JP7478374B2 - Electromagnetic wave shielding material and signal processing unit including same - Google Patents

Description

The present invention relates to an electromagnetic shielding material and a signal processing unit equipped with the same, and in particular to an electromagnetic shielding material suitable for use in a radar cover that protects a radar from the surrounding environment and does not impede radar signal transmission, and a signal processing unit equipped with the same. Note that in this specification, "shield" is used to mean at least one of absorption, i.e., reflection loss, and shielding, i.e., transmission loss.

Patent Document 1 discloses a thermoplastic resin composition for radar covers that contains 85% to 95% by weight of a thermoplastic resin, 1% to 5% by weight of carbon nanotubes, and 3% to 10% by weight of carbon black, and contains the carbon nanotubes and carbon black in a weight ratio of 3:7 to 1:7, thereby providing excellent mechanical properties and a good balance of the reflection loss and transmission loss of electromagnetic waves required for radar protection.
JP 2016-504471 A

Here, it has been found that the thermoplastic resin composition for radar covers disclosed in Patent Document 1 has room for improvement in terms of electromagnetic wave reflection loss and transmission loss in order to adequately protect the radar from the surrounding environment while not impeding radar signal transmission.

Specifically, the radar cover disclosed in Patent Document 1 is described as being able to obtain an electromagnetic wave reflection loss in the range of 2 dB to 9 dB and an electromagnetic wave transmission loss in the range of 3 dB to 12 dB (paragraph 0036), but according to the inventors' findings, in the frequency band of approximately 60 GHz to approximately 110 GHz, typically the electromagnetic wave reflection loss needs to be approximately 5 dB or more and the electromagnetic wave transmission loss needs to be approximately 15 dB or more, although this depends on the balance between the electromagnetic wave reflection loss and the electromagnetic wave transmission loss.

Based on the findings of the inventors, the reasons why the numerical values of the above conditions are necessary are as follows: In other words, when focusing on the transmission loss of electromagnetic waves, if the transmission loss of electromagnetic waves is, for example, 20 dB, the electromagnetic wave shielding rate is 90%, so that the electromagnetic waves incident on the first surface of the electromagnetic shielding material are attenuated by 90% to 10% when they are emitted from the second surface of the electromagnetic shielding material.

If the remaining electromagnetic waves collide with some other component, are reflected there, and then enter the electromagnetic shielding material again through the second surface, 90% of the waves will be attenuated to 10% when they leave the first surface of the electromagnetic shielding material. Therefore, in this example, the initial electromagnetic waves will be attenuated by 99%.

Considering this, if the transmission loss is excellent, a reflection loss of about 5 dB can be said to be sufficient. Furthermore, if one wishes to provide a highly reliable electromagnetic shielding material, it would be sufficient to provide some more electromagnetic shielding from the perspective of quality assurance for users of the electromagnetic shielding material, taking into consideration individual differences caused by manufacturing errors in the electromagnetic shielding material and the environment in which the electromagnetic shielding material is used.

Therefore, if there is something else with electromagnetic wave shielding function, such as metal, near the location where the electromagnetic shielding material is to be installed, a reflection loss of approximately 6 dB would be sufficient, and even if there is no other thing with electromagnetic wave shielding function present, a reflection loss of approximately 7 dB would be sufficient.

On the other hand, if we look at the reflection loss of electromagnetic waves, if the reflection loss of electromagnetic waves is 5 dB, the absorption rate of electromagnetic waves is 50%, and if the transmission loss is 20 dB, the absorption rate is 90%, so 50% of 100 electromagnetic waves is reflected and 90% of the remaining 50% electromagnetic waves is shielded, so that the electromagnetic waves emitted from the exit surface of the electromagnetic wave shielding material are reduced to 5%.

Therefore, it can be said that the reflection loss of electromagnetic waves must be approximately 5 dB or more, and the transmission loss of electromagnetic waves must be approximately 15 dB or more.

Note that the explanation here is based on the assumption that the electromagnetic wave transmission loss is 20 dB, but even if this is reduced to 15 dB, the electromagnetic wave shielding rate is approximately 82%, so if the reflection loss is 5 dB, the remaining approximately 18% of electromagnetic waves can be reduced to approximately 9%, and if necessary, an electromagnetic wave shielding material with a reflection loss of, for example, 6 dB can be used.

