CN115933038A - Polarizing plate with phase difference layer and image display device - Google Patents

Abstract

The invention provides a polarizing plate with a phase difference layer, which can realize wide viewing field angle in a transverse direction and can sufficiently reduce black brightness in an oblique direction intersecting with longitudinal and transverse directions. The polarizing plate with a retardation layer according to an embodiment of the present invention includes: a polarizing plate comprising a polarizer; a first phase difference layer having refractive index characteristics showing a relationship of nz > nx > ny; and a second phase difference layer having refractive index characteristics exhibiting a relationship of nx > ny = nz. The absorption axis of the polarizer is substantially orthogonal to the slow axis of the first phase difference layer, and the absorption axis of the polarizer is substantially parallel to the slow axis of the second phase difference layer. Re (550) of the first retardation layer is 280nm to 360nm, and the Nz coefficient of the first retardation layer is-1.0 to-0.1. Re (550) of the second phase difference layer is 280nm to 360nm.

Description

Polarizing plate with phase difference layer and image display device

Technical Field

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

Background

In image display devices represented by liquid crystal display devices, in general, various optical films obtained by combining a polarizer and a retardation film are used in order to compensate optical characteristics suitable for the application. For example, the following techniques are proposed: a polarizing plate including a polarizer, a first retardation layer having a refractive index characteristic showing a relationship of nz > nx > ny, and a second retardation layer having a refractive index characteristic showing a relationship of nx > ny = nz are combined such that an absorption axis of the polarizer is orthogonal to a slow axis of the first retardation layer and the absorption axis of the polarizer is parallel to the slow axis of the second retardation layer, thereby widening a viewing angle (see, for example, patent document 1).

However, in recent years, the use of image display devices has been diversified. As an example of such an application, an in-vehicle display is given. In particular, wide viewing angles in the lateral direction (left-right direction) are required for the in-vehicle display. However, even if the technique described in patent document 1 is applied to an in-vehicle display, there is a limit to the wide viewing angle in the lateral direction, and there is a problem that when the black display of the in-vehicle display is viewed from an oblique direction (for example, obliquely upward right) intersecting both the longitudinal and lateral directions, the black display does not become sufficiently black (that is, the black luminance does not become sufficiently small).

Documents of the prior art

Patent literature

Patent document 1: japanese laid-open patent publication No. 2021-76759

Disclosure of Invention

Problems to be solved by the invention

The present invention has been made to solve the above conventional problems, and a main object thereof is to provide a polarizing plate with a retardation layer, which can realize a wide viewing angle in a lateral direction (a predetermined plane direction of an image display surface) and can sufficiently reduce black luminance in an oblique direction intersecting with both the longitudinal and transverse directions, in an image display device.

Means for solving the problems

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

An image display device according to another aspect of the present invention includes: an image display unit; and the polarizing plate with a retardation layer, the polarizing plate with a retardation layer being disposed on the opposite side of the visible side with respect to the image display unit.

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

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

Effects of the invention

According to the embodiments of the present invention, it is possible to realize a polarizing plate with a retardation layer that can realize a wide viewing angle in the lateral direction (predetermined plane direction of an image display surface) of an image display device and can sufficiently reduce black luminance in an oblique direction intersecting with both the longitudinal and lateral directions.

Drawings

Fig. 1 is a schematic cross-sectional view of a polarizing plate with a retardation layer according to an embodiment of the present invention.

Fig. 2 is a schematic cross-sectional view of an image display device according to an embodiment of the present invention.

Fig. 3 is a luminance distribution diagram at the time of black display of the image display device of example 1.

Fig. 4 is a luminance distribution diagram at the time of black display of the image display device of comparative example 1.

Description of the symbols

10. First polarizing plate

11. First polarizer

20. First retardation layer

30. Second phase difference layer

40. Second polarizing plate

60. Image display unit

60a liquid crystal cell

100. Polarizing plate with phase difference layer

101. Image display device

Detailed Description

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)

The terms and symbols in the present specification are defined as follows.

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

"nx" is a refractive index in a direction in which a refractive index in a plane becomes maximum (i.e., slow axis direction), "ny" is a refractive index in a direction orthogonal to the slow axis in a plane (i.e., fast axis direction), and "nz" is a refractive index in a thickness direction.

(2) In-plane retardation (Re) and front retardation (R) ₀ )

"Re (. Lamda)" is an in-plane retardation measured at 23 ℃ with light of wavelength. Lamda.nm. For example, "Re (550)" is an in-plane retardation measured at 23 ℃ with light having a wavelength of 550 nm. The "in-plane retardation Re (550)" may be referred to as "front retardation R ₀ ". When the thickness of the layer (film) is set to d (nm), re (λ) is represented by the formula: re (λ) = (nx-ny) × d.

(3) Retardation in thickness direction (Rth)

"Rth (. Lamda)" is a retardation in the thickness direction measured at 23 ℃ with light having a wavelength of. Lamda.nm. For example, "Rth (550)" is a phase difference in the thickness direction measured at 23 ℃ with light having a wavelength of 550 nm. When the thickness of the layer (film) is set to d (nm), rth (λ) is represented by the formula: rth (λ) = (nx-nz) × d.

(4) Coefficient of Nz

The Nz coefficient was obtained from Nz = Rth/Re.

(5) Substantially parallel or orthogonal

The expressions "substantially orthogonal" and "substantially orthogonal" include the case where the angle formed by the two directions is 90 ° ± 10 °, preferably 90 ° ± 7 °, and more preferably 90 ° ± 5 °. The expressions "substantially parallel" and "substantially parallel" include the case where the angle formed by the two directions is 0 ° ± 10 °, preferably 0 ° ± 7 °, and more preferably 0 ° ± 5 °. In the present specification, simply "orthogonal" or "parallel" is considered to include a substantially orthogonal state or a substantially parallel state.

A. Integral constitution of polarizing plate with phase difference layer

Fig. 1 is a schematic cross-sectional view of a polarizing plate with a retardation layer according to an embodiment of the present invention. The polarizing plate 100 with a phase difference layer illustrated in the figure includes: a first polarizing plate 10 including a first polarizer 11; a first retardation layer 20 having refractive index characteristics showing a relationship nz > nx > ny; and a second phase difference layer 30 whose refractive index characteristic shows 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 polarizer 10 with respect to the first retardation layer 20. In the present specification, "adjacently disposed" means directly laminated or laminated only via an adhesive layer (for example, an adhesive layer or an adhesive layer). That is, it means that no optical function layer (for example, another retardation layer) is interposed between the first polarizing plate 10 and the first retardation layer 20, and between the first retardation layer 20 and the second retardation layer 30.

The absorption axis (first absorption axis direction) of the first polarizer 11 is substantially orthogonal to the slow axis (first slow axis direction) of the first retardation layer 20. 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 parallel.

