JP2001290024A - Polarizing plate and liquid crystal display device having the same - Google Patents

Abstract

(57) [Summary] Liquid crystal display device (LCD) with improved display unevenness
The present invention provides a polarizing plate and a liquid crystal display device used for the above. SOLUTION: In a polarizing plate manufactured by dyeing and crosslinking a polyvinyl alcohol (PVA) film, light transmittance (single transmittance) of one polarizing plate and polarization of two polarizing plates are obtained. A polarizing plate that satisfies all of the following equations calculated from the light transmittance (orthogonal transmittance) when the axes (polarization axes) are made orthogonal to each other. (Single transmittance) / (Orthogonal transmittance) of wavelength 440 nm> 6
00 (Single transmittance) / (Orthogonal transmittance) of wavelength 550 nm> 3
000 (Single transmittance) / (Orthogonal transmittance) of 610 nm wavelength> 1
1000

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art A polarizing plate used for a display device (especially LCD) is, for example, a polyvinyl alcohol film (hereinafter, referred to as a polyvinyl alcohol film).
Sometimes abbreviated as PVA film. ), Iodine or dichroic dye, a dyeing step of dyeing with a dichroic dye, a cross-linking step of cross-linking with boric acid or borax, and a stretching step of uniaxial stretching (each step of dyeing, crosslinking, stretching, The steps need not be performed separately and may be performed at the same time, and the order of each step is not particularly specified.), Then, dried, and then triacetylcellulose film (hereinafter sometimes abbreviated as TAC film). It is manufactured by laminating with such a protective layer.

[0003] LCDs are used in personal computers and the like.
In recent years, it has increased rapidly. LCD applications are expanding and are being used for monitor applications. However, the LCD for a monitor has a larger screen size and a larger panel brightness (brightness) than a personal computer. Therefore, if the polarizing plate used for personal computer applications is used as it is, when displaying neutral colors such as black and gray, unevenness in dyeing of the polarizing plate and the raw material of the polarizing plate The unevenness of the phase difference of PVA is seen in the stretching axis direction.
This is a display problem.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a polarizing plate and a liquid crystal display for use in an LCD with improved display unevenness in order to solve the above-mentioned conventional problems.

[0005]

In order to achieve the above object, a polarizing plate of the present invention comprises polyvinyl alcohol (PV).
A) In a polarizing plate manufactured by dyeing and crosslinking a film, the light transmittance (single transmittance) of one polarizing plate,
It is characterized by satisfying all of the following expressions calculated from the transmittance of light (orthogonal transmittance) when the axes of polarization (polarization axes) of the two polarizing plates are orthogonal. (Single transmittance) / (Orthogonal transmittance) of wavelength 440 nm> 6
00 (Single transmittance) / (Orthogonal transmittance) of wavelength 550 nm> 3
000 (Single transmittance) / (Orthogonal transmittance) of 610 nm wavelength> 1
1000 In the present invention, the light transmittance (parallel transmittance) when the axes of polarization (polarization axes) of the two polarizing plates are parallel, and 2
It is preferable to satisfy all of the following expressions calculated from the transmittance of light (orthogonal transmittance) when the axes of polarization (polarization axes) of the polarizing plates are orthogonal. (Parallel transmittance) / (Orthogonal transmittance) of wavelength 440 nm> 7
00 (parallel transmittance) / (cross transmittance) of wavelength 550 nm> 3
000 wavelength (610 nm) (parallel transmittance) / (cross transmittance)> 1
1000 In the present invention, the luminosity correction transmittance Y obtained by the JIS Z 87012 degree visual field XYZ system is 42.
It is preferably 5% or more (however, the standard light is a C light source, and the visibility is corrected (700 to 400 nm: every 10 nm))
use).

The present invention also provides any one of the above polarizing plates,
It is also possible to use a reflective polarizing plate or a transflective polarizing plate in which a reflecting plate and a transflective reflecting plate are bonded.

Further, the present invention may be an elliptical or circular polarizing plate obtained by laminating a retardation plate or a λ plate to any of the above polarizing plates.

The present invention may also be a polarizing plate obtained by laminating a viewing angle compensation film on any of the above-mentioned polarizing plates.