Based on the above considerations, the objective of the present invention is to provide an electromagnetic wave shielding material that can achieve shielding performance of at least 90%.

In order to solve the above problems, the electromagnetic shielding material and the signal processing unit including the same according to the present invention are
The main component is resin,
an electromagnetic wave shielding material 1 contained in the resin in an amount such that the reflection loss of electromagnetic waves is 50% or more;
an electromagnetic wave shielding material 2 contained in the resin in an amount such that the electromagnetic wave transmission loss is 80% or more;
including.

The resin may be a thermoplastic resin, and each of the electromagnetic wave shielding materials may be nanocarbon.

More specifically, the resin may be any one of polyolefin, polyphenylene sulfide, polyamide, polycarbonate, polybutylene, polyetherimide, etc., or any combination of several of these. The electromagnetic wave shielding materials may be any combination of an electromagnetic wave shielding material 1 that contributes to an increase in the reflection loss of electromagnetic waves and an electromagnetic wave shielding material 2 that contributes to an increase in the transmission loss of electromagnetic waves, among carbon nanotubes, carbon black, carbon nanocoils, carbon nanofibers, graphene, fullerene, etc., or any combination of several of these materials.

The resin may also contain a dispersant that disperses the electromagnetic wave shielding materials in the resin. The dispersant may be any of natural, semi-synthetic, and synthetic waxes. In more detail, the dispersant may be any of paraffin wax, montan wax, amide wax, ethylene-bis-stearamide, fatty acid metal salts, silicone, polyolefin wax, etc., or any combination of these.

The manufacturing process of the electromagnetic shielding material of the present invention is not limited, and may be, for example, press processing or injection processing. When press processing is used, the surface resistivity of the electromagnetic shielding material is generally 250 Ω/□ to 750 Ω/□, and it has been found that a surface resistivity of about 300 Ω/□ to 500 Ω/□ has suitable shielding performance when the thickness of the electromagnetic shielding material is 2 mm to 6 mm.

In addition, the signal processing unit of the present invention can be used as an automotive proximity radar having electromagnetic shielding material, communication devices including mobile phones, smartphones, PDAs, tablet terminals, and personal computers, and various proximity radars.

FIG. 4 is a diagram showing the transmission loss of the electromagnetic shielding material of Example 1. FIG. 4 is a diagram showing the reflection loss of the electromagnetic shielding material of Example 1. FIG. 11 is a diagram showing the transmission loss of the electromagnetic shielding material of Example 2. FIG. 11 is a diagram showing the reflection loss of the electromagnetic shielding material of Example 2. FIG. 11 is a diagram showing the transmission loss of the electromagnetic shielding material of Example 3. FIG. 11 is a diagram showing the reflection loss of the electromagnetic shielding material of Example 3. FIG. 11 is a diagram showing the transmission loss of the electromagnetic shielding material of Example 4. FIG. 11 is a diagram showing the reflection loss of the electromagnetic shielding material of Example 4. FIG. 13 is a diagram showing the transmission loss of the electromagnetic shielding material of Example 5. FIG. 13 is a diagram showing the reflection loss of the electromagnetic shielding material of Example 5. FIG. 13 is a diagram showing the transmission loss of the electromagnetic shielding material of Example 6. FIG. 13 is a diagram showing the reflection loss of the electromagnetic shielding material of Example 6. FIG. 13 is a diagram showing the transmission loss of the electromagnetic shielding material of Example 7. FIG. 13 is a diagram showing the reflection loss of the electromagnetic shielding material of Example 7. FIG. 13 is a diagram showing the transmission loss of the electromagnetic shielding material of Example 8. FIG. 13 is a diagram showing the reflection loss of the electromagnetic shielding material of Example 8. FIG. 13 is a diagram showing the transmission loss of the electromagnetic shielding material of Example 9. FIG. 13 is a diagram showing the reflection loss of the electromagnetic shielding material of Example 9.

Below, an embodiment of the present invention is explained using diagrams and charts.

