Adhesive composition, adhesive layer and adhesive sheet

Abstract

This invention provides an adhesive composition and an adhesive sheet, which can form an adhesive layer with low dielectric constant and dielectric loss at high frequencies, suitable for bonding to components constituting millimeter-wave antennas. The adhesive composition of this invention has a dielectric constant of 2.0 to 5.0 at 28 GHz or at 60 GHz, and comprises: a mixture of methacrylate compounds having a hydrocarbon group having 6 or more carbon atoms and (meth)acrylate compounds having crosslinking functional groups, or a portion thereof as a polymer or copolymer.

Description

[Technical Field]

[0001] This invention relates to an adhesive composition, an adhesive layer, and an adhesive sheet. More specifically, this invention relates to an adhesive composition, an adhesive layer, and an adhesive sheet suitable for bonding components of a millimeter-wave antenna. [Previous Technology]

[0002] In recent years, the speed and capacity of communication in portable communication devices such as smartphones have been improving year by year. The industry expects that in the fifth generation (5G), which is the next generation of ultra-high-speed data communication standard, it will be able to achieve 100 times the ultra-high speed and capacity of the fourth generation (4G), 1 / 10 the low latency, and more than 10 times the number of simultaneous connections compared with the fourth generation (4G).

[0003] In order to achieve the ultra-high speed, high capacity communication, low latency, and multiple simultaneous connections in 5G as described above, high-frequency electromagnetic waves with frequencies exceeding 24 GHz, known as millimeter waves, are used. By shortening the wavelength to the millimeter level, a large amount of data can be transmitted at once.

[0004] On the other hand, compared with the frequency band used by 4G, millimeter waves are more prone to attenuation due to resonance absorption by rain or oxygen and water molecules in the air, have stronger linearity, and are more easily reflected. Therefore, the antennas used in millimeter wave communication (hereinafter, sometimes referred to as "millimeter wave antennas") require antenna gain that is higher than that of previous 4G communication.

[0005] Patent Document 1 discloses a millimeter-wave antenna mounted on a portable communication device such as a smartphone, which has a structure in which a cover member is laminated on a substrate on which an antenna element is provided, and an adhesive is used to bond the substrate and the cover member.

[0006] As such an adhesive, Patent Document 2 discloses, for example, an adhesive containing a polymer formed by polymerizing a mixture of monomers including 2-ethylhexyl acrylate, a specific alkyl methacrylate, and a hydroxyl-containing monomer, which can form an adhesive layer with a dielectric constant of 3.5 or less at a frequency of 100 kHz.

[0007] Furthermore, Patent Document 3 discloses an adhesive layer containing a specific acrylic polymer, a vinyl monomer having a polyepoxide chain, a photopolymerization initiator, and a crosslinking agent, and having a relative permittivity of 3.5 or less at a frequency of 1 MHz. (Prior Art Documents, Patent Documents)

[0008] Patent Document 1: Japanese Patent Application Publication No. 2019-186942; Patent Document 2: Japanese Patent Application Publication No. 2015-183178; Patent Document 3: Japanese Patent Application Publication No. 2020-007570 [Summary of the Invention]

[0009] [The problem the invention aims to solve]

[0010] It is known that for components constituting millimeter-wave antennas, the dielectric loss of the materials used reduces the millimeter-wave gain. In order not to reduce the antenna gain, low dielectric constant, especially low dielectric loss, is required in the high-frequency band of millimeter waves. The adhesives used to bond the components constituting the millimeter-wave antennas also require low dielectric constant and low dielectric loss in the high-frequency band.

[0011] Although the adhesive in Patent Document 2 has a low dielectric constant at low frequencies (100 kHz), its dielectric loss is not low enough at high frequencies. Similarly, although the adhesive layer in Patent Document 3 has a low relative dielectric constant at low frequencies (1 MHz), its dielectric loss is not low enough at high frequencies. Furthermore, the description only relates to the dielectric constant at low frequencies and does not disclose information related to dielectric loss at high frequencies, nor does it provide a solution to the problem addressed in this application.

[0012] This invention was conceived based on the circumstances described above. The object of this invention is to provide an adhesive composition capable of forming an adhesive layer with low dielectric constant and low dielectric loss at high frequencies, suitable for bonding components constituting millimeter-wave antennas. Another object of this invention is to provide an adhesive layer with low dielectric constant and low dielectric loss at high frequencies, suitable for bonding components constituting millimeter-wave antennas. Furthermore, another object of this invention is to provide an adhesive sheet having an adhesive layer with low dielectric constant and low dielectric loss at high frequencies, suitable for bonding components constituting millimeter-wave antennas. [Technical Means for Solving the Problem]

[0013] That is, the present invention provides an adhesive composition of the first state, having a dielectric constant of 2.0 to 5.0 at a frequency of 28 GHz and a dielectric loss of 0.0001 to 0.05 at a frequency of 28 GHz, and comprising a mixture of a methacrylate compound having a hydrocarbon group having 6 or more carbon atoms and a (meth)acrylate compound having a crosslinking functional group, and a portion thereof as a polymer or copolymer.

[0014] In the adhesive composition of the first embodiment of the present invention, the dielectric constant of 2.0 to 5.0 at a frequency of 28 GHz is preferably configured to improve the antenna gain of the millimeter-wave antenna using the adhesive composition to bond the constituent components.

[0015] The dielectric constant of the adhesive composition of the first state of the present invention is preferably 2.0 to 5.0 at a frequency of 60 GHz. This configuration is preferable in terms of improving the antenna gain of the millimeter-wave antenna using the adhesive composition of the first state of the present invention to bond the structural member.

[0016] Furthermore, the present invention provides a second-state adhesive composition having a dielectric constant of 2.0 to 5.0 at a frequency of 60 GHz and a dielectric loss of 0.0001 to 0.05 at a frequency of 60 GHz, and comprising a mixture of a methacrylate compound having a hydrocarbon group having 6 or more carbon atoms and a (meth)acrylate compound having a crosslinking functional group, and a portion thereof as a polymer or copolymer.

[0017] In the adhesive composition of the second state of the present invention, the dielectric constant of 2.0 to 5.0 at a frequency of 60 GHz is preferably configured to improve the antenna gain of the millimeter-wave antenna using the adhesive composition to bond the constituent components.

[0018] Preferably, the above-mentioned hydrocarbon group has an aliphatic group, contains an alicyclic group or contains an aromatic cyclic group.

[0019] The content of the methacrylate compound having a hydrocarbon group having 6 or more carbon atoms, or the structural unit derived from the compound, in the above mixture, a portion thereof, or copolymer thereof is preferably 25% by mass or more.

[0020] The content of the above-mentioned (meth)acrylate compound having crosslinking functional groups, or structural units derived from the compound, in the above-mentioned mixture, a portion thereof, or copolymer is preferably 0.1 to 30% by mass.

[0021] Preferably, the above-mentioned hydrocarbon group has an alicyclic group or an aromatic group at the end.

[0022] Furthermore, the present invention provides an adhesive layer formed from the above-described adhesive composition.

[0023] Furthermore, the present invention provides an adhesive sheet having the above-mentioned adhesive layer.

[0024] Furthermore, the present invention provides a millimeter-wave antenna, which at least includes the aforementioned adhesive sheet and a substrate, wherein the substrate has an antenna element on at least one side, and the adhesive sheet is attached to the side of the substrate having the antenna element. [Effects of the Invention]

[0025] The adhesive composition and adhesive layer of the present invention can exhibit lower dielectric constant and dielectric loss in the high-frequency band of millimeter waves, thereby suppressing the radiation loss of millimeter waves to a lower level. Therefore, by using the adhesive sheet of the present invention to bond the constituent components of a millimeter-wave antenna, it is possible to efficiently manufacture a millimeter-wave antenna exhibiting higher antenna gain.

Implementation Method

[0027] [Adhesive Composition] The adhesive composition of the first state of the present invention has a dielectric constant of 2.0 to 5.0 at a frequency of 28 GHz and a dielectric loss of 0.0001 to 0.05 at a frequency of 28 GHz, and comprises a mixture of a methacrylate compound having a hydrocarbon group having 6 or more carbon atoms and a (meth)acrylate compound having a crosslinking functional group, and a portion thereof as a polymer or copolymer.

[0028] The adhesive composition of the second state of the present invention has a dielectric constant of 2.0 to 5.0 at a frequency of 60 GHz and a dielectric loss of 0.0001 to 0.05 at a frequency of 60 GHz, and comprises a mixture of a methacrylate compound having a hydrocarbon group having 6 or more carbon atoms and a (meth)acrylate compound having a crosslinking functional group, and a portion thereof as a polymer or copolymer.

[0029] The adhesive composition of the present invention may have any form, for example: solvent type, emulsion type, hot melt type (hot melt type), solvent-free type (active energy line hardening type, such as monomer mixture, or monomer mixture and part of polymer, etc.).

[0030] As described above, the adhesive composition of the present invention may be solvent-based, that is, it may contain organic solvents.

[0031] As the above-mentioned organic solvent, any organic compound that can be used as a solvent may be used, such as: hydrocarbon solvents such as cyclohexane, hexane, heptane, and methylcyclohexane; aromatic solvents such as toluene and xylene; ester solvents such as butyl acetate, ethyl acetate, and methyl acetate; ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; and alcohol solvents such as methanol, ethanol, propanol, butanol, and isopropanol. The above-mentioned organic solvent may also be a mixed solvent containing two or more organic solvents.

[0032] The dielectric constant of the adhesive composition of the first state of the present invention is controlled to be low at 28 GHz, which can suppress the radiation loss of millimeter waves. The dielectric constant of the adhesive composition of the first state of the present invention at a frequency of 28 GHz is 5.0 or less, preferably 4.5 or less, more preferably 4.0 or less, further preferably 3.5 or less, further preferably 3.4 or less, particularly preferably 3.3 or less, and most preferably 3.2 or less, 3.1 or less, 3.0 or less, or 2.9 or less. The lower limit value is not particularly limited, and may be 2.0 or more, or 2.1 or more, or 2.2 or more. Furthermore, it is preferable that the dielectric constant of the adhesive composition of the second state at a frequency of 28 GHz is within the above range.

[0033] In this specification, the dielectric constant is determined by the method described in the embodiments disclosed below. Furthermore, the "relative dielectric constant" is the value obtained by dividing the "dielectric constant" by the "vacuum dielectric constant," but since the "vacuum dielectric constant" is 1, in this specification, the "dielectric constant" and the "relative dielectric constant" are treated as synonyms. Also, sometimes the adhesive composition of the first state sample of the present invention and the adhesive composition of the second state sample of the present invention are collectively referred to as "the adhesive composition of the present invention."

[0034] The adhesive composition of the first embodiment of the present invention preferably has a low dielectric loss at 28 GHz, which is advantageous in suppressing the radiation loss of millimeter waves. The dielectric loss of the adhesive composition of the first embodiment of the present invention at a frequency of 28 GHz is 0.050 or less, preferably 0.045 or less, more preferably 0.040 or less, further preferably 0.035 or less, further preferably 0.030 or less, particularly preferably 0.025 or less, and most preferably 0.020 or less. The lower limit value is 0.0001 or more, and may also be 0.0005 or more or 0.0010 or more. Furthermore, it is preferable that the dielectric loss of the adhesive composition of the second embodiment of the present invention at a frequency of 28 GHz is within the above-mentioned range.

[0035] The adhesive composition of the second state of the present invention has a low dielectric constant at 60 GHz, which can suppress the radiation loss of millimeter waves. The dielectric constant of the adhesive composition of the second state of the present invention at a frequency of 60 GHz is 5.0 or less, preferably 4.5 or less, more preferably 4.0 or less, further preferably 3.5 or less, further preferably 3.4 or less, particularly preferably 3.3 or less, and most preferably 3.2 or less, 3.1 or less, 3.0 or less, or 2.9 or less. The lower limit value is not particularly limited, and may be 2.0 or more, or 2.1 or more, or 2.2 or more. Furthermore, it is preferable that the dielectric constant of the adhesive composition of the first state of the present invention at a frequency of 60 GHz is within the above range.

[0036] The adhesive composition of the second state of the present invention preferably has a low dielectric loss at 60 GHz, which is advantageous in suppressing the radiation loss of millimeter waves. The dielectric loss of the adhesive composition of the second state of the present invention at a frequency of 60 GHz is 0.050 or less, preferably 0.045 or less, more preferably 0.040 or less, further preferably 0.035 or less, further preferably 0.030 or less, particularly preferably 0.025 or less, and most preferably 0.020 or less, 0.019 or less, 0.018 or less, 0.017 or less, 0.016 or less, 0.015 or less, 0.014 or less, 0.013 or less, or 0.012 or less. The lower limit of the dielectric loss at a frequency of 60 GHz is 0.0001 or more, and may also be 0.0005 or more, or 0.0010 or more. Furthermore, it is preferable that the dielectric loss of the adhesive composition of the first state of the present invention is within the above-mentioned range at a frequency of 60 GHz.

[0037] Preferably, the adhesive composition of the present invention has a low saturated moisture absorption rate. If the saturated moisture absorption rate is low, the attenuation of millimeter waves such as resonant absorption from water molecules can be suppressed, thus exhibiting excellent water resistance when used as an adhesive layer in millimeter wave antennas, etc., and is better at suppressing the radiation loss of millimeter waves. The adhesive composition of the present invention preferably has a saturated moisture absorption rate of 2.8% or less at 25°C and 90%RH, more preferably 2.7% or less, further preferably 2.6% or less, further preferably 2.5% or less, particularly preferably 2.4% or less, and most preferably 2.3% or less, 2.2% or less, 2.1% or less, 2.0% or less, 1.9% or less, 1.8% or less, 1.7% or less, 1.6% or less, 1.5% or less, 1.4% or less, 1.3% or less, 1.2% or less, 1.1% or less, 1.0% or less, 0.9% or less, 0.8% or less, 0.7% or less, or 0.6% or less. A lower saturated moisture absorption rate at 25°C and 90%RH can suppress the radiation loss of millimeter waves near room temperature. The lower limit of the saturated moisture absorption rate is not particularly limited. For example, it can be 0.3% or more, or 0.4% or more, or 0.5% or more.

[0038] The saturated moisture absorption rate of the adhesive composition of the present invention at 65°C and 90%RH is preferably 2.8% or less, more preferably 2.6% or less, further preferably 2.4% or less, further preferably 2.3% or less, particularly preferably 2.2% or less, and most preferably 2.1% or less, 2.0% or less, 1.9% or less, 1.8% or less, 1.7% or less, 1.6% or less, 1.5% or less, 1.4% or less, 1.3% or less, 1.2% or less, 1.1% or less, 1.0% or less, 0.9% or less, 0.8% or less, or 0.7% or less. The lower limit of the above-mentioned saturated moisture absorption rate is not particularly limited; for example, it may be 0.4% or more, or 0.5% or more, or 0.6% or more. If the saturated moisture absorption rate is low at 65°C and 90%RH, then even when placed in a high-temperature environment with adhesive layers applied, the radiation loss of millimeter waves can be suppressed.

[0039] The saturated moisture absorption rate of the adhesive composition of the present invention at 85°C and 85%RH is preferably 5.0% or less, more preferably 4.0% or less, further preferably 3.5% or less, further preferably 3.0% or less, particularly preferably 2.8% or less, and most preferably 2.6% or less, 2.4% or less, 2.2% or less, 2.0% or less, 1.8% or less, 1.6% or less, 1.4% or less, 1.2% or less, 1.0% or less, or 0.8% or less. The lower limit of the above-mentioned saturated moisture absorption rate is not particularly limited; for example, it can be 0.4% or more, or 0.5% or more, or 0.6% or more. If the saturated moisture absorption rate at 85°C and 85%RH is low, even when placed in a high-temperature environment while in the state of applying an adhesive layer, the radiation loss of millimeter waves can be suppressed.

[0040] The aforementioned saturated moisture absorption rate under various temperature and humidity conditions can be calculated, for example, from the weight of the sample in a dry state (w1) and the weight (w2) at the point when the sample stops changing weight in an atmosphere of 65°C and 90%RH (when the moisture absorption rate is saturated), using the following formula. It can also be calculated separately under conditions of 25°C and 90%RH and 85°C and 85%RH. Furthermore, the values ​​of w1 and w2 are assumed to be measured under the same temperature and humidity. Saturated moisture absorption rate (%) = {(w2 - w1) / w1} × 100

[0041] The adhesive composition of the present invention preferably has a low change in dielectric loss due to moisture absorption, which is advantageous in suppressing the radiation loss of millimeter waves and its change over time. The change in dielectric loss due to moisture absorption of the adhesive composition of the present invention at a frequency of 28 GHz is preferably 0.006 or less, more preferably 0.005 or less, and even more preferably 0.004 or less. The lower limit of the change in dielectric constant due to moisture absorption is not particularly limited, and may be, for example, 0.0001 or more, 0.0002 or more, or 0.0003 or more.

