Adhesive sheets, optical laminates, and image display devices

Abstract

To provide an adhesive sheet which can suppress changes in the dimensions of an optical film included in an optical laminate and is suitable for securing durability and transparency.SOLUTION: There is provided an adhesive sheet wherein when 10 evaluation areas of 1.5 μm square are arbitrarily set for a cross-sectional view of the adhesive sheet and an island-shaped area having a short diameter of 100 nm or more is defined as a first domain, the number of the evaluation areas in which the first domain is present is 5 or less and the adhesive sheet has a haze of 0.1% or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] In recent years, image display devices, such as liquid crystal displays and electroluminescent (EL) displays (e.g., organic EL displays and inorganic EL displays), have become rapidly widespread. These various image display devices typically have a laminated structure comprising an image-forming layer, such as a liquid crystal layer or an EL light-emitting layer, and an optical laminate including an optical film and an adhesive sheet. The adhesive sheet is mainly used for bonding between films included in the optical laminate and for bonding between the image-forming layer and the optical laminate. Examples of optical films include polarizing plates, phase difference films, and polarizing plates with phase difference films that integrate a polarizing plate and a phase difference film. Patent documents 1 and 2 disclose an example of an optical laminate. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2008-031214 [Patent Document 2] Japanese Patent Publication No. 2009-98665 [Overview of the Initiative] [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 might consider increasing the elastic modulus of the adhesive sheet included in the optical laminate. However, simply increasing the elastic modulus can reduce the durability of the adhesive sheet, making it unable to keep up with dimensional changes, and may also impair the transparency desired for optical adhesive sheets.

[0005] The present invention aims to provide an adhesive sheet that can suppress changes in the dimensions of optical films contained in optical laminates, while also ensuring durability and transparency. [Means for solving the problem]

[0006] The present invention It is an adhesive sheet, When 10 evaluation regions of 1.5 μm square are arbitrarily set in the cross-sectional image of the adhesive sheet, and island-like regions having a short axis of 100 nm or more are defined as the first domain, the number of evaluation regions in which the first domain exists is 5 or less. Having haze of 0.1% or more, Adhesive sheet, To provide.

[0007] In another aspect, the present invention is An optical laminate comprising the adhesive sheet of the present invention described above and an optical film, To provide.

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

[0009] According to the present invention, it is possible to provide a pressure-sensitive adhesive sheet that can suppress dimensional changes of an optical film included in an optical laminate and is suitable for ensuring durability and transparency. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] [Figure 1] FIG. 1 is a cross-sectional view schematically showing an example of the pressure-sensitive adhesive sheet of the present invention. [Figure 2] FIG. 2 is a cross-sectional view schematically showing an example of an optical laminate provided with the pressure-sensitive adhesive sheet of the present invention. [Figure 3] FIG. 3 is a cross-sectional view schematically showing an example of an optical laminate provided with the pressure-sensitive adhesive sheet of the present invention. [Figure 4] FIG. 4 is a cross-sectional view schematically showing an example of an optical laminate provided with the pressure-sensitive adhesive sheet of the present invention. [Figure 5] FIG. 5 is a cross-sectional view schematically showing an example of an optical laminate provided with the pressure-sensitive adhesive sheet of the present invention. [Figure 6] FIG. 6 is a cross-sectional view schematically showing an example of an image display device provided with the pressure-sensitive adhesive sheet of the present invention. [Figure 7A] FIG. 7A is a diagram showing a cross-sectional image of the pressure-sensitive adhesive sheet produced in Example 3, observed by a transmission electron microscope (TEM). [Figure 7B] FIG. 7B is a diagram showing a cross-sectional TEM image of the pressure-sensitive adhesive sheet produced in Example 8. [Figure 7C] FIG. 7C is a diagram showing a cross-sectional TEM image of the pressure-sensitive adhesive sheet produced in Example 9. [Figure 7D] FIG. 7D is a diagram showing a cross-sectional TEM image of the pressure-sensitive adhesive sheet produced in Comparative Example 3. MODE FOR CARRYING OUT THE INVENTION

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

[0012] In this specification, "(meth)acrylic" means acrylic and methacrylic. Similarly, "(meth)acrylate" means acrylate and methacrylate.

[0013] [Adhesive sheet] An example of the adhesive sheet of this embodiment is shown in Figure 1. In the adhesive sheet 1 of Figure 1, when 10 evaluation regions of 1.5 μm square are arbitrarily set on the cross-sectional image of the adhesive sheet 1, and island-like regions with a short axis of 100 nm or more are defined as the first domain, the number of evaluation regions in which the first domain exists is 5 or less. In addition, the adhesive sheet 1 has a haze of 0.1% or more.

[0014] To increase the elastic modulus of an adhesive sheet, for example, additives can be incorporated into the adhesive composition that forms the adhesive sheet. Since it is difficult for the materials contained in the adhesive composition, typically the main polymer component, and the additives to be completely compatible, it is thought that the haze of the adhesive sheet increases when additives are incorporated. According to the inventors' studies, it has been found that when domains of a certain size or larger are formed in an adhesive sheet with increased haze, the durability and transparency of the adhesive sheet tend to decrease. The formation of domains can cause whitening of the adhesive sheet due to light scattering and reflection at the domain interface, and it is also thought that when the adhesive sheet is deformed by an external force, peeling progresses at the domain interface, causing voids to form. Further studies have shown that an adhesive sheet 1 having a haze of 0.1% or more and having the domains in the above state can suppress changes in the dimensions of the optical film and is suitable for ensuring durability and transparency.

[0015] In this specification, the haze of adhesive sheet 1 is the value when the sheet has a thickness of 75 μm and can be measured in accordance with Japanese Industrial Standards (formerly Japanese Industrial Standards; JIS) K7136:1981.

[0016] The haze of adhesive sheet 1 may be 0.2% or more. The upper limit of the haze is, for example, 1% or less, and may be 0.9% or less, 0.8% or less, 0.7% or less, 0.6% or less, 0.5% or less, less than 0.5%, 0.45% or less, less than 0.43%, 0.4% or less, and even less than 0.37%.

[0017] In this specification, a domain refers to an island-like region of a sea-island structure that the adhesive sheet 1 may have. A domain may contain substances derived from additives. The minor axis of a domain can be determined as the length of the shortest imaginary line segment when an imaginary line segment passing through the centroid of the domain and having the outer perimeter of the domain as both ends is assumed on the cross-sectional image. It is preferable that each evaluation region set in the cross-sectional image does not overlap with one another. The cross-sectional image can be obtained, for example, by a transmission electron microscope (TEM). The magnification of the obtained cross-sectional image is, for example, 10,000 to 30,000 times.

[0018] The number of evaluation regions in which the first domain exists may be 4 or less, 3 or less, 2 or less, 1 or less, or even 0.

[0019] For all first domains observed in the 10 evaluation areas set in the cross-sectional image of the adhesive sheet 1, the shortest distance between adjacent first domains may be 300 nm or more, 500 nm or more, or even 800 nm or more. A larger shortest distance means that the density of the domains in the adhesive sheet 1 is low. The distance between adjacent domains can be defined as the distance between their outer edges.

[0020] When island-like regions having a short axis of 50 nm or more and less than 100 nm are defined as second domains, the number of evaluation regions in the 10 evaluation regions set in the cross-sectional image of the adhesive sheet 1 in which the number of second domains is 10 or less may be 3 or more, 4 or more, 5 or more, 6 or more, 7 or more, 8 or more, 9 or more, and even 10. According to the inventors' studies, the second domains can affect the durability and transparency of the adhesive sheet 1, although not to the same extent as the first domains.

[0021] When an island-like region having a short axis of 50 nm or more and less than 100 nm is defined as a second domain, for all second domains observed in the 10 evaluation regions set in the cross-sectional image of the adhesive sheet 1, the shortest distance between adjacent second domains may be 150 nm or more, 175 nm or more, or even 200 nm or more.

[0022] When an island-like region having a short axis of 50 nm or more and less than 100 nm is defined as a second domain, the proportion (percentage by number) of second domains observed in the 10 evaluation regions set in the cross-sectional image of the adhesive sheet 1 in which the shortest distance between adjacent second domains is 100 nm or more may be 50% or more, 60% or more, or even 70% or more.

[0023] The state of the domains in adhesive sheet 1 can be evaluated, for example, by image analysis of a cross-sectional image. Various software such as ImageJ can be used for image analysis.

