WO2006120971A1

WO2006120971A1 - Process for producing polarizing plate, polarizing plate produced by said process, and optical film and image display device using said polarizing plate

Info

Publication number: WO2006120971A1
Application number: PCT/JP2006/309145
Authority: WO
Inventors: Naoyuki Nitta; Yuuji Saiki; Hiroaki Mizushima; Takemichi Yoshida
Original assignee: Nitto Denko Corporation
Priority date: 2005-05-06
Filing date: 2006-05-02
Publication date: 2006-11-16
Also published as: JP2006313205A; TW200700782A

Abstract

This invention provides a polarizing plate in which the occurrence of peripheral unevenness has been suppressed by suppressing of the shrinkage of the polarizing plate. At least a polarizing film and a protective film are stacked on top of each other. In such a state that a tension of 60 N/m to 450 N/m is applied to the laminated film, the laminated film is heated at a temperature of 60ºC to 120ºC. This heat treatment can provide a polarizing plate which undergoes a percentage dimensional change between before and after standing of the polarizing plate at 60ºC for 24 hr of, for example, -0.28% to 0%, has no residual stress in the polarizing film, and has suppressed shrinkage. By virtue of the suppressed peripheral unevenness and excellent optical properties, the polarizing plate is useful for various image display devices including liquid crystal display devices.

Description

Specification

Manufacturing method of polarizing plate, polarizing plate obtained thereby, optical film and image display device using the same

Technical field

The present invention relates to a method for producing a polarizing plate, a polarizing plate obtained thereby, an optical film using the same, and an image display device.

Background art

In general, a liquid crystal display device is provided with a polarizing plate. The polarizing plate is a laminate of a polarizer (hereinafter also referred to as “polarizing film”) and a protective film. The manufacturing method is, for example, as follows (see, for example, Patent Documents 1 and 2). That is, first, a polybulal alcohol (PVA) film is dyed with dichroic iodine or a dichroic dye, cross-linked with borosilicate or borax, and stretched to produce a polarizer. Then, using the adhesive, a transparent film such as triacetyl cellulose is attached to the polarizer as a protective film to produce a polarizing plate.

When a liquid crystal display device using such a polarizing plate is left in an environment of high temperature and high humidity, the periphery of the screen becomes a frame shape due to a shift in the axial angle due to contraction and expansion stress of the polarizing plate. If there is a depolarization phenomenon (hereinafter referred to as “peripheral unevenness” or “white skip”) that becomes brighter, that is, the vicinity of the middle point of each side becomes particularly bright, and the display quality deteriorates! . In order to solve this problem, in the production of a polarizing film, a PVA film is dyed with a dichroic substance, washed with water, and then subjected to a tension and temperature condition that satisfies a certain relationship. A manufacturing method for performing a drying treatment has been studied (for example, see Patent Document 3). However, there was a problem that the depolarization phenomenon could not be effectively solved even by such a method!

Patent Document 1: Japanese Patent Laid-Open No. 10-68821

Patent Document 2: Japanese Patent Laid-Open No. 2002-169024

Patent Document 3: Japanese Patent Laid-Open No. 2001-174634

Disclosure of the invention Problems to be solved by the invention

Therefore, an object of the present invention is to provide a method for producing a polarizing plate that can produce a polarizing plate in which the depolarization phenomenon in the peripheral portion is more effectively prevented.

Means for solving the problem

[0005] In order to achieve the above object, the production method of the present invention is a method for producing a polarizing plate, comprising a calorific heat treatment step of performing heat treatment on a laminated film including at least a polarizing film and a protective film, Heat treatment process is 60ΝΖπ on the laminated film! It is characterized in that the heat treatment is performed at a heating temperature of 60 ° C to 120 ° C with a tension of ~ 450 NZm.

The invention's effect

[0006] In order to achieve the above object, the present inventors have made a series of studies. In the process, we obtained the knowledge that if the heat treatment was performed with at least a polarizing film and a protective film laminated, the dimensional change of the obtained polarizing plate was suppressed, and further research was repeated. As a result, 60ΝΖπ! It has been found that the depolarization phenomenon can be prevented more effectively than before in the obtained polarizing plate by applying a very weak tension of ˜450 NZm and performing the heat treatment in the predetermined temperature range. That is, conventionally, a polarizing film and a protective film are laminated, and in order to evaporate and remove the solvent of the adhesive used for the lamination, the laminated body is subjected to a drying treatment while being scraped off with a roll or the like. However, since the tension at that time is large, the present inventors have found that the stress remaining in the polarizing film cannot be resolved. And in view of this point, when the tension during the heat treatment was examined, it was found that the residual stress of the polarizing film was sufficiently eliminated within the range of the tension, and the present invention was achieved. The range of the tension of the present invention is extremely small as compared with the tension during drying of the conventional polarizing plate.

Brief Description of Drawings

[0007] FIG. 1 is a photograph showing an image of unevenness in the periphery of a polarizing plate obtained in an example of the present invention. 2) FIG. 2 shows the unevenness in the periphery of a polarizing plate obtained in a comparative example. It is a photograph showing an image of FIG. 3 shows the brightness indicated by each color in a photograph showing an image of the peripheral unevenness. BEST MODE FOR CARRYING OUT THE INVENTION

[0008] Next, the production method of the present invention will be described with examples.

