Polarizing plate with phase retardation layer and image display device

Abstract

The objective of this invention is to provide a polarizing plate with a phase retardation layer capable of realizing an image display device that achieves a wide viewing angle in the horizontal direction and sufficiently reduces the black brightness in the diagonal directions intersecting the horizontal and vertical directions. An embodiment of the present invention comprises: a polarizing plate including a polarizing element; a first phase retardation layer whose refractive index characteristics show the relationship nz > nx > ny; and a second phase retardation layer whose refractive index characteristics show the relationship nx > ny = nz. The absorption axis of the polarizing element is substantially orthogonal to the slow axis of the first phase retardation layer, and the absorption axis of the polarizing element is substantially parallel to the slow axis of the second phase retardation layer. The Re(550) of the first phase retardation layer is 280 nm or more and 360 nm or less, and the Nz coefficient of the first phase retardation layer is -1.0 or more and -0.1 or less. The Re(550) of the second phase retardation layer is 280 nm or more and 360 nm or less.

Description

Technical Field

[0001] This invention relates to a polarizing plate with a phase retardation layer and an image display device. Prior Technology

[0002] In image display devices, such as liquid crystal displays, various optical films obtained by combining polarizing elements and retardation films are generally used to compensate for optical characteristics suitable for the application. For example, the following technique has been proposed: by combining a polarizing plate containing a polarizing element, a first retardation layer whose refractive index characteristics show the relationship nz>nx>ny, and a second retardation layer whose refractive index characteristics show the relationship nx>ny=nz, in such a way that the absorption axis of the polarizing element is orthogonal to the slow axis of the first retardation layer, and the absorption axis of the polarizing element is parallel to the slow axis of the second retardation layer, the viewing angle is widened (see, for example, Patent Document 1). However, in recent years, the applications of image display devices have been diversifying. One example of such applications is automotive displays. For automotive displays, a wide viewing angle in the horizontal direction (left-right direction) is particularly desirable. However, even when the technology described in Patent Document 1 is applied to automotive displays, the horizontal viewing angle is limited, and there is a problem that the black display on the automotive display is not dark enough (i.e., the black brightness is insufficient) when viewed from an angle intersecting the horizontal and vertical directions (e.g., diagonally upward to the right). [Previous Technical Documents] [Patent Literature]

[0003] Patent Document 1: Japanese Patent Application Publication No. 2021-76759 Summary of the Invention

[0004] [The problem the invention aims to solve]

[0005] The present invention was made to solve the aforementioned prior problems. Its main objective is to provide a polarizing plate with a phase difference layer that can realize the following image display device, which can achieve wide viewing angle in the horizontal direction (the specified surface direction of the image display surface) and can sufficiently reduce the black brightness in the diagonal direction that intersects with both the horizontal and vertical directions. [Technical means to solve the problem]

[0006] An embodiment of the present invention provides a polarizing plate with a phase retardation layer comprising: a first polarizing plate including a first polarizing element; a first phase retardation layer having refractive index characteristics showing the relationship nz>nx>ny; and a second phase retardation layer having refractive index characteristics showing the relationship nx>ny=nz. The first phase retardation layer is disposed adjacent to the first polarizing plate, and the second phase retardation layer is disposed adjacent to the first phase retardation layer. The absorption axis of the first polarizing element is substantially orthogonal to the slow axis of the first phase retardation layer, and the absorption axis of the first polarizing element is substantially parallel to the slow axis of the second phase retardation layer. The in-plane phase difference Re(550) of the first phase retardation layer is 280 nm or more and 360 nm or less, and the Nz coefficient of the first phase retardation layer is -1.0 or more and -0.1 or less. The in-plane phase difference Re(550) of the second phase retardation layer is 280 nm or more and 360 nm or less. Another aspect of the present invention provides an image display device comprising: an image display unit; and a polarizing plate with a phase retardation layer, which is disposed on the opposite side of the viewing side relative to the image display unit. In one embodiment, the image display unit is a liquid crystal unit, and the driving mode of the liquid crystal unit is IPS mode. In one embodiment, the image display device includes a second polarizing plate, which is disposed on the opposite side of the polarizing plate with the retardation layer relative to the image display unit. The second polarizing plate includes a second polarizing element. The absorption axis of the first polarizing element is substantially orthogonal to the initial alignment direction of the liquid crystal cell, and the absorption axis of the second polarizing element is substantially parallel to the initial alignment direction of the liquid crystal cell. [Effects of the Invention]

[0007] According to an embodiment of the present invention, a polarizing plate with a phase retardation layer can be realized, which can realize wide viewing angle in the horizontal direction (the specified surface direction of the image display surface) of the image display device and can sufficiently reduce the black brightness in the diagonal direction intersecting the horizontal and vertical directions. Simple Explanation of the Diagram

[0008] Figure 1 is a schematic cross-sectional view of a polarizing plate with a phase retardation layer according to one embodiment of the present invention. Figure 2 is a schematic cross-sectional view of an image display device according to one embodiment of the present invention. Figure 3 is a brightness distribution diagram of the image display device of Embodiment 1 when displaying black. Figure 4 is a brightness distribution diagram of the image display device of Comparative Example 1 when displaying black. Implementation

[0009] The following describes representative embodiments of the present invention, but the present invention is not limited to these embodiments.

[0010] (Definitions of terms and symbols) The definitions of terms and symbols used in this specification are as follows. (1) Refractive index (nx, ny, nz) "nx" refers to the refractive index in the direction where the in-plane refractive index reaches its maximum (i.e., the slow axis direction), "ny" refers to the refractive index in the direction orthogonal to the slow axis (i.e., the fast axis direction), and "nz" refers to the refractive index in the thickness direction. (2) In-plane phase difference (Re) and frontal phase difference (R0) "Re(λ)" refers to the in-plane phase difference measured at 23°C using light with a wavelength of λ nm. For example, "Re(550)" refers to the in-plane phase difference measured at 23°C using light with a wavelength of 550 nm. Furthermore, the "in-plane phase difference Re(550)" is sometimes called the "front-side phase difference R0". When the thickness of the layer (film) is set to d (nm), Re(λ) is obtained by the formula: Re(λ) = (nx - ny) × d. (3) Phase difference (Rth) in the thickness direction "Rth(λ)" is the phase difference in the thickness direction measured at 23°C using light with a wavelength of λ nm. For example, "Rth(550)" is the phase difference in the thickness direction measured at 23°C using light with a wavelength of 550 nm. When the thickness of the layer (film) is set to d (nm), Rth(λ) is obtained from the formula: Rth(λ) = (nx - nz) × d. (4) Nz coefficient The Nz coefficient is obtained by Nz = Rth / Re. (5) In fact, they are parallel or orthogonal. The expressions "substantially orthogonal" and "approximately orthogonal" include the case where the angle between the two directions is 90°±10°, preferably 90°±7°, and even more preferably 90°±5°. The expressions "substantially parallel" and "approximately parallel" include the case where the angle between the two directions is 0°±10°, preferably 0°±7°, and even more preferably 0°±5°. Furthermore, in this specification, the simple use of the terms "orthogonal" or "parallel" may include states that are substantially orthogonal or substantially parallel.

