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

Abstract

The present invention provides an adhesive sheet capable of suppressing occurrence of peeling and undulation of layers constituting a flexible image display device having a display portion that can be wound around a shaft member, even in the case where the device is returned to a flat state after being kept in a high-temperature environment in a state where the display portion is wound around the shaft member. The adhesive sheet of the present invention has a loss tangent tan δ of 0.32 or less at 85°C and a gel fraction of 75% or more. The adhesive sheet can be used in a laminate in a flexible image display device having a display portion that can be wound around.

Description

Technical Field

[0001] The present invention relates to an adhesive sheet for a laminate in a flexible image display device, a laminate for 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 that includes, for example, an image display panel and an optical film (e.g., Patent Document 1). The bonding of the layers constituting the image display device is generally achieved using adhesive sheets.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2014-157745 Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] In developing a novel flexible image display device with a rollable display section, the inventors studied the adhesive sheet used in this device. Through their research, the inventors discovered that, for a flexible image display device with a rollable display section, when it is held in a state wound around a roller or other axial member and then restored to a flat state, the layers bonded by the adhesive sheet tend to peel off, or the layers may develop unevenness. Furthermore, the problems of peeling and unevenness tend to be particularly pronounced in high-temperature environments.

[0008] Therefore, the present invention provides an adhesive sheet for a flexible image display device having a rollable display section, which can suppress peeling and undulation of the layers constituting the device even when the device is restored to a flat state after being kept in a high-temperature environment while being wound around a shaft member.

[0009] Problem Solving Methods

[0010] This invention provides an adhesive sheet for use in a laminate within a flexible image display device having a rollable display portion.

[0011] The adhesive sheet has a loss tangent tanδ of less than 0.32 at 85°C and a gel fraction of more than 75%.

[0012] Furthermore, the present invention provides a laminate for a flexible image display device having a rollable display portion, the laminate comprising:

[0013] The aforementioned adhesive sheet, and

[0014] The substrate supporting the adhesive sheet.

[0015] Furthermore, the present invention provides a flexible image display device having a rollable display portion, comprising:

[0016] The aforementioned stacked bodies, and

[0017] Image display panel,

[0018] The aforementioned stacked body is located closer to the visible side than the aforementioned image display panel.

[0019] The effects of the invention

[0020] According to the present invention, an adhesive sheet can be provided for a flexible image display device having a rollable display section, which can suppress peeling and undulation of the layers constituting the device even when the device is restored to a flat state after being kept in a high-temperature environment while being wound around a shaft member. Attached Figure Description

[0021] Figure 1 This is a cross-sectional view of a laminated body and a flexible image display device according to one embodiment of the present invention.

[0022] Figure 2 This is a cross-sectional view of a laminated body and a flexible image display device for another embodiment of the present invention.

[0023] Figure 3 This is a schematic diagram illustrating an example of an image display system.

[0024] Figure 4 This diagram illustrates the manufacturing method of the phase retardation film.

[0025] Figure 5A This is a diagram illustrating the winding retention test.

[0026] Figure 5B This is a diagram illustrating the winding retention test. Detailed Implementation

[0027] The present invention will now be described in detail, but the present invention is not limited to the following embodiments. It can be implemented in any way without departing from the spirit of the present invention.

[0028] (Implementation method of adhesive sheet)

[0029] The adhesive sheet of this embodiment is a component of a laminate in a flexible image display device having a rollable display section. The adhesive sheet has a loss tangent tanδ of 0.32 or less at 85°C and a gel content of 75% or more.

[0030] The tanδ of the adhesive sheet at 85°C can be determined by the following method. First, prepare a test sample that can be made from the material constituting the adhesive sheet. The test sample is disc-shaped. The diameter of the bottom surface of the test sample is 8 mm and the thickness is 2 mm. The test sample can be obtained by punching a disc shape from a laminate of multiple adhesive sheets. Next, perform a dynamic viscoelasticity test on the test sample. The dynamic viscoelasticity test can be performed, for example, using the "Advanced Rheometric Expansion System (ARES)" manufactured by Rheometric Scientific. The conditions for the dynamic viscoelasticity test are as follows.

[0031] (Measurement conditions)

[0032] Frequency: 1Hz

[0033] Deformation mode: Torsion

[0034] Measurement temperature: -70℃~150℃

[0035] Heating rate: 5℃ / min

[0036] The storage modulus G' (MPa) and loss modulus G' (MPa) at 85°C were determined based on the results of dynamic viscoelasticity measurements. The ratio of loss modulus G' to storage modulus G', G' / G', can be considered as the tanδ of the adhesive sheet at 85°C.

[0037] The tanδ of the adhesive sheet at 85°C is preferably 0.30 or less, more preferably 0.28 or less, further preferably 0.25 or less, particularly preferably 0.20 or less, especially preferably 0.18 or less, and may also be 0.15 or less, or even 0.13 or less. For flexible image display devices equipped with adhesive sheets, from the viewpoint of suppressing residual marks such as creases, the tanδ of the adhesive sheet at 85°C is preferably 0.07 or more, more preferably 0.08 or more, further preferably 0.09 or more, particularly preferably 0.10 or more, and especially preferably 0.11 or more. The tanδ of the adhesive sheet at 85°C can be 0.11 to 0.32, or 0.11 to 0.20.

[0038] The gel fraction of the adhesive sheet can be evaluated, for example, by the following method. First, a portion of the adhesive sheet is scraped off to obtain a small piece. Next, the small piece is wrapped with a stretched porous membrane of polytetrafluoroethylene (PTFE) and tied with kite string, thus obtaining a test piece. Next, the total weight of the small piece of adhesive sheet, the stretched porous membrane, and the kite string is measured (weight A). It should be noted that the total weight of the stretched porous membrane and kite string used is defined as weight B. Next, the test piece is immersed in a container filled with ethyl acetate and left to stand at 23°C for 1 week. After standing, the test piece is removed from the container and dried in a desiccator set to 130°C for 2 hours, and the weight C of the test piece is measured. Based on the following formula, the gel fraction of the adhesive sheet can be calculated from weight A, weight B, and weight C.

[0039] Gel fraction (wt%) = (C - B) / (A - B) × 100

[0040] The gel fraction of the adhesive sheet is preferably 80% or more, more preferably 83% or more, further preferably 85% or more, particularly preferably 88% or more, especially preferably 90% or more, and may also be 92% or more. There is no particular upper limit to the gel fraction of the adhesive sheet; for example, it may be 99%, 97%, 95%, or 94%.

[0041] By ensuring that the tanδ of the adhesive sheet of this embodiment is 0.32 or less at 85°C and that the gel content is 75% or more, high cohesion and adhesion can be maintained even in high-temperature environments. Furthermore, the adhesive sheet of this embodiment is less prone to deformation due to stress generated when the flexible image display device is wound around a shaft member. Therefore, according to the adhesive sheet of this embodiment, even after the flexible image display device has been kept in a high-temperature environment while wound around a shaft member and then restored to a flat state, peeling and unevenness of the layers constituting the device can be suppressed.

[0042] The storage modulus G' of the adhesive sheet at 25°C is not particularly limited, but 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 adhesive sheet at 25°C is not particularly limited, but is, for example, 0.50 MPa, preferably 0.40 MPa, and more preferably 0.35 MPa. The storage modulus G' of the adhesive sheet at 25°C can be determined based on the results of the dynamic viscoelasticity measurement described above.

[0043] The storage modulus G' of the adhesive sheet at 85°C is not particularly limited, but is, for example, 0.04 MPa or more, preferably 0.05 MPa or more, more preferably 0.063 MPa or more, further preferably 0.07 MPa or more, and particularly preferably 0.1 MPa or more. The upper limit of the storage modulus G' of the adhesive sheet at 85°C is not particularly limited, but is, for example, 0.50 MPa, preferably 0.30 MPa, and more preferably 0.20 MPa. The storage modulus G' of the adhesive sheet at 85°C can be determined based on the results of the dynamic viscoelasticity measurement described above.

[0044] The 100% modulus of the adhesive sheet is, for example, 0.05 N / mm. 2 The above. The 100% modulus of an adhesive sheet refers to a characteristic expressed by dividing the initial cross-sectional area of ​​the adhesive sheet by the following stress (tensile stress), which is the stress generated in the adhesive sheet when a tensile force is applied in one direction to impart 100% elongation. The 100% modulus of the adhesive sheet can be evaluated as follows.

[0045] First, the adhesive sheet to be evaluated is cut into strips of 30mm × 40mm. Next, the cut adhesive sheet is wound along its long side without introducing air bubbles, resulting in a cylindrical test piece with a height of 30mm corresponding to the length of the short side. Then, the obtained test piece is placed on a tensile testing machine such as a universal tensile testing machine, and a uniaxial tensile test is performed on its height direction to obtain the elongation-stress curve of the adhesive sheet. It should be noted that the preparation of the test piece and the uniaxial tensile test are carried out at room temperature (23℃), with the initial chuck distance set to 10mm and the tensile speed set to 300mm / min. Based on the obtained elongation-stress curve, the stress at 100% elongation (when the chuck distance is 20mm) is calculated, and this stress is divided by the initial cross-sectional area of ​​the test piece to obtain the 100% modulus of the adhesive sheet.

[0046] The preferred 100% modulus of the adhesive sheet is 0.10 N / mm. 2 The above, and more preferably, is 0.14 N / mm 2 The above can also be 0.18 N / mm. 2 The above can also be 0.20 N / mm 2 That's all. There is no specific upper limit to the 100% modulus of the adhesive sheet, for example, 0.80 N / mm. 2 It can be 0.50 N / mm 2 It can also be 0.30 N / mm 2 .

[0047] The 500% modulus of the adhesive sheet is, for example, 0.05 N / mm. 2The above. The 500% modulus of the adhesive sheet refers to a characteristic expressed by dividing the initial cross-sectional area of ​​the adhesive sheet by the following stress (tensile stress), which is the stress generated in the adhesive sheet when a tensile force in one direction imparts a 500% elongation. The 500% modulus of the adhesive sheet can be evaluated using the method described above for the 100% modulus of the adhesive sheet.

