Radio wave antireflection sheet, belt, and vehicle member

Abstract

A radio wave anti-reflection sheet having a first major surface that is substantially non-tacky and an opposing second major surface that is substantially tacky, and comprising a first polymeric foam layer disposed between the first and second major surfaces, and a second polymeric foam layer disposed between the second major surface and the first polymeric foam layer. The first polymeric foam has a thickness of 0.05 mm to 3.0 mm and a density of 0.20 g / cm 3 to 0.90 g / cm 3 . The second polymeric foam layer has a thickness of 0.05 mm to 3.0 mm and a density greater than 0.10 g / cm 3 and less than the density of the first polymeric foam layer. A tape includes the radio wave anti-reflection sheet disposed on a release liner. A vehicle component includes a multi-layered substrate and the radio wave anti-reflection sheet disposed on the multi-layered substrate.

Description

Background Technology

[0001] Efforts are underway to equip cars with radar devices to improve vehicle safety and further advance the practical application of autonomous driving. Summary of the Invention

[0002] This invention relates to radio wave antireflective sheets, strips including radio wave antireflective sheets, and vehicle components including radio wave antireflective sheets. The radio wave antireflective sheets can be configured to reduce the reflection of radio waves from a multilayer substrate and can include a higher-density foam layer and a lower-density foam layer, wherein the lower-density foam layer is configured to face the substrate. For example, the lower-density foam layer may have an adhesive surface for bonding to the substrate, or an adhesive layer may be disposed on the lower-density foam layer for bonding to the substrate.

[0003] In some aspects, this specification provides a radio wave antireflective sheet comprising a substantially non-adhesive first main surface and an opposing substantially adhesive second main surface; a first polymer foam layer disposed between the first main surface and the second main surface, wherein the first polymer foam layer has a thickness of 0.05 mm to 3.0 mm and a density of 0.20 g / cm³. 3 Up to 0.90 g / cm 3 ; and a second polymer foam layer disposed between the second main surface and the first polymer foam layer, wherein the thickness of the second polymer foam layer is 0.05 mm to 3.0 mm and the density is greater than 0.10 g / cm³. 3 And less than the density of the first polymer foam layer. The strip may include a radio wave antireflective sheet disposed on the release surface of the release liner. The vehicle component may include a multi-layer body portion including a first layer disposed between a second layer and a third layer, wherein the first layer has a lower density than each of the second layer and the third layer; and a radio wave antireflective sheet, the second main surface of which is disposed on and bonded to the outermost main surface of the multi-layer body portion.

[0004] These and other aspects will become apparent from the detailed description that follows. However, in no way should this brief overview be construed as limiting the subject matter for which protection may be claimed. Attached Figure Description

[0005] Figures 1A to 1B This is a schematic cross-sectional view of a radio wave antireflector according to some implementation schemes.

[0006] Figure 2 This is a schematic cross-sectional view of a radio wave antireflective sheet including an adhesive layer, according to some embodiments.

[0007] Figures 3A to 3B This is a schematic cross-sectional view of a radio wave antireflective sheet including an adhesive layer and a protective layer according to some embodiments.

[0008] Figure 3C According to some implementation schemes, this includes being installed on the peeling liner. Figure 3A A schematic cross-sectional view of the strip material of a radio wave antireflective sheet.

[0009] Figures 4A to 4B It is a schematic cross-sectional view of a radio wave antireflective sheet comprising at least three foam layers according to some embodiments.

[0010] Figure 5A This is a schematic graph showing the density of the foam layer of a radio wave antireflective sheet according to some embodiments.

[0011] Figure 5B This is a schematic graph showing the relative permittivity of the foam layer of a radio wave antireflective sheet according to some embodiments.

[0012] Figures 6A to 6B This is a schematic cross-sectional view of a vehicle component including a radio wave anti-reflective sheet according to some implementation schemes.

[0013] Figure 7A It is a schematic cross-sectional view of radiation incident on an exemplary metal surface.

[0014] Figure 7B It is a schematic cross-sectional view of radiation incident on an exemplary vehicle component excluding radio wave antireflectors.

[0015] Figure 8 It is a graph showing the reflection frequency of a 3-layer substrate with and without various radio wave anti-reflection sheets disposed on the 3-layer substrate. Detailed Implementation

[0016] Reference is made in the following description to the accompanying drawings, which form part of the invention and illustrate various embodiments by way of example. The drawings are not necessarily drawn to scale. It should be understood that other embodiments may be conceived and practiced without departing from the scope or spirit of this specification. Therefore, the following detailed description should not be considered limiting.

[0017] It is generally desirable for radar devices installed in automobiles to detect not only four-wheeled vehicles and large commercial vehicles in the surrounding area, but also pedestrians and small vehicles such as two-wheeled vehicles. However, reflected waves from people and small vehicles are typically weak, and therefore radar devices are susceptible to noise interference when detecting these targets. In particular, when a radar device is placed inside a cover member (e.g., part of the main body of a vehicle component, which may include a housing for mounting the radar device), it is often difficult to detect people and the like with high precision due to waves reflected by the cover member. Therefore, in order to use a radar device located inside the cover member to detect weak reflected waves from people and the like with high precision, it is desirable to suppress reflected waves from the cover member.

[0018] Traditionally, double-layer antireflective sheets for reducing reflections from a substrate comprise a higher-density layer facing the substrate and a lower-density layer facing away from the substrate, wherein the density of the higher-density layer is less than the density of the substrate, and the density of the lower-density layer is greater than the density of air. However, it has been found that for multilayer substrates comprising a lower-density (and / or lower-dielectric-constant) layer between two higher-density (and / or higher-dielectric-constant) layers, such double-layer antireflective sheets have limited effectiveness due to additional reflections at the interfaces between the lower-density and higher-density layers of the multilayer substrate. Such multilayer substrates can be used in the body portion of vehicle components that may include a housing for a radar device. According to some embodiments of this specification, it has been found that radio wave antireflective sheets using a lower-density layer facing the substrate and a higher-density layer facing away from the substrate can effectively reduce reflections from multilayer substrates. In some embodiments, the radio wave antireflective sheet generates reflections at various interfaces (e.g., between layers of the sheet, between the sheet and the multilayer substrate, and / or between air and the sheet), which, combined with reflections from the various interfaces of the multilayer substrate, result in low reflections due to destructive interference. In some implementations, radio wave antireflectors significantly reduce reflected waves from multilayer substrates in desired regions of the E-band frequency band, from approximately 60 GHz to 90 GHz.

