Polarizing plate

Abstract

A polarizing plate is provided, wherein protective films are adhered to both sides of a polarizing film, and the plate is not prone to curling or has minimal curling even when placed in a high-humidity environment. The polarizing plate further comprises, in sequence, a first protective film, a first adhesive layer, a polarizing film, a second adhesive layer, and a second protective film. The first adhesive layer is a cured layer of a first cationic polymeric adhesive containing one or more cationic polymerization initiators. The second adhesive layer is a cured layer of a second cationic polymeric adhesive containing one or more cationic polymerization initiators. The first cationic polymeric adhesive contains one or more cationic polymerization initiators, including a first cationic polymerization initiator. The first cationic polymerization initiator is a borate containing a cationic component and an anionic component as shown in formula (i). The molecular weight of the first cationic polymerization initiator is greater than the molecular weight of the aforementioned one or more cationic polymerization initiators contained in the second cationic polymeric adhesive.

Description

Technical Field

[0001] The present invention relates to a polarizing plate having a protective film bonded to both sides of a polarizing film by means of an adhesive layer. Background Technology

[0002] Polarizing plates, widely used in image display devices such as liquid crystal displays, typically have a structure in which a protective film is laminated on both sides of a polarizing film. Adhesives are usually used to bond the polarizing film and the protective film. Known adhesives for bonding the protective film include water-based adhesives and active energy radiation-cured adhesives.

[0003] Japanese Patent Application Publication No. 2015-140374 (Patent Document 1) discloses a radiation-curable composition and a polarizing plate formed by bonding a polarizing film and a protective film using the composition. The radiation-curable composition comprises: (A) a compound containing an ester group and having two or more alicyclic epoxy groups in the molecule; (B) a photocationic polymerization initiator having a fluoroalkyl fluorophosphate anion or a pentafluorophenyl borate anion; and (C) a compound having three or more hydroxyl groups in the molecule.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2015-140374 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] Typically, polarizing plates are manufactured into long strips (polarizing plate rolls) using a roll-to-roll method. These strips are then cut into individual polarizing plate sheets, each the size corresponding to the screen size of the image display device to which they are applied, and bonded to the image display element, thus assembling the device. After being cut into individual sheets, the polarizing plates are sometimes stored or transported for a period before being assembled into the image display device. During this time, the storage or transport environment may become relatively humid. Polarizing plate sheets exposed to high humidity are prone to curling (warping).

[0009] The purpose of this invention is to provide a polarizing plate with protective films attached to both sides of the polarizing film, which is less prone to curling or has a smaller degree of curling even when placed in a high humidity environment.

[0010] Methods for solving problems

[0011] The present invention provides the following polarizing plate.

[0012] [1] A polarizing plate, comprising, in sequence, a first protective film, a first adhesive layer, a polarizing film, a second adhesive layer, and a second protective film.

[0013] The aforementioned first adhesive layer is a cured layer of a first cationic polymeric adhesive containing one or more cationic polymerization initiators.

[0014] The aforementioned second adhesive layer is a cured layer of a second cationic polymeric adhesive containing one or more cationic polymerization initiators.

[0015] The first cationic polymeric adhesive contains one or more cationic polymerization initiators, including the first cationic polymerization initiator.

[0016] The first cationic polymerization initiator mentioned above is a borate containing a cationic component and an anionic component as shown in formula (i) below.

[0017] [Chemical Formula 1]

[0018] [(Y) k B(Phf) 4-k ] - (i)

[0019] (In the formula, Y represents an aryl group with 6 to 30 carbon atoms or a heterocyclic group with 4 to 30 carbon atoms, or a halogen atom, which may have substituents (excluding groups containing halogen atoms). Phf represents a phenyl group in which at least one hydrogen atom is substituted by at least one of perfluoroalkyl, perfluoroalkoxy, and halogen atoms. k is any integer from 0 to 4.)

[0020] The molecular weight of the first cationic polymerization initiator is greater than the molecular weight of the one or more cationic polymerization initiators contained in the second cationic polymerization adhesive.

[0021] [2] According to the polarizing plate described in [1], the above-mentioned cation component is arylsulfonium ion.

[0022] [3] According to the polarizing plate described in [1] or [2], wherein the first cationic polymeric adhesive and the second cationic polymeric adhesive further comprise cationic polymeric compounds.

[0023] The content of the above-mentioned one or more cationic polymerization initiators contained in the first cationic polymeric adhesive and the content of the above-mentioned one or more cationic polymerization initiators contained in the second cationic polymeric adhesive are 0.5 parts by mass or more and 5 parts by mass or less relative to 100 parts by mass of the above-mentioned cationic polymeric compound.

[0024] [4] The polarizing plate described in any one of [1] to [3], wherein the first protective film is formed of (meth)acrylic resin or cellulose ester resin.

[0025] [5] The polarizing plate described in any one of [1] to [4] further comprises an adhesive layer on the side of the second protective film opposite to the side of the second adhesive layer.

[0026] Invention Effects

[0027] A polarizing plate with protective films bonded to both sides of the polarizing film can be provided. This polarizing plate is not prone to curling or has a small degree of curling even when placed in a high humidity environment. Attached Figure Description

[0028] Figure 1 This is a schematic cross-sectional view illustrating an example of the layer structure of the polarizing plate of the present invention. Detailed Implementation

[0029] The polarizing plate (hereinafter also referred to as "polarizing plate") of the present invention will be described in detail below.

[0030] (1) Structure of polarizing plate

[0031] like Figure 1 As shown, the polarizing plate sequentially comprises a first protective film 10, a first adhesive layer 15, a polarizing film 30, a second adhesive layer 25, and a second protective film 20. That is, the first protective film 10 is laminated on one side of the polarizing film 30 by the first adhesive layer 15, and the second protective film 20 is laminated on the other side of the polarizing film 30 by the second adhesive layer 25.

[0032] The first adhesive layer 15 is preferably in contact with the first protective film 10 and the polarizing film 30. The second adhesive layer 25 is preferably in contact with the polarizing film 30 and the second protective film 20.

[0033] Not limited to Figure 1 For example, the polarizing plate may contain other layers besides those described above. Specific examples of other layers include: an adhesive layer laminated to the outer surface of the first protective film 10 and / or the second protective film 20; a release film (also called a "release film") laminated to the outer surface of the adhesive layer; a protective film (also called a "surface protective film") laminated to the outer surface of the first protective film 10 and / or the second protective film 20; and an optically functional film laminated to the outer surface of the first protective film 10 and / or the second protective film 20 by means of an adhesive layer and an adhesive layer, etc.

[0034] The polarizing plate of the present invention can be a polarizing plate that is not prone to curling or has a small degree of curling even when placed in a high humidity environment. Hereinafter, the degree to which it is not prone to curling is also referred to as "curling resistance", and the degree to which it is not prone to curling or has a small degree of curling is also referred to as "good curling resistance".

[0035] The polarizing plate can be a strip or a roll of material having the aforementioned layers, or it can be a single sheet. A single sheet refers to a single sheet cut to a specified size from the aforementioned strip or roll, and it is usually rectangular, square, or other square shapes.

[0036] When the polarizing plate is a strip or its winding, curl resistance refers to its resistance to curling of a single piece cut from the strip or its winding. When the polarizing plate is a single piece, curl resistance refers to its resistance to curling of that single piece or a smaller single piece cut from that single piece.

[0037] (2) Polarizing film

[0038] The polarizing film 30 is a film that selectively transmits linearly polarized light in a certain direction from natural light. Examples include: an iodine-based polarizing film formed by adsorbing iodine onto a polyvinyl alcohol-based resin film and orienting it; a dye-based polarizing film formed by adsorbing dichroic dyes onto a polyvinyl alcohol-based resin film and orienting them; and a coated polarizing film formed by coating a dichroic dye in a lyotropic liquid crystal state and then orienting and immobilizing it. These polarizing films selectively transmit linearly polarized light in one direction from natural light and absorb linearly polarized light in another direction, and are therefore called absorption-type polarizing films.

