WO2022158088A1 - Polarizing plate manufacturing method, image display device manufacturing method, and method for adjusting transmittance of polarizing film - Google Patents

Polarizing plate manufacturing method, image display device manufacturing method, and method for adjusting transmittance of polarizing film Download PDF

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Publication number
WO2022158088A1
WO2022158088A1 PCT/JP2021/041182 JP2021041182W WO2022158088A1 WO 2022158088 A1 WO2022158088 A1 WO 2022158088A1 JP 2021041182 W JP2021041182 W JP 2021041182W WO 2022158088 A1 WO2022158088 A1 WO 2022158088A1
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Prior art keywords
polarizing film
film
based resin
weight
pva
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PCT/JP2021/041182
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French (fr)
Japanese (ja)
Inventor
周作 後藤
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日東電工株式会社
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Priority to CN202180091355.4A priority Critical patent/CN116802529A/en
Priority to KR1020237024445A priority patent/KR20230129452A/en
Publication of WO2022158088A1 publication Critical patent/WO2022158088A1/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C55/00—Shaping by stretching, e.g. drawing through a die; Apparatus therefor
    • B29C55/02—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C55/00—Shaping by stretching, e.g. drawing through a die; Apparatus therefor
    • B29C55/02—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets
    • B29C55/04—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets uniaxial, e.g. oblique
    • B29C55/06—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets uniaxial, e.g. oblique parallel with the direction of feed
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
    • C08J5/18—Manufacture of films or sheets
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/30—Polarising elements
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
    • G02F1/133528—Polarisers
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B33/00—Electroluminescent light sources
    • H05B33/02—Details
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B33/00—Electroluminescent light sources
    • H05B33/10—Apparatus or processes specially adapted to the manufacture of electroluminescent light sources
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K59/00—Integrated devices, or assemblies of multiple devices, comprising at least one organic light-emitting element covered by group H10K50/00
    • H10K59/80—Constructional details
    • H10K59/8793—Arrangements for polarized light emission
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2329/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an alcohol, ether, aldehydo, ketonic, acetal, or ketal radical; Hydrolysed polymers of esters of unsaturated alcohols with saturated carboxylic acids; Derivatives of such polymer
    • C08J2329/02—Homopolymers or copolymers of unsaturated alcohols
    • C08J2329/04—Polyvinyl alcohol; Partially hydrolysed homopolymers or copolymers of esters of unsaturated alcohols with saturated carboxylic acids
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K59/00—Integrated devices, or assemblies of multiple devices, comprising at least one organic light-emitting element covered by group H10K50/00
    • H10K59/80—Constructional details
    • H10K59/8791—Arrangements for improving contrast, e.g. preventing reflection of ambient light

Definitions

  • the present invention relates to a method for manufacturing a polarizing plate, a method for manufacturing an image display device, and a method for adjusting the transmittance of a polarizing film.
  • liquid crystal display devices eg, organic EL display devices and inorganic EL display devices
  • EL electroluminescence
  • a liquid crystal display device has polarizing plates arranged on both sides of a liquid crystal cell due to its image forming method.
  • problems such as external light reflection and background reflection can be prevented by placing a circularly polarizing plate including a ⁇ /4 plate on the viewing side of the organic EL cell (for example, Patent Documents 1 and 2).
  • a polarizing plate usually has a structure in which a protective layer is arranged on at least one side of a polarizing film prepared by dyeing and stretching a polyvinyl alcohol-based resin film. It is attached to an image display cell such as an EL cell.
  • the protective layer is laminated after the protective layer is laminated or is attached to the image display cell. After that, it has been desired to develop a method for adjusting the transmittance of the polarizing film.
  • the present invention has been made to solve the conventional problems described above, and its main purpose is to provide a method for adjusting the transmittance of a polarizing film after it has been produced.
  • the primary polarizing film is dried until the moisture content becomes 15% by weight or less. and contacting the surface of the primary polarizing film with an aqueous solvent to change the transmittance to obtain a secondary polarizing film, in this order.
  • the aqueous solvent is brought into contact with the exposed surface of the primary polarizing film with one surface exposed and the other surface protected.
  • a polyvinyl alcohol-based resin film containing a halide and a polyvinyl alcohol-based resin is placed in the air in a state of a laminate with a long thermoplastic resin substrate. It includes subjecting the laminate to auxiliary stretching treatment, dyeing treatment, stretching treatment in an aqueous boric acid solution, and drying shrinkage treatment in this order. shrinking to 2% or more and drying until the water content of the polyvinyl alcohol resin film becomes 15% by weight or less.
  • the halide is iodide or sodium chloride.
  • the primary polarizing film has a thickness of 12 ⁇ m or less.
  • a polarizing film made of a polyvinyl alcohol resin film containing a dichroic substance and having a moisture content of 15% by weight or less, a protective layer, and an adhesive layer are included in this order.
  • a method for manufacturing an image display device comprising the step of bringing an aqueous solvent into contact with the substrate to change the transmittance, in this order.
  • the image display device is a liquid crystal display device or an organic EL display device.
  • the polarizing film comprises a step of bringing an aqueous solvent into contact with the surface of a polarizing film composed of a polyvinyl alcohol-based resin film containing a dichroic substance and having a moisture content of 15% by weight or less.
  • a method for adjusting the permeability of a membrane is provided.
  • the transmittance of the polarizing film can be changed ex post by bringing an aqueous solvent into contact with the surface of the polarizing film produced by dyeing and stretching the polyvinyl alcohol resin film.
  • the surface of the polarizing film whose appearance has been stabilized by drying until the moisture content becomes a predetermined value or less is brought into contact with an aqueous solvent to change the transmittance. Fine adjustment of the rate is possible.
  • variations in luminance between image display devices can be reduced, and when it is desired to match the appearance of multiple display screens, particularly when displaying images by combining multiple display screens (large public display). , digital signage, etc.).
  • FIG. 4 is a schematic diagram showing an example of drying shrinkage treatment using a heating roll. It is a schematic sectional drawing explaining an example of the polarizing plate which can be produced in the process of producing a polarizing plate. It is a schematic sectional drawing explaining an example of the polarizing plate which can be produced in the process of producing a polarizing plate. It is a schematic sectional drawing explaining an example of the polarizing plate which can be produced in the process of producing a polarizing plate.
  • FIG. 4A is a schematic cross-sectional view of an example of a polarizing plate that can be produced by a process of protecting the exposed surface of a secondary polarizing film; FIG. 4A is a schematic cross-sectional view of an example of a polarizing plate that can be produced by a process of protecting the exposed surface of a secondary polarizing film;
  • the polarizing plate obtained by the polarizing plate manufacturing method according to the embodiment of the present invention includes at least a polarizing film, and preferably includes a polarizing film and a protective layer disposed on one side or both sides thereof.
  • A. Method for producing polarizing plate In the method for producing a polarizing plate according to an embodiment of the present invention, a polyvinyl alcohol (PVA)-based resin film is dyed and stretched in an aqueous boric acid solution (stretched in boric acid solution), followed by A step of drying to a moisture content of 15% by weight or less to obtain a primary polarizing film, and contacting the surface of the primary polarizing film with an aqueous solvent to change the transmittance and form a secondary polarizing film. the step of obtaining in this order.
  • PVA polyvinyl alcohol
  • the surface of the polarizing film (primary polarizing film) once produced is decolorized by bringing an aqueous solvent into contact with the surface, thereby changing the transmittance afterward and adjusting it to a desired value.
  • the polarizing film (primary polarizing film) in a state of being highly oriented and having a stabilized appearance through stretching treatment in boric acid solution and drying treatment to contact with an aqueous solvent, the degree of polarization is excessively lowered and wrinkles are formed. It is possible to suitably adjust the transmittance while avoiding the generation, dissolution, etc. of
  • the transmittance may be changed by contacting only one surface of the primary polarizing film with an aqueous solvent, or by contacting both surfaces with an aqueous solvent to change the transmittance. You may let
  • the exposed surface of the primary polarizing film is brought into contact with an aqueous solvent to reduce the transmittance. change.
  • the method for producing the polarizing plate of the present embodiment for example, between the step of obtaining the primary polarizing film and the step of obtaining the secondary polarizing film, one surface of the primary polarizing film is exposed and the other surface is protected.
  • a step of making a layer-protected polarizer can be included.
  • Step of obtaining the primary polarizing film the PVA-based resin film is subjected to dyeing treatment and stretching treatment in boric acid solution, and then dried until the moisture content becomes 15% by weight or less.
  • the primary polarizing film may be produced using a single-layer PVA-based resin film, or may be produced using a laminate of two or more layers including a PVA-based resin layer (PVA-based resin film).
  • a primary polarizing film produced using a laminate of two or more layers avoids the occurrence of wrinkles and the like even after contact with an aqueous solvent, and exhibits excellent optical properties (typically, single transmittance and polarization degree) can be suitably maintained.
  • A-1-1 Production of a primary polarizing film using a laminate of two or more layers
  • the production of a primary polarizing film using a laminate of two or more layers is, for example, a PVA-based resin film containing a halide and a PVA-based resin that is formed into a long shape.
  • a laminate with a thermoplastic resin substrate it can be subjected to an auxiliary stretching treatment in air, a dyeing treatment, a stretching treatment in an aqueous boric acid solution, and a drying shrinkage treatment in this order.
  • a laminate of a thermoplastic resin substrate and a PVA-based resin film includes, for example, a PVA-based resin layer (PVA-based resin film) containing a halide and a PVA-based resin on one side of a long thermoplastic resin substrate. is obtained by forming a laminate.
  • the drying shrinkage treatment for example, the laminate of the long thermoplastic resin substrate and the PVA-based resin film is heated while being transported in the longitudinal direction, thereby shrinking the laminate by 2% or more in the width direction, and the PVA-based resin film. It includes drying until the moisture content of the system resin film becomes 15% by weight or less.
  • the content of the halide in the PVA-based resin layer is preferably 5 to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin.
  • the drying shrinkage treatment is preferably performed using a heating roll, and the temperature of the heating roll is preferably 60°C to 120°C. According to such a manufacturing method, it is possible to obtain a primary polarizing film having a high degree of orientation of the PVA-based resin and excellent optical properties.
  • A-1-1-1 Production of Laminate Any appropriate method can be adopted as a method for producing a laminate of a thermoplastic resin substrate and a PVA-based resin layer.
  • a coating liquid containing a halide and a PVA-based resin is applied to the surface of the thermoplastic resin substrate and dried to form a PVA-based resin layer on the thermoplastic resin substrate.
  • the content of the halide in the PVA-based resin layer is preferably 5 to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin.
  • any appropriate method can be adopted as the method of applying the coating liquid. Examples thereof include roll coating, spin coating, wire bar coating, dip coating, die coating, curtain coating, spray coating, and knife coating (comma coating, etc.).
  • the coating/drying temperature of the coating liquid is preferably 50° C. or higher.
  • the thickness of the PVA-based resin layer is preferably 3 ⁇ m to 40 ⁇ m, more preferably 3 ⁇ m to 20 ⁇ m.
  • the thermoplastic resin substrate Before forming the PVA-based resin layer, the thermoplastic resin substrate may be surface-treated (for example, corona treatment, etc.), or an easy-adhesion layer may be formed on the thermoplastic resin substrate. By performing such treatment, the adhesion between the thermoplastic resin substrate and the PVA-based resin layer can be improved.
  • surface-treated for example, corona treatment, etc.
  • an easy-adhesion layer may be formed on the thermoplastic resin substrate.
  • the thickness of the thermoplastic resin substrate is preferably 20 ⁇ m to 300 ⁇ m, more preferably 50 ⁇ m to 200 ⁇ m. If the thickness is less than 20 ⁇ m, it may be difficult to form the PVA-based resin layer. If it exceeds 300 ⁇ m, for example, in the later-described underwater stretching treatment, it may take a long time for the thermoplastic resin substrate to absorb water, and an excessive load may be required for stretching.
  • the thermoplastic resin substrate preferably has a water absorption of 0.2% or more, more preferably 0.3% or more.
  • Thermoplastic resin substrates can absorb water and be plasticized with the water acting like a plasticizer. As a result, the stretching stress can be greatly reduced, and the film can be stretched at a high draw ratio.
  • the water absorption rate of the thermoplastic resin substrate is preferably 3.0% or less, more preferably 1.0% or less.
  • thermoplastic resin substrate can be adjusted, for example, by introducing a modifying group into the constituent material.
  • the water absorption is a value determined according to JIS K 7209.
  • the glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 120°C or less.
  • Tg The glass transition temperature of the thermoplastic resin substrate.
  • the temperature is preferably 100° C. or lower, more preferably 90° C. or lower.
  • the glass transition temperature of the thermoplastic resin substrate is preferably 60°C or higher.
  • the PVA-based resin layer can be satisfactorily stretched at a suitable temperature (for example, about 60°C).
  • the glass transition temperature of the thermoplastic resin substrate can be adjusted, for example, by heating using a crystallization material that introduces a modifying group into the constituent material.
  • the glass transition temperature (Tg) is a value determined according to JIS K 7121.
  • thermoplastic resin can be adopted as a constituent material of the thermoplastic resin base material.
  • thermoplastic resins include ester resins such as polyethylene terephthalate resins, cycloolefin resins such as norbornene resins, olefin resins such as polypropylene, polyamide resins, polycarbonate resins, and copolymer resins thereof. is mentioned. Among these, norbornene-based resins and amorphous polyethylene terephthalate-based resins are preferred.
  • an amorphous (not crystallized) polyethylene terephthalate resin is preferably used.
  • amorphous (difficult to crystallize) polyethylene terephthalate resin is particularly preferably used.
  • Specific examples of amorphous polyethylene terephthalate resins include copolymers further containing isophthalic acid and/or cyclohexanedicarboxylic acid as dicarboxylic acids, and copolymers further containing cyclohexanedimethanol or diethylene glycol as glycols.
  • the thermoplastic resin base material is composed of a polyethylene terephthalate resin having an isophthalic acid unit.
  • a thermoplastic resin substrate is extremely excellent in stretchability and can suppress crystallization during stretching. This is probably because the introduction of the isophthalic acid unit gives the main chain a large bend.
  • a polyethylene terephthalate-based resin has a terephthalic acid unit and an ethylene glycol unit.
  • the isophthalic acid unit content is preferably 0.1 mol % or more, more preferably 1.0 mol % or more, relative to the total of all repeating units. This is because a thermoplastic resin base material having extremely excellent stretchability can be obtained.
  • the isophthalic acid unit content is preferably 20 mol % or less, more preferably 10 mol % or less, relative to the total of all repeating units.
  • the degree of crystallinity can be favorably increased in the drying shrinkage treatment described later.
  • the thermoplastic resin substrate may be stretched in advance (before forming the PVA-based resin layer). In one embodiment, it is stretched in the transverse direction of the elongated thermoplastic resin substrate.
  • the lateral direction is preferably a direction perpendicular to the stretching direction of the laminate described below.
  • perpendicular also includes the case of being substantially perpendicular.
  • substantially orthogonal includes 90° ⁇ 5.0°, preferably 90° ⁇ 3.0°, more preferably 90° ⁇ 1.0°.
  • the stretching temperature of the thermoplastic resin substrate is preferably Tg-10°C to Tg+50°C with respect to the glass transition temperature (Tg).
  • the draw ratio of the thermoplastic resin substrate is preferably 1.5 to 3.0 times.
  • thermoplastic resin base material Any appropriate method can be adopted as a method for stretching the thermoplastic resin base material.
  • the drawing may be fixed end drawing or free end drawing.
  • the stretching method may be a dry method or a wet method.
  • the stretching of the thermoplastic resin substrate may be performed in one step or in multiple steps. When performing in multiple stages, the above-mentioned draw ratio is the product of the draw ratios in each step.
  • the coating liquid contains a halide and a PVA-based resin, as described above.
  • the coating liquid is typically a solution in which the halide and the PVA-based resin are dissolved in a solvent.
  • solvents include water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. These can be used alone or in combination of two or more. Among these, water is preferred.
  • the concentration of the PVA-based resin in the solution is preferably 3 to 20 parts by weight with respect to 100 parts by weight of the solvent. With such a resin concentration, it is possible to form a uniform coating film in close contact with the thermoplastic resin substrate.
  • the content of the halide in the coating liquid is preferably 5 to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin.
  • Additives may be added to the coating liquid.
  • additives include plasticizers and surfactants.
  • plasticizers include polyhydric alcohols such as ethylene glycol and glycerin.
  • Surfactants include, for example, nonionic surfactants. These can be used for the purpose of further improving the uniformity, dyeability and stretchability of the obtained PVA-based resin layer.
  • any appropriate resin can be adopted as the PVA-based resin.
  • Examples include polyvinyl alcohol and ethylene-vinyl alcohol copolymers.
  • Polyvinyl alcohol is obtained by saponifying polyvinyl acetate.
  • An ethylene-vinyl alcohol copolymer is obtained by saponifying an ethylene-vinyl acetate copolymer.
  • the degree of saponification of the PVA-based resin is usually 85 mol% to 100 mol%, preferably 95.0 mol% to 99.95 mol%, more preferably 99.0 mol% to 99.93 mol%. .
  • the degree of saponification can be determined according to JIS K 6726-1994. By using a PVA-based resin having such a degree of saponification, a polarizing film having excellent durability can be obtained. If the degree of saponification is too high, gelation may occur.
  • the average degree of polymerization of the PVA-based resin can be appropriately selected according to the purpose.
  • the average degree of polymerization is usually 1,000 to 10,000, preferably 1,200 to 4,500, more preferably 1,500 to 4,300.
  • the average degree of polymerization can be determined according to JIS K 6726-1994.
  • halide any appropriate halide can be adopted as the halide.
  • examples include iodide and sodium chloride.
  • Iodides include, for example, potassium iodide, sodium iodide, and lithium iodide. Among these, potassium iodide is preferred.
  • the amount of the halide in the coating liquid is preferably 5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the PVA resin, and more preferably 10 parts by weight to 15 parts by weight with respect to 100 parts by weight of the PVA resin. Department. If the amount of the halide exceeds 20 parts by weight with respect to 100 parts by weight of the PVA-based resin, the halide may bleed out and the finally obtained polarizing film may become cloudy.
  • the orientation of the polyvinyl alcohol molecules in the PVA-based resin layer increases. orientation may be disturbed and the orientation may be lowered.
  • the laminate is stretched in boric acid water at a relatively high temperature in order to stabilize the stretching of the thermoplastic resin substrate.
  • the film is stretched, the tendency of the degree of orientation to decrease is remarkable.
  • the stretching of a single PVA film in boric acid water is generally carried out at 60° C.
  • the stretching of a laminate of A-PET (thermoplastic resin substrate) and a PVA-based resin layer is It is carried out at a high temperature of about 70° C., and in this case, the orientation of PVA at the initial stage of stretching may be lowered before it is increased by stretching in water.
  • the crystallization of the PVA-based resin in the PVA-based resin layer of the laminate after auxiliary stretching can be promoted.
  • the PVA-based resin layer is immersed in a liquid, the disturbance of the orientation of the polyvinyl alcohol molecules and the deterioration of the orientation can be suppressed compared to the case where the PVA-based resin layer does not contain a halide.
  • This can improve the optical properties of the polarizing film obtained through treatment steps such as dyeing treatment and underwater stretching treatment in which the laminate is immersed in a liquid.
  • A-1-1-2 Aerial Auxiliary Stretching
  • a two-stage stretching method combining dry stretching (auxiliary stretching) and stretching in boric acid solution is selected.
  • auxiliary stretching such as two-step stretching, it is possible to stretch while suppressing crystallization of the thermoplastic resin substrate, and excessive crystallization of the thermoplastic resin substrate in the subsequent stretching in boric acid water. It is possible to solve the problem that stretchability is reduced by stretching, and stretch the laminate at a higher magnification.
  • the stretching method of the in-air auxiliary stretching may be fixed edge stretching (e.g., a method of stretching using a tenter stretching machine) or free edge stretching (e.g., a method of uniaxially stretching the laminate through rolls having different peripheral speeds).
  • free-end drawing may be positively employed in order to obtain high optical properties.
  • the in-air stretching process includes a heating roll stretching step in which the laminate is stretched by a peripheral speed difference between heating rolls while being conveyed in the longitudinal direction.
  • the air drawing process typically includes a zone drawing process and a hot roll drawing process.
  • the order of the zone stretching process and the heating roll stretching process is not limited, and the zone stretching process may be carried out first, or the heating roll stretching process may be carried out first.
  • the zone drawing step may be omitted. In one embodiment, the zone drawing step and the heated roll drawing step are performed in this order.
  • the laminate is stretched by gripping the ends of the laminate and widening the distance between the tenters in the machine direction in a tenter stretching machine (the widening of the distance between the tenters is the stretching ratio). At this time, the distance between the tenters in the width direction (perpendicular to the machine direction) is set to be arbitrarily close.
  • the draw ratio in the machine direction can be set to be closer to the free end draw.
  • the shrinkage ratio in the width direction is calculated by (1/stretching ratio) 1/2 .
  • Aerial auxiliary stretching may be performed in one step or in multiple steps. When it is carried out in multiple stages, the draw ratio is the product of the draw ratios in each step.
  • the stretching direction in the in-air auxiliary stretching is preferably substantially the same as the stretching direction in the underwater stretching.
  • the draw ratio in the in-air auxiliary drawing is preferably 2.0 to 3.5 times.
  • the maximum draw ratio when the auxiliary drawing in the air and the drawing in water are combined is preferably 5.0 times or more, more preferably 5.5 times or more, and still more preferably 6.0 times the original length of the laminate. That's it.
  • the term "maximum draw ratio" refers to the draw ratio immediately before the laminate breaks, and is 0.2 lower than the draw ratio at which the laminate breaks.
  • the stretching temperature for the in-air auxiliary stretching can be set to any appropriate value depending on the material for forming the thermoplastic resin base material, the stretching method, and the like.
  • the stretching temperature is preferably the glass transition temperature (Tg) of the thermoplastic resin substrate or higher, more preferably the glass transition temperature (Tg) of the thermoplastic resin substrate + 10°C or higher, and particularly preferably Tg + 15°C or higher.
  • the upper limit of the stretching temperature is preferably 170°C.
  • the crystallization index of the PVA-based resin after auxiliary stretching in air is preferably 1.3 to 1.8, more preferably 1.4 to 1.7.
  • an insolubilization treatment is performed after the auxiliary stretching treatment in the air and before the stretching treatment in water or the dyeing treatment.
  • the insolubilization treatment is typically performed by immersing the PVA-based resin layer in an aqueous boric acid solution.
  • the insolubilization treatment imparts water resistance to the PVA-based resin layer, and prevents deterioration of the orientation of the PVA when immersed in water.
  • the concentration of the boric acid aqueous solution is preferably 1 to 4 parts by weight with respect to 100 parts by weight of water.
  • the liquid temperature of the insolubilizing bath is preferably 20°C to 50°C.
  • the dyeing treatment is typically performed by dyeing the PVA-based resin layer with a dichroic substance (typically iodine). Specifically, it is carried out by allowing the PVA-based resin layer to adsorb iodine.
  • adsorption method include a method of immersing the PVA-based resin layer (laminate) in a dyeing solution containing iodine, a method of coating the PVA-based resin layer with the dyeing solution, and a method of applying the dyeing solution to the PVA-based resin layer.
  • a spraying method and the like can be mentioned.
  • a preferred method is to immerse the laminate in a dyeing solution (dyeing bath). This is because iodine can be well adsorbed.
  • the staining solution is preferably an iodine aqueous solution.
  • the amount of iodine compounded is preferably 0.05 to 0.5 parts by weight per 100 parts by weight of water.
  • an iodide to the iodine aqueous solution.
  • iodides include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. etc.
  • potassium iodide is preferred.
  • the amount of iodide compounded is preferably 0.1 to 10 parts by weight, more preferably 0.3 to 5 parts by weight, per 100 parts by weight of water.
  • the liquid temperature of the dyeing liquid during dyeing is preferably 20° C. to 50° C. in order to suppress dissolution of the PVA-based resin.
  • the immersion time is preferably 5 seconds to 5 minutes, more preferably 30 seconds to 90 seconds, in order to ensure the transmittance of the PVA-based resin layer.
  • the dyeing conditions can be set so that the single transmittance of the finally obtained polarizing film has the desired value.
  • the content ratio of iodine and potassium iodide in the aqueous iodine solution is preferably 1:5 to 1:10.
  • the boric acid contained in the treatment bath is mixed into the dyeing bath.
  • the boric acid concentration in the dyeing bath may change over time, resulting in unstable dyeability.
  • the upper limit of the boric acid concentration in the dyeing bath is preferably 4 parts by weight, more preferably 2 parts by weight with respect to 100 parts by weight of water. adjusted.
  • the lower limit of the boric acid concentration in the dyeing bath is preferably 0.1 parts by weight, more preferably 0.2 parts by weight, and still more preferably 0.5 parts by weight with respect to 100 parts by weight of water. is.
