CN100410697C - Manufacturing method of polarizing plate with wide viewing angle - Google Patents

Abstract

The invention provides a method for manufacturing a high-contrast polarizing plate with a wide viewing angle, a polarizing plate with a wide viewing angle obtained by the method, an optical film equipped with the polarizing plate with a wide viewing angle, and a polarizing plate with the wide viewing angle or optical film image display device. The manufacturing method of the wide viewing angle polarizing plate of the present invention is a manufacturing method of a wide viewing angle polarizing plate having an optical compensation film and a polarizer, wherein the optical compensation film has a liquid crystal polymer on at least one side of the transparency protective layer. The birefringent layer constituted is characterized in that it has the step of heat-treating the optical compensation film in the range of 68° C. to 125° C., and using the transparent protective layer as an adhesive surface and applying the adhesive to the optical compensation film. The process of laminating the polarizer and the optical compensation film.

Description

Manufacturing method of polarizing plate with wide viewing angle

technical field

The present invention relates to a method for manufacturing a wide viewing angle polarizing plate with improved front contrast, a wide viewing angle polarizing plate obtained by the manufacturing method, an optical film having the wide viewing angle polarizing plate, and a wide viewing angle polarizing plate having the wide viewing angle polarizing plate or optical film image display device.

Background technique

In recent years, liquid crystal display devices have been widely used, but compared with CRT (cathode ray tube, Cathode Ray Tube), it lacks a viewing angle with good visibility, so it is necessary to expand the viewing angle. As a method of enlarging the viewing angle, a method of arranging and attaching a birefringent layer on a liquid crystal cell has been proposed (for example, refer to Patent Document 1). However, it is well known that when this method is used, the viewing angle is greatly enlarged, but in terms of front contrast, it is inferior to a polarizing plate not provided with a birefringent layer.

Patent Document 1: Japanese Unexamined Patent Publication No. 6-174918

Contents of the invention

The present invention has been made to solve the above-mentioned problems, and its object is to provide a method for manufacturing a polarizing plate with a high front contrast ratio, a polarizing plate with a wide viewing angle obtained by the manufacturing method, and a polarizing plate having the wide viewing angle. An optical film of an angular polarizing plate and an image display device comprising the wide viewing angle polarizing plate or the optical film.

The inventors of the present application conducted intensive studies to solve the above-mentioned conventional problems. As a result, they have found that the object can be achieved by a method for producing a wide viewing angle polarizing plate, a wide viewing angle polarizing plate, and an image display device including the wide viewing angle polarizing plate as described below, and completed the present invention.

In order to solve the above-mentioned problems, the manufacturing method of the wide viewing angle polarizing plate of the present invention is a manufacturing method of a wide viewing angle polarizing plate having an optical compensation film and a polarizer, wherein the optical compensation film is on at least one side of the transparency protective layer. It has a birefringent layer composed of a liquid crystal polymer, and is characterized in that it has a step of heat-treating the above-mentioned optical compensation film in the range of 68°C to 125°C, and using the above-mentioned transparent protective layer as an adhesive surface and using an adhesive A step of laminating the above-mentioned polarizer and the above-mentioned optical compensation film.

In addition, prior to the above-mentioned heat treatment, it is preferable to include a step of saponifying the transparent protective layer provided with the above-mentioned birefringent layer.

Furthermore, as the liquid crystal polymer, a discotic liquid crystal polymer is preferably used.

Furthermore, it is preferable to use a cellulose triacetate film as the above-mentioned transparency protective layer.

Moreover, in order to solve the said subject, the wide viewing angle polarizing plate of this invention is characterized by being manufactured using the manufacturing method of a wide viewing angle polarizing plate.

Moreover, in order to solve the above-mentioned problems, the optical film of the present invention is characterized in that at least one of the above-mentioned wide viewing angle polarizing plates is laminated.

In addition, in order to solve the above-mentioned problems, the image display device of the present invention is characterized by using the above-mentioned wide viewing angle polarizing plate or optical film.

In the manufacturing method of the wide viewing angle polarizing plate of the present invention, the transparent protective layer (hereinafter, referred to as an optical compensation film) on which the birefringent layer is formed is subjected to heat treatment in the range of 68° C. to 125° C. The refractive index difference of the refraction layer becomes low, so that the phase difference in the front direction is reduced. As a result, it is possible to obtain a wide viewing angle polarizing plate in which the occurrence of light leakage is reduced and the reduction in contrast in the front direction is suppressed.

In addition, prior to the above-mentioned heat treatment, a step of saponifying the transparent protective layer provided with the above-mentioned birefringent layer is performed to introduce hydroxyl groups on the surface of the transparent protective layer. When the transparency protective layer is, for example, cellulose triacetate, etc., when the transparency protective layer and the polarizer are glued by introducing hydroxyl groups to its surface and using an adhesive, the hydroxyl group on the surface of the transparency protective layer and the hydroxyl group of the adhesive can form hydrogen bonds. As a result, the adhesive effect of the adhesive is further improved. In addition, by performing the heat treatment step, it is possible to omit the drying step that is generally required after the saponification treatment. As a result, an increase in production efficiency is realized.

In addition, a liquid crystal display device including a wide viewing angle polarizing plate obtained by the above production method has a wide viewing angle and is excellent in display characteristics such as high contrast even in the front direction of the display screen.

Detailed ways

Embodiments of the present invention will be described below.

The present invention is a method for manufacturing a polarizer with an optical compensation film and a polarizer, wherein the optical compensation film has a birefringent layer composed of a liquid crystal polymer on at least one side of a transparency protective layer, It includes a step of heat-treating the optical compensation film in the range of 68°C to 125°C, and a step of bonding the polarizer and the optical compensation film together with an adhesive using the transparent protective layer as an adhesive surface.