[0039] The polarizing film 30 is not limited to an absorptive polarizing film. It can also be a reflective polarizing film that selectively transmits linearly polarized light in one direction and reflects linearly polarized light in another direction from natural light, or a scattering polarizing film that scatters linearly polarized light in another direction. From the perspective of excellent visibility, an absorptive polarizing film is preferred. Among these, an iodine-based polarizing film with excellent polarization degree and transmittance is more preferred.

[0040] The polarizing film 30 can be manufactured by the following method, which includes: a step of uniaxially stretching a polyvinyl alcohol (PVA) resin film; a step of adsorbing a dichroic pigment by dyeing the PVA resin film with a dichroic pigment; a step of treating the PVA resin film with the adsorbed dichroic pigment with a boric acid aqueous solution (crosslinking treatment); and a step of washing with water after the boric acid aqueous solution treatment. The stretching ratio is typically around 3 to 8 times.

[0041] After washing with water, a drying process is performed to obtain a polarizing film 30. The drying process can be carried out using a hot air dryer or a far-infrared heater. By applying a protective film to both sides of the polarizing film 30 with an adhesive, a polarizing plate can be obtained.

[0042] The thickness of the polarizing film 30 can be set to 40 μm or less, preferably 30 μm or less (e.g., 20 μm or less). It should be noted that, according to the methods described in Japanese Patent Application Publication Nos. 2000-338329 and 2012-159778, the thin-film polarizing film 30 can be manufactured more easily, and the thickness of the polarizing film 30 can be set to, for example, 20 μm or less, and further, 10 μm or less. The thickness of the polarizing film 30 is typically 2 μm or more. Reducing the thickness of the polarizing film 30 is advantageous for the thinning of polarizing plates and even image display devices.

[0043] (3) Protective film

[0044] The first protective film 10 and the second protective film 20 are respectively resin films comprising: a light-transmitting (preferably optically transparent) thermoplastic resin, such as a chain polyolefin resin (polypropylene resin, etc.), a cyclic polyolefin resin (norbornene resin, etc.); a cellulose ester resin such as triacetylcellulose or diacetylcellulose; a polyester resin such as polyethylene terephthalate, polyethylene naphthalate, or polybutylene terephthalate; a polycarbonate resin; a (meth)acrylic resin; or a mixture or copolymer thereof.

[0045] The first protective film 10 and the second protective film 20 are preferably formed from resins selected from polyester resins, polycarbonate resins, polyolefin resins, (meth)acrylic resins and cellulose ester resins, respectively.

[0046] In this specification, "(meth)acrylic acid" refers to methacrylic acid and / or acrylic acid, and "(meth)" when referred to as "(meth)acrylate" has the same meaning.

[0047] The first protective film 10 and the second protective film 20 can each be an unstretched film or a film stretched uniaxially or biaxially. Biaxial stretching can be simultaneous biaxial stretching in two stretching directions, or sequential biaxial stretching where stretching occurs in a specified direction followed by stretching in other directions. The first protective film 10 and / or the second protective film 20 can also be a protective film with optical functions, such as a phase retardation film. A phase retardation film is an optically functional film used to compensate for phase differences caused by liquid crystal cells used as image display elements. For example, by stretching a film containing the aforementioned thermoplastic resin (uniaxial stretching or biaxial stretching, etc.) or forming a liquid crystal layer on the film, a phase retardation film with arbitrary phase difference values ​​can be produced.

[0048] In addition to homopolymers of chain olefins such as polyethylene resin and polypropylene resin, copolymers containing two or more chain olefins can also be cited as examples of chain olefin resins.

[0049] Cyclic polyolefin resins are a general term for resins that use cyclic olefins, such as norbornene, tetracyclododecene (also known as dimethyl-bridged octahydronaphthalene), or their derivatives, as polymerizing units. Specific examples of cyclic polyolefin resins include: ring-opening (copolymers) of cyclic olefins and their hydrogenated derivatives, addition polymers of cyclic olefins, copolymers of cyclic olefins with chain olefins such as ethylene and propylene, or aromatic compounds having vinyl groups, and modified (copolymers) obtained by modifying them with unsaturated carboxylic acids or their derivatives. Among these, norbornene-based resins that use norbornene monomers, such as norbornene or polycyclic norbornene monomers, as cyclic olefins are preferred.

[0050] Cellulose ester resins are resins in which at least a portion of the hydroxyl groups in cellulose are esterified with acetate, or they can be mixed esters in which some are esterified with acetate and others with other esters. Cellulose ester resins are preferably acetylcellulose-based resins. Specific examples of acetylcellulose-based resins include triacetylcellulose, diacetylcellulose, cellulose acetate propionate, and cellulose acetate butyrate.

[0051] Polyester resins are resins containing ester bonds, other than the cellulose ester resins mentioned above, and typically comprise condensations of polycarboxylic acids or their derivatives with polyols. Specific examples of polyester resins include: polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polyethylene terephthalate, polypropylene terephthalate, polypropylene naphthalate, polycyclohexanedimethyl terephthalate, and polycyclohexanedimethyl terephthalate. Polyethylene terephthalate is preferred. Polyethylene terephthalate refers to a resin in which 80 mol% or more of the repeating units are composed of polyethylene terephthalate.

[0052] Polycarbonate resins are polyesters formed from carbonic acid and glycols or bisphenols.

[0053] (Meth)acrylic resins can be polymers with methacrylate as the main monomer (containing more than 50% by mass), preferably copolymers with a small amount of other copolymer components copolymerized thereon. (Meth)acrylic resins are more preferably copolymers of methyl methacrylate and methyl acrylate, and may also be further copolymerized with a third monofunctional monomer.

[0054] Examples of third-functional monomers include: methyl methacrylates other than methyl methacrylates, such as ethyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, benzyl methacrylate, 2-ethylhexyl methacrylate, and 2-hydroxyethyl methacrylate; acrylates 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 styrene such as chlorostyrene and bromostyrene; substituted styrene such as vinyltoluene and α-methylstyrene; unsaturated nitrile such as acrylonitrile and methacrylonitrile; unsaturated anhydrides such as maleic anhydride and citrate anhydride; and unsaturated imides such as phenylmaleimide and cyclohexylmaleimide. The third functional monomer can be used alone or in combination of two or more.

[0055] (Meth)acrylic resins can be further copolymerized with multifunctional monomers. Examples of multifunctional monomers 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, and tetradecaethylene glycol di(meth)acrylate, which are substances obtained by esterifying the terminal hydroxyl groups of ethylene glycol or its oligomers with (meth)acrylic acid; substances obtained by esterifying the terminal hydroxyl groups of propylene glycol or its oligomers with (meth)acrylic acid; and neopentyl glycol di(meth)acrylate, hexanediol di(meth)acrylate, and butanediol di(meth)acrylate, which are substances obtained by esterifying the hydroxyl groups of a dihydric alcohol with (meth)acrylic acid. Substances formed by esterification of the terminal hydroxyl groups of bisphenol A, its alkyl oxide adducts, or their halogenated derivatives with (meth)acrylic acid; substances formed by esterification of polyols such as trimethylolpropane and pentaerythritol with (meth)acrylic acid, and substances formed by ring-opening addition of the epoxy group of (meth)acrylic acid to their terminal hydroxyl groups; substances formed by ring-opening addition of the epoxy group of (meth)acrylic acid to dicarboxylic acids such as succinic acid, adipic acid, terephthalic acid, phthalic acid, their halogenated derivatives, and their alkyl oxide adducts; aromatic (meth)acrylic acid esters; aromatic divinyl compounds such as divinylbenzene, etc. Ethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, and neopentyl glycol dimethacrylate are preferred.

[0056] (Meth)acrylic resins can be modified by further reactions between the functional groups present in the copolymer. Examples of such reactions include: intramethanol condensation reaction of the methyl ester group of methyl acrylate with the hydroxyl group of 2-(hydroxymethyl)acrylate, and intramolecular dehydration condensation reaction of the carboxyl group of acrylic acid with the hydroxyl group of 2-(hydroxymethyl)acrylate.

[0057] The glass transition temperature of (meth)acrylic resins is preferably 80–160 °C. The glass transition temperature can be controlled by adjusting the polymerization ratio of methacrylate monomers to acrylate monomers, the carbon chain length of each ester group, the types of functional groups they possess, and the polymerization ratio of polyfunctional monomers to all monomers. Furthermore, introducing a ring structure into the polymer backbone is also an effective method for increasing the glass transition temperature of (meth)acrylic resins. The ring structure is preferably a heterocyclic structure such as a cyclic anhydride structure, a cyclic imide structure, or a lactone structure.

