Optical laminates, adhesive sheets, and image display devices

Abstract

To provide an optical laminate including an adhesive sheet having a sufficient gel fraction and having improved durability.SOLUTION: There is provided an optical laminate which comprises an adhesive sheet having a gel fraction of 70% or more and an optical film. The maximum value of the frequency in the histogram prepared by the following test method is 1400 or more. Test method: a histogram of elastic modulus with a class width of 0.1 MPa is prepared by measuring the elastic modulus so that the number of measurement points is 65536 for the range of 500 nm (length) × 500 nm (width) on the surface of an adhesive sheet using an atomic force microscope.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

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

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

[0004] Excessive dimensional changes in 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 approach is to increase the elastic modulus of the adhesive sheet contained in the optical laminate. One way to increase the elastic modulus of the adhesive sheet is to increase its gel fraction. 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, the present invention aims to provide an optical laminate containing an adhesive sheet having a sufficient gel fraction and improved durability. [Means for solving the problem]

[0006] The present invention It comprises an adhesive sheet having a gel fraction of 70% or more, and an optical film. The present invention provides an optical laminate in which the maximum frequency in the histogram created by the following test method is 1400 or higher. Test method: Using an atomic force microscope, the elastic modulus is measured over a 500 nm x 500 nm area on the surface of the adhesive sheet, with 65,536 measurement points. A histogram of the elastic modulus is then created with a class width of 0.1 MPa.

[0007] Furthermore, the present invention, An adhesive sheet having a gel fraction of 70% or more, The present invention provides an adhesive sheet in which the maximum frequency in the histogram created by the following test method is 1400 or higher. Test method: Using an atomic force microscope, the elastic modulus is measured over a 500 nm x 500 nm area on the surface of the adhesive sheet, with 65,536 measurement points. A histogram of the elastic modulus is then created with a class width of 0.1 MPa.

[0008] Further, the present invention provides an optical laminate comprising the above pressure-sensitive adhesive sheet and an optical film.

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

[0010] Further, the present invention provides a pressure-sensitive adhesive sheet having a gel fraction of 70% or more, wherein the coefficient of variation of elastic modulus measured by the following test method is less than 0.08. Test method: Using an atomic force microscope, the elastic modulus is measured in an area of 500 nm long × 500 nm wide on the surface of the pressure-sensitive adhesive sheet such that the number of measurement points is 65536. Effects of the Invention

[0011] According to the present invention, an optical laminate including a pressure-sensitive adhesive sheet having a sufficient gel fraction and improved durability can be provided. Brief Description of Drawings

[0012] [Figure 1] FIG. 1 is a cross-sectional view schematically showing an example of the optical laminate of the present invention. [Figure 2] FIG. 2 is a cross-sectional view schematically showing an example of the pressure-sensitive adhesive sheet of the present invention. [Figure 3A] FIG. 3A is a diagram showing an example of an atomic force microscope image of the surface of a pressure-sensitive adhesive sheet. [Figure 3B] FIG. 3B is a diagram showing an example of a histogram of elastic modulus measured by atomic force microscopy. [Figure 4] FIG. 4 is a cross-sectional view schematically showing an example of the optical laminate of the present invention. [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] Figure 7 is a schematic cross-sectional view showing an example of the image display device of the present invention. [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 optical laminate) An example of the optical laminate of this embodiment is shown in Figure 1. The optical laminate 10A in Figure 1 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.

[0015] (Adhesive sheet) Adhesive sheet 1 has a gel fraction of 70% or more. Furthermore, the maximum frequency F in the histogram created by the following test method. max The number is 1400 or more. Test method: Using an atomic force microscope (AFM), measurements were taken at 2 measurement points in a 500 nm x 500 nm area on the surface of adhesive sheet 1. 16 The modulus of elasticity is measured to be (65536), and a histogram of modulus of elasticity with a class width of 0.1 MPa is created.

[0016] The gel fraction of adhesive sheet 1 can be determined by the following method. First, an adhesive sheet 1 (for example, Figure 2) that has been prepared for more than one week is prepared as a sample for measurement. This adhesive sheet 1 has been stored in an environment of 23°C and 55% RH for more than one week since preparation. If adhesive sheet 1 is formed from an adhesive composition containing a crosslinking agent, the reaction by the crosslinking agent has progressed sufficiently after more than one week since preparation. In other words, the reaction by the crosslinking agent is complete. The completion of the reaction by the crosslinking agent can be confirmed, for example, by Fourier transform infrared spectroscopy (FT-IR). Next, a small piece is obtained by scraping off a part of adhesive sheet 1. Next, the obtained small piece is wrapped in a stretched porous film 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 film, and the kite string is measured. The total weight of the stretched porous film and kite string used is defined as weight B. Next, the test specimen is immersed in a container filled with ethyl acetate and left to stand at 23°C for one week. After standing, the test specimen is removed from the container and dried in a drying oven set to 130°C for two hours, and then the weight C of the test specimen 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

[0017] The gel fraction of the adhesive sheet 1 is 70% or more, preferably 80% or more, more preferably 90% or more, even more preferably 94% or more, particularly preferably 95% or more, and may be 96% or more, 97% or more, 98% or more, or even 100%. The adhesive sheet 1 with a gel fraction of 70% or more tends to have excellent processability and process stability, and is less likely to cause dents, for example, during storage. This adhesive sheet 1 is also suitable for suppressing changes in the dimensions of the optical film.

