Double-sided adhesive sheet, double-sided adhesive sheet with release film, laminate for image display device using the same, and image display device

Abstract

The present invention provides the following as a double-sided adhesive sheet that has excellent impact resistance and tends not to leave any marks during bonding.　A double-sided adhesive sheet having an adhesive layer obtained by curing an adhesive composition containing a (meth)acrylic copolymer (A), wherein: a stress-strain curve obtained for a test piece of 20 mm × 70 mm of the adhesive sheet when a tensile test is performed at a tension rate of 300 mm / min and a chuck distance of 20 mm indicates that the tensile elastic modulus (E') at 25°C, which is calculated as the slope of the strain section from 10% to 200%, is 1.0-20 MPa; and the elastic modulus ratio (E' / G') of the tensile elastic modulus (E') at 25°C to the shear storage elastic modulus (G') at 25°C obtained by dynamic viscoelasticity measurement in the shear mode at a frequency of 1 Hz is 15-100.

Description

Double-sided adhesive sheet, double-sided adhesive sheet with release film, laminate for image display device using same, and image display device

[0001] The present invention relates to a double-sided pressure-sensitive adhesive sheet, a double-sided pressure-sensitive adhesive sheet with a release film, and a laminate for an image display device and an image display device using the same.

[0002] In recent years, in order to improve the visibility of image display devices, the gap between an image display panel such as a liquid crystal display (LCD), a plasma display (PDP), or an electroluminescence display (ELD) and a protective panel or touch panel member placed on the front side (viewing side) of the image display panel has been filled with a resin such as an adhesive or glue to suppress reflection of incident light and outgoing light from the displayed image at the air layer interface.

[0003] For example, Patent Document 1 discloses a method for manufacturing a component laminate for an image display device, which has a configuration in which an image display device component is laminated on at least one side of a transparent double-sided adhesive sheet, in which an adhesive sheet that has been primarily crosslinked by ultraviolet light is attached to the image display device component, and then the adhesive sheet is irradiated with ultraviolet light through the image display device component to cause secondary curing.

[0004] Furthermore, Patent Document 2 discloses a pressure-sensitive adhesive sheet containing a (meth)acrylic copolymer having an ultraviolet-crosslinkable site, as a pressure-sensitive adhesive sheet useful for displays and touch panels.

[0005] Patent No. 4971529 Patent No. 6062740

[0006] In recent years, with the need for energy-saving, lightweight, and thin image display devices, organic electroluminescence (EL) panels are becoming increasingly popular as image display panels, replacing conventional liquid crystal panels. Furthermore, during the assembly process of an image display device, when components such as image display panels are bonded together, the unevenness and irregularities of the bonding components can be transferred to the front side (viewing side) of the image display panel, resulting in a poor appearance. For this reason, pressure-sensitive adhesive sheets used to bond image display device components are required to be resistant to marks caused by the unevenness and irregularities of the image display device components themselves during the process of creating a laminate for the image display device. Furthermore, mobile electronic devices are often at risk of damage due to impact due to their usage, and pressure-sensitive adhesive sheets themselves are required to be impact-resistant to protect the components inside the image display device from external impacts.

[0007] The pressure-sensitive adhesive sheets in Patent Documents 1 and 2 were developed for laminated structures using conventional image display device components, and did not address the aforementioned problem of poor appearance. Furthermore, conventional flexible pressure-sensitive adhesive sheets are prone to transferring unevenness and irregularities from the laminating components. While the pressure-sensitive adhesive sheet needs to be rigid to prevent deformation, simply making it too rigid results in poor impact resistance. This problem becomes more pronounced as image display panels become thinner. Therefore, for image display devices that are becoming thinner, pressure-sensitive adhesive sheets that have excellent impact resistance but are less likely to leave marks during lamination are required. Furthermore, image display devices that do not use polarizing plates have become increasingly popular in recent years. These polarizing plate-free configurations are thinner and lighter than conventional polarizing plate-based configurations, making the above-mentioned problem even more pronounced.

[0008] The present invention was conceived under these circumstances, and provides a double-sided pressure-sensitive adhesive sheet, a double-sided pressure-sensitive adhesive sheet with a release film, a laminate for an image display device, and an image display device that have excellent impact resistance and are less likely to leave marks when attached.

[0009] However, in light of these circumstances, the present inventor conducted extensive research and discovered that by setting the tensile modulus of elasticity (E') at 25°C of a double-sided pressure-sensitive adhesive sheet within a specific range, and further setting the modulus ratio (E' / G') of the tensile modulus of elasticity at 25°C (E') to the shear storage modulus of elasticity at 25°C (G') within a specific range, it is possible to obtain a double-sided pressure-sensitive adhesive sheet that has excellent impact resistance and is less likely to leave marks when applied.

[0010] That is, the present invention has the following aspects: [1] A double-sided pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed by curing a pressure-sensitive adhesive composition containing a (meth)acrylic copolymer (A), wherein the double-sided pressure-sensitive adhesive sheet has a tensile modulus (E') at 25°C of 1.0 to 20 MPa, calculated as the slope in the 10 to 200% strain section in a stress-strain curve obtained by a tensile test performed on a 20 mm x 70 mm test piece at a pulling rate of 300 mm / min and a chuck distance of 20 mm, and a modulus ratio (E' / G') of the tensile modulus (E') at 25°C to the shear storage modulus (G') at 25°C, obtained by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz, of 15 to 100. [2] The double-sided pressure-sensitive adhesive sheet according to [1], wherein the pressure-sensitive adhesive layer has a stress relaxation rate (X) of 0.50 or less, calculated by the following formula (I) from the initial elastic modulus (G'(0)) 0.1 seconds after application of a 25% strain at 70°C and the relaxed elastic modulus (G'(300)) 300 seconds after application of a 25% strain at 70°C: Stress relaxation rate (X) = (G'(300) / G'(0)) (I) [3] The double-sided pressure-sensitive adhesive sheet according to [1] or [2], wherein the pressure-sensitive adhesive composition comprises a crosslinking agent (B) and a photoinitiator (C). [4] The double-sided pressure-sensitive adhesive sheet according to any of [1] to [3], wherein the pressure-sensitive adhesive composition comprises an ultraviolet absorber (D). [5] The double-sided pressure-sensitive adhesive sheet according to any of [1] to [4], wherein the double-sided pressure-sensitive adhesive sheet has a gel fraction of 30 to 90%. [6] The double-sided pressure-sensitive adhesive sheet according to any one of [1] to [5], having a glass transition temperature (Tg) of -10°C or lower, defined as the maximum value of Tan δ, obtained by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz. [7] The double-sided pressure-sensitive adhesive sheet according to any one of [1] to [6], wherein the (meth)acrylic copolymer (A) contains, as structural units, a hydroxyl group-containing (meth)acrylate monomer (a1) and / or a nitrogen atom-containing (meth)acrylate monomer (a2). [8] The double-sided pressure-sensitive adhesive sheet according to [3], wherein the photoinitiator (C) is a hydrogen abstraction photoinitiator. [9] The double-sided pressure-sensitive adhesive sheet according to any one of [1] to [8], having a laminated pressure-sensitive adhesive layer in which two or more pressure-sensitive adhesive layers having different shear storage moduli (G') at 25°C are laminated adjacently.

[10] The double-sided pressure-sensitive adhesive sheet according to [9], wherein the laminated pressure-sensitive adhesive layer comprises a first pressure-sensitive adhesive layer having a lower shear storage modulus (G') at 25°C than the adjacent pressure-sensitive adhesive layer, and a second pressure-sensitive adhesive layer having a higher shear storage modulus (G') at 25°C than the adjacent pressure-sensitive adhesive layer.

[11] The double-sided pressure-sensitive adhesive sheet according to [9] or

[10] , wherein the laminated pressure-sensitive adhesive layer has a three-layer structure in which the first pressure-sensitive adhesive layer, the second pressure-sensitive adhesive layer, and the first pressure-sensitive adhesive layer are laminated in this order.

[12] The double-sided pressure-sensitive adhesive sheet according to

[10] or

[11] , wherein the pressure-sensitive adhesive composition forming the second pressure-sensitive adhesive layer contains an ultraviolet absorber (D).

[13] The double-sided pressure-sensitive adhesive sheet according to any of

[10] to

[13] , wherein the content of crosslinking agent (B) contained in the pressure-sensitive adhesive composition forming the second pressure-sensitive adhesive layer is higher than the content of crosslinking agent (B) contained in the pressure-sensitive adhesive composition forming the first pressure-sensitive adhesive layer.

[14] The double-sided pressure-sensitive adhesive sheet according to any one of

[10] to

[14] , wherein the ratio (t2 / t1) of the thickness (t1) of the first pressure-sensitive adhesive layer to the thickness (t2) of the second pressure-sensitive adhesive layer is 0.2 or more.

[15] A double-sided pressure-sensitive adhesive sheet with a release film, comprising the double-sided pressure-sensitive adhesive sheet according to any one of [1] to

[14] , and a release film laminated on the double-sided pressure-sensitive adhesive sheet.

[16] A laminate for an image display device, comprising two image display device components and the double-sided pressure-sensitive adhesive sheet according to any one of [1] to

[14] interposed between the two image display device components.

[17] An image display device, comprising the laminate for an image display device according to

[16] .

[0011] The double-sided pressure-sensitive adhesive sheet of the present invention has excellent impact resistance and is less likely to leave marks when attached, making it suitable for use as a double-sided pressure-sensitive adhesive sheet in image display devices, particularly organic EL image display devices.

[0012] An example of an embodiment of the present invention will be described in detail below. However, the present invention is not limited to the embodiment described below. In the present invention, the term "film" conceptually includes a sheet, a film, and a tape. Furthermore, when the term "panel" is used, such as an image display panel or a protective panel, it includes a plate, a sheet, and a film.

[0013] 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 includes the meaning of "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. Furthermore, "x and / or y (x and y are any configurations)" means at least one of x and y, and can mean three possibilities: x only, y only, or x and y. Regarding the numerical ranges described in stages in this specification, the upper or lower limit of a certain numerical range can be arbitrarily combined with the upper or lower limit of another numerical range. Furthermore, in the numerical ranges described in the present invention, the upper or lower limit of the numerical range can also be replaced with the values ​​shown in the examples. In this specification, "(meth)acrylic" refers to a compound that includes both acrylic and methacrylic, "(meth)acrylate" refers to a compound that includes both acrylate and methacrylate, and "(meth)acryloyl" refers to a compound that includes both acryloyl and methacryloyl. In this specification, "main component" refers to a component that has a significant effect on the properties of the material, and the content of the component is usually 50% by mass or more, preferably 70% by mass or more, and particularly preferably 90% by mass or more of the entire material.

[0014] <<Adhesive Sheet>> A double-sided pressure-sensitive adhesive sheet according to one embodiment of the present invention (hereinafter referred to as "the present pressure-sensitive adhesive sheet") has a pressure-sensitive adhesive layer formed by curing a pressure-sensitive adhesive composition containing a (meth)acrylic copolymer (A), and has a tensile modulus (E') at 25°C of 1.0 to 20 MPa, and a modulus ratio (E' / G') of the tensile modulus (E') at 25°C to the shear storage modulus (G') at 25°C, obtained by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz, of 15 to 100. The present pressure-sensitive adhesive sheet will now be described.

[0015] The pressure-sensitive adhesive sheet has a tensile modulus (E') at 25°C, calculated as the slope in the 10 to 200 strain range in a stress-strain curve obtained by a tensile test using a 20 mm x 70 mm test piece at a tension speed of 300 mm / min and a chuck distance of 20 mm, of 1.0 to 20 MPa, preferably 2 to 18 MPa, more preferably 2.5 to 15 MPa, particularly preferably 3.0 to 12 MPa, and most preferably 5.0 to 9.0 MPa. When the tensile modulus (E') at 25°C is within the above range, the pressure-sensitive adhesive sheet has appropriate elasticity and is resistant to marking during application. Furthermore, when the tensile modulus (E') at 25°C is equal to or greater than the above lower limit, the pressure-sensitive adhesive sheet has excellent cohesion and is resistant to indentations and dents due to localized pressure. When the tensile modulus (E') is equal to or less than the above upper limit, the pressure-sensitive adhesive sheet has appropriate flexibility and stress relaxation properties and is resistant to step absorption.

[0016] Examples of methods for adjusting the tensile modulus (E') at 25°C include adjusting the composition or molecular weight of the (meth)acrylic copolymer (A) contained in the pressure-sensitive adhesive composition described below, the type or content of the crosslinking agent (B) or the photoinitiator (C), and adjusting the amount of active energy ray irradiation. However, the methods are not limited to these. The tensile modulus (E') at 25°C can also be determined by the method described in the Examples.

[0017] The pressure-sensitive adhesive sheet preferably has a shear storage modulus (G') at 25°C, as determined by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz, of 80 to 1000 kPa, more preferably 100 to 900 kPa, even more preferably 120 to 800 kPa, particularly preferably 140 to 700 kPa, and most preferably 160 to 600 kPa. If the shear storage modulus (G') at 25°C is equal to or greater than the lower limit, the pressure-sensitive adhesive sheet tends to have excellent cohesive strength and be less susceptible to indentations or dents due to localized pressure, whereas if it is equal to or less than the upper limit, the pressure-sensitive adhesive sheet tends to have adequate flexibility and stress relaxation properties, and to have excellent impact resistance and step absorbency.

[0018] The shear storage modulus (G') at 25°C is measured, for example, as follows. The pressure-sensitive adhesive sheet is repeatedly laminated to a thickness of 0.7 to 1.2 mm (e.g., 0.8 mm), and then a circular sample with a diameter of 8 mm is punched out. The obtained sample is subjected to dynamic viscoelasticity measurement using a rheometer under the following conditions: measuring jig: 8 mm diameter parallel plates, frequency: 1 Hz, measuring temperature: -50 to 150°C, and heating rate: 5°C / min, and the shear storage modulus (G') at 25°C is read.

[0019] To accurately measure the shear storage modulus (G'), it is necessary to avoid fluctuations in the value due to the influence of measurement conditions. By adjusting the thickness of the measurement sample to a range of 0.7 to 1.2 mm, the shear storage modulus (G') can be accurately measured without being affected by the thickness of the pressure-sensitive adhesive sheet. The phrase "adjusting the thickness to a range of 0.7 to 1.2 mm" means that if the thickness of the pressure-sensitive adhesive sheet used as the measurement sample is less than this range, the thickness of the measurement sample is adjusted to this range by stacking several sheets, etc. This also applies when the thickness of the measurement sample is specified in other tests in this specification. Furthermore, the smaller the size of the parallel plates, the easier it is to reduce fluctuations in values ​​due to the influence of the measurement jig, but slippage is more likely to occur between the sample and the measurement jig. To reduce measurement errors due to this slippage, it is preferable to increase the size of the parallel plates to increase the contact area between the sample and the measurement jig and suppress slippage. This allows the shear storage modulus (G') to be accurately measured without being affected by the measurement jig.

[0020] Examples of methods for adjusting the shear storage modulus (G') at 25°C include a method for adjusting the composition or molecular weight of the (meth)acrylic copolymer (A) contained in the pressure-sensitive adhesive composition described below, or the type or amount of the crosslinking agent (B) or the photoinitiator (C) added, as well as a method for adjusting the amount of active energy ray irradiation, but the methods are not limited to these.

