JP2023054647A - Polarizing plate with phase difference layer and image display device - Google Patents

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 nx>ny≥nz; and a second phase difference layer having refractive index characteristics indicating a relationship of nz≥nx>ny. 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 orthogonal to each other. The Re(550) of the first phase difference layer is 35 nm or more and 115 nm or less, and the Re(550) of the second phase difference layer is 30 nm or more and 135 nm or less.SELECTED DRAWING: Figure 1

Description

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

2. Description of the Related Art Image display devices typified by liquid crystal display devices generally use various optical films in which a polarizer and a retardation film are combined in order to compensate for optical characteristics suitable for the application. For example, a polarizing plate containing 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. is combined so that the absorption axis of the polarizer and the slow axis of the first retardation layer are orthogonal, and the absorption axis of the polarizer and the slow axis of the second retardation layer are parallel, Techniques for widening the viewing angle have been proposed (see Patent Document 1, for example).
By the way, in recent years, the applications of image display devices have been diversified. An example of such an application is an in-vehicle display. In-vehicle displays are required to have a wide viewing angle, particularly in the horizontal direction (left-right direction). However, even if the technology described in Patent Document 1 is applied to an in-vehicle display, there is a limit to widening the viewing angle in the horizontal direction. There is a problem that it does not become sufficiently black (that is, the black luminance does not become sufficiently small) when viewed from the upper right).

JP 2021-76759 A

The present invention has been made to solve the above-mentioned conventional problems, and its main purpose is to widen the viewing angle in the horizontal direction (predetermined plane direction of the image display surface), An object of the present invention is to provide a polarizing plate with a retardation layer that can realize an image display device capable of sufficiently reducing black brightness in an oblique direction intersecting both directions.

A polarizing plate with a retardation layer according to an embodiment of the present invention includes a first polarizing plate containing a first polarizer; and a second retardation layer whose index characteristic exhibits a relationship of nz≧nx>ny. The first retardation layer is arranged adjacent to the first polarizing plate, and the second retardation layer is arranged 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 substantially perpendicular to the phase axis. The in-plane retardation Re(550) of the first retardation layer is 35 nm or more and 115 nm or less, and the in-plane retardation Re(550) of the second retardation layer is 30 nm or more and 135 nm or less.
An image display device according to another aspect of the present invention comprises: an image display cell; and the retardation layer-attached polarizing plate disposed on the opposite side of the image display cell from the viewing side.
In one embodiment, the image display cell is a liquid crystal cell, and the driving mode of the liquid crystal cell is IPS mode.
In one embodiment, the image display device includes a second polarizing plate arranged on the opposite side of the image display cell from the polarizing plate with the retardation layer. The second polarizer includes a second polarizer. The absorption axis of the first polarizer and the initial alignment direction of the liquid crystal cell are substantially orthogonal, and the absorption axis of the second polarizer and the initial alignment direction of the liquid crystal cell are substantially orthogonal. are doing.

According to the embodiment of the present invention, it is possible to widen the viewing angle in the horizontal direction (predetermined surface direction of the image display surface) in the image display device, and sufficiently reduce the black brightness in the oblique direction that intersects both the vertical and horizontal directions. A polarizing plate with a retardation layer can be realized.

1 is a schematic cross-sectional view of a polarizing plate with a retardation layer according to one embodiment of the present invention; FIG. 1 is a schematic cross-sectional view of an image display device according to one embodiment of the present invention; FIG. 4 is a luminance distribution diagram of the image display device of Example 1 during black display. FIG. 10 is a luminance distribution diagram of the image display device of Comparative Example 1 during black display; FIG.

Although representative embodiments of the present invention will be described below, the present invention is not limited to these embodiments.

(Definition of terms and symbols)
Definitions of terms and symbols used herein are as follows.
(1) refractive index (nx, ny, nz)
"nx" is the refractive index in the direction in which the in-plane refractive index is maximum (i.e., slow axis direction), and "ny" is the in-plane direction orthogonal to the slow axis (i.e., fast axis direction) and "nz" is the refractive index in the thickness direction.
(2) In-plane retardation (Re) and in-plane retardation (R ₀ )
“Re(λ)” is an in-plane retardation measured at 23° C. with light having a wavelength of λ nm. For example, "Re(550)" is the in-plane retardation measured with light having a wavelength of 550 nm at 23°C. The “in-plane phase difference Re(550)” may be referred to as the “front phase difference R ₀ ”. Re(λ) is obtained by the formula: Re(λ)=(nx−ny)×d, where d (nm) is the thickness of the layer (film).
(3) Thickness direction retardation (Rth)
“Rth(λ)” is the retardation in the thickness direction measured at 23° C. with light having a wavelength of λ nm. For example, “Rth(550)” is the retardation in the thickness direction measured at 23° C. with light having a wavelength of 550 nm. Rth(λ) is determined 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 orthogonal” include cases 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 cases where the angle formed by two directions is 0°±10°, preferably 0°±7°, more preferably 0°± 5°. Further, references herein to simply "orthogonal" or "parallel" are intended to include substantially orthogonal or substantially parallel states.

A. Overall Configuration of Retardation Layer-Equipped Polarizing Plate FIG. 1 is a schematic cross-sectional view of a retardation layer-attached polarizing plate according to one embodiment of the present invention. The polarizing plate 100 with a retardation layer in the illustrated example includes a first polarizing plate 10 including a first polarizer 11; and a second retardation layer 30 whose refractive index characteristics exhibit a relationship of nz≧nx>ny.
The first retardation layer 20 is arranged adjacent to the first polarizing plate 10 . The second retardation layer 30 is arranged 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 . As used herein, “adjacently arranged” means being directly laminated or laminated only via an adhesive layer (for example, an adhesive layer or a pressure-sensitive adhesive layer). That is, 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, an optical function layer (for example, another position) retardation layer) is not interposed.
The absorption axis (first absorption axis direction) of the first polarizer 11 and the slow axis (first slow axis direction) of the first retardation layer 20 are substantially perpendicular to each other. The absorption axis (first absorption axis direction) of the first polarizer 11 and the slow axis (second slow axis direction) of the second retardation layer 30 are substantially perpendicular to each other.
The in-plane retardation Re(550) of the first retardation layer 20 is 35 nm or more and 115 nm or less, preferably 45 nm or more and 105 nm or less, more preferably 50 nm or more and 95 nm or less, and still more preferably 60 nm or more and 80 nm. It is below.
The in-plane retardation Re(550) of the second retardation layer 30 is 30 nm or more and 135 nm or less, preferably 40 nm or more and 125 nm or less, more preferably 50 nm or more and 115 nm or less, and still more preferably 80 nm or more and 110 nm or less. It is below.
When each of Re (550) of the first retardation layer and Re (550) of the second retardation layer satisfies the above range, in the image display device comprising the polarizing plate with the retardation layer, It is possible to widen the viewing angle in the horizontal direction (predetermined surface direction of the image display surface), and sufficiently reduce the black brightness in the oblique direction intersecting both the vertical and horizontal directions. 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 surface direction X of the image display device shown in FIG. 3) is changed to the vertical direction (for example, the first surface direction X shown in FIG. can be made wider than the viewing angle in the second surface direction Y orthogonal to the ), and the black display of the image display device can be made in the horizontal direction (first surface direction X) and the vertical direction (second surface direction Y) can sufficiently reduce the black luminance when viewed from an oblique direction crossing both directions of .
More specifically, the black display of the image display device is measured at a polar angle of 40° to 42° and an azimuth angle of 20° to 25°, 155° to 160°, and 190° to 195° using any suitable luminance meter. 0.00060 or less, preferably 0.00055 or less, more preferably 0.00050 or less, and most preferably 0.00040 or less when measured in the respective ranges of 0.00060° and 345° to 350°. In this specification, the luminance measured in the range of the polar angle and the azimuth angle is defined as area A luminance. The lower limit of area A luminance is typically 0.00001 or more.

