Polarizing plate with phase retardation layer and image display device

Abstract

This invention provides a polarizing plate with a phase retardation layer for an image display device capable of achieving a wide viewing angle in the horizontal direction and sufficiently reducing the black brightness in the diagonal direction intersecting the horizontal and vertical directions. The polarizing plate with a phase retardation layer according to an embodiment of this invention comprises: a polarizing plate including a polarizing element; a first phase retardation layer whose refractive index characteristics show a relationship of nz > nx > ny; and a second phase retardation layer whose refractive index characteristics show a relationship of 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 170 nm or more and 250 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 185 nm or more and 265 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] For image display devices, such as liquid crystal displays, various optical films combining polarizing elements and retardation films are generally used to compensate for optical characteristics suitable for the application. For example, a technique has been proposed that combines a polarizing plate containing a polarizing element, a first retardation layer with refractive index characteristics showing the relationship nz>nx>ny, and a second retardation layer with refractive index characteristics showing 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, thereby expanding the viewing angle (see, for example, Patent Document 1). Furthermore, in recent years, the applications of image display devices have been diversifying. One example of this application is in-vehicle displays. For in-vehicle displays, a wide viewing angle in the horizontal (left-right) direction is particularly desirable. However, even when the technology described in Patent Document 1 is applied to in-vehicle displays, the wide viewing angle in the horizontal direction is limited. Moreover, when viewing the black display of an in-vehicle display from a diagonal direction intersecting the horizontal and vertical directions (e.g., from the upper right), there is a problem of insufficient blackness (i.e., the black brightness is not sufficiently reduced). [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 for 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 brightness in the diagonal direction that intersects the horizontal and vertical directions. [Technical means to solve the problem]

[0006] The polarizing plate with a phase retardation layer according to an embodiment of the present invention comprises: 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 170 nm or more and 250 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 185 nm or more and 265 nm or less. Another aspect of the image display device of the present invention includes: an image display unit; and a polarizing plate with a phase difference layer disposed on the viewing side of 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 (In-Plane Switching) mode. In one embodiment, the image display device includes a second polarizing plate disposed on the side of the image display unit opposite to the polarizing plate with the phase retardation layer. The second polarizing plate includes a second polarizing element. The absorption axis of the first polarizing element is substantially parallel 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 achieve a wide viewing angle of the image display device in the horizontal direction (a specific surface direction of the image display surface) and can sufficiently reduce the black brightness in the diagonal direction that intersects 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 displayed in black. Figure 4 is a brightness distribution diagram of the image display device of Comparative Example 1 when displaying in 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 is maximized (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. In addition, the "in-plane phase difference Re(550)" is sometimes referred to as the "front-side phase difference R0". Re(λ) is calculated using the formula: Re(λ) = (nx - ny) × d when the thickness of the layer (film) is set to d (nm). (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 λnm. For example, "Rth(550)" is the phase difference in the thickness direction measured at 23°C using light with a wavelength of 550 nm. Rth(λ) is calculated using the formula: Rth(λ) = (nx - nz) × d when the thickness of the layer (film) is set to d (nm). (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, when simply referred to as "orthogonal" or "parallel," it means a state that may include 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 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 from the first polarizing plate 10. In this specification, "disposed adjacently" means direct lamination or lamination only via an adhesive layer (e.g., an adhesive layer or bonding agent layer). That is, it means that no optical functional layer (e.g., other retardation layers) exists 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 (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 170 nm or more and 250 nm or less, preferably 180 nm or more and 240 nm or less, more preferably 190 nm or more and 230 nm or less, and even more preferably 200 nm or more and 220 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 -0.7 and below -0.4. The in-plane phase difference Re(550) of the second phase difference layer 30 is 185 nm or more and 265 nm or less, preferably 195 nm or more and 255 nm or less, more preferably 205 nm or more and 245 nm or less, and even more preferably 215 nm or more and 235 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 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 specific surface direction of the image display surface) can be achieved, and the black brightness in the diagonal 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, which is 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 diagonal direction intersecting the horizontal (first surface direction X) and vertical (second surface direction Y) directions can be sufficiently reduced. More specifically, when the brightness of the black display of the image display device is measured using any suitable luminance meter within the ranges of polar angle 40°~42° and azimuth angle 20°~25°, 155°~160°, 190°~195°, and 345°~350°, it is preferably less than 0.00080, more preferably less than 0.00070, and even more preferably less than 0.00060. Furthermore, in this specification, the brightness measured within the aforementioned polar angle and azimuth angle range is defined as the brightness of region A. The lower limit of the brightness of region A is representatively greater than or equal to 0.00001.

