JP2010122487A - Polarizing plate having high elasticity adhesive layer and image display device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarizing plate having reduced thermal ununiformity in an image display region. <P>SOLUTION: The polarizing plate obtained by laminating a transparent protective layer on one surface of a polarizer comprising a polyvinyl alcohol based resin film, laminating a first adhesive layer directly laminated on the other surface and laminating a transparent polymer film and a second adhesive layer on the first adhesive layer in this order, is provided. In such a case, the first adhesive layer has 0.15-10 MPa storage modulus in a range of 23-80°C. The polarizing plate obtained in this way is used as a rectangular polarizing plate having ≥7 inch diagonal line length. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a polarizing plate used in an image display device such as a liquid crystal display device, and an image display device using the same.

  Conventionally, liquid crystal display devices have been used in desktop calculators, electronic timepieces, and the like, but their use has been rapidly expanding in recent years. That is, liquid crystal display devices have been used from mobile devices such as mobile phones to large televisions regardless of screen size. In addition to liquid crystal display devices, organic electroluminescence (organic EL) display devices also tend to increase mainly in mobile applications. The polarizing plates used in these image display apparatuses are not only in increasing demand but also required to have performance suitable for each application.

  The polarizing plate generally used in the image display apparatus as described above is a triacetyl cellulose film via a liquid adhesive on both sides of a polarizer in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol resin film. It is manufactured with the structure which laminated | stacked the transparent protective layer represented by. This polarizing plate is often applied to an image display device in a form in which a transparent polymer film having optical properties is bonded depending on the application and required performance. For example, an elliptical polarization mode or a circular polarization mode is used. When a polarizing plate is used, an image display device is obtained by laminating a retardation film such as a 1 / 2λ plate or a 1 / 4λ plate to an image display element such as a liquid crystal cell or an organic EL display element. The

  FIG. 3 is a cross-sectional schematic view showing a general example of such a polarizing plate with a retardation film. That is, the transparent protective layers 2 and 2 a are provided on both surfaces of the polarizer 1 to constitute the polarizing plate 15. Then, the retardation film 4 is bonded to the transparent protective layer 2a side of the polarizing plate 15 via the pressure-sensitive adhesive layer 3, and the second pressure-sensitive adhesive layer for bonding to the image display element on the outer side. 5 to obtain a polarizing plate 14 with a retardation film. When distributed in this state, a separator 6 is usually provided outside the second pressure-sensitive adhesive layer 5 in the retardation film-attached polarizing plate 14 to protect the surface temporarily until it is bonded to the image display element. It is.

  Further, in order to meet the recent demand for thinner and lighter image display devices, as shown in FIG. 1, instead of the configuration in which the transparent protective layers 2 and 2a are provided on both surfaces of the polarizer 1 as shown in FIG. The transparent protective layer (corresponding to 2a in FIG. 3) to be bonded to the retardation film 4 is omitted, and the pressure-sensitive adhesive layer 3 is provided directly on the polarizer 1, and the retardation film is interposed through the pressure-sensitive adhesive layer. A configuration in which 4 is laminated is also being studied.

  When these polarizing films 14 and 7 with retardation film are placed in a high temperature environment, stress is applied to the retardation film 4 due to the contraction of the polarizer 1, and retardation unevenness (hereinafter referred to as heat unevenness) occurs. There is. In particular, the polarizing plate 7 having the configuration shown in FIG. 1 has no transparent protective layer on the side to be bonded to the retardation film 4, and the pressure-sensitive adhesive layer 3 that is more easily expanded and contracted than the transparent protective layer is in direct contact with the polarizer 1. Therefore, compared with the polarizing plate 14 having the configuration shown in FIG. 3, the contraction of the polarizer 1 under a high temperature environment is large, and as a result, the stress applied to the retardation film 4 is increased and thermal unevenness is likely to occur. . This heat unevenness is more likely to occur at the edge than the center of the polarizing plate. When this unevenness extends to the image display area (usually a region that is several millimeters or more inward from the periphery of the polarizing plate), There is a problem in that light leakage (white spots) occurs during display, black luminance increases, and display quality deteriorates. In particular, when the screen of the image display device is large, heat unevenness easily reaches the image display area.

  As a technique for reducing the thermal unevenness as described above, for example, Japanese Patent Application Laid-Open No. 2003-167120 (Patent Document 1) discloses a composite polarizing plate in which a linear polarizing plate and a retardation plate are laminated. It is disclosed that the arrangement angle of the optical axis of the phase difference plate with respect to is in a specific range. However, this arrangement angle is optimized depending on the characteristics of the image display element to be bonded, and the above method may not be applied depending on the structure of the image display element, and lacks versatility.

  Japanese Patent Laying-Open No. 2006-309130 (Patent Document 2) discloses that in a polarizing plate having a polarizer and first, second, and third optical compensation layers, photoelasticity is applied to the first and second optical compensation layers. In addition to using a material having a small absolute value of the coefficient, it is disclosed that the third optical compensation layer is thinned. However, there are limitations on the material and manufacturing method, and it is not always easy to realize in consideration of cost and labor.

  Furthermore, Japanese Patent Application Laid-Open No. 2003-207637 (Patent Document 3) discloses that a polarizing film is thinned in a polarizing plate in which protective films are bonded to both surfaces of the polarizing film. However, in order to obtain a thin polarizing film, it is necessary to increase the stretching ratio of the original film or to stretch the thin original film, and there is a problem that it is difficult to obtain a uniform polarizing film.