[0024] The state of the domains in the adhesive sheet 1 changes based on the manufacturing conditions of the adhesive sheet 1 (including the heating conditions described later). Furthermore, the state of the domains may change based on the composition of the adhesive composition (I), the composition and properties (e.g., glass transition temperature) of the (meth)acrylic polymer (A), the type and amount of crosslinking agent (B), and the type and amount of additives.

[0025] The thickness of the adhesive sheet 1 is, for example, 1 to 200 μm, and may be 5 to 150 μm, 10 to 100 μm, 10 to 75 μm, 10 to 50 μm, 10 to 40 μm, 10 to 30 μm, or even 10 to 20 μm.

[0026] The storage modulus G'(25°C) of the adhesive sheet 1 is, for example, 0.15 MPa or higher, and may be 0.16 MPa or higher, 0.17 MPa or higher, or even 0.18 MPa or higher. The upper limit of the storage modulus G'(25°C) is, for example, 5 MPa or lower, and may be 3.0 MPa or lower, 2.5 MPa or lower, 2.0 MPa or lower, 1.5 MPa or lower, 1.0 MPa or lower, 0.8 MPa or lower, 0.6 MPa or lower, 0.5 MPa or lower, or even less than 0.5 MPa. The adhesive sheet 1 with a storage modulus G' within the above range is particularly suitable for suppressing changes in the dimensions of the optical film.

[0027] The storage modulus (25°C) of adhesive sheet 1 can be evaluated by the following method. First, a measurement sample made of the material constituting adhesive sheet 1 is prepared. The shape of the measurement sample is disc-shaped. The measurement sample has a base diameter of 8 mm and a thickness of 2 mm. The measurement sample may also be a disc-shaped cutout of a laminate of multiple adhesive sheets 1 stacked together. Next, dynamic viscoelasticity measurement is performed on the measurement sample. For dynamic viscoelasticity measurement, for example, an ARES-G2 manufactured by TA Instruments can be used. From the results of the dynamic viscoelasticity measurement, the storage modulus G' of adhesive sheet 1 at 25°C can be determined. The conditions for dynamic viscoelasticity measurement are as follows. • Measurement conditions Frequency: 1Hz Transformation mode: Twist Measurement temperature: -70℃~150℃ Heating rate: 5°C / min

[0028] The gel fraction of the adhesive sheet 1 may be, for example, 60% or more, 65% or more, or even 70% or more. The upper limit of the gel fraction may be, for example, 99% or less, 98% or less, or even 95% or less. The adhesive sheet 1 with a gel fraction within the above range is particularly suitable for suppressing changes in the dimensions of the optical film.

[0029] The gel fraction of adhesive sheet 1 can be evaluated by the following method. First, approximately 0.2 g is scraped off from adhesive sheet 1 to obtain a small piece. Next, the obtained small piece is wrapped in a stretched porous polytetrafluoroethylene membrane (NTF1122, manufactured by Nitto Denko, with an average pore size of 0.2 μm) and tied with kite string to form a test specimen. Next, the weight A of the obtained test specimen is measured. Weight A is the sum of the weights of the adhesive sheet piece, the stretched porous membrane, and the kite string. The total weight B of the stretched porous membrane and kite string used should be measured in advance. Next, the test specimen is immersed in a 50 mL container filled with ethyl acetate and left to stand at 23°C for one week. After standing, the test specimen is removed from the container and dried in a dryer set to 130°C for two hours, and then the weight C of the test specimen is measured. From the measured weights A, B, and C, the gel fraction of adhesive sheet 1 is calculated using the formula: Gel fraction (weight %) = (CB) / (AB) × 100 (%).

[0030] The adhesive sheet 1 may be formed from an adhesive composition (I) that mainly contains a (meth)acrylic polymer (A) and further contains an isocyanate crosslinking agent (B). However, the composition of the adhesive sheet 1 is not limited to the above example.

[0031] [Adhesive composition (I)] The adhesive composition (I) contains a (meth)acrylic polymer (A) and an isocyanate crosslinking agent (B). The (meth)acrylic polymer (A) is included in the adhesive composition (I) as the main component. In other words, the adhesive composition (I) is an acrylic adhesive composition. The main component means the component with the highest content in the composition. The content of the main component is, for example, 50% by weight or more, and may be 60% by weight or more, 70% by weight or more, 73% by weight or more, or even 75% by weight or more.

[0032] ((meth)acrylic polymer (A)) The (meth)acrylic polymer (A) preferably has as its main unit a structural unit derived from a (meth)acrylic monomer (A1) having an alkyl group having 1 to 30 carbon atoms in its side chain. The alkyl group may be linear or branched. The (meth)acrylic polymer (A) may have one or more structural units derived from the (meth)acrylic monomer (A1). Examples of (meth)acrylic monomers (A1) include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, isobutyl (meth)acrylate, n-pentyl (meth)acrylate, isopentyl (meth)acrylate, n-hexyl (meth)acrylate, isohexyl (meth)acrylate, isoheptyl (meth)acrylate These are 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate, n-dodecyl (meth)acrylate (lauryl (meth)acrylate), n-tridecyl (meth)acrylate, and n-tetradecyl (meth)acrylate. In this specification, "principal unit" means a unit that accounts for, for example, 50% by weight or more, preferably 60% by weight or more, more preferably 70% by weight or more, and even more preferably 80% by weight or more of the total constituent units of the polymer.

[0033] The (meth)acrylic polymer (A) may have constituent units derived from a (meth)acrylic monomer (A1) having a long-chain alkyl group as a side chain. An example of such monomer (A1) is n-dodecyl (meth)acrylate (lauryl (meth)acrylate). In this specification, "long-chain alkyl group" means an alkyl group having 6 to 30 carbon atoms.

[0034] The (meth)acrylic polymer (A) may have constituent units derived from a (meth)acrylic monomer (A1) whose glass transition temperature (Tg) is in the range of -70 to -20°C when it is a homopolymer. An example of such monomer (A1) is n-butyl acrylate.

[0035] The (meth)acrylic polymer (A) may have constituent units other than those derived from the (meth)acrylic monomer (A1). These constituent units are derived from monomers (A2) copolymerizable with the (meth)acrylic monomer (A1). The (meth)acrylic polymer (A) may have one or more of these constituent units.

[0036] An example of monomer (A2) is an aromatic ring-containing monomer. The aromatic ring-containing monomer may also be an aromatic ring-containing (meth)acrylic monomer. Examples of aromatic ring-containing monomers are phenyl (meth)acrylate, phenoxyethyl (meth)acrylate, benzyl (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, ethylene oxide-modified nonylphenol (meth)acrylate, hydroxyethylated β-naphthol (meth)acrylate, and biphenyl (meth)acrylate. The content of constituent units derived from aromatic ring-containing monomers in (meth)acrylic polymer (A) is, for example, 0 to 50% by weight, and may be 1 to 30% by weight, 5 to 25% by weight, 8 to 20% by weight, 10 to 18% by weight, 11 to 17% by weight, or even 12 to 16% by weight. The presence of constituent units derived from aromatic ring-containing monomers in the (meth)acrylic polymer (A) can contribute to improving the compatibility between the (meth)acrylic polymer (A) and the crosslinking agent (B) and its self-polymers.

[0037] Another example of monomer (A2) is a hydroxyl group-containing monomer. The hydroxyl group-containing monomer may also be a hydroxyl group-containing (meth)acrylic monomer. Examples of hydroxyl group-containing monomers include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, and 12-hydroxylauryl (meth)acrylate, as well as (4-hydroxymethylcyclohexyl)-methyl acrylate. Note that the hydroxyl group can react with various crosslinking agents. From the viewpoint of improving the uniformity of the cross-linked structure formed, the content of constituent units derived from hydroxyl group-containing monomers in the (meth)acrylic polymer (A) may be 1% by weight or less, 0.5% by weight or less, even 0.1% by weight or less, or even 0% by weight (i.e., it may not contain such constituent units at all).

[0038] Monomer (A2) may be a carboxyl group-containing monomer, an amino group-containing monomer, or an amide group-containing monomer. Examples of carboxyl group-containing monomers are (meth)acrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, and crotonic acid. Examples of amino group-containing monomers are N,N-dimethylaminoethyl (meth)acrylate and N,N-dimethylaminopropyl (meth)acrylate. Examples of amide group-containing monomers include acrylamide monomers such as (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N-isopropylacrylamide, N-methyl(meth)acrylamide, N-butyl(meth)acrylamide, N-hexyl(meth)acrylamide, N-methylol(meth)acrylamide, N-methylol-N-propane(meth)acrylamide, aminomethyl(meth)acrylamide, aminoethyl(meth)acrylamide, mercaptomethyl(meth)acrylamide, and mercaptoethyl(meth)acrylamide; N-acryloyl heterocyclic monomers such as N-(meth)acryloylmorpholine, N-(meth)acryloylpiperidine, and N-(meth)acryloylpyrrolidine; and N-vinyl group-containing lactam monomers such as N-vinylpyrrolidone and N-vinyl-ε-caprolactam. The (meth)acrylic polymer (A) contains constituent units derived from carboxyl group-containing monomers, particularly acrylic acid, which can enhance the self-polymerization properties of, for example, isocyanate-based crosslinking agents (B). Improving the self-polymerization properties of crosslinking agent (B) can contribute, in particular, to suppressing the peeling of adhesive sheets in humid environments and stabilizing the physical properties of adhesive sheets in systems with a high content of crosslinking agent (B).

