Pressure sensitive adhesive sheet, optical laminate and picture display unit

Abstract

To provide a pressure sensitive adhesive sheet suitable for suppressing a size change of an optical film included in an optical laminate while securing durability.SOLUTION: In the pressure sensitive adhesive sheet, a peak value (peak top stress Xmax) of stress X is 0.5 MPa or more, in a stress-strain curve obtained by the following evaluation test to the pressure sensitive adhesive sheet. Evaluation test includes: making an edge face of an evaluation probe (in a columnar shape with a diameter of 5 mm, made of stainless steel) contact with an adhesive face of the pressure sensitive adhesive sheet adhered onto a glass plate; holding for 300 sec while applying a contact load of 100 N in a thickness direction of the pressure sensitive adhesive sheet; putting the evaluation probe and the pressure sensitive adhesive sheet tightly together; then displacing the evaluation probe at a constant speed of 2 μm / min in a direction vertically away from the pressure sensitive adhesive sheet; measuring the stress X and a strain Y in the thickness direction of the pressure sensitive adhesive sheet generated in the pressure sensitive adhesive sheet by the displacing of the evaluation probe; and obtaining the curve from the measured stress X and the strain Y.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a pressure-sensitive adhesive sheet, an optical laminate, and an image display device. [Background technology]

[0002] In recent years, image display devices, such as liquid crystal display devices and electroluminescence (EL) display devices (e.g., organic EL display devices and inorganic EL display devices), have rapidly become popular. These various image display devices typically have a laminated structure of an image-forming layer, such as a liquid crystal layer or an EL light-emitting layer, and an optical laminate including an optical film and an adhesive sheet. The adhesive sheet is mainly used to bond between films included in the optical laminate or to bond between the image-forming layer and the optical laminate. Examples of optical films include polarizing plates, retardation films, and polarizing plates with retardation films, which are formed by integrating a polarizing plate and a retardation film. Patent Document 1 discloses an example of an optical laminate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-031214 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-98665 Summary of the Invention [Problem to be solved by the invention]

[0004] Excessive dimensional changes in optical films due to temperature changes can cause light leakage and color unevenness in image display devices. Light leakage and color unevenness are particularly likely to occur in relatively large image display devices that use polarizing plates with retardation films. In addition, image display devices designed with narrow bezels (narrow frame designs) are becoming more common, making it increasingly important to suppress dimensional changes. One way to suppress dimensional changes is to increase the elastic modulus of the pressure-sensitive adhesive sheet included in the optical laminate. However, simply increasing the elastic modulus can reduce the durability of the pressure-sensitive adhesive sheet, making it unable to follow dimensional changes.

[0005] An object of the present invention is to provide a pressure-sensitive adhesive sheet that is suitable for suppressing dimensional changes in an optical film included in an optical laminate and that also ensures durability. [Means for solving the problem]

[0006] The present invention provides Peak top stress X max A pressure-sensitive adhesive sheet that satisfies the following formula (1): to provide. X max ≧0.5MPa (1) However, the peak top stress X max is determined by the following evaluation tests on the adhesive sheet. This is the peak value of stress X in the stress-strain curve obtained. -Evaluation test- The end face of an evaluation probe (cylindrical, stainless steel, 5 mm in diameter) is brought into contact with the adhesive surface of the adhesive sheet attached to a glass plate, and a contact load of 100 N is applied in the thickness direction of the adhesive sheet while maintaining this for 300 seconds to bring the evaluation probe and the adhesive sheet into close contact. Next, the evaluation probe is displaced at a constant rate of 2 μm / min in a direction perpendicular to and away from the adhesive sheet. The stress X and strain Y in the thickness direction of the adhesive sheet caused by the displacement of the evaluation probe are measured, and a stress-strain curve is obtained from the measured stress X and strain Y.

[0007] In another aspect, the present invention provides a method for producing a composition comprising: An optical laminate comprising the pressure-sensitive adhesive sheet of the present invention and an optical film; to provide.

[0008] In another aspect, the present invention provides a method for producing a composition comprising: An image display device comprising the optical laminate of the present invention. to provide. [Effects of the Invention]

[0009] The pressure-sensitive adhesive sheet according to the present invention is a sheet that is suitable for suppressing dimensional changes in the optical film contained in the optical laminate, and also ensures durability. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a cross-sectional view schematically showing an example of the pressure-sensitive adhesive sheet of the present invention. [Figure 2A] FIG. 2A is a schematic diagram illustrating an evaluation test for determining the stress-strain curve of a pressure-sensitive adhesive sheet. [Figure 2B] FIG. 2B is a schematic diagram for explaining an evaluation test for determining the stress-strain curve of the pressure-sensitive adhesive sheet. [Figure 2C] FIG. 2C is a schematic diagram for explaining an evaluation test for determining the stress-strain curve of the pressure-sensitive adhesive sheet. [Figure 2D] FIG. 2D is an enlarged view of area A in FIG. 2C. [Figure 3] FIG. 3 is a graph showing an example of a stress-strain curve of a pressure-sensitive adhesive sheet. [Figure 4] FIG. 4 is a schematic diagram for explaining the change in the volume of the pressure-sensitive adhesive sheet accompanying the change in the dimensions of the optical film. [Figure 5] FIG. 5 is a cross-sectional view schematically showing an example of the optical layered body of the present invention. [Figure 6] FIG. 6 is a cross-sectional view schematically showing an example of the optical layered body of the present invention. [Figure 7] FIG. 7 is a cross-sectional view schematically showing an example of the optical layered body of the present invention. [Figure 8]FIG. 8 is a cross-sectional view schematically showing an example of the optical layered body of the present invention. [Figure 9] FIG. 9 is a cross-sectional view schematically showing an example of an image display device of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the accompanying drawings, but is not limited to the following embodiments.

[0012] [Adhesive sheet] An example of the pressure-sensitive adhesive sheet of this embodiment is shown in Fig. 1. The pressure-sensitive adhesive sheet 1 of Fig. 1 has a peak top stress X max satisfies the following formula (1). X max ≧0.5MPa (1) However, the peak top stress X max is determined by the following evaluation test for adhesive sheet 1. is the peak value of stress X in the stress-strain curve.

[0013] [Evaluation test] An evaluation test for determining the stress-strain curve of the adhesive sheet 1 will be described with reference to Figs. 2A to 2D. First, an end face 53 of an evaluation probe 52 (cylindrical, 5 mm in diameter, made of stainless steel) is brought into contact with the adhesive surface 11 (exposed surface) of the adhesive sheet 1 attached to a glass plate 51, and a contact load 54 of 100 N is applied in the thickness direction of the adhesive sheet 1 while maintaining this for 300 seconds, thereby bringing the evaluation probe 52 into close contact with the adhesive sheet 1 (Figs. 2A and 2B). The end face 53 is the bottom face of the probe 52, and its diameter is 5 mm. In order to measure the stress X and strain Y with high accuracy, it is preferable that the thickness of the attached adhesive sheet 1 is 200 µm or more. If the thickness is less than 200 µm, two or more adhesive sheets 1 are stacked and autoclaved or the like. The thickness may be 200 μm or more by bonding the adhesive sheet 1 to the glass plate 51 using heating I. The glass plate 51 may be selected so that the surface to which the adhesive sheet 1 is attached is flat and the adhesive sheet 1 will not peel off during the evaluation test. The adhesive sheet 1 is attached to the glass plate 51 in such a manner that the adhesive sheet 1 will not peel off during the evaluation test. If necessary, the bonding state between the adhesive sheet 1 and the glass plate 51 may be stabilized by heating II using an autoclave or the like. The conditions for heating I and heating II are, for example, 30 to 90°C and 0.5 to 4 hours. When an autoclave is used, the conditions are, for example, 30 to 70°C, 5 to 30 minutes, and 2 to 10 atmospheres (absolute pressure). Heating I and heating II may be performed simultaneously while the overlapping adhesive sheets 1 are attached to the glass plate 51. A probe for a probe tack test conforming to the specifications of ASTM D-2979 can be used as the evaluation probe 52.

[0014] Next, the evaluation probe 52 is displaced in a direction perpendicular to the surface of the adhesive sheet 1 and away from the adhesive sheet 1 (FIG. 2C). This direction usually coincides with the thickness direction of the adhesive sheet 1. The displacement speed is kept constant at 2 μm / min. The stress X and strain Y in the thickness direction caused in the adhesive sheet 1 by the displacement of the evaluation probe 52 are measured, and from the measured stress X and strain Y, a stress-strain curve is obtained with strain Y on the horizontal axis and stress X on the vertical axis. For example, a tensile tester can be used for the evaluation test. Stress X can be measured, for example, by a load cell of the tensile tester connected to the evaluation probe 52. Strain Y is calculated by dividing the thickness (initial thickness) of the adhesive sheet 1 before the displacement of the evaluation probe 52 by t0 (μm), and the displacement of the evaluation probe 52 from the start of the displacement by t0 (μm). where d (μm) (see Figure 2D, which is an enlarged view of area A in Figure 2C), the strain is expressed as Y = d / t0. The amount of displacement d corresponds to the amount of deformation t1 in the thickness direction of the adhesive sheet 1 caused by the displacement of the evaluation probe 52.

[0015] An example of a stress-strain curve of an adhesive sheet is shown in FIG. 3. In FIG. 3, stress-strain curves 101, 102, 103, and 104 are shown for four types of adhesive sheets. The adhesive sheets 1 showing curves 101, 103, and 104 satisfy formula (1). The adhesive sheet showing curve 102 does not satisfy formula (1). For curve 101, X max is achieved at its vertex A will be done.