[0011] A. Overall structure of the polarizing plate with phase retardation layer Figure 1 is a schematic cross-sectional view of a polarizing plate with a phase retardation layer according to one embodiment of the present invention. The polarizing plate 100 with a phase retardation layer in the figure example has: a first polarizing plate 10 including a first polarizing element 11; a first phase retardation layer 20 whose refractive index characteristics show the relationship nz>nx>ny; and a second phase retardation layer 30 whose refractive index characteristics show the relationship nx>ny=nz. The first phase retardation layer 20 is disposed adjacent to the first polarizing plate 10. The second phase retardation layer 30 is disposed adjacent to the first phase retardation layer 20. The second phase retardation layer 30 is located on the opposite side of the first polarizing plate 10 relative to the first phase retardation layer 20. In this specification, "disposed adjacently" means direct lamination or lamination only via an adhesive layer (e.g., an adhesive layer or a bonding agent layer). That is, it means that no optical functional layer (e.g., other phase retardation layers) is sandwiched between the first polarizing plate 10 and the first phase retardation layer 20, and between the first phase retardation layer 20 and the second phase retardation layer 30. The absorption axis (direction of the first absorption axis) of the first polarizing element 11 is substantially orthogonal to the slow axis (direction of the first slow axis) of the first retardation layer 20. The absorption axis (direction of the first absorption axis) of the first polarizing element 11 is substantially parallel to the slow axis (direction of the second slow axis) of the second retardation layer 30. The in-plane phase difference Re(550) of the first phase difference 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 even more preferably 310 nm or more and 330 nm or less. The Nz coefficient of the first phase difference layer 20 is above -1.0 and below -0.1, preferably above -0.9 and below -0.2, more preferably above -0.8 and below -0.3, and even more preferably above -0.8 and below -0.6. The in-plane phase difference Re(550) of the second phase difference 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 even more preferably 310 nm or more and 330 nm or less. If the Re(550) and Nz coefficients of the first phase retardation layer and the Re(550) of the second phase retardation layer respectively satisfy the above-mentioned ranges, then in an image display device equipped with a polarizing plate with a phase retardation layer, a wide viewing angle in the horizontal direction (a defined surface direction of the image display surface) can be achieved, and the black brightness in the oblique direction intersecting the horizontal and vertical directions can be sufficiently reduced. That is, in an image display device equipped with a polarizing plate with a phase retardation layer, the viewing angle in the horizontal direction (e.g., the first surface direction X of the image display device shown in FIG3) can be wider than the viewing angle in the vertical direction (e.g., the second surface direction Y orthogonal to the first surface direction X shown in FIG3), and the black brightness when viewing the black display of the image display device from the oblique direction intersecting the horizontal (first surface direction X) and vertical (second surface direction Y) directions can be sufficiently reduced. More specifically, using any suitable luminance meter, the luminance of the image display device when displaying black is measured within various ranges of polar angle 40°~42° and azimuth angles of 20°~25°, 155°~160°, 190°~195°, and 345°~350°. For example, the luminance is 0.00074 or less, preferably 0.00070 or less, and more preferably 0.00068 or less. Furthermore, in this specification, the luminance measured within the aforementioned polar angle and azimuth angle range is defined as the luminance of region A. The lower limit of the luminance of region A is representatively 0.00001 or more.

[0012] In one embodiment, the Nz coefficient of the second phase retardation layer 30 is, for example, 0.5 or more and 1.5 or less, preferably 0.6 or more and 1.4 or less, more preferably 0.7 or more and 1.3 or less, and even more preferably 0.8 or more and 1.2 or less. If the Nz coefficient of the second phase retardation layer is within the range described above, then in an image display device equipped with a polarizing plate with a phase retardation layer, a wide viewing angle in the horizontal direction (the defined surface direction of the image display surface) can be stably achieved, and the black brightness in the diagonal direction intersecting the horizontal and vertical directions can be stably reduced.

[0013] The polarizing plate with a phase retardation layer may further have a conductive layer or an isotropic substrate (not shown) with a conductive layer. The conductive layer or the isotropic substrate with a conductive layer is typically disposed outside the second phase retardation layer (on the opposite side to the first polarizing plate). When a conductive layer or an isotropic substrate with a conductive layer is disposed, the polarizing plate with a phase retardation layer can be applied to a so-called internal touch panel type input display device in which a touch sensor is incorporated between an image display unit (e.g., a liquid crystal unit, an organic EL unit) and the first polarizing plate.

[0014] The polarizing plate with the retardation layer can also contain other retardation layers. The optical properties (such as refractive index, in-plane retardation, Nz coefficient, photoelastic coefficient), thickness, and placement of other retardation layers can be appropriately set according to the purpose.

[0015] The polarizing plate with the retardation layer can be a single sheet or a strip. In this specification, "strip" refers to a long, thin shape that is sufficiently long relative to its width, such as a long shape that is 10 times or more, preferably 20 times or more, than its width. The strip-shaped polarizing plate with the retardation layer can be rolled into a cylinder.

[0016] In practical applications, an adhesive layer (not shown) is provided on the side of the second retardation layer opposite to the first polarizer, allowing the polarizer with the retardation layer to be attached to the image display unit. Furthermore, it is preferable that a release liner is temporarily adhered to the surface of the adhesive layer until the polarizer with the retardation layer is supplied for use. By temporarily adhering the release liner, the adhesive layer can be protected, and a roll can be formed.

[0017] B. Overall Structure of the Image Display Device Figure 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 shown in the figure includes: an image display unit 60; and a polarizing plate 100 with a phase retardation layer disposed on the opposite side of the viewing side relative to the image display unit 60. In the image display device 101, a first phase retardation layer 20 is located between the first polarizing plate 100 and the image display unit 60, and a second phase retardation layer 30 is located between the first phase retardation layer 20 and the image display unit 60.

[0018] The image display device 101 in the illustration further includes a second polarizing plate 40 disposed on the opposite side (viewing side) of the polarizing plate 100 with the phase retardation layer, relative to the image display unit 60. The second polarizing plate 40 includes a second polarizing element 41.

[0019] Image display unit 60 is typically a liquid crystal unit 60a, and image display device 101 is typically a liquid crystal display device. The liquid crystal display device is typically of E-mode. An "E-mode liquid crystal display device" refers to a device in which the absorption axis (first absorption axis direction) of the polarizing element (in this embodiment, the first polarizing element 11) disposed on the opposite side (back side) of the viewing side of the liquid crystal unit is substantially orthogonal to the initial alignment direction of the liquid crystal unit. The "initial alignment direction of the liquid crystal unit" refers to the direction in which the in-plane refractive index of the liquid crystal layer reaches its maximum (i.e., the slow axis direction) when the liquid crystal molecules contained in the liquid crystal layer, described later, align in the absence of an electric field.

[0020] In one embodiment, the absorption axis (second absorption axis direction) of the polarizing element (second polarizing element 41 in this embodiment) disposed 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 polarizing element 11 and the absorption axis direction of the second polarizing element 41 are substantially orthogonal. According to the configuration described above, excellent visibility can be achieved even when viewing the displayed image through a polarizing lens such as polarized sunglasses.

[0021] In practical applications, 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 also include any other suitable components (e.g., diffuser, prism). In the example shown, the backlight unit 90 uses edge illumination, but the backlight unit 90 may also employ any other suitable method (e.g., direct illumination).

[0022] The image display device (liquid crystal display device) may also include any other suitable components. For example, other optical compensation layers (phase retardation layers) may be further configured. The optical characteristics, number, combination, and placement of other optical compensation layers may be appropriately selected according to the purpose and desired optical characteristics. Matters not described in this specification may be handled using configurations of image display devices (liquid crystal display devices) well known and conventional in the art.

[0023] The image display device described above is suitable for applications that require a wide horizontal viewing angle and reduced brightness in area A when displaying black (especially applications requiring high definition and the ability for multiple users to share the screen). Typical examples of image display devices include automotive displays, medical monitors, and gaming monitors, with automotive displays being particularly preferred.

[0024] The following describes the components that constitute the polarizing plate with the phase difference layer and the image display device.

[0025] C. Polarizing plate C-1. Polarizing element The first polarizing element 11 of the first polarizing plate 10 and the second polarizing element 41 of the second polarizing plate 40 (hereinafter sometimes referred to together as polarizing elements) can be any suitable polarizing element. For example, the resin film forming the polarizing element can be a single-layer resin film or a laminate of two or more layers.

[0026] Specific examples of polarizing elements composed of a single-layer resin film include those obtained by dyeing and stretching hydrophilic polymer films such as polyvinyl alcohol (PVA) films, partially formalized PVA films, and partially saponified ethylene-vinyl acetate copolymer films using dichroic substances such as iodine or dichroic dyes; and polyene alignment films such as dehydrated PVA products or dehydrochlorinated polyvinyl chloride products. From the viewpoint of superior optical properties, it is preferable to use a polarizing element obtained by dyeing a PVA film with iodine and then uniaxially stretching it.

