JP2023051589A - Radio wave absorber, article with radio wave absorber, and laminate for radio wave absorber - Google Patents

Abstract

To provide a radio wave absorber advantageous from the viewpoint of suppressing degradation of radio wave absorption performance due to moisture release from an adherend in moisture absorption state.SOLUTION: A radio wave absorber 1a includes a resistive layer 10, a reflector 30, a dielectric layer 20, and an adhesive layer 40. The reflector 30 reflects radio waves. The dielectric layer 20 is positioned between the resistive layer 10 and the reflector 30 in a thickness direction of the resistive layer 10. The resistive layer 10 is positioned between the dielectric layer 20 and the adhesive layer 40 in the thickness direction of the resistive layer 10. Under conditions of 100°C, a tensile shear load T is applied along a direction parallel to a surface of a plate 2 to the radio wave absorber 1a attached to the plate 2 with the adhesive layer 40 in contact with the surface of the plate 2. In this case, the shear adhesive strength F100 of the adhesive layer 40 is 10.0 N/cm2 or higher.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to a radio wave absorber, an article with a radio wave absorber, and a laminate for a radio wave absorber.

A radio wave absorber having a dielectric layer between a resistive layer and a radio wave reflector is conventionally known.

For example, Patent Literature 1 describes a radio wave absorber including a resistive film, a radio wave reflector, and a dielectric layer. The resistive film contains ultrafine conductive fibers. The radio wave absorber has a dielectric layer between the resistive film and the radio wave reflector, and the thickness of the dielectric layer is designed based on the λ/4 radio wave absorber theory.

Japanese Patent Application Laid-Open No. 2005-311330

A λ/4 type radio wave absorber includes a resistive layer, a reflector for reflecting radio waves, and a dielectric layer having a thickness corresponding to λ/4. A dielectric layer is disposed between the resistive layer and the reflector. λ is the wavelength of the radio wave to be absorbed.

It is conceivable to attach the λ/4 type radio wave absorber to a predetermined adherend using an adhesive layer. According to the studies of the present inventors, an adhesive layer is formed between the resistance layer of the λ/4 type electromagnetic wave absorber and the adherend, and the λ/4 type electromagnetic wave absorber is attached to the adherend by this adhesive layer. It is also envisioned that the . In this case, the resistive layer is arranged between the dielectric layer and the adhesive layer in the thickness direction of the resistive layer. On the other hand, Patent Literature 1 does not specifically consider such a case.

Further investigation by the present inventors revealed that when the radio wave absorber is attached to the adherend by means of an adhesive layer formed between the resistance layer of the radio wave absorber and the adherend, the adherend in the moisture absorbing state It was newly found that the effects of water release from the body need to be considered. Specifically, it was newly found that the release of moisture may degrade the performance of the radio wave absorber.

Therefore, the present invention prevents the deterioration of radio wave absorption performance due to the release of moisture from a moisture-absorbing adherend even if the resistance layer is arranged between the dielectric layer and the adhesive layer in the thickness direction of the resistance layer. To provide a radio wave absorber that is advantageous from the viewpoint of suppression.

The present invention
A radio wave absorber,
a resistive layer;
a reflector that reflects radio waves;
a dielectric layer disposed between the resistive layer and the reflector in the thickness direction of the resistive layer;
and an adhesive layer,
The resistance layer is arranged between the dielectric layer and the adhesive layer in the thickness direction of the resistance layer,
The adhesive layer is applied to the electromagnetic wave absorber attached to the plate material in a state in which the adhesive layer is in contact with the surface of the plate material having a surface formed of polycarbonate under the condition of 100° C. in a direction parallel to the surface. has a shear adhesive strength of 10.0 N/cm ^or more when a tensile shear load is applied along
A radio wave absorber is provided.

In addition, the present invention
the radio wave absorber;
an adherend to which the radio wave absorber is attached while the adhesive layer is in contact;
An article with a radio wave absorber is provided.

In addition, the present invention
A laminate for a radio wave absorber,
a resistive layer;
a dielectric layer having a first main surface and a second main surface, wherein the first main surface is formed closer to the resistance layer than the second main surface in the thickness direction of the resistance layer;
and an adhesive layer,
The resistance layer is arranged between the dielectric layer and the adhesive layer in the thickness direction of the resistance layer,
At least a portion forming the second main surface of the dielectric layer has adhesiveness,
The adhesive layer is attached to the surface of a plate material having a surface made of polycarbonate in a state where the adhesive layer is in contact with the surface of the plate material. having a shear adhesive strength of 10.0 N/cm ² or more when a tensile shear load is applied along a parallel direction;
A laminate for a radio wave absorber is provided.

In the above radio wave absorber, although the resistance layer is arranged between the dielectric layer and the adhesive layer in the thickness direction of the resistance layer, the radio wave absorption performance decreases due to the release of moisture from the adherend in a moisture-absorbing state. is advantageous from the viewpoint of suppressing

FIG. 1 is a cross-sectional view showing an example of a radio wave absorber according to the present invention. FIG. 2A is a plan view schematically showing a method for measuring the shear adhesive strength of the adhesive layer. FIG. 2B is a cross-sectional view of the test piece taken along line BB of FIG. 2A. FIG. 3 is a cross-sectional view showing an example of an article with a radio wave absorber according to the present invention. FIG. 4 is a cross-sectional view showing another example of the radio wave absorber according to the present invention. FIG. 5 is a cross-sectional view showing another example of an article with a radio wave absorber according to the present invention. FIG. 6 is a cross-sectional view showing an example of the radio wave absorber laminate according to the present invention. FIG. 7 is a cross-sectional view showing another example of an article with a radio wave absorber according to the present invention. FIG. 8 is a cross-sectional view showing another example of the radio wave absorber laminate according to the present invention. FIG. 9 is a diagram schematically showing a method of measuring return loss.

