JP2023051591A - 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 peeling from a release liner.SOLUTION: A radio wave absorber 1a includes a radio wave absorption layer 10, an adhesive layer 40, a reflective layer 30, and a release liner 50. The reflective layer 30 is positioned between the adhesive layer 40 and the radio wave absorption layer 10 in a thickness direction of the adhesive layer 40. The adhesive layer 40 is positioned between the release liner 50 and the reflective layer 30 in the thickness direction of the adhesive layer 40. The radio wave absorber 1a includes a body 2 containing the radio wave absorption layer 10, the reflective layer 30, and the adhesive layer 40. The 90° peel strength Np of the body 2 from the release liner 50 is 5.0 N/20 mm or less.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to a radio wave absorber and a laminate for a radio wave absorber.

Conventionally, radio wave absorbers are 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.

Patent Document 2 describes an electromagnetic wave absorber for millimeter waves. This millimeter-wave electromagnetic wave absorber includes a heat-resistant sheet and a metal layer. Heat-resistant sheets include a matrix made of rubber or plastic. A soft magnetic metal powder is embedded in the matrix. A metal layer covers either surface of the heat-resistant sheet.

Japanese Patent Application Laid-Open No. 2005-311330 Japanese Patent Application Laid-Open No. 2002-118008

It is conceivable to install the radio wave absorber by attaching it to a predetermined adherend using an adhesive layer. The radio wave absorber has a reflective layer that reflects radio waves. It is conceivable to dispose an adhesive layer near the reflective layer in the radio wave absorber. When a radio wave absorber is attached to an adherend using an adhesive layer, the adhesive layer may be protected with a release liner before the radio wave absorber is attached to the adherend. In this case, it is necessary to separate the radio wave absorber from the release liner before attaching the radio wave absorber to the adherend. On the other hand, Patent Literatures 1 and 2 do not specifically consider such a case.

According to the studies of the present inventors, when attaching a radio wave absorber to an adherend, peeling off the main body of the radio wave absorber from the release liner that protects the adhesive layer does not affect the radio wave absorption performance of the radio wave absorber. newly discovered that there is a possibility that

Accordingly, the present invention provides a radio wave absorber that is advantageous from the viewpoint of suppressing deterioration in radio wave absorption performance due to separation from the release liner when the radio wave absorber is adhered to an adherend.

The present invention
a radio wave absorbing layer;
an adhesive layer;
a reflective layer that is disposed between the adhesive layer and the radio wave absorbing layer in the thickness direction of the adhesive layer and reflects radio waves;
a release liner;
The adhesive layer is arranged between the release liner and the reflective layer in the thickness direction of the adhesive layer,
The main body including the electromagnetic wave absorbing layer, the reflective layer, and the adhesive layer has a 90° peeling adhesive strength from the release liner of 5.0 N/20 mm or less.
A radio wave absorber is provided.

In addition, the present invention
a radio wave absorbing layer including an adhesive layer;
a release liner;
The adhesive layer is arranged in contact with the release liner in the thickness direction of the adhesive layer,
The main body including the radio wave absorbing layer has a 90° peeling adhesive strength from the release liner of 5.0 N/20 mm or less.
A laminate for a radio wave absorber is provided.

The radio wave absorber described above is advantageous from the viewpoint of suppressing deterioration in radio wave absorption performance due to separation from the release liner when the radio wave absorber is adhered to an adherend.

FIG. 1 is a cross-sectional view showing an example of a radio wave absorber according to the present invention. FIG. 2A is a side view showing a state in which the main body of the radio wave absorber according to the reference example is separated from the release liner. FIG. 2B is a side view showing a state in which the main body of the electromagnetic wave absorber according to the present invention is peeled off from the release liner. FIG. 3 is a cross-sectional view showing an example of an article with a radio wave absorber. FIG. 4 is a cross-sectional view showing an example of the radio wave absorber laminate according to the present invention. FIG. 5 is a cross-sectional view showing another example of an article with a radio wave absorber. FIG. 6 is a cross-sectional view showing another example of the radio wave absorber laminate according to the present invention. FIG. 7 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 radio wave absorbing layer 10, an adhesive layer 40, a reflective layer 30, and a release liner 50. As shown in FIG. The reflective layer 30 is arranged between the adhesive layer 40 and the radio wave absorbing layer 10 in the thickness direction of the adhesive layer 40 . The adhesive layer 40 is arranged between the release liner 50 and the reflective layer 30 in the thickness direction of the adhesive layer 40 . The radio wave absorber 1a has a main body 2 including a radio wave absorbing layer 10, a reflective layer 30, and an adhesive layer 40. As shown in FIG. The 90° peeling adhesive strength Np of the main body 2 from the release liner 50 is 5.0 N/20 mm or less. The 90° peeling adhesive strength Np can be measured, for example, with reference to the description of Japanese Industrial Standard JIS Z 0237:2009.

