KR20230048606A - Polarizing plate with retardation layer, and image display device - Google Patents

Abstract

The present invention provides a polarizing plate with a retardation layer attached which can realize an image display device capable of achieving a wide viewing angle in a horizontal direction and sufficiently reducing black luminance in an oblique direction crossing both vertical and horizontal directions. The polarizing plate with a retardation layer attached according to an embodiment of the present invention comprises: a polarizing plate including a polarizer; a first retardation layer whose refractive index characteristics exhibit a relationship nz > nx > ny; and a second retardation layer whose refractive index characteristics exhibit a relationship nx > ny = nz. In addition, an absorption axis of the polarizer and a slow axis of the first retardation layer are substantially orthogonal, and the absorption axis of the polarizer and a slow axis of the second retardation layer are substantially parallel. Moreover, Re (550) of the first retardation layer is 280 nm or more and 360 nm or less and an Nz coefficient of the first retardation layer is -1.0 or more and -0.1 or less, and Re (550) of the second phase difference layer is 280 nm or more and 360 nm or less.

Description

Polarizing plate and image display device with retardation layer {POLARIZING PLATE WITH RETARDATION LAYER, AND IMAGE DISPLAY DEVICE}

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

BACKGROUND OF THE INVENTION [0002] In image display devices typified by liquid crystal display devices, various optical films in which a polarizer and a retardation film are combined are generally used in order to compensate for optical properties suitable for the application. For example, a polarizing plate including a polarizer, a first retardation layer having a refractive index characteristic of nz>nx>ny, and a second retardation layer having a refractive index characteristic of nx>ny=nz are combined with the absorption axis of the polarizer A technique for widening the viewing angle by combining the slow axis of the first retardation layer so that the slow axis of the first retardation layer is orthogonal and the absorption axis of the polarizer and the slow axis of the second retardation layer are parallel has been proposed (eg, see Patent Document 1).

By the way, in recent years, the use of an image display device is diversifying. An example of such a use is a vehicle-mounted display. In vehicle-mounted displays, a wide viewing angle in the horizontal direction (left-right direction) is particularly required. However, even if the technology described in Patent Literature 1 is applied to a vehicle-mounted display, there is a limit to the wide viewing angle in the horizontal direction, and furthermore, the black display of the vehicle-mounted display is applied in an oblique direction intersecting the vertical and horizontal directions (e.g. There is a problem that it does not become sufficiently black (i.e., the black luminance does not become sufficiently low) when viewed from above the diagonal line on the right.

Japanese Unexamined Patent Publication No. 2021-76759

The present invention has been made to solve the above conventional problems, and its main object is to achieve a wide viewing angle in the horizontal direction (a predetermined surface direction of the image display surface), and to intersect the vertical and horizontal directions. It is to provide a polarizing plate with a retardation layer capable of realizing an image display device capable of sufficiently reducing black luminance in an oblique direction.

A polarizing plate with a retardation layer according to an embodiment of the present invention includes: a first polarizing plate including a first polarizer; a first retardation layer having a refractive index characteristic of nz>nx>ny; A second retardation layer having a refractive index characteristic of nx>ny=nz is included. The first retardation layer is disposed adjacent to the first polarizing plate, and the second retardation layer is disposed adjacent to the first retardation layer. An absorption axis of the first polarizer and a slow axis of the first retardation layer are substantially orthogonal, and an absorption axis of the first polarizer and a slow axis of the second retardation layer are substantially parallel. The in-plane retardation Re (550) of the first retardation layer is 280 nm or more and 360 nm or less, and the Nz coefficient of the first retardation layer is -1.0 or more -0.1 or less. The in-plane retardation Re (550) of the second retardation layer is 280 nm or more and 360 nm or less.

An image display device according to another aspect of the present invention includes an image display cell; The polarizing plate with the retardation layer disposed on the side opposite to the viewing side with respect to the image display cell is provided.

In one embodiment, the image display cell is a liquid crystal cell, and the driving mode of the liquid crystal cell is an IPS mode.

In one embodiment, the image display device includes a second polarizing plate arranged on the opposite side of the image display cell to the polarizing plate with a retardation layer. The second polarizing plate includes a second polarizer. An absorption axis of the first polarizer and an initial alignment direction of the liquid crystal cell are substantially orthogonal, and an absorption axis of the second polarizer and an initial alignment direction of the liquid crystal cell are substantially parallel.

According to the embodiment of the present invention, a wide viewing angle can be achieved in the horizontal direction (predetermined plane direction of the image display surface) in the image display device, and the black luminance in the oblique direction crossing the vertical and horizontal directions can be sufficiently reduced. 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.
2 is a schematic cross-sectional view of an image display device according to one embodiment of the present invention.
Fig. 3 is a luminance distribution diagram of the image display device of Example 1 at the time of black display.
4 is a luminance distribution diagram of the image display device of Comparative Example 1 at the time of black display.

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

(Definition of Terms and Symbols)

Definitions of terms and symbols in this specification are as follows.

(1) Refractive index (nx, ny, nz)

'nx' is the refractive index in the direction in which the in-plane refractive index is maximized (ie, the slow axis direction), 'ny' is the refractive index in the direction orthogonal to the slow axis within the plane (ie, the fast axis direction), and 'nz' is is the refractive index in the thickness direction.

(2) In-plane retardation (Re) and face-to-face retardation (R ₀ )

'Re(λ)' is an in-plane retardation measured with light having a wavelength of λ nm at 23°C. For example, 'Re(550)' is an in-plane retardation measured with light having a wavelength of 550 nm at 23°C. In addition, 'in-plane retardation Re(550)' is sometimes referred to as 'front retardation (R ₀ )'. Re(λ) can be obtained by the formula: Re(λ)=(nx-ny)×d when the thickness of the layer (film) is set to d(nm).

(3) Phase difference in thickness direction (Rth)

'Rth(λ)' is the phase difference in the thickness direction measured with light having a wavelength of λ nm at 23°C. For example, 'Rth (550)' is the phase difference in the thickness direction measured with light having a wavelength of 550 nm at 23°C. Rth(λ) can be obtained by the formula: Rth(λ)=(nx-nz)×d when the thickness of the layer (film) is d (nm).

(4) Nz factor

The Nz coefficient can be obtained by Nz=Rth/Re.

(5) substantially parallel or orthogonal

The expressions 'substantially orthogonal' and 'approximately orthogonal' include the case where the angle formed by the two directions is 90°±10°, preferably 90°±7°, and more preferably 90°±5°. is ° The expressions 'substantially parallel' and 'approximately parallel' include the case where the angle formed by the two directions is 0°±10°, preferably 0°±7°, and more preferably 0°±5°. is ° In addition, when simply referring to 'orthogonal' or 'parallel' in this specification, a substantially orthogonal or substantially parallel state may be included.

