Adhesive sheet, optical laminate, image display device, and method for manufacturing an adhesive sheet

Abstract

To provide an adhesive sheet which has a sufficient storage elastic modulus and is improved in durability.SOLUTION: There is provided an adhesive sheet having a storage modulus G' at 25°C of 0.4 MPa or more. When a cross-section of the adhesive sheet is observed by transmission electron microscopy, the maximum diameter of the domain within the range of 6 μm in length×6 μm in width is 170 nm or less. The adhesive sheet contains, for example, two or more kinds of polymers.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an adhesive sheet, an optical laminate, an image display device, and a method for manufacturing an adhesive sheet. [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 containing 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 integrated phase difference films. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2004-051825 [Overview of the project] [Problems that the invention aims to solve]

[0004] Excessive changes in the dimensions of optical films due to temperature fluctuations 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 phase difference films. Furthermore, with the increasing prevalence of image display devices with narrow bezels, suppressing dimensional changes is becoming increasingly important. To suppress dimensional changes, one might consider increasing the elastic modulus of the adhesive sheet included in the optical laminate. However, simply increasing the elastic modulus may reduce the durability of the adhesive sheet, making it unable to keep up with dimensional changes.

[0005] Therefore, an object of the present invention is to provide an adhesive sheet having a sufficient storage elastic modulus and improved durability.

Means for Solving the Problems

[0006] When the storage elastic modulus of the adhesive sheet is increased, the polymer contained in the adhesive sheet tends to partially precipitate and a sea-island structure tends to be formed. In particular, when the blending amount of the crosslinking agent in the adhesive composition is increased to increase the storage elastic modulus of the adhesive sheet, problems of compatibility tend to occur significantly. For example, Patent Document 1 discloses an adhesive sheet having a sea-island structure. Patent Document 1 discloses that the maximum length of the island phase (domain) of the sea-island structure in the adhesive sheet is 0.3 μm to 1.0 μm. As a result of intensive studies, the present inventors newly found that the size of the domain affects the durability of the adhesive sheet, and further studies were conducted based on this finding, leading to the completion of the present invention.

[0007] The present invention provides an adhesive sheet having a storage elastic modulus G' at 25°C of 0.4 MPa or more, wherein when the cross section of the adhesive sheet is observed with a transmission electron microscope, the maximum diameter of the domain within a range of 6 μm in length and 6 μm in width is 170 nm or less.

[0008] Furthermore, the present invention provides an optical laminate including the above adhesive sheet and an optical film.

[0009] Furthermore, the present invention provides an image display device including the above optical laminate.

[0010] Furthermore, the present invention provides a method for manufacturing the above adhesive sheet, the method including: applying an adhesive composition containing a (meth)acrylic polymer (A) and an isocyanate-based crosslinking agent to a substrate to form a coating film; drying the coating film. The present invention provides a method for manufacturing an adhesive sheet.

Effects of the Invention

[0011] According to the present invention, it is possible to provide an adhesive sheet having a sufficient storage elastic modulus and improved durability.

Brief Description of the Drawings

[0012] [Figure 1] FIG. 1 is a cross-sectional view schematically showing an example of the adhesive sheet of the present invention. [Figure 2A] FIG. 2A is a schematic diagram for explaining an evaluation test for obtaining the stress-strain curve of the adhesive sheet. [Figure 2B] FIG. 2B is a schematic diagram for explaining an evaluation test for obtaining the stress-strain curve of the adhesive sheet. [Figure 2C] FIG. 2C is a schematic diagram for explaining an evaluation test for obtaining the stress-strain curve of the adhesive sheet. [Figure 2D] FIG. 2D is an enlarged view of region A in FIG. 2C. [Figure 3] FIG. 3 is a graph showing an example of the stress-strain curve of the adhesive sheet. [Figure 4] FIG. 4 is a schematic diagram for explaining the change in the volume of the 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 laminate of the present invention. [Figure 6] FIG. 6 is a cross-sectional view schematically showing an example of the optical laminate of the present invention. [Figure 7] FIG. 7 is a cross-sectional view schematically showing an example of the optical laminate of the present invention. [Figure 8] FIG. 8 is a cross-sectional view schematically showing an example of the optical laminate of the present invention. [Figure 9] FIG. 9 is a cross-sectional view schematically showing an example of the image display device of the present invention. [Figure 10] FIG. 10 is a transmission electron microscope (TEM) image of the cross-section of the adhesive sheet of Example 1. [Figure 11]Figure 11 is a TEM image of the cross-section of the adhesive sheet of Example 2. [Figure 12] Figure 12 is a TEM image of the cross-section of the adhesive sheet of Example 3. [Figure 13] Figure 13 is a TEM image of the cross-section of the adhesive sheet of Comparative Example 1. [Figure 14] Figure 14 is a TEM image of the cross-section of the adhesive sheet of Comparative Example 2. [Modes for carrying out the invention]

[0013] The present invention will be described in detail below, but the present invention is not limited to the following embodiments and can be modified and implemented as appropriate without departing from the spirit of the invention.

[0014] (Embodiment of an adhesive sheet) An example of the adhesive sheet of this embodiment is shown in Figure 1. The adhesive sheet 1 of this embodiment has a storage modulus G' of 0.4 MPa or higher at 25°C. Furthermore, when the cross-section of the adhesive sheet 1 is observed with a transmission electron microscope (TEM), the maximum diameter of the domains within a range of 6 μm x 6 μm is 170 nm or less. In this specification, a domain refers to the island-like phase of a sea-island structure formed in the adhesive sheet. Domains are usually observed as substantially circular island-like regions.

[0015] The storage modulus G' of adhesive sheet 1 at 25°C can be determined by the following method. First, a measurement sample made of the material constituting adhesive sheet 1 is prepared. 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, TA Instruments' "ARES-G2" 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

[0016] The storage modulus G' of the adhesive sheet 1 at 25°C is preferably 0.5 MPa or higher, more preferably 0.8 MPa or higher, 1.0 MPa or higher, and even more preferably 1.2 MPa or higher. The upper limit of the storage modulus G' of the adhesive sheet 1 at 25°C is not particularly limited, and is, for example, 5 MPa. The high modulus adhesive sheet 1 with a storage modulus G' within the above range is suitable for suppressing changes in the dimensions of the optical film.

[0017] The maximum diameter of a domain can be determined by the following method. First, the adhesive sheet 1 is cut and the cross-section is observed with a TEM. The magnification at this time is, for example, 20,000x. In the TEM image, domains located within a range of 6 μm vertically and 6 μm horizontally are identified. For each identified domain, the diameter (the diameter of the smallest circle that can enclose the domain) is determined. The largest value among the identified diameters can be considered the maximum diameter of the domain.

[0018] The maximum diameter of the domains is preferably 160 nm or less, more preferably 120 nm or less, even more preferably 100 nm or less, and particularly preferably 50 nm or less. In this embodiment, it is particularly preferable that no domains are visible at a magnification of 20,000 times when the cross-section of the adhesive sheet 1 is observed with a TEM. In this specification, when no domains are visible, the maximum diameter of the domains may be expressed as 0 nm.

[0019] According to the inventors' research, when domains with a large maximum diameter exist within the adhesive sheet, the hardness of the adhesive sheet tends to become uneven. Furthermore, when the adhesive sheet deforms due to dimensional changes in the optical film, regions where adhesive components are absent, such as voids, are likely to occur at the domain interfaces. When these regions occur, the adhesive strength of the adhesive sheet decreases, making it easier for the components to peel apart. In the adhesive sheet 1 of this embodiment, since the maximum diameter of the domains is 170 nm or less, the occurrence of regions where adhesive components are absent is sufficiently suppressed. As a result, the durability of the adhesive sheet 1 is improved.

