millimeter wave antenna

Abstract

To provide a millimeter-wave antenna with low dielectric constant and dielectric loss in a high frequency band, low radiation loss, and excellent antenna gain, and also provide a millimeter-wave antenna that is placed on a display, which has both low dielectric constant and low dielectric loss in the high frequency band and a high dielectric constant to some extent in the low frequency band, has low radiation loss, is excellent in antenna gain, and has the sensitivity of the touch sensor.SOLUTION: A millimeter-wave antenna 1A according to the present invention include a cover member 12, an adhesive layer 10, and a substrate 11 laminated in this order. The substrate 11 includes an antenna element 2 on at least one side thereof. The adhesive layer 10 is laminated on the surface of the substrate 11 on the side having the antenna element 2. The dielectric constant of the adhesive layer 10 at a frequency of 28 GHz or a frequency of 60 GHz is 2 to 5. The dielectric loss of the adhesive layer 10 at 28 GHz or a frequency of 60 GHz is 0.0001 to 0.05.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a millimeter-wave antenna, and more particularly to a millimeter-wave antenna with low radiation loss and excellent antenna gain. [Background technology]

[0002] In recent years, the speed and capacity of communications on mobile communication devices such as smartphones have been increasing year by year, and the next generation of ultra-high speed data communications standard, fifth generation (5G), is expected to enable ultra-high speed and high capacity communications 100 times faster than fourth generation (4G), with one-tenth the latency, and more than 10 times the number of simultaneous connections.

[0003] To enable the ultra-high speed, large capacity communications, low latency, and multiple simultaneous connections described above in 5G, high frequency electromagnetic waves with frequencies above 24 GHz called millimeter waves are used, and by shortening the wavelength to the millimeter order, it becomes possible to send large amounts of data at once.

[0004] On the other hand, compared to the frequency bands used for 4G, millimeter waves are more susceptible to attenuation due to resonant absorption with rain, oxygen in the air, and water molecules, and they also have a tendency to travel in a more directional direction and are more likely to reflect. Therefore, antennas used for millimeter wave communications (hereinafter sometimes referred to as "millimeter wave antennas") are required to have a higher antenna gain than those used for conventional 4G communications.

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

[0006] A large antenna area is required for stable reception of millimeter waves, and because millimeter waves are highly directional, reception from the upper part of the space is thought to be ideal. Since the displays of portable communication devices such as smartphones are often facing upward when in use, and larger screens have also secured a larger area, it is expected that reception efficiency will be improved if a millimeter wave antenna is placed on the display. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2019-186942 Summary of the Invention [Problem to be solved by the invention]

[0008] It is known that millimeter-wave components of millimeter-wave antennas are attenuated by their inherent dielectric loss, and so to avoid reducing antenna gain, they are required to have a low dielectric constant, especially low dielectric loss, in the high-frequency band of millimeter waves.The adhesive used to bond the components of millimeter-wave antennas is also required to have a low dielectric constant and low dielectric loss in the high-frequency band.

[0009] On the other hand, capacitive touch sensors are widely used in smartphone displays, but capacitive touch panels require a relatively high dielectric constant in the low frequency band to improve sensitivity. Therefore, when placing a millimeter-wave antenna on a display, it is necessary to achieve both low dielectric constant and dielectric loss in the high frequency band to improve antenna gain, and a relatively high dielectric constant in the low frequency band to improve touch sensor sensitivity.

[0010] The present invention has been devised in light of the above circumstances, and an object of the present invention is to provide a millimeter-wave antenna that has a low dielectric constant and dielectric loss in the high frequency band, low radiation loss, and excellent antenna gain. Another object of the present invention is to provide a millimeter-wave antenna placed on a display that has both a low dielectric constant and low dielectric loss in the high frequency band and a relatively high dielectric constant in the low frequency band, has low radiation loss, excellent antenna gain, and ensures touch sensor sensitivity. [Means for solving the problem]

[0011] A first aspect of the present invention is a millimeter-wave antenna including a cover member, a pressure-sensitive adhesive layer, and a substrate laminated in this order, the substrate has an antenna element on at least one surface; the pressure-sensitive adhesive layer is laminated on a surface of the substrate on the side having the antenna element; The pressure-sensitive adhesive layer has a dielectric constant of 2 to 5 at a frequency of 28 GHz, The pressure-sensitive adhesive layer has a dielectric loss of 0.0001 to 0.05 at 28 GHz. A millimeter wave antenna is provided.

[0012] In the millimeter-wave antenna according to the first aspect of the present invention, the pressure-sensitive adhesive layer having a dielectric constant of 2 to 5 at a frequency of 28 GHz is preferred in that it can reduce radiation loss of the received millimeter waves and improve the antenna gain of the millimeter-wave antenna according to the first aspect of the present invention.

[0013] In the millimeter-wave antenna according to the first aspect of the present invention, the pressure-sensitive adhesive layer having a dielectric loss of 0.0001 to 0.05 at a frequency of 28 GHz is preferred in that it can reduce radiation loss of the received millimeter waves and improve the antenna gain of the millimeter-wave antenna according to the first aspect of the present invention.

[0014] In the millimeter-wave antenna according to the first aspect of the present invention, the pressure-sensitive adhesive layer preferably has a dielectric constant at a frequency of 60 GHz of 2 to 5. This configuration is preferable in that it can reduce radiation loss of the received millimeter waves and improve the antenna gain of the millimeter-wave antenna according to the first aspect of the present invention.

[0015] In the millimeter-wave antenna according to the first aspect of the present invention, the pressure-sensitive adhesive layer preferably has a dielectric loss of 0.0001 to 0.05 at a frequency of 60 GHz. This configuration is preferable in that it can reduce radiation loss of the received millimeter waves and improve the antenna gain of the millimeter-wave antenna according to the first aspect of the present invention.

[0016] A second aspect of the present invention is a millimeter-wave antenna including a cover member, a pressure-sensitive adhesive layer, and a substrate laminated in this order, the substrate has an antenna element on at least one surface; the pressure-sensitive adhesive layer is laminated on a surface of the substrate on the side having the antenna element; The pressure-sensitive adhesive layer has a dielectric constant of 2 to 5 at a frequency of 60 GHz, The pressure-sensitive adhesive layer has a dielectric loss of 0.0001 to 0.05 at 60 GHz. A millimeter wave antenna is provided.

[0017] In the millimeter-wave antenna according to the second aspect of the present invention, the pressure-sensitive adhesive layer having a dielectric constant of 2 to 5 at a frequency of 60 GHz is preferred in that it can reduce radiation loss of the received millimeter waves and improve the antenna gain of the millimeter-wave antenna according to the second aspect of the present invention.

[0018] In the millimeter-wave antenna according to the second aspect of the present invention, the pressure-sensitive adhesive layer having a dielectric loss of 0.0001 to 0.05 at a frequency of 60 GHz is preferred in that it can reduce radiation loss of the received millimeter waves and improve the antenna gain of the millimeter-wave antenna according to the second aspect of the present invention.

[0019] A third aspect of the present invention is a millimeter-wave antenna including a cover member, a pressure-sensitive adhesive layer, a substrate, and an image display panel laminated in this order, the substrate has an antenna element on at least one surface; the pressure-sensitive adhesive layer is laminated on a surface of the substrate on the side having the antenna element; The pressure-sensitive adhesive layer has a dielectric constant of 2 to 5 at a frequency of 28 GHz, the pressure-sensitive adhesive layer has a dielectric constant of 2 to 8 at 100 kHz; The pressure-sensitive adhesive layer has a dielectric loss of 0.0001 to 0.05 at 28 GHz. A millimeter wave antenna is provided.

[0020] In the millimeter-wave antenna according to the third aspect of the present invention, a configuration in which the basic antenna structure comprising the cover member, the adhesive layer, and the substrate is disposed on an image display panel allows the antenna to be disposed on a display that occupies a large area in a portable communication device such as a smartphone, and is preferable from the viewpoint of stable reception of millimeter waves. Furthermore, because millimeter waves are highly directional, reception from the upper part of space is considered ideal. However, the displays of portable communication devices such as smartphones are often facing upward when in use, and large screens provide a large area. Therefore, a configuration in which the millimeter-wave antenna is disposed on the display is preferable in that reception efficiency can be dramatically improved.

[0021] In the millimeter-wave antenna according to the third aspect of the present invention, the pressure-sensitive adhesive layer having a dielectric constant of 2 to 5 at a frequency of 28 GHz is preferred in that it can reduce radiation loss of the received millimeter waves and improve the antenna gain of the millimeter-wave antenna according to the third aspect of the present invention.

[0022] In the millimeter-wave antenna according to the third aspect of the present invention, a configuration in which the pressure-sensitive adhesive layer has a dielectric constant of 2 to 8 at a frequency of 100 kHz is preferable in that touch sensor sensitivity can be ensured in the millimeter-wave antenna according to the third aspect of the present invention.

[0023] In the millimeter-wave antenna according to the third aspect of the present invention, the pressure-sensitive adhesive layer having a dielectric loss of 0.0001 to 0.05 at a frequency of 28 GHz is preferred in that it can reduce radiation loss of the received millimeter waves and improve the antenna gain of the millimeter-wave antenna according to the third aspect of the present invention.

[0024] In the millimeter-wave antenna according to the third aspect of the present invention, the pressure-sensitive adhesive layer preferably has a dielectric constant at a frequency of 60 GHz of 2 to 5. This configuration is preferable in that it can reduce radiation loss of the received millimeter waves and improve the antenna gain of the millimeter-wave antenna according to the third aspect of the present invention.

[0025] In the millimeter-wave antenna according to the third aspect of the present invention, the pressure-sensitive adhesive layer preferably has a dielectric loss of 0.0001 to 0.05 at a frequency of 60 GHz. This configuration is preferable in that it can reduce radiation loss of the received millimeter waves and improve the antenna gain of the third millimeter-wave antenna according to the present invention.

[0026] In the millimeter-wave antenna according to the third aspect of the present invention, the configuration described above, which achieves both a low dielectric constant and low dielectric loss in high frequency bands such as 28 GHz and 60 GHz and a relatively high dielectric constant in low frequency bands such as 100 kHz, is preferable because it can achieve both improved antenna gain by keeping the radiation loss of the received millimeter waves low and improved touch sensor sensitivity by exhibiting a relatively high dielectric constant in the low frequency band.

[0027] A fourth aspect of the present invention is a millimeter-wave antenna including a cover member, a pressure-sensitive adhesive layer, a substrate, and an image display panel laminated in this order, the substrate has an antenna element on at least one surface; the pressure-sensitive adhesive layer is laminated on a surface of the substrate on the side having the antenna element; The pressure-sensitive adhesive layer has a dielectric constant of 2 to 5 at a frequency of 60 GHz, the pressure-sensitive adhesive layer has a dielectric constant of 2 to 8 at 100 kHz; The pressure-sensitive adhesive layer has a dielectric loss of 0.0001 to 0.05 at 60 GHz. A millimeter wave antenna is provided.

[0028] In the millimeter-wave antenna according to the fourth aspect of the present invention, a configuration in which the basic antenna structure comprising the cover member, adhesive layer, and substrate is disposed on an image display panel allows the antenna to be disposed on a display that occupies a large area in a portable communication device such as a smartphone, and is preferable from the viewpoint of stable reception of millimeter waves. Furthermore, because millimeter waves are highly directional, reception from the upper part of space is considered ideal, but the displays of portable communication devices such as smartphones are often facing upward when in use, and large screens provide a large area, so a configuration in which the millimeter-wave antenna is disposed on the display is preferable in that it can dramatically improve reception efficiency.

[0029] In the millimeter-wave antenna according to the fourth aspect of the present invention, the pressure-sensitive adhesive layer having a dielectric constant of 2 to 5 at a frequency of 60 GHz is preferred in that it can reduce radiation loss of the received millimeter waves and improve the antenna gain of the millimeter-wave antenna according to the fourth aspect of the present invention.

[0030] In the millimeter-wave antenna according to the fourth aspect of the present invention, a configuration in which the pressure-sensitive adhesive layer has a dielectric constant of 2 to 8 at a frequency of 100 kHz is preferable in that touch sensor sensitivity can be ensured in the millimeter-wave antenna according to the fourth aspect of the present invention.

[0031] In the millimeter-wave antenna according to the fourth aspect of the present invention, the pressure-sensitive adhesive layer having a dielectric loss of 0.0001 to 0.05 at a frequency of 60 GHz is preferred in that it can reduce radiation loss of the received millimeter waves and improve the antenna gain of the millimeter-wave antenna according to the fourth aspect of the present invention.

[0032] In the millimeter-wave antenna according to the third aspect of the present invention and the millimeter-wave antenna according to the fourth aspect of the present invention, the image display panel preferably has a touch sensor. This configuration is preferable in that it eliminates the need to arrange a touch sensor on the substrate, thereby increasing the degree of freedom in arranging the antenna element on the substrate.

[0033] In the millimeter-wave antenna according to the third aspect of the present invention and the millimeter-wave antenna according to the fourth aspect of the present invention, it is preferable that an adhesive layer is further laminated between the substrate and the image display panel. This configuration is preferable in that it allows the image display panel to be stably laminated on the substrate and makes it easier to ensure sensitivity when the image display panel has a touch sensor. [Effects of the Invention]

[0034] In the millimeter-wave antenna according to the first aspect of the present invention and the millimeter-wave antenna according to the second aspect of the present invention, the pressure-sensitive adhesive layer exhibits low dielectric constant and dielectric loss in the high frequency band of millimeter waves, and can suppress radiation loss of millimeter waves to a low level. Therefore, the millimeter-wave antenna according to the first aspect of the present invention and the millimeter-wave antenna according to the second aspect of the present invention can suppress radiation loss of received millimeter waves to a low level and exhibit high antenna gain. Furthermore, in the millimeter-wave antenna according to the third aspect of the present invention and the millimeter-wave antenna according to the fourth aspect of the present invention, the pressure-sensitive adhesive layer exhibits a low dielectric constant and dielectric loss in the high frequency band of millimeter waves and a relatively high dielectric constant in the low frequency band, thereby suppressing millimeter-wave radiation loss to a low level and ensuring touch sensor sensitivity. Therefore, the millimeter-wave antenna according to the third aspect of the present invention and the millimeter-wave antenna according to the fourth aspect of the present invention can achieve both excellent antenna gain and touch sensor sensitivity by being disposed on the display of an electronic communication device such as a smartphone. [Brief explanation of the drawings]

[0035] [Figure 1] FIG. 1 is a schematic diagram (cross-sectional view) showing an embodiment of a millimeter-wave antenna according to a first aspect of the present invention and a millimeter-wave antenna according to a second aspect of the present invention. [Figure 2] FIG. 2 is a schematic diagram (cross-sectional view) showing an embodiment of the millimeter-wave antenna according to the third aspect of the present invention and the millimeter-wave antenna according to the fourth aspect of the present invention. [Figure 3] Figure 3 is a schematic diagram (cross-sectional view) showing the antenna laminate used in the evaluation of transmission and reception characteristics, where Figure 3(a) is a side cross-sectional view and Figure 3(b) is a top projection view. DETAILED DESCRIPTION OF THE INVENTION

[0036] [1. Millimeter wave antenna] The millimeter-wave antenna of the first aspect of the present invention comprises a cover member, a pressure-sensitive adhesive layer, and a substrate laminated in this order, the substrate having an antenna element on at least one side, the pressure-sensitive adhesive layer laminated on the side of the substrate having the antenna element, and the pressure-sensitive adhesive layer having a dielectric constant of 2 to 5 at a frequency of 28 GHz and a dielectric loss of 0.0001 to 0.05 at 28 GHz, but is not otherwise particularly limited. The millimeter-wave antenna of the second aspect of the present invention comprises a cover member, a pressure-sensitive adhesive layer, and a substrate laminated in this order, the substrate having an antenna element on at least one surface thereof, the pressure-sensitive adhesive layer laminated on the surface of the substrate having the antenna element, and the pressure-sensitive adhesive layer having a dielectric constant of 2 to 5 at a frequency of 60 GHz and a dielectric loss of 0.0001 to 0.05 at 60 GHz, but is not otherwise particularly limited. Furthermore, a millimeter-wave antenna according to a third aspect of the present invention comprises a cover member, a pressure-sensitive adhesive layer, a substrate, and an image display panel laminated in this order, the substrate having an antenna element on at least one surface thereof, the pressure-sensitive adhesive layer laminated on the surface of the substrate having the antenna element, and the pressure-sensitive adhesive layer having a dielectric constant of 2 to 5 at a frequency of 28 GHz, a dielectric constant of 2 to 8 at 100 kHz, and a dielectric loss of 0.0001 to 0.05 at 28 GHz, but is not otherwise particularly limited. A millimeter-wave antenna according to a fourth aspect of the present invention comprises a cover member, a pressure-sensitive adhesive layer, a substrate, and an image display panel laminated in this order, the substrate having an antenna element on at least one surface thereof, the pressure-sensitive adhesive layer laminated on the surface of the substrate having the antenna element, and the pressure-sensitive adhesive layer having a dielectric constant of 2 to 5 at a frequency of 60 GHz, a dielectric constant of 2 to 8 at 100 kHz, and a dielectric loss of 0.0001 to 0.05 at 60 GHz, but is not otherwise particularly limited. In this specification, the millimeter-wave antenna according to the first aspect of the present invention and the millimeter-wave antenna according to the second aspect of the present invention may be collectively referred to as "millimeter-wave antenna A," and the millimeter-wave antenna according to the third aspect of the present invention and the millimeter-wave antenna according to the fourth aspect of the present invention may be collectively referred to as "millimeter-wave antenna B." Furthermore, in this specification, unless otherwise specified, the term "millimeter-wave antenna of the present invention" includes both "millimeter-wave antenna A" and "millimeter-wave antenna B."

[0037] The millimeter-wave antennas (millimeter-wave antenna A and millimeter-wave antenna B) of the present invention refer to antennas suitable for millimeter-wave communication. In this specification, "millimeter waves" refers to electromagnetic waves in the frequency band of 20 GHz to 300 GHz, and "millimeter wave communication" refers to communication using millimeter waves.

[0038] [1-1. Circuit board] The substrate constituting the millimeter-wave antenna (millimeter-wave antenna A and millimeter-wave antenna B) of the present invention is a substrate having an antenna element on at least one surface (hereinafter, may be referred to as "antenna substrate").

[0039] Examples of materials constituting the antenna substrate include plastic materials such as polyester resins such as polyethylene terephthalate (PET), (meth)acrylic resins such as polymethyl methacrylate (PMMA), polycarbonate, triacetyl cellulose (TAC), polysulfone, polyarylate, polyimide, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, ethylene-propylene copolymers, cyclic olefin polymers such as "ARTON (cyclic olefin polymer, manufactured by JSR Corporation)" and "ZEONOR (cyclic olefin polymer, manufactured by Zeon Corporation)," and fluorine-based polymers. These plastic materials may be used alone or in combination of two or more. From the viewpoint of suppressing radiation loss of millimeter waves, materials with low dielectric constant and low dielectric loss are preferred, and cyclic olefin polymers such as "ARTON (cyclic olefin polymer, manufactured by JSR Corporation)" and "ZEONOR (cyclic olefin polymer, manufactured by Zeon Corporation)" are particularly preferred.

[0040] From the viewpoint of suppressing radiation loss of millimeter waves, the dielectric constant of the 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, even more preferably 2.2 to 3.4, even more preferably 2.2 to 3.3, even more preferably 2.2 to 3.2, even more preferably 2.2 to 3.1, and particularly preferably 2.2 to 3.0. Furthermore, from the viewpoint of suppressing radiation loss of millimeter waves, the dielectric loss of the antenna substrate at 28 GHz and / or 60 GHz is preferably 0.0001 to 0.05, more preferably 0.001 to 0.02, even more preferably 0.002 to 0.019, even more preferably 0.003 to 0.018, even more preferably 0.004 to 0.017, even more preferably 0.005 to 0.016, even more preferably 0.006 to 0.015, even more preferably 0.007 to 0.014, even more preferably 0.008 to 0.013, even more preferably 0.009 to 0.012, and particularly preferably 0.01 to 0.011.

[0041] The antenna substrate is preferably transparent. The total light transmittance (according to JIS K7361-1) of the antenna substrate in the visible light wavelength region 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, even more preferably 91% or more, and particularly preferably 92% or more. The haze (according to JIS K7136) of the antenna substrate 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.

[0042] The thickness of the antenna substrate is preferably 5 to 250 μm from the viewpoint of suppressing radiation loss of millimeter waves while mounting an antenna element. The antenna substrate may have either a single layer or a multi-layer structure. The surface of the antenna substrate may be appropriately subjected to a known or commonly used surface treatment, such as a physical treatment such as corona discharge treatment, plasma treatment, or electron beam treatment, a chemical treatment such as a primer treatment, or a coating layer such as a hard coating.

[0043] [1-2. Antenna elements] The antenna element included in the antenna substrate is not particularly limited as long as it can transmit and receive millimeter waves. Hereinafter, an antenna element for transmitting and receiving millimeter waves may be referred to as a "millimeter-wave antenna element." A phased array antenna is preferably used as the millimeter-wave antenna element from the viewpoint of efficiently receiving millimeter waves in a mobile communication device such as a smartphone. A phased array antenna is an antenna in which multiple antenna elements are arranged in an array and the phase of each antenna element is controlled to enable transmission and reception in a desired direction. In other words, a phased array antenna can transmit and receive radio waves in a desired direction by electronically controlling the phase of each antenna element (beam steering) regardless of the antenna direction.

[0044] As the millimeter-wave antenna element, any known antenna can be used without particular limitation, including, for example, a loop antenna structure, a patch antenna structure, a stacked patch antenna structure, a patch antenna structure having a parasitic element, an inverted-F antenna structure, a slot antenna structure, a planar inverted-F antenna structure, a monopole, a dipole, a helical antenna structure, a Yagi (Yagi-Uda) antenna structure, a surface integrated waveguide structure, and an antenna element having a resonant element formed from a hybrid of these designs. Different types of millimeter-wave antenna elements may be used for different combinations of frequency bands. From the perspective of efficiently receiving millimeter waves in mobile communication devices such as smartphones, a phased array antenna in which patch antenna elements are arranged in an array is preferred.

