JP2004233972A - Optical film, elliptic polarizing plate, and image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical film capable of displaying an image, where the coloring of a display image is suppressed even if the display image is seen from an oblique direction to the normal direction of a screen and an inversive gradation region is small. <P>SOLUTION: In a laminated optical film, when a direction where the inplane refractive index of the film becomes maximum is set to be an X axis; a direction vertical to the X axis is set to be a Y axis; the thickness direction of the film is set to be a Z axis; and refractive indexes in respective axial directions are set to be nx<SB>1</SB>, ny<SB>1</SB>, and nz<SB>1</SB>, the optical film (1), where a three-dimensional refractive index is controlled so that an Nz coefficient expressed by Nz=(nx<SB>1</SB>-nz<SB>1</SB>)/(nx<SB>1</SB>-ny<SB>1</SB>) meets Nz≤0.9, is laminated to the optical film (2) formed of a material that shows an optically negative uniaxiality and is inclined and oriented. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a laminated optical film. The laminated optical film of the present invention may be used alone or in combination with other optical films to form various optical films such as a retardation plate, a viewing angle compensation film, an optical compensation film, an elliptically polarizing plate (including a circularly polarizing plate), and a brightness enhancement film. Can be used as In particular, the laminated optical film of the present invention is useful when laminated with a polarizing plate and used as an elliptically polarizing plate. The present invention also relates to an image display device such as a liquid crystal display device, an organic EL (electroluminescence) display device, and a PDP using the laminated optical film, the elliptically polarizing plate or the like. As described above, the laminated optical film and the elliptically polarizing plate of the present invention can be applied to various liquid crystal display devices and the like, but are particularly applicable to a portable information communication device, a transflective liquid crystal display device that can be mounted on a personal computer, and the like. It is preferably used.

  2. Description of the Related Art Conventionally, a wide-band retardation plate functioning as a λ / 4 plate or a λ / 2 plate with respect to incident light (a visible light region) having a wide-band wavelength region is suitably used for a transflective liquid crystal display device or the like. Have been. As such a broadband retardation plate, a laminated film in which a plurality of polymer films having optical anisotropy are laminated with their optical axes crossing each other has been proposed. In these laminated films, the optical axis of two or more stretched films is crossed to realize a wider band (for example, see Patent Documents 1, 2, and 3).

However, even when the wide-band retardation films having the configurations of Patent Documents 1 to 3 described above are used, when the display image is viewed from the upper, lower, left and right directions with respect to the normal direction of the screen, the display is not performed. It has the disadvantage that the color appearance of the image changes and that the white image and the black image are inverted, that is, the gradation is inverted.
JP-A-5-100114 JP-A-10-68816 JP-A-10-90521

  The present invention provides an optical film capable of displaying an image having a small number of gradation inversion regions, in which coloring of the display image is suppressed even when the display image is viewed from an oblique direction with respect to the normal direction of the screen. The purpose is to provide.

  Another object of the present invention is to provide an elliptically polarizing plate obtained by laminating the optical film and a polarizing plate. Still another object of the present invention is to provide an image display device using the optical film and the elliptically polarizing plate.

  Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above problems, and have found that the above object can be achieved by using the following laminated optical film, and have completed the present invention.

That is, in the present invention, the direction in which the refractive index in the film plane is maximum is the X axis, the direction perpendicular to the X axis is the Y axis, the thickness direction of the film is the Z axis, and the refractive index in each axial direction is nx _1. , Ny ₁ , nz ₁ ,
_{Nz = (nx 1 -nz 1)} / Nz coefficient expressed by (nx ₁ -ny ₁₎ is,
An optical film (1) whose three-dimensional refractive index is controlled so as to satisfy Nz ≦ 0.9,
An optical film (2), which is formed of a material having an optically negative uniaxial property and in which the material is obliquely oriented, is laminated.

  The laminated optical film of the present invention is obtained by laminating an optical film (1) having a controlled three-dimensional refractive index and an optical film (2) obtained by tilting an optically negative uniaxial material. This is useful as a phase difference plate that compensates for a wide band and a wide viewing angle. An image display device such as a liquid crystal display device to which the laminated optical film is applied can realize a wide viewing angle, and even when the display screen is viewed from an oblique direction, display coloring is suppressed, and the gradation inversion region is reduced. A small number of images can be displayed.

The optical film (1) whose three-dimensional refractive index is controlled has an Nz coefficient defined as above, where Nz ≦ 0.9. When the Nz coefficient satisfies Nz> 0.9, it is difficult to achieve a wide viewing angle, display coloring cannot be sufficiently suppressed when the display screen is viewed from an oblique direction, and the contrast from the oblique direction is reversed. Gradation inversion occurs. The smaller the Nz coefficient, the better, and preferably satisfies Nz ≦ 0.3. Further, it is preferable to satisfy Nz ≦ 0.2. Note that the optical film (1) includes the case where (nx ₁ −nz ₁ ) <0, and the Nz coefficient may be negative. However, it is preferable to control the Nz coefficient so as to be -1 or more, and more preferably -0.5 or more, in view of expanding the viewing angle in the vertical and horizontal directions.