[0019] Figure 1AThis is a schematic cross-sectional view of a radio wave antireflective sheet 101 having a substantially non-adhesive first main surface S1 and a relatively substantially adhesive second main surface S2, according to some embodiments. The surface is substantially adhesive when the adhesion at room temperature is sufficient to bond the radio wave antireflective sheet to the polymer substrate with sufficient strength such that the adhesion can at least support the weight of the radio wave antireflective sheet (e.g., when vertically oriented or with the radio wave antireflective sheet facing down). The surface is substantially non-adhesive when the adhesion at room temperature is weak enough that the weight of the radio wave antireflective sheet allows it to be easily separated from the polymer substrate (e.g., when the sheet is vertically oriented or with the radio wave antireflective sheet facing down). The term "room temperature" has its conventional meaning and refers to a temperature of 20°C–25°C. The substantially adhesive second main surface S2 is adapted to be bonded to the substrate, while the second layer S1 faces away from the substrate.

[0020] Sheet 101 includes a first polymer foam layer 11 disposed between a first main surface and a second main surface, and the first polymer foam layer has a thickness of 0.05 mm to 3.0 mm and a density of 0.20 g / cm³. 3 Up to 0.90 g / cm 3 ; and a second polymer foam layer 12, which is disposed between the second main surface and the first polymer foam layer 11, and the second polymer foam layer has a thickness of 0.05 mm to 3.0 mm and a density greater than 0.10 g / cm³. 3 And the density is less than that of the first polymer foam layer 11. In some embodiments, the difference between the density of the first polymer foam layer 11 and the density of the second polymer foam layer 12 is, for example, greater than 0.05 g / cm³. 3 or greater than 0.08 g / cm 3 or greater than 0.1 g / cm 3 More generally, the density difference between adjacent polymer foam layers in a radio wave antireflector can be within any of these ranges. The densities (and / or relative permittivity) of the first polymer foam layer 11 and the second polymer foam layer 12 can be selected to result in low or minimal reflection from the radio wave antireflector for predetermined frequencies in the E-band frequency range, for example, when disposed on a multilayer substrate as further described elsewhere herein. In some embodiments, the density of the first polymer foam layer 11 is, for example, 0.40 g / cm³. 3 Up to 0.90 g / cm 3 or 0.50g / cm 3 Up to 0.90 g / cm 3 or 0.60g / cm 3 Up to 0.90 g / cm 3 or 0.70g / cm 3Up to 0.85 g / cm 3 In some such embodiments, or in others, the density of the second polymer foam layer 12 is, for example, 0.10 g / cm³. 3 Up to 0.85 g / cm 3 or 0.20g / cm 3 Up to 0.80 g / cm 3 or 0.30g / cm 3 Up to 0.80 g / cm 3 or 0.40 g / cm 3 Up to 0.80 g / cm 3 or 0.40g / cm 3 Up to 0.70 g / cm 3 or 0.50g / cm 3 Up to 0.70 g / cm 3 In some embodiments, the density of each polymer foam layer in the radio wave antireflective sheet is, for example, 0.30 g / cm³. 3 Up to 0.90 g / cm 3 Or 0.50g / cm 3 Up to 0.85 g / cm 3 Within the range.

[0021] The thicknesses of the first polymer foam layer 11 and the second polymer foam layer 12 can also be selected to result in low or minimal reflection from the radio wave antireflector at predetermined frequencies in the E-band frequency range, for example, when disposed on a multilayer substrate as further described elsewhere herein. In some embodiments, the thickness of at least one of the first polymer foam layer 11 and the second polymer foam layer 12 is at least 0.10 mm, or at least 0.20 mm, or at least 0.30 mm, or at least 0.40 mm, or at least 0.50 mm, and this thickness may, for example, not exceed 2.00 mm, or not exceed 1.50 mm, or not exceed 1.00 mm, or not exceed 0.90 mm. In some embodiments, the thickness of each of the first polymer foam layer 11 and the second polymer foam layer 12 is within at least one of these ranges. In some embodiments, each polymer foam layer of the radio wave antireflector has a thickness within at least one of these ranges.

[0022] The thickness and density of the polymer foam layer used to reduce reflections from a predetermined multilayer substrate at a predetermined wavelength can be determined as follows. When a radio wave antireflection sheet is disposed on a predetermined multilayer substrate, conventional modeling techniques can be used to calculate the reflection of radio waves at a predetermined frequency from the radio wave antireflection sheet as a function of the relative permittivity and thickness of the polymer foam layer of the radio wave antireflection sheet. This allows for the establishment of the desired relative permittivity and thickness of the polymer foam layer that results in low or minimal reflection. The relationship between the relative permittivity and density can be established by measuring the relative permittivity of a polymer foam layer with a certain density range at a predetermined frequency. Based on the calculated desired relative permittivity and the relationship between the relative permittivity and density, the desired density of the polymer foam layer can be determined.

[0023] The polymer foam layer is typically a foam layer comprising a continuous polymer phase. In some embodiments, the first polymer foam layer 11 and the second polymer foam layer 12 comprise respective cells 112 and 122 dispersed in respective polymer matrices 111 and 121. Figure 1B This is a schematic cross-sectional view of a radio wave antireflective sheet 101 according to some embodiments, schematically showing the pores. As further described elsewhere herein, pores 112 and / or 122 can be bubbles, hollow particles, or combinations thereof. Hollow particles can be, for example, hollow microspheres and / or expanded microspheres. For example, polymer matrices 111 and 121 can be (meth)acrylate matrices. For example, in some embodiments, a second polymer foam layer 12 (and optionally a first polymer foam layer 11) comprises a (meth)acrylate matrix; and bubbles, hollow particles, or combinations thereof dispersed in the matrix. In some such embodiments, the second polymer foam layer (and optionally the first polymer foam layer 11) comprises hollow particles dispersed in the matrix, wherein the hollow particles are or comprise hollow (e.g., glass or polymer) microspheres. The densities ρ1 and ρ2 of the respective first polymer foam layer 11 and second polymer foam layer 12 are schematically shown. Since the volume of the pores in layer 12 is greater than the volume of the pores in layer 11, density ρ2 can be less than density ρ1. Similarly, the relative permittivity ε1 and ε2 of the corresponding first polymer foam layer 11 and second polymer foam layer 12 are schematically shown. Since the volume of the pores in layer 12 is larger than that in layer 11, the relative permittivity ε2 can be smaller than the relative permittivity ε1.

