JP2004133356A - Polarizing plate, optical element and image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image display device having an excellent viewing angle expanding characteristic and capable of preventing the occurrence of image blurring. <P>SOLUTION: The polarizing plate has a transparent protective film at least on one side of a polarizer. Also, in the polarizing plate, there is installed a light diffusing layer between the polarizer and the transparent protective film. <P>COPYRIGHT: (C)2004,JPO

Description

表１の結果から明らかなように、偏光子と透明保護フィルムとの間に光拡散層を有する光学素子（実施例１、２）は、視野角が拡大し、かつ画像のぼやけもほとんど認められず鮮明性が良好であった。一方、視認側表面に光拡散層を有する光学素子（比較例１）は、視野角は拡大したが、画像のぼやけが発生し、鮮明性が悪かった。また、液晶セル側に光拡散層を有する偏光板（比較例２）は、視野角が拡大し、かつ画像のぼやけもほとんど認められず鮮明性が良好であったが、偏光解消によるコントラストの低下が起こった。光拡散層を設けなかった光学素子（比較例３）は、視野角特性及び画像の鮮明性のいずれも不良であった。
【図面の簡単な説明】
【図１】本発明の光学素子の断面図の一例である。
【図２】比較例１の光学素子の断面図の一例である。
【図３】比較例２の偏光板の断面図の一例である。
【符号の説明】
１：偏光子
２：透明保護フィルム
３：微粒子
４：光拡散層
５：接着剤層
６：接着層
７：偏光板
８：光学素子[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a polarizing plate used in various image display devices such as a liquid crystal display (LCD), an EL, and a PDP to increase a viewing angle and suppress a decrease in visibility of a screen, and an optical element using the polarizing plate. And an image display device.
[0002]
[Prior art]
The liquid crystal display device has been securing a solid position as a display through recent research and development. However, the LCD has a problem that the display characteristics change depending on the viewing angle and show good display characteristics when the LCD is viewed from the front, but become extremely difficult to see when viewed from an oblique direction. It is important to improve the viewing angle characteristics when using a TV for TV. As a method of improving the viewing angle characteristics, there are a method of providing a layer for canceling anisotropy in the liquid crystal layer and a method of changing a driving method of the liquid crystal, but any of these methods can obtain a sufficient viewing angle expanding effect. Not. There has also been proposed a method of providing a light diffusion layer on the front of a display.
[0003]
However, if the light diffusing property is provided until a sufficient viewing angle enlargement effect is obtained, image blur occurs. This is a problem because the visibility of a display device such as an LCD is reduced.
[0004]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION It is an object of the present invention to provide a polarizing plate having good viewing angle enlargement characteristics and little blurring of an image. Still another object is to provide an optical element provided with the polarizing plate and an image display device equipped with the optical element.
[0005]
[Means for Solving the Problems]
The present inventors have conducted intensive studies to solve the above problems, and as a result, have found that the above object can be achieved by the following polarizing plate and the like, and have completed the present invention.
[0006]
That is, the present invention relates to a polarizing plate having a transparent protective film on at least one surface of a polarizer, wherein the polarizing plate has a light diffusion layer between the polarizer and the transparent protective film.
[0007]
As described above, the polarizing plate of the present invention has the light diffusion layer provided between the polarizer and the transparent protective film. As a result, the viewing angle can be increased while suppressing blurring of the image.
[0008]
The present invention also relates to a polarizing plate having a transparent protective film on both surfaces of a polarizer and a light diffusion layer on one surface of the polarizer and between the polarizer and the transparent protective film.
[0009]
The polarizing plate preferably has a haze value of 70% or more. By setting the haze value to 70% or more, the viewing angle can be sufficiently expanded.
[0010]
In the polarizing plate, it is preferable that the light diffusion layer is made of a polyurethane resin containing fine particles. Polyurethane-based resins are preferably used because they have high adhesion to polarizers and transparent protective films, etc., have good cohesiveness of the resins themselves, and can efficiently form a light diffusion layer by a simple processing operation.
[0011]
Further, the present invention relates to an optical element using the polarizing plate.
[0012]
In the optical element, when the optical element is divided at a boundary surface between the light diffusion layer and the polarizer, a thickness from the boundary surface to a surface of the optical element including the polarizer is preferably 150 μm or less. By setting the thickness to 150 μm or less, blurring of an image can be effectively suppressed.
[0013]
Further, the present invention relates to an image display device equipped with the polarizing plate or the optical element.
[0014]
The present invention also relates to a liquid crystal display device having the polarizing plate or the optical element mounted on the viewing side of a liquid crystal cell.
[0015]
Furthermore, the present invention relates to a liquid crystal display device in which the polarizing plate or the optical element in which a light diffusion layer is disposed on the viewing side with respect to the polarizer is mounted on the viewing side of a liquid crystal cell.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an optical element 8 in which an adhesive layer 6 is formed on one surface of a polarizing plate 7 having a transparent protective film 2 on both surfaces of a polarizer 1. A light diffusion layer 4 containing fine particles 3 is formed on one surface of the polarizer 1 and between the polarizer 1 and the transparent protective film 2. On the other surface of the polarizer 1, an adhesive layer 5 is formed. L is the thickness from the boundary surface to the surface of the optical element including the polarizer 1 when the optical element 8 is divided at the boundary surface between the light diffusion layer 4 and the polarizer 1. FIG. 1 shows a case where the light diffusion layer 4 is formed on one side of the polarizer 1 and the adhesive layer 5 is formed on the other side. However, the light diffusion layers 4 are formed on both sides. You may.
