JP7684181B2 - Polarizing plate with phase difference layer and image display device - Google Patents

Description

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

In image display devices, such as liquid crystal display devices, various optical films that combine a polarizer and a retardation film are generally used to compensate for optical characteristics suitable for the application. For example, a technology has been proposed in which a polarizing plate including a polarizer, a first retardation layer whose refractive index characteristics show the relationship of nz>nx>ny, and a second retardation layer whose refractive index characteristics show the relationship of nx>ny=nz are combined so that the absorption axis of the polarizer and the slow axis of the first retardation layer are perpendicular to each other and the absorption axis of the polarizer and the slow axis of the second retardation layer are parallel to each other, thereby widening the viewing angle (see, for example, Patent Document 1).
In recent years, the applications of image display devices have become more diverse. One example of such applications is an in-vehicle display. In-vehicle displays are particularly required to have a wide viewing angle in the horizontal direction (left-right direction). However, even if the technology described in Patent Document 1 is applied to an in-vehicle display, there is a limit to the wide viewing angle in the horizontal direction. In addition, there is a problem that the black display of the in-vehicle display is not sufficiently black (i.e., the black luminance is not sufficiently small) when viewed from an oblique direction (e.g., diagonally upward to the right) that intersects both the vertical and horizontal directions.

JP 2021-76759 A

The present invention has been made to solve the above-mentioned problems of the conventional art, and its main objective is to provide a polarizing plate with a retardation layer that can realize an image display device that can achieve a wide viewing angle in the horizontal direction (a specific surface direction of the image display surface) and can sufficiently reduce the black luminance in the diagonal direction that intersects both the vertical and horizontal directions.

The retardation layer-attached polarizing plate according to an embodiment of the present invention has a first polarizing plate including a first polarizer; a first retardation layer whose refractive index characteristics show a relationship of nz>nx>ny; and a second retardation layer whose refractive index characteristics show a relationship of nx>ny=nz. The first retardation layer is disposed adjacent to the first polarizing plate, and the second retardation layer is disposed adjacent to the first retardation layer. The absorption axis of the first polarizer and the slow axis of the first retardation layer are substantially perpendicular to each other, and the absorption axis of the first polarizer and the slow axis of the second retardation layer are substantially parallel. The in-plane retardation Re(550) of the first retardation layer is 280 nm or more and 360 nm or less, and the Nz coefficient of the first retardation layer is -1.0 or more and -0.1 or less. The in-plane retardation Re(550) of the second retardation layer is 280 nm or more and 360 nm or less.
An image display device according to another aspect of the present invention includes: an image display cell; and the above-described retardation layer-attached polarizing plate disposed on the opposite side to the viewing side with respect to the image display cell.
In one embodiment, the image display cell is a liquid crystal cell, and the driving mode of the liquid crystal cell is an IPS mode.
In one embodiment, the image display device includes a second polarizing plate disposed on the opposite side of the image display cell to the retardation layer-attached polarizing plate. The second polarizing plate includes a second polarizer. The absorption axis of the first polarizer is substantially perpendicular to the initial alignment direction of the liquid crystal cell, and the absorption axis of the second polarizer is substantially parallel to the initial alignment direction of the liquid crystal cell.

According to an embodiment of the present invention, it is possible to realize a polarizing plate with a retardation layer that can achieve a wide viewing angle in the horizontal direction (a specific surface direction of the image display surface) in an image display device and can sufficiently reduce the black luminance in the diagonal direction that intersects both the vertical and horizontal directions.

1 is a schematic cross-sectional view of a retardation layer-attached polarizing plate according to one embodiment of the present invention. 1 is a schematic cross-sectional view of an image display device according to one embodiment of the present invention. FIG. 4 is a luminance distribution diagram of the image display device according to the first embodiment when displaying black. FIG. 11 is a luminance distribution diagram of the image display device of Comparative Example 1 during black display.

Representative embodiments of the present invention are described below, but the present invention is not limited to these embodiments.

(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 retardation (Re) and front retardation (R ₀ )
"Re(λ)" is an in-plane retardation measured with light having a wavelength of λ nm at 23° C. For example, "Re(550)" is an in-plane retardation measured with light having a wavelength of 550 nm at 23° C. Incidentally, "in-plane retardation Re(550)" is sometimes referred to as "front retardation R ₀ ". 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).
(4) Nz Coefficient The Nz coefficient is calculated by Nz=Rth/Re.
(5) Substantially Parallel or Orthogonal The terms "substantially orthogonal" and "approximately orthogonal" include cases where the angle between two directions is 90°±10°, preferably 90°±7°, and more preferably 90°±5°. The terms "substantially parallel" and "approximately parallel" include cases where the angle between two directions is 0°±10°, preferably 0°±7°, and more preferably 0°±5°. Furthermore, when the terms "orthogonal" or "parallel" are used in this specification, they may include a substantially orthogonal or substantially parallel state.

A. Overall configuration of retardation layer-attached polarizing plate Fig. 1 is a schematic cross-sectional view of a retardation layer-attached polarizing plate according to one embodiment of the present invention. The retardation layer-attached polarizing plate 100 of the illustrated example has a first polarizing plate 10 including a first polarizer 11; a first retardation layer 20 having a refractive index characteristic of nz>nx>ny; and a second retardation layer 30 having a refractive index characteristic of nx>ny=nz.
The first retardation layer 20 is disposed adjacent to the first polarizing plate 10. The second retardation layer 30 is disposed adjacent to the first retardation layer 20. The second retardation layer 30 is located on the opposite side of the first retardation layer 20 to the first polarizing plate 10. In this specification, "disposed adjacent to" means that they are directly laminated or laminated only through an adhesive layer (e.g., an adhesive layer or a pressure-sensitive adhesive layer). That is, it means that no optical functional layer (e.g., another retardation layer) is interposed between the first polarizing plate 10 and the first retardation layer 20 and between the first retardation layer 20 and the second retardation layer 30.
The absorption axis (first absorption axis direction) of the first polarizer 11 and the slow axis (first slow axis direction) of the first retardation layer 20 are substantially perpendicular to each other. The absorption axis (first absorption axis direction) of the first polarizer 11 and the slow axis (second slow axis direction) of the second retardation layer 30 are substantially parallel to each other.
The in-plane retardation Re(550) of the first retardation layer 20 is 280 nm or more and 360 nm or less, preferably 290 nm or more and 350 nm or less, more preferably 300 nm or more and 340 nm or less, and further preferably 310 nm or more and 330 nm or less.
The Nz coefficient of the first retardation layer 20 is −1.0 or more and −0.1 or less, preferably −0.9 or more and −0.2 or less, more preferably −0.8 or more and −0.3 or less, and further preferably −0.8 or more and −0.6 or less.
The in-plane retardation Re(550) of the second retardation layer 30 is 280 nm or more and 360 nm or less, preferably 290 nm or more and 350 nm or less, more preferably 300 nm or more and 340 nm or less, and further preferably 310 nm or more and 330 nm or less.
When the Re(550) and Nz coefficient of the first retardation layer and the Re(550) of the second retardation layer each satisfy the above range, in an image display device equipped with a retardation layer-attached polarizing plate, it is possible to achieve a wide viewing angle in the horizontal direction (a predetermined surface direction of the image display surface), and to sufficiently reduce the black luminance in the oblique direction intersecting both the vertical and horizontal directions. That is, in an image display device equipped with a retardation layer-attached polarizing plate, it is possible to make the viewing angle in the horizontal direction (for example, the first surface direction X of the image display device shown in FIG. 3) wider than the viewing angle in the vertical direction (for example, the second surface direction Y perpendicular to the first surface direction X shown in FIG. 3), and it is possible to sufficiently reduce the black luminance when the black display of the image display device is viewed from an oblique direction intersecting both the horizontal direction (first surface direction X) and the vertical direction (second surface direction Y).
More specifically, the luminance of the black display of the image display device measured by any appropriate luminance meter at a polar angle of 40° to 42° and at azimuth angles of 20° to 25°, 155° to 160°, 190° to 195°, and 345° to 350° is, for example, 0.00074 or less, preferably 0.00070 or less, and more preferably 0.00068 or less. In this specification, the luminance measured in the above polar angle and azimuth angle ranges is referred to as area A luminance. The lower limit of area A luminance is typically 0.00001 or more.

