Adhesive sheets, optical laminates, and image display devices

Abstract

To provide an adhesive sheet which is suitable for suppressing dimensional variation of an optical film included in an optical laminate and which has ensured durability.SOLUTION: An adhesive sheet has a peak value of stress X (peak top stress Xmax) in a stress-strain curve measured by the evaluation test for the adhesive sheet of 0.5 MPa or more. The evaluation test: A probe for evaluation and the adhesive sheet are tightly stuck to each other by bringing an end face of the probe for evaluation (columnar shape with diameter of 5 mm, made of stainless steel) into contact with an adhesive face of the adhesive sheet stuck to a glass plate and kept for 300 seconds while adding a contact load of 100 N to the thickness direction of the adhesive sheet. Next, the probe for evaluation is displaced in a direction vertically removing from the adhesive sheet with a constant speed of 2 μm / minute. The stress X and the strain Y in the thickness direction of the adhesive sheet generated by the displacement of the probe for evaluation on the adhesive sheet is measured, and the curve is obtained from the measured stress X and strain Y.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] In recent years, image display devices, such as liquid crystal displays and electroluminescent (EL) displays (e.g., organic EL displays and inorganic EL displays), have become rapidly widespread. These various image display devices typically have a laminated structure comprising 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 for bonding between films included in the optical laminate and for bonding between the image-forming layer and the optical laminate. Examples of optical films include polarizing plates, phase difference films, and polarizing plates with phase difference films that integrate a polarizing plate and a phase difference film. Patent Document 1 discloses an example of an optical laminate. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2008-031214 [Patent Document 2] Japanese Patent Publication No. 2009-98665 [Overview of the project] [Problems that the invention aims to solve]

[0004] Excessive dimensional change of an optical film accompanying temperature change causes light leakage and color unevenness in an image display device. Light leakage and color unevenness are particularly likely to occur in image display devices having a relatively large size that use a polarizing plate with a retardation film. In addition, image display devices designed with narrow frames (bezels) (narrow bezel designs) are becoming widespread, and suppression of dimensional change has become increasingly important. In order to suppress dimensional change, it is conceivable to increase the elastic modulus of the pressure-sensitive adhesive sheet included in the optical laminate. However, merely increasing the elastic modulus may lower the durability of the pressure-sensitive adhesive sheet and make 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 change of an optical film included in an optical laminate and also ensures durability. [Means for Solving the Problem]

[0006] The present invention provides a pressure-sensitive adhesive sheet whose peak top stress X max satisfies the following formula (1), . X max ≧0.5MPa (1) provided that the peak top stress X max is the peak value of the stress X in a stress-strain curve obtained by the following evaluation test performed on the pressure-sensitive adhesive sheet. - Evaluation Test - An end face of an evaluation probe (cylindrical shape with a diameter of 5 mm, made of stainless steel) is brought into contact with the pressure-sensitive adhesive surface of the pressure-sensitive adhesive sheet attached to a glass plate, and the probe is held for 300 seconds while applying a contact load of 100 N in the thickness direction of the pressure-sensitive adhesive sheet to bring the evaluation probe and the pressure-sensitive adhesive sheet into close contact with each other. Next, the evaluation probe is displaced at a constant speed of 2 μm / min in a direction vertically away from the pressure-sensitive adhesive sheet. The stress X and strain Y in the thickness direction of the pressure-sensitive adhesive sheet generated in the pressure-sensitive adhesive sheet 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 An optical laminate comprising the adhesive sheet of the present invention described above and an optical film, To provide.

[0008] In another aspect, the present invention is Image display device comprising the optical laminate of the present invention described above, To provide. [Effects of the Invention]

[0009] The adhesive sheet according to the present invention is suitable for suppressing changes in the dimensions of optical films contained in optical laminates, while also ensuring durability. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a schematic cross-sectional view showing an example of the adhesive sheet of the present invention. [Figure 2A] Figure 2A is a schematic diagram illustrating an evaluation test for determining the stress-strain curve of an adhesive sheet. [Figure 2B] Figure 2B is a schematic diagram illustrating an evaluation test for determining the stress-strain curve of an adhesive sheet. [Figure 2C] Figure 2C is a schematic diagram illustrating an evaluation test for determining the stress-strain curve of an adhesive sheet. [Figure 2D] Figure 2D is an enlarged view of area A in Figure 2C. [Figure 3] Figure 3 is a graph showing an example of a stress-strain curve for an adhesive sheet. [Figure 4] Figure 4 is a schematic diagram illustrating the change in the volume of the adhesive sheet due to a change in the dimensions of the optical film. [Figure 5] Figure 5 is a schematic cross-sectional view showing an example of the optical laminate of the present invention. [Figure 6] Figure 6 is a schematic cross-sectional view showing an example of the optical laminate of the present invention. [Figure 7] Figure 7 is a schematic cross-sectional view showing an example of the optical laminate of the present invention. [Figure 8]Figure 8 is a schematic cross-sectional view showing an example of the optical laminate of the present invention. [Figure 9] Figure 9 is a schematic cross-sectional view showing an example of the image display device of the present invention. [Modes for carrying out the invention]

[0011] Embodiments of the present invention will be described below with reference to the drawings. The present invention is not limited to the embodiments shown below.

[0012] [Adhesive sheet] An example of the adhesive sheet of this embodiment is shown in Figure 1. The adhesive sheet 1 in Figure 1 has a peak top stress X max This satisfies equation (1) below. X max ≥0.5MPa (1) However, peak top stress X max This is the peak value of stress X in the stress-strain curve obtained by the following evaluation test for adhesive sheet 1.

[0013] [Evaluation Test] The evaluation test for determining the stress-strain curve of the adhesive sheet 1 will be explained with reference to Figures 2A to 2D. First, the end face 53 of the evaluation probe 52 (cylindrical, stainless steel, 5 mm in diameter) is brought into contact with the adhesive surface 11 (exposed surface) of the adhesive sheet 1 attached to the glass plate 51. A contact load 54 of 100 N is applied in the thickness direction of the adhesive sheet 1 and held for 300 seconds to ensure close contact between the evaluation probe 52 and the adhesive sheet 1 (Figures 2A and 2B). The end face 53 is the bottom surface of the probe 52, and its diameter is 5 mm. To accurately measure stress X and strain Y, it is preferable that the thickness of the adhesive sheet 1 to be attached be 200 μm or more. If the thickness does not reach 200 μm, two or more adhesive sheets 1 may be stacked and joined together by heating I using an autoclave or the like to achieve a thickness of 200 μm or more. The glass plate 51 can be selected to have a flat surface to which the adhesive sheet 1 is attached and to prevent the adhesive sheet 1 from peeling off during the evaluation test. The adhesive sheet 1 should be attached to the glass plate 51 in a manner that prevents it from peeling 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, and if an autoclave is used, 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 with the stacked adhesive sheets 1 attached to the glass plate 51. For the evaluation probe 52, a probe tack test probe conforming to the provisions of ASTM D-2979 can be used.