At this time, if the above-mentioned optical compensation film is provided on at least one surface of the polarizer, it can be used as a polarizer with a wide viewing angle, but in order to protect the polarizer on the opposite side, add optical functions, etc., it is preferable to make An optical film laminated with suitable layers. Examples of such laminated layers include the above-mentioned optical compensation film, the above-mentioned transparent protective film, an adhesive layer, a retardation film, a hard coat layer, a reflective layer, or a brightness-improving film. When these layers are laminated, they can be laminated by a direct coating method or an appropriate method using an adhesive or an adhesive agent or the like indirectly.

An optical compensation film in which a birefringent layer is laminated on the transparent protective layer can be produced by various conventionally known methods. For example, after forming an alignment film in which a transparency protective layer has been polished, a liquid crystal polymer or the like is coated on the alignment film, followed by heat treatment or ultraviolet curing. Thereby, a birefringent layer comprising a liquid crystal polymer in a predetermined orientation state can be formed. In addition, the transparency protective layer and the birefringent layer are preferably in an adhesive state. In addition, lamination of birefringent layers may be performed on both surfaces of the transparency protective layer. In this case, another transparent protective layer can be further provided on the side of the adhesive surface with the polarizer.

The birefringent layer has a function of optically compensating for birefringence (deflection of light) that occurs when light passes through the liquid crystal cell through the retardation of the film. The retardation characteristics and the like of the birefringent layer can be appropriately set by controlling the layer thickness thereof. The retardation of the birefringent layer can be controlled by the alignment state of the liquid crystal polymer in the thickness direction or the in-plane direction, the tilt angle between the main refractive index direction in the thickness direction and the normal direction of the liquid crystal layer, or layer thickness.

The layer thickness of the birefringent layer is preferably within a range of 1 to 5 μm, more preferably within a range of 2 to 3 μm. When the layer thickness is within these ranges, it is possible to achieve a widening of the viewing angle with good visibility due to the compensation effect against the change in the viewing angle, or to realize the identification due to the prevention of coloring due to the wavelength dispersion of the birefringence difference. Good expansion of the angle of view. In addition, the retardation in the front direction is preferably in the range of 10 to 200 nm, more preferably in the range of 15 to 150 nm.

The above-mentioned liquid crystal polymer is not particularly limited, and conventionally known polymers can be used, but a discotic liquid crystal polymer is preferable in the present invention. When the birefringent layer is constituted by a discotic liquid crystal polymer, the birefringent layer has a structure in which the discotic liquid crystal polymer has an oblique orientation or a mixed orientation. Among them, the discotic liquid crystal polymer changes the direction of the retardation axis according to the improvement effect of the visibility, that is, the change of the viewing angle from the vertical direction of the liquid crystal cell, thereby making the difference between the transmission axis and the wide viewing angle polarizer. Misalignment occurs in the parallel relationship or the vertical relationship of the retardation axis, and optical anisotropy (phase difference corresponding to compensation) is generated according to the amount of the misalignment.

Examples of the above-mentioned discotic liquid crystalline polymers include those represented by the following chemical formulas.

化1

Chemical 1

(where R is nC ₇ H ₁₅ COO-.)

A discotic liquid crystal layer based on a liquid crystal polymer can be formed on one or both sides of the transparent protective layer. For example, if necessary, the liquid crystal polymer can be developed on the transparent protective layer that has been subjected to an orientation treatment to form a predetermined orientation. The layering method of the liquid crystal layer is performed by a conventional method. Therefore, when the liquid crystal polymer is developed, it can be formed into a solution based on a solvent, a molten liquid by heating, or the like as necessary. In addition, when orienting the cured layer of the liquid crystal polymer on the discotic liquid crystal layer, heat treatment to a glass transition temperature or higher may be performed as necessary.

Among them, as the orientation treatment carried out on the above-mentioned transparent protective film, it is possible to set a polyimide, polyvinyl alcohol, polyester, polyarylate, polyamideimide, or polyetherimide with rayon cloth, for example. Orientation film after buffing of attached film, suitable orientation film made of oblique vapor deposition layer such as SiO ₂ , etc., and oblique etching by ion beam, etc.

From the viewpoint of controllability of the direction of the retardation axis during polarizing plate formation, a birefringent layer made of a liquid crystal polymer is usually provided on a transparent protective layer and used to form a polarizing plate. The thickness of the provided birefringent layer can be appropriately determined by retardation characteristics, etc., and the retardation can be determined by the alignment state of the liquid crystal polymer in the thickness direction or the in-plane direction, the main refractive index direction in the thickness direction, and the normal line of the liquid crystal layer. The inclination angle of the direction, or the thickness of the layer, etc. are controlled.

However, when birefringent layers are provided on both surfaces of the transparent protective layer, each birefringent layer may be formed as a layer in which liquid crystal polymers of the same type or different types are overlapped.

The transparent protective layer is suitably formed as a plastic coating layer, a laminate of protective films, or the like. In particular, plastics excellent in transparency, mechanical strength, thermal stability, moisture barrier performance, isotropy, and the like are preferably used. As the material of the transparency protective layer, polyester polymers such as polyethylene terephthalate and polyethylene naphthalate, polystyrene or acrylonitrile-styrene copolymer (AS Resin) and other styrene-based polymers, cellulose-based polymers such as cellulose diacetate and cellulose triacetate, polyethersulfone-based polymers, polycarbonate-based polymers, polyamide-based polymers, polyimides Polymers, polyolefin polymers, or acrylic polymers such as polymethyl methacrylate, etc. In addition, polyolefin-based polymers such as polyethylene, polypropylene, polyolefins having a cyclic or norbornene structure, ethylene-propylene copolymers, vinyl chloride-based polymers, nylon or aromatic polyamides, etc. Amide polymers, imide polymers, sulfone polymers, polyethersulfone polymers, polyether ether ketone polymers, polyphenylene sulfide polymers, vinyl alcohol polymers, vinylidene chloride Polymers, polyvinyl butyral polymers, polyarylate polymers, polyoxymethylene polymers, epoxy polymers, or mixtures of the above polymers. In addition, thermosetting or ultraviolet curable resins such as acrylic, urethane, acrylic urethane, epoxy, or silicone are also exemplified.

