CN116761861A

CN116761861A - polarizing plate

Info

Publication number: CN116761861A
Application number: CN202180087399.XA
Authority: CN
Inventors: 岩田智; 阪上智惠
Original assignee: Sumitomo Chemical Co Ltd
Current assignee: Sumitomo Chemical Co Ltd
Priority date: 2020-12-28
Filing date: 2021-12-24
Publication date: 2023-09-15

Abstract

Provided is a polarizing plate wherein protective films are bonded to both surfaces of a polarizing film, and curling is less likely to occur or the degree of curling is small even when the polarizing plate is placed in a high-humidity environment. Provided is a polarizing plate comprising, in order, a 1 st protective film, a 1 st adhesive layer, a polarizing film, a 2 nd adhesive layer, and a 2 nd protective film, wherein the 1 st adhesive layer is a cured product layer of a 1 st cationic polymerization type adhesive comprising 1 or more cationic polymerization initiators, the 2 nd adhesive layer is a cured product layer of a 2 nd cationic polymerization type adhesive comprising 1 or more cationic polymerization initiators, 1 st cationic polymerization initiators contained in the 1 st cationic polymerization type adhesive comprise the 1 st cationic polymerization initiator, the 1 st cationic polymerization initiator is a borate comprising a cationic component and an anionic component represented by formula (i), and the molecular weight of the 1 st cationic polymerization initiator is greater than the molecular weight of the 1 st cationic polymerization initiator contained in the 2 nd cationic polymerization type adhesive.

Description

Polarizing plate

Technical Field

The present invention relates to a polarizing plate having a protective film bonded to both surfaces of a polarizing film via an adhesive layer.

Background

Polarizing plates widely used in image display devices typified by liquid crystal display devices generally have a structure in which protective films are laminated on both surfaces of a polarizing film. An adhesive is generally used for bonding the polarizing film and the protective film. As an adhesive for bonding a protective film, an aqueous adhesive and an active energy ray-curable adhesive are known.

Japanese patent application laid-open No. 2015-140374 (patent document 1) discloses a radiation curable composition including: (A) a compound having an ester group and having 2 or more alicyclic epoxy groups in the molecule, (B) a photo-cation polymerization initiator having a fluoroalkyl fluorophosphate anion or a pentafluorophenyl borate anion, and (C) a compound having 3 or more hydroxyl groups in the molecule.

Prior art literature

Patent literature

Patent document 1: japanese patent application laid-open No. 2015-140374

Disclosure of Invention

Problems to be solved by the invention

In general, a polarizing plate is manufactured in a roll-to-roll manner into a long product (polarizing plate roll), and then, for example, is cut into a polarizing plate single piece having a size corresponding to the screen size of an image display device to be applied, and is attached to an image display element, thereby being assembled into the image display device. After the polarizing plate is cut into a single piece, the polarizing plate may be stored or transported for a certain period of time before being assembled into the image display device, and at this time, the storage and transport environment may become relatively wet. The polarizing plate monolithic body exposed to a high humidity environment is liable to curl (warp).

The purpose of the present invention is to provide a polarizing plate, wherein a protective film is bonded to both sides of a polarizing film, and curling is not easily generated or the degree of curling is small even when the polarizing plate is placed in a high-humidity environment.

Means for solving the problems

The present invention provides the following polarizing plate.

[1] A polarizing plate comprising, in order, a 1 st protective film, a 1 st adhesive layer, a polarizing film, a 2 nd adhesive layer, and a 2 nd protective film,

the 1 st adhesive layer is a cured product layer of a 1 st cationic polymerization adhesive containing 1 or more cationic polymerization initiators,

the 2 nd adhesive layer is a cured product layer of a 2 nd cationic polymerization adhesive containing 1 or more cationic polymerization initiators,

the 1 st cationic polymerization initiator or more contained in the 1 st cationic polymerization type adhesive includes a 1 st cationic polymerization initiator,

the 1 st cationic polymerization initiator is a borate comprising a cationic component and an anionic component represented by the following formula (i),

[ chemical formula 1]

[(Y) _k B(Phf) _4-k ] ^- (i)

(wherein Y represents an aryl group having 6 to 30 carbon atoms or a heterocyclic group having 4 to 30 carbon atoms which may have a substituent (excluding a group containing a halogen atom), or a halogen atom Phf represents a phenyl group wherein at least 1 of hydrogen atoms is substituted with at least 1 selected from perfluoroalkyl groups, perfluoroalkoxy groups and halogen atoms, k is any integer of 0 to 4),

The molecular weight of the 1 st cationic polymerization initiator is larger than the molecular weight of the 1 or more cationic polymerization initiators contained in the 2 nd cationic polymerization adhesive.

[2] The polarizing plate according to [1], wherein the cation component is an aryl sulfonium ion.

[3] The polarizing plate according to [1] or [2], wherein the 1 st cation polymerizable adhesive and the 2 nd cation polymerizable adhesive further comprise a cation polymerizable compound,

the content of the 1 or more cationic polymerization initiators contained in the 1 st cationic polymerization adhesive and the content of the 1 or more cationic polymerization initiators contained in the 2 nd cationic polymerization adhesive are 0.5 parts by mass or more and 5 parts by mass or less relative to 100 parts by mass of the cationic polymerizable compound.

[4] The polarizing plate according to any one of [1] to [3], wherein the 1 st protective film is formed of a (meth) acrylic resin or a cellulose ester resin.

[5] The polarizing plate according to any one of [1] to [4], wherein an adhesive layer is further provided on a side of the 2 nd protective film opposite to the 2 nd adhesive layer side.

Effects of the invention

A polarizing plate having protective films bonded to both surfaces of a polarizing film, which is less likely to cause curling or a small degree of curling even when placed in a high-humidity environment, can be provided.

Drawings

Fig. 1 is a schematic cross-sectional view showing an example of the layer structure of the polarizing plate of the present invention.

Detailed Description

Hereinafter, the polarizing plate (hereinafter, also simply referred to as "polarizing plate") of the present invention will be described in detail.

(1) Structure of polarizing plate

As shown in fig. 1, the polarizing plate includes, in order, a 1 st protective film 10, a 1 st adhesive layer 15, a polarizing film 30, a 2 nd adhesive layer 25, and a 2 nd protective film 20. That is, the 1 st protective film 10 is laminated on one surface of the polarizing film 30 via the 1 st adhesive layer 15, and the 2 nd protective film 20 is laminated on the other surface of the polarizing film 30 via the 2 nd adhesive layer 25.

The 1 st adhesive layer 15 is preferably in contact with the 1 st protective film 10 and the polarizing film 30. The 2 nd adhesive layer 25 is preferably in contact with the polarizing film 30 and the 2 nd protective film 20.

The polarizing plate may include other layers than those described above, not limited to the example of fig. 1. Specific examples of other layers include: an adhesive layer laminated on the outer surface of the 1 st protective film 10 and/or the 2 nd protective film 20; a release film (also referred to as a "release film") laminated to an outer surface of the adhesive layer; a protective film (also referred to as a "surface protective film") laminated on the outer surface of the 1 st protective film 10 and/or the 2 nd protective film 20; an optically functional film or the like laminated on the outer surface of the 1 st protective film 10 and/or the 2 nd protective film 20 via an adhesive layer or an adhesive layer.

The polarizing plate of the present invention can be a polarizing plate which is less likely to cause curling or a small degree of curling even when placed in a high humidity environment. Hereinafter, the degree to which curl is less likely to occur is also referred to as "curl resistance", and the degree to which curl is less likely to occur or curl is also referred to as "good curl resistance".

The polarizing plate may be a long product or a wound roll thereof having the polarizing plate formed of the above layers, or may be a single sheet. The sheet body is a sheet body cut into a predetermined size from the long article or a wound roll thereof, and generally has a square shape such as a rectangle or a square.

In the case where the polarizing plate is a long article or a wound roll thereof, the curl resistance means: curl resistance of a sheet cut from a long article or a wound roll thereof. In the case where the polarizing plate is a monolithic body, the curl resistance means: curl resistance for the singlets or smaller sized singlets cut from the singlets.

(2) Polarizing film

The polarizing film 30 is a film having a function of selectively transmitting linearly polarized light in a certain direction from natural light. For example, there may be mentioned: an iodine-based polarizing film in which iodine is adsorbed to a polyvinyl alcohol-based resin film and oriented; a dye-based polarizing film in which a dichroic dye is adsorbed to a polyvinyl alcohol-based resin film and is oriented; and a coated polarizing film in which a dichroic dye in a lyotropic liquid crystal state is coated and aligned and immobilized. These polarizing films selectively transmit linear polarized light in one direction from natural light and absorb linear polarized light in the other direction, and are therefore called absorption-type polarizing films.

