JP2020031121A - Radio wave absorption laminate, radio wave absorber, and millimeter wave radar - Google Patents

Abstract

To provide a radio wave absorption laminate suitable for constituting a λ/4 type radio wave absorber having a good durability, including a dielectric layer having good adhesion to an adherend containing metal.SOLUTION: A radio wave absorption laminate (1) includes a resistance layer (10), a first dielectric layer (21), and a second dielectric layer (22). The resistance layer (10) contains a metal or a metal compound. The first dielectric layer (21) is in close contact with the resistance layer (10). The second dielectric layer (22) contains an acid component and has adhesiveness. The first dielectric layer (21) is arranged between the resistance layer (10) and the second dielectric layer (22) in a thickness direction of the first dielectric layer (21). The content of the mass-based acid component in the first dielectric layer (21) is lower than the content of the mass-based acid component in the second dielectric layer (22).SELECTED DRAWING: Figure 1

Description

  The present invention relates to a radio wave absorbing laminate, a radio wave absorber, and a millimeter wave radar.

  2. Description of the Related Art Conventionally, techniques for absorbing unnecessary radio waves are known.

  For example, Patent Document 1 discloses a millimeter wave radar device including an antenna, a control circuit, a housing, a radome, and a shielding member, wherein the shielding member is a radio wave absorbing material for absorbing radio waves. It is composed of The shielding member is disposed between the antenna and the control circuit. Thus, unnecessary radio waves such as power supply noise from the control circuit can be cut off. The shielding member includes a dielectric loss layer or a magnetic loss layer having a larger dielectric loss than the radome. A conductor layer is laminated on the outer side surface of the shielding member to improve the radio wave absorption characteristics.

  Patent Document 2 discloses a millimeter wave radar including an antenna base, a housing, and a radome, and a radio wave absorbing layer is provided on an inner surface of the radome. The radio wave absorption layer is a layer having a larger dielectric loss than the radome or a magnetic loss layer. A conductor layer is provided outside the radio wave absorption layer. The side lobe transmitted from the transmitting antenna is absorbed by the radio wave absorbing layer.

  Patent Document 3 describes a millimeter-wave electromagnetic wave absorber including a heat-resistant sheet and a metal layer covering any surface of the sheet. In a heat-resistant sheet, a soft magnetic metal powder is embedded in a rubber or plastic matrix. By disposing the millimeter-wave electromagnetic wave absorber at a predetermined position on the housing of the millimeter-wave radar, unnecessary millimeter waves can be reliably absorbed.

  Patent Literature 4 describes a radio wave absorbing sheet attached to a ceiling surface of a shield case of a high-frequency communication device. The surface of the shield case is formed of metal.

  Patent Documents 1 to 3 disclose a dielectric loss type radio wave absorber or a magnetic loss type radio wave absorber. As a radio wave absorber, a λ / 4 type radio wave absorber is also known. For example, Patent Literature 4 describes a λ / 4 type radio wave absorbing sheet. For example, as shown in Patent Document 5, a λ / 4 type radio wave absorber includes, for example, a radio wave reflection layer (conductive layer), a dielectric layer having a thickness corresponding to λ / 4, and a resistive thin film layer (resistance layer). Layer). A dielectric layer is disposed between the conductive layer and the resistive layer. Here, λ is the wavelength of the radio wave to be absorbed.

JP 2007-74662 A JP-A-2004-77399 JP 2002-118008 A JP 2012-199463 A JP-A-2017-163141

  Patent Documents 1 to 3 do not describe a λ / 4 type radio wave absorber. On the other hand, Patent Literatures 4 and 5 describe a λ / 4 type radio wave absorber, and Patent Literature 4 suggests that a radio wave absorbing sheet is attached to a metal. However, in Patent Document 4, it is not clear which part of the radio wave absorbing sheet is to be brought into contact with the metal surface of the shield case. Patent Literatures 1 to 5 disclose that a dielectric layer of a laminate including a resistance layer and a dielectric layer is brought into contact with an adherend containing a metal to form a λ / 4 type radio wave absorber. Absent.

  Therefore, the present invention provides a λ / 4 type radio wave absorber having a good durability, comprising a dielectric layer having good adhesion to an adherend containing a metal and a resistance layer. To provide a laminated body for electromagnetic wave absorption suitable for the electromagnetic wave. In addition, the present invention provides a radio wave absorber provided with such a laminate for a radio wave absorber, and a millimeter wave radar provided with the radio wave absorber.

The present disclosure
A resistance layer containing a metal or a metal compound,
A first dielectric layer in close contact with the resistance layer,
An adhesive second dielectric layer containing an acid component,
The first dielectric layer is disposed between the resistance layer and the second dielectric layer in a thickness direction of the first dielectric layer,
The content of the mass-based acid component in the first dielectric layer is lower than the content of the mass-based acid component in the second dielectric layer.
Provided is a laminate for radio wave absorption.

Also, the present invention
An adherend containing a metal,
The second dielectric layer was adhered to the adherend, the above-mentioned radio wave absorption laminate, comprising:
Provide a radio wave absorber.

Further, the present invention provides
A millimeter-wave radar including the above-described radio wave absorber is provided.