[0042] The change in dielectric loss due to moisture absorption of the adhesive composition of the present invention at a frequency of 60 GHz is preferably 0.003 or less, more preferably 0.002 or less, and even more preferably 0.001 or less. The lower limit of the change in dielectric constant due to moisture absorption is not particularly limited, and may be, for example, 0.0001 or more, or 0.0002 or more, 0.0003 or more, 0.0004 or more, 0.0005 or more, 0.0006 or more, 0.0007 or more, 0.0008 or more, or 0.0009 or more.

[0043] The changes in dielectric loss at the aforementioned frequencies of 28 GHz and 60 GHz were maintained for more than 5 days in an atmosphere of 65°C and 90%RH, and then restored to conditions of 23±1°C and 52%±1%RH (time elapsed = 0 minutes). Dielectric loss was measured every 10 minutes from 4 minutes to 180 minutes. The maximum value (Dfmax) and minimum value (Dfmin) of each frequency were calculated using the following formula: Change in dielectric loss = Dfmax - Dfmin

[0044] Because the water vapor transmission rate of the adhesive composition of the present invention is controlled to be low, the movement of water molecules in the adhesive composition can be suppressed, thereby suppressing variations in the radiation loss of millimeter waves. The water vapor transmission rate of the adhesive composition of the present invention at 40°C and 92%RH is preferably 430 g / m² / day or less, more preferably 300 g / m² / day or less, further preferably 250 g / m² / day or less, further preferably 200 g / m² / day or less, particularly preferably 150 g / m² / day or less, and most preferably 100 g / m² / day or less, 50 g / m² / day or less, or 30 g / m² / day or less. The lower limit of the water vapor transmission rate is not particularly limited; for example, it can be 10 g / m² / day or more, or 20 g / m² / day or more, or 25 g / m² / day or more.

[0045] The above-mentioned water vapor transmission rate (WVTR) is based on the cup method. It can be determined by measuring the weight (w1) of the dry calcium chloride in the adhesive layer that has been isolated from the outside, and the weight (w2) of the sample after a specified time (when the moisture absorption rate is saturated) in an atmosphere of 40°C and 92%RH. The weight change is then converted into the unit area (1 m2) of the adhesive layer per unit time (1 day).

[0046] The dielectric constant or dielectric loss, saturated moisture absorption rate, change in dielectric loss due to moisture absorption, and water vapor transmission rate of the adhesive composition of the present invention at 28 GHz or 60 GHz can be adjusted by adjusting the monomer composition, the type or content of additives, etc. In this specification, the dielectric constant or dielectric loss at 28 GHz or 60 GHz is determined by the method described in the examples disclosed below.

[0047] Furthermore, the dielectric constant, dielectric loss, saturated moisture absorption rate and water vapor transmission rate of the adhesive composition of the present invention refer to the dielectric constant, dielectric loss, saturated moisture absorption rate and water vapor transmission rate of the adhesive layer formed by the adhesive composition of the present invention.

[0048] The adhesive composition of the present invention, by comprising a mixture, a portion thereof, or a copolymer of a specific methacrylate compound and a (meth)acrylate compound, can control the dielectric constant and dielectric loss at high frequencies to be low, and suppress moisture absorption, which is a cause of dielectric loss deterioration. Furthermore, the aforementioned "mixture, a portion thereof, or a copolymer" is sometimes referred to as a methacrylate copolymer. Also, "methacrylate compound" refers to a compound having a "methacrylic acid" group, and "(meth)acrylate compound" refers to a compound having at least one of "acrylic acid" and "methacrylic acid". Also, "(meth)acrylic acid" means any one or both of "acrylic acid" and "methacrylic acid".

[0049] The above-mentioned partial polymer means a composition in which one or more monomer components constituting the above-mentioned mixture are partially polymerized.

[0050] The content of the above-mentioned methacrylic acid copolymer in the adhesive composition of the present invention is not particularly limited, but it is preferably 75% by mass or more (e.g., 75 to 99.9% by mass), and more preferably 85% by mass or more (e.g., 85 to 99.9% by mass).

[0051] [Mixtures, a portion thereof, or copolymers (methacrylic acid copolymers)] The adhesive composition of the present invention is a methacrylic acid adhesive composition using a mixture, a portion thereof, or copolymers (methacrylic acid copolymers) as the base polymer. The content of the aforementioned methacrylic acid copolymer is not particularly limited, but is preferably 75% by mass or more (e.g., 75 to 99.9% by mass) relative to 100% of the total amount of the adhesive composition of the present invention, and preferably 85% by mass or more (e.g., 85 to 99.9% by mass).

[0052] Examples of adhesive compositions of the present invention include water-dispersible compositions (emulsion compositions) that use the above-mentioned copolymer as an essential component, or active energy line hardening compositions that use the above-mentioned mixture or a portion thereof as an essential component, wherein, a composition that uses the mixture or a portion thereof as an essential component is preferred.

[0053] The methacrylic copolymer of the present invention comprises a methacrylate compound having a hydrocarbon group having 6 or more carbon atoms and a (meth)acrylate compound having a crosslinking functional group as constituent monomers.

[0054] <Methacrylate compound having 6 or more carbon groups> The methacrylate compound used in the above-mentioned methacrylate copolymer contains a hydrocarbon group having 6 or more carbon groups. Preferably, the hydrocarbon group having 6 or more carbon groups in the above-mentioned methacrylate compound is an aliphatic group, an alicyclic group, or an aromatic ring group. The methacrylate compound having such hydrocarbon groups can be used alone or in combination of two or more.

[0055] Since the main structural unit of the above-mentioned methacrylic acid copolymer is derived from methacrylate compounds and has α-methyl groups, the polarization near the main chain is reduced compared to the case where it is derived from acrylate compounds. As a result, the dielectric loss is considered to be reduced. Furthermore, compared to acrylonitrile groups, methacrylic acid groups are more hydrophobic, and moisture absorption is suppressed. Therefore, the deterioration and change in dielectric loss at high frequencies caused by moisture absorption can be suppressed.

[0056] If the above-mentioned methacrylate compound has an alicyclic or aromatic group, it is easy to obtain moderate cohesive force and strong adhesion in the methacrylate copolymer. Furthermore, increasing the gel fraction makes it easy to obtain excellent foaming peel resistance. Moreover, it is easy to obtain moderate softness, excellent stress relief, and excellent step followability in the adhesive layer.

[0057] When the hydrocarbon group with 6 or more carbon atoms is an aliphatic group, the number of carbon atoms in the hydrocarbon group is preferably 8 or more, more preferably 9 or more, and even more preferably 10 or more. The number of carbon atoms in the hydrocarbon group is preferably 22 or less, more preferably 20 or less, and even more preferably 16 or less.

[0058] Examples of methacrylate compounds in which the hydrocarbon group having 6 or more carbon atoms is an aliphatic group include: hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, isooctyl methacrylate, nonyl methacrylate, isononyl methacrylate, decyl methacrylate, isodecanyl methacrylate, undecyl methacrylate, lauryl methacrylate, tridecyl methacrylate, tetradecyl methacrylate, pentadecyl methacrylate, hexadecyl methacrylate, heptadecanyl methacrylate, octadecyl methacrylate, isostearyl methacrylate, stearyl methacrylate, nonadecanyl methacrylate, eicosyl methacrylate, etc. Among these, lauryl methacrylate, tridecyl methacrylate, and isodecanyl methacrylate are preferred.

[0059] The content of the methacrylate compound in the methacrylate copolymer of the present invention, wherein the hydrocarbon group having 6 or more carbon atoms is an aliphatic group, is not particularly limited. It is preferably 25% by mass or more, more preferably 25.0 to 99.5% by mass, and even more preferably 30.0 to 99.3% by mass, and even more preferably 40.0 to 99.0% by mass, relative to 100% by mass of all structural units. From the perspective of reducing the dielectric constant and dielectric loss at high frequencies, it is preferable to use 25% by mass or more.

[0060] When the hydrocarbon group with 6 or more carbon atoms is an alicyclic group, the number of carbon atoms in the hydrocarbon group is preferably 6 or more, more preferably 8 or more. The number of carbon atoms in the hydrocarbon group is preferably 22 or less, more preferably 16 or less.

[0061] Examples of methacrylate compounds whose hydrocarbon group with 6 or more carbon atoms is an alicyclic group include: cycloalkyl methacrylates having cycloalkane rings (cyclopentane ring, cyclohexane ring, cycloheptane ring, cyclooctane ring, etc.), methacrylates having bicyclic hydrocarbon rings (pinene, pinene, succinate, norsuccinate, norcamphene, etc.), and methacrylates having tricyclic or more aliphatic hydrocarbon rings (bicyclopentane ring, bicyclopentene ring, adamantane ring, tricyclopentane ring, tricyclopentene ring, etc.).

[0062] Examples of the above-mentioned cycloalkyl methacrylates include: cyclohexyl methacrylate, 3,3,5-trimethylcyclohexyl methacrylate, cycloheptyl methacrylate, cyclooctyl methacrylate, etc.

[0063] Examples of the above-mentioned methacrylates having a bicyclic hydrocarbon ring include methacrylate, isomethacrylate, etc.

[0064] Examples of methacrylates having three or more hydrocarbon rings include: dicyclopentyl methacrylate, dicyclopentoxyethyl methacrylate, tricyclopentyl methacrylate, 1-adamantyl methacrylate, 2-methyl-2-adamantyl methacrylate, 2-ethyl-2-adamantyl methacrylate, etc.

[0065] When the hydrocarbon group with 6 or more carbon atoms is an aromatic ring group, the number of carbon atoms in the hydrocarbon group is preferably 6 to 14, and more preferably 6 to 10.

[0066] The methacrylate compound whose hydrocarbon group with 6 or more carbon atoms is an aromatic ring group can be exemplified by compounds having an aromatic carbon ring (e.g., a monocyclic carbon ring such as a benzene ring, or a condensed carbon ring such as a naphthalene ring). Specific examples include benzyl methacrylate, phenyl methacrylate, naphthyl methacrylate, and 6-(1,1'-biphenyl-4-oxy)hexyl methacrylate.

[0067] The total content of methacrylate compounds containing alicyclic or aromatic ring groups of the hydrocarbon groups with 6 or more carbons in the methacrylate copolymer of the present invention is not particularly limited, but is preferably 1.0 to 60.0% by mass relative to 100% of all structural units, more preferably 5.0 to 55.0% by mass, and even more preferably 10.0 to 50.0% by mass.

[0068] The above-mentioned methacrylate compound may have a (poly)oxyalkyl chain. When a (poly)oxyalkyl chain is present, the hydrocarbon group having 6 or more carbon atoms is preferably located at the end of the ester portion of the above-mentioned methacrylate compound. The number of oxygen atoms in the (poly)oxyalkyl chain (i.e., the number of repetitions of the alkyl group) is preferably 1 to 10, more preferably 1 to 3. The hydrocarbon group having 6 or more carbon atoms at the end may be any one of an aliphatic group, an alicyclic group, or an aromatic group, but is preferably an alicyclic group or an aromatic group, and even more preferably an aromatic group.

[0069] The content of the methacrylate compound having (poly)oxyalkyl chain in the methacrylate copolymer of the present invention is not particularly limited, but is preferably 1.0 to 30.0% by mass relative to 100% of all structural units, more preferably 5.0 to 25.0% by mass, and even more preferably 10.0 to 20.0% by mass.

[0070] In the above-mentioned methacrylate compounds having (poly)oxyalkyl chains, when an aromatic group is present at the end, the polarizability of the repeating unit as a whole is reduced, thus being more effective in reducing dielectric loss in the high-frequency band.

[0071] Relative to 100% by mass of all structural units, the total content of the methacrylate compounds having 6 or more carbon groups in the above-mentioned methacrylate copolymer is preferably 25% by mass or more, more preferably 25.0 to 99.5% by mass, further preferably 30.0 to 99.3% by mass, and even more preferably 40.0 to 99.0% by mass. From the perspective of reducing the dielectric constant and reducing the dielectric loss at high frequencies, it is preferable to use 25% by mass or more.

[0072] <(Meth)acrylate compound containing crosslinking functional groups> The above-mentioned methacrylate copolymer contains (meth)acrylate compounds with crosslinking functional groups in the ester portion. Therefore, when a crosslinking agent is used, crosslinking occurs, increasing the gel fraction and easily obtaining excellent foaming peel resistance. Furthermore, since good cohesive force is easily obtained, strong adhesion is easily achieved. Moreover, whitening of adhesive sheets in high humidity environments is easily suppressed.

[0073] The crosslinking functional groups in the aforementioned (meth)acrylate compounds containing crosslinking functional groups, from the perspective of easily adjusting the gel fraction, can be exemplified by: hydroxyl, carboxyl, anhydride, glycidyl, and other epoxy-containing groups, isocyanate, aziridinyl, etc. Among these, hydroxyl is preferred from the perspective of easily adjusting the gel fraction. The aforementioned (meth)acrylate compounds containing crosslinking functional groups can be used alone or in combination of two or more.

[0074] Examples of (meth)acrylate compounds containing crosslinking functional groups with hydroxyl groups include: 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, hydroxyoctyl (meth)acrylate, hydroxydecyl (meth)acrylate, hydroxylauryl (meth)acrylate, and 4-hydroxymethylcyclohexyl (meth)acrylate. Among these, 2-hydroxyethyl (meth)acrylate is preferred from the perspective of easily obtaining good agglomeration strength and reliable adhesion at high temperatures.

[0075] Relative to 100% mass of all structural units, the content of the above-mentioned (meth)acrylate compound containing crosslinking functional groups in the methacrylate copolymer of the present invention is preferably 0.1 to 30.0% by mass, more preferably 0.2 to 20.0% by mass, further preferably 0.3 to 10.0% by mass, and even more preferably 0.5 to 5.0% by mass. From the perspective of adjusting the gel fraction, it is preferable to use 0.1% by mass or more, and from the perspective of reducing the dielectric constant and reducing the dielectric loss at high frequencies, it is preferable to use 30.0% by mass or less.

[0076] <Comonomer> In addition to the methacrylate compounds having 6 or more carbon groups and the (meth)acrylate compounds containing crosslinking functional groups, the above-mentioned methacrylate copolymers may also contain comonomers. Comonomers may be used alone or in combination of two or more.

[0077] Examples of the aforementioned comonomers include: acrylate compounds having hydrocarbon groups of 1 to 24 carbon atoms; methacrylate compounds having hydrocarbon groups of 1 to 5 carbon atoms; substituted methylene compounds in which all carbons of the repeating unit of the main chain have side chains; heterocyclic monomers; carboxyl monomers; nitrile monomers; isocyanate monomers; amide monomers; amino monomers; alkoxyalkyl esters of (meth)acrylate having alkoxy groups of 5 or fewer carbon atoms; sulfonic acid monomers; phosphate monomers; vinyl esters (vinyl acetate, vinyl propionate, etc.); aromatic vinyl compounds (styrene, vinyltoluene, etc.); olefins or dienes (ethylene, propylene, butadiene, isoprene, isobutylene, etc.); vinyl ethers (vinyl alkyl ethers, etc.); vinyl chloride; vinyl alcohol; macromonomers with a weight average molecular weight of 30,000 or less; and polyfunctional monomers having two or more polymerizable functional groups. These can be used alone or in combination of two or more.

[0078] Furthermore, the adhesive composition of the present invention is preferably free of or substantially free of acidic monomers (e.g., carboxyl monomers, sulfonyl monomers, phosphate monomers, etc.). This configuration is preferable in that it can achieve excellent corrosion protection for antenna elements or wiring. Furthermore, the content of acidic monomers is preferably 0.05% by weight or less (e.g., 0 to 0.05% by weight), more preferably 0.01% by weight or less (e.g., 0 to 0.01% by weight), and even more preferably 0.001% by weight or less (e.g., 0 to 0.001% by weight), which can be considered substantially free of them relative to the total amount of the adhesive composition.

[0079] Among the above-mentioned copolymer monomers, heterocyclic monomers, carboxyl monomers, amide monomers, amino monomers, sulfonic acid monomers, and phosphate monomers are better at obtaining moderate cohesive force in the adhesive layer, and are better at increasing the 180° peel adhesion to glass plates or acrylic plates and obtaining strong adhesion. From the perspective of preventing metal corrosion, heterocyclic monomers are preferred.

[0080] Examples of the methacrylate compounds having a hydrocarbon group having 1 to 5 carbon atoms include: methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, amyl methacrylate, isopropyl methacrylate, isobutyl methacrylate, dibutyl methacrylate, tributyl methacrylate, isoamyl methacrylate, etc.

[0081] Examples of the above-mentioned acrylate compounds having hydrocarbon groups having 1 to 24 carbon atoms include: methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate, dibutyl acrylate, tributyl acrylate, pentyl acrylate, isoamyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, isooctyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, isodecanyl acrylate, undecyl acrylate, dodecyl acrylate, lauryl acrylate, tridecyl acrylate, tetradecyl acrylate, pentadecyl acrylate, acrylic acid Hexadecyl acrylate, heptadecanyl acrylate, octadecyl acrylate, isostearyl acrylate, stearyl acrylate, nonadecanyl acrylate, eicosyl acrylate, cyclohexyl acrylate, 3,3,5-trimethylcyclohexyl acrylate, cycloheptyl acrylate, cyclooctyl acrylate, urethane acrylate, isourethane acrylate, dicyclopentyl acrylate, dicyclopentoxyethyl acrylate, tricyclopentyl acrylate, 1-adamantyl acrylate, 2-methyl-2-adamantyl acrylate, 2-ethyl-2-adamantyl acrylate, phenyl acrylate, naphthyl acrylate, 6-(1,1'-biphenyl-4-oxy)hexyl acrylate, etc.

