Adhesive sheet, multilayer body, and device

Abstract

[Problem] To provide an adhesive sheet which is capable of securing flexibility of an adhesive layer at low temperatures and is capable of suppressing variation in the degree of deformation even in cases where the adhesive layer is deformed in a specific temperature range. [Solution] An adhesive sheet which has an adhesive layer for bonding a first member and a second member, wherein the Shore hardness of the adhesive layer at -20°C is 70 HS or less as measured with a type E durometer, and the recovery rate of the adhesive layer at 23°C is 70% or more.

Description

Adhesive sheet, laminate and device

[0001] The present invention relates to a pressure-sensitive adhesive sheet, a laminate, and a device.

[0002] Input devices using touch panels are used as input interfaces for electronic devices such as information devices. These input devices detect the position (pressed position) pressed by a finger or the like, acquire position information, and execute a predetermined process in the information device based on the position information, outputting the result to a display or the like. Methods for detecting the pressed position include a resistive film method and a capacitive method.

[0003] In recent years, touch panels have been required to detect not only the pressure position but also the pressure. Detecting the pressure and performing processing based on the pressure information will enable a richer input interface.

[0004] One example of a method for detecting pressure is to use a piezoelectric element that can convert mechanical displacement into electrical displacement and vice versa. When a piezoelectric element is pressed, it deforms and distorts. This distortion (mechanical displacement) is converted into electrical displacement, and a voltage corresponding to the distortion is generated in the piezoelectric element. By detecting this voltage, pressure information can be obtained.

[0005] A touch panel is constructed by laminating a piezoelectric body and other components (electrodes, protective panels, etc.). Furthermore, since touch panels are often integrated with a display, the components of the touch panel, including the piezoelectric body, are laminated with components that constitute the display (display components such as liquid crystal elements and organic EL elements, electrodes, optical components, etc.). Such a laminate of a piezoelectric body and other components is generally formed by bonding the piezoelectric body and other components together using an adhesive layer of an adhesive sheet.

[0006] As described above, in a touch panel including a piezoelectric element, the piezoelectric element deforms, and therefore the adhesive layer that bonds the piezoelectric element to another member needs to have flexibility that does not hinder the deformation of the piezoelectric element and does not cause peeling from the other member.

[0007] In addition, touch panels or displays that do not contain piezoelectric materials may also be required to be flexible. For example, flexible displays have been proposed, such as stationary displays that are curved and installed on a cylindrical pillar, and mobile displays that can be folded or rolled up for portability. The adhesive layer that constitutes such flexible displays must also be flexible enough to allow bending and prevent peeling from other components.

[0008] Patent Document 1 discloses a touch panel including a piezoelectric sheet, and describes that this touch panel can detect position information and pressure information by pressing the piezoelectric sheet.

[0009] JP 2011-253517 A

[0010] As electronic devices become smaller and more powerful, portable devices such as smartphones and tablet terminals have become widespread. Such portable devices, external displays, etc. are used in external environments exposed to temperature changes. Therefore, in order to maintain constant input sensitivity, flexibility, etc. even when exposed to temperature changes, it is required that the pressure-sensitive adhesive layer have small variations in the degree of deformation within a specified temperature range.

[0011] In general, the flexibility of a pressure-sensitive adhesive layer for bonding members to each other is highly dependent on temperature changes. In particular, the flexibility of the pressure-sensitive adhesive layer tends to decrease when the temperature is low. That is, it is necessary to ensure the flexibility of the pressure-sensitive adhesive layer at low temperatures.

[0012] The touch panel disclosed in Patent Document 1 has a piezoelectric sheet and a surface protection film, etc., bonded together via an adhesive or pressure-sensitive adhesive. However, there is a problem in that no consideration is given to the flexibility of the pressure-sensitive adhesive layer at low temperatures or the degree of deformation of the adhesive or pressure-sensitive adhesive within a specified temperature range.

[0013] The present invention has been made in consideration of the above-described circumstances, and aims to provide an adhesive sheet that can ensure the flexibility of the adhesive layer at low temperatures and suppress variation in the degree of deformation, even when the adhesive layer is deformed within a specified temperature range.

[0014] The aspects of the present invention are as follows.

[0015] [1] A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer for bonding a first member and a second member, wherein the pressure-sensitive adhesive layer has a Shore hardness of 70 HS or less at -20°C as measured with an E-type durometer, and the pressure-sensitive adhesive layer has a recovery rate of 70% or more at 23°C. [2] The pressure-sensitive adhesive sheet according to [1], wherein the pressure-sensitive adhesive layer has a gel fraction of 40% or more. [3] The pressure-sensitive adhesive sheet according to [1] or [2], wherein the pressure-sensitive adhesive layer has a recovery rate of 70% or more at -20°C. [4] The pressure-sensitive adhesive sheet according to any one of [1] to [3], wherein the pressure-sensitive adhesive layer has a distortion rate after 10 seconds at -20°C of 10% or more. [5] The pressure-sensitive adhesive sheet according to any one of [1] to [4], wherein at least one selected from the first member and the second member is a member containing a piezoelectric material. [6] The pressure-sensitive adhesive sheet according to any one of [1] to [5], wherein at least one selected from the first member and the second member is a flexible member. [7] The pressure-sensitive adhesive sheet according to any one of [1] to [6], wherein the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer is an acrylic pressure-sensitive adhesive. [8] The pressure-sensitive adhesive sheet according to [7], wherein the acrylic pressure-sensitive adhesive contains a (meth)acrylic acid ester polymer and a crosslinking agent.

[0016] [9] A laminate comprising a first member, a second member, and a pressure-sensitive adhesive layer bonding the first member and the second member to each other, wherein the pressure-sensitive adhesive layer is the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet according to any one of [1] to [8].

[10] The laminate according to [9], wherein at least one selected from the first member and the second member is a member containing a piezoelectric material.

[11] The laminate according to [9] or

[10] , wherein at least one selected from the first member and the second member is a flexible member.

[0017]

[12] A device comprising the laminate according to any one of [9] to

[11] .

[0018] According to the present invention, it is possible to provide a pressure-sensitive adhesive sheet that ensures the flexibility of the pressure-sensitive adhesive layer at low temperatures and suppresses variation in the degree of deformation, even when the pressure-sensitive adhesive layer is deformed within a specified temperature range.

[0019] Fig. 1 is a cross-sectional view of a pressure-sensitive adhesive sheet according to one embodiment of the present invention. Fig. 2 is a cross-sectional view of a laminate according to one embodiment of the present invention. Fig. 3 is a cross-sectional view of a device according to one embodiment of the present invention. Fig. 4 is a schematic view for explaining a static bending test in the examples. Fig. 5 is a schematic view for explaining the amount of deformation of a test piece in a static bending test in the examples.

[0020] The present invention will be described in detail below based on specific embodiments.

[0021] (1. Pressure-Sensitive Adhesive Sheet) As shown in FIG. 1 , the pressure-sensitive adhesive sheet 1 according to this embodiment includes a pressure-sensitive adhesive layer 10, a first release sheet 11, and a second release sheet 12. The pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer 10 will be described later. Two release sheets (the first release sheet 11 and the second release sheet 12) support the pressure-sensitive adhesive layer 10, and are arranged so that their release surfaces contact both main surfaces 10a, 10b of the pressure-sensitive adhesive layer, allowing for peeling from the pressure-sensitive adhesive layer. In other words, the pressure-sensitive adhesive layer 10 is releasably sandwiched between the two release sheets (the first release sheet 11 and the second release sheet 12). In this specification, the release surface of a release sheet refers to the surface of the release sheet that has releasability, and includes both a surface that has been subjected to a release treatment and a surface that exhibits releasability even without a release treatment. Release sheets will be described later.

[0022] The pressure-sensitive adhesive sheet according to this embodiment is used to bond a first member and a second member. At least one member selected from the first member and the second member is preferably a member containing a piezoelectric material. Also, at least one member selected from the first member and the second member is preferably a bendable member (flexible member). Furthermore, at least one member selected from the first member and the second member may be a flexible member containing a piezoelectric material.

[0023] A member including a piezoelectric body is a member in which a distortion occurs in the piezoelectric body when pressed, etc., and a voltage due to this distortion is generated in the piezoelectric body. Examples of members including a piezoelectric body include film-like members having piezoelectricity.

[0024] A flexible member is a member that maintains its function even when deformed by bending such as folding or by being pushed in. Examples of flexible members include members that are molded to bend during the manufacture of a device that includes the flexible member and that maintain the bent state, and members that are repeatedly bent during the use of a device that includes the flexible member.

[0025] Therefore, the adhesive layer bonding the piezoelectric member or the flexible member is also deformed. When a device including a piezoelectric member and / or a flexible member is a portable device or a device installed in an external environment, such a device is exposed to temperature changes during use. For example, in an environment where the temperature is about -20°C, or where the temperature is 40°C or higher and the temperature of the device rises to about 70°C due to heat generation, the adhesive layer is also exposed to such temperature changes.

[0026] However, in the above-mentioned wide temperature range, the physical properties of the adhesive constituting the adhesive layer may change. For example, at low temperatures, the flexibility of the adhesive tends to decrease. When the flexibility of the adhesive decreases, the adhesive becomes less likely to deform. As a result, at low temperatures, even when the same pressing force is applied, the input sensitivity of the touch panel may decrease, and the force required to bend the display may increase, resulting in a sense of incongruity compared to operation at normal temperatures.

[0027] Therefore, it is necessary to ensure the flexibility of the pressure-sensitive adhesive layer at low temperatures and to suppress variations in the degree of deformation of the pressure-sensitive adhesive layer within a predetermined temperature range.

[0028] To address the above-mentioned problems, in the pressure-sensitive adhesive sheet according to this embodiment, the hardness of the pressure-sensitive adhesive layer at low temperatures is maintained low, and the physical properties of the pressure-sensitive adhesive layer are controlled so that even if the pressure-sensitive adhesive layer is repeatedly deformed, the amount of recovery from the deformation is large, thereby suppressing variation in the degree of deformation of the pressure-sensitive adhesive layer within a predetermined temperature range. The components of the pressure-sensitive adhesive sheet according to this embodiment will be described in detail below.

[0029] (1.1. Pressure-sensitive adhesive layer) The pressure-sensitive adhesive layer bonds the first member and the second member. As described above, it is preferable that the first member and the second member are bonded to a member including a piezoelectric body and / or a flexible member.

[0030] The pressure-sensitive adhesive layer may be composed of one layer (single layer) or two or more layers. When the pressure-sensitive adhesive layer has multiple layers, these multiple layers may be the same or different from each other, and the combination of layers constituting these multiple layers is not particularly limited.

[0031] The thickness of the pressure-sensitive adhesive layer 10 is preferably 1 to 1000 μm, more preferably 5 to 500 μm, even more preferably 10 to 250 μm, particularly preferably 20 to 100 μm, and even more preferably 30 to 70 μm. This provides adhesiveness that allows the first and second members to be satisfactorily bonded together, and, even if deformation occurs due to bending or pressure, a laminate that exhibits good indentation properties and is less likely to leave indentation marks, coupled with physical properties such as Shore hardness and recovery, which will be described later, can be provided.

[0032] (1.2. Physical Properties of Pressure-Sensitive Adhesive Layer) In this embodiment, the pressure-sensitive adhesive layer 10 has the following physical properties.

[0033] In the present specification, "the Shore hardness (Shore E) measured on the surface of a pressure-sensitive adhesive layer at temperature T (°C) using an E-type durometer" may be expressed as "Shore E (T)." Specifically, when the temperature T (°C) is -20°C, it may be expressed as "Shore E (-20)," when it is 23°C, it may be expressed as "Shore E (23)," and when it is 70°C, it may be expressed as "Shore E (70)."

