JP2002258042A - Polarizing plate and liquid crystal display device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizing plate with no variation in parallel and vertical transmittance and capable of providing a bright liquid crystal display device with excellent color reproducibility and a liquid crystal display device using the same. SOLUTION: The polarizing plate comprises a polarizer formed of a polyvinyl alcohol type film with a protective film laminated on at least one surface of it and has a >=43.0% transmittance as a single substance and a >=99.8% polarization degree. With respect to the polarizing plate, parallel transmittance at 440 nm wavelength Tp 440, vertical transmittance at 440 nm wavelength Tc 440, parallel transmittance at 550 nm wavelength Tp 550 and parallel transmittance at 610 nm wavelength Tp 610 simultaneously satisfy following inequalities (1), (2) and (3). 0.85<=Tp 440/Tp 550<=1.10 (1) 0.90<=Tp 610/Tp 550<=1.10 (2) 1,000<=Tp 440/Tc 440 (3).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Liquid crystal display devices 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 composed of a polyvinyl alcohol-based film in which iodine or a dichroic dye is adsorbed and oriented, a protective film such as triacetyl cellulose is laminated on both sides, and a liquid crystal that is bright and has good color reproducibility. In order to provide a display device, a polarizing plate having both high transmittance and a high degree of polarization is required.

In order to provide a liquid crystal display device which is bright and has good color reproducibility, a single unit transmittance and contrast are high, and a light transmittance (parallel transmittance) when two sheets are overlapped with their absorption axes parallel. In addition, it is necessary that the transmittance (orthogonal transmittance) of light when two sheets are overlapped with their absorption axes orthogonal to each other is small regardless of the wavelength in the visible light region. The preferred hue range of the display device is XY in white and black display.
0.27 ≦ x ≦ on the Z color system (CIE1931 color system)
0.31, 0.27 ≦ y ≦ 0.31.

Generally, a backlight used for a liquid crystal display device has emission line peaks at three wavelengths of 440 nm, 550 nm, and 610 nm. Therefore, it is necessary to make the transmittance at these three wavelengths the same to improve color reproducibility. It is an important point to do. In addition, in order to have sufficient brightness and degree of polarization, it is necessary that the single transmittance is 43.0% or more and the degree of polarization is 99.8% or more.

However, the polarizing plate obtained by the conventional technique is
In the visible light region, the dichroism on the long wavelength side is excellent, but it is difficult to increase the dichroism on the short wavelength side, and it is very difficult to produce a polarizing plate that has no parallel transmittance or cross transmittance at the same time. It was difficult. For example, 440 nm, 550 n
m, the parallel transmittance at 610 nm is the same,
The orthogonal transmittance of 40 nm becomes large, and the orthogonal hue becomes bluish. Conversely, if the orthogonal transmittances are made equal, there is a problem that the parallel transmittance at 440 nm decreases, and the parallel hue becomes yellowish.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the parallel transmittance and the orthogonal transmittance do not vary at the same time.
As a result of intensive studies to provide a liquid crystal display device which is bright and has good color reproducibility, it is necessary that the single transmittance of the polarizing plate is 43.0% or more, the degree of polarization is 99.8% or more, and the parallel transmittance is Satisfies the relationship of 0.85 ≦ Tp440 / Tp550 ≦ 1.10 and 0.90 ≦ Tp610 / Tp550 ≦ 1.10. When the backlight has three wavelengths having bright line peaks, the dispersion is small and 1000 ≦ When the dichroic ratio on the short wavelength side as Tp440 / Tc440 is high, the orthogonal transmittance was sufficiently low, and it was found that there was no problem in color reproducibility for practical use, and the present invention was completed.

