Polarizing plate and image display device

Abstract

To provide a polarizing plate that can be suitably used for bendable or foldable image display devices, and to provide an image display device.SOLUTION: A polarizing plate according to an embodiment of the present invention comprises a polarizer and a protective layer. The protective layer is provided at least on one surface of the polarizer. The protective layer has an indentation modulus of 3.0 GPa or greater.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a polarizing plate and an image display device. [Background technology]

[0002] Image display devices, such as liquid crystal display devices and electroluminescence (EL) display devices (e.g., organic EL display devices and inorganic EL display devices), are rapidly becoming popular. Image display devices typically use a polarizing plate that includes a polarizer and a protective layer (see, for example, Patent Document 1). In recent years, the applications of image display devices have become more diverse, and efforts have been made to make image display devices more flexible and bendable. However, when the polarizing plate described in Patent Document 1 is applied to a bendable or foldable image display device, the bendability of the image display device may become insufficient. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-200339 Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention has been made to solve the above-mentioned problems of the conventional art, and a main object of the present invention is to provide a polarizing plate and an image display device that can be suitably applied to a bendable or foldable image display device. [Means for solving the problem]

[0005] [1] A polarizing plate according to one embodiment of the present invention includes a polarizer and a protective layer disposed on at least one side of the polarizer, the protective layer having an indentation modulus of 3.0 GPa or more. [2] An image display device according to another aspect of the present invention includes the polarizing plate according to [1] above and a bendable image display panel, in this order. [3] In the image display device described in [2] above, the thickness ratio of the protective layer to the thickness of the image display panel may be 1-2. [Effects of the Invention]

[0006] According to the embodiments of the present invention, it is possible to realize a polarizing plate and an image display device that can be suitably applied to a bendable or foldable image display device. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic cross-sectional view of a polarizing plate according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic cross-sectional view of a polarizing plate according to another embodiment of the present invention. [Figure 3] FIG. 3 is a schematic cross-sectional view of an image display device including the polarizing plate of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0008] Representative embodiments of the present invention will be described below, but the present invention is not limited to these embodiments. In addition, in order to clarify the explanation, the width, thickness, shape, etc. of each part may be shown schematically in the drawings compared to the embodiments, but these are merely examples and do not limit the interpretation of the present invention.

[0009] (Definition of terms and symbols) The definitions of terms and symbols used in this specification are as follows. (1) Refractive index (nx, ny, nz) "nx" is the refractive index in the direction in which the in-plane refractive index is greatest (i.e., the slow axis direction), "ny" is the refractive index in the direction perpendicular to the slow axis in the plane (i.e., the fast axis direction), and "nz" is the refractive index in the thickness direction. (2) In-plane phase difference (Re) "Re(λ)" is the in-plane retardation measured with light of wavelength λ nm at 23°C. For example, "Re(550)" is the in-plane retardation measured with light of wavelength 550 nm at 23°C. Re(λ) is calculated by the formula: Re(λ)=(nx-ny)×d, where d (nm) is the thickness of the layer (film). (3) Retardation in the thickness direction (Rth) "Rth(λ)" is the retardation in the thickness direction measured with light of wavelength λ nm at 23°C. For example, "Rth(550)" is the retardation in the thickness direction measured with light of wavelength 550 nm at 23°C. Rth(λ) is calculated by the formula: Rth(λ) = (nx - nz) × d, where d (nm) is the thickness of the layer (film).

[0010] A. Overall structure of polarizing plate FIG. 1 is a schematic cross-sectional view of a polarizing plate according to one embodiment of the present invention. As shown in FIG. 1, the polarizing plate 100 includes a polarizer 2 and a protective layer 1. The protective layer 1 is disposed on at least one side of the polarizer 2. The protective layer 1 is typically flexible. The indentation modulus of the protective layer 1 is 3.0 GPa or more. The indentation modulus can be measured, for example, in accordance with JIS Z 2255. When the indentation modulus of the protective layer is 3.0 GPa or more, a polarizing plate including the protective layer and the polarizer can be provided with sufficient bending durability. Such a polarizing plate is applicable to bendable image display devices (e.g., liquid crystal display devices, organic EL display devices, inorganic EL display devices), preferably foldable image display devices, more preferably foldable organic EL display devices.

[0011] The indentation modulus of the protective layer 1 is preferably 3.10 GPa or more, more preferably 3.20 GPa or more. If the indentation modulus of the protective layer is equal to or more than this lower limit, the bending durability of the polarizing plate can be further improved. On the other hand, the indentation modulus of the protective layer 1 is, for example, 7.00 GPa or less, preferably 6.00 GPa or less, more preferably 4.00 GPa or less, and even more preferably 3.50 GPa or less. When the indentation modulus of the protective layer is equal to or less than such an upper limit, cracking of the protective layer when bent can be suppressed.