JP 2003-167120 A JP 2006-309130 A JP 2003-207637 A

  An object of the present invention is a polarizing plate in which a transparent polymer film typified by a retardation film is bonded as described above, in particular, a diagonal line length is relatively large, such as 7 inches or more, and generally heat unevenness is an image. An object of the present invention is to provide a polarizing plate that easily extends to the display area, which has reduced heat unevenness in the image display area and is advantageous in terms of versatility, ease of manufacture, and cost. An object of the present invention is to provide an image display device using this polarizing plate, in which light leakage during black display is suppressed, black luminance is reduced, and display quality is excellent.

  In order to achieve the above object, the polarizing plate of the present invention is a rectangular polarizing plate having a diagonal length of 7 inches or more, and a transparent protective layer on one surface of a polarizer made of a polyvinyl alcohol-based resin film. The first pressure-sensitive adhesive layer is directly laminated on the other surface, and the transparent polymer film and the second pressure-sensitive adhesive layer are laminated in this order on the first pressure-sensitive adhesive layer. The storage elastic modulus of the layer is 0.15 to 10 MPa in a temperature range of 23 to 80 ° C. In this way, as a polarizing plate having a predetermined size or more, a polarizing plate having a configuration shown in FIG. 1 which is generally more likely to cause thermal unevenness than the polarizing plate having the configuration shown in FIG. By providing a hard pressure-sensitive adhesive layer exhibiting a high storage elastic modulus as a pressure-sensitive adhesive layer between the polarizer and the transparent polymer film, it is possible to reduce heat unevenness in the image display region.

  In the polarizing plate of the present invention, the thickness of the first pressure-sensitive adhesive layer is preferably 3 to 25 μm. The second pressure-sensitive adhesive layer has removability, and it is preferable that a separator treated with a release agent such as silicone is present on the exposed surface.

  In the polarizing plate of the present invention, the transparent polymer film formed on the other surface of the polarizer via the first pressure-sensitive adhesive layer preferably has an in-plane retardation.

  In the polarizing plate of the present invention, an optical layer exhibiting another optical function can be further laminated on the transparent protective layer. For example, when this polarizing plate is disposed on the display surface (viewing side) of the image display element, a surface treatment layer such as a hard coat layer, an antireflection layer, or an antiglare layer may be provided on the transparent protective layer. it can. When this polarizing plate is disposed on the side opposite to the display surface of the liquid crystal cell (rear side), a reflective plate or a transflective plate is laminated on the transparent protective layer to provide a reflective or transflective reflector. A thin polarizing plate can be obtained, or a brightness enhancement film can be attached to form a thin polarizing plate that can be used for a brightness enhancement system.

  Furthermore, the polarizing plate of the present invention has a rectangular shape and is defined as follows when heat treatment is performed at 85 ° C. for 500 hours in a state of being bonded to a glass plate via the second pressure-sensitive adhesive layer. The shrinkage amount ratio H to be applied is preferably 1.8 or more.

H = (D1-D1 ′) / (D2-D2 ′)
D1: In the polarizing plate before the heat treatment, when the point taken at the midpoint of one long side is M1, and the point taken at the midpoint of the other long side is M2, before the heat treatment In the polarizing plate, the length of the line segment connecting M1 and M2.
D1 ′: The length of the line segment connecting M1 and M2 in the polarizing plate after the heat treatment.
D2: In the polarizing plate before the heat treatment, a point taken from M1 to the center of the polarizing plate at a linear distance of 10 mm is defined as M1 ′, and from M2 to the center of the polarizing plate at a linear distance of 10 mm. The length of the line segment connecting M1 ′ and M2 ′ in the polarizing plate before the heat treatment when the taken point is M2 ′.
D2 ′: The length of the line connecting M1 ′ and M2 ′ in the polarizing plate after the heat treatment.

  In the image display device of the present invention, the polarizing plate is bonded to an image display element such as a liquid crystal cell or an organic EL display element via the second pressure-sensitive adhesive layer. In the display device, the image display element is preferably a VA mode, ECB mode, OCB mode, or IPS mode liquid crystal cell.

  The polarizing plate of the present invention has reduced heat unevenness in the image display region, and by using this, an image display device having excellent display quality can be obtained.

  Hereinafter, the present invention will be described in detail with appropriate reference to the accompanying drawings. FIG. 1 is a schematic cross-sectional view showing an example of the layer structure of the polarizing plate of the present invention. The polarizing plate 7 has a transparent protective layer 2 formed on one side of the polarizer 1, and a first pressure-sensitive adhesive layer 3, a transparent polymer film 4, and a second pressure-sensitive adhesive layer 5 are formed on the other side of the polarizer 1. They are provided in this order. And the 1st adhesive layer 3 is comprised by what shows the storage elastic modulus of 0.15-10 MPa in the temperature range of 23-80 degreeC. Usually, the separator 6 is disposed on the exposed surface of the pressure-sensitive adhesive layer 5 and the surface thereof is temporarily protected until it is bonded to another member.

Here, “showing a storage elastic modulus of 0.15 to 10 MPa in a temperature range of 23 to 80 ° C.” means that the storage elastic modulus takes a value in the above range at any temperature within this range. Since the storage elastic modulus usually decreases gradually as the temperature rises, if both the storage elastic modulus at 23 ° C. and 80 ° C. are within the above range, the storage elastic modulus in the above range is exhibited at the temperature in this range. You can see.