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

[0015] Figure 3 shows examples of stress-strain curves for adhesive sheets. Figure 3 shows stress-strain curves 101, 102, 103, and 104 for four types of adhesive sheets. Adhesive sheet 1, which shows curves 101, 103, and 104, satisfies equation (1). Adhesive sheet 1, which shows curve 102, does not satisfy equation (1). Note that for curve 101, X max This is achieved at vertex A.

[0016] As shown in Figure 4, when the dimensions of the optical film 111 change, the volume of the adhesive sheet 112 bonded to it also changes. In the example in Figure 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 indicate the edges of the optical film 111 before and after expansion, respectively, and reference numeral 113 indicates the adherend such as a glass substrate). Peak top stress X maxWhen the value is 0.5 MPa or more, it means that the stress of the pressure-sensitive adhesive sheet 1 against the volume change is sufficiently large, which can suppress the dimensional change of the optical film 111 while ensuring its durability. The above evaluation test, in which the evaluation probe 52 is displaced at a very low speed (2 µm / min), is considered to well reflect the volume change mode of the pressure-sensitive adhesive sheet 112 accompanying the dimensional change of the optical film 111.

[0017] X max may be 0.6 MPa or more, 0.8 MPa or more, 0.9 MPa or more, 1.0 MPa or more, 1.2 MPa or more, 1.4 MPa or more, and even 1.5 MPa or more. X max has an upper limit of, for example, 5 MPa or less.

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

[0019] The pressure-sensitive adhesive sheet 1 represented by curves 101 and 104 in FIG. 3 satisfies formula (2). Y of curve 101 m is achieved at vertex A. When Y m is 0.05 or more, even when the volume of the pressure-sensitive adhesive sheet 1 changes to a greater extent, it can resist such change. Y m may be 0.07 or more, 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, and even 0.16 or more. Y m has an upper limit of, for example, 0.3.

[0020] In a stress-strain curve, after the stress X reaches the peak top stress X max and then drops to 0.15 MPa, the strain Y 0.15 may satisfy the following formula (3). Y 0.15 ≧0.28 (3)

[0021] The adhesive sheet 1 showing curve 101 satisfies equation (3). Y of curve 101 0.15 This is achieved at point B. 0.15 A value of 0.28 or higher means that even after the stress of the adhesive sheet 1 resisting volume changes has exceeded its peak, a constant stress can be maintained up to a greater strain, for example, by suppressing the generation of regions within the adhesive sheet 1 where adhesive components are absent (voids, etc.). 0.15 It may be 0.29 or higher, 0.30 or higher, 0.31 or higher, 0.32 or higher, or even 0.33 or higher. 0.15 The upper limit is, for example, 1.00 or less.

[0022] Y 0.15 The above range is satisfied, and the distortion Y m Adhesive sheet 1 with a value of 0.09 or higher, especially 0.13 or higher, is particularly suitable for improving durability. Also, Y 0.15 The above range is satisfied, and the peak top stress X max Adhesive sheets 1 with a value of 0.9 or higher, especially 1 or higher, 1.1 or higher, and even 1.2 or higher, are particularly suitable for balancing the suppression of dimensional changes with ensuring durability.

[0023] In the stress-strain curve, stress X is the peak top stress X max Distortion Y when it reaches m The stress X is the peak top stress X max After reaching this point, the strain Y when it drops to 0.15 MPa. 0.15 Ratio Y 0.15 / Y m The following equation (4) may also be satisfied. Y 0.15 / Y m ≥2 (4)

[0024] The adhesive sheet 1 showing curve 101 in Figure 3 satisfies equation (4). Ratio Y 0.15 / Y m A ratio of 2 or greater means that the generation and rate of generation of voids, etc., can be suppressed until a greater strain occurs after the stress of the adhesive sheet 1, which resists the change in volume, has exceeded its peak.0.15 / Y m The ratio Y may be 2.1 or greater. 0.15 / Y m The upper limit is, for example, 10 or less.

[0025] X of adhesive sheet 1 max , Y m and Y 0.15 This can vary based on various factors, such as the type of base polymer, glass transition temperature (Tg), and composition contained in the adhesive composition; the type and amount of crosslinking agent; the type and amount of additives such as tackifiers; and the drying (curing) conditions for forming an adhesive sheet from the adhesive composition.

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

[0027] The storage modulus G'(25°C) of the adhesive sheet 1 is, for example, 0.15 MPa or higher, and may be 0.2 MPa or higher, 0.25 MPa or higher, 0.3 MPa or higher, 0.5 MPa or higher, 0.6 MPa or higher, 0.7 MPa or higher, 0.8 MPa or higher, 0.9 MPa or higher, 1.0 MPa or higher, 1.1 MPa or higher, and even 1.2 MPa or higher. The upper limit of the storage modulus G'(25°C) is, for example, 5 MPa or lower, and may be 3.0 MPa or lower, 2.5 MPa or lower, and even 2.0 MPa or lower. The high modulus adhesive sheet 1 with a storage modulus G' within the above range is suitable because it suppresses changes in the dimensions of the optical film.

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

[0029] The gel fraction of the 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. The adhesive sheet 1 with a gel fraction within the above range is suitable because it suppresses changes in the dimensions of the optical film.

[0030] The gel fraction of adhesive sheet 1 can be evaluated by the following method. First, approximately 0.2 g is scraped off from 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, with an average pore size of 0.2 μm) and tied with kite string to form a test specimen. Next, the weight A of the obtained test specimen is measured. Weight A is the sum of the weights of the adhesive sheet piece, the stretched porous membrane, and the kite string. The total weight B of the stretched porous membrane and kite string used should be measured in advance. Next, the test specimen 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 specimen is removed from the container and dried in a dryer set to 130°C for two hours, and then the weight C of the test specimen is measured. From the measured weights A, B, and C, the gel fraction of adhesive sheet 1 is calculated using the formula: Gel fraction (weight %) = (CB) / (AB) × 100 (%).