[0016] As shown in Fig. 4, when the dimensions of the optical film 111 change, the volume of the adhesive sheet 112 bonded thereto also changes. In the example of Fig. 4, as the optical film 111 expands in the in-plane direction, the volume of the adhesive sheet 112 increases by the amount of the expanded region 115 (note that reference numerals 114 and 116 denote the ends of the optical film 111 before and after expansion, respectively, and reference numeral 113 denotes an adherend such as a glass substrate). Peak top stress X max is 0.5M Pa or more means that the stress of the adhesive sheet 1 against the volume change is sufficiently large, thereby ensuring durability while suppressing dimensional changes in the optical film 111. Note that the above evaluation test, in which the evaluation probe 52 is displaced at an extremely small speed (2 μm / min), is thought to well reflect the mode of volume change in the adhesive sheet 112 accompanying dimensional changes in the optical film 111.

[0017] X max is 0.6MPa or more, 0.8MPa or more, 0.9MPa or more, 1.0MPa or more It may be 1.2 MPa or more, 1.4 MPa or more, or even 1.5 MPa or more. max The upper limit is, for example, 5 MPa or less.

[0018] In the stress-strain curve, the peak top stress X max Strain Y when stress X reaches m may satisfy the following formula (2): Y m ≧0.05 (2)

[0019] The adhesive sheet 1 showing the curves 101 and 104 in FIG. 3 satisfies the formula (2). m is achieved at vertex A. Y m When the value is 0.05 or more, the volume of the adhesive sheet 1 becomes larger. Even if the change is large, it can withstand the change. m is 0.07 or more, It may be 0.08 or more, 0.09 or more, 0.10 or more, 0.11 or more, 0.12 or more, 0.13 or more, 0.14 or more, 0.15 or more, or even 0.16 or more. m The upper limit of For example, 0.3.

[0020] In the stress-strain curve, stress X is the peak top stress X max After reaching 0.15M Distortion Y when the pressure drops to Pa 0.15 may satisfy the following formula (3): Y 0.15 ≧0.28 (3)

[0021] The adhesive sheet 1 showing the curve 101 satisfies the formula (3). 0.15 is achieved at point B. Y 0.15 A value of 0.28 or greater means that even after the stress of the adhesive sheet 1 resisting the change in volume has peaked, a certain level of stress can be maintained up to a larger strain, for example, by suppressing the generation of regions (voids, etc.) within the adhesive sheet 1 where no adhesive component is present. 0.15 Y may be 0.29 or more, 0.30 or more, 0.31 or more, 0.32 or more, or even 0.33 or more. 0.15 The upper limit is, for example, 1.00 or less.

[0022] Y 0.15 The above range is satisfied for the strain Y m is 0.09 or more, especially 0.13 or more A certain PSA sheet 1 is particularly suitable for improving durability. 0.15 The above range is satisfied, and the peak top stress X maxis 0.9 or more, especially 1 or more, 1.1 or more, and even 1 Adhesive sheets 1 with a modulus of 0.2 or higher are particularly suitable for achieving a balance between suppressing dimensional changes and ensuring durability.

[0023] In the stress-strain curve, stress X is the peak top stress X max Distortion Y when reaching m Stress X is the peak top stress X max When the pressure drops to 0.15 MPa after reaching Distortion Y 0.15 The ratio of Y 0.15 / Y m may satisfy the following formula (4): Y 0.15 / Y m ≧2 (4)

[0024] The pressure-sensitive adhesive sheet 1 showing the curve 101 in FIG. 3 satisfies the formula (4). 0.15 / Y m is 2 or more This means that the generation and rate of voids and the like can be suppressed until the stress of the pressure-sensitive adhesive sheet 1 resisting the change in volume reaches a peak and a larger strain is reached. 0.15 / Y m The ratio Y may be 2.1 or more. 0.15 / Y m The upper limit is, for example, 10 or less.

[0025] 1 x adhesive sheet max , Y m and Y 0.15 varies depending on various factors such as the type, glass transition temperature (Tg) and composition of the base polymer contained in the pressure-sensitive adhesive composition; the type and amount of crosslinking agent; the type and amount of additives such as tackifier; and the drying (curing) conditions for forming a pressure-sensitive adhesive sheet from the pressure-sensitive adhesive composition.

[0026] The thickness of the pressure-sensitive adhesive sheet 1 is, for example, 1 to 200 μm, and may be 5 to 150 μm, or even 10 to 100 μm.

[0027] The storage modulus G' (25°C) of the pressure-sensitive adhesive sheet 1 is, for example, 0.15 MPa or more, and may be 0.2 MPa or more, 0.25 MPa or more, 0.3 MPa or more, 0.5 MPa or more, 0.6 MPa or more, 0.7 MPa or more, 0.8 MPa or more, 0.9 MPa or more, 1.0 MPa or more, 1.1 MPa or more, or even 1.2 MPa or more. The upper limit of the storage modulus G' (25°C) is, for example, 5 MPa or less, and may be 3.0 MPa or less, 2.5 MPa or less, or even 2.0 MPa or less. A high-modulus pressure-sensitive adhesive sheet 1 having a storage modulus G' within the above range is more suitable for suppressing dimensional changes in optical films.

[0028] The storage modulus (25°C) of the adhesive sheet 1 can be evaluated by the following method. A measurement sample made of the material that constitutes the sheet 1 is prepared. The measurement sample is disc-shaped. The measurement sample has a bottom diameter of 8 mm and a thickness of 2 mm. The measurement sample may be a disc-shaped punched-out laminate of multiple adhesive sheets 1. Next, dynamic viscoelasticity measurement is performed on the measurement sample. For example, an ARES-G2 manufactured by TA Instruments can be used for the dynamic viscoelasticity measurement. The storage modulus G' of the adhesive sheet 1 at 25°C can be determined from the results of the dynamic viscoelasticity measurement. The conditions for the dynamic viscoelasticity measurement are as follows: Measurement conditions Frequency: 1Hz Deformation mode: Torsion Measurement temperature: -70℃~150℃ Heating rate: 5°C / min

[0029] The gel fraction of the pressure-sensitive adhesive sheet 1 is, for example, 60% or more, and may be 65% or more, or even 70% or more. The upper limit of the gel fraction is, for example, 99% or less, and may be 98% or less, 97% or less, 96% or less, or even 95% or less. Pressure-sensitive adhesive sheets 1 with a gel fraction within the above range are more suitable for suppressing dimensional changes in optical films.

[0030] The gel fraction of the pressure-sensitive adhesive sheet 1 can be evaluated by the following method. First, approximately 0.2 g is scraped off from the pressure-sensitive adhesive sheet 1 to obtain a small piece. Next, the obtained small piece is wrapped in a stretched porous polytetrafluoroethylene membrane (NTF1122 manufactured by Nitto Denko, average pore size 0.2 μm) and tied with kite string to obtain a test piece. Next, the weight A of the obtained test piece is measured. Weight A is the total weight of the pressure-sensitive adhesive sheet piece, the stretched porous membrane, and the kite string. The total weight B of the stretched porous membrane and kite string used is measured in advance. Next, the test piece is immersed in a 50 mL container filled with ethyl acetate and left to stand at 23°C for one week. After standing, the test piece is removed from the container and dried for two hours in a dryer set at 130°C, after which the weight C of the test piece is measured. The gel fraction of the pressure-sensitive adhesive sheet 1 is calculated from the measured weights A, B, and C using the formula: gel fraction (wt %)=(CB) / (AB)×100(%).

[0031] The pressure-sensitive adhesive sheet 1 can be used, for example, for optical applications. The pressure-sensitive adhesive sheet 1 may be used in an optical laminate and / or an image display device. The pressure-sensitive adhesive sheet 1 is suitable for use in image displays in which suppression of dimensional changes in the optical film is particularly required, such as image displays with narrow frames or image displays with relatively large screen sizes. Use in these image displays, for example, suppresses peeling of the film included in the optical laminate.

[0032] The pressure-sensitive adhesive sheet 1 can be formed from the pressure-sensitive adhesive composition, for example, as follows. For a solvent-based pressure-sensitive adhesive composition, for example, the pressure-sensitive adhesive composition or a mixture of the pressure-sensitive adhesive composition and a solvent is applied to a substrate film, and the resulting coating film is dried to form the pressure-sensitive adhesive sheet 1. The pressure-sensitive adhesive composition is thermally cured by the heat generated during drying. For an active energy ray-curable (photocurable) pressure-sensitive adhesive composition, for example, a mixture containing a monomer(s) that will become a pressure-sensitive adhesive polymer upon polymerization, and optionally a partially polymerized product of the monomer(s), a polymerization initiator, an additive such as a crosslinking agent, and a solvent is applied to a substrate film, and the substrate film is then irradiated with active energy rays to form the pressure-sensitive adhesive sheet 1. The solvent may be removed by drying before irradiating with active energy rays. The substrate film may be a film (release film) whose coating surface has been subjected to a release treatment. However, the type of pressure-sensitive adhesive composition is not limited to the above examples.

[0033] The type of the pressure-sensitive adhesive composition may be, for example, an emulsion type or a hot-melt type. From the viewpoint of forming a pressure-sensitive adhesive sheet 1 with superior durability, the pressure-sensitive adhesive composition may be a solvent type. A solvent-type pressure-sensitive adhesive composition may not contain a photo-curing agent such as an ultraviolet curing agent.