According to the study of the present inventors, when attaching a radio wave absorber to a predetermined adherend, before attaching the radio wave absorber to the adherend, a shape suitable for the place where the radio wave absorber is to be attached has been found. Radio wave absorbers may be processed. Such processing is desirably performed while the adhesive layer is protected with a release liner. A high 90° peeling adhesive strength from the release liner of the main body of the radio wave absorber is desirable from the viewpoint of making it difficult for the release liner to peel off from the adhesive layer in such processing. On the other hand, when the present inventors proceed with their studies, it is possible that the detachment of the main body of the radio wave absorber from the release liner may cause damage to a predetermined portion of the radio wave absorber, thereby degrading the performance of the radio wave absorber. I learned something new.

FIG. 2A schematically shows the state of the main body 2 of the radio wave absorber 1x according to the reference example when the main body 2 is separated from the release liner 50. FIG. The radio wave absorber 1x is configured in the same manner as the radio wave absorber 1a, except for the parts that are particularly described. Components of the radio wave absorber 1x that are the same as or correspond to the components of the radio wave absorber 1a are given the same reference numerals. In the radio wave absorber 1x, the 90° peeling adhesive force Np from the release liner 50 of the main body 2 exceeds 5.0 N/20 mm. When the main body 2 of the radio wave absorber 1x is to be separated from the release liner 50 for release, compressive stress is applied to the portion in contact with the first main surface 2a of the main body 2, and tensile stress is applied to the second main surface 2b of the main body 2. It takes The second main surface 2b is formed of an adhesive layer 40, for example. Considering the elasticity of the adhesive layer 40, such tensile stress is unlikely to affect the radio wave absorption performance of the radio wave absorber 1a. On the other hand, at least a portion of the radio wave absorbing layer 10 is included in the portion in contact with the first principal surface 2a, and a compressive stress is applied to at least a portion of the radio wave absorbing layer 10 . The 90° peeling adhesive strength Np of the radio wave absorber 1x exceeds 5.0 N/20 mm. Therefore, when the end surface 2e of the main body 2 is separated from the release liner 50 by a predetermined distance D1 in order to separate the main body 2 of the radio wave absorber 1x, the area of the second main surface 2b exposed away from the release liner 50 is is relatively small, and the deflection of the main body 2 tends to increase. Therefore, a large compressive stress is applied to at least a portion of the radio wave absorbing layer 10 included in the portion in contact with the first principal surface 2a, and at least a portion of the radio wave absorbing layer 10 is likely to be damaged. As a result, the radio wave absorption performance of the radio wave absorber 1x is likely to deteriorate due to the separation of the main body 2 of the radio wave absorber 1x from the release liner 50 .

FIG. 2B schematically shows the state of the main body 2 of the radio wave absorber 1a when the main body 2 is separated from the release liner 50. As shown in FIG. In the radio wave absorber 1a, the main body 2 has a 90° peeling adhesive strength Np from the release liner 50 of 5.0 N/20 mm or less. Therefore, when the end surface 2e of the main body 2 is separated from the release liner 50 by a predetermined distance D1 in order to separate the main body 2 of the radio wave absorber 1a, the area of the second main surface 2b exposed away from the release liner 50 is is relatively large, and the deflection of the main body 2 tends to be small. Therefore, the compressive stress applied to at least a portion of the radio wave absorbing layer 10 included in the portion in contact with the first main surface 2a tends to be small. Therefore, the radio wave absorbing layer 10 is less likely to be damaged. As a result, even if the main body 2 is separated from the release liner 50 in the radio wave absorber 1a, the radio wave absorption performance of the radio wave absorber 1a is unlikely to deteriorate.