[0039] Monomer (A2) may be a polyfunctional monomer. Examples of polyfunctional monomers include polyfunctional acrylates such as hexanediol di(meth)acrylate (1,6-hexanediol di(meth)acrylate), butanediol di(meth)acrylate, (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethane tri(meth)acrylate, allyl(meth)acrylate, vinyl(meth)acrylate, epoxy acrylate, polyester acrylate and urethane acrylate; and divinylbenzene. The polyfunctional acrylate is preferably 1,6-hexanediol diacrylate or dipentaerythritol hexa(meth)acrylate.

[0040] The total content of constituent units derived from carboxyl group-containing monomers, amino group-containing monomers, amide group-containing monomers, and polyfunctional monomers in the (meth)acrylic polymer (A) is preferably 20% by weight or less, more preferably 10% by weight or less, and even more preferably 8% by weight or less. If the (meth)acrylic polymer (A) contains such constituent units, the total content may be, for example, 0.01% by weight or more, and may also be 0.05% by weight or more. The (meth)acrylic polymer (A) does not have to contain constituent units derived from polyfunctional monomers.

[0041] Other examples of monomers (A2) include alkoxyalkyl esters of (meth)acrylates such as 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, methoxytriethylene glycol (meth)acrylate, 3-methoxypropyl (meth)acrylate, 3-ethoxypropyl (meth)acrylate, 4-methoxybutyl (meth)acrylate and 4-ethoxybutyl (meth)acrylate; epoxy group-containing monomers such as glycidyl (meth)acrylate and methylglycidyl (meth)acrylate; and sodium vinyl sulfonate. These include monomers containing sulfonic acid groups such as lium; monomers containing phosphate groups; (meth)acrylic acid esters having alicyclic hydrocarbon groups such as cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, and isobornyl (meth)acrylate; vinyl esters such as vinyl acetate and vinyl propionate; aromatic vinyl compounds such as styrene and vinyltoluene; olefins or dienes such as ethylene, propylene, butadiene, isoprene, and isobutylene; vinyl ethers such as vinyl alkyl ethers; and vinyl chloride.

[0042] The total content of constituent units derived from the above-mentioned other monomers (A2) in the (meth)acrylic polymer (A) is, for example, 30% by weight or less, may be 10% by weight or less, and preferably 0% by weight (not containing the constituent units).

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] The active energy rays used in active energy ray polymerization include, for example, ionizing radiation such as alpha rays, beta rays, gamma rays, neutron rays, and electron beams, as well as ultraviolet rays. Ultraviolet rays are preferred as the active energy rays. Polymerization by irradiation with ultraviolet rays is also called photopolymerization. The polymerization system for active energy ray polymerization typically includes a photopolymerization initiator. The polymerization conditions for active energy polymerization are not limited as long as a (meth)acrylic polymer (A) is formed.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] The weight-average molecular weight (Mw) of the (meth)acrylic polymer (A) is, for example, 1 million to 2.8 million, and may be 1.2 million or more, or even 1.4 million or more, from the viewpoint of durability and heat resistance of the adhesive sheet. The weight-average molecular weight (Mw) of polymers and oligomers in this specification is a value (polystyrene equivalent) based on GPC (gel permeation chromatography) measurement.

[0052] The content of the (meth)acrylic polymer (A) in the adhesive composition (I) is, for example, 50% by weight or more in terms of solid content, and may be 60% by weight or more, 70% by weight or more, or even 80% by weight or more. The upper limit of the content is, for example, 99% by weight or less, and may be 97% by weight or less, 95% by weight or less, 93% by weight or less, or even 90% by weight or less.

[0053] (Isocyanate-based crosslinking agent (B)) Isocyanate-based crosslinking agents (B) are a type of additive to adhesive compositions. Crosslinking agent (B) contains isocyanate groups as crosslinking reactive groups. Crosslinking agent (B) is typically a polyfunctional crosslinking agent having two or more crosslinking reactive groups per molecule. Crosslinking agent (B) may also be a trifunctional or more crosslinking agent having three or more crosslinking reactive groups per molecule. The upper limit of the number of crosslinking reactive groups per molecule is, for example, five.

[0054] The isocyanate crosslinking agent (B) may be an aromatic isocyanate compound, an alicyclic isocyanate compound, or an aliphatic isocyanate compound.

[0055] Examples of aromatic isocyanate compounds that can be used as crosslinking agents (B) include phenylenediisocyanate, 2,4-tolylenediisocyanate, 2,6-tolylenediisocyanate, 2,2'-diphenylmethanediisocyanate, 4,4'-diphenylmethanediisocyanate, 4,4'-toluidinediisocyanate, 4,4'-diphenyletherdiisocyanate, 4,4'-diphenyldiisocyanate, and 1,5-naphthalenediisocyanate and xylylenediisocyanate.

[0056] Examples of alicyclic isocyanate compounds that can be used as crosslinking agents (B) include 1,3-cyclopentene diisocyanate, 1,3-cyclohexane diisocyanate, 1,4-cyclohexane diisocyanate, isophorone diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated xylylene diisocyanate, hydrogenated tolylene diisocyanate, and hydrogenated tetramethylxylylene diisocyanate.

[0057] Examples of aliphatic isocyanate compounds that can be used as crosslinking agents (B) include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylene diisocyanate, 1,3-butylene diisocyanate, dodecamethylene diisocyanate, and 2,4,4-trimethylhexamethylene diisocyanate.

[0058] The crosslinking agent (B) may be a derivative of the above-mentioned isocyanate compound. Examples of derivatives include polymers (dimers, trimers, pentamers, etc.), adducts obtained by adding to polyhydric alcohols such as trimethylolpropane, urea-modified compounds, biuret-modified compounds, allophanate-modified compounds, isocyanurate-modified compounds, carbodiimide-modified compounds, and urethane prepolymers obtained by adding to polyether polyols, polyester polyols, acrylic polyols, polybutadiene polyols, polyisoprene polyols, etc.

[0059] The crosslinking agent (B) is preferably an aromatic isocyanate compound and its derivatives, and more preferably tolylene diisocyanate and its derivatives (in other words, a tolylene diisocyanate-based (TDI-based) crosslinking agent). TDI-based crosslinking agents exhibit superior reaction uniformity compared to xylylene diisocyanate and its derivatives (in other words, xylylene diisocyanate-based (XDI-based) crosslinking agents). An example of a TDI-based crosslinking agent is an adduct of tolylene diisocyanate and a polyfunctional alcohol, and a more specific example is a trimethylolpropane / tolylene diisocyanate trimer adduct.

[0060] Commercially available products can be used as the crosslinking agent (B). Examples of commercially available products include Millionate MT, Millionate MTL, Millionate MR-200, Millionate MR-400, Coronate L, Coronate HL and Coronate HX (all manufactured by Tosoh Corporation; all are trade names), and Takenate D-102, Takenate D-103, Takenate D-110N, Takenate D-120N, Takenate D-140N, Takenate D-160N, Takenate D-165N, Takenate D-170HN, Takenate D-178N, Takenate 500 and Takenate 600 (all manufactured by Mitsui Chemicals Corporation; all are trade names). For the crosslinking agent (B), Coronate L, Takenate D-102, and Takenate D-103 (all trimethylolpropane / tolylene diisocyanate trimer adducts) can be preferably used.

[0061] The amount of crosslinking agent (B) in the adhesive composition (I) is, for example, 1.5 parts by weight or more, and may be 2 parts by weight or more, or even 2.5 parts by weight or more, per 100 parts by weight of (meth)acrylic polymer (A). The upper limit of the amount is, for example, 25 parts by weight or less, and may be 20 parts by weight or less, 15 parts by weight or less, 12 parts by weight or less, 10 parts by weight or less, 7 parts by weight or less, 5 parts by weight or less, or even 4 parts by weight or less.

[0062] The adhesive composition (I) may contain one or more crosslinking agents (B).

