JP2002174728A - Polarizing plate and liquid crystal display device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizing plate which can display a whitely displayed portion in a white color and can display a blackly displayed portion in the crossed state of polarization (black display) in a black color and to provide a liquid crystal display device which uses the polarizing plate. SOLUTION: The polarizing plate is obtained by laminating a protective film on at least one surface of a polarizer made of a polyvinylalcohol film and satisfies the relation of [Ta/Tc]/[Tb/Td]>1.5, wherein Ta and Tb are transmittances at 440 nm and at 690 nm, respectively, when two identical polarizing plates are overlapped with the absorption axes parallel to each other and Tc and Td are transmittances at 440 nm and 690 nm, respectively, when two identical polarizing plates are overlapped with the absorption axes perpendicular to each other. The polarizing plate shows <=5.0 Hunger-b value for the hue with parallel absorption axes. The polarizer is preferably a polyvinyl alcohol film in which iodine is absorbed and the protective film is preferably a triacetyl cellulose film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizing plate used in a liquid crystal display device (hereinafter, may be abbreviated as LCD) and a liquid crystal display device using the same.

[0002]

2. Description of the Related Art Liquid crystal display devices (LCDs) are used in desk-top electronic calculators, electronic watches, personal computers, word processors, and the like, and in recent years, their demand has been rapidly increasing. The use of LCDs is also expanding, and they are also being used for monitors. LCDs used outdoors, such as mobile phones and PDAs, are also increasing rapidly. The required characteristics of polarizers used for reflective or transflective LCDs used outdoors are different from those used for transmissive LCDs represented by personal computers, etc. Improvements have been made in LCDs and reflective or transflective LCDs with the aim of realizing a white display (paper white) like paper.

Among them, it has been found that as a method of changing the optical characteristics of the polarizing plate so as to approach a white display such as paper white, it is preferable to lower the hunter b (single hue b) which is the hue of the polarizing plate. ing. But,
In the conventional polarizing plate, if the single hue b, which is the hunter b of one polarizing plate, is lowered, the polarization characteristics deteriorate, and the orthogonal hue b, which is the hunter b when the two polarizing plates are in the orthogonal state, is reduced. There is a problem that it becomes large on the minus side and falls out to blue. Conversely, if the single hue b, which is the hunter b of one polarizing plate, is sacrificed, the polarization characteristics are also good, and the orthogonal hue b, which is the hunter b when the two polarizing plates are placed in the orthogonal state, approaches zero and the blue hue is reduced. Although the omission is reduced, the white display becomes yellow, and there is a problem that white display such as paper white cannot be performed.

[0004]

Therefore, it is desired to develop a polarizing plate which is excellent in polarization characteristics and excellent in contrast and capable of displaying black in black and white in white in a liquid crystal color display. In order to solve the above-mentioned conventional problems, the present invention provides a method of combining a parallel hue (a hue when two identical polarizers are superposed so that their absorption axes are parallel) and an orthogonal hue (two identical polarizers). As a result of intensive studies to develop a polarizing plate in which the parallel hues are white and the orthogonal hues are black, the polarizing plate having a certain characteristic value solves the above problem. They have found that they can be solved, and have completed the present invention.

[0005]

The present invention has been made to solve the above-mentioned problems, and is a polarizing plate comprising a polarizer formed of a polyvinyl alcohol-based film and a protective film laminated on at least one surface of the polarizer. The measured parallel transmittance (the transmittance when two identical polarizing plates are overlapped so that their absorption axes are parallel) and the orthogonal transmittance (two identical polarizing plates so that the absorption axes are perpendicular to each other) (The transmittance when combined) has a certain relationship. That is, the present invention provides a polarizing plate in which the parallel transmittance Ta and the orthogonal transmittance Tc at 440 nm and the parallel transmittance Tb and the orthogonal transmittance Td at 690 nm satisfy the following formula (I). [Ta / Tc] / [Tb / Td]> 1.5 (I)