[0034] In the present specification, the "restoration rate of the pressure-sensitive adhesive layer at temperature T (°C)" may be expressed as "restoration rate R(T)." Specifically, when the temperature T (°C) is -20°C, it may be expressed as "restoration rate R(-20)," when it is 23°C, it may be expressed as "restoration rate R(23)," and when it is 70°C, it may be expressed as "restoration rate R(70)."

[0035] In the present specification, the "distortion rate of the pressure-sensitive adhesive layer after 10 seconds at a temperature T (°C)" may be expressed as a "distortion rate (T)." Specifically, when the temperature T (°C) is -20°C, it may be expressed as a "distortion rate (-20)," when it is 23°C, it may be expressed as a "distortion rate (23)," and when it is 70°C, it may be expressed as a "distortion rate (70)."

[0036] (1.2.1. Shore Hardness of Pressure-Sensitive Adhesive Layer) In this embodiment, the Shore E (-20°C) is preferably 70HS or less. This makes it easier to ensure flexibility of the pressure-sensitive adhesive layer even at low temperatures. Typically, the Shore hardness of the pressure-sensitive adhesive layer at room temperature (e.g., 23°C) and at high temperatures (e.g., 70°C) tends to be lower than the Shore hardness of the pressure-sensitive adhesive layer at low temperature (-20°C). Therefore, the pressure-sensitive adhesive layer can be kept flexible over a wide temperature range, and for example, a laminate including such a pressure-sensitive adhesive layer exhibits good press-in properties even at low temperatures, similar to those at room temperature.

[0037] From the above viewpoints, the Shore E(-20) is preferably 1 to 67 HS, and more preferably 15 to 64 HS. From the viewpoint of achieving both the recovery rate and blister resistance described below, the Shore E(-20) is preferably 25 to 60 HS, more preferably 30 to 55 HS, particularly preferably 36 to 50 HS, and of these, 41 to 46 HS is preferred.

[0038] Furthermore, the Shore E(23) is preferably 70HS or less. In addition to the Shore E(-20) being within the above range, the Shore E(23) being within the above range makes it easy to ensure the flexibility of the pressure-sensitive adhesive layer at room temperature. As a result, the pressure-sensitive adhesive layer can be kept flexible over a wide temperature range, and a laminate including such a pressure-sensitive adhesive layer, for example, exhibits good press-in properties.

[0039] From the above viewpoints, the Shore E(23) is preferably 1 to 65 HS, more preferably 10 to 60 HS, and even more preferably 16 to 55 HS. From the viewpoint of achieving both a recovery rate and blister resistance, which will be described later, the Shore E(23) is preferably 22 to 50 HS, particularly preferably 28 to 45 HS, and of these, preferably 31 to 40 HS.

[0040] Furthermore, the Shore E(70) is preferably 70HS or less. In addition to the Shore E(-20) being within the above range, the Shore E(70) being within the above range makes it easy to ensure the flexibility of the pressure-sensitive adhesive layer at high temperatures. As a result, the pressure-sensitive adhesive layer can be kept flexible over a wide temperature range, and a laminate including such a pressure-sensitive adhesive layer, for example, exhibits good press-in properties.

[0041] From the above viewpoints, the Shore E(70) is preferably 1 to 55 HS, more preferably 8 to 40 HS, and even more preferably 16 to 35 HS. From the viewpoint of achieving both the recovery rate and blister resistance described below, the Shore E(70) is particularly preferably 20 to 30 HS, and of these, 23 to 26 HS is preferred.

[0042] From the viewpoint of being able to maintain the flexibility of the pressure-sensitive adhesive layer over a wide temperature range, it is preferable that the Shore hardness of the pressure-sensitive adhesive layer at 23°C and 70°C, in addition to -20°C, be within the above ranges.

[0043] The Shore hardness of the pressure-sensitive adhesive layer can be adjusted, for example, by changing the composition of the pressure-sensitive adhesive (the type and amount of reactive functional groups, the molecular structure and glass transition temperature of the monomer composition used, etc.), the molecular weight of the material constituting the pressure-sensitive adhesive, etc. Specific methods for measuring the Shore hardness will be described in detail in the Examples below. In this specification, when the pressure-sensitive adhesive layer is active energy ray-curable, the Shore hardness of the pressure-sensitive adhesive layer is the Shore hardness after exposure to active energy rays.

[0044] (1.2.2. Recovery rate of pressure-sensitive adhesive layer) In this embodiment, the recovery rate R(23) is preferably 70% or more. The recovery rate indicates the percentage of recovery of the state of the pressure-sensitive adhesive layer 60 seconds after the pressure-sensitive adhesive layer in a bent and deformed state is released, relative to the state of the pressure-sensitive adhesive layer before deformation and not being bent. In other words, if the state of the pressure-sensitive adhesive layer 60 seconds after the pressure-sensitive adhesive layer in a bent and deformed state is the same as the state of the pressure-sensitive adhesive layer before deformation and not being bent, the recovery rate is 100%. The recovery rate is an index of the degree of recovery from deformation.

[0045] When the recovery rate R(23) is within the above range, the deformed and undeformed states of the pressure-sensitive adhesive layer are similar at 23°C, and the deformation of the pressure-sensitive adhesive layer is sufficiently recovered. Therefore, for example, when the surface of a laminate formed via the pressure-sensitive adhesive layer is pressed with a finger, a touch pen, or the like, the deformation of the pressure-sensitive adhesive layer at the pressed location recovers after the pressing, and an indentation is unlikely to remain. Such a pressure-sensitive adhesive layer is suitable for laminates that undergo deformation such as bending or pressing. Furthermore, when the recovery rate R(23) is within the above range, the recovery rates of the pressure-sensitive adhesive layer at low temperatures (e.g., −20°C) and high temperatures (e.g., 70°C) tend to exhibit values ​​equivalent to the recovery rate R(23). Therefore, variation in the degree of deformation of the pressure-sensitive adhesive layer can be suppressed over a wide temperature range.

[0046] From the above viewpoints, the restoration rate R(23) is preferably 80% or more, more preferably 84% or more, even more preferably 88% or more, particularly preferably 90% or more, and most preferably 91% or more. The upper limit of the restoration rate R(23) is usually preferably 100% or less.

[0047] Furthermore, the restoration rate R(-20) is preferably 70% or more. In addition to the restoration rate R(23) being within the above range, the restoration rate R(-20) being within the above range reliably suppresses variation in the degree of deformation of the pressure-sensitive adhesive layer at low temperatures. As a result, variation in the degree of deformation of the pressure-sensitive adhesive layer can be suppressed over a wide temperature range.

[0048] From the above viewpoints, the restoration rate R(-20) is preferably 80% or more, more preferably 84% or more, even more preferably 88% or more, particularly preferably 90% or more, and of these, preferably 91% or more. The lower limit of the restoration rate R(-20) is preferably 100% or less.

[0049] Furthermore, the restoration rate R(70) is preferably 70% or more. In addition to the restoration rate R(23) being within the above range, the restoration rate R(70) being within the above range reliably suppresses variation in the degree of deformation of the pressure-sensitive adhesive layer at high temperatures. As a result, variation in the degree of deformation of the pressure-sensitive adhesive layer can be suppressed over a wide temperature range.

[0050] From the above viewpoints, the restoration rate R(70) is preferably 75% or more, more preferably 80% or more, even more preferably 85% or more, particularly preferably 90% or more, and most preferably 93% or more. On the other hand, the lower limit of the restoration rate R(70) is preferably 100% or less.

[0051] From the viewpoint of being able to suppress variations in the degree of deformation of the pressure-sensitive adhesive layer over a wide temperature range, it is preferable that the recovery rates of the pressure-sensitive adhesive layer be within the above ranges not only at 23°C but also at −20°C and 70°C.

[0052] The restoration rate of the pressure-sensitive adhesive layer can be adjusted, for example, by changing the composition of the pressure-sensitive adhesive (the type and amount of reactive functional groups, the molecular structure and glass transition temperature of the monomer composition used, etc.), the molecular weight of the material constituting the pressure-sensitive adhesive, etc. Specific methods for measuring the restoration rate will be described in detail in the Examples below. In this specification, when the pressure-sensitive adhesive layer is active energy ray-curable, the restoration rate of the pressure-sensitive adhesive layer is the restoration rate after irradiation with active energy rays.

[0053] (1.2.3. Distortion Rate After 10 Seconds) In this embodiment, the distortion rate (-20) is preferably 10% or more. This makes it easier to achieve the desired Shore E(-20) range and ensure the flexibility of the pressure-sensitive adhesive layer even at low temperatures. Typically, the distortion rate of a pressure-sensitive adhesive layer at room temperature and high temperatures (e.g., 70°C) tends to be higher than at low temperatures (e.g., -20°C). Therefore, the pressure-sensitive adhesive layer can be kept flexible over a wide temperature range, and a laminate including such a pressure-sensitive adhesive layer exhibits good pressurization properties at low temperatures similar to those at room temperature. The distortion rate after 10 seconds in this specification refers to the distortion rate of the pressure-sensitive adhesive layer 10 seconds after the start of applying a constant stress to the pressure-sensitive adhesive layer using a viscoelasticity measuring device at a temperature of -20°C. Specific measurement methods will be described later.

[0054] From the above viewpoints, the distortion rate (-20) is preferably 12 to 200%, more preferably 13 to 120%. From the viewpoints of easily achieving the above-mentioned Shore E(-20) within a desired range and of achieving both the recovery rate and blister resistance, the distortion rate (-20) is preferably 14 to 60%, more preferably 15 to 50%, particularly preferably 16 to 40%, and of these, 17 to 30% is preferred.

[0055] The distortion (23) is preferably 10% or more, which makes it easier for the Shore E (23) to fall within the desired range and ensures flexibility of the pressure-sensitive adhesive layer at room temperature.

[0056] From the above viewpoints, the strain (23) is preferably 20 to 300%, more preferably 30 to 200%. From the viewpoints of making it easier for the Shore E (23) to satisfy the desired range and of achieving both the recovery rate and blister resistance, the strain (23) is further preferably 35 to 170%, preferably 40 to 130%, particularly preferably 45 to 100%, and of these, preferably 50 to 80%.

[0057] The strain (70) is preferably 10% or more, which makes it easier for the Shore E(70) to fall within the desired range and also makes it easier to ensure that the pressure-sensitive adhesive layer has both the cohesive strength and flexibility at high temperatures.

[0058] From the above viewpoints, the strain (70) is preferably 20 to 600%, more preferably 30 to 400%. From the viewpoints of making it easier for the Shore E(70) to satisfy the desired range and of achieving both the recovery rate and blister resistance, the strain (70) is further preferably 35 to 300%, preferably 40 to 200%, particularly preferably 45 to 150%, and of these, preferably 50 to 120%.

[0059] From the viewpoint of being able to maintain the flexibility of the pressure-sensitive adhesive layer over a wide temperature range, it is preferable that the strain rate of the pressure-sensitive adhesive layer at 23°C and 70°C, in addition to -20°C, be within the above range.

[0060] The distortion rate of the pressure-sensitive adhesive layer can be adjusted, for example, by changing the composition of the pressure-sensitive adhesive (the type and amount of reactive functional groups, the molecular structure and glass transition temperature of the monomer composition used, etc.), the molecular weight of the material constituting the pressure-sensitive adhesive, etc. Specific methods for measuring the distortion rate will be described in detail in the Examples below. In this specification, when the pressure-sensitive adhesive layer is active energy ray-curable, the distortion rate of the pressure-sensitive adhesive layer is the distortion rate after irradiation with active energy rays.