In the radio wave absorber 1a, the 90° peeling adhesive force Np from the release liner 50 of the main body 2 may be 4.8 N/20 mm or less, 4.6 N/20 mm or less, or 4.4 N /20 mm or less, or 4.2 N/20 mm or less. The lower limit of the 90° peeling adhesive strength Np is not limited to a specific value. The 90° peeling adhesive strength Np is, for example, 0.01 N/20 mm or more. In this case, when the radio wave absorber 1a is processed into a shape suitable for the place where the main body 2 is to be attached before the main body 2 of the radio wave absorber 1a is attached to the adherend, the main body 2 is less likely to peel off from the release liner 50. . The 90° peeling adhesive strength Np may be 0.1 N/20 mm or more, or may be 0.2 N/20 mm or more.

As shown in FIG. 1, in the radio wave absorber 1a, the adhesive layer 40 is in contact with the release liner 50, for example. As long as the 90° peeling adhesive strength Np is 5.0 N/20 mm or less, the difference θ1 - θ2 obtained by subtracting the contact angle θ2 of the water droplet on the contact surface 52 from the contact angle θ1 of the water droplet on the contact surface 42 is a specific value. Not limited. The contact surface 42 is the contact surface of the adhesive layer 40 with the release liner 50 . The contact surface 52 is the contact surface of the release liner 50 with the adhesive layer 40 . The difference θ1−θ2 is, for example, 4.0° or less. In this case, the radio wave absorbing layer 10 is less likely to be damaged when the main body 2 is separated from the release liner 50, and the radio wave absorption performance of the radio wave absorber 1a is less likely to deteriorate even if the main body 2 is separated from the release liner 50. .

The difference θ1−θ2 may be 3.5° or less, 3.0° or less, 2.5° or less, or 2.0° or less, It may be 1.5° or less. The lower limit of the difference θ1-θ2 is not limited to a specific value. The difference θ1−θ2 is, for example, −15° or more, may be −10° or more, or may be −8.0° or more.

The contact angle θ1 is not limited to a specific value. The contact angle θ1 is, for example, 95-115°. The contact angle θ1 may be 96° or more, 97° or more, 98° or more, 99° or more, or 100° or more, It may be 101° or more. The contact angle θ1 may be 114° or less, 112° or less, 110° or less, or 108° or less.

The contact angle θ2 is not limited to a specific value. The contact angle θ2 is, for example, 95-115°. The contact angle θ2 may be 96° or more, 97° or more, 98° or more, or 99° or more. The contact angle θ2 may be 114° or less, 113° or less, 112° or less, or 111° or less.

The radio wave absorbing layer 10 is not limited to a specific configuration as long as the desired radio wave absorbing performance can be exhibited in the radio wave absorber 1a. As shown in FIG. 1, the radio wave absorbing layer 10 includes a resistive layer 11 and a dielectric layer 12. As shown in FIG. The dielectric layer 12 is arranged between the resistive layer 11 and the reflective layer 30 in the thickness direction of the dielectric layer 12 .

When a radio wave with a wavelength λ _O to be absorbed enters the radio wave absorber 1a, the radio wave reflected by the surface of the resistance layer 11 (surface reflection) interferes with the radio wave reflected by the reflective layer 30 (back surface reflection). , the radio wave absorber 1a is designed. In other words, the radio wave absorber 1a is a λ/4 type radio wave absorber. In this case, the resistance layer 11 is less likely to be damaged when the main body 2 is separated from the release liner 50, and the radio wave absorption performance of the radio wave absorber 1a is less likely to deteriorate even if the main body 2 is separated from the release liner 50.

The radio wave absorber 1a may be configured as a radio wave absorber other than the λ/4 type radio wave absorber. For example, the radio wave absorber 1a may be constructed as a radio wave absorber using a dielectric absorber or a magnetic absorber.