By arranging a polarizing plate satisfying the above characteristics on at least one side of a liquid crystal cell to form a liquid crystal display device, a liquid crystal panel having a white white display and a black black display and having excellent color display characteristics. A display device can be provided. In order to more effectively achieve the object of the present invention, a polarizing plate satisfying the following formula (II) is preferable. [Ta / Tc] / [Tb / Td]> 1.7 (II)

The polarizing plate of the present invention has a single light transmittance of 42 to 46%, a degree of polarization of 99.5% or more, and a light transmittance of 29.5% or more.
It is preferable that the parallel hue Hunter b value measured by a spectrophotometer when the same polarizing plates are overlapped so that the absorption axes are parallel is 5.0 or less. When the polarizing plate has such a characteristic value, the polarizing characteristics are good and a white display can be a white polarizing plate. In order to satisfy the above characteristics, it is preferable that in the configuration of the polarizing plate, the polarizer is a polyvinyl alcohol-based film on which iodine is adsorbed, and the protective film is a triacetyl cellulose film.

Further, the present invention provides a liquid crystal display device in which the polarizing plate is arranged on at least one side of a liquid crystal cell.

In the present invention, the transmittance at 440 nm and 690 nm when two identical polarizing plates are superposed in parallel or orthogonally is employed as a parameter in evaluating the characteristics as a polarizing plate. Since 440 nm is close to the wavelength of blue, if the orthogonal transmittance Tc at this wavelength is low, blue omission is reduced. In addition, in order to approach white display, it is required that the orthogonal transmittance in the vicinity of green (550 nm) and red (610 nm), which are the three primary colors of other light, is also low. The orthogonal transmittance Td at 690 nm with good measurement accuracy is measured. Therefore, when blue omission of the polarizing plate is large, [Ta / T
Since the value of [c] tends to be small, the above formula (I) cannot be satisfied. When the blue omission is small, [Ta
/ Tc] increases, but when white display is poor, the orthogonal transmittance Td at 690 nm decreases,
Since the value of [Tb / Td] becomes large, the above formula (I) cannot be satisfied.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION A polarizing plate satisfying the above formula (I) of the present invention is protected on at least one side (one side or both sides) of a polarizer formed from a polyvinyl alcohol-based film via an appropriate adhesive layer. Films are laminated.

The polarizer (polarizing film) is made of a polyvinyl alcohol-based polymer such as polyvinyl alcohol or partially formalized polyvinyl alcohol and has a thickness of 75 μm.
m, swelling treatment, dyeing treatment, crosslinking treatment,
An appropriate stretched material that transmits linearly polarized light when natural light is incident thereon can be used. staining,
The processing steps of crosslinking and stretching do not need to be performed separately but may be performed simultaneously, and the order of the respective steps may be arbitrary. In general, one obtained by uniaxially stretching to a stretching ratio of 3 to 7 times and drying is used.

In the swelling treatment, a polyvinyl alcohol-based film is heated in a water bath or the like at 10 to 50 ° C. for 0.1 to 5 minutes.
Swell for a minute.

In the dyeing treatment, the polyvinyl alcohol-based film is placed in a dyeing bath at 10 to 50 ° C. to which a dichroic substance such as iodine or a dichroic dye is added for 20 seconds to 15 hours.
Soak for iodine and dichroic dyes for a minute. The concentration of iodine or dichroic dye in the dye bath is generally 0.01
To 1% by mass, preferably 0.02 to 0.5% by mass
It is. Above all, those dyed with iodine are preferred because of their high transmittance and high polarization, that is, high dichroism. In the dyeing bath, potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, titanium iodide, etc. 0.05 to 15% by mass of an auxiliary such as iodide, preferably 0.02 to
It may be added in an amount of 10% by mass, which is particularly preferable for increasing the dyeing efficiency. Further, the stretching treatment can be performed while performing the dyeing treatment.

