JP5580348B2 - A set of polarizing plates arranged on a normally black liquid crystal panel and a liquid crystal display device using the set of polarizing plates - Google Patents

Description

The present invention relates to a set of polarizing plates composed of two polarizing plates having different transmittances arranged in a normally black liquid crystal panel, and a liquid crystal display device using the set of polarizing plates .

  A liquid crystal display device (hereinafter referred to as LCD) is an element 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). 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 the following set of polarizing plates, and have completed the present invention.

The set of polarizing plates of the present invention comprises a first polarizing plate and a second polarizing plate, and is a set of polarizing plates disposed on a normally black liquid crystal panel, wherein the first polarizing plate is , a first polarizer, and a first protective layer disposed on one side of the polarizer of the first, the refractive index ellipsoid of the first protective layer, nx>ny> nz relationship The transmittance (T ₁ ) of the _first polarizing plate is larger than the transmittance (T ₂ ) of the _second polarizing plate, and the transmittance (T ₁ ) of the _first polarizing plate , The difference (ΔT = T ₁ −T ₂ ) from the transmittance (T ₂ ) of the second polarizing plate is 0.1% to 2.0%, and the first polarizing plate and the second polarized light The degree of polarization of the plate is 99.8% or more.

In a preferred embodiment, the second polarizing plate is arranged on a viewer side of the liquid crystal cell included in the liquid crystal panel, the first polarizing plate is arranged on the side opposite to the viewing side of the liquid crystal cell It becomes.

In a preferred embodiment, the difference (ΔI = I ₂ −I ₁ ) between the iodine content (I ₂ ) of the _second polarizer and the iodine content (I ₁ ) of the first polarizer is 0.1% by weight to 1.4 % by weight.

  In a preferred embodiment, the iodine content of the first polarizer and the second polarizer is 1.8 wt% to 5.0 wt%.

  In a preferred embodiment, the slow axis direction of the first protective layer is substantially perpendicular to the absorption axis direction of the first polarizer.

The normally black liquid crystal panel using the set of polarizing plates of the present invention has a higher contrast ratio in the front direction than a conventional liquid crystal panel by using two polarizing plates having different transmittances. Can be provided.

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. 1 is a schematic cross-sectional view of a liquid crystal display device according to a preferred embodiment of the present invention.

<Definition of terms and symbols>
The definitions of terms and symbols in this specification are as follows.
(1) Transmittance of polarizing plate The transmittance (T) is a Y value of tristimulus values based on the 2-degree field of JlS Z 8701-1995.
(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]) is an in-plane retardation value at a wavelength λ (nm) at 23 ° C. Re [λ] is obtained by Re [λ] = (nx−ny) × d where the thickness of the sample is d (nm).
(4) Thickness direction retardation value:
The thickness direction retardation value (Rth [λ]) is a thickness direction retardation value at 23 ° C. and a wavelength λ (nm). Rth [λ] is obtained by Rth [λ] = (nx−nz) × d where the thickness of the sample is d (nm).
(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. Here, Rth [λ] represents a retardation value in the thickness direction at a wavelength λ (nm) at 23 ° C., and d represents a thickness (nm) of the film.
(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 °.
(9) In this specification, for example, the subscript “1” represents the first polarizing plate, and the subscript “2” represents the second polarizing plate.

<A. Overview of LCD panel>
The liquid crystal panel of the present invention includes at least a liquid crystal cell, a first polarizing plate disposed on one side of the liquid crystal cell, and a second polarizing plate disposed on the other side of the liquid crystal cell. The first polarizing plate includes a first polarizer and a first protective layer disposed on the liquid crystal cell side of the first polarizer, and the refractive index ellipsoid of the first protective layer is , Nx>ny> nz. The transmittance (T ₁ ) of the first polarizing plate is larger than the transmittance (T ₂ ) of the second polarizing plate. The liquid crystal panel is normally black. 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 difference (ΔT = T ₁ −T ₂ ) between the transmittance (T ₁ ) of the _first polarizing plate and the transmittance (T ₂ ) of the second 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 0.3% to 2.5%. . By using two polarizing plates having a transmittance difference in the above range, a liquid crystal display device having a higher contrast ratio in the front direction can be obtained.

  The liquid crystal panel of the present invention has a significantly higher contrast ratio in the front direction than conventional liquid crystal panels (typically, the transmittance of the two polarizing plates arranged on both sides of the liquid crystal cell is the same). It has the feature of being high. In this way, two polarizing plates having different transmittances are arranged in a specific positional relationship, and one polarizing plate includes a protective layer showing a relationship of a specific refractive index ellipsoid, so that The ability to provide a liquid crystal display device having a high contrast ratio is a finding that has been found for the first time by the present inventors, and is an unexpectedly excellent effect. Such an effect is particularly remarkable in a normally black liquid crystal panel that performs black display without driving liquid crystal molecules in the liquid crystal cell. It is considered that the effect obtained by using two polarizing plates having different transmittances is not hindered by driving of liquid crystal molecules.