[0045] The material constituting the millimeter-wave antenna element is not particularly limited, and examples thereof 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, and metal oxides such as ITO (oxide of indium and tin), zinc oxide, and tin oxide. Further examples include materials containing two or more of these metals or metal oxides, and alloys containing these metals as the main component. Among these, silver, copper, and ITO are preferred from the viewpoint of conductivity, and ITO is more preferred from the viewpoints of transparency and visibility. In other words, it is particularly preferred that the millimeter-wave antenna element be made of ITO. Furthermore, when the antenna element is made of a metal such as silver or copper, the antenna element may be subjected to a blackening treatment 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.

[0046] The millimeter-wave antenna element may include a transmission line path on the surface of or inside the antenna substrate for transferring a signal to be transmitted or received to a 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), a transmission line formed from a combination of these types of transmission lines, etc. The material constituting the transmission line path is also not particularly limited, and the material constituting the millimeter-wave antenna element may be used.

[0047] [1-3. Cover material] The cover member constituting the millimeter-wave antenna (millimeter-wave antenna A and millimeter-wave antenna B) of the present invention is a member laminated on the antenna substrate to protect the millimeter-wave antenna elements arranged on the antenna substrate. The cover member is not particularly limited, but optical films such as glass and plastic films can be used. Examples of materials for plastic films include polyester resins such as polyethylene terephthalate (PET), (meth)acrylic resins such as polymethyl methacrylate (PMMA), polycarbonate, triacetyl cellulose (TAC), polysulfone, polyarylate, polyimide, transparent polyimide, polyvinyl chloride, polyvinyl acetate, fluorine-based resins, polyethylene, polypropylene, ethylene-propylene copolymers, and cyclic olefin polymers such as "ARTON (cyclic olefin polymer, manufactured by JSR Corporation)" and "ZEONOR (cyclic olefin polymer, manufactured by Zeon Corporation)." These plastic materials may be used alone or in combination.

[0048] From the viewpoint of suppressing radiation loss of millimeter waves, 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, even more preferably 2.2 to 3.4, even more preferably 2.2 to 3.3, even more preferably 2.2 to 3.2, even more preferably 2.2 to 3.1, and particularly preferably 2.2 to 3.0. Furthermore, from the viewpoint of suppressing radiation loss of millimeter waves, the dielectric loss of the cover member at 28 GHz and / or 60 GHz is preferably 0.0001 to 0.05, more preferably 0.001 to 0.02, even more preferably 0.002 to 0.019, even more preferably 0.003 to 0.018, even more preferably 0.004 to 0.017, even more preferably 0.005 to 0.016, even more preferably 0.006 to 0.015, even more preferably 0.007 to 0.014, even more preferably 0.008 to 0.013, even more preferably 0.009 to 0.012, and particularly preferably 0.01 to 0.011.

[0049] The cover member is preferably transparent. The total light transmittance (according to JIS K7361-1) of the cover member in the visible light wavelength region 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, even more preferably 91% or more, and particularly preferably 92% or more. The haze (according to JIS K7136) of the cover member 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.

[0050] The thickness of the cover member is preferably 0.025 to 1.5 mm from the viewpoint of suppressing radiation loss of millimeter waves. The cover member may have either a single layer or multiple layers. The surface of the cover member may be appropriately subjected to a known or commonly used surface treatment, such as a physical treatment such as corona discharge treatment or plasma treatment, a chemical treatment such as a primer treatment, or a coating layer such as a hard coating.

[0051] [1-4. Image display panel] The image display panel constituting the millimeter wave antenna B is not particularly limited, and examples thereof include a liquid crystal display panel, an organic EL panel, a plasma display panel, and a micro LED panel. The image display panel preferably has a touch sensor, which is preferable in that the touch sensor does not need to be disposed on the substrate, thereby increasing the degree of freedom in disposing the antenna element on the substrate.

[0052] [1-5. Adhesive layer] In this specification, the pressure-sensitive adhesive layer constituting millimeter-wave antenna A may be referred to as "pressure-sensitive adhesive layer A," and the pressure-sensitive adhesive layer constituting millimeter-wave antenna B may be referred to as "pressure-sensitive adhesive layer B." Furthermore, in this specification, the term "pressure-sensitive adhesive layer of the present invention" includes both pressure-sensitive adhesive layer A and pressure-sensitive adhesive layer B, unless otherwise specified.

[0053] The pressure-sensitive adhesive layers of the present invention (pressure-sensitive adhesive layer A and pressure-sensitive adhesive layer B) are laminated between the cover member and the substrate, and are laminated on the surface of the substrate on the side having the antenna element. The pressure-sensitive adhesive layer A in the millimeter-wave antenna according to the first aspect of the present invention is not particularly limited as long as it has a dielectric constant of 2 to 5 at a frequency of 28 GHz and a dielectric loss of 0.0001 to 0.05 at a frequency of 28 GHz. The pressure-sensitive adhesive layer A in the millimeter-wave antenna according to the second aspect of the present invention is not particularly limited as long as it has a dielectric constant of 2 to 5 at a frequency of 60 GHz and a dielectric loss of 0.0001 to 0.05 at a frequency of 60 GHz. The pressure-sensitive adhesive layer B in the millimeter-wave antenna of the third aspect of the present invention is not particularly limited as long as it has a dielectric constant of 2 to 5 at a frequency of 28 GHz, a dielectric constant of 2 to 8 at a frequency of 100 kHz, and a dielectric loss of 0.0001 to 0.05 at a frequency of 28 GHz. The pressure-sensitive adhesive layer B in the millimeter-wave antenna of the fourth aspect of the present invention is not particularly limited as long as it has a dielectric constant of 2 to 5 at a frequency of 60 GHz, a dielectric constant of 2 to 8 at a frequency of 100 kHz, and a dielectric loss of 0.0001 to 0.05 at a frequency of 60 GHz.

[0054] [1-5-1. Dielectric constant and dielectric loss of adhesive layer] The pressure-sensitive adhesive layer of the present invention has low dielectric constant and dielectric loss in high frequency bands such as millimeter waves, and can therefore suppress radiation loss of millimeter waves. As a result, the millimeter-wave antennas of the present invention (millimeter-wave antenna A and millimeter-wave antenna B) can suppress radiation loss of received millimeter waves and achieve high antenna gain.

[0055] Furthermore, the pressure-sensitive adhesive layer B of the present invention has a relatively high dielectric constant in the low frequency band (100 kHz), which ensures the sensitivity of the touch sensor when the millimeter-wave antenna B is disposed on the image display panel.

[0056] The pressure-sensitive adhesive layer of the present invention has a dielectric constant at a frequency of 28 GHz of preferably 5 or less, more preferably 4.5 or less, even more preferably 4 or less, still more preferably 3.5 or less, and may be 3.4 or less, 3.3 or less, 3.2 or less, 3.1 or less, 3.0 or less, or 2.9 or less. The lower limit of the dielectric constant at a frequency of 28 GHz is not particularly limited, but is preferably 2 or more, and may be 2.1 or more, or 2.2 or more.

[0057] The dielectric constant at 28 GHz of the adhesive layer of the present invention can be adjusted by adjusting the type of base polymer constituting the adhesive composition for forming the adhesive layer, the monomer composition, the type and content of additives, etc. In this specification, the dielectric constant is measured by the method described in the examples below. Note that the "dielectric constant" is the value obtained by dividing the "dielectric constant" by the "dielectric constant of a vacuum," but since the "dielectric constant of a vacuum" is 1, in this specification, the "dielectric constant" and the "dielectric constant" are treated as synonymous.

[0058] The pressure-sensitive adhesive layer B of the present invention has a dielectric constant at 100 kHz that is controlled to a relatively high level, thereby improving the sensitivity of touch sensors (particularly capacitive touch sensors). The pressure-sensitive adhesive layer B of the present invention preferably has a dielectric constant at a frequency of 100 kHz of 2 or more, more preferably 2.1 or more, and even more preferably 2.2 or more, and may be 2.3 or more, 2.4 or more, 2.5 or more, 2.6 or more, 2.7 or more, 2.8 or more, 2.9 or more, 3.0 or more, 3.5 or more, or 4.0 or more. The upper limit of the dielectric constant at a frequency of 100 kHz is not particularly limited, but from the viewpoint of suppressing malfunction of the touch panel, it is preferably 8 or less, and may be 7.5 or less, or 7 or less.

[0059] The dielectric constant at 100 kHz of the adhesive layer B of the present invention can be adjusted by adjusting the type of base polymer constituting the adhesive composition for forming the adhesive layer B, the monomer composition, the type and content of additives, etc.

[0060] The pressure-sensitive adhesive layer of the present invention has a low dielectric loss at 28 GHz, and can suppress millimeter wave radiation loss. The pressure-sensitive adhesive layer of the present invention has a dielectric loss at a frequency of 28 GHz of preferably 0.05 or less, more preferably 0.045 or less, even more preferably 0.04 or less, even more preferably 0.035 or less, even more preferably 0.03 or less, even more preferably 0.025 or less, and particularly preferably 0.02 or less. The lower limit of the dielectric loss at a frequency of 28 GHz is not particularly limited, but is preferably 0.0001 or more, and may be 0.0005 or more, or 0.001 or more.

[0061] The dielectric loss at 28 GHz in the adhesive layer of the present invention can be adjusted by adjusting the type of base polymer constituting the adhesive composition for forming the adhesive layer, the monomer composition, the type and content of additives, etc. In this specification, the dielectric loss is measured by the method described in the examples below.

[0062] The pressure-sensitive adhesive layer of the present invention preferably has a low dielectric constant at 60 GHz, which is preferable in that it can suppress millimeter wave radiation loss. The pressure-sensitive adhesive layer of the present invention has a dielectric constant at a frequency of 60 GHz that is not particularly limited, but is preferably 5 or less, more preferably 4.5 or less, even more preferably 4 or less, and even more preferably 3.5 or less, and may be 3.4 or less, 3.3 or less, 3.2 or less, 3.1 or less, 3.0 or less, or 2.9 or less. The lower limit of the dielectric constant at a frequency of 60 GHz is not particularly limited, but is preferably 2 or more, and may be 2.1 or more, or 2.2 or more.

[0063] The dielectric constant at 60 GHz of the adhesive layer of the present invention can be adjusted by adjusting the type of base polymer constituting the adhesive composition for forming the adhesive layer, the monomer composition, the type and content of additives, etc.

[0064] The pressure-sensitive adhesive layer of the present invention preferably has a low dielectric loss at 60 GHz, which is preferable in that it can suppress millimeter wave radiation loss. The pressure-sensitive adhesive layer of the present invention has a dielectric loss at a frequency of 60 GHz that is not particularly limited, but is preferably 0.05 or less, more preferably 0.045 or less, even more preferably 0.04 or less, even more preferably 0.035 or less, even more preferably 0.03 or less, even more preferably 0.025 or less, and particularly preferably 0.02 or less, and may be 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 not particularly limited, but is preferably 0.0001 or more, and may be 0.0005 or more, or 0.001 or more.

[0065] The dielectric loss at 60 GHz in the adhesive layer of the present invention can be adjusted by adjusting the type of base polymer constituting the adhesive composition for forming the adhesive layer, the monomer composition, the type and content of additives, etc.

[0066] [1-5-2. Haze and total light transmittance of adhesive layer] The pressure-sensitive adhesive layer of the present invention (pressure-sensitive adhesive layer A and pressure-sensitive adhesive layer B) is transparent or has transparency. Therefore, the pressure-sensitive adhesive layer has excellent visibility and appearance through the pressure-sensitive adhesive layer. Thus, the pressure-sensitive adhesive layer of the present invention is suitable for optical use.

[0067] The haze of the pressure-sensitive 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. A haze of 1.2% or less is preferable because excellent transparency and excellent appearance can be obtained. The haze can be measured, for example, by forming a pressure-sensitive adhesive layer (thickness: 100 μm), leaving it at room temperature (23° C., 50% RH) for at least 24 hours, and then bonding it to a slide glass (e.g., one with a total light transmittance of 91.8% and a haze of 0.4%) to form a sample, using a haze meter (manufactured by Murakami Color Research Laboratory Co., Ltd., product name "HM-150").

[0068] The total light transmittance (according to JIS K7361-1) in the visible light wavelength region of the pressure-sensitive adhesive layer of the present invention 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, even more preferably 91% or more, and particularly preferably 92% or more. A total light transmittance of 85% or more is preferable because excellent transparency and excellent appearance can be obtained. The total light transmittance can be measured, for example, by forming a pressure-sensitive adhesive layer (thickness: 100 μm), leaving it at room temperature (23° C., 50% RH) for at least 24 hours, peeling off the separator, if any, and bonding it to a slide glass (e.g., one with a total light transmittance of 91.8% and a haze of 0.4%) to form a sample, using a haze meter (manufactured by Murakami Color Research Laboratory Co., Ltd., product name "HM-150").

[0069] The haze and total light transmittance of the pressure-sensitive adhesive layer of the present invention can be adjusted by adjusting the type of base polymer constituting the pressure-sensitive adhesive composition for forming the pressure-sensitive adhesive layer, the monomer composition, the type and content of additives, etc.

[0070] [1-5-3. Gel fraction of adhesive layer] The gel fraction (proportion of insoluble components) of the pressure-sensitive adhesive layers (pressure-sensitive adhesive layer A and pressure-sensitive adhesive layer B) of the present invention is not particularly limited, but is preferably 30 to 95%, more preferably 35 to 90%, even more preferably 40 to 85%, even more preferably 45 to 80%, and particularly preferably 50 to 75%. A gel fraction of 30% or more improves the cohesive strength of the pressure-sensitive adhesive layer, reduces the likelihood of dents during handling, and inhibits foaming and peeling at the interface with the adherend in high-temperature environments, making it easier to achieve excellent foaming and peeling resistance, which is preferable. A gel fraction of 95% or less is preferable because it provides appropriate flexibility, improves adhesion and step-conforming ability, and reduces the likelihood of foreign matter absorption.

[0071] (gel fraction) Specifically, the gel fraction (proportion of solvent-insoluble components) is a value calculated by the following "Method for measuring gel fraction," for example.

[0072] Approximately 0.1 g of the adhesive layer was sampled from the adhesive sheet, wrapped in a porous tetrafluoroethylene sheet (trade name "NTF1122", manufactured by Nitto Denko Corporation) with an average pore size of 0.2 μm, and then tied with kite string. The weight at this time was measured, and this weight was designated the pre-immersion weight (Z). The pre-immersion weight was the total weight of the adhesive layer (the adhesive layer sampled above), the tetrafluoroethylene sheet, and the kite string. The total weight of the tetrafluoroethylene sheet and the kite string was also measured, and this weight was designated the wrapping weight (Y). Next, the pressure-sensitive adhesive layer is wrapped in a tetrafluoroethylene sheet and tied with kite string (referred to as the "sample"), which is placed in a 50 ml container filled with ethyl acetate or toluene and left to stand for 7 days at 23° C. Thereafter, the sample (after ethyl acetate or toluene treatment) is removed from the container, transferred to an aluminum cup, and dried in a dryer at 130° C. for 2 hours to remove the ethyl acetate or toluene, after which the sample is weighed and this weight is defined as the post-immersion weight (X). Then, the gel fraction is calculated using the following formula. Gel fraction [% (weight%)] = (XY) / (ZY) × 100

[0073] The gel fraction can be controlled, for example, by the monomer composition of the base polymer (e.g., an acrylic polymer) of the pressure-sensitive adhesive composition for forming the pressure-sensitive adhesive layer, the weight-average molecular weight, the amount (addition amount) of the crosslinking agent used, the types and amounts of other additives used, etc.

[0074] [1-5-4. Storage modulus of adhesive layer] The storage modulus of the pressure-sensitive adhesive layer (pressure-sensitive adhesive layer A and pressure-sensitive adhesive layer B) of the present invention at 25°C is not particularly limited, but is preferably 0.01 MPa or more, more preferably 0.02 MPa or more, even more preferably 0.03 MPa or more, even more preferably 0.04 MPa or more, even more preferably 0.05 MPa or more, and particularly preferably 0.1 MPa or more. A storage modulus of 0.01 MPa or more is preferable because it reduces the likelihood of dents during handling and facilitates good adhesion reliability. Furthermore, from the viewpoints of conformability to uneven surfaces and foreign matter absorption, the storage modulus of the pressure-sensitive adhesive layer at 25°C is preferably 5 MPa or less, more preferably 4.5 MPa or less, even more preferably 4.0 MPa or less, even more preferably 3.5 MPa or less, even more preferably 3.0 MPa or less, even more preferably 2.5 MPa or less, and particularly preferably 2.0 MPa or less. The storage modulus of the pressure-sensitive adhesive layer is measured when dynamic viscoelasticity is performed at a frequency of 1 Hz. The storage modulus is the real part of the shear modulus expressed as a complex number, and can be converted to the tensile modulus, etc., taking into account the Poisson's ratio of the sample.

[0075] The storage modulus of the pressure-sensitive adhesive layer of the present invention can be controlled by the monomer composition of the base polymer (acrylic polymer), the weight average molecular weight, the amount (addition amount) of the crosslinking agent used, and the types and amounts of other additives used.

[0076] [1-5-5. 300% tensile residual stress of adhesive layer] The 300% tensile residual stress of the pressure-sensitive adhesive layer (pressure-sensitive adhesive layer A and pressure-sensitive adhesive layer B) of the present invention is not particularly limited, but is preferably 2 to 24 N / cm 2 is preferable, and more preferably 2.5 to 20 N / cm 2 , and more preferably 3 to 16 N / cm 2 The above 300% tensile residual stress is 2N / cm 2 When the 300% tensile residual stress is 24 N / cm or more, good resistance to foaming and peeling can be easily obtained, which is preferable. 2 If it is equal to or less, good stress relaxation properties can be obtained, and good step conformability can be easily obtained, which is preferable.

[0077] The pressure-sensitive adhesive layer of the present invention, having a 300% tensile residual stress within a specific range, is likely to exhibit excellent stress relaxation properties and excellent step-conforming ability, for example, even for large steps (e.g., steps having a height of about 45 μm, particularly steps having a height of 20 to 50 μm).

[0078] The 300% tensile residual stress is determined by pulling the adhesive layer in the length direction to an elongation (strain) of 300% in an environment of 23°C and 50% RH, maintaining the elongation, and determining the tensile load applied to the adhesive layer 300 seconds after the end of pulling, and dividing the tensile load by the initial cross-sectional area of ​​the adhesive layer (the cross-sectional area before pulling) (N / cm 2 ) The initial elongation of the adhesive layer is 100%.

[0079] The 300% tensile residual stress of the pressure-sensitive adhesive layer of the present invention can be controlled by the monomer composition of the base polymer (acrylic polymer), the weight average molecular weight, the amount (addition amount) of crosslinking agent used, and the types and amounts of other additives used.

[0080] [1-5-6. Thickness of adhesive layer] The thickness of the pressure-sensitive adhesive layer (pressure-sensitive adhesive layer A and pressure-sensitive adhesive layer B) 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 particularly preferably 12 to 300 μm. A thickness of at least a certain level is preferred because it improves step-following ability and adhesive reliability. On the other hand, a thickness of less than a certain level is preferred because it is less likely to absorb foreign matter during handling and is particularly easy to manufacture.

[0081] [1-5-7. Method for manufacturing adhesive layer] The method for producing the pressure-sensitive adhesive layer (pressure-sensitive adhesive layer A and pressure-sensitive adhesive layer B) of the present invention is not particularly limited, but examples thereof include coating (applying) the pressure-sensitive adhesive composition for forming the pressure-sensitive adhesive layer of the present invention onto a substrate or a release liner, and then drying, curing, or drying and curing as necessary. Curing can be carried out by irradiation with active energy rays, heating, drying, etc.

[0082] The pressure-sensitive adhesive composition may be applied (coated) using a known coating method, such as a gravure roll coater, reverse roll coater, kiss roll coater, dip roll coater, bar coater, knife coater, spray coater, comma coater, or direct coater.

[0083] [1-6. Pressure-sensitive adhesive composition] In this specification, the pressure-sensitive adhesive composition for forming pressure-sensitive adhesive layer A may be referred to as "pressure-sensitive adhesive composition A," and the pressure-sensitive adhesive composition for forming pressure-sensitive adhesive layer B may be referred to as "pressure-sensitive adhesive composition B." Furthermore, in this specification, the term "pressure-sensitive adhesive composition of the present invention" includes both pressure-sensitive adhesive composition A and pressure-sensitive adhesive composition B, unless otherwise specified.

[0084] The pressure-sensitive adhesive compositions of the present invention (pressure-sensitive adhesive composition A and pressure-sensitive adhesive composition B) may have any form, such as a solvent type, an emulsion type, a hot-melt type, or a solventless type (active energy ray curable type, for example, a monomer mixture, or a partial polymer of a monomer mixture and the like).

[0085] As described above, the pressure-sensitive adhesive composition of the present invention may be solvent-based, i.e., it may contain an organic solvent. The organic solvent is not particularly limited as long as it is an organic compound used as a solvent, but 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 organic solvent may also be a mixed solvent containing two or more organic solvents.

[0086] The pressure-sensitive adhesive compositions of the present invention (pressure-sensitive adhesive composition A and pressure-sensitive adhesive composition B) have a low dielectric constant at 28 GHz, and are able to suppress millimeter-wave radiation loss in the pressure-sensitive adhesive layer of the present invention. The pressure-sensitive adhesive composition in the millimeter-wave antenna according to the first aspect of the present invention and the millimeter-wave antenna according to the third aspect of the present invention has a dielectric constant at a frequency of 28 GHz of 5 or less, preferably 4.5 or less, more preferably 4 or less, and even more preferably 3.5 or less, and may be 3.4 or less, 3.3 or less, 3.2 or less, 3.1 or less, 3.0 or less, or 2.9 or less. The lower limit of the dielectric constant at a frequency of 28 GHz is not particularly limited, but is preferably 2 or more, and may be 2.1 or more, or 2.2 or more. Furthermore, the pressure-sensitive adhesive composition in the millimeter-wave antenna according to the second aspect of the present invention and the millimeter-wave antenna according to the fourth aspect of the present invention preferably has a dielectric constant at a frequency of 28 GHz within the above range.

