JP2002333522A - Polarizing film, polarizing plate and liquid crystal display device using them - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizing film and a polarizing plate with little variation of chromaticity even when an angle of incidence is varied and a liquid crystal display device using them. SOLUTION: The polarizing film is an iodine type polarizing film with <20 μm thickness and <=0.06 birefringence (Δn) at 900 nm wavelength obtained by stretching a polyvinyl alcohol type film. When two sheets of the polarizing films are superimposed in crossed Nicols, the polarizing films exhibit <0.09 chromaticity variation Δxy in the case chromaticity of transmitted light of incident light from the normal direction and chromaticity of transmitted light of incident light from a direction forming an angle of 40 deg. to 45 deg. direction with respect to the direction of the axis of polarization are represented by x0 , y0 and x40 , y40 respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizing film and 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 LCDs are used in personal computers and the like, and the demand for LCDs has been rapidly increasing in recent years. The polarizing plate used for the LCD is, for example, a dyeing step of dyeing a polyvinyl alcohol (hereinafter sometimes abbreviated as PVA) film with dichroic iodine or a dichroic dye,
It is manufactured by drying after a crosslinking step of crosslinking with boric acid, borax, or the like, and a stretching step of uniaxial stretching, and bonding it to a protective layer such as a triacetyl cellulose (hereinafter sometimes abbreviated as TAC) film. I have. In addition, dyeing, crosslinking,
The stretching steps need not be performed separately but may be performed simultaneously, and the order of the steps may be arbitrary.

[0003]

However, the polarizing film used in the conventional liquid crystal display has sufficient optical characteristics, but has a thickness of only 20 μm or more. The chromaticity of the transmitted light of the light incident from the normal direction is x ₀ , y ₀ , and the chromaticity of the transmitted light of the light incident from the angle of 45 degrees in the direction of the polarization axis at an angle of 40 degrees is x ₄₀ , y ₄₀ . Sometimes, the chromaticity change amount Δx
y is Δxy> 0.09. Here, the chromaticity change amount is Δxy = SQRT [(x ₀ −x ₄₀ ) ² + (y ₀ −y ₄₀ )
² ]. Such a large chromaticity change means that the chromaticity of the polarizing film is affected when light is incident at an angle of 40 degrees with respect to the 45-degree azimuth in the polarization axis direction due to the influence of the phase difference of the polarizing film. , Which means that the color change of the display panel becomes large. Therefore, there is a demand for a polarizing film having less change in chromaticity even when the incident angle of light is changed.

As described above, the polarizing plate is manufactured by swelling, dyeing with iodine, crosslinking, stretching and drying the PVA film, and forming a triacetyl film on both sides of the polarizing film as a protective layer, as described above. Cellulose membrane is attached. Conventionally, a PVA film, which is a raw material of a polarizing film, has a thickness of about 75 μm.
m thickness. In addition, when a high-magnification (6.5 times or more) stretching is performed to produce a thinner polarizing film, a conventional stretching method is used to obtain optical characteristics that can sufficiently satisfy the user's requirements. Stretching breakage occurs.

Therefore, the present inventors have proposed to use a PVA film having an initial thickness of 50 μm or less,
A polarizing film having a film thickness of less than 20 μm after stretching can be produced, and by improving the stretching method, a polarizing film capable of sufficiently satisfying the user's requirements even with a thin PVA film can be produced. The inventors have found that the present invention can be performed, and have completed the present invention.

SUMMARY OF THE INVENTION An object of the present invention is to provide a polarizing film, a polarizing plate and a liquid crystal display using the same, which have a small change in chromaticity even if the incident angle of light is changed in order to solve the above-mentioned conventional problems. .

[0007]

In order to achieve the above object, a polarizing film of the present invention has a thickness of less than 20 μm and a birefringence (Δn) at a wavelength of 900 nm of 0, which is obtained by stretching a polyvinyl alcohol-based film. 0.06 or less, wherein when the two polarizing films are stacked in a crossed Nicols state, the chromaticity of transmitted light of light incident from the normal direction is x ₀ , y ₀ , and the polarization axis The chromaticity change amount Δxy is less than 0.09, where x ₄₀ and y ₄₀ are the chromaticities of the transmitted light of the light incident from the direction of 45 degrees with respect to the direction at an angle of 40 degrees.

