JP2008009388A - Liquid crystal panel and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal device having a high contrast ratio in a forward direction. <P>SOLUTION: The liquid crystal device comprises a liquid crystal cell, a first polarizing plate arranged on one side of the liquid crystal cell, a second polarizing plate arranged on the other side of the liquid crystal cell, and a phase difference layer arranged between the liquid crystal cell and the second polarizing plate. The liquid crystal device uses a liquid crystal panel, in which a refractive index ellipsoid of the phase difference layer indicates relations of nx≥ny≥nz and in which the second polarizing plate has a transmittivity (T<SB>2</SB>) larger than the transmittivity (T<SB>1</SB>) of the first polarizing plate. This liquid crystal panel exhibits such display characteristics as have a drastically higher and more excellent contrast ratio in the forward direction than that of the liquid crystal panel of the prior art, in which two polarizing plates arranged on the two sides of the liquid crystal cell have equal transmittivities. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a liquid crystal panel including a polarizing plate with adjusted transmittance and a retardation layer.

A liquid crystal display device (hereinafter referred to as LCD) is a device that displays characters and images using the electro-optical characteristics of liquid crystal molecules. The LCD normally uses a liquid crystal panel in which polarizing plates are arranged on both sides of the liquid crystal cell. For example, in the normally black method, a black image can be displayed in a state where no voltage is applied. The LCD has a problem that the contrast ratio in the front and oblique directions is low. In order to solve this problem, a liquid crystal panel using a retardation film is disclosed (for example, see Patent Document 1). However, the market demands higher performance of the LCD, and as one of them, there is a demand for a liquid crystal display device having a higher contrast ratio capable of clearly drawing characters and images.
Japanese Patent No. 3648240

  An object of the present invention is to provide a liquid crystal display device having a high contrast ratio in the front direction.

  As a result of intensive studies, the present inventors have found that the above object can be achieved by a liquid crystal panel shown below, and have completed the present invention.

The liquid crystal panel of the present invention comprises a liquid crystal cell,
A first polarizing plate disposed on one side of the liquid crystal cell;
A second polarizing plate disposed on the other side of the liquid crystal cell;
Comprising at least a retardation layer disposed between the liquid crystal cell and the second polarizing plate;
The refractive index ellipsoid of the retardation layer shows a relationship of nx ≧ ny> nz,
The transmittance (T ₂ ) of the _second polarizing plate is larger than the transmittance (T ₁ ) of the _first polarizing plate.

In a preferred embodiment, the difference (ΔT = T ₂ −T ₁ ) between the transmittance (T ₂ ) of the _second polarizing plate and the transmittance (T ₁ ) of the first polarizing plate is 0. 1% to 6.0%.

  In a preferred embodiment, the liquid crystal cell includes liquid crystal molecules aligned in a homeotropic alignment.

  In a preferred embodiment, the first polarizing plate is disposed on the viewing side of the liquid crystal cell, and the second polarizing plate is disposed on the side opposite to the viewing side of the liquid crystal cell.

Preferably, the first polarizer includes a first polarizer, the second polarizer includes a second polarizer, and each of the first polarizer and the second polarizer is iodine. The main component is a polyvinyl alcohol-based resin containing

In a preferred embodiment, the difference (ΔI = I ₁ −I ₂ ) between the iodine content (I ₁ ) of the _first polarizer and the iodine content (I ₂ ) of the second polarizing plate is 0.1% by weight to 2.6% by weight.

  In preferable embodiment, the iodine content of a said 1st polarizer and a said 2nd polarizer is 1.8 weight%-5.0 weight%, respectively.

  In a preferred embodiment, the retardation value (Rth [590]) in the thickness direction at a wavelength of 590 nm of the retardation layer is 100 nm to 400 nm.

  In a preferred embodiment, the Nz coefficient of the retardation layer is more than 1.1 and 8 or less.

  In a preferred embodiment, the retardation layer is a retardation film containing a polyimide resin or a norbornene resin.

  According to another aspect of the present invention, a liquid crystal display device is provided. The liquid crystal display device includes the liquid crystal panel.

  The liquid crystal display device including the liquid crystal panel of the present invention has a contrast ratio in the front direction that is significantly higher than that of a conventional liquid crystal panel by using two polarizing plates with adjusted transmittance and a retardation layer. Excellent display characteristics.

<Definition of terms and symbols>
The definitions of terms and symbols in this specification are as follows.
(1) The transmittance transmittance (T) of the polarizing plate is a Y value obtained by correcting the visibility with a 2-degree visual field (C light source) of JlS Z 8701-1982.
(2) Refractive index (nx, ny, nz):
“Nx” is the refractive index in the direction in which the in-plane refractive index is maximum (ie, the slow axis direction), and “ny” is the direction orthogonal to the slow axis in the plane (ie, the fast axis direction). “Nz” is the refractive index in the thickness direction.
(3) In-plane retardation value:
The in-plane retardation value (Re [λ]) refers to the in-plane retardation value of the film at a wavelength λ (nm) at 23 ° C. Re [λ] is obtained by Re [λ] = (nx−ny) × d, where d (nm) is the thickness of the film.
(4) Thickness direction retardation value:
The retardation value in the thickness direction (Rth [λ]) refers to the retardation value in the thickness direction of the film at 23 ° C. and the wavelength λ (nm). Rth [λ] is determined by Rth [λ] = (nx−nz) × d, where d (nm) is the thickness of the film.
(5) Birefringence in the thickness direction:
The birefringence (Δn _xz [λ]) in the thickness direction is a value calculated by the formula: Rth [λ] / d.
(6) Nz coefficient:
The Nz coefficient is a value calculated by the formula: Rth [590] / Re [590].
(7) In this specification, the description “nx = ny” or “ny = nz” includes not only the case where they are completely the same, but also the case where they are substantially the same. Therefore, for example, the description of nx = ny includes the case where Re [590] is less than 10 nm.
(8) In this specification, “substantially orthogonal” includes a case where an angle formed by two optical axes is 90 ° ± 2 °, and preferably 90 ° ± 1 °. “Substantially parallel” includes a case where an angle formed by two optical axes is 0 ° ± 2 °, and preferably 0 ° ± 1 °.

<A. Overview of LCD panel>
The liquid crystal panel of the present invention includes a liquid crystal cell, a first polarizing plate disposed on one side of the liquid crystal cell, a second polarizing plate disposed on the other side of the liquid crystal cell, and the first At least a retardation layer (A) disposed between the second polarizing plate and the second polarizing plate. In the retardation layer (A), the refractive index ellipsoid shows a relationship of nx ≧ ny> nz. The transmittance (T ₂ ) of the _second polarizing plate is larger than the transmittance (T ₁ ) of the _first polarizing plate. Such a liquid crystal panel has a significantly higher contrast ratio in the front direction than a conventional liquid crystal panel (typically, the transmittance of two polarizing plates arranged on both sides of a liquid crystal cell is the same). It has the feature of being high. As described above, the present inventors have found for the first time that the contrast ratio in the front direction is greatly improved by using two polarizing plates whose transmittances are adjusted on both sides of the liquid crystal cell and the retardation layer. This is an unexpectedly superior effect.

The difference (ΔT = T ₂ −T ₁ ) between the transmittance (T ₂ ) of the _second polarizing plate and the transmittance (T ₁ ) of the first polarizing plate is preferably 0.1% to 6 0.0%, more preferably 0.1% to 4.5%, particularly preferably 0.2% to 3.0%, and most preferably 0.2% to 1.5%. . By using two polarizing plates having a transmittance difference in the above range, the liquid crystal panel of the present invention can obtain a liquid crystal display device having a higher contrast ratio in the front direction.

  FIG. 1 is a schematic sectional view of a liquid crystal panel of the present invention. It should be noted that, for the sake of easy understanding, the ratio of the vertical, horizontal, and thickness of each component shown in FIG. 1 is different from the actual ratio. A liquid crystal panel 100 of FIG. 1 includes a liquid crystal cell 10, a first polarizing plate 21 disposed on one side of the liquid crystal cell 10, and a second polarizing plate 22 disposed on the other side of the liquid crystal cell 10. And at least a retardation layer 30 disposed between the liquid crystal cell 10 and the second polarizing plate 22. The illustrated example shows a configuration in which the first polarizing plate 21 is on the upper side and the second polarizing plate 22 is on the lower side. However, the liquid crystal panel of the present invention is an inverted version of this configuration. May be. Practically, an arbitrary adhesive layer and / or other optical member (not shown) is provided between the liquid crystal cell 10 and the first polarizing plate 21 and between the liquid crystal cell 10 and the second polarizing plate 22. Are arranged).

