JP2003121644A - Polarizer and liquid crystal display element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizer exhibiting little camber of a substrate in sticking to the substrate, in particular to the plastics substrate and a liquid crystal display element using the same. SOLUTION: When the polarizer is stuck to the plastics substrate with 0.4 mm thickness and a modulus of elasticity in 1.4×10<3> -3.5×10<3> N/mm<2> range so as to make the absorption axis form 90 deg. angle via an adhesive layer and let to stand for 24 hours at 70 deg.C in the stuck state, camber stress of the plastics substrate is in 0.04-0.48 N/m<3> range. When the camber stress of the plastics substrate is within the range, the camber of a panel is reduced to a level of no practical problem and color irregularity in the panel surface is eliminated.

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 sometimes abbreviated as LCD) and a liquid crystal display element using the polarizing plate.

[0002]

2. Description of the Related Art Liquid crystal display devices are used for desk computers, electronic clocks, personal computers, word processors,
It is used for measuring instruments of automobiles and machines, and a polarizing plate is used for this liquid crystal display device. As a polarizing plate,
Generally, triacetyl cellulose (hereinafter abbreviated as “TAC”) is formed on both surfaces of a polarizing film made of a polyvinyl alcohol (hereinafter sometimes abbreviated as “PVA”) film in which iodine or a dichroic dye is adsorbed and oriented. A protective film such as a protective film is used.

Conventionally, as a method for producing a polarizing plate, a polyvinyl alcohol film has been dyed mainly with dichroic iodine or a dichroic dye, and stretched 5 times or more in order to arrange molecules, and then stretched. In order to maintain the above state, the film is cross-linked with a cross-linking agent such as boric acid or borax, dried to prepare a polarizing film, and a protective film is attached thereto.
The steps of dyeing, crosslinking and stretching need not be performed separately and may be performed simultaneously, and the order of each step may be arbitrary.

[0004]

However, a polarizing plate comprising a laminate of polymer films shows a dimensional change when it is left under heating and humidifying conditions. In particular, under heating conditions, change of 1.0% or more at maximum occurs. At present, glass substrates are often used in liquid crystal cells, and even if the dimensions of the polarizing plate change, the cell itself cannot be deformed. Concentrate on the panel, which causes color unevenness when the panel is lit.
In recent years, there has been a movement to use a plastic substrate for a liquid crystal panel for a mobile phone or a PDA as an alternative to a glass cell because it is thin, light, and does not break, but the plastic substrate is more flexible than glass. However, there is a problem in that the substrate is warped in accordance with the dimensional behavior of the polarizing plate.

In order to solve the above-mentioned conventional problems, the present invention provides a polarizing plate having a small amount of substrate warpage when bonded to a substrate, especially a plastic substrate, and a liquid crystal display device using the same. To aim.

[0006]

The inventors of the present invention have found that even polarizing plates having the same dimensional change have a difference in color unevenness in the panel surface or in a warpage phenomenon occurring in a liquid crystal cell using a plastic substrate. It was clarified that this phenomenon is due to the stress difference generated when the dimension of the polarizing plate changes. Then, according to the method described in the present specification, by considering the force generated when the dimension of the polarizing plate changes as the force that warps the plastic substrate, it becomes possible to measure the stress that occurs when the dimension of the polarizing plate changes. This is based on the finding that the behavior of a polarizing plate, which could be expressed only by a dimensional change, can be confirmed in more detail on the shrinkability of the polarizing plate by applying the above-mentioned measuring method.

To achieve the above object, the polarizing plate of the present invention has a thickness of 0.4 mm and an elastic modulus of 1.4 × 10 ^{3 to} 3.5.
The plastic substrate in the range of × 10 ³ N / mm ² was attached to the plastic substrate via the adhesive layer so that the absorption axis was 90 °, and the plastic substrate was warped when left in the attached state at 70 ° C for 24 hours. Stress is 0.04 to 0.48 N / m
It is characterized by being in the range of ³ . When the warp stress of the plastic substrate is within the above range, the warp of the panel can be reduced to a level where there is no practical problem, and color unevenness in the panel surface can be eliminated.

In the polarizing plate of the present invention, it is preferable to use a polarizing plate formed by laminating protective films on both sides of a polarizer formed by dyeing, crosslinking, stretching and drying a polyvinyl alcohol film. This achieves the object of the present invention more effectively.

In the above polarizing plate, an adhesive layer is preferably formed on at least one surface of the polarizing plate, and the thickness of the adhesive layer is preferably 5 to 30 μm.

The present invention also provides a polarizing plate, particularly a circular polarizing plate, comprising a laminate of the above polarizing plate and a retardation plate.