[0021] This PSA sheet has a modulus ratio (E' / G') of the tensile modulus (E') at 25°C to the shear storage modulus (G') at 25°C, as determined by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz, of 15 to 100, preferably 18 to 90, more preferably 21 to 80, particularly preferably 23 to 70, and most preferably 25 to 60. When the modulus ratio (E' / G') is within the above range, the double-sided PSA sheet has both moderate elasticity and excellent flexibility, and exhibits high levels of both indentation resistance and impact resistance.

[0022] If the elastic modulus ratio (E' / G') is above the lower limit, the double-sided pressure-sensitive adhesive sheet will have appropriate flexibility and stress relaxation properties, and will have excellent impact resistance and step absorption properties, and if it is below the upper limit, the double-sided pressure-sensitive adhesive sheet will have excellent cohesive strength, handling properties, and indentation resistance.

[0023] Methods for adjusting the elastic modulus ratio (E' / G') within the above range include, for example, forming the adhesive layer of the present pressure-sensitive adhesive sheet as a laminated adhesive layer in which two or more adhesive layers having different shear storage moduli (G') at 25°C are laminated adjacent to each other, or forming the adhesive layer into a structure having a gradient structure in the thickness direction. The reason why the above design improves indentation resistance and impact resistance is unclear, but the following mechanism is thought to be the cause. In a viscoelastic body such as a pressure-sensitive adhesive sheet, the tensile modulus (E') and shear storage modulus (G') obtained in dynamic viscoelasticity measurement under the same temperature and frequency conditions usually satisfy the relationship E'≦3G'. However, when the adhesive layer is a laminated adhesive layer or has a gradient structure in the thickness direction, as described above, this relationship no longer holds (E'>3G'). The inventors of the present invention have found that, upon careful observation of the state of samples after lamination tests and impact resistance tests, the elastic modulus in the large deformation region accompanied by plastic deformation, as well as the small deformation region (elastic deformation) observed in dynamic viscoelasticity measurements, is important for the susceptibility to indentation and impact resistance. Further expanding the relationship between the tensile modulus (E') and shear storage modulus (G') in dynamic viscoelasticity measurements, the inventors have found that by designing a specific relationship between the tensile modulus (E') calculated as the slope in the large deformation region, i.e., the 10 to 200% strain range, and the shear storage modulus (G') determined by dynamic viscoelasticity measurements, not only can indentation resistance be improved but also superior impact resistance can be achieved. Furthermore, when the pressure-sensitive adhesive layer is a laminated pressure-sensitive adhesive layer, increasing the difference in the shear storage modulus (G') of each layer tends to increase the elastic modulus ratio (E' / G').

[0024] From the viewpoint of reducing adhesive extrusion, the pressure-sensitive adhesive sheet has an initial modulus of elasticity (G'(0)) of typically 5 to 100 kPa, preferably 10 to 60 kPa, more preferably 15 to 50 kPa, and even more preferably 20 kPa, 0.1 seconds after application of a 25% strain at 70°C. When the lower limit of the initial modulus of elasticity (G'(0)) is equal to or greater than the above-mentioned value, the pressure-sensitive adhesive sheet has a moderate cohesive force, is excellent in handleability, and is less likely to crush the peripheral edge of the pressure-sensitive adhesive sheet when attached to a member, which tends to reduce or eliminate adhesive extrusion at the edge. Furthermore, when the adherend has unevenness, when the adherend has unevenness, the unevenness of the surface tends to be filled in during attachment.

[0025] The elastic modulus (G'(0)) is measured, for example, as follows: PSA sheets are repeatedly laminated to a thickness of 0.7 to 1.2 mm (for example, about 0.8 mm), and then punched out to a diameter of 8 mm. A strain of 25% is applied to the obtained sample at 70°C using a rheometer, and the elastic modulus (G') is read after 0.1 seconds.

[0026] Examples of methods for adjusting the initial elastic modulus (G'(0)) include a method for adjusting the composition or molecular weight of the (meth)acrylic copolymer (A) contained in the pressure-sensitive adhesive composition described below, or the type or amount of the crosslinking agent (B) or photoinitiator (C) added, as well as a method for adjusting the amount of active energy ray irradiation. However, the methods are not limited to these.

[0027] The present pressure-sensitive adhesive sheet has a relaxation modulus (G'(300)) after 300 seconds of application of a 25% strain at 70°C of typically 0.1 to 20 kPa, preferably 0.2 to 15 kPa, more preferably 0.5 to 10 kPa, and even more preferably 1 to 5 kPa. When the lower limit of the relaxation modulus (G'(300)) is equal to or greater than the above-mentioned value, the present pressure-sensitive adhesive sheet tends to have an appropriate cohesive strength, is excellent in handleability, and is less likely to crush the peripheral edges of the pressure-sensitive adhesive sheet when attached to a member, which tends to reduce or eliminate adhesive extrusion at the edges. Furthermore, when the upper limit of the relaxation modulus (G'(300)) is equal to or less than the above-mentioned value, there is a tendency for the sheet to maintain appropriate flexibility and ensure wettability to the adherend.

[0028] The relaxation modulus (G'(300)) is measured, for example, as follows. PSA sheets are repeatedly laminated to a thickness of 0.7 to 1.2 mm (for example, about 0.8 mm), and punched out to a diameter of 8 mm. A strain of 25% is applied to the obtained sample at 70°C using a rheometer, and the modulus (G') is read after 300 seconds.

[0029] Examples of methods for adjusting the relaxation modulus (G'(300)) include, but are not limited to, methods for adjusting the composition or molecular weight of the (meth)acrylic copolymer (A) contained in the pressure-sensitive adhesive composition described below, the type or content of the crosslinking agent (B) or the photoinitiator (C), and methods for adjusting the amount of active energy ray irradiation.

[0030] The present pressure-sensitive adhesive sheet preferably has a stress relaxation rate (X) calculated by the following formula (I) from the initial elastic modulus (G'(0)) 0.1 seconds after application of a 25% strain at 70°C and the relaxed elastic modulus (G'(300)) 300 seconds after application of a 25% strain at 70°C. The stress relaxation rate (X) is preferably 0.50 or less, more preferably 0.40 or less, even more preferably 0.30 or less, particularly preferably 0.20 or less, and especially preferably 0.10 or less. From the viewpoint of suppressing adhesive extrusion during lamination, the stress relaxation rate (X) is preferably 0.01 or more, more preferably 0.02 or more, even more preferably 0.03 or more, and particularly preferably 0.04 or more. The range of the stress relaxation rate (X) is, for example, 0.01 to 0.50. Stress relaxation rate (X) = (G'(300) / G'(0)) (I)

[0031] In laminates requiring precision lamination, such as laminates for image display devices, finishing lamination using a heat and pressure treatment in an autoclave is commonly performed when laminating components. After the autoclave process is completed or after the product begins to be used, air bubbles may form at the peripheral edge. One of the main causes of such bubbles is thought to be the infiltration of air present in the autoclave oven between the laminating components and the pressure-sensitive adhesive sheet due to the high pressure inside the autoclave oven during the lamination process. Conventionally, such air bubbles were not visible on the outside because the peripheral edge of a display was covered by a concealing layer such as a printed layer or a bezel. However, in recent years, due to demands for narrower display frames and frameless designs, the peripheral edge has become narrower, and there is a strong demand for improved bubble resistance at the peripheral edge of the pressure-sensitive adhesive sheet. When the stress relaxation rate (X) is within the above range, the stress relaxation rate is excellent, resulting in excellent absorption of foreign matter and defects that can cause bubbles and facilitating the diffusion of air trapped during lamination of the components. As a result, air bubbles are less likely to remain when the pressure-sensitive adhesive sheet is laminated, and the pressure-sensitive adhesive sheet tends to have excellent resistance to foaming during lamination.

[0032] Examples of methods for adjusting the stress relaxation rate (X) include, but are not limited to, a method for adjusting the composition or molecular weight of the (meth)acrylic copolymer (A) contained in the pressure-sensitive adhesive composition described below, or a method for adjusting the type or content of the crosslinking agent (B) or photoinitiator (C).

[0033] The PSA sheet preferably has a glass transition temperature (Tg) defined by the maximum value of the loss tangent (Tan δ) obtained by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz, of -10°C or lower, more preferably -15°C or lower, even more preferably -20°C or lower, and particularly preferably -25°C or lower. Having a glass transition temperature (Tg) above the lower limit tends to provide good impact resistance and stress relaxation properties. On the other hand, from the viewpoint of obtaining a double-sided PSA sheet with excellent handling properties and adhesive extrusion resistance, the lower limit is preferably -70°C or higher, more preferably -60°C or higher, even more preferably -50°C or higher, particularly preferably -40°C or higher, and most preferably -30°C or higher. The glass transition temperature (Tg) can range, for example, from -70 to -10°C.

[0034] The glass transition temperature (Tg) can be obtained by reading the temperature at which the loss tangent (Tan δ) becomes a maximum value, i.e., the peak temperature, from dynamic viscoelasticity spectrum data in a shear mode obtained in the same manner as in the measurement of the shear storage modulus (G′(25° C.)) at 25° C. described above.

[0035] The method for adjusting the glass transition temperature can be, for example, the method for adjusting the composition or molecular weight of the (meth)acrylic copolymer (A) contained in the pressure-sensitive adhesive composition described later, the method for adjusting the type or amount of the crosslinking agent (B) and the photoinitiator (C), as well as the method for adjusting the amount of active energy ray irradiation.In addition, when the pressure-sensitive adhesive sheet is a multi-layer pressure-sensitive adhesive sheet described later, the glass transition temperature of the pressure-sensitive adhesive sheet can also be adjusted by adjusting the glass transition temperature of each layer constituting the pressure-sensitive adhesive sheet.However, the method is not limited to these methods.

[0036] The present pressure-sensitive adhesive sheet preferably has a gel fraction of 30 to 90%, more preferably 35 to 87%, even more preferably 40 to 86%, and particularly preferably 45 to 85%. When the gel fraction is equal to or greater than the lower limit, a moderate cohesive strength tends to be obtained, and when the gel fraction is equal to or less than the upper limit, stress relaxation properties tend to be obtained. Furthermore, when the gel fraction of the present pressure-sensitive adhesive sheet is within the above range, it tends to have a moderate cohesive strength and excellent handleability and shape stability. The gel fraction can be measured by the method described in the Examples below.

[0037] The adhesive strength of this pressure-sensitive adhesive sheet to soda-lime glass at a temperature of 23°C and a peeling speed of 60 mm / min is typically 1 N / cm or more, preferably 3 N / cm or more, more preferably 5 N / cm or more, and particularly preferably 7 N / cm or more. The upper limit of the adhesive strength is preferably 50 N / cm or less, more preferably 30 N / cm or less. The range of the adhesive strength is, for example, 1 to 50 N / cm. When the adhesive strength of the pressure-sensitive adhesive sheet is equal to or greater than the above-mentioned numerical value, peeling of the edge surface of the pressure-sensitive adhesive sheet does not occur, and excellent lamination reliability at the peripheral edge tends to be obtained.

[0038] The adhesive strength is measured, for example, as follows. A 100 μm thick polyethylene terephthalate (PET) film and the adhesive layer of this adhesive sheet are laminated, and the other side is roll-pressed onto soda lime glass to form a laminate. The laminate is then autoclaved (temperature 60°C, gauge pressure 0.2 MPa, 20 minutes) to obtain a finished laminated sample for adhesive strength measurement. This sample is used to peel at a peel angle of 180° and a peel rate of 60 mm / min under an environment of 23°C and 50% RH, and the peel force (N / cm) is taken as the adhesive strength.

[0039] Examples of methods for adjusting the gel fraction and adhesive strength include a method for adjusting the composition and molecular weight of the (meth)acrylic copolymer (A) contained in the pressure-sensitive adhesive composition described below, or the type and amount of the crosslinking agent (B) and photoinitiator (C) added, as well as a method for adjusting the amount of active energy ray irradiation, but the methods are not limited to these.

[0040] The light transmittance of this pressure-sensitive adhesive sheet at a wavelength of 380 nm is usually 10% or less, preferably 6% or less, more preferably 5% or less, and particularly preferably 4% or less. When the light transmittance at a wavelength of 380 nm is within the above range, it tends to be easier to protect components of an image display device from deterioration due to ultraviolet rays. The light transmittance can be measured by the method described in the Examples below.

[0041] Examples of methods for adjusting the light transmittance include, but are not limited to, methods for adjusting the type and amount of ultraviolet absorber (D) contained in the pressure-sensitive adhesive composition described below.

[0042] As described above, the pressure-sensitive adhesive sheet has a pressure-sensitive adhesive layer formed by curing a pressure-sensitive adhesive composition containing a (meth)acrylic copolymer (A). The pressure-sensitive adhesive composition contains the (meth)acrylic copolymer (A) as a main component (preferably 50% by mass or more, more preferably 60% by mass or more, and particularly preferably 70% by mass or more). The pressure-sensitive adhesive composition also contains the (meth)acrylic copolymer (A) as a main component (preferably 70% by mass or more, more preferably 80% by mass or more, and particularly preferably 90% by mass or more) in a resin component. Furthermore, the pressure-sensitive adhesive composition preferably contains a crosslinking agent (B) and a photoinitiator (C), and also preferably contains an ultraviolet absorber (D). Each component contained in the pressure-sensitive adhesive composition will be described in detail below.

[0043] [(Meth)acrylic Copolymer (A)] Examples of the (meth)acrylic copolymer (A) include copolymers obtained by polymerizing a monomer component copolymerizable with an alkyl (meth)acrylate. Among these, it is preferable that the (meth)acrylic copolymer (A) contains two or more copolymerization components, and at least one of the copolymerization components is an alkyl (meth)acrylate (a1) having an alkyl group with 3 to 30 carbon atoms (hereinafter, sometimes referred to as "alkyl (meth)acrylate (a1)").

[0044] More specifically, the (meth)acrylic copolymer (A) may be a copolymer of a copolymerization component containing an alkyl(meth)acrylate (a1) and at least one copolymerizable monomer selected from the group consisting of alkyl(meth)acrylate (a1) and copolymerizable therewith, such as a hydroxyl group-containing monomer (a2), a nitrogen-containing monomer (a3), a carboxy group-containing monomer (a4), an epoxy group-containing monomer (a5), a vinyl monomer (a6), an alkyl(meth)acrylate monomer (a7) having an alkyl group with 1 or 2 carbon atoms, an alicyclic monomer (a8), a macromonomer (a9), and other copolymerizable monomers (a10) (hereinafter, sometimes referred to as "copolymerizable monomers (a2) to (a10)"). Such a (meth)acrylic copolymer (A) preferably has, in addition to the structural units derived from the alkyl(meth)acrylate (a1), structural units derived from the copolymerizable monomers (a2) to (a10) contained in the copolymerization component. In particular, the (meth)acrylic copolymer (A) preferably contains a hydroxyl group-containing monomer (a2) and / or a nitrogen-containing monomer (a3) ​​as a structural unit, since this allows for corrosion resistance, adhesion, and resistance to wet heat whitening when the adherend contains a corrosive component such as a metal, and it is particularly preferred that the (meth)acrylic copolymer (A) contains structural units derived from the hydroxyl group-containing monomer (a2) and the nitrogen-containing monomer (a3), since this further enhances cohesion. Furthermore, when the adherend contains a corrosive component such as a metal, from the viewpoint of corrosion resistance, it is preferred that the (meth)acrylic copolymer (A) does not contain structural units derived from the carboxyl group-containing monomer (a4).

