Adhesive sheet for use in laminate in flexible image display device, laminate for use in flexible image display device, and flexible image display device

Abstract

To provide a pressure sensitive adhesive sheet capable of preventing, in a flexible picture display unit having a display part that can be rolled up, a layer composing the unit from separating or waving, after being held under hot environment in a state of being rolled up onto a shaft member and then returned into a flat state.SOLUTION: In a pressure sensitive adhesive sheet, a loss tangent tanδ at 85°C is 0.32 or less, and a gel fraction is 75% or more. The pressure sensitive adhesive sheet is to be used for a laminate inside a flexible picture display unit having a display part that can be rolled up.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Various thin image display devices such as liquid crystal displays and organic EL displays have a laminated structure including, for example, an image display panel and an optical film (see, for example, Patent Document 1). An adhesive sheet is generally used to bond the layers that make up the image display device. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-157745 Summary of the Invention [Problem to be solved by the invention]

[0004] The present inventors have been developing a new flexible image display device having a rollable display unit, and have been studying the adhesive sheet used in the device. The inventors' studies have revealed that when a flexible image display device having a rollable display unit is held in a state where it is wound around an axial member such as a roller and then returned to a flat state, the layers bonded by the adhesive sheet peel off or the layers become wavy. The peeling and wavy problems tend to be particularly pronounced in high-temperature environments.

[0005] Therefore, the present invention aims to provide an adhesive sheet that can suppress peeling and undulation of the layers constituting a flexible image display device having a rollable display unit, even when the device is wound around an axis member and held in a high-temperature environment and then returned to a flat state. [Means for solving the problem]

[0006] The present invention provides The loss tangent tanδ at 85°C is 0.32 or less, Provided is a pressure-sensitive adhesive sheet for use in a laminate in a flexible image display device having a rollable display section, which has a gel fraction of 75% or more.

[0007] Furthermore, the present invention provides The above adhesive sheet, a substrate supporting the pressure-sensitive adhesive sheet; The present invention provides a laminate for use in a flexible image display device having a rollable display section, comprising:

[0008] Furthermore, the present invention provides The laminate described above; an image display panel; Equipped with The laminate is provided as a flexible image display device having a rollable display section located on the viewing side of the image display panel. [Effects of the Invention]

[0009] According to the present invention, an adhesive sheet can be provided that can suppress peeling and undulation of the layers constituting a flexible image display device having a rollable display unit, even when the device is wound around an axial member and held in a high-temperature environment and then returned to a flat state. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view of a laminate used in a flexible image display device according to one embodiment of the present invention and the flexible image display device. [Figure 2] FIG. 10 is a cross-sectional view of a laminate used in a flexible image display device and a flexible image display device according to another embodiment of the present invention. [Figure 3] FIG. 1 is a schematic diagram illustrating an example of an image display system. [Figure 4] 1A to 1C are diagrams illustrating a method for manufacturing a retardation film. [Figure 5A] FIG. 10 is a diagram for explaining a winding and retention test. [Figure 5B] FIG. 10 is a diagram for explaining a winding and retention test. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention will be described in detail below, but the present invention is not limited to the following embodiments and can be implemented in any modified form without departing from the gist of the present invention.

[0012] (Embodiment of Pressure-Sensitive Adhesive Sheet) The pressure-sensitive adhesive sheet of this embodiment is a component used in a laminate in a flexible image display device having a rollable display unit, and has a loss tangent tanδ at 85°C of 0.32 or less and a gel fraction of 75% or more.

[0013] The tan δ of a pressure-sensitive adhesive sheet at 85°C can be determined by the following method. First, a measurement sample made of the material that constitutes the pressure-sensitive adhesive sheet is prepared. The measurement sample is disc-shaped. The evaluation sample has a bottom diameter of 8 mm and a thickness of 2 mm. The measurement sample may be obtained by punching out a disc from a laminate of multiple pressure-sensitive adhesive sheets. Next, dynamic viscoelasticity measurement is performed on the measurement sample. For dynamic viscoelasticity measurement, for example, an "Advanced Rheometric Expansion System (ARES)" manufactured by Rheometric Scientific can be used. The conditions for dynamic viscoelasticity measurement are as follows: (Measurement conditions) Frequency: 1Hz Deformation mode: Torsion Measurement temperature: -70℃~150℃ Heating rate: 5°C / min

[0014] From the results of the dynamic viscoelasticity measurement, the storage modulus G' (MPa) and loss modulus G" (MPa) at 85°C are determined. The ratio G" / G' of the loss modulus G" to the storage modulus G' can be considered to be the tan δ of the PSA sheet at 85°C.

[0015] The tan δ of the pressure-sensitive adhesive sheet at 85°C is preferably 0.30 or less, more preferably 0.28 or less, even more preferably 0.25 or less, particularly preferably 0.20 or less, especially preferably 0.18 or less, and may be 0.15 or less, or may be 0.13 or less. In a flexible image display device including the pressure-sensitive adhesive sheet, from the viewpoint of suppressing the leaving of traces such as curling, the tan δ of the pressure-sensitive adhesive sheet at 85°C is preferably 0.07 or more, more preferably 0.08 or more, even more preferably 0.09 or more, especially preferably 0.10 or more, and especially preferably 0.11 or more. The tan δ of the pressure-sensitive adhesive sheet at 85°C may be 0.11 to 0.32, or may be 0.11 to 0.20.

[0016] The gel fraction of a pressure-sensitive adhesive sheet can be evaluated, for example, by the following method. First, a portion of the pressure-sensitive adhesive sheet is scraped off to obtain a small piece. Next, the obtained small piece is wrapped in a stretched porous polytetrafluoroethylene membrane and tied with kite string. This results in a test piece. Next, the total weight (weight A) of the pressure-sensitive adhesive sheet piece, the stretched porous membrane, and the kite string is measured. The total weight of the stretched porous membrane and the kite string used is defined as weight B. Next, the test piece is immersed in a container filled with ethyl acetate and left to stand at 23°C for one week. After standing, the test piece is removed from the container and dried for two hours in a dryer set at 130°C, and then the weight C of the test piece is measured. The gel fraction of the pressure-sensitive adhesive sheet can be calculated from weight A, weight B, and weight C using the following formula. Gel fraction (wt%) = (CB) / (AB) × 100

[0017] The gel fraction of the pressure-sensitive adhesive sheet is preferably 80% or more, more preferably 83% or more, even more preferably 85% or more, particularly preferably 88% or more, and especially preferably 90% or more, and may be 92% or more. The upper limit of the gel fraction of the pressure-sensitive adhesive sheet is not particularly limited, and may be, for example, 99%, 97%, 95%, or 94%.

[0018] The pressure-sensitive adhesive sheet of this embodiment has a tan δ of 0.32 or less at 85°C and a gel fraction of 75% or more, and thus can maintain high cohesive strength and adhesive strength even in a high-temperature environment. Furthermore, the pressure-sensitive adhesive sheet of this embodiment is less likely to deform due to stress generated when a flexible image display device is wound around a shaft member. Therefore, the pressure-sensitive adhesive sheet of this embodiment can suppress peeling and undulation in the layers constituting the device, even when the flexible image display device is held in a high-temperature environment while wound around a shaft member and then returned to a flat state.

[0019] The storage modulus G' of the pressure-sensitive adhesive sheet at 25°C is not particularly limited and is, for example, 0.05 MPa or more, preferably 0.08 MPa or more, more preferably 0.10 MPa or more, even more preferably 0.13 MPa or more, and particularly preferably 0.15 MPa or more. The upper limit of the storage modulus G' of the pressure-sensitive adhesive sheet at 25°C is not particularly limited and is, for example, 0.50 MPa, preferably 0.40 MPa, and more preferably 0.35 MPa. The storage modulus G' of the pressure-sensitive adhesive sheet at 25°C can be determined from the results of the dynamic viscoelasticity measurement described above.

[0020] The storage modulus G' of the pressure-sensitive adhesive sheet at 85°C is not particularly limited and is, for example, 0.04 MPa or more, preferably 0.05 MPa or more, more preferably 0.063 MPa or more, even more preferably 0.07 MPa or more, and particularly preferably 0.1 MPa or more. The upper limit of the storage modulus G' of the pressure-sensitive adhesive sheet at 85°C is not particularly limited and is, for example, 0.50 MPa, preferably 0.30 MPa, and more preferably 0.20 MPa. The storage modulus G' of the pressure-sensitive adhesive sheet at 85°C can be determined from the results of the dynamic viscoelasticity measurement described above.

[0021] The 100% modulus of the adhesive sheet is, for example, 0.05 N / mm 2 That's all. The 100% modulus of an adhesive sheet is a property expressed by the value obtained by dividing the stress (tensile stress) generated in the adhesive sheet when the adhesive sheet is stretched 100% by a tensile force in one direction by the initial cross-sectional area of ​​the adhesive sheet. The 100% modulus of an adhesive sheet can be evaluated as follows.

[0022] First, the pressure-sensitive adhesive sheet to be evaluated is cut into a 30 mm x 40 mm strip. Next, the cut-out pressure-sensitive adhesive sheet is rolled in the direction of the long side to prevent air bubbles from being trapped, to obtain a cylindrical test piece with a height of 30 mm corresponding to the length of the short side. The obtained test piece is then placed in a tensile tester such as a Tensilon, and a uniaxial tensile test is performed in the height direction to obtain an elongation-stress curve of the pressure-sensitive adhesive sheet. Note that the preparation of the test piece and the uniaxial tensile test are performed at room temperature (23°C), with an initial chuck distance of 10 mm and a tensile speed of 300 mm / min. From the obtained elongation-stress curve, the stress at 100% elongation (when the chuck distance is 20 mm) is calculated, and this is divided by the initial cross-sectional area of ​​the test piece to obtain the 100% modulus of the pressure-sensitive adhesive sheet.

[0023] The 100% modulus of the adhesive sheet is preferably 0.10 N / mm 2 or more, and more preferably 0.14 N / mm 2 or more, 0.18N / mm 2 It may be 0.20N / mm or more.2 The upper limit of the 100% modulus of the pressure-sensitive adhesive sheet is not particularly limited, and may be, for example, 0.80 N / mm 2 and 0.50N / mm 2 may be 0.30 N / mm 2 may be.

[0024] The 500% modulus of the adhesive sheet is, for example, 0.05 N / mm 2 That's all. The 500% modulus of a pressure-sensitive adhesive sheet is a property expressed by the value obtained by dividing the stress (tensile stress) generated in the pressure-sensitive adhesive sheet when the pressure-sensitive adhesive sheet is stretched 500% by a tensile force in one direction by the initial cross-sectional area of ​​the pressure-sensitive adhesive sheet. The 500% modulus of a pressure-sensitive adhesive sheet can be evaluated in accordance with the method described above for the 100% modulus of a pressure-sensitive adhesive sheet.