[0034] The pressure-sensitive adhesive sheet 1 formed on the base film can be transferred to any layer. The base film may also be an optical film, in which case an optical laminate containing the pressure-sensitive adhesive sheet 1 and the optical film is obtained.

[0035] The coating onto the substrate film can be carried out by a known method, such as roll coating, kiss roll coating, gravure coating, reverse coating, roll brushing, spray coating, dip roll coating, bar coating, knife coating, air knife coating, curtain coating, lip coating, or extrusion coating using a die coater.

[0036] For the solvent-curable adhesive, the drying temperature after application is, for example, 40 to 200°C. For the adhesive composition (I) described below, the drying temperature may be 160°C or lower, 150°C or lower, 130°C or lower, 120°C or lower, or even 100°C or lower. For example, a combination of the adhesive composition (I) and a drying temperature of 130°C or lower, 120°C or lower, or even 100°C or lower can provide an adhesive sheet 1 with better durability. In other words, the adhesive sheet 1 can be obtained by drying a coating film containing the adhesive composition (I) at a temperature of 130°C or lower, 120°C or lower, or even 100°C or lower. The drying time is, for example, 5 seconds to 20 minutes, or may be 5 seconds to 10 minutes, or even 10 seconds to 5 minutes. For the active energy ray-curable adhesive, the drying temperature and drying time when drying is performed after application may be within the above ranges.

[0037] The composition or mixture to be applied to the substrate film preferably has a viscosity suitable for handling and coating. For this reason, in the case of an active energy ray curable type, the mixture to be applied preferably contains a partial polymer of the monomer(s).

[0038] In one example of the release film, the coated surface is subjected to release treatment with a silicone compound.

[0039] The pressure-sensitive adhesive sheet 1 may be an acrylic pressure-sensitive adhesive sheet formed from an acrylic pressure-sensitive adhesive composition.

[0040] The pressure-sensitive adhesive composition (I) will be described as an example of a pressure-sensitive adhesive composition that can form the pressure-sensitive adhesive sheet 1. However, the pressure-sensitive adhesive composition for forming the pressure-sensitive adhesive sheet 1 is not limited to the pressure-sensitive adhesive composition (I).

[0041] [Adhesive composition (I)] The pressure-sensitive adhesive composition (I) contains a (meth)acrylic polymer (A) and a crosslinking agent (B). The (meth)acrylic polymer (A) is contained in the composition as a main component. In other words, the pressure-sensitive adhesive composition (I) is an acrylic pressure-sensitive adhesive composition. The pressure-sensitive adhesive sheet 1 formed from the pressure-sensitive adhesive composition (I) contains, for example, a crosslinked product of the (meth)acrylic polymer (A).

[0042] In this specification, "(meth)acrylic" means acrylic and methacrylic, and "(meth)acrylate" means acrylate and methacrylate.

[0043] The main component refers to the component with the largest content in the composition. The content of the main component is, for example, 50% by weight or more, and may be 60% by weight or more, 70% by weight or more, or even 75% by weight or more.

[0044] [(Meth)acrylic polymer (A)] The (meth)acrylic polymer (A) preferably has, as a main unit, a structural unit derived from a (meth)acrylic monomer (A1) having an alkyl group having 1 to 30 carbon atoms on the side chain. The alkyl group may be linear or branched. (Meth)acrylic The polymer (A) may have one or more structural units derived from a (meth)acrylic monomer (A1). Examples of the (meth)acrylic monomer (A1) include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, isobutyl (meth)acrylate, n-pentyl (meth)acrylate, isopentyl (meth)acrylate, n-hexyl (meth)acrylate, isohexyl (meth)acrylate, and isoheptyl (meth)acrylate. acrylate, 2-ethylhexyl(meth)acrylate, n-octyl(meth)acrylate, isooctyl(meth)acrylate, n-nonyl(meth)acrylate, isononyl(meth)acrylate, n-decyl(meth)acrylate, isodecyl(meth)acrylate, n-dodecyl(meth)acrylate (lauryl(meth)acrylate), n-tridecyl(meth)acrylate, and n-tetradecyl(meth)acrylate. In this specification, the term "main unit" refers to a unit that accounts for, for example, 50% by weight or more, preferably 60% by weight or more, more preferably 70% by weight or more, and even more preferably 80% by weight or more of all the structural units contained in the polymer.

[0045] The (meth)acrylic polymer (A) may have a structural unit derived from a (meth)acrylic monomer (A1) having a long-chain alkyl group on the side chain. An example of the monomer (A1) is n-dodecyl (meth)acrylate (lauryl (meth)acrylate). In this specification, the term "long-chain alkyl group" refers to an alkyl group having 6 to 30 carbon atoms.

[0046] The (meth)acrylic polymer (A) may have a structural unit derived from a (meth)acrylic monomer (A1) which, when made into a homopolymer, has a glass transition temperature (Tg) in the range of −70 to −20° C. An example of the monomer (A1) is n-butyl acrylate.

[0047] The (meth)acrylic polymer (A) may contain a structural unit other than the structural unit derived from the (meth)acrylic monomer (A1). The structural unit is derived from a monomer (A2) copolymerizable with the (meth)acrylic monomer (A1). The (meth)acrylic polymer (A) may contain one or more types of such structural units.

[0048] An example of the monomer (A2) is an aromatic ring-containing monomer. The aromatic ring-containing monomer may be an aromatic ring-containing (meth)acrylic monomer. Examples of the aromatic ring-containing monomer include phenyl(meth)acrylate, phenoxyethyl(meth)acrylate, benzyl(meth)acrylate, phenoxydiethylene glycol(meth)acrylate, ethylene oxide-modified nonylphenol(meth)acrylate, hydroxyethylated β-naphthol(meth)acrylate, and biphenyl(meth)acrylate. The content of the structural unit derived from the aromatic ring-containing monomer in the (meth)acrylic polymer (A) is, for example, 0 to 50% by weight, and may be 1 to 30% by weight, 5 to 25% by weight, 8 to 20% by weight, 10 to 18% by weight, or even 12 to 16% by weight. The (meth)acrylic polymer (A) having a structural unit derived from an aromatic ring-containing monomer can, for example, improve the compatibility between the (meth)acrylic polymer (A) and the crosslinking agent (B). Improved compatibility can lead to the formation of a highly uniform crosslinked structure and suppression of precipitation of the crosslinking agent (B) or its self-polymer in the pressure-sensitive adhesive sheet 1. In other words, improved compatibility can contribute to further improving the durability of the pressure-sensitive adhesive sheet 1. Furthermore, the above-mentioned effect of improved compatibility is particularly advantageous when the amount of crosslinking agent (B) is increased in order to achieve high elasticity, for example.

[0049] Another example of the monomer (A2) is a hydroxyl group-containing monomer. The hydroxyl group-containing monomer may be a hydroxyl group-containing (meth)acrylic monomer. Examples of the hydroxyl group-containing monomer include 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, and 10-hydroxydecyl (meth)acrylate. hydroxyalkyl (meth)acrylates such as 12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)-methyl acrylate The hydroxyl groups can react with the crosslinking agent (B). From the viewpoint of increasing the uniformity of the crosslinked structure, the content of the structural units derived from the hydroxyl group-containing monomer in the (meth)acrylic polymer (A) may be 1% by weight or less, 0.5% by weight or less, or even 0.1% by weight or less, or may even be 0% by weight (no such structural units may be contained).

[0050] Monomer (A2) may be a carboxyl group-containing monomer, an amino group-containing monomer, or an amide group-containing monomer. Examples of the carboxyl group-containing monomer are (meth)acrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, and crotonic acid. Examples of the amino group-containing monomer are N,N-dimethylaminoethyl (meth)acrylate and N,N-dimethylaminopropyl (meth)acrylate. Examples of the amide group-containing monomer include acrylamide-based monomers such as (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N-isopropylacrylamide, N-methyl(meth)acrylamide, N-butyl(meth)acrylamide, N-hexyl(meth)acrylamide, N-methylol(meth)acrylamide, N-methylol-N-propane(meth)acrylamide, aminomethyl(meth)acrylamide, aminoethyl(meth)acrylamide, mercaptomethyl(meth)acrylamide, and mercaptoethyl(meth)acrylamide; N-acryloyl heterocyclic monomers such as N-(meth)acryloylmorpholine, N-(meth)acryloylpiperidine, and N-(meth)acryloylpyrrolidine; and N-vinyl group-containing lactam-based monomers such as N-vinylpyrrolidone and N-vinyl-ε-caprolactam. The (meth)acrylic polymer (A) having a structural unit derived from a carboxyl group-containing monomer, particularly acrylic acid, can, for example, enhance the self-polymerization property of the crosslinking agent (B). The improved self-polymerization property of the crosslinking agent (B) can contribute to suppressing peeling of the PSA sheet, particularly in a humid environment, and stabilizing the physical properties of the PSA sheet in a system with a high content of the crosslinking agent (B).

[0051] Monomer (A2) may be a polyfunctional monomer. Examples of polyfunctional monomers include polyfunctional acrylates such as hexanediol di(meth)acrylate (1,6-hexanediol di(meth)acrylate), butanediol di(meth)acrylate, (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethane tri(meth)acrylate, allyl (meth)acrylate, vinyl (meth)acrylate, epoxy acrylate, polyester acrylate, and urethane acrylate; and divinylbenzene. The polyfunctional acrylate is preferably 1,6-hexanediol diacrylate or dipentaerythritol hexa(meth)acrylate.