[0045] [Alkyl (meth)acrylate (a1)] The alkyl (meth)acrylate (a1) is a linear or branched alkyl (meth)acrylate having an alkyl group with 3 to 30 carbon atoms, and is represented by the following formula (Chemical Formula 1): CH═C(R 1 )-COO(R 2 )...(Chemical formula 1) (In Chemical formula 1, R 1 represents a hydrogen atom or a methyl group, R 2 represents a linear or branched alkyl group having 3 to 30 carbon atoms.

[0046] Examples of the alkyl(meth)acrylate represented by the formula (Chemical Formula 1) include linear alkyl(meth)acrylates such as n-propyl(meth)acrylate, n-butyl(meth)acrylate, n-pentyl(meth)acrylate, n-hexyl(meth)acrylate, n-heptyl(meth)acrylate, n-octyl(meth)acrylate, n-nonyl(meth)acrylate, n-decyl(meth)acrylate, undecyl(meth)acrylate, lauryl(meth)acrylate, n-tridecyl(meth)acrylate, n-tetradecyl(meth)acrylate, cetyl(meth)acrylate, stearyl(meth)acrylate, icosyl(meth)acrylate, henicosyl(meth)acrylate, and behenyl(meth)acrylate; isopropyl(meth)acrylate, sec-butyl(meth)acrylate, and the like. Examples of branched alkyl (meth)acrylates include isobutyl (meth)acrylate, t-butyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, isodecyl (meth)acrylate, isobornyl (meth)acrylate, isostearyl (meth)acrylate, isoicosyl (meth)acrylate, butyloctyl (meth)acrylate, isomyristyl (meth)acrylate, isocetyl (meth)acrylate, hexyldecyl (meth)acrylate, isostearyl (meth)acrylate, octyldecyl (meth)acrylate, octyldodecyl (meth)acrylate, and isobehenyl (meth)acrylate. These may be used alone or in combination of two or more.

[0047] Among these, linear alkyl (meth)acrylates are preferred from the viewpoint of obtaining flexibility. Furthermore, from the viewpoint of balancing adhesiveness and flexibility, linear alkyl (meth)acrylates having an alkyl group of 3 to 20 carbon atoms, more preferably 5 to 18, particularly 6 to 16, and even more particularly 7 to 14 carbon atoms are preferred, and examples thereof include n-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, n-octyl (meth)acrylate, n-nonyl (meth)acrylate, decyl (meth)acrylate, and lauryl (meth)acrylate.

[0048] Among these, branched alkyl(meth)acrylates, i.e., alkyl(meth)acrylates containing a tertiary carbon atom in the alkyl group, are preferred because they readily undergo a hydrogen abstraction reaction (described later) upon irradiation with active energy rays, thereby enabling efficient formation of a crosslinked structure. Among these, branched alkyl(meth)acrylates having an alkyl group with 3 to 20 carbon atoms, more preferably 5 to 18, particularly 6 to 16, and even more particularly 7 to 14 carbon atoms are preferred, and examples thereof include isopropyl(meth)acrylate, sec-butyl(meth)acrylate, isobutyl(meth)acrylate, t-butyl(meth)acrylate, isopentyl(meth)acrylate, neopentyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, isooctyl(meth)acrylate, isononyl(meth)acrylate, isodecyl(meth)acrylate, and isobornyl(meth)acrylate, with 2-ethylhexyl(meth)acrylate and isobornyl(meth)acrylate being particularly preferred.

[0049] The proportion of the structural units derived from the alkyl (meth)acrylate (a1) relative to the (meth)acrylic copolymer (A) is usually 5 to 95% by mass, preferably 10 to 90% by mass, more preferably 15 to 85% by mass, and particularly preferably 20 to 80% by mass. If the proportion of the structural units derived from the alkyl (meth)acrylate (a1) is equal to or greater than the lower limit, the flexibility tends to be excellent and the conformability to irregularities tends to be excellent when the adherend has irregularities. If the proportion is equal to or less than the upper limit, the effect of the copolymerizable monomer described below is easily obtained and the adhesive strength and cohesive strength tend to be excellent.

[0050] [Hydroxyl Group-Containing Monomer (a2)] Examples of the hydroxyl group-containing monomer (a2) include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, and 8-hydroxyoctyl (meth)acrylate; caprolactone-modified hydroxy (meth)acrylates such as caprolactone-modified 2-hydroxyethyl (meth)acrylate; diethylene glycol (meth)acrylate; polyethylene glycol (meth)acrylate; polypropylene glycol (meth)acrylate; polytetramethylene glycol (meth)acrylate; polyoxyethylene poly(meth)acrylate; Examples of suitable monomers include (meth)acrylates having an oxyalkylene structure such as propylene glycol (meth)acrylate, primary hydroxyl group-containing (meth)acrylates such as 2-acryloyloxyethyl-2-hydroxyethyl phthalate, secondary hydroxyl group-containing (meth)acrylates such as 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and 3-chloro-2-hydroxypropyl (meth)acrylate, tertiary hydroxyl group-containing (meth)acrylates such as 2,2-dimethyl 2-hydroxyethyl (meth)acrylate, and vinyl ethers such as 2-hydroxyethyl vinyl ether, diethylene glycol monovinyl ether, and 4-hydroxybutyl vinyl ether. These may be used alone or in combination of two or more. The hydroxyl group-containing monomer (a2) improves the adhesive strength of the pressure-sensitive adhesive sheet and can suppress whitening under heat and humidity. Furthermore, when the pressure-sensitive adhesive composition contains a thermal crosslinking agent, as described below, it serves as a crosslinking reaction site.

[0051] Among the hydroxyl group-containing monomers (a2), preferred are hydroxyl group-containing monomers having a hydroxyalkyl group having 1 to 10, more preferably 1 to 6, and even more preferably 2 to 4 carbon atoms, such as 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxyethyl vinyl ether, diethylene glycol monovinyl ether, and 4-hydroxybutyl vinyl ether, and particularly preferred are primary hydroxyl group-containing (meth)acrylates, such as 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate.

[0052] When the (meth)acrylic copolymer (A) has a structural unit derived from a hydroxyl group-containing monomer (a2), the content thereof is usually 3 to 30 mass%, preferably 5 to 25 mass%, particularly preferably 7 to 20 mass%, relative to the (meth)acrylic copolymer (A), from the viewpoint of imparting adhesive strength and resistance to wet heat whitening.

[0053] [Nitrogen-Containing Monomer (a3)] Examples of the nitrogen-containing monomer (a3) ​​include amino group-containing monomers, amide group-containing monomers, isocyanate group-containing monomers, and (meth)acrylonitrile. These may be used alone or in combination of two or more. The nitrogen-containing monomer (a3) ​​improves the cohesive strength of the pressure-sensitive adhesive sheet and can suppress wet heat whitening. Furthermore, when a hydrogen abstraction photoinitiator described below is used, it is preferable that the acrylic polymer (A) has a structural unit derived from the nitrogen-containing monomer (a3). When a hydrogen abstraction photoinitiator described below is used, the nitrogen-containing monomer (a3) ​​has the effect of promoting the hydrogen abstraction reaction.

[0054] Examples of the amino group-containing monomer include primary amino group-containing (meth)acrylates such as aminomethyl (meth)acrylate and aminoethyl (meth)acrylate; secondary amino group-containing (meth)acrylates such as t-butylaminoethyl (meth)acrylate and t-butylaminopropyl (meth)acrylate; tertiary amino group-containing (meth)acrylates such as diethylaminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylate, diethylaminopropyl (meth)acrylate, and dimethylaminopropylacrylamide; and monomers such as N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine, (meth)acryloylmorpholine, N-vinylacetamides, and N-vinylcaprolactam.

[0055] Examples of the amide group-containing monomer include (meth)acrylamide; N-alkyl(meth)acrylamides such as N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-propyl(meth)acrylamide, N-n-butyl(meth)acrylamide, diacetone(meth)acrylamide, and N,N'-methylenebis(meth)acrylamide; N,N-dialkyl(meth)acrylamides such as N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dipropyl(meth)acrylamide, N,N-ethylmethylacrylamide, and N,N-diallyl(meth)acrylamide; hydroxyalkyl(meth)acrylamides such as N-hydroxymethyl(meth)acrylamide and N-hydroxyethyl(meth)acrylamide; alkoxyalkyl(meth)acrylamides such as N-methoxymethyl(meth)acrylamide and N-(n-butoxymethyl)(meth)acrylamide; maleimide or a derivative thereof. Among these, (meth)acrylamide is preferred.

[0056] Examples of the isocyanate group-containing monomer include 2-(meth)acryloyloxyethyl isocyanate and alkylene oxide adducts thereof, etc. The isocyanate group may be protected with a blocking agent such as methyl ethyl ketone oxime, 3,5-dimethylpyrazole, 1,2,4-triazole, or diethyl malonate.

[0057] Among these, those having a tertiary nitrogen atom are preferred, as they have a sensitizing effect on the hydrogen abstraction reaction by the hydrogen abstraction photoinitiator described below, and as a result, can efficiently form a crosslinked structure. Tertiary amino group-containing (meth)acrylates, N,N-dialkyl(meth)acrylamides, N-vinylpyrrolidone, acryloylmorpholine, and the like are particularly preferred.

[0058] When the (meth)acrylic copolymer (A) has a structural unit derived from the nitrogen-containing monomer (a3), the content thereof is usually 1 to 45% by mass, preferably 3 to 40% by mass, particularly preferably 5 to 35% by mass, and particularly preferably 7 to 30% by mass, relative to the (meth)acrylic copolymer (A), from the viewpoint of imparting cohesive strength and resistance to wet heat whitening.

[0059] [Carboxy Group-Containing Monomer (a4)] Examples of the carboxy group-containing monomer (a4) include (meth)acrylic acid, 2-(meth)acryloyloxyethyl hexahydrophthalic acid, 2-(meth)acryloyloxypropyl hexahydrophthalic acid, 2-(meth)acryloyloxyethyl phthalic acid, 2-(meth)acryloyloxypropyl phthalic acid, 2-(meth)acryloyloxyethyl maleic acid, 2-(meth)acryloyloxypropyl maleic acid, 2-(meth)acryloyloxyethyl succinic acid, 2-(meth)acryloyloxypropyl succinic acid, crotonic acid, fumaric acid, maleic acid, itaconic acid, etc. These may be used alone or in combination of two or more.

[0060] When the (meth)acrylic copolymer (A) has a structural unit derived from a carboxy group-containing monomer (a4), the content thereof is usually 0.1 to 15 mass%, preferably 0.3 to 13 mass%, more preferably 0.5 to 10 mass%, and particularly preferably 1 to 6 mass%, based on the (meth)acrylic copolymer (A).

[0061] [Epoxy Group-Containing Monomer (a5)] Examples of the epoxy group-containing monomer (a5) include glycidyl (meth)acrylate, methyl glycidyl (meth)acrylate, 3,4-epoxycyclohexylmethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate glycidyl ether, etc. These may be used alone or in combination of two or more.

[0062] When the (meth)acrylic copolymer (A) has a structural unit derived from an epoxy group-containing monomer (a5), the content thereof is usually 0.1 to 15 mass%, preferably 0.3 to 13 mass%, more preferably 0.5 to 10 mass%, and particularly preferably 1 to 6 mass%, based on the (meth)acrylic copolymer (A).

[0063] [Vinyl Monomer (a6)] Examples of the vinyl monomer (a6) include compounds having a vinyl group in the molecule. Examples of such compounds include vinyl ester monomers such as vinyl acetate, vinyl propionate, vinyl laurate, and vinyl stearate, as well as aromatic vinyl monomers such as styrene, chlorostyrene, chloromethylstyrene, α-methylstyrene, and other substituted styrenes. These may be used alone or in combination of two or more.

[0064] When the (meth)acrylic copolymer (A) has a constituent moiety derived from the vinyl monomer (a6), the content thereof is, from the viewpoint of imparting cohesive strength to the PSA sheet, usually 1 to 40 mass %, preferably 5 to 35 mass %, more preferably 8 to 30 mass %, and particularly preferably 10 to 25 mass %, relative to the (meth)acrylic copolymer (A).

[0065] [Alkyl(meth)acrylate Monomer (a7) in Which the Alkyl Group Has 1 or 2 Carbon Atoms] Examples of the alkyl(meth)acrylate monomer (a7) in Which the alkyl group has 1 or 2 carbon atoms include methyl(meth)acrylate and ethyl(meth)acrylate. These may be used alone or in combination of two or more.

[0066] When the (meth)acrylic copolymer (A) has a structural unit derived from an alkyl (meth)acrylate monomer (a7) in which the alkyl group has 1 or 2 carbon atoms, the content thereof is, from the viewpoint of imparting cohesive strength to the PSA sheet, usually 1 to 60 mass %, preferably 5 to 55 mass %, particularly preferably 10 to 50 mass %, and especially preferably 15 to 45 mass %, relative to the (meth)acrylic copolymer (A).

[0067] [Alicyclic Monomer (a8)] Examples of the alicyclic monomer (a8) include cyclohexyl (meth)acrylate, 3,3,5-trimethylcyclohexyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate, adamantyl (meth)acrylate, etc. These may be used alone or in combination of two or more.

[0068] When the (meth)acrylic copolymer (A) has a structural unit derived from an alicyclic monomer (a8), the content thereof is, from the viewpoint of imparting cohesive strength to the PSA sheet, usually 0.1 to 15 mass%, preferably 0.5 to 13 mass%, particularly preferably 1 to 10 mass%, and especially preferably 2 to 7 mass%, relative to the (meth)acrylic copolymer (A).

[0069] [Macromonomer (a9)] The macromonomer (a9) is a monomer that, when polymerized into the (meth)acrylic copolymer (A), can easily increase the number of carbon atoms in the side chain of the (meth)acrylic copolymer (A), for example, to 20 or more. By using the macromonomer (a9) as a copolymerization component, the (meth)acrylic copolymer (A) can be made into a graft copolymer having a constituent portion (segment) derived from the macromonomer (a9). Furthermore, by changing the blending ratio of the macromonomer (a9) to other monomers, the properties of the main chain and side chain of the graft copolymer can be changed.

[0070] The macromonomer (a9) has a radically polymerizable functional group or a functional group such as a hydroxy group, an isocyanate group, an epoxy group, a carboxy group, an amino group, an amide group, or a thiol group. The macromonomer (a9) may have these functional groups alone or in combination of two or more. Among these, the macromonomer (a9) preferably has a radically polymerizable functional group copolymerizable with other monomers. The macromonomer (a9) may have one or more radically polymerizable functional groups, with one being particularly preferred. Furthermore, even when the macromonomer (a9) has a functional group, the macromonomer may have one or more functional groups, with one being particularly preferred.