[0058] (Meth)acrylic resins may contain additives as needed. Examples of additives include lubricants, anti-blocking agents, heat stabilizers, antioxidants, antistatic agents, lightfastness agents, impact modifiers, and surfactants. These additives may also be included in protective films containing thermoplastic resins other than (meth)acrylic resins.

[0059] From the perspective of membrane-forming properties and impact resistance, (meth)acrylic resins can contain acrylic rubber particles as impact modifiers. Acrylic rubber particles refer to particles that use an elastic polymer with acrylate as the main component as an essential component. Examples include single-layer acrylic rubber particles that are essentially composed only of this elastic polymer, and multi-layer acrylic rubber particles that use this elastic polymer as one layer.

[0060] The first protective film 10 and / or the second protective film 20 may contain an ultraviolet absorber. When a polarizing plate is applied to an image display device such as a liquid crystal display device, by placing the protective film containing the ultraviolet absorber on the visible side of the image display element (e.g., a liquid crystal cell), degradation of the image display element caused by ultraviolet radiation can be suppressed. Examples of ultraviolet absorbers include salicylate compounds, benzophenone compounds, benzotriazole compounds, cyanoacrylate compounds, and nickel complex salt compounds.

[0061] The first protective film 10 and the second protective film 20 can be films formed from the same resin or films formed from different resins. In addition, the first protective film 10 and the second protective film 20 can be the same or different in terms of thickness, presence or absence of additives, type of additives, phase difference characteristics, etc.

[0062] The first protective film 10 and / or the second protective film 20 may have surface treatment layers (coatings) such as hard coating, anti-glare layer, anti-reflection layer, light diffusion layer, antistatic layer, anti-fouling layer, and conductive layer on their outer surface (the surface opposite to the polarizing film 30).

[0063] The thicknesses of the first protective film 10 and the second protective film 20 are typically 5–200 μm, preferably 10–120 μm, and more preferably 10–85 μm. Reducing the thickness of the first protective film 10 and the second protective film 20 is advantageous for the thinning of polarizing plates and even image display devices. The thinner the protective film, the easier it is to reduce the curl resistance, but according to the present invention, even if the thickness of the first protective film 10 and the second protective film 20 is thin, the curl resistance of the polarizing plate can be effectively improved.

[0064] (4) Adhesive layer

[0065] The first adhesive layer 15 is a cured layer of a first cationic polymeric adhesive containing one or more cationic polymerization initiators, and the second adhesive layer 25 is a cured layer of a second cationic polymeric adhesive containing one or more cationic polymerization initiators.

[0066] The first and second cationic polymeric adhesives typically contain cationic polymeric compounds and cationic polymerization initiators, respectively.

[0067] Cationic polymerization initiators generate cationic species or Lewis acids by irradiation with active energy rays such as visible light, ultraviolet light, X-rays, or electron beams, which then initiate the polymerization reaction of cationic curable compounds.

[0068] The first cationic polymerization initiator contained in the first cationic polymerization adhesive includes one or more of the aforementioned cationic polymerization initiators. The first cationic polymerization initiator is a borate comprising a cationic component and an anionic component as shown in formula (i) below.

[0069] [Chemical Formula 2]

[0070] [(Y) k B(Phf) 4-k ] - (i)

[0071] (In the formula, Y represents an aryl group with 6 to 30 carbon atoms or a heterocyclic group with 4 to 30 carbon atoms, or a halogen atom, which may have substituents (excluding groups containing halogen atoms). Phf represents a phenyl group in which at least one hydrogen atom is substituted by at least one of perfluoroalkyl, perfluoroalkoxy, and halogen atoms. k is any integer from 0 to 4. When there are multiple Ys, the multiple Ys may be the same or different. When there are multiple Phfs, the multiple Rhfs may be the same or different.)

[0072] The first cationic polymerization initiator and the second cationic polymerization adhesive are selected such that the molecular weight of the first cationic polymerization initiator is greater than the molecular weight of the first cationic polymerization initiator contained in the second cationic polymerization adhesive. "The molecular weight of the first cationic polymerization initiator being greater than the molecular weight of the first cationic polymerization initiator contained in the second cationic polymerization adhesive" means that the molecular weight of the first cationic polymerization initiator is greater than the molecular weight of any cationic polymerization initiator contained in the second cationic polymerization adhesive.

[0073] The first cationic polymerizable adhesive may contain two or more first cationic polymerization initiators. When the first cationic polymerizable adhesive contains two or more first cationic polymerization initiators, it is acceptable as long as the molecular weight of at least one first cationic polymerization initiator is greater than the molecular weight of any cationic polymerization initiator contained in the second cationic polymerizable adhesive. From the viewpoint of providing a polarizing plate with good resistance to curling even when placed in a high-humidity environment, it is preferable that the molecular weight of all first cationic polymerization initiators is greater than the molecular weight of any cationic polymerization initiator contained in the second cationic polymerizable adhesive.

[0074] According to the present invention, a polarizing plate with good resistance to curling even when placed in a high-humidity environment can be provided, and in particular, it can effectively suppress curling where the first protective film 10 side becomes concave and the second protective film 20 side becomes convex. This effect is believed to be due to the use of the aforementioned borate as the first cationic polymerization initiator, and the fact that the molecular weight of the cationic polymerization initiator satisfies the aforementioned relationship.

[0075] (4-1) Cationic polymerization initiator

[0076] The first cationic polymeric adhesive forming the first adhesive layer 15 comprises one or more cationic polymerization initiators, including a first cationic polymerization initiator. The first cationic polymerization initiator is a borate comprising a cationic component and an anionic component as shown in formula (i) above.

[0077] The first cationic polymerization initiator may contain one or more cationic components, or one or more anionic components as shown in formula (i).

[0078] Examples of perfluoroalkyl groups in formula (i) include: straight-chain perfluoroalkyl groups with 1 to 8 carbon atoms, preferably 1 to 4, such as trifluoromethyl, pentafluoroethyl, heptafluoropropyl, nonafluorobutyl, perfluoropentyl, and perfluorooctyl; branched perfluoroalkyl groups with 3 to 8 carbon atoms, preferably 3 to 4, such as heptafluoroisopropyl and nonafluoroisobutyl; and perfluorocyclopropyl and perfluorocyclobutyl groups with 3 to 8 carbon atoms, preferably 3 to 4.

[0079] Examples of perfluoroalkoxy groups in formula (i) include linear perfluoroalkoxy groups with 1 to 8 carbon atoms, preferably 1 to 4, such as trifluoromethoxy, pentafluoroethoxy, heptafluoropropoxy, nonafluorobutoxy, perfluoropentoxy, and perfluorooctoxy; and branched perfluoroalkoxy groups with 3 to 8 carbon atoms, preferably 3 to 4, such as heptafluoroisopropoxy and nonafluoroisobutoxy.

[0080] Examples of halogen atoms in formula (i) include fluorine, chlorine, bromine, and iodine atoms.

[0081] Examples of Rhf include: pentafluorophenyl (C6F5), trifluorophenyl (C6H2F3), tetrafluorophenyl (C6HF4), trifluoromethylphenyl (CF3C6H4), bis(trifluoromethyl)phenyl ((CF3)2C6H3), pentafluoroethylphenyl (CF3CF2C6H4), bis(pentafluoroethyl)phenyl ((CF3CF2)2C6H3), fluoro-trifluoromethylphenyl (CF3C6H3F), fluoro-bis(trifluoromethyl)phenyl ((CF3)2C6H2F), fluoro-pentafluoroethylphenyl (CF3CF2C6H3F), fluoro-bis(pentafluoroethyl)phenyl ((CF3CF2)2C6H2F), etc.

[0082] Rhf is preferably a phenyl group in which at least one hydrogen atom is replaced by a halogen atom, and more preferably a phenyl group in which at least one hydrogen atom is replaced by a fluorine atom.