[0025] The 500% modulus of the adhesive sheet is preferably 0.10 N / mm 2 More preferably, it is 0.20 N / mm 2 More preferably, it is 0.30 N / mm 2 More preferably, it is 0.35 N / mm 2 or more, 0.60N / mm 2 It may be 1.0N / mm or more. 2 The upper limit of the 500% modulus of the pressure-sensitive adhesive sheet is not particularly limited, and may be, for example, 10 N / mm 2 is.

[0026] The 700% modulus of the adhesive sheet is, for example, 0.07 N / mm 2 That's all. The 700% modulus of a pressure-sensitive adhesive sheet is a property expressed by the value obtained by dividing the stress (tensile stress) generated in the pressure-sensitive adhesive sheet when the pressure-sensitive adhesive sheet is stretched 700% by a tensile force in one direction by the initial cross-sectional area of ​​the pressure-sensitive adhesive sheet. The 700% modulus of a pressure-sensitive adhesive sheet can be evaluated in accordance with the method described above for the 100% modulus of a pressure-sensitive adhesive sheet.

[0027] The 700% modulus of the adhesive sheet is preferably 0.10 N / mm 2More preferably, it is 0.20 N / mm 2 More preferably, it is 0.30 N / mm 2 More preferably, it is 0.40 N / mm 2 or more, 0.60N / mm 2 The upper limit of the 700% modulus of the pressure-sensitive adhesive sheet is not particularly limited, and may be, for example, 10 N / mm 2 is.

[0028] The 1000% modulus of the adhesive sheet is, for example, 0.15 N / mm 2 That's all. The 1000% modulus of a pressure-sensitive adhesive sheet is a property expressed by the value obtained by dividing the stress (tensile stress) generated in the pressure-sensitive adhesive sheet when the pressure-sensitive adhesive sheet is stretched 1000% by a tensile force in one direction by the initial cross-sectional area of ​​the pressure-sensitive adhesive sheet. The 1000% modulus of a pressure-sensitive adhesive sheet can be evaluated in accordance with the method described above for the 100% modulus of a pressure-sensitive adhesive sheet.

[0029] The 1000% modulus of the adhesive sheet is preferably 0.20 N / mm 2 More preferably, it is 0.40 N / mm 2 More preferably, it is 0.50 N / mm 2 More preferably, it is 0.60 N / mm 2 The upper limit of the 1000% modulus of the pressure-sensitive adhesive sheet is not particularly limited, and may be, for example, 10 N / mm 2 is.

[0030] The glass transition temperature (Tg) of the pressure-sensitive adhesive sheet is preferably 5° C. or lower, more preferably −20° C. or lower, and even more preferably −25° C. or lower. When the Tg of the pressure-sensitive adhesive sheet is within this range, the pressure-sensitive adhesive sheet is less likely to harden, and a flexible image display device with excellent stress relaxation properties can be realized.

[0031] The total light transmittance (according to JIS K7136:2000) of the pressure-sensitive adhesive sheet in the visible light wavelength region is preferably 85% or more, more preferably 90% or more.

[0032] Examples of adhesives that constitute the adhesive sheet include acrylic adhesives, rubber adhesives, vinyl alkyl ether adhesives, silicone adhesives, polyester adhesives, polyamide adhesives, urethane adhesives, fluorine-based adhesives, epoxy adhesives, and polyether adhesives. The adhesives that constitute the adhesive sheet may be used alone or in combination of two or more. However, from the standpoints of transparency, processability, durability, adhesion, and the like, it is preferable to use an acrylic adhesive (composition) containing a (meth)acrylic polymer alone. In other words, it is preferable that the adhesive sheet contains a (meth)acrylic polymer.

[0033] [(Meth)acrylic polymer] When an acrylic pressure-sensitive adhesive is used as the pressure-sensitive adhesive composition, it preferably contains a (meth)acrylic polymer containing, as a monomer unit, a (meth)acrylic monomer having a linear or branched alkyl group having 1 to 30 carbon atoms. In this specification, "(meth)acrylic polymer" means an acrylic polymer and / or a methacrylic polymer, and "(meth)acrylate" means an acrylate and / or a methacrylate.

[0034] Specific examples of the (meth)acrylic monomer having a linear or branched alkyl group having 1 to 30 carbon atoms that constitutes the main skeleton of the (meth)acrylic polymer 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, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, and isobutyl (meth)acrylate. Examples of suitable monomers include octyl (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. Among these, preferred are (meth)acrylic monomers having a linear or branched alkyl group with 6 to 30 carbon atoms (hereinafter sometimes referred to as "(meth)acrylic monomers having long-chain alkyl groups"), with n-dodecyl (meth)acrylate (lauryl (meth)acrylate) being more preferred. The use of a (meth)acrylic monomer having a long-chain alkyl group reduces entanglement of the polymer, making it more susceptible to deformation in response to minute strains. From the viewpoint of adhesion at low temperatures, it is also preferable to use a (meth)acrylic monomer whose homopolymer has a glass transition temperature (Tg) of −70 to −20° C., and among these, it is more preferable to use 2-ethylhexyl acrylate. One or more kinds of (meth)acrylic monomers can be used.

[0035] The (meth)acrylic monomer having a linear or branched alkyl group having 1 to 30 carbon atoms is the main component of all the monomers constituting the (meth)acrylic polymer. Here, the main component means that the (meth)acrylic monomer having a linear or branched alkyl group having 1 to 30 carbon atoms accounts for 50 to 100% by weight, more preferably 80 to 100% by weight, even more preferably 90 to 99.9% by weight, and particularly preferably 94 to 99.9% by weight, of all the monomers constituting the (meth)acrylic polymer.

[0036] The monomer components constituting the (meth)acrylic polymer may contain a copolymerizable monomer (copolymerizable monomer) in addition to a (meth)acrylic monomer having a linear or branched alkyl group having 1 to 30 carbon atoms. The copolymerizable monomer may be used alone or in combination of two or more kinds.

[0037] The copolymerizable monomer is not particularly limited, but is preferably a hydroxyl group-containing monomer having a reactive functional group. By using a hydroxyl group-containing monomer, a pressure-sensitive adhesive sheet with excellent adhesion tends to be obtained. The hydroxyl group-containing monomer is, for example, a compound that contains a hydroxyl group in its structure and a polymerizable unsaturated double bond such as a (meth)acryloyl group or a vinyl group.

[0038] Specific 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. Among the hydroxyl group-containing monomers, 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate are preferred from the viewpoints of durability and adhesion. One or more types of hydroxyl group-containing monomers can be used.

[0039] The copolymerizable monomer may contain a monomer having a reactive functional group, such as a carboxyl group-containing monomer, an amino group-containing monomer, or an amide group-containing monomer. The use of these monomers is preferred from the viewpoint of adhesion in humid or high-temperature environments.

[0040] When an acrylic pressure-sensitive adhesive is used as the pressure-sensitive adhesive composition, the pressure-sensitive adhesive composition may contain a (meth)acrylic polymer containing a carboxyl group-containing monomer having a reactive functional group as a monomer unit. The use of a carboxyl group-containing monomer tends to produce a pressure-sensitive adhesive sheet with excellent adhesion even in humid or high-temperature environments. The carboxyl group-containing monomer is a compound that contains a carboxyl group in its structure and a polymerizable unsaturated double bond such as a (meth)acryloyl group or a vinyl group.

[0041] Specific examples of carboxyl group-containing monomers include (meth)acrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, and crotonic acid.

[0042] When an acrylic pressure-sensitive adhesive is used as the pressure-sensitive adhesive composition, the pressure-sensitive adhesive composition may contain, as a monomer unit, a (meth)acrylic polymer containing an amino group-containing monomer having a reactive functional group. The use of an amino group-containing monomer tends to result in a pressure-sensitive adhesive sheet with excellent adhesion even in humid or high-temperature environments. The amino group-containing monomer is a compound that contains an amino group in its structure and a polymerizable unsaturated double bond such as a (meth)acryloyl group or a vinyl group.

[0043] Specific examples of amino group-containing monomers include N,N-dimethylaminoethyl (meth)acrylate and N,N-dimethylaminopropyl (meth)acrylate.

[0044] When an acrylic pressure-sensitive adhesive is used as the pressure-sensitive adhesive composition, the pressure-sensitive adhesive composition may contain, as a monomer unit, a (meth)acrylic polymer containing an amide group-containing monomer having a reactive functional group. The use of the amide group-containing monomer tends to result in a pressure-sensitive adhesive sheet with excellent adhesion. The amide group-containing monomer is a compound that contains an amide group in its structure and a polymerizable unsaturated double bond such as a (meth)acryloyl group or a vinyl group.

[0045] Specific examples of amide group-containing monomers include acrylamide-based monomers such as (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N-isopropylacrylamide, N-methyl(meth)acrylamide, N-butyl(meth)acrylamide, N-hexyl(meth)acrylamide, N-methylol(meth)acrylamide, N-methylol-N-propane(meth)acrylamide, aminomethyl(meth)acrylamide, aminoethyl(meth)acrylamide, mercaptomethyl(meth)acrylamide, and mercaptoethyl(meth)acrylamide; N-acryloyl heterocyclic monomers such as N-(meth)acryloylmorpholine, N-(meth)acryloylpiperidine, and N-(meth)acryloylpyrrolidine; and N-vinyl group-containing lactam-based monomers such as N-vinylpyrrolidone and N-vinyl-ε-caprolactam.

[0046] Further, examples of copolymerizable monomers include polyfunctional monomers. When a polyfunctional monomer is contained, a crosslinking effect is obtained by polymerization, making it easy to adjust the gel fraction and improve the cohesive strength. This makes it easier to cut the pressure-sensitive adhesive sheet, and tends to improve processability. Furthermore, peeling of the pressure-sensitive adhesive sheet due to cohesive failure can be more effectively prevented. The polyfunctional monomer is not particularly limited, but examples include 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( Examples of suitable polyfunctional (meth)acrylates include polyfunctional (meth)acrylates such as trimethylolpropane tri(meth)acrylate, tetramethylolmethane tri(meth)acrylate, allyl (meth)acrylate, vinyl (meth)acrylate, epoxy acrylate, polyester acrylate, and urethane acrylate, as well as divinylbenzene. Among these, preferred polyfunctional (meth)acrylates are 1,6-hexanediol diacrylate and dipentaerythritol hexa(meth)acrylate. The polyfunctional monomers may be used alone or in combination of two or more.

[0047] In the monomer units constituting the (meth)acrylic polymer, the blending ratio (total amount) of the monomer having a reactive functional group and the polyfunctional monomer is preferably 20% by weight or less, more preferably 10% by weight or less, even more preferably 0.01 to 8% by weight, particularly preferably 0.01 to 5% by weight, and most preferably 0.05 to 3% by weight, of all the monomers constituting the (meth)acrylic polymer. If it exceeds 20% by weight, the number of crosslinking points increases, and the flexibility of the pressure-sensitive adhesive (sheet) is lost, which tends to result in poor stress relaxation properties.