The polarizing film 30 is not limited to an absorption-type polarizing film, but may be a reflection-type polarizing film that selectively transmits linear polarized light in one direction from natural light and reflects linear polarized light in the other direction, or a scattering-type polarizing film that scatters linear polarized light in the other direction, and is preferably an absorption-type polarizing film in view of excellent visibility. Among them, an iodine-based polarizing film excellent in polarization degree and transmittance is more preferable.

Polarizing film 30 may be manufactured by a method comprising: a step of uniaxially stretching a polyvinyl alcohol resin film; a step of adsorbing a dichroic dye by dyeing a polyvinyl alcohol resin film with the dichroic dye; a step of treating (crosslinking treatment) the polyvinyl alcohol resin film having the dichroic dye adsorbed thereon with an aqueous boric acid solution; and a step of washing with water after the treatment with the aqueous boric acid solution. The stretching ratio is usually about 3 to 8 times.

After washing with water, a drying treatment was performed to obtain a polarizing film 30. The drying treatment may be performed using a hot air dryer or a far infrared heater. A polarizing plate can be obtained by bonding protective films to both surfaces of the polarizing film 30 with an adhesive.

The thickness of the polarizing film 30 may be 40 μm or less, preferably 30 μm or less (for example, 20 μm or less). According to the methods described in japanese patent application laid-open nos. 2000-338329 and 2012-159778, the polarizing film 30 of the thin film can be produced more easily, and the thickness of the polarizing film 30 may be 20 μm or less, for example, or may be 10 μm or less. The thickness of the polarizing film 30 is usually 2 μm or more. Reducing the thickness of the polarizing film 30 is advantageous for thinning of the polarizing plate, even the image display device.

(3) Protective film

The first protective film 10 and the second protective film 20 are each a resin film including: a thermoplastic resin having light transmittance (preferably, optical transparency), for example, a polyolefin resin such as a linear polyolefin resin (polypropylene resin or the like) or a cyclic polyolefin resin (norbornene resin or the like); cellulose ester resins such as triacetyl cellulose and diacetyl cellulose; polyester resins such as polyethylene terephthalate, polyethylene naphthalate and polybutylene terephthalate; a polycarbonate resin; (meth) acrylic resins; or mixtures, copolymers, etc. thereof.

Among them, the 1 st protective film 10 and the 2 nd protective film 20 are preferably formed of a resin selected from the group consisting of polyester-based resins, polycarbonate-based resins, polyolefin-based resins, (meth) acrylic resins and cellulose ester-based resins, respectively.

In the present specification, "(meth) acrylic acid" means methacrylic acid and/or acrylic acid, and "(meth)" means "(meth) acrylic acid ester" and the like.

The 1 st protective film 10 and the 2 nd protective film 20 may be any one of an unstretched film or a uniaxially or biaxially stretched film, respectively. The biaxial stretching may be simultaneous biaxial stretching in which stretching is performed simultaneously in 2 stretching directions, or sequential biaxial stretching in which stretching is performed in a predetermined direction and then stretching is performed in other directions. The 1 st protective film 10 and/or the 2 nd protective film 20 may be a protective film having an optical function such as a retardation film. The retardation film is an optical functional film used for the purpose of compensating a phase difference or the like caused by a liquid crystal cell as an image display element. For example, a retardation film to which an arbitrary phase difference value is imparted can be produced by stretching a film containing the thermoplastic resin (uniaxial stretching, biaxial stretching, or the like) or forming a liquid crystal layer or the like on the film.

The chain polyolefin resin includes a homopolymer of a chain olefin such as a polyethylene resin or a polypropylene resin, and a copolymer containing 2 or more chain olefins.

The cyclic polyolefin resin is a general term for resins containing a cyclic olefin represented by norbornene, tetracyclododecene (alias: dimethylbridged octahydronaphthalene) or a derivative thereof as a polymerization unit. Specific examples of the cyclic polyolefin resin include: ring-opened (co) polymers of cyclic olefins and hydrogenated products thereof, addition polymers of cyclic olefins, copolymers of cyclic olefins with chain olefins such as ethylene and propylene or aromatic compounds having a vinyl group, and modified (co) polymers obtained by modifying them with unsaturated carboxylic acids or derivatives thereof. Among them, preferably, use is made of: norbornene-based resins using norbornene-based monomers such as norbornene and polycyclic norbornene-based monomers as cyclic olefins.

The cellulose ester resin is a resin in which at least a part of hydroxyl groups in cellulose is esterified with acetic acid, and may be a mixed ester in which a part of hydroxyl groups is esterified with acetic acid and a part of hydroxyl groups is esterified with other acids. The cellulose ester resin is preferably an acetyl cellulose resin. Specific examples of the acetylcellulose resin include triacetylcellulose, diacetylcellulose, cellulose acetate propionate, and cellulose acetate butyrate.

The polyester resin is a resin having an ester bond and other than the cellulose ester resin, and generally contains a polycondensate of a polycarboxylic acid or a derivative thereof and a polyhydric alcohol. Specific examples of the polyester resin include: polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polypropylene terephthalate, polypropylene naphthalate, polymethyl cyclohexane terephthalate, and polymethyl cyclohexane naphthalate. Among them, polyethylene terephthalate is preferable. Polyethylene terephthalate refers to a resin comprising ethylene terephthalate in which 80 mol% or more of the repeating units are present.

The polycarbonate resin is a polyester formed from carbonic acid and a diol or bisphenol.

The (meth) acrylic resin may be a polymer containing methacrylate as a main monomer (50 mass% or more), and is preferably a copolymer having a small amount of other copolymerization component copolymerized thereon. The (meth) acrylic resin is more preferably a copolymer of methyl methacrylate and methyl acrylate, and the third monofunctional monomer may be further copolymerized.

Examples of the third monofunctional monomer include: methacrylates other than methyl methacrylate such as ethyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, benzyl methacrylate, 2-ethylhexyl methacrylate, and 2-hydroxyethyl methacrylate; acrylic esters such as ethyl acrylate, butyl acrylate, cyclohexyl acrylate, phenyl acrylate, benzyl acrylate, 2-ethylhexyl acrylate, and 2-hydroxyethyl acrylate; hydroxyalkyl acrylates such as methyl 2- (hydroxymethyl) acrylate, methyl 2- (1-hydroxyethyl) acrylate, ethyl 2- (hydroxymethyl) acrylate, and butyl 2- (hydroxymethyl) acrylate; unsaturated acids such as methacrylic acid and acrylic acid; halogenated styrenes such as chlorostyrene and bromostyrene; substituted styrenes such as vinyl toluene and α -methylstyrene; unsaturated nitriles such as acrylonitrile and methacrylonitrile; unsaturated anhydrides such as maleic anhydride and citraconic anhydride; unsaturated imides such as phenylmaleimide and cyclohexylmaleimide. The third monofunctional monomer may be used alone or in combination of 1 or more than 2.

The (meth) acrylic resin may further be copolymerized with a polyfunctional monomer. Examples of the polyfunctional monomer include: ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, nonaethylene glycol di (meth) acrylate, tetradecanediol di (meth) acrylate, and the like, in which both terminal hydroxyl groups of ethylene glycol or an oligomer thereof are esterified with (meth) acrylic acid; a substance obtained by esterifying both terminal hydroxyl groups of propylene glycol or an oligomer thereof with (meth) acrylic acid; a substance obtained by esterifying a hydroxyl group of a 2-membered alcohol with (meth) acrylic acid, such as neopentyl glycol di (meth) acrylate, hexanediol di (meth) acrylate, and butanediol di (meth) acrylate; a bisphenol A, an alkylene oxide adduct of bisphenol A, or a halogen-substituted product thereof, both terminal hydroxyl groups of which are esterified with (meth) acrylic acid; a substance obtained by esterifying a polyhydric alcohol such as trimethylolpropane or pentaerythritol with (meth) acrylic acid, or a substance obtained by ring-opening addition of an epoxy group of glycidyl (meth) acrylate to a terminal hydroxyl group of the polyhydric alcohol; a substance obtained by ring-opening addition of an epoxy group of glycidyl (meth) acrylate to a dibasic acid such as succinic acid, adipic acid, terephthalic acid, phthalic acid, or a halogen substituent thereof, or an alkylene oxide adduct thereof; aryl (meth) acrylates; aromatic divinyl compounds such as divinylbenzene, and the like. Among them, ethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, neopentyl glycol dimethacrylate are preferably used.

The (meth) acrylic resin may be a (meth) acrylic resin modified by further reacting functional groups of the copolymer. Examples of the reaction include: and (3) a polymer chain internal demethylating condensation reaction of methyl acrylate groups and hydroxyl groups of 2- (hydroxymethyl) methyl acrylate, a polymer chain internal dehydration condensation reaction of carboxyl groups of acrylic acid and hydroxyl groups of 2- (hydroxymethyl) methyl acrylate, and the like.

