JP2017181871A - Polarizing plate set and IPS mode liquid crystal display device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a set of polarizing plates for a specific IPS mode liquid crystal cell capable of ensuring good visibility even in an environment with strong external light, and an IPS mode liquid crystal display device using the same. An absorption axis of a viewing-side polarizing plate and a back-side polarizing plate are orthogonal to each other, the viewing-side polarizing plate has a first polarizer and a λ / 4 plate, and the λ / 4 plate has a first. It is arranged between the polarizer and the liquid crystal cell, the angle between the absorption axis of the viewing side polarizing plate and the slow axis of the λ / 4 plate is 45 °, and the back side polarizing plate is the second polarizing element. And λ / 2 plate, the λ / 2 plate is arranged between the second polarizer and the liquid crystal cell, and forms the absorption axis of the back side polarizing plate and the slow axis of the λ / 2 plate. The angle is 45 °, the slow axis of the λ / 4 plate and the slow axis of the λ / 2 plate are parallel, and the Nz coefficient of the λ / 4 plate and the λ / 2 plate is -0.5 or more and 0.5. A set of polarizing plates in which the slow axis of the λ / 4 plate is arranged in a relationship orthogonal to the initial orientation direction of the IPS mode liquid crystal cell. [Selection diagram] Fig. 2

Description

  The present invention relates to a polarizing plate and an IPS mode liquid crystal display device using the same.

  In recent years, low-power consumption, low-voltage, light-weight and thin liquid crystal displays are rapidly spreading as information display devices such as mobile phones, portable information terminals, computer monitors, and televisions. With the development of liquid crystal technology, liquid crystal displays in various modes have been proposed, and problems with liquid crystal displays such as response speed, contrast, and narrow viewing angle are being solved.

  As mobile phones and personal digital assistants are used outdoors, when external light such as sunlight is strong, external light is not used in liquid crystal display devices equipped with a conventional liquid crystal cell and a conventional polarizing plate set. The problem is that the LCD screen is so strong that it is difficult to see the LCD screen.

  As such measures, measures are taken to reduce external light reflection by providing a low reflection layer on the surface of the viewing side polarizing plate to reduce external light reflection or by using a circular polarizing plate for the viewing side polarizing plate. It is customary.

  However, the visibility is remarkably lowered in an environment where the illuminance of outside light exceeds 5000 lux only with the low reflection layer. In the IPS mode liquid crystal, the in-plane retardation value is usually 250 nm to 380 nm, and it is difficult to dispose a circularly polarizing plate as the viewing side polarizing plate.

JP 2005-128498 A

  An object of the present invention is to provide a set of polarizing plates for a specific IPS mode liquid crystal cell and an IPS mode liquid crystal display device using the same, which can ensure good visibility even in an environment where the illuminance of external light exceeds 5000 lux. There is to do.

[1] A set of polarizing plates for bonding to both surfaces of an IPS mode liquid crystal cell having an in-plane retardation value of 100 nm to 200 nm, comprising a viewing side polarizing plate and a back side polarizing plate,
The absorption axis of the viewing side polarizing plate and the absorption axis of the back side polarizing plate are substantially orthogonal,
The viewing side polarizing plate has a first polarizer and a λ / 4 plate,
The λ / 4 plate is disposed between the first polarizer and the liquid crystal cell,
The angle formed by the absorption axis of the viewing side polarizing plate and the slow axis of the λ / 4 plate is approximately 45 °,
The back side polarizing plate has a second polarizer and a λ / 2 plate,
The λ / 2 plate is disposed between the second polarizer and the liquid crystal cell,
The angle formed by the absorption axis of the back side polarizing plate and the slow axis of the λ / 2 plate is approximately 45 °,
The slow axis of the λ / 4 plate and the slow axis of the λ / 2 plate are substantially parallel;
The Nz coefficient of the λ / 4 plate and the Nz coefficient of the λ / 2 plate are both −0.5 or more and 0.5 or less,
A set of polarizing plates in which the slow axis of the λ / 4 plate is disposed in a substantially perpendicular relationship to the initial alignment direction of the IPS mode liquid crystal cell.
[2] Three layers in which the λ / 4 plate and the λ / 2 plate are formed with a skin layer made of a (meth) acrylic resin composition containing rubber particles on both surfaces of a core layer made of a styrene resin. The set of polarizing plates according to [1], which is a retardation film having a structure.
[3] The set of polarizing plates according to [2], wherein the glass transition temperature of the core layer is 120 ° C. or higher, and the glass transition temperature of the skin layer is 120 ° C. or lower.
[4] An IPS mode liquid crystal display device in which the set of polarizing plates according to any one of [1] to [3] is arranged in an IPS mode liquid crystal cell having an in-plane retardation value of 100 nm to 200 nm.
[5] The IPS mode liquid crystal display device according to [4], wherein the IPS mode liquid crystal display device has a diagonal size of 15 inches or less.

  According to the set of polarizing plates of the present invention, it is possible to provide a liquid crystal display device that can suppress reflection of external light and ensure good visibility even in an environment with strong external light such as outdoors. .

It is a schematic sectional drawing which shows the example of the preferable layer structure in the set of the polarizing plate which concerns on this invention. It is the schematic which shows the example of the preferable axial structure in the IPS liquid crystal display device which concerns on this invention.

  Hereinafter, a set of polarizing plates according to the present invention and a liquid crystal panel using the same will be described with reference to the drawings, but the present invention is not limited to these embodiments.

  FIG. 1 shows a schematic cross-sectional view of an example of a preferred layer structure in a polarizing plate according to the present invention. The polarizing plate of the present invention will be described with reference to FIG. The polarizing plate set shown in FIG. 1 has a λ / 4 plate laminated on one side of a polarizing plate 30 as a viewing side polarizing plate, and a λ / 2 plate 54 on one side of a polarizing plate 50 as a back side polarizing plate. It includes a laminate in which the brightness enhancement film 60 is laminated on the other surface of the polarizing plate 50.

[Each member constituting the viewing side polarizing plate and the back side polarizing plate]
The viewing side polarizing plate and the back side polarizing plate of the present invention include a polarizing plate 30 and a polarizing plate 50.

[Polarizer]
The first polarizer 32 and the second polarizer 52 usually adsorb the dichroic dye by uniaxially stretching the polyvinyl alcohol-based resin film, and dyeing the polyvinyl alcohol-based resin film with the dichroic dye. It is manufactured through a step, a step of treating a polyvinyl alcohol-based resin film adsorbed with a dichroic dye with an aqueous boric acid solution, and a step of washing with water after the treatment with the aqueous boric acid solution.