Further, in the present invention, a polarizing plate may be formed by bonding a brightness enhancement film to any of the above-mentioned polarizing plates using an adhesive or a pressure-sensitive adhesive.

[0010] Further, a liquid crystal display device having any one of the above polarizing plates on at least one side of a liquid crystal cell may be provided.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Generally, a polarizing film is prepared by dyeing a PVA film in dirt containing iodine or a dye having dichroism characteristics, and a boring acid or borax. Can be roughly divided into three steps: a "crosslinking step" in which crosslinking is performed in a PVA crosslinking agent, and a "stretching step" in which PVA is stretched. Incidentally, the “stretching step” usually includes the “dyeing step” and “
Although it is often performed simultaneously with the “crosslinking step”, it may be performed in a separate step. Alternatively, the dyeing step and the crosslinking step may be performed simultaneously. After the above three steps, the polarizing film is dried and protected. It is manufactured by laminating with a film such as a TAC (triacetyl cellulose) film to be a layer.

The basic structure of the polarizing plate used in the present invention is as follows.
A suitable adhesive layer on one or both sides of a polarizer made of a dichroic substance-containing polyvinyl alcohol-based polarizing film,
For example, it is formed by bonding a transparent protective film serving as a protective layer via an adhesive layer made of a vinyl alcohol-based polymer or the like.

As a polarizer (polarizing film), a dichroic substance made of iodine, a dichroic dye, or the like may be used, for example, on a film made of a suitable vinyl alcohol-based polymer such as polyvinyl alcohol or partially formalized polyvinyl alcohol. , A suitable treatment such as a stretching treatment, a cross-linking treatment, or the like is performed in an appropriate order or manner, and an appropriate material that transmits linearly polarized light when natural light is incident thereon can be used. Above all, those having excellent light transmittance and degree of polarization are preferable.

As a protective film material to be a transparent protective layer provided on one side or both sides of a polarizer (polarizing film), an appropriate transparent film can be used. As an example of the polymer, an acetate resin such as triacetylcellulose is generally used, but is not limited thereto.

A transparent protective film that can be particularly preferably used in view of polarization characteristics and durability is a triacetyl cellulose film whose surface is saponified with an alkali or the like. When transparent protective films are provided on both sides of the polarizing film, transparent protective films made of different polymers or the like may be used on both sides.

The transparent protective film used for the protective layer includes:
As long as the object of the present invention is not impaired, a hard coat treatment, an anti-reflection treatment, a treatment for preventing sticking, diffusion or anti-glare, or the like may be performed. The hard coat treatment is performed for the purpose of preventing the surface of the polarizing plate from being scratched. For example, a hardened film excellent in hardness and slipperiness by an appropriate ultraviolet curable resin such as a silicone resin is coated on the surface of the transparent protective film. Can be formed.

On the other hand, the antireflection 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 antireflection film or the like according to the related art. In addition, sticking prevention is for the purpose of preventing adhesion with the adjacent layer,
The anti-glare treatment is performed for the purpose of preventing external light from being reflected on the surface of the polarizing plate and hindering the visibility of light transmitted through the polarizing plate, and is, for example, a roughening method using a sandblasting method or an embossing method. The transparent protective film can be formed by giving a fine uneven structure to the surface of the transparent protective film by an appropriate method such as a method of mixing 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. Fine particles may be used, or organic fine particles composed of crosslinked or uncrosslinked polymer particles or the like may be used. The use amount of the transparent fine particles is generally 2 to 70 parts by weight, particularly 5 to 50 parts by weight, per 100 parts by weight of the transparent resin.

The anti-glare 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 these layers, separately from the transparent protective layer.

In the present invention, the bonding treatment between the polarizer (polarizing film) and the transparent protective film as the protective layer is not particularly limited. For example, an adhesive composed of a vinyl alcohol polymer or boric acid Or borax,
It can be carried out via an adhesive comprising at least a water-soluble cross-linking agent of a vinyl alcohol-based polymer such as glutaraldehyde, melamine, and oxalic acid. Such an adhesive layer can be formed as a coating and drying layer of an aqueous solution, but when preparing the aqueous solution, if necessary, other additives,
A catalyst such as an acid can also be blended.