In one embodiment, the Nz coefficient of the first retardation layer 20 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. It is 1.3 or less, more preferably 0.8 or more and 1.2 or less.
Further, when the refractive index characteristics of the second retardation layer 30 show the relationship of nz>nx>ny, the Nz coefficient of the second retardation layer 30 is, for example, −1.5 or more and −0.5 or less. , preferably -1.4 or more and -0.6 or less, more preferably -1.3 or more and -0.7 or less, and still more preferably -1.2 or more and -0.8 or less.
When the Nz coefficient of the first retardation layer 20 and/or the Nz coefficient of the second retardation layer are in such a range, in an image display device equipped with a polarizing plate with a retardation layer, in the horizontal direction (image display surface (predetermined surface direction of (2)) can be stably widened, and the black brightness in the oblique direction intersecting both the vertical and horizontal directions can be stably reduced.

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

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

The retardation layer-attached polarizing plate may be sheet-shaped or elongated. As used herein, the term "long shape" means an elongated shape whose length is sufficiently long relative to its width, for example, an elongated shape whose length is 10 times or more, preferably 20 times or more, its width. include. The elongated retardation layer-attached polarizing plate can be wound into a roll.

Practically, an adhesive layer (not shown) is provided on the side opposite to the first polarizing plate of the second retardation layer, and the polarizing plate with the retardation layer can be attached to the image display cell. ing. Furthermore, it is preferable that a release liner is temporarily attached to the surface of the pressure-sensitive adhesive layer until the polarizing plate with a retardation layer is used. Temporarily attaching the release liner protects the pressure-sensitive adhesive layer and enables roll formation.

B. Overall Configuration of Image Display Device FIG. 2 is a schematic cross-sectional view of an image display device according to one embodiment of the present invention. The image display device 101 of the illustrated example includes an image display cell 60; and a polarizing plate 100 with a retardation layer disposed on the opposite side of the image display cell 60 from the viewing side. 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 the first retardation layer. 20 and the image display cell 60 .

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

The image display cell 60 is typically a liquid crystal cell 60a, and the image display device 101 is typically a liquid crystal display device. Liquid crystal display devices are typically of so-called E mode. The term “E-mode liquid crystal display device” refers to the absorption axis (first absorption axis direction) and the initial alignment direction of the liquid crystal cell are substantially perpendicular to each other. The "initial alignment direction of the liquid crystal cell" is the 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 becomes maximum (that is, the slow axis direction).

In one embodiment, the absorption axis (second absorption axis direction) of the polarizer (second polarizer 41 in this embodiment) placed on the viewing side of the liquid crystal cell and the initial alignment direction of the liquid crystal cell are substantially orthogonal to each other. 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.

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 other appropriate members (eg, diffusion sheet, prism sheet). Although the backlight unit 90 is edge-lit in the illustrated example, any other suitable backlight unit 90 (eg, direct type) may be employed.

The image display device (liquid crystal display device) may further include any other appropriate member. For example, another optical compensation layer (retardation layer) may be further arranged. The optical properties, number, combination, arrangement position, etc. of the separate optical compensation layers can be appropriately selected according to the purpose, desired optical properties, and the like. 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 can be adopted.

Such an image display device is used for applications that particularly require a wide viewing angle in the horizontal direction and a reduction in area A luminance during black display (in particular, high definition is required, and a screen can be shared by multiple people. use). Typical image display devices include in-vehicle displays, medical monitors, and gaming monitors, with in-vehicle displays being particularly preferred.

Each member constituting the polarizing plate with the retardation layer and the image display device will be described below.

C. Polarizing plate C-1. Polarizer As the first polarizer 11 provided in the first polarizing plate 10 and the second polarizer 41 provided in the second polarizing plate 40 (hereinafter sometimes simply referred to as polarizers), any A suitable polarizer may be employed. For example, the resin film forming the polarizer may be a single-layer resin film or a laminate of two or more layers.

Specific examples of the polarizer composed 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. In addition, oriented polyene films such as those dyed with dichroic substances such as iodine and dichroic dyes and stretched, and dehydrated PVA and dehydrochlorinated polyvinyl chloride films. A polarizer obtained by dyeing a PVA-based film with iodine and uniaxially stretching the film is preferably used because of its excellent optical properties.

The dyeing with iodine is performed by, for example, immersing the PVA-based film in an aqueous iodine solution. The draw ratio of the uniaxial drawing is preferably 3 to 7 times. Stretching may be performed after the dyeing treatment, or may be performed while dyeing. Moreover, you may dye after extending|stretching. If necessary, the PVA-based film is subjected to swelling treatment, cross-linking treatment, washing treatment, drying treatment, and the like. For example, by immersing the PVA-based film in water and washing it with water before dyeing, not only can dirt and anti-blocking agents on the surface of the PVA-based film be washed away, but also the PVA-based film can be swollen to remove uneven dyeing. can be prevented.

Specific examples of the polarizer obtained using a laminate include a laminate of a resin substrate and a PVA-based resin layer (PVA-based resin film) laminated on the resin substrate, or a resin substrate and the resin A polarizer obtained by using a laminate with a PVA-based resin layer formed by coating on a substrate can be mentioned. A polarizer obtained by using a laminate of a resin base material and a PVA-based resin layer formed by coating on the resin base material is obtained, for example, by applying a PVA-based resin solution to the resin base material and drying the resin base material. forming a PVA-based resin layer thereon to obtain a laminate of a resin substrate and a PVA-based resin layer; stretching and dyeing the laminate to use the PVA-based resin layer as a polarizer; obtain. In this embodiment, stretching typically includes immersing the laminate in an aqueous boric acid solution and stretching. Furthermore, stretching may further include stretching the laminate in air at a high temperature (eg, 95° C. or higher) before stretching in an aqueous boric acid solution, if necessary. The obtained resin substrate/polarizer laminate 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 resin substrate/polarizer laminate. Then, any appropriate protective layer may be laminated on the release surface according to the purpose. Details of the method for manufacturing such a polarizer are described in, for example, Japanese Patent Application Laid-Open No. 2012-73580 and Japanese Patent No. 6470455. These publications are incorporated herein by reference in their entirety.