[0063] When an adhesive sheet 1 is formed using an adhesive composition containing the crosslinking agent (B), the first domain and / or the second domain may contain a polymer of the crosslinking agent (B). An example of such a polymer is a self-polymer of the crosslinking agent (B).

[0064] When considering the self-polymerization (C) of the isocyanate-based crosslinking agent (B), the Hansen solubility parameter (HSP) distance Ra between the (meth)acrylic polymer (A) and the self-polymer (C) may be 15 or less. Due to the heat generated when forming the adhesive sheet 1, the isocyanate-based crosslinking agents (B) may react with each other to form a self-polymer of the crosslinking agent (B). The formation of the self-polymer can contribute to the formation of an adhesive sheet that can suppress changes in the dimensions of the optical film by increasing the cohesive force of the adhesive sheet. However, if the compatibility between the (meth)acrylic polymer (A) and the self-polymer is low, it is conceivable that independent domains rich in the self-polymer are likely to form inside the adhesive sheet. According to the inventors' studies, a distance Ra of 15 or less can contribute to the formation of the first and / or second domains in the above state.

[0065] The distance Ra may be 14.5 or less, 14 or less, 13.5 or less, 13 or less, 12.5 or less, or even 12 or less. The lower limit of the distance Ra is, for example, 6 or more.

[0066] The Hansen solubility parameter (HSP) is a solubility parameter introduced by Hildebrand, divided into three components: the dispersion term δD, the polarization term δP, and the hydrogen bonding term δH. δD represents the energy derived from intermolecular dispersion forces. δP represents the energy derived from intermolecular polar forces. δH represents the energy derived from intermolecular hydrogen bonding forces. The units for each component are typically MPa. 1 / 2 Therefore, the above three components define a point (vector) in the three-dimensional space known as Hansen space. The distance Ra corresponds to point (D) in the above space to the (meth)acrylic polymer (A). A , P A H A ) and the point corresponding to the self-polymer (C) (DC , P C , H C ), which is the distance between them, represented by the formula: {4×(δD A -δD B ) 2 +(δP A -δP B ) 2 +(δH A -δH B ) 2} 1 / 2 can be calculated by the formula. Details of Hansen solubility parameters are disclosed in "Hansen Solubility Parameters; A Users Handbook (CRC Press, 2007)". The δD, δP and δH of a polymer can be determined by calculation based on the constitutional units of the polymer and the content ratio of these units in the polymer using, for example, known software such as HSPiP (version 5). More specifically, δD, δP and δH of each constitutional unit are calculated individually, and the weighted average value obtained by weighting the calculated δD, δP and δH according to the content ratio of the unit can be used as δD, δP and δH of the polymer. Provided that the calculation is performed at a temperature of 23° C. Note that the calculated values of δD, δP and δH may differ slightly depending on the software used. However, this difference is usually negligible when determining Ra. For crosslinking agents, the Hansen solubility parameter is calculated only for those that form a self-polymer.

[0067] The self-polymer (C) assumed in the calculation of the distance Ra is a homopolymer composed of constitutional units derived from the isocyanate-based crosslinking agent (B). Provided that the self-polymer of the crosslinking agent (B) actually contained in the pressure-sensitive adhesive sheet formed from the pressure-sensitive adhesive composition (I) may contain constitutional units other than the constitutional units derived from the crosslinking agent (B).

[0068] ((Meth)acrylic oligomer) The pressure-sensitive adhesive composition (I) may further contain a (meth)acrylic oligomer (D).

[0069] The (meth)acrylic oligomer (D) may have the same composition as the (meth)acrylic polymer (A) described above, except that it has a different weight-average molecular weight (Mw). The weight-average molecular weight (Mw) of the (meth)acrylic oligomer (D) may be, for example, 1000 or more, and may be 2000 or more, 3000 or more, or even 4000 or more. The upper limit of the weight-average molecular weight (Mw) of the (meth)acrylic oligomer may be, for example, 30000 or less, and may be 15000 or less, 10000 or less, or even 7000 or less.

[0070] (Meth)acrylic oligomers (D) have, for example, one or more constituent units derived from each of the following monomers: methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate. Alkyl (meth)acrylates such as acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, and dodecyl (meth)acrylate; esters of (meth)acrylic acid with alicyclic alcohols such as cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and dicyclopentanyl (meth)acrylate; aromatic ring-containing (meth)acrylates such as phenyl (meth)acrylate and benzyl (meth)acrylate; and (meth)acrylates obtained from terpene compound derivative alcohols.

[0071] The (meth)acrylic oligomer (D) preferably has constituent units derived from a (meth)acrylic monomer having a relatively bulky structure. In this case, the adhesion of the adhesive sheet can be further improved. Examples of such acrylic monomers include alkyl (meth)acrylates having branched alkyl groups such as isobutyl (meth)acrylate and t-butyl (meth)acrylate; esters of (meth)acrylic acid with alicyclic alcohols such as cyclohexyl (meth)acrylate, isobornyl (meth)acrylate and dicyclopentanyl (meth)acrylate; and aromatic ring-containing (meth)acrylates such as phenyl (meth)acrylate and benzyl (meth)acrylate. The monomer preferably has a cyclic structure, and more preferably has two or more cyclic structures. Furthermore, when ultraviolet irradiation is performed during the polymerization of (meth)acrylic oligomer (D) and / or during the formation of the adhesive sheet, the progress of polymerization and / or formation is less likely to be inhibited. Therefore, it is preferable that the monomer does not have unsaturated bonds. For example, alkyl (meth)acrylates having a branched alkyl group, or esters of (meth)acrylic acid and alicyclic alcohols can be used.

[0072] Specific examples of (meth)acrylic oligomers (D) include copolymers of butyl acrylate, methyl acrylate, and acrylic acid; copolymers of cyclohexyl methacrylate and isobutyl methacrylate; copolymers of cyclohexyl methacrylate and isobornyl methacrylate; copolymers of cyclohexyl methacrylate and acryloyl morpholine; copolymers of cyclohexyl methacrylate and diethylacrylamide; copolymers of 1-adamantyl acrylate and methyl methacrylate; copolymers of dicyclopentanyl methacrylate and isobornyl methacrylate; copolymers of at least one selected from dicyclopentanyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, isobornyl acrylate, and cyclopentanyl methacrylate with methyl methacrylate; homopolymers of dicyclopentanyl acrylate, homopolymers of 1-adamantyl methacrylate, and homopolymers of 1-adamantyl acrylate.

[0073] The polymerization method for the (meth)acrylic polymer (A) described above can be used for the polymerization of the (meth)acrylic oligomer (D).

[0074] If the adhesive composition (I) contains a (meth)acrylic oligomer (D), the amount of D is, for example, 70 parts by weight or less, 50 parts by weight or less, or even 40 parts by weight or less, per 100 parts by weight of the (meth)acrylic polymer (A). The lower limit of the amount is, for example, 1 part by weight or more, 2 parts by weight or more, or even 3 parts by weight or more, per 100 parts by weight of the (meth)acrylic polymer (A). The adhesive composition (I) does not have to contain a (meth)acrylic oligomer (D).

[0075] (Additives) The adhesive composition (I) may contain other additives. Examples of additives include crosslinking agents other than isocyanate-based crosslinking agents (B), silane coupling agents, colorants such as pigments and dyes, surfactants, plasticizers, tackifiers, surface lubricants, leveling agents, rework improvers, softeners, antioxidants, anti-aging agents, light stabilizers, UV absorbers, polymerization inhibitors, antistatic agents (such as alkali metal salts, ionic liquids, and ionic solids, which are ionic compounds), inorganic fillers, organic fillers, powders, particles, and foils such as metal powders. Additives can be blended in an amount of, for example, 10 parts by weight or less, preferably 5 parts by weight or less, and more preferably 1 part by weight or less, per 100 parts by weight of (meth)acrylic polymer (A).

[0076] Examples of crosslinking agents other than isocyanate-based crosslinking agents (B) include peroxide-based crosslinking agents, epoxy-based crosslinking agents, imine-based crosslinking agents, and polyfunctional metal chelates. When the adhesive composition (I) contains crosslinking agents other than isocyanate-based crosslinking agents (B), the total amount of these agents is preferably 0.1 to 5 parts by weight, more preferably 0.1 to 3 parts by weight, 0.1 to 2 parts by weight, and 0.1 to 1 part by weight, in that order, per 100 parts by weight of (meth)acrylic polymer (A). The adhesive composition (I) does not have to contain crosslinking agents other than isocyanate-based crosslinking agents (B), such as epoxy-based crosslinking agents.