  The second dielectric layer of the above-described radio wave absorbing laminate has good adhesiveness to an adherend containing a metal, and the radio wave absorbing laminate has good durability. Suitable for making up the body.

FIG. 1 is a cross-sectional view showing an example of a radio wave absorbing laminate according to the present invention. FIG. 2 is a sectional view showing an example of the radio wave absorber according to the present invention. FIG. 3 is a cross-sectional view showing another example of the radio wave absorbing laminate according to the present invention.

  The present inventors have devised a radio wave absorption laminate according to the present invention based on the following new findings regarding a λ / 4 type radio wave absorber.

  The λ / 4 type radio wave absorber can adjust the thickness of the dielectric layer by adjusting the relative permittivity of the material forming the dielectric layer, and is advantageous from the viewpoint of thinning. On the other hand, when a laminate including a resistance layer, a dielectric layer, and a conductive layer is attached to an adherend with an adhesive, an adhesive layer is required in addition to the resistance layer, the dielectric layer, and the conductive layer. This cannot be said to be advantageous for promoting thinning. In the λ / 4 type radio wave absorber, one main surface of the dielectric layer may be in contact with an object having radio wave reflectivity. For this reason, if the adherend has a radio wave reflecting ability, a predetermined adhesiveness is given to the dielectric layer, and the laminate including the resistance layer and the dielectric layer is attached to the adherend, and λ / 4 It is conceivable to construct a type of electromagnetic wave absorber. As a result, the thickness of the λ / 4 type radio wave absorber can be reduced.

  In order to increase the adhesive strength of the dielectric layer to the adherend having radio wave reflecting ability, it is advantageous that the dielectric layer contains an acid component. On the other hand, the dielectric layer is also in contact with the resistance layer. The present inventors have found that when the resistance layer contains a metal or a metal compound, the thickness of the resistance layer is small, so that the acid layer contained in the dielectric layer may corrode the resistance layer and change the characteristics of the resistance layer. I found that there is. Fluctuations in the characteristics of the resistance layer cause a reduction in the radio wave absorption performance. Therefore, the present inventors have studied day and night to develop a radio wave absorbing laminate having a high adhesive strength of the dielectric layer to the adherend having radio wave reflecting ability and capable of preventing corrosion of the resistance layer. As a result of extensive trial and error, the present inventors configured the radio wave absorption laminate to include a plurality of dielectric layers, and then determined the content of the acid component in the plurality of dielectric layers in a predetermined relationship. It has been newly found that a desired electromagnetic wave absorbing laminate can be obtained by the above method.

  An embodiment of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the following embodiments.

  As shown in FIG. 1, the radio wave absorption laminate 1a includes a resistance layer 10, a first dielectric layer 21, and a second dielectric layer 22. The resistance layer 10 contains a metal or a metal compound. The first dielectric layer 21 is in close contact with the resistance layer 10. In the present specification, the term “adhesion” means that in the 180 ° peeling test described in the examples, the particles adhere with an adhesive force of 3 [N / 20 mm] or more. The second dielectric layer 22 contains an acid component and has adhesiveness. The first dielectric layer 21 is disposed between the resistance layer 10 and the second dielectric layer 22 in the thickness direction of the first dielectric layer 21. The content of the mass-based acid component in the first dielectric layer 21 is lower than the content of the mass-based acid component in the second dielectric layer 22. In the present specification, amphoteric compounds such as aluminum hydroxide do not fall under the “acid component”.

  A λ / 4 type radio wave absorber can be provided using the radio wave absorption laminate 1a. As shown in FIG. 2, the radio wave absorber 2 includes an adherend 30 and a radio wave absorbing laminate 1a. The adherend 30 contains a metal and has a radio wave reflecting ability. In the radio wave absorber 2, the radio wave absorption laminate 1 a is adhered to the adherend 30. Since the second dielectric layer 22 has adhesiveness, the radio wave absorbing laminate 1a can be adhered to the adherend 30 by pressing the second dielectric layer 22 against the adherend 30. .

When a radio wave having a wavelength (λ _O ) to be absorbed enters the radio wave absorber 2, a radio wave due to reflection on the surface of the resistance layer 10 (surface reflection) and a radio wave due to reflection at the adherend 30 (back surface reflection) are generated. The electromagnetic wave absorbing laminate 1a is designed so that the interference occurs. In a λ / 4 type radio wave absorber, the wavelength (λ) of the radio wave to be absorbed is determined by the thickness (t) of the dielectric layer and the relative permittivity (ε _r ) of the dielectric layer as shown in the following equation (1). _O ) is determined. That is, by appropriately adjusting the material and thickness of the dielectric layer, it is possible to set a radio wave having a wavelength to be absorbed. In equation (1), sqrt (ε _r ) means the square root of the relative permittivity (ε _r ).
λ _O = 4t × sqrt (ε _r ) Equation (1)

  Since the second dielectric layer 22 contains an acid component, it can exhibit a high adhesive strength to the adherend 30. The second dielectric layer 22 is formed, for example, on a sample composed of a part of the second dielectric layer 22 by using an acid determined according to “3.1 Neutralization titration method” of Japanese Industrial Standard (JIS) K 0070-1992. An acid component is contained so that the value becomes 5 or more. Thereby, the second dielectric layer 22 can more reliably exhibit a high adhesive strength to the adherend 30. The content of the acid component on a mass basis in the second dielectric layer 22 is, for example, 10% or more, preferably 15% or more. The content ratio of the acid component on a mass basis in the second dielectric layer 22 is, for example, 80% or less.

