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 a breaking elongation of 20 mm or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to polarizing plates and image display devices. [Background technology]

[0002] Image display devices, such as liquid crystal displays and electroluminescent (EL) displays (e.g., organic EL displays and inorganic EL displays), are rapidly becoming widespread. Typically, image display devices use polarizing plates comprising a polarizer and a protective layer (see, for example, Patent Document 1). In recent years, the applications of image display devices have diversified, and the flexibility and bendability of image display devices are being considered. However, when the polarizing plate described in Patent Document 1 is applied to a bendable or foldable image display device, the flexibility of the image display device may be insufficient. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2018-200339 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] The present invention was made to solve the above-mentioned conventional problems, and its main objective is to provide a polarizing plate and an image display device that can be suitably applied to a flexible or foldable image display device. [Means for solving the problem]

[0005] [1] A polarizing plate according to one embodiment of the present invention comprises a polarizer and a protective layer. The protective layer is located on at least one side of the polarizer. The elongation at break of the protective layer at 25°C is 20 mm or more. [2]An image display device according to another aspect of the present invention includes, in this order, the polarizing plate described in [1] above and a bendable image display panel. [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 to 2. [Advantages of the Invention]

[0006] According to an embodiment of the present invention, a polarizing plate and an image display device that can be suitably applied to a bendable or foldable image display device can be realized. [Brief Description 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. 2. [Modes for Carrying Out the Invention]

[0008] Hereinafter, representative embodiments of the present invention will be described, but the present invention is not limited to these embodiments. Also, for the sake of clarity in the description, the drawings may schematically represent the width, thickness, shape, etc. of each part as compared with the embodiments, but this is merely an example and does not limit the interpretation of the present invention. [[ID=​​​​​​​​​​​"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) can be obtained 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) can be obtained by the formula: Rth(λ) = (nx - nz) × d, where d (nm) is the thickness of the layer (film).

[0010] A. Overall structure of the 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 typically has flexibility. The elongation at break of the protective layer 1 at 25°C is 20 mm or more. The elongation at break can be measured, for example, in accordance with JIS K 7127. When the elongation at break of the protective layer is 20 mm or more, sufficient bending durability can be imparted to the polarizing plate including the protective layer and the polarizer. With such a polarizing plate, it is applicable to a bendable (bendable) image display device (for example, a liquid crystal display device, an organic EL display device, an inorganic EL display device), preferably a foldable (foldable) image display device, more preferably a foldable (foldable) organic EL display device.

[0011] The elongation at break of the protective layer 1 is preferably 25 mm or more, more preferably 30 mm or more. If the elongation at break of the protective layer is above such a lower limit, the bending durability of the polarizing plate can be further improved. On the other hand, the elongation at break of the protective layer 1 is, for example, 150 mm or less, preferably 130 mm or less, more preferably 100 mm or less, and even more preferably 50 mm or less. If the elongation at break of the protective layer is below such an upper limit, deformation of the protective layer 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 or less, preferably 13×10 -2 or less, more preferably 10×10 -2 or less, and even more preferably 7.0×10 -2 or less. 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 . The loss tangent tanδ of the protective layer 1 at 100°C is, for example, 15×10 -2 or less, preferably 13×10 -2 or less, more preferably 10×10 -2 or less, and even more preferably 8.0×10 -2 or less, and particularly preferably 6.0×10 -2 or less. 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 . Incidentally, the tanδ 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 tanδ of the protective layer is above such a lower limit, stress relaxation during bending works, and failure modes such as cracks due to residual stress and the like can be improved. If the tanδ of the protective layer is below such an upper limit, good image display can be maintained without creases even after bending multiple times.

[0013] The thickness of protective layer 1 is, for example, 10 μm or more, preferably 20 μm or more. If the thickness of the protective layer is above this lower limit, excellent bending durability can be stably imparted to the polarizing plate. On the other hand, the thickness of 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 especially preferably 30 μm or less. If the thickness of the protective layer is below this upper limit, excellent bending durability can be stably imparted to the polarizing plate, and the polarizing plate can be made thinner.