[0020] The storage modulus G' and maximum domain diameter of the adhesive sheet 1 at 25°C vary depending on various factors such as the type of crosslinking agent included in the adhesive composition for forming the adhesive sheet 1, the amount of crosslinking agent, the glass transition temperature (Tg) of the base polymer included in the adhesive composition, the constituent units of the base polymer, the presence or absence of additives such as tackifiers, and the drying conditions of the adhesive composition when forming the adhesive sheet 1. It can be seen from the examples and comparative examples in Patent Document 1 that the maximum domain length in the adhesive sheet can be reduced to 0.3 to 1 μm by using an adhesive composition containing an amine compound with multiple hydroxyl groups. However, it is difficult to produce the adhesive sheet 1 of this embodiment by using only this amine compound.

[0021] In this embodiment, when the cross-section of the adhesive sheet 1 is observed with a TEM, if multiple domains exist within a range of 6 μm vertically × 6 μm horizontally, it is preferable that the shortest distance D between two of these multiple domains, each having a diameter of 80% or more of the maximum diameter mentioned above, is 350 nm or more.

[0022] The shortest distance D can be determined by the following method. First, the maximum diameter of the domain is determined by the method described above. In the TEM image, among multiple domains located within a 6 μm x 6 μm area, a domain with a diameter of 80% or more of the maximum diameter is identified. The distance between two selected domains is measured. Distance measurements are performed for all combinations of the identified domains. The minimum value of the obtained measurements can be considered as the shortest distance D. The shortest distance D is more preferably 400 nm or greater, and even more preferably 500 nm or greater. The upper limit of the shortest distance D is not particularly limited, for example, 2000 nm.

[0023] In this embodiment, when the cross-section of the adhesive sheet 1 is observed with a TEM, the number of domains having a diameter of 80% or more of the maximum diameter within a range of 6 μm vertically × 6 μm horizontally is, for example, 20 or less, preferably 15 or less, and more preferably 10 or less. When the cross-section of the adhesive sheet 1 is observed with a TEM, if no domains are observed at a magnification of 20,000 times, the number of domains is 0.

[0024] In this embodiment, when the cross-section of the adhesive sheet 1 is observed with a TEM, it is preferable that the ratio R of the area of ​​domains having a diameter of 80% or more of the maximum diameter mentioned above within a range of 6 μm vertically × 6 μm horizontally is 0.7% or less.

[0025] The ratio R can be determined by the following method. First, the maximum diameter of the domain is determined using the method described above. In the TEM image, among the domains located within a 6 μm x 6 μm area, domains with a diameter of 80% or more of the maximum diameter are identified. For each identified domain, the area is calculated by image processing, and the sum of these areas, T, is determined. Area of ​​the observation range (36 μm) 2The ratio of the total value T to ) can be considered as the ratio R. The ratio R is more preferably 0.6% or less, and even more preferably 0.5% or less. When the cross-section of the adhesive sheet 1 is observed with TEM, if no domains are visible at a magnification of 20,000 times, the ratio R is 0%.

[0026] In the adhesive sheet 1 of this embodiment, the gel fraction is not particularly limited and is, for example, 60% to 99%. The gel fraction of the adhesive sheet 1 is preferably 80% or more, more preferably 90% or more, even more preferably 94% or more, and particularly preferably 95% or more. The gel fraction of the adhesive sheet 1 can be evaluated, for example, by the following method. First, a small piece is obtained by scraping off a part of the adhesive sheet 1. Next, the obtained small piece is wrapped in a stretched porous membrane of polytetrafluoroethylene and tied with kite string. This gives a test piece. Next, the total weight (weight A) of the small piece of adhesive sheet 1, the stretched porous membrane, and the kite string is measured. The total weight of the stretched porous membrane and kite string used is defined as weight B. Next, the test piece is immersed in a 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 in a dryer set to 130°C for two hours, and then the weight C of the test piece is measured. Based on the following formula, the gel fraction of adhesive sheet 1 can be calculated from weights A, B, and C. Gel fraction (weight %) = (CB) / (AB) × 100

[0027] The adhesive sheet 1 preferably has high transparency. When the thickness of the adhesive sheet 1 is 15 μm, the haze of the adhesive sheet 1 is, for example, 1% or less, preferably 0.8% or less, and more preferably 0.5% or less.

[0028] Adhesive sheet 1 has peak top stress X max It may also satisfy the following equation (1). X max ≥0.5MPa (1) However, peak top stress X maxThis is the peak value of stress X in the stress-strain curve obtained by the following evaluation test for adhesive sheet 1.

[0029] [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.

[0030] 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 amount of deformation t1 in the thickness direction of the adhesive sheet 1 due to the displacement of the evaluation probe 52.

[0031] 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.

[0032] 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 maxBeing 0.5 MPa or more means that the stress of the adhesive sheet 1 against the change in the above volume is sufficiently large, and thereby, while suppressing the change in the dimensions of the optical film 111, its durability can also be ensured. Note that the above evaluation test of displacing the evaluation probe 52 at a very small speed (2 μm / min) is considered to well reflect the mode of the volume change of the adhesive sheet 112 accompanying the change in the dimensions of the optical film 111.

[0033] 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 further 1.5 MPa or more. X max The upper limit is, for example, 5 MPa or less.

[0034] In the stress-strain curve, the peak top stress X max When the stress X reaches the stress X m the strain Y Y m may satisfy the following formula (2).

[0035] The adhesive sheet 1 showing the curves 101 and 104 in FIG. 3 satisfies the formula (2). The Y of the curve 101 m is achieved at the apex A. Y m When Y is 0.05 or more, even when the volume of the adhesive sheet 1 changes more greatly, it can resist the 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 further 0.16 or more. Y m The upper limit is, for example, 0.3.

[0036] In the stress-strain curve, after the stress X reaches the peak top stress X max when it drops to 0.15 MPa, the strain Y 0.15 may satisfy the following formula (3). Y 0.15 ≧0.28 (3)

[0037] 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.

[0038] 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.

[0039] 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)

[0040] 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.

[0041] The thickness of the adhesive sheet 1 is not particularly limited, and is, for example, about 1 to 100 μm, preferably 2 to 50 μm, more preferably 2 to 40 μm, and even more preferably 5 to 35 μm.

[0042] The composition of the adhesive sheet 1 is not particularly limited as long as the storage modulus G' at 25°C and the maximum diameter of the domains are within the range described above, but it is preferable that it contains two or more types of polymers. In this case, the domains may be formed by the precipitation of at least one of the two or more types of polymers contained in the adhesive sheet 1.

[0043] As an example, adhesive sheet 1 is formed from an adhesive composition comprising a (meth)acrylic polymer (A) and a crosslinking agent. The crosslinking agent is typically an isocyanate-based crosslinking agent. The adhesive sheet 1 formed from this adhesive composition may contain a crosslinked product of the (meth)acrylic polymer (A) and a polymer (B) whose main component is a structural unit derived from the isocyanate-based crosslinking agent. In this specification, "main component" means the structural unit that is present in the largest amount by weight among all structural units constituting the polymer. In polymer (B), the content of structural units derived from the isocyanate-based crosslinking agent is, for example, 70% by weight or more, preferably 90% by weight or more. Polymer (B) consists, for example, substantially only of structural units derived from the isocyanate-based crosslinking agent. In adhesive sheet 1, the crosslinked product of the (meth)acrylic polymer (A) and polymer (B) may constitute an interpenetrating network (IPN) structure. This IPN structure is suitable for increasing the elastic modulus of the adhesive sheet 1 while improving durability.