The polymer film described in JP-A-2001-343529 (WO01/37007) can be exemplified by (A) a thermoplastic resin having a substituted and/or unsubstituted imino group on the side chain, and (B) a side chain A resin composition of a thermoplastic resin having substituted and/or unsubstituted phenyl and nitrile groups. A specific example includes 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 co-extruded product of the resin composition or the like can be used. These films have a small phase difference and a small photoelastic coefficient, so defects such as unevenness caused by the deflection of the polarizer can be eliminated, and the moisture permeability is small, so the humidity durability is excellent.

As a transparent protective layer, the smaller the phase difference, the better. In addition, in consideration of this point of view, polarization characteristics, durability, etc., it is preferable to use a cellulose-based polymer. Furthermore, cellulose triacetate is preferable among cellulosic polymers. In addition, a transparent protective layer in which fine concavo-convex structures are formed on the surface by containing fine particles can be used.

In addition, the thinner the transparency protective layer, the better. This is because the phase difference is determined by the product (Δnd) of the refractive index difference (Δn: nx-ny) and the layer thickness (d) of the optical compensation film. The thickness of the transparent protective layer is usually 500 μm or less, preferably 5 to 300 μm, and more preferably 10 to 200 μm, in consideration of the protection of the polarizer and the like.

Wherein, when the transparent protective layer is provided on both surfaces of the polarizer, the transparent protective layer composed of the same polymer can be formed inside and outside, and the transparent protective layer composed of different polymer materials or the like can also be used.

The method for producing a wide viewing angle polarizing plate of the present invention can saponify the transparent protective layer provided with the birefringent layer before the heat treatment step. The saponification treatment is performed, for example, by immersing the transparency protective layer in an alkaline aqueous solution. Thereby, hydroxyl groups can be introduced on the surface of the transparency protective layer, and the adhesion effect can be improved in adhesion with a polarizer using an adhesive agent described later. The base used is not particularly limited, for example, potassium hydroxide or sodium hydroxide is preferably used. In this step, water washing or acid neutralization may be performed as necessary.

The step of heat-treating the transparent protective layer including the birefringent layer, that is, the optical compensation film, is performed with the most important purpose of reducing the front phase retardation (Δnd) of the birefringent layer. That is, heat treatment to rearrange the liquid crystal polymer on the birefringent layer. Therefore, the rearrangement of the liquid crystal polymer can reduce the alignment disorder and make the alignment state more regular than that before heat treatment. For this reason, the refractive index difference of the birefringent layer is reduced and the phase difference in the front direction is reduced. For example, the hysteresis (in The difference in the value of the phase difference in the front direction) decreases. Thereby, the first light can be compensated by the optical compensation film as much as possible, and the emission to the outside can be suppressed. As a result, it is possible to obtain a wide viewing angle polarizing plate that reduces the occurrence of light leakage and suppresses a decrease in contrast in the front direction.

In addition, this step can also be performed for the purpose of drying the alkaline aqueous solution after the saponification treatment. Accordingly, the birefringent layer can be heat-treated without increasing the number of steps, and a reduction in production efficiency can be suppressed.

The temperature of the heat treatment is preferably performed in the range of 68°C to 125°C, more preferably in the range of 90°C to 110°C, and particularly preferably in the range of 95°C to 105°C. When the temperature of the above-mentioned heat treatment is lower than 68° C., there is a problem that the reduction of the so-called front phase difference is insufficient and the contrast cannot be improved. On the other hand, when exceeding 125°C, the thermal shrinkage of the optical compensation film increases. As a result, when the wide viewing angle polarizing plate is manufactured by bonding the transparent protective layer and the polarizer together, the end face of the wide viewing angle polarizing plate is damaged and the display becomes defective. When the heat treatment time is long, display defects occur for the same reason as above, so it is necessary to set an appropriate time. It is preferably in the range of 1 to 300 seconds, more preferably in the range of 10 to 120 seconds. Wherein, when the heat treatment is performed under the above heat treatment conditions, the retardation value (Δnd) in the front direction of the optical compensation film can be reduced by about 20 to 40%. For example, when the retardation in the front direction is initially 30 nm, it becomes 20 to 25 nm after heat treatment.

The lamination step of the above-mentioned polarizer and the transparent protective layer provided with the above-mentioned birefringent layer is performed using an adhesive agent with the transparent protective layer as an adhesive surface. This is because adhesion and fixation are required in order to prevent misalignment of the axial relationship between the retardation axis of the birefringent layer and the transmission axis of the polarizer. In addition, bonding is carried out so that the retardation axis of the birefringent layer and the transmission axis of the polarizer are substantially parallel or perpendicular. At this time, the application of the adhesive agent may be performed on either the polarizer side or the transparent protective layer side, or may be performed on both sides.

This step is preferably performed immediately after heat treatment. More specifically, it is preferably performed within 2 hours after the heat treatment, and even more preferably within 1 minute. This is because the effect of the heat treatment disappears due to the influence of moisture absorption of the optical compensation film when this step is carried out 2 hours after the heat treatment. However, if moisture absorption of the optical compensation film can be prevented, the heat-treated optical compensation film may be bonded to the polarizer after rewinding.

The adhesive is not particularly limited, and specifically, suitable adhesives such as transparent pressure-sensitive adhesives made of acrylic, silicone, polyester, polyurethane, polyether, or rubber can be used. Among these adhesives, in order to prevent changes in the optical properties of polarizers or optical compensation films, those that do not require high-temperature treatment and long-term curing treatment or drying are preferred when the adhesive is cured or dried. In addition, adhesives that do not peel off under heating or humidification are also preferred.

