Adhesive sheet for antenna substrate and antenna substrate

Abstract

To provide an adhesive sheet which has excellent adhesive force and is suitable for use in antenna substrate applications, and to provide an antenna substrate.SOLUTION: The present invention is the adhesive sheet for an antenna substrate including a dielectric and a conductor layer, the adhesive sheet including an adhesive layer having a dielectric loss tangent (tanδ) at a frequency of 5 GHz of 0.003 or less. The antenna substrate according to the present invention includes the adhesive sheet for an antenna substrate and has a structure in which a conductor layer is bonded onto at least one surface of a dielectric via the adhesive sheet. The adhesive sheet for an antenna substrate according to the present invention has excellent adhesive force, is suitable for use in antenna substrate applications, and allows, for example, an antenna substrate having low transmission loss to be constructed.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a pressure-sensitive adhesive sheet for an antenna substrate and an antenna substrate. [Background technology]

[0002] In recent years, the capacity of wireless communication has been increasing, and there is a strong demand for the development of antenna devices with high efficiency and wideband characteristics. Therefore, it is also important to improve the performance of the antenna substrate used to form the antenna device. In general, the antenna substrate has a structure in which a conductor layer is bonded to at least one surface of a dielectric material via the adhesive sheet.

[0003] Known methods for bonding a substrate (dielectric) and a conductor include using a thermoplastic resin for the substrate, roughening the surfaces of the substrate and the conductor, and then directly bonding them by thermocompression bonding, and bonding the substrate and the conductor with an adhesive. Patent Document 1 also discloses a technology for bonding a dielectric and a conductor with an acrylic adhesive layer (adhesive sheet) containing voids to reduce the dielectric loss tangent, thereby suppressing transmission loss of electrical signals. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-145187 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in high-frequency communications, the method of roughening the surface and bonding is often unsuitable for antenna substrates because the surface roughness of the conductor reduces the conductivity, making it unsuitable for use as an antenna substrate. Furthermore, the need to use a thermoplastic resin for the substrate and the surrounding materials also require heat resistance to withstand thermocompression bonding limits the types of materials that can be used, posing challenges for practical application. Furthermore, methods using adhesives have problems such as low flexibility, which can lead to cracking and warping due to environmental changes, and poor productivity due to the inability to produce roll-to-roll products. Furthermore, even when bonding with an adhesive sheet, as disclosed in Patent Document 1, there are still problems, such as reduced transparency due to voids, uneven dispersion, and the resulting anisotropy, as well as insufficient adhesion at room temperature.

[0006] The present invention has been made in view of the above, and has an object to provide a pressure-sensitive adhesive sheet that has excellent adhesive strength and is suitable for use as an antenna substrate. [Means for solving the problem]

[0007] As a result of extensive research to achieve the above object, the inventors discovered that the above object can be achieved by applying an adhesive layer with a low dielectric tangent to an adhesive sheet, and thus completed the present invention.

[0008] That is, the present invention includes, for example, the subject matter described in the following sections. Item 1 An adhesive sheet for an antenna substrate having a dielectric and a conductor layer, An adhesive sheet for antenna substrates, comprising an adhesive layer having a dielectric loss tangent (tan δ) of 0.003 or less at a frequency of 5 GHz. Section 2 Item 2. The pressure-sensitive adhesive sheet for antenna substrates according to Item 1, wherein the pressure-sensitive adhesive layer contains an olefin-based resin. Section 3 Item 3. The pressure-sensitive adhesive sheet for antenna substrates according to Item 1 or 2, wherein the olefin-based resin includes an ethylene-propylene copolymer. Section 4 Item 4. The pressure-sensitive adhesive sheet for antenna substrates according to any one of items 1 to 3, having an adhesive strength to fluororesin of 5 N / 25 mm or more. Section 5 Item 5. The pressure-sensitive adhesive sheet for an antenna substrate according to any one of items 1 to 4, having a haze of 1% or less. Section 6 Item 6. The pressure-sensitive adhesive sheet for an antenna substrate according to any one of items 1 to 5, having a thickness of 5 to 200 μm. Section 7 Item 7. The pressure-sensitive adhesive sheet for an antenna substrate according to any one of items 1 to 6, wherein the pressure-sensitive adhesive layer does not contain an acid component. Section 8 An antenna substrate comprising the pressure-sensitive adhesive sheet for antenna substrates according to any one of items 1 to 7, An antenna substrate having a structure in which a conductor layer is adhered to at least one surface of a dielectric body via the adhesive sheet. [Effects of the Invention]

[0009] The pressure-sensitive adhesive sheet for antenna substrates according to the present invention has excellent adhesive strength and is suitable for use as antenna substrates. DETAILED DESCRIPTION OF THE INVENTION

[0010]

[0023] In the present specification, the terms "contain" and "comprise" include the concepts of "contain," "comprise," "consist essentially of," and "consist only of."

