Radio wave absorption sheet

Abstract

To provide a radio wave absorber in which deviation due to a vibration load when fixed to an antenna is suppressed and the risk of overlapping with an antenna slot is reduced.SOLUTION: A radio wave absorption sheet 10 includes an opening 11 for an antenna slot, and after being attached to a SUS plate, it is pulled for 60 mm or more at a peel angle of 90 degrees and a pulling speed of 300 mm / min in an environment of 25°C and 50% RH, and the peel strength measured by recording the average value (N / 25 mm) of the load (N) detected by a load cell is 15 N / 25 mm or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electromagnetic wave absorbing sheet and the like. [Background technology]

[0002] The accuracy of radar signals decreases due to multiple reflections between the radome or bumper and the antenna surface, and interference between the transmitting and receiving antennas. To address this problem, a resin molded product with radio wave absorbing properties is fixed to the antenna surface. Since the laminated structure is manufactured by thermal caulking during the antenna manufacturing process, the radio wave absorber is also fixed to the antenna surface by thermal caulking (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2020 / 234981 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, waveguide antennas have been developed that radiate electromagnetic waves through holes called antenna slots. When radars are installed in automobiles and other vehicles, they are subject to vibration and temperature changes. When conventional methods of fixing waveguide antennas using thermal caulking are used, the thermal caulking can come loose due to the load, potentially causing the radio wave absorber to peel off or shift. As a result, the transmitter / receiver (antenna slot) of the waveguide antenna and the radio wave absorber can overlap, potentially impairing the functionality of the waveguide antenna. Given the increasing adoption of autonomous driving assistance technologies and safe driving assistance technologies such as collision avoidance, the demand for reliable radar accuracy is expected to become even more important. For this reason, the present inventors focused on the vibration load resistance of radio wave absorbers fixed to antennas.

[0005] An object of the present invention is to provide a radio wave absorber that is prevented from shifting due to vibration load when fixed to an antenna, and that reduces the risk of overlapping with the antenna slot. [Means for solving the problem]

[0006] The present inventors have conducted research in light of the above-mentioned issues and problems, and have focused on the use of a sheet-like radio wave absorber (radio wave absorbing sheet) having an opening for an antenna slot. The present inventors have further pursued research and found that the above-mentioned problems can be solved by a radio wave absorbing sheet having an opening for an antenna slot, which, after being attached to a stainless steel plate, has a peel strength of 15 N / 25 mm or more, as measured by pulling the sheet for 60 mm or more at a peel angle of 90° and a pulling rate of 300 mm / min under an environment of 25°C and 50% RH, and recording the average value (N / 25 mm) of the load (N) detected by a load cell. Based on this finding, the present inventors have conducted further research and have completed the present invention. Specifically, the present invention encompasses the following aspects.

[0007] Item 1. Having an opening for an antenna slot, After bonding to a SUS plate, the peel strength is measured by pulling the tape for 60 mm or more at a peel angle of 90 degrees and a pulling speed of 300 mm / min under an environment of 25°C and 50% RH, and recording the average value (N / 25 mm) of the load (N) detected by the load cell. The peel strength is 15 N / 25 mm or more. Radio wave absorbing sheet.

[0008] Item 2. The radio wave absorbing sheet according to Item 1, which is a λ / 4 type radio wave absorbing sheet having a resistive layer, a dielectric layer, a reflective layer, and an adhesive layer in this order.

[0009] Item 3. The radio wave absorbing sheet according to Item 2, wherein the antenna slot opening is an opening that penetrates through the resistive layer, the dielectric layer, the reflective layer, and the adhesive layer in the stacking direction.

[0010] Item 4. The radio wave absorbing sheet according to Item 3, comprising a support, the support, the resistive layer, the dielectric layer, the reflective layer, and the adhesive layer being laminated in this order, and the antenna slot opening is an opening that penetrates through the support, the resistive layer, the dielectric layer, the reflective layer, and the adhesive layer in the lamination direction.

[0011] Item 5. A radio wave absorber sheet according to Item 2, wherein the minimum value of the return loss for radio waves of 55 to 90 GHz incident at normal incidence is −15 dB or less, and the value shown by equation 1: |(minimum value of return loss for radio waves of 55 to 90 GHz incident at normal incidence before vibration test (ISO 16750-3(2012) Test 4 - sprung masses (vehicle body)))−(minimum value of return loss for radio waves of 55 to 90 GHz incident at normal incidence after vibration test (ISO 16750-3(2012) Test 4 - sprung masses (vehicle body)))| is 5 dB or less.

[0012] Item 6. The radio wave absorbing sheet according to Item 1, which has a peel strength of 15 N / 25 mm or more after a vibration test (ISO 16750-3 (2012) Test 4 - sprung masses (vehicle body)).

[0013] Item 7. A waveguide antenna with a radio wave absorbing sheet, comprising a waveguide antenna having an antenna slot and the radio wave absorbing sheet according to any one of Items 1 to 6, wherein an opening for an antenna slot of the radio wave absorbing sheet is arranged above the antenna slot.

[0014] Item 8. A resistive layer and an adhesive dielectric layer are included, having an opening for an antenna slot, After bonding to a SUS plate, the peel strength is measured by pulling the tape for 60 mm or more at a peel angle of 90 degrees and a pulling speed of 300 mm / min under an environment of 25°C and 50% RH, and recording the average value (N / 25 mm) of the load (N) detected by the load cell. The peel strength is 15 N / 25 mm or more. Components for radio wave absorbing sheets.