  In the laminated optical film, the optically negative uniaxial material forming the optical film (2) is preferably a discotic liquid crystal compound. A material having an optically negative uniaxial property is not particularly limited, but a discotic liquid crystal compound is preferable in that the tilt alignment is well controlled and the cost is relatively low with a general material.

  In the laminated optical film, the optically negative uniaxial material forming the optical film (2) has a tilt angle of 5 ° to an average optical axis and a normal direction of the optical film (2). It is preferable that the film is tilt-oriented in a range of 50 °.

  As described above, the optical film (2) is used as a laminated optical film in combination with the optical film (1) having a controlled three-dimensional refractive index, and the tilt angle of the optical film (2) is controlled to 5 ° or more. Thereby, the effect of expanding the viewing angle when mounted on a liquid crystal display device or the like is large. On the other hand, by controlling the inclination angle to 50 ° or less, the viewing angle becomes good in any of the upper, lower, left, and right directions (four directions), and depending on the direction, the viewing angle becomes better or worse. Can be suppressed. From such a viewpoint, the inclination angle is preferably 10 ° to 30 °.

  Note that the tilt alignment state of an optical material having optically negative uniaxiality (for example, discotic liquid crystal molecules) may be a uniform tilt (tilt) alignment that does not change with the distance from the film surface. It may change with the distance between the material and the plane of the film.

Further, the present invention provides the laminated optical film,
Further, the direction in which the refractive index in the film plane is the maximum is the X axis, the direction perpendicular to the X axis is the Y axis, the thickness direction of the film is the Z axis, and the refractive indexes in the respective axial directions are nx ₃ and ny _3. , Nz ₃ ,
An optical film (3) that satisfies nx ₃ > ny ₃ ≒ nz ₃ and that has optically positive uniaxiality.

  The optical film (1) having the controlled three-dimensional refractive index and the optical film (2) obtained by obliquely orienting a material having an optically negative uniaxial property are further laminated on the laminated optical film. By laminating the optical film (3) showing the property, an image display device such as a liquid crystal display device to which the laminated optical film is applied can realize a wider viewing angle, and display when the display screen is viewed from an oblique direction. Coloring can be suppressed, and an image with few gradation inversion regions can be displayed.

  The laminated optical film obtained by laminating the optical film (3) is composed of an optical film (3) having optically positive uniaxiality and an optical film (2) obtained by obliquely orienting a material having optically negative uniaxiality. The arrangement of the optical film (1) having a controlled three-dimensional refractive index can realize a wide viewing angle and more effectively suppress the grayscale inversion area when viewed from an oblique direction. Above.

  The present invention also relates to an elliptically polarizing plate, wherein the laminated optical film and a polarizing plate are laminated. The elliptically polarizing plate is a laminated optical film obtained by laminating an optical film (3), wherein the polarizing plate is laminated on the optical film (3) side, when viewed from a wide viewing angle and obliquely. It is preferable from the point of the gradation inversion area.

  Further, the present invention relates to an image display device having the laminated optical film or the elliptically polarizing plate laminated thereon.

  Hereinafter, the laminated optical film of the present invention will be described with reference to the drawings. As shown in FIG. 1, the laminated optical film of the present invention comprises an optical film (1) having a controlled three-dimensional refractive index and an optical film (2) obtained by tilt-orientating a material having an optically negative uniaxial property. Are laminated. FIGS. 2 to 4 show a laminated optical film in which an optical film (3) having optically positive uniaxiality is further laminated on the laminated optical film. In FIG. 2, the optical film (3) is laminated on the optical film (1) side, while in FIG. 3, the optical film (3) is laminated on the optical film (2) side. In FIG. 4, the optical film (3) is laminated between the optical film (1) and the optical film (2). The laminating position of the optical film (3) may be on the optical film (2) side and / or the optical film (1) side, or any between them. However, as shown in FIG. ) Side, and the optical film (1) is preferably laminated between the optical film (2) and the optical film (3).

  Further, a polarizing plate (P) may be laminated on the laminated optical film to form an elliptically polarizing plate. FIGS. 5 to 7 show an elliptically polarizing plate (P1) in which a polarizing plate (P) is laminated on the laminated optical film shown in FIGS. The laminating position of the polarizing plate (P) with respect to the laminated optical film is not particularly limited. However, when the polarizing plate (P) is mounted on a liquid crystal display device, the optical film (3) is spread as shown in FIGS. It is preferable to laminate a polarizing plate (P) on the side. Particularly, the case of FIG. 5 is preferable.

  In FIGS. 1 to 7, each optical film and polarizing plate are laminated via an adhesive layer (a). The pressure-sensitive adhesive layer (a) may be a single layer or two or more layers.