The glass transition temperature of the (meth) acrylic resin is preferably 80 to 160 ℃. The glass transition temperature can be controlled by adjusting the polymerization ratio of the methacrylate-based monomer and the acrylate-based monomer, the carbon chain length of each ester group and the kind of functional group they have, and the polymerization ratio of the polyfunctional monomer to the entire monomers. In addition, as a method for increasing the glass transition temperature of the (meth) acrylic resin, it is also effective to introduce a ring structure into the main chain of the polymer. The ring structure is preferably a heterocyclic structure such as a cyclic anhydride structure, a cyclic imide structure, or a lactone structure.

The (meth) acrylic resin may contain additives as required. Examples of the additives include lubricants, antiblocking agents, heat stabilizers, antioxidants, antistatic agents, light-resistant agents, impact modifiers, and surfactants. These additives may be contained in a protective film containing a thermoplastic resin other than the (meth) acrylic resin.

The (meth) acrylic resin may contain acrylic rubber particles as an impact modifier from the viewpoints of film formability of a film to be formed, impact resistance of a film, and the like. The acrylic rubber particles are particles containing an elastic polymer mainly composed of an acrylic ester as an essential component, and examples thereof include acrylic rubber particles having a single-layer structure substantially composed of only the elastic polymer, and acrylic rubber particles having a multilayer structure in which the elastic polymer is used as 1 layer.

The 1 st protective film 10 and/or the 2 nd protective film 20 may contain an ultraviolet absorber. In the case of applying the polarizing plate to an image display device such as a liquid crystal display device, the deterioration of the image display device due to ultraviolet rays can be suppressed by disposing the protective film containing the ultraviolet absorber on the visible side of the image display device (for example, a liquid crystal cell). Examples of the ultraviolet absorber include salicylate-based compounds, benzophenone-based compounds, benzotriazole-based compounds, cyanoacrylate-based compounds, and nickel complex-based compounds.

The 1 st protective film 10 and the 2 nd protective film 20 may be films formed of the same resin or films formed of different resins. The 1 st protective film 10 and the 2 nd protective film 20 may be the same or different in thickness, presence or absence of additives, kinds thereof, phase difference characteristics, and the like.

The 1 st protective film 10 and/or the 2 nd protective film 20 may have a surface treatment layer (coating layer) such as a hard coat layer, an antiglare layer, an antireflection layer, a light diffusion layer, an antistatic layer, an antifouling layer, a conductive layer, and the like on the outer surface thereof (the surface on the opposite side from the polarizing film 30).

The thickness of the 1 st protective film 10 and the 2 nd protective film 20 is usually 5 to 200. Mu.m, preferably 10 to 120. Mu.m, more preferably 10 to 85. Mu.m, respectively. Reducing the thickness of the 1 st protective film 10 and the 2 nd protective film 20 is advantageous for thinning of the polarizing plate, even the image display device. The curl resistance is more likely to be reduced as the protective film is thinner, but according to the present invention, the curl resistance of the polarizing plate can be effectively improved even if the thicknesses of the 1 st protective film 10 and the 2 nd protective film 20 are thin.

(4) Adhesive layer

The 1 st adhesive layer 15 is a cured product layer of the 1 st cationic polymerization type adhesive containing 1 or more cationic polymerization initiators, and the 2 nd adhesive layer 25 is a cured product layer of the 2 nd cationic polymerization type adhesive containing 1 or more cationic polymerization initiators.

The 1 st and 2 nd cation polymerizable adhesives generally contain a cation polymerizable compound and a cation polymerization initiator, respectively.

The cationic polymerization initiator generates a cationic species or a lewis acid by irradiation with active energy rays such as visible rays, ultraviolet rays, X rays, or electron beams, and initiates polymerization of the cationically curable compound.

The 1 st cationic polymerization initiator or more contained in the 1 st cationic polymerization type adhesive contains the 1 st cationic polymerization initiator. The 1 st cationic polymerization initiator is a borate comprising a cationic component and an anionic component represented by the following formula (i),

[ chemical formula 2]

[(Y) _k B(Phf) _4-k ] ^- (i)

(wherein Y represents an aryl group having 6 to 30 carbon atoms or a heterocyclic group having 4 to 30 carbon atoms which may have a substituent (excluding a group containing a halogen atom), or a halogen atom Phf represents a phenyl group in which at least 1 of hydrogen atoms is substituted with at least 1 selected from a perfluoroalkyl group, a perfluoroalkoxy group and a halogen atom, and k is any one integer of 0 to 4.

The 1 st cationic polymerization initiator and the 1 st cationic polymerization initiator or more contained in the 2 nd cationic polymerization adhesive are selected so that the molecular weight of the 1 st cationic polymerization initiator is larger than the molecular weight of the 1 st cationic polymerization initiator or more contained in the 2 nd cationic polymerization adhesive. The molecular weight of the 1 st cationic polymerization initiator being larger than the molecular weight of the 1 st or more cationic polymerization initiators contained in the 2 nd cationic polymerization adhesive means that: the molecular weight of the 1 st cationic polymerization initiator is larger than the molecular weight of any cationic polymerization initiator contained in the 2 nd cationic polymerization adhesive.

The 1 st cationic polymerization type adhesive may contain 2 or more 1 st cationic polymerization initiators. In the case where the 1 st cationic polymerization type adhesive contains 2 or more 1 st cationic polymerization initiators, it is preferable that the molecular weight of at least one 1 st cationic polymerization initiator is larger than the molecular weight of any cationic polymerization initiator contained in the 2 nd cationic polymerization type adhesive, from the viewpoint of providing a polarizing plate excellent in curl resistance even when placed in a high humidity environment, the molecular weight of all 1 st cationic polymerization initiators is preferably larger than the molecular weight of any cationic polymerization initiator contained in the 2 nd cationic polymerization type adhesive.

According to the present invention, it is possible to provide a polarizing plate excellent in curl resistance even when placed in a high-humidity environment, and in particular, it is possible to effectively suppress curling in which the 1 st protective film 10 side becomes concave and the 2 nd protective film 20 side becomes convex. It is considered that such an effect is caused by using the above-described predetermined borate as the 1 st cationic polymerization initiator, and that the molecular weight of the cationic polymerization initiator satisfies the above-described predetermined relationship.

(4-1) cationic polymerization initiator

The 1 st cationic polymerization type adhesive forming the 1 st adhesive layer 15 contains 1 or more cationic polymerization initiators, and the 1 st cationic polymerization initiator contains the 1 st cationic polymerization initiator. The 1 st cationic polymerization initiator is a borate comprising a cationic component and an anionic component represented by the above formula (i).

The 1 st cationic polymerization initiator may contain 1 or 2 or more cationic components, or may contain 1 or 2 or more anionic components represented by the formula (i).

Examples of the perfluoroalkyl group in the formula (i) include: linear perfluoroalkyl groups having 1 to 8 carbon atoms, preferably 1 to 4 carbon atoms, such as trifluoromethyl, pentafluoroethyl, heptafluoropropyl, nonafluorobutyl, perfluoropentyl, perfluorooctyl, etc.; branched perfluoroalkyl groups having 3 to 8 carbon atoms, preferably 3 to 4 carbon atoms, such as heptafluoroisopropyl and nonafluoroisobutyl; perfluorocycloalkyl having 3 to 8 carbon atoms, preferably 3 to 4 carbon atoms, such as perfluorocyclopropyl and perfluorocyclobutyl.

Examples of the perfluoroalkoxy group in the formula (i) include: linear perfluoroalkoxy groups having 1 to 8 carbon atoms, preferably 1 to 4 carbon atoms, such as trifluoromethoxy groups, pentafluoroethoxy groups, heptafluoropropoxy groups, nonafluorobutoxy groups, perfluoropentyloxy groups, perfluorooctyloxy groups and the like; branched perfluoroalkoxy groups having 3 to 8 carbon atoms, preferably 3 to 4 carbon atoms, such as a heptafluoroisopropoxy group and a nonafluoroisobutoxy group.

Examples of the halogen atom in the formula (i) include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

Examples of Rhf include: pentafluorophenyl (C) ₆ F ₅ ) Trifluorophenyl (C) ₆ H ₂ F ₃ ) Tetrafluorophenyl group (C) ₆ HF ₄ ) Trifluoromethylphenyl (CF) ₃ C ₆ H ₄ ) Bis (trifluoromethyl) phenyl ((CF) ₃ ) ₂ C ₆ H ₃ ) Pentafluoroethylphenyl (CF) ₃ CF ₂ C ₆ H ₄ ) Bis (pentafluoroethyl) phenyl ((CF) ₃ CF ₂ ) ₂ C ₆ H ₃ ) Fluoro-trifluoromethylphenyl (CF) ₃ C ₆ H ₃ F) Fluoro-bis (trifluoromethyl) phenyl ((CF) ₃ ) ₂ C ₆ H ₂ F) Fluoro-pentafluoroethyl phenyl (CF) ₃ CF ₂ C ₆ H ₃ F) Fluoro-bis (pentafluoroethyl) phenyl ((CF) ₃ CF ₂ ) ₂ C ₆ H ₂ F) Etc.

