JP2017161940A - Method of manufacturing polarizing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a polarizing plate having little surface irregularities with no loss in production efficiency even when using a thin transparent protection film for adhering to each surface of a polarizing film using an epoxy adhesive.SOLUTION: A method of manufacturing a polarizing plate involving adhesion of a transparent protection film on each surface of a polyvinyl alcohol polarizing film includes: a composite protection film producing step for producing a composite protection film by adhering a surface protection film on one surface of each transparent protection film to be adhered onto each surface of the polarizing film; an adhesion step for adhering a surface opposite to the surface protection film of the composite protection film obtained in the composite protection film producing step onto each surface of the polarizing film using an epoxy adhesive containing an active energy ray curable or heat curable epoxy compound; and a curing step for curing the epoxy adhesive to be performed in the described order.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a polarizing plate suitably used for a liquid crystal display device.

  Liquid crystal display devices are used in various display devices by taking advantage of features such as low power consumption, operation at a low voltage, light weight and thinness. The liquid crystal display device is composed of many optical members such as a liquid crystal cell, a polarizing plate, a retardation film, a light collecting sheet, a diffusion film, a light guide plate, and a light reflecting sheet. Therefore, it is possible to improve the production efficiency and brightness of the liquid crystal display device, and further reduce the weight and thickness by improving the number of films or sheets constituting these optical members and reducing the film thickness. Such research is actively conducted.

Polarizers are widely used as polarized light supply and detection elements in liquid crystal display devices.
Generally, a polarizing plate is a liquid crystal display in a form in which a transparent protective film having optical characteristics is bonded to a polarizing film in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol resin, depending on the display mode and required characteristics. Often used in equipment.

  With the improvement of the display quality of liquid crystal display devices, there is an increasing demand for the appearance quality of polarizing plates, and proposals have been made to improve the surface appearance. For example, in JP 2008-89725 A (Patent Document 1), when a transparent protective film is bonded to a polarizing film, in order to avoid a surface defect (referred to as a “knic defect” in the same document) due to contamination of foreign matters, A technique is disclosed in which a surface protective film is bonded in advance to one surface of a transparent protective film to form a laminated film, and the transparent protective film side of the laminated film is bonded to a polarizing film. In this document, a polyvinyl alcohol adhesive, specifically, an adhesive made of an aqueous solution of a polyvinyl alcohol resin is used for laminating the polarizing film and the transparent protective film, and the surface protective film is provided on one side of the transparent protective film. The upper adhesive is applied to the opposite side of the laminated film to the surface protective film, and two laminated films (transparent protective film) are bonded to both sides of the polarizing film via the adhesive. However, when a laminated film in which a surface protective film is bonded to one side of a transparent protective film is bonded to both surfaces of a polarizing film via an adhesive made of an aqueous solution of a polyvinyl alcohol resin, subsequent drying of the adhesive is difficult. There were problems such as becoming.

  On the other hand, with the widespread use of liquid crystal display devices, improvement in production efficiency of polarizing plates is also required. Therefore, for the purpose of shortening the bonding time between the polarizing film and the transparent protective film, a technique using an epoxy-based adhesive containing an epoxy compound that is cured by irradiation with active energy rays or heating is also used as an adhesive for bonding the both. Are known. For example, in Japanese Patent Application Laid-Open No. 2004-245925 (Patent Document 2), a transparent protective film is pasted on a polyvinyl alcohol polarizing film via an adhesive composed of an epoxy compound containing no aromatic ring as a main component. In other words, a technique for forming a polarizing plate is disclosed. JP-A-2009-251284 (Patent Document 3) discloses an epoxy adhesive containing an epoxy compound that cures a polarizing film and a retardation film made of an olefin resin by irradiation with active energy rays or heating. A technique of using and laminating is disclosed. JP 2010-139703 (Patent Document 4) includes a core layer made of a styrene resin and a skin layer made of a (meth) acrylic resin composition containing rubber particles laminated on both surfaces thereof. A technique is disclosed in which a polarizing film is bonded to a retardation film having a three-layer structure by using an epoxy adhesive containing an epoxy compound that is cured by irradiation with active energy rays or heating.

  By using such an epoxy adhesive, a drying step is not necessary, and the production efficiency of the polarizing plate can be increased. However, with the thinning of the transparent protective film, when using a transparent protective film having a thickness of 50 μm or less, such a thin transparent protective film is bonded to the polarizing film using an epoxy adhesive, Nonuniform surface irregularities may remain on the polarizing plate after the adhesive is cured, resulting in poor appearance.

  In particular, when a polyvinyl alcohol resin aqueous solution is used as an adhesive, and it is attached to a polarizing film, even if it is a transparent protective film with a thickness that does not cause a problem, an epoxy curable adhesive is used. When pasted together, there was a case where a remarkable appearance defect occurred.

JP 2008-89725 A JP 2004-245925 A JP 2009-251284 A JP 2010-139703 A

  An object of the present invention is to provide a method for producing a polarizing plate in which surface unevenness hardly remains without impairing production efficiency even when a thin transparent protective film is used.

  The inventor made a composite protective film by preliminarily attaching a surface protective film to one side of the transparent protective film to be bonded to the polarizing film, and manufacturing a polarizing plate using this composite protective film. Even when the thickness is as thin as 50 μm or less, it has been found that unevenness hardly remains on the surface of the obtained polarizing plate, and the present invention has been completed.

  That is, according to the present invention, there is provided a method for producing a polarizing plate by laminating a transparent protective film on both surfaces of a polarizing film having a dichroic dye adsorbed and oriented on a polyvinyl alcohol resin; Protective film compounding step for producing a composite protective film by bonding a surface protective film on one side to each of the transparent protective films bonded on both sides; each composite protective film obtained in the above protective film combining step A bonding step of bonding the surface opposite to the surface protective film to both surfaces of the polarizing film via an epoxy adhesive containing an epoxy compound that is cured by irradiation with active energy rays or heating; and There is provided a method for producing a polarizing plate comprising a curing step for curing an epoxy adhesive in this order.

  The protective film composite step is preferably performed so that the resultant composite protective film has a thickness of 40 μm or more and 150 μm or less. Moreover, it is preferable that the epoxy-type adhesive agent used at said bonding process contains the epoxy compound which has at least one epoxy group couple | bonded with the alicyclic ring in a molecule | numerator.

  These methods can be applied even when the transparent protective film bonded to both surfaces of the polarizing film is composed of the same resin, but is also effective when composed of different resins. For example, when the transparent protective film bonded to one surface of the polarizing film is made of a cellulose-based resin and the transparent protective film bonded to the other surface of the polarizing film is formed of a cyclic olefin-based resin Also, it can be applied effectively.

  According to this invention, even if the transparent protective film bonded on both surfaces of a polarizing film becomes thin, a polarizing plate with few surface unevenness | corrugations can be produced efficiently.

  The present invention provides a method for bonding a polarizing film and a transparent protective film using an epoxy adhesive containing an epoxy compound that is cured by irradiation with active energy rays or heating in order to improve the production efficiency of a polarizing plate. Adopting a surface protective film on the transparent protective film in advance for the problem that unevenness tends to remain on the surface of the produced polarizing plate with the thinning of the transparent protective film to be bonded to the polarizing film. Thus, the surface smoothness of the polarizing plate was successfully improved.

  Hereinafter, embodiments of the present invention will be described in detail. In this specification, a film that is directly bonded to a polarizing film having a dichroic dye adsorbed and oriented on a polyvinyl alcohol-based resin, protects the surface of the polarizing film, and is maintained as it is when used as a polarizing plate is “transparent”. A protective film is called a “protective film”, which is bonded to one side of the transparent protective film and serves to reinforce the transparent protective film when bonded to a polarizing film. And distinguish between the two. First, each member constituting the polarizing plate will be described, and then each step constituting the polarizing plate manufacturing method will be described.