The electromagnetic wave shielding material of this embodiment is
(1) a resin as a main component;
(2) an electromagnetic wave shielding material contained in the resin;
It is essential to include
Furthermore, a dispersant for dispersing the electromagnetic shielding material in the resin may be optionally included. Note that the electromagnetic shielding material of this embodiment itself does not contain any metal material.

The electromagnetic shielding material of this embodiment has a reflection loss of about 6 dB or more and a transmission loss of about 15 dB or more, so that even if there are manufacturing errors or individual differences in the electromagnetic shielding material, almost all manufactured products can achieve approximately 90% shielding of electromagnetic waves when viewed overall. It has been found that when an electromagnetic shielding body with such performance is manufactured by press processing, the surface resistivity is about 300 Ω/□ to about 500 Ω/□. However, other processes such as injection processing can be used instead of press processing. In this case, there will be a large change in the surface resistivity, but theoretically there will be no change in the volume resistivity and conductivity.

In addition, in order to clarify the differences between the electromagnetic wave shielding material of this embodiment and the thermoplastic resin composition for radar covers disclosed in Patent Document 1, the performance disclosed in Patent Document 1 will be described in addition, with respect to Examples 1 to 3, the reflection losses are 6 dB, 5 dB, and 3 dB, and the transmission losses are 3 dB, 3 dB, and 5 dB or more, respectively.

Comparing the two, while Example 1 achieved a reflection loss of 6 dB, its transmission loss was only 3 dB, and Examples 2 and 3 did not achieve better performance in terms of reflection loss or transmission loss than the present embodiment. In any case, it can be seen that the thermoplastic resin composition for radar covers disclosed in Patent Document 1 has significantly different shielding properties from the electromagnetic wave shielding material of the present embodiment.

The resin may be a thermoplastic resin, and more specifically, examples of the resin may include polyolefin, polyphenylene sulfide, polyamide, polyimide, polyamideimide, polycarbonate, polyacetal, polyethersulfone, polybutylene, polyetherimide, polyetherketone, polyetherimide, polyalkylene terephthalate, polysulfone, polystyrene, syndiotactic polystyrene, acrylonitrile butadiene styrene, polyphenylene oxide, acrylic resins, liquid crystal polymer resins, etc., or any combination of these.

Furthermore, the electromagnetic wave shielding material may be one or several kinds of nanocarbons that contribute to increasing the reflection loss and transmission loss of electromagnetic waves. Typically, among carbon nanotubes, carbon black, carbon nanocoils, carbon nanofibers, graphene, fullerene, etc., those that contribute to increasing the reflection loss of electromagnetic waves and those that contribute to increasing the transmission loss of electromagnetic waves may be arbitrarily combined, but a single nanocarbon may also be selected.

Among these, carbon nanotubes contribute to an increase in the reflection loss of electromagnetic waves, and carbon black contributes to an increase in the transmission loss of electromagnetic waves, and are easily available on the market. Carbon nanotubes can have an average inner diameter of 0.5 nm to 20 nm. Carbon black can have an average secondary particle diameter of 10 μm to 200 μm.

Furthermore, the dispersant that can be selectively included in the electromagnetic shielding material can be any of natural, semi-synthetic, or synthetic waxes, and can be any of paraffin wax, montan wax, amide wax, ethylene-bis-stearamide, fatty acid metal salts, silicone, polyolefin wax, etc., or any combination of several of these.

The mixing ratio of resin and electromagnetic shielding material, when using polypropylene as the resin, carbon nanotubes as electromagnetic shielding material 1, and carbon black as electromagnetic shielding material 2, can be [resin: electromagnetic shielding material 1: electromagnetic shielding material 2 = approximately 90% by weight: approximately 0.1% by weight to approximately 1% by weight: approximately 10% by weight]. When using a dispersant, the amount of resin can be reduced by approximately 5% to 40%, and the dispersant can be mixed in instead.

However, according to the inventors' considerations, polyethylene wax is an easy choice as a dispersant when market availability and price are taken into consideration. When polyethylene wax or a similar dispersant is selected, the amount of resin can be reduced by about 5% to 20%, depending on the material selected as the resin, etc., and polyethylene wax, etc. can be mixed in instead.

