JP2002236213A - Polarizing plate and liquid crystal display device which uses the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizing plate having more excellent durability and a liquid crystal display device which uses the polarizing plate. SOLUTION: The polarizing plate is produced by laminating a protective film on a polarizer formed by dyeing, crosslinking, stretching and drying a synthetic resin film. When the polarizing plate is left to stand for 120 hours under 70 deg.C heating condition, both of the dimensional change rate in the direction of the absorption axis and the dimensional change rate in the direction of the polarization axis of the polarizing plate are within ±0.6%. When the polarizing plate is left to stand for 120 hours under 70 deg.C heating condition, the dimensional change rate A in the direction of the absorption axis and the dimensional change rate B in the direction of the polarization axis of the polarizing plate satisfy the relation of -0.1<(dimensional change rate A-dimensional change rate B)<+0.1.

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 for 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 include desk-top electronic calculators, electronic clocks, personal computers, word processors,
It is used for instruments of automobiles and machines, and a polarizing plate is used in this liquid crystal display device. As a polarizing plate,
A polarizing film made of a polyvinyl alcohol-based film in which iodine or a dichroic dye is adsorbed and aligned, and a protective film such as triacetyl cellulose is used on both sides of the polarizing film. In order to provide a polarizing plate, a polarizing plate having both a high transmittance and a high degree of polarization is required.

The polarizing plate is, for example, a polyvinyl alcohol (hereinafter sometimes abbreviated as PVA) film.
After dyeing with iodine or dichroic dye having dichroism, stretching to arrange molecules, crosslinking with a crosslinking agent such as boric acid or borax to keep the stretched state, and drying,
It is manufactured by laminating with a protective film such as a triacetyl cellulose (hereinafter sometimes abbreviated as TAC) film.

By the way, a PVA film is dyed, cross-linked,
The stress generated during stretching remains in the polarizing film formed by stretching and drying. Therefore, when a heating stress is applied to the polarizing plate, the polarizing film cannot withstand the residual stress and contracts and deforms. As a result, there is a problem that the dimensions of the polarizing plate itself also change, causing a change in the hue of the liquid crystal display device.

[0005] In particular, in recent years, a plastic substrate has been used as a cell of a small-sized liquid crystal display device. In the case of using a conventional glass cell, even if the dimensions of the polarizing plate change due to heating or humidification, warpage does not easily occur due to the low flexibility of the glass, but in the case of a liquid crystal display device using this plastic substrate, However, plastic substrates have a smaller specific gravity and are thinner than glass substrates, so they have the advantage of being significantly lighter and thinner.On the other hand, plastic has higher flexibility than glass, and cells have to be made with the deformation of the polarizing plate. Deformation and warpage occur. Therefore, a polarizing plate with a small dimensional change is desired.

[0006]

However, there has been a problem that the conventional polarizing plate cannot always sufficiently satisfy the above requirements. That is, as a result of the shrinkage of the polarizing film due to the residual stress existing in the polarizing film, the polarizing plate itself also undergoes dimensional change, resulting in a change in the hue of the LCD, etc., or a defect in workability in the assembly process of the final product. There was a problem that occurs.

That is, an object of the present invention is to provide a polarizing plate having more excellent durability and a liquid crystal display device using the same.

[0008]

Means for Solving the Problems To achieve the above object, a polarizing plate of the present invention is constituted by laminating a protective film with a polarizer formed by dyeing, crosslinking, stretching and drying a synthetic resin film. A polarizing plate, wherein the polarizing plate is heated to 70 ° C.
And the dimensional change rate of the polarizing plate in the absorption axis direction and the dimensional change rate in the polarization axis direction are both within ± 0.6% when the heating is performed for 120 hours.

