JP2021076814A - Polarizing plate - Google Patents

Abstract

To provide a polarizing plate in which discoloration of the polarizing plate is suppressed even under severe environment.SOLUTION: There is provided a polarizing plate in which a thermoplastic film is stuck to at least one surface of a polarizing film through an adhesive layer. The adhesive is a cured product of a photocurable composition containing a cationic polymerizable compound and a photo-cation polymerization initiator, and contains 0.5-1.5 pts.mass of the photo-cation polymerization initiator based on 100 pts.mass of the cationic polymerizable compound, and the cationic polymerizable compound contains 10-70 mass% of a bi-functional oxetane compound based on the total mass of the cationic polymerizable compound.SELECTED DRAWING: None

Description

The present invention relates to a polarizing plate in which a thermoplastic resin film is bonded to a polarizing film.

The polarizing plate is useful as one of the optical components constituting the liquid crystal display device. The polarizing plate usually has a structure in which a protective film is laminated on at least one surface of the polarizing film, and is incorporated in a liquid crystal display device. Further, as a method for producing a polarizing film, a method in which a uniaxially stretched polyvinyl alcohol-based resin film dyed with a dichroic dye is treated with boric acid, and then washed with water and dried is widely adopted.

Usually, the polarizing film is bonded with a protective film immediately after the above-mentioned washing treatment and drying treatment. This is because the polarizing film after drying has a weak physical strength, and once it is wound up, there is a problem that it is easily torn in the processing direction. Therefore, usually, an adhesive is immediately applied to the polarizing film after the drying treatment, and protective films are simultaneously attached to both sides of the polarizing film via the adhesive.

As the adhesive, a water-based adhesive containing a water-soluble resin such as a polyvinyl alcohol-based resin as a main component and an active energy ray-curable adhesive are generally used. As an active energy ray-curable adhesive, Patent Document 1 describes a photocurable adhesive in which an alicyclic epoxy compound and an epoxy compound having no alicyclic epoxy group are combined and blended together with a photocationic polymerization initiator. Are listed. A technique used for adhering a polarizing film and a protective film is disclosed.

Japanese Unexamined Patent Publication No. 2008-257199

In recent years, due to the diversification of mobile devices, durability in harsher environments is required. It has been found that the polarizing plate described in Patent Document 1 has a problem that the polarizing plate is discolored in a harsh environment (for example, when it is stored in a high temperature environment for a long time).
Therefore, an object of the present invention is to provide a polarizing plate in which discoloration of the polarizing plate is suppressed even in a harsh environment.

The present invention includes the following inventions.
[1] A polarizing plate in which a thermoplastic resin film is bonded to at least one surface of a polarizing film via an adhesive layer.
The adhesive layer is a cured product of a photocurable composition containing a cationically polymerizable compound and a photocationic polymerization initiator.
The photocurable composition contains 0.5 to 1.5 parts by mass of a photocationic polymerization initiator with respect to 100 parts by mass of the cationically polymerizable compound.
The cationically polymerizable compound is a polarizing plate containing 10 to 70% by mass of a bifunctional oxetane compound with respect to the total mass of the cationically polymerizable compound.
[2] The polarizing plate according to [1], wherein the cationically polymerizable compound further contains 10 to 70% by mass of an aliphatic epoxy compound with respect to the total mass of the cationically polymerizable compound.
[3] The thermoplastic resin film, the temperature 40 ° C., a moisture permeability at a relative humidity of 90% is 300g / (m ² · 24hr) or less, the polarizing plate according to [1] or [2].

The polarizing plate of the present invention suppresses discoloration of the polarizing plate even in a harsh environment.

Hereinafter, the present invention will be described in detail. The polarizing plate of the present invention is obtained by laminating a thermoplastic resin film on at least one surface of a polarizing film via an adhesive made of a photocurable composition. Each member and component constituting the polarizing plate will be described in order.

[Polarizing film]
The polarizing film is composed of a polyvinyl alcohol-based resin film in which a dichroic dye is adsorbed and oriented. The polyvinyl alcohol-based resin constituting the polarizing film can be obtained by saponifying the polyvinyl acetate-based resin. Examples of the polyvinyl acetate-based resin include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable therewith. Examples of other monomers copolymerized with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids and the like. The degree of saponification of the polyvinyl alcohol-based resin is usually 85 to 100 mol%, preferably 98 mol% or more. The polyvinyl alcohol-based resin may be modified, and for example, polyvinyl formal or polyvinyl acetal modified with aldehydes may be used. The degree of polymerization of the polyvinyl alcohol-based resin is usually in the range of 1,000 to 10,000, preferably 1,500 to 5,000.

The above-mentioned polarizing film has a step of uniaxially stretching a polyvinyl alcohol-based resin film, a step of dyeing a polyvinyl alcohol-based resin film with a bicolor dye and adsorbing the bicolor dye, and a step of adsorbing the bicolor dye. It is produced through a step of treating a polyvinyl alcohol-based resin film with an aqueous boric acid solution.

The uniaxial stretching step may be performed before dyeing with the dichroic dye, at the same time as dyeing with the dichroic dye, or after dyeing with the dichroic dye. When the uniaxial stretching is performed after dyeing with a dichroic dye, the uniaxial stretching may be performed before the boric acid treatment or during the boric acid treatment. It is also possible to perform uniaxial stretching at these multiple stages. For uniaxial stretching, it may be stretched through rolls having different peripheral speeds, or it may be stretched by sandwiching it with thermal rolls. Further, it may be a dry stretching performed in the air, or a wet stretching performed in a state of being swollen with a solvent. The draw ratio is usually about 4 to 8 times.

To dye the polyvinyl alcohol-based resin film with a dichroic dye, for example, the polyvinyl alcohol-based resin film may be immersed in an aqueous solution containing the dichroic dye. Specifically, iodine or a dichroic organic dye is used as the dichroic dye.

When iodine is used as the dichroic dye, a method of immersing a polyvinyl alcohol-based resin film in an aqueous solution containing iodine and potassium iodide for dyeing is usually adopted. The content of iodine in this aqueous solution is about 0.01 to 0.5 parts by weight per 100 parts by weight of normal water, and the content of potassium iodide is about 0.5 to 10 parts by weight per 100 parts by weight of normal water. Is. The temperature of this aqueous solution is usually about 20 to 40 ° C., and the immersion time (staining time) in this aqueous solution is usually about 30 to 300 seconds.

On the other hand, when a dichroic organic dye is used as the dichroic dye, a method of immersing a polyvinyl alcohol-based resin film in an aqueous solution containing a water-soluble dichroic organic dye and dyeing is usually adopted. The content of the dichroic organic dye in this aqueous solution is usually about 1 × 10 ^-3 to 1 × 10 ⁻² parts by weight per 100 parts by weight of water. This aqueous solution may contain an inorganic salt such as sodium sulfate. The temperature of this aqueous solution is usually about 20 to 80 ° C., and the immersion time (staining time) in this aqueous solution is usually about 30 to 300 seconds.

The boric acid treatment after dyeing with a dichroic dye is performed by immersing the dyed polyvinyl alcohol-based resin film in an aqueous boric acid solution. The content of boric acid in the boric acid aqueous solution is usually about 2 to 15 parts by weight, preferably about 5 to 12 parts by weight, per 100 parts by weight of water. When iodine is used as the dichroic pigment, this boric acid aqueous solution preferably contains potassium iodide. The content of potassium iodide in the boric acid aqueous solution is usually about 2 to 20 parts by weight, preferably 5 to 15 parts by weight, per 100 parts by weight of water. The immersion time in the boric acid aqueous solution is usually about 100 to 1,200 seconds, preferably about 150 to 600 seconds, and more preferably about 200 to 400 seconds. The temperature of the boric acid aqueous solution is usually 50 ° C. or higher, preferably 50 to 85 ° C.

The polyvinyl alcohol-based resin film after the boric acid treatment is usually washed with water. The water washing treatment is performed, for example, by immersing a boric acid-treated polyvinyl alcohol-based resin film in water. After washing with water, it is dried to produce a polarizing film. The temperature of water in the washing treatment is usually about 5 to 40 ° C., and the immersion time is usually about 2 to 120 seconds. Subsequent drying treatments are usually performed using a hot air dryer or a far-infrared heater. The drying temperature is usually 40 to 100 ° C. The drying treatment time is usually about 120 to 600 seconds.

The thickness of the polarizing film made of the polyvinyl alcohol-based resin thus obtained can be about 10 to 50 μm.

[Thermoplastic resin film]
The polarizing plate of the present invention is obtained by laminating a thermoplastic resin film on a polarizing film made of the polyvinyl alcohol-based resin film described above via a photocurable composition and curing the photocurable composition. Be done.

The thermoplastic resin film is preferably formed of a transparent resin. The thermoplastic resin film may be either a non-stretched film or a uniaxially or biaxially stretched film.