[Polarizer]
The polarizer 1 is a film having a function of extracting linearly polarized light from incident natural light, and a polarizing film in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based resin film can be used. The polyvinyl alcohol resin constituting the polarizer 1 can be obtained by saponifying a polyvinyl acetate resin. Examples of the polyvinyl acetate resin include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable therewith. Examples of other monomers copolymerized with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and acrylamides having an ammonium group. The saponification degree of the polyvinyl alcohol resin is usually about 85 to 100 mol%, preferably 98 mol% or more. This polyvinyl alcohol-based resin may be further modified, and for example, polyvinyl formal and polyvinyl acetal modified with aldehydes may be used. Moreover, the polymerization degree of polyvinyl alcohol-type resin is about 1,000-10,000 normally, Preferably it is about 1,500-5,000.

  A film obtained by forming such a polyvinyl alcohol resin is used as a raw film of the polarizer 1. The method for forming a polyvinyl alcohol-based resin is not particularly limited, and can be formed by a known method. Although the film thickness of the raw film which consists of polyvinyl alcohol-type resin is not specifically limited, For example, it is about 1 micrometer-150 micrometers. Considering easiness of stretching, the film thickness is preferably 10 μm or more.

  The polarizer 1 has a step of uniaxially stretching such a polyvinyl alcohol resin film, a step of dyeing the polyvinyl alcohol resin film with a dichroic dye and adsorbing the dichroic dye, and a dichroic dye being adsorbed. It is manufactured through a step of treating the polyvinyl alcohol-based resin film with a boric acid aqueous solution and a step of washing with water after the treatment with the boric acid aqueous solution. As the dichroic dye, iodine or a dichroic organic dye is used.

[Transparent protective layer]
The transparent protective layer 2 provided on one side of the polarizer 1 can be composed of an appropriate transparent film. Among them, a film made of a resin excellent in transparency, optical property uniformity, mechanical strength, thermal stability, etc. is preferably used. For example, cellulose resin films such as triacetyl cellulose and diacetyl cellulose, polyester resin films such as polyethylene terephthalate and polyethylene isophthalate, polybutylene terephthalate, acrylic resin films such as polymethyl (meth) acrylate and polyethyl (meth) acrylate, Examples thereof include a polycarbonate resin film, a polyethersulfone resin film, a polysulfone resin film, a polyimide resin film, a polyolefin resin film, and a cyclic olefin resin film having a cyclic olefin as a monomer such as norbornene. An adhesive or a pressure-sensitive adhesive can be used for bonding the transparent protective layer 2 and the polarizer 1.

[Transparent polymer film]
The transparent polymer film 4 can be composed of various resins exemplified as the resin constituting the transparent protective layer 2. In particular, it is advantageous that the transparent polymer film 4 has an in-plane retardation and has a function as a retardation film. The transparent polymer film 4 having in-plane retardation is preferably selected to have characteristics required as a retardation film, that is, its birefringence is optically uniform, and the protective function of the polarizer 1 and the liquid crystal panel Is used for the purpose of compensating for the phase difference due to (including the meaning of viewing angle compensation). For example, those used in image display devices can be used without limitation, and birefringent films made of stretched films of various transparent polymers, discotic liquid crystals and nematic liquid crystals are aligned and fixed. And films having the above-mentioned liquid crystal layer formed on a film substrate. When the liquid crystal layer is fixed on the film substrate, a cellulose resin film such as triacetyl cellulose is preferably used as the film substrate for supporting the oriented liquid crystal layer.

  Examples of the polymer forming the birefringent film include, for example, polycarbonate, polyvinyl alcohol, polystyrene, polymethyl methacrylate, polyolefin such as polypropylene, polyarylate, polyamide, and cyclic olefin such as norbornene. And cyclic polyolefins. The stretched film may be processed by an appropriate method such as uniaxial or biaxial. Moreover, the birefringent film which controlled the refractive index of the thickness direction of a film by applying shrinkage force and / or extending | stretching force under adhesion | attachment with a heat-shrinkable film can also be used.

  In particular, in the case of an elliptically or circularly polarizing plate used in an image display device for mobile use, a 1 / 2λ plate or a 1 / 4λ plate is effectively used. The polarizing plate in the elliptical polarization mode or the circular polarization mode has a function of changing the incident polarized light to elliptically polarized light or circularly polarized light when the polarized light is linearly polarized light, and changing it to linearly polarized light when the incident polarized light is elliptically polarized light or circularly polarized light. is doing. In particular, as a retardation film capable of changing elliptically polarized light or circularly polarized light into linearly polarized light and linearly polarized light into elliptically polarized light or circularly polarized light, a phase difference of 1/4 wavelength with respect to the wavelength of incident light, called a 1 / 4λ plate, is used. What is shown is used. The 1 / 2λ plate has a function of changing the direction of linearly polarized light. Furthermore, a 1 / 2λ plate and a 1 / 4λ plate are laminated so that the optical axes intersect at a predetermined angle to form a broadband 1 / 4λ plate that exhibits a 1/4 wavelength phase difference over a wide wavelength range. You can also.

  The elliptically polarizing mode polarizing plate is effective for preventing a coloring phenomenon caused by liquid crystal birefringence in a liquid crystal display device. The circularly polarizing mode polarizing plate is a reflective or transflective liquid crystal display device. Is effectively used for the purpose of improving the luminance. The circularly polarizing mode polarizing plate also has an antireflection function.