[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 in this range, 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 specific 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 (opposite to the first polarizing plate). When a conductive layer or an isotropic substrate with a conductive layer is to be 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 assembled between an image display unit (e.g., a liquid crystal unit, an organic EL unit) and the first polarizing plate.

[0014] A polarizing plate with a phase retardation layer may further include other phase retardation layers. The optical properties (such as refractive index, in-plane phase retardation, Nz coefficient, photoelastic coefficient), thickness, and placement of other phase 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 with a length that is sufficiently long relative to its width, for example, including long, thin shapes with a length that is more than 10 times, preferably more than 20 times, the length relative to its width. The strip-shaped polarizing plate with the retardation layer can be rolled into a roll.

[0016] In practical use, 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 to temporarily attach a release liner to the surface of the adhesive layer before the polarizer with the retardation layer is put into use. By temporarily attaching 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 viewing side of 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 example further includes a second polarizing plate 40 disposed on the image display unit 60 on the opposite side (opposite to the viewing side) of the polarizing plate 100 with the phase difference layer. 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 in so-called O-mode. "O-mode liquid crystal display device" refers to a liquid crystal display device in which the absorption axis (second absorption axis direction) of the polarizing element (in this embodiment, the second polarizing element 41) disposed on the opposite side (back side) of the viewing side of the liquid crystal unit is substantially parallel to the initial alignment direction of the liquid crystal unit. "Initial alignment direction of the liquid crystal unit" refers to the direction in which, in the absence of an electric field, the liquid crystal molecules contained in the liquid crystal layer align, resulting in the liquid crystal layer having the maximum in-plane refractive index (i.e., the slow axis direction).

[0020] In one embodiment, the absorption axis (direction of the first absorption axis) of the polarizing element (the first polarizing element 11 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 is substantially parallel to the absorption axis direction of the second polarizing element 41. With this configuration, excellent visibility can be achieved even when viewing the displayed image through a polarizing lens such as polarized sunglasses.

[0021] In practical use, 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 suitable other components (e.g., diffuser, prism). In the example shown, the backlight unit 90 is an edge-illuminated type; however, any suitable other type (e.g., direct-lit type) may be used as the backlight unit 90.

[0022] The image display device (liquid crystal display device) may further include any other suitable components. For example, other optical compensation layers (phase retardation layers) may be further configured. The optical characteristics, number, combination, and configuration position of other optical compensation layers may be appropriately selected according to the target and desired optical characteristics. Matters not described in this specification may be constructed using image display devices (liquid crystal display devices) that are well known and commonly used in the art.

[0023] This type of image display device is suitable for applications that particularly require a wide horizontal viewing angle and reduced brightness in area A when displaying black (especially applications requiring high resolution and the ability for multiple people to share the screen). Representative examples of image display devices include: automotive displays, medical monitors, and gaming screens, with automotive displays being a particularly good example.

[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 simply referred to as polarizing element) 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 polarizing elements made 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 perspective of superior optical properties, polarizing elements obtained by dyeing PVA films with iodine and then uniaxially stretching them are preferred.

[0027] The aforementioned dyeing using iodine can be 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 needs, the PVA membrane may undergo swelling, cross-linking, washing, or drying treatments. For example, immersing the PVA membrane in water for washing before dyeing not only removes surface contaminants and 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, thereby obtaining a laminate of the resin substrate and the PVA-based resin layer; and then stretching and dyeing the laminate to form a polarizing element from the PVA-based resin layer. In this embodiment, typically, stretching includes immersing the laminate in an aqueous boric acid solution for stretching. Furthermore, stretching may, if necessary, further 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 also 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 for the desired purpose can be laminated on the peeled surface for use. Detailed descriptions of this method for manufacturing a polarizing element 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, further preferably 3 μm to 12 μm, and even more preferably 3 μm to 8 μm. If the thickness of the polarizing element is within this range, 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 Each of the first polarizing plate 10 and the second polarizing plate 40 may further include 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 includes a protective layer 12 disposed on the viewing side of the first polarizing element 11, and the second polarizing plate 40 includes a protective layer 42 disposed on the side opposite to 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. Additionally, 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. Furthermore, examples include, for instance, glassy polymers such as silicate polymers. Additionally, polymer films described in Japanese Patent Application Publication No. 2001-343529 (WO01 / 37007) can also be used. As the material for this membrane, for example, a resin composition containing a thermoplastic resin having substituted or unsubstituted amide groups on the side chains, and a thermoplastic resin having substituted or unsubstituted phenyl and nitrile groups on the side chains can be used. Examples include resin compositions having alternating copolymers formed from 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 exhibit a relationship of nz>nx>ny. Layers (films) exhibiting this refractive index characteristic are sometimes referred to as "positive biaxial plates," "positive B plates," etc.