Rhf is preferably a phenyl group in which at least 1 hydrogen atom is substituted with a halogen atom, and more preferably a phenyl group in which at least 1 hydrogen atom is substituted with a fluorine atom.

Examples of the aryl group having 6 to 30 carbon atoms in Y in the formula (i) include phenyl, biphenyl, naphthyl, anthryl, phenanthryl and the like.

The heterocyclic group having 4 to 30 carbon atoms in Y in the formula (i) is a group obtained by removing 1 hydrogen atom from a heterocyclic ring having 4 to 30 carbon atoms. Examples of the heterocycle include: heterocyclic rings containing an oxygen atom such as oxetane ring, tetrahydrofuran ring and morpholine ring; a sulfur atom-containing heterocyclic ring such as a thiophene ring and a thiazole ring; heterocyclic rings containing nitrogen atoms such as pyrrole rings, imidazoline rings and indole rings.

The substituent that Y may have is a group other than a group containing a halogen atom, and examples thereof include: alkyl group having 1 to 12 carbon atoms, cycloalkyl group having 3 to 6 carbon atoms, alkoxy group having 1 to 6 carbon atoms, alkylthio group having 1 to 6 carbon atoms, arylthio group having 6 to 12 carbon atoms, alkylcarbonyl group having 2 to 7 carbon atoms, etc. In the case where Y has a plurality of substituents, these substituents may be the same or different.

k is preferably an integer of 0 to 2, more preferably an integer of 0 or 1, and even more preferably 0.

When Phf is present in plural numbers (k represents an integer of 0 to 2), the plural numbers Rhf are preferably the same group, and more preferably all Rhf are phenyl groups in which at least 1 hydrogen atom is replaced with a fluorine atom.

Among them, from the viewpoint of the curl resistance of the polarizing plate, the anionic component represented by formula (i) is preferably an anionic component having k of 0 and Rhf being phenyl group substituted with at least 1 halogen atom among hydrogen atoms, more preferably k of 0 and Rhf being pentafluorophenyl (C ₆ F ₅ ) Is an anionic component of (a). The anionic component of the 1 st cationic polymerization initiator is preferably tetrakis (pentafluorophenyl) borate anion B (C) ₆ F ₅ )4 ^- Etc.

The cationic component of the 1 st cationic polymerization initiator includes: aryl sulfonium ions, aryl iodonium ions, aryl diazonium ions, and the like. Examples of the aryl sulfonium ion include triphenylsulfonium cation, and 4,4' -bis (diphenylsulfonium) diphenyl sulfide cation. Examples of the aryl iodonium ion include diphenyliodonium cation. Examples of the aryl diazonium ion include a benzene diazonium cation.

Among them, aryl sulfonium ions are preferable from the viewpoint of curl resistance of the polarizing plate. From the viewpoint of curl resistance of the polarizing plate, the cation component of the 1 st cationic polymerization initiator more preferably contains 4,4' -bis (diphenylsulfonium) diphenyl sulfide cation.

From the viewpoint of curl resistance of the polarizing plate, the 1 st cationic polymerization type adhesive preferably contains only the 1 st cationic polymerization initiator as the cationic polymerization initiator.

The 1 st cationic polymerization initiator may have a molecular weight of 900 or more, 1000 or more, 1500 or more, 1900 or more, 3000 or less, or 2500 or less.

The 2 nd cationic polymerization type adhesive forming the 2 nd adhesive layer 25 contains 1 or more cationic polymerization initiators. As described above, the cationic polymerization initiator contained in the 2 nd cationic polymerization type adhesive is selected so that the molecular weight of the 1 st cationic polymerization initiator is larger than the molecular weight of the 1 st or more cationic polymerization initiators contained in the 2 nd cationic polymerization type adhesive. Hereinafter, 1 or more cationic polymerization initiators contained in the 2 nd cationic polymerization type adhesive are also collectively referred to as "2 nd cationic polymerization initiators".

The 2 nd cationic polymerization initiator may contain 1 or 2 or more cationic components, or may contain 1 or 2 or more anionic components.

Specifically, examples of the 2 nd cationic polymerization initiator include aryl sulfonium salts, aryl iodonium salts, aryl diazonium salts, iron-aromatic hydrocarbon complexes, and the like.

Examples of the cation component constituting the aryl sulfonium salt include aryl sulfonium ions such as triphenylsulfonium cation and 4,4' -bis (diphenylsulfonium) diphenylsulfide cation. Examples of the cation component constituting the aryl iodonium salt include aryl iodonium ions such as diphenyl iodonium cation. Examples of the cation component constituting the aryl diazonium salt include aryl diazonium ions such as benzene diazonium cations. The iron-arene complex is for example a cyclopentadienyl iron (II) arene cationic complex salt.

In the 1 st preferred embodiment, the cation component of the 1 st cation polymerization initiator and the cation component of the 2 nd cation polymerization initiator are both aryl sulfonium ions from the viewpoints of the curl resistance of the polarizing plate and the adhesion of the polarizing film to the protective film. In 1 preferred embodiment, the cationic component of the 1 st cationic polymerization initiator and the cationic component of the 2 nd cationic polymerization initiator are both triphenylsulfonium cations and/or 4,4' -bis (diphenylsulfonium) diphenylsulfide cations.

As the anion component constituting the 2 nd cation polymerization initiator, there is a specific phosphorus anion [ (Rf) _n PF _6-n ] ^- (n represents an integer of 1 to 6, rf represents a haloalkyl group), hexafluorophosphate anion PF ₆ ^- Hexafluoroantimonate anions SbF ₆ ^- Pentafluorohydroxy antimonate anions SbF ₅ (OH) ^- Hexafluoroarsenate anion AsF ₆ ^- Tetrafluoroborate anions BF ₄ ^- Tetrakis (pentafluorophenyl) borate anion B (C) ₆ F ₅ ) ₄ ^- Etc. A preferred example is hexafluorophosphate anion PF ₆ ^- 。

From the viewpoint of curl resistance of the polarizing plate, in 1 preferred embodiment, the 1 st cationic polymerization initiator has an anion represented by the above formula (i), and the 2 nd cationic polymerization initiator has an anion of PF ₆ ^- . From the viewpoint of curl resistance of the polarizing plate, in 1 preferred embodiment, the 1 st cationic polymerization initiator has an anionic component of B (C ₆ F ₅ ) ₄ ^- And the anionic component of the 2 nd cationic polymerization initiator is PF ₆ ^- 。

From the viewpoint of curl resistance of the polarizing plate, the cation polymerization initiator contained in the 2 nd cation polymerization type adhesive preferably contains an anion component other than the anion represented by the above formula (i), more preferably not a borate anion.

The molecular weight of the 2 nd cationic polymerization initiator is not particularly limited as long as it is smaller than that of the 1 st cationic polymerization initiator, and may be 1000 or less, 800 or less, 600 or less, or 200 or more.

The content of the cationic polymerization initiator contained in the 1 st cationic polymerization type adhesive (the total content of the cationic polymerization initiators in the case of containing 2 or more cationic polymerization initiators) and the content of the cationic polymerization initiator contained in the 2 nd cationic polymerization type adhesive (the total content of the cationic polymerization initiators in the case of containing 2 or more cationic polymerization initiators) are usually 0.5 parts by mass or more and 10 parts by mass or less, preferably 0.5 parts by mass or more and 5 parts by mass or less, more preferably 1.0 part by mass or more and 5 parts by mass or less, respectively, with respect to 100 parts by mass of the cationic polymerization compound. The content is more preferably 1.3 parts by mass or more from the viewpoint of the wet heat durability of the polarizing plate.

If the amount of the cationic polymerization initiator is too large, the ionic substance in the adhesive layer increases, and the hygroscopicity of the adhesive layer increases, and the durability of the polarizing plate may decrease.