[0027] The aforementioned dyeing using iodine is performed, for example, by immersing the PVA membrane in an aqueous iodine solution. The preferred uniaxial stretching ratio is 3 to 7 times. Stretching can be performed after dyeing, or simultaneously with dyeing. Alternatively, dyeing can be performed after stretching. Depending on the requirements, the PVA membrane may undergo swelling, cross-linking, washing, or drying treatments. For example, immersing the PVA membrane in water before dyeing not only removes surface contaminants or anti-blocking agents but also swells the PVA membrane to prevent uneven dyeing.

[0028] As a specific example of a polarizing element obtained using a laminate, examples include a laminate consisting of a resin substrate and a PVA-based resin layer (PVA-based resin film) deposited on the resin substrate, or a laminate consisting of a resin substrate and a PVA-based resin layer coated on the resin substrate. A polarizing element obtained using a laminate consisting of a resin substrate and a PVA-based resin layer coated on the resin substrate can be manufactured, for example, by coating a PVA-based resin solution onto a resin substrate, drying it to form a PVA-based resin layer on the resin substrate, obtaining a laminate of the resin substrate and the PVA-based resin layer; and then stretching and dyeing the laminate to use the PVA-based resin layer as a polarizing element. In this embodiment, stretching typically includes immersing the laminate in an aqueous boric acid solution. Furthermore, stretching may, as needed, include air stretching of the laminate at a high temperature (e.g., above 95°C) prior to stretching in the aqueous boric acid solution. The resulting resin substrate / polarizing element laminate can be used directly (i.e., the resin substrate can be used as a protective layer for the polarizing element), or the resin substrate can be peeled off from the resin substrate / polarizing element laminate, and any suitable protective layer can be laminated on the peeled surface according to the purpose. Detailed descriptions of the manufacturing method of the polarizing element as described above are, for example, described in Japanese Patent Application Publication No. 2012-73580 and Japanese Patent No. 6470455. The entire contents of these publications are incorporated herein by reference.

[0029] The thickness of the polarizing element 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 polarizing element is within the range described above, curling during heating can be well suppressed, and good appearance durability during heating can be obtained.

[0030] The polarizing element preferably exhibits absorption dichroism at any wavelength from 380 nm to 780 nm. The transmittance of the polarizing element is, for example, 41.5% to 46.0%, more preferably 43.0% to 46.0%, and even more preferably 44.5% to 46.0%. The polarization degree of the polarizing element is preferably 97.0% or higher, more preferably 99.0% or higher, and even more preferably 99.9% or higher.

[0031] C-2. Protective layer The first polarizing plate 10 and the second polarizing plate 40 may each further have a protective layer. The protective layer may be disposed on at least one side of the polarizing element, or on both sides of the polarizing element. In the image display device 101, the first polarizing plate 10 has a protective layer 12 disposed on the side opposite to the viewing side of the first polarizing element 11, and the second polarizing plate 40 has a protective layer 42 disposed on the viewing side of the second polarizing element 41.

[0032] The protective layer is formed from any suitable film that can be used as a protective layer for a polarizing element. Specific examples of materials that are the main components of this film include cellulose resins such as triacetyl cellulose (TAC), polyester resins, polyvinyl alcohol resins, polycarbonate resins, polyamide resins, polyimide resins, polyether resins, polyurethane resins, polystyrene resins, polynorbornene resins, polyolefin resins, (meth)acrylic acid resins, acetate resins, and other transparent resins. Also examples include thermosetting resins or UV-curing resins such as (meth)acrylic acid resins, urethane resins, (meth)acrylate urethane resins, epoxy resins, and polysiloxane resins. In addition, examples include glassy polymers such as silicate polymers. Furthermore, polymer films described in Japanese Patent Application Publication No. 2001-343529 (WO01 / 37007) can also be used. As a material for the membrane, for example, a resin composition can be used, which contains a thermoplastic resin having substituted or unsubstituted amide groups in the side chains and a thermoplastic resin having substituted or unsubstituted phenyl and nitrile groups in the side chains. Examples include resin compositions comprising alternating copolymers of isobutylene and N-methylmaleimide, and acrylonitrile-styrene copolymers. The polymer membrane can be, for example, an extruded product of the above resin composition.

[0033] When the polarizing element disposed on the viewing side of the image display unit 60 has a protective layer located on the outermost surface of the image display device, surface treatments such as hard coating, anti-reflection treatment, anti-sticking treatment, and anti-glare treatment can be applied to the protective layer as needed.

[0034] The thickness of the protective layer is typically less than 5 mm, preferably less than 1 mm, more preferably 1 μm to 500 μm, and even more preferably 5 μm to 150 μm. Furthermore, when a surface treatment has been performed, the thickness of the protective layer includes the thickness of the surface treatment layer.

[0035] D. First phase difference layer As described above, the refractive index characteristics of the first phase retardation layer 20 show a relationship of nz>nx>ny. The layer (film) showing the refractive index characteristics described above is sometimes also called a "positive biaxial plate" or "positive B plate".

[0036] The thickness of the first retardation layer is typically 3 μm or more, preferably 5 μm or more, typically 30 μm or less, preferably 20 μm or less, and more preferably 15 μm or less. By keeping the thickness of the first retardation layer within the range described above, the manufacturability during manufacturing is excellent, and the optical uniformity of the resulting image display device can be improved.

[0037] The first retardation layer can have any suitable configuration. Specifically, it can be a single retardation film or a laminate of two or more retardation films, either identical or different. In the case of a laminate, the first retardation layer may include an adhesive layer or bonding agent layer for bonding two or more retardation films. Preferably, the first retardation layer is a single retardation film. By adopting the configuration described above, the deviation or unevenness of the phase difference value caused by the shrinkage stress of the polarizing element and / or the heat of the light source can be reduced, and it can contribute to the thinning of the resulting image display device.

[0038] The optical properties of the retardation film can be set to any suitable value depending on the composition of the first retardation layer. For example, when the first retardation layer is a separate retardation film, its optical properties are preferably equal to those of the first retardation layer. Therefore, when this retardation film is laminated in a polarizing element and / or a second retardation layer, the phase difference value of the adhesive layer, bonding agent layer, etc., used is preferably as small as possible.

[0039] As a retardation film, it is preferable to use a film with excellent transparency, mechanical strength, thermal stability, and moisture-blocking properties, and one that is not easily deformed to produce optical non-uniformity. As a retardation film, it is preferable to use an extended film of a polymer film with thermoplastic resin as the main component. As the thermoplastic resin, it is preferable to use a polymer exhibiting negative birefringence. By using a polymer exhibiting negative birefringence, a retardation film with a refractive index ellipsoid of nz>nx>ny can be easily obtained. Here, "exhibiting negative birefringence" means that when the polymer is aligned by extension or the like, the refractive index in the extension direction is relatively smaller. In other words, it means that the refractive index in the direction orthogonal to the extension direction is larger. Examples of polymers exhibiting negative birefringence include polymers with highly polarized anisotropic chemical bonds or functional groups such as aromatic rings or carbonyl groups introduced into the side chains. Specifically, examples include acrylic resins, styrene resins, and maleimide resins.

[0040] The aforementioned acrylic resins can be obtained, for example, by addition polymerization of acrylate monomers. Examples of acrylic resins include polymethyl methacrylate (PMMA), polybutyl methacrylate, and polycyclohexyl methacrylate.

[0041] The aforementioned styrene-based resins can be obtained, for example, by addition polymerization of styrene-based monomers. Examples of styrene-based monomers include styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, p-chlorostyrene, p-nitrostyrene, p-aminostyrene, p-carboxystyrene, p-phenylstyrene, 2,5-dichlorostyrene, and p-tert-butylstyrene.