[0052] The total content of structural units derived from carboxyl group-containing monomers, amino group-containing monomers, amide group-containing monomers, and polyfunctional monomers in the (meth)acrylic polymer (A) is preferably 20% by weight or less, more preferably 10% by weight or less, and even more preferably 8% by weight or less. When the (meth)acrylic polymer (A) contains these structural units, the total content is, for example, 0.01% by weight or more, and may be 0.05% by weight or more. The (meth)acrylic polymer (A) does not necessarily have to contain structural units derived from polyfunctional monomers.

[0053] Examples of other monomers (A2) are 2-methoxyethyl (meth)acrylate, (meth)acrylate alkoxyalkyl (meth)acrylates such as 2-ethoxyethyl acrylate, methoxytriethylene glycol (meth)acrylate, 3-methoxypropyl (meth)acrylate, 3-ethoxypropyl (meth)acrylate, 4-methoxybutyl (meth)acrylate, and 4-ethoxybutyl (meth)acrylate; epoxy group-containing monomers such as glycidyl (meth)acrylate and methyl glycidyl (meth)acrylate; sulfonic acid group-containing monomers such as sodium vinyl sulfonate; phosphate group-containing monomers; (meth)acrylic acid esters having alicyclic hydrocarbon groups such as cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, and isobornyl (meth)acrylate; vinyl esters such as vinyl acetate and vinyl propionate; aromatic vinyl compounds such as styrene and vinyltoluene; olefins or dienes such as ethylene, propylene, butadiene, isoprene, and isobutylene; vinyl ethers such as vinyl alkyl ethers; and vinyl chloride.

[0054] The total content of the structural units derived from the other monomers (A2) in the (meth)acrylic polymer (A) is, for example, 30% by weight or less, may be 10% by weight or less, and is preferably 0% by weight (not including such structural units).

[0055] The (meth)acrylic polymer (A) can be formed by polymerizing one or more of the above-mentioned monomers by a known method. A monomer and a partial polymer of the monomer may also be polymerized. The polymerization can be carried out, for example, by solution polymerization, emulsion polymerization, bulk polymerization, thermal polymerization, or active energy ray polymerization. Solution polymerization and active energy ray polymerization are preferred because they allow the formation of a pressure-sensitive adhesive sheet 1 with excellent optical transparency. The polymerization is preferably carried out while avoiding contact between the monomer and / or the partial polymer and oxygen. For this purpose, for example, polymerization in an inert gas atmosphere such as nitrogen, or polymerization in a state where oxygen is blocked by a resin film or the like, can be employed. The (meth)acrylic polymer (A) formed may be in any form, such as a random copolymer, a block copolymer, or a graft copolymer.

[0056] The polymerization system for forming the (meth)acrylic polymer (A) may contain one or more polymerization initiators. The type of polymerization initiator can be selected depending on the polymerization reaction, and may be, for example, a thermal polymerization initiator or a photopolymerization initiator.

[0057] Examples of solvents used in solution polymerization include esters such as ethyl acetate and n-butyl acetate; aromatic hydrocarbons such as toluene and benzene; aliphatic hydrocarbons such as n-hexane and n-heptane; alicyclic hydrocarbons such as cyclohexane and methylcyclohexane; and ketones such as methyl ethyl ketone and methyl isobutyl ketone. However, the solvent is not limited to the above examples. The solvent may be a mixed solvent of two or more solvents.

[0058] Examples of polymerization initiators used in solution polymerization include azo polymerization initiators, peroxide polymerization initiators, and redox polymerization initiators. Examples of peroxide polymerization initiators include dibenzoyl peroxide and t-butyl permaleate. Among these, the azo polymerization initiators disclosed in JP-A-2002-69411 are preferred. Examples of the azo polymerization initiator include 2,2'-azobisisobutyronitrile (AIBN), 2,2'-azobis-2-methylbutyronitrile, 2,2'-azobis(2-methylpropionate)dimethyl, and 4,4'-azobis-4-cyanovaleric acid. However, the polymerization initiator is not limited to the above examples. The amount of the azo polymerization initiator used is, for example, 0.05 to 0.5 parts by weight, or may be 0.1 to 0.3 parts by weight, per 100 parts by weight of the total amount of monomers.

[0059] The active energy rays used in the active energy ray polymerization include, for example, ionizing radiation such as α rays, β rays, γ rays, neutron rays, and electron beams, as well as ultraviolet rays. The active energy rays are preferably ultraviolet rays. Polymerization by irradiation with ultraviolet rays is also called photopolymerization. The polymerization system for active energy ray polymerization typically contains a photopolymerization initiator. The polymerization conditions for the active energy polymerization are (meth)acrylic acid, ... There are no limitations as long as the acrylic polymer (A) is formed.

[0060] Examples of the photopolymerization initiator include a benzoin ether-based photopolymerization initiator, an acetophenone-based photopolymerization initiator, an α-ketol-based photopolymerization initiator, an aromatic sulfonyl chloride-based photopolymerization initiator, a photoactive oxime-based photopolymerization initiator, a benzoin-based photopolymerization initiator, a benzyl-based photopolymerization initiator, a benzophenone-based photopolymerization initiator, a ketal-based photopolymerization initiator, and a thioxanthone-based photopolymerization initiator, although the photopolymerization initiator is not limited to the above examples.

[0061] Examples of benzoin ether-based photopolymerization initiators include benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, benzoin isopropyl ether, benzoin isobutyl ether, 2,2-dimethoxy-1,2-diphenylethan-1-one, and anisole methyl ether. Examples of acetophenone-based photopolymerization initiators include 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexyl phenyl ketone, 4-phenoxydichloroacetophenone, and 4-(t-butyl)dichloroacetophenone. Examples of α-ketol-based photopolymerization initiators include 2-methyl-2-hydroxypropiophenone and 1-[4-(2-hydroxyethyl)phenyl]-2-methylpropan-1-one. Examples of aromatic sulfonyl chloride-based photopolymerization initiators include 2-naphthalenesulfonyl chloride. An example of a photoactive oxime-based photopolymerization initiator is 1-phenyl-1,1-propanedione-2-(o-ethoxycarbonyl)-oxime. An example of a benzoin-based photopolymerization initiator is benzoin. An example of a benzyl-based photopolymerization initiator is benzil. An example of a benzophenone-based photopolymerization initiator is benzophenone, benzoylbenzoic acid, 3,3'-dimethyl-4-methoxybenzophenone, polyvinylbenzophenone, or α-hydroxycyclohexyl phenyl ketone. An example of a ketal-based photopolymerization initiator is benzil dimethyl ketal. An example of a thioxanthone-based photopolymerization initiator is thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 2,4-diisopropylthioxanthone, or dodecylthioxanthone.

[0062] The amount of the photopolymerization initiator used is, for example, 0.01 to 1 part by weight, and may be 0.05 to 0.5 parts by weight, relative to 100 parts by weight of the total amount of the monomers.

[0063] The weight average molecular weight (Mw) of the (meth)acrylic polymer (A) is, for example, 1,000,000 to 2,500,000, and from the viewpoint of the durability and heat resistance of the PSA sheet, may be 1,200,000 or more, or even 1,400,000 or more. The weight average molecular weight (Mw) of the polymer and oligomer in this specification is a value (polystyrene equivalent) based on measurement by GPC (gel permeation chromatography).

[0064] The content of the (meth)acrylic polymer (A) in the pressure-sensitive adhesive composition (I) is, for example, 50% by weight or more, 60% by weight or more, 70% by weight or more, or even 80% by weight or more, in terms of solid content. The upper limit of the content is, for example, 99% by weight or less, 97% by weight or less, 95% by weight or less, 93% by weight or less, or even 90% by weight or less.

[0065] [Crosslinking agent (B)] The crosslinking agent (B) is typically a polyfunctional crosslinking agent having two or more crosslinking reactive groups per molecule. The crosslinking agent (B) may also be a trifunctional or higher crosslinking agent having three or more crosslinking reactive groups per molecule. The upper limit of the number of crosslinking reactive groups per molecule is, for example, five.

[0066] The crosslinking agent (B) is, for example, an isocyanate-based crosslinking agent. The isocyanate-based crosslinking agent contains an isocyanate group as a crosslinking reactive group. The isocyanate-based crosslinking agent (B) is an aromatic isocyanate compound, an alicyclic isocyanate compound, or an aliphatic isocyanate compound. It's okay to have one.

[0067] Examples of aromatic isocyanate compounds that can be used in the crosslinking agent (B) include phenylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 2,2'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-toluidine diisocyanate, 4,4'-diphenyl ether diisocyanate, 4,4'-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, and xylylene diisocyanate.

[0068] Examples of the alicyclic isocyanate compound that can be used in the crosslinking agent (B) include 1,3-cyclopentene diisocyanate, 1,3-cyclohexane diisocyanate, 1,4-cyclohexane diisocyanate, isophorone diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated xylylene diisocyanate, hydrogenated tolylene diisocyanate, and hydrogenated tetramethylxylylene diisocyanate.

[0069] Examples of aliphatic isocyanate compounds that can be used in the crosslinking agent (B) are trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylene diisocyanate, 1,3-butylene diisocyanate, dodecamethylene diisocyanate, and 2,4,4-trimethylhexamethylene diisocyanate.

