JP7305392B2 - λ/4 type wave absorber - Google Patents

Description

The present invention relates to a λ/4 type radio wave absorber and the like.

In recent years, the spread of mobile communication devices such as mobile phones and smartphones is progressing rapidly, and many electronic devices are being installed in automobiles. Problems such as malfunctions of other electronic devices are occurring frequently. Various radio wave absorbers have been studied as measures for preventing such radio wave interference, malfunction, and the like.

JP 2017-199931 A

In the λ/4 type electromagnetic wave absorber, a resistive film having a sheet resistance of 300 to 400Ω/□ is usually used from the viewpoint of electromagnetic wave absorption. However, especially in in-vehicle and outdoor applications, the surface resistance value of the resistive film changes due to humidity, heat, etc., and the problem that the radio wave absorbency of the λ/4 type radio wave absorber decreases becomes conspicuous. Become.

Patent Document 1 discloses a λ/4 electromagnetic wave absorber using indium tin oxide as a resistive film. However, considering the above problems, its resistance to moist heat was insufficient.

Accordingly, an object of the present invention is to provide a λ/4 electromagnetic wave absorber with higher resistance to moisture and heat.

The inventors of the present invention have found in the course of their research that the wet heat resistance can be improved by optimizing the rate of increase in the surface resistance value in the acid resistance test of the resistive film. Then, as a result of further intensive research based on this knowledge, the present inventor has a resistive film including a resistive layer, a dielectric layer, and a reflective layer, and has a surface resistance value according to an acid resistance test of the resistive film The present inventors have found that the above problem can be solved with a λ/4 type electromagnetic wave absorber having an increase rate of 30% or less. Based on this finding, the inventors have further studied and completed the present invention.

That is, the present invention includes the following aspects.

Item 1. A λ/4 type radio wave absorber comprising a resistive film including a resistive layer, a dielectric layer, and a reflective layer, and having a surface resistance increase rate of 30% or less in an acid resistance test of the resistive film.

Section 2. Item 2. A λ/4 type radio wave absorber according to item 1, wherein the resistance layer contains indium tin oxide having a SnO ₂ content of 1 to 5% by weight.

Item 3. Item 3. The λ/4 electromagnetic wave absorber according to Item 1 or 2, wherein the resistive film further includes a barrier layer having a thickness of 10 nm or less.

Section 4. Item 4. The λ/4 electromagnetic wave absorber according to any one of items 1 to 3, wherein the average particle size of the metal particles or metal oxide particles on the surface of the resistance layer is 20 nm or more.

Item 5. Item 5. The λ/4 type radio wave absorber according to any one of Items 1 to 4, wherein the layer in contact with the upper surface of the resistance layer has an average surface roughness [Ra] of 0.5 to 3 nm on the surface in contact with the resistance layer. .

Item 6. Item 6. A millimeter wave radar comprising the λ/4 type wave absorber according to any one of items 1 to 5.

Item 7. A member for a λ/4 type radio wave absorber, comprising a resistive film including a resistive layer and a dielectric layer, wherein the resistive film has a surface resistance increase rate of 30% or less in an acid resistance test.

ADVANTAGE OF THE INVENTION According to this invention, the (lambda)/4 type|mold electromagnetic wave absorber with higher moist heat resistance can be provided.

As used herein, the expressions "contain" and "include" include the concepts "contain", "include", "consist essentially of" and "consist only of".

In one aspect, the present invention has a resistive film including a resistive layer, a dielectric layer, and a reflective layer, and the surface resistance value increase rate of the resistive film in an acid resistance test is 30% or less, λ/ It relates to a type 4 radio wave absorber (in this specification, it may be indicated as "the radio wave absorber of the present invention"). This will be explained below.

<1. Characteristics>
The radio wave absorber of the present invention has the characteristic that the surface resistance value increase rate of the resistive film in the acid resistance test is within 30% (in this specification, it may be referred to as the "characteristic of the present invention"). . By having this characteristic, it is possible to exhibit sufficient heat and humidity resistance. More specifically, for example, it is possible to suppress changes in the surface resistance value of the resistive film and deterioration in the radio wave absorbency of the radio wave absorber under wet and heat conditions, and keep these within a certain range.

The properties of the invention can be measured by the following methods.

The sheet resistance value (Ro) of the resistive film in the radio wave absorber is measured with a non-destructive type (eddy current method) sheet resistance measuring instrument (EC-80P) (Napson Co., Ltd.). After that, it is immersed in a 5 wt % HCl aqueous solution for 30 minutes. After washing the radio wave absorber with pure water, the sheet resistance value (R) is measured in the same manner, and the surface resistance value increase rate is calculated by ((R−R0)/Ro)×100.