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 absorber 1a includes a resistance layer 10, a reflector 30, a dielectric layer 20, and an adhesive layer (first adhesive layer) 40. As shown in FIG. The reflector 30 reflects radio waves. The dielectric layer 20 is arranged between the resistive layer 10 and the reflector 30 in the thickness direction of the resistive layer 10 . The resistance layer 10 is arranged between the dielectric layer 20 and the adhesive layer 40 in the thickness direction of the resistance layer 10 . As shown in FIGS. 2A and 2B, a tensile shear load T is applied along a direction parallel to the surface of the plate 2 to the radio wave absorber 1a attached to the plate 2 while the adhesive layer 40 is in contact with the surface of the plate 2. By adding, the shear adhesive force F ₁₀₀ of the adhesive layer 40 is measured. This measurement is made at 100°C. The surface of the plate member 2 is made of polycarbonate (PC). The shear adhesive force F ₁₀₀ [N/cm ² ] of the adhesive layer 40 is the breaking force [N] when the bond between the electromagnetic wave absorber 1a and the plate member 2 is broken, and the bonding surface between the electromagnetic wave absorber 1a and the plate member 2. It can be determined by dividing by the area of Sa [cm ² ]. The adhesive layer 40 has a shear adhesive strength F ₁₀₀ of 10.0 N/cm ² or more. The shear adhesive strength F ₁₀₀ of the adhesive layer 40 can be measured, for example, with reference to the description of Japanese Industrial Standard JIS K 6850:1999.

When a radio wave with a wavelength λ _O to be absorbed enters the radio wave absorber 1a, the radio wave reflected on the surface of the resistance layer 10 (surface reflection) interferes with the radio wave reflected on the reflector 30 (back surface reflection). , the radio wave absorber 1a is designed. Radio waves that can be absorbed by the radio wave absorber 1a are not limited to specific radio waves. Radio waves that can be absorbed by the radio wave absorber 1a are, for example, millimeter waves or submillimeter waves in a specific frequency band.

Examples of the frequency range of radio waves that can be absorbed by the radio wave absorber 1a are as follows. The following radio waves are being considered for use as 5G radio waves in various countries.
27.5-29.5GHz
27.5-28.35GHz
24.25-24.45GHz
24.75-25.25GHz
37-38.6GHz
38.6-40GHz
47.2-48.2GHz
64-71GHz
24.25-27.5GHz
40.5-43.5GHz
66-71GHz
24.75-27.5GHz
37-42.5GHz
27.5-29.5GHz
31.8-33.4GHz
37-40.5GHz

Another example of the frequency range of radio waves that can be absorbed by the radio wave absorber 1a is as follows. The following radio waves can be used as radio waves for millimeter wave radar.
21.65-26.65GHz
60-61GHz
76-77GHz
77-81GHz
94.7-95GHz
139-140GHz

Using the radio wave absorber 1a, for example, an article 5a with a radio wave absorber shown in FIG. 3 can be provided. The radio wave absorber-attached article 5a includes, for example, a radio wave absorber 1a and an adherend 3. As shown in FIG. The radio wave absorber 1a is attached to the adherend 3 with the adhesive layer 40 in contact therewith.

The radio wave absorber-attached article 5a can be used in various environments. For example, it is assumed that the article 5a with a radio wave absorber is used in a state where the adherend 3 has absorbed moisture. When moisture is released from a hygroscopic adherend, air bubbles are likely to be generated between the adherend and the adhesive layer in contact with the adherend, resulting in large voids. In the λ/4 type electromagnetic wave absorber, when the resistance layer is arranged between the dielectric layer and the adhesive layer in the thickness direction of the resistance layer, if such a large gap occurs, the electromagnetic wave to be absorbed will be an electromagnetic wave. It is possible to pass through this gap when entering the absorber. As a result, the radio wave absorption performance of the λ/4 type radio wave absorber can be significantly degraded. The inventors of the present invention conducted extensive trial and error to develop a new radio wave absorber in which such large voids are less likely to occur between the adherend and the adhesive layer in contact with the adherend. As a result, by adjusting the shear adhesive force F ₁₀₀ of the adhesive layer 40 at 100° C. to 10.0 N/cm ² or more, the adhesive layer 40 in contact with the adherend 3 and the adherend 3 have a large shear strength. It was found that voids are less likely to occur. The inventors also measured the shear adhesive strength of the adhesive layer at 23°C. However, it has also been found that even with the use of an adhesive layer that exhibits a high shear adhesive strength at 23°C, it is sometimes difficult to suppress the deterioration of radio wave absorption performance due to the release of moisture from a moisture-absorbing adherend.

The adherend 3 in the radio wave absorber-attached article 5a is not limited to a specific article. The adherend 3 is, for example, a resin product. In this case, the amount of moisture absorbed by the adherend 3 tends to increase. However, since the shear adhesive force F ₁₀₀ of the adhesive layer 40 is adjusted to 10.0 N/cm ² or more, even if the moisture absorbed by the adherend 3, which is a resin product, is released, A large gap is less likely to occur between the adherend 3 and the adhesive layer 40 in the article 5a.

The material forming the adherend 3 is not limited to a specific material. The adherend 3 includes, for example, at least one selected from the group consisting of polycarbonate (PC), polyamide (PA), polybutylene terephthalate (PBT), polyethylene terephthalate (PET), and polypropylene (PP). In this case, the amount of moisture absorbed by the adherend 3 tends to increase. However, since the shear adhesive strength F ₁₀₀ of the adhesive layer 40 is adjusted to 10.0 N/cm ² or more, the adherend 3 containing at least one selected from the group consisting of PC, PBT, and PP absorbs moisture. Even if the moisture is released, a large gap is less likely to occur between the adherend 3 and the adhesive layer 40 in the article 5a with a radio wave absorber.