[0031] The adhesive sheet 1 can be used, for example, in optical applications. The adhesive sheet 1 may also be used in optical laminates and / or image display devices. The adhesive sheet 1 is suitable for use in image display devices where it is particularly important to suppress dimensional changes in the optical film, such as narrow-bezel image display devices and image display devices with relatively large screen sizes. By using it in these image display devices, for example, peeling of the film contained in the optical laminate is suppressed.

[0032] The adhesive sheet 1 can be formed from an adhesive composition, for example, as follows: For solvent-type adhesive compositions, for example, the adhesive composition or a mixture of the adhesive composition and a solvent is applied to a base film, and the formed coating film is dried to form the adhesive sheet 1. The adhesive composition is heat-cured by the heat during drying. For active energy ray-curable (photocurable) adhesive compositions, for example, a mixture containing monomers (group) that become adhesive polymers by polymerization, and optionally partially polymerized monomers (group), polymerization initiators, crosslinking agents, and other additives and solvents is applied to a base film, and the adhesive sheet 1 is formed by irradiation with active energy rays. The solvent may be removed by drying before irradiation with active energy rays. The base film may be a film (release film) with a release treatment applied to the coated surface. However, the type of adhesive composition is not limited to the above examples.

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

[0034] The 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 adhesive sheet 1 and the optical film is obtained.

[0035] For coating the base film, known methods can be employed. Coating can be carried out by, for example, 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, die coating, or other extrusion coating methods.

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

[0037] The composition and mixture to be applied to the base film preferably have a viscosity suitable for handling and coating. For this reason, in the case of active energy ray curing type, the mixture to be applied preferably contains partially polymerized monomers (groups).

[0038] In one example of a release film, the coated surface is treated with a silicone compound for release.

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

[0040] Adhesive composition (I) is described as an example of an adhesive composition that can form an adhesive sheet 1. However, the adhesive composition for forming the adhesive sheet 1 is not limited to adhesive composition (I).

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

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

[0043] The main component refers to the component that makes up the largest proportion of the composition. The content of the main component may be, for example, 50% by weight or more, but may also 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 its main unit a structural unit derived from a (meth)acrylic monomer (A1) having an alkyl group having 1 to 30 carbon atoms in its side chain. The alkyl group may be linear or branched. The (meth)acrylic polymer (A) may have one or more structural units derived from the (meth)acrylic monomer (A1). Examples of (meth)acrylic monomers (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, isoheptyl (meth)acrylate These are 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, "principal unit" means 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 the total constituent units of the polymer.

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

[0046] The (meth)acrylic polymer (A) may have constituent units derived from a (meth)acrylic monomer (A1) whose glass transition temperature (Tg) is in the range of -70 to -20°C when it is a homopolymer. An example of such monomer (A1) is n-butyl acrylate.

[0047] The (meth)acrylic polymer (A) may have constituent units other than those derived from the (meth)acrylic monomer (A1). These constituent units are derived from monomers (A2) copolymerizable with the (meth)acrylic monomer (A1). The (meth)acrylic polymer (A) may have one or more of these constituent units.

[0048] An example of monomer (A2) is an aromatic ring-containing monomer. The aromatic ring-containing monomer may also be an aromatic ring-containing (meth)acrylic monomer. Examples of aromatic ring-containing monomers are 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 constituent units derived from aromatic ring-containing monomers in (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) contains constituent units derived from aromatic ring-containing monomers, which can improve the compatibility between the (meth)acrylic polymer (A) and the crosslinking agent (B). Improved compatibility can lead to the formation of a crosslinked structure with excellent uniformity and suppress the precipitation of the crosslinking agent (B) or its self-polymers in the adhesive sheet 1. In other words, improved compatibility can contribute to further improvement in the durability of the adhesive sheet 1. Furthermore, the above-mentioned effects of improved compatibility are particularly advantageous when the amount of crosslinking agent (B) is increased, for example, to achieve high elasticity.

[0049] Another example of monomer (A2) is a hydroxyl group-containing monomer. The hydroxyl group-containing monomer may also be a hydroxyl group-containing (meth)acrylic monomer. Examples of hydroxyl group-containing monomers include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate and 12-hydroxylauryl (meth)acrylate, as well as (4-hydroxymethylcyclohexyl)-methyl acrylate. Note that the hydroxyl group can react with the crosslinking agent (B). From the viewpoint of improving the uniformity of the crosslinked structure, the content of constituent units derived from hydroxyl group-containing monomers in the (meth)acrylic polymer (A) may be 1% by weight or less, 0.5% by weight or less, even 0.1% by weight or less, or even 0% by weight (meaning it may not contain such constituent units).

[0050] Monomer (A2) may be a carboxyl group-containing monomer, an amino group-containing monomer, or an amide group-containing monomer. Examples of carboxyl group-containing monomers are (meth)acrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, and crotonic acid. Examples of amino group-containing monomers are N,N-dimethylaminoethyl (meth)acrylate and N,N-dimethylaminopropyl (meth)acrylate. Examples of amide group-containing monomers include acrylamide 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 monomers such as N-vinylpyrrolidone and N-vinyl-ε-caprolactam. The (meth)acrylic polymer (A) contains constituent units derived from carboxyl group-containing monomers, particularly acrylic acid, which can enhance the self-polymerization properties of the crosslinking agent (B), for example. Improving the self-polymerization properties of the crosslinking agent (B) can contribute, in particular, to suppressing the peeling of adhesive sheets in humid environments and stabilizing the physical properties of adhesive sheets in systems with a high content of 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 constituent 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. If the (meth)acrylic polymer (A) contains such constituent units, the total content may be, for example, 0.01% by weight or more, and may also be 0.05% by weight or more. The (meth)acrylic polymer (A) does not have to contain constituent units derived from polyfunctional monomers.