In this specification, the surface resistance value can be measured by a four-probe method using a surface resistance meter (manufactured by MITSUBISHI CHEMICAL ANALYTECH, trade name “Loresta-EP”).

The surface resistance value increase rate is preferably 0 to 10%, more preferably 0 to 5%, and still more preferably 0 to 1%.

In the radio wave absorber of the present invention, the layer in contact with the upper surface of the resistance layer preferably has an average surface roughness Ra of 0.8 to 4.0 nm on the surface in contact with the resistance layer. With the above average surface roughness, it is possible to further suppress changes in the surface resistance value of the resistance layer. The average surface roughness Ra of the surface in contact with the resistance layer is more preferably 0.5 to 3.0 nm, still more preferably 0.5 to 2.5 nm.

The average surface roughness Ra of the surface in contact with the resistance layer can be measured using an atomic force microscope (SPM9700 manufactured by Shimadzu Corporation, or equivalent).

Note that the "upper surface of the resistance layer" means the surface of the resistance layer opposite to the surface in contact with the dielectric, and the "layer in contact with the upper surface of the resistance layer" specifically includes a support or a barrier layer, which will be described later. etc.

<2. Configuration>
A radio wave absorber of the present invention has a structure comprising a resistive film including a resistive layer, a dielectric layer, and a reflective layer. Each configuration will be described below.

<2-1. Resistance film>
The resistive film is not particularly limited as long as it includes a layer that can function as a resistive layer in the radio wave absorber.

The surface resistance value of the resistive film is not particularly limited as long as it can satisfy the characteristics of the present invention. The surface resistance value of the resistive film is, for example, 100 to 1000Ω/□. Within this range, it is preferably 200 to 700 Ω/□, more preferably 250 to 600 Ω/□.

The thickness of the resistive film is not particularly limited. The thickness of the resistive film is, for example, 5-100 nm, preferably 7-70 nm, more preferably 510-50 nm.

The layer structure of the resistive film is not particularly limited. The resistive film may be composed of a single layer, or may be a combination of two or more layers.

<2-1-1. Resistance layer>
The resistive layer is not particularly limited as long as it can satisfy the characteristics of the present invention. It is considered that the characteristics of the present invention reflect the crystallinity of the resistive film and resistive layer. Although it is not intended to be a restrictive interpretation, it is thought that if the resistance film has low crystallinity, the electrical resistance will deteriorate due to acid generated from other layers (for example, the dielectric layer) under moist heat conditions. Therefore, various materials can be used for the resistive layer as long as they have a certain level of crystallinity or more and can satisfy the characteristics of the present invention. In addition, the characteristics of the present invention can be adjusted by a treatment for improving crystallinity (for example, an annealing treatment), etc., in addition to the material of the resistance layer.

From the viewpoint of further improving moist heat resistance, the average particle size of the metal particles or metal oxide particles on the surface of the resistance layer is preferably 20 nm or more. The average particle size is preferably 10 to 100 nm, more preferably 12 to 80 nm, still more preferably 15 to 50 nm.

The average particle size can be measured by the following method.

Using a field emission scanning electron microscope (S4800 type field emission scanning electron microscope (manufactured by Hitachi High-Technologies Corporation) or equivalent), the surface of the resistance layer is observed at an acceleration voltage of 5 kV. In the 2 × 2 μm square SEM image of the obtained resistance layer surface, 6 particles obtained by excluding the upper 2 particles and the lower 2 particles in terms of the length in the longitudinal direction from arbitrary 10 particles visible Let the number average value of the long-axis direction length about particle|grains be an average particle diameter.

The resistance value of the resistance layer is not particularly limited. The resistance value of the resistance layer is, for example, 100 to 1000Ω/□. Within this range, it is preferably 200 to 700 Ω/□, more preferably 250 to 600 Ω/□.

The thickness of the resistance layer is not particularly limited. The thickness of the resistance layer is, for example, 2-100 nm, preferably 3-70 nm, more preferably 5-50 nm.

The layer structure of the resistance layer is not particularly limited. The resistance layer may be composed of a single resistance layer, or may be a combination of two or more resistance layers.

The resistance layer typically includes an ITO-containing resistance layer, a molybdenum-containing resistance layer, and the like. Among them, the ITO-containing resistance layer is preferable from the viewpoint that uniform and stable film formation can be performed. These are described below.

<2-1-1-1. ITO-containing resistance layer>
For example, indium tin oxide (hereinafter referred to as “ITO”) is used as the resistive layer. Among them, indium tin oxide having a SnO ₂ content of 1 to 5% by weight is preferably used from the viewpoint that high crystallinity can be easily realized. The content of ITO in the resistance layer is, for example, 50% by mass or more, preferably 70% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, and usually less than 100% by mass.