[0070] The crosslinking agent (B) may be a derivative of the isocyanate compound. Examples of the derivative include multimers (dimers, trimers, pentamers, etc.), adducts obtained by addition to polyhydric alcohols such as trimethylolpropane, urea-modified products, biuret-modified products, allophanate-modified products, isocyanurate-modified products, carbodiimide-modified products, and urethane prepolymers obtained by addition to polyether polyols, polyester polyols, acrylic polyols, polybutadiene polyols, polyisoprene polyols, etc.

[0071] The crosslinking agent (B) is preferably an aromatic isocyanate compound or a derivative thereof, more preferably tolylene diisocyanate or a derivative thereof (i.e., a tolylene diisocyanate (TDI) crosslinking agent). TDI crosslinking agents have better reaction uniformity than xylylene diisocyanate or a derivative thereof (i.e., a xylylene diisocyanate (XDI) crosslinking agent). An example of a TDI crosslinking agent is an adduct of tolylene diisocyanate and a polyfunctional alcohol, and a more specific example is a trimethylolpropane / tolylene diisocyanate trimer adduct.

[0072] Commercially available crosslinking agents (B) can be used, such as Millionate MT, Millionate MTL, Millionate MR-200, Millionate MR-400, Coronate L, Coronate HL, and Coronate HX (all manufactured by Tosoh Corporation; all trade names), and Takenate D-102, Takenate D-103, Takenate D-110N, Takenate D-120N, Takenate D-140N, Takenate D-160N, Takenate D-165N, Takenate D-170HN, Takenate D-178N, Takenate 500, and Takenate 600 (all manufactured by Mitsui Chemicals; all trade names). As the crosslinking agent (B), Coronate L, Takenate D-102 and Takenate D-103 (all of which are trimethylolpropane / tolylene diisocyanate trimer adducts) can be preferably used.

[0073] The pressure-sensitive adhesive composition (I) may contain one or more crosslinking agents (B).

[0074] The amount of the crosslinking agent (B) in the pressure-sensitive adhesive composition (I) is, for example, 0.5 parts by weight or more and 30 parts by weight or less, and 1 part by weight or more, relative to 100 parts by weight of the (meth)acrylic polymer (A). It may be up to 28 parts by weight, 5 parts by weight or more and 25 parts by weight or less, 8 parts by weight or more and 20 parts by weight or less, 10 parts by weight or more and 18 parts by weight or less, more than 10 parts by weight or more and 15 parts by weight or less, or 11 parts by weight or more and 13 parts by weight or less.

[0075] According to the studies of the present inventors, when the blending amount of crosslinking agent (B) is 5 parts by weight or more, particularly 8 parts by weight or more, 10 parts by weight or more, or even 11 parts by weight or more, crosslinking agents (B) react with each other during the formation of the pressure-sensitive adhesive sheet 1, and a self-polymer of the crosslinking agent (B), in other words, a polymer containing structural units derived from the crosslinking agent (B) as a main component, is easily formed. In the self-polymer, the content of structural units derived from the crosslinking agent (B) is, for example, 70% by weight or more, and may be 90% by weight or more, 95% by weight or more, or even 99% by weight or more. The self-polymer may be composed only of structural units derived from the crosslinking agent (B). The formation of the self-polymer imparts sufficient cohesive force to the pressure-sensitive adhesive sheet 1, thereby increasing the peak top stress X max Achievement of The pressure-sensitive adhesive sheet 1 may also have an interpenetrating network (IPN) structure of a crosslinked product of the (meth)acrylic polymer (A) and a self-polymer of the crosslinking agent (B). The IPN structure is suitable for improving the durability of the pressure-sensitive adhesive sheet 1.

[0076] Other examples of the crosslinking agent (B) include peroxide-based crosslinking agents, epoxy-based crosslinking agents, imine-based crosslinking agents, and polyfunctional metal chelates. However, the crosslinking agent (B) is preferably an isocyanate-based crosslinking agent. When the pressure-sensitive adhesive composition (I) contains a crosslinking agent (B) other than an isocyanate-based crosslinking agent, the total amount of the crosslinking agent (B) is preferably 0.1 to 5 parts by weight, more preferably 0.1 to 3 parts by weight, 0.1 to 2 parts by weight, and 0.1 to 1 part by weight, per 100 parts by weight of the (meth)acrylic polymer (A). The pressure-sensitive adhesive composition (I) does not necessarily need to contain a crosslinking agent (B) other than an isocyanate-based crosslinking agent, such as an epoxy-based crosslinking agent.

[0077] [(Meth)acrylic oligomer] The pressure-sensitive adhesive composition (I) may further contain a (meth)acrylic oligomer (D).

[0078] The (meth)acrylic oligomer (D) may have the same composition as the above-mentioned (meth)acrylic polymer (A) except for the weight-average molecular weight (Mw). The weight-average molecular weight (Mw) of the (meth)acrylic oligomer (D) may be, for example, 1,000 or more, 2,000 or more, 3,000 or more, or even 4,000 or more. The upper limit of the weight-average molecular weight (Mw) of the (meth)acrylic oligomer may be, for example, 30,000 or less, 15,000 or less, 10,000 or less, or even 7,000 or less.

[0079] The (meth)acrylic oligomer (D) has, for example, one or more structural units derived from the following monomers: methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, alkyl (meth)acrylates such as methyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, and dodecyl (meth)acrylate; esters of (meth)acrylic acid and alicyclic alcohols such as cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and dicyclopentanyl (meth)acrylate; aromatic ring-containing (meth)acrylates such as phenyl (meth)acrylate and benzyl (meth)acrylate; and (meth)acrylates obtained from terpene compound derivative alcohols.

[0080] The (meth)acrylic oligomer (D) preferably has a structural unit derived from a (meth)acrylic monomer having a relatively bulky structure. In this case, the adhesiveness of the pressure-sensitive adhesive sheet can be further improved. Examples of such acrylic monomers include alkyl (meth)acrylates having an alkyl group with a branched structure, such as isobutyl (meth)acrylate and t-butyl (meth)acrylate; esters of (meth)acrylic acid and alicyclic alcohols, such as cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and dicyclopentanyl (meth)acrylate; and aromatic ring-containing (meth)acrylates, such as phenyl (meth)acrylate and benzyl (meth)acrylate. The monomer preferably has a cyclic structure, and more preferably has two or more cyclic structures. Furthermore, when ultraviolet irradiation is carried out during polymerization of the (meth)acrylic oligomer (D) and / or during formation of the pressure-sensitive adhesive sheet, it is preferable that the above-mentioned monomer does not have an unsaturated bond, since this makes it less likely that the progress of polymerization and / or formation will be inhibited. For example, an alkyl (meth)acrylate having an alkyl group with a branched structure, or an ester of (meth)acrylic acid and an alicyclic alcohol can be used.

[0081] Specific examples of the (meth)acrylic oligomer (D) include a copolymer of butyl acrylate, methyl acrylate, and acrylic acid, a copolymer of cyclohexyl methacrylate and isobutyl methacrylate, a copolymer of cyclohexyl methacrylate and isobornyl methacrylate, a copolymer of cyclohexyl methacrylate and acryloylmorpholine, a copolymer of cyclohexyl methacrylate and diethylacrylamide, a copolymer of 1-adamantyl acrylate and methyl methacrylate, a copolymer of dicyclopentanyl methacrylate and isobornyl methacrylate, a copolymer of methyl methacrylate and at least one selected from dicyclopentanyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, isobornyl acrylate, and cyclopentanyl methacrylate, a homopolymer of dicyclopentanyl acrylate, a homopolymer of 1-adamantyl methacrylate, and a homopolymer of 1-adamantyl acrylate.

[0082] For the polymerization of the (meth)acrylic oligomer (D), the above-mentioned method for polymerizing the (meth)acrylic polymer (A) can be used.

[0083] When the pressure-sensitive adhesive composition (I) contains the (meth)acrylic oligomer (D), the blending amount thereof may be, for example, 70 parts by weight or less, 50 parts by weight or less, or even 40 parts by weight or less, per 100 parts by weight of the (meth)acrylic polymer (A). The lower limit of the blending amount may be, for example, 1 part by weight or more, 2 parts by weight or more, or even 3 parts by weight or more, per 100 parts by weight of the (meth)acrylic polymer (A). The pressure-sensitive adhesive composition (I) does not necessarily contain the (meth)acrylic oligomer (D).

[0084] [Additives] The pressure-sensitive adhesive composition (I) may contain other additives. Examples of the additives include silane coupling agents, colorants such as pigments and dyes, surfactants, plasticizers, tackifiers, surface lubricants, leveling agents, rework improvers, softeners, antioxidants, antiaging agents, light stabilizers, UV absorbers, polymerization inhibitors, antistatic agents (alkali metal salts, which are ionic compounds, ionic liquids, ionic solids, etc.), inorganic fillers, organic fillers, powders such as metal powders, particles, and foil-like materials. The additives may be present in an amount of, for example, 10 parts by weight or more per 100 parts by weight of the (meth)acrylic polymer (A). The amount of the hydroxybenzoate can be in the range of 0.5 to 5 parts by weight, preferably 5 parts by weight or less, and more preferably 1 part by weight or less.