  • the dyeing process is performed using a dyeing bath pre-blended with boric acid. This can reduce the rate of change in boric acid concentration when the boric acid in the treatment bath is mixed into the dyeing bath.
  • the amount of boric acid blended in advance in the dyeing bath (that is, the content of boric acid not derived from the treatment bath) is preferably 0.1 to 2 parts by weight with respect to 100 parts by weight of water. , more preferably 0.5 to 1.5 parts by weight.
  • A-1-1-5 A-1-1-5.
  • Crosslinking Treatment If necessary, a crosslinking treatment is applied after the dyeing treatment and before the underwater stretching treatment.
  • the cross-linking treatment is typically performed by immersing the PVA-based resin layer in an aqueous solution of boric acid.
  • the cross-linking treatment imparts water resistance to the PVA-based resin layer, and prevents deterioration of the orientation of the PVA when immersed in high-temperature water in the subsequent underwater stretching.
  • the concentration of the boric acid aqueous solution is preferably 1 to 5 parts by weight with respect to 100 parts by weight of water.
  • the amount of iodide compounded is preferably 1 to 5 parts by weight per 100 parts by weight of water. Specific examples of iodides are as described above.
  • the liquid temperature of the cross-linking bath is preferably 20°C to 50°C.
  • thermoplastic resin substrate and the PVA-based resin layer can be stretched at a temperature lower than the glass transition temperature (typically, about 80° C.), and the PVA-based resin layer undergoes its crystallization. can be stretched at a high magnification while suppressing the As a result, a polarizing film having excellent optical properties can be produced.
  • any appropriate method can be adopted as the method for stretching the laminate. Specifically, fixed-end stretching or free-end stretching (for example, a method of uniaxially stretching a laminate by passing it between rolls having different peripheral speeds) may be used. Free-end drawing is preferably chosen.
  • the laminate may be stretched in one step or in multiple steps. When the stretching is performed in multiple stages, the draw ratio (maximum draw ratio) of the laminate described below is the product of the draw ratios in each step.
  • the stretching in water is typically performed by immersing the laminate in an aqueous boric acid solution (stretching in boric acid water).
  • an aqueous boric acid solution as the stretching bath, the PVA-based resin layer can be imparted with rigidity to withstand tension applied during stretching and water resistance that does not dissolve in water.
  • boric acid can form a tetrahydroxyborate anion in an aqueous solution and crosslink with a PVA-based resin through hydrogen bonding.
  • rigidity and water resistance can be imparted to the PVA-based resin layer, which can be satisfactorily stretched, and a primary polarizing film having excellent optical properties can be produced.
  • the boric acid aqueous solution is preferably obtained by dissolving boric acid and/or a borate salt in water as a solvent.
  • the boric acid concentration is preferably 1 part by weight to 10 parts by weight, more preferably 2.5 parts by weight to 6 parts by weight, and particularly preferably 3 parts by weight to 5 parts by weight with respect to 100 parts by weight of water. is.
  • an aqueous solution obtained by dissolving a boron compound such as borax, glyoxal, glutaraldehyde, or the like in a solvent can also be used.
  • an iodide is added to the stretching bath (boric acid aqueous solution).
  • iodide elution of iodine adsorbed on the PVA-based resin layer can be suppressed.
  • Specific examples of iodides are as described above.
  • the concentration of iodide is preferably 0.05 to 15 parts by weight, more preferably 0.5 to 8 parts by weight, per 100 parts by weight of water.
  • the stretching temperature (liquid temperature of the stretching bath) is preferably 40°C to 85°C, more preferably 60°C to 75°C. At such a temperature, the film can be stretched at a high magnification while suppressing dissolution of the PVA-based resin layer.
  • the glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 60° C. or higher in relation to the formation of the PVA-based resin layer. In this case, if the stretching temperature is lower than 40° C., it may not be possible to stretch well even if the plasticization of the thermoplastic resin base material by water is considered.
  • the higher the temperature of the stretching bath the higher the solubility of the PVA-based resin layer, which may make it impossible to obtain excellent optical properties.
  • the immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.
  • the draw ratio by underwater drawing is preferably 1.5 times or more, more preferably 3.0 times or more.
  • the total draw ratio of the laminate is preferably 5.0 times or more, more preferably 5.5 times or more, relative to the original length of the laminate.
  • A-1-1-7 Dry shrinkage treatment
  • the laminate of the long thermoplastic resin substrate and the PVA-based resin film is heated while being transported in the longitudinal direction, thereby shrinking the laminate by 2% or more in the width direction. and drying until the water content of the PVA-based resin film becomes 15% by weight or less. From the viewpoint of obtaining a stable appearance, it is preferable to dry to a moisture content of 12% by weight or less, more preferably 10% by weight or less, and even more preferably 1% to 5% by weight.
  • the drying shrinkage treatment may be performed by zone heating performed by heating the entire zone, or by heating the transport roll (using a so-called heating roll) (heating roll drying method). Preferably both are used.
  • heating roll heating roll drying method
  • the crystallization of the thermoplastic resin substrate can be efficiently promoted and the crystallinity can be increased by drying the laminate while it is placed along the heating roll. Even at the drying temperature, the crystallinity of the thermoplastic resin substrate can be increased satisfactorily.
  • the thermoplastic resin base material has increased rigidity and is in a state capable of withstanding shrinkage of the PVA-based resin layer due to drying, thereby suppressing curling.
  • the layered product can be dried while being maintained in a flat state, so that not only curling but also wrinkling can be suppressed.
  • the laminate can be shrunk in the width direction by drying shrinkage treatment, thereby improving the optical properties. This is because the orientation of PVA and PVA/iodine complex can be effectively enhanced.
  • the shrinkage ratio of the laminate in the width direction due to drying shrinkage treatment is preferably 1% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%.
  • FIG. 1 is a schematic diagram showing an example of drying shrinkage treatment.
  • the laminate 200 is dried while being transported by transport rolls R1 to R6 heated to a predetermined temperature and guide rolls G1 to G4.
  • the transport rolls R1 to R6 are arranged so as to alternately and continuously heat the surface of the PVA-based resin layer and the surface of the thermoplastic resin substrate.
  • the transport rolls R1 to R6 may be arranged so as to continuously heat only the plastic resin substrate surface).
  • the drying conditions can be controlled by adjusting the heating temperature of the transport rolls (the temperature of the heating rolls), the number of heating rolls, the contact time with the heating rolls, and so on.
  • the temperature of the heating roll is preferably 60°C to 120°C, more preferably 65°C to 100°C, and particularly preferably 70°C to 80°C.
  • the degree of crystallinity of the thermoplastic resin can be favorably increased, curling can be favorably suppressed, and an optical laminate having extremely excellent durability can be produced.
  • the temperature of the heating roll can be measured with a contact thermometer. In the illustrated example, six transport rolls are provided, but there is no particular limitation as long as the number of transport rolls is plural. Conveying rolls are usually 2 to 40, preferably 4 to 30 in number.
  • the contact time (total contact time) between the laminate and the heating roll is preferably 1 to 300 seconds, more preferably 1 to 20 seconds, still more preferably 1 to 10 seconds.
  • the heating roll may be provided in a heating furnace (for example, an oven), or may be provided in a normal production line (under room temperature environment). Preferably, it is provided in a heating furnace equipped with air blowing means.
  • a heating furnace equipped with air blowing means.
  • the temperature for hot air drying is preferably 30°C to 100°C.
  • the hot air drying time is preferably 1 second to 300 seconds.
  • the wind speed of the hot air is preferably about 10m/s to 30m/s. The wind speed is the wind speed in the heating furnace and can be measured with a mini-vane digital anemometer.
  • A-1-1-8 Other Treatments
  • a washing treatment is performed after the underwater stretching treatment and before the drying shrinkage treatment.
  • the cleaning treatment is typically performed by immersing the PVA-based resin layer in an aqueous solution of potassium iodide.
  • A-1-2. Production of primary polarizing film using single-layer PVA-based resin film Production of a primary polarizing film using a single-layer PVA-based resin film is self-supporting (that is, does not require support by a substrate).
  • a strip-shaped PVA-based resin film is dyed and stretched in boric acid water (typically, uniaxially stretched by a roll stretching machine), and then the water content is 15% by weight or less, preferably 12% by weight or less, more preferably 10% by weight. This can be done by drying to a weight % or less, more preferably 1 to 5 weight %.
  • the dyeing is performed by, for example, immersing the PVA-based resin film in an iodine aqueous solution.
  • the draw ratio of the uniaxial drawing is preferably 3 to 7 times. Stretching may be performed after the dyeing treatment, or may be performed while dyeing. Moreover, you may dye after extending
  • the primary polarizing film preferably exhibits absorption dichroism at any wavelength of 380 nm to 780 nm.
  • the transmittance of the primary polarizing film (single transmittance: Ts) is preferably 41.5% or more, more preferably 42.0% or more, still more preferably 42.5% or more.
  • the transmittance of the primary polarizing film is preferably 46.0% or less, more preferably 45.0% or less.
  • the degree of polarization of the primary polarizing film is preferably 98.0% or more, more preferably 99.0% or more, still more preferably 99.9% or more.
  • the degree of polarization of the primary polarizing film is preferably 99.998% or less.
  • the transmittance is typically a Y value measured using an ultraviolet-visible spectrophotometer and subjected to visibility correction.
  • the degree of polarization is typically obtained by the following formula based on the parallel transmittance Tp and the orthogonal transmittance Tc measured using an ultraviolet-visible spectrophotometer and subjected to visibility correction.
  • Degree of polarization (%) ⁇ (Tp-Tc)/(Tp+Tc) ⁇ 1/2 ⁇ 100
  • the transmittance of a thin polarizing film of 12 ⁇ m or less is typically the polarizing film (surface refractive index: 1.53) and the protective layer (protective film) (refractive index: 1.50 ) is measured using an ultraviolet-visible spectrophotometer.
  • the reflectance at each layer interface may change, resulting in a change in the measured transmittance.
  • the transmittance measurements may be corrected according to the refractive index of the surface of the protective layer that is in contact with the air interface.
  • the transmittance correction value C is expressed by the following formula using the reflectance R 1 (transmission axis reflectance) of polarized light parallel to the transmission axis at the interface between the protective layer and the air layer.
  • C R 1 -R 0
  • R 0 ((1.50 ⁇ 1) 2 /(1.50+1) 2 ) ⁇ (T 1 /100)
  • R 1 ((n 1 ⁇ 1) 2 /(n 1 +1) 2 ) ⁇ (T 1 /100)
  • R 0 is the transmission axis reflectance when a protective layer having a refractive index of 1.50 is used
  • n 1 is the refractive index of the protective layer used
  • T 1 is the transmittance of the polarizing film. is.
  • the correction amount C is approximately 0.2%.
  • the transmittance when using a polarizing film with a surface refractive index of 1.53 and a protective layer with a refractive index of 1.50 It is possible to convert to a rate.
  • the amount of change in the correction value C when the transmittance T1 of the polarizing film is changed by 2 % is 0.03% or less, and the transmittance of the polarizing film is equal to the correction value C has a limited effect on the value of Moreover, when the protective layer has absorption other than surface reflection, appropriate correction can be performed according to the amount of absorption.
  • the thickness of the primary polarizing film is typically 25 ⁇ m or less, preferably 12 ⁇ m or less, more preferably 1 ⁇ m to 8 ⁇ m, even more preferably 1 ⁇ m to 7 ⁇ m, still more preferably 2 ⁇ m to 5 ⁇ m.
  • the thickness is small, there is an advantage that wrinkles are less likely to occur in the polarizing film when it is brought into contact with an aqueous solvent.
  • the moisture content of the primary polarizing film is typically 15% by weight or less, preferably 12% by weight or less, more preferably 10% by weight or less, and still more preferably 1% to 5% by weight. If the moisture content is within the above range, the transmittance can be changed without significantly impairing the appearance when contacted with an aqueous solvent.
  • a polarizing plate having a configuration in which a protective layer and optionally a functional layer are laminated on one side of a primary polarizing film and the other side is an exposed surface is produced.
  • Any appropriate functional layer can be selected as the functional layer depending on the purpose, and specific examples thereof include a retardation layer, an adhesive layer, and the like.
  • the process of manufacturing the said polarizing plate is an arbitrary process. Therefore, depending on the purpose, the laminate having the structure of [thermoplastic resin substrate/primary polarizing film] produced by the method described in Section A-1-1 or the single layer described in Section A-1-2
  • the primary polarizing film prepared using the PVA-based resin film of No. 1 can be directly subjected to the step of obtaining the secondary polarizing film.
  • FIG. 2A to 2C are schematic cross-sectional views explaining an example of a polarizing plate that can be produced in the process of producing a polarizing plate.
  • the polarizing plate 100A shown in FIG. 2A includes a polarizing film (primary polarizing film) 10 and a protective layer 20 disposed on one side thereof, and the polarizing film (primary polarizing film) 10 on the side on which the protective layer 20 is provided. The opposite side is the exposed surface.
  • the polarizing plate 100A is, for example, an adhesive layer or a It can be obtained by laminating a protective layer via an adhesive layer and then peeling off the thermoplastic resin substrate. Alternatively, the polarizing plate 100A can be obtained by laminating a protective layer on one surface of the primary polarizing film produced by the method described in Section A-1-2 via an adhesive layer or a pressure-sensitive adhesive layer. .
  • the polarizing plate 100B shown in FIG. 2B includes a polarizing film (primary polarizing film) 10, a protective layer 20, a retardation layer 30, and an adhesive layer 40 in this order. is provided and the opposite side is an exposed surface.
  • the retardation layer 30 is attached to the protective layer 20 side surface of the polarizing plate 100A via an adhesive layer or a pressure-sensitive adhesive layer, and then the pressure-sensitive adhesive layer 40 is provided on the surface of the retardation layer 30.
  • the retardation layer 30 is provided on the thermoplastic resin substrate side surface of the laminate having the configuration of [thermoplastic resin substrate/primary polarizing film] via an adhesive layer or a pressure-sensitive adhesive layer. It can also be obtained by laminating and then providing the pressure-sensitive adhesive layer 40 on the surface of the retardation layer 30 .
  • the thermoplastic resin substrate functions as the protective layer 20 .
  • the retardation layer 30 in the illustrated example may have a single-layer structure, or may have a laminated structure in which two or more retardation layers are laminated.
  • the polarizing plate 100C shown in FIG. 2C includes a polarizing film (primary polarizing film) 10, a protective layer 20, and an adhesive layer 40 in this order. and the opposite side is the exposed surface.
  • the polarizing plate 100C can be obtained, for example, by providing an adhesive layer 40 on the protective layer 20 side surface of the polarizing plate 100A.
  • the polarizing plate 100C can also be obtained by providing an adhesive layer 40 on the thermoplastic resin substrate side surface of the laminate having the structure [thermoplastic resin substrate/primary polarizing film]. In this case, the thermoplastic resin substrate functions as the protective layer 20 .
  • a release film is temporarily attached to the surface of the adhesive layer 40 until the polarizing plate is used.
  • the protective layer 20 is formed of any appropriate film that can be used as a protective layer for polarizing films.
  • the retardation layer 30 can be, for example, a thermoplastic resin film or a liquid crystal alignment fixed layer. Any appropriate adhesive can be used as the adhesive that forms the adhesive layer 40, and among them, an acrylic adhesive having an acrylic polymer as a base polymer is preferably used.
  • Such protective layer, retardation layer and pressure-sensitive adhesive layer are well known to those skilled in the art, and thus detailed description thereof will be omitted.
  • Step of Obtaining Secondary Polarizing Film In the step of obtaining the secondary polarizing film, the surface of the primary polarizing film is brought into contact with an aqueous solvent to change the transmittance of the primary polarizing film. Specifically, a secondary polarizing film having a desired transmittance can be obtained by decolorizing the primary polarizing film by bringing it into contact with an aqueous solvent.
  • aqueous solvent can be used as the aqueous solvent as long as it can elute the dichroic substance from the primary polarizing film.
  • the aqueous solvent can be, for example, water or a mixture of water and a water-soluble organic solvent.
  • Preferred examples of the water-soluble organic solvent include lower monoalcohols having 1 to 4 carbon atoms such as methanol, ethanol, n-propyl alcohol and isopropyl alcohol, and polyhydric alcohols such as glycerin and ethylene glycol.
  • the content of the water-soluble organic solvent in the aqueous solvent is, for example, 20% by weight or less, preferably 10% by weight or less, and more preferably 5% by weight or less.
  • the method of contact with the aqueous solvent is not particularly limited, and any suitable method such as immersion, spraying, coating, etc. can be used. Spraying or coating is preferred for partial transmittance adjustment, and immersion is preferred for overall transmittance adjustment.
  • the contact time with the aqueous solvent and the temperature of the aqueous solvent during contact can be appropriately set according to the desired change in transmittance. Increasing the contact time or increasing the temperature of the aqueous solvent tends to increase the amount of change in transmittance.
  • the contact time can be, for example, 10 minutes or less, preferably 1 second to 5 minutes, more preferably 2 seconds to 3 minutes.
  • the temperature of the aqueous solvent can be preferably 20°C to 70°C, more preferably 30°C to 65°C, even more preferably 40°C to 60°C.
  • the polarizing film may be dried after contact with the aqueous solvent.
  • the drying temperature can be, for example, 30°C to 100°C, preferably 30°C to 80°C.
  • the moisture content of the dried polarizing film (secondary polarizing film) is typically 15% by weight or less, preferably 12% by weight or less, more preferably 10% by weight or less, and still more preferably 1% by weight. % to 5% by weight.
  • the secondary polarizing film preferably exhibits absorption dichroism at any wavelength of 380 nm to 780 nm.
  • the transmittance of the secondary polarizing film (single transmittance: Ts) can be appropriately adjusted depending on the purpose.
  • the transmittance of the secondary polarizing film is preferably 41.5% or more, more preferably 42% or more, still more preferably 42.5% or more.
  • the transmittance of the secondary polarizing film is, for example, 70% or less, preferably 50% or less, more preferably 46% or less.
  • the secondary polarizing film can have a transmission that is, for example, 0.1% to 1.5% higher than the primary polarizing film.
  • the degree of polarization of the secondary polarizing film is, for example, 90% or more, preferably 92.0% or more, more preferably 94.0% or more, still more preferably 96.0% or more, and still more. It is preferably 99.0% or more, still more preferably 99.5% or more, and preferably 99.998% or less.
  • the above transmittance and degree of polarization are values obtained in the same manner as the transmittance and degree of polarization of the primary polarizing film.
  • the thickness of the secondary polarizing film is typically 25 ⁇ m or less, preferably 12 ⁇ m or less, more preferably 1 ⁇ m to 8 ⁇ m, still more preferably 1 ⁇ m to 7 ⁇ m, still more preferably 2 ⁇ m to 5 ⁇ m.
  • the thickness of the secondary polarizing film can be substantially the same as the primary polarizing film.
  • the method for manufacturing the polarizing plate may further include any appropriate steps as necessary.
  • the step of changing the transmittance by contacting the surface of the secondary polarizing film with an aqueous solvent may be further included.
  • the step of changing the transmittance can be repeated two or more times.
  • any suitable layer (protective layer, retardation layer, adhesive layer, etc.) is laminated on the exposed surface of the finally obtained polarizing film (e.g., secondary polarizing film) to protect the exposed surface.
  • polarizing film e.g., secondary polarizing film
  • the polarizing plate 100D includes a first protective layer 20a, a polarizing film (secondary polarizing film) 10, a second protective layer 20b, a retardation layer 30, and an adhesive layer 40 in this order.
  • the polarizing plate 100D is obtained by, for example, forming a second protective layer 20b, a retardation layer 30 and an adhesive layer 40 in this order on the exposed surface of the polarizing film 10 of the polarizing plate 100A (FIG. 2A) that has undergone the step of obtaining a secondary polarizing film.
  • FIG. 2A a polarizing film 10 of the polarizing plate 100A
  • FIG. 2B the polarizing plate 100B
  • the polarizing plate 100E includes a first protective layer 20a, a polarizing film (secondary polarizing film) 10, a second protective layer 20b, and an adhesive layer 40 in this order.
  • the second protective layer 20b may have a desired retardation and function as a retardation layer (for example, a ⁇ /4 plate), as described later.
  • the polarizing plate 100E can be obtained, for example, by providing the second protective layer 20b and the adhesive layer 40 in this order on the exposed surface of the polarizing film 10 of the polarizing plate 100A (FIG. 2A) that has undergone the process of changing the transmittance. .
  • it can be obtained by bonding the first protective layer 20a to the exposed surface of the polarizing film 10 of the polarizing plate 100C (FIG. 2C) that has undergone the process of changing the transmittance.
  • the adhesive layer 40 is used to bond the polarizing plates 100D and 100E to an image display cell (eg liquid crystal cell, organic EL cell).
  • the first protective layer 20a serves as a protective layer (outer protective layer) arranged on the side opposite to the image display cell when the polarizing plate is applied to the image display device, and serves as the second protective layer.
  • the layer 20b becomes a protective layer (inner protective layer) arranged on the image display cell side.
  • the thickness of the outer protective layer is typically 300 ⁇ m or less, preferably 100 ⁇ m or less, more preferably 5 ⁇ m to 80 ⁇ m, still more preferably 10 ⁇ m to 60 ⁇ m.
  • the thickness of the outer protective layer is the thickness including the thickness of the surface treatment layer.
  • the thickness of the inner protective layer is preferably 5 ⁇ m to 200 ⁇ m, more preferably 10 ⁇ m to 100 ⁇ m, still more preferably 10 ⁇ m to 60 ⁇ m.
  • the inner protective layer is optically isotropic.
  • “optically isotropic” means that the in-plane retardation Re (550) is 0 nm to 10 nm, and the thickness direction retardation Rth (550) is ⁇ 10 nm to +10 nm.
  • nx is the refractive index in the direction in which the in-plane refractive index is maximized (that is, the slow axis direction)
  • ny is the in-plane direction orthogonal to the slow axis (that is, the fast is the refractive index in the axial direction)
  • 'nz' is the refractive index in the thickness direction
  • 'd' is the layer (film) thickness (nm).
  • the inner protective layer is a retardation layer having any suitable retardation value.
  • the in-plane retardation Re(550) of the inner protective layer in this embodiment can be, for example, 110 nm to 150 nm.
  • the angle between the slow axis of the inner protective layer and the slow axis of the absorption axis of the polarizing film is clockwise or counterclockwise, for example, 35° to 55°, preferably 38°. ⁇ 52°, more preferably 40° to 50°, more preferably 42° to 48°, and particularly preferably 44° to 46°, thereby functioning as a circularly polarizing plate can.
  • the retardation layer 30 may be a retardation layer having a desired in-plane retardation and/or thickness direction retardation depending on the purpose.
  • the in-plane retardation Re(550) of the retardation layer can be 110 nm to 150 nm.
  • the angle between the slow axis and the slow axis of the absorption axis of the polarizing film is clockwise or counterclockwise, for example, 35° to 55°, preferably 38°. ⁇ 52°, more preferably 40° to 50°, more preferably 42° to 48°, and particularly preferably 44° to 46°, thereby functioning as a circularly polarizing plate can.
  • a method for manufacturing an image display device includes a polarizing film made of a polyvinyl alcohol resin film containing a dichroic substance and having a moisture content of 15% by weight or less, and a protective layer. and an adhesive layer in this order, laminated on the image display cell via the adhesive layer, and the surface of the polarizing film opposite to the side on which the protective layer is arranged is exposed. and step (II) of bringing an aqueous solvent into contact with the exposed surface of the polarizing film to change the transmittance, in this order.
  • the polarizing plate laminated on the image display cell is composed of a polyvinyl alcohol-based resin film containing a dichroic substance, and includes a polarizing film having a moisture content of 15% by weight or less, a protective layer, and an adhesive layer in this order.
  • a polarizing film having a moisture content of 15% by weight or less As long as the surface of the polarizing film on which the protective layer is not arranged can be exposed, it can have any configuration.
  • the polarizing plate may be attached to the image display cell with the exposed surface of the polarizing film protected by a surface protective film, and the polarizing film may be exposed by peeling off the surface protective film before contact with the aqueous solvent. .
  • the polarizing plate laminated on the image display cell may further include a retardation layer.
  • the polarizing plates having the configurations illustrated in FIGS. 2B and 2C can be exemplified. Further, the description of the primary polarizing film, protective layer, retardation layer and adhesive layer described in section A can be applied to the polarizing film, protective layer, retardation layer and adhesive layer contained in the polarizing plate.
  • a liquid crystal display device or an organic EL display device can be preferably exemplified as the image display device manufactured by the above manufacturing method. Therefore, a liquid crystal cell or an organic EL cell can be preferably used as the image display cell.
  • a plurality of image display devices may be combined to display one image as a whole and used as digital signage.