<2-1-1-2. Molybdenum-containing resistance layer>
The lower limit of the molybdenum content is not particularly limited, but from the viewpoint of further improving durability, it is preferably 5% by weight, more preferably 7% by weight, still more preferably 9% by weight, even more preferably 11% by weight, and 13% by weight. % is particularly preferred, 15% by weight is highly preferred and 16% by weight is most preferred. The upper limit of the molybdenum content is preferably 30% by weight, more preferably 25% by weight, and still more preferably 20% by weight, from the viewpoint of facilitating adjustment of the surface resistance value.

When the resistive layer contains molybdenum, it more preferably contains nickel and chromium. By containing nickel and chromium in addition to molybdenum in the resistive layer, a radio wave absorber with more excellent durability can be obtained. Examples of alloys containing nickel, chromium and molybdenum include Hastelloy B-2, B-3, C-4, C-2000, C-22, C-276, G-30, N, W, X, etc. Various grades are mentioned.

When the resistive layer contains molybdenum, nickel and chromium, it is preferable that the content of molybdenum is 5% by weight or more, the content of nickel is 40% by weight or more, and the content of chromium is 1% by weight or more. When the contents of molybdenum, nickel, and chromium are within the above ranges, a radio wave absorber with more excellent durability can be obtained. More preferably, the molybdenum, nickel and chromium contents are 7% by weight or more, 45% by weight or more for nickel, and 3% by weight or more for chromium. More preferably, the molybdenum, nickel and chromium contents are 9% by weight or more, 47% by weight or more for nickel, and 5% by weight or more for chromium. More preferably, the molybdenum, nickel and chromium contents are 11% by weight or more, 50% by weight or more for nickel, and 10% by weight or more for chromium. Regarding the contents of molybdenum, nickel and chromium, it is particularly preferable that the molybdenum content is 13% by weight or more, the nickel content is 53% by weight or more, and the chromium content is 12% by weight or more. With respect to the contents of molybdenum, nickel and chromium, it is very preferable that the molybdenum content is 15% by weight or more, the nickel content is 55% by weight or more, and the chromium content is 15% by weight or more. As for the contents of molybdenum, nickel and chromium, it is most preferable that the molybdenum content is 16% by weight or more, the nickel content is 57% by weight or more, and the chromium content is 16% by weight or more. The content of nickel is preferably 80% by weight or less, more preferably 70% by weight or less, and even more preferably 65% by weight or less. The upper limit of the chromium content is preferably 50% by weight or less, more preferably 40% by weight or less, and even more preferably 35% by weight or less.

The resistive layer may contain metals other than molybdenum, nickel and chromium. Examples of such metals include iron, cobalt, tungsten, manganese, titanium and the like. When the resistance layer contains molybdenum, nickel and chromium, the upper limit of the total content of metals other than molybdenum, nickel and chromium is preferably 45% by weight, more preferably 40% by weight, from the viewpoint of durability of the resistance layer. % by weight, more preferably 35% by weight, even more preferably 30% by weight, particularly preferably 25% by weight, very preferably 23% by weight. The lower limit of the total content of metals other than molybdenum, nickel and chromium is, for example, 1% by weight or more.

When the resistance layer contains iron, the upper limit of the content is preferably 25% by weight, more preferably 20% by weight, still more preferably 15% by weight, from the viewpoint of durability of the resistance layer. 1% by weight. When the resistance layer contains cobalt and/or manganese, from the viewpoint of durability of the resistance layer, the upper limit of the content is preferably 5% by weight, more preferably 4% by weight, and more preferably 4% by weight. 3% by weight, and the preferred lower limit is 0.1% by weight. When the resistance layer contains tungsten, the upper limit of the content is preferably 8% by weight, more preferably 6% by weight, still more preferably 4% by weight, from the viewpoint of durability of the resistance layer. 1% by weight.

The resistive layer may contain silicon and/or carbon. When the resistance layer contains silicon and/or carbon, the content of silicon and/or carbon is preferably 1% by weight or less, more preferably 0.5% by weight or less. . Further, when the resistance layer contains silicon and/or carbon, the content of silicon and/or carbon is preferably 0.01% by weight or more.

<2-1-2. Barrier layer>
From the viewpoint of durability, the resistive film preferably further includes a barrier layer. A barrier layer is disposed on at least one surface of the resistive layer. If the barrier layer is only one-sided, the barrier layer is preferably arranged on the surface opposite to the dielectric layer side. Barrier layers are described in detail below.

