阅读说明：本技术 电磁波吸收体和带电磁波吸收体的成形品 (Electromagnetic wave absorber and molded article with electromagnetic wave absorber ) 是由 山形一斗 待永广宣 上田惠梨 请井博一 宇井丈裕 于 2018-03-27 设计创作，主要内容包括：电磁波吸收体(1)具备电介质层(10)、电阻层(20)和导电层(30)。电阻层(20)设置在电介质层(10)的一个主表面上。导电层(30)设置在电介质层(10)的另一个主表面上,具有比电阻层(20)的薄层电阻更低的薄层电阻。电阻层(20)具有200～600Ω/□的薄层电阻。在对电阻层(20)进行将电阻层(20)在5重量％的NaOH水溶液中浸渍5分钟的浸渍处理的情况下,浸渍处理前的电阻层(20)的薄层电阻与浸渍处理后的电阻层(20)的薄层电阻之差的绝对值小于100Ω/□。(The electromagnetic wave absorber (1) comprises a dielectric layer (10), a resistive layer (20), and a conductive layer (30), wherein the resistive layer (20) is provided on main surfaces of the dielectric layer (10), the conductive layer (30) is provided on the other main surfaces of the dielectric layer (10), and has a sheet resistance lower than that of the resistive layer (20), the resistive layer (20) has a sheet resistance of 200-600 Ω/□, and in the case where the resistive layer (20) is subjected to an immersion treatment in a 5 wt% aqueous NaOH solution for 5 minutes, the absolute value of the difference between the sheet resistance of the resistive layer (20) before the immersion treatment and the sheet resistance of the resistive layer (20) after the immersion treatment is less than 100 Ω/□.)

1, kinds of electromagnetic wave absorbers, comprising:

a dielectric layer;

a resistive layer disposed on major surfaces of the dielectric layer, and,

a conductive layer disposed on the other major surfaces of the dielectric layer and having a sheet resistance lower than that of the resistive layer,

the resistance layer has a sheet resistance of 200-600 Ω/□,

in the case where the resistance layer is subjected to an immersion treatment in a 5 wt% NaOH aqueous solution for 5 minutes, the absolute value of the difference between the sheet resistance of the resistance layer before the immersion treatment and the sheet resistance of the resistance layer after the immersion treatment is less than 100 Ω/□.

2. The electromagnetic wave absorber of claim 1, wherein the resistive layer contains of any one of tin oxide, titanium oxide, and indium oxide as a main component.

3. The electromagnetic wave absorber of claim 2, wherein the resistive layer further contains a dopant of at least 1 element other than the metal element having the main component.

4. The electromagnetic wave absorber of any of claims 1-3, wherein the resistive layer has a thickness of 5 x 10^-4Resistivity of not less than Ω · cm.

5. The electromagnetic wave absorber of any of claims 1-4, wherein the resistive layer has a thickness of 15-500 nm.

6. The electromagnetic wave absorber of any of claims 1-5, wherein a surface of the resistive layer opposite to the surface in contact with the dielectric layer is laminated on a polymer film.

7. The electromagnetic wave absorber of any of claims 1-6, wherein the dielectric layer has a relative permittivity of 1-10.

8. The electromagnetic wave absorber of any of claims 1-7, wherein the dielectric layer is formed of a polymer material.

9. The electromagnetic wave absorber of any of claims 1-8, wherein the conductive layer has a sheet resistance of 0.001-30 Ω/□.

10. The electromagnetic wave absorber of any of claims 1-9, wherein the conductive layer is formed from at least 1 of aluminum, an aluminum alloy, aluminum nitride, copper, a copper alloy, a nitride of copper, and indium tin oxide.

11, A molded article with an electromagnetic wave absorber, comprising:

molded article, and

an electromagnetic wave absorber as claimed in any of claims 1 to 10 attached to said molded article.

Technical Field

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

Background

In recent years, electromagnetic waves in the millimeter wave and submillimeter wave regions having a wavelength of about 1 to 10mm and a frequency of 30 to 300GHz have been used as information communication media. The use of such electromagnetic waves for collision avoidance systems is being investigated. The collision avoidance system is a system that detects an obstacle in a vehicle and automatically brakes the vehicle, or measures the speed of a surrounding vehicle and the distance between vehicles to adjust the speed of the vehicle and the distance between vehicles. In order for the collision avoidance system to operate properly, it is important to avoid receiving unwanted electromagnetic waves as much as possible to prevent false identifications. Therefore, it is conceivable to use an electromagnetic wave absorber for absorbing unnecessary electromagnetic waves in a collision avoidance system.