[0048] When an acrylic pressure-sensitive adhesive is used as the pressure-sensitive adhesive composition, other copolymerizable monomers can be introduced as monomer units in addition to the monomer having a reactive functional group and the polyfunctional monomer, as long as the effects of the present invention are not impaired.

[0049] Other copolymerizable monomers include, for example, (meth)acrylic acid alkoxyalkyl esters [e.g., 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, methoxytriethylene glycol (meth)acrylate, 3-methoxypropyl (meth)acrylate, 3-ethoxypropyl (meth)acrylate, 4-methoxybutyl (meth)acrylate, 4-ethoxybutyl (meth)acrylate, etc.]; epoxy group-containing monomers [e.g., glycidyl (meth)acrylate, methyl glycidyl (meth)acrylate, etc.]; sulfonic acid group-containing monomers [e.g., sodium vinyl sulfonate, etc.]; phosphate group-containing monomers; (meth)acrylic acid monomers having an alicyclic hydrocarbon group, p) acrylic acid esters [for example, cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, etc.]; (meth)acrylic acid esters having an aromatic hydrocarbon group [for example, phenyl (meth)acrylate, phenoxyethyl (meth)acrylate, benzyl (meth)acrylate, etc.]; vinyl esters [for example, vinyl acetate, vinyl propionate, etc.]; aromatic vinyl compounds [for example, styrene, vinyl toluene, etc.]; olefins or dienes [for example, ethylene, propylene, butadiene, isoprene, isobutylene, etc.]; vinyl ethers [for example, vinyl alkyl ether, etc.]; vinyl chloride, etc.

[0050] The blending ratio of the other copolymerization monomer is not particularly limited, but is preferably 30% by weight or less, more preferably 10% by weight or less, and even more preferably zero, of all the monomers constituting the (meth)acrylic polymer. If it exceeds 30% by weight, particularly when a monomer other than a (meth)acrylic monomer is used, the number of reaction sites between the pressure-sensitive adhesive sheet and other layers (film, substrate) tends to decrease, and the adhesion strength tends to decrease.

[0051] The pressure-sensitive adhesive sheet is formed from a pressure-sensitive adhesive composition, and the pressure-sensitive adhesive composition may be in any form, such as an emulsion type, a solvent type (solution type), an active energy ray curable type, a hot melt type, etc. Among these, preferred examples of the pressure-sensitive adhesive composition include a solvent type pressure-sensitive adhesive composition and an active energy ray curable type pressure-sensitive adhesive composition.

[0052] A preferred example of a solvent-based pressure-sensitive adhesive composition is a pressure-sensitive adhesive composition containing a (meth)acrylic polymer as an essential component. A preferred example of an active energy ray-curable pressure-sensitive adhesive composition is a pressure-sensitive adhesive composition containing, as an essential component, a mixture of monomer components constituting a (meth)acrylic polymer (monomer mixture) or a partially polymerized product thereof. Note that the term "partially polymerized product" refers to a composition in which one or more of the monomer components contained in the monomer mixture are partially polymerized. The term "monomer mixture" includes a composition containing only one type of monomer component.

[0053] In particular, from the viewpoints of productivity, environmental impact, and ease of obtaining a thick adhesive sheet, the adhesive composition is preferably an active energy ray-curable adhesive composition containing, as an essential component, a mixture of monomer components constituting a (meth)acrylic polymer (monomer mixture) or a partially polymerized product thereof.

[0054] (Meth)acrylic polymers are obtained by polymerizing monomer components. More specifically, they are obtained by polymerizing the monomer components, a monomer mixture, or a partially polymerized product thereof by a known, commonly used method. Examples of polymerization methods include solution polymerization, emulsion polymerization, bulk polymerization, and polymerization by heat or active energy ray irradiation (thermal polymerization, active energy ray polymerization). Among these, solution polymerization and active energy ray polymerization are preferred in terms of transparency, water resistance, cost, etc. Note that the polymerization is preferably carried out while avoiding contact with oxygen in order to suppress polymerization inhibition by oxygen. For example, it is preferable to carry out the polymerization under a nitrogen atmosphere or by blocking oxygen with a release film (separator). The resulting (meth)acrylic polymer may be any of a random copolymer, a block copolymer, a graft copolymer, etc.

[0055] Examples of active energy rays irradiated during active energy ray polymerization (photopolymerization) include ionizing radiation such as α-rays, β-rays, γ-rays, neutron beams, and electron beams, as well as ultraviolet rays, with ultraviolet rays being particularly preferred. The irradiation energy, irradiation time, irradiation method, and the like of the active energy rays are not particularly limited as long as they can activate the photopolymerization initiator and cause a reaction of the monomer components.

[0056] When carrying out solution polymerization, various common solvents can be used. Examples of such solvents include organic solvents such as 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. The solvents may be used alone or in combination of two or more.

[0057] When carrying out polymerization, a polymerization initiator such as a photopolymerization initiator (photoinitiator) or a thermal polymerization initiator may be used depending on the type of polymerization reaction. The polymerization initiator may be used alone or in combination of two or more kinds.

[0058] The photopolymerization initiator is not particularly limited, but examples thereof 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.

[0059] Examples of benzoin ether-based photopolymerization initiators include benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, benzoin isopropyl ether, benzoin isobutyl ether, 2,2-dimethoxy-1,2-diphenylethan-1-one, and anisole methyl ether. Examples of acetophenone-based photopolymerization initiators include 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexyl phenyl ketone, 4-phenoxydichloroacetophenone, and 4-(t-butyl)dichloroacetophenone. Examples of α-ketol-based photopolymerization initiators include 2-methyl-2-hydroxypropiophenone and 1-[4-(2-hydroxyethyl)phenyl]-2-methylpropan-1-one. Examples of aromatic sulfonyl chloride-based photopolymerization initiators include 2-naphthalenesulfonyl chloride. Examples of photoactive oxime-based photopolymerization initiators include 1-phenyl-1,1-propanedione-2-(o-ethoxycarbonyl)-oxime. Examples of benzoin-based photopolymerization initiators include benzoin. Examples of benzyl-based photopolymerization initiators include benzil. Examples of benzophenone-based photopolymerization initiators include benzophenone, benzoylbenzoic acid, 3,3'-dimethyl-4-methoxybenzophenone, polyvinylbenzophenone, and α-hydroxycyclohexyl phenyl ketone. Examples of ketal-based photopolymerization initiators include benzil dimethyl ketal. Examples of thioxanthone-based photopolymerization initiators include thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 2,4-diisopropylthioxanthone, and dodecylthioxanthone.

[0060] The amount of the photopolymerization initiator used is not particularly limited, but is preferably 0.01 to 1 part by weight, more preferably 0.05 to 0.5 parts by weight, relative to 100 parts by weight of the total amount of the monomer components.

[0061] Examples of polymerization initiators used in solution polymerization include azo polymerization initiators, peroxide polymerization initiators (e.g., dibenzoyl peroxide, tert-butyl permaleate, etc.), and redox polymerization initiators. Among these, the azo polymerization initiators disclosed in JP-A-2002-69411 are preferred. Examples of the azo polymerization initiator include 2,2'-azobisisobutyronitrile (AIBN), 2,2'-azobis-2-methylbutyronitrile, 2,2'-azobis(2-methylpropionate)dimethyl, and 4,4'-azobis-4-cyanovaleric acid.

[0062] The amount of the azo-based polymerization initiator used is not particularly limited, but is preferably 0.05 to 0.5 parts by weight, more preferably 0.1 to 0.3 parts by weight, relative to 100 parts by weight of the total amount of the monomer components.

[0063] The polyfunctional monomer (polyfunctional (meth)acrylate) used as the copolymerization monomer can also be used in a solvent-based or active energy ray-curable pressure-sensitive adhesive composition. For example, when a solvent-based pressure-sensitive adhesive composition is used by mixing the polyfunctional monomer (polyfunctional (meth)acrylate) and a photopolymerization initiator, the composition is thermally dried and then cured with active energy rays.

[0064] The weight-average molecular weight (Mw) of the (meth)acrylic polymer used in the solvent-based pressure-sensitive adhesive composition is typically in the range of 1,000,000 to 2,000,000. Considering durability, particularly heat resistance, it is preferably 1,200,000 to 2,000,000, more preferably 1,400,000 to 1,800,000. If the weight-average molecular weight is less than 1,000,000, when crosslinking polymer chains to ensure durability, the number of crosslinking points increases compared to a weight-average molecular weight of 1,000,000 or more. This results in a loss of flexibility of the pressure-sensitive adhesive (sheet). This makes it difficult to alleviate the strain on the outer (convex) and inner (concave) sides of the bend that occurs between the layers (films) constituting the image display device during winding, potentially leading to breakage of each layer. If the weight-average molecular weight is greater than 2,500,000, a large amount of dilution solvent is required to adjust the viscosity to a level suitable for coating, which increases costs, and is undesirable. Furthermore, the entanglement of the polymer chains of the resulting (meth)acrylic polymer becomes complex, resulting in poor flexibility and potentially leading to breakage of each layer (film) during winding. The weight average molecular weight (Mw) is a value measured by GPC (gel permeation chromatography) and calculated in terms of polystyrene.

[0065] [(Meth)acrylic oligomer] The pressure-sensitive adhesive composition can contain a (meth)acrylic oligomer. The (meth)acrylic oligomer is preferably a polymer having a weight-average molecular weight (Mw) smaller than that of the (meth)acrylic polymer. By using such a (meth)acrylic oligomer, the (meth)acrylic oligomer is interposed between the (meth)acrylic polymers, reducing entanglement of the (meth)acrylic polymers and making the composition more susceptible to deformation in response to minute strain.

[0066] Examples of monomers constituting the (meth)acrylic oligomer include 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, nonyl (meth)acrylate, Examples of the (meth)acrylate include alkyl (meth)acrylates such as acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, and dodecyl (meth)acrylate; esters of (meth)acrylic acid and alicyclic alcohols such as cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and dicyclopentanyl (meth)acrylate; aryl (meth)acrylates such as phenyl (meth)acrylate and benzyl (meth)acrylate; and (meth)acrylates obtained from terpene compound derivative alcohols. These (meth)acrylates can be used alone or in combination of two or more.