[0053] Other examples of monomers (A2) include alkoxyalkyl esters of (meth)acrylates such as 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, methoxytriethylene glycol (meth)acrylate, 3-methoxypropyl (meth)acrylate, 3-ethoxypropyl (meth)acrylate, 4-methoxybutyl (meth)acrylate and 4-ethoxybutyl (meth)acrylate; epoxy group-containing monomers such as glycidyl (meth)acrylate and methylglycidyl (meth)acrylate; and sodium vinyl sulfonate. These include monomers containing sulfonic acid groups such as lium; monomers containing phosphate groups; (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 constituent units derived from the above-mentioned 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 preferably 0% by weight (not containing the constituent units).

[0055] The (meth)acrylic polymer (A) can be formed by polymerizing one or more of the above-mentioned monomers by known methods. The monomers and partial polymers of the monomers may also be polymerized. Polymerization can be carried out by, for example, 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 for the formation of an adhesive sheet 1 with excellent optical transparency. Polymerization is preferably carried out while avoiding contact between the monomers and / or partial polymers and oxygen. For this purpose, polymerization can be carried out, for example, under an inert gas atmosphere such as nitrogen, or under conditions where oxygen is blocked by a resin film or the like. The (meth)acrylic polymer (A) to be formed may be in any form such as a random copolymer, block copolymer, or graft copolymer.

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

[0057] Solvents used in solution polymerization include, for example, 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 mixture of two or more solvents.

[0058] Polymerization initiators used in solution polymerization include, for example, 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 initiator disclosed in Japanese Patent Application Publication No. 2002-69411 is preferred. Examples of such azo polymerization initiators include 2,2'-azobisisobutyronitrile (AIBN), 2,2'-azobis-2-methylbutyronitrile, 2,2'-azobis(2-methylpropionic acid)dimethyl, and 4,4'-azobis-4-cyanovaleric acid. However, the polymerization initiator is not limited to the above examples. The amount of azo polymerization initiator used is, for example, 0.05 to 0.5 parts by weight per 100 parts by weight of the total amount of monomer, and may also be 0.1 to 0.3 parts by weight.

[0059] The active energy rays used in active energy ray polymerization include, for example, ionizing radiation such as alpha rays, beta rays, gamma rays, neutron rays, and electron beams, as well as ultraviolet rays. Ultraviolet rays are preferred as the active energy rays. Polymerization by irradiation with ultraviolet rays is also called photopolymerization. The polymerization system for active energy ray polymerization typically includes a photopolymerization initiator. The polymerization conditions for active energy polymerization are not limited as long as a (meth)acrylic polymer (A) is formed.

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

[0061] Benzoin ether-based photopolymerization initiators include, for example, benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, benzoin isopropyl ether, benzoin isobutyl ether, 2,2-dimethoxy-1,2-diphenylethane-1-one, and anisole methyl ether. Acetophenone-based photopolymerization initiators include, for example, 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexylphenyl ketone, 4-phenoxydichloroacetophenone, and 4-(t-butyl)dichloroacetophenone. Alpha-ketol-based photopolymerization initiators include, for example, 2-methyl-2-hydroxypropiophenone and 1-[4-(2-hydroxyethyl)phenyl]-2-methylpropan-1-one. Aromatic sulfonyl chloride-based photopolymerization initiators include, for example, 2-naphthalenesulfonyl chloride. Photoactive oxime-based photopolymerization initiators include, for example, 1-phenyl-1,1-propanedione-2-(o-ethoxycarbonyl)-oxime. Benzoin-based photopolymerization initiators include, for example, benzoin. Benzyl-based photopolymerization initiators include, for example, benzyl. Benzophenone-based photopolymerization initiators include, for example, benzophenone, benzoylbenzoic acid, 3,3'-dimethyl-4-methoxybenzophenone, polyvinylbenzophenone, and α-hydroxycyclohexylphenyl ketone. Ketal-based photopolymerization initiators include, for example, benzyldimethylketal. Thioxanthone-based photopolymerization initiators include, for example, thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 2,4-diisopropylthioxanthone, and dodecylthioxanthone.

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

[0063] The weight-average molecular weight (Mw) of the (meth)acrylic polymer (A) is, for example, 1 million to 2.5 million, and may be 1.2 million or more, or even 1.4 million or more, from the viewpoint of durability and heat resistance of the adhesive sheet. The weight-average molecular weight (Mw) of polymers and oligomers in this specification is a value (polystyrene equivalent) based on GPC (gel permeation chromatography) measurements.

[0064] The content of the (meth)acrylic polymer (A) in the adhesive composition (I) is, for example, 50% by weight or more in terms of solid content, and may be 60% by weight or more, 70% by weight or more, or even 80% by weight or more. The upper limit of the content is, for example, 99% by weight or less, and may be 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 more crosslinking agent having three or more crosslinking reactive groups per molecule. The upper limit for 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 the crosslinking reaction group. The isocyanate-based crosslinking agent (B) may be an aromatic isocyanate compound, an alicyclic isocyanate compound, or an aliphatic isocyanate compound.

[0067] Examples of aromatic isocyanate compounds that can be used as crosslinking agents (B) include phenylenediisocyanate, 2,4-tolylenediisocyanate, 2,6-tolylenediisocyanate, 2,2'-diphenylmethanediisocyanate, 4,4'-diphenylmethanediisocyanate, 4,4'-toluidinediisocyanate, 4,4'-diphenyletherdiisocyanate, 4,4'-diphenyldiisocyanate, and 1,5-naphthalenediisocyanate and xylylenediisocyanate.

[0068] Examples of alicyclic isocyanate compounds that can be used as crosslinking agents (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 as crosslinking agents (B) include 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 above-mentioned isocyanate compound. Examples of derivatives include polymers (dimers, trimers, pentamers, etc.), adducts obtained by adding to polyhydric alcohols such as trimethylolpropane, urea-modified compounds, biuret-modified compounds, allophanate-modified compounds, isocyanurate-modified compounds, carbodiimide-modified compounds, and urethane prepolymers obtained by adding to polyether polyols, polyester polyols, acrylic polyols, polybutadiene polyols, polyisoprene polyols, etc.