[0012] The loss tangent tanδ of the protective layer 1 at 85°C and 85% RH (relative humidity) is, for example, 15×10 -2 Below 13 x 10, preferably -2 Less than or equal to 10×10 -2 or less, more preferably 7.0 × 10 -2 On the other hand, the lower limit of the loss tangent tanδ of the protective layer 1 at 85°C and 85% RH (relative humidity) is typically 4.0 × 10 -2 is. The loss tangent tanδ of the protective layer 1 at 100°C is, for example, 15×10 -2 Below 13 x 10 -2 Less than or equal to 10×10 -2 or less, more preferably 8.0 × 10 -2 Below, particularly preferably 6.0 × 10 -2 On the other hand, the lower limit of the loss tangent tanδ of the protective layer 1 at 100°C is typically 3.0 × 10 -2 The tan δ of the protective layer is observed, for example, by measuring the dynamic viscoelasticity in a tensile mode at a measurement frequency of 5 Hz. If the tan δ of the protective layer is equal to or greater than this lower limit, stress relaxation upon bending can be achieved, and failure modes such as cracking due to residual stress, etc. can be improved. If the tan δ of the protective layer is equal to or less than this upper limit, no creases are formed even after multiple bending, and good image display can be maintained.

[0013] The thickness of the protective layer 1 is, for example, 10 μm or more, preferably 20 μm or more. If the thickness of the protective layer is at least this lower limit, excellent bending durability can be stably imparted to the polarizing plate. On the other hand, the thickness of the protective layer 1 is, for example, 130 μm or less, preferably 100 μm or less, more preferably 80 μm or less, even more preferably 47 μm or less, particularly preferably 42 μm or less, and particularly preferably 30 μm or less. If the thickness of the protective layer is at most this upper limit, excellent bending durability can be stably imparted to the polarizing plate, and the polarizing plate can be made thinner.

[0014] 2, in one embodiment, protective layers 1 are disposed on both sides of a polarizer 2. Hereinafter, the protective layer 1 disposed on one side of the polarizer 2 may be referred to as a first protective layer 1a, and the protective layer 1 disposed on the other side of the polarizer 2 may be referred to as a second protective layer 1b to distinguish them from each other.

[0015] The components of the polarizing plate will be described in detail below.

[0016] B. Polarizer Any appropriate polarizer can be adopted as the polarizer 2. For example, the resin film forming the polarizer may be composed of a single-layer resin film, or may be prepared using a laminate of two or more layers.

[0017] Specific examples of polarizers made of a single-layer resin film include hydrophilic polymer films such as polyvinyl alcohol (PVA) films, partially formalized PVA films, and partially saponified ethylene-vinyl acetate copolymer films that have been dyed with iodine or a dichroic substance such as a dichroic dye and stretched, as well as polyene-based oriented films such as dehydrated PVA films and dehydrochlorinated polyvinyl chloride films. Polarizers obtained by dyeing PVA films with iodine and uniaxially stretching them are preferred because of their excellent optical properties.

[0018] Specific examples of polarizers obtained using laminates include a laminate of a resin substrate and a PVA-based resin layer (PVA-based resin film) laminated on the resin substrate, or a polarizer obtained using a laminate of a resin substrate and a PVA-based resin layer coated on the resin substrate. A polarizer obtained using a laminate of a resin substrate and a PVA-based resin layer coated on the resin substrate can be produced, for example, by applying a PVA-based resin solution to the resin substrate and drying the resin substrate to form a PVA-based resin layer on the resin substrate, thereby obtaining a laminate of the resin substrate and the PVA-based resin layer, and then stretching and dyeing the laminate to convert the PVA-based resin layer into a polarizer. In one embodiment of the present invention, a polyvinyl alcohol-based resin layer containing a halide and a polyvinyl alcohol-based resin is preferably formed on one side of the resin substrate. Stretching typically involves immersing the laminate in an aqueous boric acid solution and stretching it. Furthermore, stretching can optionally further include in-air stretching the laminate at an elevated temperature (e.g., 95°C or higher) before stretching in the aqueous boric acid solution. Additionally, in one embodiment of the present invention, the laminate is preferably subjected to a drying shrinkage treatment in which the laminate is heated while being transported in the longitudinal direction, thereby shrinking the laminate by 2% or more in the width direction. Typically, the manufacturing method of this embodiment includes subjecting the laminate to an in-air auxiliary stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment, in this order. By introducing auxiliary stretching, it is possible to increase the crystallinity of PVA, even when PVA is coated on a thermoplastic resin, thereby achieving high optical properties. Furthermore, by simultaneously increasing the orientation of PVA in advance, problems such as a decrease in orientation or dissolution of PVA when immersed in water in the subsequent dyeing or stretching steps can be prevented, thereby achieving high optical properties. Furthermore, when the PVA-based resin layer is immersed in a liquid, the disordering of the orientation of polyvinyl alcohol molecules and the decrease in orientation can be suppressed compared to when the PVA-based resin layer does not contain a halide. This can improve the optical properties of a polarizer obtained through treatment steps in which the laminate is immersed in a liquid, such as a dyeing treatment and an underwater stretching treatment. Furthermore, the optical properties can be improved by shrinking the laminate in the width direction through drying shrinkage treatment.The obtained resin substrate / polarizer laminate may be used as is (i.e., the resin substrate may be used as a protective layer for the polarizer), or the resin substrate may be peeled off from the resin substrate / polarizer laminate and any appropriate protective layer depending on the purpose may be laminated on the peeled surface. Details of such a polarizer manufacturing method are described in, for example, JP 2012-73580 A and Japanese Patent No. 6470455 A. The entire disclosures of these publications are incorporated herein by reference.