The polarizing plate according to 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 One or two 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 including the polarizer of the present invention and the protective layer described above includes: Further, a reflection plate or a reflection type polarizing plate or a semi-transmission reflection type polarizing plate in which a transflective reflection plate is laminated, a retardation plate is further laminated on the above-mentioned polarizing plate comprising the polarizer of the present invention and a protective layer. An elliptical or circular polarizer, a polarizer comprising the polarizer and the protective layer of the present invention described above, and a polarizing plate further laminated with a viewing angle compensation film, or the polarizer and the protective layer of the present invention described above. Brightness enhancement film on the polarizing plate Polarizing plates are preferred.

The reflection plate will be described. The reflection plate is provided on a polarizing plate to form a reflection-type polarizing plate. The reflection-type polarizing plate is usually provided on the back side of a liquid crystal cell, and is visible. It is possible to form a liquid crystal display device of the type that reflects and reflects incident light from the side (display side), and has the advantage that the built-in light source such as a backlight can be omitted and the thickness of the liquid crystal display device can be easily reduced. .

The reflection type polarizing plate can be formed by an appropriate method such as a method in which a reflection layer made of metal or the like is provided on one side of the polarizing plate via the transparent protective film or the like as necessary. Incidentally, a specific example thereof includes a transparent protective film which has been subjected to a mat treatment as required, and a reflective layer formed by attaching a foil or a vapor-deposited film made of a reflective metal such as aluminum on one surface.

Further, there is also a reflection type polarizing plate having a reflective layer reflecting the fine unevenness on the transparent protective film having a fine unevenness on the surface by containing fine particles. The reflective layer with a fine surface irregularity structure diffuses the incident light by irregular reflection to prevent directivity and glare,
It has an advantage that light and dark unevenness can be suppressed. The formation of the reflective layer of the fine uneven structure reflecting the fine uneven structure on the surface of the transparent protective film is performed by, for example, making the metal transparent by an appropriate method such as an evaporation method such as a vacuum evaporation method, an ion plating method, or a sputtering method, or a plating method. It can be performed by a method of directly attaching to the surface of the protective film.

The reflecting plate can be used as a reflecting sheet in which a reflecting layer is provided on an appropriate film conforming to the transparent protective film, instead of directly attaching the reflective plate to the transparent protective film described above. . Since the reflection layer of the reflection plate is usually made of a metal, the use form in which the reflection surface is covered with a film, a polarizing plate, or the like is intended to prevent a decrease in the reflectance due to oxidation and to maintain the initial reflectance for a long time. It is preferable from the viewpoint of avoiding separately providing a protective layer.

The transflective polarizing plate can be obtained by forming the reflective layer as a transflective reflective layer such as a half mirror that reflects and transmits light. A transflective polarizing plate is usually provided on the back side of a liquid crystal cell. When a liquid crystal display device or the like is used in a relatively bright atmosphere, an image is displayed by reflecting incident light from the viewing side (display side). In a relatively dark atmosphere, it is possible to form a liquid crystal display device that displays an image using a built-in light source such as a backlight built in the back side of a transflective polarizing plate. That is, the transflective polarizing plate can save energy for use of a light source such as a backlight in a bright atmosphere, and can be used for forming a liquid crystal display device or the like that can be used with a built-in light source even in a relatively dark atmosphere. Useful.

Next, an elliptical or circular polarizing plate in which a retardation plate is further laminated on the above-described polarizing plate comprising the polarizer of the present invention and a protective layer will be described.

When changing linearly polarized light into elliptical or circularly polarized light, or changing elliptical or circularly polarized light into linearly polarized light, or changing the polarization direction of linearly polarized light, a phase difference plate or the like is used. Is a so-called quarter-wave plate (also referred to as a λ / 4 plate) as a retardation plate that changes into elliptical or circularly polarized light, or changes elliptical or circularly polarized light into linearly polarized light.
Is used. A half-wave plate (also called a λ / 2 plate)
It is usually used to change the polarization direction of linearly polarized light.