  FIG. 1 is a schematic cross-sectional view of a liquid crystal panel in 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. 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. Is provided. The first polarizing plate 21 includes a first polarizer 31 and a first protective layer 33 disposed on the liquid crystal cell side of the first polarizer 31. The second polarizing plate 22 includes a second polarizer 32 and a second protective layer 34 disposed on the liquid crystal cell side of the second polarizer 32. In the illustrated example, a configuration is shown in which the first polarizing plate 21 is disposed below the liquid crystal cell 10 and the second polarizing plate 22 is disposed above the liquid crystal cell. It may be a configuration in which is turned upside down.

  Practically, any other protective layer or any surface treatment layer may be disposed on the side of the first and / or second polarizer opposite to the side including the liquid crystal cell. Further, an arbitrary adhesive layer may be provided between the constituent members of the liquid crystal panel. The “adhesive layer” refers to a layer that joins surfaces with adjacent members and integrates them with practically sufficient adhesive force and adhesion time. Examples of the material for forming the adhesive layer include an adhesive, a pressure-sensitive adhesive, and an anchor coating agent. The adhesive layer may have a multilayer structure in which an anchor coating agent is formed on the surface of an adherend and an adhesive layer or a pressure-sensitive adhesive layer is formed thereon. Further, it may be a thin layer (also referred to as a hairline) that cannot be visually recognized. Hereinafter, although the detail of the structural member of this invention is demonstrated, this invention is not limited only to the following specific embodiment.

<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 active 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. Means 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, the 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 exhibits a relationship of nz> nx = ny. As the liquid crystal cell in which the refractive index ellipsoid shows a relationship of nz> nx = ny, according to the drive mode classification, for example, a vertical alignment (VA) mode, a twisted nematic (TN) mode, a vertical alignment type, An electric field control birefringence (ECB) mode, an optical compensation birefringence (OCB) mode, and the like can be given. In the present invention, the driving mode of the liquid crystal cell is particularly preferably 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.

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>
The first polarizing plate used in the present invention includes a first polarizer and a first protective layer disposed on the liquid crystal cell side of the first polarizer. The second polarizing plate preferably includes a second polarizer and a second protective layer disposed on the liquid crystal cell side of the second polarizer. 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 of the polarizing plate is usually 20 μm to 500 μm.

  Preferably, the second polarizing plate is disposed on the viewing side of the liquid crystal cell, and the first 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.

The transmittance (T ₁ ) of the first 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 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 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 ₂ by the above range, further, it is possible to contrast ratio in the front direction obtain high liquid crystal display device.

  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 preparing 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 P in 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. These transmittances are Y values of tristimulus values based on the 2-degree field of JlS Z 8701-1995.

<D. Polarizer>
In this specification, the “polarizer” refers to one that converts natural light or polarized light into linearly polarized light. Any appropriate polarizer can be selected. Preferably, the polarizer has a function of separating incident light into two orthogonal polarization components, transmitting one polarization component, and absorbing, reflecting, and / or scattering the other polarization component.

  The first polarizer and the second polarizer used in the present invention are preferably composed mainly of a polyvinyl alcohol-based resin containing iodine. The first and second polarizers can usually be obtained by stretching a polymer film containing as a main component a polyvinyl alcohol-based resin containing iodine. 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 polarizer is preferably I ₂ > I ₁ . The difference (ΔI = I ₂ −I ₁ ) between the iodine content (I ₂ ) of the _second polarizer and the iodine content (I ₁ ) of the first polarizer 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 1.2% 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 wt% to 5.0 wt%, more preferably 2.0 wt% to 4.0 wt%. is there. The iodine content of the first 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. The iodine content of the second polarizer is preferably 2.3 wt% to 5.0 wt%, more preferably 2.5 wt% to 4.5 wt%, and particularly preferably 2. wt%. 5% to 4.0% 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, the first polarizer and the second polarizer further contain 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, the first polarizer and the second polarizer further contain 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 for obtaining a polarizing plate having excellent optical properties is preferably 0.01 parts by weight to 0.15 parts by weight with respect to 100 parts by weight of water. More preferably, it is 0.01 weight part-0.05 weight part. 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 to the first crosslinking bath and the second crosslinking bath for obtaining a polarizing plate having excellent optical properties is preferably 0.1% with respect to 100 parts by weight of water. 5 to 10 parts by weight, more preferably 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 amounts of potassium iodide and boric acid to be in the above ranges, a polarizing plate having a preferable range of transmittance and a high degree of polarization can be obtained.

