JP2001296428A - Method for manufacturing polarizing plate and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a polarizing plate making high transmittance and high polarization degree compatible with each other and a liquid crystal display device. SOLUTION: The method for manufacturing the polarizing plate comprises a step for dyeing a polyvinyl alcohol(PVA) film with iodine or a dye having dichroism, a step for cross-linking the PVA film with a cross-linking agent and a step for stretching the PVA film with rolls in either of the steps. In cross-linking the PVA film in a bath containing the cross-linking agent after dyeing it in a dyeing bath, the stretch ratio is kept in the range of 1.01-4.5 times the length of a PVA film raw sheet for the film raw sheet to dyeing treatment finish. Immersion treatment at least in a bath containing 4-20 wt.% iodide is carried out after the cross-linking treatment in the bath containing the cross-linking agent, and at the same time and stretch ratio after the cross- linking treatment in the bath is kept in the range of <=3 times the previous length. Furthermore, the total stretch ratio from the PVA film raw sheet to the final product is kept in the range of 4.5-8 times the initial length.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a polarizing plate used for a liquid crystal display device (hereinafter, may be abbreviated as LCD) and a liquid crystal display device provided with the polarizing plate obtained by the method. More specifically, the present invention relates to a method for manufacturing a polarizing plate having a high light transmittance and a high polarization rate, and a liquid crystal display device.

[0002]

2. Description of the Related Art LCDs are used in personal computers and the like, and have been rapidly increasing in recent years. The use of LCDs is expanding, and in recent years, LCDs are also being used for monitors.

[0003] A polarizing plate is prepared by dyeing a PVA film with dichroic iodine or a dye and then crosslinking the film with boric acid or borax. In addition, uniaxial stretching is performed in the dyeing step and the crosslinking step. This stretching may be performed during the step, or may be performed before or after the step. After the dyeing step and the cross-linking step, it is usually dried using a drier or the like, and bonded to a protective layer such as a triacetyl cellulose (TAC) film using an adhesive.

A polarizing plate used for a liquid crystal display device is
It is required to increase both the transmittance and the degree of polarization (rate). That is, when the transmittance of a polarizing plate used in a display device such as an LCD is low, the degree of polarization increases, but the amount of transmitted light decreases and the display becomes dark. Conversely, when the transmittance is increased, the degree of polarization decreases and the contrast deteriorates. Therefore, a polarizing plate having high transmittance and high polarization degree characteristics is required. However, the transmittance and the degree of polarization (rate) of the polarizing plate are required. Various attempts have been made to raise the value of both, but it has not been easy.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing a polarizing plate and a liquid crystal display device, which have both a high light transmittance and a high polarization, in order to solve the above-mentioned conventional problems. I do.

[0006]

In order to achieve the above object, a method for producing a polarizing plate according to the present invention is a method for dyeing a polyvinyl alcohol (PVA) film with iodine or a dye having dichroic properties and using a crosslinking agent. Cross-linking, a method of producing a polarizing plate by stretching using a roll in any of these steps, dyeing the film in a dye bath containing iodine or a dye having dichroic properties, then cross-linking When cross-linking in a bath containing the agent, the stretching ratio from the PVA film raw material to after the dyeing treatment is in the range of 1.01 to 4.5 times (however, the case where the cross-linking agent is contained in the dyeing bath is also included in the dyeing ), At least one bath after the cross-linking treatment bath containing a cross-linking agent is immersed by containing 4 to 20% by weight of iodide, and the draw ratio after the cross-linking treatment bath is set to 3 times or less,
In addition, the total stretching ratio from the PVA film raw material to the final product is set to a range of 4.5 to 8 times.

In the above, “after the crosslinking treatment bath” means:
In addition to the cross-linking bath, it also includes other baths and stretching other than the bath (eg, stretching during drying of the polarizer).

[0008] In the above method, the iodide is preferably at least one compound selected from potassium iodide, hydrogen iodide, lithium iodide, sodium iodide and zinc iodide.

In the above method, the temperature of the dyeing bath is 2
It is preferably in the range of 0 to 45 ° C.

In the above method, the crosslinking bath temperature is 5
It is preferably in the range of 0 to 70 ° C.

In the above method, the crosslinking agent is preferably boric acid or borax.

In the present invention, a reflective plate or a semi-transmissive reflective plate may be bonded to the polarizer produced by the above method to form a reflective polarizer or a transflective polarizer.

Further, an elliptic or circular polarizing plate can be formed by laminating a retardation plate or a λ plate to the polarizing plate manufactured by the above method.