  • Step (II) In the step of changing the transmittance, the exposed surface of the polarizing film is brought into contact with an aqueous solvent to change the transmittance. Specifically, the transmittance of the polarizing film can be changed and adjusted to a desired value by decolorizing the dichroic substance through contact with an aqueous solvent. As for the step of changing the transmittance, the same explanation as in Section A-3 can be applied. From the viewpoint of preventing the image display cell from coming into contact with the aqueous solvent, coating or spraying can be preferably used as the method of contact with the aqueous solvent. For the polarizing film after changing the transmittance, the description of the secondary polarizing film described in Section A-3 can be applied.
  • the method for manufacturing the image display device may further include a step of protecting the exposed surface of the polarizing film after the step of changing the transmittance, if necessary. Protection of the exposed surface of the polarizing film can be carried out by laminating a protective layer, a supporting substrate, or the like on the exposed surface via an adhesive layer such as an adhesive layer or pressure-sensitive adhesive layer.
  • an aqueous solvent is brought into contact with the surface of the polarizing film which is composed of a PVA-based resin film containing a dichroic substance and has a moisture content of 15% by weight or less.
  • a method for adjusting the transmittance of a polarizing film is provided, which includes the step of causing a According to the method for adjusting the transmittance of the polarizing film, the transmittance of the polarizing film can be adjusted (typically increased) to a desired value as a result of decolorization of the polarizing film by contact with the aqueous solvent.
  • the primary polarizing film described in Section A-1 is preferably used. Also, the same description as in Section A-3 can be applied to the contact between the polarizing film and the aqueous solvent.
  • Ts, Tp and Tc of the polarizing film were used as Ts, Tp and Tc of the polarizing film, respectively.
  • Ts, Tp and Tc are Y values measured with a 2-degree field of view (C light source) according to JIS Z8701 and subjected to visibility correction.
  • the refractive index of the protective layer was 1.53, and the refractive index of the surface of the polarizing film opposite to the protective layer was 1.53. From the obtained Tp and Tc, the degree of polarization P was determined by the following formula.
  • Example 1-1 A long roll of a 30 ⁇ m-thick PVA-based resin film (manufactured by Kuraray, product name “PE3000”) was immersed in a water bath at 30° C. and stretched 2.2 times in the conveying direction. , while being immersed in an aqueous solution of 0.3% by weight of potassium at 30° C. and dyed, the film was stretched 3 times with respect to the unstretched film (original length). Next, while immersing this stretched film in an aqueous solution of 3% by weight of boric acid and 3% by weight of potassium iodide at 30° C., the stretched film is further stretched to 3.3 times its original length.
  • a polarizing film (primary polarizing film) having a thickness of 12 ⁇ m was produced.
  • the obtained primary polarizing film had a moisture content of 10% by weight.
  • the single transmittance of the polarizing film was 42.5%.
  • a PVA-based resin aqueous solution manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name “GOSEFIMER (registered trademark) Z-200”, resin concentration: 3% by weight
  • GOSEFIMER registered trademark
  • resin concentration: 3% by weight was applied, and a cycloolefin-based A film (Zeonor, thickness: 25 ⁇ m, manufactured by Nippon Zeon Co., Ltd.) was laminated to obtain a polarizing plate (before treatment) having a structure of [primary polarizing film/protective layer].
  • the above polarizing plate (before treatment) was cut into a size of 100 mm ⁇ 100 mm and attached to a glass plate so that the surface on the primary polarizing film side was exposed via an acrylic adhesive layer (thickness 15 ⁇ m) at 55 ° C. of water for 6 minutes. Then, by drying at 50° C. for 5 minutes, a polarizing plate (after treatment) having a configuration of [secondary polarizing film/protective layer] was obtained.
  • Example 1-2 A polarizing plate having a [secondary polarizing film/protective layer] configuration ( after treatment).
  • Example 1-3 A polarizing plate having a [secondary polarizing film/protective layer] configuration ( after treatment).
  • Example 1-4 A polarizing plate having a [secondary polarizing film/protective layer] configuration ( after treatment).
  • Example 2-1 A long amorphous isophthalic copolymerized polyethylene terephthalate film (thickness: 100 ⁇ m) having a Tg of about 75° C. was used as the thermoplastic resin substrate, and one side of the resin substrate was subjected to corona treatment.
  • Polyvinyl alcohol degree of polymerization: 4,200, degree of saponification: 99.2 mol%
  • acetoacetyl-modified PVA manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOSEFIMER" were mixed at a ratio of 9:1, and 100 parts by weight of PVA-based resin.
  • aqueous PVA solution (coating solution).
  • the above PVA aqueous solution was applied to the corona-treated surface of the resin base material and dried at 60° C. to form a PVA-based resin layer having a thickness of 13 ⁇ m, thereby producing a laminate.
  • the resulting laminate was uniaxially stretched 2.4 times in the machine direction (longitudinal direction) in an oven at 130° C. (in-air auxiliary stretching treatment).
  • the laminate was immersed in an insolubilizing bath (an aqueous boric acid solution obtained by mixing 4 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40° C.
  • the finally obtained polarizing plate was placed in a dyeing bath (iodine aqueous solution obtained by blending iodine and potassium iodide at a weight ratio of 1:7 with respect to 100 parts by weight of water) at a liquid temperature of 30 ° C. It was immersed for 60 seconds while adjusting the concentration so that the single transmittance (Ts) was 42.3% (dyeing treatment). Next, it was immersed for 30 seconds in a cross-linking bath at a liquid temperature of 40°C (an aqueous solution of boric acid obtained by blending 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with respect to 100 parts by weight of water).
  • crosslinking treatment After that, while immersing the laminate in an aqueous solution of boric acid (boric acid concentration: 4% by weight, potassium iodide concentration: 5% by weight) at a liquid temperature of 70° C., the laminate was moved vertically (longitudinally) between rolls with different peripheral speeds. Uniaxial stretching was performed so that the stretching ratio was 5.5 times (underwater stretching treatment). After that, the laminate was immersed in a washing bath (aqueous solution obtained by blending 4 parts by weight of potassium iodide with 100 parts by weight of water) at a liquid temperature of 20° C. (washing treatment).
  • a washing bath aqueous solution obtained by blending 4 parts by weight of potassium iodide with 100 parts by weight of water
  • a polarizing film (primary polarizing film) having a moisture content of 4.5% by weight and a thickness of 5 ⁇ m is formed on the resin substrate, and a cycloolefin film (manufactured by Nippon Zeon Co., Ltd.) is formed on the surface of the primary polarizing film.
  • the above polarizing plate (before treatment) was cut into a size of 100 mm ⁇ 100 mm and attached to a glass plate so that the surface on the primary polarizing film side became an exposed surface via an acrylic pressure-sensitive adhesive layer (thickness 15 ⁇ m). of water for 9 minutes. Then, by drying at 50° C. for 5 minutes, a polarizing plate (after treatment) having a configuration of [secondary polarizing film/protective layer] was obtained.
  • Example 2-2 A polarizing plate having a [secondary polarizing film/protective layer] configuration ( after treatment).
  • Example 2-3 A polarizing plate having a [secondary polarizing film/protective layer] configuration ( after treatment).
  • Example 2-4 A polarizing plate having a [secondary polarizing film/protective layer] configuration ( after treatment).
  • Example 2-5 A polarizing plate having a [secondary polarizing film/protective layer] configuration ( after treatment).
  • Example 3-1 Configuration of [primary polarizing film/protective layer] in the same manner as in Example 2-1 except that the iodine concentration in the dyeing bath was changed and the transmittance of the resulting polarizing film was adjusted to 44.3%. A polarizing plate (before treatment) having was obtained. The obtained primary polarizing film had a moisture content of 4.5% by weight.
  • the above polarizing plate (before treatment) was cut into a size of 100 mm ⁇ 100 mm, and attached to a glass plate so that the surface on the primary polarizing film side became an exposed surface via an acrylic pressure-sensitive adhesive layer (thickness: 15 ⁇ m). °C water for 6 minutes. Then, by drying at 50° C. for 5 minutes, a polarizing plate (after treatment) having a configuration of [secondary polarizing film/protective layer] was obtained.
  • Example 3-2 A polarizing plate having a configuration of [secondary polarizing film/protective layer] in the same manner as in Example 3-1 except that it was immersed in water at 55 ° C. for 3 minutes instead of immersing in water at 50 ° C. for 6 minutes ( after treatment).
  • the transmittance of the polarizing film can be changed after the protective layer is laminated to manufacture the polarizing plate.
  • the method for producing a polarizing plate of the present invention is suitably used in the production of image display devices.

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Abstract

The present invention provides a method for adjusting the transmittance of a polarizing film after producing the same. A polarizing plate manufacturing method according to the present invention comprises, in the order given, a step for obtaining a primary polarizing film by subjecting a polyvinyl alcohol–based resin film to a dyeing treatment and to a stretching treatment in a boric acid aqueous solution and thereafter drying the film until the moisture content reaches 15 wt% or less, and a step for obtaining a secondary polarizing film by bringing the surface of the primary polarizing film into contact with an aqueous solvent and thereby altering the transmittance of the film.

Description

偏光板の製造方法、画像表示装置の製造方法および偏光膜の透過率の調整方法Method for manufacturing polarizing plate, method for manufacturing image display device, and method for adjusting transmittance of polarizing film
　本発明は、偏光板の製造方法、画像表示装置の製造方法および偏光膜の透過率の調整方法に関する。 The present invention relates to a method for manufacturing a polarizing plate, a method for manufacturing an image display device, and a method for adjusting the transmittance of a polarizing film.
　近年、液晶表示装置およびエレクトロルミネセンス（ＥＬ）表示装置（例えば、有機ＥＬ表示装置、無機ＥＬ表示装置）に代表される画像表示装置が急速に普及している。液晶表示装置には、その画像形成方式に起因して、液晶セルの両側に偏光板が配置されている。また、有機ＥＬ表示装置では、λ／４板を含む円偏光板を有機ＥＬセルの視認側に配置することにより、外光反射や背景の映り込み等の問題を防ぐことが知られている（例えば、特許文献１および２）。 In recent years, image display devices represented by liquid crystal display devices and electroluminescence (EL) display devices (eg, organic EL display devices and inorganic EL display devices) have rapidly spread. A liquid crystal display device has polarizing plates arranged on both sides of a liquid crystal cell due to its image forming method. In addition, it is known that in an organic EL display device, problems such as external light reflection and background reflection can be prevented by placing a circularly polarizing plate including a λ/4 plate on the viewing side of the organic EL cell ( For example, Patent Documents 1 and 2).
　偏光板は、通常、ポリビニルアルコール系樹脂膜を染色および延伸することによって作製された偏光膜の少なくとも一方の側に保護層が配置された構成を有し、粘着剤層を介して液晶セル、有機ＥＬセル等の画像表示セルに貼り合わせられる。 A polarizing plate usually has a structure in which a protective layer is arranged on at least one side of a polarizing film prepared by dyeing and stretching a polyvinyl alcohol-based resin film. It is attached to an image display cell such as an EL cell.
特開２００２－３１１２３９号公報JP-A-2002-311239 特開２００２－３７２６２２号公報Japanese Patent Application Laid-Open No. 2002-372622
　従来、偏光膜の作製後にその透過率を調整する方法は知られておらず、よって、偏光板を画像表示セルに貼り合わせた後に偏光膜の透過率を調整することはできなかった。その一方で、画像表示セルやバックライトユニット等の品質個体差に起因して画像表示装置の輝度にばらつきが生じ得ることから、保護層が積層された後、あるいは、画像表示セルに貼り合わせられた後において、偏光膜の透過率を調整する方法の開発が望まれていた。 Conventionally, there is no known method for adjusting the transmittance of the polarizing film after it is produced, and therefore it was not possible to adjust the transmittance of the polarizing film after the polarizing plate was attached to the image display cell. On the other hand, since the luminance of the image display device may vary due to individual differences in the quality of the image display cell, the backlight unit, etc., the protective layer is laminated after the protective layer is laminated or is attached to the image display cell. After that, it has been desired to develop a method for adjusting the transmittance of the polarizing film.
　本発明は上記従来の課題を解決するためになされたものであり、その主たる目的は、偏光膜の作製後にその透過率を調整する方法を提供することにある。 The present invention has been made to solve the conventional problems described above, and its main purpose is to provide a method for adjusting the transmittance of a polarizing film after it has been produced.
　本発明の１つの局面によれば、、ポリビニルアルコール系樹脂膜を染色処理およびホウ酸水溶液中での延伸処理に供した後に、水分率が１５重量％以下となるまで乾燥させて、一次偏光膜を得る工程、および、該一次偏光膜の表面に水性溶媒を接触させることにより、透過率を変化させて、二次偏光膜を得る工程、を、この順に含む、偏光板の製造方法が提供される。
　１つの実施形態において、一方の面が露出しており、他方の面が保護されている状態の上記一次偏光膜の露出面に上記水性溶媒を接触させる。
　１つの実施形態において、上記一次偏光膜を得る工程が、ハロゲン化物とポリビニルアルコール系樹脂とを含むポリビニルアルコール系樹脂膜を、長尺状の熱可塑性樹脂基材との積層体の状態で、空中補助延伸処理、染色処理、ホウ酸水溶液中での延伸処理および乾燥収縮処理にこの順に供することを含み、該乾燥収縮処理が、該積層体を長手方向に搬送しながら加熱することにより、幅方向に２％以上収縮させるとともに該ポリビニルアルコール系樹脂膜の水分率が１５重量％以下となるまで乾燥させることを含む。
　１つの実施形態において、上記ハロゲン化物がヨウ化物または塩化ナトリウムである。
　１つの実施形態において、上記一次偏光膜の厚みが１２μｍ以下である。
　本発明の別の局面によれば、二色性物質を含むポリビニルアルコール系樹脂膜で構成され、水分率が１５重量％以下である偏光膜と、保護層と、粘着剤層とをこの順に含む偏光板を、該粘着剤を介して画像表示セルに積層して、該偏光膜の該保護層が配置された側と反対側の表面を露出面とする工程、および、該偏光膜の露出面に水性溶媒を接触させて透過率を変化させる工程、をこの順で含む、画像表示装置の製造方法が提供される。
　１つの実施形態において、上記画像表示装置が、液晶表示装置または有機ＥＬ表示装置である。
　本発明のさらに別の局面によれば、二色性物質を含むポリビニルアルコール系樹脂膜で構成され、水分率が１５重量％以下である偏光膜の表面に水性溶媒を接触させる工程を含む、偏光膜の透過率の調整方法が提供される。 According to one aspect of the present invention, after subjecting the polyvinyl alcohol-based resin film to dyeing treatment and stretching treatment in an aqueous boric acid solution, the primary polarizing film is dried until the moisture content becomes 15% by weight or less. and contacting the surface of the primary polarizing film with an aqueous solvent to change the transmittance to obtain a secondary polarizing film, in this order. be.
In one embodiment, the aqueous solvent is brought into contact with the exposed surface of the primary polarizing film with one surface exposed and the other surface protected.
In one embodiment, in the step of obtaining the primary polarizing film, a polyvinyl alcohol-based resin film containing a halide and a polyvinyl alcohol-based resin is placed in the air in a state of a laminate with a long thermoplastic resin substrate. It includes subjecting the laminate to auxiliary stretching treatment, dyeing treatment, stretching treatment in an aqueous boric acid solution, and drying shrinkage treatment in this order. shrinking to 2% or more and drying until the water content of the polyvinyl alcohol resin film becomes 15% by weight or less.
In one embodiment, the halide is iodide or sodium chloride.
In one embodiment, the primary polarizing film has a thickness of 12 μm or less.
According to another aspect of the present invention, a polarizing film made of a polyvinyl alcohol resin film containing a dichroic substance and having a moisture content of 15% by weight or less, a protective layer, and an adhesive layer are included in this order. a step of laminating a polarizing plate on an image display cell via the adhesive so that the surface of the polarizing film opposite to the side on which the protective layer is arranged is exposed; and the exposed surface of the polarizing film. A method for manufacturing an image display device is provided, comprising the step of bringing an aqueous solvent into contact with the substrate to change the transmittance, in this order.
In one embodiment, the image display device is a liquid crystal display device or an organic EL display device.
According to still another aspect of the present invention, the polarizing film comprises a step of bringing an aqueous solvent into contact with the surface of a polarizing film composed of a polyvinyl alcohol-based resin film containing a dichroic substance and having a moisture content of 15% by weight or less. A method for adjusting the permeability of a membrane is provided.
　本発明によれば、ポリビニルアルコール系樹脂膜を染色および延伸することによって作製された偏光膜の表面に水性溶媒を接触させることによって、偏光膜の透過率を事後的に変化させることができる。また、ホウ酸水溶液中での延伸後に水分率が所定の値以下になるまで乾燥させることによって外観が安定化した状態の偏光膜の表面に水性溶媒を接触させて透過率を変化させるので、透過率の微調整が可能となる。その結果、例えば、画像表示装置間の輝度のばらつきを低減することができ、複数の表示画面の外観を揃えたい場合、特に、複数の表示画面を組み合わせて画像を表示する場合（大型のパブリックディスプレイ、デジタルサイネージ等）に有用である。 According to the present invention, the transmittance of the polarizing film can be changed ex post by bringing an aqueous solvent into contact with the surface of the polarizing film produced by dyeing and stretching the polyvinyl alcohol resin film. In addition, after stretching in an aqueous boric acid solution, the surface of the polarizing film whose appearance has been stabilized by drying until the moisture content becomes a predetermined value or less is brought into contact with an aqueous solvent to change the transmittance. Fine adjustment of the rate is possible. As a result, for example, variations in luminance between image display devices can be reduced, and when it is desired to match the appearance of multiple display screens, particularly when displaying images by combining multiple display screens (large public display). , digital signage, etc.).
加熱ロールを用いた乾燥収縮処理の一例を示す概略図である。FIG. 4 is a schematic diagram showing an example of drying shrinkage treatment using a heating roll. 偏光板を作製する工程で作製され得る偏光板の一例を説明する概略断面図である。It is a schematic sectional drawing explaining an example of the polarizing plate which can be produced in the process of producing a polarizing plate. 偏光板を作製する工程で作製され得る偏光板の一例を説明する概略断面図である。It is a schematic sectional drawing explaining an example of the polarizing plate which can be produced in the process of producing a polarizing plate. 偏光板を作製する工程で作製され得る偏光板の一例を説明する概略断面図である。It is a schematic sectional drawing explaining an example of the polarizing plate which can be produced in the process of producing a polarizing plate. 二次偏光膜の露出面を保護する工程によって作製され得る偏光板の一例の概略断面図である。FIG. 4A is a schematic cross-sectional view of an example of a polarizing plate that can be produced by a process of protecting the exposed surface of a secondary polarizing film; 二次偏光膜の露出面を保護する工程によって作製され得る偏光板の一例の概略断面図である。FIG. 4A is a schematic cross-sectional view of an example of a polarizing plate that can be produced by a process of protecting the exposed surface of a secondary polarizing film;
　以下、本発明の実施形態について説明するが、本発明はこれらの実施形態には限定されない。なお、本発明の実施形態による偏光板の製造方法によって得られる偏光板は、少なくとも偏光膜を含み、好ましくは偏光膜とその片側または両側に配置された保護層とを含む。 Embodiments of the present invention will be described below, but the present invention is not limited to these embodiments. The polarizing plate obtained by the polarizing plate manufacturing method according to the embodiment of the present invention includes at least a polarizing film, and preferably includes a polarizing film and a protective layer disposed on one side or both sides thereof.
Ａ．偏光板の製造方法
　本発明の実施形態による偏光板の製造方法は、ポリビニルアルコール（ＰＶＡ）系樹脂膜を染色処理およびホウ酸水溶液中での延伸処理（ホウ酸水中延伸処理）に供した後に、水分率が１５重量％以下となるまで乾燥させて、一次偏光膜を得る工程、および、該一次偏光膜の表面に水性溶媒を接触させることにより、透過率を変化させて、二次偏光膜を得る工程を、この順に含む。当該偏光板の製造方法によれば、一旦作製された偏光膜（一次偏光膜）の表面に水性溶媒を接触させて脱色することにより、透過率を事後的に変化させて所望の値に調整することができる。また、ホウ酸水中延伸処理および乾燥処理を介して高配向化かつ外観が安定化した状態の偏光膜（一次偏光膜）を水性溶媒との接触に供することにより、偏光度の過度の低下、シワの発生、溶解等を回避しつつ透過率の調整を好適に行うことができる。 A. Method for producing polarizing plate In the method for producing a polarizing plate according to an embodiment of the present invention, a polyvinyl alcohol (PVA)-based resin film is dyed and stretched in an aqueous boric acid solution (stretched in boric acid solution), followed by A step of drying to a moisture content of 15% by weight or less to obtain a primary polarizing film, and contacting the surface of the primary polarizing film with an aqueous solvent to change the transmittance and form a secondary polarizing film. the step of obtaining in this order. According to the manufacturing method of the polarizing plate, the surface of the polarizing film (primary polarizing film) once produced is decolorized by bringing an aqueous solvent into contact with the surface, thereby changing the transmittance afterward and adjusting it to a desired value. be able to. In addition, by subjecting the polarizing film (primary polarizing film) in a state of being highly oriented and having a stabilized appearance through stretching treatment in boric acid solution and drying treatment to contact with an aqueous solvent, the degree of polarization is excessively lowered and wrinkles are formed. It is possible to suitably adjust the transmittance while avoiding the generation, dissolution, etc. of
　本発明の実施形態による偏光板の製造方法においては、一次偏光膜の一方の面のみに水性溶媒を接触させて透過率を変化させてもよく、両面に水性溶媒を接触させて透過率を変化させてもよい。 In the method for producing a polarizing plate according to an embodiment of the present invention, the transmittance may be changed by contacting only one surface of the primary polarizing film with an aqueous solvent, or by contacting both surfaces with an aqueous solvent to change the transmittance. You may let
　本発明の１つの実施形態による偏光板の製造方法においては、一方の面が露出しており、他方の面が保護されている状態の一次偏光膜の露出面に水性溶媒を接触させて透過率を変化させる。本実施形態の偏光板の製造方法は、例えば、一次偏光膜を得る工程と二次偏光膜を得る工程との間に、一次偏光膜の一方の表面が露出面とされ、他方の面が保護層で保護された偏光板を作製する工程を含むことができる。 In the method for manufacturing a polarizing plate according to one embodiment of the present invention, the exposed surface of the primary polarizing film, one surface of which is exposed and the other surface of which is protected, is brought into contact with an aqueous solvent to reduce the transmittance. change. In the method for producing the polarizing plate of the present embodiment, for example, between the step of obtaining the primary polarizing film and the step of obtaining the secondary polarizing film, one surface of the primary polarizing film is exposed and the other surface is protected. A step of making a layer-protected polarizer can be included.
Ａ－１．一次偏光膜を得る工程
　一次偏光膜を得る工程においては、ＰＶＡ系樹脂膜を染色処理およびホウ酸水中延伸処理に供した後に、水分率が１５重量％以下となるまで乾燥させて、一次偏光膜を得る。一次偏光膜は、単層のＰＶＡ系樹脂膜を用いて作製されてもよく、ＰＶＡ系樹脂層（ＰＶＡ系樹脂膜）を含む二層以上の積層体を用いて作製されてもよい。二層以上の積層体を用いて作製された一次偏光膜は、水性溶媒との接触後においても、シワ等の発生を回避しつつ、優れた光学特性（代表的には、単体透過率および偏光度）を好適に維持し得る。 A-1. Step of obtaining the primary polarizing film In the step of obtaining the primary polarizing film, the PVA-based resin film is subjected to dyeing treatment and stretching treatment in boric acid solution, and then dried until the moisture content becomes 15% by weight or less. get The primary polarizing film may be produced using a single-layer PVA-based resin film, or may be produced using a laminate of two or more layers including a PVA-based resin layer (PVA-based resin film). A primary polarizing film produced using a laminate of two or more layers avoids the occurrence of wrinkles and the like even after contact with an aqueous solvent, and exhibits excellent optical properties (typically, single transmittance and polarization degree) can be suitably maintained.