[0042] The aforementioned maleimide-based resins can be obtained, for example, by addition polymerization of maleimide monomers. Examples of maleimide monomers 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, and N-(2,6-dipropylphenyl)maleimide. 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, N-(2-cyanophenyl)maleimide. Maleimide monomers are available, for example, from Tokyo Chemical Industry Co., Ltd.

[0043] In the above addition polymerization, after polymerization, the birefringence properties of the obtained resin can also be controlled by substituting the side chains, or by subjecting them to maleicimide or grafting reactions.

[0044] The polymers exhibiting negative birefringence described above can also be copolymerized with other monomers. Copolymerization with other monomers can improve brittleness, processability, and heat resistance. Examples of such other monomers include, for instance, 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.

[0045] When the polymer exhibiting negative birefringence is a copolymer of the aforementioned styrene monomer and other monomers, the preferred blending ratio of the styrene monomer is 50 mol% to 80 mol%. When the polymer exhibiting negative birefringence is a copolymer of the aforementioned maleimide monomer and other monomers, the preferred blending ratio of the maleimide monomer is 2 mol% to 50 mol%. By blending within the range described above, a polymer film with excellent toughness and processability can be obtained.

[0046] As polymers exhibiting negative birefringence as described above, styrene-maleic anhydride copolymers, styrene-acrylonitrile copolymers, styrene-(meth)acrylate copolymers, styrene-maleimide copolymers, ethylene ester-maleimide copolymers, and olefin-maleimide copolymers are preferred. These can be used alone or in combination of two or more. These polymers exhibit high negative birefringence and excellent heat resistance. These polymers are available, for example, from Novartis Chemicals Japan Co., Ltd., or Arakawa Chemical Industry Co., Ltd.

[0047] As for the polymer exhibiting negative birefringence as described above, a polymer having repeating units as shown in the following general formula (I) is preferred. The polymer described above can exhibit higher negative birefringence and excellent heat resistance and mechanical strength. The polymer described above can be obtained, for example, by using an N-phenyl-substituted maleimide: an N-substituent is introduced into a maleimide monomer that is a starting material with a phenyl group having a substituent at least at the ortho position. [Chemistry 1]

[0048] In the above general formula (I), R1 to R5 independently represent hydrogen, halogen atom, carboxylic acid, carboxylic acid ester, hydroxyl, nitro, or straight-chain or branched alkyl or alkoxy with 1 to 8 carbon atoms (wherein R1 and R5 are not hydrogen atoms at the same time), R6 and R7 represent hydrogen or straight-chain or branched alkyl or alkoxy with 1 to 8 carbon atoms, and n represents an integer of 2 or more.

[0049] The polymers exhibiting negative birefringence are not limited to those described above. For example, cyclic olefin copolymers disclosed in Japanese Patent Application Publication No. 2005-350544 may also be used. Furthermore, compositions containing polymers and inorganic microparticles disclosed in Japanese Patent Application Publication No. 2005-156862 and Japanese Patent Application Publication No. 2005-227427 may also be used well. Moreover, as polymers exhibiting negative birefringence, one may be used alone, or two or more may be mixed. Furthermore, they may be modified by copolymerization, branching, crosslinking, molecular end modification (or capping), and stereoregular modification.

[0050] The aforementioned polymer film may further contain any suitable additives as needed. Specific examples of additives include plasticizers, heat stabilizers, light stabilizers, lubricants, antioxidants, UV absorbers, flame retardants, colorants, antistatic agents, compatibilizers, crosslinking agents, and tackifiers. The type and content of additives can be appropriately set according to the purpose. The additive content is typically about 3 to 10 parts by weight relative to 100 parts by weight of the total solids content of the polymer film. Excessive additive content may impair the transparency of the polymer film or cause the additives to seep out from the surface of the polymer film.

[0051] As a method for forming the aforementioned polymer film, any suitable forming method can be used. 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 preferred. This is because they can produce phase difference films with high smoothness and good optical uniformity. Specifically, extrusion molding involves heating and melting the resin composition containing thermoplastic resin, plasticizer, additives, etc., and extruding it into a thin film on the surface of a casting roller through a T-die, etc., and then cooling it to form a film. Solvent casting involves defoaming a concentrated solution (viscous substance; dope) in a solvent containing the aforementioned resin composition, uniformly casting it into a thin film on the surface of a metallic annular belt or drum, or a plastic substrate, etc., and then evaporating the solvent to form a film. Furthermore, the forming conditions can be appropriately set according to the composition or type of resin used, the forming process, etc.

[0052] The aforementioned phase décor film (extended film) can be obtained by extending the aforementioned polymer film under any suitable extension conditions. Specific examples of extension methods include longitudinal uniaxial extension, transverse uniaxial extension, longitudinal-transverse successive biaxial extension, and simultaneous longitudinal-transverse biaxial extension. Transverse uniaxial extension, longitudinal-transverse successive biaxial extension, and simultaneous longitudinal-transverse biaxial extension are preferred because they allow for the production of biaxial phase difference films. In the aforementioned polymers exhibiting negative birefringence, as described above, since the refractive index in the extension direction is relatively smaller, in the case of transverse uniaxial extension, there is a slow axis in the transport direction of the polymer film (the refractive index in the transport direction is nx). In the cases of longitudinal-transverse successive biaxial extension and simultaneous longitudinal-transverse biaxial extension, both the transport direction and the width direction can be set as slow axes depending on the ratio of the longitudinal and transverse extension ratios. Specifically, if the longitudinal (transport) extension ratio is relatively increased, the transverse (width) direction becomes the slow axis; conversely, if the transverse (width) extension ratio is relatively increased, the longitudinal (transport) direction becomes the slow axis. As the stretching device used in the above-mentioned stretching, any suitable stretching device can be used. Specific examples include roll stretching machines, tenter stretching machines, and biaxial stretching machines with scaling or linear motors. When stretching is performed while heating, the temperature can be changed continuously or in a stepwise manner. In addition, the stretching step can be divided into two or more steps.

[0053] Furthermore, by adjusting the thickness of the polymer film (original film thickness), the stretching temperature, and the stretching ratio, the Re(550) and Nz coefficients of the first phase difference layer can be adjusted to the above range. The thickness of the polymer film (original film thickness) is typically 30 μm or more, preferably 40 μm or more, even more preferably 80 μm or more, typically less than 300 μm, preferably less than 200 μm, even more preferably less than 120 μm.

[0054] The stretching temperature (the temperature inside the stretching oven during stretching of the polymer film) is preferably near the glass transition temperature (Tg) of the polymer film. Specifically, it is preferably (Tg-10)℃ to (Tg+30)℃, more preferably Tg to (Tg+25)℃, and particularly preferably (Tg+5)℃ to (Tg+20)℃. If the stretching temperature is too low, the phase difference or the direction of the slow axis may become uneven, 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 phase difference may become insufficient. The stretching temperature is typically 110~200℃. Furthermore, the glass transition temperature can be determined by DSC method according to JIS K7121-1987.

[0055] The temperature inside the extended oven can be controlled by any suitable method. For example, methods such as using an air-circulating constant temperature oven with hot or cold air circulation, heaters using microwaves or far-infrared rays, and rollers, heat pipe rollers, or metal belts for temperature regulation can be used.

[0056] Regarding the stretching ratio when stretching polymer films, it can be set to any appropriate value based on the composition of the polymer film, the types of volatile components, the residual amount of volatile components, and the desired phase difference. Preferably, it is 1.05 to 5.00 times, more preferably 2.45 to 5.00 times. Furthermore, from the viewpoint of the mechanical precision and stability of the stretching device, the feed speed during stretching is preferably 0.5 m / min to 20 m / min.

