JP2002372621A - Polarizing plate and display device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizing plate and a display device using the plate which is thin and excellent in durability with little warpage. SOLUTION: The polarizing plate is produced by laminating a protective film on at least one surface of a polarizer so that the total thickness of the polarizer and the protective film is <=135 μm. The polarizing plate has at least one resin layer between the polarizer and the protective film layer or on the surface of the polarizing plate. When the polarizing plate is left to stand for 120 hours under the heating and moisturizing conditions of at 60 deg.C and 90%RH, the dimensional change rate in the direction along the absorption axis of the polarizing plate is <=0.40%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to various display devices,
In particular, the present invention relates to a polarizing plate used for a liquid crystal display device (hereinafter, may be abbreviated as LCD) and a display device using the same.

[0002]

2. Description of the Related Art Liquid crystal display devices (LCDs) are used in desk-top electronic calculators, electronic watches, personal computers, word processors, instruments for automobiles and machines, etc., but their use has been expanding, and in recent years they have been used as monitors. And T
V applications tend to increase. In addition, flat displays (FPDs) other than LCDs, such as plasma display panels (PDPs), organic light emitting diodes (OLEDs), and field emission display (FED) panels, are also on the rise. The screen size is increasing for monitors and TV applications. However, when the screen size of the LCD is increased, the polarizing plate used in the LCD is naturally also increased in size.

[0003]

However, when the size of the polarizing plate is increased, the liquid crystal panel is warped due to environmental changes such as humidification and heating, and the warpage of the panel causes display unevenness at the periphery of the screen. And the display quality is degraded.

[0004] Further, LCDs are characterized by being thin and lightweight, and there is a demand for further reduction in the thickness of glass and polarizing plates used in liquid crystal cells. However, when the glass thickness is reduced, the rigidity of the liquid crystal cell decreases, and the amount of warpage of the liquid crystal panel tends to increase. On the other hand, in order to reduce the thickness of the polarizing plate, a protective layer (a triacetate film) of the polarizing plate is used. Even if the thickness of ()) is reduced, the amount of warpage of the liquid crystal panel tends to increase. Therefore, development of a polarizing plate which is thin and lightweight but has a small amount of warpage is required.

An object of the present invention is to provide a polarizing plate which is thin, durable and has a small amount of warpage, and a display device using the same, in order to solve the above problems.

[0006]

According to the present invention, a thin polarizing plate is formed by forming a thin resin layer on a protective film or the like constituting the polarizing plate so as not to affect the thickness of the polarizing plate. The dimensional change rate of the polarizing plate under heating and humidifying conditions can be suppressed to a certain value or less.
This is based on the finding that the liquid crystal panel has a small warpage and the display unevenness of the panel is improved, and is characterized in that the thickness of the polarizing plate is as thin as 135 μm or less.

That is, the polarizing plate of the present invention is designed such that the total thickness of the polarizer and the protective film is 135 μm or less.
A polarizing plate in which a protective film is attached to at least one surface of a polarizer, wherein the polarizing plate has at least one resin layer between the polarizer and the protective film or on the surface of the polarizing plate, and The dimensional change in the absorption axis direction of the polarizing plate when the polarizing plate is allowed to stand for 120 hours under a heating and humidifying condition of 60 ° C. and 90% RH is 0.40% or less.

In the polarizing plate of the present invention, the ratio of the thickness of the polarizer to the total thickness of the protective film (polarizer thickness / total thickness of the protective film) is preferably 0.25 or more and 0.38 or less.

In the polarizing plate, it is preferable that the resin layer is formed from a thermosetting resin.

Further, a polarizing plate of the present invention is characterized in that a reflecting plate or a semi-transmissive reflecting plate is bonded to the above-mentioned polarizing plate.

Further, a polarizing plate of the present invention is characterized in that a retardation plate or a λ plate is bonded to the above-mentioned polarizing plate.

Further, a polarizing plate of the present invention is characterized in that a viewing angle compensation film is bonded to the polarizing plate.

Further, the polarizing plate of the present invention is characterized in that a brightness enhancement film is bonded to the above-mentioned polarizing plate.

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

Further, an organic light emitting diode of the present invention is provided with the above-mentioned polarizing plate.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The polarizing plate of the present invention is a polarizing plate in which a protective film (protective layer) is attached to at least one surface of a polarizer, and the total thickness of the polarizer and the protective film is 135 μm or less. Thin, the polarizing plate has at least one
A resin layer is provided between the polarizer and the protective film or on the surface of the polarizing plate. In addition, the polarizing plate is
When left standing for 120 hours under heating and humidification conditions of 90 ° C. and 90% RH, the dimensional change rate of the polarizing plate in the absorption axis direction is as follows:
0.40% or less.