[0011] 1. Adhesive sheet for antenna substrate The pressure-sensitive adhesive sheet for antenna substrates of the present invention is used for antenna substrates comprising a dielectric and a conductor layer, and comprises a pressure-sensitive adhesive layer having a dielectric dissipation factor (tanδ) of 0.003 or less at a frequency of 5 GHz. The pressure-sensitive adhesive sheet for antenna substrates of the present invention has excellent adhesive strength and is suitable for use in antenna substrate applications, making it possible to construct, for example, an antenna substrate with low transmission loss. Hereinafter, the pressure-sensitive adhesive sheet for antenna substrates of the present invention will be referred to simply as "pressure-sensitive adhesive sheet."

[0012] (Adhesive layer) The pressure-sensitive adhesive sheet includes a pressure-sensitive adhesive layer having a dielectric loss tangent (tanδ) of 0.003 or less at a frequency of 5 GHz, which makes the sheet suitable for use as an antenna substrate, for example, by reducing the problems of reduced conductivity and limitations on the types of substrates that can be used.

[0013] The pressure-sensitive adhesive layer preferably has a dielectric loss tangent (tan δ) of 0.003 or less, more preferably 0.001 or less at a frequency of 5 GHz.

[0014] The pressure-sensitive adhesive layer has a dielectric constant of 3.0 or less, more preferably 2.7 or less at a frequency of 5 GHz.

[0015] The adhesive layer can be formed from various materials as long as the dielectric loss tangent (tanδ) at a frequency of 5 GHz is 0.003 or less. However, it is preferable that the adhesive layer contains an olefin-based resin, because it is easy to achieve a desired dielectric loss tangent (tanδ), has excellent corrosion prevention properties for conductors due to its low water vapor permeability, and has a refractive index close to that of glass compared to acrylic, which is expected to improve visibility due to anti-reflection. The adhesive layer can contain 50% by mass or more of the olefin-based resin, and particularly preferably 80% by mass or more. The adhesive layer may be composed solely of an olefin-based resin.

[0016] The type of the olefin-based resin is not particularly limited, and a wide range of known olefin-based resins and olefin-based elastomers can be used, for example. The olefin-based elastomer is, for example, a polymer containing units derived from an α-olefin, and examples thereof include poly-α-olefin-based elastomers obtained by polymerizing an α-olefin.

[0017] Examples of the olefin resin include propylene / ethylene copolymer, ethylidenenorbornene / ethylene / propylene copolymer, propylene / ethylene / 1-butene copolymer, 1-butene homopolymer, 1-butene / ethylene copolymer, 1-butene / propylene copolymer, 4-methylpentene-1 homopolymer, 4-methylpentene-1 / propylene copolymer, 4-methylpentene-1 / 1-butene copolymer, 4-methylpentene-1 / propylene-1-butene copolymer, propylene / 1-butene copolymer, and cyclic olefin polymer. The olefin resin may be an elastomer containing an unsaturated bond in the polymer chain, such as 2-methyl-1,3-butadiene homopolymer (polyisoprene), 2-methyl-1,3-butadiene copolymer, or 1,3-butadiene homopolymer (polybutadiene). In particular, those without an unsaturated bond are more preferable from the viewpoint of light resistance.

[0018] The olefin resin may be a block copolymer. The block copolymer may contain a block obtained by polymerizing an α-olefin and a block composed of another polymer. In this case, examples of the block composed of another polymer include a block composed of a styrene polymer and a block composed of a (meth)acrylic acid ester polymer.

[0019] The olefin resin preferably contains an ethylene-propylene copolymer. In this case, the dielectric loss tangent (tanδ) at a frequency of 5 GHz can be easily adjusted to 0.003 or less, and the adhesive strength is particularly excellent. The ethylene-propylene copolymer may be a random copolymer, a block copolymer, or a graft copolymer.

