Polarizing plate with retardation layer and image display device

Abstract

To provide a polarizing plate with a retardation layer and an image display device with which it is possible to reduce a decrease in black luminance in a diagonal direction in the image display device.SOLUTION: A polarizing plate with a retardation layer according to the present invention comprises: a polarizing plate that includes a polarizer; and a retardation layer located adjacent to the polarizing plate, the refractive index characteristic of which indicates the relationship nx>nz>ny. The absorption axis of the polarizer and the slow axis of the retardation layer are practically parallel or practically orthogonal. The polarizing plate with the retardation layer satisfies the relationship of formula (1) below. (In formula (1), a to j represent the constant selected from the relationship between the absorption axis and the slow axis, R0 represents the front phase difference of the retardation layer at a wavelength of 550 nm, and NZ represents the Nz coefficient of the retardation layer.)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 technology]

[0002] In recent years, image display devices, such as liquid crystal display devices, have rapidly become widespread. Known examples of such image display devices include a liquid crystal display device that includes an elliptically polarizing plate having a polarizing plate and a retardation plate, and a liquid crystal cell (see, for example, Patent Document 1). Such image display devices are used in various industrial products, and the required characteristics vary depending on the application, and visibility from oblique directions is sometimes particularly required. However, the image display device described in Patent Document 1 has a problem in that the black luminance from oblique directions is not sufficiently small (i.e., the black display does not become sufficiently black when viewed from an oblique direction). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 5-157911 Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention has been made to solve the above-mentioned conventional problems, and its object is to provide a polarizing plate with a retardation layer that can realize an image display device in which the black luminance in the oblique direction is sufficiently small. [Means for solving the problem]

[0005] The polarizing plate with a retardation layer of the present invention comprises a polarizing plate containing a polarizer; and a retardation layer disposed adjacent to the polarizing plate, the refractive index characteristics of which satisfy the relationship nx>nz>ny. The absorption axis of the polarizer and the slow axis of the retardation layer are substantially parallel or substantially perpendicular to each other. The polarizing plate with a retardation layer satisfies the relationship of the following formula (1):

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[0006] According to the embodiment of the present invention, it is possible to realize a polarizing plate with a retardation layer that can reduce the black luminance in an oblique direction in an image display device. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a schematic cross-sectional view of a retardation layer-attached polarizing plate according to one embodiment of the present invention. [Figure 2] 1 is a schematic cross-sectional view of an image display device according to one embodiment of the present invention. [Figure 3] FIG. 10 is a schematic cross-sectional view of an image display device according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

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

[0009] (Definition of terms and symbols) The definitions of terms and symbols used in this specification are as follows. (1) Refractive index (nx, ny, nz) "nx" is the refractive index in the direction in which the in-plane refractive index is greatest (i.e., the slow axis direction), "ny" is the refractive index in the direction perpendicular to the slow axis in the plane (i.e., the fast axis direction), and "nz" is the refractive index in the thickness direction. (2) In-plane retardation (Re) and front retardation (R0) "Re(λ)" is the in-plane retardation measured with light having a wavelength of λ nm at 23°C. For example, "Re(550)" is the in-plane retardation (front retardation) measured with light having a wavelength of 550 nm at 23°C. In this specification, "Re(550)" may be referred to as "R0". Re(λ) can be calculated by the formula: Re=(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 calculated by the formula: Rth=(nx-nz)×d, where d (nm) is the thickness of the layer (film). (4) Nz coefficient The Nz coefficient is calculated by Nz=Rth / Re. (5) Substantially perpendicular or parallel The expressions "substantially perpendicular" and "approximately perpendicular" include the case where the angle between two directions is 90°±10°, preferably 90°±7°, and more preferably 90°±5°. The expressions "substantially parallel" and "approximately parallel" include the case where the angle between two directions is 0°±10°, preferably 0°±7°, and more preferably 0°±5°. Furthermore, when simply referring to "orthogonal" or "parallel" in this specification, this can include the state of being substantially perpendicular or substantially parallel.

[0010] A. Overall structure of polarizing plate with 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 illustrated polarizing plate with a retardation layer 1 comprises a polarizing plate 2 including a polarizer 21; and a retardation layer 3 disposed adjacent to the polarizing plate 2, the retardation layer 3 having refractive index characteristics satisfying the relationship nx>nz>ny. The absorption axis of the polarizer 21 and the slow axis of the retardation layer 3 are substantially parallel to or substantially perpendicular to each other. The retardation layer-attached polarizing plate 1 satisfies the relationship of the following formula (1). The retardation layer 3 may be in direct contact with the polarizing plate 2, or may be attached to the polarizing plate 2 via an adhesive or pressure-sensitive adhesive.