The barrier layer is not particularly limited as long as it is a layer capable of protecting the resistance layer and suppressing its deterioration. Materials for the barrier layer include, for example, metal compounds, metalloid compounds, preferably metal or metalloid oxides, nitrides, nitride oxides, and the like. The barrier layer may contain components other than the above materials as long as the effects of the present invention are not significantly impaired. In that case, the amount of the material in the barrier layer is, for example, 80% by mass or more, preferably 90% by mass or more, more preferably 95% by mass or more, still more preferably 99% by mass or more, and usually less than 100% by mass. .

Metal elements contained in the barrier layer include, for example, titanium, aluminum, niobium, cobalt, and nickel. Examples of metalloid elements contained in the barrier layer include silicon, germanium, antimony, and bismuth.

Examples of the oxide include MO _X [wherein X is a number that satisfies the formula: n/100≦X≦n/2 (where n is the valence of a metal or semimetal), and M is a metal element or It is a metalloid element. ] The compound represented by is mentioned.

Examples of the nitride include MN _y [wherein Y is a number that satisfies the formula: n/100 ≤ Y ≤ n/3 (where n is the valence of a metal or semimetal), and M is a metal element or It is a metalloid element. ] The compound represented by is mentioned.

Examples of the nitride oxide include MO _X N _y [wherein X and Y are n/100≦X, n/100≦Y, and X+Y≦n/2 (n is the valence of the metal or semimetal). ) and M is a metallic or metalloid element. ] The compound represented by is mentioned.

Regarding the oxidation number X of the oxide or nitride oxide, the cross section of the layer containing, for example, MO _x or MO _x N _y is subjected to elemental analysis by FE-TEM-EDX (for example, “JEM-ARM200F” manufactured by JEOL Ltd.). Then, the valence of oxygen atoms can be calculated by calculating X from _the element ratio of M and O per cross-sectional area of the layer containing _MOx or _MOxNy .

Regarding the nitridation number Y of the nitride or nitride oxide, the cross section of the layer containing, for example, MN _y or MO _x N _y is analyzed by FE-TEM-EDX (for example, "JEM-ARM200F" manufactured by JEOL Ltd.). By analyzing and calculating Y from the element ratio of M and _N per cross-sectional area of the layer containing _MNy or _MOxNy , the valence of the nitrogen atom can be calculated.

Specific examples _{of materials} for the barrier layer include _SiO2 , _SiOx , _Al2O3 , _MgAl2O4 , CuO, CuN, _TiO2 , TiN, and AZO (aluminum-doped zinc oxide).

The thickness of the barrier layer is not particularly limited. The thickness of the barrier layer is, for example, 0.1-40 nm, preferably 0.5-30 nm, more preferably 1-20 nm. From the viewpoint of productivity, the thickness is preferably 5 nm or less.

The layer structure of the barrier layer is not particularly limited. The barrier layer may be composed of a single barrier layer, or may be a combination of two or more barrier layers.

The average surface roughness [Ra] of the barrier layer is preferably 0.5 to 4.0 nm, more preferably 1.0 to 3.0 nm, and more preferably 1.0 to 2.0 nm on the surface in contact with the upper surface of the resistance layer. 0.5 nm is more preferred. With the above average surface roughness, it is possible to further suppress changes in the surface resistance value of the resistance layer.

The average surface roughness of the barrier layer can be adjusted by adjusting the amount of Ar gas during sputtering.

<2-2. Dielectric layer>
The dielectric layer is not particularly limited as long as it can function as a dielectric for the target wavelength in the radio wave absorber. Examples of the dielectric layer include, but are not limited to, a resin sheet, an adhesive, and the like.

The resin sheet is not particularly limited as long as it is a sheet-like one containing resin as a raw material. The resin sheet may contain components other than the resin as long as the effects of the present invention are not significantly impaired. In that case, the total amount of the resin in the resin sheet is, for example, 50% by mass or more, preferably 70% by mass or more, more preferably 90% by mass or more, and still more preferably 95% by mass or more, and usually less than 100% by mass. be.

The resin is not particularly limited, and examples include ethylene vinyl acetate copolymer (EVA), vinyl chloride, urethane, acrylic, acrylic urethane, polyolefin, polyethylene, polypropylene, silicone, polyethylene terephthalate, polyester, polystyrene, polyimide, polycarbonate, polyamide. Synthesis of synthetic resins such as polysulfone, polyethersulfone, and epoxy, as well as polyisoprene rubber, polystyrene-butadiene rubber, polybutadiene rubber, chloroprene rubber, acrylonitrile-butadiene rubber, butyl rubber, acrylic rubber, ethylene-propylene rubber, and silicone rubber. It is preferable to use a rubber material as the resin component. These can be used singly or in combination of two or more.