A. Overall configuration of polarizing plate with retardation layer

1 is a schematic cross-sectional view of a polarizing plate with a retardation layer according to one embodiment of the present invention. The polarizing plate 100 with a retardation layer in the illustrated example includes a first polarizing plate 10 including a first polarizer 11; a first retardation layer 20 having a refractive index characteristic of nz>nx>ny; It includes the second retardation layer 30 whose refractive index characteristics show a relationship of nx>ny=nz.

The first retardation layer 20 is disposed adjacent to the first polarizing plate 10 . The second retardation layer 30 is disposed adjacent to the first retardation layer 20 . The second retardation layer 30 is located on the opposite side of the first polarizing plate 10 with respect to the first retardation layer 20 . In this specification, 'arranged adjacently' means that they are directly laminated or laminated with only an adhesive layer (eg, an adhesive layer or a pressure-sensitive adhesive layer) interposed therebetween. That is, an optical functional layer (eg, another retardation layer) 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 ) means that it does not intervene.

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 orthogonal. The absorption axis of the first polarizer 11 (in the direction of the first absorption axis) and the slow axis of the second retardation layer 30 (in the direction of the second slow axis) are substantially parallel.

The in-plane retardation Re (550) of the first retardation layer 20 is 280 nm or more and 360 nm or less, preferably 290 nm or more and 350 nm or less, more preferably 300 nm or more and 340 nm or less, still more preferably is 310 nm or more and 330 nm or less.

The Nz coefficient of the first retardation layer 20 is -1.0 or more -0.1 or less, preferably -0.9 or more -0.2 or less, more preferably -0.8 or more -0.3 or less, still more preferably -0.8 or more. -0.6 or less.

The in-plane retardation Re (550) of the second retardation layer 30 is 280 nm or more and 360 nm or less, preferably 290 nm or more and 350 nm or less, more preferably 300 nm or more and 340 nm or less, still more preferably is 310 nm or more and 330 nm or less.

If each of the Re (550) and Nz coefficients of the first retardation layer and the Re (550) of the second retardation layer satisfy the above ranges, in an image display device having a polarizing plate with a retardation layer, in the horizontal direction (image display A wide viewing angle can be achieved in a predetermined surface direction of the surface), and black luminance in an oblique direction crossing the vertical and horizontal directions can be sufficiently reduced. That is, in an image display device including a polarizing plate with a retardation layer, the viewing angle in the horizontal direction (eg, the first surface direction X of the image display device shown in FIG. 3) is set in the vertical direction (eg, the first surface direction shown in FIG. X) can be made wider than the viewing angle in the second surface direction (Y) orthogonal to, and the black display of the image display device can be displayed in the horizontal direction (first surface direction X) and in the vertical direction (second surface direction). The black luminance when viewed from an oblique direction intersecting both directions of the direction (Y) can be sufficiently reduced.

More specifically, black display of the image display device is measured by any suitable luminance meter at polar angles of 40° to 42° and azimuth angles of 20° to 25°, 155° to 160°, 190° to 195°, and 345°. The luminance measured in each range of ° to 350 ° is, for example, 0.00074 or less, preferably 0.00070 or less, and more preferably 0.00068 or less. In this specification, the luminance measured in the range of the polar angle and the azimuthal angle is referred to as area A luminance. The lower limit of the area A luminance is typically 0.00001 or more.

In one embodiment, the Nz coefficient of the second retardation layer 30 is, for example, 0.5 or more and 1.5 or less, preferably 0.6 or more and 1.4 or less, more preferably 0.7 or more and 1.3 or less, and still more preferably 0.8 or more. 1.2 or less. When the Nz coefficient of the second retardation layer is in such a range, wide viewing angles in the horizontal direction (predetermined surface direction of the image display surface) can be stably achieved in an image display device including a polarizing plate with a retardation layer, and Black luminance in an oblique direction intersecting both directions can be stably reduced.

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

The polarizing plate with a retardation layer may further contain other retardation layers. Other optical characteristics of the retardation layer (eg, refractive index characteristics, in-plane retardation, Nz coefficient, photoelastic coefficient), thickness, placement position, etc. may be appropriately set depending on the purpose.

The polarizing plate with the retardation layer may be in the form of a single sheet or a long picture. In the present specification, 'elongate' means an elongate shape in which the length is sufficiently long with respect to the width, and includes, for example, an elongate shape in which the length is 10 times or more, preferably 20 or more times the width. A long polarizing plate with a retardation layer can be wound in a roll shape.

Practically, an adhesive layer (not shown) is provided on the opposite side of the second retardation layer to the first polarizing plate, and the polarizing plate with the retardation layer can be attached to the image display cell. Further, it is preferable that a release liner is temporarily attached to the surface of the pressure-sensitive adhesive layer until the polarizing plate with the retardation layer is put into use. Roll formation becomes possible while protecting an adhesive layer by temporarily attaching a peeling liner.

B. Overall composition of the image display device

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; A polarizing plate 100 with a retardation layer disposed on the side opposite to the viewing side with respect to the image display cell 60 is provided. 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 disposed on the opposite side (view side) of the polarizing plate 100 with a phase difference layer to the image display cell 60 . The second polarizing plate 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. A liquid crystal display device is, typically, a so-called E mode. 'E-mode liquid crystal display device' refers to the absorption axis (first absorption axis direction) of a polarizer (in this embodiment, the first polarizer 11) disposed on the opposite side (rear side) of the viewing side of the liquid crystal cell , means that the initial orientation direction of the liquid crystal cell is substantially orthogonal. The term 'initial alignment direction of the liquid crystal cell' refers to the direction in which the in-plane refractive index of the liquid crystal layer formed as a result of alignment of the liquid crystal molecules included in the liquid crystal layer to be described later is maximized (ie, the slow axis direction) in the absence of an electric field. say

In one embodiment, the absorption axis (second absorption axis direction) of the polarizer (in this embodiment, the second polarizer 41) disposed on the viewing side of the liquid crystal cell and the initial orientation direction of the liquid crystal cell are substantially parallel 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 orthogonal. According to such a configuration, even when the display screen is viewed through a polarizing lens such as polarized sunglasses, excellent visibility can be realized.

In practical terms, 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 appropriate other member (eg, a diffusion sheet, a prism sheet). In the illustrated example, the backlight unit 90 is of an edge light type, but any suitable other type (for example, a direct type) may be employed as the backlight unit 90 .