[0087] The dielectric constant at 28 GHz of the pressure-sensitive adhesive composition of the present invention can be adjusted by adjusting the type of base polymer constituting the pressure-sensitive adhesive composition, the monomer composition, the type and content of additives, and the like.

[0088] The dielectric constant of the pressure-sensitive adhesive composition B at 100 kHz is controlled to a relatively high level, and can improve the sensitivity of a touch sensor (particularly a capacitive touch sensor) using the millimeter-wave antenna of the present invention. The dielectric constant of the pressure-sensitive adhesive composition B at a frequency of 100 kHz is preferably 2 or more, more preferably 2.1 or more, and even more preferably 2.2 or more, and may be 2.3 or more, 2.4 or more, 2.5 or more, 2.6 or more, 2.7 or more, 2.8 or more, 2.9 or more, 3.0 or more, 3.5 or more, or 4.0 or more. The upper limit of the dielectric constant at a frequency of 100 kHz is not particularly limited, but from the viewpoint of suppressing malfunction of the touch panel, it is preferably 8 or less, and may be 7.5 or less, or 7 or less.

[0089] The dielectric constant at 100 kHz of the adhesive composition B can be adjusted by adjusting the type of base polymer constituting the adhesive composition B, the monomer composition, the type and content of additives, and the like.

[0090] The pressure-sensitive adhesive composition of the present invention has a low controlled dielectric loss at 28 GHz, and can suppress millimeter-wave radiation loss in the pressure-sensitive adhesive layer of the present invention. The pressure-sensitive adhesive composition in the millimeter-wave antenna according to the first aspect of the present invention and the millimeter-wave antenna according to the third aspect of the present invention has a dielectric loss at a frequency of 28 GHz of 0.05 or less, preferably 0.045 or less, more preferably 0.04 or less, even more preferably 0.035 or less, even more preferably 0.03 or less, still more preferably 0.025 or less, and particularly preferably 0.02 or less. The lower limit of the dielectric loss at a frequency of 28 GHz is not particularly limited, but is preferably 0.0001 or more, and may be 0.0005 or more, or 0.001 or more. Furthermore, the pressure-sensitive adhesive composition in the millimeter-wave antenna according to the second aspect of the present invention and the millimeter-wave antenna according to the fourth aspect of the present invention preferably has a dielectric loss at a frequency of 28 GHz within the above range.

[0091] The dielectric loss at 28 GHz of the pressure-sensitive adhesive composition of the present invention can be adjusted by adjusting the type of base polymer constituting the pressure-sensitive adhesive composition, the monomer composition, the type and content of additives, and the like.

[0092] The pressure-sensitive adhesive composition of the present invention is preferred in that it has a low dielectric constant at 60 GHz and can suppress millimeter-wave radiation loss in the pressure-sensitive adhesive layer of the present invention. The pressure-sensitive adhesive composition in the millimeter-wave antenna according to the second aspect of the present invention and the millimeter-wave antenna according to the fourth aspect of the present invention has a dielectric constant at a frequency of 60 GHz of 5 or less, preferably 4.5 or less, more preferably 4 or less, and even more preferably 3.5 or less, and may be 3.4 or less, 3.3 or less, 3.2 or less, 3.1 or less, 3.0 or less, or 2.9 or less. The lower limit of the dielectric constant at a frequency of 60 GHz is not particularly limited, but is preferably 2 or more, and may be 2.1 or more, or 2.2 or more. Furthermore, the pressure-sensitive adhesive composition in the millimeter-wave antenna according to the first aspect of the present invention and the millimeter-wave antenna according to the third aspect of the present invention preferably has a dielectric constant at a frequency of 60 GHz within the above range.

[0093] The dielectric constant at 60 GHz of the pressure-sensitive adhesive composition of the present invention can be adjusted by adjusting the type of base polymer constituting the pressure-sensitive adhesive composition, the monomer composition, the type and content of additives, and the like.

[0094] The pressure-sensitive adhesive composition of the present invention is preferred in that it has a low dielectric loss at 60 GHz and can suppress millimeter-wave radiation loss in the pressure-sensitive adhesive layer of the present invention. The pressure-sensitive adhesive composition in the millimeter-wave antenna of the second aspect of the present invention and the millimeter-wave antenna of the fourth aspect of the present invention has a dielectric loss at a frequency of 60 GHz of 0.05 or less, preferably 0.045 or less, more preferably 0.04 or less, even more preferably 0.035 or less, even more preferably 0.03 or less, still more preferably 0.025 or less, and particularly preferably 0.02 or less, and may be 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 not particularly limited, but is preferably 0.0001 or more, and may be 0.0005 or more, or 0.001 or more. The pressure-sensitive adhesive composition in the millimeter-wave antenna according to the first aspect of the present invention and the millimeter-wave antenna according to the third aspect of the present invention preferably has a dielectric loss at a frequency of 60 GHz within the above range.

[0095] The dielectric loss at 60 GHz of the pressure-sensitive adhesive composition of the present invention can be adjusted by adjusting the type of base polymer constituting the pressure-sensitive adhesive composition, the monomer composition, the type and content of additives, and the like.

[0096] The base polymer constituting the pressure-sensitive adhesive composition of the present invention is not particularly limited, and examples thereof include an acrylic polymer contained as a base polymer in an acrylic pressure-sensitive adhesive composition, a rubber polymer contained as a base polymer in a rubber-based pressure-sensitive adhesive composition (such as a natural rubber-based pressure-sensitive adhesive composition or a synthetic rubber-based pressure-sensitive adhesive composition), a silicone polymer contained as a base polymer in a silicone-based pressure-sensitive adhesive composition, a polyester polymer contained as a base polymer in a polyester-based pressure-sensitive adhesive composition, a urethane polymer contained as a base polymer in a urethane-based pressure-sensitive adhesive composition, a polyamide polymer contained as a base polymer in a polyamide-based pressure-sensitive adhesive composition, an epoxy polymer contained as a base polymer in an epoxy-based pressure-sensitive adhesive composition, a vinyl alkyl ether polymer contained as a base polymer in a vinyl alkyl ether-based pressure-sensitive adhesive composition, and a fluorine-based polymer contained as a base polymer in a fluorine-based pressure-sensitive adhesive composition. Among these, acrylic polymers and rubber-based polymers are preferred as the base polymer in terms of controlling the dielectric constant and dielectric loss low in the high frequency band and transparency, weather resistance, adhesion reliability, etc. That is, the pressure-sensitive adhesive composition of the present invention is preferably an acrylic pressure-sensitive adhesive composition containing an acrylic polymer described below as a base polymer, or a rubber pressure-sensitive adhesive composition containing a rubber polymer described below as a base polymer. The base polymer may be used alone or in combination of two or more kinds.

[0097] In this specification, the term "base polymer" refers to the main component (the component with the largest blending ratio; the same applies hereinafter) among the polymer components contained in the pressure-sensitive adhesive composition, and typically refers to a component that accounts for more than 50% by weight of the above polymer components. In addition, in this specification, the term "base polymer" includes "a mixture of monomer components constituting the base polymer or a partial polymer of the mixture of monomer components constituting the base polymer." In this specification, the "mixture of monomer components" includes a mixture consisting of a single monomer component and a mixture consisting of two or more monomer components. Furthermore, the "partially polymerized product of the mixture of monomer components" refers to a composition in which one or more of the constituent monomer components of the "mixture of monomer components" are partially polymerized.

[0098] The content of the base polymer in the pressure-sensitive adhesive composition of the present invention is not particularly limited, but is preferably 75% by weight or more (for example, 75 to 99.9% by weight), and more preferably 85% by weight or more (for example, 85 to 99.9% by weight).

[0099] The pressure-sensitive adhesive composition of the present invention preferably does not contain or substantially does not contain an acidic group-containing monomer (e.g., a carboxyl group-containing monomer, a sulfo group-containing monomer, a phosphate group-containing monomer, etc.). This configuration is preferable in that it can provide excellent corrosion prevention effects for antenna elements or wiring. The content of the acidic group-containing monomer is preferably 0.05 wt % or less (e.g., 0 to 0.05 wt %), more preferably 0.01 wt % or less (e.g., 0 to 0.01 wt %), and even more preferably 0.001 wt % or less (e.g., 0 to 0.001 wt %), relative to the total amount of the pressure-sensitive adhesive composition, and it can be said that the pressure-sensitive adhesive composition is substantially free of such monomers.

[0100] [1-6-1. Acrylic polymer (A)] The pressure-sensitive adhesive composition of the present invention is preferably an acrylic pressure-sensitive adhesive composition containing an acrylic polymer as a main component. In this specification, the acrylic polymer contained as a base polymer in the acrylic pressure-sensitive adhesive composition may be referred to as "acrylic polymer (A)." The specific content of the acrylic polymer (A) is not particularly limited, but is preferably 75 wt % or more (e.g., 75 to 99.9 wt %), and more preferably 85 wt % or more (e.g., 85 to 99.9 wt %), relative to the total amount of the pressure-sensitive adhesive composition of the present invention (total weight, 100 wt %).

[0101] The pressure-sensitive adhesive composition containing the acrylic polymer (A) as the main component is not particularly limited, but examples thereof include a composition containing the acrylic polymer (A) as an essential component; a composition containing a mixture of monomer components constituting the acrylic polymer (A) (sometimes referred to as a "monomer mixture") or a composition containing a partially polymerized product thereof as an essential component; and the like. Examples of the former include, but are not limited to, so-called solvent-based and water-dispersed compositions (emulsion-based compositions), and examples of the latter include so-called active energy ray-curable compositions. The pressure-sensitive adhesive composition may contain other additives as needed.

[0102] The "monomer mixture" includes a mixture composed of a single monomer component and a mixture composed of two or more monomer components. The "partially polymerized product" refers to a composition in which one or more of the components of the monomer mixture are partially polymerized. Among these, the pressure-sensitive adhesive composition is preferably a composition containing a monomer mixture or a partially polymerized product thereof as an essential component.

[0103] The monomer component may be a macromonomer. A macromonomer is a high-molecular-weight monomer formed by polymerizing a plurality of the above-mentioned monomer components. When a macromonomer is used, structural units derived from the monomer components constituting the macromonomer are present in the base polymer in a certain degree of continuity. Therefore, by using the macromonomer, a high-order structure derived from the macromonomer can be introduced into the base polymer, and the properties required for the pressure-sensitive adhesive (adhesive strength, cohesive strength, step-conforming ability, etc.) can be easily adjusted. The weight-average molecular weight of the macromonomer is preferably 3,000 to 35,000, more preferably 4,000 to 30,000, even more preferably 5,000 to 25,000, and particularly preferably 6,000 to 20,000.

[0104] The acrylic polymer (A) is a polymer containing an acrylic monomer as an essential monomer unit (monomer unit, monomer constituent unit). In other words, the acrylic polymer (A) is a polymer containing a constituent unit derived from an acrylic monomer as a constituent unit. In other words, the acrylic polymer (A) is a polymer constituted (formed) with an acrylic monomer as an essential monomer component.

[0105] The acrylic polymer (A) is preferably a polymer containing, as an essential monomer unit, a (meth)acrylic acid alkyl ester having a linear or branched alkyl group (hereinafter, sometimes simply referred to as "(meth)acrylic acid alkyl ester"). In this specification, "(meth)acrylic" refers to either or both of "acrylic" and "methacrylic", and the same applies to others.

[0106] The acrylic polymer (A) is preferably a polymer containing, as monomer units, a (meth)acrylic acid alkyl ester having a branched alkyl group having 10 to 24 carbon atoms (hereinafter sometimes referred to as "(meth)acrylic acid alkyl ester (A1)") and / or a methacrylic acid ester having a hydrocarbon group having 6 or more carbon atoms (hereinafter sometimes referred to as "methacrylic acid ester (A2)"). That is, the acrylic polymer (A) is preferably obtained by polymerizing a monomer component containing a (meth)acrylic acid alkyl ester having a long-chain branched alkyl group such as the (meth)acrylic acid alkyl ester (A1) or a methacrylic acid ester having a long-chain hydrocarbon group such as the methacrylic acid ester (A2). The long-chain branched alkyl group, the long-chain hydrocarbon group, and the methacrylic moiety enable the realization of a pressure-sensitive adhesive layer having a low dielectric constant and low dielectric loss in the high frequency band. Even when the pressure-sensitive adhesive layer of the present invention is attached to a substrate equipped with a millimeter-wave antenna, the low dielectric constant and low dielectric loss of the pressure-sensitive adhesive layer of the present invention in the high frequency band can suppress millimeter-wave radiation loss. The (meth)acrylic acid alkyl ester (A1) and the methacrylic acid ester (A2) may each contain a compound that falls into any of these categories.

[0107] According to the Clausius-Mossotti equation, reducing the molecular dipole moment and increasing the molar volume is believed to be sufficient to reduce the dielectric constant and dielectric loss in the high frequency band. When the base polymer, which is the main component of the pressure-sensitive adhesive composition of the present invention, is an acrylic polymer (A), using a (meth)acrylic acid alkyl ester (A1) as the main monomer unit increases the molar volume of the pressure-sensitive adhesive layer obtained from the pressure-sensitive adhesive composition of the present invention due to the presence of a long-chain branched alkyl group, and furthermore, the branched alkyl group is believed to reduce the dipole moment. Thus, a pressure-sensitive adhesive composition having a balance between increasing the molar volume and reducing the dipole moment is believed to be achieved when using a (meth)acrylic acid alkyl ester (A1) having a branched alkyl group with 10 to 24 carbon atoms as the alkyl group.

[0108] Furthermore, when the base polymer, which is the main component of the pressure-sensitive adhesive composition of the present invention, is an acrylic polymer (A), if a methacrylic acid ester (A2) is used as the main monomer unit, polarization is biased toward the acrylic moiety, which is the side chain of an acrylic acid alkyl ester, whereas the methacrylic moiety in the methacrylic acid ester (A2) has an α-methyl group, which reduces polarization near the main chain, and as a result, dielectric loss is thought to be reduced. This is also thought to be because the methacrylic moiety is more hydrophobic than the acrylic moiety, and deterioration of dielectric loss due to moisture absorption can be suppressed.

[0109] The Tg of the homopolymer of the (meth)acrylic acid alkyl ester (A1) (a (meth)acrylic acid alkyl ester having a branched alkyl group with 10 to 24 carbon atoms) is preferably −80 to 0°C, and more preferably −70 to −10°C. When the Tg of the homopolymer is −80°C or higher, the elastic modulus of the pressure-sensitive adhesive layer at room temperature can be prevented from decreasing too much. When the Tg of the homopolymer is 0°C or lower, appropriate adhesive strength can be ensured. The Tg of the homopolymer is a value measured by a differential scanning calorimeter (DSC). Furthermore, the branched alkyl group has 10 to 24 carbon atoms in order to satisfy the dielectric constant, dielectric loss, and appropriate elastic modulus in the high frequency band, but an alkyl (meth)acrylate having a suitable alkyl group can be appropriately selected depending on the production method of the acrylic polymer (A). For example, when the (meth)acrylic polymer (A) is produced by solution polymerization or the like, the alkyl group preferably has 10 to 18 carbon atoms, more preferably 10 to 16 carbon atoms, and even more preferably 10 to 14 carbon atoms. When the acrylic polymer (A) is produced by radiation polymerization or the like, the alkyl group preferably has 12 to 18 carbon atoms, and even more preferably 14 to 18 carbon atoms. Even if the Tg of the homopolymer relating to the (meth)acrylic acid alkyl ester is −80 to 0° C., if the alkyl group is linear or has 9 or less carbon atoms, the effect of reducing the dielectric constant and dielectric loss of the pressure-sensitive adhesive layer of the present invention in the high frequency band is not significant.

[0110] Examples of the (meth)acrylic acid alkyl ester (A1) include isodecyl acrylate (C10, homopolymer Tg = -60°C, hereinafter simply referred to as Tg), isodecyl methacrylate (C10, Tg = -41°C), isomistyryl acrylate (C14, Tg = -56°C), isostearyl acrylate (C18, Tg = -18°C), 2-propylheptyl acrylate, isoundecyl acrylate, isododecyl acrylate, isotridecyl acrylate, isopentadecyl acrylate, isohexadecyl acrylate, isoheptadecyl acrylate, and the above-exemplified methacrylate monomers. The (meth)acrylic acid alkyl ester (A1) can be used alone or in combination of two or more.

[0111] Among the branched alkyl groups having 10 to 24 carbon atoms, those having a branched alkyl group such as a t-butyl group at the terminal of the ester group are particularly preferred because they are thought to increase the molar volume and reduce the dipole moment, thereby providing a pressure-sensitive adhesive composition with a good balance between the two. They are also preferred because they have excellent compatibility with the acrylic polymer (A) and the additives described below. As the branched alkyl group at the terminal of the ester group, branched alkyl groups having 4 to 6 carbon atoms such as a t-butyl group, neopentyl group, and t-butyl group are preferred, with a t-butyl group being particularly preferred. A preferred example of the (meth)acrylic acid alkyl ester (A1) having a t-butyl group at the terminal of the ester group is isostearyl acrylate, as represented by the following formula: [ka]

[0112] Furthermore, as the (meth)acrylic acid alkyl ester (A1), methacrylic acid alkyl ester is preferable to acrylic acid alkyl ester in terms of the effect of lowering the dielectric constant and dielectric loss of the pressure-sensitive adhesive layer of the present invention in the high frequency band due to an increase in molar volume and a decrease in dipole moment. On the other hand, acrylic acid alkyl ester is preferable to methacrylic acid alkyl ester in terms of the ability to shorten the polymerization time of the acrylic polymer (A) and improve productivity. In particular, acrylic acid alkyl ester is suitable when the acrylic polymer (A) is cured by radiation polymerization.

[0113] The content (proportion) of the (meth)acrylic acid alkyl ester (A1) in all monomer units of the acrylic polymer (A) (total amount of monomer components constituting the acrylic polymer (A)) is not particularly limited, but is preferably 3 to 60% by weight, more preferably 5 to 55% by weight, and even more preferably 10 to 50% by weight, based on the total amount (100% by weight) of monomer components constituting the acrylic polymer (A). Using 3% by weight or more is preferred in terms of lowering the dielectric constant and dielectric loss in the high frequency band, while using 60% by weight or less is preferred in terms of maintaining adhesive strength and unevenness conformability.

[0114] The methacrylic acid ester (A2) has a hydrocarbon group having 6 or more carbon atoms in the ester moiety. Examples of the hydrocarbon group having 6 or more carbon atoms in the methacrylic acid ester (A2) include an aliphatic group, an alicyclic group, and an aromatic ring-containing group. Examples of the aliphatic group include linear or branched aliphatic groups.

[0115] 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.

[0116] Examples of the methacrylic acid ester (A2) in which the hydrocarbon group having 6 or more carbon atoms is an aliphatic group include alkyl methacrylates such as 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.

[0117] 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 8 or more, more preferably 10 or more. The number of carbon atoms in the hydrocarbon group is preferably 22 or less, more preferably 16 or less.

[0118] Examples of the methacrylic acid ester (A2) in which the hydrocarbon group having 6 or more carbon atoms is an alicyclic group include methacrylic acid cycloalkyl esters having a cycloalkane ring (such as a cyclopentane ring, a cyclohexane ring, a cycloheptane ring, or a cyclooctane ring), methacrylic acid esters having a bicyclic hydrocarbon ring (such as a pinane ring, a pinene ring, a bornane ring, a norbornane ring, or a norbornene ring), and methacrylic acid esters having a tricyclic or higher aliphatic hydrocarbon ring (such as a dicyclopentane ring, a dicyclopentene ring, an adamantane ring, a tricyclopentane ring, or a tricyclopentene ring).

[0119] Examples of the cycloalkyl methacrylate include cyclohexyl methacrylate, 3,3,5-trimethylcyclohexyl methacrylate, cycloheptyl methacrylate, and cyclooctyl methacrylate. Examples of the methacrylic acid ester having a bicyclic hydrocarbon ring include alkyl methacrylates such as bornyl methacrylate and isobornyl methacrylate. Examples of the methacrylic acid ester having a hydrocarbon ring with three or more rings include alkyl methacrylates such as dicyclopentanyl methacrylate, dicyclopentanyloxyethyl methacrylate, tricyclopentanyl methacrylate, 1-adamantyl methacrylate, 2-methyl-2-adamantyl methacrylate, and 2-ethyl-2-adamantyl methacrylate.

[0120] When the hydrocarbon group having 6 or more carbon atoms is an aromatic ring-containing group, the hydrocarbon group preferably has 6 to 14 carbon atoms, and more preferably 6 to 10 carbon atoms.

[0121] Examples of the methacrylic acid ester (A2) in which the hydrocarbon group having 6 or more carbon atoms is an aromatic ring-containing group include compounds having an aromatic carbon ring (for example, a monocyclic carbon ring such as a benzene ring, or a fused carbon ring such as a naphthalene ring), and specific examples thereof include methacrylic acid esters such as benzyl methacrylate, phenyl methacrylate, naphthyl methacrylate, and 6-(1,1'-biphenyl-4-yloxy)hexyl methacrylate.

[0122] The methacrylic acid ester (A2) may have a (poly)oxyalkylene chain. When the methacrylic acid ester (A2) has a (poly)oxyalkylene chain, the hydrocarbon group having 6 or more carbon atoms is preferably present at the terminal of the ester moiety in the methacrylic acid ester (A2). The number of oxygen atoms in the (poly)oxyalkylene chain (i.e., the number of repeating oxyalkylene groups) is preferably 1 to 10, more preferably 1 to 3. The hydrocarbon group having 6 or more carbon atoms at the terminal may be an aliphatic group, an alicyclic group, or an aromatic group, but is preferably an alicyclic group or an aromatic group.

[0123] Examples of the methacrylic acid ester (A2) having a (poly)oxyalkylene chain and a hydrocarbon group having 6 or more carbon atoms include 2-phenoxyethyl methacrylate.