[0024] In some embodiments, for at least one frequency in the range of 60 GHz to 90 GHz, the relative permittivity of the first polymer foam layer 11 is 1.2 to 4.0, or 1.5 to 3.0, or 1.8 to 2.5, and the relative permittivity of the second polymer foam layer 12 is greater than 1.1 and less than the relative permittivity of the first polymer foam layer. In some embodiments, for at least one frequency in the range of 60 GHz to 90 GHz, the relative permittivity of the second polymer foam layer 12 is 1.1 to 3.0, or 1.4 to 2.5, or 1.6 to 2.1. In some embodiments, the difference between the relative permittivity of the first polymer foam layer 11 and the second polymer foam layer 12 is, for example, greater than 0.05, or greater than 0.1, or greater than 0.15, or greater than 0.2. More generally, the difference between the relative permittivity of adjacent polymer foam layers in a radio wave antireflective sheet can be within any of these ranges. The relative permittivity of the first polymer foam layer 11 and the second polymer foam layer 12 can be selected, for example, when disposed on a multilayer substrate as further described elsewhere herein, to result in low or minimal reflection from the radio wave antireflector at predetermined frequencies in the E-band frequency range.

[0025] In some embodiments, the polymer of polymer matrix 121 may be formulated as a pressure-sensitive adhesive (e.g., a (meth)acrylate pressure-sensitive adhesive), while the polymer of polymer matrix 111 may be formulated as a non-adhesive (e.g., a non-sticky polymer at room temperature). In some embodiments, the polymer of polymer matrix 121 is not an adhesive and includes an additional adhesive layer to provide a substantially tacky second primary surface S2. In some embodiments, the polymer of polymer matrix 111 may be formulated as a pressure-sensitive adhesive and includes a non-tacky layer (e.g., a protective layer) to provide a substantially non-tacky first primary surface S1.

[0026] In some embodiments, the second polymer foam layer 12 includes a second primary surface S2. In other embodiments, an additional adhesive layer is included, which includes the second primary surface S2. Figure 2This is a schematic cross-sectional view of a radio wave antireflective sheet 102, which may correspond to a radio wave antireflective sheet 101, but also includes an adhesive layer 20 (e.g., pressure-sensitive) disposed on a second polymer foam layer 12 and including a second main surface S2. The adhesive layer 20 can be used to attach the radio wave antireflective sheet to a substrate surface, such as a body portion of a vehicle. Any suitable adhesive, such as a pressure-sensitive adhesive or a curable adhesive, can be used. Suitable pressure-sensitive adhesives include, for example, pressure-sensitive adhesives based on (meth)acrylates. Other examples of suitable pressure-sensitive adhesives include silicone pressure-sensitive adhesives. Examples of curable adhesives include photochemical radiation (e.g., ultraviolet) curable adhesives and thermosetting adhesives. In some embodiments, the thickness of the adhesive layer 20 is, for example, at least 2 μm, or at least 5 μm, or at least 10 μm. In some such embodiments, or in other embodiments, the thickness of the adhesive layer 20 is, for example, no more than 200 μm, or no more than 100 μm, or no more than 50 μm. The thickness of the adhesive layer 20 can be small compared to the thickness of the polymer foam layer of the radio wave antireflection sheet, so that the adhesive layer 20 has a small or negligible effect on reducing radio wave reflection. In some embodiments, the thickness of the adhesive layer 20 is less than 0.2 times, 0.1 times, or 0.075 times the thickness of the second polymer foam layer 12.

[0027] In some embodiments, the first polymer foam layer 11 includes a first main surface S1. In other embodiments, an additional layer is disposed on the first polymer foam layer 11 and includes the first main surface S1. Figure 3A This is a schematic cross-sectional view of a radio wave antireflective sheet 103 including a protective layer 30 disposed on a first polymer foam layer 11 and including a first main surface S1. The material forming the protective layer 30 is not particularly limited, but can be a material that is non-adhesive at room temperature and exhibits a high level of adhesion to the first polymer layer 11. For example, the protective layer 30 can be formed from polymethyl methacrylate (PMMA) resin. The protective layer 30 may contain, for example, a silicone-based or fluoropolymer-based antifouling coating agent. The thickness of the protective layer 30 can be, for example, from 0.1 μm to 50 μm, or from 1 μm to 40 μm. The thickness of the protective layer 30 can be small compared to the thickness of the polymer foam layer of the radio wave antireflective sheet, such that the protective layer 30 has a small or negligible effect on reducing radio wave reflection. In some embodiments, the thickness of the protective layer 30 is less than 0.2 times, 0.1 times, or 0.05 times the thickness of the first polymer foam layer 11. The protective layer 30 can be formed, for example, by a method including coating the first polymer foam layer 11 with various coatings used to form the protective layer.

[0028] Radio wave antireflective sheet may optionally include one or more additional layers. For example, radio wave antireflective sheet may include a light-emitting layer disposed between the first main surface S1 and the second main surface S2 and / or between layers 30 and 20 (e.g., between the first polymer foam layer 11 and the second polymer foam layer 12, or between layers 20 and 12, or between layers 11 and 30). Figure 3B This is a schematic cross-sectional view of a radio wave antireflective sheet 103', which may correspond to the radio wave antireflective sheet 103 except that a light-emitting layer 40 is disposed between the first polymer foam layer 11 and the second polymer foam layer 12. For example, the light-emitting layer may allow the radio wave antireflective sheet to be easily detected from the outside. The light-emitting layer may include a photoluminescent material. The light-emitting layer may be formed, for example, by printing using ink containing a photoluminescent material. The thickness of the light-emitting layer may be set within a range that sufficiently maintains the reflection reduction function. For example, the thickness of the light-emitting layer may be from 1 μm to 20 μm. In some embodiments, the thickness of the light-emitting layer 40 is less than 0.2 times, or 0.1 times, or 0.05 times the thickness of each of the first polymer foam layer 11 and the second polymer foam layer 12.

[0029] Figure 3C This is a schematic cross-sectional view of a strip 103 including a radio wave antireflective sheet 103 disposed on an optional release liner 21. More generally, the strip may include the release liner 21 and any one of the radio wave antireflective sheets described herein, wherein a second primary surface S2 of the radio wave antireflective sheet is disposed on the release surface 22 of the release liner 21. The release liner typically has a release coating, such as a silicone coating or a fluorocarbon coating, to provide a release surface. Various release liners are commercially available.