In the polarizing film of the present invention, the transmittance of one polarizing film is 42.0% or more and the degree of polarization is 9
It is preferably at least 9.0%.

Further, in the polarizing film of the present invention,
The thickness of the polyvinyl alcohol-based film is preferably 50 μm or less.

Next, the polarizing plate of the present invention is characterized in that:
3. A polarizing plate comprising the polarizing film according to any one of 3. above, wherein one polarizing plate has a transmittance of 42.5% or more and a degree of polarization of 99% or more.

Further, the polarizing plate of the present invention comprises the polarizing plate according to claim 4 and at least one optical layer selected from a retardation plate, a reflector, a semi-transmissive reflector, a viewing angle compensation film and a brightness enhancement film. Are laminated.

Further, the polarizing plate of the present invention is characterized in that an adhesive layer is provided on the polarizing plate according to the fourth or fifth aspect.

Further, a liquid crystal display device according to the present invention is characterized in that the polarizing plate according to any one of claims 4 to 6 is arranged on at least one side of a liquid crystal cell.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The polarizing film of the present invention is iodine
Stretched polyvinyl alcohol-based film containing
Obtained thickness less than 20 μm and wavelength of 900 nm
Polarizing filter with birefringence (Δn) of 0.06 or less
And the two polarizing films are in a crossed Nicols state.
Color of transmitted light of light incident from the normal direction when superimposed on
Degree x ₀, Y₀, 45 degrees azimuth to polarization axis direction 40 degrees
The chromaticity of transmitted light of light incident from an angle of x₄₀, Y₄₀age
The chromaticity change Δxy is less than 0.09.
You. When the chromaticity change is 0.09 or more, when the panel is lit
Color change can be visually confirmed.
No. The transmittance of one polarizing film is 42.0%.
Or more, and the degree of polarization is 99.0% or more, which is practically sufficient.
It has excellent optical characteristics. Where the chromaticity change
Is Δxy = SQRT [(x₀-X₄₀)^Two+ (Y₀-Y₄₀)
^Two], The larger the value of Δxy, the larger the value
The larger the color change of the display panel and the smaller Δxy, the light
Polarization filter with less chromaticity change even if the incident angle of
It becomes.

Further, the polarizing plate of the present invention is a polarizing plate on which the above-mentioned polarizing film is laminated, wherein one polarizing plate has a transmittance of 42.5% or more and a degree of polarization of 99.0% or more. It has practically sufficient optical characteristics.

The polarizing film of the present invention is obtained by employing a characteristic manufacturing method. Specifically, a polyvinyl alcohol-based film having a thickness of 50 μm or less is dyed and crosslinked with iodine by an ordinary method. , Stretched and dried. The thickness of the polarizing film is
Although not particularly limited, 5 to 40 μm is preferable. If the thickness is less than 5 μm, the mechanical strength decreases, and if it exceeds 40 μm, the optical characteristics deteriorate. Further, the polarizing plate of the present invention is formed by bonding a transparent protective film serving as a protective layer to one or both sides of the polarizing film via an appropriate adhesive layer, for example, an adhesive layer made of a vinyl alcohol-based polymer or the like. . Hereinafter, the details will be described.

As the polyvinyl alcohol-based film used in the present invention, for example, a hydrophilic polymer film such as polyvinyl alcohol or partially formalized polyvinyl alcohol is preferable. In particular, a polyvinyl alcohol-based film is preferable because of its good dyeability with iodine. preferable. 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 degree of polymerization of the polyvinyl alcohol resin used is 100 to 5
000 is preferable, and 1400 to 4000 is more preferable. The thickness of the polyvinyl alcohol-based film is 5
0 μm or less, and preferably 20 to 50 μm.
When the thickness exceeds 50 μm, the color change of the display panel becomes large when the display panel is mounted on a liquid crystal display device. On the other hand, when the film thickness is too thin, stretching becomes difficult.

