Adhesive composition, adhesive layer, and adhesive sheet

Abstract

The present invention provides an adhesive composition and an adhesive sheet that have low dielectric constant and dielectric loss in the high-frequency band and can form an adhesive layer suitable for bonding components constituting a millimeter-wave antenna. [Solution] The adhesive composition of the present invention comprises a mixture, partial polymer or copolymer thereof of a methacrylate compound having a dielectric constant of 2.0 to 5.0 at a frequency of 28 GHz or a dielectric constant of 5.0 at a frequency of 60 GHz and having a hydrocarbon group with 6 or more carbon atoms, and a (meth)acrylate compound having a crosslinkable functional group.

Description

Technical Field

[0001] The present invention relates to an adhesive composition, an adhesive layer, and an adhesive sheet. More specifically, it relates to an adhesive composition, an adhesive layer, and an adhesive sheet suitable for bonding components of a millimeter-wave antenna.

Background Art

[0002] In recent years, the high-speed and large-capacity communication in mobile communication devices such as smartphones has been progressing year by year. In the fifth generation (5G), which is the next-generation ultra-high-speed data communication standard, it is expected to enable ultra-high-speed and large-capacity communication 100 times faster than the fourth generation (4G), low latency of 1 / 10, and connection of more than 10 times as many devices simultaneously.

[0003] In order to enable the ultra-high-speed and large-capacity communication, low latency, and connection of multiple devices simultaneously in 5G, electromagnetic waves in the high-frequency band exceeding 24 GHz, called millimeter waves, are used. By shortening the wavelength to the millimeter order, it becomes possible to transmit a large amount of data at once.

[0004] On the other hand, millimeter waves are more likely to be attenuated due to resonance absorption with rain, oxygen in the air, water molecules, etc. compared to the frequency band used in 4G, and have the properties of strong straightness and easy reflection. For antennas used in millimeter-wave communication (hereinafter sometimes referred to as "millimeter-wave antennas"), a higher antenna gain than that of conventional 4G communication is required.

[0005] Patent Document 1 discloses a configuration in which a cover member is laminated on a base material provided with antenna elements as a millimeter-wave antenna mounted on a mobile communication device such as a smartphone, and an adhesive is used for bonding these base materials and cover members.

[0006] As such an adhesive, for example, Patent Document 2 discloses an adhesive containing a polymer formed by polymerizing a monomer mixture containing 2-ethylhexyl acrylate, a specific alkyl (meth)acrylate, and a hydroxyl group-containing monomer, and capable of forming an adhesive layer having a dielectric constant of 3.5 or less at a frequency of 100 kHz.

[0007] Further, Patent Document 3 discloses an adhesive layer containing a specific acrylic polymer, a vinyl monomer having a polyalkylene oxide chain, a photopolymerization initiator, and a crosslinking agent, and having a relative dielectric constant of 3.5 or less at a frequency of 1 MHz.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0009] It is known that millimeter waves are reduced due to the dielectric loss of the material of the members constituting the millimeter wave antenna. In order not to reduce the antenna gain, characteristics of low dielectric constant, particularly low dielectric loss, in the high frequency band of millimeter waves are required. Adhesives used for bonding the members constituting the millimeter wave antenna are also required to have characteristics of low dielectric constant and low dielectric loss in the high frequency band.

[0010] Although the adhesive described in Patent Document 2 has a low dielectric constant at low frequencies (100 kHz), its dielectric loss at high frequencies is not sufficiently low. Similarly, the adhesive layer described in Patent Document 3 has a low relative dielectric constant at low frequencies (1 MHz), but its dielectric loss at high frequencies is not sufficiently low. Furthermore, the documents only describe the dielectric constant at low frequencies and do not disclose any information regarding dielectric loss at high frequencies, thus failing to provide a solution to the problem addressed by this application.

[0011] The present invention was conceived under the circumstances described above, and its object is to provide an adhesive composition that can form an adhesive layer suitable for bonding components of a millimeter-wave antenna, having low dielectric constant and dielectric loss in the high-frequency band. Another object of the present invention is to provide an adhesive layer suitable for bonding components of a millimeter-wave antenna, having low dielectric constant and dielectric loss in the high-frequency band. Another object of the present invention is to provide an adhesive sheet having an adhesive layer suitable for bonding components of a millimeter-wave antenna, having low dielectric constant and dielectric loss in the high-frequency band. [Means for solving the problem]

[0012] In other words, the present invention provides a first side adhesive composition comprising a mixture, a partial polymer thereof, or a copolymer of a methacrylate compound having a hydrocarbon group with 6 or more carbon atoms and a crosslinkable functional group, 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 a (meth)acrylate compound having a crosslinkable functional group.

[0013] In the adhesive composition of the second aspect of the present invention, a configuration in which the dielectric constant at a frequency of 28 GHz is 2.0 to 5.0 is preferable in that it can improve the antenna gain of a millimeter-wave antenna to which components are bonded using the adhesive composition.

[0014] The first side adhesive composition of the present invention preferably has a dielectric constant of 2.0 to 5.0 at a frequency of 60 GHz. This configuration is preferable because it can improve the antenna gain of a millimeter-wave antenna in which components are bonded together using the first side adhesive composition of the present invention.

[0015] The present invention also provides an adhesive composition of a second aspect, comprising a mixture, partial polymer or copolymer thereof of a methacrylate compound 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 a (meth)acrylate compound having a hydrocarbon group with 6 or more carbon atoms, and a crosslinkable functional group.

[0016] In the adhesive composition of the second aspect of the present invention, a configuration in which the dielectric constant at a frequency of 60 GHz is 2.0 to 5.0 is preferable in that it can improve the antenna gain of a millimeter-wave antenna to which components are bonded using the adhesive composition.

[0017] The hydrocarbon group described above preferably has an aliphatic group, an alicyclic group, or an aromatic ring group.

[0018] Preferably, the content of the methacrylate compound having 6 or more carbon atoms or the constituent units derived from said compound in the above mixture, its partially polymerized product, or copolymer is 25% by mass or more.

[0019] The content of the (meth)acrylate compound having the crosslinkable functional group or the constituent units derived from the compound in the above mixture, partially polymerized thereof, or copolymer is preferably 0.1 to 30% by mass.

[0020] The above hydrocarbon group preferably has an alicyclic or aromatic group at its terminus.

[0021] The present invention also provides an adhesive layer formed by the above-mentioned adhesive composition.

[0022] The present invention also provides an adhesive sheet having the above-mentioned adhesive layer.

[0023] The present invention also provides a millimeter-wave antenna having at least the above-mentioned adhesive sheet and 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 that has the antenna element. [Effects of the Invention]

[0024] The adhesive composition and adhesive layer of the present invention exhibit low dielectric constant and dielectric loss in the high-frequency band of millimeter waves, thereby suppressing millimeter-wave radiation loss. Therefore, by using the adhesive sheet of the present invention to bond the components of a millimeter-wave antenna, a millimeter-wave antenna exhibiting high antenna gain can be efficiently manufactured. [Brief explanation of the drawing]

[0025] [Figure 1] Figure 1 is a schematic diagram (cross-sectional view) showing one embodiment of the millimeter-wave antenna of the present invention. [Figure 2] Figure 2 is a schematic diagram (cross-sectional view) showing one embodiment of the millimeter-wave antenna of the present invention. [Figure 3] Figure 3 is a schematic diagram (cross-sectional view) showing one embodiment of the millimeter-wave antenna of the present invention. [Figure 4] Figure 4 is a schematic diagram (cross-sectional view) of the antenna stack used in the transmission and reception characteristics evaluation. Figure 4(a) is a lateral cross-sectional view, and Figure 4(b) is a top projection view. [Modes for carrying out the invention]

[0026] [Adhesive composition] The adhesive composition of the first side of the present invention comprises a mixture, partial polymer or copolymer thereof of a methacrylate compound having a hydrocarbon group with 6 or more carbon atoms and a (meth)acrylate compound having a crosslinkable functional group, 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 a (meth)acrylate compound having a crosslinkable functional group.

[0027] The adhesive composition of the second aspect of the present invention comprises a mixture, partial polymer or copolymer thereof of a methacrylate compound having a hydrocarbon group with 6 or more carbon atoms and a (meth)acrylate compound having a crosslinkable functional group, 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 a (meth)acrylate compound having a crosslinkable functional group.

[0028] The adhesive composition of the present invention may have any form, for example, a solvent type, an emulsion type, a hot melt type, or a solvent-free type (active energy ray curing type, for example, a monomer mixture, or a monomer mixture and its partial polymer).

[0029] As described above, the adhesive composition of the present invention may be solvent-based, that is, it may contain an organic solvent.

[0030] The above-mentioned organic solvent can be any organic compound used as a solvent, and examples include 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 isopropyl alcohol. The above-mentioned organic solvent may also be a mixed solvent containing two or more organic solvents.

[0031] The adhesive composition for the first side of the present invention has a low dielectric constant at 28 GHz, which can suppress millimeter-wave radiation loss. The dielectric constant of the adhesive composition for the first side 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, even more preferably 3.5 or less, even more preferably 3.4 or less, particularly preferably 3.3 or less, most preferably 3.2 or less, 3.1 or less, 3.0 or less, or 2.9 or less. The lower limit is not particularly limited, but is 2.0 or more, and may be 2.1 or more or 2.2 or more. Furthermore, it is preferable that the dielectric constant of the adhesive composition for the second side at a frequency of 28 GHz is within the above range.

[0032] In this specification, the dielectric constant is measured by the method described in the examples below. Note that "relative dielectric constant" is the value obtained by dividing "dielectric constant" by "dielectric constant of vacuum," but since "dielectric constant of vacuum" is 1, "dielectric constant" and "relative dielectric constant" are treated as synonymous in this specification. Furthermore, the adhesive composition for the first side of the present invention and the adhesive composition for the second side of the present invention may be collectively referred to as "the adhesive composition of the present invention."

[0033] The first side adhesive composition of the present invention is preferably characterized by low dielectric loss at 28 GHz, which is preferable in that it can suppress millimeter-wave radiation loss. The dielectric loss of the first side adhesive composition 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, even more preferably 0.035 or less, even more preferably 0.030 or less, particularly preferably 0.025 or less, and most preferably 0.020 or less. The lower limit is 0.0001 or more, and may be 0.0005 or more or 0.0010 or more. Furthermore, the second side adhesive composition of the present invention is preferably characterized by a dielectric loss at a frequency of 28 GHz within the above range.

[0034] The adhesive composition for the second side of the present invention has a low dielectric constant at 60 GHz, which can suppress millimeter-wave radiation loss. The dielectric constant of the adhesive composition for the second side 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, even more preferably 3.5 or less, even more preferably 3.4 or less, particularly preferably 3.3 or less, most preferably 3.2 or less, 3.1 or less, 3.0 or less, or 2.9 or less. The lower limit is not particularly limited, but is 2.0 or more, and may be 2.1 or more or 2.2 or more. Furthermore, it is preferable that the dielectric constant of the adhesive composition for the first side of the present invention at a frequency of 60 GHz is within the above range.

[0035] The adhesive composition for the second side of the present invention is preferable in that its dielectric loss at 60 GHz is controlled to be low, and it can suppress millimeter-wave radiation loss. The dielectric loss of the adhesive composition for the second side 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, even more preferably 0.035 or less, even more preferably 0.030 or less, particularly preferably 0.025 or less, 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 be 0.0005 or more or 0.0010 or more. Furthermore, it is preferable that the dielectric loss of the adhesive composition for the first side of the present invention at a frequency of 60 GHz is within the above range.

[0036] The adhesive composition of the present invention preferably has a low and controlled saturation moisture absorption rate. A low saturation moisture absorption rate is preferable because it suppresses attenuation such as resonance absorption of millimeter waves originating from water molecules, resulting in excellent water resistance when applied as an adhesive layer to millimeter-wave antennas, etc., and suppressing radiation loss of millimeter waves. The saturation moisture absorption rate of the adhesive composition of the present invention at 25°C and 90%RH is preferably 2.8% or less, more preferably 2.7% or less, even more preferably 2.6% or less, even more preferably 2.5% or less, particularly preferably 2.4% or less, 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 saturation moisture absorption rate at 25°C and 90%RH can suppress millimeter-wave radiation loss near room temperature. The lower limit of the saturation moisture absorption rate is not particularly limited, but may be, for example, 0.3% or higher, 0.4% or higher, or 0.5% or higher.

[0037] 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, even more preferably 2.4% or less, even more preferably 2.3% or less, particularly preferably 2.2% or less, 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 saturated moisture absorption rate is not particularly limited, but may be, for example, 0.4% or more, 0.5% or more, or 0.6% or more. A low saturated moisture absorption rate at 65°C and 90%RH can suppress millimeter-wave radiation loss even when the adhesive layer or the like is applied in a high-temperature environment.

[0038] 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, even more preferably 3.5% or less, even more preferably 3.0% or less, particularly preferably 2.8% or less, 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 saturated moisture absorption rate is not particularly limited, but may be, for example, 0.4% or more, 0.5% or more, or 0.6% or more. A low saturated moisture absorption rate at 85°C and 85%RH can suppress millimeter-wave radiation loss even when the adhesive layer or the like is applied in a high-temperature environment.

[0039] The saturated moisture absorption rate under each temperature and humidity environment can be determined, for example, from the weight of the dry sample (w1) and the weight (w2) of the sample when it has stopped changing weight after being left in an atmosphere of 65°C and 90% RH (when the moisture absorption rate is saturated), using the following formula. It can also be determined under the conditions of 25°C and 90% RH, and 85°C and 85% RH. Note that the values ​​of w1 and w2 are assumed to have been measured at the same temperature and humidity. Saturated moisture absorption rate (%)={(w2-w1) / w1}×100

[0040] The adhesive composition of the present invention is preferable in that the change in dielectric loss due to moisture absorption is controlled to a low degree, and is preferable in that it can suppress millimeter-wave radiation loss 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, but may be, for example, 0.0001 or more, 0.0002 or more, or 0.0003 or more.

[0041] The amount of change in the dielectric loss of the adhesive composition of the present invention due to moisture absorption 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 amount of change in the dielectric constant due to moisture absorption is not particularly limited, but may be, for example, 0.0001 or more, 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.