[0017]
The polarizer 1 is not particularly limited, and various types can be used. Examples of the polarizer include a hydrophilic polymer film such as a polyvinyl alcohol-based film, a partially formalized polyvinyl alcohol-based film, an ethylene-vinyl acetate copolymer-based partially saponified film, and a dichromatic dye such as iodine or a dichroic dye. And uniaxially stretched by adsorbing a reactive substance, and a polyene-based oriented film such as a dehydrated product of polyvinyl alcohol and a dehydrochlorinated product of polyvinyl chloride. Among these, a polarizer comprising a dichroic substance such as a polyvinyl alcohol film and iodine is preferable. The thickness of these polarizers is not particularly limited, but is generally about 5 to 22 μm.
[0018]
A polarizer obtained by dyeing a polyvinyl alcohol-based film with iodine and uniaxially stretching can be produced by, for example, dyeing polyvinyl alcohol by immersing it in an aqueous solution of iodine and stretching the film to 3 to 7 times its original length. If necessary, it can be immersed in an aqueous solution of boric acid or potassium iodide. Further, if necessary, the polyvinyl alcohol-based film may be immersed in water and washed with water before dyeing. By washing the polyvinyl alcohol film with water, dirt on the surface of the polyvinyl alcohol film and an anti-blocking agent can be washed, and by swelling the polyvinyl alcohol film, it also has an effect of preventing unevenness such as uneven dyeing. is there. Stretching may be performed after dyeing with iodine, may be performed while dyeing, or may be dyed with iodine after stretching. Stretching can be performed in an aqueous solution of boric acid or potassium iodide or in a water bath.
[0019]
The light diffusion layer 4 is a layer having a viewing angle expansion characteristic and a light diffusion property, and further has an effect as an adhesive for bonding the polarizer 1 and the transparent protective film 2. The light diffusion layer 4 is made of the same resin as the adhesive layer 5 and differs from the adhesive layer 5 in that the light diffusion layer 4 contains the fine particles 3. Note that an adhesive layer may be separately provided between the light diffusion layer 4 and the polarizer 1 and / or the transparent protective film 2.
[0020]
As the resin forming the light diffusion layer 4, the fine particles 3 can be dispersed, the adhesion to the polarizer and the transparent protective film is high, the cohesiveness of the resin itself is good, and the transparent one is not particularly limited. Can be used. Examples of the resin include a polyurethane resin, a polyvinyl alcohol resin, and an aqueous polyester resin. In the present invention, it is preferable to use a polyurethane resin, and it is particularly preferable to use a water-soluble polyurethane resin. The resin is usually used as an adhesive composed of an aqueous solution.
[0021]
The polarizing plate 7 of the present invention is manufactured by, for example, bonding the transparent protective film 2 and the polarizer 1 using the adhesive. The application of the adhesive may be performed on either the transparent protective film 2 or the polarizer 1, or may be performed on both. After bonding, a drying step is performed to form the light diffusion layer 4 composed of a coating and drying layer. The bonding of the polarizer 1 and the transparent protective film 2 can be performed by a roll laminator or the like. The thickness of the light diffusion layer 4 is not particularly limited, but is usually about 1 to 50 μm. The adhesive layer 5 can also be formed by the same method as described above, and the thickness of the adhesive layer 5 is not particularly limited, but is usually about 1 to 50 μm.
[0022]
As the fine particles 3 to be dispersed in the light diffusion layer 4, those having transparency such as various metal oxides, glass, and plastics and having a different refractive index from the resin forming the light diffusion layer can be used without any particular limitation. be able to. For example, inorganic fine particles that may have conductivity such as silica, alumina, titania, zirconia, calcium oxide, tin oxide, indium oxide, cadmium oxide, antimony oxide, polymethyl methacrylate, polystyrene, polyurethane, and acrylic-styrene copolymer Or crosslinked or uncrosslinked organic fine particles or silicone fine particles made of various polymers such as benzoguanamine, melamine, and polycarbonate. Among these, spherical silica particles, spherical glass beads and spherical silicone particles are preferred. One or two or more of these fine particles 3 can be appropriately selected and used.
[0023]
The particle diameter of the fine particles 3 is not particularly limited as long as the particle diameter is smaller than the thickness of the light diffusion layer 4, and is appropriately adjusted so as to be equal to or less than the thickness of the light diffusion layer 4. Preferably it is 1 to 50 μm, more preferably 2 to 10 μm. If the particle diameter of the fine particles 3 is larger than the thickness of the light diffusion layer 4, the surface of the light diffusion layer becomes uneven, which is not preferable.
[0024]
The content of the fine particles 3 in the light diffusion layer 4 is not particularly limited as long as the effects of the present invention can be sufficiently exhibited, but is preferably 1 to 100 parts by weight, and more preferably 10 to 100 parts by weight with respect to 100 parts by weight of the light diffusion layer forming resin. It is preferably from 50 to 50 parts by weight. If the amount is less than 1 part by weight, a sufficient light diffusion function cannot be obtained, and if it exceeds 100 parts by weight, the adhesive strength of the light diffusion layer tends to decrease.