  The liquid crystal panel is preferably of a normally black type. In this specification, the “normally black method” refers to a liquid crystal panel that is designed so that the transmittance is minimized when the voltage is not applied (the screen becomes black) and the transmittance is increased when the voltage is applied. Say. The effect of improving the front contrast ratio is particularly remarkable in a normally black liquid crystal panel that performs black display when no voltage is applied. It is considered that the effect obtained by using two polarizing plates having different transmittances is not hindered by driving of liquid crystal molecules.

<B. Liquid crystal cell>
Any appropriate liquid crystal cell may be employed as the liquid crystal cell used in the present invention. Examples of the liquid crystal cell include an active matrix type using a thin film transistor and a simple matrix type used in a super twist nematic liquid crystal display device.

  The liquid crystal cell preferably includes a pair of substrates and a liquid crystal layer as a display medium sandwiched between the pair of substrates. One substrate (active matrix substrate) includes a switching element (typically a TFT) for controlling the 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. Provided. The other substrate (color filter substrate) is provided with a color filter.

  The color filter may be provided on the active matrix substrate. Alternatively, when an RGB three-color light source (which may further include a multicolor light source) is used as the illumination means of the liquid crystal display device as in the field sequential method, the color filter can be omitted. The distance between the two substrates is controlled by a spacer. For example, an alignment film made of polyimide is provided on the side of each substrate in contact with the liquid crystal layer. Alternatively, for example, when the initial alignment of liquid crystal molecules is controlled using a fringe electric field formed by a patterned transparent electrode, the alignment film can be omitted.

  The liquid crystal cell preferably includes liquid crystal molecules aligned in a homeotropic alignment. In this specification, “homeotropic alignment” means a state in which the alignment vector of liquid crystal molecules is aligned perpendicularly (in the normal direction) to the substrate plane as a result of the interaction between the alignment-treated substrate and the liquid crystal molecules. Refers to things. The homeotropic alignment includes a case where the alignment vector of the liquid crystal molecules is slightly inclined with respect to the normal direction of the substrate, that is, a case where the liquid crystal molecules have a pretilt. When the liquid crystal molecules have a pretilt, the pretilt angle (angle from the substrate normal) is preferably 5 ° or less. By setting the pretilt angle in the above range, a liquid crystal display device with a high contrast ratio can be obtained.

  In the liquid crystal cell, the refractive index ellipsoid preferably has a relationship of nz> nx = ny. As a drive mode using a liquid crystal cell in which the refractive index ellipsoid has a relationship of nz> nx = ny, for example, a vertical alignment (VA) mode, a twisted nematic (TN) mode, a vertical alignment type electric field control birefringence ( ECB) mode, optical compensation birefringence (OCB) mode, and the like. Preferably, the liquid crystal cell is in a vertical alignment (VA) mode.

The VA mode liquid crystal cell utilizes a voltage-controlled birefringence effect, and makes liquid crystal molecules aligned in a homeotropic alignment respond to the substrate with an electric field in a normal direction in the absence of an electric field. Specifically, as described in, for example, Japanese Patent Application Laid-Open No. 62-210423 and Japanese Patent Application Laid-Open No. 4-153621, in the case of a normally black method, liquid crystal molecules are formed on a substrate in the absence of an electric field. Therefore, when the upper and lower polarizing plates are arranged orthogonally, a black display can be obtained. On the other hand, in the presence of an electric field, the liquid crystal molecules operate so as to tilt in a 45 ° azimuth direction with respect to the absorption axis of the polarizing plate, whereby the transmittance increases and white display is obtained.

The VA mode liquid crystal cell can be multi-domained by using a substrate having slits formed on electrodes or a substrate having projections formed on the surface as described in JP-A-11-258605, for example. It may be what you did. Such a liquid crystal cell is, for example, an ASV (Advanced Super View) mode manufactured by Sharp Corporation, a CPA (Continuous Pinwheel Alignment) mode manufactured by the same company, an MVA (Multi-domain Vertical Alignment mode) manufactured by Fujitsu Limited, or the like. PVA (Patterned Vertical Alignment) mode manufactured by Co., Ltd., EVA (Enhanced Vertical Alignment) mode manufactured by the same company, SURVIVAL (Super Ranged Viewing by Vertical Alignment) mode manufactured by Sanyo Electric Co., Ltd., etc.

Rth _LC [590] of the above liquid crystal cell in the absence of an electric field is preferably −500 nm to −200 nm, more preferably −400 nm to −200 nm. The Rth _LC [590] is appropriately set depending on the birefringence of the liquid crystal molecules and the cell gap. The cell gap (substrate interval) of the liquid crystal cell is usually 1.0 μm to 7.0 μm.

  As the liquid crystal cell, the one mounted on a commercially available liquid crystal display device may be used as it is. Commercially available liquid crystal display devices including VA mode liquid crystal cells include, for example, Sharp Corporation liquid crystal television product name “AQUIS series”, Sony liquid crystal television product name “BRAVIA series”, and SUMSUNG 32V type wide display. Liquid crystal television product name “LN32R51B”, Nanao Co., Ltd. liquid crystal television product name “FORIS SC26XD1”, AU Optronics liquid crystal television product name “T460HW01”, and the like.

<C. Polarizing plate>
As the polarizing plate (the first polarizing plate and the second polarizing plate) used in the present invention, any appropriate one can be adopted as long as the transmittance satisfies the above relationship. In the present specification, the “polarizing plate” refers to a material that converts natural light or polarized light into linearly polarized light. Preferably, the polarizing plate has a function of separating incident light into two orthogonally polarized components, transmitting one polarized component, and absorbing, reflecting and / or scattering the other polarized component.

  Preferably, the first polarizing plate is disposed on the viewing side of the liquid crystal cell, and the second polarizing plate is disposed on the side opposite to the viewing side of the liquid crystal cell. If a polarizing plate with high transmittance is arranged on the backlight side and the backlight light is incident on the liquid crystal cell as much as possible, high brightness (white brightness) can be easily obtained when displaying a white image or color display. Because. On the other hand, when a black image is displayed by arranging a polarizing plate with low transmittance on the viewing side so that the light from the backlight is not leaked to the viewing side as much as possible, the luminance (black luminance) can be kept low. . As a result, a liquid crystal display device with a high contrast ratio can be obtained. Preferably, the absorption axis direction of the first polarizing plate is substantially orthogonal to the absorption axis direction of the second polarizing plate.

  The thickness in particular of the said polarizing plate is not restrict | limited, The general concept of a thin film, a film, and a sheet is included. The thickness of the polarizing plate is usually 1 μm to 250 μm, preferably 20 μm to 250 μm. By setting the thickness of the polarizing plate in the above range, a material having excellent mechanical strength can be obtained.

The polarizing plate may be a single layer having a polarizing function (also referred to as a polarizer) or a laminate composed of a plurality of layers. When the polarizing plate is a laminate, examples of the configuration thereof include (a) a laminate including a polarizer and a protective layer (for example, the configuration of Examples), and (b) a polarizer, a protective layer, and a surface treatment. And a laminate including two or more polarizers, and the like. The polarizing plate may have two or more surface treatment layers.

The transmittance (T ₁ ) of the first polarizing plate is preferably 38.3% to 43.3%, more preferably 38.6% to 43.2%, and particularly preferably 38.9. % To 43.1%, most preferably 39.2% to 43.0%. The T ₁ by the above range, further, it is possible to contrast ratio in the front direction obtain high liquid crystal display device.

The transmittance (T ₂ ) of the second polarizing plate is preferably 41.1% to 44.3%, more preferably 41.4% to 44.3%, and particularly preferably 41.7%. % To 44.2%, and most preferably 42.0% to 44.2%. The T ₂ by the above range, further, it is possible to contrast ratio in the front direction obtain high liquid crystal display device.

  The liquid crystal panel of the present invention can be produced by, for example, selecting commercially available polarizing plates having different transmittances and combining them appropriately. Preferably, the liquid crystal panel of the present invention is produced by appropriately adjusting the transmittance of the polarizing plate so as to increase the contrast ratio in the front direction in accordance with the driving mode and application of the liquid crystal cell.

  As a method for increasing or decreasing the transmittance of the polarizing plate, for example, when a polarizer mainly composed of a polyvinyl alcohol resin containing iodine is used for the polarizing plate, the content of iodine in the polarizer The method of adjusting is mentioned. Specifically, if the iodine content in the polarizer is increased, the transmittance of the polarizing plate can be lowered, and if the iodine content in the polarizer is decreased, the transmittance of the polarizing plate is increased. can do. This method can be applied to the production of a roll-shaped polarizing plate and the production of a polarizing plate for each leaf. The polarizer will be described later.

  The degree of polarization (P) of the first polarizing plate and / or the second polarizing plate is preferably 99% or more, more preferably 99.5% or more, and further preferably 99.8%. is there. By setting the degree of polarization (P) within the above range, a liquid crystal display device having a higher contrast ratio in the front direction can be obtained.