The optical film (1) in which the three-dimensional refractive index is controlled has an X axis as a direction in which the refractive index in the film plane is maximum, a Y axis as a direction perpendicular to the X axis, a Z axis as a thickness direction of the film, When the refractive indexes in the respective axial directions are nx ₁ , ny ₁ , and nz ₁ ,
_{Nz = (nx 1 -nz 1)} / Nz coefficient expressed by (nx ₁ -ny ₁₎ is, Nz ≦ 0.9, can be used without particular limitation to satisfy.

  The method for producing the optical film (1) is not particularly limited. For example, a method of stretching a polymer film biaxially in a plane direction, a method of stretching uniaxially or biaxially in a plane direction, and a method of stretching also in a thickness direction And the like. Further, there is a method in which a heat-shrinkable film is adhered to a polymer film and the polymer film is subjected to a stretching treatment and / or a shrinkage treatment under the action of the shrinkage force caused by heating. The orientation state is controlled by controlling the refractive index in the thickness direction by these methods so that the three-dimensional refractive index of the stretched film satisfies Nz ≦ 0.9.

  Examples of the polymer forming the optical film (1) include polyolefins such as polycarbonate and polypropylene, polyesters such as polyethylene terephthalate and polyethylene naphthalate, norbornene polymers, polyvinyl alcohol, polyvinyl butyral, polymethyl vinyl ether, and polyhydroxyethyl. Cellulose polymers such as acrylate, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, polyarylate, polysulfone, polyether sulfone, polyphenylene sulfide, polyphenylene oxide, polyallyl sulfone, polyvinyl alcohol, polyamide, polyimide, polyvinyl chloride, triacetyl cellulose, etc. , Acrylic polymer, styrene polymer These binary and ternary various copolymers, graft copolymers, and any blend thereof.

The optical film (1) satisfies Nz ≦ 0.9, and its front phase difference ((nx ₁ −ny ₁ ) × d ₁ (thickness: nm)) is preferably 10 to 400 nm, More preferably, it is 50 to 200 nm. The thickness direction retardation ((nx ₁ −nz ₁ ) × d ₁ ) is preferably 10 to 400 nm, more preferably 50 to 300 nm.

The thickness (d ₁ ) of the optical film (1) is not particularly limited, but is preferably from 1 to 150 μm, more preferably from 5 to 50 μm.

  The material that forms the optical film (2) and has an optically negative uniaxial property refers to a material in a three-dimensional refractive index ellipsoid in which the refractive index of the principal axis in one direction is smaller than the refractive index in the other two directions. Show.

  Examples of the material exhibiting optically negative uniaxiality include a liquid crystal material such as a polyimide material and a discotic liquid crystal compound. In addition, a material in which these materials are used as a main component and mixed and reacted with other oligomers or polymers to fix a state in which a material exhibiting negative uniaxial orientation is obliquely oriented to form a film can be used. When a discotic liquid crystal compound is used, the tilt alignment state of the liquid crystal molecules depends on the molecular structure, the type of alignment film, and additives appropriately added to the optically anisotropic layer (eg, plasticizer, binder, surfactant). ) Can be controlled.

The direction in which the refractive index in the film plane of the optical film (2) is the maximum is the X axis, the direction perpendicular to the X axis is the Y axis, the thickness direction of the film is the Z axis, and the refractive index in each axial direction is nx. _{In the case where 2} , ny ₂ and nz ₂ are used, the front phase difference ((nx ₂ −ny ₂ ) × d ₂ (thickness: nm)) of the optical film (2) is preferably 0 to 200 nm, More preferably, it is 1 to 150 nm. The retardation in the thickness direction ((nx ₂ −nz ₂ ) × d ₂ ) is preferably from 10 to 400 nm, more preferably from 50 to 300 nm.

The thickness of the optical film ₍₂₎ (d 2) is not particularly limited but is preferably 1 to 200 [mu] m, more preferably 2～150Myuemu.

  The lamination of the optical film (1) and the optical film (2) is preferably performed such that the smaller angle of each slow axis is 70 ° to 90 °. More preferably, it is 80 ° to 90 °.

An optical film (3) that exhibits optically positive uniaxiality has an X axis as a direction in which the refractive index in the film plane is maximum, a Y axis as a direction perpendicular to the X axis, and a Z axis as a thickness direction of the film. , the refractive index of the respective axial when the _{nx 3, ny 3, nz 3} , nx 3> ny 3 ≒ nz 3, can be used without particular limitation to satisfy. That is, a material having optically positive uniaxiality refers to a material in a three-dimensional refractive index ellipsoid in which the refractive index of the principal axis in one direction is larger than the refractive indexes in the other two directions.

  The optical film (3) having optically positive uniaxiality can be obtained, for example, by subjecting the high-molecular polymer film exemplified as the optical film (1) to uniaxial stretching in the plane direction. Further, a rod-like nematic liquid crystal compound can also be used. The rod-like nematic liquid crystal compound can be tilt-aligned, and the tilt alignment state depends on the molecular structure, the type of alignment film, and additives appropriately added to the optically anisotropic layer (for example, a plasticizer, a binder, an interface). (Activator).