[0025]
The transparent protective film 2 preferably has excellent transparency, mechanical strength, heat stability, moisture shielding property, isotropy, and the like. For example, polyester polymers such as polyethylene terephthalate and polyethylene naphthalate, diacetyl cellulose, triacetyl Examples of the film include films made of transparent polymers such as cellulose polymers such as cellulose, polycarbonate polymers, and acrylic polymers such as polymethyl methacrylate. Styrene polymers such as polystyrene and acrylonitrile / styrene copolymer; polyethylene, polypropylene, polyolefins having a cyclic or norbornene structure; olefin polymers such as ethylene / propylene copolymer; vinyl chloride polymers; nylon and aromatic polyamides And a film made of a transparent polymer such as an amide-based polymer. Furthermore, imide polymers, sulfone polymers, polyethersulfone polymers, polyetheretherketone polymers, polyphenylene sulfide polymers, vinyl alcohol polymers, vinylidene chloride polymers, vinyl butyral polymers, arylate polymers, polyoxymethylene polymers Films made of transparent polymers such as polymers, epoxy polymers and blends of the above polymers are also included. In particular, those having low optical birefringence are preferably used. As the transparent protective film, a transparent protective film made of the same polymer material on the front and back may be used, or a transparent protective film made of a different polymer material or the like may be used.
[0026]
Although the thickness of the transparent protective film 2 can be determined as appropriate, it is generally about 10 to 200 μm, and particularly preferably 20 to 100 μm, from the viewpoints of strength, workability such as handleability, thinness, and the like.
[0027]
The surface of the transparent protective film 2 on which the light diffusion layer 4 is not adhered may be a hard coat layer or a surface which has been subjected to sticking prevention or a desired treatment. The hard coat treatment is performed for the purpose of preventing scratches on the surface of the polarizing plate, for example, by applying a suitable ultraviolet-curable resin such as an acrylic resin or a silicone resin to a cured film having excellent hardness and sliding properties, etc., as a transparent protective film. It can be formed by a method of adding to the surface of. In addition, the anti-sticking treatment is performed for the purpose of preventing adhesion to an adjacent layer. The hard coat layer, the anti-sticking layer and the like can be provided on the transparent protective film itself, or can be separately provided as an optical layer separately from the transparent protective film. Further, a low refractive index layer having an antireflection function can be provided. The material of the low refractive index layer is not particularly limited as long as it has a lower refractive index than that of the transparent protective film 2. For example, a low refractive index material such as fluorine-containing polysiloxane can be used. The thickness of the low refractive index layer is not particularly limited, but is preferably about 0.05 to 0.3 μm, particularly preferably 0.1 to 0.3 μm. An antireflection function can be provided by the low refractive index layer, and irregular reflection on the image surface of a display or the like can be effectively suppressed.
[0028]
In the present invention, the haze value of the polarizing plate having the light diffusion layer is preferably 70% or more, and more preferably 80% or more. When the haze value is 70% or more, a good viewing angle expanding effect is obtained.
[0029]
In practical use, another optical layer can be laminated on the polarizing plate to form an optical element. The optical layer is not particularly limited. For example, the optical layer is used for forming a liquid crystal display device such as a reflection plate, a semi-transmission plate, a retardation plate (including a wavelength plate such as 1/2 or 1/4), and a viewing angle compensation film. One or more optical layers that may be used may be used. In particular, a reflective polarizing plate or a semi-transmitting polarizing plate in which a reflecting plate or a transflective reflecting plate is further laminated on a polarizing plate, an elliptically polarizing plate or a circular polarizing plate in which a retardation plate is further laminated on a polarizing plate, a polarized light A wide viewing angle polarizing plate in which a viewing angle compensating film is further laminated on a plate, or a polarizing plate in which a brightness enhancement film is further laminated on a polarizing plate is preferable.
[0030]
The reflection type polarizing plate is provided with a reflection layer on a polarizing plate, and is used to form a liquid crystal display device of a type that reflects incident light from a viewing side (display side) and displays the reflected light. There is an advantage that the built-in light source can be omitted, and the liquid crystal display device can be easily made thinner. The reflection type 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 via the transparent protective film or the like, if necessary.
[0031]
Specific examples of the reflective polarizing plate include those in which a reflective layer formed by attaching a foil or a vapor-deposited film made of a reflective metal such as aluminum to one surface of a transparent protective film that has been matted as necessary.
[0032]
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 film, instead of the method of directly applying the reflection film to the transparent protective film of the polarizing plate. Since the reflective layer is usually made of a metal, the use form in which the reflective surface is covered with a transparent protective film, a polarizing plate, or the like is intended to prevent a decrease in reflectance due to oxidation, and to maintain the initial reflectance over a long period of time. It is more preferable to avoid separately providing a protective layer.
[0033]
The transflective polarizing plate can be obtained by forming a transflective reflective layer such as a half mirror that reflects and transmits light with 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 of a type that displays an image using a built-in light source such as a backlight built in the back side of a transflective polarizing plate can be formed. That is, the transflective polarizing plate can save energy for use of a light source such as a backlight in a bright atmosphere, and is useful for forming a liquid crystal display device of a type that can be used with a built-in light source even in a relatively dark atmosphere. It is.