[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 making the thickness of the first retardation layer within this range, the manufacturability during manufacturing is excellent, and the optical uniformity of the obtained 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 this configuration, the phase difference shift and unevenness caused by the shrinkage stress of the polarizing element and / or the heat of the light source can be reduced, and it can help to achieve a thinner 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, it is preferable that the optical properties of the retardation film are the same as those of the first retardation layer. Therefore, the phase difference value of the adhesive layer, bonding agent layer, etc., used when the retardation film is deposited on the polarizing element and / or the second retardation layer, 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 water resistance, and one that is not easily affected by optical inhomogeneities due to strain. 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 becomes relatively small. In other words, it means that the refractive index in the direction orthogonal to the extension direction becomes large. 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, the birefringence properties of the obtained resin can also be controlled by substituting the side chains or carrying out maleicimization or grafting reactions after polymerization.

[0044] The above demonstrates that polymers with negative birefringence can also be copolymerized with other monomers. Copolymerization with other monomers can improve brittleness, processability, and heat resistance. 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.

[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 this range, a polymer film with excellent toughness and processability can be obtained.

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

[0047] As for the polymer exhibiting negative birefringence, it is preferable to use a polymer having repeating units represented by the following general formula (I). Such a polymer can exhibit higher negative birefringence and has excellent heat resistance and mechanical strength. Such a polymer can be obtained, for example, by using N-phenyl-substituted maleimide, wherein the N-phenyl-substituted maleimide is introduced into a maleimide monomer with an N-substituent having at least a substituent at the ortho position as a starting material. [Chemical Formula 1]

[0048] In the above general formula (I), R1 to R5 independently represent hydrogen, halogen atoms, carboxylic acids, carboxylic acid esters, hydroxyl groups, nitro groups, or straight-chain or branched alkyl or alkoxy groups 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 groups with 1 to 8 carbon atoms, and n represents an integer of 2 or more.

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

[0050] The aforementioned polymer film may also contain any appropriate 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 leach from the surface of the polymer film.

[0051] Any suitable forming method can be used as the forming method for the aforementioned polymer film. Examples include: compression molding, transfer molding, injection molding, extrusion molding, blow molding, powder molding, FRP (fiber reinforced plastics) 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 is a method in which a resin composition containing the aforementioned thermoplastic resin, plasticizer, additives, etc., is heated and melted, and then extruded in thin film form on the surface of a casting roller using a T-die or the like, and then cooled to form a film. Solvent casting is a method in which the aforementioned resin composition is dissolved in a solvent, the resulting viscous solution (concentrate) is degassed, and then uniformly cast in thin film form on the surface of a metallic belt, rotating roller, or plastic substrate, and the solvent is evaporated to form a film. Furthermore, the molding conditions can be appropriately set according to the composition and type of the resin used, the molding process, etc.

[0052] The aforementioned phase retardation 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. This is because a biaxial phase difference film can be appropriately obtained. For the polymer exhibiting negative birefringence, as mentioned above, the refractive index in the extension direction is relatively smaller. Therefore, 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 become slow axes depending on the ratio of the longitudinal to transverse extension ratios. Specifically, if the extension ratio in the longitudinal (transport) direction is relatively increased, the transverse (width) direction becomes a slow axis; if the extension ratio in the transverse (width) direction is relatively increased, the longitudinal (transport) direction becomes a slow axis. As the stretching device used in the above-mentioned stretching, any suitable stretching device can be used. Specific examples include: roller stretching machines, tenter stretching machines, and biaxial stretching machines with telescopic or linear motors. When stretching is performed while heating, the temperature can be changed continuously or in stages. In addition, the stretching step can be divided into two or more steps.