[0061] (1.2.4. Gel Fraction) In this embodiment, the gel fraction of the pressure-sensitive adhesive layer is preferably 40 to 100%, more preferably 50 to 95%, even more preferably 60 to 90%, particularly preferably 70 to 86%, and of these, preferably 73 to 82%. This results in a pressure-sensitive adhesive with suitable cohesive properties, making it easier to adjust the physical properties described above and the adhesive strength described below to within desired ranges. In addition, good blister resistance is likely to be exhibited.

[0062] When the pressure-sensitive adhesive layer is active energy ray-curable, the gel fraction before active energy ray irradiation is preferably 40 to 90%, more preferably 48 to 85%, even more preferably 56 to 80%, and particularly preferably 60 to 75%. On the other hand, the gel fraction after active energy ray irradiation is preferably 50 to 100%, more preferably 60 to 95%, even more preferably 70 to 90%, and particularly preferably 75 to 85%. This results in a pressure-sensitive adhesive with suitable cohesive properties, making it easier to adjust the physical properties described above and the adhesive strength described below to desired ranges. Furthermore, good blister resistance is also easily exhibited.

[0063] (1.2.5. Adhesion Strength of Pressure-Sensitive Adhesive) In this embodiment, the adhesive strength of the pressure-sensitive adhesive to soda-lime glass is preferably 0.1 to 60 N / 25 mm, more preferably 0.5 to 40 N / 25 mm, even more preferably 1 to 20 N / 25 mm, particularly preferably 3 to 15 N / 25 mm, and of these, preferably 6 to 10 N / 25 mm. This improves adhesion to adherends such as optical components, and, together with the gel fraction range described above, makes it easier to exhibit good blister resistance.

[0064] When the pressure-sensitive adhesive layer is active energy ray-curable, the adhesive strength of the pressure-sensitive adhesive to soda-lime glass before exposure to active energy rays is preferably 0.1 to 60 N / 25 mm, more preferably 1 to 40 N / 25 mm, even more preferably 5 to 20 N / 25 mm, and particularly preferably 10 to 15 N / 25 mm. On the other hand, the adhesive strength of the pressure-sensitive adhesive to soda-lime glass after exposure to active energy rays is preferably 1 to 100 N / 25 mm, more preferably 5 to 75 N / 25 mm, even more preferably 10 to 50 N / 25 mm, and particularly preferably 15 to 40 N / 25 mm, with 20 to 30 N / 25 mm being preferred. This improves adhesion to adherends such as optical components, and, together with the gel fraction range described above, facilitates the achievement of good blister resistance.

[0065] The adhesive strength may be measured by a 180-degree peeling method in accordance with JIS Z0237: 2009. A specific measurement method is as shown in the test examples described below.

[0066] (1.2.6. Total Light Transmittance of Pressure-Sensitive Adhesive Layer) In this embodiment, the total light transmittance of the pressure-sensitive adhesive layer is preferably 80% or more, more preferably 90% or more, even more preferably 95% or more, and particularly preferably 98% or more. This is suitable when transparency is required for the pressure-sensitive adhesive layer for optical applications. The upper limit of the total light transmittance is usually 100% or less. In this specification, when the pressure-sensitive adhesive layer is active energy ray-curable, the total light transmittance of the pressure-sensitive adhesive layer is the total light transmittance after irradiation with active energy rays. Note that the total light transmittance in this specification is a value measured in accordance with JIS K7361-1:1997.

[0067] (1.2.7. Haze Value) In this embodiment, the haze value of the pressure-sensitive adhesive layer is preferably 10% or less, more preferably 1% or less, even more preferably 0.5% or less, and particularly preferably 0.2% or less. This is suitable when transparency of the pressure-sensitive adhesive layer is required for optical applications. The lower limit of the haze value is usually 0% or more. In this specification, when the pressure-sensitive adhesive layer is active energy ray-curable, the haze value of the pressure-sensitive adhesive layer is the haze value after exposure to active energy rays. Note that the haze value in this specification is a value measured in accordance with JIS K7136:2000.

[0068] (1.3. Composition of Pressure-Sensitive Adhesive) As long as the pressure-sensitive adhesive layer has the above-described physical properties, the composition of the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer is not particularly limited. For example, it may be any of an acrylic pressure-sensitive adhesive, a polyester pressure-sensitive adhesive, a polyurethane pressure-sensitive adhesive, a rubber pressure-sensitive adhesive, a silicone pressure-sensitive adhesive, etc. Furthermore, the pressure-sensitive adhesive may be any of an emulsion type, a solvent type, or a solventless type. Furthermore, the pressure-sensitive adhesive may or may not have a cross-linked structure. Furthermore, the pressure-sensitive adhesive may be active energy ray-curable or non-active energy ray-curable.

[0069] In this embodiment, from the viewpoint of ease of realizing the above-mentioned physical properties, and from the viewpoint of adhesive properties, optical properties, etc., an acrylic adhesive is preferred as the adhesive, and an acrylic adhesive having a crosslinked structure is more preferred.

[0070] Specifically, the adhesive is preferably an adhesive obtained by crosslinking an adhesive composition (hereinafter sometimes referred to as "adhesive composition P") containing a (meth)acrylic acid ester polymer (A) and a crosslinking agent (B). Such an adhesive is likely to satisfy the above-mentioned physical properties and easily obtain good adhesive strength. Furthermore, from the perspective of the SDGs, the adhesive may be made of a material with a high biomass content, a material that can be recycled or reused, or a recycled or reused material. In this specification, (meth)acrylic acid means both acrylic acid and methacrylic acid. The same applies to other similar terms. Furthermore, the term "polymer" also includes the concept of "copolymer."

[0071] (1.3.1. (Meth)acrylic acid ester polymer (A)) The (meth)acrylic acid ester polymer (A) preferably contains, as monomer units constituting the polymer, a (meth)acrylic acid alkyl ester and a monomer having a reactive functional group in the molecule (reactive functional group-containing monomer). This makes it easier to obtain a pressure-sensitive adhesive having a crosslinked structure and good adhesiveness.

[0072] Furthermore, the (meth)acrylic acid ester polymer (A) preferably contains an aromatic ring-containing monomer as a monomer unit constituting the polymer, which makes it easier to obtain the above-mentioned physical properties.

[0073] Furthermore, the (meth)acrylic acid ester polymer (A) preferably contains a nitrogen atom-containing monomer as a monomer unit constituting the polymer, which makes it easier to obtain the above-mentioned physical properties.

[0074] Therefore, the (meth)acrylic acid ester polymer (A) preferably contains, as monomer units constituting the polymer, a (meth)acrylic acid alkyl ester, a reactive functional group-containing monomer, and an aromatic ring-containing monomer, and also preferably contains a (meth)acrylic acid alkyl ester, a reactive functional group-containing monomer, an aromatic ring-containing monomer, and a nitrogen atom-containing monomer.

[0075] By including a (meth)acrylic acid alkyl ester, the resulting pressure-sensitive adhesive can exhibit desirable adhesiveness. As the (meth)acrylic acid alkyl ester, a (meth)acrylic acid alkyl ester having an alkyl group having 1 to 20 carbon atoms is preferred. The alkyl group may be linear or branched, or may have a cyclic structure.

[0076] Examples of (meth)acrylic acid alkyl esters having an alkyl group containing 1 to 20 carbon atoms include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, n-decyl (meth)acrylate, n-dodecyl (meth)acrylate, myristyl (meth)acrylate, palmityl (meth)acrylate, and stearyl (meth)acrylate.

[0077] Among these, (meth)acrylic acid esters in which the alkyl group has 1 to 8 carbon atoms are preferred, and (meth)acrylic acid esters in which the alkyl group has 4 to 8 carbon atoms are particularly preferred. Specifically, n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and n-octyl (meth)acrylate are preferred, and n-butyl acrylate, 2-ethylhexyl acrylate, and n-octyl acrylate are particularly preferred. These may be used alone or in combination of two or more.

[0078] The (meth)acrylic acid ester polymer (A) preferably contains 60 to 99.9 mass% of (meth)acrylic acid alkyl esters having an alkyl group containing 1 to 20 carbon atoms as monomer units constituting the polymer, more preferably 70 to 99 mass%, even more preferably 80 to 98.5 mass%, and particularly preferably 90 to 98 mass%. This allows the resulting pressure-sensitive adhesive layer to be endowed with suitable resilience and adhesiveness. Furthermore, desired amounts of other monomer components can be incorporated into the (meth)acrylic acid ester polymer (A), making it easier to design pressure-sensitive adhesives that exhibit desired performance.

[0079] The (meth)acrylic acid ester polymer (A) contains a reactive functional group-containing monomer as a monomer unit constituting the polymer, and thus the (meth)acrylic acid ester polymer (A) reacts with the crosslinking agent (B) described below via the reactive functional group derived from the reactive functional group-containing monomer, forming a crosslinked structure (three-dimensional network structure) in the pressure-sensitive adhesive. As a result, a pressure-sensitive adhesive having the desired cohesive strength is obtained, and the pressure-sensitive adhesive is more likely to satisfy the above-mentioned physical properties.

[0080] Preferred examples of reactive functional group-containing monomers include monomers having a hydroxyl group in the molecule (hydroxyl group-containing monomers), monomers having a carboxyl group in the molecule (carboxyl group-containing monomers), and monomers having an amino group in the molecule (amino group-containing monomers). These reactive functional group-containing monomers may be used alone or in combination of two or more. Among these, hydroxyl group-containing monomers or carboxyl group-containing monomers are preferred, and hydroxyl group-containing monomers are particularly preferred.

[0081] Examples of hydroxyl group-containing monomers include (meth)acrylic acid hydroxyalkyl esters such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate. Among these, (meth)acrylic acid hydroxyalkyl esters having a hydroxyalkyl group having 1 to 4 carbon atoms are preferred. Specific examples include 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate, and particularly 2-hydroxyethyl acrylate or 4-hydroxybutyl acrylate are preferred. These may be used alone or in combination of two or more.

[0082] Examples of the carboxyl group-containing monomer include ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, itaconic acid, and citraconic acid. Among these, acrylic acid is preferred from the viewpoint of the adhesive strength of the resulting (meth)acrylic acid ester polymer (A). These may be used alone or in combination of two or more.

[0083] The (meth)acrylic acid ester polymer (A) preferably contains 0.1 to 30 mass% of a reactive functional group-containing monomer as a monomer unit constituting the polymer, more preferably 0.3 to 20 mass%. When used in combination with an aromatic ring-containing monomer, it is preferably contained in an amount of 0.6 to 10 mass%, even more preferably 0.8 to 5 mass%, and particularly preferably 0.9 to 2 mass%. When no aromatic ring-containing monomer is used in combination, it is preferably contained in an amount of 1 to 18 mass%, more preferably 5 to 16 mass%, and particularly preferably 10 to 15 mass%. This allows the cohesive strength of the pressure-sensitive adhesive obtained by the crosslinking reaction with the crosslinking agent (B) to be appropriate, making it easier to satisfy the above-mentioned physical properties.

[0084] It is also preferable that the (meth)acrylic acid ester polymer (A) does not contain a carboxy group-containing monomer as a monomer unit constituting the polymer. Since a carboxy group is an acid component, by not containing a carboxy group-containing monomer, even when the target to which the pressure-sensitive adhesive is applied includes a material that is susceptible to problems caused by acid, such as a transparent conductive film such as tin-doped indium oxide (ITO), a metal film, or a metal mesh, problems caused by acid (corrosion, resistance change, etc.) can be suppressed.