[Each member constituting polarizing plate]
<Polarized film>
The polarizing film is usually a step of uniaxially stretching a polyvinyl alcohol resin film by a known method, a step of adsorbing a dichroic dye by dyeing the polyvinyl alcohol resin film with a dichroic dye, dichroism The polyvinyl alcohol resin film on which the dye is adsorbed is produced through a step of treating with a boric acid aqueous solution and a step of washing with water after the treatment with the boric acid aqueous solution.

  As the polyvinyl alcohol resin, a saponified polyvinyl acetate resin can be used. The polyvinyl acetate resin may be a copolymer with other monomers copolymerizable with vinyl acetate, in addition to polyvinyl acetate, which is a homopolymer of vinyl acetate. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and acrylamides having an ammonium group.

  The saponification degree of the polyvinyl alcohol resin is usually about 85 to 100 mol%, preferably 98 mol% or more. This polyvinyl alcohol-based resin may be modified, and for example, polyvinyl formal and polyvinyl acetal modified with aldehydes can also be used. The degree of polymerization of the polyvinyl alcohol resin is usually about 1,000 to 10,000, preferably 1,500 or more, and preferably 5,000 or less.

  What formed such a polyvinyl alcohol-type resin into a film is used as a raw film of a polarizing film. The method for forming a polyvinyl alcohol-based resin is not particularly limited, and can be formed by a known method. The film thickness of the polyvinyl alcohol-based raw film is not particularly limited, but is, for example, about 10 to 150 μm.

  Uniaxial stretching of the polyvinyl alcohol-based resin film can be performed before dyeing with the dichroic dye, simultaneously with dyeing, or after dyeing. When uniaxial stretching is performed after dyeing, this uniaxial stretching may be performed before boric acid treatment or during boric acid treatment. Moreover, you may uniaxially stretch in these several steps.

  In uniaxial stretching, it may be uniaxially stretched between rolls having different peripheral speeds, or may be uniaxially stretched using a hot roll. The uniaxial stretching may be dry stretching in which stretching is performed in the air, or may be wet stretching in which stretching is performed in a state where a polyvinyl alcohol-based resin film is swollen using a solvent. The draw ratio is usually about 3 to 8 times.

The polyvinyl alcohol resin film can be dyed with the dichroic dye by, for example, a method of immersing the polyvinyl alcohol resin film in an aqueous solution containing the dichroic dye. Specifically, iodine or a dichroic organic dye is used as the dichroic dye.
In addition, it is preferable that the polyvinyl alcohol-type resin film performs the immersion process to water before a dyeing process.

When iodine is used as the dichroic dye, a method of dyeing a polyvinyl alcohol-based resin film in an aqueous solution containing iodine and potassium iodide is usually employed.
The content of iodine in this aqueous solution is usually about 0.01 to 1 part by weight per 100 parts by weight of water. The content of potassium iodide is usually about 0.5 to 20 parts by weight per 100 parts by weight of water. The temperature of the aqueous solution used for dyeing is usually about 20 to 40 ° C. The immersion time (dyeing time) in this aqueous solution is usually about 20 to 1,800 seconds.

On the other hand, when a dichroic organic dye is used as the dichroic dye, a method of immersing and dyeing a polyvinyl alcohol-based resin film in an aqueous solution containing a water-soluble dichroic organic dye is usually employed. The content of the dichroic dye in this aqueous solution is usually about 1 × 10 ⁻⁴ to 10 parts by weight, preferably about 1 × 10 ⁻³ to 1 part by weight per 100 parts by weight of water. This aqueous solution may contain an inorganic salt such as sodium sulfate as a dyeing assistant. The temperature of the aqueous dye solution used for dyeing is usually about 20 to 80 ° C. The immersion time (dyeing time) in this aqueous solution is usually about 10 to 1,800 seconds.

  The boric acid treatment after dyeing with a dichroic dye can be usually performed by a method of immersing a dyed polyvinyl alcohol-based resin film in a boric acid-containing aqueous solution.

  The amount of boric acid in the boric acid-containing aqueous solution is usually about 2 to 15 parts by weight per 100 parts by weight of water, preferably 5 parts by weight or more, and preferably 12 parts by weight or less. When iodine is used as the dichroic dye, the boric acid-containing aqueous solution preferably contains potassium iodide. The amount of potassium iodide in the boric acid-containing aqueous solution is usually about 0.1 to 15 parts by weight, preferably 5 parts by weight or more and preferably 12 parts by weight or less per 100 parts by weight of water. The immersion time in the boric acid-containing aqueous solution is usually about 60 to 1,200 seconds, preferably 150 seconds or longer, more preferably 200 seconds or longer, and preferably 600 seconds or shorter, further 400 seconds or shorter. The temperature of the boric acid-containing aqueous solution is usually 50 ° C or higher, preferably 60 ° C or higher, more preferably 85 ° C or lower, and further 80 ° C or lower.

  The polyvinyl alcohol resin film after the boric acid treatment is usually washed with water. The water washing treatment can be performed, for example, by a method of immersing a boric acid-treated polyvinyl alcohol resin film in water. The temperature of water in the water washing treatment is usually about 5 to 40 ° C. The immersion time is usually about 1 to 120 seconds.

  After washing with water, a drying process is performed to obtain a polarizing film. The drying process can be performed using a hot air dryer or a far infrared heater. The temperature of the drying treatment is usually about 30 to 100 ° C, preferably 50 ° C or higher, and preferably 80 ° C or lower. The drying time is usually about 60 to 600 seconds, preferably 120 to 600 seconds.

  By the drying process, the moisture content of the polarizing film is reduced to a practical level. The moisture content is usually 5 to 20% by weight, preferably 8% by weight or more, and preferably 15% by weight or less. When the moisture content of the polarizing film is less than 5% by weight, flexibility is lost, and the polarizing film may be damaged or broken after drying. Moreover, when the moisture content exceeds 20 weight%, it may become inferior to thermal stability.

  Thus, the thickness of the polarizing film obtained by adsorbing and orienting the dichroic dye on the polyvinyl alcohol-based resin film can be set to about 5 to 40 μm, for example.

<Transparent protective film placed on both sides of the polarizing film>
The transparent protective film bonded to both surfaces of the polarizing film is preferably composed of a thermoplastic resin that is excellent in transparency, mechanical strength, thermal stability, moisture shielding properties, retardation value stability, and the like. Examples of the thermoplastic resin constituting such a transparent protective film include, for example, (meth) acrylic resins typically represented by methyl methacrylate resins, polyolefin resins typically represented by polypropylene resins, and cyclic olefin resins. , Polyvinyl chloride resin, cellulose resin, styrene resin, acrylonitrile / butadiene / styrene resin, acrylonitrile / styrene resin, polyvinyl acetate resin, polyvinylidene chloride resin, polyamide resin, polyacetal resin, polycarbonate Resin, modified polyphenylene ether resin, polyethylene terephthalate resin, polybutylene terephthalate resin, polysulfone resin, polyethersulfone resin, polyarylate resin, polyamideimide resin, polyimide resin, etc. And the like.

These resins can be used alone or in combination of two or more.
In addition, these resins can be used after any appropriate polymer modification. Examples of the polymer modification include copolymerization, crosslinking, molecular terminal, stereoregularity control, and reaction between different polymers. Modifications such as mixing including cases may be mentioned.