In one embodiment, the Nz coefficient of the second retardation layer 30 is, for example, 0.5 to 1.5, preferably 0.6 to 1.4, more preferably 0.7 to 1.3, and even more preferably 0.8 to 1.2. When the Nz coefficient of the second retardation layer is in such a range, in an image display device equipped with a retardation layer-attached polarizing plate, a wide viewing angle in the horizontal direction (a specific surface direction of the image display surface) can be stably achieved, and the black luminance in the diagonal direction intersecting both the vertical and horizontal directions can be stably reduced.

The polarizing plate with a retardation layer may further have a conductive layer or a conductive layer-attached isotropic substrate (not shown). The conductive layer or the conductive layer-attached isotropic substrate is typically provided on the outside of the second retardation layer (opposite the first polarizing plate). When a conductive layer or a conductive layer-attached isotropic substrate is provided, the polarizing plate with a retardation layer can be applied to a so-called inner touch panel type input display device in which a touch sensor is incorporated between an image display cell (e.g., a liquid crystal cell, an organic EL cell) and the first polarizing plate.

The polarizing plate with a retardation layer may further include other retardation layers. The optical properties (e.g., refractive index properties, in-plane retardation, Nz coefficient, photoelastic coefficient), thickness, arrangement position, etc. of the other retardation layers can be appropriately set according to the purpose.

The polarizing plate with a retardation layer may be in the form of a sheet or a long sheet. In this specification, "long sheet" means a long and narrow shape whose length is sufficiently longer than its width, and includes, for example, a long and narrow shape whose length is 10 times or more, preferably 20 times or more, larger than its width. A long polarizing plate with a retardation layer can be wound into a roll.

For practical purposes, an adhesive layer (not shown) is provided on the side of the second retardation layer opposite the first polarizing plate, so that the retardation layer-attached polarizing plate can be attached to an image display cell. Furthermore, it is preferable that a release liner is temporarily attached to the surface of the adhesive layer until the retardation layer-attached polarizing plate is used. By temporarily attaching the release liner, the adhesive layer is protected and roll formation is possible.

B. Overall Configuration of Image Display Device FIG. 2 is a schematic cross-sectional view of an image display device according to one embodiment of the present invention. The image display device 101 in the illustrated example includes an image display cell 60 and a retardation layer-attached polarizing plate 100 arranged on the opposite side of the viewing side with respect to the image display cell 60. In the image display device 101, the first retardation layer 20 is located between the first polarizing plate 10 and the image display cell 60, and the second retardation layer 30 is located between the first retardation layer 20 and the image display cell 60.

The image display device 101 in the illustrated example further includes a second polarizing plate 40 arranged on the opposite side (viewing side) of the retardation layer-attached polarizing plate 100 with respect to the image display cell 60. The second polarizing plate 40 includes a second polarizer 41.

The image display cell 60 is typically a liquid crystal cell 60a, and the image display device 101 is typically a liquid crystal display device. The liquid crystal display device is typically a so-called E mode. An "E mode liquid crystal display device" refers to a device in which the absorption axis (first absorption axis direction) of a polarizer (in this embodiment, the first polarizer 11) arranged on the opposite side (back side) of the viewing side of the liquid crystal cell is substantially perpendicular to the initial alignment direction of the liquid crystal cell. The "initial alignment direction of the liquid crystal cell" refers to the direction in which the in-plane refractive index of the liquid crystal layer, which is generated as a result of the alignment of the liquid crystal molecules contained in the liquid crystal layer described later, becomes maximum in the absence of an electric field (i.e., the slow axis direction).

In one embodiment, the absorption axis (second absorption axis direction) of the polarizer (in this embodiment, the second polarizer 41) arranged on the viewing side of the liquid crystal cell is substantially parallel to the initial alignment direction of the liquid crystal cell. That is, in the image display device 101, the absorption axis direction of the first polarizer 11 and the absorption axis direction of the second polarizer 41 are typically substantially perpendicular to each other. With this configuration, excellent visibility can be achieved even when the display screen is viewed through polarized lenses such as polarized sunglasses.

For practical purposes, the image display device 101 further includes a backlight unit 90. The backlight unit 90 includes a light source 91 and a light guide plate 92. The backlight unit 90 may further include any other appropriate members (e.g., a diffusion sheet, a prism sheet). In the illustrated example, the backlight unit 90 is of an edge light type, but any other appropriate type (e.g., a direct type) may be adopted as the backlight unit 90.

The image display device (liquid crystal display device) may further include any other appropriate members. For example, another optical compensation layer (retardation layer) may be further disposed. The optical properties, number, combination, arrangement position, etc. of the other optical compensation layer may be appropriately selected according to the purpose and desired optical properties, etc. For matters not described in this specification, the configuration of an image display device (liquid crystal display device) that is well known and commonly used in the industry may be adopted.

Such an image display device is suitable for use in applications where a wide horizontal viewing angle and reduced area A luminance during black display are particularly required (particularly applications where high definition is required and the screen may be shared by multiple people). Representative examples of image display devices include in-vehicle displays, medical monitors, and gaming monitors, with in-vehicle displays being particularly preferred.

Below, we will explain each component that makes up the retardation layer-attached polarizing plate and the image display device.

C. Polarizing Plate C-1. Polarizer Any appropriate polarizer may be adopted as the first polarizer 11 included in the first polarizing plate 10 and the second polarizer 41 included in the second polarizing plate 40 (hereinafter, they may be collectively referred to as polarizers). For example, the resin film forming the polarizer may be a single-layer resin film or 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 iodine or a dichroic substance such as a dichroic dye and stretched, and polyene-based oriented films such as dehydrated PVA and dehydrochlorinated polyvinyl chloride. Preferably, a polarizer obtained by dyeing a PVA-based film with iodine and stretching it uniaxially is used because of its excellent optical properties.

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 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.