[0030] Optionally, an additional polymer foam layer may be included to provide an additional interface for reflection, which, when disposed on a multilayer substrate, may further reduce the overall reflection of the radio wave antireflector (e.g., via destructive interference of various reflected radio waves) and / or further increase the frequency range in which the radio wave antireflector's reflection is significantly reduced. Figure 4A This is a schematic cross-sectional view of a radio wave antireflective sheet 104 including a third polymer foam layer 13 according to some embodiments. More generally, the radio wave antireflective sheet includes at least a first polymer foam layer 11 and a second polymer foam layer 12, and may include any number of additional layers. Figure 4B This is a schematic cross-sectional view of a radio wave antireflective sheet 104 comprising a first polymer foam layer 11 and a second polymer foam layer 12, and further comprising a plurality of additional optional polymer foam layers 13-1 to 13-n, according to some embodiments. In some embodiments, the total number of polymer foam layers included in the radio wave antireflective sheet is, for example, 2, 3, 4, or 5.

[0031] Figure 5A This is a schematic graph illustrating the relative density of foam layers comprising up to four layers (layer 1 to layer 4) of a radio wave antireflective sheet according to some embodiments. One two-layer embodiment, three three-layer embodiments, and one four-layer embodiment are shown. For comparison, a conventional two-layer comparative example is also shown. The relative permittivity of the individual layers generally follows the same pattern as the density of the individual layers (e.g., the permittivity of a lower-density foam having the same polymer matrix as the higher-density foam will also generally be lower than that of the higher-density foam). Figure 5B This is a schematic graph showing the relative permittivity of a foam layer comprising up to four layers of radio wave antireflective sheet according to some embodiments. Figure 5B The relative permittivity in the figure can be understood as being evaluated at the same frequency (e.g., in the range of 60 GHz to 90 GHz).

[0032] In some embodiments, the radio wave antireflective sheet includes a third polymer foam layer 13 with a thickness of 0.05 mm to 3.0 mm, wherein a second polymer foam layer 12 is disposed between a first polymer foam layer 11 and a third polymer foam layer 13 (or 13-1). In some embodiments, the density of the third polymer foam layer 13 is greater than the density of the second polymer foam layer 12 but not greater than the density of the first polymer foam layer 11. In some embodiments, the density of the third polymer foam layer is greater than the density of the first polymer foam layer but not greater than 0.95 g / cm³. 3 In some embodiments, the density of the third polymer foam layer 13 (or 13-1) is less than the density of the second polymer foam layer 12 and greater than 0.05 g / cm³. 3 In some such embodiments, or in others, the radio wave antireflective sheet further includes a fourth polymer foam layer 13-2 with a thickness of 0.05 mm to 3.0 mm, wherein a third polymer foam layer 13-1 is disposed between the second polymer foam layer 12 and the fourth polymer foam layer 13-2, and wherein the density of the fourth polymer foam layer 13-2 is less than the density of the third polymer foam layer 13-1 and greater than 0.05 g / cm³. 3 In some embodiments, the density of the third polymer foam layer 13-1 is not greater than the density of the first polymer foam layer 11, and the density of the fourth polymer foam layer 13-2 is less than each of the densities of the second polymer foam layer 12 and the third polymer foam layer 13-1 (e.g., less than 0.05 g / cm³). 3 And greater than 0.05 g / cm 3 In some embodiments, the density of the third polymer foam layer 13-1 is less than the density of the second polymer foam layer 12 (e.g., less than 0.05 g / cm³). 3(or the amount within the range described elsewhere in this document). The thickness of the third and / or fourth polymer foam layers may be within any range described elsewhere in this document for foam layers.

[0033] The polymer material of any of the polymer foam layers (e.g., 11 or 12) may include, for example, a curable resin composition, a thermoplastic resin, or a cured product of both. The “curable resin composition” comprises at least one monomeric compound and is polymerized by polymerizing at least one monomeric compound, thereby curing the curable resin composition.

[0034] The thermoplastic resin used to form the first polymer foam layer 11 or the second polymer foam layer 12 can be, for example, polyolefins such as polypropylene and polyethylene, polycarbonate, acrylonitrile vinyl styrene (AES) or acrylonitrile butadiene styrene (ABS).

[0035] The resin composition used to form the polymer foam layers (e.g., the first polymer foam layer 11 and / or the second polymer foam layer 12) may contain hollow particles or a blowing agent for generating bubbles, or both. The blowing agent for generating bubbles may be a thermally expanding blowing agent. The thermally expanding blowing agent may include, for example, a shell containing a thermoplastic resin and a liquid component encapsulated within the shell. Thermally expanding blowing agents are sometimes referred to as thermally expanding microspheres or thermally expanding microcapsules. The blowing agent for generating bubbles may be a chemical blowing agent. The hollow particles may be, for example, hollow glass particles or hollow resin particles. When the content of the blowing agent and hollow particles is high, the percentage of bubbles in the polymer foam layer increases, and therefore, the density of the foam layer decreases. Therefore, the density of each polymer foam layer in the polymer foam layer can be controlled based on the content of the blowing agent and / or hollow particles. The relative permittivity can similarly vary with the percentage of cells (e.g., bubbles) in the polymer foam layer. Therefore, the relative permittivity of each polymer foam layer in the polymer foam layer can be controlled based on the content of the blowing agent and / or hollow particles. Depending on the requirements, the polymer foam layer may also contain other components, such as dispersants.

[0036] Suitable glass microspheres include hollow glass bubbles, such as those available from 3M Company (St. Paul, MN). Expandable microspheres (which can expand by applying heat during the formation of a foam layer) may comprise a shell formed of thermoplastic resin and a low-boiling-point liquid hydrocarbon encapsulated within the shell. Suitable expandable microspheres include those available from Kureha Corporation, those available from Matsumoto Yushi-Seiyaku Co., Ltd., and those available under the trade name Expansion from Nouryon. Microspheres are typically spherical and have a diameter less than about 1 mm and typically greater than about 1 micrometer. In some embodiments, the median particle size of the microspheres is, for example, from 1 micrometer to 200 micrometers, or from 5 micrometers to 150 micrometers.

[0037] The term "(meth)acrylate monomer" refers to an acrylate or methacrylate monomer of an alcohol. Acrylates and methacrylate monomers or oligomers or polymers are collectively referred to herein as "(meth)acrylate". A (meth)acrylate composition may contain at least one (meth)acrylate monomer and may contain additional (meth)acrylate or non-(meth)acrylate copolymerizable olefinic unsaturated monomers. A majority (i.e., greater than 50% by weight) of the (meth)acrylate may consist of (meth)acrylate monomers. Suitable materials for the first polymer foam layer and / or the second polymer foam layer and / or other polymer foam layers include a (meth)acrylate matrix; and hollow microspheres dispersed in the matrix. In some embodiments, (at least) the second polymer foam layer comprises a (meth)acrylate matrix; and hollow microspheres dispersed in the matrix. Hollow microspheres may include, for example, hollow glass microspheres and / or polymer (e.g., expanded) microspheres.