From the above viewpoints, acrylic pressure-sensitive adhesives are particularly preferred. In addition, acrylic pressure-sensitive adhesives are superior in transparency, weather resistance, heat resistance, and the like compared with other adhesives, and are therefore preferable from these points. Such acrylic pressure-sensitive adhesives are not particularly limited, and monomers like butyl (meth)acrylate, methyl (meth)acrylate, ethyl (meth)acrylate, and (meth)acrylic acid can be exemplified as As a component, the base polymer is made of an acrylic polymer having a weight average molecular weight of 100,000 or more and a glass transition temperature of 0° C. or less. Among them, when the birefringent layer and the transparent protective layer have different refractive indices, from the viewpoint of suppressing reflection loss, as the above-mentioned adhesive agent, a material showing an intermediate value of both refractive indices is preferable.

As the polarizer, an appropriate polarizer that can obtain light in a predetermined polarization state can be used. Particularly preferred is a polarizer that can obtain transmitted light in a linearly polarized state. The polarizer is not particularly limited, and examples thereof include hydrophilic polymer films such as polyvinyl alcohol-based films, partially formalized polyvinyl alcohol-based films, and ethylene-vinyl acetate copolymer-based partially saponified films. On, a film that absorbs dichroic dyes such as iodine and/or dichroic dyes and stretches them; a polyolefin-based oriented film such as a dehydrated polyvinyl alcohol-based product or a dehydrochlorinated acid-treated product of polyvinyl chloride, etc. Among these polarizers, polarizers made of dichroic substances such as stretched polyvinyl alcohol-based films that adsorb iodine and dichroic dyes are particularly preferable. This is because linearly polarized light with a high degree of polarization can be obtained.

As the polyvinyl alcohol-based film, any method such as a casting method, a casting method, and an extrusion method by casting a stock solution obtained by dissolving a polyvinyl alcohol-based resin in water or an organic solvent to form a film can be suitably used. film of film. The degree of polymerization of the polyvinyl alcohol-based resin is preferably about 100 to 5,000, and more preferably 1,400 to 4,000.

Here, the surface of the above-mentioned transparent protective layer to which the polarizer is not adhered may be subjected to a step of forming a hard coat layer, anti-reflection treatment, anti-blocking, treatment for the purpose of diffusion or anti-glare.

The purpose of the hard coat treatment is to prevent damage to the surface of the polarizer, for example, by adding an appropriate ultraviolet curable resin such as acrylic or silicone to the surface of the transparent protective layer to improve the hardness, sliding properties, etc. Formation of the cured film, etc. In addition, the purpose of antireflection treatment is to prevent reflection of external light on the surface of the polarizing plate, and it can be accomplished by forming a conventional antireflection film or the like. In addition, the purpose of anti-blocking treatment is to prevent close contact with adjacent layers.

In addition, the purpose of implementing anti-glare treatment is to prevent external light from being reflected on the surface of the polarizer and disturbing the visibility of the light transmitted by the polarizer. For example, it can be formed by imparting a fine concave-convex structure to the surface of the transparency protective layer by an appropriate method such as roughening by sandblasting or embossing, or by adding transparent fine particles. As the microparticles contained in the formation of the above-mentioned surface fine uneven structure, for example, those made of silica, alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide, Transparent particles such as conductive inorganic particles composed of antimony or the like, organic particles composed of cross-linked or non-cross-linked polymers, etc. When forming the surface fine uneven structure, the amount of fine particles used is usually about 2 to 70 parts by weight, preferably 5 to 50 parts by weight, based on 100 parts by weight of the transparent resin for forming the surface fine uneven structure. The anti-glare layer may also be used as a diffusion layer that diffuses light transmitted by the polarizer to widen the viewing angle (viewing angle widening function, etc.).

In addition, the above-mentioned antireflection layer, antiblocking layer, diffusion layer, and antiglare layer can be provided separately from the transparent protective layer as an optical layer for other purposes besides being provided on the transparent protective layer itself.

In the above-mentioned form, the wide viewing angle polarizing plate of the present invention can be used as a transmissive polarizing plate. However, the present invention is not limited thereto, and can be used as an optical film laminated with other optical layers depending on the application or the like. There are no particular restrictions on the optical layer, for example, one or more layers of reflective plates, semi-transparent plates, retardation plates (including 1/2 and 1/4 wavelength plates) and the like can be used for optical applications such as liquid crystal display devices. layer. More specifically, the wide viewing angle polarizing plate of the present invention can be used as a reflective polarizing plate or a semi-transmitting polarizing plate by laminating a reflecting plate or a semi-transmitting plate. In addition, a retardation plate can be laminated on the wide viewing angle polarizing plate of the present invention to be used as an elliptically polarizing plate or a circular polarizing plate. Furthermore, it is also possible to use a polarizing plate in which a brightness improving film is laminated on the wide viewing angle polarizing plate of the present invention.

A reflective polarizing plate is formed by providing a reflective layer on a wide viewing angle polarizing plate, and can be used to form a liquid crystal display device or the like that reflects incident light from the viewing side (display side) to display. Formation of the reflective polarizer can be performed by an appropriate method such as attaching a reflective layer made of metal or the like to the transparent protective layer on the side on which the birefringent layer is laminated and on the opposite side. More specifically, it can be exemplified as a polarizing plate obtained by attaching a foil or vapor-deposited film made of a reflective metal such as aluminum on one side of a transparent protective layer such as a matte-treated transparent protective layer if necessary. wait. In addition, a polarizer may be exemplified in which a metal reflective layer is provided by an appropriate method such as vapor deposition or plating on the fine concave-convex structure of the surface caused by the particles contained in the above-mentioned transparent protective layer. The reflective layer with the above-mentioned fine uneven structure diffuses incident light by diffuse reflection, has the advantages of preventing reflection and diffuse reflection, and suppressing unevenness in light and shade. In addition, the transparent protective layer containing fine particles has the advantage of further suppressing the unevenness of light and shade through diffusion when incident light and its reflected light pass through it. The formation of the reflective layer of the micro-concave-convex structure reflecting the surface micro-concave-convex structure of the transparency protective layer can be carried out by appropriate methods such as vapor deposition methods such as vacuum evaporation methods, ion plating methods, and sputtering methods, or coating methods. A method such as a method of directly attaching a metal on the surface of the protective layer.