The image display device (liquid crystal display device) may further include any appropriate other members. For example, another optical compensation layer (retardation layer) may be further disposed. The optical characteristics, number, combination, arrangement position, and the like of the different optical compensation layers can be appropriately selected depending on the purpose and desired optical characteristics and the like. For matters not described in this specification, a configuration of an image display device (liquid crystal display device) that is well known and commonly used in the art may be employed.

Such an image display device is suitable for applications in which wide viewing angles in the horizontal direction and reduction of area A luminance during black display are particularly required (in particular, applications in which high image quality is required and a screen can be shared by a plurality of people). are used appropriately Examples of the image display device include a vehicle-mounted display, a medical monitor, and a gaming monitor as typical examples, and a vehicle-mounted display is particularly preferred.

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

C. Polarizer

C-1. polarizer

As the first polarizer 11 included in the first polarizing plate 10 and the second polarizer 41 included in the second polarizing plate 40 (hereinafter, collectively referred to simply as polarizers), any 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.

As a specific example of a polarizer composed of a single-layer resin film, iodine or dichroic (two Color property: Polyene oriented films, such as what was dyed and stretched with a dichroic substance, such as dye, and the dehydration process of PVA, and the dehydrochlorination process of polyvinyl chloride, etc. are mentioned. Preferably, a polarizer obtained by dyeing a PVA-based film with iodine and uniaxially stretching is used because of its excellent optical properties.

The dyeing with iodine is performed, for example, by immersing the PVA-based film in an aqueous solution of iodine. The draw ratio of the said uniaxial stretching is preferably 3 to 7 times. Stretching may be performed after dyeing treatment, or may be performed while dyeing. Moreover, you may dye after extending|stretching. Swelling treatment, crosslinking treatment, washing treatment, drying treatment, etc. are given to the PVA-based film as necessary. For example, by immersing and washing the PVA-based film in water before dyeing, stains on the surface of the PVA-based film and anti-blocking agent can be washed away, as well as swelling of the PVA-based film to prevent staining and the like.

As a specific example of a polarizer obtained using a laminate, 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 a PVA-based resin layer coated on the resin substrate. A polarizer obtained using a layered product of and is mentioned. A polarizer obtained by using a laminate of a resin substrate and a PVA-based resin layer coated and formed on the resin substrate, for example, by applying a PVA-based resin solution to the resin substrate, drying it, forming a PVA-based resin layer on the resin substrate, Obtaining a laminated body of a resin substrate and a PVA-based resin layer; It can be produced by: stretching and dyeing the layered product to make the PVA-based resin layer a polarizer. In this embodiment, extending|stretching typically includes immersing a layered product in boric acid aqueous solution and extending|stretching. Further, the stretching may further include, if necessary, air stretching of the laminate at a high temperature (eg, 95° C. or higher) prior to stretching in a boric acid aqueous solution. The obtained laminate of the resin substrate/polarizer may be used as it is (that is, the resin substrate may be used as a protective layer for the polarizer), and the resin substrate is peeled from the laminate of the resin substrate/polarizer, and the peel surface is used for the purpose. Any suitable protective layer according to the above may be laminated and used. The details of the manufacturing method of such a polarizer are described, for example in Unexamined-Japanese-Patent No. 2012-73580 and Japanese Patent No. 6470455. As for these publications, the entire description is incorporated herein by reference.

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. It is ㎛ ~ 8㎛. When the thickness of the polarizer is within such a range, curling at the time of heating can be suppressed satisfactorily, and favorable appearance durability at the time of heating can be obtained.

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%, 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, still more preferably 99.9% or more.

C-2. protective layer

Each of the first polarizing plate 10 and the second polarizing plate 40 may further include a protective layer. A protective layer may be provided on at least one surface of a polarizer, and may be provided on both surfaces of a polarizer. In the image display device 101, the first polarizing plate 10 includes a protective layer 12 provided on a surface opposite to the viewing side of the first polarizer 11, and the second polarizing plate 40, A protective layer 42 provided on the surface of the second polarizer 41 on the visual side is provided.

The protective layer is formed of any appropriate film that can be used as a protective layer for a polarizer. Specific examples of the material serving as 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 transparent resins such as polysulfone, polystyrene, polynorbornene, polyolefin, (meth)acrylic, and acetate resins. Further, thermosetting resins such as (meth)acrylic, urethane-based, (meth)acrylurethane-based, epoxy-based, and silicone-based resins or ultraviolet curable resins may be used. In addition, glassy type polymers, such as a siloxane type polymer, are also mentioned, for example. Moreover, the polymer film of Unexamined-Japanese-Patent No. 2001-343529 (WO01/37007) can also be used. As the material of this film, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in its side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in its side chain can be used. For example, isobutene and and a resin composition containing an alternating copolymer of N-methylmaleimide and an acrylonitrile/styrene copolymer. The polymer film may be, for example, an extrusion molding of the resin composition.

When the polarizer disposed on the viewing side of the image display cell 60 has a protective layer located on the outermost surface of the image display device, the protective layer is optionally subjected to hard coat treatment, antireflection treatment, and sticking. Surface treatment such as prevention treatment and antiglare treatment may be performed.

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. The first retardation layer

As described above, the first retardation layer 20 has a refractive index characteristic of nz>nx>ny. A layer (film) exhibiting such refractive index characteristics is sometimes referred to as a 'positive biaxial plate' or a 'positive B plate'.

The thickness of the first retardation layer is typically 3 µm or more, preferably 5 µm or more, and is typically 30 µm or less, preferably 20 µm or less, and more preferably 15 µm or less. When the thickness of the first retardation layer is within this range, the handling property at the time of manufacture is excellent, and the optical uniformity of the obtained image display device can be improved.

The first retardation layer may be of any suitable configuration. Specifically, the retardation film alone may be used, or a laminate of two or more identical or different retardation films may be used. In the case of a laminate, the first retardation layer may include a pressure-sensitive adhesive layer or an adhesive layer for attaching two or more retardation films. Preferably, the first retardation layer is a single retardation film. By adopting such a structure, shift or non-uniformity of the phase difference value due to the shrinkage stress of the polarizer and/or the heat of the light source can be reduced, and it can contribute to thinning of the obtained image display device.