[0042] The amount of change in the dielectric loss at the above frequencies of 28 GHz and 60 GHz is measured after being held in an atmosphere of 65 °C and 90% R.H. for 5 days or more, and then returned to the conditions of 23 ± 1 °C and 52 ± 1% R.H. (elapsed time = 0 minutes). After 4 minutes have elapsed, the dielectric loss at each frequency is measured every 10 minutes until 180 minutes have elapsed, and the maximum value (D fmax ) and the minimum value (D fmin ) among them can be obtained by the following formula. Amount of change in dielectric loss = D fmax - D fmin

[0043] Since the water vapor permeability of the adhesive composition of the present invention is low and controlled, the movement of water molecules in the adhesive composition can be suppressed, and the fluctuation of the radiation loss of millimeter waves can be suppressed. The water vapor permeability of the adhesive composition of the present invention at 40 °C and 92% R.H. is preferably 430 g / m 2 / day or less, more preferably 300 g / m 2 / day or less, even more preferably 250 g / m 2 / day or less, even more preferably 200 g / m 2 / day or less, particularly preferably 150 g / m 2 / day or less, most preferably 100 g / m 2 / day or less, 50 g / m 2 / day or less, or 30 g / m 2 / day or less. The lower limit of the water vapor permeability is not particularly limited, but may be, for example, 10 g / m 2 / day or more, 20 g / m 2 / day or more, or 22 It can be more than / day.

[0044] The above water vapor transmission rate (WVTR) is a value measured based on the cup method. The weight of the dry calcium chloride isolated from the outside by the adhesive layer (w1), and the weight of the sample after a predetermined time has elapsed (when the moisture absorption rate is saturated) after being left in an atmosphere of 40°C and 92%RH (w2) are measured, and the weight change is measured per unit time (1 day) and per unit area (1 m²) of the adhesive layer. 2 It can be calculated by converting to ).

[0045] The dielectric constant or dielectric loss, saturation moisture absorption rate, change in dielectric loss due to moisture absorption, and water vapor permeability of the adhesive composition of the present invention at 28 GHz or 60 GHz can be adjusted by adjusting the monomer composition, the type and content of additives, etc. In this specification, the dielectric constant or dielectric loss at 28 GHz or 60 GHz is measured by the method described in the examples below.

[0046] Furthermore, the dielectric constant, dielectric loss, saturated moisture absorption rate, and water vapor permeability of the adhesive composition of the present invention refer to the dielectric constant, dielectric loss, saturated moisture absorption rate, and water vapor permeability of the adhesive layer formed by the adhesive composition of the present invention.

[0047] The adhesive composition of the present invention contains a mixture, partial polymer thereof, or copolymer of a specific methacrylate compound and a (meth)acrylate compound, thereby controlling the dielectric constant and dielectric loss at high frequencies and suppressing moisture absorption, which is a cause of deterioration of dielectric loss. The above-mentioned "mixture, partial polymer thereof, or copolymer" may be referred to as a methacrylic copolymer. Furthermore, "methacrylate compound" refers to a compound having a "methacryloyl group," and "(meth)acrylate compound" refers to a compound having at least one of an "acryloyl group" and a "methacryloyl group." Furthermore, "(meth)acrylic" refers to either or both of "acrylic" and "methacrylic."

[0048] The above-mentioned partially polymerized product means a composition in which one or more monomer components of the above mixture are partially polymerized.

[0049] The content of the methacrylic copolymer in the adhesive composition of the present invention is not particularly limited, but is preferably 75% by mass or more (for example, 75 to 99.9% by mass), and more preferably 85% by mass or more (for example, 85 to 99.9% by mass).

[0050] [Mixtures, partially polymerized or copolymerized thereof (methacrylic copolymers)] The adhesive composition of the present invention is a methacrylic adhesive composition using a mixture, a partially polymer thereof, or a copolymer (methacrylic copolymer) as the base polymer. The content of the methacrylic copolymer is not particularly limited, but is preferably 75% by mass or more (for example, 75 to 99.9% by mass) and more preferably 85% by mass or more (for example, 85 to 99.9% by mass) based on 100% by mass of the total amount of the adhesive composition of the present invention.

[0051] Examples of adhesive compositions of the present invention include water-dispersible compositions (emulsion-type compositions) in which the above copolymer is an essential component, and active energy ray-curable compositions in which the above mixture or a partial polymer thereof is an essential component. Among these, compositions in which the mixture or a partial polymer thereof is an essential component are preferred.

[0052] The methacrylic copolymer according to the present invention comprises a methacrylate compound having a hydrocarbon group with 6 or more carbon atoms, and a (meth)acrylate compound having a crosslinkable functional group as constituent monomers.

[0053] <Methacrylate compounds having hydrocarbon groups with 6 or more carbon atoms> The methacrylate compound used in the above-mentioned methacrylate copolymer contains a hydrocarbon group having 6 or more carbon atoms. The hydrocarbon group having 6 or more carbon atoms in the above-mentioned methacrylate compound is preferably an aliphatic group, an alicyclic group, or an aromatic ring group. These methacrylate compounds having hydrocarbon groups can be used alone or in combination of two or more.

[0054] The above methacrylic copolymer is thought to reduce dielectric loss because its main constituent unit is derived from a methacrylate compound and has an α-methyl group, thus reducing polarization near the main chain compared to the case derived from an acrylate compound. Furthermore, the methacryloyl group is more hydrophobic than the acryloyl group, suppressing moisture absorption, which can suppress the deterioration and change in dielectric loss at high frequencies caused by moisture absorption.

[0055] When the above-mentioned methacrylate compound has an alicyclic or aromatic group, it becomes easier to obtain appropriate cohesive force in the methacrylic copolymer, making it easier to obtain strong adhesion. In addition, it becomes easier to increase the gel fraction and obtain excellent foaming resistance and peeling properties. Furthermore, it becomes easier to obtain appropriate flexibility in the adhesive layer, making it easier to obtain excellent stress relaxation and excellent step-following properties.

[0056] When the hydrocarbon group having 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.

[0057] 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, isodecyl methacrylate, undecyl methacrylate, lauryl methacrylate, tridecyl methacrylate, tetradecyl methacrylate, pentadecyl methacrylate, hexadecyl methacrylate, heptadecyl methacrylate, octadecyl methacrylate, isostearyl methacrylate, stearyl methacrylate, nonadecyl methacrylate, and eicosyl methacrylate. Among these, lauryl methacrylate, tridecyl methacrylate, and isodecyl methacrylate are preferred.

[0058] The content of the methacrylate compound in the methacrylic copolymer according to the present invention, in which the hydrocarbon group having 6 or more carbon atoms is an aliphatic group, is not particularly limited, but is preferably 25% by mass or more, more preferably 25.0 to 99.5% by mass, even more preferably 30.0 to 99.3% by mass, and even more preferably 40.0 to 99.0% by mass, based on 100% by mass of the total constituent units. Using 25% by mass or more is preferable from the viewpoint of lowering the dielectric constant and lowering the dielectric loss in the high frequency band.

[0059] When the hydrocarbon group having 6 or more carbon atoms is an alicyclic group, the number of carbon atoms in the hydrocarbon group is preferably 6 or more, and more preferably 8 or more. The number of carbon atoms in the hydrocarbon group is preferably 22 or less, and more preferably 16 or less.

[0060] Examples of methacrylate compounds in which the hydrocarbon group having 6 or more carbon atoms is an alicyclic group include cycloalkyl methacrylates having a cycloalkane ring (cyclopentane ring, cyclohexane ring, cycloheptane ring, cyclooctane ring, etc.), methacrylate esters having a bicyclic hydrocarbon ring (pinane, pinene, bornane, norbornane, norbornene, etc.), and methacrylate esters having three or more aliphatic hydrocarbon rings (dicyclopentane ring, dicyclopentene ring, adamantane ring, tricyclopentane ring, tricyclopentene ring, etc.).

[0061] Examples of the cycloalkyl methacrylates mentioned above include cyclohexyl methacrylate, 3,3,5-trimethylcyclohexyl methacrylate, cycloheptyl methacrylate, and cyclooctyl methacrylate.

[0062] Examples of methacrylic acid esters having the above-mentioned bicyclic hydrocarbon ring include bornyl methacrylate and isobornyl methacrylate.

[0063] Examples of methacrylic acid esters having three or more hydrocarbon rings include dicyclopentanyl methacrylate, dicyclopentanyloxyethyl methacrylate, tricyclopentanyl methacrylate, 1-adamantyl methacrylate, 2-methyl-2-adamantyl methacrylate, and 2-ethyl-2-adamantyl methacrylate.

[0064] When the hydrocarbon group having 6 or more carbon atoms is an aromatic ring-containing group, the number of carbon atoms in the hydrocarbon group is preferably 6 to 14, and more preferably 6 to 10.

[0065] Examples of methacrylate compounds in which the hydrocarbon group having 6 or more carbon atoms is an aromatic ring-containing group include compounds having aromatic carbon rings (for example, monocyclic carbon rings such as benzene rings, or condensed carbon rings such as naphthalene rings). Specific examples include benzyl methacrylate, phenyl methacrylate, naphthyl methacrylate, and 6-(1,1'-biphenyl-4-yloxy)hexyl methacrylate.

[0066] The total content of methacrylate compounds in the methacrylic copolymer according to the present invention, in which the hydrocarbon group having 6 or more carbon atoms is an alicyclic group or an aromatic ring group, is not particularly limited, but is preferably 1.0 to 60.0% by mass, more preferably 5.0 to 55.0% by mass, and even more preferably 10.0 to 50.0% by mass, based on 100% by mass of the total constituent units.

[0067] The above methacrylate compound may have a (poly)oxyalkylene chain. If it has a (poly)oxyalkylene chain, the hydrocarbon group having 6 or more carbon atoms is preferably located at the end of the ester portion of the methacrylate compound. The number of oxygen atoms in the (poly)oxyalkylene chain (i.e., the number of repeating oxyalkylene groups) is preferably 1 to 10, and more preferably 1 to 3. The hydrocarbon group having 6 or more carbon atoms at the end may be an aliphatic group, an alicyclic group, or an aromatic group, but is preferably an alicyclic group or an aromatic group, and is particularly preferred to be an aromatic group.

[0068] The content of the methacrylate compound having the (poly)oxyalkylene chain in the methacrylic copolymer according to the present invention is not particularly limited, but is preferably 1.0 to 30.0% by mass, more preferably 5.0 to 25.0% by mass, and even more preferably 10.0 to 20.0% by mass, based on 100% by mass of the total constituent units.

[0069] Among the methacrylate compounds having the above-mentioned (poly)oxyalkylene chains, those with an aromatic group at the terminal end are effective in reducing dielectric loss in the high-frequency range because the polarizability of the entire repeating unit is reduced.

[0070] The total content of the methacrylate compound having a hydrocarbon group with 6 or more carbon atoms in the above methacrylic copolymer is preferably 25% by mass or more, more preferably 25.0 to 99.5% by mass, even more preferably 30.0 to 99.3% by mass, and particularly preferably 40.0 to 99.0% by mass, based on 100% by mass of the total constituent units. Using 25% by mass or more is preferable from the viewpoint of lowering the dielectric constant and lowering the dielectric loss in the high frequency band.

[0071] <(meth)acrylate compounds containing crosslinking functional groups> The above methacrylic copolymer contains a crosslinkable functional group-containing (meth)acrylate compound with a crosslinkable functional group in the ester portion. Therefore, when a crosslinking agent is used, it is crosslinked, increasing the gel fraction and making it easier to obtain excellent foaming resistance and peeling properties. In addition, it is easier to obtain good cohesive force, making it easier to obtain strong adhesion. Furthermore, it is easier to suppress the whitening of adhesive sheets that occurs in high humidity environments.

[0072] The crosslinkable functional groups in the above-mentioned crosslinkable functional group-containing (meth)acrylate compounds include, for example, hydroxyl groups, carboxyl groups, acid anhydride groups, epoxy group-containing groups such as glycidyl groups, isocyanate groups, and aziridyl groups, due to their ease of adjusting the gel fraction. Among these, hydroxyl groups are preferred due to their ease of adjusting the gel fraction. The above-mentioned crosslinkable functional group-containing (meth)acrylate compounds can be used alone or in combination of two or more types.

[0073] Examples of (meth)acrylate compounds containing the above-mentioned crosslinkable functional group having a hydroxyl group 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 because it makes it easier to obtain good cohesive force and improves adhesion reliability at high temperatures.

[0074] The content of the crosslinkable functional group-containing (meth)acrylate compound in the methacrylic copolymer according to the present invention is preferably 0.1 to 30.0% by mass, more preferably 0.2 to 20.0% by mass, even more preferably 0.3 to 10.0% by mass, and particularly preferably 0.5 to 5.0% by mass, based on 100% by mass of the total constituent units. Using 0.1% by mass or more is preferable from the viewpoint of adjusting the gel fraction, and using 30.0% by mass or less is preferable from the viewpoint of lowering the dielectric constant and lowering the dielectric loss in the high frequency band.

[0075] <Copolymerizable monomers> The above-mentioned methacrylic copolymer may also contain copolymerizable monomers in addition to the methacrylate compound having a hydrocarbon group with 6 or more carbon atoms and the (meth)acrylate compound containing a crosslinkable functional group. The copolymerizable monomers can be used alone or in combination of two or more.

[0076] Examples of the copolymerizable monomers mentioned above include acrylate compounds having hydrocarbon groups with 1 to 24 carbon atoms, methacrylate compounds having hydrocarbon groups with 1 to 5 carbon atoms, substituted methylene compounds in which all carbon atoms in the repeating units of the main chain have side chains, heterocyclic monomers, carboxyl group monomers, nitrile group monomers, isocyanate group monomers, amide group monomers, amino group monomers, (meth)acrylate alkoxyalkyl esters having alkoxy groups with 5 or fewer carbon atoms, sulfonic acid group monomers, phosphate group 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 individually or in combination of two or more.

[0077] Furthermore, it is preferable that the adhesive composition of the present invention does not contain or substantially contains acidic group-containing monomers (for example, carboxyl group-containing monomers, sulfo group-containing monomers, phosphate group-containing monomers, etc.). This configuration is preferable in that it can obtain an excellent corrosion prevention effect on antenna elements or wiring. The content of acidic group-containing monomers is preferably 0.05% by weight or less (for example, 0 to 0.05% by weight) of the total amount of the adhesive composition, more preferably 0.01% by weight or less (for example, 0 to 0.01% by weight), and even more preferably 0.001% by weight or less (for example, 0 to 0.001% by weight) can be said to be substantially absent.

[0078] Among the copolymerizable monomers mentioned above, heterocyclic monomers, carboxyl group monomers, amide group monomers, amino group monomers, sulfonic acid group monomers, and phosphate group monomers are preferred because they easily provide a suitable cohesive force to the adhesive layer, increasing the 180° peel adhesion to glass plates and acrylic plates, and thus making it easier to obtain strong adhesion. From the viewpoint of preventing metal corrosion, heterocyclic monomers are more preferred.

[0079] Examples of methacrylate compounds having a hydrocarbon group with 1 to 5 carbon atoms include methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, pentyl methacrylate, isopropyl methacrylate, isobutyl methacrylate, s-butyl methacrylate, t-butyl methacrylate, and isopentyl methacrylate.