[0014] As shown in Figure 2, in one embodiment, the protective layer 1 is arranged on both sides of the polarizer 2. Hereinafter, the protective layer 1 arranged on one side of the polarizer 2 may be referred to as the first protective layer 1a, and the protective layer 1 arranged on the other side of the polarizer 2 may be referred to as the second protective layer 1b.

[0015] The following describes the components of a polarizing plate in detail.

[0016] B. Polarizer Any suitable polarizer can be used as polarizer 2. For example, the resin film forming the polarizer may consist of a single layer of resin film, or it may be prepared using a laminate of two or more layers.

[0017] Specific examples of polarizers composed of a single layer of resin film include hydrophilic polymer films such as polyvinyl alcohol (PVA) films, partially formalized PVA films, and partially saponified ethylene-vinyl acetate copolymer films, which have been subjected to dyeing and stretching treatments with dichroic substances such as iodine or dichroic dyes, as well as polyene-based oriented films such as dehydrated PVA or dehydrochlorinated polyvinyl chloride. Preferably, polarizers obtained by dyeing a PVA film with iodine and uniaxially stretching are used because they have excellent optical properties.

[0018] Specific examples of polarizers obtained using a laminate 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 a resin substrate, drying it to form a PVA-based resin layer on the resin substrate, and obtaining a laminate of the resin substrate and the PVA-based resin layer; or by stretching and dyeing the laminate to make the PVA-based resin layer a polarizer. In one embodiment of the present invention, preferably, a polyvinyl alcohol-based resin layer containing a halide and a polyvinyl alcohol-based resin is formed on one side of the resin substrate. Stretching typically includes immersing the laminate in an aqueous boric acid solution and stretching it. Furthermore, stretching may optionally include air stretching the laminate at a high temperature (e.g., 95°C or higher) before stretching in the aqueous boric acid solution. In addition, in one embodiment of the present invention, the laminate is preferably subjected to a drying shrinkage treatment in which it shrinks by 2% or more in the width direction by heating while being transported in the longitudinal direction. Typically, the manufacturing method of this embodiment includes applying an air-assisted stretching treatment, a dyeing treatment, a water-based stretching treatment, and a drying shrinkage treatment to the laminate 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, making it possible to achieve high optical properties. At the same time, by increasing the orientation of PVA in advance, it is possible to prevent problems such as a decrease in the orientation of PVA and dissolution when immersed in water in the subsequent dyeing and stretching processes, making it possible to achieve high optical properties. Furthermore, when the PVA-based resin layer is immersed in a liquid, the disorder 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 halides. This makes it possible to improve the optical properties of polarizers obtained through processing steps that involve immersing the laminate in a liquid, such as dyeing and water-based stretching. Furthermore, by shrinking the laminate in the width direction through a drying shrinkage treatment, the optical properties can be improved.The resulting 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 may be laminated onto the peeled surface according to the purpose. Details of such polarizer manufacturing methods are described, for example, in Japanese Patent Application Publication No. 2012-73580 and Japanese Patent No. 6470455. The entire contents of these publications are incorporated herein by reference.

[0019] The above-mentioned iodine dyeing is carried out, for example, by immersing the PVA film in an iodine aqueous solution. The stretching ratio for the above-mentioned uniaxial stretching is preferably 3 to 7 times. Stretching may be performed after the dyeing treatment, or during the dyeing process. Alternatively, dyeing may be performed after stretching. If necessary, the PVA film may be subjected to swelling, crosslinking, washing, drying, etc. For example, immersing the PVA film in water and washing it before dyeing can not only clean dirt and anti-blocking agents from the surface of the PVA film, but also swell the PVA film to prevent uneven dyeing.

[0020] The thickness of 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] Polarizer 2 typically exhibits absorption dichroism at wavelengths between 380 nm and 780 nm. The transmittance of 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 polarizer 2 is preferably 97.0% or higher, more preferably 99.0% or higher, and even more preferably 99.9% or higher.