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 a resin substrate and a PVA-based resin layer; and stretching and dyeing the laminate to make the PVA-based resin layer into a polarizer. In this embodiment, stretching typically includes immersing the laminate in an aqueous solution of boric acid and stretching it. Furthermore, stretching may further include air-stretching the laminate at a high temperature (e.g., 95°C or higher) before stretching in the aqueous solution of boric acid, as necessary. The obtained resin substrate/polarizer laminate may be used as is (i.e., the resin substrate may be used as a protective layer for the polarizer), or the resin substrate may be peeled off from the resin substrate/polarizer laminate, and any suitable protective layer may be laminated on the peeled surface depending on the purpose. Details of the method for producing such a polarizer are described in, for example, JP-A-2012-73580 and Japanese Patent No. 6,470,455. The entire disclosures of these publications are incorporated herein by reference.

The thickness of the polarizer is, for example, 1 μm to 80 μm, preferably 1 μm to 15 μm, more preferably 1 μm to 12 μm, even more preferably 3 μm to 12 μm, and particularly preferably 3 μm to 8 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 preferably exhibits absorption dichroism at any wavelength between 380 nm and 780 nm. The single transmittance of the polarizer 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 is preferably 97.0% or more, more preferably 99.0% or more, and even more preferably 99.9% or more.

C-2. Protective layer Each of the first polarizing plate 10 and the second polarizing plate 40 may further include a protective layer. The protective layer may be provided on at least one surface of the polarizer, or may be provided on both surfaces of the polarizer. In the image display device 101, the first polarizing plate 10 includes a protective layer 12 provided on the surface opposite to the viewing side of the first polarizer 11, and the second polarizing plate 40 includes a protective layer 42 provided on the viewing side surface of the second polarizer 41.

The protective layer is formed of any suitable film that can be used as a protective layer for a polarizer. Specific examples of materials that are the main components of the film include cellulose-based resins such as triacetyl cellulose (TAC), and transparent resins such as polyesters, polyvinyl alcohols, polycarbonates, polyamides, polyimides, polyethersulfones, polysulfones, polystyrenes, polynorbornenes, polyolefins, (meth)acrylics, and acetates. Other examples include thermosetting resins or ultraviolet-curing resins such as (meth)acrylics, urethanes, (meth)acrylic urethanes, epoxy resins, and silicones. Other examples include glassy polymers such as siloxane polymers. Polymer films described in JP 2001-343529 A (WO01/37007) can also be used. The material for this film can be, 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, such as a resin composition having an alternating copolymer of isobutene and N-methylmaleimide, and an acrylonitrile-styrene copolymer. The polymer film can be, for example, an extrusion molded product of the above resin composition.

When the polarizer arranged on the viewing side of the image display cell 60 has a protective layer located on the outermost surface of the image display device, the protective layer may be subjected to surface treatment such as hard coat treatment, anti-reflection treatment, anti-sticking treatment, and anti-glare treatment, as necessary.

The thickness of the protective layer is typically 5 mm or less, preferably 1 mm or less, more preferably 1 μm to 500 μm, and even more preferably 5 μm to 150 μm. If a surface treatment has been applied, the thickness of the protective layer includes the thickness of the surface treatment layer.

D. First Retardation Layer The first retardation layer 20 has a refractive index characteristic of nz>nx>ny as described above. A layer (film) exhibiting such refractive index characteristics may be called a "positive biaxial plate" or a "positive B plate".

The thickness of the first retardation layer is typically 3 μm or more, preferably 5 μm or more, and typically 30 μm or less, preferably 20 μm or less, and more preferably 15 μm or less. By having the thickness of the first retardation layer within such a range, the handling during manufacturing is excellent, and the optical uniformity of the obtained image display device can be improved.

The first retardation layer may have any appropriate configuration. Specifically, it may be a retardation film alone, or may be a laminate of two or more identical or different retardation films. When it is a laminate, the first retardation layer may include a pressure-sensitive adhesive layer or an adhesive layer for adhering two or more retardation films. Preferably, the first retardation layer is a single retardation film. By adopting such a configuration, it is possible to reduce the shift or unevenness of the retardation value due to the shrinkage stress of the polarizer and/or the heat of the light source, and it is also possible to contribute to making the image display device obtained thinner.

The optical characteristics of the retardation film can be set to any appropriate value depending on the configuration of the first retardation layer. For example, when the first retardation layer is a retardation film alone, it is preferable that the optical characteristics of the retardation film are equal to the optical characteristics of the first retardation layer. Therefore, it is preferable that the retardation value of the pressure-sensitive adhesive layer, adhesive layer, etc. used when laminating the retardation film to the polarizer and/or the second retardation layer, etc. is as small as possible.

As the retardation film, a film that is excellent in transparency, mechanical strength, thermal stability, moisture shielding properties, etc., and is unlikely to cause optical unevenness due to distortion is preferably used. As the retardation film, a stretched film of a polymer film mainly composed of a thermoplastic resin is preferably used. As the thermoplastic resin, a polymer exhibiting negative birefringence is preferably used. By using a polymer exhibiting negative birefringence, a retardation film having an index ellipsoid of nz>nx>ny can be easily obtained. Here, "exhibiting negative birefringence" means that when a polymer is oriented by stretching, etc., the refractive index in the stretching direction becomes relatively small. In other words, it means that the refractive index in the direction perpendicular to the stretching direction becomes large. Examples of polymers exhibiting negative birefringence include polymers in which chemical bonds or functional groups with large polarization anisotropy, such as aromatic rings or carbonyl groups, are introduced into the side chains. Specifically, acrylic resins, styrene resins, maleimide resins, etc. are mentioned.

The acrylic resin can be obtained, for example, by addition polymerization of acrylate monomers. Examples of acrylic resins include polymethyl methacrylate (PMMA), polybutyl methacrylate, and polycyclohexyl methacrylate.

The styrene-based resin can be obtained, for example, by addition polymerization of a styrene-based monomer. Examples of the styrene-based monomer include styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, p-chlorostyrene, p-nitrostyrene, p-aminostyrene, p-carboxystyrene, p-phenylstyrene, 2,5-dichlorostyrene, and p-t-butylstyrene.

The maleimide resin can be obtained, for example, by addition polymerization of a maleimide monomer. Examples of the maleimide monomer include N-ethylmaleimide, N-cyclohexylmaleimide, N-phenylmaleimide, N-(2-methylphenyl)maleimide, N-(2-ethylphenyl)maleimide, N-(2-propylphenyl)maleimide, N-(2-isopropylphenyl)maleimide, N-(2,6-dimethylphenyl)maleimide, N-(2,6-dipropylphenyl)maleimide, N-(2,6-diisopropylphenyl)maleimide, N-(2-methyl-6-ethylphenyl)maleimide, N-(2-chlorophenyl)maleimide, N-(2,6-dichlorophenyl)maleimide, N-(2-bromophenyl)maleimide, N-(2,6-dibromophenyl)maleimide, N-(2-biphenyl)maleimide, and N-(2-cyanophenyl)maleimide. Maleimide monomers can be obtained, for example, from Tokyo Chemical Industry Co., Ltd.

In the above addition polymerization, the birefringence properties of the resulting resin can be controlled by substituting the side chains after polymerization, or by carrying out maleimidization or grafting reactions.

The polymer exhibiting negative birefringence may be copolymerized with other monomers. By copolymerizing other monomers, brittleness, moldability, and heat resistance can be improved. Examples of such other monomers include olefins such as ethylene, propylene, 1-butene, 1,3-butadiene, 2-methyl-1-butene, 2-methyl-1-pentene, and 1-hexene; acrylonitrile; (meth)acrylates such as methyl acrylate and methyl methacrylate; maleic anhydride; and vinyl esters such as vinyl acetate.