In the present invention, the total thickness of the polarizer and the protective film constituting the polarizing plate is limited to 135 μm or less. Is difficult to obtain. With this configuration, even if the thickness of the protective layer of the polarizing plate is reduced, the amount of warpage of the liquid crystal panel is 0.2 mm or less,
The size can be reduced so as not to affect the display. Further, the thickness ratio of the polarizer to the total thickness of the protective film (polarizer thickness / total thickness of the protective film) is 0.25 or more.
It is preferably 38 or less. If the ratio is less than 0.25, it is necessary to make the polarizer thin, which makes production difficult. If the ratio exceeds 0.38, the dimensional change of the polarizing plate tends to increase.

Here, the dimensional change rate was determined by cutting a polarizing plate having an absorption axis of 0 ° into a square of 10 cm × 10 cm and leaving the polarizing plate at 23 ° C. and 65% RH for 48 hours.
The polarizing plate was left standing for 120 hours under the humidifying condition of 60 ° C. and 90% RH, and the dimensions of the polarizing plate in the absorption axis direction before and after the humidification were measured and calculated by the following equation. Dimensional change rate (%) = [(dimension after humidification-dimension before humidification) / dimension before humidification] x 100

Next, the details of the polarizing plate of the present invention will be described.

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

The polarizer is formed by swelling a synthetic resin film in a water bath or the like before dyeing, if necessary, and then dyeing, crosslinking, stretching and drying by a conventional method. The thickness of the polarizer is not particularly limited, but is preferably 5 to
It is 60 μm, and particularly preferably 10 to 40 μm. If the thickness is less than 5 μm, it will be easy to break during stretching,
If the ratio exceeds swelling, uneven swelling occurs, and it is impossible to swell uniformly.

When the synthetic resin film is stretched, the total stretch ratio is preferably set in the range of 3 to 7 times, and particularly preferably in the range of 4 to 6 times. When the total stretching ratio is less than 3 times, it becomes impossible to obtain a polarizing plate having a high degree of polarization, and when the total stretching ratio exceeds 7 times, the film is easily broken. The stretching method and the number of stretching are not particularly limited, and may be performed in each step of dyeing and crosslinking, or may be performed in only one of the steps. Further, it may be performed plural times in the same step.

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-based film is particularly preferable in that the dyeability with iodine is good. Polyvinyl alcohol-based film, a polyvinyl alcohol-based resin, a casting method of casting an undiluted solution dissolved in water or an organic solvent, a casting method,
A film formed by an arbitrary method such as an extrusion method can be appropriately used. The degree of polymerization of the polyvinyl alcohol resin used is preferably from 100 to 5000, and from 1400 to 4
000 is more preferred. Further, the thickness of the polyvinyl alcohol-based film is preferably from 10 to 200 μm, particularly preferably from 30 to 120 μm. If the thickness exceeds 200 μm, it is difficult to dry during film formation and defects such as foaming are likely to occur. On the other hand, if the thickness is less than 10 μm, stretching becomes difficult.

The drying of the polarizer is carried out at a temperature of 10 to 50.
C., preferably at 20 to 45.degree. C., for 0.5 to 30 minutes, preferably 1 to 20 minutes.

An appropriate transparent film can be used as a protective film material serving as a transparent protective layer provided on one or both sides of a polarizer (polarizing film). 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 polyether sulfone resin, a polycarbonate resin, a polyamide resin, a polyimide resin, a polyolefin resin, a polynorbornene resin, and an acrylic resin. And the like, but are not limited thereto.

A transparent protective film that can be particularly preferably used in view of polarization characteristics and durability is a triacetyl cellulose film whose surface is saponified with an alkali or the like. The thickness of the transparent protective film is arbitrary, but is preferably from 20 to 130 μm, and particularly preferably from 30 to 100 μm, from the viewpoint of reducing the thickness of the polarizing plate. When transparent protective films are provided on both sides of the polarizing film, transparent protective films made of different polymers or the like may be used on the front and back sides.

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.