[0022] C. Protective layer The protective layer 1 is composed of a resin film containing a resin material as its main component. Specific examples of the resin material include cycloolefin (COP) resins such as polynorbornene; polyester resins such as polyethylene terephthalate (PET); cellulose resins such as triacetylcellulose (TAC); polycarbonate (PC) resins; (meth)acrylic resins; polyvinyl alcohol resins; polyamide resins; polyimide resins; polyethersulfone resins; polysulfone resins; polystyrene resins; polyolefin resins; and transparent resins such as acetate resins. Thermosetting resins or UV-curing resins such as (meth)acrylic resins, urethane resins, (meth)acrylic urethane resins, epoxy resins, and silicone resins can also be used. "(meth)acrylic resin" refers to acrylic resins and / or methacrylic resins. In addition, glassy polymers such as siloxane polymers can also be used. Furthermore, the polymer film described in Japanese Patent Application Publication No. 2001-343529 (WO01 / 37007) can also be used. As materials for this film, for example, a resin composition containing a thermoplastic resin having substituted or unsubstituted imide groups in its side chains, and a thermoplastic resin having substituted or unsubstituted phenyl groups and nitrile groups in its side chains can be used. Examples include a resin composition having an alternating copolymer of isobutene and N-methylmaleimide, and an acrylonitrile-styrene copolymer. The polymer film may be, for example, an extruded product of the above resin composition. The materials for the resin film can be used individually or in combination.

[0023] Among such resin materials, PC-based resins are preferred.

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

[0025] Here, any compound having the bonding structure represented by structural formula (1) can be used as the dihydroxy compound, as long as it has two alcoholic hydroxyl groups, contains a linking group -CH2-O- in the molecule, and can react with dicarbonate diester in the presence of a polymerization catalyst to produce polycarbonate. Multiple types can also be used in combination.

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

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

[0028] Specifically, dihydroxy compounds (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) Compounds having aromatic groups in the side chain and ether groups bonded to the aromatic groups in the main chain, as exemplified by )-3-cyclohexylphenyl)fluorene, 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, and 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] [(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-(2-hydroxyethoxy) [Sopropylphenyl]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;Dihydroxyalkoxydiaryl ethers, such as 4,4'-bis(2-hydroxyethoxy)diphenyl ether and 4,4'-bis(2-hydroxyethoxy)-3,3'-dimethyldiphenyl ether; bishydroxyalkoxyaryl sulfides, such as 4,4'-bis(2-hydrochyethoxyphenyl) sulfide and 4,4'-bis[4-(2-dihydroxyethoxy)-3-methylphenyl] sulfide; bishydroxyalkoxyaryl sulfoxides, such as 4,4'-bis(2-hydrochyethoxyphenyl) sulfoxide and 4,4'-bis[4-(2-dihydroxyethoxy)-3-methylphenyl] sulfoxide; 4,4'-bis(2-hydrochyethoxyphenyl) sulfone, 4,4'-bis[4-(2- Examples include bishydroxyalkoxyaryl sulfones, such as dihydroxyethoxy)-3-methylphenyl]sulfone; 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; anhydrous sugar alcohols, such as dihydroxy compounds represented by formula (2) below; and compounds having a cyclic ether structure, such as spiroglycols represented by general formula (3) below. Dihydroxy compounds (A) can be used alone or in combination.

[0029] [ka]

[0030] [ka]

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

[0032] The proportion of structural units derived from dihydroxy compound (A) to the total dihydroxy compound-derived structural units 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 structural units derived from 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 dihydroxy compound (A) is within the above range, the elongation at break of the protective layer can be stably adjusted to the above range.

[0033] (Dihydroxy compound (B)) As dihydroxy compounds that form the structural units of PC resins, dihydroxy compound (A) and dihydroxy compound (B) can be used together. When dihydroxy compounds (A) and (B) are used in combination, the elongation at break of the protective layer can be more stably adjusted to the above range.

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

[0035] The alicyclic dihydroxy compound is not particularly limited, but preferably includes compounds that typically contain a five-membered ring structure or a six-membered ring structure. The six-membered ring structure may also be fixed in a chair or boat shape by covalent bonds. The five-membered ring 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 in the alicyclic dihydroxy compound is, for example, 70 or less, preferably 50 or less, and more preferably 30 or less.