<E. First protective layer>
The first protective layer used in the present invention is disposed between the first polarizer and the liquid crystal cell. The first protective layer is used, for example, to prevent the first polarizer from contracting or expanding. The first protective layer is preferably bonded to the first polarizer through an adhesive layer. The first protective layer may be a single layer or a laminate composed of a plurality of layers. The thickness of the first protective layer is preferably 10 μm to 200 μm. The transmittance (T [590]) at a wavelength of 590 nm of the first protective layer is preferably 90% or more.

  In the first protective layer, the refractive index ellipsoid exhibits a relationship of nx> ny> nz (negative biaxiality). As the first protective layer, a retardation film exhibiting any appropriate optical anisotropy may be used as long as the refractive index ellipsoid shows a relationship of nx> ny> nz as the whole layer. The first protective layer may be formed of, for example, (1) one or a plurality of retardation films whose refractive index ellipsoid shows a relationship of nx> ny> nz. Or (2) one or a plurality of retardation films whose refractive index ellipsoid shows a relationship of nx> ny = nz and one or a plurality of retardation films whose refractive index ellipsoid shows a relationship of nx = ny> nz You may form from retardation film. Alternatively, (3) one or a plurality of retardation films in which the refractive index ellipsoid shows a relationship of nx> ny> nz, and the refractive index ellipsoid has a relationship of nx = ny> nz or a relationship of nx> ny = nz. May be formed from one or a plurality of retardation films.

  The liquid crystal cell can be optically compensated only by disposing a layer having a refractive index ellipsoid of nx> ny> nz between the first polarizer and the second polarizer. For this reason, there is an advantage that a thin and low-cost liquid crystal panel can be obtained. Such a liquid crystal panel that compensates using only one layer having optical anisotropy is also referred to as a “single-layer compensation liquid crystal panel”.

  Preferably, the slow axis direction of the first protective layer is substantially orthogonal to the absorption axis direction of the first polarizer. The angle formed by the slow axis direction of the first protective layer and the absorption axis of the first polarizer is preferably within 90 ° ± 2 °, and more preferably within 90 ° ± 1 °. . By setting the angle formed by the two optical axes within the above range, a liquid crystal display device having a higher contrast ratio in the front direction can be obtained.

  The thickness direction retardation value (Rth [590]) of the first protective layer at a wavelength of 590 nm is larger than the in-plane retardation value (Re [590]). The difference between Rth [590] and Re [590] (Rth [590] −Re [590]) is preferably 10 nm to 400 nm or more, more preferably 30 nm to 300 nm, and particularly preferably 50 nm to 250 nm. It is.

  Re [590] of the first protective layer is preferably 10 nm or more, more preferably 20 nm to 160 nm, and particularly preferably 30 nm to 80 nm. Rth [590] of the first protective layer is preferably 50 nm to 500 nm, more preferably 100 nm to 400 nm, and particularly preferably 150 nm to 300 nm. By setting Re [590] and Rth [590] in the above ranges, a liquid crystal display device having a high contrast ratio in the oblique direction in addition to the front direction and having excellent display characteristics can be obtained.

  The Nz coefficient of the first protective 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-layer compensation type liquid crystal panel can be obtained. Furthermore, a liquid crystal display device having a high contrast ratio in an oblique direction in addition to the front direction and having excellent display characteristics can be obtained.

  As the material for forming the first protective layer, any appropriate material can be adopted as long as the refractive index ellipsoid shows a relationship of nx> ny> nz. Preferably, the first protective layer is at least one thermoplastic resin selected from the group consisting of polyimide resins, cellulose resins, norbornene resins, polycarbonate resins, polyamide resins, and polyester resins. Is a retardation film containing. The retardation film preferably contains 60 to 100 parts by weight of the thermoplastic resin with respect to 100 important parts of the total solid content.

  In the present specification, the “thermoplastic resin” includes a polymer having a polymerization degree of 20 or more and a large weight average molecular weight (so-called high polymer), and further having a polymerization degree of 2 or more and less than 20, and having a weight average. Includes low polymers (so-called oligomers) having a molecular weight of about several thousand. In the present specification, the “resin” may be a homopolymer obtained from one type of monomer or a copolymer obtained from two or more types of monomers.