[0085] Examples of the silane coupling agent include epoxy group-containing silane coupling agents such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; 3-aminopropyltrimethoxysilane, N-2-(aminopropyltriethoxysilane); amino group-containing silane coupling agents such as 3-acryloxypropyltrimethoxysilane and 3-methacryloxypropyltriethoxysilane; and isocyanate group-containing silane coupling agents such as 3-isocyanatepropyltriethoxysilane.

[0086] When the pressure-sensitive adhesive composition (I) contains a silane coupling agent, the blending amount thereof is, for example, 5 parts by weight or less, and may be 3 parts by weight or less, 1 part by weight or less, 0.5 parts by weight or less, 0.2 parts by weight or less, 0.1 parts by weight or less, or even 0.05 parts by weight or less, relative to 100 parts by weight of the (meth)acrylic polymer (A). The pressure-sensitive adhesive composition (I) does not necessarily contain a silane coupling agent.

[0087] The pressure-sensitive adhesive composition (I) may be, for example, an emulsion type, a solvent type (solution type), an active energy ray curable type (photocurable type), or a hot melt type. From the viewpoint of forming a pressure-sensitive adhesive sheet 1 having superior durability, the pressure-sensitive adhesive composition (I) may be a solvent type. The solvent-type pressure-sensitive adhesive composition (I) may not contain a photocuring agent such as an ultraviolet curing agent.

[0088] [Optical laminate] An example of the optical laminate of this embodiment is shown in Fig. 5. The optical laminate 10A in Fig. 5 includes an adhesive sheet 1 and an optical film 2. The adhesive sheet 1 and the optical film 2 are laminated together. The optical laminate 10A can be used as an optical film with an adhesive sheet.

[0089] Examples of the optical film 2 include a polarizing plate, a retardation film, and a laminated film including a polarizing plate and / or a retardation film. However, the optical film 2 is not limited to the above examples. The optical film 2 may also include a glass film.

[0090] The polarizing plate includes a polarizer. A polarizer protective film may be bonded to at least one surface of the polarizer. Any pressure-sensitive adhesive or adhesive may be used to bond the polarizer and the polarizer protective film. An adhesive sheet 1 may be used for bonding. The polarizer is typically a polyvinyl alcohol (PVA) film in which iodine has been oriented by stretching, such as in-air stretching (dry stretching) or stretching in boric acid water.

[0091] A retardation film is a film having birefringence in the in-plane direction and / or the thickness direction, and is, for example, a stretched resin film or a film in which a liquid crystal material is oriented and fixed.

[0092] The retardation film may be a λ / 4 plate, a λ / 2 plate, an anti-reflection retardation film (see, for example, paragraphs 0221, 0222, and 0228 of JP 2012-133303 A), a viewing angle compensation retardation film (see, for example, paragraphs 0225 and 0226 of JP 2012-133303 A), or an obliquely oriented viewing angle compensation retardation film (see, for example, paragraph 0227 of JP 2012-133303 A). The retardation film is not limited to the above examples, as long as it has birefringence in the in-plane direction and / or the thickness direction. The retardation value, arrangement angle, three-dimensional birefringence, whether the retardation film is single-layer or multi-layer, and the like are also not limited. Known films can be used as the retardation film.

[0093] The thickness of the optical film 2 is, for example, 1 to 200 μm. The thickness of the optical film 2, which is a polarizing plate, is, for example, 1 to 150 μm, and may be 100 μm or less, 75 μm or less, 50 μm or less, 20 μm or less, or even 15 μm or less. The lower limit of the thickness may be 10 μm or more, 20 μm or more, 50 μm or more, 75 μm or more, or even 100 μm or more.

[0094] The optical film 2 may be a single layer or a laminated film composed of two or more layers. When the optical film 2 is a laminated film, the pressure-sensitive adhesive sheet 1 may be used to bond the layers together.

[0095] Another example of the optical laminate of the present embodiment is shown in Fig. 6. The optical laminate 10B in Fig. 6 has a laminated structure in which a separator 3, a pressure-sensitive adhesive sheet 1, and an optical film 2 are laminated in this order. By peeling off the separator 3, the optical laminate 10B can be used as an optical film with a pressure-sensitive adhesive sheet.

[0096] The separator 3 is typically a resin film. Examples of resins that can be used to form the separator 3 include polyesters such as polyethylene terephthalate (PET), polyolefins such as polyethylene and polypropylene, polycarbonate, acrylic, polystyrene, polyamide, and polyimide. The surface of the separator 3 that comes into contact with the pressure-sensitive adhesive sheet 1 may be subjected to a release treatment. The release treatment may be, for example, a treatment using a silicone compound. However, the separator 3 is not limited to the above examples. The separator 3 is peeled off when the optical laminate 10B is used, for example, when it is attached to the image-forming layer.

[0097] Another example of the optical laminate of this embodiment is shown in Fig. 7. The optical laminate 10C in Fig. 7 has a laminated structure in which a separator 3, a pressure-sensitive adhesive sheet 1, a retardation film 2A, an interlayer pressure-sensitive adhesive 4, and a polarizing plate 2B are laminated in this order. After peeling off the separator 3, the optical laminate 10C can be used by being attached to, for example, an image-forming layer.

[0098] A known adhesive can be used for the interlayer adhesive 4. The adhesive sheet 1 may be used as the interlayer adhesive 4.

[0099] Another example of the optical laminate of this embodiment is shown in Fig. 8. The optical laminate 10D in Fig. 8 has a laminated structure in which a separator 3, an adhesive sheet 1, a retardation film 2A, an interlayer adhesive 4, a polarizing plate 2B, and a protective film 5 are laminated in this order. After peeling off the separator 3, the optical laminate 10D can be used by being attached to, for example, an image forming layer.

[0100] The protective film 5 has the function of protecting the optical film 2 (polarizing plate 2B), which is the outermost layer, during distribution and storage of the optical laminate 10D and when the optical laminate 10D is incorporated into an image display device. The protective film 5 may also function as a window to the external space when incorporated into an image display device. The protective film 5 is typically a resin film. Examples of resins constituting the protective film 5 include polyesters such as PET, polyolefins such as polyethylene and polypropylene, acrylics, cycloolefins, polyimides, and polyamides, with polyesters being preferred. However, the protective film 5 is not limited to the above examples. The protective film 5 may also be a glass film or a laminated film including a glass film. The protective film 5 may be subjected to surface treatments such as anti-glare, anti-reflection, and anti-static.

[0101] The protective film 5 may be bonded to the optical film 2 with any adhesive. Bonding with an adhesive sheet 1 is also possible.

[0102] The optical laminate of this embodiment can be distributed and stored, for example, as a rolled body obtained by rolling up a strip-shaped optical laminate, or as a sheet-shaped optical laminate.

[0103] The optical laminate of this embodiment is typically used in image display devices. Image display devices include, for example, EL displays such as liquid crystal displays, organic EL displays, and inorganic EL displays. It is a display.

[0104] [Image display device] An example of an image display device of this embodiment is shown in Fig. 9. The image display device 20 of Fig. 9 has a laminated structure in which a substrate 7, an image forming layer (e.g., an organic EL layer or a liquid crystal layer) 6, an adhesive sheet 1, a retardation film 2A, an interlayer adhesive 4, a polarizing plate 2B, and a protective film 5 are laminated in this order. The image display device 20 has the optical laminates 10A, 10B, 10C, and 10D of Figs. 5 to 8 (excluding the separator 3). The substrate 7 and the image forming layer 6 may have the same configurations as the substrate and the image forming layer, respectively, of known image display devices.

[0105] The image display device 20 in Fig. 9 may be an organic EL display or a liquid crystal display. However, the image display device 20 is not limited to this example. The image display device 20 may also be an electroluminescence (EL) display, a plasma display (PD), a field emission display (FED), or the like. The image display device 20 may be used for home appliances, in-vehicle applications, public information displays (PID), and the like.

[0106] The image display device of this embodiment can have any configuration as long as it includes the optical laminate of this embodiment. [Example]

[0107] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the examples shown below.

[0108] First, the evaluation methods for the (meth)acrylic polymers and pressure-sensitive adhesive sheets produced in the examples and comparative examples will be described.

[0109] [Weight average molecular weight (Mw)] The weight average molecular weight (Mw) of the (meth)acrylic polymer was evaluated by GPC under the following conditions. Analytical equipment: Waters, Acquity APC Column: Tosoh G7000HXL+GMHXL+GMHXL Column temperature: 40℃ Eluent: tetrahydrofuran (acid added) ·Flow rate: 0.8mL / min ·Injection volume: 100μL Detector: Differential refractometer (RI) Standard sample: Agilent, polystyrene (PS)

[0110] Stress-Strain Curve The stress-strain curve of the pressure-sensitive adhesive sheet was determined by the above-mentioned evaluation test using a tacking tester (TAC1000, manufactured by Rhesca). However, Corning Eagle XG was used for the glass plate 51. The evaluation sheet, which had been laminated on the glass plate 51 by stacking the prepared pressure-sensitive adhesive sheet and then bonding it to each other by heating I using an autoclave (50°C, 5 atmospheres (absolute pressure), 15 minutes) to ensure a thickness of 200 μm or more, was attached. After bonding, the bonding between the evaluation sheet and the glass plate 51 was stabilized by heating II using an autoclave (50°C, 5 atmospheres (absolute pressure), 15 minutes). A 5 mm diameter probe (SUS) manufactured by Rhesca, conforming to the ASTM D-2979 standard, was used for the evaluation probe 52. From the obtained curves, the peak top stress X max , distortion Y m and distortion Y 0.15 and the ratio Y 0.15 / Y m The evaluation test was carried out in an atmosphere of 23°C and 55% RH.