Ａ－１－１．二層以上の積層体を用いた一次偏光膜の作製
　二層以上の積層体を用いた一次偏光膜の作製は、例えば、ハロゲン化物とＰＶＡ系樹脂とを含むＰＶＡ系樹脂膜を、長尺状の熱可塑性樹脂基材との積層体の状態で、空中補助延伸処理、染色処理、ホウ酸水溶液中での延伸処理および乾燥収縮処理にこの順に供することを含む方法によって行われ得る。熱可塑性樹脂基材とＰＶＡ系樹脂膜との積層体は、例えば、長尺状の熱可塑性樹脂基材の片側に、ハロゲン化物とＰＶＡ系樹脂とを含むＰＶＡ系樹脂層（ＰＶＡ系樹脂膜）を形成して積層体とすることによって得られる。乾燥収縮処理は、例えば、該長尺状の熱可塑性樹脂基材とＰＶＡ系樹脂膜との積層体を長手方向に搬送しながら加熱することにより、幅方向に２％以上収縮させるとともに、該ＰＶＡ系樹脂膜の水分率が１５重量％以下となるまで乾燥させることを含む。ＰＶＡ系樹脂層におけるハロゲン化物の含有量は、好ましくは、ＰＶＡ系樹脂１００重量部に対して５重量部～２０重量部である。乾燥収縮処理は、加熱ロールを用いて処理することが好ましく、加熱ロールの温度は、好ましくは、６０℃～１２０℃である。このような製造方法によれば、ＰＶＡ系樹脂の配向度が高く、優れた光学特性を有する一次偏光膜を得ることができる。 A-1-1. Production of a primary polarizing film using a laminate of two or more layers The production of a primary polarizing film using a laminate of two or more layers is, for example, a PVA-based resin film containing a halide and a PVA-based resin that is formed into a long shape. In the state of a laminate with a thermoplastic resin substrate, it can be subjected to an auxiliary stretching treatment in air, a dyeing treatment, a stretching treatment in an aqueous boric acid solution, and a drying shrinkage treatment in this order. A laminate of a thermoplastic resin substrate and a PVA-based resin film includes, for example, a PVA-based resin layer (PVA-based resin film) containing a halide and a PVA-based resin on one side of a long thermoplastic resin substrate. is obtained by forming a laminate. In the drying shrinkage treatment, for example, the laminate of the long thermoplastic resin substrate and the PVA-based resin film is heated while being transported in the longitudinal direction, thereby shrinking the laminate by 2% or more in the width direction, and the PVA-based resin film. It includes drying until the moisture content of the system resin film becomes 15% by weight or less. The content of the halide in the PVA-based resin layer is preferably 5 to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin. The drying shrinkage treatment is preferably performed using a heating roll, and the temperature of the heating roll is preferably 60°C to 120°C. According to such a manufacturing method, it is possible to obtain a primary polarizing film having a high degree of orientation of the PVA-based resin and excellent optical properties.
Ａ－１－１－１．積層体の作製
　熱可塑性樹脂基材とＰＶＡ系樹脂層との積層体を作製する方法としては、任意の適切な方法が採用され得る。好ましくは、熱可塑性樹脂基材の表面に、ハロゲン化物とＰＶＡ系樹脂とを含む塗布液を塗布し、乾燥することにより、熱可塑性樹脂基材上にＰＶＡ系樹脂層を形成する。上記のとおり、ＰＶＡ系樹脂層におけるハロゲン化物の含有量は、好ましくは、ＰＶＡ系樹脂１００重量部に対して５重量部～２０重量部である。 A-1-1-1. Production of Laminate Any appropriate method can be adopted as a method for producing a laminate of a thermoplastic resin substrate and a PVA-based resin layer. Preferably, a coating liquid containing a halide and a PVA-based resin is applied to the surface of the thermoplastic resin substrate and dried to form a PVA-based resin layer on the thermoplastic resin substrate. As described above, the content of the halide in the PVA-based resin layer is preferably 5 to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin.
　塗布液の塗布方法としては、任意の適切な方法を採用することができる。例えば、ロールコート法、スピンコート法、ワイヤーバーコート法、ディップコート法、ダイコート法、カーテンコート法、スプレーコート法、ナイフコート法（コンマコート法等）等が挙げられる。上記塗布液の塗布・乾燥温度は、好ましくは５０℃以上である。 Any appropriate method can be adopted as the method of applying the coating liquid. Examples thereof include roll coating, spin coating, wire bar coating, dip coating, die coating, curtain coating, spray coating, and knife coating (comma coating, etc.). The coating/drying temperature of the coating liquid is preferably 50° C. or higher.
　ＰＶＡ系樹脂層の厚みは、好ましくは、３μｍ～４０μｍ、さらに好ましくは３μｍ～２０μｍである。 The thickness of the PVA-based resin layer is preferably 3 μm to 40 μm, more preferably 3 μm to 20 μm.
　ＰＶＡ系樹脂層を形成する前に、熱可塑性樹脂基材に表面処理（例えば、コロナ処理等）を施してもよいし、熱可塑性樹脂基材上に易接着層を形成してもよい。このような処理を行うことにより、熱可塑性樹脂基材とＰＶＡ系樹脂層との密着性を向上させることができる。 Before forming the PVA-based resin layer, the thermoplastic resin substrate may be surface-treated (for example, corona treatment, etc.), or an easy-adhesion layer may be formed on the thermoplastic resin substrate. By performing such treatment, the adhesion between the thermoplastic resin substrate and the PVA-based resin layer can be improved.
　熱可塑性樹脂基材の厚みは、好ましくは２０μｍ～３００μｍ、より好ましくは５０μｍ～２００μｍである。２０μｍ未満であると、ＰＶＡ系樹脂層の形成が困難になるおそれがある。３００μｍを超えると、例えば、後述の水中延伸処理において、熱可塑性樹脂基材が水を吸収するのに長時間を要するとともに、延伸に過大な負荷を要するおそれがある。 The thickness of the thermoplastic resin substrate is preferably 20 µm to 300 µm, more preferably 50 µm to 200 µm. If the thickness is less than 20 μm, it may be difficult to form the PVA-based resin layer. If it exceeds 300 μm, for example, in the later-described underwater stretching treatment, it may take a long time for the thermoplastic resin substrate to absorb water, and an excessive load may be required for stretching.
　熱可塑性樹脂基材は、好ましくは、その吸水率が０．２％以上であり、さらに好ましくは０．３％以上である。熱可塑性樹脂基材は、水を吸収し、水が可塑剤的な働きをして可塑化し得る。その結果、延伸応力を大幅に低下させることができ、高倍率に延伸することができる。一方、熱可塑性樹脂基材の吸水率は、好ましくは３．０％以下、さらに好ましくは１．０％以下である。このような熱可塑性樹脂基材を用いることにより、製造時に熱可塑性樹脂基材の寸法安定性が著しく低下して、得られる偏光膜の外観が悪化するなどの不具合を防止することができる。また、水中延伸時に基材が破断したり、熱可塑性樹脂基材からＰＶＡ系樹脂層が剥離したりするのを防止することができる。なお、熱可塑性樹脂基材の吸水率は、例えば、構成材料に変性基を導入することにより調整することができる。吸水率は、ＪＩＳ　Ｋ　７２０９に準じて求められる値である。 The thermoplastic resin substrate preferably has a water absorption of 0.2% or more, more preferably 0.3% or more. Thermoplastic resin substrates can absorb water and be plasticized with the water acting like a plasticizer. As a result, the stretching stress can be greatly reduced, and the film can be stretched at a high draw ratio. On the other hand, the water absorption rate of the thermoplastic resin substrate is preferably 3.0% or less, more preferably 1.0% or less. By using such a thermoplastic resin substrate, it is possible to prevent problems such as deterioration in the appearance of the obtained polarizing film due to a marked decrease in the dimensional stability of the thermoplastic resin substrate during production. Moreover, it is possible to prevent breakage of the base material and separation of the PVA-based resin layer from the thermoplastic resin base material during stretching in water. The water absorption rate of the thermoplastic resin substrate can be adjusted, for example, by introducing a modifying group into the constituent material. The water absorption is a value determined according to JIS K 7209.
　熱可塑性樹脂基材のガラス転移温度（Ｔｇ）は、好ましくは１２０℃以下である。このような熱可塑性樹脂基材を用いることにより、ＰＶＡ系樹脂層の結晶化を抑制しながら、積層体の延伸性を十分に確保することができる。さらに、水による熱可塑性樹脂基材の可塑化と、水中延伸を良好に行うことを考慮すると、１００℃以下、さらには９０℃以下であることがより好ましい。一方、熱可塑性樹脂基材のガラス転移温度は、好ましくは６０℃以上である。このような熱可塑性樹脂基材を用いることにより、上記ＰＶＡ系樹脂を含む塗布液を塗布・乾燥する際に、熱可塑性樹脂基材が変形（例えば、凹凸やタルミ、シワ等の発生）するなどの不具合を防止して、良好に積層体を作製することができる。また、ＰＶＡ系樹脂層の延伸を、好適な温度（例えば、６０℃程度）にて良好に行うことができる。なお、熱可塑性樹脂基材のガラス転移温度は、例えば、構成材料に変性基を導入する、結晶化材料を用いて加熱することにより調整することができる。ガラス転移温度（Ｔｇ）は、ＪＩＳ　Ｋ　７１２１に準じて求められる値である。 The glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 120°C or less. By using such a thermoplastic resin substrate, it is possible to sufficiently secure the stretchability of the laminate while suppressing the crystallization of the PVA-based resin layer. Furthermore, considering the plasticization of the thermoplastic resin substrate with water and the satisfactory stretching in water, the temperature is preferably 100° C. or lower, more preferably 90° C. or lower. On the other hand, the glass transition temperature of the thermoplastic resin substrate is preferably 60°C or higher. By using such a thermoplastic resin substrate, deformation of the thermoplastic resin substrate (for example, generation of unevenness, sagging, wrinkles, etc.) occurs when the coating liquid containing the PVA-based resin is applied and dried. It is possible to prevent the problem of and produce a good laminate. Moreover, the PVA-based resin layer can be satisfactorily stretched at a suitable temperature (for example, about 60°C). The glass transition temperature of the thermoplastic resin substrate can be adjusted, for example, by heating using a crystallization material that introduces a modifying group into the constituent material. The glass transition temperature (Tg) is a value determined according to JIS K 7121.
　熱可塑性樹脂基材の構成材料としては、任意の適切な熱可塑性樹脂が採用され得る。熱可塑性樹脂としては、例えば、ポリエチレンテレフタレート系樹脂等のエステル系樹脂、ノルボルネン系樹脂等のシクロオレフィン系樹脂、ポリプロピレン等のオレフィン系樹脂、ポリアミド系樹脂、ポリカーボネート系樹脂、これらの共重合体樹脂等が挙げられる。これらの中でも、好ましくは、ノルボルネン系樹脂、非晶質のポリエチレンテレフタレート系樹脂である。 Any appropriate thermoplastic resin can be adopted as a constituent material of the thermoplastic resin base material. Examples of thermoplastic resins include ester resins such as polyethylene terephthalate resins, cycloolefin resins such as norbornene resins, olefin resins such as polypropylene, polyamide resins, polycarbonate resins, and copolymer resins thereof. is mentioned. Among these, norbornene-based resins and amorphous polyethylene terephthalate-based resins are preferred.
　１つの実施形態においては、非晶質の（結晶化していない）ポリエチレンテレフタレート系樹脂が好ましく用いられる。中でも、非晶性の（結晶化しにくい）ポリエチレンテレフタレート系樹脂が特に好ましく用いられる。非晶性のポリエチレンテレフタレート系樹脂の具体例としては、ジカルボン酸としてイソフタル酸および／またはシクロヘキサンジカルボン酸をさらに含む共重合体や、グリコールとしてシクロヘキサンジメタノールやジエチレングリコールをさらに含む共重合体が挙げられる。 In one embodiment, an amorphous (not crystallized) polyethylene terephthalate resin is preferably used. Among them, amorphous (difficult to crystallize) polyethylene terephthalate resin is particularly preferably used. Specific examples of amorphous polyethylene terephthalate resins include copolymers further containing isophthalic acid and/or cyclohexanedicarboxylic acid as dicarboxylic acids, and copolymers further containing cyclohexanedimethanol or diethylene glycol as glycols.
　好ましい実施形態においては、熱可塑性樹脂基材は、イソフタル酸ユニットを有するポリエチレンテレフタレート系樹脂で構成される。このような熱可塑性樹脂基材は延伸性に極めて優れるとともに、延伸時の結晶化が抑制され得るからである。これは、イソフタル酸ユニットを導入することで、主鎖に大きな屈曲を与えることによるものと考えられる。ポリエチレンテレフタレート系樹脂は、テレフタル酸ユニットおよびエチレングリコールユニットを有する。イソフタル酸ユニットの含有割合は、全繰り返し単位の合計に対して、好ましくは０．１モル％以上、さらに好ましくは１．０モル％以上である。延伸性に極めて優れた熱可塑性樹脂基材が得られるからである。一方、イソフタル酸ユニットの含有割合は、全繰り返し単位の合計に対して、好ましくは２０モル％以下、より好ましくは１０モル％以下である。このような含有割合に設定することで、後述の乾燥収縮処理において結晶化度を良好に増加させることができる。 In a preferred embodiment, the thermoplastic resin base material is composed of a polyethylene terephthalate resin having an isophthalic acid unit. This is because such a thermoplastic resin substrate is extremely excellent in stretchability and can suppress crystallization during stretching. This is probably because the introduction of the isophthalic acid unit gives the main chain a large bend. A polyethylene terephthalate-based resin has a terephthalic acid unit and an ethylene glycol unit. The isophthalic acid unit content is preferably 0.1 mol % or more, more preferably 1.0 mol % or more, relative to the total of all repeating units. This is because a thermoplastic resin base material having extremely excellent stretchability can be obtained. On the other hand, the isophthalic acid unit content is preferably 20 mol % or less, more preferably 10 mol % or less, relative to the total of all repeating units. By setting such a content ratio, the degree of crystallinity can be favorably increased in the drying shrinkage treatment described later.
　熱可塑性樹脂基材は、予め（ＰＶＡ系樹脂層を形成する前）、延伸されていてもよい。１つの実施形態においては、長尺状の熱可塑性樹脂基材の横方向に延伸されている。横方向は、好ましくは、後述の積層体の延伸方向に直交する方向である。なお、本明細書において、「直交」とは、実質的に直交する場合も包含する。ここで、「実質的に直交」とは、９０°±５．０°である場合を包含し、好ましくは９０°±３．０°、さらに好ましくは９０°±１．０°である。 The thermoplastic resin substrate may be stretched in advance (before forming the PVA-based resin layer). In one embodiment, it is stretched in the transverse direction of the elongated thermoplastic resin substrate. The lateral direction is preferably a direction perpendicular to the stretching direction of the laminate described below. In addition, in this specification, "perpendicular" also includes the case of being substantially perpendicular. Here, "substantially orthogonal" includes 90°±5.0°, preferably 90°±3.0°, more preferably 90°±1.0°.
　熱可塑性樹脂基材の延伸温度は、ガラス転移温度（Ｔｇ）に対し、好ましくはＴｇ－１０℃～Ｔｇ＋５０℃である。熱可塑性樹脂基材の延伸倍率は、好ましくは１．５倍～３．０倍である。 The stretching temperature of the thermoplastic resin substrate is preferably Tg-10°C to Tg+50°C with respect to the glass transition temperature (Tg). The draw ratio of the thermoplastic resin substrate is preferably 1.5 to 3.0 times.
　熱可塑性樹脂基材の延伸方法としては、任意の適切な方法が採用され得る。具体的には、固定端延伸でもよいし、自由端延伸でもよい。延伸方式は、乾式でもよいし、湿式でもよい。熱可塑性樹脂基材の延伸は、一段階で行ってもよいし、多段階で行ってもよい。多段階で行う場合、上述の延伸倍率は、各段階の延伸倍率の積である。 Any appropriate method can be adopted as a method for stretching the thermoplastic resin base material. Specifically, the drawing may be fixed end drawing or free end drawing. The stretching method may be a dry method or a wet method. The stretching of the thermoplastic resin substrate may be performed in one step or in multiple steps. When performing in multiple stages, the above-mentioned draw ratio is the product of the draw ratios in each step.
　塗布液は、上記のとおり、ハロゲン化物とＰＶＡ系樹脂とを含む。上記塗布液は、代表的には、上記ハロゲン化物および上記ＰＶＡ系樹脂を溶媒に溶解させた溶液である。溶媒としては、例えば、水、ジメチルスルホキシド、ジメチルホルムアミド、ジメチルアセトアミド、Ｎ－メチルピロリドン、各種グリコール類、トリメチロールプロパン等の多価アルコール類、エチレンジアミン、ジエチレントリアミン等のアミン類が挙げられる。これらは単独で、または、二種以上組み合わせて用いることができる。これらの中でも、好ましくは、水である。溶液のＰＶＡ系樹脂濃度は、溶媒１００重量部に対して、好ましくは３重量部～２０重量部である。このような樹脂濃度であれば、熱可塑性樹脂基材に密着した均一な塗布膜を形成することができる。塗布液におけるハロゲン化物の含有量は、好ましくは、ＰＶＡ系樹脂１００重量部に対して５重量部～２０重量部である。 The coating liquid contains a halide and a PVA-based resin, as described above. The coating liquid is typically a solution in which the halide and the PVA-based resin are dissolved in a solvent. Examples of solvents include water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. These can be used alone or in combination of two or more. Among these, water is preferred. The concentration of the PVA-based resin in the solution is preferably 3 to 20 parts by weight with respect to 100 parts by weight of the solvent. With such a resin concentration, it is possible to form a uniform coating film in close contact with the thermoplastic resin substrate. The content of the halide in the coating liquid is preferably 5 to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin.
　塗布液に、添加剤を配合してもよい。添加剤としては、例えば、可塑剤、界面活性剤等が挙げられる。可塑剤としては、例えば、エチレングリコールやグリセリン等の多価アルコールが挙げられる。界面活性剤としては、例えば、非イオン界面活性剤が挙げられる。これらは、得られるＰＶＡ系樹脂層の均一性や染色性、延伸性をより一層向上させる目的で使用され得る。 Additives may be added to the coating liquid. Examples of additives include plasticizers and surfactants. Examples of plasticizers include polyhydric alcohols such as ethylene glycol and glycerin. Surfactants include, for example, nonionic surfactants. These can be used for the purpose of further improving the uniformity, dyeability and stretchability of the obtained PVA-based resin layer.
　上記ＰＶＡ系樹脂としては、任意の適切な樹脂が採用され得る。例えば、ポリビニルアルコールおよびエチレン－ビニルアルコール共重合体が挙げられる。ポリビニルアルコールは、ポリ酢酸ビニルをケン化することにより得られる。エチレン－ビニルアルコール共重合体は、エチレン－酢酸ビニル共重合体をケン化することにより得られる。ＰＶＡ系樹脂のケン化度は、通常８５モル％～１００モル％であり、好ましくは９５．０モル％～９９．９５モル％、さらに好ましくは９９．０モル％～９９．９３モル％である。ケン化度は、ＪＩＳ　Ｋ　６７２６－１９９４に準じて求めることができる。このようなケン化度のＰＶＡ系樹脂を用いることによって、耐久性に優れた偏光膜が得られ得る。ケン化度が高すぎる場合には、ゲル化してしまうおそれがある。 Any appropriate resin can be adopted as the PVA-based resin. Examples include polyvinyl alcohol and ethylene-vinyl alcohol copolymers. Polyvinyl alcohol is obtained by saponifying polyvinyl acetate. An ethylene-vinyl alcohol copolymer is obtained by saponifying an ethylene-vinyl acetate copolymer. The degree of saponification of the PVA-based resin is usually 85 mol% to 100 mol%, preferably 95.0 mol% to 99.95 mol%, more preferably 99.0 mol% to 99.93 mol%. . The degree of saponification can be determined according to JIS K 6726-1994. By using a PVA-based resin having such a degree of saponification, a polarizing film having excellent durability can be obtained. If the degree of saponification is too high, gelation may occur.
　ＰＶＡ系樹脂の平均重合度は、目的に応じて適切に選択し得る。平均重合度は、通常１０００～１００００であり、好ましくは１２００～４５００、さらに好ましくは１５００～４３００である。なお、平均重合度は、ＪＩＳ　Ｋ　６７２６－１９９４に準じて求めることができる。 The average degree of polymerization of the PVA-based resin can be appropriately selected according to the purpose. The average degree of polymerization is usually 1,000 to 10,000, preferably 1,200 to 4,500, more preferably 1,500 to 4,300. The average degree of polymerization can be determined according to JIS K 6726-1994.
　上記ハロゲン化物としては、任意の適切なハロゲン化物が採用され得る。例えば、ヨウ化物および塩化ナトリウムが挙げられる。ヨウ化物としては、例えば、ヨウ化カリウム、ヨウ化ナトリウム、およびヨウ化リチウムが挙げられる。これらの中でも、好ましくは、ヨウ化カリウムである。 Any appropriate halide can be adopted as the halide. Examples include iodide and sodium chloride. Iodides include, for example, potassium iodide, sodium iodide, and lithium iodide. Among these, potassium iodide is preferred.
　塗布液におけるハロゲン化物の量は、好ましくは、ＰＶＡ系樹脂１００重量部に対して５重量部～２０重量部であり、より好ましくは、ＰＶＡ系樹脂１００重量部に対して１０重量部～１５重量部である。ＰＶＡ系樹脂１００重量部に対するハロゲン化物の量が２０重量部を超えると、ハロゲン化物がブリードアウトし、最終的に得られる偏光膜が白濁する場合がある。 The amount of the halide in the coating liquid is preferably 5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the PVA resin, and more preferably 10 parts by weight to 15 parts by weight with respect to 100 parts by weight of the PVA resin. Department. If the amount of the halide exceeds 20 parts by weight with respect to 100 parts by weight of the PVA-based resin, the halide may bleed out and the finally obtained polarizing film may become cloudy.
　一般に、ＰＶＡ系樹脂層が延伸されることによって、ＰＶＡ系樹脂層中のポリビニルアルコール分子の配向性が高くなるが、延伸後のＰＶＡ系樹脂層を、水を含む液体に浸漬すると、ポリビニルアルコール分子の配向が乱れ、配向性が低下する場合がある。特に、熱可塑性樹脂基材とＰＶＡ系樹脂層との積層体をホウ酸水中延伸する場合において、熱可塑性樹脂基材の延伸を安定させるために比較的高い温度で上記積層体をホウ酸水中で延伸する場合、上記配向度低下の傾向が顕著である。例えば、ＰＶＡフィルム単体のホウ酸水中での延伸が６０℃で行われることが一般的であるのに対し、Ａ－ＰＥＴ（熱可塑性樹脂基材）とＰＶＡ系樹脂層との積層体の延伸は７０℃前後の温度という高い温度で行われ、この場合、延伸初期のＰＶＡの配向性が水中延伸により上がる前の段階で低下し得る。これに対して、ハロゲン化物を含むＰＶＡ系樹脂層と熱可塑性樹脂基材との積層体を作製し、積層体をホウ酸水中で延伸する前に空気中で高温延伸（補助延伸）することにより、補助延伸後の積層体のＰＶＡ系樹脂層中のＰＶＡ系樹脂の結晶化が促進され得る。その結果、ＰＶＡ系樹脂層を液体に浸漬した場合において、ＰＶＡ系樹脂層がハロゲン化物を含まない場合に比べて、ポリビニルアルコール分子の配向の乱れ、および配向性の低下が抑制され得る。これにより、染色処理および水中延伸処理など、積層体を液体に浸漬して行う処理工程を経て得られる偏光膜の光学特性を向上し得る。 In general, when the PVA-based resin layer is stretched, the orientation of the polyvinyl alcohol molecules in the PVA-based resin layer increases. orientation may be disturbed and the orientation may be lowered. In particular, when a laminate of a thermoplastic resin substrate and a PVA-based resin layer is stretched in boric acid water, the laminate is stretched in boric acid water at a relatively high temperature in order to stabilize the stretching of the thermoplastic resin substrate. When the film is stretched, the tendency of the degree of orientation to decrease is remarkable. For example, the stretching of a single PVA film in boric acid water is generally carried out at 60° C., whereas the stretching of a laminate of A-PET (thermoplastic resin substrate) and a PVA-based resin layer is It is carried out at a high temperature of about 70° C., and in this case, the orientation of PVA at the initial stage of stretching may be lowered before it is increased by stretching in water. On the other hand, by preparing a laminate of a PVA-based resin layer containing a halide and a thermoplastic resin substrate and stretching the laminate at a high temperature (auxiliary stretching) in air before stretching in boric acid water, , the crystallization of the PVA-based resin in the PVA-based resin layer of the laminate after auxiliary stretching can be promoted. As a result, when the PVA-based resin layer is immersed in a liquid, the disturbance of the orientation of the polyvinyl alcohol molecules and the deterioration of the orientation can be suppressed compared to the case where the PVA-based resin layer does not contain a halide. This can improve the optical properties of the polarizing film obtained through treatment steps such as dyeing treatment and underwater stretching treatment in which the laminate is immersed in a liquid.