[0018] Maximum frequency F maxThe elastic modulus can be determined in detail by the following method. First, an adhesive sheet 1 (for example, Figure 2) that has been prepared for more than one week is prepared as a measurement sample. Next, the adhesive sheet 1 is cut into strips to make test pieces. At this time, the thickness of the test piece is adjusted to about 100 nm. The surface of the obtained test piece can be considered as the surface of the adhesive sheet 1. Next, the test piece is placed on a substrate such as a Si wafer. Using an AFM, the elastic modulus is measured over a 500 nm x 500 nm area on the surface of the test piece, so that the number of measurement points is 65536. At this time, the spacing between adjacent measurement points is adjusted to about 2 nm. The elastic modulus is measured over the entire 500 nm x 500 nm area on the surface of the test piece, for example. The elastic modulus of the test piece can be determined by vibrating the cantilever probe of the AFM on the surface of the test piece and measuring the repulsive force generated between the test piece and the probe. As an AFM, for example, the MFP-3D-SA manufactured by Oxford Instruments can be used. As a cantilever, for example, the Olympus OMCL-AC240TS (spring constant 3 N / m) can be used. The details of the measurement conditions for the modulus of elasticity are as follows. • Measurement conditions Measurement mode: AM-FM viscoelastic mapping Measurement range: 500nm (vertical) x 500nm (horizontal) Scan speed: 3Hz Set point: 0.8V Target Amplitude: 2V Measurement temperature: 25℃

[0019] The above measurements allow us to obtain elastic modulus data for multiple locations on the surface of the test specimen. By mapping this data, we can obtain an AFM image like the one shown in Figure 3A. In this AFM image, each pixel is assigned color-based visual information based on the elastic modulus value. The size of one pixel in the AFM image corresponds to the size of the cantilever probe. The number of pixels that make up the AFM image is equal to the number of measurement points.

[0020] Next, a histogram of elastic modulus with a class width of 0.1 MPa is prepared (FIG. 3B). In this histogram, the horizontal axis represents elastic modulus, and the vertical axis represents frequency (the number of measurement points). As shown in FIG. 3B, for example, one peak P is present in the histogram. Peak P is typically unimodal. The frequency corresponding to the apex of this peak P is defined as maximum value F max In some cases, the histogram may have a plurality of peaks or multimodal peaks. However, in such cases, the maximum frequency value F max tends to be less than 1400.

[0021] Maximum value F max is preferably 1600 or more, more preferably 1800 or more, and may be 2000 or more, 2200 or more, 2400 or more, or 2600 or more. The maximum value F max has no particular limitation on its upper limit, and is 3500 for example.

[0022] Maximum value F max can be used as an indicator of the variation in elastic modulus in pressure-sensitive adhesive sheet 1. It can be said that the larger maximum value F is, the more the variation in elastic modulus is suppressed in pressure-sensitive adhesive sheet 1. According to studies by the present inventors, pressure-sensitive adhesive sheet 1 which has a sufficient gel fraction and maximum value F max of 1400 or more, with suppressed variation in elastic modulus, tends to have improved durability. Note that variation in elastic modulus is generally caused by fluctuations in the concentration of materials (such as polymers) constituting the pressure-sensitive adhesive sheet, and tends to occur prominently in pressure-sensitive adhesive sheets with a high gel fraction. max

[0023] In the histogram described above, the elastic modulus G corresponding to maximum value F max corresponds to the mode value. Elastic modulus G max is not particularly limited, and is, for example, in the range of 10 to 100 MPa. max

[0024] ​​Furthermore, in the histogram above, the maximum value F is relative to the total frequency. max Corresponding elastic modulus G max The ratio R of the sum of frequencies T within the range of (MPa) to ±2.0 MPa is not particularly limited, and is, for example, 70% or more, preferably 75% or more, more preferably 80% or more, even more preferably 85% or more, and may be 90% or more or 95% or more. The upper limit of the ratio R is not particularly limited, and is, for example, 99%.

[0025] In the ratio R, the total frequency corresponds to, for example, the integral value of the entire peak P, and is equal to the total number of measurement points by AFM. The sum T is G max -2.0 MPa to G max This corresponds to the integral value of peak P in the range up to +2.0 MPa. In a histogram, the integral value of peak P represents the area under peak P. Therefore, in this specification, the ratio R is sometimes referred to as the "area ratio".

[0026] The full width at half maximum (FWHM) of the peak P is not particularly limited; for example, it may be 4.0 MPa or less, 3.5 MPa or less, or 3.0 MPa or less. The lower limit of the FWHM of the peak P is not particularly limited; for example, it is 1.0 MPa.

[0027] At peak P, the peak width at a frequency of 5 is not particularly limited, and is, for example, 15 MPa or less, preferably 10 MPa or less, and may also be 9 MPa or less, or 8 MPa or less. The lower limit of the peak width is not particularly limited, and is, for example, 5 MPa.

[0028] In this embodiment, it is preferable that the coefficient of variation of the elastic modulus measured by the following test method is less than 0.08. Specifically, the measurement of the elastic modulus is performed using the maximum value F of the frequency. max This can be done by the method described above. Test method: Using an atomic force microscope (AFM), the elastic modulus is measured over a 500 nm x 500 nm area on the surface of adhesive sheet 1, so that the number of measurement points is 65,536.

[0029] The smaller the coefficient of variation of the elastic modulus, the more effectively the variation in the elastic modulus is suppressed in the adhesive sheet 1. The coefficient of variation of the elastic modulus is more preferably 0.078 or less, even more preferably 0.075 or less, and may also be 0.073 or less, or 0.07 or less. The lower limit of the coefficient of variation of the elastic modulus is not particularly limited. The coefficient of variation of the elastic modulus may be 0.02 or more, 0.035 or more, 0.04 or more, 0.05 or more, 0.06 or more, 0.065 or more, or 0.067 or more. Note that the coefficient of variation of the elastic modulus represents the ratio of the standard deviation to the mean value of the elastic modulus.

[0030] The storage modulus G' of the adhesive sheet 1 at 25°C is not particularly limited, and is, for example, 0.1 MPa or more, preferably 0.15 MPa or more, more preferably 0.2 MPa or more, even more preferably 0.5 MPa or more, particularly preferably 0.8 MPa or more, and may also be 1.0 MPa or more. 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. An adhesive sheet 1 having a storage modulus G' of 0.1 MPa or more, particularly 0.15 MPa or more, is suitable for suppressing changes in the dimensions of an optical film. An adhesive sheet 1 having a storage modulus G' of 0.1 MPa or more, particularly 1.0 MPa or more, tends to sufficiently suppress changes in appearance when, for example, an optical laminate is bonded to an image forming layer or the like.

[0031] 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

[0032] The adhesive sheet 1 preferably has high transparency. The haze of the adhesive sheet 1 is, for example, 1.0% or less, preferably 0.8% or less, and more preferably 0.6% or less. The lower limit of the haze of the adhesive sheet 1 is not particularly limited, but is, for example, 0.1%. In this specification, the haze of the adhesive sheet 1 is the value when the thickness is 25 μm and can be measured in accordance with Japanese Industrial Standards (formerly Japanese Industrial Standards; JIS) K7136:1981.