Further, in the polarizing plate of the present invention, when the polarizing plate is placed under heating conditions of 70 ° C. for 120 hours,
It is preferable that the dimensional change rate A in the absorption axis direction and the dimensional change rate B in the polarization axis direction of the polarizing plate satisfy the following relationship. −0.1 <(dimensional change rate A−dimensional change rate B) <+ 0.1

In the polarizing plate of the present invention, the dimensional behavior of the polarizing plate upon heating is small in the anisotropy of the change in the absorption axis direction and the change in the polarization axis direction of the polarizing plate. The load applied in the plane becomes uniform, and the warpage of the odd-shaped panel, which is a problem in assembling the liquid crystal display device, is eliminated. Accordingly, it is more preferable that the dimensional change rate A of the polarizing plate in the absorption axis direction and the dimensional change rate B in the polarization axis direction satisfy the following relationship. −0.05 <(dimensional change rate A−dimensional change rate B) <+ 0.
05

Further, in the polarizing plate of the present invention, it is preferable that the synthetic resin film is a polyvinyl alcohol film, and the protective film is a triacetyl cellulose film.

Further, in the polarizing plate of the present invention, it is preferable that the polarizer has a thickness of 7 to 40 μm.

The polarizing plate of the present invention is preferably provided with an adhesive layer.

The polarizing plate of the present invention is preferably provided with an anti-glare layer.

It is preferable that a reflector or a transflector is attached to the polarizing plate of the present invention.

Preferably, a retardation plate or a λ plate is attached to the polarizing plate of the present invention.

It is preferable that a viewing angle compensation film is attached to the polarizing plate of the present invention.

Further, it is preferable to bond a brightness enhancement film to the polarizing plate of the present invention.

Next, the liquid crystal display device of the present invention is characterized in that the above-mentioned polarizing plate is arranged on at least one side of the liquid crystal cell.

In the liquid crystal display of the present invention,
Preferably, the liquid crystal cell is a plastic substrate liquid crystal cell.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION The polarizing plate of the present invention has a small stress remaining in the polarizing plate at the time of formation, a small dimensional change of the polarizer when the polarizing plate is subjected to a heating stress, etc. A change in hue during mounting can also be suppressed. Thereby, a polarizing plate having excellent durability can be obtained, and as a result, a higher-performance liquid crystal display device can be provided.

That is, the polarizing plate of the present invention is a polarizing plate formed by laminating a protective film with a polarizer formed by dyeing, crosslinking, stretching and drying a synthetic resin film. The basic configuration of the polarizing plate is that a synthetic resin film is dyed, cross-linked, stretched and dried, and is appropriately bonded to one or both sides of a polarizer made of a dichroic substance-containing polyvinyl alcohol-based polarizing film or the like. A transparent protective film serving as a protective layer is bonded via a layer, for example, an adhesive layer made of a vinyl alcohol-based polymer or the like.

As a polarizer (polarizing film), a synthetic resin film may be subjected to an appropriate treatment such as a dyeing treatment with a dichroic substance such as iodine or a dichroic dye, a stretching treatment and a crosslinking treatment in an appropriate order. It is possible to use an appropriate material that transmits linearly polarized light when natural light is incident thereon. In particular, those having excellent light transmittance and degree of polarization are preferable.

The polarizer of the present invention is formed by dyeing, cross-linking, stretching and drying the above-mentioned synthetic resin film by a conventional method, and its thickness is not particularly limited. It is generally from 80 to 80 µm, and particularly preferably from 7 to 40 µm. If the thickness is less than 5 μm, the mechanical strength decreases, and if it exceeds 80 μm, the optical characteristics deteriorate. The synthetic resin film may be swelled in a water bath or the like before dyeing.

When the synthetic resin film is stretched, the total stretching ratio is preferably set in the range of 3.5 to 6.5 times, and particularly preferably in the range of 4.0 to 5.5 times. Is preferred. When the total stretching ratio is less than 3.5 times, it becomes impossible to obtain a polarizing plate having a high degree of polarization, and when it exceeds 6.5 times, the film is easily broken. The stretching method and the number of stretching are not particularly limited, and may be performed in each step of dyeing and crosslinking, or may be performed in only one of the steps. Further, it may be performed a plurality of times in the same step.