The front retardation ((nx ₃ −ny ₃ ) × d ₃ (thickness: nm)) of the optical film (3) is preferably from 0 to 500 nm, more preferably from 1 to 350 nm. The thickness direction retardation ((nx ₃ −nz ₃ ) × d ₃ ) is preferably 0 to 500 nm, more preferably 1 to 350 nm.

The thickness (d ₃ ) of the optical film (3) is not particularly limited, but is preferably from 1 to 200 μm, more preferably from 2 to 80 μm.

  The polarizing plate (P) usually has a protective film on one or both sides of a polarizer. The polarizer 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 or a dehydrochlorinated product of polyvinyl chloride. Among these, those obtained by stretching a polyvinyl alcohol-based film and adsorbing and orienting a dichroic material (iodine, dye) are preferably used. Although the thickness of the polarizer is not particularly limited, it is generally about 5 to 80 μm.

  A polarizer obtained by dyeing a polyvinyl alcohol-based film with iodine and uniaxially stretching can be produced, for example, by 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-based film with water, dirt on the surface of the polyvinyl alcohol-based film and an anti-blocking agent can be washed, and by swelling the polyvinyl alcohol-based film, the effect of preventing unevenness such as uneven dyeing can be obtained. 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.

  The protective film provided on one or both sides of the polarizer preferably has excellent transparency, mechanical strength, heat stability, moisture shielding property, isotropy, and the like. Examples of the material of the protective film include polyester polymers such as polyethylene terephthalate and polyethylene naphthalate; cellulose polymers such as diacetyl cellulose and triacetyl cellulose; acrylic polymers such as polymethyl methacrylate; and polystyrene and acrylonitrile / styrene copolymers. Styrene-based polymers such as (AS resin) and polycarbonate-based polymers. In addition, polyethylene, polypropylene, polyolefin having a cyclo- or norbornene structure, polyolefin-based polymer such as ethylene-propylene copolymer, vinyl chloride-based polymer, amide-based polymer such as nylon or aromatic polyamide, imide-based polymer, and sulfone-based polymer , Polyether sulfone polymer, polyether ether ketone polymer, polyphenylene sulfide polymer, vinyl alcohol polymer, vinylidene chloride polymer, vinyl butyral polymer, arylate polymer, polyoxymethylene polymer, epoxy polymer, or the above Blends of polymers are examples of polymers forming the protective film. In addition, a film formed from a thermosetting or ultraviolet curable resin such as an acrylic, urethane, acrylic urethane, epoxy, or silicone resin may be used.

  Further, polymer films described in JP-A-2001-343529 (WO 01/37007), for example, (A) a thermoplastic resin having a substituted and / or unsubstituted imide group in the side chain, and (B) a thermoplastic resin having a side chain And / or an unsubstituted phenyl and a resin composition containing a thermoplastic resin having a nitrile group. A specific example is a film of a resin composition containing an alternating copolymer of isobutylene and N-methylmaleimide and an acrylonitrile / styrene copolymer. As the film, a film composed of a mixed extruded product of a resin composition or the like can be used.

  A 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. Although the thickness of the protective film can be determined as appropriate, it is generally about 10 to 500 μm from the viewpoints of strength, workability such as handleability, and thin layer properties. In particular, 20 to 300 μm is preferable, and 30 to 200 μm is more preferable.

  Further, it is preferable that the protective film has as little coloring as possible. Therefore, Rth = [(nx + ny) / 2−nz] · d (where nx and ny are the main refractive indices in the film plane, nz is the refractive index in the film thickness direction, and d is the film thickness). A protective film having a retardation value in the film thickness direction of -90 nm to +75 nm is preferably used. By using a film having a retardation value (Rth) in the thickness direction of -90 nm to +75 nm, coloring (optical coloring) of the polarizing plate caused by the protective film can be substantially eliminated. The thickness direction retardation value (Rth) is more preferably -80 nm to +60 nm, and particularly preferably -70 nm to +45 nm.

  As the protective film, a cellulosic polymer such as triacetyl cellulose is preferable from the viewpoints of polarization characteristics and durability. Particularly, a triacetyl cellulose film is preferable. In the case where protective films are provided on both sides of the polarizer, a protective film made of the same polymer material may be used on both sides thereof, or a protective film made of a different polymer material may be used. Usually, the polarizer and the protective film are in close contact with each other via a water-based adhesive or the like. Examples of the water-based adhesive include a polyvinyl alcohol-based adhesive, a gelatin-based adhesive, a vinyl latex-based, an aqueous polyurethane, and an aqueous polyester.

  As the protective film, a hard coat layer or a film subjected to an antireflection treatment, a treatment for preventing sticking, or a treatment for diffusion or antiglare can be used.