(4-2) cationically polymerizable Compound

The cation polymerizable compound contained in the 1 st cation polymerizable adhesive and the 2 nd cation polymerizable adhesive is a compound or oligomer which undergoes a cation polymerization reaction and is cured by irradiation with active energy rays such as ultraviolet rays, visible light, electron beams, X rays, and the like, and examples thereof include epoxy compounds, oxetane compounds, vinyl compounds, and the like. Among them, the preferred cationically polymerizable compound is an epoxy compound. The epoxy compound means a compound having 1 or more, preferably 2 or more epoxy groups in the molecule. The epoxy compound may be used alone or in combination of at least 2 kinds. Examples of the epoxy compound include alicyclic epoxy compounds, aromatic epoxy compounds, hydrogenated epoxy compounds, and aliphatic epoxy compounds. Among them, from the viewpoints of weather resistance, curing speed and adhesiveness, the epoxy compound preferably contains an alicyclic epoxy compound and an aliphatic epoxy compound, and more preferably contains an alicyclic epoxy compound.

The 1 st cation polymerizable adhesive and the 2 nd cation polymerizable adhesive may contain 1 or 2 or more cation polymerizable compounds.

The alicyclic epoxy compound is a compound having 1 or more epoxy groups bonded to an alicyclic ring in the molecule. The "epoxy group bonded to an alicyclic ring" means a bridged oxygen atom-O-in the structure represented by the following formula (I). In the following formula (I), m is an integer of 2 to 5.

[ chemical formula 3]

Removing (CH) in the above formula (I) ₂ ) _m Groups of the form after 1 or more hydrogen atoms and othersThe chemically bonded compound may be an alicyclic epoxy compound. (CH) ₂ ) _m The hydrogen atom of 1 or more of them may be appropriately substituted with a linear alkyl group such as methyl or ethyl.

Among them, the alicyclic epoxy compound having a cyclopentane structure [ structure of m=3 in the above formula (I) ] or a cyclohexane structure [ structure of m=4 in the above formula (I) ] is advantageous in that the glass transition temperature of the cured product thereof is high, and in that it is advantageous in increasing the glass transition temperature of the adhesive layer and in that it is advantageous in the adhesion between the polarizing film and the protective film. Specific examples of the alicyclic epoxy compound are given below. Here, the compound names are first listed, then, the corresponding chemical formulas are shown, and the compound names and the chemical formulas corresponding thereto are given the same symbols.

A:3, 4-epoxycyclohexylmethyl 3, 4-epoxycyclohexylcarboxylate,

B:3, 4-epoxy-6-methylcyclohexyl carboxylic acid 3, 4-epoxy-6-methylcyclohexyl methyl ester,

C: ethylene bis (3, 4-epoxycyclohexyl formate),

D: bis (3, 4-epoxycyclohexylmethyl) adipate,

E: bis (3, 4-epoxy-6-methylcyclohexyl methyl) adipate,

F: diethylene glycol bis (3, 4-epoxycyclohexylmethyl ether),

G: ethylene glycol bis (3, 4-epoxycyclohexylmethyl ether),

H:2,3,14, 15-diepoxy-7,11,18,21-tetraoxatrispiro [5.2.2.5.2.2] heneicosane,

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.

[ chemical formula 4]

[ chemical formula 5]

The aromatic epoxy compound is a compound having an aromatic ring and an epoxy group in a molecule. Specific examples thereof include: bisphenol type epoxy compounds such as diglycidyl ether of bisphenol a, diglycidyl ether of bisphenol F, diglycidyl ether of bisphenol S, or oligomers thereof; phenolic epoxy resins such as phenol novolac epoxy resin, cresol novolac epoxy resin, hydroxybenzaldehyde phenol novolac epoxy resin and the like; multifunctional epoxy compounds such as glycidyl ethers of 2,2', 4' -tetrahydroxydiphenylmethane and glycidyl ethers of 2,2', 4' -tetrahydroxybenzophenone; and epoxy resins having a multifunctional function such as epoxidized polyvinyl phenol.

The hydrogenated epoxy compound is a glycidyl ether of a polyol having an alicyclic ring, and may be: the aromatic polyol is subjected to selective hydrogenation of an aromatic ring under pressure in the presence of a catalyst to obtain a nuclear hydrogenated polyol, and the nuclear hydrogenated polyol is subjected to glycidyletherification to obtain the compound. Specific examples of the aromatic polyol include, for example: bisphenol compounds such as bisphenol a, bisphenol F, and bisphenol S; phenolic resins such as phenol novolac resins, cresol novolac resins, hydroxybenzaldehyde phenol novolac resins, and the like; and multifunctional compounds such as tetrahydroxydiphenylmethane, tetrahydroxybenzophenone, and polyvinylphenol. The glycidyl ether can be produced by reacting epichlorohydrin with an alicyclic polyol obtained by hydrogenation of the aromatic ring of an aromatic polyol. Preferred among the hydrogenated epoxy compounds are diglycidyl ethers of hydrogenated bisphenol A.

Aliphatic epoxy compounds are compounds having at least 1 oxirane ring (3-membered cyclic ether) bonded to an aliphatic carbon atom in the molecule. Examples include: monofunctional epoxy compounds such as butyl glycidyl ether and 2-ethylhexyl glycidyl ether; 2-functional epoxy compounds such as 1, 4-butanediol diglycidyl ether, 1, 6-hexanediol diglycidyl ether, neopentyl glycol diglycidyl ether, and 1, 4-cyclohexanedimethanol diglycidyl ether; epoxy compounds having 3 or more functions such as trimethylolpropane triglycidyl ether and pentaerythritol tetraglycidyl ether; and epoxy compounds having 1 epoxy group directly bonded to an alicyclic ring and an oxirane ring bonded to an aliphatic carbon atom, such as 4-vinylcyclohexene dioxide and limonene dioxide. Among them, from the viewpoint of adhesion between the polarizing film and the protective film, a 2-functional epoxy compound having 2 oxirane rings bonded to aliphatic carbon atoms in the molecule (also referred to as an aliphatic diepoxy compound) is preferable. The suitable aliphatic diepoxy compound can be represented by the following formula (II), for example.

[ chemical formula 6]

Y in the formula (II) is an alkylene group having 2 to 9 carbon atoms, an alkylene group having 4 to 9 total carbon atoms with an ether bond interposed therebetween, or a C6-18 2-valent hydrocarbon group having an alicyclic structure.

Specifically, the aliphatic diepoxy compound represented by the above formula (II) is a diglycidyl ether of an alkylene glycol, a diglycidyl ether of an oligoalkylene glycol having a repetition number of about 4 or less, or a diglycidyl ether of an alicyclic glycol.

Specific examples of the diol (glycol) capable of forming the aliphatic di-epoxy compound represented by the above formula (II) are shown below. Examples of the alkylene glycol include ethylene glycol, propylene glycol, 1, 3-propylene glycol, 2-methyl-1, 3-propylene glycol, 2-butyl-2-ethyl-1, 3-propylene glycol, 1, 4-butanediol, neopentyl glycol, 3-methyl-2, 4-pentanediol, 1, 5-pentanediol, 3-methyl-1, 5-pentanediol, 2-methyl-2, 4-pentanediol, 2, 4-diethyl-1, 5-pentanediol, 1, 6-hexanediol, 1, 7-heptanediol, 3, 5-heptanediol, 1, 8-octanediol, 2-methyl-1, 8-octanediol, and 1, 9-nonanediol. Examples of the oligoalkylene glycol include diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, and the like. Examples of the alicyclic diol include cyclohexanediols such as 1, 2-cyclohexanediol, 1, 3-cyclohexanediol, and 1, 4-cyclohexanediol, cyclohexanedimethanol such as 1, 2-cyclohexanedimethanol, 1, 3-cyclohexanedimethanol, and 1, 4-cyclohexanedimethanol.

An oxetane compound which is one of the cation polymerizable compounds is a compound having 1 or more oxetane rings (oxetanyl groups) in the molecule, and specific examples thereof include: 3-ethyl-3-hydroxymethyl oxetane (also known as oxetan), 2-ethylhexyl oxetane, 1, 4-bis [ { (3-ethyloxetan-3-yl) methoxy } methyl ] benzene (also known as xylylenedioxetan), 3-ethyl-3 [ { (3-ethyloxetan-3-yl) methoxy } methyl ] oxetan, 3-ethyl-3- (phenoxymethyl) oxetan, 3- (cyclohexyloxy) methyl-3-ethyloxetan. The oxetane compound may be used as a main component of the cationically polymerizable compound, or may be used in combination with an epoxy compound. The combination of oxetane compounds may improve curing speed and adhesion.