The optical characteristics of the retardation film may be set to any suitable value depending on the configuration of the first retardation layer. For example, when the first retardation layer is a single retardation film, the optical properties of the retardation film are preferably the same as those of the first retardation layer. Therefore, it is preferable that the retardation value of the adhesive layer, adhesive layer, etc. used when laminating the said retardation film to a polarizer and/or a 2nd retardation layer etc. 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 does not cause optical unevenness due to deformation is preferably used. As the retardation film, preferably, a stretched film of a polymer film containing a thermoplastic resin as a main component is used. As the thermoplastic resin, a polymer exhibiting negative birefringence is preferably used. By using a polymer exhibiting negative birefringence, a retardation film having a refractive index ellipsoid of nz>nx>ny can be easily obtained. Here, "showing negative birefringence" means that when a polymer is oriented by stretching or the like, its 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 increases. Examples of polymers exhibiting negative birefringence include polymers in which a chemical bond or a functional group having a large polarization anisotropy such as an aromatic ring or a carbonyl group is introduced into a side chain. Specifically, an acrylic resin, a styrene resin, a maleimide resin, etc. are mentioned.

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

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

The maleimide-based resin can be obtained by, for example, addition polymerization of a maleimide-based monomer. Examples of maleimide-based monomers include N-ethylmaleimide, N-cyclohexylmaleimide, N-phenylmaleimide, N-(2-methylphenyl)maleimide, N-(2-ethylphenyl)maleimide, and 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 Mid, N-(2-bromophenyl)maleimide, N-(2,6-dibromophenyl)maleimide, N-(2-biphenyl)maleimide, N-(2-cyanophenyl)maleimide Mead can be heard. The maleimide-based monomer can be obtained from, for example, Tokyo Chemical Industry Co., Ltd.

In the above addition polymerization, the birefringence properties of the obtained resin can also be controlled by substituting the side chain after polymerization, maleimide or grafting reaction, and the like.

The polymer exhibiting negative birefringence may be copolymerized with other monomers. By copolymerizing other monomers, brittleness, molding processability, 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; (meth)acrylates such as methyl acrylate and methyl methacrylate; maleic anhydride; Vinyl esters, such as vinyl acetate, are mentioned.

When the polymer exhibiting negative birefringence is a copolymer of the styrenic monomer and the other monomer, the blending ratio of the styrenic 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 within this range, a polymer film having excellent toughness and molding processability can be obtained.

Preferably, the polymer exhibiting negative birefringence is a styrene-maleic anhydride copolymer, a styrene-acrylonitrile copolymer, a styrene-(meth)acrylate copolymer, a styrene-maleimide copolymer, and a vinyl ester-maleic acid copolymer. Mid copolymers, olefin-maleimide copolymers and the like are used. These can be used individually or in combination of 2 or more types. These polymers exhibit high negative birefringence and can also have excellent heat resistance. These polymers can be obtained from, for example, Nova Chemical Japan or Arakawa Chemical Industry Co., Ltd.

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

In the general formula (I), R _{1 to} R ₅ each independently represent hydrogen, a halogen atom, a carboxylic acid, a carboxylic acid ester, a hydroxyl group, a nitro group, or a linear or branched alkyl or alkoxy group having 1 to 8 carbon atoms ( provided that R ₁ and R ₅ are not hydrogen atoms at the same time), R ₆ and R ₇ is represents hydrogen or a straight-chain or branched alkyl group 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 the above, and a cyclic olefin-based copolymer disclosed in, for example, Japanese Unexamined Patent Publication No. 2005-350544 and the like can also be used. In addition, compositions containing polymers and inorganic fine particles as disclosed in Japanese Unexamined Patent Publication No. 2005-156862, Japanese Unexamined Patent Publication No. 2005-227427, and the like can also be suitably used. In addition, as a polymer exhibiting negative birefringence, one type may be used independently, or two or more types may be mixed and used. Further, they may be used after being modified by copolymerization, branching, crosslinking, molecular terminal modification (or capping), tactic modification, and the like.

The polymer film may further contain any appropriate additives, if necessary. Specific examples of additives include plasticizers, heat stabilizers, light stabilizers, lubricants, antioxidants, ultraviolet absorbers, flame retardants, colorants, antistatic agents, compatibilizers, crosslinking agents, and thickeners. The type and content of additives may be appropriately set depending on 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.

As a method for forming the polymer film, any suitable method may be employed. Examples 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, the extrusion molding method is a method of heating and melting a resin composition containing the thermoplastic resin, plasticizer, additives, etc., extruding this into a thin film form on the surface of a casting roll by a T die or the like, and cooling it to form a film am. In the solvent casting method, a concentrated solution (dope) in which the above resin composition is dissolved in a solvent is degassed, cast uniformly on the surface of a metallic endless belt, rotary drum, or plastic substrate in a thin film form, and the solvent is evaporated to form a film. How to shape the . In addition, molding conditions can be appropriately set according to the composition or type of resin used, molding processing method, and the like.

The retardation film (stretched film) may be obtained by stretching the polymer film under any appropriate stretching conditions.

Specific examples of the stretching method include a longitudinal uniaxial stretching method, a transverse uniaxial stretching method, a vertical and horizontal sequential biaxial stretching method, and a vertical and horizontal simultaneous biaxial stretching method. Preferably, a transverse uniaxial stretching method, vertical and horizontal sequential biaxial stretching method, and vertical and horizontal simultaneous biaxial stretching method are used. It is because a biaxial retardation film can be obtained suitably. As described above, in the polymer exhibiting negative birefringence, the refractive index in the stretching direction is relatively small, so in the case of the transverse uniaxial stretching method, the polymer film has a slow axis in the conveying direction (the refractive index in the conveying direction is nx do). In the case of the vertical and horizontal sequential biaxial stretching method and the vertical and horizontal simultaneous biaxial stretching method, depending on the ratio of the vertical and horizontal stretching ratios, both the conveying direction and the width direction can be set as the slow axis. Specifically, when the draw ratio in the longitudinal (transport) direction is relatively increased, the transverse (width) direction becomes the slow axis, and when the draw ratio in the transverse (width) direction is relatively increased, the longitudinal (transport) direction becomes the slow axis. becomes an axis

As the stretching device used for the stretching, any appropriate stretching device may be used. As a specific example, a roll stretching machine, a tenter stretching machine, a pantograph type or a linear motor type biaxial stretching machine can be mentioned. When stretching is performed while heating, the temperature may be changed continuously or may be changed stepwise. Moreover, you may divide|segment an extending process into two or more times.

In addition, the Re (550) and Nz coefficients of the first retardation layer can be adjusted within the above ranges 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 30 μm or more, preferably 40 μm or more, more preferably 80 μm or more, and typically 300 μm or less, preferably 200 μm or less, more preferably is less than 120 μm.

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, particularly preferably (Tg + 5) ° C to (Tg + 20 ° C) ) ℃. If the stretching temperature is too low, the retardation value or direction of the slow axis may become non-uniform, or the polymer film may crystallize (cloudy). On the other hand, if the stretching temperature is excessively high, there is a possibility that the polymer film melts or expression of the retardation becomes insufficient. The stretching temperature is typically 110 to 200°C. In addition, the glass transition temperature can be obtained by the DSC method according to JISK7121-1987.