[0071] The crosslinking agent (B) is preferably an aromatic isocyanate compound and its derivatives, and more preferably tolylene diisocyanate and its derivatives (in other words, a tolylene diisocyanate-based (TDI-based) crosslinking agent). TDI-based crosslinking agents exhibit superior reaction uniformity compared to xylylene diisocyanate and its derivatives (in other words, xylylene diisocyanate-based (XDI-based) crosslinking agents). An example of a TDI-based 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 products can be used as the crosslinking agent (B). Examples of commercially available products include Millionate MT, Millionate MTL, Millionate MR-200, Millionate MR-400, Coronate L, Coronate HL and Coronate HX (all manufactured by Tosoh Corporation; all are 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 Corporation; all are trade names). For the crosslinking agent (B), Coronate L, Takenate D-102, and Takenate D-103 (all trimethylolpropane / tolylene diisocyanate trimer adducts) can be preferably used.

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

[0074] The amount of crosslinking agent (B) in the adhesive composition (I) is, for example, 0.5 parts by weight or more and 30 parts by weight or less per 100 parts by weight of (meth)acrylic polymer (A), and may be 1 part by weight or more and 28 parts by weight or less, 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 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 inventors' studies, when the 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, and even 11 parts by weight or more, the crosslinking agent (B) reacts with each other during the formation of the adhesive sheet 1, making it easier to form a self-polymer of the crosslinking agent (B), in other words, a polymer mainly composed of structural units derived from the crosslinking agent (B). In the self-polymer, the content of structural units derived from the crosslinking agent (B) may be, for example, 70% by weight or more, and may be 90% by weight or more, 95% by weight or more, and even 99% by weight or more. The self-polymer may consist only of structural units derived from the crosslinking agent (B). The formation of the self-polymer is achieved by applying sufficient cohesive force to the adhesive sheet 1, thereby increasing the peak top stress X max This can contribute to achieving the above. Furthermore, the adhesive sheet 1 may have an interpenetrating network (IPN) structure between a crosslinked product of the (meth)acrylic polymer (A) and an autopolymer of the crosslinking agent (B). The IPN structure is suitable for improving the durability of the adhesive sheet 1.

[0076] Other examples of crosslinking agents (B) include peroxide-based crosslinking agents, epoxy-based crosslinking agents, imine-based crosslinking agents, and polyfunctional metal chelates. However, crosslinking agent (B) is preferably isocyanate-based. If the adhesive composition (I) contains crosslinking agents (B) other than isocyanate-based, the total amount of such crosslinking agents 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, in that order, per 100 parts by weight of (meth)acrylic polymer (A). The adhesive composition (I) does not have to contain crosslinking agents (B) other than isocyanate-based, such as epoxy-based crosslinking agents.

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

[0078] The (meth)acrylic oligomer (D) may have the same composition as the (meth)acrylic polymer (A) described above, except that it has a different weight-average molecular weight (Mw). The weight-average molecular weight (Mw) of the (meth)acrylic oligomer (D) may be, for example, 1000 or more, and may be 2000 or more, 3000 or more, or even 4000 or more. The upper limit of the weight-average molecular weight (Mw) of the (meth)acrylic oligomer may be, for example, 30000 or less, and may be 15000 or less, 10000 or less, or even 7000 or less.

[0079] (Meth)acrylic oligomers (D) have, for example, one or more constituent units derived from each of 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 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 with 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 constituent units derived from a (meth)acrylic monomer having a relatively bulky structure. In this case, the adhesion of the adhesive sheet can be further improved. Examples of such acrylic monomers include alkyl (meth)acrylates having branched alkyl groups such as isobutyl (meth)acrylate and t-butyl (meth)acrylate; esters of (meth)acrylic acid with 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 performed during the polymerization of (meth)acrylic oligomer (D) and / or during the formation of the adhesive sheet, the progress of polymerization and / or formation is less likely to be inhibited. Therefore, it is preferable that the monomer does not have unsaturated bonds. For example, alkyl (meth)acrylates having a branched alkyl group, or esters of (meth)acrylic acid and alicyclic alcohols can be used.

[0081] Specific examples of (meth)acrylic oligomers (D) include copolymers of butyl acrylate, methyl acrylate, and acrylic acid; copolymers of cyclohexyl methacrylate and isobutyl methacrylate; copolymers of cyclohexyl methacrylate and isobornyl methacrylate; copolymers of cyclohexyl methacrylate and acryloyl morpholine; copolymers of cyclohexyl methacrylate and diethylacrylamide; copolymers of 1-adamantyl acrylate and methyl methacrylate; copolymers of dicyclopentanyl methacrylate and isobornyl methacrylate; copolymers of at least one selected from dicyclopentanyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, isobornyl acrylate, and cyclopentanyl methacrylate with methyl methacrylate; homopolymers of dicyclopentanyl acrylate, homopolymers of 1-adamantyl methacrylate, and homopolymers of 1-adamantyl acrylate.

[0082] The polymerization method for the (meth)acrylic polymer (A) described above can be used for the polymerization of the (meth)acrylic oligomer (D).

[0083] If the adhesive composition (I) contains a (meth)acrylic oligomer (D), the amount of D is, 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 amount is, 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 adhesive composition (I) does not have to contain a (meth)acrylic oligomer (D).

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

[0085] Examples of silane coupling agents include epoxy group-containing silane coupling agents such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; amino group-containing silane coupling agents such as 3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, and N-phenyl-γ-aminopropyltrimethoxysilane; (meth)acrylic group-containing silane coupling agents such as 3-acryloxypropyltrimethoxysilane and 3-methacryloxypropyltriethoxysilane; and isocyanate group-containing silane coupling agents such as 3-isocyanatetopropyltriethoxysilane.

[0086] If the adhesive composition (I) contains a silane coupling agent, the amount of the silane coupling agent is, for example, 5 parts by weight or less per 100 parts by weight of the (meth)acrylic polymer (A), 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. The adhesive composition (I) does not have to contain a silane coupling agent.

[0087] The type of adhesive composition (I) may be, for example, emulsion type, solvent type (solution type), active energy ray curing type (photocuring type), or thermal melt type (hot melt type). From the viewpoint of forming an adhesive sheet 1 with superior durability, the adhesive composition (I) may be of the solvent type. The solvent type adhesive composition (I) does not need to 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 Figure 5. The optical laminate 10A in Figure 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 optical film 2 include polarizers, phase difference films, and laminated films comprising polarizers and / or phase difference films. However, optical film 2 is not limited to the above examples. Optical film 2 may also include glass films.

