JP7692009B2 - Polarizing plate and image display device - Google Patents

Description

The present invention relates to a polarizing plate and an image display device.

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 widespread. Typically, image display devices use a polarizing plate including a polarizer and a protective layer (see, for example, Patent Document 1).
In recent years, applications of image display devices have become more diverse, and efforts have been made to make image display devices 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.

JP 2022-153440 A

The present invention has been made to solve the above-mentioned problems in the conventional art, and its main objective is to provide a polarizing plate and an image display device that can be suitably applied to a bendable or foldable image display device.

[1] A polarizing plate according to one embodiment of the present invention includes a polarizer and a protective layer. The protective layer is disposed on at least one side of the polarizer. The number of flexions of the protective layer in an MIT test is 200 or more.
[2] An image display device according to another aspect of the present invention includes the polarizing plate according to the above [1] and a bendable image display panel, in this order.
[3] In the image display device according to the above [2], a ratio of a thickness of the protective layer to a thickness of the image display panel may be 1 to 2.

According to an embodiment 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.

FIG. 1 is a schematic cross-sectional view of a polarizing plate according to one embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of a polarizing plate according to another embodiment of the present invention. FIG. 3 is a schematic cross-sectional view of an image display device including the polarizing plate of FIG.

Representative embodiments of the present invention are described below, but the present invention is not limited to these embodiments. In addition, in order to make the description clearer, the drawings may show the width, thickness, shape, etc. of each part more diagrammatically than in the embodiments, but these are merely examples and do not limit the interpretation of the present invention.

(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 maximum (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 having a wavelength of λ nm at 23° C. For example, "Re(550)" is the in-plane retardation measured with light having a wavelength of 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 having a wavelength of λ nm at 23° C. For example, "Rth(550)" is the retardation in the thickness direction measured with light having a wavelength of 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).

A. Overall Configuration 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 typically has flexibility. The number of flexions in an MIT test (hereinafter, referred to as the MIT flexion number) of the protective layer 1 is 200 or more. The MIT test can be performed in accordance with, for example, JIS P 8115.
When the MIT bending number of the protective layer is 200 or more, sufficient bending durability can be imparted to a polarizing plate including the protective layer and the polarizer. Such a polarizing plate is applicable to a bendable image display device (e.g., a liquid crystal display device, an organic EL display device, an inorganic EL display device), preferably a foldable image display device, more preferably a foldable organic EL display device.

The MIT flexion number of the protective layer 1 is preferably 500 or more, more preferably 800 or more, and further preferably 1000 or more. When the MIT flexion number of the protective layer is equal to or more than such a lower limit, the flexion durability of the polarizing plate can be further improved.
On the other hand, the MIT bending number of the protective layer 1 is, for example, 6000 times or less, preferably 3000 times or less, and more preferably 2000 times or less.

The indentation modulus of the protective layer 1 is, for example, 3.00 GPa or more, preferably 3.10 GPa or more, and more preferably 3.20 GPa or more. When the indentation modulus of the protective layer is equal to or more than such a 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. If the indentation modulus of the protective layer is equal to or less than such an upper limit, cracking of the protective layer during bending can be suppressed. The indentation modulus can be measured, for example, in accordance with JIS Z 2255.

The breaking elongation of the protective layer 1 at 25° C. is, for example, 20 mm or more, preferably 25 mm or more, and more preferably 30 mm or more. When the breaking elongation of the protective layer is equal to or more than such a lower limit, the bending durability of the polarizing plate can be further improved.
On the other hand, the breaking elongation 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 breaking elongation of the protective layer is equal to or less than such an upper limit, deformation of the protective layer can be suppressed. The breaking elongation can be measured, for example, in accordance with JIS K 7127.

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 tan δ 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, 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 tan δ of the protective layer 1 at 100° C. is typically 3.0×10 ⁻² . Note that 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 higher than the lower limit, stress relaxation during bending can be achieved, and failure modes such as cracks due to residual stress, etc. If the tan δ of the protective layer is equal to or lower than the upper limit, no creases are formed even after bending multiple times, and good image display can be maintained.