In addition, with regard to the thermoplastic resin composition for radar covers disclosed in Patent Document 1, there is no discussion or mention of dispersants in Patent Document 1, so this point is not clear, but the composition is [thermoplastic resin: carbon nanotubes: carbon black = 85% by weight to 95% by weight: 1% by weight to 5% by weight: 3% by weight to 10% by weight] and the weight ratio is [carbon nanotubes: carbon black = 3:7 to 1:7].

Therefore, the electromagnetic wave shielding material of this embodiment differs from the thermoplastic resin composition for radar covers disclosed in Patent Document 1 in that the composition ratio of carbon nanotubes is relatively small. And since carbon nanotubes are generally expensive among the components that make up an electromagnetic wave shielding material, being able to relatively reduce the amount of carbon nanotubes mixed means that the electromagnetic wave shielding material of this embodiment can be realized at low cost.

Below, the electromagnetic shielding material of the embodiment of the present invention will be described using as an example a resin mainly composed of polypropylene, carbon nanotubes as electromagnetic shielding material 1, and carbon black as electromagnetic shielding material 2. In addition, in Examples 1 to 4, the thickness of the electromagnetic shielding material was approximately 2 mm, and in Examples 5 to 9, the thickness of the electromagnetic shielding material was approximately 6 mm.

The reason for setting this thickness is that a thickness of 2 mm is assumed to be suitable for use in cases where there is something else with electromagnetic wave shielding function, such as metal, near the location where the electromagnetic shielding material is to be installed, such as an ADAS radar, and the installation space for the electromagnetic shielding material is relatively small.

In addition, with regard to the 6 mm thickness, we have only assumed conditions under which the electromagnetic shielding material can be suitably used when there is another object with electromagnetic wave shielding function, such as metal, near the location where the electromagnetic shielding material is to be installed, such as a radar unit in which an ADAS radar is integrated with a mounting portion for attaching the radar to an automobile, and the installation space for the electromagnetic shielding material is relatively large.

In addition, in order to prevent the back lobe emitted from the radar antenna from reaching the electronic control unit (ECU), it is possible to use an electromagnetic shielding material. One example, but not limited to this, is to attach the electromagnetic shielding material to the electronic control unit itself.

In addition, in the case of a radar unit, it is conceivable that the label may be attached to the mounting portion, or may be used as a part or all of the material of the mounting portion. Furthermore, if the radar is equipped with a horn-type antenna, it is conceivable that the label may be attached to the outside of the antenna.

It should be noted that, as stated above, setting the thickness of the electromagnetic shielding material to 2 mm or 6 mm does not mean much from a technical point of view, and therefore the thickness is not limited to these thicknesses. Therefore, it is sufficient to select from Examples 1 to 9 an electromagnetic shielding material that satisfies the shielding performance required depending on the application and installation environment of the material, and provide it in the signal processing unit.

However, it should be noted that the manufacturing conditions shown in Examples 1 to 9 are illustrative, and it is not excluded that an electromagnetic shielding material manufactured under conditions in which the amount of carbon nanotubes mixed is less than that in Example 1 but more than that in Example 2 can be used in a signal processing unit.

Example 1
Resin: Approximately 88.80 wt%
Electromagnetic wave shielding material 1: about 1.200 wt%
Electromagnetic wave shielding material 2: about 10.00 wt%
The mixture was mixed and appropriately stirred using a twin-screw extruder so as to disperse the mixture uniformly, and then pressed into an electromagnetic shielding material having a thickness of about 2 mm by a known method.

When the electrical conductivity and surface resistivity of the electromagnetic shielding material of Example 1 were measured, the electrical conductivity was approximately 2.00 S/m and the surface resistivity was approximately 250 Ω/□.

Figure 1 is a diagram showing the transmission loss of the electromagnetic shielding material of Example 1. The horizontal axis of Figure 1 shows frequency [GHz], and the vertical axis of Figure 1 shows transmission loss [dB]. As shown in Figure 1, it can be seen that the electromagnetic shielding material of Example 1 has a transmission loss of 20 dB or more over the entire frequency band from 75 GHz to 110 GHz.

