JP2019004003A - Electromagnetic wave absorber and molded article with electromagnetic wave absorber - Google Patents

Abstract

An electromagnetic wave absorber that can be easily attached to a non-flat surface and has excellent electromagnetic wave absorption performance in a wide bandwidth. An electromagnetic wave absorber (1a) includes a first layer (10) and a conductive layer (20). The first layer (10) is a dielectric layer or a magnetic layer. The conductive layer (20) is provided on at least one side of the first layer and includes a conductive functional layer (22). The conductive functional layer (22) is a metal vapor-deposited film or a metal foil having a thickness of 50 μm or less. The product of the Young's modulus of the first layer (10) and the thickness of the first layer (10) is 0.1 to 1000 MPa · mm. The relative dielectric constant of the first layer (10) is 1-10. [Selection] Figure 1

Description

  The present invention relates to an electromagnetic wave absorber and a molded article with an electromagnetic wave absorber.

  In recent years, electromagnetic waves in a millimeter wave or quasi-millimeter wave region having a wavelength of about 1 to 10 mm and a frequency of 30 to 300 GHz have been used as information communication media. Use of such electromagnetic waves for collision prevention systems is being studied. The collision prevention system is, for example, a system that detects an obstacle in a vehicle and automatically brakes or adjusts the speed and distance between the vehicles by measuring the speed and distance between surrounding vehicles. In order for the collision prevention system to operate normally, it is important to avoid receiving unnecessary electromagnetic waves as much as possible in order to prevent misidentification. Therefore, it is conceivable to use an electromagnetic wave absorber that absorbs unnecessary electromagnetic waves in the collision prevention system.

  There are various types of electromagnetic wave absorbers according to the principle of electromagnetic wave absorption. For example, an electromagnetic wave absorber provided with an electromagnetic wave reflection layer, a dielectric layer having a thickness of λ / 4 (λ is the wavelength of an electromagnetic wave to be absorbed), and a resistive thin film layer (“λ / 4 type electromagnetic wave absorber”) Can be manufactured at low cost because the material is relatively inexpensive and easy to design. For example, Patent Document 1 proposes an electromagnetic wave absorber that exhibits excellent characteristics of functioning over a wide range of incident angles as a λ / 4 type electromagnetic wave absorber. Patent Document 2 describes an electromagnetic wave absorber having a magnetic layer.

JP 2003-198179 A JP 2012-94764 A

  In Patent Document 1 and Patent Document 2, the shape of the article to which the electromagnetic wave absorber is attached is not specifically examined, and the electromagnetic wave absorption performance in a wide bandwidth is not specifically examined.

  Therefore, the present invention provides an electromagnetic wave absorber that is advantageous for mounting on a non-flat surface and that is excellent in electromagnetic wave absorption performance in a wide bandwidth.

The present invention
A first layer that is a dielectric layer or a magnetic layer;
A conductive layer provided on at least one side of the first layer and including a conductive functional layer that is a metal vapor-deposited film or a metal foil having a thickness of 50 μm or less, and
The product of the Young's modulus of the first layer and the thickness of the first layer is 0.1 to 1000 MPa · mm,
The relative dielectric constant of the first layer is 1-10.
An electromagnetic wave absorber is provided.

The present invention also provides:
Molded products,
The electromagnetic wave absorber attached to the molded article,
A molded article with an electromagnetic wave absorber is provided.

  The above-mentioned electromagnetic wave absorber is easy to attach to a non-flat surface and has excellent electromagnetic wave absorption performance in a wide bandwidth (for example, a bandwidth of 2 GHz or more included in a frequency band of 50 to 100 GHz).

FIG. 1 is a cross-sectional view showing an example of the electromagnetic wave absorber of the present invention. FIG. 2 is a side view showing an example of the molded article with an electromagnetic wave absorber of the present invention. FIG. 3 is a cross-sectional view showing another example of the electromagnetic wave absorber of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, the following description demonstrates this invention exemplarily and this invention is not necessarily limited to the following embodiment.

  If the electromagnetic wave absorber can be attached to a non-flat surface such as a curved surface, the use of the electromagnetic wave absorber is expanded. As an example of the use of the electromagnetic wave absorber, a collision prevention system mounted on an automobile can be cited. Conventional millimeter wave radars of collision prevention systems often radiate millimeter waves in front of automobiles, and electromagnetic wave absorbers are often attached to a flat surface. However, if it is possible to detect an obstacle by irradiating the millimeter wave obliquely forward or obliquely behind the automobile, the safety of the automobile can be further improved. Therefore, it is conceivable to arrange the millimeter wave radar at the corner of the automobile. In this case, in order to prevent electromagnetic interference, it is desirable to affix an electromagnetic wave absorber to the end of an automobile part such as a bumper, and it is expected that the demand for an electromagnetic wave absorber that can be easily affixed to an uneven surface such as a curved surface will increase. The

  Further, in the millimeter wave radar of the collision prevention system, in order to increase the resolution of the radar, an attempt is made to widen the use frequency. For example, in a millimeter wave radar of a collision prevention system using an electromagnetic wave having a frequency of 76 GHz and a millimeter wave radar of a collision prevention system using an electromagnetic wave having a frequency of 79 GHz, the use bands may be set to 1 GHz and 4 GHz, respectively. For this reason, it is desirable that the electromagnetic wave absorber can exhibit good electromagnetic wave absorption performance in a wide bandwidth (for example, a bandwidth of 2 GHz or more included in a frequency band of 50 to 100 GHz).