[0044] If the adhesive sheet 1 contains a crosslinked (meth)acrylic polymer (A) and polymer (B), the above domains are formed, for example, by the precipitation of polymer (B) and are substantially composed of polymer (B). However, the domains may contain impurities other than polymer (B).

[0045] [(Meth)acrylic polymer (A)] (Meth)acrylic polymer (A) can function as a base polymer for acrylic adhesives. Acrylic adhesives tend to have excellent optical transparency, suitable wettability, cohesiveness, and adhesive properties, as well as excellent weather resistance and heat resistance. (Meth)acrylic polymer (A) contains, for example, constituent units derived from alkyl (meth)acrylate as its main component. In this specification, "(meth)acrylate" means acrylate and / or methacrylate.

[0046] The number of carbon atoms in the alkyl group contained in the alkyl (meth)acrylate for forming the main skeleton of the (meth)acrylic polymer (A) is not particularly limited, and is, for example, 1 to 30. This alkyl group may be linear, branched, or cyclic. Examples of alkyl groups include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, amyl, hexyl, cyclohexyl, heptyl, 2-ethylhexyl, isooctyl, nonyl, decyl, isodecyl, dodecyl, isomyristyl, lauryl, tridecyl, pentadecyl, hexadecyl, heptadecyl, and octadecyl groups. Alkyl (meth)acrylates can be used alone or in combination. The average number of carbon atoms in the alkyl group is preferably 3 to 9. The alkyl (meth)acrylate is preferably butyl acrylate.

[0047] In the (meth)acrylic polymer (A), the content of constituent units derived from alkyl (meth)acrylate is, from the viewpoint of improving the adhesion of the adhesive sheet 1, 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.

[0048] Besides alkyl (meth)acrylates, the monomers constituting the (meth)acrylic polymer (A) include at least one copolymer monomer selected from the group consisting of aromatic ring-containing monomers, amide group-containing monomers, carboxyl group-containing monomers, and hydroxyl group-containing monomers. The copolymer monomers can be used individually or in combination.

[0049] The (meth)acrylic polymer (A) preferably contains constituent units derived from an aromatic ring-containing monomer. The aromatic ring-containing monomer is a compound that contains an aromatic ring structure in its structure and also contains polymerizable unsaturated double bonds such as a (meth)acryloyl group or a vinyl group. Examples of aromatic rings include a benzene ring, a naphthalene ring, and a biphenyl ring. The aromatic ring-containing monomer is preferably an aromatic ring-containing (meth)acrylate.

[0050] Examples of aromatic ring-containing (meth)acrylates include benzyl (meth)acrylate, phenyl (meth)acrylate, o-phenylphenol (meth)acrylate, phenoxy (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxypropyl (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, ethylene oxide-modified nonylphenol (meth)acrylate, ethylene oxide-modified cresol (meth)acrylate, phenol ethylene oxide-modified (meth)acrylate, 2-hydroxy- Examples include those having a benzene ring, such as 3-phenoxypropyl (meth)acrylate, methoxybenzyl (meth)acrylate, chlorobenzyl (meth)acrylate, cresyl (meth)acrylate, and polystyrene (meth)acrylate; those having a naphthalene ring, such as hydroxyethylated β-naphthol acrylate, 2-naphthoethyl (meth)acrylate, 2-naphthoxyethyl acrylate, and 2-(4-methoxy-1-naphthoxy)ethyl (meth)acrylate; and those having a biphenyl ring, such as biphenyl (meth)acrylate. Among these, benzyl (meth)acrylate and phenoxyethyl (meth)acrylate are preferred, and benzyl acrylate is more preferred, from the viewpoint of improving the adhesive properties and durability of the adhesive sheet 1.

[0051] The (meth)acrylic polymer (A) may contain structural units derived from an amide group-containing monomer. The amide group-containing monomer is a compound that contains an amide group in its structure and also contains polymerizable unsaturated double bonds such as a (meth)acryloyl group or a vinyl group. 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. Among these, N-vinyl group-containing lactam monomers are preferred from the viewpoint of improving the durability of the adhesive sheet 1.

[0052] The (meth)acrylic polymer (A) may contain structural units derived from carboxyl group-containing monomers. Carboxyl group-containing monomers are compounds that contain a carboxyl group in their structure and also contain polymerizable unsaturated double bonds such as (meth)acryloyl groups and vinyl groups. Examples of carboxyl group-containing monomers include (meth)acrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, and crotonic acid. Among these, acrylic acid is preferred from the viewpoint of copolymerizability, cost, and improving the adhesive properties of adhesive sheet 1. By having structural units derived from carboxyl group-containing monomers, particularly acrylic acid, in the (meth)acrylic polymer (A), the self-polymerization properties of the crosslinking agent can be improved, for example. Improving the self-polymerization properties of the crosslinking agent can contribute, in particular, to suppressing peeling of the adhesive sheet in humid environments and stabilizing the physical properties of the adhesive sheet in systems with a high crosslinking agent content.

[0053] The (meth)acrylic polymer (A) may contain constituent units derived from hydroxyl group-containing monomers. Hydroxyl group-containing monomers are compounds that contain a hydroxyl group in their structure and also contain polymerizable unsaturated double bonds such as (meth)acryloyl groups and vinyl groups. Examples of hydroxyl group-containing monomers include hydroxyl group-containing alkyl (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; and hydroxyl group-containing cycloalkyl (meth)acrylates such as (4-hydroxymethylcyclohexyl)-methyl acrylate. Among these, 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate are preferred.

[0054] Among copolymer monomers, aromatic ring-containing monomers and carboxyl group-containing monomers are preferred from the viewpoint of adhesion and durability, with aromatic ring-containing monomers being particularly preferred. (Meth)acrylic polymer (A) containing structural units derived from carboxyl group-containing monomers tends to promote the reaction between isocyanate crosslinking agents by incorporating water molecules from the surrounding atmosphere. Aromatic ring-containing monomers are suitable for improving the compatibility between (meth)acrylic polymer (A) and polymer (B) and suppressing the formation of domains in the adhesive sheet 1. This also tends to improve the durability of the optical laminate in high-temperature and high-humidity environments.

[0055] In the (meth)acrylic polymer (A), the content of constituent units derived from copolymer monomers is not particularly limited, and may be, for example, 0 to 40% by weight, 0.1 to 30% by weight, or 0.1 to 20% by weight.

[0056] In the (meth)acrylic polymer (A), the content of constituent units derived from aromatic ring-containing monomers is not particularly limited, and is, for example, 3 to 25% by weight, more preferably 22% by weight or less, and even more preferably 20% by weight or less. This content is more preferably 8% by weight or more, and even more preferably 12% by weight or more.

[0057] In the (meth)acrylic polymer (A), the content of constituent units derived from amide group-containing monomers is not particularly limited, for example, 0.1 to 10% by weight, more preferably 0.2 to 8% by weight, and even more preferably 0.6 to 6% by weight.

[0058] In the (meth)acrylic polymer (A), the content of constituent units derived from carboxyl group-containing monomers is not particularly limited, and is, for example, 0.1 to 25% by weight, with 3% by weight or more being more preferred. This content is preferably 20% by weight or less, and more preferably 10% by weight or less.

[0059] Furthermore, in the (meth)acrylic polymer (A), it is preferable that the content of constituent units derived from copolymer monomers having active hydrogen that is highly reactive with isocyanate crosslinking agents, such as hydroxyl group-containing monomers, is low. In the (meth)acrylic polymer (A), the content of constituent units derived from hydroxyl group-containing monomers is, for example, 1% by weight or less, more preferably 0.5% by weight or less, and even more preferably 0.2% by weight or less. The (meth)acrylic polymer (A) may not contain substantially any constituent units derived from hydroxyl group-containing monomers.