More preferably, the first protective layer contains a retardation film (A) containing a polyimide resin or a cellulose resin, or a retardation film (b ₁ ) containing a polyimide resin and a cellulose resin. a retardation film _{(b 2)} and the laminate (B). The laminate (B) is a film in which a retardation film containing a polyimide resin is bonded to a retardation film containing a cellulose resin via an adhesive layer, or contains a polyimide resin. It is preferable that the retardation film to be formed is directly formed on the surface of the retardation film containing a cellulose resin by a method such as welding.

In the laminate (B), the retardation film (b ₁ ) containing a polyimide resin often exhibits a property that the retardation becomes smaller as the wavelength increases (so-called positive wavelength dispersion characteristic). The retardation film (b ₂ ) to be contained often exhibits a property (so-called reverse wavelength dispersion characteristic) in which the retardation increases as the wavelength increases. In this case, for example, by appropriately changing the thickness ratio of the retardation films (b ₁ ) and (b ₂ ) of the laminate (B), the wavelength dispersion characteristics of the laminate (B) can be changed. The liquid crystal cell can be made suitable for optical compensation.

[Polyimide resin]
When the polyimide-based resin is formed into a sheet by the solvent casting method, since the molecules are likely to be spontaneously oriented in the process of evaporation of the solvent, a film in which the refractive index ellipsoid shows a relationship of nx = ny> nz, It can be made very thin. The retardation film in which the refractive index ellipsoid shows a relationship of nx>ny> nz is obtained by shrinking and / or stretching the film in which the refractive index ellipsoid shows the relationship of nx = ny> nz in at least one direction. be able to. If a polyimide resin is used as a material for forming the retardation film, desired optical anisotropy can be obtained without using a complicated stretching method. For this reason, for example, 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 axis misalignment does not occur even if it is attached to a polarizer. small. As a result, a liquid crystal display device with a high contrast ratio in the front direction can be obtained.

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.

  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). Since polyimide resins containing these repeating units are excellent in solubility in general-purpose solvents, film formation by a solvent casting method is possible. Furthermore, a thin layer of the polyimide resin can be formed on a substrate having poor solvent resistance such as a triacetyl cellulose film without excessively eroding the surface.

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 produced by stretching a 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 film is stretched (stretching temperature) is preferably 120 ° C to 200 ° C. Moreover, the magnification (stretching ratio) for stretching the film is preferably more than 1 and not more than 3 times.

[Cellulosic resin]
Arbitrary appropriate things can be employ | adopted for the said cellulose resin. The cellulose resin is preferably a cellulose organic acid ester or a cellulose mixed organic acid ester in which some or all of the hydroxyl groups of cellulose are substituted with acetyl groups, propionyl groups, and / or butyl groups. Examples of the cellulose organic acid ester include cellulose acetate, cellulose propionate, and cellulose butyrate. Examples of the cellulose mixed organic acid ester include cellulose acetate propionate and cellulose acetate butyrate. The cellulose resin can be obtained, for example, by the method described in JP-A-2001-188128 [0040] to [0041].

  The acetyl substitution degree of the cellulose acetate is preferably 2.0 to 3.0, more preferably 2.5 to 3.0. The propionyl substitution degree of the cellulose propionate is preferably 2.0 to 3.0, more preferably 2.5 to 3.0. When the cellulose resin is a mixed organic acid ester in which a part of the hydroxyl groups of cellulose is substituted with an acetyl group and a propionyl group, the total of the acetyl substitution degree and the propionyl substitution degree is preferably 2.0 to 3. It is 0, More preferably, it is 2.5-3.0. In this case, the degree of acetyl substitution is preferably 0.1 to 2.9, and the degree of propionyl substitution is preferably 0.1 to 2.9.

  In the present specification, the acetyl substitution degree (or propionyl substitution degree) indicates the number of hydroxyl groups attached to carbons at the 2, 3, 6 positions in the cellulose skeleton with acetyl groups (or propionyl groups). The acetyl group (or propionyl group) may be biased to any of the carbons at the 2, 3 and 6 positions of the cellulose skeleton, and may be present on average in each carbon. The said acetyl substitution degree can be calculated | required by ASTM-D817-91 (test methods, such as a cellulose acetate). Moreover, the said propionyl substitution degree can be calculated | required by ASTM-D817-96 (test methods, such as a cellulose acetate).

  The weight average molecular weight (Mw) of the cellulose resin is preferably 20,000 to 1,000,000, as measured by gel permeation chromatography (polystyrene standard) using a tetrahydrofuran solvent. The glass transition temperature (Tg) of the cellulose resin is preferably 110 ° C to 185 ° C. The glass transition temperature (Tg) can be determined by a DSC method according to JIS K7121. If it is said resin, it has the outstanding thermal stability and the film excellent in mechanical strength can be obtained.