[0085] Here, "not containing a carboxy group-containing monomer" means that the carboxy group-containing monomer is substantially not contained, and includes not only the case where the carboxy group-containing monomer is not contained at all, but also the case where the carboxy group-containing monomer is contained to an extent that the carboxy group does not cause corrosion of the transparent conductive film, metal wiring, etc. Specifically, the (meth)acrylic acid ester polymer (A) may contain the carboxy group-containing monomer as a monomer unit in an amount of 0.1% by mass or less, preferably 0.01% by mass or less, and more preferably 0.001% by mass or less.

[0086] Examples of aromatic ring-containing monomers include phenyl (meth)acrylate, 2-phenylethyl (meth)acrylate, benzyl (meth)acrylate, naphthyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, phenoxybutyl (meth)acrylate, ethoxylated-o-phenylphenol acrylate, phenoxydiethylene glycol (meth)acrylate, phenoxypolyethylene glycol (meth)acrylate, biphenyl di(meth)acrylate, pentafluorobenzyl (meth)acrylate, etc. Among these, from the viewpoint of easily satisfying the above-mentioned physical properties, phenyl (meth)acrylate, 2-phenylethyl (meth)acrylate, benzyl (meth)acrylate, naphthyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, and phenoxybutyl (meth)acrylate are preferred, and from the viewpoint of easily achieving favorable Shore hardness and recovery, 2-phenoxyethyl (meth)acrylate is more preferred, and 2-phenoxyethyl acrylate is particularly preferred. These may be used alone or in combination of two or more.

[0087] The (meth)acrylic acid ester copolymer (A) preferably contains 0.1 to 20 mass% of an aromatic ring-containing monomer as a monomer unit constituting the polymer, more preferably 0.4 to 10 mass%, even more preferably 0.8 to 5 mass%, particularly preferably 1.0 to 3 mass%, and most preferably 1.2 to 2 mass%. This makes it easier to satisfy the above-mentioned physical properties. Note that, if the aromatic ring-containing monomer causes the resulting PSA to emit an odor, it is preferable to adjust the content ratio to a level at which the odor is not emitted. For example, when 2-phenoxyethyl acrylate is contained as the aromatic ring-containing monomer, it is preferable to adjust the content ratio so that the PSA does not emit an odor.

[0088] The nitrogen atom-containing monomer may be a monomer having an amino group, a monomer having an amide group, or a monomer having a nitrogen-containing heterocycle, among which a monomer having a nitrogen-containing heterocycle is preferred.In addition, from the viewpoint of increasing the degree of freedom of the nitrogen atom-containing monomer-derived portion in the higher-order structure of the pressure-sensitive adhesive, it is preferred that the nitrogen atom-containing monomer does not contain a reactive unsaturated double bond group other than one polymerizable group used in polymerization to form the (meth)acrylic acid ester polymer (A).The nitrogen atom-containing monomer may be used alone or in combination of two or more.

[0089] Examples of the monomer having an amino group include monomethylaminoethyl (meth)acrylate, monoethylaminoethyl (meth)acrylate, monomethylaminopropyl (meth)acrylate, monoethylaminopropyl (meth)acrylate, and dimethylaminoethyl (meth)acrylate.

[0090] Examples of monomers having an amide group include (meth)acrylamide, N-methyl(meth)acrylamide, N-methylol(meth)acrylamide, N-tert-butyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N-ethyl(meth)acrylamide, N,N-dimethylaminopropyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N-phenyl(meth)acrylamide, N-(n-butoxymethyl)(meth)acrylamide, dimethylaminopropyl(meth)acrylamide, and N-vinylcaprolactam.

[0091] Examples of monomers having a nitrogen-containing heterocycle include N-(meth)acryloylmorpholine, N-vinyl-2-pyrrolidone, N-(meth)acryloylpyrrolidone, N-(meth)acryloylpiperidine, N-(meth)acryloylpyrrolidine, N-(meth)acryloylaziridine, aziridinylethyl (meth)acrylate, 2-vinylpyridine, 4-vinylpyridine, 2-vinylpyrazine, 1-vinylimidazole, N-vinylcarbazole, and N-vinylphthalimide. Among these, N-(meth)acryloylmorpholine is preferred, and N-acryloylmorpholine is particularly preferred.

[0092] The (meth)acrylic acid ester polymer (A) preferably contains, as a monomer unit constituting the polymer, a nitrogen atom-containing monomer in an amount of 0.1 to 20 mass %, more preferably 0.5 to 12 mass %, and even more preferably 1 to 6 mass %, which makes it easier to satisfy the above-mentioned physical properties.

[0093] It is also preferable that the (meth)acrylic acid ester polymer (A) contains a monomer having an alicyclic structure in the molecule (alicyclic structure-containing monomer) as a monomer unit constituting the polymer. Since the alicyclic structure-containing monomer is bulky, its presence in the polymer is presumed to increase the spacing between polymer molecules, making the resulting pressure-sensitive adhesive excellent in flexibility. This improves the above-mentioned physical properties.

[0094] The carbon ring of the alicyclic structure in the alicyclic structure-containing monomer may be a saturated structure or may partially contain an unsaturated bond. The alicyclic structure may be a monocyclic alicyclic structure or a polycyclic alicyclic structure (polycyclic structure) such as a bicyclic or tricyclic structure. From the viewpoint of optimizing the distance between the resulting (meth)acrylic acid ester polymer (A) and imparting high stress relaxation properties and recovery properties to the PSA, the alicyclic structure is preferably a polycyclic structure. Furthermore, in consideration of the compatibility of the (meth)acrylic acid ester polymer (A) with other components, the polycyclic structure is particularly preferably a bicyclic to tetracyclic structure. Similarly, from the viewpoint of imparting stress relaxation properties and compatibility, the number of carbon atoms in the alicyclic structure (meaning the total number of carbon atoms in the ring, or the total number of carbon atoms in the case of multiple independent rings) is preferably 5 to 15, more preferably 7 to 10.

[0095] Specific examples of alicyclic structure-containing monomers include cyclohexyl (meth)acrylate, dicyclopentanyl (meth)acrylate, adamantyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentenyl (meth)acrylate, and dicyclopentenyloxyethyl (meth)acrylate. Among these, dicyclopentanyl (meth)acrylate (alicyclic structure carbon number: 10), adamantyl (meth)acrylate (alicyclic structure carbon number: 10), or isobornyl (meth)acrylate (alicyclic structure carbon number: 7) are preferred, as they exhibit superior adhesiveness. From the viewpoint of easily satisfying the above-mentioned physical properties, isobornyl (meth)acrylate is more preferred, and isobornyl acrylate is particularly preferred. These may be used alone or in combination of two or more.

[0096] The (meth)acrylic acid ester polymer (A) preferably contains an alicyclic structure-containing monomer as a monomer unit constituting the polymer in an amount of 1 to 30 mass %, more preferably 4 to 24 mass %, even more preferably 8 to 18 mass %, and particularly preferably 11 to 16 mass %, which makes it easier to satisfy the above-mentioned physical properties.

[0097] In this embodiment, the (meth)acrylic acid ester polymer (A) may contain other monomers as monomer units constituting the polymer, if desired. As the other monomers, monomers that do not contain reactive functional groups are preferred so as not to inhibit the above-mentioned action of the reactive functional group-containing monomer. Examples of such monomers include (meth)acrylic acid alkoxyalkyl esters such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate, vinyl acetate, and styrene. These may be used alone or in combination of two or more.

[0098] The polymerization mode of the (meth)acrylic acid ester polymer (A) may be a random copolymer or a block copolymer.

[0099] The weight-average molecular weight of the (meth)acrylic acid ester polymer (A) is preferably 200,000 to 3,000,000, more preferably 300,000 to 2,500,000. When an aromatic ring-containing monomer is contained, it is preferably 500,000 to 2,000,000, even more preferably 700,000 to 1,800,000, and particularly preferably 900,000 to 1,600,000, and of these, 1,000,000 to 1,300,000 is preferred. When an aromatic ring-containing monomer is not contained, it is preferably 350,000 to 1,600,000, more preferably 400,000 to 1,200,000, and particularly preferably 450,000 to 800,000. This makes it easier for the resulting adhesive to satisfy the above-mentioned physical properties. The weight-average molecular weight in this specification is a value measured by gel permeation chromatography (GPC) in terms of standard polystyrene.

[0100] In the pressure-sensitive adhesive composition P, the (meth)acrylic acid ester polymer (A) may be used alone or in combination of two or more.

[0101] (1.3.2. Crosslinking agent (B)) The crosslinking agent (B) crosslinks the (meth)acrylic acid ester polymer (A) and forms a crosslinked structure (three-dimensional network structure) when the pressure-sensitive adhesive composition P containing the crosslinking agent (B) is heated, etc. As a result, the cohesive strength of the resulting pressure-sensitive adhesive is improved, and the above-mentioned physical properties are more likely to be satisfied.

[0102] The crosslinking agent (B) may be any agent that reacts with the reactive group of the (meth)acrylic acid ester polymer (A). Examples include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, amine-based crosslinking agents, melamine-based crosslinking agents, aziridine-based crosslinking agents, hydrazine-based crosslinking agents, aldehyde-based crosslinking agents, oxazoline-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, and ammonium salt-based crosslinking agents. Among these, it is preferable to use an isocyanate-based crosslinking agent that has excellent reactivity with reactive functional group-containing monomers. The crosslinking agent (B) may be used alone or in combination of two or more.

[0103] The isocyanate crosslinking agent contains at least a polyisocyanate compound, such as aromatic polyisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and xylylene diisocyanate, aliphatic polyisocyanates such as hexamethylene diisocyanate, alicyclic polyisocyanates such as isophorone diisocyanate and hydrogenated diphenylmethane diisocyanate, and biuret and isocyanurate forms thereof, as well as adducts thereof that are reaction products with low-molecular-weight active hydrogen-containing compounds such as ethylene glycol, propylene glycol, neopentyl glycol, trimethylolpropane, and castor oil.

[0104] The content of the crosslinking agent (B) in the pressure-sensitive adhesive composition P is preferably 0.01 to 2 parts by mass, more preferably 0.10 to 1 part by mass or more, even more preferably 0.15 to 0.8 parts by mass, particularly preferably 0.20 to 0.6 parts by mass, and of these, preferably 0.25 to 0.4 parts by mass, relative to 100 parts by mass of the (meth)acrylic acid ester polymer (A). This makes it easier for the above-mentioned physical properties to be satisfied.

[0105] When the resulting pressure-sensitive adhesive layer is active energy ray-curable, the content of the crosslinking agent (B) in the pressure-sensitive adhesive composition P is preferably 0.01 to 2 parts by mass, more preferably 0.05 to 1 part by mass or more, still more preferably 0.08 to 0.6 parts by mass, particularly preferably 0.10 to 0.3 parts by mass, and of these, preferably 0.12 to 0.2 parts by mass, relative to 100 parts by mass of the (meth)acrylic acid ester polymer (A). This makes it easier for the above-mentioned physical properties to be satisfied.

[0106] (1.3.3. Silane Coupling Agent (C)) The pressure-sensitive adhesive composition P according to this embodiment preferably contains a silane coupling agent (C), which improves adhesion to the adherend.

[0107] The silane coupling agent is preferably an organosilicon compound having at least one alkoxysilyl group in the molecule, which has good compatibility with the adhesive component, particularly the (meth)acrylic acid ester polymer (A), and has optical transparency.