In the crosslinking treatment, the polyvinyl alcohol film is immersed in a crosslinking bath at 20 to 70 ° C. to which a PVA crosslinking agent such as boric acid or borax is added for 5 seconds to 10 minutes to crosslink the polyvinyl alcohol. I do. The concentration of boric acid or the like is generally 2 to 10% by mass, preferably 2 to 8% by mass.
% By mass. In the crosslinking bath, potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, titanium iodide, etc. Aid such as iodide of 0.05 to 15% by mass, preferably 0.5 to 8%
% May be added, which is particularly preferable in that uniform properties in the plane are obtained. Further, the stretching treatment can be performed while performing the dyeing treatment.

The polyvinyl alcohol-based film which has been dyed, cross-linked and stretched is appropriately washed with water, and dried at a temperature of 10 to 50 ° C., preferably 20 to 45 ° C. to obtain a polarizer. The thickness of the polarizer (polarizing film) is 5 to 80.
Although μm is generally used, it is particularly preferably 10 to 30 μm in order to effectively achieve the object of the present invention. Also, the method for adjusting the thickness of the polarizer is not particularly limited, and a normal method such as tenter, roll stretching or rolling can be used.

Examples of the polyvinyl alcohol-based polymer include those obtained by polymerizing vinyl acetate and then saponifying the polymer.
Those obtained by copolymerizing vinyl acetate with a small amount of copolymerizable monomers such as unsaturated carboxylic acid, unsaturated sulfonic acid, and cationic monomer, and the like. The degree of polymerization of the polyvinyl alcohol-based polymer is not particularly limited, and any one can be used. From the viewpoint of the solubility of the film in water, the average degree of polymerization is preferably from 500 to 10,000, more preferably from 1,000 to 6,000. It is. The saponification degree is preferably at least 75 mol%, more preferably from 98 to 100 mol%.

In the present invention, a protective layer is provided on one or both sides of a polarizer made of a polyvinyl alcohol-based polarizing film containing a dichroic substance via an appropriate adhesive layer, for example, an adhesive layer made of a vinyl alcohol-based polymer or the like. After the transparent protective film is bonded, heat treatment is performed to produce a polarizing plate.

The adhesive treatment between the polarizer and the transparent protective film as the protective layer may be performed, for example, using an adhesive made of a vinyl alcohol-based polymer or a vinyl alcohol-based material such as boric acid, borax, glutaraldehyde, melamine, or oxalic acid. A temperature of 20 to 65 is applied to one or both sides of the polarizer via an adhesive or the like made of a water-soluble crosslinking agent of the polymer.
The protective layer is bonded at a temperature of preferably from 40 to 60 ° C. Such an adhesive layer is formed as a coating and drying layer of an aqueous solution, and at the time of preparing the aqueous solution, other additives and a catalyst such as an acid can be added as necessary. After bonding the polarizer and the protective layer, a heat treatment is performed at a temperature of 40 to 75 ° C, preferably 50 to 70 ° C. By heat treatment,
The adhesive used to bond the polarizer and the protective layer can be cured to increase the adhesiveness.
Annealing treatment of the polarizing plate can also be performed.

As the protective film provided on one side or both sides of the polarizer (polarizing film), an appropriate transparent film can be used. Among them, a film made of a polymer which has low birefringence and is excellent in transparency, mechanical strength, heat stability, moisture shielding property and the like is preferably used. Examples of the polymer include acetate resins such as triacetyl cellulose, polycarbonate resins, polyester resins such as polyarylate and polyethylene terephthalate, polyimide resins, polysulfone resins, polyethersulfone resins, polystyrene resins, polyethylene, and polypropylene. And the like, polyolefin resins, polyvinyl alcohol resins, polyvinyl chloride resins, polynorbornene resins, polymethyl methacrylate resins, liquid crystal polymers, and the like. The film may be manufactured by any of a casting method, a calendar method, and an extrusion method. A triacetylcellulose film is preferable from the viewpoint of polarization characteristics and the like, and a triacetylcellulose film or the like whose surface is saponified with an alkali or the like is used. The thickness of the protective film is optional, but is generally 500 μm or less, preferably 5 to 300 μm for the purpose of thinning the polarizing plate.
μm, particularly preferably 5 to 150 μm. In addition,
When providing a transparent protective film on both sides of the polarizing film,
A transparent protective film made of a different polymer or the like on the front and back can also be used.