When the polymer exhibiting negative birefringence is a copolymer of the styrene monomer and the other monomer, the blending ratio of the styrene monomer is preferably 50 mol% to 80 mol%. When the polymer exhibiting negative birefringence is a copolymer of the maleimide monomer and the other monomer, the blending ratio of the maleimide monomer is preferably 2 mol% to 50 mol%. By blending in such a range, a polymer film with excellent toughness and moldability can be obtained.

Preferably, the polymer exhibiting the negative birefringence is a styrene-maleic anhydride copolymer, a styrene-acrylonitrile copolymer, a styrene-(meth)acrylate copolymer, a styrene-maleimide copolymer, a vinyl ester-maleimide copolymer, an olefin-maleimide copolymer, or the like. These may be used alone or in combination of two or more. These polymers exhibit high negative birefringence and may have excellent heat resistance. These polymers are available, for example, from Nova Chemical Japan and Arakawa Chemical Industries Co., Ltd.

As the polymer exhibiting negative birefringence, a polymer having a repeating unit represented by the following general formula (I) is preferably used. Such a polymer exhibits even higher negative birefringence and can have excellent heat resistance and mechanical strength. Such a polymer can be obtained, for example, by using an N-phenyl-substituted maleimide in which a phenyl group having a substituent at least at the ortho position is introduced as the N-substituent of the maleimide monomer as the starting material.

In the above general formula (I), R ₁ to R ₅ each independently represent hydrogen, a halogen atom, a carboxylic acid, a carboxylate, a hydroxyl group, a nitro group, or a linear or branched alkyl or alkoxy group having 1 to 8 carbon atoms (provided that R ₁ and R ₅ are not simultaneously hydrogen atoms), R ₆ and R ₇ represent hydrogen or a linear or branched alkyl or alkoxy group having 1 to 8 carbon atoms, and n represents an integer of 2 or greater.

The polymer exhibiting negative birefringence is not limited to the above, and for example, a cyclic olefin copolymer as disclosed in JP-A-2005-350544 can also be used. Furthermore, compositions containing a polymer and inorganic fine particles as disclosed in JP-A-2005-156862, JP-A-2005-227427, etc. can also be suitably used. Furthermore, as the polymer exhibiting negative birefringence, one type may be used alone, or two or more types may be used in combination. Furthermore, these may be modified by copolymerization, branching, crosslinking, molecular end modification (or sealing), stereoregular modification, etc. before use.

The polymer film may further contain any suitable additives as necessary. Specific examples of additives include plasticizers, heat stabilizers, light stabilizers, lubricants, antioxidants, UV absorbers, flame retardants, colorants, antistatic agents, compatibilizers, crosslinking agents, and thickeners. The type and content of additives may be appropriately set depending on the purpose. The content of additives is typically about 3 to 10 parts by mass per 100 parts by mass of the total solid content of the polymer film. If the content of additives is excessively high, the transparency of the polymer film may be impaired or the additives may bleed from the surface of the polymer film.

Any suitable molding method can be used as the molding method for the polymer film. Examples include compression molding, transfer molding, injection molding, extrusion molding, blow molding, powder molding, FRP molding, and solvent casting. Among these, extrusion molding and solvent casting are preferably used. This is because a retardation film having high smoothness and good optical uniformity can be obtained. Specifically, the extrusion molding method is a method in which a resin composition containing the above-mentioned thermoplastic resin, plasticizer, additives, etc. is heated and melted, and then extruded into a thin film on the surface of a casting roll using a T-die or the like, and cooled to form a film. The solvent casting method is a method in which a concentrated solution (dope) in which the resin composition is dissolved in a solvent is degassed, and cast into a uniform thin film on the surface of a metallic endless belt or rotating drum, or a plastic substrate, etc., and the solvent is evaporated to form a film. The molding conditions can be appropriately set depending on the composition and type of the resin used, the molding method, etc.

The retardation film (stretched film) can be obtained by stretching the polymer film under any appropriate stretching conditions.
Specific examples of the stretching method include a longitudinal uniaxial stretching method, a transverse uniaxial stretching method, a longitudinal and transverse sequential biaxial stretching method, and a longitudinal and transverse simultaneous biaxial stretching method. Preferably, a transverse uniaxial stretching method, a longitudinal and transverse sequential biaxial stretching method, and a longitudinal and transverse simultaneous biaxial stretching method are used. This is because a biaxial retardation film can be suitably obtained. In the polymer exhibiting the above negative birefringence, the refractive index in the stretching direction is relatively small as described above, so in the case of the transverse uniaxial stretching method, the polymer film has a slow axis in the transport direction (the refractive index in the transport direction is nx). In the case of the longitudinal and transverse sequential biaxial stretching method and the longitudinal and transverse simultaneous biaxial stretching method, both the transport direction and the width direction can be the slow axis depending on the ratio of the longitudinal and transverse stretching ratios. Specifically, when the stretching ratio in the longitudinal (transport) direction is relatively large, the transverse (width) direction becomes the slow axis, and when the stretching ratio in the transverse (width) direction is relatively large, the longitudinal (transport) direction becomes the slow axis.
Any suitable stretching device may be used for the stretching. Specific examples include a roll stretching machine, a tenter stretching machine, and a pantograph-type or linear motor-type biaxial stretching machine. When stretching is performed while heating, the temperature may be changed continuously or stepwise. The stretching process may be divided into two or more steps.

In addition, by adjusting the thickness of the polymer film (thickness of the original film), the stretching temperature and the stretching ratio, the Re(550) and the Nz coefficient of the first retardation layer can be adjusted to be within the above-mentioned range.
The thickness of the polymer film (original thickness) is typically 30 μm or more, preferably 40 μm or more, more preferably 80 μm or more, and typically 300 μm or less, preferably 200 μm or less, more preferably 120 μm or less.

The stretching temperature (the temperature in the stretching oven when stretching the polymer film) is preferably near the glass transition temperature (Tg) of the polymer film. Specifically, it is preferably (Tg-10)°C to (Tg+30)°C, more preferably Tg to (Tg+25)°C, and particularly preferably (Tg+5)°C to (Tg+20)°C. If the stretching temperature is too low, the retardation value and the direction of the slow axis may become nonuniform, or the polymer film may crystallize (become cloudy). On the other hand, if the stretching temperature is too high, the polymer film may melt or the retardation may not be fully expressed. The stretching temperature is typically 110 to 200°C. The glass transition temperature can be determined by DSC in accordance with JIS K7121-1987.

Any appropriate method can be used to control the temperature inside the stretching oven. For example, there are methods using an air-circulating thermostatic oven in which hot or cold air is circulated, a heater using microwaves or far infrared rays, a roll heated for temperature control, a heat pipe roll, or a metal belt.

The stretching ratio when stretching a polymer film can be set to any appropriate value depending on the composition of the polymer film, the type of volatile components, etc., the residual amount of volatile components, etc., the desired retardation value, etc. It is preferably 1.05 to 5.00 times, and more preferably 2.45 to 5.00 times. In addition, the feed speed during stretching is preferably 0.5 m/min to 20 m/min from the viewpoint of the mechanical accuracy and stability of the stretching device, etc.