The shear adhesive strength F ₁₀₀ of the adhesive layer 40 may be 10.5 N/cm ² or more, 11.0 N/cm ² or more, or 12.0 N/cm ² or more, It may be 13.0 N/cm ² or more. The shear adhesive force F ₁₀₀ of the adhesive layer 40 is, for example, 50 N/cm ² or less. The radio wave absorber 1a may be peeled off from the adherend 3 during maintenance of the radio wave absorber-attached article 5a or recycling of the radio wave absorber-attached article 5a. If the shear adhesive strength F ₁₀₀ of the adhesive layer 40 is 50 N/cm ² or less, the electromagnetic wave absorber 1a can be peeled off the adherend 3 during maintenance or recycling of the article 5a with the electromagnetic wave absorber. Cheap. The shear adhesive force F ₁₀₀ of the adhesive layer 40 may be 40 N/cm ² or less, or may be 30 N/cm ² or less.

The surface of the plate material 2 used for measuring the shear adhesive force F ₁₀₀ of the adhesive layer 40 is, for example, a smooth surface. The surface of the plate material 2 has, for example, an arithmetic mean roughness _Ra of 5 μm or less. Arithmetic mean roughness _Ra is a value based on JIS B 0601:2013.

The shear adhesive strength _F23 of the adhesive layer 40 can be measured in the same manner as the shear adhesive strength F100 of the adhesive layer 40 except that the 100°C condition is changed to ₂₃ °C. As long as the shear adhesive strength F ₁₀₀ is 10.0 N/cm ² or more, the shear adhesive strength F ₂₃ is not limited to a specific value. The shear adhesive force F ₂₃ is, for example, 40-100 N/cm ² . The shear adhesive strength F ₂₃ may be 45 N/cm ² or more, or 50 N/cm ² or more. The shear adhesive strength F ₂₃ may be 90 N/cm ² or less, or may be 80 N/cm ² or less.

The thickness of the adhesive layer 40 is not limited to a specific value as long as the shear adhesive strength F ₁₀₀ is 10.0 N/cm ² or more. The adhesive layer 40 has a thickness of, for example, 15-750 μm. According to such a configuration, the shear adhesive strength F ₁₀₀ of the adhesive layer 40 can be easily adjusted within a desired range, and it is easy to suppress deterioration in radio wave absorption performance due to release of moisture from the adherend 3 in a moisture-absorbing state. In addition, the influence of the adhesive layer 40 on the radio wave absorption performance of the radio wave absorber 1a can be easily reduced, and the radio wave absorber 1a can easily exhibit high radio wave absorption performance.

The thickness of the adhesive layer 40 may be 20 μm or more, 25 μm or more, 30 μm or more, 35 μm or more, 40 μm or more, or 45 μm or more. It may be 50 μm or more. The thickness of the adhesive layer 40 may be 740 μm or less, 730 μm or less, 720 μm or less, 700 μm or less, 650 μm or less, or 600 μm or less. There may be. The thickness of the adhesive layer 40 may be 550 μm or less, 500 μm or less, 450 μm or less, 400 μm or less, or 350 μm or less.

The adhesive layer 40 may be an adhesive layer provided with a substrate, or may be an adhesive layer without a substrate. The material forming the base is not limited to a specific material. The material forming the base material may be a plastic film such as a PET film, a nonwoven fabric, a woven fabric, a foam, or paper such as Japanese paper. There may be.

The base resin contained in the adhesive layer 40 is not limited to a specific resin. The adhesive layer 40 contains acrylic resin, for example. In this case, the shear adhesive strength F ₁₀₀ of the adhesive layer 40 can be easily adjusted within a desired range, and the reduction in radio wave absorption performance due to the release of moisture from the adherend 3 in a moisture-absorbing state can be more easily suppressed.

The adhesive layer 40 further contains, for example, a tackifier. The tackifier is not limited to any particular tackifier. Tackifiers are, for example, rosin-based resins, terpene-based resins, aliphatic petroleum resins, aromatic petroleum resins, hydrogenated petroleum resins, coumarone-indene resins, styrene-based resins, alkylphenol resins, or xylene resins. Rosin-based resins are, for example, rosin, hydrogenated rosin, rosin ester, hydrogenated rosin ester, rosin phenolic resin, or polymerized rosin. Terpene-based resins are, for example, terpene resins, terpene phenolic resins, aromatic modified terpene resins, or hydrogenated terpene resins.

As long as the shear adhesive strength F ₁₀₀ is 10.0 N/cm ² or more, the difference Δt between the thickness of the sample after the high temperature test and the thickness of the sample before the high temperature test is not limited to a specific value. The sample subjected to the high temperature test was a polycarbonate plate stored for 125 hours at a temperature of 85°C and a relative humidity of 85%. It is made by pasting on a board. The surface of the polycarbonate plate is smooth. A high temperature test is done by keeping the environment of the sample at 140° C. for 48 hours. The thickness of the sample prior to high temperature testing can be determined by arithmetically averaging the measurements at 5 or more randomly selected locations. After the high-temperature test, the locations where the thickness of the sample varies greatly are identified by visual inspection. The thickness at that point is determined as the thickness of the sample after the high temperature test. The difference Δt is, for example, 0.30 mm or less. According to such a configuration, even if moisture is released from the adherend in a hygroscopic state, radio waves to be absorbed are less likely to pass through large gaps when incident on the radio wave absorber 1a. Therefore, even if moisture is released from the adherend in a hygroscopic state, the radio wave absorbing performance of the radio wave absorber 1a is less likely to deteriorate.

The difference Δt is preferably 0.29 mm or less, more preferably 0.28 mm or less, even more preferably 0.27 mm or less.