[0071] The macromonomer (a9) preferably has a backbone component composed of a (meth)acrylic copolymer or a vinyl polymer. Examples of backbone components of the macromonomer (a9) include the alkyl(meth)acrylate (a1), the vinyl monomer (a6), the alkyl(meth)acrylate monomer (a7) having 1 or 2 carbon atoms in the alkyl group, and the alicyclic monomer (a8). These may be used alone or in combination of two or more. Among these, the use of an alkyl(meth)acrylate or alicyclic monomer having 1 to 8 carbon atoms in the alkyl group, or an aromatic monomer such as styrene as the backbone component is preferred, as it allows for a pressure-sensitive adhesive sheet with excellent cohesion. On the other hand, the use of an alkyl(meth)acrylate having 9 to 30 carbon atoms is preferred, as it allows for a pressure-sensitive adhesive sheet with excellent flexibility.

[0072] The number average molecular weight of the macromonomer (a9) is usually 1,000 to 40,000, preferably 1,500 to 20,000, and more preferably 2,000 to 15,000. The number average molecular weight of the macromonomer (a9) is a value measured by gel permeation chromatography (GPC) in terms of standard polystyrene.

[0073] As the macromonomer (a9), a generally produced macromonomer (for example, a macromonomer manufactured by Toagosei Co., Ltd.) can be used appropriately.

[0074] When the (meth)acrylic copolymer (A) has a structural unit derived from macromonomer (a9), the content thereof is usually 1 to 30% by mass, preferably 3 to 20% by mass, and more preferably 5 to 18% by mass, relative to the (meth)acrylic copolymer (A). If the content is equal to or greater than the lower limit, the phase separation force between the segment containing the structural unit derived from macromonomer (a9) and the segment formed by the other structural units becomes stronger, and the cohesive strength of the PSA sheet tends to be better. If the content is equal to or less than the upper limit, the phase-separated structure tends to collapse more easily during lamination, and the unevenness-following ability tends to be better.

[0075] [Other Copolymerizable Monomers (a10)] Examples of the other copolymerizable monomers (a10) include (meth)acrylates having an alkoxyalkylene glycol skeleton, such as methoxydiethylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, butoxypolyethylene glycol (meth)acrylate, methoxypolypropylene glycol (meth)acrylate, butoxypolypropylene glycol (meth)acrylate, methoxypolytetramethylene glycol (meth)acrylate, butoxypolytetramethylene glycol (meth)acrylate, methoxypolyoxyethylene polyoxypropylene glycol (meth)acrylate, and butoxypolyoxyethylene polyoxypropylene glycol (meth)acrylate; phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenyldiethylene glycol (meth)acrylate, phenoxypolyethylene glycol (meth)acrylate, and phenoxypolyethylene glycol-polypropylene glycol-(meth)acrylate; aromatic (meth)acrylates such as nonylphenol ethylene oxide adduct (meth)acrylate, 4-acryloyloxybenzophenone, 4-acryloyloxyethoxybenzophenone, 4-acryloyloxy-4'-methoxybenzophenone, 4-acryloyloxyethoxy-4'-methoxybenzophenone, 4-acryloyloxy-4'-bromobenzophenone, 4-acryloyloxyethoxy-4'-bromobenzophenone, 4-methacryloyloxybenzophenone, Examples of the benzophenone-containing (meth)acrylate include (meth)acrylates having a benzophenone structure such as benzophenone, 4-methacryloyloxyethoxybenzophenone, 4-methacryloyloxy-4'-methoxybenzophenone, 4-methacryloyloxyethoxy-4'-methoxybenzophenone, 4-methacryloyloxy-4'-bromobenzophenone, 4-methacryloyloxyethoxy-4'-bromobenzophenone, and mixtures thereof, and heterocycle-containing (meth)acrylates such as tetrahydrofurfuryl (meth)acrylate. These may be used alone or in combination of two or more.

[0076] When the (meth)acrylic copolymer (A) has a structural unit derived from another copolymerizable monomer (a10), the content thereof is usually 1 to 30 mass%, preferably 3 to 20 mass%, more preferably 5 to 15 mass%, based on the (meth)acrylic copolymer (A).

[0077] The method for producing the (meth)acrylic copolymer (A) is not particularly limited, and may be, for example, by polymerizing copolymerization components including an alkyl (meth)acrylate (a1) and, if necessary, at least one selected from the group consisting of copolymerizable monomers (a2) to (a10).

[0078] Examples of the polymerization method include conventionally known methods such as solution polymerization, suspension polymerization, bulk polymerization, and emulsion polymerization. Among these, solution polymerization is preferred in that it can safely and stably produce an acrylic resin with any monomer composition. Thus, the (meth)acrylic copolymer (A) can be obtained.

[0079] The (meth)acrylic copolymer (A) may have a photoactive moiety, such as a polymerizable carbon-carbon double bond group, introduced into a side chain thereof, thereby improving the crosslinking efficiency of the pressure-sensitive adhesive composition and enabling the pressure-sensitive adhesive composition to be crosslinked in a shorter time, thereby increasing productivity.

[0080] Examples of a method for introducing a polymerizable carbon-carbon double bond group into the side chain of the (meth)acrylic copolymer (A) include a method in which a copolymer containing a functional group-containing ethylenically unsaturated monomer such as the above-mentioned hydroxyl group-containing monomer (a2), nitrogen atom-containing monomer (a3), carboxy group-containing monomer (a4), or epoxy group-containing monomer (a5) is prepared, and then a compound having a polymerizable carbon-carbon double bond group and a functional group reactive with the functional group is subjected to a condensation or addition reaction while maintaining the activity of the polymerizable carbon-carbon double bond group.

[0081] Examples of combinations of these functional groups include an epoxy group (glycidyl group) and a carboxy group, an amino group and a carboxy group, an amino group and an isocyanate group, an epoxy group (glycidyl group) and an amino group, a hydroxyl group and an epoxy group, and a hydroxyl group and an isocyanate group. Among these combinations of functional groups, a combination of a hydroxyl group and an isocyanate group is preferred because of the ease of reaction control. Among these, a combination in which the copolymer has a hydroxyl group and the compound has an isocyanate group is preferred.

[0082] Examples of the isocyanate compound having a polymerizable carbon-carbon double bond group include the above-mentioned 2-(meth)acryloyloxyethyl isocyanate and alkylene oxide adducts thereof.

[0083] From the viewpoint of improving adhesiveness and stress relaxation properties, the content of the compound having a functional group reactive with the functional group and a polymerizable carbon-carbon double bond group is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, even more preferably 1 part by mass or less, and particularly preferably 0.1 parts by mass or less, relative to 100 parts by mass of the (meth)acrylic copolymer (A). The lower limit is usually 0 part by mass.

[0084] The weight-average molecular weight (Mw) of the (meth)acrylic copolymer (A) is typically 50,000 to 1,500,000, preferably 70,000 to 1,000,000, more preferably 100,000 to 800,000, and even more preferably 150,000 to 600,000. When the weight-average molecular weight (Mw) is equal to or greater than the lower limit, the pressure-sensitive adhesive sheet tends to have high cohesive strength. Furthermore, when the weight-average molecular weight (Mw) is equal to or less than the upper limit, the pressure-sensitive adhesive sheet tends to have excellent handleability and uniform stirring properties. The weight-average molecular weight of the (meth)acrylic copolymer (A) is a value measured by gel permeation chromatography (GPC) in terms of standard polystyrene.

[0085] [Crosslinking Agent (B)] The pressure-sensitive adhesive composition preferably contains a crosslinking agent (B) from the viewpoint of promoting the crosslinking reaction. This allows the pressure-sensitive adhesive composition to efficiently form a crosslinked structure. Furthermore, when a crosslinked structure is formed in a pressure-sensitive adhesive sheet using the pressure-sensitive adhesive composition, adhesive extrusion during storage or application can be prevented, and good adhesion and cohesive strength can be obtained. However, when the (meth)acrylic copolymer (A) undergoes a hydrogen abstraction reaction due to the action of a photoinitiator (C) described below, etc., and a sufficient crosslinked structure can be formed within the (meth)acrylic copolymer (A) and / or between the (meth)acrylic copolymers (A), the crosslinking agent (B) is not necessarily required.

[0086] Examples of the crosslinking agent (B) include acrylic crosslinking agents, isocyanate crosslinking agents, epoxy crosslinking agents, aziridine crosslinking agents, melamine crosslinking agents, aldehyde crosslinking agents, amine crosslinking agents, and metal chelate crosslinking agents. Among these, isocyanate crosslinking agents are preferred because of their excellent reactivity with the (meth)acrylic copolymer (A). On the other hand, acrylic crosslinking agents are preferred, and polyfunctional (meth)acrylates are particularly preferred, from the viewpoints of ease of reaction control and active energy ray curability.

[0087] Examples of the polyfunctional (meth)acrylate include polyfunctional (meth)acrylic monomers and polyfunctional (meth)acrylic oligomers having two or more (meth)acryloyl groups, which may be used alone or in combination of two or more.

[0088] Examples of the polyfunctional (meth)acrylic monomer include pentanediol di(meth)acrylate, hexadiol di(meth)acrylate, heptanediol di(meth)acrylate, octanediol di(meth)acrylate, nonanediol di(meth)acrylate, decanediol di(meth)acrylate, undecanediol di(meth)acrylate, dodecanediol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, glycerin di(meth)acrylate, neopentyl glycol di(meth)acrylate, glycerin glycidyl ether di(meth)acrylate, tricyclodecane dimethacrylate, tricyclodecane dimethanol di(meth)acrylate, bisphenol A polyethoxy di(meth)acrylate, bisphenol A polypropoxy di(meth)acrylate, bisphenol F polyethoxy di(meth)acrylate, ethylene glycol di(meth)acrylate tri(meth)acrylate, neopentyl glycol di(meth)acrylate, trimethylolpropane trioxyethyl(meth)acrylate, ε-caprolactone-modified tris(2-hydroxyethyl)isocyanurate tri(meth)acrylate, pentaerythritol tri(meth)acrylate, propoxylated pentaerythritol tri(meth)acrylate, ethoxylated pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, propoxylated pentaerythritol Erythritol tetra(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, tris(acryloxyethyl)isocyanurate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol penta(meth)acrylate, tris(acryloxyethyl)isocyanurate Examples of such an acrylate include tripentaerythritol hexa(meth)acrylate, tripentaerythritol penta(meth)acrylate, neopentyl glycol hydroxypivalate di(meth)acrylate, di(meth)acrylate of an ε-caprolactone adduct of neopentyl glycol hydroxypivalate, trimethylolpropane tri(meth)acrylate, trimethylolpropane polyethoxytri(meth)acrylate, and ditrimethylolpropane tetra(meth)acrylate.

[0089] Examples of the polyfunctional (meth)acrylic oligomer include polyester (meth)acrylate oligomers, epoxy (meth)acrylate oligomers, urethane (meth)acrylate oligomers, and polyether (meth)acrylate oligomers.

[0090] Among these crosslinking agents (B), polyfunctional (meth)acrylate monomers and oligomers having a glycol structure are preferred from the viewpoint of imparting appropriate flexibility to the cured product, and acrylic acid adducts of pentaerythritol and dipentaerythritol, and alkoxylated products thereof are preferred from the viewpoint of imparting cohesive strength.

[0091] When the pressure-sensitive adhesive composition contains a crosslinking agent (B), the content thereof is typically 0.1 to 25 parts by mass, preferably 0.5 to 22 parts by mass, more preferably 0.7 to 20 parts by mass, and particularly preferably 1 to 18 parts by mass, per 100 parts by mass of the (meth)acrylic copolymer (A), from the viewpoint of imparting shape stability to the pressure-sensitive adhesive sheet and durability when formed into a laminate for an image display device. If the content of the crosslinking agent (B) is at or above the lower limit, shape stability of the pressure-sensitive adhesive sheet and durability when formed into a laminate for an image display device tend to be imparted. Furthermore, if the content of the crosslinking agent (B) is at or below the upper limit, flexibility of the pressure-sensitive adhesive sheet tends to be maintained.

[0092] When the pressure-sensitive adhesive sheet has two or more pressure-sensitive adhesive layers, the crosslinking agent (B) may be contained in the pressure-sensitive adhesive composition forming at least one of the layers, or may be contained in the pressure-sensitive adhesive composition forming all of the pressure-sensitive adhesive layers. In this case, the content of the crosslinking agent (B) is based on the total mass of the (meth)acrylic copolymer (A) in all of the pressure-sensitive adhesive layers constituting the pressure-sensitive adhesive sheet.

[0093] Furthermore, when the pressure-sensitive adhesive sheet has a first pressure-sensitive adhesive layer and a second pressure-sensitive adhesive layer described below, it is preferable that the content of the crosslinking agent (B) contained in the pressure-sensitive adhesive composition forming the second pressure-sensitive adhesive layer is greater than the content of the crosslinking agent (B) contained in the pressure-sensitive adhesive composition forming the first pressure-sensitive adhesive layer. Such a configuration tends to facilitate adjustment of the elastic modulus ratio (E' / G') described above, and facilitate functional separation of trade-off physical properties such as stress relaxation property and shape retention property for each layer.

[0094] Furthermore, when the present pressure-sensitive adhesive sheet has a configuration having at least three layers, namely, a surface layer, a back layer, and an intermediate layer, which will be described later, it is preferable that the intermediate layer is formed from a pressure-sensitive adhesive composition having a higher content of crosslinking agent (B) than the surface layer and the back layer, from the viewpoint of achieving both cutting processability and lamination reliability.

[0095] [Photoinitiator (C)] The pressure-sensitive adhesive composition preferably contains a photoinitiator (C). The photoinitiator (C) is a compound that generates radicals when exposed to active energy rays. The pressure-sensitive adhesive composition can be photocured by including the photoinitiator (C). The photoinitiator (C) is broadly classified into two types based on the radical generation mechanism. More specifically, they are broadly classified into cleavage-type photoinitiators, which can generate radicals by cleaving and decomposing the single bond of the photoinitiator itself, and hydrogen-abstraction-type photoinitiators, which can generate radicals by the excited initiator abstracting hydrogen from a hydrogen donor in the system. These photoinitiators may be used alone or in combination of two or more. The cleavage-type photoinitiator is preferred because it has high photosensitivity. On the other hand, the hydrogen-abstraction-type photoinitiator is preferred because it does not generate photodecomposition products and can incorporate the (meth)acrylic copolymer (A) into a crosslinked structure through a hydrogen abstraction reaction.

[0096] Examples of the hydrogen abstraction photoinitiator include benzophenone, 4-methylbenzophenone, 2,4,6-trimethylbenzophenone, 4-phenylbenzophenone, 3,3'-dimethyl-4-methoxybenzophenone, methyl 2-benzoylbenzoate, 4-[(4-methylphenyl)thio]benzophenone, 4-acryloyloxybenzophenone, 4-acryloyloxyethoxybenzophenone, 4-acryloyloxy-4'-methoxybenzophenone, 4-acryloyloxyethoxy-4'-methoxybenzophenone, 4-acryloyloxy-4'-bromobenzophenone, 4-acryloyloxyethoxy-4'-bromobenzophenone, 4-methacryloyloxy-4'-bromobenzophenone, Examples of suitable photoinitiators include intermolecular hydrogen abstraction photoinitiators such as acryloyloxybenzophenone, 4-methacryloyloxyethoxybenzophenone, 4-methacryloyloxy-4'-methoxybenzophenone, 4-methacryloyloxyethoxy-4'-methoxybenzophenone, 4-methacryloyloxy-4'-bromobenzophenone, and 4-methacryloyloxyethoxy-4'-bromobenzophenone; and intramolecular hydrogen abstraction photoinitiators such as methylbenzoyl formate, methyl benzoylformate, oxyphenylacetic acid-2-(2-oxo-2-phenyl-acetoxy-ethoxy)ethyl ester, and oxyphenylacetic acid-2-(2-hydroxy-ethoxy)ethyl ester. These may be used alone or in combination of two or more.

