Phase difference layer-equipped polarizing plate and image display device

Abstract

To provide a polarizing plate with a phase difference layer that can achieve an image display device that can widen a viewing angle in a transverse direction and sufficiently reduce black luminance in an oblique direction intersecting both the vertical and transverse directions.SOLUTION: A polarizing plate with a phase difference layer according to an embodiment of the present invention has: a polarizing plate including a polarizer; a first phase difference layer having refractive index characteristics indicating a relationship of nz>nx>ny; and a second phase difference layer having refractive index characteristics indicating a relationship of nx>ny=nz. An absorption axis of the polarizer and a slow axis of the first phase difference layer are substantially orthogonal to each other, and an absorption axis of the polarizer and a slow axis of the second phase difference layer are substantially parallel to each other. The Re(550) of the first phase difference layer is 170 nm or more and 250 nm or less, and an Nz coefficient of the first phase difference layer is -1.0 or more and -0.1 or less. The Re(550) of the second phase difference layer is 185 nm or more and 265 nm or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a polarizing plate with a retardation layer and an image display device.

Background Art

[0002] In image display devices typified by liquid crystal display devices, various optical films combining a polarizer and a retardation film are generally used to compensate for optical characteristics suitable for the application. For example, a polarizing plate including a polarizer, a first retardation layer having a refractive index characteristic of nz > nx > ny, and a second retardation layer having a refractive index characteristic of nx > ny = nz are combined such that the absorption axis of the polarizer is orthogonal to the slow axis of the first retardation layer and the absorption axis of the polarizer is parallel to the slow axis of the second retardation layer, and a technique for expanding the viewing angle has been proposed (see, for example, Patent Document 1). By the way, in recent years, the applications of image display devices have been diversifying. As an example of such applications, an in-vehicle display can be mentioned. In an in-vehicle display, in particular, a wider viewing angle in the horizontal direction (left-right direction) is required. However, even when the technique described in Patent Document 1 is applied to an in-vehicle display, there is a limit to expanding the viewing angle in the horizontal direction, and in addition, there is a problem that the black display of the in-vehicle display does not become sufficiently black (that is, the black luminance does not become sufficiently small) when viewed from an oblique direction (for example, diagonally upward to the right) intersecting both the vertical and horizontal directions.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The present invention has been made to solve the above-described conventional problems, and its main object is to provide a retardation film - attached polarizing plate capable of achieving a wide viewing angle in the horizontal direction (a predetermined plane direction of the image display surface) and sufficiently reducing the black luminance in an oblique direction intersecting both the vertical and horizontal directions, and realizing an image display device with such capabilities.

Means for Solving the Problems

[0005] The retardation film - attached polarizing plate according to an embodiment of the present invention includes a first polarizing plate including a first polarizer, a first retardation layer having a refractive index characteristic showing a relationship of nz > nx > ny, and a second retardation layer having a refractive index characteristic showing a relationship of nx > ny = nz. The first retardation layer is disposed adjacent to the first polarizing plate, and the second retardation layer is disposed adjacent to the first retardation layer. The absorption axis of the first polarizer and the slow axis of the first retardation layer are substantially orthogonal, and the absorption axis of the first polarizer and the slow axis of the second retardation layer are substantially parallel. The in - plane retardation Re(550) of the first retardation layer is 170 nm or more and 250 nm or less, and the Nz coefficient of the first retardation layer is - 1.0 or more and - 0.1 or less. The in - plane retardation Re(550) of the second retardation layer is 185 nm or more and 265 nm or less. An image display device according to another aspect of the present invention includes an image display cell and the above - described retardation film - attached polarizing plate disposed on the viewing side with respect to the image display cell. In one embodiment, the image display cell is a liquid crystal cell, and the driving mode of the liquid crystal cell is an IPS mode. In one embodiment, the image display device includes a second polarizing plate disposed on the side opposite to the retardation film - attached polarizing plate with respect to the image display cell. The second polarizing plate includes a second polarizer. The absorption axis of the first polarizer and the initial alignment direction of the liquid crystal cell are substantially parallel, and the absorption axis of the second polarizer and the initial alignment direction of the liquid crystal cell are substantially parallel.

Effects of the Invention

[0006] According to an embodiment of the present invention, it is possible to achieve a wide viewing angle conversion in the horizontal direction (a predetermined plane direction of the image display surface) in an image display device, and to realize a polarizing plate with a retardation layer that can sufficiently reduce the black luminance in an oblique direction intersecting both the vertical and horizontal directions.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0008] Hereinafter, representative embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

[0009] (Definitions of Terms and Symbols) The definitions of terms and symbols in this specification are as follows. (1) Refractive Index (nx, ny, nz) “nx” is the refractive index in the direction where the in-plane refractive index is maximum (i.e., the slow axis direction), “ny” is the refractive index in the direction orthogonal to the slow axis in the plane (i.e., the fast axis direction), and “nz” is the refractive index in the thickness direction. (2) In-Plane Retardation (Re) and Front Retardation (R 0 ) “Re(λ)” is the in-plane retardation measured with light of wavelength λ nm at 23°C. For example, “Re(550)” is the in-plane retardation measured with light of wavelength 550 nm at 23°C. Note that “in-plane retardation Re(550)” is “front retardation R 0It may be referred to as "". Re(λ) is obtained by the formula: Re(λ) = (nx - ny) × d, where d (nm) is the thickness of the layer (film). (3) Retardation in the thickness direction (Rth) "Rth(λ)" is the retardation in the thickness direction measured with light of wavelength λ nm at 23°C. For example, "Rth(550)" is the retardation in the thickness direction measured with light of wavelength 550 nm at 23°C. Rth(λ) is obtained by the formula: Rth(λ) = (nx - nz) × d, where d (nm) is the thickness of the layer (film). (4) Nz coefficient The Nz coefficient is obtained by Nz = Rth / Re. (5) Substantially parallel or orthogonal The expressions "substantially orthogonal" and "substantially perpendicular" include the case where the angle formed by two directions is 90° ± 10°, preferably 90° ± 7°, and more preferably 90° ± 5°. The expressions "substantially parallel" and "substantially parallel" include the case where the angle formed by two directions is 0° ± 10°, preferably 0° ± 7°, and more preferably 0° ± 5°. Further, when simply referred to as "orthogonal" or "parallel" in this specification, it shall include a substantially orthogonal or substantially parallel state.