[0108] Examples of such silane coupling agents include polymerizable unsaturated group-containing silicon compounds such as vinyltrimethoxysilane, vinyltriethoxysilane, and methacryloxypropyltrimethoxysilane; silicon compounds having an epoxy structure such as 3-glycidoxypropyltrimethoxysilane and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; and mercapto group-containing silicon compounds such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, and 3-mercaptopropyldimethoxymethylsilane. Examples of such silane compounds include amino group-containing silicon compounds such as 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, and N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, 3-chloropropyltrimethoxysilane, and 3-isocyanatepropyltriethoxysilane, as well as condensates of at least one of these with alkyl group-containing silicon compounds such as methyltriethoxysilane, ethyltriethoxysilane, methyltrimethoxysilane, and ethyltrimethoxysilane. These compounds may be used alone or in combination of two or more.

[0109] The content of the silane coupling agent (C) relative to 100 parts by mass of the (meth)acrylic acid ester polymer (A) is preferably 0.01 to 2 parts by mass, more preferably 0.1 to 1 part by mass, even more preferably 0.15 to 0.5 parts by mass, and particularly preferably 0.18 to 0.25 parts by mass. This makes it easier to achieve the above-mentioned properties.

[0110] (1.3.4. Active energy ray curable component (D)) When the adhesive component constituting the adhesive layer is active energy ray curable, the adhesive composition P preferably contains an active energy ray curable component (D). It is presumed that by curing the adhesive obtained by crosslinking the adhesive composition P with active energy rays, the active energy ray curable components (D) polymerize with each other, and the polymerized active energy ray curable components (D) become entangled in the crosslinked structure (three-dimensional network structure) of the (meth)acrylic acid ester polymer (A). An adhesive having such a higher order structure can exhibit excellent properties.

[0111] The active energy ray-curable component (D) is not particularly limited as long as it is a component that can be cured by irradiation with active energy rays and can obtain the above-mentioned effects and the optical properties and adhesive properties described above, and may be any of a monomer, oligomer, or polymer, or a mixture thereof. Among these, monofunctional acrylate monomers and polyfunctional acrylate monomers are preferred, and polyfunctional acrylate monomers are preferred from the viewpoint that the resulting adhesive exhibits excellent adhesiveness and durability while maintaining the above-mentioned optical properties and adhesive properties. The polyfunctional acrylate monomer preferably has a molecular weight of less than 1000 from the viewpoint of compatibility with the adhesive component, especially the (meth)acrylic acid ester polymer (A), and from the viewpoint that the resulting adhesive easily satisfies the above-mentioned physical properties.

[0112] As the polyfunctional acrylate monomer, bifunctional, trifunctional, tetrafunctional, pentafunctional, and hexafunctional acrylate monomers are preferred. Among these, from the viewpoint that the resulting PSA readily satisfies the above-mentioned physical properties, polyfunctional acrylate monomers containing an isocyanurate structure in the molecule, such as di(acryloxyethyl)isocyanurate, tris(acryloxyethyl)isocyanurate, and ε-caprolactone-modified tris-(2-(meth)acryloxyethyl)isocyanurate, or polyfunctional acrylate monomers containing a cyclic structure (particularly a cycloalkane structure) in the molecule, such as tricyclodecane dimethanol (meth)acrylate, are preferred. These may be used alone or in combination of two or more.

[0113] From the viewpoint of the adhesiveness of the adhesive before active energy ray curing, the content of the active energy ray-curable component (D) in the adhesive composition P is preferably 0.1 to 50 parts by mass, more preferably 0.5 to 35 parts by mass, and even more preferably 1 to 20 parts by mass, relative to 100 parts by mass of the (meth)acrylic acid ester polymer (A). From the viewpoint of making it easier to satisfy the above-mentioned physical properties, the content is preferably 1 to 10 parts by mass, more preferably 2 to 8 parts by mass, and even more preferably 3 to 6 parts by mass.

[0114] (1.3.5. Photopolymerization initiator (E)) When ultraviolet rays are used as the active energy rays for curing the pressure-sensitive adhesive composition P, it is preferable that the pressure-sensitive adhesive composition P further contains a photopolymerization initiator (E) in addition to the active energy ray-curable component (D). This makes it possible to efficiently polymerize the active energy ray-curable component (D) and reduce the polymerization and curing time and the exposure dose of active energy rays.

[0115] Examples of the photopolymerization initiator (E) include benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin-n-butyl ether, benzoin isobutyl ether, acetophenone, dimethylaminoacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2,2-diethoxy-2-phenylacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-hydroxycyclohexyl phenyl ketone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propan-1-one, 4-(2-hydroxyethoxy)phenyl-2-(hydroxy-2-propyl)ketone, benzophenone, p-phenylbenzophenone, 4,4 Examples of suitable benzoxanthraquinones include 2-methyl-2-hydroxybenzoyl-1-methyl-1-methyl-2-methyl-1 ...

[0116] Among the above, phosphine oxide-based photopolymerization initiators are preferred from the viewpoint of ease of cleavage upon UV irradiation and ease of reliable curing of the pressure-sensitive adhesive. Specifically, 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, etc. are preferred. Some optical components to be adherends have UV-shielding properties, but even when UV rays are irradiated through such UV-shielding components that are difficult for UV rays to pass through, the above-mentioned phosphine oxide-based photopolymerization initiators can promote curing of the active energy ray-curable component (D).

[0117] The content of the photopolymerization initiator (E) in the adhesive composition P is preferably 1 to 30 parts by mass, more preferably 4 to 22 parts by mass, and even more preferably 8 to 16 parts by mass, relative to 100 parts by mass of the active energy ray-curable component (D).

[0118] (1.3.6. Other Additives) The adhesive composition P may contain additives that are commonly used in acrylic adhesives, if necessary. Examples of such additives include ultraviolet absorbers, infrared absorbers, antistatic agents, tackifiers, antioxidants, light stabilizers, softeners, rust inhibitors, fillers, colorants, and refractive index adjusters. Note that polymerization solvents and dilution solvents, which will be described later, are not included in the additives that constitute the adhesive composition P.

[0119] (1.4. Release Sheet) As shown in Figure 1, release sheets 11 and 12 protect the pressure-sensitive adhesive layer 10 until the pressure-sensitive adhesive sheet 1 is used, and are peeled off when the pressure-sensitive adhesive sheet 1 (pressure-sensitive adhesive layer 10) is to be used. In the pressure-sensitive adhesive sheet 1 according to this embodiment, one or both of release sheets 11 and 12 are not necessarily required.

[0120] Examples of materials that can be used as the release sheets 11 and 12 include polyethylene films, polypropylene films, polybutene films, polybutadiene films, polymethylpentene films, polyvinyl chloride films, vinyl chloride copolymer films, polyethylene terephthalate films, polyethylene naphthalate films, polybutylene terephthalate films, polyurethane films, ethylene vinyl acetate films, ionomer resin films, ethylene-(meth)acrylic acid copolymer films, ethylene-(meth)acrylic acid ester copolymer films, polystyrene films, polycarbonate films, polyimide films, and fluororesin films. Crosslinked films of these materials can also be used. Furthermore, laminated films of these materials may also be used. From the perspective of the SDGs, the material constituting the release sheets may be a material with a high biomass content, a recyclable or reusable material, or a recycled or reused material.

[0121] The release surfaces of the release sheets 11, 12 (particularly the surfaces that come into contact with the pressure-sensitive adhesive layer 10) are preferably subjected to a release treatment. Examples of release agents used for the release treatment include alkyd-based, silicone-based, fluorine-based, unsaturated polyester-based, polyolefin-based, and wax-based release agents. It is preferable that one of the release sheets 11, 12 is a heavy-release type release sheet with a high release strength, and the other is a light-release type release sheet with a low release strength.

[0122] There is no particular limitation on the thickness of the release sheets 11 and 12, but it is usually about 20 to 150 μm.

[0123] (1.5. Production of Pressure-Sensitive Adhesive Composition) The pressure-sensitive adhesive composition P can be produced, for example, by first producing a (meth)acrylic acid ester polymer (A) and then mixing the resulting (meth)acrylic acid ester polymer (A) with a crosslinking agent (B). If necessary, a silane coupling agent (C), an active energy ray-curable component (D), a photopolymerization initiator (E), and other additives may be added.

[0124] The (meth)acrylic acid ester polymer (A) can be produced, for example, by polymerizing a mixture of monomers constituting the polymer using a conventional radical polymerization method. The polymerization of the (meth)acrylic acid ester polymer (A) can be carried out by a solution polymerization method, using a polymerization initiator as needed. Polymerizing the (meth)acrylic acid ester polymer (A) using a solution polymerization method facilitates increasing the molecular weight of the resulting polymer and adjusting the molecular weight distribution, and also makes it possible to reduce the production of low molecular weight compounds. As a result, a pressure-sensitive adhesive that is excellent in recovery from deformation due to bending or pressure can be easily obtained.

[0125] Examples of polymerization solvents used in solution polymerization include ethyl acetate, n-butyl acetate, isobutyl acetate, toluene, acetone, hexane, and methyl ethyl ketone. One type of polymerization solvent may be used, or two or more types may be used in combination. Examples of polymerization initiators include azo compounds and organic peroxides, and two or more types may be used in combination. In the polymerization step, the weight average molecular weight of the resulting polymer can be adjusted by adding a chain transfer agent such as 2-mercaptoethanol.

[0126] Once the (meth)acrylic acid ester polymer (A) is obtained, the crosslinking agent (B), and, if necessary, the silane coupling agent (C), the active energy ray-curable component (D), the photopolymerization initiator (E), other additives, the dilution solvent, etc. are added to the solution of the (meth)acrylic acid ester polymer (A) and mixed thoroughly to obtain a solvent-diluted adhesive composition P (coating solution). Note that, when a solid component is used for any of the above components, or when precipitation occurs when mixed with other components in an undiluted state, that component may be dissolved or diluted alone in a dilution solvent before being mixed with other components.

[0127] Examples of dilution solvents include aliphatic hydrocarbons such as hexane, heptane, and cyclohexane; aromatic hydrocarbons such as toluene and xylene; halogenated hydrocarbons such as methylene chloride and ethylene chloride; alcohols such as methanol, ethanol, propanol, butanol, and 1-methoxy-2-propanol; ketones such as acetone, methyl ethyl ketone, 2-pentanone, isophorone, and cyclohexanone; esters such as ethyl acetate and butyl acetate; and cellosolve-based solvents such as ethyl cellosolve.

[0128] The concentration and viscosity of the coating solution prepared in this manner may be within a range that allows coating, and can be appropriately selected depending on the situation. For example, the adhesive composition P is diluted so that the concentration is 10 to 60 mass %. Note that the addition of a dilution solvent or the like is not a necessary condition for obtaining the coating solution, and as long as the adhesive composition P has a viscosity that allows coating, the addition of a dilution solvent is not necessary. In this case, the adhesive composition P becomes a coating solution in which the polymerization solvent for the (meth)acrylic acid ester polymer (A) is used as the dilution solvent.

[0129] (1.6. Production of adhesive) The adhesive constituting the adhesive layer is preferably obtained by crosslinking the above-mentioned adhesive composition P. Crosslinking of the adhesive composition P can usually be carried out by heat treatment. This heat treatment can also serve as a drying treatment for volatilizing diluent solvents and the like from a coating film of the adhesive composition P applied to a desired object. In addition, such an adhesive layer can also be preferably formed by applying the adhesive composition P to a desired object, heat treating it, and then curing the adhesive composition P by irradiating it with active energy rays.

[0130] The heating temperature for the heat treatment is preferably 50 to 150° C., more preferably 70 to 120° C. The heating time is preferably 10 seconds to 10 minutes, more preferably 50 seconds to 2 minutes.