[0080] Examples of acrylate compounds having a hydrocarbon group with 1 to 24 carbon atoms include methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate, s-butyl acrylate, t-butyl acrylate, pentyl acrylate, isopentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, isooctyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, isodecyl acrylate, undecyl acrylate, dodecyl acrylate, lauryl acrylate, tridecyl acrylate, tetradecyl acrylate, pentadecyl acrylate, hexadecyl acrylate, heptyl acrylate. Examples include tadecyl, octadecyl acrylate, isostearyl acrylate, stearyl acrylate, nonadecyl acrylate, eicosyl acrylate, cyclohexyl acrylate, 3,3,5-trimethylcyclohexyl acrylate, cycloheptyl acrylate, cyclooctyl acrylate, bornyl acrylate, isobornyl acrylate, dicyclopentanyl acrylate, dicyclopentanyloxyethyl acrylate, tricyclopentanyl acrylate, 1-adamantyl acrylate, 2-methyl-2-adamantyl acrylate, 2-ethyl-2-adamantyl acrylate, phenyl acrylate, naphthyl acrylate, and 6-(1,1'-biphenyl-4-yloxy)hexyl acrylate.

[0081] The heterocycle-containing monomers mentioned above are copolymerizable monomers having heterocycles such as heterocycles having only a nitrogen atom as a heteroatom (e.g., pyrrolidine, pyrrole, imidazole, pyrazole, piperidine, pyridine, pyrimidine, pyrroline, piperazine, pyrazine, etc.), heterocycles having both a nitrogen atom and an oxygen atom (e.g., pyrrolidone, oxazole, isoxazole, morpholine, morpholinone, piperidone, lactam, oxazine, morpholindione, succinimide, itaconimide, etc.), heterocycles having both a nitrogen atom and a sulfur atom (e.g., thiazole, isothiazole, thiazine), heterocycles having an oxygen atom (e.g., lactone, tetrahydrofuran, furan, tetrahydropyran, dioxane, etc.), and heterocycles having a sulfur atom (e.g., tetrahydrothiophene, thiophene, tetrahydrothiopyran, thiopyran, etc.).

[0082] When the methacrylic copolymer according to the present invention contains a heterocyclic monomer, appropriate flexibility can be obtained in the adhesive layer, making it easier to obtain excellent stress relaxation and excellent step-following properties.

[0083] Examples of heterocycle-containing monomers having a heterocycle with only a nitrogen atom as the heteroatom include N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-(meth)acryloylpiperidine, N-(meth)acryloylpyrrolidine, and N-vinylpyrazole.

[0084] Examples of heterocycle-containing monomers having a heterocycle with nitrogen and oxygen atoms as heteroatoms include N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-(meth)acryloyl-2-pyrrolidone, N-vinyloxazole, N-vinylisoxazole, N-vinylmorpholine, N-vinyl-3-morpholinone, N-vinyl-2-caprolactam, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, and N-vinyl-1,3-oxazine-2. Examples include -one, N-vinyl-3,5-morpholinedione, N-(meth)acryloyloxymethylenesuccinimide, N-(meth)acryloyl-6-oxyhexamethylenesuccinimide, N-(meth)acryloyl-8-oxyhexamethylenesuccinimide, N-methylitaconimide, N-ethylitaconimide, N-butylitaconimide, N-octylitaconimide, N-2-ethylhexylitaconimide, N-cyclohexylitaconimide, and N-laurylitaconimide.

[0085] Examples of heterocycle-containing monomers having a heterocycle containing a nitrogen atom and a sulfur atom as the heteroatoms include N-vinylthiazole and N-vinylisothiazole.

[0086] Among these, N-vinyl-2-pyrrolidone is particularly preferred.

[0087] Examples of the carboxyl group-containing monomers mentioned above include (meth)acrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid. Furthermore, the carboxyl group-containing monomers may also include acid anhydride group-containing monomers such as maleic anhydride and itaconic anhydride. Derivatives formed by esterification with, for example, itaconic acid may also be included.

[0088] Examples of the above-mentioned nitrile group-containing monomers include (meth)acrylonitrile.

[0089] Examples of the above-mentioned isocyanate group-containing monomers include 2-isocyanate ethyl (meth)acrylate.

[0090] Examples of the above amide group-containing monomers include (meth)acrylamide; N,N-dialkyl(meth)acrylamides such as 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(t-butyl)(meth)acrylamide; N-alkyl(meth)acrylamides such as N-ethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N-butyl(meth)acrylamide, Nn-butyl(meth)acrylamide; N-vinyl carboxylic acid amides such as N-vinylacetamide; monomers having a hydroxyl group and an amide group, for example, N-(2-hydroxyethyl)(meth)acrylamide Examples include N-hydroxyalkyl(meth)acrylamides such as 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 an alkoxy group and an amide group, such as N-alkoxyalkyl(meth)acrylamides such as N-methoxymethyl(meth)acrylamide, N-methoxyethyl(meth)acrylamide, and N-butoxymethyl(meth)acrylamide; and others such as N,N-dimethylaminopropyl(meth)acrylamide and N-(meth)acryloylmorpholine.

[0091] Furthermore, the above-mentioned (meth)acrylamides also include, for example, various N-alkoxyalkyl (meth)acrylamides, such as N-methoxymethyl (meth)acrylamide and N-butoxymethyl (meth)acrylamide.

[0092] Examples of the above-mentioned amino group-containing monomers include aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, and t-butylaminoethyl (meth)acrylate.

[0093] Examples of the above-mentioned alkoxyalkyl (meth)acrylate esters having an alkoxy group with 5 or fewer carbon atoms include 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, methoxytriethylene glycol (meth)acrylate, 3-methoxypropyl (meth)acrylate, 3-ethoxypropyl (meth)acrylate, 4-methoxybutyl (meth)acrylate, and 4-ethoxybutyl (meth)acrylate.

[0094] Examples of the above-mentioned sulfonic acid group-containing monomers include sodium vinyl sulfonate.

[0095] The above macromonomer is a high molecular weight monomer formed by the polymerization of multiple monomer components. When a macromonomer is used, the constituent units derived from the monomer components that make up the macromonomer exist continuously to a certain extent within the base polymer. Therefore, by using a macromonomer, a higher-order structure derived from the macromonomer can be introduced into the base polymer, and the properties required for an adhesive (adhesion, cohesiveness, step-following ability, etc.) can be easily adjusted. The weight-average molecular weight of the above macromonomer is preferably 3,000 to 35,000, more preferably 4,000 to 30,000, even more preferably 5,000 to 25,000, and even more preferably 6,000 to 20,000.

[0096] Examples of polyfunctional monomers having two or more polymerizable functional groups include hexanediol di(meth)acrylate, butanediol di(meth)acrylate, (poly)ethylene glycol di(meth)acrylate, (poly)propylene 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(meth)acrylate, vinyl(meth)acrylate, divinylbenzene, polyester acrylate, and urethane acrylate. Polyfunctional monomers can be used individually or in combination of two or more.

[0097] The content of the polyfunctional monomer in the methacrylic copolymer according to the present invention is not particularly limited, but is preferably 0.5% by mass or less (for example, 0 to 0.5% by mass), more preferably 0 to 0.35% by mass, and even more preferably 0 to 0.2% by mass, based on 100% by mass of the total constituent units. When the content of the polyfunctional monomer is 0.5% by mass or less, the adhesive layer has appropriate cohesive force, which is preferable as it easily improves adhesive strength and step absorption. In the case of using a crosslinking agent, the polyfunctional monomer may not be used, but in the case of not using a crosslinking agent, the content of the polyfunctional 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.

[0098] The total content of the copolymerizable monomers in the above methacrylic copolymer is not particularly limited, but is preferably 30.0% by mass or less, and more preferably 15.0% by mass or less, based on 100% by mass of the total constituent units.

[0099] The above-mentioned methacrylic copolymer can be obtained by mixing or polymerizing the above-mentioned methacrylate compound having a hydrocarbon group with 6 or more carbon atoms, a crosslinkable functional group-containing (meth)acrylate compound, and copolymerizable monomer by known or conventional polymerization methods. Examples of the polymerization methods include solution polymerization, emulsion polymerization, bulk polymerization, and polymerization by active energy ray irradiation (active energy ray polymerization). Among these, solution polymerization and active energy ray polymerization are preferred in terms of transparency, water resistance, and cost of the adhesive layer, and active energy ray polymerization is more preferred.

[0100] Examples of active energy rays used in the above-mentioned active energy ray polymerization (photopolymerization) include ionizing radiation such as alpha rays, beta rays, gamma rays, neutron rays, and electron beams, as well as ultraviolet rays, with ultraviolet rays being particularly preferred. Furthermore, the irradiation energy, irradiation time, and irradiation method of the active energy rays are not particularly limited, as long as they can activate the photopolymerization initiator and cause a reaction of the monomer components.

[0101] Various common solvents may be used in the polymerization of the above-mentioned methacrylic copolymer. Examples of such solvents include organic solvents such as esters (ethyl acetate, n-butyl acetate, etc.), aromatic hydrocarbons (toluene, benzene, etc.), aliphatic hydrocarbons (n-hexane, n-heptane, etc.), alicyclic hydrocarbons (cyclohexane, methylcyclohexane, etc.), and ketones (methyl ethyl ketone, methyl isobutyl ketone, etc.). The solvents can be used individually or in combination of two or more.

[0102] Furthermore, when polymerizing the above-mentioned methacrylic copolymer, polymerization initiators such as thermal polymerization initiators and photopolymerization initiators (photoinitiators) may be used depending on the type of polymerization reaction. Polymerization initiators can be used alone or in combination of two or more types.

[0103] The above-mentioned photopolymerization initiators are not particularly limited, but examples include benzoin ether-based photopolymerization initiators, acetophenone-based photopolymerization initiators, α-ketol-based photopolymerization initiators, aromatic sulfonyl chloride-based photopolymerization initiators, photoactive oxime-based photopolymerization initiators, benzoin-based photopolymerization initiators, benzyl-based photopolymerization initiators, benzophenone-based photopolymerization initiators, ketal-based photopolymerization initiators, thioxanthone-based photopolymerization initiators, and the like. The photopolymerization initiators can be used alone or in combination of two or more.

[0104] Examples of the above-mentioned 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 the above-mentioned acetophenone-based photopolymerization initiators include 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexylphenyl ketone, 4-phenoxydichloroacetophenone, and 4-(t-butyl)dichloroacetophenone. Examples of the above-mentioned α-ketol-based photopolymerization initiators include 2-methyl-2-hydroxypropiophenone and 1-[4-(2-hydroxyethyl)phenyl]-2-methylpropan-1-one. Examples of the above-mentioned aromatic sulfonyl chloride-based photopolymerization initiators include 2-naphthalenesulfonyl chloride. Examples of the above-mentioned photoactive oxime-based photopolymerization initiators include 1-phenyl-1,1-propanedione-2-(o-ethoxycarbonyl)-oxime. Examples of the above-mentioned benzoin-based photopolymerization initiators include benzoin. Examples of the above-mentioned benzyl-based photopolymerization initiators include benzyl. Examples of the above-mentioned benzophenone-based photopolymerization initiators include benzophenone, benzoylbenzoic acid, 3,3'-dimethyl-4-methoxybenzophenone, polyvinylbenzophenone, α-hydroxycyclohexylphenyl ketone. Examples of the above-mentioned ketal-based photopolymerization initiators include benzyldimethylketal. Examples of the above-mentioned thioxanthone-based photopolymerization initiators include thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 2,4-diisopropylthioxanthone, dodecylthioxanthone, etc.

[0105] The amount of the above-mentioned photopolymerization initiator used is not particularly limited, but for example, it is preferably 0.001 to 10.0 parts by mass, and more preferably 0.01 to 5.0 parts by mass, per 100 parts by mass of the total constituent units of the methacrylic copolymer.

[0106] Furthermore, examples of the above-mentioned thermal polymerization initiators include azo polymerization initiators, peroxide polymerization initiators (e.g., dibenzoyl peroxide, tert-butyl permaleate, 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 above-mentioned azo polymerization initiators include 2,2'-azobisisobutyronitrile (AIBN), 2,2'-azobis-2-methylbutyronitrile (AMBN), 2,2'-azobis(2-methylpropionic acid)dimethyl, and 4,4'-azobis-4-cyanovaleric acid.

[0107] The amount of the above-mentioned thermal polymerization initiator used is preferably 0.05 to 0.5 parts by mass, and more preferably 0.1 to 0.3 parts by mass, per 100 parts by mass of the total constituent units of the methacrylic copolymer, in the case of the above-mentioned azo polymerization initiator.

[0108] 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 weight-average molecular weight of 100,000 or more is preferred because it improves adhesive strength and retention properties, and enhances resistance to foaming and peeling. A weight-average molecular weight of 5,000,000 or less is preferred because it makes it easier to achieve high adhesive strength and enhances resistance to foaming and peeling.

[0109] The weight-average molecular weight (Mw) of the above copolymer can be determined by converting it to polystyrene equivalent using the GPC method. For example, it can be measured using a high-speed GPC instrument (product name "HPLC-8120GPC", manufactured by Tosoh Corporation) under the following conditions. • Column: TSKgel SuperHZM-H / HZ4000 / HZ3000 / HZ2000 • Solvent: tetrahydrofuran ·Flow rate: 0.6ml / min

[0110] The glass transition temperature (Tg) of the above copolymer is preferably -70 to 100°C, more preferably -65 to 50°C, and even more preferably -60 to 10°C. A glass transition temperature of -70°C or higher for the above methacrylic copolymer is preferable because it improves cohesive strength and easily enhances foaming resistance and peeling properties. Furthermore, a glass transition temperature of 100°C or lower is preferable because it allows the adhesive composition to have appropriate flexibility, making it easier to obtain good adhesive strength and good step absorption, and thus easier to obtain excellent adhesive reliability.

[0111] The glass transition temperature (Tg) of the above copolymer is the glass transition temperature (theoretical value) expressed by the following FOX equation. In the following equation, Tg is the glass transition temperature of the above copolymer (unit: K), Tg i This is the glass transition temperature (unit: K) when monomer i forms a homopolymer, W i represents the mass fraction of monomer i in the total amount of monomer components (i = 1, 2, .... n). 1 / Tg = W1 / Tg1 + W2 / Tg2 + ... + W n / Tg n

[0112] The following values ​​can be used as the Tg of the monomer homopolymer constituting the above copolymer. • Lauryl methacrylate -65℃ • 2-ethylhexyl methacrylate -10℃ • Lauryl acrylate 0℃ • 2-ethylhexyl acrylate -70°C Isodecyl methacrylate -41℃ 2-hydroxyethyl methacrylate 55℃ Methyl methacrylate 105℃ • Cyclohexyl methacrylate 66℃ Isobornyl methacrylate 173℃ • Dicyclopentanyl methacrylate 175℃ Methacrylic acid 228℃ • N-vinylpyrrolidone 86℃ • 2-phenoxyethyl methacrylate 5℃ Benzyl methacrylate 54℃ • 2-(2-methoxyethoxy)ethyl methacrylate -3℃

[0113] Furthermore, for monomer homopolymers not listed above, the Tg values ​​listed in the "Polymer Handbook" (3rd edition, John Wiley & Sons, Inc., 1989) can be used. In addition, for monomer homopolymers not listed in the above literature, the values ​​obtained by the measurement method described above (tanδ peak top temperature by viscoelasticity test) can be used.