Furthermore, the present invention provides a liquid crystal display device characterized in that the polarizing plate is attached to at least one surface of a liquid crystal cell. In particular, the object of the present invention is most effectively achieved in a combination of the polarizing plate of the present invention and a liquid crystal cell made of a plastic substrate.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The polarizing plate of the present invention has a thickness of 0.4 mm and an elastic modulus of 1.4 × 10 ^{3 to} 3.5 × 10 ³ N.
The absorption axis is 90 on the plastic substrate in the range of / mm ²
The warp stress of the plastic substrate is in the range of 0.04 to 0.48 N / m ³ when the substrates are attached to each other via the adhesive layer so that the temperature becomes 0 ° and left in the attached state at 70 ° C. for 24 hours. The warp stress is preferably in the range of 0.1 to 0.45 N / m ³ . When the warp stress of the plastic substrate is within the above range, the dimensional change of the polarizing plate is extremely small, and for example, the dimensional change rate in the MD direction can be suppressed within the range of 1.0% or less.

FIG. 1 is a front view schematically showing the warp stress measuring method of the present invention, and FIG. 2 is a sectional view. The polarizing plate 2 is attached to the plastic substrate 1 so that the absorption axis is 90 ° with respect to the fixed end to form a liquid crystal display element.
A heating test is performed by leaving it at 0 ° C. for 24 hours. At this time, the size of the plastic substrate is 105 × 105 mm, and the size of the polarizing plate is 100 × 100 mm. After the test is completed, one ends of the plastic substrate 1 and the polarizing plate 2 are fixed by the fixing plate 3, and the warp of the plastic substrate is measured by the force gauge 5. 7
Since the plastic substrate 1 and the polarizing plate 2 after the 0 ° C. heating test are warped in the state shown in FIG. 2, the substrate is placed on a horizontal table, and a force gauge 5 is applied to the end of the warped plastic substrate, The warp force is the value of the force gauge when the warp amount becomes 0 mm. Warpage stress (N / m ³ ) = force gauge value (N) / plastic substrate volume (m ³ ).

In order to eliminate color unevenness in the panel surface, the warp amount of the plastic substrate after the 70 ° C. heating test is 1
It is preferably 2 mm or less, more preferably 8 m
m or less, particularly preferably 5 mm or less. When the maximum amount of warpage is equal to or less than the above value, color unevenness in the panel surface is practically no problem, but the smaller the amount of warpage, the more preferable.

The polarizing plate used in the present invention may be formed by dyeing, crosslinking, stretching, and drying a synthetic resin film, and a polarizer made of a polyvinyl alcohol-based polarizing film containing a dichroic substance, or the like, on one side or both sides of the polarizer. The transparent protective film serving as a protective layer is adhered via the adhesive layer of (1), for example, an adhesive layer composed of a vinyl alcohol polymer or the like.

As the polarizer (polarizing film), a synthetic resin film is subjected to an appropriate treatment such as a dyeing treatment with a dichroic substance such as iodine or a dichroic dye, a stretching treatment and a crosslinking treatment in an appropriate order or It is possible to use an appropriate material which is applied by a method and which transmits linearly polarized light when natural light is made incident, and in particular, one having excellent light transmittance and polarization degree is preferable.
The thickness of the polarizer is not particularly limited, but 1 to
The thickness is generally 80 μm, and particularly preferably 5 to 40 μm. This is because when the thickness is less than 5 μm, the mechanical strength decreases, and when it exceeds 40 μm, the optical characteristics deteriorate.

As the synthetic resin film, for example, a hydrophilic polymer film such as polyvinyl alcohol or partially formalized polyvinyl alcohol is preferable, and a polyvinyl alcohol film is particularly preferable since it has good dyeability with iodine. The polyvinyl alcohol-based film is a casting method in which a polyvinyl alcohol-based resin is cast to form an undiluted solution obtained by dissolving it in water or an organic solvent.
A film formed by any method such as an extrusion method can be appropriately used. The degree of polymerization of the polyvinyl alcohol resin used is preferably 100 to 5000, and 1400 to 4
000 is more preferable. The thickness of the polyvinyl alcohol-based film is generally 80 μm or less, and preferably 35 to 76 μm. When it exceeds 80 μm, the color change of the display panel becomes large when it is mounted on the liquid crystal display device, while when it is too thin, the stretching becomes difficult.

The polarizing film can be manufactured, for example, by the following method.

In the dyeing step, the polyvinyl alcohol film is usually immersed in a dyeing bath containing iodine or a dichroic dye at 20 to 70 ° C. for 1 to 20 minutes to adsorb the iodine or the dichroic dye. , 2 to 4 times. The concentration of iodine or dichroic dye in the dyeing bath is usually 0.1 to 1.0 part by mass per 100 parts by mass of water. 2 to 20 parts by mass of an auxiliary agent such as potassium iodide may be added to the dyeing bath, and a small amount of an organic solvent compatible with water may be contained in addition to the water solvent. Further, the polyvinyl alcohol-based film is dyed in an aqueous solution containing iodine or a dichroic dye at 20 to 60 ° C. in a water bath or the like before dyeing in an aqueous solution containing iodine.
Swelling treatment may be performed for 1 to 10 minutes.

