JP7178825B2 - Radio wave absorbing laminate, radio wave absorber, and millimeter wave radar - Google Patents

Description

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

Conventionally, techniques for absorbing unnecessary radio waves are known.

For example, Patent Literature 1 describes a millimeter-wave radar device including an antenna, a control circuit, a housing, a radome, and a shielding member, and the shielding member is a radio wave absorbing material for absorbing radio waves. consists of The shielding member is arranged between the antenna and the control circuit. As a result, unnecessary radio waves such as power supply noise from the control circuit can be cut off. The shield member has a dielectric loss layer or a magnetic loss layer with a dielectric loss greater than that of the radome. A conductive layer is laminated on the outer side surface of the shielding member to improve the radio wave absorption characteristics.

Patent Document 2 describes a millimeter-wave radar that includes an antenna base, a housing, and a radome, and a radio wave absorption layer is provided on the inner surface of the radome. The radio wave absorbing layer is a layer having a dielectric loss greater than that of the radome or a magnetic loss layer. A conductor layer is provided outside the radio wave absorbing layer. Side lobes transmitted from the transmitting antenna are absorbed by the radio wave absorbing layer.

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

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

Patent Documents 1 to 3 describe a dielectric loss type radio wave absorber or a magnetic loss type radio wave absorber, and a λ/4 type radio wave absorber is also known as a radio wave absorber. For example, Patent Document 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 reflecting layer (conductive layer), a dielectric layer having a thickness corresponding to λ/4, a resistive thin film layer (resistive layer). A dielectric layer is disposed between the conductive layer and the resistive layer. λ is the wavelength of the radio wave to be absorbed.

JP 2007-74662 A Japanese Unexamined Patent Application Publication No. 2004-77399 Japanese Patent Application Laid-Open No. 2002-118008 JP 2012-199463 A JP 2017-163141 A

Patent Documents 1 to 3 do not describe a λ/4 type radio wave absorber. On the other hand, Patent Documents 4 and 5 describe a λ/4 type radio wave absorber, and Patent Document 4 suggests attaching a radio wave absorbing sheet to a metal. However, in Patent Document 4, it is not clear which part of the radio wave absorbing sheet is brought into contact with the metal surface of the shield case. Patent Documents 1 to 5 describe forming a λ/4 type radio wave absorber by bringing a dielectric layer of a laminate including a resistive layer and a dielectric layer into contact with an adherend containing metal. do not have.

Accordingly, the present invention provides a λ/4 type radio wave absorber having good durability, comprising a dielectric layer having good adhesiveness to an adherend containing metal and a resistive layer. To provide a radio wave absorbing laminate suitable for In addition, the present invention provides a radio wave absorber provided with such a radio wave absorber laminate and a millimeter wave radar provided with this radio wave absorber.

This disclosure is
a resistive layer comprising a metal or metal compound;
a first dielectric layer in intimate contact with the resistive layer;
an adhesive second dielectric layer containing an acid component;
The first dielectric layer is arranged between the resistance 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 first dielectric layer is lower than the content of the acid component on a mass basis in the second dielectric layer,
A radio wave absorbing laminate is provided.

In addition, the present invention
an adherend containing a metal;
the radio wave absorbing laminate, wherein the second dielectric layer adheres to the adherend;
A radio wave absorber is provided.

Furthermore, the present invention provides
Provided is a millimeter wave radar comprising the radio wave absorber described above.

The second dielectric layer of the radio wave absorbing laminate has good adhesiveness to an adherend containing metal, and the radio wave absorbing laminate has good durability. Suitable for body composition.

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

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

A λ/4 type radio wave absorber is advantageous from the viewpoint of thinning because the thickness of the dielectric layer can be adjusted by adjusting the dielectric constant of the material forming the dielectric layer. On the other hand, when attaching a laminate including a resistive layer, a dielectric layer and a conductive layer to an adherend with an adhesive, an adhesive layer is required in addition to the resistive layer, the dielectric layer and the conductive layer. It is hard to say that this is favorable 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 radio wave reflectivity, the dielectric layer is given a predetermined adhesiveness, and the laminated body including the resistance layer and the dielectric layer is attached to the adherend. It is conceivable to construct a radio wave absorber of the type. This makes it possible to promote thinning of the λ/4 type radio wave absorber.