  In addition, it is assumed that a plurality of millimeter wave radars using electromagnetic waves of different frequencies are used in the collision prevention system. In this case, preparing different types of electromagnetic wave absorbers for each millimeter wave radar may increase the number of parts of the collision prevention system and increase the manufacturing cost. In addition, preparing different types of electromagnetic wave absorbers for each millimeter wave radar may increase the total weight of the collision prevention system. Therefore, when multiple millimeter wave radars that use electromagnetic waves of different frequencies are used in the collision prevention system, if there is an electromagnetic wave absorber that can exhibit good electromagnetic wave absorption performance in a wide bandwidth, a different type for each millimeter wave radar There is no need to prepare an electromagnetic wave absorber.

  In view of such circumstances, the present inventors have conducted day and night studies on an electromagnetic wave absorber that can be easily attached to a non-flat surface and has excellent electromagnetic wave absorption performance in a wide bandwidth. As a result, the electromagnetic wave absorber according to the present invention was devised. In addition, the collision prevention system in a motor vehicle is only an example of the use of an electromagnetic wave absorber.

  As shown in FIG. 1, the electromagnetic wave absorber 1 a includes a first layer 10 and a conductive layer 20. The first layer 10 is a dielectric layer or a magnetic layer. The conductive layer 20 is provided on at least one side of the first layer 10 and includes a conductive functional layer 22. The conductive functional layer 22 is a metal vapor deposition film or a metal foil having a thickness of 50 μm or less. The product of the Young's modulus (tensile modulus) of the first layer 10 and the thickness of the first layer 10 is 0.1 to 1000 MPa · mm. In addition, the relative dielectric constant of the first layer 10 is 1-10. The conductive functional layer 22 is a metal vapor deposition film or a metal foil having a thickness of 50 μm or less, and the product of the Young's modulus of the first layer 10 and the thickness of the first layer is 0.1 to 1000 MPa · mm. Therefore, the electromagnetic wave absorber 1a can be easily attached to a non-flat surface. In addition, since the relative permittivity of the first layer 10 is 1 to 10, the electromagnetic wave absorber 1a has good electromagnetic wave absorption in a wide bandwidth (for example, a bandwidth of 2 GHz or more included in a frequency band of 50 to 100 GHz). Performance can be demonstrated. In the present specification, the Young's modulus of the first layer 10 means a value measured at room temperature in accordance with Japanese Industrial Standard (JIS) K7161-1. The relative dielectric constant of the first layer 10 can be measured by a cavity resonator perturbation method.

  The electromagnetic wave absorber 1a has, for example, an electromagnetic wave absorption amount of 20 dB or more in a bandwidth of 2 GHz or more included in the frequency band of 50 to 100 GHz. Thus, the electromagnetic wave absorber 1a can exhibit good electromagnetic wave absorption performance with a wide bandwidth. The electromagnetic wave absorption amount of the electromagnetic wave absorber 1a can be measured in accordance with JIS R 1679 by setting the incident angle to 15 ° and irradiating the electromagnetic wave absorber 1a with the electromagnetic wave.

  From the viewpoint of improving the ease of attachment to the non-flat surface of the electromagnetic wave absorber 1a, when the conductive functional layer 22 is a metal foil, the thickness is desirably 50 μm or less, more desirably 30 μm or less, It is desirably 20 μm or less, and particularly desirably 10 μm or less. Further, from the viewpoint of further enhancing the ease of attachment of the electromagnetic wave absorber 1a to a non-flat surface, it is extremely desirable that the conductive functional layer 22 is a metal vapor deposition film.

  From the viewpoint of increasing the ease of attachment to the non-flat surface of the electromagnetic wave absorber 1a, the product of the Young's modulus of the first layer 10 and the thickness of the first layer is preferably 0.1 to 500 MPa · mm, more The pressure is desirably 0.1 to 100 MPa · mm, more desirably 0.1 to 50 MPa · mm, and particularly desirably 0.1 to 20 MPa · mm.

  From the viewpoint of adjusting the product of the Young's modulus of the first layer 10 and the thickness of the first layer 10 to 0.1 to 1000 MPa · mm, the Young's modulus of the first layer 10 is desirably 2000 MPa or less. Thereby, even when the thickness of the first layer 10 cannot be changed greatly, the product of the Young's modulus of the first layer 10 and the thickness of the first layer can be easily adjusted to 0.1 to 1000 MPa · mm.

  The first layer 10 includes, for example, a polymer material. The polymer material contained in the first layer 10 is, for example, acrylic resin, ethylene vinyl acetate copolymer (EVA), polyvinyl chloride, polyurethane, acrylic urethane resin, ionomer, polyolefin, polypropylene, polyethylene, silicone resin, polyester, Synthetic resins (including thermoplastic elastomers) such as polystyrene, polyimide, polyamide, polysulfone, polyethersulfone, and epoxy resin, or polyisoprene rubber, polystyrene-butadiene rubber, polybutadiene rubber, chloroprene rubber, acrylonitrile butadiene rubber, butyl rubber , Synthetic rubbers such as acrylic rubber, ethylene propylene rubber, and silicone rubber. These can be used alone or in combination of two or more as the polymer material contained in the first layer 10.

  The first layer 10 may be a foam, for example. In this case, the relative dielectric constant of the first layer 10 tends to be low. In addition, the first layer 10 can be reduced in weight.