In the crosslinking step, the dyed polyvinyl alcohol film is usually stretched in a boron compound-containing aqueous solution at a total stretching ratio of 5 to 7 times. The composition of the boron compound-containing aqueous solution to be crosslinked is usually 100% water.
1 to 1 parts by weight of PVA crosslinking agent such as boric acid, borax, glyoxal, glutaraldehyde, etc., alone or as a mixture
It is 0 part by mass. An auxiliary agent such as potassium iodide may be added to the crosslinking bath in an amount of 0.05 to 15% by mass, which is particularly preferable from the viewpoint of obtaining uniform in-plane characteristics. The temperature of the aqueous solution is usually 2
It is in the range of 0 to 70 ° C, preferably 40 to 60 ° C. The immersion time is not particularly limited, but is usually 1 second to 15 minutes. In addition to the water solvent, a small amount of an organic solvent compatible with water may be contained.

When the polyvinyl alcohol film is stretched, the stretching method, the number of times of stretching and the like are not particularly limited, and it may be performed in each step of dyeing and crosslinking,
It may be performed only in any one step. Moreover, you may perform in the same process multiple times.

A polyvinyl alcohol-based film that has been subjected to an iodine adsorption orientation treatment or the like is further placed in an aqueous iodide solution such as potassium iodide having a water temperature of 10 to 60 ° C., preferably 30 to 40 ° C. and a concentration of 0.1 to 10% by mass. After dipping for 1 second to 1 minute, it is washed with water and dried at 20 to 80 ° C. for 1 minute to 10 minutes to obtain a polarizing film. An auxiliary agent such as zinc sulfate or zinc chloride may be added to the iodide aqueous solution.

An appropriate transparent film can be used as the protective film material which becomes the transparent protective layers provided on both sides of the polarizer (polarizing film). Above all, a film made of a polymer having excellent transparency, mechanical strength, thermal stability, moisture shielding property and the like is preferably used. Examples of the polymer include polyester resin, acetate resin, polynorbornene resin, polyether sulfone resin, polycarbonate resin, polyamide resin, polyimide resin, polyolefin resin, acrylic resin, or acrylic resin. Examples thereof include thermosetting or ultraviolet curable resins such as resins, urethanes, epoxies, and silicones. Among them, an acetate resin is preferable from the viewpoint of transparency, and a triacetyl cellulose film whose surface is saponified with alkali or the like is particularly preferable from the viewpoint of polarization characteristics and durability.

The thickness of the transparent protective film is optional, but generally 500 μm or less for the purpose of thinning the polarizing plate,
The thickness is preferably 5 to 300 μm. When transparent protective films are provided on both sides of the polarizing film, transparent protective films made of different polymers may be used on the front and back sides. Further, the transparent protective film used for the protective layer,
As long as the object of the present invention is not impaired, a hard coat treatment, an antireflection treatment, a treatment for the purpose of preventing sticking, diffusion or antiglare, or the like may be applied.

The adhesive treatment between the polarizing film and the transparent protective film as the protective layer is not particularly limited, but for example, an adhesive made of a vinyl alcohol polymer, boric acid, borax, or glutaraldehyde. Alternatively, it can be carried out via an adhesive or the like made of at least a water-soluble cross-linking agent of a vinyl alcohol polymer such as melamine or oxalic acid. Such an adhesive layer can be formed as a coating / drying layer of an aqueous solution, but other additives and a catalyst such as an acid can be blended, if necessary, in the preparation of the aqueous solution. In particular, it is preferable to use an adhesive made of polyvinyl alcohol because it has the best adhesiveness with PVA (polarizing film).

The plastic substrate used in the present invention is not particularly limited, and any conventionally known one can be used. As the resin forming the plastic substrate, for example, thermoplastic resins such as polycarbonate, polyarylate, polyether sulfone, polyester, polysulfone, polymethylmethacrylate, polyetherimide, polyamide, epoxy resin, unsaturated polyester,
Examples thereof include thermosetting resins such as polydiallyl phthalate and polyisobornyl methacrylate. These resins can be used alone or in combination of two or more, and can also be used as a copolymer or mixture with other components.

Among the above-mentioned resins for forming a substrate, it is excellent in transparency and impact resistance, and in view of durability in the case of a liquid crystal cell, chemical resistance, optical isotropy, low absorption, low moisture permeability, From the viewpoint of excellent gas barrier properties against oxygen and the like, it is preferable to use an epoxy resin (particularly an alicyclic epoxy resin) and a cured product of an epoxy composition containing an acid anhydride curing agent and a phosphorus curing catalyst. . As the alicyclic epoxy resin, various kinds can be used and are not particularly limited.

Examples of the acid anhydride-based curing agent include phthalic anhydride, maleic anhydride, trimellitic anhydride, pyromellitic anhydride, nadic acid anhydride, glutaric anhydride, tetrahydrophthalic anhydride, methyltetrahydrophthalic acid. Anhydrous, hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, methylnadic acid anhydride, dodecenylsuccinic anhydride, dichlorosuccinic anhydride, benzophenonetetracarboxylic acid anhydride, chlorendic acid anhydride, etc. Can be mentioned. In particular, colorless or pale yellow acid anhydrides such as tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, hexahydrophthalic anhydride, and methylhexahydrophthalic anhydride are preferable. The compounding amount of the acid anhydride curing agent is preferably 0.5 to 1.3 equivalents per 1 epoxy equivalent of the epoxy resin.