[0010] A. Overall configuration of the polarizing plate with a retardation layer FIG. 1 is a schematic cross-sectional view of a polarizing plate with a retardation layer according to one embodiment of the present invention. The polarizing plate with a retardation layer 100 in the illustrated example includes a first polarizer 10 including a first polarizer 11; a first retardation layer 20 having a refractive index characteristic showing a relationship of nz > nx > ny; and a second retardation layer 30 having a refractive index characteristic showing a relationship of nx > ny = nz. The first retardation layer 20 is disposed adjacent to the first polarizing plate 10. The second retardation layer 30 is disposed adjacent to the first retardation layer 20. The second retardation layer 30 is located on the side opposite to the first polarizing plate 10 with respect to the first retardation layer 20. In this specification, "disposed adjacent" means being directly laminated or being laminated via only an adhesive layer (for example, an adhesive agent layer or an adhesive layer). That is, it means that no optical functional layer (for example, another retardation layer) is interposed between the first polarizing plate 10 and the first retardation layer 20, and between the first retardation layer 20 and the second retardation layer 30. The absorption axis (the first absorption axis direction) of the first polarizer 11 and the slow axis (the first slow axis direction) of the first retardation layer 20 are substantially orthogonal. The absorption axis (the first absorption axis direction) of the first polarizer 11 and the slow axis (the second slow axis direction) of the second retardation layer 30 are substantially parallel. The in-plane retardation Re(550) of the first retardation 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 still more preferably 200 nm or more and 220 nm or less. The Nz coefficient of the first retardation layer 20 is -1.0 or more and -0.1 or less, preferably -0.9 or more and -0.2 or less, more preferably -0.8 or more and -0.3 or less, and still more preferably -0.7 or more and -0.4 or less. The in-plane retardation Re(550) of the second retardation 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 still more preferably 215 nm or more and 235 nm or less. When the Re(550) and Nz coefficients of the first retardation layer and the Re(550) of the second retardation layer each satisfy the above ranges, in an image display device including a polarizing plate with a retardation layer, a wide viewing angle in the horizontal direction (a predetermined plane direction of the image display surface) can be achieved, and the black luminance in the diagonal direction intersecting both the vertical and horizontal directions can be sufficiently reduced. That is, in an image display device including a polarizing plate with a retardation layer, the viewing angle in the horizontal direction (for example, the first plane direction X of the image display device shown in FIG. 3) can be made wider than the viewing angle in the vertical direction (for example, the second plane direction Y orthogonal to the first plane direction X shown in FIG. 3), and the black display of the image display device can sufficiently reduce the black luminance when viewed from the diagonal direction intersecting both the horizontal direction (the first plane direction X) and the vertical direction (the second plane direction Y). More specifically, when the black display of the image display device is measured by any appropriate luminance meter at a polar angle of 40° to 42° and in each of the ranges of azimuth angles of 20° to 25°, 155° to 160°, 190° to 195°, and 345° to 350°, the luminance is, for example, less than 0.00080, preferably 0.00070 or less, more preferably 0.00060 or less. In this specification, the luminance measured in the above ranges of the polar angle and the azimuth angle is defined as the area A luminance. The lower limit of the area A luminance is typically 0.00001 or more.

[0011] In one embodiment, the Nz coefficient of the second 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 still more preferably 0.8 or more and 1.2 or less. When the Nz coefficient of the second retardation layer is within such a range, in an image display device including a polarizing plate with a retardation layer, a wide viewing angle in the horizontal direction (a predetermined plane direction of the image display surface) can be stably achieved, and the black luminance in the diagonal direction intersecting both the vertical and horizontal directions can be stably reduced.

[0012] The retardation layer - attached polarizing plate may further have a conductive layer or an isotropic substrate with a conductive layer (not shown). The conductive layer or the isotropic substrate with a conductive layer is typically provided on the outer side of the second retardation layer (the side opposite to the first polarizing plate). When the conductive layer or the isotropic substrate with a conductive layer is provided, the retardation layer - attached polarizing plate can be applied to a so - called inner touch panel type input display device in which a touch sensor is incorporated between an image display cell (e.g., a liquid crystal cell, an organic EL cell) and the first polarizing plate.

[0013] The retardation layer - attached polarizing plate may further contain other retardation layers. The optical properties (e.g., refractive index property, in - plane retardation, Nz coefficient, photo - elastic coefficient), thickness, arrangement position, etc. of the other retardation layers can be appropriately set according to the purpose.

[0014] The retardation layer - attached polarizing plate may be in a sheet form or a long - strip form. In this specification, "long - strip form" means an elongated shape in which the length is sufficiently long with respect to the width, for example, an elongated shape in which the length is 10 times or more, preferably 20 times or more the width. The long - strip retardation layer - attached polarizing plate can be wound into a roll.

[0015] Practically, an adhesive layer (not shown) is provided on the side of the second retardation layer opposite to the first polarizing plate, and the retardation layer - attached polarizing plate can be attached to the image display cell. Further, it is preferable that a release liner is temporarily attached to the surface of the adhesive layer until the retardation layer - attached polarizing plate is put into use. By temporarily attaching the release liner, the adhesive layer is protected and roll formation becomes possible.

[0016] B. Overall Configuration 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 in the illustrated example includes an image display cell 60 and a retardation layer - attached polarizing plate 100 disposed on the viewing side with respect to the image display cell 60. In the image display device 101, the first retardation layer 20 is located between the first polarizing plate 10 and the image display cell 60, and the second retardation layer 30 is located between the first retardation layer 20 and the image display cell 60.

[0017] The image display device 101 in the illustrated example further includes a second polarizing plate 40 disposed on the side opposite to the polarizing plate 100 with a retardation layer (the side opposite to the viewing side) with respect to the image display cell 60. The second polarizing plate 40 includes a second polarizer 41.

[0018] The image display cell 60 is typically a liquid crystal cell 60a, and the image display device 101 is typically a liquid crystal display device. The liquid crystal display device is typically in a so-called O mode. The "liquid crystal display device in O mode" refers to a device in which the absorption axis (the second absorption axis direction) of a polarizer (the second polarizer 41 in this embodiment) disposed on the side opposite to the viewing side (the back side) of the liquid crystal cell is substantially parallel to the initial alignment direction of the liquid crystal cell. The "initial alignment direction of the liquid crystal cell" refers to the direction (i.e., the slow axis direction) in which the in-plane refractive index of the liquid crystal layer resulting from the alignment of the liquid crystal molecules contained in the liquid crystal layer described later is maximized in a state where no electric field exists.

[0019] In one embodiment, the absorption axis (the first absorption axis direction) of the polarizer (the first polarizer 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 polarizer 11 and the absorption axis direction of the second polarizer 41 are typically substantially parallel. According to such a configuration, excellent visibility can be realized even when the display screen is viewed through a polarizing lens such as polarized sunglasses.

[0020] Practically, 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 members (for example, a diffusion sheet, a prism sheet). In the illustrated example, the backlight unit 90 is an edge-lit type, but any suitable other type (for example, a direct-lit type) may be adopted as the backlight unit 90.

[0021] The image display device (liquid crystal display device) may further include any appropriate other members. For example, another optical compensation layer (retardation layer) may be further disposed. The optical characteristics, number, combination, arrangement position, etc. of the other optical compensation layer can be appropriately selected according to the purpose and desired optical characteristics, etc. As for matters not described in this specification, the configurations of image display devices (liquid crystal display devices) well-known and commonly used in the art can be adopted.

[0022] Such an image display device is suitably used for applications where a wide viewing angle in the horizontal direction and reduction of the luminance of area A during black display are particularly required (especially applications that require high definition and allow multiple people to share the screen). Representative examples of the image display device include in-vehicle displays, medical monitors, and gaming monitors, and particularly preferably in-vehicle displays.

[0023] Hereinafter, the polarizing plate with a retardation layer and each member constituting the image display device will be described.

[0024] C. Polarizing plate C-1. Polarizer As the first polarizer 11 included in the first polarizing plate 10 and the second polarizer 41 included in the second polarizing plate 40 (hereinafter, may be simply collectively referred to as a polarizer), any appropriate polarizer can be adopted. For example, the resin film forming the polarizer may be a single-layer resin film or a laminate of two or more layers.

[0025] Specific examples of the polarizer composed of a single-layer resin film include hydrophilic polymer films such as polyvinyl alcohol (PVA)-based films, partially formalized PVA-based films, and ethylene-vinyl acetate copolymer-based partially saponified films, which are subjected to dyeing treatment with dichroic substances such as iodine and dichroic dyes and stretching treatment, and polyene-based alignment films such as dehydrated products of PVA and dehydrochlorinated products of polyvinyl chloride. Preferably, a polarizer obtained by dyeing a PVA-based film with iodine and uniaxially stretching it is used because of its excellent optical characteristics.