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 equal to or greater than this lower limit, it is possible to stably impart excellent bending durability 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 55 μm or less, particularly preferably 47 μm or less, particularly preferably 42 μm or less, and most preferably 30 μm or less. If the thickness of the protective layer is equal to or less than this upper limit, it is possible to stably impart excellent bending durability to the polarizing plate and to make the polarizing plate thinner.

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

The components of the polarizing plate are explained in detail below.

B. Polarizer Any appropriate polarizer may 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.

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

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 and drying the substrate to form a PVA-based resin layer on the resin substrate to obtain a laminate of the resin substrate and the PVA-based resin layer; stretching and dyeing the laminate to make 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 to stretch it. Furthermore, the stretching may further include air-stretching the laminate at a high temperature (e.g., 95°C or higher) before stretching in the boric acid aqueous solution, as necessary. In addition, 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 conveyed 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 air-assisted stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment in this order. By introducing the auxiliary stretching, it is possible to increase the crystallinity of the PVA even when the PVA is applied onto the thermoplastic resin, and it is possible to achieve high optical properties. At the same time, by increasing the orientation of the PVA in advance, problems such as a decrease in the orientation of the PVA or dissolution when the PVA is immersed in water in the subsequent dyeing step or stretching step can be prevented, and it is possible to achieve high optical properties. Furthermore, when the PVA-based resin layer is immersed in a liquid, the disorder of the orientation of the polyvinyl alcohol molecules and the decrease in the orientation can be suppressed compared to when the PVA-based resin layer does not contain a halide. This can improve the optical properties of the polarizer obtained by immersing the laminate in a liquid in a treatment process such as a dyeing process and an underwater stretching process. Furthermore, the optical properties can be improved by shrinking the laminate in the width direction by a drying shrinkage process. The obtained resin substrate/polarizer laminate may be used as it 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 suitable protective layer according to the purpose may be laminated on the peeled surface. Details of the manufacturing method of such a polarizer are described in, for example, JP 2012-73580 A and JP 6470455 A. The entire disclosures of these publications are incorporated herein by reference.

The dyeing with iodine is carried out, for example, by immersing the PVA-based 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 process, or may be carried out while dyeing. Alternatively, the film may be stretched and then dyed. If necessary, the PVA-based film may be subjected to a swelling process, a crosslinking process, a washing process, a drying process, or the like. For example, by immersing the PVA-based film in water and washing it with water before dyeing, it is possible to wash off dirt and antiblocking agents on the surface of the PVA-based film, and also to swell the PVA-based film and prevent uneven dyeing, etc.

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. If the thickness of the polarizer is within this range, curling during heating can be effectively suppressed, and good appearance durability during heating can be obtained.

The polarizer 2 typically exhibits absorption 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.

C. Protective layer The protective layer 1 is made of a resin film containing a resin material as a main component. Specific examples of the resin material include cycloolefin (COP)-based resins such as polynorbornene-based resins; polyester-based resins such as polyethylene terephthalate (PET)-based resins; cellulose-based resins such as triacetyl cellulose (TAC)-based resins; polycarbonate (PC)-based resins; (meth)acrylic-based resins; polyvinyl alcohol-based resins; polyamide-based resins; polyimide-based resins; polyethersulfone-based resins; polysulfone-based resins; polystyrene-based resins; polyolefin-based resins; and transparent resins such as acetate-based resins. In addition, examples of the resin material include thermosetting resins or ultraviolet-curing resins such as (meth)acrylic-based resins, urethane-based resins, (meth)acrylic urethane-based resins, epoxy-based resins, and silicone-based resins. The term "(meth)acrylic resin" refers to acrylic resins and/or methacrylic resins. In addition, examples of the resin material include glassy polymers such as siloxane-based polymers. Also usable is the polymer film described in JP 2001-343529 A (WO 01/37007). As the material of this film, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in the side chain, and a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in the side chain can be used, and for example, a resin composition containing an alternating copolymer of isobutene and N-methylmaleimide, and an acrylonitrile-styrene copolymer can be mentioned. The polymer film can be, for example, an extrusion molded product of the above-mentioned resin composition. The materials of the resin film can be used alone or in combination.