[0131] After the heat treatment, a curing period of about 1 to 2 weeks may be provided at room temperature (e.g., 23°C, relative humidity 50%), if necessary. If curing is required, a pressure-sensitive adhesive having a crosslinked structure is obtained after the curing period has elapsed. If curing is not required, a pressure-sensitive adhesive having a crosslinked structure is obtained after the heat treatment has been completed. In this specification, "relative humidity α%" may also be expressed as "α% RH" (RH; Relative humidity).

[0132] In this specification, the term "active energy rays" refers to electromagnetic waves or charged particle beams that have an energy quantum, and specific examples thereof include ultraviolet rays, electron beams, etc. Among active energy rays, ultraviolet rays are particularly preferred because they are easy to handle.

[0133] The ultraviolet irradiation can be performed using a high-pressure mercury lamp, a Heraeus H lamp, a xenon lamp, or the like, and the amount of ultraviolet irradiation is set to an illuminance of 50 to 1000 mW / cm. 2 The light intensity is preferably 50 to 10,000 mJ / cm. 2 is preferably 80 to 5000 mJ / cm 2 More preferably, it is 300 to 2000 mJ / cm 2 On the other hand, the electron beam irradiation can be carried out by an electron beam accelerator or the like, and the irradiation dose of the electron beam is preferably about 10 to 1000 krad.

[0134] As long as the effects of the present invention can be obtained, the pressure-sensitive adhesive after curing by irradiation with active energy rays may contain the photopolymerization initiator (E) that has not been cleaved by irradiation with active energy rays. In this embodiment, the remaining amount of the photopolymerization initiator (E) in the pressure-sensitive adhesive after curing is preferably 0.1 mass % or less, and more preferably 0.01 mass % or less.

[0135] (1.7. Production of Pressure-Sensitive Adhesive Sheet) The method for producing the pressure-sensitive adhesive sheet 1 is not particularly limited, and it may be produced by a known method. For example, a coating solution of the above-mentioned pressure-sensitive adhesive composition P is applied to the release surface of one of the first release sheets 11 (or the second release sheet 12), and a heat treatment is carried out to crosslink the pressure-sensitive adhesive composition P, thereby forming a coating layer having a predetermined thickness. The release surface of the other second release sheet 12 (or the first release sheet 11) is then superimposed on the formed coating layer. If curing is required, the coating layer will become the pressure-sensitive adhesive layer 10 after a predetermined curing period has elapsed. Alternatively, if curing is not required, the coating layer will become the pressure-sensitive adhesive layer 10 as is. In this way, the pressure-sensitive adhesive sheet 1 is obtained.

[0136] In another method for producing the pressure-sensitive adhesive sheet 1, the release surface of one of the first release sheets 11 is coated with a coating liquid of the above-mentioned pressure-sensitive adhesive composition P, and a heat treatment is performed to crosslink the pressure-sensitive adhesive composition P and form a coating layer, thereby obtaining a first release sheet 11 with a coating layer. The release surface of the other of the second release sheets 12 is coated with a coating liquid of the above-mentioned pressure-sensitive adhesive composition P, and a heat treatment is performed to crosslink the pressure-sensitive adhesive composition P and form a coating layer, thereby obtaining a second release sheet 12 with a coating layer. The first release sheet 11 with the coating layer and the second release sheet 12 with the coating layer are then bonded together so that the two coating layers are in contact with each other. If curing is required, the coating layer becomes the pressure-sensitive adhesive layer 10 after a predetermined curing period. If curing is not required, the coating layer becomes the pressure-sensitive adhesive layer 10 as is. This produces the pressure-sensitive adhesive sheet 1. This production method allows stable production even when the pressure-sensitive adhesive layer 10 is thick.

[0137] Examples of methods for applying the coating solution of the adhesive composition P include bar coating, knife coating, roll coating, blade coating, die coating, and gravure coating.

[0138] (2. Laminate) As shown in FIG. 2 , the laminate 2 according to this embodiment is configured to include a first member 21, a second member 22, a third member 23, a fourth member 24, a pressure-sensitive adhesive layer 10A located between them and bonding the first member 21 and the second member 22 to each other, a pressure-sensitive adhesive layer 10B that bonds the second member 22 and the third member 23 to each other, and a pressure-sensitive adhesive layer 10C that bonds the first member 21 and the fourth member 24 to each other.

[0139] The pressure-sensitive adhesive layers 10A, 10B and 10C in the laminate 2 are the pressure-sensitive adhesive layer 10 of the pressure-sensitive adhesive sheet 1 described above.

[0140] An example of manufacturing the laminate 2 will be described below. First, the second release sheet on one side of the pressure-sensitive adhesive sheet is peeled off, and the exposed pressure-sensitive adhesive layer 10A of the pressure-sensitive adhesive sheet is attached to one surface of the first member 21.

[0141] Thereafter, the other first release sheet is peeled from pressure-sensitive adhesive layer 10A of the pressure-sensitive adhesive sheet 1, and the exposed pressure-sensitive adhesive layer 10A of the pressure-sensitive adhesive sheet 1 is bonded to second member 22. Similarly, pressure-sensitive adhesive layer 10B of another pressure-sensitive adhesive sheet is used to bond second member 22 to third member 23, and pressure-sensitive adhesive layer 10C of another pressure-sensitive adhesive sheet is used to bond first member 21 to fourth member 24, thereby obtaining laminate 2. As another example, the order in which first member 21, second member 22, third member 23, and fourth member 24 are bonded may be reversed.

[0142] A case will be described in which the laminate 2 is a touch panel including a piezoelectric material. In this case, the first member 21 is a member including a piezoelectric material, the second member 22 and the third member 23 are electrodes, and the fourth member 24 is a cover material.

[0143] The member containing the piezoelectric body is not limited as long as it exhibits piezoelectricity, but is preferably a film-like piezoelectric film. An example of the piezoelectric film is a film made of a polymeric piezoelectric material. A film made of a polymeric piezoelectric material is highly transparent and has excellent flexibility, making it suitable as a component of a touch panel. Examples of the polymeric piezoelectric material include fluorine-based polyolefin and polylactic acid.

[0144] The electrodes detect the strain generated in the piezoelectric body as a voltage. They may be electrodes for detecting the pressed position, electrodes for detecting the pressed force information, or electrodes for detecting the pressed position and pressed force information. The electrodes are preferably made of a highly transparent material, and examples of such materials include ITO (indium tin oxide) and conductive polymers.

[0145] Examples of the cover material include highly transparent glass materials, resin materials, etc. The cover material may be in the form of a film.

[0146] Since the adhesive layer used to bond the components constituting the laminate is the above-mentioned adhesive layer, even when the piezoelectric sensor is exposed to an external environment with large temperature changes, the adhesive layer remains flexible even at low temperatures and fully recovers to its original state from a deformed state, thereby suppressing variations in the degree of deformation of the adhesive layer over a wide temperature range.

[0147] It is also preferable that each member of the laminate 2 is composed of a flexible member. Such a laminate 2 is preferably a flexible device itself or a member constituting a part of a flexible device. The flexible device may be a device including a member that is bent once during manufacturing and maintains the bent state, or a device including a member that can be repeatedly bent (including folded). The flexible device is preferably a display, but is not limited thereto. Examples of flexible devices include organic electroluminescence (organic EL) displays, electrophoretic displays (electronic paper), liquid crystal displays using a plastic substrate (film) as a substrate, light-emitting diode (LED) displays, foldable displays, stretchable displays, rollable displays, and the like. These may include touch panels.

[0148] Examples of flexible materials include cover films, barrier films, hard coat films, polarizing films (polarizing plates), polarizers, retardation films (retardation plates), viewing angle compensation films, brightness enhancement films, contrast enhancement films, diffusion films, semi-transmitting reflective films, electrode films, transparent conductive films, metal mesh films, film sensors (touch sensor films), liquid crystal polymer films, light-emitting polymer films, film-like liquid crystal modules, organic EL modules (organic EL films, organic EL elements), electronic paper modules (film-like electronic paper), and TFT (Thin Film Transistor) substrates.

[0149] The Young's modulus of each flexible member is preferably 0.1 to 10 GPa, more preferably 0.5 to 7 GPa, and even more preferably 1 to 5 GPa, which makes it easy to repeatedly deform each flexible member by bending, pressing, etc.

[0150] The thickness of each flexible member is preferably 10 to 3000 μm, more preferably 25 to 1000 μm, and even more preferably 50 to 500 μm, which makes it easy to repeatedly deform each flexible member by bending, pressing, etc.

[0151] The interlayer adhesion (adhesive strength) between flexible members is preferably 1 to 30 N / 25 mm, particularly preferably 2 to 25 N / 25 mm, and even more preferably 5 to 20 N / 25 mm. This makes it possible to suppress peeling between members even when the members are repeatedly deformed by bending, pressing, etc., and also provides excellent reworkability, so that even if a bonding error occurs between flexible members, the two can be easily peeled away, making it possible to reuse flexible members (especially expensive flexible members).

[0152] Here, the interlayer adhesion (adhesive strength) in this specification basically refers to an adhesive strength measured by a 180-degree peel method in accordance with JIS Z0237:2009, and the measurement sample is 25 mm wide and 100 mm long, and a laminate is prepared by bonding the flexible members to be measured together with an adhesive layer, and the laminate is pressurized at 0.5 MPa and 50°C for 20 minutes, and then left to stand for 24 hours under conditions of normal pressure, 23°C, and 50% RH, and then measured at a peel speed of 300 mm / min.

[0153] (3. Device) The device according to this embodiment includes the above-described laminate 2, and may consist of only the laminate 2, or may be configured with one or more laminates 2 and other members. When one laminate 2 is laminated with another laminate 2, or when a laminate 2 is laminated with other members, it is preferable to laminate them via the pressure-sensitive adhesive layer 10 of the pressure-sensitive adhesive sheet 1 described above.

[0154] In the device according to this embodiment, the components are bonded together using the adhesive layer described above. Therefore, even when the device is used in an environment with large temperature changes and the adhesive layer is repeatedly deformed, the adhesive layer maintains its flexibility and variation in the degree of deformation is suppressed.

[0155] An example of a device in this embodiment is shown in Fig. 3. However, the device according to the present invention is not limited to this device.

[0156] 3, the device 3 according to this embodiment is configured by laminating, from top to bottom, a cover film 31, a first adhesive layer 32, a first electrode 33, a second adhesive layer 34, a piezoelectric film 35, a third adhesive layer 36, a second electrode 37, a fourth adhesive layer 38, an organic EL element 39, a fifth adhesive layer 40, and a TFT substrate 41. That is, the device 3 has a configuration in which a touch panel including a piezoelectric material as the laminate 2 and a flexible display as the laminate 2 are bonded together via the fourth adhesive layer. When the touch panel including a piezoelectric material is configured from a flexible material, the device shown in FIG. 3 is a flexible device including an input device and a display device.

[0157] At least one of the first pressure-sensitive adhesive layer 32, the second pressure-sensitive adhesive layer 34, the third pressure-sensitive adhesive layer 36, the fourth pressure-sensitive adhesive layer 38, and the fifth pressure-sensitive adhesive layer 40 is preferably the pressure-sensitive adhesive layer 10 of the pressure-sensitive adhesive sheet 1. It is preferable that two or more of the first pressure-sensitive adhesive layer 32, the second pressure-sensitive adhesive layer 34, the third pressure-sensitive adhesive layer 36, the fourth pressure-sensitive adhesive layer 38, and the fifth pressure-sensitive adhesive layer 40 are the pressure-sensitive adhesive layer 10 of the pressure-sensitive adhesive sheet 1, and it is most preferable that all of the pressure-sensitive adhesive layers 32, 34, 36, 38, and 40 are the pressure-sensitive adhesive layer 10 of the pressure-sensitive adhesive sheet 1.