[0083] Examples of aryl groups with 6 to 30 carbon atoms in Y in formula (i) include phenyl, biphenyl, naphthyl, anthraceneyl, phenanthrene, etc.

[0084] In formula (i), the heterocyclic group with 4 to 30 carbon atoms in Y is a group obtained by removing one hydrogen atom from a heterocycle with 4 to 30 carbon atoms. Examples of such heterocycles include: oxobutane rings, tetrahydrofuran rings, morpholine rings, and other heterocycles containing oxygen atoms; thiophene rings, thiazole rings, and other heterocycles containing sulfur atoms; and pyrrole rings, imidazoline rings, indole rings, and other heterocycles containing nitrogen atoms.

[0085] Y can have substituents other than those containing halogen atoms, such as: alkyl groups with 1 to 12 carbon atoms, cycloalkyl groups with 3 to 6 carbon atoms, alkoxy groups with 1 to 6 carbon atoms, alkylthio groups with 1 to 6 carbon atoms, arylthio groups with 6 to 12 carbon atoms, and alkylcarbonyl groups with 2 to 7 carbon atoms. When Y has multiple substituents, these substituents can be the same or different.

[0086] k is preferably an integer from 0 to 2, more preferably an integer of 0 or 1, and even more preferably 0.

[0087] When multiple Phfs are present (where k represents an integer from 0 to 2), the multiple Rhfs are preferably the same group, and more preferably all Rhfs are phenyl groups in which at least one hydrogen atom is replaced by a fluorine atom.

[0088] From the viewpoint of the polarizing plate's resistance to curling, the anionic component shown in formula (i) is preferably an anionic component with k=0 and Rhf being a phenyl group in which at least one hydrogen atom is substituted by a halogen atom, more preferably an anionic component with k=0 and Rhf being a pentafluorophenyl (C6F5). The anionic component of the first cationic polymerization initiator is preferably tetratetra(pentafluorophenyl)borate anion B(C6F5)4. - wait.

[0089] Examples of cationic components that can serve as first cationic polymerization initiators include arylsulfonium ions, aryliodonium ions, and aryldiazo ions. Examples of arylsulfonium ions include triphenylsulfonium cations and 4,4'-bis(diphenylsulfonyl)diphenyl sulfide cations. Examples of aryliodonium ions include diphenyliodonium cations. Examples of aryldiazo ions include benzenediazo cations.

[0090] From the viewpoint of the polarizing plate's resistance to curling, arylsulfonium ions are preferred. From the viewpoint of the polarizing plate's resistance to curling, the cationic component of the first cationic polymerization initiator more preferably includes 4,4'-bis(diphenylsulfonyl)diphenyl sulfide cation.

[0091] From the viewpoint of the polarizing plate's resistance to curling, the first cationic polymeric adhesive preferably contains only the first cationic polymerization initiator as a cationic polymerization initiator.

[0092] The molecular weight of the first cationic polymerization initiator can be above 900, above 1000, above 1500, above 1900, or below 3000 or below 2500.

[0093] The second cationic polymerizable adhesive forming the second adhesive layer 25 includes one or more cationic polymerization initiators. As described above, the cationic polymerization initiators included in the second cationic polymerizable adhesive are selected such that the molecular weight of the first cationic polymerization initiator is greater than the molecular weight of the aforementioned one or more cationic polymerization initiators included in the second cationic polymerizable adhesive. Hereinafter, the one or more cationic polymerization initiators included in the second cationic polymerizable adhesive will also be collectively referred to as "second cationic polymerization initiators".

[0094] The second cationic polymerization initiator may contain one or more cationic components, or one or more anionic components.

[0095] Specifically, examples of second cationic polymerization initiators include aryl sulfonium salts, aryl iodonium salts, aryl diazonium salts, and iron-aromatic complexes.

[0096] Examples of aryl sulfonium ions that constitute aryl sulfonium salts include triphenylsulfonium cations and 4,4'-bis(diphenylsulfonyl)diphenyl sulfide cations. Examples of aryl iodomonium ions that constitute aryl iodomonium salts include diphenyliodomonium cations. Examples of aryl diazonium ions that constitute aryl diazonium salts include benzenediazonium cations. Iron-aromatic complexes are, for example, cyclopentadienyl iron(II)aromatic cation complexes.

[0097] From the viewpoint of the polarizing plate's resistance to curling and the adhesion between the polarizing film and the protective film, in a preferred embodiment, the cationic components of both the first and second cationic polymerization initiators are arylsulfonium ions. In another preferred embodiment, the cationic components of both the first and second cationic polymerization initiators are triphenylsulfonium cations and / or 4,4'-bis(diphenylsulfonyl)diphenyl sulfide cations.

[0098] As anionic components constituting the second cationic polymerization initiator, there are special phosphorus-based anions [(Rf]]. n PF 6-n ] - (n represents an integer from 1 to 6, Rf represents a haloalkyl group), hexafluorophosphate anion PF6 - SbF6, anion of hexafluoroantimonate - The pentafluorohydroxyantimonate anion SbF5(OH) - AsF6 hexafluoroarsenate anion - Tetrafluoroborate anion BF4 - Tetra(pentafluorophenyl)borate anion B(C6F5)4 - Etc. A preferred example is the hexafluorophosphate anion PF6.- .

[0099] From the viewpoint of the polarizing plate's resistance to curling, in a preferred embodiment, the anionic component of the first cationic polymerization initiator is the anionic component shown in formula (i) above, and the anionic component of the second cationic polymerization initiator is PF6. - From the viewpoint of the polarizing plate's resistance to curling, in a preferred embodiment, the anionic component of the first cationic polymerization initiator is B(C6F5)4. - Furthermore, the anionic component of the second cationic polymerization initiator is PF6. - .

[0100] From the viewpoint of the polarizing plate's resistance to curling, the cationic polymerization initiator contained in the second cationic polymeric adhesive preferably does not contain the anionic component shown in the above formula (i), and more preferably does not contain the borate anion.

[0101] There are no particular restrictions on the molecular weight of the second cationic polymerization initiator as long as it is less than that of the first cationic polymerization initiator. It can be less than 1000, less than 800, less than 600, or more than 200.

[0102] Relative to 100 parts by mass of the cationic polymerizable compound, the content of the cationic polymerization initiator contained in the first cationic polymerizable adhesive (the total content of two or more cationic polymerization initiators) and the content of the cationic polymerization initiator contained in the second cationic polymerizable adhesive (the total content of two or more cationic polymerization initiators) are typically 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 parts by mass or more and 5 parts by mass or less. From the viewpoint of the damp heat durability of the polarizing plate, the above-mentioned content is more preferably 1.3 parts by mass or more.

[0103] It should be noted that if the amount of cationic polymerization initiator is too large, the ionic substances in the adhesive layer will increase, thereby increasing the hygroscopicity of the adhesive layer and potentially reducing the durability of the polarizing plate.

[0104] (4-2) Cationic polymeric compounds

[0105] The cationic polymerizable compounds contained in the first and second cationic polymerizable adhesives refer to compounds or oligomers that undergo cationic polymerization and are cured by irradiation with active energy rays such as ultraviolet light, visible light, electron beams, and X-rays. Examples include epoxy compounds, oxetane compounds, and vinyl compounds. Among these, epoxy compounds are preferred. An epoxy compound is a compound having one or more, preferably two or more, epoxy groups in its molecule. An epoxy compound may be used alone or in combination of two or more. Examples of epoxy compounds include alicyclic epoxy compounds, aromatic epoxy compounds, hydrogenated epoxy compounds, and aliphatic epoxy compounds. From the viewpoints of weather resistance, curing speed, and adhesion, epoxy compounds preferably include alicyclic epoxy compounds and aliphatic epoxy compounds, and more preferably include alicyclic epoxy compounds.

[0106] The first cationic polymeric adhesive and the second cationic polymeric adhesive may contain one or more cationic polymeric compounds.

[0107] Alicyclic epoxy compounds are compounds having one or more epoxy groups bonded to an alicyclic ring within the molecule. "Epoxy group bonded to an alicyclic ring" refers to the bridging oxygen atom -O- in the structure shown in formula (I) below. In formula (I) below, m is an integer from 2 to 5.