  The combination of the transparent protective films bonded to both surfaces of the polarizing film may be the same material on both surfaces, or may be a material with different surfaces. Among the resins exemplified above, transparent protective film materials include cyclic olefin resins, methyl methacrylate resins (meth) acrylic resins, polyethylene terephthalate resins, polypropylene resins, and cellulose resins. Is preferably used.

  Examples of cyclic olefin resins include resins obtained by ring-opening metathesis polymerization using cyclopentadiene and olefins by Diels-Alder reaction or a derivative thereof as a monomer, followed by hydrogenation, and dicyclopentadiene and olefin. Resins, norbornene, tetracyclododecene, and derivatives thereof obtained by performing ring-opening metathesis polymerization using tetracyclododecene or its derivative obtained from Diethyl-Alder reaction from monomers or methacrylates as monomers , Or other cyclic olefin monomers, and a resin obtained by carrying out ring-opening metathesis copolymerization and subsequent hydrogenation, norbornene, tetracyclododecene or derivatives thereof , And the like other polymerizable monomer and a resin obtained by copolymerizing by addition polymerization of such an aromatic compound having a vinyl group.

  The methyl methacrylate resin is a polymer containing 50% by weight or more of methyl methacrylate units. The content of methyl methacrylate units is preferably 70% by weight or more, and may be 100% by weight. A polymer having a methyl methacrylate unit of 100% by weight is a methyl methacrylate homopolymer obtained by polymerizing methyl methacrylate alone. A methyl methacrylate resin is usually polymerized by coexisting a monofunctional monomer mainly composed of methyl methacrylate, a radical polymerization initiator and a chain transfer agent in the presence of a polyfunctional monomer as necessary. By doing it.

  Monofunctional monomers that can be copolymerized with methyl methacrylate include, for example, ethyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, benzyl methacrylate, 2-ethylhexyl methacrylate, and 2-hydroxy methacrylate. Methacrylic esters other than methyl methacrylate such as ethyl; methyl acrylate, ethyl acrylate, butyl acrylate, cyclohexyl acrylate, phenyl acrylate, benzyl acrylate, 2-ethylhexyl acrylate, and 2-hydroxy acrylate Acrylic esters such as ethyl; methyl 2- (hydroxymethyl) acrylate, methyl 2- (2-hydroxyethyl) acrylate, ethyl 2- (hydroxymethyl) acrylate, and 2- (hydroxymethyl) ) 2- (hydroxyalkyl) acrylic esters such as butyl acrylate; unsaturated acids such as acrylic acid and methacrylic acid; styrene; halogenated styrenes such as chlorostyrene and bromostyrene; vinyltoluene and α- Alkyl-substituted styrenes such as methylstyrene; unsaturated nitriles such as acrylonitrile and methacrylonitrile; unsaturated acid anhydrides such as maleic anhydride and citraconic anhydride; unsaturated imides such as phenylmaleimide and cyclohexylmaleimide And the like. These monomers to be copolymerized may be used alone or in combination of two or more.

  Examples of polyfunctional monomers that can be copolymerized with methyl methacrylate include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, and tetraethylene glycol di (meth) acrylate. , Nonaethylene glycol di (meth) acrylate, and tetradecaethylene glycol di (meth) acrylate, which are esterified with acrylic acid or methacrylic acid at both terminal hydroxyl groups of ethylene glycol or an oligomer thereof; propylene glycol or an oligomer thereof Esterified with both hydroxyl groups of acrylic acid or methacrylic acid; neopentyl glycol di (meth) acrylate, hexanediol di (meth) acrylate, and butanediol di (meth) ) A hydroxyl group of a dihydric alcohol such as acrylate esterified with acrylic acid or methacrylic acid; Bisphenol A, an alkylene oxide adduct of bisphenol A, or both terminal hydroxyl groups of these halogen-substituted products with acrylic acid or methacrylic acid Esterified with polyhydric alcohols such as trimethylolpropane and pentaerythritol with acrylic acid or methacrylic acid; ring opening addition of epoxy groups of glycidyl acrylate or glycidyl methacrylate to the terminal hydroxyl groups of these polyhydric alcohols Dibasic acids such as succinic acid, adipic acid, phthalic acid, terephthalic acid, and their halogen substitution products, or alkylene oxide adducts of these dibasic acids with glycidyl acrylate or glycidyl meta The epoxy groups of relations that were ring-opening addition; like dialkenyl compounds such as divinylbenzene; (meth) acrylic acid allyl. When copolymerizing a polyfunctional monomer, among them, ethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, and neopentyl glycol di (meth) acrylate are preferably used.

  The methyl methacrylate resin may be further modified by a reaction between copolymerized functional groups. As the reaction, for example, demethanol condensation reaction in the polymer chain between the methyl ester site of methyl acrylate and the hydroxyl group of 2- (hydroxymethyl) methyl acrylate, or the carboxyl group of acrylic acid and 2- (hydroxy) Methyl) and intramolecular dehydration condensation reaction between hydroxyl groups of methyl acrylate.

  The polyethylene terephthalate resin means a resin in which 80 mol% or more of repeating units are composed of ethylene terephthalate, and may contain other dicarboxylic acid components or other diol components. Examples of other dicarboxylic acid components include isophthalic acid, 4,4′-dicarboxydiphenyl, 4,4′-dicarboxybenzophenone, bis (4-carboxyphenyl) ethane, adipic acid, sebacic acid, 1,4 -Dicarboxycyclohexane etc. are mentioned. Examples of other diol components include propylene glycol, butanediol, neopentyl glycol, diethylene glycol, cyclohexanediol, ethylene oxide adduct of bisphenol A, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and the like. These dicarboxylic acid components and diol components can be used in combination of two or more if necessary.

  Further, a hydroxycarboxylic acid such as p-hydroxybenzoic acid or p-β-hydroxyethoxybenzoic acid can be used in combination. Further, a small amount of a dicarboxylic acid component or a diol component having an amide bond, a urethane bond, an ether bond, or a carbonate bond may be copolymerized.

  Polyethylene terephthalate resin is a method of directly polycondensing terephthalic acid and ethylene glycol (and other dicarboxylic acids or other diols as required), dialkyl esters of terephthalic acid and ethylene glycol (and other dicarboxylic acids as needed). A method in which a dialkyl ester of an acid or other diol) is subjected to a transesterification reaction and then polycondensation, an ethylene glycol ester of terephthalic acid (and other dicarboxylic acid if necessary) (and another diol ester if necessary) Is produced by a polycondensation in the presence of a catalyst. In addition, if necessary, solid-state polymerization can be performed to improve the molecular weight or reduce the low molecular weight component.

  Polypropylene resin is obtained by polymerizing a chain olefin monomer in which 80% by weight or more of a repeating unit is propylene among chain olefin resins using a polymerization catalyst. Among them, a homopolymer of propylene and a copolymer obtained by copolymerizing propylene as a main component and a comonomer copolymerizable therewith at a rate of 1 to 20% by weight, particularly at a rate of 3 to 10% by weight. Among propylene homopolymers, propylene homopolymers having a component (CXS (cold xylene soluble) component) soluble in xylene at 20 ° C. of 1% by weight or less are more preferred, and the CXS component is 0.5% or less. More preferred.

  When a propylene copolymer is used, ethylene, 1-butene, and 1-hexene are preferred as comonomers copolymerizable with propylene. Especially, since it is comparatively excellent in transparency, what copolymerized ethylene in the ratio of 3 to 10 weight% is preferable. By setting the copolymerization ratio of ethylene to 1% by weight or more, an effect of increasing transparency appears. On the other hand, when the ratio exceeds 20% by weight, the melting point of the resin is lowered, and the heat resistance required for the transparent protective film may be impaired.