The transparent protective film may be subjected to a hard coat treatment, an antireflection treatment, a treatment for preventing sticking, a diffusion or an antiglare, or the like, as long as the object of the present invention is not impaired. The hard coat treatment is performed for the purpose of preventing the surface of the polarizing plate from being scratched, and for example, transparently protects a cured film excellent in hardness and slipperiness by an appropriate ultraviolet curable resin such as a silicone or acrylic resin. It can be formed by a method of adding to the surface of the film.

On the other hand, the anti-reflection treatment is performed for the purpose of preventing reflection of external light on the surface of the polarizing plate, and can be achieved by forming an anti-reflection film or the like according to the related art.
In addition, anti-sticking is performed to prevent adhesion between adjacent layers, and anti-glare treatment is performed to prevent external light from being reflected on the surface of the polarizing plate and hindering the visibility of light transmitted through the polarizing plate. For example, it can be formed by providing a fine uneven structure on the surface of the transparent protective film by an appropriate method such as a roughening method such as a sand blast method or an embossing method or a method of blending transparent fine particles.

Examples of the transparent fine particles include silica, alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide, and antimony oxide having an average particle size of 0.5 to 20 μm. Organic fine particles may be used, and organic fine particles made of crosslinked or uncrosslinked polymer particles or the like may be used. The amount of the transparent fine particles to be used is generally 2 to 70 parts by mass, particularly 5 to 50 parts by mass per 100 parts by mass of the transparent resin.

Further, the antiglare layer containing the transparent fine particles can be provided as the transparent protective layer itself or as a coating layer on the surface of the transparent protective layer. The anti-glare layer may also serve as a diffusion layer (such as a viewing angle compensation function) for diffusing light transmitted through the polarizing plate to increase the viewing angle. The above-described anti-reflection layer, anti-sticking layer, diffusion layer, anti-glare layer and the like can be provided as an optical layer made of a sheet or the like provided with such a layer, separately from the transparent protective layer.

The polarizing plate of the present invention can be used as an optical member laminated with another optical layer in practical use. The optical layer is not particularly limited. For example, a reflector, a transflector, a retardation plate (including a λ plate such as a 波長 wavelength plate and a 板 wavelength plate), a viewing angle compensation film, and a brightness enhancement film For example, one or more appropriate optical layers that may be used for forming a liquid crystal display device or the like can be used. In particular, a polarizing plate comprising the polarizer of the present invention and the protective layer described above, a reflective plate, or a reflective polarizer or a semi-transmissive reflective polarizer obtained by laminating a transflective reflector, the polarizer described above. A polarizing plate comprising a protective layer, an elliptically polarizing plate or a circularly polarizing plate wherein a retardation plate is further laminated, a polarizing plate comprising a polarizer and a protective layer described above, and a polarizing plate further comprising a viewing angle compensation film, Alternatively, a polarizing plate in which a brightness enhancement film is further laminated on the above-described polarizing plate comprising a polarizer and a protective layer is preferable.

The polarizing plate may be formed by laminating a polarizing plate and two or three or more optical layers, such as a polarized light separating type polarizing plate. Therefore, a reflective elliptically polarizing plate or a transflective elliptically polarizing plate obtained by combining the above-mentioned reflective polarizing plate, semi-transmissive polarizing plate and retardation plate may be used. An optical member in which two or three or more optical layers are laminated can be formed by a method in which the optical members are sequentially laminated separately in a manufacturing process of a liquid crystal display device or the like. This has the advantage that the stability of quality and the workability of assembling are excellent and the manufacturing efficiency of a liquid crystal display device or the like can be improved. Note that an appropriate bonding means such as an adhesive layer can be used for lamination.