The material forming the resistance layer 10 is not limited to a specific material as long as the radio wave absorber 1a can absorb desired radio waves. The resistance layer 10 contains, for example, at least one selected from the group consisting of metal oxides, alloys, conductive polymers, carbon black, multi-walled carbon nanotubes (MWNT), and single-walled carbon nanotubes (SWNT). A conductive polymer is not limited to a specific polymer. Conductive polymers are, for example, polythiophene, polypyrrole, polyaniline, or PEDOT/PSS. A metal oxide is, for example, a metal oxide containing at least one metal element selected from the group consisting of indium, tin, and zinc. The metal oxide may be indium tin oxide (ITO). The alloy contains molybdenum, for example. The alloy may contain nickel and chromium in addition to molybdenum.

The resistance layer 10 can be formed by a method such as sputtering, vapor deposition, ion plating, or curing of a coating film of a coating liquid.

The sheet resistance of the resistance layer 10 is not limited to a specific value as long as the radio wave absorber 1a can absorb desired radio waves. The sheet resistance of the resistive layer 10 is, for example, 200Ω/square to 600Ω/square. The sheet resistance of the resistive layer 10 may be 220Ω/square or more, 240Ω/square or more, 260Ω/square or more, 280Ω/square or more, or 300Ω/square. It may be □ or more, 320 Ω/□ or more, or 340 Ω/□ or more. The sheet resistance of the resistance layer 10 may be 580 Ω/□ or less, 560 Ω/□ or less, 540 Ω/□ or less, 520 Ω/□ or less, or 500 Ω/□ or less. □ or less, or 450Ω/□ or less.

The reflector 30 is not limited to a specific mode as long as it can reflect the radio waves to be absorbed. As shown in FIG. 1, the reflector 30 is formed in layers, for example. In this case, the reflector 30 has a sheet resistance lower than that of the resistive layer 10 . The reflector 30 may have a shape other than a layered shape.

The reflector 30 includes, for example, conductive materials such as metals, alloys, metal oxides, and carbon materials. The reflector 30 may contain at least one selected from the group consisting of aluminum, copper, iron, an aluminum alloy, a copper alloy, and an iron alloy, or may contain a transparent conductive material such as ITO.

The dielectric constant of the dielectric layer 20 is not limited to a specific value as long as the radio wave absorber 1a can absorb desired radio waves. The dielectric layer 20 has a dielectric constant of, for example, 2.0 to 20.0. In this case, it is easy to adjust the thickness of the dielectric layer 20 and adjust the radio wave absorption performance of the radio wave absorber 1a. The dielectric constant of the dielectric layer 20 is, for example, the dielectric constant at 10 GHz measured according to the cavity resonance method.

Dielectric layer 20 may be formed as a layer made of a single material, or may be formed as a laminate of a plurality of layers. For example, when the dielectric layer 20 has n layers (n is an integer of 2 or more), the dielectric constant of the dielectric layer 20 is determined as follows, for example. The dielectric constant ε _i of each layer is measured (i is an integer from 1 to n). Next, the relative permittivity ε _i of each layer measured is multiplied by the ratio of the thickness t _i of the layer to the entire dielectric layer 20 to obtain ε _i ×(t _i /T). The dielectric constant of dielectric layer 20 can be determined by summing ε _i ×(t _i /T) for all layers. When the thickness of a specific layer in the dielectric layer 20 is sufficiently smaller than the thickness T of the dielectric layer 20 as a whole, for example, when the thickness of the specific layer is 1% or less of the thickness T, the thickness of the specific layer The dielectric constant of the dielectric layer 20 may be determined by ignoring the dielectric constant.

The material forming the dielectric layer 20 is not limited to a specific value as long as the radio wave absorber 1a can absorb desired radio waves. Dielectric layer 20 includes, for example, an organic polymer. Organic polymers are not limited to specific polymers. Organic polymers include, for example, ethylene vinyl acetate copolymer, vinyl chloride resin, urethane resin, acrylic resin, acrylic urethane resin, polyethylene, polypropylene, silicone, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polycarbonate (PC). , polyimide (PI), and at least one selected from the group consisting of cycloolefin polymer (COP).

If the reflector 30 is layered, the dielectric layer 20 may comprise a layer of PET, PEN, acrylic resin (PMMA), PC, PI, or COP in contact with the reflector 30. good. In this case, this layer can serve as a support for reflector 30 . Among others, the layer of the dielectric layer 20 in contact with the reflector 30 is desirably a PET layer from the viewpoint of a balance between good heat resistance, dimensional stability and manufacturing cost. The layered reflector 30 can be deposited using methods such as, for example, sputtering, ion plating, or coating (eg, bar coating). The layered reflector 30 may be a metal foil attached to a support such as by an adhesive.

The thickness of the dielectric layer 20 is not limited to a specific value as long as the radio wave absorber 1a can absorb desired radio waves. The thickness of the dielectric layer 20 is, for example, 50-2000 μm, preferably 100-1000 μm. This makes it easy to achieve both high dimensional accuracy and low cost.

If dielectric layer 20 comprises a layer in contact with layered reflector 30, the thickness of that layer is not limited to any particular value. The thickness of the layer is, for example, 5-150 μm, and may be 5-100 μm.

As shown in FIG. 1, the radio wave absorber 1a further includes an intermediate layer 15, for example. The intermediate layer 15 is arranged between the resistance layer 10 and the adhesive layer 40 in the thickness direction of the resistance layer 10 . In this case, since the resistance layer 10 is not in direct contact with the adhesive layer 40 , it is possible to prevent the components contained in the adhesive layer 40 from affecting the properties of the resistance layer 10 .

A material forming the intermediate layer 15 is not limited to a specific material. An intermediate layer 15 comprises, for example, an organic polymer and supports the resistive layer 10 . Therefore, it is easy to uniformly adjust the thickness of the resistance layer 10 by the intermediate layer 15 . For example, the resistance layer 10 can be formed on one main surface of the intermediate layer 15 by a method such as sputtering, vapor deposition, ion plating, or curing a coating film of a coating liquid. Intermediate layer 15 may be omitted.