[0048] The 500% modulus of the adhesive sheet is preferably 0.10 N / mm. 2 The above, and more preferably, is 0.20 N / mm 2 The above, and more preferably, is 0.30 N / mm 2 The above, and especially preferred, value is 0.35 N / mm. 2 The above can also be 0.60 N / mm. 2 The above can also be 1.0 N / mm 2 That's all. There is no specific upper limit to the 500% modulus of the adhesive sheet; for example, it could be 10 N / mm. 2 .

[0049] The 700% modulus of the adhesive sheet is, for example, 0.07 N / mm. 2 The above. The 700% modulus of the adhesive sheet refers to a characteristic expressed by dividing the initial cross-sectional area of ​​the adhesive sheet by the following stress (tensile stress), which is the stress generated in the adhesive sheet when a tensile force in one direction imparts an elongation of 700%. The 700% modulus of the adhesive sheet can be evaluated using the method described above for the 100% modulus of the adhesive sheet.

[0050] The 700% modulus of the adhesive sheet is preferably 0.10 N / mm. 2 The above, and more preferably, is 0.20 N / mm 2 The above, and more preferably, is 0.30 N / mm 2 The above, and especially preferred, value is 0.40 N / mm. 2 The above can also be 0.60 N / mm. 2 That's all. There is no specific upper limit to the 700% modulus of the adhesive sheet; for example, it could be 10 N / mm. 2 .

[0051] The 1000% modulus of the adhesive sheet is, for example, 0.15 N / mm. 2The above. The 1000% modulus of the adhesive sheet refers to a characteristic expressed by dividing the following stress (tensile stress) by the initial cross-sectional area of ​​the adhesive sheet: the stress generated in the adhesive sheet when a tensile force is applied in one direction to impart 1000% elongation. The 1000% modulus of the adhesive sheet can be evaluated using the method described above for the 100% modulus of the adhesive sheet.

[0052] The preferred 1000% modulus of the adhesive sheet is 0.20 N / mm. 2 The above, and more preferably, is 0.40 N / mm 2 The above, and more preferably, is 0.50 N / mm 2 The above, and especially preferred, value is 0.60 N / mm. 2 That's all. There is no specific upper limit to the 1000% modulus of the adhesive sheet; for example, it could be 10 N / mm. 2 .

[0053] The glass transition temperature (Tg) of the adhesive sheet is preferably below 5°C, more preferably below -20°C, and even more preferably below -25°C. When the Tg of the adhesive sheet is in such a range, the adhesive sheet is less prone to hardening, enabling the realization of a flexible image display device with excellent stress relaxation properties.

[0054] The total transmittance of the adhesive sheet in the visible light wavelength region (according to JIS K7136:2000) is preferably 85% or more, more preferably 90% or more.

[0055] Examples of adhesives constituting the adhesive sheet include acrylic adhesives, rubber adhesives, vinyl alkyl ether adhesives, silicone adhesives, polyester adhesives, polyamide adhesives, urethane adhesives, fluorinated adhesives, epoxy adhesives, and polyether adhesives. It should be noted that the adhesives constituting the adhesive sheet can be used alone or in combination of two or more. However, from the perspectives of transparency, processability, durability, and adhesion, it is preferable to use an acrylic adhesive (composition) containing a (meth)acrylic polymer alone. In other words, the adhesive sheet preferably contains a (meth)acrylic polymer.

[0056] [(Meth)acrylic polymers]

[0057] When using acrylic adhesives as the adhesive composition, it is preferable to include a (meth)acrylic polymer, wherein the (meth)acrylic polymer comprises (meth)acrylic monomers having linear or branched alkyl groups having 1 to 30 carbon atoms as monomer units. It should be noted that in this specification, "(meth)acrylic polymer" refers to acrylic polymers and / or methacrylic polymers, and "(meth)acrylate" refers to acrylates and / or methacrylates.

[0058] Specific examples of (meth)acrylate monomers having straight-chain or branched alkyl groups with 1 to 30 carbon atoms as the main backbone of (meth)acrylate polymers include methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, sec-butyl methacrylate, tert-butyl methacrylate, isobutyl methacrylate, n-pentyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, isohexyl methacrylate, isoheptyl methacrylate, 2-ethylhexyl methacrylate, n-octyl methacrylate, etc. The monomers used include isooctyl methacrylate, nonyl methacrylate, isononyl methacrylate, decyl methacrylate, isodecyl methacrylate, dodecyl methacrylate (lauryl methacrylate), tridecyl methacrylate, and tetradecyl methacrylate. Preferably, (meth)acrylate monomers have straight-chain or branched alkyl groups having 6 to 30 carbon atoms (hereinafter, sometimes referred to as "(meth)acrylate monomers with long-chain alkyl groups"), and more preferably, dodecyl methacrylate (lauryl methacrylate). By using (meth)acrylate monomers with long-chain alkyl groups, polymer entanglement is reduced, and deformation due to small strain is easier. From the viewpoint of low-temperature adhesion, (meth)acrylate monomers with a glass transition temperature (Tg) of -70 to -20°C are also preferred, and 2-ethylhexyl acrylate is more preferably used. One or more (meth)acrylate monomers can be used.

[0059] (Meth)acrylic acid monomers having linear or branched alkyl groups having 1 to 30 carbon atoms are the main components of all monomers constituting (meth)acrylic acid polymers. Here, "main component" means that, among all monomers constituting (meth)acrylic acid polymers, the (meth)acrylic acid monomer having linear or branched alkyl groups having 1 to 30 carbon atoms accounts for 50 to 100% by weight, more preferably 80 to 100% by weight, further preferably 90 to 99.9% by weight, and particularly preferably 94 to 99.9% by weight.

[0060] In addition to (meth)acrylic acid monomers having straight-chain or branched alkyl groups with 1 to 30 carbon atoms, the monomer components constituting (meth)acrylic acid polymers may also include copolymerizable monomers (copolymerizable monomers). It should be noted that copolymerizable monomers can be used alone or in combination of two or more.

[0061] There are no particular limitations on the copolymerizable monomer, but hydroxyl-containing monomers with reactive functional groups are preferred. By using hydroxyl-containing monomers, there is a tendency to obtain adhesive sheets with excellent adhesion. Hydroxyl-containing monomers are, for example, compounds that contain hydroxyl groups in their structure and include polymerizable unsaturated double bonds such as (meth)acryloyl groups and vinyl groups.

[0062] Specific examples of hydroxyl-containing monomers include: 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylaurate (meth)acrylate, and hydroxyalkyl (meth)acrylates, as well as methyl (4-hydroxymethylcyclohexyl)acrylate. Among hydroxyl-containing monomers, 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate are preferred from the perspectives of durability and adhesion. It should be noted that one or more hydroxyl-containing monomers may be used.

[0063] Comonomers can contain monomers with reactive functional groups, such as carboxyl-containing monomers, amino-containing monomers, and amide-containing monomers. From the viewpoint of adhesion in humidified and high-temperature environments, these monomers are preferred.

[0064] When using acrylic adhesives as the adhesive composition, the adhesive composition may contain a (meth)acrylic polymer, which comprises a carboxyl-containing monomer having a reactive functional group as the monomer unit. By using carboxyl-containing monomers, there is a tendency to obtain adhesive sheets with excellent adhesion in humidified and high-temperature environments. Carboxyl-containing monomers are compounds that contain a carboxyl group in their structure and include polymerizable unsaturated double bonds such as (meth)acryloyl groups and vinyl groups.

[0065] Specific examples of carboxyl-containing monomers include: (meth)acrylic acid, (meth)acrylic acid carboxyethyl ester, (meth)acrylic acid carboxypentyl ester, itaconic acid, maleic acid, fumaric acid, butenoic acid, etc.

[0066] When using acrylic adhesives as the adhesive composition, the adhesive composition may contain a (meth)acrylic polymer, which comprises an amino-containing monomer having a reactive functional group as the monomer unit. By using amino-containing monomers, there is a tendency to obtain adhesive sheets with excellent adhesion in humidified and high-temperature environments. Amino-containing monomers are compounds that contain an amino group in their structure and also contain polymerizable unsaturated double bonds such as (meth)acryloyl groups and vinyl groups.

[0067] Specific examples of amino-containing monomers include N,N-dimethylaminoethyl methacrylate and N,N-dimethylaminopropyl methacrylate.

[0068] When using acrylic adhesives as the adhesive composition, the adhesive composition may contain a (meth)acrylic polymer, which comprises an amide-containing monomer having a reactive functional group as the monomer unit. By using amide-containing monomers, there is a tendency to obtain adhesive sheets with excellent adhesion. Amide-containing monomers are compounds that contain an amide group in their structure, and also contain polymerizable unsaturated double bonds such as (meth)acryloyl groups and vinyl groups.

[0069] Specific examples of amide-containing monomers include (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-hydroxymethyl(meth)acrylamide, N-hydroxymethyl-N-propyl(meth)acrylamide, aminomethyl(meth)acrylamide, aminoethyl(meth)acrylamide, mercaptomethyl(meth)acrylamide, mercaptoethyl(meth)acrylamide, and other acrylamide monomers; N-(meth)acryloylmorpholine, N-(meth)acryloylpiperidine, N-(meth)acryloylpyrrolidine, and other N-acryloyl heterocyclic monomers; and N-vinylpyrrolidone, N-vinyl-ε-caprolactam, and other N-vinyl lactam monomers.

[0070] Furthermore, multifunctional monomers can be used as comonomers. If multifunctional monomers are included, cross-linking effects can be achieved through polymerization, allowing for easy adjustment of the gel fraction and improvement of cohesive strength. Therefore, cutting the adhesive sheet becomes easier, improving processability. Additionally, peeling caused by the agglomeration and breakdown of the adhesive sheet can be prevented. As a multifunctional monomer, there are no particular limitations, but examples include: hexanediol di(meth)acrylate (1,6-hexanediol di(meth)acrylate), butanediol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, trihydroxypropane tri(meth)acrylate, tetrahydroxymethane tri(meth)acrylate, allyl methacrylate, ethylene methacrylate, epoxy acrylate, polyester acrylate, urethane acrylate, and other multifunctional (meth)acrylates, divinylbenzene, etc. Among these, 1,6-hexanediol diacrylate and dipentaerythritol hexa(meth)acrylate are preferred as multifunctional (meth)acrylates. It should be noted that multifunctional monomers can be used alone or in combination of two or more.