[Adhesive layer]
In FIG. 1, the 1st adhesive layer 3 which adhere | attaches the polarizer 1 and the transparent polymer film 4, and the 2nd adhesive layer 5 which is arrange | positioned on the outermost side of a polarizing plate and is bonded together by an image display element. Can be formed based on various adhesives conventionally used for image display devices. For example, those having a base polymer such as acrylic, rubber, urethane, silicone, and polyvinyl ether are used. Moreover, an energy beam curing type, a thermosetting type, etc. may be sufficient. Among these, a pressure-sensitive adhesive having an acrylic resin excellent in transparency, weather resistance, heat resistance and the like as a base polymer is preferable.

  The acrylic pressure-sensitive adhesive is not particularly limited, but (meth) acrylate such as butyl (meth) acrylate, ethyl (meth) acrylate, isooctyl (meth) acrylate, (2-ethylhexyl (meth) acrylate) ) An acrylic ester base polymer and a copolymer base polymer using two or more of these (meth) acrylic esters are preferably used. Furthermore, polar monomers are copolymerized in these base polymers. Examples of polar monomers include (meth) acrylic acid, 2-hydroxypropyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, (meth) acrylamide, and 2-N, N-dimethylaminoethyl (meth). Mention may be made of monomers having a carboxy group, a hydroxyl group, an amide group, an amino group, an epoxy group and the like, such as acrylate and glycidyl (meth) acrylate.

  These acrylic pressure-sensitive adhesives can of course be used alone, but usually a crosslinking agent is used in combination. As the crosslinking agent, a divalent or polyvalent metal ion that forms a carboxylic acid metal salt with a carboxyl group, a polyamine compound that forms an amide bond with a carboxyl group, Examples thereof include polyepoxy compounds and polyol compounds that form an ester bond with a carboxyl group, and polyisocyanate compounds that form an amide bond with a carboxyl group. Of these, polyisocyanate compounds are widely used as organic crosslinking agents.

  The energy ray curable adhesive has the property of being cured by irradiation with energy rays such as ultraviolet rays and electron beams, and has adhesiveness even before irradiation with energy rays to adhere to an adherend such as a film. It is a pressure-sensitive adhesive that has the property of being adhered and cured by irradiation with energy rays to adjust the adhesion. As the energy ray curable adhesive, it is particularly preferable to use an ultraviolet curable adhesive. The energy beam curable pressure-sensitive adhesive generally comprises an acrylic pressure-sensitive adhesive and an energy beam polymerizable compound as main components. Usually, a crosslinking agent is further blended, and a photopolymerization initiator and a photosensitizer can be blended as necessary.

  In addition to the above base polymer and crosslinking agent, the pressure-sensitive adhesive composition used for forming the pressure-sensitive adhesive layer includes, as necessary, the pressure-sensitive adhesive strength, cohesive force, viscosity, elastic modulus, glass transition temperature, etc. In order to adjust, for example, natural or synthetic resins, tackifying resins, antioxidants, dyes, pigments, antifoaming agents, corrosive agents, photopolymerization initiators, and other appropriate additives are added. You can also. Furthermore, it can also be set as the adhesive layer which contains microparticles | fine-particles and shows light-scattering property. The pressure-sensitive adhesive layer may contain an antioxidant or an ultraviolet absorber. Examples of ultraviolet absorbers include salicylic acid ester compounds, benzophenone compounds, benzotriazole compounds, cyanoacrylate compounds, and nickel complex compounds.

[Storage modulus of adhesive layer]
And in this invention, the 1st adhesive layer 3 which adhere | attaches the polarizer 1 and the transparent polymer film 4 shows the storage elastic modulus of 0.15-10 MPa in the temperature range of 23-80 degreeC, ie, a hard thing. Constitute. The storage elastic modulus of the pressure-sensitive adhesive can be measured using a commercially available viscoelasticity measuring device, for example, a viscoelasticity measuring device “DYNAMIC ANALYZER RDA II” manufactured by REOMETRIC as shown in the examples described later. The pressure-sensitive adhesive used in a normal image display device or an optical film therefor has a storage elastic modulus of about 0.1 MPa at most, and compared with that, the storage elasticity of the first pressure-sensitive adhesive layer 3 defined in the present invention. The rate of 0.15 to 10 MPa is a high value. By using such a hard adhesive that exhibits a high storage elastic modulus, it is possible to suppress thermal unevenness from reaching the image display area.

  The means for setting the storage elastic modulus of the first pressure-sensitive adhesive layer 3 for bonding the polarizer 1 and the transparent polymer film 4 to a high value as described above is not particularly limited. For example, the normal pressure-sensitive adhesive composition as described above is used. In addition, it is effective to blend an oligomer, specifically, a urethane acrylate oligomer. Preferably, such a urethane acrylate oligomer blended and then cured by irradiation with energy rays exhibits a high storage elastic modulus. A pressure-sensitive adhesive composition containing a urethane acrylate-based oligomer, or a film-like pressure-sensitive adhesive obtained by coating it on a support film and curing it with ultraviolet rays is known and can be obtained from a pressure-sensitive adhesive manufacturer.

  The pressure-sensitive adhesive layer 5 disposed on the outermost side may be composed of a material having a high storage elastic modulus, similar to the first pressure-sensitive adhesive layer 3 that bonds the polarizer 1 and the transparent polymer film 4, Although it may be composed of a general material having a lower storage elastic modulus than that of the first pressure-sensitive adhesive layer 3, the constitution of a material having a high storage elastic modulus suppresses the rising of the end portion of the polarizing plate accompanying the contraction of the polarizer. In addition, it is preferable.