[0009] The laminated film used in the present invention is obtained, for example, by laminating a protective film on at least one surface of a polarizing film.

[0010] As the polarizing film, a film obtained by dying a polymer film such as a polybulal alcohol (PVA) film with a dichroic substance such as iodine or a dichroic dye and uniaxially stretching is usually used. . Although the thickness of the polarizing film is not particularly limited, for example, 5π! Is about 120 μm, preferably about 7 μm to 80 μm. Among them, a polarizing film having a thickness of about 15 μm to 40 μm is particularly preferably used. If the thickness of the polarizing film is too thick (for example, 120 / zm or more), for example, the stress generated during stretching increases, and the dimensional change rate of the resulting polarizing plate may become extremely large. For example, less than δ μ ηι), for example, there is a possibility that stretch breakage is likely to occur.

[0011] As the optical characteristics of the polarizing film, for example, it is preferable that the single transmittance power is 3% or more when measured with the polarizing film alone, and the range of 43.3% to 45.0% is more preferable. Good. In practice, it is preferable that the orthogonal transmittance is smaller. In practice, it is preferably 0.00% or more and 0.05% or less, more preferably 0.030% or less. The orthogonal transmittance can be measured, for example, by preparing two polarizing films and superimposing them so that their absorption axes are orthogonal (90 °). The polarization degree of the polarizing film is practically preferably 99.90% or more and 100% or less, and particularly preferably 99.9% or more and 100% or less. Even when measured as a polarizing plate, it is preferable to obtain optical properties substantially equivalent to this.

[0012] The polymer film is not particularly limited, and for example, a film having translucency can be used. Specific examples include polybulal alcohol (PVA) film, polyethylene terephthalate (PET) film, ethylene-acetate copolymer film, partially saponified film, and cellulose film. Examples include molecular oriented films, PVA dehydrated products and polychlorinated vinyl dehydrochlorinated products such as polyene oriented films. Among these, for example, a PVA film is preferable because it is more excellent in dyeability with a dichroic substance such as iodine. [0013] The degree of polymerization of the polymer as the material of the polymer film is, for example, 500 to 10,000, preferably 100 to 6,000 force, more preferably 1,400 to 4,000 force! /. The Ken degree polymer may be used as the polymer. For example, from the viewpoint of solubility in water, it is preferably 75 mol% or more and 100 mol% or less, more preferably 98 mol% or more. and 100 mol% or less, particularly preferably 98.3 mol% to 99. 8 mol ^_0/0.

[0014] The PVA film is not particularly limited. For example, the PVA film may be any casting method, casting method, extrusion method, etc., in which a stock solution in which a film material is dissolved in water or an organic solvent is cast. A film formed by the method can be used as appropriate. Above all, the phase difference value is 5ηπ! A PVA film of ~ lOOnm is preferably used. In addition, for example, since a polarizing film having a more uniform in-plane can be obtained, it is preferable that the phase difference variation within the PVA film is as small as possible.For example, 10 nm or less is preferable at the measurement wavelength lOOOnm. It is preferable.

[0015] The method for producing a polarizing film is generally not limited to these forces that can be roughly divided into a dry stretching method and a wet stretching method. The dry stretching method is a method of stretching in a high-temperature gas atmosphere, and the wet stretching method is a method of stretching a film that has been immersed and swollen in a liquid in the liquid.

[0016] The manufacturing process of the polarizing film by the wet stretching method is not particularly limited, and a process according to necessary conditions can be appropriately used. In general, the manufacturing method is a method of manufacturing a PVA film by a series of processing steps including swelling, dyeing, crosslinking, stretching, washing with water, and drying power. It is preferable to carry out while immersing in a bath containing the treatment solution. The order of the processes, the number of times, the presence / absence of execution, and the like are not particularly limited. For example, the stretching process may be performed after the dyeing process, or may be performed simultaneously with the swelling process and the dyeing process, or may be performed after the stretching process. It is also preferable to perform the bridge treatment before and after the stretching treatment. The method for the stretching treatment is not particularly limited, and a conventionally known method can be used. For example, in the case of roll stretching, the film can be stretched by a difference in peripheral speed between rolls provided in the film stretching direction. The treatment solution may optionally contain additives such as boric acid, borax, or potassium iodide. others Therefore, the obtained polarizing film may contain boric acid, zinc sulfate, zinc chloride, potassium iodide and the like, if necessary. Further, in some treatments, a water washing treatment may be performed for each treatment that may be stretched in the flow direction (MD direction or film longitudinal direction) or the width direction (TD direction or film width direction) as appropriate.

[0017] The swelling treatment step is not particularly limited !, but for example, is a step of immersing the polymer film in a treatment bath (swelling bath) filled with water. By this step, the polymer film is washed with water, so that the dirt on the surface of the polymer film and the anti-blocking agent can be washed, and by swelling the polymer film, for example, uneven film conditions such as unevenness can be further alleviated. In the swelling bath, for example, glycerin, potassium iodide, and the like may be appropriately added and the concentration is not particularly limited, but glycerin is preferably 5% by mass or less, and potassium iodide is preferably 10% by mass or less. The temperature of the swelling bath is, for example, about 20 ° C to 45 ° C, and the immersion time in the swelling bath is, for example, about 2 seconds to 180 seconds. Further, the draw ratio at which the polymer film may be drawn in the swelling bath is, for example, about 1.1 to 3.5 times.