[0007]

According to the present invention, there is provided a polarizing plate comprising a polarizer formed of a polyvinyl alcohol film and a protective film laminated on at least one surface of the polarizer.
A polarizing plate having a polarizing transmittance of 3.0% or more and a polarization degree of 99.8% or more, wherein the parallel transmittance T of the polarizing plate at a wavelength of 440 nm;
p440, the orthogonal transmittance Tc440 at a wavelength of 440 nm,
The parallel transmittance Tp550 at a wavelength of 550 nm and the wavelength 61
The parallel transmittance Tp610 at 0 nm is expressed by the following equation (1):
(2) and (3) are simultaneously satisfied. 0.85 ≦ Tp440 / Tp550 ≦ 1.10 (1) 0.90 ≦ Tp610 / Tp550 ≦ 1.10 (2) 1000 ≦ Tp440 / Tc440 (3)

In the polarizing plate of the present invention, the polarizer is preferably a polyvinyl alcohol-based film on which iodine has been adsorbed, and the protective film is preferably a triacetyl cellulose film.

Further, the polarizing plate of the present invention comprises a laminate of the above polarizing plate 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. It is characterized by becoming.

Further, the liquid crystal display device of the present invention is characterized in that any one of the polarizing plates is arranged on at least one side of a liquid crystal cell.

[0011]

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a polarizing plate comprising a polarizer formed of a polyvinyl alcohol-based film and a protective film laminated on at least one surface of the polarizer. Is satisfied, a polarizing plate with less variation in parallel transmittance and orthogonal transmittance can be obtained, and as a result, a liquid crystal display device which is bright and has good color reproducibility can be provided.

That is, the characteristics of a polarizing plate in which a protective film is laminated on at least one surface of a polarizer formed of a polyvinyl alcohol-based film have a single transmittance of 43.0% or more.
At a polarization degree of 99.8% or more, the parallel transmittance Tp440 at a wavelength of 440 nm, the orthogonal transmittance Tc440 at a wavelength of 440 nm, and the parallel transmittance Tp550 at a wavelength of 550 nm.
It was confirmed that the polarizing plate satisfying the following formulas (1), (2) and (3) at the same time with the parallel transmittance Tp610 at a wavelength of 610 nm has a bright liquid crystal display and good color reproducibility. 0.85 ≦ Tp440 / Tp550 ≦ 1.10 (1) 0.90 ≦ Tp610 / Tp550 ≦ 1.10 (2) 1000 ≦ Tp440 / Tc440 (3)

In (3), if 1000 ≦ Tp440 / Tc440, the orthogonal transmittance is sufficiently low, and there is no problem in color reproducibility in practice, but more preferably 10,000 ≦ Tp440 / Tc440.

In the present invention, the polarizing plate is formed by laminating a transparent protective film as a protective layer on one or both sides of a polarizer made of a dichroic substance-containing polyvinyl alcohol-based polarizing film or the like via an appropriate adhesive layer. Consist of things.

The polarizer (polarizing film) is a film having a thickness of 200 μm or less made of a polyvinyl alcohol-based polymer such as polyvinyl alcohol or partially formalized polyvinyl alcohol, and swelling-treated, and made of iodine or a dichroic dye. Dyeing treatment, stretching treatment, and cross-linking treatment with a dichroic substance may be performed in an appropriate order and manner, and dried. Each of the steps of dyeing, stretching and crosslinking need not be performed separately, but may be performed simultaneously. In general, any material that transmits linearly polarized light when natural light is incident thereon may be used. In particular, a material having excellent light transmittance and degree of polarization is preferable. Although the thickness of the polarizer is not particularly limited, it is generally 5 to 80 μm, and particularly preferably 10 to 40 μm.

Examples of the polyvinyl alcohol polymer include a polymer obtained by polymerizing vinyl acetate and then saponified, and a polymer obtained by copolymerizing vinyl acetate with a small amount of a copolymerizable monomer such as unsaturated carboxylic acid or unsaturated sulfonic acid. No. The average degree of polymerization is 5 in terms of the solubility of the film in water.
It is preferably from 100 to 10,000, more preferably from 1000 to 60
The saponification degree is preferably at least 75 mol%, more preferably at least 98 mol%.