[0034]
An elliptically polarizing plate or a circularly polarizing plate in which a retardation plate is further laminated on a polarizing plate will be described. When changing linearly polarized light to elliptically or circularly polarized light, changing elliptically or circularly polarized light to linearly polarized light, or changing the polarization direction of linearly polarized light, a phase difference plate or the like is used. 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 circularly polarized light or converts circularly polarized light into linearly polarized light. A half-wave plate (also referred to as a λ / 2 plate) is usually used to change the polarization direction of linearly polarized light.
[0035]
The elliptically polarizing plate compensates (prevents) coloring (blue or yellow) caused by the birefringence of the liquid crystal layer of the Spartist Nematic (STN) type liquid crystal display device, and is effectively used in the case of black-and-white display without the coloring. Can be Further, the one in which the three-dimensional refractive index is controlled is preferable because coloring which occurs when the screen of the liquid crystal display device is viewed from an oblique direction can be compensated (prevented). The circularly polarizing plate is effectively used, for example, when adjusting the color tone of an image of a reflection type liquid crystal display device that displays an image in color, and also has an antireflection function. Specific examples of the above retardation plate include a birefringent film obtained by stretching a film made of a suitable polymer such as polycarbonate, polyvinyl alcohol, polystyrene, polymethyl methacrylate, polypropylene and other polyolefins, polyarylate and polyamide. And an alignment film of a liquid crystal polymer, and an alignment layer of a liquid crystal polymer supported by a film. The retardation plate may have an appropriate retardation depending on the purpose of use, such as, for example, a color plate due to birefringence of various wave plates or a liquid crystal layer, or a target for compensation of a viewing angle or the like. A retardation plate may be laminated to control optical characteristics such as retardation.
[0036]
Further, the elliptically polarizing plate or the reflection type elliptically polarizing plate is obtained by laminating a polarizing plate or a reflection type polarizing plate and a retardation plate in an appropriate combination. Such an elliptically polarizing plate or the like may be formed by sequentially and separately laminating a (reflection type) polarizing plate and a retardation plate in the process of manufacturing a liquid crystal display device so as to form a combination. An optical film such as a polarizing plate has an advantage that it is excellent in quality stability, laminating workability, and the like, and can improve manufacturing efficiency of a liquid crystal display device and the like.
[0037]
The viewing angle compensation film is a film for widening the viewing angle so that an image can be seen relatively clearly even when the screen of the liquid crystal display device is viewed from a direction not perpendicular to the screen but slightly oblique. Such a viewing angle compensating retardation plate includes, for example, a retardation film, an alignment film such as a liquid crystal polymer, and a transparent substrate on which an alignment layer such as a liquid crystal polymer is supported. A normal retardation plate is a polymer film having birefringence uniaxially stretched in the plane direction, whereas a retardation plate used as a viewing angle compensation film is biaxially stretched in the plane direction. A birefringent polymer film such as a polymer film having birefringence, a birefringent polymer uniaxially stretched in the plane direction, and a birefringent polymer in which the refractive index in the thickness direction is also stretched in the thickness direction, or a tilted oriented film is used. Used. Examples of the inclined alignment 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 aligning a liquid crystal polymer. No. As the raw material polymer of the retardation plate, the same polymer as described in the above retardation plate is used to prevent coloring or the like due to a change in the viewing angle based on the phase difference due to the liquid crystal cell and to enlarge the viewing angle for good visibility. Any appropriate one for the purpose can be used.
[0038]
In addition, from the viewpoint of achieving a wide viewing angle with good visibility, the optical compensation position in which the optically anisotropic layer composed of the liquid crystal polymer alignment layer, particularly the tilted alignment layer of the discotic liquid crystal polymer is supported by a triacetyl cellulose film. A phase difference plate is preferably used.
[0039]
A polarizing plate obtained by laminating a polarizing plate and a brightness enhancement film is usually used by being provided on the back side of a liquid crystal cell. The brightness enhancement film reflects linearly polarized light of a predetermined polarization axis or circularly polarized light of a predetermined direction when natural light enters due to reflection from a backlight or a back side of a liquid crystal display device, and has a characteristic of transmitting other light. A polarizing plate obtained by laminating a brightness enhancement film and a polarizing plate, while receiving light from a light source such as a backlight to obtain transmitted light of a predetermined polarization state, is reflected without transmitting light other than the predetermined polarization state. You. The light reflected on the surface of the brightness enhancement film is further inverted through a reflection layer or the like provided on the rear side thereof and re-entered on the brightness enhancement film, and a part or all of the light is transmitted as light in a predetermined polarization state to thereby improve brightness. The brightness can be improved by increasing the amount of light transmitted through the enhancement film and by increasing the amount of light that can be used for liquid crystal display image display by supplying polarized light that is hardly absorbed by the polarizer. In other words, when light is incident through a polarizer from the back side of a liquid crystal cell with a backlight or the like without using a brightness enhancement film, light having a polarization direction that does not match the polarization axis of the polarizer is almost completely polarized. Is 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 decreases, and the image becomes darker. The brightness enhancement film is such that light having a polarization direction that is absorbed by the polarizer is once reflected by the brightness enhancement film without being incident on the polarizer, and further inverted through a reflection layer or the like provided on the rear side thereof. The brightness enhancement film transmits only the polarized light whose polarization direction has been changed so that the polarization direction of the light reflected and inverted between the two can pass through the polarizer. Since light is supplied to the polarizer, light from a backlight or the like can be efficiently used for displaying an image on the liquid crystal display device, and the screen can be brightened.