As a method of controlling the temperature in the stretching oven, any suitable method may be employed. For example, an air circulation constant temperature oven in which hot or cold air circulates, a heater using microwaves or far-infrared rays, and a method using a heated roll, heat pipe roll, or metal belt for temperature control.

The stretching ratio when stretching the polymer film may be set to any suitable value depending on the composition of the polymer film, the type of volatile components, etc., the residual amount of volatile components, etc., and a desired retardation value. Preferably they are 1.05 times - 5.00 times, More preferably, they are 2.45 times - 5.00 times. In addition, the conveying speed at the time of stretching is preferably 0.5 m/min to 20 m/min from the viewpoint of mechanical accuracy and stability of the stretching device.

In the above, the method of obtaining the retardation film using a polymer exhibiting negative birefringence has been described, but the retardation film can also be obtained using a polymer exhibiting positive birefringence. As a method for obtaining a retardation film using a polymer exhibiting positive birefringence, for example, disclosed in Japanese Unexamined Patent Publication Nos. 2000-231016, 2000-206328, and 2002-207123 A stretching method that increases the refractive index in the thickness direction can be used. Specifically, a method in which a heat-shrinkable film is adhered to one side or both sides of a film containing a polymer exhibiting positive birefringence and subjected to heat treatment is exemplified. The refractive index in the thickness direction can be increased by shrinking the film under the action of the shrinking force of the heat-shrinkable film by heat treatment and shrinking the film in the longitudinal direction and the width direction, and a refractive index ellipsoid having nz > nx > ny can be obtained. A retardation film having

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

As the retardation film used for the first retardation layer, in addition to the above-mentioned film, a commercially available optical film can be used as it is. In addition, a film obtained by subjecting a commercially available optical film to secondary processing such as stretching 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 more, more preferably 85% or more, and particularly preferably 90% or more. The theoretical upper limit of the light transmittance is 100%, but since surface reflection occurs due to the difference in refractive index between air and the retardation film, the feasible upper limit of the light transmittance is generally 94%. It is preferable that the entire first retardation layer has 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, still 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 within such a range, an image display device having excellent optical uniformity, small change in optical properties even in environments such as high temperature and high humidity, and excellent durability can be obtained. The lower limit of the photoelastic coefficient is not particularly limited, but is generally 5.0 × 10 ^-13 (m 2 /N) or more, and preferably 1.0 × 10 ^-12 (m 2 /N) or more. When the photoelastic coefficient is excessively small, there is a possibility that the appearance of phase difference becomes small. The photoelastic coefficient is a value unique to chemical structures such as polymers, but the photoelastic coefficient can be reduced by copolymerizing or mixing a plurality of components having different signs (positive and negative) of the photoelastic coefficient.

E. Second retardation layer

As described above, the second retardation layer 30 has a refractive index characteristic of nx>ny=nz. A layer (film) exhibiting such refractive index characteristics is sometimes referred to as a 'positive uniaxial plate' or a 'positive A plate'. 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.

As the material forming the second retardation layer, any suitable material can be employed as long as the above characteristics are obtained. Specifically, the second retardation layer may be an alignment-fixed layer of a liquid crystal compound (liquid-crystal alignment-fixed layer) or a retardation film (stretched film of a polymer film).

When the second retardation layer is a liquid crystal alignment solidified layer, by using a liquid crystal compound, since the difference between nx and ny of the retardation layer obtained can be significantly increased compared to non-liquid crystal materials, a retardation layer for obtaining a desired in-plane retardation thickness can be significantly reduced. As a result, further thinning of the polarizing plate with the retardation layer (as a result, the image display device) can be realized. In this specification, the 'alignment fixed layer' refers to a layer in which liquid crystal compounds are aligned in a predetermined direction within the layer and the alignment state is fixed. In addition, the 'alignment hardened layer' is a concept including an alignment hardened layer obtained by curing a liquid crystal monomer as will be described later. In this embodiment, the rod-shaped liquid crystal compounds are typically aligned in a state aligned in the direction of the slow axis of the second retardation layer (homogeneous alignment).

As a liquid crystal compound, the liquid crystal compound (nematic liquid crystal) whose liquid crystal phase is a nematic phase is mentioned, for example. As such a liquid crystal compound, for example, a liquid crystal polymer or a liquid crystal monomer can be used. The liquid crystalline expression mechanism of the liquid crystal compound may be either lyotropic or thermotropic. The liquid crystal polymer and the liquid crystal monomer may be used alone or in combination.

When the liquid crystal compound is a liquid crystal 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 crosslinking the liquid crystalline monomer. After aligning the liquid crystalline monomers, for example, when the liquid crystalline monomers are polymerized or crosslinked, the alignment state can be fixed. Here, a polymer is formed by polymerization and a three-dimensional network structure is formed by crosslinking, which is non-liquid crystal. Therefore, the formed second retardation layer does not undergo transition to a liquid crystal phase, a glass phase, or a crystal phase due to a temperature change peculiar to a liquid crystal compound, for example. As a result, the formed second retardation layer becomes a retardation layer that is not affected by temperature change and has extremely excellent stability.

The specific example of a liquid crystal compound and the detail of the formation method of a liquid crystal alignment hardening layer are described in Unexamined-Japanese-Patent No. 2006-163343 and Unexamined-Japanese-Patent No. 2006-178389, for example. Descriptions of these publications are incorporated herein by reference.

As described above, the second retardation layer may be a stretched film of a polymer film. Specifically, by appropriately selecting the type of polymer, stretching conditions (eg, stretching temperature, stretching ratio, stretching direction), and stretching method (eg, transverse uniaxial stretching), the desired optical properties (eg, refractive index characteristics, in-plane) A second retardation layer having a retardation, a retardation in the thickness direction) can be obtained. In particular, Re (550) of the second retardation layer can be adjusted within the above range by adjusting the thickness (original thickness) of the polymer film, the stretching temperature, and the stretching ratio.

The thickness (original thickness) of the polymer film is typically 10 µm or more, preferably 15 µm or more, and is typically 50 µm or less, preferably 40 µm or less, and 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 1.37 times to 3.00 times, more preferably 1.60 times to 2.50 times.

As the resin forming the polymer film, any appropriate resin may be employed. Specific examples include resins constituting positively birefringent films such as norbornene-based resins, polycarbonate-based resins, cellulose-based resins, polyvinyl alcohol-based resins, and polysulfone-based resins. Among them, norbornene-based resins and polycarbonate-based resins are preferable.