As a protective film material to be a transparent protective layer provided on one side or both sides of a polarizer (polarizing film), an appropriate transparent film can be used. 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, and particularly preferably 5 to 1 μm for the purpose of reducing the thickness of the polarizing plate.
It is 50 μm. 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.

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 polarizing plate surface and the like.
A cured film excellent in hardness, slipperiness and the like made of a suitable ultraviolet-curable resin such as a urethane-based, acrylic-based, or epoxy-based resin can be formed by a method of adding to the surface of the transparent protective film.

On the other hand, the antireflection treatment is performed for the purpose of preventing reflection of external light on the surface of the polarizing plate, and can be achieved by forming an antireflection film or the like according to the related art. In addition, 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 also be used.
The amount of the transparent fine particles used is 2 per 100 parts by mass of the transparent resin.
It is generally from 70 to 70 parts by weight, especially from 5 to 50 parts by weight.

The anti-glare layer containing the transparent fine particles can be provided as the transparent protective film itself or as a coating layer on the surface of the transparent protective film. 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 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 film.

The polarizing plate of the present invention can be produced, for example, by the following method.

[0024] First, I ^- to adjust the ionic content ^- I in the polarizer by a method such as immersing in an aqueous solution containing ions. In the dyeing treatment, the polyvinyl alcohol-based film is immersed in a dyeing bath at 20 to 70 ° C. to which a dichroic substance composed of iodine or a dichroic dye is added for 1 to 20 minutes, Adsorb. The concentration of iodine or dichroic dye in the dyeing bath is usually from 0.1 to 1.0 part by mass per 100 parts by mass of water. Above all, those dyed with iodine are preferred because of their high transmittance and high polarization, that is, high dichroism. During the dyeing bath,
Potassium iodide, lithium iodide, sodium iodide,
An auxiliary agent such as zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and an iodide such as titanium iodide may be added in an amount of 2 to 20 parts by mass. It is particularly preferable for enhancing the dyeing efficiency. Further, the stretching treatment can be performed while performing the dyeing treatment. In addition to the water solvent, a small amount of an organic solvent compatible with water may be contained. Before dyeing in an aqueous solution containing iodine or a dichroic dye, the polyvinyl alcohol-based film may be subjected to a swelling treatment at 20 to 60 ° C. for 0.1 to 10 minutes in a water bath or the like.

The stretching in an aqueous solution containing iodine or a dichroic dye (dye bath) may be performed, for example, by stretching a polyvinyl alcohol-based film 3 to 7 times while immersing the film in an aqueous solution containing iodine or a dichroic dye. . Alternatively, a method may be used in which an aqueous solution containing iodine or a dichroic dye is applied to a polyvinyl alcohol-based film and stretched while spraying. The stretching method is not particularly limited. For example, the stretching can be performed by a method of appropriately adjusting the tension applied to the film.

Next, the stretched polyvinyl alcohol-based film is preferably stretched in a boron compound-containing aqueous solution so that the total stretching ratio becomes 3 to 7 times. If the stretching ratio is less than 3 times, it becomes impossible to obtain a polarizing plate having a high degree of polarization, and wrinkles are likely to occur due to swelling of the film. On the other hand, when the ratio exceeds 7 times, stretching breakage is apt to occur, and it is difficult to obtain a film having a high degree of polarization stably.

The composition of the boron compound-containing aqueous solution to be subjected to the above-mentioned crosslinking treatment is usually 1 to 10 parts by mass of a PVA crosslinking agent such as boric acid, borax, glyoxal, glutaraldehyde or the like, alone or as a mixture, per 100 parts by mass of water. . In the crosslinking bath, potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, titanium iodide, etc. 0.05 to 1 of an auxiliary such as iodide
It may be added in an amount of 5% by mass, preferably 0.5 to 8% by mass, and is particularly preferable in that in-plane uniform characteristics are obtained. The temperature of the aqueous solution is usually in the range of 20 to 70C. The immersion time is
Although not particularly limited, it is generally 1 second to 15 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.