  As the polyvinyl alcohol resin, a saponified polyvinyl acetate resin can be used. Examples of the polyvinyl acetate resin include, in addition to polyvinyl acetate, which is a homopolymer of vinyl acetate, copolymers with other monomers copolymerizable with vinyl acetate. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and acrylamides having an ammonium group.

  The saponification degree of the polyvinyl alcohol resin is usually about 85 to 100 mol%, preferably 98 mol% or more. This polyvinyl alcohol resin may be modified, and for example, polyvinyl formal and polyvinyl acetal modified with aldehydes can also be used. Moreover, the polymerization degree of polyvinyl alcohol-type resin is about 1,000-10,000 normally, and about 1,500-5,000 are preferable.

  A film obtained by forming such a polyvinyl alcohol-based resin is used as a raw film of the first polarizer 32 and the second polarizer 52. The method for forming a polyvinyl alcohol-based resin is not particularly limited, and can be formed by a known method. The film thickness of the polyvinyl alcohol-based raw film is not particularly limited, but is, for example, about 10 μm to 150 μm.

  Uniaxial stretching of the polyvinyl alcohol-based resin film can be performed before dyeing of the dichroic dye, simultaneously with dyeing, or after dyeing. When uniaxial stretching is performed after dyeing, this uniaxial stretching may be performed before boric acid treatment or during boric acid treatment. Moreover, you may uniaxially stretch in these several steps.

  In uniaxial stretching, it may be uniaxially stretched between rolls having different peripheral speeds, or may be uniaxially stretched using a hot roll. Further, the uniaxial stretching may be dry stretching in which stretching is performed in the air, or may be wet stretching in which stretching is performed in a state where a solvent is used and the polyvinyl alcohol-based resin film is swollen. The draw ratio is usually about 3 to 8 times.

  As a method of dyeing the polyvinyl alcohol resin film with the dichroic dye, for example, a method of immersing the polyvinyl alcohol resin film in an aqueous solution containing the dichroic dye is employed. Specifically, iodine or a dichroic dye is used as the dichroic dye. In addition, it is preferable that the polyvinyl alcohol-type resin film performs the immersion process to water before a dyeing process.

  When iodine is used as the dichroic dye, a method of dyeing a polyvinyl alcohol-based resin film in an aqueous solution containing iodine and potassium iodide is usually employed. The content of iodine in this aqueous solution is usually about 0.01 to 1 part by weight per 100 parts by weight of water. The content of potassium iodide is usually about 0.5 to 20 parts by weight per 100 parts by weight of water. The temperature of the aqueous solution used for dyeing is usually about 20 to 40 ° C. Moreover, the immersion time (dyeing time) in this aqueous solution is usually about 20 to 1800 seconds.

On the other hand, when a dichroic dye is used as the dichroic dye, a method of immersing and dyeing a polyvinyl alcohol-based resin film in an aqueous solution containing a water-soluble dichroic dye is usually employed. The content of the dichroic dye in this aqueous solution is usually about 1 × 10 ⁻⁴ to 10 parts by weight and preferably about 1 × 10 ⁻³ to 1 part by weight per 100 parts by weight of water. This aqueous solution may contain an inorganic salt such as sodium sulfate as a dyeing assistant. The temperature of the aqueous dichroic dye solution used for dyeing is usually about 20 to 80 ° C. Moreover, the immersion time (dyeing time) in this aqueous solution is usually about 10 to 1,800 seconds.

  The boric acid treatment after dyeing with a dichroic dye can usually be performed by immersing the dyed polyvinyl alcohol-based resin film in a boric acid-containing aqueous solution.

  The amount of boric acid in the boric acid-containing aqueous solution is usually about 2 to 15 parts by weight and preferably 5 to 12 parts by weight per 100 parts by weight of water. When iodine is used as the dichroic dye, the boric acid-containing aqueous solution preferably contains potassium iodide. The amount of potassium iodide in the boric acid-containing aqueous solution is usually about 0.1 to 15 parts by weight and preferably about 5 to 12 parts by weight per 100 parts by weight of water. The immersion time in the boric acid-containing aqueous solution is usually about 60 to 1,200 seconds, preferably about 150 to 600 seconds, and more preferably about 200 to 400 seconds. The temperature of the boric acid-containing aqueous solution is usually 50 ° C or higher, preferably 50 to 85 ° C, and more preferably 60 to 80 ° C.

  The polyvinyl alcohol resin film after the boric acid treatment is usually washed with water. The water washing treatment can be performed, for example, by immersing a boric acid-treated polyvinyl alcohol resin film in water. The temperature of water in the water washing treatment is usually about 5 to 40 ° C. Further, the immersion time is usually about 1 to 120 seconds.

  After washing with water, a drying process is performed to obtain the first polarizer 32 and the second polarizer 52. The drying process can be performed using a hot air dryer or a far infrared heater. The temperature of the drying treatment is usually about 30 to 100 ° C, and preferably 50 to 80 ° C. The time for the drying treatment is usually about 60 to 600 seconds, and preferably 120 to 600 seconds.

  By the drying process, the moisture content of the first polarizer 32 and the second polarizer 52 is reduced to a practical level. The water content is usually 5 to 20% by weight, preferably 8 to 15% by weight. When the moisture content is less than 5% by weight, the flexibility of the first polarizer 32 and the second polarizer 52 is lost, and the first polarizer 32 and the second polarizer 52 are damaged after drying. Or it may break. Further, if the moisture content exceeds 20% by weight, the thermal stability of the first polarizer 32 and the second polarizer 52 may be inferior.

  As described above, a polarizer in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based resin film can be produced.

  Further, the stretching, dyeing, boric acid treatment, water washing step, and drying step of the polyvinyl alcohol resin film in the production process of the polarizer may be performed in accordance with, for example, the method described in JP2012-159778A. . In the method described in this document, it is also useful to use a method of forming a polyvinyl alcohol resin layer to be a polarizer by coating a base film with a polyvinyl alcohol resin.

  In order to keep the contraction force of the polarizer under a high temperature environment low, the thickness of the polarizer is preferably 15 μm or less, and more preferably 12 μm or less. The thickness of the polarizer is usually 3 μm or more in that good optical properties can be imparted.

  By using a polarizer with reduced shrinkage in a high temperature environment, it is possible to suppress changes in phase difference due to distortion of the λ / 2 plate and λ / 4 plate due to the shrinkage of the polarizer. Sometimes a polarizing plate with small display unevenness can be obtained.