In order to increase the adhesion of the dielectric layer to the adherend having radio wave reflectivity, it is advantageous for the dielectric layer to contain an acid component. On the other hand, the dielectric layer also contacts the resistive layer. The present inventors have found that if the resistance layer contains a metal or metal compound, the thickness of the resistance layer is thin, and the acid component contained in the dielectric layer may corrode the resistance layer and change the characteristics of the resistance layer. newly discovered that there is Fluctuations in the properties of the resistive layer result in deterioration of radio wave absorption performance. Therefore, the present inventors have made extensive efforts to develop a radio wave absorbing laminate that has a dielectric layer with high adhesion to an adherend having radio wave reflectivity and that can prevent the resistance layer from corroding. As a result of extensive trial and error, the inventors of the present invention constructed a radio wave absorbing laminate having a plurality of dielectric layers, and then adjusted the content of the acid component in the plurality of dielectric layers to a predetermined relationship. It was newly discovered that a desired electromagnetic wave absorbing laminate can be obtained by

An embodiment of the present invention will be described with reference to the drawings. In addition, this invention is not limited to the following embodiment.

As shown in FIG. 1, the radio wave absorbing laminate 1a includes a resistance layer 10, a first dielectric layer 21, and a second dielectric layer 22. As shown in FIG. The resistive layer 10 contains a metal or metal compound. The first dielectric layer 21 is in close contact with the resistive layer 10 . As used herein, the term "adhesion" means sticking with an adhesive strength of 3 [N/20 mm] or more in the 180° peeling test described in the Examples. 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 the thickness direction of the first dielectric layer 21 . The mass-based content of the acid component in the first dielectric layer 21 is lower than the mass-based content of the acid component in the second dielectric layer 22 . In the present specification, amphoteric compounds such as aluminum hydroxide do not correspond to "acid component".

A λ/4 type radio wave absorber can be provided by using the radio wave absorbing 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 metal and has radio wave reflectivity. In the radio wave absorber 2 , the radio wave absorbing laminate 1 a adheres to the adherend 30 . Since the second dielectric layer 22 has adhesiveness, the electromagnetic 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 with a wavelength (λ _O ) to be absorbed is incident on the radio wave absorber 2, the radio wave is reflected by the surface of the resistance layer 10 (surface reflection) and the radio wave is reflected by the adherend 30 (back surface reflection). The electromagnetic wave absorbing laminated body 1a is designed so that the . In the λ/4 type radio wave absorber, as shown in the following formula (1), the wavelength ( _{λ O} ) is determined. That is, by appropriately adjusting the material and thickness of the dielectric layer, it is possible to set the radio wave of the wavelength to be absorbed. In Equation (1), sqrt(ε _r ) means the square root of 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 high adhesion to the adherend 30 . The second dielectric layer 22 is, for example, an acid determined according to "3.1 Neutralization titration method" of Japanese Industrial Standards (JIS) K 0070-1992 for a sample consisting of a part of the second dielectric layer 22 It contains an acid component so that the value is 5 or more. As a result, the second dielectric layer 22 can exhibit high adhesive strength to the adherend 30 more reliably. The mass-based content of the acid component in the second dielectric layer 22 is, for example, 10% or more, preferably 15% or more. The content 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 acid component on a mass basis in the first dielectric layer 21 is lower than the content of acid component on a mass basis in the second dielectric layer 22, corrosion of the resistive layer 10 containing a metal or metal compound is prevented. can be prevented. As a result, the radio wave absorbing laminate 1a and, in turn, the radio wave absorber 2 have high durability.

The mass-based content of the acid component in the first dielectric layer 21 is not limited to a specific content as long as it is lower than the mass-based content of the 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%, preferably 5% or less. More desirably, first dielectric layer 21 is substantially free of acid components. Thereby, corrosion of the resistance layer 10 can be prevented more reliably. “Substantially free of acid component” means that a trace amount of acid component is allowed as long as the properties of the resistive layer 10 are maintained within the desired range. For example, after storing the radio wave absorbing laminate 1a for 500 hours in an environment with a temperature of 85° C. and a relative humidity of 85%, the amount of change in the sheet resistance of the resistance layer 10 before and after storage is 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 it contains a small amount of acid component. Most preferably, the first dielectric layer 21 does not contain any acid component.

The first dielectric layer 21 has a thickness of 5 μm or more, for example. 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 prevented more reliably. 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 any 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 mass-based content of the flame retardant in the second dielectric layer 22 is, for example, 60 to 90%. As a result, desired flame retardancy can be easily imparted to the radio wave absorbing laminate 1a, and the adhesion of the second dielectric layer 22 to the adherend 30 can be kept high. The mass-based content of the flame retardant in the second dielectric layer 22 is desirably 65-80%, more desirably 70-75%.