The stretching in the boron compound-containing aqueous solution may be performed, for example, by immersing the stretched polyvinyl alcohol-based film in the boron compound-containing aqueous solution. Alternatively, a method may be used in which a boron compound-containing aqueous solution is applied to a relaxed polyvinyl alcohol-based film and stretched while spraying. The stretching method is not particularly limited. For example, the film can be stretched by a method of appropriately adjusting the tension applied to the film, a method of stretching with a fixed ratio, or a method of performing them in multiple stages. The tension is adjusted according to the type of the boron compound, the temperature and concentration of the aqueous solution containing the boron compound, the average degree of polymerization and the type of the polyvinyl alcohol-based film, and the like.

The polyvinyl alcohol-based film subjected to the above-mentioned adsorption orientation treatment is further immersed in an aqueous solution of iodide such as potassium iodide having a water temperature of 10 to 60 ° C. and a concentration of 0.1 to 10% by mass for 1 second to 1 minute. After washing with water and drying at 20 to 80 ° C. for 1 to 10 minutes, a polarizer is obtained.

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 or the like comprising at least a water-soluble crosslinking agent of a vinyl alcohol polymer such as sand, glutaraldehyde, melamine, and oxalic acid. Such an adhesive layer is formed as a coating and drying layer of an aqueous solution, and at the time of preparing the aqueous solution, other additives and a catalyst such as an acid can be blended as necessary.

After the polarizer and the protective layer are bonded to each other, the temperature is preferably 20 to 90 ° C., and more preferably 30 to 90 ° C., so that the polarizer and the protective layer are not easily peeled off by the influence of humidity or heat and have excellent light transmittance and degree of polarization.
Dry at 60 ° C. When the drying temperature is lower than 20 ° C., it takes a long time to dry or cannot be sufficiently dried, and the durability against heating is reduced. When the drying temperature is higher than 90 ° C., the color is changed or the durability against humidification is reduced. . The drying time is
Generally, it is 1 to 20 minutes, preferably 3 to 10 minutes.

Further, after bonding the polarizer and the protective layer, the light transmittance and the degree of polarization are preferably adjusted to 40 to 40%.
80 ° C, preferably 50 to 70 ° C, humidity 50 to 100%
RH, preferably 60 to 95% RH, for 1 minute to
Humidify for 24 hours. The humidification treatment time depends on the characteristics of the polarizing plate before humidification and humidification conditions. However, when the single transmittance of the polarizing plate before humidification treatment is 42 to 45% and the degree of polarization is 99.5% or more, 60 ° C. It is preferable to leave under humidification of 90% RH for 30 minutes to 10 hours.

The drying and humidification of the polarizing plate may be performed either alone or both. By carrying out both, the object of the present invention can be further achieved. The reason why the hue of the polarizing plate is improved by these methods is not clear, but the polarizing plate obtained by drying at a low temperature or humidifying the dried polarizing plate by heating at a temperature higher than 60 ° C. after the TAC bonding. The plate has more freedom in the presence of iodine (complex or ion) present in the polarizer, PVA molecules surrounding iodine and water molecules or other molecules and ions, and the absorption wavelength range of iodine is expanded. it is conceivable that.

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.
Λ plate such as a 波長 wavelength plate and a 波長 wavelength plate), a reflective plate, a semi-transmissive reflective plate, a viewing angle compensation film, a brightness enhancement film, and other suitable liquid crystal display devices. One or two or more optical layers can be used. In particular, an elliptically polarizing plate or a circularly polarizing plate in which a retardation plate is further laminated on the polarizing plate including the above-described polarizer and protective layer, and a reflecting plate or semi-transmissive reflection on the above-described polarizing plate including the polarizer and the protective layer. A reflective polarizer or transflective polarizer in which plates are laminated, a polarizer in which a viewing angle compensation film is further laminated on the polarizer including the polarizer and the protective layer described above, or the polarizer and protective described above. A polarizing plate in which a brightness enhancement film is further laminated on a polarizing plate composed of layers is preferable.