[0071] In the monomer units constituting (meth)acrylic acid polymers, the proportion (total amount) of monomers having reactive functional groups and polyfunctional monomers is preferably 20% by weight or less, more preferably 10% by weight or less, further preferably 0.01 to 8% by weight, particularly preferably 0.01 to 5% by weight, and most preferably 0.05 to 3% by weight. If it exceeds 20% by weight, the number of crosslinking sites increases, the flexibility of the adhesive (sheet) is lost, and therefore there is a tendency for it to become lacking in stress relaxation properties.

[0072] When using acrylic adhesives as the adhesive composition, other comonomers may be introduced as monomer units, in addition to monomers with reactive functional groups and polyfunctional monomers, without impairing the effects of the present invention.

[0073] Other comonomers include, for example: alkoxyalkyl esters of (meth)acrylate [e.g., 2-methoxyethyl ester, 2-ethoxyethyl ester, methoxytriethylene glycol ester, 3-methoxypropyl ester, 3-ethoxypropyl ester, 4-methoxybutyl ester, 4-ethoxybutyl ester, etc.]; epoxy-containing monomers [e.g., glycidyl ester, methyl glycidyl ester, etc.]; sulfonic acid-containing monomers [e.g., sodium vinyl sulfonate, etc.]; phosphate-containing monomers; and monomers with... Alicyclic hydrocarbon (meth)acrylates [e.g., cyclopentyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, etc.]; (meth)acrylates with aromatic hydrocarbon groups [e.g., phenyl methacrylate, phenoxyethyl methacrylate, benzyl methacrylate, etc.]; vinyl esters [e.g., vinyl acetate, vinyl propionate, etc.]; aromatic vinyl compounds [e.g., styrene, vinyltoluene, etc.]; olefins or dienes [e.g., ethylene, propylene, butadiene, isoprene, isobutylene, etc.]; vinyl ethers [e.g., vinyl alkyl ethers, etc.]; vinyl chloride, etc.

[0074] The proportion of other comonomers is not particularly limited, but preferably 30% or less by weight, more preferably 10% or less by weight, and even more preferably not including other comonomers in all monomers constituting the (meth)acrylic polymer. When it exceeds 30% by weight, especially when using monomers other than (meth)acrylic, the number of reaction points between the adhesive sheet and other layers (films, substrates) decreases, and there is a tendency for the adhesion to decrease.

[0075] The adhesive sheet is formed from an adhesive composition, which can be of any form, such as emulsion type, solvent type (solution type), active energy ray curable type, hot-melt type, etc. Among these, solvent-based adhesive compositions and active energy ray curable adhesive compositions are preferred.

[0076] As solvent-based adhesive compositions, adhesive compositions containing (meth)acrylic polymers as essential components are preferably listed. As active energy ray-curable adhesive compositions, adhesive compositions containing mixtures (monomer mixtures) or portions thereof of monomeric components constituting (meth)acrylic polymers as essential components are preferably listed. It should be noted that "portionate polymer" refers to a composition formed by the partial polymerization of one or more monomeric components contained in a monomer mixture. The term "monomer mixture" may also refer to the case where only one monomeric component is included.

[0077] In particular, considering productivity, environmental impact, and ease of obtaining adhesive sheets of thickness, the adhesive composition is preferably an active energy ray-curable adhesive composition containing a mixture (monomer mixture) of monomer components constituting (meth)acrylic polymers or a portion thereof as an essential component.

[0078] (Meth)acrylic acid polymers can be obtained by polymerizing monomer components. More specifically, they can be obtained by polymerizing monomer components, monomer mixtures, or a portion thereof using known and conventional methods. Examples of polymerization methods include solution polymerization, emulsion polymerization, bulk polymerization, and polymerization using heat or active energy radiation (thermal polymerization, active energy radiation polymerization). Among these, solution polymerization and active energy radiation polymerization are preferred considering factors such as transparency, water resistance, and cost. It should be noted that, to suppress polymerization hindrance caused by oxygen, polymerization is preferably carried out without contact with oxygen. For example, polymerization is preferably carried out in a nitrogen atmosphere or by using a release membrane (diaphragm) to block oxygen. Furthermore, the obtained (meth)acrylic acid polymer can be any copolymer such as random copolymer, block copolymer, or graft copolymer.

[0079] Examples of active energy rays used for irradiation during photopolymerization include ionizing rays such as alpha rays, beta rays, gamma rays, neutron rays, and electron rays, as well as ultraviolet rays, with ultraviolet rays being particularly preferred. There are no particular limitations on the irradiation energy, irradiation time, or irradiation method of the active energy rays, as long as they can activate the photopolymerization initiator and cause the monomer components to react.

[0080] Various common solvents can be used in solution polymerization. Examples of such solvents include: 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. It should be noted that solvents can be used alone or in combination of two or more.

[0081] During polymerization, polymerization initiators such as photopolymerization initiators and thermal polymerization initiators can be used depending on the type of polymerization reaction. It should be noted that polymerization initiators can be used alone or in combination of two or more.

[0082] As a photopolymerization initiator, there are no particular limitations, but examples include: benzoin ether photopolymerization initiators, acetophenone photopolymerization initiators, α-ol ketone photopolymerization initiators, aromatic sulfonyl chloride photopolymerization initiators, photoactive oxime photopolymerization initiators, benzoin photopolymerization initiators, benzoyl photopolymerization initiators, ketal photopolymerization initiators, and thioxanone photopolymerization initiators.

[0083] 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-diphenylethane-1-one, and anisole methyl ether. Examples of acetophenone-based photopolymerization initiators include: 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexylphenyl ketone, 4-phenoxydichloroacetophenone, and 4-(tert-butyl)dichloroacetophenone. Examples of α-olone-based photopolymerization initiators include: 2-methyl-2-hydroxyphenylacetone and 1-[4-(2-hydroxyethyl)phenyl]-2-methylpropane-1-one. Examples of aromatic sulfonyl chloride-based photopolymerization initiators include: 2-naphthalenesulfonyl chloride. Examples of photoactive oxime photopolymerization initiators include 1-phenyl-1,1-propanedione-2-(O-ethoxycarbonyl oxime). Examples of benzoin-based photopolymerization initiators include benzoin. Examples of benzoyl-based photopolymerization initiators include benzoyl. Examples of benzophenone-based photopolymerization initiators include benzophenone, benzoylbenzoic acid, 3,3'-dimethyl-4-methoxybenzophenone, polyvinylbenzophenone, and α-hydroxycyclohexylphenyl ketone. Examples of ketal-based photopolymerization initiators include benzoyldimethyl ketal. Examples of thioxanthone-based photopolymerization initiators include thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 2,4-diisopropylthioxanthone, and dodecylthioxanthone.

[0084] The amount of photopolymerization initiator 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 monomer components.

[0085] Examples of polymerization initiators used for solution polymerization include azo polymerization initiators, peroxide polymerization initiators (e.g., benzoyl peroxide, tert-butyl maleate peroxide, etc.), and redox polymerization initiators. Among these, the azo polymerization initiators disclosed in Japanese Patent Application Publication No. 2002-69411 are preferred. Examples of the aforementioned azo polymerization initiators include 2,2'-azobisisobutyronitrile (AIBN), 2,2'-azobis-2-methylbutyronitrile, dimethyl 2,2'-azobis(2-methylpropionic acid) ester, and 4,4'-azobis-4-cyanopentanoic acid.

[0086] There is no particular limitation on the amount of azo polymerization initiator, but it 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 monomer components.

[0087] It should be noted that the multifunctional monomer (polyfunctional (meth)acrylate) used as a comonomer can also be used in solvent-based or active energy ray-cured adhesive compositions, but in the case of mixing the multifunctional monomer (polyfunctional (meth)acrylate) and photopolymerization initiator in, for example, solvent-based adhesive compositions, active energy ray curing is performed after heat drying.

[0088] The weight-average molecular weight (Mw) of (meth)acrylic polymers used in solvent-based adhesive compositions is typically in the range of 1 million to 2 million. Considering durability, particularly heat resistance, a weight-average molecular weight of 1.2 million to 2 million is preferred, and more preferably 1.4 million to 1.8 million. If the weight-average molecular weight is less than 1 million, when the polymer chains are cross-linked to ensure durability, there are more cross-linking sites compared to cases with a weight-average molecular weight of 1 million or more. This results in a loss of flexibility in the adhesive (sheet), making it difficult to relax the strain on the outer (convex) and inner (concave) sides of the bending between the layers (films) constituting the image display device during winding, sometimes leading to breakage of the layers. When the weight-average molecular weight is greater than 2.5 million, a large amount of diluent is required to adjust the viscosity suitable for coating, increasing costs and making it less desirable. Furthermore, the resulting (meth)acrylic polymer chains become more complexly intertwined, resulting in poor flexibility and sometimes making the layers (films) prone to breakage during winding. It should be noted that the weight-average molecular weight (Mw) refers to the value determined by GPC (gel permeation chromatography) and calculated using polystyrene.

[0089] (Meth)acrylic acid oligomers

[0090] (Meth)acrylic oligomers may be included in the adhesive composition. Preferably, the (meth)acrylic oligomers are polymers with a lower weight-average molecular weight (Mw) than the (meth)acrylic polymers. By using the (meth)acrylic oligomers, the (meth)acrylic oligomers are intercalated between the (meth)acrylic polymers, reducing the entanglement of the (meth)acrylic polymers and making them more susceptible to deformation by small strains.

[0091] Examples of monomers constituting (meth)acrylate oligomers include: methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, isobutyl methacrylate, sec-butyl methacrylate, tert-butyl methacrylate, amyl methacrylate, isoamyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, heptyl methacrylate, octyl methacrylate, isooctyl methacrylate, and so on. Alkyl methacrylates such as nonyl acrylate, isononyl methacrylate, decyl methacrylate, isodecyl methacrylate, undecyl methacrylate, and dodecyl methacrylate; esters formed from methacrylic acid and alicyclic alcohols such as cyclohexyl methacrylate, isobornyl methacrylate, and dicyclopentyl methacrylate; aryl methacrylates such as phenyl methacrylate and benzyl methacrylate; methacrylates obtained from terpene compound derivative alcohols; and so on. Such methacrylates can be used alone or in combination of two or more.