[0097] Among the intermolecular hydrogen abstraction photoinitiators, 4-methylbenzophenone, 2,4,6-trimethylbenzophenone, and photoinitiators (c1) having a radically polymerizable functional group having a carbon-carbon double bond and a structure that generates radicals in the molecule, such as 4-acryloyloxybenzophenone, 4-methacryloyloxybenzophenone, 4-acryloyloxyethoxybenzophenone, 4-acryloyloxy-4'-methoxybenzophenone, 4-acryloyloxyethoxy-4'-methoxybenzophenone, and 4-methacryloyloxybenzophenone are preferred, and 4-methylbenzophenone, 2,4,6-trimethylbenzophenone, 4-methacryloyloxybenzophenone, and 4-methacryloyloxybenzophenone are more preferred. The photoinitiator (c1) having a radical-polymerizable functional group having a carbon-carbon double bond and a structure that generates radicals in its molecule is incorporated into the polymerization structure after photoreaction, which tends to suppress bleed-out of the photoinitiator and improve the cohesive strength of the PSA sheet. Furthermore, intramolecular hydrogen abstraction photoinitiators are preferred because they can act not only as hydrogen donors in the system but also as starting points for radical generation, with methylbenzoyl formate being more preferred.

[0098] Examples of the cleavage-type photoinitiator include 2,2-dimethoxy-1,2-diphenylethan-1-one, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, 1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propan-1-one, 2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)benzyl]phenyl}-2-methyl-propan-1-one, oligo(2-hydroxy-2-methyl-1-(4-(1-methylvinyl)phenyl)propanone), 2-benzyl-2-dimethylamino-1-(4-morpholino) Examples of suitable amines include 2-(4-(4-morpholinophenyl)-2-butan-1-one, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, 2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, (2,4,6-trimethylbenzoyl)ethoxyphenylphosphine oxide, bis(2,6-dimethoxybenzoyl)2,4,4-trimethylpentylphosphine oxide, and derivatives thereof.

[0099] In the present invention, it is preferable that the photoinitiator (C) is a hydrogen abstraction photoinitiator from the viewpoint of increasing the cohesive strength of the pressure-sensitive adhesive sheet.

[0100] In the present invention, it is also preferred that the photoinitiator (C) contains an intermolecular hydrogen abstraction photoinitiator and an intramolecular hydrogen abstraction photoinitiator, from the viewpoint of increasing the cohesive strength of the pressure-sensitive adhesive sheet.

[0101] Furthermore, in the present invention, the photoinitiator (C) preferably includes a photoinitiator (c1) having a radical-polymerizable functional group having a carbon-carbon double bond and a structure that generates radicals in its molecule, and a hydrogen-abstraction photoinitiator (c2) other than the photoinitiator (c1). By including the photoinitiator (c1) having a radical-polymerizable functional group having a carbon-carbon double bond and a structure that generates radicals in its molecule, and a hydrogen-abstraction photoinitiator (c2) other than the photoinitiator (c1), the cohesive strength of the pressure-sensitive adhesive sheet can be increased, and if the pressure-sensitive adhesive sheet is active energy ray-curable, the pressure-sensitive adhesive sheet can have excellent secondary curing properties after being attached to an adherend. Note that the hydrogen-abstraction photoinitiator (c2) refers to a hydrogen-abstraction photoinitiator other than the photoinitiator (c1) having a radical-polymerizable functional group having a carbon-carbon double bond and a structure that generates radicals in its molecule, among the above-mentioned hydrogen-abstraction photoinitiators. Among the hydrogen abstraction photoinitiators (c2), intramolecular hydrogen abstraction photoinitiators are preferred because they can act not only as hydrogen donors in the system but also as starting points for radical generation, and methylbenzoyl formate is more preferred.

[0102] When the pressure-sensitive adhesive composition contains a photoinitiator (C), the content thereof is usually 10 parts by mass or less, preferably 5 parts by mass or less, more preferably 4 parts by mass or less, and particularly preferably 3 parts by mass or less, relative to 100 parts by mass of the (meth)acrylic copolymer (A). The lower limit is usually 0.1 parts by mass. The content of the photoinitiator (C) ranges, for example, from 0.1 to 10 parts by mass. When two or more types of photoinitiators (C) are used in combination, the above content refers to the total amount of the photoinitiators (C) used. The lower and upper limits of the content of the photoinitiator (C) can be combined in any manner.

[0103] When the photoinitiator (C) contains a compound (c1) having, in the molecule, a radical-polymerizable functional group having a carbon-carbon double bond and a structure capable of generating a radical, and a hydrogen abstraction photoinitiator (c2) other than the photoinitiator (c1), the mass ratio (c2 / c1) of the photoinitiator (c2) to the photoinitiator (c1) is usually 0.5 to 10, preferably 1 to 8, and more preferably 2 to 6.

[0104] [Ultraviolet absorber (D)] The pressure-sensitive adhesive composition preferably contains an ultraviolet absorber (D). By containing the ultraviolet absorber (D), deterioration of the pressure-sensitive adhesive sheet itself and the adherend due to ultraviolet rays tends to be suppressed. When the pressure-sensitive adhesive composition contains the ultraviolet absorber (D), it is preferable to photocure the composition by using light having a wavelength other than the absorption wavelength of the ultraviolet absorber (D).

[0105] Examples of the ultraviolet absorber (D) include benzophenone-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, triazine-based ultraviolet absorbers, salicylic acid-based ultraviolet absorbers, cyanoacrylate-based ultraviolet absorbers, etc. These ultraviolet absorbers (D) can be used alone or in combination of two or more.

[0106] Examples of the benzophenone-based ultraviolet absorbers include 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-octoxybenzophenone, 2-hydroxy-4-benzyloxybenzophenone, 2-hydroxy-4-methoxy-5-sulfoxybenzophenone, 2-hydroxy-4-methoxy-5-sulfoxytrihydridolate benzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, 2,2',4,4'-tetrahydroxybenzophenone, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, 2,2'-dihydroxy-4,4'-dimethoxy-5-sodium sulfoxybenzophenone, bis(5-benzoyl-4-hydroxy-2-methoxyphenyl)methane, 2-hydroxy-4-n-dodecyloxybenzophenone, and 2-hydroxy-4-methoxy-2'-carboxybenzophenone.

[0107] Examples of the benzotriazole-based ultraviolet absorbers include 2-(2-hydroxy-5-methylphenyl)benzotriazole, 2-(2-hydroxy-5-tert-octylphenyl)benzotriazole, 2-(2-hydroxy-3,5-dicumylphenyl)phenylbenzotriazole, 2-(2-hydroxy-3-tert-butyl-5-methylphenyl)-5-chlorobenzotriazole, 2,2′-methylenebis[4-(1,1,3,3-tetramethylbutyl)-6-(2H-benzotriazol-2-yl)phenol], 2-(2-hydroxy-3,5-di-tert-butylphenyl)benzotriazole, 2-(2-hydroxy-3,5-di-tert-butylphenyl)benzotriazole, phenyl)-5-chlorobenzotriazole, 2-(2-hydroxy-3,5-di-tert-amylphenyl)benzotriazole, 2-(2-hydroxy-5-tert-octylphenyl)benzotriazole, 2-(2-hydroxy-5-tert-butylphenyl)benzotriazole, 2-(2-hydroxy-4-octoxyphenyl)benzotriazole, 2,2'-methylenebis(4-cumyl-6-benzotriazolephenyl), 2,2'-p-phenylenebis(1,3-benzoxazin-4-one, 2-[2-hydroxy-3-(3,4,5,6-tetrahydrophthalimidomethyl)-5-methylphenyl]benzotriazole, and the like.

[0108] Examples of the triazine-based ultraviolet absorber include 2-(2-hydroxy-4-methoxyphenyl)-4,6-diphenyl-1,3,5-triazine, 2-(2-hydroxy-4-ethoxyphenyl)-4,6-diphenyl-1,3,5-triazine, 2-(2-hydroxy-4-propoxyphenyl)-4,6-diphenyl-1,3,5-triazine, 2-(2-hydroxy-4-butoxyphenyl)-4,6-diphenyl-1,3,5-triazine, and 2-(2-hydroxy-4-hexyloxyphenyl)-4,6-diphenyl-1,3,5-triazine. triazine, 2-(2-hydroxy-4-octyloxyphenyl)-4,6-diphenyl-1,3,5-triazine, 2-(2-hydroxy-4-dodecyloxyphenyl)-4,6-diphenyl-1,3,5-triazine, 2-(2-hydroxy-4-benzyloxyphenyl)-4,6-diphenyl-1,3,5-triazine, 2,4-bis(2-hydroxy-4-butoxyphenyl)-6-(2,4-dibutoxyphenyl)-1,3-5-triazine, 2,4,6-tris(2-hydroxy-4-hexyloxy-3-methylphenyl)-1, 3,5-triazine, 2-(2-hydroxy-4-[1-octyloxycarbonylethoxy]phenyl)-4,6-bis(4-phenylphenyl)-1,3,5-triazine, 2-[4-[(2-hydroxy-3-dodecyloxypropyl)oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, 2-[4-[(2-hydroxy-3-tridecyloxypropyl)oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, 2-[4-[ (2-hydroxy-3-(2'-ethyl)hexyl)oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, 2,4-bis(2,4-dimethylphenyl)-6-[2-hydroxy-4-(3-octyloxy-2-hydroxypropyloxy)-5-α-cumylphenyl]-s-triazine, 2,4-bis(2,4-dimethylphenyl)-6-[2-hydroxy-4-(3-nonyloxy-2-hydroxypropyloxy)-5-α-cumylphenyl]-s-triazine, 2,4-bis(2,Examples include 2-(2-hydroxy-4-(3-decyloxy-2-hydroxypropyloxy)-5-α-cumylphenyl)-s-triazine, 2-(2-hydroxy-4-acryloyloxyethoxyphenyl)-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, etc.

[0109] Examples of the salicylic acid-based ultraviolet absorbers include phenyl salicylate, p-tert-butylphenyl salicylate, and p-octylphenyl salicylate.

[0110] Examples of the cyanoacrylate ultraviolet absorber include 2-ethylhexyl-2-cyano-3,3'-diphenylacrylate and ethyl-2-cyano-3,3'-diphenylacrylate.

[0111] Among these, from the viewpoint of effectively suppressing ultraviolet degradation of the PSA sheet itself and the adherend, benzophenone-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, and triazine-based ultraviolet absorbers are preferred, and among these, triazine-based ultraviolet absorbers containing a triazine structure are more preferred from the viewpoint of excellent heat resistance.

[0112] The content of the ultraviolet absorber (D) is preferably usually 0.1 to 15 parts by mass, preferably 0.3 to 12 parts by mass, more preferably 0.5 to 10 parts by mass, particularly preferably 1 to 8 parts by mass, and most preferably 3 to 7 parts by mass, relative to 100 parts by mass of the (meth)acrylic copolymer (A). When the content of the ultraviolet absorber (D) is equal to or greater than the lower limit, lightfastness reliability tends to improve. On the other hand, when the content of the ultraviolet absorber (D) is equal to or less than the upper limit, bleed-out tends to be suppressed and yellowing resistance tends to improve.

[0113] The content of the ultraviolet absorber (D) in the pressure-sensitive adhesive composition is usually 0.1 to 15 mass%, preferably 0.3 to 12 mass%, more preferably 0.5 to 10 mass%, particularly preferably 1 to 8 mass%, and most preferably 2.5 to 7 mass%, based on the total mass of the pressure-sensitive adhesive composition. When the content of the ultraviolet absorber (D) is equal to or greater than the lower limit, lightfastness reliability tends to be improved. When the content of the ultraviolet absorber (D) is equal to or less than the upper limit, bleed-out tends to be suppressed and yellowing resistance tends to be improved.

[0114] In addition, when the present pressure-sensitive adhesive sheet has a laminated pressure-sensitive adhesive layer described below, the ultraviolet absorber (D) may be contained in at least one layer, and it is preferable that the ultraviolet absorber (D) is contained in the pressure-sensitive adhesive composition forming the second pressure-sensitive adhesive layer from the viewpoints of facilitating the progress of the photocuring reaction and suppressing bleed-out of the ultraviolet absorber (D). In this case, the content of the ultraviolet absorber (D) is based on the total mass of the (meth)acrylic copolymer (A) contained in all pressure-sensitive adhesive layers constituting the present pressure-sensitive adhesive sheet or the total mass of all pressure-sensitive adhesive compositions constituting the pressure-sensitive adhesive sheet.

[0115] [Monofunctional (meth)acrylate] The pressure-sensitive adhesive composition may further contain a monofunctional (meth)acrylate having one (meth)acryloyl group, if necessary. By containing a monofunctional (meth)acrylate having one (meth)acryloyl group, the molecular weight between crosslinking points of the cured product can be increased, which is preferable in that the degree of freedom of movement of the molecular chain is increased and it becomes easier to obtain a cured product with excellent stress relaxation properties.

[0116] Examples of the monofunctional (meth)acrylate include ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, amyl (meth)acrylate, isoamyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, and dodecyl (meth)acrylate. (meth)acrylate, isododecyl (meth)acrylate, tetradecyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, behenyl (meth)acrylate, cyclopropyl (meth)acrylate, cyclobutyl (meth)acrylate, cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, cyclooctyl (meth)acrylate, cyclononyl (meth)acrylate, cyclodecyl (meth)acrylate, isobornyl (meth)acrylate acrylate, norbornyl (meth)acrylate, adamantyl (meth)acrylate, tricyclodecane dimethanol acrylate, ethoxylated-o-phenylphenol acrylate, 2-hydroxy-o-phenylphenol propyl acrylate, methoxypolyethylene glycol (meth)acrylate, methoxypolypropylene glycol (meth)acrylate, polyethylene glycol (meth)acrylate, polypropylene glycol (meth)acrylate, phenoxyethylene glycol (meth)acrylate, phenoxydiethylene glycol benzyl (meth)acrylates such as chol (meth)acrylate, phenoxy polyethylene glycol (meth)acrylate, 2-hydroxy-o-phenylphenol propyl acrylate, 2-(meth)acryloyloxyethyl succinate, 2-(meth)acryloyloxyethyl tetrahydrophthalate, 2-(meth)acryloyloxyethyl hexahydrophthalate, 2-(meth)acryloyloxypropyl phthalate, 2-(meth)acryloyloxypropyl hydrophthalate, and 2-(meth)acryloyloxypropyl hexahydrophthalate;Benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxyethylene glycol (meth)acrylate, 2-naphthyl (meth)acrylate, 9-anthracenyl (meth)acrylate, 1-pyrenylmethyl (meth)acrylate, benzyl (meth)acrylate, tricyclodecane dimethanol monoacrylate monocarboxylic acid, dicyclopentanyl acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, trimethylolpropane mono(meth)acrylate, glycerin mono(meth)acrylate, pentaerythritol mono(meth)acrylate, diglycerin mono(meth)acrylate, ditrimethylolpropane mono(meth)acrylate, di Examples include pentaerythritol mono(meth)acrylate, ethoxylated trimethylolpropane mono(meth)acrylate, propoxylated trimethylolpropane mono(meth)acrylate, ethoxylated glycerin mono(meth)acrylate, propoxylated glycerin mono(meth)acrylate, ethoxylated pentaerythritol mono(meth)acrylate, propoxylated pentaerythritol mono(meth)acrylate, ethoxylated ditrimethylolpropane mono(meth)acrylate, propoxylated ditrimethylolpropane mono(meth)acrylate, alkylene oxide-modified diglycerin mono(meth)acrylate, and alkylene oxide-modified dipentaerythritol mono(meth)acrylate, as well as monofunctional oligomers such as monofunctional urethane (meth)acrylate, monofunctional epoxy (meth)acrylate, and monofunctional polyester (meth)acrylate. These may be used alone or in combination of two or more.