In the dyeing step, the polyvinyl alcohol-based film is immersed in a dye bath containing iodine at 20 to 70 ° C. for 1 to 20 minutes to adsorb iodine. The iodine concentration in the dyeing bath is usually 0.1 per 100 parts by mass of water.
To 1.0 part by mass. In the dyeing bath, potassium iodide, lithium iodide, sodium iodide, zinc iodide,
An auxiliary agent such as aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, iodide such as titanium iodide is used in an amount of 2 to 20 parts by mass, preferably 0.02 parts by mass.
It may be added in an amount of 2 to 10 parts by mass, which is particularly preferable for increasing the dyeing efficiency. In addition to the water solvent, a small amount of an organic solvent compatible with water may be contained. In addition, before dyeing the polyvinyl alcohol-based film in an aqueous solution containing iodine or a dichroic dye, the polyvinyl alcohol-based film is placed in a water bath or the like at 20 to 60 ° C. for 0.1 hour.
Swelling treatment may be performed for 10 to 10 minutes.

In the crosslinking step, the dyed polyvinyl alcohol-based film is stretched in an aqueous solution containing a boron compound. The composition of the boron compound-containing aqueous solution for performing the crosslinking treatment is usually boric acid, borax,
The amount of a PVA crosslinking agent such as glioxal or glutaraldehyde is 1 to 10 parts by mass alone or as a mixture. In the crosslinking bath, potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide,
An auxiliary agent such as an iodide such as titanium iodide may be added in an amount of 0.05 to 15% by mass, preferably 0.5 to 8% by mass, and is particularly preferable in that uniform properties in a plane are obtained. The temperature of the aqueous solution is usually in the range of 20 to 70C, preferably 40 to 60C. The immersion time is not particularly limited, but is usually 1 second to 1
5 minutes, preferably 5 seconds to 10 minutes. In addition to the water solvent, a small amount of an organic solvent compatible with water may be contained.

In the drying step, the polyvinyl alcohol-based film which has been subjected to the iodine adsorption orientation treatment is further subjected to a water temperature of 10 to 60 ° C., preferably 30 to 40 ° C., and a concentration of 0.1.
1 to 10% by mass of an aqueous solution of iodide such as potassium iodide
After soaking for 1 to 1 minute, wash with water and at 20 to 80 ° C for 1 minute to
After drying for 10 minutes, a polarizing film is obtained. Auxiliary agents such as zinc sulfate and zinc chloride may be added to the aqueous iodide solution.

When the polyvinyl alcohol-based 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,
If 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 plural times in the same step.

The water content of the polarizing film (the water content of the polarizing film relative to the total weight of the polarizing film) when the polarizing film is bonded to the protective film depends on the thickness of the polarizing film, but is generally less than 20% by mass. And 5 to 20
It is 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.

The polarizing plate of the present invention is obtained by bonding a transparent protective film as a protective layer to one or both sides of the above-mentioned polarizing film via an appropriate adhesive layer, for example, an adhesive layer made of a vinyl alcohol polymer or the like. is there. As a protective film material to be a transparent protective layer provided on one or both sides of the 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. Further, the transparent protective film used for the protective layer is subjected to a hard coat treatment, an antireflection treatment, a treatment for preventing sticking, diffusion or antiglare, and the like, as long as the object of the present invention is not impaired. Is also good.

The bonding treatment between the 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, borax, glutaraldehyde, or the like can be used. And an adhesive comprising at least a water-soluble crosslinking agent of a vinyl alcohol polymer such as melamine or 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 of the present invention can be used as an optical member laminated with another optical layer in practical use. The optical layer is not particularly limited, and examples thereof include a reflector, a transflector, a retardation plate (including a λ plate such as a 波長 wavelength plate and a １ ／ wavelength plate), a viewing angle compensation film, a brightness enhancement film, and the like. 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, the above-described polarizing plate comprising the polarizing film of the present invention and a protective film includes: Further, a reflective polarizing plate or a transflective polarizing plate in which a reflecting plate or a transflective reflecting plate is laminated, an elliptically polarized light in which a retardation plate is further laminated on the above-described polarizing plate composed of a polarizing film and a protective film. Plate or circular polarizing plate, a polarizing plate comprising a polarizing film and a protective film as described above, and a polarizing plate further laminated with a viewing angle compensation film, or a polarizing film and a protective film as described above The optical plate, further polarizing plate brightness enhancement film is laminated is preferred.