For example, an electromagnetic wave absorber (sometimes referred to as "λ/4 type electromagnetic wave absorber") including an electromagnetic wave reflecting layer, a dielectric layer having a thickness of λ/4(λ is the wavelength of an electromagnetic wave to be absorbed), and a resistive thin film layer is relatively inexpensive and easy to design, and thus can be produced at low cost, and for example, in patent document 1, types of electromagnetic wave absorbers exhibiting characteristics of functioning in a wide incident angle region have been proposed as λ/4 type electromagnetic wave absorbers.

Disclosure of Invention

Problems to be solved by the invention

In patent document 1, durability (e.g., chemical resistance) peculiar to the use environment of the electromagnetic wave absorber is not specifically studied.

Accordingly, the present invention provides types of electromagnetic wave absorbers comprising a resistive layer which is advantageous for exhibiting excellent chemical resistance, and further provides a molded article with an electromagnetic wave absorber comprising such an electromagnetic wave absorber.

Means for solving the problems

The present invention provides kinds of electromagnetic wave absorbers, which are provided with:

a dielectric layer;

a resistive layer disposed on major surfaces of the aforementioned dielectric layer, and,

a conductive layer provided on the other major surfaces of the dielectric layer and having a sheet resistance lower than that of the resistive layer,

the resistive layer has a sheet resistance of 200 to 600 Ω/□,

when the resistance layer is subjected to an immersion treatment in a 5 wt% aqueous solution of NaOH for 5 minutes, the absolute value of the difference between the sheet resistance of the resistance layer before the immersion treatment and the sheet resistance of the resistance layer after the immersion treatment is less than 100 Ω/□.

The present invention also provides a molded article with an electromagnetic wave absorber, which comprises the molded article, and

the electromagnetic wave absorber is attached to the molded article.

ADVANTAGEOUS EFFECTS OF INVENTION

In the electromagnetic wave absorber, the resistance layer has good chemical resistance.

Drawings

Fig. 1 is a cross-sectional view showing examples of the electromagnetic wave absorber of the present invention.

Fig. 2 is a side view showing examples of the molded article with an electromagnetic wave absorber of the present invention.

Detailed Description

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following description is an exemplary description of the present invention, and the present invention is not limited to the following embodiments.

The present inventors have newly found the following technical problems in the course of studying the use of an electromagnetic wave absorber for an anti-collision system. For example, in the case where an electromagnetic wave absorber is used for a collision avoidance system, the electromagnetic wave absorber is installed in a vehicle such as an automobile. In some cases, chemicals such as detergents are used for maintenance of the vehicle. For example, alkaline solutions are sometimes used for vehicle cleaning. Therefore, the electromagnetic wave absorber provided on the vehicle is highly likely to come into contact with such chemicals during the washing process of the vehicle. In particular, the resistance layer in the λ/4 type electromagnetic wave absorber is located near the surface of the electromagnetic wave absorber, and is therefore susceptible to such chemicals. Therefore, if the resistance layer of the electromagnetic wave absorber has good chemical resistance, a λ/4 type electromagnetic wave absorber having a high added value can be provided.

Therefore, the present inventors have determined, through repeated tests, a material capable of imparting excellent chemical resistance to the resistive layer. Based on this new finding, the present inventors have devised an electromagnetic wave absorber of the present invention. The present inventors have studied whether ITO used in the technical fields of flat panel displays, solar cells, and the like can provide a resistance layer of a λ/4 type electromagnetic wave absorber with excellent chemical resistance. As a result of the study, it was found that it is difficult to impart good chemical resistance to the resistance layer by such ITO.

As shown in fig. 1, an electromagnetic wave absorber 1 includes a dielectric layer 10, a resistive layer 20, and a conductive layer 30, the resistive layer 20 is provided on major surfaces of the dielectric layer 10, the conductive layer 30 is provided on the other major surfaces of the dielectric layer 10, and has a sheet resistance lower than that of the resistive layer 20, the resistive layer 20 has a sheet resistance of 200 to 600 Ω/□ in the electromagnetic wave absorber 1, in the case where the resistive layer 20 is subjected to an immersion treatment in a 5 wt% aqueous NaOH solution for 5 minutes, the absolute value of the difference between the sheet resistance of the resistive layer 20 before the immersion treatment and the sheet resistance of the resistive layer 20 after the immersion treatment is less than 100 Ω/□, and thus, even if the resistive layer 20 comes into contact with a chemical such as an alkaline detergent, the sheet resistance of the resistive layer 20 is not easily changed, and the electromagnetic wave absorber 1 can maintain a desired electromagnetic wave absorption characteristic after coming into contact with the chemical.