The thickness of the polarizer is, for example, 1 μm to 80 μm, preferably 1 μm to 15 μm, more preferably 1 μm to 12 μm, even more preferably 3 μm to 12 μm, particularly preferably 3 μm to 8 μm. If the thickness of the polarizer is within such a range, it is possible to satisfactorily suppress curling during heating, and obtain excellent durability in appearance during heating.

The polarizer preferably exhibits absorption dichroism at any wavelength 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%, more preferably 44.5% to 46.0%. The degree of polarization of the polarizer is preferably 97.0% or higher, more preferably 99.0% or higher, still more preferably 99.9% or higher.

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 the protective layer 12 provided on the surface opposite to the viewing side of the first polarizer 11, and the second polarizing plate 40 is the second polarizer. A protective layer 42 is provided on the surface of the viewing side of 41 .

The protective layer is formed of any suitable film that can be used as a protective layer for polarizers. Specific examples of the material that is the main component of the film include cellulose-based resins such as triacetyl cellulose (TAC), polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, polyimide-based, polyethersulfone-based, and polysulfone-based resins. , polystyrene-based, polynorbornene-based, polyolefin-based, (meth)acrylic-based, and acetate-based transparent resins. Thermosetting resins such as (meth)acrylic, urethane, (meth)acrylic urethane, epoxy, and silicone, or ultraviolet curable resins may also be used. In addition, for example, a glassy polymer such as a siloxane-based polymer can also be used. Further, polymer films described in JP-A-2001-343529 (WO01/37007) can also be used. Materials for this film include, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in a side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and nitrile group in a side chain. can be used, for example, a resin composition comprising an alternating copolymer of isobutene and N-methylmaleimide and an acrylonitrile/styrene copolymer. The polymer film can be, for example, an extrudate of the resin composition.

When the polarizer arranged on the viewing side of the image display cell 60 is provided with a protective layer positioned on the outermost surface of the image display device, the protective layer may be subjected to hard coating treatment, antireflection treatment, sticking, as necessary. Surface treatment such as anti-glare treatment and anti-glare treatment may be applied. Additionally/or, the protective layer 42 may optionally be treated to improve visibility when viewed through polarized sunglasses (typically, imparting (elliptically) polarizing function, ultra-high retardation ) may be applied. By performing such processing, excellent visibility can be achieved even when the display screen is viewed through polarized lenses such as polarized sunglasses.

The thickness of the protective layer is typically 5 mm or less, preferably 1 mm or less, more preferably 1 μm to 500 μm, still more preferably 5 μm to 150 μm. In addition, when the surface treatment is performed, the thickness of the protective layer is the thickness including the thickness of the surface treatment layer.

D. First Retardation Layer As described above, the first retardation layer 20 exhibits a refractive index characteristic of nx>ny≧nz. That is, the refractive index characteristics of the first retardation layer 20 may be nx>ny=nz or nx>ny>nz.
A layer (film) whose refractive index characteristics exhibit a relationship of nx>ny=nz is sometimes called a “positive uniaxial plate”, a “positive A plate”, or the like. Here, "ny=nz" includes not only the case where ny and nz are strictly equal, but also the case where ny and nz are substantially equal. Specifically, it means that the Nz coefficient is more than 0.9 and less than 1.1.
A layer (film) whose refractive index characteristics exhibit a relationship of nx>ny>nz is sometimes called a “negative biaxial plate”, a “negative B plate”, or the like.

D-1. First Retardation Layer Exhibiting Refractive Index Characteristics nx>ny=nz As a material for forming the first retardation layer exhibiting refraction index characteristics nx>ny=nz, the above characteristics Any suitable material can be employed as long as it provides Specifically, the first retardation layer may be an alignment fixed layer of a liquid crystal compound (liquid crystal alignment fixed layer) or a retardation film (stretched polymer film).

When the first retardation layer is a liquid crystal alignment fixed layer, by using a liquid crystal compound, the difference between nx and ny of the obtained retardation layer can be remarkably increased compared to a non-liquid crystal material. The thickness of the retardation layer for obtaining the desired in-plane retardation can be significantly reduced. As a result, the polarizing plate with a retardation layer (as a result, the image display device) can be made thinner. As used herein, the term "fixed alignment layer" refers to a layer in which a liquid crystal compound is aligned in a predetermined direction and the alignment state is fixed. In addition, the "alignment fixed layer" is a concept including an alignment cured layer obtained by curing a liquid crystal monomer as described later. In the present embodiment, typically, rod-like liquid crystal compounds are aligned in the slow axis direction of the first retardation layer (homogeneous alignment).

Examples of liquid crystal compounds include liquid crystal compounds whose liquid crystal phase is a nematic phase (nematic liquid crystal). As such a liquid crystal compound, for example, a liquid crystal polymer or a liquid crystal monomer can be used. Either lyotropic or thermotropic mechanism may be used to develop the liquid crystallinity of the liquid crystal compound. The liquid crystal polymer and liquid crystal monomer may be used alone or in combination.

When the liquid crystal compound is a liquid crystalline monomer, it is preferably a polymerizable monomer and/or a crosslinkable monomer, for example. This is because the alignment state of the liquid crystalline monomer can be fixed by polymerizing or cross-linking the liquid crystalline monomer. After aligning the liquid crystalline monomers, for example, the alignment state can be fixed by polymerizing or cross-linking the liquid crystalline monomers. Here, a polymer is formed by polymerization and a three-dimensional network structure is formed by cross-linking, but these are non-liquid crystalline. Therefore, the formed first retardation layer does not undergo a transition to a liquid crystal phase, a glass phase, or a crystal phase due to a change in temperature, which is peculiar to liquid crystalline compounds. As a result, the formed first retardation layer becomes a retardation layer with extremely excellent stability that is not affected by temperature changes.

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

The first retardation layer may be a stretched polymer film as described above. Specifically, the desired optical properties (e.g., refraction index characteristics, in-plane retardation, thickness direction retardation) can be obtained. In particular, the Re(550) of the first retardation layer can be adjusted within the range described above by adjusting the thickness (original thickness) of the polymer film, the stretching temperature and the stretching ratio.
The thickness of the polymer film (original thickness) is typically 10 μm or more, preferably 15 μm or more, and typically 50 μm or less, preferably 40 μm or less, more preferably 30 μm or less.
The stretching temperature is preferably 110°C to 170°C, more preferably 130°C to 150°C. The draw ratio is preferably 1.05 to 2.00 times, more preferably 1.10 to 1.50 times.

Any appropriate resin can be adopted as the resin that forms the polymer film. Specific examples include resins that constitute positive birefringent films, such as norbornene-based resins, polycarbonate-based resins, cellulose-based resins, polyvinyl alcohol-based resins, and polysulfone-based resins.
When the refractive index characteristics of the first retardation layer show the relationship of nx>ny=nz, preferable resins for forming the polymer film include norbornene-based resins and polycarbonate-based resins.