[0082] The above-mentioned heterocyclic monocyclic system has the following heterocyclic copolymerizable monomers: heterocycles with only nitrogen atoms as heteroatoms (pyrrolidine, pyrrole, imidazole, pyrazole, piperidine, pyridine, pyrimidine, pyrrololine, piperidine, pyridine, etc.), heterocycles with both nitrogen and oxygen atoms (pyrrolidone, acetazole, isoacetazole, morpholine, morpholinone, piperidinone, lactone, acetazole, morpholinodione, succinimide, succinimide, etc.), heterocycles with both nitrogen and sulfur atoms (thiazole, isothiazole, thiazolinone, etc.), heterocycles with oxygen atoms (lactone, tetrahydrofuran, furan, tetrahydropiperan, diazonium, etc.), and heterocycles with sulfur atoms (tetrahydrothiophene, thiophene, tetrahydrothioran, thioran, etc.).

[0083] If the methacrylic acid copolymer of the present invention contains heterocyclic monomers, moderate flexibility can be obtained in the adhesive layer, and excellent stress relief and excellent step follow properties can be easily obtained.

[0084] Examples of heterocyclic monomers having only nitrogen atoms as heteroatoms include: N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperidone, N-vinylpyridine, N-vinylpyrrole, N-vinylpyrrole, N-vinylimidazol, N-(meth)acrylpiperidine, N-(meth)acrylpyrroleidine, N-vinylpyrazole, etc.

[0085] Examples of heterocyclic monomers having a nitrogen atom and an oxygen atom as heteroatoms include: N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-(meth)acryl-2-pyrrolidone, N-vinyl acetazole, N-vinyl isoacetazole, N-vinylmorpholine, N-vinyl-3-morpholinone, N-vinyl-2-caprolactone, N,N-dimethyl(meth)acrylamide, and N,N-diethyl(meth)acrylamide. Amines, N-vinyl-1,3-vinyl-2-one, N-vinyl-3,5-morpholinidone, N-(meth)propenyloxymethylene succinyldiimide, N-(meth)propenyl-6-oxyhexamethylene succinyldiimide, N-(meth)propenyl-8-oxyhexamethylene succinyldiimide, N-methyl succinyldiimide, N-ethyl succinyldiimide, N-butyl succinyldiimide, N-octyl succinyldiimide, N-2-ethylhexyl succinyldiimide, N-cyclohexyl succinyldiimide, N-lauryl succinyldiimide, etc.

[0086] Examples of heterocyclic monomers having a heterocycle containing nitrogen and sulfur atoms as heteroatoms include N-vinylthiazole and N-vinylisothiazole.

[0087] Of these, N-vinyl-2-pyrrolidone is particularly preferred.

[0088] Examples of the aforementioned carboxyl-containing monomers include (meth)acrylic acid, itaconic acid, maleic acid, fumaric acid, butenoic acid, and isobutenoic acid. Furthermore, the aforementioned carboxyl-containing monomers may include, for example, maleic anhydride and itaconic anhydride. Also, derivatives formed by ester bonding with itaconic acid or the like may also be examples.

[0089] Examples of the above-mentioned nitrile-containing monomers include (meth)acrylonitrile, etc.

[0090] Examples of the isocyanate-containing monomers mentioned above include ethyl 2-isocyanate of (meth)acrylate.

[0091] Examples of the above-mentioned monomers containing amide groups include: (meth)acrylamides; N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dipropyl(meth)acrylamide, N,N-diisopropyl(meth)acrylamide, N,N-di(n-butyl)(meth)acrylamide, N,N-di(tert-butyl)( N,N-dialkyl(meth)acrylamides such as methyl)acrylamide; N-alkyl(meth)acrylamides such as N-ethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N-butyl(meth)acrylamide, and N-n-butyl(meth)acrylamide; N-vinylcarboxylates such as N-vinylacetamide; monomers having hydroxyl and acetyl groups, such as N-(2- N-hydroxyalkyl (meth)acrylamides, such as hydroxyethyl (meth)acrylamide, N-(2-hydroxypropyl (meth)acrylamide), N-(1-hydroxypropyl (meth)acrylamide), N-(3-hydroxypropyl (meth)acrylamide), N-(2-hydroxybutyl (meth)acrylamide), N-(3-hydroxybutyl (meth)acrylamide), and N-(4-hydroxybutyl (meth)acrylamide); monomers having alkoxy and acrylamide groups, such as N-methoxymethyl (meth)acrylamide, N-methoxyethyl (meth)acrylamide, and N-butoxymethyl (meth)acrylamide; and N-alkoxyalkyl (meth)acrylamides, such as N,N-dimethylaminopropyl (meth)acrylamide and N-(meth)acrylamide morpholine.

[0092] Furthermore, the above-mentioned (meth)acrylamides also include various N-alkoxyalkyl (meth)acrylamides, such as N-methoxymethyl (meth)acrylamide, N-butoxymethyl (meth)acrylamide, etc.

[0093] Examples of the above-mentioned amino-containing monomers include: (meth)acrylate aminoethyl ester, (meth)acrylate N,N-dimethylaminoethyl ester, (meth)acrylate tributylaminoethyl ester, etc.

[0094] Examples of alkoxyalkyl esters of (meth)acrylate having an alkoxy group of 5 or fewer carbon atoms include: 2-methoxyethyl ester of (meth)acrylate, 2-ethoxyethyl ester of (meth)acrylate, methoxytriethylene glycol ester of (meth)acrylate, 3-methoxypropyl ester of (meth)acrylate, 3-ethoxypropyl ester of (meth)acrylate, 4-methoxybutyl ester of (meth)acrylate, 4-ethoxybutyl ester of (meth)acrylate, etc.

[0095] As the above-mentioned sulfonic acid group-containing monomer, examples include sodium vinyl sulfonate, etc.

[0096] The above-described macromonomer system is a high molecular weight monomer synthesized by polymerizing a plurality of the above-described monomer components. When using macromonomers, the structural units derived from the monomer components constituting the macromonomers will exist to a certain extent continuously in the base polymer. Therefore, by using macromonomers, higher-order structures derived from macromonomers can be introduced into the base polymer, and the properties required as an adhesive (adhesion or cohesive force, step follower, etc.) can be easily adjusted. The weight average molecular weight of the above-described macromonomers is preferably 3,000 to 35,000, more preferably 4,000 to 30,000, further preferably 5,000 to 25,000, and further preferably 6,000 to 20,000.

[0097] Examples of multifunctional monomers having two or more polymerizable functional groups include: hexanediol di(meth)acrylate, butanediol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethane tri(meth)acrylate, allyl methacrylate, ethylene methacrylate, divinylbenzene, polyester acrylate, and urethane acrylate. Multifunctional monomers can be used alone or in combination of two or more.

[0098] The content of the aforementioned multifunctional monomer in the methacrylic acid copolymer of the present invention is not particularly limited, but is preferably 0.5% by mass or less (e.g., 0 to 0.5% by mass), more preferably 0 to 0.35% by mass, and even more preferably 0 to 0.2% by mass, relative to 100% by mass of all structural units. If the content of the aforementioned multifunctional monomer is 0.5% by mass or less, the adhesive layer has appropriate cohesive force, and the adhesion or step absorption is easily improved, which is preferable. Furthermore, when a crosslinking agent is used, the multifunctional monomer may not be used. When a crosslinking agent is not used, the content of the multifunctional monomer is preferably 0.001 to 0.5% by mass, more preferably 0.001 to 0.35% by mass, and even more preferably 0.002 to 0.2% by mass.

[0099] The total content of the copolymeric monomers in the above-mentioned methacrylic acid copolymer is not particularly limited, but is preferably 30.0% by mass or less, and more preferably 15.0% by mass or less, relative to 100% by mass of all structural units.

[0100] The above-mentioned methacrylate copolymer can be obtained by mixing a methacrylate compound having a hydrocarbon group having 6 or more carbon atoms, a (meth)acrylate compound containing a crosslinking functional group, and a comonomer, or by polymerization using a known or conventional polymerization method. Examples of such polymerization methods include solution polymerization, emulsion polymerization, bulk polymerization, and polymerization using active energy line irradiation (active energy line polymerization). Among these, solution polymerization and active energy line polymerization are preferred, and active energy line polymerization is even more preferred, considering the transparency, water resistance, and cost of the adhesive layer.

[0101] Examples of active energy rays used in the above-mentioned active energy line polymerization (photopolymerization) include ionizing radiation such as alpha rays, beta rays, gamma rays, neutron rays, and electron beams, or ultraviolet rays, with ultraviolet rays being particularly preferred. Furthermore, there are no particular limitations on the irradiation energy, irradiation time, or irradiation method of the active energy rays, as long as they can activate the photopolymerization initiator and produce monomer components.

[0102] Various common solvents can also be used in the polymerization of the above-mentioned methacrylic acid copolymers. Examples of such solvents include: esters (ethyl acetate, n-butyl acetate, etc.), aromatic hydrocarbons (toluene, benzene, etc.), aliphatic hydrocarbons (n-hexane, n-heptane, etc.), alicyclic hydrocarbons (cyclohexane, methylcyclohexane, etc.), ketones (methyl ethyl ketone, methyl isobutyl ketone, etc.). Solvents can be used alone or in combination of two or more.

[0103] Furthermore, during the polymerization of the above-mentioned methacrylic acid copolymers, polymerization initiators such as thermal polymerization initiators or photopolymerization initiators (photoinitiators) may be used, depending on the type of polymerization reaction. Polymerization initiators may be used alone or in combination of two or more.

[0104] There are no particular limitations on the above-mentioned photopolymerization initiators. Examples include: benzoin ether-based photopolymerization initiators, acetophenone-based photopolymerization initiators, α-keto alcohol-based photopolymerization initiators, aromatic sulfonyl chloride-based photopolymerization initiators, photoactive oxime-based photopolymerization initiators, benzoin-based photopolymerization initiators, benzophenone-based photopolymerization initiators, ketal-based photopolymerization initiators, and 9-oxosulfuron-based photopolymerization initiators. Photopolymerization initiators can be used alone or in combination of two or more.

[0105] Examples of benzoin ether-based photopolymerization initiators include: benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, benzoin isopropyl ether, benzoin isobutyl ether, 2,2-dimethoxy-1,2-diphenylethane-1-one, and anisole methyl ether. Examples of acetophenone-based photopolymerization initiators include: 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexylphenyl ketone, 4-phenoxydichloroacetophenone, and 4-(tert-butyl)dichloroacetophenone. Examples of α-ketool-based photopolymerization initiators include: 2-methyl-2-hydroxyphenylacetone and 1-[4-(2-hydroxyethyl)phenyl]-2-methylpropane-1-one. Examples of aromatic sulfonyl chloride-based photopolymerization initiators include: 2-naphthalenesulfonyl chloride. Examples of photoactive oxime-based photopolymerization initiators include 1-phenyl-1,1-propanedione-2-(O-ethoxycarbonyl)-oxime. Examples of benzoin-based photopolymerization initiators include benzoin. Examples of benzoin-based photopolymerization initiators include benzoin. Examples of benzophenone-based photopolymerization initiators include benzoin. Examples of benzophenone-based photopolymerization initiators include benzophenone, benzoylbenzoic acid, 3,3'-dimethyl-4-methoxybenzophenone, polyvinylbenzophenone, and α-hydroxycyclohexylphenyl ketone. Examples of ketal-based photopolymerization initiators include benzophenone dimethyl ketal. Examples of 9-oxosulfuric acid (OSA) photopolymerization initiators include: 9-oxosulfuric acid, 2-chloro-9-oxosulfuric acid, 2-methyl-9-oxosulfuric acid, 2,4-dimethyl-9-oxosulfuric acid, isopropyl-9-oxosulfuric acid, 2,4-diisopropyl-9-oxosulfuric acid, dodecyl-9-oxosulfuric acid, etc.

[0106] There is no particular limitation on the amount of the above-mentioned photopolymerization initiator used. For example, it is more preferably 0.001 to 10.0 parts by mass relative to 100 parts by mass of all structural units of the above-mentioned methacrylic acid copolymer, and more preferably 0.01 to 5.0 parts by mass.

[0107] Furthermore, examples of the aforementioned thermal polymerization initiators include: azo polymerization initiators, peroxide polymerization initiators (e.g., benzoyl peroxide, tributyl maleate peroxide, etc.), and redox polymerization initiators. Among these, the azo polymerization initiator disclosed in Japanese Patent Application Publication No. 2002-69411 is preferred. Examples of the aforementioned azo polymerization initiators include: 2,2'-azobisisobutyronitrile (AIBN), 2,2'-azobis-2-methylbutyronitrile (AMBN), dimethyl 2,2'-azobis(2-methylpropionic acid), and 4,4'-azobis-4-cyanopentanoic acid.

[0108] Regarding the amount of the above-mentioned thermal polymerization initiator, for example, in the case of the above-mentioned azo polymerization initiator, it is preferably 0.05 to 0.5 parts by mass relative to 100 parts by mass of all structural units of the above-mentioned methacrylic acid copolymer, and more preferably 0.1 to 0.3 parts by mass.

[0109] The weight-average molecular weight (Mw) of the copolymer forming the adhesive layer of the present invention is preferably 100,000 to 5,000,000, more preferably 200,000 to 4,000,000, and even more preferably 300,000 to 3,000,000. A composition with a weight-average molecular weight of 100,000 or more is preferred for improved adhesion or retention properties and improved resistance to foaming and peeling. A composition with a weight-average molecular weight of 5,000,000 or less is preferred for easily improved adhesion and improved resistance to foaming and peeling.

[0110] The weight-average molecular weight (Mw) of the above copolymer can be obtained by converting polystyrene using GPC (Gel Permeation Chromatography). For example, a high-speed GPC apparatus (product name "HPLC-8120GPC", manufactured by Tosoh Corporation) can be used for determination under the following conditions: • Column: TSKgel SuperHZM-H / HZ4000 / HZ3000 / HZ2000 • Solvent: Tetrahydrofuran • Flow rate: 0.6 ml / min

[0111] The glass transition temperature (Tg) of the above-mentioned copolymer is preferably -70 to 100°C, more preferably -65 to 50°C, and even more preferably -60 to 10°C. If the glass transition temperature of the above-mentioned methacrylic acid copolymer is above -70°C, the cohesive strength is improved, and the foaming peel resistance is easily improved, which is preferable. Furthermore, if the glass transition temperature is below 100°C, the adhesive composition has moderate flexibility, and it is easy to obtain good adhesion or good step absorption, and it is easy to obtain excellent bonding reliability, which is preferable.

[0112] The glass transition temperature (Tg) of the above copolymer is the glass transition temperature (theoretical value) expressed by the following FOX formula. In the following formula, Tg represents the glass transition temperature of the above copolymer (unit: K), Tgi monomer i represents the glass transition temperature when forming the homopolymer (unit: K), and Wi represents the mass fraction of monomer i in the total monomer composition (i = 1, 2, ..., n). 1 / Tg = W1 / Tg1 + W2 / Tg2 + ... + Wn / Tgn

[0113] The Tg of the homopolymer of the monomer constituting the above copolymer can be the following values: • Lauryl methacrylate -65℃ • 2-Ethylhexyl methacrylate -10℃ • Lauryl acrylate 0℃ • 2-Ethylhexyl methacrylate -70℃ • Isodecyl methacrylate -41℃ • 2-Hydroxyethyl methacrylate 55℃ • Methyl methacrylate 105℃ • Cyclohexyl methacrylate 66℃ • Isomethyl methacrylate 173℃ • Dicyclopentyl methacrylate 175℃ • Methacrylate 228℃ • N-Vinylpyrrolidone 86℃ • 2-Phenoxyethyl methacrylate 5℃ • Benzyl methacrylate 54℃ • 2-(2-Methoxyethoxy)ethyl methacrylate -3℃

[0114] Furthermore, the Tg of the homopolymer of the monomer not described above can be the value recorded in the "Polymer Handbook" (3rd edition, John Wiley & Sons, Inc., 1989). Moreover, the Tg of the homopolymer of the monomer not described in the aforementioned literature can be the value obtained by the above-described measurement method (based on the peak temperature of tanδ in the viscoelasticity test).

[0115] In the polymerization of the above-mentioned methacrylic acid copolymers, a chain transfer agent may be used to adjust the molecular weight. Examples of such chain transfer agents include: 2-mercaptoethanol, α-thioglycerol, 2,3-dimercapto-1-propanol, octylthiol, nonylthiol, dodecylthiol (laurylthiol), tri-dodecylthiol, glycidylthiol, thioglycolic acid, methyl thioglycolate, ethyl thioglycolate, propyl thioglycolate, butyl thioglycolate, tributyl thioglycolate, 2-ethylhexyl thioglycolate, octyl thioglycolate, isooctyl thioglycolate, decyl thioglycolate, dodecyl thioglycolate, ethylene glycol thioglycolate, neopentyl glycol thioglycolate, pentaerythritol thioglycolate, α-methylstyrene dimer, etc. Among these, considering the suppression of whitening of adhesive sheets caused by humidification, α-thioglycerol and methyl thioglycolate are preferred, with α-thioglycerol being particularly preferred. Chain transfer agents can be used alone or in combination of two or more.