The organic polymer contained in intermediate layer 15 is not limited to a specific polymer. The organic polymer is for example polyethylene terephthalate (PET), polyethylene naphthalate (PEN), acrylic resin (PMMA), polycarbonate (PC), polyimide (PI) or cycloolefin polymer (COP). Among them, the organic polymer contained in the intermediate layer 15 is desirably PET from the viewpoint of the balance between good heat resistance, dimensional stability and manufacturing cost.

The thickness of intermediate layer 15 is not limited to a specific value. The thickness of the intermediate layer 15 is, for example, 5-200 μm. Since the intermediate layer 15 has a thickness of 5 μm or more, wrinkles are less likely to occur in the intermediate layer 15 when forming the resistance layer 10 on the intermediate layer 15 and when laminating the resistance layer 10 and the dielectric layer 20 . When the thickness of the intermediate layer 15 is 200 μm or less, the intermediate layer 15 or the laminate including the intermediate layer 15 can be easily wound around a roll. In addition, the electromagnetic wave absorber 1a can be deformed and arranged along the uneven surface of the adherend or the curved surface of the adherend.

The thickness of the intermediate layer 15 may be 10 μm or more, 20 μm or more, or 30 μm or more. The thickness of the intermediate layer 15 may be 150 μm or less, 100 μm or less, or 75 μm or less.

As shown in FIG. 3, radio waves absorbed by the radio wave absorber 1a pass through the adherend 3, the adhesive layer 40, and the intermediate layer 15 before reaching the resistance layer 10. FIG. The sheet resistance of the resistive layer 10, the dielectric constant of the dielectric layer 20, and the thickness of the dielectric layer 20 in the radio wave absorber 1a can be set according to transmission line theory. In this case, the thicknesses and dielectric constants of the adherend 3, the adhesive layer 40, and the intermediate layer 15 are also considered, and the sheet resistance of the resistance layer 10, the dielectric constant of the dielectric layer 20, and the dielectric layer 20 thickness is set.

The radio wave absorber 1a can be modified from various viewpoints. The radio wave absorber 1a may be changed, for example, to a radio wave absorber 1b shown in FIG. The radio wave absorber 1b is constructed in the same manner as the radio wave absorber 1a except for the parts that are particularly described. Components of the radio wave absorber 1b that are the same as or correspond to the components of the radio wave absorber 1a are given the same reference numerals, and detailed description thereof will be omitted. The description regarding the radio wave absorber 1a also applies to the radio wave absorber 1b as long as there is no technical contradiction.

As shown in FIG. 4, the radio wave absorber 1b further includes a second adhesive layer 45. As shown in FIG. The reflector 30 is arranged between the dielectric layer 20 and the second adhesive layer 45 in the thickness direction of the dielectric layer 20 . The adhesive contained in the second adhesive layer 45 is not limited to a specific adhesive. The adhesive may be an acrylic adhesive, a rubber adhesive, a urethane adhesive, or a silicone adhesive.

The second adhesive layer 45 may be an adhesive layer provided with a substrate, or may be an adhesive layer without a substrate. The material forming the base is not limited to a specific material. The material forming the base material may be a plastic film such as a PET film, a nonwoven fabric, a woven fabric, a foam, or paper such as Japanese paper. There may be.

An intermediate layer (not shown) may be arranged between the second adhesive layer 45 and the reflector 30 in the radio wave absorber 1b. This intermediate layer contains, for example, an organic polymer. The organic polymer contained in this intermediate layer is not limited to a specific polymer. The organic polymer is for example polyethylene terephthalate (PET), polyethylene naphthalate (PEN), acrylic resin (PMMA), polycarbonate (PC), polyimide (PI) or cycloolefin polymer (COP). Among others, the organic polymer contained in the intermediate layer is desirably PET from the viewpoint of the balance between good heat resistance, dimensional stability and production cost.

Using the radio wave absorber 1b, for example, an article 5b with a radio wave absorber shown in FIG. 5 can be provided. The radio wave absorber 5b includes a radio wave absorber 1b, an adherend 3, and an adherend 4. As shown in FIG. The radio wave absorber 1b is arranged between the adherend 3 and the adherend 4 . The adherend 4 is, for example, a resin product. The radio wave absorber 1 b is attached to the adherend 3 while the first adhesive layer 40 is in contact with the adherend 3 . In addition, the radio wave absorber 1 b is attached to the adherend 3 while the second adhesive layer 45 is in contact with the adherend 4 .

As shown in FIG. 6, a laminate 1c can be provided. The laminate 1c is a laminate for a radio wave absorber. The laminate 1c is constructed in the same manner as the radio wave absorber 1a, except for parts that are particularly described. Components that are the same as or correspond to those of the radio wave absorber 1a are denoted by the same reference numerals, and detailed description thereof will be omitted. The description regarding the electromagnetic wave absorber 1a also applies to the laminate 1c as long as there is no technical contradiction.

The laminate 1c includes a resistive layer 10, a dielectric layer 20, and an adhesive layer 40. As shown in FIG. In the laminate 1c, the dielectric layer 20 has a first main surface 20a and a second main surface 20b. The first main surface 20 a is formed at a position closer to the resistance layer 10 than the second main surface 20 b in the thickness direction of the resistance layer 10 . In the dielectric layer 20, at least the part forming the second main surface 20b has adhesiveness. The shear adhesion force F ₁₀₀ of the adhesive layer 40 of the laminate 1c is measured in the same manner as for the radio wave absorber 1a except that the laminate 1c is used instead of the radio wave absorber 1a. The description regarding the shear adhesive force F ₁₀₀ of the adhesive layer 40 of the radio wave absorber 1a also applies to the shear adhesive force F ₁₀₀ of the adhesive layer 40 of the laminate 1c.