The water content of the polarizer (the weight ratio of the water content in the polarizer to the total weight of the polarizer) when the polarizer is bonded to the protective film depends on the thickness of the polarizer.
It is preferably less than 0% by mass and preferably in the range of 13 to 17% by mass. When the water content exceeds 20% by mass, the amount of change in water after the production of the polarizing plate increases, and the dimensional change increases.

As the synthetic resin film used in the present invention, for example, a hydrophilic polymer film such as polyvinyl alcohol or partially formalized polyvinyl alcohol is preferable, and a polyvinyl alcohol-based film is particularly preferable in that the dyeability with iodine is good. . As the polyvinyl alcohol-based film, a film formed by an arbitrary method such as a casting method, a casting method, and an extrusion method for casting a stock solution obtained by dissolving a polyvinyl alcohol-based resin in water or an organic solvent is appropriately used. be able to. The polymerization degree of the polyvinyl alcohol resin used is preferably from 100 to 5,000, more preferably from 1,400 to 4,000. The thickness of the polyvinyl alcohol-based film is preferably 120 μm or less, more preferably 80 μm or less, and particularly preferably 20 to 50 μm.
μm is preferred. If the thickness exceeds 120 μm, the stress generated at the time of stretching increases, and the dimensional change of the polarizing plate after fabrication increases. On the other hand, if the film thickness is too thin, stretching becomes difficult.

As a protective film material to be a transparent protective layer provided on one or both sides of a polarizer (polarizing film), an appropriate transparent film can be used. Above all, a film made of a polymer having excellent transparency, mechanical strength, heat stability, moisture shielding property and the like is preferably used. Examples of the polymer include an acetate resin such as triacetyl cellulose, a polyester resin, a polyethersulfone resin, a polycarbonate resin, a polyamide resin, a polyimide resin, a polyolefin resin, and an acrylic resin. However, the present invention is not limited to this.

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. The thickness of the transparent protective film is arbitrary, but is generally 500 μm or less, preferably 5 to 300 μm for the purpose of reducing the thickness of the polarizing plate. 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 the front and back sides. In order to suppress the residual stress generated in the polarizer during the production of the polarizer (during stretching), the thickness of the protective film is preferably 15 μm or more, and particularly preferably 20 μm or more.
90 μm is preferred. In particular, when the polarizing plate is subjected to heat stress, the load on the protective layer due to the residual stress of the polarizer is the same as before, but the load on the entire polarizer decreases due to the increase in the thickness of the protective layer. There is a merit that it is done. As a result, the dimensional change of the polarizing plate is reduced,
The warpage of the panel at the time of mounting the liquid crystal panel using the plastic substrate is improved, and the change in the hue of the panel is also improved by reducing the warpage.

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 scratches on the surface of the polarizing plate, for example, by applying a cured film having an excellent hardness and slipperiness with an appropriate ultraviolet curable resin such as a silicone resin to the surface of the transparent protective film. Can be formed.

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, 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 roughening method by 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. Fine particles may be used, or organic fine particles composed 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.

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 is
It may also serve as a diffusion layer (viewing angle compensation function, etc.) 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 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, boric acid or boric acid may be used. It can be carried out via an adhesive comprising at least a water-soluble crosslinking agent of a vinyl alcohol-based polymer such as sand, glutaraldehyde, melamine, and oxalic acid. Such an adhesive layer can be formed as a coating and drying layer of an aqueous solution or the like. When the aqueous solution is prepared, other additives or a catalyst such as an acid can be blended as necessary. In particular, it is preferable to use an adhesive made of polyvinyl alcohol in that the adhesiveness to PVA (polarizing film) is the best.