[0026] The above iodine staining is performed, for example, by immersing a PVA-based film in an aqueous iodine solution. The draw ratio of the above uniaxial drawing is preferably 3 to 7 times. The drawing may be performed after the staining treatment, or may be performed while staining. Further, staining may be performed after drawing. If necessary, the PVA-based film is subjected to a swelling treatment, a crosslinking treatment, a washing treatment, a drying treatment, etc. For example, by immersing the PVA-based film in water and washing it before staining, not only can the dirt on the surface of the PVA-based film and the anti-blocking agent be washed, but also the PVA-based film can be swollen to prevent uneven staining and the like.

[0027] Specific examples of the polarizer obtained using the laminate include a laminate of a resin substrate and a PVA-based resin layer (PVA-based resin film) laminated on the resin substrate, or a laminate of a resin substrate and a PVA-based resin layer formed by coating on the resin substrate. The polarizer obtained using the laminate of a resin substrate and a PVA-based resin layer formed by coating on the resin substrate can be produced, for example, by applying a PVA-based resin solution to the resin substrate and drying it to form a PVA-based resin layer on the resin substrate to obtain a laminate of the resin substrate and the PVA-based resin layer; stretching and staining the laminate to make the PVA-based resin layer a polarizer. In the present embodiment, the stretching typically includes immersing the laminate in an aqueous boric acid solution and stretching it. Further, the stretching may further include, if necessary, air stretching the laminate at a high temperature (for example, 95 °C or higher) before stretching in the aqueous boric acid solution. The obtained laminate of the resin substrate / polarizer may be used as it is (that is, the resin substrate may be used as a protective layer for the polarizer), or the resin substrate may be peeled off from the laminate of the resin substrate / polarizer, and an arbitrary appropriate protective layer according to the purpose may be laminated on the peeled surface and used. Details of such a method for manufacturing a polarizer are described, for example, in JP-A-2012-73580 and Patent No. 6470455. The entire descriptions of these publications are incorporated herein by reference.

[0028] The thickness of the polarizer is, for example, 1 μm to 80 μm, preferably 1 μm to 15 μm, more preferably 1 μm to 12 μm, still more preferably 3 μm to 12 μm, and particularly preferably 3 μm to 8 μm. When the thickness of the polarizer is within such a range, curling during heating can be suppressed well, and good appearance durability during heating can be obtained.

[0029] The polarizer preferably exhibits absorption dichroism at any wavelength in the range of 380 nm to 780 nm. The single transmittance of the polarizer is, for example, 41.5% to 46.0%, preferably 43.0% to 46.0%, and more preferably 44.5% to 46.0%. The degree of polarization of the polarizer is preferably 97.0% or more, more preferably 99.0% or more, and still more preferably 99.9% or more.

[0030] C-2. Protective layer Each of the first polarizing plate 10 and the second polarizing plate 40 may further include a protective layer. The protective layer may be provided on at least one surface of the polarizer, or may be provided on both surfaces of the polarizer. In the image display device 101, the first polarizing plate 10 includes a protective layer 12 provided on the viewing-side surface of the first polarizer 11, and the second polarizing plate 40 includes a protective layer 42 provided on the surface opposite to the viewing-side of the second polarizer 41.

[0031] The protective layer is formed of any suitable film that can be used as a protective layer for a polarizer. Specific examples of the material that is the main component of the film include cellulose-based resins such as triacetyl cellulose (TAC), and transparent resins such as polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, polyimide-based, polyethersulfone-based, polysulfone-based, polystyrene-based, polynorbornene-based, polyolefin-based, (meth)acrylic-based, acetate-based, etc. Also, thermosetting resins or ultraviolet curable resins such as (meth)acrylic-based, urethane-based, (meth)acrylic urethane-based, epoxy-based, silicone-based, etc. can be mentioned. In addition to this, for example, glassy polymers such as siloxane-based polymers can also be mentioned. Also, the polymer film described in Japanese Patent Application Laid-Open No. 2001-343529 (WO01 / 37007) can be used. As the material of this film, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in the side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in the side chain can be used, and for example, a resin composition having an alternating copolymer composed of isobutene and N-methylmaleimide and an acrylonitrile-styrene copolymer can be mentioned. The polymer film can be, for example, an extruded product of the above resin composition.

[0032] When the polarizer disposed on the viewing side of the image display cell 60 includes a protective layer located on the outermost surface of the image display device, the protective layer may be subjected to surface treatments such as hard coat treatment, antireflection treatment, anti-sticking treatment, antiglare treatment, etc. as necessary.

[0033] The thickness of the protective layer is typically 5 mm or less, preferably 1 mm or less, more preferably 1 μm to 500 μm, and even more preferably 5 μm to 150 μm. When surface treatment is performed, the thickness of the protective layer is the thickness including the thickness of the surface treatment layer.

[0034] D. First retardation layer The first retardation layer 20 exhibits a refractive index characteristic of nz > nx > ny as described above. A layer (film) having such a refractive index characteristic may be referred to as a "positive biaxial plate", a "positive B plate", or the like.

[0035] The thickness of the first retardation layer is typically 3 μm or more, preferably 5 μm or more, and typically 30 μm or less, preferably 20 μm or less, more preferably 15 μm or less. When the thickness of the first retardation layer is within such a range, it has excellent handling properties during manufacturing and can enhance the optical uniformity of the resulting image display device.

[0036] The first retardation layer can have any suitable configuration. Specifically, it may be a retardation film alone, or a laminate of two or more retardation films that are the same or different. In the case of a laminate, the first retardation layer may include an adhesive layer or an adhesive agent layer for attaching two or more retardation films. Preferably, the first retardation layer is a single retardation film. By adopting such a configuration, it is possible to reduce the shrinkage stress of the polarizer and / or the deviation or unevenness of the retardation value due to the heat of the light source, and it can contribute to the thinning of the resulting image display device.

[0037] The optical properties of the retardation film can be set to any suitable values according to the configuration of the first retardation layer. For example, when the first retardation layer is a retardation film alone, it is preferable that the optical properties of the retardation film are equal to the optical properties of the first retardation layer described above. Therefore, it is preferable that the retardation value of the adhesive layer, the adhesive agent layer, etc. used when laminating the retardation film to the polarizer and / or the second retardation layer, etc. is as small as possible.

[0038] As the retardation film, a film that is excellent in transparency, mechanical strength, thermal stability, moisture shielding property, etc., and is less likely to cause optical unevenness due to distortion is preferably used. As the retardation film, preferably, a stretched film of a polymer film mainly composed of a thermoplastic resin is used. As the thermoplastic resin, preferably, a polymer showing negative birefringence is used. By using a polymer showing negative birefringence, a retardation film having a refractive index ellipsoid of nz>nx>ny can be easily obtained. Here, "showing negative birefringence" means that when the polymer is oriented by stretching or the like, the refractive index in the stretching direction becomes relatively small. In other words, it means that the refractive index in the direction orthogonal to the stretching direction becomes large. Examples of the polymer showing negative birefringence include polymers in which a chemical bond or functional group having a large polarization anisotropy such as an aromatic ring or a carbonyl group is introduced into the side chain. Specifically, acrylic resins, styrene resins, maleimide resins, etc. are mentioned.

[0039] The above acrylic resin can be obtained, for example, by addition polymerization of an acrylate monomer. Examples of the acrylic resin include polymethyl methacrylate (PMMA), polybutyl methacrylate, and polycyclohexyl methacrylate.

[0040] The above styrene resin can be obtained, for example, by addition polymerization of a styrene monomer. Examples of the styrene monomer include styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, p-chlorostyrene, p-nitrostyrene, p-aminostyrene, p-carboxystyrene, p-phenylstyrene, 2,5-dichlorostyrene, and p-t-butylstyrene.