[0018] The dyeing treatment step is not particularly limited. For example, the dyeing treatment step is a step of dyeing the polymer film by immersing it in a treatment bath (dye bath) containing a dichroic substance such as iodine. As the dichroic substance, conventionally known substances can be used, and examples thereof include iodine and dichroic dyes. Examples of the dichroic dye include Red BR, Red LR, Let R, Pink LB, Rubin BL, Bordeaux GS, Sky Blue LG, Lemon Yellow, Blue BR, Blue 2R, Navy RY, Green LG, Violet LB, Violet Black H, Black B, Black GSP, Yellow 3G, Yellow R, Orange LR, Orange 3R, Scarlet GL, Scarlet KGL, Congo Red, Brilliant Violet BK, Spura Blue G, Spura Blue GL, Spura Orange GL, Direct Sky Blue, Direct First Orange S, First Black, etc. can be used. These dichroic substances may be used alone or in combination of two or more. Among these, iodine is preferable because optical properties such as the degree of polarization are further excellent and a durability improving effect is easily obtained.

[0019] As the dye bath solution, for example, a solution in which the dichroic substance is dissolved in a solvent can be used. The solvent is generally compatible with force water in which water (for example, pure water) is used. It may be an aqueous solution containing an organic solvent. The concentration of the dichroic substance is, for example,

It is about 010% by mass to 10% by mass. The immersion time of the polymer film in the dye bath is not particularly limited, but is, for example, about 0.5 to 20 minutes, and the temperature of the dye bath is, for example, about 5 ° C to 42 ° C. The polymer film may be stretched in this dyeing bath. The stretch ratio is, for example, about 1.1 to 3.5 times as the cumulative stretch ratio integrated with the stretch ratio in the previous treatment step.

[0020] When iodine is used as the dichroic substance, for example, it is preferable that the dyeing bath further contains an iodide because dyeing efficiency can be further improved. Examples of the iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, yowi aluminum, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, Examples thereof include titanium iodide, and among these, potassium iodide is preferable. The ratio of the iodide may be, for example, about 0.001% by mass to 10% by mass in the dyeing bath. Among them, the ratio (a: b, weight ratio) that it is preferable to use iodine (a) and potassium iodide (b) in combination is preferably in the range of 1: 5 to 1: 100. Furthermore, for example, in order to further improve the in-plane uniformity of the film, the dyeing bath may appropriately contain a crosslinking agent such as a boron compound.

[0021] The dyeing treatment may be performed by, for example, a method of applying or spraying an aqueous solution containing a dichroic substance to the polymer film, in addition to the immersion in the dyeing bath as described above, It may be a method in which dichroic materials are sometimes mixed together.

[0022] The crosslinking treatment step is not particularly limited. For example, the crosslinking treatment step is a step of immersing the polymer film in a treatment bath (crosslinking bath) containing a crosslinking agent. As the crosslinking agent, conventionally known substances can be used, and examples thereof include boron compounds such as boric acid and borax, darioxal, and glutaraldehyde. One kind of these may be used, or two or more kinds may be used in combination. When two or more types are used in combination, the preferred ratio (c: d, molar ratio) of boric acid (c) and borax (d) is about 4: 6 to 9: 1, for example. It is. As the solvent of the crosslinking bath, water (for example, pure water) is generally used, but an aqueous solution containing an organic solvent compatible with water may be used. The concentration of the crosslinking agent in the crosslinking bath is, for example, about 1% by mass to 10% by mass.

[0023] The crosslinking bath, for example, can obtain a polarizing film having further excellent in-plane uniformity, It may further contain iodide. The iodide is, for example, as described above, and the content thereof is, for example, 0.05% by mass to 15% by mass, and preferably 0.5% by mass to 8% by mass. Among them, the ratio (a: b, weight ratio) of the preferred combination of boric acid (a) and potassium iodide (b) is preferably in the range of 1: 0.1-1: 3.5. The range of 0.5 to 1: 2.5 is more preferable. The temperature of the crosslinking bath is, for example, 20 ° C to 70 ° C, and the immersion time is, for example, about 1 second to 15 minutes. The cross-linking treatment may be performed by a method of applying or spraying a cross-linking agent-containing solution in the same manner as the dyeing treatment. Further, the draw ratio at which the film may be stretched in the crosslinking bath is, for example, about 1.1 to 3.5 times as the cumulative draw ratio.

[0024] In the case of the wet stretching method, the stretching treatment step is, for example, a step of stretching while immersed in a treatment bath (stretching bath), and the stretching ratio is, for example, 3 times as the cumulative stretching ratio. It is preferably about 7 times. As the solution for the stretching bath, for example, a solution containing a solvent such as water, ethanol or various organic solvents and a compound such as various metal salts, iodine, boron and zinc is preferable. Among them, the preferred content of a solution containing boric acid and Z or potassium iodide is preferably about 2% by mass to 18% by mass, respectively. When boric acid and potassium iodide are used in combination, the content ratio (weight ratio) is preferably about 1: 0.1-1: 4. In addition, the temperature of the stretching bath in the stretching process is preferably about 40 ° C to 67 ° C.