The polarizing plate can be used as an optical member laminated with another optical layer in practical use. The optical layer is not particularly limited, and examples thereof include a reflector, a transflector, a retardation plate (including a λ plate such as a 波長 wavelength plate and a 、 wavelength plate), a visual compensation film, and a brightness enhancement film. One or more suitable optical layers that may be used for forming a liquid crystal display device or the like can be used. In particular, the above-described polarizing plate comprising the polarizer of the present invention and a protective layer further includes A reflective polarizing plate or a transflective polarizing plate in which a reflecting plate or a transflective reflecting plate is laminated, an elliptically polarizing plate in which a retardation plate is further laminated on the above-described polarizing plate including a polarizer and a protective layer, Or a circular polarizing plate, a polarizing plate comprising the above-mentioned polarizer and a protective layer, a polarizing plate further laminated with a visual compensation film, or a polarizing plate comprising the above-described polarizer and a protective layer, further comprising a brightness enhancement film. The laminated polarizing plate Masui.

The reflection plate is described below. 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. It is possible to form a liquid crystal display device of a type that reflects and reflects incident light from the viewing side (display side), and it is possible to omit the incorporation of a light source such as a backlight and to easily reduce the thickness of the liquid crystal display device. Have.

The reflective 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. . Specific examples thereof include a transparent protective film that has been matted as necessary, 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, a reflective polarizing plate having a reflective layer on which the fine uneven structure is reflected on the transparent protective film having a fine uneven structure on the surface by containing fine particles may be used. The reflection layer having the fine surface irregularity structure has the advantage that the directivity can be relaxed by diffusing incident light by irregular reflection, glare can be prevented, and uneven brightness 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 carried out by a method of directly attaching to the surface of the protective film.

In addition, the reflecting plate may 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 to the transparent protective film of the polarizing plate described above. it can. 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 a transflective reflective layer such as a half mirror that reflects and transmits light on the reflective layer. The transflective polarizing plate is usually provided on the back side of the liquid crystal cell, and when a liquid crystal display device or the like is used in a relatively bright atmosphere,
An image is displayed by reflecting the incident light from the viewing side (display side). In a relatively dark atmosphere, the image is displayed using a built-in light source such as a backlight built in the back side of the transflective polarizing plate. A liquid crystal display device or the like of a type that displays the same can be formed. That is, the transflective polarizing plate can save energy for use of a light source such as a backlight in a bright atmosphere, and is useful for forming a liquid crystal display device of a type that can be used with a built-in light source even in a relatively dark atmosphere. It is.

Next, an elliptically polarizing plate or a circularly polarizing plate in which a retardation plate is further laminated on the above-mentioned polarizing plate comprising a polarizer and a protective layer will be described.

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

The elliptically polarizing plate compensates (prevents) coloring (blue or yellow) caused by birefringence of the liquid crystal layer of a super twisted nematic (STN) type liquid crystal display device to provide a monochrome display without the coloring. It is used effectively for such purposes. Further, the one in which the three-dimensional refractive index is controlled is preferable because coloring which occurs when the screen of the liquid crystal display device is viewed from an oblique direction can be compensated (prevented). 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.

Specific examples of the retardation plate include birefringence obtained by stretching a film made of an appropriate polymer such as polycarbonate, polyvinyl alcohol, polystyrene, polymethyl methacrylate, polypropylene, other polyolefin, polyarylate, or polyamide. And an alignment film of a liquid crystal polymer and a film in which an alignment layer of a liquid crystal polymer is supported by a film. 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 liquid crystal polymer obliquely oriented. And the like.

Next, a polarizing plate in which a viewing angle compensation film is further laminated on the above-mentioned polarizing plate comprising a polarizer 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 from a direction not perpendicular to the screen but slightly oblique.