[0041] The maleimide-based resin can be obtained, for example, by addition polymerization of a maleimide-based monomer. Examples of the maleimide-based monomer include N-ethylmaleimide, N-cyclohexylmaleimide, N-phenylmaleimide, N-(2-methylphenyl)maleimide, N-(2-ethylphenyl)maleimide, N-(2-propylphenyl)maleimide, N-(2-isopropylphenyl)maleimide, N-(2,6-dimethylphenyl)maleimide, N-(2,6-dipropylphenyl)maleimide, N-(2,6-diisopropylphenyl)maleimide, N-(2-methyl-6-ethylphenyl)maleimide, N-(2-chlorophenyl)maleimide, N-(2,6-dichlorophenyl)maleimide, N-(2-bromophenyl)maleimide, N-(2,6-dibromophenyl)maleimide, N-(2-biphenyl)maleimide, and N-(2-cyanophenyl)maleimide. The maleimide-based monomer can be obtained, for example, from Tokyo Chemical Industry Co., Ltd.

[0042] In the above addition polymerization, after polymerization, the birefringence characteristics of the obtained resin can also be controlled by, for example, substituting the side chain, performing a maleimidation or grafting reaction, or the like.

[0043] The polymer exhibiting the above negative birefringence may be copolymerized with other monomers. By copolymerizing with other monomers, brittleness, moldability, and heat resistance can be improved. Examples of the 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.

[0044] When the polymer exhibiting the above negative birefringence is a copolymer of the above styrene monomer and the above other monomer, the blending ratio of the styrene monomer is preferably 50 mol% to 80 mol%. When the polymer exhibiting the above negative birefringence is a copolymer of the above maleimide monomer and the above other monomer, the blending ratio of the maleimide monomer is preferably 2 mol% to 50 mol%. By blending in such a range, a polymer film excellent in toughness and moldability can be obtained.

[0045] As the polymer exhibiting the above negative birefringence, preferably, styrene-maleic anhydride copolymer, styrene-acrylonitrile copolymer, styrene-(meth)acrylate copolymer, styrene-maleimide copolymer, vinyl ester-maleimide copolymer, olefin-maleimide copolymer, etc. are used. These can be used alone or in combination of two or more. These polymers exhibit high negative birefringence and can be excellent in heat resistance. These polymers can be obtained, for example, from Nova Chemical Japan or Arakawa Chemical Industries, Ltd.

[0046] As the polymer exhibiting the above negative birefringence, preferably, a polymer having a repeating unit represented by the following general formula (I) is also used. Such a polymer can exhibit even higher negative birefringence and can be excellent in heat resistance and mechanical strength. Such a polymer can be obtained, for example, by using an N-phenyl-substituted maleimide in which a phenyl group having a substituent at least in the ortho position is introduced as the N-substituent of the starting maleimide monomer. [Chemical formula]

[0047] In the above general formula (I), R 1 ~R 5 each independently represents hydrogen, a halogen atom, a carboxylic acid, a carboxylic acid ester, a hydroxyl group, a nitro group, or a linear or branched alkyl group or alkoxy group having 1 to 8 carbon atoms (provided that R 1 and R5 (which is not a hydrogen atom at the same time), R 6 and R 7 represents hydrogen or a linear or branched alkyl or alkoxy group having 1 to 8 carbon atoms, and n represents an integer of 2 or more.

[0048] The polymer exhibiting the above negative birefringence is not limited to the above. For example, a cyclic olefin copolymer as disclosed in JP-A-2005-350544 can also be used. Further, a composition containing a polymer and inorganic fine particles as disclosed in JP-A-2005-156862, JP-A-2005-227427, etc. can also be preferably used. Further, as the polymer exhibiting negative birefringence, one kind may be used alone, or two or more kinds may be mixed and used. Further, these can also be used after being modified by copolymerization, branching, crosslinking, molecular end modification (or capping), and stereoregular modification, etc.

[0049] The above polymer film may further contain any appropriate additive as necessary. Specific examples of the additive include a plasticizer, a heat stabilizer, a light stabilizer, a lubricant, an antioxidant, an ultraviolet absorber, a flame retardant, a colorant, an antistatic agent, a compatibilizer, a crosslinking agent, and a thickener. The type and content of the additive can be appropriately set according to the purpose. The content of the additive is typically about 3 to 10 parts by mass with respect to 100 parts by mass of the total solid content of the polymer film. If the content of the additive becomes excessively large, the transparency of the polymer film may be impaired, or the additive may ooze out from the surface of the polymer film.

[0050] As the method for forming the above-mentioned polymer film, any appropriate forming method can be adopted. For example, compression molding method, transfer molding method, injection molding method, extrusion molding method, blow molding method, powder molding method, FRP molding method, solvent casting method can be mentioned. Among these, the extrusion molding method and the solvent casting method are preferably used. This is because a retardation film having high smoothness and good optical uniformity can be obtained. Specifically, the extrusion molding method is a method of heating and melting a resin composition containing the above-mentioned thermoplastic resin, plasticizer, additive, etc., extruding this in a thin film shape onto the surface of a casting roll by a T-die or the like, and cooling it to form a film. The solvent casting method is a method of defoaming a concentrated solution (dope) in which the resin composition is dissolved in a solvent, casting it uniformly in a thin film shape on the surface of a metallic endless belt or a rotating drum, or a plastic substrate, etc., and evaporating the solvent to form a film. In addition, the molding conditions can be appropriately set according to the composition and type of the resin used, the molding process method, etc.

[0051] The above-mentioned retardation film (stretched film) can be obtained by stretching the above-mentioned polymer film under any appropriate stretching conditions. Specific examples of the stretching method include uniaxial stretching method in the longitudinal direction, uniaxial stretching method in the transverse direction, sequential biaxial stretching method in the longitudinal and transverse directions, and simultaneous biaxial stretching method in the longitudinal and transverse directions. Preferably, the uniaxial stretching method in the transverse direction, the sequential biaxial stretching method in the longitudinal and transverse directions, and the simultaneous biaxial stretching method in the longitudinal and transverse directions are used. This is because a biaxial retardation film can be suitably obtained. In the polymer showing the above-mentioned negative birefringence, since the refractive index in the stretching direction becomes relatively small as described above, in the case of the uniaxial stretching method in the transverse direction, the slow axis is in the conveying direction of the polymer film (the refractive index in the conveying direction is nx). In the case of the sequential biaxial stretching method in the longitudinal and transverse directions and the simultaneous biaxial stretching method in the longitudinal and transverse directions, depending on the ratio of the stretching ratios in the longitudinal and transverse directions, either the conveying direction or the width direction can be the slow axis. Specifically, when the stretching ratio in the longitudinal (conveying) direction is relatively large, the transverse (width) direction becomes the slow axis, and when the stretching ratio in the transverse (width) direction is relatively large, the longitudinal (conveying) direction becomes the slow axis. As the stretching device used for the above stretching, any appropriate stretching device can be used. Specific examples include a roll stretching machine, a tenter stretching machine, a pantograph type or a linear motor type biaxial stretching machine. When stretching while heating, the temperature may be continuously changed or may be changed stepwise. Further, the stretching process may be divided into two or more times.

[0052] Further, by adjusting the thickness (original web thickness) of the polymer film, the stretching temperature, and the stretching ratio, Re(550) and the Nz coefficient of the first retardation layer can be adjusted to the above-mentioned ranges. The thickness (original web thickness) of the polymer film is typically 10 μm or more, preferably 20 μm or more, more preferably 30 μm or more, and typically 200 μm or less, preferably 100 μm or less, more preferably 80 μm or less.