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

[0091] A phase difference film is a film that exhibits birefringence in the in-plane direction and / or in the thickness direction. Examples of phase difference films include stretched resin films and films in which liquid crystal materials are oriented and immobilized.

[0092] The phase difference film may be a λ / 4 plate, a λ / 2 plate, an anti-reflective phase difference film (see, for example, paragraphs 0221, 0222, and 0228 of Japanese Patent Application Publication No. 2012-133303), a viewing angle compensation phase difference film (see, for example, paragraphs 0225 and 0226 of Japanese Patent Application Publication No. 2012-133303), or a tilted orientation phase difference film for viewing angle compensation (see, for example, paragraph 0227 of Japanese Patent Application Publication No. 2012-13303). The phase difference film is not limited to the above examples, as long as it has birefringence in the in-plane direction and / or in the thickness direction. The phase difference value, arrangement angle, three-dimensional birefringence, whether it is single-layer or multi-layer, etc. of the phase difference film are also not limited. Known films can be used as the phase difference 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. If the optical film 2 is a laminated film, an adhesive sheet 1 may be used to bond each layer.

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

[0096] The separator 3 is typically a resin film. Examples of resins that make up the separator 3 include polyester 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 adhesive sheet 1 may be treated with a release agent. The release agent is, for example, treated with 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 Figure 7. The optical laminate 10C in Figure 7 has a laminated structure in which a separator 3, an adhesive sheet 1, a phase difference film 2A, an interlayer adhesive 4, and a polarizing plate 2B are laminated in this order. The optical laminate 10C can be used by peeling off the separator 3 and, for example, attaching it to an image forming layer.

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

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

[0100] The protective film 5 has the function of protecting the outermost optical film 2 (polarizing plate 2B) during the 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 outside space when incorporated into an image display device. The protective film 5 is typically a resin film. The resin constituting the protective film 5 is, for example, polyester such as PET, polyolefin such as polyethylene and polypropylene, acrylic, cycloolefin, polyimide, and polyamide, with polyester being preferred. However, the protective film 5 is not limited to the above examples. The protective film 5 may 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-reflective, and anti-static properties.

[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 wound body formed by winding a strip-shaped optical laminate, or as a single-sheet optical laminate.

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

[0104] [Image display device] An example of an image display device of this embodiment is shown in Figure 9. The image display device 20 in Figure 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 phase difference film 2A, an interlayer adhesive 4, a polarizing plate 2B, and a protective film 5 are stacked in this order. The image display device 20 has optical laminates 10A, 10B, 10C, and 10D as shown in Figures 5 to 8 (except for the separator 3). The substrate 7 and the image forming layer 6 only need to have the same configuration as the substrate and image forming layer of a known image display device.

[0105] The image display device 20 in Figure 9 may be an organic EL display or a liquid crystal display. However, the image display device 20 is not limited to these examples. The image display device 20 may be an electroluminescent (EL) display, a plasma display (PD), a field emission display (FED), etc. The image display device 20 may be used for home appliance applications, automotive applications, public information display (PID) applications, etc.

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

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

[0108] First, the evaluation methods for the (meth)acrylic polymers and adhesive sheets prepared in the examples and comparative examples are shown.

[0109] [Weight average molecular weight (Mw)] The weight-average molecular weight (Mw) of (meth)acrylic polymers was evaluated by GPC under the following conditions. • Analytical equipment: Waters Acquity APC • Columns: Tosoh Corporation, G7000HXL + GMHXL + GMHXL Column temperature: 40°C • Eluent: Tetrahydrofuran (with acid added) ·Flow rate: 0.8mL / min ·Injection volume: 100μL • Detector: Differential refractometer (RI) • Standard sample: Polystyrene (PS) manufactured by Agilent.

[0110] [Stress-strain curve] The stress-strain curves of the adhesive sheets were obtained by the evaluation test described above using a tacking tester (Lesca, TAC1000). However, Corning Eagle XG glass plates 51 were used. An evaluation sheet with a thickness of 200 μm or more was attached to the glass plate 51 by layering the fabricated adhesive sheets and bonding them together using autoclave heating I (50°C, 5 atm (absolute pressure), 15 minutes). After attachment, the bond between the evaluation sheet and the glass plate 51 was stabilized by autoclave heating II (50°C, 5 atm (absolute pressure), 15 minutes). For the evaluation probe 52, a Lesca 5 mmΦ probe (SUS) conforming to ASTM D-2979 was used. From the obtained curves, the peak top stress X was determined for each adhesive sheet. max , distortion Y m and distortion Y 0.15 We will find the ratio Y 0.15 / Y m The following was calculated. The evaluation test was conducted at 23°C and in a 55% RH atmosphere.

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

[0112] [Gel fraction] The gel fraction of the adhesive sheet was evaluated using the method described above.

[0113] [Humidity durability] The humidification durability of the adhesive sheets (equivalent to an accelerated durability test) was evaluated by the following method. First, a circular polarizing plate with an adhesive sheet was formed, with each adhesive sheet prepared in the examples and comparative examples attached to one exposed surface. Next, the circular polarizing plate was fixed to the surface of a glass plate (Corning Eagle XG) via the adhesive sheet. The fixing of the circular polarizing plate was carried out in an atmosphere of 23°C and 50%RH. Next, after being treated in an autoclave at 50°C and 5 atmospheres (absolute pressure) for 15 minutes, it was left to cool to 23°C to stabilize the bonding of the circular polarizing plate to the glass plate, and then left in a heated and humidified atmosphere of 60°C and 95%RH for 500 hours. After the period, it was returned to an atmosphere of 23°C and 50%RH, and the humidification durability was evaluated as follows by visually checking for peeling of the circular polarizing plate from the glass plate and for the occurrence of foaming between the glass plate and the circular polarizing plate. A: No visible changes such as foaming or peeling are observed. B: There is slight peeling or foaming at the edges, but it is within a range that does not pose a practical problem. C: At the edges, slight continuous peeling or foaming is observed, but it is within a range that does not pose a practical problem. D: Significant peeling or foaming is observed at the edges, which poses a practical problem.

[0114] The following describes the method for forming the circular polarizing plate with adhesive sheet used to evaluate its humidification durability.