Examples of the phosphorus-based curing catalyst include alkylphosphines, phosphine oxides and phosphonium salts. The blending amount is 0.2 to 10 parts by mass, preferably 0.5 to 4 parts by mass, per 100 parts by mass of the acid anhydride curing agent curing agent.

The plastic substrate is formed by an appropriate method such as casting molding method, casting molding method, injection molding method, roll coating molding method, extrusion molding method, transfer molding method, and reaction injection molding method (RIM). It can be carried out. In the formation thereof, if necessary, additives such as dyes, modifiers, discoloration preventing agents, antioxidants, ultraviolet absorbers, release agents, reactive diluents and non-reactive diluents may be added to improve transparency. It can be blended within a range that does not impair it.

In the present invention, the thickness of the plastic substrate is 5 in view of thinning, lightness, strength, deformation prevention and the like.
0 μm or more and 800 μm or less, preferably 100 μm
m or more and 700 μm or less. Therefore, the thickness of the plastic substrate may be achieved as a laminate of two layers or three or more layers made of the same or different resins.

The polarizing plate and liquid crystal display device 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 may be, for example, a reflection plate, a semi-transmission reflection plate, a retardation plate (1/2 wavelength plate, 1
(Including a λ plate such as a / 4 wavelength plate), a viewing angle compensation film, a brightness enhancement film, and the like, and one or two or more suitable optical layers that may be used for forming a liquid crystal display device can be used. . In particular, a polarizing plate comprising the polarizing film of the present invention described above and a protective film, a reflection type polarizing plate or a semi-transmissive reflection type polarizing plate obtained by further laminating a reflecting plate or a semi-transmissive reflecting plate, the above-mentioned polarizing film and protection. An elliptical polarizing plate or a circular polarizing plate in which a retardation plate is further laminated on a polarizing plate comprising a film, and a viewing angle compensation film is further laminated on a polarizing plate comprising the above-mentioned polarizing film and a protective film. Alternatively, a polarizing plate in which a brightness enhancement film is further laminated on the polarizing plate composed of the polarizing film and the protective film described above is preferable.

A reflective polarizing plate or a semi-transmissive reflective plate type polarizing plate in which a reflective plate or a semi-transmissive reflective plate is further laminated on the above-mentioned polarizing plate will be described.

The reflector is provided on the polarizing plate to form a reflective polarizing plate. The reflective polarizing plate is usually disposed on the back side of the liquid crystal cell, and forms a liquid crystal display device (reflective liquid crystal display device) of the type that reflects and displays incident light from the viewing side (display side). The reflective polarizer is
It has an advantage that a light source such as a backlight can be omitted and the liquid crystal display device can be easily thinned. 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 attached to one surface of the polarizing plate. Specific examples thereof include a transparent protective film that is mat-treated if necessary, and a reflective layer formed by attaching a foil or a vapor deposition film made of a reflective metal such as aluminum to one surface of the transparent protective film.

Further, there may be mentioned a reflection type polarizing plate having a reflective layer reflecting the fine concavo-convex structure on the above transparent protective film containing fine particles and having a fine concavo-convex structure on the surface. The reflective layer having a fine surface irregularity structure has an advantage of diffusing incident light by diffuse reflection, preventing directivity and glare, and suppressing uneven brightness. The transparent protective film can be formed by a method of directly attaching a metal to the surface of the transparent protective film by an appropriate method such as a vacuum vapor deposition method, an ion plating method, a vapor deposition method such as a sputtering method or a plating method. .

Further, the reflection plate may be used as a reflection sheet in which an appropriate film conforming to the transparent protective film is provided with a reflection layer instead of the method of directly attaching to the transparent protective film of the polarizing plate. it can. Since the reflective layer of the reflective plate is usually made of metal, the use form in which the reflective surface is covered with a film or a polarizing plate is to prevent reduction of the reflectance due to oxidation, and thus to maintain the initial reflectance for a long time. Also, it is preferable from the viewpoint of avoiding the additional provision of the protective layer.

The semi-transmissive polarizing plate is a semi-transmissive reflective layer in the above reflective polarizing plate, and examples thereof include a half mirror that reflects and transmits light at the reflective layer.
The semi-transmissive polarizing plate is usually provided on the back side of the liquid crystal cell, and when a liquid crystal display device is used in a relatively bright atmosphere, it reflects incident light from the viewing side (display side) to display an image. In a relatively dark atmosphere, a liquid crystal display device of the type that displays an image using a built-in light source such as a backlight built in the back side of a semi-transmissive polarizing plate is formed. That is, the semi-transmissive polarizing plate is useful for forming a liquid crystal display device of a type that can save energy for using a light source such as a backlight in a bright atmosphere and can be used with a built-in light source in a relatively dark atmosphere. Is.