[0117] When the monofunctional (meth)acrylate component is contained, the content thereof is preferably 2 parts by mass or more, more preferably 4 parts by mass or more, and particularly preferably 6 parts by mass or more, per 100 parts by mass of the (meth)acrylic copolymer (A), from the viewpoint of adjusting the crosslinking density and imparting appropriate flexibility to the cured product. The upper limit is preferably 20 parts by mass or less, more preferably 18 parts by mass or less, and particularly preferably 15 parts by mass or less. The content of the monofunctional (meth)acrylate component ranges, for example, from 2 to 20 parts by mass.

[0118] [Other Components] The pressure-sensitive adhesive composition may contain various additives, such as silane coupling agents, plasticizers, tackifiers, antioxidants, light stabilizers, metal deactivators, anti-aging agents, moisture absorbents, rust inhibitors, and inorganic particles, as needed, as long as the effects of the present invention are not impaired. Furthermore, the pressure-sensitive adhesive composition may contain reaction catalysts, such as tertiary amine compounds, quaternary ammonium compounds, and tin laurate compounds, as needed. These may be used alone or in combination of two or more. These may be used alone or in combination of two or more. It is particularly preferred that the pressure-sensitive adhesive composition contain a silane coupling agent.

[0119] [Silane coupling agent] The silane coupling agent is an organosilicon compound that contains one or more reactive functional groups and one or more alkoxy groups bonded to silicon atoms in its structure.The reactive functional groups include, for example, epoxy group, (meth)acryloyl group, mercapto group, hydroxyl group, carboxy group, amino group, amide group, and isocyanate group.Among these, epoxy group and mercapto group are preferred from the viewpoint of balance of durability.

[0120] The alkoxy group bonded to the silicon atom preferably contains an alkoxy group having 1 to 8 carbon atoms, from the viewpoint of durability and storage stability, and is particularly preferably a methoxy group or an ethoxy group. The silane coupling agent may also contain an organic substituent other than the reactive functional group and the alkoxy group bonded to the silicon atom, such as an alkyl group or a phenyl group.

[0121] Examples of the silane coupling agent include monomeric epoxy group-containing silane coupling agents, which are silane compounds such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; and silane coupling agents in which a part of the silane compound is hydrolyzed and condensed, or in which the silane compound is polymerized with methyltriethoxysilane, ethyltriethoxysilane, oligomeric epoxy group-containing silane coupling agents which are silane compounds obtained by co-condensation of alkyl group-containing silane compounds such as methyltrimethoxysilane and ethyltrimethoxysilane; monomeric mercapto group-containing silane coupling agents which are silane compounds such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, γ-mercaptopropyldimethoxymethylsilane and 3-mercaptopropylmethyldimethoxysilane; and silane coupling agents which are obtained by hydrolysis and condensation polymerization of a part of the silane compounds or by condensation polymerization of the silane compounds with methyl groups. oligomeric mercapto group-containing silane coupling agents which are silane compounds obtained by co-condensation of alkyl group-containing silane compounds such as 3-acryloxypropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane; (meth)acryloyl group-containing silane coupling agents such as 3-acryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane; coupling agents: amino group-containing silane coupling agents such as N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethyl-butylidene)propylamine, and N-phenyl-3-aminopropyltrimethoxysilane; isocyanate group-containing silane coupling agents such as 3-isocyanatepropyltriethoxysilane;Examples of suitable silane coupling agents include vinyl group-containing silane coupling agents such as vinyltrimethoxysilane and vinyltriethoxysilane. These may be used alone or in combination of two or more.

[0122] Among these, epoxy group-containing silane coupling agents and mercapto group-containing silane coupling agents are preferably used because of their excellent durability, and among these, epoxy group-containing silane coupling agents are particularly preferred.

[0123] When the pressure-sensitive adhesive composition contains a silane coupling agent, the content thereof is usually 0.005 to 10 parts by mass, preferably 0.01 to 5 parts by mass, and particularly preferably 0.05 to 1 part by mass, relative to 100 parts by mass of the (meth)acrylic copolymer (A). When the content is within the above range, adhesive strength and durability tend to be improved.

[0124] [Plasticizer] The plasticizer may be, but is not limited to, at least one selected from the group consisting of polyisobutylene, polyisoprene, polybutadiene, amorphous polyolefins and their copolymers, silicone, polyacrylate, oligomeric polyurethane, ethylene-propylene copolymer, etc., or any combination or mixture thereof. Among these, polyisobutylene is preferred. The polyisobutylene plasticizer may be, for example, one selected from the OPPANOLB series, which is commercially available from BASF under the trade name OPPANOL.

[0125] When the pressure-sensitive adhesive composition contains a plasticizer, the content thereof is not particularly limited and is usually 0.1 to 20 parts by mass, preferably 0.5 to 15 parts by mass, per 100 parts by mass of the (meth)acrylic copolymer (A).

[0126] [Tackifier] The PSA composition may contain a tackifier to improve the adhesive strength of the PSA sheet. Examples of tackifiers include terpene resins such as polyterpenes (e.g., α-pinene resins, β-pinene resins, and limonene resins) and aromatic-modified polyterpene resins (e.g., phenol-modified polyterpene resins), coumaran-indene resins, petroleum-based resins such as C5 hydrocarbon resins, C9 hydrocarbon resins, C5 / C9 hydrocarbon resins, and dicyclopentadiene resins, and rosins such as modified rosin, hydrogenated rosin, polymerized rosin, and rosin esters.

[0127] When the pressure-sensitive adhesive composition contains a tackifier, the content thereof is not particularly limited and is usually 0.1 to 20 parts by mass, preferably 0.5 to 15 parts by mass, per 100 parts by mass of the (meth)acrylic copolymer (A).

[0128] [Rust inhibitor] The pressure-sensitive adhesive composition may contain a rust inhibitor to prevent corrosion when the adherend includes a corrosive portion such as metal wiring, etc. Examples of the rust inhibitor include triazoles, benzotriazoles, etc.

[0129] When the pressure-sensitive adhesive composition contains a rust inhibitor, the content thereof is usually 0.01 to 5 parts by mass, preferably 0.1 to 3 parts by mass, per 100 parts by mass of the (meth)acrylic copolymer (A).

[0130] <Method for producing the present pressure-sensitive adhesive sheet> Next, a method for producing the present pressure-sensitive adhesive sheet will be described. However, the following description is an example of a method for producing the present pressure-sensitive adhesive sheet, and the present pressure-sensitive adhesive sheet is not limited to sheets produced by this method.

[0131] The present pressure-sensitive adhesive sheet can be produced by preparing a pressure-sensitive adhesive composition containing a (meth)acrylic copolymer (A), preferably a crosslinking agent (B), a photoinitiator (C), an ultraviolet absorber (D), and other components as necessary, forming the pressure-sensitive adhesive composition into a sheet, curing it by crosslinking, i.e., polymerization reaction, and then processing it appropriately as necessary.

[0132] The pressure-sensitive adhesive composition may be prepared by kneading the raw materials using a temperature-controllable kneader (for example, a single-screw extruder, a twin-screw extruder, a planetary mixer, a twin-screw mixer, a pressure kneader, etc.). When kneading the various raw materials, various additives such as a silane coupling agent and an antioxidant may be blended together with a resin in advance and then fed to the kneader, or all materials may be melt-mixed in advance and then fed, or a masterbatch in which only the additives are concentrated in a resin may be prepared in advance and then fed.

[0133] The pressure-sensitive adhesive composition can be formed into a sheet by any known method, such as wet lamination, dry lamination, extrusion casting using a T-die, extrusion lamination, calendaring, inflation, injection molding, and liquid injection curing. Among these, when producing a sheet, wet lamination, extrusion casting, and extrusion lamination are preferred.

[0134] The pressure-sensitive adhesive composition can be cured by irradiation with active energy rays, and the pressure-sensitive adhesive sheet can be produced by irradiating a molded product of the pressure-sensitive adhesive composition, for example, a sheet, with active energy rays. In addition to irradiation with active energy rays, further curing can be achieved by heating.

[0135] Furthermore, the irradiation energy, irradiation time, irradiation method, etc. of the active energy ray are not particularly limited, as long as they can activate the photoinitiator (C) and polymerize photoreactive components such as (meth)acrylic acid ester compounds. When a hydrogen abstraction photoinitiator is used as the photoinitiator (C), a hydrogen abstraction reaction also occurs from the (meth)acrylic copolymer (A), and the (meth)acrylic copolymer (A) is incorporated into the crosslinked structure, forming a crosslinked structure with many crosslinking points. Therefore, it is preferable that the pressure-sensitive adhesive sheet is cured using a hydrogen abstraction photoinitiator.

[0136] Examples of the active energy rays in the active energy ray irradiation include light rays such as far ultraviolet rays, ultraviolet rays, near ultraviolet rays, infrared rays, and visible light rays, as well as ionizing radiation such as X-rays, α-rays, β-rays, γ-rays, electron beams, proton beams, and neutron beams. Among these, ultraviolet rays are preferred from the viewpoints of suppressing damage to optical device components and controlling reactions. Furthermore, ultraviolet rays are preferred from the viewpoints of curing speed, ease of availability of an irradiation device, cost, and the like.

[0137] Examples of light sources for ultraviolet irradiation include high-pressure mercury lamps, ultra-high-pressure mercury lamps, low-pressure mercury lamps, carbon arc lamps, metal halide lamps, xenon lamps, chemical lamps, electrodeless discharge lamps, and LED lamps, all of which emit light in the wavelength range of 150 to 450 nm. Of these, it is preferable to use high-pressure mercury lamps, metal halide lamps, and LED lamps.

[0138] The amount of active energy ray irradiation (cumulative light amount) is 100 to 10,000 mJ / cm from the viewpoint of curing. 2 is preferred, and more preferably 200 to 5000 mJ / cm 2 , and more preferably 300 to 4000 mJ / cm 2 , especially 400 to 3000 mJ / cm 2 , and even more particularly, 500 to 2000 mJ / cm 2 It is preferable to carry out the reaction under the following conditions.

[0139] The present pressure-sensitive adhesive sheet can also be provided as a pressure-sensitive adhesive sheet with a release film laminated on one or both sides. In particular, from the viewpoint of preventing blocking and adhesion of foreign matter, it is preferable to coat both sides of the present pressure-sensitive adhesive sheet with a release film.

[0140] When release films are provided on both sides of the present pressure-sensitive adhesive sheet, it is preferable to use a laminate configuration in which a light-release film with a relatively low release strength and a heavy-release film with a relatively high release strength are laminated together. When using a pressure-sensitive adhesive sheet with release films provided on both sides, first, one release film (light-release film) is peeled off to expose one side of the pressure-sensitive adhesive sheet, which is then bonded to a component of an image display device (referred to as a first component), and the other release film (heavy-release film) is peeled off to expose the other side of the pressure-sensitive adhesive sheet, which is then bonded to a component of an image display device (referred to as a second component).

[0141] As such a release film, a known release film can be appropriately used. As the base material for the release film, for example, a film such as a polyester film, a polyolefin film, a polycarbonate film, a polystyrene film, an acrylic film, a triacetyl cellulose film, or a fluororesin film that has been subjected to a release treatment by coating with a release agent such as a silicone resin, or release paper, etc., can be appropriately selected and used. Among these, polyester film is preferred, polyethylene terephthalate (PET) film is more preferred, and biaxially oriented PET film is particularly preferred because of its excellent transparency, mechanical strength, heat resistance, flexibility, etc. Furthermore, a release film can be used in which a release layer formed by curing a curable silicone-based release agent containing a silicone resin as a main component is provided on the above-mentioned base material.

[0142] The thickness of the release film is not particularly limited, but from the viewpoint of processability and handling, the thickness is preferably 10 to 250 μm, more preferably 25 to 200 μm, and particularly preferably 35 to 190 μm.

[0143] In another embodiment of the method for producing the pressure-sensitive adhesive sheet, the pressure-sensitive adhesive composition is dissolved in an appropriate solvent and various coating methods are used. When a coating method is used, the pressure-sensitive adhesive sheet can be obtained by curing with heat in addition to the above-mentioned active energy ray irradiation. When a coating method is used, the thickness of the pressure-sensitive adhesive sheet can be adjusted by the coating thickness and the solids concentration of the coating liquid.

[0144] The coating method may be a conventional method such as roll coating, die coating, gravure coating, comma coating, screen printing, or bar coating.

[0145] To produce the present pressure-sensitive adhesive sheet using the coating method, for example, the pressure-sensitive adhesive composition can be dissolved in a solvent, coated on the release film, dried, and cured by active energy ray irradiation to form the present pressure-sensitive adhesive sheet. Furthermore, a release film may be laminated, if necessary. In this case, the pressure-sensitive adhesive composition may be coated on a release film, dried, cured by active energy ray irradiation, and a release film may be laminated thereon. Alternatively, the pressure-sensitive adhesive sheet may be formed by coating on a release film, drying, laminating a release film, and then curing by active energy ray irradiation.

[0146] The solvent is not particularly limited as long as it dissolves the pressure-sensitive adhesive composition, and examples thereof include ester solvents such as methyl acetate, ethyl acetate, butyl acetate, methyl acetoacetate, and ethyl acetoacetate; ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; aromatic solvents such as toluene and xylene; and alcohol solvents such as methanol, ethanol, and propyl alcohol. These can be used alone or in combination of two or more. Among them, ethyl acetate, acetone, methyl ethyl ketone, and toluene are preferred in terms of solubility, drying properties, cost, and the like, and ethyl acetate is particularly preferred.

[0147] The content of the solvent is usually 1 to 600 parts by mass, preferably 50 to 500 parts by mass, more preferably 100 to 400 parts by mass, and particularly preferably 150 to 300 parts by mass, relative to 100 parts by mass of the (meth)acrylic copolymer (A) in terms of drying properties.

[0148] The solvent content in the pressure-sensitive adhesive composition after drying is preferably 1% by mass or less, more preferably 0.5% by mass or less, particularly preferably 0.1% by mass or less, and most preferably 0% by mass.

[0149] The drying temperature is usually 40 to 150° C., more preferably 45 to 140° C., even more preferably 50 to 130° C., and particularly preferably 55 to 120° C. When the temperature is within this range, the solvent can be removed efficiently and relatively safely while suppressing thermal deformation of the release film.

[0150] The drying time is usually 1 to 30 minutes, more preferably 3 to 25 minutes, and even more preferably 5 to 20 minutes. When the drying time is within this range, the solvent can be removed efficiently and sufficiently.