To explain the above-mentioned reflector, the reflector is provided on a polarizing plate to form a reflective polarizing plate, and the reflecting polarizer 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 reflection type polarizing plate having a reflective layer reflecting the fine uneven structure on the transparent protective film having a fine uneven structure on the surface by containing fine particles may also be used. The reflection layer having the fine surface irregularity structure has the advantage of diffusing incident light by irregular reflection, preventing directivity and glaring appearance, and suppressing unevenness in brightness and darkness. 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 conforming to the transparent protective film, instead 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 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 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 changes 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 a suitable polymer such as polycarbonate, polyvinyl alcohol, polystyrene, polymethyl methacrylate, polypropylene and other polyolefins, polyarylate and 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 slightly oblique rather than 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 the ordinary retardation plate, a polymer film having birefringence uniaxially stretched in the plane direction is used,
The retardation plate used as a viewing angle compensating film includes a birefringent polymer film that is biaxially stretched in a plane direction or a refractive index in a thickness direction that is uniaxially stretched in a plane direction and also stretched in a thickness direction. For example, a bidirectionally stretched film such as an obliquely oriented polymer film having a controlled thickness 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.

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, An appropriate material such as a material exhibiting a characteristic of transmitting light can be used.

Therefore, in a brightness enhancement film of a type that transmits linearly polarized light having a predetermined polarization axis, the transmitted light is directly incident on the polarization plate with the polarization axis aligned, thereby efficiently absorbing the polarization plate while suppressing the absorption loss. 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, 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 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 is 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 more optical layers, such as a polarized light separating type polarizing plate. Therefore, a reflective elliptically polarizing plate or a transflective elliptically polarizing plate obtained by combining the above-mentioned reflective polarizing plate, semi-transmissive polarizing plate and retardation plate may be used. An optical member in which two or three or more optical layers are laminated can be formed by a method in which the optical members are sequentially laminated separately in a manufacturing process of a liquid crystal display device or the like. This has the advantage that the stability of quality and the workability of assembling are excellent and the manufacturing efficiency of a liquid crystal display device or the like can be improved. Note that an appropriate bonding means such as an adhesive layer can be used for lamination.

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

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

The layers such as the polarizing film and the transparent protective film, the optical layer and the adhesive layer which form the above-mentioned polarizing plate and 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 a compound or a nickel complex salt-based compound or the like may be used.

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

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

[0057]

The present invention will be described more specifically below with reference to examples and comparative examples. (Example 1) A polyvinyl alcohol (PVA) film having an average degree of polymerization of 2400 was swollen with warm water at 30 ° C for 1 minute, and potassium iodide / iodine (mass ratio: 10:
1) It was immersed in an aqueous solution and stretched three times. At this time, the concentration of the potassium iodide / iodine (mass ratio 10: 1) aqueous solution was set to an iodine concentration of 0.3% by mass. Then, 4% by mass at 50 ° C.
The film is stretched in a boric acid aqueous solution so that the total stretching ratio becomes 6.2 times, and 5% in a 4% by mass aqueous solution of potassium iodide at 30 ° C.
After immersion for 2 seconds, it was dried by heating at 50 ° C. for 4 minutes to obtain a polarizer. On both sides of the obtained polarizer,
Using a PVA-based adhesive, triacetyl cellulose (TA
C) The films were laminated and dried by heating at 80 ° C. for 4 minutes to produce a polarizing plate. Further, the obtained polarizing plate was left at 60 ° C. and 90% RH for 4 hours to obtain a polarizing plate.