[0033] The adhesive strength of adhesive sheet 1 is, for example, 0.5 N / 25 mm or more, preferably 2 N / 25 mm or more, and more preferably 5 N / 25 mm or more. The upper limit of the adhesive strength of adhesive sheet 1 is, for example, 10 N / 25 mm from the viewpoint of reworkability. The adhesive strength of adhesive sheet 1 can be measured by the following method. First, adhesive sheet 1 is cut to a width of 25 mm and a length of 150 mm to make a test piece. Next, a stainless steel test plate and an evaluation sheet are placed on top of each other with adhesive sheet 1 in between, and a 2 kg roller is passed back and forth once to press them together. The evaluation sheet has a size of width of 30 mm and a length of 150 mm and is not particularly limited as long as it does not peel off from adhesive sheet 1 during the test. As the evaluation sheet, for example, ITO film (such as 125 Tetrilite OES (manufactured by Oike Kogyo Co., Ltd.)) can be used. Next, using a commercially available tensile testing machine, the average peel force obtained when peeling adhesive sheet 1 from a stainless steel test plate at a peel angle of 180° and a tensile speed of 300 mm / min while gripping the evaluation sheet is determined as the adhesive strength of adhesive sheet 1. The above test is performed in an atmosphere of 23°C.

[0034] The indentation hardness of the adhesive sheet 1 at 25°C is preferably adjusted to an appropriate range. The indentation hardness can be determined by numerically processing the displacement-load hysteresis curve obtained by pressing a diamond Berkovich-type (triangular pyramidal) probe perpendicularly against the surface of the adhesive sheet 1 using software (triboscan) attached to the measuring device. Specifically, the indentation hardness is measured using a nanoindenter (Triboindenter TI-950, manufactured by Hysitron Inc.) with a single indentation method at 25°C, under conditions of an indentation speed of 500 nm / sec and an indentation depth of 3000 nm.

[0035] The thickness of the adhesive sheet 1 is not particularly limited and may be, for example, 1 to 200 μm, 5 to 150 μm, or even 10 to 100 μm.

[0036] The composition of adhesive sheet 1 is determined by the gel fraction and the maximum value F. maxWhile not particularly limited as long as it is within the range described above, it is preferable to include two or more types of polymers. As an example, adhesive sheet 1 is formed from an adhesive composition comprising a (meth)acrylic polymer (A) and a crosslinking agent (B). Examples of crosslinking agent (B) include isocyanate-based crosslinking agents and polyfunctional (meth)acrylate-based crosslinking agents. Adhesive sheet 1 formed from this adhesive composition may contain a crosslinked product of the (meth)acrylic polymer (A) and a polymer (C) mainly composed of structural units derived from the crosslinking agent (B). 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 (C), the content of structural units derived from the crosslinking agent (B) is, for example, 70% by weight or more, preferably 90% by weight or more. Polymer (C) consists, for example, substantially only of structural units derived from the crosslinking agent (B). In the adhesive sheet 1, the crosslinked (meth)acrylic polymer (A) and polymer (C) may form an interpenetrating network (IPN) structure or a semi-interpenetrating network (semi-IPN) structure. This IPN structure (or semi-IPN structure) is suitable for increasing the elastic modulus of the adhesive sheet 1 while improving its durability.

[0037] [(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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] The (meth)acrylic polymer (A) may contain constituent 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.

[0044] 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. The (meth)acrylic polymer (A) having structural units derived from carboxyl group-containing monomers, particularly acrylic acid, can enhance the self-polymerization properties of crosslinking agents (B), particularly isocyanate-based crosslinking agents, for example. Improving the self-polymerization properties of the crosslinking agent (B) can contribute, in particular, to suppressing the peeling of the adhesive sheet 1 in humid environments and to stabilizing the physical properties of the adhesive sheet 1 in systems with a high content of crosslinking agent (B).

[0045] 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.

[0046] 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 reactions between isocyanate crosslinking agents, for example, by incorporating water molecules from the surrounding atmosphere. Aromatic ring-containing monomers also tend to improve the compatibility between (meth)acrylic polymer (A) and polymer (C), thereby improving the durability of optical laminates in high-temperature and high-humidity environments.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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. From the viewpoint of suppressing reaction with isocyanate-based crosslinking agents, this content is preferably 20% by weight or less, and more preferably 10% by weight or less.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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 1 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.

[0057] The (meth)acrylic polymer (A) can be formed by polymerizing one or more of the above-mentioned monomers by known methods. The monomers and partial polymers of the monomers may also be polymerized. Polymerization can be carried out by, for example, solution polymerization, emulsion polymerization, bulk polymerization, thermal polymerization, or active energy ray polymerization. Solution polymerization and active energy ray polymerization are preferred because they can form adhesive sheets with excellent optical transparency. Polymerization is preferably carried out while avoiding contact between the monomers and / or partial polymers and oxygen. For this purpose, polymerization can be carried out in an inert gas atmosphere such as nitrogen, or under conditions where oxygen is blocked by a resin film or the like. The (meth)acrylic polymer (A) to be formed may be in any form such as a random copolymer, block copolymer, or graft copolymer.

[0058] The polymerization system that forms the (meth)acrylic polymer (A) may contain one or more polymerization initiators. The type of polymerization initiator can be selected based on the polymerization reaction, and may be, for example, a thermal polymerization initiator or a photopolymerization initiator.

[0059] Solvents used in solution polymerization include, for example, esters such as ethyl acetate and n-butyl acetate; aromatic hydrocarbons such as toluene and benzene; aliphatic hydrocarbons such as n-hexane and n-heptane; alicyclic hydrocarbons such as cyclohexane and methylcyclohexane; and ketones such as methyl ethyl ketone and methyl isobutyl ketone. However, the solvent is not limited to the above examples. The solvent may be a mixture of two or more solvents.