  In the first layer 10, at least one of a dielectric and a magnetic material may be dispersed. In this case, for example, the above polymer material functions as a matrix. By adjusting the type and amount of the dielectric or magnetic material dispersed in the first layer 10, the electromagnetic wave absorber 1a can exhibit desired electromagnetic wave absorption characteristics. The dielectric material dispersed in the first layer 10 is, for example, an inorganic material such as carbon, titanium oxide, alumina, and barium titanate. The amounts of the dielectric and magnetic material dispersed in the first layer 10 are adjusted so that the relative dielectric constant of the first layer 10 is 1-10.

  The metal contained in the conductive functional layer 22 is, for example, copper, nickel, zinc, or an alloy thereof, aluminum, gold, or stainless steel. In addition, in this specification, an alloy is contained in a metal. The conductive functional layer 22 is preferably made of aluminum. In this case, the manufacturing cost or the acquisition cost of the conductive layer 20 is low. When the conductive functional layer 22 is a metal foil, the metal foil is, for example, an aluminum foil, a copper foil, a gold foil, a titanium foil, a nickel foil, a magnesium foil, an aluminum alloy foil, a copper alloy foil, a gold alloy foil, a titanium alloy foil, Nickel alloy foil, magnesium alloy foil, or stainless steel foil. Among these, aluminum foil is desirably used as the metal foil. This is because aluminum foil can be obtained at a low cost and the manufacturing cost of the electromagnetic wave absorber 1a can be reduced.

  The conductive layer 20 may be configured only by the conductive functional layer 22, but may further include, for example, a non-conductive layer that is in contact with the conductive functional layer 22. For example, the conductive layer 20 further includes a support 25 that supports the conductive layer 22 as shown in FIG. The support body 25 is disposed between the first layer 10 and the conductive functional layer 22 to protect the conductive functional layer 22. For example, when the conductive functional layer 22 is in direct contact with the first layer 10, components contained in the first layer 10 may diffuse into the conductive functional layer 22 and the conductive functional layer 22 may deteriorate. In addition, when the adhesive or pressure-sensitive adhesive for attaching the first layer 10 to the conductive functional layer 22 is attached to the conductive functional layer 22, the conductive functional layer 22 is deteriorated by the components contained in the adhesive or pressure-sensitive adhesive. There is a possibility that. Furthermore, when the electromagnetic wave absorber 1a is attached to a non-flat surface, the conductive function layer 22 is bent and the thickness of the conductive function layer 22 is small. However, since the conductive functional layer 22 is protected by the support 25, the conductive functional layer 22 is unlikely to deteriorate, and the electromagnetic wave absorber 1a easily exhibits desired electromagnetic wave absorbing performance over a long period of time.

  As described above, the support 25 has a role of supporting the conductive functional layer 22 and protecting the conductive functional layer 22. For this reason, it is desirable that the support 25 is made of a material having good heat resistance and good chemical durability. For this reason, the support body 25 is made of a polyester resin such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN).

  As shown in FIG. 1, the electromagnetic wave absorber 1 a further includes a resistance layer 30, for example. The resistance layer 30 is provided on at least one side of the first layer 10. In this case, the first layer 10 is a dielectric layer, and is disposed between the resistance layer 30 and the conductive layer 20. In other words, the electromagnetic wave absorber 1a is a λ / 4 type electromagnetic wave absorber.

When the electromagnetic wave absorber 1a is a λ / 4 type electromagnetic wave absorber, when an electromagnetic wave having a wavelength to be absorbed (λ _O ) is incident, the electromagnetic wave caused by reflection (surface reflection) on the surface of the resistance layer 30 and the conductive layer 20 It is designed to interfere with electromagnetic waves caused by reflection (back surface reflection). For this reason, if the sheet resistance of the conductive layer 20 is high, electromagnetic waves are transmitted through the conductive layer 20a, and the amount of electromagnetic waves absorbed by the electromagnetic wave absorber 1a is reduced. In the λ / 4 type electromagnetic wave absorber, as shown in the following formula (1), absorption is performed by the thickness (t) of the first layer 10 as a dielectric layer and the relative dielectric constant (ε _r ) of the dielectric layer. The wavelength (λ _O ) of the target electromagnetic wave is determined. That is, by appropriately adjusting the material and thickness of the first layer 10 that is a dielectric layer, an electromagnetic wave having a wavelength to be absorbed can be set. In the formula (1), sqrt (ε _r ) means the square root of the relative dielectric constant (ε _r ).
λ _O = 4t × sqrt (ε _r ) Equation (1)

  As described above, the resistance layer 30 is disposed to reflect an electromagnetic wave having a wavelength to be absorbed near the surface of the electromagnetic wave absorber 1a. The resistance layer 30 has, for example, a sheet resistance of 200 to 600 Ω / □, and preferably a sheet resistance of 360 to 500 Ω / □. In this case, the electromagnetic wave absorber 1a can easily selectively absorb an electromagnetic wave having a wavelength widely used in millimeter wave radar or quasi-millimeter wave radar. For example, the electromagnetic wave absorber 1a can effectively attenuate an electromagnetic wave having a frequency of 50 to 100 GHz, particularly 60 to 90 GHz used for millimeter wave radar.

The resistance layer 30 is, for example, any one of a metal oxide, a conductive polymer, a carbon nanotube, a metal nanowire, and a metal mesh whose main component is at least one selected from the group consisting of indium, tin, and zinc. (Hereinafter referred to as “resistive function layer”). In particular, the resistance functional layer of the resistance layer 30 is preferably made of indium tin oxide (ITO) from the viewpoint of stability of sheet resistance in the resistance layer 30 and durability of the resistance layer 30. In this case, the material forming the resistance functional layer of the resistance layer 30 is preferably ITO containing 20 to 40% by weight of SnO ₂ , more preferably ITO containing 25 to 35% by weight of SnO _2. . ITO containing SnO _{2 in} such a range has an extremely stable amorphous structure, and can suppress variations in the sheet resistance of the resistance layer 30 even in a high temperature and high humidity environment. The sheet resistance of the resistance layer 30 means, for example, a value measured with respect to a surface defined by the resistance function layer. In this specification, the “main component” means a component that is contained most on a mass basis.