The electromagnetic wave absorber 1 is a λ/4 type electromagnetic wave absorber. In the lambda/4 type electromagnetic wave absorber, it is designed to be a wavelength (lambda) to be absorbed₀) When the electromagnetic wave of (2) is incident, the electromagnetic wave reflected by the surface of the resistive layer 20 (surface reflection) interferes with the electromagnetic wave reflected by the conductive layer 30 (back reflection). In the λ/4 type electromagnetic wave absorber, the thickness (t) of the dielectric layer 10 and the dielectric layer 1 are determined by the following formula (1)Relative dielectric constant (. epsilon.) of 0_r) Determining the wavelength (lambda) of the electromagnetic wave of an absorption object₀). That is, by appropriately adjusting the material and thickness of the dielectric layer 10, the electromagnetic wave of the wavelength to be absorbed can be set. In the formula (1), sqrt (epsilon)_r) Refers to the relative dielectric constant (. epsilon.)_r) The square root of (a).

λ₀＝4t×sqrt(ε_r) Formula (1)

In the λ/4 type electromagnetic wave absorber, the closer the sheet resistance of the resistive layer is to the characteristic impedance of air (about 377 Ω/□), the more easily good electromagnetic wave absorption characteristics are obtained. Therefore, the resistance layer 20 is less likely to change in sheet resistance even if the resistance layer 20 is in contact with a chemical, which is extremely important for maintaining desired electromagnetic wave absorption characteristics even after the electromagnetic wave absorber 1 is in contact with a chemical.

The resistance layer 20 contains of tin oxide, titanium oxide, and indium oxide, for example, as a main component, and in this specification, "main component" means a component contained at the maximum on a weight basis.

In the case where the resistive layer 20 contains of tin oxide, titanium oxide, and indium oxide as the main component, of tin oxide, titanium oxide, and indium oxide may be contained alone, and in the case where the resistive layer 20 contains of tin oxide, titanium oxide, and indium oxide as the main component, a dopant of at least 1 element other than a metal element having the main component may be contained.

The element contained in the above-mentioned dopant is, for example, at least 1 element selected from the group consisting of tin, silicon, magnesium, titanium, nitrogen, fluorine, antimony, and niobium.

In the case where the main component of the resistance layer 20 is tin oxide, the element contained in the dopant is, for example, fluorine or antimony. When the main component of the resistive layer 20 is titanium oxide, the element contained in the dopant is, for example, niobium. In the case where the main component of the resistive layer 20 is indium oxide, the element contained in the dopant is, for example, tin, silicon, magnesium, titanium, or nitrogen. This makes it easier to adjust the resistivity of the material for forming the resistive layer 20 to a desired range.

As described above, the resistive layer 20 has a sheet resistance of 200 to 600 Ω/□, whereby the sheet resistance of the resistive layer 20 is close to the characteristic impedance of air, and the electromagnetic wave absorber 1 can exert a good electromagnetic wave absorption performance, for example, an electromagnetic wave of a wavelength used in the range of in a millimeter wave radar or a submillimeter wave radar can be easily and selectively absorbed, for example, the electromagnetic wave absorber 1 can be effectively used for attenuating an electromagnetic wave of a frequency of 50 to 100GHz, particularly 60 to 90GHz in the millimeter wave radar.

The resistive layer 20 preferably has a sheet resistance of 260 to 500 Ω/□. This enables the electromagnetic wave absorber 1 to more reliably exhibit excellent electromagnetic wave absorption performance.

The resistive layer 20 has, for example, a thickness of 5 × 10^-4Resistivity of not less than Ω · cm. Accordingly, even if the resistive layer 20 has a thickness of a predetermined value (for example, 15nm) or more, the resistive layer 20 has a desired sheet resistance. As a result, the resistive layer 20 has good chemical resistance.

The resistive layer 20 has, for example, 100 × 10^-4Resistivity of not more than Ω · cm. In this case, the thickness of the resistive layer 20 for giving a desired sheet resistance can be adjusted to a prescribed value (for example, 500nm) or less, and the time required for forming the resistive layer 20 can be shortened. The resistivity of the resistive layer 20 is preferably 50 × 10^-4Omega cm or less, more preferably 30X 10^-4Omega cm or less.

The resistive layer 20 has a thickness of, for example, 15 to 500 nm. This allows the resistive layer 20 to have good chemical resistance and the time required to form the resistive layer 20 to be shortened. The resistive layer 20 preferably has a thickness of 15 to 200 nm.