[0060] Polymerization initiators used in solution polymerization include, for example, azo polymerization initiators, peroxide polymerization initiators, and redox polymerization initiators. Examples of peroxide polymerization initiators include dibenzoyl peroxide and t-butyl permaleate. Among these, the azo polymerization initiator disclosed in Japanese Patent Application Publication No. 2002-69411 is preferred. Examples of such azo polymerization initiators include 2,2'-azobisisobutyronitrile (AIBN), 2,2'-azobis-2-methylbutyronitrile, 2,2'-azobis(2-methylpropionic acid)dimethyl, and 4,4'-azobis-4-cyanovaleric acid. However, the polymerization initiator is not limited to the above examples. The amount of azo polymerization initiator used is, for example, 0.05 to 0.5 parts by weight per 100 parts by weight of the total amount of monomer, and may also be 0.1 to 0.3 parts by weight.

[0061] The active energy rays used in active energy ray polymerization include, for example, ionizing radiation such as alpha rays, beta rays, gamma rays, neutron rays, and electron beams, as well as ultraviolet rays. Ultraviolet rays are preferred as the active energy rays. Polymerization by irradiation with ultraviolet rays is also called photopolymerization. The polymerization system for active energy ray polymerization typically includes a photopolymerization initiator. The polymerization conditions for active energy ray polymerization are not limited as long as a (meth)acrylic polymer (A) is formed.

[0062] Examples of photopolymerization initiators include benzoin ether-based photopolymerization initiators, acetophenone-based photopolymerization initiators, α-ketol-based photopolymerization initiators, aromatic sulfonyl chloride-based photopolymerization initiators, photoactive oxime-based photopolymerization initiators, benzoin-based photopolymerization initiators, benzyl-based photopolymerization initiators, benzophenone-based photopolymerization initiators, ketal-based photopolymerization initiators, and thioxanthone-based photopolymerization initiators. However, the photopolymerization initiators are not limited to the examples above.

[0063] Benzoin ether-based photopolymerization initiators include, for example, benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, benzoin isopropyl ether, benzoin isobutyl ether, 2,2-dimethoxy-1,2-diphenylethane-1-one, and anisole methyl ether. Acetophenone-based photopolymerization initiators include, for example, 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexylphenyl ketone, 4-phenoxydichloroacetophenone, and 4-(t-butyl)dichloroacetophenone. Alpha-ketol-based photopolymerization initiators include, for example, 2-methyl-2-hydroxypropiophenone and 1-[4-(2-hydroxyethyl)phenyl]-2-methylpropan-1-one. Aromatic sulfonyl chloride-based photopolymerization initiators include, for example, 2-naphthalenesulfonyl chloride. Photoactive oxime-based photopolymerization initiators include, for example, 1-phenyl-1,1-propanedione-2-(o-ethoxycarbonyl)-oxime. Benzoin-based photopolymerization initiators include, for example, benzoin. Benzyl-based photopolymerization initiators include, for example, benzyl. Benzophenone-based photopolymerization initiators include, for example, benzophenone, benzoylbenzoic acid, 3,3'-dimethyl-4-methoxybenzophenone, polyvinylbenzophenone, and α-hydroxycyclohexylphenyl ketone. Ketal-based photopolymerization initiators include, for example, benzyldimethylketal. Thioxanthone-based photopolymerization initiators include, for example, thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 2,4-diisopropylthioxanthone, and dodecylthioxanthone.

[0064] The amount of photopolymerization initiator used is, for example, 0.01 to 1 part by weight per 100 parts by weight of the total amount of monomer, and may also be 0.05 to 0.5 parts by weight.

[0065] The content of (meth)acrylic polymer (A) in the adhesive composition is, for example, 50% by weight or more in terms of solid content, and may be 60% by weight or more, 70% by weight or more, or even 80% by weight or more. The upper limit of the content is, for example, 99% by weight or less, and may be 97% by weight or less, 95% by weight or less, 93% by weight or less, or even 90% by weight or less.

[0066] [Crosslinking agent (B)] The crosslinking agent (B) is typically a polyfunctional crosslinking agent having two or more crosslinking reactive groups per molecule. The crosslinking agent (B) may also be a trifunctional or more crosslinking agent having three or more crosslinking reactive groups per molecule. The upper limit for the number of crosslinking reactive groups per molecule is, for example, five.

[0067] The crosslinking agent (B) preferably has good compatibility with the (meth)acrylic polymer (A). By using a crosslinking agent (B) with good compatibility with the (meth)acrylic polymer (A), it is easy to suppress the clouding of the adhesive sheet 1 after it has been prepared. For example, as will be described later, when an isocyanate-based crosslinking agent is used as the crosslinking agent (B), the adhesive composition tends to exhibit lower critical solution temperature (LCST) type phase separation behavior. In this case, if the crosslinking agent (B) and the (meth)acrylic polymer (A) have good compatibility, the clouding of the adhesive sheet 1 can be suppressed even when the adhesive composition is dried at a relatively high temperature. That is, the range of applicable drying temperatures for the adhesive composition tends to be wide. In particular, when the (meth)acrylic polymer (A) contains constituent units derived from aromatic ring-containing monomers or constituent units derived from monomers with relatively small molecular weights such as methyl acrylate and ethyl acrylate, the compatibility between the (meth)acrylic polymer (A) and the crosslinking agent (B) tends to be good.

[0068] The crosslinking agent (B) comprises, for example, at least one selected from the group consisting of isocyanate-based crosslinking agents and polyfunctional (meth)acrylate-based crosslinking agents, and preferably comprises an isocyanate-based crosslinking agent. Isocyanate-based crosslinking agents are suitable for solvent-type adhesive compositions. Polyfunctional (meth)acrylate-based crosslinking agents are suitable for active energy ray-curable adhesive compositions.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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. From the viewpoint of compatibility with (meth)acrylic polymers (A), it is preferable that the isocyanate-based crosslinking agent contains a long-chain alkyl group.

[0074] Preferred examples of isocyanate-based crosslinking agents are aromatic isocyanate compounds and their derivatives, and more specifically, tolylene diisocyanate (TDI) crosslinking agents (tolylene diisocyanate and its derivatives) and diphenylmethane diisocyanate (MDI) crosslinking agents (diphenylmethane diisocyanate and its derivatives). However, the isocyanate-based crosslinking agent may also be a hexamethylene diisocyanate (HDI) crosslinking agent (hexamethylene diisocyanate and its derivatives). The isocyanate-based crosslinking agent is particularly preferably a TDI crosslinking agent. Compared to HDI crosslinking agents, TDI crosslinking agents and MDI crosslinking agents react more readily with each other and are suitable for producing an adhesive sheet 1 having an IPN structure.