[0020] The olefin resin may consist solely of an ethylene-propylene copolymer, or may contain, for example, 20 to 60 mass% of an ethylene-propylene copolymer. It is particularly preferred that the olefin resin contain 30 to 50 mass% or more of an ethylene-propylene copolymer. The remainder may be, for example, a cyclic olefin polymer. That is, the olefin resin may be a mixture of an ethylene-propylene copolymer and a cyclic olefin polymer.

[0021] Examples of cyclic olefin polymers include hydrogenated C5 petroleum resins, C9 petroleum resins, dicyclopentadiene petroleum resins, and petroleum resin mixtures thereof. The softening point of the cyclic olefin polymer is preferably 80 to 150°C, and the mass average molecular weight is preferably 300 to 2,000, more preferably 500 to 1,000. Examples of cyclic olefin polymers include the Alcon P series (trade name: manufactured by Arakawa Chemical Industries), the T-REZ-H series (trade name: manufactured by TonenGeneral), ESCOREZ (trade name: manufactured by Exxon Chemical Company), and EASTOTAC (trade name: manufactured by Eastman Chemical Company).

[0022] In the ethylene-propylene copolymer, the content of ethylene units is not particularly limited, and for example, the content ratio of ethylene units to the total amount of ethylene units and propylene units is 70 mass% or less, particularly preferably 60 mass% or less. Examples of ethylene-propylene copolymers include the EP series (trade name: manufactured by JSR Corporation) and the EPT series (trade name: manufactured by Mitsui Chemicals, Inc.).

[0023] The pressure-sensitive adhesive layer may contain other components in addition to the olefin-based resin, such as an acrylic monomer, a photopolymerization initiator, a light stabilizer, an antioxidant, and a preservative.

[0024] Furthermore, since the pressure-sensitive adhesive layer is attached to a conductor, it is desirable that the pressure-sensitive adhesive layer does not contain an acid component.

[0025] The adhesive layer has a dielectric loss tangent (tanδ) of 0.003 or less at a frequency of 5 GHz, making it possible to apply the adhesive layer to adhesive applications for antenna substrates without introducing voids using foam or the like, or without including fillers with low dielectric loss tangents.

[0026] The method for forming the pressure-sensitive adhesive layer is not particularly limited, and for example, methods for forming pressure-sensitive adhesive layers in conventional pressure-sensitive adhesive sheets can be widely adopted in the present invention. For example, a pressure-sensitive adhesive layer can be formed using a pressure-sensitive adhesive composition.

[0027] The pressure-sensitive adhesive composition may contain, in addition to the olefin-based resin, at least one selected from the group consisting of a solvent, a polyfunctional monomer, a photopolymerization initiator, and a monofunctional monomer.

[0028] Examples of the solvent include hydrocarbons such as hexane, heptane, octane, toluene, xylene, ethylbenzene, cyclohexane, and methylcyclohexane; halogenated hydrocarbons such as dichloromethane, trichloroethane, trichloroethylene, tetrachloroethylene, and dichloropropane; alcohols such as methanol, ethanol, propanol, isopropyl alcohol, butanol, isobutyl alcohol, and diacetone alcohol; ethers such as diethyl ether, diisopropyl ether, dioxane, and tetrahydrofuran; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, isophorone, and cyclohexanone; esters such as methyl acetate, ethyl acetate, butyl acetate, isobutyl acetate, amyl acetate, and ethyl butyrate; and polyols such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monomethyl ether acetate, propylene glycol monomethyl ether, propylene glycol monoethyl ether, and propylene glycol monomethyl ether acetate, and derivatives thereof.

[0029] When the pressure-sensitive adhesive composition contains the solvent, the concentration of the nonvolatile content is preferably 20% by mass or more, more preferably 30% by mass or more, and is preferably 80% by mass or less, more preferably 60% by mass or less.

[0030] A polyfunctional monomer is a polymerizable monomer having two or more polymerizable double bonds in the molecule. The polyfunctional monomer preferably contains two to five polymerizable double bonds, more preferably two to three. The polyfunctional monomer is preferably a (meth)acrylic monomer. In this specification, "(meth)acrylic" means "acrylic" or "methacrylic", and "(meth)acrylate" means "acrylate" or "methacrylate".