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

As long as the 90° peeling adhesive strength Np is 5.0 N/20 mm or less, the adhesive contained in the adhesive layer 40 is not limited to a specific adhesive. The adhesive contained in the adhesive layer 40 may be an acrylic adhesive, a silicone adhesive, a urethane adhesive, or a rubber adhesive. good too.

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.

The thickness of the adhesive layer 40 is not limited to a specific value as long as the 90° peeling adhesive strength Np is 5.0 N/20 mm or less. The thickness of the adhesive layer 40 is, for example, 10-2000 μm. The thickness of the adhesive layer 40 may be 20 μm or more, 30 μm or more, 40 μm or more, or 50 μm or more. The thickness of the adhesive layer 40 may be 1800 μm or less, 1600 μm or less, 1400 μm or less, 1200 μm or less, or 1000 μm or less.

The adhesive layer 40 may have a substrate or may be an adhesive layer without a substrate. When the adhesive layer 40 has a substrate, the adhesive layer 40 has adhesive-containing layers formed on both sides of the substrate. The material forming the base is not limited to a specific material. The substrate may be a plastic film such as a polyethylene terephthalate (PET) film, a nonwoven fabric, a woven fabric, a foam, or paper such as Japanese paper. may be When the adhesive layer 40 is substrate-less, the adhesive layer is provided only with an adhesive-containing layer.

The release liner 50 is not limited to a specific mode as long as the 90° peeling adhesive strength Np is 5.0 N/20 mm or less. For example, a release agent layer is formed on the surface of the release liner 50 . The release agent contained in the release agent layer is, for example, a long-chain alkyl group-containing polymer, a fluorine atom-containing polymer, or a silicone polymer.

Release liner 50 further comprises, for example, a substrate that supports the release agent layer. The material forming the base material of the release liner 50 is not limited to a specific material. The base material of the release liner 50 may be a plastic film such as PET film and polyethylene (PE) film, or may be paper.

The thickness of release liner 50 is not limited to any particular value. The thickness of the release liner 50 is, for example, 16-200 μm.

The material forming the resistance layer 11 is not limited to a specific material as long as the radio wave absorber 1a can absorb desired radio waves. The resistance layer 11 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 11 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 resistive layer 11 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 11 is, for example, 200Ω/square to 600Ω/square. The sheet resistance of the resistive layer 11 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 resistive layer 11 may be 580Ω/□ or less, 560Ω/□ or less, 540Ω/□ or less, 520Ω/□ or less, or 500Ω/□. It may be less than or equal to 450Ω/□ or less.

The reflective layer 30 is not limited to a specific mode as long as it can reflect the radio wave to be absorbed. The reflective layer 30 has a sheet resistance lower than that of the resistive layer 11, for example.

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

The dielectric constant of the dielectric layer 12 is not limited to a specific value as long as the radio wave absorber 1a can absorb desired radio waves. The dielectric layer 12 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 12 and adjust the radio wave absorption performance of the radio wave absorber 1a. The dielectric constant of the dielectric layer 12 is, for example, the dielectric constant at 10 GHz measured according to the cavity resonance method.

The dielectric layer 12 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 12 has n layers (n is an integer of 2 or more), the dielectric constant of the dielectric layer 12 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 measured dielectric constant ε _i of each layer is multiplied by the ratio of the thickness t _i of the layer to the entire dielectric layer 12 to obtain ε _i ×(t _i /T). The dielectric constant of dielectric layer 12 can be determined by summing ε _i ×(t _i /T) for all layers. When the thickness of a specific layer in the dielectric layer 12 is sufficiently smaller than the thickness T of the dielectric layer 12 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 12 may be determined by ignoring the dielectric constant.

The material forming the dielectric layer 12 is not limited to a specific value as long as the radio wave absorber 1a can absorb desired radio waves. Dielectric layer 12 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 dielectric layer 12 is formed as a laminate of multiple layers, the layer in contact with the reflective layer 30 may be, for example, a layer of PET, PEN, acrylic resin (PMMA), PC, PI, or COP. be. In this case, this layer can serve as a support for the reflective layer 30 . Among others, the layer in contact with the reflective layer 30 in the dielectric layer 12 is desirably a PET layer from the viewpoint of the balance between good heat resistance, dimensional stability and manufacturing cost. The reflective layer 30 can be deposited using methods such as sputtering, ion plating, or coating (eg, bar coating).