[0151] Drying methods include, for example, drying with a dryer, drying with a heated roll, drying by blowing hot air onto the film, etc. Among these, using a dryer is preferred because it allows for uniform and easy drying. These methods can be used alone or in combination of two or more.

[0152] In yet another embodiment of the method for producing the present pressure-sensitive adhesive sheet, a pressure-sensitive adhesive composition may be prepared, coated onto a component of an image display device described below, and the pressure-sensitive adhesive composition may be cured to produce the present pressure-sensitive adhesive sheet, although the method is not limited to this.

[0153] Furthermore, the present pressure-sensitive adhesive sheet may be a single-layer pressure-sensitive adhesive sheet consisting only of a pressure-sensitive adhesive layer formed by curing a pressure-sensitive adhesive composition, or may be a multi-layer pressure-sensitive adhesive sheet in which a plurality of the pressure-sensitive adhesive layers and other pressure-sensitive adhesive layers formed from pressure-sensitive adhesive compositions other than the pressure-sensitive adhesive composition are laminated. Among these, the present pressure-sensitive adhesive sheet preferably has a laminated pressure-sensitive adhesive layer in which two or more pressure-sensitive adhesive layers are laminated adjacent to each other, more preferably has at least three layers: an outermost layer, an innermost layer, and an intermediate layer, and it is particularly preferred that the outermost layer and the innermost layer are pressure-sensitive adhesive layers formed by curing a pressure-sensitive adhesive composition containing a (meth)acrylic copolymer (A). This layer structure tends to result in a pressure-sensitive adhesive sheet that is excellent in impact resistance and is resistant to indentations and dents even when localized pressure is applied.

[0154] When the pressure-sensitive adhesive sheet has a laminated pressure-sensitive adhesive layer in which two or more pressure-sensitive adhesive layers are laminated adjacently, the laminated pressure-sensitive adhesive layer is preferably a laminated pressure-sensitive adhesive layer in which two or more pressure-sensitive adhesive layers are laminated adjacently and have different shear storage moduli (G') at 25° C. Furthermore, the laminated pressure-sensitive adhesive layer preferably has a first pressure-sensitive adhesive layer having a lower shear storage modulus (G') at 25° C. than the adjacent pressure-sensitive adhesive layer, and a second pressure-sensitive adhesive layer having a higher shear storage modulus (G') at 25° C. than the adjacent pressure-sensitive adhesive layer.

[0155] The first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer may be formed by curing a pressure-sensitive adhesive composition containing a (meth)acrylic copolymer (A) of the same composition, or may be formed by curing a pressure-sensitive adhesive composition containing a (meth)acrylic copolymer (A) of different composition, particularly a pressure-sensitive adhesive composition containing a (meth)acrylic copolymer (A) of different composition as a main component. Among these, from the viewpoints of easily adjusting the elastic modulus ratio (E' / G') and functionally separating the conflicting physical properties such as stress relaxation and shape retention for each layer, it is preferred that the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer be formed by curing a pressure-sensitive adhesive composition containing a (meth)acrylic copolymer (A) of different composition, particularly a pressure-sensitive adhesive composition containing a (meth)acrylic copolymer (A) of different composition as a main component. On the other hand, from the viewpoint of ease of production, it is preferred that the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer be formed by curing a pressure-sensitive adhesive composition containing a (meth)acrylic copolymer (A) of the same composition as a main component.

[0156] When the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer are formed by curing pressure-sensitive adhesive compositions containing (meth)acrylic copolymers (A) having different compositions as main components, it is preferable that the theoretical Tg (Tg1) of the (meth)acrylic copolymer (A) contained in the pressure-sensitive adhesive composition forming the first pressure-sensitive adhesive layer and the theoretical Tg (Tg2) of the (meth)acrylic copolymer (A) contained in the pressure-sensitive adhesive composition forming the second pressure-sensitive adhesive layer satisfy the relationship Tg2 > Tg1.

[0157] Furthermore, the difference (Tg2-Tg1) between the theoretical Tg (Tg1) of the acrylic copolymer (A) contained in the pressure-sensitive adhesive composition forming the first pressure-sensitive adhesive layer and the theoretical Tg (Tg2) of the acrylic copolymer (A) contained in the pressure-sensitive adhesive composition forming the second pressure-sensitive adhesive layer is usually 10 to 80°C, preferably 15 to 75°C, more preferably 20 to 70°C, particularly preferably 30 to 65°C, and most preferably 40 to 60°C.

[0158] The theoretical Tg of the (meth)acrylic copolymer (A) contained in the pressure-sensitive adhesive composition forming the first pressure-sensitive adhesive layer or the second pressure-sensitive adhesive layer is a value calculated by applying the glass transition temperature (Tg) and mass fraction of each homopolymer formed from each monomer constituting the acrylic copolymer (A) to the Fox's equation shown below.

[0159] Here, the glass transition temperature (Tg) of the homopolymer formed from the monomers constituting the (meth)acrylic copolymer (A) is usually a value measured by a differential scanning calorimeter (DSC) according to a method in accordance with JIS K7121-1987 or JIS K6240, or a value listed in a catalog.

[0160] Furthermore, the first pressure-sensitive adhesive layer preferably has a glass transition temperature (Tg) defined by the maximum value of loss tangent (Tan δ) obtained by dynamic viscoelasticity measurement in the shear mode, which is lower than the glass transition temperature of the second pressure-sensitive adhesive layer. The glass transition temperature (Tg1) defined by the maximum value of loss tangent (Tan δ) of the first pressure-sensitive adhesive layer is usually −80 to −10°C, preferably −70 to −15°C, more preferably −50 to −17°C, and even more preferably −40 to −20°C.

[0161] The second pressure-sensitive adhesive layer has a glass transition temperature (Tg2) defined by the maximum value of the loss tangent (Tan δ) obtained by the dynamic viscoelasticity measurement in the shear mode, which is usually −25 to 60° C., preferably −15 to 40° C., more preferably −10 to 30° C., and even more preferably 0 to 20° C.

[0162] When the present pressure-sensitive adhesive sheet has at least three layers, namely, a surface layer, a back layer, and an intermediate layer, it is preferable that the surface layer and / or the back layer is formed from a first pressure-sensitive adhesive layer, and the intermediate layer is formed from a second pressure-sensitive adhesive layer, and it is even more preferable that the pressure-sensitive adhesive layer has a three-layer structure in which the first pressure-sensitive adhesive layer, the second pressure-sensitive adhesive layer, and the first pressure-sensitive adhesive layer are laminated in this order.

[0163] Furthermore, when the present pressure-sensitive adhesive sheet has a laminated structure including a first pressure-sensitive adhesive layer and a second pressure-sensitive adhesive layer, the ratio (t2 / t1) of the thickness (t1) of the first pressure-sensitive adhesive layer to the thickness (t2) of the second pressure-sensitive adhesive layer is preferably 0.2 or more, more preferably 0.5 to 10, and particularly preferably 1.0 to 5. By setting the ratio (t2 / t1) of the thickness (t1) of the first pressure-sensitive adhesive layer to the thickness (t2) of the second pressure-sensitive adhesive layer within the above range, a pressure-sensitive adhesive sheet with excellent foam resistance during lamination, lamination suitability such as level difference absorbency, and impact resistance tends to be obtained. Note that when the present pressure-sensitive adhesive sheet has a three-layer structure in which the first pressure-sensitive adhesive layer, the second pressure-sensitive adhesive layer, and the first pressure-sensitive adhesive layer are laminated in this order, the thickness (t1) of the first pressure-sensitive adhesive layer represents the combined thickness of the two first pressure-sensitive adhesive layers.

[0164] The pressure-sensitive adhesive sheet thus obtained is an optically transparent transparent pressure-sensitive adhesive sheet. Here, "optically transparent" means that the total light transmittance is 80% or more, preferably 85% or more, and more preferably 90% or more. In addition, the haze value of the pressure-sensitive adhesive sheet is preferably 10% or less, more preferably 5% or less, and particularly preferably 3% or less.

[0165] The thickness of the present pressure-sensitive adhesive sheet is preferably 50 to 1000 μm, more preferably 60 to 500 μm, and particularly preferably 75 to 300 μm.

[0166] Furthermore, the pressure-sensitive adhesive sheet may be embossed or processed to have various irregularities (such as conical, pyramidal, or hemispherical shapes) as needed. Furthermore, in order to improve adhesion to various members, the surface may be subjected to various surface treatments such as corona treatment, plasma treatment, and primer treatment.

[0167] <Preferred use of the present pressure-sensitive adhesive sheet> The present pressure-sensitive adhesive sheet is suitably used for bonding optical components.Specifically, it is suitably used for bonding components constituting a display, particularly components used for manufacturing a display, and is suitably used as a pressure-sensitive adhesive sheet for bonding image display panel and image display device components such as a protective panel or touch panel disposed on its front side (viewing side), or components constituting the image display device components.In addition, the same components as those described below can be used for the image display device components.

[0168] <<Laminate for Image Display Device>> A laminate for an image display device according to one example of the embodiment of the present invention (hereinafter, may be referred to as "the present laminate for an image display device") is a laminate for an image display device having a configuration in which two components of the image display device are laminated with the present pressure-sensitive adhesive sheet interposed therebetween. The present laminate for an image display device is preferably a laminate for an image display device having a configuration in which two components of the image display device are laminated with the present pressure-sensitive adhesive sheet interposed therebetween.

[0169] Of the components of the laminate for an image display device, the pressure-sensitive adhesive sheet has been described above, and the components other than the pressure-sensitive adhesive sheet will be described below.

[0170] <Image Display Device Components> Examples of image display device components constituting the present laminate for an image display device include flat panel image display device components, curved image display device components, and flexible image display device components. Examples of such image display device components include image display panels such as liquid crystal displays and organic electroluminescence (EL) displays, surface protection panels (surface protection films), polarizing plates, polarizing elements, retardation films, color filters, barrier films, viewing angle compensation films, brightness enhancement films, contrast enhancement films, diffusion films, semi-transmitting reflective films, electrode films, transparent conductive films, metal mesh films, and touch sensor films. Any one of these may be used alone or in combination. Examples include a combination of a surface protection panel with another image display device component, or a combination with another image display device component.

[0171] Preferably, one of the two image display device components is a surface protection panel, and the other is a component consisting of one or a combination of two or more components selected from the group consisting of a touch sensor film, an image display panel, a color filter, a polarizing element, and a retardation film. It is more preferable that the surface protection panel has a frame-shaped concealing portion on its periphery, with the frame having a portion with a width of 3 mm or less. With this configuration, the effects of the present invention can be particularly achieved. From this perspective, a panel having a portion with a frame width of 2 mm or less is particularly preferable, and a panel having a portion with a width of 1.5 mm or less is particularly preferable.

[0172] <Method for manufacturing the present laminate for an image display device> The method for manufacturing the present laminate for an image display device is not particularly limited, and as described above, for example, the pressure-sensitive adhesive composition may be applied to a component of an image display device to form a pressure-sensitive adhesive sheet, or a pressure-sensitive adhesive sheet with a release film may be formed in advance and then laminated to a component of an image display device.

[0173] <<Image Display Device>> An image display device according to an embodiment of the present invention (hereinafter, sometimes referred to as the "image display device") incorporates a laminate for an image display device, which has a configuration in which two image display device components are bonded together via the present pressure-sensitive adhesive sheet. For example, an image display device may have a structure in which a laminate for an image display device, which has a configuration in which two image display device components are bonded together via the present pressure-sensitive adhesive sheet, is combined with other image display device components. In this case, "other image display device components" may include, for example, FPC cables, reflective sheets, light guide plates and light sources, diffusion films, prism sheets, liquid crystal panels, organic EL panels, anti-reflection films, color filters, polarizing plates, retardation plates, glass substrates, surface protection films, and integrated composites of these components. Specific examples of the image display device include liquid crystal displays, organic EL displays, inorganic EL displays, electronic paper, plasma displays, and microelectromechanical system (MEMS) displays used in personal computers, mobile devices, game consoles, televisions (TVs), car navigation systems, touch panels, pen tablets, etc.

[0174] The present invention will be explained in more detail below by way of examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention.

[0175] Prior to the examples, the following raw materials were prepared.

[0176] (Meth)acrylic Copolymer (A) (Meth)acrylic copolymers (A-1) to (A-3) were prepared with the copolymer component compositions shown in Table 1 below.

[0177]

[0178] [Crosslinking agent (B)] (B-1): Polypropylene glycol #400 diacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., "NK Ester APG-400") (B-2): Pentaerythritol tri- and tetraacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., "NK Ester A-TMM-3L")

[0179] [Photoinitiator (C)] (C-1): Mixture of 2,4,6-trimethylbenzophenone and 4-methylbenzophenone ("Esacure TZT" manufactured by IGM) (C-2): Methylbenzoyl formate ("Omnirad MBF" manufactured by IGM) (C-3): 4-methacryloyloxybenzophenone ("MBP" manufactured by Shinryo Corporation) (C-4): Ethyl (2,4,6-trimethylbenzoyl)-phenylphosphinate ("Omnirad TPO-L" manufactured by IGM)

[0180] [Ultraviolet absorber (D)] (D-1): 5,5'-bis(2-ethylhexyloxy)-2,2'-[6-(4-methoxyphenyl)-1,3,5-triazine-2,4-diyl]diphenol ("Tinosorb S" manufactured by BASF)

[0181] [Silane Coupling Agent] (E-1): 3-glycidyloxypropyltrimethoxysilane ("KBM-403" manufactured by Shin-Etsu Chemical Co., Ltd.)

[0182] Example 1 100 parts by mass of a (meth)acrylic polymer (A-2), 1.5 parts by mass of a crosslinking agent (B-1), 0.83 parts by mass of a photoinitiator (C-1), 0.45 parts by mass of a photoinitiator (C-3), and 0.2 parts by mass of a silane coupling agent (E-1) were prepared and uniformly mixed to form a pressure-sensitive adhesive composition for a surface layer. On the other hand, 100 parts by mass of a (meth)acrylic polymer (A-1), 20 parts by mass of a crosslinking agent (B-2), 1.5 parts by mass of a photopolymerization initiator (C-4), and 2.5 parts by mass of an ultraviolet absorber (D-1) were prepared and uniformly mixed to form a pressure-sensitive adhesive composition for an intermediate layer. The pressure-sensitive adhesive composition for the surface layer and the pressure-sensitive adhesive composition for the intermediate layer were each supplied to two extruders, and co-extruded in a layer structure of two types and three layers (surface layer / intermediate layer / surface layer, thickness ratio 1:1:1) to be hot-melt molded into a sheet having a thickness of 130 μm.

[0183] Next, the sheet-like pressure-sensitive adhesive composition was sandwiched between two polyethylene terephthalate films (manufactured by Mitsubishi Chemical Corporation, thickness 75 μm) whose surfaces had been treated with silicone release agent, i.e., two release films, to obtain a laminate consisting of release film / pressure-sensitive adhesive composition / release film. Thereafter, using a metal halide lamp, the laminate was exposed to an integrated light intensity of 3000 mJ / cm at a wavelength of 365 nm. 2 Both surfaces of the sheet-like pressure-sensitive adhesive composition were irradiated with active energy rays through the release film to obtain a double-sided pressure-sensitive adhesive sheet with release films consisting of release film / pressure-sensitive adhesive sheet / release film.