Using the laminate 1c, for example, a radio wave absorber 1d and an article 5c with a radio wave absorber shown in FIG. 7 can be provided. The radio wave absorber 1 d includes a laminate 1 c and an adherend 4 . The adherend 4 also serves as a reflector 30 and reflects radio waves. The adherend 4 contains metal, for example. Since at least the portion forming the second main surface 20b in the dielectric layer 20 has adhesiveness, the laminate 1c can be adhered to the adherend 4 by pressing the second main surface 20b against the adherend 4. can.

In the radio wave absorber-attached article 5c, the laminate 1c is arranged between the adherend 3 and the adherend 4. As shown in FIG. The laminate 1 c is attached to the adherend 3 while the first adhesive layer 40 is in contact with the adherend 3 .

In the laminate 1c, the laminate 1c is not limited to a specific configuration as long as at least the part forming the second main surface 20b has adhesiveness. For example, the dielectric layer 20 may comprise a first dielectric layer 21 and a second dielectric layer 22, as shown in FIG. The dielectric layer 20 of the laminate 1c has a layer structure of the dielectric layer 20, a material forming the dielectric layer 20, a thickness of the dielectric layer 20, etc., as long as at least a portion forming the second main surface 20b has adhesiveness. 2, it may be configured in the same manner as the dielectric layer 20 of the radio wave absorber 1a.

The thickness of the second dielectric layer 22 is not limited to a specific value as long as the radio wave absorber 1d has desired radio wave absorption performance.

Dielectric layer 20 may comprise another dielectric layer disposed between first dielectric layer 21 and second dielectric layer 22 in the thickness direction of first dielectric layer 21 .

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. First, evaluation methods for Examples and Comparative Examples will be described.

[Shear adhesive strength]
A test piece was prepared by cutting the sample according to each example and each comparative example into a rectangular shape having a short side of 10 mm and a long side of 60 mm in plan view. At room temperature of 20° C.±15° C., the adhesive layer of the test piece was attached to a polycarbonate (PC) plate having a thickness of 2 mm. As a PC board, polycarbonate PC1600 manufactured by Takiron was used. The arithmetic mean roughness R _a of the surface of the PC board was 5 μm or less. The joint surface between the test piece and the PC board had a square shape with one side of 10 mm including one end in the longitudinal direction of the test piece. The test piece was stored for 30 minutes in a 100° C. environment with the test piece attached to the PC board. While maintaining the environment of the test piece at 100 ° C., apply a tensile shear load to the test piece and the PC plate in the direction parallel to the surface of the PC plate at a tensile speed of 50 mm / min with reference to the description of JIS K 6850: 1999, The bond between the test piece and the PC board was broken. The direction of the tensile shear load coincided with the longitudinal direction of the specimen. ^Each sample at 100 ° C. of the adhesive layer was _determined . In addition, the same as the measurement of shear adhesive strength F ₁₀₀ except that the environmental temperature of the test piece when storing the test piece for 30 minutes and the environmental temperature of the test piece when applying the tensile shear load were changed from 100 ° C to 23 ° C. to determine the shear adhesive strength F ₂₃ of the adhesive layer of each sample at 23°C. Table 1 shows the results.

[High temperature test]
A PC board having a thickness of 2 mm was stored for 125 hours at a temperature of 85° C. and a relative humidity of 85% for moisture absorption treatment to obtain a moisture-absorbed PC board. A high-temperature test sample was prepared by contacting the adhesive layer of each sample according to each example and each comparative example to the surface of the PC board and attaching each sample to the PC board. In the high temperature test sample, the entire surface of the adhesive layer was in contact with the surface of the PC board. High temperature testing was performed by maintaining the environment of the high temperature test sample at 140° C. for 48 hours.

[Return loss]
A PC board having a thickness of 2 mm and not subjected to moisture absorption treatment was prepared. At normal temperature of 20° C.±15° C., the surface of the PC board was brought into contact with the adhesive layer of the sample according to each example and each comparative example, and each sample was adhered to the PC board to prepare a normal sample.

Using a radio wave transmitter/receiver EAS02 manufactured by Keycom Co., Ltd., and referring to JIS R 1679:2007, the return loss Rn of normal samples according to each example and each comparative example at 70 to 90 GHz was measured according to the following procedure. As shown in FIG. 9, a sample holder SH, a transmitter/receiver TR, and a millimeter wave lens L are arranged, and radio waves are transmitted and received while a stainless metal plate is arranged on the sample holder SH. The metal plate had a diameter of 150 mm and a thickness of 2 mm. A state in which all the radio waves are reflected by the metal plate and the return loss is 0 dB was taken as the standard, and the return loss was measured when the radio wave was vertically incident on the flat plate of each normal sample. Each normal sample was placed on the sample holder SH instead of the metal plate, radio waves were transmitted and received, and the return loss was measured. The samples were typically arranged so that the PC board was closest to the transceiver TR in the sample. Table 1 shows the maximum return loss Rn at 70 to 90 GHz.

The return loss Rh of the high temperature test sample after the high temperature test was measured at 70 to 90 GHz in the same manner as the measurement of the return loss Rn except that the high temperature test sample after the high temperature test was used instead of the normal sample. Table 1 shows the maximum return loss Rh at 70 to 90 GHz.

[Thickness of sample for high temperature test]
Using vernier calipers, the thickness tp of the high temperature test sample before the high temperature test and the thickness tq of the high temperature test sample after the high temperature test were measured. The thickness tp of the high temperature test sample before the high temperature test was determined by arithmetically averaging the measured values at 5 or more randomly selected locations in each sample. Each measured value was almost constant regardless of the location of the sample. For the thickness tq of the high-temperature test sample after the high-temperature test, each sample was visually inspected to identify three locations where the thickness varied greatly. The thickness of the high temperature test sample was measured at these three locations, and the maximum value of the three measured values was determined as the thickness of the high temperature test sample after the high temperature test. Table 1 shows the difference Δt between the thickness tq and the thickness tp of each sample.