  In the cellulose resin, part or all of the hydrogen atoms in the hydroxyl group of cellulose obtained from raw material cellulose such as cotton linter and wood pulp (hardwood pulp, conifer pulp) is substituted with an acetyl group, a propionyl group and / or a butyryl group. It is a cellulose organic acid ester or a cellulose mixed organic acid ester. Examples thereof include cellulose acetate, propionate, butyrate, and mixed esters thereof. Among them, preferred are triacetyl cellulose, diacetyl cellulose, cellulose acetate propionate, cellulose acetate butyrate and the like.

The above-described cyclic olefin-based resin, methyl methacrylate-based resin, polyethylene terephthalate-based resin, polypropylene-based resin, or cellulose-based resin can be formed into a transparent protective film that is bonded to the polarizing film. As the film forming method, a method corresponding to each resin may be appropriately selected. For example, a solvent cast method in which a resin dissolved in a solvent is cast onto a metal band or drum, and the solvent is removed by drying to obtain a film. The resin is heated above its melting temperature, melt kneaded and extruded from a die. A melt extrusion method for obtaining a film by cooling is suitably employed. In the melt extrusion method, it can be extruded as a single layer film or a multilayer film can be extruded simultaneously. The latter is also called coextrusion.
Moreover, in order to give a predetermined characteristic, these transparent protective films may be extended | stretched.

  These resins can be easily obtained as commercial products. For example, cyclic olefin resins are manufactured under the trade name TOPAS ADVANCED POLYMERS GmbH and sold in Japan from Polyplastics Co., Ltd. "TOPAS", "Arton" sold by JSR Corporation, "ZEONOR" and "ZEONEX" sold by ZEON Corporation, "APEL" sold by Mitsui Chemicals, Inc. "and so on. Methyl methacrylate resins are sold under the trade name “Sumipex” sold by Sumitomo Chemical Co., Ltd., “Acrypet” sold by Mitsubishi Rayon Co., Ltd., and Asahi Kasei Co., Ltd. "Delpet", "Parapet" sold by Kuraray Co., Ltd., "Acryviewer" sold by Nippon Shokubai Co., Ltd.

  Films made of these resins are also on sale. Among the above cyclic olefin resins, JSR's “Arton” is the product name of “Arton Film”, and Nippon Zeon's “ “Zeonoa” is also sold under the trade name “Zeonoa Film”. In addition, for polyethylene terephthalate resin films, there are "Novaclear" sold by Mitsubishi Chemical Corporation and "Teijin A-PET Sheet" sold by Teijin Chemicals Ltd., respectively. For polypropylene resin films, “FILMAX CPP film” sold by FILMAX, “Santox” sold by Sun Tox Co., Ltd. "Tosero", "Toyobo Pyrene Film" sold by Toyobo Co., Ltd., "Trephan" sold by Toray Film Processing Co., Ltd., "Nihon Polyace" sold by Nippon Polyace Co., Ltd. "Dazai FC" sold by Futamura Chemical Co., Ltd. For cellulosic resin films, there are “Fujitac TD” series sold by Fuji Film Co., Ltd. and “Konica Minolta TAC Film KC” series sold by Konica Minolta Advanced Layer Co., Ltd. .

  An antiglare property (haze) can also be imparted to the transparent protective film. As a method for imparting antiglare properties, for example, a method in which inorganic or organic fine particles are mixed into a raw material resin to form a film, a multilayer extrusion method (coextrusion method), and a resin in which fine particles are mixed on one side And a method of forming a two-layer film from a resin not mixed with fine particles on the other side, or forming a three-layer film with a resin mixed with fine particles outside, and inorganic or organic fine particles are cured on one side of the film A method of coating a coating solution mixed with a functional binder resin and curing the binder resin to provide an antiglare layer can be employed.

  Examples of inorganic fine particles for imparting antiglare properties include silica, colloidal silica, alumina, alumina sol, aluminosilicate, alumina-silica composite oxide, kaolin, talc, mica, calcium carbonate, calcium phosphate, and the like. Examples of the organic fine particles include cross-linked polyacrylic acid particles, methyl methacrylate / styrene copolymer resin particles, cross-linked polystyrene particles, cross-linked polymethyl methacrylate particles, silicone resin particles, and polyimide particles.

  The transparent protective film to which the antiglare property is imparted preferably has a haze value in the range of 6 to 45%. If the haze value of the antiglare protective film is less than 6%, a sufficient antiglare effect may not appear. On the other hand, if the haze value exceeds 45%, the screen of the liquid crystal display device to which this film is applied may become white and the image quality may be deteriorated.

  The haze value is a value determined in accordance with JIS K7136: 2000 “Plastic—How to determine haze of transparent material”. An example of a commercially available haze / transmittance meter compliant with this standard is “HM-150” sold by Murakami Color Research Laboratory. In measuring the haze value, in order to prevent warping of the film, for example, a measurement sample in which the film surface is bonded to a glass substrate using an optically transparent adhesive so that the antiglare property-imparting surface becomes the surface. Is preferably used.

  On the transparent protective film, functional layers such as a conductive layer, a hard coat layer, and a low reflection layer can be further formed. A resin composition having these functions can also be selected as the binder resin used for imparting antiglare properties as described above.

  The transparent protective film is preferably subjected to easy adhesion treatment such as saponification treatment, corona treatment, and plasma treatment prior to bonding with the polarizing film.

  The transparent protective film preferably has a thickness of 1 to 50 μm, more preferably 10 μm or more, especially 20 μm or more, and more preferably 45 μm or less, particularly 40 μm or less. If the thickness is within this range, by sticking a surface protective film to be described later on one side, there is no inconvenience when pasting to the polarizing film through an adhesive, and the polarizing film is mechanically protected, Even when exposed to high temperature and high humidity, the polarizing film does not shrink and stable optical characteristics can be maintained.

<Surface protection film>
The surface protective film is usually composed of a transparent base resin film provided with a pressure-sensitive adhesive layer. As the transparent base resin film, for example, a film made of polyester such as polyethylene terephthalate or polyethylene naphthalate can be used.

  The pressure-sensitive adhesive used for the surface protective film is composed of a polymer such as acrylic, urethane, or rubber. Of these, acrylic pressure-sensitive adhesives are preferably used because of their excellent transparency. Acrylic adhesives are generally based on one or more acrylate esters, such as butyl acrylate, ethyl acrylate, isooctyl acrylate, or 2-ethylhexyl acrylate, to which a polar monomer is copolymerized. It is composed of the polymer made. Examples of polar monomers include (meth) acrylic acid, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, (meth) acrylamide, N, N-dimethylaminoethyl (meth) acrylate, and glycidyl. Examples thereof include monomers having a functional group such as a carboxyl group, a hydroxyl group, an amino group, and an epoxy group, such as (meth) acrylate. Moreover, crosslinking agents, such as a polyisocyanate compound, an epoxy compound, and an aziridine compound, are mix | blended with the adhesive.

[Production method of polarizing plate]
In the present invention, the polarizing plate is produced by laminating the transparent protective film described above on both sides of the polarizing film described above. Each transparent protective film is subjected to a protective film compounding step in which the surface protective film described above is bonded to one surface to prepare a composite protective film before being bonded to the polarizing film. Each composite protective film obtained in the protective film composite step contains an epoxy compound that cures the surface opposite to the surface protective film, that is, the surface on the transparent protective film side, by irradiation with active energy rays or heating. It is used for the bonding process which bonds together on both surfaces of a polarizing film through an epoxy adhesive. Then, a polarizing film and the transparent protective film arrange | positioned on both surfaces are adhere | attached through the hardening process which hardens the epoxy adhesive, and a polarizing plate is manufactured. The surface protective film bonded to the transparent protective film is usually peeled and removed after that, but the surface opposite to the adhesive layer provided for bonding to one surface protective film, particularly to other members such as liquid crystal cells. The protective film can be held as it is to protect the surface until use.