Among these resin materials, PC resin is preferred.

The PC resin contains at least a structural unit derived from a dihydroxy compound having a bond structure represented by the following structural formula (1) and is produced by reacting a dihydroxy compound containing at least a dihydroxy compound having at least one bond structure -CH ₂ -O- in the molecule with a carbonate diester in the presence of a polymerization catalyst. In other words, the PC resin contains a structural unit derived from a dihydroxy compound and a carbonate group derived from a carbonate diester.

Here, as the dihydroxy compound having a bond structure represented by structural formula (1), any compound can be used as long as it has two alcoholic hydroxyl groups, contains a structure having a linking group -CH ₂ -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 of compounds may be used in combination.

In addition, a dihydroxy compound that does not have the bond structure represented by the above structural formula (1) may be used in combination as a dihydroxy compound for use in a PC-based resin. Hereinafter, a dihydroxy compound that has the bond structure represented by structural formula (1) may be abbreviated as dihydroxy compound (A), and a dihydroxy compound that does not have the bond structure represented by structural formula (1) may be abbreviated as dihydroxy compound (B).

(Dihydroxy Compound (A))
The "linking group -CH ₂ -O-" in the dihydroxy compound (A) means a structure which bonds with atoms other than hydrogen atoms 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 a carbon atom and an oxygen atom can be bonded simultaneously is preferably a carbon atom. The number of "linking groups -CH ₂ -O-" in the dihydroxy compound (A) is preferably 1 or more, more preferably 2 to 4.

Specific examples of 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)-3-cyclohexylphenyl)fluorene. compounds having an aromatic group in a side chain and an ether group bonded to the aromatic group in a 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, and 9,9-bis(4-(3-hydroxy-2,2-dimethylpropoxy)phenyl)fluorene; 1,1-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]-3,3,5-trimethylcyclohexane, 1,1-bis[4-(2-hydroxyethoxy)phenyl]- 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]butane, bis(hydroxyalkoxyaryl)alkanes, such as exemplified by 1,1-bis[4-(2-hydroxyethoxy)phenyl]cyclohexane, 1,1-bis[3-cyclohexyl-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, and 2,2-bis[3-cyclohexyl-4-(2-hydroxyethoxy)phenyl]propane; bis(hydroxyalkoxyaryl)cycloalkanes, such as 1,1-bis[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; 4,4'-bis(2-hydroxyethoxyphenyl)sulfide and 4,4'-bis[4-(2-dihydroxyethoxy)-3-methylphenyl]sulfide. bishydroxyalkoxyaryl sulfides such as 4,4'-bis(2-hydroxyethoxyphenyl)sulfoxide and 4,4'-bis[4-(2-dihydroxyethoxy)-3-methylphenyl]sulfoxide; bishydroxyalkoxyaryl sulfones such as 4,4'-bis(2-hydroxyethoxyphenyl)sulfone and 4,4'-bis[4-(2-dihydroxyethoxy)-3-methylphenyl]sulfone; bishydroxyalkoxyaryl sulfones such as 1,4-bishydroxyethoxybenzene; Examples of the dihydroxy compounds include hydroxyalkoxybenzenes; 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 those exemplified by the dihydroxy compounds represented by the following formula (2); and compounds having a cyclic ether structure such as those exemplified by the spiro glycol represented by the following general formula (3). The dihydroxy compounds (A) may be used alone or in combination.

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 isoidite, which are stereoisomeric, and these may be used alone or in combination of two or more.
Among the dihydroxy compounds (A), isosorbide obtained by dehydration condensation of sorbitol produced from various starches, which are abundant and easily available as resources, is most preferred in terms of availability, ease of production, optical properties, and moldability.

The ratio of the structural units derived from the dihydroxy compound (A) to the total structural units derived from the dihydroxy compound 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 ratio 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 ratio of the dihydroxy compound (A) is in the above range, the MIT bending number of the protective layer can be stably adjusted to the above range.