[0015] Item 9. A waveguide antenna with a member for a radio wave absorbing sheet, comprising: a waveguide antenna having an antenna slot; and the member for a radio wave absorbing sheet according to Item 8, which is placed on a metal surface of the waveguide antenna; and the opening for the antenna slot of the radio wave absorbing sheet is placed above the antenna slot. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide a radio wave absorber that is prevented from shifting due to vibration load when fixed to an antenna, and that reduces the risk of overlapping with the antenna slot. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a perspective view schematically illustrating an example of an electromagnetic wave absorbing sheet of the present invention. [Figure 2] 1 is a perspective view schematically illustrating an example of an electromagnetic wave absorbing sheet of the present invention. [Figure 3] 2 is a cross-sectional view taken along the line AA' in FIG. [Figure 4] FIG. 1 is a perspective view schematically illustrating an exploded view of an example of a waveguide antenna. DETAILED DESCRIPTION OF THE INVENTION

[0018] In this specification, the expressions "contain" and "comprise" include the concepts of "contain", "include", "consist essentially of" and "consist only of".

[0019] In one aspect, the present invention relates to a radio wave absorbing sheet (sometimes referred to in this specification as "the radio wave absorbing sheet of the present invention") which has an opening for an antenna slot, and which has a peel strength of 15 N / 25 mm or more as measured by attaching the sheet to a SUS plate, pulling the sheet for 60 mm or more at a peel angle of 90 degrees, a pulling rate of 300 mm / min, and recording the average value (N / 25 mm) of the load (N) detected by a load cell in an environment of 25°C and 50% RH. This will be explained below.

[0020] <1. Shape and characteristics> The radio wave absorbing sheet of the present invention is in a sheet form. The sheet form facilitates weight reduction, and, combined with a predetermined peel strength, makes it possible to suppress displacement due to vibration load. From this perspective, the thickness of the radio wave absorbing sheet of the present invention is desirably relatively thin, for example, 3000 μm or less, preferably 2000 μm or less, and more preferably 1000 μm or less. The lower limit of the thickness is not particularly limited as long as the desired radio wave absorbing performance is exhibited, and is, for example, 100 μm, 300 μm, or 500 μm.

[0021] The area of ​​the radio wave absorbing sheet of the present invention is not particularly limited as long as the intended radio wave absorbing performance is exhibited. From the viewpoint of use in an on-vehicle radar for which the radio wave absorbing sheet of the present invention is suitable, the area is, for example, 3 cm 2 More than 240cm 2 Less than 5cm, preferably 2 More than 120cm 2 Less than 10cm, preferably 2 More than 40cm 2 The above area includes the area of ​​an opening for an antenna slot, which will be described later.

[0022] The radio wave absorbing sheet of the present invention has an antenna slot opening. An antenna slot is a hole arranged on the surface of a waveguide antenna for transmitting and receiving electromagnetic waves. An example of an antenna slot is shown in FIG. 4. A plurality of antenna slots 21 are provided in a radiation layer 22 constituting the surface of a waveguide antenna 20. The antenna slot opening is a cut-out area in the radio wave absorbing sheet provided so as not to block one or more antenna slots (e.g., 1 to 20, 2 to 12, 3 to 10, 4 to 7) when the radio wave absorbing sheet of the present invention is arranged on the waveguide antenna, and penetrates the radio wave absorbing sheet in the thickness direction (FIG. 3). An example of the antenna slot opening is shown in FIG. 1. An antenna slot opening 11 is formed so as not to block the plurality of antenna slots 21 shown in FIG. 4. The antenna slot opening may be closed as shown in FIG. 1 or open as shown in FIG. 2.

[0023] The area of ​​one antenna slot opening can be adjusted appropriately depending on the area and number of antenna slots in the area where the opening is located. 2 More than 1cm 2 Less than 0.15cm, preferably 2 More than 0.7cm 2 Less than 0.3cm, preferably 0.3cm 2 More than 0.4cm 2 The following is the result.

[0024] The number of antenna slot openings that the radio wave absorber sheet of the present invention has is not particularly limited, but may be, for example, 2 or more and 24 or less, 4 or more and 14 or less, or 6 or more and 10 or less.

[0025] The ratio of the total area of ​​the antenna slot openings (the area of ​​one antenna slot opening if there is one, or the total area if there are multiple antenna slot openings) to 100% of the area of ​​the radio wave absorbing sheet of the present invention (the area including the antenna slot opening as described above) is preferably 1% or more and 50% or less, more preferably 3% or more and 30% or less, and even more preferably 5% or more and 15% or less, from the viewpoints of radio wave absorption performance, strength of the radio wave absorbing sheet, etc.

[0026] The electromagnetic wave absorbing sheet of the present invention has a peel strength of 15 N / 25 mm or more, as measured by attaching at least one surface to a SUS plate, pulling the sheet at 25°C and 50% RH, peeling at a 90° angle, at a pulling rate of 300 mm / min, and pulling the sheet for 60 mm or more, and recording the average value (N / 25 mm) of the load (N) detected by a load cell. This, combined with its sheet-like form, makes it possible to suppress slippage due to vibration load. The peel strength is preferably 20 N / 25 mm or more, more preferably 25 N / 25 mm or more. There is no particular upper limit to the peel strength, but it may be, for example, 100 N / 25 mm, 50 N / 25 mm, or 35 N / 25 mm. The electromagnetic wave absorbing sheet of the present invention is in sheet form, and can be designed to have a reduced thickness for all or some of the layers, thereby making the entire sheet more compact.

[0027] The peel strength measurement method is as follows: The electromagnetic wave absorbing sheet is cut into a strip measuring 25 mm wide and 150 mm long to create a test specimen. The dielectric layer of the test specimen is then bonded to a stainless steel plate to create the measurement sample. The test specimen is bonded to the stainless steel plate by rolling a 2 kg roller back and forth twice at a speed of 10 ± 0.5 mm / s. After bonding, the specimen is left in an environment of 25°C and 50% RH for 24 hours. One end of the test specimen is then fixed in the chuck of a tensile testing machine (A&D Corporation's "Tensilon Universal Material Testing Machine"). The specimen is then pulled for 60 mm or more at a peel angle of 90° and a tensile speed of 300 mm / min in an environment of 25°C and 50% RH, and the average load (N) detected by the load cell is recorded (N / 25 mm). Similar measurements are performed three times, and the average of the three points is used as the peel strength.