[0031] Examples of polyfunctional monomers include (meth)acrylic acid esters of polyhydric alcohols such as ethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, 1,3-butylene glycol di(meth)acrylate, 1,4-butylene glycol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,6-hexanediol diacrylate, polybutylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, diacrylate of bisphenol A diglycidyl ether, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and pentaerythritol tetra(meth)acrylate; and vinyl methacrylate.

[0032] The polyfunctional monomer can be obtained by a known production method or can be obtained from a commercially available product, such as dimethyloltricyclodecane diacrylate (Light Acrylate DCP-A, manufactured by Kyoeisha Chemical Co., Ltd.) or bisphenol A ethylene oxide-modified diacrylate (Aronix M-211B, manufactured by Toagosei Co., Ltd.).

[0033] When the pressure-sensitive adhesive composition contains a polyfunctional monomer, the content of the polyfunctional monomer is preferably 0.05 mass% or more, more preferably 0.1 mass% or more, and is preferably 20 mass% or less, more preferably 10 mass% or less, relative to the total mass of the pressure-sensitive adhesive composition.

[0034] The photopolymerization initiator can be, for example, an initiator that initiates polymerization of a polyfunctional monomer by irradiation with active energy rays, and a wide variety of known photopolymerization initiators can be used. Here, "active energy rays" refers to electromagnetic waves or charged particle rays that have an energy quantum, and examples thereof include ultraviolet rays, electron beams, visible light, X-rays, and ion beams. Among these, ultraviolet rays or electron beams are preferred from the viewpoint of versatility, and ultraviolet rays are particularly preferred.

[0035] Examples of photopolymerization initiators include acetophenone-based initiators, benzoin ether-based initiators, benzophenone-based initiators, hydroxyalkylphenone-based initiators, thioxanthone-based initiators, amine-based initiators, and acylphosphine oxide-based initiators. Specific examples of acetophenone-based initiators include diethoxyacetophenone and benzyl dimethyl ketal. Specific examples of benzoin ether-based initiators include benzoin and benzoin methyl ether. Specific examples of benzophenone-based initiators include benzophenone, methyl o-benzoylbenzoate, 2,4,6-trimethylbenzophenone, and 4-methylbenzophenone. Specific examples of hydroxyalkylphenone-based initiators include 1-hydroxycyclohexylphenyl ketone (manufactured by IGM Resins Co., Ltd., commercially available as Omnirad 184). Specific examples of thioxanthone-based initiators include 2-isopropylthioxanthone and 2,4-dimethylthioxanthone. Specific examples of the amine initiator include triethanolamine and ethyl 4-dimethylbenzoate.Specific examples of the acylphosphine oxide initiator include phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (manufactured by IGM Resins Co., Ltd., commercially available as Omnirad819).

[0036] When the pressure-sensitive adhesive composition contains a photopolymerization initiator, the proportion of the photopolymerization initiator is preferably 0.1 mass% or more, more preferably 0.2 mass% or more, and is preferably 15 mass% or less, more preferably 10 mass% or less, relative to the total mass of the pressure-sensitive adhesive composition.

[0037] The monofunctional monomer is a compound having one polymerizable double bond in the molecule. Examples of the monofunctional monomer include (meth)acrylic monomers, such as alkyl (meth)acrylates such as isobornyl (meth)acrylate, isostearyl (meth)acrylate, methyl (meth)acrylate, ethyl (meth)acrylate, and butyl (meth)acrylate; and other examples include benzyl (meth)acrylate, N-(meth)acryloyloxyethylhexahydrophthalimide, (meth)acrylamide, N,N-dimethyl (meth)acrylamide, N,N-diethyl (meth)acrylamide, (meth)acryloylmorpholine, and vinylpyrrolidone.

[0038] The pressure-sensitive adhesive composition may contain other optional components, such as a silane coupling agent, a tackifier, an oil component, a softener, an antioxidant, a crosslinking agent, and a pigment. The method for producing the pressure-sensitive adhesive composition is not particularly limited, and for example, a wide variety of known methods can be used, or the pressure-sensitive adhesive composition can be obtained from a commercially available product (for example, Aica Kogyo Co., Ltd.'s olefin-based pressure-sensitive adhesive Z-585VB3).