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

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

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

If the Re (550) and Nz coefficients of the first retardation layer and the Re (550) of the second retardation layer each satisfy the above-described ranges, a wide viewing angle in the lateral direction (predetermined plane direction of the image display surface) can be realized in the image display device having the polarizing plate with a retardation layer, and the black luminance in the oblique direction intersecting with both the longitudinal and transverse directions can be sufficiently reduced. That is, in the image display device having the polarizing plate with the phase difference layer, the angle of view in the lateral direction (for example, the first surface direction X of the image display device shown in fig. 3) can be made wider than the angle of view in the longitudinal direction (for example, the second surface direction Y orthogonal to the first surface direction X shown in fig. 3), and the black luminance when the image display device is viewed in black display from an oblique direction intersecting both the lateral direction (the 1 st surface direction X) and the longitudinal direction (the 2 nd surface direction Y) can be sufficiently reduced.

More specifically, the luminance of the image display device when black display is performed is measured at a polar angle of 40 ° to 42 ° and in each range of azimuth angles of 20 ° to 25 °, 155 ° to 160 °, 190 ° to 195 °, and 345 ° to 350 ° by an arbitrary appropriate luminance meter, and is, for example, 0.00074 or less, preferably 0.00070 or less, and more preferably 0.00068 or less. In the present specification, the luminance measured in the range of the polar angle and the azimuth angle is set as the luminance of the area a. The lower limit of the luminance of the area a is typically 0.00001 or more.

In one embodiment, the Nz coefficient of the second phase difference layer 30 is, for example, 0.5 to 1.5, preferably 0.6 to 1.4, more preferably 0.7 to 1.3, and still more preferably 0.8 to 1.2. If the Nz coefficient of the second retardation layer is within the above range, in the image display device having the polarizing plate with a retardation layer, it is possible to stably realize a wide viewing angle in the lateral direction (predetermined plane direction of the image display surface), and to stably reduce black luminance in an oblique direction intersecting with both the lateral and longitudinal directions.

The polarizing plate with a phase difference layer may further have a conductive layer or an isotropic substrate with a conductive layer (not shown). The conductive layer or the isotropic substrate with the conductive layer is typically disposed outside the second phase difference layer (opposite side to the first polarizer). In the case where a conductive layer is provided or an isotropic substrate with a conductive layer is provided, a polarizing plate with a phase difference layer can be applied to a so-called inner touch panel type input display device in which a touch sensor is embedded between an image display unit (for example, a liquid crystal cell, an organic EL cell) and a first polarizing plate.

The polarizing plate with a retardation layer may further comprise another retardation layer. The optical properties (for example, refractive index properties, in-plane retardation, nz coefficient, photoelastic coefficient), thickness, arrangement position, and the like of the other retardation layers can be appropriately set according to the purpose.

The polarizing plate with a retardation layer may be a single sheet or a long sheet. In the present specification, the "elongated shape" refers to an elongated shape having a length sufficiently long with respect to the width, and includes, for example, an elongated shape having a length 10 times or more, preferably 20 times or more with respect to the width. The long polarizing plate with a retardation layer can be wound in a roll shape.

In practice, an adhesive layer (not shown) is provided on the second phase difference layer on the side opposite to the first polarizing plate, so that the polarizing plate with the phase difference layer can be stuck on the image display unit. Further, it is preferable that a release liner is temporarily adhered to the surface of the pressure-sensitive adhesive layer until the polarizing plate with the retardation layer is used. By temporarily adhering the release liner, a roll can be formed while protecting the adhesive layer.

B. Integral structure of image display device

Fig. 2 is a schematic cross-sectional view of an image display device according to an embodiment of the present invention. The image display apparatus 101 of the illustrated example has: an image display unit 60; and a polarizing plate 100 with a retardation layer disposed on the opposite side of the image display unit 60 from the viewing side. In the image display device 101, the first phase difference layer 20 is located between the first polarizing plate 10 and the image display unit 60, and the second phase difference layer 30 is located between the first phase difference layer 20 and the image display unit 60.

The image display device 101 illustrated in the figure further has a second polarizing plate 40 disposed on the opposite side (viewing side) of the polarizing plate 100 with a phase difference layer with respect to the image display unit 60. The second polarizer 40 comprises a second polarizer 41.

The image display unit 60 is representatively a liquid crystal unit 60a, and the image display device 101 is representatively a liquid crystal display device. The liquid crystal display device is typically a so-called E-mode. The "E-mode liquid crystal display device" refers to a device in which the absorption axis (first absorption axis direction) of a polarizer (in the present embodiment, the first polarizer 11) disposed on the opposite side (back side) of the visible side of the liquid crystal cell is substantially orthogonal to the initial alignment direction of the liquid crystal cell. The "initial alignment direction of the liquid crystal cell" refers to a direction in which the in-plane refractive index of a liquid crystal layer, which is generated by aligning liquid crystal molecules contained in a liquid crystal layer described later in a state where no electric field is present, is maximized (i.e., a slow axis direction).

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 is substantially parallel to the initial alignment direction of the liquid crystal cell. That is, in the image display device 101, the absorption axis direction of the first polarizer 11 and the absorption axis direction of the second polarizer 41 are typically substantially orthogonal. With the above configuration, even when the display screen is viewed through a polarizing lens such as a polarizing sunglass, excellent visibility can be achieved.

In practical use, the image display apparatus 101 also has a backlight unit 90. The backlight unit 90 includes a light source 91 and a light guide plate 92. The backlight unit 90 may also have any suitable other components (e.g., diffuser sheet, prism sheet). In the illustrated example, the backlight unit 90 is of an edge-lit type, but any other suitable type (for example, a direct type) may be adopted as the backlight unit 90.

The image display device (liquid crystal display device) may further include any appropriate other member. For example, other optical compensation layers (phase difference layers) may be further provided. The optical characteristics, the number, the combination, the arrangement position, and the like of the other optical compensation layers can be appropriately selected according to the purpose, the desired optical characteristics, and the like. The configuration of an image display device (liquid crystal display device) which is conventionally known in the art can be used as items which are not described in the present specification.

Such an image display device is suitable for applications in which wide field angle in the horizontal direction and reduction in luminance of the area a during black display are particularly required (particularly, applications in which high definition is required and a screen can be shared by a plurality of people). The image display device is typically an in-vehicle display, a medical monitor, or a game monitor, and is preferably an in-vehicle display.

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

C. Polarizing plate

C-1 polarizer

As the first polarizer 11 included in the first polarizing plate 10 and the second polarizer 41 included in the second polarizing plate 40 (hereinafter, may be collectively referred to simply as polarizers), any appropriate polarizers may be used. 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 polarizers obtained by subjecting hydrophilic polymer films such as polyvinyl alcohol (PVA) -based films, partially formalized PVA-based films, and ethylene-vinyl acetate copolymer-based partially saponified films to dyeing treatment and stretching treatment with a dichroic substance such as iodine or a dichroic dye, and polyolefin-based oriented films such as dehydrated PVA products and desalted polyvinyl chloride products. From the viewpoint of excellent optical properties, it is preferable to use a polarizer obtained by dyeing a PVA-based film with iodine and uniaxially stretching the PVA film.