[0116] Relative to 100 parts by mass of all structural units of the above-mentioned methacrylic acid copolymer, the content of the chain transfer agent is preferably 0.1 to 20 parts by mass, more preferably 0.2 to 15 parts by mass, and even more preferably 0.3 to 10 parts by mass. By setting the content (amount) of the chain transfer agent within the above range, a methacrylic acid copolymer with a weight average molecular weight controlled between 1,000 and 30,000 can be easily obtained.

[0117] The adhesive composition of the present invention preferably contains a crosslinking agent. If a crosslinking agent is included in the adhesive composition, the base polymer undergoes crosslinking, increasing the gel fraction and easily improving foam peel resistance. Examples of such crosslinking agents include: isocyanate-based crosslinking agents, epoxy-based crosslinking agents, melamine-based crosslinking agents, peroxide-based crosslinking agents, urea-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, carbodiimide-based crosslinking agents, aziridine-based crosslinking agents, amine-based crosslinking agents, etc. Among these, isocyanate-based crosslinking agents and epoxy-based crosslinking agents are preferred for improving foam peel resistance, and isocyanate-based crosslinking agents are more preferred. The crosslinking agent can be used alone or in combination of two or more.

[0118] Examples of the above-mentioned isocyanate-based crosslinking agents (polyfunctional isocyanate compounds) include: lower aliphatic polyisocyanates such as 1,2-epoxyethyl diisocyanate, 1,4-epoxybutyl diisocyanate, and 1,6-hexamethylene diisocyanate; alicyclic polyisocyanates such as epoxycyclopentyl diisocyanate, epoxycyclohexyl diisocyanate, isophorone diisocyanate, hydrogenated toluene diisocyanate, and hydrogenated xylene diisocyanate; and aromatic polyisocyanates such as 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, and phenyl dimethyl diisocyanate. Furthermore, examples of commercially available isocyanate-based crosslinking agents include: trimethylolpropane / toluene diisocyanate adduct (trade name "Coronate L", manufactured by Nippon Polyurethane Industries, Ltd.), trimethylolpropane / hexamethylene diisocyanate adduct (trade name "Coronate HL", manufactured by Nippon Polyurethane Industries, Ltd.), and trimethylolpropane / phenylenedimethyl diisocyanate adduct (trade name "Takenate D-110N", manufactured by Mitsui Chemicals Co., Ltd.).

[0119] Examples of the above-mentioned epoxy crosslinking agents (multifunctional epoxy compounds) include: N,N,N',N'-tetraglycidyl-m-phenylenediamine, diglycidyl-aniline, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, neopentyl glycol diglycidyl ether, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, and polypropylene glycol diglycidyl ether. Oil ethers, sorbitol polyglycidyl ether, glycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitan anhydride polyglycidyl ether, trimethylolpropane polyglycidyl ether, diglycidyl adipate, diglycidyl phthalate, tri(2-hydroxyethyl)isocyanurate triglycidyl ether, resorcinol diglycidyl ether, bisphenol S diglycidyl ether, and other epoxy resins having two or more epoxy groups within their molecules. Furthermore, as the aforementioned epoxy crosslinking agents, examples include commercially available products such as "Tetrad C" (manufactured by Mitsubishi Gas Chemical Co., Ltd.).

[0120] The content of the crosslinking agent in the above-mentioned adhesive composition is, for example, 0.001 to 10 parts by weight, more preferably 0.01 to 5 parts by weight, relative to 100 parts by weight of the above-mentioned methacrylic copolymer. If the content of the crosslinking agent is 0.001 parts by weight or more, the foaming peel resistance is easily improved, which is preferable. On the other hand, if the content of the crosslinking agent is 10 parts by weight or less, the adhesive layer has moderate softness, and the adhesion is easily improved, which is also preferable.

[0121] From the perspective of further reducing the dielectric constant and dielectric loss at high frequencies, the adhesive composition of the present invention may include, in addition to the aforementioned base polymer, inorganic microparticles, organic microparticles, and polymer materials other than the base polymer. These may be used alone or in combination of two or more. As for the aforementioned inorganic microparticles and organic microparticles, from the perspective of reducing the dielectric constant and dielectric loss at high frequencies, those exhibiting insulating properties (insulating fillers) are preferred.

[0122] (Inorganic microparticles) Examples of inorganic microparticles that can be incorporated into the adhesive composition of the present invention include: metal oxides such as silicon dioxide, aluminum oxide, zirconium oxide, and titanium oxide; metal salts such as aluminum borate and aluminum hydroxide; minerals such as mica; and inorganic microparticles with a hollow structure such as hollow nano-silica. These can be used alone or in combination of two or more.

[0123] Considering the dispersibility in the base polymer, the aforementioned inorganic microparticles can also be surface-treated. As a surface treatment agent, known or conventional agents can be used without limitation, such as silane coupling agents, titanium coupling agents, organic acids, polyols, polysiloxanes, etc., with silane coupling agents being preferred. Examples of silane coupling agents include: vinyltrimethoxysilane, vinyltriethoxysilane, dimethylvinylmethoxysilane, dimethylvinylethoxysilane, methylvinyldimethoxysilane, methylvinyldiethoxysilane, vinyltri(2-methoxy)silane, vinyltriethoxysilane, 2-methacryloxyethyltriethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, triethoxyphenylsilane, trimethoxyphenylsilane, dimethoxydiphenylsilane, methyldiethoxyphenylsilane, dimethoxymethylphenylsilane, etc.

[0124] Considering the low dielectric constant, low dielectric loss, and transparency of the adhesive composition at high frequencies, the particle size (D50) of the aforementioned inorganic microparticles is preferably 1–100 nm, more preferably 5–80 nm, and even more preferably 10–50 nm. The aforementioned median particle size refers to the particle size (median diameter) at which the cumulative value of the particle size distribution measured by laser diffraction and scattering methods reaches 50%.

[0125] When the adhesive composition of the present invention contains inorganic microparticles, considering the low dielectric constant, low dielectric loss, and transparency of the adhesive composition at high frequencies, the content of the inorganic microparticles is preferably 0.01 to 30 parts by weight, more preferably 0.05 to 25 parts by weight, even more preferably 0.10 to 20 parts by weight, even more preferably 0.15 to 10 parts by weight, and particularly preferably 0.2 to 5 parts by weight, relative to 100 parts by weight of the above-mentioned methacrylic copolymer.

[0126] (Organic Microparticles) Examples of organic microparticles that can be formulated into the adhesive composition of the present invention include, for example, microparticles comprising polymers such as styrene-based resins, acrylic resins, polysiloxane resins, acrylic-styrene resins, vinyl chloride resins, vinylidene chloride resins, amide resins, carbamate resins, phenolic resins, styrene-conjugated diene resins, acrylic-conjugated diene resins, olefin resins, and fluorine resins, or cross-linked polymers thereof, and further comprising microparticles of such polymer-polymer cross-linked polymers in a hollow structure. These can be used alone or in combination of two or more.

[0127] Considering the low dielectric constant, low dielectric loss, and transparency of the adhesive composition at high frequencies, the particle size (D50) of the aforementioned organic microparticles is preferably 1–100 nm, more preferably 5–80 nm, and even more preferably 10–50 nm. The aforementioned median particle size refers to the particle size (median diameter) at which the cumulative value of the particle size distribution measured by laser diffraction or scattering methods reaches 50%.

[0128] When the adhesive composition of the present invention contains organic microparticles, considering the low dielectric constant, low dielectric loss, and transparency of the adhesive composition at high frequencies, the content of the organic microparticles is generally 0.01 to 30 parts by mass relative to 100 parts by mass of the methacrylic acid copolymer, preferably 0.05 to 25 parts by mass, more preferably 0.1 to 20 parts by mass, and even more preferably 0.15 to 10 parts by mass, and even more preferably 0.2 to 5 parts by mass.

[0129] (Polymer Material) Preferably, the polymer material that can be formulated into the adhesive composition of the present invention is one with a low dielectric constant and dielectric loss, and is compatible with the base polymer. Examples include: fluoropolymers, fluororubbers, fluorinated (meth)acrylates, polyethylene, polypropylene, polystyrene, polycarbonate, norcamphene resins or addition copolymers with olefins, polyphenylene ether, dicis-butenediamine-trisyl resin, polyetherimide, polyimide, polyetheretherketone (PEEK), liquid crystal polymers, rubber elastomers, hydrogenated polyolefin resins, terpenes, isoprene, terpene phenol resins, aromatic modified terpene resins, and hydrogenated resins thereof. These can be used alone or in combination of two or more.

[0130] When the adhesive composition of the present invention contains a polymer material, its content is not particularly limited. Considering the low dielectric constant, low dielectric loss and transparency of the adhesive composition at high frequency bands, the content is usually 0.01 to 50 parts by mass relative to 100 parts by mass of the above-mentioned methacrylic copolymer, preferably 0.05 to 40 parts by mass, and more preferably 0.1 to 30 parts by mass.

[0131] (Rust Inhibitor) The adhesive composition of the present invention may further contain a rust inhibitor. If a rust inhibitor is included in the adhesive composition, it is better to obtain excellent anti-corrosion effect for antenna elements and metal wiring.

[0132] Rust inhibitors are compounds that prevent metals from rusting or corroding. Examples of rust inhibitors include amine compounds, benzotriazole compounds, and nitrites. Other examples include ammonium benzoate, ammonium phthalate, ammonium stearate, ammonium palmitate, ammonium oleate, ammonium carbonate, dicyclohexylamine benzoate, urea, hexamethylenetetramine, thiourea, phenyl carbamate, and N-cyclohexylaminocarbamate (CHC). Rust inhibitors can be used alone or in combination of two or more.

[0133] Examples of the aforementioned amine compounds include: hydroxyl-containing amine compounds such as 2-amino-2-methyl-1-propanol, monoethanolamine, monoisopropanolamine, diethylethanolamine, ammonia or ammonia water; cyclic amines such as morpholine; cyclic alkylamine compounds such as cyclohexylamine; and linear alkylamines such as 3-methoxypropylamine. Examples of nitrites include: dicyclohexylammonium nitrite (DICHAN), diisopropylammonium nitrite (DIPAN), sodium nitrite, potassium nitrite, and calcium nitrite.

[0134] Regarding the content of the aforementioned rust inhibitor, it is preferable to include 0.02 to 15 parts by weight relative to 100 parts by weight of the aforementioned methacrylic acid copolymer. If the content is 0.02 parts by weight or more, it is easier to obtain good anti-corrosion performance, which is preferable. On the other hand, if the content is 15 parts by weight or less, it is easier to ensure transparency, and also easier to ensure adhesion reliability such as foaming peel resistance, which is preferable.

[0135] In view of obtaining excellent appearance, the rust inhibitor is preferably a benzotriazole compound, which can achieve a high level of adhesion reliability, transparency and corrosion resistance for the above-mentioned methacrylic copolymer in a balanced manner.

[0136] As for the above-mentioned benzotriazole compounds, there is no particular limitation as long as they are compounds having a benzotriazole skeleton. From the viewpoint of obtaining a better anti-corrosion effect, it is preferable to have the structure represented by the following formula (1). [Chemical 1] (wherein, in the above formula (1), R1 and R2 are the same or different, R1 is a substituent on the benzene ring, representing an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, an aryl group having 6 to 14 carbon atoms, an amino group, a mono- or di-C1-10 alkylamino group, an amino-C1-6 alkyl group, a mono- or di-C1-10 alkylamino-C1-6 alkyl group, a mercapto group, an alkoxy carbonyl group having 1 to 6 carbon atoms, or an alkoxy group having 1 to 6 carbon atoms, etc. The value is an integer from 0 to 4. When n is 2 or more, the n R1s can be the same or different. R2 represents a hydrogen atom, an alkyl group with 1 to 12 carbon atoms, an alkoxy group with 1 to 12 carbon atoms, an aryl group with 6 to 14 carbon atoms, an amino group, a mono- or di-C1-10 alkylamino group, an amino-C1-6 alkyl group, a mono- or di-C1-10 alkylamino-C1-6 alkyl group, a mercapto group, an alkoxycarbonyl group with 1 to 12 carbon atoms, or an alkoxy group with 1 to 12 carbon atoms, etc.

[0137] From the viewpoint of obtaining a superior anti-corrosion effect, R1 is preferably an alkyl group with 1 to 3 carbon atoms, an alkoxycarbonyl group, etc., and more preferably a methyl group. Also, n is preferably 0 or 1. From the same viewpoint, R2 is preferably a hydrogen atom, a mono- or di-C1-10 alkylamino-C1-6 alkyl group, etc., and more preferably a hydrogen atom, a di-C1-8 alkylamino-C1-4 alkyl group, etc.

[0138] Relative to 100 parts by weight of the above-mentioned methacrylic acid copolymer, the content of the above-mentioned benzotriazole compound is preferably 0.02 to 3 parts by weight, more preferably 0.02 to 2.5 parts by weight, and even more preferably 0.02 to 2 parts by weight. If the amount of the benzotriazole compound is within a certain range, the adhesion reliability, such as foaming peel resistance, can be reliably ensured, and the increase in haze of the adhesive sheet can also be reliably prevented.

[0139] (Silane Coupling Agent) The adhesive composition of the present invention may further contain a silane coupling agent. If a silane coupling agent is included in the adhesive composition, it is preferable to easily obtain excellent adhesion to glass (especially excellent adhesion reliability to glass under high temperature and high humidity).

[0140] Examples of the aforementioned silane coupling agents include: γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-aminopropyltrimethoxysilane, and N-phenylaminopropyltrimethoxysilane. Among these, γ-glycidoxypropyltrimethoxysilane is preferred. Examples of commercially available silane coupling agents include, for example, "KBM-403" (manufactured by Shin-Etsu Chemical Co., Ltd.). The silane coupling agent can be used alone or in combination of two or more.

[0141] From the perspective of improving the reliability of glass bonding, the content of the silane coupling agent is preferably 0.01 to 1 part by weight, and more preferably 0.03 to 0.5 parts by weight, relative to 100 parts by weight of the methacrylic acid copolymer.

[0142] (Other Additives) The adhesive composition of the present invention may, as needed and without impairing the characteristics of the present invention, include known additives such as antioxidants, crosslinking accelerators, crosslinking delay agents, adhesion-improving resins (rosin derivatives, polyterpene resins, oil-soluble phenols, etc.), anti-aging agents, colorants (pigments or dyes, etc.), ultraviolet absorbers, chain transfer agents, plasticizers, softeners, surfactants, and antistatic agents. These additives may be used alone or in combination of two or more.

[0143] When the adhesive composition of the present invention contains an adhesive-improving agent, from the viewpoint of imparting appropriate adhesion, the content of the adhesive-improving agent is preferably 0.01 parts by weight or more, and more preferably 0.05 parts by weight or more, relative to 100 parts by weight of the above-mentioned methacrylic acid copolymer. Furthermore, from the viewpoint of avoiding excessively high peel strength, the content is preferably 50 parts by weight or less, and more preferably 40 parts by weight or less.

[0144] [Adhesive Layer] The adhesive layer of the present invention is formed from the adhesive composition of the present invention, and therefore exhibits low dielectric constant and low dielectric loss in the high-frequency band (28-60 GHz) millimeter waves. That is, the adhesive layer of the present invention can suppress the radiation loss of millimeter waves.

[0145] The adhesive layer of the present invention has a low dielectric constant at 28 GHz, which is advantageous in suppressing the radiation loss of millimeter waves. The dielectric constant of the adhesive layer of the present invention at a frequency of 28 GHz is preferably 2.00 to 5.00, more preferably 2.05 to 4.50, further preferably 2.10 to 4.00, further preferably 2.15 to 3.50, particularly preferably 2.20 to 3.40, and most preferably 2.20 to 3.30, 2.20 to 3.20, 2.20 to 3.10, 2.20 to 3.00, or 2.20 to 2.90.

[0146] The dielectric constant of the adhesive layer of the present invention at 28 GHz can be adjusted by adjusting the type of base polymer, monomer composition, type or content of additives, etc., of the adhesive composition used to form the adhesive layer.

[0147] The adhesive layer of the present invention has a low dielectric loss at 28 GHz, which is advantageous in suppressing the radiation loss of millimeter waves. The dielectric loss of the adhesive layer of the present invention at a frequency of 28 GHz is preferably 0.050 or less, more preferably 0.045 or less, further preferably 0.040 or less, further preferably 0.035 or less, particularly preferably 0.030 or less, and most preferably 0.025 or less or 0.020 or less. The lower limit value is not particularly limited, but is preferably 0.0001 or more, and may also be 0.0005 or more or 0.0010 or more.