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. For a normal retardation plate, a polymer film having birefringence uniaxially stretched in the plane direction is used, whereas a retardation plate used as a viewing angle compensation film is biaxially stretched in the plane direction. Such as a polymer film having birefringence,
A bidirectionally stretched film such as an obliquely oriented polymer film having a controlled refractive index in the thickness direction, which is uniaxially stretched in the plane direction and also stretched in the thickness direction, is used. As described above, as described above, for example, as described above, a heat-shrinkable film is adhered to a polymer film, and the polymer film is stretched or / and shrunk under the action of the heat-induced shrinkage. Oriented ones are exemplified. 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-mentioned polarizing plate comprising a polarizer and a protective layer is usually used by being provided on the back side of a 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. In addition to increasing the amount of light transmitted through the enhancement film, it is also possible to improve the luminance 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. That is,
When light is incident from the back side of the liquid crystal cell through a polarizer with a backlight or the like without using a brightness enhancement film, light having a polarization direction that does not match the polarization axis of the polarizer is almost absorbed by the polarizer. And does not pass through the polarizer. That is, although it depends on the characteristics of the polarizer used, about 50% of the light is absorbed by the polarizer,
As a result, the amount of light that can be used 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 thereof. The brightness enhancement film transmits only 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 light is supplied to the polarizer, 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. Such as a cholesteric liquid crystal layer, particularly an alignment film of a cholesteric liquid crystal polymer or a film in which the alignment liquid crystal layer is supported on a film substrate, reflecting either left-handed or right-handed circularly polarized light, Any suitable light such as a light-transmitting 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 with the polarization axis aligned as it is, thereby suppressing absorption loss by the polarization plate. It can be transmitted efficiently. 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, from the viewpoint of suppressing absorption loss, the transmitted circularly polarized light is linearly polarized through a retardation plate. It is preferable that the light is incident on the polarizing plate. By using a quarter-wave plate as the retardation plate, circularly polarized light can be converted to 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.

Note that the cholesteric liquid crystal layer also
By combining two or more layers having different reflection wavelengths and having an arrangement structure in which two or more layers are overlapped, it is possible to obtain one that reflects circularly polarized light in a wide wavelength range such as a visible light region,
Based on this, it is possible to obtain transmitted circularly polarized light in a wide wavelength range.

Further, the polarizing plate 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. 2
An optical member in which layers or three or more optical layers are laminated can also be formed by a method in which layers are separately laminated in a manufacturing process of a liquid crystal display device or the like. The liquid crystal display has an advantage that it is excellent in quality stability, assembling workability, and the like, and can improve manufacturing efficiency of a liquid crystal display device and the like. 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 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 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 pressure-sensitive adhesive layer provided on the polarizing plate or the optical member is exposed on the surface, it is preferable to temporarily cover the pressure-sensitive adhesive layer with a separator until practical use of the pressure-sensitive 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 forming 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 absorbent such as a compound or a nickel complex compound may be used.

The polarizing plate of the present invention can be preferably used for forming various devices such as a liquid crystal display device and the like. In particular, a reflection type or a semi-transmission type in which the polarizing plate is arranged on one side or both sides of a liquid crystal cell. It can be preferably used for a liquid crystal 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. Furthermore, 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 diffusion plate, and a backlight can be arranged at appropriate positions.

[0059]

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

(Example 1) As a synthetic resin film, a polyvinyl alcohol film (PVA) film having a degree of polymerization of 1700 and a thickness of 40 µm was swollen in a warm water bath at 30 ° C, and then was swollen from an aqueous solution of iodine and potassium iodide. Become 3
The film is stretched about 3 times in a dyeing bath at 0 ° C., and then stretched in a crosslinking bath containing boric acid and potassium iodide so that the total stretching ratio becomes 4.5 times, washed with water, and dried. A polarizer having a thickness of 20 μm was obtained. At this time, the water content of the polarizer was 15% by mass.
Met. Next, 7% by mass of PV was applied to both surfaces of the polarizer.
An adhesive consisting of an aqueous solution A is applied, and as a protective film, the bonding surface is saponified with an aqueous solution of caustic soda.
The polarizer is stuck between two 0 μm triacetyl cellulose (TAC) films so that the total thickness is 1
An 80 μm polarizing plate was produced.