[0025] The water washing treatment step is not particularly limited, and is, for example, a step of immersing the polymer film in a treatment bath (water washing bath). By this step, for example, unnecessary residues such as boric acid adhered in the previous treatment can be washed away. The aqueous solution may contain iodide. As the iodide, those described above can be used, and among them, sodium iodide and potassium iodide are preferable. The temperature of the washing bath is, for example, about 10 ° C to 60 ° C. The number of water washing treatments is not particularly limited, and may be, for example, once or multiple times. The type and concentration of the additive in each washing bath are not particularly limited and can be adjusted as appropriate.

[0026] The drying treatment step is not particularly limited, and can be performed by a conventionally known drying method such as natural drying, air drying, and heat drying. In the case of heat drying, for example, the heating temperature is about 10 ° C to 90 ° C, preferably about 20 ° C to 80 ° C, more preferably about 30 ° C to 80 ° C. The time is about 1 to 10 minutes. Also, this drying process In the physical process, it may be extended as appropriate! /.

[0027] In the drying treatment step, for example, the drying treatment is preferably performed in a state where a tension of 500 NZm or more is applied. For example, in the case of a film stretched by a wet stretch method so that the final stretch ratio (total stretch ratio) in the polarization absorption axis direction is 5.0 times to 7.0 times, a state in which such high tension is applied For example, the power of obtaining a polarizing film in which the unevenness in the film is further suppressed can be obtained by performing the drying process. The tension is preferably 550 N Zm or more. The upper limit value is not particularly limited, and can be appropriately set to such an extent that the film is not excessively stretched according to the elastic modulus of the film, for example, and preferably about 1200 NZm. The tension can be measured in the same manner as in the case of a laminated film described later.

[0028] The total draw ratio of the polarizing film produced through the above treatment steps is preferably 3.0 times to 7.0 times, more preferably 5.0 times to 7.0 times, . 5 times to 6. 5 times is particularly preferable. If the total draw ratio is 3.0 times or more, for example, it is easier to obtain a polarizing film having a high degree of polarization, and if it is 7.0 times or less, for example, film breakage can be sufficiently prevented. .

[0029] The polarizing film may be a polarizing film obtained by another manufacturing method without being limited to the above manufacturing method. The polarizing film may be, for example, a film obtained by kneading a dichroic substance into a polymer film such as polyethylene terephthalate (PET), forming a film, and stretching, or using a liquid crystal aligned in a uniaxial direction as a host. E-type film using dichroic dye as guest (US Patent No. 5,523,863, Japanese Patent Publication No. 3-503322), dichroic lyo-mouth pick liquid crystal, etc. Type film (US Pat. No. 6,049,428) and the like.

[0030] The moisture content of the polarizing film can be appropriately determined depending on, for example, the thickness and material of the film, but is preferably less than 20% by mass, more preferably 13% by mass to 17% by mass. The moisture content can be calculated as follows, for example. First, a 1 Ocm × 10 cm sample is cut out from the polarizing film, and its weight (W1) is measured. Then, the sample is dried at 120 ° C for 10 hours, and its weight (W2) is measured again. Using the weight before drying (W1) and the weight after drying (W2), determine the moisture content (%) from the following formula. Moisture content (%) = {(Wl -W2) / Wl} X 100

[0031] The protective film is not particularly limited, and a conventionally known transparent film can be used. Among them, a film having excellent transparency, mechanical strength, thermal stability, isotropy, and the like is preferable. Specific examples of the material for the protective film include triacetyl cellulose (TAC), etc., one-cell type resin, polyester type resin, polycarbonate type resin, polyamide type resin, polyimide type resin, Examples thereof include transparent resins such as polyethersulfone resin, polysulfone resin, polystyrene resin, polynorbornene resin, polyolefin resin, acrylic resin, and acetate resin. Further, as the protective film, for example, the thermosetting resin such as the talyl-based resin, urethane-based resin, acrylic urethane-based resin, epoxy-based resin, silicone-based resin, or ultraviolet-curable resin. Can be given. The protective film may be a saponified film. Among these, TAC film that has a strong point of improving adhesion that TAC film is preferred in terms of polarization characteristics and durability is more preferred.

[0032] In addition, a polymer film described in JP-A-2001-343529 (WO01 / 37007) may be used as the protective phenol. Examples of the polymer material include a thermoplastic resin having a substituted or unsubstituted imide group in the side chain, and a thermoplastic resin having a substituted or unsubstituted phenyl group and a -tolyl group in the side chain. The contained rosin composition can be used. A specific example is a resin composition having an alternating copolymer of isobutene and N-methylmaleimide and an acrylonitrile / styrene copolymer. The polymer film may be an extruded product of the resin composition, for example.

[0033] The thickness of the protective film is not particularly limited, and is, for example, 500 μm or less, preferably 5 / z πι to 300 / ζ m. For example, residual stress of the polarizing film and liquid crystal panel mounting Since warpage of the panel at the time can be further suppressed, it is more preferably 15 μm to 300 μm, and further preferably 20 μm to 90 μm.