[0184] Examples 2 to 5, Comparative Example 3 Double-sided PSA sheets with release films were prepared in the same manner as in Example 1, except that the formulation, thickness, layer structure and integrated light amount were changed as shown in Table 2 below.

[0185] Comparative Example 1 A pressure-sensitive adhesive composition was prepared by uniformly mixing 100 parts by mass of a (meth)acrylic polymer (A-2), 1.5 parts by mass of a crosslinking agent (B-1), 0.83 parts by mass of a photoinitiator (C-1), 1.67 parts by mass of a photoinitiator (C-3), and 0.2 parts by mass of a silane coupling agent (E-1).

[0186] Next, the pressure-sensitive adhesive composition was spread in a sheet form on a 75 μm-thick release film (PET film manufactured by Mitsubishi Chemical Corporation) that had been subjected to a silicone release treatment so that the thickness of the pressure-sensitive adhesive composition was 130 μm. Thereafter, a 75 μm-thick release film (PET film manufactured by Mitsubishi Chemical Corporation) that had been subjected to a silicone release treatment was laminated on the sheet-like pressure-sensitive adhesive composition. Using a metal halide lamp, an integrated light intensity of 1500 mJ / cm at a wavelength of 365 nm was obtained. 2 Both surfaces of the sheet-like pressure-sensitive adhesive composition were irradiated with active energy rays through the release film to obtain a double-sided pressure-sensitive adhesive sheet with release films consisting of release film / pressure-sensitive adhesive sheet / release film.

[0187] Comparative Example 2 A double-sided PSA sheet with a release film of Comparative Example 2 was produced in the same manner as Comparative Example 1, except that the composition, thickness, and integrated light amount were changed to those shown in Table 2 below.

[0188]

[0189] [Measurement and Evaluation of Physical Properties] The pressure-sensitive adhesive sheets prepared in the above Examples and Comparative Examples were subjected to the following various measurements and evaluations. The evaluation results are summarized in Table 3 below.

[0190] [Tensile modulus (E')] The double-sided PSA sheets with release films produced in the Examples and Comparative Examples were cut to a width of 20 mm and a length of 70 mm. The release films were removed from the double-sided PSA sheets with release films, and the double-sided PSA sheets were set in a tensile tester so that the distance between chucks was 20 mm. A tensile test was performed using the tensile tester at a speed of 300 mm / min in an environment of 25°C. The slope of the stress-strain curve obtained in the tensile test in the section from 10 to 200% strain was calculated to determine the tensile modulus (E').

[0191] [Shear storage modulus (G')] The release film on one side was removed from the double-sided PSA sheets with release film prepared in the Examples and Comparative Examples, and the sheets were repeatedly laminated with a hand roller to a thickness of approximately 0.8 mm, and then punched out into circles with a diameter of 8 mm to prepare samples. The obtained samples were placed in a rheometer ("DHR-2" manufactured by T.A. Instruments) and subjected to dynamic viscoelasticity measurement under the conditions of measurement jig: 8 mm diameter parallel plates, frequency: 1 Hz, measurement temperature: -50 to 150°C, and heating rate: 5°C / min, and the shear storage modulus (G') value at 25°C was read.

[0192] [Elastic modulus ratio (E' / G')] The elastic modulus ratio (E' / G') was calculated from the tensile modulus (E') at 25°C obtained in the tensile test and the shear storage modulus (G') obtained in the dynamic viscoelasticity measurement.

[0193] [Stress Relaxation Rate (X)] The release film on one side of the double-sided PSA sheet with release film prepared in the Examples and Comparative Examples was removed, and the sheet was repeatedly laminated with a hand roller to a thickness of approximately 0.8 mm. A circle with a diameter of 25 mm was punched out to serve as a sample. A viscoelasticity measuring device ("DHR2" manufactured by T.A. Instruments) was used to measure the obtained sample. A 25% strain was applied at 70 ° C. using a 25 mm diameter parallel plate. The storage modulus after 0.1 seconds was measured as the initial modulus (G'(0)). A 25% strain was also applied at 70 ° C., and the storage modulus after 300 seconds was measured as the relaxation modulus (G'(300)). The values ​​of the initial modulus (G'(0)) and the relaxation modulus (G'(300)) were substituted into the following formula (I) to determine the stress relaxation rate (X). Stress relaxation rate (X) = (G'(300) / G'(0))...(I)

[0194] [Gel Fraction] For the double-sided PSA sheets with release film prepared in the Examples and Comparative Examples, approximately 0.1 g of PSA sheet fragments were collected from the PSA sheets after peeling off the release film. The collected PSA sheet fragments were wrapped in a bag-shaped SUS mesh (#150) with a mass (X), and the bag was closed to prepare a sample, and the mass (Y) of the sample was measured. The sample was immersed in ethyl acetate and stored in a dark place at 23°C for 24 hours, then removed and heated at 70°C for 4.5 hours to evaporate the ethyl acetate, and the mass (Z) of the dried sample was measured. The measured masses were substituted into the following formula to calculate the gel fraction before light irradiation: Gel Fraction (%) = [(Z-X) / (Y-X)] x 100 (II)

[0195] [Glass transition temperature (Tg)] The release film on one side was removed from the pressure-sensitive adhesive sheets with release film prepared in the Examples and Comparative Examples, and the sheets were repeatedly laminated with a hand roller to a thickness of approximately 0.9 mm. A sample was then punched out into a circle with a diameter of 8 mm. The obtained sample was placed in a rheometer ("DHR-2" manufactured by T.A. Instruments) and subjected to dynamic viscoelasticity measurement under the following conditions: measurement jig: 8 mm diameter parallel plate; frequency: 1 Hz; measurement temperature: -50 to 150 ° C; heating rate: 5 ° C / min. From the Tan δ spectrum obtained by the dynamic viscoelasticity measurement, the temperature at which Tan δ reached its maximum value was read and used as the glass transition temperature (Tg).

[0196] [Adhesive Strength] The release film on one side of the double-sided PSA sheets with release film prepared in the Examples and Comparative Examples was removed, and a PET film (Cosmoshine A4300, manufactured by Toyobo Co., Ltd., thickness 100 μm) was attached as a backing film using a hand roller. This was cut into strips measuring 10 mm wide x 150 mm long, and the remaining release film was peeled off, resulting in the exposed PSA sheet surface being attached to the surface of soda-lime glass using a hand roller. The resulting laminate was autoclaved (60°C, gauge pressure 0.2 MPa, 20 minutes) for finish attachment to prepare an adhesive strength measurement sample. The resulting adhesive strength measurement sample was pulled at an angle of 180° at a peel rate of 60 mm / min at 23°C and 50% RH, and the PSA sheet and backing film were peeled off from the soda-lime glass. The tensile strength (N / cm) was measured using a load cell to determine the adhesive strength.

[0197] [Light Transmittance] One release film was peeled off from each of the double-sided PSA sheets with release film prepared in the Examples and Comparative Examples, and the exposed adhesive surface was roll-pressed onto a soda lime glass (82 mm x 53 mm x 0.5 mm thick). The remaining release film was then peeled off, and the sheet was roll-pressed onto a soda lime glass (82 mm x 53 mm x 0.5 mm thick). This sheet was then autoclaved (60°C, 0.2 MPa gauge pressure, 20 minutes) for finish bonding to produce a laminate for evaluation. The spectral transmittance (%) of the above evaluation laminate was measured at wavelengths of 300 nm to 800 nm using a spectrophotometer (Shimadzu Corporation's "UV2000"), and the light transmittance at a wavelength of 380 nm was read.

[0198] [Lamination Appearance] The release film on one side of the pressure-sensitive adhesive sheets with release film prepared in the Examples and Comparative Examples was peeled off and the sheet was laminated to a 0.18 mm thick foam sheet. The remaining release film was peeled off, and the exposed adhesive surface was roll-pressed onto the entire surface of a soda-lime glass (68 mm x 155 mm x 0.55 mm thick) using a hand roller, with one stroke across the entire surface. A sample for evaluating the lamination appearance was prepared. The maximum height (Sz) of the surface of the soda-lime glass side of the sample was measured using a laser microscope (OLYMPUS Corporation, "LEXT OLS4000") in accordance with ISO 25178. Measurements were performed at three locations, one at each point in the longitudinal direction of the sample, using a 5x objective lens and a Gaussian filter. The average value of the three locations was taken as the maximum height (Sz1) of the sample.

[0199] A reference sample was also prepared by laminating the foam sheet onto the entire surface of a soda lime glass (68 mm x 155 mm x 0.55 mm thick) using a hand roller. The maximum height (Sz0) of the reference sample was measured in the same manner as for the sample for evaluating laminate appearance, and was found to be 660 μm. The measured value was substituted into the following formula to calculate the reduction rate of the maximum height (Sz): Maximum height (Sz) reduction rate (%) = (Sz0 - Sz1) / (Sz0) x 100 (III) A maximum height reduction rate of 65% or more was rated as "S," 60% or more but less than 65% as "A," and less than 60% as "B."

[0200] [Impact Resistance] For the double-sided PSA sheets with release film prepared in the Examples and Comparative Examples, one side of the release film was peeled off, and a 0.05 mm thick polyimide film was roll-pressed onto the exposed adhesive surface using a hand roller. The remaining release film was peeled off, and pressure-sensitive paper (Fujifilm Corporation's "Prescale MS Type") was attached to the exposed adhesive surface to prepare a sample for impact resistance measurement. The sample was placed on soda-lime glass (0.55 mm thick) with the polyimide film side facing up, and a 0.5 g iron ball was dropped from a height of 4 cm above the center of the sample. The pressure-sensitive paper subjected to the impact of the falling ball through the polyimide film and double-sided PSA sheet was observed at 100x magnification using a digital microscope (Leica "DVM6"), and the diameter of the circle surrounding the area that developed color due to the impact of the falling ball was measured. Circles with a diameter of 700 μm or less were rated as "S", circles with a diameter of more than 700 μm and 750 μm or less were rated as "A", and circles with a diameter of more than 750 μm were rated as "B".

[0201]

[0202] The double-sided PSA sheets of the Examples had tensile modulus (E') and modulus ratio (E' / G') at 25°C within the specified ranges, and were excellent in lamination appearance and impact resistance. On the other hand, the double-sided PSA sheet of Comparative Example 1 had a low tensile modulus (E') at 25°C, and was therefore poor in the effect of reducing the unevenness of the lamination members, resulting in poor lamination appearance. The double-sided PSA sheet of Comparative Example 2 had values ​​for both the tensile modulus (E') and modulus ratio (E' / G') at 25°C that were outside the specified ranges, and therefore was insufficient in both lamination appearance and impact resistance. The value of the modulus ratio (E' / G') of Comparative Example 3 was outside the specified range, and therefore was unable to achieve both lamination appearance and impact resistance.

[0203] Although the above examples show specific embodiments of the present invention, the examples are merely illustrative and should not be construed as limiting. Various modifications that are obvious to those skilled in the art are intended to fall within the scope of the present invention.

[0204] The double-sided pressure-sensitive adhesive sheet of the present invention is suitable for use in bonding optical members, specifically, for bonding members constituting a display, particularly members used in manufacturing a display.

Claims

1. A double-sided pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed by curing a pressure-sensitive adhesive composition containing a (meth)acrylic copolymer (A), wherein the double-sided pressure-sensitive adhesive sheet has a tensile modulus (E') at 25°C of 1.0 to 20 MPa, calculated as the slope in the 10 to 200% strain range in a stress-strain curve obtained by a tensile test conducted on a 20 mm x 70 mm test piece at a tension speed of 300 mm / min and a chuck distance of 20 mm, and wherein the modulus ratio (E' / G') of the tensile modulus (E') at 25°C to the shear storage modulus (G') at 25°C obtained by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz is 15 to 100.

2. The double-sided pressure-sensitive adhesive sheet according to claim 1, wherein the pressure-sensitive adhesive layer has a stress relaxation rate (X) of 0.50 or less, calculated by the following formula (I) from the initial elastic modulus (G'(0)) 0.1 seconds after applying a 25% strain at 70°C and the relaxed elastic modulus (G'(300)) 300 seconds after applying a 25% strain at 70°C: Stress relaxation rate (X) = (G'(300) / G'(0)) (I):

3. The double-sided pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the pressure-sensitive adhesive composition comprises a crosslinking agent (B) and a photoinitiator (C).

4. The double-sided pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the pressure-sensitive adhesive composition contains an ultraviolet absorber (D).

5. The double-sided pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the gel fraction of the double-sided pressure-sensitive adhesive sheet is 30 to 90%.

6. The double-sided pressure-sensitive adhesive sheet according to claim 1 or 2, which has a glass transition temperature (Tg) defined as the maximum value of Tan δ obtained by dynamic viscoelasticity measurement in shear mode at a frequency of 1 Hz, of -10°C or lower.

7. A double-sided pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the (meth)acrylic copolymer (A) contains a hydroxyl group-containing (meth)acrylate monomer (a1) and / or a nitrogen atom-containing (meth)acrylate monomer (a2) as a structural unit.

8. The double-sided pressure-sensitive adhesive sheet according to claim 3, wherein the photoinitiator (C) is a hydrogen abstraction photoinitiator.

9. The double-sided pressure-sensitive adhesive sheet according to claim 1 or 2, which has a laminated pressure-sensitive adhesive layer in which two or more pressure-sensitive adhesive layers having different shear storage moduli (G') at 25°C are laminated adjacent to each other.

10. The double-sided pressure-sensitive adhesive sheet according to claim 9, wherein the laminated pressure-sensitive adhesive layer has a first pressure-sensitive adhesive layer having a lower shear storage modulus (G') at 25°C than an adjacent pressure-sensitive adhesive layer, and a second pressure-sensitive adhesive layer having a higher shear storage modulus (G') at 25°C than an adjacent pressure-sensitive adhesive layer.

11. The double-sided pressure-sensitive adhesive sheet according to claim 10, wherein the laminated pressure-sensitive adhesive layer has a three-layer structure in which the first pressure-sensitive adhesive layer, the second pressure-sensitive adhesive layer, and the first pressure-sensitive adhesive layer are laminated in this order.

12. The double-sided pressure-sensitive adhesive sheet according to claim 10, wherein the pressure-sensitive adhesive composition forming the second pressure-sensitive adhesive layer contains an ultraviolet absorber (D).

13. The double-sided pressure-sensitive adhesive sheet according to claim 10, wherein the content of the crosslinking agent (B) contained in the pressure-sensitive adhesive composition forming the second pressure-sensitive adhesive layer is greater than the content of the crosslinking agent (B) contained in the pressure-sensitive adhesive composition forming the first pressure-sensitive adhesive layer.

14. The double-sided pressure-sensitive adhesive sheet according to claim 10, wherein the ratio (t2 / t1) of the thickness (t1) of the first pressure-sensitive adhesive layer to the thickness (t2) of the second pressure-sensitive adhesive layer is 0.2 or greater.

15. A double-sided pressure-sensitive adhesive sheet with a release film, comprising the double-sided pressure-sensitive adhesive sheet according to claim 1 or 2 and a release film laminated on the double-sided pressure-sensitive adhesive sheet.

16. A laminate for an image display device, comprising two components of an image display device and the double-sided pressure-sensitive adhesive sheet according to claim 1 or 2 interposed between the two components of the image display device.

17. An image display device comprising the laminate for an image display device according to claim 16.

Images