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[0011] In one embodiment, a to j in the above formula (1) represent constants selected from the relationship between the absorption axis of the polarizer 21 and the slow axis of the retardation layer 3 in Table 1 above, and the absorption axis of the polarizer 21 and the slow axis of the retardation layer 3 are substantially parallel. In this case, R0 of the retardation layer 3 is typically 210 nm or more and 270 nm or less, and preferably 250 nm or less. The Nz coefficient of the retardation layer 3 is typically 0.38 or more and 0.53 or less. According to such a configuration, when the polarizing plate with a retardation layer is used in an O-mode liquid crystal display device described later and the absorption axis of the polarizer 21 and the slow axis of the retardation layer 3 are substantially parallel to each other, the black luminance in the oblique direction can be stably reduced.

[0012] In one embodiment, a to j in the above formula (1) represent constants selected from the relationship between the absorption axis of the polarizer 21 and the slow axis of the retardation layer 3 in Table 1 above, and the absorption axis of the polarizer 21 and the slow axis of the retardation layer 3 are substantially perpendicular to each other. In this case, R0 of the retardation layer 3 is typically 270 nm or more, preferably 290 nm or more, and typically 360 nm or less. The Nz coefficient of the retardation layer 3 is typically 0.42 or more and 0.68 or less. According to such a configuration, when the polarizing plate with a retardation layer is used in an O-mode liquid crystal display device described later and the absorption axis of the polarizer 21 and the slow axis of the retardation layer 3 are substantially perpendicular to each other, the black luminance in the oblique direction can be stably reduced.

[0013] In one embodiment, a to j in the above formula (1) represent constants selected from the relationship between the absorption axis of the polarizer 21 and the slow axis of the retardation layer 3 in Table 2 above, and the absorption axis of the polarizer 21 and the slow axis of the retardation layer 3 are substantially perpendicular to each other. In this case, R0 of the retardation layer 3 is typically 210 nm or more, preferably 230 nm or more, and typically 270 nm or less. The Nz coefficient of the retardation layer 3 is typically 0.42 or more and 0.53 or less. According to such a configuration, when the polarizing plate with a retardation layer is used in an E-mode liquid crystal display device described later and the absorption axis of the polarizer 21 and the slow axis of the retardation layer 3 are substantially perpendicular to each other, the black luminance in the oblique direction can be stably reduced.

[0014] In one embodiment, a to j in the above formula (1) represent constants selected from the relationship between the absorption axis of the polarizer 21 and the slow axis of the retardation layer 3 in Table 2 above, and the absorption axis of the polarizer 21 and the slow axis of the retardation layer 3 are substantially parallel. In this case, R0 of the retardation layer 3 is typically 270 nm or more and 360 nm or less. The Nz coefficient of the retardation layer 3 is typically 0.47 or more and 0.63 or less. According to such a configuration, when the polarizing plate with a retardation layer is used in an E-mode liquid crystal display device described later and the absorption axis of the polarizer 21 and the slow axis of the retardation layer 3 are substantially parallel to each other, the black luminance in the oblique direction can be stably reduced.

[0015] B. Overall structure of polarizing plate with retardation layer 2 is a schematic cross-sectional view of an image display device according to one embodiment of the present invention. The image display device 10 shown in the figure includes an image display cell 6 and a retardation layer-attached polarizing plate 1 disposed on the viewing side of the image display cell 6 (one side in the thickness direction of the retardation layer-attached polarizing plate 1). In this embodiment, preferably, The absorption axis of the polarizer 21 of the first polarizing plate 2 and the slow axis of the retardation layer 3 are substantially parallel, R0 of the retardation layer 3 is 210 nm or more and 270 nm or less, and the Nz coefficient of the retardation layer 3 is 0.38 or more and 0.53 or less, The absorption axis of the polarizer 21 of the first polarizing plate 2 and the slow axis of the retardation layer 3 are substantially perpendicular to each other, R0 of the retardation layer 3 is 270 nm or more and 360 nm or less, and the Nz coefficient of the retardation layer 3 is 0.42 or more and 0.68 or less, or The absorption axis of the polarizer 21 of the first polarizing plate 2 and the slow axis of the retardation layer 3 are substantially perpendicular to each other, the R0 of the retardation layer 3 is 210 nm or more and 270 nm or less, and the Nz coefficient of the retardation layer 3 is 0.42 or more and 0.53 or less.

[0016] The image display device 10 shown in the figure further includes a second polarizing plate 4 disposed on the opposite side of the image display cell 6 from the viewing side (opposite side to the retardation layer-attached polarizing plate 1). For convenience, hereinafter, the polarizing plate 2 will be referred to as the first polarizing plate 2 to distinguish it from the second polarizing plate 4. The second polarizing plate 4 includes a polarizer 41. The absorption axis direction of the polarizer 21 included in the first polarizing plate 2 and the absorption axis direction of the polarizer 41 included in the second polarizing plate 4 are typically substantially perpendicular to each other. In practice, the image display device 10 (liquid crystal display device) further includes a backlight unit 9. The backlight unit 9 includes a light source 7 and a light guide plate 8. The backlight unit 9 may further include any other appropriate members (for example, a diffusion sheet, a prism sheet). In the illustrated example, the backlight unit 9 is of an edge-light type, but any other appropriate type (for example, a direct type) may also be adopted as the backlight unit 9.