  The resistance functional layer of the resistance layer 30 has a thickness of 10 to 100 nm, for example, and preferably has a thickness of 25 to 50 nm. Thereby, even if it uses for a long time in the state where electromagnetic wave absorber 1a was attached to the surface which is not flat, the sheet resistance of resistance layer 30 tends to be stabilized.

  The resistance layer 30 may further include, for example, a support that supports the resistance functional layer. In this case, the resistance layer 30 can be produced, for example, by forming a resistance functional layer on a support by a film forming method such as sputtering or coating (for example, bar coating). In this case, the support also serves as an auxiliary material that can adjust the thickness of the resistance functional layer with high accuracy. Examples of the material for the support of the resistance layer 30 include polyester resins such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), acrylic resin, polycarbonate (PC), polyolefin, polyethylene (PE), polypropylene (PP), cyclohexane. It is an olefin polymer (COP), polyurethane, urethane acrylic resin, biaxially oriented polypropylene (CPP), or vinylidene chloride resin. The material of the support of the resistance layer 30 may be the same as the material of the support of the conductive layer 20, or may be a different material. Especially, the material of the support body of the resistance layer 30 is desirably PET from the viewpoint of a balance between good heat resistance, dimensional stability, and cost. If necessary, the support in the resistance layer 30 can be omitted.

  When the resistance layer 30 includes a support, in the resistance layer 30, the resistance functional layer may be disposed at a position closer to the first layer 10 than the support, or the support is the first layer than the resistance functional layer. It may be arranged at a position close to 10.

  The support of the resistance layer 30 has a thickness of, for example, 10 to 150 μm, desirably 20 to 100 μm, and more desirably 30 to 80 μm. Thereby, the bending rigidity of the resistance layer 30 is low, and the formation or deformation of wrinkles can be suppressed when the resistance functional layer of the resistance layer 30 is formed.

  The first layer 10 that is a dielectric layer may be a single layer or a laminate of a plurality of layers. When the first layer 10 is a laminate of a plurality of layers, the relative dielectric constant of the first layer 10 is determined by measuring the relative dielectric constant of each layer, and the relative thickness of the obtained first layer 10 is the thickness of the first layer 10 It can be calculated by multiplying the ratio of the thickness of each layer to and adding these.

  When the electromagnetic wave absorber 1a is a λ / 4 type electromagnetic wave absorber and a dielectric layer is disposed outside the resistance layer 30, the dielectric layer is only a non-porous layer having a relative dielectric constant of 2 or more. Be placed. In addition, when a porous body is installed on the surface of the electromagnetic wave absorber, the electromagnetic wave absorbability of the electromagnetic wave absorber may be reduced due to moisture absorption when left for a long time in a high humidity environment.

  As shown in FIG. 1, the electromagnetic wave absorber 1a further includes an adhesive layer 40, for example. In this case, the adhesive layer 40 is disposed outside the conductive layer 20. Thereby, the electromagnetic wave absorber 1a can be easily attached to an article such as a molded product.

  The adhesive layer 40 includes, for example, an adhesive such as an acrylic adhesive, a rubber adhesive, a silicone adhesive, and a urethane adhesive.

  As shown in FIG. 2, for example, a molded article 100 with an electromagnetic wave absorber can be manufactured using the electromagnetic wave absorber 1 a. The molded product 100 with an electromagnetic wave absorber includes a molded product 70 and an electromagnetic wave absorber 1 a attached to the molded product 70. The molded product 70 is, for example, an automobile part such as a bumper.

  An example of the manufacturing method of the electromagnetic wave absorber 1a will be described. A resistance functional layer is formed on a support formed into a sheet shape by a film forming method such as vapor deposition, sputtering, and coating (for example, bar coating), and the resistance layer 30 is manufactured. Among these, from the viewpoint of strictly adjusting the sheet resistance of the resistance layer 30 and the thickness of the resistance functional layer of the resistance layer 30, the resistance functional layer of the resistance layer 30 is desirably formed by sputtering. As the conductive layer 20, for example, a laminate including the support 25 and the conductive functional layer 22 is prepared.

  Next, a resin composition for forming the first layer 10 having a predetermined thickness is placed on one main surface of the conductive layer 20 (for example, the main surface formed by the support 25). Thereafter, one main surface of the resistance layer 30 is overlaid on the resin composition forming the first layer 10. If necessary, the resin composition is cured. Thereby, the electromagnetic wave absorber 1a can be manufactured. According to this method, since the thickness of the first layer 10 can be easily controlled, the electromagnetic wave absorber 1a can be manufactured so as to effectively absorb an electromagnetic wave having a wavelength to be absorbed. Moreover, since the resistance layer 30 and the conductive layer 20 are formed separately, the time required for manufacturing the electromagnetic wave absorber 1a is short, and the manufacturing cost of the electromagnetic wave absorber 1a is low. In addition, as the conductive layer 20, a layer composed only of the conductive functional layer 22 may be used, or an adhesive or a pressure-sensitive adhesive may be used to attach the first layer 10 to the conductive layer 20 or the resistance layer 30.