The reflecting plate is described below. The reflecting plate is provided on a polarizing plate to form a reflecting polarizing plate. The reflecting 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 reflection type polarizing plate can be formed by an appropriate method such as a method in which a reflecting 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, there may be mentioned a reflection type polarizing plate having a reflective layer on which the fine unevenness structure is reflected on the transparent protective film having a fine unevenness surface containing fine particles. 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 performed by a method of directly attaching to the surface of the protective film.

The reflecting plate may be used as a reflecting sheet in which a reflecting layer is provided on an appropriate film according to the transparent protective film, instead of the method of directly attaching the reflecting plate to the transparent protective film. 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 information 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 polarizing film and a protective film 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 retardation 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.

An elliptically polarizing plate compensates (prevents) coloring (blue or yellow) caused by birefringence of a 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 inclined alignment 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 shrinkage treatment under the action of the shrinkage force caused by heating, or a liquid crystal polymer obliquely oriented. And the like.

Next, a description will be given of a polarizing plate in which a viewing angle compensation film is further laminated on the above-mentioned polarizing plate comprising a polarizing film and a protective film.

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 slightly oblique direction, not perpendicular to the screen.

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-described polarizing plate comprising a polarizing film and a protective film 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 composed of the above-described polarizing film and a protective layer, the light from a light source such as a backlight is incident to obtain transmitted light of a predetermined polarization state, and the predetermined polarization state is obtained. 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 increase the amount of light that can be used for liquid crystal image display and the like by supplying polarized light that is hardly absorbed by the polarizing film, thereby improving the luminance. In other words, when light is incident through the polarizing film from the back side of the liquid crystal cell 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 polarizing film is hardly polarized film. And does not pass through the polarizing film. That is, although it differs depending on the characteristics of the polarizing film used, about 50% of the light is absorbed by the polarizing film, and accordingly, the amount of light available for liquid crystal image display and the like decreases, and the image becomes dark. The brightness enhancement film is reflected once by the brightness enhancement film without causing the light having the polarization direction to be absorbed by the polarizing film to enter the polarizing film,
Further, the light is repeatedly inverted and re-incident on the brightness enhancement plate via a reflection layer or the like provided on the rear side thereof, so that the polarization direction of the light reflected and inverted between the two can pass through the polarizing film. Since only the polarized light with the proper polarization direction is transmitted through the brightness enhancement film and supplied to the polarizing film,
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 a brightness enhancement film of the type that transmits linearly polarized light having a predetermined polarization axis, the transmitted light is incident on the polarizing plate as it is with the polarization axis aligned, thereby suppressing absorption loss by the polarizing plate. It can be transmitted efficiently. On the other hand, in the case of a brightness enhancement film that transmits circularly polarized light, such as a cholesteric liquid crystal layer, it can be directly incident on the polarizing film.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 the course of manufacturing a liquid crystal display device or the like. The liquid crystal display device 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. Further, 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 as needed.For example, if a protective layer of a polarizing plate composed of a polarizing film and a protective layer is referred to, an adhesive layer may be provided on one or both sides of the protective layer, if necessary. May be provided.

When the adhesive layer provided on the polarizing plate or the optical member is exposed on the surface, it is preferable to temporarily cover the adhesive layer with a separator until 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 on a suitable thin leaf according to the transparent protective film or the like as necessary. 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.
The present invention can be used for a liquid crystal display device of a reflection type, a semi-transmission type, or a transmission / reflection type in which a polarizing plate is disposed on one side or both sides of a liquid crystal cell. The liquid crystal cell forming the liquid crystal display device is optional, for example, an appropriate type such as an active matrix drive type represented by a thin film transistor type, a simple matrix drive 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. Next, the present invention will be specifically described with reference to examples.