The main component of the thermoplastic resin film is preferably at least one resin selected from the group consisting of cellulose-based resins, acrylic-based resins, amorphous polyolefin-based resins, polyester-based resins, and polycarbonate-based resins.

The polyester-based resin is not particularly limited, but polyethylene terephthalate is particularly preferable in terms of mechanical properties, solvent resistance, scratch resistance, cost, and the like. The polyethylene terephthalate means a resin in which 80 mol% or more of the repeating unit is composed of ethylene terephthalate, and may contain a constituent unit derived from other copolymerization components.

Examples of other copolymerization components include a dicarboxylic acid component and a diol component. The dicarboxylic acid components include isophthalic acid, p-β-hydroxyethoxybenzoic acid, 4,4'-dicarboxydiphenyl, 4,4'-dicarboxybenzophenone, bis (4-carboxyphenyl) ethane, adipic acid, and sebacic acid. , 5-Sodium sulfoisophthalic acid, 1,4-dicarboxycyclohexane and the like. Examples of the diol component include propylene glycol, butanediol, neopentyl glycol, diethylene glycol, cyclohexanediol, ethylene oxide adduct of bisphenol A, polyethylene glycol, polypropylene glycol, polytetramethylene glycol and the like. Two or more of these dicarboxylic acid components and diol components can be used in combination, if necessary. Further, it is also possible to use a hydroxycarboxylic acid such as p-hydroxybenzoic acid in combination with the above dicarboxylic acid component and diol component. As the other copolymerization component, a small amount of a dicarboxylic acid component and / or a diol component having an amide bond, a urethane bond, an ether bond, a carbonate bond and the like may be used.

The polyethylene terephthalate resin means a resin in which 80 mol% or more of the repeating unit is composed of ethylene terephthalate, and may contain a structural unit derived from other copolymerization components. Other copolymerization components include isophthalic acid, 4,4'-dicarboxydiphenyl, 4,4'-dicarboxybenzophenone, bis (4-carboxyphenyl) ethane, adipic acid, sebacic acid, 5-sodium sulfoisophthalic acid. Dicarboxylic acid components such as acid and 1,4-dicarboxycyclohexane; propylene glycol, butanediol, neopentyl glycol, diethylene glycol, cyclohexanediol, ethylene oxide adduct of bisphenol A, polyethylene glycol, polypropylene glycol, polytetramethylene glycol and the like. A diol component can be mentioned. If necessary, two or more of these dicarboxylic acid components and diol components can be used in combination. Further, it is also possible to use a hydroxycarboxylic acid such as p-hydroxybenzoic acid or p-β-hydroxyethoxybenzoic acid in combination with the above dicarboxylic acid component or diol component. As the other copolymerization component, a dicarboxylic acid component and / or a diol component containing a small amount of amide bond, urethane bond, ether bond, carbonate bond and the like may be used.

By forming the above polyethylene terephthalate resin into a film and then applying the stretching treatment as described above as a protective film, the mechanical properties, solvent resistance, scratch resistance, cost, etc. are excellent and the thickness is reduced. The rolled polarizing plate can be obtained.

Polycarbonate-based resins are polyesters formed from carbonic acid and glycols or bisphenols. Among them, aromatic polycarbonate having a diphenylalkane in the molecular chain is preferably used because it is excellent in heat resistance, weather resistance and acid resistance. Examples of such polycarbonates include 2,2-bis (4-hydroxyphenyl) propane (also known as bisphenol A), 2,2-bis (4-hydroxyphenyl) butane, and 1,1-bis (4-hydroxyphenyl) cyclohexane. Polycarbonates derived from bisphenols, such as 1,1-bis (4-hydroxyphenyl) isobutane, or 1,1-bis (4-hydroxyphenyl) ethane, are exemplified.

As a method for producing the polycarbonate-based resin film, any method such as a casting film forming method or a melt extrusion method may be used. As an example of a specific production method, a polycarbonate resin is dissolved in an appropriate organic solvent to prepare a polycarbonate resin solution, which is cast on a metal support to form a web, and the web is formed into the metal support. A method of obtaining a film by hot-air drying the stripped web after stripping from polycarbonate can be mentioned.

The acrylic resin is not particularly limited, but is generally a polymer containing a methacrylic acid ester as a main monomer, and a copolymer in which a small amount of other comonomer components are copolymerized with the polymer is preferable. This copolymer can usually be obtained by polymerizing a monofunctional monomer containing methyl methacrylate and methyl acrylate in the presence of a radical polymerization initiator and a chain transfer agent. In addition, the acrylic resin can be copolymerized with a third monofunctional monomer.

Third monofunctional monomers capable of copolymerizing with methyl methacrylate and methyl acrylate include, for example, ethyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, benzyl methacrylate, 2-ethylhexyl methacrylate. , And methacrylic acid esters other than methyl methacrylate, such as 2-hydroxyethyl methacrylate; ethylacrylic acid, butyl acrylate, cyclohexyl acrylate, phenyl acrylate, benzyl acrylate, 2-ethylhexyl acrylate, and 2 acrylate. Acrylic acids such as −hydroxyethyl; methyl 2- (hydroxymethyl) acrylate, methyl 2- (1-hydroxyethyl) acrylate, ethyl 2- (hydroxymethyl) acrylate, and 2- (hydroxymethyl) acrylic Hydroxyalkylacrylic acid esters such as butyl acid; unsaturated acids such as methacrylic acid and acrylic acid; halogenated styrenes such as chlorostyrene and bromostyrene; substituted styrenes such as vinyltoluene and α-methylstyrene; acrylonitrile and methacrylic acid. Unsaturated nitriles such as ronitrile; unsaturated acid anhydrides such as maleic anhydride and citraconic anhydride; unsaturated imides such as phenylmaleimide and cyclohexylmaleimide can be mentioned. Each of these may be used alone, or a plurality of different types may be used in combination.

When the polyfunctional monomer is copolymerized, examples of the polyfunctional monomer that can be copolymerized with methyl methacrylate and methyl acrylate include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, and triethylene. Acrylate or the hydroxyl groups at both ends of ethylene glycol such as glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, nonaethylene glycol di (meth) acrylate, and tetradecaethylene glycol di (meth) acrylate Esterated with methacrylic acid; esterified at both terminal hydroxyl groups of propylene glycol or its oligomer with acrylic acid or methacrylic acid; neopentyl glycol di (meth) acrylate, hexanediol di (meth) acrylate, and butanediol di The hydroxyl group of a dihydric alcohol such as (meth) 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 substituents are acrylic acid or methacrylic acid. Esterated with acrylate: Polyhydric alcohols such as trimethylolpropane and pentaerythritol esterified with acrylic acid or methacrylic acid, and glycidyl acrylate or glycidyl methacrylate epoxy group added to these terminal hydroxyl groups by ring opening; Dibasic acids such as succinic acid, adipic acid, terephthalic acid, phthalic acid, halogen substituents thereof, and alkylene oxide adducts thereof to which an epoxy group of glycidyl acrylate or glycidyl methacrylate is ring-opened; aryl ( Meta) Acrylate; Examples thereof include aromatic divinyl compounds such as divinylbenzene. Of these, ethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, and neopentyl glycol dimethacrylate are preferably used.

The acrylic resin having such a composition may be further modified by reacting between the functional groups of the copolymer. Examples of the reaction include a demethanol condensation reaction in a polymer chain between a methyl ester group of methyl acrylate and a hydroxyl group of methyl 2- (hydroxymethyl) acrylate, and a carboxyl group of acrylate and 2- (hydroxymethyl) acrylic. Examples thereof include a dehydration condensation reaction in a polymer chain with a hydroxyl group of methyl acid.

The glass transition temperature of the acrylic resin is preferably in the range of 80 to 120 ° C. In order to adjust the glass transition temperature of an acrylic resin within the above range, the polymerization ratio of the methacrylic acid ester-based monomer and the acrylic acid ester-based monomer, the carbon chain length of each ester group, and the functional group thereof are usually used. A method of appropriately selecting the polymerization ratio of the polyfunctional acrylic monomer with respect to the entire monomer is adopted.

The acrylic resin may contain a known additive, if necessary. Known additives include, for example, lubricants, antiblocking agents, heat stabilizers, antioxidants, antistatic agents, lightfasteners, impact resistance improvers, surfactants and the like. However, since transparency is required as a protective film laminated on the polarizing film, it is preferable to keep the amount of these additives to a minimum.

As a method for producing the acrylic resin film, any method such as a melt casting method, a melt extrusion method such as a T-die method or an inflation method, or a calendar method may be used. Among them, a method of melt-extruding a raw material resin from, for example, a T-die and bringing at least one side of the obtained film-like material into contact with a roll or a belt to form a film is preferable in that a film having good surface properties can be obtained.