[0017] The image display cell 6 is typically a liquid crystal cell 6a, and the image display device 10 is typically a liquid crystal display device. The liquid crystal display device may be of the so-called O mode or the so-called E mode. An "O mode liquid crystal display device" refers to one in which the absorption axis direction of a polarizer (polarizer 41 in this embodiment) arranged on the opposite side of the viewing side (back side) of the liquid crystal cell is substantially parallel to the initial alignment direction of the liquid crystal cell. An "E mode liquid crystal display device" refers to one in which the absorption axis direction of a polarizer arranged on the opposite side of the viewing side (back side) of the liquid crystal cell is substantially perpendicular to the initial alignment direction of the liquid crystal cell. The "initial alignment direction of the liquid crystal cell" refers to the direction (i.e., the slow axis direction) in which the in-plane refractive index of the liquid crystal layer, which is described below, is maximized as a result of the alignment of liquid crystal molecules contained in the liquid crystal layer in the absence of an electric field. When the liquid crystal display device is in O mode, a to j in the above formula (1) typically represent constants selected from the relationship between the absorption axis of the polarizer 21 and the slow axis of the retardation layer 3 in Table 1 above, and when the liquid crystal display device is in E mode, a to j in the above formula (1) typically represent constants selected from the relationship between the absorption axis of the polarizer 21 and the slow axis of the retardation layer 3 in Table 2 above.

[0018] In the image display device 10, the polarizing plate with a retardation layer 1 is arranged on the viewing side of the image display cell 6 (liquid crystal cell 6a), but the polarizing plate with a retardation layer 1 may also be positioned on the opposite side of the viewing side of the image display cell 6 (liquid crystal cell 6a). 3 is a schematic cross-sectional view of an image display device according to another embodiment of the present invention. The image display device 11 shown in the figure includes an image display cell 6 and a retardation layer-attached polarizing plate 1 arranged on the opposite side of the image display cell 6 from the viewing side. In this embodiment, preferably, the absorption axis of the polarizer 21 of the first polarizing plate 2 and the slow axis of the retardation layer 3 are substantially parallel, R0 of the retardation layer 3 is 270 nm or more and 260 nm or less, and the Nz coefficient of the retardation layer 3 is 0.47 or more and 0.63 or less. The image display device 11 is typically a liquid crystal display device, similar to the image display device 10. In this embodiment, the liquid crystal display device is preferably an E mode.

[0019] The image display device 11 (liquid crystal display device) further includes a second polarizing plate 4 disposed on the viewing side of the image display cell 6 (liquid crystal cell 6a). Similarly to the image display device 10, the image display device 11 (liquid crystal display device) further includes a backlight unit 9 in practical use.

[0020] The image display device (liquid crystal display device) may further include any other appropriate components. For example, another optical compensation layer (retardation layer) may be further disposed. The optical properties, number, combination, and arrangement position of the other optical compensation layer may be appropriately selected depending on the purpose and desired optical properties. For matters not described in this specification, the configuration of an image display device (liquid crystal display device) well known and commonly used in the art may be adopted.

[0021] Hereinafter, each member constituting the retardation layer-attached polarizing plate and the image display device will be described.

[0022] C. Polarizing plate C-1.Polarizer Any appropriate polarizer may be adopted as the polarizer 21 included in the first polarizing plate 2 and the polarizer 41 included in the second polarizing plate 4 (hereinafter, they may be collectively referred to as polarizers). For example, the resin film forming the polarizer may be a single-layer resin film or a laminate of two or more layers.

[0023] Specific examples of polarizers made of a single-layer resin film include hydrophilic polymer films such as polyvinyl alcohol (PVA) films, partially formalized PVA films, and partially saponified ethylene-vinyl acetate copolymer films that have been dyed with iodine or a dichroic substance such as a dichroic dye and stretched, as well as polyene-based oriented films such as dehydrated PVA films and dehydrochlorinated polyvinyl chloride films. Polarizers obtained by dyeing a PVA film with iodine and uniaxially stretching it are preferred because of their excellent optical properties.