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

The retardation plate is used for converting linearly polarized light into elliptically polarized light or circularly polarized light, changing elliptically polarized light or circularly polarized light into linearly polarized light, or changing the polarization direction of linearly polarized light. In particular, a so-called quarter-wave plate (also referred to as a λ / 4 plate) is used as a retardation plate that changes linearly polarized light into elliptically polarized light or circularly polarized light, or changes elliptically polarized light or circularly polarized light into linearly polarized light. Half-wave plate (also called λ / 2 plate)
Is usually used when changing the polarization direction of linearly polarized light.

The above-mentioned elliptically polarizing plate compensates (prevents) coloring (blue or yellow) generated by the birefringence of the liquid crystal layer of the super twisted nematic (STN) type liquid crystal display device to obtain the above black and white display without coloring. It is effectively used when doing. Further, the one in which the three-dimensional refractive index is controlled is preferable because it can also compensate (prevent) coloring that occurs when the screen of the liquid crystal display device is viewed from an oblique direction. Further, the circularly polarizing plate is effectively used, for example, when adjusting the color tone of an image of a reflective liquid crystal display device in which an image is displayed in color, and also has a function of preventing reflection.

As the retardation plate, a birefringent film obtained by stretching a polymer film such as polycarbonate, polyvinyl alcohol, polystyrene, polymethylmethacrylate, polypropylene and other polyolefins, polyarylate, polyamide and polynorbornene, Examples include an oriented film of a liquid crystal polymer and a film in which an oriented layer of a liquid crystal polymer is supported.

The retardation plate is used for various purposes such as various wavelength plates such as 1/2 and 1/4, and those for the purpose of compensating for coloring due to birefringence of the liquid crystal layer and for compensating the viewing angle such as widening the viewing angle. It may have a corresponding retardation, and may be a tilt-oriented film having a controlled refractive index in the thickness direction. Also,
It may be one in which two or more kinds of retardation plates are laminated to control optical characteristics such as retardation.

The tilt-oriented film may be formed by, for example, adhering 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 being slanted It can be obtained by a method of orienting.

Next, a polarizing plate in which a viewing angle compensation film is further laminated on the above-mentioned polarizing plate will be described.

The viewing angle compensating film is a film for widening the viewing angle so that the 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 triacetyl cellulose film coated with a discotic liquid crystal or a retardation plate is used.
Ordinary retardation plate, uniaxially stretched in its plane direction, while a polymer film having birefringence is used,
The retardation plate used as a viewing angle compensation film has a birefringent polymer film biaxially stretched in the plane direction and a refractive index in the thickness direction uniaxially stretched in the plane direction and also in the thickness direction. A bidirectionally stretched film such as the above-mentioned inclined orientation polymer film is used. As the inclined orientation film, for example, a film obtained by adhering 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 its shrinkage force by heating, or a liquid crystal polymer which is obliquely oriented, etc. Is mentioned. As the raw material polymer of the retardation plate, the same polymer as that used in the above retardation plate is used.

Next, a polarizing plate in which a brightness enhancement film is further laminated on the above-mentioned polarizing plate will be described.

This polarizing plate is usually used by being provided on the back side of the liquid crystal cell. The brightness enhancement film has a property of reflecting linearly polarized light of a predetermined polarization axis or circularly polarized light of a predetermined direction when natural light is incident, due to reflection from a backlight of a liquid crystal display device or the back side, and transmitting other light. Is. Inject light from a light source such as a backlight,
The transmitted light having a predetermined polarization state is obtained, and the light other than the predetermined polarization state is reflected without being transmitted. The light reflected on the surface of the brightness enhancement film is further re-incident on the brightness enhancement plate by reversing it through a reflection layer or the like provided on the back side thereof, and a part or all of the light is transmitted as light having a predetermined polarization state, The brightness can be improved by increasing the amount of light transmitted through the brightness enhancement film and by supplying polarized light that is difficult to be absorbed by the polarizer to increase the amount of light that can be used for liquid crystal image display and the like. When light enters from the back side of the liquid crystal cell through a polarizer without using a brightness enhancement film, almost all light with a polarization direction that does not match the polarization axis of the polarizer is absorbed by the polarizer. It will not be transmitted through the polarizer. That is, although depending on the characteristics of the polarizer used, about 50% of light is absorbed by the polarizer, and the amount of light that can be used for liquid crystal image display and the like is reduced accordingly, and the image becomes dark. The brightness enhancement film allows light having a polarization direction that is absorbed by the polarizer to be reflected by the brightness enhancement film once without entering the polarizer and then inverted through a reflection layer or the like provided behind it. And then re-incident on the brightness enhancement plate. Then, the polarization direction of the light reflected and inverted between the both is transmitted only to the polarization whose polarization direction is such that it can pass through the polarizer, and is supplied to the polarizer. It can be efficiently used for displaying an image on a liquid crystal display device, and the screen can be brightened.

The brightness enhancement film is not particularly limited, and other materials such as a multilayered thin film of a dielectric or a multilayered laminate of thin films having different refractive index anisotropies can be transmitted through linearly polarized light having a predetermined polarization axis. The light may be one that exhibits a characteristic of being reflected. In addition, a cholesteric liquid crystal layer, in particular, an oriented film of a cholesteric liquid crystal polymer or one in which the oriented liquid crystal layer is supported on a film substrate, shows a property of reflecting circularly polarized light on one of the left and right sides and transmitting other light. May be.