The acrylic resin may contain acrylic rubber particles which are impact improving agents from the viewpoint of film forming property on the film and impact resistance of the film. The acrylic rubber particles referred to here are particles containing an elastic polymer mainly composed of an acrylic acid ester as an essential component, and have a single-layer structure substantially consisting of only this elastic polymer, or this elastic polymer. There is a multi-layered structure having one layer. Examples of such an elastic polymer include a crosslinked elastic copolymer containing an alkyl acrylate as a main component and copolymerizing another copolymerizable vinyl monomer and a crosslinkable monomer. Examples of the alkyl acrylate that is the main component of the elastic polymer include those having an alkyl group having about 1 to 8 carbon atoms, such as methyl acrylate, ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate, and in particular, carbon. An acrylate having an alkyl group of several 4 or more is preferably used. Examples of other vinyl monomers copolymerizable with this alkyl acrylate include compounds having one polymerizable carbon-carbon double bond in the molecule, and more specifically, methacrylic acid such as methyl methacrylate. Examples thereof include esters, aromatic vinyl compounds such as styrene, vinyl cyan compounds such as acrylonitrile, and the like. Further, examples of the crosslinkable monomer include a crosslinkable compound having at least two polymerizable carbon-carbon double bonds in the molecule, and more specifically, ethylene glycol di (meth) acrylate and butanediol. Examples thereof include (meth) acrylates of polyhydric alcohols such as di (meth) acrylates, alkenyl esters of (meth) acrylic acids such as allyl (meth) acrylates, and divinylbenzene.

Further, a laminate of a film made of an acrylic resin containing no rubber particles and a film made of an acrylic resin containing rubber particles can be used as a protective film. Acrylic resins can be easily obtained on the market. For example, Sumipex (manufactured by Sumitomo Chemical Co., Ltd.), Acrypet (manufactured by Mitsubishi Rayon Co., Ltd.), and Delpet (manufactured by Asahi Kasei Co., Ltd.) (Manufactured by), Parapet (manufactured by Kuraray Co., Ltd.), Acrylic (manufactured by Nippon Shokubai Co., Ltd.), etc.

The amorphous polyolefin resin is a resin obtained by ring-opening metathesis polymerization using norbornene or a derivative thereof obtained by a deal alder reaction from cyclopentadiene and olefins as a monomer, followed by hydrogenation; dicyclopentadiene and olefin. A resin obtained by ring-opening metathesis polymerization using tetracyclododecene or a derivative thereof obtained by a deal alder reaction with a class or methacrylic acid ester as a monomer, followed by water addition; norbornene, tetracyclododecene and their derivatives. A resin obtained by similarly performing ring-opening metathesis copolymerization using two or more selected from derivatives and other cyclic polyolefin monomers and subsequent hydrogenation; to norbornene, tetracyclododecene or derivatives thereof. , A resin obtained by addition-copolymerizing an aromatic compound having a vinyl group or the like. Examples of commercially available amorphous polyolefin resins include "Arton" from JSR Corporation, "ZEONEX" and "ZEONOR" from Zeon Corporation, and "APO" and "APO" from Mitsui Chemicals, Inc. There is "Apel" and so on. When an amorphous polyolefin resin is formed into a film, a known method such as a solvent casting method or a melt extrusion method is appropriately used for the film formation.

The cellulosic resin may be a resin in which at least a part of the hydroxyl groups in cellulose is acetic acid esterified, and a mixed ester in which a part is acetic acid esterified and a part is esterified with another acid. .. The cellulosic resin is preferably a cellulosic ester resin, and more preferably an acetyl cellulosic resin. Specific examples of the acetyl cellulose-based resin include triacetyl cellulose, diacetyl cellulose, cellulose acetate propionate, and cellulose acetate butyrate. Examples of commercially available films made of such acetyl cellulose-based resins include "Fujitac TD80", "Fujitac TD80UF" and "Fujitac TD80UZ" manufactured by Fujifilm Co., Ltd., and "KC8UX2M" manufactured by Konica Minolta Opto Co., Ltd. "And" KC8UY "and the like.

A cellulosic resin film to which an optical compensation function is provided can also be used. Examples of such an optical compensation film include a film in which a cellulosic resin contains a compound having a phase difference adjusting function, a film in which a compound having a phase difference adjusting function is coated on the surface of the cellulosic resin, and a cellulosic resin uniaxially or biaxially. Examples thereof include a film obtained by stretching on a shaft. Examples of commercially available cellulosic resin optical compensation films are "Wide View Film WV BZ 438" and "Wide View Film WV EA" manufactured by FUJIFILM Corporation, and Konica Minolta Opto Co., Ltd. There are "KC4FR-1" and "KC4HR-1" and the like.

The thermoplastic resin film attached to one surface of the polarizing film may contain an ultraviolet absorber. This is because the liquid crystal cell can be protected from deterioration due to ultraviolet rays by arranging the protective film containing the ultraviolet absorber on the visible side of the liquid crystal cell.

In the present invention, the above-mentioned thermoplastic resin film is bonded to at least one surface of the polarizing film using a photocurable composition. When the thermoplastic resin film is bonded to only one side of the polarizing film, for example, an adhesive layer for bonding to another member such as a liquid crystal cell is directly provided on the other surface of the polarizing film. You can also do it.

On the other hand, when the thermoplastic resin films are bonded to both sides of the polarizing film, the respective thermoplastic resin films may be of the same type or different types.

The thermoplastic resin film bonded to one surface of the polarizing film is adhered using a photocurable composition described later, but the thermoplastic resin film bonded to the other surface of the polarizing film is other. It may be adhered using an adhesive layer formed from the photocurable composition of.

Prior to bonding the thermoplastic resin film to the polarizing film, the bonded surface may be subjected to an easy-adhesion treatment such as a saponification treatment, a corona treatment, a priming treatment, or an anchor coating treatment. Further, various treated layers such as a hard coat layer, an antireflection layer, and an antiglare layer may be provided on the surface of the thermoplastic resin film opposite to the bonding surface to the polarizing film. The thickness of the thermoplastic resin film is usually in the range of about 5 to 200 μm, preferably 10 to 120 μm, and more preferably 10 to 100 μm.

The thermoplastic resin film, the temperature 40 ° C., preferably the moisture permeability condition of relative humidity of 90% or less ^{300g / (m 2 · 24hr)} , more preferably 200g / (m ² · 24hr) or less , and more preferably 100g / (m ² · 24hr) or less. If the moisture permeability is at 300g / (m ² · 24hr) or less, preferably because it can suppress the hue change under the transmittance change and a high-temperature environment in humidity environment for example high temperature and high.
If laminating a thermoplastic resin film on both surfaces of a polarizing film, at least the viewing side (outermost surface) of the temperature 40 ° C., the thermoplastic moisture permeability at a relative humidity of 90% for is 300g / (m ² · 24hr) or less preferably to be bonded to the resin film, both surfaces to a temperature 40 ° C. of the polarizing film, that moisture permeability at a relative humidity of 90% for condition laminating the thermoplastic resin film is 300g / (m ² · 24hr) or less More preferred.

[Adhesive layer]
The polarizing plate of the present invention is obtained by laminating a thermoplastic resin film on one surface of the above-mentioned polarizing film via an adhesive layer. This adhesive layer is formed from a photocurable composition in which a cationically polymerizable compound and a photocationic polymerization initiator are blended in a predetermined ratio.

(Cation-polymerizable compound)
The cationically polymerizable compound is the main component of the photocurable composition, and is a component that imparts adhesive strength by polymerization curing. The cationically polymerizable compound includes a bifunctional oxetane compound.

(Bifunctional oxetane compound)
The bifunctional oxetane compound is a compound having two 4-membered ring ethers (oxetanyl groups) in the molecule, and examples thereof include the following compounds.

Bis [(3-ethyloxetane-3-yl) methyl] ether, bis [(3-methyloxetane-3-yl) methyl] ether, bis [(oxetane-3-yl) methyl] ether, 1,4-bis [[(3-Ethyloxetane-3-yl) methoxy] methyl] benzene, 1,4-bis [(3-ethyloxetane-3-yl) methoxy] benzene, 1,3-bis [(3-ethyloxetane-) 3-Il) methoxy] benzene, 1,2-bis [(3-ethyloxetane-3-yl) methoxy] benzene, 4,4'-bis [(3-ethyloxetane-3-yl) methoxy] biphenyl, 2 , 2'-bis [(3-ethyloxetane-3-yl) methoxy] biphenyl, 1,1,1-tris [(3-ethyloxetane-3-yl) methoxymethyl] propane, 1,2-bis [( 3-Ethyloxetane-3-yl) methoxy] ethane, 1,2-bis [(3-ethyloxetane-3-yl) methoxy] propane, 1,4-bis [(3-ethyloxetane-3-yl) methoxy ] Butane and 1,6-bis [(3-ethyloxetane-3-yl) methoxy] hexane and the like.