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

  As the retardation film, a commercially available film can be used as it is. Alternatively, a commercially available film subjected to secondary processing such as stretching and / or shrinking can be used. As a polymer film containing a commercially available cellulose resin, for example, Fuji Photo Film Co., Ltd. Fujitac series (trade name: ZRF80S, TD80UF, TDY-80UL), Konica Minolta Opto Co., Ltd. trade name “KC8UX2M” Or the like.

  The retardation film used as the first protective layer 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 main resin.

<F. Second protective layer>
The second protective layer used in the present invention is disposed between the second polarizer and the liquid crystal cell. The second protective layer is used, for example, to prevent the second polarizer from contracting or expanding. The second protective layer is preferably bonded to the second polarizer through an adhesive layer. The second protective layer may be a single layer or a laminate composed of a plurality of layers. The thickness of the second protective layer is preferably 10 μm to 200 μm. The transmittance (T [590]) at a wavelength of 590 nm of the second protective layer is preferably 90% or more.

  In the second protective layer, the refractive index ellipsoid preferably has a relationship of nx = ny> nz or nx = ny = nz. In the present specification, “nx = ny” means that Re [590] of the second protective layer is less than 10 nm, preferably 5 nm or less. In addition, “nx = nz” means that | Rth [590] | of the second protective layer is less than 10 nm, preferably less than 5 nm.

  When the refractive index ellipsoid of the second protective layer shows a relationship of nx = ny> nz, preferably Rth [590] of the second protective layer is equal to Rth [590] of the first protective layer. ], The liquid crystal cell can be appropriately set so as to be optically compensated. Rth [590] of the second protective layer is preferably 20 nm to 80 nm.

  Any appropriate material can be adopted as the material for forming the second protective layer. Preferably, the second 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.

<G. Other protective layers>
The first polarizing plate used in the present invention includes a third protective layer on the side opposite to the liquid crystal cell side of the first polarizer, and the second polarizing plate is a liquid crystal of the second polarizer. A fourth protective layer is provided on the side opposite to the cell side. The third and fourth protective layers are used, for example, to prevent the polarizer from contracting or expanding, or to prevent deterioration due to ultraviolet rays. The third and fourth protective layers may be the same or different.

  Any appropriate layer can be adopted as the third and fourth protective layers. The thicknesses of the third and fourth protective layers are preferably 10 μm to 200 μm. The transmittance (T [590]) at a wavelength of 590 nm of the third and fourth protective layers is preferably 90% or more. Any appropriate material can be adopted as the material for forming the third and fourth protective layers. Preferably, the third and fourth protective layers are polymer films containing a cellulose resin, a norbornene resin, or an acrylic resin.

  The third and fourth protective layers may have a surface treatment layer on the side opposite to the polarizer side. The surface treatment layer can be appropriately treated according to the purpose. Examples of the surface treatment layer include treatment layers such as hard coat treatment, antistatic treatment, antireflection treatment (also referred to as antireflection treatment), and diffusion treatment (also referred to as antiglare treatment). 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 formed by fixing a treatment agent for forming the treatment layer on the surface of a base film. The base film may also serve as the protective layer. Further, the surface treatment layer may have a multilayer structure in which, for example, a hard coat treatment layer is laminated on an antistatic treatment layer.

  As the third and fourth protective layers, commercially available polymer films provided with a surface treatment layer can be used as they are. Alternatively, a commercially available polymer film can be used after any surface treatment. Examples of the diffusion treatment (antiglare treatment) include AG150, AGS1, and AGS2 manufactured by Nitto Denko Corporation. Examples of the antireflection treatment (anti-reflection treatment) 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. Examples of the commercially available surface treatment layer that has been subjected to the antireflection treatment include ReaLook series manufactured by NOF Corporation.

<H. Liquid crystal display>
The liquid crystal display device of the present invention includes the liquid crystal panel. FIG. 3 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. 3 is different from the actual one. 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. It should be noted that the optical member illustrated in FIG. 3 may be partially omitted depending on the application, such as the illumination method of the liquid crystal display device and the driving mode of the liquid crystal cell, as long as the effects of the present invention are exhibited. 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 the Y value of the tristimulus value based on the 2-degree field of JlS Z 8701-1995.
(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 Corporation. 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.
-Sample: A sample was dissolved in tetrahydrane to prepare a 0.1 wt% solution.
-Pretreatment: After standing for 8 hours, it was filtered through 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 (differential refractometer)
-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 Corporation, the lens is placed at a position 50 cm above the panel to display a white image and a black image. In this case, the Y value of the XYZ display system was measured. From the Y value (Y _W ; white luminance) in the white image and the Y value (Y _B ; black luminance) in the black image, the contrast ratio “Y _W / Y _B ” in the front direction was calculated.