The norbornene-based resin is a resin that is polymerized using a norbornene-based monomer as a polymerization unit. The norbornene-based monomers include, for example, norbornene and its alkyl and/or alkylidene-substituted products such as 5-methyl-2-norbornene, 5-dimethyl-2-norbornene, 5-ethyl-2-norbornene, 5-butyl -2-norbornene, 5-ethylidene-2-norbornene and the like, polar group-substituted products thereof such as halogen; dicyclopentadiene, 2,3-dihydrodicyclopentadiene and the like; dimethanooctahydronaphthalene, its alkyl and/or alkylidene substituents, and polar group substituents such as halogen, for example, 6-methyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6- ethyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-ethylidene-1,4:5,8-dimethano-1,4, 4a,5,6,7,8,8a-octahydronaphthalene, 6-chloro-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-cyano-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-pyridyl-1,4:5,8-dimethano-1, 4,4a,5,6,7,8,8a-octahydronaphthalene, 6-methoxycarbonyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octa hydronaphthalene, etc.; tri- to tetra-mers of cyclopentadiene, such as 4,9:5,8-dimethano-3a,4,4a,5,8,8a,9,9a-octahydro-1H-benzoindene, 4, 11:5,10:6,9-trimethano-3a,4,4a,5,5a,6,9,9a,10,10a,11,11a-dodecahydro-1H-cyclopentanthracene. The norbornene-based resin may be a copolymer of norbornene-based monomers and other monomers.

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

The first retardation layer is preferably a stretched polymer film, more preferably a stretched norbornene-based resin film.
The thickness of the first retardation layer whose refractive index characteristics exhibit a relationship of nx>ny=nz can be set so as to obtain desired optical characteristics. When the first retardation layer is a liquid crystal alignment fixed 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 first retardation layer is a stretched polymer film, the thickness is preferably 5 μm to 55 μm, more preferably 10 μm to 50 μm, still more preferably 15 μm to 45 μm.

D-2. First Retardation Layer Showing Refractive Index Characteristics nx>ny>nz The first retardation layer showing refractive index characteristics nx>ny>nz is typically obtained by stretching It's a film. Such a stretched polymer film is prepared by stretching the polymer film at the stretching temperature and stretching ratio described in the above section D-1. The thickness of the polymer film (original fabric thickness) is typically 30 μm or more, preferably 45 μm or more, more preferably 80 μm or more, and is typically 300 μm or less, preferably 200 μm or less, more preferably 120 μm or less. be. Examples of stretching methods include lateral uniaxial stretching, fixed-end biaxial stretching, and sequential biaxial stretching.

Examples of the resin for forming the polymer film include the same resins as those described in the above item D-1. When the refractive index characteristics of the first retardation layer show the relationship of nx>ny>nz, preferable resins for forming the polymer film include norbornene-based resins and cellulose-based resins. The norbornene-based resin is as described in section D-1 above.

The cellulose resin is preferably a cellulose organic acid ester or a cellulose mixed organic acid ester in which some or all of the hydroxyl groups of cellulose are substituted with acetyl groups, propionyl groups and/or butyl groups. Examples of the cellulose organic acid ester include cellulose acetate, cellulose propionate, and cellulose butyrate. Examples of the cellulose mixed organic acid ester include cellulose acetate propionate and cellulose acetate butyrate. The cellulose resin can be obtained, for example, by the method described in [0040] to [0041] of JP-A-2001-188128. The degree of acetyl substitution of the cellulose acetate is preferably 2.0 to 3.0, more preferably 2.5 to 3.0. The degree of propionyl substitution of the cellulose propionate is preferably 2.0 to 3.0, more preferably 2.5 to 3.0. When the cellulose-based resin is a mixed organic acid ester in which some hydroxyl groups of cellulose are substituted with acetyl groups and some are substituted with propionyl groups, the sum of the degree of acetyl substitution and the degree of propionyl substitution is preferably 2. 0 to 3.0, more preferably 2.5 to 3.0. In this case, the degree of acetyl substitution is preferably between 0.1 and 2.9 and the degree of propionyl substitution is preferably between 0.1 and 2.9.

The thickness of the first retardation layer whose refractive index characteristics exhibit a relationship of nx>ny>nz can be set so as to obtain desired optical characteristics. The thickness of the first retardation layer is preferably 10 μm to 100 μm, more preferably 20 μm to 90 μm, still more preferably 60 μm to 80 μm.

E. Second Retardation Layer As described above, the second retardation layer 30 exhibits a refractive index characteristic of nz≧nx>ny. That is, the refractive index characteristics of the second retardation layer 30 may satisfy nz>nx>ny or nz=nx>ny.
A layer (film) whose refractive index characteristics exhibit a relationship of nz>nx>ny is sometimes called a “positive biaxial plate”, a “positive B plate”, or the like.
A layer (film) whose refractive index characteristics exhibit a relationship of nz=nx>ny is sometimes called a “negative uniaxial plate”, a “negative A plate”, or the like. Here, "nz=nx" includes not only the case where nz and nx are strictly equal, but also the case where nz and nx are substantially equal. Specifically, it means that the Nz coefficient exceeds -0.1 and is less than 0.1.

The thickness of the second retardation layer is preferably 1 μm to 170 μm, more preferably 2 μm to 150 μm, even more preferably 3 μm to 120 μm, particularly preferably 2 μm to 40 μm. When the thickness of the second retardation layer is within such a range, it is possible to improve the optical uniformity of the obtained image display device while being excellent in handleability during production.

E-1. Second Retardation Layer Exhibiting Refractive Index Characteristics of nz>nx>ny The second retardation layer of which refractive index characteristics exhibit the relationship of nz>nx>ny may have any appropriate configuration. Specifically, it may be a single retardation film, or a laminate of two or more same or different retardation films. In the case of a laminate, the second retardation layer may include a pressure-sensitive adhesive layer or an adhesive layer for adhering two or more retardation films. Preferably, the second retardation layer is a single retardation film. By adopting such a configuration, it is possible to reduce deviation and unevenness in the retardation value due to the contraction stress of the polarizer and/or the heat of the light source, and it is possible to contribute to the thinning of the obtained image display device.

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

As the retardation film, a film that is excellent in transparency, mechanical strength, thermal stability, moisture shielding property, etc., and hardly causes optical unevenness due to distortion is preferably used. As the retardation film, a stretched polymer film containing a thermoplastic resin as a main component is preferably used. A polymer exhibiting negative birefringence is preferably used as the thermoplastic resin. A retardation film having a refractive index ellipsoid satisfying nz>nx>ny can be easily obtained by using a polymer exhibiting negative birefringence. Here, the term "exhibiting negative birefringence" means that when a 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 is increased. Polymers exhibiting negative birefringence include, for example, polymers in which chemical bonds or functional groups with large polarization anisotropy such as aromatic rings and carbonyl groups are introduced into side chains. Specific examples include acrylic resins, styrene resins, and maleimide resins.