[0108] [Chemical Formula 3]

[0109]

[0110] Remove (CH2) from equation (I) above. m Compounds in which one or more hydrogen atoms are followed by functional groups that bond with other chemical structures can become alicyclic epoxides. (CH2) m One or more hydrogen atoms in it can be appropriately substituted by straight-chain alkyl groups such as methyl or ethyl.

[0111] Among them, alicyclic epoxy compounds having an epoxycyclopentane structure (the structure where m=3 in formula (I) above) and an epoxycyclohexane structure (the structure where m=4 in formula (I) above) have high glass transition temperatures in their cured products, which is advantageous in increasing the glass transition temperature of the adhesive layer. Furthermore, they are also advantageous in terms of adhesion between the polarizing film and the protective film. Specific examples of alicyclic epoxy compounds are given below. Here, the compound names are listed first, followed by their corresponding chemical formulas, with the same symbols used for both the compound names and their corresponding chemical formulas.

[0112] A: 3,4-Epoxycyclohexylcarboxylic acid, 3,4-epoxycyclohexylmethyl ester

[0113] B: 3,4-Epoxy-6-methylcyclohexylcarboxylic acid, 3,4-epoxy-6-methylcyclohexylmethyl ester

[0114] C: Ethylenebis(3,4-epoxycyclohexyl carboxylate),

[0115] D: Bis(3,4-epoxycyclohexyl methyl adipic acid)

[0116] E: Bis(3,4-epoxy-6-methylcyclohexyl) adipic acid bis(3,4-epoxy-6-methylcyclohexyl)

[0117] F: Diethylene glycol bis(3,4-epoxycyclohexyl methyl ether)

[0118] G: Ethylene glycol bis(3,4-epoxycyclohexyl methyl ether)

[0119] H: 2,3,14,15-diepoxy-7,11,18,21-tetraoxatrispiro[5.2.2.5.2.2]cosicosane,

[0120] I: 3-(3,4-epoxycyclohexyl)-8,9-epoxy-1,5-dioxaspiro[5.5]undecane,

[0121] J: 4-Vinylcyclohexene dioxide,

[0122] K: Limonene dioxide,

[0123] L: Bis(2,3-epoxycyclopentyl) ether,

[0124] M: Dicyclopentadiene dioxide.

[0125] [Chemical Formula 4]

[0126]

[0127] [Chemical Formula 5]

[0128]

[0129] Aromatic epoxy compounds are compounds that have an aromatic ring and an epoxy group within their molecules. Specific examples include: bisphenol-type epoxy compounds or their oligomers, such as bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, and bisphenol S diglycidyl ether; phenolic epoxy resins, such as phenol-formaldehyde epoxy resin, cresol-formaldehyde epoxy resin, and hydroxybenzaldehyde-formaldehyde epoxy resin; multifunctional epoxy compounds, such as 2,2',4,4'-tetrahydroxydiphenylmethane glycidyl ether and 2,2',4,4'-tetrahydroxybenzophenone glycidyl ether; and multifunctional epoxy resins, such as epoxidized polyvinylphenol.

[0130] Hydrogenated epoxy compounds are glycidyl ethers of polyols having alicyclic rings. They can be obtained by selectively hydrogenating the aromatic ring of an aromatic polyol under pressure in the presence of a catalyst to obtain a nucleus-hydrogenated polyhydroxy compound, followed by glycidyl etherification of this nucleus-hydrogenated polyhydroxy compound. Specific examples of aromatic polyols include: bisphenol-type compounds such as bisphenol A, bisphenol F, and bisphenol S; phenolic resins such as phenol-formaldehyde resin, cresol-formaldehyde resin, and hydroxybenzaldehyde-phenol-formaldehyde resin; and multifunctional compounds such as tetrahydroxydiphenylmethane, tetrahydroxybenzophenone, and polyvinylphenol. Glycidyl ethers can be prepared by reacting an alicyclic polyol obtained by hydrogenating the aromatic ring of an aromatic polyol with epichlorohydrin. A preferred compound among hydrogenated epoxy compounds is the diglycidyl ether of hydrogenated bisphenol A.

[0131] Aliphatic epoxides are compounds that have at least one ethylene oxide ring (a 3-membered cyclic ether) bonded to an aliphatic carbon atom within their molecule. Examples include: monofunctional epoxides such as butyl glycidyl ether and 2-ethylhexyl glycidyl ether; difunctional epoxides such as 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, neopentyl glycol diglycidyl ether, and 1,4-cyclohexanediethanol diglycidyl ether; trifunctional or more functional epoxides such as trimethylolpropane triglycidyl ether and pentaerythritol tetraglycidyl ether; and epoxides such as 4-vinylcyclohexene dioxide and limonene dioxide, which have one epoxy group directly bonded to an alicyclic ring and an ethylene oxide ring bonded to an aliphatic carbon atom. From the viewpoint of adhesion between the polarizing film and the protective film, a difunctional epoxy compound (also known as an aliphatic diepoxide compound) having two ethylene oxide rings bonded to aliphatic carbon atoms within the molecule is preferred. Such a suitable aliphatic diepoxide compound can be represented, for example, by the following formula (II).

[0132] [Chemical Formula 6]

[0133]

[0134] In the above formula (II), Y is an alkylene group with 2 to 9 carbon atoms, an alkylene group with 4 to 9 carbon atoms containing ether bonds, or a divalent hydrocarbon group with 6 to 18 carbon atoms having an alicyclic structure.

[0135] Specifically, the aliphatic diepoxide compound represented by formula (II) above is a diglycidyl ether of an alkyl diol, a diglycidyl ether of an oligoalkylene diol with a repeat number of about 4 or less, or a diglycidyl ether of an alicyclic diol.

[0136] The following are specific examples of glycols that can form the aliphatic diepoxides shown in formula (II) above. Examples of alkyl glycols include ethylene glycol, propylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,4-butanediol, neopentyl glycol, 3-methyl-2,4-pentanediol, 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 oligomeric alkylene glycols include diethylene glycol, triethylene glycol, tetraethylene glycol, and dipropylene glycol. As alicyclic diols, there are cyclohexanediols such as 1,2-cyclohexanediol, 1,3-cyclohexanediol, and 1,4-cyclohexanediol, as well as cyclohexanediols such as 1,2-cyclohexanediethanol, 1,3-cyclohexanediethanol, and 1,4-cyclohexanediethanol.

[0137] Oxetane compounds, as cationic polymerizable compounds, are compounds containing one or more oxetane rings (oxetane alkyl groups) within their molecules. Specific examples include: 3-ethyl-3-hydroxymethyloxetane (also known as oxetane alcohol), 2-ethylhexyloxetane, 1,4-bis[{(3-ethyloxetane-3-yl)methoxy}methyl]benzene (also known as xylenedioxetane), 3-ethyl-3[{(3-ethyloxetane-3-yl)methoxy}methyl]oxetane, 3-ethyl-3-(phenoxymethyl)oxetane, and 3-(cyclohexyloxy)methyl-3-ethyloxetane. Oxetane compounds can be used as the main component of cationic polymerizable compounds or in combination with epoxy compounds. By using oxetane compounds in combination, the curing speed and adhesion can sometimes be improved.

[0138] Vinyl compounds that can be cationic polymerizable include aliphatic or alicyclic vinyl ether compounds, such as: vinyl ethers of alkyl alcohols or alkenyl alcohols with 5 to 20 carbon atoms, including 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, oleyl vinyl ether, etc.; hydroxyl-containing vinyl ethers such as 2-hydroxyethyl vinyl ether, 3-hydroxypropyl vinyl ether, 4-hydroxybutyl vinyl ether; vinyl ethers of monohydric alcohols having aliphatic or aromatic rings such as cyclohexyl vinyl ether, 2-methylcyclohexyl vinyl ether, cyclohexylmethyl vinyl ether, benzyl vinyl ether; glycerol monovinyl ether, 1 Mono- and polyvinyl ethers of polyols such as 4-butanediol monovinyl ether, 1,4-butanediol divinyl ether, 1,6-hexanediol divinyl ether, neopentyl glycol divinyl ether, pentaerythritol 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- and divinyl ethers such as diethylene glycol divinyl ether, triethylene glycol divinyl ether, and diethylene glycol monobutyl monovinyl ether; and other vinyl ethers such as glycidyl vinyl ether and ethylene glycol vinyl ether methacrylate. Vinyl compounds can be used as the main component of cationic polymerizable compounds, or in combination with epoxy compounds, or epoxy compounds and oxetane compounds. By using vinyl compounds in combination, it is sometimes possible to improve the curing speed and reduce the viscosity of the adhesive.