  Since the content of the mass-based acid component in the first dielectric layer 21 is lower than the content of the mass-based acid component in the second dielectric layer 22, the corrosion of the resistance layer 10 containing a metal or a metal compound is prevented. Can be prevented. As a result, the radio wave absorbing laminate 1a and, consequently, the radio wave absorber 2 have high durability.

  The content of the mass-based acid component in the first dielectric layer 21 is not limited to a specific content as long as it is lower than the content of the mass-based acid component in the second dielectric layer 22. The content of the acid component on a mass basis in the first dielectric layer 21 is, for example, less than 10%, and desirably 5% or less. More desirably, the first dielectric layer 21 does not substantially contain an acid component. Thereby, corrosion of the resistance layer 10 can be more reliably prevented. The expression "substantially does not contain an acid component" means that a trace amount of an acid component is allowed as long as the characteristics of the resistance layer 10 are maintained in a desired range. For example, after storing the radio wave absorbing laminate 1a in an environment of a temperature of 85 ° C. and a relative humidity of 85% for 500 hours, the amount of change in the sheet resistance of the resistance layer 10 before and after storage is changed by the sheet resistance of the resistance layer 10 before storage. If it is less than 20%, it can be said that the first dielectric layer 21 does not substantially contain an acid component even if a small amount of an acid component is contained. Particularly preferably, the first dielectric layer 21 does not contain any acid component.

  The first dielectric layer 21 has a thickness of, for example, 5 μm or more. In this case, the acid component contained in the second dielectric layer 21 can be prevented from passing through the first dielectric layer 21 and reaching the resistance layer 10. As a result, corrosion of the resistance layer 10 can be more reliably prevented. The thickness of the first dielectric layer 21 may be 10 μm or more, or may be 15 μm or more.

  The second dielectric layer 22 contains, for example, a flame retardant. It is desirable that the radio wave absorbing laminate 1a has flame retardancy. If the second dielectric layer 22 contains a flame retardant, the radio wave absorbing laminate 1a tends to have desired flame retardancy. The flame retardant contained in the second dielectric 22 is not limited to a specific flame retardant, and may be a known flame retardant. For example, the flame retardant is an inorganic flame retardant such as aluminum hydroxide. The flame retardant may be an organic flame retardant.

  The content based on mass of the flame retardant in the second dielectric layer 22 is, for example, 60 to 90%. Thereby, it is easy to impart desired flame retardancy to the radio wave absorbing laminate 1a, and the adhesive strength of the second dielectric layer 22 to the adherend 30 can be kept high. The content based on mass of the flame retardant in the second dielectric layer 22 is preferably 65 to 80%, more preferably 70 to 75%.

  The first dielectric layer 21 does not substantially contain, for example, a flame retardant. The flame retardant may reduce the adhesion of the first dielectric layer 21 to the resistance layer 10. However, if the first dielectric layer 21 does not substantially contain a flame retardant, good adhesion of the first dielectric layer 21 to the resistance layer 10 is maintained. “Substantially does not contain a flame retardant” means that a small amount of a flame retardant is allowed if the first dielectric layer 21 is in close contact with the resistance layer 10. Desirably, the first dielectric layer 21 does not contain any flame retardant.

  The first dielectric layer 21 has a thickness of, for example, less than 80 μm. In this case, even if the first dielectric layer 21 does not contain a flame retardant, the radio wave absorbing laminate 1a tends to have a desired flame retardancy. The thickness of the first dielectric layer 21 preferably has a thickness of 75 μm or less, and more preferably has a thickness of 70 μm or less.

  The radio wave absorbing laminate 1a conforms to, for example, UL94 V-1 of the UL standard. In this case, the radio wave absorbing laminate 1a has desired flame retardancy.

  In the design of the λ / 4 type radio wave absorber, the sheet resistance of the resistance layer 10 is determined so that the impedance viewed from the front surface of the resistance layer 10 using transmission theory becomes equal to the characteristic impedance. The sheet resistance required for the resistance layer 10 can vary depending on the assumed incident angle of the radio wave incident on the λ / 4 type radio wave absorber. The resistance layer 10 has a sheet resistance of, for example, 180 to 750 Ω / □.

As described above, the resistance layer 10 contains a metal or a metal compound. The metal included in the resistance layer 10 is not particularly limited, but is, for example, at least one selected from the group consisting of indium, tin, zinc, and silver. The metal compound contained in the resistance layer 10 is not particularly limited, but is, for example, at least one oxide selected from the group consisting of indium, tin, and zinc. The resistance layer 10 is, for example, a layer containing any one of a metal compound, metal nanowires, and a metal mesh mainly containing at least one oxide selected from the group consisting of indium, tin, and zinc. From the viewpoint of the stability of the sheet resistance of the resistance layer 10 and the durability of the resistance layer 10, the resistance layer 10 desirably contains indium tin oxide (ITO) as a main component. In this case, the content of SnO ₂ in the resistance layer 10 is desirably 20 to 40% by weight, and more desirably 25 to 35% by weight. Such a resistance layer 10 has an extremely stable amorphous structure, and can suppress a change in the sheet resistance of the resistance layer 10 in a high-temperature and high-humidity environment. In addition, in this specification, the "main component" means a component contained most on a mass basis.