[Other explanation about adhesive layer]
The first pressure-sensitive adhesive layer 3 and the second pressure-sensitive adhesive layer 5 are formed, for example, by dissolving or dispersing the pressure-sensitive adhesive composition in an organic solvent such as toluene or ethyl acetate to obtain a solution having a concentration of 10 to 40% by weight. The method of laminating the separator 6 made of a resin film after directly applying to the surface of the film on which the pressure-sensitive adhesive layer is to be formed and drying, or after forming the pressure-sensitive adhesive layer on the separator 6, It can be performed by a method of transferring to the surface of the film to be formed. When forming the pressure-sensitive adhesive layer on the film, a treatment for improving the adhesion, for example, corona treatment, is performed on the surface (one or both) on which the film and the pressure-sensitive adhesive layer are bonded as necessary. You may give it.

The separator 6 temporarily protects the surface of the second pressure-sensitive adhesive layer 5 until the polarizing plate 7 is bonded to an image display element. For example, a silicone-based film made of a transparent resin such as polyethylene terephthalate is used. Those subjected to treatment with a release agent such as are used.
[Polarizer]

  The polarizing plate of the present invention is employed as a rectangular polarizing plate having a diagonal length of 7 inches or more. Typically, a screen size image display apparatus ranging from a relatively large mobile device to a large television is used in a square shape or a rectangular shape. As described above, by adopting the predetermined polarizing plate having the hard first pressure-sensitive adhesive layer in the configuration shown in FIG. 1 as a polarizing plate that is relatively large and generally has a thermal unevenness that easily reaches the image display region, Thermal unevenness in the image display area can be reduced. Further, when it is adopted as a polarizing plate having a smaller size than this, heat unevenness easily reaches the image display region.

  Further, the polarizing plate of the present invention is rectangular, and when the heat treatment is performed at 85 ° C. for 500 hours in a state of being bonded to the glass plate via the second pressure-sensitive adhesive layer, The shrinkage ratio H is preferably 1.8 or more. When the shrinkage amount ratio H is 1.8 or more, it is possible to more effectively suppress the thermal unevenness from reaching the image display area.

[Other optical layers]
The polarizing plate of the present invention is configured as described above, and an optical layer having other optical functions can be laminated on the transparent protective layer 2 as necessary.

  For example, when this polarizing plate is disposed on the display surface (viewing side) of the image display element, a surface treatment layer such as a hard coat layer, an antireflection layer, or an antiglare layer is provided on the transparent protective layer. May be. The hard coat layer is formed to prevent scratches on the surface of the polarizing plate. The hard coat layer is mainly composed of an ultraviolet curable resin, for example, an acrylic resin or a silicone resin, and the adhesiveness to the transparent protective layer 2. Those having excellent hardness are appropriately selected and can be formed on the surface of the transparent protective layer 2.

  The antireflection layer is formed for the purpose of preventing reflection of external light on the surface of the polarizing plate, and can be formed by a known method. The anti-glare layer is formed to prevent disturbance of visibility caused by external light reflected on the surface of the polarizing plate, for example, a roughening method such as a sand blast method or an embossing method, In general, the surface of the transparent protective layer 2 is formed to have a concavo-convex structure by, for example, a method of applying and curing a coating liquid in which transparent fine particles are mixed with an ultraviolet curable resin.

  On the other hand, when this polarizing plate is disposed on the opposite side (rear side) of the display surface of the liquid crystal cell, on the transparent protective layer 2, a reflective layer, a transflective layer, a light diffusing layer, a light collector, and a luminance improvement A film or the like can be laminated.

  The reflective polarizing plate is used in a liquid crystal display device of a type that reflects and displays external light incident from the viewing side. Since a light source such as a backlight can be omitted, the liquid crystal display device can be easily thinned. The transflective polarizing plate is used in a liquid crystal display device that displays as a reflective type in a bright place and as a transmissive type using a light source such as a backlight in a dark place. The reflective layer for making a reflective polarizing plate can be formed by attaching a foil or a vapor deposition film made of a metal such as aluminum to the protective layer 2 on the polarizer 1, for example. The semi-transmissive reflective layer for making a semi-transmissive reflective polarizing plate is a method of using the reflective layer as a half mirror, or a reflective plate containing a pearl pigment or the like and exhibiting light transmittance is adhered to the polarizing plate. It can be formed by a method or the like.

  The diffusion type polarizing plate has a function of diffusing incident light. For the light diffusion layer used for that purpose, various methods such as a method of applying a mat treatment to the transparent protective layer 2 on the polarizer 1, a method of applying a resin containing fine particles, and a method of adhering a film containing fine particles are used. Formed.

  Further, the reflection / diffusion polarizing plate is obtained by providing a diffusion reflection layer, for example, by providing a reflection layer reflecting the uneven structure on the fine uneven structure surface of the diffusion type polarizing plate. The reflective layer having a fine concavo-convex structure has advantages such that incident light is diffused by irregular reflection, directivity and glare can be prevented, and unevenness in brightness and darkness can be suppressed. In addition, the resin layer or film containing fine particles has an advantage that incident light and its reflected light are diffused when passing through the layer, and brightness unevenness can be further suppressed. The reflective layer reflecting the surface fine concavo-convex structure can be formed, for example, by directly attaching a metal to the surface of the fine concavo-convex structure by a method such as vapor deposition such as vacuum deposition, ion plating, sputtering, or plating. Examples of the fine particles to be blended for forming the surface fine concavo-convex structure include silica, aluminum oxide, titanium oxide, zirconium oxide, tin oxide, indium oxide, cadmium oxide, and oxide having an average particle diameter of 0.1 to 30 μm. Inorganic fine particles made of antimony or the like, organic fine particles made of a crosslinked or uncrosslinked polymer, or the like can be used.