[0034] The moisture content of the protective film can be appropriately determined depending on, for example, the thickness and material of the film, and is not particularly limited. For example, when the protective film is a TAC film, the moisture content is, for example, about 0.1% by mass to 10% by mass. The moisture content of the protective film can be calculated in the same manner as the polarizing film. [0035] The protective film may be, for example, a film having a viewing angle compensation function. The viewing angle compensation function is, for example, a function that can widen the viewing angle so that the image looks relatively clear even when the screen of the liquid crystal display device is viewed from an oblique direction that is perpendicular to the screen. It is. Examples of the film having such a function include a film obtained by applying a discotic liquid crystal nematic liquid crystal to the TAC film, a polymer film having birefringence that is biaxially stretched in the plane direction, and a uniaxial stretch in the plane direction. In addition, a bi-directionally stretched film such as a gradient oriented polymer film with a controlled refractive index in the thickness direction, which is also stretched in the thickness direction, can be used. Examples of the obliquely oriented polymer film include a film obtained by bonding a heat-shrinkable film to the polymer film and subjecting the polymer film to a stretching treatment or a shrinking treatment, or a liquid crystal polymer under the action of the shrinkage force by heating. Examples include films. Further, as the film having the viewing angle compensation function, for example, a film of a polymer such as polycarbonate, polybutyl alcohol, polystyrene, polymethyl methacrylate, polypropylene and other polyolefins, polyarylate, polyamide, polynorbornene and the like. Examples thereof include a birefringent film subjected to a stretching treatment, a liquid crystal polymer alignment film, and a laminated film in which a liquid crystal polymer alignment layer is supported by a film.

[0036] The protective film may be laminated on at least one surface of the polarizing film, but preferably on both sides. When laminating on both sides, the protective film may be of the same type or different types. The method for laminating the polarizing film and the protective film is not particularly limited. For example, an adhesive or the like is applied or dropped between the polarizing film and the protective film, and the both are continuously provided between adjacent rolls. The method of crimping can be increased by passing it through. The adhesive can be appropriately determined depending on the material of the protective film and the polarizing film, for example, an adhesive made of a polymer such as acrylic, butyl alcohol, silicone, polyester, polyurethane, or polyether. Agents and rubber adhesives can be used. Among these, it is more preferable to use, for example, a PVA polymer adhesive or a urethane polymer adhesive, for which a material excellent in hygroscopicity and heat resistance is preferred. Further, as the adhesive, for example, a general pressure-sensitive adhesive can also be used.

[0037] The polymer used in the PVA-based polymer adhesive is not particularly limited. For example, PVA having an average degree of polymerization of about 100 to 3000 and an average degree of saponification of about 85 mol% to 100 mol% is preferable from the viewpoint of adhesiveness. As the adhesive, for example, an adhesive containing a PVA-based polymer having a acetoacetyl group is more preferable because the adhesiveness and durability can be further improved. Further, the concentration of the aqueous adhesive solution is not particularly limited, but 0.1% by mass to 15% by mass is preferable, and 0.5% by mass to 10% by mass is more preferable. The thickness of the adhesive layer is preferably about 30 nm to 1000 nm, more preferably 50 nm to 300 nm force after drying.

[0038] Then, on the laminated film including at least the polarizing film and the protective film, 60 ΝΖπ! Apply heat treatment under conditions of heating temperature of 60 ° C to 120 ° C with a tension of ~ 450NZm. This heat treatment is preferably carried out while collecting and collecting the heated laminated film. If the tension exceeds 450 NZm, the dimensional change rate described later increases, and unevenness in the periphery cannot be suppressed. If the tension is less than 60 NZm, it is difficult to collect and collect the laminated film. If the temperature is too low (for example, less than 60 ° C), the laminated film cannot be sufficiently shrunk, resulting in a large dimensional change after the heat treatment and too high (for example, 120 ° C or more). In addition, the optical properties such as the hue of the polarizing plate are inferior. When the heat treatment in the present invention is used as a polarizing film, a film obtained by stretching at a high magnification (for example, a total stretching magnification of 5.0 to 7.0 times) and drying at a high tension is used. Very effective.

[0039] The tension of the heat treatment is preferably 70ΝΖπ! ~ 350NZm, more preferably 9ΟΝΖπ! ~ 320NZm, more preferably 90ΝΖπ! ~ 300NZm. The magnitude of the tension can be adjusted by, for example, the torque of the roll, and the application method is not particularly limited. For example, when the laminated film is fed by a roll and subjected to continuous heat treatment, the feeding direction Can be granted. The tension can be measured by, for example, a load cell type tension pick-up roll that can be measured by a load applied to the conveyance tool.

[0040] The temperature of the heat treatment is preferably 60 ° C to 90 ° C, more preferably 60 ° C to 85 ° C, still more preferably 60 ° C to 80 ° C, and particularly preferably. Is between 63 ° C and 80 ° C. The humidity of the heat treatment is not particularly limited, but is preferably 20% to 80%, for example. 30% to 70%. The time for the heat treatment is not particularly limited, but is, for example, 60 seconds to 600 seconds, preferably 120 seconds to 480 seconds.

[0041] In the polarizing plate of the present invention obtained as described above, the dimensional change rate is, for example, 0.28% to 0%. Peripheral unevenness can be sufficiently suppressed in the device. Further, the dimensional change rate is preferably -0.25% to 0%, more preferably 0.23% to 0%. In addition, the said dimensional change rate can be calculated | required with the following method, for example. First, a square sample of lOcm × 10 cm is cut out from the polarizing plate so that one side is parallel to the absorption axis direction of the polarizing film, and the dimension in the absorption axis direction is measured. The sample is allowed to stand for 24 hours at a temperature of 60 ° C (reliability test), and the dimension in the absorption axis direction is measured again. Then, using the dimension (A) before leaving and the dimension (B) after leaving, determine the dimensional change rate (C (%)) from the following formula. In this dimensional change rate, the humidity during the leaving treatment is not particularly limited, but is, for example, in the range of 0% to 20%.