[0024] The dyeing with iodine is carried out, for example, by immersing the PVA film in an aqueous iodine solution. The stretching ratio of the uniaxial stretching is preferably 3 to 7 times. The stretching may be carried out after the dyeing treatment or while dyeing. Alternatively, the PVA film may be stretched and then dyed. If necessary, the PVA film may be subjected to a swelling treatment, a crosslinking treatment, a washing treatment, a drying treatment, or the like. For example, by immersing the PVA film in water and washing it before dyeing, it is possible to wash away dirt and antiblocking agents on the surface of the PVA film, and also to swell the PVA film, thereby preventing uneven dyeing.

[0025] Specific examples of polarizers obtained using laminates include a laminate of a resin substrate and a PVA-based resin layer (PVA-based resin film) laminated on the resin substrate, or a polarizer obtained using a laminate of a resin substrate and a PVA-based resin layer coated on the resin substrate. A polarizer obtained using a laminate of a resin substrate and a PVA-based resin layer coated on the resin substrate can be produced, for example, by applying a PVA-based resin solution to the resin substrate and drying the resin substrate 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 convert the PVA-based resin layer into a polarizer. In this embodiment, stretching typically involves immersing the laminate in an aqueous boric acid solution and stretching it. Furthermore, stretching can optionally further include in-air stretching the laminate at an elevated temperature (e.g., 95°C or higher) before stretching in the aqueous boric acid solution. The obtained resin substrate / polarizer laminate may be used as is (i.e., the resin substrate may be used as a protective layer for the polarizer), or the resin substrate may be peeled off from the resin substrate / polarizer laminate and any appropriate protective layer depending on the purpose may be laminated on the peeled surface. Details of such a polarizer manufacturing method are described in, for example, JP 2012-73580 A and Japanese Patent No. 6470455 A. The entire disclosures of these publications are incorporated herein by reference.

[0026] 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 this range, curling during heating can be well suppressed, and good appearance durability during heating can be obtained.

[0027] The polarizer preferably exhibits absorption dichroism at any wavelength between 380 nm and 780 nm. The single transmittance of the polarizer is, for example, 41.5% to 46.0%, preferably 43.0% to 46.0%, and more preferably 44.5% to 46.0%. The degree of polarization of the polarizer is preferably 97.0% or more, more preferably 99.0% or more, and even more preferably 99.9% or more.

[0028] C-2.Protective layer Each of the first polarizing plate 2 and the second polarizing plate 4 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 10, the first polarizing plate 2 includes a protective layer 22 provided on the viewing side surface of the polarizer 21, and the second polarizing plate 4 includes a protective layer 42 provided on the surface of the polarizer 41 opposite to the viewing side. In the image display device 11, the protective layer 22 is provided on the surface of the polarizer 21 opposite to the viewing side, and the protective layer 42 is provided on the viewing side surface of the polarizer 41.

[0029] The protective layer is formed of any suitable film that can be used as a protective layer for a polarizer. Specific examples of materials that can be the main component of the film include cellulose-based resins such as triacetyl cellulose (TAC), and transparent resins such as polyesters, polyvinyl alcohols, polycarbonates, polyamides, polyimides, polyethersulfones, polysulfones, polystyrenes, polynorbornenes, polyolefins, (meth)acrylics, and acetates. Other examples include thermosetting or ultraviolet-curing resins such as (meth)acrylics, urethanes, (meth)acrylic urethanes, epoxy resins, and silicones. Other examples include glassy polymers such as siloxane polymers. Polymer films described in JP 2001-343529 A (WO 01 / 37007) can also be used. Examples of materials that can be used for this film include a resin composition containing a thermoplastic resin having substituted or unsubstituted imide groups in its side chains and a thermoplastic resin having substituted or unsubstituted phenyl and nitrile groups in its side chains, such as a resin composition containing an alternating copolymer of isobutene and N-methylmaleimide and an acrylonitrile-styrene copolymer.The polymer film can be, for example, an extrusion molded product of the above resin composition.

[0030] When the polarizer arranged on the viewing side of the image display cell 6 has a protective layer located on the outermost surface of the image display device, the protective layer may be subjected to surface treatment such as hard coating treatment, anti-reflection treatment, anti-sticking treatment, anti-glare treatment, etc., as necessary.

[0031] The thickness of the protective layer is typically 5 mm or less, preferably 1 mm or less, more preferably 1 μm to 500 μm, and even more preferably 5 μm to 150 μm. If a surface treatment is applied, the thickness of the protective layer includes the thickness of the surface treatment layer.

[0032] D. Retardation layer As described above, the retardation layer 3 exhibits refractive index characteristics of nx>nz>ny. The Re(550) of the retardation layer 3 is typically 210 nm or more and 360 nm or less. If the Re(550) of the retardation layer 3 is in this range, the movement distance on the Poincaré sphere is short, thereby achieving excellent hue and luminance characteristics and reducing the deviation due to the retardation component of the TFT (switching element).