[0067] The (meth)acrylic oligomer preferably contains, as a monomer unit, an acrylic monomer having a relatively bulky structure, such as alkyl (meth)acrylates with a branched alkyl group, such as isobutyl (meth)acrylate and t-butyl (meth)acrylate; esters of (meth)acrylic acid and alicyclic alcohol, such as cyclohexyl (meth)acrylate and isobornyl (meth)acrylate dicyclopentanyl (meth)acrylate; or (meth)acrylates with a cyclic structure, such as aryl (meth)acrylates, such as phenyl (meth)acrylate and benzyl (meth)acrylate. By imparting such a bulky structure to the (meth)acrylic oligomer, the adhesiveness of the pressure-sensitive adhesive sheet tends to be further improved. In particular, those with a cyclic structure are highly effective in terms of bulkiness, and those containing multiple rings are even more effective. When ultraviolet light is used to synthesize a (meth)acrylic oligomer or to prepare a pressure-sensitive adhesive sheet, a monomer having a saturated bond is preferred because it is less likely to cause polymerization inhibition, and an alkyl (meth)acrylate in which the alkyl group has a branched structure, or an ester with an alicyclic alcohol can be suitably used as a monomer constituting the (meth)acrylic oligomer.

[0068] From this point of view, suitable (meth)acrylic oligomers include, for example, a copolymer of butyl acrylate (BA), methyl acrylate (MA), and acrylic acid (AA), a copolymer of cyclohexyl methacrylate (CHMA) and isobutyl methacrylate (IBMA), a copolymer of cyclohexyl methacrylate (CHMA) and isobornyl methacrylate (IBXMA), a copolymer of cyclohexyl methacrylate (CHMA) and acryloylmorpholine (ACMO), a copolymer of cyclohexyl methacrylate (CHMA) and diethylacrylamide (DEAA), a copolymer of 1-adamantyl acrylate (ADA) and methyl Examples of the copolymer include a copolymer of dicyclopentanyl methacrylate (DCPMA) and methyl methacrylate (MMA), a copolymer of dicyclopentanyl methacrylate (DCPMA) and isobornyl methacrylate (IBXMA), a copolymer of dicyclopentanyl methacrylate (DCPMA), cyclohexyl methacrylate (CHMA), isobornyl methacrylate (IBXMA), isobornyl acrylate (IBXA), a copolymer of cyclopentanyl methacrylate (DCPMA) and methyl methacrylate (MMA), and homopolymers of dicyclopentanyl acrylate (DCPA), 1-adamantyl methacrylate (ADMA), and 1-adamantyl acrylate (ADA).

[0069] Similar to the (meth)acrylic polymer, polymerization methods for the (meth)acrylic oligomer include solution polymerization, emulsion polymerization, bulk polymerization, emulsion polymerization, and polymerization by heat or active energy ray irradiation (thermal polymerization, active energy ray polymerization). Among these, solution polymerization and active energy ray polymerization are preferred in terms of transparency, water resistance, cost, etc. The resulting (meth)acrylic oligomer may be any of a random copolymer, a block copolymer, a graft copolymer, etc.

[0070] Like the (meth)acrylic polymer, the (meth)acrylic oligomer can be used in a solvent-based pressure-sensitive adhesive composition or an active energy ray-curable pressure-sensitive adhesive composition. For example, an active energy ray-curable pressure-sensitive adhesive composition can be prepared by mixing a (meth)acrylic oligomer with a mixture (monomer mixture) of monomer components constituting a (meth)acrylic polymer or a partial polymer thereof. When the (meth)acrylic oligomer is dissolved in a solvent, the pressure-sensitive adhesive composition can be thermally dried to volatilize the solvent, and then the active energy ray curing can be completed to obtain a pressure-sensitive adhesive sheet.

[0071] The weight-average molecular weight (Mw) of the (meth)acrylic oligomer used in the solvent-based pressure-sensitive adhesive composition is preferably 1,000 or more, more preferably 2,000 or more, even more preferably 3,000 or more, and particularly preferably 4,000 or more. The weight-average molecular weight (Mw) of the (meth)acrylic oligomer is preferably 30,000 or less, more preferably 15,000 or less, even more preferably 10,000 or less, and particularly preferably 7,000 or less. By adjusting the weight-average molecular weight (Mw) of the (meth)acrylic oligomer to fall within the above range, for example, when used in combination with a (meth)acrylic polymer, the (meth)acrylic oligomer is interposed between the (meth)acrylic polymers, reducing entanglement of the (meth)acrylic polymer. This makes the pressure-sensitive adhesive sheet more susceptible to deformation in response to minute strain, and tends to reduce strain on other layers constituting the image display device. This tends to further suppress cracking of each layer and peeling between the pressure-sensitive adhesive sheet and other layers. The weight average molecular weight (Mw) of the (meth)acrylic oligomer is measured by GPC (gel permeation chromatography) in the same manner as the (meth)acrylic polymer, and is calculated in terms of polystyrene.

[0072] When a (meth)acrylic oligomer is used in the pressure-sensitive adhesive composition, its amount is not particularly limited, but is preferably 70 parts by weight or less, more preferably 1 to 70 parts by weight, even more preferably 2 to 50 parts by weight, even more preferably 3 to 40 parts by weight, and even more preferably 20 parts by weight or less, per 100 parts by weight of the (meth)acrylic polymer. By adjusting the amount of the (meth)acrylic oligomer to fall within the above range, the (meth)acrylic oligomer is appropriately interposed between the (meth)acrylic polymers, reducing entanglement of the (meth)acrylic polymers and making the pressure-sensitive adhesive sheet more susceptible to deformation due to slight strain. This reduces strain on other layers constituting the image display device and tends to suppress cracking of each layer and peeling between the pressure-sensitive adhesive sheet and other layers.

[0073] [Crosslinking agent] The pressure-sensitive adhesive composition may contain a crosslinking agent. As the crosslinking agent, organic crosslinkers or polyfunctional metal chelates can be used in both solvent-based and active energy ray-curable pressure-sensitive adhesive compositions. Examples of organic crosslinkers include isocyanate-based crosslinkers, peroxide-based crosslinkers, epoxy-based crosslinkers, and imine-based crosslinkers. In polyfunctional metal chelates, polyvalent metals are covalently or coordinately bonded to organic compounds. Examples of polyvalent metal atoms include Al, Cr, Zr, Co, Cu, Fe, Ni, V, Zn, In, Ca, Mg, Mn, Y, Ce, Sr, Ba, Mo, La, Sn, and Ti. Examples of atoms in the organic compound that form covalent or coordinate bonds include oxygen atoms, and examples of organic compounds include alkyl esters, alcohol compounds, carboxylic acid compounds, ether compounds, and ketone compounds. For solvent-based pressure-sensitive adhesive compositions, peroxide-based crosslinkers and isocyanate crosslinkers are preferred. Peroxide-based crosslinking agents generate radicals by abstracting hydrogen atoms from the side chains of a (meth)acrylic polymer, promoting crosslinking between the side chains of the (meth)acrylic polymer. Therefore, compared with crosslinking using an isocyanate-based crosslinking agent (e.g., a polyfunctional isocyanate-based crosslinking agent), the crosslinked state tends to be relatively loose, maintaining ease of deformation in response to minute strain while increasing cohesive strength. This tends to suppress cracking of the layers constituting the image display device and peeling between the pressure-sensitive adhesive sheet and other layers. Isocyanate-based crosslinking agents (especially trifunctional isocyanate-based crosslinking agents) are preferred in terms of durability. Furthermore, peroxide-based crosslinking agents and isocyanate-based crosslinking agents (especially bifunctional isocyanate-based crosslinking agents) are preferred in terms of winding properties. While peroxide-based crosslinking agents and bifunctional isocyanate-based crosslinking agents both form flexible two-dimensional crosslinks, trifunctional isocyanate-based crosslinking agents form stronger three-dimensional crosslinks. When winding, two-dimensional crosslinking, which is a more flexible crosslinking, is advantageous. However, two-dimensional crosslinking alone may result in poor durability and prone to peeling, so a hybrid crosslinking of two-dimensional and three-dimensional crosslinking is preferable. Therefore, it may be preferable to use a trifunctional isocyanate-based crosslinking agent in combination with a peroxide-based crosslinking agent or a bifunctional isocyanate-based crosslinking agent.In terms of productivity and thick-film coating, it is preferable to obtain a crosslinking effect by polymerization using a polyfunctional monomer for the active energy ray-curable pressure-sensitive adhesive composition. However, the above-mentioned crosslinking agent may be used or may be used in combination with the polyfunctional monomer. For example, a crosslinking agent may be mixed with a mixture (monomer mixture) of monomer components constituting a (meth)acrylic polymer or a partial polymer thereof, and the reaction of the crosslinking agent may be completed by thermal drying before or after curing the pressure-sensitive adhesive composition with active energy rays.

[0074] The amount of the crosslinking agent used is, for example, preferably 0.1 to 10 parts by weight, more preferably 0.2 to 5 parts by weight, per 100 parts by weight of the (meth)acrylic polymer.

[0075] When a peroxide-based crosslinking agent is used alone, the amount of peroxide-based crosslinking agent blended is preferably 0.5 to 10 parts by weight, more preferably 1 to 5 parts by weight, per 100 parts by weight of the (meth)acrylic polymer. Within this range, the adhesive sheet tends to be able to maintain its ease of deformation in response to minute strain while sufficiently increasing cohesive strength and improving durability.

[0076] When the isocyanate crosslinking agent is used alone, the amount of the isocyanate crosslinking agent added is preferably 0.5 to 10 parts by weight, more preferably 1 to 5 parts by weight, per 100 parts by weight of the (meth)acrylic polymer.

[0077] When a peroxide-based crosslinking agent and an isocyanate-based crosslinking agent are used in combination, the lower limit of the weight ratio of the peroxide-based crosslinking agent to the isocyanate-based crosslinking agent (peroxide-based crosslinking agent / isocyanate-based crosslinking agent) is preferably 0.02 or more, more preferably 1 or more, and even more preferably 5 or more. The upper limit of this weight ratio is preferably 500 or less, more preferably 100 or less, even more preferably 50 or less, and particularly preferably 40 or less. Within the above range, the pressure-sensitive adhesive sheet tends to be able to maintain ease of deformation in response to minute strain while sufficiently increasing cohesive strength.

[0078] When a polyfunctional monomer (particularly a polyfunctional (meth)acrylate) is used as a crosslinking agent, the amount of the polyfunctional monomer is preferably 0.1 to 1 part by weight, more preferably 0.2 to 0.5 parts by weight, per 100 parts by weight of the (meth)acrylic polymer.

[0079] [Additives] Furthermore, the pressure-sensitive adhesive composition may contain other known additives, for example, various silane coupling agents, polyether compounds of polyalkylene glycols such as polypropylene glycol, colorants, powders such as pigments, dyes, surfactants, plasticizers, tackifiers, surface lubricants, leveling agents, softeners, antioxidants, antiaging agents, light stabilizers, UV absorbers, polymerization inhibitors, antistatic agents (such as alkali metal salts, ionic liquids, and ionic solids, which are ionic compounds), inorganic or organic fillers, metal powders, particles, foil-like materials, etc. May be added appropriately depending on the application. A redox system containing a reducing agent added within a controllable range may also be used.