[0114] When polymerizing the above methacrylic copolymer, a chain transfer agent may be used to adjust the molecular weight. Examples of the above chain transfer agent include 2-mercaptoethanol, α-thioglycerol, 2,3-dimercapto-1-propanol, octyl mercaptan, t-nonyl mercaptan, dodecyl mercaptan (lauryl mercaptan), t-dodecyl mercaptan, glycidyl mercaptan, thioglycolic acid, methyl thioglycolate, ethyl thioglycolate, propyl thioglycolate, butyl thioglycolate, t-butyl thioglycolate, 2-ethylhexyl thioglycolate, octyl thioglycolate, isooctyl thioglycolate, decyl thioglycolate, dodecyl thioglycolate, thioglycolic acid ester of ethylene glycol, thioglycolic acid ester of neopentyl glycol, thioglycolic acid ester of pentaerythritol, α-methylstyrene dimer, and the like. In particular, α-thioglycerol and methyl thioglycolate are preferred, with α-thioglycerol being especially preferred, because they suppress whitening of the adhesive sheet due to humidification. The chain transfer agent can be used alone or in combination of two or more types.

[0115] The content of the above-mentioned 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, per 100 parts by mass of the total constituent units of the above-mentioned methacrylic copolymer. By setting the content (amount used) of the chain transfer agent within the above range, a methacrylic copolymer with a weight-average molecular weight controlled to 1000 to 30000 can be easily obtained.

[0116] The adhesive composition of the present invention preferably contains a crosslinking agent. When a crosslinking agent is included in the adhesive composition, the base polymer crosslinks, increasing the gel fraction and improving foaming resistance and peeling properties. Examples of the above crosslinking agents include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, melamine-based crosslinking agents, peroxide-based crosslinking agents, as well as urea-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, carbodiimide-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, and amine-based crosslinking agents. Among these, isocyanate-based crosslinking agents and epoxy-based crosslinking agents are preferred in terms of improving foaming resistance and peeling properties, and isocyanate-based crosslinking agents are more preferred. The crosslinking agents can be used alone or in combination of two or more types.

[0117] Examples of the above-mentioned isocyanate-based crosslinking agents (polyfunctional isocyanate compounds) include lower aliphatic polyisocyanates such as 1,2-ethylene diisocyanate, 1,4-butylene diisocyanate, and 1,6-hexamethylene diisocyanate; alicyclic polyisocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate, isophorone diisocyanate, hydrogenated tolylene diisocyanate, and hydrogenated xylene diisocyanate; and aromatic polyisocyanates such as 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, and xylylene diisocyanate. In addition, commercially available isocyanate-based crosslinking agents include, for example, trimethylolpropane / tolylene diisocyanate adduct (product name "Coronate L", manufactured by Nippon Polyurethane Industry Co., Ltd.), trimethylolpropane / hexamethylene diisocyanate adduct (product name "Coronate HL", manufactured by Nippon Polyurethane Industry Co., Ltd.), and trimethylolpropane / xylylene diisocyanate adduct (product name "Takenate D-110N", manufactured by Mitsui Chemicals, Inc.).

[0118] Examples of the epoxy crosslinking agents (polyfunctional epoxy compounds) mentioned above include N,N,N',N'-tetraglycidyl-m-xylenediamine, diglycidylaniline, 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, polypropylene glycol diglycidyl ether, sorbitol polypropylene Examples of epoxy crosslinking agents include lysidyl ether, glycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitan polyglycidyl ether, trimethylolpropane polyglycidyl ether, diglycidyl adipate ester, diglycidyl o-phthalate ester, triglycidyl-tris(2-hydroxyethyl) isocyanurate, resorcinol diglycidyl ether, bisphenol-S-diglycidyl ether, and epoxy resins having two or more epoxy groups in the molecule. In addition, commercially available epoxy crosslinking agents such as the trade name "Tetrad C" (manufactured by Mitsubishi Gas Chemical Co., Ltd.) can also be used.

[0119] The crosslinking agent content in the above adhesive composition is preferably 0.001 to 10 parts by mass, and more preferably 0.01 to 5 parts by mass, per 100 parts by mass of the methacrylic copolymer. A crosslinking agent content of 0.001 parts by mass or more is preferable because it tends to improve foaming resistance and peeling. On the other hand, a crosslinking agent content of 10 parts by mass or less is preferable because it allows the adhesive layer to have appropriate flexibility and tends to improve adhesive strength.

[0120] The adhesive composition of the present invention may contain, in addition to the base polymer, inorganic fine particles, organic fine particles, or polymer materials other than the base polymer, from the viewpoint of further reducing dielectric constant and dielectric loss in the high frequency range. These can be used individually or in combination of two or more. As the inorganic fine particles and organic fine particles, those exhibiting insulating properties (insulating fillers) are preferred from the viewpoint of reducing dielectric constant and dielectric loss in the high frequency range.

[0121] (Inorganic fine particles) Examples of inorganic fine particles that can be incorporated into the adhesive composition of the present invention include metal oxides such as silica, alumina, zirconia, and titania; metal salts such as aluminum borate and aluminum hydroxide; minerals such as mica; and inorganic fine particles having a hollow structure such as hollow nanosilica. These can be used individually or in combination of two or more.

[0122] The inorganic fine particles described above may be surface-treated in terms of their dispersibility in the base polymer. Known or conventional surface treatment agents can be used without limitation, including, for example, silane coupling agents, titanium coupling agents, organic acids, polyols, and silicones, with silane coupling agents being preferred. Examples of silane coupling agents include vinyltrimethoxysilane, vinyltriethoxysilane, dimethylvinylmethoxysilane, dimethylvinylethoxysilane, methylvinyldimethoxysilane, methylvinyldiethoxysilane, vinyl-tris(2-methoxy)silane, vinyltriacetoxysilane, 2-methacryloxyethyltriethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, triethoxyphenylsilane, trimethoxyphenylsilane, dimethoxydiphenylsilane, methyldiethoxyphenylsilane, and dimethoxymethylphenylsilane.

[0123] The particle size (D50) of the above inorganic fine particles is preferably 1 to 100 nm, more preferably 5 to 80 nm, and even more preferably 10 to 50 nm, from the viewpoint of low dielectric constant, low dielectric loss, and transparency in the high frequency band of the adhesive composition. The above central particle size refers to the particle size (median diameter) at 50% of the integrated value in the particle size distribution measured by laser diffraction and scattering method.

[0124] When the adhesive composition of the present invention contains inorganic fine particles, the amount thereof is preferably 0.01 to 30 parts by mass, more preferably 0.05 to 25 parts by mass, even more preferably 0.10 to 20 parts by mass, even more preferably 0.15 to 10 parts by mass, and particularly preferably 0.2 to 5 parts by mass, per 100 parts by weight of the methacrylic copolymer, from the viewpoint of lowering the dielectric constant, lowering the dielectric loss, and improving transparency in the high-frequency range of the adhesive composition.

[0125] (Organic fine particles) Examples of organic fine particles that can be incorporated into the adhesive composition of the present invention include polymers such as styrene resins, acrylic resins, silicone resins, acrylic-styrene resins, vinyl chloride resins, vinylidene chloride resins, amide resins, urethane resins, phenolic resins, styrene-conjugated diene resins, acrylic-conjugated diene resins, olefin resins, and fluororesins, or fine particles composed of crosslinked polymers, and further fine particles composed of these polymers or polymer crosslinked polymers to have a hollow structure. These can be used individually or in combination of two or more.

[0126] The particle size (D50) of the above organic fine particles is preferably 1 to 100 nm, more preferably 5 to 80 nm, and even more preferably 10 to 50 nm, from the viewpoint of low dielectric constant, low dielectric loss, and transparency in the high frequency band of the adhesive composition. The above central particle size refers to the particle size (median diameter) at 50% of the integrated value in the particle size distribution measured by laser diffraction-scattering method.

[0127] When the adhesive composition of the present invention contains organic fine particles, the amount thereof is usually 0.01 to 30 parts by mass, preferably 0.05 to 25 parts by mass, more preferably 0.1 to 20 parts by mass, even more preferably 0.15 to 10 parts by mass, and particularly preferably 0.2 to 5 parts by mass, per 100 parts by mass of the methacrylic copolymer, from the viewpoint of lowering the dielectric constant, lowering dielectric loss, and transparency of the adhesive composition in the high-frequency band.

[0128] (Polymer materials) The polymer materials that can be incorporated into the adhesive composition of the present invention are preferably those with low dielectric constant and dielectric loss and compatibility with the base polymer. Examples include fluororesins, fluororubber, fluorine-containing functional group (meth)acrylates, polyethylene, polypropylene, polystyrene, polycarbonate, norbornene-based resins or addition copolymer resins with olefins, polyphenylene ethers, bismaleimide / triazine resins, polyetherimide, polyimide, polyetheretherketone (PEEK), liquid crystal polymers, rubber / elastomers, hydrogenated polyolefin resins, terpenes, isoprene, terpene phenol resins, aromatically modified terpene resins, and hydrogenated resins thereof. These can be used individually or in combination of two or more.

[0129] When the adhesive composition of the present invention contains a polymer material, its content is not particularly limited, but from the viewpoint of lowering the dielectric constant, lowering the dielectric loss, and improving transparency in the high-frequency range of the adhesive composition, it is usually 0.01 to 50 parts by mass, preferably 0.05 to 40 parts by mass, and more preferably 0.1 to 30 parts by mass, per 100 parts by mass of the methacrylic copolymer.

[0130] (Rust inhibitor) The adhesive composition of the present invention may further contain a rust inhibitor. The inclusion of a rust inhibitor in the adhesive composition is preferable because it provides excellent corrosion prevention for antenna elements and metal wiring.

[0131] Rust inhibitors are compounds that prevent metal rust and corrosion. 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, urotropin, thiourea, phenyl carbamate, and cyclohexylammonium-N-cyclohexylcarbamate (CHC). Rust inhibitors can be used alone or in combination of two or more.

[0132] Examples of the amine compounds mentioned above include 2-amino-2-methyl-1-propanol, monoethanolamine, monoisopropanolamine, diethylethanolamine, hydroxyl group-containing amine compounds such as ammonia and aqueous ammonia; cyclic amines such as morpholine; cyclic alkylamine compounds such as cyclohexylamine; and linear alkylamines such as 3-methoxypropylamine. Examples of nitrites include dicyclohexylammonium nitride (DICHAN), diisopropylammonium nitride (DIPAN), sodium nitrite, potassium nitrite, and calcium nitrite.

[0133] The rust inhibitor is preferably contained in an amount of 0.02 to 15 parts by mass per 100 parts by mass of the methacrylic copolymer. A content of 0.02 parts by mass or more is preferable because it makes it easier to obtain good corrosion prevention performance. On the other hand, a content of 15 parts by mass or less is preferable because it makes it easier to ensure transparency and to ensure adhesive reliability such as resistance to foaming and peeling.

[0134] In particular, the above-mentioned rust inhibitor is preferably a benzotriazole compound because it can provide a good balance of high levels of adhesion reliability, transparency, and corrosion prevention properties to the above-mentioned methacrylic copolymer, and can also provide excellent appearance.

[0135] The above-mentioned benzotriazole compound is not particularly limited as long as it has a benzotriazole skeleton, but it is preferable from the viewpoint of obtaining a better corrosion prevention effect if it has the structure represented by the following formula (1). [ka] (However, in the above formula (1), R 1 and R 2 They are the same or different, R 1 is a substituent on a benzene ring, and is a C1-C6 alkyl group, a C1-C6 alkoxy group, a C6-C14 aryl group, an amino group, a mono or diC 1-10 Alkylamino group, amino-C 1-6 Alkyl alkyl groups, mono-C1, or di-C1 1-10 Alkylamino-C 1-6 The substituents include alkyl groups, mercapto groups, alkoxycarbonyl groups having 1 to 6 carbon atoms, or alkoxy groups having 1 to 6 carbon atoms, where n is an integer from 0 to 4, and if n is 2 or more, there are n R 1 They may be the same or different, R 2 This includes hydrogen atoms, C1-C12 alkyl groups, C1-C12 alkoxy groups, C6-C14 aryl groups, amino groups, mono- or di-C12 groups. 1-10 Alkylamino group, amino-C 1-6 Alkyl alkyl groups, mono-C1, or di-C1 1-10 Alkylamino-C 1-6 (This indicates substituents such as alkyl groups, mercapto groups, alkoxycarbonyl groups having 1 to 12 carbon atoms, or alkoxy groups having 1 to 12 carbon atoms.)

[0136] From the perspective of obtaining a better corrosion prevention effect, R 1 Preferably, the C1-C3 alkyl group or alkoxycarbonyl group is preferred, and a methyl group is more preferred. Also, n is preferably 0 or 1. From a similar perspective, R 2 Examples include hydrogen atoms, mono- or di-C atoms. 1-10 Alkylamino-C 1-6 Alkyl alkyl groups are preferred, as are hydrogen atoms and diC. 1-8 Alkylamino C1-4 Alkyl alkyl groups are more preferable.

[0137] The content of the benzotriazole compound is preferably 0.02 to 3 parts by mass, more preferably 0.02 to 2.5 parts by mass, and even more preferably 0.02 to 2 parts by mass, per 100 parts by mass of the methacrylic copolymer. When the amount of the benzotriazole compound is within a certain range, adhesive reliability such as resistance to foaming and peeling can be reliably ensured, and the increase in haze of the adhesive sheet can also be reliably prevented.

[0138] (Silane coupling agent) The adhesive composition of the present invention may further contain a silane coupling agent. The inclusion of a silane coupling agent in the adhesive composition is preferable because it facilitates obtaining excellent adhesion to glass (particularly excellent adhesive reliability to glass at high temperatures and high humidity).

[0139] Examples of the silane coupling agents mentioned above include γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-aminopropyltrimethoxysilane, and N-phenyl-aminopropyltrimethoxysilane. Among these, γ-glycidoxypropyltrimethoxysilane is preferred. Examples of the silane coupling agents include commercially available products such as the trade name "KBM-403" (manufactured by Shin-Etsu Chemical Co., Ltd.). The silane coupling agents can be used alone or in combination of two or more.