Among them, in the case of bis [(3-ethyloxetane-3-yl) methyl] ether, the reactivity of the photocurable composition is high, and the elastic modulus of the obtained cured product at high temperature can be increased. Therefore, the durability of the polarizing plate under high temperature conditions and high temperature and high humidity is increased, which is preferable.

The bifunctional oxetane compound preferably has a molecular weight of 550 or less, preferably at a molecular weight of 150 to 400, in that the photocurable composition has a low viscosity and the cured product of the photocurable composition has excellent adhesive strength. It is more preferable to have a molecular weight of 150 to 300.

As the bifunctional oxetane compound, one kind may be used, or two or more kinds may be used.

It is preferable to add the bifunctional oxetane compound in a proportion of 10 to 70% by mass based on the total mass of the cationically polymerizable compound. When the content of the bifunctional oxetane compound is 10% by mass or less, the curability of the photocurable composition is lowered, and when it is 70% by mass or more, the adhesive force to the thermoplastic resin film is lowered. The preferred content of the bifunctional oxetane compound is 15 to 65% by mass, more preferably 25 to 55% by mass, based on the total amount of the cationically polymerizable compound.

(Aliphatic epoxy compound)
The photocurable composition in the present invention may further contain an aliphatic epoxy compound as the cationically polymerizable compound. When a bifunctional oxetane compound and an aliphatic epoxy compound are used in combination as a cationically polymerizable compound, the adhesion between the polarizing film and the protective film is further improved while maintaining a high storage elastic modulus of the cured product of the photocurable composition. Can be enhanced. The aliphatic epoxy compound referred to here is a compound in which one carbon atom of two carbon atoms contained in an epoxy group is bonded to another aliphatic carbon atom. Examples thereof include polyglycidyl ether of alkane polyol and polyglycidyl ether of polyalkylene glycol.

Examples of polyalkylene glycol polyglycidyl ethers include diethylene glycol diglycidyl ether, triethylene glycol diglycidyl ether, dipropylene glycol diglycidyl ether, and tripropylene glycol diglycidyl ether.

A specific example of the polyglycidyl ether of an alkane polyol is a compound represented by the following formula (IV).

In the above formula (IV), Z represents an alkylene group having 2 to 10 carbon atoms, and Z may be a straight chain, a branched chain, or a ring structure. Z preferably has 2 to 6 carbon atoms, and more preferably 4 to 6 carbon atoms.

Examples of the compound represented by the above formula (IV) include ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, 1,3-propanediol diglycidyl ether, 1,4-butanediol diglycidyl ether, and neopentyl glycol diglycidyl. Examples thereof include ether, 1,6-hexanediol diglycidyl ether, 1,9-nonanediol diglycidyl ether, cyclohexanedimethanol diglycidyl ether, and 1,4-cyclohexanedimethanol diglycidyl ether.

Other aliphatic epoxy compounds include triglycidyl ether of glycerin, triglycidyl ether of trimethylolpropane, pentaerythritol polyglycidyl ether and dipentaerythritol polyglycidyl ether, 2-ethylhexyl glycidyl ether, hydroquinone diglycidyl ether, and resorcin. Diglycidyl ether, etc. can be mentioned.

The aliphatic epoxy compound is preferably a compound represented by the formula (IV) because it is easily available and has a great effect of enhancing the adhesion between the polarizing film and the thermoplastic resin film. Specifically, compounds having 4 to 6 carbon atoms of Z such as 1,4-butanediol diglycidyl ether, neopentyl glycol diglycidyl ether and 1,6-hexanediol diglycidyl ether are preferably used.

As the aliphatic epoxy compound, one kind may be used, or two or more kinds may be used.

When the bifunctional oxetane compound and the aliphatic epoxy compound are used in combination, the mixing ratio of both is preferably 10 to 90% by mass based on the total amount of the cationically polymerizable compound, and 15 It is more preferably ~ 80% by mass, and even more preferably 15 to 50% by mass. Of course, the total of these does not exceed 100% by mass. By blending an aliphatic epoxy compound (for example, a compound represented by the above formula (IV)) in a proportion of 10% by mass or more of the total amount of the cationically polymerizable compound, the compound has excellent adhesive strength to the thermoplastic resin film. It becomes. From the viewpoint of lowering the viscosity and adhesive strength of the photocurable composition, it is preferable that the amount of the aliphatic epoxy compound is large, but if it exceeds 90% by mass, the storage elastic modulus of the cured product of the photocurable composition at 80 ° C. is low. Therefore, the durability of the polarizing plate in which the polarizing film and the protective film are bonded to each other in the thermal shock test is deteriorated.

(Other cationic curable components)
The photocurable composition may contain other cationic curable components. Examples of other cationic curable components include aromatic epoxy compounds, hydrogenated epoxy compounds in which the aromatic ring of the aromatic epoxy compound is hydrogenated, alicyclic epoxy compounds, and monofunctional oxetane compounds.

In the present invention, the aromatic epoxy compound represents a compound in which a glycidyl ether group or a glycidyl ester group is directly bonded to an aromatic ring. Specific examples thereof include bisphenol A type epoxy, bisphenol F type epoxy resin, bisphenol S type epoxy, bisphenol A, bisphenol F and epichlorohydrin polycondensed epoxy resin, phenol novolac type epoxy resin, cresol novolac type epoxy resin, and bisphenol A. Examples thereof include novolak type epoxy resin and bisphenol F novolak type epoxy resin.

From the viewpoint of adhesiveness to the thermoplastic resin film, the number of epoxy groups contained in one molecule of the aromatic epoxy compound is preferably 2 or more. For the same reason, the weight average molecular weight of the aromatic epoxy compound (hereinafter referred to as “Mw”) is preferably 400 to 50,000, more preferably 1,000 to 10,000. It is more preferably 2,000 to 5,000. In addition, Mw in this invention means polystyrene-equivalent Mw measured by gel permeation chromatography (GPC).

The aromatic epoxy compound may be used alone or in combination of two or more.

When an aromatic epoxy compound is used in combination, the content thereof is preferably 1 to 25% by mass with respect to the total mass of the cationically polymerizable compound. When the content is 1% by mass or more, the adhesion to the thermoplastic resin film is improved. On the other hand, when the content exceeds 25% by mass, the viscosity of the composition becomes high and the coatability deteriorates. The preferable content is 3 to 20% by mass, more preferably 5 to 15% by mass, based on the total mass of the cationically polymerizable compound.

The hydrogenated epoxy compound selectively hydrogenates an aromatic polyhydroxy compound having at least two phenolic hydroxyl groups in the molecule, which is a raw material of the above aromatic epoxy compound, under pressure in the presence of a catalyst. The hydrogenated polyhydroxy compound thus obtained is glycidyl etherified. Specific examples thereof include diglycidyl ether of hydrogenated bisphenol A, diglycidyl ether of hydrogenated bisphenol F, and diglycidyl ether of hydrogenated bisphenol S.

The alicyclic epoxy compound means a compound containing at least two alicyclic epoxy groups in the molecule. The alicyclic epoxy group is a group represented by the following formula (II) (representing an integer of m = 2 to 5 in the formula (II)), and specifically, an epoxycyclopentyl group and an epoxycyclohexyl group. And so on.

（式中、Ｒ^１及びＲ^２は、それぞれ独立して、炭素数１〜６のアルキル基を表す。）
式（ＩＩＩ）で表される化合物としては、３，４−エポキシシクロヘキシルメチル ３，４−エポキシシクロヘキサンカルボキシレート、３，４−エポキシ−６−メチルシクロヘキシルメチル ３，４−エポキシ−６−メチルシクロヘキサンカルボキシレート等が挙げられる。 The alicyclic epoxy compound is preferably a compound represented by the formula (III).

(In the formula, R ¹ and R ² each independently represent an alkyl group having 1 to 6 carbon atoms.)
Examples of the compound represented by the formula (III) include 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate and 3,4-epoxy-6-methylcyclohexylmethyl 3,4-epoxy-6-methylcyclohexanecarboxylate. The rate etc. can be mentioned.

When the alicyclic epoxy compound is used in combination, the content of the alicyclic epoxy compound is preferably small from the viewpoint of moisture and heat resistance. Specifically, the alicyclic epoxy compound is preferably less than 30% by mass, more preferably less than 15% by mass, and further preferably 1 to 10% by mass with respect to the total mass of the cationically polymerizable compound. preferable.