[0092] As (meth)acrylic acid oligomers, monomers containing acrylic acid monomers with relatively large bulk structures are preferred as monomer units. Representative examples of such acrylic acid monomers include: alkyl (meth)acrylic acid esters with branched alkyl structures, such as isobutyl (meth)acrylate and tert-butyl (meth)acrylate; esters formed from (meth)acrylic acid and alicyclic alcohols, such as cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and dicyclopentyl (meth)acrylate; and aryl (meth)acrylic acid esters with cyclic structures, such as phenyl (meth)acrylate and benzyl (meth)acrylate. By possessing such large bulk structures in (meth)acrylic acid oligomers, there is a tendency to further improve the adhesive properties of the adhesive sheet. Especially in terms of bulk size, monomers with cyclic structures are more effective, and monomers containing multiple rings are even more effective. When using ultraviolet light to synthesize (meth)acrylic oligomers and make adhesive sheets, monomers with saturated bonds are preferred from the perspective of minimizing polymerization hindrance. More preferably, alkyl esters of (meth)acrylic acid with branched alkyl structures or esters formed with alicyclic alcohols are suitable as monomers constituting (meth)acrylic oligomers.

[0093] Considering these aspects, suitable (meth)acrylic oligomers include, for example: copolymers of butyl acrylate (BA), methyl acrylate (MA), and acrylic acid (AA); copolymers of cyclohexyl methacrylate (CHMA) and isobutyl methacrylate (IBMA); copolymers of cyclohexyl methacrylate (CHMA) and isobornyl methacrylate (IBXMA); copolymers of cyclohexyl methacrylate (CHMA) and acrylamide (ACMO); copolymers of cyclohexyl methacrylate (CHMA) and diethylacrylamide (DEAA); and 1-adamantane acrylate (A... Copolymers of DA and methyl methacrylate (MMA), copolymers of dicyclopentyl methacrylate (DCPMA) and isobornyl methacrylate (IBXMA), copolymers of dicyclopentyl methacrylate (DCPMA), cyclohexyl methacrylate (CHMA), isobornyl methacrylate (IBXMA), isobornyl acrylate (IBXA), cyclopentyl methacrylate (DCPMA) and methyl methacrylate (MMA), and various homopolymers of dicyclopentyl acrylate (DCPA), 1-adamantane methacrylate (ADMA), and 1-adamantane acrylate (ADA).

[0094] As for polymerization methods for (meth)acrylic acid oligomers, similar to those for (meth)acrylic acid polymers, examples include solution polymerization, emulsion polymerization, bulk polymerization, and polymerization using heat or active energy radiation (thermal polymerization, active energy radiation polymerization). Among these, solution polymerization and active energy radiation polymerization are preferred considering factors such as transparency, water resistance, and cost. The resulting (meth)acrylic acid oligomers can be any copolymer, including random copolymers, block copolymers, and graft copolymers.

[0095] (Meth)acrylic acid oligomers, like (meth)acrylic acid polymers, can be used in solvent-based adhesive compositions and active energy radiation-cured adhesive compositions. For example, as an active energy radiation-cured adhesive composition, (meth)acrylic acid oligomers can be further mixed into a mixture (monomer mixture) of monomer components constituting a (meth)acrylic acid polymer or a portion thereof. When the (meth)acrylic acid oligomer is dissolved in a solvent, the adhesive composition can be cured by heat drying to evaporate the solvent, followed by active energy radiation curing to obtain an adhesive sheet.

[0096] The weight-average molecular weight (Mw) of the (meth)acrylic acid oligomer used in solvent-based adhesive compositions is preferably 1000 or more, more preferably 2000 or more, further preferably 3000 or more, and particularly preferably 4000 or more. The weight-average molecular weight (Mw) of the (meth)acrylic acid oligomer is preferably 30000 or less, more preferably 15000 or less, further preferably 10000 or less, and particularly preferably 7000 or less. By adjusting the weight-average molecular weight (Mw) of the (meth)acrylic acid oligomer to the above range, when used, for example, in combination with a (meth)acrylic acid polymer, the (meth)acrylic acid oligomer is positioned between the (meth)acrylic acid polymers, reducing the entanglement of the (meth)acrylic acid polymers. The adhesive sheet becomes more easily deformed by small strains, and there is a tendency to reduce the strain applied to other layers constituting the image display device. Therefore, there is a tendency to further suppress the cracking of each layer and the peeling between the adhesive sheet and other layers. It should be noted that the weight-average molecular weight (Mw) of (meth)acrylic acid oligomers, like that of (meth)acrylic acid polymers, refers to the value determined by GPC (gel permeation chromatography) and calculated using polystyrene conversion.

[0097] When using (meth)acrylic acid oligomers in the adhesive composition, the amount is not particularly limited, but is preferably 70 parts by weight or less, more preferably 1 to 70 parts by weight, further 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, relative to 100 parts by weight of the (meth)acrylic acid polymer. By adjusting the amount of (meth)acrylic acid oligomers within the above range, the (meth)acrylic acid oligomers are moderately positioned between the (meth)acrylic acid polymers, reducing the entanglement of the (meth)acrylic acid polymers and preventing the adhesive sheet from easily deforming due to small strains. This reduces the strain applied to other layers constituting the image display device, and tends to suppress cracking of individual layers and peeling between the adhesive sheet and other layers.

[0098] [Cross-linking agent]

[0099] The adhesive composition may contain a crosslinking agent. As a crosslinking agent, organic crosslinking agents and polyfunctional metal chelates can be used in any composition of solvent-based or active energy radiation-cured adhesive compositions. Examples of organic crosslinking agents include isocyanate crosslinking agents, peroxide crosslinking agents, epoxy crosslinking agents, and imine crosslinking agents. In polyfunctional metal chelates, a multivalent metal is covalently or coordinately bonded to an organic compound. Examples of multivalent 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 covalently or coordinately bonded organic compound include oxygen atoms, and examples of organic compounds include: alkyl esters, alcohol compounds, carboxylic acid compounds, ether compounds, and ketone compounds. In the case of solvent-based adhesive compositions, peroxide crosslinking agents and isocyanate crosslinking agents are preferred. Peroxide-based crosslinking agents, for example, generate free radicals by abstracting hydrogen from the side chains of (meth)acrylic acid polymers, enabling crosslinking between the side chains of the (meth)acrylic acid polymers. Therefore, compared to crosslinking using isocyanate-based crosslinking agents (e.g., polyfunctional isocyanate-based crosslinking agents), the crosslinking state is more gradual, tending to maintain flexibility to small strains and improve cohesion. This results in a tendency to suppress cracking of the layers constituting the image display device and peeling between the adhesive sheet and other layers. From a durability perspective, isocyanate-based crosslinking agents (especially trifunctional isocyanate-based crosslinking agents) are preferred. Furthermore, from a winding perspective, peroxide-based crosslinking agents and isocyanate-based crosslinking agents (especially difunctional isocyanate-based crosslinking agents) are preferred. Peroxide-based crosslinking agents and difunctional isocyanate-based crosslinking agents form soft two-dimensional crosslinks, while trifunctional isocyanate-based crosslinking agents form stronger three-dimensional crosslinks. During winding, two-dimensional crosslinking, being a softer crosslinking method, is advantageous. However, in the case of two-dimensional crosslinking alone, there is a lack of durability and easy peeling. Therefore, mixed crosslinking of two-dimensional and three-dimensional crosslinking is preferred. Therefore, it is sometimes preferable to use trifunctional isocyanate crosslinking agents and peroxide crosslinking agents, or difunctional isocyanate crosslinking agents in combination. It should be noted that, from the viewpoint of productivity and thick film coating, it is preferable to obtain the crosslinking effect by using the polymerization of multifunctional monomers as the adhesive composition. However, the above-mentioned crosslinking agents can also be used, or used in combination with multifunctional monomers. For example, the crosslinking agent can be mixed into a mixture of monomer components constituting (meth)acrylic polymers (monomer mixture) or a portion thereof, and the crosslinking agent reaction can be terminated by heat drying before and after the adhesive composition is cured by active energy rays.

[0100] The amount of crosslinking agent used is preferably 0.1 to 10 parts by weight, more preferably 0.2 to 5 parts by weight, relative to 100 parts by weight of (meth)acrylic polymer.

[0101] When using a peroxide-based crosslinking agent alone, the amount of the peroxide-based crosslinking agent is preferably 0.5 to 10 parts by weight, more preferably 1 to 5 parts by weight, relative to 100 parts by weight of the (meth)acrylic polymer. Within the above range, the adhesive sheet tends to maintain ease of deformation to small strains, and can sufficiently improve cohesion and durability.

[0102] When using isocyanate crosslinking agents alone, the amount of isocyanate crosslinking agent is preferably 0.5 to 10 parts by weight, more preferably 1 to 5 parts by weight, relative to 100 parts by weight of (meth)acrylic polymer.

[0103] When using a combination of peroxide-based and isocyanate-based crosslinking agents, 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 ranges, the adhesive sheet tends to maintain ease of deformation to small strains and can sufficiently improve cohesion.

[0104] When a multifunctional monomer (especially a multifunctional (meth)acrylate) is used as a crosslinking agent, the amount of the multifunctional monomer is preferably 0.1 to 1 part by weight, more preferably 0.2 to 0.5 parts by weight, relative to 100 parts by weight of the (meth)acrylate polymer.

[0105] [additive]

[0106] The adhesive composition may further contain other known additives, such as various silane coupling agents, polyether compounds like polyalkylene glycols such as polypropylene glycol, colorants, pigments and other powders, dyes, surfactants, plasticizers, tackifiers, surface lubricants, leveling agents, softeners, antioxidants, anti-aging agents, light stabilizers, UV absorbers, polymerization inhibitors, antistatic agents (alkali metal salts, ionic liquids, ionic solids, etc. as ionic compounds), inorganic or organic fillers, metal powders, particles, foils, etc., depending on the intended use. Redox compounds with added reducing agents may also be used within a controllable range.