Example 2 A polyvinyl alcohol (PVA) film having an average degree of polymerization of 2400 was swollen with warm water at 30 ° C. for 1 minute, and immersed in an aqueous solution of potassium iodide / iodine (mass ratio 10: 1) at 30 ° C. The film was stretched three times. At this time, the concentration of the potassium iodide / iodine (mass ratio 10: 1) aqueous solution was set to an iodine concentration of 0.3% by mass. Then, at 50 ° C
In a 4% by mass aqueous solution of boric acid, the film is stretched so that the total stretching ratio becomes 6.2 times, immersed in a 4% by mass aqueous solution of potassium iodide at 30 ° C. for 5 seconds, and then heated at 50 ° C. for 4 minutes. By drying, a polarizer was obtained. A triacetyl cellulose (TAC) film was attached to both sides of the obtained polarizer using a PVA-based adhesive, and dried by heating at 60 ° C. for 4 minutes to produce a polarizing plate.

Comparative Example 1 PVA having an average degree of polymerization of 2400
The film was swollen with warm water at 30 ° C. for 1 minute, immersed in a 30 ° C. aqueous solution of potassium iodide / iodine (mass ratio 10: 1), and stretched three times. At this time, the concentration of the potassium iodide / iodine (mass ratio 10: 1) aqueous solution was set to an iodine concentration of 0.3% by mass. Next, the film is stretched in a 4% by mass aqueous solution of boric acid at 50 ° C. so that the total stretching ratio becomes 6.2 times.
Immersed in a 3% by mass aqueous solution of potassium iodide for 5 seconds, and dried by heating at 50 ° C. for 4 minutes.
A polarizer was obtained. A TAC film was attached to both surfaces of the obtained polarizer using a PVA-based adhesive, and dried by heating at 80 ° C. for 4 minutes to produce a polarizing plate.

Comparative Example 2 PVA having an average degree of polymerization of 2400
The film was swollen with warm water at 30 ° C. for 1 minute, immersed in a 30 ° C. aqueous solution of potassium iodide / iodine (mass ratio 10: 1), and stretched three times. At this time, the concentration of the potassium iodide / iodine (mass ratio 10: 1) aqueous solution was set to an iodine concentration of 0.3% by mass. Next, the film is stretched in a 2% by mass aqueous boric acid solution at 50 ° C. so that the total stretching ratio becomes 6.2 times.
Immersed in a 3% by mass aqueous solution of potassium iodide for 5 seconds, and dried by heating at 50 ° C. for 4 minutes.
A polarizer was obtained. A TAC film was adhered to both surfaces of the obtained polarizer using a PVA-based adhesive, and dried by heating at 80 ° C. for 4 minutes to produce a polarizing plate. Further, the obtained polarizing plate was left at 60 ° C. and 90% RH for 4 hours to obtain a polarizing plate.

Comparative Example 3 PVA having an average degree of polymerization of 2400
The film was swollen with warm water at 30 ° C. for 1 minute, immersed in a 30 ° C. aqueous solution of potassium iodide / iodine (mass ratio 10: 1), and stretched three times. At this time, the concentration of the potassium iodide / iodine (mass ratio 10: 1) aqueous solution was set to an iodine concentration of 0.3% by mass. Next, the film is stretched in a 6% by mass aqueous solution of boric acid at 50 ° C. so that the total stretching ratio becomes 6.2 times.
Immersed in a 3% by mass aqueous solution of potassium iodide for 5 seconds, and dried by heating at 50 ° C. for 4 minutes.
A polarizer was obtained. A TAC film was adhered to both surfaces of the obtained polarizer using a PVA-based adhesive, and dried by heating at 80 ° C. for 4 minutes to produce a polarizing plate. Further, the obtained polarizing plate was left at 60 ° C. and 90% RH for 4 hours to obtain a polarizing plate.

[Evaluation] The individual transmittance, parallel transmittance, and orthogonal transmittance of the polarizing plates prepared in Examples and Comparative Examples were measured at each wavelength, and Tp440 / Tp550 was measured. , Tp610 / Tp550,
Tp440 / Tc440 was calculated. The degree of polarization was calculated from each transmittance. Table 1 shows the results. The measurement was performed by the following method.