  Hereinafter, the protective film compositing step, the bonding step, and the curing step constituting the polarizing plate manufacturing method will be described in order.

<Protective film composite process>
In the protective film compounding step, a surface protective film is bonded to one side of each of the transparent protective films bonded to both sides of the polarizing film to produce a composite protective film. This step may be performed so that the surface protective film is bonded to one surface of the transparent protective film bonded to both surfaces of the polarizing film, and the method itself may be appropriately selected. Among them, the method of paying out the transparent protective film from the long roll, paying out the surface protective film from another long roll, aligning both the long side directions, and continuously bonding using a bonding roll, Since the composite protective film can be produced with high productivity, it is preferably employed.

  The composite protective film obtained in this step preferably has a thickness of 40 μm or more and 150 μm or less. More preferably, it is 70 μm or more and 120 μm or less. If the thickness is less than 40 μm, wrinkles may occur due to poor handling. If the thickness exceeds 150 μm, the film thickness difference between the films constituting the composite protective film becomes large and the film warps. Therefore, when the composite protective film and the polarizing film are bonded, air bubbles are easily generated between the layers. .

<Bonding process>
The composite protective film obtained in the protective film compounding step is an epoxy containing an epoxy compound that cures the surface opposite to each surface protective film, that is, the surface on the transparent protective film side, by irradiation with active energy rays or heating. It is used for the bonding process which bonds together on both surfaces of a polarizing film through a system adhesive. The epoxy compound constituting the adhesive has at least two epoxy groups in the molecule.

  The epoxy compound constituting the adhesive is preferably one that does not contain an aromatic ring in the molecule from the viewpoints of weather resistance, refractive index, cationic polymerization, and the like. Examples of epoxy compounds that do not contain an aromatic ring in the molecule include hydrogenated epoxy compounds, alicyclic epoxy compounds, and aliphatic epoxy compounds. Examples of the epoxy compound suitably used for the adhesive include, for example, Patent Documents 2 to 4 (JP 2004-245925 A, JP 2009-251284 A, and JP 2010-139703 A) described above in detail. Although described, an overview will be given here as well.

  The hydrogenated epoxy compound is a glycidyl compound obtained by subjecting an aromatic polyhydroxy compound, which is a raw material of an aromatic epoxy compound, to a nuclear hydrogenated polyhydroxy compound obtained by selectively performing a nuclear hydrogenation reaction in the presence of a catalyst and under pressure. It can be etherified. Examples of the aromatic polyhydroxy compound that is a raw material of the aromatic epoxy compound include bisphenols such as bisphenol A, bispheel F and bisphenol S; Type resins; polyfunctional compounds such as tetrahydroxydiphenylmethane, tetrahydroxybenzophenone and polyvinylphenol. A glycidyl ether can be obtained by performing a nuclear hydrogenation reaction on such an aromatic polyhydroxy compound and reacting the resulting hydrogenated polyhydroxy compound with epichlorohydrin. Suitable hydrogenated epoxy compounds include hydrogenated glycidyl ether of bisphenol A.

  An alicyclic epoxy compound is a compound having at least one epoxy group bonded to an alicyclic ring in the molecule. Here, the “epoxy group bonded to the alicyclic ring” means a bridging oxygen atom —O— in the structure represented by the following formula, wherein m is an integer of 2 to 5.

A compound in which one or more hydrogen atoms in (CH ₂ ) _m in this formula are removed and bonded to another chemical structure can be an alicyclic epoxy compound. Further, one or more hydrogen atoms in (CH ₂ ) _m forming the alicyclic ring may be appropriately substituted with a linear alkyl group such as a methyl group or an ethyl group. Among alicyclic epoxy compounds, an epoxy compound having an oxabicyclohexane ring (m = 3 in the above formula) or an oxabicycloheptane ring (m = 4 in the above formula) has excellent adhesion. It is preferably used from the indication. Specific examples of the alicyclic epoxy compound are listed below. Here, the compound names are given first, and then the chemical formulas corresponding to each are shown, and the same reference numerals are given to the compound names and the chemical formulas corresponding thereto.

A: 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate,
B: 3,4-epoxy-6-methylcyclohexylmethyl 3,4-epoxy-6-methylcyclohexanecarboxylate,
C: ethylene bis (3,4-epoxycyclohexanecarboxylate),
D: Bis (3,4-epoxycyclohexylmethyl) adipate,
E: bis (3,4-epoxy-6-methylcyclohexylmethyl) adipate,
F: diethylene glycol bis (3,4-epoxycyclohexyl methyl ether), G: ethylene glycol bis (3,4-epoxycyclohexyl methyl ether),
H: 2,3,14,15-diepoxy-7,11,18,21-tetraoxatrispiro [5.2.2.2.5.2] henicosane,
I: 3- (3,4-epoxycyclohexyl) -8,9-epoxy-1,5-dioxaspiro [5.5] undecane,
J: 4-vinylcyclohexene dioxide,
K: Limonene dioxide
L: bis (2,3-epoxycyclopentyl) ether,
M: Dicyclopentadiene dioxide and the like.

  The aliphatic epoxy compound can be a polyglycidyl ether of an aliphatic polyhydric alcohol or an alkylene oxide adduct thereof. More specifically, diglycidyl ether of propylene glycol; diglycidyl ether of 1,4-butanediol; diglycidyl ether of 1,6-hexanediol; triglycidyl ether of glycerin; triglycidyl ether of trimethylolpropane; ethylene Polyglycidyl ether of polyether polyol (for example, diglycidyl ether of polyethylene glycol) obtained by adding alkylene oxide (ethylene oxide or propylene oxide) to aliphatic polyhydric alcohol such as glycol, propylene glycol and glycerin It is done.

  An epoxy compound may be used individually by 1 type, and may use 2 or more types together. Among these, this epoxy compound preferably contains an alicyclic epoxy compound having at least one epoxy group bonded to the alicyclic ring in the molecule.

  The epoxy compound used in the adhesive has an epoxy equivalent usually in the range of 30 to 3,000 g / equivalent, but this epoxy equivalent is preferably 50 g / equivalent or more, and preferably 1,500 g / equivalent or less. . When the epoxy equivalent is less than 30 g / equivalent, there is a possibility that the flexibility of the polarizing plate obtained after curing is lowered or the adhesive strength is lowered. On the other hand, when the epoxy equivalent exceeds 3,000 g / equivalent, compatibility with other components contained in the adhesive may be lowered.

From the viewpoint of reactivity, cationic polymerization is preferably used as the curing reaction of the epoxy compound. For this purpose, the epoxy adhesive preferably contains a cationic polymerization initiator.
The cationic polymerization initiator generates a cationic species or a Lewis acid by irradiation or heating of active energy rays such as visible light, ultraviolet rays, X-rays, and electron beams, and starts an epoxy group polymerization reaction. Regardless of the type of cationic polymerization initiator, it is preferable from the viewpoint of workability that latency is imparted. Hereinafter, a cationic polymerization initiator that generates a cationic species or a Lewis acid by irradiation of active energy rays and initiates a polymerization reaction of an epoxy group is referred to as a “photo cationic polymerization initiator”, and generates a cationic species or a Lewis acid by heat. The cationic polymerization initiator that initiates the polymerization reaction of the epoxy group is referred to as “thermal cationic polymerization initiator”.