Examples of the vinyl compound which can be a cationically polymerizable compound include aliphatic or alicyclic vinyl ether compounds, and specific examples thereof include: vinyl ethers of alkyl or alkenyl alcohols having 5 to 20 carbon atoms such as n-pentyl vinyl ether, isopentyl vinyl ether, n-hexyl vinyl ether, n-octyl vinyl ether, 2-ethylhexyl vinyl ether, n-dodecyl vinyl ether, stearyl vinyl ether and oleyl vinyl ether; hydroxyl-containing vinyl ethers such as 2-hydroxyethyl vinyl ether, 3-hydroxypropyl vinyl ether and 4-hydroxybutyl vinyl ether; vinyl ethers of monohydric alcohols having an aliphatic or aromatic ring such as cyclohexyl vinyl ether, 2-methylcyclohexyl vinyl ether, cyclohexylmethyl vinyl ether and benzyl vinyl ether; mono-to poly-vinyl ethers of polyhydric alcohols such as glycerol monovinyl ether, 1, 4-butanediol divinyl ether, 1, 6-hexanediol divinyl ether, neopentyl glycol divinyl ether, pentaerythritol tetravinyl ether, trimethylolpropane divinyl ether, trimethylolpropane trivinyl ether, 1, 4-dihydroxycyclohexane monovinyl ether, 1, 4-dihydroxycyclohexane divinyl ether, 1, 4-dihydroxymethylcyclohexane monovinyl ether, and 1, 4-dihydroxymethylcyclohexane divinyl ether; polyalkylene glycol mono-divinyl ethers such as diethylene glycol divinyl ether, triethylene glycol divinyl ether, diethylene glycol monobutyl monovinyl ether, and the like; other vinyl ethers such as glycidyl vinyl ether and ethylene glycol vinyl ether methacrylate. The vinyl compound may be used as a main component of the cationically polymerizable compound, or may be used in combination with an epoxy compound, or an epoxy compound and an oxetane compound. By using a vinyl compound in combination, the curing speed and the viscosity of the adhesive can be improved in some cases.

The cationically polymerizable adhesive may further contain a cationically polymerizable compound other than the above, such as a cyclic lactone compound, a cyclic acetal compound, a cyclic thioether compound, and a spiro orthoester compound.

From the viewpoint of adhesion between the polarizing film and the protective film, in the 1 st and 2 nd cation polymerizable adhesives, the content of the cation polymerizable compound (the total content of all the cation polymerizable compounds contained in the cation polymerizable adhesive, in the case of containing 2 or more cation polymerizable compounds) is preferably 50% by mass or more, more preferably 60% by mass or more, still more preferably 80% by mass or more, still more preferably 90% by mass or more, and particularly preferably 100% by mass, when the total amount of the curable compounds contained in the cation polymerizable adhesive is 100% by mass.

The cation polymerizable compound contained in the 1 st cation polymerizable adhesive and the cation polymerizable compound contained in the 2 nd cation polymerizable adhesive may be the same kind or different kinds.

(4-3) additives

The 1 st and/or 2 nd cationic polymerization type adhesive may contain other additives as needed. Examples of the additives include ion capturing agents, antioxidants, chain transfer agents, polymerization accelerators (polyols, etc.), sensitizers, sensitizing aids, light stabilizers, tackifiers, thermoplastic resins, fillers, flow control agents, plasticizers, antifoaming agents, leveling agents, silane coupling agents, pigments, antistatic agents, and ultraviolet absorbers.

(4-4) application of adhesive and adhesion of polarizing film to protective film

The 1 st protective film 10 is laminated and bonded on one surface of the polarizing film 30 via the 1 st adhesive layer 15, and the 2 nd protective film 20 is laminated and bonded on the other surface of the polarizing film 30 via the 2 nd adhesive layer 25, thereby obtaining the polarizing plate of the present invention. The 1 st protective film 10 and the 2 nd protective film 20 (they are also collectively referred to simply as "protective films") may be bonded layer by layer in a stepwise manner, or the protective films on both sides may be bonded in one stage.

Specifically, the adhesion of the polarizing film 30 to the protective film can be performed as follows: an adhesive is applied to the bonding surface of the polarizing film 30 and/or the bonding surface of the protective film, and the films are laminated with each other with the adhesive applied therebetween, and then the laminated films are pressed from the top and bottom by using, for example, a laminating roller or the like, and then the laminated films are cured by irradiation with active energy rays. When the active energy ray-curable adhesive is used, the heat treatment may be performed simultaneously with or after the irradiation of the active energy ray. One or both of the bonding surfaces of the polarizing film 30 and the protective film may be subjected to an easy-to-adhere treatment such as a saponification treatment, a corona discharge treatment, a plasma treatment, a flame treatment, a primer treatment, and an anchor coating treatment before the adhesive coating layer is formed.

The adhesive coating layer can be formed by various coating methods such as a blade, a bar, a die coater, a comma coater, and a gravure coater. In addition, it is also possible to employ: the adhesive is cast between the polarizing film 30 and the protective film while continuously feeding them so that the bonding surfaces of the two are inside.

From the viewpoint of coatability, the adhesive forming the 1 st adhesive layer 15 and the 2 nd adhesive layer 25 is preferably low in viscosity. Specifically, the viscosity at 25℃is preferably 1000 mPas or less, more preferably 500 mPas or less, and still more preferably 100 mPas or less. The adhesive may be solvent-free, but may contain an organic solvent in order to adjust the viscosity to be suitable for the application method used.

The light source for active energy rays may be any light source that generates ultraviolet rays, electron beams, X-rays, or the like, for example. The active energy ray is preferably ultraviolet ray. The ultraviolet light source is preferably a light source having a light emission distribution at a wavelength of 400nm or less, and examples thereof include a low-pressure mercury lamp, a medium-pressure mercury lamp, a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, a chemical lamp, a black light lamp, a microwave-excited mercury lamp, and a metal halide lamp.

The irradiation intensity of active energy rays to the adhesive layer is determined for each adhesive composition, and it is preferable that the irradiation intensity of light in a wavelength region effective for activation of the photopolymerization initiator is 0.1 to 1000mW/cm ² . If the light irradiation intensity is too small, the reaction time becomes too long, while if the light irradiation intensity is too large, yellowing of the adhesive layer, deterioration of the polarizing film 30, or surface defects of the protective film may occur due to heat radiated from the lamp and heat generated during the polymerization of the adhesive. The irradiation time of the adhesive is controlled according to each adhesive composition, and it is preferable that the cumulative light amount expressed as the product of the irradiation intensity and the irradiation time is 10 to 5000mJ/cm ² Is set by the mode of (2). If the cumulative light amount is too small, generation of active species from the photopolymerization initiator is insufficient, and there is a possibility that curing of the obtained adhesive layer becomes insufficient, whereas if the cumulative light amount is too large, the light irradiation time becomes extremely long, which is liable to be disadvantageous in improving productivity.

The timing of laminating the protective film on the polarizing film 30 via the coating layer of the adhesive and the timing of curing the coating layer are not particularly limited. For example, after one protective film is laminated, the coating layer may be cured continuously, and then another protective film may be laminated, so that the coating layer is cured. Alternatively, after two protective films are laminated in sequence or simultaneously, the coating layers on both sides may be cured simultaneously. The irradiation with active energy rays may be performed from any of the protective films. For example, when one protective film contains an ultraviolet absorber and the other protective film does not contain an ultraviolet absorber, it is preferable to irradiate active energy rays from the protective film side not containing an ultraviolet absorber. By performing the irradiation in this way, the active energy rays irradiated can be effectively utilized, and the curing speed can be increased.

The thickness of the 1 st and 2 nd adhesive layers 15, 25 after curing is usually 20 μm or less, preferably 10 μm or less, more preferably 5 μm or less, still more preferably less than 5 μm, and particularly preferably 3 μm or less. If the thicknesses of the 1 st and 2 nd adhesive layers 15, 25 are too large, the reactivity of the adhesive tends to decrease, and the wet-heat durability of the polarizing plate tends to be deteriorated. The thickness of the 1 st and 2 nd adhesive layers 15, 25 is usually 0.01 μm or more, preferably 0.1 μm or more, more preferably 0.5 μm or more. If the thicknesses of the 1 st and 2 nd adhesive layers 15 and 25 are too small, if there are fine defects (fine waste, fine dust, etc.) on the polarizing film 30, there are cases where fine defects are also caused to other layers (the 1 st protective film 10, the 2 nd protective film 20, etc.) laminated by the 1 st adhesive layer and the 2 nd adhesive layer. The thickness of the 1 st adhesive layer 15 and the 2 nd adhesive layer 25 may be the same or different.

(5) Preferred constitution of polarizing plate

The polarizing plate preferably has the following structure, for example, from the viewpoint that the curl-resistant effect can be effectively obtained even when placed under a high-humidity environment, and particularly, the curl of the 1 st protective film 10 side becoming concave and the 2 nd protective film 20 side becoming convex can be effectively suppressed.

The 1 st protective film 10 and the 2 nd protective film 20 are films formed of different resins.

In [ a ], the 1 st protective film 10 is a (meth) acrylic resin film or a cellulose ester resin film.

In [ b ], the 2 nd protective film 20 is a cyclic polyolefin resin film.