  The thickness of the resistance layer 10 is not particularly limited, but is, for example, 20 to 90 nm. As described above, when the thickness of the resistance layer 10 is small, the resistance layer 10 is easily corroded by a small amount of an acid component. However, as described above, since the content of the acid component in the first dielectric layer 21 is low, even if the thickness of the resistance layer 10 is small, the resistance layer 10 is hardly corroded.

  The material forming the first dielectric layer 21 is not limited to a specific material as long as the first dielectric layer 21 can adhere to the resistance layer 10. The first dielectric layer 21 contains, for example, a predetermined elastomer as a main component or a matrix. The elastomer contained in the first dielectric layer 21 may be a natural rubber, a synthetic rubber, an acrylic elastomer, a silicone rubber, or a urethane elastomer. The first dielectric layer 21 may include a component such as a tackifier, if necessary.

  The material forming the second dielectric layer 22 is not limited to a specific material as long as it contains an acid component and has adhesiveness. The second dielectric layer 22 contains, for example, an elastomer which is chemically stable to an acid component as a main component. The elastomer contained in the second dielectric layer 22 may be a natural rubber, a synthetic rubber, an acrylic elastomer, a silicone rubber, or a urethane elastomer. The elastomer contained in the second dielectric layer 22 is desirably an acrylic elastomer. The second dielectric layer 22 may include a component such as a tackifier, if necessary.

  The acid component contained in the second dielectric layer 22 is, for example, at least one of an inorganic acid such as phosphoric acid and an organic acid such as acrylic acid. By including such an acid component in the second dielectric layer 22, a sample composed of a part of the second dielectric layer 22 is subjected to JIS K 0070-1992 “3.1 Neutralization titration method”. The determined acid value is likely to be 5 or more. As a result, the second dielectric layer 22 tends to more reliably exhibit a high adhesive strength to the adherend 30.

  As shown in FIG. 1, the radio wave absorption laminate 1 a further includes, for example, a support 12. The support 12 supports the resistance layer 10. In this case, the resistance layer 10 can be manufactured by, for example, forming a film on the support 12 using a method such as sputtering, ion plating, or coating (for example, bar coating). The support 12 is arranged, for example, at a position farther from the adherend 30 than the resistance layer 10 in the radio wave absorber 2. For this reason, the resistance layer 10, the first dielectric layer 21, and the second dielectric layer 22 are protected by the support 12, and the radio wave absorber 2 has high durability. In addition, the support 12 also serves as an auxiliary material for adjusting the thickness of the resistance layer 10 with high precision. The material of the support 12 is, for example, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide (PI), acrylic resin, polycarbonate (PC), polyolefin, polyethylene (PE), polypropylene (PP), cycloolefin polymer (COP), polyurethane, urethane acrylic resin, non-axially oriented polypropylene (CPP), or vinylidene chloride resin. Above all, the material of the support 12 is desirably PET or PI from the viewpoint of a balance between good heat resistance, dimensional stability, and manufacturing cost.

  The support 12 has a thickness of, for example, 10 to 150 μm, preferably has a thickness of 15 to 100 μm, and more preferably has a thickness of 20 to 80 μm. Thereby, the bending rigidity of the support body 12 is low, and generation or deformation of wrinkles in the support body 12 when the resistance layer 10 is formed can be suppressed.

  In the radio wave absorber 2, for example, the surface of the adherend 30 to be bonded to the radio wave absorbing laminate 1a is formed of metal. Thereby, the adherend 30 has radio wave reflecting ability on the adherend surface. The metal forming the adhered surface of the adherend 30 with the radio wave absorbing laminate 1a is not particularly limited, but is, for example, aluminum, copper, nickel, an aluminum alloy, a copper alloy, or a nickel alloy.

  The radio wave absorbing laminate 1a can be changed from various viewpoints. The radio wave absorbing laminate 1a may be changed, for example, to a radio wave absorbing laminate 1b shown in FIG. The radio wave absorbing laminate 1b has the same configuration as the radio wave absorbing laminate 1a, unless otherwise specified. The components of the radio wave absorbing laminate 1b that are the same as or correspond to the components of the radio wave absorbing laminate 1a are denoted by the same reference numerals, and detailed description thereof is omitted. The description of the radio wave absorbing laminate 1a also applies to the radio wave absorbing laminate 1b unless technically contradictory. Note that the radio wave absorber 2 may include a radio wave absorption laminate 1b instead of the radio wave absorption laminate 1a.

  The radio wave absorption laminate 1b further includes a third dielectric layer 23. The third dielectric layer 23 is disposed between the first dielectric layer 21 and the second dielectric layer 22 in the thickness direction of the first dielectric layer 21. The content of the mass-based acid component in the third dielectric layer 23 is lower than the content of the mass-based acid component in the second dielectric layer 22. According to the radio wave absorbing laminate 1b, the acid component contained in the second dielectric layer 22 can be prevented from reaching the resistance layer 10 by the third dielectric layer 23, and the corrosion of the resistance layer 10 can be prevented.