[0033] The retardation layer 3 may exhibit an inverse wavelength dispersion characteristic in which the retardation value increases according to the wavelength of the measurement light, a positive wavelength dispersion characteristic in which the retardation value decreases according to the wavelength of the measurement light, or a flat wavelength dispersion characteristic in which the retardation value hardly changes depending on the wavelength of the measurement light. The retardation layer 3 preferably exhibits a flat wavelength dispersion characteristic.

[0034] The retardation layer 3 has a photoelastic coefficient of, for example, 10×10 -12 m 2 / N or more, preferably 1.0 × 10 -12 m 2 / N or more, e.g., 100×10 -12 m 2 / N or less, preferably 60 × 10 -12 m 2 / N or less, preferably 30 × 10 -12 m 2 When the photoelastic coefficient of the retardation layer 3 is equal to or less than the upper limit, deviation or unevenness in the retardation value caused by shrinkage stress of the polarizer or heat from the backlight can be suppressed, and an image display device (liquid crystal display device) with good display uniformity can be obtained.

[0035] The thickness of the retardation layer 3 is typically 20 μm or more, preferably 30 μm or more, more preferably 40 μm or more, and typically 200 μm or less, preferably 150 μm or less.

[0036] The retardation layer 3 is typically a retardation film formed of any appropriate resin capable of realizing the above-mentioned properties. Examples of resins that form the retardation layer 3 include polyarylates, polyamides, polyimides, polyesters, polyaryletherketones, polyamideimides, polyesterimides, polyvinyl alcohols, polyfumarates, polyethersulfones, polysulfones, cycloolefin resins, polycarbonate resins, cellulose resins, and polyurethanes. These resins may be used alone or in combination. A cycloolefin resin is preferably used, and more preferably a norbornene resin, as the resin forming the retardation layer 3. Specific examples of the norbornene resin include "cycloolefin resin obtained by hydrogenating a ring-opening polymer of a norbornene monomer" described in JP-A-2006-208925.

[0037] The retardation layer 3 can be produced, for example, by laminating a high-shrinkage film (e.g., a polypropylene film) to both sides of a polymer film mainly composed of the above-mentioned resin, and then heat-stretching the film using a longitudinal uniaxial stretching method with a roll stretching machine. The high-shrinkage film is used to impart a shrinkage force in a direction perpendicular to the stretching direction during heat-stretching, thereby increasing the refractive index (nz) in the thickness direction of the retardation layer 3. There are no particular restrictions on the method for laminating the high-shrinkage films to both sides of the polymer film, but a method in which an acrylic pressure-sensitive adhesive layer containing an acrylic polymer as a base polymer is provided between the polymer film and the high-shrinkage film to bond them is preferred from the viewpoints of excellent workability and economy.

[0038] Furthermore, by adjusting the thickness of the polymer film (thickness of the original film), the stretching temperature and the stretching ratio, the front retardation R0 and the Nz coefficient of the retardation layer 3 can be adjusted to fall within the above-mentioned ranges. The thickness of the polymer film (raw thickness) is typically 80 μm or more, preferably 100 μm or more, and typically 500 μm or less, preferably 400 μm or less, more preferably 300 μm or less. The stretching temperature is typically 120°C or higher, preferably 130°C or higher, and typically 180°C or lower, preferably 170°C or lower. The stretching ratio ((stretching direction dimension of retardation layer−stretching direction dimension of polymer film) / stretching direction dimension of polymer film×100) is typically 0.1% or more, preferably 0.3% or more, and typically 80% or less, preferably 70% or less.

[0039] E. Liquid crystal cell The liquid crystal cell 6a has a first substrate 62, a second substrate 63, and a liquid crystal layer 61 sandwiched between them and containing liquid crystal molecules aligned in a homogeneous array in the absence of an electric field. In a typical configuration, one substrate (typically the first substrate 62) is provided with a color filter and a black matrix, while the other substrate (typically the second substrate 63) is provided with switching elements that control the electro-optical properties of the liquid crystal, scanning lines that provide gate signals to the switching elements, signal lines that provide source signals, pixel electrodes, and counter electrodes. The distance between the substrates (cell gap) is controlled by spacers or the like. An alignment film made of, for example, polyimide, can be provided on the side of the substrate that contacts the liquid crystal layer.

[0040] The Rth(550) of the first substrate 62 and the second substrate 63 is −10 nm to 100 nm. In one embodiment, the Rth(550) of at least one of the first substrate 62 and the second substrate 63 is preferably 8 nm to 90 nm, more preferably 15 nm to 80 nm, even more preferably 20 nm to 70 nm, and particularly preferably 30 nm to 60 nm. In another embodiment, the Rth(550) of at least one of the first substrate 62 and the second substrate 63 is preferably −0.1 nm or less, more preferably −5 nm to −50 nm. According to an embodiment of the present invention, when the substrates have such a thickness direction retardation, the black luminance in the oblique direction can be sufficiently reduced in a liquid crystal display device including a liquid crystal cell with homogeneous alignment.