[0040]
The brightness enhancement film has a property of transmitting linearly polarized light having a predetermined polarization axis and reflecting other light, such as a multilayer thin film of a dielectric or a multilayer laminate of thin films having different refractive index anisotropy. As shown in the figure, such as an alignment film of a cholesteric liquid crystal polymer and an alignment liquid crystal layer supported on a film substrate, it exhibits a characteristic of reflecting either left-handed or right-handed circularly polarized light and transmitting other light. Any suitable one such as one can be used.
[0041]
Therefore, in a brightness enhancement film of the type that transmits linearly polarized light having a predetermined polarization axis, the transmitted light is incident on the polarization plate as it is, with the polarization axis aligned, thereby efficiently transmitting the light while suppressing absorption loss by the polarization plate. Can be done. On the other hand, in a brightness enhancement film of the type that emits circularly polarized light, such as a cholesteric liquid crystal layer, it can be directly incident on a polarizer, but from the viewpoint of suppressing absorption loss, the circularly polarized light is linearly polarized through a retardation plate. It is preferable that the light is incident on a polarizing plate. By using a quarter-wave plate as the retardation plate, circularly polarized light can be converted to linearly polarized light.
[0042]
A retardation plate that functions as a quarter-wave plate in a wide wavelength range such as a visible light region exhibits, for example, a retardation layer that functions as a quarter-wave plate for light-color light having a wavelength of 550 nm and other retardation characteristics. It can be obtained by a method of superimposing a retardation layer, 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 composed of one or more retardation layers.
[0043]
The cholesteric liquid crystal layer is also configured such that two or three or more cholesteric liquid crystal layers are superimposed on each other to reflect circularly polarized light in a wide wavelength range such as a visible light region. Based on this, it is possible to obtain circularly polarized light transmitted in a wide wavelength range.
[0044]
Further, the polarizing plate may be formed by laminating a polarizing plate and two or three or more optical layers as in the above-mentioned polarized light separating type polarizing plate. Therefore, a reflective elliptically polarizing plate or a transflective elliptically polarizing plate obtained by combining the above-mentioned reflective polarizing plate, semi-transmissive polarizing plate, and retardation plate may be used.
[0045]
The lamination of various optical layers on the polarizing plate can also be performed by a method of sequentially laminating the optical layers in a manufacturing process of a liquid crystal display device or the like. There is an advantage that it is excellent in work and the like and can improve a manufacturing process of a liquid crystal display device or the like. For the lamination, an appropriate bonding means such as an adhesive layer can be used. When bonding the above-mentioned polarizing plate and other optical layers, their optical axes can be arranged at an appropriate angle depending on the intended retardation characteristics and the like.
[0046]
At least one surface of the above-mentioned polarizing plate or an optical element having at least one layer of the polarizing plate laminated thereon may be provided with an adhesive layer for bonding to another member such as a liquid crystal cell. Although the adhesive forming the adhesive layer is not particularly limited, for example, an acrylic polymer, a silicone polymer, a polyester, a polyurethane, a polyamide, a polyether, and a polymer having a fluorine-based or rubber-based polymer as a base polymer are appropriately selected. Can be used. In particular, those having excellent optical transparency such as an acrylic adhesive, exhibiting appropriate wettability, cohesiveness and adhesive adhesive properties, and having excellent weather resistance and heat resistance can be preferably used.
[0047]
In addition to the above, prevention of foaming and peeling phenomena due to moisture absorption, reduction of optical characteristics due to thermal expansion difference and the like, prevention of warpage of the liquid crystal cell, and, in view of the formability of a liquid crystal display device having high quality and excellent durability, etc. An adhesive layer having low moisture absorption and excellent heat resistance is preferred.
[0048]
The adhesive layer is, for example, a natural or synthetic resin, in particular, a tackifier resin, or a filler, a pigment, a colorant, an antioxidant, or the like made of glass fiber, glass beads, metal powder, other inorganic powder, or the like. May be added to the adhesive layer. The attachment of an adhesive layer to an optical element such as a polarizing plate can be performed by an appropriate method. For example, an adhesive solution of about 10 to 40% by weight is prepared by dissolving or dispersing the base polymer or its composition in a solvent composed of a single solvent or a mixture of appropriate solvents such as toluene and ethyl acetate. A method in which it is directly attached to the optical element by an appropriate development method such as a casting method or a coating method, or a method in which an adhesive layer is formed on a separator according to the above and transferred to the optical element. can give. The adhesive layer may be provided as a superimposed layer of different compositions or types in each layer. The thickness of the adhesive layer can be appropriately determined depending on the purpose of use, adhesive strength, and the like, and is generally 1 to 500 μm, preferably 5 to 200 μm, and particularly preferably 10 to 100 μm.