  The method of curing the adhesive by irradiation with active energy rays using a cationic photopolymerization initiator enables curing at room temperature, reducing the need to consider the heat resistance of the polarizing film or distortion due to expansion, and transparent protection This is advantageous because the film and the polarizing film can be bonded well. In addition, since the cationic photopolymerization initiator acts catalytically by light, it is excellent in storage stability and workability even when mixed with an epoxy compound.

  Examples of the photocationic polymerization initiator include aromatic diazonium salts; onium salts such as aromatic iodonium salts and aromatic sulfonium salts; iron-arene complexes.

Examples of the aromatic diazonium salt include the following compounds.
Benzenediazonium hexafluoroantimonate,
Benzenediazonium hexafluorophosphate,
Benzenediazonium hexafluoroborate, etc.

Examples of the aromatic iodonium salt include the following compounds.
Diphenyliodonium tetrakis (pentafluorophenyl) borate,
Diphenyliodonium hexafluorophosphate,
Diphenyliodonium hexafluoroantimonate,
Bis (4-nonylphenyl) iodonium hexafluorophosphate and the like.

Examples of the aromatic sulfonium salt include the following compounds.
Triphenylsulfonium hexafluorophosphate,
Triphenylsulfonium hexafluoroantimonate,
Triphenylsulfonium tetrakis (pentafluorophenyl) borate,
4,4'-bis (diphenylsulfonio) diphenyl sulfide bis (hexafluorophosphate),
4,4′-bis [di (β-hydroxyethoxy) phenylsulfonio] diphenyl sulfide bis (hexafluoroantimonate),
4,4′-bis [di (β-hydroxyethoxy) phenylsulfonio] diphenyl sulfide bis (hexafluorophosphate),
7- [di (p-toluyl) sulfonio] -2-isopropylthioxanthone hexafluoroantimonate,
7- [di (p-toluyl) sulfonio] -2-isopropylthioxanthone tetrakis (pentafluorophenyl) borate,
4-phenylcarbonyl-4'-diphenylsulfonio-diphenyl sulfide hexafluorophosphate,
4- (p-tert-butylphenylcarbonyl) -4'-diphenylsulfonio-diphenyl sulfide hexafluoroantimonate,
4- (p-tert-butylphenylcarbonyl) -4'-di (p-toluyl) sulfonio-diphenyl sulfide tetrakis (pentafluorophenyl) borate and the like.

Moreover, as an iron-arene complex, the following compounds are mentioned, for example.
Xylene-cyclopentadienyl iron (II) hexafluoroantimonate,
Cumene-cyclopentadienyl iron (II) hexafluorophosphate,
Xylene-cyclopentadienyl iron (II) tris (trifluoromethylsulfonyl) methanide.

These photocationic polymerization initiators can be easily obtained as commercial products. Examples of commercially available photo-cationic polymerization initiators are “Kayarad PCI-220” and “Kayarad PCI-620” sold by Nippon Kayaku Co., Ltd. and Union Carbide, respectively. "UVI-6990", "Adekaoptomer SP-150" and "Adekaoptomer SP-170" sold by ADEKA Corporation, "CI-5102" sold by Nippon Soda Co., Ltd. "," CIT-1370 "," CIT-1682 "," CIP-1866S "," CIP-2048S "and" CIP-2064S "," DPI-101 "and" DPI "sold by Midori Chemical Co., Ltd. -102 ”,
“DPI-103”, “DPI-105”, “MPI-103”, “MPI-105”, “BBI-101”, “BBI-102”,
“BBI-103”, “BBI-105”, “TPS-101”, “TPS-102”, “TPS-103”, “TPS-105”,
"MDS-103", "MDS-105", "DTS-102", "DTS-103", "PI-2074" sold by Rhodia, etc.

  These photocationic polymerization initiators may be used alone or in combination of two or more. Among these, aromatic sulfonium salts are particularly preferable since they have ultraviolet absorption characteristics even in a wavelength region of 300 nm or more, and thus can provide a cured product having excellent curability and good mechanical strength and adhesive strength. Used.

The compounding quantity of a photocationic polymerization initiator is 0.5-20 weight part normally with respect to 100 weight part of epoxy compounds, Preferably it is 1 weight part or more, Preferably, it is 15 weight part or less.
When the blending amount of the cationic photopolymerization initiator is less than 0.5 parts by weight with respect to 100 parts by weight of the epoxy compound, curing becomes insufficient and mechanical strength and adhesive strength tend to decrease. Moreover, when the compounding quantity of a photocationic polymerization initiator exceeds 20 weight part with respect to 100 weight part of epoxy compounds, the hygroscopic property of hardened | cured material will become high because the ionic substance in hardened | cured material will increase, and durability performance. May be reduced.

  When using a photocationic polymerization initiator, the epoxy adhesive may further contain a photosensitizer as necessary. By using a photosensitizer, the reactivity of cationic polymerization is improved, and the mechanical strength and adhesive strength of the cured product can be improved. Examples of the photosensitizer include carbonyl compounds, organic sulfur compounds, persulfides, redox compounds, azo and diazo compounds, halogen compounds, and photoreductive dyes.

  More specific examples of photosensitizers include benzoin derivatives such as benzoin methyl ether, benzoin isopropyl ether, and α, α-dimethoxy-α-phenylacetophenone; benzophenone, 2,4-dichlorobenzophenone, o- Benzophenone derivatives such as methyl benzoylbenzoate, 4,4'-bis (dimethylamino) benzophenone, and 4,4'-bis (diethylamino) benzophenone; thioxanthone derivatives such as 2-chlorothioxanthone and 2-isopropylthioxanthone; 2 Anthraquinone derivatives such as chloroanthraquinone and 2-methylanthraquinone; acridone derivatives such as N-methylacridone and N-butylacridone; other α, α-diethoxyacetophenone, benzyl, There are fluorenone, xanthone, uranyl compounds, halogen compounds and the like. These photosensitizers may be used alone or in combination of two or more. The photosensitizer is preferably contained within a range of 0.1 to 20 parts by weight with respect to 100 parts by weight of all solids constituting the epoxy adhesive.

  On the other hand, examples of the thermal cationic polymerization initiator include benzylsulfonium salt, thiophenium salt, thioranium salt, benzylammonium, pyridinium salt, hydrazinium salt, carboxylic acid ester, sulfonic acid ester, and amine imide. Commercially available products of these thermal cationic polymerization initiators can also be easily obtained. Examples of commercially available thermal cationic polymerization initiators are all trade names of “ADEKA OPTON CP77” and “ADEKA OPTON CP66” sold by ADEKA Co., Ltd., and sold by Nippon Soda Co., Ltd. There are "CI-2639" and "CI-2624", "Sun-Aid SI-60L", "Sun-Aid SI-80L" and "Sun-Aid SI-100L" sold by Sanshin Chemical Industry Co., Ltd.

  The epoxy compound constituting the adhesive may be cured by either photocationic polymerization or thermal cationic polymerization, or may be cured by combining photocationic polymerization and thermal cationic polymerization. In the latter case, it is preferable to use a photocationic polymerization initiator and a thermal cationic polymerization initiator in combination.

  The epoxy adhesive may further contain a compound that promotes cationic polymerization, such as oxetanes and polyols.