[0107] There are no particular limitations on the preparation method of the adhesive composition; known methods can be used. For example, as described above, solvent-based acrylic adhesive compositions are prepared by mixing (meth)acrylic polymers with desired added components (e.g., (meth)acrylic oligomers, crosslinking agents, silane coupling agents, solvents, additives, etc.). As described above, active energy ray-curable acrylic adhesive compositions are prepared by mixing monomer mixtures or a portion thereof with desired added components (e.g., photopolymerization initiators, multifunctional monomers, (meth)acrylic oligomers, crosslinking agents, silane coupling agents, solvents, additives, etc.).

[0108] The adhesive composition preferably has a viscosity suitable for handling and application. Therefore, the active energy radiation-curable acrylic adhesive composition preferably contains a portion of the polymer from the monomer mixture. The polymerization rate of the polymer is not particularly limited, but is preferably 5–20% by weight, more preferably 5–15% by weight.

[0109] The polymerization rate of a fractional polymer can be determined as follows: A portion of the fractional polymer is sampled as a test specimen. The test specimen is accurately weighed, and its weight is recorded as the "weight of the fractional polymer before drying". Next, the test specimen is dried at 130°C for 2 hours, and the dried test specimen is accurately weighed, and its weight is recorded as the "weight of the fractional polymer after drying". Then, based on the "weight of the fractional polymer before drying" and the "weight of the fractional polymer after drying", the weight reduction of the test specimen due to drying at 130°C for 2 hours is calculated, as the "weight reduction" (weight of volatile components and unreacted monomers). Based on the obtained "weight of the fractional polymer before drying" and "weight reduction", the polymerization rate (wt%) of the monomer components of the fractional polymer is calculated using the following formula.

[0110] The polymerization rate (wt%) of the monomer component of the polymer is calculated as follows: [1 - (weight loss) / (weight of the polymer before drying)] × 100

[0111] [Formation of the adhesive sheet]

[0112] Examples of methods for forming adhesive sheets include: coating a solvent-based adhesive composition onto a release diaphragm (release film) after a release treatment, drying off the polymerizing solvent, etc., to form an adhesive sheet; coating a solvent-based adhesive composition onto a polarizing film, etc., drying off the polymerizing solvent, etc., to form an adhesive sheet on the polarizing film, etc.; and coating an active energy radiation-curable adhesive composition onto a release diaphragm, etc., and irradiating it with active energy radiation to form an adhesive layer, etc. It should be noted that, depending on the need, in addition to active energy radiation irradiation, heating drying can also be performed. When coating the adhesive composition, other solvents besides the polymerizing solvent can be added.

[0113] As the release liner, a silicone release liner is preferred. When coating the adhesive composition onto such a liner and drying it to form an adhesive sheet, a suitable method for drying the adhesive can be employed depending on the purpose. A method of heating and drying the coated film is preferred. For example, in the case of preparing an acrylic adhesive using a (meth)acrylic polymer, the heating and drying temperature is preferably 40–200°C, more preferably 50–180°C, and particularly preferably 70–170°C. By setting the heating temperature within the above range, there is a tendency to obtain an adhesive sheet with excellent adhesive properties.

[0114] The drying time can be appropriately selected. For example, in the case of preparing an acrylic adhesive using (meth)acrylic polymers, 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.

[0115] Various methods can be used as coating methods for adhesive compositions. Specifically, examples include: roller coating, licking coating, gravure coating, reverse coating, roller brush coating, spraying, dip-roll coating, bar coating, doctor blade coating, air knife coating, curtain coating, die lip coating, and extrusion coating using a die coating machine, etc.

[0116] The thickness of the adhesive sheet is preferably 1–200 μm, more preferably 5–150 μm, and even more preferably 10–100 μm. The adhesive sheet can be a single layer or have a laminated structure. Within the above range, it does not hinder the winding of the flexible image display device, and is also preferred from the viewpoint of adhesion (maintaining performance).

[0117] The following methods can be cited as methods for manufacturing the adhesive sheet of this embodiment.

[0118] First, the method for using a solvent-based adhesive composition (solvent-based methods 1 to 4) will be described. In solvent-based method 1, a (meth)acrylic polymer copolymerized from (meth)acrylic monomers having long-chain alkyl groups is used. Here, in solvent-based method 1, the (meth)acrylic monomers having long-chain alkyl groups are preferably set to 40% by weight or more and 99% by weight or less relative to all monomers.

[0119] In the solvent-based second method, isocyanate crosslinking agent is used alone as a crosslinking agent, and is added at least 0.1 parts by weight and less than 10 parts by weight relative to 100 parts by weight of (meth)acrylic polymer.

[0120] In the solvent-based third 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 set to be 0.02 or more and 500 or less, and the amount of peroxide-based crosslinking agent added is set to be 0.1 parts by weight or more relative to 100 parts by weight of the (meth)acrylic polymer.

[0121] For the fourth solvent-based method, in the first to third solvent-based methods, 1 to 70 parts by weight of (meth)acrylic acid oligomer are further added as described above, relative to 100 parts by weight of (meth)acrylic acid polymer.

[0122] Next, a method for using an active energy ray-curable adhesive composition (Active Energy Ray Curable Method 1 to Method 3) will be described. In the Active Energy Ray Curable Method 1, a mixture (monomer mixture) containing a (meth)acrylic acid monomer having a long-chain alkyl group as the main component and comprising an alkyl group having 1 or more carbon atoms or a monomer having a functional group, or a portion thereof, is polymerized together with a multifunctional monomer.

[0123] For the second method of active energy ray curing, in the first method of active energy ray curing, as a (meth)acrylic monomer having a long-chain alkyl group, a mixture (monomer mixture) of an alkyl (meth)acrylic monomer having 10 or more and 30 or less carbon atoms and an alkyl (meth)acrylic monomer having 6 or more and 9 or less carbon atoms is used.

[0124] For the third method of active energy ray curing, in the first method of active energy ray curing, a multifunctional (meth)acrylate is used as a multifunctional monomer, and is added at least 0.1 parts by weight and less than 1 part by weight relative to 100 parts by weight of (meth)acrylate polymer.

[0125] Here, in the first to third methods of active energy ray curing, it is preferable to set the content of (meth)acrylic monomers having long-chain alkyl groups in all monomers to 50% by weight or more, more preferably 60% by weight or more, and on the other hand, preferably 100% by weight or less, more preferably 99% by weight or less. Furthermore, when using a mixture of (meth)acrylic monomers having alkyl groups having 10 or more and 30 or less carbon atoms and (meth)acrylic monomers having alkyl groups having 6 or more and 9 or less carbon atoms, it is preferable to set the mixing ratio to ((meth)acrylic monomers having alkyl groups having 10 or more and 30 or less carbon atoms): ((meth)acrylic monomers having alkyl groups having 6 or more and 9 or less carbon atoms) = 40:60 to 90:10.

[0126] (Implementation of Flexible Image Display Device and Laminated Structure)

[0127] like Figure 1 As shown, the flexible image display device 100 of this embodiment includes a laminate 10 and an image display panel 3, with the laminate 10 disposed closer to the viewable side than the image display panel 3.

[0128] [Layered Body]

[0129] The laminate 10 is a component for the flexible image display device 100, and it includes the adhesive sheet 1 and the substrate 2 described above. The substrate 2 supports the adhesive sheet 1, for example, and is in contact with the adhesive sheet 1. The substrate 2 may also not be directly in contact with the adhesive sheet 1. The laminate 10 is mounted to the image display panel 3 using the adhesive sheet 1. The laminate 10, for example, does not include the polarizing film described later.

[0130] [Substrate]

[0131] The substrate 2 also functions as a protective film for the components included in the protective laminate 10. Figure 1 In this process, the substrate 2 is located on the outermost side of the laminate 10, and therefore, for example, it also functions as a window.

[0132] The substrate 2 is made of, for example, a transparent resin. Examples of transparent resins include cyclic olefin resins such as norbornene resins, olefin resins such as polyethylene and polypropylene, polyester resins, (meth)acrylic resins, and polyimide resins.

[0133] The thickness of the substrate 2 is, for example, 5–60 μm, preferably 10–40 μm, and more preferably 10–30 μm. When the thickness of the substrate 2 is within the above range, the substrate 2 does not easily hinder the winding of the flexible image display device. Surface treatments such as anti-glare, anti-reflection, and antistatic treatments can be applied to the substrate 2.

[0134] [Image Display Panel]

[0135] The image display panel 3 constitutes the display section of the flexible image display device 100. In the flexible image display device 100, the display section constituted by the image display panel 3 can be rolled up. The image display panel 3 is typically an organic EL display panel. A touch sensor can be incorporated into 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 embedded flexible image display device.

[0136] 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 composed of the image display panel 3 is, for example, 50% or more and 90% or less.

[0137] [Transparent Conductive Layer]

[0138] The laminate 10 may further include a transparent conductive layer constituting a touch sensor. The transparent conductive layer may be located between the adhesive sheet 1 and the substrate 2, or between the adhesive sheet 1 and the image display panel 3. The transparent conductive layer may be configured, for example, in a flexible manner.

[0139] The constituent material of the transparent conductive layer is not particularly limited, and can be at least one metal or metal oxide selected from indium, tin, zinc, gallium, antimony, titanium, silicon, zirconium, magnesium, aluminum, gold, silver, copper, palladium, and tungsten, or an organic conductive polymer such as polythiophene. The metal oxide may further contain the metal atoms described above as needed. For example, indium oxide (ITO) containing tin oxide, tin oxide containing antimony, etc., are preferred, and ITO is particularly preferred. ITO preferably contains 80-99% by weight of indium oxide and 1-20% by weight of tin oxide.

[0140] As for ITO, examples include crystalline ITO and amorphous (non-crystalline) ITO. Crystalline ITO can be obtained by increasing the sputtering temperature and further heating amorphous ITO.

[0141] The thickness of the transparent conductive layer is preferably 0.005–10 μm, more preferably 0.01–3 μm, and even more preferably 0.01–1 μm. When the thickness of the transparent conductive layer is less than 0.005 μm, there is a tendency for the resistance value of the transparent conductive layer to increase. On the other hand, when the thickness is greater than 10 μm, there is a tendency for the productivity of the transparent conductive layer to decrease, the cost to increase, and consequently, the optical properties to decrease.

[0142] 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.