Although the method for obtaining a retardation film using a polymer exhibiting negative birefringence has been described above, a retardation film can also be obtained using a polymer exhibiting positive birefringence. As a method for obtaining a retardation film using a polymer exhibiting positive birefringence, for example, a stretching method for increasing the refractive index in the thickness direction, such as those disclosed in JP-A-2000-231016, JP-A-2000-206328, and JP-A-2002-207123, can be used. Specifically, a method in which a heat-shrinkable film is adhered to one or both sides of a film containing a polymer exhibiting positive birefringence and a heat treatment is performed can be mentioned. The film is shrunk under the action of the shrinking force of the heat-shrinkable film by the heat treatment, and the film is shrunk in the length direction and width direction, so that the refractive index in the thickness direction can be increased, and a retardation film having an index ellipsoid of nz>nx>ny can be obtained.

In this way, the positive B plate used in the first retardation layer can be manufactured using a polymer that exhibits either positive or negative birefringence. In general, the use of a polymer that exhibits positive birefringence has the advantage that there are many types of polymers to choose from, and the use of a polymer that exhibits negative birefringence has the advantage that a retardation film with excellent uniformity in the slow axis direction can be easily obtained due to the stretching method, compared to the use of a polymer that exhibits positive birefringence.

In addition to the above-mentioned films, commercially available optical films can be used as the retardation film for the first retardation layer. In addition, commercially available optical films that have been subjected to secondary processing such as stretching and/or relaxation can also be used.

The light transmittance of the above retardation film at a wavelength of 550 nm is preferably 80% or more, more preferably 85% or more, and particularly preferably 90% or more. The theoretical upper limit of light transmittance is 100%, but since surface reflection occurs due to the refractive index difference between air and the retardation film, the upper limit of light transmittance that can be realized is approximately 94%. It is preferable that the first retardation layer as a whole has a similar light transmittance.

The absolute value of the photoelastic coefficient of the retardation film is preferably 1.0×10 ⁻¹⁰ (m ² /N) or less, more preferably 5.0×10 ⁻¹¹ (m ² /N) or less, even more preferably 3.0×10 ⁻¹¹ (m ² /N) or less, and particularly preferably 1.5×10 ⁻¹¹ (m ² /N) or less. By setting the photoelastic coefficient in such a range, an image display device having excellent optical uniformity, small changes in optical properties even in high temperature and high humidity environments, and excellent durability can be obtained. The lower limit of the photoelastic coefficient is not particularly limited, but is generally 5.0×10 ⁻¹³ (m ² /N) or more, preferably 1.0×10 ⁻¹² (m ² /N) or more. If the photoelastic coefficient is excessively small, the expression of retardation may be reduced. The photoelastic coefficient is a value inherent to the chemical structure of a polymer or the like, but the photoelastic coefficient can be reduced by copolymerizing or mixing a plurality of components with photoelastic coefficients of different signs (positive or negative).

E. Second retardation layer As described above, the second retardation layer 30 has a refractive index characteristic of nx>ny=nz. A layer (film) that exhibits such a refractive index characteristic may be called a "positive uniaxial plate", a "positive A plate", etc. Here, "ny=nz" includes not only the case where ny and nz are strictly equal, but also the case where ny and nz are substantially equal. Specifically, it means that the Nz coefficient is greater than 0.9 and less than 1.1.

As the material for forming the second retardation layer, any appropriate material may be used as long as the above-mentioned characteristics are obtained. Specifically, the second retardation layer may be a layer of a liquid crystal compound with a solidified orientation (liquid crystal alignment solidified layer) or a retardation film (a stretched film of a polymer film).

When the second retardation layer is a liquid crystal alignment solidified layer, the difference between nx and ny of the obtained retardation layer can be significantly increased compared to non-liquid crystal materials by using a liquid crystal compound, and therefore the thickness of the retardation layer for obtaining a desired in-plane retardation can be significantly reduced. As a result, a polarizing plate with a retardation layer (and, as a result, an image display device) can be further thinned. In this specification, the "alignment solidified layer" refers to a layer in which the liquid crystal compound is aligned in a predetermined direction within the layer and the alignment state is fixed. Note that the "alignment solidified layer" is a concept that includes an alignment hardened layer obtained by hardening a liquid crystal monomer as described later. In this embodiment, typically, rod-shaped liquid crystal compounds are aligned in the slow axis direction of the second retardation layer (homogeneous alignment).

An example of a liquid crystal compound is a liquid crystal compound whose liquid crystal phase is a nematic phase (nematic liquid crystal). For example, a liquid crystal polymer or a liquid crystal monomer can be used as such a liquid crystal compound. The mechanism by which the liquid crystallinity of the liquid crystal compound is expressed may be either lyotropic or thermotropic. The liquid crystal polymer and the liquid crystal monomer may be used alone or in combination.

When the liquid crystal compound is a liquid crystal monomer, it is preferably, for example, a polymerizable monomer and/or a crosslinkable monomer. This is because the orientation state of the liquid crystal monomer can be fixed by polymerizing or crosslinking the liquid crystal monomer. After the liquid crystal monomer is aligned, for example, the liquid crystal monomers can be polymerized or crosslinked with each other, thereby fixing the above-mentioned orientation state. Here, a polymer is formed by polymerization, and a three-dimensional network structure is formed by crosslinking, but these are non-liquid crystal. Therefore, the formed second retardation layer does not undergo, for example, a transition to a liquid crystal phase, a glass phase, or a crystalline phase due to a temperature change specific to a liquid crystal compound. As a result, the formed second retardation layer becomes a retardation layer that is not affected by temperature changes and has extremely excellent stability.

Specific examples of liquid crystal compounds and details of the method for forming the liquid crystal alignment solidified layer are described, for example, in JP-A-2006-163343 and JP-A-2006-178389. The descriptions in these publications are incorporated herein by reference.

The second retardation layer may be a stretched film of a polymer film as described above. Specifically, by appropriately selecting the type of polymer, stretching conditions (e.g., stretching temperature, stretching ratio, stretching direction), and stretching method (e.g., horizontal uniaxial stretching), the second retardation layer having the desired optical properties (e.g., refractive index characteristics, in-plane retardation, thickness direction retardation) can be obtained. In particular, by adjusting the thickness (original thickness), stretching temperature and stretching ratio of the polymer film, the Re (550) of the second retardation layer can be adjusted to the above range.
The thickness of the polymer film (original thickness) is typically 10 μm or more, preferably 15 μm or more, and typically 50 μm or less, preferably 40 μm or less, more preferably 30 μm or less.
The stretching temperature is preferably 110° C. to 170° C., more preferably 130° C. to 150° C. The stretching ratio is preferably 1.37 times to 3.00 times, more preferably 1.60 times to 2.50 times.

Any suitable resin may be used as the resin forming the polymer film. Specific examples include resins that form positive birefringence films, such as norbornene-based resins, polycarbonate-based resins, cellulose-based resins, polyvinyl alcohol-based resins, and polysulfone-based resins. Of these, norbornene-based resins and polycarbonate-based resins are preferred.