(Dihydroxy Compound (B))
As the dihydroxy compound that is a structural unit of the PC resin, the dihydroxy compound (B) can be used together with the dihydroxy compound (A). By using the dihydroxy compounds (A) and (B) in combination, the MIT bending number of the protective layer can be more stably adjusted to the above range.

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 compound (B) can be used alone or in combination.
Of the dihydroxy compounds (B), preferably, an alicyclic dihydroxy compound is used.

The alicyclic dihydroxy compound is not particularly limited, but preferably includes a compound that typically contains a 5-membered ring structure or a 6-membered ring structure. The 6-membered ring structure may be fixed to a chair or boat shape by a covalent bond. When the alicyclic dihydroxy compound has a 5-membered ring or a 6-membered ring structure, the heat resistance of the resulting PC resin can be improved. 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.

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).
HOCH ₂ -R ¹ -CH ₂ OH (I)
HO-R ² -OH (II)
(In formulas (I) and (II), R ¹ and R ² each represent a cycloalkylene group having 4 to 20 carbon atoms.)

Cyclohexanedimethanol ^, which is an alicyclic dihydroxy compound represented by the above general formula (I), includes various isomers represented by the following general formula (Ia) in which R ¹ in general formula (I) is 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.

Tricyclodecane dimethanol or pentacyclopentadecanedimethanol, which is an alicyclic dihydroxy compound represented by the above general formula (I), includes various isomers in which R ¹ in general formula (I) is represented by the following general formula (Ib) (wherein n is 0 or 1).

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

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

Adamantane dimethanol, which is an alicyclic dihydroxy compound represented by general formula (I), includes various isomers in which R ¹ in general formula (I) is represented by the following general formula (Ie), specifically, 1,3-adamantanedimethanol.

Cyclohexanediol, which is an alicyclic dihydroxy compound represented by the above general formula (II), includes various isomers represented by the following general formula (IIa) in which ^R2 in the general formula (II) is 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.

Tricyclodecanediol or pentacyclopentadecanediol, which is an alicyclic dihydroxy compound represented by the above general formula (II), includes various isomers in which ^R2 in the general formula (II) is represented by the following general formula (IIb) (wherein n is 0 or 1).

Decalindiol or tricyclotetradecanediol, which is an alicyclic dihydroxy compound represented by the above general formula (II), includes various isomers in which ^R2 in general formula (II) is represented by the following general formula (IIc) (wherein m is 0 or 1). Specific examples of such isomers include 2,6-decalindiol, 1,5-decalindiol, and 2,3-decalindiol.

Norbornanediol, which is an alicyclic dihydroxy compound represented by the above general formula (II), includes various isomers in which ^R2 in general formula (II) is represented by the following general formula (IId). Specific examples of such isomers include 2,3-norbornanediol and 2,5-norbornanediol.

The adamantanediol, which is an alicyclic dihydroxy compound represented by the above general formula (II), includes various isomers in which ^R2 in the general formula (II) is represented by the following general formula (IIe). A specific example of such an isomer is 1,3-adamantanediol.

Among the specific examples of the alicyclic dihydroxy compounds listed above, preferred are cyclohexane dimethanols, tricyclodecane dimethanols, adamantane diols, and pentacyclopentadecanedimethanols. From the viewpoints of availability and ease of handling, more preferred are 1,4-cyclohexane dimethanol, 1,3-cyclohexane dimethanol, 1,2-cyclohexane dimethanol, and tricyclodecane dimethanol, and even more preferred is tricyclodecane dimethanol.

The ratio of the structural units derived from dihydroxy compound (B) to the total 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 ratio of the 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.

Details of these PC resins are described, for example, in JP 2012-31370 A (Patent No. 5448264). The disclosure of this patent document is incorporated herein by reference.