[0038] The terms "Tg" and "glass transition temperature" are used interchangeably. If measured, unless otherwise specified, the Tg value is determined by differential scanning calorimetry (DSC) at a scan rate of 10 °C / min. Typically, the Tg value of the (meth)acrylate copolymer is not measured; instead, it is calculated using the well-known Fox formula, using the homopolymer Tg value provided by the monomer supplier, as understood by those skilled in the art. The homopolymer Tg value may be measured, for example, for monomers that are not commercially available. In some embodiments, the (meth)acrylate matrix has an acid content of 2% by weight or less and a Tg of -35 °C or higher, or -25 °C or higher. The Tg of the (meth)acrylate matrix can be, for example, at most 50 °C or at most 40 °C. For example, (meth)acrylates with a Tg in the range of -35 °C to 50 °C may have desired properties, such as low water vapor transmission rate. However, in other embodiments, the Tg may be less than -35 °C or greater than 50 °C. As will be understood by those skilled in the art, Tg can be adjusted by appropriately selecting monomers in the (meth)acrylate composition used as the matrix.

[0039] In some embodiments, at least one polymer foam layer (e.g., a first polymer foam layer and / or a second polymer foam layer) is hydrophobic. As will be understood by those skilled in the art, the foam layer can be made hydrophobic by selecting, for example, a hydrophobic monomer in the (meth)acrylate composition used as the matrix. The hydrophobicity of the foam layer or radio wave antireflective sheet can be measured in various ways, typically by exposing it to controlled heat and humidity conditions for a period of time and determining the water absorption rate. In some embodiments, the water absorption rate of the foam layer or radio wave antireflective sheet after 24 hours at 85°C and 85% relative humidity is less than 9000 ppm, or less than 7400 ppm, or less than 5000 ppm.

[0040] International application IB2021 / 052188, filed on March 16, 2021, describes a related foam layer having a matrix with a Tg of -25°C or higher and / or a water absorption rate of less than 7400 ppm after 24 hours at 85°C and 85% relative humidity. Other related foam layers are described in international application IB2021 / 052189, filed on March 16, 2021.

[0041] The term "alkyl" refers to a monovalent group that is an alkane group, where the alkane is a saturated hydrocarbon. Alkyl groups can be straight-chain, branched, cyclic, or combinations thereof, and typically have 1 to 20 carbon atoms. In some embodiments, the alkyl group contains 1 to 18, 1 to 12, 1 to 10, 1 to 8, 1 to 6, or 1 to 4 carbon atoms. Examples of alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, cyclohexyl, n-heptyl, n-octyl, and ethylhexyl ester.

[0042] The term "aryl" refers to a monovalent group consisting of an aromatic ring and a carbocyclic ring. An aryl group can have one to five rings attached to or fused with an aromatic ring. Other ring structures can be aromatic, non-aromatic, or combinations thereof. Examples of aryl groups include, but are not limited to, phenyl, biphenyl, terphenyl, anthryl, naphthyl, acenaphthenic, anthraquinone, phenanthryl, anthracenyl, pyrene, peryl, and fluorenyl.

[0043] In some embodiments, the (meth)acrylates used for polymer foam layers (e.g., layer 11 and / or layer 12) are prepared by providing a reaction mixture comprising at least two (meth)acrylate monomers, optionally 2% by weight or less of an acidic (meth)acrylate monomer, and at least one initiator. In some embodiments, the (meth)acrylate monomers may be selected to obtain polymers with a Tg of -35°C or higher, or -25°C or higher. A variety of (meth)acrylate monomers are suitable for the reaction mixture. Typically, the (meth)acrylate monomers are alkyl (meth)acrylate or aryl (meth)acrylate monomers, wherein the alkyl or aryl groups of the (meth)acrylate have an average of 1 to 20 carbon atoms. Since the reaction mixture may contain at least two (meth)acrylate monomers, multiple combinations are suitable. Typically, the reaction mixture comprises a first (meth)acrylate monomer having a relatively low homopolymer Tg and a second (meth)acrylate monomer having a relatively high homopolymer Tg. Generally, the first (meth)acrylate monomer has an alkyl group containing about 4 to about 18 or about 14 carbon atoms and has a homopolymer Tg of 0°C or lower. Examples include, but are not limited to, butyl acrylate, isooctyl acrylate, lauryl acrylate, isostearyl acrylate, 4-methyl-2-pentyl acrylate, isoamyl acrylate, sec-butyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate, n-decyl acrylate, isodecanyl acrylate, isodecanyl methacrylate, and isononyl acrylate. Generally, the second (meth)acrylate monomer is an alkyl (meth)acrylate or aryl (meth)acrylate with a homopolymer Tg higher than 0°C, typically higher than 10°C. Examples include, but are not limited to, methyl acrylate, methyl methacrylate, isobornyl acrylate, biphenyl acrylate, tert-butylphenyl acrylate, cyclohexyl acrylate, 4-tert-butylcyclohexyl acrylate, cyclic trimethylolpropane formal acrylate, dicyclopentyl acrylate, dicyclopentenyl acrylate, dicyclopentenyloxyethyl acrylate, dimethyl adamantyl acrylate, 2-naphthyl acrylate, phenyl acrylate, N,N-dimethylacrylamide, N,N-diethylacrylamide, acrylmorpholine, N-hydroxyethylacrylamide, N-isopropylacrylamide, N,N-dimethylaminopropylacrylamide, N-vinylpyrrolidone, and N-vinylcaprolactam. If a hydrophobic (meth)acrylate is required and if a hydrophilic monomer is used as the second (meth)acrylate monomer, the amount of such monomer is typically less than 10%, more typically less than 5%, so that the copolymer retains its hydrophobic properties. Optionally, the reaction mixture may also contain, for example, up to 2% by weight of an acid-functionalized monomer. Examples of acid-functionalized monomers include acrylic acid, methacrylic acid, and itaconic acid. The reaction mixture typically also contains at least one initiator. Often, one or more initiators include photoinitiators, meaning that the initiator is activated by light, typically ultraviolet (UV) light.Examples of suitable free radical photoinitiators include DAROCURE 4265, IRGACURE 184, IRGACURE 651, IRGACURE 1173, IRGACURE 819, LUCIRIN TPO, and LUCIRIN TPO-L, which are commercially available from BASF, Charlotte, NC, North Carolina. Generally, the photoinitiator is used in amounts from 0.01 parts by weight to 1 part by weight relative to 100 parts by weight of total reactive components.