[0143] The density of the transparent conductive layer is preferably 1.0–10.5 g / cm³. 3 More preferably, it is 1.3–3.0 g / cm³. 3.

[0144] The surface resistivity 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 / □.

[0145] There are no particular limitations on the method for forming the transparent conductive layer, and existing known methods can be used. Specifically, examples include vacuum evaporation, sputtering, and ion plating. In addition, appropriate methods can be used depending on the required film thickness.

[0146] If necessary, a primer layer, an oligomer prevention layer, etc., can be further provided between the transparent conductive layer and the substrate 2.

[0147] [Conductive layer (antistatic layer)]

[0148] The laminate 10 may further include a conductive layer (conductive layer, antistatic layer). Since the laminate 10 can be formed with a very thin structure, it is easily damaged by minor static electricity generated during manufacturing processes. When the laminate 10 has a conductive layer, there is a tendency to significantly reduce the burden caused by static electricity during manufacturing processes.

[0149] When a flexible image display device 100 including the laminate 10 is wound, static electricity may sometimes be generated in the wound portion. When the laminate 10 has a conductive layer, there is a tendency to quickly remove the static electricity generated due to winding.

[0150] The conductive layer can be a base coating with conductive properties, an adhesive containing an ionic compound as a conductive component or an antistatic agent, or a surface treatment layer containing a conductive component. For example, the conductive layer can be formed from an antistatic agent composition containing a conductive polymer such as polythiophene and an adhesive. The laminate 10 preferably has one or more conductive layers, but may also contain two or more conductive layers.

[0151] Characteristics of Flexible Image Display Devices

[0152] As described above, according to the adhesive sheet 1, even when the flexible image display device 100 is kept in a high-temperature environment while wound around a shaft member and then restored to a flat state, peeling and unevenness of the layers constituting the device 100 can be suppressed. For example, according to the adhesive sheet 1, when the flexible image display device 100 is kept at 85°C for 48 hours while wound around a roller with a diameter of 20 mm forming a circle from its sides and then restored to a flat state, the components (e.g., the substrate 2) bonded using the adhesive sheet 1 will not peel off.

[0153] Applications of flexible image display devices

[0154] The flexible image display device 100 of the present invention is suitable for use as a flexible liquid crystal display device, an organic EL (electroluminescent) display device, electronic paper, and other image display devices. The flexible image display device 100 can be used independently of resistive film methods, capacitive methods, or other similar touch panel methods.

[0155] (Examples of flexible image display devices and laminates)

[0156] The laminate 10 of the flexible image display device 100 may include multiple adhesive sheets 1 and multiple substrates 2, and may further include an optical film. Figure 2 The laminate 11 of the flexible image display device 110 shown includes a first adhesive sheet 1a and a second adhesive sheet 1b as adhesive sheet 1. The laminate 11 includes a first substrate 2a and a second substrate 2b as substrate 2. The laminate 11 further includes an optical film 20. Except as described above, the structure of the laminate 11 is the same as that of the laminate 10 of the flexible image display device 100. Therefore, reference numerals are used to denote common elements in the laminate 10 of the flexible image display device 100 and the laminate 11 of this embodiment, and their descriptions are sometimes omitted. In this specification, the laminate 11 is sometimes referred to as an optical film with an adhesive layer.

[0157] As described below, the first substrate 2a is a component contained in the optical film 20. The second substrate 2b is located, for example, closer to the visible side 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 or different from each other.

[0158] The first adhesive sheet 1a is located between the optical film 20 and the image display panel 3, bonding these components together. The second adhesive sheet 1b is located between the second substrate 2b and the optical film 20, bonding these components together. The first adhesive sheet 1a and the second adhesive sheet 1b may be the same or different from each other.

[0159] [Optical film]

[0160] The optical film 20, for example, includes 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, for example, is located closer to the visible 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, for example, generate circularly polarized light to compensate for the viewing angle. The circularly polarized light is used to prevent light incident from the visible side of the polarizing film 4 from being internally reflected and emitted back to the visible side.

[0161] The thickness of the optical film 20 is preferably 92 μm or less, more preferably 60 μm or less, and even more preferably 10 to 50 μm. Within the above range, the optical film 20 does not easily obstruct the winding of the flexible image display device 110.

[0162] As long as the required properties of the polarizing film 4 can be maintained, the polarizing film 4 and the first substrate 2a can also be bonded together by an adhesive layer (not shown). Examples of adhesives constituting the adhesive layer include isocyanate adhesives, polyvinyl alcohol adhesives, gelatin adhesives, vinyl latex adhesives, and waterborne polyesters. The adhesive is usually used in the form of an aqueous solution, for example, having a solid content concentration of 0.5 to 60% by weight. Examples of adhesives constituting the adhesive layer include UV-curable adhesives and electron beam-curable adhesives. Electron beam-curable adhesives exhibit suitable adhesion to the first substrate 2a. The adhesive may contain a metal compound filler.

[0163] [Polarizing film]

[0164] As the polarizing film 4, for example, a polyvinyl alcohol (PVA) resin can be used that is stretched and oriented by stretching processes such as stretching in a gas atmosphere (dry stretching) or stretching in a boric acid aqueous solution.

[0165] A representative method for manufacturing polarizing film 4 is the method described in Japanese Patent Application Publication No. 2004-341515, which includes a dyeing process and a stretching process for a single layer of PVA resin. Other methods for manufacturing polarizing film 4 include those described in Japanese Patent Application Publication Nos. 51-069644, 2000-338329, 2001-343521, International Publication No. 2010 / 100917, 2012-073563, and 2011-2816, which include a stretching process and a dyeing process for a laminate of a PVA resin layer and a stretching resin substrate. If this method is used, the PVA resin layer is supported by the stretching resin substrate. Therefore, even if the PVA resin layer is thin, it can suppress defects such as breakage caused by stretching.

[0166] As a manufacturing method that includes both stretching and dyeing of the laminate, examples include the gas atmosphere stretching (dry stretching) method described in Japanese Patent Application Publication Nos. 51-069644, 2000-338329, and 2001-343521. Considering the ability to perform stretching at high magnification and easily improve polarization properties, the manufacturing method described in International Publication No. 2010 / 100917 and Japanese Patent Application Publication No. 2012-073563, which includes a stretching step in a boric acid aqueous solution, is preferred. Particularly preferred is the manufacturing method described in Japanese Patent Application Publication No. 2012-073563, which involves performing an auxiliary stretching step in a gas atmosphere before stretching in the boric acid aqueous solution (two-step stretching method). The method described in Japanese Patent Application Publication No. 2011-2816, which involves stretching a laminate of a PVA-type resin layer and a stretching resin substrate, then over-dyeing the PVA-type resin layer, and finally decolorizing it (over-dyeing and decolorization method), is also preferred. Examples of polarizing film 4 include, for instance, the polarizing film obtained by stretching a polyvinyl alcohol resin oriented to iodine using a two-step stretching process consisting of assisted stretching in a gas atmosphere and stretching in a boric acid aqueous solution. As polarizing film 4, the polarizing film prepared by over-dyeing a laminate of a stretched PVA-type resin layer and a stretching resin substrate using an iodine-oriented polyvinyl alcohol resin, and then decolorizing it, can also be used.

[0167] 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, even 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.

[0168] [Phase difference film]

[0169] As the retardation film 5, a film obtained by stretching a polymer film or a film obtained by aligning and immobilizing a liquid crystal material can be used. In this specification, the retardation film 5 has birefringence in the in-plane and / or thickness direction.

[0170] Examples of phase retardation films 5 include anti-reflection phase retardation films (see Japanese Patent Application Publication No. 2012-133303

[0221] ,

[0222] ,

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

[0225] ,

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

[0227] ).

[0171] As for the phase retardation film 5, as long as it is a phase retardation film that substantially has the above-mentioned functions, there are no particular limitations on aspects such as phase difference value, configuration angle, three-dimensional birefringence, single layer or multiple layers, and known phase retardation films can be used.

[0172] The thickness of the phase retardation film 5 is preferably 20 μm or less, more preferably 10 μm or less, even more preferably 1 to 9 μm, and particularly preferably 3 to 8 μm. Within the above range, the winding of the laminate 11 is hardly hindered.

[0173] The phase retardation film 5 is, for example, a phase retardation film composed of two layers: a quarter-wave plate and a half-wave plate, obtained by aligning and immobilizing liquid crystal material.

[0174] (Implementation methods of image display systems)

[0175] like Figure 3 As shown, the image display system 500 of this embodiment includes a flexible image display device 100 (or 110) and a shaft member 45. The flexible image display device 100 can be designed to be wound around the shaft member 45 and introduced in a bent manner. Compared to Figure 3 Furthermore, by introducing the flexible image display device 100, the device 100 is wound into a spiral shape. The shaft member 45 is, for example, a roller. The flexible image display device 100 functions as a so-called wound image display device.

[0176] The image display system 500 may also include a storage section (not shown) for housing the shaft member 45. For example, the storage section can house the flexible image display device 100 wound around the shaft member 45 along with the shaft member 45. The storage section may have an opening. When the flexible image display device 100 wound around the shaft member 45 is to be removed, for example, the device 100 can be removed from the storage section through the opening.

[0177] 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 it is pulled out from the shaft member 45. The holding mechanism may be a plate supporting the flexible image display device 100 or a frame surrounding the surface of the flexible image display device 100. When the flexible image display device 100 is housed in a storage compartment, the holding mechanism may also be configured to be housed together with the device 100 in the storage compartment.

[0178] 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, 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, for example, it is 5 mm. When the shaft member 45 is a roller, the minimum bending radius of the flexible image display device 100 is equivalent to the radius r of the circle defined by the side of the roller.

[0179] Example

[0180] The present invention will now be described in more detail by way of examples, but the present invention is not limited to the examples shown below.

[0181] [(Meth)acrylic polymer A1]

[0182] A monomer mixture containing 99 parts by weight of butyl acrylate (BA) and 1 part by weight of 4-hydroxybutyl acrylate (HBA) was added to a four-necked flask equipped with a stirring blade, thermometer, nitrogen inlet tube, and condenser. Further, relative to 100 parts by weight of the monomer mixture, 0.1 parts by weight of 2,2'-azobisisobutyronitrile (AIBN) as a polymerization initiator was added together with ethyl acetate. Nitrogen purging was performed by slowly stirring and introducing nitrogen gas. The liquid temperature in the flask was then maintained at approximately 55°C, and the polymerization reaction was carried out for 7 hours. Then, ethyl acetate was added to the resulting reaction solution to prepare a solution of (meth)acrylic acid polymer A1 with a weight average molecular weight of 1.6 million and a solids concentration adjusted to 30%.