[0140] The content of the silane coupling agent is preferably 0.01 to 1 part by mass, and more preferably 0.03 to 0.5 parts by mass, per 100 parts by mass of the methacrylic copolymer, from the viewpoint of improving adhesion reliability to glass.

[0141] (Other additives) The adhesive composition of the present invention may optionally contain known additives such as antioxidants, crosslinking promoters, crosslinking retarders, tackifying resins (rosin derivatives, polyterpene resins, oil-soluble phenols, etc.), anti-aging agents, colorants (pigments, dyes, etc.), ultraviolet absorbers, chain transfer agents, plasticizers, softeners, surfactants, and antistatic agents, to the extent that they do not impair the properties of the present invention. These can be used individually or in combination of two or more.

[0142] When the adhesive composition of the present invention contains a tackifier, the amount of the tackifier is preferably 0.01 parts by mass or more, and more preferably 0.05 parts by mass or more, per 100 parts by mass of the methacrylic copolymer, in order to impart appropriate tackiness. Furthermore, in order to avoid excessively high peel strength, the amount is preferably 50 parts by mass or less, and more preferably 40 parts by mass or less.

[0143] [Adhesive layer] Because the adhesive layer of the present invention is formed from the adhesive composition of the present invention, it exhibits low dielectric constant and low dielectric loss in the high-frequency band (28-60 GHz) of millimeter waves. In other words, the adhesive layer of the present invention can suppress millimeter wave radiation loss.

[0144] The adhesive layer of the present invention is preferable in that it has a low dielectric constant at 28 GHz and can suppress millimeter-wave radiation loss. 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, even more preferably 2.10 to 4.00, even more preferably 2.15 to 3.50, particularly preferably 2.20 to 3.40, 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.

[0145] The dielectric constant at 28 GHz in the adhesive layer of the present invention can be adjusted by adjusting the type of base polymer, monomer composition, and type and content of additives that constitute the adhesive composition for forming the adhesive layer.

[0146] The adhesive layer of the present invention is preferable in that its dielectric loss at 28 GHz is low and controlled, and it can suppress millimeter-wave radiation loss. 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, even more preferably 0.040 or less, even more 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 is not particularly limited, but is preferably 0.0001 or more, and may be 0.0005 or more or 0.0010 or more.

[0147] The dielectric loss at 28 GHz in the adhesive layer of the present invention can be adjusted by adjusting the type of base polymer, monomer composition, and type and content of additives that constitute the adhesive composition for forming the adhesive layer.

[0148] The adhesive layer of the present invention is preferable in that it has a low dielectric constant at 60 GHz and can suppress millimeter-wave radiation loss. 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, even more preferably 2.2 to 4.0, even more preferably 2.2 to 3.5, particularly preferably 2.2 to 3.4, 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.

[0149] The dielectric constant at 60 GHz in the adhesive layer of the present invention can be adjusted by adjusting the type of base polymer, monomer composition, and type and content of additives that constitute the adhesive composition for forming the adhesive layer.

[0150] The adhesive layer of the present invention is preferably characterized by low dielectric loss at 60 GHz, which is preferable in that it can suppress millimeter-wave radiation loss. 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, even more preferably 0.040 or less, even more 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 be 0.0005 or more or 0.0010 or more.

[0151] The dielectric loss at 60 GHz in the adhesive layer of the present invention can be adjusted by adjusting the type of base polymer, monomer composition, and type and content of additives that constitute the adhesive composition for forming the adhesive layer.

[0152] The adhesive layer of the present invention is transparent or has transparency. Therefore, it offers excellent visibility and appearance through the adhesive composition. Thus, the adhesive layer of the present invention is suitably used for optical applications.

[0153] 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, even more preferably 1.0% or less, even more preferably 0.9% or less, and particularly preferably 0.8% or less. When the haze is, for example, 1.2% or less, excellent transparency and excellent appearance are easily obtained. The above haze can be measured, for example, by setting the adhesive layer thickness to 25 μm, leaving it to stand at room temperature (23°C, 50% RH) for at least 24 hours, and then laminating it onto a glass slide (for example, total light transmittance 91.8%, haze 0.4%) as a sample, and measuring it using a haze meter (product name "HM-150", manufactured by Murakami Color Technology Laboratory Co., Ltd.).

[0154] The total light transmittance of the adhesive layer of the present invention in the visible light wavelength range (according to JIS K7361-1) is not particularly limited, but is preferably 85% or more, more preferably 88% or more, even more preferably 89% or more, even more preferably 90% or more, particularly preferably 91% or more, and most preferably 92% or more. When the total light transmittance is 85% or more, excellent transparency and excellent appearance are easily obtained. The above total light transmittance can be measured, for example, by setting the adhesive layer thickness to 25 μm, leaving it at normal conditions (23°C, 50% RH) for at least 24 hours, peeling off the separator if one is present, and attaching it to a glass slide (for example, total light transmittance 91.8%, haze 0.4%) as a sample, and measuring it using a haze meter (product name "HM-150", manufactured by Murakami Color Technology Laboratory Co., Ltd.).

[0155] 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, and type and content of additives that constitute the adhesive composition for forming the adhesive layer.

[0156] The gel fraction (proportion of insoluble components) of the adhesive layer of the present invention is preferably 30-95%, more preferably 35-90%, even more preferably 40-85%, even more preferably 45-80%, and particularly preferably 50-75%. When the gel fraction is 30% or more, the cohesive force of the adhesive layer is improved, making it less likely to cause dents during handling, and foaming and peeling at the interface with the adherend in high-temperature environments are suppressed, making it easier to obtain excellent foaming and peeling resistance, which is preferable. When the gel fraction is 95% or less, a moderate flexibility is obtained, further improving adhesion and step-following ability, and it becomes less likely to absorb foreign matter, which is preferable.

[0157] The gel fraction (proportion of solvent-insoluble components) can be calculated, for example, as follows.

[0158] Approximately 0.1 g is taken from the adhesive layer, wrapped in a porous tetrafluoroethylene sheet with an average pore size of 0.2 μm (product name "NTF1122", manufactured by Nitto Denko Corporation), tied with kite string, and the mass at this time is measured and defined as the mass before immersion (Z). This mass before immersion is the total mass of the adhesive layer, the tetrafluoroethylene sheet, and the kite string. The total mass of the tetrafluoroethylene sheet and the kite string is also measured and defined as the package mass (Y). Next, the adhesive layer wrapped in the tetrafluoroethylene sheet and tied with kite string (referred to as the "sample") is placed in a 50 ml container filled with ethyl acetate or toluene and left to stand at 23°C for 7 days. After that, the sample (after ethyl acetate or toluene treatment) is removed from the container, transferred to an aluminum cup, dried in a drying oven at 130°C for 2 hours to remove the ethyl acetate or toluene, and then the mass is measured and defined as the mass after immersion (X). Then, the gel fraction is calculated using the following formula. Gel fraction (%) = {(XY) / (ZY)} × 100

[0159] 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, and the type and amount of other additives used.

[0160] The storage modulus of the adhesive layer of the present invention at 25°C is preferably 0.01 MPa or higher, more preferably 0.02 MPa or higher, even more preferably 0.03 MPa or higher, even more preferably 0.04 MPa or higher, particularly preferably 0.05 MPa or higher, and most preferably 0.10 MPa or higher. A storage modulus of 0.01 MPa or higher is preferable because it reduces the likelihood of dents occurring during handling and makes it easier to obtain good adhesive reliability. Furthermore, from the viewpoint of step-following ability and foreign matter absorption, the storage modulus of the adhesive layer at 25°C is preferably 5 MPa or lower, more preferably 4.5 MPa or lower, even more preferably 4.0 MPa or lower, even more preferably 3.5 MPa or lower, particularly preferably 3.0 MPa or lower, and most preferably 2.5 MPa or lower or 2.0 MPa or lower. The storage modulus of the adhesive layer is measured when dynamic viscoelasticity is performed at a frequency of 1 Hz. The above storage modulus is the real part of the shear modulus expressed as a complex number, and can be converted from the tensile modulus, etc., by considering the Poisson's ratio of the sample.

[0161] The storage modulus of the adhesive layer of the present invention can be controlled by the monomer composition, weight-average molecular weight, the amount of crosslinking agent used (amount added), and the type and amount of other additives used.

[0162] The 300% tensile residual stress of the adhesive layer of the present invention is not particularly limited, but is between 2 and 24 N / cm². 2 Preferably, the density is 2.5 to 20 N / cm². 2 More preferably 3 to 16 N / cm² 2 The above 300% tensile residual stress is 2 N / cm. 2 With the above specifications, good resistance to foam peeling is easily obtained, and the load capacity is 24 N / cm². 2 The following conditions are preferable, as they lead to good stress relaxation and easier acquisition of good step-following ability.

[0163] When the 300% tensile residual stress of the adhesive layer of the present invention is within the above range, it becomes easier to obtain excellent stress relaxation properties and exhibit excellent step-following properties, and can follow large steps (approximately 45 μm, for example, with a height of 20 to 50 μm) well.

[0164] This involves stretching the adhesive layer in the length direction to 300% elongation (strain) under conditions of 23°C and 50% RH, maintaining that elongation, and determining the tensile load applied to the adhesive layer 300 seconds after the end of stretching. The value obtained by dividing this tensile load by the initial cross-sectional area of ​​the adhesive layer (cross-sectional area before stretching) is calculated (N / cm²). 2 ). Furthermore, the initial elongation of the adhesive layer is 100%.

[0165] 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 (amount added), and the type and amount of other additives used.

[0166] The adhesive layer of the present invention has a low and controlled saturation moisture absorption rate, which can suppress millimeter-wave radiation loss. The saturation 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, even more preferably 2.6% or less, even more preferably 2.5% or less, particularly preferably 2.4% or less, 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 saturation moisture absorption rate at 25°C and 90%RH can suppress millimeter-wave radiation loss near room temperature. The lower limit of the saturated moisture absorption rate is not particularly limited, but may be, for example, 0.3% or more, 0.4% or more, or 0.5% or more.

[0167] The saturation 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, even more preferably 2.4% or less, even more preferably 2.3% or less, particularly preferably 2.2% or less, 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 saturation moisture absorption rate is not particularly limited, for example, it may be 0.4% or more, 0.5% or more, or 0.6% or more. A low saturation moisture absorption rate at 65°C and 90%RH can suppress millimeter-wave radiation loss even when exposed to high-temperature environments.

[0168] 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, even more preferably 3.5% or less, even more preferably 3.0% or less, particularly preferably 2.8% or less, 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 saturated moisture absorption rate is not particularly limited, for example, it may be 0.4% or more, 0.5% or more, or 0.6% or more. A low saturated moisture absorption rate at 85°C and 85%RH can suppress millimeter-wave radiation loss even when exposed to high-temperature environments.

[0169] The saturated moisture absorption rate under each temperature and humidity environment can be determined, for example, from the weight of the sample in a dry state (w1) and the weight of the sample when it stops changing weight after being left in an atmosphere of 65°C and 90%RH (when the moisture absorption rate is saturated) (w2) using the following formula. It can also be determined under the conditions of 25°C and 90%RH, and 85°C and 85%RH. Note that the values ​​of w1 and w2 are assumed to have been measured at the same temperature and humidity. Saturated moisture absorption rate (%)={(w2-w1) / w1}×100

[0170] The adhesive layer of the present invention suppresses millimeter-wave radiation loss because the change in dielectric loss due to moisture absorption is controlled to a low extent. The change in dielectric loss due to moisture absorption at a frequency of 28 GHz of the adhesive layer of the present invention 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 saturation moisture absorption rate is not particularly limited, but may be, for example, 0.0001 or more, 0.0002 or more, or 0.0003 or more.

[0171] The change in dielectric loss due to moisture absorption at a frequency of 60 GHz in the adhesive layer of the present invention 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 saturation moisture absorption rate is not particularly limited, but may be, for example, 0.0001 or more, 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.

[0172] The change in dielectric loss at the above frequencies of 28 GHz and 60 GHz was measured by holding the facility in an atmosphere of 65°C and 90% RH for more than 5 days, then returning it to conditions of 23 ± 1°C and 52 ± 1% RH (elapsed time = 0 minutes), and measuring the dielectric loss at each frequency every 10 minutes from 4 minutes to 180 minutes, with the maximum value (D) being measured among them. fmax ) and the minimum value (D fmin ) can be calculated using the following formula. Change in dielectric loss = D fmax -D fmin

[0173] The adhesive layer of the present invention has a low and controlled water vapor permeability, which can suppress millimeter-wave radiation loss. The water vapor permeability of the adhesive layer of the present invention at 40°C and 92% RH is 430 g / m². 2 Preferably less than / day, and more preferably 300 g / m² 2 Less than / day, and even more preferably 250g / m² 2 Less than / day, and even more preferably 200g / m² 2Less than or equal to / day, particularly preferably 150g / m² 2 Less than or equal to / day, most preferably 100g / m² 2 / day or less, 50g / m 2 / day or less or 30g / m 2 It is less than / day. Low water vapor permeability at 40°C and 92%RH improves the water resistance of the adhesive layer and suppresses millimeter-wave radiation loss within the adhesive layer. The lower limit of water vapor permeability is not particularly limited, but for example, 10 g / m 2 It is acceptable to have a minimum of / day and a 20g / m² 2 / day or more, or 25g / m² 2 It can be more than / day.

[0174] The above water vapor transmission rate (WVTR) is a value measured based on the cup method. The weight of calcium chloride in a dry state (w1) isolated from the outside by an adhesive layer, and the weight (w2) of the sample after a predetermined time has elapsed when left in an atmosphere of 40°C and 92% RH (when the moisture absorption rate is saturated) are measured, and the weight change is measured per unit time (1 day) and per unit area (1 m²). 2 It can be calculated by converting to ).

[0175] The dielectric constant or dielectric loss, saturation 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 and content of additives, etc.

[0176] The thickness of the adhesive layer of the present invention is not particularly limited, but is preferably 10 to 500 μm, more preferably 11 to 400 μm, even more preferably 12 to 350 μm, and even more preferably 12 to 300 μm. A thickness above a certain level tends to improve step-following ability and adhesive reliability. Conversely, a thickness below a certain level tends to reduce the absorption of foreign matter during handling and improve manufacturability.

[0177] The method for manufacturing the adhesive layer described above is not particularly limited, but for example, it may involve applying the adhesive composition onto a substrate or release liner, and then drying, curing, or drying and curing as necessary. Curing can be performed by irradiation with active energy rays, heating and drying, etc.

[0178] Furthermore, known coating methods may be used for applying (coating) the above adhesive composition. For example, coaters such as gravure roll coaters, reverse roll coaters, kiss roll coaters, dip roll coaters, bar coaters, knife coaters, spray coaters, comma coaters, and direct coaters may be used.