The elliptically polarizing plate is effectively used for compensating for coloring (blue or yellow) caused by the birefringence of the liquid crystal layer of the STN type liquid crystal display device to make a monochrome display without the coloring. Further, the one in which the three-dimensional refractive index is controlled can also compensate (prevent) coloring that occurs when the screen of the liquid crystal display device is viewed from an oblique direction, and is preferable. The circularly polarizing plate is effectively used, for example, when adjusting the color tone of an image of a reflection type liquid crystal display device for displaying an image in color, and also has an antireflection function.

Incidentally, specific examples of the retardation plate include:
Birefringent film, liquid crystal polymer alignment film, liquid crystal polymer alignment film obtained by stretching a film made of a suitable polymer such as polycarbonate, polyvinyl alcohol, polystyrene, polymethyl methacrylate, polypropylene and other polyolefins, polyarylate and polyamide. One in which the layer is supported by a film is exemplified. Examples of the obliquely oriented film include, for example, a film obtained by bonding a heat shrinkable film to a polymer film and subjecting the polymer film to a stretching treatment and / or a shrinking treatment under the action of the shrinkage force caused by heating, or a film obtained by obliquely aligning a liquid crystal polymer. Is raised.

Next, a polarizing plate in which a viewing angle compensation film is further laminated on the above-mentioned polarizing plate comprising the polarizer of the present invention and a protective layer will be described.

The viewing angle compensation film is a film for widening the viewing angle so that an image can be seen relatively clearly even when the screen of the liquid crystal display device is viewed not in a direction perpendicular to the screen but in a slightly oblique direction.

As such a viewing angle compensation film, a film obtained by coating a discotic liquid crystal on a triacetyl cellulose film or the like, or a retardation plate is used. Whereas a polymer film having a birefringence in which a normal retardation plate is uniaxially stretched in the plane direction is used, a retardation plate used as a viewing angle compensation film is a birefringent film which is biaxially stretched in the plane direction. Or a bidirectionally stretched film such as an obliquely oriented polymer film which is uniaxially stretched in the plane direction and stretched in the thickness direction and has a controlled refractive index in the thickness direction. As described above, for example, as described above, the heat-shrinkable film is adhered to the polymer film, and the polymer film is stretched or / and shrunk under the action of the heat-induced shrinkage force. And the like. As the raw material polymer for the retardation plate, the same polymer as the polymer described for the retardation plate is used.

A polarizing plate obtained by laminating a brightness enhancement film on the above-described polarizing plate comprising the polarizer of the present invention and a protective layer is as follows:
Usually, it is provided and used on the back side of the liquid crystal cell. The brightness enhancement film reflects linearly polarized light having a predetermined polarization axis or circularly polarized light having a predetermined direction when natural light is incident due to reflection from a backlight or a back side of a liquid crystal display device, and has a property of transmitting other light. A polarizing plate obtained by laminating a brightness enhancement film with a polarizing plate comprising the above-described polarizer and a protective layer, while allowing light from a light source such as a backlight to enter to obtain transmitted light of a predetermined polarization state and the predetermined polarization state. Other light is reflected without transmitting. The light reflected on the surface of the brightness enhancement film is further inverted via a reflection layer or the like provided on the rear side thereof and re-incident on the brightness enhancement plate, and a part or all of the light is transmitted as light of a predetermined polarization state to achieve brightness. The brightness can be improved by increasing the amount of light transmitted through the enhancement film and by supplying polarized light that is hardly absorbed by the polarizer to increase the amount of light that can be used for liquid crystal image display and the like. In other words, when light is incident through a polarizer from the back side of a liquid crystal cell with a backlight or the like without using a brightness enhancement film, light having a polarization direction that does not coincide with the polarization axis of the polarizer is hardly generated. Is absorbed by
Does not pass through the polarizer. That is, although it differs depending on the characteristics of the polarizer used, about 50% of the light is absorbed by the polarizer, and accordingly, the amount of light available for liquid crystal image display and the like decreases, and the image becomes darker. The brightness enhancement film is such that light having a polarization direction that is absorbed by the polarizer is once reflected by the brightness enhancement film without being incident on the polarizer, and further inverted through a reflection layer or the like provided on the rear side. Repeatedly re-entering the brightness enhancement plate, the brightness enhancement film transmits the polarized light whose polarization direction has been changed so that the polarization direction of the light reflected and inverted between the two can pass through the polarizer. Since the light is supplied to the child, light from a backlight or the like can be efficiently used for displaying an image on the liquid crystal display device, and the screen can be brightened.