A method for forming a resin layer on the surface of the protective layer is as follows.
Although not particularly limited, for example, a solution obtained by diluting the resin material to an appropriate concentration with a solvent and adding an appropriate amount of a conventionally known polymerization initiator or the like as needed using a bar coater or the like is used. It can be manufactured by applying a coating on the surface of the above-mentioned protective film to form a coating. The coating method is not particularly limited, and a brush coating method, a spray coating method, a dipping method, a flow coating method, or the like can be employed. After the application, a suitable heat treatment is performed to remove the solvent, thereby forming a resin layer on the film surface. The thickness of the resin layer after drying does not affect the thickness of the polarizing plate,
It is preferably formed to be 1 to 10 μm,
Particularly preferably, it is 2 to 8 μm. Further, from the viewpoint of increasing the film strength, it is preferable that the resin layer is solidified by performing irradiation treatment with ultraviolet rays or the like as necessary after drying.

The resin material is not particularly limited, and any resin material can be used as long as it has high transparency and does not impair the optical characteristics of the polarizing plate. For example, a UV-curable urethane acrylate monomer, a thermosetting resin, or the like can be used.

The polarizing plate may have at least one resin layer between the polarizer and the protective layer or on the surface of the polarizing plate. Therefore, as described above, the polarizing plate of the present invention can be manufactured by forming a resin layer on one or both surfaces of the protective film and bonding the protective film on which the resin layer is formed to a polarizer. Alternatively, it can be manufactured by a method in which a resin layer is formed on the surface of a protective film or the like after bonding the polarizer and the protective film. In consideration of adhesiveness and the like, a method in which a resin layer is formed on one surface of the protective film, and the protective film is bonded to one or both surfaces of the polarizer with the surface on which the resin layer is formed facing outward is preferable.

The bonding treatment between the polarizer (polarizing film) and the transparent protective film as the protective layer is not particularly limited. For example, an adhesive composed of a vinyl alcohol polymer or boric acid Or an adhesive comprising at least a water-soluble cross-linking agent of a vinyl alcohol polymer such as borax, glutaraldehyde, melamine, and oxalic acid. Such an adhesive layer,
It can be formed as a coating and drying layer of an aqueous solution, etc. In preparing the aqueous solution, other additives and a catalyst such as an acid can be blended as necessary. In particular, it is preferable to use an adhesive made of polyvinyl alcohol in that the adhesiveness to PVA (polarizing film) is the best. After bonding the polarizer and the protective layer, at a temperature of 40 to 75 ° C,
The heat treatment is preferably performed at 60 to 75 ° C. The heat treatment is performed at the above temperature for 0.2 to 2 hours, preferably 0.5 to 2 hours.
It is better to do it for one hour.

The polarizing plate of the present invention has a total thickness of 135 μm or less and a dimensional change rate of 0.40 in the absorption axis direction of the polarizing plate when left standing for 120 hours under heating and humidification conditions of 60 ° C. and 90% RH. % Or less. The dimensional change rate includes the stretching ratio of the PVA film, the elastic modulus of the protective layer (that is, the type and the method of forming the protective film), the surface treatment conditions of the protective layer, and the drying conditions of the polarizer and the polarizing plate (drying temperature, drying time). ), Stretching conditions (stretching ratio, stretching speed) in a dyeing bath, a crosslinking bath, etc., and various conditions such as the thickness of a polarizer, etc., and can be achieved by adjusting these conditions.

Next, a polarizing plate in which a reflecting plate or a transflective plate, a retardation plate or a λ plate, a viewing angle compensation film and a brightness enhancement film are laminated on the polarizing plate of the present invention will be described.

The polarizing plate can be used as an optical member laminated with another optical layer in practical use. The optical layer is not particularly limited, and examples thereof include a reflection plate, a semi-transmission reflection plate, a retardation plate (including a λ plate such as a 波長 wavelength plate and a 波長 wavelength plate), a visual compensation film and a brightness enhancement film. One or more suitable optical layers that may be used for forming a liquid crystal display device or the like can be used. In particular, a polarizing plate of the present invention is further provided with a reflective plate or a transflective plate. Reflective polarizer or transflector polarizer,
An elliptically polarizing plate or a circular polarizing plate obtained by further laminating a retardation plate or a λ plate on the polarizing plate of the present invention, a polarizing plate obtained by further laminating a visual compensation film on the polarizing plate of the present invention, or the polarized light of the present invention A polarizing plate in which a brightness enhancement film is further laminated on the plate is preferable.