[0139] Cationic polymeric adhesives may further include other cationic polymeric compounds besides those mentioned above, such as cyclic lactone compounds, cyclic acetal compounds, cyclic sulfide compounds, and spirocyclic orthoester compounds.

[0140] From the viewpoint of adhesion between the polarizing film and the protective film, in the first and second cationic polymeric adhesives, when the total amount of curing compounds contained in the cationic polymeric adhesive is set to 100% by mass, the content of cationic polymeric compounds (the content of all cationic polymeric compounds contained in the cationic polymeric adhesive, or their total content when two or more cationic polymeric compounds are contained) is preferably 50% by mass or more, more preferably 60% by mass or more, further preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 100% by mass.

[0141] The cationic polymeric compounds contained in the first cationic polymeric adhesive and the cationic polymeric compounds contained in the second cationic polymeric adhesive may be of the same type or different types.

[0142] (4-3) Additives

[0143] The first and / or second cationic polymeric adhesive may contain other additives as needed. Examples of additives include, for instance, ion traps, antioxidants, chain transfer agents, polymerization accelerators (polyols, etc.), sensitizers, sensitizing aids, light stabilizers, tackifiers, thermoplastic resins, fillers, flow modifiers, plasticizers, defoamers, leveling agents, silane coupling agents, pigments, antistatic agents, and UV absorbers.

[0144] (4-4) Application of adhesive and bonding of polarizing film and protective film

[0145] A first protective film 10 is laminated and bonded to one side of the polarizing film 30 using a first adhesive layer 15, and a second protective film 20 is laminated and bonded to the other side of the polarizing film 30 using a second adhesive layer 25, thereby obtaining the polarizing plate of the present invention. The first protective film 10 and the second protective film 20 (also collectively referred to as "protective film") can be laminated and bonded in stages, one side at a time, or the protective films on both sides can be laminated and bonded in one stage.

[0146] Specifically, the bonding of the polarizing film 30 and the protective film can be performed as follows: an adhesive is applied to the bonding surfaces of the polarizing film 30 and / or the protective film; the two films are overlapped through the adhesive coating layer; they are then pressed together from above and below using, for example, a bonding roller; and cured by irradiation with active energy rays. When using an active energy ray-curable adhesive, heat treatment can be performed simultaneously with or after irradiation with active energy rays. Before forming the adhesive coating layer, one or both of the bonding surfaces of the polarizing film 30 and the protective film can be subjected to an easy-to-bond treatment such as saponification, corona discharge, plasma treatment, flame treatment, primer treatment, or anchor coating.

[0147] The adhesive coating layer can be formed using various coating methods, such as scraper, wire bar, die coater, comma coater, and gravure coater. Alternatively, the adhesive can be cast between the polarizing film 30 and the protective film, with their bonding surfaces facing inwards.

[0148] From a coating point of view, the adhesive forming the first adhesive layer 15 and the second adhesive layer 25 preferably has a low viscosity. Specifically, the viscosity at 25°C is preferably 1000 mPa·s or less, more preferably 500 mPa·s or less, and even more preferably 100 mPa·s or less. The adhesive can be solvent-free, but it may also contain an organic solvent to adjust the viscosity to suit the coating method used.

[0149] The source of active energy rays can be any light source that generates ultraviolet rays, electron beams, X-rays, etc. Ultraviolet rays are preferred. As an ultraviolet light source, a light source with a luminous distribution at a wavelength below 400 nm is preferred; examples include 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, and metal halide lamps.

[0150] The intensity of the active energy radiation irradiation on the adhesive layer is determined according to each adhesive composition, preferably in the wavelength range effective for activating the photopolymerization initiator, at 0.1–1000 mW / cm². 2 If the light intensity is too low, the reaction time becomes too long. On the other hand, if the light intensity is too high, 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 adhesive polymerization. Furthermore, the light irradiation time for the adhesive is controlled according to each adhesive composition. Preferably, the cumulative light intensity, expressed as the product of light intensity and light irradiation time, is 10–5000 mJ / cm². 2 The setting is done in a certain way. If the cumulative light intensity is too low, the generation of active species from the photopolymerization initiator will be insufficient, and there is a possibility that the curing of the obtained adhesive layer will be insufficient. On the other hand, if the cumulative light intensity is too high, the light irradiation time will become very long, which is not conducive to improving productivity.

[0151] There are no particular restrictions on the timing of laminating the protective film onto the polarizing film 30 using an adhesive coating layer, or on the timing of curing the coating layer. For example, after laminating one protective film, the coating layer can be cured, and then another protective film can be laminationed and the coating layer cured. Alternatively, two protective films can be laminationed sequentially or simultaneously, and the coating layers on both sides can be cured simultaneously. Furthermore, irradiation with active energy rays can be performed from either side of the protective film. For example, if one protective film contains an ultraviolet absorber and the other does not, it is preferable to irradiate with active energy rays from the side of the protective film that does not contain an ultraviolet absorber. By irradiating in this way, the irradiated active energy rays can be utilized effectively, increasing the curing speed.

[0152] The thickness of the cured first and second adhesive layers 15 and 25 is typically 20 μm or less, preferably 10 μm or less, more preferably 5 μm or less, further preferably less than 5 μm, and particularly preferably 3 μm or less. If the thickness of the first and second adhesive layers 15 and 25 is too large, there is a tendency for the adhesive reaction rate to decrease and the damp heat durability of the polarizing plate to deteriorate. The thickness of the first and second adhesive layers 15 and 25 is typically 0.01 μm or more, preferably 0.1 μm or more, and more preferably 0.5 μm or more. If the thickness of the first and second adhesive layers 15 and 25 is too thin, in the case of fine defects (fine waste, fine dust, etc.) on the polarizing film 30, it may sometimes also affect other layers (first protective film 10, second protective film 20, etc.) that are stacked by the first and second adhesive layers. The thicknesses of the first adhesive layer 15 and the second adhesive layer 25 can be the same or different.

[0153] (5) Preferred configuration of polarizing plate

[0154] From the perspective that it can effectively obtain anti-curling effect even when placed in a high humidity environment, especially from the perspective that it can effectively suppress the curling angle of the first protective film 10 side becoming concave and the second protective film 20 side becoming convex, the polarizing plate preferably has the following configuration, for example.

[0155] [a] The first protective film 10 and the second protective film 20 are films formed of different resins.

[0156] [b] In [a] above, the first protective film 10 is a (meth)acrylic resin film or a cellulose ester resin film.

[0157] [c] In [b] above, the second protective film 20 is a cyclic polyolefin resin film.

[0158] [d] In any of [a] to [c] above, the first cationic polymerization initiator is a borate comprising a cationic component as an arylsulfonium ion and an anionic component as shown in formula (i) above, and the second cationic polymerization initiator comprises PF6 - Cationic polymerization initiators as anionic components.

[0159] [e] In [d] above, the first cationic polymerization initiator comprises a cationic component as an arylsulfonium ion and a B(C6F5)4 ion as a cationic component. - The anionic component of borate.

[0160] [f] In [d] or [e] above, the second cationic polymerization initiator contains a cationic component comprising an arylsulfonium ion and PF6. - Cationic polymerization initiators with anionic components.

[0161] [g] In any of [a] to [f] above, the first cationic polymeric adhesive contains only the first cationic polymerization initiator, and the second cationic polymeric adhesive contains only a cationic component comprising an arylsulfonium ion and PF6. - Cationic polymerization initiators with anionic components.

[0162] [h] In [g] above, the cationic component of the first cationic polymerization initiator is triphenylsulfonium cationic and / or 4,4'-bis(diphenylsulfonyl)diphenyl sulfide cationic, and the cationic component of the cationic polymerization initiator contained in the second cationic polymerization adhesive is triphenylsulfonium cationic and / or 4,4'-bis(diphenylsulfonyl)diphenyl sulfide cationic.