The dyeing with iodine is performed by, for example, immersing the PVA-based film in an aqueous iodine solution. The stretching ratio of the uniaxial stretching is preferably 3 to 7 times. The stretching may be performed after the dyeing treatment or simultaneously with the dyeing. Further, dyeing may be performed after stretching. The PVA-based film is subjected to swelling treatment, crosslinking treatment, washing treatment, drying treatment, and the like as necessary. For example, the PVA film may be washed with water by immersing in water before dyeing, whereby not only dirt and an anti-blocking agent on the surface of the PVA film can be washed but also the PVA film can be swollen to prevent uneven dyeing.

Specific examples of the polarizer obtained using the laminate include a laminate of a resin substrate and a PVA-based resin layer (PVA-based resin film) laminated on the resin substrate, and a polarizer obtained using a laminate of a resin substrate and a PVA-based resin layer formed by coating on the resin substrate. A polarizer obtained using a laminate of a resin substrate and a PVA-based resin layer formed on the resin substrate by coating can be produced, for example, by the following steps: coating a PVA-based resin solution on a resin base material, and drying the solution to form a PVA-based resin layer on the resin base material, thereby obtaining a laminate of the resin base material and the PVA-based resin layer; the laminate was stretched and dyed, and the PVA-based resin layer was used as a polarizer. In the present embodiment, the stretching typically includes immersing the laminate in an aqueous boric acid solution to perform stretching. The stretching may further include, if necessary, subjecting the laminate to in-air stretching at a high temperature (for example, 95 ℃ or higher) before stretching in the aqueous boric acid solution. 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 a polarizer), or the resin substrate may be peeled from the resin substrate/polarizer laminate and an arbitrary appropriate protective layer may be laminated on the peeled surface according to the purpose. Details of the method for producing such a polarizer are described in, for example, japanese patent laid-open No. 2012-73580 and japanese patent No. 6470455. The entire disclosures of these publications are incorporated herein by reference.

The thickness of the polarizer is, for example, 1 to 80 μm, preferably 1 to 15 μm, more preferably 1 to 12 μm, still more preferably 3 to 12 μm, and particularly preferably 3 to 8 μm. If the thickness of the polarizer is within the above range, the curling during heating can be favorably suppressed, and favorable durability of appearance during heating can be obtained.

Preferably, the polarizer exhibits absorption dichroism at any wavelength of 380nm to 780 nm. The polarizer has a monomer transmittance of, for example, 41.5 to 46.0%, preferably 43.0 to 46.0%, and more preferably 44.5 to 46.0%. The polarization degree of the polarizer is preferably 97.0% or more, more preferably 99.0% or more, and further 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. The protective layer can be arranged on at least one surface of the polarizer and can also be arranged on two surfaces of the polarizer. In the image display device 101, the first polarizing plate 10 has a protective layer 12 provided on a surface opposite to the visible side of the first polarizer 11, and the second polarizing plate 40 has a protective layer 42 provided on a surface of the second polarizer 41 on the visible side.

The protective layer is formed of any suitable film that can be used as a protective layer for a polarizer. Specific examples of the material that becomes the main component of the film include cellulose resins such as triacetyl cellulose (TAC), and transparent resins such as polyester, polyvinyl alcohol, polycarbonate, polyamide, polyimide, polyether sulfone, polysulfone, polystyrene, polynorbornene, polyolefin, (meth) acrylic, and acetate resins. Further, there may be mentioned thermosetting resins such as (meth) acrylic, urethane, (meth) acrylic urethane, epoxy, silicone, and the like, ultraviolet-curable resins, and the like. In addition, for example, a glassy polymer such as a siloxane polymer can be cited. Further, the polymer film described in Japanese patent application laid-open No. 2001-343529 (WO 01/37007) may be used. As a material of the film, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide in a side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in a side chain, for example, a resin composition having an alternating copolymer of isobutylene and N-methylmaleimide and an acrylonitrile-styrene copolymer can be used. The polymer film may be, for example, an extrusion-molded product of the resin composition.

When the polarizer disposed on the viewing side of the image display device 60 includes a protective layer located on the outermost surface of the image display device, the protective layer may be subjected to surface treatment such as hard coat treatment, antireflection treatment, anti-sticking treatment, and antiglare treatment as needed.

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

d. First phase difference layer

As described above, the refractive index characteristic of the first retardation layer 20 shows the relationship nz > nx > ny. The layer (film) exhibiting such refractive index characteristics as described above is also 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 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 the above range, the workability in the production is excellent, and the optical uniformity of the obtained image display device can be improved.

The first retardation layer may have any suitable configuration. Specifically, the retardation film may be a single retardation film, or may be a laminate of 2 or more retardation films which may be the same or different. In the case of a laminate, the first retardation layer may include an adhesive layer or an adhesive layer for bonding 2 or more retardation films. Preferably, the first retardation layer is a single retardation film. With such a configuration, it is possible to reduce the variation and unevenness of the phase difference value due to the shrinkage stress of the polarizer and/or the heat of the light source, and to contribute to the thinning of the obtained image display device.

The optical properties of the retardation film can be set to any appropriate values depending on the configuration of the first retardation layer. For example, when the first retardation layer is a single retardation film, the optical characteristics of the retardation film are preferably equal to those of the first retardation layer. Therefore, the retardation value of the adhesive layer, or the like used when the retardation film is laminated on the polarizer, the second retardation layer, or the like is preferably as small as possible.

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

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

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

The maleimide resin can be obtained by, for example, addition polymerization of a maleimide monomer. Examples of the maleimide monomer include: n-ethylmaleimide, N-cyclohexylmaleimide, N-phenylmaleimide, N- (2-methylphenyl) maleimide, N- (2-ethylphenyl) maleimide, N- (2-propylphenyl) maleimide, N- (2-isopropylphenyl) maleimide, N- (2, 6-dimethylphenyl) maleimide, N- (2, 6-dipropylphenyl) maleimide, N- (2, 6-diisopropylphenyl) maleimide, N- (2-methyl-6-ethylphenyl) maleimide, N- (2-chlorophenyl) maleimide, N- (2, 6-dichlorophenyl) maleimide, N- (2-bromophenyl) maleimide, N- (2, 6-dibromophenyl) maleimide, N- (2-biphenyl) maleimide, N- (2-cyanophenyl) maleimide. The maleimide monomer is available, for example, from Tokyo chemical industry Co.

In the above addition polymerization, the birefringence characteristics of the resin obtained can also be controlled by substituting the side chain after polymerization, or subjecting it to maleimide reaction, graft reaction, or the like.