The cationic polymerization initiator 1 in any one of the above [ a ] to [ c ] is a borate comprising a cationic component as an aryl sulfonium ion and an anionic component represented by the above formula (i), the 1 st2 cationic polymerization initiator comprises PF ₆ ^- A cationic polymerization initiator as an anionic component.

In the above [ d ], the 1 st cationic polymerization initiator is a cationic component comprising an aryl sulfonium ion and B (C) ₆ F ₅ ) ₄ ^- Is a borate of the anionic component of (a).

In the above [ d ] or [ e ], the 2 nd cationic polymerization initiator contains a cationic component containing an aryl sulfonium ion as an aryl sulfonium ion and PF as the cationic component ₆ ^- A cationic polymerization initiator of an anionic component of (a).

In any one of the above [ a ] to [ f ], the 1 st cationic polymerization type adhesive contains only the 1 st cationic polymerization initiator, and the 2 nd cationic polymerization type adhesive contains only a cationic component containing an aryl sulfonium ion and PF ₆ ^- A cationic polymerization initiator of an anionic component of (a).

In the above [ g ], the cation component of the 1 st cationic polymerization initiator is triphenylsulfonium cation and/or 4,4 '-bis (diphenylsulfonium) diphenylsulfide cation, and the cation component of the cationic polymerization initiator contained in the 2 nd cationic polymerization adhesive is triphenylsulfonium cation and/or 4,4' -bis (diphenylsulfonium) diphenylsulfide cation.

When the polarizing plate is assembled in the image display device, the polarizing plate is typically disposed such that the 1 st protective film 10 side is a visible side and the 2 nd protective film 20 side is an image display element side.

(6) Other constituent elements of polarizing plate

(6-1) optically functional film

The polarizing plate may be provided with an optical functional film other than the polarizing film 30 for imparting a desired optical function, and a suitable example thereof is a retardation film. As described above, the 1 st protective film 10 and/or the 2 nd protective film 20 may also serve as a phase difference film, but the phase difference film may be laminated separately from the protective films. In the latter case, the retardation film may be laminated on the outer surface of the 1 st protective film 10 and/or the 2 nd protective film 20 via an adhesive layer or an adhesive layer.

Specific examples of the retardation film include: a birefringent film comprising a stretched film of a thermoplastic resin having light transmittance, a film in which a discotic liquid crystal or a nematic liquid crystal is oriented and fixed, and a retardation film in which the liquid crystal layer is formed on a base film. The base film is usually a thermoplastic resin film, and as the thermoplastic resin, a cellulose ester resin such as triacetyl cellulose is preferably used.

Examples of other optically functional films (optical members) that may be included in the polarizing plate are a light condensing plate, a brightness enhancement film, a reflective layer (reflective film), a semi-transmissive reflective layer (semi-transmissive reflective film), a light diffusion layer (light diffusion film), and the like. They are generally provided in the case where the polarizing plate is a polarizing plate disposed on the back side (backlight side) of the liquid crystal cell.

(6-2) adhesive layer

The polarizing plate of the present invention may include an adhesive layer for bonding the polarizing plate to an image display element such as a liquid crystal cell or other optical member. The adhesive layer may be laminated on the outer surface of the protective film. The adhesive layer may be laminated on the outer surface of the 1 st protective film or on the outer surface of the 2 nd protective film.

In the case where the polarizing plate has an adhesive layer, the polarizing plate preferably has an adhesive layer on the side of the 2 nd protective film 20 opposite to the 2 nd adhesive layer 25 side. The adhesive layer is typically an adhesive layer for attaching the polarizing plate to the image display element.

As the adhesive used in the adhesive layer, an adhesive based on a (meth) acrylic resin, a silicone resin, a polyester resin, a polyurethane resin, a polyether resin, or the like can be used. Among them, a (meth) acrylic adhesive is preferably used from the viewpoints of transparency, adhesion, reliability, weather resistance, heat resistance, reworkability, and the like. In the (meth) acrylic pressure-sensitive adhesives, a (meth) acrylic resin obtained by blending an alkyl (meth) acrylate having an alkyl group having 20 or less carbon atoms such as a methyl group, an ethyl group, and a butyl group with a functional group-containing (meth) acrylic monomer such as (meth) acrylic acid, and hydroxyethyl (meth) acrylate, the (meth) acrylic monomer having a glass transition temperature of preferably 25 ℃ or less, more preferably 0 ℃ or less, and the weight average molecular weight of the (meth) acrylic resin is 10 ten thousand or more, is useful as a base polymer.

The formation of the adhesive layer on the polarizing plate can be performed, for example, by the following means: a method in which a 10 to 40 mass% solution is prepared by dissolving or dispersing the pressure-sensitive adhesive composition in an organic solvent such as toluene or ethyl acetate, and the solution is directly applied to the target surface of the polarizing plate to form a pressure-sensitive adhesive layer; the release film subjected to the release treatment is formed in advance with an adhesive layer in a sheet form, and is then attached to the target surface of the polarizing plate. The thickness of the pressure-sensitive adhesive layer is determined by its adhesive strength and the like, and is preferably in the range of about 1 to 50. Mu.m, more preferably 2 to 40. Mu.m.

The polarizing plate may include the above-described barrier film. The separator may be a film containing polyethylene resin such as polyethylene, polypropylene resin such as polypropylene, polyester resin such as polyethylene terephthalate, or the like. Among them, a stretched film of polyethylene terephthalate is preferable.

Glass fibers, glass beads, resin beads, fillers including metal powder and other inorganic powder, pigments, colorants, antioxidants, ultraviolet absorbers, antistatic agents, and the like may be blended in the pressure-sensitive adhesive layer as necessary.

(6-3) protective film

The polarizing plate of the present invention may include a protective film for temporarily adhering and protecting a surface thereof (a protective film surface). The protective film is peeled off together with the pressure-sensitive adhesive layer provided on the polarizing plate, for example, after the polarizing plate is bonded to the image display element or other optical member.

The protective film is composed of a base film and an adhesive layer laminated thereon. The above description is cited as to the adhesive layer. The resin forming the base film may be, for example: polyethylene resins such as polyethylene, polypropylene resins such as polypropylene, polyester resins such as polyethylene terephthalate and polyethylene naphthalate, and thermoplastic resins such as polycarbonate resins. Polyester resins such as polyethylene terephthalate are preferable.

The polarizing plate of the present invention can be bonded to an image display element such as a liquid crystal cell via an adhesive layer. Examples of the liquid crystal cell include IPS type and VA type. The polarizing plate of the present invention may be bonded to an organic EL panel with an adhesive layer interposed therebetween as an antireflection polarizing plate.

Examples

Hereinafter, the present invention will be described more specifically by way of examples and comparative examples, but the present invention is not limited to these examples. In the following examples, the following were used as the cationic polymerizable compound and the cationic polymerization initiator constituting the cationic polymerization type adhesive.

[ 1 ] cationically polymerizable Compound A-1:3, 4-epoxycyclohexylformic acid-3 ',4' -epoxycyclohexylmethyl ester (trade name "CEL2021P", manufactured by Daicel Co., ltd.)

[ 2 ] cationically polymerizable Compound A-2: neopentyl glycol diglycidyl ether (trade name "EX-211L", manufactured by Nagase ChemteX Co., ltd.)

[ 3 ] cationically polymerizable Compound A-3: 4-hydroxybutyl vinyl ether (manufactured by CARBIDE, japan, trade name "HBVE")

[ 4 ] cationically polymerizable Compound A-4: methyl methacrylate-glycidyl methacrylate copolymer (cationically polymerizable Polymer) (manufactured by Niday oil under the trade name "MARPROOF G-01100")

[ 5 ] cationic polymerization initiator B-1: a cationic polymerization initiator comprising the following cationic component and anionic component. Mixtures of compounds having molecular weight 1050 and compounds having molecular weight 1915 (manufactured by ESTCHEM, inc.; trade name "PAG-20008")

[ chemical formula 7]

[ 6 ] cationic polymerization initiator B-2: a cationic polymerization initiator comprising the following cationic component and anionic component. Molecular weight 517 (trade name "CPI-100P", manufactured by San-Apro Co., ltd.)

[ chemical formula 8]

Production examples 1 to 14: preparation of cationic polymeric Adhesives

The cationically polymerizable compounds and the cationic polymerization initiators described in Table 1 were mixed in the mixing ratio described in Table 1, and deaerated to prepare liquid cationically polymerizable adhesives A to N, respectively. The numerical values in table 1 represent parts by mass. The cationic polymerization initiators B-1 and B-2 were blended in the form of a 50 mass% propylene carbonate solution, and the values shown in Table 1 were amounts as solid components contained therein.