  The hard coat treatment is performed for the purpose of preventing scratches on the polarizing plate surface and the like.For example, an acrylic or silicone-based appropriate ultraviolet-curable resin is used to form a cured film having excellent hardness and sliding properties on the protective film. It can be formed by a method of adding to the surface. The anti-reflection treatment is performed for the purpose of preventing the reflection of external light on the polarizing plate surface, and can be achieved by forming an anti-reflection film or the like according to the related art. In addition, the anti-sticking treatment is performed for the purpose of preventing adhesion to an adjacent layer.

  The anti-glare treatment is performed for the purpose of preventing external light from being reflected on the surface of the polarizing plate and hindering the visibility of light transmitted through the polarizing plate, and is, for example, a roughening method using a sand blast method or an embossing method. The protective film can be formed by providing a fine uneven structure on the surface of the protective film by an appropriate method such as a method of blending transparent fine particles or the like. As the fine particles to be contained in the formation of the surface fine uneven structure, for example, a conductive material composed of silica, alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide, antimony oxide and the like having an average particle size of 0.5 to 50 μm. Transparent fine particles such as inorganic fine particles that may be used and organic fine particles made of a crosslinked or uncrosslinked polymer or the like are used. When forming the fine surface unevenness structure, the amount of the fine particles to be used is generally about 2 to 50 parts by weight, preferably 5 to 25 parts by weight, per 100 parts by weight of the transparent resin forming the fine surface unevenness structure. The anti-glare layer may also serve as a diffusion layer (such as a viewing angle expanding function) for diffusing light transmitted through the polarizing plate to increase the viewing angle or the like.

  The anti-reflection layer, anti-sticking layer, diffusion layer, anti-glare layer and the like can be provided on the protective film itself, or can be provided as an optical layer separately from the transparent protective layer.

  The pressure-sensitive adhesive forming the pressure-sensitive adhesive layer (a) is not particularly limited. For example, a pressure-sensitive adhesive having an acrylic polymer, silicone polymer, polyester, polyurethane, polyamide, polyether, fluorine-based or rubber-based polymer as a base polymer Can be appropriately selected and used. In particular, an acrylic adhesive having excellent optical transparency, exhibiting appropriate wettability, cohesiveness and adhesive adhesive properties and having excellent weather resistance and heat resistance can be preferably used.

  The formation of the pressure-sensitive adhesive layer can be performed by an appropriate method. As an example thereof, for example, an adhesive solution of about 10 to 40% by weight is prepared by dissolving or dispersing a base polymer or a composition thereof in a solvent composed of a single solvent or a mixture of appropriate solvents such as toluene and ethyl acetate, It is directly applied on the substrate or the liquid crystal film by an appropriate development method such as a casting method or a coating method, or an adhesive layer is formed on a separator according to the above and transferred to the liquid crystal layer. And the like.

  In the pressure-sensitive adhesive layer, for example, natural or synthetic resins, in particular, a tackifier resin, a filler, a pigment, a coloring agent, a glass fiber, a glass bead, a metal powder, and other inorganic powders. It may contain an additive such as an inhibitor that is added to the adhesive layer. Further, a pressure-sensitive adhesive layer containing fine particles and exhibiting light diffusibility may be used.

  The thickness of the pressure-sensitive 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.

  A separator is temporarily attached to the exposed surface of the pressure-sensitive adhesive layer for the purpose of preventing contamination and the like until the pressure-sensitive adhesive layer is put to practical use. This can prevent the adhesive layer from coming into contact with the adhesive layer in a normal 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 sheet 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 a long-chain alkyl-based, fluorine-based, or molybdenum sulfide, may be used.

  In addition, each layer such as the optical film and the pressure-sensitive adhesive layer may be treated with an ultraviolet absorbent such as a salicylate compound, a benzophenol compound, a benzotriazole compound, a cyanoacrylate compound, or a nickel complex salt compound. UV-absorbing ability can be provided by the above method.

  The elliptically polarizing plate of the present invention is suitably used in an image display device. For example, it can be preferably used for forming various devices such as a transflective liquid crystal display device. A transflective liquid crystal display device or the like is suitably used as a portable information communication device or a personal computer. When forming a reflective transflective liquid crystal display device, the elliptically polarizing plate according to the present invention is arranged on the backlight side of the liquid crystal cell.

  FIG. 9 shows a case where the elliptically polarizing plate (P1) of the present invention shown in FIGS. 5 to 7 is connected to the backlight (BL) side of the liquid crystal cell (L) via an adhesive layer in a transflective liquid crystal display device. It is arranged. The side of the elliptically polarizing plate (P1) stacked on the lower (backlight side) liquid crystal cell (L) is not particularly limited, but the polarizing plate (P) of the elliptically polarizing plate (P1) is positioned from the liquid crystal cell (L) side. It is preferred that they are furthest apart. Liquid crystal is sealed in the liquid crystal cell (L). The upper liquid crystal cell substrate is provided with a transparent electrode, and the lower liquid crystal cell substrate is provided with a reflective layer also serving as an electrode. On the upper part of the upper liquid crystal cell substrate, an elliptically polarizing plate (P2) and various optical films used for a transflective liquid crystal display device are provided. It is preferable that the elliptically polarizing plate (P2) is also arranged such that the polarizing plate (P) is farthest from the liquid crystal cell (L) side.