(Photocationic polymerization initiator)
The photocurable composition undergoes cationic polymerization by irradiation with active energy rays and is cured to provide an adhesive layer. The photocationic polymerization initiator is one that generates a cationic species or Lewis acid by irradiation with active energy rays such as visible light, ultraviolet rays, X-rays, or electron beams, and initiates the polymerization reaction of the cationically polymerizable compound. Good. Since the photocationic polymerization initiator acts catalytically with light, it does not affect the storage stability and workability even when mixed with the cationically polymerizable compound. Examples of the photocationic polymerization initiator include aromatic diazonium salts, onium salts such as aromatic iodonium salts and aromatic sulfonium salts, and iron-allene 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,
Di (4-nonylphenyl) iodonium hexafluorophosphate Di (4-alkylphenyl) iodonium hexafluorophosphate,
Trillcumyl iodonium tetrakis (pentafluorophenyl) borate,
Di (4-t-butylphenyl) iodonium hexafluorophosphate,
Di (4-t-Butylphenyl) Iodonium Hexafluoroantimonate,
(4-Methylphenyl) [4- (2-methylpropyl) phenyl] -hexafluoroophosphate 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] diphenylsulfide bishexafluorophosphate,
4,4'-Bis [di (β-hydroxyethoxy) phenylsulfonio] diphenylsulfide bishexafluoroantimonate,
4,4'-Bis [di (β-hydroxyethoxy) phenylsulfonio] diphenylsulfide bishexafluorophosphate,
7- [Di (p-toluyl) sulfonio] -2-isopropylthioxanthone hexafluoroantimonate,
7- [di (p-toluyl) sulfonio] -2-isopropylthioxanthone tetrakis (pentafluorophenyl) borate,
4-Phenylcarbonyl-4'-diphenylsulfonio-diphenylsulfide hexafluorophosphate,
4- (p-tert-Butylphenylcarbonyl) -4'-diphenylsulfonio-diphenylsulfide hexafluoroantimonate,
4- (p-tert-butylphenylcarbonyl) -4'-di (p-toluyl) sulfonio-diphenylsulfide tetrakis (pentafluorophenyl) borate 4- (phenylthio) phenyldiphenylsulfonium tris (pentafluoroethyl) trifluorophosphate 4 -(Phenylthio) Phenyldiphenylsulfonium Hexafluorophosphate 4- (Phenylthio) Phenyldiphenylsulfonium Trifluoromethanesulfonate, etc.

Examples of the iron-arene complex include the following compounds.
Xylene-Cyclopentadienyl Iron (II) Hexafluoroantimonate,
Cumene-Cyclopentadienyl Iron (II) Hexafluorophosphate,
Xylene-cyclopentadienyl iron (II) tris (trifluoromethylsulfonyl) metanide, etc.

These photocationic polymerizable initiators are available as commercial products. For example, ADEKA PUTMER SP-100, SP-150, SP-152, SP-170, SP-172 [manufactured by ADEKA Corporation], Photoinitiator 2074 (manufactured by Rhodia), Kayarad PCI-220, PCI-620. [Nippon Kayaku Co., Ltd.], Irgacure 250 (manufactured by Ciba Japan), CPI-100P, CPI-110P, CPI-101A, CPI-200K, CPI-210S [manufactured by Sun Appro Co., Ltd.), WPI-113 , WPI-116 [manufactured by Wako Pure Chemical Industries, Ltd.]), BBI-102, BBI-103, TPS-102, TPS-103, DTS-102, DTS-103 [manufactured by Midori Kagaku Co., Ltd.], etc. Be done.

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

The blending amount of the photocationic polymerization initiator is 0.5 to 1.5 parts by mass with respect to 100 parts by mass of the cationically polymerizable compound. By blending 0.5 parts by mass or more (more preferably 0.7 parts by mass or more) of the photocationic polymerization initiator per 100 parts by mass of the cationically polymerizable compound, the cationically polymerizable compound can be sufficiently cured. The obtained polarizing plate is provided with high mechanical strength and adhesive strength, and has excellent durability in a high temperature and high humidity environment. On the other hand, when the amount is large, the residual amount of the unreacted initiator, the solvent used as necessary for dissolving the initiator, or the decomposition product of the initiator is increased, so that the physical properties of the cured product are impaired. , The polarizing plate discolors in a high temperature environment. Therefore, the amount of the photocationic polymerization initiator is preferably 1.5 parts by mass or less per 100 parts by mass of the cationically polymerizable compound.

(Other ingredients)
The photocurable composition may contain other components in addition to the cationically polymerizable compound and the photocationic polymerization initiator described above. Examples of other ingredients that can be blended include photosensitizers, photosensitizers, thermal cationic polymerization initiators, chain transfer agents, thermoplastic resins, flow modifiers, defoamers, leveling agents, organic solvents. , Solvent coupling agents, polymers, etc. Depending on the type of protective film attached to the polarizing film, it may be preferable to add a photosensitizer and further a photosensitizer.

The photosensitizer is a compound that exhibits maximum absorption at a wavelength longer than the maximum absorption wavelength indicated by the photocationic polymerization initiator and promotes the polymerization initiation reaction by the photocationic polymerization initiator. As such a photosensitizer, an anthracene-based compound is preferably used. As anthracene compounds that can be photosensitizers, 9,10-dimethoxyanthracene, 9,10-diethoxyanthracene, 9,10-dipropoxyanthracene, 9,10-diisopropoxyanthracene, 9,10-dibutoxyanthracene , 9,10-Dipentyloxyanthracene, 9,10-dihexyloxyanthracene and the like.

The photosensitizer is a compound that further promotes the action of the photosensitizer. As such a photosensitizer, a naphthalene compound is preferably used. As naphthalene compounds that can be photosensitizers, 1,4-dimethoxynaphthalene, 1-ethoxy-4-methoxynaphthalene, 1,4-diethoxynaphthalene, 1,4-dipropoxynaphthalene, 1,4-dibutoxy Examples include naphthalene.

When these other components are blended, the amount thereof is, for example, from a range of 10 parts by mass or less with respect to 100 parts by mass of the cationically polymerizable compound which is the main component of the photocurable composition, according to the blending purpose. It may be selected as appropriate.

The viscosity of the photocurable composition in the present invention is not particularly limited, but is preferably 10 to 1000 mPa · s at 25 ° C. From the viewpoint of coatability and thinning of the coating layer, it is more preferably 15 to 500 mPa · s, and further preferably 20 to 100 mPa · s. The viscosity in the present invention is a value measured by an E-type viscometer.

The water content of the photocurable composition is preferably 3% by mass or less, more preferably 2% by mass or less, and preferably 1% by mass or less, based on the total amount of the photocurable composition. It is more preferably 0.5% by mass or less, and particularly preferably 0.5% by mass or less. When the water content of the photocurable composition exceeds 3% by mass, the curability of the photocurable composition tends to deteriorate. Therefore, the adhesion between the thermoplastic resin film and the polarizing film immediately after the production of the polarizing plate is lowered, and there is a tendency for fluffiness and peeling to occur.

[Preparation of polarizing plate]
The thermoplastic resin film is bonded to the polarizing film via an adhesive layer formed from the photocurable composition to form a polarizing plate. In this bonding, a coating layer of the photocurable composition described above is formed on one or both of the bonding surfaces of the polarizing film and the thermoplastic resin film, and the polarizing film and the protection thereof are formed through the coating layer. This is done by laminating the films, curing the coating layer of the uncured photocurable composition by irradiating it with active energy rays, and fixing these thermoplastic resin films on the polarizing film.

For the formation of the coating layer of the photocurable composition, various coating methods such as a doctor blade, a wire bar, a die coater, a comma coater, and a gravure coater can be used. It is also possible to adopt a method in which the polarizing film and the thermoplastic resin film are continuously supplied so that the bonding surface of both is on the inside, and the photocurable composition is cast between them. Since each coating method has an optimum viscosity range, it is also a useful technique to adjust the viscosity using a solvent. The type of solvent for this purpose is not particularly limited as long as it dissolves the photocurable composition well without deteriorating the optical performance of the polarizing film. For example, organic solvents such as hydrocarbons typified by toluene and esters typified by ethyl acetate can be used.

When adhering the polarizing film and the thermoplastic resin film, corona discharge treatment, plasma treatment, flame treatment, and primer treatment are performed on one or both of the bonding surfaces of the two before forming a coating layer of the photocurable composition. , An easy-adhesion treatment such as an anchor coating treatment may be applied.