Therefore, in a brightness enhancement film of the type that transmits linearly polarized light of a predetermined polarization axis, the transmitted light is directly incident on the polarizing plate with its polarization axis aligned, and the absorption loss due to the polarizing plate is suppressed and the efficiency is improved. Can be transmitted. On the other hand, in a brightness enhancement film of a type that transmits circularly polarized light like a cholesteric liquid crystal layer, it can be directly incident on a polarizer, but 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 ¼ wavelength plate as the retardation plate, circularly polarized light can be converted into linearly polarized light.

A retardation plate that functions as a quarter-wave plate in a wide wavelength range such as a visible light region is a retardation layer that functions as a quarter-wave plate for monochromatic light such as light having a wavelength of 550 nm. It can be obtained by a method of superimposing a retardation layer showing the retardation characteristic of (for example, a retardation layer functioning as a half-wave plate). Therefore, the retardation plate disposed between the polarizing plate and the brightness enhancement film may be one layer or two or more retardation layers. The cholesteric liquid crystal layers can also have a structure in which two or more layers are superposed by combining layers having different reflection wavelengths. Thereby, it is possible to obtain a circularly polarized light that reflects in a wide wavelength range such as a visible light region, and based on that, it is possible to obtain a 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. Therefore, it may be a reflective elliptical polarizing plate or a semi-transmissive elliptical polarizing plate in which the above reflective polarizing plate or semi-transmissive polarizing plate is combined with a retardation plate.

The optical member having two or three or more optical layers laminated can be formed by a method of sequentially laminating separately in the manufacturing process of a liquid crystal display device or the like. The optical member is excellent in quality stability and assembling workability, and has an advantage of being able to improve manufacturing efficiency of liquid crystal display devices and the like. In addition, an appropriate adhesion means such as an adhesive layer can be used for the lamination.

An adhesive layer for adhering to other members such as a liquid crystal cell may be provided on the above-mentioned polarizing plate or optical member. The pressure-sensitive adhesive layer can be formed from a suitable conventional pressure-sensitive adhesive such as acrylic. In particular, in terms of prevention of foaming phenomenon and peeling phenomenon due to moisture absorption, deterioration of optical characteristics due to thermal expansion difference and the like, prevention of warpage of liquid crystal cells, and further formation of a liquid crystal display device having high quality and excellent durability, the moisture absorption rate is high. The adhesive layer is preferably low and has excellent heat resistance. It is also possible to form an adhesive layer containing fine particles and exhibiting light diffusivity. The pressure-sensitive adhesive layer may be provided on a necessary surface as necessary. For example, if a protective layer of a polarizing plate comprising a polarizing film and a protective layer is mentioned, a pressure-sensitive adhesive layer may be provided on one side or both sides of the protective layer, if necessary. Should be provided.

The thickness of the pressure-sensitive adhesive layer is not particularly limited, but is preferably 5 to 30 μm, more preferably 10 to 25 μm, and particularly preferably 15 to 25 μm. By setting the thickness of the adhesive layer in this range, the stress generated when the polarizing plate behaves in a dimensional manner is relaxed,
This is because it is possible to prevent a phenomenon in which the surface of the polarizing plate is stained by the adhesive.

When the pressure-sensitive adhesive layer provided on the polarizing plate or the like is exposed on the surface, it is preferable to cover the pressure-sensitive adhesive layer with a separator for the purpose of preventing contamination until practical use. The separator is formed by a method in which a suitable thin sheet conforming to the above-mentioned transparent protective film or the like is provided with a release coat using a suitable release agent such as silicone-based or long-chain alkyl-based, fluorine-based or molybdenum sulfide as necessary. be able to.

Each layer such as the polarizing film and the transparent protective film forming the polarizing plate and the optical member, the optical layer and the pressure-sensitive adhesive layer is, for example, a salicylate compound, a benzophenone compound, a benzotriazole compound or a cyanoacrylate compound. It may be one having an ultraviolet absorbing ability by an appropriate method such as a method of treating with an ultraviolet absorber such as a compound or a nickel complex salt compound.

The polarizing plate and the liquid crystal display element of the present invention can be preferably used for forming various devices such as a liquid crystal display device. For example, a reflective type in which a polarizing plate is arranged on one side or both sides of a liquid crystal cell is used. It can be used for a semi-transmissive type or a transmissive / reflective type liquid crystal display device. The liquid crystal cell forming the liquid crystal display device is arbitrary, and 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 twist nematic type or a super twist nematic type, etc. The liquid crystal cell 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, when forming the liquid crystal display device, one or two or more layers can be arranged at appropriate positions with appropriate components such as a prism array sheet, a lens array sheet, a light diffusion plate, and a backlight.

[0059]

EXAMPLES Next, the present invention will be described with reference to Examples and Comparative Examples.
A more specific description will be given. In the following examples and the like, "mass%" and "parts by mass" are abbreviated as "%" and "parts", respectively, unless otherwise specified.