[0057] The above describes a method for obtaining a retardation film using a polymer exhibiting negative birefringence. However, a retardation film can also be obtained using a polymer exhibiting positive birefringence. For example, methods for increasing the refractive index in the thickness direction can be used, as disclosed in Japanese Patent Application Publications Nos. 2000-231016, 2000-206328, and 2002-207123. Specifically, a method can be exemplified by attaching a heat-shrinkable film to one or both sides of a film containing a polymer exhibiting positive birefringence and then performing a heat treatment. By shrinking the film under the contraction force of the heat-shrinkable film caused by the heat treatment, the film shrinks in both the length and width directions, thereby increasing the refractive index in the thickness direction and obtaining a retardation film with a refractive index ellipsoid of nz>nx>ny.

[0058] Thus, the positive B-plate used for the first retardation layer can be manufactured using any type of birefringent polymer exhibiting both positive and negative refraction. Generally speaking, when using a polymer exhibiting positive birefringence, there is an advantage in the variety of polymers that can be selected. When using a polymer exhibiting negative birefringence, compared to using a polymer exhibiting positive birefringence, there is an advantage in the ease of obtaining a retardation film with excellent uniformity in the slow axis direction due to its stretching method.

[0059] In addition to the films mentioned above, commercially available optical films can also be used as the retardation film for the first retardation layer. Furthermore, films that have undergone secondary processing such as stretching and / or relaxation treatments on commercially available optical films can also be used.

[0060] The aforementioned retardation film preferably has a transmittance of 80% or higher at a wavelength of 550 nm, more preferably 85% or higher, and particularly preferably 90% or higher. The theoretical upper limit of transmittance is 100%, but due to surface reflection caused by the difference in refractive index between air and the retardation film, the achievable upper limit of transmittance is approximately 94%. The first retardation layer as a whole also preferably has the same transmittance.

[0061] The absolute value of the photoelastic coefficient of the aforementioned retardation film is preferably 1.0 × 10⁻¹⁰ (m² / N) or less, more preferably 5.0 × 10⁻¹¹ (m² / N) or less, further preferably 3.0 × 10⁻¹¹ (m² / N) or less, and particularly preferably 1.5 × 10⁻¹¹ (m² / N) or less. By setting the photoelastic coefficient to the range described above, an image display device with excellent optical uniformity and minimal changes in optical properties, even in environments with high temperature and high humidity, can be obtained, resulting in excellent durability. There is no particular limitation on the lower limit of the photoelastic coefficient, but it is generally 5.0 × 10⁻¹³ (m² / N) or more, and preferably 1.0 × 10⁻¹² (m² / N) or more. If the photoelastic coefficient is too small, the performance of the phase difference may be reduced. The photoelasticity coefficient is an inherent value of the chemical structure of polymers, etc., but by copolymerizing or mixing multiple components with different signs (positive and negative) of the photoelasticity coefficient, the photoelasticity coefficient can be reduced.

[0062] E. Second phase difference layer As described above, the refractive index characteristics of the second phase retardation layer 30 show a relationship of nx > ny = nz. Layers (films) exhibiting this refractive index characteristic are sometimes called "positive uniaxial plates," "positive A plates," 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 refers to a Nz coefficient exceeding 0.9 but not reaching 1.1.

[0063] As the material for forming the second phase retardation layer, any suitable material can be used, as long as the aforementioned properties can be obtained. Specifically, the second phase retardation layer can be an alignment and curing layer of a liquid crystal compound (liquid crystal alignment and curing layer), or it can be a phase retardation film (an extension film of a polymer film).

[0064] When the second retardation layer is a liquid crystal alignment and curing layer, by using a liquid crystal compound, the difference between nx and ny in the resulting retardation layer can be significantly increased compared to non-liquid crystal materials. Therefore, the thickness of the retardation layer used to obtain the desired in-plane retardation can be significantly reduced. As a result, the polarizing plate with the retardation layer (and consequently, the image display device) can be further thinned. In this specification, "alignment and curing layer" refers to a layer in which the liquid crystal compound is aligned in a predetermined direction and its alignment state is fixed. Furthermore, "alignment and curing layer" includes the concept of an alignment and curing layer obtained by curing liquid crystal monomers as described later. In this embodiment, typically, rod-shaped liquid crystal compounds are aligned in a state of being aligned along the slow axis direction of the second retardation layer (plane alignment).

[0065] Examples of liquid crystal compounds include those with a nematic phase (nematic liquid crystals). As described above, liquid crystal polymers or liquid crystal monomers can be used, for example. The liquid crystal properties of the liquid crystal compound can be lyotropic or thermotropic. Liquid crystal polymers and liquid crystal monomers can be used individually or in combination.

[0066] When the liquid crystal compound is a liquid crystal monomer, it is preferably a polymerizable monomer and / or a crosslinking monomer. This is because by polymerizing or crosslinking the liquid crystal monomer, its alignment state can be fixed. After aligning the liquid crystal monomer, for example, if the liquid crystal monomers are polymerized or crosslinked together, this alignment state can be fixed. Here, although a polymer is formed by polymerization and a three-dimensional network structure is formed by crosslinking, these are non-liquid crystals. Therefore, the formed second retardation layer does not undergo the transformation to a liquid crystal phase, glassy phase, or crystalline phase due to temperature changes, as is characteristic of liquid crystal compounds. As a result, the formed second retardation layer becomes a retardation layer with extremely excellent stability, unaffected by temperature changes.

[0067] Specific examples of liquid crystal compounds and detailed methods for forming liquid crystal alignment and curing layers are described, for example, in Japanese Patent Application Publication Nos. 2006-163343 and 2006-178389. The contents of these publications are incorporated herein by reference.

[0068] As described above, the second retardation layer can also be an extended film of a polymer film. Specifically, by appropriately selecting the type of polymer, the stretching conditions (e.g., stretching temperature, stretching ratio, stretching direction), and the stretching method (e.g., transverse uniaxial stretching), a second retardation layer with the aforementioned desired optical properties (e.g., refractive index characteristics, in-plane phase difference, and phase difference in the thickness direction) can be obtained. In particular, by adjusting the thickness of the polymer film (original film thickness), the stretching temperature, and the stretching ratio, the Re(550) of the second retardation layer can be adjusted to the aforementioned range. The thickness of the polymer film (original film thickness) is typically 10 μm or more, preferably 15 μm or more, typically 50 μm or less, preferably 40 μm or less, and even more preferably 30 μm or less. The preferred elongation temperature is 110℃~170℃, and more preferably 130℃~150℃. The preferred elongation ratio is 1.37x~3.00x, and more preferably 1.60x~2.50x.

[0069] Any suitable resin can be used as the resin for forming the aforementioned polymer film. Specific examples include norcamphene-based resins, polycarbonate-based resins, cellulose-based resins, polyvinyl alcohol-based resins, and polyurethane-based resins, which constitute positive birefringent films. Among these, norcamphene-based resins and polycarbonate-based resins are preferred.

[0070] The aforementioned nobornene-based resins are resins polymerized using nobornene monomers as polymerization units. Examples of nobornene monomers include nobornene and its alkyl and / or alkylene-substituted derivatives, such as 5-methyl-2-norbornene, 5-dimethyl-2-norbornene, 5-ethyl-2-norbornene, 5-butyl-2-norbornene, 5-ethylene-2-norbornene, and their halogenated or other polar derivatives; dicyclopentadiene, 2,3-dihydrodicyclopentadiene, etc.; dimethylbridged octahydronaphthalene, and its alkyl and / or alkylene-substituted derivatives. Alkylene-substituted derivatives and polar-substituted derivatives such as halogens, for example, 6-methyl-1,4:5,8-dimethylbridged-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-ethyl-1,4:5,8-dimethylbridged-1,4,4a,5,6,7,8,8a-octahydronaphthalene, and 6-ethylene-1,4:5,8-dimethylbridged-1,4,4a,5,6,7,8,8a-octahydronaphthalene. 6-Chloro-1,4:5,8-Dimethylbridged-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-Cyano-1,4:5,8-Dimethylbridged-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-Pyridyl-1,4:5,8-Dimethylbridged-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-Methoxycarbonyl-1,4:5,8-Dimethylbridged-1 4,4a,5,6,7,8,8a-octahydronaphthalene; 3- to 4-polymers of cyclopentadiene, such as 4,9:5,8-dimethylbridged-3a,4,4a,5,8,8a,9,9a-octahydro-1H-benzo[a]indene, 4,11:5,10:6,9-trimethylbridged-3a,4,4a,5,5a,6,9,9a,10,10a,11,11a-dodecylhydro-1H-cyclopentaenthracene. The above-mentioned nobornene resins can also be copolymers of nobornene monomers with other monomers.