In addition, for reflective polarizers, instead of being directly formed on the transparent protective layer of the above-mentioned wide viewing angle polarizer, it can be used as a reflective layer formed by providing a reflective layer on an appropriate film such as the transparent protective layer. tablet use. Also, since the reflective layer is usually made of metal, the reflective surface is covered with a transparent protective layer or a wide viewing angle polarizer to prevent a decrease in reflectance due to oxidation. Furthermore, the initial reflectance is maintained for a long period of time, and it is possible to avoid laminating a protective layer separately on the reflective layer.

Among the above, the semi-transmissive polarizing plate can be obtained by forming a semi-transmissive reflective layer such as a half mirror that reflects and transmits light with a reflective layer. The transflective polarizing plate is usually provided on the back side of the liquid crystal cell. When using a transflective liquid crystal display device equipped with such a transflective polarizer in a bright environment, the external light incident from the recognition side (display surface side) is used as display light. When used in a downlight, light from a backlight or the like is used as display light. Thereby, the power consumption can be reduced.

Next, an elliptically polarizing plate or a circular polarizing plate formed by further laminating a retardation plate on a wide viewing angle polarizing plate will be described. In the case of changing linearly polarized light into elliptically polarized light or circularly polarized light, or changing elliptically polarized light or circularly polarized light into linearly polarized light, or changing the polarization direction of linearly polarized light, a retardation plate or the like can be used. In particular, as a retardation plate that changes linearly polarized light into circularly polarized light or vice versa, a so-called 1/4 wavelength plate (also referred to as a λ/4 plate) can be used. A 1/2 wavelength plate (also called a λ/2 plate) is usually used in the case of changing the polarization direction of linearly polarized light.

Elliptical polarizers can be effectively used in the following cases to compensate (prevent) the coloring (blue or yellow) caused by the birefringence of the liquid crystal layer in an STN (SuperTwisted Nematic) mode liquid crystal display device, thereby performing the above-mentioned white and black without coloring displayed, etc. In addition, a polarizing plate that controls the three-dimensional refractive index can also compensate (prevent) coloring that occurs when viewing the screen of a liquid crystal display device from an oblique direction, and is therefore preferable. The circular polarizing plate is effectively used, for example, to adjust the color tone of an image of a reflective liquid crystal display device that displays an image in color, and also has a function of preventing reflection. Specific examples of the aforementioned retardation plate include those made of polycarbonate, polyvinyl alcohol, polystyrene, polymethyl methacrylate, polypropylene or other polyolefins, polyarylates, and polyamides. A birefringent film formed by stretching a film made of a polymer, an alignment film of a liquid crystal polymer, a member supporting an alignment layer of a liquid crystal polymer with a film, etc. The phase difference plate may have an appropriate phase difference corresponding to the purpose of use of the member for the purpose of compensating, for example, the coloring caused by the birefringence of various wavelength plates or liquid crystal layers, or the viewing angle, and may be stacked 2 A member that controls optical characteristics such as phase difference by using more than one type of phase difference plate.

In addition, the above-mentioned elliptically polarizing plate or reflective elliptically polarizing plate is formed by laminating a wide viewing angle polarizing plate or reflective polarizing plate and a phase difference plate in an appropriate combination. Such elliptically polarizing plates and the like can also be formed by sequentially stacking (reflective) polarizing plates and retardation plates in sequence during the manufacture of liquid crystal display devices to form a combination of (reflective) polarizing plates and retardation plates, and as above As mentioned above, members preliminarily formed as optical films such as elliptically polarizing plates are excellent in quality stability and lamination workability, and have the advantages of improving the production efficiency of liquid crystal display devices and the like.

A polarizing plate obtained by laminating a wide viewing angle polarizing plate and a brightness improving film is usually installed and used on the back side of a liquid crystal cell. Brightness-improving film is a film that exhibits the property of reflecting linearly polarized light of a predetermined polarization axis or circularly polarized light of a predetermined direction when natural light enters from a backlight of a liquid crystal display device or the like or by reflection from the back side, etc. light while allowing other light to pass through. Therefore, the polarizing plate formed by laminating the brightness-improving film and the wide viewing angle polarizing plate can make the light from the light source such as the backlight incident, and obtain the transmitted light of the specified polarization state. The light is not transmitted but is reflected. The light reflected on the surface of the brightness-improving film is further reversed by means of a reflective layer on the rear side thereof, and it is incident on the brightness-improving film again, so that part or all of it is transmitted as light in a prescribed polarization state. By doing this, the light transmitted through the brightness improving film is increased, and at the same time, polarized light that is difficult to absorb is supplied to the polarizer, thereby increasing the amount of light that can be utilized in liquid crystal display image display, etc., and thus the brightness can be improved. That is, in the case where 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 improving film, light having a polarization direction inconsistent with the polarization axis of the polarizer is basically captured by the polarizer. Absorbed and therefore cannot pass through polarizers. That is, although depending on the characteristics of the polarizer, about 50% of the light is absorbed by the polarizer, so the amount of light that can be used in liquid crystal image displays and the like decreases, resulting in darker images. Because the brightness improvement film repeatedly performs the following operations, that is, the light with the polarization direction that can be absorbed by the polarizer is not incident on the polarizer, but the light is reflected on the brightness improvement film, and then by means of the The reflective layer etc. on the side are reversed, and the light is incident on the brightness improving film again, so that the brightness improving film only changes the polarization direction of the light reflected and reversed between the two to pass through the polarizer. Since the polarized light in the polarization direction is transmitted and supplied to the polarizer, light such as a backlight can be effectively used for displaying an image on a liquid crystal display device, and the screen can be brightened.