[0124] The content (proportion) of the methacrylic acid ester (A2) in all monomer units of the acrylic polymer (A) (total amount of monomer components constituting the acrylic polymer (A)) is not particularly limited, but is preferably 10% by weight or more (e.g., 10 to 99.9% by weight), more preferably 15% by weight or more (e.g., 15 to 99.7% by weight), and even more preferably 20% by weight or more (e.g., 20 to 99.5% by weight) relative to the total amount (100% by weight) of monomer components constituting the acrylic polymer (A). Using 15% by weight or more is preferred in terms of achieving a low dielectric constant and low dielectric loss in the high frequency band. Using 99.9% by weight or less is preferred in terms of maintaining adhesive strength and conformability to uneven surfaces.

[0125] The total content (proportion) of the (meth)acrylic acid alkyl ester (A1) and the methacrylic acid ester (A2) in all monomer units of the acrylic polymer (A) (total amount of monomer components constituting the acrylic polymer (A)) is not particularly limited, but is preferably 3 to 99.9 wt %, more preferably 5 to 99.7 wt %, and even more preferably 10 to 99.5 wt %, based on the total amount (100 wt %) of monomer components constituting the acrylic polymer (A). Using 3 wt % or more is preferred in terms of lowering the dielectric constant and dielectric loss in the high frequency band, while using 99.9 wt % or less is preferred in terms of maintaining adhesive strength and unevenness conformability.

[0126] The acrylic polymer (A) may contain, as a monomer component, a (meth)acrylic acid alkyl ester other than the (meth)acrylic acid alkyl ester (A1) and the methacrylic acid ester (A2) (hereinafter, sometimes referred to as "(meth)acrylic acid alkyl ester (B)"), together with the (meth)acrylic acid alkyl ester (A1) and / or the methacrylic acid ester (A2), or instead of the (meth)acrylic acid alkyl ester (A1) and / or the methacrylic acid ester (A2). By containing the (meth)acrylic acid alkyl ester (B), it is possible to adjust the Tg of the acrylic polymer (A) itself, to control the cohesive strength and adhesive strength of the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention, and to improve stress relaxation properties and step-conformability.

[0127] Examples of the (meth)acrylic acid alkyl ester (B) include acrylic acid alkyl esters having a linear alkyl group with 1 to 24 carbon atoms, acrylic acid alkyl esters having a branched alkyl group with 3 to 9 carbon atoms, methacrylic acid alkyl esters having a linear alkyl group with 1 to 5 carbon atoms, and methacrylic acid alkyl esters having a branched alkyl group with 3 to 5 carbon atoms, and from the viewpoint of realizing a low dielectric constant and low dielectric loss in the high frequency band of the pressure-sensitive adhesive layer of the present invention, acrylic acid alkyl esters having a linear alkyl group with 10 to 24 carbon atoms are preferred. The (meth)acrylic acid alkyl esters (B) can be used singly or in combination of two or more.

[0128] Examples of the alkyl acrylate ester having a linear alkyl group having 1 to 24 carbon atoms include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate (n-butyl acrylate), pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, nonyl acrylate, decyl acrylate, undecyl acrylate, dodecyl acrylate, tridecyl acrylate, tetradecyl acrylate, pentadecyl acrylate, hexadecyl acrylate, heptadecyl acrylate, octadecyl acrylate, nonadecyl acrylate, and eicosyl acrylate.

[0129] Examples of alkyl acrylates having a branched alkyl group having 3 to 9 carbon atoms include isopropyl acrylate, isobutyl acrylate, s-butyl acrylate, t-butyl acrylate, isopentyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, and isononyl acrylate.

[0130] Examples of the alkyl methacrylate ester having a linear alkyl group having 1 to 5 carbon atoms include methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate (n-butyl methacrylate), pentyl methacrylate, etc. Examples of the alkyl methacrylate ester having a branched alkyl group having 3 to 5 carbon atoms include isopropyl methacrylate, isobutyl methacrylate, s-butyl methacrylate, t-butyl methacrylate, isopentyl methacrylate, etc.

[0131] The Tg of the homopolymer of (meth)acrylic acid alkyl ester (B) is not particularly limited, but is preferably −100°C or higher (for example, −100 to 150°C), more preferably −90 to 140°C, and even more preferably −90 to 120°C. The Tg of the homopolymer may be −30°C or lower, or may be −40°C or lower. When the homopolymer has a Tg of −100°C or higher, it is possible to prevent the elastic modulus of the pressure-sensitive adhesive layer at room temperature from decreasing too much. By using a mixture of the acrylic polymer (A) and the meth)acrylic acid alkyl ester (B) having a high homopolymer Tg, it is possible to adjust the cohesive strength and adhesive strength of the pressure-sensitive adhesive layer and appropriately impart stress relaxation properties and step-conforming properties.

[0132] Among these, from the viewpoint of improving the stress relaxation properties of the pressure-sensitive adhesive layer and adjusting the step-conforming ability, the (meth)acrylic acid alkyl ester (B) is preferably an acrylic acid alkyl ester having a branched alkyl group with 6 to 9 carbon atoms, more preferably an acrylic acid alkyl ester having a branched alkyl group with 7 to 9 carbon atoms, and particularly 2-ethylhexyl acrylate (branched alkyl group with 8 carbon atoms, Tg = -70°C).Furthermore, from the viewpoint of reducing the dielectric constant and dielectric loss in the high frequency band, the (meth)acrylic acid alkyl ester is preferably an acrylic acid alkyl ester having a linear alkyl group with 8 to 24 carbon atoms, more preferably an acrylic acid alkyl ester having a linear alkyl group with 10 to 24 carbon atoms, and particularly lauryl acrylate (linear alkyl group with 12 carbon atoms, Tg = -50°C).

[0133] Furthermore, as the (meth)acrylic acid alkyl ester (B), methacrylic acid alkyl ester is preferable to acrylic acid alkyl ester in terms of the effect of lowering the dielectric constant and dielectric loss of the pressure-sensitive adhesive layer of the present invention in the high frequency band due to an increase in molar volume and a decrease in dipole moment. On the other hand, acrylic acid alkyl ester is preferable to methacrylic acid alkyl ester in terms of the ability to shorten the polymerization time of the acrylic polymer (A) and improve productivity. In particular, acrylic acid alkyl ester is suitable when the acrylic polymer (A) is cured by radiation polymerization.

[0134] The content (proportion) of the (meth)acrylic acid alkyl ester (B) in all monomer units of the acrylic polymer (A) (total amount of monomer components constituting the acrylic polymer (A)) is not particularly limited, but is preferably 1% by weight or more (for example, 1 to 95% by weight, more preferably 3 to 93% by weight, even more preferably 10 to 90% by weight, and particularly preferably 20 to 85% by weight) relative to the total amount (100% by weight) of monomer components constituting the acrylic polymer (A). Using 1% by weight or more is preferred in terms of adhesive strength, conformability to unevenness, and low dielectric constant and low dielectric loss of the pressure-sensitive adhesive layer of the present invention in the high frequency band (28 to 60 GHz).

[0135] The total content (proportion) of alkyl acrylates having a linear alkyl group containing 1 to 24 carbon atoms (more preferably alkyl acrylates having a linear alkyl group containing 10 to 24 carbon atoms) and alkyl methacrylates having a linear alkyl group containing 1 to 5 carbon atoms in all monomer units of the acrylic polymer (A) (total amount of monomer components constituting the acrylic polymer (A)) is not particularly limited, but is preferably 0.1 wt% or more (e.g., 0.1 to 97 wt%), more preferably 1 to 95 wt%, even more preferably 3 to 90 wt%, even more preferably 10 to 80 wt%, even more preferably 15 to 75 wt%, and particularly preferably 20 to 70 wt% relative to the total amount (100 wt%) of monomer components constituting the acrylic polymer (A). Using 0.1 wt% or more is preferred in terms of reducing the dielectric constant and dielectric loss of the pressure-sensitive adhesive layer of the present invention in the high frequency range (28 to 60 GHz).

[0136] The total content (proportion) of the alkyl acrylate having a branched alkyl group containing 3 to 9 carbon atoms (preferably an alkyl acrylate having a branched alkyl group containing 6 to 9 carbon atoms) and the alkyl methacrylate having a branched alkyl group containing 3 to 5 carbon atoms in all monomer units of the acrylic polymer (A) (total amount of monomer components constituting the acrylic polymer (A)) is not particularly limited, but is preferably 0.1 wt% or more (e.g., 0.1 to 80 wt%), more preferably 1 to 70 wt%, even more preferably 3 to 60 wt%, even more preferably 10 to 60 wt%, and particularly preferably 20 to 50 wt%, relative to the total amount (100 wt%) of the monomer components constituting the acrylic polymer (A). Using 0.1 wt% or more is preferred in terms of adhesive strength and conformability to uneven surfaces.

[0137] The acrylic polymer (A) may contain, as monomer units, a copolymerizable monomer (copolymerizable monomer) in addition to the (meth)acrylic acid alkyl ester (A1), the methacrylic acid ester (A2), and the (meth)acrylic acid alkyl ester (B). That is, the acrylic polymer (A) may contain a copolymerizable monomer as a constituent monomer component. The copolymerizable monomer may be used alone or in combination of two or more kinds.

[0138] Examples of the copolymerizable monomer include hydroxyl-containing monomers. When the acrylic polymer (A) contains a hydroxyl-containing monomer as a monomer unit, the constituent monomer components are more easily polymerized, and good cohesive strength is more easily obtained. This makes it easier to obtain strong adhesion, and also makes it easier to increase the gel fraction and obtain excellent foaming and peeling resistance. Furthermore, it makes it easier to suppress whitening of the pressure-sensitive adhesive sheet, which can occur in high-humidity environments. On the other hand, when the acrylic polymer (A) contains a large amount of hydroxyl-containing monomer as a monomer unit, the dielectric constant and dielectric loss of the pressure-sensitive adhesive layer of the present invention tend to increase in the high-frequency band.

[0139] The content (ratio) of the hydroxyl group-containing monomer relative to the total amount (100 wt%) of the monomer components constituting the acrylic polymer (A) is not particularly limited. A certain amount of the hydroxyl group-containing monomer contributes to improved cohesive strength, adhesion, adhesive reliability such as foam-peeling resistance, and dielectric constant in the low frequency band (100 kHz) of the pressure-sensitive adhesive layer B. The lower limit of the content of the hydroxyl group-containing monomer is preferably 0.01 wt% or more, more preferably 0.05 wt% or more, even more preferably 0.1 wt% or more, still more preferably 0.5 wt% or more, and particularly preferably 1 wt% or more. To achieve a low dielectric constant and low dielectric loss in the high frequency band of the pressure-sensitive adhesive layer of the present invention, the content of the hydroxyl group-containing monomer is preferably 30 wt% or less, more preferably 25 wt% or less, even more preferably 20 wt% or less, and particularly preferably 15 wt% or less. In some embodiments of the present invention, the acrylic polymer (A) may not contain a hydroxyl group-containing monomer.

[0140] Further, examples of the copolymerizable monomer include nitrogen-containing monomers. When the acrylic polymer (A) contains a nitrogen-containing monomer as a monomer unit, it is easier to obtain a moderate cohesive strength. This increases the 180° peel adhesion strength to a glass plate and the 180° peel adhesion strength to an acrylic plate, making it easier to obtain strong adhesion, and also increases the gel fraction, making it easier to obtain excellent anti-foaming / peeling properties. Furthermore, it makes it easier to obtain moderate flexibility in the pressure-sensitive adhesive layer, adjusts the 300% tensile residual stress within a specific range, and makes it easier to obtain excellent stress relaxation properties and excellent step-following properties. It is also preferable from the viewpoint of improving the dielectric constant of the pressure-sensitive adhesive layer B in the low frequency band (100 kHz). The rust inhibitors described below have selectivity in solubility in monomers. For example, benzotriazole-based compounds, which are one type of rust inhibitor, have good solubility in nitrogen-containing monomers.

[0141] When the acrylic polymer (A) contains the nitrogen-atom-containing monomer as a monomer component constituting the polymer, the proportion of the nitrogen-atom-containing monomer in the total monomer components (100 wt%) constituting the acrylic polymer (A) is not particularly limited, but is preferably 1 wt% or more, more preferably 3 wt% or more, and even more preferably 5 wt% or more. A proportion of 1 wt% or more is preferred from the viewpoints of easily achieving good cohesive strength and adhesive reliability at high temperatures. Furthermore, this is preferred because it further suppresses clouding and improves durability in high-humidity environments, thereby achieving higher adhesive reliability to adherends. It is also preferred from the viewpoint of improving the dielectric constant of the pressure-sensitive adhesive layer B in the low-frequency band (100 kHz). Furthermore, the proportion of the nitrogen-atom-containing monomer is preferably 30 wt% or less, more preferably 25 wt% or less, even more preferably 20 wt% or less, even more preferably 15 wt% or less, and particularly preferably 10 wt% or less, from the viewpoints of obtaining a pressure-sensitive adhesive layer having appropriate flexibility and excellent transparency.

[0142] Furthermore, the copolymerizable monomer may be an alicyclic structure-containing monomer. When the acrylic polymer (A) contains an alicyclic structure-containing monomer as a monomer unit, it is easier to obtain a moderate cohesive strength. As a result, it is easier to obtain strong adhesion by increasing the 180° peel adhesive strength to a glass plate and the 180° peel adhesive strength to an acrylic plate, and it is easier to obtain strong adhesion. It is also easier to obtain excellent foaming and peel resistance by increasing the gel fraction. Furthermore, it is easier to obtain moderate flexibility in the pressure-sensitive adhesive layer, and it is easier to adjust the 300% tensile residual stress within a specific range, making it easier to obtain excellent stress relaxation properties and excellent step-conforming properties.

[0143] When the acrylic polymer (A) contains the alicyclic structure-containing monomer as a monomer component constituting the polymer, the proportion of the alicyclic structure-containing monomer in the total monomer components (100 wt%) constituting the acrylic polymer (A) is not particularly limited, but is preferably 1 wt% or more, more preferably 5 wt% or more, and even more preferably 10 wt% or more, from the viewpoint of improving durability and obtaining high adhesive reliability. Furthermore, the proportion of the alicyclic structure-containing monomer is preferably 50 wt% or less, more preferably 45 wt% or less, even more preferably 40 wt% or less, even more preferably 30 wt% or less, even more preferably 25 wt% or less, and particularly preferably 20 wt% or less, from the viewpoint of obtaining a pressure-sensitive adhesive layer having appropriate flexibility. Furthermore, in some embodiments of the present invention, the acrylic polymer (A) may not contain the alicyclic structure-containing monomer.

[0144] The acrylic polymer (A) can be obtained by polymerizing the monomer units (monomer components) by a known or conventional polymerization method. Examples of the polymerization method for the acrylic polymer (A) include solution polymerization, emulsion polymerization, bulk polymerization, and polymerization by active energy ray irradiation (active energy ray polymerization). Among these, in terms of transparency, water resistance, cost, etc. of the pressure-sensitive adhesive layer, solution polymerization and active energy ray polymerization are preferred, and active energy ray polymerization is more preferred.

[0145] Examples of the active energy rays irradiated during the active energy ray polymerization (photopolymerization) include ionizing radiation such as α-rays, β-rays, γ-rays, neutron beams, and electron beams, as well as ultraviolet rays, with ultraviolet rays being particularly preferred. The irradiation energy, irradiation time, irradiation method, and the like 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.

[0146] Various common solvents may be used in the polymerization of the acrylic polymer (A). Examples of such solvents include organic solvents such as esters such as ethyl acetate and n-butyl acetate; aromatic hydrocarbons such as toluene and benzene; aliphatic hydrocarbons such as n-hexane and n-heptane; alicyclic hydrocarbons such as cyclohexane and methylcyclohexane; and ketones such as methyl ethyl ketone and methyl isobutyl ketone. The solvents may be used alone or in combination of two or more.

[0147] In addition, when polymerizing the acrylic polymer (A), a polymerization initiator such as a thermal polymerization initiator or a photopolymerization initiator (photoinitiator) may be used depending on the type of polymerization reaction. The polymerization initiator may be used alone or in combination of two or more kinds.

[0148] The photopolymerization initiator is not particularly limited, and examples thereof 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, etc. The photopolymerization initiators may be used alone or in combination of two or more.

[0149] Examples of the benzoin ether-based photopolymerization initiator include benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, benzoin isopropyl ether, benzoin isobutyl ether, 2,2-dimethoxy-1,2-diphenylethan-1-one, and anisole methyl ether. Examples of the acetophenone-based photopolymerization initiator include 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexyl phenyl ketone, 4-phenoxydichloroacetophenone, and 4-(t-butyl)dichloroacetophenone. Examples of the α-ketol-based photopolymerization initiator include 2-methyl-2-hydroxypropiophenone and 1-[4-(2-hydroxyethyl)phenyl]-2-methylpropan-1-one. Examples of the aromatic sulfonyl chloride-based photopolymerization initiator include 2-naphthalenesulfonyl chloride. Examples of the photoactive oxime-based photopolymerization initiator include 1-phenyl-1,1-propanedione-2-(o-ethoxycarbonyl)-oxime. Examples of the benzoin-based photopolymerization initiator include benzoin. Examples of the benzyl-based photopolymerization initiator include benzil. Examples of the benzophenone-based photopolymerization initiator include benzophenone, benzoylbenzoic acid, 3,3'-dimethyl-4-methoxybenzophenone, polyvinylbenzophenone, and α-hydroxycyclohexyl phenyl ketone. Examples of the ketal-based photopolymerization initiator include benzil dimethyl ketal. Examples of the thioxanthone-based photopolymerization initiator include thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 2,4-diisopropylthioxanthone, and dodecylthioxanthone.

[0150] The amount of the photopolymerization initiator used is not particularly limited, but is preferably 0.001 to 1 part by weight, and more preferably 0.01 to 0.50 parts by weight, relative to 100 parts by weight of all monomer units of the acrylic polymer (A) (total amount of monomer components constituting the acrylic polymer (A)).

[0151] The thermal polymerization initiator is not particularly limited, but examples thereof include azo polymerization initiators, peroxide polymerization initiators (e.g., dibenzoyl peroxide, tert-butyl permaleate, etc.), and redox polymerization initiators. Among these, the azo polymerization initiators disclosed in JP-A-2002-69411 are preferred. Examples of the azo polymerization initiator include 2,2'-azobisisobutyronitrile (hereinafter sometimes referred to as "AIBN"), 2,2'-azobis-2-methylbutyronitrile (hereinafter sometimes referred to as "AMBN"), 2,2'-azobis(2-methylpropionate) dimethyl, and 4,4'-azobis-4-cyanovaleric acid.

[0152] The amount of the thermal polymerization initiator used is not particularly limited, but for example, in the case of the azo-based polymerization initiator, it is preferably 0.05 to 0.5 parts by weight, and more preferably 0.1 to 0.3 parts by weight, per 100 parts by weight of all monomer units of the acrylic polymer (A) (total amount of monomer components constituting the acrylic polymer (A)).

[0153] [1-6-2. Carboxyl group-containing monomers, etc.] When the pressure-sensitive adhesive composition of the present invention contains an acrylic polymer (A) as a base polymer, it may contain a carboxyl group-containing monomer as a monomer component constituting the acrylic polymer (A). However, it is preferable that the acrylic polymer (A) is substantially free of carboxyl group-containing monomers. Here, "substantially free of" means that the acrylic polymer (A) is not actively blended except in cases where it is inevitably mixed in. Furthermore, a carboxyl group-containing monomer refers to a monomer having at least one carboxyl group in its molecule. From the viewpoint of obtaining a more excellent corrosion prevention effect, specifically, a carboxyl group-containing monomer content of preferably 0.05 wt% or less (e.g., 0 to 0.05 wt%), more preferably 0.01 wt% or less (e.g., 0 to 0.01 wt%), and even more preferably 0.001 wt% or less (e.g., 0 to 0.001 wt%), based on the total amount (100 wt%) of the monomer components constituting the acrylic polymer (A), can be said to be substantially free of carboxyl group-containing monomers. Examples of the carboxyl group-containing monomer include (meth)acrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid. The carboxyl group-containing monomer also includes acid anhydride group-containing monomers such as maleic anhydride and itaconic anhydride. The carboxyl group-containing monomer may also be a derivative formed by ester bonding with itaconic acid or the like.

[0154] When the pressure-sensitive adhesive composition of the present invention contains an acrylic polymer (A) as a base polymer, from the viewpoint of obtaining even more excellent corrosion prevention effects, it is preferable that the monomer components constituting the acrylic polymer (A) are not substantially containing carboxyl group-containing monomers, and that the monomer components constituting the acrylic polymer (A) are also substantially free of monomers having acidic groups other than carboxyl groups (e.g., sulfo groups, phosphate groups). That is, the acrylic polymer (A) preferably contains substantially no carboxyl group-containing monomers or other monomers having acidic groups as its constituent monomer components. Specifically, the acrylic polymer (A) can be said to be substantially free when the total amount of the carboxyl group-containing monomers and other monomers having acidic groups as its constituent monomer components is preferably 0.05 wt% or less (e.g., 0 to 0.05 wt%), more preferably 0.01 wt% or less (e.g., 0 to 0.01 wt%), and even more preferably 0.001 wt% or less (e.g., 0 to 0.001 wt%), based on the total amount (100 wt%) of the monomer components constituting the acrylic polymer (A).

[0155] From the same viewpoint, the pressure-sensitive adhesive composition of the present invention preferably does not contain or substantially does not contain acidic group-containing monomers as monomer components constituting polymers other than the acrylic polymer (A). For example, it preferably does not substantially contain carboxyl group-containing monomers. The meaning and preferable degree of "substantially does not contain," and monomers having acidic groups other than carboxyl groups, etc., are the same as those in the case of the monomer components constituting the acrylic polymer (A).