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

The styrenic resin can be obtained, for example, by addition polymerization of styrenic monomers. Styrenic monomers include, for example, styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, p-chlorostyrene, p-nitrostyrene, p-aminostyrene, p-carboxystyrene, p-phenylstyrene, 2,5-dichlorostyrene and pt-butylstyrene can be mentioned.

The maleimide-based resin can be obtained, for example, by addition polymerization of a maleimide-based monomer. Maleimide-based monomers include, for example, 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, N-(2-cyanophenyl)maleimide. A maleimide-based monomer can be obtained from Tokyo Kasei Kogyo Co., Ltd., for example.

In the above addition polymerization, the birefringence properties of the resulting resin can be controlled by substituting the side chains, maleimidation, grafting, or the like after the polymerization.

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

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

When the refractive index characteristics of the second retardation layer exhibit a relationship of nz>nx>ny, the polymer exhibiting negative birefringence is preferably a styrene-maleic anhydride copolymer or a styrene-acrylonitrile copolymer. Copolymers, styrene-(meth)acrylate copolymers, styrene-maleimide copolymers, vinyl ester-maleimide copolymers, olefin-maleimide copolymers, and the like are used. These can be used alone or in combination of two or more. These polymers can exhibit high negative birefringence and excellent heat resistance. These polymers are available from Nova Chemical Japan and Arakawa Chemical Industries, Ltd., for example.

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

In general formula (I) above, R ₁ to R ₅ each independently represent a hydrogen atom, a halogen atom, a carboxylic acid, a carboxylic acid ester, a hydroxyl group, a nitro group, or a linear or branched chain having 1 to 8 carbon atoms. represents an alkyl group or an alkoxy group (provided that R ₁ and R ₅ are not hydrogen atoms at the same time), and R ₆ and R ₇ are 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.

The polymer exhibiting negative birefringence is not limited to those described above, and for example, a cyclic olefin copolymer as disclosed in JP-A-2005-350544 can also be used. Furthermore, compositions containing polymers and inorganic fine particles, as disclosed in JP-A-2005-156862, JP-A-2005-227427, etc., can also be preferably used. As the polymer exhibiting negative birefringence, one type may be used alone, or two or more types may be mixed and used. Further, these can be modified by copolymerization, branching, cross-linking, molecular terminal modification (or capping), stereoregular modification, and the like.

The polymer film may further contain any appropriate additive as necessary. Specific examples of additives include plasticizers, heat stabilizers, light stabilizers, lubricants, antioxidants, ultraviolet absorbers, flame retardants, colorants, antistatic agents, compatibilizers, cross-linking agents, and thickeners. mentioned. 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 is excessively high, the transparency of the polymer film may be impaired, or the additive may exude from the surface of the polymer film.

Any appropriate molding method can be adopted as the method for molding the polymer film. Examples thereof include compression molding, transfer molding, injection molding, extrusion molding, blow molding, powder molding, FRP molding, and solvent casting. 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, in the extrusion molding method, the resin composition containing the above thermoplastic resin, plasticizer, additives, etc. is heated and melted, and this is extruded into a thin film on the surface of a casting roll using a T-die or the like, It is a method of forming a film by cooling. In the solvent casting method, a concentrated solution (dope) obtained by dissolving the resin composition in a solvent is degassed, and cast uniformly in a thin film on the surface of a metal endless belt or rotating drum, or a plastic substrate. , a method of forming a film by evaporating a solvent. The molding conditions can be appropriately set according to the composition and type of resin to be used, the molding method, and the like.

The retardation film (stretched film) can be obtained by stretching the polymer film under any appropriate stretching conditions.
Specific examples of the stretching method include a vertical uniaxial stretching method, a horizontal uniaxial stretching method, a vertical and horizontal successive biaxial stretching method, and a vertical and horizontal simultaneous biaxial stretching method. Preferably, a horizontal uniaxial stretching method, a vertical and horizontal successive biaxial stretching method, and a vertical and horizontal simultaneous biaxial stretching method are used. This is because a biaxial retardation film can be suitably obtained. In the polymer exhibiting negative birefringence, as described above, the refractive index in the stretching direction is relatively small. The refractive index in the transport direction is nx). In the case of the longitudinal and transverse sequential biaxial stretching method and the longitudinal and transverse simultaneous biaxial stretching method, both the transport direction and the width direction can be the slow axes depending on the ratio of longitudinal and transverse stretching ratios. Specifically, when the draw ratio in the longitudinal (conveyance) direction is relatively increased, the horizontal (width) direction becomes the slow axis, and when the draw ratio in the transverse (width) direction is relatively increased, the longitudinal (conveyance) The direction is the slow axis.
Any appropriate stretching device can be used as the stretching device used for the stretching. Specific examples include a roll stretching machine, a tenter stretching machine, and a pantograph type or linear motor type biaxial stretching machine. When stretching is performed while heating, the temperature may be changed continuously or stepwise. Moreover, you may divide|segment the extending|stretching process into 2 times or more.

Also in the preparation of such a second retardation layer, Re (550) of the second retardation layer is adjusted by adjusting the thickness of the polymer film (original film thickness), the stretching temperature and the stretching ratio. It can be adjusted within the above range.
The thickness of the polymer film (original thickness) is typically 3 μm or more, preferably 5 μm or more, and typically 70 μm or less, preferably 60 μm or less, more preferably 50 μm or less.

The stretching temperature (the temperature in the stretching oven when stretching the polymer film) is preferably around the glass transition temperature (Tg) of the polymer film. Specifically, it is preferably (Tg-10)°C to (Tg+30)°C, more preferably Tg to (Tg+25)°C, and particularly preferably (Tg+5)°C to (Tg+20)°C. If the stretching temperature is too low, the retardation value and the direction of the slow axis may become non-uniform, and the polymer film may crystallize (white turbidity). On the other hand, if the stretching temperature is excessively high, the polymer film may be melted or the retardation may be insufficiently developed. The stretching temperature is typically 110-200°C. The glass transition temperature can be determined by the DSC method according to JISK7121-1987.

Any appropriate method can be adopted for controlling the temperature in the stretching oven. Examples thereof include a method using an air circulation type constant temperature oven in which hot air or cold air circulates, a heater using microwaves or far infrared rays, a roll heated for temperature control, a heat pipe roll, a metal belt, or the like.

The stretching ratio for stretching the polymer film is set to any appropriate value depending on the composition of the polymer film, the type of volatile components, the amount of residual volatile components, etc., and the desired retardation value. can be It is preferably 1.05 to 5.00 times. Further, the feeding speed during stretching is preferably 0.5 m/min to 20 m/min from the viewpoint of mechanical accuracy of the stretching apparatus, stability and the like.