[0080] The method for preparing the pressure-sensitive adhesive composition is not particularly limited, and known methods can be used. For example, as described above, a solvent-type acrylic pressure-sensitive adhesive composition is prepared by mixing a (meth)acrylic polymer and components that are added as needed (e.g., a (meth)acrylic oligomer, a crosslinking agent, a silane coupling agent, a solvent, additives, etc.). As described above, an active energy ray-curable acrylic pressure-sensitive adhesive composition is prepared by mixing a monomer mixture or a partially polymerized product thereof and components that are added as needed (e.g., a photopolymerization initiator, a polyfunctional monomer, a (meth)acrylic oligomer, a crosslinking agent, a silane coupling agent, a solvent, additives, etc.).

[0081] The pressure-sensitive adhesive composition preferably has a viscosity suitable for handling and coating. Therefore, the active energy ray-curable acrylic pressure-sensitive adhesive composition preferably contains a partial polymer of the monomer mixture. The polymerization rate of the partial polymer is not particularly limited, but is preferably 5 to 20 wt %, more preferably 5 to 15 wt %.

[0082] The polymerization rate of the partial polymer is determined as follows. A portion of the partial polymer is sampled and used as a sample. The sample is precisely weighed to determine its weight, which is defined as the "weight of the partial polymer before drying." Next, the sample is dried at 130°C for 2 hours, and the dried sample is precisely weighed to determine its weight, which is defined as the "weight of the partial polymer after drying." The weight of the sample lost by drying at 130°C for 2 hours is then determined from the "weight of the partial polymer before drying" and the "weight of the partial polymer after drying," and this is defined as the "weight loss" (weight of volatile content, unreacted monomer). The polymerization rate (% by weight) of the partial polymer of the monomer component is determined from the obtained "weight of the partial polymer before drying" and "weight loss" using the following formula: Conversion rate (wt%) of partial polymer of monomer component = [1 - (weight loss) / (weight of partial polymer before drying)] × 100

[0083] [Adhesive sheet formation] Examples of methods for forming a pressure-sensitive adhesive sheet include a method in which a solvent-based pressure-sensitive adhesive composition is applied to a release-treated separator (release film) or the like, and the polymerization solvent and the like are dried and removed to form a pressure-sensitive adhesive sheet; a method in which a solvent-based pressure-sensitive adhesive composition is applied to a polarizing film or the like, and the polymerization solvent and the like are dried and removed to form a pressure-sensitive adhesive sheet on the polarizing film or the like; and a method in which an active energy ray-curable pressure-sensitive adhesive composition is applied to a release-treated separator or the like, and the like, and the like is irradiated with active energy rays to form a pressure-sensitive adhesive sheet. Note that, if necessary, heat drying may be performed in addition to the active energy ray irradiation. When applying the pressure-sensitive adhesive composition, a solvent other than the polymerization solvent may be newly added.

[0084] A silicone release liner is preferably used as the release-treated separator. When a pressure-sensitive adhesive composition is applied to such a liner and dried to form a pressure-sensitive adhesive sheet, a suitable method can be adopted as a method for drying the pressure-sensitive adhesive, depending on the purpose. Preferably, a method is used in which the coating film is heated and dried. For example, when preparing an acrylic pressure-sensitive adhesive using a (meth)acrylic polymer, the heat-drying temperature is preferably 40 to 200°C, more preferably 50 to 180°C, and particularly preferably 70 to 170°C. By setting the heating temperature within the above range, a pressure-sensitive adhesive sheet with excellent adhesive properties tends to be obtained.

[0085] The drying time can be appropriately selected. For example, when preparing an acrylic pressure-sensitive adhesive using a (meth)acrylic polymer, the drying time is preferably 5 seconds to 20 minutes, more preferably 5 seconds to 10 minutes, and particularly preferably 10 seconds to 5 minutes.

[0086] Various methods can be used to apply the pressure-sensitive adhesive composition, specifically, 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, extrusion coating using a die coater, etc.

[0087] The thickness of the pressure-sensitive adhesive sheet is preferably 1 to 200 μm, more preferably 5 to 150 μm, and even more preferably 10 to 100 μm. The pressure-sensitive adhesive sheet may be a single layer or may have a laminated structure. A thickness within the above range is preferable from the viewpoint of adhesion (holding resistance) as it does not hinder the winding of the flexible image display device.

[0088] The pressure-sensitive adhesive sheet of this embodiment can be produced by the following method.

[0089] First, the methods using a solvent-based pressure-sensitive adhesive composition (solvent-based methods 1 to 4) will be described. In the solvent-based method 1, a (meth)acrylic polymer obtained by copolymerizing a (meth)acrylic monomer having a long-chain alkyl group is used. Here, in the solvent-based method 1, it is preferable that the (meth)acrylic monomer having a long-chain alkyl group accounts for 40% by weight or more and 99% by weight of all monomers.

[0090] In the second solvent-based method, an isocyanate crosslinking agent is used alone as the crosslinking agent, and is added in an amount of 0.1 to 10 parts by weight per 100 parts by weight of the (meth)acrylic polymer.

[0091] In the third solvent-based method, a peroxide-based crosslinking agent and an isocyanate-based crosslinking agent are used in combination as crosslinking agents, the weight ratio of the peroxide-based crosslinking agent to the isocyanate-based crosslinking agent (peroxide-based crosslinking agent / isocyanate-based crosslinking agent) is 0.02 or more and 500 or less, and the amount of peroxide-based crosslinking agent added is 0.1 parts by weight or more per 100 parts by weight of the (meth)acrylic polymer.

[0092] In the fourth solvent-based method, in the first to third solvent-based methods, 1 part by weight or more and 70 parts by weight or less of a (meth)acrylic oligomer is further added to 100 parts by weight of the (meth)acrylic polymer, as described above.

[0093] Next, methods using an active energy ray-curable pressure-sensitive adhesive composition (first to third active energy ray-curable methods) will be described. In the first active energy ray-curable method, a mixture (monomer mixture) containing a (meth)acrylic monomer having a long-chain alkyl group as the main component and a monomer having an alkyl group or a functional group having 1 to 5 carbon atoms, or a partial polymer of the mixture, is polymerized together with a polyfunctional monomer.

[0094] In the second active energy ray curing method, in the first active energy ray curing method, the (meth)acrylic monomer having a long-chain alkyl group is a mixture (monomer mixture) of a (meth)acrylic monomer having an alkyl group having from 10 to 30 carbon atoms and a (meth)acrylic monomer having an alkyl group having from 6 to 9 carbon atoms, or a partial polymer of the mixture.

[0095] In the third active energy ray curing method, in the first active energy ray curing method, a polyfunctional (meth)acrylate is used as the polyfunctional monomer, and 0.1 to 1 part by weight of the polyfunctional (meth)acrylate is added to 100 parts by weight of the (meth)acrylic polymer.

[0096] In the first to third active energy ray-curable methods, the content of (meth)acrylic monomers having long-chain alkyl groups in all monomers is preferably 50% by weight or more, more preferably 60% by weight or more, and on the other hand, is preferably 100% by weight or less, more preferably 99% by weight or less. Furthermore, when using a mixture of a (meth)acrylic monomer having an alkyl group with 10 to 30 carbon atoms and a (meth)acrylic monomer having an alkyl group with 6 to 9 carbon atoms, the mixing ratio is preferably ((meth)acrylic monomer having an alkyl group with 10 to 30 carbon atoms):((meth)acrylic monomer having an alkyl group with 6 to 9 carbon atoms)=40:60 to 90:10.

[0097] (Embodiments of flexible image display devices and laminates) As shown in FIG. 1, a flexible image display device 100 of this embodiment includes a laminate 10 and an image display panel 3, and the laminate 10 is disposed on the viewer side of the image display panel 3.

[0098] [Laminate] The laminate 10 is a component used in the flexible image display device 100, and includes the above-described adhesive sheet 1 and substrate 2. The substrate 2 supports the adhesive sheet 1 and is in contact with the adhesive sheet 1, for example. The substrate 2 does not have to be in direct contact with the adhesive sheet 1. The laminate 10 is attached to the image display panel 3 by the adhesive sheet 1. The laminate 10 does not include, for example, a polarizing film, which will be described later.

[0099] [Base material] The substrate 2 also functions as a protective film that protects the components included in the laminate 10. In Fig. 1, the substrate 2 is located on the outermost side of the laminate 10, and therefore also functions as, for example, a window.

[0100] The substrate 2 is made of, for example, a transparent resin. Examples of the transparent resin include cycloolefin resins such as norbornene resins, olefin resins such as polyethylene and polypropylene, polyester resins, (meth)acrylic resins, and polyimide resins.

[0101] The thickness of the substrate 2 is, for example, 5 to 60 μm, preferably 10 to 40 μm, and more preferably 10 to 30 μm. If the thickness of the substrate 2 is within the above range, the substrate 2 is less likely to interfere with the winding up of the flexible image display device. The substrate 2 may be subjected to surface treatment such as anti-glare, anti-reflection, and anti-static treatment.

[0102] [Image display panel] The image display panel 3 constitutes a display unit of the flexible image display device 100. In the flexible image display device 100, the display unit constituted by the image display panel 3 is rollable. The image display panel 3 is typically an organic EL display panel. A touch sensor may be incorporated in the image display panel 3. When the image display panel 3 has a built-in touch sensor, the flexible image display device 100 is a so-called in-cell type flexible image display device.

[0103] In the flexible image display device 100, the ratio of the area of ​​the rollable display portion to the area of ​​the entire display portion formed by the image display panel 3 is, for example, 50% or more and 90% or less.

[0104] [Transparent conductive layer] The laminate 10 may further include a transparent conductive layer that constitutes a touch sensor. The transparent conductive layer may be located between the adhesive sheet 1 and the substrate 2, or may be located between the adhesive sheet 1 and the image display panel 3. The transparent conductive layer is configured to be, for example, flexible.

[0105] The material for the transparent conductive layer is not particularly limited, and may be at least one metal or metal oxide selected from the group consisting of indium, tin, zinc, gallium, antimony, titanium, silicon, zirconium, magnesium, aluminum, gold, silver, copper, palladium, tungsten, and molybdenum, or an organic conductive polymer such as polythiophene. The metal oxide may further contain a metal atom listed in the above group, as necessary. For example, indium oxide (ITO) containing tin oxide and tin oxide containing antimony are preferably used, with ITO being particularly preferred. ITO preferably contains 80 to 99% by weight of indium oxide and 1 to 20% by weight of tin oxide.

[0106] ITO can be crystalline or amorphous. Crystalline ITO can be obtained by increasing the sputtering temperature or by further heating amorphous ITO.

[0107] The thickness of the transparent conductive layer is preferably 0.005 to 10 μm, more preferably 0.01 to 3 μm, and even more preferably 0.01 to 1 μm. If the thickness of the transparent conductive layer is less than 0.005 μm, the change in the electrical resistance value of the transparent conductive layer tends to be large. On the other hand, if the thickness exceeds 10 μm, the productivity of the transparent conductive layer decreases, the cost increases, and the optical properties also tend to deteriorate.