Ａ－１－１－２．空中補助延伸処理
　特に、高い光学特性を得るためには、乾式延伸（補助延伸）とホウ酸水中延伸を組み合わせる、２段延伸の方法が選択される。２段延伸のように、補助延伸を導入することにより、熱可塑性樹脂基材の結晶化を抑制しながら延伸することができ、後のホウ酸水中延伸において熱可塑性樹脂基材の過度の結晶化により延伸性が低下するという問題を解決し、積層体をより高倍率に延伸することができる。さらには、熱可塑性樹脂基材上にＰＶＡ系樹脂を塗布する場合、熱可塑性樹脂基材のガラス転移温度の影響を抑制するために、通常の金属ドラム上にＰＶＡ系樹脂を塗布する場合と比べて塗布温度を低くする必要があり、その結果、ＰＶＡ系樹脂の結晶化が相対的に低くなり、十分な光学特性が得られない、という問題が生じ得る。これに対して、補助延伸を導入することにより、熱可塑性樹脂基材上にＰＶＡ系樹脂を塗布する場合でも、ＰＶＡ系樹脂の結晶性を高めることが可能となり、高い光学特性を達成することが可能となる。また、同時にＰＶＡ系樹脂の配向性を事前に高めることで、後の染色処理や延伸処理で水に浸漬された時に、ＰＶＡ系樹脂の配向性の低下や溶解などの問題を防止することができ、高い光学特性を達成することが可能になる。 A-1-1-2. Aerial Auxiliary Stretching In order to obtain particularly high optical properties, a two-stage stretching method combining dry stretching (auxiliary stretching) and stretching in boric acid solution is selected. By introducing auxiliary stretching, such as two-step stretching, it is possible to stretch while suppressing crystallization of the thermoplastic resin substrate, and excessive crystallization of the thermoplastic resin substrate in the subsequent stretching in boric acid water. It is possible to solve the problem that stretchability is reduced by stretching, and stretch the laminate at a higher magnification. Furthermore, when applying the PVA-based resin on the thermoplastic resin substrate, in order to suppress the influence of the glass transition temperature of the thermoplastic resin substrate, compared to the case of applying the PVA-based resin on a normal metal drum As a result, the crystallization of the PVA-based resin becomes relatively low, which may cause a problem that sufficient optical properties cannot be obtained. On the other hand, by introducing auxiliary stretching, it is possible to increase the crystallinity of the PVA-based resin even when the PVA-based resin is applied onto a thermoplastic resin substrate, thereby achieving high optical properties. It becomes possible. At the same time, by increasing the orientation of the PVA-based resin in advance, it is possible to prevent problems such as deterioration of the orientation and dissolution of the PVA-based resin when it is immersed in water in the subsequent dyeing treatment or stretching treatment. , making it possible to achieve high optical properties.
　空中補助延伸の延伸方法は、固定端延伸（たとえば、テンター延伸機を用いて延伸する方法）でもよいし、自由端延伸（たとえば、周速の異なるロール間に積層体を通して一軸延伸する方法）でもよいが、高い光学特性を得るためには、自由端延伸が積極的に採用され得る。１つの実施形態においては、空中延伸処理は、上記積層体をその長手方向に搬送しながら、加熱ロール間の周速差により延伸する加熱ロール延伸工程を含む。空中延伸処理は、代表的には、ゾーン延伸工程と加熱ロール延伸工程とを含む。なお、ゾーン延伸工程と加熱ロール延伸工程の順序は限定されず、ゾーン延伸工程が先に行われてもよく、加熱ロール延伸工程が先に行われてもよい。ゾーン延伸工程は省略されてもよい。１つの実施形態においては、ゾーン延伸工程および加熱ロール延伸工程がこの順に行われる。また、別の実施形態では、テンター延伸機において、積層体端部を把持し、テンター間の距離を流れ方向に広げることで延伸される（テンター間の距離の広がりが延伸倍率となる）。この時、幅方向（流れ方向に対して、垂直方向）のテンターの距離は、任意に近づくように設定される。好ましくは、流れ方向の延伸倍率に対して、自由端延伸により近くなるように設定され得る。自由端延伸の場合、幅方向の収縮率＝（１/延伸倍率）１／２で計算される。 The stretching method of the in-air auxiliary stretching may be fixed edge stretching (e.g., a method of stretching using a tenter stretching machine) or free edge stretching (e.g., a method of uniaxially stretching the laminate through rolls having different peripheral speeds). Although good, free-end drawing may be positively employed in order to obtain high optical properties. In one embodiment, the in-air stretching process includes a heating roll stretching step in which the laminate is stretched by a peripheral speed difference between heating rolls while being conveyed in the longitudinal direction. The air drawing process typically includes a zone drawing process and a hot roll drawing process. The order of the zone stretching process and the heating roll stretching process is not limited, and the zone stretching process may be carried out first, or the heating roll stretching process may be carried out first. The zone drawing step may be omitted. In one embodiment, the zone drawing step and the heated roll drawing step are performed in this order. In another embodiment, the laminate is stretched by gripping the ends of the laminate and widening the distance between the tenters in the machine direction in a tenter stretching machine (the widening of the distance between the tenters is the stretching ratio). At this time, the distance between the tenters in the width direction (perpendicular to the machine direction) is set to be arbitrarily close. Preferably, the draw ratio in the machine direction can be set to be closer to the free end draw. In the case of free end stretching, the shrinkage ratio in the width direction is calculated by (1/stretching ratio) 1/2 .
　空中補助延伸は、一段階で行ってもよいし、多段階で行ってもよい。多段階で行う場合、延伸倍率は、各段階の延伸倍率の積である。空中補助延伸における延伸方向は、好ましくは、水中延伸の延伸方向と略同一である。 Aerial auxiliary stretching may be performed in one step or in multiple steps. When it is carried out in multiple stages, the draw ratio is the product of the draw ratios in each step. The stretching direction in the in-air auxiliary stretching is preferably substantially the same as the stretching direction in the underwater stretching.
　空中補助延伸における延伸倍率は、好ましくは２．０倍～３．５倍である。空中補助延伸と水中延伸とを組み合わせた場合の最大延伸倍率は、積層体の元長に対して、好ましくは５．０倍以上、より好ましくは５．５倍以上、さらに好ましくは６．０倍以上である。本明細書において「最大延伸倍率」とは、積層体が破断する直前の延伸倍率をいい、別途、積層体が破断する延伸倍率を確認し、その値よりも０．２低い値をいう。 The draw ratio in the in-air auxiliary drawing is preferably 2.0 to 3.5 times. The maximum draw ratio when the auxiliary drawing in the air and the drawing in water are combined is preferably 5.0 times or more, more preferably 5.5 times or more, and still more preferably 6.0 times the original length of the laminate. That's it. As used herein, the term "maximum draw ratio" refers to the draw ratio immediately before the laminate breaks, and is 0.2 lower than the draw ratio at which the laminate breaks.
　空中補助延伸の延伸温度は、熱可塑性樹脂基材の形成材料、延伸方式等に応じて、任意の適切な値に設定することができる。延伸温度は、好ましくは熱可塑性樹脂基材のガラス転移温度（Ｔｇ）以上であり、さらに好ましくは熱可塑性樹脂基材のガラス転移温度（Ｔｇ）＋１０℃以上、特に好ましくはＴｇ＋１５℃以上である。一方、延伸温度の上限は、好ましくは１７０℃である。このような温度で延伸することで、ＰＶＡ系樹脂の結晶化が急速に進むのを抑制して、当該結晶化による不具合（例えば、延伸によるＰＶＡ系樹脂層の配向を妨げる）を抑制することができる。空中補助延伸後のＰＶＡ系樹脂の結晶化指数は、好ましくは１．３～１．８であり、より好ましくは１．４～１．７である。ＰＶＡ系樹脂の結晶化指数は、フーリエ変換赤外分光光度計を用い、ＡＴＲ法により測定することができる。具体的には、偏光を測定光として測定を実施し、得られたスペクトルの１１４１ｃｍ－１および１４４０ｃｍ－１の強度を用いて、下記式に従って結晶化指数を算出する。
　　　結晶化指数＝（ＩＣ／ＩＲ）
ただし、
ＩＣ ：測定光を入射して測定したときの１１４１ｃｍ－１の強度
ＩＲ　：測定光を入射して測定したときの１４４０ｃｍ－１の強度
である。 The stretching temperature for the in-air auxiliary stretching can be set to any appropriate value depending on the material for forming the thermoplastic resin base material, the stretching method, and the like. The stretching temperature is preferably the glass transition temperature (Tg) of the thermoplastic resin substrate or higher, more preferably the glass transition temperature (Tg) of the thermoplastic resin substrate + 10°C or higher, and particularly preferably Tg + 15°C or higher. On the other hand, the upper limit of the stretching temperature is preferably 170°C. By stretching at such a temperature, it is possible to suppress rapid crystallization of the PVA-based resin and suppress problems caused by the crystallization (for example, hindrance of orientation of the PVA-based resin layer due to stretching). can. The crystallization index of the PVA-based resin after auxiliary stretching in air is preferably 1.3 to 1.8, more preferably 1.4 to 1.7. The crystallization index of the PVA-based resin can be measured by the ATR method using a Fourier transform infrared spectrophotometer. Specifically, measurement is performed using polarized light as measurement light, and the crystallization index is calculated according to the following formula using the intensities at 1141 cm −1 and 1440 cm −1 of the obtained spectrum.
Crystallization index = (IC/ IR )
however,
I C : Intensity at 1141 cm −1 when measurement light is incident and measured I R : Intensity at 1440 cm −1 when measurement light is incident and measured.
Ａ－１－１－３．不溶化処理
　必要に応じて、空中補助延伸処理の後、水中延伸処理や染色処理の前に、不溶化処理を施す。上記不溶化処理は、代表的には、ホウ酸水溶液にＰＶＡ系樹脂層を浸漬することにより行う。不溶化処理を施すことにより、ＰＶＡ系樹脂層に耐水性を付与し、水に浸漬した時のＰＶＡの配向低下を防止することができる。当該ホウ酸水溶液の濃度は、水１００重量部に対して、好ましくは１重量部～４重量部である。不溶化浴（ホウ酸水溶液）の液温は、好ましくは２０℃～５０℃である。 A-1-1-3. Insolubilization Treatment If necessary, an insolubilization treatment is performed after the auxiliary stretching treatment in the air and before the stretching treatment in water or the dyeing treatment. The insolubilization treatment is typically performed by immersing the PVA-based resin layer in an aqueous boric acid solution. The insolubilization treatment imparts water resistance to the PVA-based resin layer, and prevents deterioration of the orientation of the PVA when immersed in water. The concentration of the boric acid aqueous solution is preferably 1 to 4 parts by weight with respect to 100 parts by weight of water. The liquid temperature of the insolubilizing bath (boric acid aqueous solution) is preferably 20°C to 50°C.
Ａ－１－１－４．染色処理
　上記染色処理は、代表的には、ＰＶＡ系樹脂層を二色性物質（代表的には、ヨウ素）で染色することにより行う。具体的には、ＰＶＡ系樹脂層にヨウ素を吸着させることにより行う。当該吸着方法としては、例えば、ヨウ素を含む染色液にＰＶＡ系樹脂層（積層体）を浸漬させる方法、ＰＶＡ系樹脂層に当該染色液を塗工する方法、当該染色液をＰＶＡ系樹脂層に噴霧する方法等が挙げられる。好ましくは、染色液（染色浴）に積層体を浸漬させる方法である。ヨウ素が良好に吸着し得るからである。 A-1-1-4. Dyeing Treatment The dyeing treatment is typically performed by dyeing the PVA-based resin layer with a dichroic substance (typically iodine). Specifically, it is carried out by allowing the PVA-based resin layer to adsorb iodine. Examples of the adsorption method include a method of immersing the PVA-based resin layer (laminate) in a dyeing solution containing iodine, a method of coating the PVA-based resin layer with the dyeing solution, and a method of applying the dyeing solution to the PVA-based resin layer. A spraying method and the like can be mentioned. A preferred method is to immerse the laminate in a dyeing solution (dyeing bath). This is because iodine can be well adsorbed.
　上記染色液は、好ましくは、ヨウ素水溶液である。ヨウ素の配合量は、水１００重量部に対して、好ましくは０．０５重量部～０．５重量部である。ヨウ素の水に対する溶解度を高めるため、ヨウ素水溶液にヨウ化物を配合することが好ましい。ヨウ化物としては、例えば、ヨウ化カリウム、ヨウ化リチウム、ヨウ化ナトリウム、ヨウ化亜鉛、ヨウ化アルミニウム、ヨウ化鉛、ヨウ化銅、ヨウ化バリウム、ヨウ化カルシウム、ヨウ化錫、ヨウ化チタン等が挙げられる。これらの中でも、好ましくは、ヨウ化カリウムである。ヨウ化物の配合量は、水１００重量部に対して、好ましくは０．１重量部～１０重量部、より好ましくは０．３重量部～５重量部である。染色液の染色時の液温は、ＰＶＡ系樹脂の溶解を抑制するため、好ましくは２０℃～５０℃である。染色液にＰＶＡ系樹脂層を浸漬させる場合、浸漬時間は、ＰＶＡ系樹脂層の透過率を確保するため、好ましくは５秒～５分であり、より好ましくは３０秒～９０秒である。 The staining solution is preferably an iodine aqueous solution. The amount of iodine compounded is preferably 0.05 to 0.5 parts by weight per 100 parts by weight of water. In order to increase the solubility of iodine in water, it is preferable to add an iodide to the iodine aqueous solution. Examples of iodides include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. etc. Among these, potassium iodide is preferred. The amount of iodide compounded is preferably 0.1 to 10 parts by weight, more preferably 0.3 to 5 parts by weight, per 100 parts by weight of water. The liquid temperature of the dyeing liquid during dyeing is preferably 20° C. to 50° C. in order to suppress dissolution of the PVA-based resin. When the PVA-based resin layer is immersed in the staining solution, the immersion time is preferably 5 seconds to 5 minutes, more preferably 30 seconds to 90 seconds, in order to ensure the transmittance of the PVA-based resin layer.
　染色条件（濃度、液温、浸漬時間）は、最終的に得られる偏光膜の単体透過率が所望の値となるように設定することができる。このような染色条件としては、好ましくは、染色液としてヨウ素水溶液を用い、ヨウ素水溶液におけるヨウ素およびヨウ化カリウムの含有量の比を、１：５～１：２０とする。ヨウ素水溶液におけるヨウ素およびヨウ化カリウムの含有量の比は、好ましくは１：５～１：１０である。これにより、後述のような光学特性を有する一次偏光膜が得られ得る。 The dyeing conditions (concentration, liquid temperature, immersion time) can be set so that the single transmittance of the finally obtained polarizing film has the desired value. As for such dyeing conditions, it is preferable to use an iodine aqueous solution as a dyeing solution and to set the content ratio of iodine and potassium iodide in the iodine aqueous solution to 1:5 to 1:20. The content ratio of iodine and potassium iodide in the aqueous iodine solution is preferably 1:5 to 1:10. Thereby, a primary polarizing film having optical properties as described later can be obtained.
　ホウ酸を含有する処理浴に積層体を浸漬する処理（代表的には、不溶化処理）の後に連続して染色処理を行う場合、当該処理浴に含まれるホウ酸が染色浴に混入することにより染色浴のホウ酸濃度が経時的に変化し、その結果、染色性が不安定になる場合がある。上記のような染色性の不安定化を抑制するために、染色浴のホウ酸濃度の上限は、水１００重量部に対して、好ましくは４重量部、より好ましくは２重量部となるように調整される。一方で、染色浴のホウ酸濃度の下限は、水１００重量部に対して、好ましくは０．１重量部であり、より好ましくは０．２重量部であり、さらに好ましくは０．５重量部である。１つの実施形態においては、予めホウ酸が配合された染色浴を用いて染色処理を行う。これにより、上記処理浴のホウ酸が染色浴に混入した場合のホウ酸濃度の変化の割合を低減し得る。予め染色浴に配合されるホウ酸の配合量（すなわち、上記処理浴に由来しないホウ酸の含有量）は、水１００重量部に対して、好ましくは０．１重量部～２重量部であり、より好ましくは０．５重量部～１．５重量部である。 When dyeing treatment is performed continuously after the treatment of immersing the laminate in a treatment bath containing boric acid (typically, insolubilization treatment), the boric acid contained in the treatment bath is mixed into the dyeing bath. The boric acid concentration in the dyeing bath may change over time, resulting in unstable dyeability. In order to suppress the destabilization of dyeability as described above, the upper limit of the boric acid concentration in the dyeing bath is preferably 4 parts by weight, more preferably 2 parts by weight with respect to 100 parts by weight of water. adjusted. On the other hand, the lower limit of the boric acid concentration in the dyeing bath is preferably 0.1 parts by weight, more preferably 0.2 parts by weight, and still more preferably 0.5 parts by weight with respect to 100 parts by weight of water. is. In one embodiment, the dyeing process is performed using a dyeing bath pre-blended with boric acid. This can reduce the rate of change in boric acid concentration when the boric acid in the treatment bath is mixed into the dyeing bath. The amount of boric acid blended in advance in the dyeing bath (that is, the content of boric acid not derived from the treatment bath) is preferably 0.1 to 2 parts by weight with respect to 100 parts by weight of water. , more preferably 0.5 to 1.5 parts by weight.
Ａ－１－１－５．架橋処理
　必要に応じて、染色処理の後、水中延伸処理の前に、架橋処理を施す。上記架橋処理は、代表的には、ホウ酸水溶液にＰＶＡ系樹脂層を浸漬させることにより行う。架橋処理を施すことにより、ＰＶＡ系樹脂層に耐水性を付与し、後の水中延伸で、高温の水中へ浸漬した際のＰＶＡの配向低下を防止することができる。当該ホウ酸水溶液の濃度は、水１００重量部に対して、好ましくは１重量部～５重量部である。また、上記染色処理後に架橋処理を行う場合、さらに、ヨウ化物を配合することが好ましい。ヨウ化物を配合することにより、ＰＶＡ系樹脂層に吸着させたヨウ素の溶出を抑制することができる。ヨウ化物の配合量は、水１００重量部に対して、好ましくは１重量部～５重量部である。ヨウ化物の具体例は、上述のとおりである。架橋浴（ホウ酸水溶液）の液温は、好ましくは２０℃～５０℃である。 A-1-1-5. Crosslinking Treatment If necessary, a crosslinking treatment is applied after the dyeing treatment and before the underwater stretching treatment. The cross-linking treatment is typically performed by immersing the PVA-based resin layer in an aqueous solution of boric acid. The cross-linking treatment imparts water resistance to the PVA-based resin layer, and prevents deterioration of the orientation of the PVA when immersed in high-temperature water in the subsequent underwater stretching. The concentration of the boric acid aqueous solution is preferably 1 to 5 parts by weight with respect to 100 parts by weight of water. Moreover, when cross-linking treatment is carried out after the dyeing treatment, it is preferable to further add an iodide. By blending iodide, elution of iodine adsorbed on the PVA-based resin layer can be suppressed. The amount of iodide compounded is preferably 1 to 5 parts by weight per 100 parts by weight of water. Specific examples of iodides are as described above. The liquid temperature of the cross-linking bath (boric acid aqueous solution) is preferably 20°C to 50°C.
Ａ－１－１－６．水中延伸処理
　水中延伸処理は、積層体を延伸浴に浸漬させて行う。水中延伸処理によれば、上記熱可塑性樹脂基材やＰＶＡ系樹脂層のガラス転移温度（代表的には、８０℃程度）よりも低い温度で延伸し得、ＰＶＡ系樹脂層を、その結晶化を抑えながら、高倍率に延伸することができる。その結果、優れた光学特性を有する偏光膜を製造することができる。 A-1-1-6. Underwater Stretching Treatment Underwater stretching treatment is performed by immersing the laminate in a stretching bath. According to the underwater stretching treatment, the thermoplastic resin substrate and the PVA-based resin layer can be stretched at a temperature lower than the glass transition temperature (typically, about 80° C.), and the PVA-based resin layer undergoes its crystallization. can be stretched at a high magnification while suppressing the As a result, a polarizing film having excellent optical properties can be produced.
　積層体の延伸方法は、任意の適切な方法を採用することができる。具体的には、固定端延伸でもよいし、自由端延伸（例えば、周速の異なるロール間に積層体を通して一軸延伸する方法）でもよい。好ましくは、自由端延伸が選択される。積層体の延伸は、一段階で行ってもよいし、多段階で行ってもよい。多段階で行う場合、後述の積層体の延伸倍率（最大延伸倍率）は、各段階の延伸倍率の積である。 Any appropriate method can be adopted as the method for stretching the laminate. Specifically, fixed-end stretching or free-end stretching (for example, a method of uniaxially stretching a laminate by passing it between rolls having different peripheral speeds) may be used. Free-end drawing is preferably chosen. The laminate may be stretched in one step or in multiple steps. When the stretching is performed in multiple stages, the draw ratio (maximum draw ratio) of the laminate described below is the product of the draw ratios in each step.
　水中延伸は、代表的には、ホウ酸水溶液中に積層体を浸漬させて行う（ホウ酸水中延伸）。延伸浴としてホウ酸水溶液を用いることで、ＰＶＡ系樹脂層に、延伸時にかかる張力に耐える剛性と、水に溶解しない耐水性とを付与することができる。具体的には、ホウ酸は、水溶液中でテトラヒドロキシホウ酸アニオンを生成してＰＶＡ系樹脂と水素結合により架橋し得る。その結果、ＰＶＡ系樹脂層に剛性と耐水性とを付与して、良好に延伸することができ、優れた光学特性を有する一次偏光膜を製造することができる。 The stretching in water is typically performed by immersing the laminate in an aqueous boric acid solution (stretching in boric acid water). By using an aqueous boric acid solution as the stretching bath, the PVA-based resin layer can be imparted with rigidity to withstand tension applied during stretching and water resistance that does not dissolve in water. Specifically, boric acid can form a tetrahydroxyborate anion in an aqueous solution and crosslink with a PVA-based resin through hydrogen bonding. As a result, rigidity and water resistance can be imparted to the PVA-based resin layer, which can be satisfactorily stretched, and a primary polarizing film having excellent optical properties can be produced.
　上記ホウ酸水溶液は、好ましくは、溶媒である水にホウ酸および／またはホウ酸塩を溶解させることにより得られる。ホウ酸濃度は、水１００重量部に対して、好ましくは１重量部～１０重量部であり、より好ましくは２．５重量部～６重量部であり、特に好ましくは３重量部～５重量部である。ホウ酸濃度を１重量部以上とすることにより、ＰＶＡ系樹脂層の溶解を効果的に抑制することができ、より高特性の偏光膜を製造することができる。なお、ホウ酸またはホウ酸塩以外に、ホウ砂等のホウ素化合物、グリオキザール、グルタルアルデヒド等を溶媒に溶解して得られた水溶液も用いることができる。 The boric acid aqueous solution is preferably obtained by dissolving boric acid and/or a borate salt in water as a solvent. The boric acid concentration is preferably 1 part by weight to 10 parts by weight, more preferably 2.5 parts by weight to 6 parts by weight, and particularly preferably 3 parts by weight to 5 parts by weight with respect to 100 parts by weight of water. is. By setting the boric acid concentration to 1 part by weight or more, the dissolution of the PVA-based resin layer can be effectively suppressed, and a polarizing film with higher properties can be produced. In addition to boric acid or borate salts, an aqueous solution obtained by dissolving a boron compound such as borax, glyoxal, glutaraldehyde, or the like in a solvent can also be used.
　好ましくは、上記延伸浴（ホウ酸水溶液）にヨウ化物を配合する。ヨウ化物を配合することにより、ＰＶＡ系樹脂層に吸着させたヨウ素の溶出を抑制することができる。ヨウ化物の具体例は、上述のとおりである。ヨウ化物の濃度は、水１００重量部に対して、好ましくは０．０５重量部～１５重量部、より好ましくは０．５重量部～８重量部である。 Preferably, an iodide is added to the stretching bath (boric acid aqueous solution). By blending iodide, elution of iodine adsorbed on the PVA-based resin layer can be suppressed. Specific examples of iodides are as described above. The concentration of iodide is preferably 0.05 to 15 parts by weight, more preferably 0.5 to 8 parts by weight, per 100 parts by weight of water.
　延伸温度（延伸浴の液温）は、好ましくは４０℃～８５℃、より好ましくは６０℃～７５℃である。このような温度であれば、ＰＶＡ系樹脂層の溶解を抑制しながら高倍率に延伸することができる。具体的には、上述のように、熱可塑性樹脂基材のガラス転移温度（Ｔｇ）は、ＰＶＡ系樹脂層の形成との関係で、好ましくは６０℃以上である。この場合、延伸温度が４０℃を下回ると、水による熱可塑性樹脂基材の可塑化を考慮しても、良好に延伸できないおそれがある。一方、延伸浴の温度が高温になるほど、ＰＶＡ系樹脂層の溶解性が高くなって、優れた光学特性が得られないおそれがある。積層体の延伸浴への浸漬時間は、好ましくは１５秒～５分である。 The stretching temperature (liquid temperature of the stretching bath) is preferably 40°C to 85°C, more preferably 60°C to 75°C. At such a temperature, the film can be stretched at a high magnification while suppressing dissolution of the PVA-based resin layer. Specifically, as described above, the glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 60° C. or higher in relation to the formation of the PVA-based resin layer. In this case, if the stretching temperature is lower than 40° C., it may not be possible to stretch well even if the plasticization of the thermoplastic resin base material by water is considered. On the other hand, the higher the temperature of the stretching bath, the higher the solubility of the PVA-based resin layer, which may make it impossible to obtain excellent optical properties. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.