<Modification>
The electromagnetic wave absorber 1a may be modified like the electromagnetic wave absorber 1b shown in FIG. The electromagnetic wave absorber 1b is configured in the same manner as the electromagnetic wave absorber 1a unless otherwise described. The same or corresponding components of the electromagnetic wave absorber 1b as those of the electromagnetic wave absorber 1a are denoted by the same reference numerals, and detailed description thereof is omitted. The description regarding the electromagnetic wave absorber 1a also applies to the electromagnetic wave absorber 1b unless there is a technical contradiction.

As shown in FIG. 3, the electromagnetic wave absorber 1 b includes the first layer 10 and the conductive layer 20, but does not include the resistance layer 30. The first layer 10 is a dielectric layer or a magnetic layer. When the first layer 10 is a dielectric layer, the electromagnetic wave absorber 1b is a dielectric loss type electromagnetic wave absorber that absorbs an electromagnetic wave by using dielectric loss caused by molecular polarization. In a dielectric loss type electromagnetic wave absorber, the polarization of the molecule cannot follow the change in the electric field, and the energy of the electromagnetic wave is lost as heat. In this case, in the first layer 10, for example, the dielectric material such as carbon particles or barium titanate (BaTiO ₃ ) particles in the above-described synthetic resin or synthetic rubber mentioned as the polymer material of the first layer 10 that is a dielectric layer. Particles are dispersed. The content of dielectric particles in the first layer 10 is adjusted so that the relative dielectric constant of the first layer 10 is 1-10.

  When the first layer 10 is a magnetic layer, the electromagnetic wave absorber 1b is a magnetic loss type electromagnetic wave absorber that absorbs electromagnetic waves due to magnetic loss of the magnetic material. In the magnetic loss type electromagnetic wave absorber, the magnetic moment cannot follow the change of the magnetic field, and the energy of the electromagnetic wave is lost as heat. In this case, in the first layer 10, for example, particles of a magnetic material such as ferrite, iron, or nickel are dispersed in the above synthetic resin or synthetic rubber cited as the polymer material of the first layer 10 that is a dielectric layer. ing. The content of the magnetic particles in the first layer 10 is adjusted so that the relative dielectric constant of the first layer 10 is 1-10.

  Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited to the following examples.

<Example 1>
Sputtering on a film-like support made of polyester (Mitsubishi Chemical Polyester, Mitsubishi Diafoil, thickness: 38 μm thickness) using ITO containing 30% by weight of SnO ₂ so that the sheet resistance is 380Ω / □. Thus, a resistance functional layer was formed, and a resistance layer according to Example 1 was manufactured. As the conductive layer according to Example 1, an aluminum vapor-deposited film (manufactured by Mitsui Chemicals, Inc., product name: CP WS20, base material: biaxially oriented polypropylene (CPP) film, base material thickness: 20 μm) was prepared. An acrylic resin (Kuraray Co., Ltd., Clarity LA2330) press-molded to a thickness of 560 μm, which is the dielectric layer according to Example 1, was placed on the aluminum deposited film of the conductive layer according to Example 1. Next, the resistance layer according to Example 1 was overlaid on the acrylic resin (dielectric layer) with the main surface formed by the support of the resistance layer facing the acrylic resin. Thus, the electromagnetic wave absorber which concerns on Example 1 was obtained. The dielectric constant of the dielectric layer in the electromagnetic wave absorber according to Example 1 was 2.55.

<Example 2>
As a conductive layer according to Example 2, a PET film with aluminum foil manufactured by UACJ having a two-layer structure of a PET layer having a thickness of 25 μm and an aluminum foil having a thickness of 7 μm was prepared. An electromagnetic wave absorber according to Example 2 was obtained in the same manner as in Example 1 except that the conductive layer according to Example 2 was used instead of the conductive layer according to Example 1. The conductive layer according to Example 2 and the dielectric layer according to Example 1 were overlapped with the aluminum foil of the conductive layer according to Example 2 facing the dielectric layer according to Example 1.

<Example 3>
Transparent having a thickness of 0.025 mm on the surface of an aluminum vapor-deposited film (made by Mitsui Chemicals, Inc., product name: CP WS20, base material: biaxially oriented polypropylene (CPP) film, base material thickness: 20 μm) An adhesive sheet (manufactured by Nitto Denko Corporation, CS9861US) was bonded, and a PET film having a thickness of 11 μm (manufactured by Toray Industries Inc., product name: Lumirror S10) was laminated and pasted on the transparent adhesive sheet. In this way, a conductive layer according to Example 3 was obtained. An electromagnetic wave absorber according to Example 3 was obtained in the same manner as in Example 1 except that the conductive layer according to Example 3 was used instead of the conductive layer according to Example 1. The conductive layer according to Example 3 and the dielectric layer according to Example 1 were overlapped with the PET film of the conductive layer according to Example 3 facing the dielectric layer according to Example 1.

<Example 4>
As a conductive layer according to Example 4, a PET layer having a thickness of 25 μm, an aluminum foil having a thickness of 7 μm, and a PET layer having a thickness of 9 μm are laminated in this order. A PET film was prepared. An electromagnetic wave absorber according to Example 4 was obtained in the same manner as in Example 1 except that the conductive layer according to Example 4 was used instead of the conductive layer according to Example 1. The conductive layer according to Example 4 and the dielectric layer according to Example 1 were overlapped with the PET film having the thickness of 25 μm of the conductive layer according to Example 4 directed to the dielectric layer according to Example 1.