[0060] In addition to alkyl (meth)acrylate and the copolymer monomers mentioned above, other copolymer monomers having polymerizable functional groups containing unsaturated double bonds, such as (meth)acryloyl groups or vinyl groups, can be used as monomer components to improve the adhesion and heat resistance of the adhesive sheet 1. These other copolymer monomers can be used alone or in combination.

[0061] Other copolymer monomers include, for example, acid anhydride group-containing monomers such as maleic anhydride and itaconic anhydride; caprolactone adducts of acrylic acid; sulfonic acid group-containing monomers such as allyl sulfonic acid, 2-(meth)acrylamide-2-methylpropanesulfonic acid, (meth)acrylamidepropanesulfonic acid, and sulfopropyl (meth)acrylate; phosphate group-containing monomers such as 2-hydroxyethyl acryloyl phosphate; aminoethyl (meth)acrylate and N,N-dimethylaminoethyl (meth)acrylate. Alkylaminoalkyl(meth)acrylates such as t-butylaminoethyl(meth)acrylate; alkoxyalkyl(meth)acrylates such as methoxyethyl(meth)acrylate and ethoxyethyl(meth)acrylate; succinimide monomers such as N-(meth)acryloyloxymethylenesuccinimide, N-(meth)acryloyl-6-oxyhexamethylenesuccinimide, and N-(meth)acryloyl-8-oxyoctamethylenesuccinimide; N-cyclohexylmaleimide, N- Maleimide monomers such as sopropylmaleimide, N-laurylmaleimide, and N-phenylmaleimide; itaconimide monomers such as N-methylitaconimide, N-ethylitaconimide, N-butylitaconimide, N-octylitaconimide, N-2-ethylhexylitaconimide, N-cyclohexylitaconimide, and N-laurylitaconimide; vinyl monomers such as vinyl acetate and vinyl propionate; cyanoacrylate monomers such as acrylonitrile and methacrylonitrile; glycidyl (meth)acrylates containing epoxy groups such as (meth)acrylate; glycol-based (meth)acrylates such as polyethylene glycol (meth)acrylate, polypropylene glycol (meth)acrylate, methoxyethylene glycol (meth)acrylate, and methoxypolypropylene glycol (meth)acrylate; (meth)acrylate monomers such as tetrahydrofurfuryl (meth)acrylate, fluorine (meth)acrylate, silicone (meth)acrylate, and 2-methoxyethyl acrylate;Examples include silane monomers containing silicon atoms, such as 3-acryloxypropyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, 4-vinylbutyltrimethoxysilane, 4-vinylbutyltriethoxysilane, 8-vinyloctyltrimethoxysilane, 8-vinyloctyltriethoxysilane, 10-methacryloyloxydecyltrimethoxysilane, 10-acryloyloxydecyltrimethoxysilane, 10-methacryloyloxydecyltriethoxysilane, and 10-acryloyloxydecyltriethoxysilane.

[0062] Furthermore, other copolymer monomers include, for example, polyfunctional monomers having two or more unsaturated double bonds, such as tripropylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, bisphenol A diglycidyl ether di(meth)acrylate, neopentyl glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and caprolactone-modified dipentaerythritol hexa(meth)acrylate.

[0063] When using other copolymer monomers as monomer components, the content of constituent units derived from other copolymer monomers in the (meth)acrylic polymer (A) is preferably 10% by weight or less, more preferably 7% by weight or less, and even more preferably 5% by weight or less.

[0064] The weight-average molecular weight of (meth)acrylic polymer (A) is typically 300,000 to 4,000,000. From the viewpoint of durability, the weight-average molecular weight of (meth)acrylic polymer (A) is preferably 300,000 to 3,000,000, and more preferably 400,000 to 2,200,000. A weight-average molecular weight of 300,000 or more is preferable in terms of heat resistance. If the weight-average molecular weight is 4,000,000 or less, the adhesive sheet tends not to harden easily and peeling is less likely to occur. The weight-average molecular weight (Mw) / number-average molecular weight (Mn), which represents the molecular weight distribution, is preferably 1.8 to 10, more preferably 1.8 to 7, and even more preferably 1.8 to 5. A molecular weight distribution (Mw / Mn) of 10 or less is preferable in terms of durability. The weight-average molecular weight and molecular weight distribution (Mw / Mn) are determined from values ​​calculated by GPC (gel permeation chromatography) and converted to polystyrene equivalent.

[0065] (Meth)acrylic polymer (A) can be produced by known polymerization methods such as solution polymerization, radiation polymerization such as electron beam or UV, bulk polymerization, emulsion polymerization, and various radical polymerization methods. The resulting (meth)acrylic polymer (A) may be a random copolymer, block copolymer, graft copolymer, or any other type.

[0066] In solution polymerization, polymerization solvents such as ethyl acetate and toluene are used. Solution polymerization is carried out under reaction conditions of approximately 50-70°C for 5-30 hours, for example, by adding a polymerization initiator under a stream of an inert gas such as nitrogen.

[0067] The polymerization initiators, chain transfer agents, emulsifiers, etc., used in radical polymerization are not particularly limited and can be selected and used as appropriate. The weight-average molecular weight of the (meth)acrylic polymer (A) can be controlled by the amount of polymerization initiator and chain transfer agent used, the reaction conditions, etc. Therefore, the amount of polymerization initiator and chain transfer agent used is adjusted as appropriate according to their composition.

[0068] Examples of polymerization initiators include azo-based initiators such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-amidinopropane)dihydrochloride, 2,2'-azobis[2-(5-methyl-2-imidazolin-2-yl)propane]dihydrochloride, 2,2'-azobis(2-methylpropionamidine)disulfate, 2,2'-azobis(N,N'-methyleneisobutylamidine), and 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine]hydrate (manufactured by Wako Pure Chemical Industries, Ltd., VA-057); persulfates such as potassium persulfate and ammonium persulfate; di(2-ethylhexyl)peroxydicarbonate, di(4-t-butylcyclohexyl)peroxydicarbonate, and di-sec-butylperoxy Examples of peroxide initiators include, but are not limited to, dicarbonates, t-butyl peroxyneodecanoate, t-hexyl peroxypivalate, t-butyl peroxypivalate, dilauroyl peroxide, di-n-octanoyl peroxide, 1,1,3,3-tetramethylbutyl peroxy-2-ethylhexanoate, di(4-methylbenzoyl) peroxide, dibenzoyl peroxide, t-butyl peroxyisobutyrate, 1,1-di(t-hexyl peroxy)cyclohexane, t-butyl hydroperoxide, and hydrogen peroxide; as well as redox initiators combining peroxides with reducing agents, such as combinations of persulfates and sodium bisulfite, and combinations of peroxides and sodium ascorbate.

[0069] Polymerization initiators can be used alone or in combination, but the total amount used is preferably about 0.005 to 1 part by weight, and more preferably about 0.02 to 0.5 parts by weight, per 100 parts by weight of monomer components.

[0070] Examples of chain transfer agents include lauryl mercaptan, glycidyl mercaptan, mercaptoacetic acid, 2-mercaptoethanol, thioglycolic acid, 2-ethylhexyl thioglycolate, and 2,3-dimercapto-1-propanol. Chain transfer agents may be used individually or in combination of two or more, but the total amount used should be approximately 0.1 parts by weight or less per 100 parts by weight of monomer components.

[0071] Examples of emulsifiers used in emulsion polymerization include anionic emulsifiers such as sodium lauryl sulfate, ammonium lauryl sulfate, sodium dodecylbenzenesulfonate, ammonium polyoxyethylene alkyl ether sulfate, and sodium polyoxyethylene alkylphenyl ether sulfate; and nonionic emulsifiers such as polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene fatty acid esters, and polyoxyethylene-polyoxypropylene block polymers. Emulsifiers can be used alone or in combination.