The norbornene-based resin is a resin that is polymerized using a norbornene-based monomer as a polymerization unit. Examples of the norbornene-based monomer include norbornene and its alkyl and/or alkylidene substituents such as 5-methyl-2-norbornene, 5-dimethyl-2-norbornene, 5-ethyl-2-norbornene, 5-butyl-2-norbornene, 5-ethylidene-2-norbornene, etc., these halogen-substituted polar groups; dicyclopentadiene, 2,3-dihydrodicyclopentadiene and the like; Dimethanooctahydronaphthalene, its alkyl and/or alkylidene substituents, and polar substituents such as halogen, such as 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-ethyl Iden-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-chloro-1,4:5,8-dimethano- 1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-cyano-1,4:5,8-dimethano-1,4,4a,5,6,7,8 ,8a-octahydronaphthalene, 6-pyridyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-methoxycarbonyl -1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, etc.; Tri-tetramers 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-cyclopentaanthracene. there is. The norbornene-based resin may be a copolymer of a norbornene-based monomer and another monomer.

As the polycarbonate-based resin, an aromatic polycarbonate is preferably used. Aromatic polycarbonate can typically be obtained by a reaction between a carbonate precursor and an aromatic dihydric phenol compound. Specific examples of the carbonate precursor include phosgene, bischloroformate of dihydric phenols, diphenyl carbonate, di-p-tolyl carbonate, phenyl-p-tolyl carbonate, di-p-chlorophenyl carbonate, and dinaphthyl carbonate. can Among these, phosgene and diphenyl carbonate are preferable. Specific examples of the aromatic dihydric phenol compound include 2,2-bis(4-hydroxyphenyl)propane, 2,2-bis(4-hydroxy-3,5-dimethylphenyl)propane, and bis(4-hydroxyphenyl). ) methane, 1,1-bis(4-hydroxyphenyl)ethane, 2,2-bis(4-hydroxyphenyl)butane, 2,2-bis(4-hydroxy-3,5-dimethylphenyl)butane , 2,2-bis(4-hydroxy-3,5-dipropylphenyl)propane, 1,1-bis(4-hydroxyphenyl)cyclohexane, 1,1-bis(4-hydroxyphenyl)- 3,3,5-trimethylcyclohexane is exemplified. You may use these individually or in combination of 2 or more types. Preferably, 2,2-bis(4-hydroxyphenyl)propane, 1,1-bis(4-hydroxyphenyl)cyclohexane, 1,1-bis(4-hydroxyphenyl)-3,3, 5-Trimethylcyclohexane is used. In particular, it is preferable to use 2,2-bis(4-hydroxyphenyl)propane and 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane together.

The second retardation layer is preferably a stretched film of a polymer film, more preferably a stretched film of a norbornene-based resin film.

The thickness of the second retardation layer can be set so that desired optical characteristics are obtained. When the second retardation layer is a liquid crystal alignment solidified layer, the thickness is preferably 0.5 μm to 10 μm, more preferably 0.5 μm to 8 μm, still more preferably 0.5 μm to 5 μm. When the second 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.

F. A laminate of the first retardation layer and the second retardation layer

A laminate of the first retardation layer and the second retardation layer preferably satisfies the following relationship:

Re(450)/Re(550)>0.82

Re(650)/Re(550)<1.18.

Re(450)/Re(550) of the laminate is more preferably 1.0 to 1.2, still more preferably 1.0 to 1.1. Re(650)/Re(550) of the laminate is more preferably from 0.8 to 1.0, still more preferably from 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 inverse dispersion characteristics, the luminance in the oblique direction during black display is small, and the color shift in the oblique direction is A polarizing plate with a retardation layer capable of realizing a small image display device can be obtained.

G. liquid crystal cell

The liquid crystal cell 60a includes a first substrate 62, a second substrate 63, and a liquid crystal layer 61 sandwiched therebetween including liquid crystal molecules aligned in a homogeneous arrangement in the absence of an electric field. ). In a general configuration, a color filter and a black matrix are provided on one substrate (typically, the first substrate 62), and an electro-optical liquid crystal is provided on the other substrate (typically, the second substrate 63). A switching element for controlling characteristics, a scanning line for giving a gate signal to the switching element, a signal line for giving a source signal, a pixel electrode, and a counter electrode are provided. The distance between the substrates (cell gap) is controlled by a spacer or the like. On the side of the substrate in contact with the liquid crystal layer, for example, an alignment film made of polyimide or the like may be provided.

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 an embodiment of the present invention, when the substrate has such a phase difference in the thickness direction, black luminance in an oblique direction can be sufficiently reduced in a liquid crystal display device including liquid crystal cells of homogeneous alignment.

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

As described above, the liquid crystal layer 61 includes liquid crystal molecules aligned in a homogeneous arrangement in the absence of an electric field. 'Liquid crystal molecules aligned in a homogeneous arrangement' refers to a state in which the alignment vectors of the liquid crystal molecules are aligned parallel to and equally aligned with the plane of the substrate as a result of the interaction between the liquid crystal molecules and the substrate subjected to alignment treatment. Such a liquid crystal layer (result, a liquid crystal cell) typically exhibits a refractive index characteristic of nx>ny=nz. Here, 'ny = nz' includes not only a case where ny and nz are completely equal, but also a case where ny and nz are substantially equal. 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.

In one embodiment, the liquid crystal molecules of the liquid crystal layer have a pretilt. That is, the orientation vector of the liquid crystal molecules is slightly inclined with respect to the substrate plane. The pretilt angle is preferably 0.1° to 1.0°, more preferably 0.2° to 0.7°.

As a drive mode of such a liquid crystal cell 60a, an in-plane switching (IPS) mode and a fringe field switching (FFS) mode are exemplified. Further, 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. Further, 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. As the driving mode of the liquid crystal cell 60a, an in-plane switching (IPS) mode is preferably used.

If the driving mode of the liquid crystal cell 60a is the IPS mode, the visibility in the oblique direction of the liquid crystal display device can be improved.

H. Backlight unit

The light source 91 is disposed at a position corresponding to the side surface of the light guide plate 92 . As the light source, for example, an LED light source configured by arranging a plurality of LEDs can be used. As the light guide plate 92, any appropriate light guide plate can be used. For example, a light guide plate in which a lens pattern is formed on the rear surface side and a prism shape or the like formed on the rear surface side and/or the viewer side are used so that light from the horizontal direction can be deflected in the thickness direction. Preferably, a light guide plate in which prism shapes are formed on the rear side and the viewer side is used. In the light guide plate, the prism shape formed on the back side and the prism shape formed on the viewer side are preferably orthogonal to each other in the ridge direction. If such a light guide plate is used, light that is more easily condensed can be made incident on a prism sheet (not shown).