<Example 5>
EVA resin (Evaflex EV250 manufactured by Mitsui DuPont, Inc., relative dielectric constant: 2.45) was press-molded at 120 ° C. to obtain a dielectric layer according to Example 5 having a thickness of 560 μm. An electromagnetic wave absorber according to Example 5 was obtained in the same manner as Example 4 except that the dielectric layer according to Example 5 was used instead of the dielectric layer according to Example 1.

<Example 6>
50 parts by weight of barium titanate powder (manufactured by Sakai Chemical Industry Co., Ltd., product name: BT-01) was added to 100 parts by weight of EVA resin (Mitsui DuPont, Evaflex EV250), and kneaded with a mixing roll. . Thereafter, the kneaded material was press-molded at 120 ° C. to obtain a dielectric layer according to Example 6 having a thickness of 456 μm. The dielectric constant of the dielectric layer according to Example 6 was 3.90. An electromagnetic wave absorber according to Example 6 was obtained in the same manner as Example 4 except that the dielectric layer according to Example 6 was used instead of the dielectric layer according to Example 1.

<Example 7>
100 parts by weight of EVA resin (Mitsui DuPont, EVAFLEX EV250) was added 100 parts by weight of barium titanate powder (manufactured by Sakai Chemical Industry Co., Ltd., product name: BT-01) and kneaded with a mixing roll. . Thereafter, the kneaded material was press-molded at 120 ° C. to obtain a dielectric layer according to Example 7 having a thickness of 397 μm. The dielectric constant of the dielectric layer according to Example 7 was 5.19. An electromagnetic wave absorber according to Example 7 was obtained in the same manner as Example 4 except that the dielectric layer according to Example 7 was used instead of the dielectric layer according to Example 1.

<Example 8>
200 parts by weight of barium titanate powder (manufactured by Sakai Chemical Industry Co., Ltd., product name: BT-01) was added to 100 parts by weight of EVA resin (Mitsui DuPont, EVAFLEX EV250), and kneaded with a mixing roll. . Thereafter, the kneaded material was press-molded at 120 ° C. to obtain a dielectric layer according to Example 8 having a thickness of 336 μm. The dielectric constant of the dielectric layer according to Example 8 was 7.25. An electromagnetic wave absorber according to Example 8 was obtained in the same manner as Example 4 except that the dielectric layer according to Example 8 was used instead of the dielectric layer according to Example 1.

<Example 9>
An olefin-based foam (manufactured by Nitto Denko Corporation, product name: SCF 100, relative dielectric constant: 1.07) was sliced to obtain a dielectric layer according to Example 9 having a thickness of 0.82 mm. The dielectric layer according to Example 9 is formed by interposing an acrylic adhesive having a thickness of 30 μm between the PET layer having a thickness of 25 μm of the conductive layer according to Example 4 and the dielectric layer according to Example 9. The conductive layer according to Example 4 was attached. Next, the dielectric layer according to Example 9 and the resistance layer according to Example 1 with the main surface formed by the support of the resistance layer according to Example 1 facing the dielectric layer according to Example 9 The dielectric layer according to Example 9 and the resistance layer according to Example 1 were bonded together with an acrylic adhesive having a thickness of 30 μm interposed therebetween. Thus, the electromagnetic wave absorber which concerns on Example 9 was obtained.

<Example 10>
A polyester foam (manufactured by Nitto Denko Corporation, product name: SCF T100, relative dielectric constant: 1.09) was sliced to obtain a dielectric layer according to Example 10 having a thickness of 0.79 mm. The dielectric layer according to Example 10 with an acrylic adhesive having a thickness of 30 μm interposed between the PET layer having a thickness of 25 μm of the conductive layer according to Example 4 and the dielectric layer according to Example 10; The conductive layer according to Example 4 was attached. Next, the dielectric layer according to Example 10 and the resistance layer according to Example 1 with the main surface formed by the support of the resistance layer according to Example 1 facing the dielectric layer according to Example 10 The dielectric layer according to Example 10 and the resistance layer according to Example 1 were adhered to each other with an acrylic adhesive having a thickness of 30 μm interposed therebetween. Thus, the electromagnetic wave absorber which concerns on Example 10 was obtained.

<Example 11>
To 100 parts by weight of acrylic resin (Kuraray, Clarity LA2330), 300 parts by weight of carbonyl iron powder YW1 made by New Metals End Chemicals was added, kneaded with a mixing roll, and then press molded at 120 ° C. to a thickness of 1200 μm. A sheet-like dielectric layer having a thickness (dielectric layer according to Example 11) was produced. The dielectric constant of the dielectric layer according to Example 11 was 6.60. The dielectric layer according to Example 11 was overlaid on the conductive layer according to Example 4 with the support of the conductive layer according to Example 4 directed toward the dielectric layer according to Example 11. Thus, the electromagnetic wave absorber which concerns on Example 11 was obtained.

<Example 12>
An ionomer resin (Mitsui / DuPont Polychemical Co., Ltd., product name: High Milan 1855) was kneaded with a mixing roll and then press molded at 120 ° C. to produce a dielectric layer according to Example 12 having a thickness of 565 μm. The dielectric constant of the dielectric layer according to Example 12 was 2.44. An electromagnetic wave absorber according to Example 12 was obtained in the same manner as in Example 4 except that the dielectric layer according to Example 12 was used instead of the dielectric layer according to Example 1.

<Example 13>
Dielectric layer according to Example 13 having a thickness of 580 μm after kneading a linear low density polyethylene (LLDPE) (manufactured by Prime Polymer Co., Ltd., product name: ULT ZEXX 2022L) with a mixing roll and press molding at 120 ° C. Was made. The dielectric constant of the dielectric layer according to Example 13 was 2.30. An electromagnetic wave absorber according to Example 13 was obtained in the same manner as in Example 9 except that the dielectric layer according to Example 13 was used instead of the dielectric layer according to Example 9.