[0049]
In the present invention, the polarizer has a transparent protective film on both surfaces, and on one side of the polarizer, and an optical element having a light diffusion layer between the polarizer and the transparent protective film, the optical element and the light diffusion layer When divided at the interface with the polarizer, the thickness from the interface to the surface of the optical element including the polarizer is preferably 150 μm or less, and more preferably 100 μm or less. By setting the thickness to 150 μm or less, blurring of an image can be effectively suppressed. In addition, when the optical element has another optical layer and / or an adhesive layer on the surface of the polarizing plate including the polarizer from the boundary surface, the thickness is different from that of the other optical layer and / or the adhesive layer. It also means the thickness including.
[0050]
A separator is temporarily attached to the exposed surface of the adhesive layer for the purpose of preventing contamination and the like until the surface is put to practical use, and covered. As a result, it is possible to prevent the contact with the adhesive layer in the usual handling state. Except for the above thickness conditions, the separator may be, for example, a plastic film, a rubber sheet, paper, cloth, a nonwoven fabric, a net, a foamed sheet or a metal foil, a suitable thin body such as a laminate thereof, or a silicone-based material as necessary. Appropriate conventional ones, such as those coated with an appropriate release agent such as long mirror alkyl, fluorine or molybdenum sulfide, can be used.
[0051]
In the present invention, each layer such as a polarizer, a transparent protective film, an optical layer, or the like, which forms the above-described optical element, and a layer such as an adhesive layer include, for example, a salicylate compound, a benzophenol compound, a benzotriazole compound, and a cyanoacrylate. It may be a compound having an ultraviolet absorbing ability by a method such as a method of treating with an ultraviolet absorbent such as a system compound and a nickel complex compound.
[0052]
The optical element of the present invention can be preferably used for forming various image display devices such as a liquid crystal display device. The formation of the liquid crystal display device can be performed according to a conventional method. That is, a liquid crystal display device is generally formed by appropriately assembling components such as a liquid crystal cell and an optical element and, if necessary, an illumination system and incorporating a drive circuit. There is no particular limitation except that an element is used, and it can be in accordance with the prior art. As for the liquid crystal cell, any type such as TN type, STN type and π type can be used.
[0053]
An appropriate liquid crystal display device such as a liquid crystal display device in which the optical element is arranged on one side or both sides of a liquid crystal cell, or an illumination system using a backlight or a reflector can be formed. In that case, the optical element according to the present invention can be installed on one side or both sides of the liquid crystal cell. When optical elements are provided on both sides, they may be the same or different. Further, when forming the liquid crystal display device, for example, a suitable component such as a diffusion plate, an anti-glare layer, an antireflection film, a protection plate, a prism array, a lens array sheet, a light diffusion plate, a backlight, etc. Two or more layers can be arranged.
[0054]
It is preferable that the liquid crystal display device of the present invention has the polarizing plate or the optical element mounted on the viewing side of a liquid crystal cell. Further, it is preferable that the polarizing plate or the optical element in which the light diffusion layer is disposed on the viewing side with respect to the polarizer is mounted on the viewing side of the liquid crystal cell. On the viewing side of the polarizer, the image is more likely to be blurred than on the liquid crystal cell side, and when a light diffusion layer is provided on the liquid crystal cell side of the polarizer, depolarization tends to occur due to the light diffusion layer. is there.
[0055]
Next, an organic electroluminescence device (organic EL display device) will be described. In general, in an organic EL display device, a luminous body (organic electroluminescent luminous body) is formed by sequentially laminating a transparent electrode, an organic luminescent layer, and a metal electrode on a transparent substrate. Here, the organic light emitting layer is a laminate of various organic thin films, for example, a laminate of a hole injection layer made of a triphenylamine derivative or the like, and a light emitting layer made of a fluorescent organic solid such as anthracene, Alternatively, a configuration having various combinations such as a stacked body of such a light emitting layer and an electron injection layer made of a perylene derivative, or a stacked body of a hole injection layer, a light emitting layer, and an electron injection layer thereof is known. Has been.
[0056]
In an organic EL display device, holes and electrons are injected into an organic light emitting layer by applying a voltage to a transparent electrode and a metal electrode, and energy generated by recombination of these holes and electrons excites a fluorescent substance. Then, light is emitted on the principle that the excited fluorescent substance emits light when returning to the ground state. The mechanism of recombination on the way is the same as that of a general diode, and as can be expected from this, the current and the emission intensity show strong nonlinearity accompanied by rectification with respect to the applied voltage.
[0057]
In an organic EL display device, at least one of the electrodes must be transparent in order to extract light emitted from the organic light emitting layer. Usually, a transparent electrode formed of a transparent conductor such as indium tin oxide (ITO) is used as an anode. Used as On the other hand, in order to facilitate electron injection and increase luminous efficiency, it is important to use a material having a small work function for the cathode, and usually a metal electrode such as Mg-Ag or Al-Li is used.
[0058]
In the organic EL display device having such a configuration, the organic light emitting layer is formed of a very thin film having a thickness of about 10 nm. Therefore, the organic light emitting layer transmits light almost completely, similarly to the transparent electrode. As a result, when light is incident from the surface of the transparent substrate during non-light emission, light transmitted through the transparent electrode and the organic light-emitting layer and reflected by the metal electrode again exits to the surface side of the transparent substrate, and when viewed from the outside, The display surface of the organic EL display device looks like a mirror surface.