A method for obtaining a retardation film using a polymer exhibiting negative birefringence has been described above, but the retardation film can also be obtained using a polymer exhibiting positive birefringence. Methods for obtaining a retardation film using a polymer exhibiting positive birefringence include, for example, JP-A-2000-231016, JP-A-2000-206328, and JP-A-2002-207123. In addition, a drawing method that increases the refractive index in the thickness direction can be used. Specifically, there is a method of adhering a heat-shrinkable film to one side or both sides of a film containing a polymer exhibiting positive birefringence, followed by heat treatment. The film is shrunk under the action of the shrinkage force of the heat-shrinkable film due to heat treatment to shrink the film in the length and width directions, thereby increasing the refractive index in the thickness direction, where nz>nx. A retardation film having an index ellipsoid of >ny can be obtained.

Thus, the positive B plate used for the second retardation layer can be manufactured using a polymer exhibiting either positive or negative birefringence. In general, when using a polymer exhibiting positive birefringence, there is an advantage in that there are many types of polymers that can be selected. is advantageous in that a retardation film having excellent uniformity in the slow axis direction can be easily obtained due to the stretching method.

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

The light transmittance of the retardation film at a wavelength of 550 nm is preferably 80% or higher, more preferably 85% or higher, particularly preferably 90% or higher. The theoretical upper limit of light transmittance is 100%, but surface reflection occurs due to the difference in refractive index between air and the retardation film, so the achievable upper limit of light transmittance is approximately 94%. . It is preferable that the first retardation layer as a whole also have the same light transmittance.

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

E-2. Second Retardation Layer Exhibiting Refractive Index Characteristic Relationship of nz=nx>ny The second retardation layer having refractive index ellipsoid exhibiting the relationship of nz=nx>ny may have any appropriate configuration. The second retardation layer is typically a stretched polymer film containing a polymer exhibiting negative birefringence as a main component. The polymer exhibiting negative birefringence is as described in section E-1 above.
Such a second retardation layer is, for example, a polymer film containing a polymer exhibiting negative birefringence as a main component, under the stretching conditions described in E-1 above (e.g., original film thickness, stretching temperature , stretch ratio). More specifically, the polymer film is heated and stretched by a longitudinal uniaxial stretching method using a roll stretching machine. A shrinkable film may be pasted on both sides of the polymer film before stretching. A shrinkable film is used to impart shrinkage force in a direction perpendicular to the stretching direction during heating and stretching to increase the refractive index (nz) in the thickness direction. Details of the method for forming the stretched film constituting the second retardation layer of the present embodiment are described in JP-A-2007-193365. The description of the publication is incorporated herein by reference. The second retardation layer can also be produced by continuously obliquely stretching the long resin film in a direction at a predetermined angle with respect to the longitudinal direction. In this case, it is preferably produced by laminating a resin film obtained by laminating the shrinkable film on a support substrate, diagonally stretching this laminate, and transferring the diagonally stretched resin film to another layer. be.

F. Laminate of first retardation layer and second retardation layer The laminate of the first retardation layer and 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, still more preferably 0.9 to 1.0. According to the embodiment of the present invention, although the first retardation layer and the second retardation layer as a whole do not exhibit ideal reverse dispersion characteristics, the luminance in the oblique direction during black display is small, Moreover, it is possible to obtain a polarizing plate with a retardation layer that can realize an image display device with a small color shift in an oblique direction.

G. Liquid Crystal Cell The liquid crystal cell 60a has a first substrate 62, a second substrate 63, and a liquid crystal layer 61 sandwiched between them containing liquid crystal molecules aligned in a homogeneous alignment in the absence of an electric field. In a general configuration, one substrate (typically, the first substrate 62) is provided with a color filter and a black matrix, and the other substrate (typically, the second substrate 63) is provided with A switching element for controlling the electro-optical characteristics of the liquid crystal, a signal line for applying a gate signal and a source signal to the switching element, a pixel electrode and a counter electrode are provided. The spacing (cell gap) between the substrates is controlled by a spacer or the like. An alignment film made of polyimide, for example, can be provided on the side of the substrate that is in contact with the liquid crystal layer.

Rth(550) of the first substrate 62 and the second substrate 63 is -10 nm to 100 nm, respectively. In one embodiment, 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, 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 retardation in the thickness direction, the black luminance in the oblique direction can be sufficiently reduced in the liquid crystal display device including the homogeneously aligned liquid crystal cell.

In one embodiment, at least one of the first substrate 62 and the second substrate 63 satisfies the relationship Rth(450)>Rth(550), preferably both the first substrate 62 and the second substrate 63 are It satisfies the relationship Rth(450)>Rth(550). More preferably, at least one of first substrate 62 and second substrate 63 further satisfies the relationship Rth(550)>Rth(650), and even more preferably both first substrate 62 and second substrate 63 have Rth It further satisfies the relationship of (550)>Rth(650). According to the embodiment of the present invention, even when the substrate has such a wavelength dispersion characteristic, it is possible to sufficiently reduce the black luminance in the oblique direction in a liquid crystal display device including a homogeneously aligned liquid crystal cell.

The liquid crystal layer 61 contains liquid crystal molecules aligned in a homogeneous alignment in the absence of an electric field, as described above. "Liquid crystal molecules oriented in a homogeneous alignment" means a state in which the alignment vectors of the above liquid crystal molecules are oriented parallel and uniformly with respect to the plane of the substrate as a result of the interaction between the liquid crystal molecules and the substrate that has undergone alignment treatment. Say. Such a liquid crystal layer (resulting in 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 completely 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, between 300 nm and 400 nm. The Nz coefficient of the liquid crystal layer can be, for example, 0.9-1.1.

In one embodiment, the liquid crystal molecules of 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°, more preferably 0.2° to 0.7°.

Driving modes of such a liquid crystal cell 60a include, for example, an in-plane switching (IPS) mode and a fringe field switching (FFS) mode. The IPS mode includes a super-in-plane switching (S-IPS) mode and an advanced super-in-plane switching (AS-IPS) mode employing V-shaped electrodes or zigzag electrodes. The FFS mode includes an advanced fringe field switching (A-FFS) mode and an ultra fringe field switching (U-FFS) mode employing V-shaped electrodes or zigzag electrodes. The driving mode of the liquid crystal cell 60a is preferably an in-plane switching (IPS) mode.
When the drive mode of the liquid crystal cell 60a is the IPS mode, it is possible to improve the visibility of the liquid crystal display device in oblique directions.

H. Backlight Unit The light source 91 is arranged at a position corresponding to the side surface of the light guide plate 92 . As the light source, for example, an LED light source configured by arranging a plurality of LEDs can be used. Any appropriate light guide plate can be used as the light guide plate 92 . For example, a light guide plate in which a lens pattern is formed on the back side and a light guide plate in which a prism shape or the like is formed on the back side and/or the viewing side is used so that light from the lateral direction can be deflected in the thickness direction. . Preferably, a light guide plate having a prism shape formed on the rear surface side and the viewing side is used. In the light guide plate, it is preferable that the prism shape formed on the rear surface side and the prism shape formed on the viewing side are perpendicular to each other. By using such a light guide plate, it is possible to make light that is more easily condensed enter the prism sheet (not shown).