The norbornene-based resin is a resin polymerized using norbornene-based monomers as polymerization units. Examples of the norbornene-based monomers include norbornene and its alkyl and/or alkylidene substituted derivatives, such as 5-methyl-2-norbornene, 5-dimethyl-2-norbornene, 5-ethyl-2-norbornene, 5-butyl-2-norbornene, 5-ethylidene-2-norbornene, and polar group substituted derivatives thereof, such as halogen; dicyclopentadiene, 2,3-dihydrodicyclopentadiene, and the like; dicyclopentadiene, 2,3-dihydrodicyclopentadiene, and the like; Octahydronaphthalene, its alkyl and/or alkylidene substituted derivatives, and polar group substituted derivatives such as halogen, for example, 6-methyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-ethyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-ethylidene-1,4:5,8-dimethano-1,4,4a,5,6,7 ,8,8a-octahydronaphthalene, 6-chloro-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-cyano-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-pyridyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-methoxycarbonyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene norbornene-1,4,4a,5,6,7,8,8a-octahydronaphthalene; trimers and tetramers of cyclopentadiene, such as 4,9:5,8-dimethano-3a,4,4a,5,8,8a,9,9a-octahydro-1H-benzoindene and 4,11:5,10:6,9-trimethano-3a,4,4a,5,5a,6,9,9a,10,10a,11,11a-dodecahydro-1H-cyclopentaanthracene. The norbornene-based resin may be a copolymer of a norbornene-based monomer and another monomer.

As the polycarbonate resin, an aromatic polycarbonate is preferably used. Aromatic polycarbonate can be obtained, typically, by reacting a carbonate precursor with an aromatic dihydric phenol compound. Specific examples of carbonate precursors include phosgene, bischloroformates of dihydric phenols, diphenyl carbonate, di-p-tolyl carbonate, phenyl-p-tolyl carbonate, di-p-chlorophenyl carbonate, and dinaphthyl carbonate. Among these, phosgene and diphenyl carbonate are preferred. Specific examples of aromatic dihydric phenol compounds include 2,2-bis(4-hydroxyphenyl)propane, 2,2-bis(4-hydroxy-3,5-dimethylphenyl)propane, bis(4-hydroxyphenyl)methane, 1,1-bis(4-hydroxyphenyl)ethane, 2,2-bis(4-hydroxyphenyl)butane, 2,2-bis(4-hydroxy-3,5-dimethylphenyl)butane, 2,2-bis(4-hydroxy-3,5-dipropylphenyl)propane, 1,1-bis(4-hydroxyphenyl)cyclohexane, and 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane. These may be used alone or in combination of two or more. Preferably, 2,2-bis(4-hydroxyphenyl)propane, 1,1-bis(4-hydroxyphenyl)cyclohexane, and 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane are used. In particular, it is preferable to use 2,2-bis(4-hydroxyphenyl)propane and 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane together.

The second retardation layer is preferably a stretched polymer film, and more preferably a stretched norbornene resin film.
The thickness of the second retardation layer can be set so as to obtain desired optical characteristics. When the second retardation layer is a liquid crystal alignment solidified layer, the thickness is preferably 0.5 μm to 10 μm, more preferably 0.5 μm to 8 μm, and even more preferably 0.5 to 5 μm. When the second retardation layer is a stretched film of a polymer film, the thickness is preferably 5 μm to 55 μm, more preferably 10 μm to 50 μm, and even more preferably 15 μm to 45 μm.

F. Laminate of the First Retardation Layer and the Second Retardation Layer The laminate of the first retardation layer and the second retardation layer preferably satisfies the following relationship:
Re(450)/Re(550)>0.82
Re(650)/Re(550)<1.18.
The Re(450)/Re(550) of the laminate is more preferably 1.0 to 1.2, and even more preferably 1.0 to 1.1. The Re(650)/Re(550) of the laminate is more preferably 0.8 to 1.0, and even more preferably 0.9 to 1.0. According to the embodiment of the present invention, it is possible to obtain a retardation layer-attached polarizing plate capable of realizing an image display device having small luminance in an oblique direction during black display and small color shift in an oblique direction, even though the first retardation layer and the second retardation layer do not show ideal reverse dispersion characteristics as a whole.

G. Liquid crystal cell The liquid crystal cell 60a has a first substrate 62, a second substrate 63, and a liquid crystal layer 61 sandwiched between them and containing liquid crystal molecules aligned in a homogeneous arrangement in the absence of an electric field. In a typical configuration, one substrate (typically, the first substrate 62) is provided with a color filter and a black matrix, and the other substrate (typically, the second substrate 63) is provided with switching elements for controlling the electro-optical properties of the liquid crystal, scanning lines for providing gate signals to the switching elements, signal lines for providing source signals, pixel electrodes, and counter electrodes. The spacing (cell gap) between the substrates is controlled by spacers or the like. An alignment film made of, for example, polyimide, can be provided on the side of the substrate that contacts the liquid crystal layer.

The Rth(550) of the first substrate 62 and the second substrate 63 is -10 nm to 100 nm. In one embodiment, the Rth(550) of at least one of the first substrate 62 and the second substrate 63 is preferably 8 nm to 90 nm, more preferably 15 nm to 80 nm. In another embodiment, the Rth(550) of at least one of the first substrate 62 and the second substrate 63 is preferably -0.1 nm or less, more preferably -5 nm to -50 nm. According to an embodiment of the present invention, when the substrate has such a thickness direction retardation, the black luminance in the oblique direction can be sufficiently reduced in a liquid crystal display device including a homogeneously aligned liquid crystal cell.

In one embodiment, at least one of the first substrate 62 and the second substrate 63 satisfies the relationship Rth(450)>Rth(550), and preferably, both the first substrate 62 and the second substrate 63 satisfy the relationship Rth(450)>Rth(550). More preferably, at least one of the first substrate 62 and the second substrate 63 further satisfies the relationship Rth(550)>Rth(650), and even more preferably, both the first substrate 62 and the second substrate 63 further satisfies the relationship Rth(550)>Rth(650). According to an embodiment of the present invention, even if the substrate has such wavelength dispersion characteristics, the black luminance in the oblique direction can be sufficiently reduced in a liquid crystal display device including a homogeneously aligned liquid crystal cell.

As described above, the liquid crystal layer 61 contains liquid crystal molecules aligned in a homogeneous arrangement in the absence of an electric field. "Liquid crystal molecules aligned in a homogeneous arrangement" refers to a state in which the alignment vector of the liquid crystal molecules is aligned parallel and uniformly to the substrate plane as a result of the interaction between the alignment-treated substrate and the liquid crystal molecules. Such a liquid crystal layer (and thus the liquid crystal cell) typically exhibits a refractive index characteristic of nx>ny=nz. Here, "ny=nz" includes not only the case where ny and nz are completely identical, but also the case where ny and nz are substantially identical. The Re(550) of the liquid crystal layer may be, for example, 300 nm to 400 nm. The Nz coefficient of the liquid crystal layer may be, for example, 0.9 to 1.1.

In one embodiment, the liquid crystal molecules of the liquid crystal layer have a pretilt, i.e., the director of the liquid crystal molecules is slightly tilted with respect to the substrate plane. The pretilt angle is preferably 0.1° to 1.0°, more preferably 0.2° to 0.7°.