Figure 2 is a diagram showing the reflection loss of the electromagnetic shielding material of Example 1. The horizontal axis of Figure 2 shows frequency [GHz], and the vertical axis of Figure 2 shows reflection loss [dB]. As shown in Figure 2, it can be seen that the electromagnetic shielding material of Example 1 has a reflection loss of 6 dB or more over the entire frequency band from 75 GHz to 110 GHz.

Example 2
Resin: Approximately 89.30 wt%
Electromagnetic wave shielding material 1: about 0.700 wt%
Electromagnetic wave shielding material 2: about 10.00 wt%
The mixture was mixed and appropriately stirred using a twin-screw extruder so as to disperse the mixture uniformly, and then pressed into an electromagnetic shielding material having a thickness of about 2 mm by a known method.

When the electrical conductivity and surface resistivity of the electromagnetic shielding material of Example 2 were measured, the electrical conductivity was approximately 1.67 S/m and the surface resistivity was approximately 300 Ω/□.

Figure 3 is a diagram showing the transmission loss of the electromagnetic shielding material of Example 2. The horizontal axis of Figure 3 shows frequency [GHz], and the vertical axis of Figure 3 shows transmission loss [dB]. As shown in Figure 3, it can be seen that the electromagnetic shielding material of Example 2 has a transmission loss of 20 dB or more over the entire frequency band from 75 GHz to 110 GHz.

Figure 4 is a diagram showing the reflection loss of the electromagnetic shielding material of Example 2. The horizontal axis of Figure 4 shows frequency [GHz], and the vertical axis of Figure 4 shows reflection loss [dB]. As shown in Figure 4, it can be seen that the electromagnetic shielding material of Example 2 has a reflection loss of 6 dB or more over the entire frequency band from 60 GHz to 90 GHz.

Example 3
Resin: Approximately 89.40 wt%
Electromagnetic wave shielding material 1: about 0.600 wt%
Electromagnetic wave shielding material 2: about 10.00 wt%
The mixture was mixed and appropriately stirred using a twin-screw extruder so as to disperse the mixture uniformly, and then pressed into an electromagnetic shielding material having a thickness of about 2 mm by a known method.

When the electrical conductivity and surface resistivity of the electromagnetic shielding material of Example 3 were measured, the electrical conductivity was approximately 1.25 S/m and the surface resistivity was approximately 400 Ω/□.

Figure 5 is a diagram showing the transmission loss of the electromagnetic shielding material of Example 3. The horizontal axis of Figure 5 shows frequency [GHz], and the vertical axis of Figure 5 shows transmission loss [dB]. As shown in Figure 5, it can be seen that the electromagnetic shielding material of Example 3 has a transmission loss of approximately 20 dB or more over the entire frequency band from 75 GHz to 110 GHz.

Figure 6 is a diagram showing the reflection loss of the electromagnetic shielding material of Example 3. The horizontal axis of Figure 6 shows frequency [GHz], and the vertical axis of Figure 6 shows reflection loss [dB]. As shown in Figure 6, it can be seen that the electromagnetic shielding material of Example 3 has a reflection loss of 6 dB or more over the entire frequency band from 60 GHz to 90 GHz.

Example 4
Resin: about 89.37 wt%
Electromagnetic wave shielding material 1: about 0.630 wt%
Electromagnetic wave shielding material 2: about 10.00 wt%
The mixture was mixed and appropriately stirred using a twin-screw extruder so as to disperse the mixture uniformly, and then pressed into an electromagnetic shielding material having a thickness of about 2 mm by a known method.

When the electrical conductivity and surface resistivity of the electromagnetic shielding material of Example 4 were measured, the electrical conductivity was approximately 1.00 S/m and the surface resistivity was approximately 500 Ω/□.

Figure 7 is a diagram showing the transmission loss of the electromagnetic shielding material of Example 4. The horizontal axis of Figure 7 shows frequency [GHz], and the vertical axis of Figure 7 shows transmission loss [dB]. As shown in Figure 7, it can be seen that the electromagnetic shielding material of Example 4 has a transmission loss of 15 dB or more over the entire frequency band from 75 GHz to 110 GHz.