[0148] The dielectric loss of the adhesive layer of the present invention at 28 GHz can be adjusted by adjusting the type of base polymer, monomer composition, type or content of additives, etc. of the adhesive composition used to form the adhesive layer.

[0149] The adhesive layer of the present invention has a low dielectric constant at 60 GHz, which is advantageous in suppressing the radiation loss of millimeter waves. The dielectric constant of the adhesive layer of the present invention at a frequency of 60 GHz is preferably 2.0 to 5.0, more preferably 2.1 to 4.5, further preferably 2.2 to 4.0, even more preferably 2.2 to 3.5, particularly preferably 2.2 to 3.4, and most preferably 2.2 to 3.3, 2.2 to 3.2, 2.2 to 3.1, 2.2 to 3.0, or 2.2 to 2.9.

[0150] The dielectric constant of the adhesive layer of the present invention at 60 GHz can be adjusted by adjusting the type of base polymer, monomer composition, type or content of additives, etc. of the adhesive composition used to form the adhesive layer.

[0151] The adhesive layer of the present invention preferably has a low dielectric loss at 60 GHz, which is advantageous in suppressing the radiation loss of millimeter waves. The dielectric loss of the adhesive layer of the present invention at a frequency of 60 GHz is preferably 0.050 or less, more preferably 0.045 or less, further preferably 0.040 or less, further preferably 0.035 or less, particularly preferably 0.030 or less, and most preferably 0.025 or less or 0.020 or less. The lower limit of the dielectric loss at a frequency of 60 GHz is preferably 0.0001 or more, and may also be 0.0005 or more or 0.0010 or more.

[0152] The dielectric loss of the adhesive layer of the present invention at 60 GHz can be adjusted by adjusting the type of base polymer, monomer composition, type or content of additives, etc. of the adhesive composition used to form the adhesive layer.

[0153] The adhesive layer of the present invention is transparent or has transparency. Therefore, it provides excellent visibility or appearance of the adhesive composition described above. Thus, the adhesive layer of the present invention can be suitably used for optical applications.

[0154] The haze of the adhesive layer of the present invention (according to JIS K7136) is not particularly limited, but is preferably 1.2% or less, more preferably 1.1% or less, further preferably 1.0% or less, further preferably 0.9% or less, and even more preferably 0.8% or less. If the haze is, for example, 1.2% or less, excellent transparency or excellent appearance can be easily obtained. The above-mentioned haze can be set, for example, to an adhesive layer thickness of 25 μm, and then left to stand at normal temperature (23°C, 50%RH) for at least 24 hours. After that, it is attached to a glass slide (e.g., total light transmittance 91.8%, haze 0.4%), and the result is used as a sample. The haze is measured using a haze meter (product name "HM-150", manufactured by Murakami Color Technology Research Institute Co., Ltd.).

[0155] The total light transmittance (according to JIS K7361-1) of the adhesive layer of the present invention in the visible light wavelength region is not particularly limited, but is preferably 85% or more, more preferably 88% or more, further preferably 89% or more, further preferably 90% or more, particularly preferably 91% or more, and most preferably 92% or more. If the total light transmittance is 85% or more, excellent transparency or excellent appearance can be easily obtained. The above-mentioned total light transmittance can be set, for example, with an adhesive layer thickness of 25 μm, and left to stand at normal temperature (23°C, 50%RH) for at least 24 hours. After that, it is peeled off with spacers and attached to a glass slide (e.g., total light transmittance 91.8%, haze 0.4%). The result is used as a sample and measured using a haze meter (product name "HM-150", manufactured by Murakami Color Technology Research Institute Co., Ltd.).

[0156] The haze and total light transmittance of the adhesive layer of the present invention can be adjusted by adjusting the type of base polymer, monomer composition, type or content of additives, etc. of the adhesive composition used to form the adhesive layer.

[0157] The gel fraction (ratio of insoluble components) of the adhesive layer of the present invention is preferably 30-95%, more preferably 35-90%, further preferably 40-85%, further preferably 45-80%, and even more preferably 50-75%. If the gel fraction is 30% or more, the cohesive force of the adhesive layer is improved, and it is less likely to produce indentations during operation. In addition, foaming or peeling at the interface with the substrate is suppressed under high temperature conditions, and it is easier to obtain excellent foaming and peeling resistance. If the gel fraction is 95% or less, moderate softness can be obtained, adhesion and step followability are further improved, and it is less likely to absorb foreign matter.

[0158] The gel fraction (the ratio of solvent-insoluble components) mentioned above can be calculated, for example, in the following manner.

[0159] Approximately 0.1 g of the self-adhesive layer was wrapped in a porous tetrafluoroethylene sheet (trade name "NTF1122", manufactured by Nitto Denko Corporation) with an average pore size of 0.2 μm. The sheet was then secured with kite string, and the mass at this point was measured. This mass was designated as the mass before impregnation (Z). The mass before impregnation was the total mass of the adhesive layer, the tetrafluoroethylene sheet, and the kite string. The combined mass of the tetrafluoroethylene sheet and the kite string was also measured beforehand and designated as the packaging mass (Y). Next, the sample (referred to as the "sample"), which was wrapped with the adhesive layer in the tetrafluoroethylene sheet and secured with kite string, was placed in a 50 ml container filled with ethyl acetate or toluene and left to stand at 23°C for 7 days. Afterward, the sample (treated with ethyl acetate or toluene) was removed from the container, transferred to an aluminum cup, and dried in a desiccator at 130°C for 2 hours to remove the ethyl acetate or toluene. The mass was then measured and designated as the mass after impregnation (X). Furthermore, the gel fraction is calculated using the following formula: Gel fraction (%) = {(X-Y) / (Z-Y)} × 100

[0160] The gel fraction of the adhesive layer of the present invention can be controlled, for example, by the monomer composition, weight average molecular weight, amount of crosslinking agent used, type or amount of other additives used.

[0161] The storage modulus of the adhesive layer of the present invention at 25°C is preferably 0.01 MPa or more, more preferably 0.02 MPa or more, further preferably 0.03 MPa or more, further preferably 0.04 MPa or more, particularly preferably 0.05 MPa or more, and most preferably 0.10 MPa or more. If the storage modulus is 0.01 MPa or more, it is less likely to produce dents during operation, and good adhesion reliability is easily obtained, which is preferred. Furthermore, considering step followability and foreign matter absorption, the storage modulus of the adhesive layer at 25°C is preferably 5 MPa or less, more preferably 4.5 MPa or less, further preferably 4.0 MPa or less, further preferably 3.5 MPa or less, particularly preferably 3.0 MPa or less, and most preferably 2.5 MPa or less or 2.0 MPa or less. The storage modulus of the adhesive layer was measured during dynamic viscoelasticity testing at a frequency of 1 Hz. The storage modulus mentioned above is the real part of the shear modulus expressed as a miscellaneous number; the tensile modulus, etc., can be converted by taking into account the Poisson's ratio of the sample.

[0162] The storage modulus of the adhesive layer of the present invention can be controlled by monomer composition, weight average molecular weight, amount of crosslinking agent used (addition amount), type or amount of other additives, etc.

[0163] The 300% tensile residual stress of the adhesive layer of the present invention is not particularly limited, but is preferably 2 to 24 N / cm2, more preferably 2.5 to 20 N / cm2, and even more preferably 3 to 16 N / cm2. If the above-mentioned 300% tensile residual stress is 2 N / cm2 or more, good foaming peel resistance can be easily obtained, and if it is 24 N / cm2 or less, good stress relief can be obtained, and good step followability can be easily obtained, which is preferable.

[0164] If the 300% tensile residual stress of the adhesive layer of the present invention is within the above range, it is easy to obtain excellent stress relief and excellent step follow-up performance, for example, it can follow well even for larger step differences (around 45 μm, for example, a height of 20 to 50 μm).

[0165] The aforementioned 300% tensile residual stress is as follows (N / cm2): It is obtained by stretching the adhesive layer along its length to an elongation (strain) of 300% at 23°C and 50% RH, maintaining this elongation, calculating the tensile load applied to the adhesive layer 300 seconds after the end of the stretching, and dividing this tensile load by the initial cross-sectional area of ​​the adhesive layer (the cross-sectional area before stretching). Furthermore, the initial elongation of the adhesive layer is 100%.

[0166] The 300% tensile residual stress of the adhesive layer of the present invention can be controlled by the monomer composition of the base polymer, the weight average molecular weight, the amount of crosslinking agent used (addition amount), the type or amount of other additives, etc.

[0167] The adhesive layer of the present invention has a low saturated moisture absorption rate, thus suppressing the radiation loss of millimeter waves. The saturated moisture absorption rate of the adhesive layer of the present invention at 25°C and 90%RH is preferably 2.8% or less, more preferably 2.7% or less, further preferably 2.6% or less, further preferably 2.5% or less, particularly preferably 2.4% or less, and most preferably 2.3% or less, 2.2% or less, 2.1% or less, 2.0% or less, 1.9% or less, 1.8% or less, 1.7% or less, 1.6% or less, 1.5% or less, 1.4% or less, 1.3% or less, 1.2% or less, 1.1% or less, 1.0% or less, 0.9% or less, 0.8% or less, 0.7% or less, or 0.6% or less. A low saturated moisture absorption rate at 25°C and 90%RH can suppress the radiation loss of millimeter waves near room temperature. The lower limit of the saturated moisture absorption rate is not particularly limited. For example, it can be 0.3% or more, or 0.4% or more, or 0.5% or more.

[0168] The saturated moisture absorption rate of the adhesive layer of the present invention at 65°C and 90%RH is preferably 2.8% or less, more preferably 2.6% or less, further preferably 2.4% or less, further preferably 2.3% or less, particularly preferably 2.2% or less, and most preferably 2.1% or less, 2.0% or less, 1.9% or less, 1.8% or less, 1.7% or less, 1.6% or less, 1.5% or less, 1.4% or less, 1.3% or less, 1.2% or less, 1.1% or less, 1.0% or less, 0.9% or less, 0.8% or less, or 0.7% or less. The lower limit of the above-mentioned saturated moisture absorption rate is not particularly limited; for example, it can be 0.4% or more, or 0.5% or more, or 0.6% or more. If the saturated moisture absorption rate at 65°C and 90%RH is low, then even when placed in a high-temperature environment, the radiation loss of millimeter waves can be suppressed.

[0169] The saturated moisture absorption rate of the adhesive layer of the present invention at 85°C and 85%RH is preferably 5.0% or less, more preferably 4.0% or less, further preferably 3.5% or less, further preferably 3.0% or less, particularly preferably 2.8% or less, and most preferably 2.6% or less, 2.4% or less, 2.2% or less, 2.0% or less, 1.8% or less, 1.6% or less, 1.4% or less, 1.2% or less, 1.0% or less, or 0.8% or less. The lower limit of the above-mentioned saturated moisture absorption rate is not particularly limited; for example, it can be 0.4% or more, or 0.5% or more, or 0.6% or more. If the saturated moisture absorption rate at 85°C and 85%RH is low, then even when placed in a high-temperature environment, the radiation loss of millimeter waves can be suppressed.

[0170] The aforementioned saturated moisture absorption rate under various temperature and humidity conditions can be calculated, for example, from the weight of the sample in its dry state (w1) and the weight (w2) at the point when the sample stops changing weight in an atmosphere of 65°C and 90%RH (when the moisture absorption rate is saturated), using the following formula. It can also be calculated separately under conditions of 25°C and 90%RH and 85°C and 85%RH. Furthermore, the values ​​of w1 and w2 are assumed to be measured under the same temperature and humidity. Saturated moisture absorption rate (%) = {(w2 - w1) / w1} × 100

[0171] The adhesive layer of the present invention can suppress the emission loss of millimeter waves because the change in dielectric loss due to moisture absorption is controlled to be low. The change in dielectric loss due to moisture absorption of the adhesive layer of the present invention at a frequency of 28 GHz is preferably 0.006 or less, more preferably 0.005 or less, and even more preferably 0.004 or less. The lower limit of the saturated moisture absorption rate is not particularly limited, and may be, for example, 0.0001 or more, 0.0002 or more, or 0.0003 or more.

[0172] The change in dielectric loss of the adhesive layer of the present invention at a frequency of 60 GHz due to moisture absorption is preferably 0.003 or less, more preferably 0.002 or less, and even more preferably 0.001 or less. The lower limit of the saturated moisture absorption rate is not particularly limited, and may be, for example, 0.0001 or more, or 0.0002 or more, 0.0003 or more, 0.0004 or more, 0.0005 or more, 0.0006 or more, 0.0007 or more, 0.0008 or more, or 0.0009 or more.

[0173] The changes in dielectric loss at the aforementioned frequencies of 28 GHz and 60 GHz were maintained for more than 5 days in an atmosphere of 65°C and 90%RH. Afterward, the conditions were restored to 23±1°C and 52%±1%RH (time elapsed = 0 minutes). Dielectric loss was measured every 10 minutes from 4 minutes to 180 minutes. The maximum value (Dfmax) and minimum value (Dfmin) of each frequency were calculated using the following formula: Change in dielectric loss = Dfmax - Dfmin

[0174] The adhesive layer of the present invention can suppress the radiation loss of millimeter waves because its water vapor permeability is controlled to be low. The water vapor permeability of the adhesive layer of the present invention at 40°C and 92%RH is preferably below 430 g / m² / day, more preferably below 300 g / m² / day, even more preferably below 250 g / m² / day, even more preferably below 200 g / m² / day, particularly preferably below 150 g / m² / day, and most preferably below 100 g / m² / day, below 50 g / m² / day, or below 30 g / m² / day. If the water vapor permeability at 40°C and 92%RH is low, the water resistance of the adhesive layer is improved, which can suppress the radiation loss of millimeter waves in the adhesive layer. There is no particular limitation on the lower limit of water vapor permeability. For example, it can be above 10 g / m2 / day, or above 20 g / m2 / day, or above 25 g / m2 / day.

[0175] The above-mentioned water vapor transmission rate (WVTR) is based on the cup method. It can be determined by measuring the weight (w1) of the dry calcium chloride layer separating the adhesive layer from the outside, and the weight (w2) of the sample after a specified time (when the moisture absorption rate is saturated) in an atmosphere of 40°C and 92%RH. The weight change is then converted into unit time (1 day) and unit area (1 m2).

[0176] The dielectric constant or dielectric loss, saturated moisture absorption rate, change in dielectric loss due to moisture absorption, and water vapor permeability of the adhesive layer of the present invention at 28 GHz or 60 GHz can be adjusted by adjusting the monomer composition, the type or content of additives, etc.

[0177] The thickness of the adhesive layer in this invention is not particularly limited, but is preferably 10–500 μm, more preferably 11–400 μm, and even more preferably 12–350 μm, and even more preferably 12–300 μm. If the thickness is above a certain value, the step followability or bonding reliability can be easily improved. Furthermore, if the thickness is below a certain value, foreign matter is less likely to be absorbed during operation, and there is a tendency for excellent manufacturability.

[0178] There are no particular limitations on the method for manufacturing the adhesive layer described above. For example, the following method can be used: applying the adhesive composition described above to a substrate or release liner, and drying, hardening, or both as needed. Hardening can be carried out by irradiation with active energy lines, heating and drying, etc.

[0179] Furthermore, the coating (application) of the above-mentioned adhesive composition can also be performed using known coating methods. For example, gravure roller coating machines, reverse roller coating machines, contact roller coating machines, dip roller coating machines, rod coating machines, doctor blade coating machines, spray coating machines, corner wheel coating machines, direct coating machines, and other coating machines can also be used.

[0180] [Adhesive sheet] The adhesive sheet of the present invention only needs to have the adhesive layer of the present invention, and there are no other particular limitations.

[0181] The adhesive sheet of the present invention can be a double-sided adhesive sheet with adhesive layers on both sides, or a single-sided adhesive sheet with adhesive layers on only one side. From the perspective of bonding two components together, a double-sided adhesive sheet is preferred. Furthermore, in this specification, the term "adhesive sheet" is used to refer to a strip, that is, "adhesive strip" is also included. Also, in this specification, the adhesive layer surface is sometimes referred to as the "adhesive surface".

[0182] The adhesive sheet of the present invention may also have a spacer (peeling pad) provided on the adhesive surface before use.

[0183] The adhesive sheet of the present invention can be a so-called "substrate-free" adhesive sheet that does not have a substrate (substrate layer) (hereinafter, sometimes referred to as "substrate-free adhesive sheet"), or it can be an adhesive sheet with a substrate (hereinafter, sometimes referred to as "substrate-attached adhesive sheet"). Examples of the above-mentioned substrate-free adhesive sheet include, for example, a double-sided adhesive sheet that only includes the above-mentioned adhesive layer, or a double-sided adhesive sheet that includes the above-mentioned adhesive layer and an adhesive layer other than the above-mentioned adhesive layer (sometimes referred to as "other adhesive layers"). On the other hand, examples of substrate-attached adhesive sheets include adhesive sheets that have the above-mentioned adhesive layer on at least one side of the substrate. Among these, a substrate-free adhesive sheet (substrate-free double-sided adhesive sheet) is preferred, and a substrate-free double-sided adhesive sheet that only includes the above-mentioned adhesive layer is even more preferred. Furthermore, it is also preferable to have an adhesive sheet (a double-sided adhesive sheet with a substrate) having the aforementioned adhesive layers on both sides of the substrate. The adhesive layers on both sides of the aforementioned double-sided adhesive sheet with a substrate may both be the adhesive layers of the present invention, or one side may be the adhesive layer of the present invention and the other side may be another adhesive layer. Moreover, the aforementioned "substrate (substrate layer)" does not include spacers that are peeled off during the use (application) of the adhesive sheet.