Examples of driving modes for such liquid crystal cell 60a include an in-plane switching (IPS) mode and a fringe field switching (FFS) mode. The IPS mode includes a super in-plane switching (S-IPS) mode and an advanced super in-plane switching (AS-IPS) mode that employ a V-shaped electrode or a zigzag electrode. The FFS mode includes an advanced fringe field switching (A-FFS) mode and an ultra fringe field switching (U-FFS) mode that employ a V-shaped electrode or a zigzag electrode. A preferred driving mode for the liquid crystal cell 60a is the in-plane switching (IPS) mode.
When the driving mode of the liquid crystal cell 60a is the IPS mode, the visibility in oblique directions of the liquid crystal display device can be improved.

H. Backlight Unit The light source 91 is disposed at a position corresponding to the side of the light guide plate 92. For example, an LED light source configured by arranging a plurality of LEDs may be used as the light source. Any suitable light guide plate may be used as the light guide plate 92. For example, a light guide plate having a lens pattern formed on the back side, and a light guide plate having a prism shape or the like formed on the back side and/or the viewing side may be used so that light from the lateral direction can be deflected in the thickness direction. Preferably, a light guide plate having a prism shape formed on the back side and the viewing side is used. In the light guide plate, it is preferable that the prism shape formed on the back side and the prism shape formed on the viewing side have their ridge directions perpendicular to each other. By using such a light guide plate, light that is more easily condensed can be made incident on the prism sheet (not shown).

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) Measurement of Retardation Value The in-plane retardation of the first retardation layer and the second retardation layer used in the examples and comparative examples was automatically measured using KOBRA-WPR manufactured by Oji Scientific Instruments Co., Ltd. The measurement wavelength was 550 nm and the measurement temperature was 23°C.
(2) Luminance during black display A black screen was displayed on the image display devices obtained in the examples and comparative examples, and the luminance was measured using a luminance meter (manufactured by AUTONIC-MELCHERS, product name "Conoscope"). Specifically, the luminance was measured by changing the polar angle from 0° to 80° and the azimuth angle from 0° to 360°.
In addition, among the luminances measured as described above, the luminance when the polar angle was 40° and the azimuth angle was any of 20°, 25°, 155°, 160°, 190°, 195°, 345°, and 350° was defined as area A luminance (unit: cd/ ^m2 ), and the maximum luminance among them was defined as area A maximum luminance (unit: cd/ ^m2 ).

<Preparation of Polarizing Plate>
<<Production 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 weight of potassium iodide to 100 parts by weight 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 weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40° C. for 30 seconds (insolubilizing treatment).
Next, the film was immersed in a dye bath (an aqueous iodine solution obtained by mixing iodine and potassium iodide in a weight ratio of 1:7 with 100 parts by weight 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 plate was immersed in a crosslinking bath (a boric acid aqueous solution obtained by mixing 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with 100 parts by weight 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 weight of potassium iodide with 100 parts by weight 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.
A HC-TAC film (thickness: 20 μm) was attached as a protective layer to the polarizer surface (the surface opposite to the resin substrate) of the obtained laminate. The resin substrate was then peeled off to obtain a polarizing plate having a protective layer/polarizer structure. The obtained polarizing plate was then punched out to a size corresponding to a liquid crystal cell described below.

<Preparation of Retardation Film (Positive B Plate) with Refractive Index Characteristics of nz>nx>ny>
<<Production Example 2>>
A pellet-shaped resin of styrene-maleic anhydride copolymer (manufactured by Nova Chemical Japan, product name "Dylark D232") was extruded at 270°C using a single screw extruder and a T-die, and the sheet-shaped molten resin was cooled on a cooling drum to obtain a film having a thickness of 100 μm. This film was uniaxially stretched at the free end in the conveying direction at a temperature of 130°C and a stretch ratio of 2.5 times using a roll stretching machine to obtain a film having a fast axis in the conveying direction (longitudinal stretching process).
The obtained film was uniaxially stretched with fixed ends in the width direction at a temperature of 135° C. using a tenter stretching machine so that the film width was 4.5 times the film width after the longitudinal stretching, to obtain a retardation film (biaxially stretched film, positive B plate) having a thickness of 14 μm (transverse stretching step). Thereafter, the obtained retardation film was punched out to a size corresponding to the liquid crystal cell described later.
The retardation film (positive B plate) thus obtained had a fast axis in the conveying direction (a slow axis in the width direction), and the refractive index characteristics showed the relationship nz>nx>ny. The in-plane retardation Re(550), thickness direction retardation Rth(550) and Nz coefficient of the retardation film (positive B plate) are shown in Table 1.
<<Production Example 3>>
A retardation film (positive B plate) was obtained in the same manner as in Production Example 2, except that the longitudinal stretching ratio was changed to 1.7 times and the transverse stretching ratio was changed to 1.8 times.
<<Production Example 4>>
A retardation film (positive B plate) was obtained in the same manner as in Production Example 2, except that the longitudinal stretching ratio was changed to 1.5 times and the transverse stretching ratio was changed to 1.5 times.
<<Production Example 5>>
A retardation film (positive B plate) was obtained in the same manner as in Production Example 2, except that the longitudinal stretching ratio was changed to 1.4 times and the transverse stretching ratio was changed to 1.4 times.
<<Production Example 6>>
A retardation film (positive B plate) was obtained in the same manner as in Production Example 2, except that the longitudinal stretching ratio was changed to 2.2 times and the transverse stretching ratio was changed to 2.4 times.

<Preparation of Retardation Film (Positive A Plate) with Refractive Index Characteristics of nx>ny=nz>
<<Production Example 7>>
A long norbornene-based resin film (manufactured by Zeon Corporation, product name Zeonor, thickness 40 μm, photoelastic coefficient 3.10×10 ⁻¹² m ² /N) was uniaxially stretched 2.0 times at 135° C. to produce a retardation film with a thickness of 28 μm. The obtained retardation film was then punched out to a size corresponding to the liquid crystal cell described below.
The retardation film thus obtained had a slow axis in the transport direction, and the refractive index characteristics showed the relationship of nx>ny=nz. The in-plane retardation Re(550), thickness direction retardation Rth(550) and Nz coefficient of the retardation film (positive A plate) are shown in Table 1.
<<Production Example 8>>
A retardation film (positive A plate) was obtained in the same manner as in Production Example 7, except that the stretching ratio was changed to 1.5 times.
<<Production Example 9>>
A retardation film (positive A plate) was obtained in the same manner as in Production Example 7, except that the stretching ratio was changed to 1.43 times.
<<Production Example 10>>
A retardation film (positive A plate) was obtained in the same manner as in Production Example 7, except that the stretching ratio was changed to 1.37 times.
<<Production Example 11>>
A retardation film (positive A plate) was obtained in the same manner as in Production Example 7, except that the stretching ratio was changed to 1.2 times.

<Preparation of Retardation Film (Positive C Plate) with Refractive Index Characteristics of nz>nx=ny>
<<Production Example 12>>
A retardation film (positive C plate) was obtained in the same manner as in Production Example 6 of Japanese Patent No. 6896118, except that the retardation Rth in the thickness direction was changed to −86 nm. The obtained retardation film was then punched out to a size corresponding to a liquid crystal cell described later.
The retardation film thus obtained had a slow axis in the transport direction, and the refractive index characteristics showed the relationship nz>nx=ny. The in-plane retardation Re(550) and thickness direction retardation Rth(550) of the retardation film (positive C plate) are shown in Table 1.
<<Production Example 13>>
A retardation film (positive C plate) was obtained in the same manner as in Production Example 12, except that the retardation in the thickness direction Rth was changed to −66 nm.