[0053] In addition, by adjusting the thickness of the polymer film (preform 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 (preform thickness) is typically 10 μm or more, preferably 20 μm or more, even more preferably 30 μm or more, typically less than 200 μm, preferably less than 100 μm, even more preferably less than 80 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 even more preferably (Tg+5)℃ to (Tg+20)℃. If the stretching temperature is too low, there is a risk that the phase difference value and the direction of the slow axis will become uneven, or the polymer film may crystallize (become cloudy). On the other hand, if the stretching temperature is too high, there is a risk that the polymer film will melt or the phase difference will become insufficient. A representative stretching temperature is 110~200℃. Furthermore, the glass transition temperature can be determined by the 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 that circulates hot or cold air, heaters that utilize microwaves or far-infrared rays, heated temperature regulating rollers, heat pipe rollers, or metal belts can be used.

[0056] The stretching ratio for stretching a polymer membrane can be set to any appropriate value based on the composition of the polymer membrane, 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 1.20 to 1.65 times. Furthermore, considering the mechanical precision and stability of the stretching device, the conveying 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. As a method for obtaining a retardation film using a polymer exhibiting positive birefringence, for example, methods for increasing the refractive index in the thickness direction disclosed in Japanese Patent Application Publications Nos. 2000-231016, 2000-206328, and 2002-207123 can be used. 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 causing the film to shrink under the shrinkage force of the heat-shrinkable film resulting from the heat treatment, the film shrinks in both the length and width directions, thereby increasing the refractive index in the thickness direction, and a retardation film with a refractive index ellipsoid of nz>nx>ny can be obtained.

[0058] Thus, the positive B-plate used in the first retardation layer can also be manufactured using a polymer that exhibits either positive or negative birefringence. Generally, when using a polymer exhibiting positive birefringence, there is an advantage in that more types of polymers can be selected; when using a polymer exhibiting negative birefringence, compared to using a polymer exhibiting positive birefringence, the retardation film with excellent uniformity in the slow axis direction can be easily obtained due to its stretching method, which is advantageous from this perspective.

[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. Alternatively, films that have undergone secondary processing, such as stretching and / or relaxation processing, can also be used.

[0060] The aforementioned retardation film preferably has a light transmittance of 80% or more at a wavelength of 550 nm, more preferably 85% or more, and even more preferably 90% or more. The theoretical upper limit of light transmittance is 100%, but considering the surface reflection caused by the difference in refractive index between air and the retardation film, the achievable upper limit of light transmittance is approximately 94%. Preferably, the first retardation layer has a uniform light transmittance throughout.

[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 even more preferably 1.5 × 10⁻¹¹ (m² / N) or less. By setting the photoelastic coefficient within this range, an image display device with excellent optical uniformity and minimal changes in optical properties even under high temperature and high humidity environments, as well as excellent durability, can be obtained. There is no particular limitation on the lower limit of the photoelastic coefficient, but it is typically 5.0 × 10⁻¹³ (m² / N) or more, 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. The photoelasticity coefficient can be reduced by copolymerizing or mixing multiple components with different signs (positive and negative) of the photoelasticity coefficient.

[0062] E. Second phase difference layer As described above, the refractive index characteristics of the second phase retardation layer 30 exhibit a relationship of nx > ny = nz. Layers (films) exhibiting this refractive index characteristic are sometimes referred to as "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 for the material forming the second retardation layer, any suitable material can be used as long as the properties described above are obtained. Specifically, the second retardation layer can be an alignment and curing layer of a liquid crystal compound (liquid crystal alignment and curing layer) or a 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 of the obtained retardation layer can be made significantly greater than that of a non-liquid crystal material. 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 (resulting in an 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 specific direction and the 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 below. In this embodiment, typically, rod-shaped liquid crystal compounds are aligned (horizontally aligned) in a state where they are aligned along the slow axis direction of the second retardation layer.