As the above-mentioned brightness improving film, for example, a multilayer thin film of a dielectric or a multilayer laminate of thin films having different refractive index anisotropies transmits linearly polarized light having a predetermined polarization axis and reflects other light. The cholesteric liquid crystal layer, especially the cholesteric liquid crystal polymer oriented film or the one that supports the oriented liquid crystal layer on a film substrate, reflects either left-handed or right-handed circularly polarized light. Other appropriate light, such as one exhibiting a characteristic of transmitting other light, may be used.

Therefore, in the brightness enhancement film of the type which transmits the linearly polarized light having the predetermined polarization axis, the transmitted light is incident on the polarizing plate as it is, with the polarization axis aligned, so that the absorption loss by the polarizing plate can be suppressed and efficiently. Can be transmitted. On the other hand, a brightness enhancement film that transmits circularly polarized light, such as a cholesteric liquid crystal layer, can be directly incident on a polarizer.However, rather than suppressing absorption loss, the transmitted circularly polarized light is converted to linearly polarized light through a retardation plate. It is preferable to make the light incident on the polarizing plate. Incidentally, by using a quarter-wave plate as the retardation plate, circularly polarized light can be converted into linearly polarized light.

A retardation plate that functions as a quarter-wave plate in a wide wavelength range such as a visible light region is, for example, a retardation layer that functions as a quarter-wave plate for monochromatic light such as light having a wavelength of 550 nm. , For example, a method of superimposing a retardation layer functioning as a half-wave plate with the retardation layer exhibiting the above retardation characteristic. Therefore, the retardation plate disposed between the polarizing plate and the brightness enhancement film may be composed of one or more retardation layers.

The cholesteric liquid crystal layer is also configured such that two or three or more cholesteric liquid crystal layers having different reflection wavelengths are overlapped with each other to reflect circularly polarized light in a wide wavelength range such as a visible light region. Thus, it is possible to obtain circularly polarized light transmitted in a wide wavelength range.

The polarizing plate of the present invention may be formed by laminating a polarizing plate and two or three or more optical layers as in the above-mentioned 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,
Although it can be formed by a method of sequentially laminating layers sequentially in the manufacturing process of a liquid crystal display device or the like, those which are preliminarily laminated as an optical member are excellent in stability of quality and workability of assembly, etc. There is an advantage that the manufacturing efficiency of the device or the like can be improved. For the lamination, an appropriate adhesive means such as an adhesive layer can be used.

The polarizing plate or the optical member according to the present invention 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. Above all, from the viewpoint of preventing foaming and peeling phenomena due to moisture absorption, deterioration of optical characteristics due to difference in thermal expansion, prevention of liquid crystal cell warpage, and formation of a high quality and durable liquid crystal display device, the moisture absorption rate It is preferable that the pressure-sensitive adhesive layer has low heat resistance and excellent heat resistance. In addition, an adhesive layer or the like which contains fine particles and exhibits light diffusibility can be used. The adhesive layer may be provided on a necessary surface if necessary.For example, if mention is made of the protective layer of the polarizing plate comprising the polarizer and the protective layer of the present invention, if necessary, one or both surfaces of the protective layer May be provided with an adhesive layer.

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 practical use of the adhesive layer 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, a salicylic acid ester compound, a benzophenone compound, a benzotriazole compound or a cyanoacrylate compound. Alternatively, a material having an ultraviolet absorbing ability by an appropriate method such as a method of treating with an ultraviolet absorbing agent such as a nickel complex compound may be used.

The polarizing plate according to the present invention can be preferably used for forming various devices such as a liquid crystal display device. The liquid crystal display device is a transmission type or reflection type in which the polarizing plate according to the present invention is disposed on one side or both sides of a liquid crystal cell, or a transmission type or a reflection type.
It can be formed as a device having an appropriate structure according to the related art such as a dual-purpose type. Therefore, the liquid crystal cell forming the liquid crystal display device is arbitrary, and may be 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, and the like. A liquid crystal cell of a type 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.