[0156] [1-6-3. Basic group-containing monomers] When the pressure-sensitive adhesive composition of the present invention contains an acrylic polymer (A) as the base polymer, it is preferable that the monomer components constituting the acrylic polymer (A) do not contain or substantially do not contain basic group-containing monomers. Furthermore, it is also preferable that the monomer components constituting polymers other than the acrylic polymer (A) do not substantially contain basic group-containing monomers. Even if a basic group-containing monomer is not a monomer component constituting various polymers, it is preferable that the pressure-sensitive adhesive layer does not substantially contain a basic group-containing monomer, just as in the case of a carboxyl group-containing monomer. The meaning and preferred degree of "substantially not containing" also apply similarly.

[0157] [1-6-4. Hydroxyl group-containing monomers] A hydroxyl group-containing monomer refers to a monomer having at least one hydroxyl group in the molecule. A monomer having at least one hydroxyl group and at least one carboxyl group in the molecule is a carboxyl group-containing monomer, but not a hydroxyl group-containing monomer. The hydroxyl group-containing monomer is not particularly limited, but specific examples include hydroxyl group-containing (meth)acrylic acid esters such as 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; vinyl alcohol; and allyl alcohol. Among these, the hydroxyl group-containing monomer is preferably a hydroxyl group-containing (meth)acrylic acid ester, more preferably 2-hydroxyethyl acrylate (HEA), 2-hydroxypropyl (meth)acrylate (HPA), or 4-hydroxybutyl acrylate (4HBA), from the viewpoint of facilitating obtaining good cohesive strength and facilitating obtaining adhesive reliability at high temperatures. The hydroxyl group-containing monomer may be used alone or in combination of two or more kinds.

[0158] [1-6-5. Nitrogen-containing monomers] A nitrogen atom-containing monomer refers to a monomer having at least one nitrogen atom in the molecule (per molecule). However, the hydroxyl group-containing monomer does not include the nitrogen atom-containing monomer. In other words, in this specification, a monomer having a hydroxyl group and a nitrogen atom in the molecule is included in the nitrogen atom-containing monomer. Furthermore, a monomer having at least one nitrogen atom in the molecule and at least one carboxyl group in the molecule is a carboxyl group-containing monomer, but is not a nitrogen atom-containing monomer.

[0159] As the nitrogen atom-containing monomer, from the viewpoint of improving resistance to foaming and peeling, N-vinyl cyclic amides, (meth)acrylamides, etc. The nitrogen atom-containing monomers may be used alone or in combination of two or more kinds.

[0160] The N-vinyl cyclic amide is preferably an N-vinyl cyclic amide represented by the following formula (1), from the viewpoint that good cohesive strength can be easily obtained and adhesive reliability at high temperatures can be easily obtained. [ka] (In formula (1), R 1 indicates a divalent organic group)

[0161] R in the above formula (1) 1 is a divalent organic group, preferably a divalent saturated or unsaturated hydrocarbon group, and more preferably a divalent saturated hydrocarbon group (for example, an alkylene group having 3 to 5 carbon atoms).

[0162] As the N-vinyl cyclic amide represented by the above formula (1), from the viewpoint of further improving foaming and peeling resistance and compatibility with benzotriazole-based compounds, N-vinyl-2-pyrrolidone (NVP), N-vinyl-2-piperidone, N-vinyl-2-caprolactam, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N-vinyl-3-morpholinone, N-vinyl-1,3-oxazin-2-one, N-vinyl-3,5-morpholinedione, etc. are preferred, more preferably N-vinyl-2-pyrrolidone, N-vinyl-2-caprolactam, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, and even more preferably N-vinyl-2-pyrrolidone.

[0163] Examples of the (meth)acrylamides include (meth)acrylamide, N-alkyl(meth)acrylamide, and N,N-dialkyl(meth)acrylamide. Examples of the N-alkyl(meth)acrylamide include N-ethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, Nn-butyl(meth)acrylamide, and N-octylacrylamide. Furthermore, the N-alkyl(meth)acrylamides also include (meth)acrylamides having an amino group, such as dimethylaminoethyl(meth)acrylamide, diethylaminoethyl(meth)acrylamide, and dimethylaminopropyl(meth)acrylamide. Examples of the N,N-dialkyl(meth)acrylamide include 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, and N,N-di(t-butyl)(meth)acrylamide.

[0164] The (meth)acrylamides also include, for example, various N-hydroxyalkyl(meth)acrylamides. Examples of the N-hydroxyalkyl(meth)acrylamides include N-methylol(meth)acrylamide, N-(2-hydroxyethyl)(meth)acrylamide, N-(2-hydroxypropyl)(meth)acrylamide, N-(1-hydroxypropyl)(meth)acrylamide, N-(3-hydroxypropyl)(meth)acrylamide, N-(2-hydroxybutyl)(meth)acrylamide, N-(3-hydroxybutyl)(meth)acrylamide, N-(4-hydroxybutyl)(meth)acrylamide, and N-methyl-N-2-hydroxyethyl(meth)acrylamide.

[0165] The (meth)acrylamides also include, for example, various N-alkoxyalkyl(meth)acrylamides, such as N-methoxymethyl(meth)acrylamide and N-butoxymethyl(meth)acrylamide.

[0166] Furthermore, examples of nitrogen atom-containing monomers other than the N-vinyl cyclic amides and the (meth)acrylamides include amino group-containing monomers such as aminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylate, and t-butylaminoethyl (meth)acrylate; cyano group-containing monomers such as acrylonitrile and methacrylonitrile; (meth)acryloylmorpholine, N-vinylpiperazine, N-vinylpyrrole, N-vinylimidazole, N-vinylpyrazine, N-vinylmorpholine, N-vinylpyrazole, vinylpyridine, vinylpyrimidine, vinyloxazole, vinylisoxazole, vinylthiazole, vinylisothiazole, vinylpyridazine, (meth)acryloylpyrrolidone, (meth)acryloylpyrrolidine, (meth)acryloylpiperidine, N- Examples of the monomer include heterocycle-containing monomers such as methylvinylpyrrolidone; maleimide-based monomers such as N-cyclohexylmaleimide, N-isopropylmaleimide, N-laurylmaleimide, and N-phenylmaleimide; itaconimide-based monomers such as N-methylitaconimide, N-ethylitaconimide, N-butylitaconimide, N-octylitaconimide, N-2-ethylhexylitaconimide, N-laurylitaconimide, and N-cyclohexylitaconimide; and succinimide-based monomers such as N-(meth)acryloyloxymethylenesuccinimide, N-(meth)acryloyl-6-oxyhexamethylenesuccinimide, and N-(meth)acryloyl-8-oxyoctamethylenesuccinimide; and imide group-containing monomers such as 2-(meth)acryloyloxyethylisocyanate.

[0167] [1-6-6. Alicyclic structure-containing monomers] The alicyclic structure-containing monomer refers to a monomer having a polymerizable functional group with an unsaturated double bond, such as a (meth)acryloyl group or a vinyl group, and having an alicyclic structure (excluding those corresponding to the methacrylic acid ester (A2)). For example, a (meth)acrylic acid alkyl ester having a cycloalkyl group is included in the above alicyclic structure-containing monomer. However, a monomer having at least one alicyclic structure in the molecule and at least one carboxyl group in the molecule is a carboxyl group-containing monomer, but is not an alicyclic structure-containing monomer. The alicyclic structure-containing monomer may be used alone or in combination of two or more types.

[0168] The alicyclic structure in the alicyclic structure-containing monomer is a cyclic hydrocarbon structure, preferably having 5 or more carbon atoms, more preferably 6 to 24 carbon atoms, still more preferably 6 to 15 carbon atoms, and particularly preferably 6 to 10 carbon atoms.

[0169] Examples of the alicyclic structure-containing monomer include (meth)acrylic monomers such as cyclopropyl (meth)acrylate, cyclobutyl (meth)acrylate, cyclopentyl (meth)acrylate, cyclohexyl acrylate, 3,3,5-trimethylcyclohexyl acrylate, cycloheptyl acrylate, cyclooctyl acrylate, isobornyl acrylate, dicyclopentanyl acrylate, HPMPA represented by the following formula (2), TMA-2 represented by the following formula (3), and HCPA represented by the following formula (4). In the following formula (4), the bonding position between the cyclohexyl ring connected by a line and the structural formula in parentheses is not particularly limited. Among these, isobornyl acrylate, cyclohexyl acrylate, and 3,3,5-trimethylcyclohexyl acrylate are preferred. [ka] [ka] [ka]

[0170] [1-6-7. Other copolymerizable monomers] Examples of copolymerizable monomers for the acrylic polymer (A), in addition to the above-mentioned nitrogen atom-containing monomers, hydroxyl group-containing monomers, and alicyclic structure-containing monomers, include (meth)acrylic acid alkoxyalkyl esters [e.g., 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, methoxytriethylene glycol (meth)acrylate, 3-methoxypropyl (meth)acrylate, 3-ethoxypropyl (meth)acrylate, 4-methoxybutyl (meth)acrylate, 4-ethoxybutyl (meth)acrylate, 2-(2-methoxyethoxy)ethyl (meth)acrylate, etc.]; epoxy group-containing monomers [e.g., glycidyl (meth)acrylate, methylglycidyl (meth)acrylate, etc.]; Examples of the monomer include sulfonic acid group-containing monomers [e.g., sodium vinyl sulfonate, etc.]; phosphate group-containing monomers; (meth)acrylic acid esters having aromatic hydrocarbon groups (excluding those corresponding to the methacrylic acid ester (A2)) [e.g., phenyl acrylate, phenoxyethyl acrylate, benzyl acrylate, etc.]; vinyl esters [e.g., vinyl acetate, vinyl propionate, etc.]; aromatic vinyl compounds [e.g., styrene, vinyl toluene, etc.]; olefins or dienes [e.g., ethylene, propylene, butadiene, isoprene, isobutylene, etc.]; vinyl ethers [e.g., vinyl alkyl ether, etc.]; vinyl chloride; and substituted methylene compounds in which all carbon atoms in the repeating units of the main chain have side chains.

[0171] Furthermore, the copolymerizable monomer in the acrylic polymer (A) may also be a polyfunctional monomer. The polyfunctional monomer acts as a crosslinking component. Examples of the polyfunctional monomer 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, epoxy acrylate, polyester acrylate, and urethane acrylate. The polyfunctional monomer may be used alone or in combination of two or more.

[0172] The content (proportion) of the polyfunctional monomer in all monomer units of the acrylic polymer (A) is not particularly limited, but is preferably 0.5 wt% or less (e.g., 0 to 0.5 wt%), more preferably 0 to 0.35 wt%, and even more preferably 0 to 0.2 wt%, relative to the total amount (100 wt%) of monomer components constituting the acrylic polymer (A). A polyfunctional monomer content of 0.5 wt% or less is preferred because the pressure-sensitive adhesive layer has adequate cohesive strength, and adhesive strength and level difference absorbency are likely to be improved. When a crosslinking agent is used, the polyfunctional monomer does not need to be used; however, when a crosslinking agent is not used, the polyfunctional monomer content is preferably 0.001 to 0.5 wt%, more preferably 0.001 to 0.35 wt%, and even more preferably 0.002 to 0.2 wt%.

[0173] The weight-average molecular weight (Mw) of the acrylic polymer (A) is preferably 100,000 to 5,000,000, more preferably 500,000 to 4,000,000, and even more preferably 750,000 to 3,000,000. A configuration in which the weight-average molecular weight of the acrylic polymer (A) is 100,000 or more is preferred in terms of improving adhesive strength and retention properties, and improving foaming-peeling resistance. On the other hand, a configuration in which the weight-average molecular weight of the acrylic polymer (A) is 5,000,000 or less is preferred in terms of easily increasing adhesive strength and improving foaming-peeling resistance.

[0174] The weight average molecular weight (Mw) of the acrylic polymer (A) can be determined in terms of polystyrene by GPC, for example, using a high-speed GPC device "HPLC-8120GPC" manufactured by Tosoh Corporation under the following conditions: Column: TSKgel SuperHZM-H / HZ4000 / HZ3000 / HZ2000 Solvent: tetrahydrofuran Flow rate: 0.6ml / min

[0175] The glass transition temperature (Tg) of the acrylic polymer (A) is not particularly limited, but is preferably −70 to 100° C., more preferably −65 to 50° C., and even more preferably −60 to 10° C. When the glass transition temperature of the acrylic polymer (A) is −70° C. or higher, the cohesive strength is improved and foaming peel resistance is likely to be improved, which is preferable. Furthermore, when the glass transition temperature of the acrylic polymer (A) is 100° C. or lower, the pressure-sensitive adhesive layer has appropriate flexibility, and good adhesive strength and good level difference absorbency are likely to be obtained, which makes it easier to obtain excellent adhesion reliability, which is preferable.

[0176] The glass transition temperature (Tg) of the acrylic polymer (A) is a theoretical value represented by the following FOX formula. 1 / Tg = W1 / Tg1+W2 / Tg2++W n / Tg n In the above formula, Tg is the glass transition temperature (unit: K) of the acrylic polymer (A), Tgi is the glass transition temperature (unit: K) when monomer i forms a homopolymer, W i represents the weight fraction of monomer i in the total amount of monomer components (i = 1, 2, . . . n). The following values ​​can be used as the Tg of the homopolymer of the monomer constituting the acrylic polymer (A). 2-Ethylhexyl acrylate -70℃ n-Hexyl acrylate -65℃ n-Octyl acrylate -65℃ Isononyl acrylate -60℃ n-Nonyl acrylate -58℃ n-Butyl acrylate -55℃ Ethyl acrylate -20℃ Lauryl acrylate 0℃ 2-Ethylhexyl methacrylate -10℃ Methyl acrylate 8℃ n-Butyl methacrylate 20℃ Methyl methacrylate 105℃ Lauryl methacrylate -65℃ Isodecyl methacrylate -41℃ Cyclohexyl methacrylate 66℃ Isobornyl methacrylate 173℃ Dicyclopentanyl methacrylate 175℃ 2-phenoxyethyl methacrylate 5℃ Benzyl methacrylate 54℃ 2-(2-methoxyethoxy)ethyl methacrylate -3℃ 2-Hydroxyethyl methacrylate 55℃ Acrylic acid 106℃ Methacrylic acid 228℃ N-vinylpyrrolidone 86℃ Vinyl acetate 32℃ Styrene 100℃

[0177] For the Tg of a homopolymer of a monomer not described above, the value described in "Polymer Handbook" (3rd Edition, John Wiley & Sons, Inc., 1989) can be used. Furthermore, for the Tg of a homopolymer of a monomer not described in the above literature, the value obtained by the above-mentioned measurement method (peak top temperature of tan δ in a viscoelasticity test) can be used.

[0178] [1-6-8. Acrylic polymer (B)] When the pressure-sensitive adhesive composition of the present invention contains an acrylic polymer (A) as a base polymer, the pressure-sensitive adhesive composition preferably contains, in addition to the acrylic polymer (A), an acrylic polymer (B) having a weight-average molecular weight of 1,000 to 30,000. When the pressure-sensitive adhesive composition contains the acrylic polymer (B), the adhesiveness to the adherend at the interface of the pressure-sensitive adhesive sheet is improved, making it easier to obtain strong adhesion and excellent foaming-peel resistance. In this specification, the "acrylic polymer (B) having a weight-average molecular weight of 1,000 to 30,000" may be simply referred to as the "acrylic polymer (B)."

[0179] The acrylic polymer (B) is preferably an acrylic polymer constituted by a (meth)acrylic acid ester having a cyclic structure in the molecule as an essential monomer component, and more preferably an acrylic polymer constituted by a (meth)acrylic acid ester having a cyclic structure in the molecule and a (meth)acrylic acid alkyl ester having a linear or branched alkyl group as essential monomer components. That is, the acrylic polymer (B) is preferably an acrylic polymer containing a (meth)acrylic acid ester having a cyclic structure in the molecule as a monomer unit, and more preferably an acrylic polymer containing a (meth)acrylic acid ester having a cyclic structure in the molecule and a (meth)acrylic acid alkyl ester having a linear or branched alkyl group as a monomer unit.

[0180] The cyclic structure (ring) of the (meth)acrylic acid ester having a cyclic structure in the molecule (within one molecule) (hereinafter, sometimes referred to as "ring-containing (meth)acrylic acid ester") may be either an aromatic ring or a non-aromatic ring, and is not particularly limited. Examples of the aromatic ring include an aromatic carbocycle (for example, a monocyclic carbocycle such as a benzene ring, or a fused carbocycle such as a naphthalene ring), various aromatic heterocycles, etc. Examples of the non-aromatic ring include non-aromatic aliphatic rings (non-aromatic alicyclic rings) [for example, cycloalkane rings such as a cyclopentane ring, a cyclohexane ring, a cycloheptane ring, and a cyclooctane ring; cycloalkene rings such as a cyclohexene ring], non-aromatic bridged rings [for example, bicyclic hydrocarbon rings such as a pinane ring, a pinene ring, a bornane ring, a norbornane ring, and a norbornene ring; tricyclic or higher aliphatic hydrocarbon rings (bridged hydrocarbon rings) such as an adamantane ring], and non-aromatic heterocycles [for example, an epoxy ring, an oxolane ring, and an oxetane ring].

[0181] Examples of the tricyclic or higher aliphatic hydrocarbon ring (tricyclic or higher bridged hydrocarbon ring) include a dicyclopentanyl group represented by the following formula (5a), a dicyclopentenyl group represented by the following formula (5b), an adamantyl group represented by the following formula (5c), a tricyclopentanyl group represented by the following formula (5d), and a tricyclopentenyl group represented by the following formula (5e). [ka]

[0182] That is, examples of the ring-containing (meth)acrylic acid esters include (meth)acrylic acid cycloalkyl esters such as cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, and cyclooctyl (meth)acrylate; (meth)acrylic acid esters having a bicyclic aliphatic hydrocarbon ring such as isobornyl (meth)acrylate; dicyclopentanyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, tricyclopentanyl (meth)acrylate, 1-adamanyl (meth)acrylate, and the like. and (meth)acrylic acid esters having an aromatic ring, such as (meth)acrylic acid esters having three or more aliphatic hydrocarbon rings, such as butyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, and 2-ethyl-2-adamantyl (meth)acrylate; (meth)acrylic acid esters having an aromatic ring, such as (meth)acrylic acid aryl esters, such as phenyl (meth)acrylate; (meth)acrylic acid aryloxyalkyl esters, such as phenoxyethyl (meth)acrylate; and (meth)acrylic acid arylalkyl esters, such as benzyl (meth)acrylate. Among these, the ring-containing (meth)acrylic acid esters are particularly preferably non-aromatic ring-containing (meth)acrylic acid esters, more preferably cyclohexyl acrylate (CHA), cyclohexyl methacrylate (CHMA), dicyclopentanyl acrylate (DCPA), and dicyclopentanyl methacrylate (DCPMA), and even more preferably dicyclopentanyl acrylate (DCPA) and dicyclopentanyl methacrylate (DCPMA). The ring-containing (meth)acrylic acid esters may be used alone or in combination of two or more kinds.

[0183] Among the above non-aromatic ring-containing (meth)acrylic acid esters, the use of (meth)acrylic acid esters having a tricyclic or higher aliphatic hydrocarbon ring (particularly a tricyclic or higher bridged hydrocarbon ring) is particularly preferred because they are less likely to cause polymerization inhibition. Furthermore, the use of (meth)acrylic acid esters having a dicyclopentanyl group represented by the above formula (5a), an adamantyl group represented by the above formula (5c), or a tricyclopentanyl group represented by the above formula (5d), which have no unsaturated bond, can further enhance foaming and peeling resistance, and can also significantly improve adhesion to low-polarity adherends such as polyethylene and polypropylene.

[0184] The content (proportion) of the ring-containing (meth)acrylic ester in all monomer units of the acrylic polymer (B) (total amount of monomer components constituting the acrylic polymer (B)) is not particularly limited, but is preferably 10 to 90 wt %, more preferably 20 to 80 wt %, relative to the total amount (100 wt %) of monomer components constituting the acrylic polymer (B). A content of the ring-containing (meth)acrylic ester of 10 wt % or more is preferred because foaming and peeling resistance is easily improved. Furthermore, a content of 90 wt % or less is preferred because the pressure-sensitive adhesive layer has appropriate flexibility and adhesion strength, step absorbency, and the like are easily improved.

[0185] Furthermore, examples of the (meth)acrylic acid alkyl ester having a linear or branched alkyl group as a monomer unit of the acrylic polymer (B) include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, and 2-ethyl (meth)acrylate. Examples of the (meth)acrylic acid alkyl ester include alkyl esters having an alkyl group having 1 to 20 carbon atoms, such as hexyl, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate. Among these, methyl methacrylate (MMA) is preferred because of its good compatibility with the acrylic polymer (A). The above alkyl (meth)acrylates may be used alone or in combination of two or more.

[0186] The content (proportion) of the (meth)acrylic acid alkyl ester having the linear or branched alkyl group in all monomer units of the acrylic polymer (B) (total amount of monomer components constituting the acrylic polymer (B)) is not particularly limited, but from the viewpoint of foaming and peeling resistance, it is preferably 10% by weight or more (e.g., 10 to 90% by weight), more preferably 20 to 80% by weight, and even more preferably 20 to 60% by weight, relative to the total amount (100% by weight) of monomer components constituting the acrylic polymer (B). A content of 10% by weight or more is preferred because it tends to improve adhesive strength, particularly to adherends made of acrylic resin or polycarbonate.

[0187] The monomer units of the acrylic polymer (B) may include, in addition to the ring-containing (meth)acrylic acid ester and the (meth)acrylic acid alkyl ester having a linear or branched alkyl group, a monomer copolymerizable with these monomers (copolymerizable monomers). The content (proportion) of the copolymerizable monomer in all monomer units of the acrylic polymer (B) (total amount of monomer components constituting the acrylic polymer (B)) is not particularly limited, but is preferably 49.9 wt% or less (e.g., 0 to 49.9 wt%), more preferably 30 wt% or less, based on the total amount (100 wt%) of monomer components constituting the acrylic polymer (B). The copolymerizable monomers may be used alone or in combination of two or more.