  The polarizer preferably has a contraction force of 2 N / 2 mm or less per 2 mm width in the absorption axis direction when held at a temperature of 80 ° C. for 240 minutes. If the shrinkage force is greater than 2N / 2 mm, the amount of dimensional change under a high temperature environment increases, and the shrinkage force of the polarizer increases, so that the λ / 2 plate and the λ / 4 plate are easily distorted. Tends to cause cracks in the polarizer. The contraction force of the polarizer tends to be 2N / 2 mm or less when the draw ratio is lowered and when the thickness of the polarizer is reduced. The measuring method of contraction force follows the method of the below-mentioned Example.

A protective film is preferably laminated on at least one surface of the polarizer, and may have a protective film on both surfaces. The protective films 31a, 31b, 51a, 51b can be made of a transparent resin film. In particular, it is preferable to use a material that is excellent in transparency, mechanical strength, thermal stability, moisture shielding properties, and the like. In this specification, the transparent resin film means a resin film having a single transmittance of 80% or more in the visible light region.

  The protective films 31b and 51b are effective means for reducing the thickness of the polarizing plate by giving the λ / 4 plate 34 or the λ / 2 plate 54 a role as a protective film. Similarly, omitting the protective film 51a by providing the brightness enhancement film 60 as a protective film is also an effective means for reducing the thickness of the polarizing plate.

  As the protective films 31a, 31b, 51a, 51b, cellulose-based resins, chain polyolefin-based resins, cyclic polyolefin-based resins, acrylic resins, polyimide-based resins, polycarbonate-based resins, polyester-based resins, and the like have been conventionally used in this field. A film formed from a material widely used as a forming material can be used.

  These resins may contain appropriate additives as long as the transparency is not impaired. Additives such as antioxidants, ultraviolet absorbers, antistatic agents, lubricants, nucleating agents, antifogging agents, antiblocking agents, phase difference reducing agents, stabilizers, processing aids, plasticizers, impact aids , Matting agents, antibacterial agents, fungicides and the like. A plurality of these additives may be used in combination.

  Any optimum method may be appropriately selected as a method for forming a film from the resin as described above. For example, a solvent cast method in which a resin dissolved in a solvent is cast on a metal band or drum, and the solvent is removed by drying to obtain a film. The resin is heated above its melting temperature, kneaded and extruded from a die. A melt extrusion method for obtaining a film by cooling can be used. In the melt extrusion method, a single layer film can be extruded or a multilayer film can be coextruded.

  Moreover, you may use for the protective film 31a the phase difference plate which extended | stretched the said film for improving the visibility when seeing a screen through polarized sunglasses. From the viewpoint of improving visibility, it is desirable to arrange the retardation plate so that the angle formed by the slow axis of the λ / 4 plate and the absorption axis of the polarizing film is about 45 °. Moreover, when laminating | stacking with the polarizing film on long, when the angle | corner with respect to a long long side direction is extended | stretched to about 45 degrees or 135 degrees, since a polarizing plate can be produced by roll-to-roll, it is preferable.

[Surface Treatment Layer 35 of Protective Film 31a]
The protective film 31a may have a surface treatment layer 35 on the surface opposite to the surface bonded to the polarizer 32. Examples of the surface treatment layer 35 include a hard coat layer having a fine surface irregularity shape. The hard coat layer preferably has a pencil hardness higher than H. If the pencil hardness is H or smaller, the surface is likely to be scratched, and if the pencil hardness is scratched, the visibility of the liquid crystal display device is deteriorated. The pencil hardness is determined according to JIS K 5600-5-4: 1999 “General test methods for paints – Part 5: Mechanical properties of coating films – Section 4: Scratch hardness (pencil method)”. It is represented by the hardness of the hardest pencil that does not cause scratches when scratched with a pencil.

  The protective film 31a having the surface treatment layer 35 preferably has a haze value of 0.1 to 45%, more preferably 5 to 40%. When the haze value is larger than 45%, the reflection of external light can be reduced, but the black display screen is reduced. On the other hand, if the haze value is less than 0.1%, sufficient antiglare performance cannot be obtained and external light is reflected on the screen, which is not preferable. Here, the haze value is determined according to JIS K 7136: 2000 “Plastics—How to determine haze of transparent material”.

  The hard coat layer with fine surface irregularities forms a method of forming a coating film containing organic fine particles or inorganic fine particles on the surface of the resin film, or a coating film containing or not containing organic fine particles or inorganic fine particles. Then, it can be formed by a method of pressing against a roll having an uneven shape, such as an embossing method. Such a coating film can be formed by, for example, a method of applying a coating liquid (curable resin composition) containing a binder component made of a curable resin and organic fine particles or inorganic fine particles to the surface of the resin film. .

  In addition to the antiglare treatment (haze imparting treatment) that also serves as a hard coat layer, the protective film 31a has various additional surface treatments such as an antireflection layer, an antistatic treatment, an antifouling treatment, or an antibacterial treatment. It may be applied, and a coating layer made of a liquid crystalline compound or a high molecular weight compound thereof may be formed. In particular, when an antireflection layer of 3% or less is formed, it is preferably used because visibility can be maintained even at 10000 Lux or more. In addition to the surface treatment, the antistatic function may be imparted to other portions of the polarizing plate such as an adhesive layer.

[Protective films 31b and 51b]
As the protective films 31b and 51b, a cellulose resin or a cyclic polyolefin resin is preferable because the retardation value can be easily controlled and is easily available.

  The cellulose resin may be an organic acid ester or mixed organic acid ester of cellulose in which part or all of the hydrogen atoms in the hydroxyl group of cellulose are substituted with an acetyl group, a propionyl group, and / or a butyryl group. Examples include cellulose acetate, propionate, butyrate, and mixed esters thereof. Of these, triacetyl cellulose, diacetyl cellulose, cellulose acetate propionate, cellulose acetate butyrate and the like are preferable.

  The cyclic polyolefin-based resin is obtained by polymerizing cyclic olefin monomers such as norbornene and other cyclopentadiene derivatives in the presence of a catalyst. When such a cyclic polyolefin-based resin is used, a protective film having a predetermined retardation value described later can be easily obtained.

  As the cyclic polyolefin-based resin, for example, ring-opening metathesis polymerization is performed from cyclopentadiene and olefins or (meth) acrylic acid or esters thereof using norbornene obtained by Diels-Alder reaction or a derivative thereof as a monomer. Resin obtained by hydrogenation; ring-opening metathesis polymerization using dicyclopentadiene and olefins or (meth) acrylic acid or esters thereof by tetracyclododecene or a derivative thereof obtained by Diels-Alder reaction, Resin obtained by subsequent hydrogenation; ring-opening metathesis copolymerization of at least two monomers selected from norbornene, tetracyclododecene, derivatives thereof, and other cyclic olefin monomers, Resins obtained by hydrogenation; resins obtained by addition copolymerization of aromatic compounds having chain olefins and / or vinyl groups with cyclic olefins such as norbornene, tetracyclododecene, or derivatives thereof Can be mentioned.