When the resistive layer 20 contains only indium oxide, or when the resistive layer 20 contains oxygenIn the case of ITO containing indium oxide as a main component and less than 13 wt% of tin oxide, it is desirable that the resistive layer 20 has a polycrystalline structure. Thus, the resistive layer 20 has good chemical resistance even with a small thickness. When the resistive layer 20 is ITO containing tin oxide in an amount of 5 wt% or more and less than 13 wt%, the resistive layer 20 preferably further contains a dopant of silicon, magnesium, titanium, or nitrogen. Thus, even if the resistance layer 20 has a polycrystalline structure, the resistivity of the resistance layer 20 is easily 5 × 10^-4Omega cm or more. In the case where the resistive layer 20 is ITO containing indium oxide as a main component and containing 25 wt% or more of tin oxide, the resistive layer 20 typically has an amorphous structure. In this case, the amorphous structure of ITO is extremely stable, and when the resistance layer 20 is formed of such ITO, the resistance layer 20 has good chemical resistance.

The resistive layer 20 can be formed by sputtering such as DC magnetron sputtering, a physical vapor deposition method such as a vacuum deposition method, an ion plating method, and a pulsed laser deposition method, a chemical vapor deposition method such as a thermal CVD method, or a spray pyrolysis method, for example, depending on the material of the resistive layer 20.

In the case where the resistive layer 20 is ITO having a polycrystalline structure, the resistive layer 20 having a polycrystalline structure may be formed by performing heat treatment (annealing treatment) on a film having an amorphous structure formed by sputtering. It is to be noted that the resistive layer 20 formed of ITO having a polycrystalline structure may be formed by adjusting sputtering conditions such as a film formation temperature without performing a heating process after sputtering.

As shown in fig. 1, for example, the surface of the resistive layer 20 opposite to the surface in contact with the dielectric layer 10 is laminated on the polymer film 25, the polymer film 25 functions as a support for the resistive layer 20, and it is preferable that the polymer film 25 is formed of a material having heat resistance capable of withstanding heating at the time of film formation or at the time of subsequent annealing treatment and providing a smooth surface, for example, when the resistive layer 20 is manufactured by sputtering, in addition, since the polymer film 25 is provided so as to cover the resistive layer 20, if the polymer film 25 has high chemical resistance, the electromagnetic wave absorber 1 also has high chemical resistance, and therefore, the material of the polymer film 25 is, for example, a polyester resin such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), an acrylic resin such as polymethyl methacrylate (PMMA), a Polycarbonate (PC), a cycloolefin polymer (COP), an aromatic polyether ether ketone such as polyether ether ketone, an aromatic polyamide (aramid), or a polyimide, and the support for the polymer film 20 is preferably a PET material from the viewpoint of good chemical resistance, a balance between dimensional stability and cost.

The polymer thin film 25 has a thickness of, for example, 10 to 150 μm, preferably 20 to 100 μm, and more preferably 30 to 80 μm. This reduces the bending rigidity of the polymer film 25, and suppresses the occurrence of wrinkles or deformation when the resistive layer 20 is formed on the polymer film 25.

The dielectric layer 10 has a relative dielectric constant of, for example, 1 to 10. Thus, the electromagnetic wave absorber 1 can exhibit excellent electromagnetic wave absorption performance over a wide bandwidth (for example, a bandwidth of 2GHz or more included in a frequency band of 50 to 100 GHz). The relative permittivity of the dielectric layer 10 can be determined, for example, by cavity resonator perturbation.

The dielectric layer 10 may be a single layer or a laminate of a plurality of layers. In the case where the dielectric layer 10 is a laminate of a plurality of layers, the relative permittivity of the dielectric layer 10 can be calculated as follows: the relative dielectric constant of each layer is measured, and the obtained relative dielectric constant of each layer is multiplied by the ratio of the thickness of each layer to the thickness of the entire dielectric layer 10, and the sum of the values is calculated.

The dielectric layer 10 is not particularly limited, and is formed of, for example, a polymer material. For example, the polymer material of the dielectric layer 10 is: synthetic resins (including thermoplastic elastomers) such as acrylic resins, ethylene vinyl acetate copolymers (EVA), polyvinyl chloride, polyurethane, acrylic urethane resins, polyolefins, polypropylene, polyethylene, silicone resins, polyethylene terephthalate, polyesters, polystyrene, polyimides, polycarbonates, polyamides, polysulfones, polyether sulfones, and epoxy resins; or synthetic rubbers such as polyisoprene rubber, polystyrene-butadiene rubber, polybutadiene rubber, chloroprene rubber, acrylonitrile butadiene rubber, butyl rubber, acrylic rubber, ethylene propylene rubber, and silicone rubber. These polymer materials may be used alone or in combination of 2 or more as the polymer material of the dielectric layer 10.