[0028] The radio wave absorbing sheet of the present invention preferably has a peel strength of 15 N / 25 mm or more, as measured by bonding at least one surface of the sheet to a SUS plate after a vibration test (ISO 16750-3 (2012) Test 4 - sprung masses (vehicle body)), pulling the sheet for 60 mm or more at a peel angle of 90° and a pulling rate of 300 mm / min in an environment of 25°C and 50% RH, and recording the average value (N / 25 mm) of the load (N) detected by a load cell. The peel strength is preferably 20 N / 25 mm or more, and more preferably 25 N / 25 mm or more. There is no particular upper limit to the peel strength, but it may be, for example, 100 N / 25 mm, 50 N / 25 mm, or 35 N / 25 mm.

[0029] The rate of change (unit: %) in peel strength of the radio wave absorbing sheet of the present invention due to the vibration test (ISO 16750-3(2012) Test 4 - sprung masses (vehicle body)) (= (peel strength after vibration test (ISO 16750-3(2012) Test 4 - sprung masses (vehicle body)) / peel strength before vibration test (ISO 16750-3(2012) Test 4 - sprung masses (vehicle body))) × 100) is preferably 10% or more and 200% or less, more preferably 30% or more and 150% or less, even more preferably 50% or more and 130% or less, still more preferably 70% or more and 130% or less, and even more preferably 90% or more and 125% or less.

[0030] The vibration test method is as follows: The electromagnetic wave absorbing sheet is fixed to a SUS plate (0.5 mm thick, SUS304BA) via an adhesive layer in accordance with JIS standards, and this is then fixed to a PPS plate (5 mm thick) via adhesive tape. A vibration tester (IMV A30 / EM3HM), a thermostatic chamber (IMV Syn-3HW-70-VH), and an acceleration sensor (IMV VP-32(9132U)) are used in accordance with ISO 16750-3(2012) Test 4 - Sprung Masses (Vehicle Body). The test is conducted at Tmax = 125°C, in accordance with ISO 16750-3(2012) Test 4 - Sprung Masses (Vehicle Body). The sample is attached to three sides of a cube jig, and the test is conducted in three directions, changing the attachment side, for eight hours each. Each sample is fixed to the PPS plate with screws in two or four holes.

[0031] The radio wave absorbing sheet of the present invention preferably has a minimum return loss of −5 dB or less for normally incident radio waves of 55 to 90 GHz, more preferably −10 dB or less, and even more preferably −15 dB or less.

[0032] The details of the method for measuring the minimum return loss are as follows. A radio wave absorption measurement device is constructed using a PNA microwave network analyzer N5227A (Keysight), a PNA-X Series 2-port millimeter-wave controller N5261A (Keysight), and a horn antenna FSS-07 (HVS). Using this radio wave absorption measurement device, the radio wave absorption amount of the radio wave absorbing sheet from 55 GHz to 90 GHz is measured in accordance with JIS R1679. The radio wave absorbing sheet is set so that the radio wave incidence direction is vertical and incident from the support side. The minimum return loss value for vertically incident radio waves from 55 to 90 GHz is calculated.

[0033] The radio wave absorbing sheet of the present invention preferably has a value of 5 dB or less, as determined by the formula 1: |(minimum value of return loss for vertically incident radio waves of 55 to 90 GHz before the vibration test (vibration test conditions)) - (minimum value of return loss for vertically incident radio waves of 55 to 90 GHz after the vibration test (vibration test conditions))|.

[0034] <2. Configuration> The configuration of the radio wave absorbing sheet of the present invention is not particularly limited, and any known configuration of a radio wave absorber that can be made into a sheet form can be adopted.

[0035] In one embodiment, the radio wave absorbing sheet of the present invention is a λ / 4 type radio wave absorbing sheet having a resistive layer, a dielectric layer, a reflective layer, and an adhesive layer in this order. In this embodiment, the antenna slot opening is preferably an opening that penetrates through the resistive layer, the dielectric layer, the reflective layer, and the adhesive layer in the stacking direction.

[0036] In the above embodiment, the radio wave absorbing sheet of the present invention preferably includes a support, and the support, resistive layer, dielectric layer, reflective layer, and adhesive layer are laminated in this order. In this case, the opening for the antenna slot is preferably an opening that penetrates through the support, resistive layer, dielectric layer, reflective layer, and adhesive layer in the lamination direction.

[0037] <2-1.Support> The support is not particularly limited as long as it is in a sheet form. Examples of the support include, but are not particularly limited to, a resin substrate. The support can protect the resistive layer and enhance the durability of the radio wave absorber.

[0038] The resin substrate is not particularly limited as long as it is a substrate containing a resin as a material and is in a sheet form. The resin substrate may contain components other than resin as long as the radio wave absorption performance is not significantly impaired. For example, titanium oxide may be contained to adjust the relative dielectric constant. In this case, the total amount of 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, and even more preferably 99% by mass or more, and is usually less than 100% by mass.

[0039] The resin is not particularly limited, and examples thereof include polyester resins such as polyethylene terephthalate (PET), polyethylene naphthalate, and modified polyester, polyolefin resins such as polyethylene (PE) resin, polypropylene (PP) resin, polystyrene resin, and cyclic olefin resin, 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, polyethersulfone (PES) resin, polycarbonate (PC) resin, polyamide resin, polyimide resin, acrylic resin, triacetyl cellulose (TAC) resin, etc. These can be used alone or in combination of two or more.

[0040] Among these, from the viewpoints of productivity and strength, polyester resins are preferred, and polyethylene terephthalate is more preferred.