  Any optimum method may be appropriately selected as a method for forming a film from the resin as described above. For example, a solvent cast method in which a resin dissolved in a solvent is cast on a metal band or drum, and the solvent is removed by drying to obtain a film. The resin is heated above its melting temperature, kneaded and extruded from a die. A melt extrusion method for obtaining a film by cooling can be used. In the melt extrusion method, a single layer film can be extruded or a multilayer film can be coextruded.

In order to suppress a decrease in the degree of polarization due to depolarization of the protective films 31b and 51b, the thickness direction retardation value Rth is preferably 10 nm or less. The retardation value Rth in the thickness direction is a value obtained by multiplying the value obtained by subtracting the refractive index in the thickness direction from the in-plane average refractive index, and is defined by the following formula (a). The in-plane retardation value Re is preferably 10 nm or less. The in-plane retardation value Re is a value obtained by multiplying the in-plane refractive index difference by the film thickness, and is defined by the following formula (b).
Rth = _{[(n x + n y) /} 2-n z ] × d (a)
_{Re = (n x -n y)} × d (b)

Wherein, n _x is a refractive index in x-axis direction in the film plane (in-plane slow axis direction), n _y is a y-axis direction (in-plane fast axis direction in the film plane, the plane In the direction perpendicular to the x-axis), _nz is the refractive index in the z-axis direction (thickness direction) perpendicular to the film surface, and d is the thickness of the film.

  Here, the phase difference value can be a value at an arbitrary wavelength in the range of about 500 to 650 nm near the center of visible light, but in this specification, the phase difference value at a wavelength of 590 nm is used as a standard. The retardation value Rth in the thickness direction and the in-plane retardation value Re can be measured using various commercially available retardation meters.

  Examples of a method for controlling the in-plane and thickness direction retardation value Rth of the resin film within a range of 10 nm or less include a method of minimizing the distortion remaining in the in-plane and thickness directions as much as possible. . For example, in the solvent casting method, a method of relaxing residual shrinkage strain in the plane and in the thickness direction generated when the cast resin solution is dried by heat treatment can be employed. On the other hand, in the melt extrusion method, the distance from the die to the cooling drum is reduced as much as possible in order to prevent the resin film from being drawn from the die and cooled, and the extrusion amount and the rotation speed of the cooling drum are reduced. A method of controlling the film so that the film is not stretched can be employed. Moreover, the method of relieving the distortion which remains in the obtained film by heat processing similarly to the solvent casting method is also employable.

[λ / 4 plate 34]
The λ / 4 plate 34 is particularly preferably made of a material excellent in transparency, mechanical strength, thermal stability, moisture shielding properties, and the like. The material of the λ / 4 plate can be composed of a resin that forms the protective film, but it is preferable to use a styrene-based material. Styrenic materials are desirable because they satisfy the refractive index relational expression nz> nx ≧ ny, but are not suitable for use alone due to their brittleness. Therefore, in the present invention, a retardation film having a three-layer structure in which a skin layer made of a (meth) acrylic resin composition containing rubber particles is formed on both surfaces of a core layer made of a styrene resin is used. Is preferred.
The retardation film is also preferable because it has positive wavelength dispersion.

Here, positive wavelength dispersion means that the following formula (c) is satisfied. The number in parentheses is the measurement wavelength (unit: nm) of the phase difference value.

Re (450)> Re (590)> Re (650) (c)

In the present invention, the retardation value of the λ / 4 plate means that the retardation value Re is 120 nm to 160 nm at the measurement wavelength of 590 nm. In the present invention, the λ / 4 plate has an Nz coefficient defined by the following formula (d) in the range of −0.5 to 0.5, preferably in the range of −0.2 to 0.2. is there.

Nz = (nx−nz) / (nx−ny) = Re / Rth + 0.5 (d)

  The λ / 4 plate may be blended with an appropriate additive as long as the transparency is not impaired. Additives such as antioxidants, ultraviolet absorbers, antistatic agents, lubricants, nucleating agents, antifogging agents, antiblocking agents, phase difference reducing agents, stabilizers, processing aids, plasticizers, impact aids , Matting agents, antibacterial agents, fungicides and the like. A plurality of these additives may be used in combination.

  The styrenic resin constituting the core layer can be a homopolymer of styrene or a derivative thereof, and is a binary or higher copolymer of styrene or a derivative thereof and another copolymerizable monomer. You can also Here, the styrene derivative is a compound in which another group is bonded to styrene, such as o-methylstyrene, m-methylstyrene, p-methylstyrene, 2,4-dimethylstyrene, o-ethylstyrene, Alkyl styrene such as p-ethyl styrene, hydroxy styrene, tert-butoxy styrene, vinyl benzoic acid, o-chloro styrene, p-chloro styrene, benzene nucleus of styrene, hydroxyl group, alkoxy group, carboxyl group, halogen And substituted styrene and the like into which is introduced. A terpolymer as disclosed in JP-A-2003-90912 or JP-A-2004-167823 can also be used. The styrenic resin is preferably a copolymer of styrene or a styrene derivative and at least one monomer selected from acrylonitrile, maleic anhydride, methyl methacrylate, and butadiene. The styrenic resin of the core layer is preferably composed of a heat-resistant one, and generally its Tg is 100 ° C. or higher. A more preferable Tg of the styrene resin is 120 ° C. or more.

  The core layer made of styrene resin is desirably set so that its thickness is 10 to 100 μm. If the thickness is less than 10 μm, a sufficient retardation value may not easily be exhibited by stretching. On the other hand, if the thickness exceeds 100 μm, the impact strength of the film tends to be weak and the retardation change due to external stress tends to increase, and white spots are likely to occur when applied to a liquid crystal display device. Display performance is likely to deteriorate.

The skin layers disposed on both surfaces of the core layer made of the styrene resin are made of a (meth) acrylic resin composition in which rubber particles are blended with a (meth) acrylic resin.
Examples of the (meth) acrylic resin include a methacrylic acid alkyl ester or a homopolymer of an acrylic acid alkyl ester, and a copolymer of a methacrylic acid alkyl ester and an acrylic acid alkyl ester. Specific examples of the alkyl methacrylate include methyl methacrylate, ethyl methacrylate, and propyl methacrylate. Specific examples of the alkyl acrylate include methyl acrylate, ethyl acrylate, and propyl acrylate. . As such a (meth) acrylic resin, a commercially available (meth) acrylic resin can be used. Some (meth) acrylic resins are called impact-resistant (meth) acrylic resins, and high heat-resistant (meth) acrylic resins having a glutaric anhydride structure or lactone ring structure in the main chain Also called.