[0036] Examples of alicyclic dihydroxy compounds containing a five-membered ring structure or a six-membered ring structure include alicyclic dihydroxy compounds represented by the following general formulas (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 these represents a cycloalkylene group with 4 to 20 carbon atoms.

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

[0038] [ka]

[0039] Tricyclodecanedimethanol or pentacyclopentadecanedimethanol, which are alicyclic dihydroxy compounds represented by the above general formula (I), are defined as R in general formula (I).1 This includes various isomers represented by the following general formula (Ib) (wherein n represents 0 or 1).

[0040] [ka]

[0041] Decalindimethanol or tricyclotetradecanedimethanol, which are alicyclic dihydroxy compounds represented by the above general formula (I), are, in general formula (I), R 1 This includes various isomers represented by the following general formula (Ic) (wherein m represents 0 or 1). Specifically, such isomers include 2,6-decalingimethanol, 1,5-decalingimethanol, and 2,3-decalingimethanol.

[0042] [ka]

[0043] Norbornane dimethanol, an alicyclic dihydroxy compound represented by the above general formula (I), has R in general formula (I). 1 This includes various isomers represented by the following general formula (Id). Specifically, examples of such isomers include 2,3-norbornanedimethanol and 2,5-norbornanedimethanol.

[0044] [ka]

[0045] Adamantane dimethanol, an alicyclic dihydroxy compound represented by general formula (I), has R in general formula (I). 1 This includes various isomers represented by the following general formula (Ie). Specifically, one such example is 1,3-adamantanedimethanol.

[0046] [ka]

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

[0048] [ka]

[0049] Tricyclodecanediol or pentacyclopentadecanediol, which are alicyclic dihydroxy compounds represented by the above general formula (II), are defined as R in general formula (II). 2 This includes various isomers represented by the following general formula (IIb) (wherein n represents 0 or 1).

[0050] [ka]

[0051] Decalindiol or tricyclotetradecanediol, which are alicyclic dihydroxy compounds represented by the above general formula (II), are, in general formula (II), R 2 This includes various isomers represented by the following general formula (IIc) (wherein m represents 0 or 1). Specifically, such isomers include 2,6-decalindiol, 1,5-decalindiol, and 2,3-decalindiol.

[0052] [ka]

[0053] Norbornanediol, an alicyclic dihydroxy compound represented by the above general formula (II), has R in general formula (II). 2 This includes various isomers represented by the following general formula (IId). Specifically, examples of such isomers include 2,3-norbornanediol and 2,5-norbornanediol.

[0054] [ka]

[0055] Adamantanediol, an alicyclic dihydroxy compound represented by the above general formula (II), has R in general formula (II). 2 This includes various isomers represented by the following general formula (IIe). Specifically, 1,3-adamantanediol is one such example.

[0056] [ka]

[0057] Among the specific examples of the alicyclic dihydroxy compounds described above, preferred examples include cyclohexanedimethanol, tricyclodecanedimethanol, adamantanediol, and pentacyclopentadecanedimethanol. More preferably, from the viewpoint of availability and ease of handling, are 1,4-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,2-cyclohexanedimethanol, and tricyclodecanedimethanol, and even more preferably tricyclodecanedimethanol.

[0058] The proportion of structural units derived from dihydroxy compound (B) to the total dihydroxy compound-derived structural units 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 structural units derived from 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-based resins are described, for example, in Japanese Patent Publication No. 2012-31370 (Japanese Patent No. 5448264). The description in said patent document is incorporated herein by reference.