　水中延伸による延伸倍率は、好ましくは１．５倍以上、より好ましくは３．０倍以上である。積層体の総延伸倍率は、積層体の元長に対して、好ましくは５．０倍以上であり、さらに好ましくは５．５倍以上である。このような高い延伸倍率を達成することにより、光学特性に極めて優れた一次偏光膜を製造することができる。このような高い延伸倍率は、水中延伸方式（ホウ酸水中延伸）を採用することにより、達成し得る。 The draw ratio by underwater drawing is preferably 1.5 times or more, more preferably 3.0 times or more. The total draw ratio of the laminate is preferably 5.0 times or more, more preferably 5.5 times or more, relative to the original length of the laminate. By achieving such a high draw ratio, it is possible to produce a primary polarizing film with extremely excellent optical properties. Such a high draw ratio can be achieved by adopting an underwater drawing method (boric acid solution drawing).
Ａ－１－１－７．乾燥収縮処理
　上記乾燥収縮処理は、例えば、該長尺状の熱可塑性樹脂基材とＰＶＡ系樹脂膜との積層体を長手方向に搬送しながら加熱することにより、幅方向に２％以上収縮させるとともに、該ＰＶＡ系樹脂膜の水分率が１５重量％以下となるまで乾燥させることを含む。安定した外観を得る観点から、水分率が１２重量％以下、より好ましくは１０重量％以下、さらに好ましくは１重量％～５重量％となるまで乾燥させることが好ましい。 A-1-1-7. Dry shrinkage treatment In the dry shrinkage treatment, for example, the laminate of the long thermoplastic resin substrate and the PVA-based resin film is heated while being transported in the longitudinal direction, thereby shrinking the laminate by 2% or more in the width direction. and drying until the water content of the PVA-based resin film becomes 15% by weight or less. From the viewpoint of obtaining a stable appearance, it is preferable to dry to a moisture content of 12% by weight or less, more preferably 10% by weight or less, and even more preferably 1% to 5% by weight.
　乾燥収縮処理は、ゾーン全体を加熱して行うゾーン加熱により行っても良いし、搬送ロールを加熱する（いわゆる加熱ロールを用いる）ことにより行う（加熱ロール乾燥方式）こともできる。好ましくは、その両方を用いる。加熱ロールを用いて乾燥させることにより、効率的に積層体の加熱カールを抑制して、外観に優れた一次偏光膜を製造することができる。具体的には、加熱ロールに積層体を沿わせた状態で乾燥することにより、上記熱可塑性樹脂基材の結晶化を効率的に促進させて結晶化度を増加させることができ、比較的低い乾燥温度であっても、熱可塑性樹脂基材の結晶化度を良好に増加させることができる。その結果、熱可塑性樹脂基材は、その剛性が増加して、乾燥によるＰＶＡ系樹脂層の収縮に耐え得る状態となり、カールが抑制される。また、加熱ロールを用いることにより、積層体を平らな状態に維持しながら乾燥できるので、カールだけでなくシワの発生も抑制することができる。この時、積層体は、乾燥収縮処理により幅方向に収縮させることにより、光学特性を向上させることができる。ＰＶＡおよびＰＶＡ／ヨウ素錯体の配向性を効果的に高めることができるからである。乾燥収縮処理による積層体の幅方向の収縮率は、好ましくは１％～１０％であり、より好ましくは２％～８％であり、特に好ましくは４％～６％である。加熱ロールを用いることにより、積層体を搬送しながら連続的に幅方向に収縮させることができ、高い生産性を実現することができる。 The drying shrinkage treatment may be performed by zone heating performed by heating the entire zone, or by heating the transport roll (using a so-called heating roll) (heating roll drying method). Preferably both are used. By drying using a heating roll, it is possible to efficiently suppress heat curling of the laminate and to produce a primary polarizing film excellent in appearance. Specifically, the crystallization of the thermoplastic resin substrate can be efficiently promoted and the crystallinity can be increased by drying the laminate while it is placed along the heating roll. Even at the drying temperature, the crystallinity of the thermoplastic resin substrate can be increased satisfactorily. As a result, the thermoplastic resin base material has increased rigidity and is in a state capable of withstanding shrinkage of the PVA-based resin layer due to drying, thereby suppressing curling. Moreover, by using a heating roll, the layered product can be dried while being maintained in a flat state, so that not only curling but also wrinkling can be suppressed. At this time, the laminate can be shrunk in the width direction by drying shrinkage treatment, thereby improving the optical properties. This is because the orientation of PVA and PVA/iodine complex can be effectively enhanced. The shrinkage ratio of the laminate in the width direction due to drying shrinkage treatment is preferably 1% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%. By using the heating roll, the laminate can be continuously shrunk in the width direction while being transported, and high productivity can be achieved.
　図１は、乾燥収縮処理の一例を示す概略図である。乾燥収縮処理では、所定の温度に加熱された搬送ロールＲ１～Ｒ６と、ガイドロールＧ１～Ｇ４とにより、積層体２００を搬送しながら乾燥させる。図示例では、ＰＶＡ系樹脂層の面と熱可塑性樹脂基材の面を交互に連続加熱するように搬送ロールＲ１～Ｒ６が配置されているが、例えば、積層体２００の一方の面（たとえば熱可塑性樹脂基材面）のみを連続的に加熱するように搬送ロールＲ１～Ｒ６を配置してもよい。 FIG. 1 is a schematic diagram showing an example of drying shrinkage treatment. In the drying shrinkage process, the laminate 200 is dried while being transported by transport rolls R1 to R6 heated to a predetermined temperature and guide rolls G1 to G4. In the illustrated example, the transport rolls R1 to R6 are arranged so as to alternately and continuously heat the surface of the PVA-based resin layer and the surface of the thermoplastic resin substrate. The transport rolls R1 to R6 may be arranged so as to continuously heat only the plastic resin substrate surface).
　搬送ロールの加熱温度（加熱ロールの温度）、加熱ロールの数、加熱ロールとの接触時間等を調整することにより、乾燥条件を制御することができる。加熱ロールの温度は、好ましくは６０℃～１２０℃であり、さらに好ましくは６５℃～１００℃であり、特に好ましくは７０℃～８０℃である。熱可塑性樹脂の結晶化度を良好に増加させて、カールを良好に抑制することができるとともに、耐久性に極めて優れた光学積層体を製造することができる。なお、加熱ロールの温度は、接触式温度計により測定することができる。図示例では、６個の搬送ロールが設けられているが、搬送ロールは複数個であれば特に制限はない。搬送ロールは、通常２個～４０個、好ましくは４個～３０個設けられる。積層体と加熱ロールとの接触時間（総接触時間）は、好ましくは１秒～３００秒であり、より好ましくは１～２０秒であり、さらに好ましくは１～１０秒である。 The drying conditions can be controlled by adjusting the heating temperature of the transport rolls (the temperature of the heating rolls), the number of heating rolls, the contact time with the heating rolls, and so on. The temperature of the heating roll is preferably 60°C to 120°C, more preferably 65°C to 100°C, and particularly preferably 70°C to 80°C. The degree of crystallinity of the thermoplastic resin can be favorably increased, curling can be favorably suppressed, and an optical laminate having extremely excellent durability can be produced. The temperature of the heating roll can be measured with a contact thermometer. In the illustrated example, six transport rolls are provided, but there is no particular limitation as long as the number of transport rolls is plural. Conveying rolls are usually 2 to 40, preferably 4 to 30 in number. The contact time (total contact time) between the laminate and the heating roll is preferably 1 to 300 seconds, more preferably 1 to 20 seconds, still more preferably 1 to 10 seconds.
　加熱ロールは、加熱炉（例えば、オーブン）内に設けてもよいし、通常の製造ライン（室温環境下）に設けてもよい。好ましくは、送風手段を備える加熱炉内に設けられる。加熱ロールによる乾燥と熱風乾燥とを併用することにより、加熱ロール間での急峻な温度変化を抑制することができ、幅方向の収縮を容易に制御することができる。熱風乾燥の温度は、好ましくは３０℃～１００℃である。また、熱風乾燥時間は、好ましくは１秒～３００秒である。熱風の風速は、好ましくは１０ｍ／ｓ～３０ｍ／ｓ程度である。なお、当該風速は加熱炉内における風速であり、ミニベーン型デジタル風速計により測定することができる。 The heating roll may be provided in a heating furnace (for example, an oven), or may be provided in a normal production line (under room temperature environment). Preferably, it is provided in a heating furnace equipped with air blowing means. By using both heating roll drying and hot air drying, abrupt temperature changes between the heating rolls can be suppressed, and shrinkage in the width direction can be easily controlled. The temperature for hot air drying is preferably 30°C to 100°C. Moreover, the hot air drying time is preferably 1 second to 300 seconds. The wind speed of the hot air is preferably about 10m/s to 30m/s. The wind speed is the wind speed in the heating furnace and can be measured with a mini-vane digital anemometer.
Ａ－１－１－８．その他の処理
　好ましくは、水中延伸処理の後、乾燥収縮処理の前に、洗浄処理を施す。上記洗浄処理は、代表的には、ヨウ化カリウム水溶液にＰＶＡ系樹脂層を浸漬させることにより行う。 A-1-1-8. Other Treatments Preferably, a washing treatment is performed after the underwater stretching treatment and before the drying shrinkage treatment. The cleaning treatment is typically performed by immersing the PVA-based resin layer in an aqueous solution of potassium iodide.
Ａ－１－２．単層のＰＶＡ系樹脂膜を用いた一次偏光膜の作製
　単層のＰＶＡ系樹脂膜を用いた一次偏光膜の作製は、自己支持性を有する（すなわち、基材による支持を必要としない）長尺状のＰＶＡ系樹脂膜を染色およびホウ酸水中延伸（代表的には、ロール延伸機による一軸延伸）し、次いで、水分率が１５重量％以下、好ましくは１２重量％以下、より好ましくは１０重量％以下、さらに好ましくは１重量％～５重量％となるまで乾燥させることによって行われ得る。上記染色は、例えば、ＰＶＡ系樹脂膜をヨウ素水溶液に浸漬することにより行われる。上記一軸延伸の延伸倍率は、好ましくは３～７倍である。延伸は、染色処理後に行ってもよいし、染色しながら行ってもよい。また、延伸してから染色してもよい。必要に応じて、ＰＶＡ系樹脂膜に、膨潤処理、架橋処理、洗浄処理等が施される。例えば、染色の前にＰＶＡ系樹脂膜を水に浸漬して水洗することで、ＰＶＡ系樹脂膜表面の汚れやブロッキング防止剤を洗浄することができるだけでなく、ＰＶＡ系樹脂膜を膨潤させて染色ムラ等を防止することができる。 A-1-2. Production of primary polarizing film using single-layer PVA-based resin film Production of a primary polarizing film using a single-layer PVA-based resin film is self-supporting (that is, does not require support by a substrate). A strip-shaped PVA-based resin film is dyed and stretched in boric acid water (typically, uniaxially stretched by a roll stretching machine), and then the water content is 15% by weight or less, preferably 12% by weight or less, more preferably 10% by weight. This can be done by drying to a weight % or less, more preferably 1 to 5 weight %. The dyeing is performed by, for example, immersing the PVA-based resin film in an iodine aqueous solution. The draw ratio of the uniaxial drawing is preferably 3 to 7 times. Stretching may be performed after the dyeing treatment, or may be performed while dyeing. Moreover, you may dye after extending|stretching. If necessary, the PVA-based resin film is subjected to swelling treatment, cross-linking treatment, washing treatment, and the like. For example, by immersing the PVA-based resin film in water and washing it with water before dyeing, it is possible not only to wash away stains and anti-blocking agents on the surface of the PVA-based resin film, but also to swell the PVA-based resin film for dyeing. Unevenness and the like can be prevented.
Ａ－１－３．一次偏光膜
　一次偏光膜は、好ましくは、波長３８０ｎｍ～７８０ｎｍのいずれかの波長で吸収二色性を示す。一次偏光膜の透過率（単体透過率：Ｔｓ）は、好ましくは４１．５％以上であり、より好ましくは４２．０％以上であり、さらに好ましくは４２．５％以上である。一方、一次偏光膜の透過率は、好ましくは４６．０％以下であり、より好ましくは４５．０％以下である。一次偏光膜の偏光度は、好ましくは９８．０％以上であり、より好ましくは９９．０％以上、さらに好ましくは９９．９％以上である。一方、一次偏光膜の偏光度は、好ましくは９９．９９８％以下である。上記透過率は、代表的には、紫外可視分光光度計を用いて測定し、視感度補正を行なったＹ値である。上記偏光度は、代表的には、紫外可視分光光度計を用いて測定して視感度補正を行なった平行透過率Ｔｐおよび直交透過率Ｔｃに基づいて、下記式により求められる。
　　　偏光度（％）＝｛（Ｔｐ－Ｔｃ）／（Ｔｐ＋Ｔｃ）｝１／２×１００ A-1-3. Primary Polarizing Film The primary polarizing film preferably exhibits absorption dichroism at any wavelength of 380 nm to 780 nm. The transmittance of the primary polarizing film (single transmittance: Ts) is preferably 41.5% or more, more preferably 42.0% or more, still more preferably 42.5% or more. On the other hand, the transmittance of the primary polarizing film is preferably 46.0% or less, more preferably 45.0% or less. The degree of polarization of the primary polarizing film is preferably 98.0% or more, more preferably 99.0% or more, still more preferably 99.9% or more. On the other hand, the degree of polarization of the primary polarizing film is preferably 99.998% or less. The transmittance is typically a Y value measured using an ultraviolet-visible spectrophotometer and subjected to visibility correction. The degree of polarization is typically obtained by the following formula based on the parallel transmittance Tp and the orthogonal transmittance Tc measured using an ultraviolet-visible spectrophotometer and subjected to visibility correction.
Degree of polarization (%) = {(Tp-Tc)/(Tp+Tc)} 1/2 × 100
　１つの実施形態においては、１２μｍ以下の薄型の偏光膜の透過率は、代表的には、偏光膜（表面の屈折率：１．５３）と保護層（保護フィルム）（屈折率：１．５０）との積層体を測定対象として、紫外可視分光光度計を用いて測定される。偏光膜の表面の屈折率および／または保護層の空気界面に接する表面の屈折率に応じて、各層の界面での反射率が変化し、その結果、透過率の測定値が変化する場合がある。したがって、例えば、屈折率が１．５０ではない保護層を用いる場合、保護層の空気界面に接する表面の屈折率に応じて透過率の測定値を補正してもよい。具体的には、透過率の補正値Ｃは、保護層と空気層との界面における透過軸に平行な偏光の反射率Ｒ１（透過軸反射率）を用いて、以下の式で表わされる。
Ｃ＝Ｒ１－Ｒ０
Ｒ０＝（（１．５０－１）２／（１．５０＋１）２）×（Ｔ１／１００）　
Ｒ１＝（（ｎ１－１）２／（ｎ１＋１）２）×（Ｔ１／１００）
ここで、Ｒ０は、屈折率が１．５０である保護層を用いた場合の透過軸反射率であり、ｎ１は使用する保護層の屈折率であり、Ｔ１は偏光膜の透過率である。例えば、表面屈折率が１．５３である基材（シクロオレフィン系フィルム、ハードコート層付きフィルムなど）を保護層として用いる場合、補正量Ｃは約０．２％となる。この場合、測定により得られた透過率に０．２％を加算することで、表面の屈折率が１．５３である偏光膜を屈折率が１．５０である保護層を用いた場合の透過率に換算することが可能である。なお、上記式に基づく計算によれば、偏光膜の透過率Ｔ１を２％変化させたときの補正値Ｃの変化量は０．０３％以下であり、偏光膜の透過率が補正値Ｃの値に与える影響は限定的である。また、保護層が表面反射以外の吸収を有する場合は、吸収量に応じて適切な補正を行うことができる。 In one embodiment, the transmittance of a thin polarizing film of 12 μm or less is typically the polarizing film (surface refractive index: 1.53) and the protective layer (protective film) (refractive index: 1.50 ) is measured using an ultraviolet-visible spectrophotometer. Depending on the refractive index of the surface of the polarizing film and/or the refractive index of the protective layer contacting the air interface, the reflectance at each layer interface may change, resulting in a change in the measured transmittance. . Thus, for example, if a protective layer with a refractive index other than 1.50 is used, the transmittance measurements may be corrected according to the refractive index of the surface of the protective layer that is in contact with the air interface. Specifically, the transmittance correction value C is expressed by the following formula using the reflectance R 1 (transmission axis reflectance) of polarized light parallel to the transmission axis at the interface between the protective layer and the air layer.
C=R 1 -R 0
R 0 = ((1.50−1) 2 /(1.50+1) 2 )×(T 1 /100)
R 1 = ((n 1 −1) 2 /(n 1 +1) 2 )×(T 1 /100)
Here, R 0 is the transmission axis reflectance when a protective layer having a refractive index of 1.50 is used, n 1 is the refractive index of the protective layer used, and T 1 is the transmittance of the polarizing film. is. For example, when a substrate having a surface refractive index of 1.53 (a cycloolefin film, a film with a hard coat layer, etc.) is used as the protective layer, the correction amount C is approximately 0.2%. In this case, by adding 0.2% to the transmittance obtained by the measurement, the transmittance when using a polarizing film with a surface refractive index of 1.53 and a protective layer with a refractive index of 1.50 It is possible to convert to a rate. According to the calculation based on the above formula, the amount of change in the correction value C when the transmittance T1 of the polarizing film is changed by 2 % is 0.03% or less, and the transmittance of the polarizing film is equal to the correction value C has a limited effect on the value of Moreover, when the protective layer has absorption other than surface reflection, appropriate correction can be performed according to the amount of absorption.
　一次偏光膜の厚みは、代表的には２５μｍ以下であり、好ましくは１２μｍ以下であり、より好ましくは１μｍ～８μｍであり、さらに好ましくは１μｍ～７μｍ、さらにより好ましくは２μｍ～５μｍである。厚みが小さい場合、水性溶媒と接触させた際に偏光膜にシワが発生し難いという利点がある。 The thickness of the primary polarizing film is typically 25 μm or less, preferably 12 μm or less, more preferably 1 μm to 8 μm, even more preferably 1 μm to 7 μm, still more preferably 2 μm to 5 μm. When the thickness is small, there is an advantage that wrinkles are less likely to occur in the polarizing film when it is brought into contact with an aqueous solvent.
　一次偏光膜の水分率は、代表的には１５重量％以下であり、好ましくは１２重量％以下であり、より好ましくは１０重量％以下、さらに好ましくは１重量％～５重量％である。水分率が上記範囲であれば、水性溶媒と接触させた際に大きく外観を損なうことなく、透過率を変化させることができる。 The moisture content of the primary polarizing film is typically 15% by weight or less, preferably 12% by weight or less, more preferably 10% by weight or less, and still more preferably 1% to 5% by weight. If the moisture content is within the above range, the transmittance can be changed without significantly impairing the appearance when contacted with an aqueous solvent.
Ａ－２．偏光板を作製する工程
　偏光板を作製する工程においては、一次偏光膜の一方の側に保護層および任意に機能層が積層され、他方の側が露出面とされた構成を有する偏光板を作製する。機能層としては、目的に応じて任意の適切な機能層が選択され得、その具体例としては、位相差層、粘着剤層等が挙げられる。なお、当該偏光板を作製する工程は、任意の工程である。よって、目的に応じて、Ａ－１－１項に記載の方法で作製された［熱可塑性樹脂基材／一次偏光膜］の構成を有する積層体またはＡ－１－２項に記載の単層のＰＶＡ系樹脂膜を用いて作成された一次偏光膜をそのまま、二次偏光膜を得る工程に供することもできる。 A-2. Step of Producing Polarizing Plate In the step of producing a polarizing plate, a polarizing plate having a configuration in which a protective layer and optionally a functional layer are laminated on one side of a primary polarizing film and the other side is an exposed surface is produced. . Any appropriate functional layer can be selected as the functional layer depending on the purpose, and specific examples thereof include a retardation layer, an adhesive layer, and the like. In addition, the process of manufacturing the said polarizing plate is an arbitrary process. Therefore, depending on the purpose, the laminate having the structure of [thermoplastic resin substrate/primary polarizing film] produced by the method described in Section A-1-1 or the single layer described in Section A-1-2 The primary polarizing film prepared using the PVA-based resin film of No. 1 can be directly subjected to the step of obtaining the secondary polarizing film.
　図２Ａ～図２Ｃはそれぞれ、偏光板を作製する工程で作製され得る偏光板の一例を説明する概略断面図である。図２Ａに示される偏光板１００Ａは、偏光膜（一次偏光膜）１０とその片側に配置された保護層２０とを含み、偏光膜（一次偏光膜）１０の保護層２０が設けられた側と反対側が露出面とされている。偏光板１００Ａは、例えば、Ａ－１－１項に記載の方法で作製された［熱可塑性樹脂基材／一次偏光膜］の構成を有する積層体の一次偏光膜側表面に、接着剤層または粘着剤層を介して保護層を貼り合わせ、次いで、熱可塑性樹脂基材を剥離することによって得られ得る。あるいは、偏光板１００Ａは、Ａ－１－２項に記載の方法で作製された一次偏光膜の一方の表面に、接着剤層または粘着剤層を介して保護層を貼り合わせることによって得られ得る。 2A to 2C are schematic cross-sectional views explaining an example of a polarizing plate that can be produced in the process of producing a polarizing plate. The polarizing plate 100A shown in FIG. 2A includes a polarizing film (primary polarizing film) 10 and a protective layer 20 disposed on one side thereof, and the polarizing film (primary polarizing film) 10 on the side on which the protective layer 20 is provided. The opposite side is the exposed surface. The polarizing plate 100A is, for example, an adhesive layer or a It can be obtained by laminating a protective layer via an adhesive layer and then peeling off the thermoplastic resin substrate. Alternatively, the polarizing plate 100A can be obtained by laminating a protective layer on one surface of the primary polarizing film produced by the method described in Section A-1-2 via an adhesive layer or a pressure-sensitive adhesive layer. .
　図２Ｂに示される偏光板１００Ｂは、偏光膜（一次偏光膜）１０と保護層２０と位相差層３０と粘着剤層４０とをこの順に含み、偏光膜（一次偏光膜）１０の保護層２０が設けられた側と反対側が露出面とされている。偏光板１００Ｂは、例えば、偏光板１００Ａの保護層２０側表面に接着剤層または粘着剤層を介して位相差層３０を貼り合わせ、次いで、位相差層３０の表面に粘着剤層４０を設けることによって得られ得る。あるいは、偏光板１００Ｂは、上記［熱可塑性樹脂基材／一次偏光膜］の構成を有する積層体の熱可塑性樹脂基材側表面に、接着剤層または粘着剤層を介して位相差層３０を貼り合わせ、次いで、位相差層３０の表面に粘着剤層４０を設けることによっても得られ得る。この場合、熱可塑性樹脂基材が保護層２０として機能する。なお、図示例の位相差層３０は、単層構造であってもよく、２層以上の位相差層が積層された積層構造であってもよい。 The polarizing plate 100B shown in FIG. 2B includes a polarizing film (primary polarizing film) 10, a protective layer 20, a retardation layer 30, and an adhesive layer 40 in this order. is provided and the opposite side is an exposed surface. For the polarizing plate 100B, for example, the retardation layer 30 is attached to the protective layer 20 side surface of the polarizing plate 100A via an adhesive layer or a pressure-sensitive adhesive layer, and then the pressure-sensitive adhesive layer 40 is provided on the surface of the retardation layer 30. can be obtained by Alternatively, in the polarizing plate 100B, the retardation layer 30 is provided on the thermoplastic resin substrate side surface of the laminate having the configuration of [thermoplastic resin substrate/primary polarizing film] via an adhesive layer or a pressure-sensitive adhesive layer. It can also be obtained by laminating and then providing the pressure-sensitive adhesive layer 40 on the surface of the retardation layer 30 . In this case, the thermoplastic resin substrate functions as the protective layer 20 . The retardation layer 30 in the illustrated example may have a single-layer structure, or may have a laminated structure in which two or more retardation layers are laminated.
　図２Ｃに示される偏光板１００Ｃは、偏光膜（一次偏光膜）１０と保護層２０と粘着剤層４０とをこの順に含み、偏光膜（一次偏光膜）１０の保護層２０が設けられた側と反対側が露出面とされている。偏光板１００Ｃは、例えば、偏光板１００Ａの保護層２０側表面に粘着剤層４０を設けることによって得られ得る。あるいは、偏光板１００Ｃは、上記［熱可塑性樹脂基材／一次偏光膜］の構成を有する積層体の熱可塑性樹脂基材側表面に、粘着剤層４０を設けることによっても得られ得る。この場合、熱可塑性樹脂基材が保護層２０として機能する。 The polarizing plate 100C shown in FIG. 2C includes a polarizing film (primary polarizing film) 10, a protective layer 20, and an adhesive layer 40 in this order. and the opposite side is the exposed surface. The polarizing plate 100C can be obtained, for example, by providing an adhesive layer 40 on the protective layer 20 side surface of the polarizing plate 100A. Alternatively, the polarizing plate 100C can also be obtained by providing an adhesive layer 40 on the thermoplastic resin substrate side surface of the laminate having the structure [thermoplastic resin substrate/primary polarizing film]. In this case, the thermoplastic resin substrate functions as the protective layer 20 .