With the polarizing plate of the present invention, unevenness due to the polarizing plate is not visible even in an LCD for high-brightness monitoring and the like.

[0046]

The present invention will be described more specifically with reference to the following examples.

(Comparative Example 1) Kuraray-made PVA (9 × 75R)
S), while performing 3.2-fold stretching in a dyeing bath (aqueous solution containing iodine and KI), dyeing, and then 1.9-fold stretching in a cross-linking bath containing boric acid (total stretching ratio of 6.
08 times), and then dried with a dryer at 50 ° C. to produce a polarizer. After that, a TAC (triacetylcellulose) film and a PVA-based adhesive are bonded together,
A polarizing plate having a visibility correction transmittance of 44.13% and a degree of polarization of 99.94% was obtained.

Comparative Example 2 PVA made by Kuraray (9 × 75R)
S), while performing stretching three times in a dyeing bath (aqueous solution containing iodine and KI), dyeing, and then performing 1.5 times stretching in the first cross-linking bath containing boric acid, followed by boric acid The film was stretched 1.34 times (total stretching ratio 6.03 times) in the second bath of the containing crosslinking bath, and then dried with a dryer at 50 ° C to produce a polarizer. Thereafter, the TAC (triacetylcellulose) film and a pva-based adhesive were used to bond together, and a luminosity corrected transmittance of 43.35% and a degree of polarization of 99.97.
% Polarizing plate was obtained.

Example 1 Kuraray PVA (9 × 75R)
Dyeing bath using S) (aqueous solution containing iodine and KI)
The film was dyed while being stretched 3.2 times in the above, and then stretched 1.2 times in the first bath of the cross-linking bath containing boric acid, and further stretched 1.7 times in the second bath of the cross-linking bath containing boric acid. (Total stretch ratio 6.5 times), and then dried with a dryer at 50 ° C. to produce a polarizer. After that, a TAC (triacetylcellulose) film and a PVA-based adhesive are bonded together,
A polarizing plate having a visibility correction transmittance of 43.25% and a degree of polarization of 99.98% was obtained.

Example 2 Kuraray-made PVA (9 × 75R)
Dyeing bath using S) (aqueous solution containing iodine and KI)
Then, the dye was dyed while being stretched 3 times in the first step, and then stretched 1.4 times in the first bath of the cross-linking bath containing boric acid, and further stretched 1.6 times in the second bath of the cross-linking bath containing boric acid. (Stretching ratio: 6.72 times), and then dried with a dryer at 50 ° C to produce a polarizer. Thereafter, the TAC (triacetylcellulose) film and a PVA-based adhesive were bonded together to obtain a polarizing plate having a visibility correction transmittance of 43.35% and a degree of polarization of 99.99%.

The transmittance of the polarizing plate was measured with an integrating sphere spectral transmittance meter DO-3 (manufactured by Murakami Color Research Laboratory). (Evaluation method 1 for unevenness of polarizing plate) Illuminance 33,000 in dark room
When two polarizing plates to be evaluated were placed on a backlight of Lux such that the polarization axes were orthogonal to each other, it was confirmed whether striped unevenness was visually observed in a direction perpendicular to the polarization axis. (Evaluation method 2 for unevenness of polarizing plate) Illuminance 33,000 in dark room
On a Lux backlight, two polarizing plates are arranged so that their polarization axes are parallel to each other, and the polarizing plate to be evaluated between the two polarizing plates is placed in an orthogonal state. It was confirmed whether unevenness was observed in the direction perpendicular to the polarization axis. (Evaluation method 3 for unevenness of polarizing plate) The upper and lower polarizing plates attached to the liquid crystal cell of a commercially available 18.1 inch LCS monitor (300 candela) were peeled off, and the polarizing plate to be evaluated was evaluated using an adhesive. After bonding, the display on the monitor was changed to a black display, and the viewing angle at which the monitor was viewed was changed, and it was confirmed whether streaks (stripes) were seen in the direction perpendicular to the polarization axis of the polarizing plate.