[0163] When a polarizer is assembled into an image display device, the polarizer is typically configured such that the side with the first protective film 10 is the visible side and the side with the second protective film 20 is the image display element side.

[0164] (6) Other components of the polarizing plate

[0165] (6-1) Optical functional film

[0166] The polarizer may have other optically functional films besides the polarizing film 30 to impart the desired optical function; a suitable example is a retardation film. As mentioned above, the first protective film 10 and / or the second protective film 20 may also serve as retardation films, but they may also be laminated separately from the protective films. In the latter case, the retardation film may be laminated onto the outer surface of the first protective film 10 and / or the second protective film 20 by means of an adhesive layer or bonding agent layer.

[0167] Specific examples of retardation films include: birefringent films made of a stretched film of a light-transmitting thermoplastic resin; films in which dish-shaped liquid crystals or nematic liquid crystals are oriented and fixed; and retardation films on which the aforementioned liquid crystal layers are formed on a substrate film. The substrate film is typically a thermoplastic resin film, and cellulose ester resins such as triacetyl cellulose are preferably used as the thermoplastic resin.

[0168] Examples of other optical functional films (optical components) that may be included in a polarizing plate include a light-concentrating plate, a brightness enhancement film, a reflective layer (reflective film), a semi-transparent reflective layer (semi-transparent reflective film), and a light-diffusing layer (light-diffusing film). These are typically provided when the polarizing plate is disposed on the back side (backlight side) of the liquid crystal cell.

[0169] (6-2) Adhesive layer

[0170] The polarizing plate of the present invention may include an adhesive layer for attaching it to an image display element such as a liquid crystal cell or other optical components. The adhesive layer may be laminated on the outer surface of a protective film. The adhesive layer may be laminated on the outer surface of a first protective film or on the outer surface of a second protective film.

[0171] When the polarizer has an adhesive layer, the polarizer preferably has an adhesive layer on the side of the second protective film 20 opposite to the side of the second adhesive layer 25. This adhesive layer is typically used to attach the polarizer to an image display element.

[0172] As an adhesive used in the adhesive layer, adhesives based on polymers such as (meth)acrylic resins, silicone resins, polyester resins, polyurethane resins, and polyether resins can be used. Among these, (meth)acrylic adhesives are preferred from the viewpoints of transparency, adhesion, reliability, weather resistance, heat resistance, and reprocessability. In (meth)acrylic adhesives, it is useful to use a (meth)acrylic resin as the base polymer, which is formulated by combining alkyl (meth)acrylates having alkyl groups such as methyl, ethyl, or butyl with alkyl (meth)acrylates containing 20 or fewer carbon atoms with (meth)acrylic acid, hydroxyethyl (meth)acrylate, or other functionalized (meth)acrylic acid monomers, preferably with a glass transition temperature of 25°C or lower, more preferably 0°C or lower, and having a weight-average molecular weight of 100,000 or higher.

[0173] Forming an adhesive layer on a polarizing plate can be achieved, for example, by dissolving or dispersing an adhesive composition in an organic solvent such as toluene or ethyl acetate to prepare a 10-40% by mass solution, and then directly applying the solution to the target surface of the polarizing plate to form an adhesive layer; or by pre-forming the adhesive layer into a sheet on a release film that has undergone a release treatment, and then transferring it to the target surface of the polarizing plate. The thickness of the adhesive layer is determined based on its adhesive strength, etc., and a range of about 1-50 μm is appropriate, preferably 2-40 μm.

[0174] The polarizing plate may include the aforementioned separator film. The separator film may be a film containing polyethylene-based resins such as polyethylene, polypropylene-based resins such as polypropylene, or polyester-based resins such as polyethylene terephthalate. Preferably, it is a stretched polyethylene terephthalate film.

[0175] The adhesive layer may contain glass fibers, glass beads, resin beads, fillers including metal powder and other inorganic powders, pigments, colorants, antioxidants, ultraviolet absorbers, antistatic agents, etc., as needed.

[0176] (6-3) Protective film

[0177] The polarizing plate of the present invention may include a protective film for temporarily bonding and protecting its surface (protective film surface). The protective film, for example, is peeled off together with its adhesive layer after the polarizing plate is attached to an image display element or other optical component.

[0178] The protective film comprises a substrate film and an adhesive layer laminated thereon. Regarding the adhesive layer, the description above is cited. The resin forming the substrate film can be, for example, a polyethylene-based resin such as polyethylene, a polypropylene-based resin such as polypropylene, a polyester-based resin such as polyethylene terephthalate or polyethylene naphthalate, or a thermoplastic resin such as polycarbonate. A polyester-based resin such as polyethylene terephthalate is preferred.

[0179] The polarizing plate of the present invention can be bonded to image display elements such as liquid crystal cells via an adhesive layer. Examples of liquid crystal cells include IPS type and VA type. Furthermore, the polarizing plate of the present invention can also be used as an anti-reflective polarizing plate and bonded to organic EL panels via an adhesive layer.

[0180] Example

[0181] The present invention will now be described in more detail with examples and comparative examples, but the invention is not limited to these examples. In the following examples, the following substances are used as cationic polymerizable compounds and cationic polymerization initiators constituting cationic polymerizable adhesives.

[0182] [1] Cationic polymeric compound A-1: ​​3,4-epoxycyclohexylcarboxylic acid-3',4'-epoxycyclohexylmethyl ester (manufactured by Daicel Corporation, trade name "CEL2021P")

[0183] [2] Cationic polymeric compound A-2: Neopentyl glycol diglycidyl ether (manufactured by Nagase ChemteX Co., Ltd., trade name "EX-211L")

[0184] [3] Cationic polymeric compound A-3: 4-hydroxybutylvinyl ether (manufactured by CARBIDE, Japan, trade name "HBVE")

[0185] [4] Cationic polymeric compound A-4: Methyl methacrylate-glycidyl methacrylate copolymer (cationic polymer) (Nippon Oil Manufacturing Co., Ltd., trade name "MARPROOF G-01100")

[0186] [5] Cationic polymerization initiator B-1: A cationic polymerization initiator containing the following cationic and anionic components. A mixture of a compound with a molecular weight of 1050 and a compound with a molecular weight of 1915 (manufactured by ESTCHEM Co., Ltd., trade name "PAG-20008").

[0187] [Chemical Formula 7]

[0188]

[0189] [6] Cationic polymerization initiator B-2: A cationic polymerization initiator containing the following cationic and anionic components. Molecular weight 517 (manufactured by San-Apro Corporation, trade name "CPI-100P")

[0190] [Chemical Formula 8]

[0191]

[0192] <Manufacturing Examples 1-14: Preparation of Cationic Polymer Adhesives>

[0193] The cationic polymerizable compounds and cationic polymerization initiators listed in Table 1 were mixed in the proportions listed in Table 1, and degassed to prepare liquid cationic polymerizable adhesives A to N. The values ​​in Table 1 represent parts by mass. Cationic polymerization initiators B-1 and B-2 were formulated as a 50% by mass propylene carbonate solution; the values ​​shown in Table 1 are the amounts of solid components contained therein.

[0194] [Table 1]

[0195]

[0196] <Examples 1-7, Comparative Examples 1-2>

[0197] (1) Fabrication of polarizing plates

[0198] Corona discharge treatment was applied to one side of the first protective film shown in Table 2. On this corona-discharge treated side, the first cationic polymeric adhesive shown in Table 2 was applied using a bar coater to a cured thickness of approximately 5 μm. Next, a polyvinyl alcohol (PVA)-iodine polarizing film with a thickness of 25 μm was laminated onto this coated side. Next, corona discharge treatment was applied to one side of the second protective film shown in Table 2. On this corona-discharge treated side, the second cationic polymeric adhesive shown in Table 2 was applied using a bar coater to a cured thickness of approximately 5 μm. On this coated side, the polarizing film with the first protective film was overlapped on the polarizing film side, and pressed and laminated using a laminating roller to obtain a laminate. For this laminate, an ultraviolet irradiation device with a conveyor belt (using a "D BULB" lamp manufactured by Fusion UV Systems) was used, with a cumulative light intensity of 200 mJ / cm² from the second protective film side. 2 A polarizing plate is made by irradiating ultraviolet light (UVB) on both sides to cure the adhesive layers.