The above-mentioned polarizing plate or optical member may be provided with an adhesive layer for bonding to another member such as a liquid crystal cell. The pressure-sensitive adhesive layer can be formed with an appropriate pressure-sensitive adhesive, such as an acrylic resin, according to the related art. In particular, from the viewpoint of preventing foaming and peeling phenomena due to moisture absorption, deterioration of optical characteristics due to thermal expansion difference and the like, prevention of liquid crystal cell warpage, and, in view of the formability of a liquid crystal display device having high quality and excellent durability, the moisture absorption rate is high. It is preferable that the pressure-sensitive adhesive layer is low and has excellent heat resistance. In addition, an adhesive layer or the like that contains fine particles and exhibits light diffusivity can also be used. The adhesive layer may be provided on a necessary surface if necessary.For example, if mention is made of a protective layer of a polarizing plate comprising a polarizer and a protective layer, if necessary, an adhesive layer may be provided on one or both sides of the protective layer. May be provided.

When the adhesive layer provided on the polarizing plate or the optical member is exposed on the surface, it is preferable to temporarily cover the adhesive layer with a separator until the adhesive layer is put to practical use for the purpose of preventing contamination and the like. The separator is formed by a method of providing a release coat with a suitable release agent such as a silicone-based or long-chain alkyl-based, fluorine-based or molybdenum sulfide as necessary, on a suitable thin leaf according to the transparent protective film or the like. be able to.

The layers such as the polarizing film and the transparent protective film, the optical layer and the adhesive layer which form the polarizing plate and the optical member are made of, for example, salicylic acid ester compounds, benzophenone compounds, benzotriazole compounds and cyanoacrylate compounds. Compounds having an ultraviolet absorbing ability by an appropriate method such as a method of treating with an ultraviolet absorber such as a compound or a nickel complex compound may be used.

The polarizing plate of the present invention can be used for forming various devices such as a liquid crystal display device. In particular, a reflective or semi-transmissive liquid crystal in which a polarizing plate is arranged on one side or both sides of a liquid crystal cell. It can be preferably used for a display device. The liquid crystal cell forming the liquid crystal display device is arbitrary, for example, an appropriate type such as an active matrix driving type represented by a thin film transistor type, a simple matrix driving type represented by a twisted nematic type or a super twisted nematic type, or the like. May be used.

When polarizing plates and optical members are provided on both sides of the liquid crystal cell, they may be the same or different. Further, in forming the liquid crystal display device, one or more layers of appropriate components such as a prism array sheet, a lens array sheet, a light diffusing plate, and a backlight can be arranged at appropriate positions.
Next, the present invention will be specifically described with reference to examples.

[0031]

Example 1 A polyvinyl alcohol (PVA) film having a thickness of 75 μm was swollen in a bath containing water for 2 minutes, and then dyed in a dye bath comprising an aqueous solution containing iodine and potassium iodide. After immersion in a water bath for 5 seconds, the film was immersed in a cross-linking bath containing boric acid and potassium iodide (concentration: 6% by mass) for 1 minute. The film was stretched so that the stretching ratio became 6.5 times. After the polarizer surface was washed with water, it was dried with a dryer at 30 ° C. to produce a polarizer. This was bonded to a saponified TAC (triacetyl cellulose) film using a PVA-based adhesive, and heated at 60 ° C. to produce a polarizing plate.

Example 2 A polarizing plate was produced in the same manner as in Example 1 except that the PVA film was stretched in a crosslinking bath so that the stretching ratio from the initial stage was 6.0 times.

Example 3 The same 75 μm P as in Example 1
After swelling the VA film in a bath of water for 2 minutes,
It is stretched to 3.3 times while dyeing in a dye bath comprising an aqueous solution containing iodine and potassium iodide, and then immersed in a water bath for 5 seconds, and then boric acid and potassium iodide (concentration 5.5% by mass). Immersed in a cross-linking bath for 1 minute, and stretched in the cross-linking bath so that the initial draw ratio was 6.0 times. After the polarizer surface was washed with water, it was dried with a dryer at 30 ° C. to produce a polarizer. This is combined with a saponified TAC (triacetyl cellulose) film and PVA
A polarizing plate was produced by bonding using a system adhesive and heating at 62 ° C.