[0115] <Fabrication of polarizing plate P1> (Fabrication of polarizers) A 12 μm thick polarizer was produced by uniaxially stretching a long polyvinyl alcohol (PVA) resin film (manufactured by Kuraray, product name "PE3000", thickness 30 μm) in the longitudinal direction using a roll stretcher (total stretching ratio 5.9 times). Simultaneously, the resin film was subjected to swelling, dyeing, crosslinking, washing, and drying in sequence. 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 transmittance of the polarizer produced was 45.0%. A two-stage crosslinking treatment was employed. In the first stage of crosslinking, the resin film was stretched 1.2 times while being treated with an aqueous solution at 40°C containing boric acid and potassium iodide. In the first crosslinking stage, the boric acid content in the aqueous solution was 5.0% by weight, and the potassium iodide content was 3.0% by weight. In the second crosslinking stage, the resin film was stretched 1.6 times while being treated with an aqueous solution of boric acid and potassium iodide dissolved in it at 65°C. In the aqueous solution used for the second crosslinking stage, the boric acid content was 4.3% by weight, and the potassium iodide content was 5.0% by weight. For the washing stage, an aqueous solution of potassium iodide at 20°C was used. In the aqueous solution used for the washing stage, the potassium iodide content was 2.6% by weight. The drying stage was carried out under drying conditions of 70°C for 5 minutes.

[0116] (Fabrication of polarizing plate P1) A triacetylcellulose (TAC) film (manufactured by Konica Minolta, product name "KC2UA", thickness 25 μm) was bonded to each main surface of the polarizer fabricated above using a polyvinyl alcohol-based adhesive. However, a hard coat (thickness 7 μm) was formed on the main surface opposite to the polarizer side of the TAC film bonded to one of the main surfaces. In this way, a polarizer plate P1 having the configuration of a hard-coated protective layer / polarizer / protective layer (without hard coat) was obtained.

[0117] <Preparation of phase difference film R1> (Preparation of the first phase difference 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 added to the reaction vessel and dissolved under a nitrogen atmosphere (for about 15 minutes). At this time, the temperature of the heat medium in the reaction vessel was set to 150°C, and stirring was carried out as needed. Next, the pressure in the reaction vessel was reduced to 13.3 kPa, and the temperature of the heat medium was raised to 190°C over 1 hour. The phenol generated as the temperature of the heat medium rose 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, then the pressure inside the reaction vessel was changed to 6.67 kPa, and the heat medium temperature was increased to 230°C over 15 minutes. When the stirring torque of the stirrer equipped with the reaction vessel increased, the heat 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 reactants were extruded into water and pelletized. In this way, a polycarbonate resin having 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 obtained polycarbonate resin was 136.6°C, and the reduced viscosity was 0.395 dL / g.

[0118] After vacuum-drying the prepared polycarbonate resin pellets at 80°C for 5 hours, a long resin film with a thickness of 120 μm was obtained using a film-making apparatus equipped with a single-screw extruder (manufactured by Isuzu Chemical Machinery, screw diameter 25 mm, cylinder setting temperature 220°C), a T-die (width 200 mm, setting temperature 220°C), a chill roll (setting temperature 120-130°C), and a winding machine. Next, the obtained resin film was stretched in the width direction using a tenter stretcher at a stretching temperature of 137-139°C and a stretching ratio of 2.5 times to obtain a first phase difference film.

[0119] (Preparation of the second phase difference 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 are the mole percent of each constituent unit), 80 parts by weight of a polymerizable liquid crystal exhibiting a nematic liquid crystal phase (BASF, trade name "Paliocolor LC242"), and 5 parts by weight of a photopolymerization initiator (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 (Nippon Zeon, trade name "Zeonex"), which was the base film, using a bar coater, and then heated and dried at 80°C for 4 minutes to orient the liquid crystals contained in the coated film. Next, the coated film was cured by irradiation with ultraviolet light to form a liquid crystal solidification layer (thickness 0.58 μm), which is a second phase difference film, on the base film. The in-plane phase difference Re of the liquid crystal solidified layer for light with a wavelength of 550 nm was 0 nm, and the phase difference Rth in the thickness direction was -71 nm (nx=1.5326, ny=1.5326, nz=1.6550). The liquid crystal solidified layer exhibited refractive index characteristics such as nz>nx=ny.

[0120] [ka]

[0121] (Preparation of phase difference film R1) Phase difference film R1 was fabricated by bonding one side of the first phase difference film prepared above to the liquid crystal solidification layer of the second phase difference film via an adhesive.

[0122] <Fabrication of circular polarizing plates with adhesive sheets> (Preparation of interlayer adhesive) 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 was charged into a four-necked flask equipped with a stirring blade, thermometer, nitrogen gas inlet tube, and condenser. Next, 0.1 parts by weight of 2,2'-azoisobutyronitrile was added to 100 parts by weight of the monomer mixture along with ethyl acetate as a polymerization initiator. After introducing nitrogen gas to purge the flask with nitrogen while gently stirring, the polymerization reaction was carried out for 7 hours while maintaining the liquid temperature in the flask at around 55°C. Next, ethyl acetate was added to the resulting reaction solution to adjust the solid content concentration to 30% by weight, obtaining a solution of (meth)acrylic polymer to be used as an interlayer adhesive. The weight-average molecular weight of the obtained polymer was 2.2 million.

[0123] Next, to the obtained (meth)acrylic polymer solution, 0.5 parts by weight of 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 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, Cyryl SAT10) were mixed per 100 parts by weight of the solid content of the solution to obtain an adhesive composition PSA1 to be used as an interlayer adhesive for bonding a polarizing plate P1 and a phase difference film R1.

[0124] (Fabrication of polarizing plates with interlayer adhesive layer) The adhesive composition PSA1 prepared above was applied to the release surface of a 38 μm thick polyethylene terephthalate (PET) film (Mitsubishi Chemical Polyester Films, MRF38), which is a release film with a silicone treatment on the release surface, so that the thickness of the dried layer was 12 μm. The film was then dried at 155°C for 1 minute to form an interlayer adhesive layer. Next, the formed interlayer adhesive layer was transferred to the protective layer (without hard coat) side of the polarizing plate P1 to obtain a polarizing plate with an interlayer adhesive layer.