It is also possible to provide a diffusion plate between the luminance improving film and the above-mentioned reflective layer or the like. The light in the polarized state reflected by the luminance improving film is directed toward the above-mentioned reflective layer, etc., and the diffuser is provided to uniformly diffuse the passing light while canceling the polarized state into a non-polarized state. That is, the diffuser returns the polarized light to its original natural light state. The operation of irradiating the light in the unpolarized state, that is, the natural light state, to the reflective layer, etc., is reflected by the reflective layer, and then passes through the diffusion plate again to enter the brightness improving film is repeated. In this way, by providing a diffuser plate between the brightness improving film and the reflective layer, which restores the polarized light to its original natural light state, the brightness of the display screen can be maintained while the unevenness of the brightness of the display screen can be reduced, thereby providing Uniform and bright picture. By arranging the diffusion plate, the number of repeated reflections of the first incident light can be appropriately increased, and a uniform and bright display image can be provided by utilizing the diffusion function of the diffusion plate.

As the aforementioned brightness improving film, for example, a dielectric multilayer film or a film multilayer laminate having different refractive index anisotropy, which exhibits the property of transmitting linearly polarized light with a specific polarization axis and reflecting other light, can be used. Films, alignment films of cholesteric liquid crystal polymers, or films supporting the alignment liquid crystal layer on a film substrate, which reflect either left-handed or right-handed circularly polarized light and transmit other light Suitable films such as films with special properties.

Therefore, by using the brightness improving film of the type that transmits the linearly polarized light of the above-mentioned predetermined polarization axis, the transmitted light is directly incident on the wide viewing angle polarizing plate along the direction consistent with the polarization axis, and it can be suppressed by While absorbing the loss caused by the polarizer with a wide viewing angle, the light is transmitted efficiently. On the other hand, using a brightness-improving film that transmits circularly polarized light, such as a cholesteric liquid crystal layer, can directly make light incident on a polarizer, but from the viewpoint of suppressing absorption loss, it is preferable to use a phase The circularly polarized light is linearly polarized by the difference plate, and then incident on the wide field of view polarizer. Furthermore, by using a 1/4 wavelength plate as the retardation plate, it is possible to convert circularly polarized light into linearly polarized light.

A phase difference plate that can function as a 1/4 wavelength plate in a wide wavelength range such as the visible light region can be obtained, for example, by using a light-colored light with a wavelength of 550nm that can function as a 1/4 wavelength plate. The retardation layer and the retardation layer exhibiting other retardation characteristics, for example, a method in which the retardation layer can function as a 1/2 wavelength plate is overlapped, and the like. Therefore, the retardation plate disposed between the wide viewing angle polarizing plate and the brightness improving film may be composed of one or more retardation layers.

In addition, as far as the cholesteric liquid crystal layer is concerned, it is also possible to combine materials with different reflection wavelengths to form a configuration structure in which two or more layers overlap, thereby obtaining circularly polarized light reflected in a wider wavelength range such as the visible light region. components. As a result, transmitted circularly polarized light over a wide wavelength range can be obtained.

In addition, the wide viewing angle polarizing plate may be composed of a lamination of a wide viewing angle polarizing plate and two or more optical layers, like the above-mentioned polarized light separation type polarizing plate. Therefore, a reflection type elliptically polarizing plate or a semi-transmitting type elliptically polarizing plate obtained by combining the above-mentioned reflective polarizing plate or semi-transmitting type polarizing plate with a retardation plate may also be used.

An optical film in which the above-mentioned optical layer is laminated on a wide viewing angle polarizing plate can be formed by sequentially and independently laminating in a manufacturing process of a liquid crystal display device or the like. However, a polarizing plate laminated in advance to form an optical film is excellent in quality stability, assembly work, etc., and can improve the production efficiency of liquid crystal display devices and the like. Appropriate adhesive means, such as an adhesive layer, can be used for lamination. When gluing the wide-field-angle polarizing plate and other optical films, their optical axes can be arranged at appropriate angles according to the target retardation characteristics and the like.

An adhesive layer for bonding other components such as a liquid crystal cell can also be provided on the above-mentioned wide viewing angle polarizing plate or an optical film on which at least one wide viewing angle polarizing plate is laminated. There is no particular limitation on the adhesive forming the adhesive layer. A material using a polymer such as an acrylic polymer, a silicone polymer, polyester, polyurethane, polyamide, polyether, fluorine, or rubber as the base polymer can be appropriately selected. It is particularly preferable to use a material that is excellent in optical transparency like an acrylic adhesive, exhibits moderate wettability, cohesiveness, and adhesive adhesive properties, and is excellent in weather resistance, heat resistance, and the like.

In addition, in addition to the above, from the prevention of foaming or peeling caused by moisture absorption, the reduction of optical characteristics due to thermal expansion differences, or the curling of liquid crystal cells, and the formation of high-quality liquid crystal display devices with excellent durability From the viewpoint of the like, an adhesive layer having low hygroscopicity and excellent heat resistance is preferable.

The adhesive layer may contain additives. Examples of such additives include natural or synthetic resins, particularly tackifier resins, fillers made of glass fibers, glass beads, metal powder, and other inorganic powders, or pigments, colorants, and antioxidants. wait. In addition, fine particles may be contained to impart light diffusing properties to the adhesive layer.

Adhesive layers can be attached to one side or both sides of the wide viewing angle polarizing plate or optical film in an appropriate manner. As an example of this, for example, a method in which 10 to 40% by mass of the base polymer or its composition is dissolved or dispersed in a solvent composed of a pure substance or a mixture of a suitable solvent such as toluene or ethyl acetate can be mentioned. adhesive solution, and then directly attach it to a polarizer or an optical film with a wide viewing angle through a suitable spreading method such as casting or coating; or based on the above-mentioned formation of an adhesive layer on the separator The way it is transferred and pasted on a polarizer or optical film with a wide viewing angle, etc.

The adhesive layer can also be provided on one or both surfaces of a wide viewing angle polarizing plate or an optical film as a superimposed layer of members having different compositions or types. In addition, when provided on both sides, it is also possible to provide adhesive layers of different compositions, types, thicknesses, etc. on the front and back surfaces of the wide viewing angle polarizing plate or optical film. The thickness of the adhesive layer can be appropriately determined depending on the purpose of use, adhesive force, etc., and is generally 1 to 500 μm, preferably 5 to 200 μm, particularly preferably 10 to 100 μm.