A polarizing plate can also be formed by laminating a viewing angle compensation film on the polarizing plate manufactured by the above method.

Further, a polarizing plate can be formed by laminating a brightness enhancement film to the polarizing plate manufactured by the above method using an adhesive or a pressure-sensitive adhesive.

Next, a liquid crystal display device according to the present invention is characterized in that a polarizing plate manufactured by the above method is provided on at least one side of a liquid crystal cell.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION In the process for producing a polarizing plate of the present invention, a PVA film, which is a raw material of the polarizing plate, is subjected to swelling, dyeing, stretching, cross-linking, drying, etc. to obtain a polarizer having a polarizing function. Then, a film such as TAC or polyethylene terephthalate (PET) is attached as a protective layer to the polarizer using an adhesive or a pressure-sensitive adhesive to obtain a polarizing plate.

In the manufacturing process of the polarizer, swelling, dyeing,
The order of the four steps of stretching and crosslinking is not particularly limited, and the four steps may be performed separately or in combination. That is, the “stretching step”
Usually, it is often performed simultaneously with the “dyeing step” and “crosslinking step”, but may be performed in another step. Further, the dyeing step and the crosslinking step may be performed simultaneously. The polarizing film is made of the above 3
After the step, the film is dried, and is manufactured by laminating with a film such as a TAC (triacetylcellulose) film or a PET film to be a protective layer.

In the present invention, the stretching ratio after dyeing with an iodine-containing dyeing bath having dichroic properties (hereinafter referred to as "pre-stretching ratio") is in the range of 1.01 to 4.5 times. "Pre-stretching"
This includes stretching in the case where treatments such as washing, swelling, humidity control, and rolling are performed before the dyeing bath. The stretching ratio after the subsequent crosslinking treatment bath (hereinafter referred to as “post-stretching ratio”) is performed at 3 times or less, and the total stretching ratio of the pre-stretching ratio and the post-stretching ratio is 4.5 to 8 times or less. It is manufactured as. Here, the reason why the pre-stretching ratio is in the range of 1.01 to 4.5 times is that there is no occurrence of sagging or wrinkling of the film due to the dyeing treatment, and the unevenness of stretching is reduced. 1.01
If the ratio is less than twice, the film sags, and there is an inconvenience that the portion becomes uneven in dyeing at the time of dyeing. Also, 4.
If it exceeds 5 times, there is a disadvantage that the stretching is likely to be non-uniform in the plane of the film being stretched and unevenness of the stretching is likely to occur.

The reason why the post-stretching ratio is set to 3 times or less is that the orientation of iodine in the PVA is good and cutting of the stretched film hardly occurs. There is an inconvenience that it becomes easier.

The polarizing plate thus obtained has both characteristics of high transmittance and high degree of polarization. When a crosslinking agent is contained in the dyeing bath, it is treated as a dyeing bath and not treated as a crosslinking bath. That is, it is included in “pre-stretching”.

The immersion treatment is carried out by adding 4 to 20% by weight, preferably 2 to 10% by weight of iodide in at least one bath after the crosslinking treatment bath containing the crosslinking agent after dyeing. Iodide
The compound is preferably at least one compound selected from potassium iodide, hydrogen iodide, lithium iodide, sodium iodide and zinc iodide. It is particularly preferable to use potassium iodide.

The dyeing bath is preferably a bath having a concentration of iodine or a dye having a dichroic property of 0.02% by weight or more.

The stretching ratio after the crosslinking treatment (“post-stretching ratio”) is not the stretching ratio in the crosslinking bath alone, but
For example, when a washing bath is provided after the crosslinking bath, the stretching ratio during the washing bath is also included, and when the polarizer is dried, the stretching ratio during the drying process is also included. In other words, it defines the stretching ratio after the crosslinking bath until the polarizer is produced.

The total stretching ratio is the total stretching ratio from the raw material at the time of PVA film formation to the production of the polarizer.
If the total stretching ratio exceeds 8 times, PVA
The film is likely to be cut, which is not preferable in terms of quality.

An appropriate transparent film can be used as a protective film material serving as a transparent protective layer provided on one or both sides of a polarizer (polarizing film). 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 is
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 external light from being reflected 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 can be visually recognized. 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 reflective 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 a reflection type polarizing plate having a reflection layer reflecting the fine unevenness on the transparent protective film having a fine unevenness on the surface 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 the method in which the reflecting plate is directly attached to the transparent protective film of the polarizing plate. . 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 elliptic or circular polarizing plate in which a retardation plate is further laminated on the above-mentioned polarizing plate comprising the polarizer of the present invention and a protective layer will be described.