[0041] The relative dielectric constant of the support is, for example, 1 or more and 20 or less, preferably 1 or more and 15 or less, and more preferably 1 or more and 10 or less.

[0042] For the purpose of adjusting the relative dielectric constant of the support, it is preferable to contain an additive such as titanium oxide, silica, barium titanate, alumina, zirconium oxide, etc. From the viewpoint of weather resistance, titanium oxide is preferred.

[0043] The content of the additive in the support is not particularly limited, but is preferably 8 to 20% by weight, more preferably 9 to 15% by weight. From the viewpoint of strength, it is preferably 20% or less, and from the viewpoint of weather resistance, it is preferably 8% or more.

[0044] The thickness of the support is, for example, from 5 μm to 500 μm, preferably from 10 μm to 300 μm, and more preferably from 20 μm to 300 μm.

[0045] The layer structure of the support is not particularly limited, and the support may be composed of a single type of support, or may be a combination of two or more types of supports.

[0046] <2-2. Resistance layer> The resistive layer is not particularly limited as long as it can function as a resistive layer in the radio wave absorber.

[0047] The resistance value of the resistive layer is not particularly limited and may be, for example, 100 Ω / □ or more and Ω / □ or less, preferably 150 Ω / □ or more and 1000 Ω / □ or less, more preferably 200 Ω / □ or more and 600 Ω / □ or less, and even more preferably 250 Ω / □ or more and 450 Ω / □ or less.

[0048] The resistance value of the resistive layer can be measured by a four-terminal method using a surface resistance meter (manufactured by MITSUBISHI CHEMICAL ANALYTECH, trade name "Loresta-EP").

[0049] The thickness of the resistive layer is not particularly limited and is, for example, 1 nm to 200 nm, preferably 2 nm to 100 nm, and more preferably 2 nm to 50 nm.

[0050] The layer structure of the resistive layer is not particularly limited, and may be composed of a single resistive layer or a combination of two or more resistive layers.

[0051] <2-1-1.ITO-containing resistance layer> For example, indium tin oxide (hereinafter referred to as "ITO") is used as the resistive layer. Among them, ITO containing 20 to 40 wt % SnO2, more preferably 25 to 35 wt % SnO2, is preferably used because the amorphous structure is extremely stable and fluctuations in the sheet resistance of the resistive layer can be suppressed even in a high-temperature and high-humidity environment (for example, 50 wt % or more, preferably 70 wt % or more, more preferably 90 wt % or more, and even more preferably 95 wt % or more, and usually less than 100 wt % in the resistive layer).

[0052] <2-1-2. Molybdenum-containing resistive layer> As the resistive layer, a resistive layer containing molybdenum is preferably used from the viewpoints of durability and ease of adjusting resistivity. The lower limit of the molybdenum content is not particularly limited, but from the viewpoint of further improving durability, it is preferably 5 wt %, more preferably 7 wt %, even more preferably 9 wt %, even more preferably 11 wt %, particularly preferably 13 wt %, very preferably 15 wt %, and most preferably 16 wt %. Furthermore, from the viewpoint of ease of adjusting the surface resistivity, the upper limit of the molybdenum content is preferably 30 wt %, more preferably 25 wt %, and even more preferably 20 wt %.

[0053] When the resistive layer contains molybdenum, it is more preferable that it further contains nickel and chromium. By containing nickel and chromium in addition to molybdenum in the resistive layer, a λ / 4 type radio wave absorber with superior durability can be obtained. Examples of alloys containing nickel, chromium, and molybdenum include various grades such as Hastelloy B-2, B-3, C-4, C-2000, C-22, C-276, G-30, N, W, and X.

[0054] When the resistive layer contains molybdenum, nickel, and chromium, the molybdenum content is preferably 5 wt% or more, the nickel content is 40 wt% or more, and the chromium content is 1 wt% or more. By having the molybdenum, nickel, and chromium contents within the above ranges, a λ / 4 type radio wave absorber with superior durability can be obtained. The molybdenum, nickel, and chromium contents are more preferably 7 wt% or more, 45 wt% or more, and 3 wt% or more. The molybdenum, nickel, and chromium contents are even more preferably 9 wt% or more, 47 wt% or more, and 5 wt% or more. The molybdenum, nickel, and chromium contents are even more preferably 11 wt% or more, 50 wt% or more, and 10 wt% or more. The molybdenum, nickel, and chromium contents are particularly preferably 13 wt% or more, 53 wt% or more, and 12 wt% or more. The molybdenum, nickel, and chromium contents are very preferably 15 wt% or more, 55 wt% or more, and 15 wt% or more. The molybdenum, nickel, and chromium contents are most preferably 16 wt% or more, 57 wt% or more, and 16 wt% or more. The nickel content is preferably 80 wt% or less, more preferably 70 wt% or less, and even more preferably 65 wt% or less. The upper limit of the chromium content is preferably 50 wt% or less, more preferably 40 wt% or less, and even more preferably 35 wt% or less.

[0055] The resistive layer may contain metals other than molybdenum, nickel, and chromium. Examples of such metals include iron, cobalt, tungsten, manganese, and titanium. When the resistive layer contains molybdenum, nickel, and chromium, the upper limit of the total content of the metals other than molybdenum, nickel, and chromium is preferably 45% by weight, more preferably 40% by weight, even more preferably 35% by weight, even more preferably 30% by weight, particularly preferably 25% by weight, and very preferably 23% by weight, from the viewpoint of durability of the resistive layer. The lower limit of the total content of the metals other than molybdenum, nickel, and chromium is, for example, 1% by weight or more.