  The ratio of the thickness of the third dielectric layer 23 to the thickness of the second dielectric layer 22 is not particularly limited as long as the relationship of the formula (1) is satisfied.

  The content of the mass-based acid component in the third dielectric layer 23 is not limited to a specific content as long as it is lower than the content of the mass-based acid component in the second dielectric layer 22. The content of the acid component on a mass basis in the third dielectric layer 23 is, for example, less than 10%, and desirably 5% or less. More preferably, the third dielectric layer 23 does not substantially contain an acid component. Thereby, corrosion of the resistance layer 10 can be more reliably prevented. The expression "substantially does not contain an acid component" means that a trace amount of an acid component is allowed as long as the characteristics of the resistance layer 10 are maintained in a desired range. For example, after storing the radio wave absorption laminate 1b in an environment of a temperature of 85 ° C. and a relative humidity of 85% for 500 hours, the amount of change in the sheet resistance of the resistance layer 10 before and after the storage is changed. If it is less than 20%, it can be said that the first dielectric layer 23 does not substantially contain an acid component even if a small amount of an acid component is contained. Particularly preferably, the first dielectric layer 23 does not contain any acid component.

  In the radio wave absorption laminate 1b, the third dielectric layer 23 contains, for example, a flame retardant. Thereby, the radio wave absorbing laminate 1b tends to have desired flame retardancy.

  The flame retardant contained in the third dielectric 23 is not limited to a specific flame retardant, and may be a known flame retardant. For example, the flame retardant is an inorganic flame retardant such as aluminum hydroxide. The flame retardant may be an organic flame retardant. The content based on mass of the flame retardant in the third dielectric layer 23 is, for example, 60 to 90%. This makes it easier for the radio wave absorbing laminate 1b to have the desired flame retardancy more reliably. The content based on mass of the flame retardant in the third dielectric layer 23 is desirably 65 to 80%, and more desirably 70 to 75%.

  For example, a millimeter wave radar including the radio wave absorber 2 can be provided by using the radio wave absorption laminate 1a or the radio wave absorption laminate 1b. In this case, a component including a metal of the millimeter wave radar may correspond to the adherend 30.

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

<Example 1>
(Production of laminate for radio wave absorption)
On a polyethylene terephthalate (PET) film having a thickness of 23 μm, a target material containing 30% by weight of SnO ₂ and 2.5% by weight of SiO ₂ and the balance being indium oxide was used to resist by sputtering. A layer was formed. Thus, a PET film with a resistance layer was obtained. The initial sheet resistance of the resistance layer was 390Ω / □. The sheet resistance of the resistance layer was measured according to an eddy current method using a non-contact type sheet resistance measuring device (manufactured by Napson, product name: NC-80MAP).

  Mixing roll of a mixture obtained by adding 10% by weight of a polymerized rosin ester (manufactured by Arakawa Chemical Industries, product name: Pencel C) as a tackifier to an acrylic block copolymer (manufactured by Kuraray Co., Ltd., product name: Clarity LA2330) And stirred. Thereafter, the mixture was heated and pressed at 150 ° C. to obtain a sheet having a thickness of 70 μm. Thus, the first dielectric layer sheet according to Example 1 was obtained. The sheet for the first dielectric layer according to Example 1 did not contain an acid component.

  A laminate having three layers of a double-sided tape (manufactured by Nitto Denko Corporation, product name: TR-5920FS, thickness: 200 μm) containing an acrylic adhesive was heated and pressed at 100 ° C. to obtain a sheet having a thickness of 400 μm. . Thus, a second dielectric layer sheet according to Example 1 was obtained. The sheet for the second dielectric layer according to Example 1 contained 18% by mass of acrylic acid as an acid component, and contained 72% by mass of aluminum hydroxide as a flame retardant.

  The radio wave absorbing laminate according to Example 1 is obtained by stacking the first dielectric layer sheet on the resistance layer of the PET film with the resistance layer, and further stacking the second dielectric layer sheet on the first dielectric layer sheet. I got a body.

(Preparation of specimen A)
The PET film with the resistance layer was cut out to obtain a strip having a width of 20 mm. In addition, the first dielectric layer sheet was cut out to obtain a small piece having a width of 20 mm. A double-sided adhesive tape (product name: No. 5000N, manufactured by Nitto Denko Corporation) was attached to the surface of a plate made of SUS304BA. On the double-sided pressure-sensitive adhesive tape, a small piece of the first dielectric layer sheet was laminated and stuck. Next, the end portion of the resistive layer in the length direction of the strip of the PET film with the resistive layer was overlapped and stuck on the small piece of the first dielectric layer sheet. This state was maintained in an environment of 23 ° C. for 30 minutes to obtain a test piece A according to Example 1.

(Preparation of specimen B)
A PET film having a thickness of 23 μm was cut out to obtain a strip having a width of 20 mm. Further, the sheet for the second dielectric layer was cut out to obtain a small piece having a width of 20 mm. A small piece of the second dielectric layer sheet was attached to the end of the strip of the PET film in the length direction. Next, a small piece of the second dielectric layer sheet was attached to the surface of a SUS304BA plate material. This state was maintained for 30 minutes in an environment of 23 ° C. to obtain a test piece B according to Example 1.