Here, when a polarizing plate is laminated with a reflecting plate or a transflective plate, a retardation plate or a λ plate, a viewing angle compensation film, a brightness enhancement film, or the like, an appropriate bonding means such as an adhesive or a pressure-sensitive adhesive is used. Can be bonded together. As the adhesive or pressure-sensitive adhesive, for example, an acrylic, silicone, polyester, polyurethane, polyether, rubber-based or the like can be used, and among them, from the viewpoint of heat resistance and optical characteristics, etc. Acrylic materials are preferably used. The lamination of the polarizing plate and the reflection plate can be performed by a method of sequentially and separately laminating in the manufacturing process of the liquid crystal display device, but they may be laminated in advance. Thereby, there is an advantage that the stability of quality, the laminating workability, and the like are excellent, and the manufacturing efficiency of the liquid crystal display device can be improved.

Next, a description will be given of a reflective polarizing plate or a transflective polarizing plate in which a reflecting plate or a semi-transmissive reflecting plate is further laminated on the above-mentioned polarizing plate comprising a polarizer and a protective layer.

The reflector is provided on a polarizing plate to form a reflective polarizing plate. The reflection type polarizing plate is usually arranged on the back side of the liquid crystal cell, and forms a liquid crystal display device (reflection type liquid crystal display device) which reflects incident light from the viewing side (display side) to display. The reflective polarizer is
There is an advantage that the incorporation of a light source such as a backlight can be omitted and the thickness of the liquid crystal display device can be easily reduced. 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 surface of the polarizing plate. Specific examples thereof include a transparent protective film that has been matted as required, and a reflective layer formed by attaching a foil or a vapor-deposited film made of a reflective metal such as aluminum on one surface.

Further, a reflective polarizing plate having a reflective layer on which the fine uneven structure is reflected on the transparent protective film having a fine uneven structure on the surface by containing fine particles may be used. The reflection layer having the fine surface irregularity structure has an advantage that diffused incident light is diffused by irregular reflection, directivity and glare can be prevented, and uneven brightness can be suppressed. 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 an evaporation method such as a vacuum evaporation method, an ion plating method, and a sputtering method, and a plating method. . Further, the reflection plate can be used as a reflection sheet or the like in which a reflection layer is provided on an appropriate film conforming to the transparent protection film, instead of directly attaching the reflection plate to the transparent protection film.

The transflective polarizing plate is a transflective reflective layer in the above-mentioned reflective polarizer, and includes a half mirror that reflects and transmits light on the reflective layer.
A transflective polarizing plate is usually provided on the back side of a liquid crystal cell. When a liquid crystal display device or the like is used in a relatively bright atmosphere, an image is displayed by reflecting incident light from the viewing side (display side). In a relatively dark atmosphere, a liquid crystal display device or the like that displays an image using a built-in light source such as a backlight built in the back side of a transflective polarizing plate is 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 or a λ plate is further laminated on the above-mentioned polarizing plate comprising a polarizer and a protective layer will be described.

The phase difference plate is used to change linearly polarized light to elliptically polarized light or circularly polarized light, to change elliptically polarized light or circularly polarized light to linearly polarized light, or to change 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. 1/2 wavelength plate (also called λ / 2 plate)
Is usually used to change the polarization direction of linearly polarized light.

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

Here, examples of the retardation plate include a birefringent film formed by stretching a polymer film, an alignment film of a liquid crystal polymer, and an alignment layer of a liquid crystal polymer supported by a film. As a polymer,
Examples include polycarbonate, polyvinyl alcohol, polystyrene, polymethyl methacrylate, polypropylene and other polyolefins, polyarylate, polyamide, polynorbornene, 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 a normal retardation plate, a polymer film having birefringence, which is uniaxially stretched in the plane direction, is used,
The retardation plate used as a viewing angle compensation film controls the birefringent polymer film biaxially stretched in the plane direction and the refractive index in the thickness direction stretched uniaxially in the plane direction and also stretched in the thickness direction. A bidirectionally stretched film such as a tilted oriented polymer film is used. Examples of the obliquely oriented film include 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, and a film obtained by obliquely orienting a liquid crystal polymer. Is mentioned. As the raw material polymer of the retardation plate, the same polymer as the polymer used in the above retardation plate is used.

Next, a polarizing plate in which a brightness enhancement film is further laminated on the above-described polarizing plate comprising a polarizer and a protective layer will be described.