[0075] The isocyanate-based crosslinking agent preferably includes, as a TDI-based crosslinking agent, an adduct of a polyhydric alcohol and tolyleneisocyanate, or an isocyanurate-modified tolyleneisocyanate. Specific examples of the adduct of a polyhydric alcohol and tolyleneisocyanate include the trimethylolpropane / tolyleneisocyanate trimer adduct.

[0076] Examples of commercially available isocyanate-based crosslinking agents include Mitsui Chemicals' product names "Takenate D-101E," "Takenate D-262," "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," and Tosoh Corporation's product names "Millionate MT," "Millionate MTL," "Millionate MR-200," "Millionate MR-400," "Coronate L," "Coronate HL," and "Coronate HX," with Takenate D-101E and Takenate D-262 being preferred.

[0077] The isocyanate crosslinking agents may be used individually or in combination of two or more types.

[0078] As a polyfunctional (meth)acrylate crosslinking agent, a compound having at least two (meth)acryloyl groups (polyfunctional (meth)acrylate compound) can be used. Examples of polyfunctional (meth)acrylate compounds include polyalkylene glycol di(meth)acrylates such as polypropylene glycol di(meth)acrylate and polyethylene glycol di(meth)acrylate; alkyldiol di(meth)acrylates such as 1,6-hexanediol di(meth)acrylate and neopentyl glycol di(meth)acrylate; (meth)acrylic acid adducts of diglycidyl ether compounds such as bisphenol A diglycidyl ether di(meth)acrylate; and compounds having three or more (meth)acryloyl groups such as trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, and dipentaerythritol hexa(meth)acrylate, with polypropylene glycol di(meth)acrylate being preferred.

[0079] Examples of commercially available polyfunctional (meth)acrylate crosslinking agents include "APG-400" manufactured by Shin-Nakamura Chemical Co., Ltd.

[0080] The polyfunctional (meth)acrylate crosslinking agents may be used individually or in combination of two or more of the above-mentioned agents.

[0081] The crosslinking agent (B) is not limited to isocyanate-based crosslinking agents and polyfunctional (meth)acrylate-based crosslinking agents. Other examples of crosslinking agent (B) include peroxide-based crosslinking agents, epoxy-based crosslinking agents, imine-based crosslinking agents, and polyfunctional metal chelates. Two or more of these crosslinking agents may be used in mixture form. For example, a polyfunctional (meth)acrylate-based crosslinking agent and an epoxy-based crosslinking agent may be used in mixture form.

[0082] The amount of crosslinking agent (B) is, for example, 2 parts by weight or more, preferably 3 parts by weight or more, more preferably 5 parts by weight or more, even more preferably 8 parts by weight or more, particularly preferably 10 parts by weight or more, and may be 12 parts by weight or more, per 100 parts by weight of (meth)acrylic polymer (A). The amount of crosslinking agent (B) is, for example, 30 parts by weight or less, preferably 25 parts by weight or less, and may be less than 20 parts by weight, per 100 parts by weight of (meth)acrylic polymer (A).

[0083] As an example, if the crosslinking agent (B) is an adduct of trimethylolpropane and an isocyanate compound containing a long-chain alkyl group, the amount blended is preferably about 10 parts by weight per 100 parts by weight of (meth)acrylic polymer (A). If the crosslinking agent (B) is an isocyanurate modified form of an isocyanate compound containing a long-chain alkyl group, the amount blended is preferably about 5 parts by weight per 100 parts by weight of (meth)acrylic polymer (A). If the crosslinking agent (B) is a bifunctional (meth)acrylate crosslinking agent, the amount blended is preferably about 20 parts by weight per 100 parts by weight of (meth)acrylic polymer (A). If the crosslinking agent (B) is a tetrafunctional (meth)acrylate crosslinking agent, the amount blended is preferably about 10 parts by weight per 100 parts by weight of (meth)acrylic polymer (A). When the crosslinking agent (B) is a hexafunctional (meth)acrylate crosslinking agent, the amount blended is preferably about 7 parts by weight per 100 parts by weight of the (meth)acrylic polymer (A). However, the amount of crosslinking agent (B) is not limited to the above and can be appropriately adjusted depending on the molecular weight and structure of the crosslinking agent (B).

[0084] In an adhesive composition, when the amount of crosslinking agent (B) is approximately 2 parts by weight or more per 100 parts by weight of (meth)acrylic polymer (A), when the adhesive sheet 1 is made, the crosslinking agents (B) may react with each other, forming a polymer (C) that mainly contains structural units derived from the crosslinking agents (B). Polymer (C) is suitable for suppressing dimensional changes of the adhesive sheet 1 by imparting sufficient cohesive force to the adhesive sheet 1. In other words, polymer (C) is suitable for suppressing display unevenness and light leakage in image display devices. Furthermore, the combination of (meth)acrylic polymer (A) and polymer (C) is suitable for improving the durability of the adhesive sheet 1 in high-temperature and high-humidity environments.

[0085] [Other ingredients] 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] The (meth)acrylic oligomer preferably has constituent units derived from a (meth)acrylic monomer having a relatively bulky structure. In this case, the adhesion of the adhesive sheet 1 can be further enhanced. Examples of such acrylic monomers include alkyl (meth)acrylates having branched alkyl groups such as isobutyl (meth)acrylate and t-butyl (meth)acrylate; esters of (meth)acrylic acid with alicyclic alcohols such as cyclohexyl (meth)acrylate, isobornyl (meth)acrylate and dicyclopentanyl (meth)acrylate; and aromatic ring-containing (meth)acrylates such as phenyl (meth)acrylate and benzyl (meth)acrylate. The monomer preferably has a cyclic structure, and more preferably has two or more cyclic structures. Furthermore, when ultraviolet irradiation is performed during the polymerization of (meth)acrylic 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, polyfunctional alcohols, 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, antistatic agents (such as alkali metal salts, ionic liquids, and ionic solids, which are ionic compounds), inorganic or organic fillers, metal powders, particles, and foils. 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 contain a polyfunctional alcohol. The molecular weight of the polyfunctional alcohol is, for example, 240 or less, and may be 230 or less, 220 or less, 210 or less, 200 or less, 190 or less, 180 or less, 170 or less, 160 or less, and even 150 or less. The lower limit of the molecular weight is, for example, 60 or more, and may be 80 or more, 90 or more, and even 100 or more.