[0050]

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

(Example 1) Degree of polymerization 1700, thickness 38μ
m polyvinyl alcohol film (PVA) film is swollen in a 30 ° C. warm water bath, stretched about three times in a 30 ° C. dyeing bath composed of an aqueous solution of iodine and potassium iodide, and then boric acid And 50 with potassium iodide
The film was stretched and crosslinked in a crosslinking bath at a temperature of 5 ° C. so that the total stretching ratio became 5.5 times. This was immersed in an aqueous potassium iodide solution at 35 ° C. for 10 seconds to adjust the hue. Further, the film was washed with water and dried to obtain a polarizing film having a thickness of 17 μm. The water content of this polarizing film was 15% by mass. Also,
The birefringence (Δn) at a wavelength of 900 nm is 0.048.
5. The transmittance was 43.0% and the degree of polarization was 99.9%. Next, an adhesive consisting of a 7% by mass aqueous solution of PVA was applied to both surfaces of the polarizing film, and two 80 μm-thick triacetylcellulose (TAC) whose adhesive surfaces were saponified with an aqueous sodium hydroxide solution were used as protective films. ) Attaching this polarizing film so as to sandwich it with a film, total thickness of 17
A 7 μm polarizing plate was produced. The obtained polarizing plate had a single transmittance of 42.7% and a degree of polarization of 99.9%. In addition,
The measurement was performed by the following method.

(Birefringence index) A phase difference value (Δnd) is obtained from the light having a wavelength of 900 nm using a parallel Nicol rotation method.
This is a value obtained by dividing by the thickness d.

(Transmittance) Measured using a spectrophotometer (DOT-3, manufactured by Murakami Color Research Laboratory) and measured by JISZ 870.
Y whose luminosity is corrected by a 1-degree field of view (C light source).
Value.

(Degree of Polarization) Two identical polarizing plates have flat polarization axes.
Transmittance (H ₀)
The transmittance (H₉₀), The above transmission
The degree of polarization is measured according to the following formula.
I did. The parallel transmittance (H₀) And the transmittance (H
₉₀) Is the Y value corrected for visibility.

[0055]

(Equation 1)

(Comparative Example 1) Degree of polymerization: 1700, thickness: 75 μm
m in accordance with Example 1, except that a polyvinyl alcohol film (PVA) film was used.
The film was stretched 6 times to obtain a polarizing film having a thickness of 17 μm. The birefringence (Δn) at a wavelength of 900 nm of this polarizing film was 0.0765, the transmittance was 43.8%, and the degree of polarization was 98.0%. Next, on both surfaces of this polarizing film, as in Example 1, two polarizing plates of 80 μm in thickness were sandwiched between two triacetyl cellulose (TAC) films to produce a polarizing plate having a total thickness of 177 μm. did. The single transmittance of the obtained polarizing plate is 43.5.
%, And the degree of polarization was 98.4%.

(Comparative Example 2) Degree of polymerization: 1700, thickness: 75 μm
m, except that a polyvinyl alcohol film (PVA) film having a total stretching ratio of 5.5 m was used.
The film was stretched twice to obtain a polarizing film having a thickness of 27 μm. The birefringence (Δn) at a wavelength of 900 nm of this polarizing film was 0.0464, the transmittance was 42.9%, and the degree of polarization was 99.93%. Next, on both surfaces of this polarizing film, as in Example 1, two polarizing plates of 80 μm in thickness were sandwiched between two triacetyl cellulose (TAC) films to produce a polarizing plate having a total thickness of 187 μm. did. The obtained polarizing plate has a single transmittance of 42.6.
% And the degree of polarization were 99.9%.

(Evaluation) The transmittance of the polarizing films produced in Examples and Comparative Examples during crossed Nicols was measured with a spectrophotometer equipped with an integrating sphere (UV-2400, manufactured by Shimadzu Corporation).
The xy chromaticity was determined. In the measurement, the chromaticity (x ₀ , y ₀ ) of transmitted light of light incident from the normal direction in a crossed Nicols state
And the chromaticity (x ₄₀ , y ₄₀ ) of the transmitted light of the light incident at an angle of 45 degrees with respect to the polarization axis direction at an angle of 40 degrees, and using this value, the chromaticity change amount Δxy is obtained from the following equation. Was calculated.
Table 1 shows the results together with the characteristics of the polarizing film. Δxy = SQRT [(x ₀ −x ₄₀ ) ² + (y ₀ −y ₄₀ ) ² ]

[0059]

[Table 1] Birefringence Thickness (μm) Chromaticity (x ₀ , y ₀ ) Chromaticity (x ₄₀ , y ₄₀ ) Chromaticity change Example 1 0.0485 17 0.209, 0.187 0.280, 0.290 0.082 Comparative Example 1 0.0765 17 0.203, 0.157 0.301, 0.295 0.117 Comparative Example 2 0.0464 27 0.201, 0.156 0.291, 0.292 0.108