[0111] [Storage modulus G' (25℃)] The storage modulus G' (25°C) of the PSA sheet was evaluated using the method described above. However, the measurement sample was prepared by punching out a disc from a laminate obtained by stacking the manufactured PSA sheets. The dynamic viscoelasticity of the measurement sample was measured using an ARES-G2 manufactured by TA Instruments.

[0112] [Gel fraction] The gel fraction of the pressure-sensitive adhesive sheet was evaluated by the method described above.

[0113] [Humidity durability] The humidity durability (corresponding to an accelerated durability test) of the pressure-sensitive adhesive sheet was evaluated using the following method. First, a circularly polarizing plate with a pressure-sensitive adhesive sheet was formed, with one exposed surface of each of the pressure-sensitive adhesive sheets produced in the Examples and Comparative Examples. Next, the circularly polarizing plate was fixed to the surface of a glass plate (Corning Eagle XG) via the pressure-sensitive adhesive sheet. The circularly polarizing plate was fixed in an atmosphere of 23°C and 50% RH. Next, the plate was treated in an autoclave at 50°C and 5 atmospheres (absolute pressure) for 15 minutes, and then left to cool to 23°C to stabilize the bonding of the circularly polarizing plate to the glass plate. After that, the plate was left in a heated and humidified atmosphere at 60°C and 95% RH for 500 hours. After leaving the plate, the atmosphere was returned to 23°C and 50% RH, and the presence of peeling of the circularly polarizing plate from the glass plate and the formation of bubbles between the glass plate and the circularly polarizing plate were visually confirmed, and the humidity durability was evaluated as follows. A: No changes in appearance such as foaming or peeling are observed. B: A small amount of isolated peeling or bubbling was observed at the edge, but this was within the range that would not cause any problems in practical use. C: Slight continuous peeling or bubbling is observed at the edge, but is within a range that does not cause any practical problems. D: Significant peeling or bubbling is observed at the edge, and there is a problem in practical use.

[0114] The method for forming the circularly polarizing plate with the adhesive sheet used for evaluating the humidity durability is described below.

[0115] <Preparation of Polarizing Plate P1> (Fabrication of polarizer) A long polyvinyl alcohol (PVA) resin film (manufactured by Kuraray, product name "PE3000", thickness 30 μm) was uniaxially stretched in the longitudinal direction (total stretching ratio 5.9 times) using a roll stretching machine. At the same time, the resin film was subjected to the following treatments in order: swelling, dyeing, crosslinking, washing, and drying. A 12 μm-thick polarizer was produced. In the swelling treatment, the resin film was stretched 2.2 times while being treated with pure water at 20°C. In the dyeing treatment, the resin film was stretched 1.4 times while being treated with an aqueous solution at 30°C containing iodine and potassium iodide in a weight ratio of 1:7. The iodine concentration in the aqueous solution was adjusted so that the single transmittance of the produced polarizer would be 45.0%. A two-stage crosslinking treatment was used. In the first stage of the crosslinking treatment, the resin film was stretched 1.2 times while being treated with an aqueous solution at 40°C containing boric acid and potassium iodide. The aqueous solution used in the first crosslinking treatment had a boric acid content of 5.0 wt % and a potassium iodide content of 3.0 wt %. In the second crosslinking treatment, the resin film was stretched 1.6 times while being treated with a 65°C aqueous solution containing dissolved boric acid and potassium iodide. The aqueous solution used in the second crosslinking treatment had a boric acid content of 4.3 wt % and a potassium iodide content of 5.0 wt %. A potassium iodide aqueous solution at 20°C was used for the washing treatment. The potassium iodide content of the aqueous solution used for the washing treatment was 2.6 wt %. The drying treatment was carried out at 70°C for 5 minutes.

[0116] (Preparation of polarizing plate P1) A triacetyl cellulose (TAC) film was applied to each of the main surfaces of the polarizer. A TAC film (Konica Minolta, product name "KC2UA", thickness 25 μm) was attached to the polarizer using a polyvinyl alcohol adhesive. However, the TAC film attached to one of the main surfaces had a hard coat (thickness 7 μm) formed on the main surface opposite the polarizer side. In this way, a polarizing plate P1 having a configuration of protective layer with hard coat / polarizer / protective layer (without hard coat) was obtained.

[0117] <Preparation of Retardation Film R1> (Preparation of First Retardation Film) 26.2 parts by weight of isosorbide (ISB), 100.5 parts by weight of 9,9-[4-(2-hydroxyethoxy)phenyl]fluorene (BHEPF), 10.7 parts by weight of 1,4-cyclohexanedimethanol (1,4-CHDM), 105.1 parts by weight of diphenyl carbonate (DPC), and 0.591 parts by weight of cesium carbonate (0.2 wt % aqueous solution) as a catalyst were charged into a reaction vessel and dissolved under a nitrogen atmosphere (approximately 15 minutes). The heat transfer temperature in the reaction vessel was set to 150°C, and stirring was performed as necessary. Next, the pressure inside the reaction vessel was reduced to 13.3 kPa, and the heat transfer temperature was increased to 190°C over 1 hour. Phenol evolved as the heat transfer temperature increased was removed from the reaction vessel (the same applies below). Next, the temperature inside the reaction vessel was maintained at 190°C for 15 minutes, after which the pressure inside the reaction vessel was changed to 6.67 kPa and the heat transfer medium temperature was increased to 230°C over 15 minutes. When the stirring torque of the reactor's agitator increased, the heat transfer medium temperature was increased to 250°C over 8 minutes, and the pressure inside the reaction vessel was further reduced to 0.200 kPa or less. After reaching the predetermined stirring torque, the reaction was terminated, and the resulting reaction product was extruded into water and pelletized. In this way, a polycarbonate resin with a composition of BHEPF / ISB / 1,4-CHDM = 47.4 mol% / 37.1 mol% / 15.5 mol% was obtained. The glass transition temperature of the resulting polycarbonate resin was 136.6°C and the reduced viscosity was 0.395 dL / g.

[0118] The prepared polycarbonate resin pellets were vacuum-dried at 80°C for 5 hours, and then a long resin film with a thickness of 120 μm was obtained using a film-forming device equipped with a single-screw extruder (manufactured by Isuzu Chemical Engineering, screw diameter 25 mm, cylinder temperature setting 220°C), a T-die (width 200 mm, temperature setting 220°C), a chill roll (temperature setting 120-130°C), and a winder. Next, the obtained resin film was stretched in the width direction using a tenter stretching machine at a stretching temperature of 137-139°C and a stretch ratio of 2.5 times to obtain a first retardation film.

[0119] (Preparation of second retardation film) A liquid crystal coating solution was prepared by dissolving 20 parts by weight of a side-chain liquid crystal polymer (weight average molecular weight 5000) represented by the following chemical formula (I) (wherein 65 and 35 represent the mol% of each structural unit), 80 parts by weight of a polymerizable liquid crystal exhibiting a nematic liquid crystal phase (manufactured by BASF, trade name "Paliocolor LC242"), and 5 parts by weight of a photopolymerization initiator (manufactured by Ciba Specialty Chemicals, trade name "Irgacure 907") in 200 parts by weight of cyclopentanone. Next, the prepared liquid crystal coating solution was applied to the surface of a norbornene-based resin film (manufactured by Nippon Zeon, trade name "Zeonex"), which is a substrate film, using a bar coater, and then heated and dried at 80 ° C for 4 minutes to align the liquid crystal contained in the coating film. Next, the coating film was cured by irradiation with ultraviolet light, and a liquid crystal solidified layer (thickness 0.58 μm) serving as a second retardation film was formed on the substrate film. The in-plane retardation Re of the liquid crystal solidified layer for light with a wavelength of 550 nm was 0 nm, and the retardation Rth in the thickness direction was -71 nm (nx=1.5326, ny=1.5326, nz=1.6550), and the liquid crystal solidified layer exhibited refractive index characteristics of nz>nx=ny.

[0120] [ka]

[0121] (Preparation of retardation film R1) One surface of the first retardation film prepared above was attached to the liquid crystal solidified layer of the second retardation film via an adhesive to prepare a retardation film R1.

[0122] <Preparation of a circularly polarizing plate with an adhesive sheet> (Preparation of interlayer adhesive) A four-neck flask equipped with a stirring blade, thermometer, nitrogen gas inlet, and condenser was charged with a monomer mixture containing 79.9 parts by weight of butyl acrylate, 15 parts by weight of benzyl acrylate, 5 parts by weight of acrylic acid, and 0.1 parts by weight of 4-hydroxybutyl acrylate. Next, 0.1 parts by weight of 2,2'-azoisobutyronitrile as a polymerization initiator was added to 100 parts by weight of the monomer mixture along with ethyl acetate. Nitrogen gas was introduced into the flask with gentle stirring to replace the atmosphere with nitrogen. The temperature in the flask was maintained at around 55°C, and the polymerization reaction was allowed to proceed for 7 hours. Ethyl acetate was then added to the resulting reaction solution to adjust the solids concentration to 30% by weight, yielding a (meth)acrylic polymer solution for use as an interlayer adhesive. The weight-average molecular weight of the resulting polymer was 2.2 million.