[0096] Examples of polyfunctional alcohols include alkylene glycols such as ethylene glycol and propylene glycol and their polymers; ether glycols such as diethylene glycol and their polymers; trimethylolethane; trimethylolpropane; glycerin; and sugar alcohols such as pentaerythritol and sorbitol. The polyfunctional alcohols are preferably trimethylolpropane, glycerin, and diethylene glycol and their polymers, and more preferably trimethylolpropane.

[0097] Polyfunctional alcohols may have three or more functional properties. Examples of trifunctional polyfunctional alcohols are trimethylolpropane and glycerin.

[0098] The polyfunctional alcohol does not need to have any reactive groups other than the hydroxyl group that react with the crosslinking agent (B). The reactive group is, for example, at least one selected from an amino group, a carboxyl group, and an epoxy group, and is particularly an amino group.

[0099] The amount of polyfunctional alcohol in the adhesive composition is, for example, 0.5 parts by weight or more and 20 parts by weight or less per 100 parts by weight of (meth)acrylic polymer (A). The upper limit of the amount may be 15 parts by weight or less, 10 parts by weight or less, 8 parts by weight or less, 5 parts by weight or less, 4 parts by weight or less, or even 3 parts by weight or less.

[0100] The adhesive composition can be of an emulsion type, solvent type (solution type), active energy ray curing type (photocuring type), or hot melt type. From the viewpoint of forming an adhesive sheet 1 with excellent durability, the adhesive composition may be solvent type or active energy ray curing type, or it may be solvent type. Solvent-type adhesive compositions do not need to contain photocuring agents such as ultraviolet curing agents.

[0101] The adhesive sheet 1 can be prepared from the adhesive composition by the following method. For the solvent type, for example, the adhesive composition or a mixture of the adhesive composition and a solvent is applied to a base film to form a coating film, and the formed coating film is dried to form the adhesive sheet 1. The adhesive composition is thermocured by the heat during drying. For the active energy ray curing type (photocuring type), for example, a mixture of monomers (group) that become (meth)acrylic polymers (A) by polymerization, a crosslinking agent (B), and optionally, partially polymerized monomers (group), polymerization initiators, oligomers, additives, and solvents is applied to a base film, and the formed coating film is irradiated with active energy rays to form the adhesive sheet 1. Before irradiation with active energy rays, the coating film may be dried to remove the solvent. The base film may be a film (peel liner) with a release treatment applied to the coated surface.

[0102] The adhesive sheet 1 formed on the base film can be transferred to any layer. The base film may also be an optical film, in which case an optical laminate containing the adhesive sheet 1 and the optical film is obtained.

[0103] For coating the base film, known methods can be employed. Coating can be carried out by, for example, roll coating, kiss roll coating, gravure coating, reverse coating, roll brushing, spray coating, dip roll coating, bar coating, knife coating, air knife coating, curtain coating, lip coating, die coating, or other extrusion coating methods.

[0104] Solvent-type adhesive compositions, particularly those containing isocyanate-based crosslinking agents, tend to exhibit lower critical solution temperature (LCST) phase separation behavior. Therefore, when using solvent-type adhesive compositions, the drying temperature of the coated film is preferably 200°C or lower, and may also be 160°C or lower, 150°C or lower, 130°C or lower, 120°C or lower, or even 100°C or lower. When the drying temperature is 130°C or lower, the reaction rate of the crosslinking agent (B), particularly the isocyanate-based crosslinking agent, can be appropriately adjusted, and the compatibility between the (meth)acrylic polymer (A) and polymer (C) can be well maintained, which tends to reduce variations in the elastic modulus of the adhesive sheet 1. The lower limit of the drying temperature of the coated film is not particularly limited and may be, for example, 40°C or 60°C. The drying time of the coated film can be appropriately adjusted according to the drying temperature, etc., and may be, for example, 5 seconds to 20 minutes, 5 seconds to 10 minutes, or even 10 seconds to 5 minutes. When setting a high drying temperature, it is preferable to set a short drying time from the viewpoint of reducing variations in the elastic modulus of the adhesive sheet 1. Drying of the coating film is preferably carried out in an environment with relatively high humidity. This tends to cause the reaction of the crosslinking agent (B), particularly the isocyanate-based crosslinking agent, in the coating film to proceed quickly and uniformly. The relative humidity at the drying temperature of the coating film is, for example, 0%RH or higher, and may be 5%RH or higher, 10%RH or higher, 20%RH or higher, or even 30%RH or higher.

[0105] Active energy ray curable adhesive compositions, particularly adhesive compositions containing polyfunctional (meth)acrylate crosslinking agents, tend to exhibit Upper Critical Solution Temperature (UCST) phase separation behavior. Therefore, when using an active energy ray curable adhesive composition, the coated film may be irradiated with active energy rays, or a drying treatment may be performed before or after irradiation. The drying temperature of the coated film is preferably 60°C or higher, and may be 80°C or higher, 100°C or higher, 110°C or higher, or even 120°C or higher. Setting a high drying temperature for the coated film tends to maintain good compatibility between the (meth)acrylic polymer (A) and polymer (C), particularly polymer (C) containing constituent units derived from the polyfunctional (meth)acrylate crosslinking agent, thereby reducing variations in the elastic modulus of the adhesive sheet 1. The upper limit of the drying temperature of the coated film is not particularly limited, and is, for example, 200°C. The drying time of the coating film can be adjusted as appropriate depending on the drying temperature, for example, from 5 seconds to 20 minutes, or from 5 seconds to 10 minutes, or even from 10 seconds to 5 minutes.

[0106] (Optical film) 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.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] 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.

[0117] 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.

[0118] 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.

[0119] 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] ).

[0120] 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.

[0121] 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.

[0122] 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.