[0188] Examples of the copolymerizable monomer as a monomer unit of the acrylic polymer (B) (the copolymerizable monomer constituting the acrylic polymer (B)) include (meth)acrylic acid alkoxyalkyl esters [e.g., 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, methoxytriethylene glycol (meth)acrylate, 3-methoxypropyl (meth)acrylate, 3-ethoxypropyl (meth)acrylate, 4-methoxybutyl (meth)acrylate, 4-ethoxybutyl (meth)acrylate, etc.]; hydroxyl group (hydroxyl group)-containing monomers [e.g., hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, etc.]; vinyl alcohol; allyl alcohol, etc.); amide group-containing monomers [e.g., (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N-methylol(meth)acrylamide, N-methoxymethyl(meth)acrylamide, N-butoxymethyl(meth)acrylamide, N-hydroxyethyl(meth)acrylamide, etc.]; amino group-containing monomers [e.g., aminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, t-butylaminoethyl (meth)acrylate, etc.]; cyano group-containing monomers [e.g., acrylonitrile, methacrylonitrile, etc.]; sulfonic acid group-containing monomers [e.g., sodium vinyl sulfonate, etc.]; phosphate group-containing monomers [e.g., 2-hydroxyethyl acryloyl phosphate, etc.]; isocyanate group-containing monomers [e.g., 2-methacryloyloxyethyl isocyanate, etc.], imide group-containing monomers [cyclohexylmaleimide, isopropylmaleimide, etc.], etc.

[0189] As described above, the acrylic polymer (B) is preferably an acrylic polymer containing, as monomer units, a (meth)acrylic acid ester having a cyclic structure in the molecule and a (meth)acrylic acid alkyl ester having a linear or branched alkyl group. Among these, an acrylic polymer containing, as monomer units, a ring-containing (meth)acrylic acid ester and the above-mentioned (meth)acrylic acid alkyl ester having a linear or branched alkyl group is preferred. In the acrylic polymer containing, as monomer units, a ring-containing (meth)acrylic acid ester and a (meth)acrylic acid alkyl ester having a linear or branched alkyl group, the amount of the ring-containing (meth)acrylic acid ester relative to the total amount (100% by weight) of the monomer components constituting the acrylic polymer (B) is not particularly limited, but is preferably 10 to 90% by weight, more preferably 20 to 80% by weight. Furthermore, the content of the (meth)acrylic acid alkyl ester having a linear or branched alkyl group is not particularly limited, but is preferably 10 to 90 parts by weight, more preferably 20 to 80% by weight, even more preferably 20 to 60% by weight.

[0190] Furthermore, a particularly preferred specific configuration of the acrylic polymer (B) is an acrylic polymer containing, as monomer units, (1) at least one monomer selected from the group consisting of dicyclopentanyl acrylate, dicyclopentanyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate, and (2) methyl methacrylate. In the acrylic polymer (B) of the particularly preferred specific configuration, the content of (1) dicyclopentanyl acrylate, dicyclopentanyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate (the total amount when two or more types are included) in all monomer units of the acrylic polymer (B) is preferably 30 to 70 wt % and the content of (2) methyl methacrylate is preferably 30 to 70 wt % relative to the total amount (100 wt %) of the monomer components constituting the acrylic polymer (B). However, the acrylic polymer (B) is not limited to the specific configuration described above.

[0191] The acrylic polymer (B) can be obtained by polymerizing the above-mentioned monomer components by a known or conventional polymerization method. Examples of the polymerization method for the acrylic polymer (B) include a solution polymerization method, an emulsion polymerization method, a bulk polymerization method, and a polymerization method using active energy ray irradiation (active energy ray polymerization method). Among these, the bulk polymerization method and the solution polymerization method are preferred, and the solution polymerization method is more preferred.

[0192] Various common solvents may be used in the polymerization of the acrylic polymer (B). Examples of the solvent include organic solvents such as esters such as ethyl acetate and n-butyl acetate; aromatic hydrocarbons such as toluene and benzene; aliphatic hydrocarbons such as n-hexane and n-heptane; alicyclic hydrocarbons such as cyclohexane and methylcyclohexane; and ketones such as methyl ethyl ketone and methyl isobutyl ketone. These solvents may be used alone or in combination of two or more.

[0193] Furthermore, when polymerizing the acrylic polymer (B), a known or commonly used polymerization initiator (for example, a thermal polymerization initiator or a photopolymerization initiator) may be used. The polymerization initiator may be used alone or in combination of two or more kinds.

[0194] Examples of the thermal polymerization initiator include 2,2'-azobisisobutyronitrile (AIBN), 2,2'-azobis-2-methylbutyronitrile (AMBN), 2,2'-azobis(2-methylpropionic acid) dimethyl, 4,4'-azobis-4-cyanovaleric acid, 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 1,1'-azobis(cyclohexane-1- Examples of suitable initiators include azo initiators such as 2,2'-azobis(2,4,4-trimethylpentane) and benzoyl peroxide, t-butyl hydroperoxide, di-t-butyl peroxide, t-butyl peroxybenzoate, dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane and 1,1-bis(t-butylperoxy)cyclododecane. When solution polymerization is performed, it is preferable to use an oil-soluble polymerization initiator. The thermal polymerization initiators may be used alone or in combination of two or more.

[0195] The amount of the thermal polymerization initiator used is not particularly limited, but is, for example, 0.1 to 15 parts by weight per 100 parts by weight of all monomer units of the acrylic polymer (B) (total amount of monomer components constituting the acrylic polymer (B)).

[0196] The photopolymerization initiator is not particularly limited, but examples thereof include the same photopolymerization initiators as those used in the polymerization of the acrylic polymer (A) described above. The amount of the photopolymerization initiator used is not particularly limited and is selected appropriately.

[0197] During polymerization of the acrylic polymer (B), a chain transfer agent may be used to adjust the molecular weight (specifically, to adjust the weight average molecular weight to 1,000 to 30,000). Examples of the 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 esters of ethylene glycol, thioglycolic acid esters of neopentyl glycol, thioglycolic acid esters of pentaerythritol, and α-methylstyrene dimer. Of these, from the viewpoint of suppressing whitening of the PSA sheet due to humidification, α-thioglycerol and methyl thioglycolate are preferred, and α-thioglycerol is particularly preferred. The chain transfer agents may be used alone or in combination of two or more.

[0198] The content (amount used) of the chain transfer agent is not particularly limited, but is preferably 0.1 to 20 parts by weight, more preferably 0.2 to 15 parts by weight, even more preferably 0.3 to 10 parts by weight, even more preferably 0.5 to 5 parts by weight, and particularly preferably 0.75 to 3 parts by weight, relative to 100 parts by weight of all monomer units of the acrylic polymer (B) (total amount of monomer components constituting the acrylic polymer (B)). By setting the content (amount used) of the chain transfer agent within the above range, an acrylic polymer having a weight-average molecular weight controlled to 1,000 to 30,000 can be easily obtained.

[0199] The weight-average molecular weight (Mw) of the acrylic polymer (B) is 1,000 to 30,000, preferably 1,000 to 20,000, more preferably 1,500 to 10,000, even more preferably 2,000 to 8,000, and particularly preferably 4,000 to 6,000. Since the weight-average molecular weight of the acrylic polymer (B) is 1,000 or more, adhesive strength and retention properties are improved, and foaming-peeling resistance is improved. Meanwhile, since the weight-average molecular weight of the acrylic polymer (B) is 30,000 or less, adhesive strength can be easily increased, and foaming-peeling resistance is improved.

[0200] The weight average molecular weight (Mw) of the acrylic polymer (B) can be determined in terms of polystyrene by GPC, for example, using a high-speed GPC device "HPLC-8120GPC" manufactured by Tosoh Corporation under the following conditions: Column: TSKgel SuperHZM-H / HZ4000 / HZ3000 / HZ2000 Solvent: tetrahydrofuran Flow rate: 0.6ml / min

[0201] The glass transition temperature (Tg) of the acrylic polymer (B) is not particularly limited, but is preferably 20 to 300°C, more preferably 30 to 250°C, even more preferably 40 to 200°C, even more preferably 50 to 150°C, even more preferably 60 to 120°C, even more preferably 70 to 100°C, and particularly preferably 80 to 90°C. A glass transition temperature of 20°C or higher of the acrylic polymer (B) is preferred because it tends to improve foaming and peeling resistance. Furthermore, a glass transition temperature of 300°C or lower of the acrylic polymer (B) is preferred because it tends to provide the pressure-sensitive adhesive layer with adequate flexibility, favorable adhesive strength and favorable level difference absorbency, and favorable adhesion reliability.

[0202] The glass transition temperature (Tg) of the acrylic polymer (B) is the glass transition temperature (theoretical value) represented by the above FOX formula. The Tg of a homopolymer of a monomer constituting the acrylic polymer (B) can be a value listed in Table 1 below. Furthermore, the Tg of a homopolymer of a monomer not listed in Table 1 can be a value listed in "Polymer Handbook" (3rd edition, John Wiley & Sons, Inc., 1989). Furthermore, the Tg of a homopolymer of a monomer not listed in the above literature can be a value obtained by the above-mentioned measurement method (peak top temperature of tan δ in a viscoelasticity test).

[0203] [Table 1] In Table 1, the copolymer "DCPMA / MMA=60 / 40" means a copolymer of 60 parts by weight of DCPMA and 40 parts by weight of MMA.

[0204] When the pressure-sensitive adhesive composition of the present invention contains acrylic polymers (A) and (B), the content of the acrylic polymer (B) is not particularly limited, but is preferably 1 to 30 parts by weight, more preferably 2 to 20 parts by weight, even more preferably 2 to 10 parts by weight, and even more preferably 2 to 5 parts by weight, relative to 100 parts by weight of the acrylic polymer (A). That is, the content of the acrylic polymer (B) in the pressure-sensitive adhesive composition is not particularly limited, but is preferably 1 to 30 parts by weight, more preferably 2 to 20 parts by weight, even more preferably 2 to 10 parts by weight, and even more preferably 2 to 5 parts by weight, relative to 100 parts by weight of all monomer units of the acrylic polymer (A). The content of the acrylic polymer (B) in the pressure-sensitive adhesive composition of the present invention is not particularly limited, but is, for example, preferably 1 to 30 parts by weight, more preferably 2 to 20 parts by weight, even more preferably 2 to 10 parts by weight, and even more preferably 2 to 5 parts by weight, relative to 100 parts by weight of the monomer mixture. When the content of the acrylic polymer (B) is 1 part by weight or more, excellent adhesion and excellent resistance to foaming and peeling can be easily obtained, which is preferable, and when the content of the acrylic polymer (B) is 30 parts by weight or less, excellent transparency and adhesive reliability can be easily obtained, which is preferable.

[0205] The method for preparing the pressure-sensitive adhesive composition containing the acrylic polymers (A) and (B) is not particularly limited. For example, the pressure-sensitive adhesive composition can be prepared by adding, as necessary, the acrylic polymer (B), additives, etc. to a mixture of monomer components constituting the acrylic polymer (A) or a partial polymer of the mixture of monomer components constituting the acrylic polymer (A) (the monomer mixture forming the acrylic polymer (A) or its partial polymer), and mixing them.

[0206] [1-6-9. Rubber-based polymers] Another preferred embodiment of the pressure-sensitive adhesive composition of the present invention is a rubber-based pressure-sensitive adhesive composition primarily composed of a rubber-based polymer. Examples of rubber-based polymers include natural rubber, styrene-butadiene rubber (SBR), polyisoprene (PIP), polyisobutylene (PIB), butene-based polymers primarily composed of butene (1-butene and cis- or trans-2-butene) and / or 2-methylpropene (isobutylene), and ABA block copolymer rubbers and their hydrogenated products, such as styrene-butadiene-styrene block copolymer rubber (SBS), styrene-isoprene-styrene block copolymer rubber (SIS), styrene-isobutylene-styrene block copolymer rubber (SIBS), styrene-vinyl-isoprene-styrene block copolymer rubber (SVIS), hydrogenated SBS product styrene-ethylene-butylene-styrene block copolymer rubber (SEBS), and hydrogenated SIS product styrene-ethylene-propylene-styrene block copolymer rubber (SEPS). These rubber-based polymers can be used alone or in combination of two or more.

[0207] From the viewpoint of further reducing the dielectric constant and dielectric loss in the high frequency band and / or controlling the dielectric constant in the low frequency band, the pressure-sensitive adhesive composition of the present invention may contain, in addition to the base polymer, inorganic fine particles, organic fine particles, and polymer materials other than the base polymer, which may be contained alone or in combination of two or more. As the inorganic fine particles and organic fine particles, those exhibiting insulating properties (insulating filler) are preferred from the viewpoint of reducing the dielectric constant and dielectric loss in the high frequency band.

[0208] [1-6-10. Inorganic fine particles] The inorganic fine particles that can be blended in the pressure-sensitive adhesive composition of the present invention are not particularly limited, but examples thereof 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, and these may be used alone or in combination of two or more.

[0209] The inorganic fine particles may be surface-treated from the viewpoint of dispersibility in the base polymer. As the surface treatment agent, known or conventional ones can be used without limitation, for example, silane coupling agents, titanium coupling agents, organic acids, polyols, silicones, etc., and silane coupling agents are 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, dimethoxymethylphenylsilane, etc.

[0210] The particle size (D50) of the inorganic fine particles is not particularly limited, but from the viewpoints of reducing the dielectric constant and dielectric loss in the high frequency band of the pressure-sensitive adhesive layer of the present invention, controlling the dielectric constant in the low frequency band, and transparency, it is preferably 1 to 100 nm, more preferably 5 to 80 nm, and even more preferably 10 to 50 nm. The median particle size refers to the particle size (median diameter) at 50% of the cumulative value in the particle size distribution measured by laser diffraction / scattering method.

[0211] When the pressure-sensitive adhesive composition of the present invention contains inorganic fine particles, the content thereof is not particularly limited, but from the viewpoints of reducing the dielectric constant and dielectric loss in the high frequency band of the pressure-sensitive adhesive layer of the present invention, controlling the dielectric constant in the low frequency band, and transparency, the content is usually 0.01 to 30 parts by weight, preferably 0.05 to 25 parts by weight, more preferably 0.1 to 20 parts by weight, even more preferably 0.15 to 10 parts by weight, and particularly preferably 0.2 to 5 parts by weight, relative to the base polymer (100 parts by weight).

[0212] [1-6-11.Organic fine particles] The organic fine particles that can be incorporated into the pressure-sensitive adhesive composition of the present invention are not particularly limited, and examples thereof include fine particles composed of polymers such as styrene-based resins, acrylic-based resins, silicone-based resins, acrylic-styrene-based resins, vinyl chloride-based resins, vinylidene chloride-based resins, amide-based resins, urethane-based resins, phenol-based resins, styrene-conjugated diene-based resins, acrylic-conjugated diene-based resins, olefin-based resins, and fluorine-based resins, or crosslinked products of these polymers, and further fine particles composed of these polymer-polymer crosslinked products so as to have a hollow structure, and these may be used alone or in combination of two or more.

[0213] The particle size (D50) of the organic fine particles is not particularly limited, but from the viewpoints of reducing the dielectric constant and dielectric loss in the high frequency band of the pressure-sensitive adhesive layer of the present invention, controlling the dielectric constant in the low frequency band, and transparency, it is preferably 1 to 100 nm, more preferably 5 to 80 nm, and even more preferably 10 to 50 nm. The median particle size refers to the particle size (median diameter) at 50% of the cumulative value in the particle size distribution measured by a laser diffraction / scattering method.

[0214] When the pressure-sensitive adhesive composition of the present invention contains organic fine particles, the content thereof is not particularly limited, but from the viewpoints of lowering the dielectric constant and dielectric loss of the pressure-sensitive adhesive layer of the present invention in the high frequency band, controlling the dielectric constant of the pressure-sensitive adhesive layer B in the low frequency band, and transparency, it is usually 0.01 to 30 parts by weight, preferably 0.05 to 25 parts by weight, more preferably 0.1 to 20 parts by weight, even more preferably 0.15 to 10 parts by weight, and particularly preferably 0.2 to 5 parts by weight, relative to the base polymer (100 parts by weight).

[0215] [1-6-12. Polymer Materials] The polymer material that can be blended into the pressure-sensitive adhesive composition of the present invention is not particularly limited, but is preferably one that has a low dielectric constant and dielectric loss and is compatible with the base polymer. Examples include fluororesins, fluororubbers, polyethylene, polypropylene, polystyrene, polycarbonate, norbornene resins or addition copolymer resins with olefins, polyphenylene ether, bismaleimide-triazine resins, polyetherimides, polyimides, polyetheretherketone (PEEK), liquid crystal polymers, rubber elastomers, hydrogenated polyolefin resins, terpenes, isoprene, terpene phenol resins, aromatic modified terpene resins, and hydrogenated resins thereof, and these may be used alone or in combination of two or more.

[0216] When the pressure-sensitive adhesive composition of the present invention contains a polymer material, the content thereof is not particularly limited, but from the viewpoints of achieving a low dielectric constant and low dielectric loss in the high frequency band of the pressure-sensitive adhesive layer of the present invention, controlling the dielectric constant of pressure-sensitive adhesive layer B in the low frequency band, and transparency, the content is usually 0.01 to 50 parts by weight, preferably 0.05 to 40 parts by weight, more preferably 0.1 to 30 parts by weight, even more preferably 0.15 to 20 parts by weight, and particularly preferably 0.2 to 10 parts by weight, relative to the base polymer (100 parts by weight).

[0217] [1-6-13. Rust inhibitors] The pressure-sensitive adhesive composition of the present invention preferably further contains a rust inhibitor. When the pressure-sensitive adhesive layer contains a rust inhibitor, it is preferable in that an excellent corrosion prevention effect can be obtained for the antenna element and metal wiring.

[0218] Rust inhibitors are compounds that prevent metal rust and corrosion. Rust inhibitors are not particularly limited, but examples include amine compounds, benzotriazole-based compounds, and nitrites. Other examples include ammonium benzoate, ammonium phthalate, ammonium stearate, ammonium palmitate, ammonium oleate, ammonium carbonate, dicyclohexylamine benzoate, urea, urotropine, thiourea, phenyl carbamate, and cyclohexylammonium-N-cyclohexylcarbamate (CHC). Rust inhibitors can be used alone or in combination of two or more.

[0219] Examples of the amine compounds include hydroxyl-containing amine compounds such as 2-amino-2-methyl-1-propanol, monoethanolamine, monoisopropanolamine, diethylethanolamine, 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 nitrite (DICHAN), diisopropylammonium nitrite (DIPAN), sodium nitrite, potassium nitrite, and calcium nitrite.

[0220] The content of the rust inhibitor is not particularly limited, but is preferably 0.02 to 15 parts by weight per 100 parts by weight of the base polymer. A content of 0.02 parts by weight or more is preferred because it facilitates obtaining good corrosion prevention performance. On the other hand, a content of less than 15 parts by weight is preferred because it facilitates ensuring transparency and adhesive reliability such as anti-foaming and peeling properties.

[0221] Among these, the rust inhibitor is preferably a benzotriazole-based compound from the viewpoints of compatibility with the base polymer and transparency, and is particularly preferably a benzotriazole-based compound from the viewpoints of achieving a well-balanced and high level of adhesive reliability, transparency, and corrosion prevention properties, and of achieving excellent appearance.

[0222] The content of the benzotriazole compound is not particularly limited, but is preferably 0.02 to 3 parts by weight, more preferably 0.02 to 2.5 parts by weight, and even more preferably 0.02 to 2 parts by weight, relative to 100 parts by weight of the base polymer. Because the amount of the benzotriazole compound is below a certain level, adhesive reliability such as foaming and peeling resistance can be reliably ensured, and an increase in haze of the pressure-sensitive adhesive sheet can also be reliably prevented.

[0223] The benzotriazole-based compound is not particularly limited as long as it has a benzotriazole skeleton, but it is preferable that the compound has a structure represented by the following formula (6) from the viewpoint of obtaining a more excellent corrosion prevention effect. [ka] (However, in the above formula (6), R 2 and R 3 are the same or different, and R 2 is a substituent on a benzene ring, and is an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, an aryl group having 6 to 14 carbon atoms, an amino group, a mono- or di-C 1-10 Alkylamino group, amino-C 1-6 Alkyl group, mono or di C 1-10 Alkylamino-C 1-6 represents a substituent such as an alkyl group, a mercapto group, an alkoxycarbonyl group having 1 to 6 carbon atoms, or an alkoxy group having 1 to 6 carbon atoms, and n is an integer of 0 to 4. When n is 2 or more, n R 2 may be the same or different, and R 3 is a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, an aryl group having 6 to 14 carbon atoms, an amino group, a mono- or di-C1-10 Alkylamino group, amino-C 1-6 Alkyl group, mono or di C 1-10 Alkylamino-C 1-6 It represents a substituent such as an alkyl group, a mercapto group, an alkoxycarbonyl group having 1 to 12 carbon atoms, or an alkoxy group having 1 to 12 carbon atoms.

[0224] From the viewpoint of obtaining a better corrosion prevention effect, R 2 As the group, an alkyl group or an alkoxycarbonyl group having 1 to 3 carbon atoms is preferred, and a methyl group is more preferred. From a similar perspective, R 3 As the C 1-10 Alkylamino-C 1-6 Alkyl groups are preferred, and hydrogen atoms and diC 1~8 Alkylamino C 1~4 An alkyl group is more preferred.

[0225] [1-6-14. Silane coupling agents] The pressure-sensitive adhesive composition of the present invention preferably further contains a silane coupling agent. When the pressure-sensitive adhesive layer contains a silane coupling agent, excellent adhesion to glass (particularly excellent adhesion reliability to glass under high temperature and high humidity) can be easily obtained, which is preferable.

[0226] The silane coupling agent is not particularly limited, but examples thereof include γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-aminopropyltrimethoxysilane, and N-phenylaminopropyltrimethoxysilane. Of these, γ-glycidoxypropyltrimethoxysilane is preferred. Furthermore, examples of the silane coupling agent include commercially available products such as "KBM-403" (manufactured by Shin-Etsu Chemical Co., Ltd.). The silane coupling agents may be used alone or in combination of two or more.

[0227] The content of the silane coupling agent is not particularly limited, but from the viewpoint of improving the adhesive reliability to glass, it is preferably 0.01 to 1 part by weight, more preferably 0.03 to 0.5 parts by weight, per 100 parts by weight of the base polymer.