　図示しないが、粘着剤層４０の表面には、偏光板が使用に供されるまで、剥離フィルムが仮着されていることが好ましい。 Although not shown, it is preferable that a release film is temporarily attached to the surface of the adhesive layer 40 until the polarizing plate is used.
　保護層２０は、偏光膜の保護層として使用できる任意の適切なフィルムで形成される。位相差層３０は、例えば、熱可塑性樹脂フィルムまたは液晶配向固化層であり得る。また、粘着剤層４０を形成する粘着剤としては、任意の適切な粘着剤を用いることができ、なかでも、アクリル系ポリマーをベースポリマーとするアクリル系粘着剤が好ましく用いられる。このような保護層、位相差層および粘着剤層は、当業者に周知であるので、その詳細な説明は省略する。 The protective layer 20 is formed of any appropriate film that can be used as a protective layer for polarizing films. The retardation layer 30 can be, for example, a thermoplastic resin film or a liquid crystal alignment fixed layer. Any appropriate adhesive can be used as the adhesive that forms the adhesive layer 40, and among them, an acrylic adhesive having an acrylic polymer as a base polymer is preferably used. Such protective layer, retardation layer and pressure-sensitive adhesive layer are well known to those skilled in the art, and thus detailed description thereof will be omitted.
Ａ－３．二次偏光膜を得る工程
　二次偏光膜を得る工程においては、一次偏光膜の表面に水性溶媒を接触させることにより、該一次偏光膜の透過率を変化させる。具体的には、水性溶媒と接触させて一次偏光膜を脱色することによって、所望の透過率を有する二次偏光膜を得ることができる。 A-3. Step of Obtaining Secondary Polarizing Film In the step of obtaining the secondary polarizing film, the surface of the primary polarizing film is brought into contact with an aqueous solvent to change the transmittance of the primary polarizing film. Specifically, a secondary polarizing film having a desired transmittance can be obtained by decolorizing the primary polarizing film by bringing it into contact with an aqueous solvent.
　水性溶媒としては、一次偏光膜から二色性物質を溶出させ得る限りにおいて、任意の適切な水性溶媒が用いられ得る。水性溶媒は、例えば、水または水と水溶性有機溶媒との混合物であり得る。水溶性有機溶媒としては、メタノール、エタノール、ｎ－プロピルアルコール、イソプロピルアルコール等の炭素数が１個～４個の低級モノアルコールおよびグリセリン、エチレングリコール等の多価アルコールが好ましく例示できる。 Any appropriate aqueous solvent can be used as the aqueous solvent as long as it can elute the dichroic substance from the primary polarizing film. The aqueous solvent can be, for example, water or a mixture of water and a water-soluble organic solvent. Preferred examples of the water-soluble organic solvent include lower monoalcohols having 1 to 4 carbon atoms such as methanol, ethanol, n-propyl alcohol and isopropyl alcohol, and polyhydric alcohols such as glycerin and ethylene glycol.
　水性溶媒中における水溶性有機溶媒の含有割合は、例えば２０重量％以下であり、好ましくは１０重量％以下であり、より好ましくは５重量％以下である。 The content of the water-soluble organic solvent in the aqueous solvent is, for example, 20% by weight or less, preferably 10% by weight or less, and more preferably 5% by weight or less.
　水性溶媒との接触方法としては、特に制限されず、浸漬、噴霧、塗布等の任意の適切な方法が用いられ得る。部分的な透過率の調整には噴霧または塗布が好ましく、全面的な透過率の調整には浸漬が好ましい。 The method of contact with the aqueous solvent is not particularly limited, and any suitable method such as immersion, spraying, coating, etc. can be used. Spraying or coating is preferred for partial transmittance adjustment, and immersion is preferred for overall transmittance adjustment.
　水性溶媒との接触時間および接触時の水性溶媒の温度は、所望する透過率の変化量に応じて適切に設定され得る。接触時間を長くすることまたは水性溶媒の温度を高くすることにより、透過率の変化量が大きくなる傾向にある。接触時間は、例えば１０分以下、好ましくは１秒～５分、より好ましくは２秒～３分であり得る。水性溶媒の温度は、好ましくは２０℃～７０℃、より好ましくは３０℃～６５℃、さらに好ましくは４０℃～６０℃であり得る。 The contact time with the aqueous solvent and the temperature of the aqueous solvent during contact can be appropriately set according to the desired change in transmittance. Increasing the contact time or increasing the temperature of the aqueous solvent tends to increase the amount of change in transmittance. The contact time can be, for example, 10 minutes or less, preferably 1 second to 5 minutes, more preferably 2 seconds to 3 minutes. The temperature of the aqueous solvent can be preferably 20°C to 70°C, more preferably 30°C to 65°C, even more preferably 40°C to 60°C.
　必要に応じて、水性溶媒と接触させた後に偏光膜を乾燥させてもよい。乾燥温度は、例えば３０℃～１００℃、好ましくは３０℃～８０℃であり得る。乾燥後の偏光膜（二次偏光膜）の水分率は、代表的には１５重量％以下であり、好ましくは１２重量％以下であり、より好ましくは１０重量％以下であり、さらに好ましくは１重量％～５重量％である。 If necessary, the polarizing film may be dried after contact with the aqueous solvent. The drying temperature can be, for example, 30°C to 100°C, preferably 30°C to 80°C. The moisture content of the dried polarizing film (secondary polarizing film) is typically 15% by weight or less, preferably 12% by weight or less, more preferably 10% by weight or less, and still more preferably 1% by weight. % to 5% by weight.
　二次偏光膜は、好ましくは、波長３８０ｎｍ～７８０ｎｍのいずれかの波長で吸収二色性を示す。二次偏光膜の透過率（単体透過率：Ｔｓ）は、目的に応じて、適切に調整され得る。二次偏光膜の透過率は、好ましくは４１．５％以上であり、より好ましくは４２％以上であり、さらに好ましくは４２．５％以上である。一方、二次偏光膜の透過率は、例えば７０％以下であり、好ましくは５０％以下、より好ましくは４６％以下である。１つの実施形態において、二次偏光膜は、一次偏光膜よりも例えば０．１％～１．５％高い透過率を有し得る。また、二次偏光膜の偏光度は、例えば９０％以上、好ましくは９２．０％以上であり、より好ましくは９４．０％以上であり、さらに好ましくは９６．０％以上であり、さらにより好ましくは９９．０％以上であり、さらにより好ましくは９９．５％以上であり、好ましくは９９．９９８％以下である。上記透過率および偏光度は、一次偏光膜の透過率および偏光度と同様にして得られる値である。 The secondary polarizing film preferably exhibits absorption dichroism at any wavelength of 380 nm to 780 nm. The transmittance of the secondary polarizing film (single transmittance: Ts) can be appropriately adjusted depending on the purpose. The transmittance of the secondary polarizing film is preferably 41.5% or more, more preferably 42% or more, still more preferably 42.5% or more. On the other hand, the transmittance of the secondary polarizing film is, for example, 70% or less, preferably 50% or less, more preferably 46% or less. In one embodiment, the secondary polarizing film can have a transmission that is, for example, 0.1% to 1.5% higher than the primary polarizing film. Further, the degree of polarization of the secondary polarizing film is, for example, 90% or more, preferably 92.0% or more, more preferably 94.0% or more, still more preferably 96.0% or more, and still more. It is preferably 99.0% or more, still more preferably 99.5% or more, and preferably 99.998% or less. The above transmittance and degree of polarization are values obtained in the same manner as the transmittance and degree of polarization of the primary polarizing film.
　二次偏光膜の厚みは、代表的には２５μｍ以下であり、好ましくは１２μｍ以下であり、より好ましくは１μｍ～８μｍであり、さらに好ましくは１μｍ～７μｍ、さらにより好ましくは２μｍ～５μｍである。二次偏光膜の厚みは、一次偏光膜と実質的に同じであり得る。 The thickness of the secondary polarizing film is typically 25 μm or less, preferably 12 μm or less, more preferably 1 μm to 8 μm, still more preferably 1 μm to 7 μm, still more preferably 2 μm to 5 μm. The thickness of the secondary polarizing film can be substantially the same as the primary polarizing film.
Ａ－４．他の工程
　上記偏光板の製造方法は、必要に応じて、任意の適切な工程をさらに含み得る。例えば、二次偏光膜を得る工程の後に、二次偏光膜の表面に水性溶媒を接触させることにより、透過率を変化させる工程をさらに含んでもよい。当該透過率を変化させる工程は、２回以上繰り返すことができる。また例えば、最終的に得られた偏光膜（例えば、二次偏光膜）の露出面に任意の適切な層（保護層、位相差層、粘着剤層等）を積層して当該露出面を保護する工程を含むことができる。 A-4. Other Steps The method for manufacturing the polarizing plate may further include any appropriate steps as necessary. For example, after the step of obtaining the secondary polarizing film, the step of changing the transmittance by contacting the surface of the secondary polarizing film with an aqueous solvent may be further included. The step of changing the transmittance can be repeated two or more times. Further, for example, any suitable layer (protective layer, retardation layer, adhesive layer, etc.) is laminated on the exposed surface of the finally obtained polarizing film (e.g., secondary polarizing film) to protect the exposed surface. can include the step of
　図３Ａおよび３Ｂはそれぞれ、偏光膜の露出面を保護する工程後に得られ得る偏光板の一例の概略断面図である。偏光板１００Ｄは、第１の保護層２０ａと偏光膜（二次偏光膜）１０と第２の保護層２０ｂと位相差層３０と粘着剤層４０とをこの順に備える。偏光板１００Ｄは、例えば、二次偏光膜を得る工程を経た偏光板１００Ａ（図２Ａ）の偏光膜１０の露出面に第２の保護層２０ｂ、位相差層３０および粘着剤層４０をこの順に設けることによって得られ得る。あるいは、二次偏光膜を得る工程を経た偏光板１００Ｂ（図２Ｂ）の偏光膜１０の露出面に第１の保護層２０ａを貼り合わせることによって得られ得る。 3A and 3B are schematic cross-sectional views of an example of a polarizing plate that can be obtained after the step of protecting the exposed surface of the polarizing film. The polarizing plate 100D includes a first protective layer 20a, a polarizing film (secondary polarizing film) 10, a second protective layer 20b, a retardation layer 30, and an adhesive layer 40 in this order. The polarizing plate 100D is obtained by, for example, forming a second protective layer 20b, a retardation layer 30 and an adhesive layer 40 in this order on the exposed surface of the polarizing film 10 of the polarizing plate 100A (FIG. 2A) that has undergone the step of obtaining a secondary polarizing film. can be obtained by providing Alternatively, it can be obtained by bonding the first protective layer 20a to the exposed surface of the polarizing film 10 of the polarizing plate 100B (FIG. 2B) that has undergone the step of obtaining the secondary polarizing film.
　偏光板１００Ｅは、第１の保護層２０ａと偏光膜（二次偏光膜）１０と第２の保護層２０ｂと粘着剤層４０とをこの順に備える。偏光板１００Ｅにおいて、第２の保護層２０ｂは、後述するように、所望の位相差を有し、位相差層（例えば、λ／４板）として機能し得るものであってもよい。偏光板１００Ｅは、例えば、透過率を変化させる工程を経た偏光板１００Ａ（図２Ａ）の偏光膜１０の露出面に第２の保護層２０ｂおよび粘着剤層４０をこの順に設けることによって得られ得る。あるいは、透過率を変化させる工程を経た偏光板１００Ｃ（図２Ｃ）の偏光膜１０の露出面に第１の保護層２０ａを貼り合わせることによって得られ得る。 The polarizing plate 100E includes a first protective layer 20a, a polarizing film (secondary polarizing film) 10, a second protective layer 20b, and an adhesive layer 40 in this order. In the polarizing plate 100E, the second protective layer 20b may have a desired retardation and function as a retardation layer (for example, a λ/4 plate), as described later. The polarizing plate 100E can be obtained, for example, by providing the second protective layer 20b and the adhesive layer 40 in this order on the exposed surface of the polarizing film 10 of the polarizing plate 100A (FIG. 2A) that has undergone the process of changing the transmittance. . Alternatively, it can be obtained by bonding the first protective layer 20a to the exposed surface of the polarizing film 10 of the polarizing plate 100C (FIG. 2C) that has undergone the process of changing the transmittance.
　１つの実施形態において、粘着剤層４０は、画像表示セル（例えば、液晶セル、有機ＥＬセル）に偏光板１００Ｄおよび１００Ｅを貼り合わせるために用いられる。本実施形態においては、第１の保護層２０ａが、偏光板を画像表示装置に適用したときに画像表示セルとは反対側に配置される保護層（外側保護層）になり、第２の保護層２０ｂが画像表示セル側に配置される保護層（内側保護層）になる。 In one embodiment, the adhesive layer 40 is used to bond the polarizing plates 100D and 100E to an image display cell (eg liquid crystal cell, organic EL cell). In the present embodiment, the first protective layer 20a serves as a protective layer (outer protective layer) arranged on the side opposite to the image display cell when the polarizing plate is applied to the image display device, and serves as the second protective layer. The layer 20b becomes a protective layer (inner protective layer) arranged on the image display cell side.
　上記外側保護層の厚みは、代表的には３００μｍ以下であり、好ましくは１００μｍ以下、より好ましくは５μｍ～８０μｍ、さらに好ましくは１０μｍ～６０μｍである。なお、表面処理が施されている場合、外側保護層の厚みは、表面処理層の厚みを含めた厚みである。 The thickness of the outer protective layer is typically 300 μm or less, preferably 100 μm or less, more preferably 5 μm to 80 μm, still more preferably 10 μm to 60 μm. In addition, when the surface treatment is performed, the thickness of the outer protective layer is the thickness including the thickness of the surface treatment layer.
　上記内側保護層の厚みは、好ましくは５μｍ～２００μｍ、より好ましくは１０μｍ～１００μｍ、さらに好ましくは１０μｍ～６０μｍである。 The thickness of the inner protective layer is preferably 5 µm to 200 µm, more preferably 10 µm to 100 µm, still more preferably 10 µm to 60 µm.
　１つの実施形態において、内側保護層は、光学的に等方性である。なお、本明細書において「光学的に等方性である」とは、面内位相差Ｒｅ（５５０）が０ｎｍ～１０ｎｍであり、厚み方向の位相差Ｒｔｈ（５５０）が－１０ｎｍ～＋１０ｎｍであることをいう。ここで、「Ｒｅ（５５０）」は、２３℃における波長５５０ｎｍの光で測定した面内位相差であり、式：Ｒｅ＝（ｎｘ－ｎｙ）×ｄにより求められる。また、「Ｒｔｈ（５５０）」は、２３℃における波長５５０ｎｍの光で測定した厚み方向の位相差であり、式：Ｒｔｈ（λ）＝（ｎｘ－ｎｚ）×ｄによって求められる。ここで、「ｎｘ」は面内の屈折率が最大になる方向（すなわち、遅相軸方向）の屈折率であり、「ｎｙ」は面内で遅相軸と直交する方向（すなわち、進相軸方向）の屈折率であり、「ｎｚ」は厚み方向の屈折率であり、「ｄ」は層（フィルム）の厚み（ｎｍ）である。 In one embodiment, the inner protective layer is optically isotropic. In this specification, “optically isotropic” means that the in-plane retardation Re (550) is 0 nm to 10 nm, and the thickness direction retardation Rth (550) is −10 nm to +10 nm. Say things. Here, “Re(550)” is an in-plane retardation measured with light having a wavelength of 550 nm at 23° C., and is obtained by the formula: Re=(nx−ny)×d. "Rth(550)" is the retardation in the thickness direction measured with light having a wavelength of 550 nm at 23° C., and is obtained by the formula: Rth(λ)=(nx−nz)×d. Here, “nx” is the refractive index in the direction in which the in-plane refractive index is maximized (that is, the slow axis direction), and “ny” is the in-plane direction orthogonal to the slow axis (that is, the fast is the refractive index in the axial direction), 'nz' is the refractive index in the thickness direction, and 'd' is the layer (film) thickness (nm).
　別の実施形態においては、内側保護層は、任意の適切な位相差値を有する位相差層である。本実施形態における内側保護層の面内位相差Ｒｅ（５５０）は、例えば１１０ｎｍ～１５０ｎｍであり得る。このような内側保護層を、その遅相軸と偏光膜の吸収軸との遅相軸とのなす角度が、時計回りまたは反時計回りに、例えば３５°～５５°であり、好ましくは３８°～５２°であり、より好ましくは４０°～５０°であり、さらに好ましくは４２°～４８°であり、特に好ましくは４４°～４６°となるように配置することにより、円偏光板として機能し得る。 In another embodiment, the inner protective layer is a retardation layer having any suitable retardation value. The in-plane retardation Re(550) of the inner protective layer in this embodiment can be, for example, 110 nm to 150 nm. The angle between the slow axis of the inner protective layer and the slow axis of the absorption axis of the polarizing film is clockwise or counterclockwise, for example, 35° to 55°, preferably 38°. ~52°, more preferably 40° to 50°, more preferably 42° to 48°, and particularly preferably 44° to 46°, thereby functioning as a circularly polarizing plate can.
　位相差層３０は、目的に応じて所望の面内位相差および／または厚み方向の位相差を有する位相差層であってよい。例えば、内側保護層が光学的に等方性である場合、位相差層の面内位相差Ｒｅ（５５０）は、１１０ｎｍ～１５０ｎｍであり得る。このような位相差層を、その遅相軸と偏光膜の吸収軸との遅相軸とのなす角度が、時計回りまたは反時計回りに、例えば３５°～５５°であり、好ましくは３８°～５２°であり、より好ましくは４０°～５０°であり、さらに好ましくは４２°～４８°であり、特に好ましくは４４°～４６°となるように配置することにより、円偏光板として機能し得る。 The retardation layer 30 may be a retardation layer having a desired in-plane retardation and/or thickness direction retardation depending on the purpose. For example, when the inner protective layer is optically isotropic, the in-plane retardation Re(550) of the retardation layer can be 110 nm to 150 nm. In such a retardation layer, the angle between the slow axis and the slow axis of the absorption axis of the polarizing film is clockwise or counterclockwise, for example, 35° to 55°, preferably 38°. ~52°, more preferably 40° to 50°, more preferably 42° to 48°, and particularly preferably 44° to 46°, thereby functioning as a circularly polarizing plate can.
Ｂ．画像表示装置の製造方法
　本発明の実施形態による画像表示装置の製造方法は、二色性物質を含むポリビニルアルコール系樹脂膜で構成され、水分率が１５重量％以下である偏光膜と、保護層と、粘着剤層とをこの順に含む偏光板を、当該粘着剤層を介して画像表示セルに積層して、該偏光膜の該保護層が配置された側と反対側の表面を露出面とする工程（Ｉ）、および、該偏光膜の露出面に水性溶媒を接触させて透過率を変化させる工程（ＩＩ）、をこの順で含む。このような画像表示装置の製造方法によれば、画像表示セルに貼り合わせた後に偏光膜の透過率を調整することができることから、画像表示セルやバックライトユニット等の品質個体差に関わらず、所望の輝度を有する画像表示装置を得ることができる。 B. Method for manufacturing an image display device A method for manufacturing an image display device according to an embodiment of the present invention includes a polarizing film made of a polyvinyl alcohol resin film containing a dichroic substance and having a moisture content of 15% by weight or less, and a protective layer. and an adhesive layer in this order, laminated on the image display cell via the adhesive layer, and the surface of the polarizing film opposite to the side on which the protective layer is arranged is exposed. and step (II) of bringing an aqueous solvent into contact with the exposed surface of the polarizing film to change the transmittance, in this order. According to such an image display device manufacturing method, since the transmittance of the polarizing film can be adjusted after being bonded to the image display cell, regardless of individual differences in quality of the image display cell, backlight unit, etc., An image display device having desired luminance can be obtained.
Ｂ－１．工程（Ｉ）
　画像表示セルに積層する偏光板は、二色性物質を含むポリビニルアルコール系樹脂膜で構成され、水分率が１５重量％以下である偏光膜と、保護層と、粘着剤層とをこの順に含み、偏光膜の保護層が配置されていない側の面が露出可能とされている限りにおいて、任意の構成を有し得る。例えば、偏光膜の露出面を表面保護フィルムで保護した状態で偏光板を画像表示セルに貼り合わせ、水性溶媒との接触前に表面保護フィルムを剥離することにより、偏光膜を露出させてもよい。 B-1. Step (I)
The polarizing plate laminated on the image display cell is composed of a polyvinyl alcohol-based resin film containing a dichroic substance, and includes a polarizing film having a moisture content of 15% by weight or less, a protective layer, and an adhesive layer in this order. , as long as the surface of the polarizing film on which the protective layer is not arranged can be exposed, it can have any configuration. For example, the polarizing plate may be attached to the image display cell with the exposed surface of the polarizing film protected by a surface protective film, and the polarizing film may be exposed by peeling off the surface protective film before contact with the aqueous solvent. .
　１つの実施形態において、画像表示セルに積層する偏光板は、位相差層をさらに含んでもよい。画像表示セルに積層する偏光板としては、図２Ｂおよび２Ｃに例示した構成の偏光板が例示できる。また、当該偏光板に含まれる偏光膜、保護層、位相差層および粘着剤層についてはそれぞれ、Ａ項に記載の一次偏光膜、保護層、位相差層および粘着剤層の説明が適用できる。 In one embodiment, the polarizing plate laminated on the image display cell may further include a retardation layer. As the polarizing plate laminated on the image display cell, the polarizing plates having the configurations illustrated in FIGS. 2B and 2C can be exemplified. Further, the description of the primary polarizing film, protective layer, retardation layer and adhesive layer described in section A can be applied to the polarizing film, protective layer, retardation layer and adhesive layer contained in the polarizing plate.
　上記製造方法で製造される画像表示装置としては、液晶表示装置または有機ＥＬ表示装置が好ましく例示できる。よって、上記画像表示セルとしては、液晶セルまたは有機ＥＬセルが好ましく用いられ得る。複数の画像表示装置が全体として１つの画像を表示するように組み合わされて、デジタルサイネージとして用いられてもよい。 A liquid crystal display device or an organic EL display device can be preferably exemplified as the image display device manufactured by the above manufacturing method. Therefore, a liquid crystal cell or an organic EL cell can be preferably used as the image display cell. A plurality of image display devices may be combined to display one image as a whole and used as digital signage.
Ｂ－２．工程（ＩＩ）
　透過率を変化させる工程においては、偏光膜の露出面に水性溶媒を接触させて透過率を変化させる。具体的には、水性溶媒との接触を介した二色性物質の脱色によって、偏光膜の透過率を変化させて所望の値に調整することができる。透過率を変化させる工程については、Ａ－３項と同様の説明を適用することができる。画像表示セルが水性溶媒と接触することを防ぐ観点から、水性溶媒との接触方法としては、塗布または噴霧が好ましく用いられ得る。透過率を変化させた後の偏光膜については、Ａ－３項に記載の二次偏光膜の説明が適用され得る。 B-2. Step (II)
In the step of changing the transmittance, the exposed surface of the polarizing film is brought into contact with an aqueous solvent to change the transmittance. Specifically, the transmittance of the polarizing film can be changed and adjusted to a desired value by decolorizing the dichroic substance through contact with an aqueous solvent. As for the step of changing the transmittance, the same explanation as in Section A-3 can be applied. From the viewpoint of preventing the image display cell from coming into contact with the aqueous solvent, coating or spraying can be preferably used as the method of contact with the aqueous solvent. For the polarizing film after changing the transmittance, the description of the secondary polarizing film described in Section A-3 can be applied.
　上記画像表示装置の製造方法は、必要に応じて、透過率を変化させる工程の後に、偏光膜の露出面を保護する工程をさらに含み得る。偏光膜の露出面の保護は、保護層、支持基材等を接着剤層、粘着剤層等の接着層を介して露出面に積層することによって行われ得る。 The method for manufacturing the image display device may further include a step of protecting the exposed surface of the polarizing film after the step of changing the transmittance, if necessary. Protection of the exposed surface of the polarizing film can be carried out by laminating a protective layer, a supporting substrate, or the like on the exposed surface via an adhesive layer such as an adhesive layer or pressure-sensitive adhesive layer.
Ｃ．偏光膜の透過率の調整方法
　本発明の別の局面によれば、二色性物質を含むＰＶＡ系樹脂膜で構成され、水分率が１５重量％以下である偏光膜の表面に水性溶媒を接触させる工程を含む、偏光膜の透過率の調整方法が提供される。当該偏光膜の透過率の調整方法によれば、水性溶媒との接触によって偏光膜が脱色する結果、偏光膜の透過率を所望の値に調整（代表的には、増大）することができる。 C. Method for Adjusting Transmittance of Polarizing Film According to another aspect of the present invention, an aqueous solvent is brought into contact with the surface of the polarizing film which is composed of a PVA-based resin film containing a dichroic substance and has a moisture content of 15% by weight or less. A method for adjusting the transmittance of a polarizing film is provided, which includes the step of causing a According to the method for adjusting the transmittance of the polarizing film, the transmittance of the polarizing film can be adjusted (typically increased) to a desired value as a result of decolorization of the polarizing film by contact with the aqueous solvent.