[0060] In one embodiment, the PC resin includes structural units derived from a dihydroxy compound (A) represented by formula (2) above, structural units derived from an alicyclic dihydroxy compound (B) represented by general formula (I) above, and carbonate groups connecting them. When a PC resin containing these structural units is applied to a resin film, the elongation at break of the protective layer can be adjusted to the above range with greater stability. In such a PC-based resin, the molar ratio (A:B) of structural units derived from the dihydroxy compound (A) represented by formula (2) above and structural units derived from the alicyclic dihydroxy compound (B) represented by the general formula (I) above is, for example, 5:5 to 9:1, and preferably 6:4 to 8:2. In such PC resins, the combination of the dihydroxy compound (A) represented by formula (2) and the alicyclic dihydroxy compound (B) represented by the general formula (I) is preferably a combination of isosorbide and tricyclodecanedimethanol.

[0061] In addition to the resin material described above, protective layer 1 may contain any suitable additives. Examples of additives include antioxidants, ultraviolet absorbers, light stabilizers, nucleating agents, fillers, pigments, surfactants, and antistatic agents. The surface of protective layer 1 (the surface opposite to polarizer 2) may be provided with any suitable surface treatment layer. Examples of surface treatment layers include hard coat layers, easy-adhesion layers, easy-slip layers, anti-blocking layers, antistatic layers, anti-reflective layers, and oligomer-preventing layers.

[0062] The protective layer 1 is typically optically isotropic. In this specification, "optically isotropic" means that the in-plane phase difference Re(550) and the thickness-direction phase difference Rth(550) are within the following ranges. The in-plane phase difference 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 phase difference Re(550) of the protective layer 1 is typically 0 nm. The phase difference Rth(550) in the thickness direction of the protective layer 1 is, for example, -10nm to +10nm, preferably -5nm to +5nm.

[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 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 especially preferably 0.3% or less. The lower limit of the haze value of protective layer 1 is typically 0.05%. If the total light transmittance and / or haze value of the protective layer are within this range, the protective layer may suppress its influence on the optical properties of the polarizer.

[0064] D. Adhesive layer (tack layer or adhesive layer) Although not shown in the diagram, protective layer 1 is typically attached to polarizer 2 via an adhesive layer (tack layer or adhesive layer).

[0065] Examples of adhesives that constitute 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 individually or in combination of two or more types. Among the adhesives, (meth)acrylic adhesives are preferred.

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

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

[0068] Examples of adhesives that constitute the adhesive layer include thermosetting adhesives and active energy ray curing adhesives, with ultraviolet curing adhesives being preferred. The thickness of the adhesive layer is, for example, 0.4 μm to 3.0 μm. Among these adhesive layers, an adhesive layer is preferred.

[0069] E. Image display device In one embodiment, the polarizing plates described in sections A to D above are used by being attached to a flexible image display panel. Figure 3 is a schematic cross-sectional view of an image display device equipped with the polarizing plate shown in Figure 2. The illustrated example image display device 200 is equipped with a polarizing plate 100 and a flexible image display panel 5 in that order.

[0070] The polarizing plate 100 is typically positioned 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 suitable adhesive layer (adhesive layer or bonding layer). The flexible image display panel 5 typically includes an image display cell. Examples of flexible image display panels 5 include liquid crystal display panels, organic EL panels, and inorganic EL panels, with organic EL panels being preferred. Flexible image display panels 5 are described, for example, in Japanese Patent Application Publication No. 2017-126061. The entire descriptions of these publications are incorporated herein by reference. Preferably, the adhesive layer used to attach the polarizing plate 100 to the image display panel 5 is the adhesive layer described above, and more preferably, an adhesive layer made of an acrylic adhesive.

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

[0072] Such an image display device 200 is flexible or foldable, as described above. Note that the image display device may be referred to as an optical display device, the image display panel as an optical display panel, and the image display cell as an optical display cell. [Examples]

[0073] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. The measurement methods for each characteristic are as follows.

[0074] (1) Elongation at break of the protective layer (resin film) In the examples and comparative examples, the resin film used as the protective layer was cut into a dumbbell shape (10 mm wide, 100 mm long) to obtain test samples. Next, the test samples were subjected to tensile testing using an Autograph AGS-50D tensile testing machine (manufactured by Shimadzu Corporation) with a chuck spacing of 10 mm and a tensile speed of 60 mm / min, and the stress-strain curve was determined. The stress at which the test sample fractured was determined as the fracture strength, and the strain (elongation) at which the test sample fractured was determined as the fracture elongation. The results are shown in Table 1.