[0179] [Adhesive sheet] The adhesive sheet of the present invention only needs to have the adhesive layer of the present invention, and is not particularly limited in any other respect.

[0180] The adhesive sheet of the present invention may be a double-sided adhesive sheet in which both sides are adhesive layer surfaces, or a single-sided adhesive sheet in which only one side is an adhesive layer surface. Of these, a double-sided adhesive sheet is preferable in terms of bonding two members together. In this specification, the term "adhesive sheet" also includes tape-like materials, i.e., "adhesive tape." In this specification, the surface of the adhesive layer may be referred to as the "adhesive surface."

[0181] The adhesive sheet of the present invention may have a separator (release liner) on the adhesive surface until it is in use.

[0182] The adhesive sheet of the present invention may be a so-called "substrate-less type" adhesive sheet (hereinafter sometimes referred to as "substrate-less adhesive sheet") that does not have a base material (substrate layer), or it may be an adhesive sheet of the type that has a base material (hereinafter sometimes referred to as "adhesive sheet with base material"). Examples of the substrate-less adhesive sheet include a double-sided adhesive sheet consisting only of the adhesive layer, and a double-sided adhesive sheet consisting of the adhesive layer and an adhesive layer other than the adhesive layer (sometimes referred to as "other adhesive layer"). On the other hand, examples of an adhesive sheet with a base material include an adhesive sheet having the adhesive layer on at least one side of the base material. Among these, the substrate-less adhesive sheet (substrate-less double-sided adhesive sheet) is preferred, and more preferably, the substrate-less double-sided adhesive sheet consisting only of the adhesive layer. An adhesive sheet having the adhesive layer on both sides of the base material (double-sided adhesive sheet with base material) is also preferred. In the double-sided adhesive sheet with base material, both adhesive layers may be the adhesive layer of the present invention, or one may be the adhesive layer of the present invention and the other may be another adhesive layer. Note that the above-mentioned "substrate (substrate layer)" does not include the separator that is peeled off when the adhesive sheet is used (applied).

[0183] The adhesive sheet of the present invention is preferably a substrate-less adhesive sheet in order to avoid millimeter-wave radiation loss due to the substrate. However, if the substrate is made of a material with low dielectric constant and low dielectric loss, it may be an adhesive sheet with a substrate. Since it is desirable that the substrate can be used regardless of the polarization state of the millimeter waves, an unstretched substrate, and especially an isotropic substrate, is preferred.

[0184] The 180° peel-off adhesive strength of the adhesive sheet of the present invention against a glass plate at a tensile speed of 300 mm / min (particularly the 180° peel-off adhesive strength of the adhesive surface provided by the adhesive layer of the present invention against the glass plate) is not particularly limited, but a higher adhesive strength ensures sufficient adhesion to the antenna element, so it is preferably 3N / 20mm or more, more preferably 3.5N / 20mm or more, even more preferably 4N / 20mm or more, even more preferably 5N / 20mm, particularly preferably 6N / 20mm or more, most preferably 7N / 20mm or more, 8N / 20mm or more, 9N / 20mm or more, or 10N / 20mm or more. If the above peel-off adhesive strength is above a certain value, the adhesion to glass and the ability to suppress lifting at steps are further improved. The upper limit of the 180° peel adhesive strength of the adhesive sheet of the present invention to a glass plate at a tensile speed of 300 mm / min is not particularly limited, but for example, it is preferably 30 N / 20 mm or less, more preferably 25 N / 20 mm or less, even more preferably 22 N / 20 mm or less, even more preferably 20 N / 20 mm, particularly preferably 19 N / 20 mm or less, 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 adhesive strength to a glass plate at a tensile speed of 300 mm / min is determined by the 180° peel adhesive strength measurement method described below.

[0185] Examples of the glass plates mentioned above include the product name "Soda-Lime Glass #0050" (manufactured by Matsunami Glass Industry Co., Ltd.). Other examples include alkali-free glass and chemically strengthened glass.

[0186] The 180° peel adhesion strength to a glass plate at a tensile speed of 300 mm / min is determined by the following measurement method: The adhesive side of the adhesive sheet is attached to the substrate, and pressure is applied using a 2 kg roller for one back-and-forth motion. After aging for 30 minutes in an atmosphere of 23°C and 50% RH, the adhesive sheet is peeled from the substrate in accordance with JIS Z0237 at an atmosphere of 23°C and 50% RH, a tensile speed of 300 mm / min, and a peel angle of 180°, and the 180° peel adhesion strength (N / 20 mm) is measured.

[0187] The 180° peel-off adhesive strength 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 (amount added), and the type and amount of other additives used.

[0188] The thickness (total thickness) of the adhesive sheet of the present invention is not particularly limited, but is preferably 10 to 500 μm, more preferably 11 to 400 μm, even more preferably 12 to 350 μm, and even more preferably 12 to 300 μm. A thickness above a certain level makes it less likely for peeling to occur at stepped areas. A thickness below a certain level makes it easier to maintain an excellent appearance during manufacturing. Note that the thickness of the adhesive sheet of the present invention does not include the thickness of the separator.

[0189] 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, even more preferably 1.0% or less, even more preferably 0.9% or less, and particularly preferably 0.8% or less. When the haze is 1.2% or less, excellent transparency and excellent appearance are easily obtained. The above haze can be measured, for example, by setting the adhesive layer thickness to 25 μm, leaving it to stand at room temperature (23°C, 50% RH) for at least 24 hours, and then laminating it onto a glass slide (for example, total light transmittance 91.8%, haze 0.4%) as a sample, and measuring it using a haze meter (product name "HM-150", manufactured by Murakami Color Technology Laboratory Co., Ltd.).

[0190] The total light transmittance of the adhesive sheet of the present invention in the visible light wavelength range (according to JIS K7361-1) is preferably 85% or higher, more preferably 88% or higher, even more preferably 89% or higher, even more preferably 90% or higher, particularly preferably 91% or higher, and most preferably 92% or higher. When the total light transmittance is 85% or higher, excellent transparency and excellent appearance are easily obtained. The above total light transmittance can be measured, for example, by setting the adhesive layer thickness to 25 μm, leaving it at normal conditions (23°C, 50% RH) for at least 24 hours, peeling off the separator if present, and attaching it to a glass slide (for example, total light transmittance 91.8%, haze 0.4%) as a sample, and measuring it using a haze meter (product name "HM-150", manufactured by Murakami Color Technology Laboratory Co., Ltd.).

[0191] The haze and total light transmittance of the adhesive layer of the present invention can be adjusted by adjusting the monomer composition, the type and content of additives, etc.

[0192] The adhesive sheet of the present invention is not particularly limited, but is preferably manufactured according to known or conventional manufacturing methods. For example, if the adhesive sheet of the present invention is a substrate-less adhesive sheet, it can be obtained by forming the adhesive layer on a separator by the method described above. If 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 transfer method), or by first forming the adhesive layer on a separator and then transferring (bonding) it to the substrate to provide the adhesive layer on the substrate (transfer method).

[0193] The adhesive sheet of the present invention may have other layers in addition to the adhesive layer described above. 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, undercoat layers, etc. The adhesive sheet of the present invention may have two or more other layers.

[0194] When the adhesive sheet of the present invention is an adhesive sheet with a substrate, examples of the substrate include various optical films such as plastic films, anti-reflective (AR) films, polarizing plates, and phase difference plates. Examples of materials such as the plastic film include polyester resins such as polyethylene terephthalate (PET), (meth)acrylic resins such as polymethyl methacrylate (PMMA), polycarbonate, triacetylcellulose (TAC), polysulfone, polyarylate, polyimide, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, ethylene-propylene copolymer, cyclic olefin polymers such as the trade name "Arton (cyclic olefin polymer, manufactured by JSR Corporation)" and the trade name "Zeonor (cyclic olefin polymer, manufactured by Nippon Zeon Co., Ltd.)", and fluorine polymers. These plastic materials can be used individually or in combination of two or more. Furthermore, the "substrate" mentioned above refers to the portion that is attached to the adherend together with the adhesive layer when the adhesive sheet is attached to the adherend. The separator (release liner) that is peeled off when the adhesive sheet is used (applied) is not included in the "base material".

[0195] The above substrate is preferably transparent. The total light transmittance of the above substrate in the visible light wavelength region (according to JIS K7361-1) is preferably 85% or more, more preferably 88% or more, even more preferably 89% or more, even more preferably 90% or more, particularly preferably 91% or more, and most preferably 92% or more. The haze of the above substrate (according to JIS K7136) is preferably 1.0% or less, and more preferably 0.8% or less. Examples of such transparent substrates include PET film and non-oriented films such as those traded as "Arton" and "Zeonor". Non-oriented films are particularly preferred because their properties do not depend on the direction of the millimeter-wave electric field.

[0196] The thickness of the above-mentioned substrate is not particularly limited, but is preferably, for example, 12 to 500 μm. The above-mentioned substrate may be in the form of a single layer or multiple layers. Furthermore, the surface of the above-mentioned substrate may be appropriately subjected to known and conventional surface treatments, such as physical treatments such as corona discharge treatment, plasma treatment, or electron beam treatment, or chemical treatments such as undercoating.

[0197] The adhesive sheet of the present invention may have a separator (release liner) on the adhesive surface until use. If the adhesive sheet of the present invention is a double-sided adhesive sheet, each adhesive surface may be protected by two separators, or it may be protected by a single separator with release surfaces on both sides, wound in a roll shape. The separator is used as a protective material for the adhesive layer and is removed when the sheet is applied to the substrate. Furthermore, if the adhesive sheet of the present invention is a substrate-less adhesive sheet, the separator also serves as a support for the adhesive layer. Note that the separator is not necessarily required.

[0198] The separator described above is not particularly limited and can be any conventional release paper. Examples include a substrate having a release treatment layer, a low-adhesion substrate made of a fluoropolymer, or a low-adhesion substrate made of a nonpolar polymer. Examples of substrates having a release treatment layer include plastic films and paper surface-treated with release agents such as silicone-based, long-chain alkyl-based, fluorine-based, or molybdenum sulfide. Examples of fluorine-based polymers in the low-adhesion substrate made of a fluoropolymer include polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, and chlorofluoroethylene-vinylidene fluoride copolymer. Examples of nonpolar polymers include olefin resins (e.g., polyethylene, polypropylene, etc.), and polyester substrates (polyethylene terephthalate substrates, polyethylene naphthalate substrates, polybutylene terephthalate substrates, etc.) can also be used. The separator can be formed by known or conventional methods. The thickness of the separator is also not particularly limited.

[0199] The adhesive sheet of the present invention, having the adhesive layer of the present invention, exhibits excellent adhesion and resistance to foaming and peeling, as well as excellent stress relaxation and step-following properties. Therefore, it offers superior adhesive reliability, particularly at high temperatures. Furthermore, it boasts excellent appearance.

[0200] Therefore, the adhesive sheet of the present invention is useful for bonding materials that are prone to foaming at the interface at high temperatures. For example, polymethyl methacrylate (PMMA) may contain unreacted monomers, making it prone to foaming due to foreign matter at high temperatures. Also, polycarbonate (PC) is prone to outgassing of water and carbon dioxide at high temperatures. Since the adhesive sheet of the present invention has excellent foaming resistance and peeling resistance, it can be useful for bonding plastic substrates containing such resins.

[0201] Furthermore, the adhesive sheet of the present invention can be useful not only for adherends with a low coefficient of linear expansion, but also for adherends with a high coefficient of linear expansion. Examples of adherends with a low coefficient of linear expansion include glass plates (coefficient of linear expansion 0.3 × 10⁻⁶). -5 ~0.8 × 10 -5 ( / °C), polyethylene terephthalate substrate (PET film, coefficient of linear expansion 1.5 × 10⁻⁶) -5 ~2×10 -5 Examples include the coefficient of thermal expansion ( / °C). Furthermore, examples of adherends with a large coefficient of thermal expansion include resin substrates with a large coefficient of thermal expansion, and more specifically, polycarbonate resin substrates (PC, coefficient of thermal expansion 7 × 10). -5 ~8×10 -5 ( / °C), polymethyl methacrylate resin substrate (PMMA, coefficient of linear expansion 7 × 10) -5 ~8×10 -5 ( / °C), cycloolefin polymer substrate (COP, coefficient of linear expansion 6 × 10⁻⁶) -5 ~7×10 -5 Examples include products such as "Zeonoa" (manufactured by Nippon Zeon Co., Ltd.) and "Arton" (manufactured by JSR Corporation).

[0202] The adhesive sheet of the present invention is useful for bonding a substrate with a low coefficient of thermal expansion to a substrate with a high coefficient of thermal expansion. Specifically, the adhesive sheet of the present invention is preferably used for bonding a glass substrate (e.g., a glass plate, chemically strengthened glass, a glass lens, etc.) to a resin substrate with a high coefficient of thermal expansion.

[0203] Thus, the adhesive sheet of the present invention is useful for bonding various materials together, and is particularly useful for bonding glass substrates to plastic substrates. The plastic substrate may be an optical film, such as a plastic film having an ITO (indium tin oxide) layer on its surface.

[0204] Furthermore, the adhesive sheet of the present invention can be useful not only for adherends with smooth surfaces but also for adherends with steps on their surfaces. In particular, the adhesive sheet of the present invention can be useful for bonding a glass adherend to a resin substrate with a high coefficient of thermal expansion, even if at least one of the glass adherend or the resin substrate with a high coefficient of thermal expansion has steps on its surface.

[0205] The adhesive sheet of the present invention is preferably used in the manufacture of portable electronic devices. Examples of such portable electronic devices include mobile phones, PHS phones, smartphones, tablets (tablet computers), mobile computers (mobile PCs), personal digital assistants (PDAs), electronic organizers, portable broadcast receivers such as portable televisions and portable radios, portable game consoles, portable audio players, portable DVD players, cameras such as digital cameras, and camcorder-type video cameras.

[0206] The adhesive sheet of the present invention is preferably used, for example, for bonding components and modules that constitute portable electronic devices to each other, or for fixing components and modules that constitute portable electronic devices to the housing. More specifically, examples include bonding cover glass or lenses (especially glass lenses) to touch panels, touch sensors, and antenna modules; fixing cover glass or lenses (especially glass lenses) to the housing; fixing display panels to the housing; fixing antenna modules to the housing; fixing input devices such as sheet keyboards and touch panels to the housing; bonding protective panels for information display sections to the housing; bonding housings to each other; bonding housings to decorative sheets; and fixing and bonding various components and modules that constitute portable electronic devices. In this specification, a display panel refers to a structure that is at least composed of a lens (especially a glass lens) and a touch panel. Furthermore, the term "lens" in this specification includes both transparent materials that exhibit light refraction and transparent materials that do not exhibit light refraction. In other words, the term "lens" in this specification also includes simple window panels that do not exhibit light refraction.