  When the laminated optical film or elliptically polarizing plate of the present invention is mounted on a liquid crystal display device or the like, in the optical film (2), the average optical axis of a material having optically negative uniaxiality (tilted orientation). It is preferable that the liquid crystal molecules are arranged so that the liquid crystal molecules are oriented in the same direction as the liquid crystal molecules at the center (midplane) in the thickness direction of the liquid crystal cell in which voltage is applied vertically. In this case, the orientation of the liquid crystal cell may be a twist type or a non-twist type.

  The reflective transflective liquid crystal display device shown in FIG. 9 is an example of a liquid crystal cell, and the laminated optical film and elliptically polarizing plate of the present invention can be applied to other various liquid crystal display devices.

  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.

  A polarizing plate obtained by bonding a polarizing plate and a brightness enhancement film is usually provided on the back side of a liquid crystal cell and used. The brightness enhancement film reflects linearly polarized light of a predetermined polarization axis or circularly polarized light of a predetermined direction when natural light is incident due to reflection from a backlight or a back side of a liquid crystal display device, and has a property of transmitting other light. A polarizing plate obtained by laminating a brightness enhancement film and a polarizing plate, while transmitting light from a light source such as a backlight to obtain a transmission light in 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-incident on the brightness enhancement film, and a part or all of the light is transmitted as light of a predetermined polarization state to thereby obtain brightness. In addition to increasing the amount of light transmitted through the enhancement film, it is also possible to improve the luminance by supplying polarized light that is hardly absorbed by the polarizer to increase the amount of light that can be used for liquid crystal display image display and the like. In other words, when light is incident through the polarizer from the back side of the liquid crystal cell with a backlight or the like without using a brightness enhancement film, light having a polarization direction that does not match the polarization axis of the 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 as 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 behind the same. 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.

  A diffusion plate may be provided between the brightness enhancement film and the above-mentioned reflection layer or the like. The light in the polarization state reflected by the brightness enhancement film goes to the reflection layer and the like, but the diffuser provided uniformly diffuses the light passing therethrough, and at the same time, eliminates the polarization state and becomes a non-polarization state. That is, the diffuser returns the polarized light to the original natural light state. The light in the non-polarized state, that is, the light in the natural light state is repeatedly directed to the reflection layer and the like, reflected through the reflection layer and the like, again passed through the diffusion plate and re-incident on the brightness enhancement film. Thus, while maintaining the brightness of the display screen by providing a diffusion plate that returns polarized light to the original natural light state between the brightness enhancement film and the reflective layer, etc., at the same time, reducing unevenness in the brightness of the display screen, A uniform and bright screen can be provided. It is considered that by providing such a diffusion plate, the number of repetitions of the reflection of the first incident light is moderately increased, and a uniform bright display screen can be provided in combination with the diffusion function of the diffusion plate.

  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 anisotropies. As shown in the figure, such as a cholesteric liquid crystal polymer oriented film or a film in which the oriented liquid crystal layer is supported on a film substrate, it exhibits a property of reflecting either left-handed or right-handed circularly polarized light and transmitting other light. Any suitable one such as one can be used.

  Therefore, in the brightness enhancement film of the type that transmits linearly polarized light having the 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 the 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.

  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.

  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.

  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.

  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, an optical element, and an illumination system as needed, and incorporating a drive circuit. There is no particular limitation except that the elliptically polarizing plate of the present invention is used, and it can be in accordance with the conventional art. As for the liquid crystal cell, any type such as TN type, STN type and π type can be used.

  On the back side of the liquid crystal cell, an appropriate liquid crystal display device such as one using a backlight or a reflector for an illumination system can be formed. In that case, the elliptically polarizing plate of 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.

  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. Have been.

  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.

  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.

  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.

  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.

  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 phase difference plate is composed of a 1/4 wavelength plate and the angle between the polarization directions of the polarizing plate and the phase difference plate is adjusted to π / 4, the mirror surface of the metal electrode can be completely shielded. .

  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 a phase difference plate, but is particularly circularly polarized light when the phase difference plate is a quarter-wave plate and the angle between the polarization directions of the polarization plate and the phase difference plate is π / 4. .

  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.

  Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited thereto. In each example, parts are parts by weight.

  In addition, the measurement of the refractive index and the phase difference of each optical film is performed by measuring the main refractive indices nx, ny, and nz in the film plane and in the thickness direction by using an automatic birefringence measurement device (manufactured by Oji Scientific Instruments; ), The characteristics at λ = 590 nm were measured.