[0053] The stretching temperature (the temperature in the stretching oven when stretching the polymer film) is preferably near the glass transition temperature (Tg) of the polymer film. Specifically, it is preferably (Tg - 10)°C to (Tg + 30)°C, more preferably Tg to (Tg + 25)°C, and particularly preferably (Tg + 5)°C to (Tg + 20)°C. If the stretching temperature is too low, there is a risk that the retardation value and the direction of the slow axis become non-uniform, or the polymer film crystallizes (becomes cloudy). On the other hand, if the stretching temperature is excessively high, there is a risk that the polymer film melts or the development of retardation becomes insufficient. The stretching temperature is typically 110 to 200°C. The glass transition temperature can be determined by the DSC method in accordance with JIS K7121-1987.

[0054] As the method for controlling the temperature in the above stretching oven, any appropriate method can be adopted. For example, methods using an air circulation type constant temperature oven in which hot air or cold air circulates, a heater using microwaves or far-infrared rays, etc., a roll heated for temperature adjustment, a heat pipe roll, or a metal belt can be mentioned.

[0055] When stretching the polymer film, the stretching ratio can be set to any appropriate value according to the composition of the polymer film, the types of volatile components, etc., the residual amount of volatile components, etc., the desired retardation value, etc. Preferably, it is 1.05 to 5.00 times, more preferably 1.20 to 1.65 times. Also, the feeding speed during stretching is preferably 0.5 m / min to 20 m / min from the viewpoints of the mechanical accuracy, stability, etc. of the stretching apparatus.

[0056] As described above, the method for obtaining a retardation film using a polymer showing negative birefringence has been described. However, a retardation film can also be obtained using a polymer showing positive birefringence. As a method for obtaining a retardation film using a polymer showing positive birefringence, for example, a stretching method for increasing the refractive index in the thickness direction as disclosed in JP-A-2000-231016, JP-A-2000-206328, and JP-A-2002-207123 can be used. Specifically, a method of bonding a heat-shrinkable film to one or both surfaces of a film containing a polymer showing positive birefringence and performing a heat treatment can be mentioned. By shrinking the film under the action of the shrinking force of the heat-shrinkable film by heat treatment and shrinking the length direction and width direction of the film, the refractive index in the thickness direction can be increased, and a retardation film having a refractive index ellipsoid of nz>nx>ny can be obtained.

[0057] Thus, the positive B plate used for the first retardation layer can be manufactured using a polymer showing either positive or negative birefringence. Generally, when using a polymer showing positive birefringence, it has an advantage in that there are many types of polymers that can be selected. When using a polymer showing negative birefringence, compared with the case of using a polymer showing positive birefringence, there is an advantage in that a retardation film excellent in the uniformity in the slow axis direction can be easily obtained due to the stretching method.

[0058] As the retardation film used for the first retardation layer, in addition to the films described above, commercially available optical films can be used as they are. Further, films obtained by subjecting commercially available optical films to secondary processing such as stretching treatment and / or relaxation treatment can also be used.

[0059] The light transmittance of the above retardation film at a wavelength of 550 nm is preferably 80% or more, more preferably 85% or more, and particularly preferably 90% or more. Although the theoretical upper limit of the light transmittance is 100%, surface reflection occurs due to the refractive index difference between air and the retardation film, so the practically achievable upper limit of the light transmittance is approximately 94%. It is also preferable that the entire first retardation layer has a similar light transmittance.

[0060] The absolute value of the photoelastic coefficient of the above retardation film is preferably 1.0×10 -10 (m 2 / N) or less, more preferably 5.0×10 -11 (m 2 / N) or less, still more preferably 3.0×10 -11 (m 2 / N) or less, and particularly preferably 1.5×10 -11 (m 2 / N) or less. By setting the photoelastic coefficient within such a range, an image display device excellent in optical uniformity, with small changes in optical characteristics even in environments such as high temperature and high humidity, and excellent in durability can be obtained. The lower limit value of the photoelastic coefficient is not particularly limited, but generally it is 5.0×10 -13 (m 2 / N) or more, preferably 1.0×10 -12 (m 2 / N) or more. If the photoelastic coefficient is excessively small, there is a risk that the manifestation of retardation will be small. The photoelastic coefficient is a value inherent to the chemical structure such as a polymer, but the photoelastic coefficient can be reduced by copolymerizing or mixing a plurality of components having different signs (positive or negative) of the photoelastic coefficient.

[0061] E. Second retardation layer The second retardation layer 30 exhibits a refractive index characteristic of nx > ny = nz as described above. A layer (film) having such a refractive index characteristic may be referred to as a "positive uniaxial plate", a "positive A plate", etc. Here, "ny = nz" includes not only the case where ny and nz are exactly equal, but also the case where ny and nz are substantially equal. Specifically, it means that the Nz coefficient exceeds 0.9 and is less than 1.1.

[0062] As the material for forming the second retardation layer, any appropriate material can be adopted as long as the above-described characteristics can be obtained. Specifically, the second retardation layer may be an alignment and solidification layer (liquid crystal alignment and solidification layer) of a liquid crystal compound, or may be a retardation film (stretched film of a polymer film).

[0063] When the second retardation layer is an alignment and solidification layer of a liquid crystal compound, by using a liquid crystal compound, the difference between nx and ny of the obtained retardation layer can be made significantly larger than that of a non-liquid crystal material, so that the thickness of the retardation layer for obtaining a desired in-plane retardation can be significantly reduced. As a result, further thinning of the retardation layer-containing polarizing plate (and as a result, the image display device) can be achieved. In this specification, the "alignment and solidification layer" refers to a layer in which a liquid crystal compound is aligned in a predetermined direction within the layer and the alignment state is fixed. Note that the "alignment and solidification layer" is a concept that includes an alignment and curing layer obtained by curing a liquid crystal monomer as described later. In the present embodiment, typically, rod-shaped liquid crystal compounds are aligned in the direction of the slow axis of the second retardation layer (homogeneous alignment).

[0064] Examples of the liquid crystal compound include a liquid crystal compound having a nematic liquid crystal phase (nematic liquid crystal). As such a liquid crystal compound, for example, a liquid crystal polymer or a liquid crystal monomer can be used. The mechanism for expressing the liquid crystallinity of the liquid crystal compound may be either lyotropic or thermotropic. The liquid crystal polymer and the liquid crystal monomer may be used alone or in combination.

[0065] When the liquid crystal compound is a liquid crystal monomer, for example, it is preferably a polymerizable monomer and / or a crosslinkable monomer. This is because by polymerizing or crosslinking the liquid crystal monomer, the alignment state of the liquid crystal monomer can be fixed. After the liquid crystal monomer is aligned, for example, if the liquid crystal monomers are polymerized or crosslinked with each other, the above alignment state can be fixed thereby. Here, a polymer is formed by polymerization, and a three-dimensional network structure is formed by crosslinking, but these are non-liquid crystalline. Therefore, in the formed second retardation layer, for example, no transition from a liquid crystal phase, a glass phase, or a crystal phase due to a temperature change peculiar to the liquid crystal compound occurs. As a result, the formed second retardation layer becomes an extremely stable retardation layer that is not affected by temperature changes.

[0066] Specific examples of the liquid crystal compound and details of the method for forming the liquid crystal alignment fixing layer are described, for example, in JP-A-2006-163343 and JP-A-2006-178389. The descriptions in these publications are incorporated herein by reference.