As is clear from Table 1, the polarizing film of the present invention has a thickness of 17 μm, a birefringence of 0.0485, and a small chromaticity change of less than 0.09. On the other hand, the polarizing film of Comparative Example 1 had a thickness of 17 μm.
However, since the film thickness is reduced by stretching a conventional thickness polyvinyl alcohol-based film at a high stretching ratio, the birefringence increases due to the influence of in-plane retardation, and the hue changes. The amount is 0.09 or more. Further, the polarizing film of Comparative Example 2 has a birefringence of 0.0464, but has a large thickness. Therefore, the chromaticity change amount is 0.09 or more, and the effect of reducing the hue change amount is not obtained. Therefore, it can be seen that the polarizing film according to the present invention has a small chromaticity change when the incidence of light changes in the range of 0 to 40 degrees during crossed Nicols.

[0061]

As described above, the polarizing film of the present invention is obtained by stretching an iodine-containing polyvinyl alcohol-based film to a thickness of less than 20 μm and a wavelength of 900 μm.
By setting the birefringence (Δn) in nm to 0.06 or less, the chromaticity of transmitted light of light incident from the normal direction is x ₀ when the two polarizing films are stacked in a crossed Nicols state. y ₀ , the chromaticity change Δxy satisfies less than 0.09, where x ₄₀ and y ₄₀ are the chromaticities of the transmitted light of the light incident from the angle of 40 degrees in the azimuth of 45 degrees with respect to the polarization axis direction. Things. Accordingly, it is possible to provide a polarizing film, a polarizing plate, and a liquid crystal display device using the same, which have a small change in chromaticity even when the incident angle of light is changed. Therefore, its industrial value is great.

 ──────────────────────────────────────────────────続 き Continued on front page (72) Inventor Naofumi Mihara 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation (72) Inventor Atsushi Kitagawa 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation (72) Inventor ▲ Hama ▼ Eiji Moto 1-2-1, Shimohozumi, Ibaraki City, Osaka Prefecture Nitto Denko Corporation (72) Inventor Seiichi Kusumoto 1-1-1, Shimohozumi, Ibaraki City, Osaka Prefecture No. Nitto Denko F-term (reference) 2H049 BA02 BA03 BA04 BA06 BA07 BA27 BB03 BB33 BB43 BB52 BB63 BC03 BC09 BC22 2H091 FA08X FA08Z FA11X FA14Z FB02 FC02 FC06 FC07 GA16 GA17 LA02 LA12

Claims (7)

[Claims] 1. A film obtained by stretching a polyvinyl alcohol-based film, having a thickness of less than 20 μm and a wavelength of 900 n.
the iodine-based polarizing film having a birefringence (Δn) of 0.06 or less at m, wherein when the two polarizing films are stacked in a crossed Nicols state, the chromaticity of transmitted light of light incident from the normal direction To x ₀ ,
y ₀ , when the chromaticity of the transmitted light of the light incident from the angle of 40 degrees in the 45-degree azimuth with respect to the polarization axis direction is x ₄₀ , y ₄₀ ,
A polarizing film having a chromaticity change Δxy of less than 0.09. 2. The transmittance of one polarizing film is 42.0%.
The polarizing film according to claim 1, which has a degree of polarization of 99.0% or more. 3. The polarizing film according to claim 1, wherein the thickness of the polyvinyl alcohol-based film is 50 μm or less. 4. A polarizing plate on which the polarizing film according to claim 1 is laminated, wherein the transmittance of one polarizing plate is 42.5% or more and the degree of polarization is 99.0%. A polarizing plate characterized by the above. 5. A polarizing plate according to claim 4, and a retardation plate,
A polarizing plate characterized by laminating at least one optical layer selected from a reflector, a transflector, a viewing angle compensation film and a brightness enhancement film. 6. A polarizing plate, wherein the polarizing plate according to claim 4 is provided with an adhesive layer. 7. A liquid crystal display device, wherein the polarizing plate according to claim 4 is arranged on at least one side of a liquid crystal cell.