[0123] Another example of the optical laminate of this embodiment is shown in Figure 4. The optical laminate 10B in Figure 4 has a laminated structure in which a release liner 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 release liner 3.

[0124] Examples of materials that can be used to construct the release liner 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.

[0125] 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.

[0126] The thickness of the release liner 3 is typically 5 to 200 μm, preferably about 5 to 100 μm. The release liner 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 release liner 3.

[0127] As mentioned above, the release film used when preparing the adhesive sheet 1 may also be used as the release liner 3.

[0128] Another example of the optical laminate of this embodiment is shown in Figure 5. The optical laminate 10C in Figure 5 has a laminated structure in which a release liner 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 release liner 3 and then attaching it to, for example, an image forming layer.

[0129] Any known adhesive can be used for the interlayer adhesive 4. The adhesive sheet 1 may also be used as the interlayer adhesive 4.

[0130] Another example of the optical laminate of this embodiment is shown in Figure 6. The optical laminate 10D in Figure 6 has a laminated structure in which a release liner 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 release liner 3 and then attaching it to, for example, an image forming layer.

[0131] 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.

[0132] The protective film 5 may be bonded to the optical film 2 with any adhesive. Bonding with an adhesive sheet 1 is also possible.

[0133] 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.

[0134] 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.

[0135] (Embodiment of an image display device) An example of an image display device of this embodiment is shown in Figure 7. The image display device 11 in Figure 7 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 laminated in this order. The image display device 11 has an optical laminate 10B, 10C, or 10D as shown in Figures 4 to 6 (except for the release liner 3). The substrate 7 and the image forming layer 6 may have the same configuration as the substrate and image forming layer of a known image display device.

[0136] The image display device 11 in Figure 7 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 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.

[0137] The image display device of this embodiment may have any configuration as long as it includes the optical laminate of this embodiment. [Examples]

[0138] 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.

[0139] [(meth)acrylic polymer A1] A monomer mixture containing 81.9 parts by weight of butyl acrylate, 4.8 parts by weight of acrylic acid, 0.1 parts by weight of 4-hydroxybutyl acrylate, and 13.2 parts by weight of benzyl 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 concentration to 30% by weight, obtaining a solution of (meth)acrylic polymer A1.

[0140] [(meth)acrylic polymer A2] A monomer mixture containing 94.9 parts by weight of butyl acrylate, 5.0 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 AIBN was added to 100 parts by weight of the monomer mixture as a polymerization initiator, and nitrogen gas was introduced while gently stirring to purge the flask with nitrogen. The polymerization reaction was then 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 12% by weight to obtain a solution of (meth)acrylic polymer A2.

[0141] [Table 1]

[0142] The abbreviations used in Table 1 are as follows: BA: n-butyl acrylate AA: Acrylic acid HBA: 4-hydroxybutyl acrylate BzA: Benzyl acrylate AIBN: Azo polymerization initiator, 2,2'-azobisisobutyronitrile (manufactured by Kishida Chemical Co., Ltd.)

[0143] [Making adhesive sheets] (Examples 1-3 and Comparative Examples 1-2) A solvent-type adhesive composition was obtained by mixing (meth)acrylic polymers and crosslinking agents 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 (release liner), so that the thickness of the adhesive sheet after drying would be 25 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 1-3 and Comparative Examples 1-2.

[0144] (Example 4) An active energy ray-curable 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 a base film (release liner), so that the thickness of the adhesive sheet was 25 μm. A fountain coater was used to apply the adhesive composition. A release liner was then laminated onto the surface of the resulting coated film. After drying the coated film at 130°C, illuminance was set to 4 mW / cm². 2 , light intensity 1200mJ / cm 2 Ultraviolet irradiation was performed under these conditions. This caused the coating film to harden, and the adhesive sheet of Example 4 was obtained.

[0145] [Table 2]

[0146] The abbreviations used in Table 2 are as follows: D262: Isocyanurate-modified form of tolylene diisocyanate (manufactured by Mitsui Chemicals, Inc., product name: Takenate D-262) D101E: Trimethylolpropane / tolide diisocyanate adduct (manufactured by Mitsui Chemicals, product name: Takenate D-101E) APG400: Polypropylene glycol diacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., product name: APG-400) Tetrad C: 1,3-Bis(N,N-Diglycidylaminomethyl)cyclohexane (Polyfunctional epoxy crosslinking agent; manufactured by Mitsubishi Gas Chemical Company, Tetrad C) Omnirad 651: Photopolymerization initiator, 2,2-dimethoxy-1,2-diphenylethane-1-one (manufactured by IGM Resins BV)

[0147] [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

[0148] <Thickness> The thickness of adhesive sheets and other materials was measured using a dial gauge (manufactured by Mitutoyo).

[0149] <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.

[0150] <Adhesive strength> The adhesive strength of the fabricated adhesive sheets was evaluated using the method described above. A Shimadzu Autograph AG-IS tensile testing machine was used.

[0151] <Hayes> The haze of the fabricated adhesive sheets was measured in accordance with JIS K7136:1981 using a Suga Test Instruments HZ-V3 haze meter in a 25°C atmosphere. The measurement was performed with the adhesive sheet being evaluated attached to a Matsunami Glass Industry S012140 slide glass (1.3 mm thick).

[0152] <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.

[0153] <Atomic force microscopy measurement> Using the method described above, the elastic modulus was measured using an AFM (Automated Microscope Function) over a 500nm x 500nm area on the surface of the adhesive sheet, with 65,536 measurement points. The AFM used was an MFP-3D-SA manufactured by Oxford Instruments. The cantilever used was an Olympus OMCL-AC240TS (spring constant 3 N / m). A histogram of elastic moduli with a class width of 0.1 MPa was created, and the maximum frequency F was calculated. max These factors were identified. Furthermore, the mean and standard deviation of the elastic modulus were calculated, and the coefficient of variation was determined.

[0154] <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. A sample measuring 100 mm in length and 40 mm in width was prepared as the circular polarizing plate with an adhesive sheet. 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 foaming between the glass plate and the circular polarizing plate. A: No visible changes such as foaming or peeling are observed. C: Significant peeling or foaming is observed at the edges, which poses a practical problem.