[0071] As the aforementioned polycarbonate resin, aromatic polycarbonate is preferred. Aromatic polycarbonate can be typically obtained by reacting a carbonate precursor with an aromatic diphenol compound. Specific examples of carbonate precursors include phosgene, dichloroformate of diphenols, diphenyl carbonate, di-p-toluene carbonate, phenyl-p-toluene carbonate, di-p-chlorophenyl carbonate, and dinaphthalene carbonate. Among these, phosgene and diphenyl carbonate are preferred. Specific examples of aromatic diphenolic 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 can be used alone or in combination of two or more. 2,2-bis(4-hydroxyphenyl)propane, 1,1-bis(4-hydroxyphenyl)cyclohexane, and 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane are preferred. It is particularly preferred to use 2,2-bis(4-hydroxyphenyl)propane and 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane simultaneously.

[0072] The second phase difference layer is preferably an extension of a polymer membrane, and more preferably an extension of a norcamphene-based resin membrane. The thickness of the second retardation layer can be set in a manner that allows for the attainment of desired optical properties. When the second retardation layer is a liquid crystal alignment and curing 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 an extended 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.

[0073] F. Stack of the first phase difference layer and the second phase difference layer The stack volume of the first phase difference layer and the second phase difference layer preferably satisfies the following relationship: Re(450) / Re(550)>0.82 Re(650) / Re(550)<1.18. The Re(450) / Re(550) ratio of the laminate is preferably 1.0 to 1.2, and more preferably 1.0 to 1.1. The Re(650) / Re(550) ratio of the laminate is preferably 0.8 to 1.0, and more preferably 0.9 to 1.0. According to an embodiment of the present invention, a polarizing plate with a phase retardation layer can be obtained, which, although the first phase retardation layer and the second phase retardation layer as a whole do not exhibit ideal inverse dispersion characteristics, can realize an image display device with low oblique brightness and low oblique color shift when displaying black.

[0074] G. Liquid Crystal Unit The liquid crystal cell 60a includes a first substrate 62, a second substrate 63, and a liquid crystal layer 61 sandwiched between them. The liquid crystal layer 61 contains liquid crystal molecules aligned planarly in the absence of an electric field. In a typical configuration, a color filter and a black matrix are provided on one substrate (typically the first substrate 62), and the other substrate (typically the second substrate 63) provides: a switching element for controlling the electro-optical properties of the liquid crystal; a scan line providing a gate signal to the switching element and a signal line providing a source signal; and a pixel electrode and a counter electrode. The spacing between the substrates (cell gap) is controlled by pads. For example, an alignment film containing polyimide may be provided on the side of the substrate in contact with the liquid crystal layer.

[0075] The Rth (550) of the first substrate 62 and the second substrate 63 are -10 nm to 100 nm, respectively. 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 the thickness direction phase difference as described above, the oblique black brightness can be sufficiently reduced in a liquid crystal display device including liquid crystal cells with planar alignment.

[0076] In one embodiment, at least one of the first substrate 62 and the second substrate 63 satisfies the relationship Rth(450)>Rth(550), 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 satisfy the relationship Rth(550)>Rth(650). According to the embodiments of the present invention, even when the substrate has the wavelength dispersion characteristics described above, the oblique black brightness can be sufficiently reduced in a liquid crystal display device including liquid crystal cells with planar alignment.

[0077] As described above, the liquid crystal layer 61 contains liquid crystal molecules aligned along the surface in the absence of an electric field. "Liquid crystal molecules aligned along the surface" refers to a state where, due to the interaction between the aligned substrate and the liquid crystal molecules, the alignment vectors of the liquid crystal molecules are parallel to and aligned with respect to the substrate plane. The liquid crystal layer (resulting in liquid crystal cells) described above typically exhibits a refractive index characteristic of nx > ny = nz. Here, "ny = nz" includes not only the case where ny and nz are exactly the same, but also the case where ny and nz are substantially the same. The Re(550) of the liquid crystal layer can be, for example, 300 nm to 400 nm. The Nz coefficient of the liquid crystal layer can be, for example, 0.9 to 1.1.

[0078] In one embodiment, the liquid crystal molecules of the liquid crystal layer have a pretilt. That is, the alignment vector of the liquid crystal molecules is slightly tilted relative to the substrate plane. The pretilt angle is preferably 0.1° to 1.0°, more preferably 0.2° to 0.7°.

[0079] As for the driving mode of the liquid crystal cell 60a as described above, examples include the in-plane switching (IPS) mode and the edge field switching (FFS) mode. Furthermore, the IPS mode includes the super-flat switching (S-IPS) mode using V-shaped electrodes or sawtooth electrodes, or the advanced super-flat switching (AS-IPS) mode. Similarly, the FFS mode includes the advanced edge field switching (A-FFS) mode using V-shaped electrodes or sawtooth electrodes, or the ultra-edge field switching (U-FFS) mode. As for the driving mode of the liquid crystal cell 60a, the in-plane switching (IPS) mode is preferred. If the driving mode of the liquid crystal cell 60a is IPS mode, then the visibility of the liquid crystal display device at an angle can be improved.

[0080] H. Backlight unit The light source 91 is positioned corresponding to the side of the light guide plate 92. For example, an LED light source composed of a plurality of LEDs can be used. As the light guide plate 92, any suitable light guide plate can be used. For example, in order to deflect light from the lateral direction in the thickness direction, a light guide plate with a lens pattern formed on the back side, or a light guide plate with a prism shape formed on the back side and / or the viewing side, can be used. Preferably, a light guide plate with a prism shape formed on both the back side and the viewing side is used. In this light guide plate, it is preferable that the prism shapes formed on the back side and the prism shapes formed on the viewing side have orthogonal ridge directions. If a light guide plate as described above is used, light that is more easily focused can be incident on the prism (not shown). [Example]

[0081] The present invention will now be specifically described through examples, but the present invention is not limited to these examples. The methods for measuring each characteristic are described below.

[0082] (1) Measurement of phase difference The in-plane phase difference between the first and second phase retardation layers used in the embodiments and comparative examples was automatically measured using a KOBRA-WPR manufactured by Oji Measurement & Control Co., Ltd. The measurement wavelength was 550 nm, and the measurement temperature was 23°C. (2) Brightness when displaying black In the examples and comparative examples, a black screen was displayed on the image display device, and the brightness was measured using a luminance meter (manufactured by AUTRONIC-MELCHERS, trade name "Conoscope"). Specifically, the brightness was measured by varying the polar angle from 0° to 80° and the azimuth angle from 0° to 360°. Furthermore, the brightness measured as described above, with a polar angle of 40° and an azimuth angle of any one of 20°, 25°, 155°, 160°, 190°, 195°, 345°, and 350°, is taken as the brightness of region A (unit: cd / m 2), and the maximum brightness among them is taken as the maximum brightness of region A (unit: cd / m 2).