The degree of polarization can be measured using a spectrophotometer [product name “DOT-3” manufactured by Murakami Color Research Laboratory Co., Ltd.]. As a specific method for measuring the degree of polarization, the parallel transmittance (H ₀ ) and orthogonal transmittance (H ₉₀ ) of the polarizing plate are measured, and the formula: degree of polarization (%) = {(H ₀ -H ₉₀ ) / (H ₀ + H ₉₀ )} ^1/2 × 100. The parallel transmittance (H ₀ ) is a transmittance value of a parallel laminated polarizing plate produced by superposing two identical polarizing plates so that their absorption axes are parallel to each other. The orthogonal transmittance (H ₉₀ ) is a value of the transmittance of an orthogonal laminated polarizing plate produced by superposing two identical polarizing plates so that their absorption axes are orthogonal to each other. In addition, these transmittance | permeability is Y value which performed visibility correction | amendment by the 2 degree visual field (C light source) of JlS Z 8701-1982.

<C-1. Polarizer>
Any appropriate polarizer may be employed as the polarizer used in the present invention. Preferably, the first polarizer includes a first polarizer, the second polarizer includes a second polarizer, and each of the first polarizer and the second polarizer is iodine. The main component is a polyvinyl alcohol-based resin containing The polarizer can be usually obtained by stretching a polymer film containing as a main component a polyvinyl alcohol-based resin containing iodine. A polarizing plate including such a polarizer is excellent in optical characteristics.

The relationship between the iodine content (I ₁ ) of the first polarizer and the iodine content (I ₂ ) of the second polarizing plate is preferably I ₁ > I ₂ . The difference (ΔI = I ₁ −I ₂ ) between the iodine content (I ₁ ) of the _first polarizer and the iodine content (I ₂ ) of the second polarizing plate is preferably 0.1 weight. % To 2.6% by weight, more preferably 0.1% to 2.0% by weight, particularly preferably 0.1% to 1.4% by weight, and most preferably 0.15%. % By weight to 0.8% by weight. By making the relationship of the iodine content of each polarizer into the above range, a polarizing plate having a transmittance relationship in a preferable range can be obtained, and a liquid crystal display device having a high contrast ratio in the front direction can be obtained.

The iodine content of the first polarizer and the second polarizer is preferably 1.8% by weight to 5.0% by weight, more preferably 2.0% by weight to 4.0% by weight, respectively. %. The iodine content of the first polarizer is preferably 2.3% to 5.0% by weight, more preferably 2.5% to 4.5% by weight, and particularly preferably 2.% by weight. 5% to 4.0% by weight. The iodine content of the second polarizer is preferably 1.8% to 3.5% by weight, more preferably 1.9% to 3.2% by weight, and particularly preferably 2.% by weight. 0% by weight to 2.9% by weight. By setting the iodine content of each polarizer in the above range, a polarizing plate having a transmittance in a preferable range can be obtained, and a liquid crystal display device having a high contrast ratio in the front direction can be obtained.

Preferably, each of the first polarizer and the second polarizer further contains potassium. The potassium content is preferably 0.2% by weight to 1.0% by weight, more preferably 0.3% by weight to 0.9% by weight, and particularly preferably 0.4% by weight to 0.00%. 8% by weight. By making potassium content into the said range, the polarizing plate which has the transmittance | permeability of a preferable range and has high polarization degree can be obtained.

Preferably, each of the first polarizer and the second polarizer further contains boron. The boron content is preferably 0.5 wt% to 3.0 wt%, more preferably 1.0 wt% to 2.8 wt%, and particularly preferably 1.5 wt% to 2. wt%. 6% by weight. By setting the boron content in the above range, a polarizing plate having a transmittance in a preferable range and a high degree of polarization can be obtained.

  The polyvinyl alcohol resin can be obtained by saponifying a vinyl ester polymer obtained by polymerizing a vinyl ester monomer. The saponification degree of the polyvinyl alcohol resin is preferably 95.0 mol% to 99.9 mol%. The saponification degree can be determined according to JIS K 6726-1994. By using a polyvinyl alcohol resin having a saponification degree in the above range, a polarizer having excellent durability can be obtained.

  As the average degree of polymerization of the polyvinyl alcohol-based resin, an appropriate value can be appropriately selected according to the purpose. The average degree of polymerization is preferably 1200 to 3600. The average degree of polymerization can be determined according to JIS K 6726-1994.

  Any appropriate forming method can be adopted as a method for obtaining the polymer film containing the polyvinyl alcohol resin as a main component. Examples of the molding method include the method described in JP 2000-315144 A [Example 1].

  The polymer film containing the vinyl alcohol polymer as a main component preferably contains a plasticizer and / or a surfactant. Examples of the plasticizer include polyhydric alcohols such as ethylene glycol and glycerin. As said surfactant, a nonionic surfactant is mentioned, for example. The content of the plasticizer and the surfactant is preferably more than 1 and 10 parts by weight with respect to 100 parts by weight of the vinyl alcohol polymer. The polyhydric alcohol and the surfactant are used for the purpose of further improving the dyeability and stretchability of the polarizer.

  A commercially available film can be used as it is as the polymer film containing the polyvinyl alcohol resin as a main component. Examples of the polymer film mainly composed of a commercially available polyvinyl alcohol-based resin include, for example, “Kuraray Vinylon Film” manufactured by Kuraray Co., Ltd., “Toselo Vinylon Film” manufactured by Tosero Co., Ltd., Nippon Synthetic Chemical Industry Product name “Nippon Vinylon Film”, etc., may be mentioned.

  An example of a method for manufacturing a polarizer will be described with reference to FIG. FIG. 2 is a schematic view showing the concept of a typical production process of a polarizer used in the present invention. For example, a polymer film 301 mainly composed of a polyvinyl alcohol-based resin is fed from a feeding unit 300 and immersed in a swelling bath 310 containing pure water and a dyeing bath 320 containing an aqueous iodine solution, and rolls 311 having different speed ratios. , 312, 321 and 322, swelling treatment and dyeing treatment are performed while tension is applied in the longitudinal direction of the film. Next, the film subjected to the swelling treatment and the dyeing treatment is immersed in the first crosslinking bath 330 containing potassium iodide and the second crosslinking bath 340, and is rolled with rolls 331, 332, 341 and 342 having different speed ratios. While tension is applied in the longitudinal direction of the film, a crosslinking treatment and a final stretching treatment are performed. The film subjected to the crosslinking treatment is immersed in a washing bath 350 containing pure water by rolls 351 and 352, and subjected to a washing treatment. The water-washed film is dried by the drying means 360, so that the moisture content is adjusted to, for example, 10% to 30%, and is wound by the winding unit 380. The polarizer 370 can be obtained by stretching the polymer film containing the polyvinyl alcohol-based resin as a main component to 5 to 7 times the original length through these steps.

  In the dyeing step, the amount of iodine added to the dyeing bath is preferably 0.01 parts by weight to 0.15 parts by weight, more preferably 0.01 parts by weight to 0.05 parts by weight with respect to 100 parts by weight of water. Parts by weight. By adjusting the amount of iodine added to the dyeing bath in the above range, a polarizing plate having excellent optical properties can be obtained. When the amount of iodine added to the dyeing bath is increased within the above range, a polarizing plate having a low transmittance can be obtained as a result. Moreover, when the addition amount of the iodine of a dyeing bath is reduced in said range, a polarizing plate with a high transmittance | permeability can be obtained as a result.

  The amount of potassium iodide added to the dyeing bath is preferably 0.05 parts by weight to 0.5 parts by weight, more preferably 0.1 parts by weight to 0.3 parts by weight with respect to 100 parts by weight of water. It is. By setting the amount of potassium iodide to be in the above range, a polarizing plate having a preferable range of transmittance and a high degree of polarization can be obtained.

  In the dyeing step, the amount of potassium iodide added in the first crosslinking bath and the second crosslinking bath is preferably 0.5 to 10 parts by weight, more preferably 100 parts by weight of water. Is 1 to 7 parts by weight. The amount of boric acid added in the first crosslinking bath and the second crosslinking bath is preferably 0.5 to 10 parts by weight, more preferably 1 to 7 parts by weight. By setting the addition amounts of potassium iodide and boric acid in the above ranges, a polarizing plate having a preferable range of transmittance and high optical properties with a high degree of polarization can be obtained.

<C-2. Protective layer>
The polarizing plate used in the present invention preferably includes at least a polarizer and protective layers disposed on both sides of the polarizer. For example, the protective layer can prevent the polarizer from contracting or expanding, or can prevent deterioration due to ultraviolet rays, and a highly durable polarizing plate can be obtained.