  The rubber particles blended in the (meth) acrylic resin are preferably acrylic. Acrylic rubber particles are particles having rubber elasticity obtained by polymerizing in the presence of a polyfunctional monomer mainly composed of an alkyl acrylate ester such as butyl acrylate or 2-ethylhexyl acrylate. Such rubber elastic particles may be formed as a single layer, or may be a multilayer structure having at least one rubber elastic layer. As the acrylic rubber particles having a multilayer structure, the particles having rubber elasticity as described above are used as cores, and the periphery thereof is covered with a hard alkyl methacrylate ester polymer, or a hard alkyl methacrylate ester polymer. The core is covered with an acrylic polymer having rubber elasticity as described above, and the hard core is covered with an acrylic polymer having rubber elasticity, and the periphery thereof is hard methacrylic acid. Examples thereof include those covered with an alkyl ester polymer. These rubber particles generally have an average diameter of particles formed of an elastic layer in the range of about 50 to 400 nm.

  The content of the rubber particles in the (meth) acrylic resin composition constituting the skin layer is usually about 5 to 50 parts by weight per 100 parts by weight of the (meth) acrylic resin. Since (meth) acrylic resin and acrylic rubber particles are commercially available in a state where they are mixed, commercially available products thereof can be used. Examples of commercially available (meth) acrylic resins containing acrylic rubber particles include “HT55X” and “Technoloy (registered trademark) S001” sold by Sumitomo Chemical Co., Ltd. Such a (meth) acrylic resin composition generally has a Tg of 160 ° C. or lower, but a preferable Tg is 120 ° C. or lower, and further 110 ° C. or lower.

  The skin layer made of a (meth) acrylic resin composition containing rubber particles, preferably acrylic rubber particles, is desirably made to have a thickness of 10 to 100 μm. If the thickness is to be less than 10 μm, film formation tends to be difficult. On the other hand, when the thickness exceeds 100 μm, the retardation of the (meth) acrylic resin layer tends to be ignorable.

  As described above, in the retardation film used in the present invention, the core layer made of a styrene resin preferably has a Tg of 120 ° C. or higher, while a (meth) acrylic resin composition containing rubber particles. The skin layer made of a material preferably has a Tg of 120 ° C. or lower, more preferably 110 ° C. or lower. It is preferable that the Tg of the two layers does not overlap, and the core layer made of styrene resin has a higher Tg than the skin layer made of the (meth) acrylic resin composition containing rubber particles.

  In order to produce the retardation film used in the present invention, for example, a styrene resin and a (meth) acrylic resin composition containing rubber particles may be coextruded and then stretched. In addition, after each single-layer film is produced, heat fusion can be performed by heat lamination and the film can be stretched.

  This retardation film has a three-layer structure in which a skin layer made of a (meth) acrylic resin composition containing rubber particles is formed on both surfaces of a core layer made of a styrene resin. In this three-layer structure, the skin layers arranged on both sides are usually set to substantially the same thickness. Thus, by setting it as a three-layer structure, the skin layer which consists of a (meth) acrylic-type resin composition with which the rubber particle was mix | blended works as a protective layer, and becomes excellent in mechanical strength and chemical resistance.

  The retardation film configured as described above is given in-plane retardation by stretching. Stretching can be performed by well-known longitudinal uniaxial stretching, tenter lateral uniaxial stretching, simultaneous biaxial stretching, sequential biaxial stretching, etc., and may be performed so as to obtain a desired retardation value.

  For example, when the first polarizer 32 (long shape) has an absorption axis in the longitudinal direction, the stretching process is performed so that the slow axis is in a direction of about 45 °. By doing so, the first polarizer 32 (polarizing plate) and the λ / 4 plate 34 can be continuously laminated in a roll-to-roll manner. As a result, the manufacturing process can be significantly shortened.

  In addition, in this invention, although the thickness of the 1st layer and 2nd layer which comprises a resin multilayer film is illustrated, this is the value before extending | stretching, Comprising: In retardation film after extending | stretching, The lower limit of the thickness may be slightly below the above value. However, it is more preferable to have the thickness within the above range even after stretching.

[λ / 2 plate 54]
As the λ / 2 plate 54, a retardation film made of the same material as that exemplified for the λ / 4 plate 34 can be used. The λ / 2 plate 54 and the λ / 4 plate 34 may be formed of the same material or different materials.

In the present invention, the retardation value of the λ / 2 plate means that the retardation value Re is 200 nm to 300 nm at a measurement wavelength of 590 nm. In the present invention, the λ / 2 plate has an Nz coefficient in the range of −0.5 to 0.5, and preferably in the range of −0.2 to 0.2.

  For example, when the second polarizer 52 (long shape) has an absorption axis in the longitudinal direction, the stretching process is performed so that the slow axis is in a direction of about 45 °. By doing so, the second polarizer 52 (polarizing plate) and the λ / 2 plate 54 can be continuously laminated by roll-to-roll. As a result, the manufacturing process can be significantly shortened.

[Brightness enhancement film 60]
The brightness enhancement film 60 is also referred to as a reflective polarizer, and a polarization conversion element having a function of separating outgoing light from a light source (backlight) into transmitted polarized light and reflected polarized light or scattered polarized light is used. As described above, by arranging the brightness enhancement film 60 on the polarizing plate 50, the return efficiency of the linearly polarized light emitted from the polarizing plate 50 is improved by using the retroreflected light that is reflected polarized light or scattered polarized light. Can do.

  The brightness enhancement film 60 can be, for example, an anisotropic reflective polarizer. An example of an anisotropic reflective polarizer is an anisotropic multiple thin film that transmits linearly polarized light in one vibration direction and reflects linearly polarized light in the other vibration direction, and a specific example thereof is DBEF made of 3M ( JP-A-4-268505). Another example of the anisotropic reflective polarizer is a composite of a cholesteric liquid crystal layer and a λ / 4 plate, and a specific example thereof is a PCF manufactured by Nitto Denko (JP-A-11-231130, etc.). Yet another example of the anisotropic reflective polarizer is a reflective grid polarizer, and a specific example thereof is a metal grid reflective polarizer (US) that emits reflected polarized light even in the visible light region by finely processing metal. Patent No. 6288840, etc.), a film (JP-A-8-184701) obtained by adding metal fine particles into a polymer matrix and stretching.