Production of Polarizer [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. This polarizer A had iodine content = 2.95% by weight, potassium content = 0.62% by weight, and boric acid content = 2% by weight.
<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]
Polarizer 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 0.030 parts by weight with respect to 100 parts by weight of water in the dye bath. This polarizer B had an iodine content = 2.63 wt%, a potassium content = 0.60 wt%, and a boric acid content = 2 wt%.

[Reference Example 3]
A polarizer 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. This polarizer C had an iodine content = 2.09 wt%, a potassium content = 0.58 wt%, and a boric acid content = 2 wt%.

Preparation of first protective 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%.

上記ポリイミド粉末をメチルイソブチルケトンに溶解し、１５重量％のポリイミド溶液を調製した。このポリイミド溶液を、厚み８０μｍのトリアセチルセルロースフィルム（富士写真フィルム（株）製 商品名「ＴＤ８０ＵＦ」；Ｒｅ［５９０］＝０ｎｍ、Ｒｔｈ［５９０］＝６０ｎｍ）の表面に、スロットダイコーターにてシート状に均一に流延した。次に、該フィルムを多室型の空気循環式乾燥オーブン内へ投入し、８０℃で２分間、１３５℃で５分間、１５０℃で１０分間と低温から徐々に昇温しながら溶剤を蒸発させて、ポリイミド層とトリアセチルセルロースフィルムとの積層体を得た。次に、該積層体を、テンター延伸機を用いて、固定端横一軸延伸法により、１４７℃で１．１４倍に延伸して、厚み３．４μｍのポリイミド層とトリアセチルセルロースフィルムとの積層体（Ｂ）を得た。上記積層体（Ｂ）は、屈折率楕円体がｎｘ＞ｎｙ＞ｎｚの関係を示し、Ｔ［５９０］＝９１％、Ｒｅ［５９０］＝５０ｎｍ、Ｒｔｈ［５９０］＝２７０ｎｍ、Ｎｚ係数＝４．８であった。なお、上記積層体（Ｂ）のポリイミド層部分の光学特性は、Ｒｅ［５９０］＝４８ｎｍ、Ｒｔｈ［５９０］＝２１０ｎｍ、Δｎ_ｘｚ＝０．０６であった。

The polyimide powder was dissolved in methyl isobutyl ketone to prepare a 15% by weight polyimide solution. This polyimide solution is sheeted with a slot die coater on the surface of a 80 μm thick triacetylcellulose film (trade name “TD80UF” manufactured by Fuji Photo Film Co., Ltd .; Re [590] = 0 nm, Rth [590] = 60 nm). Cast uniformly. 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. Thus, a laminate of the polyimide layer and the triacetyl cellulose film was obtained. Next, the laminate is stretched 1.14 times at 147 ° C. by a fixed-end lateral uniaxial stretching method using a tenter stretching machine, and a laminate of a polyimide layer having a thickness of 3.4 μm and a triacetyl cellulose film is laminated. A body (B) was obtained. In the laminate (B), the refractive index ellipsoid shows a relationship of nx>ny> nz, T [590] = 91%, Re [590] = 50 nm, Rth [590] = 270 nm, Nz coefficient = 4. It was 8. The optical properties of the polyimide layer portion of the laminate (B) were Re [590] = 48 nm, Rth [590] = 210 nm, and Δn _xz = 0.06.

Production of first polarizing plate [Reference Example 5]
On one side of the polarizer A obtained in Reference Example 1, via a water-soluble adhesive mainly composed of a polyvinyl alcohol-based resin (trade name “GOHSEIMER Z200” manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) In the laminate (B) obtained in Reference Example 4, the triacetylcellulose side of the laminate (B) is opposed to the polarizer A, and the slow axis direction of the laminate (B) is The polarizer A was attached so as to be orthogonal to the absorption axis direction of the polarizer A. Next, on the other side 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.) is passed through the water-soluble adhesive. Sticked. The polarizing plate A1 had a degree of polarization of 99.9% and a transmittance (T ₁ ) of 41.5%.

[Reference Example 6]
A polarizing plate B1 was produced in the same manner as in Reference Example 5 except that the polarizer B obtained in Reference Example 2 was used in place of the polarizer A. The polarizing plate B1 had a degree of polarization of 99.9% and a transmittance (T ₁ ) of 42.6%.

[Reference Example 7]
A polarizing plate C1 was produced in the same manner as in Reference Example 5 except that the polarizer C obtained in Reference Example 3 was used in place of the polarizer A. The polarizing plate C1 had a degree of polarization of 99.9% and a transmittance (T ₁ ) of 43.5%.