  In one embodiment, the first polarizing plate is preferably a first polarizer, a first protective layer disposed on the liquid crystal cell side of the first polarizer, and the first polarized light. And at least a second protective layer disposed on the side opposite to the liquid crystal cell side of the child. Furthermore, the second polarizing plate is preferably a second polarizer, a third protective layer disposed on the liquid crystal cell side of the second polarizer, and the liquid crystal cell side of the second polarizer. And at least a fourth protective layer disposed on the opposite side.

  The protective layer and the polarizer can be laminated via any appropriate adhesive layer. In this specification, the “adhesive layer” refers to a layer that joins surfaces of adjacent optical members and integrates them with practically sufficient adhesive force and adhesion time. Examples of the material for forming the adhesive layer include an adhesive and an anchor coat agent. The adhesive layer may have a multilayer structure in which an anchor coat layer is formed on the surface of an adherend and an adhesive layer is formed thereon. Further, it may be a thin layer (also referred to as a hairline) that cannot be visually recognized.

  In the case where the polarizer contains a polyvinyl alcohol resin containing iodine as a main component, the material for forming the adhesive layer is preferably a water-soluble adhesive. The water-soluble adhesive is preferably a water-soluble adhesive mainly composed of a polyvinyl alcohol resin. A commercially available adhesive can be used as it is for the adhesive layer. Or a solvent and an additive can also be mixed and used for a commercially available adhesive agent. As an adhesive mainly composed of a commercially available polyvinyl alcohol resin, for example, “GOHSEIMER Z200” manufactured by Nippon Synthetic Chemical Industry Co., Ltd. may be mentioned.

  The water-soluble adhesive may further contain a crosslinking agent as an additive. Examples of the crosslinking agent include amine compounds, aldehyde compounds, methylol compounds, epoxy compounds, isocyanate compounds, and polyvalent metal salts. A commercially available crosslinking agent can be used as it is. As a commercially available crosslinking agent, an aldehyde compound trade name “glyoxazal” manufactured by Nippon Synthetic Chemical Industry Co., Ltd. may be mentioned. The addition amount of the crosslinking agent can be appropriately adjusted according to the purpose, but is usually more than 0 and 10 parts by weight or less with respect to 100 parts by weight of the solid content of the water-soluble adhesive.

[First protective layer]
The first protective layer is disposed on the liquid crystal cell side of the first polarizer. As the thickness of the first protective layer, an appropriate value can be appropriately selected according to the purpose. The thickness of the first protective layer is preferably 20 μm to 100 μm. The transmittance (T [590]) at a wavelength of 590 nm of the first protective layer is preferably 90% or more.

  Since the first protective layer is disposed between the polarizer and the liquid crystal cell, the optical characteristics may affect the display characteristics of the liquid crystal display device. Therefore, it is preferable to use the first protective layer having an appropriate retardation value. Preferably, the refractive index ellipsoid of the first protective layer exhibits a relationship of nx = ny ≧ nz. In this specification, “showing a relationship of nx = ny ≧ nz” indicates a relationship of nx = ny> nz (also referred to as negative uniaxiality), or a relationship of nx = ny = nz (optically equivalent). It is also referred to as directionality.

  When the refractive index ellipsoid of the first protective layer shows a relationship of nx = ny> nz, Re [590] of the first protective layer is less than 10 nm, and Rth [590] is preferably It is 10 nm-80 nm, More preferably, it is 20 nm-70 nm. When the refractive index ellipsoid of the first protective layer shows a relationship of nx = ny = nz, Re [590] and Rth [590] of the first protective layer are both less than 10 nm.

  Any appropriate material can be adopted as the material for forming the first protective layer. Preferably, the protective layer is a polymer film containing a cellulose resin, a norbornene resin, or an acrylic resin. The polymer film containing the cellulose resin can be obtained, for example, by the method described in Example 1 of JP-A-7-112446. The polymer film containing the norbornene resin can be obtained, for example, by the method described in JP-A-2001-350017. The polymer film containing the acrylic resin can be obtained, for example, by the method described in Example 1 of JP-A-2004-198952.

[Second protective layer]
The second protective layer is disposed on the side opposite to the liquid crystal cell side of the first polarizer. Any appropriate layer can be adopted as the second protective layer. The thickness of the second protective layer is preferably 20 μm to 100 μm. The transmittance (T [590]) at a wavelength of 590 nm of the second protective layer is preferably 90% or more.

  Any appropriate material can be adopted as the material for forming the second protective layer. Preferably, the protective layer is a polymer film containing a cellulose resin, a norbornene resin, or an acrylic resin.

  As long as the said 2nd protective layer satisfies the said transmittance | permeability relationship, arbitrary appropriate surface treatment may be given to the surface. For example, as the protective layer, a commercially available polymer film subjected to surface treatment can be used as it is. Alternatively, a commercially available polymer film can be used after any surface treatment. Examples of the surface treatment include diffusion treatment (antiglare treatment), antireflection treatment (antireflection treatment), hard coat treatment, and antistatic treatment. Examples of commercially available diffusion-treated (antiglare-treated) products include AG150, AGS1, AGS2, and AGT1 manufactured by Nitto Denko Corporation. Examples of commercially available antireflection treatment (anti-reflection treatment) products include ARS and ARC manufactured by Nitto Denko Corporation. Examples of the commercially available film subjected to the hard coat treatment and the antistatic treatment include “KC8UX-HA” manufactured by Konica Minolta Opto Co., Ltd.

[Surface treatment layer]
If necessary, a surface treatment layer may be provided on the side of the second protective layer opposite to the side provided with the first polarizer. Any appropriate layer can be adopted as the surface treatment layer depending on the purpose. For example, a diffusion treatment (antiglare treatment) layer, an antireflection treatment (antireflection treatment) layer, a hard coat treatment layer, an antistatic treatment layer and the like can be mentioned. These surface treatment layers are used for the purpose of preventing the screen from being soiled or damaged, or preventing the display image from becoming difficult to see due to the reflection of indoor fluorescent light or sunlight on the screen. In general, the surface treatment layer is obtained by fixing the treatment agent for forming the treatment layer on the surface of the base film. The base film may also serve as the second protective layer. Furthermore, the surface treatment layer may have a multilayer structure in which, for example, a hard coat treatment layer is laminated on the antistatic treatment layer. Examples of the commercially available surface treatment layer that has been subjected to the antireflection treatment include ReaLook series manufactured by NOF Corporation.

[Third protective layer]
The third protective layer is disposed on the liquid crystal cell side of the second polarizer. As said 3rd protective layer, a suitable thing can be employ | adopted suitably from the material, characteristic, conditions, etc. which were described in the 1st protective layer mentioned above. The first protective layer and the third protective layer may be the same or different.

[Fourth protective layer]
The fourth protective layer is disposed on the side opposite to the liquid crystal cell side of the second polarizer. As the fourth protective layer, an appropriate layer can be adopted as appropriate from the materials, characteristics, conditions, and the like described in the second protective layer. The second protective layer and the fourth protective layer may be the same or different.

<D. Retardation layer>
The retardation layer used in the present invention is disposed between the first polarizing plate and the second polarizing plate. Preferably, the retardation layer is disposed between the liquid crystal cell and the second polarizing plate. In this case, more preferably, the second polarizing plate is disposed on the side opposite to the viewing side of the liquid crystal cell. In such a configuration, a liquid crystal display device with a higher contrast ratio in the front direction can be obtained. In the present specification, the “retardation layer” refers to a transparent layer having a retardation in the plane and / or in the thickness direction. The in-plane and / or thickness direction retardation value of the retardation layer at a wavelength of 590 nm is 10 nm or more. The thickness of the retardation layer is preferably 0.5 μm to 200 μm. The transmittance (T [590]) at a wavelength of 590 nm of the retardation layer is preferably 90% or more.

  Preferably, the retardation layer is disposed between the liquid crystal cell and the second polarizing plate. Preferably, the slow axis direction of the retardation layer is substantially perpendicular to the absorption axis direction of the adjacent polarizer. Therefore, when the retardation layer is disposed between the liquid crystal cell and the second polarizing plate, the slow axis direction of the retardation layer is the absorption axis direction of the second polarizer. It is preferably substantially orthogonal.

  The refractive index ellipsoid of the retardation layer shows a relationship of nx ≧ ny> nz. In this specification, “showing a relationship of nx ≧ ny> nz” means a relationship of nx = ny> nz or a relationship of nx> ny> nz (also referred to as negative biaxiality). Say.

  Preferably, in the retardation layer, the refractive index ellipsoid shows a relationship of nx> ny> nz. Because a liquid crystal cell can be highly compensated by simply placing one retardation layer between the first polarizer and the second polarizer, a thin and low-cost liquid crystal panel can be obtained. is there. Further, since the number of retardation layers is small, the slow axis of the retardation layer is less likely to deviate from a desired position, and a liquid crystal display device with a higher contrast ratio in the front direction can be obtained. A liquid crystal panel that compensates using only one retardation layer is also referred to as a “single-compensation liquid crystal panel”.