Comparative Example 1 The same 75 μm P
After swelling the VA film in a bath of water for 2 minutes,
It is stretched to 3.1 times while dyeing in a dyeing bath composed of an aqueous solution containing iodine and potassium iodide, then immersed in a water bath for 5 seconds, and then containing boric acid and potassium iodide (concentration: 6% by mass). Then, it was immersed in the crosslinking bath for 1 minute and stretched in the crosslinking bath so that the stretching ratio from the initial stage was 5.5 times. After the polarizer surface was washed with water, it was dried with a dryer at 40 ° C. to produce a polarizer. This is the T
An AC (triacetyl cellulose) film and a PVA-based adhesive were bonded together and heated at 75 ° C. to produce a polarizing plate.

(Comparative Example 2) The same 75 μm P
After swelling the VA film in a bath of water for 2 minutes,
It is stretched to 3.1 times while dyeing in a dyeing bath composed of an aqueous solution containing iodine and potassium iodide, then immersed in a water bath for 5 seconds, and then containing boric acid and potassium iodide (concentration: 3% by mass). Then, it was immersed in the crosslinking bath for 1 minute and stretched in the crosslinking bath so that the stretching ratio from the initial stage was 5.5 times. After the polarizer surface was washed with water, it was dried with a dryer at 35 ° C. to produce a polarizer. This is the T
An AC (triacetyl cellulose) film and a PVA-based adhesive were bonded together and heated at 60 ° C. to produce a polarizing plate.

(Comparative Example 3) The same 75 μm P as in Example 1.
After swelling the VA film in a bath of water for 2 minutes,
It is stretched to 3.1 times while dyeing in a dyeing bath composed of an aqueous solution containing iodine and potassium iodide, then immersed in a water bath for 5 seconds, and then containing boric acid and potassium iodide (concentration: 2% by mass). Then, it was immersed in the crosslinking bath for 1 minute and stretched in the crosslinking bath so that the stretching ratio from the initial stage was 5.0 times. After the polarizer surface was washed with water, it was dried with a dryer at 35 ° C. to produce a polarizer. This is the T
An AC (triacetyl cellulose) film and a PVA-based adhesive were attached to each other, and heated at 65 ° C. to produce a polarizing plate.

[Evaluation Method] The optical properties of the polarizing plates prepared in the examples and comparative examples and the polarizing plate used for a commercially available liquid crystal monitor were evaluated by the following methods. The results are shown in Tables 1 to 3.

(Transmittance) A case where two identical polarizing plates are superimposed so that their absorption axes are parallel using a spectrophotometer (CMS-500, manufactured by Murakami Color Research Laboratory Co., Ltd.). The transmittance at 440 nm (Ta) and the transmittance at 690 nm (T
b), 4 when superimposed so that absorption axes are orthogonal
40 nm transmittance (Tc) and 690 nm transmittance (Td)
Was measured.

(Degree of Polarization) Two identical polarizing plates have flat polarization axes.
Transmittance (H ₀)
The transmittance (H₉₀), The above spectroscopy
The degree of polarization was determined from the following equation using a photometer.
The parallel transmittance (H₀) And the transmittance (H₉₀)
Is based on the 2 degree field of view (C light source) of JIS Z8701.
This is the Y value corrected for visibility.

[0040]

(Equation 1)

(Parallel Hue Hunter b value) Two identical polarizing plates were superposed so that their polarization axes were parallel to each other, and determined by a spectrophotometer (CMS-500, manufactured by Murakami Color Research Laboratory Co., Ltd.).

(Contrast of Black and White Display) The polarizing plates on both sides of a commercially available thin-film transistor (TFT) type liquid crystal monitor are peeled off, and the above polarizing plates are laminated on both sides to obtain black display and white display. It was visually determined according to the following criteria.

