbed by carbon nanostructures 6 having a graphene structure. By covering about 3% of the total surface area of carbon fiber 4 with carbon nanostructures 6 having a graphene structure, it is possible to achieve high electromagnetic wave absorption performance of around -6 dB for electromagnetic waves of 45 to 110 GHz.

(2) Electromagnetic Wave Absorbing Molded Resin Article The electromagnetic wave absorbing molded resin article of the present invention is characterized in that the electromagnetic wave absorbing material of the present invention is present in a resin substrate.

Figure 2 shows a schematic cross-sectional view of an electromagnetic wave absorbing resin molded body of the present invention when the carbon material is carbon fiber (short carbon fiber). The electromagnetic wave absorbing resin molded body 10 is a body in which an electromagnetic wave absorbing material 2 is dispersed in a resin substrate 12. In Figure 2, the carbon material of the electromagnetic wave absorbing material 2 is carbon fiber 4, and the electromagnetic wave absorbing material 2 is uniformly dispersed in the resin substrate 12. The volume fraction of the electromagnetic wave absorbing material 2 is not particularly limited as long as it does not impair the effects of the present invention, and may be appropriately adjusted according to the desired electromagnetic wave absorbing performance, mechanical properties, moldability, etc.

For example, if the carbon material of the radio wave absorbing material 2 is long fiber, it may be arranged in any state in the resin substrate 12, and it is possible to arrange the long fiber woven fabric two-dimensionally or three-dimensionally, and it can be in a state similar to that of a general long fiber reinforced resin molded body.

The resin substrate 12 is not particularly limited as long as it does not impair the effects of the present invention, and various conventionally known resin materials can be used. As the resin substrate 12, for example, acrylic resins such as polymethyl methacrylate (PMMA), polycarbonate (PC), acrylonitrile-butadiene-styrene copolymer (ABS), polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), acrylonitrile-styrene copolymer (AS), polystyrene (PS), cycloolefin polymer (COP), acrylonitrile-butadiene-styrene copolymer (ABS), acrylonitrile-styrene-acrylate copolymer (ASA), acrylonitrile-ethylenepropyl rubber-styrene copolymer (AES), etc. can be used alone or in combination of two or more types, and additives may also be contained.

The electromagnetic wave absorbing resin molded body 10 is preferably a carbon fiber reinforced thermoplastic resin. In this case, the electromagnetic wave absorbing material 2 of the present invention may be dispersed in a general carbon fiber reinforced thermoplastic resin, or the carbon fiber 4 may be the electromagnetic wave absorbing material 2. By making the electromagnetic wave absorbing resin molded body 10 out of a carbon fiber reinforced thermoplastic resin, it is possible to obtain a lightweight and high-strength electromagnetic wave absorbing resin molded body.

The electromagnetic wave absorbing resin molded body 10 is preferably an automobile emblem or automobile bumper. The electromagnetic wave absorbing resin molded body 10 can efficiently absorb electromagnetic waves having a frequency of 45 to 110 GHz, and can be suitably used as an electromagnetic wave absorbing material for automobiles, where millimeter wave radar having a maximum frequency of 81 GHz is also a noise source. It is anticipated that electromagnetic waves in the 100 GHz band will be used in the future, and the electromagnetic wave absorbing material 2 and the electromagnetic wave absorbing resin molded body 10 can also efficiently absorb electromagnetic waves in this frequency band.

The manufacturing method of the electromagnetic wave absorbing resin molded body 10 is not particularly limited as long as it does not impair the effects of the present invention, and various conventional manufacturing methods for resin molded bodies can be used. In this case, the electromagnetic wave absorbing material 2 is dispersed in the resin substrate 12 by an appropriate method.