[0184] To avoid millimeter-wave radiation loss caused by the substrate, the adhesive sheet of the present invention is preferably a substrate-free adhesive sheet. In cases where the substrate contains a material with low dielectric constant and low dielectric loss, a substrate-attached adhesive sheet may also be used. Ideally, the substrate should be usable regardless of the millimeter-wave polarization state, and therefore preferably non-stretchable, and especially preferably isotropic.

[0185] The adhesive sheet of the present invention does not have a particular limitation on the 180° peel adhesion force of the glass plate at a tensile speed of 300 mm / min (especially the 180° peel adhesion force of the adhesive surface provided by the adhesive layer of the present invention to the glass plate). If the adhesion force is high, from the perspective of obtaining sufficient close contact with the antenna element, it is preferably 3 N / 20 mm or more, more preferably 3.5 N / 20 mm or more, more preferably 4 N / 20 mm or more, more preferably 5 N / 20 mm, particularly preferably 6 N / 20 mm or more, and most preferably 7 N / 20 mm or more, 8 N / 20 mm or more, 9 N / 20 mm or more, or 10 N / 20 mm or more. If the above-mentioned peel adhesion force is a certain value or more, the adhesion to the glass and the suppression of bulges in the step are more excellent. Furthermore, the adhesive sheet of the present invention does not particularly limit the upper limit of the 180° peel adhesion force at a tensile speed of 300 mm / min on the glass plate. For example, it is preferably 30 N / 20 mm or less, more preferably 25 N / 20 mm or less, further preferably 22 N / 20 mm or less, further preferably 20 N / 20 mm, especially preferably 19 N / 20 mm or less, and most preferably 18 N / 20 mm or less, 17 N / 20 mm or less, 16 N / 20 mm or less, 15 N / 20 mm, 14 N / 20 mm or less, 13 N / 20 mm or less, 12 N / 20 mm or less, or 11 N / 20 mm or less. The 180° peel adhesion force at a tensile speed of 300 mm / min on the glass plate is determined by the following method for measuring 180° peel adhesion force.

[0186] For example, the trade name "Soda-lime glass (SODA-LIME GLASS) ♯0050" (manufactured by Matsunami Glass Industry Co., Ltd.) can be cited as an example of the aforementioned glass sheet. Also, alkali-free glass or chemically strengthened glass can be cited as examples.

[0187] The 180° peel adhesion force of the glass plate at a tensile speed of 300 mm / min was determined by the following method. The adhesive side of the adhesive sheet was attached to the substrate and pressed under the condition of one round-trip pressing with a 2 kg roller. After aging for 30 minutes at 23°C and 50%RH, the adhesive sheet was peeled from the substrate at a tensile speed of 300 mm / min and a peel angle of 180° according to JIS Z0237. The 180° peel adhesion force (N / 20 mm) was then measured.

[0188] The 180° peel adhesion of the adhesive sheet of the present invention can be controlled by the monomer composition of the base polymer (acrylic polymer), the weight average molecular weight, the amount of crosslinking agent used (addition amount), and the type or amount of other additives.

[0189] The thickness (total thickness) of the adhesive sheet of the present invention is not particularly limited, but is preferably 10-500 μm, more preferably 11-400 μm, and even more preferably 12-350 μm, and even more preferably 12-300 μm. If the thickness is above a certain value, peeling at the stepped areas is less likely to occur. Furthermore, if the thickness is below a certain value, it is easier to maintain an excellent appearance during manufacturing. Moreover, the thickness of the adhesive sheet of the present invention does not include the thickness of the spacers.

[0190] The haze of the adhesive sheet of the present invention (according to JIS K7136) is not particularly limited, but is preferably 1.2% or less, more preferably 1.1% or less, further preferably 1.0% or less, further preferably 0.9% or less, and even more preferably 0.8% or less. If the haze is 1.2% or less, excellent transparency or excellent appearance can be easily obtained. The above-mentioned haze can be set, for example, with an adhesive layer thickness of 25 μm, and left to stand at normal temperature (23°C, 50%RH) for at least 24 hours, and then bonded to a glass slide (e.g., total light transmittance 91.8%, haze 0.4%), and the result is used as a sample, and measured using a haze meter (product name "HM-150", manufactured by Murakami Color Technology Research Institute Co., Ltd.).

[0191] The total light transmittance (according to JIS K7361-1) of the adhesive sheet of the present invention in the visible light wavelength region is preferably 85% or more, more preferably 88% or more, further preferably 89% or more, further preferably 90% or more, particularly preferably 91% or more, and most preferably 92% or more. If the total light transmittance is 85% or more, excellent transparency or excellent appearance can be easily obtained. The above-mentioned total light transmittance can be set, for example, with an adhesive layer thickness of 25 μm, and left to stand at normal temperature (23°C, 50%RH) for at least 24 hours. After that, it is peeled off with spacers and bonded to a glass slide (e.g., total light transmittance 91.8%, haze 0.4%). The result is used as a sample and measured using a haze meter (product name "HM-150", manufactured by Murakami Color Technology Research Institute Co., Ltd.).

[0192] The haze and total light transmittance of the adhesive layer of the present invention can be adjusted by adjusting the monomer composition, the type or content of additives, etc.

[0193] The adhesive sheet of the present invention is not particularly limited, but it is preferably manufactured according to a known or conventional manufacturing method. For example, when the adhesive sheet of the present invention is a substrate-free adhesive sheet, it can be obtained by forming the adhesive layer on the spacer using the above method. Furthermore, when the adhesive sheet of the present invention is a substrate-attached adhesive sheet, it can be obtained by directly forming the adhesive layer on the surface of the substrate (direct printing method), or by temporarily forming the adhesive layer on the spacer and then transferring (adhering) it to the substrate, thereby providing the adhesive layer on the substrate (transfer printing method).

[0194] In addition to the adhesive layer described above, the adhesive sheet of the present invention may also have other layers. Examples of other layers include: other adhesive layers (adhesive layers other than the adhesive layer described above, adhesive layers other than the adhesive layer formed by the adhesive composition of the present invention)), intermediate layers, base layers, etc. Furthermore, the adhesive sheet of the present invention may also have two or more other layers.

[0195] Examples of substrates used as adhesive sheets in this invention include various optical films such as plastic films, anti-reflective (AR) films, polarizing plates, and retardation plates. Examples of materials used as plastic films include polyester resins such as polyethylene terephthalate (PET); (meth)acrylic resins such as polymethyl methacrylate (PMMA); polycarbonate, triacetin cellulose (TAC), polyurethane, polyarylate, polyimide, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, ethylene-propylene copolymer, cyclic olefin polymers such as "Arton (a cyclic olefin polymer, manufactured by JSR Corporation)" and "Zeonor (a cyclic olefin polymer, manufactured by Zeon Corporation of Japan)"; and fluoropolymers. Furthermore, these plastic materials can be used alone or in combination of two or more. Furthermore, the aforementioned "substrate" refers to the portion of the adhesive sheet that is attached to the substrate along with the adhesive layer when the adhesive sheet is applied. The spacers (release liner) that are peeled off during the use of the adhesive sheet (application) are not included in the "substrate".

[0196] The aforementioned substrate is preferably transparent. The total light transmittance (according to JIS K7361-1) of the aforementioned substrate in the visible light wavelength region is preferably 85% or more, more preferably 88% or more, further preferably 89% or more, further preferably 90% or more, particularly preferably 91% or more, and most preferably 92% or more. Furthermore, the haze (according to JIS K7136) of the aforementioned substrate is preferably 1.0% or less, more preferably 0.8% or less. Examples of such transparent substrates include PET films, or non-aligned films such as those marketed under the names "Arton" and "Zeonor". Non-aligned films are particularly preferred because their characteristics do not depend on the direction of the electric field in millimeter waves.

[0197] The thickness of the above-mentioned substrate is not particularly limited, but is preferably 12 to 500 μm. Furthermore, the above-mentioned substrate may have any of the forms of single layer and multilayer. Also, the surface of the above-mentioned substrate may be subjected to physical treatments such as corona discharge treatment, plasma treatment, electron beam treatment, etc., and chemical treatments such as primer treatment, etc., which are known and commonly used surface treatments.

[0198] The adhesive sheet of the present invention may also have spacers (release pads) provided on the adhesive surface before use. Furthermore, when the adhesive sheet of the present invention is a double-sided adhesive sheet, each adhesive surface can be protected by two spacers, or by one spacer with both sides as release surfaces, wound into a roll for protection. The spacers serve as protective materials for the adhesive layer and are peeled off when attached to the substrate. Also, when the adhesive sheet of the present invention is a substrate-free adhesive sheet, the spacers also function as supports for the adhesive layer. Furthermore, spacers may not necessarily be provided.

[0199] As the aforementioned spacer, conventional release paper or the like can be used, and there are no particular limitations. Examples include: substrates with a release layer, low-adhesion substrates containing fluoropolymers, or low-adhesion substrates containing non-polar polymers. Examples of substrates with a release layer include plastic films or papers that have undergone surface treatment with release agents such as polysiloxane, long-chain alkyl, fluorine, or molybdenum sulfide. Examples of fluoropolymers in the aforementioned low-adhesion substrates containing fluoropolymers include: polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, and chlorofluoroethylene-vinylidene fluoride copolymer. Furthermore, examples of non-polar polymers include olefin resins (e.g., polyethylene, polypropylene), and polyester substrates (polyethylene terephthalate substrates, polyethylene naphthalate substrates, polybutylene terephthalate substrates, etc.) can also be used. Furthermore, the spacers can be formed using known or conventional methods. Also, there are no particular limitations on the thickness of the spacers.

[0200] The adhesive sheet of the present invention, due to having the adhesive layer of the present invention, exhibits excellent adhesion and resistance to foaming and peeling, and further, excellent stress relief and step followability. Therefore, it has excellent adhesion reliability, especially at high temperatures. Furthermore, it has excellent appearance.

[0201] Therefore, the adhesive sheet of the present invention can be usefully used for bonding components that are prone to foaming at the interface at high temperatures. For example, polymethyl methacrylate (PMMA) resin sometimes contains unreacted monomers, which are prone to foaming caused by foreign matter at high temperatures. Also, polycarbonate (PC) is prone to releasing water and carbon dioxide at high temperatures. Because of its excellent resistance to foaming and peeling, the adhesive sheet of the present invention can also be usefully used for bonding plastic substrates containing such resins.

[0202] Furthermore, the adhesive sheet of the present invention can be usefully used not only for substrates with a small coefficient of linear expansion, but also for substrates with a large coefficient of linear expansion. Furthermore, examples of substrates with a small coefficient of linear expansion include: glass plates (coefficient of linear expansion 0.3×10⁻⁵~0.8×10⁻⁵ / ℃), polyethylene terephthalate substrates (PET film, coefficient of linear expansion 1.5×10⁻⁵~2×10⁻⁵ / ℃), etc. Furthermore, as an adhesive with a relatively large coefficient of linear expansion, examples include resin substrates with a relatively large coefficient of linear expansion. More specifically, examples include: polycarbonate resin substrates (PC, coefficient of linear expansion 7×10-5~8×10-5 / ℃), polymethyl methacrylate resin substrates (PMMA, coefficient of linear expansion 7×10-5~8×10-5 / ℃), cycloolefin polymer substrates (COP, coefficient of linear expansion 6×10-5~7×10-5 / ℃), trade name "Zeonor" (manufactured by Zeon Corporation of Japan), trade name "Arton" (manufactured by JSR Corporation), etc.

[0203] The adhesive sheet of the present invention can be usefully used for bonding an adhesive with a smaller coefficient of linear expansion to an adhesive with a larger coefficient of linear expansion. Specifically, the adhesive sheet of the present invention is preferably used for bonding a glass adhesive (e.g., a glass plate, chemically strengthened glass, a glass lens, etc.) to the aforementioned resin substrate with a larger coefficient of linear expansion.

[0204] Thus, the adhesive sheet of the present invention is useful for bonding various materials to each other, and is particularly useful for bonding glass substrates to plastic substrates. Furthermore, the plastic substrate can also be an optical film such as a plastic film having an ITO (Indium Tin Oxide) layer on its surface.

[0205] Furthermore, the adhesive sheet of the present invention can be usefully used not only for substrates with smooth surfaces, but also for substrates with stepped surfaces. In particular, even if at least one of the glass substrate and the resin substrate with a large coefficient of linear expansion has a stepped surface, the adhesive sheet of the present invention can also be usefully used for bonding the glass substrate to the resin substrate with a large coefficient of linear expansion.

[0206] The adhesive sheet of the present invention is preferably used for manufacturing portable electronic devices. Examples of such portable electronic devices include: mobile phones, PHS (Personal Handyphone System), smartphones, tablets (tablet computers), mobile computers (mobile PCs), portable information terminals (PDAs), electronic notebooks, portable televisions or portable radios and other portable broadcast transceivers, portable game consoles, Walkmans, portable DVD (Digital Versatile Disc) players, digital cameras and other cameras, camcorders, etc.

[0207] The adhesive sheet of the present invention can be preferably used, for example, for attaching components or modules of portable electronic devices to each other, or for fixing components or modules of portable electronic devices to a housing. More specifically, examples include: attaching a cover glass or lens (especially a glass lens) to a touch panel or touch sensor, or an antenna module; fixing a cover glass or lens (especially a glass lens) to a housing; fixing a display panel to a housing; fixing an antenna module to a housing; fixing an input device such as a keypad or touch panel to a housing; attaching a protective panel of an information display unit to a housing; attaching housings to each other; attaching a housing to a decorative sheet; and fixing or attaching various components or modules of portable electronic devices. Furthermore, in this specification, a display panel refers to a structure that includes at least a lens (especially a glass lens) and a touch panel. Also, in this specification, a lens includes both transparent bodies that refract light and transparent bodies that do not refract light. That is, the lens in this specification also includes a simple window panel that has no refractive effect.

[0208] Furthermore, the adhesive sheet of the present invention is preferably used for optical applications. That is, the adhesive sheet of the present invention is preferably an optical adhesive sheet for optical applications. More specifically, for example, it is preferably used for bonding optical components (for bonding optical components) or for manufacturing articles using the above-mentioned optical components (optical articles), etc.

[0209] As an optical component, an example can be given of an optical component that has at least the aforementioned adhesive sheet and a substrate, wherein the substrate has a metal electrode and wiring (e.g., copper, silver, ITO wiring, etc.) on at least one side, and the adhesive layer of the present invention is adhered to the side of the substrate having the metal electrode and wiring. Furthermore, the aforementioned adhesive sheet may have spacers provided on the adhesive surface before use, but the adhesive sheet in the optical component of the present invention is an adhesive sheet for use, and therefore does not have spacers.

[0210] Furthermore, the optical component is preferably provided with the adhesive layer on the side of the substrate opposite to the side having the metal electrode and wiring, and even more preferably, the adhesive layer is attached to the surface of the substrate opposite to the side having the metal electrode and wiring.

[0211] Examples of materials constituting the aforementioned metal electrodes and wiring include: titanium, silicon, niobium, indium, zinc, tin, gold, silver, copper, aluminum, cobalt, chromium, nickel, lead, iron, palladium, platinum, tungsten, zirconium, tantalum, hafnium, etc.; and metal oxides such as ITO (oxide of indium and tin), zinc oxide, and tin oxide. Furthermore, examples include those containing two or more of these metals or metal oxides, or alloys with these metals as the main component. Among these, gold, silver, copper, and ITO are preferred from a conductivity perspective; silver, copper, and ITO are more preferred from a conductivity and cost perspective; and ITO is even more preferred from a transparency perspective. That is, the aforementioned metal electrodes and wiring are preferably silver, copper, or ITO wiring, and especially ITO wiring. Furthermore, the materials constituting the millimeter-wave antenna elements described below are also the same. In order to prevent the reduction in visibility caused by metal reflection, the aforementioned metal electrodes and wiring may also be blackened by forming a film of nitrides, oxides, sulfides, etc. on the metal for the purpose of concealing the electrodes and / or wiring.

[0212] Optical components refer to components that have optical properties (such as polarization, refraction, scattering, reflection, transmittance, absorption, diffraction, rotation, visibility, electromagnetic wave transmittance, etc.). Examples of substrates constituting the aforementioned optical components include: display devices (image display devices), input devices, and other equipment (optical equipment); substrates constituting antenna modules or substrates used in such equipment; examples include: polarizing plates, waveplates, retardation plates, optical compensation films, brightness enhancement films, light guide plates, reflective films, anti-reflective films, antenna substrates, hard-coated films (films on at least one side of plastic films such as PET films with hard coating treatment), transparent conductive films (e.g., plastic films with an ITO layer on the surface (preferably PET-ITO, polycarbonate, cyclic olefin polymers, etc. ITO films)), design films, decorative films, surface protection plates, prisms, lenses, color filters, transparent substrates (glass sensors, glass display panels (LCDs, etc.), glass substrates with transparent electrodes, etc.), or substrates on which such layers are deposited (sometimes collectively referred to as "functional films"). Furthermore, these films may have metal nanowire layers or conductive polymer layers. Furthermore, fine metal lines can be screen-printed on these films. Also, antenna elements can be present on these films. Moreover, the aforementioned "plate" and "film" are respectively provided in the form of a plate, a film, or a sheet; for example, a "polarizing film" is provided to include a "polarizing plate" and a "polarizing sheet," etc. Furthermore, a "film" is provided to include a film sensor, etc.