[Table 1] Single transmittance (%) Degree of polarization (%) Parallel hue b value Example 1 44.0 99.96 4.4 Example 2 44.0 99.89 4.3 Example 3 43 7.7 99.95 4.4 Comparative Example 1 43.6 99.95 6.5 Comparative Example 2 43.9 99.55 3.8 Comparative Example 3 41.6 98.98 5.1 Commercial LCD Monitor 43.1 99.94 6.2

[Table 2] Ta (%) Tb (%) Tc (%) Td (%) Ta / Tc ÷ Tb / Td Example 1 33.89 41.21 0.06 0.15 2.04 Example 2 33.50 41.82 0.08 0.18 1.80 Example 3 32.07 42.34 0.09 0.18 1.51 Comparative Example 1 31.50 42.23 0.09 0.16 1.33 Comparative Example 2 33.48 40.07 0.52 0.02 0.03 Comparative Example 3 32.24 39.83 0.78 0.05 0.05 Commercial LCD monitor 29.51 39.28 0.04 0.02 0.38

[0045]

As is clear from Tables 1 to 3, the polarizing plates (Examples 1 to 3) produced by the method of the present invention have a high degree of polarization and excellent polarization characteristics, as well as a black display and a white display. Both are good. On the other hand, Comparative Examples 1 and 3 and the commercially available LCD monitor product have good polarization characteristics, but have a large b value and poor white display. In Comparative Example 2, the b value was small, but the polarization characteristics were poor, and the black display was also poor. Therefore, it can be understood that the black display and the white display are good in the example, while the black display and the white display are not compatible in the comparative example.

[0047]

As described above, the polarizing plate of the present invention has the parallel transmittance (the transmittance when the absorption axes of the two polarizing plates are made parallel) and the orthogonal transmittance (the transmittance of the two polarizing plates). The transmittance when the absorption axis is made orthogonal) has a constant relationship when measured at two different wavelengths, so that the polarization characteristics and hue of the polarizing plate are good, and the liquid crystal display device such as a liquid crystal monitor is used. In this case, white display can be displayed white and black in the orthogonal state (black display) can be displayed black.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yoichiro Sugino 1-1-2 Shimohozumi, Ibaraki City, Osaka Prefecture Inside Nitto Denko Corporation (72) Inventor Yuji Sumiki 1-1-2 Shimohozumi, Ibaraki City, Osaka Prefecture Item Nitto Denko Corporation (72) Inventor Seri Yoshikawa 1-1-2 Shimohozumi, Ibaraki City, Osaka Prefecture Nitto Denko Corporation (72) Inventor Naofumi Mihara 1-1-2 Shimohozumi, Ibaraki City, Osaka Prefecture F-term in Nitto Denko Corporation (reference) 2H049 BA02 BA27 BB03 BB33 BB43 BC22 2H091 FA08X FA08Z FB02 FB04 GA16 LA17 LA30

Claims (5)

[Claims] 1. A polarizing plate in which a protective film is laminated on at least one side of a polarizer formed of a polyvinyl alcohol-based film, and has a parallel transmittance T at 440 nm.
A polarizing plate, wherein a and the orthogonal transmittance Tc and the parallel transmittance Tb and the orthogonal transmittance Td at 690 nm satisfy the following formula (I). [Ta / Tc] / [Tb / Td]> 1.5 (I) 2. The polarizing plate according to claim 1, wherein the single transmittance of light is 42 to 46%, the degree of polarization is 99.5% or more, and the parallel hue hunter b value is 5.0 or less. 3. The polarizing plate according to claim 1, wherein the polarizer is a polyvinyl alcohol-based film on which iodine is adsorbed. 4. The polarizing plate according to claim 1, wherein the protective film is a triacetyl cellulose film. 5. A liquid crystal display device, wherein the polarizing plate according to claim 1 is arranged on at least one side of a liquid crystal cell.