The above-mentioned polymers exhibiting negative birefringence may also be copolymerized with other monomers. By copolymerizing with 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; (meth) acrylates such as methyl acrylate and methyl methacrylate; maleic anhydride; vinyl esters such as vinyl acetate.

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

As the above-mentioned polymer showing negative birefringence, a styrene-maleic anhydride copolymer, a styrene-acrylonitrile copolymer, a styrene- (meth) acrylate copolymer, a styrene-maleimide copolymer, a vinyl ester-maleimide copolymer, an olefin-maleimide copolymer, or the like is preferably used. They may be used alone or in combination of two or more. These polymers can exhibit high negative birefringence and are excellent in heat resistance. These polymers can be obtained, for example, from nova chemical japan, seikagawa chemical industries co.

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

In the above general formula (I), R ₁ ～R ₅ Each independently represents hydrogen, a halogen atom, a carboxylic acid, a carboxylic ester, a hydroxyl group, a nitro group, or a linear or branched alkyl or alkoxy group having 1 to 8 carbon atoms (wherein R is ₁ And R ₅ Not simultaneously hydrogen atom), R ₆ And R ₇ Represents hydrogen, a linear or branched alkyl group having 1 to 8 carbon atoms, or an alkoxy group, and n represents an integer of 2 or more.

The polymer exhibiting negative birefringence is not limited to the above-mentioned polymers, and a cycloolefin copolymer as disclosed in, for example, japanese patent application laid-open No. 2005-350544 can be used. Further, a composition containing a polymer and inorganic fine particles as disclosed in Japanese patent application laid-open Nos. 2005-156862 and 2005-227427 may be preferably used. One kind of polymer exhibiting negative birefringence may be used alone, or two or more kinds may be used in combination. Further, they may be used after modification by copolymerization, branching, crosslinking, molecular terminal modification (or capping), stereoregular modification, and the like.

The polymer film may contain any appropriate additive as needed. Specific examples of the additives include plasticizers, heat stabilizers, light stabilizers, lubricants, antioxidants, ultraviolet absorbers, flame retardants, colorants, antistatic agents, compatibilizers, crosslinking agents, and thickeners. The kind and content of the additive may be appropriately set according to the purpose. The content of the additive is typically about 3 to 10 parts by mass per 100 parts by mass of the total solid content of the polymer film. If the content of the additive is excessively increased, the transparency of the polymer film may be impaired or the additive may bleed out from the surface of the polymer film.

As the method for molding the polymer film, any appropriate molding method can be adopted. Examples thereof include compression molding, transfer molding, injection molding, extrusion molding, blow molding, powder molding, FRP molding, and solvent casting. Among them, extrusion molding and solvent casting are preferably used. This is because a retardation film having high smoothness and excellent optical uniformity can be obtained. Specifically, the extrusion molding method is a method of heating and melting a resin composition containing the above thermoplastic resin, plasticizer, additive, and the like, extruding the molten resin composition into a film shape on the surface of a casting roll by a T-die or the like, and then cooling the film to mold the film. The solvent casting method is a method of forming a film by deaerating a concentrated solution (dope) obtained by dissolving the above resin composition in a solvent, uniformly casting the solution in the form of a film on the surface of a metallic endless belt, a drum, a plastic substrate or the like, and evaporating the solvent. The molding conditions may be appropriately set according to the composition and type of the resin used, the molding method, and the like.

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

Specific examples of the stretching method include a longitudinal uniaxial stretching method, a transverse uniaxial stretching method, a longitudinal sequential biaxial stretching method, and a longitudinal simultaneous biaxial stretching method. Preferably, a transverse uniaxial stretching method, a longitudinal and transverse sequential biaxial stretching method, and a longitudinal and transverse simultaneous biaxial stretching method are used. This is because a biaxial retardation film can be obtained favorably. In the polymer exhibiting negative birefringence, since the refractive index in the stretching direction is relatively small as described above, the polymer film has a slow axis in the transport direction (the refractive index in the transport direction is nx) in the case of the transverse uniaxial stretching method. In the case of the longitudinal and transverse sequential biaxial stretching method and the longitudinal and transverse simultaneous biaxial stretching method, the slow axis can be set in both the transport direction and the width direction depending on the ratio of the longitudinal and transverse stretching magnifications. Specifically, if the stretch ratio in the vertical (conveyance) direction is relatively increased, the lateral (width) direction becomes the slow axis, and if the stretch ratio in the lateral (width) direction is relatively increased, the vertical (conveyance) direction becomes the slow axis.

As the stretching device used for the above stretching, any suitable stretching device may be used. Specific examples thereof include roll stretching machines, tenter stretching machines, pantograph type or linear motor type biaxial stretching machines. When the stretching is performed while heating, the temperature may be continuously changed or may be changed stepwise. The stretching step may be divided into 2 or more steps.

Further, by adjusting the thickness (blank thickness), stretching temperature and stretching ratio of the polymer film, the Re (550) and Nz coefficients of the first retardation layer can be adjusted to the above ranges.

The thickness (blank thickness) of the polymer film 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 120 μm or less.

The stretching temperature (temperature in the stretching oven when the polymer film is stretched) is preferably around the glass transition temperature (Tg) of the polymer film. Specifically, it is preferably (Tg-10) to (Tg + 30) deg.C, more preferably (Tg + 25) deg.C, and particularly preferably (Tg + 5) to (Tg + 20) deg.C. If the stretching temperature is too low, the retardation value or the direction of the slow axis may become uneven, or the polymer film may crystallize (become white turbid). On the other hand, if the stretching temperature is too high, the polymer film may melt or the appearance of retardation may become insufficient. The stretching temperature is typically 110 to 200 ℃. The glass transition temperature can be determined by DSC method in accordance with JIS K7121-1987.

The temperature in the stretching oven can be controlled by any appropriate method. Examples of the method include a method using the following apparatus: an air circulation type constant temperature oven in which hot air or cold air circulates, a heater using microwaves, far infrared rays, or the like, a roller for adjusting temperature to perform heating, a heat pipe roller, a metal belt, or the like.

The stretching ratio in stretching the polymer film may be set to any appropriate value depending on the composition of the polymer film, the type of volatile components and the like, the amount of volatile components and the like remaining, a desired retardation value, and the like. Preferably 1.05 times to 5.00 times, and more preferably 2.45 times to 5.00 times. In addition, the conveying speed during stretching is preferably 0.5 m/min to 20 m/min from the viewpoints of mechanical accuracy, stability, and the like of the stretching apparatus.