[0039] The method for forming a pressure-sensitive adhesive layer using the pressure-sensitive adhesive composition is not particularly limited, and for example, a wide variety of known methods can be adopted. Specifically, the pressure-sensitive adhesive layer can be formed by a step of applying the pressure-sensitive adhesive composition onto a substrate.

[0040] The method for applying the pressure-sensitive adhesive composition to the substrate is not particularly limited, and for example, a wide variety of known application methods can be used. For example, the pressure-sensitive adhesive composition can be applied using a commercially available application device such as a blade coater, an air knife coater, a roll coater, a bar coater, a gravure coater, a microgravure coater, a rod blade coater, a lip coater, a die coater, or a curtain coater. The amount of application of the pressure-sensitive adhesive composition is not particularly limited, and can be appropriately set depending on the desired thickness of the pressure-sensitive adhesive layer.

[0041] The substrate to which the pressure-sensitive adhesive composition is applied is not particularly limited, but is preferably a release sheet. Examples of the release sheet include a release laminate sheet having a release sheet substrate and a release agent layer provided on one side of the release sheet substrate, or a polyolefin film such as a polyethylene film or a polypropylene film as a low-polarity substrate. Paper or a polymer film is used as the release sheet substrate in the release laminate sheet. Examples of the release agent constituting the release agent layer include general-purpose addition or condensation type silicone-based release agents and long-chain alkyl group-containing compounds. In particular, highly reactive addition type silicone-based release agents are preferably used.

[0042] A coating film is formed by applying the pressure-sensitive adhesive composition to a substrate. A pressure-sensitive adhesive layer can be formed by subjecting this coating film to a drying process or the like. The conditions for the drying process are not particularly limited, and a wide variety of conventional methods for drying coating films of pressure-sensitive adhesive compositions can be used. Such drying processes can be carried out, for example, using a known heating device or the like. The heating temperature is preferably 50 to 200°C, more preferably 60 to 150°C. The heating time may be set so that the solvent volatilizes and the residual solvent concentration in the pressure-sensitive adhesive layer is, for example, 1000 ppm or less. Therefore, it is preferable to appropriately set the heating time within the above temperature range within a time period of about 1 to 30 minutes depending on the concentration of the pressure-sensitive adhesive composition, the desired thickness of the pressure-sensitive adhesive layer, etc.

[0043] A pressure-sensitive adhesive layer can be formed by the above method. The obtained pressure-sensitive adhesive layer can be used as a pressure-sensitive adhesive sheet. Therefore, the pressure-sensitive adhesive sheet of the present invention can be obtained by the same method as the method for forming the pressure-sensitive adhesive layer.

[0044] When the release sheet described above is used as the substrate to which the pressure-sensitive adhesive composition is applied, a pressure-sensitive adhesive sheet with a release sheet is obtained. In the pressure-sensitive adhesive sheet with a release sheet, the release sheets may be provided on both sides.

[0045] (Physical properties of adhesive sheet) The adhesive sheet of the present invention preferably has an adhesive strength to fluororesin of 5 N / 25 mm or more. In this case, the adhesive sheet of the present invention can more firmly bond the dielectric and conductor layers of the antenna substrate. The adhesive sheet of the present invention more preferably has an adhesive strength to fluororesin of 5 N / 25 mm or more, and even more preferably 10 N / 25 mm or more. Note that when the adhesive sheet is formed only of an adhesive layer, the adhesive strength corresponds to the adhesive strength of the adhesive layer.

[0046] The pressure-sensitive adhesive sheet of the present invention preferably has a haze of 1% or less, more preferably 0.7% or less, since it is likely to have high transparency. When the pressure-sensitive adhesive sheet is formed only of a pressure-sensitive adhesive layer, the haze corresponds to the haze of the pressure-sensitive adhesive layer. In particular, since the pressure-sensitive adhesive sheet of the present invention does not contain fillers or voids, as described above, it has high transparency and does not generate anisotropy.

[0047] The pressure-sensitive adhesive sheet of the present invention is not particularly limited as long as it is applicable to antenna substrates. For example, the pressure-sensitive adhesive sheet of the present invention preferably has a thickness of 5 to 200 μm, more preferably 10 to 150 μm.