[0108] The total light transmittance of the transparent conductive layer is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more.

[0109] The density of the transparent conductive layer is preferably 1.0 to 10.5 g / cm 3 and more preferably 1.3 to 3.0 g / cm 3 is.

[0110] The surface resistance value of the transparent conductive layer is preferably 0.1 to 1000 Ω / □, more preferably 0.5 to 500 Ω / □, and even more preferably 1 to 250 Ω / □.

[0111] The method for forming the transparent conductive layer is not particularly limited, and any conventionally known method can be used. Specific examples include vacuum deposition, sputtering, and ion plating. Furthermore, any appropriate method can be used depending on the required film thickness.

[0112] If necessary, an undercoat layer, an oligomer blocking layer, or the like may be further provided between the transparent conductive layer and the substrate 2 .

[0113] [Conductive layer (antistatic layer)] The laminate 10 may further include a conductive layer (conductive layer, antistatic layer). The laminate 10 can have a very thin thickness, and is therefore susceptible to damage from weak static electricity generated during the manufacturing process, etc. When the laminate 10 includes a conductive layer, the load caused by static electricity during the manufacturing process, etc. tends to be significantly reduced.

[0114] When a flexible image display device 100 including the laminate 10 is wound up, static electricity may be generated in the wound portion. When the laminate 10 has a conductive layer, static electricity generated by winding tends to be quickly removed.

[0115] The conductive layer may be a primer layer having a conductive function, a pressure-sensitive adhesive containing an ionic compound that is a conductive component or an antistatic agent, or a surface treatment layer containing a conductive component. The conductive layer may be formed from, for example, an antistatic composition containing a conductive polymer such as polythiophene and a binder. The laminate 10 preferably has one or more conductive layers, and may include two or more conductive layers.

[0116] [Characteristics of flexible image display devices] As described above, the adhesive sheet 1 can prevent peeling and undulation of the layers constituting the device 100, even when the flexible image display device 100 is held in a high-temperature environment while wound around an axial member and then returned to a flat state. As an example, when the adhesive sheet 1 is used for the flexible image display device 100, when the device is wound around a roller having a diameter of 20 mm in a circle defined by its side surfaces and held at 85°C for 48 hours, and then returned to a flat state, the adhesive sheet 1 prevents peeling of the members (e.g., the substrate 2) bonded by the adhesive sheet 1.

[0117] [Applications of flexible image display devices] The flexible image display device 100 of the present invention can be suitably used as an image display device such as a flexible liquid crystal display device, an organic EL (electroluminescence) display device, electronic paper, etc. The flexible image display device 100 can be used regardless of the type of touch panel, such as a resistive type or a capacitive type.

[0118] (Modifications of flexible image display device and laminate) The laminate 10 of the flexible image display device 100 may include a plurality of adhesive sheets 1 and a plurality of substrates 2, and may further include an optical film. The laminate 11 of the flexible image display device 110 shown in FIG. 2 includes a first adhesive sheet 1a and a second adhesive sheet 1b as the adhesive sheets 1. The laminate 11 includes a first substrate 2a and a second substrate 2b as the substrates 2. The laminate 11 further includes an optical film 20. Except for the above, the structure of the laminate 11 is the same as the structure of the laminate 10 of the flexible image display device 100. Therefore, elements common to the laminate 10 of the flexible image display device 100 and the laminate 11 of this embodiment are denoted by the same reference numerals, and their description may be omitted. In this specification, the laminate 11 may be referred to as an optical film with an adhesive layer.

[0119] As will be described later, the first substrate 2a is a member included in the optical film 20. The second substrate 2b is, for example, located closer to the viewer than the optical film 20 and is located on the outermost side of the laminate 11. The first substrate 2a and the second substrate 2b may be the same as or different from each other.

[0120] The first adhesive sheet 1a is located between the optical film 20 and the image display panel 3, and bonds these members together. The second adhesive sheet 1b is located between the second base material 2b and the optical film 20, and bonds these members together. The first adhesive sheet 1a and the second adhesive sheet 1b may be the same as or different from each other.

[0121] [Optical film] The optical film 20 has, for example, a first substrate 2a, a polarizing film 4, and a retardation film 5, with the polarizing film 4 located between the first substrate 2a and the retardation film 5. The first substrate 2a is located, for example, closer to the viewing side than the polarizing film 4 and functions as a protective film for the polarizing film 4. The polarizing film 4 and the retardation film 5 generate, for example, circularly polarized light to prevent light that has entered the interior of the polarizing film 4 from the viewing side from being internally reflected and emitted to the viewing side, thereby compensating for the viewing angle.

[0122] The thickness of the optical film 20 is preferably 92 μm or less, more preferably 60 μm or less, and further preferably 10 to 50 μm. Within the above range, the optical film 20 is less likely to interfere with the winding up of the flexible image display device 110.

[0123] As long as the properties required for the polarizing film 4 are maintained, the polarizing film 4 and the first substrate 2a may be bonded together with an adhesive layer (not shown). Examples of adhesives that can be used to form the adhesive layer include isocyanate-based adhesives, polyvinyl alcohol-based adhesives, gelatin-based adhesives, vinyl latex, and water-based polyesters. The adhesive is usually used as an aqueous solution and has a solids concentration of, for example, 0.5 to 60% by weight. Examples of adhesives that can be used to form the adhesive layer include ultraviolet-curable adhesives and electron beam-curable adhesives. Electron beam-curable adhesives exhibit suitable adhesive properties to the first substrate 2a. The adhesive may contain a metal compound filler.

[0124] [Polarizing film] The polarizing film 4 may be made of a polyvinyl alcohol (PVA) resin that has been stretched by a stretching process such as in-air stretching (dry stretching) or stretching in boric acid water, and in which iodine has been oriented.

[0125] A representative example of a method for producing the polarizing film 4 is a method (single-layer stretching method) described in JP 2004-341515 A, which includes a step of dyeing and a step of stretching a PVA-based resin monolayer. Other examples of a method for producing the polarizing film 4 include a method described in JP 51-069644 A, JP 2000-338329 A, JP 2001-343521 A, WO 2010 / 100917 A, JP 2012-073563 A, and JP 2011-2816 A, which includes a step of stretching and a step of dyeing a laminate of a PVA-based resin layer and a resin substrate for stretching. With this method, since the PVA-based resin layer is supported by the resin substrate for stretching, problems such as breakage due to stretching can be suppressed even if the PVA-based resin layer is thin.

[0126] Examples of manufacturing methods that include a step of stretching the laminate and a step of dyeing it include the in-air stretching (dry stretching) methods described in the aforementioned JP-A Nos. 51-069644, 2000-338329, and 2001-343521. In terms of enabling high-magnification stretching and easily improving polarization performance, manufacturing methods that include a step of stretching in a boric acid aqueous solution, as described in WO 2010 / 100917 and 2012-073563, are preferred, and the manufacturing method (two-stage stretching method) described in JP-A No. 2012-073563, in which a step of auxiliary in-air stretching is performed before stretching in a boric acid aqueous solution, is particularly preferred. A preferred production method (excess dyeing and bleaching method) is described in JP 2011-2816 A, in which a laminate of a PVA-based resin layer and a resin substrate for stretching is stretched, and then the PVA-based resin layer is excessively dyed and subsequently bleached. Examples of the polarizing film 4 include a polarizing film made of the above-mentioned iodine-oriented polyvinyl alcohol-based resin and stretched in a two-stage stretching process consisting of air-assisted stretching and stretching in boric acid water. Examples of the polarizing film 4 that can be used include a polarizing film made of the above-mentioned iodine-oriented polyvinyl alcohol-based resin and stretched by excessively dyeing a laminate of a PVA-based resin layer and a resin substrate for stretching, followed by bleaching.

[0127] The thickness of the polarizing film 4 is, for example, 20 μm or less, preferably 12 μm or less, more preferably 9 μm or less, still more preferably 1 to 8 μm, and particularly preferably 3 to 6 μm. Within the above range, the winding of the laminate 11 is hardly hindered.

[0128] [Retardation film] A film obtained by stretching a polymer film or a film obtained by aligning and fixing a liquid crystal material can be used as the retardation film 5. In this specification, the retardation film 5 has birefringence in the in-plane and / or thickness direction.

[0129] Examples of the retardation film 5 include anti-reflection retardation films (see JP 2012-133303 A,

[0221] ,

[0222] ,

[0228] ), viewing angle compensation retardation films (see JP 2012-133303 A,

[0225] ,

[0226] ), and tilted alignment retardation films for viewing angle compensation (see JP 2012-133303 A,

[0227] ).

[0130] The retardation film 5 is not particularly limited in terms of, for example, retardation value, arrangement angle, three-dimensional birefringence, whether it is a single layer or a multilayer, etc., as long as it substantially has the above-mentioned functions, and any known retardation film can be used.

[0131] The thickness of the retardation film 5 is preferably 20 μm or less, more preferably 10 μm or less, still more preferably 1 to 9 μm, and particularly preferably 3 to 8 μm. Within the above range, the winding of the laminate 11 is hardly hindered.

[0132] The retardation film 5 is a retardation film made up of, for example, two layers of a quarter wave plate and a half wave plate in which a liquid crystal material is aligned and fixed.

[0133] (Embodiment of Image Display System) As shown in FIG. 3, the image display system 500 of this embodiment includes a flexible image display device 100 (or 110) and an axis member 45. The flexible image display device 100 can be designed to be wound around the axis member 45 and retracted while being bent. When the flexible image display device 100 is retracted further than in FIG. 3, the device 100 is wound into a spiral shape. The axis member 45 is, for example, a roller. The flexible image display device 100 functions as a so-called rollable image display device.

[0134] The image display system 500 may further include a housing (not shown) that houses the shaft member 45. The housing can house, for example, the shaft member 45 as well as the flexible image display device 100 wound around the shaft member 45. The housing has, for example, an opening. When pulling out the flexible image display device 100 wound around the shaft member 45, for example, the device 100 can be pulled out of the housing through the opening of the housing.

[0135] The image display system 500 may further include a holding mechanism (not shown) that holds the flexible image display device 100 in a flat state when the device 100 wound around the shaft member 45 is pulled out. The holding mechanism may be a plate material that supports the flexible image display device 100, or a frame material that surrounds the surface of the flexible image display device 100. When the flexible image display device 100 is housed in the housing section, the holding mechanism may be configured to be housed in the housing section together with the device 100.

[0136] When the flexible image display device 100 is wound around the shaft member 45, the minimum bending radius of the flexible image display device 100 is, for example, 50 mm or less, and may be 30 mm or less, 20 mm or less, or 10 mm or less. The lower limit of the minimum bending radius is not particularly limited and is, for example, 5 mm. When the shaft member 45 is a roller, the minimum bending radius of the flexible image display device 100 corresponds to the radius r of a circle defined by the side surfaces of the roller. [Example]

[0137] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the examples shown below.