[0056] When the resistive layer contains iron, from the viewpoint of durability of the resistive layer, the upper limit of the content is preferably 25 wt%, more preferably 20 wt%, even more preferably 15 wt%, and the lower limit is preferably 1 wt%. When the resistive layer contains cobalt and / or manganese, from the viewpoint of durability of the resistive layer, the upper limit of the content is preferably 5 wt%, more preferably 4 wt%, even more preferably 3 wt%, and the lower limit is preferably 0.1 wt%. When the resistive layer contains tungsten, from the viewpoint of durability of the resistive layer, the upper limit of the content is preferably 8 wt%, more preferably 6 wt%, even more preferably 4 wt%, and the lower limit is preferably 1 wt%.

[0057] The resistive layer may contain silicon and / or carbon. When the resistive layer contains silicon and / or carbon, the content of each of the silicon and / or carbon is preferably 1% by weight or less, and more preferably 0.5% by weight or less. When the resistive layer contains silicon and / or carbon, the content of each of the silicon and / or carbon is preferably 0.01% by weight or more.

[0058] <2-3. 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. The dielectric layer is not particularly limited, but examples thereof include a resin sheet, an adhesive, and the like.

[0059] The resin sheet is not particularly limited as long as it is a sheet-like material containing a resin. The resin sheet may contain components other than resin as long as the effects of the present invention are not significantly impaired. In this case, the total amount of 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 even more preferably 95% by mass or more, and is usually less than 100% by mass.

[0060] The resin is not particularly limited, and examples of suitable resin components include synthetic resins such as ethylene vinyl acetate copolymer (EVA), vinyl chloride, urethane, acrylic, acrylic urethane, polyolefin, polyethylene, polypropylene, silicone, polyethylene terephthalate, polyester, polystyrene, polyimide, polycarbonate, polyamide, polysulfone, polyethersulfone, and epoxy, as well as synthetic rubber materials 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 may be used alone or in combination of two or more.

[0061] The dielectric layer may be a resin sheet, a foam, or an adhesive. From the viewpoint of thickness accuracy of the dielectric layer, a resin sheet or an adhesive is preferable.

[0062] 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 becomes a "dielectric layer." From the viewpoint of facilitating lamination with an adjacent layer, the dielectric layer preferably includes an adhesive layer.

[0063] The relative dielectric constant of the dielectric layer is not particularly limited and may be, for example, 1 or more and 20 or less, preferably 1 or more and 15 or less, and more preferably 1 or more and 10 or less.

[0064] The relative permittivity of the dielectric layer can be measured at 10 GHz by a cavity resonator perturbation method using a network analyzer, a cavity resonator, or the like.

[0065] The thickness of the dielectric layer is not particularly limited and is, for example, from 10 μm to 2000 μm, preferably from 100 μm to 1500 μm, and more preferably from 200 μm to 800 μm.

[0066] The thickness of the dielectric layer can be measured by Nikon DIGIMICRO STANDMS-11C + Nikon DIGIMICRO MFC-101.

[0067] The layer structure of the dielectric layer is not particularly limited. The dielectric layer may be composed of a single type of dielectric layer, or may be a combination of two or more types of dielectric layers. Examples include a three-layer dielectric layer composed of a non-adhesive dielectric and adhesive layers disposed on both sides of the non-adhesive dielectric layer, a single-layer dielectric layer composed of an adhesive dielectric layer, and a dielectric layer composed of multiple layers in which two or more adhesive dielectric layers are laminated.

[0068] <2-4. Reflective layer> The reflective layer is not particularly limited as long as it can function as a reflective layer for the radio wave absorber. The reflective layer is not particularly limited, but examples thereof include a metal film.

[0069] 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 metal as long as the radio wave absorption performance is not significantly impaired. In this 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, even more preferably 80% by mass or more, still more preferably 90% by mass or more, particularly preferably 95% by mass or more, and very preferably 99% by mass or more, and usually less than 100% by mass.

[0070] The metal is not particularly limited, and examples thereof include aluminum, copper, iron, silver, gold, chromium, nickel, molybdenum, gallium, zinc, tin, niobium, and indium. Metal compounds such as ITO can also be used as the material for the metal film. These may be used alone or in combination of two or more.

[0071] The thickness of the reflective layer is not particularly limited and is, for example, from 1 μm to 500 μm, preferably from 2 μm to 200 μm, and more preferably from 5 μm to 100 μm.

[0072] The layer structure of the reflective layer is not particularly limited, and may be composed of a single reflective layer or a combination of two or more reflective layers.

[0073] <2-5. Adhesive layer> The adhesive layer is a layer for attaching the radio wave absorbing sheet of the present invention to another member (the surface of the waveguide antenna in the present invention). In addition, by appropriately adjusting the adhesiveness of the adhesive layer, a predetermined peel strength can be obtained.

[0074] The adhesive layer usually contains a pressure-sensitive adhesive, and the pressure-sensitive adhesive is not particularly limited, and examples thereof include acrylic pressure-sensitive adhesives, urethane pressure-sensitive adhesives, polyolefin pressure-sensitive adhesives, polyester pressure-sensitive adhesives, vinyl alkyl ether pressure-sensitive adhesives, polyamide pressure-sensitive adhesives, rubber pressure-sensitive adhesives, silicone pressure-sensitive adhesives, and fluorine-based pressure-sensitive adhesives.

[0075] The thickness of the adhesive layer is not particularly limited and is, for example, from 5 μm to 500 μm, preferably from 10 μm to 300 μm, and more preferably from 30 μm to 150 μm.

[0076] The layer configuration of the adhesive layer is not particularly limited. The adhesive layer may be composed of a single adhesive layer, or may be a combination of two or more adhesive layers.

[0077] <2-6. Layer structure, other layers> In the radio wave absorbing sheet of the present invention, the layers are arranged in the order that allows them to exhibit radio wave absorbing performance as described above.

[0078] The radio wave absorbing sheet of the present invention may contain other layers in addition to the above-mentioned layers. The other layers may be disposed on one surface of the support, the resistive layer, the dielectric layer, or the reflective layer.