This polarizing plate is usually provided and used on the back side of a liquid crystal cell. The brightness enhancement film exhibits the property of reflecting linearly polarized light with a predetermined polarization axis or circularly polarized light in a predetermined direction when natural light is incident due to reflection from the backlight or the back side of a liquid crystal display device, etc., and transmits other light. It is. Inject light from a light source such as a backlight,
The transmitted light in the predetermined polarization state is obtained, and light other than the predetermined polarization state is reflected without transmitting. The light reflected on the surface of the brightness enhancement film is further reversed and incident again on the brightness enhancement plate via a reflection layer or the like provided on the rear side thereof, and a part or all of the light is transmitted as light in a predetermined polarization state, In addition to increasing the amount of light transmitted through the brightness enhancement film, the polarizer is supplied with polarized light that is hardly absorbed, thereby increasing the amount of light that can be used for liquid crystal image display and the like, thereby improving brightness. When light is incident from the back side of the liquid crystal cell through a polarizer with a backlight or the like without using a brightness enhancement film, light having a polarization direction that does not match the polarization axis of the polarizer is almost absorbed by the polarizer. And does not pass through the polarizer. That is, although it depends on the characteristics of the polarizer used, about 50% of the light is absorbed by the polarizer, and accordingly, the amount of light available for liquid crystal image display and the like is reduced, and the image becomes dark. The brightness enhancement film reflects light having a polarization direction that is absorbed by the polarizer into the polarizer, reflects the light once on the brightness enhancement film, and further inverts the light through a reflection layer and the like provided on the rear side. Then, re-incident on the brightness enhancement plate is repeated. Then, only the polarized light whose polarization direction is reflected and inverted between the two and has a polarization direction that can pass through the polarizer is transmitted and supplied to the polarizer. The liquid crystal display device can be efficiently used for displaying an image, and the screen can be brightened.

The brightness enhancement film is not particularly limited as long as it has a property of reflecting either left-handed or right-handed circularly polarized light and transmitting the other light. For example, a multilayer thin film of a dielectric or a multilayer laminate of thin films having different refractive index anisotropies may be used. Among them, a cholesteric liquid crystal layer, particularly an alignment film of a cholesteric liquid crystal polymer, and a film in which the alignment liquid crystal layer is supported on a film substrate are preferable. Therefore, in a brightness enhancement film of a type that transmits linearly polarized light having a predetermined polarization axis, the transmitted light is incident on the polarizing plate with the polarization axis aligned as it is, thereby efficiently transmitting the light while suppressing the absorption loss by the polarizing plate. Can be. 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 retardation layer functioning as a half-wave plate) having the above retardation characteristic. Accordingly, 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 can also be a combination of two or three or more layers having different reflection wavelengths so as to have an overlapping structure. Thereby, it is possible to obtain circularly polarized light that reflects circularly polarized light in a wide wavelength range such as a visible light range, and it is possible to obtain transmitted circularly polarized light in a wide wavelength range based on the reflected light.

The polarizing plate may be formed by laminating a polarizing plate and two or three or more optical layers. 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.
An optical member formed by laminating in advance has an advantage that it is excellent in quality stability, assembling workability, and the like, and can improve the manufacturing efficiency of a liquid crystal display device and the like. In addition, an appropriate adhesive means such as an adhesive can be used for lamination, and the same adhesive or adhesive as described above is used.

The polarizing plate and the optical member of the present invention may be provided with an adhesive layer for bonding to a member such as a liquid crystal cell. The pressure-sensitive adhesive used for forming the pressure-sensitive adhesive layer is not particularly limited,
For example, acrylic, silicone, polyester,
Appropriate materials such as polyurethane, polyether, and rubber can be used. An acrylic pressure-sensitive adhesive having a low moisture absorption rate and excellent heat resistance is preferable from the viewpoints of preventing a foaming phenomenon and a peeling phenomenon due to moisture absorption, a decrease in optical characteristics due to a difference in thermal expansion, and a prevention of warpage of a liquid crystal cell. Thus, a liquid crystal display device having high quality and excellent durability can be formed.
Further, an adhesive layer or the like which contains fine particles and exhibits light diffusibility can be used. The adhesive layer may be provided on a necessary surface as needed. For example, when referring to a protective layer of a polarizing plate comprising a polarizer and a protective layer, an adhesive layer may be provided on one side or both sides of the protective layer as needed.

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

The layers such as the polarizer and the transparent protective film, the optical layer and the adhesive layer which form the polarizing plate and the optical member are made of, for example, salicylic acid ester compounds, benzophenone compounds, benzotriazole compounds and cyanoacrylate compounds. A compound which has been treated with an ultraviolet absorbent such as a compound or a nickel complex compound and has an ultraviolet absorbing ability may be used.

The polarizing plate of the present invention can be preferably used for forming various display devices such as a liquid crystal display device. For example, a reflection type or a transflective type in which a polarizing plate is arranged on one side or both sides of a liquid crystal cell. Or a liquid crystal display device of a transmission / reflection type. 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.