Preparation of second polarizing plate [Reference Example 8]
On both sides of the polarizer A obtained in Reference Example 1, a water-soluble adhesive having a polyvinyl alcohol resin as a main component (trade name “Goseifamer Z200” manufactured by Nippon Gosei Kagaku Kogyo Co., Ltd.) is used. A polymer film containing 80 μm cellulosic resin (trade name “TD80UF” manufactured by Fuji Photo Film Co., Ltd .; Re [590] = 0 nm, Rth [590] = 60 nm) was attached to produce polarizing plate A2. . The polarizing plate A2 had a degree of polarization of 99.9% and a transmittance (T ₂ ) of 41.5%.

[Reference Example 9]
A polarizing plate B2 was produced in the same manner as in Reference Example 8, except that the polarizer B obtained in Reference Example 2 was used in place of the polarizer A. The polarizing plate B2 had a degree of polarization of 99.9% and a transmittance (T ₂ ) of 42.6%.

[Reference Example 10]
A polarizing plate C2 was produced in the same manner as in Reference Example 9 except that the polarizer C obtained in Reference Example 3 was used in place of the polarizer A. The polarizing plate C2 had a degree of polarization of 99.9% and a transmittance (T ₂ ) of 43.5%.

Preparation of liquid crystal cell [Reference Example 11]
A liquid crystal panel is taken out of a commercially available normally black liquid crystal display device [Sony 40-inch liquid crystal television product name “BRAVIA KDL-32V1000”] including a VA mode liquid crystal cell, and polarized light arranged above and below the liquid crystal cell. All optical films such as plates were 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 (I)
[Example 1]
On the viewing side of the liquid crystal cell A prepared in Reference Example 12, the polarizing plate B1 prepared in Reference Example 6 is used as the first polarizing plate, the laminate (B) side is the liquid crystal cell side, and the absorption axis of the polarizing plate B1. It was stuck via an acrylic pressure-sensitive adhesive (thickness 20 μm) so that the direction was substantially parallel to the long side direction of the liquid crystal cell A. Next, on the opposite side (backlight side) to the viewing side of the liquid crystal cell A, the polarizing plate A2 produced in Reference Example 8 is used as the second polarizing plate, and the absorption axis direction of the polarizing plate A2 is the liquid crystal. It was stuck via an acrylic adhesive (thickness 20 μm) so as to be substantially perpendicular to the long side direction of the cell A. 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 normally black liquid crystal panel A produced in this way 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 1 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 C1 produced in Reference Example 7 was used as the first polarizing plate. Table 1 shows the characteristics of the obtained liquid crystal display device B.

[Comparative Example 1]
In the same manner as in Example 1, except that the polarizing plate A1 prepared in Reference Example 5 was used as the first polarizing plate, and the polarizing plate B2 prepared in Reference Example 9 was used as the second polarizing plate. A liquid crystal panel H and a liquid crystal display device H were produced. The characteristics of the obtained liquid crystal display device H are shown in Table 1.

[Comparative Example 2]
In the same manner as in Example 1, except that the polarizing plate A1 prepared in Reference Example 5 was used as the first polarizing plate, and the polarizing plate C2 prepared in Reference Example 10 was used as the second polarizing plate. A liquid crystal panel I and a liquid crystal display device I were produced. Table 1 shows the characteristics of the obtained liquid crystal display device I.

[Comparative Example 3]
In the same manner as in Example 1, except that the polarizing plate C1 prepared in Reference Example 7 was used as the first polarizing plate, and the polarizing plate C2 prepared in Reference Example 10 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 1.

[Comparative Example 4]
In the same manner as in Example 1, except that the polarizing plate A1 prepared in Reference Example 5 was used as the first polarizing plate, and the polarizing plate A2 prepared in Reference Example 8 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.

Production of liquid crystal panel and liquid crystal display device (II)
[Example 3]
On the viewing side of the liquid crystal cell A prepared in Reference Example 12, the polarizing plate A2 prepared in Reference Example 8 is used as the second polarizing plate, and the absorption axis direction of the polarizing plate A2 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) to the viewing side of the liquid crystal cell A, the polarizing plate B1 produced in Reference Example 6 is used as the first polarizing plate, and the laminate (B) side is the liquid crystal cell side. The polarizing plate B1 was attached via an acrylic pressure-sensitive adhesive (thickness 20 μm) so that the absorption axis direction of the polarizing plate B1 was substantially orthogonal to the long side direction of the liquid crystal cell A. 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. This liquid crystal panel C was combined with the backlight unit of the original liquid crystal display device to produce a liquid crystal display device C. The characteristics of the obtained liquid crystal display device C are shown in Table 2 below.