The dielectric layer may be foam or adhesive.

The dielectric layer may be adhesive. Therefore, when a non-adhesive dielectric is laminated on another layer with an adhesive layer, the combination of the dielectric and the adhesive layer is a "dielectric layer". From the viewpoint of easy lamination with adjacent layers, the dielectric layer preferably includes an adhesive layer.

The dielectric constant of the dielectric layer is not particularly limited. The relative dielectric constant of the dielectric layer is, for example, 0.5-10, preferably 1-8, more preferably 1-5.

The dielectric constant of the dielectric layer can be measured by a cavity resonator perturbation method using a network analyzer, a cavity resonator, or the like.

The thickness of the dielectric layer is, for example, 50 to 2000 μm, preferably 100 to 1000 μm, more preferably 200 to 800 μm.

The layer structure of the dielectric layer is not particularly limited. The dielectric layer may be composed of a single dielectric layer, or may be a combination of two or more dielectric layers. Examples thereof include a three-layer dielectric layer composed of a non-adhesive dielectric and adhesive layers disposed on both sides thereof, and a one-layer dielectric layer composed of an adhesive dielectric.

<2-3. Reflective layer>
The reflective layer is not particularly limited as long as it can function as a reflective layer for radio waves in the radio wave absorber. Examples of the reflective layer include, but are not limited to, a metal film.

The metal film is not particularly limited as long as it is a layer containing metal as a material. The metal film may contain components other than metals as long as the effects of the present invention are not significantly impaired. In that case, the total amount of metal in the metal film is, for example, 30% by mass or more, preferably 50% by mass or more, more preferably 75% by mass or more, still more preferably 80% by mass or more, and even more preferably 90% by mass or more. , particularly preferably 95% by mass or more, very preferably 99% by mass or more, and usually less than 100% by mass.

Metals are not particularly limited, and examples thereof include aluminum, copper, iron, silver, gold, chromium, nickel, molybdenum, gallium, zinc, tin, niobium, and indium. A metal compound such as ITO can also be used as the material for the metal film. These may be used singly or in combination of two or more.

The thickness of the reflective layer is not particularly limited. The thickness of the reflective layer is, for example, 1 μm or more and 500 μm or less, preferably 2 μm or more and 200 μm or less, more preferably 5 μm or more and 100 μm or less.

The layer structure of the reflective layer is not particularly limited. The reflective layer may be composed of a single reflective layer, or may be a combination of two or more reflective layers.

<2-4. Support>
The radio wave absorber of the present invention preferably further has a support. Thereby, the resistance film can be protected, and the durability as a radio wave absorber can be enhanced. The support is not particularly limited as long as it is in the form of a sheet. Examples of the support include, but are not limited to, resin substrates.

The resin base material is not particularly limited as long as it is a base material containing a resin as a material and is in the form of a sheet. The resin substrate may contain components other than the resin as long as the effects of the present invention are not significantly impaired. For example, titanium oxide or the like may be contained from the viewpoint of adjusting the dielectric constant.
In that case, the total amount of the resin in the resin substrate is, for example, 80% by mass or more, preferably 90% by mass or more, more preferably 95% by mass or more, still more preferably 99% by mass or more, and usually less than 100% by mass. is.

The resin is not particularly limited, and examples include polyethylene terephthalate (PET), polyethylene naphthalate, polyester resins such as modified polyester, polyethylene (PE) resins, polypropylene (PP) resins, polystyrene resins, polyolefins such as cyclic olefin resins. vinyl resins such as polyvinyl chloride and polyvinylidene chloride, polyvinyl acetal resins such as polyvinyl butyral (PVB), polyether ether ketone (PEEK) resin, polysulfone (PSF) resin, polyether sulfone (PES) resin , polycarbonate (PC) resin, polyamide resin, polyimide resin, acrylic resin, triacetyl cellulose (TAC) resin, and the like. These can be used singly or in combination of two or more.

Among these, from the viewpoint of productivity and strength, polyester-based resins are preferred, and polyethylene terephthalate is more preferred.

The dielectric constant of the support is not particularly limited. The dielectric constant of the support is, for example, 1-20, preferably 1-15, more preferably 1-10, still more preferably 1-5.

The thickness of the support is not particularly limited. The thickness of the support is, for example, 5 μm or more and 500 μm or less, preferably 10 μm or more and 300 μm or less, more preferably 20 μm or more and 300 μm or less.

The average surface roughness [Ra] of the support is preferably 0.8 to 4.0 nm, more preferably 1.0 to 3.0 nm, on the surface in contact with the upper surface of the resistance layer (or resistance film). 1.0 to 2.5 nm is more preferable. With the above average surface roughness, it is possible to further suppress changes in the surface resistance value of the resistance layer.