[0041] In one embodiment, at least one of the first substrate 62 and the second substrate 63 satisfies the relationship Rth(450)>Rth(550), and preferably, both the first substrate 62 and the second substrate 63 satisfy the relationship Rth(450)>Rth(550). More preferably, at least one of the first substrate 62 and the second substrate 63 further satisfies the relationship Rth(550)>Rth(650), and even more preferably, both the first substrate 62 and the second substrate 63 further satisfy the relationship Rth(550)>Rth(650). According to an embodiment of the present invention, even when the substrates have such wavelength dispersion characteristics, the black luminance in oblique directions can be sufficiently reduced in a liquid crystal display device including a homogeneously aligned liquid crystal cell.

[0042] As described above, the liquid crystal layer 61 contains liquid crystal molecules that are homogeneously aligned in the absence of an electric field. "Liquid crystal molecules aligned in a homogeneous alignment" refers to a state in which the directors of the liquid crystal molecules are aligned parallel and uniformly to the substrate plane as a result of the interaction between the alignment-treated substrate and the liquid crystal molecules. Such a liquid crystal layer (and consequently, the liquid crystal cell) typically exhibits a refractive index characteristic of nx>ny=nz. Here, "ny=nz" encompasses not only the case where ny and nz are completely identical, but also the case where ny and nz are substantially identical. The Re(550) of the liquid crystal layer may be, for example, 300 nm to 400 nm. The Nz coefficient of the liquid crystal layer may be, for example, 0.9 to 1.1.

[0043] In one embodiment, the liquid crystal molecules in the liquid crystal layer have a pretilt. That is, the alignment vectors of the liquid crystal molecules are slightly tilted with respect to the substrate plane. The pretilt angle is preferably 0.1° to 1.0°, and more preferably 0.2° to 0.7°.

[0044] Examples of driving modes for such liquid crystal cell 6a include in-plane switching (IPS) mode and fringe field switching (FFS) mode. The IPS mode includes super in-plane switching (S-IPS) mode and advanced super in-plane switching (AS-IPS) mode, which employ V-shaped electrodes or zigzag electrodes. The FFS mode includes advanced fringe field switching (A-FFS) mode and ultra fringe field switching (U-FFS) mode, which employ V-shaped electrodes or zigzag electrodes. The in-plane switching (IPS) mode is preferred as the driving mode for liquid crystal cell 6a. When the liquid crystal cell 6a is driven in the IPS mode, the visibility of the liquid crystal display device in oblique directions can be improved.

[0045] F. Backlight unit The light source 7 is disposed at a position corresponding to the side surface of the light guide plate 8. For example, an LED light source configured by an array of multiple LEDs may be used as the light source. Any appropriate light guide plate may be used as the light guide plate 8. For example, a light guide plate having a lens pattern formed on the back surface side, or a light guide plate having a prism shape or the like formed on the back surface side and / or the viewing surface, may be used so as to be able to deflect light from the lateral direction in the thickness direction. Preferably, a light guide plate having a prism shape formed on the back surface side and the viewing surface is used. In the light guide plate, it is preferable that the prism shape formed on the back surface side and the prism shape formed on the viewing surface have their ridge directions perpendicular to each other. Using such a light guide plate allows light to be incident on a prism sheet (not shown) in a manner that is more easily focused. [Example]

[0046] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The evaluation items in the examples are as follows.

[0047] (1) Maximum black brightness A black screen was displayed on the image display devices obtained in the examples and comparative examples, and the luminance was measured at a polar angle of 60° and at one azimuth angle using a luminance meter (manufactured by AUTRONIC-MELCHERS, product name "Conoscope"), and the maximum value was taken as the maximum black luminance (unit: cd / m 2 ) was decided.