[0048] The pressure-sensitive adhesive sheet for antenna substrates of the present invention has excellent adhesive strength and is suitable for use in antenna substrate applications. The pressure-sensitive adhesive sheet for antenna substrates of the present invention makes it possible to construct an antenna substrate with low transmission loss, for example. For example, methods of reducing the transmission loss of antenna substrates by adding fillers or hollow particles (voids) to a pressure-sensitive adhesive sheet can result in reduced transparency and insufficient adhesiveness at room temperature, whereas the pressure-sensitive adhesive sheet for antenna substrates of the present invention makes it possible to construct an antenna substrate with low transmission loss without including fillers or voids, resulting in excellent transparency and adhesive strength and no anisotropy.

[0049] Furthermore, the pressure-sensitive adhesive sheet for antenna substrates of the present invention is less susceptible to problems such as a decrease in electrical conductivity and limitations on the types of substrates that can be used, making it suitable for use as an antenna substrate.

[0050] 2.Antenna board The antenna substrate of the present invention includes a pressure-sensitive adhesive sheet for an antenna substrate, and has a structure in which a conductor layer is adhered to at least one surface of a dielectric material via the pressure-sensitive adhesive sheet.

[0051] In the antenna substrate, the types of dielectric and conductor layers are not particularly limited, and for example, a wide range of dielectric and conductor layers used in conventional antenna substrates can be applied.

[0052] The dielectric may be formed from various insulating materials, such as fluororesins such as polytetrafluoroethylene, epoxy resins, polyamide resins, polyester resins, and polyimide resins.

[0053] The conductor layer can be formed of, for example, various metal materials. Examples of metal materials include transparent conductive films of copper, aluminum, ITO, etc. Transparent conductive films are particularly preferred because they can be combined with the pressure-sensitive adhesive sheet of the present invention to produce a transparent antenna.

[0054] The size, thickness, shape, etc. of the dielectric and conductor layers are not particularly limited, and may be the same as those of known antenna substrates, for example.

[0055] The antenna substrate of the present invention may have a conductor layer provided on at least one surface of a dielectric body via the pressure-sensitive adhesive sheet, and another member provided on the other surface, in which case the dielectric body and the other member may be bonded together by the pressure-sensitive adhesive sheet.

[0056] In the antenna substrate of the present invention, the conductor layer and the dielectric are bonded together via the adhesive sheet for the antenna substrate of the present invention, so that the conductor layer and the dielectric are firmly bonded together, and since there is no need to perform roughening treatment, a decrease in conductivity can be suppressed, and therefore the antenna substrate has low transmission loss. [Example]

[0057] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0058] Example 1 The olefin-based adhesive Z-585VB3 (manufactured by AICA Kogyo Co., Ltd., non-volatile content 32%) was applied to a first release film (heavy release separator) so that the adhesive layer would be 75 μm thick after drying, and the coating was formed by drying at 100°C for 3 minutes. Next, a second release film (light release separator) was attached to the coating, and the second release film was exposed to an illuminance of 150 mW cm. 2 Accumulated light intensity of 500mJ / cm 2 An adhesive sheet was produced by irradiating the adhesive with ultraviolet light.

[0059] Example 2 An adhesive sheet was obtained in the same manner as in Example 1, except that the thickness of the adhesive layer was changed to 150 μm and the drying time at 100° C. was changed to 10 minutes.

[0060] (Comparative Example 1) Shin-Tack Chemical's acrylic adhesive sheet "SA366" was used as the adhesive sheet.

[0061] (Evaluation method) <Dielectric constant and dielectric dissipation factor of adhesive sheet (5GHz, 24GHz)> The dielectric constant and dielectric loss tangent of the adhesive sheet at 5 GHz and 24 GHz were measured by the cylindrical cavity resonance method (TM method).

[0062] <Dielectric constant and dielectric dissipation factor of adhesive sheet (80GHz, 160GHz)> The dielectric constant and dielectric loss tangent of the adhesive sheet at 80 GHz and 160 GHz were measured by the Fabry-Perot resonator method.

[0063] <Adhesion strength of adhesive sheet to PTFE and copper plate> One release sheet was peeled off from the pressure-sensitive adhesive sheets obtained in the Examples and Comparative Examples, and a 100 μm-thick PET film was attached to the exposed surface, which was then cut to a width of 25 mm. The other release sheet was peeled off and a PTFE ("MSF-100" manufactured by Chukoh Chemical Industry Co., Ltd.) or copper plate ("C1100" manufactured by Engineering Test Services Co., Ltd.) was pressure-bonded to the exposed surface as an adherend. 24 hours after bonding, the pressure-sensitive adhesive sheet was peeled off at a peel angle of 180° and a speed of 300 mm / min in an environment of 23°C and 50% RH, and the adhesive strength to the adherend was measured.