The thickness of the dielectric layer 12 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 12 is, for example, 50-2000 μm, preferably 100-1000 μm. This makes it easy to achieve both high dimensional accuracy and low cost.

When dielectric layer 12 is formed as a laminate of multiple layers, the thickness of the layer in dielectric layer 12 that is in contact with reflective layer 30 is not limited to a specific 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 a protective layer 15, for example. The resistance layer 11 is arranged between the protective layer 15 and the dielectric layer 12 in the thickness direction of the resistance layer 11 . The protective layer 15 protects the resistive layer 11 . Protective layer 15 may function as a support for resistive layer 11 .

A material forming the protective layer 15 is not limited to a specific material. A protective layer 15 includes, for example, an organic polymer and supports the resistive layer 11 . Therefore, it is easy to uniformly adjust the thickness of the resistance layer 11 by the protective layer 15 . For example, the resistance layer 11 can be formed on one main surface of the protective layer 15 by a method such as sputtering, vapor deposition, ion plating, or curing a coating film of a coating liquid. Protective layer 15 may be omitted.

The organic polymer contained in protective 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 protective layer 15 is desirably PET from the viewpoint of the balance between good heat resistance, dimensional stability and manufacturing cost.

The thickness of protective layer 15 is not limited to a specific value. The thickness of the protective layer 15 is, for example, 5 to 200 μm. Since the thickness of the protective layer 15 is 5 μm or more, wrinkles are less likely to occur in the protective layer 15 when forming the resistive layer 11 on the protective layer 15 and laminating the resistive layer 11 and the dielectric layer 12 . Since the thickness of the protective layer 15 is 200 μm or less, the thickness of the radio wave absorber 1a tends to be small.

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

As shown in FIG. 1, the radio wave absorber 1a further includes an intermediate layer 35, for example. The intermediate layer 35 is arranged between the adhesive layer 40 and the reflective layer 30 in the thickness direction of the adhesive layer 40 . According to such a configuration, since the reflective layer 30 is not in direct contact with the adhesive layer 40, the reflective layer 30 is less likely to be affected by the components contained in the adhesive layer 40, and the radio wave absorber 1a can achieve desired durability. easy to perform.

A material forming the intermediate layer 35 is not limited to a specific material. Intermediate layer 35 includes, for example, an organic polymer. The organic polymer contained in intermediate layer 35 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 35 is desirably PET from the viewpoint of the balance between good heat resistance, dimensional stability and manufacturing cost.

The thickness of intermediate layer 35 is not limited to a specific value. The thickness of the intermediate layer 35 is, for example, 1-100 μm. Since the thickness of the intermediate layer 35 is 1 μm or more, the reflective layer 30 is less susceptible to the components contained in the adhesive layer 40 . Since the thickness of the intermediate layer 35 is 100 μm or less, the thickness of the radio wave absorber 1a tends to be small.

The thickness of the intermediate layer 35 may be 2 μm or more, 3 μm or more, or 5 μm or more. The thickness of the intermediate layer 35 may be 50 μm or less, 40 μm or less, 30 μm or less, 20 μm or less, or 15 μm or less.

As shown in FIG. 3, for example, it is possible to provide an article 5 with a radio wave absorber including a main body 2 of a radio wave absorber 1a. The radio wave absorber-attached article 5 includes an adherend 3 in addition to the main body 2 . In the radio wave absorber-attached article 5 , the main body 2 is attached to the adherend 3 while the adhesive layer 40 is in contact with the adherend 3 .

As shown in FIG. 4, a laminate 1b can be provided. The laminate 1b is a laminate for a radio wave absorber. The laminate 1b is constructed in the same manner as the radio wave absorber 1a, except for parts that are particularly described. Components of the laminate 1b that are the same as or correspond to components of the radio wave absorber 1a are denoted by the same reference numerals, and detailed description thereof is omitted. The description regarding the radio wave absorber 1a also applies to the laminate 1b as long as there is no technical contradiction.