Figure 8 is a diagram showing the reflection loss of the electromagnetic shielding material of Example 4. The horizontal axis of Figure 8 shows frequency [GHz], and the vertical axis of Figure 8 shows reflection loss [dB]. As shown in Figure 8, it can be seen that the electromagnetic shielding material of Example 4 has a reflection loss of 6 dB or more over the entire frequency band from 75 GHz to 110 GHz.

Example 5
Resin: about 89.73 wt%
Electromagnetic wave shielding material 1: about 0.270 wt%
Electromagnetic wave shielding material 2: about 10.00 wt%
The mixture was mixed and appropriately stirred using a twin-screw extruder so as to disperse the mixture uniformly, and then pressed into an electromagnetic shielding material having a thickness of about 6 mm by a known method.

When the electrical conductivity and surface resistivity of the electromagnetic shielding material of Example 5 were measured, the electrical conductivity was approximately 0.67 S/m and the surface resistivity was approximately 250 Ω/□.

Figure 9 is a diagram showing the transmission loss of the electromagnetic shielding material of Example 5. The horizontal axis of Figure 9 shows frequency [GHz], and the vertical axis of Figure 9 shows transmission loss [dB]. As shown in Figure 9, the electromagnetic shielding material of Example 5 has a transmission loss of 30 dB or more over the entire frequency band of 75 GHz to 110 GHz, and in particular, it can be seen that the shielding performance is 40 dB or more over the entire frequency band of approximately 90 GHz to 110 GHz.

Figure 10 is a diagram showing the reflection loss of the electromagnetic shielding material of Example 5. The horizontal axis of Figure 10 shows frequency [GHz], and the vertical axis of Figure 10 shows reflection loss [dB]. As shown in Figure 10, it can be seen that the electromagnetic shielding material of Example 5 has a reflection loss of 8 dB or more over the entire frequency band from 75 GHz to 110 GHz.

Example 6
Resin: about 89.76 wt%
Electromagnetic wave shielding material 1: about 0.240 wt%
Electromagnetic wave shielding material 2: about 10.00 wt%
The mixture was mixed and appropriately stirred using a twin-screw extruder so as to disperse the mixture uniformly, and then pressed into an electromagnetic shielding material having a thickness of about 6 mm by a known method.

When the electrical conductivity and surface resistivity of the electromagnetic shielding material of Example 6 were measured, the electrical conductivity was approximately 0.56 S/m and the surface resistivity was approximately 300 Ω/□.

Figure 11 is a diagram showing the transmission loss of the electromagnetic shielding material of Example 6. The horizontal axis of Figure 11 shows frequency [GHz], and the vertical axis of Figure 11 shows transmission loss [dB]. As shown in Figure 11, the electromagnetic shielding material of Example 6 has a transmission loss of 35 dB or more over the entire frequency band of 75 GHz to 110 GHz, and in particular, it can be seen that the shielding performance is 40 dB or more over the entire frequency band of approximately 90 GHz to 110 GHz.

Figure 12 is a diagram showing the reflection loss of the electromagnetic shielding material of Example 6. The horizontal axis of Figure 12 shows frequency [GHz], and the vertical axis of Figure 12 shows reflection loss [dB]. As shown in Figure 12, it can be seen that the electromagnetic shielding material of Example 6 has a reflection loss of approximately 7 dB or more over the entire frequency band from 60 GHz to 90 GHz.

(Example 7)
Resin: about 89.775 wt%
Electromagnetic wave shielding material 1: about 0.225 wt%
Electromagnetic wave shielding material 2: about 10.00 wt%
The mixture was mixed and appropriately stirred using a twin-screw extruder so as to disperse the mixture uniformly, and then pressed into an electromagnetic shielding material having a thickness of about 6 mm by a known method.

When the electrical conductivity and surface resistivity of the electromagnetic shielding material of Example 7 were measured, the electrical conductivity was approximately 0.56 S/m and the surface resistivity was approximately 400 Ω/□.

Figure 13 is a diagram showing the transmission loss of the electromagnetic shielding material of Example 7. The horizontal axis of Figure 13 shows frequency [GHz], and the vertical axis of Figure 13 shows transmission loss [dB]. As shown in Figure 13, the electromagnetic shielding material of Example 7 has a transmission loss of 30 dB or more over the entire frequency band of 75 GHz to 110 GHz, and in particular, the shielding performance is 35 dB or more over the entire frequency band of approximately 80 GHz to 100 GHz, and the shielding performance is 40 dB or more over the entire frequency band of approximately 100 GHz to 110 GHz.