[0072] Reactive emulsifiers include those incorporating radical polymerizable functional groups such as propenyl groups and allyl ether groups. Specific examples of such emulsifiers include Aqualon HS-10, HS-20, KH-10, BC-05, BC-10, BC-20 (all manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), and Adekaria Soap SE10N (manufactured by ADEKA Corporation). Reactive emulsifiers are preferred because they are incorporated into the polymer chain after polymerization, improving water resistance. The amount of emulsifier used is preferably 0.3 to 5 parts by weight per 100 parts by weight of the total amount of monomer components, and more preferably 0.5 to 1 part by weight due to polymerization stability and mechanical stability.

[0073] In radiation polymerization, monomer components are polymerized by irradiating them with radiation such as electron beams or UV to produce (meth)acrylic polymers (A). When radiation polymerization is performed using electron beams, it is not particularly necessary to include a photoinitiator in the monomer components. When radiation polymerization is performed using UV, a photoinitiator may be included in the monomer components due to the advantage of being able to shorten the polymerization time. Photoinitiators can be used alone or in combination.

[0074] The photopolymerization initiator is not particularly limited as long as it initiates photopolymerization, and commonly used photopolymerization initiators can be used. Examples of photopolymerization initiators include benzoin ether-based, acetophenone-based, α-ketol-based, photoactive oxime-based, benzoin-based, benzyl-based, benzophenone-based, ketal-based, and thioxanthone-based compounds. The amount of photopolymerization initiator used is 0.05 to 1.5 parts by weight, preferably 0.1 to 1 part by weight, per 100 parts by weight of monomer component. The photopolymerization initiator can be used alone or in combination.

[0075] [Isocyanate-based crosslinking agents] As an isocyanate crosslinking agent, a compound having at least two isocyanate groups (isocyanate compound) can be used. Preferably, the number of isocyanate groups in the isocyanate compound is three or more. The upper limit of the number of isocyanate groups is not particularly limited, but is, for example, five. Examples of isocyanate compounds include aromatic isocyanate compounds, alicyclic isocyanate compounds, and aliphatic isocyanate compounds. It is preferable that the isocyanate crosslinking agent can self-polymerize by reaction with water.

[0076] Examples of aromatic isocyanate compounds include phenylenediisocyanate, 2,4-tolylenediisocyanate, 2,6-tolylenediisocyanate, 2,2'-diphenylmethanediisocyanate, 4,4'-diphenylmethanediisocyanate, 4,4'-toluidinediisocyanate, 4,4'-diphenyletherdiisocyanate, 4,4'-diphenyldiisocyanate, 1,5-naphthalenediisocyanate, and xylylenediisocyanate.

[0077] Examples of alicyclic isocyanate compounds 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.

[0078] Examples of aliphatic isocyanate compounds 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.

[0079] Examples of isocyanate-based crosslinking agents include polymers (dimers, trimers, pentamers, etc.) of the above-mentioned isocyanate compounds, adducts obtained by adding them to polyhydric alcohols such as trimethylolpropane, urea-modified compounds, biuret-modified compounds, allophanate-modified compounds, isocyanurate-modified compounds, carbodiimide-modified compounds, urethane prepolymers obtained by adding them to polyether polyols, polyester polyols, acrylic polyols, polybutadiene polyols, polyisoprene polyols, etc.

[0080] The isocyanate crosslinking agent is preferably an aromatic isocyanate compound and its derivatives, more preferably tolylene diisocyanate and its derivatives, in other words, a tolylene diisocyanate-based (TDI-based) crosslinking agent. From the viewpoint of reactivity, TDI-based crosslinking agents are more suitable for the production of the adhesive sheet 1 of this embodiment than xylylene diisocyanate and its derivatives, in other words, xylylene diisocyanate-based (XDI-based) crosslinking agents. In particular, the isocyanate crosslinking agent preferably contains an adduct of a polyhydric alcohol and tolylene diisocyanate as a TDI-based crosslinking agent. A specific example of this adduct is the trimethylolpropane / tolylene diisocyanate trimer adduct.

[0081] Examples of commercially available isocyanate-based crosslinking agents include the following products manufactured by Tosoh Corporation: "Millionate MT," "Millionate MTL," "Millionate MR-200," "Millionate MR-400," "Coronate L," "Coronate HL," and "Coronate HX," and the following products manufactured by Mitsui Chemicals Corporation: "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," with Coronate L being preferred.

[0082] The isocyanate crosslinking agent may be used alone or in a mixture of two or more of the above-mentioned types. The amount of isocyanate crosslinking agent is, for example, 5 parts by weight or more, preferably 8 parts by weight or more, more preferably 10 parts by weight or more, and even more preferably 11 parts by weight or more, per 100 parts by weight of (meth)acrylic polymer (A). The amount of isocyanate crosslinking agent is, for example, 30 parts by weight or less, preferably 20 parts by weight or less, more preferably 15 parts by weight or less, and even more preferably 13 parts by weight or less, per 100 parts by weight of (meth)acrylic polymer (A).

[0083] In an adhesive composition, when the amount of isocyanate crosslinking agent is approximately 5 parts by weight or more per 100 parts by weight of (meth)acrylic polymer (A), when an adhesive sheet is prepared, the isocyanate crosslinking agents may react with each other, forming polymer (B) which mainly consists of structural units derived from the isocyanate crosslinking agents. In this case, the formation of polymer (B) tends to proceed more dominantly than the reaction between the isocyanate crosslinking agent and the (meth)acrylic polymer (A). Polymer (B) is suitable for suppressing dimensional changes in the adhesive sheet by imparting sufficient cohesive force to the adhesive sheet. In other words, polymer (B) is suitable for suppressing display unevenness and light leakage in image display devices. Furthermore, the combination of (meth)acrylic polymer (A) and polymer (B) is suitable for improving the durability of the adhesive sheet in high-temperature and high-humidity environments.

[0084] [Other ingredients] The adhesive composition may contain other crosslinking agents besides isocyanate-based crosslinking agents. Examples of other crosslinking agents include peroxide-based crosslinking agents, epoxy-based crosslinking agents, imine-based crosslinking agents, and polyfunctional metal chelates. The amount of other crosslinking agents is preferably 2 parts by weight or less, and more preferably 1 part by weight or less, per 100 parts by weight of (meth)acrylic polymer (A). From the viewpoint of the durability of the adhesive sheet, it is preferable that the adhesive composition substantially does not contain other crosslinking agents, especially epoxy-based crosslinking agents.

[0085] The adhesive composition may further contain a (meth)acrylic oligomer.

[0086] The (meth)acrylic oligomer may have the same composition as the (meth)acrylic polymer (A) described above, except that it differs in its weight-average molecular weight (Mw). The weight-average molecular weight (Mw) of the (meth)acrylic oligomer 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.

[0087] (Meth)acrylic oligomers 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.

[0088] (Meth)acrylic oligomers preferably have constituent units derived from (meth)acrylic monomers 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 monomers preferably have a cyclic structure, and more preferably have two or more cyclic structures. Furthermore, when ultraviolet irradiation is performed during the polymerization of (meth)acrylic oligomers and / or during the formation of adhesive sheets, the progress of polymerization and / or formation is less likely to be inhibited. Therefore, it is preferable that the monomers do 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.

[0089] Specific examples of (meth)acrylic oligomers 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.

[0090] The polymerization method for (meth)acrylic polymer (A) described above can be used for the polymerization of (meth)acrylic oligomers.

[0091] If the adhesive composition contains a (meth)acrylic oligomer, the amount of oligomer 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 (meth)acrylic polymer (A). The lower limit of the amount of oligomer 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 (meth)acrylic polymer (A). The adhesive composition does not have to contain a (meth)acrylic oligomer.