[0019] The dyeing with iodine is carried out, for example, by immersing the PVA film in an aqueous iodine solution. The stretching ratio of the uniaxial stretching is preferably 3 to 7 times. The stretching may be carried out after the dyeing treatment or while dyeing. Alternatively, the PVA film may be stretched and then dyed. If necessary, the PVA film may be subjected to a swelling treatment, a crosslinking treatment, a washing treatment, a drying treatment, or the like. For example, by immersing the PVA film in water and washing it before dyeing, it is possible to wash away dirt and antiblocking agents on the surface of the PVA film, and also to swell the PVA film, thereby preventing uneven dyeing.

[0020] The thickness of the polarizer 2 is, for example, 1 μm to 80 μm, preferably 1 μm to 15 μm, more preferably 1 μm to 12 μm, and even more preferably 3 μm to 12 μm. When the thickness of the polarizer is within this range, curling during heating can be well suppressed and good appearance durability during heating can be obtained.

[0021] The polarizer 2 typically exhibits absorptive dichroism at any wavelength between 380 nm and 780 nm. The single transmittance of the polarizer 2 is, for example, 41.5% to 46.0%, preferably 43.0% to 46.0%, and more preferably 44.5% to 46.0%. The degree of polarization of the polarizer 2 is preferably 97.0% or more, more preferably 99.0% or more, and even more preferably 99.9% or more.

[0022] C. Protective layer The protective layer 1 is composed of a resin film containing a resin material as a main component. Specific examples of the resin material include transparent resins such as cycloolefin (COP) resins such as polynorbornene; polyester resins such as polyethylene terephthalate (PET); cellulose resins such as triacetyl cellulose (TAC); polycarbonate (PC) resins; (meth)acrylic resins; polyvinyl alcohol resins; polyamides; polyimides; polyethersulfones; polysulfones; polystyrenes; polyolefins; and acetate resins. Other examples include thermosetting or ultraviolet-curing resins such as (meth)acrylic, urethane, (meth)acrylic urethane, epoxy, and silicone resins. The term "(meth)acrylic resin" refers to acrylic resins and / or methacrylic resins. Other examples include glassy polymers such as siloxane polymers. The polymer films described in JP 2001-343529 A (WO 01 / 37007) can also be used. Examples of materials for this film include resin compositions containing a thermoplastic resin with substituted or unsubstituted imide groups in its side chains and a thermoplastic resin with substituted or unsubstituted phenyl and nitrile groups in its side chains. Examples include a resin composition containing an alternating copolymer of isobutene and N-methylmaleimide and an acrylonitrile-styrene copolymer. The polymer film can be, for example, an extrusion molded product of the above resin composition. The resin film materials can be used alone or in combination.

[0023] Of these resin materials, PC resins are preferred.

[0024] PC resins contain at least structural units derived from dihydroxy compounds having a bond structure represented by the following structural formula (1), and are produced by reacting a dihydroxy compound containing at least one dihydroxy compound having at least one -CH2-O- bond in the molecule with a carbonate diester in the presence of a polymerization catalyst. In other words, PC resins contain structural units derived from dihydroxy compounds and carbonate groups derived from carbonate diesters. [ka]

[0025] Here, the dihydroxy compound having the bond structure represented by structural formula (1) can be any compound having any structure, as long as it has two alcoholic hydroxyl groups, contains a structure having a linking group -CH-O- in the molecule, and is capable of reacting with a carbonate diester in the presence of a polymerization catalyst to produce a polycarbonate, and multiple types may be used in combination.

[0026] Furthermore, a dihydroxy compound not having the bond structure represented by the structural formula (1) may be used in combination with the dihydroxy compound used in the PC resin. Hereinafter, a dihydroxy compound having the bond structure represented by the structural formula (1) may be abbreviated as dihydroxy compound (A), and a dihydroxy compound not having the bond structure represented by the structural formula (1) may be abbreviated as dihydroxy compound (B).

[0027] (Dihydroxy compound (A)) The "linking group -CH2-O-" in the dihydroxy compound (A) means a structure in which atoms other than hydrogen atoms are bonded to form a molecule. In this linking group, the atom to which at least an oxygen atom can be bonded or the atom to which both a carbon atom and an oxygen atom can be bonded is preferably a carbon atom. The number of "linking groups -CH2-O-" in the dihydroxy compound (A) is preferably 1 or more, more preferably 2 to 4.