Further, the elliptically polarizing plate or the circularly polarizing plate of the present invention can be used for a flat display (FPD) other than a liquid crystal display (LCD), for example, a plasma display panel (P).
DP), an organic light emitting diode (OLED), a field emission display (FED) panel, and the like.

[0057]

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

(Example 1) Degree of polymerization: 2400, thickness: 75 μm
m, a polyvinyl alcohol film is immersed in a dyeing bath of 40 ° C. containing iodine and potassium iodide to perform a dyeing treatment, and then a total stretching ratio in a 60 ° C. acid bath containing boric acid and potassium iodide is obtained. The stretching treatment and the cross-linking treatment were performed so as to be 5.3 times. After washing with water, the polarizer was dried at 40 ° C. to obtain a polarizer having a thickness of 28 μm. An adhesive composed of a 7% by mass aqueous solution of polyvinyl alcohol is applied to both surfaces of the polarizer, the adhesive surface is saponified on one surface with an aqueous solution of caustic soda, and the non-adhered surface is formed of a urethane acrylate resin layer (thickness). A 3 μm thick triacetyl cellulose (TAC) film having a thickness of 50 μm,
On the other surface, a 50 μm-thick triacetyl cellulose (TA) having the adhesive surface saponified with an aqueous solution of caustic soda was used.
C) After laminating the films, they were dried at 70 ° C. to produce a polarizing plate having a total thickness of 131 μm.

Incidentally, triacetyl cellulose (TAC)
The formation of the urethane acrylate resin layer on the film
The following method was used. 3.5 parts by mass of a benzophenone-based photopolymerization initiator was added to 100 parts by mass of an ultraviolet-curable urethane acrylate monomer, and a solvent for adjusting the viscosity was further added to prepare a solution having a solid content of 45% by mass. this,
One side of a TAC film having a thickness of 50 μm is coated with a bar coder, and after evaporating the solvent, it is irradiated with ultraviolet rays.
T having a urethane acrylate resin layer having a thickness of 3 μm
An AC film was obtained.

(Example 2) Degree of polymerization: 2400, thickness: 75 μm
m polyvinyl alcohol film was immersed in a 40 ° C. dyeing bath containing iodine and potassium iodide to perform a dyeing treatment, and then the total stretching ratio was increased in a 60 ° C. acid bath containing boric acid and potassium iodide. The stretching treatment and the cross-linking treatment were performed to 5.5 times. After being washed with water, it was dried at 42 ° C. to obtain a polarizer having a thickness of 27 μm. An adhesive composed of a 7% by mass aqueous solution of polyvinyl alcohol is applied to both surfaces of the polarizer, the adhesive surface is saponified on one surface with an aqueous solution of caustic soda, and the non-adhered surface is formed of a urethane acrylate resin layer (thickness). 3 μm) and a 40 μm-thick triacetyl cellulose (TAC) film,
On the other side, a 40 μm-thick triacetyl cellulose (TA) saponified on an adhesive surface with an aqueous solution of caustic soda.
C) After laminating the films, they were dried at 72 ° C. to produce a polarizing plate having a total thickness of 110 μm.

Incidentally, triacetyl cellulose (TAC)
The formation of the urethane acrylate resin layer on the film
The same method as in Example 1 was used. 3.5 parts by mass of a benzophenone-based photopolymerization initiator was added to 100 parts by mass of an ultraviolet-curable urethane acrylate monomer, and a solvent for adjusting the viscosity was further added to prepare a solution having a solid content of 45% by mass. This is placed on one side of a 40 μm thick TAC film,
After coating with a bar coder and evaporating the solvent, the film was irradiated with ultraviolet rays to obtain a TAC film having a urethane acrylate resin layer having a thickness of 3 μm.

Example 3 A polarizer having a thickness of 28 μm was manufactured in the same manner as in Example 1. On both sides of this polarizer,
An adhesive consisting of a 7% by mass aqueous solution of polyvinyl alcohol was applied, and a layer made of a urethane acrylate resin (thickness: 3 μm) was formed on one side in the same manner as in Example 1.
m), a 50 μm-thick triacetyl cellulose (TAC) film was stuck so that the urethane resin layer became an adhesive surface, and the other surface was saponified with a sodium hydroxide aqueous solution. A 50 μm-thick triacetyl cellulose (TAC) film is attached,
It dried at ° C and produced the polarizing plate of 131 micrometers in total thickness.