(Example 2) As a synthetic resin film, a polyvinyl alcohol film (PVA) film having a degree of polymerization of 1700 and a thickness of 40 µm was swollen in a warm water bath at 30 ° C, and then, from an aqueous solution of iodine and potassium iodide. Become 3
The film is stretched about 3 times in a dyeing bath at 0 ° C., and then stretched in a crosslinking bath containing boric acid and potassium iodide so that the total stretching ratio becomes 5.0 times, washed with water, and dried. A polarizer having a thickness of 16 μm was obtained. At this time, the water content of the polarizer was 17% by mass.
Met. Next, 7% by mass of PV was applied to both surfaces of the polarizer.
An adhesive consisting of an aqueous solution A is applied, and as a protective film, the bonding surface is saponified with an aqueous solution of caustic soda.
The polarizer is stuck between two 0 μm triacetyl cellulose (TAC) films so that the total thickness is 1
A 76 μm polarizing plate was produced.

(Comparative Example 1) As a synthetic resin film, a polyvinyl alcohol film (PVA) film having a degree of polymerization of 1700 and a thickness of 75 μm was swollen in a warm water bath at 30 ° C., and then a water solution of iodine and potassium iodide was used. Become 3
The film is stretched about 3 times in a dyeing bath at 0 ° C., and then stretched in a crosslinking bath containing boric acid and potassium iodide so that the total stretching ratio becomes 5.0 times, washed with water, and dried. A polarizer having a thickness of 25 μm was obtained. At this time, the water content of the polarizer was 20% by mass.
Met. Next, on both surfaces of the polarizer, 7% by mass of PV was added.
An adhesive consisting of an aqueous solution A is applied, and as a protective film, the bonding surface is saponified with an aqueous solution of caustic soda.
The polarizer is stuck between two 0 μm triacetyl cellulose (TAC) films so that the total thickness is 1
An 85 μm polarizing plate was produced.

(Comparative Example 2) As a synthetic resin film, a polyvinyl alcohol film (PVA) film having a degree of polymerization of 1700 and a thickness of 75 μm was swollen in a warm water bath at 30 ° C., and then an aqueous solution of iodine and potassium iodide was prepared. Become 3
The film is stretched about 3 times in a dyeing bath at 0 ° C., and then stretched in a crosslinking bath containing boric acid and potassium iodide so that the total stretching ratio becomes 4.0 times, washed with water, and dried. A 34 μm thick polarizer was obtained. At this time, the water content of the polarizer was 24% by mass.
Met. Next, 7% by mass of PV was applied to both surfaces of the polarizer.
An adhesive consisting of an aqueous solution A is applied, and as a protective film, the bonding surface is saponified with an aqueous solution of caustic soda.
The polarizer is stuck between two 0 μm triacetyl cellulose (TAC) films so that the total thickness is 1
A 94 μm polarizing plate was produced.

(Durability Test) The polarizing plates prepared in Examples and Comparative Examples were cut into a size of 50 mm × 50 mm and heated at a temperature of 70 ° C. for 120 hours. The dimensions (Lb) of the test piece before the heating test and the dimensions (La) after the heating test were measured for the absorption axis (MD) direction and the polarization axis (TD) direction,
The dimensional change rate (%) was determined from the following equation. Dimensional change rate = [(La−Lb) / Lb] × 100

The liquid crystal display device was formed by bonding the polarizing plates prepared in Examples and Comparative Examples to both sides of a liquid crystal cell on a plastic substrate, and the hue change was measured. The hue change was evaluated based on the following criteria for display unevenness after the durability test. Evaluation criteria: ◎ No color loss at panel edge or hue variation in panel surface ○ Little color loss at panel edge or hue variation in panel surface △ Color loss at panel edge or panel There is slight variation in in-plane hue. × There is color omission at the panel edge and in-plane hue variation.

Table 1 shows the properties of the polarizing plates produced in Examples and Comparative Examples, and Table 2 shows the evaluation results of the polarizing plates.