The first dielectric layer 21, for example, contains substantially no flame retardant. A flame retardant may reduce the adhesion of the first dielectric layer 21 to the resistive layer 10 . However, good adhesion of first dielectric layer 21 to resistive layer 10 is maintained if first dielectric layer 21 is substantially free of flame retardants. “Substantially containing no flame retardant” means that a slight amount of flame retardant is allowed as long as the first dielectric layer 21 adheres to the resistance layer 10 . Desirably, first dielectric layer 21 does not contain any flame retardants.

The first dielectric layer 21 has a thickness of less than 80 μm, for example. 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 desired flame retardancy. The thickness of the first dielectric layer 21 is preferably 75 μm or less, more preferably 70 μm or less.

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

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

As noted above, resistive layer 10 includes a metal or metal compound. The metal contained 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, a metal nanowire, and a metal mesh, the main component of which is 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 preferably contains indium tin oxide (ITO) as a main component. In this case, the SnO ₂ content in the resistive layer 10 is preferably 20-40% by weight, more preferably 25-35% by weight. Such a resistance layer 10 has an extremely stable amorphous structure, and can suppress variations in sheet resistance of the resistance layer 10 in a high-temperature, high-humidity environment. In addition, in this specification, a "main component" means the component contained most on a mass basis.

Although the thickness of the resistance layer 10 is not particularly limited, it is, for example, 20 to 90 nm. Thus, when the thickness of the resistance layer 10 is small, the resistance layer 10 is easily corroded by a small amount of acid component. However, as described above, since the content of the acid component in the first dielectric layer 21 is low, the resistance layer 10 is less likely to corrode even if the thickness of the resistance layer 10 is small.

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 matrix. The elastomer contained in the first dielectric layer 21 may be natural rubber, synthetic rubber, acrylic elastomer, silicone rubber, or urethane elastomer. The first dielectric layer 21 may contain components 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 that is chemically stable against acid components as a main component. The elastomer contained in the second dielectric layer 22 may be natural rubber, synthetic rubber, acrylic elastomer, silicone rubber, or urethane elastomer. The elastomer contained in the second dielectric layer 22 is desirably an acrylic elastomer. The second dielectric layer 22 may contain components such as a tackifier, if desired.

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 containing such an acid component in the second dielectric layer 22, a sample consisting of a part of the second dielectric layer 22 is subjected to the following "3.1 Neutralization titration method" of JIS K 0070-1992. The determined acid value tends to be 5 or more. As a result, the second dielectric layer 22 tends to more reliably exhibit high adhesion to the adherend 30 .

As shown in FIG. 1, the electromagnetic wave absorbing laminate 1a further includes a support 12, for example. A support 12 supports the resistive layer 10 . In this case, the resistive layer 10 can be produced, for example, by depositing it on the support 12 using methods such as sputtering, ion plating, or coating (eg, bar coating). The support 12 is arranged at a position farther from the adherend 30 than the resistance layer 10 in the radio wave absorber 2, for example. Therefore, the support 12 protects the resistance layer 10, the first dielectric layer 21, and the second dielectric layer 22, 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 resistive 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-oriented polypropylene (CPP), or vinylidene chloride resin. Among them, the material of the support 12 is desirably PET or PI from the viewpoint of the balance between good heat resistance, dimensional stability and manufacturing cost.

The support 12 has a thickness of, for example, 10-150 μm, preferably 15-100 μm, more preferably 20-80 μm. As a result, the bending rigidity of the support 12 is low, and wrinkling or deformation of the support 12 can be suppressed when the resistance layer 10 is formed.

In the radio wave absorber 2, for example, the adherend surface of the adherend 30 to the radio wave absorbing laminate 1a is made of metal. Thereby, the adherend 30 has radio wave reflectivity on the adherend surface. The metal forming the adherend 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 electromagnetic wave absorbing laminate 1a can be modified from various viewpoints. The radio wave absorbing laminate 1a may be modified, for example, into a radio wave absorbing laminate 1b shown in FIG. The radio wave absorbing laminate 1b is constructed in the same manner as the radio wave absorbing laminate 1a, except where otherwise specified. Components of the radio wave absorbing laminate 1b that are the same as or corresponding to those of the radio wave absorbing laminate 1a are denoted by the same reference numerals, and detailed description thereof is omitted. The description regarding the electromagnetic wave absorbing laminate 1a also applies to the electromagnetic wave absorbing laminate 1b as long as there is no technical contradiction. The radio wave absorber 2 may have a radio wave absorbing laminate 1b instead of the radio wave absorbing laminate 1a.