[0044] In some embodiments, the curable resin composition used to form the polymer foam layer (e.g., layer 11 and / or layer 12) may comprise a monomeric compound having one or more (meth)acryloyl groups. The cured product of the monomeric compound having (meth)acryloyl groups comprises an acrylic resin formed by polymerization of the monomeric compound. Examples of monomeric compounds having (meth)acryloyl groups include alkyl (meth)acrylates, (meth)acrylic acid, and aryl (meth)acrylates. The alkyl groups contained in the alkyl (meth)acrylates may have 1 to 18 or 1 to 14 carbon atoms. Specific examples of alkyl methacrylates include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, tert-butyl methacrylate, isobutyl methacrylate, n-pentyl methacrylate, n-hexyl methacrylate, cyclohexyl methacrylate, n-heptyl methacrylate, n-octyl methacrylate, isobornyl methacrylate, and 2-ethylhexyl methacrylate. The content of monomeric compounds having (meth)acryloyl groups can be from 80% by mass to 100% by mass, depending on the mass of the curable resin composition. When the content of monomeric compounds having (meth)acryloyl groups is 100% by mass, the foam layer can be formed, for example, by mechanical foaming (foaming by the inflow of an inert gas such as nitrogen). The curable resin composition containing monomeric compounds having (meth)acryloyl groups may also contain a photopolymerization initiator, a thermal polymerization initiator, or both.

[0045] The reactive composition components can be mixed using conventional methods known to those skilled in the art. Such methods include mixing, mechanical rolling, hot melt blending, etc. The reactive mixture can then be partially polymerized by exposure to UV radiation to obtain a curable, coatable slurry, as described, for example, in U.S. Patent No. 6,339,111 (Moon et al.). Because the reaction mixture is only partially polymerized, the resulting coatable slurry remains a curable composition. Foaming agents, hollow particles and / or expandable microspheres, and additional initiators can be dispersed into the curable, coatable slurry to form a filled curable, coatable slurry. The additional initiator can be the same initiator used to achieve partial polymerization, or it can be a different initiator. Generally, the photoinitiator is used in amounts of 0.01 parts by weight to 1 part by weight, more typically 0.1 parts by weight to 0.5 parts by weight, relative to 100 parts by weight of the total reactive components.

[0046] The filled, curable, coatable slurry can then be applied to the first release liner using any suitable coating technique to form a curable layer. The thickness of the curable layer can vary considerably, typically from 0.02 mm to 2.5 mm. The filled, curable, coatable layer can be covered with a second release liner to form a curable layer between the two release liners. The second release liner can be the same as or different from the first release liner. The second release liner can be added after the curable, coatable layer is formed, or it can be added during the formation of the coating. In some embodiments, the slurry is applied to the first release liner while simultaneously contacting the top surface of the coating with the second release liner. The curable layer between the two release liners can then be polymerized to form a filled, cured polymer (e.g., (meth)acrylate) matrix. Typically, the curable layer is cured by exposure to ultraviolet (UV) radiation. In embodiments including expandable microspheres, the cured layer can then be exposed to elevated temperatures to cause the expandable microspheres to expand to form a foam layer. Typically, in this case, the cured layer is placed in an oven to allow the expandable microspheres to expand. The temperature and time the cured layer is exposed depend on the nature of the expandable microspheres used and the level of microspheres present. In other embodiments, hollow particles (e.g., hollow glass microspheres) are contained in the slurry, and the heating step can be omitted.

[0047] In some embodiments, after the formation of the first foam layer, a second foam layer is formed by coating and subsequently curing a second filler of a curable, coatable slurry onto the first foam layer. In other embodiments, the two foam layers are formed separately and then bonded together (e.g., one of the foam layers may be adhesive to provide bonding between layers, or a separate adhesive layer much thinner than the foam layers may be used). In some embodiments, each polymer foam layer of the radio wave antireflective sheet is a foam layer described elsewhere herein (e.g., formed using at least one of the techniques described herein). In some embodiments, at least one polymer foam layer (e.g., a minimum density layer) is formed using the techniques described herein, and at least one other polymer foam layer (e.g., a higher density layer) is prepared by a different method. The foam layers prepared by the different methods may be acrylic foam tapes, such as the PX5000 series of acrylic foam tapes available from 3M Company, St. Paul, Minnesota. In some embodiments, the foam layers prepared by the different methods may be commercially available foam constructions, such as polypropylene foam.

[0048] Figures 6A to 6B This is a schematic cross-sectional view of a vehicle component 300 according to some embodiments. The vehicle component 300 includes a multi-layer body portion 60 comprising a first layer 61 disposed between a second layer 63 and a third layer 64, wherein for at least one frequency in the range of 60 GHz to 90 GHz, the first layer 61 has a lower density than each of the second layer 63 and the third layer 64 and / or the first layer has a lower relative permittivity than each of the second layer 63 and the third layer 64. For example, the first layer 61 may be an air layer, while each of the second layer 63 and the third layer 64 may be a polymer layer. Layer 62 may be a spacer layer separating the second layer 63 and the third layer 64. In some embodiments, the density of each of the second layer 63 and the third layer 64 is at least 1.1 g / cm³. 3 Furthermore, the density of the first layer 61 is at least 0.2 g / cm³ less than the density of each of the second layer 63 and the third layer 64. 3 Or at least 0.3 g / cm 3In some embodiments, for at least a first frequency in the 60 GHz to 90 GHz range, the relative permittivity of each of the second layer 63 and the third layer 64 is at least 2, and the first layer 61 has a relative permittivity for at least the first frequency that is at least 0.5 smaller than the relative permittivity of each of the second layer 63 and the third layer 64. In some embodiments, for at least the first frequency in the 60 GHz to 90 GHz range, the relative permittivity of the first layer 61 is less than 1.2, or less than 1.1, or less than 1.05. In some embodiments, the first layer 61 is an air layer in which the vehicle logo or another vehicle dashboard is disposed (e.g., on the surface of layer 63), and the third layer 64 is optically transparent. In some embodiments, the average thickness of the first layer 61 is, for example, less than 0.5 mm, or less than 0.3 mm, and may be greater than 0.05 mm. In some embodiments, for example, the average thickness of the first layer 61 is less than the thickness of each of the first polymer foam layer 11 and the second polymer foam layer 12, or less than half the thickness of each of the first polymer foam layer 11 and the second polymer foam layer 12, or less than one-third the thickness of each of the first polymer foam layer 11 and the second polymer foam layer 12.