  The light collector is attached for the purpose of optical path control and can be formed as a prism array sheet, a lens array sheet, a dot attached sheet, or the like.

  The brightness enhancement film has a function of transmitting a part of incident natural light as linearly polarized light or circularly polarized light and reflecting the remaining light for reuse, and is used for the purpose of improving brightness in a liquid crystal display device or the like. . Examples include a reflective linearly polarized light separation sheet, a cholesteric liquid crystal polymer alignment film designed to produce anisotropy in reflectance by laminating a plurality of thin film films having different refractive index anisotropies, and the like. Examples include a reflective circularly polarized light separating sheet in which an oriented liquid crystal layer is supported on a film substrate.

  The various optical layers as described above can be integrated with the transparent protective layer 2 using a pressure-sensitive adhesive or an adhesive, but the pressure-sensitive adhesive or the adhesive used for this purpose is not particularly limited and may be appropriately selected. You can select and use one. It is preferable to use a pressure-sensitive adhesive from the viewpoint of simplicity of bonding work and prevention of optical distortion. As an example of an adhesive, the thing similar to having demonstrated the adhesive layers 3 and 5 previously with reference to FIG. 1 can be mentioned. In addition, when the formed pressure-sensitive adhesive layer is exposed on the surface, a separator is preferably disposed for preventing contamination. As a separator, the thing similar to what was demonstrated previously can be used.

[Image display element]
The polarizing plate of this invention can be arrange | positioned at various image display elements, and can be set as an image display apparatus. For example, it can be arranged on one or both sides of a liquid crystal cell to provide a liquid crystal display device. Typically, a liquid crystal display device is formed using a liquid crystal cell of VA (Vertical Alignment) mode, ECB (Electrically Controlled Birefringence) mode, OCB (Optically Compensated Birefringence) mode, and IPS (In-plane Switching) mode. Can do. When providing the polarizing plate of this invention in the both sides of a liquid crystal cell, both may be the same and may differ.

  FIG. 2 is a schematic cross-sectional view showing an example in which the polarizing plate of the present invention is mounted on a liquid crystal panel. In this example, basically, the polarizing plate 7 shown in FIG. 1 is disposed on both surfaces of the liquid crystal cell 11. That is, from the liquid crystal cell 11 side on one side (upper side in the figure) of the liquid crystal cell 11, the second adhesive layer 5 / transparent polymer film (retardation film) 4 / first adhesive layer 3 / polarizer 1 / surface A polarizing plate 9 laminated in the order of the transparent protective layer 2 having the treatment layer 12 (the surface treatment layer 12 is on the outside) (this includes the separator 6 from the polarization plate 7 shown in FIG. It corresponds to the peeled state). Further, on the other surface (lower side of the figure) of the liquid crystal cell 11, from the liquid crystal cell 11 side, the second adhesive layer 5 / transparent polymer film (retardation film) 4 / adhesive layer 3 / polarizer 1 Polarizing plate 10 laminated in the order of transparent protective layer 2 / other optical layer 13 (this is a state in which separator 6 is peeled off from polarizing plate 7 shown in FIG. 1 except that other optical layer 13 is provided) Is equivalent). In the liquid crystal display device of this example, the upper side of the figure is the viewing side, and when a backlight is provided, it is arranged on the lower side of the figure. In this case, the surface treatment layer 12 can be a hard coat layer, an antireflection layer, an antiglare layer, or the like. The other optical layer 13 can be a reflective layer, a transflective layer, a light collector, a brightness enhancement film, or the like.

  Furthermore, the polarizing plate of the present invention is also effectively used in a circularly polarized or elliptically polarized mode having an antireflection function in an image display device other than a liquid crystal display device, for example, a flat display such as an organic EL display device. Those skilled in the art will easily understand that when the image display element is an organic EL display element, the polarizing plate of the present invention may be bonded to one side thereof, that is, the viewing side display surface. Of course, the image display apparatus to which the polarizing plate of the present invention is applied is not limited to the one exemplified here.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples. In the following examples, the storage elastic modulus of the pressure-sensitive adhesive is a value measured by the following method.

[Measurement method of storage modulus]
A cylindrical test piece of 8 mmφ × 1 mm thickness was prepared from the adhesive, and the storage elastic modulus (G ′) was determined by a torsional shear method with a frequency of 1 Hz using a measuring instrument “DYNAMIC ANALYZER RDAII” manufactured by REOMETRIC.

  In the following examples, the following were used as pressure-sensitive adhesives.

Adhesive A: A 38 μm-thick polyethylene terephthalate film having a release treatment applied to an organic solvent solution in which a urethane acrylate oligomer is blended with a copolymer of butyl acrylate and acrylic acid and an isocyanate crosslinking agent is added. A sheet-like pressure-sensitive adhesive coated on the release treatment surface of the separator) with a die coater so that the thickness after drying becomes 15 μm. The storage elastic modulus of this pressure-sensitive adhesive layer was 0.37 MPa at 23 ° C. and 0.17 MPa at 80 ° C.

Adhesive B: Polyethylene terephthalate film having a thickness of 38 μm, which is obtained by subjecting an organic solvent solution in which a urethane acrylate oligomer is blended to a copolymer of butyl acrylate and acrylic acid and an isocyanate crosslinking agent is further added thereto to a release treatment. A sheet-like pressure-sensitive adhesive coated on the release treatment surface of the separator) with a die coater so that the thickness after drying becomes 5 μm. The storage elastic modulus of this pressure-sensitive adhesive layer was 0.37 MPa at 23 ° C. and 0.17 MPa at 80 ° C.