<Example 1>
Sputtering was performed using indium tin oxide (ITO) as a target to form a resistance layer on a polyester film having a thickness of 23 μm to obtain a film with a resistance layer. The SnO ₂ content in ITO was 30% by mass. The sheet resistance of the resistive layer was 395Ω/□. The dielectric constant of the polyester film was 3.2. A film with aluminum foil was prepared comprising a PET layer with a thickness of 25 μm, a PET layer with a thickness of 9 μm, and an aluminum foil with a thickness of 7 μm placed between the PET layers. The dielectric constant of PET in the film with aluminum foil was 3.2. Acrylic resin Clarity LA2330 manufactured by Kuraray Co., Ltd. was press-molded to a thickness of 590 μm to prepare an acrylic resin sheet. The dielectric constant of the acrylic resin sheet was 2.55. An acrylic resin sheet was placed on the PET layer having a thickness of 25 μm of the film with aluminum foil. Next, the film with a resistance layer was placed on the acrylic resin sheet so that the resistance layer was in contact with the acrylic resin sheet. Next, a double-faced tape No. 5602 manufactured by Nitto Denko Corporation was adhered to the polyester film of the film with a resistance layer to form an adhesive layer, and a sample according to Example 1 was obtained. The thickness of the double-sided tape No. 5602 was 20 μm. In this double-sided tape, layers of an acrylic pressure-sensitive adhesive were formed on both sides of a PET base material.

<Example 2>
A sample according to Example 2 was prepared in the same manner as in Example 1 except that double-sided tape No. 5603 manufactured by Nitto Denko Corporation was used instead of double-sided tape No. 5602 manufactured by Nitto Denko Corporation. The thickness of the double-sided tape No. 5603 was 30 μm. In this double-sided tape, an acrylic pressure-sensitive adhesive layer was formed on both sides of a PET base material.

<Example 3>
A sample according to Example 3 was prepared in the same manner as in Example 1 except that double-sided tape No. 5605 manufactured by Nitto Denko Corporation was used instead of double-sided tape No. 5602 manufactured by Nitto Denko Corporation. The thickness of the double-sided tape No. 5605 was 50 μm. In this double-sided tape, an acrylic pressure-sensitive adhesive layer was formed on both sides of a PET base material.

<Example 4>
A sample according to Example 4 was prepared in the same manner as in Example 1 except that double-sided tape GA5905 manufactured by Nitto Denko Corporation was used instead of double-sided tape No. 5602 manufactured by Nitto Denko Corporation. The thickness of the double-sided tape GA5905 was 50 μm. This double-sided tape did not have a base material, and was formed only by a layer of an acrylic pressure-sensitive adhesive having a thickness of 50 μm.

<Example 5>
A sample according to Example 5 was prepared in the same manner as in Example 1 except that double-sided tape No. 5000NS manufactured by Nitto Denko Corporation was used instead of double-sided tape No. 5602 manufactured by Nitto Denko Corporation. The thickness of the double-sided tape No. 5000NS was 160 μm. In the double-faced tape No. 5000NS, acrylic pressure-sensitive adhesive layers were formed on both sides of the nonwoven fabric substrate.

<Example 6>
A sample according to Example 6 was prepared in the same manner as in Example 1 except that double-sided tape No. 515 manufactured by Nitto Denko Corporation was used instead of double-sided tape No. 5602 manufactured by Nitto Denko Corporation. The thickness of the double-sided tape No. 515 was 250 μm. In the double-sided tape No. 515, acrylic pressure-sensitive adhesive layers were formed on both sides of the nonwoven fabric substrate.

<Example 7>
A sample according to Example 7 was prepared in the same manner as in Example 1 except that double-sided tape No. 5000ND manufactured by Nitto Denko Corporation was used instead of double-sided tape No. 5602 manufactured by Nitto Denko Corporation. The thickness of the double-sided tape No. 5000ND was 320 µm. In the double-faced tape No. 5000ND, acrylic pressure-sensitive adhesive layers were formed on both sides of the nonwoven fabric substrate.

<Example 8>
The procedure was the same as in Example 1 except that a laminate of double-sided tape No. 5000ND manufactured by Nitto Denko Corporation and double-sided tape HYPERJOINT H7004 manufactured by Nitto Denko Corporation was used instead of double-sided tape No. 5602 manufactured by Nitto Denko Corporation. A sample according to Example 8 was produced. HYPERJOINT is a registered trademark of Nitto Denko Corporation. The double-sided tape HYPERJOINT H7004 in this laminate was in contact with the polyester film of the film with the resistance layer. The thickness of the double-sided tape HYPERJOINT H7004 was 400 µm. In this double-faced tape, the acrylic pressure-sensitive adhesive was present on both sides and inside the acrylic resin foam. The thickness of this laminate was 720 μm.

<Comparative Example 1>
A sample according to Comparative Example 1 was prepared in the same manner as in Example 1 except that double-sided tape No. 5600 manufactured by Nitto Denko Corporation was used instead of double-sided tape No. 5602 manufactured by Nitto Denko Corporation. The thickness of the double-sided tape No. 5600 was 5 μm. In this double-sided tape, an acrylic pressure-sensitive adhesive layer was formed on both sides of a PET base material.

<Comparative Example 2>
A sample according to Comparative Example 2 was prepared in the same manner as in Example 1 except that double-sided tape No. 5601 manufactured by Nitto Denko Corporation was used instead of double-sided tape No. 5602 manufactured by Nitto Denko Corporation. The thickness of the double-sided tape No. 5601 was 10 μm. In this double-sided tape, an acrylic pressure-sensitive adhesive layer was formed on both sides of a PET base material.