The radio wave absorbing laminate 1 b further includes a third dielectric layer 23 . The third dielectric layer 23 is arranged between the first dielectric layer 21 and the second dielectric layer 22 in the thickness direction of the first dielectric layer 21 . The mass-based content of the acid component in the third dielectric layer 23 is lower than the mass-based content of the acid component in the second dielectric layer 22 . According to the radio wave absorbing laminate 1b, the third dielectric layer 23 can suppress the acid component contained in the second dielectric layer 22 from reaching the resistance layer 10, 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 formula (1) is satisfied.

The mass-based content of the acid component in the third dielectric layer 23 is not limited to a specific content as long as it is lower than the mass-based content of the 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%, preferably 5% or less. More desirably, third dielectric layer 23 is substantially free of acid components. Thereby, corrosion of the resistance layer 10 can be prevented more reliably. “Substantially free of acid component” means that a trace amount of acid component is allowed as long as the properties of the resistive layer 10 are maintained within the desired range. For example, after storing the radio wave absorbing laminate 1b for 500 hours in an environment with a temperature of 85° C. and a relative humidity of 85%, the amount of change in the sheet resistance of the resistance layer 10 before and after storage is 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 23 does not substantially contain an acid component even if it contains a trace amount of acid component. Most preferably, the first dielectric layer 23 does not contain any acid component.

In the electromagnetic wave absorbing laminate 1b, the third dielectric layer 23 contains, for example, a flame retardant. This makes it easier for the radio wave absorbing laminate 1b 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 mass-based content 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 desired flame retardancy more reliably. The mass-based content of the flame retardant in the third dielectric layer 23 is desirably 65-80%, more desirably 70-75%.

For example, by using the radio wave absorbing laminate 1a or the radio wave absorbing laminate 1b, a millimeter wave radar provided with the radio wave absorber 2 can be provided. In this case, the adherend 30 may correspond to a metal-containing part of the millimeter wave radar.

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

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

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) is mixed with a roll. was stirred. Thereafter, this mixture was hot-pressed at 150° C. to obtain a sheet with a thickness of 70 μm. Thus, a first dielectric layer sheet according to Example 1 was obtained. The first dielectric layer sheet according to Example 1 did not contain an acid component.

A laminate obtained by stacking three layers of double-sided tape containing an acrylic adhesive (manufactured by Nitto Denko, product name: TR-5920FS, thickness: 200 μm) was hot-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 second dielectric layer sheet according to Example 1 contained 18% by mass of acrylic acid as the acid component and 72% by mass of aluminum hydroxide as the flame retardant.

A first dielectric layer sheet is overlaid on the resistance layer of the PET film with a resistance layer, and a second dielectric layer sheet is further overlaid on the first dielectric layer sheet to form a radio wave absorbing laminate according to Example 1. got a body

(Preparation of specimen A)
A 20 mm wide strip was obtained by cutting the PET film with the resistive layer. Also, a small piece having a width of 20 mm was obtained by cutting the first dielectric layer sheet. A double-sided adhesive tape (manufactured by Nitto Denko Corporation, product name: No. 5000N) was attached to the surface of a plate material made of SUS304BA. A small piece of the sheet for the first dielectric layer was laminated and pasted on the double-sided adhesive tape. Next, the ends of the resistive layer in the longitudinal direction of the strip of the resistive layer-attached PET film were overlapped and pasted onto the small piece of the sheet for the first dielectric layer. This state was maintained in an environment of 23° C. for 30 minutes to obtain a specimen A according to Example 1.

(Preparation of test body B)
A 20 mm wide strip was obtained by cutting a PET film with a thickness of 23 μm. Also, a small piece having a width of 20 mm was obtained by cutting the sheet for the second dielectric layer. A small piece of the second dielectric layer sheet was applied to the longitudinal end of the strip of PET film. Next, a small piece of the sheet for the second dielectric layer was attached to the surface of the SUS304BA plate material. This state was maintained in an environment of 23° C. for 30 minutes to obtain a specimen B according to Example 1.