[0199] It should be noted that when the obtained polarizing plate is assembled into an image display device, the polarizing plate is configured such that the side of the second protective film (phase difference film) becomes the image display element side and the side of the first protective film becomes the visible side.

[0200] The details of the first and second protective films shown in Table 2 are as follows.

[0201] [1] Protective film a: A 60 μm thick (meth)acrylic resin film containing an ultraviolet absorber. The (meth)acrylic resin forming the film is a copolymer obtained by copolymerizing methyl methacrylate and methyl acrylate at a mass ratio of 96:4.

[0202] [2] Protective film b: 60 μm thick cellulose ester resin film (manufactured by Fujifilm Corporation, trade name "TG")

[0203] [3] Protective film c: A phase retardation film with a thickness of 50 μm containing cyclic polyolefin resin (norbornene resin) (manufactured by ZEON Corporation, Japan, trade name "ZEONOR").

[0204] [4] Protective film d: A phase retardation film with a thickness of 40 μm containing (meth)acrylic resin (manufactured by LG Chemical Co., Ltd., trade name "GA-01").

[0205] (2) Evaluation of the polarizing plate's resistance to curling in high humidity environment

[0206] Under an environment of 25°C and 55% relative humidity, a monolith of 8cm × 8cm was cut from the polarizing plate prepared in (1) above. In this monolith, one pair of opposing sides is parallel to the absorption axis of the polarizing film. At this time, the monolith is not curled (curl amount 0mm). After placing the monolith in an environment of 25°C and 90% relative humidity for 2 hours, the curl amount of the monolith was measured. The curl amount was calculated as follows: the bent monolith was placed on a horizontal platform with a downward convex position, and the height from the platform to the four corners of the monolith was measured with a ruler. The average value of the four points was used to calculate the curl amount. Based on the obtained curl amount, the curl resistance was evaluated according to the following criteria. The evaluation results are shown in Table 2.

[0207] 5: No curling or curling amount less than 1mm

[0208] 4: Curl exceeding 1mm but less than 2mm

[0209] 3: Curl exceeding 2mm but less than 5mm

[0210] 2: Curl exceeding 5mm but less than 20mm

[0211] 1: Excessive curling causes the polarizing plate to become coiled.

[0212] (3) Formation of adhesive layer

[0213] A (meth)acrylic adhesive organic solvent solution was applied by a die coater onto the release-treated surface of a 38 μm-thick release film made of polyethylene terephthalate which had been subjected to release treatment, such that the thickness after drying reached 20 μm, thereby preparing a sheet-shaped adhesive with a release film. Next, corona discharge treatment was performed on the second protective film surface of the polarizing plate produced in (1) above, and the surface of the obtained sheet-shaped adhesive opposite to the release film (the adhesive surface) was laminated onto the corona discharge-treated surface using a laminator, followed by curing for 7 days under conditions of a temperature of 23°C and a relative humidity of 65%, thereby obtaining a polarizing plate having an adhesive layer.

[0214] (4) Evaluation of wet heat durability of polarizing plate

[0215] A 3 cm×3 cm sized single piece was cut out from the polarizing plate with an adhesive layer produced in (3) above. In this single piece, one set of two opposing sides are parallel to the absorption axis direction of the polarizing film. The release film was peeled off from the single piece, and the exposed adhesive surface was laminated onto a glass substrate. An alkali-free glass manufactured by Corning Incorporated under the trade name "Eagle XG" was used as the glass substrate. For the obtained optical layered body, an integrating sphere-equipped spectrophotometer (manufactured by JASCO Corporation, product name "V7100") was used to measure the MD transmittance and TD transmittance in the wavelength range of 380 to 780 nm, and the single body transmittance at each wavelength was calculated. For the calculated single body transmittance, visibility correction was performed in accordance with the 2-degree field of view (light source C) specified in JIS Z 8701:1999 "Method of displaying colors - XYZ color system and X 10 Y 10 Z 10 color system", to obtain the visibility-corrected single body transmittance (Ty) before the wet heat durability test. It should be noted that the optical layered body was placed in the integrating sphere-equipped spectrophotometer such that the first protective film surface side of the polarizing plate faced the detector side, and light was incident from the glass substrate side.

[0216] Single body transmittance (%) is defined by the following formula:

[0217] Single body transmittance(λ) = (Tp(λ)+Tc(λ)) / 2.

[0218] Tp(λ) is the transmittance (%) of the test sample measured when the incident linearly polarized light with wavelength λ (nm) is in a parallel Nicols relationship.

[0219] Tc(λ) is the transmittance (%) of the test sample measured when the incident linearly polarized light with wavelength λ (nm) is in a crossed Nicols relationship.

[0220] Next, the optical laminate was subjected to a damp heat durability test, which involved placing it in a humid heat environment at 80°C and 90% relative humidity for 48 hours, followed by a further 24 hours at 23°C and 60% relative humidity. After the damp heat durability test, the visibility-corrected monomer transmittance Ty was determined using the same method as before the test.

[0221] Based on the visibility-corrected monomer transmittance Ty before and after the damp heat durability test, the change in Ty is calculated using the following formula, and the damp heat durability is evaluated according to the following criteria. The evaluation results are shown in the table.

[0222] Change in Ty (%) = |Ty(after damp heat durability test) - Ty(before damp heat durability test)|

[0223] 4: The change in Ty is less than 1.0%.

[0224] 3: The change in Ty exceeds 1.0% but is less than 2.0%.

[0225] 2: The change in Ty exceeds 2.0% but is less than 3.0%.

[0226] 1: The change in Ty exceeds 3.0%.

[0227] [Table 2]

[0228]

[0229] Explanation of reference numerals in the attached figures

[0230] 10: First protective film, 15: First adhesive layer, 20: Second protective film, 25: Second adhesive layer, 30: Polarizing film.

Claims

1. A polarizing plate, comprising, in sequence, a first protective film, a first adhesive layer, a polarizing film, a second adhesive layer, and a second protective film. The first adhesive layer is a cured layer of a first cationic polymeric adhesive containing one or more cationic polymerization initiators. The second adhesive layer is a cured layer of a second cationic polymeric adhesive containing one or more cationic polymerization initiators. The first cationic polymerizable adhesive contains one or more cationic polymerization initiators, including a first cationic polymerization initiator; the second cationic polymerizable adhesive contains one or more cationic polymerization initiators, including a second cationic polymerization initiator. The second cationic polymerization initiator contains one or more cationic components and one or more anionic components; The first cationic polymerization initiator is a borate comprising a cationic component and an anionic component as shown in formula (i) below. In the formula, Y represents an aryl group with 6 to 30 carbon atoms, a heterocyclic group with 4 to 30 carbon atoms, or a halogen atom, which may be optionally substituted. The substituents do not include groups containing halogen atoms; Phf represents a phenyl group in which at least one hydrogen atom is substituted by at least one of perfluoroalkyl, perfluoroalkoxy, and halogen atoms; k is any integer from 0 to 4. Wherein, the cationic components of the first cationic polymerization initiator and the second cationic polymerization initiator are both arylsulfonium ions, and the anionic component of the second cationic polymerization initiator is a special phosphorus-based anion that is not the anion shown in formula (i) above. The special phosphorus-based anion is [(Rf)]. n PF 6-n ] - n represents an integer from 1 to 6, and Rf represents a haloalkyl group; The molecular weight of the first cationic polymerization initiator is greater than the molecular weight of the one or more cationic polymerization initiators contained in the second cationic polymerization adhesive.

2. The polarizing plate according to claim 1, wherein, The first cationic polymeric adhesive and the second cationic polymeric adhesive further comprise cationic polymeric compounds. The content of the one or more cationic polymerization initiators contained in the first cationic polymeric adhesive and the content of the one or more cationic polymerization initiators contained in the second cationic polymeric 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 polymeric compound.

3. The polarizing plate according to any one of claims 1 to 2, wherein, The first protective film is formed from (meth)acrylic resin or cellulose ester resin.

4. The polarizing plate according to claim 3, wherein, An adhesive layer is also provided on the side of the second protective film opposite to the side of the second adhesive layer.

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