(Single Transmittance) One polarizing plate was measured using a spectrophotometer (DOT-3, manufactured by Murakami Color Research Laboratory Co., Ltd.), and a 2 degree field of view (C light source) of Jls Z8701 was used. , The Y value after the visibility correction.

(Degree of Polarization) Two identical polarizers having the same polarization axis
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.

[0065]

(Equation 1)

[0066]

[Table 1] Single transmittance Polarization degree Variation of average transmittance Contrast (%) (%) Tp440 / Tp550 Tp610 / Tp550 Tp440 / Tc440 Example 1 43.5 99.99 0.87 1.00 16000 Example 2 43.2 99.99 0.86 1.00 15900 Comparative example 1 43.8 99.98 0.83 1.01 940 Comparative Example 2 44.0 99.76 0.88 0.99 49 Comparative Example 3 43.1 99.99 0.79 1.01 1957

Further, the polarizing plates produced in Examples and Comparative Examples were thin-film-transistor (TFT).
r) type liquid crystal display device, and using a luminance meter BM-5A chromaticity measuring device manufactured by Topcon Co., Ltd., a CIE1931 color system (white field X field of view X
YZ color system) was measured, and the color reproducibility was evaluated. Table 2 shows the results.

[0068]

[Table 2]

As is clear from Tables 1 and 2, the polarizing plate of the present invention is bright, has a high degree of polarization, has a low wavelength dependence of light transmittance, and has a large parallel transmittance at 440 nm. Also,
The balance between black display and white display is also good, and 0.27 ≦ x ≦ 0.31 and 0.27 ≦ y ≦ 0.31 on the XYZ color system.

[0070]

As described above, the polarizing plate of the present invention comprises:
The single transmittance is 43.0% or more, the degree of polarization is 99.8% or more, the dispersion of the parallel transmittance at 440 nm, 550 nm and 610 nm is small, and 1000 ≦ Tp440.
/ Tc440 and high dichroism on the short wavelength side. Therefore, when used for a liquid crystal display device, bright and high color reproducibility can be achieved. Therefore, its industrial value is great.

Continued on the front page (72) Inventor Yoichiro Sugino 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation F-term (reference) 2H049 BA02 BA06 BA27 BB33 BB43 BB63 BC22 2H091 FA08X FA08Z FA11X FA11Z FA14X FA14Z FA41Z FB02 FB12 KA10 LA18

Claims (5)

[The claims] 1. A polarizing plate having a protective film laminated on at least one side of a polarizer formed of a polyvinyl alcohol-based film and having a single transmittance of 43.0% or more and a degree of polarization of 99.8% or more, wherein Parallel transmittance Tp440 at a wavelength of 440 nm of the plate
The orthogonal transmittance Tc440 at a wavelength of 440 nm, the parallel transmittance Tp550 at a wavelength of 550 nm, and the wavelength 610n.
The parallel transmittance Tp610 at m is given by the following equation (1):
A polarizing plate that satisfies both (2) and (3) at the same time. 0.85 ≦ Tp440 / Tp550 ≦ 1.10 (1) 0.90 ≦ Tp610 / Tp550 ≦ 1.10 (2) 1000 ≦ Tp440 / Tc440 (3) 2. The polarizing plate according to claim 1, wherein the polarizer is a polyvinyl alcohol-based film on which iodine is adsorbed. 3. The polarizing plate according to claim 1, wherein the protective film is a triacetyl cellulose film. 4. A laminate of the polarizer according to claim 1 and at least one optical layer selected from a retardation plate, a reflector, a transflector, a viewing angle compensation film and a brightness enhancement film. A polarizing plate made of a body. 5. A liquid crystal display device, wherein the polarizing plate according to claim 1 is arranged on at least one side of a liquid crystal cell.