[0183] [(Meth)acrylic polymers A2 and A4]

[0184] The monomers used were changed as shown in Table 1. Otherwise, solutions of (meth)acrylic polymers A2 and A4 were prepared using the same method as (meth)acrylic polymer A1.

[0185] [(Meth)acrylic monomer slurry A3]

[0186] One hundred parts by weight of the monomer mixture shown in Table 1, 0.4 parts by weight of 2,2-dimethoxy-1,2-diphenylethane-1-one (trade name "Omnirad 651", manufactured by IGM Resins BV) as a photopolymerization initiator, and 0.4 parts by weight of 1-hydroxycyclohexylphenyl ketone (trade name "Omnirad 184", manufactured by IGM Resins BV) were added to a four-necked flask and photopolymerized under ultraviolet light in a nitrogen atmosphere until the viscosity reached approximately 15 Pa·s, thereby obtaining a (meth)acrylic acid monomer slurry A3 containing a partial polymer of the monomer group. It should be noted that the viscosity was measured using a Type B viscometer (BH viscometer No. 5 rotor manufactured by Tokyo Keiki Co., Ltd.) at a rotation speed of 10 rpm and a temperature of 30°C.

[0187] [(Meth)acrylic monomer slurry A5]

[0188] The monomers and polymerization initiators used were changed as shown in Table 1. Otherwise, (meth)acrylic monomer slurry A5 was prepared using the same method as (meth)acrylic monomer slurry A3.

[0189] [(Meth)acrylic acid oligomer B1]

[0190] In a four-necked flask equipped with a stirring blade, thermometer, nitrogen inlet tube, and condenser, 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-hydroxycyclohexylphenyl 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 were added. Nitrogen gas was introduced while the mixture was slowly stirred to ensure complete nitrogen purging. The liquid temperature in the flask was then maintained at approximately 70°C for 8 hours to prepare a solution of (meth)acrylic acid oligomer B1. The weight-average molecular weight of (meth)acrylic acid oligomer B1 was 4500.

[0191] [(Meth)acrylic acid oligomer B2]

[0192] The monomers and polymerization initiators used were changed as shown in Table 1. Otherwise, (meth)acrylic acid oligomer B2 was prepared using the same method as (meth)acrylic acid oligomer B1.

[0193]

[0194] The abbreviations in Table 1 are as follows.

[0195] 2EHA: 2-Ethylhexyl acrylate

[0196] BA: n-Butyl acrylate

[0197] LA: Lauryl acrylate

[0198] MA: Methyl acrylate

[0199] BzA: Benzyl acrylate

[0200] NVP: N-vinylpyrrolidone

[0201] AA: Acrylic acid

[0202] HBA: 4-Hydroxybutyl acrylate

[0203] HEA: 2-Hydroxyethyl acrylate

[0204] DCPM: Dicyclopentyl methacrylate

[0205] MMA: Methyl methacrylate

[0206] Omnirad 651: Photopolymerization initiator, 2,2-dimethoxy-1,2-diphenylethane-1-one (manufactured by IGM Resins B.V.)

[0207] Omnirad 184: Photopolymerization initiator, 1-hydroxycyclohexylphenyl ketone (manufactured by IGM Resins BV).

[0208] AIBN: Azo polymerization initiator, 2,2'-azobisisobutyronitrile (manufactured by KISHIDA Chemical Co., Ltd.)

[0209] [Making the Adhesive Sheet]

[0210] (Examples 1-5, Examples 7-8, and Comparative Example 1)

[0211] (Meth)acrylic acid polymers, (meth)acrylic acid oligomers, crosslinking agents, and additives were mixed according to the compositions shown in Table 2 below to obtain solvent-based adhesive compositions. Next, the obtained adhesive compositions were coated onto the surface of a PET film used as a substrate film (separator) and dried in an air-circulating constant-temperature oven set at 155°C for 2 minutes to form adhesive sheets of Examples 1-5, Examples 7-8, and Comparative Example 1. A fountain coater was used to coat the adhesive compositions.

[0212] (Example 6 and Comparative Example 2)

[0213] A mixture was obtained by mixing (meth)acrylic monomer slurry, (meth)acrylic oligomer, crosslinking agent, and additives in a manner that achieves the composition shown in Table 2 below. Next, the mixture was coated onto the surface of a PET film (38 μm thick) serving as a substrate film (separator). Then, another PET film was placed on top of the coated film, and the coated film was sandwiched between the two PET films. Next, an illuminance of 4 mW / cm² was applied. 2 and light intensity 1200mJ / cm 2 The coated film was cured by irradiation with ultraviolet light under irradiation conditions, forming an adhesive sheet (50 μm thick). After the adhesive sheet was formed, the other PET film was peeled off to expose the adhesive sheet. Thus, the adhesive sheets of Example 6 and Comparative Example 2 were formed.

[0214] [Table 2]

[0215]

[0216] The abbreviations in Table 2 are as follows.

[0217] D110N: Trimethylolpropane / phenylenediamine diisocyanate adduct (Mitsui Chemicals, trade name: Takenate D110N)

[0218] C / L: Trimethylolpropane / Toluene diisocyanate (manufactured by Nippon Polyurethane Kogyo Co., Ltd., trade name: Coronate L)

[0219] A-HD-N: 1,6-hexanediol diacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., trade name: A-HD-N)

[0220] Peroxide: Benzoyl peroxide (manufactured by Nippon Oil & Fat Co., Ltd., trade name: NYPER BMT)

[0221] Fabrication of optical films with adhesive layers

[0222] Next, for the laminate (a) of the substrate film and adhesive sheet obtained in each embodiment and comparative example, an optical film consisting of a λ / 4 waveplate, a λ / 2 waveplate, a polarizing film, and a substrate (protective film) stacked sequentially is bonded using the adhesive sheet to obtain an optical film A with an adhesive layer. The optical film A with the adhesive layer has a multilayer structure from the substrate film side: substrate film | adhesive sheet | λ / 4 waveplate | λ / 2 waveplate | polarizing film | protective film. It should be noted that the layers constituting the optical film and the optical film are prepared as described below.

[0223] (λ / 4 waveplate and λ / 2 waveplate)

[0224] The phase retardation film, which forms the laminate of λ / 4 and λ / 2 waveplates, was fabricated using a polymerizable liquid crystal material (BASF, Paliocolor LC242) that exhibits a nematic liquid crystal phase after the alignment film is formed. Specifically, as described above. The polymerizable liquid crystal material and a photopolymerization initiator (BASF, Irgacure 907) were dissolved in toluene. To improve coatability, 0.1–0.5% by weight of a fluorinated surfactant (DIC, Megafac) was further added based on the liquid crystal thickness to prepare a coating solution L. The solid content concentration of coating solution L was set to 25% by weight.

[0225] Next, preparations were made. Figure 4 The apparatus 200 shown is a phase retardation film manufacturing apparatus. The manufacturing apparatus 200 includes: a supply spool 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 transport roller 231; die heads 222, 229, 232, and 239; and ultraviolet irradiation devices 225, 227, 235, and 237 for irradiating ultraviolet light using a high-pressure mercury lamp. Next, a solution 210 of an ultraviolet-curable resin is coated onto one side of the PET substrate 214 drawn from the supply spool 221 using the die head 222. Next, the coated film is brought into contact with the shaping roller 230 by the pressure roller 224. While maintaining contact, the PET substrate 214 is transported along the shaping roller 230, and simultaneously, ultraviolet light is irradiated from the PET substrate 214 side using the ultraviolet irradiation device 225 to cure the coated film. Linear irregularities (extending at a 75° angle relative to the MD direction of the PET substrate) are formed on the transport surface of the PET substrate 214 in the shaping roller 230. These linear irregularities form λ / 4 waveplates when the alignment film of the polymeric liquid crystal material is further formed. Through the above-mentioned curing, a cured film of UV-curable resin with a shape corresponding to the irregularities is formed on the exposed surface. Next, the PET substrate 214 with the cured film is peeled off from the shaping roller 230 by the peeling roller 226, and a coating liquid L is applied to the exposed surface of the cured film by the die head 229. The coated film is then oriented and cured by UV irradiation by the UV irradiation device 227. In this way, a λ / 4 waveplate (3 μm thick) formed by the cured film of UV-curable resin and the alignment cured film of polymeric liquid crystal material is formed on the PET substrate 214.

[0226] Next, a PET substrate 214 with λ / 4 waveplates is transported by a transport roller 231, and a solution 212 of the aforementioned UV-curable resin is applied to the exposed surface of the λ / 4 waveplates by a die 232, thereby forming a coated film. Next, the coated film is brought into contact with a shaping roller 240 by a pressure roller 234, and the PET substrate 214 is transported along the shaping roller 240 while both are in contact. Simultaneously, UV light is irradiated from the PET substrate 214 side by a UV irradiation device 235, causing the coated film to cure. Linear irregularities (extending at a 15° angle relative to the MD direction of the PET substrate) are formed on the transport surface of the PET substrate 214 in the shaping roller 240. These linear irregularities form λ / 2 waveplates during the further formation of the alignment film of the aforementioned polymeric liquid crystal material. Through the curing process, a cured film of UV-curable resin with a shape corresponding to these irregularities is formed on the exposed surface. Next, the PET substrate 214 with the cured film formed is peeled off from the shaping roller 240 by the peeling roller 236, and a coating liquid L is applied to the exposed surface of the cured film by the die head 239. Ultraviolet light is then irradiated by the ultraviolet irradiation device 237 to oriented and cure the coating film. In this way, a λ / 2 waveplate (3 μm thick) is further formed on the λ / 4 waveplate of the PET substrate 214, consisting of a cured film of ultraviolet-curable resin and an oriented cured film of polymeric liquid crystal material, resulting in a laminate (b).