The method of obtaining a retardation film using a polymer exhibiting negative birefringence has been described above, but a retardation film may be obtained using a polymer exhibiting positive birefringence. As a method for obtaining a retardation film using a polymer exhibiting positive birefringence, for example, methods of increasing the refractive index in the thickness direction as disclosed in Japanese patent laid-open Nos. 2000-231016, 2000-206328, and 2002-207123 can be used. Specifically, a method of bonding a heat-shrinkable film to one surface or both surfaces of a film containing a polymer exhibiting positive birefringence and heat-treating the film is mentioned. By shrinking the heat-shrinkable film by a shrinking force of the film caused by heat treatment, the film is shrunk in the longitudinal direction and the width direction, whereby the refractive index in the thickness direction can be increased, and a retardation film having a refractive index ellipsoid in which nz > nx > ny can be obtained.

In this way, the positive B plate used for the first retardation layer can be produced using a polymer exhibiting birefringence of either positive or negative. In general, when a polymer showing positive birefringence is used, there is an advantage in that the number of selectable polymer types is large, and when a polymer showing negative birefringence is used, there is an advantage in that compared with the case of using a polymer showing positive birefringence, there are advantages in that: due to the stretching method, a retardation film having excellent uniformity in the slow axis direction can be easily obtained.

As the retardation film used for the first retardation layer, a commercially available optical film may be used as it is, in addition to the above-described film. Further, a commercially available optical film subjected to secondary processing such as stretching and/or relaxation may be used.

The light transmittance of the retardation film at a wavelength of 550nm 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 surface reflection is caused due to a difference in refractive index between air and the retardation film, so the achievable upper limit of the light transmittance is approximately 94%. The same light transmittance is also preferable for the entire first retardation layer.

The absolute value of the photoelastic coefficient of the retardation film is preferably 1.0 × 10 ^-10 (m ² /N) or less, more preferably 5.0X 10 ^-11 (m ² /N) or less, more preferably 3.0X 10 ^-11 (m ² /N) or less, particularly preferably 1.5X 10 ^-11 (m ² the/N) is as follows. By setting the photoelastic coefficient in such a range, an image display device having excellent optical uniformity, small change in optical characteristics even in an environment 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 5.0X 10 ^-13 (m ² /N) or more, preferably 1.0X 10 ^-12 (m ² /N) above. If the photoelastic coefficient is too small, the appearance of the phase difference may be small. The photoelastic coefficient is a value inherent to a chemical structure of a polymer or the like, and is obtained by copolymerizing or mixing plural components having different photoelastic coefficients in sign (positive or negative)Accordingly, the photoelastic coefficient can be reduced.

E. Second phase difference layer

As described above, the refractive index characteristic of the second retardation layer 30 shows the relationship of nx > ny = nz. A layer (film) exhibiting such refractive index characteristics is also sometimes referred to as a "positive uniaxial plate" or a "positive a plate". Here, "ny = nz" includes not only a case where ny and nz are strictly equal but also a case where ny and nz are substantially equal. Specifically, it means that the Nz coefficient exceeds 0.9 and is less than 1.1.

As a material for forming the second phase difference layer, any appropriate material can be used as long as the above-described characteristics can be obtained. Specifically, the second retardation layer may be an alignment cured layer of a liquid crystal compound (liquid crystal alignment cured layer) or a retardation film (stretched film of a polymer film).

In the case where the second retardation layer is a liquid crystal alignment cured layer, the difference between nx and ny of the resulting retardation layer can be made significantly larger than that of a non-liquid crystal material by using a liquid crystal compound, and therefore the thickness of the retardation layer for obtaining a desired in-plane retardation can be made significantly smaller. As a result, the polarizing plate with a retardation layer (and consequently, the image display device) can be further thinned. In the present specification, the "alignment cured layer" refers to a layer in which a liquid crystal compound is aligned in a predetermined direction within the layer and the alignment state is fixed. The "alignment cured layer" is a concept including an alignment cured layer obtained by curing a liquid crystal monomer as described below. In this embodiment, typically, the rod-like liquid crystal compound is aligned in a state of being aligned in the slow axis direction of the second phase difference layer (uniform alignment).

Examples of the liquid crystal compound include a liquid crystal compound in which a 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. The mechanism of developing the liquid crystallinity of the liquid crystal compound may be 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 crystalline monomer, for example, a polymerizable monomer and/or a crosslinkable monomer is preferable. This is because the alignment state of the liquid crystalline monomer can be fixed by polymerizing or crosslinking the liquid crystalline monomer. After the liquid crystal monomers are aligned, for example, if the liquid crystal monomers are polymerized or crosslinked with each other, the alignment state can be fixed. Here, although polymers are formed by polymerization and three-dimensional network structures are formed by crosslinking, they are non-liquid crystalline. Therefore, the second retardation layer formed does not undergo transition to a liquid crystal phase, a glass phase, or a crystal phase due to, for example, a temperature change unique to the liquid crystalline compound. As a result, the formed second retardation layer is a retardation layer which is not affected by temperature change and has extremely excellent stability.

Specific examples of the liquid crystal compound and details of the method for forming the liquid crystal alignment cured layer are described in, for example, japanese patent laid-open nos. 2006-163343 and 2006-178389. The contents of these publications are incorporated herein by reference.

As described above, the second phase difference layer may be a stretched film of a polymer film. Specifically, the second retardation layer having the desired optical properties (for example, refractive index properties, in-plane retardation, and retardation in the thickness direction) can be obtained by appropriately selecting the type of polymer, the stretching conditions (for example, stretching temperature, stretching ratio, and stretching direction), and the stretching method (for example, transverse uniaxial stretching). In particular, by adjusting the thickness (blank thickness), stretching temperature, and stretching ratio of the polymer film, re (550) of the second phase difference layer can be adjusted to the above-mentioned ranges.

The thickness of the polymer film (blank thickness) is typically 10 μm or more, preferably 15 μm or more, and typically 50 μm or less, preferably 40 μm or less, and more preferably 30 μm or less.

The stretching temperature is preferably 110 to 170 ℃ and more preferably 130 to 150 ℃. The stretch ratio is preferably 1.37 to 3.00 times, and more preferably 1.60 to 2.50 times.