[0048] [Production Example 1: Preparation of first polarizing plate] A long, amorphous isophthalic copolymerized polyethylene terephthalate film (thickness: 100 μm) having a Tg of about 75° C. was used as the thermoplastic resin substrate, and one side of the resin substrate was subjected to a corona treatment. A PVA aqueous solution (coating solution) was prepared by dissolving 100 parts by weight of a PVA-based resin made by mixing polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOHSEFFIMER") in a 9:1 ratio, to which 13 parts by weight of potassium iodide was added, in water. 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 resin layer with a thickness of 13 μm, thereby producing a laminate. The resulting laminate was uniaxially stretched 2.4 times in the machine direction (longitudinal direction) in an oven at 130°C (auxiliary in-air stretching treatment). Next, the laminate was immersed in an insolubilizing bath (a boric acid aqueous solution obtained by mixing 4 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40°C for 30 seconds (insolubilizing treatment). Next, the film was immersed in a dye bath (an aqueous iodine solution obtained by mixing iodine and potassium iodide in a weight ratio of 1:7 with 100 parts by weight of water) at a liquid temperature of 30°C for 60 seconds while adjusting the concentration so that the single transmittance (Ts) of the finally obtained polarizer would be a desired value (dyeing treatment). Next, the sample was immersed in a crosslinking bath (a boric acid aqueous solution obtained by blending 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40°C for 30 seconds (crosslinking treatment). The laminate was then immersed in a boric acid aqueous solution (boric acid concentration 4 wt %, potassium iodide concentration 5 wt %) at a liquid temperature of 70°C and uniaxially stretched in the longitudinal direction (longitudinal direction) between rolls with different peripheral speeds to a total stretch ratio of 5.5 times (underwater stretching treatment). Thereafter, the laminate was immersed in a cleaning bath (aqueous solution obtained by mixing 4 parts by weight of potassium iodide with 100 parts by weight of water) at a liquid temperature of 20° C. (cleaning treatment). Thereafter, the film was dried in an oven maintained at about 90°C, and brought into contact with a heated roll made of SUS whose surface temperature was maintained at about 75°C (drying shrinkage treatment). In this manner, a polarizer having a thickness of about 5 μm was formed on the resin substrate, and a laminate having a resin substrate / polarizer structure was obtained. An HC-TAC film was attached as a protective layer to the polarizer surface of the obtained laminate (the surface opposite to the resin substrate).The resin substrate was then peeled off to obtain a first polarizing plate having a protective layer / polarizer structure.

[0049] [Production Example 2: Preparation of second polarizing plate] A laminate having a resin substrate / polarizer structure was obtained in the same manner as in Production Example 1. A TAC film (thickness: 20 μm) was attached as a protective layer to the polarizer surface (the surface opposite to the resin substrate) of the obtained laminate. Next, the resin substrate was peeled off, and a reflective polarizer (thickness: 26 μm) was attached to the peeled surface via a pressure-sensitive adhesive layer (thickness: 12 μm) to obtain a second polarizing plate having a reflective polarizer / polarizer / protective layer structure.

[0050] [Production Example 3: Preparation of Retardation Layer] A cycloolefin (norbornene) resin film (Arton 3, manufactured by JSR Corporation) having the thickness (raw film thickness) shown in Table 3 was prepared. Next, high-shrinkage polypropylene films were attached to both sides of the cycloolefin (norbornene) resin film via acrylic adhesive layers. Thereafter, the film was held in the longitudinal direction using a roll stretching machine and stretched at the temperature and stretching ratio shown in Table 3 to produce a retardation layer exhibiting refractive index characteristics of nx>nz>ny. Table 3 shows the correlation between the front retardation R0 and Nz coefficient of the obtained retardation layer and the raw film thickness, temperature, and stretching ratio.

[0051] [Table 5]

[0052] [Manufacturing Example 4: Preparation of image display cell (liquid crystal cell)] A liquid crystal cell was removed from an IPS-mode liquid crystal display device (manufactured by Apple Inc., product name "iPad (registered trademark)"). The optical members attached to both sides of the liquid crystal cell were removed, and the removed surfaces (the outer surfaces of the substrates) were cleaned. This was used as an image display cell (liquid crystal cell). The first substrate of the liquid crystal cell had Rth(450) = 32 nm, Rth(550) = 19 nm, and Rth(650) = 23 nm; the second substrate had Rth(450) = 9 nm, Rth(550) = 0.3 nm, and Rth(650) = -6 nm.

[0053] [Examples 1 to 6 and Comparative Examples 1 to 54: O mode] The retardation layer of Production Example 3 and the first polarizing plate of Production Example 1 were laminated in this order on the viewing side of the liquid crystal cell of Production Example 4. Table 4 shows the front retardation R0 and Nz coefficient of the retardation layer in each example and comparative example. On the other hand, the second polarizing plate of Production Example 2 was laminated on the back side of the liquid crystal cell. The lamination was performed so that the absorption axis direction of the polarizer of the first polarizing plate and the absorption axis direction of the polarizer of the second polarizing plate were substantially perpendicular to each other, the absorption axis direction of the polarizer of the first polarizing plate and the slow axis direction of the retardation layer were substantially parallel to each other, and the absorption axis direction of the polarizer of the second polarizing plate and the initial alignment direction of the liquid crystal cell were substantially parallel to each other. In this way, an image display device (O-mode liquid crystal display device) was produced. The values ​​of the above formula (1) for the obtained liquid crystal display device are shown in Table 4. The liquid crystal display device was also evaluated for maximum black luminance according to the following criteria. The results are shown in Table 4. 〇:0.0072cd / m 2 less than ×:0.0072cd / m 2 That's all.