[0207] Furthermore, the adhesive sheet of the present invention is preferably used in optical applications. That is, the adhesive sheet of the present invention is preferably an optical adhesive sheet used in optical applications. More specifically, it is preferably used, for example, in applications for bonding optical components (for bonding optical components) or in the manufacture of products using the optical components (optical products).

[0208] An example of an optical component is an optical component having at least the above-mentioned adhesive sheet and substrate, wherein the substrate has metal electrodes and wiring (e.g., copper, silver, ITO wiring, etc.) on at least one side, and the adhesive layer of the present invention is attached to the side of the substrate having the metal electrodes and wiring. The above-mentioned adhesive sheet may have a separator on its adhesive surface until use, but the above-mentioned adhesive sheet in the optical component of the present invention does not have a separator because it is an adhesive sheet used during use.

[0209] Furthermore, it is preferable that the optical component has the adhesive layer on the side of the substrate opposite to the side having the metal electrodes and wiring, and it is even more preferable that the adhesive layer is attached to the surface of the substrate opposite to the side having the metal electrodes and wiring.

[0210] Examples of materials constituting the above-mentioned metal electrodes and wiring include metals such as titanium, silicon, niobium, indium, zinc, tin, gold, silver, copper, aluminum, cobalt, chromium, nickel, lead, iron, palladium, platinum, tungsten, zirconium, tantalum, and hafnium, as well as metal oxides such as ITO (indium and tin oxide), zinc oxide, and tin oxide. Furthermore, materials containing two or more of these metals or metal oxides, and alloys with these metals as the main component are also included. Among these, gold, silver, copper, and ITO are preferred in terms of conductivity, silver, copper, and ITO are more preferred in terms of conductivity and cost, and ITO is even more preferred in terms of transparency. In other words, the above-mentioned metal electrodes and wiring are preferably silver, copper, or ITO wiring, and ITO wiring is particularly preferred. The same applies to the materials constituting the millimeter-wave antenna element described later. The above-mentioned metal electrodes and wiring may be blackened by forming a film of nitride, oxide, sulfide, etc. of the metal in order to conceal the electrodes and / or wiring in order to prevent a decrease in visibility due to metal reflection.

[0211] An optical component refers to a component that possesses optical properties (for example, polarization, refractiveness, scattering, reflectivity, transmission, absorption, diffraction, optical rotation, visibility, electromagnetic wave transmission, etc.). Examples of substrates constituting the above 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, phase difference plates, optical compensation films, brightness enhancement films, light guide plates, reflective films, anti-reflective films, antenna substrates, hard coat films (films in which at least one side of a plastic film such as a PET film is hard-coated), transparent conductive films (for example, plastic films having an ITO layer on the surface (preferably ITO films such as PET-ITO, polycarbonate, or cycloolefin polymer)), decorative films, ornamental films, surface protection plates, prisms, lenses, color filters, transparent substrates (glass sensors, glass display panels (LCDs, etc.), glass substrates such as glass plates with transparent electrodes, etc.), and substrates on which these are laminated (these are sometimes collectively referred to as "functional films"). Furthermore, these films may have metal nanowire layers or conductive polymer layers. In addition, metal fine wires may be mesh-printed on these films. Furthermore, these films may have antenna elements. Furthermore, the terms "plate" and "film" above include forms such as plate-like, film-like, and sheet-like shapes, respectively. For example, "polarizing film" includes "polarizing plates" and "polarizing sheets," etc. Also, "film" includes film sensors, etc.

[0212] The above-mentioned metal wires may be blackened by forming a coating of nitrides, oxides, sulfides, etc., of the metal, in order to conceal them and prevent a decrease in visibility due to the reflection of the metal.

[0213] Examples of the above-mentioned display devices include liquid crystal displays, organic electroluminescent (EL) displays, PDPs (plasma display panels), and electronic paper. Examples of the above-mentioned input devices include touch panels. Examples of antenna modules include millimeter-wave antennas, as described later.

[0214] Examples of substrates constituting the above-mentioned optical components include substrates made of glass, (meth)acrylic resin, polycarbonate, polyethylene terephthalate, cycloolefin polymer, metal thin films, etc. (for example, sheet-shaped, film-shaped, or plate-shaped substrates). In addition, the term "optical component" in this invention also includes components that serve a decorative or protective role while maintaining the visibility of display devices and input devices (such as decorative films, surface protection films, etc.).

[0215] If the adhesive sheet of the present invention is an adhesive sheet with a base material, and the adhesive sheet constitutes a component having optical properties, then the base material can be considered equivalent to the substrate, and the adhesive sheet can be said to be an optical component of the present invention.

[0216] If the adhesive sheet of the present invention is an adhesive sheet with a base material, and the functional film described above is used as the base material, the adhesive sheet of the present invention can also be used as an "adhesive functional film" having the adhesive layer described above on at least one side of the functional film.

[0217] [Millimeter wave antenna] The adhesive sheet of the present invention has an adhesive layer (the adhesive layer of the present invention) with low dielectric constant and dielectric loss in high-frequency bands such as millimeter waves, and can suppress millimeter wave radiation loss. For this reason, the adhesive sheet of the present invention is useful for bonding components that make up antennas (millimeter wave antennas) used in millimeter wave communication.

[0218] In this specification, "millimeter-wave communication" means communication in the frequency band of 20 GHz to 300 GHz.

[0219] Components of a millimeter-wave antenna include a substrate (which may be referred to as a "millimeter-wave antenna substrate") equipped with antenna elements for transmitting and receiving millimeter waves (hereinafter sometimes referred to as "millimeter-wave antenna elements") on at least one side.

[0220] Examples of millimeter-wave antenna substrates include plastic films used as the base material for the adhesive sheets mentioned above. Materials with low dielectric constant and low dielectric loss are preferred because they can suppress millimeter-wave radiation loss. In particular, cyclic olefin polymers such as "Arton" (manufactured by JSR Corporation) and "Zeonor" (manufactured by Nippon Zeon Corporation) are preferred.

[0221] 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, from the standpoint of suppressing millimeter-wave radiation loss. Furthermore, 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, 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, from the standpoint of suppressing the radiation loss of millimeter waves.

[0222] The millimeter-wave antenna substrate is preferably transparent. The total light transmittance of the millimeter-wave antenna substrate in the visible light wavelength range (according to JIS K7361-1) is not particularly limited, but is preferably 85% or more, more preferably 88% or more, even more preferably 89% or more, even more preferably 90% or more, particularly preferably 91% or more, and most preferably 92% or more. 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, even more preferably 1.0% or less, even more preferably 0.9% or less, and particularly preferably 0.8% or less.

[0223] The thickness of the millimeter-wave antenna substrate is preferably 5 to 250 μm, from the standpoint of suppressing millimeter-wave radiation loss while mounting the millimeter-wave antenna elements. The millimeter-wave antenna substrate may be in the form of a single layer or a multi-layer structure. Furthermore, the surface of the millimeter-wave antenna substrate may be appropriately subjected to known and conventional surface treatments, such as physical treatments like corona discharge treatment or plasma treatment, chemical treatments like primer treatment, or coating layers such as hard coatings.

[0224] The millimeter-wave antenna elements on the millimeter-wave antenna substrate are not particularly limited as long as they can transmit and receive millimeter waves, but a phased array antenna is preferably used from the standpoint of efficiently receiving millimeter waves with mobile communication devices such as smartphones. A phased array antenna is an antenna that enables transmission and reception in a desired direction by arranging multiple antenna elements in an array and controlling the phase of each antenna element. In other words, a phased array antenna can transmit or receive radio waves in a desired direction by electronically controlling the phase of each antenna element (beam steering), regardless of the direction of the antenna.

[0225] Any known antenna can be used as a millimeter-wave antenna element without particular limitation. Examples include loop antenna structures, patch antenna structures, stacked patch antenna structures, patch antenna structures with parasitic elements, inverted F antenna structures, slot antenna structures, planar inverted F antenna structures, monopoles, dipoles, helical antenna structures, Yagi (Yagi-Uda) antenna structures, surface integrated waveguide structures, and antenna elements having resonant elements formed from hybrids of these designs. Different types of millimeter-wave antenna elements may be used for different combinations of frequency bands. A phased array antenna, in which patch antenna elements are arranged in an array, is preferred for efficient reception of millimeter waves by mobile communication devices such as smartphones.

[0226] The materials used to construct the millimeter-wave antenna element are not particularly limited and include, for example, metals such as titanium, silicon, niobium, indium, zinc, tin, gold, silver, copper, aluminum, cobalt, chromium, nickel, lead, iron, palladium, platinum, tungsten, zirconium, tantalum, and hafnium, as well as metal oxides such as ITO (indium and tin oxide), zinc oxide, and tin oxide. Furthermore, materials containing two or more of these metals or metal oxides, and alloys with these metals as the main component are also included. Among these, silver, copper, and ITO are preferred from the viewpoint of conductivity, and ITO is more preferred from the viewpoint of transparency and visibility. In other words, the above-mentioned millimeter-wave antenna element is particularly preferably composed of ITO.

[0227] Furthermore, if the antenna element is made of a metal such as silver or copper, it may be treated to blacken by forming a film of nitride, oxide, sulfide, or the like of the metal in order to conceal the antenna element and prevent a decrease in visibility due to reflection from the metal.

[0228] Furthermore, the millimeter-wave antenna substrate may include a transmission line path for transferring signals transmitted and received by the millimeter-wave antenna element to the transceiver circuit. The transmission line path may include a coaxial cable path, a microstrip transmission line, a stripline transmission line, an edge-coupled microstrip transmission line, an edge-coupled stripline transmission line, a waveguide structure for transmitting signals in the millimeter-wave frequency band (e.g., a coplanar waveguide or a grounded coplanar waveguide), or a transmission line formed from a combination of these types of transmission lines. The material constituting the transmission line path is not particularly limited, and the material constituting the millimeter-wave antenna element can be used.

[0229] Components of a millimeter-wave antenna include cover members laminated on the millimeter-wave antenna substrate to protect the millimeter-wave antenna elements arranged on the substrate. For example, optical films such as glass or plastic films can be used as cover members.

[0230] Examples of materials for plastic films include polyester resins such as polyethylene terephthalate (PET); (meth)acrylic resins such as polymethyl methacrylate (PMMA); polycarbonate; triacetylcellulose (TAC); polysulfone; polyarylate; polyimide; transparent polyimide; polyvinyl chloride; polyvinyl acetate; fluororesins; polyolefin resins such as polyethylene, polypropylene, and ethylene-propylene copolymers; and cyclic olefin polymers such as the trade name "Arton" (manufactured by JSR Corporation) and the trade name "Zeonor" (manufactured by Nippon Zeon Co., Ltd.). These plastic materials can be used individually or in combination of two or more.

[0231] The dielectric constant of the cover member 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, from the viewpoint of suppressing millimeter-wave radiation loss. Furthermore, the dielectric loss of the cover member 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, 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, from the standpoint of suppressing millimeter-wave radiation loss.

[0232] The cover member described above is preferably transparent. The total light transmittance of the cover member in the visible light wavelength range (according to JIS K7361-1) is preferably 85% or more, more preferably 88% or more, even more preferably 89% or more, even more preferably 90% or more, particularly preferably 91% or more, and most preferably 92% or more. The haze of the cover member (according to JIS K7136) is preferably 1.2% or less, more preferably 1.1% or less, even more preferably 1.0% or less, even more preferably 0.9% or less, and particularly preferably 0.8% or less.

[0233] The thickness of the cover member is preferably 0.025 to 1.5 mm from the standpoint of suppressing millimeter-wave radiation loss. The cover member may be in the form of a single layer or a multi-layer structure. Furthermore, the surface of the cover member may be appropriately subjected to known and conventional surface treatments, such as physical treatments like corona discharge treatment or plasma treatment, chemical treatments like primer treatment, or coating layers such as hard coatings.

[0234] The adhesive sheet of the present invention is preferably used in the manufacture of millimeter-wave antennas used in portable communication devices. Examples of such portable communication devices include mobile phones, PHS phones, smartphones, tablets (tablet computers), mobile computers (mobile PCs), and personal digital assistants (PDAs).

[0235] The millimeter-wave antenna may have components other than the millimeter-wave antenna substrate, cover member, and adhesive sheet described above. For example, it may have polarizing plates, wave plates, phase difference plates, optical compensation films, brightness enhancement films, light guide plates, reflective films, anti-reflective films, hard coat films, transparent conductive films, decorative films, surface protection plates, prisms, lenses, color filters, transparent substrates, or image display panels (e.g., liquid crystal display panels, organic EL panels, plasma display panels, etc.). The image display panel may also have a touch sensor.

[0236] The millimeter-wave antenna may be positioned anywhere on the mobile communication device, specifically on the front, back, or side. The front of the mobile communication device is the side that faces the user when the device is in use, and for example, the side with the display panel, while the back and sides are the casing. The display panel refers to a structure that consists of at least a lens (especially a glass lens) and a touch panel.

[0237] The size (area) of the millimeter-wave antenna is not limited; it may be formed on the entire surface of each side of the mobile communication device, or it may be placed only on a part of it. The shape of the millimeter-wave antenna is also not particularly limited; for example, it may be square, round, or wire-shaped. It may also be arranged in a frame-like manner. Furthermore, the number of millimeter-wave antennas placed on the mobile communication device is not limited; there may be one, or multiple antennas may be placed at arbitrary locations. If multiple millimeter-wave antennas are placed, their sizes (areas) may be the same or different. In areas of the mobile communication device where millimeter-wave antennas are not present, dummy patterns without millimeter-wave antennas may be placed to improve visibility.

[0238] The millimeter-wave antenna of the present invention is a millimeter-wave antenna having at least the above-mentioned adhesive sheet and substrate, wherein 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) that has the antenna element, and is not particularly limited in other respects. Note that the adhesive sheet in the millimeter-wave antenna of the present invention is an adhesive sheet used during operation and therefore does not have a separator.

[0239] The millimeter-wave antenna described above is preferably constructed by bonding a millimeter-wave antenna substrate to another optical component (which may or may not have the adhesive sheet, but having it is preferable as it further suppresses the radiation loss of millimeter waves). Furthermore, the other optical component may be one or more.

[0240] Examples of the manner in which the millimeter-wave antenna of the present invention is bonded to the other optical member in the above embodiment include: (1) a manner in which the millimeter-wave antenna substrate of the present invention and the other optical member are bonded via the adhesive sheet of the present invention; (2) a manner in which the adhesive sheet of the present invention, which includes or constitutes the millimeter-wave antenna substrate, is bonded to the other optical member; (3) a manner in which the millimeter-wave antenna substrate is bonded to a member other than the millimeter-wave antenna substrate via the adhesive tape of the present invention; and (4) a manner in which the adhesive tape of the present invention, which includes or constitutes the millimeter-wave antenna substrate, is bonded to a member other than the millimeter-wave antenna substrate. In embodiment (2) above, it is preferable that the adhesive sheet of the present invention is a double-sided adhesive sheet whose base material is a millimeter-wave antenna substrate.