<Comparative Example 3>
A sample according to Comparative Example 3 was prepared in the same manner as in Example 1 except that double-sided tape No. 5035K manufactured by Nitto Denko Corporation was used instead of double-sided tape No. 5602 manufactured by Nitto Denko Corporation. The thickness of the double-sided tape No. 5035K was 120 μm. In this double-sided tape, adhesive layers were formed on both sides of a nonwoven fabric substrate.

<Comparative Example 4>
A sample according to Comparative Example 4 was prepared in the same manner as in Example 1, except that the double-sided tape HYPERJOINT H7004 manufactured by Nitto Denko Corporation was used instead of the double-sided tape No. 5602 manufactured by Nitto Denko Corporation.

<Comparative Example 5>
A sample according to Comparative Example 5 was prepared in the same manner as in Example 1 except that the double-sided tape HYPERJOINT H7008 manufactured by Nitto Denko Corporation was used instead of the double-sided tape No. 5602 manufactured by Nitto Denko Corporation. The thickness of the double-sided tape HYPERJOINT H7008 was 800 μm. In this double-sided tape, the acrylic pressure-sensitive adhesive was present inside the acrylic resin foam.

As shown in Table 1, the maximum value of the return loss Rh at 70 to 90 GHz of the high temperature test sample after the high temperature test for each example was 15.0 dB or more. On the other hand, the maximum value of the return loss Rh at 70 to 90 GHz of the high temperature test sample after the high temperature test for each comparative example was less than 15.0 dB. In the high temperature test, the environment of the high temperature test sample containing the wet PC board is maintained at 140° C. for 48 hours. For this reason, it is considered that moisture is released as water vapor from the PC board. The shear adhesive strength F ₁₀₀ at 100° C. of the adhesive layer of the sample of each example was 10.0 N/cm ² or more. On the other hand, the shear adhesive strength F ₁₀₀ at 100° C. of the adhesive layer of the sample of each comparative example was less than 10.0 N/cm ² . Therefore, if the adhesive layer has a shear adhesive strength F ₁₀₀ of 10.0 N/cm ² or more at 100° C., the electromagnetic wave absorption performance of the electromagnetic wave absorber can be maintained high even if moisture is released from the adherend in a moisture-absorbing state. It was suggested that it is easy to drip.

In each comparative example, the difference Δt between the thickness tq of the high temperature test sample after the high temperature test and the thickness tp of the high temperature test sample before the high temperature test exceeded 0.30 mm. It is believed that the difference Δt exceeding 0.30 mm was caused by the release of moisture as water vapor from the PC board in a moisture-absorbing state in the high-temperature test and the formation of a large gap between the adhesive layer and the PC board. On the other hand, in each example, the difference .DELTA.t is 0.30 mm or less, although it is considered that moisture is released from the PC board. For this reason, it is understood that, in the examples, it was difficult to generate a large gap between the adhesive layer and the PC board. A comparison between the examples and the comparative examples suggests that when the difference Δt is 0.30 mm or less, the electromagnetic wave absorption performance of the electromagnetic wave absorber is likely to be kept high even if moisture is released from the adherend in a moisture-absorbing state. was done.

1a, 1b radio wave absorber 1c laminate 2 plate material 3 adherend 5a, 5b, 5c article with radio wave absorber 10 resistance layer 15 intermediate layer 20 dielectric layer 30 reflector 40 adhesive layer (first adhesive layer)

Claims (9)

A radio wave absorber,
a resistive layer;
a reflector that reflects radio waves;
a dielectric layer disposed between the resistive layer and the reflector in the thickness direction of the resistive layer;
and an adhesive layer,
The resistance layer is arranged between the dielectric layer and the adhesive layer in the thickness direction of the resistance layer,
The adhesive layer is applied to the electromagnetic wave absorber attached to the plate material in a state in which the adhesive layer is in contact with the surface of the plate material having a surface formed of polycarbonate under the condition of 100° C. in a direction parallel to the surface. has a shear adhesive strength of 10.0 N/cm ^or more when a tensile shear load is applied along
radio wave absorber. The radio wave absorber according to claim 1, wherein said adhesive layer has a thickness of 15 to 750 µm. The difference between the thickness of the sample after the high temperature test and the thickness of the sample before the high temperature test is 0.30 mm or less,
The sample was stored at a temperature of 85° C. and a relative humidity of 85% for 125 hours. made by
The high temperature test is done by keeping the environment of the sample at 140° C. for 48 hours.
The radio wave absorber according to claim 1 or 2. The radio wave absorber according to any one of claims 1 to 3, further comprising an intermediate layer disposed between said resistance layer and said adhesive layer in the thickness direction of said resistance layer. The radio wave absorber according to any one of claims 1 to 4, wherein the adhesive layer contains an acrylic resin. The radio wave absorber according to any one of claims 1 to 5, wherein said resistance layer has a sheet resistance of 200 to 600Ω/□. a radio wave absorber according to any one of claims 1 to 6;
an adherend to which the radio wave absorber is attached while the adhesive layer is in contact;
Articles with radio wave absorbers. 8. The article with a radio wave absorber according to claim 7, wherein said adherend contains at least one selected from the group consisting of polycarbonate, polyamide, polybutylene terephthalate, polyethylene terephthalate, and polypropylene. A laminate for a radio wave absorber,
a resistive layer;
a dielectric layer having a first main surface and a second main surface, wherein the first main surface is formed closer to the resistance layer than the second main surface in the thickness direction of the resistance layer;
and an adhesive layer,
The resistance layer is arranged between the dielectric layer and the adhesive layer in the thickness direction of the resistance layer,
At least a portion forming the second main surface of the dielectric layer has adhesiveness,
The adhesive layer is attached to the surface of a plate material having a surface made of polycarbonate in a state where the adhesive layer is in contact with the surface of the plate material. having a shear adhesive strength of 10.0 N/cm ² or more when a tensile shear load is applied along a parallel direction;
Laminate for radio wave absorber.

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