The average surface roughness of the support can be adjusted according to or according to a known adjustment method. For example, it can be adjusted by applying resin, particles, or the like.

The layer structure of the support is not particularly limited. The support may be composed of a single type of support, or may be a combination of two or more types of supports.

<2-5. Layer structure>
Each layer in the radio wave absorber of the present invention is arranged in the order in which the radio wave absorption performance can be exhibited. As an example, the resistive film, dielectric layer, and reflective layer are arranged in this order.

Furthermore, when the radio wave absorber of the present invention has a support, for example, the support, resistive film, dielectric layer, and reflective layer are arranged in this order.

The radio wave absorber of the present invention may contain other layers in addition to the support, resistive film, dielectric layer, and reflective layer. Other layers may be disposed on either surface of each of the support, resistive film, dielectric layer, and reflective layer.

<3. Manufacturing method>
The radio wave absorber of the present invention can be obtained by various methods, for example, according to or according to known production methods, depending on its configuration. For example, it can be obtained by a method including a step of sequentially laminating a resistive film, a dielectric layer, and a reflective layer on a support.

A lamination method is not particularly limited.

The resistance film can be formed by, for example, a sputtering method, a vacuum deposition method, an ion plating method, a chemical vapor deposition method, a pulse laser deposition method, or the like. Among these, the sputtering method is preferable from the viewpoint of film thickness controllability. The sputtering method is not particularly limited, but examples thereof include DC magnetron sputtering, high frequency magnetron sputtering, and ion beam sputtering. Also, the sputtering apparatus may be of a batch system or a roll-to-roll system.

The dielectric layer and the reflective layer can be laminated using, for example, the adhesiveness of the dielectric layer.

<4. λ/4 type radio wave absorber member>
In one aspect of the present invention, the λ/4 type radio wave absorber has a resistive film including a resistive layer and a dielectric layer, and the surface resistance value increase rate of the resistive film in an acid resistance test is within 30%. body member. The λ/4 electromagnetic wave absorber member is a member for forming a λ/4 electromagnetic wave absorber by placing it in contact with an adherend. The resistive film, dielectric layer, characteristics of the present invention, and other configurations are the same as those described for the λ/4 electromagnetic wave absorber of the present invention.

<5. Application>
The radio wave absorber of the present invention is used for the purpose of suppressing radio wave interference and reducing noise in millimeter wave radars used in intelligent transportation systems (ITS) and automobile collision prevention systems that perform information communication between automobiles, roads, and people. be able to. From this point of view, one aspect of the present invention relates to a millimeter wave radar including the radio wave absorber of the present invention.

In addition, as other applications, for example, it can be used as a radio wave countermeasure member in optical transceivers, next-generation mobile communication systems (5G), short-range wireless transfer technology, and the like.

The radio wave frequency targeted by the radio wave absorber of the present invention is, for example, 1 to 200 GHz, preferably 10 to 100 GHz, more preferably 50 to 90 GHz, further preferably 65 to 90 GHz.

EXAMPLES The present invention will be described in detail below based on examples, but the present invention is not limited by these examples.

(1) Production of λ/4 type radio wave absorber (Example 1)
A polyethylene terephthalate (PET) film (dielectric constant: 3.4) kneaded with titanium oxide and having a thickness of 125 μm was prepared as a support.

A resistive film (barrier layer 1/resistive layer) having a surface resistance of 372Ω/□ was formed on the PET film as follows. First, a gas in which the ratio of Ar and _O2 was adjusted to 1:1 by DC pulse sputtering was introduced and adjusted to 0.5 Pa to form a _SiO2 layer (barrier layer 1: thickness 8 nm). bottom. When the average surface roughness of the surface of the barrier layer 1 was measured, it was 4.0 nm. Subsequently, a resistive layer was formed on the barrier layer 1 by DC pulse sputtering. In the DC pulse sputtering, a gas with a ratio of Ar and _O adjusted to 96:4 was introduced, adjusted to 0.8 Pa, and indium tin oxide (SnO ₂ content was 2% by weight) was used as a target. was used, and the output was 5.5 kW.

The resistive film was annealed at a temperature of 150° C. for 2 hours to obtain a resistive film with a surface resistance of 372Ω/□.

Next, a dielectric made of polycarbonate with a thickness of 0.5 mm and a dielectric constant of 2.6 is laminated on the formed resistive film via an adhesive tape (acrylic double-sided adhesive tape, thickness 30 μm, dielectric constant 2.6), Further, a 10 μm-thick reflecting layer made of aluminum was laminated on the dielectric via the same adhesive tape to obtain a λ/4 type radio wave absorber.