[0213] In order to prevent the reduction in visibility caused by the reflection of the metal, the above-mentioned metal wires can also be pre-treated by forming a film of nitride, oxide, sulfide or other metal for the purpose of concealment.

[0214] Examples of the aforementioned display devices include liquid crystal displays, organic EL (electroluminescent) displays, PDP (plasma display panels), and electronic paper. Examples of the aforementioned input devices include touch panels. Examples of the antenna modules include millimeter-wave antennas disclosed below.

[0215] Examples of substrates constituting the aforementioned optical components include glass, (meth)acrylic resins, polycarbonate, polyethylene terephthalate, cyclic olefin polymers, and metal films (e.g., sheet-like, film-like, or plate-like substrates). Furthermore, the "optical components" in this invention, as described above, also include components (design films, decorative films, or surface protective films, etc.) that maintain the visibility of the display device or input device and perform decorative or protective functions.

[0216] If the adhesive sheet of the present invention is an adhesive sheet attached to a substrate, and the adhesive sheet constitutes a component with optical properties, then the substrate can be regarded in the same way as the substrate, and the adhesive sheet can also be considered as an optical component of the present invention.

[0217] When the adhesive sheet of the present invention is an adhesive sheet with a substrate and the above-mentioned functional film is used as the substrate, the adhesive sheet of the present invention can also be used as an "adhesive functional film" having the above-mentioned adhesive layer on at least one side of the functional film.

[0218] [Millimeter-wave antenna] Since the adhesive sheet of the present invention has an adhesive layer with low dielectric constant and low dielectric loss in high-frequency bands such as millimeter waves (the adhesive layer of the present invention), it can suppress the radiation loss of millimeter waves. Therefore, the adhesive sheet of the present invention can be used for bonding components that constitute an antenna for millimeter-wave communication (millimeter-wave antenna).

[0219] In this specification, "millimeter wave communication" means communication in the frequency band of 20 GHz to 300 GHz.

[0220] As a component constituting a millimeter-wave antenna, an example can be found on a substrate (hereinafter sometimes referred to as a "millimeter-wave antenna substrate") of an antenna element (hereinafter sometimes referred to as a "millimeter-wave antenna element") that is used to transmit and receive millimeter waves at least once.

[0221] As a millimeter-wave antenna substrate, the plastic film used in the substrate of the above-mentioned adhesive sheet can be exemplified. From the perspective of suppressing the radiation loss of millimeter waves, it is preferable to use a material with low dielectric constant and low dielectric loss, and it is especially preferable to use cyclic olefin polymers such as "Arton" (manufactured by JSR Corporation) and "Zeonor" (manufactured by Zeon Corporation of Japan).

[0222] From the perspective of suppressing the radiation loss of millimeter waves, the dielectric constant of the millimeter wave antenna substrate at 28 GHz and / or 60 GHz is preferably 2.0 to 5.0, more preferably 2.1 to 4.5, even more preferably 2.2 to 4.0, even more preferably 2.2 to 3.5, particularly preferably 2.2 to 3.4, and most preferably 2.2 to 3.3, 2.2 to 3.2, 2.2 to 3.1 or 2.2 to 3.0. Furthermore, considering the suppression of radiation loss in millimeter waves, the dielectric loss of the millimeter wave antenna substrate at 28 GHz and / or 60 GHz is preferably 0.0001 to 0.05, more preferably 0.001 to 0.029, even more preferably 0.002 to 0.028, even more preferably 0.003 to 0.027, particularly preferably 0.004 to 0.026, and most preferably 0.005 to 0.025, 0.006 to 0.024, 0.007 to 0.023, 0.008 to 0.022, 0.009 to 0.021, 0.010 to 0.020, 0.011 to 0.019, 0.012 to 0.018, 0.013 to 0.017, 0.014 to 0.016, or 0.014 to 0.015.

[0223] The millimeter-wave antenna substrate is preferably transparent. The total transmittance of the millimeter-wave antenna substrate in the visible light wavelength region (according to JIS K7361-1) is not particularly limited, but is preferably 85% or higher, more preferably 88% or higher, further preferably 89% or higher, further preferably 90% or higher, especially preferably 91% or higher, and most preferably 92% or higher. Furthermore, the haze of the millimeter-wave antenna substrate (according to JIS K7136) is not particularly limited, but is preferably 1.2% or less, more preferably 1.1% or less, further preferably 1.0% or less, further preferably 0.9% or less, and especially preferably 0.8% or less.

[0224] From the perspective of mounting millimeter-wave antenna elements and suppressing millimeter-wave radiation loss, the thickness of the millimeter-wave antenna substrate is preferably 5–250 μm. Furthermore, the millimeter-wave antenna substrate can have any of the forms of a single layer or multiple layers. Also, the surface of the millimeter-wave antenna substrate can be appropriately subjected to known and commonly used surface treatments such as physical treatments such as corona discharge treatment and plasma treatment; chemical treatments such as primer treatment; and coatings such as hard coating.

[0225] As for the millimeter-wave antenna elements included in the millimeter-wave antenna substrate, there are no particular limitations as long as they can transmit and receive millimeter waves. However, considering the efficient reception of millimeter waves using portable communication devices such as smartphones, a phase array antenna is preferable. A phase array antenna is an antenna that can transmit and receive in the desired direction by arranging a plurality of antenna elements in an array and controlling the phase of each antenna element. That is, regardless of the antenna's orientation, a phase array antenna can transmit or receive radio waves in the desired direction by electronically controlling the phase (beam direction) of each antenna element.

[0226] As a millimeter-wave antenna element, known antennas can be used without particular limitation. For example, an antenna element with a resonant element can be cited, which is formed by a loop antenna structure, a patch antenna structure, a stacked patch antenna structure, a patch antenna structure with parasitic elements, an inverted-F antenna structure, a slot antenna structure, a planar inverted-F antenna structure, a monopole, a dipole, a helical antenna structure, a Yagi (Yagi / Uda) antenna structure, a surface bulk waveguide structure, or a combination of these designs. Different types of millimeter-wave antenna elements can be used for different frequency band combinations. From the perspective of efficiently receiving millimeter waves using portable communication devices such as smartphones, it is preferable to arrange the patch antenna elements in an array as a phase array antenna.

[0227] The materials constituting the millimeter-wave antenna elements are not particularly limited. Examples include: titanium, silicon, niobium, indium, zinc, tin, gold, silver, copper, aluminum, cobalt, chromium, nickel, lead, iron, palladium, platinum, tungsten, zirconium, tantalum, hafnium, etc.; and metal oxides such as ITO (indium and tin oxide), zinc oxide, and tin oxide. Furthermore, examples include those containing two or more of these metals or metal oxides, or alloys with these metals as the main components. Among these, from the viewpoint of conductivity, silver, copper, and ITO are preferred, and from the viewpoint of transparency and visibility, ITO is even more preferred. That is, the above-mentioned millimeter-wave antenna elements are particularly preferably those containing ITO.

[0228] Furthermore, when the antenna element contains metals such as silver and copper, in order to conceal the antenna element and prevent the reduction in visibility caused by the reflection of the metal, a blackening treatment can be carried out in advance by forming a film of the metal such as nitride, oxide, or sulfide.

[0229] Furthermore, the millimeter-wave antenna substrate may also have a transmission line path, which is used to transmit the signals received and transmitted by the millimeter-wave antenna element to the transceiver circuit. The transmission line path may include coaxial cable paths, microstrip transmission lines, stripline transmission lines, edge-coupled microstrip transmission lines, edge-coupled stripline transmission lines, waveguide structures (e.g., coplanar waveguides or grounded coplanar waveguides) used to transmit signals using the millimeter-wave band, and transmission lines formed by combinations of these types of transmission lines. There are no particular limitations on the materials constituting the transmission line path; materials constituting millimeter-wave antenna elements may be used.

[0230] As a component constituting a millimeter-wave antenna, a cover component can be cited as an example, which is deposited on the millimeter-wave antenna substrate to protect the millimeter-wave antenna elements arranged on the millimeter-wave antenna substrate. As a cover component, optical films such as glass or plastic films can be used, for example.

[0231] Examples of materials used for plastic films include: polyester resins such as polyethylene terephthalate (PET); (meth)acrylic resins such as polymethyl methacrylate (PMMA); polycarbonate; triacetyl cellulose (TAC); polyurethane; polyarylate; polyimide; transparent polyimide; polyvinyl chloride; polyvinyl acetate; fluorinated resins; polyolefin resins such as polyethylene, polypropylene, and ethylene-propylene copolymers; and cyclic olefin polymers such as "Arton" (manufactured by JSR Corporation) and "Zeonor" (manufactured by Zeon Corporation of Japan). These plastic materials can be used alone or in combination of two or more.

[0232] From the perspective of suppressing the radiation loss of millimeter waves, the dielectric constant of the cover component at 28 GHz and / or 60 GHz is preferably 2.0 to 5.0, more preferably 2.1 to 4.5, even more preferably 2.2 to 4.0, even more preferably 2.2 to 3.5, particularly preferably 2.2 to 3.4, and most preferably 2.2 to 3.3, 2.2 to 3.2, 2.2 to 3.1 or 2.2 to 3.0. Furthermore, considering the suppression of millimeter wave radiation loss, the dielectric loss of the cover component at 28 GHz and / or 60 GHz is preferably 0.0001 to 0.050, more preferably 0.001 to 0.02, even more preferably 0.002 to 0.019, even more preferably 0.003 to 0.018, particularly preferably 0.004 to 0.017, and most preferably 0.005 to 0.016, 0.006 to 0.015, 0.007 to 0.014, 0.008 to 0.013, 0.009 to 0.012 or 0.010 to 0.011.

[0233] The aforementioned cover member is preferably transparent. The total light transmittance of the cover member in the visible light wavelength region (according to JIS K7361-1) is preferably 85% or more, more preferably 88% or more, further preferably 89% or more, further preferably 90% or more, especially preferably 91% or more, and most preferably 92% or more. Furthermore, the haze of the cover member (according to JIS K7136) is preferably 1.2% or less, more preferably 1.1% or less, further preferably 1.0% or less, further preferably 0.9% or less, and especially preferably 0.8% or less.

[0234] From the perspective of suppressing the radiation loss of millimeter waves, the thickness of the cover member is preferably 0.025 to 1.5 mm. Furthermore, the cover member can have any of the forms of single layer or multi-layer. Also, the surface of the cover member can be appropriately subjected to known and commonly used surface treatments such as physical treatment such as corona discharge treatment and plasma treatment; chemical treatment such as primer treatment; and coatings such as hard coating.

[0235] The adhesive sheet of the present invention is preferably used in the manufacture of millimeter-wave antennas for use in portable communication devices. Examples of such portable communication devices include: mobile phones, PHS, smartphones, tablets (tablet computers), mobile computers (mobile PCs), portable information terminals (PDAs), etc.

[0236] The millimeter-wave antenna may have components other than the aforementioned millimeter-wave antenna substrate, cover component, and adhesive sheet. For example, it may have a polarizing plate, waveplate, retardation plate, optical compensation film, brightness enhancement film, light guide plate, reflective film, anti-reflective film, hard coating film, transparent conductive film, design film, decorative film, surface protection plate, prism, lens, color filter, transparent substrate, or image display panel (e.g., liquid crystal display panel, organic EL panel, plasma display panel, etc.). The image display panel may have a touch sensor.

[0237] The millimeter-wave antenna can be configured at any location on the portable communication device, specifically, it can be configured on the front, back, or side of the portable communication device. Furthermore, the front of the portable communication device refers to the side facing the user when the user is using the device; for example, the side with the display panel corresponds to the front, and the casing corresponds to the back or side. Furthermore, the display panel refers to a structure that includes at least a lens (especially a glass lens) and a touch panel.

[0238] The size (area) of the millimeter-wave antenna is not limited; it can be formed on the entire surface of any surface of the portable communication device, or it can be configured on a portion of it. Furthermore, the shape of the millimeter-wave antenna is not particularly limited; for example, it can be square, circular, or wire-like. It can also be configured in a frame-like shape. Moreover, the number of millimeter-wave antennas configured on the portable communication device is not limited; it can be one, or multiple antennas can be configured at any location. When multiple millimeter-wave antennas are configured, their sizes (areas) can be the same or different. In order to improve visibility, dummy patterns without millimeter-wave antennas can also be configured on the parts of the portable communication device where no millimeter-wave antennas are configured.

[0239] The millimeter-wave antenna of the present invention has at least the aforementioned adhesive sheet and substrate. It is sufficient that the substrate has an antenna element (millimeter-wave antenna element) on one side, and the adhesive sheet is attached to the side of the substrate (millimeter-wave antenna substrate) where the antenna element is located. There are no other particular limitations. Furthermore, since the adhesive sheet in the millimeter-wave antenna of the present invention is an adhesive sheet used in practice, it does not have spacers.

[0240] As described above, the millimeter-wave antenna is preferably constructed by bonding the millimeter-wave antenna substrate with other optical components (which may or may not have the aforementioned adhesive sheet, but are preferably present to further suppress the radiation loss of the millimeter wave). Furthermore, the aforementioned other optical components may be singular or plural.

[0241] Examples of bonding the millimeter-wave antenna of the present invention with the other optical components under the above-described conditions include: (1) bonding the millimeter-wave antenna substrate of the present invention with the other optical components via the adhesive sheet of the present invention; (2) bonding the adhesive sheet of the present invention, which includes or constitutes the millimeter-wave antenna substrate, to the other optical components; (3) bonding the millimeter-wave antenna substrate to a component other than the millimeter-wave antenna substrate via the adhesive tape of the present invention; and (4) bonding the adhesive tape of the present invention, which includes or constitutes the millimeter-wave antenna substrate, to a component other than the millimeter-wave antenna substrate. Furthermore, in the above-described condition (2), the adhesive sheet of the present invention is preferably a double-sided adhesive sheet with the millimeter-wave antenna substrate as the substrate.

[0242] Next, a preferred embodiment of the millimeter-wave antenna of the present invention will be described with reference to the drawings.

[0243] Figure 1 shows a millimeter-wave antenna 1A, which is a millimeter-wave antenna having at least an adhesive sheet 10 and a substrate as a millimeter-wave antenna substrate 11, and the millimeter-wave antenna substrate 11 has a millimeter-wave antenna element 2 on one side, and the adhesive sheet 10 is attached to the side of the millimeter-wave antenna substrate 11 with the millimeter-wave antenna element 2.

[0244] Figure 2 shows a millimeter-wave antenna 1B, which sequentially comprises a cover member 12, an adhesive sheet 10, and a millimeter-wave antenna substrate 11 in a state of mutual contact. The millimeter-wave antenna substrate 11 has a millimeter-wave antenna element 2 on the side of the adhesive sheet 10, and the adhesive sheet 10 is attached to the side of the millimeter-wave antenna substrate 11 with the millimeter-wave antenna element 2. The cover member 12 is preferably made of glass, and from the perspective of low dielectric constant and low dielectric loss, the millimeter-wave antenna substrate 11 is preferably made of COP, and the millimeter-wave antenna element 2 is preferably made of copper, silver, or ITO.

[0245] Figure 3 shows a millimeter-wave antenna 1C, which, in a state of sequential contact with each other, includes a cover member 12, an adhesive sheet 10a, a millimeter-wave antenna substrate 11, an adhesive sheet 10b, and an image display panel 13. The millimeter-wave antenna substrate 11 has a millimeter-wave antenna element 2 on the side of the adhesive sheet 10a, and the adhesive sheet 10a is attached to the side of the millimeter-wave antenna substrate 11 with the millimeter-wave antenna element 2. The cover member 12 is preferably glass. Considering low dielectric constant and low dielectric loss, the millimeter-wave antenna substrate 11 is preferably COP. Considering transparency and visibility, the millimeter-wave antenna element 2 is preferably ITO, or silver or copper that has undergone blackening treatment using nitride, oxide, sulfide, or other coatings. The adhesive sheet 10b may be the adhesive sheet of this invention, or it may not be the adhesive sheet of this invention, but it is preferably the adhesive sheet of this invention. The image display panel 13 may have a touch sensor (illustration omitted).

[0246] In the millimeter-wave antennas 1A-1C of Figures 1-3, since the adhesive sheets 10, 10a, and preferably the adhesive sheet 10b contain the adhesive layer of the present invention with low dielectric constant and low dielectric loss in the high-frequency band, the emission loss of millimeter waves is suppressed, enabling efficient millimeter-wave communication. Furthermore, since efficient millimeter-wave communication is possible, the antenna area can be miniaturized, allowing for antenna miniaturization. [Example]

[0247] Hereinafter, the present invention will be described in more detail based on embodiments, but the present invention is not limited to these embodiments in any way.