[0138] [(Meth)acrylic polymer A1] A four-neck flask equipped with a stirring blade, thermometer, nitrogen gas inlet, and condenser was charged with a monomer mixture containing 99 parts by weight of butyl acrylate (BA) and 1 part by weight of 4-hydroxybutyl acrylate (HBA). Furthermore, 0.1 parts by weight of 2,2'-azobisisobutyronitrile (AIBN) as a polymerization initiator was charged along with ethyl acetate per 100 parts by weight of the monomer mixture. Nitrogen gas was introduced with gentle stirring to replace the atmosphere. The temperature in the flask was maintained at around 55°C, and the polymerization reaction was carried out for 7 hours. Ethyl acetate was then added to the resulting reaction solution to prepare a solution of (meth)acrylic polymer A1 with a weight-average molecular weight of 1.6 million, adjusted to a solids concentration of 30%.

[0139] [(Meth)acrylic polymers A2 and A4] Solutions of (meth)acrylic polymers A2 and A4 were prepared in the same manner as for (meth)acrylic polymer A1, except that the monomers used were changed as shown in Table 1.

[0140] [(Meth)acrylic monomer syrup A3] A four-neck flask was charged with 100 parts by weight of the monomer mixture shown in Table 1, 0.4 parts by weight of the photopolymerization initiators 2,2-dimethoxy-1,2-diphenylethan-1-one (trade name "Omnirad 651", manufactured by IGM Resins BV), and 0.4 parts by weight of 1-hydroxycyclohexyl phenyl ketone (trade name "Omnirad 184", manufactured by IGM Resins BV). The mixture was then photopolymerized under a nitrogen atmosphere by irradiation with ultraviolet light until the viscosity reached approximately 15 Pa s, yielding a (meth)acrylic monomer syrup A3 containing a partial polymer of the monomer groups. The viscosity was measured using a Brookfield viscometer (Tokyo Keiki BH Viscometer No. 5 rotor) at a rotation speed of 10 rpm and a temperature of 30°C.

[0141] [(Meth)acrylic monomer syrup A5] (Meth)acrylic monomer syrup A5 was prepared in the same manner as (meth)acrylic monomer syrup A3, except that the monomers and polymerization initiators used were changed as shown in Table 1.

[0142] [(Meth)acrylic oligomer B1] A four-neck flask equipped with a stirring blade, thermometer, nitrogen gas inlet tube, and condenser was charged with 95 parts by weight of butyl acrylate (BA), 2 parts by weight of acrylic acid (AA), 3 parts by weight of methyl acrylate (MA), 0.1 parts by weight of 1-hydroxycyclohexyl phenyl ketone (trade name "Omnirad 184" manufactured by IGM Resins BV) as a polymerization initiator, 0.1 parts by weight of 2,2'-azobisisobutyronitrile, and 140 parts by weight of toluene. Nitrogen gas was introduced with gentle stirring to thoroughly replace the atmosphere with nitrogen. The temperature in the flask was maintained at around 70°C, and the polymerization reaction was carried out for 8 hours to prepare a solution of (meth)acrylic oligomer B1. The weight-average molecular weight of (meth)acrylic oligomer B1 was 4500.

[0143] [(Meth)acrylic oligomer B2] (Meth)acrylic oligomer B2 was prepared in the same manner as for (meth)acrylic oligomer B1, except that the monomers and polymerization initiators used were changed as shown in Table 1.

[0144] [Table 1]

[0145] The abbreviations in Table 1 are as follows: 2EHA: 2-ethylhexyl acrylate BA: n-butyl acrylate LA: Lauryl acrylate MA: methyl acrylate BzA: benzyl acrylate NVP: N-vinylpyrrolidone AA: acrylic acid HBA: 4-hydroxybutyl acrylate HEA: 2-hydroxyethyl acrylate DCPM: dicyclopentanyl methacrylate MMA: Methyl methacrylate Omnirad 651: Photopolymerization initiator, 2,2-dimethoxy-1,2-diphenylethan-1-one (manufactured by IGM Resins BV) Omnirad 184: Photopolymerization initiator, 1-hydroxycyclohexyl phenyl ketone (manufactured by IGM Resins BV) AIBN: Azo polymerization initiator, 2,2'-azobisisobutyronitrile (Kishida Chemical Co., Ltd.)

[0146] [Preparation of adhesive sheet] (Examples 1 to 5, Examples 7 to 8, and Comparative Example 1) A solvent-based pressure-sensitive adhesive composition was obtained by mixing a (meth)acrylic polymer, a (meth)acrylic oligomer, a crosslinking agent, and additives to obtain the composition shown in Table 2. Next, the pressure-sensitive adhesive composition obtained was applied to the surface of a PET film serving as a base film (separator), and then dried for 2 minutes in an air-circulating constant-temperature oven set at 155°C, thereby forming pressure-sensitive adhesive sheets for Examples 1 to 5, Examples 7 and 8, and Comparative Example 1. A fountain coater was used to apply the pressure-sensitive adhesive composition.

[0147] (Example 6 and Comparative Example 2) A mixture was obtained by mixing a (meth)acrylic monomer syrup, a (meth)acrylic oligomer, a crosslinking agent, and additives to obtain the composition shown in Table 2 below. Next, the mixture was applied to the surface of a PET film (thickness 38 μm) that was a base film (separator), and then another PET film was placed on top of the mixture coating, and the coating film was sandwiched between the pair of PET films. Next, an illuminance of 4 mW / cm was applied. 2 and light intensity 1200mJ / cm 2 The coating film was cured by irradiating it with ultraviolet light under the irradiation conditions of , to form an adhesive sheet (thickness: 50 μm). After the adhesive sheet was formed, the additional PET film was peeled off to expose the adhesive sheet. In this way, the adhesive sheets of Example 6 and Comparative Example 2 were formed.

[0148] [Table 2]

[0149] The abbreviations in Table 2 are as follows: D110N: Trimethylolpropane / xylylene diisocyanate adduct (manufactured by Mitsui Chemicals, product name: Takenate D110N) C / L: Trimethylolpropane / tolylene diisocyanate (manufactured by Nippon Polyurethane Industry Co., Ltd., product name: Coronate L) A-HD-N: 1,6-hexanediol diacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., product name: A-HD-N) Peroxide: Benzoyl peroxide (manufactured by NOF Corporation, trade name: Nyper BMT)

[0150] [Preparation of optical film with adhesive layer] Next, an optical film comprising a quarter-wave plate (λ / 4 plate), a half-wave plate (λ / 2 plate), a polarizing film, and a substrate (protective film) laminated in this order was bonded to the laminate (a) of the substrate film and pressure-sensitive adhesive sheet obtained in each Example and Comparative Example using the pressure-sensitive adhesive sheet to obtain a pressure-sensitive adhesive layer-attached optical film A. The pressure-sensitive adhesive layer-attached optical film A has a multilayer structure of, from the substrate film side, substrate film|pressure-sensitive adhesive sheet|λ / 4 plate|λ / 2 plate|polarizing film|protective film. The layers constituting the optical film and the optical film were prepared as follows.

[0151] (λ / 4 plate and λ / 2 plate) The retardation film, a laminate of a λ / 4 plate and a λ / 2 plate, was fabricated using a polymerizable liquid crystal material (BASF, Paliocolor LC242) that exhibits a nematic liquid crystal phase after the formation of an alignment film. Specifically, the polymerizable liquid crystal material and a photopolymerization initiator (BASF, Irgacure 907) were dissolved in toluene, and then a fluorine-based surfactant (DIC, Megafac) was added at 0.1 to 0.5 wt % depending on the liquid crystal thickness to improve coating properties, to prepare coating liquid L. The solids concentration of coating liquid L was set to 25 wt %.

[0152] Next, a retardation film manufacturing apparatus 200 shown in FIG. 4 was prepared. The manufacturing apparatus 200 included a supply reel 221 for supplying a strip-shaped PET substrate 214, pressure rollers 224 and 234, shaping rollers 230 and 240, peeling rollers 226 and 236, a conveying roller 231, dies 222, 229, 232, and 239, and ultraviolet irradiation devices 225, 227, 235, and 237 for irradiating ultraviolet light from a high-pressure mercury lamp. Next, a solution 210 of ultraviolet-curable resin was applied to one side of the PET substrate 214 unwound from the supply reel 221 using the die 222. Next, the pressure roller 224 brought the coating film into contact with the shaping roller 230, and while the two were in contact, the PET substrate 214 was conveyed along the shaping roller 230, and the ultraviolet irradiation device 225 irradiated ultraviolet light from the side of the PET substrate 214 to cure the coating film. On the conveying surface of the PET substrate 214 on the shaping roller 230, linear irregularities (extending in a direction at an angle of 75° to the MD of the PET substrate) were formed, which would form a λ / 4 plate when an alignment film of the polymerizable liquid crystal material was further formed. The curing process resulted in the formation of a cured film of UV-curable resin, the exposed surface of which had a shape corresponding to the irregularities. Next, the PET substrate 214 on which the cured film had been formed was peeled off from the shaping roller 230 by the peeling roller 226. Then, a coating liquid L was applied to the exposed surface of the cured film by a die 229, and UV light was irradiated by an ultraviolet irradiation device 227 to align and cure the coating film. In this way, a λ / 4 plate (3 μm thick) consisting of a cured film of UV-curable resin and an alignment and cured film of the polymerizable liquid crystal material was formed on the PET substrate 214.

[0153] Next, the PET substrate 214 on which the λ / 4 plate had been formed was transported by transport rollers 231, and further, the ultraviolet-curable resin solution 212 was applied to the exposed surface of the λ / 4 plate by a die 232 to form a coating film. Next, the pressure roller 234 brought the coating film into contact with the shaping roller 240, and while they were in contact, the PET substrate 214 was transported along the shaping roller 240, and ultraviolet light was irradiated from the side of the PET substrate 214 by an ultraviolet irradiation device 235 to harden the coating film. On the transport surface of the PET substrate 214 on the shaping roller 240, linear irregularities (extending in a direction at an angle of 15° to the MD direction of the PET substrate) were formed, which would form the λ / 2 plate when an alignment film of the polymerizable liquid crystal material was further formed, and the curing resulted in the formation of a cured film of the ultraviolet-curable resin having a shape corresponding to the irregularities on the exposed surface. Next, the PET substrate 214 on which the cured film was formed was peeled off from the shaping roller 240 by a peeling roller 236, and then the coating liquid L was applied to the exposed surface of the cured film by a die 239, and the coating film was aligned and cured by irradiating it with ultraviolet light by an ultraviolet irradiation device 237. In this way, a λ / 2 plate (thickness 3 μm) consisting of a cured film of an ultraviolet curable resin and an aligned and cured film of a polymerizable liquid crystal material was further formed on the λ / 4 plate of the PET substrate 214, to obtain a laminate (b).