[0228] [1-6-15. Crosslinking agents] The pressure-sensitive adhesive composition of the present invention preferably further contains a crosslinking agent. When the pressure-sensitive adhesive composition contains a crosslinking agent, the base polymer is crosslinked, increasing the gel fraction and facilitating the improvement of foam-peeling resistance. For example, crosslinking an acrylic polymer can easily increase the gel fraction, thereby facilitating the improvement of foam-peeling resistance. Examples of the crosslinking agent include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, melamine-based crosslinking agents, and 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, when the pressure-sensitive adhesive layer is a pressure-sensitive adhesive composition containing an acrylic polymer as the base polymer, isocyanate-based crosslinking agents and epoxy-based crosslinking agents are preferred, and isocyanate-based crosslinking agents are more preferred, in terms of improving foam-peeling resistance. The crosslinking agents may be used alone or in combination of two or more.

[0229] Examples of the isocyanate-based crosslinking agent (polyfunctional isocyanate compound) 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. Examples of the isocyanate crosslinking agent include commercially available products such as a trimethylolpropane / tolylene diisocyanate adduct (manufactured by Nippon Polyurethane Industry Co., Ltd., product name "Coronate L"), a trimethylolpropane / hexamethylene diisocyanate adduct (manufactured by Nippon Polyurethane Industry Co., Ltd., product name "Coronate HL"), and a trimethylolpropane / xylylene diisocyanate adduct (manufactured by Mitsui Chemicals, Inc., product name "Takenate D-110N").

[0230] Examples of the epoxy crosslinking agent (polyfunctional epoxy compound) include N,N,N',N'-tetraglycidyl-m-xylylenediamine, 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 polyglycol Examples of the epoxy crosslinking agent include adipic acid diglycidyl ester, glycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitan polyglycidyl ether, trimethylolpropane polyglycidyl ether, adipic acid diglycidyl ester, o-phthalic acid diglycidyl 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. Examples of the epoxy crosslinking agent include commercially available products such as "Tetrad C" manufactured by Mitsubishi Gas Chemical Company, Inc.

[0231] The content of the crosslinking agent in the pressure-sensitive adhesive composition is not particularly limited, but for example, when the pressure-sensitive adhesive composition is a pressure-sensitive adhesive layer containing an acrylic polymer as a base polymer, the content is preferably 0.001 to 10 parts by weight, more preferably 0.01 to 5 parts by weight, per 100 parts by weight of the acrylic polymer. A crosslinking agent content of 0.001 part by weight or more is preferred because it tends to improve foaming and peeling resistance. On the other hand, a crosslinking agent content of 10 parts by weight or less is preferred because it tends to provide the pressure-sensitive adhesive layer with appropriate flexibility and improve adhesive strength.

[0232] [1-6-16. Additives] The pressure-sensitive adhesive composition of the present invention may contain, as necessary, known additives such as antioxidants, crosslinking accelerators, tackifying resins (rosin derivatives, polyterpene resins, oil-soluble phenols, etc.), antioxidants, colorants (pigments, dyes, etc.), ultraviolet absorbers, chain transfer agents, plasticizers, softeners, surfactants, antistatic agents, etc., within ranges that do not impair the properties of the present invention. These additives may be used alone or in combination of two or more.

[0233] When the pressure-sensitive adhesive composition of the present invention contains a tackifier, the content thereof is preferably 0.01 parts by weight or more, and more preferably 0.05 parts by weight or less, relative to 100 parts by weight of the base polymer in order to provide appropriate adhesiveness, and is preferably 50 parts by weight or less, and more preferably 40 parts by weight or less, relative to 100 parts by weight of the base polymer in order to avoid excessively high peel strength. In some embodiments, when the adhesive strength can be effectively controlled through the composition and Tg of the base polymer, the gel fraction of the adhesive, etc., an embodiment in which a tackifier is not used can also be preferably implemented.

[0234] [1-7. Adhesive sheet] The pressure-sensitive adhesive layer of the present invention is preferably used in the form of a pressure-sensitive adhesive sheet when laminated to the millimeter-wave antenna of the present invention. The pressure-sensitive adhesive sheet is not particularly limited in other respects as long as it has the pressure-sensitive adhesive layer of the present invention. In this specification, a pressure-sensitive adhesive sheet having the pressure-sensitive adhesive layer of the present invention may be referred to as the "pressure-sensitive adhesive sheet of the present invention."

[0235] The pressure-sensitive adhesive sheet of the present invention may be a double-sided pressure-sensitive adhesive sheet in which both sides are pressure-sensitive adhesive layer surfaces, or a single-sided pressure-sensitive adhesive sheet in which only one side is a pressure-sensitive adhesive layer surface. Among these, a double-sided pressure-sensitive adhesive sheet is preferred from the viewpoint of bonding two members together. Note that, in this specification, the term "pressure-sensitive adhesive sheet" also includes tape-like materials, i.e., "pressure-sensitive adhesive tape." Also, in this specification, the pressure-sensitive adhesive layer surface may be referred to as the "adhesive surface."

[0236] The pressure-sensitive adhesive sheet of the present invention may have a separator (release liner) provided on the adhesive surface until use.

[0237] The pressure-sensitive adhesive sheet of the present invention may be a so-called "substrate-less" pressure-sensitive adhesive sheet that does not have a substrate (substrate layer) (hereinafter, this may be referred to as a "substrate-less pressure-sensitive adhesive sheet"), or may be a pressure-sensitive adhesive sheet that has a substrate (hereinafter, this may be referred to as a "substrate-attached pressure-sensitive adhesive sheet"). Examples of the substrate-less pressure-sensitive adhesive sheet include a double-sided pressure-sensitive adhesive sheet consisting only of the pressure-sensitive adhesive layer, and a double-sided pressure-sensitive adhesive sheet consisting of the pressure-sensitive adhesive layer and a pressure-sensitive adhesive layer other than the pressure-sensitive adhesive layer (hereinafter, this may be referred to as an "other pressure-sensitive adhesive layer"). On the other hand, examples of substrate-attached pressure-sensitive adhesive sheets include pressure-sensitive adhesive sheets having the pressure-sensitive adhesive layer on at least one side of a substrate. Among these, substrate-less pressure-sensitive adhesive sheets (substrate-less double-sided pressure-sensitive adhesive sheets) are preferred, and substrate-less double-sided pressure-sensitive adhesive sheets consisting only of the pressure-sensitive adhesive layer are more preferred. Pressure-sensitive adhesive sheets having the pressure-sensitive adhesive layers on both sides of a substrate (substrate-attached double-sided pressure-sensitive adhesive sheets) are also preferred. The pressure-sensitive adhesive layers on both sides of the substrate-attached double-sided pressure-sensitive adhesive sheet may both be the pressure-sensitive adhesive layer of the present invention, or one may be the pressure-sensitive adhesive layer of the present invention and the other may be another pressure-sensitive adhesive layer. The "substrate (substrate layer)" does not include a separator that is peeled off when the pressure-sensitive adhesive sheet is used (applied).

[0238] When the pressure-sensitive adhesive sheet of the present invention is a pressure-sensitive adhesive sheet with a substrate, radiation loss of millimeter waves may occur due to the substrate, so it is preferably a substrate-less pressure-sensitive adhesive sheet. However, when the substrate is made of a material with a low dielectric constant and low dielectric loss, the pressure-sensitive adhesive sheet may be a substrate-attached pressure-sensitive adhesive sheet.

[0239] [1-7-1. 180° peel strength of adhesive sheet] The 180° peel adhesive strength of the pressure-sensitive adhesive sheet of the present invention to a glass plate at a pulling speed of 300 mm / min (particularly, the 180° peel adhesive strength of the adhesive surface provided by the pressure-sensitive adhesive layer of the present invention to a glass plate) is not particularly limited, but from the viewpoint that a high adhesive strength can be obtained, sufficient adhesion to the antenna element is preferably 3 N / 20 mm or more, more preferably 3.5 N / 20 mm or more, even more preferably 4 N / 20 mm or more, even more preferably 5 N / 20 mm, even more preferably 6 N / 20 mm or more, even more preferably 7 N / 20 mm or more, even more preferably 8 N / 20 mm or more, even more preferably 9 N / 20 mm or more, and particularly preferably 10 N / 20 mm or more. If the 180° peel adhesive strength of the pressure-sensitive adhesive sheet of the present invention to a glass plate at a pulling speed of 300 mm / min is a certain value or more, the adhesiveness to glass and the ability to prevent lifting at steps are even more excellent. The upper limit of the 180° peel adhesive strength of the pressure-sensitive adhesive sheet of the present invention to a glass plate at a pulling rate of 300 mm / min is not particularly limited, but is, for example, preferably 30 N / 20 mm or less, more preferably 25 N / 20 mm or less, even more preferably 22 N / 20 mm or less, particularly preferably 20 N / 20 mm or less, 19 N / 20 mm or less, 18 N / 20 mm or less, 17 N / 20 mm or less, 16 N / 20 mm or less, 15 N / 20 mm or less, 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 pulling rate of 300 mm / min is determined by the following 180° peel adhesive strength measurement method.

[0240] The glass plate is not particularly limited, but examples thereof 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.

[0241] (180° peel adhesive strength measurement method) The adhesive side of the adhesive sheet is attached to the adherend, pressed back and forth with a 2 kg roller, and aged for 30 minutes in an atmosphere of 23°C and 50% RH. After aging, the adhesive sheet is peeled from the adherend in accordance with JIS Z 0237 at a tensile speed of 300 mm / min and a peel angle of 180°, at an atmosphere of 23°C and 50% RH, and the 180° peel adhesive strength (N / 20 mm) is measured.

[0242] The 180° peel adhesive strength of the pressure-sensitive adhesive sheet of the present invention can be controlled by the monomer composition of the base polymer (acrylic polymer), the weight average molecular weight, the amount of crosslinking agent used (addition amount), and the types and amounts of other additives used.

[0243] [1-7-2. Thickness of adhesive sheet] The thickness (total thickness) of the pressure-sensitive 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 particularly preferably 12 to 300 μm. A thickness of at least a certain level is preferred because peeling at uneven areas is less likely to occur. A thickness of at most a certain level is also preferred because excellent appearance is more easily maintained during production. The thickness of the pressure-sensitive adhesive sheet of the present invention does not include the thickness of the separator.

[0244] [1-7-3. Haze and total light transmittance of adhesive sheets] The haze (according to JIS K7136) of the pressure-sensitive adhesive sheet of the present invention 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. A haze of 1.2% or less is preferable because excellent transparency and excellent appearance can be obtained. The haze can be measured, for example, by leaving the pressure-sensitive adhesive sheet at room temperature (23°C, 50% RH) for at least 24 hours, peeling off the separator if present, and bonding the sheet to a slide glass (e.g., one with a total light transmittance of 91.8% and a haze of 0.4%) as a sample using a haze meter (manufactured by Murakami Color Research Laboratory Co., Ltd., product name "HM-150").

[0245] The total light transmittance (according to JIS K7361-1) in the visible light wavelength region of the pressure-sensitive adhesive sheet of the present invention 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, even more preferably 91% or more, and particularly preferably 92% or more. A total light transmittance of 85% or more is preferable, as excellent transparency and excellent appearance can be obtained. The total light transmittance can be measured, for example, by leaving the pressure-sensitive adhesive sheet at room temperature (23°C, 50% RH) for at least 24 hours, peeling off the separator if present, and bonding the sheet to a slide glass (e.g., one with a total light transmittance of 91.8% and a haze of 0.4%) as a sample using a haze meter (manufactured by Murakami Color Research Laboratory Co., Ltd., product name "HM-150").

[0246] The haze and total light transmittance of the pressure-sensitive adhesive sheet of the present invention can be adjusted by adjusting the type of base polymer constituting the pressure-sensitive adhesive composition for forming the pressure-sensitive adhesive layer, the monomer composition, the type and content of additives, the type and thickness of the substrate, etc.

[0247] [1-7-4. Manufacturing method of adhesive sheet] The pressure-sensitive adhesive sheet of the present invention is not particularly limited, but is preferably produced according to a known or conventional production method. For example, when the pressure-sensitive adhesive sheet of the present invention is a substrate-less pressure-sensitive adhesive sheet, it can be obtained by forming the pressure-sensitive adhesive layer on a separator by the above-mentioned method. Furthermore, when the pressure-sensitive adhesive sheet of the present invention is a substrate-attached pressure-sensitive adhesive sheet, it can be obtained by directly forming the pressure-sensitive adhesive layer on the surface of the substrate (direct transfer method), or by first forming the pressure-sensitive adhesive layer on a separator and then transferring (laminating) it to the substrate to provide the pressure-sensitive adhesive layer on the substrate (transfer method).

[0248] [1-7-5. Other layers of adhesive sheet] The pressure-sensitive adhesive sheet of the present invention may have other layers in addition to the pressure-sensitive adhesive layer. Examples of other layers include other pressure-sensitive adhesive layers (pressure-sensitive adhesive layers other than the pressure-sensitive adhesive layer (pressure-sensitive adhesive layers other than the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention)), intermediate layers, undercoat layers, etc. The pressure-sensitive adhesive sheet of the present invention may have two or more other layers.

[0249] [1-7-6. Adhesive sheet base material] When the pressure-sensitive adhesive sheet of the present invention is a substrate-attached pressure-sensitive adhesive sheet, the substrate is not particularly limited, and examples thereof include various optical films such as plastic films, antireflection (AR) films, polarizing plates, and retardation plates. Examples of materials for the plastic films include polyester resins such as polyethylene terephthalate (PET), (meth)acrylic resins such as polymethyl methacrylate (PMMA), polycarbonate, triacetyl cellulose (TAC), polysulfone, polyarylate, polyimide, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, ethylene-propylene copolymers, cyclic olefin polymers such as "ARTON (cyclic olefin polymer, manufactured by JSR Corporation)" and "ZEONOR (cyclic olefin polymer, manufactured by Zeon Corporation)," and fluorine-based polymers. These plastic materials may be used alone or in combination of two or more. In addition, one or both sides of the substrate may be appropriately formed with a surface treatment layer having a single or multiple known and commonly used function, such as a hard coat layer, an antiblocking layer, an antireflection layer, an antistatic layer, an easy-adhesion layer, or a moisture-proof layer. The "substrate" above refers to the part that is attached to the adherend together with the adhesive layer when the pressure-sensitive adhesive sheet is attached to the adherend. The "substrate" does not include a separator (release liner) that is peeled off when the pressure-sensitive adhesive sheet is used (attached).

[0250] The substrate is preferably transparent. The total light transmittance (according to JIS K7361-1) of the substrate in the visible light wavelength region is not particularly limited, but is preferably 85% or more, more preferably 88% or more. The haze (according to JIS K7136) of the substrate 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. Examples of such transparent substrates include PET films and non-oriented films such as those sold under the trade names "Arton" and "Zeonor." Non-oriented films are particularly preferred because their properties do not depend on the direction of the millimeter-wave electric field.

[0251] The thickness of the substrate is not particularly limited, but is preferably 12 to 500 μm, for example. The substrate may have either a single layer or multiple layers. The surface of the substrate may be appropriately subjected to a known and commonly used surface treatment, such as a physical treatment such as corona discharge treatment, plasma treatment, or electron beam treatment, or a chemical treatment such as a primer treatment.

[0252] [1-7-7. Adhesive sheet separator] The pressure-sensitive adhesive sheet of the present invention may have a separator (release liner) on its adhesive surface until use. When the pressure-sensitive adhesive sheet of the present invention is a double-sided pressure-sensitive adhesive sheet, each adhesive surface may be protected by two separators, or may be protected by a single separator with release surfaces on both sides and wound into a roll. The separator is used as a protective material for the pressure-sensitive adhesive layer and is peeled off when the sheet is attached to the adherend. When the pressure-sensitive adhesive sheet of the present invention is a substrate-less pressure-sensitive adhesive sheet, the separator also serves as a support for the pressure-sensitive adhesive layer. The separator does not necessarily have to be provided.

[0253] The separator can be made of conventional release paper or the like, and is not particularly limited. Examples include substrates with a release treatment layer, low-adhesion substrates made of fluoropolymers, and low-adhesion substrates made of non-polar polymers. Examples of substrates with a release treatment layer include plastic films and papers surface-treated with release agents such as silicone-based, long-chain alkyl-based, fluorine-based, and molybdenum sulfide-based release agents. Examples of fluorine-based polymers in the low-adhesion substrates made of fluoropolymers include polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymers, and chlorofluoroethylene-vinylidene fluoride copolymers. Examples of non-polar polymers include olefin-based resins (e.g., polyethylene, polypropylene, etc.), and polyester-based substrates (polyethylene terephthalate-based substrates, polyethylene naphthalate-based substrates, polybutylene terephthalate-based substrates, etc.). The separator can be formed by known or conventional methods. The thickness of the separator is also not particularly limited.

[0254] [1-8. Manufacturing of millimeter wave antennas] The millimeter wave antenna of the present invention can be preferably produced using the pressure-sensitive adhesive sheet of the present invention.

[0255] The embodiment in which an antenna substrate and a cover member are bonded together using the pressure-sensitive adhesive sheet of the present invention is not particularly limited, and examples thereof include (1) an embodiment in which an antenna substrate and a cover member are bonded together via the pressure-sensitive adhesive sheet of the present invention, (2) an embodiment in which a pressure-sensitive adhesive sheet of the present invention that includes or constitutes an antenna substrate is bonded to a cover member, and (3) an embodiment in which a pressure-sensitive adhesive sheet of the present invention that includes or constitutes a cover member is bonded to an antenna substrate. In the above embodiment (2), the pressure-sensitive adhesive sheet of the present invention is preferably a double-sided pressure-sensitive adhesive sheet in which the substrate is the antenna substrate. In the above embodiment (3), the pressure-sensitive adhesive sheet of the present invention is preferably a double-sided pressure-sensitive adhesive sheet in which the substrate is a cover member.

[0256] The manner in which the antenna substrate and the image display panel are bonded using the pressure-sensitive adhesive sheet of the present invention is not particularly limited, and examples thereof include (1) bonding the antenna substrate and the image display panel via a pressure-sensitive adhesive sheet, (2) bonding an adhesive sheet including or constituting an antenna substrate to an image display panel, and (3) bonding an adhesive sheet including or constituting an image display panel to an antenna substrate. In the above-mentioned (2) embodiment, the pressure-sensitive adhesive sheet is preferably a double-sided pressure-sensitive adhesive sheet whose substrate is the antenna substrate. In the above-mentioned (3) embodiment, the pressure-sensitive adhesive sheet is preferably a double-sided pressure-sensitive adhesive sheet whose substrate is an image display panel. The pressure-sensitive adhesive sheet used to bond the antenna substrate and the image display panel is not particularly limited, but the pressure-sensitive adhesive sheet of the present invention is preferred from the viewpoint of realizing high antenna gain and touch sensor sensitivity.

[0257] The millimeter-wave antennas (millimeter-wave antenna A and millimeter-wave antenna B) of the present invention may include components other than the antenna substrate, cover member, adhesive sheet, and image display panel, such as a polarizing plate, a wavelength plate, a retardation plate, an optical compensation film, a brightness enhancement film, a light guide plate, a reflective film, an anti-reflection film, a hard coat film, a transparent conductive film, a design film, a decorative film, a surface protection plate, a prism, a lens, a color filter, a transparent substrate, etc. Furthermore, the millimeter-wave antenna A may include an image display panel (e.g., a liquid crystal display panel, an organic EL panel, a plasma display panel, etc.), and the image display panel may include a touch sensor.

[0258] The millimeter-wave antenna A has an adhesive layer A with low dielectric constant and dielectric loss in high frequency bands such as millimeter waves, so that radiation loss of the received millimeter waves can be kept low and high antenna gain can be achieved. Furthermore, millimeter-wave antenna B contains adhesive composition B, which has low dielectric constant and dielectric loss in high frequency bands such as millimeter waves, while its dielectric constant in low frequency bands (100 kHz) is controlled to be relatively high, and therefore exhibits high antenna gain while also exhibiting high sensitivity to touch sensors (especially capacitive touch sensors). Therefore, millimeter-wave antenna B can obtain high antenna gain without impairing the detection function of the touch sensor. Therefore, the millimeter-wave antennas (millimeter-wave antenna A and millimeter-wave antenna B) of the present invention are preferably used as transmitting and receiving antennas for mobile communication devices. Examples of the mobile communication devices include mobile phones, PHS, smartphones, tablets (tablet computers), mobile computers (mobile PCs), and personal digital assistants (PDAs). In addition, the millimeter-wave antennas can be preferably used in communication devices with edge computing functions, including IoT (Internet of Things) terminals.

[0259] The millimeter-wave antenna A may be located anywhere on the mobile communication device, specifically on the front, back, or side of the mobile communication device. The front of the mobile communication device refers to the surface facing the user when the user uses the mobile communication device, and corresponds to the surface having the display panel, for example, while the back and side correspond to the housing. The display panel refers to a structure composed of at least a lens (particularly a glass lens) and a touch panel.

[0260] The size (area) of the millimeter-wave antenna A is not limited, and it may be formed on the entire surface of each side of the mobile communication device, or may be arranged on only a part of it. The shape of the millimeter-wave antenna A is also not particularly limited, and it may be, for example, square, round, or wire-shaped. It may also be arranged in a frame shape. Furthermore, the number of millimeter-wave antennas A arranged on the mobile communication device is not limited, and it may be one, or multiple antennas may be arranged in any position. When multiple millimeter-wave antennas A are arranged, the sizes (areas) may be the same or different. In areas of the mobile communication device where no millimeter-wave antenna A is arranged, a dummy pattern without a millimeter-wave antenna may be arranged to improve visibility.

[0261] The millimeter-wave antenna B may be arranged in any position on the display (image display panel). The size (area) of the millimeter-wave antenna B is not limited, and it may be formed over the entire surface of the image display panel or may be arranged on only a part of it. The shape of the millimeter-wave antenna B is also not particularly limited, and it may be, for example, square, round, or wire-shaped. It may also be arranged in a frame-like shape on the image display panel. The number of millimeter-wave antennas B arranged on the image display panel is also not limited, and it may be one, or multiple antennas may be arranged in any position. When multiple millimeter-wave antennas B are arranged, the sizes (areas) may be the same or different. In areas of the image display panel where no millimeter-wave antenna B is arranged, a dummy pattern without a millimeter-wave antenna may be arranged to improve visibility.