Adhesive C: A commercially available sheet-like adhesive in which a release treatment surface of a 38 μm thick polyethylene terephthalate film (separator) subjected to a release treatment is provided with an acrylic adhesive layer having a thickness of 25 μm. No urethane acrylate oligomer is blended. The storage elastic modulus of this pressure-sensitive adhesive layer was 0.05 MPa at 23 ° C. and 0.04 MPa at 80 ° C.

Adhesive D: A commercially available sheet-like adhesive in which an adhesive layer having a thickness of 15 μm is provided on a release treatment surface of a 38 μm-thick polyethylene terephthalate film (separator) subjected to a release treatment. No urethane acrylate oligomer is blended. The storage elastic modulus of this pressure-sensitive adhesive layer was 0.05 MPa at 23 ° C. and 0.04 MPa at 80 ° C.

  In addition, adhesive C is applied to one side of a retardation film ("Essina film" manufactured by Sekisui Chemical Co., Ltd .: trade name) made of a norbornene resin having a thickness of 25 μm and an in-plane retardation of 140 nm. A retardation film with an adhesive was prepared.

[Example 1]
A transparent protective layer made of a triacetyl cellulose film having a thickness of 40 μm is formed on one side of a polarizer made of a film having a thickness of 25 μm in which iodine is adsorbed and oriented on polyvinyl alcohol, and made of an aqueous solution containing polyvinyl alcohol and a water-soluble epoxy resin. After bonding through an adhesive, pressure-sensitive adhesive A was bonded to the polyvinyl alcohol polarizer side to obtain a single polarizing plate corresponding to 8 in FIG.

  After separating the separator from the polarizing plate alone, on the side of the pressure-sensitive adhesive layer, on the side where the pressure-sensitive adhesive film is not provided, the optical axis is clockwise with respect to the polarizing absorption axis of the polarizing plate. Bonding was performed so as to form 45 °, and then cut out at a diagonal size of 7 inches so that the polarization absorption axis was 30 degrees with respect to the long side, to produce a front polarizing plate with a retardation film.

  In addition, after the separator is peeled off from the polarizing plate alone, the optical retardation is opposite to the polarizing absorption axis of the polarizing plate on the side where the pressure-sensitive adhesive film is not provided on the pressure-sensitive adhesive layer side. Bonded so as to form 45 ° in the clockwise direction, and then cut out with a diagonal size of 7 inches so that the polarization absorption axis is 60 degrees with respect to the long side, and a rear polarizing plate with a retardation film is produced. did.

[Example 2]
A front polarizing plate with a retardation film and a rear polarizing plate are provided in the same manner as in Example 1 except that the pressure-sensitive adhesive A attached to the polyvinyl alcohol polarizer side of the polarizing plate is changed to pressure-sensitive adhesive B. Produced.

[Example 3]
A front polarizing plate and a rear polarizing plate with a retardation film were prepared in the same manner as in Example 1 except that the polarizing plate was cut out at a diagonal size of 10 inches.

[Comparative Example 1]
A front polarizing plate with a retardation film and a rear polarizing plate are prepared in the same manner as in Example 1 except that the pressure-sensitive adhesive A attached to the polyvinyl alcohol polarizer side of the polarizing plate is changed to pressure-sensitive adhesive C. Produced.

[Comparative Example 2]
A front polarizing plate with a retardation film and a rear polarizing plate are prepared in the same manner as in Example 1 except that the pressure-sensitive adhesive A attached to the polyvinyl alcohol polarizer side of the polarizing plate alone is changed to the pressure-sensitive adhesive D. Produced.

[Comparative Example 3]
A transparent protective layer made of a triacetyl cellulose film having a thickness of 40 μm is formed on an aqueous solution containing polyvinyl alcohol and a water-soluble epoxy resin on both sides of a polarizer made of a film having a thickness of 25 μm in which iodine is adsorbed and oriented on polyvinyl alcohol. After being bonded through an adhesive, the pressure-sensitive adhesive A was bonded to one side to obtain a single polarizing plate corresponding to 15 in FIG.

  In the same manner as in Example 1, a retardation film with an adhesive was bonded to a single polarizing plate, cut out with a diagonal size of 7 inches, and a front polarizing plate and a rear polarizing plate with a retardation film were produced.

[Comparative Example 4]
A front polarizing plate and a rear polarizing plate with a retardation film were produced in the same manner as in Comparative Example 3 except that the first layer pressure-sensitive adhesive A provided on the polarizing plate single-side was changed to the pressure-sensitive adhesive B.

[Comparative Example 5]
A front polarizing plate and a rear polarizing plate with a retardation film were produced in the same manner as in Example 1 except that the polarizing plate was cut out in a 4 inch diagonal size.