Example 4 A polarizer having a thickness of 28 μm was manufactured in the same manner as in Example 1. On both sides of this polarizer,
An adhesive consisting of a 7% by mass aqueous solution of polyvinyl alcohol is applied, and the bonding surface is saponified with an aqueous solution of caustic soda.
A 50 μm thick triacetyl cellulose (TAC) film having a urethane acrylate resin layer (thickness 3 μm) provided on the non-adhesive surface is bonded to both surfaces of the polarizer, and then dried at 70 ° C. A polarizing plate having a thickness of 134 μm was produced.

Example 5 A polarizer having a thickness of 27 μm was manufactured in the same manner as in Example 2. On both sides of this polarizer,
After applying an adhesive composed of a 7% by mass aqueous solution of polyvinyl alcohol, and bonding a layer of urethane acrylate resin (thickness: 3 μm) on both sides, a 40 μm thick triacetyl cellulose (TAC) film, 7
After drying at 2 ° C., a polarizing plate having a total thickness of 119 μm was prepared.

Incidentally, triacetyl cellulose (TAC)
The formation of the urethane acrylate resin layer on the film
Using a method similar to that of Example 1, a urethane acrylate resin layer having a thickness of 3 μm was formed on both sides of a TAC film having a thickness of 40 μm.

Comparative Example 1 A polarizer having a thickness of 27 μm was produced in the same manner as in Example 2. On both sides of this polarizer,
An 80 μm-thick triacetylcellulose (TAC) film having an adhesive surface coated with a 7% by mass aqueous solution of polyvinyl alcohol and having an adhesive surface saponified with an aqueous solution of caustic soda is attached to both surfaces of the polarizer, and then heated to 70 ° C. To produce a polarizing plate having a total thickness of 187 μm.

(Comparative Example 2) The stretching ratio of the polarizer was 5.4.
A 25 μm-thick polarizer was produced in the same manner as in Example 1 except that the drying temperature was 35 ° C. An adhesive consisting of a 7% by mass aqueous solution of polyvinyl alcohol was applied to both surfaces of this polarizer, and the adhesive surface was saponified with an aqueous solution of caustic soda.
AC) After laminating the film on both sides of the polarizer, 7
By drying at 0 ° C., a polarizing plate having a total thickness of 125 μm was prepared.

Comparative Example 3 A polarizer having a thickness of 27 μm was produced in the same manner as in Example 2. On both sides of this polarizer,
An adhesive made of a 7% by mass aqueous solution of polyvinyl alcohol is applied, and a 40 μm-thick triacetylcellulose (TAC) film whose adhesive surface is saponified with an aqueous solution of caustic soda is attached to both surfaces of the polarizer. To produce a polarizing plate having a total thickness of 107 μm.

The performance of the polarizing plates produced in the examples and comparative examples was evaluated by the following methods. Tables 1 and 2 show the results together with the thicknesses of the polarizer and the protective layer.

(Dimensional change rate) The polarizing plate (absorption axis 0 degree) is set to 1
Cut into a square of 0 cm x 10 cm,
After being left for 48 hours under the condition of 5% RH, the temperature is 60 ° C. and 90%
It left still for 120 hours under the humidification condition of RH. The dimensions of the polarizing plate in the direction of the absorption axis before and after humidification were measured, and the dimensional change was calculated from the following equation. Dimensional change rate (%) = [(dimension after humidification-dimension before humidification) /
Dimension before humidification] x 100

(Amount of Warpage) The prepared polarizing plate (absorption axis 45)
Degrees) to 2 x 275 mm x 205 mm.
The sheet was cut out and two polarizing plates were bonded to both sides of a 13.3 inch liquid crystal cell such that the absorption axes were orthogonal (black display). With the polarizing plate attached to the liquid crystal cell, 6
The liquid crystal cell was left standing at 0 ° C. and 90% RH for 500 hours, and the amount of warpage of the liquid crystal cell after the test was measured. The measurement was performed by placing the liquid crystal cell 1 on the horizontal base 2 as shown in FIG. 1 and measuring the amount of warpage h (mm).

(Display Unevenness) After the above humidification test, the liquid crystal cell to which the polarizing plate was attached was placed on a backlight having an illuminance of 33000 Lux, and an experiment for confirming display unevenness of the liquid crystal cell was performed.