  When the refractive index ellipsoid of the retardation layer shows a relationship of nx = ny> nz, Re [590] of the retardation layer is less than 10 nm, preferably 5 nm or less. When the refractive index ellipsoid of the retardation layer shows a relationship of nx> ny> nz, Re [590] of the retardation layer is 10 nm or more, preferably 20 nm to 80 nm, more preferably 30 nm to It is 70 nm, and particularly preferably 30 nm to 60 nm. By setting Re [590] within the above range, a liquid crystal display device having a high contrast ratio in the front and oblique directions and excellent display characteristics can be obtained.

  Rth [590] of the retardation layer can be appropriately set according to the retardation value in the thickness direction of the liquid crystal cell. The Rth [590] is preferably 100 nm to 400 nm, more preferably 150 nm to 350 nm, and particularly preferably 150 nm to 300 nm. By setting Rth [590] in the above range, a liquid crystal display device having a high contrast ratio in an oblique direction and excellent display characteristics can be obtained.

  When the refractive index ellipsoid of the retardation layer shows a relationship of nx> ny> nz, Rth [590] is larger than Re [590]. That is, the Nz coefficient of the retardation layer is greater than 1. The Nz coefficient is preferably more than 1.1 and 8 or less, more preferably 2 to 7, and particularly preferably 3 to 6. By setting the Nz coefficient in the above range, a single-compensation type liquid crystal panel can be obtained. Furthermore, a liquid crystal display device having a high contrast ratio in the front and oblique directions and excellent display characteristics can be obtained.

  As the material for forming the retardation layer, any appropriate material can be adopted as long as the refractive index ellipsoid shows a relationship of nx ≧ ny> nz. The retardation layer is preferably a retardation film containing a polyimide resin or a norbornene resin.

[Polyimide resin]
When the polyimide resin is formed into a sheet by the solvent casting method, the refractive index ellipsoid shows a relationship of nx = ny> nz because the molecules are likely to be spontaneously oriented during the evaporation process of the solvent. The film can be made very thin. The thickness of the retardation film containing the polyimide resin is preferably 0.5 μm to 10 μm, and more preferably 1 μm to 5 μm. The birefringence (Δn _xz [590]) in the thickness direction of the retardation film containing the polyimide resin is preferably 0.01 to 0.12, and more preferably 0.02 to 0.08. Such a polyimide resin can be obtained, for example, by the method described in US Pat. No. 5,344,916.

  Furthermore, since the refractive index ellipsoid shows the relationship of nx = ny> nz as described above, the polyimide-based resin does not require a complicated stretching method, and a general longitudinal uniaxial stretching method or lateral uniaxial stretching method is used. Thus, a retardation film having a refractive index ellipsoid showing a relationship of nx> ny> nz can be obtained. For this reason, even when a wide retardation film is produced for a large-sized liquid crystal display device, the slow axis tends to be uniform in the width direction, and the axial misalignment is small even when attached to a polarizer. As a result, a liquid crystal display device with a high contrast ratio in the front direction can be obtained.

  Preferably, the polyimide resin has a hexafluoroisopropylidene group and / or a trifluoromethyl group. More preferably, the polyimide resin has at least a repeating unit represented by the following general formula (I) or a repeating unit represented by the following general formula (II). Polyimide resins containing these repeating units are excellent in transparency and solubility in general-purpose solvents, and have a large birefringence in the thickness direction.

In the above general formulas (I) and (II), G and G ′ are a covalent bond, CH ₂ group, C (CH ₃ ) ₂ group, C (CF ₃ ) ₂ group, C (CX ₃ ) ₂ group (here X is a halogen.), Each independently from the group consisting of CO, O, S, SO ₂ , Si (CH ₂ CH ₃ ) ₂ and N (CH ₃ ) groups. Represents a group selected, and may be the same or different.

  In the above general formula (I), L is a substituent, and e represents the number of substitutions. L is, for example, a halogen, an alkyl group having 1 to 3 carbon atoms, a halogenated alkyl group having 1 to 3 carbon atoms, a phenyl group, or a substituted phenyl group, and in a plurality of cases, they are the same or different. e is an integer from 0 to 3.

  In the general formula (II), Q is a substituent, and f represents the number of substitutions. Q is, for example, selected from the group consisting of hydrogen, halogen, alkyl group, substituted alkyl group, nitro group, cyano group, thioalkyl group, alkoxy group, aryl group, substituted aryl group, alkyl ester group, and substituted alkyl ester group And when Q is plural, they are the same or different. f is an integer from 0 to 4, and g and h are integers from 1 to 3, respectively.

  The said polyimide resin can be obtained by reaction of tetracarboxylic dianhydride and diamine, for example. As the repeating unit of the above general formula (I), for example, 2,2′-bis (trifluoromethyl) -4,4′-diaminobiphenyl is used as a diamine, and a tetracarboxylic acid having at least two aromatic rings. It can be obtained by reaction with dianhydride. As the repeating unit of the above general formula (II), for example, 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropanoic acid dianhydride is used as a tetracarboxylic dianhydride, and this is combined with an aromatic ring. It can be obtained by reacting with at least two diamines. The reaction may be, for example, chemical imidization that proceeds in two stages or thermal imidization that proceeds in one stage.

  Any appropriate tetracarboxylic dianhydride may be selected. Examples of the tetracarboxylic dianhydride include 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropanoic dianhydride and 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride. 2,3,3 ′, 4-benzophenone tetracarboxylic dianhydride, 2,2 ′, 3,3′-benzophenone tetracarboxylic dianhydride, 2,2′-dibromo-4,4 ′, 5 , 5′-biphenyltetracarboxylic dianhydride, 2,2′-bis (trifluoromethyl) -4,4 ′, 5,5′-biphenyltetracarboxylic dianhydride, 3,3 ′, 4,4 '-Biphenyltetracarboxylic dianhydride, 4,4'-bis (3,4-dicarboxyphenyl) ether dianhydride, 4,4'-oxydiphthalic dianhydride, 4,4'-bis (3 4-dicarboxyl Yl) sulfonic acid dianhydride, bis (2,3-carboxyphenyl) methane dianhydride, bis (3,4-carboxyphenyl) diethyl silane dianhydride, and the like.

  Any appropriate diamine may be selected. Examples of the diamine include 2,2′-bis (trifluoromethyl) -4,4′-diaminobiphenyl, 4,4′-diaminobiphenyl, 4,4′-diaminophenylmethane, 4,4 ′-( 9-fluorenylidene) -dianiline, 3,3′-dichloro-4,4′-diaminodiphenylmethane, 2,2′-dichloro-4,4′-diaminobiphenyl, 4,4′-diaminodiphenyl ether, 3,4′- Examples include diaminodiphenyl ether, 4,4′-diaminodiphenyl sulfone, 4,4′-diaminodiphenylthioether, and the like.

  The above polyimide-based resin is a polyethylene oxide standard weight average molecular weight (Mw) using a dimethylformamide solution (a solution obtained by adding 10 mM lithium bromide and 10 mM phosphoric acid to make a 1 L dimethylformamide solution). However, it is preferably 20,000 to 180,000. The imidization rate is preferably 95% or more. The imidation rate can be determined from an integral intensity ratio between a proton peak derived from polyamic acid, which is a polyimide precursor, and a proton peak derived from polyimide.

  The retardation film containing the polyimide resin can be obtained by any appropriate forming method. Preferably, the retardation film containing the polyimide resin is prepared by stretching a polymer film formed into a sheet shape by a solvent casting method, by a longitudinal uniaxial stretching method or a lateral uniaxial stretching method. The temperature at which the polymer film is stretched (stretching temperature) is preferably 120 ° C to 200 ° C. Moreover, the magnification (stretching ratio) for stretching the polymer film is preferably more than 1 and not more than 3 times.

[Norbornene resin]
Since the norbornene resin has a small absolute value (C [590]) of the photoelastic coefficient, a liquid crystal display device with small optical unevenness can be obtained. C [590] of the norbornene-based resin is preferably 1 × 10 ^{−12 to} 20 × 10 ⁻¹² , and more preferably 1 × 10 ⁻¹² to 10 × 10 ⁻¹² . In this specification, the “norbornene-based resin” refers to a (co) polymer obtained by using a norbornene-based monomer having a norbornene ring as a part or all of a starting material (monomer). The “(co) polymer” represents a homopolymer or a copolymer (copolymer).