[0065] Examples of liquid crystal compounds include those with a nematic phase (nematic liquid crystals). Liquid crystal polymers and monomers can be used as such compounds. The liquid crystal properties of the liquid crystal compound can be either lyotropic or thermotropic. Liquid crystal polymers and 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, the alignment state can be fixed simply by polymerizing or crosslinking the liquid crystal monomers. Here, a polymer is formed by polymerization, and a three-dimensional network structure is formed by crosslinking, but these are non-liquid crystals. Therefore, the formed second retardation layer does not undergo the temperature-induced phase shift to liquid crystal, glassy, ​​or crystalline phase characteristic of liquid crystal compounds. As a result, the formed second retardation layer becomes a retardation layer with 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 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 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 (preform 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 (preform 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~2.50x, and more preferably 1.42x~2.00x.

[0069] Any suitable resin can be used as the resin for forming the aforementioned polymer film. Specific examples include: nobornene-based resins, polycarbonate-based resins, cellulose-based resins, polyvinyl alcohol-based resins, and polyurethane-based resins, which constitute positive birefringent films. Among these, nobornene-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 such 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-ethylidene-2-norbornene, etc., and their halogenated or other polar substituted derivatives; dicyclopentadiene, 2,3-dihydrodicyclopentadiene, etc.; dimethylene octahydronaphthalene, its alkyl and / or alkylene-substituted derivatives, etc. Or alkylene-substituted derivatives and polar halogen-substituted derivatives, such as 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, 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, etc.; trimers to tetramers 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-cyclopentanthracene. The above-mentioned nobornene resins can be copolymers of nobornene monomers with other monomers.

[0071] As the aforementioned polycarbonate resin, aromatic polycarbonate is preferred. Aromatic polycarbonate can typically be obtained by reacting a carbonate precursor with an aromatic diphenol compound. Specific examples of carbonate precursors include: carbohydrates, dichloroformates of diphenols, diphenyl carbonate, di-p-toluene carbonate, phenyl-p-toluene carbonate, di-p-chlorophenyl carbonate, and dinaphthalene carbonate. Among these, carbohydrates 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. Preferred are 2,2-bis(4-hydroxyphenyl)propane, 1,1-bis(4-hydroxyphenyl)cyclohexane, and 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane. It is particularly advantageous to use 2,2-bis(4-hydroxyphenyl)propane together with 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane.

[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 to achieve the 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 an attached 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 achieve an image display device with low brightness in the oblique direction and low color shift in the oblique direction 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 in a planar manner 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 a switching element for controlling the electro-optical characteristics of the liquid crystal, a scan line for imparting a gate signal to the switching element, a signal line for imparting a source signal, a pixel electrode, and an opposing electrode are provided on the other substrate (typically the second substrate 63). The spacing between the substrates (cell gap) is controlled by a spacer or the like. An alignment film, for example, formed of polyimide, can 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 the embodiments of the present invention, when the substrate has such a phase difference in the thickness direction, the black brightness in the oblique direction can be sufficiently reduced in a liquid crystal display device including horizontally aligned liquid crystal cells.

[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 of 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 of 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 such wavelength dispersion characteristics, in a liquid crystal display device including horizontally aligned liquid crystal cells, the black brightness in the oblique direction can be sufficiently reduced.

[0077] As described above, the liquid crystal layer 61 comprises liquid crystal molecules aligned in a plane-oriented manner in the absence of an electric field. "Liquid crystal molecules aligned in a plane-oriented manner" refers to liquid crystal molecules in which the alignment vectors of the liquid crystal molecules are aligned parallel and uniformly with respect to the plane of the substrate due to the interaction between the aligned substrate and the liquid crystal molecules. This type of liquid crystal layer (resulting in liquid crystal cells) 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 are pre-tilted. That is, the alignment vector of the liquid crystal molecules is slightly tilted relative to the substrate plane. The pre-tilt angle is preferably 0.1° to 1.0°, more preferably 0.2° to 0.7°.