[0064] <Fabrication of antenna substrate (substrate laminate)> The adhesive sheets obtained in the Examples and Comparative Examples were bonded to both sides of a PTFE film ("MSF-100" manufactured by Chukoh Chemical Industry Co., Ltd.), and then copper foil (CF-T9DA-SV-12 manufactured by Fukuda Metal Foil and Powder Co., Ltd., thickness 12 μm, Rz0 0.85 μm) was bonded to both sides of the adhesive sheets to obtain a substrate laminate.

[0065] <Transmission loss measurement> The copper foil on one side of the obtained substrate laminate was patterned to produce a microstrip line with a wiring length of 100 mm and an impedance of 50 Ω. The transmission loss S21 parameter was measured at a measurement frequency of 5 GHz using a network analyzer (E8363B PNA series manufactured by Keysight Technologies).

[0066] [Table 1]

[0067] The evaluation results of the pressure-sensitive adhesive sheets obtained in each example and comparative example are shown in Table 1. The pressure-sensitive adhesive sheets obtained in the examples contained an ethylene-propylene copolymer and had a pressure-sensitive adhesive layer with a dielectric loss tangent (tanδ) of 0.003 or less at a frequency of 5 GHz, and had low dielectric loss tangent (tanδ) and dielectric constant, as well as excellent adhesive strength to PTFE and copper plates.

[0068] Furthermore, as shown in Table 1, it was also found that the transmission loss of the antenna substrate (substrate laminate) equipped with the adhesive sheet obtained in the example was superior to the transmission loss of the antenna substrate (substrate laminate) equipped with the adhesive sheet obtained in the comparative example (since the transmission loss of Examples 1 and 2 was superior to that of Comparative Example 1, the transmission loss of Comparative Example 1 was marked "X" and the transmission loss of Examples 1 and 2 was marked "O").

[0069] Therefore, it was found that the adhesive sheet obtained in the examples has an adhesive layer containing an ethylene-propylene copolymer, and therefore when applied to an antenna substrate, it can firmly bond the conductor layer and the dielectric and also result in low transmission loss.

Claims

1. An adhesive sheet for an antenna substrate having a dielectric and a conductor layer, A pressure-sensitive adhesive sheet for antenna substrates, comprising a pressure-sensitive adhesive layer having a dielectric dissipation factor (tanδ) of 0.003 or less at a frequency of 5 GHz, wherein the pressure-sensitive adhesive layer contains at least one olefin-based resin selected from the group consisting of ethylene-propylene copolymer, ethylidene norbornene / ethylene / propylene copolymer, propylene / ethylene / 1-butene copolymer, 1-butene homopolymer, 1-butene / ethylene copolymer, 1-butene / propylene copolymer, 4-methyl-1-pentene homopolymer, 4-methyl-1-pentene / propylene copolymer, 4-methyl-1-pentene / 1-butene copolymer, 4-methyl-1-pentene / propylene-1-butene copolymer, propylene / 1-butene copolymer, cyclic olefin-based polymer, 2-methyl-1,3-butadiene homopolymer (polyisoprene), 2-methyl-1,3-butadiene copolymer, and 1,3-butadiene homopolymer (polybutadiene).

2. 2. The pressure-sensitive adhesive sheet for antenna substrates according to claim 1, which has an adhesive strength to fluororesin of 5 N / 25 mm or more.

3. 3. The pressure-sensitive adhesive sheet for an antenna substrate according to claim 1, which has a haze of 1% or less.

4. The pressure-sensitive adhesive sheet for an antenna substrate according to any one of claims 1 to 3, which has a thickness of 5 to 200 µm.

5. The pressure-sensitive adhesive sheet for an antenna substrate according to any one of claims 1 to 4, wherein the pressure-sensitive adhesive layer does not contain an acid component.

6. An antenna substrate comprising the pressure-sensitive adhesive sheet for antenna substrates according to any one of claims 1 to 5, An antenna substrate having a structure in which a conductor layer is adhered to at least one surface of a dielectric material via the adhesive sheet.

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