The light source used to irradiate the coating layer of the photocurable composition with active energy rays may be one that generates ultraviolet rays, electron beams, X-rays, or the like. In particular, low-pressure mercury lamps, medium-pressure mercury lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, chemical lamps, black light lamps, microwave-excited mercury lamps, metal halide lamps, and the like having an emission distribution at a wavelength of 400 nm or less are preferably used. The irradiation intensity of the active energy ray on the photocurable composition is determined for each target composition and is not particularly limited, but the irradiation intensity in the wavelength region effective for activating the initiator is 0. It is preferably ¹ to 100 mW / cm 2. When the light irradiation intensity of the photocurable composition is ^{less than 0.1 mW / cm 2} , the reaction time becomes too long, ^{and when it exceeds 100 mW / cm 2} , the heat radiated from the lamp and the photocurable composition The heat generated during the polymerization may cause yellowing of the photocurable composition and deterioration of the polarizing film. The light irradiation time of the photocurable composition is controlled for each curing composition, and is not particularly limited, but the integrated light amount expressed as the product of the irradiation intensity and the irradiation time is 10 to 5, It is preferably set to 000 mJ / cm ^2. If the integrated light intensity into the photocurable composition is ^{less than 10 mJ / cm 2} , the active species derived from the initiator may not be sufficiently generated, and the resulting adhesive layer may be insufficiently cured. If the integrated light intensity ^{exceeds 5,000 mJ / cm 2} , the irradiation time becomes very long, which is disadvantageous for improving productivity.

When the thermoplastic resin films are bonded to both sides of the polarizing film, the active energy rays may be irradiated from either side of the thermoplastic resin film. For example, one of the thermoplastic resin films contains an ultraviolet absorber. When the other thermoplastic resin film does not contain an ultraviolet absorber, irradiating the active energy ray from the thermoplastic resin film side that does not contain the ultraviolet absorber effectively utilizes the irradiated active energy ray. , Preferred for increasing the curing rate.

The thickness of the adhesive layer formed by curing the photocurable composition is usually 20 μm or less, preferably 10 μm or less, and more preferably 5 μm or less. When the adhesive layer becomes thick, the durability in a heat-resistant environment and a high-temperature and high-humidity environment tends to deteriorate.

[Laminate optical member]
The polarizing plate of the present invention can be made into a laminated optical member by laminating optical layers having an optical function other than the polarizing plate. Typically, an optical layer is laminated and attached to a thermoplastic resin film of a polarizing plate via an adhesive layer or an adhesive layer to form a laminated optical member, but in addition, for example, one of the polarizing films. It is also possible to attach a thermoplastic resin film to a surface via a photocurable composition according to the present invention, and to laminate and attach an optical layer to the other surface of the polarizing film via an adhesive or an adhesive. In the latter case, a cured product of the photocurable composition specified in the present invention may be used as the adhesive layer for adhering the polarizing film and the optical layer, or it is formed from another known adhesive. An adhesive layer may be used.

To give an example of an optical layer laminated on a polarizing plate, for a polarizing plate arranged on the back side of a liquid crystal cell, reflection is laminated on the side of the polarizing plate opposite to the side facing the liquid crystal cell. There are layers, transflective layers, light diffusing layers, light collecting plates, brightness improving films, and the like. Further, for both the polarizing plate arranged on the front side of the liquid crystal cell and the polarizing plate arranged on the back side of the liquid crystal cell, a retardation plate or the like laminated on the side of the polarizing plate facing the liquid crystal cell, etc. There is.

The reflective layer, the semi-transmissive reflective layer, or the light diffusing layer is a reflective polarizing plate (optical member), a semi-transmissive reflective polarizing plate (optical member), or a diffusion type polarizing plate (optical member), respectively. It is provided in. The reflective polarizing plate is used in a liquid crystal display device of a type that reflects and displays incident light from the viewing side, and since a light source such as a backlight can be omitted, the liquid crystal display device can be easily made thinner. Further, the transflective polarizing plate is used in a liquid crystal display device of a type that displays light from a backlight in a dark place as a reflective type in a bright place. As an optical member as a reflective polarizing plate, for example, a reflective layer can be formed by attaching a foil made of a metal such as aluminum or a vapor-deposited film to a protective film on a polarizing film. The optical member as a semitransparent polarizing plate can be formed by using the above-mentioned reflective layer as a half mirror, or by adhering a reflector containing a pearl pigment or the like and exhibiting light transmission to the polarizing plate. On the other hand, as the optical member as a diffusion type polarizing plate, various methods such as a method of applying a matte treatment to a protective film on the polarizing plate, a method of applying a resin containing fine particles, and a method of adhering a film containing fine particles can be used. It is used to form a fine concavo-convex structure on the surface.

Further, it is also possible to form an optical member as a polarizing plate for both reflection and diffusion. In that case, for example, a method such as providing a reflection layer reflecting the uneven structure on the fine uneven structure surface of the diffusion type polarizing plate is adopted. it can. The reflective layer having a fine concavo-convex structure has advantages such as diffusing incident light by diffuse reflection, preventing directivity and glare, and suppressing unevenness of light and darkness. Further, the resin layer or film containing fine particles has an advantage that incident light and its reflected light are diffused when passing through the fine particle-containing layer, and uneven brightness can be suppressed. The reflective layer reflecting the surface fine uneven structure can be formed by directly attaching the metal to the surface of the fine uneven structure by, for example, a method such as vapor deposition or plating such as vacuum deposition, ion plating, and sputtering. The fine particles blended to form the surface fine uneven structure include, for example, silica, aluminum oxide, titanium oxide, zirconia, tin oxide, indium oxide, cadmium oxide, and antimony oxide having an average particle size of 0.1 to 30 μm. It can be inorganic fine particles, organic fine particles such as crosslinked or non-crosslinked polymers, and the like.

The condensing plate is used for the purpose of controlling the optical path, and can be formed as a prism array sheet, a lens array sheet, a sheet with dots, or the like.

The brightness improving film is used for the purpose of improving the brightness in a liquid crystal display device. For example, a plurality of thin films having different refractive anisotropies are laminated to cause anisotropy in reflectance. Examples thereof include a reflective polarizing separation sheet designed as described above, an oriented film of a cholesteric liquid crystal polymer, and a circularly polarized light separating sheet in which the oriented liquid crystal layer is supported on a film substrate.

On the other hand, the above-mentioned retardation plate as an optical layer is used for the purpose of compensating for the retardation by the liquid crystal cell. Examples thereof include a birefringent film made of stretched films of various plastics, a film in which a discotic liquid crystal or a nematic liquid crystal is oriented and fixed, and a film in which the above liquid crystal layer is formed on a film substrate. When a liquid crystal layer is formed on a film base material, a cellulosic resin film such as triacetyl cellulose is preferably used as the film base material.

Examples of the plastic forming the birefractive film include an amorphous polyolefin resin, a polycarbonate resin, an acrylic resin, a chain polyolefin resin such as polypropylene, polyvinyl alcohol, polystyrene, polyarylate, and polyamide. Be done. The stretched film can be processed by an appropriate method such as uniaxial or biaxial. Two or more retardation plates may be used in combination for the purpose of controlling optical characteristics such as widening the bandwidth.

In the laminated optical member, a material including a retardation plate as an optical layer other than the polarizing plate is preferably used because it can effectively guarantee the optics when applied to a liquid crystal display device. The optimum retardation value (in-plane and thickness direction) of the retardation plate may be selected according to the liquid crystal cell to be applied.

The laminated optical member can be a laminated body having two layers or three or more layers by combining a polarizing plate and one layer or two or more layers selected from the various optical layers described above according to the purpose of use. In that case, the various optical layers forming the laminated optical member are integrated with the polarizing plate by using an adhesive layer or an adhesive layer, and the adhesive or the adhesive used for that purpose is an adhesive layer or an adhesive layer. Is not particularly limited as long as it is well formed. It is preferable to use an adhesive (also called a pressure-sensitive adhesive) from the viewpoint of easiness of bonding work and prevention of occurrence of optical strain. As the pressure-sensitive adhesive, an acrylic polymer, a silicone-based polymer, a polyester, a polyurethane, a polyether, or the like as a base polymer can be used. Among them, like acrylic adhesives, it has excellent optical transparency, retains appropriate wettability and cohesiveness, has excellent adhesion to the base material, and has weather resistance and heat resistance. However, it is preferable to select and use a material that does not cause peeling problems such as floating and peeling under the conditions of heating and humidification. In acrylic pressure-sensitive adhesives, alkyl esters of (meth) acrylic acids having an alkyl group having 20 or less carbon atoms such as methyl group, ethyl group and butyl group, and hydroxyethyl (meth) acrylic acid and (meth) acrylic acid Based on an acrylic copolymer having a weight average molecular weight of 100,000 or more, which is blended with a functional group-containing acrylic monomer composed of the above so that the glass transition temperature is preferably 25 ° C. or lower, more preferably 0 ° C. or lower. Useful as a polymer.

To form the pressure-sensitive adhesive layer on the polarizing plate, for example, a pressure-sensitive adhesive composition is dissolved or dispersed in an organic solvent such as toluene or ethyl acetate to prepare a 10 to 40% by mass solution, which is directly placed on the polarizing plate. This can be done by a coating method, a method in which an adhesive layer is formed on a protective film in advance, and a method in which the pressure-sensitive adhesive layer is transferred onto a polarizing plate. The thickness of the pressure-sensitive adhesive layer is determined according to the adhesive strength and the like, but a range of about 1 to 50 μm is appropriate.