In the norbornene-based resin, a norbornene-based monomer having a norbornene ring (having a double bond in the norbornane ring) is used as a starting material. In the state of the (co) polymer, the norbornene-based resin may or may not have a norbornane ring in the structural unit. In the state of the (co) polymer, the norbornene-based resin having a norbornane ring as a structural unit is, for example, tetracyclo [4.4.1 ^2,5 . 1 ^7,10 . 0] Dec-3-ene, 8-methyltetracyclo [4.4.1 ^2,5 . 1 ^7,10 . 0] dec-3-ene, 8-methoxycarbonyltetracyclo [4.4.1 ^2,5 . 1 ^7,10 . 0] Dec-3-ene and the like. A norbornene-based resin having no norbornane ring as a structural unit in the (co) polymer state is, for example, a (co) polymer obtained using a monomer that becomes a 5-membered ring by cleavage. Examples of the monomer that becomes a 5-membered ring by cleavage include norbornene, dicyclopentadiene, 5-phenylnorbornene, and derivatives thereof. When the norbornene-based resin is a copolymer, the arrangement state of the molecules is not particularly limited, and may be a random copolymer, a block copolymer, or a graft copolymer. It may be.

  Examples of the norbornene resin include (A) a resin obtained by hydrogenating a ring-opening (co) polymer of a norbornene monomer, and (B) a resin obtained by addition (co) polymerization of a norbornene monomer. The ring-opening copolymer of the norbornene-based monomer is a resin obtained by hydrogenating a ring-opening copolymer of one or more norbornene-based monomers and α-olefins, cycloalkenes, and / or non-conjugated dienes. Includes. The resin obtained by addition copolymerization of the norbornene monomer includes a resin obtained by addition copolymerization of one or more norbornene monomers with α-olefins, cycloalkenes and / or non-conjugated dienes.

  A resin obtained by hydrogenating the ring-opening (co) polymer of the norbornene monomer is subjected to a metathesis reaction of the norbornene monomer or the like to obtain a ring-opening (co) polymer. It can be obtained by hydrogenation. Specifically, for example, the method described in paragraphs [0059] to [0060] of JP-A-11-116780, the method described in paragraphs [0035] to [0037] of JP-A-2001-350017, and the like. Can be mentioned. The resin obtained by addition (co) polymerization of the norbornene monomer can be obtained, for example, by the method described in Example 1 of JP-A No. 61-292601.

  The weight average molecular weight (Mw) of the norbornene resin is preferably 20,000 to 500,000 as measured by gel permeation chromatography (polystyrene standard) using a tetrahydrofuran solvent. The glass transition temperature (Tg) of the norbornene-based resin is preferably 120 ° C to 170 ° C. If it is said resin, it has the outstanding thermal stability and the film excellent in the drawability can be obtained. The glass transition temperature (Tg) is a value calculated by the DSC method according to JIS K7121.

  The retardation film containing the norbornene resin can be obtained by any appropriate forming method. Preferably, the retardation film containing the norbornene-based resin is obtained by subjecting a polymer film formed into a sheet shape by a solvent casting method or a melt extrusion method to a horizontal uniaxial stretching method, a vertical / horizontal simultaneous biaxial stretching method, or a vertical / horizontal sequential two-phase method. It is produced by stretching by an axial stretching method. The temperature at which the polymer film is stretched (stretching temperature) is preferably 120 ° C to 200 ° C. Moreover, the magnification (stretching ratio) for stretching the polymer film is preferably more than 1 and not more than 3 times.

  The retardation film may further contain any appropriate additive. Examples of the additive include a plasticizer, a heat stabilizer, a light stabilizer, a lubricant, an antioxidant, an ultraviolet absorber, a flame retardant, a colorant, an antistatic agent, a compatibilizer, a crosslinking agent, and a thickener. Etc. The content of the additive is preferably more than 0 and 10 parts by weight or less with respect to 100 parts by weight of the norbornene resin.

  The retardation layer may be a liquid crystal composition. When a liquid crystal composition is used, the retardation layer includes a solidified layer or a cured layer of a liquid crystal composition containing a rod-like liquid crystal compound aligned in a planar alignment, or a discotic liquid crystal compound aligned in a columnar alignment. It includes a solidified layer or a cured layer of the liquid crystal composition. If a liquid crystal compound is used, a thin retardation film can be obtained because the birefringence in the thickness direction is large.

  In this specification, “planar alignment” refers to a state in which rod-like liquid crystal compounds (calamitic liquid crystal compounds) are aligned so that the helical axes of liquid crystals are perpendicular to both substrate surfaces (for example, FIG. a)). “Columnar alignment” refers to a state in which discotic liquid crystal compounds are arranged so as to be stacked in a columnar shape (see, for example, FIG. 3B). Further, the “solidified layer” refers to a solidified state in which a liquid crystalline composition in a softened, molten or solution state is cooled. The “cured layer” is a layer in which a part or all of the liquid crystalline composition is cross-linked by heat, catalyst, light and / or radiation to be in a stable state of infusible or hardly soluble. Say. In addition, the said hardened layer includes what became the hardened layer via the solidified layer of a liquid crystalline composition.

  A retardation film comprising a solidified layer or a cured layer of a liquid crystalline composition containing a rod-like liquid crystal compound aligned in the planar arrangement can be obtained, for example, by the method described in JP-A No. 2003-287623. In addition, a retardation film comprising a solidified layer or a cured layer of a liquid crystalline composition containing a discotic liquid crystal compounded soil aligned in the columnar arrangement can be obtained, for example, by the method described in JP-A-9-117983. it can.

<E. Adhesive layer>
In a preferred embodiment, the polarizing plate (first polarizing plate and second polarizing plate) is attached to a liquid crystal panel via an adhesive layer. As a material for forming the adhesive layer, an appropriate adhesive and / or anchor coat agent can be selected according to the type and application of the adherend. Specific examples of adhesives include solvent-based adhesives, emulsion-type adhesives, pressure-sensitive adhesives, rehumidifying adhesives, polycondensation-type adhesives, solventless adhesives, and film-like adhesives according to the classification by shape. Agents, hot melt adhesives, and the like. According to the classification by chemical structure, synthetic resin adhesives, rubber adhesives, and natural product adhesives can be mentioned. The adhesive includes a viscoelastic substance (also referred to as an adhesive) that exhibits an adhesive force that can be sensed by pressure contact at room temperature.

  Preferably, the material forming the adhesive layer is a pressure-sensitive adhesive (also referred to as an acrylic pressure-sensitive adhesive) having an acrylic polymer as a base polymer. It is because it is excellent in transparency, adhesiveness, weather resistance, and heat resistance. The thickness of the acrylic pressure-sensitive adhesive layer can be appropriately adjusted according to the material and application of the adherend, but is usually 5 μm to 50 μm.

<F. Liquid crystal display>
The liquid crystal display device of the present invention includes the liquid crystal panel. FIG. 4 is a schematic cross-sectional view of a liquid crystal display device according to a preferred embodiment of the present invention. It should be noted that for the sake of easy understanding, the ratio of the vertical, horizontal, and thickness of each component shown in FIG. 4 is different from the actual ratio. The liquid crystal display device 200 includes at least a liquid crystal panel 100 and a backlight unit 80 disposed on one side of the liquid crystal panel 100. In the illustrated example, the case where the direct type is adopted as the backlight unit is shown, but this may be a side light type, for example.

  When the direct type is adopted, the backlight unit 80 preferably includes at least a light source 81, a reflection film 82, a diffusion plate 83, a prism sheet 84, and a brightness enhancement film 85. When the sidelight method is adopted, preferably, the backlight unit further includes at least a light guide plate and a light reflector in addition to the above-described configuration. In addition, as long as the optical member illustrated in FIG. 4 exhibits the effects of the present invention, a part of the optical member such as an illumination method of a liquid crystal display device or a driving mode of a liquid crystal cell may be omitted depending on the application, or others. The optical member can be replaced.

  The liquid crystal display device may be a transmissive type that irradiates light from the back side of the liquid crystal panel to view the screen, or a reflective type that irradiates light from the viewing side of the liquid crystal panel to view the screen. good. Alternatively, the liquid crystal display device may be a transflective type having both transmissive and reflective properties.

  The liquid crystal display device of the present invention is used for any appropriate application. Applications include, for example, OA equipment such as personal computer monitors, notebook computers, and copiers, mobile phones, watches, digital cameras, personal digital assistants (PDAs), portable devices such as portable game machines, video cameras, televisions, microwave ovens, etc. Home appliances, back monitors, car navigation system monitors, car audio and other in-vehicle equipment, exhibition equipment such as commercial store information monitors, security equipment such as surveillance monitors, nursing care monitors, medical monitors, etc. Nursing care / medical equipment.

  Preferably, the use of the liquid crystal display device of the present invention is a television. The screen size of the television is preferably a wide 17 type (373 mm × 224 mm) or more, more preferably a wide 23 type (499 mm × 300 mm) or more, and particularly preferably a wide 32 type (687 mm × 412 mm) or more. .