[0028] Specific examples of the dihydroxy compound (A) include 9,9-bis(4-(2-hydroxyethoxy)phenyl)fluorene, 9,9-bis(4-(2-hydroxyethoxy)-3-methylphenyl)fluorene, 9,9-bis(4-(2-hydroxyethoxy)-3-isopropylphenyl)fluorene, 9,9-bis(4-(2-hydroxyethoxy)-3-isobutylphenyl)fluorene, 9,9-bis(4-(2-hydroxyethoxy)-3-tert-butylphenyl)fluorene, and 9,9-bis(4-(2-hydroxyethoxy)phenyl)fluorene. a compound having an aromatic group in a side chain and an ether group bonded to the aromatic group in the main chain, such as 9,9-bis(4-(2-hydroxyethoxy)-3-phenylphenyl)fluorene, 9,9-bis(4-(2-hydroxyethoxy)-3,5-dimethylphenyl)fluorene, 9,9-bis(4-(2-hydroxyethoxy)-3-tert-butyl-6-methylphenyl)fluorene, or 9,9-bis(4-(3-hydroxy-2,2-dimethylpropoxy)phenyl)fluorene;Bis[4-(2-hydroxyethoxy)phenyl]methane, bis[4-(2-hydroxyethoxy)phenyl]diphenylmethane, 1,1-bis[4-(2-hydroxyethoxy)phenyl]ethane, 1,1-bis[4-(2-hydroxyethoxy)phenyl]-1-phenylethane, 2,2-bis[4-(2-hydroxyethoxy)phenyl]propane, 2,2-bis[4-(2-hydroxyethoxy)-3-methylphenyl]propane, 2,2-bis[3,5-dimethyl-4-(2-hydroxyethoxy)phenyl]propane 1,1-bis[4-(2-hydroxyethoxy)phenyl]propane, 1,1-bis[4-(2-hydroxyethoxy)phenyl]-3,3,5-trimethylcyclohexane, 1,1-bis[4-(2-hydroxyethoxy)phenyl]cyclohexane, 1,4-bis[4-(2-hydroxyethoxy)phenyl]cyclohexane, 1,3-bis[4-(2-hydroxyethoxy)phenyl]cyclohexane, 2,2-bis[4-(2-hydroxyethoxy)-3-phenylphenyl]propane, 2,2-bis[(2-hydroxyethoxy)-3- isopropylphenyl]propane, 2,2-bis[3-tert-butyl-4-(2-hydroxyethoxy)phenyl]propane, 2,2-bis[4-(2-hydroxyethoxy)phenyl]butane, 2,2-bis[4-(2-hydroxyethoxy)phenyl]-4-methylpentane, 2,2-bis[4-(2-hydroxyethoxy)phenyl]octane, 1,1-bis[4-(2-hydroxyethoxy)phenyl]decane, 2,2-bis[3-bromo-4-(2-hydroxyethoxy)phenyl]propane bis(hydroxyalkoxyaryl)alkanes, such as 2,2-bis[3-cyclohexyl-4-(2-hydroxyethoxy)phenyl]propane; bis(hydroxyalkoxyaryl)cycloalkanes, such as 1,1-bis[4-(2-hydroxyethoxy)phenyl]cyclohexane, 1,1-bis[3-cyclohexyl-4-(2-hydroxyethoxy)phenyl]cyclohexane, and 1,1-bis[4-(2-hydroxyethoxy)phenyl]cyclopentane;Dihydroxyalkoxy diaryl ethers, such as 4,4'-bis(2-hydroxyethoxy)diphenyl ether and 4,4'-bis(2-hydroxyethoxy)-3,3'-dimethyldiphenyl ether; bishydroxyalkoxy aryl sulfides, such as 4,4'-bis(2-hydroxyethoxyphenyl) sulfide and 4,4'-bis[4-(2-dihydroxyethoxy)-3-methylphenyl] sulfide; bishydroxyalkoxy aryl sulfoxides, such as 4,4'-bis(2-hydroxyethoxyphenyl) sulfoxide and 4,4'-bis[4-(2-dihydroxyethoxy)-3-methylphenyl] sulfoxide; 4,4'-bis(2-hydroxyethoxyphenyl) sulfone, 4,4'-bis[4-(2- Examples of the dihydroxy compound (A) include bishydroxyalkoxyarylsulfones, such as 1,4-bishydroxyethoxybenzene; bishydroxyalkoxybenzenes, such as 1,4-bishydroxyethoxybenzene; 1,3-bis[2-[4-(2-hydroxyethoxy)phenyl]propyl]benzene; 1,4-bis[2-[4-(2-hydroxyethoxy)phenyl]propyl]benzene; 4,4'-bis(2-hydroxyethoxy)biphenyl; 1,3-bis[4-(2-hydroxyethoxy)phenyl]-5,7-dimethyladamantane; anhydrosugar alcohols, such as the dihydroxy compound represented by the following formula (2); and compounds having a cyclic ether structure, such as the spiroglycol represented by the following general formula (3). The dihydroxy compound (A) may be used alone or in combination.

[0029] [ka]

[0030] [ka]

[0031] Of these dihydroxy compounds (A), preferred is the dihydroxy compound represented by the above formula (2). Examples of the dihydroxy compound represented by the above formula (2) include isosorbide, isomannide, and isoidet, which are stereoisomers, and these may be used alone or in combination of two or more. Among the dihydroxy compounds (A), isosorbide, which is obtained by dehydration condensation of sorbitol produced from various starches that are abundant and easily available as resources, is most preferred in terms of availability, ease of production, optical properties, and moldability.

[0032] The proportion of the structural units derived from the dihydroxy compound (A) relative to all structural units derived from dihydroxy compounds contained in the PC resin is, for example, 10 mol% or more, preferably 40 mol% or more, and more preferably 60 mol% or more. On the other hand, the proportion of the structural units derived from the dihydroxy compound (A) is, for example, 100 mol% or less, preferably 90 mol% or less, more preferably 80 mol% or less, and even more preferably 70 mol% or less. When the proportion of the dihydroxy compound (A) is within the above range, the indentation modulus of the protective layer can be stably adjusted to be within the above range.