Further, as necessary, the pressure-sensitive adhesive layer contains a filler composed of glass fiber, glass beads, resin beads, metal powder or other inorganic powder, a pigment or a colorant, an antioxidant, an antioxidant, and an ultraviolet absorber. Etc. may be blended. Examples of the ultraviolet absorber include salicylate ester compounds, benzophenone compounds, benzotriazole compounds, cyanoacrylate compounds, and nickel complex salt compounds.

Examples of the antistatic agent include ionic compounds, conductive fine particles, and conductive polymers. From these, appropriate antistatic agents can be used alone or in combination of two or more. Of course, two or more antistatic agents classified as ionic compounds can be used in combination, or two or more antistatic agents classified as conductive fine particles can be used in combination, and the conductivity is high. It is also possible to use two or more antistatic agents classified as molecules in combination.

Among the antistatic agents described above, an ionic compound is preferably used because it has excellent compatibility with a solvent.

The ionic compound can be classified into an ionic compound having an organic cation, an ionic compound having an inorganic cation, an ionic compound having an organic anion, and an ionic compound having an inorganic anion. Examples of the organic cation include pyridinium cation, imidazolium cation, ammonium cation, sulfonium cation, phosphonium cation and the like. Examples of the indefinite cation include lithium and potassium. The cation component constituting the ionic compound may be an inorganic anion or an organic anion, but is preferably an organic cation from the viewpoint of compatibility with the (meth) acrylic resin. On the other hand, the anion component constituting the ionic compound may be an inorganic anion or an organic anion, but an anion component containing a fluorine atom is preferable because it provides an ionic compound having excellent antistatic performance. The anionic component containing a fluorine atom, hexafluorophosphate anion [(PF ₆ ^-)], bis (trifluoromethanesulfonyl) imide anion _{[(CF 3 SO 2) 2} N -] anion, bis (fluorosulfonyl) imide anion [ (FSO _{2) 2} N ^-] anion, and the like.

The laminated optical member can be arranged on one side or both sides of the liquid crystal cell. The liquid crystal cell used is arbitrary, and a liquid crystal display device using various liquid crystal cells such as an active matrix drive type represented by a thin film transistor type and a simple matrix drive type represented by a super twisted nematic type. Can be formed. An adhesive is usually used to bond the laminated optical member and the liquid crystal cell.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples. In the examples, "parts" and "%" indicating the content or the amount used are based on mass unless otherwise specified. The cationically polymerizable compounds, photocationic polymerization initiators, and leveling agents used in the following examples are as follows, and are indicated by the respective symbols below.

(A) Cationic Polymerizable Compound (a1) 3-Ethyl-3 {[(3-Ethyloxetane-3-yl) methoxy] Methyl} Oxetane: Obtained from Toa Synthetic Co., Ltd., trade name "OXT-221". In Table 1 described later, it is abbreviated as "(a1)".
(A2) 1,4-Butanediol diglycidyl ether: Obtained from Nagase ChemteX Corporation, trade name "EX-214L". In Table 1 described later, it is abbreviated as "(a2)".

(B) Photocationic polymerization initiator (b1) 4- (Phenylthio) Phenyldiphenylsulfonium Hexafluorophosphate: Obtained from San-Apro Co., Ltd., trade name "CPI-100P". In Table 1 described later, it is abbreviated as "(b1)". CPI-100P was used as a 50% propylene carbonate solution, and the solid content thereof is shown in Table 1.

[Examples 1 to 3 and Comparative Example 1]
[Preparation Examples 1 to 4]
(1) Preparation of Photocurable Compositions Each component was mixed at the blending ratio shown in Table 1 and then defoamed to prepare photocurable compositions 1 to 3.

(2) Fabrication of polarizing plate
[Example 1]
A polarizing plate was prepared using the above photocurable composition 1. The surface of a 50 μm-thick cycloolefin film [trade name “ZEONOR” manufactured by Nippon Zeon Corporation] is subjected to corona discharge treatment, and the corona discharge treated surface is subjected to the above photocurable composition using a bar coater. Object 1 was coated so that the film thickness after curing was about 1.5 μm. A polyvinyl alcohol-iodine-based polarizing film was attached to the coated surface of the photocurable composition. In addition, a protective film made of (meth) acrylic resin (PMMA) [trade name "Technoloy S001", manufactured by Sumitomo Chemical Co., Ltd.] containing an ultraviolet absorber and having a thickness of 80 μm is subjected to corona discharge treatment. The same photocurable composition 1 used for the cycloolefin-based film was coated on the corona discharge-treated surface with a bar coater so that the film thickness after curing was about 1.5 μm. A polarizing film in which the cycloolefin film prepared above was bonded to one side was bonded to the coated surface of the photocurable composition on the polarizing film side to prepare a laminate. From the cycloolefin film side of this laminate, use an ultraviolet irradiation device with a belt conveyor (the lamp uses a "D valve" manufactured by Fusion UV Systems) so that the integrated light amount (UVB) is 200 mJ / cm ^2. To cure the photocurable composition to form an adhesive layer. In this way, a polarizing plate in which a protective film was bonded to both sides of the polarizing film via an adhesive was produced.

[Example 2]
A polarizing plate was prepared using the above photocurable composition 1. The surface of a 50 μm-thick cycloolefin film [trade name “ZEONOR” manufactured by Nippon Zeon Corporation] is subjected to corona discharge treatment, and the corona discharge treated surface is subjected to the above photocurable composition using a bar coater. The object 1 was coated so that the film thickness after curing was about 1.5 μm. A polyvinyl alcohol-iodine-based polarizing film was attached to the coated surface of the photocurable composition. Further, a corona discharge treatment is applied to the bonded surface of a triacetyl cellulose (TAC) film [trade name "TD60UL", manufactured by Fuji Film Co., Ltd.] having a thickness of 60 μm containing an ultraviolet absorber, and the corona discharge treated surface is subjected to a corona discharge treatment. The same photocurable composition used for the cycloolefin film was coated with a bar coater so that the film thickness after curing was about 1.5 μm. A polarizing film in which the cycloolefin film prepared above was bonded to one side was bonded to the coated surface of the photocurable composition on the polarizing film side to prepare a laminate. From the cycloolefin film side of this laminate, use an ultraviolet irradiation device with a belt conveyor (the lamp uses a "D valve" manufactured by Fusion UV Systems) so that the integrated light amount (UVB) is 200 mJ / cm ^2. To cure the photocurable composition to form an adhesive layer. In this way, a polarizing plate in which a protective film was bonded to both sides of the polarizing film via an adhesive was produced.

[Example 3]
A polarizing plate was produced in the same manner as in Example 1 except that the photocurable composition 1 was replaced with the photocurable composition 2.

[Comparative Example 1]
A polarizing plate was produced in the same manner as in Example 1 except that the photocurable composition 1 was replaced with the photocurable composition 3.

The moisture permeability of the thermoplastic resin film at a temperature of 40 ° C. and a relative humidity of 90% was measured by the cup method specified in JIS Z 0208.
^{PMMA: 60g / (m 2 ·} 24hr)
^{TAC: 520g / (m 2 ·} 24hr)
^{COP: 5.8g / (m 2 ·} 24hr)

(3) Preparation of Polarizing Plate with Adhesive Layer The cycloolefin film surface of the polarizing plate prepared in (2) above is subjected to corona treatment, and an acrylic pressure-sensitive adhesive having a thickness of 25 μm is bonded with a laminator, and then the temperature is increased. A polarizing film with an adhesive was obtained by curing for 7 days under the conditions of 23 ° C. and 65% relative humidity.

(4) Evaluation of Optical Characteristics of Polarizing Plate The polarizing plate with adhesive produced in (3) above is cut into a size of 30 mm × 30 mm and bonded to non-alkali glass [trade name “EAGLE XG” manufactured by Corning Inc.]. Then, the b value of each transparent hue was measured. The measurement was performed using an ultraviolet visible spectrophotometer "UV-2450" manufactured by Shimadzu Corporation with an optional accessory "film holder with polarizing film" set, and the transmission of the polarizing plate in the wavelength range of 380 nm to 780 nm. The spectrum was obtained, and the b value of the transmitted hue was calculated by the software "UV-Probe" attached to the spectrophotometer.