The present invention will be further described using the above examples and comparative examples. In addition, this invention is not limited only to these Examples. In addition, each analysis method used in the Example is as follows.
(1) Transmittance of polarizing plate:
The transmittance (T) is a Y value obtained by correcting the visibility with a 2-degree visual field (C light source) of JlS Z 8701-1982.
(2) Measuring method of each element (I, K) content:
Each element content was calculated | required with the analytical curve created beforehand using the standard sample from the X-ray intensity measured on the following conditions by the fluorescent X-ray analysis on the circular sample of diameter 10mm.
・ Analyzer: X-ray fluorescence analyzer (XRF) manufactured by Rigaku Denki Kogyo Co., Ltd. Product name “ZSX100e”
-Counter cathode: Rhodium-Spectral crystal: Lithium fluoride-Excitation light energy: 40 kV-90 mA
・ Iodine measurement line: I-LA
・ Potassium measurement line: K-KA
Quantitative method: FP method 2θ angle peak: 103.078 deg (iodine), 136.847 deg (potassium)
Measurement time: 40 seconds (3) Measuring method of phase difference values (Re [λ], Rth [λ]), Nz coefficient, T [590]:
Measurement was performed at 23 ° C. using a trade name “KOBRA21-ADH” manufactured by Oji Scientific Instruments. In addition, the value measured using the Abbe refractometer [Atago Co., Ltd. product name "DR-M4"] was used for the average refractive index.
(4) Measuring method of thickness:
When the thickness was less than 10 μm, measurement was performed using a thin film spectrophotometer [manufactured by Otsuka Electronics Co., Ltd., “instant multiphotometry system MCPD-2000”]. When the thickness was 10 μm or more, measurement was performed using an Anritsu digital micrometer “KC-351C type”.
(5) Method for measuring molecular weight of polyimide resin:
Polyethylene oxide was calculated as a standard sample by a gel permeation chromatograph (GPC) method. The equipment, instruments and measurement conditions are as follows.
Sample: A sample was dissolved in an eluent to prepare a 0.1% by weight solution.
-Pretreatment: After standing for 8 hours, it was filtered through a 0.45 µm membrane filter.
・ Analyzer: “HLC-8020GPC” manufactured by Tosoh Corporation
-Column: Tosoh GMH _XL + GMH _XL + G2500H _XL
Column size: 7.8 mmφ x 30 cm each (total 90 cm)
Eluent: Dimethylformamide (added with 10 mM lithium bromide and 10 mM phosphoric acid to make up to 1 L dimethylformamide solution)
-Flow rate: 0.8 ml / min.
・ Detector: RI (differential refractometer)
-Column temperature: 40 ° C
・ Injection volume: 100 μl
(6) Method for measuring molecular weight of norbornene resin:
Polystyrene was calculated as a standard sample by the gel permeation chromatograph (GPC) method. Specifically, it measured with the following apparatuses, instruments, and measurement conditions. The sample is
Measurement sample: The sample was dissolved in tetrahydrane to give a 0.1% by weight solution, allowed to stand overnight, and then filtered using a 0.45 μm membrane filter.
・ Analyzer: “HLC-8120GPC” manufactured by TOSOH
Column: TSKgel Super HM-H / H4000 / H3000 / H2000
Column size: 6.0 mmI. D. × 150mm
-Eluent: Tetrahydrofuran-Flow rate: 0.6 ml / min.
・ Detector: RI
-Column temperature: 40 ° C
・ Injection volume: 20 μl
(7) Measuring method of glass transition temperature:
Using a differential scanning calorimeter [Seiko Co., Ltd. product name “DSC-6200”], it was determined by a method according to JIS K 7121 (1987) (measurement method of plastic transition temperature). Specifically, a 3 mg powder sample was heated twice (heating rate: 10 ° C./min) in a nitrogen atmosphere (gas flow rate: 80 ml / min) and measured twice, and the second data was adopted. The calorimeter corrected the temperature using a standard material (indium).
(8) Measuring method of absolute value (C [590]) of photoelastic coefficient:
Using a spectroscopic ellipsometer [product name “M-220” manufactured by JASCO Corporation], the sample (size 2 cm × 10 cm) is sandwiched at both ends and stress (5 to 15 N) is applied to the phase difference at the center of the sample. The value (23 ° C./wavelength 590 nm) was measured and calculated from the slope of the function of stress and retardation value.
(9) Measuring method of contrast ratio in front direction of liquid crystal display device:
After 30 minutes have passed since the backlight was turned on in a dark room at 23 ° C, using the product name “BM-5” manufactured by Topcon, the lens was placed at a position 50 cm above the panel, and a white image and a black image were displayed. In this case, the Y value of the XYZ display system was measured. The contrast ratio “YW / YB” in the front direction was calculated from the Y value (YW: white luminance) in the white image and the Y value (YB: black luminance) in the black image.

Preparation of polarizing plate [Reference Example 1]
A polymer film (trade name “VF-PS # 7500”, manufactured by Kuraray Co., Ltd.) having a 75 μm-thick polyvinyl alcohol resin as a main component is placed in 5 baths under the following conditions [1] to [5] in the longitudinal direction of the film. The film was immersed while applying tension, and stretched so that the final stretching ratio was 6.2 times the original film length. The stretched film was dried in an air circulation drying oven at 40 ° C. for 1 minute to produce a polarizer A. On both sides of the polarizer A, a polymer film containing a cellulose resin having a thickness of 80 μm (trade name “TD80UF” manufactured by Fuji Photo Film Co., Ltd .; Re [590] = 0 nm, Rth [590] = 60 nm), A polarizing plate A was prepared by adhering via a water-soluble adhesive (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name “Gosefimer Z200”) mainly composed of a polyvinyl alcohol resin. The characteristics of the polarizing plate A are shown in Table 1 below.
<Conditions>
[1] Swelling bath: 30 ° C. pure water.
[2] Dye bath: An aqueous solution at 30 ° C. containing 0.032 parts by weight of iodine with respect to 100 parts by weight of water and 0.2 parts by weight of potassium iodide with respect to 100 parts by weight of water.
[3] First cross-linking bath: 40 ° C. aqueous solution containing 3% by weight of potassium iodide and 3% by weight of boric acid.
[4] Second crosslinking bath: 60 ° C. aqueous solution containing 5% by weight of potassium iodide and 4% by weight of boric acid.
[5] Washing bath: A 25 ° C. aqueous solution containing 3% by weight of potassium iodide.

[Reference Example 2]
A polarizing plate B was produced under the same conditions and method as in Reference Example 1 except that the amount of iodine added under condition [2] was 0.031 parts by weight with respect to 100 parts by weight of water in the dye bath. The characteristics of the polarizing plate B are shown in Table 1 below.

[Reference Example 3]
Polarizing plate C was produced under the same conditions and method as in Reference Example 1 except that the amount of iodine added under condition [2] was 0.027 parts by weight with respect to 100 parts by weight of water in the dye bath. The characteristics of the polarizing plate C are shown in Table 1 below.

Production of retardation layer [Reference Example 4]
2,2'-bis (3,4-dicarboxyphenyl) hexafluoropropanoic acid dianhydride in a reaction vessel (500 mL) equipped with a mechanical stirrer, Dean-Stark device, nitrogen inlet tube, thermometer and condenser tube [Clariant Japan Co., Ltd.] 17.77 g (40 mmol) and 2,2-bis (trifluoromethyl) -4,4′-diaminobiphenyl [Wakayama Seika Kogyo Co., Ltd.] 12.81 g (40 mmol) added. Subsequently, a solution in which 2.58 g (20 mmol) of isoquinoline was dissolved in 275.21 g of m-cresol was added, and the mixture was stirred at 23 ° C. for 1 hour (600 rpm) to obtain a uniform solution. Next, the reaction vessel was heated using an oil bath so that the temperature in the reaction vessel became 180 ± 3 ° C., and stirred for 5 hours while maintaining the temperature to obtain a yellow solution. After further stirring for 3 hours, heating and stirring were stopped, and the mixture was allowed to cool to room temperature.

  Acetone was added to the yellow solution in the reaction vessel to completely dissolve the gel to prepare a diluted solution (7% by weight). When this diluted solution was gradually added to 2 L of isopropyl alcohol while stirring, a white powder was precipitated. This powder was collected by filtration and poured into 1.5 L of isopropyl alcohol for washing. Further, the same operation was repeated once again for washing, and then the powder was collected again by filtration. This was dried for 48 hours in an air circulation type constant temperature oven at 60 ° C., and then dried at 150 ° C. for 7 hours to obtain a polyimide powder of the following structural formula (III) in a yield of 85%. The polyimide had a polymerization average molecular weight (Mw) of 124,000 and an imidation ratio of 99.9%.