  An optical layer such as a hard coat layer, an antiglare layer, a light diffusion layer, or a retardation layer having a retardation value of ¼ wavelength may be provided on the surface of the brightness enhancement film 60 opposite to the polarizing plate 50. Good. By forming the optical layer, the adhesion to the backlight tape and the uniformity of the display image can be improved. Although the thickness of the brightness enhancement film 61 can be about 10 to 100 μm, it is preferably 10 to 50 μm, more preferably 10 to 30 μm from the viewpoint of thinning the polarizing plate.

[Adhesion of each layer]
Any appropriate pressure-sensitive adhesive layer or adhesive layer is preferably provided between the members constituting the polarizing plate of the present invention. Moreover, in order to bond a polarizing plate to a liquid crystal cell, it is preferable that an adhesive layer is provided on the surface of a polarizing plate. In the present embodiment, for example, an adhesive can be provided outside the λ / 4 plate 34 and an adhesive layer can be provided outside the λ / 2 plate 54. Examples of the adhesive that forms the adhesive layer include water-based adhesives and active energy ray-curable adhesives that are cured by irradiation with ultraviolet rays or electron beams. Examples of the active energy ray-curable adhesive include a composition containing a radical polymerizable compound such as an acrylic compound and a composition containing a cationic polymerizable compound such as an epoxy compound. Each of these compositions preferably contains a radical polymerization initiator or a cationic polymerization initiator. As an adhesive, the adhesive (acrylic adhesive) containing acrylic resin is preferable.

[Liquid crystal cell]
The liquid crystal cell includes a pair of substrates and a liquid crystal layer as a display medium sandwiched between the substrates. One substrate (color filter substrate) is provided with a color filter and a black matrix. The other 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, a signal line for supplying a source signal, and a pixel. Electrodes. Note that the color filter may be provided on the active matrix substrate side. The distance between the substrates (cell gap) is controlled by a spacer. An alignment film made of, for example, polyimide is provided on the side of the substrate in contact with the liquid crystal layer.

As a driving mode of the liquid crystal cell for arranging the set of polarizing plates of the present invention, an IPS (In-Plane Switching) mode having an in-plane retardation value of 100 to 200 nm at a wavelength of 590 nm is employed. Since the liquid crystal cell itself has an in-plane retardation value close to λ / 4 wavelength, it becomes possible to arrange a circularly polarizing plate as a viewing side polarizing plate, and greatly reduce reflection of external light. it can.

  As a method of setting the in-plane retardation of the liquid crystal cell to 100 nm to 200 nm at a wavelength of 590 nm, it can be produced by adjusting the thickness of the liquid crystal of the liquid crystal cell. For example, a liquid crystal cell having a desired in-plane retardation value can be produced by adjusting the thickness of the liquid crystal of the liquid crystal cell to about 1 to 2 μm.

[Liquid Crystal Display]
The liquid crystal display device of the present invention includes the set of polarizing plates of the present invention and the liquid crystal cell. The liquid crystal display device of the present invention is particularly suitable for small and medium-sized liquid crystal display devices because it is excellent in visibility even in the strong outdoor light. For example, it is suitable when the size of the liquid crystal display device is 15 inches diagonal.

  The shaft configuration of each member in the liquid crystal display device of the present invention will be described with reference to FIG.

  For convenience of explanation, the initial alignment direction of the liquid crystal cell used in the present invention is defined as 0 °, and the angle in the counterclockwise direction when the rear side polarizing plate is viewed from the viewing side polarizing plate is defined as positive. . The slow axes of the λ / 4 plate 34 and the λ / 2 plate 54 are arranged at approximately 90 ° with respect to the initial alignment direction. Further, the absorption axis of the viewing side polarizing plate is arranged at about 45 ° with respect to the initial alignment direction, and the absorption axis of the back side polarizing plate is arranged at about 135 ° with respect to the initial alignment direction. Here, when it is described as approximately what degree, it represents that the value is within the range of ± 5 °, and preferably represents within the range of ± 2 °.

  In the present invention, the initial alignment direction of the liquid crystal cell means the alignment direction of the liquid crystal molecules in an initial state where no driving voltage is applied to the liquid crystal cell.

EXAMPLES Hereinafter, although an Example is shown and this invention is demonstrated further more concretely, this invention is not limited by these examples. In the examples, the parts and% representing the content or amount used are based on weight unless otherwise specified. Regarding the angle, the counterclockwise direction is positive. In addition, each physical property in the following examples was measured by the following method.

(1) Measurement of thickness:
Measurement was performed using a digital micrometer “MH-15M” manufactured by Nikon Corporation.

(2) Measurement of in-plane retardation and thickness direction retardation:
In-plane retardation and thickness direction retardation at each wavelength at a temperature of 23 ° C using a phase difference meter "KOBRA (registered trademark) -WPR" based on the parallel Nicol rotation method manufactured by Oji Scientific Instruments Co., Ltd. It was measured.

(3) Measurement of polarization degree and single transmittance of polarizing plate:
The measurement was performed using a spectrophotometer with an integrating sphere [“V7100” manufactured by JASCO Corporation, 2-degree field of view; C light source].

(4) Measurement of the contraction force of the polarizer A super cutter (Tatsuno Seiki Co., Ltd.) having a width of 2 mm and a length of 50 mm so that the direction in which the contraction force is measured (the absorption axis direction of the polarizer) is the long side. (Manufactured by Seisakusho). The obtained strip-shaped chip was used as a test piece. The shrinkage force of the test piece was measured using a thermomechanical analyzer (model II TMA / 6100, manufactured by SII Nano Technology Co., Ltd.). This measurement was performed in the constant dimension mode, and the distance between chucks was set to 10 mm. After leaving the test piece in a room at 23 ° C. and 55% for 24 hours or more, the temperature in the sample room is raised from 23 ° C. to 80 ° C. over 1 minute, and after the temperature rise, the temperature in the sample room is maintained at 80 ° C. Was set as follows. After allowing the temperature to rise for another 4 hours, the contraction force in the long side direction of the test piece was measured in an environment at 80 ° C. In this measurement, the static load was 0 mN, and a SUS probe was used as the jig.

[Production Example 1] Production of polarizer A 30 μm-thick polyvinyl alcohol film (average polymerization degree of about 2400, saponification degree of 99.9 mol% or more) is uniaxially stretched by about 4 times by dry stretching, and further maintained in a tension state. The sample was immersed in pure water at 40 ° C. for 40 seconds, and then immersed in an aqueous solution having an iodine / potassium iodide / water weight ratio of 0.052 / 5.7 / 100 at 28 ° C. for 30 seconds to perform a dyeing treatment. It was. Thereafter, it was immersed in an aqueous solution having a weight ratio of potassium iodide / boric acid / water of 11.0 / 6.2 / 100 at 70 ° C. for 120 seconds. Subsequently, after washing with pure water at 8 ° C. for 15 seconds, the film is dried at 60 ° C. for 50 seconds and then at 75 ° C. for 20 seconds while being held at a tension of 300 N, and iodine is adsorbed and oriented on the polyvinyl alcohol film. An absorption polarizer having a thickness of 12 μm was obtained. It was 2.0 N / 2mm when the contraction force of the obtained polarizer was measured.