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 together. When a PC resin containing these structural units is applied to a resin film, the MIT bending number of the protective layer can be more stably adjusted to the above range.
In such a PC resin, the molar ratio (A:B) of the structural unit derived from the dihydroxy compound (A) represented by the above formula (2) to the structural unit 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-based 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.

In addition to the resin material described above, the protective layer 1 may contain any suitable additive. Examples of the additive include antioxidants, UV absorbers, light stabilizers, nucleating agents, fillers, pigments, surfactants, and antistatic agents. Any suitable surface treatment layer may be provided on the surface of the protective layer 1 (the surface opposite 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.

The protective layer 1 typically has optical isotropy. In this specification, the term "optically isotropic" means that the in-plane retardation Re(550) and the retardation Rth(550) in the thickness direction 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 retardation Rth(550) in the thickness direction of the protective layer 1 is, for example, −10 nm to +10 nm, and preferably −5 nm to +5 nm.

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.

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

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.

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

The storage modulus (G') of the adhesive layer at 25°C is, for example, 0.01 MPa to 1.00 MPa, and 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 bendable or foldable image display device (particularly an organic EL display device) can be realized.

The adhesive constituting the adhesive layer may be, for example, a heat-curable adhesive or an active energy ray-curable adhesive, and 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 preferable.

E. Image Display Device In one embodiment, the polarizing plate described in any one of A to D above 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 of the illustrated example includes a polarizing plate 100 and a bendable image display panel 5 in this order.

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, preferably, the above-mentioned pressure-sensitive adhesive layer is used, and more preferably, a pressure-sensitive adhesive layer made of an acrylic pressure-sensitive adhesive is used.

In one embodiment, the thickness of the protective layer 1 of 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. If the thickness ratio between the protective layer and the image display panel is within this range, the image display device can be stably provided with suitable flexibility.

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

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

(1) MIT bending number of protective layer (resin film) In the examples and comparative examples, the resin film serving as the protective layer was subjected to an MIT test in accordance with JIS P 8115. Specifically, the resin film was cut into a length of 15 cm and a width of 1.5 cm to prepare a measurement sample. The measurement sample was attached to an MIT folding fatigue tester BE-202 type (manufactured by Tester Sangyo Co., Ltd.) (load 1.0 kgf, clamp R: 0.38 mm), and repeatedly bent at a test speed of 90 cpm and a bending angle of 90°, and the number of bending times at which the measurement sample broke was taken as the test value. The results are shown in Table 1.

(2) Loss tangent tan δ of 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 Measurement and Control Co., Ltd.). The results are shown in Table 1.
<Measurement conditions>
Measurement temperature: 85°C or 100°C
Measurement humidity: 85 RH% (relative humidity) ^{*Only at 85°C}
Mode: Tensile Frequency: 5Hz
Sample width: 5 mm
Chuck distance: 20 mm

(3) Flexibility of Organic EL Display Device The polarizing plates obtained in the examples and comparative examples were used as dummy bendable organic EL panels, and were attached with a transparent polyimide film (manufactured by KOLON, thickness 25 μm) using 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 sample was cut into a strip of 100 mm x 20 mm with the absorption axis direction of the polarizer as the long side. The cut sample was set in a no-load U-shaped stretch tester (Yuasa System Co., Ltd.'s "Small tabletop durability tester DLMD111LHA" and "U-shaped stretch test jig") so that the polarizer side was on 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
The number of bending times: 10,000 times. The bending property of the organic EL display device was then evaluated according to the following criteria. The results are shown in Table 1.
◯: No cracks in the polarizing plate.
x: Cracks occurred in the polarizing plate.