[0092] The adhesive composition may further contain known additives. Examples of additives include silane coupling agents, solvents, powders such as colorants and pigments, dyes, surfactants, plasticizers, tackifiers, surface lubricants, leveling agents, rework enhancers, softeners, antioxidants, anti-aging agents, light stabilizers, UV absorbers, polymerization inhibitors, inorganic or organic fillers, metal powders, particles, foils, and the like. Furthermore, a redox system with a reducing agent may be used within a controllable range. These additives can be used in amounts 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 (meth)acrylic polymer (A).

[0093] Specific 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.

[0094] If the adhesive composition 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 (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 does not need to contain a silane coupling agent.

[0095] The adhesive composition may further contain, but may not contain, an amine compound containing multiple hydroxyl groups.

[0096] The adhesive composition can be of various types, such as 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 excellent durability, the adhesive composition may be of the solvent type. The solvent type adhesive composition does not need to contain a photocuring agent such as an ultraviolet curing agent.

[0097] A method for manufacturing the adhesive sheet 1 includes, for example, applying an adhesive composition containing a (meth)acrylic polymer (A) and an isocyanate crosslinking agent to a substrate to form a coating film, and drying the obtained coating film.

[0098] For example, a release film can be used as the base material. The adhesive sheet 1 formed on the release film can be transferred to, for example, an optical film. The base material may also be an optical film. In this case, an optical laminate can be obtained by forming the adhesive sheet 1.

[0099] The release film can be used as a separator after the adhesive sheet 1 has been transferred to the optical film, until the adhesive sheet 1 is put into practical use, thus simplifying the process.

[0100] Examples of materials that can be used to construct the release film include porous materials such as plastic film, paper, cloth, and nonwoven fabric, as well as appropriate thin sheets such as nets, foamed sheets, metal foils, and laminates thereof. However, plastic film is preferably used due to its excellent surface smoothness.

[0101] The plastic film is not particularly limited and includes, for example, polyethylene film, polypropylene film, polybutene film, polybutadiene film, polymethylpentene film, polyvinyl chloride film, vinyl chloride copolymer film, polyethylene terephthalate film, polybutylene terephthalate film, polyurethane film, and ethylene-vinyl acetate copolymer film.

[0102] The thickness of the release film is typically 5 to 200 μm, preferably about 5 to 100 μm. The release film is treated with a release agent such as a silicone-based, fluorine-based, or long-chain alkyl-based agent. The release film may also be treated with a release and antifouling agent such as a fatty acid amide-based release agent or silica powder, or with an antistatic treatment such as a coating, kneading, or vapor deposition.

[0103] A solution containing the adhesive composition (adhesive solution) may be applied to the substrate. The solid content concentration of the adhesive solution is, for example, 5 to 50% by weight, preferably 10 to 40% by weight. The adhesive solution can be prepared by appropriately adding the same solvent as the polymerization solvent or a different solvent to the adhesive composition, depending on the polymerization form of the (meth)acrylic polymer (A).

[0104] Various methods can be used to apply the adhesive composition to the substrate, including, 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, and extrusion coating methods using a die coater. The amount of adhesive composition applied can be appropriately adjusted according to the desired thickness of the adhesive sheet 1.

[0105] By drying the coating film, the coating film hardens and the adhesive sheet 1 is formed. The drying temperature of the coating film is not particularly limited, but is, for example, 130°C or lower, preferably 125°C or lower, more preferably 120°C or lower, even more preferably 110°C or lower, and particularly preferably 100°C or lower. The drying temperature of the coating film may be 60°C or higher, or 80°C or higher. When the drying temperature is 60°C or higher, for example, the reaction of the isocyanate-based crosslinking agent proceeds smoothly, which tends to improve the cohesive force of the adhesive sheet 1 and reduce display unevenness in the image display device. When the drying temperature is 130°C or lower, for example, the reaction rate of the isocyanate-based crosslinking agent can be appropriately adjusted, which tends to maintain good compatibility between the (meth)acrylic polymer (A) and polymer (B) and ensure transparency. In other words, by setting the drying temperature to 130°C or lower, the maximum diameter of the domains in the adhesive sheet 1 tends to be reduced.

[0106] The drying time of the coated film can be appropriately adjusted according to the composition of the adhesive composition, preferably 30 to 300 seconds, more preferably 40 to 240 seconds, and particularly preferably 60 to 180 seconds.

[0107] (Embodiment of an 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.

[0108] 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.

[0109] A polarizing plate is, for example, a laminate including a polarizer and a transparent protective film. The transparent protective film is, for example, positioned in contact with the main surface (the surface with the largest area) of the layered polarizer. The polarizer may be positioned between two transparent protective films.

[0110] The polarizer is not particularly limited, and various types can be used. Examples of polarizers include hydrophilic polymer films such as polyvinyl alcohol-based films, partially formalized polyvinyl alcohol-based films, and partially saponified ethylene-vinyl acetate copolymer films, to which dichroic substances such as iodine or dichroic dyes are adsorbed and then uniaxially stretched; and polyene-based oriented films such as dehydrated polyvinyl alcohol products and dehydrochlorinated polyvinyl chloride products. Among these, polarizers made of polyvinyl alcohol-based films and dichroic substances such as iodine are preferred, and iodine-based polarizers containing iodine and / or iodide ions are more preferred. The thickness of the polarizer is not particularly limited, but is generally about 5 to 80 μm.

[0111] A polarizer made by dyeing a polyvinyl alcohol-based film with iodine and uniaxially stretching it can be produced, for example, by dyeing the polyvinyl alcohol by immersing it in an aqueous solution of iodine and stretching it to 3 to 7 times its original length. If necessary, the polyvinyl alcohol can also be immersed in an aqueous solution of potassium iodide containing boric acid, zinc sulfate, zinc chloride, etc. Furthermore, if necessary, the polyvinyl alcohol-based film may be washed by immersing it in water before dyeing. Washing the polyvinyl alcohol-based film with water can remove dirt and anti-blocking agents from the surface of the film, and also has the effect of suppressing the occurrence of uneven dyeing by swelling the polyvinyl alcohol-based film. The stretching of the polyvinyl alcohol-based film may be performed after dyeing with iodine, during dyeing, or before dyeing with iodine. Stretching may be performed in an aqueous solution of boric acid, potassium iodide, etc., or in a water bath.

[0112] As a polarizer, a thin polarizer with a thickness of 10 μm or less can also be used. From the viewpoint of miniaturization, the thickness of the polarizer is preferably 1 to 7 μm. Such thin polarizers are preferable because they have less thickness variation, excellent visibility, excellent durability due to minimal dimensional change, and allow for the miniaturization of the polarizing plate.

[0113] Examples of thin polarizers include those described in Japanese Patent Publication No. 51-069644, Japanese Patent Publication No. 2000-338329, International Publication No. 2010 / 100917, Japanese Patent No. 4751481, and Japanese Patent Publication No. 2012-073563. These thin polarizers can be obtained by a manufacturing method that includes a step of stretching a polyvinyl alcohol-based resin (hereinafter also referred to as PVA-based resin) layer and a stretchable resin substrate in a laminated state, and a step of dyeing. With this manufacturing method, since the PVA-based resin layer is supported by the stretchable resin substrate, even if the PVA-based resin layer is thin, problems such as breakage due to stretching can be suppressed.