The exposed surface of the adhesive layer may be temporarily covered with a spacer to prevent contamination before use. This prevents the adhesive layer from coming into contact with foreign matter in normal operating conditions. As the spacer, on the basis of satisfying the above-mentioned thickness conditions, for example, plastic film, rubber sheet, paper, cloth, Suitable sheet materials such as non-woven fabrics, nets, foam sheets, metal foils, and laminates thereof are coated and treated based on conventional suitable separators.

In addition, in the present invention, ultraviolet absorbing ability and the like may be imparted to each layer such as the polarizer, the transparent protective layer, the optical layer, and the adhesive layer constituting the above-mentioned wide viewing angle polarizing plate. For the provision of ultraviolet absorbing ability, for example, ultraviolet absorbers such as salicylate-based compounds, benzophenol-based compounds, benzotriazole-based compounds, cyanoacrylate-based compounds, and nickel complex compounds can be used. .

The wide viewing angle polarizing plate or optical film of the present invention can be applied to various image display devices such as liquid crystal display devices and electroluminescence (EL) display devices.

For example, when applied to a transmissive liquid crystal display device, the liquid crystal display device is constituted by disposing a liquid crystal cell between a pair of transmissive polarizers (or optical films). The transmissive polarizer and the optical film are bonded together with a conventionally known adhesive or the like. The front polarizing plate on the display surface side and the rear polarizing plate on the back side of the liquid crystal cell may be the same polarizing plate or different polarizing plates. In addition, when applied to a reflective liquid crystal display device or a transflective liquid crystal display device, a reflective polarizer or a transflective polarizer is provided on the back side of a liquid crystal cell for application. In addition, when making a liquid crystal display device, one or more layers such as a diffusion plate, an anti-glare layer, an anti-reflection film, a protective plate, a prism array, a lens array sheet, a light diffusion plate, and a back-illuminated layer can be arranged at an appropriate position. Lights and other suitable components.

As a display mode of a liquid crystal display device, it can be applied to TN (twisted nematic, Twisted Nematic), STN mode, or OCB (optical self-compensating birefringence, Optically self-Compensated Birefringence) mode, etc., and the optical compensation film of the present invention can be particularly preferred Used in TN mode and STN mode. In the OCB mode among these display modes, the decrease in contrast due to light leakage during black display is particularly noticeable, but the effect of the present invention can be exhibited particularly in a liquid crystal display device equipped with the above-mentioned wide viewing angle polarizing plate.

The production of the liquid crystal display device can be performed in a conventionally known manner. That is, in general, a liquid crystal display device can be made by appropriately combining a liquid crystal cell, a wide viewing angle polarizing plate or an optical film, and an illumination system added as needed, and incorporating a driving circuit. In the invention, it is not particularly limited except for the point of using the wide viewing angle polarizing plate or the optical film of the present invention, and it can be carried out in the conventional manner.

In addition, the wide viewing angle polarizing plate or optical film of the present invention can also be applied to an organic EL device. Generally, in an organic EL display device, a transparent electrode, an organic light-emitting layer, and a metal electrode are sequentially stacked on a transparent substrate to form a light emitter (organic electroluminescent body). Here, the organic light-emitting layer is a laminate of various organic thin films. For example, a laminate of a hole injection layer composed of a triphenylamine derivative or the like and a light-emitting layer composed of a fluorescent organic solid such as anthracene is known, Or a laminate of such a light-emitting layer and an electron injection layer made of a perylene derivative or the like, or a laminate of these hole injection layers, a light-emitting layer, and an electron injection layer, or various combinations thereof.

The organic EL display device emits light according to the following principle, that is, by applying a voltage to the transparent electrode and the metal electrode, holes and electrons are injected into the organic light-emitting layer, and the energy generated by the recombination of these holes and electrons excites fluorescent substances, When the excited fluorescent substance returns to the ground state, it emits light. The recombination mechanism in the middle is the same as that of a general diode. From this, it can also be inferred that the current and luminous intensity show strong nonlinearity with rectification with respect to the applied voltage.

In an organic EL display device, in order to extract light generated in the organic light-emitting layer, at least one electrode must be transparent, and a transparent electrode made of indium tin oxide (ITO) or the like is usually used as an anode. On the other hand, in order to facilitate electron injection and improve luminous efficiency, it is very important to use a substance with a small work function on the cathode, and metal electrodes such as Mg-Ag and Al-Li are usually used.

In the organic EL display device having such a configuration, the organic light-emitting layer is formed of an extremely thin film with a thickness of about 10 nm. Therefore, the organic light-emitting layer transmits light almost completely similarly to the transparent electrode. As a result, light incident from the surface of the transparent film and transmitted through the transparent electrode and the organic light-emitting layer and reflected on the metal electrode when not emitting light is emitted to the surface side of the transparent film again. Therefore, when it is recognized from the outside, the organic The display surface of the EL device is like a mirror surface.

In an organic EL display device including an organic electroluminescent body as described below, it is possible to provide a wide viewing angle polarizing plate on the surface side of the transparent electrodes while providing a phase difference between these transparent electrodes and the wide viewing angle polarizing plate In the above-mentioned organic electroluminescent body, a transparent electrode is provided on the front side of the organic light-emitting layer that emits light by applying a voltage, and a metal electrode is provided on the back side of the organic light-emitting layer.

Since the retardation plate and the wide viewing angle polarizer have the effect of polarizing the light incident from the outside and reflected by the metal electrode, the mirror surface of the metal electrode cannot be recognized from the outside due to the polarization effect. In particular, when a 1/4 wavelength plate is used to form a retardation plate and the angle between the polarizing plate and the polarizing direction of the retardation plate is adjusted to π/4, the mirror surface of the metal electrode can be completely shielded.