<Example 14>
High-density polyethylene (HDPE) (manufactured by Prime Polymer Co., Ltd., product name: Hi-Zex 2100J) was kneaded with a mixing roll and then press-molded at 120 ° C. to produce a dielectric layer according to Example 14 having a thickness of 595 μm. The dielectric constant of the dielectric layer according to Example 14 was 2.30. An electromagnetic wave absorber according to Example 14 was obtained in the same manner as Example 9 except that the dielectric layer according to Example 14 was used instead of the dielectric layer according to Example 9.

<Example 15>
EVA resin (Mitsui DuPont, EVAFLEX EV250, relative dielectric constant: 2.45) was press-molded at 120 ° C. to obtain a dielectric layer according to Example 15 having a thickness of 571 μm. As a conductive layer according to Example 15, a PET film with aluminum foil made by UACJ having a two-layer structure having a PET layer having a thickness of 9 μm and an aluminum foil having a thickness of 7 μm was prepared. Similar to Example 1, except that the dielectric layer according to Example 15 was used instead of the dielectric layer according to Example 1, and the conductive layer according to Example 15 was used instead of the conductive layer according to Example 1. Thus, an electromagnetic wave absorber according to Example 15 was obtained. The dielectric layer according to Example 15 was overlaid on the aluminum foil having a thickness of 7 μm in the conductive layer according to Example 15.

<Comparative Example 1>
An electromagnetic wave absorber according to Comparative Example 1 was obtained in the same manner as in Example 1 except that an aluminum foil having a thickness of 100 μm was used instead of the conductive layer according to Example 1.

<Comparative Example 2>
300 parts by weight of barium titanate powder (manufactured by Sakai Chemical Industry Co., Ltd., product name: BT-01) was added to 100 parts by weight of EVA resin (Mitsui DuPont, Evaflex EV250), and kneaded with a mixing roll. . Thereafter, the kneaded material was press-molded at 120 ° C. to obtain a dielectric layer according to Comparative Example 2 having a thickness of 242 μm. The dielectric constant of the dielectric layer according to Comparative Example 2 was 14.00. An electromagnetic wave absorber according to Comparative Example 2 was obtained in the same manner as in Example 4 except that the dielectric layer according to Comparative Example 2 was used instead of the dielectric layer according to Example 1.

<Comparative Example 3>
400 parts by weight of carbonyl iron powder YW1 made by New Metals End Chemicals is added to 100 parts by weight of acrylic resin (Kuraray, Clarity LA2330), kneaded with a mixing roll, and press-molded at 120 ° C. to a thickness of 1200 μm. A sheet-like dielectric layer having a thickness (dielectric layer according to Comparative Example 3) was produced. The dielectric constant of the dielectric layer according to Comparative Example 3 was 10.30. The dielectric layer according to Comparative Example 3 was overlaid on the conductive layer according to Example 4 in a state where the PET layer having a thickness of 25 μm of the conductive layer according to Example 4 was directed to the dielectric layer according to Comparative Example 3. In this way, an electromagnetic wave absorber according to Comparative Example 3 was obtained.

<Comparative example 4>
As a dielectric layer according to Comparative Example 4, a polyester film (PET film) manufactured by Toray Industries, Inc. having a thickness of 480 μm was prepared. The dielectric constant of the dielectric layer according to Comparative Example 4 was 3.20. An electromagnetic wave absorber according to Comparative Example 4 was obtained in the same manner as in Example 9 except that the dielectric layer according to Comparative Example 4 was used instead of the dielectric layer according to Example 9.

<Comparative Example 5>
A polycarbonate (PC) sheet manufactured by Sumika Acrylic Co., Ltd. having a thickness of 500 μm was prepared as a dielectric layer according to Comparative Example 5. The dielectric constant of the dielectric layer according to Comparative Example 5 was 2.90. An electromagnetic wave absorber according to Comparative Example 5 was obtained in the same manner as in Example 9, except that the dielectric layer according to Comparative Example 5 was used instead of the dielectric layer according to Example 9.

[Young's modulus]
The Young's modulus (tensile modulus) of each dielectric layer and each conductive layer used in Examples and Comparative Examples was measured in accordance with JIS K7161-1 at room temperature, and the Young's modulus in each dielectric layer and each conductive layer The product of thickness (Et) was determined. The results are shown in Table 1.

[Relative permittivity of dielectric layer]
Using a network analyzer (manufactured by Agilent Technologies, product name: N5230C) and a cavity resonator (cavity resonator CP531 manufactured by Kanto Electronics Application Development Co., Ltd.), the relative dielectric constant at 10 GHz of each dielectric layer in Examples and Comparative Examples Was measured by cavity resonator perturbation method. The results are shown in Table 1.

[Bending adhesiveness]
A state where an electromagnetic wave absorber according to an example or a comparative example is attached to a steel plate bent to R50 (curvature radius: 50 mm) using a transparent adhesive sheet (CS9862UA, manufactured by Nitto Denko Corporation) having a thickness of 0.05 mm. Each example and each comparative example were evaluated according to the following indices. The results are shown in Table 2.
a: The electromagnetic wave absorber is deformed along the curved surface of the steel plate and does not float after being attached to the steel plate.
b: Although the electromagnetic wave absorber is deformed along the curved surface of the steel plate, the electromagnetic wave absorber is broken and wrinkled.
x: The electromagnetic wave absorber cannot be deformed along the curved surface of the steel sheet and is difficult to be attached.