[Production Example 2] Preparation of water-based adhesive 3 parts by weight of carboxyl group-modified polyvinyl alcohol [trade name “KL-318” obtained from Kuraray Co., Ltd.] was dissolved in 100 parts by weight of water, and a water-soluble epoxy was dissolved in the aqueous solution. 1.5 parts by weight of a resin-based polyamide epoxy additive [trade name “Smileise Resin (registered trademark) 650 (30)” obtained from Taoka Chemical Co., Ltd., aqueous solution with a solid content of 30 wt%] was added. A water-based adhesive was prepared.

[Adhesives A and B]
The following two types of pressure-sensitive adhesives A: a sheet-like pressure-sensitive adhesive having a thickness of 25 μm [“P-3132” manufactured by Lintec Corporation]
Adhesive B: 5 μm thick sheet adhesive (“NCF # L2” manufactured by Lintec Corporation)
Prepared.

[Protective films A, B, C, D]
The following three types of protective films were prepared.
Protective film A: Triacetyl cellulose film with hard coat manufactured by Konica Minolta, Inc .; 25KCHCN-TC (thickness 32 μm)
Protective film B: Triacetyl cellulose film manufactured by Konica Minolta, Inc .; KC2UA (thickness 25 μm)
Protective film C: cyclic polyolefin resin film manufactured by ZEON Corporation; ZF14-013 (thickness 13 μm, in-plane retardation value at wavelength 590 nm = 0.8 nm, thickness direction retardation at wavelength 590 nm = 3.4 nm)
Protective film D: Anti-reflection film made of triacetylcellulose-based resin manufactured by Toppan Tomoegawa Optical Products; 40KSPLR (thickness 44 μm, Y value 1.1% according to JIS-Z8701-1982)

[Brightness enhancement film A]
The following brightness enhancement films were prepared.
Brightness enhancement film A: 26 μm thick brightness enhancement film (trade name “Advanced Polarized Film, Version 3 made by 3M”)

[Production of λ / 4 plate]
Styrene-maleic anhydride copolymer resin (“Dylark (registered trademark) D332” (Tg = 131 ° C.) manufactured by Nova Chemical Co., Ltd.) is used as a core layer, and about 20% of acrylic rubber particles having an average particle size of 200 μm are blended. Methacrylic resin (resin used in “Technoloy (registered trademark) S001” manufactured by Sumitomo Chemical Co., Ltd. (Tg = 105 ° C.)) is used as a skin layer, and three-layer coextrusion is performed. A resin three-layer film having a thickness of 60 μm and a skin layer having a thickness of 72 μm on each side was obtained. This resin three-layer film was stretched twice at 142 ° C. to obtain a negative retardation film having an in-plane retardation of 140 nm and an Nz coefficient of 0.0 at a wavelength of 590 nm.

[Production of λ / 2 plate]
Styrene-maleic anhydride copolymer resin (“Dylark (registered trademark) D332” (Tg = 131 ° C.) manufactured by Nova Chemical Co., Ltd.) is used as a core layer, and about 20% of acrylic rubber particles having an average particle size of 200 μm are blended. Methacrylic resin (resin used in “Technoloy (registered trademark) S001” manufactured by Sumitomo Chemical Co., Ltd. (Tg = 105 ° C.)) is used as a skin layer, and three-layer coextrusion is performed. A resin three-layer film having a thickness of 60 μm and a skin layer having a thickness of 72 μm on each side was obtained. This resin three-layer film was stretched 4 times at 142 ° C. to obtain a negative retardation film having an in-plane retardation of 260 nm and an Nz coefficient of 0.0 at a wavelength of 590 nm.

[Preparation of Polarizing Plate A]
The protective film A was subjected to saponification treatment, and the bonding surface of the protective film C to the polarizer was subjected to corona treatment. The protective film A, the polarizer and the protective film C are bonded with a water-based adhesive so that the triacetyl cellulose surface of the protective film A and the corona-treated surface of the protective film C become a bonding surface with the polarizer. A was obtained.

[Preparation of Polarizing Plate B]
The protective film B was subjected to saponification treatment, and the bonding surface of the protective film C with the polarizer was subjected to corona treatment. The protective film B, the polarizer, and the protective film C were bonded with a water-based adhesive so that the corona-treated surface of the protective film B and the protective film C became a bonding surface with the polarizer to obtain a polarizing plate. An adhesive B was bonded to the protective film B side of the polarizing plate B. Under the present circumstances, the corona treatment was performed to the bonding surface of the protective film B and the adhesive B. FIG. Finally, the brightness enhancement film A was bonded to the adhesive B surface of the polarizing plate to obtain a polarizing plate B.

[Production of pseudo liquid crystal cell]
Two alkali-free glass made by Corning: Eagle XG (thickness 0.7 mm, length 157 mm × width 98 mm) bonded with adhesive B was prepared. Under the present circumstances, the corona treatment was performed to the bonding surface of glass and an adhesive. Next, the previously prepared λ / 4 plate was bonded to one glass adhesive B surface. Also at this time, the corona treatment was performed on the λ / 4 plate and the adhesive B surface. Finally, the λ / 4 surface of the glass bonded with this λ / 4 plate and the adhesive B surface of the other glass were bonded to produce a pseudo liquid crystal cell. At this time, corona treatment was performed on the λ / 4 plate surface and the adhesive B bonding surface. The slow axis direction of the λ / 4 plate was prepared so as to be parallel to the short side direction of the glass.

  It is assumed that the initial alignment direction of the pseudo liquid crystal cell is parallel to the long side direction of the glass, and the pseudo liquid crystal cell is assumed to be a liquid crystal cell when a driving voltage is applied (in the case of white display). .

  Furthermore, Doraemon (Fujiko F. Fujio's “Doraemon”) appears on one glass surface of the fabricated pseudo liquid crystal cell using Himacy Blue (MO-150-MC-BL) manufactured by Zebra Corporation. I drew a portrait of a cat-shaped robot (published by Shogakukan).

[Backlight]
Google Inc. A liquid crystal panel was taken out from Nexus 7 (registered trademark) manufactured, and a backlight was obtained by lighting only the backlight.