(Preparation of test piece C)
The test piece C according to Example 1 was obtained by cutting the radio wave absorption laminate according to Example 1 into a strip having a length of 125 ± 5 mm and a width of 13 ± 0.5 mm.

<Example 2>
In the same manner as in Example 1, a first dielectric layer sheet was prepared, and a first dielectric layer sheet according to Example 2 having a thickness of 70 μm was obtained. A double-sided tape containing an acrylic pressure-sensitive adhesive (trade name: TR-5920FS, manufactured by Nitto Denko Corporation, thickness: 200 μm) was used as the second dielectric layer sheet according to Example 2. The sheet for the second dielectric layer according to Example 2 contained 18% by mass of acrylic acid as an acid component, and contained 72% by mass of aluminum hydroxide as a flame retardant.

  To 100 parts by weight of an acrylic block copolymer (manufactured by Kuraray Co., Ltd., product name: Clarity LA2330), 250 parts by weight of aluminum hydroxide-containing particles (manufactured by Showa Denko KK, product name: Heidilite H-42) were added. The mixture was stirred with a mixing roll. Thereafter, the mixture was heated and pressed at 150 ° C. to obtain a sheet having a thickness of 200 μm. Thus, a third dielectric layer sheet according to Example 2 was obtained. The third dielectric layer sheet did not contain an acid component, and contained 72% by mass of aluminum hydroxide as a flame retardant.

  The first dielectric layer sheet is stacked on the resistance layer of the PET film with the resistance layer, then the third dielectric layer sheet is stacked on the first dielectric layer sheet, and finally the third dielectric layer sheet The sheet for a second dielectric layer was overlaid on the above to obtain a radio wave absorbing laminate according to Example 2.

  Specimen A according to Example 2 was produced in the same manner as in Example 1. Specimen B according to Example 2 was produced in the same manner as in Example 1 except that the second dielectric layer sheet according to Example 2 was used instead of the second dielectric layer sheet according to Example 1. did. A test piece C according to Example 2 was produced in the same manner as in Example 1 except that the radio wave absorption laminate according to Example 2 was used instead of the radio wave absorption laminate according to Example 1.

<Comparative Example 1>
To 100 parts by weight of an acrylic block copolymer (manufactured by Kuraray Co., Ltd., product name: Clarity LA2330), 250 parts by weight of aluminum hydroxide-containing particles (manufactured by Showa Denko KK, product name: Heidilite H-42) were added. The mixture was stirred with a mixing roll. Thereafter, the mixture was heated and pressed at 150 ° C. to obtain a sheet having a thickness of 460 μm. Thus, a dielectric layer sheet according to Comparative Example 1 was obtained. The sheet for the dielectric layer according to Comparative Example 1 was overlaid on the resistance layer of the PET film with the resistance layer manufactured in the same manner as in Example 1 to obtain a radio wave absorption laminate according to Comparative Example 1. The dielectric layer sheet according to Comparative Example 1 did not contain an acid component, and contained 72% by mass of aluminum hydroxide as a flame retardant.

  Specimen A according to Comparative Example 1 was produced in the same manner as in Example 1 except that the dielectric layer sheet according to Comparative Example 1 was used instead of the first dielectric layer sheet according to Example 1. Specimen B according to Comparative Example 1 was produced in the same manner as in Example 1, except that the dielectric layer sheet according to Comparative Example 1 was used instead of the second dielectric layer sheet according to Example 1. A test piece C according to Comparative Example 1 was produced in the same manner as in Example 1, except that the radio wave absorbing laminate according to Comparative Example 1 was used instead of the radio wave absorbing laminate according to Example 1.

<Comparative Example 2>
A laminate having three layers of a double-sided tape (manufactured by Nitto Denko Corporation, product name: TR-5920FS, thickness: 200 μm) containing an acrylic adhesive was heated and pressed at 100 ° C. to obtain a sheet having a thickness of 450 μm. . Thus, a dielectric layer sheet according to Comparative Example 2 was obtained. The dielectric layer sheet according to Comparative Example 2 contained 18% by mass of acrylic acid as an acid component and 72% by mass of aluminum hydroxide as a flame retardant.

  The dielectric layer sheet according to Comparative Example 2 was overlaid on the resistive layer of the PET film with the resistive layer produced in the same manner as in Example 1 to obtain a radio wave absorbing laminate according to Comparative Example 2.

  Specimen A according to Comparative Example 2 was produced in the same manner as in Example 1 except that the dielectric layer sheet according to Comparative Example 2 was used instead of the first dielectric layer sheet according to Example 1. Specimen B according to Comparative Example 2 was produced in the same manner as in Example 1, except that the dielectric layer sheet according to Comparative Example 2 was used instead of the second dielectric layer sheet according to Example 1. A test piece C according to Comparative Example 2 was produced in the same manner as in Example 1 except that the radio wave absorbing laminate according to Comparative Example 2 was used instead of the radio wave absorbing laminate according to Example 1.