As the resin for forming the polymer film, any appropriate resin can be used. Specific examples thereof include resins constituting a positive birefringent film, 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 polymerized using a norbornene-based monomer as a polymerization unit. Examples of the norbornene-based monomer include norbornene, and alkyl and/or alkylidene substituents thereof, for example, polar group substituents such as 5-methyl-2-norbornene, 5-dimethyl-2-norbornene, 5-ethyl-2-norbornene, 5-butyl-2-norbornene, 5-ethylidene-2-norbornene, and halogen thereof; dicyclopentadiene, 2, 3-dihydrodicyclopentadiene, and the like; methyl octahydronaphthalene, alkyl and/or alkylidene substitutes thereof, and polar group substitutes such as halogen, for example, 6-methyl-1, 4:5, 8-dimethylbridge-1, 4,4a,5,6,7,8, 8a-octahydronaphthalene, 6-ethyl-1, 4:5, 8-dimethylbridge-1, 4,4a,5,6,7,8, 8a-octahydronaphthalene, 6-ethylidene-1, 4:5, 8-dimethylbridge-1, 4a,5,6,7,8 a-octahydronaphthalene, 6-chloro-1, 4:5, 8-dimethylbridge-1, 4,4a,5,6,7,8, 8a-octahydronaphthalene, 6-cyano-1, 4:5, 8-dimethylbridge-1, 4,4a,5,6,7,8, 8a-octahydronaphthalene, 6-pyridyl-1, 4:5, 8-dimethylbridge-1, 4,4a,5,6,7,8, 8a-octahydronaphthalene, 6-methoxycarbonyl-1, 4:5, 8-dimethylbridge-1, 4,4a,5,6,7,8, 8a-octahydronaphthalene; 3-4 mers of cyclopentadiene, for example, 4,9:5, 8-dimethylbridge-3a, 4,4a,5,8,8a,9, 9a-octahydro-1H-benzindene, 4, 11:5,10: 6,9-trimethylbridge-3a, 4,4a,5,5a,6,9,9a,10, 10a,11 a-dodecahydro-1H-cyclopenta-anthracene. 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. The aromatic polycarbonate is typically obtained by reacting a carbonate precursor with an aromatic dihydric phenol compound. Specific examples of the carbonate precursor include phosgene, bischloroformates of diphenols, diphenyl carbonate, di-p-tolyl carbonate, phenyl-p-tolyl carbonate, di-p-chlorophenyl carbonate and dinaphthyl carbonate. Among them, phosgene and diphenyl carbonate are preferable. As specific examples of the aromatic dihydric phenol compound, examples thereof include 2, 2-bis (4-hydroxyphenyl) propane, 2-bis (4-hydroxy-3, 5-dimethylphenyl) propane, bis (4-hydroxyphenyl) methane, 1-bis (4-hydroxyphenyl) ethane, 2-bis (4-hydroxyphenyl) butane, and the like 2, 2-bis (4-hydroxy-3, 5-dimethylphenyl) butane, 2-bis (4-hydroxy-3, 5-dipropylphenyl) propane, 1-bis (4-hydroxyphenyl) cyclohexane, 1-bis (4-hydroxyphenyl) -3, 5-trimethylcyclohexane. These may be used alone or in combination of two or more. Preference is given to using 2, 2-bis (4-hydroxyphenyl) propane, 1-bis (4-hydroxyphenyl) cyclohexane, 1-bis (4-hydroxyphenyl) -3, 5-trimethylcyclohexane. Particularly preferably, 2-bis (4-hydroxyphenyl) propane and 1, 1-bis (4-hydroxyphenyl) -3, 5-trimethylcyclohexane are used simultaneously.

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

The thickness of the second retardation layer can be set in such a manner that desired optical characteristics are obtained. When the second retardation layer is a liquid crystal alignment cured layer, the thickness is preferably 0.5 to 10 μm, more preferably 0.5 to 8 μm, and still more preferably 0.5 to 5 μm. When the second retardation layer is a stretched film of a polymer film, the thickness is preferably 5 to 55 μm, more preferably 10 to 50 μm, and still more preferably 15 to 45 μm.

F. Laminate of first retardation layer and second retardation layer

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

Re(450)/Re(550)>0.82

Re(650)/Re(550)<1.18。

the Re (450)/Re (550) of the laminate is more preferably 1.0 to 1.2, and still more preferably 1.0 to 1.1. The Re (650)/Re (550) of the laminate is more preferably 0.8 to 1.0, and still more preferably 0.9 to 1.0. According to the embodiments of the present invention, a retardation layer-equipped polarizing plate that can realize an image display device having a small luminance in an oblique direction and a small color shift in an oblique direction in black display, although the first retardation layer and the second retardation layer do not exhibit ideal inverse dispersion characteristics as a whole, 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, and the liquid crystal layer 61 includes liquid crystal molecules aligned in a uniform manner 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 the other substrate (typically, the second substrate 63) is provided with: a switching element for controlling electro-optical characteristics of the liquid crystal; a scanning line for supplying a gate signal to the switching element and a signal line for supplying a source signal to the switching element; and a pixel electrode and a counter electrode. The interval (cell gap) between the substrates is controlled by spacers. An alignment film made of, for example, polyimide may be provided on the side of the substrate that contacts the liquid crystal layer.

The Rth (550) of the first substrate 62 and the second substrate 63 are-10 nm to 100nm, respectively. In one embodiment, the Rth (550) of at least one of the first substrate 62 and the second substrate 63 is preferably 8nm to 90nm, more preferably 15nm to 80nm. In another embodiment, the Rth (550) of at least one of the first substrate 62 and the second substrate 63 is preferably-0.1 nm or less, and more preferably-5 nm to-50 nm. According to the embodiments of the present invention, when the substrate has such a thickness direction phase difference, the black luminance in an oblique direction can be sufficiently reduced in the liquid crystal display device including the liquid crystal cells in uniform alignment.

In one embodiment, at least one of the first substrate 62 and the second substrate 63 satisfies the relationship Rth (450) > Rth (550), and preferably both of the first substrate 62 and the second substrate 63 satisfy the relationship Rth (450) > Rth (550). More preferably, at least one of the first substrate 62 and the second substrate 63 further satisfies the relationship Rth (550) > Rth (650), and still more preferably, both the first substrate 62 and the second substrate 63 further satisfy the relationship Rth (550) > Rth (650). According to the embodiments of the present invention, even when the substrate has such a wavelength dispersion characteristic as described above, it is possible to sufficiently reduce the black luminance in the oblique direction in the liquid crystal display device including the liquid crystal cells in the uniform alignment.

As described above, the liquid crystal layer 61 contains liquid crystal molecules aligned to be uniformly aligned in the absence of an electric field. The term "liquid crystal molecules aligned in a uniform manner" refers to a state in which the alignment vectors of the liquid crystal molecules are aligned in parallel to the substrate plane and in the same manner as a result of the interaction between the substrate subjected to the alignment treatment and the liquid crystal molecules. The liquid crystal layer (the result is a liquid crystal cell) as described above 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. Re (550) of the liquid crystal layer may be, for example, 300nm to 400nm. The Nz coefficient of the liquid crystal layer may be, for example, 0.9 to 1.1.

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

Examples of the driving mode of the liquid crystal cell 60a include an in-plane switching (IPS) mode and a Fringe Field Switching (FFS) mode. The IPS mode includes a super-flat switch (S-IPS) mode and an advanced super-flat switch (AS-IPS) mode using V-shaped electrodes, zigzag electrodes, or the like. The FFS mode includes an advanced fringe field switching (a-FFS) mode and a super fringe field switching (U-FFS) mode using V-shaped electrodes, zigzag electrodes, or the like. As a driving mode of the liquid crystal cell 60a, an in-plane switching (IPS) mode is preferably cited.