[Example 1]
(Preparation of viewing-side polarizing plate 1)
An adhesive B was bonded to the protective film C surface of the polarizing plate A. Under the present circumstances, the corona treatment was performed to the bonding surface of the protective film C surface and the adhesive B. Next, a λ / 4 plate was laminated on the pressure-sensitive adhesive B surface of the produced polarizing plate A. Under the present circumstances, the corona treatment was performed to the bonding surface of adhesive B and (lambda) / 4 board. The angle formed between the absorption axis of the polarizing plate and the λ / 4 plate is 45 ° (λ / 4 so that the angle is 45 ° counterclockwise from the absorption axis of the polarizing plate when the protective film A surface of the polarizing plate is viewed as the upper surface. The slow axis of the plate was disposed). Furthermore, the adhesive A was bonded to the λ / 4 plate surface of the polarizing plate A. Also at this time, the λ / 4 plate of the polarizing plate A and the bonding surface of the adhesive A were subjected to corona treatment. In this way, the viewing side polarizing plate 1 was produced.

(Preparation of the back side polarizing plate 1)
The back side polarizing plate 1 was produced in the same manner as the viewing side polarizing plate except that the polarizing plate A was changed to the polarizing plate B and the λ / 4 plate was changed to the λ / 2 plate. The λ / 2 plate was placed so that the angle formed by the absorption axis of the polarizing plate B and the slow axis of the λ / 2 plate was −45 °. Next, the adhesive B was laminated on the protective film B side of the polarizing plate B. At this time, corona treatment was performed on the protective film B surface and the adhesive B bonding surface. Finally, lamination was performed on the adhesive B surface so that the transmission axis of the brightness enhancement film A was parallel to the transmission axis of the back-side polarizing plate 1. Under the present circumstances, the corona treatment was implemented to the bonding surface of the adhesive B surface and the brightness improvement film A. FIG.

  The produced viewing-side polarizing plate 1 and back-side polarizing plate 1 were cut into a size of 155 mm long × 96 mm wide. In this case, when each polarizing plate is viewed with the protective film A (viewing-side polarizing plate 1) or the protective film B (back-side polarizing plate 1) as the upper surface, the absorption axis of the polarizing plate is 45 with respect to the long side direction. Each was cut to be °.

  A viewing-side polarizing plate 1 was bonded to the glass surface on which a portrait of Doraemon of the pseudo liquid crystal cell was drawn, and a back-side polarizing plate 1 was bonded to the opposite glass surface to prepare a pseudo liquid crystal panel. At this time, the shaft configuration was as shown in FIG.

  The pseudo liquid crystal panel thus produced was placed on the produced backlight, and it was confirmed whether Doraemon was visible. When the visibility was confirmed under external light, the visibility was good even at 7500 Lux.

[Example 2]
A pseudo liquid crystal panel was prepared in the same manner except that the protective film A of the viewing-side polarizing plate 1 of Example 1 was changed to the protective film D.

  The pseudo liquid crystal panel thus produced was placed on the produced backlight, and it was confirmed whether Doraemon was visible. When the visibility was confirmed under external light, the visibility was good even at an illuminance of 10,000 Lux.

[Comparative Example 1]
Google Inc. The upper and lower polarizing plates were peeled off from the manufactured Nexus 7 (registered trademark) liquid crystal panel, and the in-plane retardation value of the liquid crystal cell was measured at a wavelength of 590 nm to be 355 nm. Subsequently, the polarizing plate A was bonded to the viewing side of the taken-out liquid crystal cell via the adhesive A, and the polarizing plate B was bonded to the back side via the adhesive A to produce a liquid crystal panel. The liquid crystal panel thus produced was mounted on Nexus 7, and an image of Doraemon was displayed on the screen, and it was confirmed that it was visible under external light. As a result, at illuminance of 5000 Lux, the visibility was remarkably lowered and it was difficult to identify the image.

  According to the set of polarizing plates of the present invention, it is possible to provide a liquid crystal display device that can suppress reflection of external light and ensure good visibility even in an environment with strong external light such as outdoors. So it is useful.

DESCRIPTION OF SYMBOLS 10 View side polarizing plate 20 Back side polarizing plate 30, 50 Polarizing plate 31a, 31b, 51a, 51b Protective film 35 Surface treatment layer 32 1st polarizer 52 2nd polarizer 34 (lambda) / 4 board 54 (lambda) / 2 board 61 Brightness-improving film 60 Liquid crystal cell 1 Absorption axis of polarizing plate 2 Slow axis of λ / 4 plate 3 Initial alignment direction of liquid crystal cell 4 Slow axis of λ / 2 5 Absorption axis of polarizing plate

Claims (5)

A set of polarizing plates for bonding to both surfaces of an IPS mode liquid crystal cell having an in-plane retardation value of 100 nm to 200 nm, comprising a viewing side polarizing plate and a back side polarizing plate,
The absorption axis of the viewing side polarizing plate and the absorption axis of the back side polarizing plate are substantially orthogonal,
The viewing side polarizing plate has a first polarizer and a λ / 4 plate,
The λ / 4 plate is disposed between the first polarizer and the liquid crystal cell,
The angle formed by the absorption axis of the viewing side polarizing plate and the slow axis of the λ / 4 plate is approximately 45 °,
The back side polarizing plate has a second polarizer and a λ / 2 plate,
The λ / 2 plate is disposed between the second polarizer and the liquid crystal cell,
The angle formed by the absorption axis of the back side polarizing plate and the slow axis of the λ / 2 plate is approximately 45 °,
The slow axis of the λ / 4 plate and the slow axis of the λ / 2 plate are substantially parallel;
The Nz coefficient of the λ / 4 plate and the Nz coefficient of the λ / 2 plate are both −0.5 or more and 0.5 or less,
A set of polarizing plates in which the slow axis of the λ / 4 plate is disposed in a substantially perpendicular relationship to the initial alignment direction of the IPS mode liquid crystal cell.   The λ / 4 plate and the λ / 2 plate have a three-layer structure in which a skin layer made of a (meth) acrylic resin composition containing rubber particles is formed on both sides of a core layer made of a styrene resin. The set of polarizing plates according to claim 1, which is a retardation film.   The set of polarizing plates according to claim 2, wherein the glass transition temperature of the core layer is 120 ° C or higher and the glass transition temperature of the skin layer is 120 ° C or lower.   An IPS mode liquid crystal display device in which the set of polarizing plates according to claim 1 is disposed in an IPS mode liquid crystal cell having an in-plane retardation value of 100 nm to 200 nm.   The IPS mode liquid crystal display device according to claim 4, wherein the size of the IPS mode liquid crystal display device is 15 inches or less diagonally.

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