[0033] (Dihydroxy compound (B)) As the dihydroxy compound that forms the structural unit of the PC resin, dihydroxy compound (A) and dihydroxy compound (B) can be used together. By using dihydroxy compounds (A) and (B) in combination, the indentation modulus of the protective layer can be more stably adjusted to fall within the above range.

[0034] The dihydroxy compound (B) is typically a dihydroxy compound other than the dihydroxy compound (A). Examples of the dihydroxy compound (B) include alicyclic dihydroxy compounds, aliphatic dihydroxy compounds, oxyalkylene glycols, aromatic dihydroxy compounds, and diols having a cyclic ether structure. The dihydroxy compounds (B) may be used alone or in combination. Of the dihydroxy compounds (B), preferred are alicyclic dihydroxy compounds.

[0035] The alicyclic dihydroxy compound is not particularly limited, but preferably includes a compound having a five-membered ring structure or a six-membered ring structure. The six-membered ring structure may be fixed in a chair or boat shape by a covalent bond. The five-membered or six-membered ring structure of the alicyclic dihydroxy compound can improve the heat resistance of the resulting PC resin. The number of carbon atoms contained in the alicyclic dihydroxy compound is, for example, 70 or less, preferably 50 or less, and more preferably 30 or less.

[0036] Specific examples of the alicyclic dihydroxy compound containing a 5-membered ring structure or a 6-membered ring structure include alicyclic dihydroxy compounds represented by the following general formula (I) or (II). HOCH2-R 1 -CH2OH (I) HO-R 2 -OH (II) (In formulas (I) and (II), R 1 and R 2 Each of the represents a cycloalkylene group having 4 to 20 carbon atoms.

[0037] Cyclohexanedimethanol, which is an alicyclic dihydroxy compound represented by the general formula (I), is a compound represented by the general formula (I) in which R 1 is represented by the following general formula (Ia) (wherein R 3 represents an alkyl group having 1 to 12 carbon atoms or a hydrogen atom. Specific examples of such isomers include 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, and 1,4-cyclohexanedimethanol.

[0038] [ka]

[0039] The alicyclic dihydroxy compound represented by the general formula (I), tricyclodecane dimethanol or pentacyclopentadecanedimethanol, is a compound represented by the general formula (I), 1 is represented by the following general formula (Ib) (wherein n is 0 or 1):

[0040] [ka]

[0041] Decalin dimethanol or tricyclotetradecane dimethanol, which is an alicyclic dihydroxy compound represented by the above general formula (I), is a compound represented by the general formula (I) in which R 1 is represented by the following general formula (Ic) (wherein m is 0 or 1). Specific examples of such isomers include 2,6-decalindimethanol, 1,5-decalindimethanol, and 2,3-decalindimethanol.

[0042] [ka]

[0043] Norbornane dimethanol, which is an alicyclic dihydroxy compound represented by the above general formula (I), is a compound represented by the general formula (I) in which R 1 The isomers include various isomers represented by the following general formula (Id): Specific examples of such isomers include 2,3-norbornane dimethanol and 2,5-norbornane dimethanol.

[0044] [ka]

[0045] Adamantane dimethanol, which is an alicyclic dihydroxy compound represented by general formula (I), is 1The general formula (Ie) includes various isomers represented by the following general formula (Ie): Specific example of such isomer is 1,3-adamantanedimethanol.

[0046] [ka]

[0047] The cyclohexanediol, which is an alicyclic dihydroxy compound represented by the general formula (II), is a compound represented by the general formula (II) in which R 2 is represented by the following general formula (IIa) (wherein R 3 represents an alkyl group having 1 to 12 carbon atoms or a hydrogen atom. Specific examples of such isomers include 1,2-cyclohexanediol, 1,3-cyclohexanediol, 1,4-cyclohexanediol, and 2-methyl-1,4-cyclohexanediol.

[0048] [ka]

[0049] The alicyclic dihydroxy compound represented by the general formula (II), tricyclodecanediol or pentacyclopentadecanediol, is a compound represented by the general formula (II), 2 includes various isomers represented by the following general formula (IIb) (wherein n is 0 or 1).

[0050] [ka]

[0051] Decalindiol or tricyclotetradecanediol, which is an alicyclic dihydroxy compound represented by the above general formula (II), is a compound represented by the general formula (II) in which R 2is represented by the following general formula (IIc) (wherein m represents 0 or 1). Specific examples of such isomers include 2,6-decalindiol, 1,5-decalindiol, and 2,3-decalindiol.

[0052] [ka]

[0053] Norbornanediol, which is an alicyclic dihydroxy compound represented by the above general formula (II), is 2 The isomers include various isomers represented by the following general formula (IId): Specific examples of such isomers include 2,3-norbornanediol and 2,5-norbornanediol.

[0054] [ka]

[0055] Adamantanediol, which is an alicyclic dihydroxy compound represented by the general formula (II), is a compound represented by the general formula (II) in which R 2 These include various isomers represented by the following general formula (IIe): Specific examples of such isomers include 1,3-adamantanediol.

[0056] [ka]

[0057] Among the specific examples of the alicyclic dihydroxy compound described above, preferred are cyclohexanedimethanols, tricyclodecane dimethanols, adamantanediols, and pentacyclopentadecanedimethanols. From the viewpoints of availability and ease of handling, more preferred are 1,4-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,2-cyclohexanedimethanol, and tricyclodecane dimethanol, and even more preferred is tricyclodecane dimethanol.