[0262] In the millimeter-wave antenna B, a preferred embodiment is one in which the antenna substrate is bonded to an image display panel (which may or may not necessarily have the pressure-sensitive adhesive sheet of the present invention, but having it is preferable from the viewpoint of further suppressing radiation loss of millimeter waves). Furthermore, an optical component other than the image display panel (for example, a polarizing plate) may be laminated. The optical component other than the image display panel may be singular or plural.

[0263] Next, preferred embodiments of the millimeter wave antenna of the present invention will be described with reference to the drawings.

[0264] FIG. 1 is a schematic diagram (cross-sectional view) showing one embodiment of a millimeter-wave antenna A, depicting a millimeter-wave antenna 1A having a cover member 12, an adhesive layer 10, and an antenna substrate 11 in contact with one another in this order. The adhesive layer 10 is composed of an adhesive layer A. The antenna substrate 11 has a millimeter-wave antenna element 2 on the surface facing the adhesive layer 10, and the adhesive layer 10 is laminated on the surface of the antenna substrate 11 having the millimeter-wave antenna element 2. The cover member 12 is preferably glass, the antenna substrate 11 is preferably COP from the viewpoints of low dielectric constant and low dielectric loss, and the millimeter-wave antenna element 2 is preferably copper, silver, or ITO.

[0265] FIG. 2 is a schematic diagram (cross-sectional view) showing one embodiment of a millimeter-wave antenna B. The millimeter-wave antenna 1B includes a cover member 12, an adhesive layer 10a, a millimeter-wave antenna substrate 11, an adhesive layer 10b, and an image display panel 13, which are in contact with one another in this order. The adhesive layer 10a is composed of the adhesive layer B. The antenna substrate 11 includes a millimeter-wave antenna element 2 on the surface of the adhesive layer 10a, and the adhesive layer 10a is laminated on the surface of the antenna substrate 11 that includes the millimeter-wave antenna element 2. The cover member 12 is preferably glass, the antenna substrate 11 is preferably COP from the viewpoints of low dielectric constant and low dielectric loss, and the millimeter-wave antenna element 2 is preferably ITO or silver or copper blackened with a coating of nitride, oxide, sulfide, or the like from the viewpoints of transparency and visibility. The adhesive layer 10b may or may not be adhesive layer B, but is preferably adhesive layer B. The image display panel 13 preferably has a touch sensor (particularly, a capacitive touch sensor) (not shown).

[0266] 1, the pressure-sensitive adhesive layer 10 is composed of the pressure-sensitive adhesive layer A, which has a low dielectric constant and dielectric loss in the high frequency band, so that radiation loss of millimeter waves 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 made finer.

[0267] In the millimeter-wave antenna 1B of Fig. 2, the adhesive sheet 10a, and preferably the adhesive sheet 10b, is made of an adhesive layer B having a low dielectric constant and dielectric loss in the high frequency band, thereby suppressing radiation loss of millimeter waves and enabling efficient millimeter-wave communication. Also, in the millimeter-wave antenna 1B of Fig. 2, the adhesive sheet 10a, and preferably the adhesive sheet 10b, is made of an adhesive layer B that is controlled to have a relatively high dielectric constant in the low frequency band, so the touch sensor of the image display panel 13 can sensitively receive touch input from, for example, the top of the cover member 12. [Example]

[0268] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples in any way.

[0269] [Example 1] A monomer mixture consisting of 43 parts by weight of 2-ethylhexyl acrylate (2EHA), 43 parts by weight of isostearyl acrylate (ISTA), 12 parts by weight of N-vinyl-2-pyrrolidone (NVP), and 1 part by weight of 4-hydroxybutyl acrylate (4HBA) was blended with 0.035 parts by weight of a photopolymerization initiator (trade name "Irgacure 184", manufactured by BASF) and 0.035 parts by weight of a photopolymerization initiator (trade name "Irgacure 651", manufactured by BASF), and then irradiated with ultraviolet light until the viscosity (BH viscometer No. 5 rotor, 10 rpm, measurement temperature 30°C) reached approximately 20 Pa·s, yielding a prepolymer composition in which some of the monomer components had polymerized. Next, 0.075 parts by weight of hexanediol diacrylate (HDDA) and 0.3 parts by weight of a silane coupling agent (trade name "KBM-403", manufactured by Shin-Etsu Chemical Co., Ltd.) were added to 100 parts by weight of the prepolymer composition and mixed to obtain a pressure-sensitive adhesive composition (pre-cured composition).

[0270] The pressure-sensitive adhesive composition was applied to a polyethylene terephthalate (PET) separator (trade name "MRF50", manufactured by Mitsubishi Chemical Corporation) to a final thickness (thickness of the pressure-sensitive adhesive layer) of 25 μm to form a coating layer (pressure-sensitive adhesive composition layer). Next, a PET separator (trade name "MRF38", manufactured by Mitsubishi Chemical Corporation) was placed on the coating layer to cover the coating layer and block oxygen. A laminate of MRF50 / coating layer (pressure-sensitive adhesive composition layer) / MRF38 was then obtained. Next, a black light (manufactured by Toshiba Corporation) was used to illuminate the laminate from the top surface (MRF38 side) of the laminate at an illuminance of 5 mW / cm. 2 The sheet was then irradiated with ultraviolet light at 1000 W for 300 seconds. The sheet was then dried in a dryer at 90°C for 2 minutes to volatilize any remaining monomers. This resulted in a substrate-less double-sided PSA sheet consisting only of a PSA layer, with both sides of the PSA layer protected by separators.

[0271] [Example 2] A substrateless double-sided PSA sheet was obtained in the same manner as in Example 1, except that a prepolymer composition was obtained using a monomer mixture consisting of 25 parts by weight of 2-ethylhexyl acrylate (2EHA), 62 parts by weight of lauryl acrylate (LA), 8 parts by weight of N-vinyl-2-pyrrolidone (NVP), and 5 parts by weight of 4-hydroxybutyl acrylate (4HBA).

[0272] [Example 3] A pressure-sensitive adhesive composition (solution) with a solids content of 13 wt% was prepared by blending 100 parts by weight of polyisobutylene (trade name "OPPANOL N80", Mw: 1,050,000, Mn: 440,000, Mw / Mn: 2.4, manufactured by BASF) and 22 parts by weight of a fully hydrogenated terpene phenol (softening point: 135°C, hydroxyl value: 160) as a tackifier in toluene. The resulting pressure-sensitive adhesive composition (solution) was applied to a PET separator (trade name "MRF50", manufactured by Mitsubishi Chemical Corporation) to a final thickness (adhesive layer thickness) of 50 μm to form a coating layer (adhesive composition layer). The coating layer was then dried at 130°C for 5 minutes to form an adhesive layer, and a pressure-sensitive adhesive sheet with an adhesive layer thickness of 50 μm was produced. A PET separator (product name "MRF38", manufactured by Mitsubishi Chemical Corporation) was attached to the adhesive surface of the pressure-sensitive adhesive sheet so that the release-treated surface was in contact with the pressure-sensitive adhesive layer, yielding a substrate-less double-sided pressure-sensitive adhesive sheet in which both sides of the pressure-sensitive adhesive layer were protected by separators.

[0273] [Example 4] A pressure-sensitive adhesive composition was prepared by mixing 100 parts by weight of polystyrene-poly(ethylene / propylene)-polystyrene block copolymer rubber (SEPS: Kuraray's "Septon 2063," styrene content: 13%) with 300 parts by weight of toluene. The pressure-sensitive adhesive composition was applied to the release-treated surface of a PET separator (trade name "MRF50," manufactured by Mitsubishi Chemical Corporation) to a thickness of 20 μm after drying, and then heated at 130°C for 5 minutes to remove the solvent, producing a pressure-sensitive adhesive sheet. A PET separator (trade name "MRF38," manufactured by Mitsubishi Chemical Corporation) was also attached to the adhesive surface of the pressure-sensitive adhesive sheet, with the release-treated surface in contact with the pressure-sensitive adhesive layer. A substrate-less double-sided pressure-sensitive adhesive sheet was obtained, with both sides of the pressure-sensitive adhesive layer protected by separators.

[0274] [Comparative Example 1] A substrateless double-sided PSA sheet was obtained in the same manner as in Example 1, except that a prepolymer composition was obtained using a monomer mixture consisting of 65 parts by weight of butyl acrylate (BA), 13 parts by weight of cyclohexyl acrylate (CHA), 7 parts by weight of 2-hydroxyethyl acrylate (HEA), and 30 parts by weight of 4-hydroxybutyl acrylate (4HBA).

[0275] [Examples 5 to 42] A reaction vessel equipped with a condenser, nitrogen inlet, thermometer, and stirrer was charged with the mixture of monomer components shown in Table 2, 0.2 parts by weight of 2,2'-azobisisobutyronitrile (AIBN) as a thermal polymerization initiator, and ethyl acetate as a polymerization solvent so that the monomer components were 70% by weight. Nitrogen gas was introduced and the atmosphere was replaced with nitrogen for approximately 1 hour while stirring. The reaction vessel was then heated to 70°C and reacted for 6 hours. The reaction vessel was then heated to 80°C and reacted for 3 hours, yielding a (meth)acrylic polymer with a weight-average molecular weight (Mw) of 400,000. To this (meth)acrylic polymer solution (100 parts by weight of solids), 0.1 parts by weight (based on solids) of an isocyanate crosslinking agent (trade name "Coronate HX", manufactured by Tosoh Corporation, solids concentration 100% by weight), 0.01 parts by weight of dioctyltin dilaurate (trade name "Envirizer OL-1", manufactured by Tokyo Fine Chemical Co., Ltd.) as a crosslinking accelerator, and 5 parts by weight of acetylacetone as a crosslinking retarder were added and mixed uniformly to prepare a pressure-sensitive adhesive composition according to this example.

[0276] The pressure-sensitive adhesive composition was applied to a polyethylene terephthalate (PET) separator (trade name "MRF38", manufactured by Mitsubishi Chemical Corporation) to a final thickness (thickness of the pressure-sensitive adhesive layer) of 25 μm to form a coating layer (pressure-sensitive adhesive composition layer). The coating was then dried in a dryer at 130°C for 120 minutes to volatilize the solvent and residual monomer. A PET separator (trade name "MRE38", manufactured by Mitsubishi Chemical Corporation) was then placed on the coating layer to obtain a substrate-less double-sided pressure-sensitive adhesive sheet consisting only of a pressure-sensitive adhesive layer, with both sides of the pressure-sensitive adhesive layer protected by separators.

[0277] The units of the values ​​shown in Table 2 are "parts by weight." The monomer components shown in Table 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 macromonomer 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

[0278] [Table 2]

[0279] [Characteristics evaluation] The substrate-less double-sided PSA sheets of the Examples and Comparative Examples were subjected to the following measurements and evaluations. The evaluation results are shown in Tables 3 and 4.

[0280] (1) Evaluation of dielectric constant and dielectric loss The pressure-sensitive adhesive layer alone (the double-sided pressure-sensitive adhesive sheet from which the silicone-treated PET separator had been peeled off) obtained in the Examples or Comparative Examples was measured for dielectric constant and dielectric loss at frequencies of 28 GHz and 60 GHz, and for dielectric constant at 100 kHz using the following equipment. Measurements at 28 GHz were carried out over a circular area with a diameter of 8 cm, and measurements at 60 GHz were carried out over a circular area with a diameter of 4 cm. Three samples were prepared for each specimen, and the averages of the measured values ​​for the three samples were used as the relative dielectric constant and dielectric loss. Measurement method: Open resonator method JIS R1660-2 Equipment: Keycom Corporation, Interferometric Resonator Method Dielectric Constant Measurement System Measurement environment: 23±1℃, 52±1%RH

[0281] (2) Total light transmittance and haze One separator was peeled off from the double-sided pressure-sensitive adhesive sheet, and the double-sided pressure-sensitive adhesive sheet was attached to a glass slide (manufactured by Matsunami Glass Industry Co., Ltd., "White Polish No. 1", thickness 0.8 to 1.0 mm, total light transmittance 92%, haze 0.2%), and the other separator was then peeled off to prepare a test piece having a layer structure of double-sided pressure-sensitive adhesive sheet (adhesive layer) / glass slide. The total light transmittance and haze of the above test pieces in the visible light region were measured using a haze meter (device name "HM-150", manufactured by Murakami Color Research Institute Co., Ltd.) in an environment of 23±1°C and 52±1% RH. Three samples were prepared for each specimen, and the averages of the measured values ​​of the three samples were used as the total light transmittance and haze in the visible light region.

[0282] (3) Transmission and reception characteristics The transmission and reception characteristics of the pressure-sensitive adhesive layers (obtained by peeling the silicone-treated PET separator from the double-sided pressure-sensitive adhesive sheet) obtained in the Examples and Comparative Examples were evaluated using a rectangular microstrip antenna as shown in Figure 3 (see Chapter 5, "Planar Antennas," Group 4, Part 2, of the Institute of Electronics, Communications, and Information Engineers, URL: http: / / www.ieice.hbkb.org / files / 04 / 04gun_02hen_05.pdf). Specifically, a millimeter-wave patch antenna 33 having the shape shown in Figure 3 was formed on the front surface of a 100-µm-thick COP substrate (trade name: Zeonor, manufactured by Zeon Corporation, Japan) as an antenna substrate 34, and a 1-µm-thick copper ground layer 35 was formed on the back surface to create an antenna film 36. The size of the millimeter-wave patch antenna 33 was adjusted to optimize lamination with the pressure-sensitive adhesive of each Example or Comparative Example (length A: 2.8-3.2 mm, width B: 4.13 mm). The adhesive layer 32 of each example and comparative example was attached to the patch antenna 33 side of the antenna film 36 while taking care to prevent the inclusion of air bubbles or foreign matter, and then this was attached to a 0.7 mm thick chemically strengthened glass (manufactured by Corning) as a cover glass 31 to create an antenna laminate 3 of cover glass 31 / adhesive layer 32 / antenna film 36. Power was supplied from a microstrip line 33a connected to the millimeter wave patch antenna 33 of each antenna laminate 3, and the transmission and reception characteristics in the 30 GHz frequency band were evaluated. A gain that was improved compared to the gain (5.7 dB) when no adhesive layer was used (antenna film 36 placed close to cover glass 31) was marked with an ◯, and a decrease (worsening) was marked with an X.

[0283] [Table 3]

[0284] [Table 4]

[0285] Variations of the present invention are listed below. [Appendix 1] A millimeter wave antenna in which a cover member, an adhesive layer, and a substrate are laminated in this order, the substrate has an antenna element on at least one side; the adhesive layer is laminated on a surface of the substrate on the side having the antenna element; The pressure-sensitive adhesive layer has a dielectric constant of 2 to 5 at a frequency of 28 GHz, The pressure-sensitive adhesive layer has a dielectric loss of 0.0001 to 0.05 at 28 GHz. Millimeter wave antenna. [Appendix 2] The pressure-sensitive adhesive layer has a dielectric constant of 2 to 5 at a frequency of 60 GHz, Attachment 1: The millimeter-wave antenna according to claim 1, wherein the pressure-sensitive adhesive layer has a dielectric loss of 0.0001 to 0.05 at a frequency of 60 GHz. [Appendix 3] A millimeter-wave antenna in which a cover member, an adhesive layer, and a substrate are laminated in this order, the substrate has an antenna element on at least one side; the adhesive layer is laminated on a surface of the substrate on the side having the antenna element; The pressure-sensitive adhesive layer has a dielectric constant of 2 to 5 at a frequency of 60 GHz, The pressure-sensitive adhesive layer has a dielectric loss of 0.0001 to 0.05 at 60 GHz. Millimeter wave antenna. [Appendix 4] A millimeter wave antenna in which a cover member, an adhesive layer, a substrate, and an image display panel are laminated in this order, the substrate has an antenna element on at least one side; the adhesive layer is laminated on a surface of the substrate on the side having the antenna element; The pressure-sensitive adhesive layer has a dielectric constant of 2 to 5 at a frequency of 28 GHz, the pressure-sensitive adhesive layer has a dielectric constant of 2 to 8 at 100 kHz; The pressure-sensitive adhesive layer has a dielectric loss of 0.0001 to 0.05 at 28 GHz. Millimeter wave antenna. [Appendix 5] The pressure-sensitive adhesive layer has a dielectric constant of 2 to 5 at a frequency of 60 GHz, 5. The millimeter-wave antenna according to claim 4, wherein the pressure-sensitive adhesive layer has a dielectric loss of 0.0001 to 0.05 at a frequency of 60 GHz. [Appendix 6] A millimeter-wave antenna in which a cover member, an adhesive layer, a substrate, and an image display panel are laminated in this order, the substrate has an antenna element on at least one side; the adhesive layer is laminated on a surface of the substrate on the side having the antenna element; The pressure-sensitive adhesive layer has a dielectric constant of 2 to 5 at a frequency of 60 GHz, the pressure-sensitive adhesive layer has a dielectric constant of 2 to 8 at 100 kHz; The pressure-sensitive adhesive layer has a dielectric loss of 0.0001 to 0.05 at 60 GHz. Millimeter wave antenna. [Supplementary Note 7] The millimeter-wave antenna according to any one of Supplementary Notes 4 to 6, wherein the image display panel has a touch sensor. [Appendix 8] The millimeter-wave antenna according to any one of Appendices 4 to 7, wherein an adhesive layer is further laminated between the substrate and the image display panel. [Explanation of symbols]

[0286] 1A, 1B millimeter wave antenna 10, 10a, 10b adhesive layer 11 Antenna board 12 Cover member 2 mm-wave antenna elements 13 Image display panel 3 Antenna stack 31 Coverslip 32 adhesive layer 33 Millimeter-wave patch antenna 33a Microstrip line 34 Antenna board 35 Copper Ground Plane 36 Antenna Film

Claims

1. A millimeter-wave antenna in which a cover member, a pressure-sensitive adhesive layer, and a substrate are laminated in this order, the substrate has an antenna element on at least one side; the adhesive layer is laminated on a surface of the substrate on the side having the antenna element; the pressure-sensitive adhesive layer has a dielectric constant of 2 to 5 at a frequency of 28 GHz; the pressure-sensitive adhesive layer has a dielectric loss of 0.0001 to 0.05 at 28 GHz; the base polymer constituting the pressure-sensitive adhesive layer is at least one selected from the group consisting of acrylic polymers, rubber polymers, silicone polymers, polyester polymers, urethane polymers, polyamide polymers, epoxy polymers, vinyl alkyl ether polymers, and fluorine-based polymers; Millimeter wave antenna.

2. the pressure-sensitive adhesive layer has a dielectric constant of 2 to 5 at a frequency of 60 GHz; 2. The millimeter-wave antenna according to claim 1, wherein the pressure-sensitive adhesive layer has a dielectric loss of 0.0001 to 0.05 at a frequency of 60 GHz.

3. A millimeter-wave antenna in which a cover member, a pressure-sensitive adhesive layer, and a substrate are laminated in this order, the substrate has an antenna element on at least one side; the adhesive layer is laminated on a surface of the substrate on the side having the antenna element; the pressure-sensitive adhesive layer has a dielectric constant of 2 to 5 at a frequency of 60 GHz; the pressure-sensitive adhesive layer has a dielectric loss of 0.0001 to 0.05 at 60 GHz; the base polymer constituting the pressure-sensitive adhesive layer is at least one selected from the group consisting of acrylic polymers, rubber polymers, silicone polymers, polyester polymers, urethane polymers, polyamide polymers, epoxy polymers, vinyl alkyl ether polymers, and fluorine-based polymers; Millimeter wave antenna.

4. A millimeter-wave antenna in which a cover member, a pressure-sensitive adhesive layer, a substrate, and an image display panel are laminated in this order, the substrate has an antenna element on at least one side; the adhesive layer is laminated on a surface of the substrate on the side having the antenna element; the pressure-sensitive adhesive layer has a dielectric constant of 2 to 5 at a frequency of 28 GHz; the pressure-sensitive adhesive layer has a dielectric constant of 2 to 8 at 100 kHz; the pressure-sensitive adhesive layer has a dielectric loss of 0.0001 to 0.05 at 28 GHz; the base polymer constituting the pressure-sensitive adhesive layer is at least one selected from the group consisting of acrylic polymers, rubber polymers, silicone polymers, polyester polymers, urethane polymers, polyamide polymers, epoxy polymers, vinyl alkyl ether polymers, and fluorine-based polymers; Millimeter wave antenna.

5. the pressure-sensitive adhesive layer has a dielectric constant of 2 to 5 at a frequency of 60 GHz; 5. The millimeter-wave antenna according to claim 4, wherein the pressure-sensitive adhesive layer has a dielectric loss of 0.0001 to 0.05 at a frequency of 60 GHz.

6. A millimeter-wave antenna in which a cover member, a pressure-sensitive adhesive layer, a substrate, and an image display panel are laminated in this order, the substrate has an antenna element on at least one side; the adhesive layer is laminated on a surface of the substrate on the side having the antenna element; the pressure-sensitive adhesive layer has a dielectric constant of 2 to 5 at a frequency of 60 GHz; the pressure-sensitive adhesive layer has a dielectric constant of 2 to 8 at 100 kHz; the pressure-sensitive adhesive layer has a dielectric loss of 0.0001 to 0.05 at 60 GHz; the base polymer constituting the pressure-sensitive adhesive layer is at least one selected from the group consisting of acrylic polymers, rubber polymers, silicone polymers, polyester polymers, urethane polymers, polyamide polymers, epoxy polymers, vinyl alkyl ether polymers, and fluorine-based polymers; Millimeter wave antenna.

7. The millimeter-wave antenna according to any one of claims 4 to 6, wherein the image display panel has a touch sensor.

8. 8. The millimeter wave antenna according to claim 4, further comprising an adhesive layer laminated between the substrate and the image display panel.

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