[0079] Examples of driving modes for this type of liquid crystal cell 60a include: Lateral Electric Field Effect (IPS) mode and Edge Field Switching (FFS) mode. Furthermore, the aforementioned IPS mode includes Super Lateral Electric Field Effect (S-IPS) mode and Advanced Super Lateral Electric Field Effect (AS-IPS) mode, which employs V-shaped electrodes or sawtooth electrodes. Additionally, the aforementioned FFS mode includes Advanced Edge Field Switching (A-FFS) mode and Ultra Edge Field Switching (U-FFS) mode, which employ V-shaped electrodes or sawtooth electrodes. Preferably, the lateral electric field effect (IPS) mode is used as the driving mode for the liquid crystal cell 60a. When the driving mode of the liquid crystal cell 60a is IPS mode, the visibility of the liquid crystal display device in the oblique direction 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 multiple LEDs arranged in a grid 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 towards 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 can be used. In this light guide plate, the prism shape formed on the back side and the prism shape formed on the viewing side are preferably orthogonal in their ridge directions. Using this type of light guide plate allows light that is more easily focused to 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. The measurement wavelength was 550 nm, and the measurement temperature was 23°C. (2) Brightness when displaying black In the image display devices obtained in the embodiments and comparative examples, a black screen was displayed, 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°. In addition, among the brightness measured in the above manner, the brightness at any angle among the polar angle of 40° and azimuth angles of 20°, 25°, 155°, 160°, 190°, 195°, 345° and 350° is set as the brightness of region A (unit: cd / m 2), and the maximum brightness among them is set 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. Potassium iodide was added to 100 parts by weight of a PVA-based resin prepared by mixing polyvinyl alcohol (degree of polymerization 4200, degree of saponification 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Japan Synthetic Chemical Industry Co., Ltd., product name "GOHSEFIMER") in a 9:1 ratio. The resulting substance was 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 obtained laminate was uniaxially stretched 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, in a dyeing bath at a liquid temperature of 30°C (an iodine aqueous solution obtained by mixing iodine and potassium iodide in a weight ratio of 1:7 relative to 100 parts by mass of water), the concentration was adjusted to make the final polarizing element's monomer transmittance (Ts) reach the desired value, while immersing for 60 seconds (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 mass of potassium iodide and 5 parts by mass of boric acid with 100 parts by mass 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, it was uniaxially stretched (water stretching treatment) in the longitudinal direction (length direction) between rollers with different circumferential speeds, with a total stretch ratio of 5.5 times. Then, the laminate is immersed (washed) in a washing bath at a liquid temperature of 20°C (an aqueous solution of 4 parts by mass of potassium iodide mixed with 100 parts by mass of water). Then, while drying in an oven maintained at approximately 90°C, it is brought into contact with SUS heated rollers whose surface temperature is maintained at approximately 75°C (drying shrinkage treatment). Thus, a first polarizing element with a thickness of about 5 μm is formed on the resin substrate, and a laminate with the structure of resin substrate / first polarizing element is obtained. An HC-TAC film (20 μm thick) is laminated as a protective layer onto the surface of the polarizing element (the side opposite to the resin substrate) of the obtained laminate. Next, the resin substrate is peeled off to obtain a first polarizing plate having the protective layer / first polarizing element / . Then, the obtained first polarizing plate is 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>> Using a uniaxial extruder and a T-die, granular resin of styrene-maleic anhydride copolymer (manufactured by NOVA Chemicals Japan, product name "DYLARK D232") was extruded at 270°C. The sheet-like molten resin was cooled using a cooling drum to obtain a film with a thickness of 50 μm. Using a roll stretcher, the film was uniaxially stretched at the free end in the conveying direction at a temperature of 130°C with an elongation ratio of 1.4 times to obtain a film with a fast axis in the conveying direction (longitudinal stretching step). Using a tenter frame, the obtained film is uniaxially stretched along its width at a fixed end at a temperature of 135°C, with the film width being 1.6 times the width of the film after longitudinal stretching, to obtain a 10 μm thick phase retardation film (biaxially stretched film, positive B-plate) (lateral stretching step). Then, the obtained phase retardation film is punched to the size corresponding to the liquid crystal cell described later. The phase retardation film (positive B-plate) thus obtained 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 phase retardation film (positive B-plate) are shown in Table 1. <<Manufacturing Example 3>> The thickness of the film before stretching was changed to 100 μm, the longitudinal stretching ratio was changed to 1.6 times, and the transverse stretching ratio was changed to 1.7 times. Otherwise, the phase difference film (positive B plate) was obtained in the same way as in manufacturing example 2. <<Manufacturing Example 4>> The longitudinal extension ratio was changed to 1.7 times, and otherwise, a phase difference film (positive B plate) was obtained in the same manner as in manufacturing example 3. <<Manufacturing Example 5>> The longitudinal elongation ratio was changed to 1.8 times and the lateral elongation ratio was changed to 1.9 times. Otherwise, the phase difference film (positive B plate) was obtained in the same manner as in manufacturing example 3. <<Manufacturing Example 6>> The longitudinal elongation ratio was changed to 2.3 times and the lateral elongation ratio was changed to 2.2 times. Otherwise, the phase difference film (positive B plate) was obtained in the same manner as in manufacturing example 3. <<Manufacturing Example 7>> The lateral extension ratio was changed to 1.8 times, and otherwise, a phase difference film (positive B plate) was obtained in the same manner as in manufacturing example 3.