[0077] 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.

[0078] If the adhesive composition (I) contains a silane coupling agent, the amount of the silane coupling agent is, for example, 5 parts by weight or less per 100 parts by weight of the (meth)acrylic polymer (A), and may be 3 parts by weight or less, 1 part by weight or less, 0.5 parts by weight or less, 0.2 parts by weight or less, 0.1 parts by weight or less, or even 0.05 parts by weight or less. The adhesive composition (I) does not have to contain a silane coupling agent.

[0079] The type of adhesive composition (I) may be, for example, emulsion type, solvent type (solution type), active energy ray curing type (photocuring type), or thermal melt type (hot melt type). From the viewpoint of forming an adhesive sheet with superior durability, the adhesive composition (I) may be of the solvent type. The solvent type adhesive composition (I) may not contain a photocuring agent such as an ultraviolet curing agent.

[0080] The adhesive sheet 1 can be used, for example, in optical applications. The adhesive sheet 1 may also be used in optical laminates and / or image display devices. The adhesive sheet 1 is suitable for use in image display devices where it is particularly important to suppress dimensional changes in the optical film, such as narrow-bezel image display devices and image display devices with relatively large screen sizes. By using it in these image display devices, for example, peeling of the film contained in the optical laminate is suppressed.

[0081] [Method for manufacturing adhesive sheets] The adhesive sheet 1 can be formed, for example, by the manufacturing method of this embodiment described below. However, the adhesive sheet 1 may also be formed by other manufacturing methods.

[0082] The manufacturing method of this embodiment includes heating a coating film of an adhesive composition (I) which mainly contains a (meth)acrylic polymer (A) and further contains an isocyanate crosslinking agent (B) to form an adhesive sheet 1 from the coating film. Hereinafter, the heating of the coating film will be referred to as the main heating. During this heating, primarily, crosslinking and curing of the adhesive composition (I) contained in the coating film proceed due to heat.

[0083] The conditions for this heating process satisfy either equation (1) or (2) below. Here, x and y are the heating temperature (°C) and time (seconds), respectively. Equation (2) means that if the heating temperature x exceeds 120°C, the heating time y should be limited to a predetermined time. The heating temperature x can be set as the highest temperature to which the coating film is exposed, for example, the set temperature of a heating device such as a heating oven used to heat the coating film (if the heating device has multiple sections with different set temperatures or if the set temperature changes over time, it can be set as the highest set temperature to which the coating film is exposed within the heating device). The heating time y can be set as the time to which the coating film is exposed to a temperature exceeding 120°C. When using a heating device, for example, time y may be set as the time the coating film is located in a space set to a temperature exceeding 120°C, or the time the coating film passes through a section set to a temperature exceeding 120°C. If there are multiple sections set to a temperature exceeding 120°C, the sum of the times the coating film passes through these sections can be set as time y. If the set temperature changes over time, the time during which the set temperature exceeds 120°C can be calculated as time y. The same applies to the preheating temperature p and time q, which will be discussed later. x ≤ 120 ···(1) x > 120, and y ≤ -2.17x + 365.83 ···(2)

[0084] According to the inventors' studies, isocyanate-based crosslinking agents (B) in monomeric form tend to lose solubility at high temperatures and gradually aggregate within the coated film. Therefore, as the temperature x increases and the time y increases, the independent domains described above are more likely to be formed in the adhesive sheet, and the size and density of the formed domains tend to increase. On the other hand, when the temperature x falls below a certain level, the formation of oligomers such as dimers and trimers through self-polymerization of the crosslinking agents (B) proceeds preferentially, and aggregation is suppressed. This heating under conditions that satisfy formula (1) or (2) above is suitable for suppressing the aggregation of crosslinking agents (B).

[0085] The lower limit of temperature x may be, for example, 80°C or higher, 85°C or higher, or even 90°C or higher. The upper limit of temperature x may be, for example, 165°C or lower, or 160°C or lower. Under conditions that satisfy equation (1), the upper limit of temperature x may be 115°C or lower, 110°C or lower, 105°C or lower, 100°C or lower, 95°C or lower, or even 90°C or lower. The temperature x of this heating may be kept constant throughout the heating process, or it may be changed during the heating process.

[0086] The lower limit of time y is, for example, 10 seconds or more, but may also be 20 seconds or more, 30 seconds or more, 35 seconds or more, 40 seconds or more, more than 40 seconds, 45 seconds or more, and even 50 seconds or more. The upper limit of time y is, for example, 300 seconds or less, but may also be 180 seconds or less, and even less than 180 seconds. The upper limit of time y under conditions that satisfy equation (2) may also be 100 seconds or less, 95 seconds or less, 90 seconds or less, 85 seconds or less, 80 seconds or less, 75 seconds or less, 70 seconds or less, 65 seconds or less, and even 60 seconds or less.

[0087] The conditions for this heating may also satisfy equation y ≤ -2.17x + 345.83 for x > 120. In heating that satisfies the above equation, the time y is further restricted compared to heating that satisfies equation (2).

[0088] The conditions for this heating process may satisfy y ≤ 80 for x > 120, and may also satisfy y ≤ 60.

[0089] The heating conditions may also satisfy y < 180 for x ≤ 120, and may also satisfy y ≤ 160, y ≤ 140, y ≤ 120, y ≤ 110, y ≤ 100, y < 100, y ≤ 95, and even y ≤ 90.

[0090] The manufacturing method of this embodiment may further include pre-heating the coating film of the adhesive composition (I) under heating conditions of temperature p (°C) and time q (seconds) before performing the main heating. The temperature p for pre-heating is lower than the temperature x for the main heating. During pre-heating, the drying of the coating film and, in the case of solvent-type adhesive compositions (I), removal of the solvent proceed mainly. Removal of the solvent can contribute to suppressing the aggregation of the isocyanate-based crosslinking agent (B). Furthermore, pre-heating can contribute to generating an oligomer of the crosslinking agent (B) by allowing the reaction with a compound having a hydroxyl group, typically water, to proceed to some extent while suppressing the melting of the isocyanate-based crosslinking agent (B).

[0091] The temperature x (°C) of the main heating and the temperature p (°C) of the preheating may satisfy the equation: xp ≤ 55. xp may be 50°C or less, 45°C or less, 40°C or less, 35°C or less, 30°C or less, less than 30°C, 25°C or less, 20°C or less, 15°C or less, and even 10°C or less. The lower limit of xp is greater than 0°C and may be 5°C or more, and even 10°C or more. A small difference between temperature x and temperature p can contribute to suppressing shrinkage of the coating film caused by rapid temperature changes.

[0092] The temperature p is, for example, 50°C or higher and less than 80°C. The lower limit of the temperature p may be 55°C or higher, 60°C or higher, 65°C or higher, or even 70°C or higher. The upper limit of the temperature p may be 75°C or lower. The preheating temperature p may be kept constant throughout the preheating process, or it may be varied during the preheating process.

[0093] Time q is, for example, 5 seconds or more, but may also be 10 seconds or more, 15 seconds or more, 20 seconds or more, 25 seconds or more, 30 seconds or more, 35 seconds or more, 40 seconds or more, and even 45 seconds or more. The upper limit of time q is, for example, 180 seconds or less, but may also be 120 seconds or less, 115 seconds or less, and even 110 seconds or less.

[0094] Time q may be set such that, when the adhesive composition (I) is solvent-type, the solvent content in the coating film is 30% or less, preferably 25% or less, and more preferably 20% or less, relative to the content before preheating.

[0095] Time q may be expressed as q / (q+y), which is the ratio of preheating time to the total preheating and main heating time, and satisfy the condition 0.2 ≤ q / (q+y) ≤ 0.6. The lower limit of q / (q+y) may be 0.25 or greater, and even 0.3 or greater. The upper limit of q / (q+y) may be 0.55 or less, 0.5 or less, 0.45 or less, and even 0.4 or less.

[0096] Preheating may be performed after a predetermined time r has elapsed since the formation of the coating film. Ensuring a time r between the formation of the coating film and the start of preheating can contribute to the efficient removal of solvents contained in the coating film. The time r is, for example, 5 to 180 seconds, and may also be 5 to 120 seconds or 10 to 60 seconds. During time r, the coating film is in a non-heated atmosphere, for example, in an atmosphere of 20 to 30°C.

[0097] Preheating and main heating may be performed consecutively. As a more specific example, a single heating device may be divided into a preheating section and a main heating section, and the coated film may be continuously transported from the preheating section to the main heating section with the temperatures x and p of each section set independently.