[0158] In this specification, when it is stated that "X to Y" (X and Y are any numbers), it means "X or more and Y or less" unless otherwise specified, and also means "preferably greater than X" or "preferably smaller than Y". Furthermore, when it is stated that "X or more" (X is any number), it means "preferably greater than X" unless otherwise specified, and when it is stated that "Y or less" (Y is any number), it also means "preferably smaller than Y" unless otherwise specified.

[0159] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and may be modified in various ways within the scope of the present invention.

[0160] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples.

[0161] Example 1 1. Preparation of (meth)acrylic acid ester polymer 48.6 parts by mass of n-butyl acrylate, 48.6 parts by mass of 2-ethylhexyl acrylate, 1.8 parts by mass of 2-phenoxyethyl acrylate, and 1 part by mass of 4-hydroxybutyl acrylate were copolymerized to prepare a (meth)acrylic acid ester polymer (A). The molecular weight of the resulting (meth)acrylic acid ester polymer (A) was measured by the method described below, and the weight average molecular weight (Mw) was found to be 1,200,000.

[0162] The weight average molecular weight (Mw) is a polystyrene-equivalent weight average molecular weight measured using gel permeation chromatography (GPC) under the following conditions (GPC measurement). (Measurement conditions) GPC measurement device: HLC-8020, manufactured by Tosoh Corporation GPC columns (passed in the following order): TSK guard column HXL-H, TSK gel GMHXL (x2), TSK gel G2000HXL, manufactured by Tosoh Corporation Measurement solvent: tetrahydrofuran Measurement temperature: 40°C

[0163] 2. Preparation of Pressure-Sensitive Adhesive Composition 100 parts by mass (solid content equivalent; the same applies hereinafter) of the (meth)acrylic acid ester polymer (A) obtained above, 0.14 parts by mass of an isocyanate-based crosslinking agent (manufactured by Soken Chemical & Engineering Co., Ltd., product name "TD-75") (B1) as the crosslinking agent (B), and 0.2 parts by mass of 3-glycidoxypropyltrimethoxysilane (C1) as the silane coupling agent (C) were mixed, thoroughly stirred, and diluted with methyl ethyl ketone to obtain a coating solution of a pressure-sensitive adhesive composition.

[0164] 3. Production of Pressure-Sensitive Adhesive Sheet The obtained coating solution of the pressure-sensitive adhesive composition was applied using a knife coater to the release-treated surface of a heavy-release type release sheet R1, one side of which had been release-treated with a silicone-based release agent for polyethylene terephthalate film. The coating layer was then heat-treated at 90°C for 1 minute to promote a crosslinking reaction, thereby forming a coating layer made of a pressure-sensitive adhesive having a crosslinked structure composed of a (meth)acrylic acid ester polymer (A) and a crosslinking agent (B).

[0165] Next, the coating layer on the release sheet R1 obtained above was bonded to a light-release type release sheet R2, which was a polyethylene terephthalate film with one side treated with a silicone-based release agent, so that the release-treated surface contacted the coating layer, and the sheet was aged for 7 days under conditions of 23°C and 50% RH to produce a pressure-sensitive adhesive sheet having a 50 μm thick adhesive layer. This pressure-sensitive adhesive sheet had a configuration of release sheet R1 / adhesive layer (thickness: 50 μm) / release sheet R2. The thickness of the adhesive layer was measured in accordance with JIS K7130 using a constant-pressure thickness gauge (manufactured by Teclock Corporation, product name "PG-02"). It was also confirmed that the release sheet R1 had a greater peel strength from the adhesive layer than release sheet R2.

[0166] (Examples 2 to 7, Comparative Examples 1 to 3) Pressure-sensitive adhesive sheets were produced by the same method as in Example 1, except that the composition and molecular weight of the (meth)acrylic acid ester polymer (A), the type and amount of the crosslinking agent (B), the amount of the silane coupling agent (C), the type and amount of the active energy ray-curable component (D), and the amount of the photopolymerization initiator (E) were changed as shown in Table 1. In Table 1, the amounts of the crosslinking agent (B), the silane coupling agent (C), the active energy ray-curable component (D), and the photopolymerization initiator (E) are expressed as amounts (solid content equivalent) relative to 100 parts by mass (solid content equivalent) of the (meth)acrylic acid ester polymer (A). The pressure-sensitive adhesive layers of the pressure-sensitive adhesive sheets of Example 5 and Comparative Example 2 were active energy ray-curable.

[0167]

[0168] Details of the abbreviations and other information listed in Table 1 are as follows: ((Meth)acrylic acid ester copolymer (A)) BA: n-butyl acrylate 2EHA: 2-ethylhexyl acrylate PhEA: 2-phenoxyethyl acrylate 4HBA: 4-hydroxybutyl acrylate ACMO: N-acryloylmorpholine IBXA: isobornyl acrylate HEA: 2-hydroxyethyl acrylate (Crosslinking agent (B)) B1: isocyanate-based crosslinking agent (manufactured by Soken Chemical & Engineering Co., Ltd., product name "TD-75") B2: isocyanate-based crosslinking agent (manufactured by Mitsui Chemicals, Inc., product name "Takenate D-101E") (Silane coupling agent (C)) C1: 3-glycidoxypropyltrimethoxysilane (Active energy ray-curable component (D)) D1: tricyclodecane dimethanol diacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., product name "NK Ester A-DCP") D2: ε-caprolactone-modified tris-(2-acryloxyethyl) isocyanurate (manufactured by Shin-Nakamura Chemical Co., Ltd., product name "NK Ester A-9300-1CL") (photopolymerization initiator (E)) E1: 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide

[0169] (Evaluation of Gel Fraction of Pressure-Sensitive Adhesive) The pressure-sensitive adhesive layers prepared in the Examples and Comparative Examples were cut to a size of 80 mm x 80 mm, and the pressure-sensitive adhesive layers were wrapped in a polyester mesh (product name: Tetron Mesh #200), and the mass thereof was weighed using a precision balance. The mass of the pressure-sensitive adhesive alone was calculated by subtracting the mass of the mesh alone from the weighed value. This mass was designated M1.

[0170] Next, the adhesive wrapped in the polyester mesh was immersed in ethyl acetate at room temperature (23°C) for 24 hours. The mesh was then removed and air-dried for 24 hours in an environment of 23°C and 50% RH, and then dried in an oven at 80°C for 12 hours. After drying, the mesh was weighed using a precision balance. The mass of the adhesive alone was calculated by subtracting the mass of the mesh alone from the weighed value. This mass was designated M2. The gel fraction was calculated using the obtained M1 and M2 according to the following formula. The results are shown in Table 2. Gel fraction (%) = (M2 / M1) x 100

[0171] For Example 5 and Comparative Example 2, the gel fractions before and after irradiation with active energy rays (ultraviolet rays; UV) were measured by the same method as above. The active energy ray irradiation conditions were the following irradiation conditions A. (Irradiation Condition A) - High-pressure mercury lamp used - Illuminance 200 mW / cm 2 , light intensity 2000mJ / cm 2 ・UV illuminance and light intensity meter used is "UVPF-A1" manufactured by iGraphics

[0172] (Measurement of adhesive strength of adhesive layer) The release sheet R2 was peeled off from the adhesive sheets obtained in the Examples and Comparative Examples, and the exposed adhesive layer was attached to an easy-adhesion layer of a polyethylene terephthalate (PET) film (manufactured by Toyobo Co., Ltd., product name "Cosmoshine A4160", thickness: 100 μm) having an easy-adhesion layer, to obtain a release sheet R1 / adhesive layer / PET film laminate. The obtained laminate was cut into a width of 25 mm and a length of 100 mm, and this was used as a sample.

[0173] The release sheet R1 was peeled from the sample under an environment of 23°C and 50% RH, and the exposed adhesive layer was attached to soda lime glass (manufactured by Nippon Sheet Glass Co., Ltd.). The sample was then pressurized in an autoclave (manufactured by Kurihara Manufacturing Co., Ltd.) at 0.5 MPa and 50°C for 20 minutes. After leaving the sample at 23°C and 50% RH for 24 hours, the adhesive strength (N / 25 mm) was measured using a tensile tester (manufactured by Orientec Co., Ltd., product name "Tensilon") at a peel rate of 300 mm / min and a peel angle of 180°. Measurements were conducted under conditions other than those described here in accordance with JIS Z0237:2009. The results are shown in Table 2. For Example 5 and Comparative Example 2, the adhesive strength was measured before and after irradiation with active energy rays (ultraviolet rays; UV) using the same method as described above. The active energy ray irradiation conditions were the same as irradiation condition A described above.

[0174] (Measurement of Total Light Transmittance) The pressure-sensitive adhesive layers of the pressure-sensitive adhesive sheets obtained in the Examples and Comparative Examples were attached to glass to prepare measurement samples. After background measurement was performed on the glass, the measurement samples were measured for total light transmittance (%) using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., product name "NDH-5000") in accordance with JIS K7361-1:1997. The results are shown in Table 2. For the pressure-sensitive adhesive layers of Example 5 and Comparative Example 2, the total light transmittance was measured using the same method as above after irradiation with active energy rays (ultraviolet rays; UV). The active energy ray irradiation conditions were the irradiation conditions A described above.

[0175] (Haze Value Measurement) The haze values ​​(%) of the pressure-sensitive adhesive layers of the pressure-sensitive adhesive sheets obtained in the Examples and Comparative Examples were measured using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., product name "NDH-5000") in accordance with JIS K7136:2000. The obtained total light haze values ​​(%) are shown in Table 2. Note that for the pressure-sensitive adhesive layers of Example 5 and Comparative Example 2, the haze values ​​were measured using the same method as above after irradiation with active energy rays (ultraviolet rays; UV). The active energy ray irradiation conditions were the irradiation conditions A described above.

[0176] (Measurement of Shore Hardness) For the pressure-sensitive adhesive sheets obtained in the Examples and Comparative Examples, the Shore hardness (HS) of the surface of the pressure-sensitive adhesive layer was measured using an E-type durometer (manufactured by Muratec KDS, product name "Rubber Hardness Meter DM-207E") in an environment of 23°C and 50% RH. The results are shown in Table 2. Furthermore, the Shore hardness of the surface of the pressure-sensitive adhesive layer was measured in an environment of -20°C and an environment of 70°C and 50% RH. The results are shown in Table 2. Note that for the pressure-sensitive adhesive layers of Example 5 and Comparative Example 2, the Shore hardness of the surface of the pressure-sensitive adhesive layer was measured using the same method as above after irradiation with active energy rays (ultraviolet rays; UV). The active energy ray irradiation conditions were the irradiation condition A described above.

[0177] (Measurement of distortion rate) A plurality of pressure-sensitive adhesive layers of the pressure-sensitive adhesive sheets obtained in Examples and Comparative Examples were laminated to form a laminate having a thickness of 0.8 mm. A cylindrical body having a diameter of 8 mm (height of 0.8 mm) was punched out from the obtained laminate to serve as a sample.