[0059]
In an organic EL display device including an organic electroluminescent luminous body having a transparent electrode on the front side of an organic luminescent layer that emits light by applying a voltage and a metal electrode on the back side of the organic luminescent layer, the surface of the transparent electrode A polarizing plate can be provided on the side, and a retardation plate can be provided between the transparent electrode and the polarizing plate.
[0060]
Since the retardation plate and the polarizing plate have a function of polarizing light incident from the outside and reflected by the metal electrode, there is an effect that the mirror surface of the metal electrode is not visually recognized by the polarizing function. In particular, if the retardation plate is formed of a 1/4 wavelength plate and the angle between the polarization directions of the polarizing plate and the retardation plate is adjusted to π / 4, the mirror surface of the metal electrode can be completely shielded. .
[0061]
That is, as for the external light incident on the organic EL display device, only the linearly polarized light component is transmitted by the polarizing plate. This linearly polarized light is generally converted into elliptically polarized light by the phase difference plate, but becomes circularly polarized light particularly when the phase difference plate is a １ wavelength plate and the angle between the polarization directions of the polarizing plate and the phase difference plate is π / 4. .
[0062]
This circularly polarized light transmits through the transparent substrate, the transparent electrode, and the organic thin film, is reflected by the metal electrode, passes through the organic thin film, the transparent electrode, and the transparent substrate again, and becomes linearly polarized light again by the phase difference plate. The linearly polarized light cannot pass through the polarizing plate because it is orthogonal to the polarizing direction of the polarizing plate. As a result, the mirror surface of the metal electrode can be completely shielded.
[0063]
【Example】
Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited to these Examples. When the optical element was divided at the interface between the light diffusion layer and the polarizer, the thickness from the interface to the surface of the optical element including the polarizer and the haze value were measured by the following methods.
[0064]
(Measurement of thickness)
Using the prepared optical element, the thickness from the boundary surface when the optical element is divided at the boundary surface between the light diffusion layer and the polarizer to the surface of the optical element on the side including the polarizer is measured by SEM (scanning electron microscope). It measured using.
[0065]
(Measurement of haze value)
It measured using HGM-2DP (made by Suga Test Instruments) according to JISK7105 using the produced polarizing plate.
[0066]
Example 1
(Production of light diffusion layer, etc.)
100 parts by weight of a polyurethane resin (manufactured by Dainippon Ink and Chemicals, Bondic 1040NS) and 20 parts by weight of fine particles (manufactured by Toshiba Silicone, Tospearl 145, average particle diameter 4.5 μm) were mixed with a mixed solvent of water and isopropyl alcohol (water: isopropyl). In addition to alcohol (1: 3), a light diffusion layer forming composition having a solid content of 15% by weight was prepared. Then, the light diffusion layer forming composition was stirred with a homogenizer for 30 minutes to disperse the fine particles. Thereafter, the composition for forming a light diffusion layer is applied on a triacetyl cellulose film (manufactured by Fuji Photo Film Co., Ltd., TD80U, thickness: 80 μm) using a wire bar so that the thickness after drying is 25 μm, dried, and dried. A transparent protective film (1) having a layer was obtained.
Further, the polyurethane resin, the mixed solvent of water and isopropyl alcohol were mixed to prepare a mixed solution (A) having a solid content of 15% by weight. Then, the mixed solution (A) is applied to a triacetyl cellulose film (manufactured by Fuji Photo Film Co., Ltd., TD80U, thickness: 80 μm) using a wire bar so that the thickness after drying is 25 μm, dried, and dried. Was obtained.
[0067]
(Production of optical element)
A polyvinyl alcohol film (Kuraray Co., Ltd., Kuraray vinylon film) was swollen and stretched in an iodine aqueous solution, and then the film was dried with hot air to remove water and produce a polarizer (thickness: 20 μm). This polarizer was sandwiched between the light diffusion layer of the transparent protective film (1) and the adhesive layer of the transparent protective film (2), and was heated and laminated to obtain a polarizing plate. Further, an adhesive solution made of an acrylic polymer was applied on the transparent protective film (2) of the polarizing plate, and dried to produce an optical element having an adhesive layer (25 μm in thickness) on the surface. FIG. 1 shows the configuration of the manufactured optical element.
[0068]
Example 2
An optical element having an adhesive layer (25 μm in thickness) on the surface was produced in the same manner as in Example 1 except that KC4UX2MW made by Konica and a thickness of 40 μm were used as the triacetyl cellulose film.
[0069]
Reference Example 1
An optical element having an adhesive layer (thickness: 25 μm) on the surface was produced in the same manner as in Example 1 except that the amount of the fine particles was changed to 4 parts by weight.
[0070]
Comparative Example 1
(Production of light diffusion layer, etc.)
In the same manner as in Example 1, a transparent protective film (1) having a light diffusion layer was obtained. Further, the mixed solvent (A) is applied to a surface of the transparent protective film (1) opposite to the surface on which the light diffusion layer is laminated using a wire bar so that the thickness after drying becomes 25 μm. After drying, a transparent protective film (3) having a light diffusion layer and an adhesive layer was obtained. Further, a transparent protective film (2) having an adhesive layer was obtained in the same manner as in Example 1.