[0083] <Making of Polarizing Plates> <<Manufacturing Example 1>> As a thermoplastic resin substrate, a strip-shaped amorphous polyethylene terephthalate copolymer film (thickness: 100 μm) with a Tg of about 75°C is used to perform corona treatment on one side of the resin substrate. In a PVA-based resin mixture of polyvinyl alcohol (degree of polymerization 4200, degree of saponification 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "Gohsefimer") in a ratio of 9:1, 13 parts by weight of potassium iodide were added. The resulting solution was then dissolved in water to prepare a PVA aqueous solution (coating solution). The above-mentioned PVA aqueous solution is coated on the corona-treated surface of the resin substrate and dried at 60°C to form a PVA-based resin layer with a thickness of 13 μm, thereby producing a laminate. The resulting laminate was stretched uniaxially to 2.4 times its original length in an oven at 130°C (air-assisted stretching process). The laminate was then immersed in an insoluble bath (an aqueous solution of boric acid prepared 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 (insoluble treatment). Subsequently, the polarizing element is immersed in a dyeing bath (an iodine aqueous solution prepared by mixing iodine and potassium iodide in a weight ratio of 1:7 relative to 100 parts by weight of water) at a liquid temperature of 30°C for 60 seconds while adjusting the concentration to achieve the desired monomer transmittance (Ts) of the final polarizing element (dyeing treatment). Subsequently, the sample was immersed in a crosslinking bath at a liquid temperature of 40°C (a boric acid aqueous solution prepared by mixing 3 parts by weight of potassium iodide and 5 parts by weight of boric acid relative to 100 parts by weight of water) for 30 seconds (crosslinking treatment). Then, while immersing the laminate in a boric acid aqueous solution (boric acid concentration of 4 wt% and potassium iodide concentration of 5 wt%) at a liquid temperature of 70°C, uniaxial stretching (water stretching treatment) is performed between rollers with different circumferential speeds along the longitudinal direction (length direction) with a total stretching ratio of 5.5 times. Then, the laminate is immersed in a washing bath at a temperature of 20°C (an aqueous solution prepared by adding 4 parts by weight of potassium iodide to 100 parts by weight of water) (washing treatment). Then, while drying in an oven maintained at approximately 90°C, it comes into contact with SUS heated rollers whose surface temperature is maintained at approximately 75°C (drying shrinkage treatment). A polarizing element with a thickness of about 5 μm is formed on a resin substrate in the manner described above, thereby obtaining a laminate having a resin substrate / polarizing element composition. On the surface of the polarizing element of the obtained laminate (the side opposite to the resin substrate), an HC-TAC film (20 μm thick) is laminated as a protective layer. Then, the resin substrate is peeled off to obtain a polarizing plate having a protective layer / polarizing element. The obtained polarizing plate is then punched to a size corresponding to the liquid crystal cell described later.

[0084] Fabrication of a phase retardation film (positive B-plate) with refractive index characteristics of nz>nx>ny <<Manufacturing Example 2>> Granular resin of styrene-maleic anhydride copolymer (manufactured by Novartis Chemicals Japan Co., Ltd., trade name "Dylark D232") was extruded at 270°C using a uniaxial extruder and a T-die. The sheet-like molten resin was cooled with a cooling drum to obtain a film with a thickness of 100 μm. The film was then uniaxially stretched at the free end in the conveying direction using a roller stretcher at 130°C and a stretch ratio of 2.5 times to obtain a film with a fast axis in the conveying direction (longitudinal stretching step). The obtained film is stretched uniaxially at a fixed end in the width direction using a stretching machine at a temperature of 135°C, so that the film width reaches 4.5 times the width of the film after longitudinal stretching, thereby obtaining a phase retardation film (biaxially stretched film, positive B plate) with a thickness of 14 μm (transverse stretching step). Then, the obtained phase retardation film is punched into a size corresponding to the liquid crystal cell described later. The retardation film (positive B-plate) obtained as described above has a fast axis in the transport direction (and a slow axis in the width direction), and its refractive index characteristics show a relationship of nz>nx>ny. The in-plane phase difference Re (550), the phase difference Rth (550) in the thickness direction, and the Nz coefficient of the retardation film (positive B-plate) are shown in Table 1. <<Manufacturing Example 3>> Except for changing the longitudinal extension ratio to 1.7 times and the transverse extension ratio to 1.8 times, the phase difference film (positive B plate) was obtained in the same manner as in manufacturing example 2. <<Manufacturing Example 4>> Except for changing the longitudinal extension ratio to 1.5 times and the transverse extension ratio to 1.5 times, the phase difference film (positive B plate) was obtained in the same manner as in manufacturing example 2. <<Manufacturing Example 5>> Except for changing the longitudinal extension ratio to 1.4 times and the transverse extension ratio to 1.4 times, the phase difference film (positive B plate) was obtained in the same manner as in manufacturing example 2. <<Manufacturing Example 6>> Except for changing the longitudinal extension ratio to 2.2 times and the transverse extension ratio to 2.4 times, the phase difference film (positive B plate) was obtained in the same manner as in manufacturing example 2.

[0085] Fabrication of a phase retardation film (positive A plate) with refractive index characteristics nx>ny=nz <<Manufacturing Example 7>> A 28 μm thick retardation film was fabricated by uniaxially stretching a strip of nobornene resin film (manufactured by ZEON Corporation, Japan, trade name Zeonor, with a thickness of 40 μm and a photoelasticity of 3.10 × 10⁻¹² m² / N) to 2.0 times its original length at 135°C. The resulting retardation film was then punched to dimensions corresponding to the liquid crystal cell described later. The phase retardation film obtained as described above has a slow axis in the transport direction, and its refractive index characteristics show a relationship of nx > ny = nz. The in-plane phase difference Re (550), the phase difference Rth (550) in the thickness direction, and the Nz coefficient of the phase retardation film (positive A plate) are shown in Table 1. <<Manufacturing Example 8>> Except for changing the elongation ratio to 1.5 times, the phase difference film (positive A plate) was obtained in the same manner as in manufacturing example 7. <<Manufacturing Example 9>> Except for changing the elongation ratio to 1.43 times, the phase difference film (positive A plate) was obtained in the same manner as in manufacturing example 7. <<Manufacturing Example 10>> Except for changing the elongation ratio to 1.37 times, the phase difference film (positive A plate) was obtained in the same manner as in manufacturing example 7. <<Manufacturing Example 11>> Except for changing the elongation ratio to 1.2 times, the phase difference film (positive A plate) was obtained in the same manner as in manufacturing example 7.

[0086] Fabrication of a phase retardation film (positive C-plate) with refractive index characteristics nz>nx=ny <<Manufacturing Example 12>> Except for changing the phase difference Rth in the thickness direction to -86 nm, a phase retardation film (positive C plate) was obtained in the same manner as Manufacturing Example 6 of Japanese Patent No. 6896118. Then, the obtained phase retardation film was punched into a size corresponding to the liquid crystal cell described later. The phase retardation film obtained as described above has a slow axis in the transport direction, and its refractive index characteristics show a relationship of nz>nx=ny. The in-plane phase difference Re(550) and the phase difference Rth(550) in the thickness direction of the phase retardation film (positive C plate) are shown in Table 1. <<Manufacturing Example 13>> Except for changing the phase difference Rth in the thickness direction to -66 nm, a phase difference film (positive C plate) was obtained in the same manner as in manufacturing example 12.

[0087] Fabrication of a phase retardation film (negative B-plate) with refractive index characteristics of nx>ny>nz <<Manufacturing Example 14>> Except for extending the fixed end laterally by 1.35 times, the phase retardation film (negative B plate) is obtained in the same manner as in Manufacturing Example 7. Then, the obtained phase retardation film is punched into a size corresponding to the liquid crystal cell described later. The refractive index characteristics of the retardation film obtained as described above show a relationship of nx>ny>nz. The in-plane phase difference Re(550) and the phase difference Rth(550) in the thickness direction of the retardation film (negative B plate) are shown in Table 1. <<Manufacturing Example 15>> Except for changing the elongation ratio to 1.3 times, the phase difference film (negative B plate) was obtained in the same manner as in manufacturing example 14. <<Manufacturing Example 16>> Except for changing the elongation ratio to 1.2 times, the phase difference film (negative B plate) was obtained in the same manner as in manufacturing example 14.