  The polyimide powder was dissolved in methyl isobutyl ketone to prepare a 15% by weight polyimide solution. This polyimide solution was uniformly cast in the form of a sheet by a slot die coater on the surface of a triacetylcellulose film (thickness 80 μm). Next, the film is put into a multi-chamber air circulation drying oven, and the solvent is evaporated while gradually raising the temperature from a low temperature of 80 ° C. for 2 minutes, 135 ° C. for 5 minutes, and 150 ° C. for 10 minutes. It was. Next, the film was stretched 1.14 times at 147 ° C. by a fixed-end lateral uniaxial stretching method using a tenter stretching machine. The triacetyl cellulose film was peeled off to obtain a polyimide layer (retardation layer A) having a thickness of 3.4 μm. In the retardation layer A, the refractive index ellipsoid has a relationship of nx> ny> nz, and T [590] = 91%, Re [590] = 50 nm, Rth [590] = 210 nm, and Nz coefficient = 4.2. Met.

Preparation of liquid crystal cell [Reference Example 5]
An optical film such as a polarizing plate disposed above and below the liquid crystal cell after taking out the liquid crystal panel from a commercially available liquid crystal display device including a VA mode liquid crystal cell [Sony's 40-inch liquid crystal television product name “BRAVIA KDL-40X1000”] Was completely removed. The front and back of the glass plate of this liquid crystal cell was washed to obtain liquid crystal cell A.

Production of liquid crystal panel and liquid crystal display device [Example 1]
On the viewing side of the liquid crystal cell A prepared in Reference Example 5, the polarizing plate A prepared in Reference Example 1 is used as the first polarizing plate. The absorption axis direction of the polarizing plate A is the long side direction of the liquid crystal cell A. And an acrylic pressure-sensitive adhesive (thickness 20 μm). Next, on the opposite side (backlight side) of the liquid crystal cell A, the retardation layer A produced in Reference Example 4 is used as the retardation layer, and the slow axis direction of the retardation layer A is the liquid crystal. It was stuck via an acrylic adhesive (thickness 20 μm) so as to be substantially parallel to the long side direction of the cell A. Next, the polarizing plate B produced in Reference Example 2 is used as the second polarizing plate on the backlight side surface of the retardation layer A, and the absorption axis direction of the polarizing plate B is the long side of the liquid crystal cell A. It stuck through the acrylic adhesive (thickness 20 micrometers) so that it might be substantially orthogonal to a direction. At this time, the absorption axis direction of the first polarizing plate and the absorption axis direction of the second polarizing plate are substantially perpendicular to each other. The slow axis direction of the retardation layer A is substantially orthogonal to the absorption axis direction of the second polarizing plate. This liquid crystal panel A was combined with the backlight unit of the original liquid crystal display device to produce a liquid crystal display device A. The characteristics of the obtained liquid crystal display device A are shown in Table 2 below.

[Example 2]
A liquid crystal panel B and a liquid crystal display device B were produced in the same manner as in Example 1 except that the polarizing plate C produced in Reference Example 3 was used as the second polarizing plate. The characteristics of the obtained liquid crystal display device B are shown in Table 2 below.

[Comparative Example 1]
A liquid crystal panel H and a liquid crystal display device H were produced in the same manner as in Example 1 except that the polarizing plate C produced in Reference Example 3 was used as the first polarizing plate and the second polarizing plate. The characteristics of the obtained liquid crystal display device H are shown in Table 2 below.

[Comparative Example 2]
A liquid crystal panel I and a liquid crystal display device I were produced in the same manner as in Example 1 except that the polarizing plate B produced in Reference Example 2 was used as the first polarizing plate. The characteristics of the obtained liquid crystal display device I are shown in Table 2 below.

[Comparative Example 3]
In the same manner as in Example 1, except that the polarizing plate C prepared in Reference Example 3 was used as the first polarizing plate, and the polarizing plate A prepared in Reference Example 1 was used as the second polarizing plate. A liquid crystal panel J and a liquid crystal display device J were produced. The characteristics of the obtained liquid crystal display device J are shown in Table 2 below.

[Comparative Example 4]
In the same manner as in Example 1, except that the polarizing plate B prepared in Reference Example 2 was used as the first polarizing plate, and the polarizing plate A prepared in Reference Example 1 was used as the second polarizing plate. A liquid crystal panel K and a liquid crystal display device K were produced. The characteristics of the obtained liquid crystal display device K are shown in Table 2 below.

[Evaluation]
As shown in Examples 1 and 2, the liquid crystal display device including the liquid crystal panel of the present invention includes a retardation layer, and the transmittance (T ₂ ) of the _second polarizing plate is transmitted through the first polarizing plate. By making it larger than the rate (T ₁ ), the contrast ratio in the front direction was much higher than that using the conventional liquid crystal panel. On the other hand, in the liquid crystal display devices of Comparative Examples 1 to 4, the transmittance (T ₂ ) of the _second polarizing plate is equal to the transmittance (T ₁ ) of the first polarizing plate, or the second polarizing plate Although the transmittance (T ₂ ) of the polarizing plate was smaller than the transmittance (T ₁ ) of the first polarizing plate, the contrast ratio in the front direction was low.

  As described above, since the liquid crystal panel of the present invention exhibits a high front contrast ratio when used in a liquid crystal display device, it is extremely useful for improving display characteristics of, for example, a liquid crystal television, a personal computer monitor, and a mobile phone. is there.

It is a schematic sectional drawing of the liquid crystal panel in preferable embodiment of this invention. It is a schematic diagram which shows the concept of the typical manufacturing process of the polarizer used for this invention. (A) is a schematic diagram explaining the planar aligned rod-like liquid crystal compound, and (b) is a schematic diagram explaining the columnar aligned discotic liquid crystal compound. 1 is a schematic cross-sectional view of a liquid crystal display device according to a preferred embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Liquid crystal cell 21 1st polarizing plate 22 2nd polarizing plate 30 Retardation layer 80 Backlight unit 81 Light source 82 Reflective film 83 Diffuser plate 84 Prism sheet 85 Brightness enhancement film 100 Liquid crystal panel 301 The main component is polyvinyl alcohol resin. Polymer film 300 Feeding part 310 Swelling bath 320 Dyeing baths 311, 312, 321, 322, 331, 332, 341, 342 Roll 330 First cross-linking bath 340 Second cross-linking bath 350 Washing bath 360 Drying means 370 Polarizer 380 Winding unit

Claims (11)

A liquid crystal cell;
A first polarizing plate disposed on one side of the liquid crystal cell;
A second polarizing plate disposed on the other side of the liquid crystal cell;
Comprising at least a retardation layer disposed between the liquid crystal cell and the second polarizing plate;
The refractive index ellipsoid of the retardation layer shows a relationship of nx ≧ ny> nz,
The liquid crystal panel in which the transmittance (T ₂ ) of the _second polarizing plate is larger than the transmittance (T ₁ ) of the first polarizing plate. The difference (ΔT = T ₂ −T ₁ ) between the transmittance (T ₂ ) of the _second polarizing plate and the transmittance (T ₁ ) of the first polarizing plate is 0.1% to 6.0. The liquid crystal panel according to claim 1, which is%.   The liquid crystal panel according to claim 1, wherein the liquid crystal cell includes liquid crystal molecules aligned in a homeotropic alignment.   The said 1st polarizing plate is arrange | positioned at the visual recognition side of the said liquid crystal cell, and the said 2nd polarizing plate is arrange | positioned at the opposite side to the visual recognition side of the said liquid crystal cell. LCD panel. The first polarizing plate includes a first polarizer, the second polarizing plate includes a second polarizer, and the first polarizer and the second polarizer each contain iodine. The liquid crystal panel according to claim 1, comprising a polyvinyl alcohol-based resin as a main component. The difference (ΔI = I ₁ −I ₂ ) between the iodine content (I ₁ ) of the _first polarizer and the iodine content (I ₂ ) of the second polarizing plate is 0.1 wt% to The liquid crystal panel according to claim 5, which is 2.6% by weight.   The liquid crystal panel according to claim 5 or 6, wherein iodine contents of the first polarizer and the second polarizer are 1.8 wt% to 5.0 wt%, respectively.   The liquid crystal panel according to claim 1, wherein a retardation value (Rth [590]) in a thickness direction at a wavelength of 590 nm of the retardation layer is 100 nm to 400 nm.   The liquid crystal panel according to claim 1, wherein an Nz coefficient of the retardation layer exceeds 1.1 and is 8 or less.   The liquid crystal panel according to claim 1, wherein the retardation layer is a retardation film containing a polyimide resin or a norbornene resin.   A liquid crystal display device comprising the liquid crystal panel according to claim 1.

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