Figure 14 is a diagram showing the reflection loss of the electromagnetic shielding material of Example 7. The horizontal axis of Figure 14 shows frequency [GHz], and the vertical axis of Figure 14 shows reflection loss [dB]. As shown in Figure 14, it can be seen that the electromagnetic shielding material of Example 7 has a reflection loss of 8 dB or more over the entire frequency band from 60 GHz to 90 GHz.

(Example 8)
Resin: Approximately 89.91 wt%
Electromagnetic wave shielding material 1: about 0.09 wt%
Electromagnetic wave shielding material 2: about 10.00 wt%
The mixture was mixed and appropriately stirred using a twin-screw extruder so as to disperse the mixture uniformly, and then pressed into an electromagnetic shielding material having a thickness of about 6 mm by a known method.

When the electrical conductivity and surface resistivity of the electromagnetic shielding material of Example 8 were measured, the electrical conductivity was approximately 0.33 S/m and the surface resistivity was approximately 500 Ω/□.

Figure 15 is a diagram showing the transmission loss of the electromagnetic shielding material of Example 8. The horizontal axis of Figure 15 shows frequency [GHz], and the vertical axis of Figure 15 shows transmission loss [dB]. As shown in Figure 15, it can be seen that the electromagnetic shielding material of Example 8 has a transmission loss of 30 dB or more over the entire frequency band from 75 GHz to 110 GHz.

Figure 16 is a diagram showing the reflection loss of the electromagnetic shielding material of Example 8. The horizontal axis of Figure 16 shows frequency [GHz], and the vertical axis of Figure 16 shows reflection loss [dB]. As shown in Figure 16, it can be seen that the electromagnetic shielding material of Example 8 has a reflection loss of 8 dB or more over the entire frequency band from 75 GHz to 110 GHz.

Example 9
Resin: Approximately 89.928 wt%
Electromagnetic wave shielding material 1: about 0.072 wt%
Electromagnetic wave shielding material 2: about 10.00 wt%
The mixture was mixed and appropriately stirred using a twin-screw extruder so as to disperse the mixture uniformly, and then pressed into an electromagnetic shielding material having a thickness of about 6 mm by a known method.

When the electrical conductivity and surface resistivity of the electromagnetic shielding material of Example 9 were measured, the electrical conductivity was approximately 0.33 S/m and the surface resistivity was approximately 750 Ω/□.

Figure 17 is a diagram showing the transmission loss of the electromagnetic shielding material of Example 9. The horizontal axis of Figure 17 shows frequency [GHz], and the vertical axis of Figure 17 shows transmission loss [dB]. As shown in Figure 17, it can be seen that the electromagnetic shielding material of Example 9 has a transmission loss of 30 dB or more over the entire frequency band from 75 GHz to 110 GHz.

Figure 18 is a diagram showing the reflection loss of the electromagnetic shielding material of Example 9. The horizontal axis of Figure 18 shows frequency [GHz], and the vertical axis of Figure 18 shows reflection loss [dB]. As shown in Figure 18, it can be seen that the electromagnetic shielding material of Example 9 has a reflection loss of 7 dB or more over the entire frequency band from 75 GHz to 110 GHz.

(Comparative Example 1)
Resin: Approximately 89.5 wt%
Electromagnetic wave shielding material 1: about 0.5 wt%
Electromagnetic wave shielding material 2: about 10.00 wt%
The above ingredients were mixed, appropriately stirred using a twin-screw extruder so that they were uniformly dispersed, and then pressed into an electromagnetic shielding material having a thickness of about 2 mm. However, the transmission loss at frequencies below 95 GHz was less than 15 dB, indicating that the required shielding performance could not be obtained.