Example 1 A polyvinyl alcohol film having a thickness of 40 μm was immersed in a dyeing bath containing iodine and potassium iodide for dyeing and stretching about 3 times, and boric acid and potassium iodide were added. After performing stretching and cross-linking treatment in the acid bath to a total of 6 times,
A polarizer having a thickness of 15 μm was obtained by drying. An adhesive consisting of a 7% polyvinyl alcohol aqueous solution was applied to both sides of this polarizer, and a triacetyl cellulose film having a thickness of 80 μm, the adhesive surface of which was saponified with a caustic soda aqueous solution, was pasted and dried under heating at 70 ° C. Total thickness by doing 1
A 75 μm polarizing plate was obtained. An adhesive having a thickness of 25 μm was applied to one side of the polarizing plate in order to attach it to the cell.

(Example 2) An adhesive consisting of a 7% aqueous solution of polyvinyl alcohol was applied to both sides of a polarizer prepared in the same manner as in Example 1, and the adhesive surface was saponified with an aqueous solution of caustic soda to give a thickness of 40 µm. A triacetyl cellulose film was attached and dried under heating at 70 ° C. to obtain a polarizing plate having a total thickness of 95 μm. An adhesive having a thickness of 25 μm was applied to one side of the polarizing plate in order to attach it to the cell.

Example 3 A polyvinyl alcohol film having a thickness of 75 μm was immersed in a dyeing bath containing iodine and potassium iodide for dyeing treatment and stretching about 3 times, and boric acid and potassium iodide were added. In the acidic bath, stretching treatment and crosslinking treatment were carried out so as to obtain a total of 4.5 times, and then it was dried to obtain a polarizer having a thickness of 28 μm. An adhesive consisting of a 7% polyvinyl alcohol aqueous solution was applied to both sides of this polarizer, and a triacetyl cellulose film having a thickness of 80 μm, the adhesive surface of which was saponified with a caustic soda aqueous solution, was pasted and dried under heating at 70 ° C. By doing so, a polarizing plate having a total thickness of 188 μm was obtained. An adhesive having a thickness of 25 μm was applied to one side of the polarizing plate in order to attach it to the cell.

Comparative Example 1 A polyvinyl alcohol film having a thickness of 75 μm was immersed in a dyeing bath containing iodine and potassium iodide for dyeing and stretching about 3 times, and boric acid and potassium iodide were added. After performing stretching and cross-linking treatment in the acid bath to a total of 6 times,
It was dried to obtain a polarizer having a thickness of 25 μm. An adhesive consisting of a 7% polyvinyl alcohol aqueous solution was applied to both sides of this polarizer, and a triacetyl cellulose film having a thickness of 80 μm, the adhesive surface of which was saponified with a caustic soda aqueous solution, was pasted and dried under heating at 70 ° C. Total thickness by doing 1
A polarizing plate of 85 μm was obtained. An adhesive having a thickness of 25 μm was applied to one side of the polarizing plate in order to attach it to the cell.

Comparative Example 2 A polarizer made in the same manner as in Example 1 was coated with an adhesive consisting of a 7% polyvinyl alcohol aqueous solution on both sides, and the adhesive surface was saponified with a caustic soda aqueous solution to give a thickness of 40 μm. A triacetyl cellulose film was attached and dried under heating at 70 ° C. to obtain a polarizing plate having a total thickness of 105 μm. An adhesive having a thickness of 25 μm was applied to one side of the polarizing plate in order to attach it to the cell.

Comparative Example 3 A polyvinyl alcohol film having a thickness of 75 μm was immersed in a dyeing bath containing iodine and potassium iodide for dyeing and stretching about 3 times, and boric acid and potassium iodide were added. After stretching and cross-linking treatment in the acidic bath to a total of 5.5 times, the film was dried to obtain a polarizer having a thickness of 26 μm. An adhesive consisting of a 7% polyvinyl alcohol aqueous solution was applied to both sides of this polarizer, and a triacetyl cellulose film having a thickness of 80 μm, the adhesive surface of which was saponified with a caustic soda aqueous solution, was pasted and dried under heating at 70 ° C. By doing so, a polarizing plate having a total thickness of 186 μm was obtained. An adhesive having a thickness of 25 μm was applied to one side of the polarizing plate in order to attach it to the cell.

The characteristics of the polarizing plates prepared in Examples and Comparative Examples were evaluated by the following methods. The evaluation results are shown in Table 1.

(Warping Stress) The polarizing plates with pressure-sensitive adhesive prepared in Examples and Comparative Examples were cut into a size of 100 mm × 100 mm, and a size of 105 × 105 mm was obtained.
It is attached to a 4 mm plastic substrate (made by Nitto Denko, epoxy resin plastic substrate) and left under heating conditions at 70 ° C. for 24 hours. The warp force of each plastic substrate with a polarizing plate after standing is measured with a force gauge to determine the warp stress [N / mm ³ ] and the warp amount [mm].

(Dimensional change during heating) The polarizing plates prepared in Examples and Comparative Examples were cut into a size of 50 mm × 50 mm and heated at 70 ° C. for 24 hours. The dimension (Lb) in the absorption axis (MD) direction before the heating test of the test piece and the dimension (La) in the absorption axis (MD) direction after the heating test were measured, and the dimensional change rate (%) was calculated from the following formula. Ask.