[0088] Fabrication of a phase retardation film (negative A plate) with refractive index characteristics nx=nz>ny <<Manufacturing Example 17>> Granular resin of styrene-maleic anhydride copolymer (manufactured by Novartis Chemicals Japan, trade name "Dylark D232") was extruded at 270°C using a uniaxial extruder and a T-die. The molten resin in sheet form was cooled with a cooling drum to obtain a film with a thickness of 30 μm. This film was then uniaxially stretched at the free end in the conveying direction at a temperature of 130°C and an elongation of 1.8 times to obtain a phase retardation film (negative A plate) with a fast axis in the conveying direction. The obtained phase retardation film was then punched to the size corresponding to the liquid crystal cell described later. The refractive index characteristics of the retardation film obtained as described above show a relationship of nx=nz>ny. The in-plane phase difference Re(550) and the phase difference Rth(550) in the thickness direction of the retardation film (negative A plate) are shown in Table 1.

[0089] Preparation of Image Display Unit (Liquid Crystal Unit) <<Manufacturing Example 18>> The liquid crystal unit is removed from an IPS-based liquid crystal display device (manufactured by Apple Inc., trade name "iPad" (registered trademark)). The optical components attached to both sides of the liquid crystal unit are removed, and the removed surface (the outer surface of the substrate) is cleaned. It is used as an image display unit (liquid crystal unit). The first substrate of the liquid crystal unit has Rth(450) = 32 nm, Rth(550) = 19 nm, and Rth(650) = 23 nm; the second substrate has Rth(450) = 9 nm, Rth(550) = 0.3 nm, and Rth(650) = -6 nm.

[0090] [Example 1] On the viewing side of the liquid crystal cell in Manufacturing Example 18, a polarizing plate (a second polarizing plate including a second polarizing element) of Manufacturing Example 1 is laminated. On the other hand, on the back side of the liquid crystal cell, a retardation film (a second retardation layer) of Manufacturing Example 7, a retardation film (a first retardation layer) of Manufacturing Example 2, and a polarizing plate (a first polarizing plate including a first polarizing element) of Manufacturing Example 1 are sequentially laminated. The lamination is performed in the following manner: the absorption axis direction of the first polarizing element is substantially orthogonal to the slow axis direction of the first retardation layer; the absorption axis direction of the first polarizing element is substantially parallel to the slow axis direction of the second retardation layer; the absorption axis direction of the first polarizing element is substantially orthogonal to the initial alignment direction of the liquid crystal cell; and the absorption axis direction of the second polarizing element is substantially parallel to the initial alignment direction of the liquid crystal cell. An image display device (an E-mode liquid crystal display device) was manufactured in the manner described above. Then, the brightness of the image display device when subjected to the aforementioned black display was measured. The brightness distribution in the image display device of Example 1 is illustrated in FIG3. Furthermore, the maximum brightness of region A in the image display device of Embodiment 1 is shown in Table 1.

[0091] [Comparative Examples 1-8] Except that the phase retardation film (second phase retardation layer) of Manufacturing Example 7 and the phase retardation film (first phase retardation layer) of Manufacturing Example 2 were replaced with the phase retardation films of the manufacturing examples shown in Table 1, an image display device (E-mode liquid crystal display device) was manufactured in the same manner as in Example 1. Then, the brightness of the image display device when subjected to the aforementioned black display was measured. The brightness distribution in the image display device of Comparative Example 1 is illustrated in FIG4. Furthermore, the maximum brightness of region A in the image display devices of Comparative Examples 1 to 8 is shown in Table 1.

[0092] [Table 1] Table 1 No. Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Comparative Example 7 Comparative Example 8 Second phase Difference layer Manufacturing example Manufacturing Example 7 Manufacturing Example 8 Manufacturing Example 9 Manufacturing Example 13 Manufacturing Example 4 Manufacturing Example 5 Manufacturing Example 6 Manufacturing Example 4 Manufacturing Example 17 Refractive index characteristics nx>ny=nz nx>ny=nz nx>ny=nz nz>nx=ny nz>nx>ny nz>nx>ny nz>nx>ny nz>nx>ny nx=nz>ny Re(550) [nm] 326 173 155 0 twenty four 12 28 twenty four 73 Rth(550) [nm] 326 173 155 -66 -75 -68 -59 -75 0 Nz coefficient 1.0 1.0 1.0 - -3.1 -5.7 -2.1 -3.1 - First phase difference layer Manufacturing example Manufacturing Example 2 Manufacturing Example 3 Manufacturing Example 12 Manufacturing Example 10 Manufacturing Example 14 Manufacturing Example 14 Manufacturing Example 15 Manufacturing Example 16 Manufacturing Example 11 Refractive index characteristics nz>nx>ny nz>nx>ny nz>nx=ny nx>ny=nz nx>ny>nz nx>ny>nz nx>ny>nz nx>ny>nz nx>ny=nz Re(550) [nm] 323 37 0 136 116 116 98 89 93 Rth(550) [nm] -226 -90 -86 136 139 139 132 142 93 Nz coefficient -0.7 -2.4 - 1.0 1.2 1.2 1.3 1.6 1.0 Maximum brightness in area A [cd / m 2] 0.000661 0.001560 0.001605 0.000945 0.002257 0.000973 0.000945 0.000988 0.000745

[0093] [evaluate] As can be seen from Table 1, Figure 3 and Figure 4, by ensuring that the Re(550) and Nz coefficients of the first phase difference layer are within the above range, and the Re(550) of the second phase difference layer are within the above range, it is possible to realize an image display device (liquid crystal display device) that ensures that the viewing angle in the horizontal direction (X, the left-right direction of the paper in Figure 3 and Figure 4) is wider than the viewing angle in the vertical direction (Y, the up-down direction of the paper in Figure 3 and Figure 4), and that the maximum brightness of the above-mentioned area A is sufficiently small. [Industrial Applicability]

[0094] The polarizing plate with a phase retardation layer according to the embodiments of the present invention can be well used in image display devices, and in particular, it can be well used in liquid crystal display devices.

[0095] 10: First polarizing plate 11: First polarizing element 12: Protective layer 20: First phase difference layer 30: Second phase difference layer 40: Second polarizing plate 41: Second polarizing element 42: Protective layer 60: Image display unit 60a: Liquid Crystal Unit 61: Liquid Crystal Layer 62: First substrate 63: Second substrate 90: Backlight unit 91: Light source 92: Light guide plate 100: Polarizing plate with phase retardation layer 101: Image display device X: Left and right directions on the paper Y: Up and down direction on the paper []

Claims

1. A polarizing plate with a phase retardation layer, comprising: a first polarizing plate including a first polarizing element; a first phase retardation layer disposed adjacent to the first polarizing plate and having a refractive index characteristic showing the relationship nz>nx>ny; and a second phase retardation layer disposed adjacent to the first phase retardation layer and having a refractive index characteristic showing the relationship nx>ny=nz; wherein the absorption axis of the first polarizing element is substantially orthogonal to the slow axis of the first phase retardation layer, the absorption axis of the first polarizing element is substantially parallel to the slow axis of the second phase retardation layer, the in-plane phase difference Re(550) of the first phase retardation layer is 300 nm or more and 340 nm or less, the Nz coefficient of the first phase retardation layer is -1.0 or more and -0.1 or less, and the in-plane phase difference Re(550) of the second phase retardation layer is 300 nm or more and 340 nm or less.

2. An image display device comprising: an image display unit; and a polarizing plate with a phase retardation layer as claimed in claim 1, disposed on the opposite side of the viewing side relative to the image display unit.

3. The image display device as claimed in claim 2, wherein the image display unit is a liquid crystal unit and the driving mode of the liquid crystal unit is IPS mode.

4. The image display device of claim 3, wherein the image display device includes a second polarizing plate, the second polarizing plate being disposed on the opposite side of the polarizing plate with the phase retardation layer relative to the image display unit, the second polarizing plate including a second polarizing element, the absorption axis of the first polarizing element being substantially orthogonal to the initial alignment direction of the liquid crystal unit, and the absorption axis of the second polarizing element being substantially parallel to the initial alignment direction of the liquid crystal unit.

Images