[Example]

Hereinafter, the present invention will be specifically described by examples, but the present invention is not limited by these examples. The measurement method of each characteristic is as follows.

(1) Measurement of phase difference 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 a KOBRA-WPR manufactured by Ohji 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 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°.

In addition, among the luminances measured as described above, the luminance when the polar angle is 40° and the azimuth angle is any of 20°, 25°, 155°, 160°, 190°, 195°, 345°, and 350° is an area It was set as A luminance (unit: cd/m<2>), and the maximum luminance in it was made into area A maximum luminance (unit: cd/m<2>).

<Production of polarizing plate>

<<Production Example 1>>

As the thermoplastic resin substrate, a long, amorphous isophthalic copolymer polyethylene terephthalate film (thickness: 100 μm) having a Tg of about 75° C. was used, and corona treatment was performed on one side of the resin substrate.

Potassium iodide 13 What was added by weight was dissolved in water to prepare a PVA aqueous solution (coating liquid).

A PVA-based resin layer having a thickness of 13 μm was formed by applying the PVA aqueous solution to the corona-treated surface of the resin substrate and drying at 60° C., thereby producing a laminate.

The obtained layered product was uniaxially stretched 2.4 times in the machine direction (longitudinal direction) in a 130°C oven (air assisted stretching treatment).

Next, the laminate was immersed in an insolubilization bath (boric acid aqueous solution obtained by blending 4 parts by weight of boric acid with respect to 100 parts by weight of water) at a liquid temperature of 40°C for 30 seconds (insolubilization treatment).

Next, in a dyeing bath (100 parts by weight of water, an iodine aqueous solution obtained by blending iodine and potassium iodide at a weight ratio of 1:7) with a liquid temperature of 30 ° C., the single transmittance (Ts) of the polarizer finally obtained is the desired value. It was immersed for 60 seconds while adjusting the concentration so as to be (dyeing treatment).

Next, it 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 respect to 100 parts by weight of water) at a liquid temperature of 40°C for 30 seconds (crosslinking treatment).

Thereafter, the laminate was immersed in an aqueous boric acid solution (boric acid concentration: 4% by weight, potassium iodide concentration: 5% by weight) at a liquid temperature of 70°C, while the total draw ratio was increased in the machine direction (longitudinal direction) between rolls having different circumferential speeds. Uniaxial stretching was performed so as to be 5.5 times (underwater stretching treatment).

Thereafter, the laminate was immersed in a washing bath (aqueous solution obtained by blending 4 parts by weight of potassium iodide with respect to 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, and a laminate having a configuration of resin substrate/polarizer was obtained.

An HC-TAC film (20 μm in thickness) was bonded as a protective layer to the polarizer surface (the surface on the opposite side to the resin substrate) of the obtained laminate. Then, the resin substrate was peeled off to obtain a polarizing plate having a configuration of a protective layer/polarizer. Then, the obtained polarizing plate was punched into a size corresponding to a liquid crystal cell described later.

<Production of retardation film (positive B plate) having nz>nx>ny refractive index characteristics>

<<Production Example 2>>

A pellet-shaped resin of a styrene-maleic anhydride copolymer (manufactured by Nova Chemical Japan Co., Ltd., trade name "Dyrac D232") was extruded at 270°C using a single screw extruder and a T die, and the sheet-like molten resin was placed in a cooling drum After cooling, a film having a thickness of 100 μm was obtained. This film was subjected to free end uniaxial stretching in the transport direction at a temperature of 130°C and a draw ratio of 2.5 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 uniaxially stretched at a fixed end in the transverse direction at a temperature of 135° C. using a tenter stretching machine so that the film width was 4.5 times the film width after longitudinal stretching, to obtain a retardation film (biaxially stretched film, Positive B plate) was obtained (transverse stretching step). Thereafter, 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 had a fast axis (slow axis in the width direction) in the conveying direction, and the refractive index characteristic showed a relationship of nz > nx > ny. Table 1 shows the in-plane retardation Re (550), thickness direction retardation Rth (550) and Nz coefficient of the retardation film (positive B plate).

<<Production Example 3>>

A phase difference film (positive B plate) was obtained in the same manner as in Production Example 2 except that the longitudinal stretch magnification was changed to 1.7 times and the transverse stretch magnification was changed to 1.8 times.

<<Production Example 4>>

A phase difference film (positive B plate) was obtained in the same manner as in Production Example 2, except that the longitudinal stretch ratio was changed to 1.5 times and the transverse stretch ratio was changed to 1.5 times.

<<Production Example 5>>

A phase difference film (positive B plate) was obtained in the same manner as in Production Example 2 except that the longitudinal stretch magnification was changed to 1.4 times and the transverse stretch magnification was changed to 1.4 times.

<<Production Example 6>>

A phase difference film (positive B plate) was obtained in the same manner as in Production Example 2, except that the longitudinal stretch magnification was changed to 2.2 times and the transverse stretch magnification was changed to 2.4 times.

<Production of retardation film (positive A plate) having refractive index characteristics nx>ny=nz>

<<Production Example 7>>

By uniaxially stretching a long norbornene-based resin film (manufactured by Nippon Zeon, trade name Zeonor, thickness 40 μm, photoelastic coefficient 3.10 × 10 ^-12 m ² /N) at 135 ° C. by 2.0 times, a phase difference film having a thickness of 28 μm is produced. did Thereafter, the obtained retardation film was punched into a size corresponding to a liquid crystal cell described later.

The retardation film obtained in this way had a slow axis in the transport direction, and the refractive index characteristic exhibited a relationship of nx>ny=nz. Table 1 shows the in-plane retardation Re (550), the retardation in the thickness direction Rth (550), and the Nz coefficient of the retardation film (positive A plate).

<<Production Example 8>>

A phase difference film (positive A plate) was obtained in the same manner as in Production Example 7 except that the draw ratio was changed to 1.5 times.

<<Production Example 9>>

A phase difference film (positive A plate) was obtained in the same manner as in Production Example 7 except that the draw ratio was changed to 1.43 times.

<<Production Example 10>>

A phase difference film (positive A plate) was obtained in the same manner as in Production Example 7 except that the draw ratio was changed to 1.37 times.

<<Production Example 11>>

A phase difference film (positive A plate) was obtained in the same manner as in Production Example 7 except that the draw ratio was changed to 1.2 times.