[Evaluation of shrinkage ratio of polarizing plate]
Each of the front polarizing plate with retardation film and the rear polarizing plate prepared in Examples 1 to 3 and Comparative Examples 1 to 5 is a glass plate having a thickness of 0.7 mm through a second pressure-sensitive adhesive layer. The two polarizers were pasted so that the absorption axes of the polarizers were orthogonal to each other, and autoclaved for 20 minutes under the conditions of a temperature of 50 ° C. and a pressure of 0.5 MPa. After natural cooling, D1 and D2 in the above formula of shrinkage ratio H for the front polarizing plate and the rear polarizing plate of each sample (glass plate with polarizing plate) are two-dimensional manufactured by Nikon Corporation. Measurement was performed using a measuring instrument “NEXIV VMR-12207”. Next, a heating test was performed in which these samples were put into an oven maintained at 85 ° C. and held for 500 hours. For the front polarizing plate and the rear polarizing plate of the sample after the heating test, D1 ′ and D2 ′ in the expression of the shrinkage amount ratio H described above are two-dimensional measuring instruments “NEXIV VMR-” manufactured by Nikon Corporation. The measurement was performed using 12072 ″, the shrinkage ratio H of the front polarizing plate and the shrinkage ratio H of the rear polarizing plate were determined, and the average value of both was shown in Tables 1-3.

[Evaluation of thermal unevenness of polarizing plate]
About the sample of the heating test in said shrinkage | contraction amount ratio evaluation of said polarizing plate, the brightness | luminance difference (DELTA) L defined below was calculated | required and the result was shown to Tables 1-3. The luminance was measured with “Eye-scale 4W” manufactured by I-System Co., Ltd.

ΔL = (L1 + L2 + L3 + L4) / 4−L5
L1, L2, L3, L4: Respective luminances measured at a portion (usually in the image display area) 10 mm inward from the center of the four sides of the polarizing plate.
L5: Luminance measured at the center of the polarizing plate.

  Here, it is determined that the smaller the value of ΔL, the smaller the luminance difference between the periphery of the display portion and the center portion, that is, the less heat unevenness.

  As shown in Table 1, the polarizing plates of the present invention obtained in Examples 1 and 2 have a high storage elastic modulus of the first pressure-sensitive adhesive layer, and ΔL is higher than that of Comparative Examples 1 and 2. It can be seen that the thermal unevenness of the image display area is reduced.

  As shown in Table 2, the polarizing plates of the present invention obtained in Examples 1 and 2 have no transparent protective layer between the polarizer and the transparent polymer film, and in Comparative Examples 3 and 4 where this is present. It can be seen that ΔL is smaller than that of the polarizing plate, and thermal unevenness in the image display area is reduced.

  As shown in Table 3, the polarizing plates of the present invention obtained in Example 1 and Example 3 have a diagonal length of 7 inches or more and a diagonal length of Comparative Example 5 of less than 7 inches. It can be seen that ΔL is smaller than that of the polarizing plate, and thermal unevenness in the image display area is reduced.

It is a cross-sectional schematic diagram which shows the example of the laminated constitution of the polarizing plate of this invention. It is a cross-sectional schematic diagram which shows the example which mounted | wore the liquid crystal panel with the polarizing plate of this invention. It is a cross-sectional schematic diagram which shows the example of the laminated constitution of the conventional polarizing plate.

Explanation of symbols

1 ... Polarizer,
2, 2a ... Transparent protective layer,
3 …… First adhesive layer,
4 …… Polymer film (retardation film),
5 …… Second adhesive layer,
6 …… Separator,
7: Polarizing plate,
8: Polarizer alone,
9 …… Front polarizing plate,
10: Rear polarizing plate,
11 …… Image display element (liquid crystal cell),
12. Other optical layer (surface treatment layer),
13. Other optical layers (such as brightness enhancement films)
14 …… Polarizing plate (conventional),
15: Polarizer alone (conventional).

Claims (7)

A rectangular polarizing plate having a diagonal length of 7 inches or more,
A transparent protective layer is laminated on one side of a polarizer made of a polyvinyl alcohol-based resin film, a first pressure-sensitive adhesive layer is laminated directly on the other side, a transparent polymer film and The second adhesive layer is laminated in this order,
A polarizing plate, wherein the storage elastic modulus of the first pressure-sensitive adhesive layer is 0.15 to 10 MPa in a temperature range of 23 to 80 ° C.   The polarizing plate according to claim 1, wherein the first pressure-sensitive adhesive layer has a thickness of 3 to 25 μm.   The polarizing plate according to claim 1, wherein the transparent polymer film has an in-plane retardation.   The polarizing plate according to claim 1, wherein an optical layer having an optical function is laminated on the transparent protective layer. When the heat treatment is performed at 85 ° C. for 500 hours in a state of being a rectangular polarizing plate and bonded to the glass plate through the second pressure-sensitive adhesive layer, the shrinkage amount ratio H defined below is 1. It is 8 or more, The polarizing plate in any one of Claims 1-4.
H = (D1-D1 ′) / (D2-D2 ′)
D1: In the polarizing plate before the heat treatment, when the point taken at the midpoint of one long side is M1, and the point taken at the midpoint of the other long side is M2, before the heat treatment In the polarizing plate, the length of the line segment connecting M1 and M2.
D1 ′: The length of the line segment connecting M1 and M2 in the polarizing plate after the heat treatment.
D2: In the polarizing plate before the heat treatment, a point taken from M1 to the center of the polarizing plate at a linear distance of 10 mm is defined as M1 ′, and from M2 to the center of the polarizing plate at a linear distance of 10 mm. The length of the line segment connecting M1 ′ and M2 ′ in the polarizing plate before the heat treatment when the taken point is M2 ′.
D2 ′: The length of the line connecting M1 ′ and M2 ′ in the polarizing plate after the heat treatment.   An image display device, wherein the polarizing plate according to claim 1 is bonded to an image display element via the second pressure-sensitive adhesive layer.   7. The image display device according to claim 6, wherein the image display element is a liquid crystal cell of VA mode, ECB mode, OCB mode or IPS mode.

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