[0052]

[Table 1]

[0053]

[Table 2]

[0054]

[Table 3]

[0055]

[Table 4]

(Evaluation results) "Evaluation results of unevenness" in Tables 1 to 4
As is clear from the above, in Examples 1 and 2, a good polarizing plate with no visible unevenness was obtained.

That is, a combination of the stretching ratio of the first and second baths containing boric acid and the increase of the total stretching ratio,
By making the transmittance near 43.2 to 43.3 and setting the degree of polarization to 99.98 or more, a good polarizing plate without unevenness was obtained.

[0058]

As described above, the polarizing plate of the present invention is manufactured by dyeing and cross-linking a polyvinyl alcohol (PVA) film, and the light transmittance (single unit) of one polarizing plate is obtained. Transmittance) and the following formula, which is calculated from the transmittance (orthogonal transmittance) of the light when the axes of polarization (polarization axes) of the two polarizing plates are made orthogonal, improves display unevenness. A polarizing plate and a liquid crystal display device to be used for a finished LCD can be provided. (Single transmittance) / (Orthogonal transmittance) of wavelength 440 nm> 6
00 (Single transmittance) / (Orthogonal transmittance) of wavelength 550 nm> 3
000 (Single transmittance) / (Orthogonal transmittance) of 610 nm wavelength> 1
1000

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Kazuki Tsuchimoto 1-2-1, Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation (72) Inventor Senri Yoshikawa 1-1-1, Shimohozumi, Ibaraki-shi, Osaka No.2 Nitto Denko Corporation (72) Inventor Seiichi Kusumoto 1-2-1, Shimohozumi, Ibaraki-shi, Osaka F-term in Nitto Denko Corporation (Reference) BA27 BA43 BB33 BB43 BB63 BB65 BB66 BC03 BC14 BC22 2H091 FA08X FA08Z FA11X FA11Z FA14Z FA37X FA37Z FC05 FC07 FD08 FD10 FD15 GA16 GA17 KA10 LA16

Claims (8)

[Claims] 1. A polarizing plate produced by dyeing and cross-linking a polyvinyl alcohol (PVA) film, comprising: a light transmittance (single transmittance) of one polarizing plate; and a polarization of two polarizing plates. A polarizing plate that satisfies all of the following expressions calculated from the transmittance of light (orthogonal transmittance) when the axes (polarization axes) are orthogonal to each other. (Single transmittance) / (Orthogonal transmittance) of wavelength 440 nm> 6
00 (Single transmittance) / (Orthogonal transmittance) of wavelength 550 nm> 3
000 (Single transmittance) / (Orthogonal transmittance) of 610 nm wavelength> 1
1000 2. The light transmittance (parallel transmittance) when the axes of polarization (polarization axes) of two polarizing plates are parallel to the axis of polarization (polarization axes) of the two polarizing plates. 2. The polarizing plate according to claim 1, wherein all of the following expressions calculated from the light transmittance (orthogonal transmittance) are satisfied. 3. (Parallel transmittance) / (Orthogonal transmittance) of wavelength 440 nm> 7
00 (parallel transmittance) / (cross transmittance) of wavelength 550 nm> 3
000 wavelength (610 nm) (parallel transmittance) / (cross transmittance)> 1
1000 3. The polarizing plate according to claim 1, wherein the luminosity-corrected transmittance Y determined by a JIS Z 87012-degree visual field XYZ system is 42.5% or more (where the standard light is a C light source, Visibility correction (700 to 400 nm: 10
nm))). 4. A reflective polarizing plate or a transflective polarizing plate comprising a polarizing plate according to claim 1 and a reflecting plate and a semi-transmissive reflecting plate bonded thereto. 5. An elliptical or circular polarizing plate comprising the polarizing plate according to claim 1 and a retardation plate or a λ plate bonded thereto. 6. A polarizing plate comprising the polarizing plate according to claim 1 and a viewing angle compensation film bonded thereto. 7. A polarizing plate comprising the polarizing plate according to claim 1 and an adhesive or a pressure-sensitive adhesive, to which a brightness enhancement film is attached. 8. A liquid crystal display device comprising the polarizing plate according to claim 1 on at least one side of a liquid crystal cell.