The laminate 1b includes a radio wave absorbing layer 10 and a release liner 50. As shown in FIG. In the laminate 1b, the radio wave absorbing layer 10 includes an adhesive layer 40. As shown in FIG. For example, in the laminate 1b, the dielectric layer 12 also serves as the adhesive layer 40. As shown in FIG. The adhesive layer 40 is arranged in contact with the release liner 50 in the thickness direction of the adhesive layer 40 . The main body 2 includes a radio wave absorbing layer 10. - 特許庁In other words, body 2 does not include a reflective layer. The 90° peeling adhesive strength of the body 2 from the release liner 50 is 5.0 N/20 mm or less.

Using the laminate 1b, for example, an article 5b with a radio wave absorber shown in FIG. 5 can be provided. The article 5b with a radio wave absorber includes a main body 2 and an adherend 3. As shown in FIG. In the radio wave absorber-attached article 5b, the main body 2 is attached to the adherend 3 while the adhesive layer 40 is in contact with the adherend 3. As shown in FIG. In the radio wave absorber-attached article 5b, the adherend 3 reflects radio waves. The adherend 3 contains metal, for example. In the article 5b with a radio wave absorber, the main body 2 and the adherend 3 constitute a radio wave absorber. In the electromagnetic wave absorber-attached article 5b, the adherend 3 can function in the same manner as the reflective layer 30 of the electromagnetic wave absorber 1a with respect to the mechanism of electromagnetic wave absorption in the electromagnetic wave absorber.

As long as the adhesive layer 40 is in contact with the release liner 50 in the thickness direction of the adhesive layer 40, the dielectric layer 12 of the laminate 1b has a layer structure of the dielectric layer 12 of the laminate 1b and a material forming the dielectric layer 12. , and the thickness of the dielectric layer 12 may be configured in the same manner as the dielectric layer 12 of the radio wave absorber 1a. For example, in the laminate 1b, the dielectric layer 12 may include a first dielectric layer 12a and an adhesive layer 40, as shown in FIG. The first dielectric layer 12 a is arranged between the resistance layer 11 and the adhesive layer 40 in the thickness direction of the resistance layer 11 . The first dielectric layer 12a is in contact with the resistive layer 11, for example.

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.

[90° peeling adhesive strength Np]
A test piece for a 90° peel test was prepared from the samples according to each example and each comparative example. The release liner in the specimen was applied to a steel plate with a thickness of 1.5 mm. In accordance with JIS Z 0237: 2009, at room temperature 20 ° C ± 15 ° C, the laminate except the release liner in each test piece was peeled off from the release liner, and the 90 ° peeling adhesive strength Np of the laminate from the release liner It was determined. The tensile speed of the test piece was 50 mm/min in the 90° peel test. In the 90° peel test, ignore the measurements corresponding to the first 10 mm length, then average the 90° peel adhesion measurements corresponding to 50 mm lengths that are peeled off the release liner by 90°. ° Determined as the peel adhesive strength Np.

[Contact angle of water droplet]
One end in the longitudinal direction of the laminate excluding the release liner was lifted in a direction perpendicular to the release liner of each of the samples of Examples and Comparative Examples having a rectangular shape having a short side of 50 mm and a long side of 100 mm in plan view. The laminate was released from the release liner. Thereafter, 2 microliters of pure water droplets were dropped on each of the contact surface of the adhesive layer with the release liner and the contact surface of the release liner with the adhesive layer. A contact angle meter Model CA X manufactured by Kyowa Interface Science Co., Ltd. was used to measure the contact angle of the water droplet 10 seconds after the water droplet was dropped. The arithmetic mean of the three measurements was determined as the contact angle of the water droplet on each contact surface. Table 1 shows the results. In Table 1, θ1 is the contact angle of water droplets on the contact surface of the adhesive layer with the release liner, and θ2 is the contact angle of water droplets on the contact surface of the release liner with the adhesive layer.