  Oxetanes are compounds having a 4-membered ring ether in the molecule. Specific examples include 3-ethyl-3-hydroxymethyloxetane and 1,4-bis [(3-ethyl-3-oxetanyl) methoxymethyl] benzene. , 3-ethyl-3- (phenoxymethyl) oxetane, bis [(3-ethyl-3-oxetanyl) methyl] ether, 3-ethyl-3- (2-ethylhexyloxymethyl) oxetane, phenol novolak oxetane, etc. be able to. These oxetanes can be easily obtained as commercial products. Examples of commercially available oxetanes are those sold by Toagosei Co., Ltd., “Aron Oxetane OXT-101”, “Aron Oxetane OXT-121”, “Aron Oxetane OXT-211” ”,“ Aron Oxetane OXT-221 ”,“ Aron Oxetane OXT-212 ”, etc. These oxetanes are usually contained in a proportion of 5 to 95% by weight, preferably 30% by weight or more, and preferably 70% by weight or less, based on the total solid content constituting the epoxy adhesive.

  Polyols are compounds having a plurality of alcoholic hydroxyl groups in the molecule, but those having no acidic groups other than phenolic hydroxyl groups are particularly preferred. For example, polyol compounds having no functional groups other than hydroxyl groups, polyester polyols Examples thereof include a compound, a polycaprolactone polyol compound, a polyol compound having a phenolic hydroxyl group, and a polycarbonate polyol. The molecular weight of the polyols is usually 48 or more, preferably 62 or more, more preferably 100 or more, and preferably 1,000 or less. These polyols are usually contained at a ratio of 50% by weight or less, preferably 30% by weight or less, based on the total solid content constituting the epoxy adhesive.

  Further, the epoxy adhesive is not limited to the effects of the present invention, and other additives such as ion trapping agents, antioxidants, chain transfer agents, sensitizers, tackifiers, thermoplastic resins, fillers Further, it can contain a flow modifier, a plasticizer, an antifoaming agent, and the like. Examples of the ion trapping agent include inorganic compounds such as powdered bismuth-based, antimony-based, magnesium-based, aluminum-based, calcium-based, titanium-based and mixed systems thereof. Examples include hindered phenol antioxidants.

  After applying the epoxy adhesive containing the epoxy compound as described above to the adhesive surface of the polarizing film or the composite protective film, or to the adhesive surface of both, the two films are pasted on the adhesive-coated surface. Then, the uncured adhesive layer is cured by irradiating active energy rays or heating, and the polarizing film and the transparent protective film are passed through the adhesive layer made of a cured epoxy adhesive. Can be bonded. The adhesive may be applied by an appropriate method in consideration of the composition and physical properties of the adhesive to be used. For example, various coating methods such as a doctor blade, a wire bar, a die coater, a comma coater, and a gravure coater. Can be adopted.

  Epoxy adhesives used for bonding polarizing films and composite protective films can basically be used as solvent-free adhesives that are substantially free of solvent components, but are optimal for each coating method. Since there is a wide viscosity range, a solvent may be included for viscosity adjustment. As the solvent, it is preferable to use a solvent that satisfactorily dissolves each component including the epoxy compound constituting the adhesive without deteriorating the optical performance of the polarizing film. Examples thereof include hydrocarbons represented by toluene. And organic solvents such as esters typified by ethyl acetate.

<Curing process>
Adhesion between the polarizing film and the transparent protective film is performed by irradiating an active energy ray or heating the coating layer of the adhesive interposed between these films, and applying a curable epoxy compound contained in the adhesive. This is done by curing. In the present invention, curing of the epoxy compound by irradiation of active energy rays or heat is preferably performed by cationic polymerization of the epoxy compound.

When curing the adhesive by irradiation with active energy rays, the light source may be one that generates active energy rays effective for curing the adhesive. For example, a low-pressure mercury lamp having a light emission distribution at a wavelength of 400 nm or less, Examples include medium-pressure mercury lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, chemical lamps, black light lamps, microwave-excited mercury lamps, and metal halide lamps. The light irradiation intensity to the epoxy adhesive may vary depending on the composition, but the irradiation intensity in the wavelength region effective for activation of the photocationic polymerization initiator should be 0.1 to 100 mW / cm ^2. Is preferred. If the light irradiation intensity is too small, the reaction time becomes too long.On the other hand, if the intensity is increased, the yellowing of the adhesive or the deterioration of the polarizing film is caused by the heat radiated from the lamp and the heat generated during the polymerization of the adhesive. May occur. The light irradiation time to the epoxy adhesive is also controlled for each composition, so that the integrated light amount expressed as the product of the irradiation intensity and the irradiation time is 10 to 5,000 mJ / cm ^2. It is preferably set. If the integrated light quantity is too small, the generation of active species derived from the photocationic polymerization initiator is not sufficient, and the adhesive may be insufficiently cured. Further, if the integrated light quantity is increased, the irradiation time becomes very long, which may be disadvantageous for improving productivity.

  When the adhesive is cured by heat, it can be heated by a generally known method, and a condition that causes proper curing may be employed. Usually, heating is performed at a temperature higher than the temperature at which the thermal cationic polymerization initiator blended in the epoxy adhesive generates cationic species or Lewis acid, and the specific heating temperature is, for example, about 50 to 200 ° C.

  Even when cured under the conditions of irradiation with active energy rays or heating, the polarization degree, transmittance and hue of the polarizing film, transparency and retardation characteristics of the transparent protective film, and various functions of the obtained polarizing plate It is preferable to cure within a range that does not decrease.

  The cured adhesive layer preferably has a thickness in the range of 0.1 to 35 μm, more preferably 0.5 μm or more and 15 μm or less. If it is this range, a float and peeling will not arise between a polarizing film and the transparent protective film bonded on both surfaces, and the adhesive force which does not have a problem practically will be obtained.

  As described above, the transparent protective film bonded to both surfaces of the polarizing film may be composed of the same material on both surfaces, or may be composed of different materials on both surfaces. In recent years, in particular, the transparent protective film on the liquid crystal cell side when applied to the liquid crystal cell has a retardation characteristic or optical compensation characteristic, and the opposite side (the side far from the liquid crystal cell) is made of a transparent resin made of another resin. A protective film is often applied. Thus, also when sticking the transparent protective film which consists of a different kind of resin on both surfaces of a polarizing film, this invention functions effectively. For example, the transparent protective film bonded to one surface of the polarizing film is made of a cellulose-based resin, and the transparent protective film bonded to the other surface of the polarizing film is formed of a cyclic olefin-based resin. Is one of the preferred ones.

[Other explanation about polarizing plate]
In this invention, although a polarizing plate is manufactured in the state which attached the surface protection film on both surfaces, these surface protection films are usually peeled and removed after that. In particular, an adhesive layer is often provided on the transparent protective film on the liquid crystal cell side when pasted on the liquid crystal cell. In this case, the adhesive layer is provided after the surface protective film is peeled off. The pressure-sensitive adhesive layer is not particularly limited as long as it is excellent in optical transparency and exhibits pressure-sensitive adhesive properties such as appropriate wettability, cohesiveness, and adhesiveness, and those having particularly excellent durability are preferably used. Specifically, for example, a pressure-sensitive adhesive made of an acrylic resin (also referred to as an acrylic pressure-sensitive adhesive) can be used.

  This acrylic pressure-sensitive adhesive is, for example, 1 (meth) acrylate such as butyl (meth) acrylate, ethyl (meth) acrylate, isooctyl (meth) acrylate, and 2-ethylhexyl (meth) acrylate. The main component is an acrylic resin which is a polymer used as a seed or two or more kinds. This acrylic resin is copolymerized with a polar monomer. Examples of polar monomers include (meth) acrylic acid, 2-hydroxypropyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, (meth) acrylamide, and 2-N, N-dimethylaminoethyl (meth). And monomers having a polar functional group such as a carboxyl group, a hydroxyl group, an amide group, an amino group, and an epoxy group, such as acrylate and glycidyl (meth) acrylate. Usually, such an acrylic resin is blended with a crosslinking agent to form an acrylic pressure-sensitive adhesive.