<Production of retardation film (positive C plate) having refractive index characteristics of nz>nx=ny>

<<Production Example 12>>

A retardation film (positive C plate) was obtained in the same manner as in Production Example 6 of Japanese Patent No. 6896118 except that the retardation Rth in the thickness direction was changed to -86 nm. Thereafter, the obtained retardation film was punched into a size corresponding to a liquid crystal cell described later.

The retardation film obtained in this way had a slow axis in the conveyance direction, and the refractive index characteristics showed a relationship of nz>nx=ny. Table 1 shows the in-plane retardation Re (550) and thickness direction retardation Rth (550) of the retardation film (positive C plate).

<<Production Example 13>>

A retardation film (positive C plate) was obtained in the same manner as in Production Example 12 except that the retardation Rth in the thickness direction was changed to -66 nm.

<Production of retardation film (negative B plate) having nx>ny>nz refractive index characteristics>

<<Production Example 14>>

A retardation film (negative B plate) was obtained in the same manner as in Production Example 7 except that the fixed-end transverse stretching was performed at a rate of 1.35 times. Thereafter, the obtained retardation film was punched into a size corresponding to a liquid crystal cell described later.

The retardation film thus obtained had a relationship of nx>ny>nz in the refractive index characteristic. Table 1 shows the in-plane retardation Re (550) and thickness direction retardation Rth (550) of the retardation film (negative B plate).

<<Production Example 15>>

A phase difference film (negative B plate) was obtained in the same manner as in Production Example 14 except that the draw ratio was changed to 1.3 times.

<<Production Example 16>>

A phase difference film (negative B plate) was obtained in the same manner as in Production Example 14 except that the draw ratio was changed to 1.2 times.

<Production of retardation film (negative A plate) having nx=nz>ny refractive index characteristics>

<<Production Example 17>>

A pellet-shaped resin of a styrene-maleic anhydride copolymer (manufactured by Nova Chemical Japan Co., Ltd., trade name "Dyrac D232") was extruded at 270 ° C. using a single screw extruder and a T die, and the sheet-like molten resin was poured into a cooling drum After cooling, a film having a thickness of 30 μm was obtained. This film was uniaxially stretched at the free end in the transport direction at a temperature of 130° C. and a draw ratio of 1.8 times using a roll stretching machine to obtain a retardation film (negative A plate) having a fast axis in the transport direction. Thereafter, the obtained retardation film was punched into a size corresponding to a liquid crystal cell described later.

The retardation film thus obtained had a relationship of nx = nz > ny in the refractive index characteristic. Table 1 shows the in-plane retardation Re (550) and the thickness-direction retardation Rth (550) of the retardation film (negative A plate).

<Preparation of image display cell (liquid crystal cell)>

<<Production Example 18>>

A liquid crystal cell was taken out from an IPS mode liquid crystal display device (manufactured by Apple, trade name "iPad (registered trademark)"). The optical member attached to both surfaces of the liquid crystal cell was removed, and the removal surface (the outer surface of the substrate) was washed. This was used as an image display cell (liquid crystal cell). The first substrate of the liquid crystal cell is Rth(450) = 32 nm, Rth(550) = 19 nm, Rth(650) = 23 nm; The second substrate was Rth(450) = 9 nm, Rth(550) = 0.3 nm, and Rth(650) = -6 nm.

[Example 1]

On the viewing side of the liquid crystal cell of Production Example 18, the polarizing plate of Production Example 1 (the second polarizing plate including the second polarizer) was laminated. On the other hand, on the rear side of the liquid crystal cell, the retardation film (second retardation layer) of Production Example 7, the retardation film (first retardation layer) of Production Example 2, and the polarizing plate (first including the first polarizer) of Production Example 1 polarizing plates) were laminated in this order. In the stacking, the absorption axis direction of the first polarizer and the slow axis direction of the first retardation layer are substantially orthogonal, the absorption axis direction of the first polarizer and the slow axis direction of the second retardation layer are substantially parallel, and the first polarizer The absorption axis direction and the initial orientation direction of the liquid crystal cell were substantially orthogonal, and the absorption axis direction of the second polarizer and the initial orientation direction of the liquid crystal cell were substantially parallel. In this way, an image display device (E-mode liquid crystal display device) was produced. Then, the image display device was subjected to the luminance measurement at the time of black display described above. A luminance distribution diagram in the image display device of Example 1 is shown in FIG. 3 . Table 1 also shows the area A maximum luminance in the image display device of Example 1.

[Comparative Examples 1 to 8]

Except for changing each of the retardation film (second retardation layer) of Production Example 7 and the retardation film (first retardation layer) of Production Example 2 to the retardation film of Production Example shown in Table 1, in the same manner as in Example 1, An image display device (liquid crystal display device in E mode) was produced. Then, the image display device was subjected to the luminance measurement at the time of black display described above. A luminance distribution diagram in the image display device of Comparative Example 1 is shown in FIG. 4 . Table 1 shows the area A maximum luminance in the image display devices of Comparative Examples 1 to 8.

[Table 1]

[evaluation]

As is clear from Table 1, FIGS. 3 and 4, Re (550) and Nz coefficient of the first retardation layer are in the above range, and Re (550) of the second retardation layer are in the above range, so that the transverse direction ( The viewing angle in the left-right direction (X) of the paper in FIGS. 3 and 4 can be secured wider than the angle of view in the vertical direction (up-and-down direction (Y) in the paper in FIGS. 3 and 4). An image display device (liquid crystal display device) having sufficiently low luminance can be realized.

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

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 disposed adjacent to the first polarizing plate and having a refractive index characteristic of nz>nx>ny;
A second retardation layer disposed adjacent to the first retardation layer and exhibiting a relationship of refractive index characteristics nx > ny = nz,
An absorption axis of the first polarizer and a slow axis of the first retardation layer are substantially orthogonal,
An absorption axis of the first polarizer and a slow axis of the second retardation layer are substantially parallel,
The in-plane retardation Re (550) of the first retardation layer is 280 nm or more and 360 nm or less,
The Nz coefficient of the first retardation layer is -1.0 or more and -0.1 or less,
The in-plane retardation Re (550) of the second retardation layer is 280 nm or more and 360 nm or less,
A polarizing plate with a retardation layer. an image display cell;
The polarizing plate with a retardation layer according to claim 1, disposed on the side opposite to the viewing side with respect to the image display cell.
An image display device having a According to claim 2,
The image display cell is a liquid crystal cell,
The driving mode of the liquid crystal cell is an IPS mode, an image display device. According to claim 3,
The image display device includes a second polarizing plate disposed on an opposite side of the image display cell from the polarizing plate with a 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,
An image display device in which an absorption axis of the second polarizer and an initial orientation direction of the liquid crystal cell are substantially parallel.

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