C = {-(A-B) / A} X 100

In the polarizing plate of the present invention, the single hue b value is, for example, preferably 4.8 NBS or less, more preferably 4. ONBS or less, and further preferably 3.5 NBS or less. Within such a range, for example, very excellent optical properties with less coloring are exhibited. The single hue b value described above is the Hunter Lab color system (Hunter, RS: J. Opt. Soc. Amer., 38, 661 (A), 1094 (A) (1948); J. Opt. Soc. Amer. 48, 985 (1958)). Specifically, for example, according to JIS K 7105 5.3, tristimulus values (Χ, Υ, Ζ) of a sample are measured using a spectrophotometer or a photoelectric colorimeter, and these values are calculated. By substituting into the Hunter equation shown below as the color difference formula in Lab space, the simple hue b value can be calculated. For this measurement, for example, a C light source can be used. For example, according to an integrating sphere type spectral transmittance measuring device (trade name DOT-3C; manufactured by Murakami Color Research Laboratory), the single hue b value can be measured together with the transmittance.

Single hue b = 7. OX (Y-0.847Ζ) / Υ ^{1 2}

[0043] Next, the optical film of the present invention is characterized by including the polarizing plate of the present invention, and other configurations and structures are not limited at all. The optical film may further include another optical layer. Examples of the optical layer include a retardation film, a liquid crystal film, a light diffusion film, and a diffraction film. In the case where a retardation film is included as the other optical layer, the retardation film is preferably laminated on the polarizing film via the protective film, for example! /.

[0044] The retardation film is used, for example, when converting linearly polarized light into elliptically polarized light or circularly polarized light, converting elliptically polarized light or circularly polarized light into linearly polarized light, or polarizing the polarization direction of linearly polarized light. can do. In particular, a retardation film that converts linearly polarized light into elliptically polarized light or circularly polarized light, and elliptically polarized light or circularly polarized light into linearly polarized light, respectively, is, for example, a λ Ζ4 plate. Examples of the phase difference film include a λ 2 plate. In addition to the various wavelength plates such as the λΖ4 plate and the λΖ2 plate, the retardation film is, for example, a film for compensation of viewing angle such as compensation of coloration due to birefringence of the liquid crystal layer and expansion of viewing angle, etc. Examples thereof include a film having a phase difference according to the purpose of use and a tilted orientation film having a controlled refractive index in the thickness direction. Also, a laminated film in which two or more kinds of retardation films are laminated and optical characteristics such as retardation are controlled may be used. Examples of the retardation film include a birefringent film obtained by stretching a polymer film such as polycarbonate, polybutyl alcohol, polystyrene, polymethyl methacrylate, polypropylene and other polyolefins, polyacrylate, polyamide, polynorbornene, and liquid crystal. Examples thereof include a polymer alignment film and a laminated film in which an alignment layer of a liquid crystal polymer is supported by a film.

[0045] In the optical film of the present invention, each constituent member is, for example, a salicylic acid ester compound, a benzophenone compound, a benzotriazole compound, a cyanoacrylate compound, a nickel complex compound, or the like. It may have a UV absorption flaw by treatment with a UV absorber.

[0046] The optical film of the present invention may be, for example, an elliptically polarizing plate or a circularly polarizing plate. The elliptically polarizing plate compensates for coloring (for example, blue or yellow) caused by birefringence of a liquid crystal layer of a super twist nematic (STN) type liquid crystal display device, for example, to obtain a monochrome display without the coloring. It is used effectively. In addition, an elliptically polarizing plate with a controlled three-dimensional refractive index is, for example, an attachment that occurs when the screen of a liquid crystal display device is viewed from an oblique direction. This is preferable because the color can also be compensated. On the other hand, the circularly polarizing plate is effective, for example, when adjusting the color tone of an image of a reflective liquid crystal display device in which the image is a color display, and also has an antireflection function.

[0047] The polarizing plate and the optical film of the present invention may include an adhesive layer for adhering to other members such as a liquid crystal cell. The adhesive layer is not particularly limited, but an adhesive layer made of a pressure-sensitive adhesive is preferably used according to the demand for rework or the like. Examples of the pressure-sensitive adhesive include known translucent pressure-sensitive adhesives such as acrylic, silicone, polyester, polyurethane, polyether, and rubber. Of these, acrylic adhesives are preferably used for polarizing plates and optical films. The thickness of the adhesive layer containing the pressure-sensitive adhesive is not particularly limited, but is generally about 1 μm to 500 μm, preferably 5 μm to 200 μm force, and more preferably 10 μm to 100 μm force. By setting the thickness of the adhesive layer within this range, for example, stress associated with the dimensional behavior of the polarizing film and the polarizing plate can be further relaxed.

[0048] The polarizing plate and the optical film of the present invention can be preferably used for forming an image display device such as a liquid crystal display device (LCD) and an electoluminescence display device (ELD).