When changing linearly polarized light to elliptical or circularly polarized light, or changing elliptical or circularly polarized light to linearly polarized light, or changing the polarization direction of linearly polarized light, a retardation 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 provide 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, as a specific example of the retardation plate,
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-described polarizing plate comprising the polarizer of the present invention and a protective layer will be described.

The viewing angle compensating 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 from a slightly oblique direction, not perpendicular to the screen.

As such a viewing angle compensating 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, linearly polarized light having a predetermined polarization axis is transmitted and other light is reflected, such as a multilayer thin film of a dielectric or a multilayer laminate of thin films having different refractive index anisotropy. 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 that transmits linearly polarized light having a predetermined polarization axis, the transmitted light is incident on the polarization plate as it is, with the polarization axis aligned, thereby efficiently suppressing absorption loss by the polarization plate. 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 with respect to 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 also has a structure in which two or three or more layers are overlapped by combining those having different reflection wavelengths, so that a layer which reflects circularly polarized light in a wide wavelength range such as a visible light region is obtained. 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 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. 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.

[0057]

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

Example 1 Kuraray-made PVA (9 × 75R)
Roll stretching was performed using S). After pre-stretching in the first dyeing bath (an aqueous solution having an iodine concentration of 0.03 wt% and a KI concentration of 0.5 wt%, at 30 ° C.) at a stretching magnification of 3 times, a second crosslinking bath (borate concentration of 5 wt% and KI concentration of 8 wt%) % Aqueous solution, 55 ° C.), stretched twice in a bath, and dried. The total stretching ratio was 6.0 times. The obtained polarizer,
A polarizing plate was produced by laminating a TAC (triacetyl cellulose) film and a PVA-based adhesive. The transmittance / polarization degree at that time was 44.1% / 99.95%.

Example 2 Kuraray-made PVA (9 × 75R)
Roll stretching was performed using S). In the first dyeing bath (an aqueous solution with an iodine concentration of 0.03 wt% and a KI concentration of 0.3 wt%, at 30 ° C.), pre-stretching is performed at a draw ratio of 3 and then a second crosslinking bath (borate concentration of 5 wt% and KI concentration of 10 wt%) % Aqueous solution, 55 ° C.) in a bath at 1.33 times post stretching.
It was stretched 5 times and dried. The total stretching ratio is 6.0.
Doubled.

The obtained polarizer was bonded to a TAC (triacetyl cellulose) film using a PVA-based adhesive to produce a polarizing plate. Transmittance / polarization degree at that time = 4
It was 4.0% / 99.96%.

Example 3 Kuraray-made PVA (9 × 75R)
Roll stretching was performed using S). Pre-stretching in the first dyeing bath (iodine concentration 0.03 wt%, KI concentration 0.3 wt% aqueous solution, 30 ° C.) up to 3 times the draw ratio, second crosslinking bath (boric acid 5 wt% aqueous solution, 55 ° C.) 1.) in the bath
The film was stretched at 0 times, immersed (1 time) in a third bath (aqueous solution with a KI concentration of 10 wt%, 55 ° C.), and stretched to a total of 6.0 times during the drying treatment to prepare a polarizer. Then TA
A polarizing plate was produced by laminating a C (triacetyl cellulose) film with a PVA-based adhesive. At that time, the transmittance / degree of polarization was 44.1% / 99.95%.

Comparative Example 1 PVA made by Kuraray (9 × 75R)
Roll stretching was performed using S). The first dyeing bath (an aqueous solution with an iodine concentration of 0.03 wt% and a KI concentration of 5 wt%,
30 ° C.), pre-stretching at a stretching magnification of 5 times, and then stretching 1.04 times in a second cross-linking bath (aqueous solution having a boric acid concentration of 5% by weight and a KI concentration of 1% by weight, 55 ° C.) followed by 1.15 times stretching. It was stretched and dried. The total stretching ratio was 6.0 times. Thereafter, a TAC (triacetyl cellulose) film and a PVA-based adhesive were attached to each other to produce a polarizing plate. Transmittance / polarization degree at that time = 44.0% / 99.6
%Met.

Comparative Example 2 PVA made by Kuraray (9 × 75R)
Roll stretching was performed using S). The first dyeing bath (an aqueous solution with an iodine concentration of 0.03 wt% and a KI concentration of 5 wt%,
At 30 ° C.), and then stretched 3.22 times in a second cross-linking bath (aqueous solution having a boric acid concentration of 5 wt% and a KI concentration of 1 wt%, 55 ° C.), followed by 1 .0
After stretching 4 times, it was dried. The total stretching ratio was 6.0 times. Thereafter, a TAC (triacetyl cellulose) film and a PVA-based adhesive were attached to each other to produce a polarizing plate. Transmittance / polarization degree at that time = 43.8
% / 99.6%.