  Various other additives may be blended in the adhesive. Suitable additives include silane coupling agents and antistatic agents. A silane coupling agent is effective in increasing the adhesive strength with glass. Antistatic agents are effective in reducing or preventing the generation of static electricity. That is, when a polarizing plate is attached to a liquid crystal cell via an adhesive layer, the release film (separator) that has been covered and temporarily protected by covering the adhesive layer is peeled off and then attached to the liquid crystal cell. The static electricity generated when the film is peeled off may cause alignment failure in the liquid crystal in the cell, resulting in display failure of the liquid crystal display device. In order to reduce or prevent the generation of such static electricity, the addition of an antistatic agent is effective.

  EXAMPLES Hereinafter, although an Example is shown and this invention is demonstrated further in detail, this invention is not limited by these examples. In the examples, “%” and “part” representing the content or amount used are based on weight unless otherwise specified.

[Example 1]
(Preparation of epoxy adhesive)
100 parts of bis (3,4-epoxycyclohexylmethyl) adipate, 25 parts of diglycidyl ether of hydrogenated bisphenol A, and 4,4'-bis (diphenylsulfonio) diphenyl sulfide bis (hexafluorophosphate as a photocationic polymerization initiator ) 2.2 parts were mixed and then defoamed to prepare an epoxy adhesive. The cationic photopolymerization initiator was blended as a 50% propylene carbonate solution. The compounding amount shown here is based on solid content.

(Protective film composite process)
An adhesive layer was formed on one side of the polyethylene terephthalate film, and a surface protective film (“NBO-D0415” manufactured by Fujimori Kogyo Co., Ltd.) having a total thickness of 53 μm including the adhesive layer was prepared.

  The adhesive layer side of the above-mentioned surface protective film “NBO-D0415” is bonded to a transparent protective film made of triacetyl cellulose having a thickness of 40 μm (“KC4UYW” manufactured by Konica Minolta Advanced Layer Co., Ltd.) A cellulose composite protective film was prepared. The adhesive layer side of the above surface protective film “NBO-D0415” is pasted on a transparent protective film made of cyclic olefin resin and having a thickness of 23 μm (“Zeonor Film ZF14-023” manufactured by Zeon Corporation). Thus, a cyclic olefin-based composite protective film was produced.

(Bonding process)
The triacetyl cellulose film surface of the triacetyl cellulose composite protective film prepared above and the cyclic olefin resin film surface of the cyclic olefin composite protective film were each subjected to corona treatment at an output of 16.8 kJ / m ² . Corona-treated surface of the above triacetyl cellulose composite protective film is on one side of the polarizing film in which iodine is adsorbed and oriented on polyvinyl alcohol, and the above cyclic olefin composite protective film is on the other side of the polarizing film. The corona-treated surfaces were superposed via the epoxy adhesive prepared above. In this state, they were bonded together by sandwiching them with a laminate roll from the composite protective film side on both sides.

(Curing process)
Thereafter, using an ultraviolet irradiation device, the upper laminated film is irradiated with ultraviolet rays so that the accumulated light amount of UV-A light in the wavelength range of 315 to 380 nm is 1500 mJ / cm ^2, and the adhesive is cured. The polarizing film and the transparent protective films on both sides were adhered to produce a polarizing plate.

(Evaluation)
When the surface protective film was peeled off from both surfaces of the obtained polarizing plate and the surface was observed, the pitch of the surface irregularities was fine and in a good state.

[Example 2]
In Example 1, the transparent protective film constituting the triacetylcellulose-based composite protective film was changed to a film having a thickness of 25 μm made of triacetylcellulose (“KC2UAW” manufactured by Konica Minolta Advanced Layer Co., Ltd.). A polarizing plate was produced in the same manner as in Example 1.

  When the surface protective film was peeled off from both sides of the obtained polarizing plate and the surface was observed, the pitch of the surface irregularities was fine and in a good state.

[Comparative Example 1]
In Example 1, the transparent protective film to be bonded to one side of the polarizing film is a film “KC4UYW” having a thickness of 40 μm made of triacetyl cellulose without the surface protective film being bonded, and is transparent to be bonded to the other side of the polarizing film. The protective film was a cyclic olefin-based composite protective film in which the same surface protective film as in Example 1 was bonded, and the other was made in the same manner as in Example 1 to produce a polarizing plate.

  When the surface protective film on the cyclic olefin-based composite protective film side was peeled off from the obtained polarizing plate and the surface of the polarizing plate was observed, the pitch of the surface unevenness was 1-2 mm, which was not uniform. It was.

[Comparative Example 2]
In Example 2, the transparent protective film to be bonded to one side of the polarizing film is a film “KC2UAW” having a thickness of 25 μm made of triacetyl cellulose without the surface protective film being bonded, and is transparent to be bonded to the other side of the polarizing film. The protective film was a cyclic olefin-based composite protective film in which the same surface protective film as in Example 2 was bonded, and the other was made in the same manner as in Example 2 to produce a polarizing plate.

  When the surface protective film on the cyclic olefin-based composite protective film side was peeled off from the obtained polarizing plate and the surface of the polarizing plate was observed, the pitch of the surface unevenness was 1-2 mm, which was not uniform. It was.

[Comparative Example 3]
In Example 1, the transparent protective film to be bonded to both surfaces of the polarizing film is not bonded to the film “KC4UYW” having a thickness of 40 μm made of triacetyl cellulose to which the surface protective film is bonded and the surface protective film. A polarizing plate was prepared in the same manner as in Example 1 except that the film was made of a cyclic olefin resin and had a thickness of 23 μm “Zeonor film ZF14-023”.

  When the surface of the obtained polarizing plate was observed, the pitch of the surface irregularities was as uneven as 1 to 2 mm, and it was not in a good state.

Claims (5)

A method for producing a polarizing plate by laminating a transparent protective film on both surfaces of a polarizing film on which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based resin,
For each of the transparent protective films to be bonded to both sides of the polarizing film, a protective film compounding step for producing a composite protective film by bonding a surface protective film to one side,
The surface opposite to the surface protective film of each composite protective film obtained in the protective film composite step, through an epoxy adhesive containing an epoxy compound that is cured by irradiation with active energy rays or heating, A laminating step for bonding to both sides of the polarizing film; a curing step for curing the epoxy adhesive;
And removing the surface protective film on the liquid crystal cell side and providing a pressure-sensitive adhesive layer on the transparent protective film in this order,
The method for producing a polarizing plate, wherein the thickness of the adhesive layer obtained by curing the epoxy adhesive is 0.5 μm or more.   The method for producing a polarizing plate according to claim 1, wherein the protective film composite step is performed so that the composite protective film to be obtained has a thickness of 40 μm or more and 150 μm or less.   The said epoxy adhesive used at the said bonding process is a manufacturing method of the polarizing plate of Claim 1 or 2 containing the epoxy compound which has at least 1 the epoxy group couple | bonded with the alicyclic ring in a molecule | numerator.   The said transparent protective film bonded on both surfaces of the said polarizing film is a manufacturing method of the polarizing plate in any one of Claims 1-3 comprised by another resin, respectively.   The transparent protective film bonded to one surface of the polarizing film is made of a cellulose resin, and the transparent protective film bonded to the other surface of the polarizing film is made of a cyclic olefin resin. The manufacturing method of the polarizing plate of Claim 4.