A state in which the electromagnetic wave absorber according to the example or the comparative example is attached to a steel sheet bent to R37 (curvature radius: 37 mm) using a transparent adhesive sheet (manufactured by Nitto Denko Corporation, CS9862UA) having a thickness of 0.05 mm. The examples and comparative examples were evaluated according to the following indices. The results are shown in Table 2.
a: The electromagnetic wave absorber is deformed along the curved surface of the steel plate and does not float after being attached to the steel plate.
b: Although the electromagnetic wave absorber is deformed along the curved surface of the steel plate, the electromagnetic wave absorber is broken and wrinkled.
x: The electromagnetic wave absorber cannot be deformed along the curved surface of the steel sheet and is difficult to be attached.

[Electromagnetic wave absorption characteristics]
Based on JIS R 1679, the amount of reflection absorption when a millimeter wave of 60 GHz to 90 GHz was incident on the electromagnetic wave absorber according to the example or the comparative example at an incident angle of 15 ° was measured for each frequency. From this measurement result, the maximum reflection absorption amount, the maximum peak frequency, and the bandwidth of the frequency at which the reflection absorption amount is 20 dB or more were determined. The results are shown in Table 2.

[Electromagnetic wave absorption characteristics after durability test]
The electromagnetic wave absorbers according to Examples and Comparative Examples in a state of being fixed along a steel plate bent to R50 (curvature radius: 50 mm) are stored for 500 hours in an environment of a temperature of 40 ° C. and a relative humidity of 92%, and a durability test is performed. did. Then, the electromagnetic wave absorber which concerns on an Example and a comparative example was removed from the steel plate. Then, in accordance with JIS R 1679, the amount of reflection absorption when a millimeter wave of 60 GHz to 90 GHz is incident on the electromagnetic wave absorber according to the example or the comparative example at an incident angle of 15 ° is measured for each frequency. The maximum reflection absorption after the durability test was determined from the results. The electromagnetic wave absorbers according to Examples and Comparative Examples were evaluated as follows from the maximum amount of reflected absorption before and after the durability test of the electromagnetic wave absorbers according to Examples and Comparative Examples. The results are shown in Table 2.
a: A decrease in the maximum reflection absorption amount is not recognized, and the maximum reflection absorption amount after the durability test is 20 dB or more.
b: Although the fall of the maximum reflection absorption amount is recognized, the maximum reflection absorption amount after an endurance test is 20 dB or more.
x: The maximum reflection absorption after the durability test is less than 20 dB.

  According to the comparison between Examples 1 to 15 and Comparative Example 1, the conductive functional layer of the conductive layer is a metal vapor-deposited film or a metal foil having a thickness of 50 μm or less, so that it has good bendability. It was suggested. In addition, according to the comparison between Examples 1 to 15 and Comparative Examples 4 and 5, the product of the Young's modulus of the dielectric layer and the thickness of the dielectric layer is 0.1 to 1000 MPa · mm. It was suggested that the electromagnetic wave absorber can be easily attached to a non-flat surface. According to the comparison between Examples 1 to 15 and Comparative Examples 2 and 3, when the relative permittivity of the dielectric layer is 10 or less, the electromagnetic wave absorber has a wide bandwidth and good reflection absorption (20 dB or more). It was suggested that it can be demonstrated. Further, according to the comparison between Example 2 and Example 3, the electromagnetic wave absorber has high durability because the support of the conductive functional layer is located between the conductive functional layer and the dielectric layer. It has been suggested.

1a, 1b Electromagnetic wave absorber 10 First layer (dielectric layer or magnetic layer)
20 conductive layer 22 conductive functional layer 25 support 30 resistance layer

Claims (11)

A first layer that is a dielectric layer or a magnetic layer;
A conductive layer provided on at least one side of the first layer and including a conductive functional layer that is a metal vapor-deposited film or a metal foil having a thickness of 50 μm or less, and
The product of the Young's modulus of the first layer and the thickness of the first layer is 0.1 to 1000 MPa · mm,
The relative dielectric constant of the first layer is 1-10.
Electromagnetic wave absorber.   The electromagnetic wave absorber according to claim 1 whose Young's modulus of said 1st layer is 2000 MPa or less.   The electromagnetic wave absorber according to claim 1, wherein the first layer includes a polymer material.   The electromagnetic wave absorber according to claim 1, wherein the first layer is a foam.   The electromagnetic wave absorber according to claim 1, wherein at least one of a dielectric and a magnetic material is dispersed in the first layer. The conductive layer further includes a support that supports the conductive functional layer,
The electromagnetic wave absorber according to claim 1, wherein the support is disposed between the first layer and the conductive functional layer to protect the conductive functional layer. A resistance layer provided on at least one side of the first layer;
The electromagnetic wave absorber according to claim 1, wherein the first layer is the dielectric layer and is disposed between the resistance layer and the conductive layer.   The electromagnetic wave absorber according to claim 7, wherein the resistance layer has a sheet resistance of 200 to 600Ω / □.   The electromagnetic wave absorber according to any one of claims 1 to 8, wherein the electromagnetic wave absorber has an electromagnetic wave absorption amount of 20 dB or more in a bandwidth of 2 GHz or more included in a frequency band of 50 to 100 GHz.   The electromagnetic wave absorber according to any one of claims 1 to 9, further comprising an adhesive layer disposed outside the conductive layer. Molded products,
The electromagnetic wave absorber according to any one of claims 1 to 10 attached to the molded article,
Molded product with electromagnetic wave absorber.

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