For each of the electromagnetic shielding materials of Examples 1 to 9, the electromagnetic wave reflection loss was measured by the free space method, and the transmission loss was measured based on ASTM D4935. Specifically, the reflection loss was determined by irradiating the electromagnetic shielding materials of Examples 1 to 9 with electromagnetic waves of 75 GHz to 110 GHz, and then measuring the difference in signal strength reflected from the surface of the specimen and the signal strength at the time of irradiation. The transmission loss was determined by irradiating the electromagnetic shielding materials of Examples 1 to 9 with electromagnetic waves of 75 GHz to 110 GHz, and then measuring the difference in signal strength transmitted through the specimen and the signal strength at the time of irradiation.

It can be seen that the electromagnetic wave reflection loss and transmission loss of the electromagnetic wave shielding materials of Examples 1 to 9 are both 6 dB or more in reflection loss and 15 dB or more in transmission loss. In addition, the electromagnetic wave shielding materials of Examples 1 to 9 tend to have flat reflection loss across the entire measured frequency band, which makes it easier to design electronic circuits.

For reference, the reflection loss was measured for the randomly selected electromagnetic shielding materials of Examples 2, 3, 6, and 7, with the lower limit of the frequency band set to 60 GHz. As a result, it was confirmed that the reflection loss for each of the electromagnetic shielding materials was 6 dB.

In this embodiment, an example of applying the electromagnetic shielding material to an automotive proximity radar has been described, but the electromagnetic shielding material can also be applied to communication devices attached to mobile phones, smartphones, PDAs, tablet terminals, personal computers, etc. that use the 73 GHz frequency band, various proximity radars of 76 GHz to 83 GHz, etc. In these cases, the electromagnetic shielding material can be attached or disposed on the electronic control unit or an equivalent member itself or in the vicinity thereof.

Claims (7)

The main component is resin,
an electromagnetic wave shielding material 1 contained in the resin, which contributes to increasing the absolute value of the reflection loss of the electromagnetic wave;
an electromagnetic wave shielding material 2 contained in the resin, which contributes to increasing the absolute value of the electromagnetic wave transmission loss;
An electromagnetic wave shielding material comprising:
a dispersant for dispersing the electromagnetic wave shielding materials (not sintered with silver fine particles) in the resin;
An electromagnetic wave shielding material having a thickness of 2 mm , the absolute value of the reflection loss being 5 dB or more and the absolute value of the transmission loss being 15 dB or more over the entire frequency band from 75 GHz to 110 GHz. The resin is a thermoplastic resin,
The electromagnetic wave shielding material according to claim 1 , wherein each of said electromagnetic wave shielding substances is nanocarbon. The resin is any one of polyamide resin, polyimide resin, polyamideimide resin, polyacetal resin, polycarbonate resin, polyethersulfone resin, polyetherketone resin, polyetherimide resin, polyalkylene terephthalate resin, acrylic resin, polysulfone resin, polyphenylene sulfide, polyolefin, polystyrene resin, syndiotactic polystyrene resin, acrylonitrile butadiene styrene resin, polyphenylene oxide resin, polybutylene, and liquid crystal polymer resin, or any combination of some of these,
2. The electromagnetic wave shielding material according to claim 1, wherein each of the electromagnetic wave shielding substances is an arbitrary combination of the electromagnetic wave shielding substance 1, which contributes to increasing the absolute value of the reflection loss of the electromagnetic wave, and the electromagnetic wave shielding substance 2, which contributes to increasing the absolute value of the transmission loss of the electromagnetic wave, selected from carbon nanotubes, carbon black, carbon nanocoils, carbon nanofibers, graphene, and fullerenes. The electromagnetic shielding material according to claim 1, wherein the dispersant is any of natural, semi-synthetic, and synthetic waxes. The electromagnetic shielding material according to claim 1, wherein the dispersant is any one of paraffin wax, montan wax, amide wax, ethylene-bis-stearamide, fatty acid metal salt, silicone, polyolefin wax, etc., or any combination of several of these. A signal processing unit comprising the electromagnetic shielding material according to any one of claims 1 to 5,
A signal processing unit, wherein the electromagnetic wave shielding material has a thickness of 2 mm or more. The signal processing unit according to claim 6 is an automobile proximity radar having the electromagnetic shielding material, a communication device including a mobile phone, a smartphone, a PDA, a tablet terminal, and a personal computer, and various proximity radars.

Images