EXAMPLES The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these Examples. The measurement method of each characteristic is as follows.

(1) Measurement of retardation value The in-plane retardation of the first retardation layer and the second retardation layer used in Examples and Comparative Examples was automatically measured using KOBRA-WPR manufactured by Oji Scientific Instruments. 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 Examples and Comparative Examples, and the luminance was measured with a luminance meter (manufactured by AUTONIC-MELCHERS, trade name "Conoscope"). Specifically, the luminance was measured by changing the polar angle from 0° to 80° and the azimuth angle from 0° to 360°.
Further, among the luminance measured as described above, the polar angle is 40° and the azimuth angle is any of 20°, 25°, 155°, 160°, 190°, 195°, 345° and 350°. The luminance at that time was defined as the area A luminance (unit: cd/m ² ), and the maximum luminance among them was defined as the area A maximum luminance (unit: cd/m ² ).

<Preparation of polarizing plate>
<<Production Example 1>>
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 corona treatment.
Polyvinyl alcohol (degree of polymerization: 4,200, degree of saponification: 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOSEFIMER") were mixed at a ratio of 9:1, and 100 parts by weight of PVA-based resin. was added with 13 parts by weight of potassium iodide and dissolved in water to prepare an aqueous PVA solution (coating solution).
The above PVA aqueous solution was applied to the corona-treated surface of the resin base material and dried at 60° C. to form a PVA-based resin layer having 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. (in-air auxiliary stretching treatment).
Next, the laminate was immersed in an insolubilizing bath (an aqueous boric acid 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).
Then, the finally obtained polarizer is added to a dyeing bath (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) at a liquid temperature of 30 ° C. It was immersed for 60 seconds while adjusting the concentration so that the single transmittance (Ts) was a desired value (dyeing treatment).
Next, it was immersed for 30 seconds in a cross-linking bath at a liquid temperature of 40°C (an aqueous solution of boric acid 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).
After that, while immersing the laminate in an aqueous solution of boric acid (boric acid concentration: 4% by weight, potassium iodide concentration: 5% by weight) at a liquid temperature of 70° C., the laminate was moved vertically (longitudinally) between rolls with different peripheral speeds. Uniaxial stretching was performed so that the stretching ratio was 5.5 times (underwater stretching treatment).
After that, the laminate was immersed in a washing bath (aqueous solution obtained by blending 4 parts by weight of potassium iodide with 100 parts by weight of water) at a liquid temperature of 20° C. (washing treatment).
Thereafter, while drying in an oven maintained at about 90° C., it was brought into contact with a heating roll made of SUS whose surface temperature was maintained at about 75° C. (dry shrinkage treatment).
In this way, a polarizer having a thickness of about 5 μm was formed on the resin substrate to obtain a laminate having a structure of resin substrate/polarizer.
An HC-TAC film (thickness: 20 μm) was attached as a protective layer to the polarizer surface (the surface opposite to the resin substrate) of the obtained laminate. Then, the resin substrate was peeled off to obtain a polarizing plate having a structure of protective layer/polarizer/. After that, the obtained polarizing plate was punched into a size corresponding to a liquid crystal cell described later.

<Preparation of Retardation Film (Positive A Plate) with Refractive Index Characteristics nx>ny=nz>
<<Production Example 2>>
By uniaxially stretching a long norbornene-based resin film (manufactured by Nippon Zeon Co., Ltd., trade name Zeonor, thickness 40 μm, photoelastic coefficient 3.10×10 ⁻¹² m ² /N) at 135° C. to 1.2 times, A retardation film having a thickness of 37 μm was produced. After that, the obtained retardation film was punched into a size corresponding to a liquid crystal cell described later.
The thus-obtained retardation film had a slow axis in the transport direction and had a refractive index characteristic of nx>ny=nz. Table 1 shows the in-plane retardation Re (550), the thickness direction retardation Rth (550) and the Nz coefficient of the retardation film (positive A plate).
<<Production Example 3>>
A retardation film (positive A plate) was obtained in the same manner as in Production Example 2, except that the draw ratio was changed to 1.3 times.
<<Production Example 4>>
A retardation film (positive A plate) was obtained in the same manner as in Production Example 2, except that the draw ratio was changed to 1.8 times.

<Preparation of Retardation Film (Negative A Plate) with Refractive Index Characteristics nz=nx>ny>
<<Production Example 5>>
Styrene-maleic anhydride copolymer (manufactured by Nova Chemical Japan, trade name "Dylark D232") pellet-shaped resin is extruded at 270 ° C. using a single-screw extruder and a T-die to form a sheet-shaped molten resin. was cooled with a cooling drum to obtain a film having a thickness of 50 μm. This film is uniaxially stretched in the transport direction at a temperature of 130° C. and a stretch ratio of 1.4 times using a roll stretching machine to obtain a retardation film (negative A plate) having a fast axis in the transport direction. Obtained. After that, the obtained retardation film was punched into a size corresponding to a liquid crystal cell described later.
The retardation film thus obtained exhibited a relationship of nz=nx>ny in terms of refractive index characteristics. Table 1 shows the in-plane retardation Re (550) and the thickness direction retardation Rth (550) of the retardation film (negative A plate).
<<Production Example 6>>
A retardation film (negative A plate) was obtained in the same manner as in Production Example 5, except that the draw ratio was changed to 1.5 times.

<Preparation of Retardation Film (Negative B Plate) with Refractive Index Properties of nx>ny>nz>
<<Production Example 7>>
A retardation film (negative 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 and the film was laterally stretched at a stretching ratio of 1.5 times. The thus-obtained retardation film exhibited a relationship of nx>ny>nz in terms of refractive index characteristics. Table 1 shows the in-plane retardation Re (550), the thickness direction retardation Rth (550) and the Nz coefficient of the retardation film (negative B plate).
<<Production Example 8>>
A retardation film (negative B plate) was obtained in the same manner as in Production Example 7, except that the thickness of the film before stretching was changed to 40 μm and the stretching ratio was changed to 1.35 times.
<<Production Example 9>>
A retardation film (negative B plate) was obtained in the same manner as in Production Example 7, except that the thickness of the film before stretching was changed to 40 μm and the stretching ratio was changed to 1.3 times.
<<Production Example 10>>
A retardation film (negative B plate) was obtained in the same manner as in Production Example 7, except that the thickness of the film before stretching was changed to 55 μm and the stretching ratio was changed to 1.35 times.