[Return loss]
Using a radio wave transmitter/receiver EAS02 manufactured by Keycom Co., Ltd., and referring to JIS R 1679:2007, the return loss at 70 to 90 GHz of the samples before and after the peeling according to each example and each comparative example was measured according to the following procedure. . When peeling from the release liner, the part of the sample between one end in the longitudinal direction of the laminate lifted in the direction perpendicular to the release liner and the position 30 mm away from the one end in the longitudinal direction was measured for return loss. It was set as a measurement target. As shown in FIG. 7, 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 when the radio waves were vertically incident on the flat plate of each sample was used as a standard for measuring the return loss. A sample before and after separation was placed on the sample holder SH instead of the metal plate, radio waves were transmitted and received, and the return loss was measured. Each sample was arranged so that the polyester film of the film with the resistance layer was closest to the transmitter/receiver TR in each sample. Based on the measurement results of the return loss, for each example and each comparative example, the maximum return loss R1 of the sample before peeling at 70 to 90 GHz, the maximum return loss at 70 to 90 GHz of the sample after peeling A value of R2 and a value of R2-R1 were determined. Table 1 shows the results.

<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, thereby obtaining a film with a resistance layer according to Example 1. 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 505 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 according to Example 1 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. 515 manufactured by Nitto Denko Co., Ltd. was adhered to the surface of the PET layer having a thickness of 9 μm of the film with aluminum foil to form an adhesive layer. A release liner α was attached to this adhesive layer. In the release liner α, the surface to which the adhesive layer was adhered was a release surface formed with a silicone-based release agent, and the contact angle θ2 of water droplets on this release surface was 106.5°C. The thickness of the release liner α was 135 μm. Thus, a sample according to Example 1 was obtained. The thickness of the double-sided tape No. 515 was 250 μm. In this double-faced tape, an acrylic pressure-sensitive adhesive-containing layer was formed on both sides of a nonwoven fabric substrate. The base material of the release liner α was paper.

<Example 2>
A sample according to Example 2 was prepared in the same manner as in Example 1, except that the release liner β was used instead of the release liner α. In the release liner β, the surface to which the adhesive layer was attached was a release surface formed with a silicone-based release agent, and the contact angle θ2 of water droplets on this release surface was 110.6°. The thickness of the release liner β was 75 μm, and the base material of the release liner β was a PET film.

<Example 3>
A sample according to Example 3 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. 515. The thickness of the double-sided tape No. 5000NS was 160 μm. In this double-sided tape, an acrylic pressure-sensitive adhesive-containing layer was formed on both sides of a nonwoven fabric substrate.

<Example 4>
A sample according to Example 4 was prepared in the same manner as in Example 1 except that double-sided tape No. 5000NS was used instead of double-sided tape No. 515 and release liner γ was used instead of release liner α. The release liner γ was a polyethylene (PE) film with a thickness of 150 μm. A low-density polyethylene resin Novatec LD UF641 manufactured by Nippon Polyethylene Co., Ltd. was used as a raw material for the release surface of the release liner γ to which the adhesive layer was adhered. The density of this low density polyethylene resin was 927 kg/m ³ . Also, as the raw material for the base layer and the back side of the release liner γ, a mixed raw material of high-density polyethylene resin HI-ZEX 3300F manufactured by Prime Polymer Co., Ltd. and low-density polyethylene resin Novatec LD LF440HB manufactured by Nippon Polyethylene Co., Ltd. was used. In this mixed raw material, the mass of high-density polyethylene resin: mass of low-density polyethylene resin was 60:40. The density of HI-ZEX 3300F was 950 kg/m ³ and the density of Novatec LD LF440HB was 925 kg/m ³ . The contact angle θ2 of water droplets on the release surface of the release liner γ was 99.9°.

<Example 5>
A sample according to Example 5 was prepared in the same manner as in Example 1, except that instead of double-sided tape No. 515, a laminate obtained by stacking five double-sided tape No. 57120B manufactured by Nitto Denko Corporation was used. The thickness of the five sheets of double-sided tape No. 57120B was 1000 μm. In the double-sided tape No. 57120B, an acrylic pressure-sensitive adhesive-containing layer was formed on the surface of the base material, which was a polyolefin foam.

<Example 6>
A sample according to Example 6 was produced in the same manner as in Example 1 except that double-sided tape AS-0221P12 was used instead of double-sided tape No. 515.