[Example 4]
A liquid crystal panel D and a liquid crystal display device D were produced in the same manner as in Example 1 except that the polarizing plate C1 produced in Reference Example 7 was used as the first polarizing plate. The characteristics of the obtained liquid crystal display device D are shown in Table 1.

[Comparative Example 5]
In the same manner as in Example 3, except that the polarizing plate B2 prepared in Reference Example 9 was used as the second polarizing plate, and the polarizing plate A1 prepared in Reference Example 5 was used as the first polarizing plate. A liquid crystal panel O and a liquid crystal display device O were produced. Table 2 shows the characteristics of the obtained liquid crystal display device O.

[Comparative Example 6]
In the same manner as in Example 3, except that the polarizing plate C2 prepared in Reference Example 10 was used as the second polarizing plate, and the polarizing plate A1 prepared in Reference Example 5 was used as the first polarizing plate. A liquid crystal panel P and a liquid crystal display device P were produced. Table 2 shows the characteristics of the obtained liquid crystal display device P.

[Comparative Example 7]
In the same manner as in Example 3, except that the polarizing plate C2 prepared in Reference Example 10 was used as the second polarizing plate, and the polarizing plate C1 prepared in Reference Example 7 was used as the first polarizing plate. A liquid crystal panel Q and a liquid crystal display device Q were produced. The characteristics of the obtained liquid crystal display device Q are shown in Table 2.

[Evaluation]
In the liquid crystal display device including the liquid crystal panel of the present invention, as shown in Examples 1 to 4, the transmittance (T ₁ ) of the first polarizing plate is larger than the transmittance (T ₂ ) of the second polarizing plate. As a result, the contrast ratio in the front direction can be remarkably increased as compared with the conventional liquid crystal display device. On the other hand, in the liquid crystal display devices of Comparative Examples 1 to 7, the transmittance (T ₁ ) of the first polarizing plate is smaller than the transmittance (T ₂ ) of the second polarizing plate, or The transmittance (T ₁ ) of the polarizing plate ₁ and the transmittance (T ₂ ) of the second polarizing plate were equal, but the contrast ratio in the front direction was small.

  As described above, since the liquid crystal panel of the present invention can increase the contrast ratio in the front direction when used in a liquid crystal display device, for example, to improve the display characteristics of a liquid crystal television, a personal computer monitor, and a mobile phone. Very useful.

DESCRIPTION OF SYMBOLS 10 Liquid crystal cell 21 1st polarizing plate 21 2nd polarizing plate 31 1st polarizer 32 2nd polarizer 33 1st protective layer 34 2nd protective layer 100 Liquid crystal panel 80 Backlight unit 81 Light source 82 Reflection Film 83 Diffusion plate 84 Prism sheet 85 Brightness enhancement film 200 Liquid crystal display device 300 Feeding section 301 Polymer film 310 Swelling baths 311, 312, 321, 322, 331, 332 Roll 320 Dyeing bath 330 First cross-linking bath 340 Second Cross-linking bath 350 Flushing bath 360 Drying means 370 Polarizer 380 Winding unit

Claims (4)

A first polarizing plate and a second polarizing plate;
The first polarizing plate includes a first polarizer and a first protective layer disposed on one side of the first polarizer, and the refractive index ellipsoid of the first protective layer is nx >Ny> nz,
The transmittance (T ₁ ) of the _first polarizing plate is larger than the transmittance (T ₂ ) of the _second polarizing plate, the transmittance (T ₁ ) of the _first polarizing plate, and the second The difference (ΔT = T ₁ −T ₂ ) from the transmittance (T ₂ ) of the polarizing plate is 0.1% to 2.0%,
Ri der degree of polarization of the first polarizing plate and second polarizing plate at least 99.8%,
The slow axis direction of the first protective layer is substantially perpendicular to the absorption axis direction of the first polarizer;
Here, the transmittance is the Y value of the tristimulus value based on the 2-degree visual field of JIS Z 8701-1995 .
A set of normally black polarizing plates for LCD panels.   The set of polarizing plates according to claim 1, wherein the second polarizing plate is a viewing side polarizing plate, and the first polarizing plate is a backlight side polarizing plate. The difference (ΔI = I ₂ −I ₁ ) between the iodine content (I ₂ ) of the _second polarizer and the iodine content (I ₁ ) of the first polarizer is 0.1 wt% to The set of polarizing plates according to claim 1 or 2, which is 1.4% by weight. The set of polarizing plates according to any one of claims 1 to 3, wherein the iodine content of the first polarizer and the second polarizer is 1.8 wt% to 5.0 wt%.

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