[0125] (Fabrication of circular polarizing plates with adhesive sheets) On the second phase difference film side of the phase difference film R1 (the norbornene-based resin film used as the base film when preparing the second phase difference film was peeled off), the adhesive sheets prepared in the examples and comparative examples were transferred from the release film and attached. Next, the polarizing plate with the interlayer adhesive layer prepared above was attached to the first phase difference film side of the phase difference film R1 via the interlayer adhesive layer to obtain a circular polarizing plate with an adhesive sheet. The attachment of the phase difference film R1 and the polarizing plate with the interlayer adhesive layer was carried out so that, when viewed from the side of the first phase difference film, the angle between the slow axis of the first phase difference film and the absorption axis of the polarizer was 45 degrees counterclockwise.

[0126] Next, the methods for producing each adhesive sheet in 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; manufactured by Tosoh Corporation, Coronate L) TetradC: 1,3-Bis(N,N-Diglycidylaminomethyl)cyclohexane (Polyfunctional epoxy crosslinking agent; manufactured by Mitsubishi Gas Chemical Company, TetradC) KBM403: 3-Glycidoxypropyltriethoxysilane (silane coupling agent; manufactured by Shin-Etsu Chemical Co., Ltd., KBM403)

[0128] [Preparation of (meth)acrylic polymer (A)] (Synthesis Example 1) A four-necked 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 was added to 100 parts by weight of the mixture of BA, AA, and HBA as a polymerization initiator. Nitrogen gas was introduced while gently stirring to purge the flask with nitrogen, and the polymerization reaction was carried out for 7 hours while maintaining the temperature of the liquid in the flask at around 55°C. Next, ethyl acetate was added to the resulting reaction solution to adjust the solid content concentration to 12% by weight to obtain a solution of (meth)acrylic polymer (A-1). The weight-average molecular weight (Mw) of (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 (meth)acrylic polymer (A-2) was 2.2 million.

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

[0131] [Table 1]

[0132] [Preparation of adhesive compositions and adhesive sheets] (Example 1) ~3、5~ 7. Comparative Examples 1, 2) As shown in Table 2 below, a solvent-type adhesive composition was obtained by mixing a crosslinking agent and the like with 100 parts by weight of the solid content of (meth)acrylic polymer (A).

[0133] [Table 2]

[0134] Next, the obtained adhesive composition was applied to the release surface of a 38 μm thick PET film (Mitsubishi Chemical Polyester Films, MRF38), which is a release film with a silicone treatment applied to the release surface, and then dried for a predetermined time in an air-circulating constant temperature oven set to a predetermined temperature, to obtain Example 1 ~3、5~ Adhesive sheets (15 μm thick) were formed for 7 and Comparative Examples 1 and 2. A fountain coater was used to apply the adhesive composition. The drying conditions during adhesive sheet formation are shown in Table 3, and the evaluation results of the formed adhesive sheets are shown in Table 4.

[0135] [Table 3]

[0136] [Table 4]

[0137] As shown in Table 4, the peak top stress X of 0.5 MPa or higher max The adhesive sheet of the embodiment having the above characteristics was more suitable for suppressing dimensional changes and exhibited higher durability compared to the adhesive sheet of the comparative example. [Industrial applicability]

[0138] The 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 Stack 11 Adhesive surface 20 Image display devices 51 Glass plate 52 Evaluation probes 53 End face 54 Contact load 101, 102, 103, 104 Stress-strain curves

Claims

1. An adhesive sheet formed from an adhesive composition comprising a (meth)acrylic polymer (A) and a crosslinking agent (B), The aforementioned adhesive composition does not contain an epoxy crosslinking agent. The (meth)acrylic polymer (A) has constituent units derived from aromatic ring-containing monomers, The content of the constituent units derived from the aromatic ring-containing monomer in the (meth)acrylic polymer (A) is 1 to 25% by weight. The adhesive sheet has a storage modulus G' of 0.15 MPa or more and 3.0 MPa or less at 25°C, measured under the condition of a frequency of 1 Hz. Peak top stress X max An adhesive sheet that satisfies the following equation (1). X max ≧0.5MPa (1) However, the peak top stress X max This is the peak value of stress X in the stress-strain curve obtained by the following evaluation test on the adhesive sheet. - Evaluation Test - The end face of an evaluation probe (cylindrical, 5 mm in 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 holding for 300 seconds to make the evaluation probe and the adhesive sheet adhere tightly together. Next, the evaluation probe is displaced at a constant speed of 2 μm / min in a direction perpendicular to the adhesive sheet. The stress X and strain Y in the thickness direction of the adhesive sheet, generated by the displacement of the evaluation probe, are measured, and a stress-strain curve is obtained from the measured stress X and strain Y. The evaluation test is carried out in an atmosphere of 23°C and 55% RH.

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

3. In the stress-strain curve, stress X is the peak top stress X max After reaching this point, the strain Y when it drops to 0.15 MPa. 0.15 The adhesive sheet according to claim 1 or 2, wherein the following formula (3) is satisfied. Y 0.15 ≧0.28 (3)

4. In the stress-strain curve, stress X is the peak top stress X max Distortion Y when it reaches m The adhesive sheet according to claim 3, wherein the ratio is 0.09 or higher.

5. Previous peak top stress X max The adhesive sheet according to claim 3 or 4, wherein the pressure is 0.9 MPa or higher.

6. In the stress-strain curve, stress X is the peak top stress X max Distortion Y when it reaches m The stress X is the peak top stress X max After reaching this point, the strain Y when it drops to 0.15 MPa. 0.15 Ratio Y 0.15 / Y m The adhesive sheet according to any one of claims 1 to 5, wherein the following formula (4) is satisfied. Y 0.15 / Y m ≧2 (4)

7. The adhesive sheet according to any one of claims 1 to 6, wherein the storage modulus G' at 25°C, measured under the condition of a frequency of 1 Hz, is 0.5 MPa or more.

8. An adhesive sheet according to any one of claims 1 to 7, comprising an acrylic adhesive.

9. The adhesive sheet according to any one of claims 1 to 8, wherein the crosslinking agent (B) is an isocyanate-based crosslinking agent.

10. The adhesive sheet according to any one of claims 1 to 9, wherein the amount of the crosslinking agent (B) blended with 100 parts by weight of the (meth)acrylic polymer (A) is 5 parts by weight or more.

11. An optical laminate comprising an adhesive sheet according to any one of claims 1 to 10 and an optical film.

12. An image display device comprising the optical laminate according to claim 11.

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