[0049] Vehicle component 300 includes a radio wave antireflector as described herein, wherein a second main surface S2 of the radio wave antireflector is disposed on and bonded to the outermost main surface 237 of the multilayer body portion 60. In an illustrated embodiment, a radio wave antireflector 103 is disposed on the multilayer body portion 60. In other embodiments, different types of radio wave antireflectors described herein are used. In an illustrated embodiment, the body portion 60 forms a receiving chamber 65 for the radar device 50 (see...). Figure 6A It can be installed in this housing. Figure 6B The radio wave 251 incident on the first main surface S1 and the reflected radio wave 253 are schematically shown.

[0050] Figures 7A to 7B This is a schematic cross-sectional view showing the reflection of radio waves from a reference article according to some embodiments. Figure 7A In this context, the reference article is a flat metal plate 276 having a metallic surface 277. The metal plate 276 can be, for example, an aluminum plate, and can have, for example, a thickness of about 3 mm. Figure 7BIn this embodiment, the reference article is a multi-layered body portion 60 without a radio wave antireflective sheet. Radio waves 251 have a frequency f in the range f1 to f2. In some embodiments, f1 is 60 GHz or 70 GHz. In some such embodiments, or in others, f2 is 90 GHz or 85 GHz. In some embodiments, the frequency f is, for example, in the range of 60 GHz to 90 GHz or 70 GHz to 85 GHz.

[0051] In some embodiments, when radio waves 251 having a first intensity Pi and a first frequency f in the range of 60 GHz to 90 GHz are irradiated from the first main surface side in a direction perpendicular to the first main surface S1, the intensity of the radio waves 253 reflected by the radio wave antireflective sheet and the multilayer main body portion is P1 (see...). Figure 6B When a radio wave 251 having a first intensity Pi and a first frequency f is used to irradiate the metal surface 277 in a direction perpendicular to the metal surface, the intensity of the radio wave 252 reflected by the flat metal surface 277 is P0. In some embodiments, P1-P0 is, for example, less than -15 dB, or less than -30 dB, or less than -40 dB. For example, P1-P0 can be as low as -80 dB or -60 dB. In some embodiments, when the radio wave antireflector is removed from the multilayer body portion 60 and the multilayer body portion 60 is irradiated with a radio wave 251 having a first intensity Pi and a first frequency f from the radio wave antireflector side (i.e., the side of the multilayer body portion 60 that was in before the radio wave antireflector was removed) in a direction perpendicular to the outermost main surface 237, the intensity of the radio wave 254 reflected by the multilayer body portion 60 is P2. In some embodiments, P1-P2 is, for example, less than -3 dB, or less than -5 dB, or less than -10 dB, or less than -15 dB. For example, P1-P2 can be as low as -40dB or -35dB. In some embodiments, the radio wave antireflector reduces the reflection of radio waves having a first frequency f in the range of 60 GHz to 90 GHz and being incident substantially perpendicularly on the multilayer body portion, for example, by at least 3dB, or at least 5dB, or at least 10dB, or at least 15dB, and in some embodiments, by at most 40dB or at most 35dB.

[0052] Example

[0053] These embodiments are for illustrative purposes only and are not intended to limit the scope of the appended claims. Unless otherwise specified, all parts, percentages, ratios, etc., in the embodiments and the remainder of the specification are by weight.

[0054] Table 1. Materials

[0055]

[0056] Weigh 0.150 g IRGACURE 651, 306.9 g 2EHA, 3.05 g AA, 96.75 g IBOA, and 96.34 g REGALREZ 6108 and place them in a 900 mL wide-mouth glass flask. Place the flask on a roller mixer overnight until REGALREZ 6108 is completely dissolved in the monomer mixture. Remove oxygen by purging the monomer mixture with nitrogen for 15 minutes, then irradiate the 900 mL wide-mouth glass flask with a 360 nm black light for 30 seconds. A viscous slurry containing the polymer is obtained. After prepolymerization, add 0.785 g IRGACURE 651 and 0.626 g HDDA to the 900 mL wide-mouth glass flask and place the flask on a roller mixer again overnight.

[0057] Add a certain amount of the slurry prepared as described above and K-15 shown in Table 2 to a 150 mL plastic cup and mix by rotating at 2000 rpm for 2 minutes using a planetary centrifuge mixer.

[0058] The slurry was poured between two pads (PUREX A50 and FILMBYNA MIB (50 μm)) on the coating line, with the coating head set to the selected gap to produce the thickness given in Table 2. The composition was then exposed to a UV light source in a UV chamber until the acrylate monomer mixture was completely polymerized into an acrylate polymer. The glass transition temperature of the acrylate polymer was calculated to be -30.5 °C according to the Fox formula. The thickness of the resulting acrylic foam was measured and recorded at four points on the sheet using a thickness gauge (Mitutoyo, code 543-390). The average thickness is shown in Table 2. The density was measured using an MDS-300 densitometer (AlfaMirage Co., Ltd., Osaka, Japan) and is shown in Table 2. The relative permittivity was determined using a KEYCOM version 1.2.2 dielectric constant analyzer (KEYCOM Corporation, Tokyo, Japan) and is shown in Table 2.

[0059] Table 2

[0060]

[0061] As shown in Table 3, various radio wave antireflective sheets are made from the layers in Table 2. The stacking notation in Table 3 indicates that Example 2, for example, comprises layers 1-2, 2-2, and 3 in sequence. Table 3 also shows the reflection level at 77 GHz and the average reflection level in the frequency range of 76 GHz to 77 GHz. The reflection level is for radiation that is incident substantially perpendicularly and relates to reflection from a metal (3 mm thick aluminum) plate.

[0062] Table 3

[0063]

[0064]

[0065] *1 The difference between the reflection from the metal plate at 77 GHz and the reflection from the metal plate at 77 GHz.

[0066] *2 Average reflection of the metal plate at 76GHz-77GHz.

[0067] Table 4 schematically summarizes the layer densities (high (H), medium (M), low (L), and lowest (LL)) of the various embodiments and comparative examples, and shows the average reduction in reflection in dB in the frequency range of 76 GHz to 77 GHz when the radio wave antireflective sheet is placed on a three-layer substrate including a 0.1 mm thick air layer between two polycarbonate layers. The polycarbonate layer facing the radio wave antireflective sheet is 2.8 mm thick, and the other polycarbonate layer is 3.0 mm thick. The polycarbonate layers are spaced apart using metal spacers near the layer edges. The average reflection from the three-layer substrate in the frequency range of 76 GHz to 77 GHz is -17.1 dB relative to reflection from an aluminum plate with a thickness of approximately 3 mm. Figures 5A to 5B As schematically shown, layers 1 to 4 are arranged from the air side to the substrate side.