<Comparative Example 3>
A mixture of 100 parts by weight of an acrylic block copolymer (manufactured by Kuraray Co., Ltd., product name: Clarity LA2330) and 250 parts by weight of aluminum hydroxide-containing particles (manufactured by Showa Denko KK, product name: Heidilite H-42) Was stirred with a mixing roll. Thereafter, the mixture was hot-pressed at 150 ° C. to obtain a sheet having a thickness of 70 μm. Thus, a first dielectric layer sheet according to Comparative Example 3 was obtained. The first dielectric layer sheet according to Comparative Example 3 did not contain an acid component and contained 72% by mass of aluminum hydroxide as a flame retardant.

  A laminate having three layers of a double-sided tape (manufactured by Nitto Denko Corporation, product name: TR-5920FS, thickness: 200 μm) containing an acrylic pressure-sensitive adhesive was heated and pressed at 100 ° C. to obtain a sheet having a thickness of 380 μm. . Thus, a second dielectric layer sheet according to Comparative Example 3 was obtained. The second dielectric layer sheet according to Comparative Example 3 contained 18% by mass of acrylic acid as an acid component, and contained 72% by mass of aluminum hydroxide as a flame retardant.

  The first dielectric layer sheet according to Comparative Example 3 was overlaid on the resistance layer of the PET film with the resistance layer produced in the same manner as in Example 1, and the first dielectric layer sheet according to Comparative Example 3 was further placed on the first dielectric layer sheet. The two dielectric layer sheets were stacked to obtain a radio wave absorbing laminate according to Comparative Example 3.

  Specimen A according to Comparative Example 3 was prepared in the same manner as in Example 1 except that the first dielectric layer sheet according to Comparative Example 3 was used instead of the first dielectric layer sheet according to Example 1. did. Specimen B according to Comparative Example 3 was produced in the same manner as in Example 1 except that the second dielectric layer sheet according to Comparative Example 3 was used instead of the second dielectric layer sheet according to Example 1. did. A test piece C according to Comparative Example 3 was obtained in the same manner as in Example 1 except that the radio wave absorbing laminate according to Comparative Example 3 was used instead of the radio wave absorbing laminate according to Example 1.

<Comparative Example 4>
In the same manner as in Comparative Example 3, a first dielectric layer sheet according to Comparative Example 4 was obtained. Four layers of a double-sided tape (manufactured by Nitto Denko Corporation, product name: CS9864, thickness: 100 µm) containing an acrylic pressure-sensitive adhesive were laminated to obtain a sheet having a thickness of 400 µm. Thus, a second dielectric layer sheet according to Comparative Example 4 was obtained. The sheet for the second dielectric layer according to Comparative Example 4 contained 42% by mass of acrylic acid as an acid component, but did not contain a flame retardant.

  The first dielectric layer sheet according to Comparative Example 4 was overlaid on the resistance layer of the PET film with a resistance layer produced in the same manner as in Example 1, and the first dielectric layer sheet according to Comparative Example 4 was further placed on the first dielectric layer sheet. The two dielectric layer sheets were stacked to obtain a radio wave absorbing laminate according to Comparative Example 4.

  Specimen A according to Comparative Example 4 was prepared in the same manner as in Example 1 except that the first dielectric layer sheet according to Comparative Example 4 was used instead of the first dielectric layer sheet according to Example 1. did. Specimen B according to Comparative Example 4 was produced in the same manner as in Example 1 except that the second dielectric layer sheet according to Comparative Example 4 was used instead of the second dielectric layer sheet according to Example 1. did. A test piece C according to Comparative Example 4 was obtained in the same manner as in Example 1, except that the radio wave absorbing laminate according to Comparative Example 4 was used instead of the radio wave absorbing laminate according to Example 1.

<Comparative Example 5>
An acrylic block copolymer (Kuraray Co., Ltd., product name: Clarity LA2330) was heated and pressed at 150 ° C. to obtain a sheet having a thickness of 560 μm. Thus, a dielectric layer sheet according to Comparative Example 5 was obtained. The dielectric layer sheet according to Comparative Example 5 did not contain an acid component and a flame retardant. The dielectric layer sheet according to Comparative Example 5 was overlaid on the resistance layer of the PET film with the resistance layer produced in the same manner as in Example 1 to obtain a radio wave absorption laminate according to Comparative Example 5.

  Specimen A according to Comparative Example 5 was produced in the same manner as in Example 1, except that the dielectric layer sheet according to Comparative Example 5 was used instead of the first dielectric layer sheet according to Example 1. Specimen B according to Comparative Example 5 was produced in the same manner as in Example 1, except that the dielectric layer sheet according to Comparative Example 5 was used instead of the second dielectric layer sheet according to Example 1. A test piece C according to Comparative Example 5 was obtained in the same manner as in Example 1, except that the radio wave absorbing laminate according to Comparative Example 5 was used instead of the radio wave absorbing laminate according to Example 1.

[Dielectric constant measurement]
Using a network analyzer (manufactured by Agilent Technologies, product name: N5230C), the relative dielectric constant at 10 GHz of the dielectric layer of the radio wave absorption laminate according to the example and each comparative example was measured according to the cavity resonance method. Table 1 shows the results.