  In the optical film (2), the average optical axis of the optical material having a tilted orientation and the tilt angle between the normal direction of the optical film (2) and the tilt angle of the optical film (2) with respect to the slow axis are defined as- The phase difference was measured with the measuring device at an angle of 50 ° to 50 °, and the absolute value of the angle showing the minimum phase difference was determined. In the above measurement, the measurement angle when the incident direction of light from the light source of the measuring instrument coincided with the normal to the film plane was set to 0 °.

Example 1
(Optical film with controlled three-dimensional refractive index (1))
A heat-shrinkable film made of a biaxially stretched polyester film was adhered to both sides of a 70 μm-thick transparent polycarbonate film via an adhesive layer. Thereafter, the film was stretched 1.1 times at 155 ° C. while being held by a simultaneous biaxial stretching machine. The obtained stretched film had a thickness of 72 μm, a front retardation of 140 nm, a retardation in the thickness direction of 70 nm, and an Nz coefficient of 0.5.

(Optical film (2) obtained by tilting and orienting a material exhibiting optically negative uniaxiality)
WVSA12B (thickness: 110 μm) manufactured by Fuji Photo Film Co., Ltd. was used. The film was prepared by applying a discotic liquid crystal to a support, and had a front phase difference of 30 nm, a thickness direction phase difference of 160 nm, and a tilt angle of a tilt-oriented average optical axis: 20 °.

(Optical film (3) showing optically positive uniaxiality)
A 100 μm-thick norbornene-based film (arton, manufactured by JSR Corporation) was uniaxially stretched 1.5 times at 170 ° C. The obtained stretched film had a thickness of 75 μm, a front retardation of 270 nm, and a retardation in the thickness direction of 270 nm.

(Laminated optical film and elliptically polarizing plate)
The optical film (1) and the optical film (2) were laminated via an adhesive layer (acrylic adhesive, thickness 30 μm) to obtain a laminated optical film (FIG. 1). Next, the optical film (3) was laminated on the optical film (1) side of the laminated optical film via an adhesive layer (acrylic adhesive, thickness 30 μm) to obtain a laminated optical film (FIG. 2). . Further, a polarizing plate (P: TEG1465DU, manufactured by Nitto Denko Corporation) is laminated on the optical film (3) side of the laminated optical film via an adhesive layer (acrylic adhesive, thickness: 30 μm) to form elliptically polarized light. A plate was obtained (FIG. 5).

Example 2
(Optical film with controlled three-dimensional refractive index (1))
A heat-shrinkable film made of a biaxially stretched polyester film was adhered to both sides of a 70 μm-thick transparent polycarbonate film via an adhesive layer. Thereafter, the film was stretched 1.05 times at 165 ° C. while being held by a simultaneous biaxial stretching machine. The obtained stretched film had a thickness of 75 μm, a front retardation of 140 nm, a retardation in the thickness direction of 0 nm, and an Nz coefficient of 0.

(Laminated optical film and elliptically polarizing plate)
In Example 1, a laminated optical film and an elliptically polarizing plate were obtained in the same manner as in Example 1, except that the stretched film produced above was used as the optical film (1).

Example 3
The optical film (1), the optical film (2), the optical film (3) and the polarizing plate (P) used in Example 1 were replaced with an optical film (1) / optical film (2) / optical film (3) / polarized light. The elliptically polarizing plate was obtained by laminating a plate (P) and a pressure-sensitive adhesive layer (acrylic pressure-sensitive adhesive, thickness 30 μm) in this order (FIG. 6).

Example 4
The optical film (1), the optical film (2), the optical film (3) and the polarizing plate (P) used in Example 1 were replaced with an optical film (1) / optical film (3) / optical film (2) / polarized light. The elliptically polarizing plate was obtained by laminating a plate (P) and a pressure-sensitive adhesive layer (acrylic pressure-sensitive adhesive, thickness 30 μm) in this order (FIG. 7).

Comparative Example 1
(Retardation film)
A 70 μm-thick transparent polycarbonate film was uniaxially stretched 1.55 times at 155 ° C. with a uniaxial stretching machine. The obtained stretched film had a thickness of 60 μm, a front retardation of 140 nm, a retardation in the thickness direction of 140 nm, and an Nz coefficient of 1.

(Laminated optical film and elliptically polarizing plate)
In Example 1, a laminated optical film and an elliptically polarizing plate were obtained in the same manner as in Example 1 except that the retardation film (stretched film) produced above was used instead of the optical film (1).

Reference Example 1
(Optical film (3) showing optically positive uniaxiality)
A 100 μm-thick norbornene-based film (arton, manufactured by JSR Corporation) was uniaxially stretched 1.3 times at 170 ° C. The obtained stretched film had a thickness of 80 μm, a front retardation of 140 nm, and a retardation in the thickness direction of 140 nm. This was used as an optical film (3-2).

(Elliptical polarizing plate)
The optical film (3) obtained in Example 1 and having optically positive uniaxiality was used as the optical film (3-1). The optical film (3-1) and the optical film (3-2) are interposed through a pressure-sensitive adhesive layer (acrylic pressure-sensitive adhesive, thickness 30 μm) as shown in FIG. 8 to obtain a polarizing plate (P: manufactured by Nitto Denko Corporation). , TEG1465DU) to obtain an elliptically polarizing plate.