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

[0076] (3) Flexibility of organic EL display devices The polarizers obtained in the examples and comparative examples were attached to a transparent polyimide film (manufactured by KOLON, 25 μm thick) using an acrylic adhesive (15 μm thick) as a dummy for a flexible organic EL panel. The ratio of the thickness 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 strips of 100 mm × 20 mm with the direction of the absorption axis of the polarizer as the longer side. The cut samples were set in a no-load U-shaped stretch test machine (Yuasa System Equipment Co., Ltd. "Small Tabletop Durability Test Machine DLMD111LHA" and "U-shaped Stretch Test Fixture") with the polarizer side facing the inside of the bend, and a bending test was performed under the following conditions. Environmental conditions: 25℃, 55%RH Test speed: 60 rpm Bending radius: R3 Number of flexions: 100,000 Subsequently, the flexibility of the organic EL display device was evaluated according to the following criteria. The results are shown in Table 1. ○: There are no cracks in the polarizing plate. ×: There is a crack in the polarizing plate.

[0077] <<Preparation Example 1: PC-based resin film>> 81.98 parts by mass of isosorbide (ISB), 47.19 parts by mass of tricyclodecanedimethanol (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 added to a reaction vessel. In the first stage of the reaction, under a nitrogen atmosphere, the heating vessel was heated to 150°C, and the raw materials were dissolved while stirring as needed (for about 15 minutes). 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 removed from the reaction vessel. After holding the entire reaction vessel at 190°C for 15 minutes, in the second stage, the pressure inside the reaction vessel was set to 6.67 kPa, and the heating vessel temperature was raised to 230°C over 15 minutes, while the generated phenol was removed from the reaction vessel. As the stirring torque of the stirrer increased, the temperature was raised to 250°C in 8 minutes, and then the pressure inside the reaction vessel was reduced to 0.200 kPa or less to remove the generated phenol. After reaching the predetermined stirring torque, the reaction was terminated, and the resulting reactants were extruded into water to obtain PC resin pellets. The obtained PC resin was vacuum dried at 100°C for 12 hours, and then a 25 μm thick PC resin film was produced using a film manufacturing apparatus equipped with a single-screw extruder (manufactured by Toshiba Machine Co., Ltd., cylinder setting temperature: 250°C), a T-die (width 1700 mm, setting temperature: 250°C), a cast roll (setting temperature: 60°C), and a winding machine. The in-plane phase difference Re(550) of the PC resin film was 3.0 nm.

[0078] <<Preparation Example 2: PC-based resin film>> A PC-based resin film was prepared in the same manner as in Preparation Example 1, except that the thickness was changed to 60 μm.