[0054] [Table 6]

[0055] [Examples 7 to 23 and Comparative Examples 55 to 109: O mode] Image display devices (O-mode liquid crystal display devices) were produced in the same manner as in Examples 1 to 6 and Comparative Examples 1 to 54, except that the layers were laminated so that the absorption axis direction of the polarizer of the first polarizing plate and the slow axis direction of the retardation layer were substantially perpendicular to each other. The values ​​of the above formula (1) for the obtained liquid crystal display devices are shown in Table 5. The liquid crystal display devices were also subjected to evaluation of maximum black luminance and evaluated according to the following criteria. The results are shown in Table 5. 〇:0.0127cd / m 2 less than ×:0.0127cd / m 2 That's all.

[0056] [Table 7]

[0057] [Examples 24 to 35 and Comparative Examples 110 to 169: E mode] The first polarizing plate of Production Example 1 was laminated on the viewing side of the liquid crystal cell of Production Example 4. On the other hand, the retardation layer of Production Example 3 and the second polarizing plate of Production Example 2 were laminated in this order on the back side of the liquid crystal cell. The lamination was performed so that the absorption axis direction of the polarizer of the first polarizing plate and the absorption axis direction of the second polarizer were substantially perpendicular, the absorption axis direction of the polarizer of the first polarizing plate and the slow axis direction of the retardation layer were substantially parallel, and the absorption axis direction of the polarizer of the second polarizing plate and the initial alignment direction of the liquid crystal cell were substantially perpendicular. In this way, an image display device (E-mode liquid crystal display device) was produced. The values ​​of the above formula (1) for the obtained liquid crystal display device are shown in Table 6. The liquid crystal display device was also subjected to evaluation of maximum black luminance and evaluated according to the following criteria. The results are shown in Table 6. 〇:0.0138cd / m 2 less than ×:0.0138cd / m 2 That's all.

[0058] [Table 8]

[0059] [Examples 36 to 38 and Comparative Examples 170 to 214: E mode] Image display devices (E-mode liquid crystal display devices) were fabricated in the same manner as in Examples 7 to 23 and Comparative Examples 55 to 109, except that the second polarizing plate was laminated so that the absorption axis direction of the polarizer and the initial alignment direction of the liquid crystal cell were substantially perpendicular to each other. The values ​​of the above formula (1) for the obtained liquid crystal display devices are shown in Table 7. The liquid crystal display devices were also subjected to evaluation of maximum black luminance, and were evaluated according to the following criteria. The results are shown in Table 7. 〇:0.0064cd / m 2 less than ×:0.0064cd / m 2 That's all.

[0060] [Table 9]

[0061] [evaluation] As is clear from Tables 4 to 7, by setting the above formula (1) to less than a predetermined value, it is possible to realize an image display device (liquid crystal display device) in which the black luminance in an oblique direction is sufficiently small. [Industrial Applicability]

[0062] The polarizing plate with a retardation layer and the image display device of the present invention can be used for various applications, including portable devices such as personal digital assistants (PDAs), mobile phones, watches, digital cameras, and portable game consoles; office automation equipment such as personal computer monitors, notebook computers, and copy machines; household electrical appliances such as video cameras, LCD televisions, and microwave ovens; in-vehicle equipment such as backup monitors, monitors for car navigation systems, and car audio; exhibition equipment such as information monitors for commercial stores; security equipment such as surveillance monitors; and nursing and medical equipment such as nursing monitors and medical monitors. [Explanation of symbols]

[0063] 1 Polarizing plate with retardation layer 2 Polarizing Plate 21 Polarizer 3 Retardation layer 6 Image display cells 10 Image display device

Claims

1. A liquid crystal cell; a retardation layer-attached polarizing plate disposed on the opposite side of the liquid crystal cell from the viewing side; a second polarizing plate disposed on the viewing side of the liquid crystal cell, The retardation layer-attached polarizing plate is a first polarizing plate including a polarizer; a retardation layer disposed adjacent to the first polarizing plate and having refractive index characteristics that satisfy the relationship of nx>nz>ny; an absorption axis of a polarizer of the first polarizing plate and a slow axis of the retardation layer are substantially parallel to each other; the second polarizing plate includes a polarizer, an absorption axis of a polarizer of the first polarizing plate and an initial alignment direction of the liquid crystal cell are substantially perpendicular to each other; R of the retardation layer ０ is 270 nm or more and 360 nm or less, the Nz coefficient of the retardation layer is 0.47 or more and 0.63 or less, An image display device that satisfies the relationship of the following formula (1): [Equation 1] (In formula (1), a to j represent constants selected from the relationship between the absorption axis and the slow axis in Table 2 below. R ０ represents the front retardation of the retardation layer at a wavelength of 550 nm, and NZ represents the Nz coefficient of the retardation layer. 【number】

2. 2. The image display device according to claim 1, wherein the driving mode of the liquid crystal cell is an IPS mode.

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