(Example 2)
A polyethylene terephthalate (PET) film (relative permittivity: 3.1) with a thickness of 125 μm was prepared as a support.

A resistive film (barrier layer 1/resistive layer) having a surface resistance of 374Ω/□ was formed on the PET film as follows. First, a gas in which the ratio of Ar and _O2 was adjusted to 1:1 by DC pulse sputtering was introduced to adjust the pressure to 0.8 Pa, and a _SiO2 layer (barrier layer 1: thickness 8 nm) was formed. bottom. When the average surface roughness of the surface of the barrier layer 1 was measured, it was 4.0 nm. Subsequently, a resistive layer was formed on the barrier layer 1 by DC pulse sputtering. In the DC pulse sputtering, a gas with a ratio of Ar and _O2 adjusted to 96:4 was introduced, adjusted to 0.8 Pa, and indium tin oxide ( _SnO2 content was 2% by weight) was used as a target. was used, and the output was 5.5 kW. The resistive film was annealed at a temperature of 150° C. for 2 hours to obtain a resistive film with a surface resistance of 374Ω/□.
Thereafter, the same procedure as in Example 1 was carried out to obtain a λ/4 electromagnetic wave absorber.

(Example 3)
A resistive film (barrier layer 1/resistive layer) having a surface resistance of 371Ω/□ was formed on the PET film used in Example 1 as follows. First, a gas in which the ratio of Ar and _O2 was adjusted to 1:1 by DC pulse sputtering was introduced and adjusted to 0.5 Pa to form a _SiO2 layer (barrier layer 1: thickness 8 nm). bottom. When the average surface roughness of the surface of the barrier layer 1 was measured, it was 3.9 nm.

Subsequently, a resistive layer was formed on the barrier layer 1 by DC pulse sputtering. In the DC pulse sputtering, a gas with a ratio of Ar and _O2 adjusted to 96:4 was introduced, adjusted to 0.8 Pa, and indium tin oxide ( _SnO2 content was 5% by weight) was used as a target. was used, and the output was 5.5 kW. The resistive film was annealed at a temperature of 150° C. for 2 hours to obtain a resistive film with a surface resistance of 371Ω/□.

Thereafter, the same procedure as in Example 1 was carried out to obtain a λ/4 electromagnetic wave absorber.

(Example 4)
A resistive film (barrier layer 1/resistive layer) having a surface resistance of 373Ω/□ was formed on the PET film used in Example 2 as follows. First, a gas in which the ratio of Ar and _O2 was adjusted to 1:1 by DC pulse sputtering was introduced to adjust the pressure to 0.8 Pa, and a _SiO2 layer (barrier layer 1: thickness 8 nm) was formed. bottom. When the average surface roughness of the surface of the barrier layer 1 was measured, it was 1.5 nm.

Subsequently, a resistive layer was formed on the barrier layer 1 by DC pulse sputtering. In the DC sputtering, a gas with a ratio of Ar and _O2 adjusted to 96:4 is introduced to adjust the pressure to 0.8 Pa, and indium tin oxide ( _SnO2 content is 5% by weight) is used as a target. , at an output of 5.5 kW. The resistive film was annealed at a temperature of 150° C. for 2 hours to obtain a resistive film with a surface resistance of 373Ω/□.

Thereafter, the same procedure as in Example 1 was carried out to obtain a λ/4 electromagnetic wave absorber.

(Comparative example 1)
On the PET film used in Example ₁ , a resistive film (barrier layer 1/resistive layer/) with a surface resistance value of 372 Ω/sq. was formed in the same manner as in Example 2, except that Thereafter, the same procedure as in Example 1 was carried out to obtain a λ/4 electromagnetic wave absorber.

(Comparative example 2)
A λ/4 type radio wave absorber was obtained in the same manner as in Example 1, except that indium tin oxide (SnO ₂ content: 11% by weight) was used as a sputtering target.

(2) Measurement of the average particle size of the surface of the resistance layer The average particle size of the surface of the resistance layer was determined as follows. Using a field emission scanning electron microscope (S4800 type field emission scanning electron microscope (manufactured by Hitachi High-Technologies Corporation) or equivalent), the surface of the resistance layer was observed at an accelerating voltage of 5 kV. In the 2 × 2 μm square SEM image of the obtained resistance layer surface, 6 particles obtained by excluding the upper 2 particles and the lower 2 particles in terms of the length in the longitudinal direction from arbitrary 10 particles visible The number average value of the longitudinal length of the particles was taken as the average particle diameter.

(3) Method of measuring average surface roughness [Ra] A layer in contact with the upper surface of the resistive film was measured using an atomic force microscope (SPM9700 manufactured by Shimadzu Corporation, or equivalent) in the range of 1 µm × 1 µm. was scanned to measure the average surface roughness (Ra).