[0085] Fabrication of a phase retardation film (positive A plate) with refractive index characteristics nx>ny=nz <<Manufacturing Example 8>> A strip of nobornene resin film (manufactured by Zeon Corporation, Japan, product name Zeonor, thickness 40 μm, photoelasticity coefficient 3.10 × 10⁻¹² m² / N) was uniaxially stretched to 1.7 times at 140°C to produce a 31 μm thick retardation film. The obtained retardation film was then punched to dimensions corresponding to the liquid crystal cell described later. The phase retardation film thus obtained 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 9>> The elongation ratio was changed to 1.39 times, and otherwise, a phase difference film (positive A plate) was obtained in the same manner as in manufacturing example 8. <<Manufacturing Example 10>> The elongation ratio was changed to 1.3 times, and otherwise, a phase difference film (positive A plate) was obtained in the same manner as in manufacturing example 8. <<Manufacturing Example 11>> The elongation ratio was changed to 1.37 times, and otherwise, a phase difference film (positive A plate) was obtained in the same manner as in manufacturing example 8.

[0086] Fabrication of a phase retardation film (positive C-plate) with refractive index characteristics nz>nx=ny <<Manufacturing Example 12>> The phase difference Rth in the thickness direction was changed to -85 nm. Otherwise, a phase difference film (positive C plate) was obtained in the same manner as in Manufacturing Example 6 of Japanese Patent No. 6896118. Then, the obtained phase difference film was punched to a size corresponding to the liquid crystal cell described later. The phase retardation film thus obtained 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>> The phase difference Rth in the thickness direction was changed to -114 nm, and otherwise 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>> The fixed end is extended laterally by 1.35 times, and otherwise, a phase retardation film (negative B plate) is obtained in the same manner as in Manufacturing Example 8. 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 phase retardation film thus obtained 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 phase retardation film (negative B plate) are shown in Table 1. <<Manufacturing Example 15>> The elongation ratio was changed to 1.3 times, and otherwise, a phase difference film (negative B plate) was obtained in the same manner as in manufacturing example 14. <<Manufacturing Example 16>> The thickness of the film before stretching was changed to 20 μm, and the stretching ratio was changed to 1.5 times. Otherwise, the phase difference film (negative B plate) was obtained in the same way 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>> Using a uniaxial extruder and a T-die, granular resin of styrene-maleic anhydride copolymer (manufactured by NOVA Chemicals Japan, product name "DYLARK D232") was extruded at 270°C. The sheet-like molten resin was cooled using a cooling drum to obtain a film with a thickness of 50 μm. Using a roll stretcher, the film was uniaxially stretched at a free end in the conveying direction at a temperature of 130°C with an elongation of 1.8 times to obtain a phase retardation film (negative A plate) with a fast axis in the conveying direction. Then, the obtained phase retardation film was punched to the size corresponding to the liquid crystal cell described later. The refractive index characteristics of the phase retardation film thus obtained 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 phase 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 was removed from an IPS-mode 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 were removed, and the removed surface (the outer surface of the substrate) was cleaned. It was then 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] The phase retardation film (second phase retardation layer) of Example 8, the phase retardation film (first phase retardation layer) of Example 2, and the polarizing plate (first polarizing plate including the first polarizing element) of Example 1 are sequentially deposited on the viewing side of the liquid crystal cell of Example 18. On the other hand, a polarizing plate (a second polarizing plate including a second polarizing element) of Example 1 is fabricated by laminating a layer on the back side of the liquid crystal cell. The lamination is performed such that 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, and the absorption axis directions of the first and second polarizing elements are substantially parallel to the initial alignment direction of the liquid crystal cell. An image display device (a liquid crystal display device in O-mode) is thus fabricated. Next, the brightness of the image display device is measured when it is displayed in black as described above. The brightness distribution of the image display device of Example 1 is illustrated in FIG3. Furthermore, the maximum brightness of region A of the image display device of Example 1 is shown in Table 1.