[0068] The following conditions and measuring apparatus are used to measure the intensity of reflected radio waves using the S-parameter method:

[0069] Network Analyzer: PNAX N5242B (Keysight Technologies)

[0070] TX Unit: MEX6090-X6 (Microwave Factory)

[0071] LO / IF power unit: MLI UNIT SER.193679 (Microwave manufacturer)

[0072] Frequency expander: MEX6090-X6 SER.193680 (Microwave manufacturer)

[0073] Horn antenna: MSGH12-25(WR-12) (Microwave Manufacturer)

[0074] Waveguide (Twist): WR-12 1-inch 45-degree Left / Right Rotation (Microwave Manufacturer)

[0075] Mixer: FS-Z90 (Rhode & Schwartz)

[0076] RF cable: SUCOFLEX 221(Tx / Rx) / 322(NA) (HUBER & SUHNER)

[0077] Compared to the 2-layer comparative example CE1, the 2-layer example 1 showed a significant reduction. Compared to the 3-layer comparative example CE2, the 3-layer examples 2 to 4 showed a significant reduction. Compared to the 4-layer comparative example CE3, the 4-layer example 5 showed a significant reduction.

[0078] Table 4

[0079]

[0080] Figure 8 It is a graph of reflection versus frequency for 3-layer substrates with and without various radio wave antireflection sheets (without strips) disposed on the 3-layer substrate, where the reflection is for radiation that is essentially perpendicularly incident and is related to the reflection from a metal (3mm thick aluminum) plate.

[0081] Terms such as “about” will be understood in the context in which they are used and described by those skilled in the art. If it is unclear to those skilled in the art in the context of their use and description of “about” to express quantities of characteristic size, quantity, and physical properties, then “about” will be understood to mean within 10% of a specified value. A quantity given a specified value as “about” can be precisely the specified value. For example, if it is unclear to those skilled in the art in the context of their use and description of this specification, a quantity having a value of about 1 means that the quantity has a value between 0.9 and 1.1, and that the value can be 1.

[0082] All cited references, patents, and patent applications are incorporated herein by reference in their entirety in a consistent manner. In the event of any inconsistency or contradiction between the incorporated references and this application, the information in the foregoing description shall prevail.

[0083] Unless otherwise stated, the description of elements in the accompanying drawings should be understood to apply equally to corresponding elements in the other drawings. While specific embodiments have been illustrated and described herein, those skilled in the art will recognize that various alternative and / or equivalent embodiments may be used instead of the illustrated and described embodiments without departing from the scope of this disclosure. This application is intended to cover any modifications, variations, or combinations of the specific embodiments discussed herein. Therefore, this disclosure is intended to be limited only by the claims and their equivalents.

Claims

1. A radio wave anti-reflection sheet, the radio wave anti-reflection sheet comprising: A substantially non-viscous first primary surface and a relatively substantially viscous second primary surface; A first polymer foam layer is disposed between the first main surface and the second main surface, and the thickness of the first polymer foam layer is 0.05 mm to 3.0 mm and the density is 0.20 g / cm³. 3 Up to 0.90 g / cm 3 ; as well as A second polymer foam layer is disposed between the second main surface and the first polymer foam layer, and the second polymer foam layer has a thickness of 0.05 mm to 3.0 mm and a density greater than 0.10 g / cm³. 3 And its density is less than that of the first polymer foam layer. The difference between the density of the first polymer foam layer and the density of the second polymer foam layer is greater than 0.05 g / cm³. 3 ,and The radio wave antireflector reduces the reflection of radio waves with frequencies in the range of 60 GHz to 90 GHz and which are incident substantially perpendicularly on the multilayer body portion by at least 3 dB.

2. The radio wave antireflective sheet according to claim 1, wherein the first polymer foam layer comprises the first main surface.

3. The radio wave antireflective sheet according to claim 1, wherein the radio wave antireflective sheet further comprises a protective layer disposed on the first polymer foam layer and including the first main surface.

4. The radio wave antireflective sheet according to claim 1, wherein the second polymer foam layer comprises the second main surface.

5. The radio wave antireflective sheet according to claim 1, wherein the radio wave antireflective sheet further comprises a pressure-sensitive adhesive layer disposed on the second polymer foam layer and including the second main surface.

6. The radio wave antireflective sheet according to claim 1, wherein the radio wave antireflective sheet further comprises a third polymer foam layer with a thickness of 0.05 mm to 3.0 mm, and the second polymer foam layer is disposed between the first polymer foam layer and the third polymer foam layer.

7. The radio wave antireflective sheet according to claim 6, wherein the density of the third polymer foam layer is greater than the density of the second polymer foam layer and not greater than the density of the first polymer foam layer.

8. The radio wave antireflective sheet according to claim 6, wherein the density of the third polymer foam layer is greater than the density of the first polymer foam layer and not greater than 0.95 g / cm³. 3 .

9. The radio wave antireflective sheet according to claim 6, wherein the density of the third polymer foam layer is less than the density of the second polymer foam layer and greater than 0.05 g / cm³. 3 .

10. The radio wave antireflective sheet according to claim 9, further comprising a fourth polymer foam layer with a thickness of 0.05 mm to 3.0 mm, wherein the third polymer foam layer is disposed between the second polymer foam layer and the fourth polymer foam layer, and the density of the fourth polymer foam layer is less than the density of the third polymer foam layer and greater than 0.05 g / cm³. 3 .

11. The radio wave antireflective sheet according to claim 1, wherein the second polymer foam layer comprises: (meth)acrylate matrix; and Bubbles, hollow particles, or combinations thereof dispersed in the matrix.

12. The radio wave antireflective sheet according to claim 11, wherein the second polymer foam layer comprises hollow particles dispersed in the matrix, the hollow particles comprising hollow microspheres.

13. A strip comprising a release liner and a radio wave antireflective sheet according to any one of claims 1 to 12, wherein a second primary surface of the radio wave antireflective sheet is disposed on the release surface of the release liner.

14. A vehicle component, the vehicle component comprising: A multi-layer body portion, the multi-layer body portion including a first layer disposed between a second layer and a third layer, the first layer having a lower density than each of the second layer and the third layer; as well as According to any one of claims 1 to 12, the second main surface of the radio wave antireflective sheet is disposed on the outermost main surface of the multilayer body portion and bonded to the outermost main surface of the multilayer body portion.

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