[Evaluation of Adhesion of Dielectric Layer to Resistance Layer]
Using the specimen A according to the example and each comparative example, the adhesiveness of the dielectric layer to the resistance layer was evaluated. In test piece A, the strip of the PET film with the resistance layer was peeled at 180 ° from the dielectric layer at a speed of 300 mm / min. The force required for this peeling was measured to determine the adhesion of the dielectric layer to the resistive layer. Table 1 shows the results.

[Evaluation of adhesion of dielectric layer to metal]
The adhesiveness of the dielectric layer to metal was evaluated using the test piece B according to the example and each comparative example. In the test piece B, the PET film strip was pulled at a speed of 300 mm / min, and the dielectric layer was peeled at 180 ° with respect to the surface of the SUS304BA plate material. The force required for this peeling was measured to determine the adhesion of the dielectric layer to the metal. Table 1 shows the results.

[Flame retardancy evaluation]
Using the test piece C according to the example and each comparative example, the flame retardancy of the electromagnetic wave absorbing laminate according to the example and each comparative example was evaluated according to the UL94V test defined in the UL standard. Table 1 shows the results. The criterion for determining the flame retardancy in the UL94V test is as shown in Table 2.

[An endurance test]
The radio wave absorption laminates according to Examples and Comparative Examples were stored for 500 hours in an environment of 85 ° C. and 85% relative humidity. The sheet resistance of the resistive layer after storage was measured according to the eddy current method using a non-contact sheet resistance measuring device (product name: NC-80MAP, manufactured by Napson Corporation). The ratio (ΔR / Ri) of the variation ΔR of the sheet resistance of the resistance layer before and after storage to the sheet resistance Ri of the initial resistance layer was determined, and the durability of the radio wave absorption laminate according to the example and each comparative example was determined according to the following criteria. The sex was evaluated. The variation ΔR is an absolute value of a difference obtained by subtracting the sheet resistance Ra of the stored resistance layer from the sheet resistance Ri of the initial resistance layer.
A +: ΔR / Ri is less than 10%.
A: ΔR / Ri is 10% or more and less than 20%.
X: ΔR / Ri is 20% or more.

  From comparison between Comparative Examples 1 and 5 and Examples 1 and 2, it is desirable that the dielectric layer that can be adhered to the metal adherend contains an acid component in order to increase the adhesion to the metal. It was suggested. On the other hand, a comparison between Examples 1 and 2 and Comparative Example 2 shows that the fact that the dielectric layer in contact with the resistance layer does not contain an acid component enhances the durability of the resistance layer and thus the durability of the radio wave absorber. Suggested that it was advantageous.

  From comparison between Comparative Examples 1, 3 and 4, and Examples 1 and 2, it is desirable that the dielectric layer in contact with the resistance layer does not contain a flame retardant in order to increase the adhesion of the dielectric layer to the resistance layer. Was suggested.

  From the comparison between Examples 1 and 2 and Comparative Examples 4 and 5, when the radio wave absorbing laminate has a dielectric layer containing no flame retardant, the thickness of the dielectric layer is not more than a predetermined thickness. It is suggested that is advantageous from the viewpoint of increasing the flame retardancy of the radio wave absorbing laminate.

REFERENCE SIGNS LIST 1 radio wave absorbing laminate 2 radio wave absorber 10 resistive layer 12 support 21 first dielectric layer 22 second dielectric layer 23 third dielectric layer 30 adherend

Claims (12)

A resistance layer containing a metal or a metal compound,
A first dielectric layer in close contact with the resistance layer,
An adhesive second dielectric layer containing an acid component,
The first dielectric layer is disposed between the resistance layer and the second dielectric layer in a thickness direction of the first dielectric layer,
The content of the mass-based acid component in the first dielectric layer is lower than the content of the mass-based acid component in the second dielectric layer.
Laminate for radio wave absorption.   The radio wave absorbing laminate according to claim 1, wherein the first dielectric layer does not substantially contain an acid component.   The radio wave absorbing laminate according to claim 1, wherein the first dielectric layer has a thickness of 5 μm or more.   The radio wave absorption laminate according to any one of claims 1 to 3, wherein the second dielectric layer contains a flame retardant.   The radio wave absorption laminate according to any one of claims 1 to 4, wherein the first dielectric layer does not substantially contain a flame retardant.   The radio wave absorption laminate according to claim 5, wherein the first dielectric layer has a thickness of less than 80 µm.   The radio wave absorbing laminate according to any one of claims 1 to 6, which conforms to UL standard UL94 V-1.   The radio wave absorption laminate according to any one of claims 1 to 7, further comprising a support that supports the resistance layer. Further comprising a third dielectric layer disposed between the first dielectric layer and the second dielectric layer in the thickness direction of the first dielectric layer,
The content of the acid component on a mass basis in the third dielectric layer is lower than the content of the acid component on a mass basis in the second dielectric layer, according to any one of claims 1 to 8. Laminate for radio wave absorption.   The radio wave absorbing laminate according to claim 9, wherein the third dielectric layer contains a flame retardant. An adherend containing a metal,
The radio wave absorption laminate according to any one of claims 1 to 10, wherein the second dielectric layer is adhered to the adherend.
Electromagnetic wave absorber.   A millimeter wave radar comprising the radio wave absorber according to claim 11.

Images