[0114] Among manufacturing methods that include a step of stretching in a laminated state and a step of dyeing, the method described in International Publication No. 2010 / 100917, Japanese Patent No. 4751481, and Japanese Patent Application Publication No. 2012-073563, which includes a step of stretching in an aqueous boric acid solution, is preferred because it can be stretched to a high magnification and improve the polarization performance. In particular, the method described in Japanese Patent No. 4751481 and Japanese Patent Application Publication No. 2012-073563, which includes a step of auxiliary air stretching before stretching in an aqueous boric acid solution, is preferred.

[0115] As the material for forming the transparent protective film provided on one or both sides of the polarizer, for example, a thermoplastic resin with excellent transparency, mechanical strength, thermal stability, moisture barrier properties, and isotropy can be used. Specific examples of such thermoplastic resins include cellulose resins such as triacetylcellulose, polyester resins, polyethersulfone resins, polysulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, (meth)acrylic resins, cyclic polyolefin resins (norbornene-based resins), polyarylate resins, polystyrene resins, polyvinyl alcohol resins, and mixtures thereof. The material of the transparent protective film may also be a thermosetting resin or UV-curing resin such as (meth)acrylic, urethane, acrylic urethane, epoxy, or silicone-based resins. When a polarizer has two transparent protective films, the materials of the two transparent protective films may be the same or different. For example, a transparent protective film made of thermoplastic resin may be bonded to one main surface of the polarizer via an adhesive, and a transparent protective film made of thermosetting resin or UV-curing resin may be bonded to the other main surface of the polarizer. The transparent protective film may contain one or more additives. Examples of additives include UV absorbers, antioxidants, lubricants, plasticizers, mold release agents, color inhibitors, flame retardants, nucleating agents, antistatic agents, pigments, and colorants. The content of thermoplastic resin in the transparent protective film is preferably 50 to 100% by weight, more preferably 50 to 99% by weight, even more preferably 60 to 98% by weight, and particularly preferably 70 to 97% by weight. When the content of thermoplastic resin in the transparent protective film is 50% by weight or more, the high transparency inherent in thermoplastic resin tends to be fully expressed.

[0116] The thickness of the transparent protective film can be determined as appropriate, but generally it is around 10 to 200 μm, considering factors such as strength, ease of handling, and thinness.

[0117] The polarizer and the transparent protective film are typically bonded together via a water-based adhesive. Examples of water-based adhesives include isocyanate adhesives, polyvinyl alcohol adhesives, gelatin adhesives, vinyl latex, water-based polyurethane, and water-based polyester. Other adhesives besides those mentioned above include UV-curing adhesives and electron beam-curing adhesives. Electron beam-curing adhesives for polarizers exhibit suitable adhesion to various transparent protective films. The adhesive may also contain metal compound fillers.

[0118] In polarizing plates, a phase difference film or the like can be formed on the polarizer instead of a transparent protective film. Furthermore, another transparent protective film, a phase difference film, or the like can be added on top of the transparent protective film.

[0119] Regarding the transparent protective film, a hard coat layer may be provided on the surface that is in contact with the polarizer and the surface that is opposite it, and treatments for purposes such as anti-reflection, anti-sticking, diffusion, and anti-glare may be applied.

[0120] As the phase difference film, one obtained by stretching a polymer film or one obtained by oriented and immobilizing a liquid crystal material can be used. The phase difference film has birefringence in the in-plane direction and / or in the thickness direction, for example.

[0121] Examples of phase difference films include anti-reflective phase difference films (see Japanese Patent Publication No. 2012-133303

[0221] ,

[0222] ,

[0228] ), phase difference films for viewing angle compensation (see Japanese Patent Publication No. 2012-133303

[0225] ,

[0226] ), and tilt-oriented phase difference films for viewing angle compensation (see Japanese Patent Publication No. 2012-133303

[0227] ).

[0122] As for the phase difference film, any known phase difference film can be used, as long as it substantially possesses the above-mentioned functions, for example, the phase difference value, arrangement angle, three-dimensional birefringence, and whether it is single-layer or multi-layer.

[0123] The thickness of the phase difference film is preferably 20 μm or less, more preferably 10 μm or less, even more preferably 1 to 9 μm, and particularly preferably 3 to 8 μm.

[0124] A phase difference film, for example, is composed of two layers: a quarter-wave plate and a half-wave plate, on which liquid crystal material is oriented and fixed.

[0125] 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.

[0126] Examples of materials that can be used to construct the separator 3 include plastic films such as polyethylene, polypropylene, polyethylene terephthalate, and polyester film; porous materials such as paper, cloth, and nonwoven fabric; nets, foamed sheets, metal foils, and suitable thin sheets such as laminates thereof. However, plastic films are preferably used due to their excellent surface smoothness.

[0127] The plastic film is not particularly limited as long as it is a film that can protect the adhesive sheet 1, and examples include polyethylene film, polypropylene film, polybutene film, polybutadiene film, polymethylpentene film, polyvinyl chloride film, vinyl chloride copolymer film, polyethylene terephthalate film, polybutylene terephthalate film, polyurethane film, ethylene-vinyl acetate copolymer film, etc.

[0128] The thickness of the separator 3 is typically 5 to 200 μm, preferably about 5 to 100 μm. The separator 3 may be subjected to release and antifouling treatments using silicone-based, fluorine-based, long-chain alkyl-based, or fatty acid amide-based release agents, silica powder, etc., as well as antistatic treatments such as coating, mixing, or vapor deposition, as needed. In particular, the release properties from the adhesive sheet 1 can be further improved by appropriately performing release treatments such as silicone treatment, long-chain alkyl treatment, or fluorine treatment on the surface of the separator 3.

[0129] As mentioned above, the release film used when preparing the adhesive sheet 1 may also be used as the separator 3.

[0130] 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.

[0131] Any known adhesive can be used for the interlayer adhesive 4. The adhesive sheet 1 may also be used as the interlayer adhesive 4.

[0132] 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.

[0133] 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.

[0134] The protective film 5 may be bonded to the optical film 2 with any adhesive. Bonding with an adhesive sheet 1 is also possible.

[0135] 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.

[0136] 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.

[0137] (Embodiment of an image display device) An example of an image display device of this embodiment is shown in Figure 9. The image display device 11 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 11 has optical laminates 10B, 10C, and 10D as shown in Figures 6 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.

[0138] The image display device 11 in Figure 9 may be an organic EL display or a liquid crystal display. However, the image display device 11 is not limited to these examples. The image display device 11 may also be an electroluminescent (EL) display, a plasma display (PD), a field emission display (FED), etc. The image display device 11 can be used for consumer electronics applications, automotive applications, public information display (PID) applications, etc.

[0139] The image display device of this embodiment may have any configuration as long as it includes the optical laminate of this embodiment. [Examples]

[0140] 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.

[0141] [(meth)acrylic polymer A1] A monomer mixture containing 94.9 parts by weight of butyl acrylate (BA), 5 parts by weight of acrylic acid (AA), 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. Furthermore, 0.1 parts by weight of 2,2'-azobisisobutyronitrile (AIBN) was added to 100 parts by weight of the monomer mixture as a polymerization initiator along with ethyl acetate. After introducing nitrogen gas and purging the mixture with nitrogen while gently stirring, the polymerization reaction was carried out for 7 hours while maintaining the temperature of the solution in the flask at around 55°C. Subsequently, ethyl acetate was added to the resulting reaction solution to adjust the solid content to 30% and obtain a solution of (meth)acrylic polymer A1.

[0142] [(meth)acrylic polymer A2] A solution of (meth)acrylic polymer A2 was prepared in the same manner as for (meth)acrylic polymer A1, except that the monomers used were changed as shown in Table 1.

[0143] [Table 1]

[0144] The abbreviations used in Table 1 are as follows: BA: n-butyl acrylate BzA: Benzyl acrylate AA: Acrylic acid HBA: 4-hydroxybutyl acrylate AIBN: Azo polymerization initiator, 2,2'-azobisisobutyronitrile (manufactured by Kishida Chemical Co., Ltd.)