(3) Manufacturing method of electromagnetic wave absorbing material The electromagnetic wave absorbing material 2 can be obtained by subjecting carbon fibers 4 to surface modification. The method of surface modification of carbon fibers 4 is characterized in that the carbon fibers 4 are irradiated with microwaves in a gas atmosphere to heat the carbon fibers 4 with microwaves, an excited state of the gas is induced by the microwaves, and the C=C bonds of the carbon fibers 4 are cut by ultraviolet light generated in the process of gas emission. Each of these constituent elements will be described in detail below.

An example of the situation in which the surface of carbon fiber 4 is modified is shown in FIG. 3. A glass tube 22 is inserted into a microwave generator 20, and carbon fiber 4 placed in an alumina boat 24 is disposed inside the glass tube 22. A gas inlet 30 and a gas outlet 32 are provided in the glass tube 22, and the inside of the glass tube 22 is a gas atmosphere.

(1-1) Carbon fiber (carbon material)
The carbon fibers 4 are not particularly limited as long as they do not impair the effects of the present invention, and various conventionally known carbon fibers can be used. The carbon fibers 4 have a diameter of 1 to 20 μm and are completely different from carbon nanotubes and carbon nanofibers.

It is preferable to use short fibers as the carbon fibers 4, and more preferable to use milled fibers. Milled fibers are carbon fibers that have been mechanically crushed to produce short fibers, and defects and distortions are introduced near the surface, which allows the formation of carbon nanostructures 6 through the cleavage and recombination of C=C bonds to proceed more efficiently.

(1-2) Gas atmosphere Surface modification of the carbon fibers 4 cannot be achieved by only micro-heating the carbon fibers 4, and it is necessary to utilize gas plasma. When the carbon fibers 4 are microwave-heated, the C=C bonds near the surface of the carbon fibers 4 are broken by ultraviolet light generated in the light emission process of the gas present inside the glass tube 22 at the same time, and as a result, carbon nanostructures 6 (carbon nanotubes, graphene, graphene oxide, etc.) having a graphene structure are densely formed on the surface of the carbon fibers 4.

As long as the C=C bonds on the surface of the carbon fiber 4 are broken by the ultraviolet light generated during the gas emission process, the type of gas filled or circulated in the glass tube 22 is not limited, but it is preferable that the gas contains at least one of air, argon, helium, nitrogen, and carbon dioxide. These gases may be used alone or in combination of two or more types. By irradiating any of air, argon, helium, nitrogen, and carbon dioxide with microwaves, ultraviolet light that contributes to breaking the C=C bonds near the surface of the carbon fiber 4 can be efficiently generated.

The gas pressure and gas flow rate inside the glass tube 22 are not particularly limited and may be adjusted as appropriate according to the desired surface state of the carbon fibers 4, but it is preferable to set the total pressure inside the glass tube 22 to less than 1000 Pa. By irradiating the inside of the glass tube 22 with microwaves at 1000 Pa, ultraviolet rays that contribute to breaking the C=C bonds near the surface of the carbon fibers 4 can be efficiently generated.

(1-3) Microwave Irradiation Conditions Microwaves are generated by the microwave generator 20 and irradiated to the carbon fiber 4 and the gas inside the glass tube 22. Here, microwaves refer to electromagnetic waves with a wavelength in the range of 100 μm to 1 m and a frequency of 30 MHz to 3 THz. For example, a general-purpose microwave oven can be used as the microwave generator 20.

The microwave output used for surface modification of carbon fiber 4 is not particularly limited and may be adjusted as appropriate depending on the amount of carbon fiber 4 inserted (amount of processing), the processing speed, the desired surface state, etc. For example, when processing 10 mg of carbon fiber 4, it is preferable to set the output to 10 to 1000 W, and more preferably 100 to 800 W.

The microwave irradiation time is not particularly limited and may be adjusted as appropriate depending on the amount of carbon fiber 4 inserted (amount of processing), the processing speed, the desired surface state, etc., but is preferably 10 seconds to 10 minutes, and more preferably 1 minute to 5 minutes. If the processing time is extended within the range of 10 seconds to 10 minutes, the amount of carbon nanostructures 6 formed on the surface of the carbon fiber 4 increases and the density increases, but if the processing time is longer than 10 minutes, in addition to causing significant damage to the carbon fiber 4, the generated carbon nanostructures 6 may also be damaged.