Table 1 shows the above results.

[0065]

[Table 1]

As is clear from Table 1, the difference between the single transmittance and the degree of polarization in Comparative Examples 1-2 and Examples 1-3 seems to be slightly smaller than the decimal point, but this difference is a large difference. is there. As a numerical value that can confirm the difference, take the ratio of "parallel transmittance" and "orthogonal transmittance" used when calculating the degree of polarization.
As shown in Table 1, it can be confirmed as a large difference between the comparative example and the example. The ratio between "parallel transmittance" and "orthogonal transmittance" can be regarded as the contrast of the polarizing plate.

[0067]

As described above, according to the present invention, a polyvinyl alcohol (PVA) film is dyed with iodine or a dye having dichroic properties, cross-linked with a cross-linking agent, and subjected to any of these steps. A method for producing a polarizing plate by stretching using a roll, wherein the film is dyed in a dyeing bath containing iodine or a dye having dichroic properties, and then crosslinked in a bath containing a crosslinking agent, PVA is used. The stretching magnification from the film forming raw material to after the dyeing treatment is 1.01 to 4.5.
The range is twice as large (however, the case where the crosslinking agent is contained in the dyeing bath is also included in the dyeing), and 4 to 20% by weight of iodide is contained in at least one bath after the crosslinking treatment bath containing the subsequent crosslinking agent. Along with the immersion treatment, the stretching ratio after the crosslinking treatment bath is 3 times or less, and by setting the total stretching ratio from the PVA film raw material to the final product in the range of 4.5 to 8 times, high light transmittance and It is possible to provide a method for manufacturing a polarizing plate and a liquid crystal display device that have both high polarization ratios.

 ──────────────────────────────────────────────────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 City, Osaka Prefecture F-term in Nitto Denko Corporation (Reference) 2H049 BA02 BA27 BB43 BB62 BB63 BC01 BC03 BC22 2H091 FA08X FA08Z FA11X FA15Z FB02 FC05 FC07 GA16 HA07 HA10 LA30

Claims (10)

[Claims] 1. A polarizing plate obtained by dyeing a polyvinyl alcohol (PVA) film with iodine or a dye having dichroic properties, cross-linking with a cross-linking agent, and stretching using a roll in any of these steps. After dyeing the film with a dye bath containing iodine or a dye having dichroic properties, and then crosslinking the film with a bath containing a crosslinking agent, from the PVA film raw material to after the dyeing treatment When the stretching ratio is 1.
The range is from 01 to 4.5 times (however, the case where a cross-linking agent is contained in the dyeing bath is also included in the dyeing), and 4 to 20 iodides are contained in at least one bath after the crosslinking treatment bath containing the cross-linking agent. In addition to the immersion treatment, the stretching ratio after the cross-linking treatment bath is 3 times or less, and the total stretching ratio from the PVA film raw material to the final product is in the range of 4.5 to 8 times. Method for manufacturing a polarizing plate. 2. The method according to claim 1, wherein the iodide is at least one compound selected from potassium iodide, hydrogen iodide, lithium iodide, sodium iodide and zinc iodide. 3. The method for producing a polarizing plate according to claim 1, wherein the dye bath temperature is in the range of 20 to 45 ° C. 4. The method for producing a polarizing plate according to claim 1, wherein the crosslinking bath temperature is in the range of 50 to 70 ° C. 5. The method according to claim 1, wherein the crosslinking agent is boric acid or borax. 6. A reflective plate or a semi-transmissive reflective plate is bonded to the polarizer produced by the method according to claim 1 to form a reflective polarizer or a transflective polarizer. Method for producing a polarizing plate. 7. A method for manufacturing a polarizing plate, comprising: attaching a retardation plate or a λ plate to the polarizing plate manufactured by the method according to claim 1 to form an elliptical or circular polarizing plate. 8. A viewing angle compensation film laminated to a polarizing plate manufactured by the method according to claim 1.
A method for manufacturing a polarizing plate for forming a polarizing plate. 9. A method for manufacturing a polarizing plate, comprising: bonding a brightness enhancement film to the polarizing plate manufactured by the method according to claim 1 using an adhesive or a pressure-sensitive adhesive to form a polarizing plate. 10. A liquid crystal display device comprising a polarizing plate manufactured by the method according to claim 1 on at least one side of a liquid crystal cell.