The dielectric layer 10 may be a foam in some cases. In this case, the relative permittivity of the dielectric layer 10 tends to be low. Further, the dielectric layer 10 can be reduced in weight. The foam is, for example, an olefin foam or a polyester foam.

The thickness of the dielectric layer 10 is, for example, 50 to 2000 μm, preferably 100 to 1000 μm. This makes it easy to achieve both high dimensional accuracy and low cost.

The conductive layer 30 reflects the electromagnetic wave to be absorbed in the electromagnetic wave absorber 1 in the vicinity of the back surface of the electromagnetic wave absorber. The conductive layer 30 has a sheet resistance of, for example, 0.001 to 30 [ omega ]/□. This makes it easy for the electromagnetic wave absorber 1 to exhibit desired electromagnetic wave absorption performance. For example, the present invention can be effectively used for attenuating electromagnetic waves having a frequency of 50 to 100GHz, particularly 60 to 90GHz, in millimeter wave radar.

The material of the conductive layer 30 includes, for example, at least 1 of aluminum, an aluminum alloy, aluminum nitride, copper, a copper alloy, a nitride of copper, and indium tin oxide. This makes it easy for the electromagnetic wave absorber 1 to exhibit desired electromagnetic wave absorption performance. When the conductive layer 30 contains ITO, the conductive layer 30 is preferably ITO containing tin oxide in an amount of 5 to 15 wt%.

As shown in fig. 1, the conductive layer 30 may be laminated on the polymer film 35. The polymer film 35 functions as a support for supporting the conductive layer 30. In this case, the material of the polymer film 35 may be the material exemplified as the material of the polymer film 25, and may be polyester, polypropylene, polyurethane, urethane acrylic resin, biaxially oriented polypropylene (CPP), or vinylidene chloride resin. The polymer film 35 may be omitted in some cases.

The major surface of any layer of the resistive layer 20 and the conductive layer 30 facing the dielectric layer 10 can be coated with a predetermined coating, thereby preventing the dielectric layer 10 from being contaminatedThe component (b) diffuses into the resistive layer 20 or the conductive layer 30 to affect the characteristics of the resistive layer 20 or the conductive layer 30. The material coated is, for example, SiO₂Silicon oxide, silicon nitride, Al₂O₃Iso-alumina, aluminum nitride (AlN), Nb₂O₅Niobium oxide, Strontium Titanate (STO), or zinc aluminum oxide (AZO) are exemplified. In the case where AlN or AZO is used as the material to be coated, it is possible to contribute to improvement in durability of the resistive layer 20 or the conductive layer 30.

As shown in fig. 1, the electromagnetic wave absorber 1 further includes, for example, an adhesive layer 40 and a separator 50. An adhesive layer 40 is disposed on the outside of the conductive layer 30. The separator 50 is disposed in contact with the adhesive layer 40. The electromagnetic wave absorber 1 can be easily attached to an article by peeling the separator 50 to expose the adhesive layer 40 and pressing the adhesive layer 40 against the article such as a molded article. In addition, before the electromagnetic wave absorber 1 is attached to an article, the adhesive layer 40 can be protected by the separator 50.

The adhesive layer 40 includes adhesives such as acrylic adhesives, rubber adhesives, silicone adhesives, and urethane adhesives.

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

examples of the method for producing the electromagnetic wave absorber 1 will be described, the resistive layer 20 is formed on the polymer thin film 25 by a film forming method such as sputtering, and a laminate having the conductive layer 30 formed on the polymer thin film 35 is prepared.

Next, a resin composition for forming the dielectric layer 10 formed to a predetermined thickness is placed on main surfaces of the conductive layer 30, thereafter main surfaces of the resistive layer 20 are laminated on the resin composition for forming the dielectric layer 10, and the resin composition is cured as necessary, whereby the electromagnetic wave absorber 1 can be manufactured, and according to this method, the thickness of the dielectric layer 10 can be easily controlled, and therefore the electromagnetic wave absorber 1 can be manufactured to efficiently absorb electromagnetic waves of a wavelength to be absorbed, and further, since the resistive layer 20 and the conductive layer 30 are formed separately, the time required for manufacturing the electromagnetic wave absorber 1 is short, and the manufacturing cost of the electromagnetic wave absorber 1 is low, and it is necessary to use an adhesive or a binder in order to bond the dielectric layer 10 to the conductive layer 30 or the resistive layer 20.