[0098] The coating film subjected to the above heating can be formed, for example, by applying an adhesive composition (I) or a mixture of adhesive composition (I) and a solvent to a base film. The base film is typically a resin film or a metal film. The base film may also be a film with a release treatment applied to the coated surface (release film). In one example of a release film, the coated surface is released using a silicone compound. The base film may also be an optical film, in which case an optical laminate including an adhesive sheet and an optical film can be formed.

[0099] 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.

[0100] The compositions and mixtures applied to the base film preferably have a viscosity suitable for handling and coating.

[0101] [Optical laminate] An example of the optical laminate of this embodiment is shown in Figure 2. The optical laminate 10A in Figure 2 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.

[0102] 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.

[0103] The polarizing plate includes a polarizer. A polarizer protective film may be bonded to at least one side of the polarizer. Any adhesive or bonding agent can be used to bond the polarizer and the polarizer protective film. Adhesive sheet 1 may be used for bonding. The polarizer is typically a polyvinyl alcohol (PVA) film in which iodine is oriented by stretching such as air stretching (dry stretching) or boric acid water stretching.

[0104] A phase difference film is a film that exhibits birefringence in the in-plane direction and / or in the thickness direction. Examples of phase difference films include stretched resin films and films in which liquid crystal materials are oriented and immobilized.

[0105] The phase difference film may be a λ / 4 plate, a λ / 2 plate, an anti-reflective phase difference film (see, for example, paragraphs 0221, 0222, and 0228 of Japanese Patent Application Publication No. 2012-133303), a viewing angle compensation phase difference film (see, for example, paragraphs 0225 and 0226 of Japanese Patent Application Publication No. 2012-133303), or a tilted orientation phase difference film for viewing angle compensation (see, for example, paragraph 0227 of Japanese Patent Application Publication No. 2012-13303). The phase difference film is not limited to the above examples, as long as it has birefringence in the in-plane direction and / or in the thickness direction. The phase difference value, arrangement angle, three-dimensional birefringence, whether it is single-layer or multi-layer, etc. of the phase difference film are also not limited. Known films can be used as the phase difference film.

[0106] The thickness of the optical film 2 is, for example, 1 to 200 μm. The thickness of the optical film 2 which is a polarizing plate is, for example, 1 to 150 μm, and may be 100 μm or less, 75 μm or less, 50 μm or less, 20 μm or less, or even 15 μm or less. The lower limit of the thickness may be 10 μm or more, 20 μm or more, 50 μm or more, 75 μm or more, or even 100 μm or more.

[0107] The optical film 2 may be a single layer or a laminated film composed of two or more layers. If the optical film 2 is a laminated film, an adhesive sheet 1 may be used to bond each layer.

[0108] Another example of the optical laminate of this embodiment is shown in Figure 3. The optical laminate 10B in Figure 3 has a laminated structure in which a separator 3, an adhesive sheet 1, and an optical film 2 are laminated in this order. The optical laminate 10B can be used as an optical film with an adhesive sheet by peeling off the separator 3.

[0109] The separator 3 is typically a resin film. Examples of resins that make up the separator 3 include polyester such as polyethylene terephthalate (PET), polyolefins such as polyethylene and polypropylene, polycarbonate, acrylic, polystyrene, polyamide, and polyimide. The surface of the separator 3 that comes into contact with the adhesive sheet 1 may be treated with a release agent. The release agent is, for example, treated with a silicone compound. However, the separator 3 is not limited to the above examples. The separator 3 is peeled off when the optical laminate 10B is used, for example, when it is attached to the image forming layer.

[0110] Another example of the optical laminate of this embodiment is shown in Figure 4. The optical laminate 10C in Figure 4 has a laminated structure in which a separator 3, an adhesive sheet 1, a phase difference film 2A, an interlayer adhesive 4, and a polarizing plate 2B are laminated in this order. The optical laminate 10C can be used by peeling off the separator 3 and, for example, attaching it to an image forming layer.

[0111] Any known adhesive can be used for the interlayer adhesive 4. The adhesive sheet 1 may also be used as the interlayer adhesive 4.

[0112] Another example of the optical laminate of this embodiment is shown in Figure 5. The optical laminate 10D in Figure 5 has a laminated structure in which a separator 3, an adhesive sheet 1, a phase difference film 2A, an interlayer adhesive 4, a polarizing plate 2B, and a protective film 5 are laminated in this order. The optical laminate 10D can be used by peeling off the separator 3 and, for example, attaching it to an image forming layer.

[0113] 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.

[0114] The protective film 5 may be bonded to the optical film 2 with any adhesive. Bonding with an adhesive sheet 1 is also possible.

[0115] The optical laminate may have any configuration as long as it includes an adhesive sheet formed by the above-described method for manufacturing the adhesive sheet.

[0116] 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.

[0117] 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.

[0118] [Image display device] An example of an image display device of this embodiment is shown in Figure 6. The image display device 11 in Figure 6 has a laminated structure in which a substrate 7, an image forming layer (e.g., an organic EL layer or a liquid crystal layer) 6, an adhesive sheet 1, a phase difference film 2A, an interlayer adhesive 4, a polarizing plate 2B, and a protective film 5 are stacked in this order. The image display device 11 has optical laminates 10A, 10B, 10C, and 10D as shown in Figures 2 to 5 (except for the separator 3). The substrate 7 and the image forming layer 6 only need to have the same configuration as the substrate and image forming layer of a known image display device.

[0119] The image display device 11 in Figure 6 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 may be used for home appliance applications, automotive applications, public information display (PID) applications, etc.

[0120] The image display device may have any configuration as long as it includes an adhesive sheet formed by the above-described method for manufacturing the adhesive sheet, and / or an optical laminate formed by the above-described method for manufacturing the optical laminate. [Examples]

[0121] 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.

[0122] First, the evaluation methods for the (meth)acrylic polymers and adhesive sheets prepared in the examples and comparative examples are shown.

[0123] [Weight average molecular weight (Mw)] The weight-average molecular weight (Mw) of (meth)acrylic polymers was evaluated by GPC under the following conditions. • Analytical equipment: Waters Acquity APC • Columns: Tosoh Corporation, G7000HXL + GMHXL + GMHXL Column temperature: 40°C • Eluent: Tetrahydrofuran (with acid added) ·Flow rate: 0.8mL / min ·Injection volume: 100μL • Detector: Differential refractometer (RI) • Standard sample: Polystyrene (PS) manufactured by Agilent.

[0124] [Distance Ra] The distance Ra was calculated using the method described above. HSPiP (version 5) was used as the software.

[0125] [Storage modulus G'(25℃)] The storage modulus G'(25°C) of the adhesive sheet was evaluated by the method described above. However, the sample for measurement was prepared by punching out a disc shape from a laminate obtained by stacking the fabricated adhesive sheets. For dynamic viscoelasticity measurements of the sample, an ARES-G2 from TA Instruments was used.

[0126] [Whitening] The degree of whitening of the adhesive sheet was evaluated based on the measurement of haze on the adhesive sheet, as follows: A smaller haze indicates a smaller degree of whitening. The haze of the adhesive sheet was measured in accordance with JIS K7136:1981 using a Suga Test Instruments HZ-V3 haze meter at a 25°C atmosphere. The measurement was performed on a Matsunami Glass Industry S012140 slide glass (thickness 1.3 mm) with five layers (adhesive sheet thickness 15 μm) or three layers (adhesive sheet thickness 25 μm) of the adhesive sheet to be evaluated bonded together (total thickness 75 μm in both cases). For the adhesive sheet of Example 21, which has a thickness of 35 μm, the measured value V in the state with two layers bonded together (total thickness 70 μm) was converted to a value corresponding to a total thickness of 75 μm using the formula: V × 75 / 70. A: Measured haze is less than 0.37% B: Measured haze is between 0.37% and less than 0.43% C: Measured haze is between 0.43% and less than 0.50% D: Measured haze is 0.50% or higher

[0127] [Domain status] The domain status of the adhesive sheet was evaluated using the evaluation method described above on the cross-sectional image of the adhesive sheet. Cross-sectional images were acquired using a TEM (Hitachi HT7820; acceleration voltage 100kV) at a magnification of 20,000x. Samples for TEM were prepared by staining the adhesive sheet to be evaluated with RuO4 heavy metals, then embedding it in resin, and finally cutting it into ultrathin sections approximately 100nm thick. Ten evaluation regions were set in the cross-sectional image so as not to overlap with each other. The status was evaluated by image analysis of the cross-sectional image, using ImageJ. The status of the evaluated domains 1 to 5, and the evaluation criteria for each status, are as follows.