　水性溶媒と接触させる偏光膜としては、Ａ－１項に記載の一次偏光膜が好ましく用いられる。また、偏光膜と水性溶媒との接触については、Ａ－３項と同様の説明を適用することができる。 As the polarizing film to be brought into contact with the aqueous solvent, the primary polarizing film described in Section A-1 is preferably used. Also, the same description as in Section A-3 can be applied to the contact between the polarizing film and the aqueous solvent.
　以下、実施例によって本発明を具体的に説明するが、本発明はこれら実施例によって限定されるものではない。各特性の測定方法は以下の通りである。なお、特に明記しない限り、実施例および比較例における「部」および「％」は重量基準である。
（１）厚み
　干渉膜厚計（大塚電子社製、製品名「ＭＣＰＤ－３０００」）を用いて測定した。
（２）単体透過率および偏光度
　実施例および比較例で得られた偏光膜と保護層との積層体（偏光板）について、偏光膜側から、紫外可視分光光度計（大塚電子社製「ＬＰＦ－２００」）を用いて測定した単体透過率Ｔｓ、平行透過率Ｔｐ、直交透過率Ｔｃをそれぞれ、偏光膜のＴｓ、ＴｐおよびＴｃとした。これらのＴｓ、ＴｐおよびＴｃは、ＪＩＳ　Ｚ８７０１の２度視野（Ｃ光源）により測定して視感度補正を行なったＹ値である。なお、保護層の屈折率は１．５３であり、偏光膜の保護層とは反対側の表面の屈折率は１．５３であった。
　得られたＴｐおよびＴｃから、下記式により偏光度Ｐを求めた。
　　　偏光度Ｐ（％）＝｛（Ｔｐ－Ｔｃ）／（Ｔｐ＋Ｔｃ）｝１／２×１００
　なお、分光光度計は、日本分光社製「Ｖ－７１００」などでも同等の測定をすることが可能であり、いずれの分光光度計を用いた場合であっても同等の測定結果が得られることが確認されている。
（３）水分率
　乾燥処理直後の一次偏光膜（積層体で延伸した場合、延伸基材は剥離する）を１００ｍｍ×１００ｍｍ以上の大きさに切り出し、電子天秤にて、処理前重量を測定する。その後１２０℃に保たれた加熱オーブンに２時間投入し、取り出し後の重量（処理後重量）を測定し、下記式により水分率を求めた。
水分率［％］＝（処理前重量－処理後重量）／処理前重量×１００ EXAMPLES The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these Examples. The measurement method of each characteristic is as follows. "Parts" and "%" in Examples and Comparative Examples are by weight unless otherwise specified.
(1) Thickness Measured using an interference film thickness meter (manufactured by Otsuka Electronics Co., Ltd., product name: "MCPD-3000").
(2) Single transmittance and degree of polarization For the laminate (polarizing plate) of the polarizing film and the protective layer obtained in Examples and Comparative Examples, from the polarizing film side, an ultraviolet-visible spectrophotometer (manufactured by Otsuka Electronics Co., Ltd. "LPF −200”) were used as Ts, Tp and Tc of the polarizing film, respectively. These Ts, Tp and Tc are Y values measured with a 2-degree field of view (C light source) according to JIS Z8701 and subjected to visibility correction. The refractive index of the protective layer was 1.53, and the refractive index of the surface of the polarizing film opposite to the protective layer was 1.53.
From the obtained Tp and Tc, the degree of polarization P was determined by the following formula.
Degree of polarization P (%) = {(Tp-Tc)/(Tp+Tc)} 1/2 × 100
Equivalent measurement can be performed with a spectrophotometer such as "V-7100" manufactured by JASCO Corporation, and equivalent measurement results can be obtained using any spectrophotometer. has been confirmed.
(3) Moisture content The primary polarizing film immediately after drying (when the laminate is stretched, the stretched substrate is peeled off) is cut into a size of 100 mm x 100 mm or more, and the weight before processing is measured with an electronic balance. After that, it was placed in a heating oven maintained at 120° C. for 2 hours, the weight after removal (weight after treatment) was measured, and the moisture content was determined by the following formula.
Moisture content [%] = (weight before treatment - weight after treatment) / weight before treatment x 100
［実施例１－１］
　厚み３０μｍのＰＶＡ系樹脂フィルム（クラレ製、製品名「ＰＥ３０００」）の長尺ロールを、３０℃水浴中に浸漬させつつ搬送方向に２．２倍に延伸した後、ヨウ素濃度０．０４重量％、カリウム濃度０．３重量％の３０℃水溶液中に浸漬して染色しながら、全く延伸していないフィルム（元長）を基準として３倍に延伸した。次いで、この延伸フィルムを、ホウ酸濃度３重量％、ヨウ化カリウム濃度３重量％の３０℃の水溶液中に浸漬しながら、元長基準で３．３倍までさらに延伸し、続いて、ホウ酸濃度４重量％、ヨウ化カリウム濃度５重量％の６０℃水溶液中に浸漬しながら、元長基準で６倍までさらに延伸し、最後に６０℃に保たれたオーブンで５分の乾燥処理を施すことによって、厚み１２μｍの偏光膜（一次偏光膜）を作製した。得られた一次偏光膜の水分率は１０重量％であった。偏光膜の単体透過率は４２．５％であった。続いて、偏光膜の片面に、ＰＶＡ系樹脂水溶液（日本合成化学工業社製、商品名「ゴーセファイマー（登録商標）Ｚ－２００」、樹脂濃度：３重量％）を塗布し、シクロオレフィン系フィルム（日本ゼオン社製、Ｚｅｏｎｏｒ、厚み：２５μｍ）を貼り合わせ、［一次偏光膜／保護層］の構成を有する偏光板（処理前）を得た。 [Example 1-1]
A long roll of a 30 μm-thick PVA-based resin film (manufactured by Kuraray, product name “PE3000”) was immersed in a water bath at 30° C. and stretched 2.2 times in the conveying direction. , while being immersed in an aqueous solution of 0.3% by weight of potassium at 30° C. and dyed, the film was stretched 3 times with respect to the unstretched film (original length). Next, while immersing this stretched film in an aqueous solution of 3% by weight of boric acid and 3% by weight of potassium iodide at 30° C., the stretched film is further stretched to 3.3 times its original length. While immersed in a 60°C aqueous solution with a concentration of 4% by weight and a concentration of potassium iodide of 5% by weight, it is further stretched to 6 times its original length, and finally dried in an oven maintained at 60°C for 5 minutes. Thus, a polarizing film (primary polarizing film) having a thickness of 12 μm was produced. The obtained primary polarizing film had a moisture content of 10% by weight. The single transmittance of the polarizing film was 42.5%. Subsequently, on one side of the polarizing film, a PVA-based resin aqueous solution (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name “GOSEFIMER (registered trademark) Z-200”, resin concentration: 3% by weight) was applied, and a cycloolefin-based A film (Zeonor, thickness: 25 μm, manufactured by Nippon Zeon Co., Ltd.) was laminated to obtain a polarizing plate (before treatment) having a structure of [primary polarizing film/protective layer].
　上記偏光板（処理前）を１００ｍｍ×１００ｍｍサイズに切断し、アクリル系粘着剤層（厚み１５μｍ）を介して一次偏光膜側表面が露出面となるようにガラス板に貼り合わせた状態で５５℃の水中に６分浸漬した。次いで、５０℃で５分乾燥することにより、［二次偏光膜／保護層］の構成を有する偏光板（処理後）を得た。 The above polarizing plate (before treatment) was cut into a size of 100 mm × 100 mm and attached to a glass plate so that the surface on the primary polarizing film side was exposed via an acrylic adhesive layer (thickness 15 μm) at 55 ° C. of water for 6 minutes. Then, by drying at 50° C. for 5 minutes, a polarizing plate (after treatment) having a configuration of [secondary polarizing film/protective layer] was obtained.
［実施例１－２］
　５５℃の水中に６分間浸漬する代わりに、５５℃の水に９分間浸漬したこと以外は実施例１－１と同様にして、［二次偏光膜／保護層］の構成を有する偏光板（処理後）を得た。 [Example 1-2]
A polarizing plate having a [secondary polarizing film/protective layer] configuration ( after treatment).
［実施例１－３］
　５５℃の水中に６分間浸漬する代わりに、６０℃の水に４分間浸漬したこと以外は実施例１－１と同様にして、［二次偏光膜／保護層］の構成を有する偏光板（処理後）を得た。 [Example 1-3]
A polarizing plate having a [secondary polarizing film/protective layer] configuration ( after treatment).
［実施例１－４］
　５５℃の水中に６分間浸漬する代わりに、６５℃の水に３分間浸漬したこと以外は実施例１－１と同様にして、［二次偏光膜／保護層］の構成を有する偏光板（処理後）を得た。 [Example 1-4]
A polarizing plate having a [secondary polarizing film/protective layer] configuration ( after treatment).
［実施例２－１］
　熱可塑性樹脂基材として、長尺状で、Ｔｇ約７５℃である、非晶質のイソフタル共重合ポリエチレンテレフタレートフィルム（厚み：１００μｍ）を用い、樹脂基材の片面に、コロナ処理を施した。
　ポリビニルアルコール（重合度４２００、ケン化度９９．２モル％）およびアセトアセチル変性ＰＶＡ（日本合成化学工業社製、商品名「ゴーセファイマー」）を９：１で混合したＰＶＡ系樹脂１００重量部に、ヨウ化カリウム１３重量部を添加したものを水に溶かし、ＰＶＡ水溶液（塗布液）を調製した。
　樹脂基材のコロナ処理面に、上記ＰＶＡ水溶液を塗布して６０℃で乾燥することにより、厚み１３μｍのＰＶＡ系樹脂層を形成し、積層体を作製した。
　得られた積層体を、１３０℃のオーブン内で縦方向（長手方向）に２．４倍に一軸延伸した（空中補助延伸処理）。
　次いで、積層体を、液温４０℃の不溶化浴（水１００重量部に対して、ホウ酸を４重量部配合して得られたホウ酸水溶液）に３０秒間浸漬させた（不溶化処理）。
　次いで、液温３０℃の染色浴（水１００重量部に対して、ヨウ素とヨウ化カリウムを１：７の重量比で配合して得られたヨウ素水溶液）に、最終的に得られる偏光板の単体透過率（Ｔｓ）が４２．３％となるように濃度を調整しながら６０秒間浸漬させた（染色処理）。
　次いで、液温４０℃の架橋浴（水１００重量部に対して、ヨウ化カリウムを３重量部配合し、ホウ酸を５重量部配合して得られたホウ酸水溶液）に３０秒間浸漬させた（架橋処理）。
　その後、積層体を、液温７０℃のホウ酸水溶液（ホウ酸濃度４重量％、ヨウ化カリウム濃度５重量％）に浸漬させながら、周速の異なるロール間で縦方向（長手方向）に総延伸倍率が５．５倍となるように一軸延伸を行った（水中延伸処理）。
　その後、積層体を液温２０℃の洗浄浴（水１００重量部に対して、ヨウ化カリウムを４重量部配合して得られた水溶液）に浸漬させた（洗浄処理）。
　その後、約９０℃に保たれたオーブン中で乾燥しながら、表面温度が約７５℃に保たれたＳＵＳ製の加熱ロールに接触させた（乾燥収縮処理）。乾燥収縮処理による積層体の幅方向の収縮率は２％であった。
　このようにして、樹脂基材上に水分率が４．５重量％であり、厚み５μｍの偏光膜（一次偏光膜）を形成し、一次偏光膜の表面にシクロオレフィン系フィルム（日本ゼオン社製、Ｚｅｏｎｏｒ、厚み：２５μｍ）をＵＶ硬化型接着剤（厚み１．０μｍ）により貼り合わせ、その後、樹脂基材を剥離して［一次偏光膜／保護層］の構成を有する偏光板（処理前）を得た。 [Example 2-1]
A long amorphous isophthalic copolymerized polyethylene terephthalate film (thickness: 100 μm) having a Tg of about 75° C. was used as the thermoplastic resin substrate, and one side of the resin substrate was subjected to corona treatment.
Polyvinyl alcohol (degree of polymerization: 4,200, degree of saponification: 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOSEFIMER") were mixed at a ratio of 9:1, and 100 parts by weight of PVA-based resin. was added with 13 parts by weight of potassium iodide and dissolved in water to prepare an aqueous PVA solution (coating solution).
The above PVA aqueous solution was applied to the corona-treated surface of the resin base material and dried at 60° C. to form a PVA-based resin layer having a thickness of 13 μm, thereby producing a laminate.
The resulting laminate was uniaxially stretched 2.4 times in the machine direction (longitudinal direction) in an oven at 130° C. (in-air auxiliary stretching treatment).
Next, the laminate was immersed in an insolubilizing bath (an aqueous boric acid solution obtained by mixing 4 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40° C. for 30 seconds (insolubilizing treatment).
Next, the finally obtained polarizing plate was placed in a dyeing bath (iodine aqueous solution obtained by blending iodine and potassium iodide at a weight ratio of 1:7 with respect to 100 parts by weight of water) at a liquid temperature of 30 ° C. It was immersed for 60 seconds while adjusting the concentration so that the single transmittance (Ts) was 42.3% (dyeing treatment).
Next, it was immersed for 30 seconds in a cross-linking bath at a liquid temperature of 40°C (an aqueous solution of boric acid obtained by blending 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with respect to 100 parts by weight of water). (crosslinking treatment).
After that, while immersing the laminate in an aqueous solution of boric acid (boric acid concentration: 4% by weight, potassium iodide concentration: 5% by weight) at a liquid temperature of 70° C., the laminate was moved vertically (longitudinally) between rolls with different peripheral speeds. Uniaxial stretching was performed so that the stretching ratio was 5.5 times (underwater stretching treatment).
After that, the laminate was immersed in a washing bath (aqueous solution obtained by blending 4 parts by weight of potassium iodide with 100 parts by weight of water) at a liquid temperature of 20° C. (washing treatment).
Thereafter, while drying in an oven maintained at about 90° C., it was brought into contact with a heating roll made of SUS whose surface temperature was maintained at about 75° C. (dry shrinkage treatment). The shrinkage rate in the width direction of the laminate due to the drying shrinkage treatment was 2%.
In this way, a polarizing film (primary polarizing film) having a moisture content of 4.5% by weight and a thickness of 5 μm is formed on the resin substrate, and a cycloolefin film (manufactured by Nippon Zeon Co., Ltd.) is formed on the surface of the primary polarizing film. , Zeonor, thickness: 25 μm) are laminated with a UV-curable adhesive (thickness: 1.0 μm), and then the resin substrate is peeled off to form a [primary polarizing film/protective layer] polarizing plate (before treatment) got
　上記偏光板（処理前）を１００ｍｍ×１００ｍｍサイズに切断し、アクリル系粘着剤層（厚み１５μｍ）を介して一次偏光膜側表面が露出面となるようにガラス板に貼り合わせた状態で５０℃の水中に９分間浸漬した。次いで、５０℃で５分乾燥することにより、［二次偏光膜／保護層］の構成を有する偏光板（処理後）を得た。 The above polarizing plate (before treatment) was cut into a size of 100 mm × 100 mm and attached to a glass plate so that the surface on the primary polarizing film side became an exposed surface via an acrylic pressure-sensitive adhesive layer (thickness 15 μm). of water for 9 minutes. Then, by drying at 50° C. for 5 minutes, a polarizing plate (after treatment) having a configuration of [secondary polarizing film/protective layer] was obtained.
［実施例２－２］
　５０℃の水中に９分間浸漬する代わりに、５５℃の水に３分間浸漬したこと以外は実施例２－１と同様にして、［二次偏光膜／保護層］の構成を有する偏光板（処理後）を得た。 [Example 2-2]
A polarizing plate having a [secondary polarizing film/protective layer] configuration ( after treatment).
［実施例２－３］
　５０℃の水中に９分間浸漬する代わりに、６０℃の水に１分間浸漬したこと以外は実施例２－１と同様にして、［二次偏光膜／保護層］の構成を有する偏光板（処理後）を得た。 [Example 2-3]
A polarizing plate having a [secondary polarizing film/protective layer] configuration ( after treatment).
［実施例２－４］
　５０℃の水中に９分間浸漬する代わりに、６０℃の水に２分間浸漬したこと以外は実施例２－１と同様にして、［二次偏光膜／保護層］の構成を有する偏光板（処理後）を得た。 [Example 2-4]
A polarizing plate having a [secondary polarizing film/protective layer] configuration ( after treatment).
［実施例２－５］
　５０℃の水中に９分間浸漬する代わりに、６０℃の水に３分間浸漬したこと以外は実施例２－１と同様にして、［二次偏光膜／保護層］の構成を有する偏光板（処理後）を得た。 [Example 2-5]
A polarizing plate having a [secondary polarizing film/protective layer] configuration ( after treatment).
［実施例３－１］
　染色浴のヨウ素濃度を変更し、得られる偏光膜の透過率が４４．３％となるように調整したこと以外は実施例２－１と同様にして、［一次偏光膜／保護層］の構成を有する偏光板（処理前）を得た。得られた一次偏光膜の水分率は４．５重量％であった。 [Example 3-1]
Configuration of [primary polarizing film/protective layer] in the same manner as in Example 2-1 except that the iodine concentration in the dyeing bath was changed and the transmittance of the resulting polarizing film was adjusted to 44.3%. A polarizing plate (before treatment) having was obtained. The obtained primary polarizing film had a moisture content of 4.5% by weight.
　上記偏光板（処理前）を１００ｍｍ×１００ｍｍサイズに切断し、、アクリル系粘着剤層（厚み１５μｍ）を介して一次偏光膜側表面が露出面となるようにガラス板に貼り合わせた状態で５０℃の水中に６分間浸漬した。次いで、５０℃で５分乾燥することにより、［二次偏光膜／保護層］の構成を有する偏光板（処理後）を得た。 The above polarizing plate (before treatment) was cut into a size of 100 mm × 100 mm, and attached to a glass plate so that the surface on the primary polarizing film side became an exposed surface via an acrylic pressure-sensitive adhesive layer (thickness: 15 µm). ℃ water for 6 minutes. Then, by drying at 50° C. for 5 minutes, a polarizing plate (after treatment) having a configuration of [secondary polarizing film/protective layer] was obtained.
［実施例３－２］
　５０℃の水中に６分間浸漬する代わりに、５５℃の水に３分間浸漬したこと以外は実施例３－１と同様にして、［二次偏光膜／保護層］の構成を有する偏光板（処理後）を得た。 [Example 3-2]
A polarizing plate having a configuration of [secondary polarizing film/protective layer] in the same manner as in Example 3-1 except that it was immersed in water at 55 ° C. for 3 minutes instead of immersing in water at 50 ° C. for 6 minutes ( after treatment).
　上記実施例で得られた偏光板（処理前）および偏光板（処理後）について透過率および偏光度を測定した。結果を表１に示す。
Figure JPOXMLDOC01-appb-T000001
 The transmittance and degree of polarization of the polarizing plate (before treatment) and the polarizing plate (after treatment) obtained in the above examples were measured. Table 1 shows the results.
Figure JPOXMLDOC01-appb-T000001
　表１から明らかなように、実施例の製造方法によれば、保護層が積層されて偏光板を作製した後に偏光膜の透過率を変化させることができる。 As is clear from Table 1, according to the manufacturing method of the example, the transmittance of the polarizing film can be changed after the protective layer is laminated to manufacture the polarizing plate.
　本発明の偏光板の製造方法は、画像表示装置の製造において好適に用いられる。 The method for producing a polarizing plate of the present invention is suitably used in the production of image display devices.
　１０　　　偏光膜
　２０　　　保護層
　３０　　　位相差層
　４０　　　粘着剤層
１００　　　偏光板 REFERENCE SIGNS LIST 10 polarizing film 20 protective layer 30 retardation layer 40 adhesive layer 100 polarizing plate

Claims (8)

  1. 　ポリビニルアルコール系樹脂膜を染色処理およびホウ酸水溶液中での延伸処理に供した後に、水分率が１５重量％以下となるまで乾燥させて、一次偏光膜を得る工程、および
    　該一次偏光膜の表面に水性溶媒を接触させることにより、透過率を変化させて、二次偏光膜を得る工程、
    　を、この順に含む、偏光板の製造方法。     A step of obtaining a primary polarizing film by subjecting a polyvinyl alcohol-based resin film to dyeing treatment and stretching treatment in an aqueous boric acid solution, followed by drying to a moisture content of 15% by weight or less, and the surface of the primary polarizing film. contacting an aqueous solvent to change the transmittance to obtain a secondary polarizing film;
    , in this order.
  2. 　一方の面が露出しており、他方の面が保護されている状態の前記一次偏光膜の露出面に前記水性溶媒を接触させる、請求項１に記載の偏光板の製造方法。 The method for producing a polarizing plate according to claim 1, wherein the aqueous solvent is brought into contact with the exposed surface of the primary polarizing film in which one surface is exposed and the other surface is protected.
  3. 　前記一次偏光膜を得る工程が、ハロゲン化物とポリビニルアルコール系樹脂とを含むポリビニルアルコール系樹脂膜を、長尺状の熱可塑性樹脂基材との積層体の状態で、空中補助延伸処理、染色処理、ホウ酸水溶液中での延伸処理および乾燥収縮処理にこの順に供することを含み、
    　該乾燥収縮処理が、該積層体を長手方向に搬送しながら加熱することにより、幅方向に２％以上収縮させるとともに該ポリビニルアルコール系樹脂膜の水分率が１５重量％以下となるまで乾燥させることを含む、請求項１または２に記載の偏光板の製造方法。     In the step of obtaining the primary polarizing film, a polyvinyl alcohol-based resin film containing a halide and a polyvinyl alcohol-based resin is laminated with a long thermoplastic resin substrate, and then subjected to auxiliary stretching in the air and dyeing. , subjecting it to stretching treatment in an aqueous boric acid solution and drying shrinkage treatment in this order,
    In the drying shrinkage treatment, the laminate is heated while being transported in the longitudinal direction, thereby shrinking in the width direction by 2% or more and drying until the moisture content of the polyvinyl alcohol resin film is 15% by weight or less. The method for producing a polarizing plate according to claim 1 or 2, comprising:
  4. 　前記ハロゲン化物がヨウ化物または塩化ナトリウムである、請求項３に記載の偏光板の製造方法。 The method for producing a polarizing plate according to claim 3, wherein the halide is iodide or sodium chloride.
  5. 　前記一次偏光膜の厚みが１２μｍ以下である、請求項１から４のいずれかに記載の偏光板の製造方法。 The method for manufacturing a polarizing plate according to any one of claims 1 to 4, wherein the primary polarizing film has a thickness of 12 µm or less.
  6. 　二色性物質を含むポリビニルアルコール系樹脂膜で構成され、水分率が１５重量％以下である偏光膜と、保護層と、粘着剤層とをこの順に含む偏光板を、該粘着剤を介して画像表示セルに積層して、該偏光膜の該保護層が配置された側と反対側の表面を露出面とする工程、および
    　該偏光膜の露出面に水性溶媒を接触させて透過率を変化させる工程、
    　をこの順で含む、画像表示装置の製造方法。     A polarizing plate composed of a polyvinyl alcohol-based resin film containing a dichroic substance and containing, in this order, a polarizing film having a moisture content of 15% by weight or less, a protective layer, and an adhesive layer is attached via the adhesive. lamination on an image display cell to expose the surface of the polarizing film opposite to the side on which the protective layer is arranged; and contacting the exposed surface of the polarizing film with an aqueous solvent to change the transmittance. the process of causing
    in this order.
  7. 　前記画像表示装置が、液晶表示装置または有機ＥＬ表示装置である、請求項６に記載の画像表示装置の製造方法。 The method for manufacturing an image display device according to claim 6, wherein the image display device is a liquid crystal display device or an organic EL display device.
  8. 　二色性物質を含むポリビニルアルコール系樹脂膜で構成され、水分率が１５重量％以下である偏光膜の表面に水性溶媒を接触させる工程を含む、偏光膜の透過率の調整方法。 A method for adjusting the transmittance of a polarizing film, comprising a step of bringing an aqueous solvent into contact with the surface of a polarizing film composed of a polyvinyl alcohol resin film containing a dichroic substance and having a moisture content of 15% by weight or less.
PCT/JP2021/041182 2021-01-22 2021-11-09 Polarizing plate manufacturing method, image display device manufacturing method, and method for adjusting transmittance of polarizing film WO2022158088A1 (en)

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WO2019235107A1 (en) * 2018-06-07 2019-12-12 日東電工株式会社 Polarizing film and polarizing plate with retardation layer
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WO2019235107A1 (en) * 2018-06-07 2019-12-12 日東電工株式会社 Polarizing film and polarizing plate with retardation layer
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