That is, of the external light incident on the organic EL display device, only the linearly polarized light component is transmitted due to the presence of the wide viewing angle polarizer. The linearly polarized light is generally converted into elliptically polarized light by a retardation plate. Especially when the retardation plate is a 1/4 wavelength plate and the included angle between the polarization directions of the wide viewing angle polarizer and the retardation plate is π/4, it will become circularly polarized light.

The circularly polarized light passes through the transparent substrate, transparent electrode, and organic thin film, is reflected on the metal electrode, and then passes through the organic thin film, transparent electrode, and transparent substrate again, and is converted into linearly polarized light by the phase difference plate again. Then, since the linearly polarized light is perpendicular to the polarization direction of the wide-field-angle polarizer, it cannot pass through the polarizer. As a result, the mirror surface of the metal electrode can be completely shielded.

Example

(Example 1)

In an aqueous NaOH solution at 60°C, an optical compensation film (Fuji Electric Co., Ltd. Photo Film Co., Ltd., product name: WVA12B, layer thickness 108 μm) was dipped for 30 seconds, and saponified. Then, it heat-dried at 100 degreeC for 40 second. At this time, the front-side retardation value (Δnd) of the optical compensation film before and after heating measured with an automatic birefringence measuring device (KOBRA21ADH, manufactured by Oji Scientific Instruments Co., Ltd.) was 31.7 nm before heating and 23.3 nm after heating. .

On the other hand, a polyvinyl alcohol film having a thickness of 75 μm was stretched in an iodine aqueous solution, and then dried to produce a polarizer.

Next, the optical compensation film and the polarizer were bonded together using an acrylic adhesive so that the transparent protective layer side of the optical compensation film was the adhesive surface. Bonding was carried out 1 minute after the optical compensation film was produced. Also on the other side of the polarizer, a cellulose triacetate film (manufactured by Fuji Photo Film Co., Ltd., product name: TD80UF) with a thickness of 80 μm was glued to form a transparent protective layer using an acrylic adhesive, and dried.

Thus, the wide viewing angle polarizing plate of Example 1 was obtained. Here, the bonding of the polarizer and the transparency protective layer is carried out so that the retardation axis of the birefringent layer and the transmission axis of the polarizer are in a substantially parallel relationship.

(Example 2)

In this Example 2, except that the heating and drying after the saponification treatment at 100°C in the above-mentioned Example 1 was replaced by 70°C, the rest were made in the same manner as in the above-mentioned Example 1. Field of view polarizer.

(Example 3)

In this Example 3, except that the heating and drying after the saponification treatment at 100°C in the above-mentioned Example 1 was replaced by 120°C, the rest were made in the same manner as in the above-mentioned Example 1. Field of view polarizer.

(comparative example 1)

In Comparative Example 1, except that the heating and drying after the saponification treatment at 100°C in the above-mentioned Example 1 was replaced at 65°C, the rest were made in the same manner as in the above-mentioned Example 1. field angle polarizer. At this time, the front-side retardation value (Δnd) of the optical compensation film before and after heating was measured in the same manner as in Example 1. As a result, it was 31.6 nm before heating and 31.4 nm after heating.

(comparative example 2)

In Comparative Example 2, except that the heating and drying after the saponification treatment at 65°C in the above-mentioned Comparative Example 1 was replaced with 130°C, the rest were made in the same manner as in the above-mentioned Comparative Example 1. field angle polarizer.

(contrast)

Contrast was evaluated by arranging the wide viewing angle polarizing plates produced in the above-mentioned Examples or Comparative Examples on both sides of a TFT liquid crystal cell (TN mode) and measuring white luminance and black luminance, respectively. A luminance meter (trade name: BM-5A, manufactured by TOPCON Corporation) was used for the luminance measurement. The contrast (white luminance/black luminance) in the front direction of the display screen is calculated from the value of luminance thus obtained. These results are shown in Table 1. It can be seen from the same table that the wide viewing angle polarizers of Examples 1 to 3 can obtain good contrast.

(end view)

The end surface observation was performed by punching out the wide viewing angle polarizing plate produced in the above-mentioned Examples or Comparative Examples into A4 size to observe the end surface. Evaluation was made as ◯ if there was no fractured surface on the end face, and as x even if there was one. The results are shown in Table 1. As can be seen from the same table, no fracture surface such as cracks was observed in the wide viewing angle polarizing plates of Examples 1 to 3. On the other hand, in the wide viewing angle polarizing plate of Comparative Example 2, a fractured surface with cracks was observed.

Table 1

Heat treatment temperature (℃) Contrast presence or absence of cracks Example 1 100 453 ○ Example 2 70 438 ○ Example 3 120 432 ○ Comparative example 1 65 412 ○ Comparative example 2 130 432 ×

Claims (7)

1. A kind of manufacture method of wide viewing angle polarizing plate is the manufacturing method of the wide viewing angle polarizing plate with optical compensation film and polarizer, and described optical compensation film has at least one side of transparency protective layer containing liquid crystal A birefringent layer made of a polymer is characterized in that it has: a step of heat-treating the optical compensation film in the range of 68°C to 125°C; and A step of laminating the polarizer and the optical compensation film with an adhesive using the transparent protective layer as an adhesive surface. 2. The manufacture method of wide viewing angle polarizing plate according to claim 1, is characterized in that, before described heat treatment, comprises the operation that saponification process is carried out to the transparency protection layer that is equipped with described birefringent layer. 3. the manufacture method of wide viewing angle polarizing plate according to claim 1 or 2, is characterized in that, as described liquid crystal polymer, uses disc liquid crystal polymer. 4. the manufacture method of wide viewing angle polarizing plate according to claim 1 and 2 is characterized in that, as described transparency protective layer, uses cellulose triacetate film. 5. A wide viewing angle polarizing plate, is characterized in that, is manufactured by the manufacturing method described in any one of claim 1～4. 6. an optical film, is characterized in that, is laminated with at least 1 wide angle of view polarizer described in claim 5. 7. An image display device, characterized in that, uses the wide viewing angle polarizer according to claim 5 or the optical film according to claim 6.