[0058] The proportion of the structural units derived from the dihydroxy compound (B) relative to all structural units derived from dihydroxy compounds contained in the PC resin is, for example, 0 mol% or more, preferably 10 mol% or more, more preferably 20 mol% or more, and even more preferably 30 mol% or more. On the other hand, the proportion of the structural units derived from the dihydroxy compound (B) is, for example, 90 mol% or less, preferably 60 mol% or less, and more preferably 40 mol% or less.

[0059] Details of these PC resins are described, for example, in JP 2012-31370 A (Patent No. 5448264), the disclosure of which is incorporated herein by reference.

[0060] In one embodiment, the PC resin contains a structural unit derived from the dihydroxy compound (A) represented by the above formula (2), a structural unit derived from the alicyclic dihydroxy compound (B) represented by the above general formula (I), and a carbonate group linking them. When a PC resin containing these structural units is used in a resin film, the indentation modulus of the protective layer can be more stably adjusted to fall within the above range. In such a PC resin, the molar ratio (A:B) of the structural units derived from the dihydroxy compound (A) represented by the above formula (2) to the structural units derived from the alicyclic dihydroxy compound (B) represented by the above general formula (I) is, for example, 5:5 to 9:1, and preferably 6:4 to 8:2. In such a PC resin, the combination of the dihydroxy compound (A) represented by the above formula (2) and the alicyclic dihydroxy compound (B) represented by the above general formula (I) is preferably a combination of isosorbide and tricyclodecane dimethanol.

[0061] The protective layer 1 may contain any appropriate additive in addition to the resin material described above. Examples of the additive include antioxidants, UV absorbers, light stabilizers, nucleating agents, fillers, pigments, surfactants, and antistatic agents. Any appropriate surface treatment layer may be provided on the surface of the protective layer 1 (the surface opposite to the polarizer 2). Examples of the surface treatment layer include a hard coat layer, an easy-adhesion layer, an easy-slip layer, an antiblocking layer, an antistatic layer, an antireflection layer, and an anti-oligomer layer.

[0062] The protective layer 1 is typically optically isotropic. In this specification, "optically isotropic" means that the in-plane retardation Re(550) and the thickness direction retardation Rth(550) are in the following ranges. The in-plane retardation Re(550) of the protective layer 1 is, for example, 10 nm or less, preferably 5 nm or less, and more preferably 3 nm or less. On the other hand, the lower limit of the in-plane retardation Re(550) of the protective layer 1 is typically 0 nm. The thickness direction retardation Rth(550) of the protective layer 1 is, for example, −10 nm to +10 nm, and preferably −5 nm to +5 nm.

[0063] The total light transmittance of the protective layer 1 is, for example, 80% or more, preferably 85% or more, more preferably 90% or more, and even more preferably 95% or more. The haze value of the protective layer 1 is, for example, 2.0% or less, preferably 1.5% or less, more preferably 1.0% or less, even more preferably 0.7% or less, particularly preferably 0.5% or less, and particularly preferably 0.3% or less. The lower limit of the haze value of the protective layer 1 is typically 0.05%. When the total light transmittance and / or haze value of the protective layer is within such range, the protective layer can be prevented from affecting the optical properties of the polarizer.

[0064] D. Adhesive layer (adhesive layer or adhesive layer) Although not shown, the protective layer 1 is typically attached to the polarizer 2 via an adhesive layer (a pressure-sensitive adhesive layer or an adhesive layer).

[0065] Examples of adhesives constituting the adhesive layer include (meth)acrylic adhesives, rubber adhesives, vinyl alkyl ether adhesives, silicone adhesives, polyester adhesives, polyamide adhesives, urethane adhesives, fluorine adhesives, epoxy adhesives, and polyether adhesives. The adhesives may be used alone or in combination of two or more. Of the adhesives, (meth)acrylic adhesives are preferred.

[0066] The thickness of the pressure-sensitive adhesive layer is typically 10 μm to 250 μm, and preferably 10 μm to 150 μm. The pressure-sensitive adhesive layer may be a single layer or may have a laminated structure.

[0067] The pressure-sensitive adhesive layer has a storage modulus (G') of, for example, 0.01 MPa to 1.00 MPa, and preferably 0.05 MPa to 0.50 MPa at 25° C. If the storage modulus of the pressure-sensitive adhesive layer is within this range, a polarizing plate with excellent flexibility can be realized, and as a result, a bendable or foldable image display device (particularly an organic EL display device) can be realized.

[0068] The adhesive layer may be made of, for example, a thermosetting adhesive or an active energy ray-curable adhesive, preferably an ultraviolet ray-curable adhesive. The thickness of the adhesive layer is, for example, 0.4 μm or more and 3.0 μm or less. Of these adhesive layers, the adhesive layer is preferred.

[0069] E. Image display device In one embodiment, the polarizing plate described in any one of the above items A to D is attached to a bendable image display panel. Fig. 3 is a schematic cross-sectional view of an image display device including the polarizing plate of Fig. 2. The image display device 200 shown in the figure includes a polarizing plate 100 and a bendable image display panel 5 in this order.