[0069] Dimensional change rate = [(La−Lb) / Lb] × 100

[0070]

[Table 1] Warp stress MD dimensional change rate Warp amount [N / mm ³ ] [%] [mm] Example 1 0.39 −0.82 5.3 Comparative Example 1 0.55 −0.83 7.9 Example 2 0.44-1.26 10.5 Comparative Example 2 0.54-1.29 13.0 Example 3 0.34-0.88 4.8 Comparative Example 3 0.50-0.81 9.0 Plastic Board only 0.04-0.15 1.9

As is clear from Table 1, comparison with Example 1
Example 1, Example 2 and Comparative Example 2, Example 3 and Comparative Example 3
Comparing each, the MD dimensional change rate is the same, but
There is a difference in bending stress, and the polarizing plate of the example
Is small and the warp amount of the substrate is also reduced. This result
And the elastic modulus is 1.4 × 10³~ 3.5 x 10³N / mm ²
Polarizing plate on 0.4mm thick plastic substrate in the range of
Plastic when laminated and subjected to 70 ° C heating test
The warp stress of the substrate is 0.04 to 0.48 N / m³In the range of
The problem of panel warpage caused by using a certain polarizing plate
It can be seen that it can be reduced to a level that does not exist.

Further, a retardation plate was adhered to the polarizing plates prepared in Examples 1 to 3 through an acrylic adhesive layer to prepare a circularly polarizing plate, and this circularly polarizing plate was attached to one side (upper side) of the STN type liquid crystal cell. The retardation plate is attached to the substrate (viewing side) so that it is on the substrate side of the liquid crystal cell, and only the polarizing plate obtained in each example is attached to the opposite side of the cell (lower substrate: backlight side). A liquid crystal display device was produced by combining them. When this display device was used for a long time, almost no color loss was observed at the edge of the panel and variation in hue within the panel surface was not observed.

[0073]

As described above, since the polarizing plate of the present invention has a warp stress of the plastic substrate of 0.04 to 0.48 N / m ³ when bonded to the plastic substrate, the polarizing plate alone is used. As compared with the case where the dimensional change rate is controlled, it is possible to realize a polarizing plate in which the load on the substrate is further reduced and the warp amount of the substrate is small. Therefore, when mounted on a liquid crystal display device, it is possible to provide a display display with a small change in hue. Therefore, it becomes possible to realize a liquid crystal display using a large-sized plastic substrate, which is of great industrial value.

[Brief description of drawings]

FIG. 1 is a conceptual diagram (front view) showing a method for measuring the amount of warpage of a plastic substrate.

FIG. 2 is a conceptual diagram (cross-sectional view) showing a method for measuring the amount of warpage of a plastic substrate.

[Explanation of symbols]

1 plastic substrate 2 Polarizer 3 plastic substrate fixing plate 4 Presser plate 5 Force gauge

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kazuhiro Higashi             1-2 1-2 Shimohozumi, Ibaraki City, Osaka Prefecture Nitto             Electric Works Co., Ltd. (72) Inventor Seiichi Kusumoto             1-2 1-2 Shimohozumi, Ibaraki City, Osaka Prefecture Nitto             Electric Works Co., Ltd. (72) Inventor Yuji Suiki             1-2 1-2 Shimohozumi, Ibaraki City, Osaka Prefecture Nitto             Electric Works Co., Ltd. F-term (reference) 2H049 BA02 BA03 BA04 BA25 BA26                       BA27 BB03 BB43 BB46 BB48                       BB49 BB54 BB62 BC03 BC14                       BC22                 2H091 FA08X FA08Z FA11X FA11Z                       FB02 FC07 FC08 FC09 FD06                       GA01 LA02 LA16 LA20

Claims (7)

[Claims] 1. An elastic modulus of 1.4 × 10 with a thickness of 0.4 mm.
^When bonded to a plastic substrate in the range of ^{3 to} 3.5 × 10 ³ N / mm ² via an adhesive layer so that the absorption axis is 90 °, and when left in the bonded state at 70 ° C. for 24 hours , The warp stress of the plastic substrate is 0.04 to 0.
A polarizing plate characterized by being in the range of 48 N / m ³ . 2. The polarizing plate according to claim 1, wherein the polarizing plate is formed by bonding protective films to both sides of a polarizer formed by dyeing, crosslinking, stretching and drying a polyvinyl alcohol film. . 3. The polarizing plate according to claim 1, wherein an adhesive layer is formed on at least one surface of the polarizing plate. 4. The polarizing plate according to claim 1, wherein the adhesive layer has a thickness of 5 to 30 μm. 5. A polarizing plate comprising a laminated body of the polarizing plate according to claim 1 and a retardation plate. 6. A liquid crystal display device comprising the polarizing plate according to claim 1 attached to at least one surface of a liquid crystal cell. 7. The liquid crystal display device according to claim 6, wherein the substrate forming the liquid crystal cell is a plastic substrate.