[0067] The second retardation layer may be a stretched film of the polymer film as described above. Specifically, by appropriately selecting the type of polymer, stretching conditions (for example, stretching temperature, stretching ratio, stretching direction), and stretching method (for example, uniaxial stretching in the transverse direction), a second retardation layer having the above-described desired optical properties (for example, refractive index characteristics, in-plane retardation, retardation in the thickness direction) can be obtained. In particular, by adjusting the thickness (original film thickness) of the polymer film, the stretching temperature, and the stretching ratio, Re(550) of the second retardation layer can be adjusted to the above-described range. The thickness (original film thickness) of the polymer film is typically 10 μm or more, preferably 15 μm or more, and typically 50 μm or less, preferably 40 μm or less, more preferably 30 μm or less. The stretching temperature is preferably 110°C to 170°C, more preferably 130°C to 150°C. The stretching ratio is preferably 1.37 times to 2.50 times, more preferably 1.42 times to 2.00 times.

[0068] As the resin for forming the above-mentioned polymer film, any suitable resin can be adopted. Specific examples include resins constituting a positive birefringence film such as norbornene resins, polycarbonate resins, cellulose resins, polyvinyl alcohol resins, polysulfone resins, etc. Among them, norbornene resins and polycarbonate resins are preferred.

[0069] The above norbornene-based resin is a resin polymerized with norbornene-based monomers as polymerization units. Examples of the norbornene-based monomers include norbornene, and its alkyl and / or alkylidene substitution products, such as 5-methyl-2-norbornene, 5-dimethyl-2-norbornene, 5-ethyl-2-norbornene, 5-butyl-2-norbornene, 5-ethylidene-2-norbornene, etc., and polar group substitution products such as halogens of these; dicyclopentadiene, 2,3-dihydrodicyclopentadiene, etc.; dimethanooctahydronaphthalene, its alkyl and / or alkylidene substitution products, and polar group substitution products such as halogens, for example, 6-methyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-ethyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-ethylidene-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-chloro-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-cyano-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-pyridyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-methoxycarbonyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, etc.; trimers to tetramers of cyclopentadiene, for example, 4,9:5,8-dimethano-3a,4,4a,5,8,8a,9,9a-octahydro-1H-benzindene, 4,11:5,10:6,9-trimethano-3a,4,4a,5,5a,6,9,9a,10,10a,11,11a-dodecahydro-1H-cyclopentaanthracene. The above norbornene-based resin may be a copolymer of a norbornene-based monomer and another monomer.

[0070] As the above-mentioned polycarbonate resin, an aromatic polycarbonate is preferably used. An aromatic polycarbonate can typically be obtained by the reaction of a carbonate precursor and an aromatic dihydric phenol compound. Specific examples of the carbonate precursor include phosgene, bis-chloroformate of dihydric phenols, diphenyl carbonate, di-p-tolyl carbonate, phenyl-p-tolyl carbonate, di-p-chlorophenyl carbonate, dinaphthyl carbonate. Among these, phosgene and diphenyl carbonate are preferred. Specific examples of the aromatic dihydric phenol compound 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, 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane. These may be used alone or in combination of two or more. Preferably, 2,2-bis(4-hydroxyphenyl)propane, 1,1-bis(4-hydroxyphenyl)cyclohexane, 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane are used. In particular, it is preferable to use both 2,2-bis(4-hydroxyphenyl)propane and 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane.

[0071] The second retardation layer is preferably a stretched film of a polymer film, more preferably a stretched film of a norbornene resin film. The thickness of the second retardation layer can be set so as to obtain desired optical properties. When the second retardation layer is a liquid crystal alignment cured layer, the thickness is preferably 0.5 μm to 10 μm, more preferably 0.5 μm to 8 μm, and still more preferably 0.5 to 5 μm. When the second retardation layer is a stretched film of a polymer film, the thickness is preferably 5 μm to 55 μm, more preferably 10 μm to 50 μm, and still more preferably 15 μm to 45 μm.

[0072] F. Laminate of the first retardation layer and the second retardation layer The laminate of the first retardation layer and the second retardation layer preferably satisfies the following relationship: Re(450) / Re(550)>0.82 Re(650) / Re(550)<1.18. Re(450) / Re(550) of the laminate is more preferably 1.0 to 1.2, and still more preferably 1.0 to 1.1. Re(650) / Re(550) of the laminate is more preferably 0.8 to 1.0, and still more preferably 0.9 to 1.0. According to an embodiment of the present invention, even though the first retardation layer and the second retardation layer do not show ideal inverse dispersion characteristics as a whole, a polarizing plate with a retardation layer capable of realizing an image display device with low luminance in the diagonal direction during black display and a small color shift in the diagonal direction can be obtained.

[0073] G. Liquid crystal cell The liquid crystal cell 60a has a first substrate 62, a second substrate 63, and a liquid crystal layer 61 sandwiched therebetween and containing liquid crystal molecules oriented in a homogeneous alignment state in the absence of an electric field. In a general 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 scanning line for supplying a gate signal to this switching element, a signal line for supplying a source signal, a pixel electrode, and a counter electrode are provided on the other substrate (typically the second substrate 63). The interval (cell gap) between the above substrates is controlled by a spacer or the like. On the side of the above substrates in contact with the liquid crystal layer, an alignment film made of, for example, polyimide can be provided.

[0074] The Rth(550) of the first substrate 62 and the second substrate 63 is -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 embodiment of the present invention, when the substrate has such a thickness direction retardation, in a liquid crystal display device including a liquid crystal cell with homogeneous alignment, the black luminance in the oblique direction can be sufficiently reduced.

[0075] In one embodiment, at least one of the first substrate 62 and the second substrate 63 satisfies the relationship of Rth(450)>Rth(550), and preferably, both the first substrate 62 and the second substrate 63 satisfy the relationship of Rth(450)>Rth(550). More preferably, at least one of the first substrate 62 and the second substrate 63 further satisfies the relationship of Rth(550)>Rth(650), and still more preferably, both the first substrate 62 and the second substrate 63 further satisfy the relationship of Rth(550)>Rth(650). According to the embodiment of the present invention, even when the substrate has such wavelength dispersion characteristics, the black luminance in the oblique direction can be sufficiently reduced in a liquid crystal display device including a liquid crystal cell with a homogeneous alignment.

[0076] As described above, the liquid crystal layer 61 includes liquid crystal molecules aligned in a homogeneous arrangement in the absence of an electric field. The "liquid crystal molecules aligned in a homogeneous arrangement" refers to a state in which the alignment vectors of the liquid crystal molecules are parallel and uniformly aligned with respect to the substrate plane as a result of the interaction between the aligned substrate and the liquid crystal molecules. Such a liquid crystal layer (and as a result, a liquid crystal cell) typically exhibits a refractive index characteristic of nx>ny=nz. Here, "ny=nz" includes not only the case where ny and nz are 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.

[0077] 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 inclined with respect to the substrate plane. The pretilt angle is preferably 0.1° to 1.0°, and more preferably 0.2° to 0.7°.

[0078] As driving modes of such a liquid crystal cell 60a, for example, an in-plane switching (IPS) mode and a fringe field switching (FFS) mode can be mentioned. Note that the above IPS mode includes a super in-plane switching (S-IPS) mode and an advanced super in-plane switching (AS-IPS) mode that employ a V-shaped electrode or a zigzag electrode, etc. Further, the above FFS mode includes an advanced fringe field switching (A-FFS) mode and an ultra fringe field switching (U-FFS) mode that employ a V-shaped electrode or a zigzag electrode, etc. As a driving mode of the liquid crystal cell 60a, preferably, an in-plane switching (IPS) mode can be mentioned. When the driving mode of the liquid crystal cell 60a is the IPS mode, the visibility in the diagonal direction of the liquid crystal display device can be improved.