[0155] The following describes the method for forming the circular polarizing plate with adhesive sheet used to evaluate its humidification durability.

[0156] <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.

[0157] (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.

[0158] <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.

[0159] 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.

[0160] (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. [ka]

[0161] (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.

[0162] <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.

[0163] Next, to the obtained (meth)acrylic polymer solution, 0.5 parts by weight of trimethylolpropane / tolylene diisocyanate trimer adduct (manufactured by Tosoh Corporation, 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.

[0164] (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 liner with a silicone treatment on the release surface, so that the thickness of the dried layer would be 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.

[0165] (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 liner 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.

[0166] [Table 3]

[0167] As can be seen from Table 3, the gel fraction is 70% or more, and the maximum frequency F in the histogram of elastic modulus is also present. max The adhesive sheets of the examples, where the ratio was 1400 or higher, showed improved durability compared to the adhesive sheets of the comparative examples. [Industrial applicability]

[0168] 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]

[0169] 1 Adhesive sheet 2 Optical film 10A, 10B, 10C, 10D Optical Stack 11 Image display device

Claims

1. It comprises an adhesive sheet having a gel fraction of 90% or more, and an optical film. The adhesive sheet is formed from an adhesive composition comprising a (meth)acrylic polymer (A) and a crosslinking agent (B), The (meth)acrylic polymer (A) comprises structural units derived from alkyl (meth)acrylate, structural units derived from aromatic ring-containing monomers, and structural units derived from carboxyl group-containing monomers. The content of the constituent units derived from the alkyl (meth)acrylate in the (meth)acrylic polymer (A) is 80% by weight or more, The content of the constituent units derived from the aromatic ring-containing monomer in the (meth)acrylic polymer (A) is 17% by weight or less. The content of the constituent units derived from the carboxyl group-containing monomer in the (meth)acrylic polymer (A) is 3% by weight or more, The amount of the crosslinking agent (B) in the adhesive composition is 10 parts by weight or more and less than 20 parts by weight per 100 parts by weight of the (meth)acrylic polymer (A). An optical laminate in which the maximum frequency in the histogram created by the following test method is 1400 or higher. Test method: Using an atomic force microscope, the elastic modulus is measured over a 500 nm x 500 nm area on the surface of the adhesive sheet, with 65,536 measurement points. A histogram of the elastic modulus with a class width of 0.1 MPa is then created.

2. An adhesive sheet having a gel fraction of 90% or more, The adhesive sheet is formed from an adhesive composition comprising a (meth)acrylic polymer (A) and a crosslinking agent (B), The (meth)acrylic polymer (A) comprises structural units derived from alkyl (meth)acrylate, structural units derived from aromatic ring-containing monomers, and structural units derived from carboxyl group-containing monomers. The content of the constituent units derived from the alkyl (meth)acrylate in the (meth)acrylic polymer (A) is 80% by weight or more, The content of the constituent units derived from the aromatic ring-containing monomer in the (meth)acrylic polymer (A) is 17% by weight or less. The content of the constituent units derived from the carboxyl group-containing monomer in the (meth)acrylic polymer (A) is 3% by weight or more, The amount of the crosslinking agent (B) in the adhesive composition is 10 parts by weight or more and less than 20 parts by weight per 100 parts by weight of the (meth)acrylic polymer (A). An adhesive sheet in which the maximum frequency in the histogram created by the following test method is 1400 or higher. Test method: Using an atomic force microscope, the elastic modulus is measured over a 500 nm x 500 nm area on the surface of the adhesive sheet, with 65,536 measurement points. A histogram of the elastic modulus with a class width of 0.1 MPa is then created.

3. In the histogram, the elastic modulus G corresponding to the maximum value max The adhesive sheet according to claim 2, wherein the pressure is in the range of 10 to 100 MPa.

4. The adhesive sheet according to claim 2 or 3, wherein the coefficient of variation of the elastic modulus measured by the above test method is less than 0.

08.

5. The adhesive sheet according to any one of claims 2 to 4, wherein the coefficient of variation of the elastic modulus measured by the above test method is 0.035 or more.

6. In the histogram, the elastic modulus G corresponding to the maximum value for the total frequency max The adhesive sheet according to any one of claims 2 to 5, wherein the ratio of the total values ​​of frequencies that fall within the range of ±2.0 MPa from (MPa) is 70% or more.

7. An adhesive sheet according to any one of claims 2 to 6, wherein the storage modulus G' at 25°C is 0.1 MPa or more.

8. An adhesive sheet according to any one of claims 2 to 7, having a haze of 1.0% or less.

9. The adhesive sheet according to any one of claims 2 to 8, wherein the crosslinking agent (B) comprises at least one selected from the group consisting of isocyanate-based crosslinking agents and polyfunctional (meth)acrylate-based crosslinking agents.

10. The adhesive sheet according to any one of claims 2 to 9, wherein the adhesive composition is solvent-based or active energy ray-curable.

11. An optical laminate comprising an adhesive sheet according to any one of claims 2 to 10 and an optical film.

12. An image display device comprising the optical laminate described in claim 11.

13. An adhesive sheet having a gel fraction of 90% or more, The adhesive sheet is formed from an adhesive composition comprising a (meth)acrylic polymer (A) and a crosslinking agent (B), The (meth)acrylic polymer (A) comprises structural units derived from alkyl (meth)acrylate, structural units derived from aromatic ring-containing monomers, and structural units derived from carboxyl group-containing monomers. The content of the constituent units derived from the alkyl (meth)acrylate in the (meth)acrylic polymer (A) is 80% by weight or more, The content of the constituent units derived from the aromatic ring-containing monomer in the (meth)acrylic polymer (A) is 17% by weight or less. The content of the constituent units derived from the carboxyl group-containing monomer in the (meth)acrylic polymer (A) is 3% by weight or more, The amount of the crosslinking agent (B) in the adhesive composition is 10 parts by weight or more and less than 20 parts by weight per 100 parts by weight of the (meth)acrylic polymer (A). An adhesive sheet having a coefficient of variation of elastic modulus less than 0.08, as measured by the test method described below. Test method: Using an atomic force microscope, the elastic modulus is measured over a 500 nm x 500 nm area on the surface of the adhesive sheet, such that the number of measurement points is 65,536.

Images