[0178] For the above sample, a constant stress was continuously applied to the sample in accordance with JIS K7244-1 using a viscoelasticity measuring device (manufactured by Anton Paar, product name "MCR302") under conditions of a measurement temperature of 23°C and a shear stress of 10 kPa, and the strain rate (%) was measured 10 seconds after the start of the stress application. The strain rate (%) was also measured in the same manner as above at measurement temperatures of -20°C and 70°C. The results are shown in Table 2. For the pressure-sensitive adhesive layers of Example 5 and Comparative Example 2, the obtained laminate was irradiated with active energy rays (ultraviolet rays; UV), and then the strain rate (%) was measured using the same method as above. The active energy ray irradiation conditions were the above-mentioned irradiation condition A.

[0179] (Restoration Rate of Pressure-Sensitive Adhesive Layer) The restoration rate of the pressure-sensitive adhesive layer was measured as follows. Under an environment of 23°C and 50% RH, the release sheet R2 was peeled from the pressure-sensitive adhesive sheets obtained in the Examples and Comparative Examples, and the exposed pressure-sensitive adhesive layer was bonded to one side of a polyimide (PI) film (manufactured by DuPont-Toray Co., Ltd., product name "Kapton 100PI", thickness: 25 μm, Young's modulus: 3.4 GPa). Next, the release sheet R1 was peeled off, and the exposed pressure-sensitive adhesive layer was bonded to the gas barrier layer surface of a gas barrier film (Young's modulus: 4.2 GPa) prepared by the method described below. Then, after pressurizing at 0.5 MPa and 50°C for 20 minutes in an autoclave (manufactured by Kurihara Manufacturing Co., Ltd.), the film was left for 24 hours under conditions of 23°C and 50% RH. The laminate consisting of the PI film / pressure-sensitive adhesive layer / gas barrier film obtained in this manner was cut into a 50 mm width and 200 mm length, which was used as test piece S. The pressure-sensitive adhesive layers of Example 5 and Comparative Example 2 were irradiated with active energy rays (ultraviolet rays; UV) from the gas barrier film side of the obtained laminate, and the resulting laminate was used as test piece S. The active energy ray irradiation conditions were the same as those of irradiation condition A described above.

[0180] The obtained test piece S was held in a bent state between two holding plates P (distance between them: 4 mm) made of upright glass plates in an environment of 23°C and 50% RH for 24 hours as shown in Fig. 4. At this time, the test piece S was bent so that the gas barrier film sides faced each other, and a static bending test was performed.

[0181] After the static bending test, the test piece S was placed on a flat plate as shown in Figure 5, and the height h from the surface of the flat plate to the apex of the bent portion (deformed portion) was measured as the static bending deformation (mm) immediately after the test and one hour after the test. The recovery rate R (%) was calculated from the static bending deformation (mm) immediately after the test and one hour after the test using the following formula. The results are shown in Table 2. Recovery rate (%) = (1 - static bending deformation after one hour of test / static bending deformation immediately after test) x 100

[0182] Furthermore, the static bending test was carried out in an environment of −20° C. and an environment of 70° C. and 50% RH, and the recovery rates of the pressure-sensitive adhesive layer at −20° C. and 70° C. were calculated from the obtained static bending deformation amounts. The results are shown in Table 2.

[0183] (Preparation of Gas Barrier Film) A polyethylene terephthalate (PET) film (manufactured by Toyobo Co., Ltd., product name "Cosmoshine A4160", thickness: 50 μm) with one side treated for easy adhesion was used as a substrate. A composition containing an ultraviolet (UV) curable resin and reactive silica (manufactured by Arakawa Chemical Industries, Ltd., product name "Opstar Z7530") was applied to one side of the substrate (the smooth side not treated for easy adhesion) using a Mayer bar to form a coating film, and the coating film was dried at 70°C for 1 minute. Then, using a conveyor-type UV light irradiation device (manufactured by Fusion Co., Ltd., product name "F600V"), the coating film was irradiated with UV under the following conditions to cure the coating film and form a 1 μm thick anchor coat layer. <UV Irradiation Conditions> UV lamp: high-pressure mercury lamp Line speed: 20 m / min Accumulated light intensity: 120 mJ / cm 2 ・Illuminance: 200mW / cm 2 ・Lamp height: 104mm

[0184] Next, a coating material containing perhydropolysilazane as a main component (manufactured by Merck Performance Materials, product name "AZ-110a-20") was applied to the surface of the anchor coat layer by spin coating. The resulting coating was then heated at 120°C for 1 minute to form a polysilazane layer containing perhydropolysilazane. The thickness of the formed polysilazane layer was 200 nm.

[0185] Then, using a plasma ion implantation device, argon (Ar) was plasma ion implanted into the surface of the polysilazane layer to form a gas barrier layer made of modified polysilazane. In this way, a gas barrier film was obtained having a gas barrier layer made of modified polysilazane on one side of the substrate (PET film). Note that the modification of polysilazane proceeds from the surface of the polysilazane layer. Therefore, the degree of modification does not affect the surface condition of the gas barrier layer, and therefore does not affect the recovery rate.

[0186] (Evaluation of indentation) The release sheet R2 was peeled off from the pressure-sensitive adhesive sheets obtained in the Examples and Comparative Examples, and the exposed pressure-sensitive adhesive layer was attached to an easy-adhesion layer of a polyethylene terephthalate (PET) film (thickness: 25 μm) having an easy-adhesion layer, and then the release sheet R1 was peeled off. Subsequently, the release sheet R2 was peeled off from another pressure-sensitive adhesive sheet, and the exposed pressure-sensitive adhesive layer was attached to the pressure-sensitive adhesive layer on the PET film, to obtain a laminate having a configuration of release sheet R1 / adhesive layer (thickness: 100 μm) / PET film.

[0187] The release sheet R1 was peeled off from the obtained laminate, and the exposed adhesive layer was attached to soda lime glass (manufactured by Nippon Sheet Glass Co., Ltd.) to obtain a sample having a configuration of soda lime glass / adhesive layer (thickness: 100 μm) / PET film. The adhesive layers of Example 5 and Comparative Example 2 were further irradiated with active energy rays (ultraviolet rays; UV) from the PET film side, and these samples were used. The active energy ray irradiation conditions were the same as those of irradiation condition A described above.

[0188] In an environment of 23°C and 50% RH, the surface of the obtained sample PET film was pressed with a probe of a constant pressure thickness measuring instrument (manufactured by Teclock, product name "PG-02") at a load of 125 gf for 60 seconds. 60 seconds after the pressing was completed, the pressed area was visually observed and the indentation was evaluated according to the following criteria. The results are shown in Table 2. A: No indentation visible B: Slight indentation visible C: Indentation visible

[0189] (Evaluation of pressability) The same samples as those used for the evaluation of indentations described above were prepared. In an environment of -20°C, 10 evaluators pressed their index fingers into the surface of the PET film of the obtained sample, and evaluated the pressability according to the following evaluation criteria. The results are shown in Table 2. In an environment of 23°C and 50% RH, all 10 evaluators judged that it was easy to press. A: 8 or more evaluators out of 10 judged that it was easy to press. B: 3 or more evaluators out of 10 judged that it was difficult to press.

[0190] (Evaluation of Odor) The release sheet R2 was peeled off from the pressure-sensitive adhesive sheets obtained in the Examples and Comparative Examples, and 10 evaluators evaluated the odor of the exposed pressure-sensitive adhesive layer according to the following criteria. The results are shown in Table 2. A: Three or fewer evaluators noticed an odor in the pressure-sensitive adhesive layer. B: Four or more evaluators noticed an odor in the pressure-sensitive adhesive layer.

[0191] (Evaluation of blister resistance) The release sheet R2 was peeled off from the pressure-sensitive adhesive sheets obtained in the Examples and Comparative Examples, and the exposed pressure-sensitive adhesive layer was attached to an ITO vapor-deposited film (manufactured by Oike Kogyo Co., Ltd., product name "Tetlite TCFKH150NMH2-125-U6 / T2"). Furthermore, the release sheet R1 was peeled off from the pressure-sensitive adhesive sheet, and the exposed pressure-sensitive adhesive layer was attached to the polycarbonate side of a resin plate (manufactured by Mitsubishi Gas Chemical Company, Inc., product name "Iupilon Sheet MR58U", containing an ultraviolet absorber, thickness: 1 mm) in which a polymethyl methacrylate resin layer was laminated on a polycarbonate resin plate, thereby obtaining an evaluation sample. Thereafter, the evaluation sample was autoclaved for 20 minutes under conditions of 50°C and 0.5 MPa.

[0192] The evaluation sample was left at normal pressure, 23°C, and 50% RH for 12 hours, and then stored under high-temperature, high-humidity conditions of 85°C and 85% RH for 72 hours. The condition of the interface between the pressure-sensitive adhesive layer and the adherend was then visually inspected, and blister resistance was evaluated according to the following criteria. The results are shown in Table 2. For Example 5 and Comparative Example 2, the pressure-sensitive adhesive layer after autoclaving was irradiated with ultraviolet light as active energy rays at an illuminance of 200 mW / cm. 2 , light intensity 1000mJ / cm 2After the adhesive layer was cured, the blister resistance was evaluated in the same manner as above. A: No bubbling B: Bubbling

[0193]

[0194] From Table 2, it was confirmed that the pressure-sensitive adhesive sheets of Examples 1 to 7 had high flexibility of the pressure-sensitive adhesive layer at low temperatures, and that within a specified temperature range, variation in the degree of deformation of the pressure-sensitive adhesive layer was suppressed.

[0195] The pressure-sensitive adhesive sheet of the present invention can be suitably used for bonding a first member and a second member, for example, for bonding members constituting a display body, and is suitable for a configuration in which the pressure-sensitive adhesive layer is subjected to repeated deformation.

[0196] REFERENCE SIGNS LIST 1... Adhesive sheet 10... Adhesive layer 11... First release sheet 12... Second release sheet 2... Laminate 10A, 10B, 10C... Adhesive layer 21... First member 22... Second member 23... Third member 24... Fourth member 3... Device 31... Cover film 32... First adhesive layer 33... First electrode 34... Second adhesive layer 35... Piezoelectric film 36... Third adhesive layer 37... Second electrode 38... Fourth adhesive layer 39... Organic EL element 40... Fifth adhesive layer 41... TFT substrate

Claims

1. An adhesive sheet having an adhesive layer for bonding a first member and a second member, wherein the Shore hardness of the adhesive layer at -20°C measured with an E-type durometer is 70HS or less, and the recovery rate of the adhesive layer at 23°C is 70% or more.

2. The pressure-sensitive adhesive sheet according to claim 1, wherein the gel fraction of the pressure-sensitive adhesive layer is 40% or more.

3. The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the pressure-sensitive adhesive layer has a recovery rate of 70% or more at -20°C.

4. The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the pressure-sensitive adhesive layer has a distortion rate after 10 seconds at -20°C of 10% or more.

5. The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein at least one selected from the first member and the second member is a member containing a piezoelectric material.

6. The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein at least one selected from the first member and the second member is a flexible member.

7. The adhesive sheet according to claim 1 or 2, wherein the adhesive constituting the adhesive layer is an acrylic adhesive.

8. The pressure-sensitive adhesive sheet according to claim 7, wherein the acrylic pressure-sensitive adhesive comprises a (meth)acrylic acid ester polymer and a crosslinking agent.

9. A laminate comprising a first member, a second member, and an adhesive layer that bonds the first member and the second member to each other, wherein the adhesive layer is the adhesive layer possessed by the adhesive sheet according to claim 1.

10. The laminate according to claim 9, wherein at least one selected from the first member and the second member is a member containing a piezoelectric material.

11. The laminate according to claim 9, wherein at least one selected from the first member and the second member is a flexible member.

12. The laminate according to claim 10, wherein at least one selected from the first member and the second member is a flexible member.

13. A device comprising a laminate according to any one of claims 9 to 12.

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