[0091] [Comparative Examples 1-9] The phase retardation film (second phase retardation layer) of Manufacturing Example 8 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. Otherwise, the image display device (O-mode liquid crystal display device) was manufactured in the same manner as in Example 1. Next, the brightness of the image display device was measured when it was displayed in black as described above. The brightness distribution of the image display device of Comparative Example 1 is illustrated in FIG4. Furthermore, the maximum brightness of region A of the image display devices of Comparative Examples 1 to 9 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 Comparative Example 9 Phase difference layer 1 Manufacturing example Manufacturing Example 2 Manufacturing Example 3 Manufacturing Example 12 Manufacturing Example 11 Manufacturing Example 14 Manufacturing Example 14 Manufacturing Example 15 Manufacturing Example 14 Manufacturing Example 15 Manufacturing Example 16 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 nx>ny>nz Re(550) [nm] 208 35 0 137 116 116 98 116 98 82 Rth(550) [nm] -104 -85 -85 137 139 139 132 139 132 90 Nz coefficient -0.5 -2.4 - 1.0 1.2 1.2 1.3 1.2 1.3 1.1 Second phase difference layer Manufacturing example Manufacturing Example 8 Manufacturing Example 9 Manufacturing Example 10 Manufacturing Example 13 Manufacturing Example 4 Manufacturing Example 5 Manufacturing Example 3 Manufacturing Example 6 Manufacturing Example 7 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 nz>nx>ny nx=nz>ny Re(550) [ nm] 226 141 124 0 32 twenty four 35 16 43 120 Rth(550) [nm] 226 141 124 -114 -87 -93 -85 -112 -90 0 Nz coefficient 1.0 1.0 1.0 - -2.7 -3.9 -2.4 -7.0 -2.1 - Maximum luminance of region A [cd / m²] 0.000532 0.000800 0.000822 0.000880 0.001312 0.001253 0.001627 0.000905 0.000913 0.000851

[0093] [evaluate] According to Table 1, Figure 3 and Figure 4, it is clear that by making the Re(550) and Nz coefficients of the first phase difference layer within the above range, and making the Re(550) of the second phase difference layer within the above range, it is possible to achieve an image display device (liquid crystal display device) that ensures a wider viewing angle in the horizontal direction (X, the left-right direction of the paper in Figure 3 and Figure 4) than 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 phase retardation layer of the present invention is suitable for image display devices, and is particularly suitable for liquid crystal display devices.

[0095] 10: 1st polarizing plate 11: First polarizing element 12 protective layers 20: First phase difference layer 30: Second phase difference layer 40: 2nd polarizing plate 41: Second polarizing element 42: Protective layer 60: Image display unit 60a: Liquid Crystal Unit 61: Liquid Crystal Layer 62: 1st substrate 63: 2nd substrate 90: Backlight unit 91: Light source 92: Light guide plate 100: Polarizing plate with phase retardation layer 101: Image display device X: Direction of the first face Y: 2nd side direction

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 exhibiting 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 exhibiting the relationship nx > ny = nz; wherein the second phase retardation layer is located on the side of the first phase retardation layer opposite to the first polarizing plate; the angle between the absorption axis of the first polarizing element and the slow axis of the first phase retardation layer is in the range of 90° ± 10°; the angle between the absorption axis of the first polarizing element and the slow axis of the second phase retardation layer is in the range of 0° ± 10°; and the in-plane phase difference Re(550) of the first phase retardation layer is 170 nm or more and 250 nm or less. The Nz coefficient of the first phase difference layer is above -1.0 and below -0.1, and the in-plane phase difference Re(550) of the second phase difference layer is above 185 nm and below 265 nm.

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 viewing side of 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 disposed on the side of the image display unit opposite to the polarizing plate with the phase retardation layer, the second polarizing plate includes a second polarizing element, the angle between the absorption axis of the first polarizing element and the initial alignment direction of the liquid crystal unit is in the range of 0°±10°, and the angle between the absorption axis of the second polarizing element and the initial alignment direction of the liquid crystal unit is in the range of 0°±10°.

Images