TABLE 1

Examples 1 to 7 and comparative examples 1 to 2 >, respectively

(1) Manufacture of polarizing plate

The 1 st cationic polymerization type adhesive shown in Table 2 was applied to one surface of the 1 st protective film shown in Table 2 by corona discharge treatment so that the thickness of the film after curing became about 5. Mu.m, using a bar coater. Next, a polyvinyl alcohol (PVA) -iodine polarizing film having a thickness of 25 μm was bonded to the coated surface. Next, a corona discharge treatment was performed on one surface of the 2 nd protective film shown in table 2, and the 2 nd cationic polymerization adhesive shown in table 2 was applied to the corona discharge treated surface by using a bar coater so that the thickness after curing became about 5 μm. The polarizing film with the 1 st protective film formed above was laminated on the coated surface, and pressed and bonded by a bonding roller to obtain a laminate. The laminate was irradiated with ultraviolet light using a belt conveyor ("D BULB" manufactured by lamp Fusion UV Systems Co., ltd.) to a cumulative light amount of 200mJ/cm from the 2 nd protective film side ² (UVB) irradiating with ultraviolet light to cure the adhesive layers on both sides, thereby producing a polarizing plate.

When the obtained polarizing plate is assembled in an image display device, the polarizing plate is disposed such that the 2 nd protective film (phase difference film) side is the image display element side and the 1 st protective film side is the visible side.

Details of the 1 st protective film and the 2 nd protective film shown in table 2 are as follows.

[ 1 ] protective film a: the ultraviolet absorber-containing (meth) acrylic resin film having a thickness of 60 μm. The (meth) acrylic resin for forming the film was prepared by mixing methyl methacrylate and methyl acrylate in a ratio of 96:4, and a copolymer obtained by copolymerizing the above materials in a mass ratio.

[ 2 ] protective film b: cellulose ester resin film (trade name "TG" manufactured by Fuji film Co., ltd.) having a thickness of 60. Mu.m

[ 3 ] protective film c: a retardation film (trade name "ZEONOR", manufactured by Japanese ZEON Co., ltd.) having a thickness of 50 μm and comprising a cyclic polyolefin-based resin (norbornene-based resin)

[ 4 ] protective film d: a retardation film (trade name "GA-01", manufactured by LG Chemical Co., ltd.) having a thickness of 40 μm and comprising a (meth) acrylic resin

(2) Evaluation of curl resistance of polarizing plate under high humidity environment

A8 cm X8 cm-sized sheet was cut out of the polarizing plate produced in the above (1) in an atmosphere having a temperature of 25℃and a relative humidity of 55%. In the monolithic body, the 2 sides of the 1 group facing each other are parallel to the absorption axis direction of the polarizing film. At this time, the single piece body was not curled (curling amount 0 mm). After the single sheet was left to stand in an atmosphere having a relative humidity of 90% at 25℃for 2 hours, the curl amount of the single sheet was measured. The curl amount was determined as follows: the curved single piece body was placed on a horizontal table so as to protrude downward, and the heights of the 4 corners from the table to the single piece body were measured with a ruler, and the heights were obtained as an average value of the obtained 4-point values. Based on the obtained curl amount, curl resistance was evaluated according to the following criteria. The evaluation results are shown in table 2.

5: no curl is generated or the curl amount is less than 1mm

4: the curl amount exceeds 1mm and is less than 2mm

3: the curl amount exceeds 2mm and is less than 5mm

2: the curl amount exceeds 5mm and is 20mm or less

1: too strong curling to make the polarizing plate in a curled state

(3) Formation of adhesive layer

The release-treated surface of a release film having a thickness of 38 μm containing polyethylene terephthalate, which was subjected to release treatment, was coated with an organic solvent solution of a (meth) acrylic adhesive by a die coater so that the thickness thereof after drying became 20. Mu.m, to prepare a sheet-like adhesive with a release film. Next, the 2 nd protective film surface of the polarizing plate produced in the above (1) was subjected to corona discharge treatment, and the surface (adhesive surface) of the sheet-like adhesive obtained above opposite to the separator was bonded to the corona discharge treated surface by a laminator, and then cured at a temperature of 23 ℃ and a relative humidity of 65% for 7 days, to obtain a polarizing plate having an adhesive layer.

(4) Evaluation of damp-heat durability of polarizing plate

A sheet having a size of 3cm X3 cm was cut out from the polarizing plate having the adhesive layer produced in the above (3). In the monolithic body, the 2 sides of the 1 group facing each other are parallel to the absorption axis direction of the polarizing film. The release film is peeled from the monolithic body, and the exposed adhesive layer is bonded to the glass substrate. The glass substrate used was an alkali-free glass product name "Eagle XG" manufactured by Corning corporation. The obtained optical laminate was measured for MD transmittance and TD transmittance in the wavelength range of 380 to 780nm using a spectrophotometer with an integrating sphere (manufactured by japan spectroscopy corporation, product name "V7100"), and the monomer transmittance at each wavelength was calculated. The calculated monomer transmittance was calculated by JIS Z8701: 1999 "color display method-XYZ color System and X ₁₀ Y ₁₀ Z ₁₀ The visibility correction (Japanese: see sensitivity correction) was performed on the 2-degree field of view (C light source) of the color system "to determine the visibility correction monomer transmittance (Ty) before the wet heat durability test. The optical laminate was set on a spectrophotometer with an integrating sphere so that light was incident from the glass substrate side with the 1 st protective film surface side of the polarizing plate as the detector side.

The monomer transmittance (%) is defined by the following formula:

Monomer transmittance (λ) = (Tp (λ) +tc (λ))/2.

Tp (λ) is the transmittance (%) of the measurement sample measured in the relationship between the incident linearly polarized light of wavelength λ (nm) and parallel nicols.

Tc (λ) is the transmittance (%) of the measurement sample measured as the relationship between the incident linearly polarized light of wavelength λ (nm) and orthogonalized Nicole.

Next, the optical laminate was subjected to a wet heat durability test in which the optical laminate was left to stand in a wet heat environment having a temperature of 80 ℃ and a relative humidity of 90% for 48 hours, and further left to stand in an environment having a temperature of 23 ℃ and a relative humidity of 60% for 24 hours. After the wet heat durability test, the visibility-corrected monomer transmittance Ty was obtained by the same method as before the wet heat durability test.

The monomer transmittance Ty was corrected based on the visibility after and before the wet heat durability test, the amount of change in Ty was calculated based on the following formula, and the wet heat durability was evaluated based on the following criteria. The evaluation results are shown in the table.

Ty change amount (%) = |ty (after wet heat durability test) -Ty (before wet heat durability test) |

4: ty variation is 1.0% or less

3: ty variation exceeds 1.0% and is 2.0% or less

2: ty variation exceeds 2.0% and is 3.0% or less

1: ty change over 3.0%

TABLE 2

Description of the reference numerals

10: 1 st protective film, 15: adhesive layer 1, 20: 2 nd protective film, 25: adhesive layer 2, 30: a polarizing film.

Claims

1. A polarizing plate comprising, in order, a 1 st protective film, a 1 st adhesive layer, a polarizing film, a 2 nd adhesive layer, and a 2 nd protective film,

the 2 nd adhesive layer is a cured product layer of a 2 nd cationic polymerization adhesive containing more than 1 cationic polymerization initiator,

the 1 st cationic polymerization initiator or more contained in the 1 st cationic polymerization adhesive contains a 1 st cationic polymerization initiator,

[(Y) _k B(Phf) _4-k ] (i)

wherein Y represents an aryl group having 6 to 30 carbon atoms or a heterocyclic group having 4 to 30 carbon atoms, which may have a substituent, or a halogen atom, wherein the substituent does not include a group containing a halogen atom; phf it is a phenyl group in which at least 1 of hydrogen atoms is substituted with at least 1 selected from perfluoroalkyl groups, perfluoroalkoxy groups, and halogen atoms; k is any integer from 0 to 4,

2. The polarizing plate according to claim 1, wherein the cation component is an aryl sulfonium ion.

3. The polarizing plate according to claim 1 or 2, wherein the 1 st cation-polymerizable adhesive and the 2 nd cation-polymerizable adhesive further comprise a cation-polymerizable compound,

the content of the 1 st cationic polymerization initiator contained in the 1 st cationic polymerization type adhesive and the content of the 1 st cationic polymerization initiator contained in the 2 nd cationic polymerization type adhesive are 0.5 parts by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the cationic polymerizable compound.

4. The polarizing plate according to any one of claims 1 to 3, wherein the 1 st protective film is formed of a (meth) acrylic resin or a cellulose ester resin.

5. The polarizing plate according to any one of claims 1 to 4, wherein an adhesive layer is further provided on a side of the 2 nd protective film opposite to the 2 nd adhesive layer side.