Generally, in the gas phase method, carbon nanostructures are formed using metal particles as a catalyst, but carbon nanostructure 6 is formed by cutting and recombining C in carbon fibers, and since no metal catalyst is used, carbon nanostructure 6 does not contain any metal elements.

The electromagnetic wave absorbing material and electromagnetic wave absorbing resin molded body of the present invention will be further explained in the following examples, but the present invention is not limited to these examples in any way.

Example 1
Carbon felt (Tsukuba Materials Information Research Institute, Ltd., e-4-1 carbon felt, A4 size, 2t) made of carbon fiber was used as the carbon material, and the surface treatment was performed in the state shown in Figure 3. Specifically, an alumina boat containing carbon felt measuring 20 mm wide x 80 mm long x 2 mm thick with 50 mg of activated carbon powder sprinkled on the surface was inserted into a glass tube, and microwaves were irradiated at an output of 700 W using a commercially available microwave oven. Here, the inside of the glass tube was an argon-substituted atmosphere of about 1 Pa, and the microwave irradiation time was 5 minutes. Note that light emission was observed during microwave irradiation.

Figure 4 shows an SEM photograph of the carbon felt after surface treatment. It can be seen that carbon nanostructures have been formed on the surface of the carbon fibers facing the surface side of the carbon felt. The formation of the carbon nanostructures was observed from the outermost surface of the carbon felt to a depth of about 100 μm. When the carbon nanostructures were observed at high magnification, complex pleated and sheet-like structures were confirmed, and it is believed that carbon nanowalls consisting of multiple graphene sheets stacked together have been formed in a dense manner.

The electromagnetic wave absorption characteristics of the surface-treated carbon felt are shown in Figure 5. For reference, the electromagnetic wave absorption characteristics of untreated carbon felt are also shown. As shown in Figure 4, the area in which the carbon nanostructures are formed is limited, but the electromagnetic wave absorption characteristics are dramatically improved compared to untreated carbon felt. Specifically, for electromagnetic waves with frequencies of 75 to 110 GHz, it has a high electromagnetic wave absorption performance of -6 dB (about 75% in terms of absorption rate). The carbon nanostructures, when converted into an application rate, are about 3% of the total surface area. The electromagnetic wave absorption characteristics were measured using a Free Space Microwave Measurement System (HVSFS) manufactured by MAC Systems Co., Ltd., using the free space method. Measurements were performed in the following bands: Band V-1 (45.0-67.0 GHz), Band V-2 (67.0-75.0 GHz), and Band W (75.0-110.0 GHz).

2. Electromagnetic wave absorbing material,
4...carbon fiber,
6... Carbon nanostructures,
10: Electromagnetic wave absorbing resin molded body 10,
12... Resin substrate,
20...Microwave generator,
22...glass tube,
24...Alumina boat,
30: Gas inlet,
32...Gas outlet.

Claims (4)

A method for absorbing electromagnetic waves having a frequency of 45 to 110 GHz using an electromagnetic wave absorbing material, comprising:
The electromagnetic wave absorbing material is
The surface of the carbon material is covered with a carbon nanostructure having a graphene structure,
The carbon nanostructure is a carbon nanowall,
The carbon material is carbon fiber,
The carbon nanostructure does not contain any metal element;
A method for absorbing electromagnetic waves, comprising: Dispersing the electromagnetic wave absorbing material in a resin substrate;
2. The method for absorbing electromagnetic waves according to claim 1 , The resin substrate is a carbon fiber reinforced thermoplastic resin;
3. The method for absorbing electromagnetic waves according to claim 2 , The resin substrate is an automobile emblem or an automobile bumper;
4. The method for absorbing electromagnetic waves according to claim 2 or 3,