[0079] H. Backlight Unit The light source 91 is disposed at a position corresponding to the side surface of the light guide plate 92. As the light source, for example, an LED light source formed by arranging a plurality of LEDs can be used. As the light guide plate 92, any appropriate light guide plate can be used. For example, a light guide plate having a lens pattern formed on the back side so that light from the lateral direction can be deflected in the thickness direction, or a light guide plate having a prism shape or the like formed on the back side and / or the viewing side is used. Preferably, a light guide plate having a prism shape formed on the back side and the viewing side is used. In the light guide plate, it is preferable that the ridge line direction of the prism shape formed on the back side and the prism shape formed on the viewing side are orthogonal to each other. By using such a light guide plate, light that is more easily condensed can be made incident on the prism sheet (not shown).

Example

[0080] Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples. The measurement methods of each characteristic are as follows.

[0081] (1) Measurement of retardation value Regarding the in-plane retardation of the first retardation layer and the second retardation layer used in the examples and comparative examples, automatic measurement was performed using the Oji Scientific Instruments KOBRA-WPR. The measurement wavelength was 550 nm, and the measurement temperature was 23°C. (2) Luminance during black display A black screen was displayed on the image display devices obtained in the examples and comparative examples, and measurement was performed using a luminance meter (manufactured by AUTRONIC-MELCHERS, product name "Conoscope"). Specifically, the luminance was measured while changing the polar angle from 0° to 80° and the azimuth angle from 0° to 360°. Among the luminances measured as described above, when the polar angle is 40° and the azimuth angle is any one of 20°, 25°, 155°, 160°, 190°, 195°, 345°, and 350°, the luminance is defined as the area A luminance (unit: cd / m 2 ), and the maximum luminance among them is defined as the area A maximum luminance (unit: cd / m 2 ).

[0082] <Production of polarizing plate> <<Production Example 1>> As a thermoplastic resin substrate, an amorphous isophthalic copolyethylene terephthalate film (thickness: 100 μm) in a long strip shape with a Tg of about 75°C was used, and one side of the resin substrate was subjected to corona treatment. 13 parts by weight of potassium iodide was added to 100 parts by weight of a PVA-based resin obtained by mixing polyvinyl alcohol (degree of polymerization 4200, degree of saponification 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., product name "Gosefimer") at a ratio of 9:1, and the mixture was dissolved in water to prepare a PVA aqueous solution (coating solution). The above PVA aqueous solution was applied to 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 2.4 times in the longitudinal direction (longitudinal direction) in an oven at 130°C (air-assisted stretching treatment). Next, the laminate was immersed in an insolubilization bath (boric acid aqueous solution obtained by mixing 4 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40°C for 30 seconds (insolubilization treatment). Next, it was immersed for 60 seconds in a dyeing bath at a liquid temperature of 30°C (an iodine aqueous solution obtained by blending iodine and potassium iodide at a weight ratio of 1:7 with respect to 100 parts by weight of water), while adjusting the concentration so that the single transmittance (Ts) of the finally obtained polarizer would reach a desired value (dyeing treatment). Next, it was immersed for 30 seconds in a crosslinking bath at a liquid temperature of 40°C (a boric acid aqueous solution obtained by blending 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with respect to 100 parts by weight of water) (crosslinking treatment). Thereafter, while immersing the laminate in a boric acid aqueous solution at a liquid temperature of 70°C (boric acid concentration 4 wt%, potassium iodide concentration 5 wt%), uniaxial stretching was performed in the longitudinal direction (lengthwise direction) between rolls with different peripheral speeds so that the total draw ratio would be 5.5 times (stretching treatment in water). Thereafter, the laminate was immersed in a washing bath at a liquid temperature of 20°C (an aqueous solution obtained by blending 4 parts by weight of potassium iodide with respect to 100 parts by weight of water) (washing treatment). Thereafter, while drying in an oven maintained at about 90°C, it was brought into contact with a SUS heating roll whose surface temperature was maintained at about 75°C (dry shrinkage treatment). In this way, a first polarizer with a thickness of about 5 μm was formed on the resin substrate, and a laminate having the structure of resin substrate / first polarizer was obtained. An HC-TAC film (thickness 20 μm) was laminated as a protective layer on the polarizer surface (the surface opposite to the resin substrate) of the obtained laminate. Next, the resin substrate was peeled off to obtain a first polarizing plate having the structure of protective layer / first polarizer / . Thereafter, the obtained first polarizing plate was punched out to a size corresponding to the liquid crystal cell described later.

[0083] <Production of a retardation film (positive B plate) with refractive index characteristics of nz > nx > ny> <<Production Example 2>> Pellet-shaped resin of styrene-maleic anhydride copolymer (manufactured by Nova Chemical Japan Co., Ltd., trade name "Dailac D232") was extruded at 270 °C using a single-screw extruder and a T-die, and the sheet-shaped molten resin was cooled by a cooling drum to obtain a film with a thickness of 50 μm. This film was uniaxially stretched in the transport direction with a free end at a temperature of 130 °C and a draw ratio of 1.4 times using a roll stretching machine to obtain a film having an optical axis advancing in the transport direction (longitudinal stretching step). The obtained film was uniaxially stretched in the width direction with a fixed end at a temperature of 135 °C using a tenter stretching machine so that the film width became 1.6 times the film width after the longitudinal stretching, to obtain a retardation film with a thickness of 10 μm (biaxially stretched film, positive B plate) (transverse stretching step). Then, the obtained retardation film was punched out to a size corresponding to the liquid crystal cell described later. The retardation film (positive B plate) thus obtained had an optical axis advancing in the transport direction (retarded axis in the width direction) and showed a refractive index characteristic relationship of nz > nx > ny. The in-plane retardation Re(550), the retardation Rth(550) in the thickness direction, and the Nz coefficient of the retardation film (positive B plate) are shown in Table 1. <<Production Example 3>> A retardation film (positive B plate) was obtained in the same manner as in Production Example 2, except that the thickness of the film before stretching was changed to 100 μm, the longitudinal draw ratio was changed to 1.6 times, and the transverse draw ratio was changed to 1.7 times. <<Production Example 4>> A retardation film (positive B plate) was obtained in the same manner as in Production Example 3, except that the longitudinal draw ratio was changed to 1.7 times. <<Production Example 5>> A retardation film (positive B plate) was obtained in the same manner as in Production Example 3, except that the longitudinal draw ratio was changed to 1.8 times and the transverse draw ratio was changed to 1.9 times. <<Production Example 6>> A retardation film (positive B plate) was obtained in the same manner as in Production Example 3, except that the longitudinal draw ratio was changed to 2.3 times and the transverse draw ratio was changed to 2.2 times. <<Production Example 7>> A retardation film (positive B plate) was obtained in the same manner as in Production Example 3, except that the horizontal elongation magnification was changed to 1.8 times.

[0084] <Production of a retardation film (positive A plate) with refractive index characteristics of nx > ny = nz> <<Production Example 8>> A long norbornene-based resin film (manufactured by Zeon Corporation, trade name Zeonor, thickness 40 μm, photoelastic coefficient 3.10 × 10 -12 m 2 / N) was uniaxially stretched 1.7 times at 140°C to produce a retardation film with a thickness of 31 μm. Thereafter, the obtained retardation film was punched out to a size corresponding to the liquid crystal cell described below. The retardation film thus obtained had a slow axis in the transport direction and showed a refractive index characteristic relationship of nx > ny = nz. The in-plane retardation Re(550), retardation Rth(550) in the thickness direction, and Nz coefficient of the retardation film (positive A plate) are shown in Table 1. <<Production Example 9>> A retardation film (positive A plate) was obtained in the same manner as in Production Example 8, except that the elongation magnification was changed to 1.39 times. <<Production Example 10>> A retardation film (positive A plate) was obtained in the same manner as in Production Example 8, except that the elongation magnification was changed to 1.3 times. <<Production Example 11>> A retardation film (positive A plate) was obtained in the same manner as in Production Example 8, except that the elongation magnification was changed to 1.37 times.