(Evaluation)
The elliptically polarizing plates manufactured in Examples and Comparative Examples were mounted as the elliptically polarizing plates (P1) on the backlight side of the transflective TFT-TN type liquid crystal display device of FIG. On the other hand, the elliptically polarizing plate produced in Reference Example 1 was mounted as a viewing-side elliptically polarizing plate (P2). Both the elliptically polarizing plate (P1) and the elliptically polarizing plate (P2) were mounted such that the polarizing plate side was located at the farthest lamination position from the liquid crystal cell (L) side.

  Next, a white image and a black image are displayed on the liquid crystal display device, and the Y value, the x value, and the y value in the XYZ display system at the front, up, down, left and right, and viewing angle of 0 to 70 ° are displayed by EZcontrast 160D manufactured by ELDIM. Was measured.

  The angle at which the value of the contrast (Y value (white image) / Y value (black image)) was 10 or more was defined as the viewing angle. Table 1 shows the results.

Further, the chromaticity change of the chromaticity (x ₄₀ , y ₄₀ ) was evaluated by comparing the chromaticity (x ₄₀ , y ₄₀ ) of the white image when the chromaticity (x ₀ , y ₀ ) in front of the screen was inclined by 40 ° up, down, left and right. The chromaticity change was determined by the following equation. Table 1 shows the results.
Chromaticity change amount = {(x ₄₀ −x ₀ ) ² + (y ₄₀ −y ₀ ) ² }

1 is an embodiment of a cross-sectional view of a laminated optical film of the present invention. 1 is an embodiment of a cross-sectional view of a laminated optical film of the present invention. 1 is an embodiment of a cross-sectional view of a laminated optical film of the present invention. 1 is an embodiment of a cross-sectional view of a laminated optical film of the present invention. 1 is an embodiment of a cross-sectional view of an elliptically polarizing plate of the present invention. 1 is an embodiment of a cross-sectional view of an elliptically polarizing plate of the present invention. 1 is an embodiment of a cross-sectional view of an elliptically polarizing plate of the present invention. FIG. 4 is an embodiment of a cross-sectional view of an elliptically polarizing plate of a reference example. It is sectional drawing of the example of a transflective liquid crystal display device of an Example.

Explanation of reference numerals

1: Optical film with controlled three-dimensional refractive index (1)
2: An optical film (2) in which a material exhibiting a negative uniaxial property is inclinedly oriented.
3: Optical film showing optically positive uniaxiality (3)
P: polarizing plate a: adhesive layer L: liquid crystal cell BL: backlight

Claims (9)

The direction in which the refractive index in the film plane is the maximum is the X axis, the direction perpendicular to the X axis is the Y axis, the thickness direction of the film is the Z axis, and the refractive indexes in the respective axial directions are nx ₁ , ny ₁ , nz _{If 1
Nz = (nx 1 -nz 1)} / Nz coefficient expressed by (nx ₁ -ny ₁₎ is,
An optical film (1) whose three-dimensional refractive index is controlled so as to satisfy Nz ≦ 0.9,
An optical film (2), which is formed of a material having an optically negative uniaxial property and in which the material is obliquely oriented, is laminated.   The laminated optical film according to claim 1, wherein the Nz coefficient of the optical film (1) whose three-dimensional refractive index is controlled satisfies Nz ≤ 0.3.   3. The laminated optical film according to claim 1, wherein the material forming the optical film (2) and exhibiting optically negative uniaxiality is a discotic liquid crystal compound.   The material that forms the optical film (2) and exhibits optically negative uniaxiality has a tilt angle between the average optical axis and the normal direction of the optical film (2) in the range of 5 ° to 50 °. The laminated optical film according to any one of claims 1 to 3, which is oriented. The laminated optical film according to any one of claims 1 to 4,
Further, the direction in which the refractive index in the film plane is the maximum is the X axis, the direction perpendicular to the X axis is the Y axis, the thickness direction of the film is the Z axis, and the refractive indexes in the respective axial directions are nx ₃ and ny _3. , Nz ₃ ,
An optical film (3) that satisfies nx ₃ > ny ₃ ≒ nz ₃ and that is optically positively uniaxial.   An optical film having a controlled three-dimensional refractive index between an optical film (3) having an optically positive uniaxial property and an optical film (2) obtained by obliquely orienting a material having an optically negative uniaxial property. The laminated optical film according to claim 5, wherein a film (1) is arranged.   An elliptically polarizing plate, comprising the laminated optical film according to claim 1 and a polarizing plate.   The elliptically polarizing plate according to claim 7, wherein a polarizing plate is laminated on the optical film (3) side of the laminated optical film according to claim 5 or 6. An image display device comprising the laminated optical film according to claim 1 or the elliptically polarizing plate according to claim 7.

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