(5) Heat resistance evaluation of the polarizing plate The polarizing plate produced in (4) above is subjected to a heating test in which it is allowed to stand in a heating environment at a temperature of 90 ° C. for 48 hours, and the transmitted hue b value of the polarizing plate after the test is measured. did. The measurement and the calculation of the b value were carried out by the same method as in (4) above. The absolute value (| Δb |) of the difference in transmitted hue before and after the heat resistance test was calculated according to the following formula.

| Δb | = | b value after heating test-b value before heating test |

Next, from the obtained values of | Δb |, the “Δb change rate (improvement rate)” (%) of each example based on | Δb | of Comparative Example 1 was obtained based on the following formula. The calculated values of the rate of change of Δb are shown in Table 1. The larger the rate of change of Δb, the better the heat resistance.
Δb change rate (%) of each example
= | {(| Δb | in each example)-(| Δb | in Comparative Example 1)} | / (| Δb | in Comparative Example 1) × 100
In each of the examples and comparative examples, Δb showed a positive value.
The results are shown in Table 1.

From Table 1, in the polarizing plate in which the thermoplastic resin film is bonded to at least one surface of the polarizing film via an adhesive, the adhesive is used, and the bifunctional oxetane compound is contained in the cationically polymerizable compound from 10 to 70. It was confirmed that good heat resistance was exhibited by containing 0.5 to 1.5 parts by mass of the photocationic polymerization initiator with respect to 100 parts by mass of the cationically polymerizable compound.

[Preparation Example 4-10]
(1) Preparation of Photocurable Compositions Each component was mixed at the blending ratio shown in Table 2 and then defoamed to prepare photocurable compositions 4 to 10.
The abbreviations in Table 2 indicate the compounds listed below.
(A) Cationic Polymerizable Compound (a1) 3-Ethyl-3 {[(3-Ethyloxetane-3-yl) methoxy] Methyl} Oxetane: Obtained from Toa Synthetic Co., Ltd., trade name "OXT-221". In Table 2, it is abbreviated as "(a1)".
(A2) 1,4-Butanediol diglycidyl ether: Obtained from Nagase ChemteX Corporation, trade name "EX-214L". In Table 2, it is abbreviated as "(a2)".
(A3) Neopentyl glycol diglycidyl ether: Obtained from Nagasechemtex Co., Ltd., trade name "EX-211L". In Table 2, it is abbreviated as "(a3)".
(A4) Pentaerythritol polyglycidyl ether: Obtained from Nagase ChemteX Corporation, trade name "EX-411". In Table 2, it is abbreviated as "(a4)".
(A5) 3', 4'-Epoxycyclohexylmethyl 3,4-Cyclohexanecarboxylate: Obtained from Daicel Chemical Co., Ltd., trade name "Ceroxide 2021P". In Table 2, it is abbreviated as "(a5)".
(B) Photocationic polymerization initiator (b1) 4- (Phenylthio) Phenyldiphenylsulfonium Hexafluorophosphate: Obtained from San-Apro Co., Ltd., trade name "CPI-100P". In Table 2, it is abbreviated as "(b1)". CPI-100P was used as a 50% propylene carbonate solution, and the solid content thereof is shown in Table 2.

[Example 4]
(2) Preparation of polarizing plate A corona discharge treatment is applied to the surface of a cycloolefin resin film having a thickness of 50 μm [trade name “ZEONOR” manufactured by Nippon Zeon Corporation], and a bar coater is applied to the corona discharge treatment surface. Using, the photocurable composition 4 was coated so that the film thickness after curing was about 1.5 μm. A polyvinyl alcohol-iodine-based polarizing film was attached to the coated surface of the photocurable composition 4. In addition, a protective film made of (meth) acrylic resin (PMMA) [trade name "Technoloy S001", manufactured by Sumitomo Chemical Co., Ltd.] containing an ultraviolet absorber and having a thickness of 80 μm is subjected to corona discharge treatment. The photocurable composition 4 was coated on the corona discharge-treated surface with a bar coater so that the film thickness after curing was about 1.5 μm. A polarizing film having the cycloolefin film prepared above bonded on one side was bonded to the coated surface of the photocurable composition 4 on the polarizing film side to prepare a laminate. From the cycloolefin film side of this laminate, use an ultraviolet irradiation device with a belt conveyor (the lamp uses a "D valve" manufactured by Fusion UV Systems) so that the integrated light amount (UVB) is 200 mJ / cm ^2. The photocurable composition was cured to form an adhesive layer, and a protective film was bonded to both sides of the polarizing film via an adhesive to prepare a polarizing plate.

[Example 5]
A polarizing plate was produced in the same manner as in Example 4 except that the photocurable composition 4 was replaced with the photocurable composition 5.

[Example 6]
A polarizing plate was produced in the same manner as in Example 4 except that the photocurable composition 4 was replaced with the photocurable composition 6.

[Example 7]
A polarizing plate was produced in the same manner as in Example 4 except that the photocurable composition 4 was replaced with the photocurable composition 7.

[Example 8]
A polarizing plate was produced in the same manner as in Example 4 except that the photocurable composition 4 was replaced with the photocurable composition 8.

[Example 9]
A polarizing plate was produced in the same manner as in Example 4 except that the photocurable composition 4 was replaced with the photocurable composition 9.

[Example 10]
A polarizing plate was produced in the same manner as in Example 4 except that the photocurable composition 4 was replaced with the photocurable composition 10.

(3) Preparation of Polarizing Plate with Adhesive Layer The cycloolefin film surface of the polarizing plate prepared in (2) above is corona-treated, and an acrylic pressure-sensitive adhesive having a thickness of 25 μm is bonded with a laminator, and then the temperature is increased. A polarizing film with an adhesive was obtained by curing for 7 days under the conditions of 23 ° C. and 65% relative humidity.

(4) Evaluation of Optical Characteristics of Polarizing Plate The polarizing plate with adhesive produced in (3) above is cut into a size of 30 mm × 30 mm and bonded to non-alkali glass [trade name “EAGLE XG” manufactured by Corning Inc.]. Then, the b value of each transparent hue was measured. The measurement was performed using an ultraviolet visible spectrophotometer "UV-2450" manufactured by Shimadzu Corporation with an optional accessory "film holder with polarizing film" set, and the transmission of the polarizing plate in the wavelength range of 380 nm to 780 nm. The spectrum was obtained, and the b value of the transmitted hue was calculated by the software "UV-Probe" attached to the spectrophotometer.

(5) Heat resistance evaluation of the polarizing plate The polarizing plate produced in (4) above is subjected to a heating test in which it is allowed to stand in a heating environment at a temperature of 90 ° C. for 48 hours, and the transmitted hue b value of the polarizing plate after the test is measured. did. The measurement and the calculation of the b value were carried out by the same method as in (4) above. The absolute value (| Δb |) of the difference in transmitted hue before and after the heat resistance test was calculated according to the following formula.
| Δb | = | b value after heating test-b value before heating test |

Next, from the obtained values of | Δb |, the “Δb change rate (improvement rate)” (%) of each example based on | Δb | of Comparative Example 1 was obtained based on the following formula. Table 2 shows the calculated values of the rate of change of Δb. The larger the rate of change of Δb, the better the heat resistance.
Δb change rate (%) of each example
= | {(| Δb | in each example)-(| Δb | in Comparative Example 1)} | / (| Δb | in Comparative Example 1) × 100
In each of the examples and comparative examples, Δb showed a positive value.
The results are shown in Table 2.

(6) Evaluation of Moisture and Heat Resistance of Polarizing Plate The polarizing plate produced in (4) above is subjected to a moisture and heat resistance test in which it is allowed to stand in a high temperature and high humidity environment at a temperature of 80 ° C. and a relative humidity of 90% for 48 hours. The luminosity factor correction single transmittance Ty value in the above was measured. The measurement and the calculation of the Ty value were carried out in the same manner as in (4) above. The absolute value (| ΔTy |) of the difference in the luminous efficiency correction single transmittance Ty before and after the moisture resistance heat test was calculated according to the following formula.
| ΔTy | = | Ty value after heating test-Ty value before heating test |
In each of the examples and comparative examples, ΔTy showed a positive value.
The results are shown in Table 3.

Claims (3)

A polarizing plate in which a thermoplastic resin film is bonded to at least one surface of a polarizing film via an adhesive layer.
The adhesive layer is a cured product of a photocurable composition containing a cationically polymerizable compound and a photocationic polymerization initiator.
The photocurable composition contains 0.5 to 1.5 parts by mass of a photocationic polymerization initiator with respect to 100 parts by mass of the cationically polymerizable compound.
The cationically polymerizable compound is a polarizing plate containing 10 to 70% by mass of a bifunctional oxetane compound with respect to the total mass of the cationically polymerizable compound. The polarizing plate according to claim 1, wherein the cationically polymerizable compound further contains 10 to 70% by mass of an aliphatic epoxy compound with respect to the total mass of the cationically polymerizable compound. The thermoplastic resin film, the temperature 40 ° C., a moisture permeability at a relative humidity of 90% is 300g / (m ² · 24hr) or less, the polarizing plate according to claim 1 or 2.