[0079] From the viewpoint of durability, the wave absorber of the present invention preferably further comprises a barrier layer on at least one surface of the resistive layer. The barrier layer will be described in detail below.

[0080] <2-6-1. Barrier layer> The barrier layer is not particularly limited as long as it can protect the resistance layer and prevent its deterioration. Examples of materials for the barrier layer include metal compounds, semimetal compounds, and preferably metal or semimetal oxides, nitrides, and nitride oxides. 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 such cases, the amount of the above materials 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, and even more preferably 99% by mass or more, and typically less than 100% by mass.

[0081] Examples of metals include titanium, aluminum, niobium, cobalt, nickel, etc. Examples of metalloids include silicon, germanium, antimony, bismuth, etc.

[0082] Examples of the oxides include MO X [wherein X is a number that satisfies the formula: n / 100≦X≦n / 2 (n is the valence of the metal), and M is a metal element.]

[0083] Examples of the nitride include MN y [wherein Y is a number that satisfies the formula: n / 100≦Y≦n / 3 (n is the valence of the metal), and M is a metal element.]

[0084] Examples of the above nitride oxide include, for example, MO X N y [In the formula, X and Y satisfy n / 100 ≤ X, n / 100 ≤ Y, and X + Y < n / 2 (where n is the valence of the metal), and M is a metal element.] Compounds represented thereby are exemplified.

[0085] Regarding the oxidation number X of the above oxide or nitride oxide, for example, for a layer containing MO x or MO x N y perform elemental analysis on the cross-section of the layer by FE-TEM-EDX (for example, "JEM-ARM200F" manufactured by JEOL Ltd.), and calculate X from the elemental ratio of M and O per unit area of the cross-section of the layer containing MO x or MO x N y Thereby, the valence of the oxygen atom can be calculated.

[0086] Regarding the nitrogenation number Y of the above nitride or nitride oxide, for example, for a layer containing MN y or MO x N y perform elemental analysis on the cross-section of the layer by FE-TEM-EDX (for example, "JEM-ARM200F" manufactured by JEOL Ltd.), and calculate Y from the elemental ratio of M and N per unit area of the cross-section of the layer containing MN y or MO x N y Thereby, the valence of the nitrogen atom can be calculated.

[0087] Specific examples of the material of the barrier layer include SiO2, SiO x , Al2O3, MgAl2O4, CuO, CuN, TiO2, TiN, AZO (aluminum-doped zinc oxide), and the like.

[0088] The thickness of the barrier layer is not particularly limited. The thickness of the barrier layer is, for example, 1 nm or more and 200 nm or less, preferably 1 nm or more and 100 nm or less, more preferably 1 nm or more and 20 nm or less.

[0089] The layer structure of the barrier layer is not particularly limited, and may be composed of a single type of barrier layer or a combination of two or more types of barrier layers.

[0090] <3. Manufacturing method> The radio wave absorbing sheet of the present invention can be obtained, for example, by a method including the steps of laminating a resistive layer, a dielectric layer, a reflective layer, and an adhesive layer in this order on a support. Alternatively, it can be obtained by a method including the steps of laminating or forming a resistive layer on one surface of a dielectric layer, laminating a support on the surface of the resistive layer opposite to the surface that contacts the dielectric layer, and laminating a reflective layer and an adhesive layer in this order on the surface of the dielectric layer opposite to the surface that contacts the resistive layer.

[0091] The lamination method is not particularly limited. The resistive layer and the barrier layer can be formed by, for example, sputtering, vacuum deposition, ion plating, chemical vapor deposition, pulsed laser deposition, etc. Among these, sputtering is preferred from the viewpoint of film thickness controllability. The sputtering method is not particularly limited, but examples thereof include direct current magnetron sputtering, radio frequency magnetron sputtering, and ion beam sputtering. The sputtering device may be a batch type or a roll-to-roll type.

[0092] The dielectric layer and the reflective layer can be laminated by utilizing the adhesiveness of the dielectric layer, for example.

[0093] <4. Radio wave absorbing sheet materials> In one aspect, the present invention relates to a member for a radio wave absorbing sheet (the member for a radio wave absorbing sheet of the present invention), which comprises a resistive layer and an adhesive dielectric layer, has an opening for an antenna slot, and has a peel strength of 15 N / 25 mm or more, as measured by attaching the member to a SUS plate, pulling the member for 60 mm or more at a peel angle of 90 degrees, a pulling rate of 300 mm / min, and recording the average value (N / 25 mm) of the load (N) detected by a load cell in an environment of 25°C and 50% RH.

[0094] The radio wave absorbing sheet member of the present invention preferably further includes a support. The radio wave absorbing sheet member of the present invention is a member for forming a radio wave absorbing sheet / radio wave absorber by placing it in contact with an adherend that can function as a reflective layer. The support, resistive film, dielectric layer, and other configurations, shapes, characteristics, etc. are the same as those described for the radio wave absorbing sheet of the present invention. By appropriately adjusting the adhesiveness of the dielectric layer, a predetermined peel strength can be obtained.

[0095] <5.Applications> The radio wave absorbing sheet of the present invention and the radio wave absorbing sheet member of the present invention are disposed on a waveguide antenna. The waveguide antenna is not particularly limited as long as it has an antenna slot, and known configurations can be used. An example of a waveguide antenna is shown in FIG. 4. The waveguide antenna 20 includes a radiation layer 22 having an antenna slot and a distribution layer 23. A waveguide antenna generally comprises a rectangular waveguide having multiple slots arranged linearly along the broadside wall of the waveguide. This broadside can be seen as the radiation layer 22, and the remaining portion of the waveguide can be seen as the distribution layer 23. The waveguide antenna can further comprise a printed circuit board (PCB) layer and a shielding layer. These waveguide antenna configurations are known; see, for example, JP-A-2023-531043.