[0227] (Laminated structure of polarizing film and protective film)

[0228] A laminate of polarizing film and protective film was fabricated as described below.

[0229] As a thermoplastic resin substrate, an amorphous IPA copolymer PET film (100 μm thick) containing 7 mol% isophthalic acid (IPA) units was prepared, and its surface was subjected to corona treatment (58 W / m). 2 / min). Furthermore, PVA (degree of polymerization 4200, degree of saponification 99.2%) obtained by adding 1% by weight of acetylated modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., GOHSEFIMER Z200, average degree of polymerization 1200, degree of saponification 98.5 mol%, degree of acetylation 5 mol%) was dissolved in water to obtain a PVA coating solution with a concentration of 5.5% by weight. Next, the above PVA coating solution was coated onto the corona-treated surface of an IPA copolymer PET film, resulting in a film thickness of 12 μm after drying. The coated film was then dried with hot air at 60°C for 10 minutes to obtain a laminate consisting of a substrate and a PVA layer on the substrate.

[0230] Next, the obtained laminate was stretched at 130°C in air with a stretching ratio of 1.8 times (assisted stretching in a gas atmosphere) to obtain a stretched laminate. Next, the stretched laminate was immersed in a boric acid-insoluble aqueous solution at 30°C for 30 seconds, thereby insolubleting the PVA layer. The boric acid content in the boric acid-insoluble aqueous solution was set to 3 parts by weight relative to 100 parts by weight of water. Next, the stretched laminate obtained by insolubleting the PVA layer was dyed to obtain a colored laminate. Dyeing was performed by immersing the stretched laminate in a dyeing solution containing iodine and potassium iodide at 30°C. In the above dyeing, the PVA layer contained in the stretched laminate was dyed with iodine. The dyeing time was adjusted to achieve a monomer transmittance of 40-44% for the PVA layer constituting the final polarizing film. The dyeing solution used was an aqueous solution with an iodine concentration of 0.1-0.4% by weight and a potassium iodide concentration of 0.7-2.8% by weight. The ratio of potassium iodide concentration to iodine concentration in the staining solution was set to 7. Next, the stained laminate was immersed in a boric acid crosslinking aqueous solution at 30°C for 60 seconds, thereby performing a crosslinking treatment to form crosslinked structures between PVA molecules in the iodine-adsorbed PVA layer. The content of boric acid and potassium iodide in the boric acid crosslinking aqueous solution was both set to 3 parts by weight relative to 100 parts by weight of water.

[0231] Next, the cross-linked colored laminate was stretched in a boric acid aqueous solution at a stretching temperature of 70°C and a stretching ratio of 3.05 times, resulting in a stretched laminate with a final stretching ratio of 5.50 times. The stretching direction in the boric acid aqueous solution was aligned with the stretching direction of the initial assisted stretching in the gas atmosphere. 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 cleaned with a potassium iodide solution (4 parts by weight relative to 100 parts by weight of water). Next, the cleaned stretched laminate was dried with hot air at 60°C, resulting in a laminate of a substrate and a polarizing film (5 μm thick) formed on the substrate.

[0232] Next, as a protective film, a stretched film of methacrylic resin with glutarimide ring units (thickness 20 μm, moisture permeability 160 g / m²) was prepared. 2 Next, the prepared protective film is bonded to the exposed surface of the polarizing film in the above-prepared laminate, resulting in a laminate (c) of a substrate and a polarizing film having a polarizing film and a protective film. A known acrylic adhesive is used to bond the polarizing film and the protective film.

[0233] Next, using the laminates (a), (b), and (c) prepared above, an optical film A with an adhesive layer was fabricated as described below. First, the substrate was peeled off from the laminate (c) to expose the polarizing film. Next, the exposed polarizing film was bonded to the λ / 2 waveplate of the laminate (b) using a known acrylic adhesive. Next, the PET substrate 214 was peeled off from the laminate (b) to expose the λ / 4 waveplate. Next, the exposed λ / 4 waveplate was bonded to the laminate (a) using an adhesive sheet, thus obtaining the optical film A with an adhesive layer.

[0234] Optical films A with adhesive layers were prepared using adhesive sheets from the various embodiments and comparative examples. Optical films B with adhesive layers were obtained, each having a multilayer structure of PET layer | adhesive sheet | λ / 4 waveplate | λ / 2 waveplate | polarizing film | protective film | adhesive sheet | polyimide (PI) layer, as described below. First, the substrate film (septum) was peeled from the optical film A with adhesive layers, exposing the adhesive sheet. Next, a 125 μm thick PET layer (corona-treated) was bonded to the exposed adhesive sheet. Next, for the exposed surface on the opposite side, i.e., the protective film (corona-treated), a PI layer (50 μm thick, corona-treated) was bonded using the same adhesive sheet used between the PET layer and the λ / 4 waveplate, thus obtaining the optical film B with adhesive layers.

[0235] [evaluate]

[0236] <Weight-average molecular weight (Mw) of (meth)acrylic acid polymers and acrylic acid oligomers>

[0237] The weight-average molecular weight (Mw) of the obtained (meth)acrylic acid polymers and acrylic acid oligomers was determined by GPC (gel permeation chromatography).

[0238] ·Analysis device: Made by Tosoh Corporation, HLC-8120GPC

[0239] ·Pillar: Made by Tosoh Corporation, G7000H XL +GMH XL +GMH XL

[0240] • Column dimensions: Each Total 90cm

[0241] Column temperature: 40℃

[0242] • Flow rate: 0.8 ml / min

[0243] Injection volume: 100μl

[0244] • Eluent: Tetrahydrofuran

[0245] • Detector: Differential refractometer (RI)

[0246] Standard sample: polystyrene

[0247] <Thickness>

[0248] The thickness of adhesive sheets, etc., was measured using a micrometer (manufactured by MITUTOYO).

[0249] <Gel fraction>

[0250] The gel fraction of the prepared adhesive sheet was evaluated using the method described above. A small piece obtained by scraping off a portion of the adhesive sheet weighed approximately 0.2 g. The stretched porous polytetrafluoroethylene membrane used was Nitto Denko NTF1122 (average pore size 0.2 μm).

[0251] <tanδ and storage modulus G'>

[0252] The tanδ at 85°C, the storage modulus G' at 25°C, and the storage modulus G' at 85°C of the prepared adhesive sheet were evaluated using the methods described above. Dynamic viscoelasticity measurements were performed using the Advanced Rheometric Expansion System (ARES) manufactured by Rheometric Scientific.

[0253] <Modulus>

[0254] The evaluation of the 100% modulus, 500% modulus, 700% modulus, and 1000% modulus of the manufactured adhesive sheet was carried out using the method described above. A Shimadzu AG-IS tensile testing machine was used. The adhesive sheet was wound while being peeled from the substrate film.

[0255] <Winding Retention Test>

[0256] Optical film B with an adhesive layer was used as an evaluation sample, and a winding and holding test was conducted. The winding and holding test was performed as follows. First, a strip of optical film B with an adhesive layer, measuring 320 mm × 25 mm, was cut to prepare test piece 15. Next, as... Figure 5A As shown, the test piece 15 is wound along its long side using the shaft member 45. At this time, a belt is used to secure the end 15a of the test piece 15, which is in contact with the shaft member 45, to the shaft member 45. Similarly, a belt is used to secure the end 15b of the test piece 15, which is in contact with the surface of the test piece 15, to the test piece 15. The shaft member 45 is a roller, and the diameter R of the circle defined by its side is 20 mm.

[0257] Next, test piece 15 was kept wound up and maintained at 85°C for 48 hours. After cooling the test piece 15 to room temperature (23°C), as follows... Figure 5B The surface was restored to a flat state as shown. At this point, the presence or absence of peeling and unevenness in the optical film B, which constitutes the adhesive layer, was confirmed by visual inspection.

[0258] The criteria for judgment are as follows.

[0259] A: No peeling or fluctuations occurred (no practical problems).

[0260] B: Slight undulations were observed at the end of the test piece (this does not pose a practical problem).

[0261] C: The test piece exhibited slight fluctuations overall (no practical problems).

[0262] D: Peeling occurred, or unevenness was created throughout the test piece (posing practical problems).

[0263]

[0264] As shown in Table 3, the optical film B (Examples 1-8) with an adhesive layer having a tanδ of less than 0.32 at 85°C and a gel content of more than 75% achieved sufficient suppression of peeling and undulation in the winding and holding test.

[0265] Industrial applicability

[0266] The adhesive sheet of the present invention is suitable for use in flexible image display devices having a rollable display portion.

Claims

1. An adhesive sheet for use in a laminate within a flexible image display device having a rollable display portion, The adhesive sheet is formed from an adhesive composition comprising a (meth)acrylic polymer and a crosslinking agent. The monomer components constituting the (meth)acrylic polymers include: (meth)acrylic monomers comprising straight-chain or branched alkyl groups having 1 to 30 carbon atoms, and comonomers. The comonomer is selected from carboxyl-containing monomers, amino-containing monomers, and amide-containing monomers with reactive functional groups. The comonomer may be used alone or in combination of two or more. The adhesive sheet has a loss tangent tanδ of less than 0.20 at 85°C and a gel fraction of more than 75%.

2. The adhesive sheet according to claim 1, wherein, The tanδ is greater than or equal to 0.

11.

3. The adhesive sheet according to claim 1, wherein, The gel fraction is over 90%.

4. The adhesive sheet according to claim 1, wherein its storage modulus G' at 25°C is 0.05 MPa or higher.

5. The adhesive sheet according to claim 1, wherein its 100% modulus is 0.05 N / mm. 2 above.

6. A laminate for a flexible image display device having a rollable display portion, the laminate comprising: The adhesive sheet according to any one of claims 1 to 5, and The substrate supporting the adhesive sheet.

7. The laminate according to claim 6, further comprising a polarizing film.

8. The laminate according to claim 6, wherein, When the laminated body is kept in a state of being wound on a roller and kept at 85°C for 48 hours and then restored to a flat state, the components joined by the adhesive sheet do not peel off, and the diameter of the circle defined by the side of the roller is 20 mm.

9. A flexible image display device having a rollable display section, comprising: The laminate according to any one of claims 6 to 8, and Image display panel, in, The stacked body is located closer to the visible side than the image display panel.

Images