[0248] (Example 1) In a reaction vessel equipped with a condenser, a nitrogen inlet pipe, a thermometer, and a stirrer, a mixture of 99.0 parts by mass of C12-13 alkyl methacrylate (manufactured by Kyoesha Chemical Co., Ltd., trade name "L-7MA"), 1.0 part by mass of hydroxyethyl methacrylate (HEMA), 0.2 parts by mass of 2,2'-azobisisobutyronitrile (AIBN) as a thermal polymerization initiator, and ethyl acetate as a polymerization solvent was added at a monomer content of 70% by mass. Nitrogen gas was introduced, and nitrogen purging was carried out for about 1 hour while stirring. Subsequently, the reaction vessel was heated to 70°C and reacted for 6 hours. Then, the reaction vessel was heated to 80°C and reacted for 3 hours to obtain a (meth)acrylic polymer with a weight average molecular weight (Mw) of 400,000. In a solution of the (meth)acrylic polymer (100 parts by weight of solids), 0.1 parts by weight of an isocyanate-based crosslinking agent (trade name "Coronate HX", manufactured by Tosoh Co., Ltd., 100% solids concentration), 0.01 parts by weight of dioctyltin dilaurate (trade name "EMBILIZEROL-1", manufactured by Tokyo Fine Chemicals Co., Ltd.) as a crosslinking promoter, and 5 parts by weight of acetone as a crosslinking delay agent were added and mixed uniformly to prepare the adhesive composition of this example.

[0249] The adhesive composition described above was coated onto a polyethylene terephthalate (PET) spacer (trade name "MRF38", manufactured by Mitsubishi Chemical Corporation) to form a coating layer (adhesive composition layer) with a final thickness (adhesive layer thickness) of 25 μm. Subsequently, the layer was dried in a dryer at 130°C for 120 minutes to allow residual monomers to evaporate. Then, a PET spacer (trade name "MRE38", manufactured by Mitsubishi Chemical Corporation) was disposed on the coating layer to obtain a substrate-free double-sided adhesive sheet. This substrate-free double-sided adhesive sheet contains only an adhesive layer, and both sides of the adhesive layer are protected by the spacer.

[0250] (Examples 2-38) Except that each monomer component was prepared in the manner shown in Tables 1 and 2, a substrate-free double-sided adhesive sheet was obtained in the same manner as in Example 1.

[0251] (Comparative Example 1) In a reaction vessel equipped with a condenser, a nitrogen inlet pipe, a thermometer, and a stirrer, 2-ethylhexyl acrylate (2EHA), isodecyl acrylate (IDA), acrylic acid (MA), 4-hydroxybutyl acrylate (4HBA), and 2,2'-azobisisobutyronitrile (AIBN) as a thermal polymerization initiator were mixed in the amounts shown in Table 2. Ethyl acetate as a polymerization solvent was added at a monomer content of 40%, nitrogen gas was introduced, and nitrogen purging was carried out for about 1 hour while stirring. Subsequently, the reaction vessel was heated to 60°C and reacted for 6 hours. Then, the reaction vessel was heated to 75°C and reacted for 2 hours to obtain an acrylic polymer. In addition, a substrate-free double-sided adhesive sheet was obtained in the same manner as in Example 1.

[0252] Furthermore, the monomers used as shown in Tables 1 and 2 are as follows: • LMA: Lauryl methacrylate • LA: Lauryl acrylate • 2-EHA: 2-Ethylhexyl acrylate • i-NA: Isononyl acrylate • L-7MA: C12-13 alkyl methacrylate • IDMA: Isodecyl methacrylate • HEMA: 2-Hydroxyethyl methacrylate • MMA: Methyl methacrylate • MMA-giant monomer: Methyl methacrylate • CHMA: Cyclohexyl methacrylate • IBXMA: Isodecyl methacrylate • MAA: Methacrylate • NVP: N-vinylpyrrolidone • PHE-1G: 2-phenoxyethyl methacrylate • BzMA: Benzyl methacrylate • M-20G: 2-(2-methoxyethoxy)ethyl methacrylate • IDA: Isodecyl acrylate • MA: Methyl acrylate • 4-HBA: 4-Hydroxybutyl acrylate

[0253] [Characteristic Evaluation] The substrate-free double-sided adhesive sheets of the Examples and Comparative Examples were subjected to the following measurements or evaluations. The evaluation results are shown in Tables 1 and 2.

[0254] (1) Evaluation of dielectric constant and dielectric loss The dielectric constant and dielectric loss of the adhesive layer monomers (the PET spacers treated with polysiloxane peeled off from the double-sided adhesive sheet) obtained in the examples or comparative examples were measured at frequencies of 28 GHz and 60 GHz using the following apparatus. For the measurement, a circular area with a diameter of 8 cm was performed at 28 GHz, and a circular area with a diameter of 4 cm was performed at 60 GHz. At least 3 samples were prepared for each specimen, and the maximum and minimum values ​​of the measured values ​​of the 3 samples were removed, and the average value was taken as the dielectric constant and dielectric loss at each frequency. ・Measurement method: Open resonator method JIS R1660-2 ・Apparatus: Interferometric resonator method dielectric constant measurement system manufactured by KEYCOM Co., Ltd. ・Measurement environment: 23±1℃, 52%±1%RH

[0255] (2) Total light transmittance and haze: A spacer was peeled off from the double-sided adhesive sheet and attached to a glass slide (manufactured by Matsunami Glass Industry Co., Ltd., "White Grinding No.1", thickness 0.8-1.0 mm, total light transmittance 92%, haze 0.2%). Then, another spacer was peeled off to create a test piece consisting of a double-sided adhesive sheet (adhesive layer) and a glass slide. The total light transmittance and haze of the test piece in the visible light region were measured using a haze meter (product name "HM-150", manufactured by Murakami Color Research Institute Co., Ltd.) at 23±1℃ and 52±1%RH. Three samples were prepared for each specimen, and the average of the measured values ​​of the three samples was taken as the total light transmittance and haze in the visible light region. Furthermore, the greater the thickness of the test piece, the lower the total light transmittance and the higher the haze.

[0256] (3) Transmission and reception characteristics The transmission and reception characteristics of the adhesive layer (the PET spacer that has been treated with polysiloxane and peeled off from the double-sided adhesive sheet) obtained in the embodiment or comparative example were evaluated using the square microstrip antenna shown in FIG4 (refer to Chapter 5, Volume 2, Group 4 of the Institute of Electronics and Information Sciences, "Planar Antennas", URL: http: / / www.ieicehbkb.org / files / 04 / 04Gun_02hen_05.pdf). Specifically, an antenna film 46 was fabricated, on which a millimeter-wave patch antenna 43 of the shape shown in FIG4 was formed on the surface of a 100 μm thick COP substrate (trade name "Zeonor", manufactured by Zeon Corporation, Japan) which serves as the antenna substrate 44, and a 1 μm thick copper ground layer 45 was formed on the back side. The dimensions of the millimeter-wave patch antenna 43 were adjusted to achieve the optimal form when laminated with the adhesive in each embodiment and comparative example (longitudinal A: 2.8–3.2 mm, transverse B: 4.13 mm). Adhesive layers 42 from each embodiment and comparative example were attached to the patch antenna 43 side of the aforementioned antenna film 46 to prevent air bubbles or foreign matter from entering, and then bonded to a 0.7 mm thick chemically strengthened glass (manufactured by Corning) serving as the cover glass 41, thus creating an antenna laminate 4 consisting of cover glass 41 / adhesive layer 42 / antenna film 46. Power was supplied from the microstrip line 43a connecting the various antenna laminates 4 to the millimeter-wave patch antenna 43, and the transmit / receive characteristics in the 30 GHz band were evaluated. Those showing an improvement in gain (5.7 dB) compared to when no adhesive layer was used (with the antenna film 46 positioned close to the cover glass 41) were rated as ○, and those showing a decrease (deterioration) were rated as ×.

[0257] [Table 1] Table 1 Example 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 Use monomers (parts by weight) LMA Quality 99.0 86.0 86.0 98.9 96.9 94.9 94.9 86.0 79.0 66.0 50.0 86.0 79.0 66.0 86.0 79.0 66.0 The 7MA 99.0 IDMA 99 HEMA 1.0 1.0 1.0 1.0 1.0 0.1 0.1 0.1 0.1 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 MMA 13.0 MMA-Big Body 13.0 CHMA 13.0 20.0 33.0 49.0 DCPMA 13.0 20.0 33.0 IBXMA 13.0 20.0 33.0 MA 1.0 3.0 5.0 NVP 5.0 AIBN (parts by weight) 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Dielectric constant 28 GHz 2.27 2.32 2.41 2.47 2.30 2.24 2.69 2.26 2.31 2.18 2.26 2.46 2.34 2.55 2.38 2.35 2.32 2.56 2.63 60 GHz 2.39 2.33 2.44 2.12 2.47 2.44 2.66 2.66 2.23 2.13 2.44 2.49 2.48 2.35 2.34 2.89 2.19 2.24 2.49 Dielectric loss 28 GHz 0.004 0.005 0.006 0.004 0.006 0.003 0.004 0.003 0.005 0.005 0.004 0.004 0.004 0.004 0.003 0.003 0.003 0.004 0.003 60 GHz 0.001 0.003 0.004 0.003 0.004 0.002 0.004 0.002 0.003 0.003 0.003 0.002 0.003 0.002 0.003 0.002 0.004 0.002 0.003 Transparency Total light transmittance % 93.0 93.0 92.8 92.8 92.6 92.9 92.7 92.8 92.8 92.4 92.8 92.6 92.5 92.8 92.7 92.7 92.8 92.7 92.6 Haze 0.20 0.30 0.40 0.60 1.20 0.20 0.60 0.80 0.30 0.40 0.50 0.70 0.88 0.30 0.50 0.20 0.40 0.50 0.80 Then force N / 20 mm 4.8 5.0 16.2 7.5 6.1 8.3 13.2 12.2 6.0 8.5 12.1 19.0 0.2 9.1 12.6 19.6 8.0 12.6 21.6 Receive characteristics ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○

[0258] [Table 2] Table 2 Example Comparative example 20 twenty one twenty two twenty three twenty four 25 26 27 28 29 30 31 32 33 34 35 36 37 38 1 Use monomers LMA Quality 86.0 79.0 86.0 79.0 86.0 95.0 90.0 80.0 84.5 79.5 74.5 49.5 24.5 74.5 74.5 36.0 50.0 44.5 DAY 24.5 2-FOUR 14.5 19.5 24.5 49.5 74.5 50.0 40.0 in case 24.5 IDMA 39.0 44.5 89.0 HEMA 1.0 1.0 1.0 1.0 1.0 5.0 10.0 20.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 CHMA 13.0 10.0 10.0 10.0 PHE-1G 13.0 20.0 BzMA 13.0 20.0 IDA 50.00 MA 9.5 4-HBA 13.0 0.5 AIBN (parts by weight) 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Dielectric constant 28 GHz 2.33 2.30 2.52 2.59 2.54 2.26 2.26 2.30 2.31 2.49 2.46 2.25 2.38 2.29 2.45 2.50 2.69 2.61 2.50 2.57 60 GHz 2.28 2.32 2.37 3.29 2.19 2.22 2.26 2.64 2.28 2.47 2.39 2.19 2.44 2.18 2.21 2.47 2.58 2.51 2.44 2.47 Dielectric loss 28 GHz 0.004 0.005 0.005 0.007 0.029 0.008 0.013 0.019 0.006 0.007 0.007 0.012 0.019 0.006 0.007 0.012 0.004 0.004 0.005 0.030 60 GHz 0.003 0.004 0.004 0.003 0.016 0.003 0.009 0.008 0.004 0.006 0.004 0.008 0.011 0.004 0.004 0.008 0.002 0.004 0.005 0.017 Transparency Total light transmittance % 92.7 92.6 92.7 92.7 92.8 92.8 92.8 92.7 92.8 92.8 92.9 93.0 92.9 92.9 92.9 92.8 92.7 92.7 92.7 92.1 Haze 0.30 0.40 0.30 0.40 0.30 0.50 0.70 0.10 0.20 0.10 0.40 0.60 0.10 0.10 0.20 0.20 0.40 0.40 0.50 0.3 Then force N / 20 mm 7.9 9.0 10.2 11.4 7.0 5.5 7.9 10.0 6.8 5.9 3.5 3.3 2.9 1.7 4.2 5.1 11.9 13.4 17.0 2.2 Receive characteristics ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ [Simplified Explanation of the Diagram]

[0026] Figure 1 is a schematic diagram (cross-sectional view) of one embodiment of the millimeter-wave antenna of the present invention. Figure 2 is a schematic diagram (cross-sectional view) of one embodiment of the millimeter-wave antenna of the present invention. Figure 3 is a schematic diagram (cross-sectional view) of one embodiment of the millimeter-wave antenna of the present invention. Figure 4 is a schematic diagram (cross-sectional view) of the antenna stack used in the evaluation of transmit and receive characteristics. Figure 4(a) is a side cross-sectional view, and Figure 4(b) is a top projection view.

Claims

1. An adhesive composition having a dielectric constant of 2.0 to 5.0 at a frequency of 28 GHz and a dielectric loss of 0.0001 to 0.05 at a frequency of 28 GHz, and comprising a mixture of a methacrylate compound having a hydrocarbon group having 6 or more carbon atoms and a methacrylate compound having a crosslinking functional group, a portion thereof, or a copolymer thereof, wherein the methacrylate compound having a hydrocarbon group having 6 or more carbon atoms satisfies at least one of the following (i), (ii), and (iii): (i) is a methacrylate compound having an aliphatic group having 10 or more carbon atoms, wherein the content of the methacrylate compound having an aliphatic group having 10 or more carbon atoms, or a structural unit derived from the compound, in the mixture, a portion thereof, or a copolymer thereof is 66% by mass or more; (ii) is a methacrylate compound having 6 or more carbon atoms and containing an alicyclic group, wherein the content of the methacrylate compound having 6 or more carbon atoms and containing an alicyclic group, or a structural unit derived from the compound, in the above mixture, some of its polymers or copolymers, is 1.0 to 60.0% by mass; (iii) is a methacrylate compound having 6 or more carbon atoms and containing an aromatic ring group, wherein the content of the methacrylate compound having 6 or more carbon atoms and containing an aromatic ring group, or a structural unit derived from the compound, in the above mixture, some of its polymers or copolymers, is 1.0 to 60.0% by mass.

2. The adhesive composition of claim 1 has a dielectric constant of 2.0 to 5.0 at a frequency of 60 GHz.

3. An adhesive composition having a dielectric constant of 2.0 to 5.0 at a frequency of 60 GHz and a dielectric loss of 0.0001 to 0.05 at a frequency of 60 GHz, and comprising a mixture of a methacrylate compound having a hydrocarbon group having 6 or more carbon atoms and a methacrylate compound having a crosslinking functional group, a portion thereof, or a copolymer thereof, wherein the methacrylate compound having a hydrocarbon group having 6 or more carbon atoms satisfies at least one of the following (i), (ii), and (iii): (i) is a methacrylate compound having an aliphatic group having 10 or more carbon atoms, wherein the content of the methacrylate compound having an aliphatic group having 10 or more carbon atoms, or a structural unit derived from the compound, in the mixture, a portion thereof, or a copolymer thereof is 66% by mass or more; (ii) is a methacrylate compound having 6 or more carbon atoms and containing an alicyclic group, wherein the content of the methacrylate compound having 6 or more carbon atoms and containing an alicyclic group, or a structural unit derived from the compound, in the above mixture, some of its polymers or copolymers, is 1.0 to 60.0% by mass; (iii) is a methacrylate compound having 6 or more carbon atoms and containing an aromatic ring group, wherein the content of the methacrylate compound having 6 or more carbon atoms and containing an aromatic ring group, or a structural unit derived from the compound, in the above mixture, some of its polymers or copolymers, is 1.0 to 60.0% by mass.

4. The adhesive composition of any one of claims 1 to 3, wherein in (ii) and (iii) above, the content of the methacrylate compound having 6 or more carbon atoms and / or the methacrylate compound having 6 or more carbon atoms and / or the structural unit derived from the compound is 25% by mass or more.

5. An adhesive composition according to any one of claims 1 to 3, wherein the content of the methacrylate compound having crosslinking functional groups in the mixture, a portion thereof, or a copolymer thereof, or a structural unit derived therefrom is 0.1 to 30 by mass.

6. An adhesive composition according to any one of claims 1 to 3, wherein the hydrocarbon is based on a terminal alicyclic or aromatic group.

7. An adhesive layer formed from an adhesive composition of any one of claims 1 to 6.

8. An adhesive sheet having an adhesive layer as claimed in claim 7.

9. A millimeter-wave antenna having at least an adhesive sheet as described in claim 8 and a substrate, wherein the substrate has an antenna element on at least one side, and the adhesive sheet is attached to the side of the substrate having the antenna element.

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