(4) Measurement of surface resistance value increase rate (%) by acid resistance test of resistive film ) (Napson Co., Ltd.). After that, it was immersed in a 5 wt % HCl aqueous solution for 30 minutes. After washing the radio wave absorber with pure water, the sheet resistance value (R) was similarly measured and calculated by ((R−R0)/Ro)×100.

(5) Radio absorption evaluation network analyzer MS4647B (manufactured by Anritsu), free space material measurement device BD1-26. A (manufactured by Keycom Co., Ltd.) was used to configure a radio wave absorption measuring apparatus. Using this radio wave absorption measuring device, the radio wave absorption amount in the 55 to 90 GHz band of the obtained λ / 4 type radio wave electromagnetic wave absorber was measured based on JIS R1679, and the radio wave absorption amount at 79 GHz before the wet heat test. . The λ/4 type radio wave absorber was set so that the direction of incidence of radio waves was perpendicular and from the substrate side.

After that, the radio wave absorber was allowed to stand still for 240 hours in an atmosphere with a temperature of 80° C. and a relative humidity of 85%. After standing, the radio wave absorber was taken out, and after standing for 1 hour at a temperature of 25 ° C. and a relative humidity of 50%, the amount of radio wave absorption at 79 GHz after the wet heat test was measured in the same manner, ((R'-Ro' )/Ro′)×100.

(6) Measurement of resistance value increase rate by wet heat test of resistive film Sheet resistance value of resistive film in radio wave absorber is measured by non-destructive type (eddy current method) sheet resistance measuring instrument (EC-80P) (Napson Co., Ltd.) (R0'). After that, it was allowed to stand for 240 hours in an atmosphere of 80° C. and 85% relative humidity. After standing still, the electromagnetic wave absorber was taken out, and after standing at a temperature of 25° C. and a relative humidity of 50% for 1 hour, the sheet resistance value (R′) was similarly measured. .

(7) Results The results are shown in Table 1.

Claims (8)

A λ / 4 type radio wave absorber having a resistive film including a resistive layer, a dielectric layer, and a reflective layer,
Sheet resistance value (Ro) of the resistive film in the λ/4 type electromagnetic wave absorber and sheet resistance value after immersing the λ/4 type electromagnetic wave absorber in a 5 wt% HCl aqueous solution for 30 minutes and washing with pure water A λ/4 type radio wave absorber having a surface resistance increase rate calculated from (R) by the formula: ((R−Ro)/Ro)×100 within 30%. 2. The λ/4 electromagnetic wave absorber according to claim 1, wherein said resistive layer comprises indium tin oxide with a SnO ₂ content of 1 to 5% by weight. 3. The λ/4 electromagnetic wave absorber according to claim 1, wherein said resistive film further includes a barrier layer having a thickness of 10 nm or less. The λ/4 electromagnetic wave absorber according to any one of claims 1 to 3, wherein the metal particles or metal oxide particles on the surface of the resistance layer have an average particle size of 20 nm or more. The λ/4 type radio wave absorber according to any one of claims 1 to 4, wherein the layer in contact with the upper surface of the resistance layer has an average surface roughness [Ra] of 0.5 to 3 nm on the surface in contact with the resistance layer. body. A λ / 4 radio wave absorber having a resistive film including a resistive layer, a dielectric layer, and a reflective layer,
Sheet resistance value (Ro) of the resistive film in the λ/4 type electromagnetic wave absorber and sheet resistance value after immersing the λ/4 type electromagnetic wave absorber in a 5 wt% HCl aqueous solution for 30 minutes and washing with pure water The surface resistance value increase rate calculated from (R) by the formula: ((R−Ro)/Ro)×100 is 0 to 10%,
The layer in contact with the upper surface of the resistance layer has an average surface roughness [Ra] of 0.5 to 3 nm on the surface in contact with the resistance layer, and
the dielectric layer comprises an adhesive layer;
λ/4 type radio wave absorber. A millimeter wave radar comprising the λ/4 type wave absorber according to any one of claims 1 to 6 . A λ/4 type radio wave absorber member having a resistive film including a resistive layer and a dielectric layer,
Sheet resistance value (Ro) of the resistive film in the λ/4-type electromagnetic wave absorber member , and after immersing the λ/4-type electromagnetic wave absorber member in a 5 wt% HCl aqueous solution for 30 minutes and washing with pure water A member for a λ/4 type radio wave absorber having a rate of increase in surface resistance value calculated from the sheet resistance value (R) of ((R−Ro)/Ro)×100 by 30% or less.