[0145] [Making adhesive sheets] (Examples 1-5 and Comparative Examples 1-2) A solvent-type adhesive composition was obtained by mixing (meth)acrylic polymers, crosslinking agents, and additives to the composition shown in Table 2 below. Next, the adhesive composition was applied to the surface of a PET film, which was the base film (separator), so that the thickness of the adhesive sheet after drying would be 15 μm. A fountain coater was used to apply the adhesive composition. The resulting coated film was dried for 1 minute in an air-circulating constant-temperature oven set to the drying temperature shown in Table 2 to form the adhesive sheets of Examples 1-5 and Comparative Examples 1-2.

[0146] [Table 2]

[0147] The abbreviations used in Table 2 are as follows: C / L: Trimethylolpropane / Tolylene diisocyanate (manufactured by Tosoh Corporation, product name: Coronate L) KBM403: γ-Glycidoxypropyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.)

[0148] [evaluation] <Weight-average molecular weight (Mw) of (meth)acrylic polymers> The weight-average molecular weight (Mw) of the obtained (meth)acrylic polymer was measured by GPC (gel permeation chromatography). • Analytical instrument: Tosoh Corporation, HLC-8120GPC • Column: Tosoh Corporation, G7000H XL +GMH XL +GMH XL • Column size: 7.8mmφ x 30cm each, total 90cm Column temperature: 40°C ·Flow rate: 0.8ml / min ·Injection volume: 100μl • Eluent: Tetrahydrofuran • Detector: Differential refractometer (RI) • Standard sample: Polystyrene

[0149] <thickness> The thickness of adhesive sheets and other materials was measured using a dial gauge (manufactured by Mitutoyo).

[0150] <Gel fraction> The gel fraction of the fabricated adhesive sheet was evaluated using the method described above. The weight of a small piece obtained by scraping off a portion of the adhesive sheet was approximately 0.2 g. For the stretched porous polytetrafluoroethylene membrane, Nitto Denko NTF1122 (average pore size 0.2 μm) was used.

[0151] <Storage modulus G'> The storage modulus G' of the adhesive sheet at 25°C was evaluated using the method described above. Dynamic viscoelasticity measurements were performed using the "ARES-G2" instrument manufactured by TA Instruments.

[0152] <Observation of the cross-section of the adhesive sheet> The cross-section of the adhesive sheet was observed using TEM in the following manner. First, the adhesive sheet was stained with heavy metal (RuO4). Next, this adhesive sheet was embedded in resin. The embedded adhesive sheet was cut using the ultrathin sectioning method to prepare measurement samples with a thickness of approximately 100 nm. The cross-section of the obtained measurement samples was observed using TEM. A Hitachi High-Tech HT7820 was used as the TEM. For TEM observation, the acceleration voltage was set to 100 kV and the magnification was set to 20,000 times.

[0153] Figures 10 and 11 are TEM images of the cross-sections of the adhesive sheets of Examples 1 and 2, respectively. As can be seen from Figures 10 and 11, no domains could be identified from the cross-sections of the adhesive sheets of Examples 1 and 2. Similarly, no domains could be identified from the cross-sections of the adhesive sheets of Examples 4 and 5.

[0154] Figures 12-14 are TEM images of the cross-sections of the adhesive sheets of Example 3, Comparative Examples 1 and 2, respectively. As can be seen from Figures 12-14, domains were identified in the cross-sections of the adhesive sheets of Example 3, Comparative Examples 1 and 2. Image processing was performed on these TEM images of the cross-sections of the adhesive sheets, and the maximum diameter of the domains, the shortest distance D between two domains with a diameter of 80% or more of the maximum diameter, the number of domains with a diameter of 80% or more of the maximum diameter, and the ratio R of the areas of domains with a diameter of 80% or more of the maximum diameter were identified using the method described above.

[0155] <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.

[0156] The following describes the method for forming the circular polarizing plate with adhesive sheet used to evaluate its humidification durability.

[0157] <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.

[0158] (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.

[0159] <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.

[0160] 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.

[0161] (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.

[0162] [ka]

[0163] (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.

[0164] <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.

[0165] 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.

[0166] (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.

[0167] (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.

[0168] [Table 3]

[0169] As can be seen from Figures 10-14 and Table 3, in the adhesive sheets of the examples, domains could not be identified, or if they could be identified, their maximum diameter was 170 nm or less, which was smaller than that of the adhesive sheets of the comparative examples. As can be seen from Table 3, the adhesive sheets of the examples, in which the maximum diameter of the domains was 170 nm or less, showed improved durability compared to the adhesive sheets of the comparative examples. [Industrial applicability]

[0170] The adhesive composition of the present invention can be suitably used in the production of adhesive sheets for image display devices such as EL displays and liquid crystal displays. [Explanation of Symbols]

[0171] 1 Adhesive sheet 2 Optical film 10A, 10B, 10C, 10D Optical Stack 11 Image display device

Claims

1. An adhesive sheet having a storage modulus G' of 0.4 MPa or more at 25°C, The adhesive sheet is formed from an adhesive composition comprising a (meth)acrylic polymer (A) and an isocyanate crosslinking agent. The (meth)acrylic polymer (A) comprises structural units derived from alkyl (meth)acrylate and structural units derived from aromatic ring-containing monomers. The amount of the isocyanate-based crosslinking agent in the adhesive composition is 5 parts by weight or more per 100 parts by weight of the (meth)acrylic polymer (A), An adhesive sheet in which, when the cross-section of the adhesive sheet is observed with a transmission electron microscope, the maximum diameter of the domains within a range of 6 μm x 6 μm is 170 nm or less.

2. The adhesive sheet according to claim 1, comprising two or more types of polymers.

3. When the cross-section of the adhesive sheet was observed with a transmission electron microscope, multiple domains were found within a range of 6 μm x 6 μm. The adhesive sheet according to claim 1 or 2, wherein the shortest distance between two of the plurality of domains having a diameter of 80% or more of the largest diameter is 350 nm or more.

4. The adhesive sheet according to any one of claims 1 to 3, wherein when the cross-section of the adhesive sheet is observed with a transmission electron microscope, the number of domains having a diameter of 80% or more of the maximum diameter within a range of 6 μm vertically × 6 μm horizontally is 20 or less.

5. The adhesive sheet according to any one of claims 1 to 4, wherein when the cross-section of the adhesive sheet is observed with a transmission electron microscope, the ratio of the area of ​​domains having a diameter of 80% or more of the maximum diameter within a range of 6 μm vertically × 6 μm horizontally is 0.7% or less.

6. The adhesive sheet according to any one of claims 1 to 5, wherein the domain is substantially composed of a polymer (B) mainly comprising a structural unit derived from the isocyanate crosslinking agent.

7. The adhesive sheet according to any one of claims 1 to 6, wherein the amount of the isocyanate crosslinking agent in the adhesive composition is 15 parts by weight or less per 100 parts by weight of the (meth)acrylic polymer (A).

8. The adhesive sheet according to any one of claims 1 to 7, wherein the isocyanate-based crosslinking agent is a tolylene diisocyanate-based crosslinking agent.

9. An optical laminate comprising an adhesive sheet according to any one of claims 1 to 8 and an optical film.

10. An image display device comprising the optical laminate described in claim 9.

11. A method for manufacturing an adhesive sheet according to any one of claims 1 to 8, The adhesive composition containing the (meth)acrylic polymer (A) and the isocyanate crosslinking agent is applied to a substrate to form a coating film. The coating film is dried at a temperature of 130°C or lower. A method for manufacturing an adhesive sheet, including the method described above.

Images