(Preparation of test piece C)
A test piece C according to Example 1 was obtained by cutting the electromagnetic wave absorbing 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>
A first dielectric layer sheet was produced in the same manner as in Example 1 to obtain a first dielectric layer sheet according to Example 2 having a thickness of 70 μm. A double-faced tape containing an acrylic adhesive (manufactured by Nitto Denko, product name: TR-5920FS, thickness: 200 μm) was used as the second dielectric layer sheet according to Example 2. The second dielectric layer sheet according to Example 2 contained 18% by mass of acrylic acid as the acid component and 72% by mass of aluminum hydroxide as the flame retardant.

250 parts by weight of aluminum hydroxide-containing particles (manufactured by Showa Denko Co., Ltd., product name: Hygilite H-42) were added to 100 parts by weight of an acrylic block copolymer (manufactured by Kuraray Co., Ltd., product name: Clarity LA2330). The mixture was stirred with a mixing roll. After that, the mixture was hot-pressed at 150° C. to obtain a sheet with 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.

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

A specimen A according to Example 2 was produced in the same manner as in Example 1. A 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 absorbing laminate according to Example 2 was used instead of the electromagnetic wave absorbing laminate according to Example 1.

<Comparative Example 1>
250 parts by weight of aluminum hydroxide-containing particles (manufactured by Showa Denko Co., Ltd., product name: Hygilite H-42) were added to 100 parts by weight of an acrylic block copolymer (manufactured by Kuraray Co., Ltd., product name: Clarity LA2330). The mixture was stirred with a mixing roll. After that, the mixture was hot-pressed at 150° C. to obtain a sheet with a thickness of 460 μm. Thus, a dielectric layer sheet according to Comparative Example 1 was obtained. A dielectric layer sheet according to Comparative Example 1 was placed on the resistance layer of a PET film with a resistance layer produced in the same manner as in Example 1 to obtain a radio wave absorbing 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.

A 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. A 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 electromagnetic wave absorbing laminate according to Comparative Example 1 was used instead of the electromagnetic wave absorbing laminate according to Example 1.

<Comparative Example 2>
A laminate obtained by stacking three layers of double-sided tape containing an acrylic adhesive (manufactured by Nitto Denko, product name: TR-5920FS, thickness: 200 μm) was hot-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 the acid component and 72% by mass of aluminum hydroxide as the flame retardant.

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

A 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. A 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 electromagnetic wave absorbing laminate according to Comparative Example 2 was used instead of the electromagnetic 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 Co., Ltd., product name: Hygilite H-42). was stirred with a mixing roll. After that, the mixture was hot-pressed at 150° C. to obtain a sheet with 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 obtained by stacking three layers of double-sided tape containing an acrylic adhesive (manufactured by Nitto Denko, product name: TR-5920FS, thickness: 200 μm) was hot-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 the acid component and 72% by mass of aluminum hydroxide as the flame retardant.

A first dielectric layer sheet according to Comparative Example 3 was placed on the resistance layer of a PET film with a resistance layer produced in the same manner as in Example 1, and a second dielectric layer sheet according to Comparative Example 3 was further placed on the first dielectric layer sheet. A radio wave absorbing laminate according to Comparative Example 3 was obtained by laminating the two dielectric layer sheets.

A specimen A according to Comparative Example 3 was produced 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. A 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 electromagnetic wave absorbing laminate according to Comparative Example 3 was used instead of the electromagnetic wave absorbing laminate according to Example 1.

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

A first dielectric layer sheet according to Comparative Example 4 was placed on the resistance layer of a PET film with a resistance layer produced in the same manner as in Example 1, and a second dielectric layer sheet according to Comparative Example 4 was further placed on the first dielectric layer sheet. A radio wave absorbing laminate according to Comparative Example 4 was obtained by stacking two dielectric layer sheets.

A specimen A according to Comparative Example 4 was produced 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. A 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 electromagnetic wave absorbing laminate according to Comparative Example 4 was used instead of the electromagnetic wave absorbing laminate according to Example 1.

<Comparative Example 5>
An acrylic block copolymer (manufactured by Kuraray Co., Ltd., product name: Clarity LA2330) was hot-pressed at 150° C. to obtain a sheet with 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. A dielectric layer sheet according to Comparative Example 5 was placed on the resistance layer of a PET film with a resistance layer produced in the same manner as in Example 1 to obtain a radio wave absorbing laminate according to Comparative Example 5.

A 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. A 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 electromagnetic wave absorbing laminate according to Comparative Example 5 was used instead of the electromagnetic wave absorbing laminate according to Example 1.

[Permittivity measurement]
Using a network analyzer (manufactured by Agilent Technologies, product name: N5230C), according to the cavity resonance method, the relative permittivity at 10 GHz of the dielectric layers of the radio wave absorbing laminates according to Examples and Comparative Examples was measured. Table 1 shows the results.