<Comparative Example 1>
A sample according to Comparative Example 1 was prepared in the same manner as in Example 1, except that the release liner γ was used instead of the release liner α.

<Comparative Example 2>
A sample according to Comparative Example 2 was prepared in the same manner as in Comparative Example 1, except that a laminate of five sheets of double-sided tape No. 57120B was used instead of double-sided tape No. 515.

<Comparative Example 3>
A sample according to Comparative Example 3 was prepared in the same manner as in Comparative Example 1, except that a laminate of double-sided tape No. 57120B was used instead of double-sided tape No. 515. The thickness of the laminate of double-sided tape No. 57120B was 2000 μm.

<Comparative Example 4>
A sample according to Comparative Example 4 was prepared in the same manner as in Comparative Example 1 except that double-sided tape No. 5620A manufactured by Nitto Denko Corporation was used instead of double-sided tape No. 515. The thickness of the double-sided tape No. 5620A was 200 µm. In this double-sided tape, an acrylic pressure-sensitive adhesive-containing layer was formed on both sides of a PET base material.

<Comparative Example 5>
A sample according to Comparative Example 5 was prepared in the same manner as in Comparative Example 1 except that double-sided tape AS-0221P12 was used instead of double-sided tape No. 515.

As shown in Table 1, the R2-R1 value of the samples according to each example was -5.0 dB or more, and the radio wave absorption performance of the samples according to each example did not easily decrease even when the release liner was peeled off. . On the other hand, the value of R2-R1 of the sample according to each comparative example was less than -5.0 dB. The 90° peeling adhesive strength Np of the sample according to each example was 5.0 N/20 mm or less, and the 90° peeling adhesive strength Np of the sample according to each comparative example exceeded 5.0 N/20 mm or less. It was suggested that the 90° peeling adhesive strength Np of 5.0 N/20 mm or less is advantageous from the viewpoint of suppressing deterioration of the radio wave absorption performance of the radio wave absorber due to peeling from the release liner.

The value of the difference θ1-θ2 in the samples according to each example was 4.0° or less, and the value of the difference θ1-θ2 in the samples according to each comparative example exceeded 4.0°. It was suggested that the value of the difference θ1−θ2 being 4.0° or less is advantageous from the viewpoint of suppressing deterioration of the radio wave absorption performance of the radio wave absorber due to separation from the release liner.

1a Radio wave absorber 1b Radio wave absorber laminate 2 Main body 3 Adherend 5, 5b Article with radio wave absorber 10 Radio wave absorption layer 11 Resistive layer 12 Dielectric layer 30 Reflective layer 40 Adhesive layer 50 Release liner

Claims (6)

a radio wave absorbing layer;
an adhesive layer;
a reflective layer that is disposed between the adhesive layer and the radio wave absorbing layer in the thickness direction of the adhesive layer and reflects radio waves;
a release liner;
The adhesive layer is arranged between the release liner and the reflective layer in the thickness direction of the adhesive layer,
The main body including the electromagnetic wave absorbing layer, the reflective layer, and the adhesive layer has a 90° peeling adhesive strength from the release liner of 5.0 N/20 mm or less.
radio wave absorber. 2. The difference obtained by subtracting the contact angle of water droplets on the contact surface of the release liner with the adhesive layer from the contact angle of water droplets on the surface of the adhesive layer with the release liner is 4.0° or less. The radio wave absorber described in . The radio wave absorbing layer includes a resistive layer and a dielectric layer,
3. The radio wave absorber according to claim 1, wherein said dielectric layer is arranged between said resistance layer and said reflective layer in the thickness direction of said dielectric layer. 4. The radio wave absorber according to claim 3, wherein said resistive layer has a sheet resistance of 200-600Ω/□. The radio wave absorber according to any one of claims 1 to 4, further comprising an intermediate layer arranged between the adhesive layer and the reflective layer in the thickness direction of the adhesive layer. a radio wave absorbing layer including an adhesive layer;
a release liner;
The adhesive layer is arranged in contact with the release liner in the thickness direction of the adhesive layer,
The main body including the radio wave absorbing layer has a 90° peeling adhesive strength from the release liner of 5.0 N/20 mm or less.
Laminate for radio wave absorber.

Images