[0071]
(Production of optical element)
A polarizer produced in the same manner as in Example 1 was sandwiched between the adhesive layer of the transparent protective film (3) and the adhesive layer of the transparent protective film (2), and was heat-laminated to diffuse light to one surface. A polarizing plate having a layer was obtained. Further, an optical element having an adhesive layer (thickness: 25 μm) on the other surface was manufactured in the same manner as in Example 1. FIG. 2 shows the structure of the manufactured optical element.
[0072]
Comparative Example 2
(Preparation of polarizing plate)
A polarizer was obtained by sandwiching both surfaces of the polarizer produced by the same method as in Example 1 with the adhesive layer of the transparent protective film (2) and laminating by heating.
[0073]
(Formation of light diffusion layer)
Acrylic polymer (weight average molecular weight: 200) obtained by solution polymerization of butyl acrylate (BA, 100 parts by weight), acrylic acid (AA, 5 parts by weight), and hydroxyethyl acrylate (HEA, 0.1 parts by weight). 100 parts by weight, 0.6 parts by weight of a polyisocyanate crosslinking agent (Coronate L, manufactured by Nippon Polyurethane), 0.1 parts by weight of a silane coupling agent (KBM403, manufactured by Shin-Etsu Silicone), and the spherical fine particles (5 parts by weight) ) Was added to toluene to prepare a light diffusion layer forming composition having a solid content of 10% by weight. Then, the light diffusion layer forming composition was stirred for 15 minutes with a disper to disperse the fine particles. Thereafter, a light-diffusing layer-forming composition is applied on one surface of the prepared polarizing plate using a wire bar so that the thickness after drying becomes 25 μm, and dried, and a polarizing plate having a light-diffusing layer on the surface Was prepared. FIG. 3 shows the structure of the manufactured polarizing plate.
[0074]
Comparative Example 3
An optical element having an adhesive layer (thickness: 25 μm) on the surface was produced in the same manner as in Example 1 except that the light diffusion layer was not formed.
[0075]
A liquid crystal display was manufactured using the optical elements and the like manufactured in the above Examples, Reference Examples, and Comparative Examples, and the viewing angle characteristics and image clarity were evaluated according to the following criteria. Table 1 shows the results.
[0076]
(Viewing angle characteristics)
The viewing angle characteristics were visually evaluated according to the following criteria.
：: The viewing angle was greatly increased compared to when the optical element was not mounted.
Δ: Viewing angle slightly increased.
X: The viewing angle did not expand at all.
[0077]
(Image sharpness)
The sharpness of the image was measured by visual observation. A case where the outline of the image was hardly blurred was regarded as good, and a case where the outline of the image was blurred was evaluated as poor.
[0078]
[Table 1]

As is clear from the results in Table 1, the optical element having the light diffusion layer between the polarizer and the transparent protective film (Examples 1 and 2) has a wide viewing angle and almost no image blur. The sharpness was good. On the other hand, in the optical element having the light diffusion layer on the viewing side surface (Comparative Example 1), the viewing angle was enlarged, but the image was blurred and the sharpness was poor. Further, the polarizing plate having the light diffusion layer on the liquid crystal cell side (Comparative Example 2) had a wide viewing angle and little image blurring, and had good sharpness, but the contrast was degraded due to depolarization. Happened. The optical element without the light diffusion layer (Comparative Example 3) had poor viewing angle characteristics and poor image clarity.
[Brief description of the drawings]
FIG. 1 is an example of a sectional view of an optical element of the present invention.
FIG. 2 is an example of a cross-sectional view of an optical element of Comparative Example 1.
FIG. 3 is an example of a cross-sectional view of a polarizing plate of Comparative Example 2.
[Explanation of symbols]
1: Polarizer 2: Transparent protective film 3: Fine particles 4: Light diffusion layer 5: Adhesive layer 6: Adhesive layer 7: Polarizing plate 8: Optical element

Claims (9)

What is claimed is: 1. A polarizing plate having a transparent protective film on at least one surface of a polarizer, comprising a light diffusion layer between the polarizer and the transparent protective film. The polarizing plate according to claim 1, wherein the polarizer has a transparent protective film on both sides and a light diffusion layer on one side of the polarizer. The haze value is 70% or more, The polarizing plate of Claim 1 or 2 characterized by the above-mentioned. The polarizing plate according to any one of claims 1 to 3, wherein the light diffusion layer is made of a polyurethane resin containing fine particles. An optical element using the polarizing plate according to claim 1. 6. The optical element according to claim 5, wherein when the optical element is divided at a boundary surface between the light diffusion layer and the polarizer, a thickness from the boundary surface to the surface of the optical element on the side including the polarizer is 150 μm or less. Optical element. An image display device comprising the polarizing plate according to claim 1 or the optical element according to claim 5. A liquid crystal display device comprising the polarizing plate according to any one of claims 1 to 4 or the optical element according to claim 5 mounted on the viewing side of a liquid crystal cell. The liquid crystal display according to claim 8, further comprising a polarizing plate according to any one of claims 1 to 4, or an optical element according to claim 5 or 6, wherein a light diffusion layer is disposed on the viewing side with respect to the polarizer. apparatus.

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