[Evaluation of Adhesiveness of Dielectric Layer to Resistive Layer]
Adhesiveness of the dielectric layer to the resistive layer was evaluated using test specimens A according to Examples and Comparative Examples. In Test Specimen A, a strip of resistive PET film was peeled off 180° to the dielectric layer at a speed of 300 mm/min. The peel force was measured to determine the adhesion of the dielectric layer to the resistive layer. Table 1 shows the results.

[Evaluation of Adhesiveness of Dielectric Layer to Metal]
Adhesiveness of the dielectric layer to metal was evaluated using the specimen B according to the example and each comparative example. In specimen B, the PET film strip was pulled at a speed of 300 mm/min to peel off the dielectric layer at 180° to the surface of the SUS304BA plate material. The peel force was measured to determine the adhesion of the dielectric layer to metal. Table 1 shows the results.

[Flame Retardant Evaluation]
The flame retardancy of the radio wave absorbing laminates according to Examples and Comparative Examples was evaluated according to the UL94V test specified in UL Standards using the test piece C according to Examples and Comparative Examples. Table 1 shows the results. In addition, the judgment criteria for flame retardancy in the UL94V test are as shown in Table 2.

[An endurance test]
The radio wave absorbing laminates of Examples and Comparative Examples were stored in an environment of 85° C. and 85% relative humidity for 500 hours. The sheet resistance of the resistance layer after storage was measured according to the eddy current method using a non-contact sheet resistance measuring device (manufactured by Napson, product name: NC-80MAP). The ratio (ΔR/Ri) of the variation amount ΔR of the sheet resistance of the resistance layer before and after storage to the initial sheet resistance Ri of the resistance layer was obtained, and the durability of the electromagnetic wave absorbing laminates according to the examples and each comparative example was determined according to the following criteria. evaluated the sex. The amount of variation ΔR is the absolute value of the difference obtained by subtracting the sheet resistance Ra of the resistance layer after storage from the initial sheet resistance Ri of the 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 the 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, from the comparison between Examples 1 and 2 and Comparative Example 2, it was found 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 the 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 adhesiveness 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 electromagnetic wave absorbing laminate has a dielectric layer containing no flame retardant, the thickness of the dielectric layer is equal to or less than a predetermined thickness. was suggested to be advantageous from the viewpoint of enhancing the flame retardancy of the electromagnetic wave absorbing laminate.

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

Claims (11)

a resistive layer comprising a metal or metal compound;
a first dielectric layer in intimate contact with the resistive layer;
an adhesive second dielectric layer containing an acid component;
a support that supports the resistive layer ;
The first dielectric layer is arranged between the resistance layer and the second dielectric layer in the thickness direction of the first dielectric layer,
The resistance layer is arranged between the support and the first dielectric layer in the thickness direction of the first dielectric layer,
The content of the acid component on a mass basis in the first dielectric layer is lower than the content of the acid component on a mass basis in the second dielectric layer,
A laminate for electromagnetic wave absorption. 2. The radio wave absorbing laminate according to claim 1, wherein said first dielectric layer does not substantially contain an acid component. 3. The electromagnetic wave absorbing laminate according to claim 1, wherein said first dielectric layer has a thickness of 5 [mu]m or more. The electromagnetic wave absorbing laminate according to any one of claims 1 to 3, wherein the second dielectric layer contains a flame retardant. The electromagnetic wave absorbing laminate according to any one of claims 1 to 4, wherein the first dielectric layer does not substantially contain a flame retardant. 6. The electromagnetic wave absorbing laminate according to claim 5, wherein said first dielectric layer has a thickness of less than 80 [mu]m. The electromagnetic wave absorbing laminate according to any one of claims 1 to 6, which conforms to UL94 V-1 of UL standards. 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;
8. The composition according to any one of claims 1 to 7 , wherein a mass-based content of the acid component in the third dielectric layer is lower than a mass-based content of the acid component in the second dielectric layer. A laminate for electromagnetic wave absorption. 9. The electromagnetic wave absorbing laminate according to claim 8 , wherein said third dielectric layer contains a flame retardant. an adherend containing a metal;
The electromagnetic wave absorbing laminate according to any one of claims 1 to 9 , wherein the second dielectric layer adheres to the adherend,
electromagnetic wave absorber. A millimeter wave radar comprising the radio wave absorber according to claim 10 .

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