[0085] <Production of a retardation film (positive C plate) with refractive index characteristics of nz > nx = ny> <<Production Example 12>> A retardation film (positive C plate) was obtained in the same manner as in Production Example 6 of Patent No. 6896118, except that the retardation Rth in the thickness direction was changed to -85 nm. Thereafter, the obtained retardation film was punched out to a size corresponding to the liquid crystal cell described below. The retardation film thus obtained had a slow axis in the transport direction and exhibited a refractive index characteristic of nz > nx = ny. The in-plane retardation Re(550) and the retardation Rth(550) in the thickness direction of the retardation film (positive C-plate) are shown in Table 1. <<Production Example 13>> A retardation film (positive C-plate) was obtained in the same manner as in Production Example 12, except that the retardation Rth in the thickness direction was changed to -114 nm.

[0086] <Production of a retardation film (negative B-plate) with a refractive index characteristic of nx > ny > nz> <<Production Example 14>> A retardation film (negative B-plate) was obtained in the same manner as in Production Example 8, except that the fixed-end lateral stretching was performed 1.35 times. Thereafter, the obtained retardation film was punched out to a size corresponding to the liquid crystal cell described later. The retardation film thus obtained exhibited a refractive index characteristic of nx > ny > nz. The in-plane retardation Re(550) and the retardation Rth(550) in the thickness direction of the retardation film (negative B-plate) are shown in Table 1. <<Production Example 15>> A retardation film (negative B-plate) was obtained in the same manner as in Production Example 14, except that the stretching ratio was changed to 1.3 times. <<Production Example 16>> A retardation film (negative B-plate) was obtained in the same manner as in Production Example 14, except that the thickness of the film before stretching was changed to 20 μm and the stretching ratio was changed to 1.5 times.

[0087] <Production of a retardation film (negative A-plate) with a refractive index characteristic of nx = nz > ny> <<Production Example 17>> Pelletized resin of styrene-maleic anhydride copolymer (manufactured by Nova Chemical Japan Co., Ltd., trade name "Dylark D232") was extruded at 270 °C using a single-screw extruder and a T-die, and the sheet-like molten resin was cooled with a cooling drum to obtain a film with a thickness of 50 μm. This film was uniaxially stretched in the transport direction with a free end at a temperature of 130 °C and a draw ratio of 1.8 times using a roll stretching machine to obtain a retardation film (negative A plate) having an optical axis in the transport direction. Thereafter, the obtained retardation film was punched into a size corresponding to the liquid crystal cell described below. The retardation film thus obtained exhibited a refractive index characteristic of nx = nz > ny. Table 1 shows the in-plane retardation Re(550) and the thickness-direction retardation Rth(550) of the retardation film (negative A plate).

[0088] <Preparation of Image Display Cell (Liquid Crystal Cell)> <<Production Example 18>> A liquid crystal cell was taken out from a liquid crystal display device of the IPS mode (manufactured by Apple Inc., trade name "iPad (registered trademark)"). The optical members attached to both surfaces of the liquid crystal cell were removed, and the removal surface (outer surface of the substrate) was cleaned. This was used as an image display cell (liquid crystal cell). For the first substrate of the liquid crystal cell, Rth(450) = 32 nm, Rth(550) = 19 nm, and Rth(650) = 23 nm; for the second substrate, Rth(450) = 9 nm, Rth(550) = 0.3 nm, and Rth(650) = -6 nm.

[0089] [Example 1] On the viewing side of the liquid crystal cell of Production Example 18, the retardation film of Production Example 8 (second retardation layer), the retardation film of Production Example 2 (first retardation layer), and the polarizing plate of Production Example 1 (first polarizing plate including the first polarizer) were laminated in this order. On one side, a polarizing plate (the second polarizing plate including the second polarizer) of Production Example 1 was laminated on the back side of the liquid crystal cell. The lamination was performed such that the absorption axis direction of the first polarizer and the slow axis direction of the first retardation layer were substantially orthogonal, the absorption axis direction of the first polarizer and the slow axis direction of the second retardation layer were substantially parallel, and the absorption axis direction of each of the first polarizer and the second polarizer and the initial alignment direction of the liquid crystal cell were substantially parallel. In this way, an image display device (O-mode liquid crystal display device) was fabricated. Next, the image display device was subjected to the above-described luminance measurement during black display. The luminance distribution diagram of the image display device of Example 1 is shown in FIG. 3. Also, the maximum luminance of Area A in the image display device of Example 1 is shown in Table 1.

[0090] [Comparative Examples 1 to 9] An image display device (O-mode liquid crystal display device) was fabricated in the same manner as in Example 1, except that the retardation film (the second retardation layer) of Production Example 8 and the retardation film (the first retardation layer) of Production Example 2 were each changed to the retardation film of the production example shown in Table 1. Next, the image display device was subjected to the above-described luminance measurement during black display. The luminance distribution diagram of the image display device of Comparative Example 1 is shown in FIG. 4. Also, the maximum luminance of Area A in the image display devices of Comparative Examples 1 to 9 is shown in Table 1.

[0091] [Table 1]

[0092] [Evaluation] As is clear from Table 1, FIGS. 3 and 4, when the Re(550) and Nz coefficient of the first retardation layer are within the above ranges and the Re(550) of the second retardation layer is within the above range, it is possible to ensure a wider viewing angle in the horizontal direction (the left-right direction X on the paper surface in FIGS. 3 and 4) than in the vertical direction (the up-down direction Y on the paper surface in FIGS. 3 and 4), and it is possible to realize an image display device (liquid crystal display device) in which the maximum luminance of Area A described above is sufficiently small. [Industrial Applicability]

[0093] The polarizing plate with a phase difference layer according to an embodiment of the present invention is suitably applicable to an image display device, and in particular, can be suitably applied to a liquid crystal display device.

Explanation of Signs

[0094] 10 First polarizing plate 11 First polarizer 20 First phase difference layer 30 Second phase difference layer 40 Second polarizing plate 60 Image display cell 60a Liquid crystal cell 100 Polarizing plate with a phase difference layer 101 Image display device

Claims

1. A first polarizing plate including a first polarizer; A first retardation layer having a refractive index characteristic of nz > nx > ny, which is directly laminated on the first polarizing plate or laminated via only an adhesive layer; A second retardation layer having a refractive index characteristic of nx > ny = nz, which is directly laminated on the first retardation layer or laminated via only an adhesive layer, and having: The angle formed by the absorption axis of the first polarizer and the slow axis of the first retardation layer is in the range of 90° ± 10°; The angle formed by the absorption axis of the first polarizer and the slow axis of the second retardation layer is in the range of 0° ± 10°; The in-plane retardation Re(550) of the first retardation layer is 180 nm or more and 240 nm or less; The Nz coefficient of the first retardation layer is -1.0 or more and -0.1 or less; The in-plane retardation Re(550) of the second retardation layer is 195 nm or more and 255 nm or less, A polarizing plate with a retardation layer.

2. An image display cell; An image display device comprising the polarizing plate with a retardation layer according to Claim 1, disposed on the viewing side with respect to the image display cell.

3. The image display cell is a liquid crystal cell, The driving mode of the liquid crystal cell is an IPS mode, the image display device according to Claim 2.

4. The image display device includes a second polarizing plate disposed on the side opposite to the polarizing plate with a retardation layer with respect to the image display cell, The second polarizing plate includes a second polarizer, The angle formed by the absorption axis of the first polarizer and the initial alignment direction of the liquid crystal cell is in the range of 0° ± 10°, The angle formed by the absorption axis of the second polarizer and the initial alignment direction of the liquid crystal cell is in the range of 0° ± 10°, the image display device according to Claim 3.

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