[0128] (State 1: Number of evaluation regions in which the first domain exists) A: Number of evaluation areas is 0 B: Number of evaluation areas is 1-2 C: Number of evaluation areas: 3-5 D: Number of evaluation areas is 6 or more

[0129] (State 2: For all first domains, the shortest distance between adjacent first domains) A: The shortest distance is 300nm or more. D: Shortest distance is less than 300nm

[0130] (State 3: For all second domains, the shortest distance between adjacent second domains) A: The shortest distance is 200 nm or more. C: Shortest distance is between 150nm and 200nm D: Shortest distance is less than 150nm

[0131] (State 4: Number of evaluation regions where the number of second domains is 10 or less) A: Number of evaluation areas is 3 or more D: Number of evaluation areas is 1-2

[0132] (State 5: Percentage of all secondary domains where the shortest distance between adjacent secondary domains is 100 nm or more) A: 50% or more D: Less than 50%

[0133] [Humidity durability] The humidification durability of the adhesive sheets (equivalent to an accelerated durability test) was evaluated by the following method. First, a circular polarizing plate with an adhesive sheet was formed, with each adhesive sheet prepared in the examples and comparative examples attached to one exposed surface. Next, the circular polarizing plate was fixed to the surface of a glass plate (Corning Eagle XG) via the adhesive sheet. The fixing of the circular polarizing plate was carried out in an atmosphere of 23°C and 50%RH. Next, after being treated in an autoclave at 50°C and 5 atmospheres (absolute pressure) for 15 minutes, it was left to cool to 23°C to stabilize the bonding of the circular polarizing plate to the glass plate, and then left in a heated and humidified atmosphere of 60°C and 95%RH for 500 hours. After the period, it was returned to an atmosphere of 23°C and 50%RH, and the humidification durability was evaluated as follows by visually checking for peeling of the circular polarizing plate from the glass plate and for the occurrence of foaming between the glass plate and the circular polarizing plate. A: No visible changes such as foaming or peeling are observed. B: There is slight peeling or foaming at the edges, but it is within a range that does not pose a practical problem. C: Slight continuous peeling or foaming is observed at the edges, but it is within a range that does not pose a practical problem. D: Significant peeling or foaming is observed at the edges, which poses a practical problem.

[0134] The following describes the method for forming the circular polarizing plate with adhesive sheet used to evaluate its humidification durability.

[0135] <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.

[0136] (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.

[0137] <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.

[0138] 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.

[0139] (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.

[0140] [ka]

[0141] (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.

[0142] <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.

[0143] Next, to the obtained (meth)acrylic polymer solution, 0.5 parts by weight of trimethylolpropane / tolylene diisocyanate trimer adduct (manufactured by Tosoh, trade name "Coronate L"), 0.1 parts by weight of benzoyl peroxide, a peroxide-based crosslinking agent, 0.2 parts by weight of epoxy group-containing silane coupling agent (manufactured by Shin-Etsu Chemical Co., Ltd., trade name "KBM-403"), and 0.5 parts by weight of a polyether compound having a reactive silyl group (manufactured by Kaneka, Cyryl SAT10) were mixed per 100 parts by weight of the solid content of the solution to obtain an adhesive composition PSA1 to be used as an interlayer adhesive for bonding a polarizing plate P1 and a phase difference film R1.

[0144] (Fabrication of polarizing plates with interlayer adhesive layer) The adhesive composition PSA1 prepared above was applied to the release surface of a 38 μm thick polyethylene terephthalate (PET) film (Mitsubishi Chemical Polyester Films, MRF38), which is a release film with a silicone treatment on the release surface, so that the thickness of the dried layer was 12 μm. The film was then dried at 155°C for 1 minute to form an interlayer adhesive layer. Next, the formed interlayer adhesive layer was transferred to the protective layer (without hard coat) side of the polarizing plate P1 to obtain a polarizing plate with an interlayer adhesive layer.

[0145] (Fabrication of circular polarizing plates with adhesive sheets) On the second phase difference film side of the phase difference film R1 (the norbornene-based resin film used as the base film when preparing the second phase difference film was peeled off), the adhesive sheets prepared in the examples and comparative examples were transferred from the release film and attached. Next, the polarizing plate with the interlayer adhesive layer prepared above was attached to the first phase difference film side of the phase difference film R1 via the interlayer adhesive layer to obtain a circular polarizing plate with an adhesive sheet. The attachment of the phase difference film R1 and the polarizing plate with the interlayer adhesive layer was carried out so that, when viewed from the side of the first phase difference film, the angle between the slow axis of the first phase difference film and the absorption axis of the polarizer was 45 degrees counterclockwise.

[0146] [Condensation marks (exterior)] The surface of the release film and coating (adhesive sheet) after heating was visually inspected to check for any droplet marks, and the condensation marks that may occur during the manufacturing of the adhesive sheet were evaluated as follows. A: No traces of liquid droplets are visible. B: There are slight traces of liquid droplets, but it is at a level that does not pose any practical problems. C: Droplet marks are visible, which poses a practical problem.

[0147] [Degree of remaining material] The residual monomer and solvent content in the adhesive sheet formed on the release sheet was determined, and the degree of residual substances was evaluated as follows. ppm is based on weight. A: The content of both residual monomers and residual solvents is below the detection limit. B: The total content of residual monomers and residual solvents is above the detection limit but 50 ppm or less. C: The total content of residual monomers and residual solvents is greater than 50 ppm but less than or equal to 100 ppm. D: The total content of residual monomers and residual solvents exceeds 100 ppm.

[0148] (Method for measuring residual monomers) Approximately 0.1 g of adhesive sheet was placed in a screw-top tube, 5 mL of acetone was added, and the tube was shaken overnight. The contents of the screw-top tube were then filtered through a membrane filter (average pore size 0.45 μm), and 1 μL of the resulting filtrate was injected into a gas chromatograph (GC) to determine the residual monomer content. The GC measurement conditions are shown below. GC system: Agilent Technologies, 6890N Column: Agilent Technologies HP-1 (0.250mmφ × 30m, df=1.0μm) Column temperature: Hold at 40°C for 1 minute, then increase to 60°C (rate 5°C / min), then increase to 140°C (rate 10°C / min), and further increase to 300°C (rate 20°C / min), and hold at 300°C for 10 minutes. Column flow rate: 2 mL / min (He) Column pressure: Constant flow mode (136kPa) Inlet temperature: 200℃ Injection volume: 1μL Injection method: Split (10:1) Detector: Flame ionization detector (FID) Detector temperature: 250℃

[0149] (Method for measuring residual solvent) Approximately 0.02 g of adhesive sheet was collected and sealed in a 20 mL headspace vial. Next, the vial containing the adhesive sheet was heated in a headspace sampler (HSS) at 150°C for 30 minutes. After heating, 1 mL of the gas phase in the vial was injected into a GC to determine the residual solvent content. The HSS conditions and GC measurement conditions are shown below. ·HSS conditions HSS device: Agilent Technologies, G1888 Heating temperature: 150℃ Heating time: 30 minutes Pressurization time: 0.20 minutes Loop filling time: 0.20 minutes Loop equilibrium time: 0.05 minutes Injection time: 0.50 minutes Sample loop temperature: 160℃ Transfer line temperature: 200℃ • GC measurement conditions (residual solvent) GC system: Agilent Technologies, 6890N Column: Agilent Technologies HP-1 (0.250mmφ × 30m, df=1.0μm) Column temperature: Hold at 40°C for 3 minutes, then increase to 120°C (rate 10°C / min), then increase to 300°C (rate 20°C / min), and hold at 300°C for 10 minutes. Column flow rate: 1 mL / min (He) Column pressure: Constant flow mode (81kPa) Inlet temperature: 250℃ Injection volume: 1mL Injection method: Split (20:1) Detector: FID Detector temperature: 250℃

[0150] [comprehensive evaluation] A comprehensive evaluation of the durability and transparency of the adhesive sheets was conducted as follows. A: The humidification durability rating is A, and the whitening rating is A to C. B: Humidity resistance is rated B, and whitening is rated A-C. C: Humidification durability is rated C, and whitening is rated A-C. D: At least one of the following evaluations is D: Humidification durability and whitening.

[0151] Next, the methods for producing each adhesive sheet in the examples and comparative examples will be described.