[0079] [Example 1] As a thermoplastic resin substrate, an amorphous isophthalic copolymer polyethylene terephthalate film (thickness: 100 μm) in a long length with a Tg of approximately 75°C was used, and one side of the resin substrate was subjected to corona treatment. A PVA aqueous solution (coating solution) was prepared by dissolving 100 parts by mass of a PVA-based resin, which was prepared by mixing polyvinyl alcohol (degree of polymerization 4200, degree of saponification 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "Gosephymer") in a 9:1 ratio, with 13 parts by mass of potassium iodide. A PVA aqueous solution was applied to the corona-treated surface of a resin substrate and dried at 60°C to form a 13 μm thick PVA-based resin layer, thereby creating a laminate. The resulting laminate was uniaxially stretched 2.4 times in the longitudinal direction (longitudinal direction) in an oven at 130°C (air-assisted stretching). Next, the laminate was immersed for 30 seconds in an insolubilization bath at a liquid temperature of 40°C (a boric acid aqueous solution obtained by mixing 4 parts by mass of boric acid with 100 parts by mass of water) (insolubilization treatment). Next, the polarizers were immersed for 60 seconds in a staining bath at a liquid temperature of 30°C (an iodine aqueous solution obtained by mixing iodine and potassium iodide in a weight ratio of 1:7 with 100 parts by mass of water) while adjusting the concentration so that the final transmittance (Ts) of the polarizers obtained would be the desired value (staining treatment). Next, the material was immersed for 30 seconds in a crosslinking bath at a liquid temperature of 40°C (a boric acid aqueous solution obtained by mixing 3 parts by mass of potassium iodide and 5 parts by mass of boric acid with 100 parts by mass of water) (crosslinking treatment). Subsequently, the laminate was immersed in a boric acid aqueous solution (boric acid concentration 4% by weight, potassium iodide concentration 5% by weight) at a liquid temperature of 70°C, and uniaxially stretched in the longitudinal direction (longitudinal direction) between rolls with different peripheral speeds to achieve a total stretch ratio of 5.5 times (underwater stretching treatment). Subsequently, the laminate was immersed in a washing bath at a liquid temperature of 20°C (an aqueous solution obtained by mixing 4 parts by mass of potassium iodide with 100 parts by mass of water) (washing treatment). Subsequently, the material was dried in an oven maintained at approximately 90°C while being brought into contact with a SUS (stainless steel) heated roll whose surface temperature was maintained at approximately 75°C (drying shrinkage treatment). In this way, a polarizer with a thickness of approximately 5 μm was formed on the resin substrate, and a laminate having a resin substrate / polarizer configuration was obtained. The polarizer surface of the obtained laminate (the side opposite to the resin substrate) and the PC-based resin film (first protective layer) obtained in Preparation Example 1 were bonded together using an adhesive (specifically, an active energy ray curing adhesive), and the adhesive was cured by irradiation with ultraviolet light. Next, the resin substrate was peeled off, and the peeled surface of the resin substrate on the polarizer was bonded to the PC-based resin film (second protective layer) obtained in Preparation Example 1 using an adhesive (specifically, an active energy ray curing adhesive), and the adhesive was cured by irradiation with ultraviolet light. Based on the above, a polarizing plate having the configuration of a 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 in Preparation Example 1 was changed to a PET film with a thickness of 40 μm (Toray Industries, Inc., product number "50U48").

[0081] [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 replaced with a COP resin film with a thickness of 50 μm (manufactured by Nippon Zeon Co., Ltd., product number ZF16).

[0082] [Comparative Example 2] A polarizing plate was obtained in the same manner as in Example 1, except that the PC resin film in Preparation Example 1 was replaced with a 25 μm thick acrylic resin film (manufactured by Kaneka Corporation, product name "HTX-Z").

[0083] [Comparative Example 3] A polarizing plate was obtained in the same manner as in Example 1, except that the PC-based resin film of Preparation Example 1 was replaced with the PC-based resin film of Preparation Example 2.

[0084] [Table 1]

[0085] [evaluation] As is clear from Table 1, if the elongation at break of the protective layer is 20 mm or more, applying a polarizing plate equipped with this protective layer to an organic EL display device can impart excellent flexibility to the organic EL display device. [Industrial applicability]

[0086] The polarizing plate of the present invention can be applied to image display devices, and is particularly suitable for use in flexible or foldable organic EL display devices. [Explanation of Symbols]

[0087] 1 protective layer 2 polarizers 100 polarizing plates 200 Image Display Devices

Claims

[Claim 1] The device comprises a polarizing plate and a flexible image display panel in this order. The polarizing plate is Polarizer and, The polarizer comprises a protective layer disposed on at least one side thereof, The elongation at break of the protective layer at 25°C, measured by the method described below, is 20 mm or more. The ratio of the thickness of the protective layer to the thickness of the image display panel is 1 to 2, for the image display device: <Method for measuring elongation at break> The protective layer was cut into a dumbbell shape (10 mm wide, 100 mm long) to be used as a test sample; The aforementioned test sample was subjected to a tensile test using a tensile testing machine with a chuck spacing of 10 mm and a tensile speed of 60 mm / min, and the stress-strain curve was determined; The strain at which the aforementioned test sample breaks is determined and defined as the elongation at break.

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