[0070] The polarizing plate 100 is typically disposed on the viewing side of the image display panel 5. In one embodiment, the polarizing plate 100 is attached to the image display panel 5 via any appropriate adhesive layer (a pressure-sensitive adhesive layer or an adhesive layer). The bendable image display panel 5 typically includes an image display cell. Examples of the bendable image display panel 5 include a liquid crystal display panel, an organic EL panel, and an inorganic EL panel, and preferably an organic EL panel. The bendable image display panel 5 is described in, for example, JP 2017-126061 A. The entire disclosures of these publications are incorporated herein by reference. As the adhesive layer for attaching the polarizing plate 100 to the image display panel 5, the above-mentioned pressure-sensitive adhesive layer is preferred, and a pressure-sensitive adhesive layer made of an acrylic pressure-sensitive adhesive is more preferred.

[0071] In one embodiment, the thickness of the protective layer 1 included in the polarizing plate 100 is, for example, 0.6 to 2.2, and preferably 1.0 to 2.0, relative to the thickness of the image display panel 5. When the thickness ratio between the protective layer and the image display panel is within this range, suitable flexibility can be stably imparted to the image display device.

[0072] As described above, such an image display device 200 is bendable or foldable. Note that an image display device may be referred to as an optical display device, an image display panel may be referred to as an optical display panel, and an image display cell may be referred to as an optical display cell. [Example]

[0073] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The methods for measuring each property are as follows.

[0074] (1) Indentation modulus of the protective layer (resin film) In the examples and comparative examples, the indentation modulus of the resin film serving as the protective layer was measured by the nanoindenter method under the following measurement conditions. Equipment: Triboindenter (manufactured by Hysitron Inc.) Sample size: 10 x 10 mm Indenter: Concial (spherical indenter: radius of curvature 10μm) Measurement method: Single indentation measurement Measurement temperature: 25℃ Indenter depth: 100 nm Analysis: Oliver Pharr analysis based on load-displacement curve The results are shown in Table 1.

[0075] (2) Loss tangent tanδ of the protective layer (resin film) The loss tangent tan δ of the resin films used in the examples and comparative examples was measured under the following conditions using a dynamic viscoelasticity measuring device (manufactured by IT Keisoku Seigyo Co., Ltd.). The results are shown in Table 1. <Measurement conditions> Measurement temperature: 85℃ or 100℃ Measured humidity: 85%RH (relative humidity) *85℃の場合のみ Mode: Tensile Frequency: 5Hz Sample width: 5mm Chuck distance: 20mm

[0076] (3) Flexibility of organic EL display devices The polarizing plates obtained in the examples and comparative examples were used as dummy bendable organic EL panels, which were attached to a transparent polyimide film (manufactured by KOLON, thickness 25 μm) with an acrylic adhesive (thickness 15 μm). The thickness ratio of the protective layer to the thickness of the organic EL panel is shown in Table 1. Next, the obtained evaluation samples were cut into 100 mm × 20 mm strips with the long side aligned with the absorption axis of the polarizer. The cut samples were placed in a no-load U-shaped stretch tester (Yuasa System Co., Ltd.'s "Small Desktop Durability Tester DLMD111LHA" and "U-shaped stretch test jig") with the polarizer side facing inward when bent, and a bending test was performed under the following conditions. Environmental conditions: 25℃, 55%RH Test speed: 60 rpm Bending radius: R3 Number of flexes: 50,000 Thereafter, the flexibility of the organic EL display device was evaluated according to the following criteria. The results are shown in Table 1. ◯: No cracks in the polarizing plate. ×: Cracks were found in the polarizing plate.

[0077] <<Preparation Example 1: PC Resin Film>> 81.98 parts by mass of isosorbide (ISB), 47.19 parts by mass of tricyclodecane dimethanol (TCDDM), 175.1 parts by mass of diphenyl carbonate (DPC), and 0.979 parts by mass of a 0.2% by mass aqueous solution of cesium carbonate as a catalyst were charged into a reaction vessel. Under a nitrogen atmosphere, the heating vessel temperature was heated to 150°C as the first step of the reaction, and the raw materials were dissolved (approximately 15 minutes) with stirring as necessary. Next, the pressure was increased from atmospheric pressure to 13.3 kPa, and the heating vessel temperature was raised to 190°C over 1 hour, while the generated phenol was withdrawn from the reaction vessel. After the entire reaction vessel was held at 190°C for 15 minutes, the pressure inside the reaction vessel was increased to 6.67 kPa, and the heating vessel temperature was raised to 230°C over 15 minutes as the second step, and the generated phenol was withdrawn from the reaction vessel. As the stirring torque of the mixer increased, the temperature was raised to 250°C in 8 minutes. Furthermore, the pressure inside the reactor was reduced to 0.200 kPa or less to remove the phenol generated. After reaching the required stirring torque, the reaction was terminated, and the resulting reaction product was extruded into water to obtain PC resin pellets. The resulting PC resin was vacuum-dried at 100°C for 12 hours. A 25 μm-thick PC resin film was then produced using a film-forming device equipped with a single-screw extruder (Toshiba Machine Co., Ltd., cylinder temperature setting: 250°C), a T-die (width: 1700 mm, temperature setting: 250°C), a cast roll (temperature setting: 60°C), and a winder. The in-plane retardation (Re(550)) of the PC resin film was 3.0 nm.