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

H. Backlight unit

The light source 91 is disposed at a position corresponding to a 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 suitable light guide plate can be used. For example, a light guide plate having a lens pattern formed on the back surface side and a light guide plate having a prism shape or the like formed on the back surface side and/or the visible side are used in order to deflect light from the lateral direction in the thickness direction. A light guide plate having prism shapes formed on the back surface side and the visible side is preferably used. In this light guide plate, it is preferable that the prism shape formed on the back surface side and the prism shape formed on the visible side have ridge line directions orthogonal to each other. If such a light guide plate as described above is used, light that is more easily condensed can be made incident to the prism sheet (not shown).

Examples

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. The measurement method of each property is as follows.

(1) Determination of phase difference

The in-plane retardation of the first retardation layer and the second retardation layer used in the examples and comparative examples was measured automatically using KOBRA-WPR manufactured by prince instruments. The measurement wavelength was 550nm and the measurement temperature was 23 ℃.

(2) Brightness in black display

The black screen was displayed on the image display devices obtained in the examples and comparative examples, and measurement was performed by a luminance meter (manufactured by AUTONIC-MELCHERS, trade name "Conscope"). Specifically, the luminance was measured by changing the polar angle from 0 ° to 80 ° and the azimuth angle from 0 ° to 360 °.

In addition, the luminance at any of 40 ° polar angle, 20 °, 25 °, 155 °, 160 °, 190 °, 195 °, 345 ° and 350 ° in the luminance measured as described above was taken as the luminance of the region A (unit: cd/m) ² ) The maximum luminance is set as the maximum luminance of the area a (unit: cd/m ² )。

< preparation of polarizing plate >

< production example 1>

As the thermoplastic resin substrate, a long-sized amorphous isophthalic acid copolymerized polyethylene terephthalate film (thickness: 100 μm) having a Tg of about 75 ℃ was used, and one surface of the resin substrate was subjected to corona treatment.

Polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (product name "Gohsefimer" manufactured by japan synthetic chemical industries) were mixed at a ratio of 9:1 to 100 parts by weight of the PVA-based resin mixed together, 13 parts by weight of potassium iodide was added, and the resultant was dissolved in water to prepare a PVA aqueous solution (coating solution).

The 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 ℃.

The resulting laminate was uniaxially stretched to 2.4 times in the longitudinal direction (longitudinal direction) in an oven at 130 ℃ (in-air assisted stretching treatment).

Next, the laminate was immersed in an insolubilization bath (an aqueous boric acid solution prepared by adding 4 parts by weight of boric acid to 100 parts by weight of water) having a liquid temperature of 40 ℃ for 30 seconds (insolubilization treatment).

Next, the resultant polarizer was immersed in a dyeing bath (an aqueous iodine solution prepared by mixing iodine and potassium iodide at a weight ratio of 1.

Subsequently, the substrate was immersed in a crosslinking bath (an aqueous boric acid solution prepared by mixing 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 ℃ for 30 seconds (crosslinking treatment).

Then, while immersing the laminate in an aqueous boric acid solution (boric acid concentration of 4 wt%, potassium iodide concentration of 5 wt%) having a liquid temperature of 70 ℃, uniaxial stretching was performed at a total stretching ratio of 5.5 times in the longitudinal direction (longitudinal direction) between rolls having different peripheral speeds (underwater stretching treatment).

Then, the laminate was immersed in a cleaning bath (aqueous solution containing 4 parts by weight of potassium iodide per 100 parts by weight of water) having a liquid temperature of 20 ℃ (cleaning treatment).

Then, drying was performed in an oven maintained at about 90 ℃ while being brought into contact with a heated roll made of SUS whose surface temperature was maintained at about 75 ℃ (drying shrinkage treatment).

In this manner, a polarizer having a thickness of about 5 μm was formed on the resin substrate, and a laminate having a structure of the resin substrate/polarizer was obtained.

An HC-TAC film (20 μm thick) was bonded as a protective layer to the polarizer surface (the surface opposite to the resin substrate) of the obtained laminate. Subsequently, the resin substrate was peeled off to obtain a polarizing plate having a protective layer/polarizer structure. Then, the obtained polarizing plate is punched out to have a size corresponding to a liquid crystal cell described later.

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

< production example 2>

A pellet-like resin of a styrene-maleic anhydride copolymer (product name: dylark D232, manufactured by Norwalk chemical Japan) was extruded at 270 ℃ using a single-screw extruder and a T-die, and the sheet-like molten resin was cooled by a cooling drum to obtain a film having a thickness of 100. Mu.m. The film was subjected to free-end uniaxial stretching in the transport direction at a temperature of 130 ℃ and a stretching ratio of 2.5 times using a roll stretcher to obtain a film having a fast axis in the transport direction (longitudinal stretching step).

The obtained film was subjected to fixed-end uniaxial stretching in the width direction at a temperature of 135 ℃ using a tenter stretcher so that the film width became 4.5 times the film width after the longitudinal stretching, to thereby obtain a retardation film (biaxially stretched film, positive B plate) having a thickness of 14 μm (transverse stretching step). Then, the obtained retardation film is punched out to have a size corresponding to a liquid crystal cell described later.

The retardation film (positive B plate) obtained in this way has a fast axis (slow axis in the width direction) in the transport direction, and the refractive index characteristic shows a relationship nz > nx > ny. The in-plane retardation Re (550), the thickness direction retardation Rth (550), and the Nz coefficient of the retardation film (positive B plate) are shown in table 1.

< production example 3>

A retardation film (positive B plate) was obtained in the same manner as in production example 2, except that the longitudinal stretching magnification was changed to 1.7 times and the transverse stretching magnification was changed to 1.8 times.

< production example 4>

A retardation film (positive B plate) was obtained in the same manner as in production example 2, except that the longitudinal stretching magnification was changed to 1.5 times and the transverse stretching magnification was changed to 1.5 times.

< production example 5>

A retardation film (positive B plate) was obtained in the same manner as in production example 2, except that the longitudinal stretching magnification was changed to 1.4 times and the transverse stretching magnification was changed to 1.4 times.

< production example 6>

A retardation film (positive B plate) was obtained in the same manner as in production example 2, except that the longitudinal stretching magnification was changed to 2.2 times and the transverse stretching magnification was changed to 2.4 times.

< production of retardation film (Positive A plate) having refractive index characteristic nx > ny = nz >

< production example 7>

A long norbornene resin film (trade name Zeonor, manufactured by ZEON Co., ltd., japan) having a thickness of 40 μm and a photoelastic coefficient of 3.10X 10 was used ^-12 m ² N) was uniaxially stretched at 135 c by a factor of 2.0 to produce a retardation film having a thickness of 28 μm. Then, the obtained retardation film is punched out to have a size corresponding to a liquid crystal cell described later.