[0067]

Table 1 Stretching ratio of PVA Polarizer Polarizer Thickness of polarizer Thickness (μm) Thickness (μm) Moisture percentage (%) (μm) Example 1 40 4.5 20 15 180 Example 2 40 5.0 16 17 176 Comparative Example 1 75 5.0 25 20 185 Comparative Example 2 75 4.0 34 24 194

[0068]

TABLE 2 Dimensional change rate Dimensional change rate Dimensional change rate A and hue change A (%) B (%) Dimensional change rate B Difference Example 1 -0.573 -0.584 0.011 Example 2 -0.491 -0.485 0.006 ◎ Comparative Example 1 -0.863 -0.642 0.221 × Comparative Example 2 -0.726 -0.508 0.218 △

As is clear from Table 2, the polarizing plate of the present invention has a dimensional change rate in the absorption axis direction and a polarizing axis of the polarizing plate when the polarizing plate is placed under heating conditions of 70 ° C. for 120 hours. The dimensional change rates in the directions are both within ± 0.6%. The dimensional change rate A in the absorption axis direction and the dimensional change rate B in the polarization axis direction of the polarizing plate of the present invention satisfy the following relationship. −0.1 <(dimensional change rate A−dimensional change rate B) <+ 0.1 The polarizing plate of the present invention that satisfies this relationship has a smaller hue change than the polarizing plate of the comparative example that does not satisfy the above relationship. You can see that. That is, it can be seen that the polarizing plate of the present invention has better durability than the conventional polarizing plate.

[0070]

As described above, the polarizing plate of the present invention has a small change in the absorption axis direction and the small change in the anisotropy of the polarization axis direction of the polarizing plate. Such a load becomes even, the warpage of the odd-shaped panel which is a problem in assembling the liquid crystal display device is eliminated, and the polarizing plate is more durable with less shrinkage when a heat stress is applied to the polarizing plate. Can be obtained. Therefore, when the polarizing plate of the present invention is mounted on a liquid crystal panel using a plastic substrate, the warpage of the panel is reduced, so that a change in panel hue can be prevented. Therefore, its industrial value is great.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Senri Yoshikawa 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation F-term (reference) 2H049 BA02 BA03 BA04 BA06 BA07 BA25 BA27 BB03 BB33 BB63 BB52 BB63 BC03 BC09 BC10 BC22 2H091 FA08X FA08Z FA11X FA11Z FA15Z FA37X FA37Z FA41Z GA16 LA30 5G435 AA04 AA14 BB12 FF03 FF05 HH03 KK07

Claims (12)

[Claims] Claims: 1. A synthetic resin film is dyed, cross-linked, stretched,
A polarizing plate formed by laminating a dried polarizer and a protective film, wherein when the polarizing plate is placed under a heating condition of 70 ° C. for 120 hours, the direction of the absorption axis of the polarizing plate is A polarizing plate, wherein a dimensional change rate and a dimensional change rate in a polarization axis direction are both within ± 0.6%. 2. The polarizing plate according to claim 1, wherein when the polarizing plate is placed under a heating condition of 70 ° C. for 120 hours, the dimensional change rate A in the absorption axis direction of the polarizing plate and the polarization axis. A polarizing plate, wherein the dimensional change rate B in the direction satisfies the following relationship. −0.1 <(dimensional change rate A−dimensional change rate B) <+ 0.1 3. The polarizing plate according to claim 1, wherein the synthetic resin film is a polyvinyl alcohol film, and the protective film is a triacetyl cellulose film. 4. The polarizing plate according to claim 3, wherein the polarizer has a thickness of 7 to 40 μm. 5. A polarizing plate comprising the polarizing plate according to claim 1 and an adhesive layer. 6. A polarizing plate comprising the polarizing plate according to claim 1 and an anti-glare layer. 7. A polarizing plate comprising the polarizing plate according to claim 1 and a reflecting plate or a transflective plate. 8. A polarizing plate comprising the polarizing plate according to claim 1 and a retardation plate or a λ plate attached to the polarizing plate. 9. A polarizing plate comprising the polarizing plate according to claim 1 and a viewing angle compensation film bonded thereto. 10. A polarizing plate obtained by laminating a brightness enhancement film on the polarizing plate according to claim 1. 11. 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. 12. The liquid crystal display according to claim 11, wherein the liquid crystal cell is a plastic substrate liquid crystal cell.