[0078] <<Preparation Example 2: PC Resin Film>> A PC resin film was produced in the same manner as in Preparation Example 1, except that the thickness was changed to 45 μm. <<Preparation Example 3: PC Resin Film>> A PC resin film was produced in the same manner as in Preparation Example 1, except that the thickness was changed to 60 μm.

[0079] [Example 1] A long, amorphous isophthalic copolymerized polyethylene terephthalate film (thickness: 100 μm) having a Tg of about 75° C. was used as the thermoplastic resin substrate, and one side of the resin substrate was subjected to a corona treatment. A PVA aqueous solution (coating liquid) was prepared by dissolving 100 parts by mass of a PVA-based resin prepared by mixing polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOHSEFFIMER") in a 9:1 ratio, to which 13 parts by mass of potassium iodide was added, in water. The above PVA aqueous solution was applied to the corona treated surface of the resin substrate and dried at 60° C. to form a PVA resin layer with a thickness of 13 μm, thereby producing a laminate. The resulting laminate was uniaxially stretched 2.4 times in the machine direction (longitudinal direction) in an oven at 130°C (auxiliary in-air stretching treatment). Next, the laminate was immersed in an insolubilizing bath (a boric acid aqueous solution obtained by mixing 4 parts by mass of boric acid with 100 parts by mass of water) at a liquid temperature of 40°C for 30 seconds (insolubilizing treatment). Next, the film was immersed in a dye bath (an aqueous iodine solution obtained by mixing iodine and potassium iodide in a weight ratio of 1:7 with 100 parts by mass of water) at a liquid temperature of 30°C for 60 seconds while adjusting the concentration so that the single transmittance (Ts) of the finally obtained polarizer would be a desired value (dyeing treatment). Next, the substrate was immersed in a crosslinking bath (a boric acid aqueous solution obtained by blending 3 parts by mass of potassium iodide and 5 parts by mass of boric acid with 100 parts by mass of water) at a liquid temperature of 40° C. for 30 seconds (crosslinking treatment). The laminate was then immersed in a boric acid aqueous solution (boric acid concentration 4 wt %, potassium iodide concentration 5 wt %) at a liquid temperature of 70°C and uniaxially stretched in the longitudinal direction (longitudinal direction) between rolls with different peripheral speeds to a total stretch ratio of 5.5 times (underwater stretching treatment). Thereafter, the laminate was immersed in a cleaning bath (aqueous solution obtained by mixing 4 parts by mass of potassium iodide with 100 parts by mass of water) at a liquid temperature of 20° C. (cleaning treatment). Thereafter, the film was dried in an oven maintained at about 90°C, and brought into contact with a heated roll made of SUS whose surface temperature was maintained at about 75°C (drying shrinkage treatment). In this manner, a polarizer having a thickness of about 5 μm was formed on the resin substrate, and a laminate having a resin substrate / polarizer structure was obtained. The polarizer surface (the surface opposite to the resin substrate) of the obtained laminate and the PC resin film (first protective layer) obtained in Preparation Example 1 were bonded together using an adhesive (specifically, an active energy ray-curable adhesive), and the adhesive was cured by irradiating it with ultraviolet light. Next, the resin substrate was peeled off, and the peeled surface of the resin substrate in the polarizer and the PC resin film (second protective layer) obtained in Preparation Example 1 were bonded together using an adhesive (specifically, an active energy ray-curable adhesive), and the adhesive was cured by irradiating it with ultraviolet light. In this way, a polarizing plate having a structure of first protective layer / polarizer / second protective layer was obtained.

[0080] [Example 2] A polarizing plate was obtained in the same manner as in Example 1, except that the PC resin film of Preparation Example 1 was changed to an acrylic resin film having a thickness of 25 μm (manufactured by Kaneka Corporation, product name "HTX-Z").

[0081] [Example 3] A polarizing plate was obtained in the same manner as in Example 1, except that the PC resin film in Preparation Example 1 was changed to a PET film having a thickness of 40 μm (manufactured by Toray Industries, Inc., product number "50U48").

[0082] [Example 4] A polarizing plate was obtained in the same manner as in Example 1, except that the PC resin film of Preparation Example 1 was changed to the PC resin film of Preparation Example 2.

[0083] [Comparative Example 1] A polarizing plate was obtained in the same manner as in Example 1, except that the PC resin film in Preparation Example 1 was changed to a COP resin film (manufactured by Nippon Zeon Co., Ltd., product number ZF16) having a thickness of 50 μm.

[0084] Comparative Example 2 A polarizing plate was obtained in the same manner as in Example 1, except that the PC resin film of Preparation Example 1 was changed to the PC resin film of Preparation Example 3.

[0085] [Table 1]

[0086] [evaluation] As is clear from Table 1, when the indentation modulus of the protective layer is 3.0 GPa or more, by applying a polarizing plate having this protective layer to an organic EL display device, it is possible to impart excellent flexibility to the organic EL display device. [Industrial Applicability]

[0087] The polarizing plate of the present invention can be applied to image display devices, and can be suitably used in particular in bendable or foldable organic EL display devices. [Explanation of symbols]

[0088] 1 protective layer 2 Polarizers 100 Polarizer 200 Image display device

Claims

[Claim 1] A polarizer; a protective layer disposed on at least one side of the polarizer, A polarizing plate, wherein the protective layer has an indentation modulus of 3.0 GPa or more.

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