[0154] (Laminate of polarizing film and protective film) The laminate of the polarizing film and the protective film was prepared as follows.

[0155] As a thermoplastic resin substrate, an amorphous IPA copolymerized PET film (thickness 100 μm) containing 7 mol% of isophthalic acid (IPA) units was prepared, and its surface was subjected to corona treatment (58 W / m 2 / min). Separately, PVA (degree of polymerization 4200, degree of saponification 99.2%) to which 1 wt% of acetoacetyl-modified PVA (Nippon Synthetic Chemical Industry, Gohsefimer Z200, average degree of polymerization 1200, degree of saponification 98.5 mol%, degree of acetoacetylation 5 mol%) was added was dissolved in water to obtain a PVA coating solution with a concentration of 5.5 wt%. Next, the PVA coating solution was applied to the corona-treated surface of the IPA copolymerized PET film so that the film thickness after drying would be 12 μm, and the coating film was dried for 10 minutes by hot air drying at 60 °C to obtain a laminate consisting of the substrate and the PVA layer on the substrate.

[0156] The resulting laminate was then free-end stretched (in-air auxiliary stretching) in air at 130°C at a stretch ratio of 1.8 to obtain a stretched laminate. The stretched laminate was then immersed in a boric acid insolubilizing aqueous solution at 30°C for 30 seconds to insolubilize the PVA layer. The boric acid content in the boric acid insolubilizing aqueous solution was 3 parts by weight per 100 parts by weight of water. The stretched laminate with the insolubilized PVA layer was then dyed to obtain a colored laminate. The dyeing was performed by immersing the stretched laminate in a dye solution containing iodine and potassium iodide at 30°C. During the dyeing, the PVA layer contained in the stretched laminate was dyed with iodine. The dyeing time was adjusted so that the PVA layer constituting the final polarizing film had a single transmittance of 40 to 44%. The dye solution used was an aqueous solution with an iodine concentration of 0.1 to 0.4 wt % and a potassium iodide concentration of 0.7 to 2.8 wt %. The ratio of potassium iodide concentration to iodine concentration in the dyeing solution was 7. Next, the colored laminate was immersed in a boric acid crosslinking aqueous solution at a liquid temperature of 30°C for 60 seconds to carry out a crosslinking treatment to form a crosslinked structure between PVA molecules in the iodine-adsorbed PVA layer. The contents of boric acid and potassium iodide in the boric acid crosslinking aqueous solution were both 3 parts by weight per 100 parts by weight of water.

[0157] Next, the crosslinked dyed laminate was stretched in a boric acid aqueous solution at a stretching temperature of 70°C and a stretching ratio of 3.05 (stretching in boric acid water) to obtain a stretched laminate with a final stretching ratio of 5.50. The stretching direction in the boric acid aqueous solution was the same as the stretching direction of the initial in-air auxiliary stretching. Next, the stretched laminate was removed from the boric acid aqueous solution, and the boric acid adhering to the surface of the PVA layer was washed with a potassium iodide solution (potassium iodide content: 4 parts by weight per 100 parts by weight of water). Next, the washed stretched laminate was dried with hot air at 60°C to obtain a laminate consisting of the substrate and a polarizing film (5 μm thick) formed on the substrate.

[0158] Next, a stretched film of methacrylic resin having a glutarimide ring unit (thickness: 20 μm, moisture permeability: 160 g / m) was used as a protective film. 2 ) was prepared. Next, a prepared protective film was bonded to the exposed surface of the polarizing film in the laminate prepared above, to obtain a laminate (c) consisting of a substrate and a polarizing film having a polarizing film and a protective film. A known acrylic adhesive was used to bond the polarizing film and the protective film.

[0159] Next, an optical film A with a pressure-sensitive adhesive layer was produced using the laminate (a), laminate (b), and laminate (c) produced above as follows. First, the substrate was peeled off from the laminate (c) to expose the polarizing film. Next, the exposed polarizing film and the λ / 2 plate of the laminate (b) were bonded together with a known acrylic adhesive. Next, the PET substrate 214 was peeled off from the laminate (b) to expose the λ / 4 plate. Next, the exposed λ / 4 plate and the laminate (a) were bonded together with the pressure-sensitive adhesive sheet of the laminate (a), to obtain an optical film A with a pressure-sensitive adhesive layer.

[0160] From the pressure-sensitive adhesive layer-attached optical film A prepared using the pressure-sensitive adhesive sheet of each Example and Comparative Example, a pressure-sensitive adhesive layer-attached optical film B having a multilayer structure of PET layer | pressure-sensitive adhesive sheet | λ / 4 plate | λ / 2 plate | polarizing film | protective film | pressure-sensitive adhesive sheet | polyimide (PI) layer was obtained as follows. First, the base film (separator) was peeled off from the pressure-sensitive adhesive layer-attached optical film A to expose the pressure-sensitive adhesive sheet. Next, a 125 μm-thick PET layer (corona-treated) was bonded to the exposed pressure-sensitive adhesive sheet. Next, a PI layer (50 μm thick, corona-treated) was bonded to the protective film (corona-treated), which was the exposed surface on the opposite side, using the same pressure-sensitive adhesive sheet as the pressure-sensitive adhesive sheet used between the PET layer and the λ / 4 plate, to obtain a pressure-sensitive adhesive layer-attached optical film B.

[0161] [evaluation] <Weight-average molecular weight (Mw) of (meth)acrylic polymer and acrylic oligomer> The weight average molecular weight (Mw) of the obtained (meth)acrylic polymer and acrylic oligomer was measured by GPC (gel permeation chromatography). Analytical equipment: Tosoh HLC-8120GPC Column: Tosoh G7000H XL +GMH XL +GMH XL Column size: 7.8mm diameter x 30cm each, total 90cm Column temperature: 40℃ ·Flow rate: 0.8ml / min ·Injection volume: 100μl Eluent: tetrahydrofuran Detector: Differential refractometer (RI) Standard sample: Polystyrene

[0162] <Thickness> The thickness of the adhesive sheet etc. was measured using a dial gauge (manufactured by Mitutoyo).

[0163] <Gel fraction> The evaluation of the gel fraction of the prepared adhesive sheet was carried out by the method described above. The weight of a small piece obtained by scraping a part of the adhesive sheet was about 0.2 g. For the stretched porous film of polytetrafluoroethylene, NTF1122 (average pore diameter 0.2 μm) manufactured by Nitto Denko Corporation was used.

[0164] <tanδ and storage modulus G'> The evaluation of tanδ at 85°C, the storage modulus G' at 25°C, and the storage modulus G' at 85°C of the prepared adhesive sheet was carried out by the method described above. The dynamic viscoelasticity measurement was performed using the "Advanced Rheometric Expansion System (ARES)" manufactured by Rheometric Scientific.

[0165] <Modulus> The evaluation of 100% modulus, 500% modulus, 700% modulus, and 1000% modulus of the prepared adhesive sheet was carried out by the method described above. An AG-IS manufactured by Shimadzu Corporation was used as the tensile testing machine. The winding of the adhesive sheet was carried out while peeling the adhesive sheet from the base film.

[0166] <Winding retention test> Using the optical film B with an adhesive layer as a test sample, a winding retention test was carried out. The winding retention test was carried out as follows. First, the optical film B with an adhesive layer was cut into a strip shape of 320 mm × 25 mm to prepare a test piece 15. Next, as shown in Fig. 5A, the test piece 15 was wound in the longitudinal direction by the shaft member 45. At this time, using a tape, the end portion 15a of the test piece 15 in contact with the shaft member 45 was fixed to the shaft member 45. Similarly, using a tape, the end portion 15b of the test piece 15 in contact with the surface of the test piece 15 was fixed to the test piece 15. The shaft member 45 was a roller, and the diameter R of the circle defined by its side surface was 20 mm.

[0167] Next, the test piece 15 was held in a wound state at 85°C for 48 hours. After cooling to room temperature (23°C), the test piece 15 was returned to a flat state as shown in Fig. 5B. At this time, the layers constituting the pressure-sensitive adhesive layer-attached optical film B were visually inspected for peeling and waviness.

[0168] The criteria for judgment are as follows: A: No peeling or undulations (no practical problems) B: A slight undulation occurred at the edge of the test piece (no practical problem) C: A slight undulation occurred on the entire test piece (no practical problems) D: Peeling occurred or waviness occurred over the entire test piece (problems in practical use)

[0169] [Table 3]

[0170] As can be seen from Table 3, in the optical film B (Examples 1 to 8) with an adhesive layer having an adhesive sheet with a tan δ of 0.32 or less at 85°C and a gel fraction of 75% or more, peeling and waviness were sufficiently suppressed in the roll-up holding test. [Industrial Applicability]

[0171] The pressure-sensitive adhesive sheet of the present invention can be suitably used in a flexible image display device having a rollable display section. [Explanation of symbols]

[0172] 1 adhesive sheet 2 Base material 3 Image display panel 4. Polarizing film 5 Retardation film 10,11 Laminate for flexible image display device 20 Optical Film 100,110 Flexible image display device

Claims

1. An adhesive sheet for use in a laminate in a flexible image display device having a rollable display section, the pressure-sensitive adhesive sheet is formed from a pressure-sensitive adhesive composition containing a (meth)acrylic polymer and a crosslinking agent, The loss tangent tanδ at 85°C is 0.32 or less, A pressure-sensitive adhesive sheet having a gel fraction of 75% or more.

2. The pressure-sensitive adhesive sheet according to claim 1 , wherein the tan δ is 0.11 or more.

3. The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the tan δ is 0.20 or less.

4. The pressure-sensitive adhesive sheet according to any one of claims 1 to 3, wherein the gel fraction is 90% or more.

5. The pressure-sensitive adhesive sheet according to any one of claims 1 to 4, which has a storage modulus G' at 25°C of 0.05 MPa or more.

6. 100% modulus is 0.05 N / mm 2 The pressure-sensitive adhesive sheet according to any one of claims 1 to 5, wherein

7. The pressure-sensitive adhesive sheet according to any one of claims 1 to 6, a substrate supporting the pressure-sensitive adhesive sheet; A laminate for use in a flexible image display device having a rollable display portion, comprising:

8. The laminate of claim 7 further comprising a polarizing film.

9. 9. The laminate according to claim 7 or 8, wherein when the laminate is wound around a roller having a diameter of 20 mm defined by its side surface, held at 85°C for 48 hours, and then returned to a flat state, the members bonded by the pressure-sensitive adhesive sheet do not peel off.

10. The laminate according to any one of claims 7 to 9, an image display panel; Equipped with The laminate is positioned on the viewing side of the image display panel, and the flexible image display device has a rollable display section.

Images