<Preparation of Retardation Film (Negative B Plate) with Refractive Index Characteristics of nx>ny>nz>
<<Production Example 14>>
A retardation film (negative B plate) was obtained in the same manner as in Production Example 7, except that the fixed-end lateral stretching was performed at 1.35 times. Thereafter, the obtained retardation film was punched out to a size corresponding to a liquid crystal cell described later.
The retardation film thus obtained had a refractive index characteristic of nx>ny>nz. The in-plane retardation Re(550) and thickness direction retardation Rth(550) of the retardation film (negative B plate) are shown in Table 1.
<<Production Example 15>>
A retardation film (negative B plate) was obtained in the same manner as in Production Example 14, except that the stretching ratio was changed to 1.3 times.
<<Production Example 16>>
A retardation film (negative B plate) was obtained in the same manner as in Production Example 14, except that the stretching ratio was changed to 1.2 times.

<Preparation of Retardation Film (Negative A Plate) with Refractive Index Characteristics of nx=nz>ny>
<<Production Example 17>>
A pellet-shaped resin of styrene-maleic anhydride copolymer (manufactured by Nova Chemical Japan, product name "Dylark D232") was extruded at 270°C using a single screw extruder and a T-die, and the sheet-shaped molten resin was cooled with a cooling drum to obtain a film having a thickness of 30 μm. This film was uniaxially stretched at a free end in the conveying direction at a temperature of 130°C and a stretching ratio of 1.8 times using a roll stretching machine to obtain a retardation film (negative A plate) having a fast axis in the conveying direction. Thereafter, the obtained retardation film was punched out to a size corresponding to the liquid crystal cell described later.
The retardation film thus obtained had a refractive index characteristic of nx=nz>ny. The in-plane retardation Re(550) and thickness direction retardation Rth(550) of the retardation film (negative A plate) are shown in Table 1.

<Preparation of image display cell (liquid crystal cell)>
<<Production Example 18>>
A liquid crystal cell was removed from an IPS mode liquid crystal display device (manufactured by Apple, product name "iPad (registered trademark)"). The optical members attached to both sides of the liquid crystal cell were removed, and the removed surfaces (outer surfaces of the substrates) were cleaned. This was used as an image display cell (liquid crystal cell). The first substrate of the liquid crystal cell had Rth(450)=32 nm, Rth(550)=19 nm, and Rth(650)=23 nm; the second substrate had Rth(450)=9 nm, Rth(550)=0.3 nm, and Rth(650)=-6 nm.

[Example 1]
The polarizing plate of Production Example 1 (second polarizing plate including a second polarizer) was laminated on the viewing side of the liquid crystal cell of Production Example 18. On the other hand, the retardation film (second retardation layer) of Production Example 7, the retardation film (first retardation layer) of Production Example 2, and the polarizing plate of Production Example 1 (first polarizing plate including a first polarizer) were laminated in this order on the back side of the liquid crystal cell. The lamination was performed so that the absorption axis direction of the first polarizer and the slow axis direction of the first retardation layer were substantially perpendicular to each other, the absorption axis direction of the first polarizer and the slow axis direction of the second retardation layer were substantially parallel to each other, the absorption axis direction of the first polarizer and the initial alignment direction of the liquid crystal cell were substantially perpendicular to each other, and the absorption axis direction of the second polarizer and the initial alignment direction of the liquid crystal cell were substantially parallel to each other. In this way, an image display device (E-mode liquid crystal display device) was produced. Next, the image display device was subjected to the above-mentioned luminance measurement during black display. A luminance distribution diagram in the image display device of Example 1 is shown in FIG. 3. Moreover, the maximum luminance of area A in the image display device of Example 1 is shown in Table 1.

[Comparative Examples 1 to 8]
An image display device (E-mode liquid crystal display device) was produced in the same manner as in Example 1, except that the retardation film (second retardation layer) of Production Example 7 and the retardation film (first retardation layer) of Production Example 2 were changed to the retardation films of the production examples shown in Table 1. Next, the image display device was subjected to the above-mentioned luminance measurement during black display. The luminance distribution diagram of the image display device of Comparative Example 1 is shown in FIG. 4. In addition, the maximum luminance of area A in the image display devices of Comparative Examples 1 to 8 is shown in Table 1.

[evaluation]
As is clear from Table 1, FIGS. 3 and 4, the Re(550) and Nz coefficient of the first retardation layer are within the above ranges, and the Re(550) of the second retardation layer is within the above ranges. This makes it possible to ensure that the viewing angle in the horizontal direction (the left-right direction X of the paper in FIGS. 3 and 4) is wider than the viewing angle in the vertical direction (the up-down direction Y of the paper in FIGS. 3 and 4), and to realize an image display device (liquid crystal display device) in which the maximum luminance of the above-mentioned area A is sufficiently small.

The polarizing plate with a retardation layer according to the embodiment of the present invention is preferably applied to an image display device, and in particular, can be preferably applied to a liquid crystal display device.

REFERENCE SIGNS LIST 10 First polarizing plate 11 First polarizer 20 First retardation layer 30 Second retardation layer 40 Second polarizing plate 60 Image display cell 60a Liquid crystal cell 100 Retardation layer-attached polarizing plate 101 Image display device

Claims (4)

a first polarizing plate including a first polarizer;
A first retardation layer having a refractive index characteristic of nz>nx>ny, which is laminated directly on the first polarizing plate or laminated only via an adhesive layer or a pressure-sensitive adhesive layer ;
A second retardation layer having a refractive index characteristic that satisfies the relationship of nx>ny=nz, which is laminated directly on the first retardation layer or laminated only via an adhesive layer or a pressure-sensitive adhesive layer;
an angle between an absorption axis of the first polarizer and a slow axis of the first retardation layer is in a range of 90°±10°;
an angle between an absorption axis of the first polarizer and a slow axis of the second retardation layer is in the range of 0°±10° ;
The in-plane retardation Re(550) of the first retardation layer is 300 nm or more and 340 nm or less ,
The Nz coefficient of the first retardation layer is −1.0 or more and −0.1 or less,
The in-plane retardation Re(550) of the second retardation layer is 300 nm or more and 340 nm or less .
Polarizing plate with retardation layer. an image display cell;
An image display device comprising: the retardation layer-attached polarizing plate according to claim 1 , which is disposed on the opposite side to the viewing side with respect to the image display cell. the image display cell is a liquid crystal cell,
3. The image display device according to claim 2, wherein a driving mode of the liquid crystal cell is an IPS mode. the image display device includes a second polarizing plate disposed on an opposite side of the image display cell to the retardation layer-attached polarizing plate,
the second polarizing plate includes a second polarizer,
an angle between an absorption axis of the first polarizer and an initial alignment direction of the liquid crystal cell is in a range of 90°±10°;
4. The image display device according to claim 3, wherein an angle between the absorption axis of the second polarizer and an initial alignment direction of the liquid crystal cell is in the range of 0°±10° .

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