[0096] In one aspect, the present invention relates to a radio wave absorbing sheet of the present invention and a waveguide antenna in which a member for a radio wave absorbing sheet of the present invention is disposed. Specifically, in one aspect, the present invention relates to a waveguide antenna with a radio wave absorbing sheet, comprising a waveguide antenna having an antenna slot and the radio wave absorbing sheet of the present invention, with an opening for an antenna slot in the radio wave absorbing sheet arranged above the antenna slot. In another aspect, the present invention relates to a waveguide antenna with a member for a radio wave absorbing sheet, comprising a waveguide antenna having an antenna slot and the member for a radio wave absorbing sheet of the present invention disposed on the metal surface of the waveguide antenna, with the opening for an antenna slot in the radio wave absorbing sheet arranged above the antenna slot. The radio wave absorbing sheet of the present invention and the member for a radio wave absorbing sheet of the present invention are disposed on the radiation layer side surface of the waveguide antenna.

[0097] The radio wave absorbing sheet of the present invention, the radio wave absorbing sheet / radio wave absorber formed from the radio wave absorbing sheet member of the present invention, and the above-mentioned waveguide antenna of the present invention have the ability to absorb unwanted electromagnetic waves, and therefore can be suitably used, for example, in millimeter-wave radar used in automobile collision prevention systems. They can also be used for other purposes, such as suppressing radio wave interference and reducing noise, in intelligent transport systems (ITS) that communicate information between automobiles, roads, and people, and in next-generation mobile communication systems (5G) that use millimeter waves.

[0098] The radio wave frequency that the radio wave absorbing sheet of the present invention and the radio wave absorbing sheet / radio wave absorber formed from the radio wave absorbing sheet member of the present invention are subject to is, for example, 20 GHz or more and 100 GHz or less, and preferably 50 GHz or more and 90 GHz or less. [Example]

[0099] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples.

[0100] (1) Manufacturing and preparation of electromagnetic wave absorbing sheets The electromagnetic wave absorbing sheet was manufactured and prepared as follows.

[0101] Example 1 A polyethylene terephthalate (PET) film (thickness: 125 μm, relative dielectric constant: 3.4) was prepared as a support. A resistive layer film (barrier layer 1 / resistive layer / barrier layer 2) with a resistance value of 320 Ω / □ was formed on the PET film as follows: First, a Si layer (barrier layer 1: thickness: 10 nm) was formed by DC pulse sputtering. Next, a resistive layer was formed on barrier layer 1 by DC pulse sputtering. The sputtering target used was Hastelloy C-276 (composition: 16.4 wt% molybdenum, 55.2 wt% nickel, 18.9 wt% chromium, 5.5 wt% iron, 3.5 wt% tungsten, and 0.5 wt% silica). Finally, a Si layer (barrier layer 2, thickness: 15 nm) was formed in the same manner as barrier layer 1. Next, multiple sheets of acrylic adhesive tape (UL-94 VTM-0, dielectric constant 3.7) were laminated onto the formed resistive film to a total thickness of 465 μm, and then a reflective layer made of an aluminum foil / PET composite film (Alpet (registered trademark)) with a thickness of 65 μm was laminated thereon, and then an acrylic adhesive tape (3M 9485PC, thickness 127 μm) was laminated as an adhesive layer to obtain a radio wave absorbing sheet.

[0102] Example 2 As in Example 1, a resistive layer and a barrier layer were formed on a PET film, and a piece of 465 μm thick acrylic adhesive tape (UL-94 HB or higher, dielectric constant 3.7) was laminated on the resistive film thus formed. Then, as in Example 1, a reflective layer and an adhesive layer were laminated to obtain a radio wave absorbing sheet.

[0103] Example 3 As in Example 1, a resistive layer and a barrier layer were formed on a PET film, and multiple sheets of acrylic adhesive tape (UL-94 VTM-0, dielectric constant 3.7) were laminated on the resistive film to a total thickness of 465 μm to obtain a radio wave absorbing sheet.

[0104] Example 4 50 μm thick electromagnetic wave absorbing sheet (Laird Eccosorb TMAn acrylic adhesive tape (3M 9485PC 127 μm) was laminated on the MMI to obtain an electromagnetic wave absorbing sheet.

[0105] Example 5 The layers up to the reflective layer were laminated in the same manner as in Example 1, and a flame-retardant tape (155 μm) was attached as an adhesive layer to obtain a radio wave absorbing sheet.

[0106] (Comparative Example 1) The layers up to the reflective layer were laminated in the same manner as in Example 1, and the strong adhesive surface of an acrylic adhesive tape (Teraoka Seisakusho No. 7692 12 μm) was attached as an adhesive layer to obtain a radio wave absorbing sheet.

[0107] (Comparative Example 2) In the same manner as in Example 1, layers up to the reflective layer were laminated to obtain an electromagnetic wave absorbing sheet.

[0108] (Comparative Example 3) The wave absorber was obtained by injection molding Laird's ReZorb JCP-PP9 to a size of 2.5 x 15 cm or 10 x 10 cm and a thickness of 3 mm.

[0109] (2) Evaluation (2-1) Vibration test Vibration tests were conducted as follows. The absorbent material prepared for the peel test was fixed to a SUS plate (0.5 mm thick, SUS304BA) via an adhesive layer in accordance with JIS, and then fixed to a PPS plate (5 mm thick) via adhesive tape. In Comparative Examples 2 and 3, the SUS and PPS plates (3 mm) were fixed by caulking. Samples for absorption measurement were prepared under the same conditions as for the peel test, except that the sample size was 10 x 10 cm. Tests were conducted in accordance with ISO 16750-3 (2012) Test 4 - Sprung Masses (Vehicle Body) at Tmax = 125 °C using a vibration tester (IMV A30 / EM3HM), a thermostatic chamber (IMV Syn-3HW-70-VH), and an acceleration sensor (IMV VP-32 (9132U)). The test was conducted in three directions, changing the mounting surface, for 8 hours each. Each sample was fixed to a PPS plate with screws in two or four holes.