<<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 0.2% by mass aqueous solution of cesium carbonate as a catalyst were charged into a reaction vessel, and in a nitrogen atmosphere, the temperature of the heating vessel was heated to 150°C as the first step of the reaction, and the raw materials were dissolved while stirring as necessary (about 15 minutes). Next, the pressure was increased from normal pressure to 13.3 kPa, and the temperature of the heating vessel was increased to 190°C in 1 hour, while the generated phenol was extracted outside the reaction vessel. After the entire reaction vessel was held at 190°C for 15 minutes, the pressure in the reaction vessel was increased to 6.67 kPa, the temperature of the heating vessel was increased to 230°C in 15 minutes, and the generated phenol was extracted outside the reaction vessel as the second step. As the stirring torque of the stirrer increases, the temperature is raised to 250 ° C. in 8 minutes, and the pressure in the reaction vessel is allowed to reach 0.200 kPa or less in order to remove the phenol generated. After reaching a predetermined stirring torque, the reaction is terminated, and the reaction product is extruded into water to obtain pellets of PC resin. The obtained PC resin is vacuum-dried at 100 ° C. for 12 hours, and then a film-forming device 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 winder is used to produce a PC resin film having a thickness of 25 μm. The in-plane retardation Re (550) of the PC resin film was 3.0 nm.

<<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.

[Example 1]
As a thermoplastic resin substrate, a long amorphous isophthalic copolymerized polyethylene terephthalate film (thickness: 100 μm) having a Tg of about 75° C. was used, and one side of the resin substrate was subjected to a corona treatment.
A PVA aqueous solution (coating solution) was prepared by adding 13 parts by mass of potassium iodide to 100 parts by mass of a PVA-based resin prepared by mixing polyvinyl alcohol (polymerization degree 4,200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., product name "GOHSEFFIMER") in a ratio of 9:1, and dissolving the resultant in water.
The above PVA aqueous solution was applied to the corona-treated surface of a resin substrate and dried at 60° C. to form a PVA-based resin layer having a thickness of 13 μm, thereby producing a laminate.
The obtained laminate was uniaxially stretched 2.4 times in the longitudinal direction (machine 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) having 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) having 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 have a desired value (dyeing treatment).
Next, the piece was immersed in a crosslinking bath (a boric acid aqueous solution obtained by mixing 3 parts by mass of potassium iodide and 5 parts by mass of boric acid with respect to 100 parts by mass of water) at a liquid temperature of 40° C. for 30 seconds (crosslinking treatment).
Thereafter, the laminate was immersed in an aqueous boric acid 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 (an 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., while being brought into contact with a SUS heated roll 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 to each other using an adhesive (specifically, an active energy ray-curable adhesive), and the adhesive was cured by irradiation with ultraviolet rays.
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 with ultraviolet rays.
In this manner, a polarizing plate having a structure of first protective layer/polarizer/second protective layer was obtained.

[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 COP resin film having a thickness of 50 μm (manufactured by Zeon Corporation, product number ZF16).

[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 an acrylic resin film having a thickness of 25 μm (manufactured by Kaneka Corporation, product name "HTX-Z").

[Example 4]
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").

[Example 5]
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.

[Comparative Example 1]
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.

[evaluation]
As is clear from Table 1, when the protective layer is bent 200 times or more in the MIT test, it is found that by applying a polarizing plate having the protective layer to an organic EL display device, excellent flexibility can be imparted to the organic EL display device.

The polarizing plate of the present invention can be applied to image display devices, and is particularly suitable for use in bendable or foldable organic EL display devices.

REFERENCE SIGNS LIST 1 protective layer 2 polarizer 100 polarizing plate 200 image display device

Claims (3)

A polarizer;
a protective layer disposed on at least one side of the polarizer;
The number of flexions in an MIT test of the protective layer is 200 or more and 6000 or less,
The total light transmittance of the protective layer is 95% or more,
the protective layer contains a polycarbonate-based resin,
The polycarbonate resin is
A structural unit derived from a dihydroxy compound (A) represented by the following formula (2),
A structural unit derived from an alicyclic dihydroxy compound (B) represented by the following general formula (I),
and a carbonate group linking them .

HOCH ₂ -R ¹ -CH ₂ OH (I)
(In formula (I), R ¹ represents a cycloalkylene group having 4 to 20 carbon atoms.) An image display device comprising, in this order, the polarizing plate according to claim 1 and a bendable image display panel. 3. The image display device according to claim 2, wherein a ratio of a thickness of said protective layer to a thickness of said image display panel is 1 to 2.

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