The retardation film obtained by the above operation has a slow axis in the transport direction, and the refractive index characteristic shows a relationship of nx > ny = nz. The in-plane retardation Re (550), the thickness direction retardation Rth (550), and the Nz coefficient of the retardation film (positive a plate) are shown in table 1.

< production example 8>

A retardation film (positive a plate) was obtained in the same manner as in production example 7, except that the stretching ratio was changed to 1.5.

< production example 9>

A retardation film (positive a plate) was obtained in the same manner as in production example 7, except that the stretching ratio was changed to 1.43 times.

< production example 10>

A retardation film (positive a plate) was obtained in the same manner as in production example 7, except that the stretching ratio was changed to 1.37 times.

< production example 11>

A retardation film (positive a plate) was obtained in the same manner as in production example 7, except that the stretching ratio was changed to 1.2 times.

< production of retardation film (Positive C plate) having refractive index characteristics 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 in the thickness direction Rth was changed to-86 nm. Then, the obtained retardation film is punched out to have a size corresponding to a liquid crystal cell described later.

The retardation film obtained by the above-described operation has a slow axis in the transport direction, and the refractive index characteristic shows a relationship of nz > nx = ny. The in-plane retardation Re (550) and the thickness direction retardation Rth (550) of the retardation film (positive C plate) are shown in table 1.

< production example 13>

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

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

< 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 was transversely stretched 1.35 times. Then, the obtained retardation film is punched out to have a size corresponding to a liquid crystal cell described later.

The refractive index characteristics of the retardation film obtained by the above-described operation show a relationship of nx > ny > nz. The in-plane retardation Re (550) and the thickness direction retardation Rth (550) of the retardation film (negative B plate) are shown in table 1.

< production example 15>

A retardation film (negative B plate) was obtained in the same manner as in production example 14, except that the stretching magnification was changed to 1.3 times.

< production example 16>

A retardation film (negative B plate) was obtained in the same manner as in production example 14, except that the stretching ratio was changed to 1.2 times.

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

< production example 17>

A pellet-like resin of a styrene-maleic anhydride copolymer (manufactured by Norwalk chemical Japan, trade name "Dylark D232") was extruded at 270 ℃ using a single-screw extruder and a T-die, and the sheet-like molten resin was cooled with a cooling drum, thereby obtaining a film having a thickness of 30 μm. The film was subjected to free-end uniaxial stretching in the conveying direction at a temperature of 130 ℃ and a stretching ratio of 1.8 times using a roll stretcher, thereby obtaining a retardation film (negative a plate) having a fast axis in the conveying direction. Then, the obtained retardation film is punched out to have a size corresponding to a liquid crystal cell described later.

The refractive index characteristics of the retardation film obtained by the above-described operation show a relationship of nx = nz > ny. The in-plane retardation Re (550) and the thickness direction retardation Rth (550) of the retardation film (negative a plate) are shown in table 1.

< preparation of image display Unit (liquid Crystal Unit) >

< production example 18>

The 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 are removed, and the removed surfaces (outer surfaces of the substrates) are cleaned. It is used as an image display unit (liquid crystal unit). Rth (450) =32nm, rth (550) =19nm, rth (650) =23nm of the first substrate of the liquid crystal cell; rth (450) =9nm, rth (550) =0.3nm, rth (650) = -6nm for the second substrate.

[ example 1]

The polarizing plate (second polarizing plate including a second polarizer) of production example 1 was laminated on the viewing side of the liquid crystal cell of production example 18. On the other hand, 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 polarizing plate including first polarizer) of production example 1 were laminated in this order on the back side of the liquid crystal cell. The lamination was performed as follows: the absorption axis direction of the first polarizer is substantially orthogonal to the slow axis direction of the first retardation layer, the absorption axis direction of the first polarizer is substantially parallel to the slow axis direction of the second retardation layer, the absorption axis direction of the first polarizer is substantially orthogonal to the initial alignment direction of the liquid crystal cell, and the absorption axis direction of the second polarizer is substantially parallel to the initial alignment direction of the liquid crystal cell. In this way, an image display device (E-mode liquid crystal display device) was produced. Next, the image display device is subjected to the luminance measurement at the time of the black display. The luminance distribution diagram in the image display device of example 1 is shown in fig. 3. In addition, the maximum luminance of the area a in the image display device of example 1 is shown in table 1.

Comparative examples 1 to 8

An image display device (E-mode liquid crystal display device) was produced in the same manner as in example 1, except that the retardation film (second retardation layer) of production example 7 and the retardation film (first retardation layer) of production example 2 were each changed to the retardation film of the production example shown in table 1. Next, the image display device is subjected to the luminance measurement at the time of the black display. The luminance distribution diagram in the image display device of comparative example 1 is shown in fig. 4. Table 1 shows the maximum luminance of the region a in the image display devices of comparative examples 1 to 8.

TABLE 1

[ evaluation ]

As is apparent from table 1, fig. 3, and fig. 4, since Re (550) and Nz coefficient of the first retardation layer are within the above-described ranges and Re (550) of the second retardation layer is within the above-described ranges, it is possible to realize an image display device (liquid crystal display device) which can secure a wider angle of view in the lateral direction (left-right direction X of the paper surface in fig. 3 and fig. 4) than that in the vertical direction (up-down direction Y of the paper surface in fig. 3 and fig. 4) and in which the maximum luminance of the above-described region a is sufficiently small.

Industrial applicability

The polarizing plate with a retardation layer according to the embodiment of the present invention is suitably used for an image display device, and particularly, is suitably used for a liquid crystal display device.

Claims (4)

1. A polarizing plate with a phase difference layer, comprising:

a first polarizer including a first polarizer;

a first retardation layer which is disposed adjacent to the first polarizer and has a refractive index characteristic exhibiting a relationship of nz > nx > ny; and

a second phase difference layer which is disposed adjacent to the first phase difference layer and has a refractive index characteristic showing a relationship of nx > ny = nz,

wherein an absorption axis of the first polarizer is substantially orthogonal to a slow axis of the first retardation layer,

the absorption axis of the first polarizer is substantially parallel to the slow axis of the second phase difference layer,

the in-plane retardation Re (550) of the first retardation layer is 280 to 360nm,

the Nz coefficient of the first phase difference layer is-1.0 to-0.1,

the in-plane retardation Re (550) of the second retardation layer is 280 to 360nm.

2. An image display device, comprising:

an image display unit; and

the polarizing plate with a retardation layer according to claim 1, which is disposed on the side opposite to the viewing side with respect to the image display unit.

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

4. The image display device according to claim 3, wherein the image display device has a second polarizing plate disposed on a side opposite to the polarizing plate with the phase difference layer with respect to the image display unit,

said second polarizer comprises a second polarizer,

the absorption axis of the first polarizer is substantially orthogonal to the initial alignment direction of the liquid crystal cell,

the absorption axis of the second polarizer is substantially parallel to the initial orientation direction of the liquid crystal cell.

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