[0241] Next, preferred embodiments of the millimeter-wave antenna of the present invention will be described with reference to the drawings.

[0242] Figure 1 shows a millimeter-wave antenna 1A having at least an adhesive sheet 10 and a substrate which is a millimeter-wave antenna substrate 11, wherein 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 that has the millimeter-wave antenna element 2.

[0243] Figure 2 shows a millimeter-wave antenna 1B having a cover member 12, an adhesive sheet 10, and a millimeter-wave antenna substrate 11 in contact with each other in this order. The millimeter-wave antenna substrate 11 has a millimeter-wave antenna element 2 on the side facing the adhesive sheet 10, and the adhesive sheet 10 is attached to the side of the millimeter-wave antenna substrate 11 that has the millimeter-wave antenna element 2. The cover member 12 is preferably made of glass, the millimeter-wave antenna substrate 11 is preferably made of COP from the viewpoint of low dielectric constant and low dielectric loss, and the millimeter-wave antenna element 2 is preferably made of copper, silver, or ITO.

[0244] Figure 3 shows a millimeter-wave antenna 1C having a cover member 12, an adhesive sheet 10a, a millimeter-wave antenna substrate 11, an adhesive sheet 10b, and an image display panel 13 in contact with each other in this order. The millimeter-wave antenna substrate 11 has a millimeter-wave antenna element 2 on the side facing the adhesive sheet 10a, and the adhesive sheet 10a is attached to the side of the millimeter-wave antenna substrate 11 that has the millimeter-wave antenna element 2. The cover member 12 is preferably made of glass, the millimeter-wave antenna substrate 11 is preferably made of COP from the viewpoint of low dielectric constant and low dielectric loss, and the millimeter-wave antenna element 2 is preferably made of ITO, or silver or copper blackened with a film of nitride, oxide, sulfide, etc. from the viewpoint of transparency and visibility. The adhesive sheet 10b may be the adhesive sheet of the present invention, or it may not be the adhesive sheet of the present invention, but it is preferably the adhesive sheet of the present invention. The image display panel 13 may have a touch sensor (not shown).

[0245] In the millimeter-wave antennas 1A to 1C shown in Figures 1 to 3, the adhesive sheets 10, 10a, and preferably adhesive sheet 10b are composed of the adhesive layer of the present invention, which has a low dielectric constant and dielectric loss in the high-frequency band. As a result, millimeter-wave radiation loss is suppressed, and millimeter-wave communication can be performed efficiently. Furthermore, because millimeter-wave communication can be performed efficiently, the antenna area can be reduced, and the antenna can be miniaturized. [Examples]

[0246] The present invention will be described in more detail below based on examples, but the present invention is not limited in any way by these examples.

[0247] (Example 1) A reaction vessel equipped with a condenser, nitrogen inlet, thermometer and stirring device contains C methacrylate. 12-13A mixture of 99.0 parts by mass of alkyl (manufactured by Kyoeisha Chemical Co., Ltd., trade name "L-7MA"), 1.0 part by mass of hydroxyethyl methacrylate (HEMA), 0.2 part by mass of 2,2'-azobisisobutyronitrile (AIBN) as a thermal polymerization initiator, and ethyl acetate as a polymerization solvent was charged so that the monomer component was 70% by mass. Nitrogen gas was flowed, and nitrogen substitution was carried out for about 1 hour while stirring. Thereafter, the reaction vessel was heated to 70°C and reacted for 6 hours. Further, the reaction vessel was heated to 80°C and reacted for 3 hours to obtain a (meth)acrylic polymer having a weight average molecular weight (Mw) of 400,000. To a solution (100 parts by mass of solid content) of this (meth)acrylic polymer, 0.1 part by mass based on the solid content of an isocyanate-based crosslinking agent (trade name "Coronate HX", manufactured by Tosoh Corporation, solid content concentration 100%), 0.01 part by mass of dioctyltin dilaurate (trade name "Envirizer OL-1", manufactured by Tokyo Fine Chemical Co., Ltd.) as a crosslinking accelerator, and 5 parts by mass of acetylacetone as a crosslinking retarder were added and uniformly mixed to prepare the adhesive composition according to this example.

[0248] The above adhesive composition was applied onto a polyethylene terephthalate (PET) separator (trade name "MRF38", manufactured by Mitsubishi Chemical Corporation) so that the final thickness (thickness of the adhesive layer) was 25 μm to form a coating layer (adhesive composition layer). Next, drying treatment was carried out in a dryer at 130°C for 120 minutes to volatilize the residual monomers. Further, a PET separator (trade name "MRE38", manufactured by Mitsubishi Chemical Corporation) was provided on the above coating layer to obtain a substrate-less double-sided adhesive sheet consisting only of an adhesive layer and having both sides of the adhesive layer protected by separators.

[0249] (Examples 2 to 38) A substrate-less double-sided adhesive sheet was obtained in the same manner as in Example 1, except that each monomer component was blended so as to have the blending amounts shown in Tables 1 and 2.

[0250] (Comparative Example 1) In a reaction vessel equipped with a condenser, nitrogen inlet tube, thermometer, and stirring device, 2-ethylhexyl acrylate (2EHA), acrylodecyl 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 was added as the polymerization solvent so that the monomer component amounted to 40%, and nitrogen gas was flowed through the mixture, followed by nitrogen purging for approximately 1 hour while stirring. The reaction vessel was then heated to 60°C and reacted for 6 hours. Furthermore, the reaction vessel was heated to 75°C and reacted for 2 hours to obtain an acrylic polymer. A substrate-less double-sided adhesive sheet was obtained in the same manner as in Example 1.

[0251] 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:C 12-13 Alkyl methacrylate • IDMA: Isodecyl methacrylate HEMA:2-hydroxyethyl methacrylate MMA: Methyl methacrylate • MMA - Macromonomer: Methyl methacrylate CHMA: Cyclohexyl methacrylate IBXMA: Isobornyl methacrylate • MAA: Methacrylic acid • 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

[0252] [Characteristic evaluation] The following measurements or evaluations were performed on the substrate-less double-sided adhesive sheets of the examples and comparative examples. The evaluation results are shown in Tables 1 and 2.

[0253] (1) Evaluation of dielectric constant and dielectric loss The dielectric constant and dielectric loss of the adhesive layer obtained in the examples or comparative examples (PET separator peeled off from a double-sided adhesive sheet after silicone treatment) were measured at frequencies of 28 GHz and 60 GHz using the following apparatus. Measurements were performed on a circular area with a diameter of 8 cm at 28 GHz and on a circular area with a diameter of 4 cm at 60 GHz. At least three samples were prepared for each specimen, and after excluding the maximum and minimum measured values ​​of these three samples, the average values ​​were taken as the dielectric constant and dielectric loss at each frequency. ·Measurement method: Open resonator method JIS R1660-2 • Equipment: Interferometric resonator dielectric constant measurement system manufactured by Keycom Co., Ltd. • Measurement environment: 23±1℃, 52±1%RH

[0254] (2) Total light transmittance and haze A test specimen was prepared by peeling off one separator from a double-sided adhesive sheet, bonding the sheet to a glass slide (Matsunami Glass Industry Co., Ltd., "White Polished No. 1", thickness 0.8-1.0 mm, total light transmittance 92%, haze 0.2%), and then peeling off the other separator to create a test specimen with a layer structure of double-sided adhesive sheet (adhesive layer) / glass slide. The total light transmittance and haze of the above test specimen in the visible light region were measured using a haze meter (product name "HM-150", Murakami Color Research Institute Co., Ltd.) under conditions of 23±1℃ and 52±1%RH. Three samples were prepared for each specimen, and the average of the measured values ​​of these three samples was taken as the total light transmittance and haze in the visible light region. Note that the greater the thickness of the test specimen, the smaller the total light transmittance and the larger the haze.

[0255] (3) Transmission and Reception Characteristics The transmission and reception characteristics of the adhesive layers obtained in the examples or comparative examples (PET separators that have been silicone-treated and peeled off from double-sided adhesive sheets) were evaluated using the rectangular microstrip antenna shown in Figure 4 (see IEICE Group 4, Part 2, Chapter 5 "Planar Antennas", URL: http: / / www.ieice hbkb.org / files / 04 / 04gun_02hen_05.pdf). Specifically, an antenna film 46 was fabricated using a COP substrate (product name "Zeonor", manufactured by Nippon Zeon Co., Ltd.) with a thickness of 100 μm as the antenna substrate 44. A millimeter-wave patch antenna 43 with the shape shown in Figure 4 was formed on the surface, and a 1 μm thick copper ground layer 45 was formed on the back surface. The size of the millimeter-wave patch antenna 43 was adjusted to be optimal when laminated with the adhesives of each example and comparative example (vertical A: 2.8~3.2 mm, horizontal B: 4.13 mm). The adhesive layer 42 of each example and comparative example was attached to the patch antenna 43 side of the antenna film 46, taking care not to include air bubbles or foreign matter. Subsequently, it was bonded to a 0.7 mm thick chemically strengthened glass (manufactured by Corning) as a cover glass 41, thereby fabricating an antenna laminate 4 consisting of cover glass 41 / adhesive layer 42 / antenna film 46. Power was supplied from a microstrip line 43a connected to the millimeter-wave patch antenna 43 of each antenna laminate 4, and the transmission and reception characteristics in the 30 GHz frequency band were evaluated. An improvement in gain compared to the case without the adhesive layer (where the antenna film 46 is placed close to the cover glass 41) (5.7 dB) was marked with ○, and a decrease (worsening) was marked with ×.

[0256] [Table 1]

[0257] [Table 2] [Explanation of symbols]

[0258] 1A, 1B, 1C millimeter-wave antennas 10, 10a, 10b Adhesive sheets 11 mm wave antenna board 12 Cover member 2 Millimeter-wave antenna element 13 Image display panel 4 Antenna laminate 41 Cover glass 42 Adhesive layer 43 Patch antenna for millimeter waves 43a Microstrip line 44 Antenna substrate 45 Copper ground layer 46 Antenna film

Claims

1. The dielectric constant at a frequency of 28 GHz is 2.0 to 5.

0. The dielectric loss at a frequency of 28 GHz is 0.0001 to 0.

05. The base polymer comprises a mixture of a methacrylate compound having a hydrocarbon group with 6 or more carbon atoms, and a (meth)acrylate compound having a crosslinkable functional group, a partially polymer thereof, or a copolymer thereof. The total content of the methacrylate compound having 6 or more carbon atoms or structural units derived from said compound in the base polymer is 86% by mass or more, based on 100% by mass of all structural units. The methacrylate compound having a hydrocarbon group with 6 or more carbon atoms satisfies at least one of the following conditions (i), (ii), and (iii): The (meth)acrylate compound having a crosslinkable functional group is a methacrylate compound containing a crosslinkable functional group having a hydroxyl group, and the content of the methacrylate compound containing a crosslinkable functional group having a hydroxyl group or constituent units derived from said compound in the mixture, a partially polymer thereof, or a copolymer thereof is 1.0 to 30.0% by mass, in an adhesive composition. (i) 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 constituent unit derived from said compound in the mixture, partially polymer thereof or copolymer is 66% by mass or more. (ii) A methacrylate compound having an alicyclic group with 6 or more carbon atoms, wherein the content of the methacrylate compound having an alicyclic group with 6 or more carbon atoms or a constituent unit derived from said compound in the mixture, partially polymer thereof, or copolymer is 10.0 to 50.0% by mass. (iii) A methacrylate compound having an aromatic ring-containing group with 6 or more carbon atoms, wherein the content of the methacrylate compound having an aromatic ring-containing group with 6 or more carbon atoms or a constituent unit derived from said compound in the mixture, partially polymer thereof, or copolymer is 10.0 to 50.0% by mass.

2. The adhesive composition according to claim 1, wherein the dielectric constant at a frequency of 60 GHz is 2.0 to 5.

0.

3. The dielectric constant at a frequency of 60 GHz is 2.0 to 5.

0. The dielectric loss at a frequency of 60 GHz is 0.0001 to 0.

05. The base polymer comprises a mixture of a methacrylate compound having a hydrocarbon group with 6 or more carbon atoms, and a (meth)acrylate compound having a crosslinkable functional group, a partially polymer thereof, or a copolymer thereof. The total content of the methacrylate compound having 6 or more carbon atoms or structural units derived from said compound in the base polymer is 86% by mass or more, based on 100% by mass of all structural units. The methacrylate compound having a hydrocarbon group with 6 or more carbon atoms satisfies at least one of the following conditions (i), (ii), and (iii): The (meth)acrylate compound having a crosslinkable functional group is a methacrylate compound containing a crosslinkable functional group having a hydroxyl group, and the content of the methacrylate compound containing a crosslinkable functional group having a hydroxyl group or constituent units derived from said compound in the mixture, a partially polymer thereof, or a copolymer thereof is 1.0 to 30.0% by mass, in an adhesive composition. (i) 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 constituent unit derived from said compound in the mixture, partially polymer thereof or copolymer is 66% by mass or more. (ii) A methacrylate compound having an alicyclic group with 6 or more carbon atoms, wherein the content of the methacrylate compound having an alicyclic group with 6 or more carbon atoms or a constituent unit derived from said compound in the mixture, partially polymer thereof, or copolymer is 10.0 to 50.0% by mass. (iii) A methacrylate compound having an aromatic ring-containing group with 6 or more carbon atoms, wherein the content of the methacrylate compound having an aromatic ring-containing group with 6 or more carbon atoms or a constituent unit derived from said compound in the mixture, partially polymer thereof, or copolymer is 10.0 to 50.0% by mass.

4. The adhesive composition according to any one of claims 1 to 3, wherein in the above (ii) and (iii), the content of the methacrylate compound having an alicyclic group having 6 or more carbon atoms and / or the methacrylate compound having an aromatic ring group having 6 or more carbon atoms, or constituent units derived from said compound, in the mixture, a partially polymer thereof or copolymer is 25% by mass or more.

5. The adhesive composition according to any one of claims 1 to 4, wherein the content of the (meth)acrylate compound having the crosslinkable functional group or a constituent unit derived from the compound in the mixture, a partially polymer thereof, or a copolymer thereof is 1.0 to 20.0% by mass.

6. The adhesive composition according to any one of claims 1 to 5, wherein the hydrocarbon group has an alicyclic group or an aromatic group at its terminus.

7. An adhesive layer formed by the adhesive composition according to any one of claims 1 to 6.

8. An adhesive sheet having the adhesive layer described in claim 7.

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

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