[0073]

[Table 1] Thickness (μm) Thickness ratio Dimensional change rate protective layer 1 Polarizer protective layer 2 Total thickness Polarizer / total protective layer (%) Example 1 53 28 50 131 0.27 0.30 Example 2 43 27 40 110 0.33 0.34 Example 3 53 28 50 131 0.27 0.35 Example 4 53 28 53 134 0.26 0.33 Example 5 46 27 46 119 0.29 0.34 Comparative Example 1 80 27 80 187 0.17 0.34 Comparative Example 2 50 25 50 125 0.25 0.45 Comparative Example 3 40 27 40 107 0.34 0.51

[0074]

Table 2 Amount of warpage of liquid crystal cell (mm) Display unevenness of liquid crystal cell Example 1 0.1 Small Example 2 0.2 Small Example 3 0.2 Small Example 4 0.1 Small Example 5 0. 2 small comparative example 1 0.1 small comparative example 2 0.4 large comparative example 3 0.6 large

As is evident from Tables 1 and 2, the polarizing plate of the present invention has a dimensional change rate in the direction of the absorption axis when the polarizing plate is placed under heating and humidification conditions of 60 ° C. and 90% RH for 120 hours. Is within 0.40%, so that the dimensional change rate is 0.40%.
%, The amount of warpage of the liquid crystal cell after the heating and humidifying treatment is smaller than that of the polarizing plate exceeding 50%. In addition, the polarizing plate of the present invention has a smaller amount of warpage of the liquid crystal cell and smaller display unevenness, similarly to the conventional polarizing plate, though it is thinner than the conventional polarizing plate (Comparative Example 1). .

[0076]

As described above, since the polarizing plate of the present invention has a small change in the absorption axis direction of the polarizing plate, the load applied to the plane of the liquid crystal cell becomes uniform due to expansion and contraction of the polarizing plate.
It is possible to eliminate the warpage of the panel, which is a problem in assembling the liquid crystal display device, and to obtain a polarizing plate having excellent durability. Therefore, even when the polarizing plate of the present invention is mounted on a large-sized liquid crystal panel, the warpage of the panel is reduced,
The display unevenness of the panel can be prevented. Therefore, its industrial value is great.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a warpage amount measurement.

[Explanation of symbols]

 1 liquid crystal cell 2 horizontal base

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[Procedure amendment]

[Submission date] August 22, 2001 (2001.8.2
2)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0048

[Correction method] Change

[Correction contents]

The brightness enhancing film is not particularly limited, and examples thereof include a multilayer thin film of a dielectric and a multilayer laminate of thin films having different refractive index anisotropies. Alternatively , a cholesteric liquid crystal layer, in particular, an oriented film of a cholesteric liquid crystal polymer, and a film in which the oriented liquid crystal layer is supported on a film substrate are preferable. Therefore, in a brightness enhancement film of a type that transmits linearly polarized light having a predetermined polarization axis, the transmitted light is incident on the polarizing plate with the polarization axis aligned as it is, thereby efficiently transmitting the light while suppressing the absorption loss by the polarizing plate. Can be. 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.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Atsushi Kitagawa 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation (72) Inventor Yuji Shiki 1-2-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation (72) Inventor Seiichi Kusumoto 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation (72) Yoichiro Sugino 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto F-term (reference) in Electric Works Co., Ltd.

Claims (9)

[Claims] 1. The total thickness of the polarizer and the protective film is 13
A polarizing plate comprising a polarizer and a protective film attached to at least one surface of the polarizer so as to have a thickness of 5 μm or less, wherein the polarizing plate includes at least one resin layer between the polarizer and the protective film or between the polarizer and the polarizing plate. The polarizing plate has a surface, and the dimensional change rate of the polarizing plate in the absorption axis direction when the polarizing plate is allowed to stand at 60 ° C. and 90% RH for 120 hours is 0.40% or less. The polarizing plate characterized by the above. 2. The thickness ratio of the polarizer to the total thickness of the protective film (polarizer thickness / total thickness of the protective film) is 0.25.
The polarizing plate according to claim 1, which is not less than 0.38. 3. The polarizing plate according to claim 1, wherein the resin layer is formed from a thermosetting resin. 4. A polarizing plate comprising the polarizing plate according to claim 1 and a reflecting plate or a semi-transmissive reflecting plate. 5. A polarizing plate comprising the polarizing plate according to claim 1 and a retardation plate or a λ plate bonded thereto. 6. A polarizing plate comprising the polarizing plate according to claim 1 and a viewing angle compensation film bonded thereto. 7. A polarizing plate comprising the polarizing plate according to claim 1 and a brightness enhancement film bonded thereto. 8. A liquid crystal display device, wherein the polarizing plate according to claim 4 is arranged on at least one side of a liquid crystal cell. 9. An organic light-emitting diode comprising the polarizing plate according to claim 5.