[0049] The polarizing plate and the optical film of the present invention can be used particularly preferably for the formation of a liquid crystal display device, for example, for example, a reflective type or a transflective type in which a polarizing plate is arranged on one side or both sides of a liquid crystal cell. It can be used for a liquid crystal display device such as a transmission / reflection type. The liquid crystal cell substrate may be, for example, a plastic substrate or a glass substrate. The liquid crystal cell forming the liquid crystal display device is arbitrary, for example, an active matrix driving type represented by a thin film transistor type, a simple matrix driving type represented by a twist nematic type or a super twist nematic type, and the like. A liquid crystal cell of a type may be used.

[0050] When polarizing plates and optical films are provided on both sides of the liquid crystal cell, they may be the same or different. Further, in the liquid crystal display device, for example, appropriate components such as a prism array sheet, a lens array sheet, a light diffusion plate, and a backlight may be included in one layer or two or more layers at an appropriate position.

[0051] The polarizing plate of the present invention is applied to an organic electroluminescence display device (organic EL display device). In the case of an organic EL display device including an organic EL light emitting device including a transparent electrode on the front surface side of the organic light emitting layer that emits light when voltage is applied and a metal electrode on the back surface side of the organic light emitting layer, the transparent electrode It is preferable to provide a polarizing plate on the surface side. This has the effect of polarizing the light incident from the outside and reflected by the metal electrode, so that there is an effect that the light caused by the specular reflection of the metal electrode is not visually recognized by the polarization operation.

[0052] Next, examples of the present invention will be described together with comparative examples. However, the present invention is not limited by the following examples and comparative examples.

Example 1

[0053] (Preparation of polarizing film)

Using a PVA film (degree of polymerization 2400) (manufactured by KURARENE), a polarizing film (thickness 25 m) was produced as follows. The PVA film was stretched in the longitudinal direction up to a draw ratio of 3.0 while being immersed in pure water at 30 ° C. to swell. The PVA film was dyed in a dyeing bath (aqueous solution containing 0.5% iodine and potassium iodide) while maintaining the above stretching ratio, and subjected to crosslinking treatment in an aqueous solution containing potassium borate iodide. The film was further stretched to a total stretching ratio of 6.0, and then washed with an aqueous potassium iodide solution at 30 ° C. The washed PVA film was dried under a temperature of 30 ° C. with a tension of 550 NZm to produce a polarizing film.

[0054] A TAC film (manufactured by Fuji Photo Film Co., Ltd.) with a surface thickness of 80 μm was prepared, and this TAC film and the polarizing film were laminated with a PVA adhesive using a pinch roll. (Thickness about 185 m). Then, this laminated film was heated for 8 minutes under a temperature of 65 ° C. with a tension of 1 OONZm in the absorption axis direction of the polarizing film, and a polarizing film in which protective films were laminated on both sides of the polarizing film. A plate was made. The tension was measured with a load cell type tension pick-up roll that can be measured with a load applied to the transport roll. Example 2

[0055] A polarizing plate was produced in the same manner as in Example 1 except that the tension during drying of the laminated film was 300 NZm.

Example 3 [0056] A polarizing plate was produced in the same manner as in Example 1 except that the temperature during heating of the laminated film was set to 70 ° C.

Example 4

[0057] A polarizing plate was produced in the same manner as in Example 1 except that the temperature when the laminated film was heated was 73 ° C.

Example 5

[0058] A polarizing plate was produced in the same manner as in Example 1 except that the temperature during heating of the laminated film was 78 ° C.

[0059] (Comparative Example 1)

A polarizing plate was produced in the same manner as in Example 1 except that the tension during heating of the laminated film was 500 NZm.

[0060] (Comparative Example 2)

A polarizing plate was produced in the same manner as in Example 1 except that the tension during heating of the laminated film was 50 NZm.

[0061] (Dimensional change rate)

A square test piece (10 cm × 10 cm) was cut out from the polarizing plate obtained as described above so that one side was parallel to the absorption axis direction. Cuts were made with a cutter at the center of the edges of the test pieces so that they were parallel to the absorption axis direction of the polarizing film, and the interval (A) between the cuts was measured using calipers. These test pieces were allowed to stand for 24 hours in a dryer (temperature: 60 ° C.) (reliability test), and the incision interval (B) was further measured. Using the interval before the reliability test (A) and the interval after the reliability test (B), the dimensional change rate (C (%)) was obtained from the following equation. The results are shown in Table 1 below.

C = {-(A-B) / A} X 100

[0062] (Optical property evaluation test)

Square test pieces (5 cm × 5 cm) were cut out from the polarizing plate obtained as described above, and these test pieces were left for 24 hours in a dryer (temperature 60 ° C.) (reliability test). Then, a single hue b value of the polarizing plate after the reliability test was measured using an integrating sphere type spectral transmittance measuring device (trade name: DOT-3C; manufactured by Murakami Color Research Laboratory). [0063] [Table 1] Heating conditions Dimensional change Single hue

Tension (N / m) Temperature CO C (%) b value (N B S)

Example 1 1 0 0 6 5 1 0. 2 4 3. 1 0 Example 2 3 0 0 6 5 1 0. 2 6 3. 2 6 Example 3 1 0 0 7 0 1 0. 2 2 3. 4 6 Example 4 1 0 0 7 3-0. 2 0 4. 0 1 Example 5 1 0 0 7 8-0. 1 3 4-7 2 Comparative Example 1 5 0 0 6 5-0. 2 9 3. 4 5 Comparative Example 2 5 0 6 5 ―-

[0064] In Comparative Example 2, the dimensional change rate and the single hue b value were not measured because wrinkle could not be removed due to the reduced tension during heating.