[0110] After the vibration test, the sample was left standing at a 90 degree angle for 1 hour, and the deviation from the pre-marked position of the radio wave absorbing sheet on the SUS plate was measured using a vernier caliper, and evaluated according to the following evaluation criteria. ○:0mm △: More than 0mm but less than 3mm ×: More than 3mm.

[0111] (2-2) Peel strength measurement The peel strength of the radio wave absorbing sheets of the examples and comparative examples was measured before and after the vibration test in (2-1) above.

[0112] Peel strength was measured as follows. The electromagnetic wave absorbing sheet was cut into a strip measuring 25 mm wide and 150 mm long to prepare a test specimen. The dielectric layer of the test specimen was then bonded to a stainless steel plate to prepare the measurement sample. The specimen was bonded to the stainless steel plate by rolling a 2 kg roller back and forth twice at a speed of 10 ± 0.5 mm / s. After bonding, the specimen was left in an environment of 25°C and 50% RH for 24 hours. One end of the specimen was then fixed in the chuck of a tensile testing machine (A&D Corporation's "Tensilon Universal Material Testing Machine"). The specimen was then pulled for 60 mm or more at a peel angle of 90° and a tensile speed of 300 mm / min under an environment of 25°C and 50% RH. The average load (N / 25 mm) detected by the load cell was recorded. Similar measurements were performed three times, and the average of the three points was used as the peel strength.

[0113] (2-3) Return loss measurement The return loss of the radio wave absorbing sheets of the examples and comparative examples was measured before and after the vibration test in (2-1) above.

[0114] The return loss was measured as follows. A radio wave absorption measurement device was constructed using a PNA microwave network analyzer N5227A (Keysight), a PNA-X Series 2-port millimeter-wave controller N5261A (Keysight), and a horn antenna FSS-07 (HVS). Using this radio wave absorption measurement device, the return loss of the radio wave absorbing sheets obtained in the examples and comparative examples at frequencies between 55 GHz and 90 GHz was measured in accordance with JIS R1679. The radio wave absorbing sheets were set so that the radio wave incidence direction was vertical and incident from the support side. The minimum return loss values ​​for vertically incident radio waves in the 55-90 GHz range were calculated before and after the vibration test, and the electromagnetic wave absorption performance was evaluated based on the minimum return loss value after the vibration test according to the following evaluation criteria. ◎: Less than -15dB. ○: -15dB or more and less than -7dB. △: -7dB or more and less than -3dB. ×: -3dB or more.

[0115] (3) Results The results are shown in Table 1.

[0116] [Table 1] [Explanation of symbols]

[0117] 10. Radio wave absorbing sheet 11 Antenna slot opening 12 resistance layer 13 Dielectric layer 14 Reflective layer 15 Adhesive layer 20 Waveguide antenna 21 Antenna slot 22 Radiation Layer 23 Distribution layer

Claims

1. having an opening for an antenna slot, After being bonded to a stainless steel plate, the film is pulled for 60 mm or more at a peel angle of 90° and a pulling speed of 300 mm / min under an environment of 25°C and 50% RH, and the average value (N / 25 mm) of the load (N) detected by the load cell is recorded. The peel strength is 15 N / 25 mm or more. Radio wave absorbing sheet.

2. 2. The radio wave absorbing sheet according to claim 1, which is a λ / 4 type radio wave absorbing sheet having a resistive layer, a dielectric layer, a reflective layer and an adhesive layer in this order.

3. 3. The radio wave absorbing sheet according to claim 2, wherein the antenna slot opening is an opening that penetrates through the resistive layer, the dielectric layer, the reflective layer, and the adhesive layer in a stacking direction.

4. 4. The radio wave absorbing sheet according to claim 3, comprising a support, the support, the resistive layer, the dielectric layer, the reflective layer, and the adhesive layer being laminated in this order, and the opening for the antenna slot is an opening that penetrates through the support, the resistive layer, the dielectric layer, the reflective layer, and the adhesive layer in the stacking direction.

5. 3. The radio wave absorbing sheet according to claim 2, wherein the minimum value of the return loss for vertically incident radio waves of 55 to 90 GHz is −15 dB or less, and the value represented by formula 1: |(minimum value of return loss for vertically incident radio waves of 55 to 90 GHz before vibration test (ISO 16750-3 (2012) Test 4 - spring masses (vehicle body))) − (minimum value of return loss for vertically incident radio waves of 55 to 90 GHz after vibration test (ISO 16750-3 (2012) Test 4 - spring masses (vehicle body))) | is 5 dB or less.

6. 2. The radio wave absorbing sheet according to claim 1, wherein the peel strength after a vibration test (ISO 16750-3 (2012) Test 4 - spring masses (vehicle body)) is 15 N / 25 mm or more.

7. A waveguide antenna with a radio wave absorbing sheet, comprising: a waveguide antenna having an antenna slot; and the radio wave absorbing sheet according to any one of claims 1 to 6, wherein an opening for an antenna slot of the radio wave absorbing sheet is arranged above the antenna slot.

8. a resistive layer and an adhesive dielectric layer; having an opening for an antenna slot, After being bonded to a stainless steel plate, the film is pulled for 60 mm or more at a peel angle of 90° and a pulling speed of 300 mm / min under an environment of 25°C and 50% RH, and the average value (N / 25 mm) of the load (N) detected by the load cell is recorded. The peel strength is 15 N / 25 mm or more. Components for radio wave absorbing sheets.

9. A waveguide antenna with a member for a radio wave absorbing sheet, comprising: a waveguide antenna having an antenna slot; and the member for a radio wave absorbing sheet according to claim 8, which is disposed on a metal surface of the waveguide antenna, and an opening for an antenna slot of the radio wave absorbing sheet is disposed above the antenna slot.

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