<Preparation of Retardation Film (Positive B Plate) with Refractive Index Properties of nz>nx>ny>
<<Production Example 11>>
Styrene-maleic anhydride copolymer (manufactured by Nova Chemical Japan, trade name "Dylark D232") pellet-shaped resin is extruded at 270 ° C. using a single-screw extruder and a T-die to form a sheet-shaped molten resin. was cooled with a cooling drum to obtain a film having a thickness of 50 µm. This film was uniaxially stretched in the transport direction at a temperature of 130° C. and a draw ratio of 1.2 times using a roll stretching machine to obtain a film having a fast axis in the transport direction (longitudinal stretching step). .
The obtained film was fixed-end uniaxially stretched in the width direction using a tenter stretching machine at a temperature of 135 ° C. so that the film width was 1.7 times the film width after the longitudinal stretching, and the thickness was 26 μm. A retardation film (biaxially stretched film, positive B plate) was obtained (transverse stretching step). After that, the obtained retardation film was punched into a size corresponding to a liquid crystal cell described later.
The retardation film (positive B plate) obtained in this way has a fast axis in the transport direction (slow axis in the width direction), and has a refractive index characteristic of nz>nx>ny. . Table 1 shows the in-plane retardation Re (550), the thickness direction retardation Rth (550) and the Nz coefficient of the retardation film (positive B plate).
<<Production Example 12>>
A retardation film (positive B plate) was obtained in the same manner as in Production Example 11, except that the transverse stretching ratio was changed to 6.1 times without performing the longitudinal stretching step.
<<Production Example 13>>
A retardation film (positive B plate) was obtained in the same manner as in Production Example 11, except that the longitudinal draw ratio was changed to 1.5 times and the transverse draw ratio was changed to 1.5 times.
<<Production Example 14>>
A retardation film (positive B plate) was obtained in the same manner as in Production Example 11, except that the longitudinal draw ratio was changed to 1.9 times and the transverse draw ratio was changed to 1.8 times.

<Preparation of Retardation Film (Positive C Plate) with Refractive Index Characteristics of nz>nx=ny>
<<Production Example 15>>
A retardation film (positive C plate) was obtained in the same manner as in Production Example 6 of Japanese Patent No. 6896118, except that the retardation Rth in the thickness direction was changed to -98 nm. After that, the obtained retardation film was punched into a size corresponding to a liquid crystal cell described later.
The retardation film thus obtained had a slow axis in the transport direction and exhibited a refractive index characteristic of nz>nx=ny. Table 1 shows the in-plane retardation Re (550) and the thickness direction retardation Rth (550) of the retardation film (positive C plate).

<Preparation of image display cell (liquid crystal cell)>
<<Production Example 16>>
A liquid crystal cell was taken out from an IPS mode liquid crystal display device (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 surfaces to be removed (the outer surface of the substrate) were washed. This was used as an image display cell (liquid crystal cell). The first substrate of the liquid crystal cell has Rth(450)=32 nm, Rth(550)=19 nm, Rth(650)=23 nm; the second substrate has Rth(450)=9 nm, Rth(550)=0. 3 nm and Rth(650)=-6 nm.

[Example 1]
The polarizing plate of Production Example 1 (second polarizing plate containing a second polarizer) was laminated on the viewing side of the liquid crystal cell of Production Example 16. On the other hand, on the back side of the liquid crystal cell, the retardation film of Production Example 5 (second retardation layer), the retardation film of Production Example 2 (first retardation layer), and the polarizing plate of Production Example 1 ( A first polarizing plate containing a first polarizer) was laminated in this order. In the lamination, the absorption axis direction of the first polarizer and the slow axis direction of the first retardation layer are substantially perpendicular to each other, and the absorption axis direction of the first polarizer and the slow axis direction of the second retardation layer are substantially perpendicular to each other. the phase axis direction is substantially orthogonal, the absorption axis direction of the first polarizer and the initial alignment direction of the liquid crystal cell are substantially orthogonal, and the absorption axis direction of the second polarizer and the initial alignment direction of the liquid crystal cell are substantially orthogonal direction was substantially orthogonal to the Thus, an image display device (E-mode liquid crystal display device) was produced. Next, the image display device was subjected to the luminance measurement during black display as described above. FIG. 3 shows a luminance distribution diagram in the image display device of Example 1. As shown in FIG. Table 1 shows the area A maximum luminance in the image display device of Example 1.

[Examples 2 and 3 and Comparative Examples 1 to 5]
Except for changing each of the retardation film (second retardation layer) of Production Example 5 and the retardation film (first retardation layer) of Production Example 2 to the retardation film of Production Example shown in Table 1 prepared an image display device (E-mode liquid crystal display device) in the same manner as in Example 1. Next, the image display device was subjected to the luminance measurement during black display as described above. FIG. 4 shows a luminance distribution diagram in the image display device of Comparative Example 1. As shown in FIG. Table 1 shows the area A maximum luminance in the image display devices of Examples 2 and 3 and Comparative Examples 1 to 5.

[evaluation]
As is clear from Table 1, FIGS. 3 and 4, Re (550) and Nz coefficient of the first retardation layer are within the above ranges, and Re (550) of the second retardation layer is within the above ranges. As a result, the viewing angle in the horizontal direction (horizontal direction X on the paper surface in FIGS. 3 and 4) can be secured wider than the viewing angle in the vertical direction (vertical direction Y on the paper surface in FIGS. 3 and 4), and the above-described An image display device (liquid crystal display device) in which the area A maximum luminance is sufficiently small can be realized.

A polarizing plate with a retardation layer according to an embodiment of the present invention can be suitably applied to an image display device, and particularly suitably applied to a liquid crystal display device.

REFERENCE SIGNS LIST 10 first polarizing plate 11 first polarizer 20 first retardation layer 30 second retardation layer 40 second polarizing plate 60 image display cell 60a liquid crystal cell 100 polarizing plate with retardation layer 101 image display device

Claims (4)

a first polarizing plate including a first polarizer;
a first retardation layer having a refractive index characteristic exhibiting a relationship of nx>ny≧nz, disposed adjacent to the first polarizing plate;
a second retardation layer arranged adjacent to the first retardation layer and having a refractive index characteristic exhibiting a relationship of nz≧nx>ny;
The absorption axis of the first polarizer and the slow axis of the first retardation layer are substantially orthogonal,
The absorption axis of the first polarizer and the slow axis of the second retardation layer are substantially orthogonal,
The in-plane retardation Re (550) of the first retardation layer is 35 nm or more and 115 nm or less,
The in-plane retardation Re(550) of the second retardation layer is 30 nm or more and 135 nm or less.
A polarizing plate with a retardation layer. an image display cell;
and the polarizing plate with a retardation layer according to claim 1, which is arranged on the opposite side of the image display cell from the viewing side. The image display cell is a liquid crystal cell,
3. The image display device according to claim 2, wherein the driving mode of said liquid crystal cell is IPS mode. The image display device comprises a second polarizing plate disposed on the opposite side of the image display cell from the polarizing plate with the retardation layer,
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 orthogonal,
4. The image display device according to claim 3, wherein the absorption axis of said second polarizer and the initial alignment direction of said liquid crystal cell are substantially perpendicular to each other.

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