[0065] As shown in Table 1, in Examples 1 to 5, since the dimensional change rates are all in the range of 0.28% to 0%, such a polarizing plate can reduce peripheral unevenness. It can be said. Moreover, since the single hue b value of the polarizing plate is within 4.8, it can be said that the optical characteristics are excellent. On the other hand, in Comparative Example 1, since the dimensional change rate is smaller than −0.28%, it can be said that peripheral unevenness occurs in such a polarizing plate. Further, in Comparative Example 2, there was a problem that the polarizing plate could not be wound! /.

[0066] (Surrounding unevenness image measurement)

A polarizing plate obtained by the method of Example 2 was cut into a size of 30 cm × 25 cm so that the angle between the absorption axis and the long side was 45 ° when the adhesive surface was down. I got a sheet. These polarizing plates were attached to both surfaces of the glass plate so that the absorption axes were perpendicular to each other to prepare measurement samples. A horizontal backlight is turned on, the sample for measurement is placed on it, and a liquid crystal color distribution measuring device (trade name: liquid crystal color distribution measuring device CA-1000: manufactured by MINOLTA Co., Ltd.) at a distance of lm from the measurement sample. ) And the brightness of the sample were measured. In addition, the measurement performed both the central force and the vertical position force of the sample. The same measurement was performed on the polarizing plate obtained by the method of Comparative Example 1. These results are shown in Figs. FIG. 1 is an image showing the luminance of the polarizing plate of Example 2, and FIG. 2 is an image showing the luminance of the polarizing plate of Comparative Example 1. The outline of the relationship between each color and brightness in these figures is shown in Table 2 below, and the details are shown in Figure 3. [0067] [Table 2] Color Luminance (cd / m ² )

Blue 0- -0. 3

Light blue 0-3- -0. 5

Yellowish green 0-5- -0.7

Yellow 0.7--0.8

Orange 0-8--1. 0

Red 1.0--1.2

Pink 1. 2--1. 4

As shown in FIG. 1, the polarizing plate obtained by the method of Example 2 was able to suppress peripheral unevenness. On the other hand, as shown in FIG. 2, the polarizing plate obtained by the method of Comparative Example 1 was particularly bright near the midpoint of each side that was bright as a whole, and peripheral unevenness occurred. From the above, it was confirmed that the polarizing plate obtained by the method of the present invention can suppress peripheral unevenness. Industrial applicability

[0069] Thus, according to the production method of the present invention, 60ΝΖπ! Residual stress of the polarizing film can be eliminated by applying heat treatment under the conditions of heating temperature of 60 ° C to 120 ° C with a tension of ~ 450 NZm, so that shrinkage is suppressed and hue is excellent A polarizing plate can be manufactured. The polarizing plate obtained by the production method of the present invention is suppressed in peripheral unevenness, has excellent optical characteristics, and can be said to be useful for various image display devices such as liquid crystal display devices.

Claims

The scope of the claims

[1] A method for producing a polarizing plate, comprising: a heat treatment step of heat-treating a laminated film including at least a polarizing film and a protective film, wherein the heat treatment step is performed on the laminated film by 60ΝΖπ! ~ Heating temperature 60 ° C ~ 120 with 450 NZm tension applied

A manufacturing method characterized by being a step of performing heat treatment under the condition of ° C.

[2] The production method according to claim 1, wherein the polarizing film is a polybulal alcohol film dyed with a dichroic substance.

[3] The method according to claim 1, wherein the polarizing film is a film stretched by a wet stretching method at a total stretching ratio of 5 to 7 times.

[4] The polarizing film is heated at a temperature of 1 with a tension of 500 NZm or more after the stretching.

4. The production method according to claim 3, wherein the film has been subjected to a drying treatment under conditions of 0 ° C. to 90 ° C.

[5] The method according to claim 1, wherein the heat treatment step is a step performed while scraping the laminated film.

6. The production method according to claim 1, wherein the protective film strength is at least one of a triacetyl cellulose film and a saponified triacetyl cellulose film.

7. The manufacturing method according to claim 1, wherein the protective film is a film having a viewing angle compensation function.

[8] A polarizing plate comprising at least a polarizing film and a protective film, wherein the polarizing plate is obtained by the production method according to claim 1.

[9] When the polarizing plate is allowed to stand for 24 hours at a temperature of 60 ° C., the dimensional change rate represented by the following formula in the absorption axis direction of the polarizing plate is 0.28% or more and 0% or less, The polarizing plate according to claim 8, wherein a single hue b value of the polarizing plate after being left standing is 4.8 NBS or less.

Dimensional change rate = (A-B) / A} X 100

In the above formula, A represents the size of the polarizing plate before being left, and B represents the size of the polarizing plate after being left.

[10] An optical film including a polarizing plate, wherein the polarizing plate is the polarizing plate according to claim 8. Optical film.

9. An image display device comprising a polarizing plate, wherein the polarizing plate is a polarizing plate according to claim 8.