[0123] Next, 0.5 parts by weight of a trimethylolpropane / tolylene diisocyanate trimer adduct (manufactured by Tosoh, trade name "Coronate L"), 0.1 parts by weight of benzoyl peroxide, a peroxide-based crosslinking agent, 0.2 parts by weight of an epoxy group-containing silane coupling agent (manufactured by Shin-Etsu Chemical Co., Ltd., trade name "KBM-403"), and 0.5 parts by weight of a polyether compound having a reactive silyl group (manufactured by Kaneka, Silyl SAT10) were mixed with the resulting (meth)acrylic polymer solution relative to 100 parts by weight of the solids content of the solution to obtain an adhesive composition PSA1 used as an interlayer adhesive for bonding the polarizing plate P1 and the retardation film R1.

[0124] (Preparation of polarizing plate with interlayer adhesive layer) The pressure-sensitive adhesive composition PSA1 prepared above was applied to the release surface of a 38 μm thick polyethylene terephthalate (PET) film (Mitsubishi Chemical Polyester Film, MRF38), a release film whose release surface was silicone-treated, so that the thickness of the layer after drying would be 12 μm, and the coating was dried at 155° C. for 1 minute to form an interlayer pressure-sensitive adhesive layer. Next, the formed interlayer pressure-sensitive adhesive layer was transferred to the protective layer (without hard coat) side of polarizing plate P1 to obtain a polarizing plate with an interlayer pressure-sensitive adhesive layer.

[0125] (Preparation of a circular polarizing plate with an adhesive sheet) Each adhesive sheet prepared in the Examples and Comparative Examples was transferred from the release film to the second retardation film side of the retardation film R1 (the norbornene-based resin film used as the substrate film when preparing the second retardation film was peeled off). Next, the polarizing plate with the interlayer adhesive layer prepared above was attached to the first retardation film side of the retardation film R1. The retardation film R1 and the polarizing plate with the interlayer adhesive layer were attached to each other so that the angle between the slow axis of the first retardation film and the absorption axis of the polarizer was 45 degrees counterclockwise when viewed from the side of the first retardation film.

[0126] Next, the method for producing each of the pressure-sensitive adhesive sheets of the Examples and Comparative Examples will be described.

[0127] The correspondence between the abbreviations or names shown in the following explanation and the compounds is as follows: BA: n-butyl acrylate BzA: benzyl acrylate AA: acrylic acid HBA: 4-hydroxybutyl acrylate AIBN: 2,2'-azobisisobutyronitrile C / L: Trimethylolpropane / tolylene diisocyanate trimer adduct (isocyanate-based crosslinking agent; Tosoh, Coronate L) TetradC: 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane (multifunctional epoxy crosslinker; TetradC, manufactured by Mitsubishi Gas Chemical Company) KBM403: 3-glycidoxypropyltriethoxysilane (silane coupling agent; Shin-Etsu Chemical Co., Ltd., KBM403)

[0128] [Preparation of (meth)acrylic polymer (A)] (Synthesis Example 1) A four-neck flask equipped with a stirring blade, thermometer, nitrogen gas inlet tube, and condenser was charged with 94.9 parts by weight of BA, 5.0 parts by weight of AA, and 0.1 parts by weight of HBA. Next, 0.1 parts by weight of AIBN as a polymerization initiator was added to 100 parts by weight of the mixture of BA, AA, and HBA. Nitrogen gas was introduced into the flask with gentle stirring to replace the atmosphere with nitrogen. The liquid temperature in the flask was maintained at around 55°C, and the polymerization reaction was allowed to proceed for 7 hours. Ethyl acetate was then added to the resulting reaction solution to adjust the solids concentration to 12% by weight, yielding a solution of (meth)acrylic polymer (A-1). The weight-average molecular weight (Mw) of the (meth)acrylic polymer (A-1) was 2.2 million.

[0129] (Synthesis Example 2) A solution of (meth)acrylic polymer (A-2) was obtained in the same manner as in Synthesis Example 1, except that the monomers used were changed to 79.9 parts by weight of BA, 15.0 parts by weight of BzA, 5.0 parts by weight of AA, and 0.1 parts by weight of HBA. The weight average molecular weight (Mw) of the (meth)acrylic polymer (A-2) was 2,200,000.

[0130] The types and amounts of the monomers and polymerization initiators used in Synthesis Examples 1 and 2, as well as the weight average molecular weights (Mw) of the resulting polymers, are summarized in Table 1 below.

[0131] [Table 1]

[0132] [Preparation of Pressure-Sensitive Adhesive Composition and Pressure-Sensitive Adhesive Sheet] (Examples 1 to 7, Comparative Examples 1 and 2) As shown in Table 2 below, a crosslinking agent and the like were mixed with 100 parts by weight of the solid content of the (meth)acrylic polymer (A) to obtain a solvent-based pressure-sensitive adhesive composition.

[0133] [Table 2]

[0134] Next, the obtained pressure-sensitive adhesive composition was applied to the release surface of a 38 μm thick PET film (Mitsubishi Chemical Polyester Film Co., Ltd., MRF38), a release film whose release surface had been silicone-treated, and then dried for a predetermined time in an air-circulating constant-temperature oven set at a predetermined temperature to form pressure-sensitive adhesive sheets (15 μm thick) for Examples 1 to 7 and Comparative Examples 1 and 2. A fountain coater was used to apply the pressure-sensitive adhesive composition. Table 3 shows the drying conditions used to form the pressure-sensitive adhesive sheets, and Table 4 shows the evaluation results of the formed pressure-sensitive adhesive sheets.

[0135] [Table 3]

[0136] [Table 4]

[0137] As shown in Table 4, the peak top stress X of 0.5 MPa or more max Adhesive of an embodiment having The sheet was more suitable for suppressing dimensional changes and showed higher durability than the pressure-sensitive adhesive sheets of the comparative examples. [Industrial Applicability]

[0138] The pressure-sensitive adhesive sheet of the present invention can be used, for example, in an image display device. [Explanation of symbols]

[0139] 1 adhesive sheet 2 Optical Film 10A, 10B, 10C, 10D Optical laminate 11 Adhesive surface 20 Image display device 51 Glass Plate 52 Evaluation probe 53 End face 54 Contact load 101,102,103,104 Stress-strain curve

Claims

1. Peak top stress X max A pressure-sensitive adhesive sheet that satisfies the following formula (1). X max ≧0.5MPa (1) However, the peak top stress X max is determined by the following evaluation tests on the adhesive sheet. The stress X is the peak value of the stress-strain curve obtained by the test. -Evaluation test- The end face of an evaluation probe (cylindrical, 5 mm diameter, made of stainless steel) is brought into contact with the adhesive surface of the adhesive sheet attached to the glass plate, and a contact load of 100 N is applied in the thickness direction of the adhesive sheet while maintaining this for 300 seconds to bring the evaluation probe and the adhesive sheet into close contact. Next, the evaluation probe is displaced perpendicularly away from the adhesive sheet at a constant speed of 2 μm / min. The stress X and strain Y in the thickness direction of the pressure-sensitive adhesive sheet, which are generated in the pressure-sensitive adhesive sheet due to the displacement of the evaluation probe, are measured, and a stress-strain curve is obtained from the measured stress X and strain Y.

2. In the stress-strain curve, the stress X is the peak top stress X max When it reaches Distortion Y m The pressure-sensitive adhesive sheet according to claim 1 , wherein: satisfies the following formula (2): Y m ≧0.05 (2)

3. In the stress-strain curve, the stress X is the peak top stress X max After reaching 0 Strain Y when the pressure drops to 15 MPa 0.15 The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein: satisfies the following formula (3): Y 0.15 ≧0.28 (3)

4. The distortion Y m The pressure-sensitive adhesive sheet according to claim 3, wherein the σ is 0.09 or more.

5. The peak top stress X max The pressure-sensitive adhesive sheet according to claim 3 or 4, wherein the σ is 0.9 or more. 。

6. In the stress-strain curve, the stress X is the peak top stress X max When it reaches Distortion Y m The stress X is the peak top stress X max After reaching 0.15 MPa, the strain Y 0.15 The ratio Y 0.15 / Y m satisfies the following formula (4): The pressure-sensitive adhesive sheet according to any one of claims 1 to 14. Y 0.15 / Y m ≧2 (4)

7. The pressure-sensitive adhesive sheet according to any one of claims 1 to 6, which has a storage modulus G' at 25°C of 0.5 MPa or more.

8. The pressure-sensitive adhesive sheet according to any one of claims 1 to 7, which comprises an acrylic pressure-sensitive adhesive.

9. The pressure-sensitive adhesive sheet according to any one of claims 1 to 8, which is formed from a pressure-sensitive adhesive composition containing a (meth)acrylic polymer (A) and a crosslinking agent (B).

10. The pressure-sensitive adhesive sheet according to claim 9 , wherein the crosslinking agent (B) is an isocyanate-based crosslinking agent.

11. The pressure-sensitive adhesive sheet according to claim 9 or 10, wherein the amount of the crosslinking agent (B) blended is 5 parts by weight or more per 100 parts by weight of the (meth)acrylic polymer (A).

12. The pressure-sensitive adhesive sheet according to any one of claims 9 to 11, wherein the (meth)acrylic polymer (A) has a structural unit derived from an aromatic ring-containing monomer.

13. An optical laminate comprising the pressure-sensitive adhesive sheet according to any one of claims 1 to 12 and an optical film.

14. An image display device comprising the optical laminate according to claim 13.

Images