[0152] The correspondence between the abbreviations or names shown in the following explanation and the compounds is as follows: BA: n-butyl acrylate BzA: Benzyl acrylate AA: Acrylic acid HBA: 4-hydroxybutyl acrylate AIBN: 2,2'-Azobisisobutyronitrile C / L: Trimethylolpropane / Tolylene diisocyanate trimer adduct (isocyanate-based crosslinking agent; manufactured by Tosoh Corporation, Coronate L) TetradC: 1,3-Bis(N,N-Diglycidylaminomethyl)cyclohexane (Polyfunctional epoxy crosslinking agent; manufactured by Mitsubishi Gas Chemical Company, TetradC) KBM403: 3-Glycidoxypropyltriethoxysilane (silane coupling agent; manufactured by Shin-Etsu Chemical Co., Ltd., KBM403)

[0153] [Preparation of (meth)acrylic polymer (A)] (Synthesis Example 1) A four-necked flask equipped with a stirring blade, thermometer, nitrogen gas inlet tube, and condenser was charged with 94.9 parts by weight of BA, 5.0 parts by weight of AA, and 0.1 parts by weight of HBA. Next, 0.1 parts by weight of AIBN was added to 100 parts by weight of the mixture of BA, AA, and HBA as a polymerization initiator. Nitrogen gas was introduced while gently stirring to purge the flask with nitrogen, and the polymerization reaction was carried out for 7 hours while maintaining the 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 (A-1). The weight-average molecular weight (Mw) of (meth)acrylic polymer (A-1) was 2.2 million. For HSP, the δD, δP, and δH of (meth)acrylic polymer (A-1) were 16.75 MPa, respectively. 1 / 2 , 3.49 MPa 1 / 2 and 5.38 MPa 1 / 2 That was the case.

[0154] (Synthesis Example 2) A solution of (meth)acrylic polymer (A-2) was obtained in the same manner as in Synthesis Example 1, except that the monomers used were changed to 79.9 parts by weight of BA, 15.0 parts by weight of BzA, 5.0 parts by weight of AA, and 0.1 parts by weight of HBA. The weight-average molecular weight (Mw) of (meth)acrylic polymer (A-2) was 2.2 million. For HSP, the δD, δP, and δH of (meth)acrylic polymer (A-2) were 17.05 MPa, respectively. 1 / 2 , 3.49 MPa 1 / 2 and 5.43 MPa 1 / 2 That was the case.

[0155] (Synthesis Example 3) A solution of (meth)acrylic polymer (A-3) was obtained in the same manner as in Synthesis Example 1, except that the monomers used were changed to 74.9 parts by weight of BA, 20.0 parts by weight of BzA, 5.0 parts by weight of AA, and 0.1 parts by weight of HBA. The weight-average molecular weight (Mw) of (meth)acrylic polymer (A-3) was 2.3 million. For HSP, the δD, δP, and δH of (meth)acrylic polymer (A-3) were 17.15 MPa, respectively. 1 / 2 , 3.49 MPa 1 / 2 and 5.44 MPa 1 / 2 That was the case.

[0156] Table 1 below summarizes the types and amounts of monomers and polymerization initiators used in Synthesis Examples 1-3, as well as the weight-average molecular weight (Mw) and HSP distance Ra of the resulting polymers. Note that the δD, δP, and δH of the C / L self-polymers are calculated at 20.50 MPa, respectively. 1 / 2 , 12.40 MPa 1 / 2 and 9.60 MPa 1 / 2 That was the case.

[0157] [Table 1]

[0158] [Preparation of adhesive compositions and adhesive sheets] (Manufacturing Examples 1-8) As shown in Table 2 below, a solvent-type adhesive composition was obtained by mixing a crosslinking agent and the like with 100 parts by weight of the solid content of (meth)acrylic polymer (A). Note that Tetrad-C did not form a self-polymer.

[0159] [Table 2]

[0160] Next, a 38 μm thick PET film (Mitsubishi Chemical Polyester Films, MRF38), which is a release film with a silicone treatment applied to its release surface, was coated with the adhesive composition prepared in each manufacturing example to form a coating film. This was then left in a 23°C environment until preheating (standing time r), and then preheating and main heating were continuously performed in an air-circulating constant-temperature oven while the base film and coating film were transported to form adhesive sheets of Examples 1 to 25 and Comparative Examples 1 to 5 having a predetermined thickness. The standing time r and the conditions for preheating and main heating are shown in Table 3 below. The temperatures for preheating and main heating are the set temperatures for the preheating section and main heating section of the oven, respectively. The times for preheating and main heating are the times for the base film and coating film to pass through the preheating section and main heating section, respectively.

[0161] [Table 3]

[0162] The evaluation results of the fabricated adhesive sheets are shown in Table 4 below. Furthermore, TEM cross-sectional images of the adhesive sheets of Examples 3, 8, 9 and Comparative Example 3 are shown in Figures 7A to 7D. The domain states 1 to 5 in Table 4 are as follows: State 1: Number of evaluation regions in which the first domain exists. State 2: For all first domains, the shortest distance between adjacent first domains. State 3: For all second domains, the shortest distance between adjacent second domains. State 4: Number of evaluation regions where the number of second domains is 10 or less. State 5: Percentage of all secondary domains where the shortest distance to an adjacent secondary domain is 100 nm or more.

[0163] [Table 4]

[0164] As shown in Table 4, the adhesive sheet of the example was more suitable for suppressing dimensional changes than the adhesive sheet of the comparative example, and also exhibited superior transparency and durability. [Industrial applicability]

[0165] The adhesive sheet of the present invention can be used, for example, as an optical adhesive sheet for use in optical laminates and / or image display devices. [Explanation of Symbols]

[0166] 1 Adhesive sheet 2 Optical film 10A, 10B, 10C, 10D Optical Stack 11 Image display device

Claims

1. An adhesive sheet formed from an adhesive composition comprising a (meth)acrylic polymer (A) and a crosslinking agent, The aforementioned adhesive composition does not contain an epoxy crosslinking agent. The amount of the crosslinking agent in the adhesive composition is 1.5 parts by weight or more and 15 parts by weight or less per 100 parts by weight of the (meth)acrylic polymer (A). The weight-average molecular weight of the (meth)acrylic polymer (A) is 1 million or more. The (meth)acrylic polymer (A) has constituent units derived from carboxyl group-containing monomers, The (meth)acrylic polymer (A) has constituent units derived from aromatic ring-containing monomers, The content of the constituent units derived from the aromatic ring-containing monomer in the (meth)acrylic polymer (A) is 1 to 25% by weight. The gel fraction of the adhesive sheet is 95% or more. The adhesive sheet has a storage modulus G' (at 25°C) of 0.15 MPa or higher, measured at a frequency of 1 Hz. When 10 evaluation regions of 1.5 μm square are arbitrarily set in the cross-sectional image of the adhesive sheet, and island-like regions having a short axis of 100 nm or more are defined as the first domain, the number of evaluation regions in which the first domain exists is 5 or less. Having haze of 0.1% or more, Adhesive sheet.

2. The adhesive sheet according to claim 1, wherein for all the first domains observed in the defined evaluation area, the shortest distance between adjacent first domains is 300 nm or more.

3. The adhesive sheet according to claim 1 or 2, wherein, when an island-like region having a short axis of 50 nm or more and less than 100 nm is defined as a second domain, the number of evaluation regions in which the number of the second domains is 10 or less is 3 or more.

4. The adhesive sheet according to any one of claims 1 to 3, wherein, when an island-like region having a short axis of 50 nm or more and less than 100 nm is defined as a second domain, the shortest distance between adjacent second domains is 150 nm or more for all second domains observed in the defined evaluation region.

5. The adhesive sheet according to any one of claims 1 to 4, wherein, when an island-like region having a short axis of 50 nm or more and less than 100 nm is defined as a second domain, the proportion of second domains among all the second domains observed in the defined evaluation region in which the shortest distance between adjacent second domains is 100 nm or more is 50% or more.

6. The adhesive sheet according to any one of claims 1 to 5, wherein the storage modulus G' (at 25°C), measured under the condition of a frequency of 1 Hz, is less than 0.5 MPa.

7. The adhesive sheet according to any one of claims 1 to 6, wherein the adhesive composition mainly comprises the (meth)acrylic polymer (A) and an isocyanate crosslinking agent (B) as the crosslinking agent.

8. The adhesive sheet according to claim 7, wherein the first domain comprises a polymer of the isocyanate-based crosslinking agent (B).

9. The adhesive sheet according to claim 7 or 8, wherein the isocyanate-based crosslinking agent (B) is a tolylene diisocyanate-based agent.

10. The adhesive sheet according to any one of claims 1 to 9, wherein the (meth)acrylic polymer (A) contains structural units derived from hydroxyl group-containing monomers in a content of 1% by weight or less.

11. The adhesive sheet according to any one of claims 1 to 10, wherein the adhesive composition is solvent-type.

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

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

Images